CN116026790A - A sensor based on a racetrack-type resonant cavity with subwavelength gratings in continuous domain bound states - Google Patents

Abstract

The present invention is a sensor based on a continuum bound state sub-wavelength grating racetrack resonant cavity. The device structure is as follows from bottom to top: the first layer is an intrinsic silicon substrate (1), and the second layer is a buried oxide layer (2), the third layer is a silicon nitride film (3), the fourth layer is a racetrack resonator (4), and the racetrack resonator includes a racetrack microring (4.1), a bus waveguide (4.2) and a grating coupler (4.3). On the waveguide supporting continuous domain bound mode, the invention realizes light-limited propagation with high quality factor by designing sub-wavelength grating structure whose period is smaller than light wavelength and parameters of racetrack resonant cavity, and is further applied as a sensor. The present invention has many advantages such as high throughput, high detection sensitivity, high quality factor, simple structure, and easy manufacture, and its application as a refractive index sensor or biosensor can provide a solution for fast, portable and cost-effective medical detection.

Description

A sensor based on subwavelength grating racetrack resonator in continuum bound state

technical field

The invention relates to the field of nanometer optical sensing, and more specifically, relates to a sensor based on a continuous domain bound state subwavelength grating racetrack resonant cavity.

Background technique

The importance of fast, portable and cost-effective medical diagnostics is increasing. Compared with traditional laboratory-based and test paper-based detection methods, nano-optical sensors have simpler detection processes, faster detection time and lower detection costs, as well as high sensitivity and accuracy, so they are favored by researchers at home and abroad. widespread attention.

Most current nano-optical sensor designs are based on silicon-on-insulator waveguides, which require difficult etching processes, small manufacturing tolerances, and high manufacturing costs. The bound state waveguide in the continuum domain can confine the optical field in the high-refractive-index film through the design of the physical structure, and route it by the low-refractive-index waveguide above, so as to realize the perfect confinement state in the continuum domain and become a substitute for silicon-on-insulator. One of the reliable options for waveguides. Unlike the previous silicon-on-insulator waveguide, this method does not need to etch single crystal material, and only needs a simple process to achieve high-precision manufacturing, which is simple, fast and economical. Therefore, continuum bound state waveguides are considered to be an effective way to develop novel nano-optical sensors.

A high-Q resonator is an important element in an optical system. Since the light will propagate around the resonator and interfere with the incident light, while obtaining enhanced light-matter interaction, the refractive index of the cladding can be adjusted to The perturbation is converted into the change of the interference spectrum, therefore, applying the high-Q resonant cavity to the field of nano-optical sensing can obtain higher detection sensitivity. The characteristic size of photonic devices with a subwavelength grating structure is smaller than the wavelength of the incident light. By designing the structural parameters of the subwavelength grating, the mode confinement of the waveguide can be flexibly controlled. In addition, the cladding material can enter the micro-nano structure, which increases the body surface area of the device. Therefore, it has practical significance for the improvement of sensor sensitivity. At present, further optimizing the manufacturing process and sensing performance of nano-optical sensors is a research hotspot at home and abroad.

Contents of the invention

Technical problem: In view of this, the object of the present invention is to provide a sensor based on a continuum-bound state subwavelength grating racetrack resonator, which uses a continuum-bound state instead of a silicon-on-insulator waveguide, which has the advantages of simple structure and easy manufacture; And further expand the subwavelength grating structure in the racetrack resonant cavity to achieve lower power consumption optical propagation and higher sensitivity sensing performance.

Technical solution: A sensor based on a continuous-domain bound state subwavelength grating racetrack resonator of the present invention, the layered structure of the device from bottom to top is as follows: the first layer is an intrinsic silicon substrate, the second layer is The oxide layer is buried, the third layer is a silicon nitride film, and the fourth layer is a racetrack-shaped resonant cavity. The racetrack-shaped resonant cavity includes a racetrack-shaped microring, a bus waveguide, and a grating coupler; The sides are distributed symmetrically along the length direction, and the grating couplers are respectively located at the four ends of the two bus waveguides.

The thickness of the intrinsic silicon substrate is 0.4-0.7 mm.

The buried oxide layer is made of silicon dioxide with a thickness of 1-3 microns.

The thickness of the silicon nitride film is 200-400 nanometers.

The racetrack-shaped resonant cavity includes a racetrack-shaped microring, a bus waveguide and a grating coupler, and the four grating couplers are respectively used as couplers for the input end, the through end, the upstream end and the downstream end of the racetrack-shaped resonant cavity.

The racetrack resonant cavity is provided with a sub-wavelength grating structure whose period is smaller than the wavelength of light, and the sub-wavelength grating structure is composed of several sub-wavelength micro-nano structural units.

The sub-wavelength micro-nano structural unit includes a high-refractive-index medium and a low-refractive-index medium, and the high-refractive-index medium is electron beam photoresist ZEP520A, whose refractive index is smaller than that of the silicon nitride film, and whose thickness is 200- 1000 nm, the low refractive index medium is gas or liquid.

The high-refractive-index medium in the linear part of the racetrack-shaped microring is a rectangular array arranged periodically; the high-refractive-index medium in the arc part is a trapezoidal array arranged periodically, wherein the base of the trapezoid outside the circle is larger than that inside the circle. The bottom side of is short, and its period is the same as that of the subwavelength grating period of the straight line part of the racetrack-shaped microring.

The high refractive index medium of the bus waveguide is a rectangular array arranged periodically, and its period is the same as that of the sub-wavelength grating in the straight line part of the racetrack microring.

The low-refractive-index medium of the grating coupler is a rectangular array that is periodically arranged and whose duty cycle changes according to a certain rule along the width direction.

The working principle is: the optical propagation mode can be divided into three types according to the frequency, including guided wave mode, radiation mode and continuum bound mode. Among them, the TE continuum mode and the TM bound mode located in the continuum domain can be fully decoupled by the low-refractive-index waveguide defined on the high-refractive-index film, thereby achieving low-loss propagation of the continuum-bound mode. The sensor based on the sub-wavelength grating structure racetrack resonant cavity in the continuum bound state realizes the high quality factor optical Limit propagation, further applied as a sensor. When the light enters the resonator bus waveguide through the input (Input) grating coupler, the light is coupled into the racetrack-shaped microring in the coupling area, and a part of the light is coupled into the bus waveguide after half a circle, and is output from the downlink (Drop) grating coupler, and the other part of the light is Continue to transmit around the ring, couple into the bus waveguide in the coupling area, and output from the through grating coupler after interfering with the input light, so the spectra of the through port and the drop port are complementary. The light that satisfies the resonant wavelength condition is coherent and constructive in the resonator, and is continuously enhanced. After passing through the microring for a week, the phase difference between the light coupled from the microring to the straight waveguide and the incident light is (2k+1)π, and the two occur Coherent and destructive, so the light intensity output from the through (Through) grating coupler becomes a minimum value, and several filter resonance peaks can be observed on the spectrum. When the concentration of the external environment, molecules and other parameters change, the effective refractive index of the light propagation mode in the resonator will also change, which will cause changes in the output spectrum of the through coupler or downlink coupler, including the resonance wavelength Offset, intensity change and phase change etc. Since the light will propagate many turns in the racetrack-shaped microring, the resonant cavity structure achieves an enhanced light-matter interaction length, which is beneficial to realize high-sensitivity sensing performance. The introduction of subwavelength gratings can flexibly control the mode confinement of the waveguide. More importantly, the cladding material can enter the micro-nano structure, which increases the body surface area of the device and helps to achieve higher sensitivity detection. Hundreds of sensors can be mass-integrated on a chip through semiconductor processing technology to achieve high-throughput and low-cost detection.

Beneficial effects: Compared with the prior art, the present invention adopts the continuous domain bound state waveguide to realize the sensor of the racetrack resonant cavity, and introduces the sub-wavelength grating structure to improve the sensing sensitivity.

The advantage of the embodiment of the present invention is:

1) The continuous domain bound state waveguide is adopted, the manufacturing process is simple, and the manufacturing cost is low.

2) The optical propagation with high quality factor is achieved through the design of the racetrack resonant cavity, and the enhanced light-matter interaction length is obtained, which is conducive to the realization of high-sensitivity detection performance

3) The introduction of subwavelength gratings can flexibly control the mode confinement of the waveguide. More importantly, the cladding material can enter the micro-nano structure, which increases the body surface area of the device and helps to achieve higher sensitivity detection.

4) Multiple sensors can be integrated on the chip to achieve high-throughput and low-cost detection.

5) The sensor has many advantages such as high throughput, high detection sensitivity, high quality factor, simple structure, and easy fabrication. The application as a refractive index sensor or biosensor can provide a solution for fast, portable and cost-effective medical detection.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

FIG. 1 is a schematic structural diagram of a sensor based on a racetrack-type resonant cavity of a continuous-domain bound state subwavelength grating provided by an embodiment of the present invention.

Fig. 2 is a top-view structure schematic diagram of a sensor based on a continuum bound state sub-wavelength grating racetrack resonator provided by an embodiment of the present invention, and the lower figure is a partial enlarged view of the wireframe in the upper figure.

Fig. 3 is a schematic diagram of a cross-sectional structure of a sensor based on a continuum bound state sub-wavelength grating racetrack resonator provided by an embodiment of the present invention.

Fig. 4 is a cross-sectional mode distribution of a sensor based on a continuum bound state subwavelength grating racetrack resonator provided by an embodiment of the present invention.

Fig. 5 is a simulated transmission spectrum diagram of a sensor based on a continuum-bound state sub-wavelength grating racetrack resonator provided by an embodiment of the present invention using a finite time-domain difference method.

In the figure: intrinsic silicon substrate 1, buried oxide layer 2, silicon nitride film 3, racetrack resonator 4, racetrack resonator 4 includes racetrack microring 4.1, bus waveguide 4.2 and grating coupler 4.3.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

As shown in Figure 1, Figure 2, and Figure 3, a racetrack resonator based on a sub-wavelength grating structure in a continuous domain bound state, the device structure is as follows from bottom to top: the first layer is the intrinsic silicon substrate 1, the second The second layer is a buried oxide layer 2, the third layer is a silicon nitride film 3, and the fourth layer is a racetrack resonator 4, which includes a racetrack microring 4.1, a bus waveguide 4.2 and a grating coupler 4.3; Wherein, the intrinsic silicon substrate 1 is arranged at the bottom, the buried oxide layer 2 is directly oxidized and formed on the intrinsic silicon substrate 1, the silicon nitride film 3 is deposited on the buried oxide layer 2, and the silicon nitride film 3 is deposited on the buried oxide layer 2. A racetrack-shaped resonant cavity 4 is arranged above the thin film 3, including a racetrack-shaped microring 4.1, a bus waveguide 4.2 and a grating coupler 4.3. The bus waveguide 4.2 is symmetrically distributed along the length direction on both sides of the racetrack-shaped microring 4.1, and the grating coupler 4.3 is respectively located at The four ends of the two-section bus waveguide 4.2.

The intrinsic silicon substrate 1 has a thickness of 0.4-0.7 millimeters, and it mainly plays a role of supporting the entire photodetector.

Buried oxide layer 2 , in this embodiment, the buried oxide substrate layer can be silicon dioxide with a thickness of 1-3 microns, which mainly plays a role in supporting the entire photodetector.

The silicon nitride film 3 is arranged on the buried oxide layer 2, its refractive index is greater than that of the racetrack resonator 4, and its thickness is 200-400 nanometers, and the incident light from the optical grating coupler is limited to the nitrogen Propagate in SiC thin film 3.

The racetrack-shaped resonant cavity 4 includes a racetrack-shaped microring 4.1, a bus waveguide 4.2 and a grating coupler 4.3, which are arranged on the silicon nitride film 3, and two bus waveguides 4.2 are symmetrically distributed on both sides of the racetrack-shaped microring 4.1 , the four grating couplers 4 are respectively located at the four ends of the two-section bus waveguide 4.2, as the input (Input), through (Through), uplink (Add) and downlink (Drop) couplers of the racetrack resonator. The incident light from the input (Input) grating coupler is guided by the resonant cavity waveguide, and is coherent and constructive in the silicon nitride film 3 directly below the racetrack-shaped microring 4.1, so as to realize enhanced light-matter interaction. The racetrack resonant cavity 4 is provided with a sub-wavelength grating structure whose period is smaller than the light wavelength, and the sub-wavelength grating structure is composed of several sub-wavelength micro-nano structural units (a sub-wavelength micro-nano structural unit is inside the black solid frame line in Fig. 1 ) composition, including high refractive index medium (dark part of black solid frame line in Figure 1) and low refractive index medium (light part of black solid frame line in Figure 1), and the high refractive index medium is electron beam photoresist ZEP520A, the refractive index is lower than that of the silicon nitride film (3), the thickness is 200-1000 nanometers, and the low refractive index medium is gas or liquid. The subwavelength grating structure can flexibly control the mode confinement of the waveguide. More importantly, the cladding material can enter the micro-nano structure, which increases the body surface area of the device and helps to achieve higher sensitivity detection.

Racetrack microring 4.1, the width is 1.4 microns, the length of the straight part is 100 microns, the high refractive index medium is a rectangular array arranged periodically; the diameter of the arc part is d=100 microns, and the high refractive index medium is periodically arranged The trapezoidal array, wherein, the base l _outer of the trapezoid outside the circle is shorter than the base l _inner inside the circle, and its period is the same as the sub-wavelength grating period Λ of the straight line part of the racetrack-type microring 4.1. The trapezoidal shape reduces the bending loss, thereby increasing the quality factor of the resonant cavity to achieve better sensing performance.

The bus waveguide 4.2 has a length of 100 microns and a width of W ₂ =1.4 microns. The high-refractive index medium is a rectangular array periodically arranged, and its period is the same as that of the sub-wavelength grating of the racetrack-shaped microring 4.1.

The grating coupler 4.3 has widths at both ends of W ₁ =2.67 microns and W ₂ =1.4 microns respectively, and the low-refractive-index medium is a rectangular array that is periodically arranged and whose duty cycle changes according to a certain rule along the width direction.

In this embodiment, the light enters the resonant cavity from the incident optical fiber through the input (Input) grating coupler, and is transmitted around the ring. When the concentration of the external environment, molecules and other parameters change, the effective refractive index of the light propagation mode in the resonator will also change, which will cause changes in the output spectrum of the through coupler or downlink coupler, including the resonance wavelength Offset, intensity change and phase change etc. Since the light will propagate many turns in the racetrack-shaped microring, the resonant cavity structure achieves an enhanced light-matter interaction length, which is beneficial to realize high-sensitivity sensing performance. The introduction of subwavelength gratings can flexibly control the mode confinement of the waveguide. More importantly, the cladding material can enter the micro-nano structure, which increases the body surface area of the device and helps to achieve higher sensitivity detection. Hundreds of sensors can be mass-integrated on a chip through semiconductor processing technology to achieve high-throughput and low-cost detection.

As shown in Figure 4, the cross-sectional mode distribution of a sensor based on a continuum-bound state subwavelength grating racetrack resonator, it can be seen that the mode of the continuum-bound waveguide is well confined in the silicon nitride film , and are routed by bound state waveguides above the continuum domain.

As shown in Figure 5, a finite time domain difference method simulation transmission spectrum diagram of a sensor based on a continuum bound state subwavelength grating racetrack resonator cavity. The material parameters in the simulation are consistent with this embodiment. The particle swarm algorithm is used to optimize the structural parameters of the sub-wavelength grating and resonant cavity to achieve high light confinement transmission. The light of 1550 nm is incident from the input grating coupler and from the through The coupler output spectrum. It can be seen that the resonant cavity has an interference peak at the resonant wavelength, the free spectral range is 1.95 nm, and the quality factor is 15000.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A sensor based on continuous domain constraint state sub-wavelength grating runway type resonant cavity is characterized in that the device sequentially comprises the following layers from bottom to top: the first layer is an intrinsic silicon substrate (1), the second layer is a buried oxide layer (2), the third layer is a silicon nitride film (3), the fourth layer is a runway-type resonant cavity (4), and the runway-type resonant cavity (4) comprises a runway-type micro-ring (4.1), a bus waveguide (4.2) and a grating coupler (4.3); the bus waveguides (4.2) are symmetrically distributed on two sides of the runway type micro-ring (4.1) along the length direction, and the grating couplers (4.3) are respectively positioned at four ends of the two sections of bus waveguides (4.2).

2. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 1, wherein the intrinsic silicon substrate (1) has a thickness of 0.4-0.7 mm.

3. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 1, wherein the buried oxide layer (2) is made of silicon dioxide and has a thickness of 1-3 microns.

4. Sensor based on a racetrack resonator of a subwavelength grating structure in the continuous domain bound state according to claim 1 characterized by the fact that the thickness of the silicon nitride film (3) is 200-400 nm.

5. The sensor based on a runway type resonant cavity with a sub-wavelength grating structure in a continuous domain bound state according to claim 1, wherein the runway type resonant cavity (4) comprises a runway type micro-ring (4.1), a bus waveguide (4.2) and grating couplers (4.3), and the four grating couplers (4.3) are respectively used as the couplers of an Input end (Input), a Through end (Through), an uplink end (Add) and a downlink end (Drop) of the runway type resonant cavity (4).

6. The sensor based on a runway type resonant cavity of a sub-wavelength grating structure in a continuous domain bound state according to claim 5, wherein the runway type resonant cavity (4) is provided with a sub-wavelength grating structure with a period smaller than the wavelength of light, and the sub-wavelength grating structure is composed of a plurality of sub-wavelength micro-nano structural units.

7. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 6, wherein the sub-wavelength micro-nano structural unit comprises a high refractive index medium and a low refractive index medium, the high refractive index medium is electron beam photoresist ZEP520A, the refractive index is smaller than that of the silicon nitride film (3), the thickness is 200-1000 nanometers, and the low refractive index medium is gas or liquid.

8. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 5, wherein the high refractive index medium of the straight line part of the runway type micro-ring (4.1) is a rectangular array which is periodically arranged; the high refractive index medium of the arc part is a periodically arranged trapezoid array, wherein the bottom edge of the trapezoid outside the circle is shorter than the bottom edge inside the circle, and the period of the trapezoid array is the same as the period of the sub-wavelength grating of the straight line part of the runway type micro-ring (4.1).

9. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 5, wherein the high refractive index medium of the bus waveguide (4.2) is a periodically arranged rectangular array, and the period of the rectangular array is the same as the period of the sub-wavelength grating of the straight line part of the runway type micro-ring (4.1).

10. The sensor based on the runway type resonant cavity of the sub-wavelength grating structure in the continuous domain confinement state according to claim 5, wherein the low refractive index medium of the grating coupler (4.3) is a rectangular array which is periodically arranged and the duty ratio of which is changed along the width direction according to a certain rule.

Images