A sensor based on a continuous domain bound state subwavelength grating racetrack resonator

Abstract

The application is a sensor based on a continuous domain bound state subwavelength grating racetrack resonator, and the device structure is sequentially from bottom to top: the first layer is intrinsic silicon substrate (1), the second layer is buried oxide layer (2), the third layer is silicon nitride film (3), and the fourth layer is racetrack resonator (4), which comprises racetrack micro-ring (4.1), bus waveguide (4.2) and grating coupler (4.3). The application realizes high-quality-factor light confinement propagation by designing subwavelength grating structure with a period less than the wavelength of light and parameters of the racetrack resonator on the waveguide supporting continuous domain bound mode, and is further applied as a sensor. The application has many advantages such as high throughput, high detection sensitivity, high quality factor, simple structure, easy manufacturing and the like, and application as a refractive index sensor or a biological sensor can provide a solution for fast, portable and cost-effective medical detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nano-optical sensing, and more particularly, to a sensor based on a continuous domain bound state subwavelength grating racetrack resonator. BACKGROUND

[0002] The importance of rapid, portable and cost-effective medical diagnosis is increasingly highlighted. Compared with traditional detection methods based on laboratories and test papers, nano-optical sensors have simpler detection processes, faster detection times and lower detection costs, while having high sensitivity and accuracy, so they have been widely valued by researchers at home and abroad.

[0003] Most of the current nano-optical sensors are designed based on silicon-on-insulator waveguides, which require a relatively difficult etching process in the manufacturing process, have small manufacturing tolerances and high manufacturing costs. The continuous domain bound state waveguide can confine the optical field in a high refractive index film by designing the physical structure, and route it from the top low refractive index waveguide, thereby realizing the perfect confinement state in the continuous domain, becoming one of the reliable choices to replace the silicon-on-insulator waveguide. Unlike the previous silicon-on-insulator waveguide, this method does not need to etch single crystal materials, and high-precision manufacturing can be achieved with a simple process, which has the characteristics of simplicity, speed and economy. Therefore, the continuous domain bound state waveguide is considered to be an effective way to develop new nano-optical sensors.

[0004] High-Q resonators are an important element in optical systems. Since light propagates around the ring in the resonator and interferes with the incident light, the high-Q resonator can convert the cladding refractive index perturbation into changes in the interference spectrum while obtaining enhanced light-matter interaction. Therefore, the application of high-Q resonators in the field of nano-optical sensing can achieve higher detection sensitivity. The characteristic size of the 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 substance can enter the micro-nano structure, increasing the volume-surface area of the device, so it has practical significance for improving the sensitivity of the sensor. At present, further optimizing the manufacturing process and sensing performance of nano-optical sensors is a research hotspot at home and abroad. SUMMARY

[0005] Technical problem: In view of this, the purpose of the present application is to provide a sensor based on a continuous domain bound state subwavelength grating racetrack resonator, which uses a continuous domain bound state instead of a silicon-on-insulator waveguide, has the advantages of simple structure and easy manufacturing; and further expands the subwavelength grating structure in the racetrack resonator to achieve lower power consumption of optical propagation and higher sensitivity of sensing performance.

[0006] Technical solution: The sensor based on the continuous domain bound state subwavelength grating racetrack resonator cavity of the application, the layered structure of the device from bottom to top is sequentially: the first layer is intrinsic silicon substrate, the second layer is buried oxide layer, the third layer is silicon nitride film, and the fourth layer is racetrack resonator cavity, the racetrack resonator cavity includes racetrack micro ring, bus waveguide and grating coupler; wherein, the bus waveguide is symmetrically distributed along the length direction on both sides of the racetrack micro ring, and the grating coupler is located at the four ends of the two bus waveguides respectively.

[0007] The intrinsic silicon substrate has a thickness of 0.4-0.7 mm.

[0008] The material of the buried oxide layer is silicon dioxide, and the thickness is 1-3 microns.

[0009] The thickness of the silicon nitride film is 200-400 nm.

[0010] The racetrack resonator cavity includes a racetrack micro ring, a bus waveguide and a grating coupler, and the four grating couplers are respectively used as the couplers of the input end, the straight-through end, the uplink end and the downlink end of the racetrack resonator cavity.

[0011] The racetrack resonator cavity is provided with a subwavelength grating structure with a period less than the wavelength of light, and the subwavelength grating structure is composed of a plurality of subwavelength micro-nano structure units.

[0012] The subwavelength micro-nano structure unit includes a high refractive index medium and a low refractive index medium, the high refractive index medium is electron beam resist ZEP520A, the refractive index is less than the refractive index of the silicon nitride film, and the thickness is 200-1000 nm, and the low refractive index medium is gas or liquid.

[0013] The high refractive index medium of the straight line part of the racetrack micro ring is a periodically arranged rectangular array; the high refractive index medium of the circular arc part is a periodically arranged trapezoidal array, wherein the bottom of the trapezoid outside the circle is shorter than the bottom inside the circle, and the period is the same as the subwavelength grating period of the straight line part of the racetrack micro ring.

[0014] The high refractive index medium of the bus waveguide is a periodically arranged rectangular array, and the period is the same as the subwavelength grating period of the straight line part of the racetrack micro ring.

[0015] The low refractive index medium of the grating coupler is a periodically arranged rectangular array with a duty cycle changing along the width direction according to certain rules.

[0016] The working principle is as follows: the optical propagation mode can be divided into three kinds according to the frequency, including guided mode, radiation mode and continuous domain bound mode. Among them, the TE continuous mode and the TM bound mode located in the continuous domain can be fully decoupled through the low refractive index waveguide defined on the high refractive index thin film, so as to realize the low-loss propagation of the continuous domain bound mode. The sensor based on the subwavelength grating structure racetrack resonator under the continuous domain bound state is on the waveguide supporting the continuous domain bound mode, the parameters of the subwavelength grating structure and the Add-Drop racetrack resonator are designed, the light confinement propagation with high quality factor is realized, and the sensor is further applied. When the light is input into the resonant cavity bus waveguide through the input (Input) grating coupler, the light is coupled into the racetrack micro-ring in the coupling area, a part of the light is coupled into the bus waveguide after circling half a circle, and the other part of the light continues to transmit in the ring and is coupled into the bus waveguide in the coupling area, and the light is output from the drop (Drop) grating coupler after interference with the input light, so the spectrum of the through (Through) port and the drop (Drop) port is complementary. The light meeting the resonant wavelength condition is coherent and enhanced in the resonant cavity, and after one circle of transmission in the micro-ring, the phase difference between the light coupled from the micro-ring to the straight waveguide and the incident light is (2k+1)π, and the two are coherent and destructive, so the light intensity output from the through (Through) grating coupler becomes a minimum, and a plurality of filtering resonance peaks can be observed on the spectrum. When the concentration, molecules and other parameters of the external environment change, the effective refractive index of the light propagation mode in the resonant cavity also changes, thereby causing the change of the output spectrum of the through (Through) coupler or the drop (Drop) coupler, including the resonant wavelength shift, the light intensity change and the phase change. Since the light propagates in the racetrack micro-ring for many circles, the resonant cavity structure realizes the enhanced light and matter interaction length, which is beneficial to realize the high-sensitivity sensing performance. The introduction of the subwavelength grating can flexibly control the mode limitation of the waveguide, and more importantly, the cladding substance can enter the micro-nano structure, thereby increasing the volume-surface area of the device, which is helpful to realize higher sensitivity detection. A plurality of sensors can be integrated on the chip through a semiconductor processing technology, so as to realize high-throughput and low-cost detection.

[0017] Beneficial effects: compared with the prior art, the sensor of the racetrack resonator is realized by using the continuous domain bound state waveguide, and the subwavelength grating structure is introduced to improve the sensing sensitivity.

[0018] The advantages of the embodiment of the present application are that:

[0019] 1) The continuous domain bound state waveguide is adopted, the manufacturing process is simple, and the manufacturing cost is low.

[0020] 2) The racetrack resonator is designed to realize the optical propagation with high quality factor, and the enhanced light and matter interaction length is obtained, which is beneficial to realize the high-sensitivity detection performance

[0021] 3) The introduction of subwavelength gratings can flexibly control the mode confinement of the waveguide, and more importantly, the cladding substance can enter the micro-nano structure, increasing the volume-surface area of the device, which helps to achieve higher sensitivity detection.

[0022] 4) Multiple sensors can be integrated on a chip to achieve high-throughput and low-cost detection.

[0023] 5) The sensor has the advantages of high throughput, high detection sensitivity, high quality factor, simple structure, easy manufacturing, etc., and as a refractive index sensor or a biosensor, it can provide a solution for fast, portable and cost-effective medical detection. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0025] Figure 1 A structure schematic diagram of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator according to an embodiment of the present application.

[0026] Figure 2 A top view structure schematic diagram of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator according to an embodiment of the present application, and the following diagram is a partial enlarged view of the frame in the above diagram.

[0027] Figure 3 A cross-sectional structure schematic diagram of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator according to an embodiment of the present application.

[0028] Figure 4 A cross-sectional mode distribution of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator according to an embodiment of the present application.

[0029] Figure 5 A finite-difference time-domain simulation transmission spectrum line graph of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator according to an embodiment of the present application.

[0030] In the figure: intrinsic silicon substrate 1, buried oxide layer 2, silicon nitride film 3, racetrack resonator 4, racetrack resonator 4 including racetrack micro-ring 4.1, bus waveguide 4.2 and grating coupler 4.3. DETAILED DESCRIPTION

[0031] The invention will now be further explained with reference to the accompanying drawings.

[0032] like Figure 1 , Figure 2 , Figure 3 The diagram illustrates a racetrack-shaped resonant cavity based on a subwavelength grating structure in a continuous domain bound state. The device structure, from bottom to top, consists of: an intrinsic silicon substrate 1, a buried oxide layer 2, a silicon nitride thin film 3, and a racetrack-shaped resonant cavity 4. The racetrack-shaped resonant cavity 4 includes a racetrack-shaped microring 4.1, a bus waveguide 4.2, and a grating coupler 4.3. The intrinsic silicon substrate 1 is located at the bottom. The buried oxide layer 2 is directly oxidized on the intrinsic silicon substrate 1. The silicon nitride thin film 3 is deposited on the buried oxide layer 2. The racetrack-shaped resonant cavity 4, including the racetrack-shaped microring 4.1, the bus waveguide 4.2, and the grating coupler 4.3, is symmetrically distributed along the length of both sides of the racetrack-shaped microring 4.1. The grating couplers 4.3 are located at the four ends of the two bus waveguides 4.2.

[0033] The intrinsic silicon substrate 1, with a thickness of 0.4-0.7 mm, mainly serves to support the entire photodetector.

[0034] The buried oxide layer 2, in this embodiment, can be silicon dioxide with a thickness of 1-3 micrometers, which mainly serves to support the entire photodetector.

[0035] A silicon nitride thin film 3 is disposed on the buried oxide layer 2. Its refractive index is greater than that of the racetrack-shaped resonant cavity 4, and its thickness is 200-400 nanometers. Light incident from the optical grating coupler is confined to propagate in the silicon nitride thin film 3.

[0036] The racetrack-shaped resonant cavity 4 includes a racetrack-shaped micro-ring 4.1, a bus waveguide 4.2, and grating couplers 4.3, disposed on the silicon nitride thin film 3. Two bus waveguides 4.2 are symmetrically distributed on both sides of the racetrack-shaped micro-ring 4.1. Four grating couplers 4 are located at the four ends of the two bus waveguides 4.2, serving as the input, through, add, and drop couplers of the racetrack-shaped resonant cavity. Light incident from the input grating coupler is guided by the resonant cavity waveguide and coherently constructively coupled in the silicon nitride thin film 3 directly below the racetrack-shaped micro-ring 4.1, thereby enhancing light-matter interaction. The racetrack-shaped resonant cavity 4 contains a subwavelength grating structure with a period smaller than the wavelength of light. This subwavelength grating structure consists of several subwavelength micro / nano structure units (…). Figure 1 The solid black frame in the middle represents a subwavelength micro / nano structure unit, comprising a high refractive index medium ( Figure 1 (the dark part within the black solid frame) and low refractive index media (Figure 1 The high refractive index medium is electron beam lithography glue ZEP520A, the refractive index is less than that of the silicon nitride film (3), the thickness is 200-1000 nanometers, and the low refractive index medium is a gas or a liquid. The subwavelength grating structure can flexibly control the mode limitation of the waveguide, and more importantly, the cladding substance can enter the micro-nano structure, thereby increasing the volume-surface area of the device and helping to realize higher sensitivity detection.

[0037] The runway-type micro-ring 4.1 has a width of 1.4 microns, a length of a straight line part of 100 microns, and a high refractive index medium that is a periodically arranged rectangular array; a circular arc part has a diameter d of 100 microns, and a high refractive index medium that is a periodically arranged trapezoidal array, wherein the base l outer of the trapezoid outside the circle is shorter than the base l inner of the trapezoid inside the circle, and the period is the same as the subwavelength grating period Lambda of the straight line part of the runway-type micro-ring 4.1. The trapezoid reduces the bending loss, thereby increasing the quality factor of the resonant cavity to achieve better sensing performance.

[0038] The bus waveguide 4.2 has a length of 100 microns, a width of W2=1.4 microns, and a high refractive index medium that is a periodically arranged rectangular array, and the period is the same as the subwavelength grating period of the straight line part of the runway-type micro-ring 4.1.

[0039] The grating coupler 4.3 has a width of W1=2.67 microns and W2=1.4 microns at two ends, and a low refractive index medium that is a periodically arranged rectangular array with a duty cycle that changes along the width direction according to a certain rule.

[0040] In the embodiment, light enters the resonant cavity from the input grating coupler through the input fiber and is transmitted around the ring. When the concentration, molecules, or other parameters of the external environment change, the effective refractive index of the light propagation mode in the resonant cavity also changes, thereby causing changes in the output spectrum of the through coupler or the drop coupler, including resonance wavelength shift, light intensity change, and phase change. Since the light propagates many times in the runway-type micro-ring, the resonant cavity structure realizes enhanced light-matter interaction length, which is conducive to realizing high-sensitivity sensing performance. The introduction of the subwavelength grating can flexibly control the mode limitation of the waveguide, and more importantly, the cladding substance can enter the micro-nano structure, thereby increasing the volume-surface area of the device and helping to realize higher sensitivity detection. Hundreds of sensors can be integrated on a chip through a semiconductor processing technology, thereby realizing high-throughput and low-cost detection.

[0041] As Figure 4As shown in the figure, the cross-sectional mode distribution of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator can be seen that the mode of the continuous domain bound state waveguide is well confined in the silicon nitride film and routed by the upper continuous domain bound state waveguide.

[0042] As shown in the figure, the cross-sectional mode distribution of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator can be seen that the mode of the continuous domain bound state waveguide is well confined in the silicon nitride film and routed by the upper continuous domain bound state waveguide. Figure 5 As shown in the figure, the cross-sectional mode distribution of a sensor based on a continuous domain bound state subwavelength grating racetrack resonator can be seen that the mode of the continuous domain bound state waveguide is well confined in the silicon nitride film and routed by the upper continuous domain bound state waveguide.

[0043] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A sensor based on a continuous domain bound state subwavelength grating racetrack resonator characterized in that, The device has a layered structure from bottom to top, which is sequentially: a first layer is an intrinsic silicon substrate (1), a second layer is a buried oxide layer (2), a third layer is a silicon nitride film (3), and a fourth layer is a racetrack resonant cavity (4). The racetrack resonant cavity (4) comprises a racetrack micro-ring (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 micro-ring (4.1), and the grating coupler (4.3) is located at the four ends of the two bus waveguides (4.2), respectively. The racetrack resonant cavity (4) comprises a racetrack micro-ring (4.1), a bus waveguide (4.2) and a grating coupler (4.3), and the four grating couplers (4.3) are used as couplers of the input end (Input), the through end (Through), the uplink end (Add) and the downlink end (Drop) of the racetrack resonant cavity (4), respectively. The racetrack resonant cavity (4) is provided with a sub-wavelength grating structure with a period less than the wavelength of light, and the sub-wavelength grating structure is composed of a plurality of sub-wavelength micro-nano structure units. The sub-wavelength micro-nano structure unit comprises a high refractive index medium and a low refractive index medium, the high refractive index medium is electron beam resist ZEP520A, the refractive index is less than the refractive index of the silicon nitride film (3), and the thickness is 200-1000 nanometers, and the low refractive index medium is a gas or a liquid.

2. The sensor based on a continuous domain bound state subwavelength grating structure racetrack resonator according to claim 1, characterized in that, The thickness of the intrinsic silicon substrate (1) is 0.4-0.7 millimeters.

3. The sensor based on a continuous domain bound state subwavelength grating structure racetrack resonator according to claim 1, characterized in that, The material of the buried oxide layer (2) is silicon dioxide, and the thickness is 1-3 micrometers.

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

5. The sensor based on a continuous domain bound state subwavelength grating structure racetrack resonator according to claim 1, characterized in that, The high refractive index medium of the straight part of the racetrack micro-ring (4.1) is a periodically arranged rectangular array; the high refractive index medium of the circular arc part is a periodically arranged trapezoidal array, wherein the bottom of the trapezoid outside the circle is shorter than the bottom inside the circle, and the period is the same as the sub-wavelength grating period of the straight part of the racetrack micro-ring (4.1).

6. The sensor based on a continuous domain bound state subwavelength grating structure racetrack resonator of claim 1, wherein, The high refractive index medium of the bus waveguide (4.2) is a periodically arranged rectangular array, and the period is the same as the sub-wavelength grating period of the straight part of the racetrack micro-ring (4.1).

7. The sensor based on a continuous domain bound state sub-wavelength grating structure racetrack resonator of claim 1, wherein, The low refractive index medium of the grating coupler (4.3) is a periodically arranged rectangular array with a duty cycle changing along the width direction according to a certain rule.

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