WO2025106793A1

WO2025106793A1 - Ultra-low loss photonic multi-waveguide interconnects

Info

Publication number: WO2025106793A1
Application number: PCT/US2024/056092
Authority: WO
Inventors: Nikhil Kumar
Original assignee: Psiquantum Corp
Current assignee: Psiquantum Corp
Priority date: 2023-11-15
Filing date: 2024-11-15
Publication date: 2025-05-22
Anticipated expiration: 2026-05-15

Abstract

A low loss photonic coupling transition includes a first photonic integrated circuit having a first plurality of waveguides that have a tilt arrangement to couple light to a second photonic integrated circuit having a second plurality of waveguides with a corresponding tilt arrangement such that the optical mode tilts at an angle, such as away from an edge of the first photonic integrated circuit.

Description

Ref. No. PSIQ-523WO / 6224.011WO1 ULTRA-LOW LOSS PHOTONIC MULTI-WAVEGUIDE INTERCONNECTS CLAIM OF PRIORITY [0001] This application claims the benefit of priority to U.S. Patent Application Serial No. 63/599,340, filed on November 15, 2023, which is incorporated by reference herein in its entirety. TECHNICAL FIELD [0002] The present disclosure generally relates to optical devices, and more particularly to coupling optical devices. BACKGROUND [0003] A photonic device can comprise waveguides that direct light. A first waveguide can couple light into a second waveguide, however optical loss can occur that can lower the performance of various photonic designs. Further, for some applications, such as high-performance quantum optics- based communications and quantum logic devices, optical loss of coupled transitions (e.g., between optical devices) can cause failure of the device to operate (e.g., due to information loss, error rates). As an example, one source of loss can arise from coupling light into a chip (e.g., from one or more fibers, from another chip). BRIEF DESCRIPTION OF THE DRAWINGS [0004] The following description includes discussion of figures having illustrations given by way of example of implementations of embodiments of the disclosure. The drawings should be understood by way of example, and not by way of limitation. As used herein, references to one or more "embodiments" are to be understood as describing a particular feature, structure, or characteristic included in at least one implementation of the inventive subject matter. Thus, phrases such as "in one embodiment" or "in an alternate embodiment" appearing herein describe various embodiments and implementations of the inventive subject matter, and do not necessarily Ref. No. PSIQ-523WO / 6224.011WO1 all refer to the same embodiment. However, they are also not necessarily mutually exclusive. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure ("FIG. ") number in which that element or act is first introduced. [0005] FIG. 1A illustrates a quantum information processing system, in accordance with some example embodiments. [0006] FIG. 1B shows example photonic embodiment of the quantum information processing system, in accordance with some example embodiments. [0007] FIG. 2 shows a photonic processing architecture of a photonic switch-based information processing system, in accordance with some example embodiments. [0008] FIG. 3 shows an example source architecture, in accordance with some example embodiments. [0009] FIG. 4 shows an example of a single photon source photonic integrated circuit, in accordance with some example embodiments. [0010] FIG. 5 shows example fabrication stack architecture, in accordance with some example embodiments. [0011] FIG. 6 shows an example supermode tilt-compensated optical coupler structure, in accordance with some example embodiments. [0012] FIG. 7 shows a cross section view of the plurality of waveguides, in accordance with some example embodiments. [0013] FIG. 8 shows a top-down view of a first photonic integrated circuit (PIC) that is placed upon the second PIC, in accordance with some example embodiments. [0014] FIG. 9 is a flowchart of an example process for implementing low loss coupling between pics having tilted arrays of waveguides for coupling, in accordance with some example embodiments. [0015] FIG. 10 shows an example interposer embodiment, in accordance with some example embodiments. [0016] Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential Ref. No. PSIQ-523WO / 6224.011WO1 embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the disclosure is provided below, followed by a more detailed description with reference to the drawings. DETAILED DESCRIPTION [0017] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide an understanding of various embodiments of the inventive subject matter. It will be evident, however, to those skilled in the art, that embodiments of the inventive subject matter may be practiced without these specific details. In general, well-known instruction instances, structures, and techniques are not necessarily shown in detail. [0018] A multi-waveguide interconnect can be implemented to efficiently optically couple light (e.g., bright light, classical light, quantum light, single photons) between photonic integrated circuits (PICs) using vertically offset waveguides. In some example embodiments, each PIC includes multiple layers of waveguides (e.g., upper layer, middle layer, lower layer) that end at different distances away from a side or edge of the PIC, thereby creating a tilt arrangement in the same direction. Light can tilt from down and propagate to another device (e.g., another PIC, an optical interposer), which has another set of multiple waveguides having a corresponding tilt to receive the light. Further, in some embodiments, a lower set of multiple waveguides can propagate light upwards from its multi-waveguide tilt arrangement to another PIC that has a corresponding set of waveguides having a corresponding tilt arrangement to receive the light. [0019] FIG. 1A illustrates a quantum information processing system 100, in accordance with some embodiments. In the illustrated example, the quantum information processing system 100 includes a classical processing system 105 (CPS) that is connected (e.g., electrically, optically) to a quantum object processing system 140 over a classical channel 135 (e.g., a plurality of classical channels, electrical connections, optical fibers, free space optics). The classical channel 135 may relay classical information between the classical processing system 105 and quantum object processing system 140. Ref. No. PSIQ-523WO / 6224.011WO1 [0020] In some embodiments, the classical processing system 105 comprises memory 115 (e.g., one or more non-transitory computer-readable memory media storing instructions that can be executed by a processor), a processor 110 (e.g., central processing unit (CPU), processing core, physical processor, virtualized processor), a power supply, an input/output (I/O) subsystem, and a communication bus interconnecting these components. The processor 110 may execute modules, programs, and/or instructions stored in memory 115 and thereby perform processing operations. The processor may comprise a dedicated processor, or it may be a field programmable gate arrays (FPGA), an application specific integrated circuit (ASIC), or a "system on a chip" that includes classical processors and memory, among other possibilities. In some embodiments, the memory 115 stores one or more programs (e.g., sets of instructions) and/or data structures and is coupled to the processor(s). [0021] Further, in some embodiments, the classical processing system 105 comprises an encoder 120 that can receive user code and/or data, (e.g., quantum application data) and encode the received data into quantum logical data, such as logical block network data for processing on the quantum object processing system 140. Further, in some embodiments, the classical processing system 105 comprises a decoder 125 that is configured to translate measurement outcome data to logical qubit data. [0022] In some example embodiments, the classical processing system 105 comprises a data pre-processor 130 to pre-process data from the encoder 120 for execution by the controller 145 in the quantum object processing system 140. In some example embodiments, the data pre-processor 130 is configured to perform data processing tasks for measurement system 150 (e.g., data formatting, cleaning, additional transformations) so that the decoder 125 can interpret the measurement data. For example, the data pre- processor 130 may perform one or more summation and modulus operations on the measurement data to format the measurement data to a format used by the decoder 125. [0023] In some example embodiments, the decoder 125 is configured to implement one or more quantum decoders (e.g., off the shelf or custom Ref. No. PSIQ-523WO / 6224.011WO1 decoders), such as Union Find or modular decoding. In some example embodiments, new decoders can be swapped to replace the decoder 125 and the data pre-processor 130 can be configured to format the measurement data from the quantum object processing system 140 to the native format of new decoder swapped in at decoder 125. [0024] The classical processing system 105 may be classical in the sense that it operates computer code represented as a plurality of classical bits that may take a value of 1 or 0. Programs may be written in the form of ordered lists of instructions and stored within the classical (e.g., digital) memory 115 and executed by the classical processor 110 (e.g., electrical digital processor) of the classical computer. The memory 115 is classical in the sense that it stores data and/or program instructions in a storage medium in the form of classical bits which have a single binary state (0 or 1) at a given point in time. The processor 110 may read instructions from the computer program in the memory 115 and/or write data into the memory 115, and the processor 110 may optionally receive input data from a source external to the classical processing system 105, such as from a user input device such as a mouse, keyboard, or any other input device. The processor 110 may execute program instructions that have been read from the memory 115 to perform computations on data read from the memory 115 and/or input from the quantum object processing system 140 and may additionally generate output from those instructions. The processor 110 may store the generated output back into the memory 115. [0025] The quantum object processing system 140 may include a controller 145, a measurement system 150, and a plurality of qubits 155. [0026] In some embodiments, the controller 145 can be configured to interface with the plurality of qubits 155 to control, direct and/or measure the qubits within the quantum circuit. The qubits 155 may be configured to evolve in time under the directed influence of the controller 145, and the measurement system 150 may at times perform quantum measurements on all or a subset of the qubits 155 to obtain quantum measurement results in the form of classical data bits (e.g., ones and zeros). Ref. No. PSIQ-523WO / 6224.011WO1 [0027] In some embodiments, the measurement system 150 comprises a plurality of measurement hardware, such as quantum hardware. The classical data from the measurement results may be intermediate results that inform behavior of the classical processing system 105 and/or the controller 145 during a quantum computation. The classical data from the measurement results may additionally include classical results of the quantum computation. The measurement results may be communicated to the classical processing system 105 and/or the controller 145. The classical processing system 105 may provide directions and/or instructions to the controller 145 and the measurement system 150 to guide the behavior of the qubits 155 to perform a quantum computation. For example, the classical processing system 105 may provide classical data signals used for quantum state preparation within the quantum object processing system 140. In response to receiving the classical data signals, the quantum object processing system 140 such as the controller 145, may prepare the states of the qubits 155 into a desired initial state for a particular quantum computation. [0028] In some embodiments, qubits 155 (e.g., physical qubits) are provided to the measurement system 150 and controller 145. In some embodiments, the measurement system 150 and the controller 145 function as a logical qubit encoder that together perform a sequence of measurements on the qubits 155 to produce a logical qubit (e.g., a logical qubit prepared in a magic state, or another type of fault-tolerant encoded logical qubit). For example, the measurement system 150 and controller 145 may perform a sequence of measurements on the qubits 155 to entangle them in such a way as to produce a logical qubit. Encoding the logical qubit will also produce syndrome graph data for the logical qubit as classical information, which is output to the classical processing system 105 via the classical channel 135. [0029] FIG. 1B shows an example photonic quantum information processing system 190, which is an example of the quantum information processing system 100, in accordance with some example embodiments. The photonic quantum information processing system 190 can be used to generate qubits (e.g., photons) in an entangled state (e.g., a 3-GHZ state, 4- GHZ state, Bell pair state, and the like), in accordance with some embodiments. In an illustrative photonic architecture, photonic quantum Ref. No. PSIQ-523WO / 6224.011WO1 information processing system 190 includes a photon source module 165 that is optically connected to entangled state generator 170. Both the photon source module 165 and the entangled state generator 170 may be coupled to the classical processing system 105, as discussed above with reference to FIG. 1A. [0030] In some example embodiments, photon source module 165 comprises a collection of single-photon sources that can generate photons that are coupled to the entangled state generator 170 by way of interconnecting waveguides 175. [0031] The entangled state generator 170 may receive the output photons, convert them to one or more entangled photonic states, and then output these entangled photonic states into output waveguides 185. In some example embodiments, the output waveguides 185 can be coupled to one or more downstream (quantum? photonic? integrated?) circuits that use the entangled states for performing quantum information processing. [0032] In some embodiments, the photonic quantum information processing system 190 may include classical channels 160 (e.g., classical channels 160A through 160D) for interconnecting and providing classical information between components. It is noted that classical channels 160A through 160D need not all be the same. For example, classical channel 160A through 160D may comprise a bi-directional communication bus carrying one or more reference signals, e.g., one or more clock signals, one or more control signals, or any other signal that carries classical information, e.g., heralding signals, photon detector readout signals, and the like. [0033] In some example embodiments, the photonic quantum information processing system 190 includes the classical processing system 105 that communicates with and/or controls the photon source module 165 and/or the entangled state generator 170. For example, in some embodiments, classical processing system 105 can be used to configure one or more circuits, e.g., using system clock that may be provided to the photon source module 165 and the entangled state generator 170, as well as any downstream quantum photonic circuits used for performing quantum information processing. In some embodiments, the quantum photonic circuits can include optical Ref. No. PSIQ-523WO / 6224.011WO1 circuits, electrical circuits, or any other types of circuits. As discussed above, in some example embodiments, the classical processing system 105 includes memory 115, one or more processor(s) 110, a power supply, an input/output (I/O) subsystem, and a communication bus for interconnection. The processor(s) 110 may execute modules, programs, and/or instructions stored in memory 115 and thereby perform processing operations. [0034] In some embodiments, memory 115 stores one or more programs (e.g., sets of instructions) and/or data structures. For example, in some embodiments, entangled state generator 170 can attempt to produce an entangled state over successive stages, any one of which may be successful in producing an entangled state. In some embodiments, memory 115 stores control instructions to determine whether a respective stage was successful and to configure the entangled state generator 170 accordingly (e.g., by configuring entangled state generator 170 to switch the photons to an output if the stage was successful or pass the photons to the next stage of the entangled state generator 170 if the stage was not yet successful). To that end, in some embodiments, memory 115 stores detection patterns (described below) from which the classical processing system 105 may determine whether a stage was successful. In addition, memory 115 can store settings that are provided to the various configurable components (e.g., switches) described herein that are configured by, e.g., setting one or more phase shifts for the component. [0035] In some embodiments, some or all of the above-described functions may be implemented with electrical circuitry included in photon source module 165 and/or entangled state generator 170. In some embodiments, photon source module 165 includes one or more controllers 180A (e.g., logic controllers) (e.g., which may comprise field programmable gate arrays (FPGAs), application specific integrated circuits (ASICS), a "system on a chip" that includes classical processors and memory, or the like). In some embodiments, controller 180A determines whether photon source module 165 was successful (e.g., for a given attempt on a given clock cycle, described below) and outputs a reference signal indicating whether photon source module 165 was successful. For example, in some embodiments, controller 180A outputs a logical high value to classical channel 160A Ref. No. PSIQ-523WO / 6224.011WO1 and/or classical channel 160C when photon source module 165 is successful and outputs a logical low value to classical channel 160A and/or classical channel 160C when photon source module 165 is not successful. In some embodiments, the output of control 180A may be used to configure hardware in controller 180B. [0036] Similarly, in some embodiments, entangled state generator 170 includes one or more controllers 180B (e.g., logical controllers) (e.g., which may comprise field programmable gate arrays (FPGAs), application specific integrated circuits (ASICS), or the like) that determine whether a respective stage of entangled state generator 170 has succeeded, perform the switching logic described above, and output a reference signal to classical channels 160B and/or 160D to inform other components as to whether the entangled state generator 170 has succeeded. [0037] In some embodiments, a system clock signal can be provided to photon source module 165 and entangled state generator 170 via an external source (not shown) or by classical processing system 105 generates via classical channels 160A and/or 160B. In some embodiments, the system clock signal provided to photon source module 165 triggers the photon source module 165 to attempt to output one photon per waveguide. In some embodiments, the system clock signal provided to entangled state generator 170 triggers, or gates, sets of detectors in entangled state generator 170 to attempt to detect photons. For example, in some embodiments, triggering a set of detectors in entangled state generator 170 to attempt to detect photons includes gating the set of detectors. [0038] It should be noted that, in some embodiments, photon source module 165 and entangled state generator 170 may have internal clocks. For example, photon source module 165 may have an internal clock generated and/or used by controller 180A and entangled state generator 170 has an internal clock generated and/or used by controller 180B. In some embodiments, the internal clock of photon source module 165 and/or entangled state generator 170 is synchronized to an external clock (e.g., the system clock provided by classical processing system 105) (e.g., through a phase-locked loop). In some embodiments, any of the internal clocks may Ref. No. PSIQ-523WO / 6224.011WO1 themselves be used as the system clock, e.g., an internal clock of the photon source may be distributed to other components in the system and used as the system clock. [0039] In some embodiments, photon source module 165 includes a plurality of probabilistic photon sources that may be spatially and/or temporally multiplexed (e.g., multiplexed single photon source). In one example, the probabilistic photon source is driven by a pump, e.g., a light pulse, which is coupled into an optical resonator which, through a nonlinear optical process (e.g., spontaneous four wave mixing, second harmonic generation, and the like) may generate zero, one, or more photons. As used herein, the term "attempt" is used to refer to the application of an optical drive signal to a photon source at a power, duration, etc., that can reach the regime of the nonlinear optical process of the optical resonator. In particular, the photon source may produce output photons non-deterministically (e.g., in response to the driving signal, the probability that the photon source will generate one or more photons may be less than 1). In some embodiments, a respective photon source may have a highest probability to produce zero photons on a respective attempt (e.g., there may be a 90% probability of producing zero photons per attempt to produce a single photon). The second most probable result for an attempt may be production of a single-photon (e.g., there may be a 9% probability of producing a single-photon per attempt to produce a single-photon). The third most probable result for an attempt may be production of two photons (e.g., there may be an approximately 1% probability of producing two photons per attempt to produce a single photon). In some circumstances, there may be less than a 1% probability of producing more than two photons. [0040] In some embodiments, the apparent efficiency of the photon sources may be increased by using a plurality of single-photon sources and multiplexing the outputs of the plurality of photon sources. The precise type of photon source used is not critical and any type of source can be used, employing any photon generating process, such as spontaneous four wave mixing (SPFW), spontaneous parametric down-conversion (SPDC), or any other process. Other classes of sources that do not necessarily require a nonlinear material can also be employed, such as those that employ atomic Ref. No. PSIQ-523WO / 6224.011WO1 and/or artificial atomic systems, e.g., quantum dot sources, color centers in crystals, and the like. In some cases, sources may or may not be coupled to photonic cavities, e.g., as can be the case for artificial atomic systems such as quantum dots coupled to photonic crystal cavities, micropillar cavities, etc. Other types of photon sources also exist for SPWM and SPDC, such as optomechanical systems and the like. In some examples, the photon sources can emit multiple photons already in an entangled state. The entangled state generator 170 can therefore receive the multiple photons already entangled and can output a larger entangled state. In some examples, with multiple photons already entangled, the entangled state generator 170 can be bypassed or omitted from photonic quantum information processing system 190. [0041] For the sake of illustration, an example which employs spatial multiplexing of several non-deterministic is described as an example of a multiplexed (mux) photon source. However, many different spatial mux architectures are possible without departing from the scope of the present disclosure. Temporal muxing can also be implemented instead of or in combination with spatial multiplexing. Mux schemes that employ log-tree, generalized Mach-Zehnder interferometers, multimode interferometers, chained sources, chained sources with dump-the-pump schemes, asymmetric multi-crystal single photon sources, or any other type of mux architecture can be used. In some embodiments, the photon source module 165 can employ a mux scheme with quantum feedback control and the like. [0042] The foregoing description provides an example of how photonic circuits can be used to implement physical qubits and operations on physical qubits using mode coupling between waveguides. In these examples, a pair of waveguide modes can be used to represent each physical qubit. Examples described below can be implemented using similar photonic circuit elements. [0043] FIG. 2 shows a photonic processing architecture 200 of a photonic switch-based information processing system, according to some example embodiments. In the example of FIG. 2, the photonic processing architecture 200 is configured as a spatial multiplexing architecture, although it is appreciated that in other example embodiments the photonic architecture can Ref. No. PSIQ-523WO / 6224.011WO1 be configured for time-based multiplexing which can implement time-binned entanglement using switches (e.g., GMZIs). [0044] In the example of FIG. 2, a plurality optical sources 205 comprise a set of probabilistic optical sources that generate single photons probabilistically (e.g., spontaneous parametric down conversion, four wave mixing, quantum dot generated single photons). In some example embodiments, the plurality optical sources 205 generate respective pairs of photons. One or more photons in the respective pairs can be detected (e.g., as herald photons), and the resulting detection signal can be used to indicate that a successful entangle-able photon has been transmitted from the plurality of optical sources 205 towards the switch network 210. In some example embodiments, the detection of heralded photons can generate electronic data bits indicating that the source succeeded or failed ("source success or fail") in generating an entangle-able photon. The data bits are electronically input into the switch network 210. The switch network 210 is configured to route (e.g., using optical switch 212) groups of the enable-able photons 215 to a photonic entanglement circuit 220 for entanglement. [0045] The photonic entanglement circuit 220 receives the entangle-able photons and generates entanglement groups 222 (e.g., photonic resource states comprising three or more entangled photons). In some example embodiments, like the plurality of optical sources 205, the photonic entanglement circuit 220 functions probabilistically and successful generation of entangled groups 222 occurs infrequently. In some example embodiments, the photonic entanglement circuit 220 implements one or more optical detections of photons in the photonic entanglement circuit 220 to generate circuit success or fail data that indicates whether a successful entanglement of a group has occurred and further indicates the location of the entangled portions of a given entanglement group 222. The circuit success or fail data is electronically communicated to a second switch network 225 for further routing. [0046] In some example embodiments, the second switch network 225 performs further entanglement operations by merging the entanglement groups 222 without detection or otherwise decoherence, such that the switch Ref. No. PSIQ-523WO / 6224.011WO1 network outputs one or more entanglement groups 230 (e.g., groups of entangled qubits, 4-GHZ state) for further non-classical optical processing (e.g., quantum communication, quantum experimentation of quantum states, quantum computing). In some example embodiments, the switch network 210, the photonic entanglement circuit 220, and the second switch network 225 implement optical switches, such as optical switch 212, to perform both routing and production of photonic entanglements. In some example embodiments, the optical switch 212 comprises a generalized Mach-Zehnder interferometer, as discussed in further detail below. [0047] In some example embodiments, a Mach Zehnder interferometer comprises a being splitter that divides an input light into 2 equal parts which travel on different paths and then combined back together again on a 2nd being splitter. The path length can be adjusted between the 2 arms can be adjusted such that the phase difference of classical light input into the Mach Zehnder interferometer can cause all of the light to be output from a single output port. In some example embodiments, the path links of the different arms are not adjusted but rather physical characteristics of one or more of the arms are modified to implement phase shifts of light traversing the given arm, thereby enabling the direction of the input light to a single output port were both output ports. When classical or “bright light” is input into a given Mach-Zehnder interferometer the device can function as a splitter or guide that guides the classical light towards one or more of the output ports. Interestingly, when non-classical light (e.g., single photons, quantum light) is input into an MZI, the photon is split and propagates as a super position of being in each arm at the same time as a propagates through the device. As an example, if the MZI is in a 50/50 splitter configuration (e.g., via path length or active phase adjustments), the super position of the single photon of quantum light is recombined at the second splitter and there is a 50/50 chance of emerging from either output port. Thus, the MZI can function as a classical and non-classical (e.g., quantum) photonic device. [0048] FIG. 3 shows an example architecture 350, in accordance with some example embodiments. The source architecture 350 is an example time-bin switch architecture for increasing a probability of photon generation using non-deterministic sources (e.g., the plurality of optical sources 205, FIG. 2) Ref. No. PSIQ-523WO / 6224.011WO1 and a switch network 370 (e.g., the first switch network 210, FIG. 2, one or more GMZIs). [0049] One technique to improve the probability of simultaneously obtaining photons from each of a set of non-deterministic photon sources involves spatial multiplexing of multiple photon sources. The source architecture 350 is configured as a N×1 (or N-to-1) multiplexing circuit having a plurality of optical sources (e.g., plurality of optical sources 205). In the example of FIG. 3, the source architecture 350 includes a set of N photon sources 353-1 through 353-N are shown, Each photon source 353-1 through 353-N has an associated detector in detectors 354-1 to 354-N and an associated signaling waveguide in signaling waveguides 373-1 to 373-N. [0050] In some example embodiments, a respective photon source can be a distinct physical device that can produce a photon pair in response to a pump pulse (e.g., laser pump pulse). For instance, a respective photon source can be a heralded single photon source as described above. Photon sources 353-1 through 353-N can be pumped, and each respective instance of the photon sources 353-1 through 353-N can define a time bin (or temporal mode). For each time bin, the respective photon source has a respective probability to generate a photon pair. [0051] In some example embodiments, in any time bin where a given photon source does produce a photon pair, one photon propagates through the associated signaling waveguide while the other photon is detected by the associated detector. [0052] P1 through P5 show different time bins represented as a time series right-to-left (e.g., P1 happens before P2, etc.), occurring for each photon source as indicated by the vertical dashed line for each time bin passing through the associated signaling waveguides 373-1 through 373-N. As shown in FIG. 3, dots 356a through 356f indicate photons that are probabilistically generated at respective time bins P1-P5. As a particular example, dot 356a can indicate that photon source 353-1 successfully generated a photon during time bin P1. Similarly, dot 356c can indicate that photon source 353-3 successfully generated a photon during time bin P2. Ref. No. PSIQ-523WO / 6224.011WO1 FIG. 3 can be regarded as an overview of the source architecture 350, wherein photons produced during respective time bins appear at different locations along the waveguides 373-1 through 373-N. [0053] In some example embodiments, the waveguides 373-1 through 373- N are input to a switch network 370, which receives the time-binned photons. In some example embodiments, the switch network 370 is implemented as a N×1 multiplexer (or “mux”) that operates as an active optical switching circuit. The switch network 370 can be an active optical switching circuit in that the switch network 370 can selectively couple one of waveguides 373-1 to 373-N to an output waveguide 386. In some example embodiments, selectable optical coupling can be provided using active optical switches or other active optical components that can be controlled to either allow or block propagation of photons. [0054] For example, a N×1 mux in the switch network 370 can be implemented as an N×1 generalized Mach-Zehnder interferometer (GMZI). In some example embodiments, an N×M (or N-to-M) GMZI is an optical circuit that can receive photons on a set of N input waveguides and can control a set of active phase shifters to selectively couple M of the received photons to a set of M output waveguides (where M is less than or equal to N). In some example embodiments, one or more of the phase shifters may be passive fixed phase shifters for preconfigured phase shifts. In the example of FIG. 3, the switch network 370 is configured as a M=1 multiplexer that has one output. [0055] In some example embodiments, the N×1 mux of the switch network 370 can be controlled by control logic 380 (e.g., controllers), which can be implemented using any suitable electronic logic circuit. In some example embodiments, control logic 380 can receive signals from respective detectors 354-1 to 354-N that indicate, for each time bin P1 through P5, whether a photon was or was not detected by each detector 354-1 to 354-N. Accordingly, control logic 380 can determine which of photon sources 353-1 through 353-N generated photons during a given time bin P1 through P5. Similarly, control logic 380 can therefore determine which of the input Ref. No. PSIQ-523WO / 6224.011WO1 waveguides 373-1 to 373-N are carrying photons for the given time bin P1 through P5. [0056] Control logic 380 can control the switch network 370 to couple one respective waveguide that carries a photon in a given time bin to output waveguide 386. As a particular example, control logic 380 can control the switch network 370 to couple waveguide 373-3 to output waveguide 386 during a time period corresponding to time bin P2 in order for a photon (represented by dot 356c) to be provided to output waveguide 386. [0057] The switch network 370 can, for example, comprise a GMZI that includes a set of active phase shifters that can be controlled to apply variable phase shifts along different optical paths, creating either constructive or destructive interference. In order to configure the desired coupling, control logic 380 can generate control signals which set the state of each active phase shifter in a GMZI implementing N×1 mux. [0058] In some example embodiments, the time bin can have any suitable duration. For example, the duration of a respective time bin can be based on characteristics of an optical circuit, can account for variability in the timing of generating photons in the photon sources 353, and so on. An interval duration between time bins can be determined to allow each time bin to be treated as an independent temporal mode. In some instances, an interval duration between time bins may be determined based on the speed at which N×1 mux operations in the switch network 370 can be switched, on a recovery time for photon sources 353-1 through 353-N and/or detectors 354- 1 through 354-N, the operating speed of electronic or photonic circuits downstream of the switch network 370, or other design considerations. [0059] As noted above, the behavior of photon sources 353 may be non- deterministic. That is, during a given time bin, the probability of a photon being generated by a given photon source can be represented as _s, where s<1. For such non-deterministic photon sources, multiplexing as shown in FIG. 3 increases the probability of successfully producing a photon in a given time bin. As shown in FIG. 3, the probability that the switch network m_{ux=1-(1- s)} ^N when N non-deterministic single-photon sources are used, with one photon source Ref. No. PSIQ-523WO / 6224.011WO1 coupled to each input of the switch network 370, where each photon source has a probability s of generating a photon for the given time bin. [0060] Thus, for a given type of photon source, a desired probability mux of providing one photon per time bin to output waveguide 386 can, at least in principle, be achieved by a suitable choice of N. [0061] FIG. 4 shows an example of a single photon source photonic integrated circuit 490, in accordance with some example embodiments. The embodiment of FIG. 4 is an example of a photonic chip that can implement the fabrication stack of FIG. 5 discussed below. As illustrated in FIG. 4, the photonic integrated circuit 490 comprises a photon source array 491 that generates photons non-deterministically. In some example embodiments, each photon source in the photon source array 491 comprises a ring resonator and an MZI, where an upper portion of the ring resonator functions as the lower arm of the MZI. In some example embodiments, each photon source in the photon source array 491 receives pump light from the input ports 400 (e.g., input waveguides) and implements one or more single photon source schemes (e.g., spontaneous four wave mixing, spontaneous parametric down conversion) to probabilistically generate single photons. In some example embodiments, each photon source in the photon source array 491 comprises a single input port and a single output port that is coupled to a filter. [0062] Each photon source outputs the pump light and one or more photon pairs into a filter array 492 for filtering. In some example embodiments, each filter in the filter array 492 comprises an optical pump rejection filter to filter out pump light such that only photon pairs (e.g., generated at the photon source array 491) are output from the filter array 492. In some example embodiments, one of the photons (e.g., signal photon) from one or more of the filters impinges on a herald detector of a plurality of herald detectors 499 to indicate that its counterpart photon (e.g., idler photon) exists and is propagating towards the switch 493. As discussed in further detail below, the switch 493 can include a first optical coupler network 494 (e.g., optical Hadamard network, beam splitter arrangement) that separates the quantum light onto a plurality of waveguide arms and a second optical Ref. No. PSIQ-523WO / 6224.011WO1 coupler network 496 that combines the quantum light in such a way (e.g., via interference) that the quantum light is output from a single output waveguide 498. In some example embodiments, the switch 493 comprises phase shifters 495 (e.g., heaters, BTO-based devices) that can change the phase of the light on one or more of the given arms to implement a N-to-1 permutations to output single photons 497 as a single-photon multiplexed source, as discussed in further detail below. [0063] FIG. 5 illustrates an example fabrication stack of a PIC wafer 500 including various photonic integrated circuit components according to certain embodiments. In the illustrated example, PIC wafer 500 includes a substrate 502, a cladding layer 504 and cladding layer 505 (e.g., BOX), a temperature sensor 506, a grating coupler 508, a ridge waveguide 510, a heater 512, a Ge photodiode 514, one or more layers of SiN waveguides 515 and 516, one or more super conducting nanowire single photon detectors (SNSPDs) 518 (e.g., a herald detector 354 in FIG. 3), SNSPD contact regions 520, and the like. [0064] As described above, the silicon-based circuit components, such as grating coupler 508, a ridge waveguide 510, temperature sensor 506, and the like, may be formed in an SOI layer deposited on cladding layer 504. SiN waveguides 515 and 516 may have different thicknesses and different losses and may be used to form various active and passive photonic integrated circuit components, such as delay lines, phase shifters, ring oscillator, interferometers, switches, filters, single photon detectors, couplers, and the like. SiN waveguides 515 and 516 may receive light from an optical fiber through edge coupling or grating coupler 508. [0065] Heater 512 may include, for example, a silicide layer (such as a nickel silicide layer), a nitride layer (e.g., TiN or NbN), or another resistive material layer, and may be used to tune silicon waveguides. The silicide layer may also be formed in other regions, such as on top of a silicon material region in the SOI layer below SNSPD 518, to form part of a scatter mitigation structure. The wafer with these devices and structures may be bonded with a wafer with phase shifters 522 (e.g., electro-optical material) for switches formed thereon. The substrate of the wafer with phase shifters Ref. No. PSIQ-523WO / 6224.011WO1 522 may subsequently be removed and the active layer of phase shifters 522 may be patterned by selective etching, in accordance with some example embodiments. [0066] Electrical contacts 524 (e.g., through-oxide vias) may be formed in the oxide layers to make electrical connections to the various devices, such as heater 512, Ge photodiode 514, SNSPDs 518, phase shifters 522, and the like. As illustrated in the example, electrical contacts 524 may include metal trenches surrounding SNSPDs 518 to form scatter mitigation structures for blocking stray light as described above. [0067] As also illustrated in FIG. 5, thermal trenches 526 and undercut regions 528 may be formed in the oxide layers and substrate 502 respectively. Additionally, or alternatively, thermal isolation trenches 530 and undercut region 532 may be formed by, for example, etching trenches in the oxide layers to expose certain regions of the SOI layer, and then selectively etching the SOI layer to remove the silicon and form an undercut region. In some embodiments, other structures, such as metal trenches 534 may be formed in the oxide layers and the substrate. [0068] After these structures are manufactured, PIC wafer 500 may be processed using the (BELO) processes to form one or more metal layers 536 and vias 538 (e.g., metal plugs or metal trenches). Some vias 538 may be aligned with some electrical contacts 524 to form the scatter mitigation structures for SNSPDs 518. In some embodiments, a trench 540 aligned with grating coupler 508 may be etched in the oxide layer to facilitate the coupling of light into the waveguides. For example, an optical fiber may be inserted into trench 540 or positioned on trench 540 to send light to grating coupler 508. [0069] As illustrated in FIG. 5, one or more etch stop layers 542 (e.g., SiCN layers) may be used as needed for etching and patterning the metal layers and other structures. The SiCN layers may also be passivation layers for the metal (e.g., copper) in the metal layers. Contact pads 550 may be formed on the top metal layer (bottom layer shown in FIG. 5) of PIC wafer 500. In the illustrated example, trenches 560 may be etched to from bonding balls (not shown in FIG. 5) for bonding contact pads 550 with an EIC wafer. Ref. No. PSIQ-523WO / 6224.011WO1 [0070] PIC wafer 500 shown in FIG. 5 includes various passive and active photonic components in a same wafer stack, such as silicon waveguides, SiN waveguides that form parts of other passive or active photonic components (e.g., splitters, filters, delay lines, phase shifters, and single photon sources), grating couplers, Ge photodetectors, single photon detectors, low power BTO-based phase shifters/switches, temperature sensors, heaters, and the like. Thus, PIC wafer 500 may be used to perform various functions for optical quantum computing, such as single photon generation, photon entanglement, fusion, qubit storage, resource state generation, single-photon and multi-photon measurement, data communication, and the like. [0071] PIC wafer 500 also includes thermal isolation structures (e.g., undercut regions 528 and trenches 526) for thermally isolating, for example, the heaters from other components. Undercut regions 528 can be formed in a large region in substrate 502 to thermally isolate components in a large region. Undercut regions (e.g., undercut region 532) may additionally or alternatively be formed in an SOI layer. PIC wafer 500 further includes scattered light mitigation structures formed by metal layers, a silicide layer, and through-oxide vias or trenches, to isolate, for example, the single photon detectors from stray light. [0072] FIG. 6 shows an example supermode tilt-compensated optical coupler structure 600, in accordance with some example embodiments. In the illustrated example of FIG. 6, a first photonic integrated circuit (PIC) 610 is connected to a second PIC 615. In some example embodiments, the first PIC 610 is connected to the second PIC 615 directly (e.g., using heat and pressure, using direct bonding; without adhesive or a bonding layer;). For example, the PICs can be bonded using direct bonding (e.g., fusion bonding), wherein the respective bonding surfaces of the PICs are cleaned and highly polished such that when the two bonding surfaces are brought near one another intermolecular actions (e.g., van der Waals force) attracts and bonds the surfaces together. In other example embodiments, an adhesive layer is used to bond the first PIC 610 to the second PIC 615. [0073] In the example of FIG. 6, light 605 is coupled from the first PIC 610 to the second PIC 615 using a first plurality of the waveguides 655 that are Ref. No. PSIQ-523WO / 6224.011WO1 coupled to a second plurality of waveguides 660. In the illustrated example, the light 605 is propagating from left to right along a propagation axis, such as the X axis as depicted in FIG. 6. However, one of ordinary skill in the art appreciates that the propagation direction can occur from right to left along the propagation axis (e.g., X axis); for example, where the light is coupled from the second PIC 615 to the first PIC 610 (e.g., from the second plurality of the waveguides 660 to the first plurality of waveguides 655). [0074] As illustrated in FIG. 6, the first plurality of waveguides 655 comprises multiple levels of waveguides that are vertically offset from one another (e.g., in the Y direction), including a first waveguide layer 640A, a second waveguide layer 640B, and a third waveguide layer 640C. In some example embodiments, to guide light being coupled between the photonic integrated circuits away from their propagation direction, the first plurality of waveguides 655 are structured in a tilt arrangement. In effect, such a structured arrangement can tilt the super mode of the light 605 propagating in the first PIC 610 downwards (from the perspective of FIG. 6) towards the second PIC 615. [0075] In particular, for example, with reference to the first plurality of waveguides 655, a tilt arrangement 630 is formed from a first waveguide in the first waveguide layer 640A extending farther than a second waveguide in the second waveguide layer 640B. The tilt arrangement 630 is further formed by the second waveguide of the second waveguide layer 640B extending farther than a third waveguide in a third waveguide layer 640C. [0076] In the illustrated example embodiment of FIG. 6, the second plurality of waveguides 660 are arranged in a corresponding tilt arrangement 635 that corresponds or otherwise matches an angle of the tilt arrangement 630. In particular, for example, a lower most waveguide in waveguide layer 645A extends farther than the waveguide in layer 645B, which extends farther than a waveguide in another waveguide layer 645C. [0077] In this way, an aggregate or super mode of the light 605 propagates along the first plurality of waveguide 655 and bends downward (e.g., propagates or refracts through material of the first PIC 610) through a first port 620 to couple into the second PIC 615 via a second port 625 (e.g., Ref. No. PSIQ-523WO / 6224.011WO1 propagates or refracts through material of the second PIC 615). This downward bending of the optical mode enables a greater vertical separation (e.g., along the Y-axis, as shown in FIG. 6) between the first plurality of waveguides 655 and the second plurality of waveguides 660 than would otherwise be available. Although ports are illustrated in figures, it is appreciated in some example embodiments a “port” can refer to an area of material of a given PIC at the interface of the PIC (e.g., bottom side). For example, light can shine through the material of the area of port 620, propagate through a low loss interface between first PIC 610 and second PIC 615 (e.g., direct bonded, bonded with thin layer of adhesive), and through the material of the area of port 620. Further, in some example embodiments, the ports may comprise optical components such as grating couplers to couple the light form one PIC to another (e.g., port 620 comprises a first grating coupler, port 625 comprises a second grating coupler). [0078] Continuing, the downward bending from the corresponding waveguide tilt arrangement 630 tilts the light towards ports 620 and 625 and away from the direction the light would otherwise continue propagating. For instance, without the tilt arrangement, much of the light 605 would continue to propagate straight (along the X axis) to an edge 650 of the first PIC 610 (e.g., causing loss, scattering out of the edge 650). [0079] Further, due to the downward bending optical mode from the corresponding tilted arrangement, the light more rapidly, x distance wise, is guided from the first PIC 610 to the second PIC 615 using less propagation or coupling distance, thereby enabling the edge to be placed nearer to the PIC to interposer coupling region, and further enabling other components to be placed on the interposer near the edge (e.g., as shown FIG. 10 and discussed in further detail below). [0080] FIG. 7 shows a cross section view of the plurality of waveguides 655, in accordance with some example embodiments. In the illustrated perspective of FIG. 7, the viewer is looking down the axis of propagation of light (e.g., the X-axis depicted in FIG. 6 is in and out of the page). An example of a supermode 700 is shown propagating through the plurality of Ref. No. PSIQ-523WO / 6224.011WO1 waveguides 655. The illustrated example of supermode 700 can extend through multiple levels of waveguides. [0081] As illustrated, the plurality of waveguides 655 comprises the first waveguide layer 640A having a plurality of first level waveguides, a second waveguide layer 640B comprising a plurality of second level waveguides, and a third waveguide layer 640C comprising a plurality of third level waveguides. In some example embodiments, as discussed above, the plurality of first level waveguides extends farther along the propagation axis than both the plurality of second level waveguides and the plurality of third level waveguides. Similarly, the plurality of second level waveguides may extend farther along the propagation axis than the plurality of third level waveguides, thereby forming the tilt arrangement 630 shown in FIG. 6. [0082] As further illustrated in FIG. 7, in some example embodiments, each layer of waveguides is split into multiple waveguides. In some example embodiments, the first PIC 610 comprises a reasonable optical splitter (e.g., MZI coupler tree, GMZI) that can direct the light from one or more subsets of the rods to new rods to further guide the light “downwards” towards the second PIC. [0083] In some example embodiments, each layer of the waveguides is formed from a different PIC material. For example, the first waveguide layer 640A can be formed from active layer material (e.g., optically active via changing its refractive index via heat, or stress applied). Additionally, the second waveguide layer 640B and the third waveguide layer 640C may be formed respectively from different materials (e.g., silicon waveguide material, silicon nitride waveguide material). It is appreciated by one of ordinary skill or that the second plurality of waveguides 660 can be further formed from different materials, and also further controlled by a tunable splitter on the second PIC 615. [0084] FIG. 8 shows a top-down view of the first PIC 610 that is placed upon the second PIC 615, in accordance with some example embodiments. From the view of FIG. 8, a first plurality of waveguides 655 comprises an elevator region 805 in which a single layer of waveguides is coupled to other vertically offset layers (e.g., higher, or lower layers) using optical elevators. Ref. No. PSIQ-523WO / 6224.011WO1 Optical elevators are waveguides that have an increasingly narrow taper in a first layer to couple light to an increasingly widening taper in a vertically offset layer, as is appreciated by one of ordinary skill in the art. [0085] The first plurality of waveguides further comprises a tapering and combining region 810 where the multi-rods of the different waveguide layers are tapered outward (e.g., tapered up and down in the perspective of FIG. 8). In the tapering and combining region 810, the light bends "downward" (into the paper from the perspective of FIG. 8) to couple to the second plurality of waveguides 660 in the second PIC 615, which may further comprise elevator and tapering regions (e.g., an upper waveguide can be positioned over a lower waveguide to transmit light to different layers in the PIC; optionally, the waveguides can have tapers to assist in coupling between the waveguides in different layers). In some example embodiments, the light propagates in an enlarged fiber-like propagation region 815 from the first plurality of waveguides 655 to the second plurality of waveguides 660 in the second PIC 615 (interposer). [0086] FIG. 9 is a flowchart of an example process 900. In some implementations, one or more process blocks of Fig. 9 may be performed by a device. As shown in Fig. 9, process 900 may include propagating light in a first plurality of waveguides in a first photonic integrated circuit along a propagation direction, the first plurality of waveguides coupled to a first port of the first photonic integrated circuit, the first plurality of waveguides having a first upper layer of waveguides and a first lower layer of waveguides that are vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port of along the propagation direction than the first lower layer of waveguides (block 905). [0087] For example, device may propagate light in a first plurality of waveguides in a first photonic integrated circuit along a propagation direction, the first plurality of waveguides coupled to a first port of the first photonic integrated circuit, the first plurality of waveguides having a first upper layer of waveguides and a first lower layer of waveguides that are Ref. No. PSIQ-523WO / 6224.011WO1 vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port of along the propagation direction than the first lower layer of waveguides, as described above. [0088] As also shown in FIG. 9, process 900 may include coupling the light from the first photonic integrated circuit to a second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides having a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper layer of waveguides, the first tilt arrangement and the second tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit (block 910). [0089] For example, device may couple the light from the first photonic integrated circuit to a second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides having a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper layer of waveguides, the first tilt arrangement and the second Ref. No. PSIQ-523WO / 6224.011WO1 tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit, as described above. [0090] As further shown in FIG. 9, process 900 may include propagating the light in the second plurality of waveguides along the propagation direction (block 915). For example, device may propagate the light in the second plurality of waveguides along the propagation direction, as described above. [0091] Although FIG. 9 shows example blocks of process 900, in some implementations, process 900 may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in FIG. 9. Additionally, or alternatively, two or more of the blocks of process 900 may be performed in parallel. [0092] FIG. 10 shown example interposer embodiment 1000, in accordance with some example embodiments. As discussed above, in some example embodiments, the second PIC 615 is an optical interposer that couples light between different photonic integrated circuits such as the first PIC 610 and a third photonic integrated circuit 1005. As illustrated, and in accordance with some example embodiments, the third photonic integrated circuit 1005 and the second PIC 615 have similarly congruent plurality of waveguides having tilt arrangements that enable greater coupling between the two photonic circuits. Further illustrated in FIG. 10 is an additional component 1010 (e.g., PIC component, ASIC, ports, power control), which can be placed closer to the edge 650 of the first PIC 610 due to the shorted coupling distance implemented from coupling from the first PIC 610 and the second PIC 615. [0093] In view of the above-described implementations of subject matter this application discloses the following list of examples, wherein one feature of an example in isolation or more than one feature of an example, taken in combination and, optionally, in combination with one or more features of one or more further examples are further examples also falling within the disclosure of this application. Ref. No. PSIQ-523WO / 6224.011WO1 [0094] Described implementations of the subject matter can include one or more features, alone or in combination as illustrated below by way of example. [0095] Example 1: A method comprising: propagating light in a first plurality of waveguides in a first photonic integrated circuit along a propagation direction, the first plurality of waveguides coupled to a first port of the first photonic integrated circuit, the first plurality of waveguides comprising a first upper layer of waveguides and a first lower layer of waveguides that are vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port of along the propagation direction than the first lower layer of waveguides; coupling the light from the first photonic integrated circuit to a second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides comprising a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper layer of waveguides, the first tilt arrangement and the second tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit; and propagating the light in the second plurality of waveguides along the propagation direction. [0096] Example 2: The method of Example 1, wherein the first photonic integrated circuit is adjacent to the second photonic integrated circuit. [0097] Example 3: The method of Example 1 or Example 2, wherein the first port and the second port are adjacent to each other. Ref. No. PSIQ-523WO / 6224.011WO1 [0098] Example 4: The method of any one of Examples 1-3, wherein the first tilt arrangement and the second tilt arrangement couple the light away from a first edge of the first photonic integrated circuit. [0099] Example 5: The method of any one of Examples 1-4, wherein the second photonic integrated circuit is connected to a third photonic integrated circuit that is positioned a distance away from the first photonic integrated circuit. [00100] Example 6: The method of any one of Examples 1-5, wherein coupling the light from the first photonic integrated circuit to the second photonic integrated circuit comprises: coupling the light from the first plurality of waveguides through first material of the first photonic integrated circuit to second material of the second photonic integrated circuit to the second plurality of waveguides. [00101] Example 7: The method of any one of Examples 1-6, wherein increased coupling from the first tilt arrangement and second tilt arrangement enables increased vertical distance between the first photonic integrated circuit and the second photonic integrated circuit. [00102] Example 8: The method of any one of Examples 1-7, wherein the light propagates in the first plurality of waveguides as a supermode that is spread amongst the first plurality of waveguides as the light propagates along the first plurality of waveguides. [00103] Example 9: The method of any one of Examples 1-8, wherein the light propagates in the second plurality of waveguides as the supermode that is further spread amongst the first plurality of waveguides as the light propagates along the second plurality of waveguides. [00104] Example 10: The method of any one of Examples 1-9, wherein the first photonic integrated circuit is connected on top of the second photonic integrated circuit, and the supermode tilts downwards out of the first port of first photonic integrated circuit towards the second port of the second photonic integrated circuit. [00105] Example 11: The method of any one of Examples 1-10, wherein the second photonic integrated circuit is an optical interposer that is optically coupled to a plurality of photonic integrated circuits that includes the first photonic integrated circuit. Ref. No. PSIQ-523WO / 6224.011WO1 [00106] Example 12: The method of any one of Examples 1-11, further comprising: coupling the light from the optical interposer to a third photonic integrated circuit. [00107] Example 13: The method of any one of Examples 1-12, wherein the third photonic integrated circuit comprises a third plurality of waveguides. [00108] Example 14: The method of any one of Examples 1-13, wherein the light comprises quantum light. [00109] Example 15: The method of any one of Examples 1-14, wherein the quantum light comprises single photons. [00110] Example 16: An apparatus comprising: a first photonic integrated circuit comprising a first plurality of waveguides that are coupled to a first port of the first photonic integrated circuit, the first photonic integrated circuit configured to propagate light in the first plurality of waveguides along a propagation direction, the first plurality of waveguides comprising a first upper layer of waveguides and a first lower layer of waveguides that are vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port of along the propagation direction than the first lower layer of waveguides; and a second photonic integrated circuit comprising a second plurality of waveguides that are coupled to a second port of the second photonic integrated circuit, the first port of the first photonic integrated circuit in the second port of the second photonic integrated circuit being configured to couple the light from the first photonic integrated circuit to the second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides comprising a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper Ref. No. PSIQ-523WO / 6224.011WO1 layer of waveguides, the first tilt arrangement and the second tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit. [00111] Example 17: The apparatus of Example 16, wherein the first photonic integrated circuit is adjacent to the second photonic integrated circuit. [00112] Example 18: The apparatus of Example 16 or Example 17, wherein the first port and the second port are adjacent to each other. [00113] Example 19: The apparatus of any one of Examples 16-18, wherein the first tilt arrangement and the second tilt arrangement couple the light away from a first edge of the first photonic integrated circuit. [00114] Example 20: The apparatus of any one of Examples 16-19, wherein the second photonic integrated circuit is connected to a third photonic integrated circuit that is positioned a distance away from the first photonic integrated circuit. [00115] Example 21: The apparatus of any one of Examples 16-20, wherein coupling the light from the first photonic integrated circuit to the second photonic integrated circuit comprises: coupling the light from the first plurality of waveguides through first material of the first photonic integrated circuit to second material of the second photonic integrated circuit to the second plurality of waveguides. [00116] Example 22: The apparatus of any one of Examples 16-21, wherein increased coupling from the first tilt arrangement and second tilt arrangement enables increased vertical distance between the first photonic integrated circuit and the second photonic integrated circuit. [00117] Example 23: The apparatus of any one of Examples 16-22, wherein the light propagates in the first plurality of waveguides as a supermode that is spread amongst the first plurality of waveguides as the light propagates along the first plurality of waveguides. [00118] Example 24: The apparatus of any one of Examples 16-23, wherein the light propagates in the second plurality of waveguides as the supermode Ref. No. PSIQ-523WO / 6224.011WO1 that is further spread amongst the first plurality of waveguides as the light propagates along the second plurality of waveguides. [00119] Example 25: The apparatus of any one of Examples 16-24, wherein the first photonic integrated circuit is connected on top of the second photonic integrated circuit, and the supermode tilts downwards out of the first port of first photonic integrated circuit towards the second port of the second photonic integrated circuit. [00120] Example 26: The apparatus of any one of Examples 16-25, wherein the second photonic integrated circuit is an optical interposer that is optically coupled to a plurality of photonic integrated circuits that includes the first photonic integrated circuit. [00121] Example 27: The apparatus of any one of Examples 16-26, wherein the apparatus further comprises a third photonic integrated circuit to couple light from the optical interposer to the third photonic integrated circuit. coupling the light from the optical interposer to a third photonic integrated circuit. [00122] Example 28: The apparatus of any one of Examples 16-27, wherein the third photonic integrated circuit comprises a third plurality of waveguides. [00123] Example 29: The apparatus of any one of Examples 16-28, wherein the light comprises quantum light. [00124] Example 30: The apparatus of any one of Examples 16-29, wherein the quantum light comprises single photons. [00125] In the foregoing detailed description, the method and apparatus of the present inventive subject matter have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the present inventive subject matter. The present specification and figures are accordingly to be regarded as illustrative rather than restrictive.

Claims

Ref. No. PSIQ-523WO / 6224.011WO1 CLAIMS What is claimed is: 1. A method comprising: propagating light in a first plurality of waveguides in a first photonic integrated circuit along a propagation direction, the first plurality of waveguides coupled to a first port of the first photonic integrated circuit, the first plurality of waveguides comprising a first upper layer of waveguides and a first lower layer of waveguides that are vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port along the propagation direction than the first lower layer of waveguides; coupling the light from the first photonic integrated circuit to a second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides comprising a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper layer of waveguides, the first tilt arrangement and the second tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit; and propagating the light in the second plurality of waveguides along the propagation direction. 2. The method of claim 1, wherein the first photonic integrated circuit is adjacent to the second photonic integrated circuit. Ref. No. PSIQ-523WO / 6224.011WO1 3. The method of claim 2, wherein the first port and the second port are adjacent to each other. 4. The method of claim 1, wherein the first tilt arrangement and the second tilt arrangement couple the light away from a first edge of the first photonic integrated circuit. 5. The method of claim 4, wherein the second photonic integrated circuit is connected to a third photonic integrated circuit that is positioned a distance away from the first photonic integrated circuit. 6. The method of claim 1, wherein coupling the light from the first photonic integrated circuit to the second photonic integrated circuit comprises coupling the light from the first plurality of waveguides through first material of the first photonic integrated circuit to second material of the second photonic integrated circuit to the second plurality of waveguides. 7. The method of claim 1, wherein increased coupling from the first tilt arrangement and second tilt arrangement enables increased vertical distance between the first photonic integrated circuit and the second photonic integrated circuit. 8. The method of claim 1, wherein the light propagates in the first plurality of waveguides as a supermode that is spread amongst the first plurality of waveguides as the light propagates along the first plurality of waveguides. 9. The method of claim 8, wherein the light propagates in the second plurality of waveguides as the supermode that is further spread amongst the first plurality of waveguides as the light propagates along the second plurality of waveguides. Ref. No. PSIQ-523WO / 6224.011WO1 10. The method of claim 8, wherein the first photonic integrated circuit is connected on top of the second photonic integrated circuit, and the supermode tilts downwards out of the first port of first photonic integrated circuit towards the second port of the second photonic integrated circuit. 11. The method of claim 1, wherein the second photonic integrated circuit is an optical interposer that is optically coupled to a plurality of photonic integrated circuits that includes the first photonic integrated circuit. 12. The method of claim 11, further comprising coupling the light from the optical interposer to a third photonic integrated circuit. 13. The method of claim 12, wherein the third photonic integrated circuit comprises a third plurality of waveguides. 14. The method of claim 1, wherein the light comprises quantum light. 15. The method of claim 14, wherein the quantum light comprises single photons. 16. An apparatus comprising: a first photonic integrated circuit comprising a first plurality of waveguides that are coupled to a first port of the first photonic integrated circuit, the first photonic integrated circuit configured to propagate light in the first plurality of waveguides along a propagation direction, the first plurality of waveguides comprising a first upper layer of waveguides and a first lower layer of waveguides that are vertically offset from the first upper layer of waveguides in the first photonic integrated circuit, the first plurality of waveguides configured in a first tilt arrangement such that the first upper layer of waveguides extends further towards the first port of along the propagation direction than the first lower layer of waveguides; and a second photonic integrated circuit comprising a second plurality of waveguides that are coupled to a second port of the second photonic integrated circuit, the first port of the first photonic integrated circuit in the second port of Ref. No. PSIQ-523WO / 6224.011WO1 the second photonic integrated circuit being configured to couple the light from the first photonic integrated circuit to the second photonic integrated circuit, the light being coupled from the first plurality of waveguides of the first photonic integrated circuit to a second plurality of waveguides in the second photonic integrated circuit, the second plurality of waveguides coupled to a second port of the second photonic integrated circuit, the second plurality of waveguides comprising a second upper layer of waveguides and a second lower layer of waveguides that are vertically offset from the second upper layer of waveguides in the second photonic integrated circuit, the second plurality of waveguides configured in a second tilt arrangement such that the second lower layer of waveguides extends further towards the second port than the second upper layer of waveguides, the first tilt arrangement and the second tilt arrangement being tilted in a same direction along the propagation direction such that the light tilts downwards from the first photonic integrated circuit to the second photonic integrated circuit to increase coupling between the first photonic integrated circuit and the second photonic integrated circuit. 17. The apparatus of claim 16, wherein the first photonic integrated circuit is adjacent to the second photonic integrated circuit. 18. The apparatus of claim 17, wherein the first port and the second port are adjacent to each other. 19. The apparatus of claim 16, wherein the first tilt arrangement and the second tilt arrangement couple the light away from a first edge of the first photonic integrated circuit. 20. The apparatus of claim 19, wherein the second photonic integrated circuit is connected to a third photonic integrated circuit that is positioned a distance away from the first photonic integrated circuit. Ref. No. PSIQ-523WO / 6224.011WO1 21. The apparatus of claim 16, wherein coupling the light from the first photonic integrated circuit to the second photonic integrated circuit comprises: coupling the light from the first plurality of waveguides through first material of the first photonic integrated circuit to second material of the second photonic integrated circuit to the second plurality of waveguides. 22. The apparatus of claim 16, wherein increased coupling from the first tilt arrangement and second tilt arrangement enables increased vertical distance between the first photonic integrated circuit and the second photonic integrated circuit. 23. The apparatus of claim 16, wherein the light propagates in the first plurality of waveguides as a supermode that is spread amongst the first plurality of waveguides as the light propagates along the first plurality of waveguides. 24. The apparatus of claim 23, wherein the light propagates in the second plurality of waveguides as the supermode that is further spread amongst the first plurality of waveguides as the light propagates along the second plurality of waveguides. 25. The apparatus of claim 23, wherein the first photonic integrated circuit is connected on top of the second photonic integrated circuit, and the supermode tilts downwards out of the first port of first photonic integrated circuit towards the second port of the second photonic integrated circuit. 26. The apparatus of claim 16, wherein the second photonic integrated circuit is an optical interposer that is optically coupled to a plurality of photonic integrated circuits that includes the first photonic integrated circuit. 27. The apparatus of claim 26, wherein the apparatus further comprises a third photonic integrated circuit to couple light from the optical interposer to the third photonic integrated circuit. Ref. No. PSIQ-523WO / 6224.011WO1 28. The apparatus of claim 27, wherein the third photonic integrated circuit comprises a third plurality of waveguides. 29. The apparatus of claim 16, wherein the light comprises quantum light. 30. The apparatus of claim 29, wherein the quantum light comprises single photons.