CN116793524A - Photon temperature sensing system and temperature measuring method thereof - Google Patents

Abstract

The application relates to a photon temperature sensing system and a temperature measuring method thereof, belongs to the technical field of temperature sensing, and solves the problem that the existing method is affected by laser frequency noise, power noise and polarization. The system comprises a laser for generating laser light; a frequency control loop for frequency controlling the laser based on the frequency feedback signal to generate a frequency stabilized laser signal; a power control loop for modulating the power of the frequency stabilized laser signal based on the power feedback signal to generate a frequency and power stabilized optical signal; a photon temperature sensing probe for providing a frequency and power stabilized optical signal to the photon temperature sensing probe to generate an output optical signal; and the first photoelectric detector is used for receiving the output optical signal and converting the output optical signal into a first electric signal so as to acquire a temperature value according to the first electric signal. Systematic errors due to laser frequency and power noise are improved.

Description

Photon temperature sensing system and temperature measuring method thereof

Technical Field

The application relates to the technical field of temperature sensing, in particular to a photon temperature sensing system and a temperature measuring method thereof.

Background

Although thermometers have been ubiquitous, they have evolved very slowly over the last decades. As a standard carrier for accurate temperature measurement, standard platinum resistance thermometers were originally developed over a century ago. In addition, many modern temperature sensors still rely on the realization of temperature sensing of a metallic film or wire resistance, which varies with temperature. While thermometers that utilize resistance to effect temperature measurement have an uncertainty of 10mK in conventional measurements, such thermometers are very sensitive to mechanical shock, which can lead to drift in resistance over time, requiring frequent offline and time consuming calibration.

In recent years, the trend of temperature sensing is realized by changing the bottom foundation of temperature sensing by a photonic device, and the photonic device is hopeful to be finally used as a substitute of a resistance thermometer. The photon device has larger temperature measurement sensitivity and strong robustness to electromagnetic interference. And the optical resonant cavity refers to a resonant cavity capable of limiting the optical field to a micro-nano level. In recent years, micro-nano processing technology and semiconductor technology are mature, and research on optical microcavities is further carried out. The optical microcavity mode has small volume and high quality factor, greatly enhances the interaction between light and substances, and has wide application in the aspects of cavity quantum electrodynamics, nonlinear optics, low-threshold lasers and high-sensitivity sensors.

The quality factor Q of the ring resonator is high, and the mode volume V is small. The quality factor, mode volume, refers to the ability of the microcavity to effectively bind photons in both the temporal and spatial dimensions. The photon temperature sensor based on the micro-ring resonant cavity has the advantages of high sensitivity and accuracy, small volume, integration, strong electromagnetic environment and the like, and is widely applied to the field of sensing. Optical sensing based on optical microcavity is realized by measuring the change of the resonance mode after the physical quantity of the sensed sensor changes or the spectral characteristics change after the disturbance of the pumping light source. It is a temperature sensing that uses temperature changes in material properties-typically a combination of thermo-optic effects and thermal expansion effects-to exhibit shifts in center wavelength in the spectrum.

In the measurement sensing of the optical cavity, if the optical signal matched with the resonant peak wavelength is used for monitoring and sensing the physical quantity, the sensing of the physical quantity is realized according to the light intensity change of the measured optical signal after the optical cavity is disturbed by the physical quantity to be measured. But the measurement scheme is limited by system noise, including laser frequency noise, power noise, and polarization effects.

Disclosure of Invention

In view of the above analysis, the embodiments of the present application aim to provide a photon temperature sensing system and a temperature measuring method thereof, which are used for solving the problem that the existing method is affected by laser frequency noise, power noise and polarization.

In one aspect, an embodiment of the present application provides a photonic temperature sensing system comprising: the device comprises a laser, a frequency control ring, a power control ring, a photon temperature sensing probe and a first photoelectric detector, wherein the laser is used for generating laser; the frequency control loop is used for performing frequency control on the laser based on a frequency feedback signal so as to generate a frequency stable laser signal; the power control loop is used for modulating the power of the frequency stabilized laser signal based on a power feedback signal to generate a frequency and power stabilized optical signal; the photon temperature sensing probe is used for providing the optical signal with stable frequency and power to the photon temperature sensing probe so as to generate an output optical signal; and the first photoelectric detector is used for receiving the output optical signal and converting the output optical signal into a first electric signal so as to acquire a temperature value according to the first electric signal.

The beneficial effects of the technical scheme are as follows: the photon temperature sensing system provided by the embodiment of the application has the functions of stabilizing the frequency and the power of the light source through the frequency control loop and stabilizing the power through the power control loop, and the frequency and the power stabilizing system can improve the system errors caused by laser frequency noise and laser power noise.

Based on a further improvement of the system, the frequency control loop comprises a first beam splitter, a wavelength meter, a data acquisition card and a personal computer, wherein the first beam splitter is used for dividing the laser into a first beam light and a second beam light; the wavemeter is used for receiving the second beam of light and providing the wavelength of the second beam of light to the personal computer through the data acquisition card; and the personal computer is used for setting a feedback frequency according to the wavelength of the second beam of light to generate a frequency feedback signal, and providing the frequency feedback signal to the laser through the data acquisition card so that the laser outputs a frequency stabilized laser signal.

Based on a further improvement of the above system, the power control loop comprises: the device comprises an acousto-optic modulator, a polarizer, a second beam splitter, a second photoelectric detector, a servo controller, a radio frequency source and a power amplifier, wherein the acousto-optic modulator is used for receiving the power feedback signal and modulating the power of the first beam of light according to the power feedback signal so as to output the first beam of light with stable power; the polarizer is used for polarizing the first beam of light with stable power; the second beam splitter is used for dividing the polarized first beam into a third beam and a fourth beam; the second photoelectric detector is used for receiving the fourth beam of light and converting the fourth beam of light into a second electric signal; the servo controller is used for generating a digital control signal according to the second electric signal; the radio frequency source is used for modulating the digital control signal into a radio frequency signal; and the power amplifier is used for amplifying the radio frequency signal to generate the power feedback signal.

Based on a further improvement of the above system, the photon temperature sensing system further comprises a polarization controller disposed between the second beam splitter and the photon temperature sensing probe for controlling a polarization direction of the third beam of light so that as much of the third beam of light passes through the photon temperature sensing probe as possible.

Based on a further improvement of the above system, the photon temperature sensing probe comprises: an optical chip, and a waveguide and a ring resonator disposed on the optical chip, wherein 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, wherein the input portion is disposed between the coupling input end and the first curved portion, and a width thereof gradually decreases from the coupling input end to the first curved portion, wherein a first width of the coupling input end is larger than a second width of the first curved portion; the first curved portion and the second curved portion having a uniform second width; the straight waveguide is arranged between the first bending part and the second bending part, and has a uniform second width; the output part is arranged between the coupling-out end and the second bending part, and the width of the output part gradually decreases from the coupling-out end to the second bending part, wherein the first width of the coupling-out end is larger than the second width of the second bending part.

Based on a further improvement of the system, the coupling-in end and the coupling-out end are arranged as shallow etched grating structures, wherein the directions of the shallow etched grating structures are perpendicular to the directions of the input part and the output part.

Based on further improvement of the system, the etching depth, the duty ratio and the period of the shallow etching grating structure are set according to the light with the specific wavelength.

Based on a further improvement of the system, the photon temperature sensing probe further comprises a transmission structure, wherein the transmission structure comprises an input optical fiber, an output optical fiber, a V-shaped groove substrate and an optical fiber cover plate, and the input optical fiber and the output optical fiber are fixed in the V-shaped groove of the V-shaped groove substrate and are covered above the V-shaped groove substrate, the input optical fiber and the output optical fiber through the optical fiber cover plate.

Based on a further improvement of the system, the angle between the normal lines of the input optical fiber and the output optical fiber and the optical chip is more than or equal to 8 degrees; and the input optical fiber and the output optical fiber are single-mode polarization maintaining optical fibers.

In another aspect, an embodiment of the present application provides a method for measuring a temperature of a photon temperature sensing system, including: generating laser light by a laser; performing frequency control on the laser based on a frequency feedback signal through a frequency control loop to generate a frequency stabilized laser signal; modulating the power of the frequency stabilized laser signal based on a power feedback signal by a power control loop to generate a frequency and power stabilized optical signal; providing the frequency and power stabilized 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 according to the first electrical signal.

Compared with the prior art, the application has at least one of the following beneficial effects:

1. the photon temperature sensing system provided by the embodiment of the application has the functions of stabilizing the frequency and the power of the light source through the frequency control loop and stabilizing the power through the power control loop, and the frequency and the power stabilizing system can improve the system errors caused by laser frequency noise and laser power noise.

2. The photon temperature sensing system provided by the embodiment of the application has the characteristics of low noise level and strong electromagnetic interference resistance, so that the photon temperature sensing system has great potential in the aerospace and micro-fluid application fields.

3. And a polaroid or a prism is added in the power control loop to stabilize the polarization of the light source, so that a polarization-power stabilizing system of the light source is constructed, and the temperature measurement resolution is improved.

In the application, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application may be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the application, like reference numerals being used to refer to like parts throughout the several views.

FIG. 1 is a block diagram of a photonic temperature sensing system in accordance with an embodiment of the present application.

FIG. 2a is a schematic diagram of a photonic temperature sensing probe according to an embodiment of the present application;

FIG. 2b is a schematic diagram of a shallow etched grating structure in a photonic temperature sensing probe according to an embodiment of the present application;

FIG. 3 is a graph of a transmission spectrum of a shallow etched grating according to an embodiment of the present application;

FIG. 4a is a three-dimensional structural diagram of a photonic temperature sensing probe according to an embodiment of the present application;

FIG. 4b is a side view of a photonic temperature sensing probe according to an embodiment of the present application;

FIG. 5 is a schematic diagram of a coupling system according to an embodiment of the present application;

FIG. 6 is a graph of normalized transmission spectra of a silicon microring coupling structure scan at room temperature in accordance with an embodiment of the present application;

FIG. 7 is a normalized graph of the scan transmission spectrum of a packaged device according to an embodiment of the present application;

FIG. 8 is a schematic diagram of a thermometry experimental apparatus according to an embodiment of the application;

FIG. 9a is a graph of resonant wavelength versus temperature according to an embodiment of the present application;

FIG. 9b is a temperature-wavelength linear graph according to an embodiment of the present application;

FIG. 10a is a diagram of 1540nm-1560nm scanning transmission peaks according to an embodiment of the present application;

FIG. 10b is a graph of 1540nm-1552nm scanning transmission peaks according to an embodiment of the application;

FIG. 10c is a graph of a swept-transmission peak after frequency and power stabilization in accordance with an embodiment of the application;

FIG. 10d is a graph of transmission peaks before frequency locking according to an embodiment of the present application;

FIG. 11 is a graph of resolution response provided by a bath providing a 10mk temperature disturbance in accordance with an embodiment of the present application;

FIG. 12 is a flow chart of a method of thermometry of a photon temperature sensing system in accordance with an embodiment of the application.

Detailed Description

Preferred embodiments of the present application will now be described in detail with reference to the accompanying drawings, which form a part hereof, and together with the description serve to explain the principles of the application, and are not intended to limit the scope of the application.

In one embodiment of the present application, a photonic temperature sensing system is disclosed, referring to FIG. 1, comprising: a laser 102, a frequency control loop 104, a power control loop 106, a photon temperature sensing probe 108, and a first photodetector 110, wherein the laser 102 is configured to generate laser light; a frequency control loop 104 for frequency controlling the laser 102 based on the frequency feedback signal to generate a frequency stabilized laser signal; a power control loop 106 for modulating the power of the frequency stabilized laser signal based on the power feedback signal to generate a frequency and power stabilized optical signal; a photon temperature sensing probe 108 for providing a frequency and power stabilized optical signal to the photon temperature sensing probe to generate an output optical signal; and a first photodetector 110 for receiving the output optical signal and converting the output optical signal into a first electrical signal to obtain a temperature value according to the first electrical signal.

Compared with the prior art, the photon temperature sensing system provided by the embodiment of the application has the functions of stabilizing the frequency and the power, stabilizing the frequency of the light source through the frequency control loop and stabilizing the power through the power control loop, and the frequency and the power stabilizing system can improve the system error caused by laser frequency noise and laser power noise.

The photon temperature sensing system comprises: 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. Hereinafter, a photonic temperature sensing system according to an embodiment of the present application will be described in detail with reference to fig. 1 to 2b, 4a, 4b, and 8.

The laser 102 is used to generate laser light. In particular, the role of a LASER (LASER) is to provide a LASER source with a power in the order of mw and a wavelength in the range 1500-1560nm that is continuously tunable.

The frequency control loop 104 is used to frequency control the laser 102 based on the frequency feedback signal to generate a frequency stabilized laser signal. Specifically, referring to fig. 8, the frequency control loop 104 includes a first beam splitter, a wavemeter WM, a data acquisition card DAQ, and a personal computer PC. The first beam splitter is used for splitting the laser into a first beam light and a second beam light; a wavelength meter for receiving the second light beam and providing the wavelength of the second light beam to the personal computer via the data acquisition card; and a personal computer for setting a feedback frequency according to the wavelength of the second beam of light to generate a frequency feedback signal, and providing the frequency feedback signal to the laser via the data acquisition card, so that the laser outputs a frequency stabilized laser signal. Specifically, the frequency of the second light beam may be acquired according to the wavelength of the second light beam, and the frequency of the second light beam is compared with a predetermined frequency to acquire a frequency difference value as the frequency feedback signal.

The power control loop 106 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 106 includes: an acousto-optic modulator AOM, a polarizer (polarizer), a second beam splitter, a second photodetector (PD 2), a servo controller PI, a radio frequency source RF and a power amplifier PA. The acousto-optic modulator is used for receiving the power feedback signal and modulating the power of the first beam of light according to the power feedback signal so as to output the first beam of light with stable power; the polarizer is used for polarizing the first light with stable power; the second beam splitter is used for dividing the polarized first beam into a third beam and a fourth beam; the second photoelectric detector is used for receiving the fourth beam of light and converting the fourth beam of light into a second electric signal; the servo controller is used for generating a digital control signal according to the second electric signal; the radio frequency source is used for modulating the digital control signal into a radio frequency signal; and a power amplifier for amplifying the radio frequency signal to generate a power feedback signal.

The polarization controller is arranged between the second beam splitter and the photon temperature sensing probe and is used for controlling the polarization direction of the third beam of light so as to enable as much third beam of light to pass through the photon temperature sensing probe as possible.

The photon temperature sensing probe 108 is used to provide a frequency and power stabilized optical signal to the photon temperature sensing probe to generate an output optical signal. Specifically, referring to fig. 2a, the photonic temperature sensing probe comprises: the optical chip and the waveguide and the ring resonant cavity arranged on the optical chip, wherein the waveguide comprises a coupling input end, an input part, a first bending part, a straight waveguide, a second bending part, an output part and a coupling output end, and the input part is arranged between the coupling input end and the first bending part, and the width of the input part is gradually reduced from the coupling input end to the first bending part. The first width of the coupling-in end is greater than the second width of the first curved portion, the first ends of the coupling-in end and the input portion each have a first width, and the second ends 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, 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 coupling-out terminal and the second curved portion, and its width becomes gradually smaller from the coupling-out terminal to the second curved portion. The first width of the coupling output end is larger than the second width of the second bending portion, specifically, the second end of the output portion has the second width and the first end of the output portion has the first width. Referring to fig. 2b, the coupling-in and coupling-out terminals are arranged as shallow etched grating structures, wherein the direction of the shallow etched grating structures is perpendicular to the direction of the input and output portions. The etching depth, duty cycle and period of the shallow etching grating structure are set according to the light with specific wavelength. For example, to maximize the transmission in the 1550nm band, the trench is etched to a depth of 70nm, the grid period is 615nm, and the duty cycle is about 0.5. The ring resonator is disposed adjacent the straight waveguide and distal from the coupling-in end and the coupling-out end. Referring to fig. 4a, the photonic temperature sensing probe further comprises a transmission structure connected to the coupling input and the coupling output via an input optical fiber and an output optical fiber, respectively. The transmission structure comprises an input optical fiber, an output optical fiber, a V-shaped groove substrate and an optical fiber cover plate, wherein the input optical fiber and the output optical fiber are fixed in the V-shaped groove of the V-shaped groove substrate and are covered above the V-shaped groove substrate, the input optical fiber and the output optical fiber through the optical fiber cover plate. The angle between the input and output fibers and the normal of the optical chip is 8 ° (see fig. 4 b); and the input optical fiber and the output optical fiber are single-mode polarization maintaining optical fibers.

The first photodetector 110 is configured to receive the output optical signal and convert the output optical signal into a first electrical signal to obtain a temperature value according to the first electrical signal. The first electrical signal is transmitted via the data acquisition card DAQ to the personal computer PC, which obtains a temperature value from the first electrical signal, in particular, the personal computer is able to obtain a frequency from the first electrical signal, and then obtains a temperature value from the graphs as shown in fig. 9a and 9 b.

In one embodiment of the application, a method of measuring temperature of a photonic temperature sensing system is disclosed. Referring to fig. 12, a method of thermometry of a photonic temperature sensing system implemented in accordance with the application includes: in step 1202, generating laser light by a laser; in step 1204, frequency controlling the laser based on the frequency feedback signal by a frequency control loop to generate a frequency stabilized laser signal; in step 1206, modulating the power of the frequency stabilized laser signal based on the power feedback signal by a power control loop to generate a frequency and power stabilized optical signal; in step 1208, providing the frequency and power stabilized 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 according to the first electrical signal.

Hereinafter, a photon temperature sensing system according to an embodiment of the present application will be described in detail by way of specific example with reference to fig. 2a to 11.

The smaller the spectral linewidth of the resonant peak of the optical cavity and the larger the slope of the linetype, the larger the change of the light intensity is caused, so that the higher the perception sensitivity is. Based on the principle, the temperature measuring system adopts an edge method to measure temperature, namely, the steepest light intensity change at a specific frequency at one side of a resonance peak edge resonance peak is measured to realize the sensing of temperature. While a small, temperature-dependent shift in the resonance frequency results in a large change in the intensity of the light. Since the resonance line type is a known quantity, the intensity variation of the transmitted-reflected spectrum can be converted into a variation of the center frequency.

The application constructs a photon temperature sensing system with a light source stabilizing function, the system mainly shows the capability of a microcavity in the aspect of temperature sensing through a silicon-based micro-ring structure, and a polarization-power stabilizing system of a light source is constructed to improve the system error caused by laser frequency noise and laser power noise, so that a complete photon temperature sensing system set is developed. The working temperature which is over 100K and the actual temperature measurement resolution is less than 10mK is realized.

The frequency control loop locks the frequency at the steepest side of the edge of the resonance peak, specifically, the wavelength meter detects the emergent light frequency of the laser, labview monitors the reading of the wavelength meter, and the feedback electric signal is fed to control the piezoelectric ceramic of the laser to realize frequency stabilization. A higher sensitivity of temperature sensing is achieved. The application builds a practical and feasible complete photon temperature sensing system, and can improve the sensitivity and the temperature measuring range of temperature sensing. The application mainly shows the capability of the microcavity in the aspect of temperature sensing through the silicon-based micro-ring structure, and constructs a polarization and power stabilizing system of the light source to improve the system error caused by laser frequency noise and laser power noise, and the complete photon temperature sensing system can realize the temperature measuring range of more than 100K and the actual temperature measuring resolution is less than 10mK.

Optical microcavity-based optical sensing is achieved by measuring the change in the resonant mode after the physical quantity of the sensed fluid changes or the pump light source perturbs. The temperature measuring system adopts an edge method to measure the steepest light intensity change at a specific frequency at one side of the resonance peak edge resonance peak so as to realize the sensing of the external temperature.

Referring to fig. 4, a six-axis piezoelectric platform and a three-axis moving platform are utilized to realize the coupling alignment of the optical chip and the coupling end, and the relative spatial positions of the optical chip and the coupling end are fixed by using ultraviolet glue with adaptive refractive index to become a packaged sensing probe. And then performing performance test, wherein the performance test scheme is to put the packaged sensing probe and a calibrated platinum resistance thermometer into a glass tube to enter a bath. Calibrating main parameters: the quality factor Q of the optical microcavity (describing the effective binding capacity of the microcavity to photons in the time dimension); a free spectral range FSR (free spectral range FSR: the frequency spacing or wavelength spacing of two whispering gallery modes with only angular quanta differing by 1); sensitivity, temperature measurement range and temperature resolution of the photon temperature sensor.

The working principle of the platinum resistance thermometer is that the temperature sensing platinum wire can freely expand and contract when the temperature changes. By measuring the resistance of the thermometer temperature sensing element, an interpolation formula of a temperature scale is utilized. Outputting a temperature curve changing with time.

Traditionally, fiber Bragg Grating (FBG) based photon thermometers employ continuous wavelength scanning techniques to measure temperature changes. In the wavelength scanning mode, the frequency region where the detection laser passes through the target is continuously scanned, the transmission and reflection spectrum is recorded, the center frequency of the transmission and reflection spectrum is calculated, and then the center frequency is converted into the temperature. The method adopts a bar grating structure, and the target frequency is locked at the steepest side of the resonance peak edge on the premise of stabilizing the frequency and the power. This may allow this to reflect changes in ambient temperature through changes in transmitted light power.

1. Photonic device fabrication

Fig. 2a and 2b depict a schematic representation of a photonic device coupled by a ring resonator to a straight waveguide, designed to have a width of 520nm, and a waveguide-microring distance of 60nm, ensuring single mode transmission, and a shallow etched grating structure. The coupling mode of the optical fiber and the device adopted in the experiment is vertical coupling, the coupling optical fiber is an array optical fiber, and the coupling part of the device is arranged into a shallow etching grating structure. The grating period is 615nm, the grating etching depth is 70nm, and the grating side wall is vertical and smooth, so that higher coupling efficiency is obtained. The purpose of the grating is to provide an efficient way of free-space light coupling into the photonic device.

The coupling mode of the optical fiber and the device adopted in the experiment is vertical coupling, the coupling optical fiber is an array optical fiber, and the coupling part of the device is arranged into a shallow etching grating structure. The coupling efficiency can be improved by designing the etching depth, duty cycle and period of the shallow etched grating structure for light of a specific wavelength. The light incidence angle has great influence on the coupling of the optical fiber and the microcavity, the light incidence angle set in the experiment is 8 degrees, namely the angle between the incident optical fiber direction and the vertical direction is 8 degrees, and the coupling efficiency is improved by adopting shallow etching bar grating through parameter setting. And designing the shallow etched grating by utilizing the FDTD software self-carried optimization process. First, fixed structure parameters such as silicon layer thickness, bottom silicon thickness, etc. are set. And then obtaining parameters such as the optimal period, duty ratio and the like under 1550nm wavelength through setting scanning optimization. Through the design optimization, the optimal coupling period of the shallow etched grating is 615nm, the duty ratio is 0.5, the grating etching depth is 60nm, the optimized parameters are designed into a complete shallow etched grating structure, two-dimensional simulation is carried out by FDTD, the obtained grating transmission spectrum is shown in figure 3, the center wavelength is 1550nm, the optimal coupling efficiency is 45.7%, and the requirements of experiments are met.

2. Preparation of coupling probe

The application uses the optical fiber to guide the light to one temperature sensing unit and senses the change of the optical condition of the temperature sensing unit, and the temperature sensing unit does not need electricity when working, thus having the advantages of good lightning resistance, electromagnetic noise resistance, convenient remote sensing and the like. The six-degree-of-freedom high-precision nanometer positioning system is used for correcting the coupling positions and angles of the chip and the end head, so that the chip and the end head have optimal coupling efficiency, and the front and back performances of the device package are basically kept consistent through photonic device coupling grating parameter setting and ultraviolet rubber powder adopting refractive index matching. Finally, the sensing device with high coupling efficiency is obtained.

In the present application, as shown in fig. 4a and 4b, two optical fibers for lighting and light transmission are fixed on a V-shaped groove substrate to form a main transmission structure with an optical fiber cover plate.

In the application, the temperature sensing unit consists of a transmission structure and an optical micro-ring optical chip matched with the transmission structure.

In particular, in the present application, the optical fiber incidence angle is preferably equal to or greater than 8 ° from the optical chip normal angle.

In particular, in the present application, the optical fiber used for transmitting the optical field is preferably a single-mode polarization maintaining optical fiber.

In particular, in the present application, the two-core optical fiber segment for temperature transmission is fixed using a V-groove base plate and an optical fiber cover plate made of quartz glass, as shown in fig. 4a and 4 b.

In the application, the probe comprises the v-shaped groove base plate and the optical fiber cover plate which are made of quartz glass, so that the sensing can be stably performed in repeated cold-hot alternation, and the sensing stability is further improved.

The sensing probe comprises two optical fibers for lighting and light transmission; a silicon-based micro-ring optical chip binds photons.

In addition, two optical fibers for lighting and light transmission are fixed on the V-shaped groove substrate, and form a main structure of the probe together with the micro-ring chip; the probe is formed by packaging a temperature measuring probe for temperature sensing.

In coupling alignment, the chip is placed on a six-axis piezoelectric platform. The nanometer positioning system is a six-degree-of-freedom high-precision nanometer positioning system, and has six motion axes, three being linear and three being rotary. The input optical fiber is fixed by using an 8-degree coupling end clamp, and the clamp is placed on a triaxial accurate nano moving platform as shown in fig. 5, so that the clamp can be accurately controlled to move back and forth, and the optical fiber and the chip can be aligned conveniently. The chip and the coupling head are fixed on the platform and the clamp through the vacuum air path air suction, so that the stability of the coupling process is ensured. The vertical relative position of the optical chip and the cross section of the coupling head was set at 20 microns. The judgment of the optimal coupling position is realized by observing the light transmission efficiency converted by the output voltage.

3. Device performance calibration

After finding the optimal coupling position of the optical fiber and the device, the performance of the device needs to be calibrated, i.e. the Q value and FSR of the device are measured. An experimental system is built, a photoelectric detector PD, an oscillograph OSC and an adaptive optical path system are connected, and the transmission spectrum line type of the resonant cavity is observed on the oscillograph OSC. First, a broad wavelength range of 1530-1560nm is scanned by a LASER, and the scanned range is recorded precisely by a wavemeter OSC.

The device transmission spectrum obtained by scanning is shown in fig. 6, and the formula is utilized:

Q＝λ/△λ

wherein lambda is the center wavelength of the resonance peak; Δλ is the line width of the resonance peak, i.e., the half-width of the line; the free spectral range FSR is the wavelength interval between two resonance peaks.

The Free Spectral Range (FSR) of the device and the Q value of the device can be obtained through fitting calculation. The free spectral range of the device was found to be 8.85nm and the Q value was found to be 76440.

After the optimal coupling position is found, the performance of the device is tested, then the device and the optical fiber head are integrally packaged by ultraviolet glue, and the relative space position of the device and the optical fiber head is fixed by ultraviolet glue with adaptive refractive index, so that a packaged sensing probe is obtained. It is worth noting that during packaging, dispensing is performed on the outer edge of the device, so that ultraviolet glue is prevented from entering the coupling area as much as possible, and the performance of the device is affected. After packaging, the performance of the device needs to be calibrated again, a transmission spectrum is obtained through broad spectrum scanning, the Q value and FSR of the packaged device are observed, and the scanning transmission spectrum after packaging is shown in fig. 7. The Q value of the packaged device is reduced to 60587, the FSR is 8.84nm, and the Q value is not much different from that before packaging.

When the temperature sensitivity of the photonic device is calibrated, the sensing probe and the platinum resistor are put into the bath together, and the mK-magnitude tiny temperature change atmosphere in special environments such as aerospace, microfluid and the like is simulated.

By controlling the bath temperature, the ambient temperature around the device is changed. A new temperature measuring system adopting an edge method is constructed, compared with the traditional temperature measuring system, the temperature measuring system is provided with a polarizer in an AOM loop for polarization stabilization, a light source stabilizing system is added to improve the power noise and the frequency noise of a light source, the resolution is improved, and a final temperature measuring experimental device is shown in a schematic diagram of FIG. 8.

The function of a LASER (LASER) is to provide a continuously tunable LASER source with a power in the order of mw and a wavelength in the range 1500-1560 nm.

One path (10% light source) is split by a 10/90 beam splitter and connected to a Wavelength Meter (WM).

The acousto-optic modulator receives the feedback signal amplified by the power amplifier to modulate the light source, so that the power of the light source is constant at a certain level.

In particular, a polaroid or a prism is added in the AOM loop to stabilize the polarization of the light source, so that the polarization stability of the light source is ensured.

The second 10/90 beam splitter divides one path (10% light source) and converts the light into an electric signal through a photoelectric detector to be connected to a servo controller (PI).

A servo controller (PI) receives the PD electrical signal and outputs a control signal to control the RF source amplitude.

A radio frequency source (RF) modulates an input digital signal into a radio frequency signal and amplifies the signal for acousto-optic modulation.

The power amplifier is used to amplify the RF signal power.

In the experiment, an external BATH (BATH) method is adopted to simulate the external environment temperature change for the sensing probe, and the BATH is used for providing a system-controllable temperature change in mK magnitude; the bath is used to simulate the atmosphere of small temperature variation of the order of mK in special environments such as aerospace, microfluidics, etc.

A Photodetector (PD) converts the optical signal into an electrical signal.

An Oscilloscope (OSC) monitors and displays the electrical signal of the PD.

The data acquisition card (DAQmax) acquires signals of the Wavemeter (WM), and the feedback control of the piezoelectric ceramic PZT of the laser is realized by matching with the frequency set by the Labview program of the PC end, so that the frequency stability is realized.

When the temperature changes, the refractive index of the material and the volume of the device change along with the change of the temperature due to the thermo-optical effect and the thermal expansion effect of the material of the device. For silicon materials, the thermo-optic coefficient is 10 ^-4 Magnitude, and thermal expansion coefficient of 10 ^-6 The magnitude, therefore, shows that the thermo-optic coefficient is two orders of magnitude higher than the thermal expansion coefficient, so that only the influence of the thermo-optic coefficient is considered. The resonant wavelength of the microcavity will vary with the refractive index of the material, so the effect of temperature on the microcavity is ultimately manifested by a shift in the resonant wavelength with temperature, as shown in fig. 9 a.

As can be seen from FIG. 9b, the temperature sensitivity of the device is 79.62pm/K, the FSR after encapsulation is 8.84nm, and the temperature measuring range of the device is about 111K and is more than 100K.

It is noted that thermal broadening of the transmission spectrum sometimes occurs during the course of the experiment. The reason for this is probably that the self-heating response of the device is caused due to the excessively high input power, so that the transmission spectrum is widened, and an attenuator is needed to be added into the line for power attenuation. After the attenuator is added, the thermal broadening phenomenon disappears.

The temperature measurement resolution of the photon temperature sensing device depends on the temperature measurement resolution of the optical microcavity, and the microcavity temperature measurement resolution refers to the minimum value which can be resolved by the microcavity when the external environment temperature is disturbed. Resistance thermometer 25 European standard platinum resistance thermometer developed by American standard office, bridge resolution 0.02mK, quartz temperature sensor resolution of China reaches 0.1mK. The experiment uses PT100 platinum resistor as temperature resolution reference temperature, the resolution is 1mK, and the temperature measuring range is-200 to 850 ℃. The scheme has the advantages that the required resolution of the microcavity temperature sensor is 10mK, when the 10mK resolution calibration measurement is carried out, the frequency is locked to the steepest position on one side of a resonance peak, and then the signal noise on the oscilloscope is overlarge.

How to quantify and improve the system noise becomes critical here, so the signal is connected to a phase noise analyzer, noise signal is analyzed, the arangena variance, etc. The frequency noise introduced by long-term drift of the laser frequency of the laser is quantified by monitoring the output power of the microring resonator and the laser wavelength as a function of time, and measuring the laser frequency.

The new method for measuring mK level temperature change by the edge method is provided, firstly, laser is controlled to scan coarsely in the frequency range of 1540nm-1560nm to find a target resonance peak as shown in figure 10a, and then fine scanning is performed in the range of 1540nm-1550nm to obtain a transmission spectrum as shown in figure 10 b. An acousto-optic modulator AOM power stabilization system is then added to stabilize the laser power at a constant power level, as shown in fig. 10c, scanning the transmission peak after frequency and power stabilization.

It is noted that the laser and polarization controller also need to be tuned to lock the frequency on the side of the formants for laser frequency scanning, and the edge level and the bond level at the center frequency of the formants are shown in fig. 10d where the transmission peak identifies the steepest side of the formants. Then the frequency control loop is turned on to stabilize the laser frequency at a higher stable frequency level, and finally the laser frequency is locked at the position with the maximum slope on the side of the resonance peak.

A resolution response line was obtained by providing a 10mK temperature disturbance through the bath, as shown in fig. 11.

As can be seen from fig. 11, when the temperature increases by 10mK, the temperature change trend is consistent with the voltage change trend of the microcavity sensor device, so that the sensor device is said to have the lowest resolution of 10mK.

In summary, the present sensing device achieves a resolution of a minimum of 10mK. The photon temperature sensing system improves the system error caused by laser frequency and laser power. The low noise level and the strong electromagnetic interference resistance of the micro-fluidic chip have great potential in the application fields of aerospace and microfluidics.

The capability of the microcavity in temperature sensing is exhibited mainly by a silicon-based micro-ring structure. A spectrum edge method temperature measurement scheme is adopted, and a polarization-power stabilizing system of a light source is constructed to improve system errors caused by laser frequency noise and laser power noise. A complete set of photonic temperature sensing systems was developed. The temperature measuring range of more than 100K is realized, and the actual temperature measuring resolution is smaller than 10mK.

After the existing photon temperature sensing device packaging technology is optimized, the Q value of the micro-ring resonant cavity is as high as 60587, and the FSR is 8.84nm.

The spectrum edge method is adopted for measuring the temperature, so that the temperature measurement resolution is improved, and the established experiment proves that the method has the lowest resolution of 10mK.

And adding a polaroid or a prism into the AOM loop to stabilize the polarization of the light source, so as to construct a polarization-power stabilizing system of the light source. Is favorable for improving the temperature measurement resolution.

Those skilled in the art will appreciate that all or part of the flow of the methods of the embodiments described above may be accomplished by way of a computer program that instructs associated hardware to perform, and that the program may be stored on a computer readable storage medium. Wherein the computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory, etc.

The foregoing is only a preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the technical scope of the present application should be covered by the present application.

Claims (10)

1. A photonic temperature sensing system comprising: the laser, the frequency control loop, the power control loop, the photon temperature sensing probe and the first photoelectric detector, wherein,

the laser is used for generating laser;

the frequency control loop is used for performing frequency control on the laser based on a frequency feedback signal so as to generate a frequency stable laser signal;

the power control loop is used for modulating the power of the frequency stabilized laser signal based on a power feedback signal to generate a frequency and power stabilized optical signal;

the photon temperature sensing probe is used for providing the optical signal with stable frequency and power to the photon temperature sensing probe so as to generate an output optical signal; and

the first photoelectric detector is used for receiving the output optical signal and converting the output optical signal into a first electric signal so as to acquire a temperature value according to the first electric signal.

2. The photonic temperature sensing system of claim 1, wherein the frequency control loop comprises a first beam splitter, a wavelength meter, a data acquisition card, a personal computer, wherein,

the first beam splitter is used for splitting the laser into a first beam light and a second beam light;

the wavemeter is used for receiving the second beam of light and providing the wavelength of the second beam of light to the personal computer through the data acquisition card; and

the personal computer is used for setting a feedback frequency according to the wavelength of the second beam of light to generate a frequency feedback signal, and providing the frequency feedback signal to the laser through the data acquisition card so that the laser outputs a frequency-stabilized laser signal.

3. The photonic temperature sensing system of claim 2, wherein the power control loop comprises: an acousto-optic modulator, a polarizer, a second beam splitter, a second photodetector, a servo controller, a radio frequency source and a power amplifier, wherein,

the acousto-optic modulator is used for receiving the power feedback signal and modulating the power of the first beam of light according to the power feedback signal so as to output the first beam of light with stable power;

the polarizer is used for polarizing the first beam of light with stable power;

the second beam splitter is used for dividing the polarized first beam into a third beam and a fourth beam;

the second photodetector is configured to receive the fourth beam of light and convert the fourth beam of light into a second electrical signal;

the servo controller is used for generating a digital control signal according to the second electric signal;

the radio frequency source is used for modulating the digital control signal into a radio frequency signal; and

the power amplifier is configured to amplify the radio frequency signal to generate the power feedback signal.

4. A photonic temperature sensing system according to claim 3, further comprising a polarization controller arranged between the second beam splitter and the photonic temperature sensing probe for controlling the polarization direction of the third beam of light such that as much third beam of light as possible passes the photonic temperature sensing probe.

5. The photonic temperature sensing system of claim 2, wherein the photonic temperature sensing probe comprises: an optical chip, and a waveguide and a ring resonator disposed on the optical chip, wherein 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 part is arranged between the coupling-in end and the first bending part, and the width of the input part gradually becomes smaller from the coupling-in end to the first bending part, wherein the first width of the coupling-in end is larger than the second width of the first bending part;

the first curved portion and the second curved portion having 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 part is arranged between the coupling-out end and the second bending part, and the width of the output part gradually becomes smaller from the coupling-out end to the second bending part, wherein the first width of the coupling-out end is larger than the second width of the second bending part.

6. The photonic temperature sensing system of claim 5, wherein the coupling-in and coupling-out terminals are provided as shallow etched grating structures, wherein the direction of the shallow etched grating structures is perpendicular to the direction of the input and output portions.

7. The photonic temperature sensing system of claim 6, wherein the etch depth, duty cycle, and period of the shallow etched grating structure are set according to a specific wavelength of light.

8. The photonic temperature sensing system of claim 6, wherein the photonic temperature sensing probe further comprises a transmission structure, wherein the transmission structure comprises 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-shaped groove of the V-shaped groove base plate

And the V-shaped groove base plate, the input optical fiber and the output optical fiber are covered by the optical fiber cover plate.

9. The photonic temperature sensing system of claim 8, wherein an angle between the input optical fiber and the output optical fiber and a normal to the optical chip is 8 ° or more; and the input optical fiber and the output optical fiber are single-mode polarization maintaining optical fibers.

10. A method of measuring temperature of a photonic temperature sensing system, comprising:

generating laser light by a laser;

performing frequency control on the laser based on a frequency feedback signal through a frequency control loop to generate a frequency stabilized laser signal;

modulating the power of the frequency stabilized laser signal based on a power feedback signal by a power control loop to generate a frequency and power stabilized optical signal;

providing the optical signal with stable frequency and power to a photon temperature sensing probe to output an optical signal; and

and receiving the output optical signal, and converting the output optical signal into a first electric signal to acquire a temperature value according to the first electric signal.