External cavity tunable semiconductor laser and method for synchronous output of uniform wave number thereof

Abstract

The application provides an external cavity tuning semiconductor laser and a uniform wave number synchronous output method thereof, rapid and accurate modulation of the angle of a feedback light beam is realized through rapid deflection of an optical galvanometer, and the method specifically comprises the following steps: synchronously collecting the deflection angle of the optical galvanometer and the instantaneous output spectrum, accurately calculating the center wavelength of each sampling point by using a Gaussian fitting method, converting the center wavelength to the wave number domain for uniform processing, and obtaining the optimized driving curve of the deflection angle of the optical galvanometer changing with time through reverse calculation, so that the laser is finally synchronously and rapidly output according to the uniform wave number; the application can effectively overcome the deficiencies of traditional motor driving or piezoelectric ceramics in terms of precision, tuning speed and scanning stroke, significantly reduce the hardware cost of the core component, and has a wide application in the scenes of coherent tomography, high-resolution spectral analysis and precise laser radar.

Description

Technical Field

[0001] This invention relates to the field of semiconductor lasers and tunable laser technology, and in particular to external cavity tunable semiconductor lasers and their uniform wavenumber synchronous output method. Background Technology

[0002] Lasers have crucial applications in atomic physics, high-resolution spectroscopy, coherent optical communication, and lidar. These fields all require laser output light to be tunable to one or more specific wavelengths. Therefore, tunable semiconductor lasers with excellent output characteristics have become indispensable optical devices. Monolithic integrated lasers, such as distributed feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers, and vertical-cavity surface-emitting lasers (VCSELs), achieve wavelength tunability through temperature or current, with a tuning range of only a few nanometers and no continuous tuning. Tunable external cavity semiconductor lasers (ECDLs) avoid these problems by achieving tunability through tuning optical elements in the external cavity. The maximum continuous tunable range can reach tens of nanometers, while simultaneously achieving narrow linewidth output.

[0003] An external cavity semiconductor laser mainly consists of three parts: a gain chip, a collimating mirror, and an optical feedback element. The external optical feedback element acts as a frequency selection unit, selecting the mode of the output light from the gain chip and achieving optical feedback. Only light meeting the conditions returns to the active region and couples with the internal optical field. Simultaneously, the modulation feedback element changes the mode selection conditions of the feedback light, thus achieving narrow linewidth and wide tunability of the optical output. A planar grating is a widely used optical feedback element, possessing a wide wavelength tuning range, high spectral resolution, and enabling fine tuning. External cavity semiconductor lasers based on planar reflective grating structures have two typical structures: the Littrow structure and the Littman structure. The Littrow structure is simple; after collimated light is incident on the grating, tunability is achieved by changing the angle of the grating relative to the resonant cavity, allowing for a wide tuning range and high output power. Compared to the Littrow structure, the Littman structure adds a mirror, making it more complex. The collimated light undergoes diffraction through the grating, and the first-order diffracted light is reflected by the mirror before being fed back to the gain chip. The beam undergoes two diffractions within the resonant cavity, resulting in a narrower linewidth. Furthermore, the Littman structure allows for tunability of the light by changing the angle of the mirrors; the output light direction of the external cavity structure is fixed, eliminating the need for an additional beam compensator. Existing Littman devices commonly use mechanical motors and piezoelectric ceramics to drive the mirrors, but these suffer from low accuracy, slow tuning speed, and insufficient travel when tuning over a wide wavelength range. Summary of the Invention

[0004] This invention proposes an external cavity tuned semiconductor laser and its method for synchronous output of uniform wavenumber, which can effectively overcome the shortcomings of traditional motor drive or piezoelectric ceramics in terms of accuracy, tuning speed and scanning stroke, and significantly reduce the hardware cost of core components. It has wide applications in scenarios such as coherence tomography, high-resolution spectral analysis and precision lidar.

[0005] The present invention adopts the following technical solution.

[0006] A method for uniform wavenumber synchronous output of an external cavity tuned semiconductor laser is disclosed. The method achieves rapid and precise modulation of the feedback beam angle through the rapid deflection of an optical mirror. Specifically, the method involves synchronously acquiring the optical mirror deflection angle and the instantaneous output spectrum, accurately determining the center wavelength of each sampling point using Gaussian fitting, converting it to the wavenumber domain for homogenization, and obtaining the optimized driving curve of the optical mirror angle changing with time through inverse calculation. Finally, the laser achieves uniform synchronous and rapid output according to the wavenumber.

[0007] An external cavity tuned semiconductor laser, using the above-described method for uniform wavenumber synchronous output of an external cavity tuned semiconductor laser, is characterized in that: the laser is a Littman-type external cavity tuned semiconductor laser employing a gain chip, and its external cavity structure adopts a Littman-Metcalf configuration, utilizing the dispersion capability of a grating for frequency selection;

[0008] The laser includes a gain chip, a laser mounting base, a collimating lens, a planar diffraction grating, an optical galvanometer, a focusing lens, a five-axis optical adjustment frame, a fiber optic connector, and an optical output and monitoring module. It also includes a host computer for controlling the laser. The laser mounting base consists of an electrical interface, a thermistor, and a semiconductor cooling chip. The optical output and monitoring module includes a 99:1 1-to-2 fiber optic splitter and a photoresistor sensor.

[0009] The zero-order diffracted light from the planar grating is coupled to the fiber optic connector through a focusing lens and input to the light output and monitoring module. The five-axis optical adjustment frame is used to adjust the relative pose between the focusing lens and the fiber optic connector so that the fiber optic connector is located at the focal point of the focusing lens and parallel to the lens, thereby reducing power loss when free space light is coupled to the fiber.

[0010] When the laser's optical path structure is working, the broadband light output from the gain chip is collimated by a collimating lens and then incident on a planar diffraction grating at a specific incident angle (e.g., near grazing incidence or Brewster's angle), resulting in the first diffraction. To ensure high-precision spectral purity, the planar diffraction grating is a holographic grating or a defined grating with a grating constant ranging from 600 lines / mm to 1800 lines / mm, balancing dispersion capability and diffraction efficiency. The zero-order diffracted light from the first diffraction serves as the laser's effective output light and is coupled into an optical fiber via the optical output and monitoring module.

[0011] The laser wavelength is controlled by feedback light formed by the reflection of first-order diffracted light through an optical mirror.

[0012] When the laser wavelength is controlled by the feedback light formed by the reflection of the first-order diffracted light through the optical mirror, the synchronous logic signal of the laser excitation is extracted in real time by combining the 99:1 fiber optic splitter and the photosensitive sensor. The host computer controls the rotation of the optical mirror to change the relative angle between the mirror lens and the diffraction grating.

[0013] Since optical galvanometers are electromechanical actuators, they have a certain mechanical inertia and response lag. The mechanical inertia and response lag of optical galvanometers are compensated by limiting the dynamic response parameters of the galvanometer and using a specific homogenization algorithm.

[0014] The excitation wavelength of the gain chip satisfies the following formula:

[0015] Formula 1;

[0016] in For the effective cavity length, It is a positive integer. For wavelength, The grating constant is The angle between the incident light and the grating. This is the relative angle between the optical galvanometer and the grating;

[0017] The laser output linewidth is expressed by the following formula:

[0018] Formula 2;

[0019] in For the linewidth of the external cavity laser, To increase the chip linewidth, The linewidth broadening factor. For phase matching factor, The reflectivity of the rear end face of the laser resonator. This represents the first-order diffraction efficiency of the diffraction grating. It is the length of the laser's internal cavity.

[0020] The method for outputting a synchronization signal from the laser is as follows: In the optical output and monitoring module, the optical fiber splitter is a 99:1 one-to-two optical fiber splitter. The optical fiber splitter is connected to an optical fiber connector. The input light is split into two paths. In one path, the splitter output with 1% intensity is directed to the photoresistor sensor as the laser status monitoring light. In the other path, the splitter output with 99% intensity is used as the laser output light.

[0021] The light intensity of a laser differs drastically between its excited and unexcited states, typically by more than three orders of magnitude. The optical galvanometer is rotated twice to put the laser into both excited and unexcited states, and the light intensity is then collected by a photoresistor sensor.

[0022] By adjusting the output threshold of the photoresistor sensor, the photoresistor sensor outputs a high level when the laser is excited and a low level when it is in the unexcited state. The output of the photoresistor is the synchronous output signal of the laser.

[0023] The method for uniform output of the laser wavenumber is as follows: control the optical galvanometer to rotate at a fixed speed so that the laser is continuously tuned and outputs light with the wavelength range covering the entire tuning band. The output light is input into a spectrometer or other spectral information detector, and the rotation angle of the galvanometer and the corresponding output spectrum are synchronously acquired through a synchronous output signal.

[0024] The center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, thus obtaining the laser wavelength output curve corresponding to the mirror rotation angle; that is, the actual wavenumber output curve.

[0025] The actual wavenumber output curve is homogenized, and the mirror angle corresponding to each sampling point during homogenization is calculated in reverse to obtain the mirror angle change curve.

[0026] By adjusting the rotation speed of the galvanometer, the galvanometer angle can be made to change non-linearly according to the curve, thereby achieving uniform wavenumber output of the laser.

[0027] In the wavenumber uniform output method, the Gaussian fitting method involves the following steps: Based on the spectral data, set a Gaussian function with a constant background and initial estimation parameters. The formula for the Gaussian function with background is as follows:

[0028] Formula 3;

[0029] in The peak signal strength, The center wavelength, Standard deviation It is a constant;

[0030] Then, by nonlinear least squares fitting, the values ​​of each parameter are obtained when the sum of squared residuals is minimized, and the center wavelength of the above spectral data is obtained.

[0031] Repeat the above steps to obtain the center wavelength of the spectral data corresponding to each rotation angle, and obtain the laser wavelength output curve corresponding to the galvanometer rotation angle;

[0032] Next, the wavelength output curve is converted to the wavenumber domain. The relationship between wavelength and wavenumber is as follows:

[0033] Formula 4;

[0034] in Wave number;

[0035] Substituting Equation 4 into Equation 1, we obtain the relationship between the laser output wavenumber and the galvanometer angle, expressed as: Formula 5.

[0036] Based on the above formula, it can be concluded that the output wavenumber of the laser has a non-linear relationship with the change of the galvanometer angle.

[0037] The wavenumber uniform output method also includes: first controlling the optical galvanometer to perform a full-range scan with a constant voltage change rate, so that the laser is continuously tuned and output, and the output light is input to a spectrometer or other spectral information detector, and synchronous acquisition is triggered by a photosensitive sensor; the output results at different wavelengths are as follows: Figure 4 As shown. Record the original driving curve of "time-mirror rotation angle";

[0038] Then, the center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, and the original "time-laser output wavelength" curve is obtained; the wavelength output curve is converted to the wavenumber domain, and the wavenumber curve is linearized by interpolation.

[0039] Then, through reverse mapping, the "time-angle drive curve" required to obtain linear wavenumber output is calculated; the optimized curve is used to generate a drive signal and the drive signal is applied to the optical galvanometer to adjust the optical galvanometer's operating conditions.

[0040] This curve not only corrects the geometric nonlinearity of the grating equation but also implicitly compensates for the mechanical hysteresis of the system at the current scanning speed. As long as the galvanometer operates within the defined linear region and bandwidth, this feedforward control method can achieve high-precision uniform wavenumber synchronization output without the need for real-time mechanical position closed-loop feedback, greatly reducing system complexity and cost. Figure 5 This is a comparison diagram of the galvanometer drive angle before and after uniform wavenumber output. Figure 6 This is a comparison chart of the laser output wavelength before and after uniform wavenumber output. Figure 7 This is a comparison chart of the laser output wavenumber before and after uniform wavenumber output.

[0041] The optical galvanometer is a high-performance closed-loop galvanometer scanning galvanometer with an integrated position sensor, providing position repeatability accuracy at the micro-radian level. To match the speed of the electronic signal in the spectral sampling and reduce nonlinear errors caused by mechanical hysteresis, the small-angle step response time of the optical galvanometer is less than 300 Å, and the closed-loop bandwidth is greater than 1 kHz.

[0042] The high bandwidth ensures that the galvanometer can quickly respond to minute changes in the driving voltage, reducing hysteresis at the hardware level. Through geometric optical path calculations, the effective mechanical deflection angle range of the galvanometer is limited to within ±5° (corresponding to an angle variation of 12.23°~14.17° in this embodiment). A smaller deflection angle helps the galvanometer operate in the region of highest linearity, further improving the accuracy of wavelength control.

[0043] This invention relates to the field of laser tuning and precision optical control, specifically providing a Littman-type external cavity tuned semiconductor laser using optical mirror tuning and its uniform wavenumber synchronous output method. This method uses a Littman external cavity tuning structure as its core, employs a gain chip, and achieves rapid and precise modulation of the feedback beam angle through the rapid deflection of the optical mirror. In terms of optical path structure, diffraction is achieved through a planar diffraction grating. The feedback light formed by the reflection of the first-order diffracted light by the mirror controls the laser wavelength, while the zero-order diffracted light serves as the output light. A 99:1 fiber optic splitter and a photosensitive sensor are used to extract the synchronization logic signal of the laser excitation in real time. At the algorithm processing level, the system synchronously acquires the mirror deflection angle and instantaneous output spectrum, accurately calculates the center wavelength of each sampling point using Gaussian fitting, converts it to the wavenumber domain for homogenization, and obtains the optimized driving curve of the mirror angle changing over time through inverse calculation, ultimately achieving uniform and rapid synchronous output of the laser according to the wavenumber. The laser can effectively overcome the shortcomings of traditional motor drives or piezoelectric ceramics in terms of accuracy, tuning speed and scanning stroke, significantly reducing the hardware cost of core components, and has wide applications in scenarios such as coherence tomography, high-resolution spectral analysis and precision lidar.

[0044] The Littman-type external cavity tuned semiconductor laser and its uniform wavenumber synchronous output method provided by this invention have the following advantages:

[0045] 1. To address the shortcomings of traditional Littman structure external cavity tuned semiconductor lasers, such as slow tuning speed, small tuning range, and high cost in different wavelength tuning mechanisms, this solution innovatively uses an optical galvanometer as the tuning mechanism for the Littman structure external cavity tuned semiconductor laser, achieving high-speed tuning output over a wide range at low cost.

[0046] 2. To improve the synchronization of the laser in measurement, processing, and other applications, this solution innovatively incorporates a light output and monitoring module, enabling synchronized output from the laser and other devices. This module also offers the advantage of low cost.

[0047] 3. The original wavenumber output curve of the laser was measured by combining the Gaussian fitting method, and the rotation angle curve of the galvanometer when the laser outputs a uniform wavenumber was calculated, so as to achieve uniform wavelength output of the laser. Attached Figure Description

[0048] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0049] Appendix Figure 1 A schematic diagram of a Littman-type external cavity tuned semiconductor laser tuned using optical galvanometers;

[0050] Appendix Figure 2 A schematic diagram of the laser mounting bracket structure;

[0051] Appendix Figure 3 This is a schematic diagram of a Littman-type external cavity tuned semiconductor laser tuned using optical galvanometers.

[0052] Appendix Figure 4 This is a schematic diagram of the output spectrum of a laser built using a gain chip with a wavelength range of 780 nm to 820 nm at different wavelengths in an embodiment of the present invention.

[0053] Appendix Figure 5 A schematic diagram comparing the mirror drive angles before and after uniform wavenumber output;

[0054] Appendix Figure 6 A schematic diagram comparing the output wavelength of the laser before and after uniform wavenumber output;

[0055] Appendix Figure 7 A schematic diagram comparing the output wavenumbers of the laser before and after uniform wavenumber output;

[0056] In the diagram: 1 is the laser mounting base, 2 is the gain chip, 3 is the collimating lens, 4 is the plane diffraction grating, 5 is the optical galvanometer, 6 is the focusing lens, 7 is the five-axis optical adjustment frame, and 8 is the fiber optic connector.

[0057] 9 is a 99:1 fiber optic splitter, 10 is a laser output connector, and 11 is a photoresistor sensor.

[0058] a1 is the electrical interface of the gain chip, a2 is the semiconductor cooling chip, and a3 is the thermistor. Detailed Implementation

[0059] As shown in the figure, a method for uniform wavenumber synchronous output of an external cavity tuned semiconductor laser is described. This method achieves rapid and precise modulation of the feedback beam angle through the rapid deflection of an optical mirror. Specifically, the method involves synchronously acquiring the optical mirror deflection angle and the instantaneous output spectrum, accurately determining the center wavelength of each sampling point using Gaussian fitting, converting it to the wavenumber domain for homogenization, and obtaining the optimized driving curve of the optical mirror angle changing with time through inverse calculation. Ultimately, this achieves uniform synchronous and rapid output of the laser according to the wavenumber.

[0060] An external cavity tuned semiconductor laser, using the above-described method for uniform wavenumber synchronous output of an external cavity tuned semiconductor laser, is characterized in that: the laser is a Littman-type external cavity tuned semiconductor laser employing a gain chip, and its external cavity structure adopts a Littman-Metcalf configuration, utilizing the dispersion capability of a grating for frequency selection;

[0061] The laser includes a gain chip 2, a laser mounting base 1, a collimating lens 3, a planar diffraction grating 4, an optical galvanometer 5, a focusing lens 6, a five-axis optical adjustment frame 7, an optical fiber connector 8, and an optical output and monitoring module. It also includes a host computer for controlling the laser. The laser mounting base consists of an electrical interface, a thermistor, and a semiconductor cooling chip. The optical output and monitoring module includes a 99:1 1-to-2 fiber optic splitter 9 and a photoresistor sensor 11.

[0062] The zero-order diffracted light from the planar grating is coupled to the fiber optic connector through a focusing lens and input to the light output and monitoring module. The five-axis optical adjustment frame is used to adjust the relative pose between the focusing lens and the fiber optic connector so that the fiber optic connector is located at the focal point of the focusing lens and parallel to the lens, thereby reducing power loss when free space light is coupled to the fiber.

[0063] When the laser's optical path structure is working, the broadband light output from the gain chip is collimated by a collimating lens and then incident on a planar diffraction grating at a specific incident angle (e.g., near grazing incidence or Brewster's angle), resulting in the first diffraction. To ensure high-precision spectral purity, the planar diffraction grating is a holographic grating or a defined grating with a grating constant ranging from 600 lines / mm to 1800 lines / mm, balancing dispersion capability and diffraction efficiency. The zero-order diffracted light from the first diffraction serves as the laser's effective output light and is coupled into an optical fiber via the optical output and monitoring module.

[0064] The laser wavelength is controlled by feedback light formed by the reflection of first-order diffracted light through an optical mirror.

[0065] When the laser wavelength is controlled by the feedback light formed by the reflection of the first-order diffracted light through the optical mirror, the synchronous logic signal of the laser excitation is extracted in real time by combining the 99:1 fiber optic splitter and the photosensitive sensor. The host computer controls the rotation of the optical mirror to change the relative angle between the mirror lens and the diffraction grating.

[0066] Since optical galvanometers are electromechanical actuators, they have a certain mechanical inertia and response lag. The mechanical inertia and response lag of optical galvanometers are compensated by limiting the dynamic response parameters of the galvanometer and using a specific homogenization algorithm.

[0067] The excitation wavelength of the gain chip satisfies the following formula:

[0068] Formula 1;

[0069] in For the effective cavity length, It is a positive integer. For wavelength, The grating constant is The angle between the incident light and the grating. This is the relative angle between the optical galvanometer and the grating;

[0070] The laser output linewidth is expressed by the following formula:

[0071] Formula 2;

[0072] in For the linewidth of the external cavity laser, To increase the chip linewidth, The linewidth broadening factor. For phase matching factor, The reflectivity of the rear end face of the laser resonator. This represents the first-order diffraction efficiency of the diffraction grating. It is the length of the laser's internal cavity.

[0073] The method for outputting a synchronization signal from the laser is as follows: In the optical output and monitoring module, the optical fiber splitter is a 99:1 one-to-two optical fiber splitter. The optical fiber splitter is connected to an optical fiber connector. The input light is split into two paths. In one path, the splitter output with 1% intensity is directed to the photoresistor sensor as the laser status monitoring light. In the other path, the splitter output with 99% intensity is used as the laser output light.

[0074] The light intensity of a laser differs drastically between its excited and unexcited states, typically by more than three orders of magnitude. The optical galvanometer is rotated twice to put the laser into both excited and unexcited states, and the light intensity is then collected by a photoresistor sensor.

[0075] By adjusting the output threshold of the photoresistor sensor, the photoresistor sensor outputs a high level when the laser is excited and a low level when it is in the unexcited state. The output of the photoresistor is the synchronous output signal of the laser.

[0076] The method for uniform output of the laser wavenumber is as follows: control the optical galvanometer to rotate at a fixed speed so that the laser is continuously tuned and outputs light with the wavelength range covering the entire tuning band. The output light is input into a spectrometer or other spectral information detector, and the rotation angle of the galvanometer and the corresponding output spectrum are synchronously acquired through a synchronous output signal.

[0077] The center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, thus obtaining the laser wavelength output curve corresponding to the mirror rotation angle; that is, the actual wavenumber output curve.

[0078] The actual wavenumber output curve is homogenized, and the mirror angle corresponding to each sampling point during homogenization is calculated in reverse to obtain the mirror angle change curve.

[0079] By adjusting the rotation speed of the galvanometer, the galvanometer angle can be made to change non-linearly according to the curve, thereby achieving uniform wavenumber output of the laser.

[0080] In the wavenumber uniform output method, the Gaussian fitting method involves the following steps: Based on the spectral data, set a Gaussian function with a constant background and initial estimation parameters. The formula for the Gaussian function with background is as follows:

[0081] Formula 3;

[0082] in The peak signal strength, The center wavelength, Standard deviation It is a constant;

[0083] Then, by nonlinear least squares fitting, the values ​​of each parameter are obtained when the sum of squared residuals is minimized, and the center wavelength of the above spectral data is obtained.

[0084] Repeat the above steps to obtain the center wavelength of the spectral data corresponding to each rotation angle, and obtain the laser wavelength output curve corresponding to the galvanometer rotation angle;

[0085] Next, the wavelength output curve is converted to the wavenumber domain. The relationship between wavelength and wavenumber is as follows:

[0086] Formula 4;

[0087] in Wave number;

[0088] Substituting Equation 4 into Equation 1, we obtain the relationship between the laser output wavenumber and the galvanometer angle, expressed as: Formula 5.

[0089] Based on the above formula, it can be concluded that the output wavenumber of the laser has a non-linear relationship with the change of the galvanometer angle.

[0090] The wavenumber uniform output method also includes: first controlling the optical galvanometer to perform a full-range scan with a constant voltage change rate, so that the laser is continuously tuned and output, and the output light is input to a spectrometer or other spectral information detector, and synchronous acquisition is triggered by a photosensitive sensor; the output results at different wavelengths are as follows: Figure 4As shown. Record the original driving curve of "time-mirror rotation angle";

[0091] Then, the center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, and the original "time-laser output wavelength" curve is obtained; the wavelength output curve is converted to the wavenumber domain, and the wavenumber curve is linearized by interpolation.

[0092] Then, through reverse mapping, the "time-angle drive curve" required to obtain linear wavenumber output is calculated; the optimized curve is used to generate a drive signal and the drive signal is applied to the optical galvanometer to adjust the optical galvanometer's operating conditions.

[0093] This curve not only corrects the geometric nonlinearity of the grating equation but also implicitly compensates for the mechanical hysteresis of the system at the current scanning speed. As long as the galvanometer operates within the defined linear region and bandwidth, this feedforward control method can achieve high-precision uniform wavenumber synchronization output without the need for real-time mechanical position closed-loop feedback, greatly reducing system complexity and cost. Figure 5 This is a comparison diagram of the galvanometer drive angle before and after uniform wavenumber output. Figure 6 This is a comparison chart of the laser output wavelength before and after uniform wavenumber output. Figure 7 This is a comparison chart of the laser output wavenumber before and after uniform wavenumber output.

[0094] The optical galvanometer is a high-performance closed-loop galvanometer scanning galvanometer with an integrated position sensor, providing position repeatability accuracy at the micro-radian level. To match the speed of the electronic signal in the spectral sampling and reduce nonlinear errors caused by mechanical hysteresis, the small-angle step response time of the optical galvanometer is less than 300 Å, and the closed-loop bandwidth is greater than 1 kHz.

[0095] The high bandwidth ensures that the galvanometer can quickly respond to minute changes in the driving voltage, reducing hysteresis at the hardware level. Through geometric optical path calculations, the effective mechanical deflection angle range of the galvanometer is limited to within ±5° (corresponding to an angle variation of 12.23°~14.17° in this embodiment). A smaller deflection angle helps the galvanometer operate in the region of highest linearity, further improving the accuracy of wavelength control.

[0096] Example:

[0097] Figure 1 This is a schematic diagram of the structure of this embodiment, including a laser mounting base, a gain chip, a collimating lens, a planar diffraction grating, an optical galvanometer, a focusing lens, a five-axis optical adjustment frame, a fiber optic connector, a 99:1 1-to-2 fiber optic splitter, a laser output connector 10, and a photoresistor sensor. The schematic diagram of the laser mounting base is shown below. Figure 2 As shown, it includes a gain chip electrical interface a1, a semiconductor cooling chip a2, and a thermistor a3. Figure 3 This is a physical image of the embodiment.

[0098] In this embodiment, the gain chip has a wavelength range of 780 nm to 820 nm, a maximum operating current of 300 mA, and a maximum operating temperature of 30 °C. Based on the gain chip parameters, the laser mounting base is set to output a constant current of 250 mA. The ambient temperature is collected by a thermistor, and a semiconductor cooling chip controls the ambient temperature to be maintained at 25 °C to ensure long-term stable operation of the laser. The output light from the gain chip is collimated by a collimating lens and then diffracted by a planar diffraction grating. The first-order diffracted light is reflected by an optical mirror to form feedback light, which is fed back to the gain chip. Inside the gain chip, it undergoes multiple reflections and excitations. The optical power in the feedback light band is much greater than in other bands, achieving wavelength frequency selection.

[0099] The planar diffraction grating used in this embodiment has a grating constant of 1200 and achieves the highest diffraction efficiency at an incident angle of 26°. By controlling the collimated light through the collimating lens to be incident at this angle, the angle between the optical galvanometer and the planar diffraction grating when the gain chip is in the excited state is calculated to be 12.23°~14.17° using formula (1).

[0100] In this embodiment, a high-performance closed-loop galvanometer scanning galvanometer is selected as the optical galvanometer. This galvanometer integrates a position sensor and possesses position repeatability accuracy at the microradian level. To match the electronic signal velocity of spectral sampling and reduce nonlinear errors caused by mechanical hysteresis, the small-angle step response time of the galvanometer is limited to less than 300°. The closed-loop bandwidth is greater than 1 kHz. This high bandwidth ensures the galvanometer can quickly respond to minute changes in the driving voltage, reducing hysteresis at the hardware level. Through geometric optical path calculations, the effective mechanical deflection angle range of the galvanometer is limited to within ±5° (corresponding to an angle variation of 12.23° to 14.17° in this embodiment). A smaller deflection angle allows the galvanometer to operate in its highest linearity region, further improving the accuracy of wavelength control.

[0101] The zero-order diffracted light from the planar diffraction grating serves as the output light, which is focused by a focusing lens onto the fiber optic connector and coupled to the laser output and status detection module. A five-axis optical adjustment frame is used to adjust the relative pose of the focusing lens and the fiber optic connector, reducing optical power loss when free-space light couples to the fiber. The output light is split into two beams by a 99:1 fiber optic splitter. 99% intensity light is used as the laser output and outputs through the laser output interface, while 1% intensity light is incident on a photodiode to monitor the laser's excitation state. The optical galvanometer is rotated twice, so that the angle between the optical galvanometer and the planar diffraction grating is once within the excitation angle range and once outside the excitation angle range, respectively putting the gain chip in the excited and unexcited states and acquiring the signal from the photoresistor sensor. The output threshold of the photoresistor sensor is adjusted so that it outputs a high level when the laser is excited and a low level when it is unexcited. The output of the photoresistor is the synchronous output signal of the laser.

[0102] The optical galvanometer is controlled to perform a full-range scan at a constant voltage change rate, allowing the laser to be continuously tuned and output. The output light is then input to a spectrometer or other spectral information detector, where a photosensitive sensor triggers synchronous acquisition. Output results at different wavelengths are shown below. Figure 4 As shown, the original driving curve of "time-mirror rotation angle" is recorded.

[0103] The center wavelength of the output light corresponding to the rotation angle at each sampling point is obtained by Gaussian fitting, resulting in the original "time-laser output wavelength" curve. The wavelength output curve is then transformed to the wavenumber domain, and linear interpolation is performed on the wavenumber curve. Through inverse mapping, the "time-angle drive curve" required to obtain linear wavenumber output is calculated. This optimized curve is then applied as the drive signal to the galvanometer. This curve not only corrects the geometric nonlinearity of the grating equation but also implicitly compensates for the mechanical hysteresis of the system at the current scanning speed. As long as the galvanometer operates within the defined linear region and bandwidth, this feedforward control method can achieve high-precision uniform wavenumber synchronous output without the need for real-time mechanical position closed-loop feedback, significantly reducing system complexity and cost. Figure 5 This is a comparison diagram of the galvanometer drive angle before and after uniform wavenumber output. Figure 6 This is a comparison chart of the laser output wavelength before and after uniform wavenumber output. Figure 7 This is a comparison chart of the laser output wavenumber before and after uniform wavenumber output.

Claims

1. A method for uniform wavenumber synchronous output of an external cavity tuned semiconductor laser, characterized in that: The method modulates the feedback beam angle by rapidly deflecting the optical galvanometer. Specifically, it involves synchronously acquiring the optical galvanometer deflection angle and instantaneous output spectrum, accurately determining the center wavelength of each sampling point using Gaussian fitting, converting it to the wavenumber domain for homogenization, and obtaining the optimized driving curve of the optical galvanometer angle changing with time through reverse calculation, thereby achieving synchronous and rapid output of the laser in a uniform wavenumber manner.

2. An external cavity tuned semiconductor laser, using the uniform wavenumber synchronous output method of the external cavity tuned semiconductor laser as described in claim 1, characterized in that: The laser is a Littman-type external cavity tuned semiconductor laser with a gain chip. Its external cavity structure adopts the Littman-Metcalf configuration and uses the dispersion capability of the grating for frequency selection. The laser includes a gain chip, a laser mounting base, a collimating lens, a planar diffraction grating, an optical galvanometer, a focusing lens, a five-axis optical adjustment frame, a fiber optic connector, and an optical output and monitoring module. It also includes a host computer for controlling the laser. The laser mounting base consists of an electrical interface, a thermistor, and a semiconductor cooling chip. The optical output and monitoring module includes a fiber optic splitter and a photoresistor sensor.

3. The external cavity tuned semiconductor laser according to claim 2, characterized in that: The zero-order diffracted light from the planar grating is coupled to the fiber optic connector through a focusing lens and input to the light output and monitoring module. The five-axis optical adjustment frame is used to adjust the relative pose between the focusing lens and the fiber optic connector so that the fiber optic connector is located at the focal point of the focusing lens and parallel to the lens, thereby reducing power loss when free space light is coupled to the fiber. When the laser's optical path structure is working, the broadband light output from the gain chip is collimated by a collimating lens and then incident on a planar diffraction grating at a specific incident angle, resulting in the first diffraction. The planar diffraction grating is either a holographic grating or a defined grating, with a grating constant ranging from 600 lines / mm to 1800 lines / mm. The zero-order diffracted light from the first diffraction serves as the effective output light of the laser and is coupled into an optical fiber via the optical output and monitoring module. The laser wavelength is controlled by feedback light formed by the reflection of first-order diffracted light through an optical mirror.

4. The external cavity tuned semiconductor laser according to claim 3, characterized in that: When the laser wavelength is controlled by the feedback light formed by the reflection of the first-order diffracted light through the optical mirror, the synchronous logic signal of the laser excitation is extracted in real time by combining the fiber optic splitter and the photosensitive sensor. The host computer controls the rotation of the optical mirror to change the relative angle between the mirror lens and the diffraction grating. The mechanical inertia and response hysteresis of the optical galvanometer are compensated by limiting the dynamic response parameters of the galvanometer and using a specific homogenization algorithm.

5. The external cavity tuned semiconductor laser according to claim 4, characterized in that: The excitation wavelength of the gain chip satisfies the following formula: Official 1; in For the effective cavity length, It is a positive integer. For wavelength, The grating constant is The angle between the incident light and the grating. This is the relative angle between the optical galvanometer and the grating; The laser output linewidth is expressed by the following formula: Official 2; in For the linewidth of the external cavity laser, To increase the chip linewidth, The linewidth broadening factor. For phase matching factor, The reflectivity of the rear end face of the laser resonator. This represents the first-order diffraction efficiency of the diffraction grating. It is the length of the laser's internal cavity.

6. The external cavity tuned semiconductor laser according to claim 5, characterized in that: The method for outputting a synchronization signal from the laser is as follows: In the optical output and monitoring module, the optical fiber splitter is a 99:1 one-to-two optical fiber splitter. The optical fiber splitter is connected to an optical fiber connector. The input light is split into two paths. In one path, the splitter output with 1% intensity is directed to the photoresistor sensor as the laser status monitoring light. In the other path, the splitter output with 99% intensity is used as the laser output light. The optical galvanometer is rotated to put the laser into an excited state and an unexcited state, respectively, and the light intensity of the photoresistor sensor is collected. By adjusting the output threshold of the photoresistor sensor, the photoresistor sensor outputs a high level when the laser is excited and a low level when it is in the unexcited state. The output of the photoresistor is the synchronous output signal of the laser.

7. The external cavity tuned semiconductor laser according to claim 5, characterized in that: The method for uniform output of the laser wavenumber is as follows: control the optical galvanometer to rotate at a fixed speed so that the laser is continuously tuned and outputs light with the wavelength range covering the entire tuning band. The output light is input into a spectrometer or other spectral information detector, and the rotation angle of the galvanometer and the corresponding output spectrum are synchronously acquired through a synchronous output signal. The center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, thus obtaining the laser wavelength output curve corresponding to the mirror rotation angle; that is, the actual wavenumber output curve. The actual wavenumber output curve is homogenized, and the mirror angle corresponding to each sampling point during homogenization is calculated in reverse to obtain the mirror angle change curve. By adjusting the rotation speed of the galvanometer, the galvanometer angle can be made to change non-linearly according to the curve, thereby achieving uniform wavenumber output of the laser.

8. The external cavity tuned semiconductor laser according to claim 7, characterized in that: In the wavenumber uniform output method, the Gaussian fitting method involves the following steps: Based on the spectral data, set a Gaussian function with a constant background and initial estimation parameters. The formula for the Gaussian function with background is as follows: Official 3; in The peak signal strength, The center wavelength, Standard deviation It is a constant; Then, by nonlinear least squares fitting, the values ​​of each parameter are obtained when the sum of squared residuals is minimized, and the center wavelength of the above spectral data is obtained. Repeat the above steps to obtain the center wavelength of the spectral data corresponding to each rotation angle, and obtain the laser wavelength output curve corresponding to the galvanometer rotation angle; Next, the wavelength output curve is converted to the wavenumber domain. The relationship between wavelength and wavenumber is as follows: Official 4; in Wave number; Substituting Equation 4 into Equation 1, we obtain the relationship between the laser output wavenumber and the galvanometer angle, expressed as: Official 5.

9. The external cavity tuned semiconductor laser according to claim 8, characterized in that: The wavenumber uniform output method also includes: first controlling the optical galvanometer to perform a full-range scan with a constant voltage change rate, so that the laser is continuously tuned and output, and the output light is input into a spectrometer or other spectral information detector, and synchronous acquisition is triggered by a photosensitive sensor; the original driving curve of "time-galvanometer rotation angle" is recorded. Then, the center wavelength of the output light corresponding to the rotation angle of each sampling point is obtained by Gaussian fitting, and the original "time-laser output wavelength" curve is obtained; the wavelength output curve is converted to the wavenumber domain, and the wavenumber curve is linearized by interpolation. Then, through reverse mapping, the "time-angle drive curve" required to obtain linear wavenumber output is calculated; the optimized curve is used to generate a drive signal and the drive signal is applied to the optical galvanometer to adjust the optical galvanometer's operating conditions.

10. The external cavity tuned semiconductor laser according to claim 2, characterized in that: The optical galvanometer is a closed-loop galvanometer scanning galvanometer with an integrated position sensor. The small-angle step response time of the optical galvanometer is less than 300° and the closed-loop bandwidth is greater than 1 kHz.

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