CN104167660B - Control method and system of laser set - Google Patents

Abstract

A control method and system for a laser group, belonging to the field of heterodyne interferometry, solves the problem of unstable laser beam difference frequency and power in a heterodyne interferometer composed of multiple lasers, and maintains the difference frequency between lasers Stable while suppressing laser power attenuation, thereby improving the performance of measurement equipment. The control method of the present invention includes an initialization step, a real-time detection step, a frequency stabilization control step, and a power control step; the control system of the present invention includes an initialization module, a real-time detection module, a frequency stabilization control module, and a power control module. The invention can realize real-time frequency feedback control, keep the difference frequency between the lasers stable and at the same time suppress the power attenuation of the lasers, so as to meet the measurement requirements of high time precision; the device involved is simple in structure, ensuring the measurement of the original system with high precision and low noise environment.

Description

A control method and system for a laser group

technical field

The invention belongs to the field of heterodyne interferometry, and in particular relates to a control method of a laser group and a system thereof.

Background technique

Heterodyne laser interferometer, also known as dual-frequency interferometer, is widely used in actual production and scientific research to meet the demand for precise parameter measurement. The beams of two different frequencies in the heterodyne interferometer can be provided by two monochromatic lasers, or by using magneto-optic, electro-optic, acousto-optic effects or the diffraction effect of a rotating grating disk. Especially in the field of scientific research or applications that require high time and space resolution, in order to obtain a higher frequency difference, two or more laser machines are often used to form a laser group to achieve interferometric measurement. The phase change of the light wave caused by the change of the measured object is carried on the difference frequency, and the interferometer with the difference frequency stabilization function can guarantee its measurement effect in the field of high-precision measurement. At the same time, controlling the output energy of the laser not to attenuate with the work can ensure that the interferometer has a better signal-to-noise ratio, and give full play to the advantages of the strong anti-interference ability of the heterodyne interferometer.

At present, there is no device and structure based on stabilizing the difference frequency of multiple lasers and simultaneously stabilizing multiple lasers in a state of high power output. The method involved in the patent CN201210211550.9 can stabilize the output frequency of each laser to obtain a stable difference frequency, and can make the laser in a strong output state. However, this method requires an additional set of laser interferometers for each laser to implement feedback. For a multi-laser system, the implementation of the feedback function is bound to become very complicated, and due to the need to scan a large resonant cavity length range for each frequency feedback, the time accuracy of the feedback cannot be made very high.

Contents of the invention

The invention provides a control method and system for a laser group, which solves the problem of unstable laser beam difference frequency and power in a heterodyne interferometer composed of multiple lasers, and keeps the difference frequency between lasers stable while suppressing Laser power attenuation improves measurement equipment performance.

The present invention is applied to a laser group consisting of N lasers, one of which is used as a frequency reference laser, and each laser is equipped with a piezoelectric ceramic converter for adjusting the cavity length of the corresponding laser resonator; and the frequency reference laser is equipped with Output laser power detector; the laser beams emitted by each laser are combined to form an interference laser beam, which enters the interference signal detector. After the interference signal detector converts the difference frequency signal of the interference laser beam into a voltage intermediate frequency signal, it is analog signal The isolator reads that the analog signal isolator has a high input impedance so that the signal energy consumed is negligible, and the coupling loop between the control signal and the detection signal is cut off, and the high-frequency noise is filtered out through the analog signal isolator amplification and filtering Finally, the analog-to-digital converter converts the intermediate frequency signal into an intermediate frequency digital signal and transmits it to the digital signal processor (DSP). At the same time, the laser power detector converts the detected laser power signal of the frequency reference laser through the analog-to-digital converter into a power digital signal. The signal is input into the digital signal processor; the power digital signal and the intermediate frequency digital signal are processed by the digital signal processor to obtain the corresponding power control quantity and frequency control quantity, and the power control quantity and each frequency control quantity are passed through a voltage holder The digital-to-analog converters are converted into voltage signals, which are respectively output to the piezoelectric ceramic converters of N lasers.

A method for controlling a laser group provided by the present invention includes an initialization step, a real-time detection step, a frequency stabilization control step and a power control step, and is characterized in that:

(1) Initialization steps:

For N lasers with the same calibrated output frequency, one of them is selected as the frequency reference laser, and the control voltage V _k =V ₀ converted into analog by the digital-to-analog converter is applied to the piezoelectric ceramic converter of the frequency reference laser, Adjust the frequency reference laser to the calibrated output frequency P ₀ ; the difference frequency signals between each two lasers together constitute the intermediate frequency signal, that is, the intermediate frequency signal contains a total of difference frequency signals, 2≤N≤6;

According to specific application requirements, predetermine the frequency difference △P _i between the output frequency of each laser among the remaining N-1 lasers and the output frequency of the frequency reference laser, i=1, 2,...N-1, △P _i =±1KHz ~±1GHz, these N-1 frequency differences △P _i must meet the requirements generated by N lasers There is a requirement that there will be no aliasing of the difference frequency signals in the frequency spectrum; at the same time, the control voltage V _i converted into analog by the digital-to-analog converter is respectively applied to the piezoelectric ceramic converters of the remaining N-1 lasers, and the remaining The output frequency of each laser in N-1 lasers is adjusted to P ₀ +△P _i , and the number of lasers with positive frequency difference and negative frequency difference is equal, so that the output frequency values of all lasers in the entire laser group are uniform distribution on the output peak to achieve the best output state, and the output frequency value of the frequency reference laser is located in the middle of the output frequency of the entire laser group; in this way, each difference frequency signal contained in the intermediate frequency signal will be on the spectrum with the already appear in known order;

The N-1 frequency differences △P _i are used as N-1 frequency setting values; and the voltage adjustment direction flag H is initialized to "1" or "0";"1" means to adjust in the direction of voltage increase , "0" means to adjust to the direction of voltage reduction;

(2) Real-time detection steps:

Real-time acquisition of the intermediate frequency digital signal and power digital signal collected by the analog-to-digital converter, the intermediate-frequency digital signal is obtained by converting the voltage intermediate-frequency signal through the analog-to-digital converter, and the voltage intermediate-frequency signal is combined by the laser beams emitted by each laser Finally, the interference laser beam is formed, and the difference frequency signal of the interference laser beam is converted and formed by the interference signal detector;

The power digital signal is formed by converting the laser power signal of the frequency reference laser through an analog-to-digital converter;

performing FFT transformation on the intermediate frequency digital signal, and extracting from the frequency spectrum obtained by FFT transformation peak frequency, the The first peak frequency is the frequency difference aliased in the intermediate frequency signal; the power digital signal is stored in the power memory so that the subsequent judgment substep (4.4) is used; then step (3) and step (4) are carried out respectively simultaneously;

(3) The frequency stabilization control step includes the following sub-steps:

(3.1) Frequency offset judgment sub-step: according to the distribution order of each difference frequency signal known in step (1), compare the N-1 frequency setting values ΔP _i with the detected Corresponding N-1 peak frequencies F _i among the peak frequencies are compared correspondingly to judge whether they are all equal, if yes, proceed to substep (3.3), otherwise proceed to substep (3.2); i=1, 2, ... N-1;

(3.2) Calculate the frequency correction voltage sub-step:

For each laser in which the frequency setting value and the peak frequency are not equal, according to the control voltage currently applied to the piezoelectric ceramic converter of each corresponding laser, find the slope K _i of the corresponding point on the frequency-voltage response curve of the laser , calculate frequency correction voltage △V1 _i =(F _i -△P _i )/K _i ;

For each laser whose frequency setting value and peak frequency are equal, set its corresponding △V1 _i to 0; i=1, 2, or N-1;

The frequency-voltage response curve of the laser is the response curve of the output frequency of the laser to the voltage change of the piezoelectric ceramic converter;

(3.3) Frequency control action sub-steps:

Calculate the amount of change in control voltage △V _i : △V _i = △V1 _i + △V2 _i ;

Among them, △V2 _i is read by the compensation voltage memory, which is used to eliminate the frequency fluctuation caused by power regulation;

Assign the value of V _i +△V _i to V _i , and then convert V _i into an analog quantity through a digital-to-analog converter, and then act on the piezoelectric ceramic converters of N-1 lasers;

Clear all the values of control voltage change △V _i , frequency correction voltage △V1 _i and frequency compensation voltage △V2 _i ; turn to step (2);

(4) power control step, including the following sub-steps:

(4.1) Delay triggering sub-step: set delay time T, T=1～10 seconds, trigger a power regulation every T seconds, carry out sub-step (4.2); this delay time T is sufficiently larger than the time scale of real-time frequency control , so that the real-time frequency control can timely suppress the frequency fluctuation caused by the power regulation action,

(4.2) Sub-step of power control action: if the voltage adjustment direction flag H is "1", assign the value of V _k + VL to V _k ; if the voltage adjustment direction flag H is "0", then assign the value of V _k - VL The value is given to V _k ; where the voltage adjustment step is VL=1mV～1V; then V _k is converted into an analog quantity through a digital-to-analog converter, and applied to the piezoelectric ceramic converter of the frequency reference laser, and the sub-step (4.3) is performed;

(4.3) Frequency compensation sub-step: perform frequency compensation on other N-1 lasers:

According to the current V _k , find the slope K _k of the corresponding point on the frequency-voltage response curve of the frequency reference laser, so as to calculate the frequency fluctuation value △P _k ＝VL·K _k produced by the frequency reference laser, and further according to △P _k , Calculate the frequency compensation voltage △V2 _i = VL·K _k /K _i of each laser; and store the frequency compensation voltage △V2 _i into the compensation voltage memory; proceed to sub-step (4.4);

(4.4) Judgment sub-step: judge whether the current voltage adjustment is keeping the output power of the frequency reference laser away from the output power peak state, if so, change the voltage adjustment direction mark H, and go to step (2), otherwise the voltage adjustment direction mark H remains unchanged Change, turn to step (2).

In the sub-step (4.3), since changing the frequency reference laser control voltage _Vk causes a slight change in the power of the frequency reference laser, its output frequency will also be slightly changed, in order to offset the frequency change of the frequency reference laser will be produced on the difference frequency signal When the frequency fluctuation of the frequency reference laser control voltage V _k changes, the other N-1 lasers are frequency compensated; the frequency compensation voltage of each laser is required to eliminate this frequency fluctuation.

The judging sub-step (4.4) of the power control step includes one of the following judging processes:

A. Calculate the current frequency reference laser output power value minus the difference ΔD of the previous power digital signal in the power memory, and judge whether ΔD<Q, the response rate threshold Q=-100～-1; if so, the frequency reference laser The output power is far away from the peak output power, otherwise the output power of the frequency reference laser is not far away from the peak output power;

B. Calculate the difference ΔS between the maximum value of all power digital signals minus the current frequency reference laser output power value after the last change of the voltage adjustment direction sign H stored in the power memory, and determine whether ΔS>G, the amount of reduction Threshold G=1-100; if yes, the output power of the frequency reference laser is far away from the peak output power; otherwise, the output power of the frequency reference laser is not far away from the peak output power.

Judgment process A, the power response rate of the frequency reference laser after the power regulation action. According to the characteristics of the output power-cavity length curve of the laser with a small slope in the output power peak range and a gradual increase in slope away from the output peak point, the preset responsivity threshold Q; More sensitive with steeper ranges;

Judgment process B, judge the working state of the laser by judging the total drop value of the laser output power after the laser crosses the output peak point; it is more sensitive when the output peak range is relatively flat.

In the judging sub-step (4.4), process A and process B can be carried out simultaneously, as long as one of them judges that the frequency reference laser is far away from the output peak point, then the judging sub-step (4.4) makes the frequency reference laser far away from the output peak judgment.

A control system for a laser group provided by the present invention includes an initialization module, a real-time detection module, a frequency stabilization control module and a power control module, and is characterized in that:

(1) Initialize the module:

For N lasers with the same calibrated output frequency, one of them is selected as the frequency reference laser, and the control voltage V _k =V ₀ converted into analog by the digital-to-analog converter is applied to the piezoelectric ceramic converter of the frequency reference laser, Adjust the frequency reference laser to the calibrated output frequency P ₀ ; the difference frequency signals between each two lasers together constitute the intermediate frequency signal, that is, the intermediate frequency signal contains a total of difference frequency signals, 2≤N≤6;

According to specific application requirements, predetermine the frequency difference △P _i between the output frequency of each laser among the remaining N-1 lasers and the output frequency of the frequency reference laser, i=1, 2,...N-1, △P _i =±1KHz ~±1GHz, these N-1 frequency differences △P _i must meet the requirements generated by N lasers There is a requirement that there will be no aliasing of the difference frequency signals in the frequency spectrum; at the same time, the control voltage V _i converted into analog by the digital-to-analog converter is respectively applied to the piezoelectric ceramic converters of the remaining N-1 lasers, and the remaining The output frequency of each laser in N-1 lasers is adjusted to P ₀ +△P _i , and the number of lasers with positive frequency difference and negative frequency difference is equal, so that the output frequency values of all lasers in the entire laser group are uniform distribution on the output peak to achieve the best output state, and the output frequency value of the frequency reference laser is located in the middle of the output frequency of the entire laser group; in this way, each difference frequency signal contained in the intermediate frequency signal will be on the spectrum with the already appear in known order;

The N-1 frequency differences △P _i are used as N-1 frequency setting values; and the voltage adjustment direction flag H is initialized to "1" or "0";"1" means to adjust in the direction of voltage increase , "0" means to adjust to the direction of voltage reduction;

(2) Real-time detection module:

Real-time acquisition of the intermediate frequency digital signal and power digital signal collected by the analog-to-digital converter, the intermediate-frequency digital signal is obtained by converting the voltage intermediate-frequency signal through the analog-to-digital converter, and the voltage intermediate-frequency signal is combined by the laser beams emitted by each laser Finally, the interference laser beam is formed, and the difference frequency signal of the interference laser beam is converted and formed by the interference signal detector;

The power digital signal is formed by converting the laser power signal of the frequency reference laser through an analog-to-digital converter;

performing FFT transformation on the intermediate frequency digital signal, and extracting from the frequency spectrum obtained by FFT transformation peak frequency, the The first peak frequency is the frequency difference aliased in the intermediate frequency signal; the power digital signal is stored in the power memory so that the subsequent judgment sub-module (4.4) uses; then perform module (3) and module (4) simultaneously;

(3) frequency stabilization control module, including the following sub-modules:

(3.1) Frequency offset judging submodule: according to the distribution order of each difference frequency signal known in step (1), compare the N-1 frequency setting values ΔP _i with the detected Corresponding N-1 peak frequencies F _i among the peak frequencies are compared correspondingly to judge whether they are all equal, if yes, proceed to submodule (3.3), otherwise proceed to submodule (3.2); i=1, 2, ... N-1;

(3.2) Calculate the frequency correction voltage sub-module:

For each laser in which the frequency setting value and the peak frequency are not equal, according to the control voltage currently applied to the piezoelectric ceramic converter of each corresponding laser, find the slope K _i of the corresponding point on the frequency-voltage response curve of the laser , calculate frequency correction voltage △V1 _i =(F _i -△P _i )/K _i ;

For each laser whose frequency setting value and peak frequency are equal, set its corresponding △V1 _i to 0; i=1, 2, or N-1;

The frequency-voltage response curve of the laser is the response curve of the output frequency of the laser to the voltage change of the piezoelectric ceramic converter;

(3.3) Frequency control action sub-module:

Calculate the amount of change in control voltage △V _i : △V _i = △V1 _i + △V2 _i ;

Among them, △V2 _i is read by the compensation voltage memory, which is used to eliminate the frequency fluctuation caused by power regulation;

Assign the value of V _i +△V _i to V _i , and then convert V _i into an analog quantity through a digital-to-analog converter, and then act on the piezoelectric ceramic converters of N-1 lasers;

Clear all the values of control voltage change △V _i , frequency correction voltage △V1 _i and frequency compensation voltage △V2 _i ; turn to module (2);

(4) Power control module, including the following sub-modules:

(4.1) Delay triggering sub-module: set the delay time T, T=1～10 seconds, trigger a power regulation every T seconds, and carry out the sub-module (4.2); the delay time T is sufficiently larger than the time scale of real-time frequency control , so that the real-time frequency control can timely suppress the frequency fluctuation caused by the power regulation action,

(4.2) Power control action sub-module: if the voltage adjustment direction flag H is "1", assign the value of V _k + VL to V _k ; if the voltage adjustment direction flag H is "0", then assign the value of V _k - VL The value is assigned to V _k ; where the voltage adjustment step is VL=1mV～1V; then V _k is converted into an analog quantity through a digital-to-analog converter, and applied to the piezoelectric ceramic converter of the frequency reference laser to perform the sub-module (4.3);

(4.3) Frequency compensation sub-module: perform frequency compensation on other N-1 lasers:

According to the current V _k , find the slope K _k of the corresponding point on the frequency-voltage response curve of the frequency reference laser, so as to calculate the frequency fluctuation value △P _k ＝VL·K _k produced by the frequency reference laser, and further according to △P _k , Calculate the frequency compensation voltage △V2 _i = VL·K _k /K _i of each laser; and store the frequency compensation voltage △V2 _i into the compensation voltage memory; carry out the sub-module (4.4);

(4.4) Judging sub-module: judging whether the current voltage adjustment is keeping the output power of the frequency reference laser away from the peak output power state, if so, change the voltage adjustment direction mark H, and go to step (2); otherwise, the voltage adjustment direction mark H remains unchanged Change, turn to module (2).

The judging submodule (4.4) of the power control module performs one of the following judging processes:

A. Calculate the current frequency reference laser output power value minus the difference ΔD of the previous power digital signal in the power memory, and judge whether ΔD<Q, the response rate threshold Q=-100～-1; if so, the frequency reference laser The output power is far away from the peak output power, otherwise the output power of the frequency reference laser is not far away from the peak output power;

B. Calculate the difference ΔS between the maximum value of all power digital signals minus the current frequency reference laser output power value after the last change of the voltage adjustment direction sign H stored in the power memory, and determine whether ΔS>G, the amount of reduction Threshold G=1-100; if yes, the output power of the frequency reference laser is far away from the peak output power; otherwise, the output power of the frequency reference laser is not far away from the peak output power.

Since the laser will have a peak output power within a small range of resonant cavity length, the present invention uses the active regulation of the frequency reference laser resonant cavity length with a fixed step size and a fixed time interval, and through the above-mentioned continuous active cavity length regulation The resulting small laser power changes determine whether the working state of the frequency reference laser is moving away from the output peak. If the judgment result is "No", continue to adjust the frequency reference laser cavity length in the current direction, so that the frequency reference laser continues to approach the output peak value; if the judgment result is "Yes", then reverse the adjustment of the frequency reference laser cavity length control direction. The above control method of making the frequency reference laser continuously approach the output peak will make the frequency reference laser always dynamically maintain the working state of the output peak power. On the basis that the frequency reference laser is controlled at the output peak value, the collected digital intermediate frequency signal is monitored in real time, and the real-time laser resonator is implemented by controlling the terminal voltage of the piezoelectric ceramic converter on each laser except the frequency reference laser. The cavity length feedback keeps the difference frequency of N-1 lasers except the frequency reference laser constant relative to the frequency reference laser, so as to achieve the purpose of stabilizing the difference frequency of the interferometer laser beam. Using the corresponding relationship between the output frequency of the laser and the cavity length of the resonator, the cavity lengths of other laser resonators under the stable control of the difference frequency will be associated with the cavity length of the frequency reference laser, so that the following frequency reference laser will always work near the output peak point. In this way, By controlling the power stability of the frequency reference laser, the function of controlling the power output stability of the entire laser group is realized.

The present invention can realize real-time frequency feedback control, keep the difference frequency between lasers stable and suppress the power attenuation of lasers at the same time, so as to meet the measurement requirements of high time precision; the device involved is simple in structure, and no additional device is required to obtain the frequency information, feedback control can be realized only by the intermediate frequency detector of the interferometer itself, and only one variable of the laser resonator is controlled, and the control amount is single; in the case of multiple lasers, the present invention only needs to detect the power information of one laser The power control of multiple lasers can be realized; since there is no need to change the original measurement system structure of the interferometer, the signal sampling port is isolated from the original measurement system by a high-impedance analog signal isolator, and the impact on the original interferometer measurement system is minimized , ensuring the high-precision and low-noise measurement environment of the original system;

Description of drawings

Fig. 1 is a block diagram of the overall control device of the present invention.

Fig. 2 is a schematic diagram of the control method of the present invention;

Fig. 3 is a schematic diagram of the control process of the present invention;

Fig. 4 is a schematic diagram of the power control method of the present invention.

detailed description

The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

As shown in Figure 1, the embodiment of the present invention is applied to a laser group composed of three lasers, one of which is used as a frequency reference laser 1, and each laser is equipped with a piezoelectric ceramic converter for adjusting the corresponding laser resonator and the frequency reference laser 1 is equipped with an output laser power detector 5; the laser beams emitted by the first laser 2, the second laser 3 and the frequency reference laser 1 combine to form an interference laser beam and enter the interference signal detector 4. The interference signal detector 4 converts the difference frequency signal of the interference laser beam into a voltage intermediate frequency signal and sends it to the control device 10, and is read by the analog signal isolator 6. The analog signal isolator 6 has a relatively high input impedance to make it The consumed signal energy is negligible, and the coupling loop between the control signal and the detection signal is cut off. After the analog signal isolator amplifies and filters out the high-frequency noise, the analog-to-digital converter 7 converts the intermediate frequency signal into an intermediate frequency digital signal and transmits it to the Digital signal processor 8 (DSP), meanwhile, laser power detector 5 converts the laser power signal of the detected frequency reference laser 1 through analog-to-digital converter 7 into a power digital signal input in digital signal processor 8; The signal and the intermediate frequency digital signal are processed by the digital signal processor 8 to obtain the corresponding power control quantity and frequency control quantity, and the power control quantity and each frequency control quantity are converted into voltage signals through the digital-to-analog converter 9 with a voltage holder , which are respectively output to the piezoelectric ceramic converters of the three lasers.

As shown in Figure 2, an embodiment of the present invention includes an initialization step, a real-time detection step, a frequency stabilization control step and a power control step, and is characterized in that:

(1) Initialization steps:

For 3 lasers with the same calibrated output frequency, select one of them as the frequency reference laser, apply the control voltage V _k = 30V converted to analog by the digital-to-analog converter on the piezoelectric ceramic converter of the frequency reference laser, adjust From the frequency reference laser to the calibrated output frequency P ₀ =694GHz; the difference frequency signals between every two lasers together form an intermediate frequency signal, that is, the intermediate frequency signal contains a total of 3 difference frequency signals;

According to specific application requirements, predetermine the frequency difference between the output frequency of each laser in the other two lasers and the output frequency of the frequency reference laser △P ₁ =-1MHz, △P ₁ =+1.5MHz, these two frequency differences △P _i meet the requirements that the difference frequency signals generated by the three lasers will not be aliased in the frequency spectrum; at the same time, the piezoelectric ceramic converters of the other two lasers are respectively applied to the analog signals converted by the digital-to-analog converter The initial control voltage is about 30V, adjust the output frequency of each of the other two lasers to P ₀ +△P _i , i=1, 2, the number of lasers with positive frequency difference and negative frequency difference is roughly equal , so that the output frequency values of all lasers in the entire laser group are evenly distributed on the output peak to achieve the best output state, and the output frequency value of the frequency reference laser is located in the middle of the output frequency of the entire laser group; thus, the intermediate frequency signal The individual beat signals included will appear in a known order on the spectrum;

Set △P ₁ =-1MHz, △P ₁ =+1.5MHz as the two frequency setting values; and initialize the voltage adjustment direction flag H to "0";"1" means to adjust to the direction of voltage increase, "0" Indicates to adjust in the direction of voltage reduction;

(2) Real-time detection steps:

Real-time acquisition of the intermediate frequency digital signal and power digital signal collected by the analog-to-digital converter, the intermediate-frequency digital signal is obtained by converting the voltage intermediate-frequency signal through the analog-to-digital converter, and the voltage intermediate-frequency signal is combined by laser beams emitted by three lasers Finally, the interference laser beam is formed, and the difference frequency signal of the interference laser beam is converted and formed by the interference signal detector;

The power digital signal is formed by converting the laser power signal of the frequency reference laser through an analog-to-digital converter;

Carry out FFT transformation to described intermediate frequency digital signal, extract 3 peak frequencies from the frequency spectrum that FFT transform obtains, and these 3 peak frequencies are the frequency difference that aliases in intermediate frequency signal; Store described power digital signal in The power storage is used for subsequent judgment sub-step (4.4); then carry out step (3) and step (4) respectively simultaneously;

(3) The frequency stabilization control step includes the following sub-steps:

(3.1) Frequency offset judgment sub-step: according to the distribution order of each difference frequency signal known in step (1), set the two frequency setting values ΔP ₁ =-1MHz, ΔP ₁ =+1.5MHz Correspondingly compared with ₂ peak frequencies F1 and F2 corresponding in the ₃ peak frequencies detected, judge whether they are all equal, if yes, proceed to substep (3.3), otherwise proceed to substep (3.2); i= 1, 2;

(3.2) Calculate the frequency correction voltage sub-step:

For each laser in which the frequency setting value and the peak frequency are not equal, according to the control voltage currently applied to the piezoelectric ceramic converter of each corresponding laser, find the slope K _i of the corresponding point on the frequency-voltage response curve of the laser , calculate frequency correction voltage △V1 _i =(F _i -△P _i )/K _i ;

For each laser whose frequency setting value and peak frequency are equal, set its corresponding △V1 _i to 0; i=1, 2;

The frequency-voltage response curve of the laser is the response curve of the output frequency of the laser to the voltage change of the piezoelectric ceramic converter;

(3.3) Frequency control action sub-steps:

Calculate the amount of change in control voltage △V _i : △V _i = △V1 _i + △V2 _i ;

Among them, △V2 _i is read by the compensation voltage memory, which is used to eliminate the frequency fluctuation caused by power regulation;

Assign the value of V _i +△V _i to V _i , and then convert V _i into an analog quantity through a digital-to-analog converter, and then act on the piezoelectric ceramic converters of N-1 lasers;

Clear all the values of control voltage change △V _i , frequency correction voltage △V1 _i and frequency compensation voltage △V2 _i ; turn to step (2);

(4) power control step, including the following sub-steps:

(4.1) Delay triggering sub-step: setting delay time T=3 seconds, triggering power regulation once every interval T seconds, and performing sub-step (4.2);

(4.2) Sub-step of power control action: if the voltage adjustment direction flag H is "1", assign the value of V _k + VL to V _k ; if the voltage adjustment direction flag H is "0", then assign the value of V _k - VL The value is given to V _k ; wherein the voltage adjustment step size VL=40mV; then V _k is converted into an analog quantity through a digital-to-analog converter, and applied to the piezoelectric ceramic converter of the frequency reference laser, and the sub-step (4.3) is performed;

(4.3) Frequency compensation sub-step: perform frequency compensation on other N-1 lasers:

According to the current V _k , find the slope K _k of the corresponding point on the frequency-voltage response curve of the frequency reference laser, so as to calculate the frequency fluctuation value △P _k ＝VL·K _k produced by the frequency reference laser, and further according to △P _k , Calculate the frequency compensation voltage △V2 _i = VL·K _k /K _i of each laser; and store the frequency compensation voltage △V2 _i into the compensation voltage memory; proceed to sub-step (4.4);

(4.4) Judgment sub-step: judge whether the current voltage adjustment is keeping the output power of the frequency reference laser away from the output power peak state, if so, change the voltage adjustment direction mark H, and go to step (2), otherwise the voltage adjustment direction mark H remains unchanged Change, turn to step (2).

In this embodiment, the judging sub-step (4.4) of the power control step includes one of the following judging processes:

A. Calculate the current frequency reference laser output power value minus the difference ΔD of the previous power digital signal in the power memory, and judge whether ΔD<Q, the responsivity threshold Q=-8; if so, the output power of the frequency reference laser is far away from output power peak value, otherwise the output power of the frequency reference laser is not far from the output power peak value;

B. Calculate the difference ΔS between the maximum value of all power digital signals minus the current frequency reference laser output power value after the last change of the voltage adjustment direction sign H stored in the power memory, and determine whether ΔS>G, the amount of reduction Threshold G=25; if yes, the output power of the frequency reference laser is far away from the peak output power; otherwise, the output power of the frequency reference laser is not far away from the peak output power.

A schematic diagram of the control effect of the present invention is shown in Fig. 3. In the figure, the horizontal axis is the cavity length of the laser resonator, the vertical axis is the laser output power, and the curve in the figure is the laser output power-cavity length curve.

Taking three lasers as an example, the cavity length of the frequency reference laser 1 is L2, and the corresponding working point on the laser output power-cavity length curve is point A; the working point of the first laser 2 is point B, and the working point of the second laser 3 Point is point C. The frequency of the operating point A of the frequency reference laser 1 is at an intermediate value among all lasers. As shown in the figure, the output energy P of the laser will appear at the output peak point S within a small range of the resonant cavity length L. The present invention continuously regulates the cavity length of the frequency reference laser 1 so that the working point A of the frequency reference laser 1 approaches the output peak point S. When the operating point A of the frequency reference laser is placed at its output peak position, and the first laser 2, the second laser 3 and the reference laser maintain a stable frequency difference F1, F2 through cavity length control, due to the difference between the laser cavity length and the output frequency Corresponding relationship, the resonant cavity length L1 of the first laser 2, the resonant cavity length L2 of the frequency reference laser 1, and the resonant cavity length L3 of the second laser 3 will be in a coupled state and maintain a relatively stable distance. In this way, the operating point B of the first laser 2 and the operating point C of the second laser 3 will follow the operating point A of the reference laser 1, and uniformly stabilize within a certain range near the output peak point S, so that by only controlling the frequency reference laser 1 power It is stable and realizes the function that the laser group of the whole interferometer is in an ideal output environment.

Fig. 4 has provided the synoptic diagram that control frequency reference laser 1 power approaches power output peak value in the present invention, among the figure, horizontal axis is laser resonator cavity long, and vertical axis is laser output power, and curve among the figure is laser output power- Magnification of the peak portion of the lumen length curve.

As mentioned above, the power regulation of the frequency reference laser 1 piezoelectric ceramic converter is adjusted with a fixed voltage change step size VL, and the action is performed once every time T. Assume that after the laser is initialized, the control voltage V _k of the frequency reference laser 1 just makes the operating point of the frequency reference laser 1 be at the W1 point, and the initialization voltage adjustment flag is "0"; the delay trigger substep (4.1) is delayed for T seconds , triggering the power control action sub-step (4.2), according to the voltage adjustment flag "0", the frequency reference laser control voltage V _k is adjusted from the current value V ₀ to V ₀ -VL, and the frequency reference laser 1 working position drops to point W2; At the same time, the frequency compensation sub-step (4.3) calculates the frequency compensation voltages △V2 ₁ and △V2 ₂ and stores them in the compensation voltage memory; since the frequency-voltage curve of the frequency reference laser 1 has a large slope at W1, the frequency reference laser 1 starts at W1 In the process of falling to W2 point, the response rate of power to voltage change is too large, so that the difference ΔD<Q between the power at point W2 minus the power at point W1, and the judgment sub-step (4.4) makes the decision "is letting the frequency With reference to the judgment that the output power of the laser is far away from the output power peak", immediately change the voltage adjustment flag to "1", then when the next delay trigger sub-step (4.1) is triggered, the power control action sub-step (4.2) will be at the same step size VL adjusts the control voltage Vk of the frequency reference laser ₁ by one step in the direction of increasing the voltage. At the same time, the frequency compensation sub-step (4.3) calculates the frequency compensation voltages △V2 ₁ and △V2 ₂ and stores them in the compensation voltage memory; since the voltage adjustment this time will make the frequency reference laser 1 return from the W2 point to the position close to the W1 point, Its power value increases, and the judging substep (4.4) will not make the judgment of "making the output power of the frequency reference laser 1 away from the output power peak value" through judging process A or B; like this, the power control step (4) will Continue to adjust the frequency reference laser 1 in the direction of increasing the control voltage. Repeat the above process, the power control step (4) will always gradually adjust the frequency reference laser 1 in the direction of increasing the control voltage, so that the output power of the frequency reference laser 1 moves to the output peak, until the operating point of the frequency reference laser 1 exceeds the output peak point M , and reach the working point R after a certain power control action sub-step (4.2); at this time, the working point of the frequency reference laser 1 has moved from W2 to the current working point R since the last time the voltage adjustment direction was changed ; In this process, the maximum value of all power values stored in the real-time detection step (2) occurs when the output peak point M is crossed. Judging sub-step (4.4) by calculating the difference between the maximum power value and the current power value, the conclusion of the difference ΔS>G is drawn, and through the judgment process B, it is made that the output power of the frequency reference laser is far away from the output power peak value ", immediately change the voltage adjustment flag to "0", so that the next voltage regulation will be carried out in the direction of reducing the control voltage. Until the operating point of the frequency reference laser 1 crosses the power output peak again and reaches a certain point Z, the judging sub-step makes a judgment that "the output power of the frequency reference laser is moving away from the output power peak" again through the judging process A and judging process B. By analogy, the frequency reference laser 1 will always be between the two points on the left and right sides of the current output peak value, which can make the judgment process A or judgment process B make the judgment of "making the output power of the frequency reference laser far away from the output power peak". Swing back and forth, thus being dynamically locked in the peak state of power output.

Claims (4)

1. a kind of control method of laser instrument group, including initialization step, real-time detection step, path length control step and power control Step processed, it is characterised in that：

(1) initialization step：

Determine output frequency identical laser instrument for N station symbols, optionally wherein one as frequency reference laser instrument, in frequency reference Control voltage V that digital to analog converter is converted to analog quantity is applied across on the piezoelectric ceramics converter of laser instrument_k=V₀, adjustment frequency Rate reference laser diode extremely demarcates output frequency P₀；Collectively form intermediate-freuqncy signal per the difference frequency signal between two laser instruments, i.e., in Frequency signal is included altogetherIndividual difference frequency signal, 2≤N≤6；

According to concrete application demand, each laser instrument output frequency and frequency reference laser in remaining N-1 platform laser instrument are predefined Frequency-splitting △ P between device output frequency_i, i=1,2 ... N-1, △ P_i=± 1KHz～± 1GHz, this N-1 frequency-splitting △P_iIt must is fulfilled for by produced by N platform laser instrumentsIndividual difference frequency signal is not in the requirement of aliasing on frequency spectrum；Meanwhile, It is applied across the control voltage that digital to analog converter is converted to analog quantity on the piezoelectric ceramics converter of remaining N-1 platform laser instrument respectively V_i, every laser instrument output frequency in remaining N-1 platform laser instrument is adjusted to into P₀+△P_i, frequency-splitting be on the occasion of and frequency-splitting Number of lasers for negative value is equal so that the output frequency value of all laser instruments of whole laser instrument group is evenly distributed in defeated Go out to reach optimal output state on peak value, and the output frequency value of frequency reference laser instrument is exported positioned at whole laser instrument group The centre position of frequency；So, each difference frequency signal included in intermediate-freuqncy signal will be on frequency spectrum with the appearance of known order；

By the N-1 frequency-splitting △ P_iAs N-1 frequency setting value；And be initialized as Voltage Cortrol Directional Sign H " 1 " or " 0 "；" 1 " represents and is adjusted to voltage augment direction, and " 0 " represents that reducing direction to voltage is adjusted；

(2) real-time detection step：

The digital intermediate frequency signal and power digital signal of analog-digital converter collection are obtained in real time, and the digital intermediate frequency signal is by voltage Intermediate-freuqncy signal Jing analog-digital converter is changed and obtained, and the voltage intermediate-freuqncy signal closes beam by the laser beam that each laser instrument is launched After form coherence laser beam, the difference frequency signal of coherence laser beam is converted by interference signal detector to be formed；

The power digital signal is changed through analog-digital converter by the laser power signal of frequency reference laser instrument and formed；

FFT is carried out to the digital intermediate frequency signal, is extracted in the frequency spectrum obtained from FFTIndividual crest frequency, shouldIndividual crest frequency is the frequency-splitting being aliasing in intermediate-freuqncy signal；The power digital signal is stored in into power memory Subsequently to judge that sub-step (4.4) is used；Then while carrying out step (3) and step (4) respectively；

(3) path length control step, including following sub-steps：

(3.1) frequency shift (FS) judges sub-step：According to the distribution sequence of known each difference frequency signal in step (1), by the N-1 Individual frequency setting value △ P_iWith detectCorresponding N-1 crest frequency F in individual crest frequency_i, correspond to compared respectively Compared with, judge that whether whole it is equal, it is to carry out sub-step (3.3), otherwise carry out sub-step (3.2)；I=1,2 ... N-1；

(3.2) frequency amendment voltage sub-step is calculated：

For wherein frequency setting value and the unequal each laser instrument of crest frequency, according to being currently applied to each corresponding laser instrument Control voltage on piezoelectric ceramics converter, finds the slope K of corresponding points in the frequency-voltage response curves of the laser instrument_i, Calculate frequency amendment voltage △ V1_i=(F_i- △ P_i)/K_i；

The each laser instrument equal for wherein frequency setting value and crest frequency, by its corresponding △ V1_iSet to 0；I=1,2 or N- 1；

Frequency-the voltage response curves of the laser instrument are that the laser instrument output frequency changes to piezoelectric ceramics transducer voltage Response curve；

(3.3) FREQUENCY CONTROL action sub-step：

Calculate control voltage knots modification △ V_i：△V_i=△ V1_i+△V2_i；

Wherein, △ V2_iRead by offset voltage memory, for eliminating the frequency fluctuation that power regulation causes；

By V_i+△V_iValue give V_i, then by V_iAnalog quantity is converted to through digital to analog converter, N-1 platform laser instruments are respectively acting on Piezoelectric ceramics converter on；

By control voltage knots modification △ V_i, frequency amendment voltage △ V1_iWith frequency compensation voltage △ V2_iValue all reset；Turn step Suddenly (2)；

(4) power control step, including following sub-steps：

(4.1) Time-delayed trigger sub-step：Setting time delay T, T=1～10 second are triggered a power regulation, are entered at interval of the T seconds Row sub-step (4.2)；

(4.2) power control actions sub-step：If voltage-regulation Directional Sign H is " 1 ", by V_kThe value of+VL gives V_k；If electric It is " 0 " that pressure adjusts Directional Sign H, then by V_kThe value of-VL gives V_k；Wherein Voltage Cortrol step-length VL=1mV～1V；Then by V_k Analog quantity is converted to through digital to analog converter, the piezoelectric ceramics converter of frequency reference laser instrument is put on, sub-step is carried out (4.3)；

(4.3) frequency compensation sub-step：Frequency compensation is carried out to other N-1 platforms laser instruments：

According to current V_k, the slope K of corresponding points is found in the frequency-voltage response curves of frequency reference laser instrument_k, so as to count Calculate the frequency fluctuation value △ P of frequency reference laser instrument generation_k=VLK_k, further according to △ P_k, calculate each laser instrument Frequency compensation voltage △ V2_i=VLK_k/K_i；And by frequency compensation voltage △ V2_iIt is stored in offset voltage memory；Carry out sub-step Suddenly (4.4)；

(4.4) sub-step is judged：Judge this voltage-regulation whether allowing frequency reference laser instrument power output away from defeated Go out power peak state, be then to change Voltage Cortrol Directional Sign H, go to step (2), otherwise Voltage Cortrol Directional Sign H keeps It is constant, go to step (2).

2. control method as claimed in claim 1, it is characterised in that：

The judgement sub-step (4.4) of the power control step is including one of following processes：

A, calculating ongoing frequency reference laser diode output power value deduct last power digital signal in the power memory Difference DELTA D, judge whether Δ D ＜ Q, responsiveness threshold value Q=-100～-1；Be then frequency reference laser instrument power output it is remote From power output peak value, otherwise the power output of frequency reference laser instrument is not away from power output peak value；

All power digital signals after the last changes of Voltage Cortrol Directional Sign H stored in B, the calculating power memory In maximum deduct difference DELTA S of ongoing frequency reference laser diode output power value, judge whether Δ S ＞ G, reduction amount threshold value G=1～100；Be the power output of then frequency reference laser instrument away from power output peak value, otherwise frequency reference laser instrument is defeated Go out power not away from power output peak value.

3. a kind of control system of laser instrument group, including initialization module, real-time detection module, path length control module and power control Molding block, it is characterised in that：

(1) initialization module：

Determine output frequency identical laser instrument for N station symbols, optionally wherein one as frequency reference laser instrument, in frequency reference Control voltage V that digital to analog converter is converted to analog quantity is applied across on the piezoelectric ceramics converter of laser instrument_k=V₀, adjustment frequency Rate reference laser diode extremely demarcates output frequency P₀；Collectively form intermediate-freuqncy signal per the difference frequency signal between two laser instruments, i.e., in Frequency signal is included altogetherIndividual difference frequency signal, 2≤N≤6；

According to concrete application demand, each laser instrument output frequency and frequency reference laser in remaining N-1 platform laser instrument are predefined Frequency-splitting △ P between device output frequency_i, i=1,2 ... N-1, △ P_i=± 1KHz～± 1GHz, this N-1 frequency-splitting △P_iIt must is fulfilled for by produced by N platform laser instrumentsIndividual difference frequency signal is not in the requirement of aliasing on frequency spectrum；Meanwhile, It is applied across the control voltage that digital to analog converter is converted to analog quantity on the piezoelectric ceramics converter of remaining N-1 platform laser instrument respectively V_i, every laser instrument output frequency in remaining N-1 platform laser instrument is adjusted to into P₀+△P_i, frequency-splitting be on the occasion of and frequency-splitting Number of lasers for negative value is equal so that the output frequency value of all laser instruments of whole laser instrument group is evenly distributed in defeated Go out to reach optimal output state on peak value, and the output frequency value of frequency reference laser instrument is exported positioned at whole laser instrument group The centre position of frequency；So, each difference frequency signal included in intermediate-freuqncy signal will be on frequency spectrum with the appearance of known order；

By the N-1 frequency-splitting △ P_iAs N-1 frequency setting value；And be initialized as Voltage Cortrol Directional Sign H " 1 " or " 0 "；" 1 " represents and is adjusted to voltage augment direction, and " 0 " represents that reducing direction to voltage is adjusted；

(2) real-time detection module：

The digital intermediate frequency signal and power digital signal of analog-digital converter collection are obtained in real time, and the digital intermediate frequency signal is by voltage Intermediate-freuqncy signal Jing analog-digital converter is changed and obtained, and the voltage intermediate-freuqncy signal closes beam by the laser beam that each laser instrument is launched After form coherence laser beam, the difference frequency signal of coherence laser beam is converted by interference signal detector to be formed；

The power digital signal is changed through analog-digital converter by the laser power signal of frequency reference laser instrument and formed；

FFT is carried out to the digital intermediate frequency signal, is extracted in the frequency spectrum obtained from FFTIndividual crest frequency, shouldIndividual crest frequency is the frequency-splitting being aliasing in intermediate-freuqncy signal；The power digital signal is stored in into power memory So that follow-up judging submodule (4.4) is used；Then while carrying out module (3) and module (4) respectively；

(3) path length control module, including following submodules：

(3.1) frequency shift (FS) judging submodule：According to the distribution sequence of known each difference frequency signal in step (1), by the N-1 Individual frequency setting value △ P_iWith detectCorresponding N-1 crest frequency F in individual crest frequency_i, correspond to compared respectively Compared with, judge that whether whole it is equal, it is to carry out submodule (3.3), otherwise carry out submodule (3.2)；I=1,2 ... N-1；

(3.2) frequency amendment voltage submodule is calculated：

For wherein frequency setting value and the unequal each laser instrument of crest frequency, according to being currently applied to each corresponding laser instrument Control voltage on piezoelectric ceramics converter, finds the slope K of corresponding points in the frequency-voltage response curves of the laser instrument_i, Calculate frequency amendment voltage △ V1_i=(F_i- △ P_i)/K_i；

The each laser instrument equal for wherein frequency setting value and crest frequency, by its corresponding △ V1_iSet to 0；I=1,2 or N- 1；

Frequency-the voltage response curves of the laser instrument are that the laser instrument output frequency changes to piezoelectric ceramics transducer voltage Response curve；

(3.3) FREQUENCY CONTROL action submodule：

Calculate control voltage knots modification △ V_i：△V_i=△ V1_i+△V2_i；

Wherein, △ V2_iRead by offset voltage memory, for eliminating the frequency fluctuation that power regulation causes；

By V_i+△V_iValue give V_i, then by V_iAnalog quantity is converted to through digital to analog converter, N-1 platform laser instruments are respectively acting on Piezoelectric ceramics converter on；

By control voltage knots modification △ V_i, frequency amendment voltage △ V1_iWith frequency compensation voltage △ V2_iValue all reset；Revolving die Block (2)；

(4) power control module, including following submodules：

(4.1) Time-delayed trigger submodule：Setting time delay T, T=1～10 second are triggered a power regulation, are entered at interval of the T seconds Row submodule (4.2)；Time delay T is sufficiently more than the time scale of real-time frequency control, so that real-time frequency control energy Enough frequency fluctuations timely suppressed caused by power regulation action,

(4.2) power control actions submodule：If voltage-regulation Directional Sign H is " 1 ", by V_kThe value of+VL gives V_k；If electric It is " 0 " that pressure adjusts Directional Sign H, then by V_kThe value of-VL gives V_k；Wherein Voltage Cortrol step-length VL=1mV～1V；Then by V_k Analog quantity is converted to through digital to analog converter, the piezoelectric ceramics converter of frequency reference laser instrument is put on, submodule is carried out (4.3)；

(4.3) frequency compensation submodule：Frequency compensation is carried out to other N-1 platforms laser instruments：

According to current V_k, the slope K of corresponding points is found in the frequency-voltage response curves of frequency reference laser instrument_k, so as to count Calculate the frequency fluctuation value △ P of frequency reference laser instrument generation_k=VLK_k, further according to △ P_k, calculate each laser instrument Frequency compensation voltage △ V2_i=VLK_k/K_i；And by frequency compensation voltage △ V2_iIt is stored in offset voltage memory；Carry out submodule Block (4.4)；

(4.4) judging submodule：Judge this voltage-regulation whether allowing frequency reference laser instrument power output away from defeated Go out power peak state, be then to change Voltage Cortrol Directional Sign H, go to step (2), otherwise Voltage Cortrol Directional Sign H keeps It is constant, revolving die block (2).

4. the control system of laser instrument group as claimed in claim 3, it is characterised in that the judgement submodule of the power control module Block (4.4) carries out one of following deterministic processes：

A, calculating ongoing frequency reference laser diode output power value deduct last power digital signal in the power memory Difference DELTA D, judge whether Δ D ＜ Q, responsiveness threshold value Q=-100～-1；Be then frequency reference laser instrument power output it is remote From power output peak value, otherwise the power output of frequency reference laser instrument is not away from power output peak value；

All power digital signals after the last changes of Voltage Cortrol Directional Sign H stored in B, the calculating power memory In maximum deduct difference DELTA S of ongoing frequency reference laser diode output power value, judge whether Δ S ＞ G, reduction amount threshold value G=1～100；Be the power output of then frequency reference laser instrument away from power output peak value, otherwise frequency reference laser instrument is defeated Go out power not away from power output peak value.