Optical waveguide temperature sensor and temperature control method based on Mach-Zehnder interferometer

Abstract

This application provides an optical waveguide temperature sensor and temperature control method based on a Mach-Zehnder interferometer, comprising: an optical waveguide and a Mach-Zehnder interferometer structure integrated in the optical waveguide, consisting of an input optical coupler, a beam splitter, an interference structure, a beam combiner, and an output optical coupler connected in sequence; a first interferometer arm comprising a first single-mode waveguide, a first mode conversion structure, a multimode waveguide, a second mode conversion structure, and a second single-mode waveguide connected in sequence; the multimode waveguide is used to support the propagation of higher-order modes, and the first and second mode conversion structures are used to perform reversible conversion between the fundamental mode and higher-order modes; the second interferometer arm is a single-mode waveguide used to support the propagation of the fundamental mode; the geometric parameters of the multimode waveguide are configured such that the refractive index of the first group of higher-order modes in the first interferometer arm and the refractive index of the second group of the fundamental mode in the second interferometer arm satisfy an approximate match, and the propagation modes in the first and second interferometer arms have different thermo-optical response coefficients.

Description

Technical Field

[0001] This application relates to the field of optical waveguide sensing and temperature control technology, and in particular to an optical waveguide temperature sensor and temperature control method based on a Mach-Zehnder interferometer. Background Technology

[0002] In related technologies, optical waveguide temperature sensors based on Mach-Zehnder interferometers mainly rely on single-mode propagation and thermo-optic effects to achieve temperature detection. Traditional structures achieve phase difference changes by adjusting the length of the interferometer arm or the waveguide width, but their temperature sensitivity is usually limited by the thermo-optic coefficient of the material and the degree of freedom of the structure, making it difficult to break through the 1 nm / K order of magnitude. Summary of the Invention

[0003] In view of this, this application provides an optical waveguide temperature sensor and temperature control method based on a Mach-Zehnder interferometer, which at least partially solves the above-mentioned technical problems.

[0004] This application provides an optical waveguide temperature sensor based on a Mach-Zehnder interferometer, comprising: an optical waveguide and a Mach-Zehnder interferometer structure integrated in the optical waveguide; the Mach-Zehnder interferometer structure includes an input optical coupler, a beam splitter, an interference structure, a beam combiner, and an output optical coupler connected in sequence; the interference structure includes a first interferometer arm and a second interferometer arm, the first interferometer arm including a first single-mode waveguide, a first mode conversion structure, a multimode waveguide, a second mode conversion structure, and a second single-mode waveguide connected in sequence; the multimode waveguide is used to support the propagation of higher-order modes and the fundamental mode, and the first mode conversion structure and the second mode conversion structure are used to perform reversible conversion between the fundamental mode and higher-order modes; the second interferometer arm is a single-mode waveguide used to support the propagation of the fundamental mode; the geometric parameters of the multimode waveguide are configured such that the refractive index of the first group of higher-order modes in the first interferometer arm and the refractive index of the second group of the fundamental mode in the second interferometer arm satisfy an approximate match, and the propagation modes in the first interferometer arm and the second interferometer arm have different thermo-optical response coefficients.

[0005] According to an embodiment of this application, the group refractive index of the higher-order mode in the first interferometer arm and the group refractive index of the fundamental mode in the second interferometer arm satisfy an approximate match, including: the absolute value of the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode is less than a preset threshold, wherein when the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode approaches zero, the sensitivity of the output interference spectrum to phase changes reaches its maximum.

[0006] According to embodiments of this application, the phase difference between the first interferometer arm and the second interferometer arm is correlated with the first effective refractive index of the higher-order mode, the second effective refractive index of the fundamental mode, the first propagation path length of the higher-order mode, the second propagation path length of the fundamental mode, and the wavelength of the output interference spectrum.

[0007] According to an embodiment of this application, the phase difference between the first interferometer arm and the second interferometer arm is formed by the difference between the first phase delay generated by the higher-order mode in the propagation path and the second phase delay generated by the fundamental mode in the propagation path; the first phase delay is related to the product of the first effective refractive index and the first propagation path length, and the second phase delay is related to the product of the second effective refractive index and the second propagation path length; the first effective refractive index and the second effective refractive index change with temperature.

[0008] According to an embodiment of this application, the rate of change of the first effective refractive index corresponding to the higher-order mode with respect to temperature is different from the rate of change of the second effective refractive index corresponding to the fundamental mode with respect to temperature.

[0009] According to an embodiment of this application, the wavelength shift corresponding to the interference peak or valley in the output interference spectrum is related to the phase difference change between the first interferometer arm and the second interferometer arm.

[0010] According to an embodiment of this application, the optical waveguide includes a substrate layer, a lower cladding layer, a waveguide core layer, and an upper cladding layer stacked sequentially; a Mach-Zehnder interferometer structure is disposed in the waveguide core layer.

[0011] According to embodiments of this application, the mode conversion structure includes one or more of a directional coupler, an adiabatic graded waveguide, or a waveguide offset coupling structure; the beam splitter and beam combiner include one or more of a multimode interference structure, a directional coupler, or an adiabatic coupler.

[0012] According to embodiments of this application, the cross-sectional dimensions of a multimode waveguide are configured to support the propagation of the fundamental mode and at least one higher-order mode, while the cross-sectional dimensions of a single-mode waveguide are configured to support only the propagation of the fundamental mode.

[0013] According to embodiments of this application, both the multimode waveguide and the single-mode waveguide are silicon-on-insulator (SiI) waveguides. The first waveguide width of the multimode waveguide is 0.8 μm to 2 μm, and the first waveguide height is 200 nm to 300 nm. The second waveguide width of the single-mode waveguide is 400 nm to 500 nm, and the second waveguide height is 200 nm to 300 nm. Both the multimode and single-mode waveguides are silicon waveguides. The first waveguide width of the multimode waveguide is 0.8 μm to 2 μm, and the first waveguide height is 200 nm to 300 nm. The waveguide height is 300nm~400nm; the second waveguide width of the single-mode waveguide is 500nm~800nm, and the second waveguide height is 300nm~400nm; both the multimode and single-mode waveguides are thin silicon nitride waveguides. The first waveguide width of the multimode waveguide is 1.5μm~3μm, and the first waveguide height is 200nm~400nm; the second waveguide width of the single-mode waveguide is 700nm~1500nm, and the second waveguide height is 200nm~400nm. The multimode and single-mode waveguides are both thick silicon nitride waveguides, with the first waveguide width of the multimode waveguide being 1.5 μm to 3 μm and the first waveguide height being 600 nm to 1000 nm. The second waveguide width of the single-mode waveguide is 1200 nm to 2500 nm and the second waveguide height is 600 nm to 1000 nm. Both the multimode and single-mode waveguides are thin-film lithium niobate waveguides, with the first waveguide width of the multimode waveguide being 1.5 μm to 400 nm. The first waveguide has a width of 300nm to 700nm and a height of 300nm to 700nm; the second waveguide of the single-mode waveguide has a width of 700nm to 1500nm and a height of 300nm to 700nm; both the multimode and single-mode waveguides are polymer waveguides. The first waveguide of the multimode waveguide has a width of 4μm to 8μm and a height of 1μm to 5μm; the second waveguide of the single-mode waveguide has a width of 1μm to 8μm and a height of 1μm to 5μm.

[0014] This application also provides a temperature control method based on an optical waveguide temperature sensor, comprising: acquiring the wavelength corresponding to the interference peak in the output interference spectrum of the optical waveguide temperature sensor; determining the temperature error between the current temperature and the target temperature based on the wavelength corresponding to the interference peak; generating a control signal based on the temperature error; driving a temperature adjustment unit to adjust the temperature of the controlled device based on the control signal; and repeating the above steps until the temperature error meets a preset condition.

[0015] The optical waveguide temperature sensor and temperature control method based on Mach-Zehnder interferometer provided in this application have at least the following technical effects.

[0016] This optical waveguide temperature sensor introduces higher-order modes into the interferometer arms and achieves reversible conversion between the fundamental mode and higher-order modes through a mode-switching structure. Simultaneously, it modulates the structural parameters of the multimode waveguide to approximately match the group refractive index of the higher-order mode with that of the fundamental mode in another interferometer arm. Furthermore, it utilizes the difference in thermo-optical response between different modes to significantly enhance the interference phase response to temperature changes. In other words, this optical waveguide temperature sensor achieves mode freedom control by introducing higher-order modes, enhances the interference response through group refractive index matching, and realizes a temperature-induced wavelength drift amplification mechanism through the synergistic effect of group refractive index matching and the difference in thermo-optical response between modes, thus significantly improving temperature sensitivity.

[0017] This optical waveguide temperature sensor does not require the introduction of heterogeneous materials, is compatible with CMOS technology, and can achieve a temperature sensitivity of over 7 nm / K. It has the advantages of high sensitivity, miniaturization, and easy integration. Attached Figure Description

[0018] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0019] Figure 1 A schematic diagram of a Mach-Zehnder interferometer-based optical waveguide temperature sensor according to an embodiment of this application is shown.

[0020] Figure 2 A schematic cross-sectional view of the first mode conversion structure according to an embodiment of this application is shown.

[0021] Figure 3 A schematic cross-sectional view of the second mode conversion structure according to an embodiment of this application is shown.

[0022] Figure 4 The diagram illustrates different implementations of the mode conversion structure according to embodiments of this application.

[0023] Figure 5 A schematic diagram illustrating an optical temperature sensor test according to an embodiment of this application is shown.

[0024] Figure 6 The illustration schematically shows the change in the output spectrum at different temperatures as the optical signal travels from the first input port to the first output port according to an embodiment of this application.

[0025] Figure 7 This illustration schematically shows a drive from an embodiment of the present application. Figure 6 The peak and valley wavelengths extracted are curves showing the shift with temperature. Detailed Implementation

[0026] The embodiments of this application will now 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 this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0027] In the process of developing this application, it was discovered that related technologies involve optimizing interference conditions through group refractive index engineering and using multimode waveguide structures for temperature sensing. Optimizing interference conditions through group refractive index engineering is still limited to single-mode systems, with limited degrees of freedom in adjustment. The use of multimode waveguide structures is mainly used to reduce temperature sensitivity and achieve temperature-stabilized devices. Optimizing the spectral response characteristics of optical waveguide interference structures through group refractive index engineering can improve device performance. However, such schemes are usually based on single-mode waveguide systems, achieving group refractive index matching or compensation by adjusting waveguide structure parameters, resulting in relatively limited design freedom. Furthermore, existing technologies also include schemes that utilize multimode waveguide structures to control device temperature characteristics. These schemes mainly compensate for temperature-induced spectral drift by introducing the propagation or thermal response characteristics of different modes, thereby reducing device temperature sensitivity and achieving temperature-stabilized design. However, these schemes primarily focus on optimizing interference conditions or suppressing temperature drift, without fully utilizing the phase changes caused by the temperature response differences between different modes to achieve temperature sensing. Therefore, there is still room for further improvement in temperature measurement sensitivity and structural design freedom.

[0028] Based on this, this application proposes an optical waveguide temperature sensor and temperature control method based on a Mach-Zehnder interferometer. By introducing dual-mode group refractive index engineering, higher-order modes are excited in a multimode waveguide, and a temperature-dependent phase difference is formed by utilizing the difference in the effective refractive index temperature change rate between the higher-order modes and the fundamental mode. This causes a measurable wavelength shift in the output interference spectrum with temperature changes, thereby achieving temperature detection. Compared to schemes based on single-mode group refractive index engineering, this application can introduce additional mode freedom, which is beneficial to improving temperature sensing sensitivity and expanding device design space, and has important application value in the field of optical waveguide temperature sensing. Specific embodiments are described below.

[0029] Figure 1 A schematic diagram of a Mach-Zehnder interferometer-based optical waveguide temperature sensor according to an embodiment of this application is shown.

[0030] like Figure 1 As shown, the optical waveguide temperature sensor based on the Mach-Zehnder interferometer in this embodiment may include: an optical waveguide and a Mach-Zehnder interferometer structure integrated in the optical waveguide.

[0031] The Mach-Zehnder interferometer structure includes an input optical coupler 1, an input single-mode waveguide 2, a beam splitter 3, an interference structure, a beam combiner 12, a first output waveguide 13, a second output waveguide 14, and an output optical coupler 15, which are connected in sequence.

[0032] The interference structure includes a first interferometer arm and a second interferometer arm. The first interferometer arm comprises, in sequence, a first interferometer arm input waveguide 4, a first mode conversion structure 6, a multimode waveguide 7, a second mode conversion structure 8, and a first interferometer arm output waveguide 10. The multimode waveguide 7 supports the propagation of higher-order modes, and the first mode conversion structure 6 and the second mode conversion structure 8 perform reversible conversions between the fundamental mode and higher-order modes. The second interferometer arm comprises, in sequence, a second interferometer arm input waveguide 5, a single-mode waveguide 9, and a second interferometer arm output waveguide 11, supporting the propagation of the fundamental mode. The geometric parameters of the multimode waveguide 7 are configured such that the refractive index of the first group of higher-order modes in the first interferometer arm approximately matches the refractive index of the second group of the fundamental mode in the second interferometer arm. The propagation modes in the first and second interferometer arms have different thermo-optical response coefficients.

[0033] According to an embodiment of this application, the first interferometer arm is a measuring arm (higher-order mode propagation), and the second interferometer arm is a reference arm (fundamental mode propagation). The higher-order mode is at least one of a transverse electric mode or a transverse magnetic mode.

[0034] According to embodiments of this application, when the temperature changes, an enhanced phase difference change occurs between the two interferometer arms due to the different thermo-optic coefficients of different modes. Simultaneously, due to group refractive index matching, the interference fringes amplify wavelength changes, thereby achieving highly sensitive temperature detection.

[0035] In some implementations, the group refractive index of the higher-order mode in the first interferometer arm and the group refractive index of the fundamental mode in the second interferometer arm satisfy an approximate match, including: the absolute value of the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode is less than a preset threshold. When the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode approaches zero, the sensitivity of the output interference spectrum to phase changes reaches its maximum.

[0036] For example, the refractive index matching error of the first group of the higher-order modes of the multimode waveguide in the first interferometer arm and the second group of the refractive index matching error of the fundamental mode of the single-mode waveguide in the second interferometer arm satisfies:

[0037] |n g,HM -n g,FM |<10 −2

[0038] Where, n g,HM n is the refractive index of the first group of higher-order modes of the multimode waveguide in the first interferometer arm. g,FMThe second group refractive index is the fundamental mode of the single-mode waveguide in the second interferometer arm. The sensitivity of the output interferometer spectrum to phase changes is maximized when the group refractive index difference between the higher-order modes and the fundamental mode approaches zero.

[0039] In some embodiments, the phase difference between the first interferometer arm and the second interferometer arm is correlated with the first effective refractive index of the higher-order mode, the second effective refractive index of the fundamental mode, the first propagation path length of the higher-order mode, the second propagation path length of the fundamental mode, and the wavelength of the output interference spectrum.

[0040] Furthermore, the phase difference between the first and second interferometer arms is formed by the difference between the first phase delay generated by the higher-order mode in the propagation path and the second phase delay generated by the fundamental mode in the propagation path. Temperature changes cause changes in the first and second effective refractive indices, which in turn change the difference between the first and second phase delays, resulting in a change in the phase difference between the first and second interferometer arms and causing a shift in the wavelengths corresponding to the interference peaks or valleys in the output interference spectrum.

[0041] The phase difference increases as the difference between the first and second phase delays increases. The first phase delay is related to the first effective refractive index and the first propagation path length, while the second phase delay is related to the second effective refractive index and the second propagation path length. When the first and second effective refractive indices change due to temperature variations, the phase difference changes accordingly, and the characteristic wavelengths that satisfy the interference conditions change accordingly, thus causing a drift in the output interference spectrum.

[0042] For example, the phase difference between the two interferometer arms satisfy:

[0043]

[0044] in, and L represents the first effective refractive index of the higher-order modes and the second effective refractive index of the fundamental mode, respectively, for different waveguide structures. HM and L FM These are the first propagation path lengths of the higher-order mode and the second propagation path lengths of the fundamental mode, respectively.

[0045] In some embodiments, the first rate of change of the first effective refractive index with temperature is not equal to the second rate of change of the second effective refractive index with temperature.

[0046] For example, the input light is coupled into the chip through input coupler 1 and input single-mode waveguide 2, and then split into two paths by beam splitter 3: one path is coupled into a higher-order mode in multimode waveguide 7 through first mode conversion structure 6, and then converted back to the fundamental mode. The other path always maintains the fundamental mode propagation. The two paths interfere at the beam combiner, and the output spectrum drifts significantly with temperature. Under a temperature change ΔT:

[0047] Refractive index change:

[0048]

[0049] Because the field distributions of higher-order modes and the fundamental mode are different, their effective refractive index temperature response rates are also different. Therefore:

[0050]

[0051] The formula for the temperature sensitivity of light output after passing through the beam combiner is:

[0052]

[0053] To improve the temperature sensitivity of the device, it is necessary to maximize the effective refractive index temperature response difference between the two arms, minimize the group refractive index difference between the two arms, and minimize the difference in arm length between the two arms. When n satisfies... g,HM ≈n g,FM At this time, phase changes are highly sensitive to wavelength changes, and temperature changes will amplify the wavelength drift.

[0054] Figure 2 A schematic cross-sectional view of the first mode conversion structure according to an embodiment of this application is shown. Figure 3 A schematic cross-sectional view of the second mode conversion structure according to an embodiment of this application is shown.

[0055] like Figure 2 and Figure 3 As shown, the optical waveguide includes a substrate layer 16, a lower cladding layer 17, a waveguide core layer 18, and an upper cladding layer 19 stacked sequentially.

[0056] The Mach-Zehnder interferometer structure is disposed in the waveguide core layer 18, namely, the first mode conversion structure 6, the multimode waveguide 7, and the single-mode waveguide 9 are disposed in the waveguide core layer 18. The material of the waveguide core layer 18 includes any one of silicon, silicon nitride, silicon dioxide, lithium niobate, etc., or it can be a polymer formed from silicon, silicon nitride, silicon dioxide, lithium niobate, etc.

[0057] Figure 4 The diagram illustrates different implementations of the mode conversion structure according to embodiments of this application.

[0058] In some embodiments, the mode transition structure may include a directional coupler (such as...) Figure 4 As shown in a), adiabatic graded waveguide (such as...) Figure 4 (as shown in b) or waveguide offset coupling structure (such as...) Figure 4 One or more of the following (as shown in c). The conversion efficiency of the mode conversion structure needs to be greater than 98% (preferably close to 100%).

[0059] In some embodiments, the beam splitter 3 and the beam combiner 12 include one or more of a multimode interference structure, a directional coupler, or a thermally insulating coupler.

[0060] In some embodiments, the material of the optical waveguide temperature sensor can be SOI, SiN, LNOI, etc. The process can employ standard photolithography, eliminating the need for heterogeneous material deposition.

[0061] In some embodiments, both the multimode waveguide and the single-mode waveguide are silicon-on-insulator waveguides. The first waveguide width of the multimode waveguide is 0.8 μm to 2 μm, and the first waveguide height is 200 nm to 300 nm. The second waveguide width of the single-mode waveguide is 400 nm to 500 nm, and the second waveguide height is 200 nm to 300 nm.

[0062] In other embodiments, both the multimode waveguide and the single-mode waveguide are silicon waveguides. The first waveguide width of the multimode waveguide is 0.8 μm to 2 μm, and the first waveguide height is 300 nm to 400 nm. The second waveguide width of the single-mode waveguide is 500 nm to 800 nm, and the second waveguide height is 300 nm to 400 nm.

[0063] In other embodiments, both the multimode waveguide and the single-mode waveguide are thin silicon nitride waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 200nm to 400nm. The second waveguide width of the single-mode waveguide is 700nm to 1500nm, and the second waveguide height is 200nm to 400nm.

[0064] In other embodiments, both the multimode waveguide and the single-mode waveguide are thick silicon nitride waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 600nm to 1000nm. The second waveguide width of the single-mode waveguide is 1200nm to 2500nm, and the second waveguide height is 600nm to 1000nm.

[0065] In other embodiments, both the multimode waveguide and the single-mode waveguide are thin-film lithium niobate waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 300nm to 700nm. The second waveguide width of the single-mode waveguide is 700nm to 1500nm, and the second waveguide height is 300nm to 700nm.

[0066] In other embodiments, both the multimode waveguide and the single-mode waveguide are polymer waveguides. The first waveguide width of the multimode waveguide is 4μm to 8μm, and the first waveguide height is 1μm to 5μm. The second waveguide width of the single-mode waveguide is 1μm to 8μm, and the second waveguide height is 1μm to 5μm.

[0067] Based on the above configuration of waveguide materials and interface dimensions, multimode waveguides can support the propagation of the fundamental mode and at least one higher-order mode, while single-mode waveguides only support the propagation of the fundamental mode.

[0068] In some embodiments, the optical waveguide temperature sensor further includes a heating control unit for adjusting the device temperature to cause the envelope peak or interference peak position of the output interference spectrum to drift, and to achieve fine control by utilizing the amplification effect.

[0069] Based on the above-described optical waveguide temperature sensor, embodiments of this application also provide a temperature control method, comprising: acquiring the wavelength corresponding to the interference peak in the output interference spectrum of the optical waveguide temperature sensor; determining the temperature error between the current temperature and the target temperature based on the wavelength corresponding to the interference peak; generating a control signal based on the temperature error; driving a temperature adjustment unit to adjust the temperature of the controlled device based on the control signal; and repeating the above steps until the temperature error meets a preset condition.

[0070] According to embodiments of this application, the differential thermo-optical response of different propagation modes is utilized to amplify the phase change caused by temperature variations in the wavelength domain, thereby improving temperature control sensitivity. The synergistic effect of group refractive index approximation and the difference in thermo-optical response of propagation modes amplifies the interference phase change caused by temperature variations in the wavelength domain. By introducing different propagation modes and their thermo-optical response differences in the first and second interferometer arms, combined with group refractive index matching conditions, an interference phase enhancement effect caused by temperature variations is achieved, resulting in a wavelength change in the output interference spectrum that is greater than the corresponding change in a single-mode interference structure. The propagation modes are not limited to a specific order or polarization form.

[0071] Figure 5 A schematic diagram illustrating an optical temperature sensor test according to an embodiment of this application is shown.

[0072] like Figure 5As shown, the optical signal is emitted from a broadband light source, passes through a polarization controller, and enters input port 1 of the sensing chip. The output optical signal of the sensing chip (an optical waveguide temperature sensor based on a Mach-Zehnder interferometer) is then processed by a spectrometer. Temperature changes in the chip can be achieved through a temperature controller at the bottom of the chip or by fabricating heating electrodes on the two arms of the Mach-Zehnder interferometer. When the ambient temperature changes, a phase difference occurs between the two interferometer arms due to the different thermo-optical responses of different propagation modes, causing a wavelength shift in the output interference spectrum. Temperature measurement is achieved by detecting changes in the peak position of the output spectrum.

[0073] Figure 6 The illustration schematically shows the output spectrum at different temperatures calculated by simulation when the optical signal travels from the first input port to the first output port according to an embodiment of this application.

[0074] like Figure 6 As shown, the peaks and valleys of the output spectrum shift with temperature changes.

[0075] Figure 7 This illustration schematically shows a drive from an embodiment of the present application. Figure 6 The peak and valley wavelengths extracted are curves showing the shift with temperature.

[0076] like Figure 7 As shown, by fitting this line ( Figure 7 (The dashed line at the midpoint) gives a slope, i.e., temperature sensitivity, of 7.103 nm / K. This demonstrates that using a multimode waveguide can indeed improve the sensitivity of the Mach-Zehnder interferometer sensor. However, in actual fabrication, the measured value may be lower than the theoretical value due to manufacturing errors.

[0077] It should be noted that the implementation details and beneficial effects of the temperature control method embodiment are the same as or similar to the implementation details and beneficial effects of the optical waveguide temperature sensor embodiment, and the specific details will not be repeated here.

[0078] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this application is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this application, and all such substitutions and modifications should fall within the scope of this application.

Claims

1. An optical waveguide temperature sensor based on a Mach-Zehnder interferometer, characterized in that, include: Optical waveguide and Mach-Zehnder interferometer structure integrated in the optical waveguide; The Mach-Zehnder interferometer structure includes an input optical coupler, a beam splitter, an interference structure, a beam combiner, and an output optical coupler connected in sequence. The interference structure includes a first interferometer arm and a second interferometer arm. The first interferometer arm includes a first interferometer arm input waveguide, a first mode conversion structure, a multimode waveguide, a second mode conversion structure, and a second interferometer arm output waveguide connected in sequence. The multimode waveguide is used to support the propagation of higher-order modes and the fundamental mode. The first mode conversion structure and the second mode conversion structure are used to perform reversible conversion between the fundamental mode and the higher-order modes. The second interferometer arm is a single-mode waveguide used to support the propagation of the fundamental mode. The geometric parameters of the multimode waveguide are configured such that the refractive index of the first group of higher-order modes in the first interferometer arm and the refractive index of the second group of the fundamental mode in the second interferometer arm are approximately matched. The propagation modes in the first interferometer arm and the propagation modes in the second interferometer arm have different thermo-optical response coefficients.

2. The optical waveguide temperature sensor according to claim 1, characterized in that, The group refractive index of the higher-order modes in the first interferometer arm and the group refractive index of the fundamental mode in the second interferometer arm satisfy an approximate match, including: The absolute value of the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode is less than a preset threshold. When the difference between the first group refractive index of the higher-order mode and the second group refractive index of the fundamental mode approaches zero, the sensitivity of the output interference spectrum to phase changes reaches its maximum.

3. The optical waveguide temperature sensor according to claim 1 or 2, characterized in that, The phase difference between the first interferometer arm and the second interferometer arm is related to the first effective refractive index of the higher-order mode, the second effective refractive index of the fundamental mode, the first propagation path length of the higher-order mode, the second propagation path length of the fundamental mode, and the wavelength of the output interference spectrum.

4. The optical waveguide temperature sensor according to claim 3, characterized in that, The phase difference is formed by the difference between the first phase delay generated by the higher-order mode in the propagation path and the second phase delay generated by the fundamental mode in the propagation path; the first phase delay is related to the product of the first effective refractive index and the first propagation path length, and the second phase delay is related to the product of the second effective refractive index and the second propagation path length; the first effective refractive index and the second effective refractive index change with temperature.

5. The optical waveguide temperature sensor according to claim 3, characterized in that, The rate of change of the first effective refractive index corresponding to the higher-order mode with respect to temperature is different from the rate of change of the second effective refractive index corresponding to the fundamental mode with respect to temperature.

6. The optical waveguide temperature sensor according to claim 3, characterized in that, The phase difference change between the first interferometer and the second interferometer results in a shift in the wavelength corresponding to the interference peak or valley in the output interference spectrum. This shift is related to the phase difference change between the first interferometer and the second interferometer.

7. The optical waveguide temperature sensor according to claim 1, characterized in that, The optical waveguide comprises a substrate layer, a lower cladding layer, a waveguide core layer, and an upper cladding layer stacked sequentially. The Mach-Zehnder interferometer structure is disposed in the waveguide core layer.

8. The optical waveguide temperature sensor according to claim 1, characterized in that, The mode conversion structure includes one or more of a directional coupler, an adiabatic graded waveguide, or a waveguide offset coupling structure. The beam splitter and beam combiner include one or more of a multimode interference structure, a directional coupler, or a thermally insulating coupler.

9. The optical waveguide temperature sensor according to claim 1, characterized in that, Both the multimode waveguide and the single-mode waveguide are silicon-on-insulator waveguides. The first waveguide width of the multimode waveguide is 0.8μm to 2μm, and the first waveguide height is 200nm to 300nm. The second waveguide width of the single-mode waveguide is 400nm to 500nm, and the second waveguide height is 200nm to 300nm. Both the multimode waveguide and the single-mode waveguide are silicon waveguides. The first waveguide width of the multimode waveguide is 0.8μm to 2μm, and the first waveguide height is 300nm to 400nm. The second waveguide width of the single-mode waveguide is 500nm to 800nm, and the second waveguide height is 300nm to 400nm. Both the multimode waveguide and the single-mode waveguide are thin silicon nitride waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 200nm to 400nm. The second waveguide width of the single-mode waveguide is 700nm to 1500nm, and the second waveguide height is 200nm to 400nm. Both the multimode waveguide and the single-mode waveguide are thick silicon nitride waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 600nm to 1000nm. The second waveguide width of the single-mode waveguide is 1200nm to 2500nm, and the second waveguide height is 600nm to 1000nm. Both the multimode waveguide and the single-mode waveguide are thin-film lithium niobate waveguides. The first waveguide width of the multimode waveguide is 1.5μm to 3μm, and the first waveguide height is 300nm to 700nm. The second waveguide width of the single-mode waveguide is 700nm to 1500nm, and the second waveguide height is 300nm to 700nm. Both the multimode waveguide and the single-mode waveguide are polymer waveguides. The first waveguide width of the multimode waveguide is 4μm to 8μm, and the first waveguide height is 1μm to 5μm. The second waveguide width of the single-mode waveguide is 1μm to 8μm, and the second waveguide height is 1μm to 5μm.

10. A temperature control method, characterized in that, The temperature control method is implemented based on the optical waveguide temperature sensor according to any one of claims 1 to 9, and includes: Obtain the wavelengths corresponding to the interference peaks in the output interference spectrum of the optical waveguide temperature sensor; The temperature error between the current temperature and the target temperature is determined based on the wavelength corresponding to the interference peak. A control signal is generated based on the temperature error; The temperature adjustment unit is driven to adjust the temperature of the controlled device according to the control signal; Repeat the above steps until the temperature error meets the preset conditions.

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