Narrow-linewidth semiconductor laser

Abstract

The present application relates to the technical field of semiconductor laser, and especially relates to a narrow linewidth semiconductor laser, which comprises a laser module containing n semiconductor laser units for outputting n laser beams, n>=2; a fast axis collimating mirror array for fast axis collimation of the n laser beams; a slow axis collimating mirror array for slow axis collimation of the fast axis collimated n laser beams; a mirror array for spatial beam combination of the fast axis and slow axis collimated n laser beams; a focusing mirror for focusing of the combined laser beams; a homogenization waveguide for homogenization of the focused laser beams; a collimating mirror for collimation of the homogenized laser beams; and a volume Bragg grating for diffraction feedback of the collimated laser beams. The present application only uses a single volume Bragg grating, and the homogenization waveguide is arranged in the internal cavity feedback loop of the volume Bragg grating to homogenize the energy of the incident laser beams, suppress the internal temperature gradient of the volume Bragg grating, and improve the linewidth narrowing effect and spectral locking precision of the multiple semiconductor laser units.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, and particularly relates to a narrow linewidth semiconductor laser. Background Technology

[0002] High-power narrow-linewidth semiconductor lasers combine high output power, sub-nanometer narrow linewidth, and excellent wavelength and power stability. In addition to being widely used as pump sources for fiber lasers, gas lasers, and disk lasers, they also have important applications in key fields such as laser processing, medical health, and national defense security.

[0003] Currently, the mainstream technology for achieving narrow linewidth and spectral locking in high-power semiconductor lasers is an external cavity feedback structure based on a bulk Bragg grating. The output beam of a freely rotating semiconductor laser is collimated and then incident on the bulk Bragg grating, utilizing its diffraction characteristics at a specific center wavelength to enhance the optical gain at that wavelength. Through a mode competition mechanism, stable output of narrow-linewidth lasers can be achieved.

[0004] The mainstream technical solutions are divided into two types: one is the single-chip single-unit Bragg grating solution, which collimates the beam emitted by the unit laser and then incident it onto the volume Bragg grating to build an external cavity feedback structure; the other is the multi-chip beam-combining single-unit Bragg grating solution, which first collimates and combines the beams of multiple lasers, and then uses a single volume Bragg grating to realize synchronous external cavity feedback of multiple lasers.

[0005] The two mainstream solutions mentioned above still have the following problems: First, the system is costly and complex to assemble and adjust. The single-chip, single-unit Bragg grating solution requires an expensive volume Bragg grating to be configured independently for each channel, and the optical path calibration process is cumbersome, which is not conducive to system integration and cost control.

[0006] Secondly, volume Bragg gratings (BBRs) are difficult to manage thermally and have poor spectral stability. BBRs exhibit significant temperature drift characteristics, and high-power laser incidence causes a redshift in their center wavelength. If multiple BBRs are subjected to precise temperature control individually, the system size and power consumption will increase. Furthermore, inconsistent temperature control among the BBRs leads to deviations in wavelength locking of the laser units, ultimately resulting in broadening of the combined beam and deterioration of spectral quality.

[0007] Third, the uneven energy distribution of the beam exacerbates the thermal effect of the volume Bragg grating, limiting the spectral locking accuracy. The initial beam of a semiconductor laser has a Gaussian distribution and poor energy uniformity, which generates a temperature gradient inside the volume Bragg grating: the temperature gradient along the optical axis causes the laser linewidth to broaden; the temperature gradient perpendicular to the optical axis causes the locking center wavelength of different laser units to shift, resulting in a multi-peak spectrum after beam combining, which severely weakens the linewidth narrowing and center wavelength locking effect.

[0008] It is evident that existing bulk Bragg grating external cavity feedback schemes have significant shortcomings in terms of cost control, thermal management, and precise spectral locking. There is an urgent need for an external cavity feedback structure that can simplify the structure, reduce thermal impact, and improve spectral locking performance. Summary of the Invention

[0009] In view of this, the present invention aims to provide a narrow linewidth semiconductor laser that combines a homogenized waveguide with a single bulk Bragg grating to achieve linewidth narrowing and spectral locking of multiple laser units, thereby reducing device cost, simplifying optical path structure, and reducing thermal management difficulty.

[0010] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A narrow linewidth semiconductor laser, comprising: A laser module comprises n semiconductor laser units, where n ≥ 2; the laser module is used to output n laser beams. A fast-axis collimating mirror array is used for fast-axis collimation of n laser beams. Slow-axis collimating mirror array, used to perform slow-axis collimation on n laser beams that have been collimated by fast axis; A mirror array is used to spatially combine n laser beams collimated along the fast and slow axes. A focusing lens is used to focus a laser beam after it has been combined in space. Homogenizing waveguides are used to homogenize focused laser light. A collimating lens is used to collimate homogenized laser light. A bulk Bragg grating is used to provide diffraction feedback for the collimated laser beam; the diffracted laser beam returns along the original optical path to each semiconductor laser unit, forming an external cavity feedback resonance.

[0011] Furthermore, the homogenizing waveguide is a solid homogenizing rod, and the cross-section of the solid homogenizing rod can be either rectangular or circular.

[0012] Furthermore, the homogenized waveguide is made of fused silica material; the light-transmitting end face of the homogenized waveguide is coated with an anti-reflection film corresponding to the working band, and its transmittance is not less than 99.5%.

[0013] Furthermore, the volume Bragg grating is a reflective volume Bragg grating with a diffraction efficiency of 7% to 13%.

[0014] Furthermore, the light-transmitting surfaces of the fast-axis collimating lens array, the slow-axis collimating lens array, the focusing lens, the collimating lens, and the volume Bragg grating are all coated with anti-reflection films corresponding to the working wavelength, with a transmittance of not less than 99.5%.

[0015] Furthermore, the semiconductor laser unit is an independent single-tube laser or a bar composed of single-tube lasers; the light-emitting end face of the semiconductor laser unit is coated with an anti-reflection film corresponding to the working wavelength, and its transmittance is not less than 99%.

[0016] Furthermore, the volume Bragg grating is equipped with a temperature control component, which includes a thermoelectric cooler and a temperature sensor. The temperature sensor is a thermistor. The thermoelectric cooler is used to adjust the temperature of the volume Bragg grating, and the thermistor is used to collect the temperature of the volume Bragg grating.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention achieves both linewidth narrowing and spectral locking of multiple semiconductor laser units simultaneously using only a single volume Bragg grating, eliminating the high device costs associated with configuring independent volume Bragg gratings for each laser unit in traditional solutions. It also avoids the cumbersome alignment and adjustment processes required for multiple independent external cavities, resulting in a more compact optical path structure and significantly reduced assembly and adjustment difficulty. Furthermore, it only requires temperature control of a single volume Bragg grating, eliminating the need for multiple sets of high-precision temperature control units for multiple volume Bragg gratings, thus reducing system size and power consumption. It also avoids the problems of center wavelength deviation and beam broadening in the combined spectrum caused by inconsistent temperature control of multiple volume Bragg gratings.

[0018] This invention places a homogenizing waveguide inside the external cavity feedback loop, at the front end of the volume Bragg grating, unlike the conventional design approach of placing homogenizing elements at the laser output end to optimize the output beam spot. In this invention, the homogenizing waveguide is used at least to improve the uniformity of laser energy incident on the volume Bragg grating and suppress the internal temperature gradient of the volume Bragg grating, rather than to reshape the laser output beam spot. After homogenization by the homogenizing waveguide, the multi-beam laser can effectively suppress the internal temperature gradient of the volume Bragg grating caused by the non-uniformity of Gaussian beam energy, avoiding the problem of center wavelength shift in each semiconductor laser unit and the generation of multiple center wavelengths after beam combining, thus improving the linewidth narrowing effect and spectral locking accuracy. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the narrow linewidth semiconductor laser described in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures: 10. Laser module; 101~10n, semiconductor laser unit; 11. Fast-axis collimating lens array; 111~11n, fast-axis collimating lens; 12. Slow-axis collimating lens array; 121~12n, slow-axis collimating lens; 13. Mirror array; 131~13n, mirror; 14. Focusing lens; 15. Homogenizing waveguide; 16. Collimating lens; 17. Volume Bragg grating. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., 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, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] like Figure 1As shown, this embodiment of the invention provides a narrow linewidth semiconductor laser, including: a laser module 10, a fast-axis collimating lens array 11, a slow-axis collimating lens array 12, a mirror array 13, a focusing lens 14, a homogenizing waveguide 15, a collimating lens 16, and a volume Bragg grating 17.

[0027] The laser module 10 includes n semiconductor laser units 101 to 10n, where n ≥ 2; each semiconductor laser unit can be an independent single-tube laser or a bar composed of single-tube lasers. The light-emitting end face of the semiconductor laser units 101 to 10n is coated with an anti-reflection film corresponding to the working wavelength, and its transmittance is not less than 99%.

[0028] The fast-axis collimating lens array 11 is set in the light output direction of the laser module 10. The fast-axis collimating lens array 11 includes n fast-axis collimating lenses, namely fast-axis collimating lenses 111~11n. One fast-axis collimating lens corresponds to one single-tube laser. The fast-axis collimating lens array 11 achieves fast-axis collimation of the n laser beams output by the laser module 10.

[0029] The slow-axis collimating lens array 12 is positioned in the emission direction of the fast-axis collimating lens array 11. The slow-axis collimating lens array 12 includes n slow-axis collimating lenses, namely slow-axis collimating lenses 121 to 12n. One slow-axis collimating lens corresponds to one fast-axis collimating lens, that is, one slow-axis collimating lens corresponds to one semiconductor laser unit. The slow-axis collimating lens array 12 realizes the slow-axis collimation of n laser beams that have passed through fast-axis collimation.

[0030] The mirror array 13 is positioned along the emission direction of the slow-axis collimating mirror array 12. The mirror array 13 comprises n mirrors, designated 131 to 13n. Each mirror corresponds to one slow-axis collimating mirror, meaning each mirror corresponds to one semiconductor laser unit. The mirror array 13 reflects the n laser beams after fast-axis and slow-axis collimation, achieving spatial beam combining. Each mirror in the mirror array 13 has a reflective coating on its reflective end face corresponding to the operating wavelength, with a reflectivity of not less than 99.5%.

[0031] The focusing mirror 14 is positioned in the reflection direction of the mirror array 13 and is used to focus the laser beam after spatial beam combining.

[0032] The homogenizing waveguide 15 is disposed in the exit direction of the focusing lens 14 and is used to homogenize the focused laser. The homogenizing waveguide 15 can be a solid homogenizing rod, the cross-section of which can be rectangular (e.g., square) or circular; furthermore, the homogenizing waveguide 15 is made of fused silica material; the light-transmitting end face of the homogenizing waveguide 15 is coated with an anti-reflection film corresponding to the working wavelength, and its transmittance is not less than 99.5%.

[0033] The collimating lens 16 is positioned in the emission direction of the homogenizing waveguide 15 and is used to collimate the homogenized laser.

[0034] A volume Bragg grating 17 is positioned in the exit direction of the collimating lens 16 to provide diffraction feedback to the collimated laser. The diffracted laser returns along the original optical path to the laser module 10, forming an external cavity feedback resonance. The volume Bragg grating 17 is a reflective volume Bragg grating with a diffraction efficiency of 7% to 13%. The volume Bragg grating 17 is equipped with a temperature control component (not shown in the figure), which includes a thermoelectric cooler and a temperature sensor. The temperature sensor is a thermistor. The thermoelectric cooler is used to adjust the temperature of the volume Bragg grating 17, and the thermistor is used to collect the temperature of the volume Bragg grating 17. By controlling the temperature of the bulk Bragg grating 17, the lattice period inside the bulk Bragg grating 17 can be adjusted, thereby changing the diffraction center wavelength of the bulk Bragg grating 17. The specific wavelength beam diffracted by the bulk Bragg grating 17 is fed back to the gain region of each semiconductor laser unit 101~10n along the original optical path. Under the mode competition of the external cavity resonance, the output wavelength of each semiconductor laser unit 101~10n is forced to approach the current diffraction center wavelength of the bulk Bragg grating 17, thereby achieving unified wavelength locking of multiple semiconductor laser units and obtaining narrow linewidth laser output.

[0035] The light-transmitting end faces of the fast-axis collimating lens array 11, the slow-axis collimating lens array 12, the focusing lens 14, the collimating lens 16, and the volume Bragg grating 17 are all coated with anti-reflection films corresponding to the working wavelength, and their transmittance is not less than 99.5%.

[0036] The narrow-linewidth semiconductor laser in this embodiment constitutes an external cavity feedback resonant cavity. To achieve lasing, the corresponding resonance conditions must be met: n semiconductor laser units 101~10n provide optical gain; the laser beam is collimated and spatially combined after passing through a fast-axis collimating mirror array 11, a slow-axis collimating mirror array 12, and a reflecting mirror array 13; then, it sequentially passes through a focusing mirror 14, a homogenizing waveguide 15, and a collimating mirror 16 before being incident on a volume Bragg grating 17; the volume Bragg grating 17 diffracts a specific wavelength of laser light, feeding back a portion of the laser power along the original optical path to the gain region of the semiconductor laser units 101~10n. When the round-trip optical gain within the external cavity feedback loop is greater than the total optical loss of the loop, the lasing threshold condition is met; utilizing the wavelength selectivity of the volume Bragg grating 17, only beams matching the diffraction center wavelength of the volume Bragg grating 17 can obtain effective feedback, suppressing other wavelengths through a mode competition mechanism, ultimately achieving wavelength locking of the multi-channel semiconductor laser units and narrow-linewidth laser output.

[0037] This invention places the homogenizing waveguide 15 inside the external cavity feedback loop, at the front end of the volume Bragg grating 17, which differs from the conventional approach in the prior art of placing homogenizing elements at the laser output end to optimize the output beam quality. The combined laser beam output from the semiconductor laser units 101~10n first undergoes homogenization processing through the homogenizing waveguide 15, making the laser energy distribution incident on the volume Bragg grating 17 more uniform, rather than reshaping the beam shape of the final output laser beam.

[0038] The original laser beams from semiconductor laser units 101-10n exhibit a Gaussian distribution, with high energy at the center and low energy at the edges. If the beams are directly incident on the bulk Bragg grating 17 without homogenization, the local absorption of laser energy by the bulk Bragg grating 17 material will simultaneously generate temperature gradients along the optical axis and perpendicular to the optical axis within the bulk Bragg grating 17. The temperature gradient along the optical axis will cause the diffraction wavelength of the bulk Bragg grating 17 to continuously shift along the optical path, resulting in inconsistent diffraction wavelengths fed back to the semiconductor laser units 101-10n, thus causing broadening of the single-path laser spectral linewidth. The temperature gradient perpendicular to the optical axis will cause the diffraction center wavelengths at different transverse positions of the bulk Bragg grating 17 to be different. When lasers from different semiconductor laser units 101-10n irradiate different transverse regions of the bulk Bragg grating 17, the received feedback wavelengths will differ, ultimately causing each semiconductor laser unit 101-10n to lock to different center wavelengths, resulting in multi-peak output spectra and spectral broadening and degradation.

[0039] This invention homogenizes the Gaussian energy fluctuations of the incident laser by homogenizing the waveguide 15, significantly reducing local energy hotspots on the light-receiving surface of the bulk Bragg grating 17, thereby simultaneously suppressing temperature gradients along both the optical axis and perpendicular to the optical axis within the bulk Bragg grating 17. Suppressing the temperature gradient along the optical axis effectively alleviates the linewidth broadening problem of a single-path laser. Suppressing the temperature gradient perpendicular to the optical axis also makes the diffraction center wavelengths at various lateral positions of the bulk Bragg grating 17 more consistent, allowing each semiconductor laser unit 101~10n to receive diffraction feedback of the same target wavelength. This avoids the phenomenon of center wavelength shifts in each semiconductor laser unit 101~10n and the generation of multiple discrete center wavelengths after beam combining, ultimately improving the linewidth narrowing effect and center wavelength locking accuracy of the multi-path semiconductor laser units.

[0040] Example 1 The laser module 10 includes 10 semiconductor laser units, each of which is a single-tube laser. In free operation, the center wavelength of the laser output by the single-tube laser is 777nm~783nm, the spectral linewidth is approximately 5nm, and the output power is approximately 10W. During free operation, the laser exhibits large divergence angles along both the fast and slow axes. The divergence angle along the fast axis is approximately 30°~60°, and the divergence angle along the slow axis is approximately 8°~12°. The 10 laser beams output from the 10 single-tube lasers are first fast-axis collimated by a fast-axis collimating lens array 11 with a focal length of 0.3mm, and then slow-axis collimated by a slow-axis collimating lens array 12 with a focal length of 20mm. After collimation, the full-angle divergence angle of each laser beam can be compressed to the order of 10mrad.

[0041] Ten independent single-tube lasers are coated with antireflective coatings in the 730nm~830nm wavelength range on their emitting ends, with a transmittance of not less than 99%. The height difference between adjacent single-tube lasers is 0.4mm. The ten laser beams are reflected by the mirror array 13 and then spatially superimposed to form a combined laser beam. The coating parameters of the mirror array 13 are as follows: when the incident laser is incident at a 45° angle, the reflectivity in the 730nm~830nm wavelength range is not less than 99.5%. The combined laser beam is focused by a focusing lens 14 with a focal length of 12mm and then coupled into a homogenizing waveguide 15, where the focused combined laser beam is homogenized. The light-transmitting end face of the homogenizing waveguide 15 is 1mm×1mm in size and 50mm in length. After homogenization, the combined laser beam is collimated by a collimating lens 16 with a focal length of 12mm and then incident on a volume Bragg grating 17. The volume Bragg grating 17 diffracts the incident laser to obtain a feedback laser, which returns to the laser module 10 along the original optical path, forming an external cavity feedback resonance.

[0042] The volume Bragg grating 17 has a diffraction center wavelength of 779.9nm~780.1nm, a diffraction efficiency of 7%~13%, a thickness of 3mm, and external dimensions of 6mm×6mm.

[0043] The fast-axis collimating lens array 11, the slow-axis collimating lens array 12, the focusing lens 14, the homogenizing waveguide 15, the collimating lens 16 and the volume Bragg grating 17 are all coated with an anti-reflection film in the 730nm~830nm band, and their transmittance is not less than 99.5%.

[0044] It should be noted that the above embodiments are specific examples of an implementable optical path according to the present invention. The specific values ​​of the number of semiconductor laser units 101~10n, the center wavelength of the output laser, the focal length, size, coating parameters, diffraction parameters, etc. of each optical element described in the embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Those skilled in the art can reasonably adjust and replace the above parameters according to actual usage scenarios and design requirements, all of which fall within the scope of protection of the present invention.

[0045] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0046] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A narrow linewidth semiconductor laser, characterized in that, include: A laser module includes n semiconductor laser units, where n ≥ 2; the laser module is used to output n laser beams. A fast-axis collimating mirror array is used for fast-axis collimation of n laser beams. Slow-axis collimating mirror array, used to perform slow-axis collimation on n laser beams that have been collimated by fast axis; A mirror array is used to spatially combine n laser beams collimated along the fast and slow axes. A focusing lens is used to focus a laser beam after it has been combined in space. Homogenizing waveguides are used to homogenize focused laser light. A collimating lens is used to collimate homogenized laser light. A volume Bragg grating is used to provide diffraction feedback for collimated laser light. The laser beam, after diffraction feedback, returns along the original optical path to each semiconductor laser unit, forming an external cavity feedback resonance.

2. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The homogenizing waveguide is a solid homogenizing rod, and the cross-section of the solid homogenizing rod can be either rectangular or circular.

3. The narrow linewidth semiconductor laser according to claim 1 or 2, characterized in that, The homogenized waveguide is made of fused silica material; the light-transmitting end face of the homogenized waveguide is coated with an anti-reflection film corresponding to the working band, and its transmittance is not less than 99.5%.

4. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The volume Bragg grating is a reflective volume Bragg grating with a diffraction efficiency of 7% to 13%.

5. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The light-transmitting surfaces of the fast-axis collimating lens array, slow-axis collimating lens array, focusing lens, collimating lens, and volume Bragg grating are all coated with anti-reflection films corresponding to the working wavelength, and their transmittance is not less than 99.5%.

6. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The semiconductor laser unit is an independent single-tube laser or a bar composed of single-tube lasers; the light-emitting end face of the semiconductor laser unit is coated with an anti-reflection film corresponding to the working wavelength, and its transmittance is not less than 99%.

7. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The volume Bragg grating is equipped with a temperature control component, which includes a thermoelectric cooler and a temperature sensor. The temperature sensor is a thermistor. The thermoelectric cooler is used to adjust the temperature of the volume Bragg grating, and the thermistor is used to collect the temperature of the volume Bragg grating.

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