A photonic temperature sensing system and a temperature measuring method thereof

Abstract

The present application relates to a kind of photonic temperature sensing system and its temperature measuring method, belong to temperature sensing technical field, solve the problem that existing method is influenced by laser frequency noise, power noise and polarization.System includes laser, for generating laser;Frequency control loop, for frequency control laser based on frequency feedback signal to generate frequency stable laser signal;Power control loop, for modulating the power of frequency stable laser signal based on power feedback signal to generate frequency and power stable optical signal;Photonic temperature sensing probe, for providing frequency and power stable optical signal to photonic temperature sensing probe to generate output optical signal;And first photoelectric detector, for receiving output optical signal, and first electrical signal is converted into output optical signal to obtain temperature value according to first electrical signal.Improve the system error caused by laser frequency and power noise.

Description

Technical Field

[0001] This invention relates to the field of temperature sensing technology, and in particular to a photonic temperature sensing system and its temperature measurement method. Background Technology

[0002] Although thermometers are now ubiquitous, their development has been very slow over the past few decades. The standard platinum resistance thermometer, the standard medium for precise temperature measurement, was first developed over a century ago. Furthermore, many modern temperature sensors still rely on the resistance of thin metal films or wires to sense temperature, a resistance that varies with temperature. While thermometers using resistance to measure temperature have an uncertainty of 10 mK in routine measurements, they are sensitive to mechanical shocks, which can cause the resistance to drift over time, requiring frequent offline calibrations that are time-consuming.

[0003] In recent years, photonic devices have been trending towards revolutionizing temperature sensing by altering its fundamental basis, potentially becoming a replacement for resistance thermometers. These photonic devices offer greater temperature sensitivity and strong robustness against electromagnetic interference. Optical resonant cavities, on the other hand, are resonant cavities that confine the light field to the micro- and nano-scale. Recent advancements in micro- and nano-fabrication technologies and semiconductor processes have furthered research into optical microcavities. These microcavities are small in size and have a high quality factor, significantly enhancing the interaction between light and matter, and have wide applications in cavity quantum electrodynamics, nonlinear optics, low-threshold lasers, and high-sensitivity sensors.

[0004] Ring resonators exhibit high quality factor Q and small mode volume V. Quality factor and mode volume describe the effective confinement of photons by a microcavity in the temporal and spatial dimensions, respectively. Photon temperature sensors based on microring resonators possess advantages such as high sensitivity and accuracy, small size, integrability, and applicability to strong electromagnetic environments, and are widely used in the sensing field. Optical sensing based on optical microcavities achieves temperature sensing by measuring changes in the spectral characteristics of the resonant mode after changes in the measured physical quantity or disturbances in the pump source. It utilizes temperature changes in material properties—typically a combination of thermo-optical effects and thermal expansion effects—to manifest a shift in the center wavelength of the spectrum.

[0005] In optical cavity measurement sensing, if an optical signal with a matched resonant peak wavelength is used to monitor and sense a physical quantity, and the change in light intensity of the measured optical signal after the optical cavity is disturbed by the physical quantity being measured is used to sense that physical quantity, this measurement scheme is limited by system noise, including laser frequency noise, power noise, and the effects of polarization. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a photonic temperature sensing system and its temperature measurement method to solve the problems of existing methods being affected by laser frequency noise, power noise and polarization.

[0007] On one hand, embodiments of the present invention provide a photonic temperature sensing system comprising: a laser, a frequency control loop, a power control loop, a photonic temperature sensing probe, and a first photodetector, wherein: the laser is used to generate laser light; the frequency control loop is used to control the frequency of the laser based on a frequency feedback signal to generate a frequency-stable laser signal; the power control loop is used to modulate the power of the frequency-stable laser signal based on a power feedback signal to generate a frequency- and power-stable optical signal; the photonic temperature sensing probe is used to provide the frequency- and power-stable optical signal to itself to generate an output optical signal; and the first photodetector is used to receive the output optical signal and convert the output optical signal into a first electrical signal to obtain a temperature value based on the first electrical signal.

[0008] The beneficial effects of the above technical solution are as follows: The photon temperature sensing system according to the embodiment of the present invention has frequency and power stabilization functions. The frequency control loop stabilizes the light source frequency and the power control loop stabilizes the power. The frequency and power stabilization system can improve the system error caused by laser frequency noise and laser power noise.

[0009] Based on further improvements to the above system, the frequency control loop includes a first beam splitter, a wavelength meter, a data acquisition card, and a personal computer. The first beam splitter is used to split the laser into a first beam and a second beam. The wavelength meter is used to receive the second beam and provide its wavelength to the personal computer via the data acquisition card. The personal computer is used to set a feedback frequency based on the wavelength of the second beam to generate a frequency feedback signal, and to provide the frequency feedback signal to the laser via the data acquisition card, thereby enabling the laser to output a frequency-stable laser signal.

[0010] Based on further improvements to the above system, the power control loop includes: an acousto-optic modulator, a polarizer, a second beam splitter, a second photodetector, a servo controller, a radio frequency source, and a power amplifier. The acousto-optic modulator is used to receive the power feedback signal and modulate the power of the first beam of light according to the power feedback signal to output a first beam of light with stable power. The polarizer is used to polarize the first beam of light with stable power. The second beam splitter is used to divide the polarized first beam of light into a third beam of light and a fourth beam of light. The second photodetector is used to receive the fourth beam of light and convert it into a second electrical signal. The servo controller is used to generate a digital control signal according to the second electrical signal. The radio frequency source is used to modulate the digital control signal into a radio frequency signal. The power amplifier is used to amplify the radio frequency signal to generate the power feedback signal.

[0011] Based on further improvements to the above system, the photonic temperature sensing system also includes a polarization controller, which is disposed between the second beam splitter and the photonic temperature sensing probe, for controlling the polarization direction of the third beam so that as much of the third beam as possible passes through the photonic temperature sensing probe.

[0012] Based on further improvements to the above system, the photonic temperature sensing probe includes: an optical chip and a waveguide and a ring resonant cavity disposed on the optical chip. The waveguide includes a coupling input end, an input portion, a first curved portion, a straight waveguide, a second curved portion, an output portion, and a coupling output end. The input portion is disposed between the coupling input end and the first curved portion, and its width gradually decreases from the coupling input end to the first curved portion. The first width of the coupling input end is greater than the second width of the first curved portion. The first curved portion and the second curved portion have a uniform second width. The straight waveguide is disposed between the first curved portion and the second curved portion and has a uniform second width. The output portion is disposed between the coupling output end and the second curved portion, and its width gradually decreases from the coupling output end to the second curved portion. The first width of the coupling output end is greater than the second width of the second curved portion.

[0013] Based on a further improvement of the above system, the coupling input terminal and the coupling output terminal are configured as shallow etched grating structures, wherein the direction of the shallow etched grating structure is perpendicular to the direction of the input portion and the output portion.

[0014] Based on further improvements to the above system, the etching depth, duty cycle, and period of the shallow etched grating structure are set according to a specific wavelength of light.

[0015] Based on further improvements to the above system, the photonic temperature sensing probe further includes a transmission structure, wherein the transmission structure includes an input optical fiber, an output optical fiber, a V-groove substrate and an optical fiber cover plate, the input optical fiber and the output optical fiber are fixed in the V-groove of the V-groove substrate and covered above the V-groove substrate, the input optical fiber and the output optical fiber by the optical fiber cover plate.

[0016] Based on further improvements to the above system, the angle between the input fiber and the output fiber and the normal of the optical chip is greater than or equal to 8°; and the input fiber and the output fiber are single-mode polarization-maintaining fibers.

[0017] On the other hand, embodiments of the present invention provide a temperature measurement method for a photonic temperature sensing system, comprising: generating laser light through a laser; controlling the frequency of the laser light through a frequency control loop based on a frequency feedback signal to generate a frequency-stable laser signal; modulating the power of the frequency-stable laser signal through a power control loop based on a power feedback signal to generate a frequency- and power-stable optical signal; providing the frequency- and power-stable optical signal to a photonic temperature sensing probe to generate an output optical signal; and receiving the output optical signal and converting the output optical signal into a first electrical signal to obtain a temperature value based on the first electrical signal.

[0018] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0019] 1. The photonic temperature sensing system according to an embodiment of the present invention has frequency and power stabilization functions. The frequency control loop stabilizes the light source frequency and the power control loop stabilizes the power. The frequency and power stabilization system can improve the system error caused by laser frequency noise and laser power noise.

[0020] 2. The photon temperature sensing system according to the embodiments of the present invention has the characteristics of low noise level and strong resistance to electromagnetic interference, which makes it have great potential in the fields of aerospace and microfluidics applications.

[0021] 3. By adding a polarizer or prism to the power control loop to stabilize the polarization of the light source, a polarization-power stabilization system for the light source is constructed, which is beneficial to improving the temperature measurement resolution.

[0022] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0024] Figure 1 This is a block diagram of a photon temperature sensing system according to an embodiment of the present invention.

[0025] Figure 2a This is a schematic diagram of the structure of a photon temperature sensing probe according to an embodiment of the present invention;

[0026] Figure 2b This is a schematic diagram of a shallowly etched grating structure in a photonic temperature sensing probe according to an embodiment of the present invention;

[0027] Figure 3 A graph showing the transmission spectrum of a shallow-etched grating according to an embodiment of the present invention;

[0028] Figure 4a A three-dimensional structural diagram of a photonic temperature sensing probe according to an embodiment of the present invention;

[0029] Figure 4b This is a side view of a photonic temperature sensing probe according to an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of a coupling system according to an embodiment of the present invention;

[0031] Figure 6 Normalized transmission spectrum of silicon microring coupling structure at room temperature according to an embodiment of the present invention;

[0032] Figure 7 This is a normalized transmission spectrum graph of a packaged device according to an embodiment of the present invention.

[0033] Figure 8 This is a schematic diagram of a temperature measuring experimental apparatus according to an embodiment of the present invention;

[0034] Figure 9a A graph illustrating the change of resonant wavelength with temperature according to an embodiment of the present invention;

[0035] Figure 9b This is a temperature-wavelength linear graph according to an embodiment of the present invention;

[0036] Figure 10a This is a diagram showing the 1540nm-1560nm scanning transmission peak according to an embodiment of the present invention;

[0037] Figure 10b This is a diagram showing the 1540nm-1552nm scanning transmission peak according to an embodiment of the present invention;

[0038] Figure 10c This is a diagram showing the transmission peak after frequency and power stabilization according to an embodiment of the present invention.

[0039] Figure 10d A diagram showing the transmission peak before frequency locking according to an embodiment of the present invention;

[0040] Figure 11 To obtain a resolution response curve by providing a 10 mk temperature disturbance through a bath according to an embodiment of the present invention;

[0041] Figure 12 This is a flowchart of a temperature measurement method for a photon temperature sensing system according to an embodiment of the present invention. Detailed Implementation

[0042] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0043] A specific embodiment of the present invention discloses a photon temperature sensing system, with reference to... Figure 1 The photonic temperature sensing system includes: a laser 102, a frequency control loop 104, a power control loop 106, a photonic temperature sensing probe 108, and a first photodetector 110. The laser 102 is used to generate laser light; the frequency control loop 104 is used to control the frequency of the laser 102 based on a frequency feedback signal to generate a frequency-stable laser signal; the power control loop 106 is used to modulate the power of the frequency-stable laser signal based on a power feedback signal to generate a frequency- and power-stable optical signal; the photonic temperature sensing probe 108 is used to provide the frequency- and power-stable optical signal to the photonic temperature sensing probe to generate an output optical signal; and the first photodetector 110 is used to receive the output optical signal and convert the output optical signal into a first electrical signal to obtain a temperature value based on the first electrical signal.

[0044] Compared with the prior art, the photonic temperature sensing system provided in this embodiment has frequency and power stabilization functions. The frequency control loop stabilizes the light source frequency and the power control loop stabilizes the power. This frequency and power stabilization system can improve the system error caused by laser frequency noise and laser power noise.

[0045] The photon temperature sensing system includes: a laser 102, a frequency control loop 104, a power control loop 106, a polarization controller, a photon temperature sensing probe 108, and a first photodetector 110. Referring below... Figures 1 to 2b , Figure 4a , Figure 4b and Figure 8 The photon temperature sensing system according to an embodiment of the present invention will be described in detail.

[0046] Laser 102 is used to generate laser light. Specifically, the laser (LASER) provides a continuously tunable laser source with power in the mW range and wavelength in the 1500-1560nm range.

[0047] The frequency control loop 104 is used to perform frequency control on the laser 102 based on the frequency feedback signal to generate a frequency-stable laser signal. Specifically, refer to... Figure 8 The frequency control loop 104 includes a first beam splitter, a wavelength meter (WM), a data acquisition card (DAQ), and a personal computer (PC). The first beam splitter splits the laser into a first beam and a second beam. The wavelength meter receives the second beam and provides its wavelength to the PC via the data acquisition card. The PC sets a feedback frequency based on the wavelength of the second beam to generate a frequency feedback signal and provides this signal to the laser via the data acquisition card, thereby stabilizing the laser output frequency. Specifically, the frequency of the second beam is obtained based on its wavelength, and this frequency is compared with a predetermined frequency to obtain the frequency difference as the frequency feedback signal.

[0048] A power control loop 106 is used to modulate the power of a frequency-stabilized laser signal based on a power feedback signal to generate a frequency- and power-stabilized optical signal. The power control loop 106 includes: an acousto-optic modulator (AOM), a polarizer, a second beam splitter, a second photodetector (PD2), a servo controller (PI), a radio frequency (RF) source, and a power amplifier (PA). The acousto-optic modulator receives the power feedback signal and modulates the power of the first beam of light according to the power feedback signal to output a power-stabilized first beam of light; the polarizer polarizes the power-stabilized first beam of light; the second beam splitter divides the polarized first beam of light into a third beam and a fourth beam; the second photodetector receives the fourth beam of light and converts it into a second electrical signal; the servo controller generates a digital control signal based on the second electrical signal; the RF source modulates the digital control signal into an RF signal; and the power amplifier amplifies the RF signal to generate a power feedback signal.

[0049] A polarization controller is positioned between the second beam splitter and the photon temperature sensing probe to control the polarization direction of the third beam so that as much of the third beam as possible passes through the photon temperature sensing probe.

[0050] The photonic temperature sensing probe 108 is used to provide a frequency- and power-stable optical signal to the photonic temperature sensing probe to generate an output optical signal. Specifically, refer to... Figure 2aThe photonic temperature sensing probe includes an optical chip and a waveguide and a ring resonant cavity disposed on the optical chip. The waveguide includes a coupled input terminal, an input portion, a first curved portion, a straight waveguide, a second curved portion, an output portion, and a coupled output terminal. The input portion is disposed between the coupled input terminal and the first curved portion, and its width gradually decreases from the coupled input terminal to the first curved portion. The first width of the coupled input terminal is greater than the second width of the first curved portion. Both the coupled input terminal and the first end of the input portion have a first width, while the second end of the input portion and the first curved portion have a second width. Specifically, the first width of the first end of the input portion is greater than the second width of the second end of the input portion, with the first width being the maximum width and the second width being the minimum width. The first curved portion and the second curved portion have a uniform second width. The straight waveguide is disposed between the first curved portion and the second curved portion and has a uniform second width. The output portion is disposed between the coupled output terminal and the second curved portion, and its width gradually decreases from the coupled output terminal to the second curved portion. The first width of the coupled output terminal is greater than the second width of the second curved portion. Specifically, the second end of the output portion has a second width, and the first end of the output portion has a first width. (Reference) Figure 2b The coupling input and coupling output terminals are configured with shallow-etched grating structures, wherein the direction of the shallow-etched grating structure is perpendicular to the directions of the input and output portions. The etching depth, duty cycle, and period of the shallow-etched grating structure are set according to the specific wavelength of light. For example, to maximize the transmittance in the 1550nm light band, the trench etching depth is 70nm, the grating period is 615nm, and the duty cycle is approximately 0.5. The ring resonator is positioned adjacent to the straight waveguide and away from the coupling input and coupling output terminals. (Reference) Figure 4a The photonic temperature sensing probe also includes a transmission structure, connected to the coupling input and coupling output ends via input and output optical fibers, respectively. The transmission structure includes an input optical fiber, an output optical fiber, a V-groove substrate, and an optical fiber cover plate. The input and output optical fibers are fixed in the V-groove of the V-groove substrate and covered by the optical fiber cover plate. The angle between the input and output optical fibers and the normal to the optical chip is greater than or equal to 8° (see [reference]). Figure 4b ); and the input and output optical fibers are single-mode polarization-maintaining fibers.

[0051] The first photodetector 110 receives the output optical signal and converts it into a first electrical signal to obtain a temperature value. The first electrical signal is transmitted to a personal computer (PC) via a data acquisition card (DAQ). The PC obtains the temperature value based on the first electrical signal. Specifically, the PC can obtain the frequency from the first electrical signal and then... Figure 9a and Figure 9bThe temperature value is obtained from the curve shown.

[0052] A specific embodiment of the present invention discloses a temperature measurement method for a photon temperature sensing system. (See reference...) Figure 12 The temperature measurement method of the photonic temperature sensing system according to the present invention includes: in step 1202, generating laser light through a laser; in step 1204, controlling the frequency of the laser light through a frequency control loop based on a frequency feedback signal to generate a frequency-stable laser signal; in step 1206, modulating the power of the frequency-stable laser signal through a power control loop based on a power feedback signal to generate a frequency- and power-stable optical signal; in step 1208, providing the frequency- and power-stable optical signal to a photonic temperature sensing probe to generate an output optical signal; and in step 1210, receiving the output optical signal and converting the output optical signal into a first electrical signal to obtain a temperature value based on the first electrical signal.

[0053] In the following text, refer to Figures 2a to 11 The photon temperature sensing system according to embodiments of the present invention will be described in detail by way of specific examples.

[0054] The smaller the spectral linewidth and the steeper the slope of the optical cavity resonance peak, the greater the change in light intensity, and thus the higher the sensing sensitivity. Based on this principle, this temperature measurement system uses the edge method, that is, measuring the change in light intensity at a specific frequency at the steepest point on one side of the resonance peak to sense the temperature. A small, temperature-dependent shift in the resonance frequency will cause a large change in light intensity. Since the resonance lineshape is a known quantity, the change in transmission and reflection spectrum intensity can be converted into a change in the center frequency.

[0055] This application constructs a photonic temperature sensing system with light source stabilization. The system primarily utilizes a silicon-based microring structure to demonstrate the temperature sensing capabilities of a microcavity. A polarization-power stabilization system for the light source is constructed to mitigate system errors caused by laser frequency and power noise. A complete photonic temperature sensing system is developed, achieving a temperature measurement range exceeding 100K with an actual temperature resolution of less than 10mK.

[0056] A frequency control loop locks the frequency at the steepest point on one side of the resonant peak. Specifically, a wavelength meter detects the frequency of the laser's emitted light, LabVIEW monitors the wavelength meter reading, and a feedback electrical signal is sent to control the piezoelectric ceramic of the laser to achieve frequency stabilization. This enables higher sensitivity temperature sensing. This invention constructs a practical and complete photonic temperature sensing system, which can improve the sensitivity and measurement range of temperature sensing. This invention mainly demonstrates the temperature sensing capabilities of microcavities through a silicon-based microring structure, and constructs a polarization and power stabilization system for the light source to improve the system errors caused by laser frequency noise and laser power noise. The complete photonic temperature sensing system can achieve a temperature measurement range of over 100K with an actual temperature measurement resolution of less than 10mK.

[0057] Optical sensing based on optical microcavities achieves its function by measuring changes in the spectral characteristics of the resonant mode after variations in the measured physical quantity or disturbances in the pump source. This temperature measurement system uses the edge method to measure the light intensity change at a specific frequency at the steepest point on one side of the resonant peak at the edge of the resonant peak, thus sensing the external temperature.

[0058] Referring to Figure 4, a six-axis piezoelectric platform and a three-axis moving platform are used to align the optical chip and the coupling end. A UV adhesive with a refractive index match is used to fix the relative spatial position of the optical chip and the coupling end, forming a packaged sensing probe. Performance testing is then conducted by placing the packaged sensing probe and a calibrated platinum resistance thermometer together in a glass tube into a bath. The main calibration parameters are: the quality factor Q of the optical microcavity (describing the effective ability of the microcavity to confine photons in the time dimension); the free spectral range (FSR) (the frequency or wavelength interval between two whispering-gallery modes that differ only by 1 in angular quantum number); and the sensitivity, temperature measurement range, and temperature resolution of the photon temperature sensor.

[0059] The working principle of a platinum resistance thermometer is that the temperature-sensing platinum wire expands and contracts freely when the temperature changes. By measuring the resistance of the thermometer's sensing element and using the interpolation formula of the temperature scale, a temperature curve changing over time is output.

[0060] Traditionally, photonic thermometers based on fiber Bragg gratings (FBGs) use continuous wavelength scanning technology to measure temperature changes. In wavelength scanning mode, the frequency region through which the probe laser passes is continuously scanned, the transmission and reflection spectra are recorded, the center frequency is calculated, and then the center frequency is converted into temperature. Here, we use a bar grating structure, and under the premise of stable frequency and power, the target frequency is locked at the steepest point on one side of the resonance peak. This allows changes in transmitted light power to reflect changes in the external ambient temperature.

[0061] 1. Fabrication of photonic devices

[0062] Figure 2a and Figure 2b A schematic diagram of the photonic device and a shallow-etched grating structure are depicted. The device consists of a ring resonator coupled to a straight waveguide with a design width of 520 nm and a waveguide-micro-ring distance of 60 nm to ensure single-mode transmission. The coupling method used in this experiment is vertical coupling between the optical fiber and the device. The coupling fiber is an array of optical fibers, and the coupling point is configured as a shallow-etched grating structure. The grating period is 615 nm, the grating etching depth is 70 nm, and the grating sidewalls are vertical and smooth to achieve high coupling efficiency. The grating provides an efficient method for coupling free-space light to the photonic device.

[0063] The coupling method used in this experiment is vertical coupling between the optical fiber and the device. The coupling fiber is an array fiber, and the coupling point of the device is set as a shallow-etched grating structure. By designing the etching depth, duty cycle, and period of the shallow-etched grating structure for a specific wavelength of light, the coupling efficiency can be improved. The incident angle of the light also has a significant impact on the coupling between the optical fiber and the microcavity. In this experiment, the incident angle is set to 8°, that is, the angle between the incident fiber direction and the vertical direction is 8°. A shallow-etched strip grating is used to improve the coupling efficiency through parameter settings. The shallow-etched grating is designed using the built-in optimization process of FDTD software. First, fixed structural parameters, such as silicon layer thickness and bottom silicon thickness, are set. Then, by setting the scan optimization, the optimal period and duty cycle parameters at a wavelength of 1550nm are obtained. Through the above design optimization, the optimal coupling period of the shallow-etched grating is 615nm, the duty cycle is 0.5, and the grating etching depth is 60nm. The optimized parameters are designed into a complete shallow-etched grating structure, and two-dimensional simulation is performed using FDTD. The grating transmission spectrum obtained is as follows. Figure 3 As shown, the center wavelength is 1550nm, and the optimal coupling efficiency is 45.7%, which meets the experimental requirements.

[0064] 2. Fabrication of the coupling probe

[0065] This invention uses optical fiber to guide light to a temperature sensing unit and sense changes in the unit's optical condition. Furthermore, this temperature sensing unit requires no electricity to operate, thus offering advantages such as good resistance to lightning strikes, electromagnetic noise, and ease of long-distance sensing. A six-degree-of-freedom high-precision nano-positioning system is used to correct the coupling position and angle of the chip and end-capsule, achieving optimal coupling efficiency. By setting the parameters of the photonic device coupling grating and using UV adhesive powder with refractive index matching, the performance of the device remains essentially consistent before and after packaging. The result is a sensor with high coupling efficiency.

[0066] In this invention, such as Figure 4a and Figure 4b As shown, the two optical fibers that collect and transmit light are fixed on the V-groove substrate and together with the optical fiber cover plate form the main transmission structure.

[0067] In this invention, the temperature sensing unit consists of a transmission structure and a matching optical microring optical chip.

[0068] In particular, in this invention, the incident angle of the optical fiber and the normal angle of the optical chip are preferably equal to or greater than 8°.

[0069] In particular, in this invention, the optical fiber used to transmit the optical field is preferably a single-mode polarization-maintaining fiber.

[0070] Specifically, in this invention, the two-core optical fiber segments used for temperature transmission are fixed using a V-groove substrate made of quartz glass and an optical fiber cover plate, such as... Figure 4a and Figure 4b As shown.

[0071] In this invention, the probe includes a V-groove substrate made of quartz glass and an optical fiber cover plate, which can perform stable sensing even under repeated hot and cold cycles, further improving the sensing stability.

[0072] The sensing probe consists of two optical fibers for light collection and transmission; and a silicon-based micro-ring optical chip for confining photons.

[0073] In addition, two optical fibers for light collection and transmission are fixed on a V-groove substrate to form the main structure of the probe together with the micro-ring chip; the probe is made by encapsulating a temperature sensing probe.

[0074] During coupling alignment, the chip is placed on a six-axis piezoelectric platform. This is a six-degree-of-freedom high-precision nanopositioning system with six axes of motion: three linear and three rotational. The input fiber is secured using an 8° coupling end clamp, which is placed on a three-axis precision nanomotion platform. Figure 5 As shown, the jig's forward and backward movement can be precisely controlled, facilitating the alignment of the optical fiber and the chip. A vacuum circuit is used to evacuate the chip and coupling head, securing them to the platform and jig to ensure stability during the coupling process. The vertical relative position between the optical chip and the coupling head cross-section is set to 20 micrometers. The optimal coupling position is determined by calculating the optical transmission efficiency based on the output voltage.

[0075] 3. Device performance calibration

[0076] After finding the optimal coupling point between the optical fiber and the device, the device's performance needs to be calibrated, specifically by measuring its Q value and FSR. An experimental system was set up, connecting a photodetector (PD), an oscilloscope (OSC), and a compatible optical path system. The transmission spectral pattern of the resonant cavity was observed on the OSC. First, a wide wavelength scan of 1530-1560 nm was performed using a laser (LASER), and the scan range was accurately recorded using a wavelength meter (OSC).

[0077] The transmission spectrum of the device was obtained by scanning as follows Figure 6 As shown, using the formula:

[0078] Q=λ / △λ

[0079] Where λ is the center wavelength of the resonant peak; Δλ is the linewidth of the resonant peak, i.e., the half-width at half maximum (FWHM) of the line shape; and the free spectrum range (FSR) is the wavelength interval between two resonant peaks.

[0080] The free spectral range (FSR) and Q value of the device can be obtained through fitting calculations. It is found that the free spectral range of the device is 8.85 nm, and the Q value is 76440.

[0081] After finding the optimal coupling position, the device performance was tested. Then, the device and fiber optic head were encapsulated using UV adhesive. A UV adhesive with a refractive index match was needed to fix their relative spatial positions, resulting in a well-encapsulated sensing probe. It is important to note that during encapsulation, the adhesive should be applied to the outer edge of the device to avoid the UV adhesive entering the coupling area and affecting device performance. After encapsulation, the device performance needs to be calibrated again. The transmission spectrum was obtained through broadband scanning, and the Q value and FSR of the encapsulated device were observed. The post-encapsulation transmission spectrum is shown below. Figure 7 As shown in the figure. Through fitting calculations, the Q value of the packaged device decreased to 60587, and the FSR was 8.84nm, which is not much different from that before packaging.

[0082] When calibrating the temperature sensitivity of photonic devices, the sensing probe and platinum resistance thermometer are placed together in a bath to simulate the atmosphere of minute temperature changes on the order of mK in special environments such as aerospace and microfluidics.

[0083] By controlling the bath temperature, the ambient temperature around the device is changed. A novel temperature measurement system using the edge method is constructed here. Compared with traditional temperature measurement systems, this system improves resolution by adding a polarizer to the AOM loop for polarization stabilization and incorporating a light source stabilization system to reduce power and frequency noise. A schematic diagram of the final temperature measurement experimental setup is shown below. Figure 8 As shown.

[0084] The function of a laser is to provide a continuously tunable laser source with power in the mW range and wavelength in the range of 1500-1560nm.

[0085] A 10 / 90 beam splitter is used to split one path (10% of the light source) and connect it to the wavelength meter (WM).

[0086] The acousto-optic modulator receives feedback signals amplified by the power amplifier and modulates the light source, keeping the power of the light source constant at a certain level.

[0087] Specifically, a polarizer or prism is added to the AOM loop to stabilize the polarization of the light source and ensure its polarization stability.

[0088] The second 10 / 90 beam splitter splits one path (10% of the light source) which is converted into an electrical signal by a photodetector and then fed into a servo controller (PI).

[0089] The servo controller (PI) receives the PD electrical signal and outputs a control signal to control the amplitude of the RF source.

[0090] Radio frequency (RF) sources modulate input digital signals into RF signals and then amplify the signals for acousto-optic modulation.

[0091] Power amplifiers are used to amplify the power of RF signals.

[0092] In the experiment, we used an external bath to simulate the temperature changes of the external environment for the sensing probe. The advantage of using a bath is that it can provide a controllable temperature change in the mK range. The bath is used to simulate the small temperature change atmosphere in the mK range in special environments such as aerospace and microfluidics.

[0093] A photodetector (PD) converts optical signals into electrical signals.

[0094] An oscilloscope (OSC) monitors and displays the electrical signals of the PD.

[0095] The data acquisition card (DAQmax) acquires signals from the wavelength meter (WM), and, in conjunction with the frequency set by the LabVIEW program on the PC, implements feedback control of the piezoelectric ceramic PZT of the laser to achieve frequency stability.

[0096] When the temperature changes, the refractive index and volume of the device material will change due to the thermo-optical effect and thermal expansion effect. For silicon materials, the thermo-optical coefficient is around 10. -4 On the order of magnitude, while the coefficient of thermal expansion is in the range of 10. -6 The thermo-optic coefficient is on the order of magnitude higher than the coefficient of thermal expansion, thus only the influence of the thermo-optic coefficient needs to be considered. The resonant wavelength of the microcavity changes with the refractive index of the material; therefore, the effect of temperature on the microcavity is ultimately reflected in the shift of the resonant wavelength with temperature, such as... Figure 9a As shown.

[0097] Depend on Figure 9b It can be seen that the temperature sensitivity of the device obtained by heating is 79.62 pm / K, and the FSR after packaging is 8.84 nm. The calculated temperature measurement range of the device is about 111 K, which is greater than 100 K.

[0098] It is worth noting that thermal broadening sometimes occurs in the transmission spectrum during the experiment. This may be due to excessively high input power causing the device to heat up, resulting in transmission spectrum broadening. In this case, an attenuator needs to be added to the circuit to reduce power. After adding the attenuator, the thermal broadening disappears.

[0099] The temperature resolution of a photonic temperature sensor depends on the temperature resolution of its optical microcavity. Microcavity temperature resolution refers to the minimum value that the microcavity can resolve when there is a disturbance in the ambient temperature. The 25-ohm standard platinum resistance thermometer developed by the US National Institute of Standards and Technology (NIST) has a bridge resolution of 0.02 mK, while quartz temperature sensors produced in my country achieve a resolution of 0.1 mK. This experiment uses a PT100 platinum resistance thermometer as the temperature resolution reference temperature, with a resolution of 1 mK and a temperature range of -200 to 850℃. This scheme aims for a resolution of 10 mK for the microcavity temperature sensor. However, during the 10 mK resolution calibration measurement, after locking the frequency to the steepest point on one side of the resonance peak, excessive signal noise appeared on the oscilloscope.

[0100] Here, quantifying and improving system noise becomes crucial. Therefore, the signal is connected to a phase noise analyzer to analyze the noise signal, Allan variance, etc. By monitoring the output power of the microring resonator as a function of the laser wavelength over time, and simultaneously measuring the laser frequency, the frequency noise introduced by the long-term drift of the laser frequency is quantified.

[0101] This paper presents a novel edge-based method for measuring temperature changes at the mK level. First, the laser is controlled to roughly scan within the frequency range of 1540nm-1560nm to locate the target resonance peak. Figure 10a As shown, further fine scanning at 1540nm-1550nm yielded the following results: Figure 10b The transmission spectrum is shown. Then, an acousto-optic modulator (AOM) power stabilization system was added to stabilize the laser power at a constant level, as shown... Figure 10c To stabilize the frequency and power, the transmission peak was scanned.

[0102] It is worth noting that the laser and polarization controller also need to be adjusted to lock the frequency to one side of the resonance peak for laser frequency scanning. The edge level at the steepest point on the side of the transmission peak and the bottom level at the center frequency of the resonance peak are as follows: Figure 10d As shown. Then, the frequency control loop is activated to stabilize the laser frequency at a higher stability level, and finally, the laser frequency is locked at the point with the maximum slope on one side of the resonance peak.

[0103] By providing a 10 mK temperature perturbation in the bath, a resolution response linearity was obtained, such as... Figure 11 As shown.

[0104] Figure 11 It can be seen that when the temperature increases by 10mK, the temperature change trend is consistent with the voltage change trend of the microcavity sensor. Therefore, it can be said that this sensor has a minimum resolution of 10mK.

[0105] In summary, this sensor achieves a minimum resolution of 10 mK. This photonic temperature sensing system mitigates system errors introduced by laser frequency and power. Its low noise level and strong immunity to electromagnetic interference make it a promising candidate for aerospace and microfluidic applications.

[0106] The microcavity's temperature sensing capabilities were primarily demonstrated through a silicon-based microring structure. A spectral edge-based temperature measurement scheme was employed, and a polarization-power stabilization system for the light source was constructed to mitigate system errors caused by laser frequency and power noise. A complete photonic temperature sensing system was developed, achieving a temperature measurement range exceeding 100K with an actual temperature resolution of less than 10mK.

[0107] After optimizing the existing photonic temperature sensor packaging technology, the Q value of the micro-ring resonator reaches 60587, and the FSR is 8.84nm.

[0108] The use of the spectral edge method for temperature measurement improves the temperature measurement resolution, and experiments have proven that it has a minimum resolution of 10 mK.

[0109] By adding a polarizer or prism to the AOM loop to stabilize the polarization of the light source, a polarization-power stabilization system for the light source is constructed. This is beneficial for improving temperature measurement resolution.

[0110] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0111] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A photonic temperature sensing system, characterized in that, include: The components include a laser, a frequency control loop, a power control loop, a photon temperature sensing probe, and a first photodetector. The laser is used to generate laser light; The frequency control loop is used to control the frequency of the laser based on a frequency feedback signal to generate a frequency-stable laser signal. The frequency control loop includes a first beam splitter, a wavelength meter, a data acquisition card, and a personal computer. The first beam splitter is used to split the laser into a first beam and a second beam. The wavelength meter is used to receive the second beam and provide its wavelength to the personal computer via the data acquisition card. The personal computer is used to set a feedback frequency according to the wavelength of the second beam to generate a frequency feedback signal and provide the frequency feedback signal to the laser via the data acquisition card, so that the laser outputs a frequency-stable laser signal. The power control loop is used to modulate the power of the frequency-stabilized laser signal based on the power feedback signal to generate a frequency- and power-stabilized optical signal. The power control loop includes: an acousto-optic modulator, a polarizer, a second beam splitter, a second photodetector, a servo controller, a radio frequency (RF) source, and a power amplifier. The acousto-optic modulator receives the power feedback signal and modulates the power of the first beam of light according to the power feedback signal to output a power-stabilized first beam of light. The polarizer polarizes the power-stabilized first beam of light. The second beam splitter divides the polarized first beam of light into a third beam and a fourth beam. The second photodetector receives the fourth beam of light and converts it into a second electrical signal. The servo controller generates a digital control signal based on the second electrical signal. The RF source modulates the digital control signal into an RF signal. The power amplifier amplifies the RF signal to generate the power feedback signal. The photonic temperature sensing probe is used to provide the frequency and power-stable optical signal to the photonic temperature sensing probe to generate an output optical signal; and The first photodetector is used to receive the output optical signal and convert the output optical signal into a first electrical signal to obtain a temperature value based on the first electrical signal.

2. The photon temperature sensing system according to claim 1, characterized in that, It also includes a polarization controller, disposed between the second beam splitter and the photon temperature sensing probe, for controlling the polarization direction of the third beam so that as much of the third beam as possible passes through the photon temperature sensing probe.

3. The photon temperature sensing system according to claim 1, characterized in that, The photonic temperature sensing probe includes: an optical chip and a waveguide and a ring resonant cavity disposed on the optical chip, wherein the waveguide includes a coupling input terminal, an input section, a first curved section, a straight waveguide, a second curved section, an output section, and a coupling output terminal. The input portion is disposed between the coupling input end and the first curved portion, and its width gradually decreases from the coupling input end to the first curved portion, wherein the first width of the coupling input end is greater than the second width of the first curved portion; The first curved portion and the second curved portion have a uniform second width; The straight waveguide is disposed between the first curved portion and the second curved portion, and has a uniform second width; The output portion is disposed between the coupled output end and the second curved portion, and its width gradually decreases from the coupled output end to the second curved portion, wherein the first width of the coupled output end is greater than the second width of the second curved portion.

4. The photon temperature sensing system according to claim 3, characterized in that, The coupling input terminal and the coupling output terminal are configured as shallow etched grating structures, wherein the direction of the shallow etched grating structure is perpendicular to the direction of the input portion and the output portion.

5. The photon temperature sensing system according to claim 4, characterized in that, in, The etching depth, duty cycle, and period of the shallow etched grating structure are set according to a specific wavelength of light.

6. The photon temperature sensing system according to claim 4, characterized in that, in, The photonic temperature sensing probe further includes a transmission structure, wherein the transmission structure includes an input optical fiber, an output optical fiber, a V-groove substrate, and an optical fiber cover plate. The input optical fiber and the output optical fiber are fixed in the V-groove of the V-groove substrate and covered by the optical fiber cover plate above the V-groove substrate, the input optical fiber and the output optical fiber.

7. The photonic temperature sensing system according to claim 6, characterized in that, in, The angle between the input fiber and the output fiber and the normal of the optical chip is greater than or equal to 8°; and the input fiber and the output fiber are single-mode polarization-maintaining fibers.

8. A temperature measurement method for a photon temperature sensing system, characterized in that, include: Laser is generated by using a laser. The laser is frequency controlled by a frequency control loop based on a frequency feedback signal to generate a frequency-stable laser signal. The power of the frequency-stable laser signal is modulated by a power control loop based on a power feedback signal to generate an optical signal with stable frequency and power. The frequency and power-stable optical signal is provided to the photonic temperature sensing probe to output an optical signal. as well as The system receives the output optical signal and converts it into a first electrical signal to obtain a temperature value based on the first electrical signal. The frequency control loop includes a first beam splitter, a wavelength meter, a data acquisition card, and a personal computer. The first beam splitter splits the laser beam into a first beam and a second beam. The wavelength meter receives the second beam and provides its wavelength to the personal computer via the data acquisition card. The personal computer sets a feedback frequency based on the wavelength of the second beam to generate a frequency feedback signal and provides the frequency feedback signal to the laser via the data acquisition card, thereby stabilizing the laser output frequency of the laser signal. The power control loop includes: an acousto-optic modulator, a polarizer, a second beam splitter, a second photodetector, a servo controller, a radio frequency (RF) source, and a power amplifier. The acousto-optic modulator receives the power feedback signal and modulates the power of the first beam of light according to the power feedback signal to output a first beam of light with stable power. The polarizer polarizes the first beam of light with stable power. The second beam splitter divides the polarized first beam of light into a third beam and a fourth beam. The second photodetector receives the fourth beam of light and converts it into a second electrical signal. The servo controller generates a digital control signal according to the second electrical signal. The RF source modulates the digital control signal into an RF signal. The power amplifier amplifies the RF signal to generate the power feedback signal.

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