A method for adjusting the external cavity wave lock of a volume grating

Abstract

This invention relates to a method for adjusting the external cavity lock-in state of a volume grating (VBG), belonging to the field of semiconductor laser technology. The adjustment method involves the following steps: first, preparing the laser; then, using a six-axis motion platform, adjusting the VBG to the lock-in position; testing the initial power and wavelength of the laser under operating current, adjustment current, and low current conditions; then, adjusting the VBG to the lock-in state; and finally, fixing the lock-in state using adhesive application, photocuring, and thermal curing. Finally, a lock-in test is performed to complete the adjustment. This invention enables rapid and simple lock-in adjustment without requiring complex equipment, and has advantages such as high efficiency, simplicity, good stability, and ease of operation.

Description

Technical Field

[0001] This invention relates to a bulk grating external cavity wave-locking modulation method, belonging to the field of semiconductor laser technology. Background Technology

[0002] Semiconductor lasers have been widely used in various sectors of the national economy due to their advantages such as small size, light weight, long lifespan, wide wavelength coverage, good monochromaticity, good directionality, good coherence, and high brightness. These applications include laser cutting, laser welding, beauty, medical devices, communications, indicators, night vision, and weapons.

[0003] Semiconductor laser devices (LDs) also have inherent limitations, including poor beam quality. They typically require a series of complex optical systems to achieve a usable beam. Semiconductor laser chips emit a wide spectrum, generally between 3-10 nm. In some specialized applications, such as ultrafast pump sources requiring narrow linewidths and high energy, the linewidth needs to be compressed to within 1 nm.

[0004] To address the issues of wavelength locking and linewidth narrowing in semiconductor lasers, an increasing number of research and development efforts are employing reflective volume Bragg gratings (R-VBG) (such as...). Figure 7 As shown in the figure, it reduces the sensitivity of the grating to ambient temperature and vibration, and has achieved significant results in wavelength stabilization and linewidth compression of high-power semiconductor lasers. Based on the angle and wavelength selectivity of the volume Bragg grating, the light wave emitted by each unit in the external cavity of the laser array is selectively fed back to the adjacent unit, thereby realizing phase-locking of the laser array external cavity. The spectral width is compressed to one-tenth of the original, and the corresponding far-field divergence angle is below 1.5 mrad, which greatly improves the beam output quality and stability, and thus has been widely used.

[0005] In the prior art, Chinese patent document CN113131336B discloses a wavelength locking method for a semiconductor laser, comprising: testing a first center wavelength of the semiconductor laser under operating current and a heat sink under operating temperature; if the first center wavelength is within the wavelength locking range of a volume grating, adjusting the current in the semiconductor laser to a first current, which is less than the operating current of the semiconductor laser, and testing a second center wavelength of the semiconductor laser while keeping the heat sink at the operating temperature; then adjusting the heat sink at the bottom of the semiconductor laser to the test temperature, so that the semiconductor laser emits laser light with a third center wavelength, the difference between the third center wavelength and a boundary of the wavelength locking range being less than or equal to a first threshold; and then adjusting the angle of the volume grating until the side lobes of the light emitted from the volume grating disappear in the spectrum. While this method simulates wavelength locking under different currents by controlling the wavelength through temperature, it requires frequent switching of the water cooling temperature and involves complex calculations. Therefore, this invention is proposed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a volume grating external cavity wave-locking adjustment method, which can quickly and easily perform wave-locking adjustment without the need for complex equipment. It has the advantages of high efficiency, simplicity, good stability, and ease of operation.

[0007] The technical solution of the present invention is as follows:

[0008] A method for adjusting the external cavity wave-locking of a volume grating includes the following steps:

[0009] (1) Laser preparation: A heat sink is set on the laser mounting platform, a semiconductor laser is set on the heat sink, and a fast axis collimator (FAC) is set on the heat sink on the light output side of the semiconductor laser for fast axis collimation.

[0010] (2) Use a six-axis motion platform to adjust the VBG to the adjustment lock position. Install a clamp on the six-axis motion platform and clamp the VBG so that the VBG is parallel to the FAC. Then place the VBG 3-5mm away from the FAC. During the clamping process, ensure that the angle of the VBG is not tilted. Set a ceramic pad on the laser mounting platform under the VBG. Then adjust the Z-axis so that the bottom of the VBG contacts the ceramic pad. Then raise the VBG by 500 micrometers as the adjustment lock position.

[0011] The six-axis motion platform has a total of six axes, denoted as X-axis, Y-axis, Z-axis, P-axis, R-axis, and YAW-axis. The X-axis and Y-axis drive forward, backward, left, and right movement. The Z-axis adjusts the vertical position of the VBG axis. The P-axis adjusts the longitudinal arc perpendicular to the X-axis. The YAW-axis adjusts the lateral position perpendicular to the X-axis. The R-axis adjusts the arc around the X-axis and is generally a fixed axis that is not adjusted after adjustment but is calibrated periodically.

[0012] (3) Power-on test wavelength: Power on the laser, use a periscope prism to export the light spot emitted by the laser and enter the integrating sphere for testing. The side wall of the integrating sphere is drilled with a power meter and a spectrometer. During the test, the VBG is raised. The power meter and spectrometer are used to test the initial power and wavelength of the laser under the working current, adjustment current and low current conditions. After the test is completed, the VBG falls back to the adjustment and locking position.

[0013] (4) Adjustment: First, adjust VBG on the P axis until a locked waveform appears. Record the range of the locked waveform L1. Then adjust the YAW axis to find the range of the locked waveform, and record it as L2. After recording, adjust the P axis of VBG to the middle position of L1 and the YAW axis to the middle position of L2 to achieve the locked waveform.

[0014] Wave lock test: Power on the laser and record the current range under wave lock state, such as 2A-15A or 5A-15A, etc.

[0015] (5) Apply UV glue to the bottom of the VBG;

[0016] (6) UV curing using LEDs, etc.;

[0017] (7) Heat curing: Remove the product with the pre-sealed wave and place it on the heating table for heat curing. The heat curing process is divided into three stages: T1 stage: uniform heating; T2 stage: heat preservation; T3 stage: natural cooling.

[0018] (8) Take out the cured product and perform a wave lock test. Test whether the wave lock current range is consistent with the record in step (4). If it is consistent, it meets the product requirements and the adjustment is completed. Otherwise, return to step (5) and repeat the adhesive coating and curing process.

[0019] According to a preferred embodiment of the present invention, in step (2), after adjusting the Z-axis so that the bottom of the VBG contacts the ceramic pad, the distance between the bottom of the VBG and the ceramic pad is measured. If the distance is 0, the VBG is adjusted to the correct position. If the distance is greater than 0, the bottom of the VBG is not in contact with the ceramic pad, and there is an error in the clamping and adjustment process. The Z-axis is further adjusted, and then the distance between the bottom of the VBG and the ceramic pad is measured until the distance between the two is 0.

[0020] According to a preferred embodiment of the present invention, in step (3), during the test, the VBG is vertically raised by 5-10cm to remove the VBG from the optical path of the laser, so as to avoid the VBG affecting the test results of the initial power and wavelength of the laser. The operating current is the maximum operating current, the adjustment current is half of the operating current, and the low current is slightly higher than the threshold current. In this application, it is fixed at 2A.

[0021] According to a preferred embodiment of the present invention, in step (4), after the P-axis and YAW-axis of VBG are adjusted, spectral information is collected, and the PIB (Power In Band) value is calculated by software. If the PIB is greater than 99%, the adjustment is considered to be correct, and the laser enters the wave-locked state.

[0022] According to a preferred embodiment of the present invention, in step (5), the specific operation is as follows: apply glue to the bottom of the VBG, spread the glue evenly on the bottom of the VBG and let it hang down naturally to the ceramic pad, and test whether the locked current range is consistent with the record in step (4). If it is consistent, proceed to the next step; otherwise, fine-tune the P-axis and YAW-axis of the VBG until the locked current range is consistent with the record in step (4) before proceeding to the next step.

[0023] According to a preferred embodiment of the present invention, in step (6), the specific photocuring process is as follows:

[0024] a. Turn the LED light on for five seconds and turn it off for one second, repeating this cycle three times (the exact number of cycles depends on the type of adhesive).

[0025] b. Turn the LED light on for 60 seconds, turn it off for 5 seconds, then turn it on again for 60 seconds. Then collect the spectral information and calculate the PIB value. If the PIB is greater than 99%, proceed to the next step; otherwise, return to step (5) to reapply the adhesive.

[0026] According to a preferred embodiment of the present invention, in step (7), the uniform heating process is 10℃ / min, and after heating to 120℃, it is kept at 120℃ for 48min, and then naturally cooled to room temperature. The heating rate, the holding temperature and the holding time can be set separately according to the type of adhesive.

[0027] The T1 process is a uniform heating process to prevent excessive stress caused by rapid heating during glue curing. The T3 cooling process should not be too fast, as this will affect the stress relief effect of glue curing. Therefore, a natural cooling method is adopted.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention provides a method for adjusting the external cavity of a volume grating, which can quickly and easily adjust the locked wave without the need for complex equipment. It has the advantages of high efficiency, simplicity, good stability, and ease of operation.

[0030] 2. The adhesive curing method of the present invention effectively reduces the stress generated during the adhesive curing process, improves the stability of the adhesive after curing, and avoids the effect of wave locking due to changes in environmental factors. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process of the present invention;

[0032] Figure 2 This is a schematic diagram of the VBG clamping mechanism of the present invention;

[0033] Figure 3 This is a schematic diagram of the VBG adjustment direction of the present invention;

[0034] Figure 4 This is a schematic diagram of the first photocuring time of the present invention;

[0035] Figure 5 This is a schematic diagram of the second photocuring time of the present invention;

[0036] Figure 6 This is a schematic diagram of the thermosetting time of the present invention;

[0037] Figure 7 This is an existing VBG wavelock structure. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0039] Example 1:

[0040] like Figure 1-3 As shown, this embodiment provides a method for adjusting the external cavity wave lock of a volume grating, the steps of which are as follows:

[0041] (1) Laser preparation: A heat sink is set on the laser mounting platform, a semiconductor laser is set on the heat sink, and a fast axis collimator (FAC) is set on the heat sink on the light output side of the semiconductor laser for fast axis collimation.

[0042] (2) Use a six-axis motion platform to adjust the VBG to the adjustment lock position. Install a clamp on the six-axis motion platform and clamp the VBG so that the VBG is parallel to the FAC. Then place the VBG 3-5mm away from the FAC. During the clamping process, ensure that the angle of the VBG is not tilted. Set a ceramic pad on the laser mounting platform under the VBG. Then adjust the Z-axis so that the bottom of the VBG contacts the ceramic pad. Measure the distance between the bottom of the VBG and the ceramic pad. If the distance is 0, the VBG is adjusted to the correct position. If the distance is greater than 0, the bottom of the VBG is not in contact with the ceramic pad, and there is an error in the clamping and adjustment process. Further adjust the Z-axis and then measure the distance between the bottom of the VBG and the ceramic pad until the distance is 0. Then raise the VBG by 500 micrometers as the adjustment lock position.

[0043] The six-axis motion platform has a total of six axes, denoted as X-axis, Y-axis, Z-axis, P-axis, R-axis, and YAW-axis. The X-axis and Y-axis drive forward, backward, left, and right movement. The Z-axis adjusts the vertical position of the VBG axis. The P-axis adjusts the longitudinal arc perpendicular to the X-axis. The YAW-axis adjusts the lateral position perpendicular to the X-axis. The R-axis adjusts the arc around the X-axis and is generally a fixed axis that is not adjusted after adjustment but is calibrated periodically.

[0044] (3) Power-on test wavelength: Power on the laser, use a periscope prism to export the light spot emitted by the laser and enter the integrating sphere for testing. The side wall of the integrating sphere is drilled with a power meter and a spectrometer. During the test, the VBG is raised. The power meter and spectrometer are used to test the initial power and wavelength of the laser under the working current, adjustment current and low current conditions. After the test is completed, the VBG falls back to the adjustment and locking position.

[0045] (4) Adjustment: First, adjust VBG on the P axis until a locked waveform appears. Record the range of the locked waveform L1. Then adjust the YAW axis to find the range of the locked waveform, and record it as L2. After recording, adjust the P axis of VBG to the middle position of L1 and the YAW axis to the middle position of L2 to achieve the locked waveform. Then collect the spectral information and calculate the PIB (Power In Band) value through software. If the PIB is greater than 99%, the adjustment is considered to be correct and the laser enters the locked waveform state.

[0046] Wave lock test: Power on the laser and record the current range under wave lock state, such as 2A-15A or 5A-15A, etc.

[0047] (5) Apply UV glue to the bottom of VBG. Spread the glue evenly on the bottom of VBG and let it hang down naturally to the ceramic pad. Test the range of the locked current with the record in step (4). If it is consistent, proceed to the next step. Otherwise, fine-tune the P-axis and YAW-axis of VBG until the range of the locked current is consistent with the record in step (4) before proceeding to the next step.

[0048] (6) UV curing is performed using LEDs, etc. The specific curing process is as follows:

[0049] a. Turn the LED light on for five seconds and off for one second, repeating this cycle three times (the exact number of cycles depends on the type of adhesive). Figure 4 As shown;

[0050] b. Turn the LED light on for 60 seconds, turn it off for 5 seconds, then turn it on again for 60 seconds. Then collect the spectral information and calculate the PIB value. If the PIB is greater than 99%, proceed to the next step; otherwise, return to step (5) to reapply the adhesive. Figure 5 As shown;

[0051] (7) Heat curing: Remove the product with the pre-sealed wave and place it on the heating table for heat curing. The heat curing process is divided into three stages: T1 stage: uniform heating; T2 stage: heat preservation; T3 stage: natural cooling.

[0052] The uniform heating rate was 10℃ / min, and after reaching 120℃, it was held for 48 minutes, then allowed to cool naturally to room temperature. Figure 6 As shown, the heating rate, holding temperature, and holding time can be set individually according to the type of adhesive.

[0053] The T1 process is a uniform heating process to prevent excessive stress caused by rapid heating during glue curing. The T3 cooling process should not be too fast, as this will affect the stress relief effect of glue curing. Therefore, a natural cooling method is adopted.

[0054] (8) Take out the cured product and perform a wave lock test. Test whether the wave lock current range is consistent with the record in step (4). If it is consistent, it meets the product requirements and the adjustment is completed. Otherwise, return to step (5) and repeat the adhesive coating and curing process.

[0055] Example 2:

[0056] In step (3), during the test, the VBG is raised vertically by 5-10cm to remove it from the laser's optical path, thus avoiding the VBG affecting the test results of the laser's initial power and wavelength. The operating current is the maximum operating current, and the adjustment current is half of the operating current. The low current is slightly higher than the threshold current, and in this embodiment, it is fixed at 2A.

[0057] For those skilled in the art, various modifications and variations can be made to this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for adjusting the external cavity wave-locking of a volume grating, characterized in that, The steps are as follows: (1) Laser preparation: A heat sink is set on the laser mounting platform, a semiconductor laser is set on the heat sink, and an FAC is set on the heat sink on the output side of the semiconductor laser for fast axis collimation. (2) Use a six-axis motion platform to adjust the VBG to the adjustment lock position. Install a clamp on the six-axis motion platform and clamp the VBG so that the VBG is parallel to the FAC. Then place the VBG 3-5mm away from the FAC. Set a ceramic pad on the laser mounting platform under the VBG. Then adjust the Z-axis so that the bottom of the VBG contacts the ceramic pad. Then raise the VBG by 500 micrometers as the adjustment lock position. The six-axis motion platform has a total of six axes, denoted as X-axis, Y-axis, Z-axis, P-axis, R-axis and YAW-axis. The X-axis and Y-axis drive forward, backward and left and right movement, the Z-axis adjusts the vertical position of VBG, the P-axis adjusts the longitudinal arc perpendicular to the X-axis, the YAW-axis adjusts the lateral position perpendicular to the X-axis, and the R-axis adjusts the arc around the X-axis. (3) Powering on the test wavelength, powering on the laser, using a periscope prism to guide the light spot emitted by the laser into the integrating sphere for testing. The integrating sphere has holes drilled in its sidewall to install a power meter and a spectrometer. During the test, the VBG is raised, and the initial power and wavelength of the laser under the working current, adjustment current and low current conditions are tested by the power meter and the spectrometer. After the test is completed, the VBG falls back to the adjustment and locking position. (4) Adjustment: First, adjust VBG on the P axis until a locked waveform appears. Record the range of the locked waveform L1. Then adjust the YAW axis to find the range of the locked waveform, and record it as L2. After recording, adjust the P axis of VBG to the middle position of L1 and the YAW axis to the middle position of L2 to achieve the locked waveform. Wave lock test: The laser is powered on, and the current range under wave lock state is recorded; (5) Apply UV adhesive to the bottom of the VBG; (6) UV curing using LEDs; (7) Heat curing: Remove the product with the pre-sealed wave and place it on the heating table for heat curing. The heat curing process is divided into three stages: T1 stage: uniform heating; T2 stage: heat preservation; T3 stage: natural cooling. (8) Take out the cured product and perform a wave lock test. Test whether the wave lock current range is consistent with the record in step (4). If it is consistent, it meets the product requirements and the adjustment is completed. Otherwise, return to step (5) and repeat the adhesive coating and curing process.

2. The volume grating external cavity wave-locking modulation method as described in claim 1, characterized in that, In step (2), adjust the Z-axis so that the bottom of VBG contacts the ceramic pad. Then measure the distance between the bottom of VBG and the ceramic pad. If the distance is 0, then VBG is adjusted to the correct position. If the distance is greater than 0, then the bottom of VBG is not in contact with the ceramic pad, and there is an error in the clamping and adjustment process. Further adjust the Z-axis and then measure the distance between the bottom of VBG and the ceramic pad until the distance between the two is 0.

3. The volume grating external cavity wave-locking modulation method as described in claim 2, characterized in that, In step (3), during the test, the VBG is raised vertically by 5-10cm to separate the VBG from the optical path of the laser. The operating current is the maximum operating current, the adjustment current is half of the operating current, and the low current is fixed at 2A.

4. The volume grating external cavity wave-locking modulation method as described in claim 3, characterized in that, In step (4), after the P-axis and YAW-axis of VBG are adjusted, spectral information is collected and the PIB value is calculated. If the PIB is greater than 99%, the adjustment is considered to be correct and the laser enters the wave-locking state.

5. The volume grating external cavity wave-locking modulation method as described in claim 4, characterized in that, In step (5), the specific operation is to apply glue to the bottom of the VBG, spread the glue evenly on the bottom of the VBG and let it hang down naturally to the ceramic pad, and test whether the range of the locked current is consistent with the record in step (4). If it is consistent, the next step can be carried out. Otherwise, the P-axis and YAW-axis of the VBG are finely adjusted until the range of the locked current is consistent with the record in step (4) before the next step is carried out.

6. The volume grating external cavity wave-locking modulation method as described in claim 5, characterized in that, In step (6), the specific photocuring process is as follows: a. The LED light is turned on for five seconds and then off for one second, repeating this cycle three times; b. Turn the LED light on for 60 seconds, turn it off for 5 seconds, then turn it on again for 60 seconds. Then collect the spectral information and calculate the PIB value. If the PIB is greater than 99%, proceed to the next step; otherwise, return to step (5) to reapply the adhesive.

7. The volume grating external cavity wave-locking modulation method as described in claim 6, characterized in that, In step (7), the uniform heating process is 10℃ / min, and after reaching 120℃, it is kept at 120℃ for 48 minutes, and then naturally cooled to room temperature.

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