External cavity semiconductor laser packaging structure based on tail fiber direct pumping

Abstract

The invention provides an external cavity semiconductor laser packaging structure based on tail fiber direct pumping. The external cavity semiconductor laser packaging structure comprises a pumping tail fiber, a heat conduction heat sink, a transparent heat sink, a gain chip and an external cavity output mirror. The pumping tail fiber penetrates into the heat conduction heat sink, is in contact with the surface of the transparent heat sink, is fixed with the transparent heat sink and is used for outputting pumping light; the heat-conducting heat sink is provided with a precise optical fiber lead-in hole which is used for leading in and fixing the pumping tail fiber; the transparent heat sink is arranged on the heat conduction heat sink and is bonded with the gain chip, and pump light output by the pump tail fiber passes through the transparent heat sink and enters an active area of the gain chip; the gain chip and the outer cavity output mirror form a basic resonant cavity structure, and output laser beams are obtained through pump light excitation. By changing the pumping structure of the VECSEL laser, compact and modular packaging of the laser can be achieved, and a low-noise and high-stability single-frequency light source and a frequency-modulated continuous wave light source can be provided.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a packaging structure for an external cavity semiconductor laser based on direct fiber-pumped laser. Background Technology

[0002] Vertical external cavity surface-emitting lasers (VECSELs) are a new type of semiconductor laser that combines high beam quality and high power density. Compared with traditional edge-emitting lasers, VECSELs offer scalable cavity designs and excellent heat dissipation, facilitating the insertion of frequency-doubling crystals, filters, or FP optical elements. Therefore, they have become an important platform for realizing single-frequency, frequency-doubled, and tunable laser output. This type of light source has broad application prospects in fields such as spectral analysis, precision measurement, interferometry, coherent communication, and lidar.

[0003] For low-to-medium power external cavity single-frequency VECSELs in the hundreds of milliwatts range, their optical structures are typically simple, often employing a linear cavity design, offering good optical tunability and high mode stability. The single-frequency stability of such systems depends more on cavity mechanical stability and thermal management than on the optical design itself. However, in practical implementation, the packaging and stability of the pump system become key bottlenecks limiting single-frequency performance and compact packaging. Currently, VECSEL pumping methods are mainly divided into two categories: fiber-free pumping and fiber-coupled pumping.

[0004] Among them, the fiberless pumping method integrates the pump diode directly inside the laser and projects the pump beam onto the surface of the gain chip through a collimating and focusing lens group. The problems it faces are: (1) The quality of the pump spot is limited by the strip-shaped light-emitting surface of the diode, and the beam is distributed in a non-uniform strip shape. After the beam is shaped and focused, it is difficult to form an ideal circular spot with uniform brightness, which will lead to a significant decrease in the output beam quality of the VECSEL; (2) The heat sources of the pump and the chip are concentrated, the local heat load is large, and the system temperature field distribution is complex, which is not conducive to high-precision temperature control and single-frequency maintenance.

[0005] Fiber-coated pumping typically utilizes pump light output from an optical fiber, which is then focused onto a gain chip via a collimating and focusing lens assembly. This approach effectively improves beam uniformity and reduces thermal coupling, making it a commonly used pumping structure. However, its main problems lie in mechanical and thermal instability: (1) The SMA905 connector and its metal ferrule structure will experience slight displacement during thermal cycling, and the thermal expansion difference between the lens and the lens barrel will cause the focal length and optical axis to drift, resulting in changes in the pump beam position over time; (2) Pump loss light will cause local thermal noise, and the metal interface and metal sleeve will absorb the lost pump light, forming random heat sources, resulting in uneven temperature distribution within the cavity and affecting single-frequency stability; (3) The package size is large, and the dimensions of the standard SMA905 connector and collimating and focusing components often exceed the entire laser cavity, which not only limits the overall compact design but also increases assembly difficulty and system thermal drift.

[0006] Therefore, whether it is a directly integrated fiberless structure or the traditional method of using SMA905 fiber coupling, it is difficult to balance spot quality, mechanical stability and compact packaging in low-to-medium power single-frequency VECSELs, which limits the potential application value of this type of laser. Summary of the Invention

[0007] This invention aims to provide a solution that allows direct optical contact between the fiber end face and a transparent heat sink, replacing the traditional collimation and focusing system. This achieves lensless coupling of the pump light and integrated packaging of the laser structure, addressing the problems of existing low-to-medium power external cavity single-frequency VECSELs, which commonly use SMA905 pigtails and collimation and focusing lenses, resulting in large size, optical axis sensitivity, and severe thermal drift. This invention achieves compact and modular packaging of linear cavity single-frequency VECSELs, providing low-noise, high-stability single-frequency light sources and frequency-modulated continuous wave light sources.

[0008] An external cavity semiconductor laser packaging structure based on direct fiber-pumped pump includes: a pump pigtail, a heat sink, a transparent heat sink, a gain chip, and an external cavity output mirror; the pump pigtail passes through the heat sink and contacts the surface of the transparent heat sink, and is fixed to the transparent heat sink for outputting pump light; the heat sink is provided with a precision fiber guide hole for introducing and fixing the pump pigtail; the transparent heat sink is mounted on the heat sink and bonded to the gain chip; the pump light output from the pump pigtail passes through the transparent heat sink and is incident on the active region of the gain chip; the gain chip and the external cavity output mirror constitute a basic resonant cavity structure, and an output laser beam is obtained by excitation by the pump light.

[0009] Furthermore, the transparent heat sink is made of silicon carbide, diamond, or sapphire.

[0010] Furthermore, the contact end between the pump pigtail and the transparent heat sink is a ceramic ferrule structure, a short-cut optical fiber end, or a bare fiber direct insertion structure, and the contact method between the pump pigtail and the transparent heat sink is direct surface contact or optical adhesive bonding.

[0011] Furthermore, the pump pigtail includes an optical fiber core, a core cladding, a coating layer, and a core protective sleeve. The optical fiber core and core cladding are used for beam transmission. The core cladding wraps around the optical fiber core. The coating layer is located outside the core cladding and is formed by coating the surface of the core cladding with a resin material. The core protective sleeve is located outside the coating layer.

[0012] Furthermore, the heat sink is equipped with a TEC temperature control module for temperature control of the gain chip.

[0013] Furthermore, it also includes: a complete housing, which is a metal housing or a ceramic housing, and the pump pigtail, heat sink, transparent heat sink, gain chip and external cavity output mirror are all sealed inside the complete housing.

[0014] Compared to existing technologies, the advantages and beneficial effects of this invention are as follows: By inserting the pump pigtail into the precision fiber guide hole of the heat-conducting heat sink to achieve optical reference and heat conduction, and fixing it with the transparent heat sink, pump light is output. The transparent heat sink is mounted on the heat-conducting heat sink and bonded to the gain chip, avoiding the formation of metal welding layers or other light-absorbing media layers, ensuring good optical contact and thermal conductivity. The pump light output from the pump pigtail passes through the transparent heat sink and is incident on the active region of the gain chip to achieve optical excitation. The gain chip and the external cavity output mirror form a basic resonant cavity structure. The output laser beam is obtained by excitation by the pump light. The direct contact between the end face of the pump pigtail and the transparent heat sink replaces the traditional collimation and focusing system, realizing lensless coupling of the pump light and integrated packaging of the laser structure, thereby significantly reducing the package size. It is especially suitable for the compact and modular packaging of linear cavity single-frequency VECSELs, realizing low-noise, high-stability single-frequency light sources and frequency-modulated continuous wave light sources, ensuring spot quality, mechanical stability and package compactness. Attached Figure Description

[0015] Figure 1 This is a cross-sectional schematic diagram of a package structure for an external cavity semiconductor laser based on direct pigtail pumping in one embodiment.

[0016] Figure 2 This is a schematic diagram of pumping light emitted from a pump pigtail in one embodiment;

[0017] Figure 3 This is a schematic cross-sectional view of the heat sink in one embodiment;

[0018] Figure 4This is a schematic cross-sectional view of the pump pigtail structure in one embodiment;

[0019] Figure 5 This is a schematic diagram of the optical path of an external cavity semiconductor laser packaging structure based on direct fiber-pumped laser tail in one embodiment.

[0020] In the attached diagram, the components are: pump pigtail 1, fiber core 11, fiber core cladding 12, coating layer 13, fiber core protective sleeve 14, heat sink 2, precision fiber inlet 21, transparent heat sink 3, gain chip 4, external cavity output mirror 5, frequency doubling crystal 6, and birefringent filter 7. Detailed Implementation

[0021] To make the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In one embodiment, such as Figure 1-3 As shown, a package structure for an external cavity semiconductor laser based on direct pumping via a pigtail is provided, including: a pump pigtail 1, a heat sink 2, a transparent heat sink 3, a gain chip 4, and an external cavity output mirror 5; the pump pigtail 1 passes through the heat sink 2 and contacts the surface of the transparent heat sink 3, and is fixed to the transparent heat sink 3 for outputting pump light; the heat sink 2 is provided with a precision fiber inlet hole 21 for introducing and fixing the pump pigtail 1; the transparent heat sink 3 is mounted on the heat sink 2 and bonded to the gain chip 4, and the pump light output from the pump pigtail 1 is incident on the active region of the gain chip 4 through the transparent heat sink 3; the gain chip 4 and the external cavity output mirror 5 constitute a basic resonant cavity structure, and the output laser beam is obtained by excitation by the pump light.

[0023] In this embodiment, the pump pigtail 1 is inserted into the precision fiber inlet 21 of the heat sink 2 to achieve optical reference and heat conduction. It is fixed to the transparent heat sink 3 and outputs pump light. The transparent heat sink 3 is mounted on the heat sink 2 and bonded to the gain chip 4 to avoid the formation of metal welding layers or other light-absorbing media layers, ensuring good optical contact and thermal conductivity. The pump light output from the pump pigtail 1 passes through the transparent heat sink 3 and is incident on the active region of the gain chip 4 to achieve optical excitation. The gain chip 4 and the external cavity output mirror 5 form a basic resonant cavity structure. The output laser beam is obtained by excitation by the pump light. The direct contact between the end face of the pump pigtail 1 and the transparent heat sink 3 replaces the traditional collimation and focusing system, realizing lensless coupling of the pump light and integrated packaging of the laser structure, thereby significantly reducing the package size. It is especially suitable for the compact and modular packaging of linear cavity single-frequency VECSELs, realizing low-noise, high-stability single-frequency light sources and frequency-modulated continuous wave light sources, ensuring spot quality, mechanical stability and package compactness.

[0024] It should be noted that the core of this invention is to provide a technical solution for a fiber-coated direct-pumped gain chip. The basic resonant cavity structure is only an exemplary structure, and corresponding optical elements, such as frequency-doubling crystals and birefringent filters, can be inserted into the cavity according to actual needs. The resonant cavity structure can also be adjusted as needed, such as a V-shaped or Z-shaped resonant cavity, to facilitate the insertion of more optical elements and improve laser performance.

[0025] Among them, the heat sink 2 is made of a high thermal conductivity material to facilitate rapid heat dissipation of the gain chip 4. For example, a copper heat sink can be used as the heat sink. Copper heat sink has high thermal conductivity, which can quickly dissipate the heat generated by the chip to the heat dissipation structure, preventing the gain chip 4 from overheating. In addition, copper heat sink also has advantages in mechanical strength and thermal management, which can effectively improve the chip performance and reliability.

[0026] The pump pigtail 1 includes an optical fiber core layer 11, a core cladding layer 12, a coating layer 13, and a core protective sleeve 14. The optical fiber core layer 11 and the core cladding layer 12 are used for beam transmission. The core cladding layer 12 wraps around the optical fiber core layer 11. The coating layer 13 is located outside the core cladding layer 12 and is formed by coating the surface of the core cladding layer 12 with resin material. The core protective sleeve 14 is located outside the coating layer 13.

[0027] Specifically, such as Figure 4 As shown, the fiber core 11 and the fiber core cladding 12 form the optical transmission channel. The surface of the fiber core cladding 12 is coated with a resin-like material to form a coating layer 13, which increases the structural strength of the optical fiber. The outermost layer of the optical fiber is a fiber core protective sleeve 14 of various types, such as Teflon or PVC.

[0028] In actual use, if there are no mechanical moving or vibrating parts inside the VECSEL laser, and the coated optical fiber has sufficient mechanical strength, the fiber core protective sleeve is not required.

[0029] Remove the fiber core protective sleeve 14 from the pump pigtail 1. The end inserted into the fiber ferrule or custom clamp needs to be polished to ensure the perpendicularity of the optical axis and low insertion loss. With the fiber ferrule or custom clamp fixed, the pump pigtail 1 is inserted into the precision fiber inlet hole 21 of the heat sink 2 and contacts the surface of the transparent heat sink 3. It is fixed with optical adhesive to achieve the effect of direct pumping at the rear end of the pigtail.

[0030] In one embodiment, typical multimode fiber structure dimensions are shown in Table 1, and the typical core diameters of the pigtails used in the low-power laser diode pump source are 105 μm and 200 μm, respectively.

[0031] Table 1: Typical Multimode Fiber Structure Dimensions (Unit: Micrometers)

[0032] Fiber core Core cladding Coating layer Fiber core protective sleeve 105 125 250 900 200 220 320 900

[0033] The contact end between the pump pigtail 1 and the transparent heat sink 3 can be a ceramic ferrule structure, a short fiber optic end, or a bare fiber direct insertion structure. The contact method between the pump pigtail 1 and the transparent heat sink 3 is direct surface contact or optical adhesive bonding.

[0034] Specifically, the contact end between the pump pigtail 1 and the transparent heat sink 3 can adopt various different structures according to actual needs. The ceramic ferrule structure can be used to fix the fiber end face and achieve alignment, so that the contact end between the pump pigtail 1 and the transparent heat sink 3 is aligned with the transparent heat sink 3; the stub fiber end has a fiber end face that has been cut and polished, so that the pump pigtail 1 contacts the transparent heat sink 3; the bare fiber direct insertion structure does not require a ceramic ferrule and is suitable for temporary or low-loss scenarios.

[0035] When the above structure is used to make the pump pigtail 1 contact the transparent heat sink 3, the contact method between the pump pigtail 1 and the transparent heat sink 3 can be direct surface contact or contact through optical adhesive with ultra-low absorption rate.

[0036] In addition, the contact ends of the pump pigtail 1 and the contact surfaces of the transparent heat sink 3 can be precision polished to improve surface quality, optimize contact performance, enhance functional performance and extend service life.

[0037] The heat sink 2 is equipped with a TEC temperature control module for temperature control of the gain chip 4.

[0038] Specifically, the heat sink 2 also includes a TEC (Thermoelectric Cooling) temperature control module. The TEC temperature control module uses the Peltier effect to precisely regulate the temperature of the gain chip 4, preventing the gain chip 4 from overheating.

[0039] Among them, the transparent heat sink 3 is not limited to silicon carbide, diamond and sapphire, but can also be other transparent heat sink sheets with high thermal conductivity and low absorption of pump light.

[0040] Specifically, using transparent materials with high thermal conductivity such as silicon carbide, diamond, or sapphire, the transparent heat sink 3 has both high thermal conductivity and high light transmittance. It can serve as a pump optical path channel and also form an efficient heat dissipation interface, ensuring the temperature stability of the gain chip 4.

[0041] To reduce optical transmission path loss and achieve efficient heat conduction of the chip, a direct bonding process is required between the transparent heat sink 3 and the gain chip 4. Therefore, silicon carbide or diamond material can be preferred for the transparent heat sink 3.

[0042] Within the resonant cavity, a frequency-doubling crystal 6 and a birefringent filter 7 can be sequentially arranged along the optical path. The frequency-doubling crystal 6 is used for laser frequency conversion; the birefringent filter 7, through its spectral filtering and polarization selection characteristics, introduces wavelength-dependent losses during the laser's round-trip oscillation, ultimately allowing a single longitudinal mode to prevail in the competition, thereby obtaining a single longitudinal mode laser output.

[0043] Of course, depending on the actual application requirements, any optical element such as an FP filter can be inserted into the resonant cavity to jointly realize the functions of laser frequency conversion, laser polarization state control, and further compression of single-frequency linewidth.

[0044] It also includes: the main unit housing, which is a metal or ceramic housing, and the pump pigtail 1, heat sink 2, transparent heat sink 3, gain chip 4 and external cavity output mirror 5 are all sealed inside the main unit housing.

[0045] Specifically, the pump pigtail 1, the heat sink 2, the transparent heat sink 3, the gain chip 4, and the external cavity output mirror 5 are all sealed inside the main housing. The main housing can be a metal housing or a ceramic housing, equipped with relevant optoelectronic interfaces, and is completely sealed. After assembly, dry nitrogen is filled in to prevent contamination and oxidation.

[0046] In the aforementioned external cavity semiconductor laser packaging structure, the pump optical path, heat conduction path, and mechanical reference are unified in the same structural system, eliminating the need for a multi-lens focusing system. This allows the pump light to be directly incident on the gain chip via a transparent heat sink, effectively eliminating focal drift and optical misalignment and simplifying the optical path. The transparent heat sink has both high thermal conductivity and high light transmittance, serving as both an optical path channel and a highly efficient heat dissipation interface, maintaining stable chip temperature and optimizing the heat dissipation channel. Ceramic ferrules or precision metal holes are used to position the pigtails, which are then sealed and fixed with low-shrinkage optical adhesive, eliminating optical axis offset caused by thermal expansion differences in traditional metal structures.

[0047] The design of the external cavity semiconductor laser packaging structure eliminates the need for a separate collimation and focusing module in the pumping system, significantly reducing the package size, improving mechanical stiffness, and simultaneously suppressing optical and thermal drift. This approach is particularly suitable for the compact and modular packaging of linear cavity single-frequency VECSELs, laying the structural foundation for realizing low-noise, high-stability single-frequency light sources and frequency-modulated continuous wave (FMCW) LiDAR light sources.

[0048] In one embodiment, the calculation steps for the spot size on the laser gain chip of the aforementioned external cavity semiconductor laser packaging structure are as follows: The output light field of the multimode fiber is a quasi-uniform angular distribution light source with a large number of superimposed modes, which can be approximated as a conical divergence model with a "uniform top cap," satisfying geometric optics sufficient for pump spot size estimation. After the pump light exits from the fiber core, it can be regarded as a spot with a divergence angle, and its spot radius can be calculated using a layered accumulation formula:

[0049]

[0050] like Figure 5 As shown, the laser gain chip is bonded to the silicon carbide surface. The VECSEL thickness is on the order of micrometers. Ignoring beam variations along this path, the beam spot on the chip is approximately the same as the beam spot on the silicon carbide exit surface. Furthermore, the pigtail ferrule and the silicon carbide (SiC) surface are precision polished, resulting in a very small gap between them during assembly (0.05 mm). Other parameters are as follows: typical VECSEL pump source: wavelength 808 nm, NA = 0.22, fiber core diameter 100 μm; SiC refractive index 2.55, thickness 350 μm.

[0051] The theoretical calculations are as follows:

[0052] 1) Diverging half-angle

[0053] Air layer:

[0054] In SiC:

[0055] 2) Fiber end radius

[0056] Initial radius: r0 = d0 / 2 = 50 μm

[0057] 3) Radius increment of each layer

[0058] Air segment extension: △r air =ztanθ air =50×0.22553=11.276μm

[0059] SiC internal expansion: △r SiC =d SiC tanθ SiC =350 × 0.0866 = 30.309 μm

[0060] 4) Target surface radius and diameter

[0061] r = r0 + Δr air +△r SiC =50+11.276+30.309=91.585μm

[0062] D = 2r = 183.171μm

[0063] Table 2 shows the pump spot results obtained by calculating different fiber core diameters and SiC thickness parameters using the above method.

[0064] Table 2 Pump spot of direct fiber optic pump in the active region of the gain chip (unit: micrometers)

[0065] Core diameter air gap SiC thickness Pump spot diameter on chip 100 50 350 183 100 50 500 209 200 50 350 283 200 50 500 309

[0066] In practical applications, the pump spot on the laser gain chip is typically smaller than millimeters. At the same pump power, a smaller spot size results in a higher carrier concentration in the quantum well, making it easier to meet the pumping conditions for laser generation. For VECSEL applications of several hundred milliwatts, under different core diameters and SiC thickness parameters, the spot sizes obtained in Table 2 all meet the application requirements, indicating that direct back-end pumping with the pigtail effectively ensures spot quality and improves the stability of the laser under high-precision requirements.

[0067] In one embodiment, a specific implementation example of an external cavity semiconductor laser packaging structure based on direct fiber-pumped laser pigtail is also provided:

[0068] The layout of optical components within the VECSEL laser resonator cavity is consistent with traditional methods. For the direct-pump section using a pigtail, the VECSEL gain chip employs an inverted growth structure, directly bonding the gain chip to a precision-polished transparent heat sink (such as a SiC wafer). Then, a chemical etching process is used to remove the matrix, exposing the laser emission window. The central opening of the heat sink facilitates the insertion and fixation of the pigtail. To ensure reliable heat dissipation of the chip, the central opening of the heat sink should be as small as possible. In specific engineering examples, there are two typical technical solutions:

[0069] The first method is to use a small-sized fiber optic ferrule to assist in the fiber core insertion mode.

[0070] Specifically, the core of the pump pigtail with a coated layer is inserted into the fiber ferrule, and the core is aligned flush with the end face of the ferrule and secured with optical adhesive. The rear end face of the ferrule is also fixed to the protective sleeve of the core to protect the fiber. The end face of the fiber inserted into the ferrule is polished using specialized fiber polishing equipment. For practical applications, a general-purpose ceramic ferrule with a diameter of 1.249mm can be selected. Correspondingly, a 1.25mm precision fiber guide hole is made in the center of the heat sink copper block to guide the ferrule, allowing the core of the pump pigtail to directly contact the silicon carbide surface; optical adhesive can also be used for fixation. To achieve better heat transfer, high thermal conductivity adhesives or indium foil can be used to assist thermal contact between the silicon carbide and the heat sink, creating a better heat transfer channel for the chip.

[0071] The aforementioned small-sized fiber ferrule-assisted fiber core mode is a mature technology with simple assembly, ensuring consistent laser performance.

[0072] It should be noted that only typical treatment methods in the structure are listed here. Various optimization schemes can be generated from this. For example, applying optical adhesive (the adhesive medium can be optical adhesive, epoxy adhesive or other transparent low-shrinkage curing materials) to the contact surface between the fiber core and silicon carbide is beneficial to contact stability and reduce losses.

[0073] The second method is to use a fiber optic connection mode without ferrules.

[0074] The coating significantly improves the mechanical strength of the bare fiber core; for example, with a core diameter of 100 μm, the coating diameter is 250 μm. Guide holes slightly larger than 250 μm are created in the copper block (heat sink). The polished fiber core is inserted into and contacts the SiC surface, and then fixed with optical adhesive. A 900 μm outer diameter fiber protective sleeve can be bonded near the through-hole of the heat sink.

[0075] The ferrule-less fiber optic access mode achieves separation of optical alignment contact and mechanical stress on the protective sleeve, resulting in better structural stability. However, this mode places higher demands on assembly and adjustment. In practical applications, either the small-size fiber ferrule-assisted fiber optic access mode or the ferrule-less fiber optic access mode can be selected based on specific needs.

[0076] As can be seen from the two specific embodiments above, the gap between the fiber core and the silicon carbide wafer should be as close as possible, thereby shortening the distance from the pump light to the gain chip; the gain chip has a good heat dissipation channel, which is beneficial to improving the laser's operating efficiency and performance.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] First, the optical path degrees of freedom are significantly reduced, resulting in passively stable pump coupling. A single coaxial reference is formed by "fiber core end face - transparent heat sink - gain region", and the optical axis no longer depends on the cooperation of multiple lens stages and lens barrel; the focal length and focusing mechanism are eliminated, and the drift of the pump spot position with time and temperature is significantly suppressed, which is conducive to maintaining a single frequency operating point for a long time; the structure is more deterministic, and it is a stable solution after assembly, reducing subsequent maintenance and readjustment.

[0079] Secondly, the pump inlet and heat dissipation interface are integrated, making it easier to obtain a stable thermal state with good repeatability. The transparent heat sink simultaneously serves as the pump injection window and heat conduction channel, with heat from the pump area being directly conducted to the heat sink along the coaxial direction. No additional heat absorbers such as metal lenses / joints are introduced at the pump end, simplifying the interface materials and path, which is conducive to forming a uniform and reproducible steady-state temperature field and reducing thermal stress and phase disturbances caused by interface differences. Temperature control only needs to maintain the overall thermal balance of this coaxial channel, making the control strategy and parameter tuning more direct.

[0080] Third, the pump interface is compact and standardized, facilitating processing, assembly, and batch consistency. It employs ceramic ferrules for positioning and low-shrinkage optical adhesive for fixation, forming a standardized coaxial pump interface compatible with common fiber optic pigtail specifications. The processing technology follows a conventional "polishing-ferrule-limiting-curing" sequence, with fewer steps, a shorter tolerance chain, and high packaging accuracy and batch consistency. It is also easy to integrate with processes such as nitrogen filling and sealing. The interface itself is independent of specific external cavity designs (linear cavity, V-cavity, and frequency doubling are all possible), facilitating reuse across different single-frequency VECSEL platforms.

[0081] In summary, this invention innovatively designs a pump structure for external cavity semiconductor laser packaging, enabling highly integrated design at the optical, thermal, and mechanical levels. It systematically solves the problems of thermal drift, focal length drift, and volume constraints that exist in the pump packaging stage of low- and medium-power single-frequency VECSELs, laying an engineeringable packaging foundation for compact, high-stability single-frequency lasers and their applications in spectral measurement, optical communication, and LiDAR.

[0082] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0083] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A packaging structure for an external cavity semiconductor laser based on direct fiber-coated laser pigtails, characterized in that, include: Pump pigtail, thermally conductive heat sink, transparent heat sink, gain chip, and external cavity output mirror; The pump pigtail is inserted into the thermally conductive heat sink and contacts the surface of the transparent heat sink, and is fixed to the transparent heat sink for outputting pump light; The heat sink is provided with a precision optical fiber inlet hole for introducing and fixing the pump pigtail. The transparent heat sink is mounted on the heat-conducting heat sink and bonded to the gain chip. The pump light output from the pump pigtail passes through the transparent heat sink and is incident on the active region of the gain chip. The gain chip and the external cavity output mirror constitute a basic resonant cavity structure, and the output laser beam is obtained by pump light excitation.

2. The packaging structure for an external cavity semiconductor laser based on direct fiber-coated pigtails according to claim 1, characterized in that, The transparent heat sink is made of silicon carbide, diamond, or sapphire.

3. The packaging structure for an external cavity semiconductor laser based on direct fiber-coated pigtails according to claim 1, characterized in that, The contact end between the pump pigtail and the transparent heat sink is a ceramic ferrule structure, a short fiber optic end, or a bare fiber direct insertion structure. The contact method between the pump pigtail and the transparent heat sink is direct surface contact or optical adhesive bonding.

4. The packaging structure for an external cavity semiconductor laser based on direct fiber-coated pigtails according to claim 1, characterized in that, The pump pigtail includes an optical fiber core, a core cladding, a coating layer, and a core protective sleeve. The optical fiber core and core cladding are used for beam transmission. The core cladding wraps around the optical fiber core. The coating layer is located outside the core cladding and is formed by coating the surface of the core cladding with a resin material. The core protective sleeve is located outside the coating layer.

5. The packaging structure for an external cavity semiconductor laser based on direct fiber-pumped laser tails according to claim 1, characterized in that, The heat sink is equipped with a TEC temperature control module for temperature control of the gain chip.

6. The packaging structure for an external cavity semiconductor laser based on direct fiber-coated pigtails according to claim 1, characterized in that, Also includes: The main housing is either a metal or ceramic housing, and the pump pigtail, heat sink, transparent heat sink, gain chip, and external cavity output mirror are all sealed inside the main housing.

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