External cavity single-frequency VECSEL structure based on quartz reference skeleton

Abstract

The invention provides an external cavity single-frequency VECSEL structure based on a quartz reference skeleton. The external cavity single-frequency VECSEL structure comprises a pumping module, a gain chip, an output mirror and the quartz reference skeleton, the pumping module and the quartz reference skeleton adopt a unified optical interface and are used for outputting pumping light to an active area of the gain chip; the gain chip is bonded on the heat conduction heat sink and then is installed on the copper heat sink. The copper heat sink is in direct sealing contact with the quartz reference skeleton. The gain chip and the output mirror form a resonant cavity, and output laser beams are obtained through pump light excitation; the quartz reference skeleton is of a quartz integrated structure and is used for fixing all optical elements in the resonant cavity and providing an optical geometric reference. According to the invention, heat flow control and optical stability can be mutually independent, the mechanical and thermal stability of the VECSEL is improved, and the length of the resonant cavity is kept stable for a long time, so that passive single-frequency output without active feedback for a long time is realized.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to an external cavity single-frequency VECSEL structure based on a quartz reference frame. Background Technology

[0002] Vertical external cavity surface-emitting lasers (VECSELs) offer flexible wavelength customization, near-diffraction-limited beam quality, and high power. By inserting elements into the external cavity, they can achieve single-frequency, frequency-doubled, and tuned outputs, making them widely applicable. The readily available 1018nm infrared VECSEL, through intracavity frequency doubling, can achieve a 509nm single-frequency output. This wavelength corresponds to the Rydberg hyperfine level structure of cesium atoms, holding significant value in Rydberg-based quantum information processing and precision measurement. Furthermore, the 509nm band exhibits a low absorption coefficient in seawater, and single-frequency lasers reduce pulse broadening caused by dispersion, thereby increasing transmission rate and distance. Therefore, single-frequency green VECSELs show promising applications in underwater communication and measurement.

[0003] Two common resonant cavity structures for VECSEL lasers are linear cavities and V-cavities. For single-frequency applications of several hundred milliwatts, linear cavities are typically used; while for high output power, a frequency-doubling crystal needs to be placed near the waist of the Gaussian beam within a V-cavity to improve frequency doubling efficiency.

[0004] The current packaging of VECSE single-frequency lasers faces the following key technical challenges:

[0005] Firstly, lasers require good temperature control.

[0006] VECSEL output lasers undergo multiple energy conversion stages, resulting in low electro-optic efficiency and a heavy system thermal load. Furthermore, the spectral characteristics and performance of VECSEL gain chips are significantly affected by temperature, and the performance of frequency doubling crystals is also temperature-dependent. Therefore, reliable packaging of this type of single-frequency laser faces challenges related to high heat generation and precise temperature control.

[0007] Secondly, the open cavity structure of VECSEL single-frequency lasers can easily lead to a significant deterioration in single-frequency performance.

[0008] While the open-cavity structure of VECSELs offers flexible layout, functional expansion, and performance enhancement, this large-scale external cavity structure significantly amplifies system instabilities, severely degrading VECSEL single-frequency performance. Even micrometer-level changes in the cavity structure can cause longitudinal mode jumps in the laser, leading to single-frequency performance failure. Therefore, VECSEL single-frequency laser packaging requires comprehensive consideration of system temperature control, thermal conduction, mechanical stability, and temperature drift characteristics.

[0009] Thirdly: the slow temperature drift characteristic introduced by the optical pumping system.

[0010] VECSELs typically use a laser diode with a pigtail output as the pump source, which, after passing through a collimation and focusing module, produces a circular focused spot. This module is not only relatively large but also absorbs some of the pump light. Furthermore, pump light not completely absorbed by the gain chip is randomly absorbed within the packaged system. The material absorbing the pump light can be considered a distributed heat source, and the system exhibits a significant thermal capacitance effect, causing the system's temperature field distribution to remain in a state of random, slow change for extended periods, making it difficult to reach a stable equilibrium state.

[0011] Fourthly, the shortcomings of traditional packaging structures.

[0012] Traditional VECSEL packaging primarily uses metal materials (aluminum alloy, stainless steel, copper, etc.) to ensure good heat transfer channels and mechanical stability. However, metal components typically have a high coefficient of thermal expansion (10⁻⁶). -5 The cavity length changes (on the order of kJ / K) caused by temperature fluctuations can lead to frequency drift and even longitudinal mode jumps. Furthermore, when using independent mechanical optical adjustment frames for optical path layout, these frames are susceptible to thermal expansion, mechanical vibration, and stress relaxation during operation, causing slight deviations in the optical axis or minute changes in the mirror tilt angle, introducing more uncertainties. Some researchers, drawing inspiration from DFB lasers, have attempted to use integrated packaging to reduce changes in the resonant cavity structure, achieving good results; however, this sacrifices the flexible layout and performance expansion of the VECSEL cavity. Moreover, such packaging requires the removal of the collimation and focusing module, often employing a spatial beam shaping mode with the laser diode pump source closely attached to the VECSEL. This not only increases the system's thermal load but also results in poor laser diode beam quality and severely uneven beam spatial distribution due to the lack of fiber homogenization, significantly deteriorating the VECSEL beam quality and single-frequency performance.

[0013] In summary, due to its open cavity structure, VECSEL is susceptible to the combined effects of mechanical vibration and changes in ambient temperature, resulting in a slow, random drift in cavity length. This severely impacts single-frequency performance and limits its application in the field of precision light sources.

[0014] Currently, the mainstream method to suppress the single-frequency performance degradation of VECSELs is to introduce closed-loop feedback control, using frequency error signals to drive devices such as temperature control, piezoelectric ceramics, or metal structure thermal compensation to achieve active stabilization. This approach not only relies on high-precision optical frequency monitoring methods, but also suffers from complex system structures, high costs, and limited long-term reliability.

[0015] Therefore, there is an urgent need for a VECSEL external cavity structure with passive stabilization characteristics, which can achieve highly stable single-frequency output without complex feedback control. Summary of the Invention

[0016] Therefore, it is necessary to provide an external cavity single-frequency VECSEL structure based on a quartz reference skeleton to address the above-mentioned technical problems.

[0017] An external cavity single-frequency VECSEL structure based on a quartz reference frame includes: a pump module, a gain chip, an output mirror, and a quartz reference frame; the pump module and the quartz reference frame adopt a unified optical interface for outputting pump light to the active region of the gain chip; the gain chip is bonded to a heat sink and then mounted on a copper heat sink, and the copper heat sink is in direct sealed contact with the quartz reference frame; the gain chip and the output mirror form a resonant cavity, and an output laser beam is obtained by excitation with pump light; the quartz reference frame is an integrated quartz structure used to fix all optical components in the resonant cavity and provide an optical geometric reference.

[0018] In one embodiment, the pump module includes a ceramic ferrule and a pump pigtail. The end face of the ceramic ferrule is precision polished to position and fix the end of the pump pigtail. The pump pigtail is inserted into the ceramic ferrule and fixed with an adhesive to output pump light.

[0019] In one embodiment, the pump module is a quartz sleeve type pump structure, including a quartz sleeve and a lens. The quartz sleeve is integrally processed with the quartz reference skeleton or precisely bonded with optical adhesive. The ceramic ferrule is embedded in the quartz sleeve, so that the pump light enters the quartz sleeve after being transmitted through the pump pigtail. The lens is disposed on a limiting shoulder inside the quartz sleeve and is used to focus the pump light onto the active region of the gain chip.

[0020] In one embodiment, the pump module is a direct pump structure at the rear end of the pigtail, and the heat sink is a transparent heat sink. One side of the transparent heat sink is bonded to the gain chip, and the other side is fixed to the copper heat sink. The copper heat sink is provided with precision mating holes for introducing and fixing the ceramic ferrule, and for directly contacting and fixing the pump pigtail to the transparent heat sink, so that the pump light is transmitted through the pump pigtail and then incident on the active region of the gain chip through the transparent heat sink.

[0021] In one embodiment, the transparent thermally conductive heat sink is diamond or silicon carbide.

[0022] In one embodiment, the resonant cavity further includes a frequency doubling crystal and a birefringent filter. The frequency doubling crystal is optically connected to the gain chip and mounted on the copper heat sink. The birefringent filter is optically connected to the frequency doubling crystal and the output mirror and is mounted on the quartz reference frame by optical adhesive or mechanical clamping.

[0023] In one embodiment, the quartz reference frame is formed by CNC precision machining or laser cutting to create an integrated optical base.

[0024] In one embodiment, a TEC module is connected below the copper heat sink for temperature control of the gain chip.

[0025] In one embodiment, a heat dissipation substrate is also included, which is located below the TEC module for heat dissipation.

[0026] In one embodiment, the mechanical clamping method of the quartz reference frame includes a quartz reference hole, a limiting step, or a stop structure.

[0027] Compared to existing technologies, the advantages and beneficial effects of this invention are as follows: the pump module and the quartz reference frame adopt a unified optical interface for outputting pump light to the active region of the gain chip; the gain chip is bonded to a heat sink and then mounted on a copper heat sink for heat dissipation; the quartz reference frame and the copper heat sink are in direct sealed contact to ensure the cavity is airtight and can be filled with dry nitrogen; the copper heat sink performs thermal management; the gain chip and the output mirror form a resonant cavity, and the output laser beam is obtained by excitation with pump light; the quartz reference frame is an integrated quartz structure used to fix all optical components in the resonant cavity; each optical component in the cavity is directly mounted on the surface of the quartz reference frame by optical adhesive or mechanical clamping, without the need for a metal adjustment frame; the quartz reference frame provides an optical geometric reference, realizing a composite system of quartz optical reference and copper thermal control at the structural level, making thermal flow control and optical stability independent of each other, improving the mechanical and thermal stability of the VECSEL, and keeping the resonant cavity length stable for a long time, thereby achieving passive single-frequency output without active feedback for a long time. Attached Figure Description

[0028] Figure 1 This is a cross-sectional view along the optical axis of an external cavity single-frequency VECSEL structure based on a quartz reference skeleton in one embodiment;

[0029] Figure 2This is a top view of an external cavity single-frequency VECSEL structure based on a quartz reference frame in one embodiment;

[0030] Figure 3 This is a schematic diagram of the assembly of the ceramic ferrule and the pump pigtail in one embodiment;

[0031] Figure 4 This is a schematic diagram of a quartz sleeve-type pump structure in one embodiment;

[0032] Figure 5 This is a schematic diagram of a direct pumping structure at the rear end of the pigtail in one embodiment.

[0033] In the attached diagram, the components are: ceramic ferrule 11, pump pigtail 12, quartz sleeve 13, lens 14, gain chip 2, heat sink 21, copper heat sink 22, output mirror 3, quartz reference frame 4, frequency doubling crystal 5, birefringent filter 6, TEC module 7, and heat dissipation substrate 8. Detailed Implementation

[0034] Before describing the specific embodiments of the present invention, the overall concept of the present invention will be explained as follows:

[0035] This invention addresses the problem that traditional metal or ceramic external cavity support structures struggle to suppress cavity length drift while maintaining thermal control performance. It proposes an external cavity single-frequency VECSEL structure based on a quartz reference framework. This structure utilizes a low-expansion quartz material to construct a unified optical support reference, achieving direct, sealed contact with a copper heat sink to ensure airtightness. Dry nitrogen is then introduced, enabling passive stability of the cavity length and long-term single-frequency output at the structural level.

[0036] 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.

[0037] In one embodiment, such as Figure 1-2As shown, an external cavity single-frequency VECSEL structure based on a quartz reference frame is provided, including: a pump module, a gain chip 2, an output mirror 3, and a quartz reference frame 4; the pump module and the quartz reference frame 4 adopt a unified optical interface for outputting pump light to the active region of the gain chip; the gain chip 2 is bonded to a heat sink 21 and then mounted on a copper heat sink 22, and the copper heat sink 22 is in direct sealed contact with the quartz reference frame 4; the gain chip 2 and the output mirror 3 form a resonant cavity, and the output laser beam is obtained by excitation by pump light; the quartz reference frame 4 is an integrated quartz structure used to fix all optical components in the resonant cavity and provide an optical geometric reference.

[0038] In this embodiment, the pump module and the quartz reference frame 4 adopt a unified optical interface for outputting pump light to the active area of ​​the gain chip 2. The gain chip 2 is bonded to the heat sink 21 and then mounted on the copper heat sink 22 for heat dissipation. The quartz reference frame 4 and the copper heat sink 22 are in direct sealed contact to ensure the cavity is airtight and can be filled with dry nitrogen. The copper heat sink 22 undertakes the thermal management function. The gain chip 2 and the output mirror 3 form a resonant cavity, and the output laser beam is obtained by excitation with pump light. The quartz reference frame 4 is an integrated quartz structure used to fix all optical components in the resonant cavity. Each optical component in the cavity is directly mounted on the surface of the quartz reference frame 4 by optical adhesive or mechanical clamping, without the need for a metal adjustment frame. The quartz reference frame 4 provides an optical geometric reference, realizing a composite system of quartz optical reference and copper thermal control at the structural level. This makes thermal flow control and optical stability independent of each other, improving the mechanical and thermal stability of the VECSEL and keeping the resonant cavity length stable for a long time, thereby realizing passive single-frequency output without active feedback for a long time.

[0039] Among them, the heat sink 21 is made of a high thermal conductivity material, such as diamond or silicon carbide, which is directly bonded to the gain chip 2, which can shorten the heat conduction path and reduce the chip operating temperature.

[0040] The copper heat sink 22 on the side of the gain chip 2 is tightly attached to the quartz reference frame 4 and fixed by a mechanical clamping structure. This ensures a reliable heat transfer path while preventing slight displacement of the gain chip 2 along the optical axis. The thermal behavior of all optical components within the resonant cavity is uniformly constrained by the quartz frame.

[0041] The entire resonant cavity can be sealed and filled with dry nitrogen gas to reduce scattering noise and prevent optical components from getting damp or contaminated. The optical inertness and low hygroscopicity of quartz material can maintain a clean environment in the cavity for a long time.

[0042] In addition, when using a collimation and focusing module, a fixed base that is integrally machined with the quartz reference frame 4 needs to be designed, and the pump light focusing input is precisely positioned by using an optical adjustment frame. After adjustment, the collimation and focusing module is fixed to the fixed base with glue.

[0043] Unlike traditional cavity structures that use metal or ceramic supports, the quartz reference frame 4 of this invention provides a unified reference both mechanically and thermally. Quartz material has an extremely low coefficient of linear expansion (approximately 0.5 × 10⁻⁶). -6 The temperature ( / K) is about an order of magnitude lower than that of aluminum alloy or stainless steel, which can effectively suppress cavity length drift caused by changes in ambient temperature. In a typical 100mm cavity, a 1K increase in temperature in an aluminum alloy structure will result in a cavity length change of about 2.3μm, equivalent to about nine longitudinal mode pitches; while the corresponding change in the quartz reference frame 4 is only about 0.055μm, about 0.2 longitudinal mode pitches, thus significantly reducing the risk of mode jump.

[0044] Since all optical components within the cavity are supported by quartz, the system does not suffer from thermal expansion mismatch issues between different materials. Even with changes in pump power or slow fluctuations in ambient temperature, the cavity length and optical axis position remain stable, achieving passive frequency locking at the structural level.

[0045] To illustrate the advantages of quartz materials in terms of thermal stability, Table 1 lists the coefficients of linear expansion of common structural materials.

[0046] Table 1 Comparison of linear expansion coefficients of common structural materials

[0047]

[0048]

[0049] As can be seen from the table, the coefficient of thermal expansion of quartz is only about 1 / 40 that of aluminum alloy, indicating that using it as a reference material for the external cavity has a significant advantage in suppressing thermal drift.

[0050] In the external cavity system designed in this invention, assuming a cavity length L = 100 mm and a working wavelength λ = 509 nm, the corresponding longitudinal mode spacing is:

[0051] FSR = c / (2L) ≈ 1.5GHz.

[0052] When the ambient temperature increases by 1K, the cavity length of the aluminum alloy outer cavity changes by ΔL=αL≈2.3μm, resulting in a resonant frequency drift of about 13.6GHz (equivalent to 9 longitudinal mode spacings); while in the quartz skeleton structure, ΔL≈0.055μm corresponds to a frequency drift of only about 0.3GHz (about 0.2 longitudinal mode spacings).

[0053] Therefore, within the range of room temperature fluctuations, the quartz skeleton structure hardly produces longitudinal mode jumps, achieving long-term stability of passive single-frequency output.

[0054] The pump module includes a ceramic ferrule 11 and a pump pigtail 12. The end face of the ceramic ferrule 11 is precision polished and used to position and fix the end of the pump pigtail 12. The pump pigtail 12 is inserted into the ceramic ferrule 11 and fixed with adhesive for outputting pump light.

[0055] Specifically, such as Figure 3 As shown, the pump module includes a ceramic ferrule 11 and a pump pigtail 12. This invention eliminates the traditional metal SMA905 plug and directly uses the ceramic ferrule 11 as the fixing and positioning unit for the end of the pump pigtail. The fiber end face inside the ceramic ferrule 11 is precision polished (during polishing, the fiber is inserted into the ceramic ferrule so that the fiber end face and the ceramic ferrule end face are flush and fixed with optical adhesive, and both are polished together), to avoid random scattering of pump light at the end face and to ensure optical axis perpendicularity and low insertion loss. The pump pigtail 12 consists of a fiber core, cladding, coating layer and outer protective sleeve. After removing part of the protective sleeve, the fiber containing the coating layer is inserted into the ceramic ferrule 11 with an outer diameter of 1.249 mm and fixed with optical adhesive.

[0056] Compared to the SAM905 structure, this invention eliminates the metal flange, threaded pressure ring, and transition cavity, resulting in a more compact assembly, higher mechanical strength, and immunity to the effects of metal thermal expansion and contraction. The ceramic ferrule 11 used in this invention possesses excellent dimensional accuracy and thermal stability, and can directly mate with the pump pigtail 12, meeting the fixing requirements for 100μm and 200μm core diameter pigtails. This assembly method significantly simplifies the pump light input structure, improves interface accuracy and repeatability, standardizes the interface structure, and makes it suitable for mass production of miniaturized, high-stability laser packages.

[0057] The pump module is a quartz sleeve type pump structure, including a quartz sleeve 13 and a lens 14. The quartz sleeve 13 is integrally processed with the quartz reference frame 4 or precisely bonded with optical adhesive. The ceramic ferrule 11 is embedded in the quartz sleeve 13, so that the pump light enters the quartz sleeve 13 after being transmitted through the pump pigtail 12. The lens 14 is set on the limiting shoulder inside the quartz sleeve 13 and is used to focus the pump light on the active area of ​​the gain chip.

[0058] Specifically, in the quartz reference frame structure, the pump light is divided into front-end side pumping and back-end pumping, which is the same as the existing VECSEL laser structure. Therefore, the pump module and the quartz reference frame 4 adopt a unified optical interface. The corresponding pump structure can be determined according to the output power level and heat dissipation requirements, which is either quartz sleeve type (corresponding to front-end side pumping in complex structures) or pigtail direct pumping type (corresponding to back-end pumping).

[0059] like Figure 4As shown, this is a quartz sleeve-type pump structure, which is suitable for medium-to-high power single-frequency VECSELs. In this case, the chip heat dissipation is better, but a sleeve-type focusing module is still needed to focus the pump light onto the gain chip 2. Therefore, the VECSEL structure also includes a quartz sleeve 13 and a lens 14. The quartz sleeve 13 is integrally machined with the quartz reference frame 4 or precisely bonded with optical adhesive. Its thermal expansion characteristics are consistent with the outer cavity frame, thus avoiding the thermal drift problem of metal collimators or threaded parts under high power.

[0060] The ceramic ferrule 11 is embedded in the quartz sleeve 13, so that the pump light is transmitted through the pump pigtail 12 and enters the quartz sleeve 13. The lens 14 is set on the limiting shoulder inside the quartz sleeve 13. The lens 14 can also be a lens group. After the pump light is focused by the lens group, it is incident on the surface of the gain chip 2 at a small angle. The spot size and energy distribution can be adjusted by changing the lens combination.

[0061] Quartz sleeve type pump structure has the advantages of high optical path stability, uniform heat dissipation and good assembly repeatability, and is suitable for high stable output under watt-level power conditions.

[0062] The pump module is a direct pump structure at the rear end of the pigtail. The heat sink 21 is a transparent heat sink. One side of the transparent heat sink is bonded to the gain chip 2, and the other side is fixed to the copper heat sink 22. The copper heat sink 22 is provided with precision mating holes for introducing and fixing the ceramic ferrule 11. The pump pigtail 12 is directly in contact with and fixed to the transparent heat sink 15, so that the pump light is transmitted through the pump pigtail 12 and then incident on the active area of ​​the gain chip 2 through the transparent heat sink.

[0063] Specifically, such as Figure 5 As shown, this is a direct pumping structure at the rear end of the pigtail, suitable for single-frequency external cavity VECSELs in the hundreds of milliwatts range. In this case, the heat sink 21 in the VECSEL structure is a transparent heat sink, which can be a silicon carbide wafer, etc. One side of the transparent heat sink is directly bonded to the gain chip 2 to avoid the presence of a metal solder layer or other light-absorbing medium, ensuring good optical contact and thermal conductivity. The other side is fixed to a copper heat sink 22, which has a precision fitting hole for inserting and fixing a ceramic ferrule 11. The outer diameter of the ceramic ferrule is 1.249 mm. The pump pigtail 12 is directly contacted and fixed to the transparent heat sink, so that the pump light is directly output through the pump pigtail and incident on the active area of ​​the gain chip 2 through the transparent heat sink.

[0064] The direct-pump structure at the back end of the pigtail eliminates the need for lenses and metal collimators, resulting in a short optical path, high alignment accuracy, and no additional heat source introduced, thus maintaining extremely low cavity drift under low power conditions.

[0065] Among them, the transparent thermally conductive heat sink is made of diamond or silicon carbide, etc.

[0066] Specifically, the transparent thermally conductive heat sink used for bonding gain chip 2 can be a transparent thermally conductive heat sink sheet with high thermal conductivity and low absorption of pump light, such as silicon carbide, diamond, or sapphire.

[0067] The resonant cavity also includes a frequency doubling crystal 5 and a birefringent filter 6. The frequency doubling crystal 5 is optically connected to the gain chip 2 and is mounted on the copper heat sink 22. The birefringent filter 6 is optically connected to the frequency doubling crystal 5 and the output mirror 3 and is mounted on the quartz reference frame 4 by optical adhesive or mechanical clamping.

[0068] Specifically, a frequency doubling crystal 5 and a birefringent filter 6 can also be installed inside the resonant cavity. The quartz reference frame 4 is an integrated structure used to support all optical components inside the resonant cavity. The copper heat sink 22 is in direct sealed contact with the quartz reference frame 4, and its front end protrudes into the resonant cavity at the frequency doubling crystal 5, providing efficient heat dissipation and temperature control for the frequency doubling crystal 5, ensuring good thermal conductivity and maintaining the airtightness of the cavity.

[0069] The birefringent filter 6 is optically connected to the frequency doubling crystal 5 and the output mirror 3. Stable linearly polarized light is obtained through the birefringent filter 6. The birefringent filter 6 is mounted on the quartz reference frame 4 by optical adhesive or mechanical clamping. The quartz reference frame 4 is used to achieve fixed spacing and coaxial positioning between optical elements in the resonant cavity.

[0070] All optical components are finely assembled using an optical precision adjustment frame. Except for the gain chip, which requires mechanical clamping on both sides, all other components can be fixed with optical adhesive.

[0071] Among them, the quartz reference frame 4 is formed by CNC precision machining or laser cutting to form an integrated optical base.

[0072] The copper heat sink 22 is connected to a TEC (Thermoelectric Cooling) module 7 below it, which is used to control the temperature of the gain chip 2.

[0073] Specifically, the copper heat sink 22 is connected to the TEC module 7 below to achieve precise temperature control of the gain chip 2. For high-power applications, the copper heat sink 22 can be embedded with high thermal conductivity materials such as heat pipes to achieve more reliable temperature control.

[0074] It also includes a heat dissipation substrate 8, which is located below the TEC module 7 and is used for heat dissipation.

[0075] Specifically, the VECSEL structure may also include a heat dissipation substrate 8, which is located below the TEC module 7 and is used to dissipate heat from the gain chip 2.

[0076] The mechanical clamping methods for the quartz reference frame include quartz reference holes, limiting steps, or stop structures.

[0077] Specifically, the quartz skeleton is an integral structure used to support all optical components inside the cavity. The installation position of each optical component inside the resonant cavity can be determined by the quartz reference hole, limiting step or stop structure, so as to achieve fixed spacing and coaxial positioning between optical components.

[0078] Through the above design, this invention achieves a high degree of integration at the mechanical, thermal, and optical levels. The quartz reference frame provides a unified optical geometric reference, while the copper heat sink and TEC module are responsible for local temperature control. This structure can maintain long-term single-frequency output without active feedback, while also possessing high assembly repeatability and mass production consistency.

[0079] It should be noted that this invention uses a linear cavity structure as an example for illustration, and the specific optical path is for illustrative purposes only. In practice, the scheme can be adjusted according to the output wavelength and functional requirements (such as single-frequency, frequency multiplication, mode-locking). For V-shaped cavities or more complex cavity structures, the same technical approach can also be used for encapsulation.

[0080] Quartz is chosen as the material in this invention because its machining process is mature, supporting resources are readily available, and its coefficient of thermal expansion is extremely low, making it suitable for high-precision optical packaging. Other materials with similar or lower coefficients of thermal expansion and equivalent mechanical stability and process feasibility (such as silicon carbide, ultra-low expansion glass, etc.) are also within the scope of protection of this invention.

[0081] Compared with existing external cavity single-frequency VECSEL lasers, this invention achieves significant improvements in structural design and material system, and has the following beneficial effects:

[0082] Firstly, it enables passive stabilization of the cavity length and long-term single-frequency output. By employing a low-expansion quartz skeleton as the external cavity optical reference, the resonant cavity length becomes insensitive to changes in ambient temperature. Within the range of normal temperature fluctuations, the cavity length drift is reduced by approximately one order of magnitude compared to traditional aluminum alloy structures, effectively avoiding longitudinal mode jumps and achieving stable single-frequency output without active feedback. Furthermore, combined with high-precision temperature control, it ensures the system maintains low-frequency drift characteristics over extended periods, providing a structural foundation for the realization of linear frequency modulated continuous wave (VECSEL).

[0083] Secondly, it can significantly reduce single-frequency flicker noise. Compared with metal or ceramic structures, this design reduces power and phase noise caused by random heat sources (quartz materials hardly absorb pump light and laser) and thermo-optic effects from the source; at the same time, the high mechanical quality factor of quartz effectively suppresses the transmission of external micro-vibrations, making the phase coupling between pump light, gain medium and external cavity more stable, thereby significantly reducing single-frequency flicker noise and improving the purity and frequency stability of the output spectrum.

[0084] Third, it achieves an integrated mechanical and thermal structure. The quartz skeleton uniformly supports all optical components, while the copper heat sink and TEC module are responsible for local temperature control. The two work together in a sealed manner to form an independent thermal circuit. Heat flow control and optical positioning do not interfere with each other. The overall structure is compact, highly stable, quick to install and debug, and easy to obtain stable product performance.

[0085] In summary, this invention systematically solves the practical application problem of single-frequency VECSELs at the structural level, and realizes a passive, stable, low-noise, and highly reliable external cavity packaging solution.

[0086] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely 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 a process, method, article, or apparatus.

[0087] 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 invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of this invention. These should also be considered within the scope of protection of this invention, and will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed by this invention 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 cavity single-frequency VECSEL structure based on a quartz reference frame, characterized in that, include: Pump module, gain chip, output mirror and quartz reference frame; The pump module and the quartz reference frame use a unified optical interface for outputting pump light to the active region of the gain chip. The gain chip is bonded to a thermally conductive heat sink and then mounted on a copper heat sink, with the copper heat sink in direct, sealed contact with the quartz reference frame. The gain chip and the output mirror form a resonant cavity, and the output laser beam is obtained by excitation with pump light. The quartz reference frame is an integrated quartz structure used to fix all optical components inside the resonant cavity and provide an optical geometric reference.

2. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 1, characterized in that, The pump module includes a ceramic ferrule and a pump pigtail. The end face of the ceramic ferrule is precision polished and used to position and fix the end of the pump pigtail. The pump pigtail is inserted into the ceramic ferrule and fixed with adhesive for outputting pump light.

3. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 2, characterized in that, The pump module is a quartz sleeve type pump structure, including a quartz sleeve and a lens. The quartz sleeve is integrally processed with the quartz reference skeleton or precisely bonded with optical adhesive. The ceramic ferrule is embedded in the quartz sleeve, so that the pump light enters the quartz sleeve after being transmitted through the pump pigtail. The lens is set on the limiting shoulder inside the quartz sleeve to focus the pump light onto the active area of ​​the gain chip.

4. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 2, characterized in that, The pump module is a direct pump structure at the rear end of the pigtail. The heat sink is a transparent heat sink. One side of the transparent heat sink is bonded to the gain chip, and the other side is fixed to the copper heat sink. The copper heat sink is provided with precision mating holes for inserting and fixing the ceramic ferrule. The pump pigtail is directly in contact with and fixed to the transparent heat sink, so that the pump light is transmitted through the pump pigtail and then incident on the active area of ​​the gain chip through the transparent heat sink.

5. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 4, characterized in that, The transparent thermally conductive heat sink is made of diamond or silicon carbide.

6. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 1, characterized in that, The resonant cavity also includes a frequency doubling crystal and a birefringent filter. The frequency doubling crystal is optically connected to the gain chip and is mounted on the copper heat sink. The birefringent filter is optically connected to the frequency doubling crystal and the output mirror and is mounted on the quartz reference frame by optical adhesive or mechanical clamping.

7. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 1, characterized in that, The quartz reference frame is formed by CNC precision machining or laser cutting to create an integrated optical base.

8. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 1, characterized in that, A TEC module is connected below the copper heat sink for temperature control of the gain chip.

9. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 8, characterized in that, It also includes a heat dissipation substrate, which is located below the TEC module and is used for heat dissipation.

10. The external cavity single-frequency VECSEL structure based on a quartz reference skeleton according to claim 1, characterized in that, The mechanical clamping methods of the quartz reference frame include quartz reference holes, limiting steps, or stop structures.

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