Silicon-based optical resonant cavity temperature sensor with wide free spectral region and preparation method of silicon-based optical resonant cavity temperature sensor

Abstract

The invention provides a wide-free-spectral-region silicon-based optical resonant cavity temperature sensor and a preparation method thereof. The wide-free-spectral-region silicon-based optical resonant cavity temperature sensor comprises a substrate; the sensing unit is prepared on the substrate and is used for converting temperature change into a narrow free spectral region resonance signal; the filtering unit is prepared on the substrate and is used for carrying out filtering processing on the resonance signal in the narrow free spectral region and outputting a sensing signal in a wide free spectral region; the temperature sensitivity of the filtering unit is an integral multiple of the sensitivity of the sensing unit; and the upper wrapping layer is the top layer of the sensor and is deposited on the sensing unit and the filtering unit. According to the invention, wide-temperature-zone temperature measurement of the silicon-based optical resonant cavity type temperature sensor can be realized, and the temperature sensor has the advantages of high sensitivity and low loss.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-based optical temperature sensors, and particularly, to a silicon-based optical resonator temperature sensor with a wide free spectral range and a preparation method thereof. Background Art

[0002] Temperature sensing and detection are widely applied in fields such as aerospace, artificial intelligence, and quantum computing. Traditional electrical temperature sensors cannot be applied to complex and harsh environments due to the influence of electromagnetic interference. Optical temperature sensors have been widely studied and applied because they have advantages such as high quality factors and electromagnetic interference resistance compared with traditional resistive temperature sensors. Among them, optical resonator temperature sensors have been widely developed due to their high sensitivity, small mode volume, and compatibility with CMOS processes.

[0003] Through a search of the prior art, it is found that Haitan Xu et al. from the Joint Quantum Institute of the University of Maryland, College Park, USA, wrote an article "Ultra-sensitive chip-based photonic temperature sensor using ring resonator structures" in Optics Express, 2014, 3. It demonstrated a silicon-based micro-ring resonator temperature sensor with a temperature sensitivity of 77 pm / K, and achieved a low noise limit of 80 μK by using different monitoring modes. However, its temperature detection range is limited to the room temperature range and cannot meet the requirements of wide-range temperature measurement and detection.

[0004] Cheng Zhang et al. from the National Institute of Metrology of China wrote an article "Soliton microcomb-assisted microring photonic thermometer with ultra-high resolution and broad range" in Photonics Research, 2023, 11. It demonstrated a silicon nitride resonator temperature sensor with a temperature measurement range of 45 K and a resolution of 58 μK, taking into account the advantages of a wide range and high resolution. However, it relies on a complex temperature measurement system built and cannot meet the needs of practical applications.

[0005] Xiantao Zhu et al. from the School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, China, published an article "Wide-range and ultra-low temperature thermometer based on a silicon resonator" in Optics Letters, 2024, 49. Their experiment proved that a silicon-based micro-ring resonator temperature sensor can be used for temperature measurement in a wide temperature range of 10K - 300K, and for the first time, the sensing temperature range was extended to the low temperature range of 10K. However, due to the limitation of the free spectral range, this micro-ring temperature sensor can actually only be used for temperature measurement in the temperature range of 10K - 240K, and cannot meet the requirements of full-range temperature measurement.

[0006] In summary, optical resonator temperature sensors utilize the dependence of the resonant wavelength on temperature and have advantages such as high sensitivity, small size, and anti-electromagnetic interference. However, the small free spectral range (FSR) of existing optical resonator temperature sensors limits the temperature sensing range. Temperature sensors with a wide free spectral range need to sacrifice the device quality factor (Q value). Therefore, there is an urgent need to propose a low-loss, high-sensitivity silicon-based optical resonator temperature sensor with a wide free spectral range that can meet full-temperature range detection. Summary of the Invention

[0007] Aiming at the defects in the prior art, the purpose of the present invention is to provide a silicon-based optical resonator temperature sensor with a wide free spectral range and a preparation method.

[0008] According to the first aspect of the present invention, there is provided a silicon-based optical resonator temperature sensor with a wide free spectral range, comprising:

[0009] A substrate;

[0010] A sensing unit, which is prepared on the substrate and converts temperature changes into resonant signals in a narrow free spectral range;

[0011] A filtering unit, which is prepared on the substrate and filters the resonant signals in the narrow free spectral range to output sensing signals in a wide free spectral range; the temperature sensitivity of the filtering unit is an integer multiple of the sensitivity of the sensing unit;

[0012] An upper cladding, which is the top layer of the sensor and is deposited on the sensing unit and the filtering unit.

[0013] Preferably, the sensing unit includes:

[0014] A resonant cavity, which is a micro-ring resonator or a nano-beam resonator;

[0015] The optical signal transmission straight waveguide is located on one side of the resonant cavity. The two ends of the optical signal transmission straight waveguide are coupling gratings to realize the input and output of optical signals. The optical signal transmission straight waveguide is critically coupled with the resonant cavity.

[0016] Preferably, the micro-ring resonator has at least one of the following characteristics:

[0017] - The waveguide width of the micro-ring resonator is the same as that of the optical signal transmission straight waveguide;

[0018] - The waveguide width ranges from 400 nm to 3 μm;

[0019] - The micro-ring resonator is critically coupled with the optical signal transmission straight waveguide, and the gap between the two ranges from 100 nm to 500 nm;

[0020] The nano-beam resonator has at least one of the following characteristics:

[0021] - The nano-beam resonator is a stacked structure with periodic defects introduced into the optical signal transmission straight waveguide;

[0022] - The resonant peak of the nano-beam resonator is adjusted by adjusting the period of the defects;

[0023] - The nano-beam resonator is connected to the optical signal transmission straight waveguide.

[0024] Preferably, the filtering unit is a cascaded micro-ring; the cascaded micro-ring includes a plurality of parallel micro-rings, and adjacent micro-rings are coupled to each other.

[0025] Preferably, the optical signal transmission straight waveguide includes an upper straight waveguide and a lower straight waveguide with the same structure; the cascaded micro-ring is located between the upper straight waveguide and the lower straight waveguide;

[0026] The cascaded micro-ring has at least one of the following characteristics:

[0027] - The upper straight waveguide structure and the lower straight waveguide structure are respectively critically coupled with the cascaded micro-ring structure;

[0028] - The gap between adjacent micro-rings among the upper straight waveguide structure, the lower straight waveguide structure and the cascaded micro-ring structure ranges from 100 nm to 300 nm;

[0029] - Each micro-ring in the cascaded micro-ring has the same size, and the diameter ranges from 1 μm to 100 μm.

[0030] Preferably, the diameter of the micro-ring can regulate the size of the free spectral range FSR of the filtering unit.

[0031] Preferably, the signal transmission between the upper straight waveguide and the lower straight waveguide adopts the Drop transmission mode.

[0032] Preferably, the filtering unit is an MZI structure of a Mach-Zehnder interferometer; the MZI structure includes two asymmetric interference arms, and the waveguide widths of the two interference arms are the same, but the lengths are different.

[0033] Preferably, the length difference between the two asymmetric interference arms of the MZI structure can regulate the temperature sensitivity of the filtering unit and the size of the free spectral range FSR.

[0034] According to the second aspect of the present invention, a method for manufacturing a wide free spectral range silicon-based optical resonator temperature sensor is provided, including:

[0035] Providing a substrate;

[0036] Fabricating a sensing unit and a filtering unit on the substrate;

[0037] Depositing a top layer on the top of the substrate to cover the sensing unit and the filtering unit.

[0038] Compared with the prior art, the embodiments of the present invention have at least one beneficial effect:

[0039] The wide free spectral range silicon-based optical resonator temperature sensor provided in the embodiments of the present invention can achieve temperature measurement in a wide temperature range through the cooperation of the sensing unit and the filtering unit, and at the same time has the advantages of high sensitivity and low loss. Description of the Drawings

[0040] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent:

[0041] Figure 1 It is a schematic diagram of the overall structure of a wide free spectral range silicon-based optical resonator temperature sensor using a microring resonator as a temperature sensing unit and a cascaded microring structure as a filtering unit in an embodiment of the present invention;

[0042] Figure 2 It is a top view of a wide free spectral range silicon-based optical resonator type temperature sensor using a microring resonator as a temperature sensing unit and a cascaded microring structure as a filtering unit in an embodiment of the present invention;

[0043] Figure 3 It is a schematic diagram of a wide free spectral range silicon-based optical resonator type temperature sensor using a microring resonator as a temperature sensing unit and an MZI structure as a filtering unit in an embodiment of the present invention;

[0044] Figure 4Flowchart of the preparation method of a silicon-based optical resonator temperature sensor with a wide free spectral range in an embodiment of the present invention;

[0045] Figure 5 Schematic diagram of the process of the preparation method in an embodiment of the present invention.

[0046] The corresponding reference numerals in the figure are: 1 is the sensing unit, 2 is the filtering unit, 3 is silicon dioxide, 4 is the signal transmission straight waveguide, 5 is the coupling grating, 5-1 and 5-2 are the signal input coupling gratings, 5-3 and 5-4 are the signal output coupling gratings, 6-1 is the upper interference arm, 6-2 is the lower interference arm, 7 is the silicon waveguide layer, and 8 is the photoresist. Specific embodiments

[0047] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0048] In the traditional single-ring structure, the temperature sensing range depends on the free spectral range, and the free spectral range is limited by the micro-ring diameter. The smaller the diameter, the larger the free spectral region, but the smaller the micro-ring diameter, the greater the device loss and the smaller the Q value, which is a contradiction. Based on this, an embodiment of the present invention provides a silicon-based optical resonator temperature sensor with a wide free spectral range, as shown in Figure 1 and 2 shown, including a substrate, a sensing unit 1, a filtering unit 2, and an upper cladding. The sensing unit 1 is fabricated on the substrate and converts the temperature change into a narrow free spectral range resonance signal; the filtering unit 2 is fabricated on the substrate and processes the narrow free spectral range resonance signal to output a sensing signal with a wide free spectral range; the temperature sensitivity of the filtering unit is an integer multiple of the temperature sensitivity of the sensing unit 1; the upper cladding is the top layer of the sensor and is deposited on the sensing unit 1 and the filtering unit 2.

[0049] Specifically, the narrow free spectral range (FSR) resonance signal refers to the wavelength or frequency interval between the resonance peaks generated by the sensing unit being relatively small. For example, in silicon-based photonic devices, the narrow FSR usually corresponds to: wavelength domain: about 0.1 nm to 1 nm (corresponding to the 1550 nm band); frequency domain: about 10 GHz to 100 GHz. The wide free spectral range (FSR) sensing signal is the signal output after the filtering unit processes the narrow FSR signal. For example, the wide FSR is usually an integer multiple of the narrow FSR (such as 2-5 times): wavelength domain: about 1 nm to 5 nm; frequency domain: about 100 GHz to 500 GHz.

[0050] The temperature sensitivity of the filtering unit is an integer multiple of the temperature sensitivity of the sensing unit, ensuring that the resonance peak of the sensing unit matches the peak of the filtering unit, thereby ensuring that the resonance peak of the sensing unit is not filtered out. In this way, the signal of the sensing unit can be detected at the signal output end to achieve temperature sensing detection.

[0051] In the above embodiments, since the filtering unit and the sensing unit are respectively provided, and the sensitivity relationship between them, the size of the filtering unit can be unrestricted, thereby achieving a wide free spectral range. The size of the sensing unit is also unrestricted. The filtering unit filters out too many resonance peaks of the sensing unit, and finally achieves a wide temperature range and high Q through the two, that is, the filtering unit achieves a wide free spectral range, and the sensing unit achieves a high Q value.

[0052] In some preferred embodiments, the filtering unit 2 is critically coupled to the shown sensing unit 1, which can minimize the critical coupling loss.

[0053] In a preferred embodiment, the sensing unit 1 includes a resonant cavity and an optical signal transmission straight waveguide 4. The resonant cavity can be a microring resonator or a nanobeam resonator; both ends of the optical signal transmission straight waveguide 4 are coupling gratings to realize the input and output of optical signals; the optical signal transmission straight waveguide 4 is critically coupled to the resonant cavity.

[0054] Furthermore, in a preferred embodiment, when the resonant cavity is a microring resonator, the waveguide width of the microring resonator is the same as that of the optical signal transmission straight waveguide, which is convenient for designing to generate a resonant signal; the waveguide width ranges from 400 nm to 3 μm; the microring resonator is critically coupled to the optical signal transmission straight waveguide, and the gap between the two ranges from 100 nm to 200 nm;

[0055] For the nanobeam resonator, the nanobeam resonator introduces periodic defects such as etched cylindrical holes and rectangular holes in the silicon straight waveguide, including but not limited to a stacked structure; the resonance peak of the nanobeam resonator is adjusted by adjusting the period of the defect; the nanobeam resonator is connected to the straight waveguide.

[0056] In the above embodiments, the microring resonator structure can be designed with different sizes and different cascaded number structures of filtering rings according to needs to control the filtering peak width; the nanobeam resonator structure can be realized by introducing defects in the straight waveguide, and the device design and preparation process is simple, and the overall size and volume of the device are smaller.

[0057] Based on the sensing unit of the above embodiments, in a preferred embodiment, the filtering unit is a cascaded microring; the cascaded microring includes a plurality of parallel microrings, and adjacent microrings are coupled to each other.

[0058] For the cascaded microring, the optical signal transmission straight waveguide includes an upper straight waveguide and a lower straight waveguide with the same structure; the cascaded microring is located between the upper straight waveguide and the lower straight waveguide; the two ends of the upper straight waveguide are respectively a signal input coupling grating 5-1 and a signal output coupling grating 5-3; the two ends of the lower straight waveguide are respectively a signal input coupling grating 5-2 and a signal output coupling grating 5-4.

[0059] Both the structure of the upper straight waveguide and the cascaded microring structure, and the structure of the lower straight waveguide and the cascaded microring structure achieve critical coupling; the gap ranges between the structure of the upper straight waveguide, the structure of the lower straight waveguide and the cascaded microring structure, and between adjacent microring structures are set to be from 100 nm to 300 nm. In the above embodiments, the achievement of critical coupling ensures that the loss is reduced to the lowest, thereby enabling the Q value of the device to be improved, and the accuracy of critical coupling depends on the gap sizes between the ring structures and between the ring structure and the straight waveguide structure.

[0060] The microrings in the cascaded microring structure have the same size, and the diameter range of each microring is 1 μm - 100 μm. The microring diameter determines the free spectral range, as shown in the following formula:

[0061]

[0062] FSR represents the free spectral range, λ is the central wavelength of the input laser signal, r represents the microring radius, and n g is the group refractive index of the microring waveguide.

[0063] In the above embodiments, the diameter of the filtering unit structure can be designed to be very small to achieve a wide free spectral region, while the microring structure diameter of the sensing unit can be very large to ensure a high Q value. The filtering unit filters out the resonant peak parts of too many sensing units, and finally achieves a wide temperature range and a high Q value through the two, that is, the filtering unit achieves a wide free spectral region and the sensing unit achieves a high Q value.

[0064] In a preferred embodiment, referring to Figure 1 and Figure 2 as shown, the wide free spectral region silicon-based optical resonator temperature sensor mainly includes the following design: coupling gratings 5 are designed at both ends of the straight waveguide to realize the input and output of optical signals. A single microring resonator structure is used as the sensing unit, and a cascaded microring resonator structure is used as the filtering unit. The optical signal enters from the input coupling grating 5-1, passes through the sensing unit and the filtering unit in sequence. The filtering unit can filter the signal of the sensing unit, and finally the signal is read at the output coupling grating 5-3 to realize low-loss and wide free spectral region temperature detection.

[0065] To achieve low loss and high temperature sensitivity of the device, the resonant cavity structure of the sensing unit is designed to be large-sized. By adjusting the diameter and cascading number of the micro-ring structure of the filtering unit 2, the free spectral range of the device is adjusted. By selecting different input signal waveguide and output signal waveguide structures, Through-mode transmission or Drop-mode transmission can be achieved. When the optical signal enters through coupling grating 5-1 and outputs through coupling grating 5-3, or enters through coupling grating 5-2 and outputs through coupling grating 5-4, Through transmission mode can be achieved. When the optical signal enters through coupling grating 5-1 and outputs through coupling grating 5-4, or enters through coupling grating 5-2 and outputs through coupling grating 5-3, Drop transmission mode can be achieved. To achieve a wide free spectral range silicon-based micro-ring temperature sensor, Drop mode should be used for signal transmission.

[0066] In another embodiment of the present invention, as Figure 3 shown, coupling gratings are designed at both ends of the straight waveguide to achieve the input and output of optical signals. A single micro-ring resonator structure is used as the sensing unit, and a Mach-Zehnder interferometer (MZI) structure is used as the filtering unit. By adjusting the length difference between the upper interference arm 6-1 and the lower interference arm 6-2 of the MZI structure, the temperature sensitivity of the filtering unit is regulated to be consistent with that of the sensing unit, and the free spectral range FSR of the device is adjusted. Specifically, the temperature sensitivity S of the MZI filtering unit and the lengths of the interference arm 1 and interference arm 2 of the MZI structure satisfy the following relational formula:

[0067]

[0068] The free spectral range FSR of the MZI filtering unit and the lengths of the interference arm 1 and interference arm 2 of the MZI structure satisfy the following relational formula:

[0069]

[0070] where λ is the central wavelength of the input laser signal, σ is the thermo-optic coefficient of the substrate material, L1, n g1 is the arm length of the first interference arm and the group refractive index of the waveguide structure, L2, n g2 is the arm length of the second interference arm and the group refractive index of the waveguide structure.

[0071] Based on the same inventive concept, in other embodiments of the present invention, a preparation method for a wide free spectral range silicon-based optical resonator temperature sensor is also provided, as Figure 4 shown, and the main steps include:

[0072] The first step is to provide a substrate;

[0073] The second step is to fabricate a sensing unit and a filtering unit on the substrate;

[0074] In the third step, a top cladding layer is deposited on the top of the substrate to cover the sensing unit and the filtering unit.

[0075] In some specific embodiments, the top cladding layer can be any one of silicon oxide, silicon nitride, or PI.

[0076] In some specific embodiments, the CMOS process is adopted. The sensing unit and the filtering unit are fabricated through electron beam lithography, development, and etching, and the top cladding layer is deposited on the surface of the device at a high temperature. Further, as Figure 5 shown, the fabrication method adopts the following steps:

[0077] S1. Provide a substrate, which includes a silicon waveguide layer 7, a silicon oxide layer 3, and a silicon waveguide layer 7 from bottom to top.

[0078] S2. After spin-coating a photoresist 8 on the substrate, patterned photoresist 8 is formed by electron beam direct writing lithography and development. Then, the unprotected area without photoresist 8 is etched with 220 nm silicon by plasma deep silicon etching to form a signal transmission straight waveguide, a sensing unit, and a filtering unit.

[0079] S3. Remove the photoresist 8.

[0080] S4. After spin-coating the photoresist 8 on the substrate again, patterned photoresist 8 is formed by electron beam direct writing lithography and development. Then, the unprotected area without photoresist 8 is etched with 70 nm silicon by plasma deep silicon etching to form a coupling grating structure.

[0081] S5. Deposit silicon oxide 3 on the surface of the device to form a silicon oxide layer, obtaining a silicon-based optical micro-ring temperature sensor.

[0082] The fabrication method of the above embodiments is compatible with the traditional complementary metal oxide semiconductor (CMOS) process, with mature processes, can be mass-produced on a large scale, and is conducive to the integration with other devices such as other sensors.

[0083] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be combined arbitrarily without conflict.

Claims

1. A silicon-based optical resonator temperature sensor with a wide free spectral range, characterized in that Comprising: A substrate; A sensing unit, which is fabricated on the substrate and converts temperature changes into a narrow free spectral range resonance signal; A filtering unit, which is fabricated on the substrate, filters the narrow free spectral range resonance signal, and outputs a sensing signal with a wide free spectral range; the temperature sensitivity of the filtering unit is an integer multiple of the sensitivity of the sensing unit; An upper cladding, which is the top layer of the sensor and is deposited on the sensing unit and the filtering unit.

2. The temperature sensor of a silicon-based optical resonator with a wide free spectral range according to claim 1, characterized in that, The sensing unit includes: A resonator, which is a micro-ring resonator or a nano-beam resonator; An optical signal transmission straight waveguide, located on one side of the resonator, with coupling gratings at both ends of the optical signal transmission straight waveguide to realize the input and output of optical signals; the optical signal transmission straight waveguide is critically coupled with the resonator.

3. The temperature sensor of a silicon-based optical resonator with a wide free spectral range according to claim 2, characterized in that, The micro-ring resonator has at least one of the following characteristics: - The waveguide width of the micro-ring resonator is the same as that of the optical signal transmission straight waveguide; - The waveguide width ranges from 400 nm to 3 μm; - The micro-ring resonator is critically coupled with the optical signal transmission straight waveguide, and the gap between them ranges from 100 nm to 500 nm; The nano-beam resonator has at least one of the following characteristics: - The nano-beam resonator is a stacked structure with periodic defects introduced in the optical signal transmission straight waveguide; - The resonance peak of the nano-beam resonator is adjusted by adjusting the period of the defects; - The nano-beam resonator is connected to the optical signal transmission straight waveguide.

4. The temperature sensor of a silicon-based optical resonator with a wide free spectral range according to claim 2, wherein, The filtering unit is a cascaded micro-ring; the cascaded micro-ring includes a plurality of parallel micro-rings, and adjacent micro-rings are coupled to each other.

5. The temperature sensor of a silicon-based optical resonator with a wide free spectral range according to claim 4, wherein, The optical signal transmission straight waveguide includes an upper straight waveguide and a lower straight waveguide with the same structure; the cascaded micro-ring is located between the upper straight waveguide and the lower straight waveguide; The cascaded micro-ring has at least one of the following characteristics: - The upper straight waveguide structure and the lower straight waveguide structure are respectively critically coupled with the cascaded micro-ring structure; - The gap between adjacent micro-rings among the upper straight waveguide structure, the lower straight waveguide structure and the cascaded micro-ring structure ranges from 100 nm to 300 nm; - Each micro-ring in the cascaded micro-ring has the same size, and the diameter ranges from 1 μm to 100 μm.

6. The temperature sensor of a silicon-based optical resonator with a wide free spectral range according to claim 5, characterized in that, The diameter of the micro-ring can control the size of the free spectral range (FSR) of the filtering unit.

7. A wide free spectral range silicon-based optical resonator temperature sensor according to claim 5, characterized in that, The signal transmission between the upper straight waveguide and the lower straight waveguide adopts the Drop transmission mode.

8. A wide free spectral range silicon-based optical resonator temperature sensor according to claim 1, characterized in that The filtering unit is an MZI structure of a Mach-Zehnder interferometer; the MZI structure includes two asymmetric interference arms, and the waveguide widths of the two interference arms are the same, but the lengths are different.

9. A silicon-based optical resonator temperature sensor with a wide free spectral range according to claim 8, characterized in that, The length difference between the two asymmetric interference arms of the MZI structure can control the temperature sensitivity of the filtering unit and the size of the free spectral range (FSR).

10. A method for preparing a wide free spectral range silicon-based optical resonator temperature sensor according to any one of claims 1-9, characterized in that, Including: Providing a substrate; Fabricating a sensing unit and a filtering unit on the substrate; Depositing an upper cladding on the top of the substrate to cover the sensing unit and the filtering unit.

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