CN102243136B - Laser gyro optical resonant cavity loss measurement system based on resonance method - Google Patents

Abstract

The invention discloses a laser gyro resonant cavity loss measurement system, which mainly solves the problem that the existing measurement system needs another system to complete nonlinear correction of piezoelectric ceramics. The entire measurement system includes a laser (1), a spherical mirror (2), a two-dimensional parallel plate (3), a polarizer (4), a 1/2 wave plate (5), a resonant cavity fixing device (6), a resonant optical signal A measurement control device (7), a main control computer (11) and a piezoelectric ceramic driver (12). The laser emits a laser beam, which enters the laser gyro resonator to be tested through a spherical mirror, a two-dimensional parallel plate, a polarizer and a 1/2 wave plate to generate resonant light. By applying different bias voltages to the piezoelectric ceramics, the piezoelectric The nonlinearity of ceramics is accurately corrected, and then the resonant cavity loss is calculated by measuring the half-maximum width of the resonant optical power spectrum. The invention has the advantages of high efficiency, low cost and accurate measurement, and is suitable for high-precision measurement of laser gyro resonant cavity loss.

Description

Laser Gyro Optical Resonator Loss Measurement System Based on Resonance Method

technical field

The invention belongs to the technical field of measurement, and relates to a measurement system of an optical resonant cavity, which is mainly used for measuring the loss of the optical resonant cavity of a laser gyroscope.

Background technique

At present, there are two main methods for measuring the loss of the laser gyro optical resonator: one is the cavity ring-down method based on the measurement of the resonator decay time constant, and the other is the resonance method based on the measurement of the free spectral range of the resonator. The optical cavity ring down method is not affected by the stability of the incident laser beam light intensity of the resonator, but it can only measure lower losses, and the measurement accuracy is reduced for higher losses; while the resonance method is generally used for middle and high Accurate measurement of losses. In addition, there is a direct measurement method based on the DF transflectometer, which is simple to measure, but only suitable for high loss measurement and low measurement accuracy.

There are many researches on the measurement of resonator loss in China. The literature "Laser Gyroscope Resonator Loss and Phase Difference Measurement" (Tian Haifeng et al., 2006, Chinese Journal of Inertial Technology) discusses the measurement method of laser gyroscope optical resonator loss based on the resonance method in The principle and device are discussed in detail. In the case of medium and high loss, this method can theoretically achieve higher accuracy, but the measurement accuracy of this method is greatly affected by the nonlinearity of piezoelectric ceramics in the frequency-swept laser. Therefore, in the actual measurement, the piezoelectric ceramics must first be corrected for nonlinearity, so that the frequency-sweeping laser outputs a laser beam whose frequency varies linearly to ensure the accuracy of the measurement; and then the resonant cavity loss is accurately measured. The current general measurement method is: in addition to the resonant cavity loss measurement system, an additional set of special measurement devices is added to measure and correct the nonlinearity of piezoelectric ceramics. This measurement system not only increases the complexity and cost of the measurement process , and reduces the measurement efficiency.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and propose a laser gyro optical resonator loss measurement system based on the resonance method, so as to simplify the measurement process, reduce the cost and improve the measurement efficiency.

To achieve the above object, the measurement system of the present invention includes: laser, spherical mirror, two-dimensional parallel plate, polarizer, 1/2 wave plate, resonant cavity fixing device, resonant optical signal measurement control device, main control computer and piezoelectric Ceramic driving circuit, wherein the laser is a single-mode frequency-sweeping laser, under the control of the piezoelectric ceramic driving circuit, the laser outputs a laser beam with a periodic and continuous linear change in frequency; the laser beam output by the laser passes through the spherical mirror in turn , a two-dimensional parallel plate, a polarizer and a 1/2 wave plate, incident into the resonator of the laser gyro to be tested placed on the resonator fixture, and multiple eigenmodes are excited in the resonator of the laser gyro to be tested to generate resonant light , the resonant light undergoes photoelectric conversion and digital-to-analog conversion through the resonant optical signal measurement and control device, and is transmitted to the main control computer; the main control computer is equipped with a USB drive module, a nonlinear correction module, a loss measurement module and a display interface module. The drive module is used to drive the command transmission and data acquisition between the main control computer and the resonant optical signal measurement control device, and display and save the collected data in real time through the display interface module; the nonlinear correction module controls the piezoelectric ceramic drive The circuit applies different bias voltages to the piezoelectric ceramics on the laser, and obtains a set of power spectral lines with different pulse widths output by the laser gyro resonator to be tested. Based on this group of spectral lines, the nonlinearity of the piezoelectric ceramics is corrected, and The loss of the resonant cavity of the laser gyro to be tested is measured by the loss measurement module.

The piezoelectric ceramic driving circuit includes two DDS signal generators and two high-voltage amplifying modules, each DDS signal generator is respectively connected to a high-voltage amplifying module, and each DDS signal generator generates an adjustable 0-5V waveform Voltage, the voltage is amplified to 0-240V through the high-voltage amplification module, and applied to the two ends of the piezoelectric ceramic on the laser as the driving voltage and bias voltage to control the change of the laser beam frequency.

The spherical reflector and the two-dimensional parallel plate are placed between the laser and the resonant cavity fixing device, and are used to adjust the angle and translation of the laser output laser beam incident on the laser gyro resonator to be tested, and improve the coupling efficiency.

The polarizer and the 1/2 wave plate are placed between the laser and the resonator fixing device, and are used to adjust the polarization state, polarization direction and light intensity of the laser beam incident to the resonator of the laser gyroscope to be measured according to the measurement requirements.

The resonant optical signal measurement control device includes a photodetector, an A/D analog-to-digital converter and a USB interface, and the A/D analog-to-digital converter converts the resonant optical signal through the photodetector for photoelectric conversion and signal amplification Digital signals are output to the main control computer through the USB interface for data processing, and the main control computer sends control signals to the piezoelectric ceramic driver through the USB interface to generate piezoelectric ceramic drive voltage.

The present invention has the following advantages:

1) The present invention adopts a single-mode frequency-sweeping laser. Under the control of a piezoelectric ceramic drive circuit, the laser outputs a laser beam whose frequency is periodically and continuously changes linearly. eigenmodes, enabling the simultaneous measurement of multiple eigenmode losses.

2) The present invention uses the laser gyro resonator loss measurement system to propose a nonlinear correction method for piezoelectric ceramics based on the FWHM of the resonant optical power spectrum, which ensures the correction accuracy and avoids the use of additional equipment for piezoelectric ceramic non-linear correction. Linear correction reduces cost, improves efficiency and simplifies the measurement process.

3) The piezoelectric ceramic drive circuit in the present invention includes two DDS signal generators and two high-voltage amplifying modules, which can flexibly adjust the output voltage waveform, and can simultaneously output two voltage signals to both ends of the piezoelectric ceramic as a driver voltage and bias voltage.

4) The present invention adopts the combination of a spherical reflector and a two-dimensional parallel plate, which can finely adjust the incident angle and translation of the laser beam incident to the resonator of the laser gyro to be tested at the same time, and carry out mode adjustment between the incident laser beam and the resonator of the laser gyro to be tested. Matching can effectively reduce cross-coupling between modes and improve coupling efficiency.

5) Due to the use of the polarizer and the 1/2 wave plate, the present invention can convert the polarization state, polarization direction and light intensity of the laser beam incident to the laser gyro resonator to be measured according to the measurement requirements, and filter out the noise interference caused by stray light, Improve measurement accuracy.

Description of drawings

Fig. 1 is a structural block diagram of the laser gyro resonator loss measurement system based on the resonance method of the present invention;

Fig. 2 is the principle schematic diagram that the present invention uses resonance method to measure laser gyro resonator loss;

Fig. 3 is the flow chart that the present invention uses resonance method to measure laser gyroscope resonator loss;

Fig. 4 is in the testing process of the present invention, when carrying out resonant cavity loss measurement, the resonant light power spectral line that the laser gyroscope resonator cavity output to be tested is output;

Fig. 5 shows the resonant optical power spectrum lines output by the laser gyroscope resonator to be tested when different bias voltages are applied to the piezoelectric ceramics on the laser during the testing process of the present invention when the nonlinear correction of the piezoelectric ceramics is performed.

Fig. 6 is a diagram of a set of resonant optical power spectra obtained by changing the bias voltage applied to the piezoelectric ceramics on the laser and through the nonlinearity of the piezoelectric ceramics.

Detailed ways

The system structure of the present invention will be described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, the measurement system of the present invention comprises an optical system, a resonant optical signal measurement control device 7, a main control computer 11 and a piezoelectric ceramic drive circuit 12, the optical system generates an optical signal, and transmits the optical signal through the resonant optical signal measurement control device 7 to The main control computer 11, the main control computer 11 controls the piezoelectric ceramic driving circuit 12 through the resonant optical signal measurement control device 7 at the same time, and applies the driving voltage and the bias voltage to the optical system. in:

The optical system includes a laser 1, a spherical mirror 2, a two-dimensional parallel plate 3, a polarizer 4, a 1/2 wave plate 5 and a resonant cavity fixing device 6. The laser 1 adopts a single-mode frequency-sweeping laser with a pressure Electric ceramics, by controlling the piezoelectric ceramics, the frequency of the laser beam output by the laser 1 can be adjusted. After the laser 1, a spherical mirror 2, a two-dimensional parallel plate 3, a polarizer 4, and a 1/2 wave plate 5 are placed in sequence. Vibrating cavity fixing device (6). The spherical reflector 2 and the two-dimensional parallel plate 3 can precisely adjust the angle and position of the incident laser beam, reduce the difficulty of optical path adjustment, and improve the coupling efficiency between the incident laser beam and the laser gyro resonator to be tested; polarizer 4 and 1/2 wave plate 5. According to the measurement requirements, the polarization state, polarization direction and light intensity of the laser beam incident to the laser gyro resonator to be tested can be adjusted and converted; the resonator fixing device (6) is used to place the laser gyro resonator to be tested; the laser 1 The output laser beam is incident on the resonator of the laser gyroscope to be measured placed on the resonator fixture (6) through the spherical mirror 2, the two-dimensional parallel plate 3, the polarizer 4 and the 1/2 wave plate 5; the incident laser beam In the process of continuous frequency change, if it is the same as the natural frequency of the laser gyro resonator to be tested, resonant light will be generated and output in the laser gyro resonator to be tested.

The resonant optical signal measurement control device 7 includes a photodetector 8, an A/D analog-to-digital converter 9 and a USB interface 10. The photodetector 8 is located at the front end of the resonant optical signal measurement control device 7 as its input, after the photodetector 8 An A/D analog-to-digital converter 9 is provided, and the A/D analog-to-digital converter 9 is connected to the USB interface 10 . The photodetector 8 converts the incident light signal into an analog electrical signal, and the analog electrical signal is converted into a digital signal by the A/D analog-to-digital converter 9 and output to the main control computer through the USB interface.

The main control computer 11 is equipped with a measurement control module, including a USB driver module, a nonlinear correction module, a loss measurement module and a display interface module. The nonlinear correction module, the loss measurement module and the display interface module are independent and connected to the USB driver module; the USB driver module is used for data acquisition and command sending with external devices through the USB interface; the nonlinear correction module realizes the piezoelectric ceramic non-linear Linear correction; the loss measurement module completes the measurement of the laser gyro resonator loss to be tested; the display interface module displays the collected data graphically.

The piezoelectric ceramic driver 12 includes two DDS signal generators and two high-voltage amplifying modules, each DDS signal generator is respectively connected to a high-voltage amplifying module, and each DDS signal generator generates a waveform adjustable voltage of 0-5V, through The high-voltage amplification module amplifies the voltage to 0-240V and outputs it.

The principle of loss measurement using the above system is explained as follows with reference to Figure 2:

Under the control of the piezoelectric ceramic driving circuit 13, the laser 14 outputs a laser beam whose frequency varies periodically and continuously linearly with time and is incident into the laser gyro resonator 15 to be tested. When the frequency of the laser beam is close to the laser gyro resonance to be tested When a certain natural frequency of the laser gyro cavity is reached, the intensity of the resonant light output by the laser gyro resonator to be tested increases, and when it is far from the natural frequency, the intensity of the resonant light output by the laser gyro resonator to be tested decreases. The resonant light output by the laser gyro resonator to be tested is photoelectrically converted by the photodetector 16, processed and displayed by the data processing system 17, and the spectral line diagram of the resonant light power changing with time can be obtained, as shown in FIG. 5 . The half-maximum width of the spectral line has the following relationship with the loss of the laser gyro resonator:

$\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; res</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; las</span>}}}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;t</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}$

Among them, δ is the resonant cavity loss, Δt is the full width at half maximum of the resonant optical power spectrum, L _res is the cavity length of the laser gyro cavity to be tested, L _las is the cavity length of the laser resonator, and T is the frequency sweep period of the laser.

It can be seen from the above formula that the loss of the resonator can be obtained by obtaining the output resonant optical power spectrum line of the laser gyro resonator cavity and measuring the half width of the spectrum line.

With reference to Fig. 3, the measuring steps of the present invention are as follows:

Step 1, correct the piezoelectric ceramic nonlinearity of the system.

With reference to Fig. 4, the concrete implementation of this step is as follows:

1.1) The main control computer 11 controls the piezoelectric ceramic driving circuit 12 through the USB interface 10, and outputs the bias voltage and the driving voltage of the sawtooth waveform. The voltage is applied to both ends of the piezoelectric ceramic on the laser 1. , so that the frequency of the laser beam output by the laser 1 changes nonlinearly;

1.2) The frequency nonlinearly changing laser beam output by the laser 1 is incident on the resonator of the laser gyro to be tested placed in the resonator fixture 6, and resonant light is generated in the resonator of the laser gyro to be tested, and the resonant light passes through the resonant optical signal The measurement control device 7 converts it into a digital signal and transmits it to the main control computer 11, and the main control computer 11 displays the spectral line diagram of the resonant optical power changing with time;

1.3) Change the bias voltage applied to the piezoelectric ceramics on the laser 1, and obtain a set of resonant optical power spectral line diagrams through the nonlinearity of the piezoelectric ceramics, as shown in Figure 6, the half-height widths of the spectral lines are different, respectively Δt1, Δt2, Δt3, Δt4, Δt5...;

1.4) The non-linear correction module on the computer 11 is based on the FWHM of a group of spectral lines obtained in 1.3), and adjusts the driving voltage waveform output by the piezoelectric ceramic driver, so that the output frequency of the laser 1 is a laser beam that changes linearly, Complete nonlinear correction of piezoelectric ceramics.

Step 2, the main control computer 11 controls the piezoelectric ceramic driving circuit 12 through the USB interface 10, and outputs the waveform-corrected driving voltage to the piezoelectric ceramic on the laser 1, so that the laser 1 outputs a laser beam whose frequency changes periodically and continuously linearly.

Step 3, the frequency linearly changing laser beam output by the laser 1 is incident into the laser gyro resonator to be tested to excite resonant light, and the resonant light signal is transmitted to the main control computer 11 through the measurement control device 7 to obtain the resonant light power spectrum.

Step 4, the main control computer 11 measures the FWHM of the resonant optical power spectrum, and calculates the resonant cavity loss value according to the following formula:

$\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; res</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; las</span>}}}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;t</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}$

Among them: Δt is the half-maximum width of the measured resonant optical power spectrum, L _res is the cavity length of the laser gyro cavity to be tested, L _las is the cavity length of the laser cavity, and T is the frequency sweep period of the laser.

Claims (1)

1. A method for measuring laser gyro cavity loss, said method adopts a laser gyro cavity loss measurement system, said system comprising: laser (1), spherical reflector (2), two-dimensional parallel flat plate (3), polarizer (4), 1/2 wave plate (5), resonant cavity fixing device (6), resonant optical signal measurement control device (7), main control computer (11) and piezoelectric ceramic drive circuit ( 12), where: The laser (1) adopts a single-mode frequency-sweeping laser. Under the control of the piezoelectric ceramic drive circuit (12), the laser outputs a laser beam whose frequency is periodically and continuously linearly changed; the laser beam output by the laser (1) is sequentially After the spherical reflector (2), two-dimensional parallel plate (3), polarizer (4) and 1/2 wave plate (5), it is incident into the resonator of the laser gyro to be tested placed on the resonator fixture (6). , a plurality of eigenmodes are excited in the resonant cavity of the laser gyro to be tested to generate resonant light, which is transmitted to the main control computer (11) through photoelectric conversion and digital-to-analog conversion through the resonant optical signal measurement control device (7) ; The main control computer (11) is equipped with a USB drive module, a nonlinear correction module, a loss measurement module and a display interface module, and the USB drive module is used to drive the command transmission between the main control computer and the resonant optical signal measurement control device (7) and data acquisition, and display and save the collected data in real time through the display interface module; the nonlinear correction module applies different bias voltages to the piezoelectric ceramics on the laser by controlling the piezoelectric ceramic drive circuit (12), and obtains the Based on a set of power spectral lines with different pulse widths output by the laser gyro resonator, the nonlinearity of the piezoelectric ceramic is corrected based on the group of spectral lines, and the loss of the laser gyro resonator to be tested is measured through the loss measurement module; The method comprises the steps of: (1) Correct the piezoelectric ceramic nonlinearity of the system: 1.1) The main control computer controls the piezoelectric ceramic driving circuit through the USB interface, and outputs the bias voltage and the driving voltage of the sawtooth waveform. The voltage is applied to both ends of the piezoelectric ceramic on the laser, and the laser output A laser beam whose frequency varies nonlinearly; 1.2) The output frequency of the laser changes nonlinearly. The laser beam is incident into the resonator of the laser gyro to be tested to generate resonant light. Time-varying spectrograms; 1.3) Change the bias voltage applied to the piezoelectric ceramics on the laser, and obtain a set of resonant optical power spectrum lines with different half-height widths through the nonlinearity of the piezoelectric ceramics; 1.4) Based on the half-height width of a group of spectral lines obtained in 1.3), adjust the driving voltage waveform output by the piezoelectric ceramic driver, so that the output frequency of the laser changes linearly, and complete the nonlinear correction of the piezoelectric ceramic; (2) The main control computer controls the piezoelectric ceramic driving circuit through the USB interface, and outputs the driving voltage after waveform correction to the piezoelectric ceramic on the laser, so that the laser output frequency is linearly changed laser beam; (3) The laser beam output by the laser is incident into the resonant cavity of the laser gyro to generate resonant light, which is converted into a digital signal by the resonant light signal measurement and control device, and transmitted to the main control computer to display the resonant light power with time changing spectral lines; (4) The main control computer calculates the loss value of the resonant cavity by measuring the full width at half maximum of the resonant optical power spectrum: Among them, δ is the resonant cavity loss, Δt is the full width at half maximum of the resonant optical power spectrum, L _res is the cavity length of the laser gyro cavity to be tested, L _las is the cavity length of the laser resonator, and T is the frequency sweep period of the laser.

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