A power feedforward control device for a high power single frequency laser

Abstract

The application relates to a power feedforward control device of a high-power single-frequency laser, which comprises a light splitting module, a photoelectric detector, an analog amplification and adjustment circuit, a low-pass filter circuit, a PID operation circuit and a current driving circuit; the high-power laser output by a laser emission module is split by the light splitting module to generate detection light which is sent into the photoelectric detector to generate an analog voltage; after amplification, adjustment and filtering treatment by the analog amplification and adjustment circuit and the low-pass filter circuit, the analog voltage is compared with an input reference value in the PID operation circuit to obtain a difference and perform PID operation, and the output signal is output to the current driving circuit to generate a power feedforward adjustment current which is directly fed into the laser emission module to realize closed-loop control of the optical power. The scheme basically does not consume the laser power of the main light path, has simple structure and small volume, and can effectively solve the problem of excessively low power adjustment bandwidth. The technology can better meet the requirements of a cold atom interferometer on the laser in actual application.

Description

Technical Field

[0001] This invention relates to the field of laser control technology, and more specifically to a power feedforward control device for a high-power single-frequency laser. Background Technology

[0002] After years of development, recent research has shown that, compared with traditional technologies, cold atom interferometers based on atomic matter waves have demonstrated significant advantages in fields such as high-precision inertial measurement and gravity measurement. Various precision instruments for acceleration and angular velocity measurement have been gradually developed, including atomic gravimeters, atomic gravity gradiometers, and atomic gyroscopes.

[0003] Cold atom interferometers utilize highly stable single-frequency lasers to manipulate atoms, and the single-frequency laser is the core component of the cold atom interferometer. The long-term stability of the single-frequency laser's frequency and power directly affects the performance indicators of the cold atom interferometer, and improving the stability of the laser's frequency and power has always been an important research goal for major research institutions and commercial companies.

[0004] Currently, the technologies for controlling laser power are mainly divided into two categories.

[0005] One type is internal control technology. This technology is mostly used in low-power lasers. It mainly controls the laser power by controlling various factors affecting laser emission (laser tube drive current, temperature, etc.). Some organizations also use a photodetector (PD) to detect the optical power after laser output, calculate the error between the current value and the target setting value, generate a power adjustment control signal, and then add this signal to the current setting signal of the constant current source. This allows the adjustment signal and the current setting signal to work together to control the laser tube drive current, forming a closed-loop control. However, the power adjustment signal being too early in the process limits the current adjustment bandwidth.

[0006] The advantages of internal control technology are its simple structure and lack of laser power attenuation. The disadvantages are: 1) The method of separately controlling the laser drive current and temperature is open-loop control, which cannot handle laser intensity noise, resulting in low laser power control performance, only reaching the 1% level; 2) The PD detection and adjustment scheme is not suitable for lasers requiring frequency stabilization, as adjusting the seed source current simultaneously causes wavelength changes, failing to meet the needs of cold atom interferometers; 3) The PD detection and adjustment scheme adds the adjustment signal to the drive current setting signal, and the adjustment signal feed point is too early, limiting the adjustment bandwidth. The noise of the single-frequency laser drive current used in cold atom interferometers has a significant impact on laser performance. Electrical design should minimize the bandwidth of the laser drive current setting signal and subsequent drive current to reduce noise. A feed point that is too early will limit the bandwidth of the power adjustment current, making this method only suitable for suppressing laser power drift caused by temperature changes, and the adjustment bandwidth often only reaches the 10Hz level.

[0007] Another type is external control technology. This technology is mostly used in high-power lasers. Various electrically tunable modulators, such as acousto-optic modulators (AOM), electro-optic modulators (EOM), or optical attenuators (VOA), are added to the main laser output path. A coupler is used to split the beam and generate detection light. A photodetector (PD) detects the optical power, and a PID controller adjusts the attenuation value of the modulators in the optical path to dynamically attenuate the main optical path power, forming a closed-loop control of the optical power. This method can achieve relatively stable power control, with reported control accuracy reaching the 0.1% level. The disadvantages are that it requires a large number of external optical components, resulting in a complex structure, high cost, and the consumption of some laser power during power adjustment, leading to significant power loss.

[0008] The current state of technology makes it impossible for single-frequency lasers to meet the requirements of size, cost, output power, and stability, thus limiting the performance improvement of cold atom interferometers. Summary of the Invention

[0009] Existing single-frequency lasers, when used in systems such as cold atom gravimeters, cannot simultaneously meet the requirements of structural simplicity, small size, output power, and stability, thus limiting further performance improvements in certain application scenarios. To address this issue, this invention provides a novel power feedforward control technology for high-power single-frequency lasers. This technology combines the advantages of traditional internal and external control techniques, featuring a simple structure, a wide laser power adjustment range, and high bandwidth, thus better meeting the practical application needs of cold atom interferometer systems.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A power feedforward control device for a high-power single-frequency laser includes: a beam splitting module, a photodetector, an analog amplification and adjustment circuit, a low-pass filter circuit, a PID calculation circuit, and a current driving circuit. The beam splitting module splits the high-power laser output from the laser emitting module into a detection beam, which is then fed into the photodetector to generate an analog voltage. After amplification, adjustment, and filtering by the analog amplification and adjustment circuit and the low-pass filter circuit, the voltage is compared with the input reference value in the PID calculation circuit, and the difference is calculated. The PID calculation is then performed, and the output signal is sent to the current driving circuit to generate a power feedforward adjustment current that is directly fed into the laser emitting module, thereby realizing closed-loop control of the optical power.

[0011] Unlike traditional internal control techniques that directly add the adjustment signal to the constant current source setting signal, this invention addresses the problem of insufficient laser power adjustment bandwidth by moving the power adjustment current feed point to the optical amplifier. The analog adjustment signal output after PID calculation generates a drive current with a certain driving capability through the drive circuit, which is directly fed into the laser emission module, thus improving the bandwidth of the power adjustment current.

[0012] Furthermore, the laser emission module includes a single-frequency laser seed source and an optical amplifier. The seed source generates low-power seed light which is injected into the optical amplifier to output high-power laser light. The power feedforward adjustment current generated by the current driving circuit is fed into the optical amplifier.

[0013] Furthermore, the beam splitting module is implemented using a combination structure of a half-wave plate and a polarizing beam splitter prism.

[0014] Furthermore, the photodetector includes a transimpedance amplifier for converting the output current of the photodetector into an output voltage, the transimpedance amplifier being constructed using an operational amplifier.

[0015] Furthermore, the low-pass filter circuit uses a passive filter to filter the analog voltage signal output by the photodetector.

[0016] Furthermore, the current drive circuit includes a reference adjustment circuit and a push-pull current drive circuit; the reference adjustment circuit processes the voltage signal calculated by the PID calculation circuit and adjusts the reference point to the drive power supply of the subsequent push-pull drive circuit.

[0017] Furthermore, the reference adjustment circuit is implemented using an adder circuit.

[0018] Furthermore, the push-pull current drive circuit is implemented based on two back-to-back current sources.

[0019] Furthermore, the push-pull current drive circuit includes an NMOS transistor and a PMOS transistor; when DRV_VCC is a negative voltage, the source of the NMOS transistor is connected to DRV_VCC through resistor R1, and the source of the PMOS transistor is grounded through resistor R2; when DRV_VCC is a positive voltage, the source of the NMOS transistor is grounded through resistor R1, and the source of the PMOS transistor is connected to DRV_VCC through resistor R2.

[0020] The beneficial effects of this invention are as follows: This invention proposes a novel power feedforward control technology for high-power single-frequency lasers used in cold atom interferometers. This technology consumes virtually no laser power in the main optical path, has a simple structure, and is small in size; it effectively solves the problem of excessively low power adjustment bandwidth. This technology can better meet the requirements of cold atom interferometers for lasers in practical applications. Attached Figure Description

[0021] Figure 1 A schematic diagram of a power feedforward control device for a high-power single-frequency laser provided in an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the current driving circuit structure provided in an embodiment of the present invention.

[0023] The attached diagram lists the components represented by each number as follows:

[0024] 1. Single-frequency laser seed source; 2. Optical amplifier; 3. Beam splitter module; 4. Photodetector; 5. Analog amplification and adjustment circuit; 6. Low-pass filter circuit; 7. PID calculation circuit; 8. Current drive circuit; 9. Amplifier tube driving constant current source; 11. Reference adjustment circuit; 12. Push-pull current drive circuit. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0027] In the description of this application, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the invention can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the invention with unnecessary detail. Therefore, the invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0028] like Figure 1As shown, this embodiment of the invention provides a power feedforward control device for a high-power single-frequency laser, including: a beam splitting module 3, a photodetector 4, an analog amplification and adjustment circuit 5, a low-pass filter circuit 6, a PID calculation circuit 7, and a current driving circuit 8. The beam splitting module splits the high-power laser output from the laser emitting module into a detection beam, which is then fed into the photodetector to generate an analog voltage. After amplification, adjustment, and filtering by the analog amplification and adjustment circuit and the low-pass filter circuit, the voltage is compared with the input reference value in the PID calculation circuit, and the difference is calculated. The PID calculation is then performed, and the output signal is sent to the current driving circuit to generate a power feedforward adjustment current that is directly fed into the laser emitting module, thereby realizing closed-loop control of the optical power.

[0029] The laser emitting module is a high-power laser, employing a two-stage MOPA structure, such as... Figure 1 Seed source 1 generates low-power seed light, which is injected into optical amplifier 2 to output high-power laser light. The power feedforward adjustment current generated by the current drive circuit 8 is fed into optical amplifier 2 to achieve closed-loop control of optical power.

[0030] The beam splitting module 3 can be implemented using a combination of a common half-wave plate and a polarizing beam splitter prism. Optionally, an optical coupler or a beam splitter flat plate can be used for beam splitting. When selecting, it is important to ensure that the polarization stability is at least higher than the output power stability requirement. The detected optical power should be able to match the input requirements of the subsequent PD tube. In this embodiment, a combination of a common half-wave plate and a polarizing beam splitter prism is used.

[0031] The photodetector (PD tube) can be a common photodetector. Attention should be paid to the operating wavelength and response sensitivity of the PD tube, and the gain of the transimpedance amplifier should be adjusted as needed. The dark current of the PD tube should be much lower than the detection photocurrent and fluctuation value incident on the PD tube under operating conditions, and the response characteristics should meet the requirements of the subsequent transimpedance amplifier.

[0032] An operational amplifier is used to build a transimpedance amplifier, converting the current of the PD transistor into the output voltage. When selecting an operational amplifier, the bias current and bias current temperature drift should be the primary considerations. The bias current should be significantly lower than the current generated by the PD transistor during normal operation. The gain-bandwidth product of the operational amplifier should also be taken into account to ensure that the gain of the transimpedance amplifier circuit meets the bandwidth requirements.

[0033] The low-pass filter circuit uses a passive filter to filter the analog voltage signal output by the photodetector. Optionally, an active filter built with an operational amplifier can be used instead of the passive filter.

[0034] In this embodiment, a high-resolution analog-to-digital converter (ADC) chip, FPGA or MCU, or digital-to-analog converter (DAC) chip can be selected to implement PID calculation. Alternatively, an analog PID circuit built with an operational amplifier can be used, or a purchased functional module can be employed.

[0035] In this embodiment, the current drive circuit includes a reference adjustment circuit and a push-pull current drive circuit; the reference adjustment circuit processes the voltage signal calculated by the PID calculation circuit and adjusts the reference point to the drive power supply of the subsequent push-pull drive circuit. This function can be implemented using an adder circuit or a similar circuit.

[0036] The push-pull drive circuit actually consists of two back-to-back current sources, each composed of an NMOS and a PMOS or similar functional transistor. This embodiment uses one NMOS and one PMOS. A schematic diagram of the current drive circuit structure is shown below. Figure 2 As shown.

[0037] In this example, DRV_VCC is a negative voltage, and its absolute value should be lower than the threshold voltage of the laser amplifier tube. When the Vin voltage is greater than 0, the NMOS tube is off and the PMOS tube is on. If the resistor values ​​configured in the operational amplifier are equal, the Iout current is determined by Vin and R2, and the current flows out. When the Vin voltage is less than 0, the PMOS is off and the NMOS is on. In this case, the Iout current is determined by Vin and R1, and the current flows in. Iout is directly connected to the current terminal of the laser amplifier tube, which allows for positive and negative current adjustment. The maximum value of Iout is approximately determined by the ratio of the difference between the DRV_VCC voltage and the amplifier tube's threshold voltage to either R1 or R2.

[0038] Optionally, resistors R1 and R2 can be smaller current sampling resistors, which are then amplified by an amplifier and adjusted to the reference point before being fed into the corresponding operational amplifier.

[0039] Optionally, if DRV_VCC is positive, the direction of the reference circuit and the two MOSFETs can be changed to make the circuit work normally.

[0040] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0041] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A power feedforward control device for a high-power single-frequency laser, characterized in that, include: The laser emission module comprises a beam splitter, a photodetector, an analog amplification and adjustment circuit, a low-pass filter circuit, a PID calculation circuit, and a current drive circuit. The laser emission module includes a single-frequency laser seed source and an optical amplifier. The seed source generates low-power seed light which is injected into the optical amplifier to output high-power laser light. The beam splitter separates the high-power laser light from the laser emission module and sends it to the photodetector to generate an analog voltage. After amplification, adjustment, and filtering by the analog amplification and adjustment circuit and the low-pass filter circuit, the voltage is compared with the input reference value in the PID calculation circuit, and a PID calculation is performed. The output signal is then sent to the current drive circuit. The laser emission module has a two-stage MOPA structure. The current drive circuit includes a reference adjustment circuit and a push-pull current drive circuit. The reference adjustment circuit processes the voltage signal after the PID calculation circuit and adjusts the reference point to the drive power supply of the subsequent push-pull current drive circuit. The push-pull current drive circuit is based on two back-to-back current sources, including an NMOS transistor and a PMOS transistor. The generated power feedforward adjustment current is directly fed into the current terminal of the amplification transistor in the optical amplifier, achieving closed-loop control of the optical power.

2. The power feedforward control device for a high-power single-frequency laser according to claim 1, characterized in that, The beam splitting module is implemented using a combination of a half-wave plate and a polarizing beam splitter prism.

3. The power feedforward control device for a high-power single-frequency laser according to claim 1, characterized in that, The photodetector includes a transimpedance amplifier for converting the output current of the photodetector into an output voltage, and the transimpedance amplifier is constructed using an operational amplifier.

4. The power feedforward control device for a high-power single-frequency laser according to claim 1, characterized in that, The low-pass filter circuit uses a passive filter to filter the analog voltage signal output by the photodetector.

5. The power feedforward control device for a high-power single-frequency laser according to claim 1, characterized in that, The reference adjustment circuit is implemented using an adder circuit.

6. The power feedforward control device for a high-power single-frequency laser according to claim 1, characterized in that, When DRV_VCC is negative, the source of the NMOS transistor is connected to DRV_VCC through resistor R1, and the source of the PMOS transistor is grounded through resistor R2; when DRV_VCC is positive, the source of the NMOS transistor is grounded through resistor R1, and the source of the PMOS transistor is connected to DRV_VCC through resistor R2.

Images