WO2024099579A1

WO2024099579A1 - Optical apparatus and method for selective wavelength switching of light

Info

Publication number: WO2024099579A1
Application number: PCT/EP2022/081660
Authority: WO
Inventors: Aurelian Dodoc
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2022-11-11
Filing date: 2022-11-11
Publication date: 2024-05-16
Anticipated expiration: 2025-05-11

Abstract

An optical apparatus (100) for selective wavelength switching of light is disclosed. The optical apparatus (100) comprises a first SLM (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels and a second SLM (160) positioned along an optical axis at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (120). Moreover, the optical apparats (100) comprises a first lens arrangement having a focal length F and positioned between the first SLM (120) and the second SLM (160), wherein the first lens arrangement is configured to redirect a light beam propagating from a point on the optical axis on the first SLM (120) towards the second SLM (160) so that the light beam intersects the optical axis in an optical axis intersection point between the first SLM (120) and the second SLM (160). The optical apparatus (100) further comprises a second lens arrangement positioned on the optical axis between the first lens arrangement and the second SLM (160) within about a quarter of the distance D from the optical axis intersection point to redirect the plurality of demultiplexed light input channels received from the first lens arrangement towards the second SLM (160).

Description

Optical apparatus and method for selective wavelength switching of light

TECHNICAL FIELD

The present disclosure relates to optical technology for optical fiber communication networks. More specifically, the present disclosure relates to an optical apparatus and method for selective wavelength switching (also referred to as cross-connecting) of light.

BACKGROUND

Optical networks are networks that use optical signals to carry data. Light sources such as lasers generate optical signals. Modulators modulate the optical signals with data to generate modulated optical signals. Various components transmit, propagate, amplify, receive, and process the modulated optical signals, such as optical fibers and optical multiplexers/demultiplexers allowing to achieve higher bandwidths for optical networks. More details about switching architectures in optical networks can be found in the review article “Survey of Photonic Switching Architectures and Technologies in Support of Spatially and Spectrally Flexible Optical Networking”, Marom Dan, et. al., JOSA, VOL. 8, No. 1 , 2017.

SUMMARY

It is an objective of the present disclosure to provide an improved optical apparatus (herein also referred to as an optical multiplexer/demultiplexer) and method for selective wavelength switching of light.

The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect an optical apparatus for selective wavelength switching of light is provided. The optical apparatus comprises a first spatial light modulator, SLM, configured to receive and redirect, i.e. steer a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams. The optical apparatus further comprises a second SLM positioned along an optical axis at a distance D from the first SLM and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM. Moreover, the optical apparatus comprises a first lens arrangement having a focal length F and positioned between the first SLM and the second SLM to redirect the plurality of demultiplexed light input waveband channels received from the first SLM in the direction of the second SLM, wherein the first lens arrangement is configured to redirect a light beam propagating from a point on the optical axis on the first SLM towards the second SLM so that the light beam intersects the optical axis in an optical axis intersection point between the first SLM and the second SLM. The optical apparatus further comprises a second lens arrangement positioned on the optical axis between the first lens arrangement and the second SLM within about a quarter of the distance D from the optical axis intersection point to redirect the plurality of demultiplexed light input waveband channels received from the first lens arrangement towards the second SLM. The optical apparatus for selective wavelength switching of light has a compact design. The ratio between the optical active diameters of the lens arrangements and the optical active diameters of the SLMs can reach beneficial values lower than 1.5, particularly lower than 1.2. Furthermore, the optical apparatus is configured for beam steering in both directions, thus X-Y steering. This allows the input ports to be arranged in a multi-dimensional array further reducing the optical active diameters and so the overall size of the optical apparatus.

In a further possible implementation form, the optical apparatus further comprises a third lens arrangement positioned within about a quarter of the distance D from a point on the optical axis halfway between the first SLM and the second SLM.

In a further possible implementation form, the first lens arrangement and the second lens arrangement comprise at least one optical element, in particular at least one lens having a positive refractive power.

In a further possible implementation form, the third lens arrangement comprises a micro-lens array.

In a further possible implementation form, the plurality of micro-lenses of the micro-lens array have a negative optical refractive power.

In a further possible implementation form, the plurality of micro-lenses of the micro-lens array have a first optical refractive power in a first symmetry plane of the optical apparatus and a second optical refractive power different to the first optical refractive power in a second symmetry plane of the optical apparatus perpendicular to the first plane of symmetry.

In a further possible implementation form, the first lens arrangement and/or the second lens arrangement comprises a micro-lens array. The micro-lenses of the micro-lens array may be implemented with an optical power based on refractive or diffractive effects, for instance, a liquid crystal. In a further possible implementation form, the plurality of micro-lenses of the micro-lens array have a positive optical refractive power.

In a further possible implementation form, the first and the second lens arrangement between the first and second SLM define an afocal optical system.

In a further possible implementation form, the distance D between the first SLM and the second SLM is an integer multiple of the focal length F.

In a further possible implementation form, the distance D between the first SLM and the second SLM is about four times the focal length F.

In a further possible implementation form, the distance D between the first SLM and the second SLM is about six times the focal length F.

In a further possible implementation form, the first SLM and/or the second SLM comprises a liquid crystal on silicon device and/or a digital mirror device.

In a further possible implementation form, the optical apparatus further comprises: a first dispersive optical element configured to disperse one or more input light beams into the plurality of light input channels and to direct the plurality of light input channels onto the first SLM; and/or a second dispersive optical element configured to receive a plurality of light output channels from the second SLM and combine the plurality of light output channels from the second SLM into one or more output light beams.

In a further possible implementation form, the first dispersive optical element and/or the second dispersive optical element comprises a grating, a prism and/or a grism.

According to a second aspect a method for operating an optical apparatus for selective wavelength switching of light is provided, wherein the optical apparatus comprises a first SLM configured to receive and redirect a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams, and a second SLM positioned along an optical axis at a distance D from the first SLM and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM. The method according to the second aspect comprises the steps of: redirecting, by a first lens arrangement having a focal length F and positioned between the first SLM and the second SLM, the plurality of demultiplexed light input waveband channels received from the first SLM in the direction of the second SLM, wherein the first lens arrangement is configured to redirect a light beam propagating from a point on the optical axis on the first SLM towards the second SLM so that the light beam intersects the optical axis in an optical axis intersection point between the first SLM and the second SLM; and redirecting, by a second lens arrangement positioned on the optical axis between the first lens arrangement and the second SLM within about a quarter of the distance D from the optical axis intersection point, the plurality of demultiplexed light input waveband channels received from the first lens arrangement towards the second SLM.

The method according to the second aspect of the present disclosure can be performed by the optical apparatus according to the first aspect of the present disclosure. Thus, further features of the method according to the second aspect of the present disclosure, result directly from the functionality of the optical apparatus according to the first aspect of the present disclosure as well as its different implementation forms described above and below.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Fig. 1 shows a schematic diagram illustrating an optical apparatus for selective wavelength switching of light according to an embodiment;

Fig. 2 shows two schematic cross-sectional side views of an optical system of a conventional optical apparatus for selective wavelength switching of light;

Fig. 3 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to an embodiment;

Fig. 4 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to an embodiment; Figs. 5a-d show tables illustrating some examples of input ports arrangements and possible waveband channels distributions on a first SLM of an optical apparatus according to an embodiment;

Fig. 6 shows a schematic diagram illustrating an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 7 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 8 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 9 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 10 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 11 shows two schematic cross-sectional side views of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Figs. 12a and 12b show two schematic cross-sectional side views of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 13 shows two schematic cross-sectional side views of an optical system of an optical apparatus for selective wavelength switching of light according to a further embodiment;

Fig. 14 shows a schematic cross-sectional side view of an optical apparatus for selective wavelength switching of light according to a further embodiment; and

Fig. 15 shows a flow diagram illustrating steps of a method for operating an optical apparatus for selective wavelength switching of light according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 shows a schematic diagram illustrating an optical apparatus (also referred to as optical multiplexer/demultiplexer) 100 for selective wavelength switching of light according to an embodiment from N input ports to N output ports. Each input and output port may contain L data carrying wavelength channels so that the optical apparatus 100 is configured to recombine and redirect NxL input data channels to N output ports. The input ports ._N may be connected to optical fibers, wherein each optical fiber transmits L data carrying wavelength channels AI._N.

More specifically, the optical apparatus 100 comprises a first spatial light modulator, SLM, 120 configured to receive and redirect a plurality of demultiplexed light input waveband channels from the input ports li._N. As will be appreciated, each light input waveband channel comprises a plurality of light beams. The optical apparatus 100 further comprises a second SLM 160 positioned along a main optical axis OA at a distance D from the first SLM 120 and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM 120. In an embodiment, the first SLM 120 and/or the second SLM 160 may be implemented as a liquid crystal on silicon device (also referred to as a LCOS device) and/or a digital mirror device.

As schematically indicated in figure 1 , the optical apparatus 100 further comprises an optical system 180 arranged between the first SLM 120 and the second SLM 160 for guiding the light emitted by a respective portion of the first SLM 120 to a selectable desired portion of the second SLM 160. By way of example, as illustrated in figure 1 , the optical system 180 of the optical apparatus 100 is configured to guide a first light input waveband channel Ai from a first input port h to a portion of the second SLM 160 associated with a first light output waveband channel Ai of the (N-1)-th output port ON-I . Several embodiments of the optical system 180 of the optical apparatus 100 will be described below.

For generating the plurality of demultiplexed light input waveband channels from the light provided by the input ports li._N, the optical apparatus 100 may further comprise a first dispersive optical element 110 (shown, for instance, in figure 11) configured to disperse the input light beams from the input ports into the plurality of light input waveband channels and to direct the plurality of light input waveband channels onto the first SLM 120. Additionally, the optical apparatus 100 may further comprise a second dispersive optical element 170 (also shown, for instance, in figure 11) configured to receive the plurality of light output waveband channels from the second SLM 160 and combine the plurality of light output waveband channels from the second SLM 160 into an output light beam further directed to a specific output port of the N output ports OI-N. In an embodiment, the first dispersive optical element 110 and/or the second dispersive optical element 170 may comprise a grating, a prism and/or a grism.

Figure 2 shows two schematic cross-sectional side views of the optical system of a conventional optical apparatus for selective wavelength switching of light. The optical system comprises a first SLM 10 in the form for example of a LCOS device, a Y-lens 30, a X-lens 40, a further Y-lens 50 and a second SLM 60 in the form for example an of a LCOS device. As will be appreciated, the optical system is a 2F system in the steering direction X-Z, where the dimension of the X-lens 40 in the steering direction X-Z is about twice the diameter of the SLMs 20, 60. This is due to the fact that in order to cover the whole extent of the SLMs 20, 60 in this direction, the beam arrangement at the first LCOS 20 has to be telecentric, i.e. the beam steered to a central point of the second LCOS 60 has to start at the first LCOS 20 parallel to the optical axis, as illustrated in figure 2. Furthermore, this conventional arrangement, does not allow steering in two dimensions but only in one, namely the X-Z plane.

In the following several embodiments of the optical system 180 of the optical apparatus 100 will be described, which provide different advantages over the conventional optical system illustrated in figure 2. A first embodiment of the optical system 180 is shown in figure 3, where the optical apparatus 100 comprises a first lens arrangement 130a having a focal length F and positioned between the first SLM 120 and the second SLM 160 to redirect the plurality of demultiplexed light input waveband channels received from the first SLM 120 in the direction of the second SLM 160. As will be described in more detail below, the first lens arrangement 130a is configured to redirect light beams propagating from a point on the optical axis OA on the first SLM 120 (illustrated as point A’ in figure 3) towards the second SLM 160 so that the light beams intersect the optical axis OA in an optical axis intersection point (illustrated as point C’ in figure 3) between the first SLM 120 and the second SLM 160. The optical system 180 of the optical apparatus 100 shown in figure 3 further comprises a second lens arrangement 150a positioned on the optical axis OA between the first lens arrangement 130a and the second SLM 160. In the embodiment shown in figure 3, the second lens arrangement 150a is positioned in the vicinity of the optical axis intersection point C’ to redirect the plurality of demultiplexed light input waveband channels received from the first lens arrangement 130a towards the second SLM 160. In further embodiments, the second lens arrangement 150a is positioned within about a quarter of the distance D from the optical axis intersection point C’ to redirect the plurality of demultiplexed light input waveband channels received from the first lens arrangement 130a towards the second SLM 160. In the embodiment shown in figure 3, the first lens arrangement 130a and the second lens arrangement 150a each comprise an optical element in the form of a lens having a positive refractive power, in particular a biconvex lens.

As will be appreciated, for the embodiment shown in figure 3 (as well as for further embodiments described in the following) the first and the second lens arrangement 130a, 150a (implemented, for example as biconvex lenses 130a, 150a) between the first and second SLM 120, 160 define an afocal optical system that allows the conservation of the waveband channel structure from the first SLM 120 to the second SLM 160 so that parallel beams emerging from the first SLM 120 infringe in parallel on the second SLM 160. The arrangement of this embodiment shown in figure 3 further allows steering both in the x and y directions (as illustrated by the different points A, A’, A” on the first SLM 120, B, B’, B” on the first lens arrangement 130a, C, C’, C” on the second lens arrangement 150a and D, D’, D” on the second SLM 160). As will be appreciated furthermore, for the embodiment shown in figure 3 the distance D between the first SLM 120 and the second SLM 160 is an integer multiple of the focal length F, in particular about six times the focal length F.

A variant of the embodiment shown in figure 3, is shown in figure 4, where the optical system 180 further comprises a third lens arrangement 140a, in particular a third lens element (for instance, a third biconvex lens 140a) positioned within about a quarter of the distance D from a point B2’ on the optical axis OA halfway between the first SLM 120 and the second SLM 160. More specifically, in the embodiment shown in figure 4, the third lens arrangement 140a is positioned at the point B2’ half-way between the first and second lens arrangement 130a, 150a, while the first and second lens arrangement 130a, 150a are located at a respective distance from the first and second SLM 120, 160 corresponding to their focal length F. Thus, in the embodiment of figure 4 the total distance D between the first SLM 120 and the second SLM 160 is four times the focal length F of the first and second lens arrangement 130a and 150a, i.e. D = 4F.

Figures 5a-d show four tables illustrating some examples of input port arrangements and possible waveband channels distributions on the first SLM 120. In a first table shown in figure 5a the input port arrangement is in a one-dimensional array of N ports li._N. Correspondingly the demultiplexed waveband channels are arranged in a two-dimensional array on the first SLM 120. The columns correspond to the different input ports ._N and the rows corresponds to the different waveband channels AI-L. This arrangement corresponds to the optical system 180 shown figure 1. In the following tables shown in figures 5b to 5d, the N input ports ._N are arranged in an array comprising multiple rows particularly two rows I11-1N/2 and I21-2N/2 with N/2 columns but with different waveband channel arrangements. In figure 5b the waveband channels from two input ports arranged in the same column are interleaved represented on the first SLM 120 in one column, so that two waveband channels with the same waveband but from different input ports are adjacent, thus A21 is following An and A2L/2 is following A1L/2. As a consequence, the wavebands An and A12 from port In and correspondingly A21 and A22 from port I21 are not connected in this configuration, in between the two subsequent waveband channels there is a wavelength gap as long as a waveband channel itself. So, in an input port, the carrying waveband channels are individual and not connected to each other. In figure 5c the sequence of connected waveband channels in an input port is larger comprising two connected wavebands so that for example the connected wavebands A21 and A22 are adjacent to the connected wavebands An and A12. In this particular case the gap is as large as two connected wavebands. In figure 5d all the waveband channels from a respective input port are connected but the waveband channels from an input port in the first row are different from the waveband channels in the second input port in the same input ports column. So, if the optical apparatus 100 is working for example in the C and L bands of wavelength, the first row of input ports may contain the C band, while the second row of input ports may contain the L band. This case corresponds also with the arrangement in table 5a where the input ports contain all C and L waveband channels. As will be appreciated, on the second SLM 160 the channel distribution will be the same. The advantage of the multi row distribution of input ports is a more compact size in one dimension.

An important consequence of the different possible port distribution illustrated in figures 5a-d is the type of steering. While the one row distribution involves one-dimensional steering, the multirow distribution usually requires a two-dimensional steering. Figure 6 shows a schematic diagram illustrating a variant of the optical apparatus 100 shown in figure 1 for selective wavelength switching of light according to the waveband channel distribution illustrated in figure 5c. In this case, since there are two rows of channels with the same wavelength on the first SLM 120, a steering in two dimensions X and Y is used in order to interconnect all channels.

Figure 7 shows two schematic cross-sectional side views of the optical system 180 of the optical apparatus 100 for selective wavelength switching of light according to a further embodiment. In the embodiment shown in figure 7, which is a variant of the embodiment shown in figure 3, the first lens arrangement may be implemented as a biconvex lens element 130a and a two-dimensional multi-lens array 130b, i.e. a X-Y matrix of lenslets (or micro-lenses). Likewise, the second lens arrangement with positive refractive power may be implemented as a biconvex lens element 150a and a multi-lens array 150b. Like in the embodiment shown in figure 3, in the embodiment shown in figure 7 the distance D between the first SLM 120 and the second SLM 160 is about six times the focal length F of both the first and second lens arrangement 130a, b, 150a, b. In an embodiment, the plurality of micro-lenses of the micro-lens array 130b, 150b may have a positive optical refractive power. In an embodiment, the plurality of micro-lenses of the micro-lens array 130b, 150b may have a first optical refractive power in a first symmetry plane of the optical apparatus 100 and a second optical refractive power different to the first optical refractive power in a second symmetry plane of the optical apparatus 100 perpendicular to the first plane of symmetry.

Figure 8 shows two schematic cross-sectional side views of the optical system 180 of the optical apparatus 100 for selective wavelength switching of light according to a further embodiment. In the embodiment shown in figure 8, which is a variant of the embodiment shown in figure 7, the first lens arrangement with a positive refractive power may be implemented as a biconvex lens 130a and a first one-dimensional multi-lens array 130b, wherein the first onedimensional multi-lens array 130b only has a refractive power in the X-Z plane. Likewise, the second lens arrangement with a positive refractive power may be implemented as a second biconvex lens 150a and a second one-dimensional multi-lens array 150b, wherein the second one-dimensional multi-lens array 150b only has a refractive power in the X-Z plane as well. In the embodiment shown in figure 8 the third lens arrangement 140a with negative optical power in the Y-Z plane and no optical power in the X-Z plane, may be implemented as a biconcave Y-lens, i.e. a biconcave lens having a refractive power only in the Y-Z plane, i.e. in a plane perpendicular to the plane, where the first and second one-dimensional multi-lens array 130b, 150b have a refractive power. Like in the embodiments shown in figures 3 and 7, in the embodiment shown in figure 8 the distance D between the first SLM 120 and the second SLM 160 is about six times the focal length F of both the first and second lens arrangement 130a,b, 150a, b.

Figure 9 shows two schematic cross-sectional side views of the optical system 180 of the optical apparatus 100 for selective wavelength switching of light according to a further embodiment. In the embodiment shown in figure 9, the first lens arrangement with positive refractive power may be implemented as a biconcave lens 130a, the second lens arrangement with positive refractive power may be implemented as a biconvex lens 150a and the third lens arrangement 140a of negative refractive power comprises an optical element 140a, wherein the optical element 140a provides on one of the surfaces, for example, the front surface thereof a one-dimensional multi-lens array only having a refractive power in the X-Z plane and on a opposite surface thereof a concave Y-lens only having a refractive power in the Y-Z plane (perpendicular to the X-Z plane). This design of the third lens arrangement 140a allows steering of the light input channels in the X-direction only. Like in the embodiments shown in figures 3, 7 and 8, in the embodiment shown in figure 9 the distance D between the first SLM 120 and the second SLM 160 is about six times the focal length F of both the first and second lens arrangement 130a, 150a. In an embodiment, the plurality of micro-lenses of the microlens array 140a of the third lens arrangement have a negative optical refractive power. Although in the embodiment shown in figure 9 the one-dimensional multi-lens array only has a refractive power in the X-Z plane, in further embodiments the plurality of micro-lenses of the micro-lens array may have a first optical refractive power in a first symmetry plane of the optical apparatus 100 (for instance the X-Z plane) and a second optical refractive power different to the first optical refractive power in a second symmetry plane of the optical apparatus 100 perpendicular to the first plane of symmetry (for instance the Y-Z plane). The lens arrays in any of the disclosed embodiments can be implemented with refractive or diffractive (ex. Liquid crystal) based optical action.

Figure 10 shows two schematic cross-sectional side views of the optical system 180 of the optical apparatus 100 for selective wavelength switching of light according to a further embodiment. In the embodiment shown in figure 10, which is a variant of the embodiment shown in figure 9, the third lens arrangement 140a comprises a two-dimensional multi-lens array 140a, i.e. a X-Y matrix of lenslets (or micro-lenses). This design of the third lens arrangement 140a allows steering of the light input channels both in the X-direction and Y- direction. Like in the embodiments shown in figures 3, 7, 8 and 9, in the embodiment shown in figure 10 the distance D between the first SLM 120 and the second SLM 160 is about six times the focal length F of both the first and second lens arrangement 130a, 150a. The position of the lens array 140a in figure 10 is about at half of the distance between the first SLM 120 and the second SLM 160 and about at half of the distance between the first and second lens arrangements. The advantage of the embodiments with only one lens array is that the beam mapping between the first SLM 120 and second SLM 160 is less complex.

Figure 11 shows two schematic cross-sectional side views of the optical apparatus 100 based on the optical system 180 shown in figure 10. As already mentioned above, the optical apparatus 100 shown in figure 11 further comprises the first dispersive optical element 110, such as a grating, prism, or grism, configured to disperse a plurality of input light beams (provided via the input ports li._N) into the plurality of light input waveband channels and to direct the plurality of light input waveband channels onto the first SLM 120 and the second dispersive optical element 170, such as a grating, prism, or grism, configured to receive the plurality of light output waveband channels from the second SLM 160 and combine the plurality of light output waveband channels from the second SLM 160 into aa plurality of output light beams, further directed to the output ports OI-N. AS illustrated in figure 11 , in this embodiment two supplementary lens arrangements 115 and 165 may be used to focus the optical beams between the first dispersive element 110 and the first SLM 120 and the optical beams between the second dispersive element 170 and the second SLM 160, respectively.

Figures 12a and 12b show two schematic cross-sectional side views of a variant of the optical apparatus 100 of figure 11. In the embodiment shown in figures 12a and 12b the optical system 180 of the optical apparatus 100 has a folded optical axis OA due to a first mirror 130b of the first lens arrangement and a second mirror 150b of the second lens arrangement. This folding lead to a very compact optical system 180 of the optical apparatus 100.

Figure 13 shows two schematic cross-sectional side views of the optical system 180 of the optical apparatus 100 for selective wavelength switching of light according to a further embodiment. In the embodiment shown in figure 13, which is a variant of the embodiment shown in figure 4, the third lens arrangement comprises in addition to a lens arrangement with positive optical power, which may be implemented as a biconvex lens 140b a two-dimensional multi-lens array 140a, i.e. a X-Y matrix of lenslets. This design of the third lens arrangement allows steering of the light input waveband channels both in the X-direction and Y-direction. Like in the embodiments shown in figure 4, in the embodiment shown in figure 13 the distance D between the first SLM 120 and the second SLM 160 is about four times the focal length F of both the first and second lens arrangement 130a, 150a. Figure 14 shows two schematic cross-sectional side views of the optical apparatus 100 based on the optical system 180 shown in figure 13. In the embodiment shown in figure 14 the optical apparatus 100 comprises the first dispersive optical element 110 in the form of a first grism 110a configured to disperse one or more input light beams into the plurality of light input waveband channels and to direct the plurality of light input channels onto the first SLM 120 and the second dispersive optical element 170 in the form of a second grism 170a configured to receive the plurality of light output channels from the second SLM 160 and combine the plurality of light output channels from the second SLM 160 into one or more output light beams. In the embodiment shown in figure 14 the first lens arrangement 130a of positive refractive power, which may be implemented as a biconvex lens 130a, is used to redirect both the light between the first SLM 120 and the third lens arrangement 140a, b and between the first SLM 120 and the first grism 110a. Likewise, the second lens arrangement 150a of positive refractive power, which may be implemented as a biconvex lens 150a, is used to redirect both the light between the third lens arrangement 140a,b and the second SLM 160, and between the second SLM 160 and the second grism 170a.

Figure 15 shows a flow diagram illustrating steps of a method 1500 for operating the optical apparatus 100 for selective wavelength switching of light according to an embodiment. As already described above, the optical apparatus 100 comprises the first SLM 120 configured to receive and redirect a plurality of demultiplexed light input waveband channels and the second SLM 160 positioned along an optical axis at a distance D from the first SLM 120 and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM 120. The method 1500 comprises a step 1501 of redirecting, by the first lens arrangement 130a,b having a focal length F and positioned between the first SLM 120 and the second SLM 160, the plurality of demultiplexed light input waveband channels received from the first SLM 120 in the direction of the second SLM 160. As already described above, the first lens arrangement 130a,b is configured to redirect a light beam propagating from a point on the optical axis on the first SLM 120 towards the second SLM 160 so that the light beam intersects the optical axis OA in an optical axis intersection point between the first SLM 120 and the second SLM 160. Moreover, the method 1500 comprises a step 1503 of redirecting, by the second lens arrangement 150a,b positioned on the optical axis OA between the first lens arrangement 130a, b and the second SLM 160 within about a quarter of the distance D from the optical axis intersection point, the plurality of demultiplexed light input waveband channels received from the first lens arrangement 130a,b towards the second SLM 160.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

1. An optical apparatus (100) for selective wavelength switching of light, wherein the optical apparatus (100) comprises: a first spatial light modulator, SLM, (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels, each light input waveband channel comprising a plurality of light beams; a second SLM (160) positioned along an optical axis (OA) at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (120); a first lens arrangement (130a,b) having a focal length F and positioned between the first SLM (120) and the second SLM (160) to redirect the plurality of demultiplexed light input waveband channels received from the first SLM (120) in the direction of the second SLM (160), wherein the first lens arrangement (130a,b) is configured to redirect a light beam propagating from a point on the optical axis (OA) on the first SLM (120) towards the second SLM (160) so that the light beam intersects the optical axis (OA) in an optical axis intersection point between the first SLM (120) and the second SLM (160); and a second lens arrangement (150a,b) positioned on the optical axis (OA) between the first lens arrangement (130a,b) and the second SLM (160) within about a quarter of the distance D from the optical axis intersection point to redirect the plurality of demultiplexed light input waveband channels received from the first lens arrangement (130a, b) towards the second SLM (160).

2. The optical apparatus (100) of claim 1 , wherein the optical apparatus (100) further comprises a third lens arrangement (140a, b) positioned within about a quarter of the distance D from a point on the optical axis (OA) halfway between the first SLM (120) and the second SLM (160).

3. The optical apparatus (100) of claim 2, wherein the first lens arrangement (130a,b) and the second lens arrangement (150a,b) comprise at least one optical element having a positive refractive power.

4. The optical apparatus (100) of claim 2 or 3, wherein the third lens arrangement (140a, b) comprises a micro-lens array (140a).

5. The optical apparatus (100) of claim 4, wherein the plurality of micro-lenses of the micro-lens array (140a) have a negative optical refractive power.

6. The optical apparatus (100) of claim 4 or 5, wherein the plurality of micro-lenses of the micro-lens array (140a) have a first optical refractive power in a first symmetry plane of the optical apparatus (100) and a second optical refractive power different to the first optical refractive power in a second symmetry plane of the optical apparatus (100) perpendicular to the first plane of symmetry.

7. The optical apparatus (100) of any one of the preceding claims, wherein the first lens arrangement (130a, b) and/or the second lens arrangement (150a, b) comprises a micro-lens array (130b, 150b).

8. The optical apparatus (100) of claim 7, wherein the plurality of micro-lenses of the micro-lens array (130b, 150b) of the first lens arrangement (130a,b) and/or the second lens arrangement (150a,b) have a positive optical refractive power.

9. The optical apparatus (100) of claim 7 or 8, wherein the plurality of micro-lenses of the micro-lens array (130b, 150b) of the first lens arrangement (130a,b) and/or the second lens arrangement (150a,b) have a first optical refractive power in a first symmetry plane of the optical apparatus (100) and a second optical refractive power different to the first optical refractive power in a second symmetry plane of the optical apparatus (100) perpendicular to the first plane of symmetry.

10. The optical apparatus (100) of any one of the preceding claims, wherein the first and the second lens arrangement (130a, b, 150a, b) between the first and second SLM (120, 160) define an afocal optical system.

11. The optical apparatus (100) of any one of the preceding claims, wherein the distance D between the first SLM (120) and the second SLM (160) is an integer multiple of the focal length F.

12. The optical apparatus (100) of claim 11, wherein the distance D between the first SLM (120) and the second SLM (160) is about four times the focal length F.

13. The optical apparatus (100) of claim 11, wherein the distance D between the first SLM (120) and the second SLM (160) is about six times the focal length F.

14. The optical apparatus (100) of any one of the preceding claims, wherein the first SLM (120) and/or the second SLM (160) comprises a liquid crystal on silicon device and/or a digital mirror device.

15. The optical apparatus (100) of any one of the preceding claims, wherein the optical apparatus (100) further comprises: a first dispersive optical element (110) configured to disperse one or more input light beams into the plurality of light input waveband channels and to direct the plurality of light input waveband channels onto the first SLM (120); and/or a second dispersive optical element (170) configured to receive a plurality of light output waveband channels from the second SLM (160) and combine the plurality of light output waveband channels from the second SLM (160) into one or more output light beams.

16. The optical apparatus (100) of claim 15, wherein the first dispersive optical element (110) and/or the second dispersive optical element (170) comprises a grating, a prism and/or a grism.

17. A method (1500) for operating an optical apparatus (100) for selective wavelength switching of light, the optical apparatus (100) comprising a first spatial light modulator, SLM, (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams, and a second SLM (160) positioned along an optical axis (OA) at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (120), wherein the method (1500) comprises: redirecting (1501), by a first lens arrangement (130a, b) having a focal length F and positioned between the first SLM (120) and the second SLM (160), the plurality of demultiplexed light input waveband channels received from the first SLM (120) in the direction of the second SLM (160), wherein the first lens arrangement (130a, b) is configured to redirect a light beam propagating from a point on the optical axis (OA) on the first SLM (120) towards the second SLM (160) so that the light beam intersects the optical axis (OA) in an optical axis intersection point between the first SLM (120) and the second SLM (160); and redirecting (1503), by a second lens arrangement (150a,b) positioned on the optical axis (OA) between the first lens arrangement (130a, b) and the second SLM (160) within about a quarter of the distance D from the optical axis intersection point, the plurality of demultiplexed light input waveband channels received from the first lens arrangement (130a,b) towards the second SLM (160).