Temperature monitoring chip of reflective asymmetric interference structure

Abstract

The present application relates to the technical field of optical sensing, and particularly relates to a temperature monitoring chip of a reflective asymmetric interference structure, which comprises an input waveguide, a Y-branch beam splitter, an asymmetric interference arm, a Y-branch combiner, an output waveguide and a total reflection structure; the asymmetric interference arm comprises an asymmetric sensing arm waveguide and a reference arm waveguide; the end of the input waveguide is connected to the head of the Y-branch beam splitter, the first end and the second end of the Y-branch beam splitter are respectively connected to the head of the sensing arm waveguide and the reference arm waveguide; the end of the sensing arm waveguide and the end of the reference arm waveguide are respectively connected to the first head and the second head of the Y-branch combiner; the total reflection structure is arranged at the end of the Y-branch combiner; the total reflection structure is used for reflecting the light wave output by the output waveguide, so that the light sensing arm waveguide and the reference arm waveguide propagate back and forth twice, thereby forming a double-path interference path and generating a fourth-order interference output. The present application effectively improves the temperature detection precision.

Description

Technical Field

[0001] This invention relates to the field of optical sensing technology, and more specifically to a temperature monitoring chip with a reflective asymmetric interference structure. Background Technology

[0002] Temperature sensing is one of the most fundamental and widely applied areas in photonic sensing, with applications in precision manufacturing, environmental monitoring, biomedicine, energy, and microsystems integration. In industrial and chemical production, temperature sensors monitor high-temperature and high-pressure environments and precision reaction processes in real time, preventing fluctuations from causing safety accidents or product deterioration. In power systems, they are used for overheating early warning of critical equipment, ensuring the safety and stability of the power grid. Daily life and medical devices also rely on temperature sensing for human comfort and health management. In agriculture, sensor networks provide optimal conditions for crop growth and animal reproduction through temperature control in greenhouses and livestock environments. The millisecond-level response requirements for temperature in scientific research and aerospace have driven the development of high-precision sensing technologies. As a bridge connecting macroscopic systems and microscopic environments, temperature monitoring technology plays an irreplaceable role in ensuring safety, improving efficiency, and supporting innovation.

[0003] With the maturation of silicon photonics technology, on-chip temperature sensors based on integrated waveguide structures have gradually become a research and application hotspot. Existing on-chip temperature sensors mainly fall into two categories: waveguide Bragg grating (WBG) type and interferometric (MZI or ring) structures. Waveguide grating type sensors rely on the drift of the reflected center wavelength caused by temperature changes for measurement, offering advantages such as high sensitivity and compact structure. However, their output signal is strongly dependent on the position of the center wavelength. Since temperature drift directly manifests as wavelength shift, the system must undergo rigorous wavelength calibration and periodic recalibration in practical applications; otherwise, measurement errors are easily accumulated. Furthermore, the grating structure has a narrow reflection spectrum, requiring extremely high light source bandwidth and demodulation accuracy, resulting in system complexity and poor scalability.

[0004] Traditional Mach-Zehnder interferometer (MZI) temperature sensors utilize the phase change caused by the optical path difference between the two arms to achieve temperature demodulation. Their advantages include independence from wavelength calibration, simple structure, and ease of on-chip integration. However, ordinary single-pass MZIs have a large interference spectrum bandwidth, flat interference peaks, and limited peak position identification accuracy, resulting in limitations on demodulation resolution and temperature measurement range. Furthermore, spectral line overlap is prone to occur when interference peaks drift with temperature, posing challenges to demodulation in multi-node systems.

[0005] In summary, while existing waveguide grating structures offer high sensitivity, they require wavelength calibration and are complex systems; traditional MZIs, although calibration-free, suffer from excessively broad spectral lines and limited resolution. Therefore, how to obtain narrowband, high-resolution interferometric spectra while maintaining the wavelength-calibration-free advantage of MZIs to improve temperature measurement range and system compatibility has become a pressing technical challenge in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a temperature monitoring chip with a reflective asymmetric interference structure. The specific technical solution adopted is as follows: This invention provides a temperature monitoring chip with a reflective asymmetric interferometric structure. The chip includes: an input waveguide, a Y-branch beamsplitter, an asymmetric interferometer arm, a Y-branch combiner, an output waveguide, and a total internal reflection structure. The asymmetric interferometer arm includes an asymmetric sensing arm waveguide and a reference arm waveguide. The end of the input waveguide is connected to the beginning of the Y-branch beamsplitter, the first end of the Y-branch beamsplitter is connected to the beginning of the sensing arm waveguide, and the second end of the Y-branch beamsplitter is connected to the beginning of the reference arm waveguide. The end of the sensing arm waveguide is connected to the first beginning of the Y-branch combiner, and the reference arm... The end of the waveguide is connected to the second head of the Y-branch beam combiner; the total internal reflection structure is disposed at the end of the Y-branch beam combiner; the fundamental mode light of the input waveguide is split into two equal-power beams by the Y-branch beam splitter and coupled to the sensing arm waveguide and the reference arm waveguide respectively, and after being coupled by the Y-branch beam combiner at the ends of the sensing arm waveguide and the reference arm waveguide, it is input to the output waveguide; the total internal reflection structure is used to reflect the light wave output from the output waveguide, so that the light wave propagates back and forth twice in the sensing arm waveguide and the reference arm waveguide, thereby forming a two-way interference path and generating a fourth-order interference output.

[0007] In some possible implementations, the asymmetric sensing arm waveguide and reference arm waveguide exhibit asymmetry in at least one parameter of length, waveguide width, or thermo-optical material; when asymmetry exists in length, the length of the sensing arm waveguide is greater than the length of the reference arm waveguide; when asymmetry exists in waveguide width, the width of the sensing arm waveguide is greater than the width of the reference arm waveguide; when asymmetry exists in thermo-optical material, the sensing arm waveguide and the reference arm waveguide are made of materials with different thermo-optical coefficients.

[0008] In some possible implementations, when there is asymmetry in length, the sensing arm waveguide is a curved waveguide and the reference arm waveguide is a straight waveguide; the first end of the sensing arm waveguide is connected to the first end of the Y-branch beam splitter through a first straight waveguide buffer, and the end of the sensing arm waveguide is connected to the first end of the Y-branch beam combiner through a second waveguide buffer.

[0009] In some possible implementations, the angle between the Y-branch beam splitter and the Y-branch beam combiner is less than or equal to a set angle threshold; and the minimum distance between the sensing arm waveguide and the reference arm waveguide is greater than or equal to a set distance threshold.

[0010] In some possible implementations, when there is asymmetry in the waveguide width, the beginning and end of the sensing arm waveguide are both configured as tapered structures, and the beginning and end of the reference arm waveguide are both configured as tapered structures.

[0011] In some possible implementations, when asymmetry exists in the thermo-optical material, the sensing arm waveguide uses silicon as the core material and the reference arm waveguide uses SU-8 polymer material as the core material.

[0012] In some possible implementations, the temperature monitoring chip is constructed based on an SOI structure, which includes a silicon substrate, a silicon dioxide cladding, and a single-crystal silicon waveguide core; the difference in direct refractive index between the cladding and the core is greater than or equal to a set refractive index threshold.

[0013] In some possible implementations, the silicon substrate has a thickness of 725 μm and a width of 1 mm, the silicon dioxide cladding has a thickness of 0.55 μm and a refractive index of 1.4447, and the monocrystalline silicon waveguide core has a thickness of 0.22 μm, a width of 0.5 μm, and a refractive index of 3.5457.

[0014] In some possible implementations, the total internal reflection structure is a distributed Bragg reflector, which is formed by alternating layers of SiO2 and Ta2O5.

[0015] In some possible implementations, the thickness deviation of the single layer of SiO2 and Ta2O5 is controlled within ±1% of the design value; and the distributed Bragg mirror has a vertically etched end face formed by anisotropic dry etching, the vertically etched end face being perpendicular to the optical transmission axis of the silicon waveguide device, with an included angle of 90°±1°.

[0016] This invention offers the following advantages: By constructing an asymmetric interference arm consisting of an asymmetric sensing arm waveguide and a reference arm waveguide, and placing a total internal reflection structure at the end of a Y-branch combiner to create a two-way interference path, the light wave crosses the MZI twice to form a higher-order interference response. This significantly compresses the 3dB bandwidth of the transmission spectrum, resulting in a steeper spectral edge and thus improving wavelength demodulation accuracy. The output signal of this structure depends on the interference phase rather than the absolute wavelength position, enabling wavelength-indiscriminate access and enhancing the system's robustness to light source fluctuations. The demodulation system can seamlessly interface with sensing units of different batches, materials, and structures without wavelength pre-calibration, thereby reducing system complexity and maintenance costs. The optical path folding design saves output waveguide length, achieving a compact structure and improved integration, while remaining compatible with existing fiber optic or photonic chip demodulation systems. Furthermore, this structure boasts advantages such as compactness, high integration, strong compatibility, and low maintenance costs. It requires no calibration, is easy to mass-produce, and is suitable for engineering scenarios such as distributed temperature monitoring and chip-level thermal field diagnostics, significantly improving system reliability, sensor deployment flexibility, and engineering applicability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the planar structure of the reflective length asymmetric MZI optical waveguide temperature sensor according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the SOI waveguide cross-section according to an embodiment of the present invention; Figure 3 This is a simplified structural diagram of a reflective waveguide width asymmetric MZI temperature sensor according to an embodiment of the present invention. Figure 4 This is a simplified structural diagram of the reflective thermo-optical material asymmetric MZI waveguide temperature sensor according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the Taper waveguide structure according to an embodiment of the present invention; Figure 6 This is a simulation diagram of the mode field at the cone opening of the Taper structure according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a bent waveguide according to an embodiment of the present invention; Figure 8 This is a simulation diagram of the optical field of the reflective length asymmetric MZI optical waveguide temperature sensor according to an embodiment of the present invention. Figure 9 This is a simulation diagram of the optical field of a reflective waveguide width-asymmetric MZI temperature sensor according to an embodiment of the present invention. Figure 10 This is a simulation diagram of the optical field of the asymmetric MZI waveguide temperature sensor made of thermo-optical material according to an embodiment of the present invention. Figure 11 This is a layout diagram of a reflective length-asymmetric MZI optical chip according to an embodiment of the present invention; Figure 12 The transmission spectra of a single-stage MZI optical chip and a reflective MZI optical chip according to an embodiment of the present invention are shown. Figure 13 The transmission spectrum of the reflective length asymmetric MZI optical chip according to an embodiment of the present invention is shown in the range of 25°C to 45°C. In the attached figures: 1 is the input straight waveguide, 2 is the 3dBY branch beamsplitter, 3 is the waveguide buffer, 4 is the reference arm waveguide, 5 is the sensor arm waveguide, 6 is the waveguide buffer, 7 is the 3dBY branch beam combiner, 8 is the output waveguide and end integrated mirror; 9 is the waveguide core layer, 10 is the silicon dioxide cladding, 11 is the buried oxide layer, 12 is the silicon substrate, 13 is the 3dBY branch beamsplitter, 14 is the tapered structure transitioning from a single-mode waveguide to a narrow waveguide, 15 is the tapered structure transitioning from a single-mode waveguide to a wide waveguide, 16 is the narrow waveguide reference arm, 17 is the wide waveguide sensor arm, 18 is the Si core material sensor arm, 19 is the SU-8 waveguide material reference arm; 20 is the tapered structure of the waveguide buffer. Detailed Implementation

[0019] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0020] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the invention. It should be understood that the accompanying drawings and embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the invention.

[0021] It should be understood that the various steps described in the method embodiments of the present invention may be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of the present invention is not limited in this respect.

[0022] The term "comprising" and its variations as used herein are open-ended inclusions, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Definitions of other terms will be given in the description below.

[0023] It should be noted that the concepts of "first" and "second" mentioned in this invention are only used to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies.

[0024] Although operations or steps are described in a specific order in the accompanying drawings in the embodiments of the present invention, this should not be construed as requiring these operations or steps to be performed in the specific order or serial order shown, or requiring all of the shown operations or steps to be performed to obtain the desired result. In the embodiments of the present invention, these operations or steps may be performed serially; they may be performed in parallel; or a portion of these operations or steps may be performed.

[0025] Furthermore, it is understood that the data involved in the technical solutions of this invention (including but not limited to the data itself, the acquisition or use of the data) shall comply with the requirements of relevant laws, regulations, and provisions. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] The following will provide a detailed description of a temperature monitoring chip with a reflective asymmetric interference structure provided by an embodiment of the present invention, with reference to the accompanying drawings.

[0027] This invention provides a temperature monitoring chip with a reflective asymmetric interferometric structure. The chip includes: an input waveguide, a Y-branch beamsplitter, an asymmetric interferometer arm, a Y-branch combiner, an output waveguide, and a total internal reflection structure. The asymmetric interferometer arm includes an asymmetric sensing arm waveguide and a reference arm waveguide. The end of the input waveguide is connected to the beginning of the Y-branch beamsplitter; the first end of the Y-branch beamsplitter is connected to the beginning of the sensing arm waveguide; the second end of the Y-branch beamsplitter is connected to the beginning of the reference arm waveguide; the end of the sensing arm waveguide is connected to the first end of the Y-branch combiner. The reference arm waveguide is connected to the second end of the Y-branch combiner. A total internal reflection structure is set at the end of the Y-branch combiner. The fundamental mode light of the input waveguide is split into two equal-power beams by the Y-branch combiner and coupled to the sensing arm waveguide and the reference arm waveguide, respectively. After being coupled by the Y-branch combiner at the ends of the sensing arm waveguide and the reference arm waveguide, they are input to the output waveguide. The total internal reflection structure is used to reflect the light wave output from the output waveguide, so that the light wave propagates back and forth twice in the sensing arm waveguide and the reference arm waveguide, thereby forming a two-way interference path and producing a fourth-order interference output.

[0028] The specific sensing principle of the temperature monitoring chip with the aforementioned reflective asymmetric interference structure is as follows: Let the incident light field be ,in, Indicates the amplitude of the input light field. Indicates the angular frequency of the input light. Indicates time. The incident light field After passing through the Y-branch beam splitter, the light field is evenly divided into the sensing arm light field. and reference arm light field The two beams of light generate a fundamental phase difference after passing through the asymmetric interferometer arm for the first time: in: The basic phase difference is the phase difference that occurs when a light wave first passes through an asymmetric structure. The center wavelength is 1550nm; , These are the phases of the sensing arm waveguide and the reference arm waveguide, respectively. , These are the effective refractive indices of the sensing arm waveguide and the reference arm waveguide, respectively. , These are the physical lengths of the sensing arm waveguide and the reference arm waveguide, respectively. When 2m When m is a positive integer, the interference light intensity reaches its maximum value, and an interference peak appears, corresponding to the wavelength. .

[0029] A reflector is integrated at the straight waveguide output of the Y-branch beam combiner, reconstructing the optical path operation mechanism. The light wave is reflected back by the reflector, splits into two paths again by the Y-branch beam combiner, passes through the asymmetric region a second time, and undergoes secondary interference at the Y-branch beam splitter. The final output light field... for: in: Reflectance.

[0030] Final output light intensity Satisfying the relation: This shows that, compared to traditional one-way MZI... Compared to the dominant term, the output signal includes a frequency harmonic term. The increased order of this term on the phase-wavelength response curve leads to a steeper main lobe slope, which is equivalent to approximately halving the 3dB bandwidth (both theoretical analysis and simulation support this conclusion). To rigorously demonstrate this point, this embodiment provides spectral comparison data of a single-pass MZI and this reflective MZI under the same device parameters and light source bandwidth, such as... Figure 12 The comparison of the 3dB bandwidth between the two is given in the text.

[0031] When the ambient temperature changes, the lengths of the sensing arm waveguide and the reference arm waveguide are affected by the thermo-optical effect and the thermal expansion effect. , and effective refractive index , The external temperature will also change. The changes in the sensing length and effective refractive index of the silicon photonic chip can be expressed as: in: The coefficient of thermal expansion of the sensor arm; The coefficient of thermal expansion of the reference arm; The thermo-optic coefficient of the sensing arm; The thermo-optic coefficient of the reference arm; T represents the initial ambient temperature (normal temperature); T represents the changed ambient temperature. , For the external environment The length of the two arms at that time; , The length of the two arms is given when the ambient temperature is T. , The ambient temperature is Effective refractive index of both arms; The effective refractive index of the two arms is given by the ambient temperature T.

[0032] When the ambient temperature rises , and , Both will increase, causing the interference peak to shift towards longer or shorter wavelengths (in this patent, it shifts towards longer wavelengths). Temperature sensitivity of characteristic wavelengths. It can be represented as: in: λ is the wavelength of the wave crest.

[0033] The aforementioned temperature monitoring chip with a reflective asymmetric interferometry structure achieves a two-way interference path and generates a fourth-order interference output by allowing light waves to propagate twice between the sensing arm waveguide and the reference arm waveguide. This significantly reduces the 3dB bandwidth of the interference spectrum compared to traditional single-way MZI, resulting in steeper spectral edges. This achieves spectral steepening and improved wavelength demodulation accuracy, thereby enhancing both wavelength demodulation accuracy and temperature measurement range. Furthermore, since the interference spectrum exhibits an overall translational response to temperature changes, the output signal depends on the interference phase rather than the absolute wavelength position. This allows for multi-node hybrid deployment within the same fiber optic link or on-chip optical network. It enables wavelength-indiscriminate access with the demodulation system, eliminating the need for wavelength calibration and periodic recalibration. Sensors with different length, width, or material differences can be plugged and played with the same demodulation system, making it suitable for distributed temperature monitoring systems with multi-node hybrid deployments.

[0034] In one possible implementation, the temperature monitoring chip is constructed based on an SOI structure, which includes a silicon substrate, a silicon dioxide cladding, and a monocrystalline silicon waveguide core layer; the refractive index difference between the cladding and the core layer is greater than or equal to a set refractive index threshold. The silicon substrate has a thickness of 725 μm and a width of 1 mm, the silicon dioxide cladding has a thickness of 0.55 μm and a refractive index of 1.4447, and the monocrystalline silicon waveguide core layer has a thickness of 0.22 μm, a width of 0.5 μm, and a refractive index of 3.5457.

[0035] Specifically, photonic chips are constructed based on a silicon-on-insulator (SOI) material system, such as... Figure 2As shown, the silicon-on-in-place (SOI) material system has a layered structure, including a silicon substrate 12, a buried oxide layer 11, a silicon dioxide cladding 10, and a single-crystal silicon waveguide core layer 9. The bottom silicon substrate 12 has a thickness of 725 μm and a width of 1 mm; the silicon dioxide cladding 10 formed on it has a thickness of 0.55 μm and a refractive index of 1.4447; the single-crystal silicon waveguide core layer 9 formed on the cladding surface has a thickness of 0.22 μm, a width of 0.5 μm, and a refractive index of 3.5457. A refractive index difference of up to 2.101 (refractive index difference Δn = 3.5457 - 1.4447) is formed between the core layer 9 and the silicon dioxide cladding 10. This high refractive index contrast produces a strong optical confinement effect, strictly confining the transmitted light field within the sub-micron scale of the silicon waveguide core layer, thereby ensuring that the optical signal coupled from the end face can be transmitted in a low-loss mode.

[0036] In one possible implementation, the total internal reflection structure is a distributed Bragg reflector (DBR) integrated at the tail of a silicon-based waveguide device. The DBR is composed of alternating layers of silicon dioxide (SiO2) and tantalum pentoxide (Ta2O5). To ensure that the center wavelength shift of the reflection spectrum meets the preset temperature sensing accuracy, the thickness deviation of the single layer of SiO2 and Ta2O5 is controlled within ±1% of the design value. Simultaneously, the DBR has an etched end face perpendicular to the waveguide transmission axis, with an end face angle of 90°±1°.

[0037] Specifically, this total internal reflection structure is a distributed Bragg reflector (DBR), fabricated using ion beam sputtering deposition (IBS). A high-precision optical monitoring system enables real-time monitoring and precise calibration of each layer's thickness, ensuring a single-layer thickness deviation of ≤±1%. After SiO2 / Ta2O5 dielectric deposition, anisotropic dry etching is performed using inductively coupled plasma etching (ICP-RIE) to form a reflective endface at the waveguide end that is strictly perpendicular to the optical transmission axis, with the perpendicularity deviation controlled within ±1°. Through the vertical coupling of high and low refractive index dielectric layers, this DBR possesses high reflectivity and low phase distortion characteristics, ensuring the stability and reliability of the interference signal.

[0038] In one possible implementation, the asymmetric sensing arm waveguide and reference arm waveguide exhibit asymmetry in at least one parameter of length, waveguide width, or thermo-optical material; when asymmetry exists in length, the length of the sensing arm waveguide is greater than the length of the reference arm waveguide; when asymmetry exists in waveguide width, the width of the sensing arm waveguide is greater than the width of the reference arm waveguide; when asymmetry exists in thermo-optical material, the sensing arm waveguide and reference arm waveguide are made of materials with different thermo-optical coefficients.

[0039] In this method, the sensing arm waveguide and the reference arm waveguide are designed to have at least one asymmetry in length, waveguide width, or thermo-optical material to introduce an initial optical path difference.

[0040] In one possible implementation, when there is asymmetry in length, the sensing arm waveguide is a curved waveguide, and the reference arm waveguide is a straight waveguide. The first end of the sensing arm waveguide is connected to the first end of the Y-branch beamsplitter via a first straight waveguide buffer, and the end of the sensing arm waveguide is connected to the first end of the Y-branch combiner via a second waveguide buffer. The included angle between the Y-branch beamsplitter and the Y-branch combiner is less than or equal to a set included angle threshold, and the minimum distance between the sensing arm waveguide and the reference arm waveguide is greater than or equal to a set distance threshold.

[0041] like Figure 1 As shown, the temperature monitoring chip with a reflective asymmetric interferometric structure provided in this embodiment is an optical waveguide temperature sensor based on reflective length asymmetric MZI. The core structure of this sensor consists of an asymmetric interferometric arm (comprising an input straight waveguide 1, a 3dBY branch beamsplitter 2, a waveguide buffer 3, a sensing arm waveguide 5, and a reference arm waveguide 4), a waveguide buffer 6, a 3dBY branch beam combiner 7, an output waveguide, and an integrated reflector 8 at the end. The input straight waveguide 1, with a length of 0.5cm, receives incident light from a broadband light source. The 3dBY branch beamsplitter 2 splits the incident light into two equal beams, which enter the sensing arm waveguide 5 and the reference arm waveguide 4, respectively. The sensing arm waveguide 5 employs a curved design, with its length L1 greater than the length L2 of the reference arm waveguide 4, forming a controllable geometric arm length difference ΔL, thereby establishing an initial optical path difference and introducing a fundamental phase shift. To achieve high-precision interferometry, a reflector is placed at the end of the output straight waveguide, forcing the light wave to propagate twice in the asymmetric interferometric arm. The 3dB Y-branch beam splitter 2 and the branch beam combiner 7 employ a small included angle design of 1.5° (or less than 1.5°) to effectively suppress bending loss to below 0.1dB / cm. Simultaneously, the minimum distance between the two arms is set to 5μm (or greater than 5μm) to eliminate directional coupling effects and ensure the purity and stability of the interference signal. During temperature sensing, changes in the ambient temperature simultaneously induce thermo-optical and thermal expansion effects in the waveguide material, causing differences in the effective refractive index and optical path length between the sensing arm waveguide 5 and the reference arm waveguide 4, resulting in a change in the effective refractive index difference Δn between the two arms. This change further modulates the interference phase, causing a measurable characteristic wavelength shift in the fourth-order interference narrowband spectrum at the output. By demodulating the shift, high-sensitivity temperature measurement can be achieved. Figure 8 Simulation results of the optical field distribution of the reflective length asymmetric MZI structure are presented. The propagation path and interference behavior of the light wave in the two arms can be observed from the simulation, which verifies that the structure can stably achieve fourth-order interference output.

[0042] In one possible implementation, when there is asymmetry in the waveguide width, both the beginning and end of the sensing arm waveguide are set to a tapered structure, and both the beginning and end of the reference arm waveguide are set to a tapered structure.

[0043] like Figure 3 As shown in the figure, the temperature monitoring chip with a reflective asymmetric interference structure provided in this embodiment is a reflective waveguide width asymmetric MZI temperature sensor. Its structural schematic diagram is shown in the figure, and the optical field simulation results are as follows. Figure 9 As shown, the main structure of the sensor includes an input single-mode waveguide, a 3dBY branch beamsplitter 13, an asymmetric interferometer arm consisting of a sensing arm waveguide (i.e., a wide waveguide sensing arm) 17 and a reference arm waveguide (i.e., a narrow waveguide reference arm) 16 with the same length but different widths, a 3dBY branch beam combiner 23, an output single-mode waveguide, and an integrated reflector 8 at the end. The width W1 of the reference arm waveguide 16 is 380nm, and the width W2 of the sensing arm waveguide 17 is 500nm. The asymmetric waveguide width structure is formed by designing W2 > W1. To achieve smooth optical mode switching, two tapered structures 15 of length L are provided at the beginning and end of the sensing arm waveguide 17, gradually increasing the waveguide width to the designed value. Similarly, the beginning and end of the reference arm waveguide 16 are equipped with corresponding tapered structures 14, achieving a decreasing width transition. The reflector 8 allows the light wave to propagate twice in the asymmetric interferometer arm. This two-way interference mechanism generates a fourth-order interference spectrum at the output, with a wavelength shift that is doubled compared to the traditional single-way structure, thus significantly improving the temperature detection range. The tapered design of the gradient conical structures 14 and 15 achieves smooth optical mode conversion between single-mode waveguides and wide / narrow waveguides through continuous gradient of geometric contours. This effectively suppresses higher-order mode excitation, reduces mode conversion loss, and achieves a single-mode transmission efficiency of ≥98%, while reducing reflection and scattering losses caused by abrupt changes in cross-section to <0.1dB / cm. Combined with the two-way interference mechanism of the end DBR, it ensures phase stability of the light wave when it travels back and forth through the asymmetric region.

[0044] In one possible implementation, when asymmetry exists in the thermo-optical material, the sensing arm waveguide uses silicon as the core material and the reference arm waveguide uses SU-8 polymer as the core material. Specifically, when asymmetry exists between the sensing arm and reference arm waveguides in the thermo-optical material, only the core material of the sensing arm and reference arm waveguides is replaced, while the rest of the structure remains unchanged.

[0045] like Figure 4 As shown, the temperature monitoring chip with a reflective asymmetric interference structure provided in this embodiment is a reflective thermo-optical material asymmetric MZI waveguide temperature sensor. Figure 10The simulation results of its optical field propagation and interference characteristics are shown in the figure. The main structure of the sensor consists of an input single-mode straight waveguide, a 3dBY branch beam splitter 13, an asymmetric interferometer arm composed of a sensing arm waveguide (i.e., a Si core material sensing arm) 18 with completely symmetrical geometric dimensions and different core materials and a reference arm waveguide (i.e., a SU-8 waveguide material reference arm) 19, a 3dBY branch beam combiner 23, an output single-mode straight waveguide, and an integrated reflector 8 at the end. The core feature of this structure is that the two interferometer arms use functional materials with significantly different thermo-optic coefficients: the sensing arm waveguide 18 uses silicon as the core material, and its thermo-optic coefficient is +1.8×10. -4 K -1 Reference arm waveguide 19 is made of SU-8 polymer material, with a thermo-optic coefficient of -1.21 × 10⁻⁶. -4 K -1 The difference in thermo-optical coefficients between the two arm materials. (dn / dT) reaches 3.01×10 -4 K -1 To achieve efficient thermal management, the lower cladding of both arms is made of high thermal conductivity silica material (thermal conductivity 1.4 W·m). -1 ·K -1 ( ), to accelerate the thermal response process.

[0046] like Figure 5 As shown, this embodiment employs a tapered structure 20 in the waveguide buffer of the MZI interferometer arm. Figure 6 Figure (a) shows the simulated mode field distribution at the tapered end of the Taper structure. It can be observed that the optical signal maintains single-mode characteristics throughout its transmission from the single-mode waveguide through the tapered gradient region to the wide waveguide. Figures (b) and (c) show the optical field distribution of the single-mode waveguide and the wide waveguide cross-section, respectively, indicating that the optical field is effectively confined within the waveguide core layer without significant energy leakage. This tapered structure achieves smooth mode transitions through continuous gradients in its geometric profile, effectively avoiding mode mismatch losses caused by abrupt changes in the waveguide cross-section. This design suppresses higher-order mode excitation while keeping reflection and scattering losses at a low level, increasing the single-mode transmission efficiency to over 98%. Combined with the secondary interference enhancement mechanism introduced by the end mirror, the tapered structure effectively ensures the phase stability of the light wave during its two round trips through the waveguide width difference region, providing the necessary waveguide morphology basis for achieving a high wavelength drift response in the fourth-order interference spectrum at the output end.

[0047] Figure 7The figure shows the cross-sectional mode distribution of the curved waveguide used in this embodiment. As can be observed, the optical energy is concentrated in the central region of the waveguide and exhibits a distribution characteristic of gradually decreasing from the inside out, consistent with the typical mode morphology of a single-mode waveguide. Within the waveguide boundary marked by the black rectangle, the optical field is effectively confined, resulting in high energy concentration; while the optical field intensity in the background region is significantly reduced, indicating that the waveguide has good lateral confinement capability for light and low leakage loss. Compared to a straight waveguide, the curved waveguide exhibits a longer light propagation path on the outer side, leading to a difference in phase accumulation and causing the optical energy distribution to shift towards the outer side of the curve. Figure 7 The bright spot in the mid-field is slightly offset to the outside of the waveguide cross-section, verifying this physical phenomenon. Although the curved structure introduces some radiation loss and mode coupling effect, no obvious energy overflow from the waveguide boundary is observed in the optical field shown in the figure, indicating that the selected bending radius is reasonable and can control the additional loss within the allowable range, meeting the sensor's design requirements for transmission loss.

[0048] like Figure 11 The diagram shown is a layout of the reflective length asymmetric MZI optical chip design in this embodiment. Figure 13 The figure shows the transmission spectrum response of the chip within a temperature range of 25℃ to 45℃. Under different temperature conditions, regular periodic interference fringes can be observed in the transmission spectrum. This phenomenon originates from the optical path difference introduced by the difference in the geometric lengths of the two interference arms in the MZI structure. When the ambient temperature changes, the thermo-optical effect and thermal expansion effect of silicon material work together, causing changes in the effective refractive index and physical length of the waveguide. Due to the initial optical path difference between the two interference arms, temperature changes will alter the interference conditions, manifested as an overall shift in the interference fringes of the transmission spectrum. The arrows in the figure clearly indicate the spectral shift trend: as the temperature increases, the characteristic resonant wavelength shifts linearly towards longer wavelengths. This wavelength shift phenomenon is mainly attributed to the thermo-optical effect of silicon material: increased temperature causes an increase in the refractive index of the silicon waveguide, thereby prolonging the equivalent propagation time of light waves in the waveguide, ultimately leading to a redshift of the resonant wavelength.

[0049] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A temperature monitoring chip with a reflective asymmetric interference structure, characterized in that, The chip includes: an input waveguide, a Y-branch beamsplitter, an asymmetric interferometer arm, a Y-branch combiner, an output waveguide, and a total internal reflection structure. The asymmetric interferometer arm includes an asymmetric sensing arm waveguide and a reference arm waveguide. The end of the input waveguide is connected to the beginning of the Y-branch beamsplitter; the first end of the Y-branch beamsplitter is connected to the beginning of the sensing arm waveguide; the second end of the Y-branch beamsplitter is connected to the beginning of the reference arm waveguide; the end of the sensing arm waveguide is connected to the first beginning of the Y-branch combiner; and the end of the reference arm waveguide is connected to the first beginning of the Y-branch combiner. The second end of the beam combiner; the total internal reflection structure is disposed at the end of the Y-branch beam combiner; the fundamental mode light of the input waveguide is split into two equal-power beams by the Y-branch beam splitter and coupled to the sensing arm waveguide and the reference arm waveguide respectively, and then coupled to the output waveguide after being coupled by the Y-branch beam combiner at the ends of the sensing arm waveguide and the reference arm waveguide; the total internal reflection structure is used to reflect the light wave output from the output waveguide, so that the light wave propagates back and forth twice in the sensing arm waveguide and the reference arm waveguide, thereby forming a two-way interference path and generating a fourth-order interference output.

2. The temperature monitoring chip with a reflective asymmetric interference structure according to claim 1, characterized in that, The asymmetric sensing arm waveguide and reference arm waveguide exhibit asymmetry in at least one parameter: length, waveguide width, or thermo-optical material. When asymmetry exists in length, the length of the sensing arm waveguide is greater than the length of the reference arm waveguide. When asymmetry exists in waveguide width, the width of the sensing arm waveguide is greater than the width of the reference arm waveguide. When asymmetry exists in thermo-optical material, the sensing arm waveguide and the reference arm waveguide are made of materials with different thermo-optical coefficients.

3. The temperature monitoring chip with a reflective asymmetric interference structure according to claim 2, characterized in that, When there is asymmetry in length, the sensing arm waveguide is a curved waveguide and the reference arm waveguide is a straight waveguide; the first end of the sensing arm waveguide is connected to the first end of the Y-branch beam splitter through a first straight waveguide buffer, and the end of the sensing arm waveguide is connected to the first end of the Y-branch beam combiner through a second waveguide buffer.

4. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 2, characterized in that, The included angle between the Y-branch beam splitter and the Y-branch beam combiner is less than or equal to a set included angle threshold; and the minimum distance between the sensing arm waveguide and the reference arm waveguide is greater than or equal to a set distance threshold.

5. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 2, characterized in that, When there is asymmetry in the waveguide width, the beginning and end of the sensing arm waveguide are both set as tapered structures, and the beginning and end of the reference arm waveguide are both set as tapered structures.

6. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 2, characterized in that, When asymmetry exists in the thermo-optical material, the sensing arm waveguide uses silicon as the core material and the reference arm waveguide uses SU-8 polymer material as the core material.

7. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 1, characterized in that, The temperature monitoring chip is constructed based on an SOI structure, which includes a silicon substrate, a silicon dioxide cladding, and a single-crystal silicon waveguide core; the difference in direct refractive index between the cladding and the core is greater than or equal to a set refractive index threshold.

8. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 7, characterized in that, The silicon substrate has a thickness of 725 μm and a width of 1 mm, the silicon dioxide cladding has a thickness of 0.55 μm and a refractive index of 1.4447, and the single-crystal silicon waveguide core has a thickness of 0.22 μm, a width of 0.5 μm, and a refractive index of 3.5457.

9. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 1, characterized in that, The total internal reflection structure is a distributed Bragg reflector, which is formed by alternating SiO2 and Ta2O5 layers.

10. A temperature monitoring chip with a reflective asymmetric interference structure according to claim 9, characterized in that, The thickness deviation of the single-layer films of the SiO2 layer and Ta2O5 layer is strictly controlled within ±1% of the design value, and the distributed Bragg reflector has a vertical etched end face formed by anisotropic dry etching. The vertical etched end face is perpendicular to the optical transmission axis of the silicon waveguide device, and the included angle is 90°±1°.

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