A common external cavity linewidth compression system based on transmission grating

Abstract

The present invention belongs to the technical field of blue light semiconductor lasers and discloses a common external cavity linewidth compression system based on a transmission grating, comprising: N blue light modules, a common external cavity module, an output coupling module and a fiber focusing output module; the common external cavity module comprises a first cubic beam splitter, a transmission grating and a first reflector; a blue light beam output by any blue light module is divided into reflected light and transmitted light after passing through the first cubic beam splitter; the reflected light passes through the transmission grating and returns along the original optical path via the first reflector and is split again at the first cubic beam splitter, with one portion of the light beam returning to the any blue light module along the original optical path, and the other portion of the light beam being transmitted to the remaining blue light modules respectively, and together with the light beam returning along the original optical path from any blue light module, forming the Littman external cavity feedback of the any blue light module, thereby achieving linewidth compression; the present invention can achieve high-power and narrow-linewidth laser output, improve the scalability of the system, and reduce the complexity of the system structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of blue light semiconductor lasers, and more specifically, relates to a common external cavity linewidth compression system based on a transmission grating. Background Art

[0002] High-brightness blue lasers are a key light source for future advanced manufacturing, with urgent application demands in power batteries, aerospace, power systems, large ship heat exchangers, and thick copper welding in new energy flat-wire motors. Linewidth compression technology can achieve semiconductor laser output with high power, high power density, and high beam quality.

[0003] At present, the linewidth compression technology of semiconductor lasers is mainly divided into two categories, namely light injection method and light feedback method. The light feedback method can be further divided into internal cavity method and external cavity method. The internal cavity method is mostly used in the manufacturing process of semiconductor lasers. The external cavity method is to couple light into an external cavity, split it by a wavelength selection device, and reflect only the useful components back into the laser's resonant cavity to achieve specific light feedback. During the reflection process in the external cavity, the laser will produce a certain phase shift, causing the phase of the reflected light to be different from the phase of the light field in the resonant cavity. Only modes with wavelengths consistent with or close to the longitudinal mode wavelength of the external cavity feedback can achieve in-phase feedback, thereby gaining an advantage in mode competition.

[0004] The effect of grating external cavity technology on the linewidth narrowing of semiconductor lasers is mainly reflected in two aspects: the laser output linewidth is inversely proportional to the square of the photon lifetime in the resonant cavity, which is proportional to the laser cavity length, so the linewidth is also inversely proportional to the square of the laser cavity length; for grating external cavity semiconductor lasers, the external cavity length is much longer than the internal cavity length of a single LD tube, so the grating external cavity has a significant effect on the linewidth narrowing of semiconductor lasers. However, the existing solutions based on the combination of grating and FP cavity to achieve narrow linewidth laser output have the following problems:

[0005] 1. The system structure is complex, including multiple optical isolators, half-wave plates, gratings, and FP cavities, and requires sophisticated feedback control equipment to maintain a narrow linewidth. This not only leads to complex optical path design, operational difficulties and high costs, but also makes adjustment and maintenance difficult.

[0006] 2. The system primarily relies on a single power amplifier and a complex feedback system to achieve high-power, narrow-linewidth laser output, lacking modular design and poor scalability. The complex optical path and numerous optical components further reduce optical path allocation efficiency, limiting the increase in output power. Summary of the Invention

[0007] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a common external cavity linewidth compression system based on a transmission grating, the purpose of which is to achieve high-power and narrow-linewidth laser output without the need for complex feedback control, improve the scalability of the system, and reduce the complexity of the system structure.

[0008] To achieve the above objectives, according to a first aspect of the present invention, a common external cavity linewidth compression system based on a transmission grating is provided, comprising: N blue light modules, N ≥ 2, a common external cavity module, an output coupling module, and a fiber focusing output module; the common external cavity module comprises a first cubic beam splitter, a transmission grating, and a first reflector;

[0009] Each blue light module simultaneously outputs a blue light beam of the same wavelength. The blue light beam output by any blue light module is divided into reflected light and transmitted light after passing through the first cubic beam splitter. The reflected light is diffracted by the transmission grating to generate diffracted light. The diffracted light is reflected by the first reflector and then returns along the original optical path and is split again at the first cubic beam splitter. Part of the light beam after the second split returns along the original optical path to the any blue light module, and the other part of the light beam is transmitted to the other N-1 blue light modules respectively, and together with the light beam from any blue light module that returns along the original optical path, constitutes the Littman external cavity feedback of the any blue light module to achieve linewidth compression. The transmitted light of the N blue light modules is coupled into a beam of light by the output coupling module and output through the optical fiber focusing output module.

[0010] Furthermore, the N blue light modules are arranged in sequence;

[0011] The common external cavity linewidth compression system further includes N-1 second cubic beam splitters corresponding one-to-one to the remaining N-1 blue light modules except the first blue light module, for splitting the blue light beam output by the corresponding blue light module into reflected light and transmitted light;

[0012] The blue light beams inputted into the common external cavity module by the remaining N-1 blue light modules are reflected lights after passing through the corresponding second cubic beam splitter;

[0013] The transmitted light of the N blue light modules includes the transmitted light of each blue light module after passing through the first cubic beam splitter and the transmitted light of the remaining N-1 blue light modules after passing through their corresponding second cubic beam splitter.

[0014] Furthermore, the blue light beam of the same wavelength output by each blue light module is a P-polarized blue light beam;

[0015] The transmission grating is a grating whose diffraction efficiency for S-polarized light in the blue light band reaches a preset threshold or above, and the diffracted light is +1-order diffracted light;

[0016] The first cubic beam splitter and the second cubic beam splitter are cubic beam splitters that reflect and transmit the P-polarized blue light beam;

[0017] The common external cavity module further includes a first half-wave plate disposed between the first cubic beam splitter and the transmission grating along the optical path, for transforming the polarization state of the blue light beam.

[0018] Furthermore, the blue light beam of the same wavelength output by each blue light module is an S-polarized blue light beam;

[0019] The transmission grating is a grating whose diffraction efficiency for P-polarized light in the blue light band reaches a preset threshold or above, and the diffracted light is +1-order diffracted light;

[0020] The first cubic beam splitter and the second cubic beam splitter are cubic beam splitters that reflect and transmit the S-polarized blue light beam;

[0021] The common external cavity module further includes a first half-wave plate disposed between the first cubic beam splitter and the transmission grating along the optical path, for transforming the polarization state of the blue light beam.

[0022] Furthermore, when N>2, the output coupling module includes a cube polarization splitter, N-1 second half-wave plates and second reflectors corresponding one-to-one to the remaining N-1 blue light modules, and a beam combining unit;

[0023] The transmitted light after passing through the second cubic beam splitter is polarized by the corresponding second half-wave plate, and then the light path direction is changed by the corresponding second reflector, and then the N-1 light beams are combined by the beam combining unit to obtain a combined light beam;

[0024] The combined light beam and the transmitted light after passing through the first cubic beam splitter are coupled into one beam of light through the cubic polarization beam splitter, and the coupled light beam serves as the output total light beam.

[0025] Furthermore, when N=2, the output coupling module includes a cube polarization beam splitter, a second half-wave plate and a second reflector;

[0026] The transmitted light beam after passing through the second cube beam splitter undergoes polarization state conversion through the second half-wave plate, and then changes the direction of the optical path through the second reflector. It is then coupled with the transmitted light after passing through the first cube beam splitter through the cube polarization beam splitter to form a beam of light, and the coupled beam serves as the output total beam.

[0027] Furthermore, a ratio of reflectivity to transmittance of the first cubic beam splitter and the second cubic beam splitter is 2:8.

[0028] Furthermore, it also includes a third reflector corresponding to the last blue light module;

[0029] The third reflector is used to reflect the transmitted light beam of the blue light beam output by the last blue light module after passing through the common external cavity module and then passing through its corresponding second cube beam splitter, so that the reflected light beam passes through its corresponding second cube beam splitter again.

[0030] Furthermore, each blue light module includes, in sequence along the optical path direction: a blue light single tube array, a fast axis collimator lens group, a slow axis collimator lens group, a 45° reflector lens group and a 45° reflector;

[0031] The blue light beam generated by the blue light single tube array passes through the fast axis collimator lens group and the slow axis collimator lens group in sequence to be collimated in the fast axis direction and the slow axis direction; the collimated light beam passes through the 45° reflector group and is shaped into a beam of light, and then passes through the 45° reflector to change the direction of the light path and output the required blue light beam.

[0032] Furthermore, the optical fiber focusing output module includes a focusing lens and an optical fiber connector;

[0033] The light beam output by the output coupling module is focused by the focusing lens and then coupled into the optical fiber connector.

[0034] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0035] (1) The transmission grating-based common external cavity linewidth compression system of the present invention adopts a design of N blue light modules in a common external cavity, using only one transmission grating as an optical feedback element. Without increasing the complexity and cost of the system, it can achieve efficient linewidth compression, improve the utilization rate of the grating and the stability of the linewidth compression. By flexibly adjusting the number N of blue light modules, the required power and narrow linewidth laser output can be achieved. This modular design eliminates the need for a single power amplifier and complex feedback system to achieve high-power and narrow linewidth laser output. It has good flexibility and scalability, reduces the complexity of the system structure, improves the efficiency of optical path distribution, and makes it easier to achieve an increase in output power.

[0036] (2) Compared with the single-module feedback, the feedback beam (target longitudinal mode) received by each blue light module not only includes the feedback light of the current blue light module, but also includes the feedback light transmitted to the current blue light module by other blue light modules, which makes the target longitudinal mode have more energy, which is conducive to the target longitudinal mode gaining an advantage in the mode competition, thereby making the optical system more stable.

[0037] (3) The present invention utilizes a Littman grating external cavity structure. When the laser is incident on the transmission grating, it undergoes a first diffraction. The diffracted light no longer returns directly to the active region (blue light module). Instead, it is incident on the first reflector, reflected back to the transmission grating, undergoes a second diffraction, and then returns along the original optical path to the laser resonant cavity. Because of the two diffractions, compared to a single-grating Littrow structure, light of a smaller wavelength range is fed back to the active region, theoretically resulting in a narrower output linewidth.

[0038] (4) Preferably, a third reflector corresponding to the last blue light module is further included, which is used to reflect the transmitted light beam of the blue light beam output by the last blue light module after passing through the common external cavity module and then passing through its corresponding second cube spectrometer, so that the reflected light beam passes through the corresponding second cube spectrometer again to avoid energy leakage.

[0039] In summary, the N blue light modules of the present invention share an external cavity feedback system (common external cavity module), which not only optimizes the beam quality, but also improves the optical efficiency of the grating. The modular design improves the reliability and maintainability of the system, while providing convenience for future power expansion. By increasing the number of modules, the output power can be linearly increased while maintaining optical performance to meet the needs of different application scenarios. Compared with the traditional single power amplifier solution, the present invention can more effectively disperse the heat load and improve the long-term stability and service life of the system. In addition, the multi-module design also provides the possibility of realizing more complex functions (such as multi-wavelength output, fast wavelength switching, etc.), further expanding the application prospects of this technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of a common external cavity linewidth compression system based on a transmission grating according to an embodiment of the present invention.

[0041] Figure 2 Schematic diagram of a blue light single tube array arrangement and beam combining module according to an embodiment of the present invention.

[0042] Figure 3 1 is a principle diagram of transmission grating characteristics according to an embodiment of the present invention.

[0043] Figure 4 This is a schematic diagram of the external cavity feedback path of the first blue light module according to an embodiment of the present invention.

[0044] Figure 5 Schematic diagram of the external cavity feedback path of the second blue light module according to an embodiment of the present invention.

[0045] Figure 6 Schematic diagram of dual-module output coupling according to an embodiment of the present invention.

[0046] Figure 72 is a schematic diagram of light focusing output according to an embodiment of the present invention.

[0047] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0048] 1-Blue light single tube array, 2-Fast axis collimator group, 3-Slow axis collimator group, 4-45° reflector group, 5-45° reflector, 6, 7-Blue light module, 8-First cube beam splitter, 9-First half-wave plate, 10-Transmission grating, 11-First reflector, 12-Second cube beam splitter, 13-Third reflector, 14-Second half-wave plate, 15-Second reflector, 16-Cube polarization beam splitter, 17-Focusing lens, 18-Fiber connector, 19-External cavity feedback path of blue light module 6, 20-External cavity feedback path of blue light module 7, 21-Output coupling module, 22-Fiber focusing output module. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0050] In the present invention, the terms "first", "second", etc. in the present invention and the accompanying drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0051] like Figure 1 As shown, the present invention provides a common external cavity linewidth compression system based on transmission grating, which mainly includes: N blue light modules, N≥2, a common external cavity module, an output coupling module 21 and a fiber focusing output module 22;

[0052] Each blue light module is used to output a corresponding blue light beam of the same wavelength. In the embodiment of the present invention, since the transmission grating 10 used is a grating with a diffraction efficiency of more than 94% for S light in the blue light band, the blue light beam is a P-polarized blue light beam as an example for description.

[0053] The common external cavity module includes a first cubic beam splitter 8, a first half-wave plate 9, a transmission grating 10 and a first reflector 11;

[0054] Each blue light module simultaneously outputs a blue light beam of the same wavelength. The blue light beam output by the i-th (i is 1, 2, ... or N) blue light module passes through the first cubic beam splitter 8 in the common external cavity module, where the P-polarized blue light beam is split into reflected light and transmitted light. The reflected light passes through the first half-wave plate 9, converting the P-polarized blue light beam into an S-polarized blue light beam. The reflected light is then diffracted by the transmission grating 10 to produce diffracted light. The first-order diffracted light is then returned along the original optical path by the first reflector 11 and split again at the first cubic beam splitter 8. Part of the split light beam returns along the original optical path to the i-th blue light module, while the other part is transmitted to the remaining N-1 blue light modules. Together with the light beam returning along the original optical path from the current i-th blue light module, it forms the Littman external cavity structure feedback of the current i-th blue light module to achieve linewidth compression.

[0055] The transmitted light of the N blue light modules is coupled into a beam of light by the output coupling module 21 and then outputted through the optical fiber focusing output module 22 .

[0056] Specifically, N blue light modules are arranged sequentially. The common external cavity linewidth compression system in this embodiment of the present invention also includes N-1 second cubic beam splitters 12 corresponding one-to-one to the remaining N-1 blue light modules excluding the first blue light module, for splitting the blue light beam output by the corresponding blue light module into reflected light and transmitted light. In this embodiment of the present invention, the first cubic beam splitter 8 and the N-1 second cubic beam splitters 12 corresponding one-to-one to the remaining N-1 blue light modules are both devices that reflect and transmit only P polarization, where the reflection:transmission ratio is 2:8.

[0057] In the remaining N−1 blue light modules, the blue light beam input into the common external cavity module is the reflected light after passing through the corresponding second cubic beam splitter 12 .

[0058] Specifically, the blue light beam output by the first blue light module passes through the first cube beam splitter 8, the first half-wave plate 9, the transmission grating 10 and the first reflector 11 in the common external cavity module in sequence, and the generated first-order diffraction light returns along the original optical path and is split again at the first cube beam splitter 8; a part of the light beam after splitting again returns to the first blue light module along the original optical path, and the other part of the light beam returns to the remaining N-1 blue light modules along the second cube beam splitter 12 corresponding to the remaining N-1 blue light modules. The blue light beam output by a certain blue light module among the remaining N-1 blue light modules is divided into reflected light and transmitted light by the corresponding second cubic beam splitter 12. The reflected light then passes through the first cubic beam splitter 8, the first half-wave plate 9, the transmission grating 10, and the first reflector 11 in the common external cavity module in sequence, and the generated +1-order diffracted light returns along the original optical path and is split again at the first cubic beam splitter 8. A portion of the light beam after the splitting again returns to the certain blue light module along the original optical path, and the other portion of the light beam is transmitted to the first blue light module and to the remaining N-2 blue light modules along the second cubic beam splitter 12 corresponding to the remaining N-2 blue light modules outside the certain blue light module.

[0059] Specifically, the transmitted light of the N blue light modules includes the transmitted light beam of each blue light module after passing through the first cubic beam splitter 8 and the transmitted light beams of the remaining N−1 blue light modules after passing through their corresponding second cubic beam splitter 12 .

[0060] Preferably, a third reflector 13 corresponding to the last blue light module is further included, which is used to reflect the transmitted light beam of the blue light beam output by the last blue light module after passing through the common external cavity module and then passing through its corresponding second cube spectrometer 12, so that the reflected light beam passes through the corresponding second cube spectrometer 12 again to avoid energy leakage.

[0061] Specifically, when N>2, the output coupling module 21 includes a cube polarization beam splitter 16, N-1 second half-wave plates 14, N-1 reflectors 15, and a beam combining unit; wherein the N-1 second half-wave plates 14 and the second reflectors 15 correspond one-to-one to the remaining N-1 blue light modules;

[0062] After passing through the second cube beam splitter 12 corresponding to the remaining N-1 blue light modules, the transmitted light beam is converted into S-polarized light after passing through the corresponding second half-wave plate 14. Then, after the light path direction is changed by the corresponding second reflector 15, the N-1 light beams are combined by the beam combining unit to obtain the combined S-polarized light, and the combined light beam is coupled with the P-polarized transmitted light beam after passing through the first cube beam splitter 8 through the cube polarization beam splitter 16 to obtain the output total light beam; wherein, the cube polarization beam splitter 16 is a spectroscopic device that transmits P light and reflects S light.

[0063] When N=2, no beam combining unit is required, and the output coupling module 21 includes a cube polarization beam splitter 16, a second half-wave plate 14 and a second reflector 15. The cube polarization beam splitter 16 is used to couple the P-polarized transmitted light beam after passing through the first cube beam splitter 8 with the S-polarized light after the optical path direction is changed by the second reflector 15 to obtain the output total light beam.

[0064] The optical fiber focusing output module 22 includes a focusing lens 17 and an optical fiber connector 18 ; the total light beam output by the output coupling module 21 is focused by the focusing lens 17 and then coupled into the optical fiber connector 18 .

[0065] like Figure 1 and Figure 2 As shown, in the embodiment of the present invention, taking N=2 as an example, among the two blue light modules 6 and 7, the blue light module 6 is the first blue light module and the blue light module 7 is the second blue light module. Each blue light module includes, in sequence along the optical path direction: a blue light single tube array 1, a fast axis collimator lens group 2, a slow axis collimator lens group 3, a 45° reflector group 4 and a 45° reflector 5;

[0066] The blue light single tube array 1 includes a plurality of blue light single tubes, each of which is used to generate blue light of a required wavelength and power. In an embodiment of the present invention, the blue light single tube array 1 includes 10 blue light single tubes with an output wavelength of approximately 444 nm and an output power of approximately 3 W, and the 10 blue light single tubes are evenly arranged in a line.

[0067] The blue light beams output by the blue light single-tube array 1 are collimated in the fast and slow axis directions by the fast-axis collimator group 2 and the slow-axis collimator group 3 in sequence to reduce the fast and slow axis divergence angles of each beam. The collimated blue light beams pass through the 45° reflector group 4 to shape each beam into a single beam. The optical path direction is then changed by the 45° reflector 5 to obtain a 30W blue light beam with a wavelength of 444nm, which is a P-polarized blue light beam.

[0068] In the embodiment of the present invention, the transmission grating 10 used is a grating with a diffraction efficiency of more than 94% for S light in the blue light band, that is, the +1 order diffraction efficiency at 444nm is about 94%. Only the 0th and +1st order diffracted light exists, and both the 0th and +1st order diffracted light of the grating exist in both transmission and reflection states. Figure 3 As shown, for this grating, when the incident light is in the P polarization state, the 0th-order diffracted transmitted light accounts for 91% of the total energy. When the incident light is in the S polarization state, the +1st-order diffracted transmitted light accounts for 94% of the total energy. Therefore, before the light enters the grating, a first half-wave plate 9 is used to convert the light into the S polarization state, and a first reflector 11 is used to select the +1st-order transmitted light. In other embodiments, other gratings whose diffraction efficiency for S light in the blue light band exceeds a preset threshold may also be used.

[0069] like Figure 4 and Figure 6 As shown, the blue light module 6 transmits a blue light beam, which is split into 20% reflected light and 80% transmitted light after passing through the first cubic beam splitter 8. The 20% reflected light is reflected upward, passes through the first half-wave plate 9 to convert the P-polarized blue light beam into an S-polarized blue light beam, and then is diffracted by the transmission grating 10 to produce +1-order diffracted light. The +1-order diffracted light is then returned along the original optical path by the first reflector 11 and split again at the first cubic beam splitter 8. A portion of the re-split light beam returns along the original optical path to the blue light single-electrode array 1 of the blue light module 6, and together with the light beam from the blue light module 7 that is re-split at the first cubic beam splitter 8 and transmitted to the blue light module 6, constitutes the Littman external cavity structure feedback of the blue light module 6, achieving linewidth compression. This process is the external cavity feedback of the blue light module 6. The other portion of the re-split light beam is transmitted downward along the second cubic beam splitter 12 of the blue light module 7 to the blue light single-electrode array 1 of the blue light module 7. 80% of the transmitted light is incident on the cube polarization beam splitter 16 toward the left, and is subsequently coupled with the light beam from the blue light module 7 that is incident on the cube polarization beam splitter 16 after passing through the second reflector 15 .

[0070] like Figure 5 and Figure 6 As shown, the blue light module 7 sends a blue light beam, which is divided into 20% reflected light and 80% transmitted light after passing through the second cube beam splitter 12; the 20% reflected light passes through the first cube beam splitter 8 upward and is again divided into reflected light and transmitted light. The transmitted light is incident on the cube polarization beam splitter 16 to the left together with the transmitted light beam of the blue light module 6. The reflected light passes through the first half-wave plate 9 upward and changes from the P polarization state to the S polarization state. After being diffracted by the transmission grating 10, a +1-order diffracted light is obtained. The +1-order diffracted light is reflected by the first reflector 11, returns along the original light path, and is split again at the first cube beam splitter 8; a part of the light beam split again at the first cube beam splitter 8 is sent along the original light path. The optical path returns to the blue light single tube array 1 of the blue light module 7, and together with the light beam from the blue light module 6 that is split again after passing through the first cubic beam splitter 8 and transmitted to the blue light module 7 along the second cubic beam splitter 12 of the blue light module 7, constitutes the Littman external cavity structure feedback of the blue light module 7, achieving linewidth compression. This process is the external cavity feedback of the blue light module 7; the other light beam that is split again at the first cubic beam splitter 8 is transmitted to the right into the blue light module 6, and together with the light beam from the blue light module 6 that is split again after passing through the first cubic beam splitter 8 and returned to the blue light module 6 along the original optical path, constitutes the Littman external cavity structure feedback of the blue light module 6. For details, see Figure 1The blue light module 6 external cavity feedback path 19 and the blue light module 7 external cavity feedback path 20. 80% of the transmitted light passes through the second half-wave plate 14 to the left, converting the P polarization state beam into the S polarization state. After being reflected by the second reflector 15, it is coupled with the 80% transmitted light of the blue light module 6 above after passing through the first cube beam splitter 8 at the cube polarization beam splitter 16 to output the total beam. In this embodiment of the present invention, Figure 1 、 Figure 4 and Figure 5 The black solid arrow in the figure indicates the direction of the output light path, and the arrow filled with slashes indicates the direction of the feedback light path.

[0071] A third reflector 13 is provided below the second cubic beam splitter 12 for reflecting the transmitted light beam after passing through the common external cavity module and then passing through the corresponding second cubic beam splitter 12 back to the second cubic beam splitter 12 to avoid energy leakage.

[0072] like Figure 6 As shown, the light beam passing through the cube polarization beam splitter 16 consists of two parts, an upper and a lower part. The first part is the transmitted light beam after passing through the first cube beam splitter 8. This part of the light beam includes 80% of the transmitted light beam of the blue light module 6 after passing through the first cube beam splitter 8, and the reflected light beam of the blue light module 7 after passing through the second cube beam splitter 12 and then passing through the first cube beam splitter 8 again. The second part is the 80% of the transmitted light beam of the blue light module 7 after passing through the second cube beam splitter 12. Both of these light beams are transmitted light beams in the P polarization state. Because the cube polarization beam splitter 16 reflects light beams in the S polarization state and transmits light beams in the P polarization state, the 80% of the transmitted light beam of the blue light module 7 after passing through the second cube beam splitter 12 is converted from the P polarization state to the S polarization state by passing through the second half-wave plate 14. After being reflected by the second reflector 15, it is coupled with the transmitted light beam after passing through the first cube beam splitter 8 at the cube polarization beam splitter 16 to output the total light beam.

[0073] It should be noted that if N>2, the second part of the light beam coupled through the cube polarization splitter 16 includes 80% of the transmitted light beams of the remaining N-1 blue light modules after passing through their corresponding second cube splitter 12. These N-1 transmitted light beams are P-polarized state transmitted light beams. The P-polarized state light beams are converted into S-polarized state through the corresponding second half-wave plate 14, and are reflected by the corresponding second reflectors 15. They are then combined by the beam combining unit. The combined light beam is coupled with the transmitted light beam of the first part after the first cube splitter 8 at the cube polarization splitter 16 to output the total light beam.

[0074] like Figure 7 As shown, the combined light beams are focused by the focusing lens 17 and then coupled into the optical fiber connector 18 .

[0075] It should be noted that the above embodiment is described using an example in which the transmission grating 10 has a diffraction efficiency of 94% or greater for S-light in the blue light band, and the blue light beam output by the blue light module is P-polarized. In other embodiments, the transmission grating 10 may also have a high diffraction efficiency for P-light in the blue light band, and the blue light output by the single blue light tube in each blue light module is an S-polarized blue light beam. The first and second cubic beam splitters 8 and 12 are cubic beam splitters that reflect and transmit the S-polarized blue light beam, while the remaining components remain unchanged. The polarization characteristics of the blue light output by the blue light module are determined specifically based on the polarization characteristics of the transmission grating 10.

[0076] In addition, whether the first half-wave plate 9 and the second half-wave plate 14 are needed to change the polarization state can be selected according to the characteristics of the cube polarization splitter 16. For example, when the blue light beam output by the blue light module is S-polarized, the cube polarization splitter 16 is a splitting device that transmits S light and reflects P light, and there is no need for a corresponding half-wave plate to change the polarization state.

[0077] The number of blue light tubes in each blue light module and the number of blue light modules are determined according to the actual power linewidth requirements; and the number, structure and size of other components in the device such as the fast-axis collimator group and the slow-axis collimator group can also be changed as needed to achieve linewidth compression of multiple modules.

[0078] The transmission grating-based shared external cavity linewidth compression system in this embodiment of the present invention utilizes a shared external cavity design with N blue light modules and a single transmission grating as the optical feedback element. This system efficiently achieves linewidth compression without increasing system complexity or cost, improving grating utilization and linewidth compression stability. By flexibly adjusting the number of blue light modules N, the desired power and narrow linewidth laser output can be achieved. This modular design eliminates the need for a single power amplifier and complex feedback system to achieve high-power, narrow linewidth laser output. This provides excellent flexibility and scalability, reduces system complexity, improves optical path allocation efficiency, and facilitates increased output power.

[0079] Compared with single-module feedback, the feedback beam (target longitudinal mode) received by each blue light module not only includes the feedback light of the current blue light module, but also the feedback light transmitted to the current blue light module by other blue light modules, which makes the target longitudinal mode have more energy, which is conducive to the target longitudinal mode gaining an advantage in mode competition, thereby making the optical system more stable.

[0080] Using a transmission grating as the optical feedback element, the system's high-efficiency diffraction properties enable narrower laser linewidths and eliminate the need for complex feedback control equipment, simplifying system design and operation. This design is closer to the classic external cavity diode laser (ECDL) structure, facilitating a wider wavelength tuning range. Compared to blazed gratings, transmission gratings offer lower diffraction losses, greater mechanical stability, and are less susceptible to temperature fluctuations.

[0081] The present invention uses a transmission grating for line width compression. An ideal diffraction grating can be considered to be composed of a group of equally spaced infinitely long and infinitely narrow slits, with the spacing between the slits being d, which is called the grating constant. When a plane wave with a wavelength of λ is incident vertically on the grating, the points on each slit act as secondary wave sources; the light emitted from these secondary wave sources propagates in all directions (i.e., spherical waves). Since the slits are infinitely long, we can only consider the situation on the plane perpendicular to the slits, that is, simplify the slits to a row of points on the plane. Then the light field along a certain direction on the plane is composed of the coherent superposition of the light emitted from each slit. When interference occurs, since the phases of the light emitted from each slit at the interference point are different, they will partially or completely cancel each other out. However, when the optical path difference between the light emitted from two adjacent slits to the interference point is an integer multiple of the wavelength of the light, the two beams of light have the same phase, and interference enhancement will occur. When a plane wave is incident at an angle of incidence θ i At incident light, the grating equation is written as:

[0082] d(sinθ m +sinθ i )=mλ

[0083] Where d is the slit spacing, i.e., the grating constant, and m is an integer with values ​​of 0, ±1, ±2, ...; θ m is the grating diffraction angle.

[0084] The diffraction angle of the grating is related to the wavelength of the incident light. The emission spectrum of a semiconductor laser has a certain width, and the laser light emitted by the laser contains multiple wavelengths. Therefore, when the laser is incident on the grating, except for the zeroth order, the longer the wavelength of the diffracted light of the same order, the larger the diffraction angle, that is, dispersion occurs. The use of higher-order diffracted light can also bring about greater angular dispersion, but in general, the diffraction efficiency of higher-order diffracted light is very small, which means that there is not enough energy to be fed back into the active area of ​​the laser resonant cavity. Therefore, in the grating external cavity technology, +1 (or -1) order diffracted light is often used. In the embodiment of the present invention, +1 order diffracted light is used.

[0085] This invention utilizes a Littman grating external cavity structure. When laser light is incident on the transmission grating 10, it undergoes a first diffraction. The +1st-order diffracted light no longer returns directly to the active area (blue light module). Instead, it is incident on the first reflector 11, reflected back to the transmission grating 10, undergoing a second diffraction. This second diffraction of the +1st-order diffracted light returns along the original optical path back to the laser resonant cavity. This double diffraction allows for a narrower wavelength range of light to be fed back to the active area compared to a single-grating Littrow structure, theoretically resulting in a narrower output linewidth.

[0086] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A common external cavity linewidth compression system based on transmission grating, characterized in that: include: N blue light modules, N≥2, a common external cavity module, an output coupling module (21) and a fiber focusing output module (22); the common external cavity module comprises a first cubic beam splitter (8), a transmission grating (10) and a first reflector (11); Each blue light module simultaneously outputs a blue light beam of the same wavelength. The blue light beam output by any blue light module is divided into reflected light and transmitted light after passing through the first cubic beam splitter (8); the reflected light is diffracted by the transmission grating (10) to generate diffracted light, and the diffracted light is reflected by the first reflector (11) and returns along the original light path, and is split again at the first cubic beam splitter (8); a portion of the light beam after splitting again returns along the original light path to the any blue light module, and the other portion of the light beam is respectively transmitted to the other N-1 blue light modules, and together with the light beam in any blue light module that returns along the original light path, constitutes the Littman external cavity feedback of the any blue light module, so as to achieve line width compression; the transmitted light of the N blue light modules is coupled into a beam of light through the output coupling module (21), and is output through the optical fiber focusing output module (22).

2. The common external cavity linewidth compression system according to claim 1, characterized in that: The N blue light modules are arranged in sequence; The common external cavity linewidth compression system further includes N-1 second cubic optical splitters (12) corresponding one-to-one to the remaining N-1 blue light modules except the first blue light module, and used for splitting the blue light beam output by the corresponding blue light module into reflected light and transmitted light; The blue light beams inputted into the common external cavity module by the remaining N-1 blue light modules are reflected lights after passing through the corresponding second cubic beam splitter (12); The transmitted light of the N blue light modules includes the transmitted light of each blue light module after passing through the first cubic beam splitter (8) and the transmitted light of the remaining N-1 blue light modules after passing through their corresponding second cubic beam splitter (12).

3. The common external cavity linewidth compression system according to claim 2, characterized in that: The blue light beam of the same wavelength output by each blue light module is a P-polarized blue light beam; The transmission grating (10) is a grating whose diffraction efficiency for S-polarized light in the blue light band reaches a preset threshold value or above, and the diffracted light is +1-order diffracted light; The first cubic beam splitter (8) and the second cubic beam splitter (12) are cubic beam splitters that reflect and transmit P-polarized blue light beams; The common external cavity module further comprises a first half-wave plate (9) arranged between the first cubic beam splitter (8) and the transmission grating (10) along the optical path direction, and is used for transforming the polarization state of the blue light beam.

4. The common external cavity linewidth compression system according to claim 2, characterized in that: The blue light beam of the same wavelength output by each blue light module is an S-polarized blue light beam; The transmission grating (10) is a grating whose diffraction efficiency for P-polarized light in the blue light band reaches a preset threshold value or above, and the diffracted light is +1-order diffracted light; The first cubic beam splitter (8) and the second cubic beam splitter (12) are cubic beam splitters that reflect and transmit S-polarized blue light beams; The common external cavity module further comprises a first half-wave plate (9) arranged between the first cubic beam splitter (8) and the transmission grating (10) along the optical path direction, and is used for transforming the polarization state of the blue light beam.

5. The common external cavity linewidth compression system according to any one of claims 2 to 4, characterized in that: When N>2, the output coupling module (21) includes a cube polarization beam splitter (16), N-1 second half-wave plates (14) and second reflectors (15) corresponding one-to-one to the remaining N-1 blue light modules, and a beam combining unit; The transmitted light after passing through the second cubic beam splitter (12) undergoes polarization state conversion through a corresponding second half-wave plate (14), and then undergoes optical path direction change through a corresponding second reflector (15), and then undergoes N-1 beams of light to be combined through the beam combining unit to obtain a combined light beam; The combined light beam and the transmitted light after passing through the first cubic beam splitter (8) are coupled into a beam of light through the cubic polarization beam splitter (16), and the coupled light beam serves as the output total light beam.

6. The common external cavity linewidth compression system according to any one of claims 2 to 4, characterized in that: When N=2, the output coupling module (21) includes a cube polarization beam splitter (16), a second half-wave plate (14) and a second reflector (15); The transmitted light beam after passing through the second cube beam splitter (12) undergoes polarization state conversion through the second half-wave plate (14), and then changes the direction of the optical path through the second reflector (15). The light beam is then coupled with the transmitted light after passing through the first cube beam splitter (8) through the cube polarization beam splitter (16) to form a beam of light, and the coupled beam serves as the output total beam.

7. The common external cavity linewidth compression system according to any one of claims 2 to 4, characterized in that: The ratio of the reflectivity to the transmittance of the first cubic beam splitter (8) and the second cubic beam splitter (12) is 2:

8.

8. The common external cavity linewidth compression system according to any one of claims 2 to 4, characterized in that: Also included is a third reflector (13) corresponding to the last blue light module; The third reflector (13) is used to reflect the transmitted light beam of the blue light beam output by the last blue light module after passing through the common external cavity module and then passing through its corresponding second cubic beam splitter (12), so that the reflected light beam passes through its corresponding second cubic beam splitter (12) again.

9. The common external cavity linewidth compression system according to any one of claims 1 to 4, characterized in that: Each blue light module comprises, in sequence along the optical path direction: a blue light single tube array (1), a fast axis collimating lens group (2), a slow axis collimating lens group (3), a 45° reflector group (4) and a 45° reflector (5); The blue light beam generated by the blue light single tube array (1) passes through the fast axis collimating lens group (2) and the slow axis collimating lens group (3) in sequence to be collimated in the fast axis direction and the slow axis direction; the collimated light beam passes through the 45° reflector group (4) to be shaped into a beam of light, and then passes through the 45° reflector (5) to change the direction of the light path and output the required blue light beam.

10. The common external cavity linewidth compression system according to any one of claims 1 to 4, characterized in that: The optical fiber focusing output module (22) includes a focusing lens (17) and an optical fiber connector (18); The light beam output by the output coupling module (21) is focused by the focusing lens (17) and then coupled into the optical fiber connector (18).

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