A high-precision thermal expansion coefficient measuring device

Abstract

The present invention discloses a high-precision thermal expansion coefficient measurement device, including a PDH frequency locking module, a reference cavity length measurement circuit control module, and a data acquisition and processing module. The present invention utilizes a first electro-optical modulator to lock the frequency of the laser on the resonance peak of the optical F-P cavity by means of PDH frequency stabilization, and at the same time applies a cavity locking modulation signal to the second electro-optical modulator, so that the frequency of the radio frequency signal output by the radio frequency signal source is locked on the free spectrum range FSR of the optical F-P cavity, and finally the thermal expansion coefficient and other parameters of the optical F-P cavity can be obtained. The present invention only needs a set of frequency-stabilized lasers to complete the measurement of the thermal expansion coefficient of the optical reference cavity, and has high measurement precision, good accuracy, high data reliability, a large measurement temperature range, and can measure a variety of solid materials.

Description

Technical Field

[0001] The invention relates to the technical field of high-precision signal measurement and control, and in particular to a high-precision thermal expansion coefficient measuring device. Background Art

[0002] From household appliances, machinery manufacturing, construction, firefighting to lithography, chemistry, metrology and astronomy, etc., all fields require the use of materials with close to zero thermal expansion over a wide temperature range. For example, Invar nickel-iron alloy is widely used in precision instruments and machinery. By measuring the expansion of materials at different temperatures, we can understand the thermal expansion properties of materials, which provides an important basis for the design and application of materials. In addition, thermal expansion coefficient measurement can also be used to evaluate the thermal stability and reliability of materials.

[0003] In the fields of basic science and precision measurement, the optical Fabry-Perot (FP) cavity, as a basic optical device in atomic, molecular and optical physics, has important applications in laser frequency stabilization, high-resolution laser spectroscopy and optical frequency standards. Since the optical path of the laser in the optical FP cavity changes with temperature, in order to reduce the long-term drift caused by temperature, the thermal expansion coefficient of the distance holder between the optical FP cavity mirrors should be as small as possible. Low expansion materials such as microcrystalline glass and ultra-low expansion (ULE) glass are good materials for making high thermal stability FP cavities. In order to reduce the temperature sensitivity of the optical FP cavity, it is very important to find its appropriate working point, the length of the material that maintains the end mirror spacing, and the precise measurement of its thermal expansion coefficient.

[0004] At present, there are many methods for measuring the thermal expansion coefficient, such as thermomechanical analysis, photoelastic analysis, ultrasonic method and interferometry. Among them, the laser interferometry method uses the Michelson interferometer to measure the glass sample, and calculates the length change of the sample according to the change of the interference fringes. However, these measurement methods are difficult to measure the thermal expansion coefficient of ultra-low thermal expansion materials, and the measurement accuracy needs to be improved. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a high-precision thermal expansion coefficient measuring device, which measures the thermal expansion coefficient of an optical FP cavity by measuring the length change of the optical FP cavity at different temperatures.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] A high-precision thermal expansion coefficient measuring device comprises a laser, wherein the laser emitted by the laser is sequentially phase-modulated by a first electro-optical modulator and a second electro-optical modulator and then incident on an optical FP cavity, and the laser emitted from the optical FP cavity is divided into a frequency-locked reference light and a cavity-locked reference light;

[0008] The frequency-locking reference light is input to the frequency-locking component, the frequency-locking component outputs a frequency-locking modulation reference signal to the electrical input end of the first electro-optical modulator, and the frequency-locking component also outputs a laser frequency fine-tuning control signal to the servo control system of the laser;

[0009] The cavity-locked reference light is input to the reference cavity length measurement circuit control module, and the reference cavity length measurement circuit control module outputs a cavity-locked modulation signal to the electrical input end of the second electro-optical modulator, and at the same time, the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module and the output signal of the frequency reference source are both input to the frequency counter;

[0010] The frequency data output by the frequency counter and the temperature detection data of the optical FP cavity are simultaneously input into the computer.

[0011] As mentioned above, the reference cavity length measurement circuit control module includes a second photodetector,

[0012] The cavity-locked reference light is input into a second photodetector, and a second analog electrical signal output by the second photodetector and a first phase modulation signal output by a sideband modulation signal source are both input into a microwave frequency locking system, and the second analog electrical signal is sequentially demodulated, filtered, and integrated by the microwave frequency locking system to output a microwave signal, and the microwave signal is divided into a cavity-locked reference microwave signal and a cavity length measurement microwave signal, and the cavity-locked reference microwave signal is input into a radio frequency signal source;

[0013] The cavity length measurement microwave signal output by the microwave frequency locking system is used as the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module;

[0014] The radio frequency signal source outputs a radio frequency signal to the phase modulator, and the cavity-locked modulation signal output by the phase modulator serves as the cavity-locked modulation signal output by the reference cavity length measurement circuit control module.

[0015] As described above, the frequency locking component includes a first photodetector, the frequency locking reference light is coupled to the first photodetector and converted into a first analog electrical signal, the signal output by the frequency locking modulation signal source is divided into a frequency locking demodulation reference signal and a frequency locking modulation reference signal, and the frequency locking demodulation reference signal and the first analog electrical signal output by the first photodetector are both input into the laser frequency locking system.

[0016] The laser frequency fine-tuning control signal output by the laser frequency locking system is used as the laser frequency fine-tuning control signal output by the frequency locking component;

[0017] The frequency-locked modulation reference signal output by the frequency-locked modulation signal source is used as the frequency-locked modulation reference signal output by the frequency-locked component.

[0018] As mentioned above, the frequency of the RF signal output by the RF signal source is equal to the free spectral range FSR of the optical FP cavity.

[0019] As mentioned above, the output frequency of the sideband modulation signal source cannot be equal to the output frequency of the frequency-locked modulation signal source, and is not an integer multiple of the output frequency of the frequency-locked modulation signal source.

[0020] As described above, the laser light emitted by the laser is phase modulated by the first electro-optic modulator and the second electro-optic modulator in sequence, and then transmitted through the polarization beam splitter prism and incident on the optical FP cavity. After that, the reflected light of the optical FP cavity is reflected and coupled to the beam splitter prism through the polarization beam splitter prism, and the beam splitter prism outputs the frequency-locked reference light and the cavity-locked reference light.

[0021] As described above, a thermistor is provided on the surface of the optical FP cavity, and a digital multimeter collects resistance data of the thermistor; the resistance data collected by the digital multimeter is input into a computer as temperature detection data, and the computer converts the resistance data into temperature data.

[0022] As mentioned above, the detection range of the first photodetector is 0.1-99 MHz, and the detection range of the second photodetector is 0.5-20 GHz.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1. The working principle of the present invention is to measure the thermal expansion coefficient of the optical FP cavity by measuring the length change at different temperatures, add a new electro-optical modulator to the optical path of the PDH frequency locking module, perform phase modulation on the laser, and convert the length and free spectral range (FSR) of the optical FP cavity into the output frequency value of the microwave, and finally directly obtain the thermal expansion coefficient and absolute length of the optical FP cavity. The device of the present invention has a simple structure and low cost.

[0025] 2. The device structure of the present invention has a large measurement range, a short measurement period, high measurement accuracy, high data reliability, and can measure a variety of solid materials. The measurement of the absolute length of the optical FP cavity is of great significance to time-frequency measurement.

[0026] 3. Compared with the existing method of measuring the thermal expansion coefficient of the optical FP cavity using PDH frequency locking, the present invention adds an electro-optic modulator to the optical path, and detects through two photodetectors after splitting, thereby improving the locking effect of the laser, reducing the overall measurement error, and improving the measurement accuracy.

[0027] 4. The present invention simplifies system operation, enhances system adaptability and expansibility, and can meet the needs of modern scientific research and engineering applications for high-precision, high-stability laser light sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the principle structure diagram of the present invention;

[0029] Figure 2 is a curve showing the variation of the absolute cavity length of the optical FP cavity used in the embodiment with temperature;

[0030] Figure 3 is a curve showing the change of thermal expansion coefficient of the optical FP cavity used in the embodiment with temperature;

[0031] Among them, 1-PDH frequency locking module; 101-laser; 102-first electro-optic modulator; 103-second electro-optic modulator; 104-polarization beam splitter; 105-optical FP cavity; 106-beam splitter; 107-first photodetector; 108-laser frequency locking system; 109-frequency locking modulation signal source;

[0032] 2-reference cavity length measurement circuit control module; 201-second photodetector; 202-microwave frequency locking system; 203-RF signal source; 204-phase modulator; 205-sideband modulation signal source;

[0033] 3-data acquisition and processing module; 301-frequency reference source; 302-frequency counter; 303-digital multimeter; 304-computer. DETAILED DESCRIPTION

[0034] In order to facilitate ordinary technicians in the field to understand and implement the present invention, the present invention is further described in detail below in combination with embodiments and with reference to the accompanying drawings. The implementation examples described herein are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

[0035] Example 1

[0036] A high-precision thermal expansion coefficient measuring device, such as Figure 1 As shown, it includes a PDH frequency locking module 1, a reference cavity length measurement circuit control module 2 and a data acquisition and processing module 3.

[0037] The PDH frequency locking module 1 includes a laser 101, a first electro-optic modulator 102, a second electro-optic modulator 103, a polarization beam splitter prism 104, an optical FP cavity 105, a beam splitter prism 106 and a frequency locking component, wherein the frequency locking component includes a first photodetector 107, a laser frequency locking system 108 and a frequency locking modulation signal source 109, wherein the optical FP cavity 105 is an optical reference cavity to be measured.

[0038] The reference cavity length measurement circuit control module 2 includes a second photodetector 201 , a microwave frequency locking system 202 , a radio frequency signal source 203 , a phase modulator 204 and a sideband modulation signal source 205 .

[0039] The data acquisition and processing module 3 includes a frequency reference source 301, a frequency counter 302, a digital multimeter 303 and a computer 304. The connection relationship of the above components is as follows:

[0040] For PDH frequency locking module 1:

[0041] The laser light emitted by the laser 101 is incident on the first electro-optic modulator 102 for phase modulation, the light modulated by the first electro-optic modulator 102 is incident on the second electro-optic modulator 103 for phase modulation again, the light modulated by the second electro-optic modulator 103 is incident on the optical FP cavity 105 through the polarization beam splitter prism 104, the light reflected by the optical FP cavity 105 is incident on the polarization beam splitter prism 104 again and reflected by the polarization beam splitter prism 104 to the beam splitter prism 106, the light beam incident on the beam splitter prism 106 is split into two paths by the beam splitter prism 106, wherein the first path of light output by the beam splitter prism 106 is used as a frequency-locking reference light, and the second path of light output by the beam splitter prism 106 is used as a cavity-locking reference light;

[0042] The frequency-locking reference light is input to the frequency-locking component, and the frequency-locking component outputs a frequency-locking modulation reference signal to the electrical input end of the first electro-optical modulator 102. The frequency-locking component also outputs a laser frequency fine-tuning control signal to the laser 101 to stabilize the laser output by the laser 101. The specific settings are as follows:

[0043] The frequency-locking reference light is coupled to the first photodetector 107 of the frequency-locking component and converted into a first analog electrical signal. The output signal of the frequency-locking modulation signal source 109 is divided into two paths, namely, a frequency-locking demodulation reference signal and a frequency-locking modulation reference signal. The frequency-locking demodulation reference signal output by the frequency-locking modulation signal source 109 and the first analog electrical signal output by the first photodetector 107 are both input into the laser frequency locking system 108 and subjected to frequency-locking processing (the frequency-locking processing includes phase demodulation, low-pass filtering and loop filtering in sequence, and the phase demodulation obtains a frequency-locking error signal, and the frequency-locking error The signal is low-pass filtered to obtain a frequency-locking error signal with high-frequency components removed, and the frequency-locking error signal with high-frequency components removed is passed through a loop filter to obtain a laser frequency fine-tuning control signal). The laser frequency fine-tuning control signal output after frequency locking is input into the servo control system of the laser 101 (the laser frequency fine-tuning control signal output by the laser frequency locking system 108 is used as the laser frequency fine-tuning control signal output by the frequency locking component). The laser 101 is servo-controlled by the laser frequency locking system 108 to lock the laser frequency output by the laser 101. The frequency-locking modulation reference signal output by the frequency-locking modulation signal source 109 is input into the electrical input end of the first electro-optical modulator 102 (the frequency-locking modulation reference signal output by the frequency-locking modulation signal source 109 is used as the frequency-locking modulation reference signal output by the frequency locking component). The frequency of the frequency-locking modulation reference signal output by the frequency-locking modulation signal source 109 performs phase modulation on the laser frequency output by the laser 101.

[0044] For reference cavity length measurement circuit control module 2:

[0045] The cavity lock reference light is input to the reference cavity length measurement circuit control module 2, and the reference cavity length measurement circuit control module 2 outputs the cavity lock modulation signal to the electrical input end of the second electro-optical modulator 103. At the same time, the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module 2 is input to the frequency counter 302. The specific settings are as follows:

[0046] The cavity-locked reference light is coupled to the second photodetector 201 and converted into a second analog electrical signal;

[0047] The phase modulation signal output by the sideband modulation signal source 205 is divided into two paths. The first phase modulation signal output by the sideband modulation signal source 205 and the second analog electrical signal output by the above-mentioned second photodetector 201 are both input into the microwave frequency locking system 202. The second analog electrical signal is sequentially demodulated, filtered and integrated by the microwave frequency locking system 202 and then output as a microwave signal. The microwave signal is divided into a cavity lock reference microwave signal and a cavity length measurement microwave signal. The cavity lock reference microwave signal output by the microwave frequency locking system 202 is input into the radio frequency signal source 203 as a frequency reference of the radio frequency signal source 203; at the same time, the cavity length measurement microwave signal output by the microwave frequency locking system 202 is input into the frequency counter 302 (the cavity length measurement microwave signal output by the microwave frequency locking system 202 is used as the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module 2). The RF signal source 203 outputs an RF signal to the phase modulator 204 (the frequency of the RF signal is equal to the free spectrum range FSR of the optical FP cavity 105), and the cavity-locked modulation signal output by the phase modulator 204 is input to the electrical input end of the second electro-optical modulator 103 (the cavity-locked modulation signal output by the phase modulator 204 is used as the cavity-locked modulation signal output by the reference cavity length measurement circuit control module 2), and the cavity-locked modulation signal output by the phase modulator 204 further modulates the light modulated by the first electro-optical modulator 102 based on the free spectrum range FSR of the optical FP cavity 105, thereby modulating the free spectrum range FSR of the optical FP cavity 105.

[0048] In this embodiment, the light reflected by the polarization beam splitter 104 includes modulated signals with different frequency ranges, wherein the high-frequency modulated signal is modulated and generated by the second electro-optical modulator 103, and the frequency range of the high-frequency modulated signal is 0.5-20GHz; the low-frequency modulated signal is modulated and generated by the first electro-optical modulator 102, and the frequency range of the low-frequency modulated signal is 0.1~99MHz; therefore, the beam splitter 106 is used for splitting and the detection is performed respectively through the first electro-optical modulator 102 and the second photodetector 201, instead of directly passing through one photodetector and then dividing the electrical signal output by the photodetector into two paths. If only one photodetector is used, it is necessary to detect both the high-frequency modulated signal and the low-frequency modulated signal at the same time; however, the laser frequency locking system 108 and the microwave frequency locking system 202 have high requirements on the noise floor of the photodetector. It is difficult for a photodetector that can detect high-frequency modulated signals to have a low noise level near the MHz frequency, resulting in a large locking noise; a photodetector that can detect low-frequency modulated signals and has low noise has too low a gain near the GHz frequency, resulting in signal attenuation and cannot be effectively detected; therefore, a solution is adopted in which two different photodetectors are used for separate detection after splitting; in this embodiment, the first photodetector 107 is used to detect low-frequency modulated signals in the detection range of 0.1 to 99 MHz, and the second photodetector 201 is used to detect high-frequency modulated signals in the detection range of 0.5-20 GHz.

[0049] The cavity lock reference microwave signal output by the microwave frequency locking system 202 includes error information (i.e. cavity lock error information) between the RF signal output by the RF signal source 203 and the actual free spectrum range FSR of the optical FP cavity 105. The cavity lock reference microwave signal is used to perform feedback adjustment on the RF signal source 203 so that the frequency of the RF signal finally output by the RF signal source 203 is equal to the free spectrum range FSR of the optical FP cavity 105. In this embodiment, the frequency of the RF signal output by the RF signal source 203 is about 1.5 GHz, which is obtained by multiplying the 10 MHz output by the microwave frequency locking system 202 by 150 times. The free spectrum range FSR of the optical FP cavity 105 is about 1.5 GHz (corresponding to the cavity length of the optical FP cavity 105 being about 10 cm, and the optical FP cavity 105 being in a vacuum environment). If the cavity lock error information is to be obtained, the sideband modulation signal source 205 is required to modulate the RF signal source 203. The second analog electrical signal output by the second photodetector 201 is demodulated by the sideband modulation signal source 205, and then the control voltage signal of the voltage-controlled crystal oscillator is obtained by low-pass filtering and integration in sequence. The voltage-controlled crystal oscillator in the microwave frequency locking system 202 outputs a 10 MHz cavity-locked reference microwave signal. The 10 MHz cavity-locked reference microwave signal is used as a reference input to the radio frequency signal source 203. The radio frequency signal source 203 then outputs a 1.5 GHz radio frequency signal. The 1.5 GHz radio frequency signal is mixed and demodulated with the sideband modulation signal source 205 to obtain a cavity-locked modulation signal. The microwave frequency locking system 202 reflects the cavity-locked error information on the change of the output 10 MHz cavity-locked reference microwave signal. Since the cavity-locked reference microwave signal output by the microwave frequency locking system 202 is a reference for the radio frequency signal source 203, the frequency of the radio frequency signal output by the radio frequency signal source 203 will also change accordingly, so that the frequency of the radio frequency signal output by the radio frequency signal source 203 is locked to the free spectrum range FSR of the optical FP cavity 105.

[0050] The present invention adopts the method of inputting the cavity-locked modulation signal output by the phase modulator 204 into the electrical input end of the second electro-optical modulator 103 separately, and simultaneously inputting the frequency-locked demodulation reference signal output by the frequency-locked modulation signal source 109 separately into the electrical input end of the first electro-optical modulator 102; if the cavity-locked modulation signal output by the phase modulator 204 and the frequency-locked demodulation reference signal output by the frequency-locked modulation signal source 109 are input into one electro-optical modulator together, an additional signal mixing device is required, which causes a large insertion loss and affects the signal-to-noise ratio. The present invention uses the first electro-optic modulator 102 and the second electro-optic modulator 103 to modulate the laser light emitted by the laser 101 twice in sequence, and the modulation amplitude can be set respectively, so that the cavity-locked modulation signal output by the phase modulator 204 and the frequency-locked demodulation reference signal output by the frequency-locked modulation signal source 109 are not restricted by each other, and the corresponding error signals can be optimized respectively, with a better locking effect, thereby reducing the entire measurement error and improving the measurement accuracy; in this embodiment, compared with the general commercial thermal expansion coefficient measurement device, the measurement accuracy is improved by two orders of magnitude, which can reach the order of 2E-8. In addition, the first electro-optic modulator 102 and the second electro-optic modulator 103 are used. Photoelectric detectors with different detection ranges work in their respective high-gain frequency bands, which can have a lower noise level and reduce the locking noise.

[0051] For data acquisition and processing module 3:

[0052] The output signal of the frequency reference source 301 and the cavity length measurement microwave signal output by the microwave frequency locking system 202 are both input to the frequency counter 302, wherein the cavity length measurement microwave signal output by the microwave frequency locking system 202 is used as the characterization value of the length change of the optical FP cavity 105, and the output signal of the frequency reference source 301 is used as the frequency reference of the frequency counter 302. The digital multimeter 303 collects the resistance data of the thermistor on the optical FP cavity 105, and the resistance data is used as the temperature detection data. The thermistor is attached to the outer surface of the optical FP cavity 105; at the same time, the temperature detection data output by the digital multimeter 303 and the frequency data output by the frequency counter 302 are both input to the computer 304, and the computer 304 performs data processing to obtain parameters such as the thermal expansion coefficient and the absolute length of the optical FP cavity 105.

[0053] In this embodiment, the optical FP cavity 105 is made of ultra-low expansion (ULE) glass and has a cavity length of about 10 cm.

[0054] In this embodiment, the frequency reference source 301 is a rubidium clock reference source.

[0055] In this embodiment, the RF signal source 203 outputs an initial RF signal with an initial frequency of 1.5 GHz (frequency fluctuation range of 50 kHz).

[0056] The output frequency of the sideband modulation signal source 205 cannot be equal to the output frequency of the frequency-locked modulation signal source 109, and is not an integer multiple of the output frequency of the frequency-locked modulation signal source 109. In this embodiment, the sideband modulation signal source 205 outputs a sinusoidal signal with a frequency of 1 MHz.

[0057] In this embodiment, the frequency-locked modulation reference signal output by the frequency-locked modulation signal source 109 is a sine signal with a frequency of 2.5 MHz, and the cavity-locked modulation signal output by the phase modulator 204 is a 1.5 GHz RF signal with phase modulation. The phase modulation frequency of the 1.5 GHz RF signal with phase modulation is 1 MHz, and the 1 MHz phase modulation signal is output by the sideband modulation signal source 205.

[0058] In this embodiment, the positions of the first electro-optic modulator 102 and the second electro-optic modulator 103 in the optical path can be interchanged, that is, the laser emitted by the laser 101 can first pass through the phase modulation of the second electro-optic modulator 103, and then pass through the phase modulation of the first electro-optic modulator 102. The electrical input end of the second electro-optic modulator 103 receives the cavity-locked modulation signal output by the phase modulator 204, and the electrical input end of the first electro-optic modulator 102 receives the frequency-locked modulation reference signal output by the frequency-locked modulation signal source 109.

[0059] In this embodiment, the optical FP cavity 105 is controlled by a temperature control system and is in a vacuum environment. The temperature control system controls the temperature of the optical FP cavity 105 to be measured so that it can cover the entire temperature range of the measurement. According to the index requirements, the temperature control system can achieve a temperature change of -50°C to 80°C. The vacuum environment is because the principle of the measurement is based on optical interferometry, and the measurement result strongly depends on the refractive index change of the air. In order to eliminate the influence of the refractive index of the air, the optical FP cavity 105 to be measured needs to be placed in a vacuum system and the vacuum degree is maintained at a level higher than E-2Pa.

[0060] The present invention belongs to an optical interference measurement system, and it is necessary to couple the light modulated by the second electro-optic modulator 103 into the optical FP cavity 105 to be measured. In this embodiment, the coupling system adopts an all-fiber optical path, and the light beam modulated by the first electro-optic modulator 102, the second electro-optic modulator 103 and the polarization beam splitter prism 104 is directly coupled into the optical FP cavity 105 through a collimator. The all-fiber optical path ensures the stability and reliability of the system. The optical fiber collimator is fixed on a five-dimensional adjustment frame, and the coupling efficiency of the system is ensured by the five-dimensional adjustment frame.

[0061] The present invention includes a frequency measurement system (implemented by a reference cavity length measurement circuit control module 2) and a temperature measurement system (implemented by a data acquisition processing module 3). Since it is necessary to measure the change in the length of the optical FP cavity 105 with temperature by measuring the change in the free spectrum range FSR with temperature, it is necessary to use an accurate frequency measurement system to measure the free spectrum range FSR, and its measurement frequency range is required to cover the range of 1MHz-100MHz, and the frequency measurement accuracy is <1mHz; at the same time, a high-precision digital multimeter 303 is used to measure the temperature change of the optical FP cavity 105 to be measured, and the digital multimeter 303 uses a multimeter with a resolution of six and a half digits or higher.

[0062] Example 2

[0063] A high-precision thermal expansion coefficient measurement method is provided, using a high-precision thermal expansion coefficient measurement device described in Example 1, locking the frequency of the radio frequency signal output by the radio frequency signal source 203 to the free spectrum range FSR of the optical FP cavity 105 through the microwave frequency locking system 202, and measuring the frequency of the microwave signal output by the microwave frequency locking system 202 after locking to measure the free spectrum range FSR of the optical FP cavity 105, thereby obtaining the absolute length of the optical FP cavity 105. By changing the temperature in the optical FP cavity 105, a data set of the absolute length of the cavity length of the optical FP cavity 105 versus the temperature is obtained.

[0064] The measurement process is as follows:

[0065] Changing the temperature in the optical FP cavity 105 by a temperature control system;

[0066] At different temperatures, the digital multimeter 303 is used to collect data from the thermistor attached to the optical FP cavity 105. The resistance value of the thermistor has a one-to-one correspondence with the temperature, so the resistance value data collected by the digital multimeter 303 can be converted into temperature data through the computer 304.

[0067] At the same time, at different temperatures, the microwave frequency locking system 202 outputs two microwave signals, wherein the cavity lock reference microwave signal is input into the RF signal source 203 as a frequency reference of the RF signal source 203, and the output cavity length measurement microwave signal is input into the frequency counter 302 for measurement, and the frequency data output by the frequency counter 302 is input into the computer 304 for processing.

[0068] The absolute cavity length of the optical FP cavity 105 is calculated by the following formula:

[0069]

[0070] Wherein, L is the absolute cavity length of the optical FP cavity 105, c is the speed of light in a vacuum, and n is the refractive index of air in the environment where the optical FP cavity 105 is located. In this embodiment, n=1. ref is the frequency of the microwave signal output by the microwave frequency locking system 202, which is directly measured by the frequency counter 302. M is the frequency division coefficient of the frequency of the microwave signal output by the microwave frequency locking system 202. In this embodiment, the frequency division coefficient is 150.

[0071] By changing the temperature in the optical FP cavity 105, a data set of absolute cavity length versus temperature of the optical FP cavity 105 is obtained, and then a data set of absolute cavity length change versus temperature of the optical FP cavity 105 is obtained. The relationship curve of absolute cavity length change versus temperature of the optical FP cavity 105 is shown in FIG. Figure 2 shown.

[0072] The absolute cavity length of the optical FP cavity 105 is L. The absolute cavity length change dL of the optical FP cavity 105 caused by the temperature change dT can be expressed as

[0073] dL=Lα(T)*dT Formula 2

[0074] Right now

[0075]

[0076] Wherein α(T) is the thermal expansion coefficient of the cavity material of the optical FP cavity 105 at a temperature of T.

[0077] Substituting the data set of the absolute cavity length of the optical FP cavity 105 and the absolute cavity length change versus temperature into Formula 3 for calculation, a data set of the thermal expansion coefficient (CTE) versus temperature of the optical FP cavity 105 is obtained, and then a curve of the thermal expansion coefficient (CTE) of the optical FP cavity 105 versus temperature can be obtained, such as: Figure 3 shown.

[0078] The present invention is not limited to the above-mentioned implementation modes. The above-mentioned embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the concept of the present invention. The implementation schemes in the above-mentioned embodiments can be further combined or replaced. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art all belong to the protection scope of the present invention.

Claims

1. A high-precision thermal expansion coefficient measuring device, comprising a laser (101), characterized in that: The laser light emitted by the laser (101) is sequentially phase-modulated by a first electro-optic modulator (102) and a second electro-optic modulator (103) and then incident on an optical FP cavity (105), and the laser light emitted from the optical FP cavity (105) is divided into a frequency-locked reference light and a cavity-locked reference light; The frequency-locking reference light is input to the frequency-locking component, the frequency-locking component outputs a frequency-locking modulation reference signal to the electrical input end of the first electro-optical modulator (102), and the frequency-locking component also outputs a laser frequency fine-tuning control signal to the servo control system of the laser (101); The cavity-locked reference light is input to a reference cavity length measurement circuit control module (2), the reference cavity length measurement circuit control module (2) outputs a cavity-locked modulation signal to an electrical input end of a second electro-optical modulator (103), and simultaneously the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module (2) and the output signal of a frequency reference source (301) are both input to a frequency counter (302); The frequency data output by the frequency counter (302) and the temperature detection data of the optical FP cavity (105) are simultaneously input into the computer (304); The reference cavity length measurement circuit control module (2) comprises a second photodetector (201), The cavity-locked reference light is input into a second photodetector (201); a second analog electrical signal output by the second photodetector (201) and a first phase modulation signal output by a sideband modulation signal source (205) are both input into a microwave frequency locking system (202); the second analog electrical signal is sequentially demodulated, filtered and integrated by the microwave frequency locking system (202) to output a microwave signal; the microwave signal is divided into a cavity-locked reference microwave signal and a cavity length measurement microwave signal; and the cavity-locked reference microwave signal is input into a radio frequency signal source (203); The cavity length measurement microwave signal output by the microwave frequency locking system (202) is used as the cavity length measurement microwave signal output by the reference cavity length measurement circuit control module (2); The radio frequency signal source (203) outputs a radio frequency signal to the phase modulator (204), and the cavity-locked modulation signal output by the phase modulator (204) serves as the cavity-locked modulation signal output by the reference cavity length measurement circuit control module (2); The frequency locking component comprises a first photodetector (107), a frequency locking reference light is coupled to the first photodetector (107) and converted into a first analog electrical signal, a signal output by a frequency locking modulation signal source (109) is divided into a frequency locking demodulation reference signal and a frequency locking modulation reference signal, and the frequency locking demodulation reference signal and the first analog electrical signal output by the first photodetector (107) are both input into a laser frequency locking system (108), The laser frequency fine-tuning control signal output by the laser frequency locking system (108) is used as the laser frequency fine-tuning control signal output by the frequency locking component; The frequency-locked modulation reference signal output by the frequency-locked modulation signal source (109) is used as the frequency-locked modulation reference signal output by the frequency-locked component.

2. A high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that: The frequency of the radio frequency signal output by the radio frequency signal source (203) is equal to the free spectrum range (FSR) of the optical FP cavity (105).

3. A high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that: The output frequency of the sideband modulation signal source (205) cannot be equal to the output frequency of the frequency-locked modulation signal source (109), and is not an integer multiple of the output frequency of the frequency-locked modulation signal source (109).

4. A high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that: The laser light emitted by the laser (101) is phase modulated by a first electro-optic modulator (102) and a second electro-optic modulator (103) in sequence, and then transmitted through a polarization beam splitter prism (104) and incident on an optical FP cavity (105). Afterwards, the reflected light of the optical FP cavity (105) is reflected and coupled to a beam splitter prism (106) through the polarization beam splitter prism (104), and the beam splitter prism (106) outputs a frequency-locked reference light and a cavity-locked reference light.

5. A high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that: A thermistor is arranged on the surface of the optical FP cavity (105), and a digital multimeter (303) collects resistance data of the thermistor; the resistance data collected by the digital multimeter (303) is input into a computer (304) as temperature detection data, and the computer (304) converts the resistance data into temperature data.

6. A high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that: The detection range of the first photodetector (107) is 0.1-99 MHz, and the detection range of the second photodetector (201) is 0.5-20 GHz.

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