On-chip waveguide gas sensor
By designing the Mach-Zendel interferometer gas sensor using a photonic crystal waveguide structure on the chip, the problem of relying on expensive equipment and special processes in the prior art is solved, and the gas detection effect with miniaturization, cost reduction and high sensitivity is achieved.
Patent Information
- Application Number
- CN202510078589.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-17
- Publication Date
- 2025-05-13
AI Technical Summary
Existing on-chip gas sensors rely on expensive equipment or special processes, are expensive and have high manufacturing process requirements, making them difficult to be compatible with standard CMOS processes.
An on-chip waveguide gas sensor was designed, using a photonic crystal waveguide structure as the sensing arm of the interferometer, combined with a single-mode straight waveguide as the reference arm, and using the interference effect of the Mach-Zendel interferometer to achieve gas detection. The sensor has a compact structure, loose process requirements, and is compatible with standard 0.18μm CMOS process.
The miniaturization and cost reduction of gas sensors are achieved, the measurement range and sensitivity are improved, and the dependence on expensive equipment and complex processes is avoided.
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Figure CN119985402A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the field of optoelectronic technology, and in particular to an on-chip waveguide gas sensor. Background Art
[0002] In recent years, photonic integration technology based on the Silicon-On-Insulator (SOI) platform has developed rapidly, which can integrate traditional independent optical devices into the same photonic chip, making it possible to realize on-chip gas sensors.
[0003] Existing on-chip gas sensors are mainly based on the principles of refractive index sensing, Raman spectroscopy sensing, and infrared absorption sensing. For example, the optimal refractive index sensor can reduce the detection limit of alcohol vapor to 1.6ppb; the detection limit of infrared absorption sensors for methane is 348.6ppm; Raman scattering sensors can detect dimethyl sulfoxide organic vapor with a detection limit of 7.6ppb. However, most of these sensors rely on expensive instruments or complex processes: refractive index sensors require tunable lasers to track the output peak, while Raman spectroscopy sensing and infrared absorption sensing rely on spectrometers to characterize gas properties. In addition, the manufacturing process requirements of these sensors are high. For example, the refractive index sensor based on subwavelength grating waveguide microrings requires electron beam lithography, which is difficult to be compatible with standard CMOS processes; MZI sensors based on metal surface plasmon waveguides require additional preparation of silver waveguides, and silver waveguides are prone to failure due to lack of coating protection; MZI sensors based on subwavelength grating waveguides require 90nm CMOS processes, and their cost is 5-10 times that of 0.18μm CMOS processes.
[0004] In summary, existing on-chip gas sensors generally have the problem of relying on expensive equipment or special processes and being high in cost. Summary of the invention
[0005] The purpose of this application is to provide an on-chip waveguide gas sensor.
[0006] The present application provides an on-chip waveguide gas sensor, comprising:
[0007] A substrate, and an incident Y-waveguide, an output Y-waveguide, a single-mode straight waveguide and a photonic crystal waveguide structure arranged on the substrate;
[0008] Two ends of the single-mode straight waveguide are respectively connected to the first branch waveguide of the incident Y waveguide and the first branch waveguide of the output Y waveguide;
[0009] Two ends of the photonic crystal waveguide structure are respectively connected to the second branch waveguide of the incident Y waveguide and the second branch waveguide of the output Y waveguide;
[0010] The single-mode straight waveguide is used as a reference arm of the interferometer, and the photonic crystal waveguide structure is used as a sensing arm of the interferometer.
[0011] In a possible implementation, the photonic crystal waveguide structure includes: an incident tapered waveguide, an incident transition structure, a two-dimensional photonic crystal waveguide, an output transition structure, and an output tapered waveguide which are sequentially connected along an optical path.
[0012] In a possible implementation, the incident transition structure and the output transition structure are symmetrically arranged;
[0013] The incident transition structure comprises a plurality of semi-elliptical waveguides arranged in parallel along the optical path direction, the semi-elliptical waveguides overlap with a portion of the two-dimensional photonic crystal waveguide, and the width of the semi-elliptical waveguides gradually decreases along the optical path direction.
[0014] In a possible implementation manner, the surface of the single-mode straight waveguide is covered with a protective layer, and the surface of the photonic crystal waveguide structure is covered with a gas sensitive coating.
[0015] In a possible implementation, the protective layer includes a silicon dioxide material, and the gas sensitive coating includes a mesoporous silicon dioxide material.
[0016] In a possible implementation, both the incident Y-waveguide and the output Y-waveguide are asymmetric Y-waveguides.
[0017] In a possible implementation, the included angle between the two branch waveguides of the asymmetric Y-waveguide is 45°.
[0018] In a possible implementation manner, a heating resistor is further disposed above the single-mode straight waveguide.
[0019] In a possible implementation manner, the width of the heating resistor is greater than the width of the single-mode straight waveguide.
[0020] In a possible implementation, the heating resistor is made of titanium nitride.
[0021] Compared with the prior art, the on-chip waveguide gas sensor provided by the present application includes a substrate, and an incident Y waveguide, an output Y waveguide, a single-mode straight waveguide and a photonic crystal waveguide structure arranged on the substrate; the two ends of the single-mode straight waveguide are respectively connected to the first branch waveguide of the incident Y waveguide and the first branch waveguide of the output Y waveguide; the two ends of the photonic crystal waveguide structure are respectively connected to the second branch waveguide of the incident Y waveguide and the second branch waveguide of the output Y waveguide; wherein the single-mode straight waveguide serves as the reference arm of the interferometer, and the photonic crystal waveguide structure serves as the sensing arm of the interferometer. It can be seen that in the on-chip waveguide gas sensor provided by the present application, the sensing arm uses a photonic crystal waveguide structure, which has a high refractive index sensitivity, a compact structure, loose process requirements, and is compatible with the standard 0.18μm CMOS process, which can miniaturize the gas sensor and reduce the sensor preparation cost. At the same time, a phase-discrimination output method is adopted to increase the measurement range of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present disclosure. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:
[0023] Figure 1 A schematic structural diagram of an on-chip waveguide gas sensor provided by the present disclosure is shown;
[0024] Figure 2 Shown Figure 1 A magnified view of the medium-incident Y-waveguide 11;
[0025] Figure 3 Shown Figure 1 An enlarged view of the incident tapered waveguide 21 and the incident transition structure 22;
[0026] Figure 4 Shown is a schematic diagram of signal modulation and processing of an on-chip waveguide gas sensor provided by the present disclosure;
[0027] Figure 5 Shown is a specific parameter diagram of the on-chip waveguide gas sensor provided by the present disclosure;
[0028] Figure 6 Shown Figure 1 An enlarged view of the single-mode straight waveguide 31 and the heating resistor 32;
[0029] Figure 7 The figure is a top view of the electric field intensity when the asymmetric Y-waveguide provided by the present disclosure inputs the TE0 mode;
[0030] Figure 8 The figure shows the relative transmittance of the two-dimensional photonic crystal waveguide with different wavelengths of TE mode input;
[0031] Fig. 9 Shown is a graph showing the relationship between different lengths of L and the extinction ratio and the refractive index sensitivity of the sensor;
[0032] Fig.10 The graph shows the relationship between the refractive index sensitivity and extinction ratio of the sensor as A changes while keeping the L width constant. DETAILED DESCRIPTION
[0033] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.
[0034] Various structural schematic diagrams according to embodiments of the present disclosure are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may further design regions / layers with different shapes, sizes, and relative positions according to actual needs.
[0035] In the context of the present disclosure, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element or an intervening layer / element may exist therebetween. In addition, if a layer / element is "on" another layer / element in one orientation, the layer / element may be "below" the other layer / element when the orientation is reversed.
[0036] When the on-chip waveguide gas sensor provided by the present invention performs gas measurement, it does not require a tunable laser and a spectrometer, but only requires a photodiode, a laser diode, and peripheral circuits for temperature control and modulation, which greatly reduces the overall volume and cost, as described below with reference to the accompanying drawings.
[0037] The on-chip waveguide gas sensor provided by the present disclosure has a detection principle based on the interference effect of a Mach-Zehnder interferometer and the property that gases of different concentrations have different refractive indices.
[0038] Please refer to Figure 1 , Figure 1 A schematic structural diagram of an on-chip waveguide gas sensor provided in an embodiment of the present application is shown.
[0039] like Figure 1 As shown, the on-chip waveguide gas sensor of the present application includes: a substrate (not shown in the figure), and an incident Y waveguide 11, an output Y waveguide 12, a single-mode straight waveguide 31 and a photonic crystal waveguide structure 20 arranged on the substrate. The surface of the single-mode straight waveguide 31 is covered with a protective layer, which can be a silicon dioxide protective layer. The surface of the photonic crystal waveguide structure 20 is covered with a gas sensitive coating, which can be a mesoporous silicon dioxide coating.
[0040] In some embodiments, Figure 2 As shown, the incident Y waveguide 11 and the output Y waveguide 12 are both asymmetric Y waveguides, and the angle between the two branch waveguides (the first branch waveguide and the second branch waveguide) of the asymmetric Y waveguide can be 45°, and of course it can also be set to other values as needed.
[0041] Specifically, Figure 2 As shown, the second branch waveguide of the asymmetric Y-waveguide can be a straight waveguide, and the first branch waveguide and the second branch waveguide form an angle of 45°.
[0042] like Figure 1 As shown, the two ends of the single-mode straight waveguide 31 are respectively connected to the first branch waveguide of the incident Y waveguide 11 and the first branch waveguide of the output Y waveguide 12. The two ends of the photonic crystal waveguide structure 20 are respectively connected to the second branch waveguide of the incident Y waveguide 11 and the second branch waveguide of the output Y waveguide 12. The single-mode straight waveguide serves as the reference arm of the interferometer, and the photonic crystal waveguide structure serves as the sensing arm of the interferometer.
[0043] In some embodiments, Figure 1 As shown, a heating resistor 32 is further disposed above the single-mode straight waveguide 31. Specifically, the width of the heating resistor 32 is greater than the width of the single-mode straight waveguide 31. The heating resistor 32 may be made of titanium nitride.
[0044] In some embodiments, Figure 1 As shown, the photonic crystal waveguide structure 20 includes: an incident tapered waveguide 21, an incident transition structure 22, a two-dimensional photonic crystal waveguide 23, an output transition structure 24, and an output tapered waveguide 25, which are sequentially connected along the optical path. Specifically, the incident tapered waveguide 21 and the output tapered waveguide 25 are symmetrically arranged, and the incident transition structure 22 and the output transition structure 24 are symmetrically arranged.
[0045] Figure 3 Shown Figure 1 An enlarged view of the incident tapered waveguide 21 and the incident transition structure 22.
[0046] like Figure 3As shown, the incident transition structure 22 includes a plurality of semi-elliptical waveguides arranged in parallel along the optical path direction, the semi-elliptical waveguides overlap with a portion of the two-dimensional photonic crystal waveguide 23, and the width of the semi-elliptical waveguides gradually decreases along the optical path direction.
[0047] In the on-chip waveguide gas sensor disclosed herein, except for the heating resistor 32 which is made of titanium nitride, the rest of the incident Y waveguide 11, the output Y waveguide 12, the single-mode straight waveguide 31 and the photonic crystal waveguide structure 20 are all made of single crystal silicon. The substrate may include silicon dioxide material.
[0048] The following is the detection principle of the above-mentioned on-chip waveguide gas sensor provided by the present disclosure.
[0049] Figure 4 A schematic diagram of signal modulation and processing of the on-chip waveguide gas sensor provided by the present disclosure.
[0050] like Figure 4 As shown, the waveguide Mach-Zehnder interferometer used in the present invention has two interference arms, namely the sensing arm and the reference arm. The single-mode laser is coupled into the incident Y waveguide by the input coupling grating, and then distributed into two beams of light by the incident Y waveguide and enter the reference arm and the sensing arm respectively. The sensing arm and the reference arm interfere with each other at the output Y waveguide. When the optical path difference between the reference arm and the sensing arm changes, the optical power of the interference output will change. The reference arm is composed of a single-mode waveguide covered with a silica protective layer, so its own optical properties are not changed by changes in the refractive index of the external gas. The sensing arm is composed of a two-dimensional photonic crystal waveguide, and the waveguide has no silica protective layer and is exposed to the external environment. At the same time, it is covered with a sensing waveguide gas sensitive coating, which enhances the property that gases of different concentrations have different refractive indices. When the gas concentration changes, the optical path of light propagating in the sensing arm will change, which will cause the phase of the output signal to change, which can be Figure 4 Detected by the method shown.
[0051] Photonic crystal is a medium with a periodically changing refractive index. Compared with ordinary waveguides, the energy of the evanescent field around the photonic crystal accounts for a larger proportion of the total propagation energy, so it has stronger sensing capabilities than ordinary waveguides.
[0052] The sensing arm disclosed in the present invention adopts a two-dimensional photonic crystal waveguide. Compared with a straight waveguide, the optical power of the evanescent field of the two-dimensional photonic crystal waveguide outside the waveguide medium is greater than that of a straight waveguide, so it is more sensitive to the refractive index change of the coating. However, the transmittance of the two-dimensional photonic crystal waveguide with the same length of 5μm under a 1550nm laser is only 17% of that of the single-mode straight waveguide with the same length. Therefore, the present invention adds a transition structure on the basis of the two-dimensional photonic crystal waveguide to effectively improve the transmittance, and the transition structure is composed of a semi-elliptical structure. The sensitivity of directly using a waveguide for alcohol vapor concentration detection is very low, and the additional mesoporous silica coating can effectively improve the sensitivity and detection limit of the sensor. The coating preparation method is simple, and a coating of a certain thickness can be prepared by spin coating.
[0053] Figure 1 The specific parameters of the on-chip waveguide gas sensor are shown in Figure 5 As shown in Figure 2, the overall length of the on-chip waveguide gas sensor is 113.4 μm and the width is 5.1 μm. The width of the input and output strip single-mode straight waveguides of the asymmetric Y-waveguide is 0.45 μm, and the length of the asymmetric Y-waveguide is 7.3 μm.
[0054] like Figure 2 As shown, the waveguide width of the asymmetric Y-waveguide is 0.45 μm, and the angle between the two branch waveguides is 45°.
[0055] like Figure 3 As shown, the overall period of the two-dimensional photonic crystal waveguide is 0.38μm and the duty cycle is 47.3%; the width of a single-layer photonic crystal is 0.3μm and the spacing between layers is 0.2μm; the tapered waveguide input port is 0.45μm and the output port is 1.8μm; the transition structure consists of a two-dimensional photonic crystal waveguide and a truncated semi-elliptical waveguide, the ellipse is 2.2μm long and the truncated port is 0.2μm wide.
[0056] Figure 6 Shown Figure 1 The enlarged view of the single-mode straight waveguide 31 and the heating resistor 32 shows that the width of the single-mode straight waveguide 31 is 0.45 μm, and the width of the heating resistor 32 is 1.28 μm.
[0057] The on-chip waveguide gas sensor provided by the present disclosure has the characteristics of small size, high sensitivity, adaptability to standard SOI process, and no need for electron beam lithography process, and has important research and application value in gas sensing.
[0058] The present disclosure uses a finite-difference time-domain method (FDTD) to simulate the on-chip waveguide gas sensor. The simulation results of the on-chip waveguide gas sensor of the present disclosure are described in detail below according to the diagrams.
[0059] Figure 7The top view of the electric field intensity when the asymmetric Y waveguide provided by the present invention is input into the TE0 mode. An infrared laser with a wavelength of 1550nm is input from the input end of the incident Y waveguide 11. Figure 7 As shown, the TE mode signal is asymmetrically distributed at the branch along the input straight waveguide, and most of the optical power is transmitted along the branch waveguide parallel to the input wave, realizing the function of asymmetric power output, and its power distribution ratio is 0.27 to 1.
[0060] Figure 8 The figure is a schematic diagram of the relative transmittance of the two-dimensional photonic crystal waveguide under the TE mode input of different wavelengths (1550nm-1600nm) (relative to the transmittance of the single-mode straight waveguide). The relative transmittance of the two-dimensional photonic crystal waveguide with a transition structure fluctuates between 30.55% and 35.21%, while the relative transmittance of the two-dimensional photonic crystal waveguide without a transition structure fluctuates between 15.07% and 17.21%. At this time, the length of the two-dimensional photonic crystal waveguide is 100.4μm.
[0061] Fig. 9 The relationship between L and the extinction ratio and the refractive index sensitivity of the sensor at different lengths is shown in Figure 2. L is the duty cycle of the two-dimensional photonic crystal waveguide. Fig. 9 Among them, A is set to 100nm. After comprehensive consideration, L is set to 180nm, which achieves a good balance between extinction ratio and sensitivity. In order to reduce the simulation time, the length of the two-dimensional photonic crystal waveguide is set to 10μm, and the actual length is 100.4μm.
[0062] Fig.10 To keep L constant at 180nm, the relationship between the sensor's refractive index sensitivity and extinction ratio as A changes. Fig.10 It can be seen that when A is 200nm, the sensitivity and extinction ratio are the highest. At this time, the refractive index sensitivity is 198nm / RIU and the extinction ratio is 4.507. When the two-dimensional photonic crystal waveguide is extended to 100.4μm, the refractive index sensitivity is 1980nm / RIU.
[0063] The above simulation results show that the on-chip waveguide gas sensor disclosed in the present invention exhibits good sensitivity and has the ability to compensate for temperature drift. The sensor does not require an external tunable laser and spectrometer, and has lower cost and smaller size. The waveguide gas sensor disclosed in the present invention has a simple and compact structure, a large process tolerance, and is compatible with CMOS silicon photonics and does not require complex processes. The present invention has important research and application value in the fields of gas sensing in optical sensors in photonic integration.
[0064] The invention is based on the standard 0.18μm CMOS process, which has the advantages of low cost and high mass production, and has broad commercial value. At the same time, the innovation points of the invention are: 1. Adding an asymmetric Y-branch waveguide to improve the sensor signal-to-noise ratio; 2. Adding a thermal phase modulator to cooperate with Figure 4 The phase-comparison output shown improves the output range of the sensor.
[0065] In order to form the same structure, those skilled in the art may also design a method that is not completely the same as the method described above. In addition, although the various embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination advantageously.
[0066] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, a person skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.
[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application.
Claims
1. An on-chip waveguide gas sensor, characterized in that: include: A substrate, and an incident Y-waveguide, an output Y-waveguide, a single-mode straight waveguide and a photonic crystal waveguide structure arranged on the substrate; Two ends of the single-mode straight waveguide are respectively connected to the first branch waveguide of the incident Y waveguide and the first branch waveguide of the output Y waveguide; Two ends of the photonic crystal waveguide structure are respectively connected to the second branch waveguide of the incident Y waveguide and the second branch waveguide of the output Y waveguide; The single-mode straight waveguide is used as a reference arm of the interferometer, and the photonic crystal waveguide structure is used as a sensing arm of the interferometer.
2. The on-chip waveguide gas sensor according to claim 1, characterized in that: The photonic crystal waveguide structure comprises: an incident tapered waveguide, an incident transition structure, a two-dimensional photonic crystal waveguide, an output transition structure and an output tapered waveguide which are sequentially connected and arranged along an optical path.
3. The on-chip waveguide gas sensor according to claim 2, characterized in that: The incident transition structure and the output transition structure are symmetrically arranged; The incident transition structure comprises a plurality of semi-elliptical waveguides arranged in parallel along the optical path direction, the semi-elliptical waveguides overlap with a portion of the two-dimensional photonic crystal waveguide, and the width of the semi-elliptical waveguides gradually decreases along the optical path direction.
4. The on-chip waveguide gas sensor according to claim 1, characterized in that: The surface of the single-mode straight waveguide is covered with a protective layer, and the surface of the photonic crystal waveguide structure is covered with a gas sensitive coating.
5. The on-chip waveguide gas sensor according to claim 4, characterized in that: The protective layer comprises a silicon dioxide material, and the gas sensitive coating comprises a mesoporous silicon dioxide material.
6. The on-chip waveguide gas sensor according to claim 1, characterized in that: The incident Y-waveguide and the output Y-waveguide are both asymmetric Y-waveguides.
7. The on-chip waveguide gas sensor according to claim 6, characterized in that: The included angle between the two branch waveguides of the asymmetric Y-waveguide is 45°.
8. The on-chip waveguide gas sensor according to claim 1, characterized in that: A heating resistor is also arranged above the single-mode straight waveguide.
9. The on-chip waveguide gas sensor according to claim 8, characterized in that: The width of the heating resistor is greater than the width of the single-mode straight waveguide.
10. The on-chip waveguide gas sensor according to claim 8, characterized in that: The heating resistor is made of titanium nitride.