Temperature sensor and optical chip based on enhanced vernier effect

Abstract

The invention relates to the field of photon integrated circuits, in particular to a temperature sensor based on an enhanced vernier effect and an optical chip, and aims to improve the structure of the temperature sensor and improve the detection sensitivity. In order to achieve the purpose, the temperature sensor comprises two Mach-Zehnder interference structures which are connected in parallel, and upper cladding layers of a sensing arm and a reference arm are made of two upper cladding layer materials with opposite thermo-optical coefficients. Through the design of the sensing arm and the reference arm which are connected in parallel, an enough separation space is formed between the two arms, different upper cladding materials can be conveniently covered, and the process difficulty is reduced; two upper cladding materials with opposite thermo-optical coefficients are adopted as the upper cladding of the sensing arm and the upper cladding of the reference arm respectively, the wavelength drift amount of the envelope of the output combined spectrum along with the temperature change can be greatly improved, and therefore the sensitivity of the temperature sensor is improved.

Description

Technical Field

[0001] This application relates to the field of photonic integrated circuits, specifically to a temperature sensor and optical chip based on the enhanced vernier effect. Background Technology

[0002] Silicon photonics chips, due to their advantages such as high integration, low cost, and compatibility with CMOS processes, have been widely used in cutting-edge fields such as data center optical interconnects, optical computing, and quantum information processing. However, the core optical performance parameters (resonant wavelength, refractive index, phase, etc.) of silicon-based photonic devices (such as microring resonators, Mach-Zehnder interferometers, and lasers) exhibit extremely high sensitivity to temperature changes. Even small temperature fluctuations can cause significant changes in the effective refractive index of the mode, leading to drift in key device parameters. This not only severely degrades the wavelength stability and phase coherence of optical signals, causing a surge in communication bit error rates and a decrease in computational accuracy, but also induces severe channel crosstalk in dense wavelength division multiplexing (DWDM) systems. Therefore, achieving in-situ, high-sensitivity, and fast-response temperature detection on-chip is crucial for real-time compensation of thermally induced optical drift, maintaining stable optical path performance, and ensuring reliable system operation.

[0003] Currently, most on-chip temperature sensors based on the vernier effect employ micro-ring resonators or cascaded Mach-Zehnder interferometer structures. While these sensors offer advantages such as small size and ease of manufacturing, their sensitivity is limited. Therefore, improving the structure of vernier effect-based temperature sensors to enhance detection sensitivity has become an urgent problem to be solved. Summary of the Invention

[0004] In order to overcome the above-mentioned defects, this application is made to solve, or at least partially solve, the technical problem of how to improve the structure of a vernier effect-based temperature sensor and enhance its detection sensitivity.

[0005] In a first aspect, a temperature sensor based on the enhanced vernier effect is provided, comprising, in sequence, a substrate, a lower cladding layer, a waveguide layer, and an upper cladding layer, wherein: The waveguide layer includes a first beamsplitter, a second beamsplitter, a third beamsplitter, a first Mach-Zehnder interference structure, a second Mach-Zehnder interference structure, and a beam combiner; wherein, the first Mach-Zehnder interference structure includes a first directional coupler, and the second Mach-Zehnder interference structure includes a second directional coupler; The two outputs of the first beam splitter are connected to the inputs of the second and third beam splitters, respectively; the two outputs of the second beam splitter are connected to the two inputs of the first directional coupler, and the output of the first directional coupler is connected to the first input of the beam combiner; the two outputs of the third beam splitter are connected to the two inputs of the second directional coupler, and the output of the second directional coupler is connected to the second input of the beam combiner. The upper cladding includes a first upper cladding and a second upper cladding. The first upper cladding has a first thermo-optic coefficient, and the second upper cladding has a second thermo-optic coefficient. Of the first and second thermo-optic coefficients, one is positive and the other is negative. The first upper cladding covers the first directional coupler, and the second upper cladding covers the second directional coupler.

[0006] In one technical solution of the above temperature sensor structure, the first Mach-Zehnder interferometer structure further includes a first waveguide, a second waveguide, and a first output waveguide; the second Mach-Zehnder interferometer structure further includes a third waveguide, a fourth waveguide, and a second output waveguide. The two outputs of the second beam splitter are connected to the two inputs of the first directional coupler via the first waveguide and the second waveguide, respectively; the output of the first directional coupler is connected to the first input of the beam combiner via the first output waveguide. The two outputs of the third beam splitter are connected to the two inputs of the second directional coupler via the third and fourth waveguides, respectively. The output of the second directional coupler is connected to the second input of the beam combiner via the second output waveguide.

[0007] In one technical solution of the above-mentioned temperature sensor structure, The first waveguide and the second waveguide have different lengths, so that there is an optical path difference between the two optical signals input to the first directional coupler; The third and fourth waveguides have different lengths to create an optical path difference between the two optical signals input to the second directional coupler.

[0008] In one technical solution of the above temperature sensor structure, the absolute values ​​of the first thermo-optic coefficient and the second thermo-optic coefficient are different.

[0009] In one technical solution of the above temperature sensor structure, the upper cladding also includes a third upper cladding with a third thermo-optic coefficient, and the third upper cladding covers the area other than the first directional coupler and the second directional coupler.

[0010] In one technical solution of the above temperature sensor structure, the absolute values ​​of the first thermo-optic coefficient and the second thermo-optic coefficient are both greater than the absolute value of the third thermo-optic coefficient.

[0011] In one technical solution of the above temperature sensor structure, the absolute values ​​of the thermo-optic coefficients in the first and second upper cladding layers are relatively small, and are the same as the absolute value of the third thermo-optic coefficient.

[0012] In a second aspect, an optical chip is provided, including a temperature sensor according to any of the above-mentioned technical solutions.

[0013] The above-mentioned technical solutions of this application have at least one or more of the following beneficial effects: The temperature sensor body adopts two parallel Mach-Zehnder interferometer structures, which provides sufficient separation space between the sensing arm and the reference arm, making it convenient to cover the sensing arm and the reference arm with cladding materials of different thermo-optic coefficients, thus reducing the difficulty of the process; Using two cladding materials with positive and negative thermo-optic coefficients as the cladding materials of the sensing arm and the reference arm (first directional coupler and second directional coupler) respectively can greatly improve the wavelength shift of the envelope of the output combined spectrum with temperature change, thereby improving the sensitivity of the temperature sensor. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a temperature sensor according to one embodiment of this application.

[0015] Figure 2 This is a cross-sectional schematic diagram of a temperature sensor according to one embodiment of this application.

[0016] Figure 3 This is a schematic diagram of a temperature measurement system according to one embodiment of this application. Detailed Implementation

[0017] Some embodiments of this application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this application and are not intended to limit the scope of protection of this application.

[0018] It should be noted that in the description of this application, terms such as "upper," "lower," "inner," and "outer," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These terms are used merely for ease of description and do not indicate or imply that a structure must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, terms such as "first," "second," and similar descriptions are used only for distinguishing purposes and should not be construed as indicating or implying relative importance.

[0019] Temperature sensors based on the vernier effect (hereinafter referred to as temperature sensors) typically have a reference arm and a sensing arm. If these two interference spectra are connected in parallel, the Free Spectral Range (FSR) of the envelope of the resulting combined spectrum is the least common multiple of the FSRs of the two independent spectra, and its wavelength shift is much greater than that of a single arm. This application improves the sensitivity of the temperature sensor by optimizing the design of the reference arm and the sensing arm and adjusting the cladding material corresponding to the regions of the two arms.

[0020] Figure 1 This is a schematic diagram of a temperature sensor according to one embodiment of this application. Figure 1 As shown, the temperature sensor of this application includes a cladding and a waveguide layer enclosed by the cladding, wherein the cladding includes an upper cladding and a lower cladding; the waveguide layer structure includes: a first beam splitter 11, a second beam splitter 12, a third beam splitter 13, a first directional coupler 14, a second directional coupler 15, and a beam combiner 16.

[0021] The incident light enters from the input end of the first beam splitter 11 via end-face coupling or grating coupling. The first beam splitter 11 splits the beam into two output beams. As an example, the beam splitting ratio can be set to 1:1. The two output ends of the first beam splitter 11 are connected to the input ends of the second beam splitter 12 and the third beam splitter 13, respectively.

[0022] The second beam splitter 12 splits the incoming beam of light into two beams, which are output from two output ports respectively. The first output port of the second beam splitter 12 is connected to the first input port of the first directional coupler 14 through the first waveguide 21; the second output port of the second beam splitter 12 is connected to the second input port of the first directional coupler 14 through the second waveguide 22.

[0023] The first waveguide 21 and the second waveguide 22 have different lengths, which causes the two beams of light entering the first directional coupler 14 to have an optical path difference. The two beams of light interfere within the first directional coupler 14, and the first interference light is output.

[0024] The first waveguide 21, the second waveguide 22, and the first directional coupler 14 constitute the first Mach-Zehnder interferometer structure or the core structure of the first Mach-Zehnder interferometer structure. The first Mach-Zehnder interferometer structure serves as the sensing arm of the temperature sensor, and the FSR of this sensing arm is denoted as FSR. sens .

[0025] The third beam splitter 13 also splits the incoming beam into two beams, which are output from two output ports respectively. The first output port of the third beam splitter 13 is connected to the first input port of the second directional coupler 15 through the third waveguide 23; the second output port of the third beam splitter 13 is connected to the second input port of the second directional coupler 15 through the fourth waveguide 24.

[0026] The third waveguide 23 and the fourth waveguide 24 have different lengths, which causes the two beams of light entering the second directional coupler 15 to have an optical path difference. The two beams of light interfere within the second directional coupler 15, and the second interference light is output.

[0027] The third waveguide 23, the fourth waveguide 24, and the second directional coupler 15 constitute the second Mach-Zehnder interferometer structure or its core structure. The second Mach-Zehnder interferometer structure serves as the reference arm for the temperature sensor, and the FSR of this reference arm is denoted as FSR. ref .

[0028] For both the first and second Mach-Zehnder interferometer structures, specifically, the directional couplers are the key components that truly play a crucial role in temperature sensing. Therefore, in both Mach-Zehnder interferometer structures, one directional coupler is considered the sensing arm, and the other is considered the reference arm. It should be noted that the terms "reference arm" and "sensing arm" are relative and interchangeable in practice. For ease of explanation, in this embodiment, the first directional coupler 14 in the first Mach-Zehnder interferometer structure is considered the sensing arm, and the second directional coupler 15 in the second Mach-Zehnder interferometer structure is considered the reference arm.

[0029] The outputs of the first directional coupler 14 and the second directional coupler 15 are respectively connected to the two input and output terminals of the beam combiner 16. The first interference light and the second interference light generate a vernier effect in the beam combiner 16. The output terminal of the beam combiner 16 outputs a combined spectrum light signal, which is the output of the temperature sensor.

[0030] Furthermore, the first Mach-Zehnder interferometer structure may also include a first output waveguide 31, and the second Mach-Zehnder interferometer structure may also include a second output waveguide 32. The output end of the first directional coupler 14 is connected to the first input end of the beam combiner 16 through the first output waveguide 31, and the output end of the second directional coupler 15 is connected to the second input end of the beam combiner 16 through the second output waveguide 32.

[0031] The FSR of the envelope of the combinatorial spectrum (hereinafter referred to as the envelope) is denoted as FSR. C FSR of the sensing arm sens FSR of reference arm ref The relationship can be represented as: (1).

[0032] Using λ C , λ sens and λ refLet represent the wavelengths of the troughs / peaks of the output spectra of the envelope, sensing arm, and reference arm, respectively. Then, the wavelength shift of the envelope can be expressed as: (2) Wherein, M1 and M2 are respectively: (3) (4).

[0033] As can be seen from equation (2), when both the sensing arm and the reference arm are affected by the ambient temperature and experience wavelength shifts in the same direction, .

[0034] If the reference arm is not affected by ambient temperature, then , At this point, M1 is the amplification factor of the vernier effect on temperature sensitivity.

[0035] When both the sensing arm and the reference arm are affected by the ambient temperature, resulting in wavelength shifts in opposite directions, (5) That is, the wavelength shift of the envelope will increase.

[0036] Therefore, this application uses two materials with opposite thermo-optic coefficients as the upper cladding of the sensing arm and the reference arm, respectively. When the temperature increases, the refractive index of the negative thermo-optic coefficient material decreases, and the effective refractive index of the waveguide layer covered by it decreases accordingly, resulting in a blue shift in the spectrum; while the refractive index of the positive thermo-optic coefficient material increases, and the effective refractive index of the waveguide layer covered by it increases accordingly, resulting in a red shift in the spectrum, which greatly increases the wavelength shift due to changes in envelope temperature.

[0037] The sensitivity of a temperature sensor can be expressed as: (6) Where T represents temperature. As can be seen from the above, the greater the envelope wavelength shift, the higher the sensitivity of the temperature sensor.

[0038] In this embodiment, the upper cladding covering the first directional coupler 14 is referred to as the first upper cladding, which has a first thermo-optic coefficient; the upper cladding covering the second directional coupler 15 is referred to as the second upper cladding, which has a second thermo-optic coefficient. The first and second upper claddings are made of different materials. More specifically, one of the first and second thermo-optic coefficients is positive, and the other is negative. More specifically, as mentioned above, since the first directional coupler 14 is considered as a sensing arm and the second directional coupler 15 is considered as a reference arm, in this embodiment, the absolute value of the second thermo-optic coefficient is less than the absolute value of the first thermo-optic coefficient.

[0039] Continue reading Figure 2 and combined Figure 1 The longitudinal structure of the temperature sensor, from bottom to top, includes: substrate 51, lower cladding 52, waveguide layer, and upper cladding.

[0040] In one feasible implementation, substrate 51 is a silicon substrate; lower cladding 52 is SiO2; waveguide layer is obtained by patterning single-crystal silicon and includes a first waveguide 21, a second waveguide 22, a third waveguide 23, a fourth waveguide 24, a first directional coupler 14, a second directional coupler 15, and multiple beam splitters; upper cladding includes a first upper cladding 41, a second upper cladding 42, and a third upper cladding 43, wherein the first upper cladding 41 covers the first directional coupler 14, the second upper cladding 42 covers the second directional coupler 15, and the third upper cladding 43 covers other areas, for example, covering the area between the first directional coupler 14 and the second directional coupler 15. The refractive indices of the first upper cladding 41, the second upper cladding 42, and the third upper cladding 43 are all greater than the refractive index of the waveguide layer (single-crystal silicon) material.

[0041] In one embodiment, the thermo-optic coefficients of the first upper cladding layer 41 and the second upper cladding layer 42 are opposite in value, wherein the first thermo-optic coefficient is positive and the second thermo-optic coefficient is negative; or, the first thermo-optic coefficient is negative and the second thermo-optic coefficient is positive; wherein the absolute value of the first thermo-optic coefficient is greater than the absolute value of the second thermo-optic coefficient. As can be seen from equation (5), the greater the difference between the absolute values ​​of the first and second thermo-optic coefficients, the better. The greater the change, the higher the sensitivity of the temperature sensor.

[0042] The absolute values ​​of the thermo-optic coefficients of the first upper cladding layer 41 and the second upper cladding layer 42 can both be greater than the absolute value of the thermo-optic coefficient of the third upper cladding layer 43. Furthermore, the smaller the absolute value of the thermo-optic coefficient of the third upper cladding layer 43, the less the temperature sensor chip is affected by temperature changes, which is beneficial to improving the stability of the temperature sensor.

[0043] As an example, the first upper cladding layer 41 is made of polydimethylsiloxane (PDMS) with a first thermo-optical coefficient of -4.5 × 10⁻⁶. -4 / ℃; the second upper cladding layer 42 is made of polymethyl methacrylate (PMMA), and its second thermo-optical coefficient is 6.0 × 10⁻⁶. -5 / °C; the third upper cladding 43 is made of silicon dioxide (SiO2), and the third thermo-optic coefficient is 6.9×10. -6 / ℃.

[0044] In this application, the main body of the temperature sensor structure adopts a parallel structure, which provides sufficient separation space for the two Mach-Zehnder interference structure branches. This facilitates covering the sensing arm and the reference arm with upper cladding layers of different thermo-optic coefficients, or covering the area between the sensing arm and the reference arm with other upper cladding layers different from the first upper cladding layer 41 and the second upper cladding layer 42.

[0045] In another embodiment, the second upper cladding layer 42 and the third upper cladding layer 43 can also be made of the same material. As an example, the first upper cladding layer 41 is made of silicone resin (REN60) with a first thermo-optical coefficient of -3.6 × 10⁻⁶. -4 / ℃; the second upper cladding 42 and the third upper cladding 43 are both made of SiO2.

[0046] Furthermore, the aforementioned temperature sensor structure can be implemented using semiconductor processes. To this end, this application also provides an optical chip, which can be fabricated based on an SOI silicon wafer or a silicon substrate.

[0047] Taking SOI substrate as an example, the fabrication process of the optical chip for the temperature sensor, which includes three types of top cladding materials, in this application is as follows: (1) Prepare a clean SOI substrate, which includes a bottom silicon layer, a buried oxide layer and a top silicon layer stacked in sequence, wherein the bottom silicon layer is the substrate and the buried oxide layer is the lower cladding layer. (2) The top silicon is patterned using standard photolithography and dry etching processes to prepare the waveguide layer, resulting in an SOI patterned wafer. The photoresist is then removed using a wet photoresist removal process. (3) The first upper cladding layer (material such as PDMS) is spin-coated onto the SOI graphic sheet using a high-speed spin coating process, and then baked at a high temperature; (4) The first upper cladding layer is patterned by using standard photolithography and dry etching processes, and the photoresist is removed by wet photoresist removal process; (5) A second top cladding material (e.g., PMMA) is deposited on the SOI pattern using plasma-enhanced chemical vapor deposition (PECVD) technology; (6) The second upper cladding layer is planarized by chemical mechanical polishing (CMP) process; (7) The second upper cladding layer is patterned by using standard photolithography and dry etching processes, and the photoresist is removed by wet photoresist removal process; (8) A silicon dioxide layer is formed on the SOI patterned chip using vapor deposition technology as the third upper cladding layer; (9) Using CMP process, grind the third upper cladding layer and stop at the same height as the first and second upper cladding layers; (10) The third upper cladding layer is patterned by using standard photolithography and dry etching processes, and the photoresist is removed by wet photoresist removal process.

[0048] It should be noted that the above process is performed in the order of the first, second, and third upper cladding layers. In actual fabrication, the process order of the three materials can be changed depending on the different film formation methods of the upper cladding layers, thereby fabricating the temperature sensor optical chip of this application. Of course, if the second and third upper cladding layers are made of the same material, but their materials are different from those of the first upper cladding layer, the above process steps can also be adjusted.

[0049] This optical chip can be used in temperature measurement systems. For example... Figure 3 As shown, Figure 3 This is a schematic diagram of a temperature measurement system according to one embodiment of this application. The temperature measurement system includes a light source 61, a photoelectric chip 62, and a temperature calculation unit 63.

[0050] The output light of the light source 61 enters the optical chip 62, which serves as a temperature sensor, through single-mode fiber coupling (e.g., end-face coupling or grating coupling). The optical signal output by the optical chip 62 is then coupled into the optical fiber and output to the temperature calculation unit 63 via the optical fiber. The temperature calculation unit 63 obtains the corresponding temperature data based on the relationship between the envelope wavelength shift of the optical chip and the temperature.

[0051] The temperature calculation unit 63 mentioned above can be, for example, an OSA spectrometer. In application, the optical chip 62 can be placed in the temperature controller to record the spectrum at different temperatures. Then, a linear fit is performed with temperature as the abscissa and the drift of the spectral envelope as the ordinate. The linear coefficient is the sensitivity of the temperature sensor.

[0052] It should be noted that the optical chip described in this application can be an optical chip that only includes the temperature sensor described in this application, used as a temperature sensor; or it can be based on the temperature sensor described in this application with the addition of other structures. For example, wavelength division multiplexing structures, large-scale optical switch arrays, etc. can be added to form an optical computing chip for use in data centers and other fields; or it can be integrated with high-speed modulators, SOA arrays, etc. to achieve on-chip transceiver integration and form a high-speed optical communication chip, etc.

[0053] The technical solution of this application has been described above with reference to one embodiment shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A temperature sensor based on the enhanced vernier effect, characterized in that, The structure consists of a substrate, a lower cladding layer, a waveguide layer, and an upper cladding layer, in that order: The waveguide layer includes a first beamsplitter, a second beamsplitter, a third beamsplitter, a first Mach-Zehnder interference structure, a second Mach-Zehnder interference structure, and a beam combiner; wherein the first Mach-Zehnder interference structure includes a first directional coupler, and the second Mach-Zehnder interference structure includes a second directional coupler; The two outputs of the first beam splitter are respectively connected to the inputs of the second beam splitter and the third beam splitter; the two outputs of the second beam splitter are respectively connected to the two inputs of the first directional coupler, and the output of the first directional coupler is connected to the first input of the beam combiner; the two outputs of the third beam splitter are respectively connected to the two inputs of the second directional coupler, and the output of the second directional coupler is connected to the second input of the beam combiner. The upper cladding layer includes a first upper cladding layer and a second upper cladding layer. The first upper cladding layer has a first thermo-optic coefficient, and the second upper cladding layer has a second thermo-optic coefficient. One of the first thermo-optic coefficient and the second thermo-optic coefficient is positive, and the other is negative. The first upper cladding layer covers the first directional coupler, and the second upper cladding layer covers the second directional coupler.

2. The temperature sensor according to claim 1, characterized in that, The first Mach-Zehnder interferometer structure further includes a first waveguide, a second waveguide, and a first output waveguide; the second Mach-Zehnder interferometer structure further includes a third waveguide, a fourth waveguide, and a second output waveguide. The two outputs of the second beam splitter are connected to the two inputs of the first directional coupler via the first waveguide and the second waveguide, respectively; the output of the first directional coupler is connected to the first input of the beam combiner via the first output waveguide. The two outputs of the third beam splitter are connected to the two inputs of the second directional coupler via the third waveguide and the fourth waveguide, respectively, and the output of the second directional coupler is connected to the second input of the beam combiner via the second output waveguide.

3. The temperature sensor according to claim 2, characterized in that, The first waveguide and the second waveguide have different lengths, so that there is an optical path difference between the two optical signals input to the first directional coupler; The third waveguide and the fourth waveguide have different lengths so that there is an optical path difference between the two optical signals input to the second directional coupler.

4. The temperature sensor according to claim 1, characterized in that, The absolute values ​​of the first thermo-optic coefficient and the second thermo-optic coefficient are different.

5. The temperature sensor according to any one of claims 1 to 4, characterized in that, The upper cladding also includes a third upper cladding with a third thermo-optic coefficient, the third upper cladding covering the area excluding the first directional coupler and the second directional coupler.

6. The temperature sensor according to claim 5, characterized in that, The absolute values ​​of the first thermo-optic coefficient and the second thermo-optic coefficient are both greater than the absolute value of the third thermo-optic coefficient.

7. The temperature sensor according to claim 5, characterized in that, The absolute values ​​of the thermo-optic coefficients in the first and second upper cladding layers are relatively small, and are the same as the absolute value of the third thermo-optic coefficient.

8. An optical chip, characterized in that, Includes a temperature sensor according to any one of claims 1 to 7.

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