High power mid-wave quantum cascade laser fiber combined laser source

Abstract

A high-power middle-wave quantum cascade laser fiber beam combining laser source, output ends of quantum cascade lasers are respectively aligned with incident surfaces of focusing lenses, output surfaces of the focusing lenses are respectively aligned with input fiber end surfaces of a fiber beam combiner, and an output end surface of the fiber beam combiner is aligned with a collimating output mirror, thereby completing beam combining of N quantum cascade lasers; the quantum cascade lasers, the focusing lenses, and the fiber input end surfaces are integrated on a heat sink; the quantum cascade lasers are all located in a middle-wave infrared waveband, and the emitted laser is subjected to power synthesis in the fiber beam combiner; the fiber beam combiner is prepared based on a chalcogenide fiber, the input end is composed of N chalcogenide fibers, a first infrared light-transmitting window sheet is bonded to the chalcogenide fibers through first liquid glass, the output end surface is bonded to a chalcogenide end cap through second liquid glass, the chalcogenide end cap is bonded to a second infrared light-transmitting window sheet through third liquid glass, and the first, second, and third liquid glasses are used for refractive index matching.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more particularly to a high-power mid-wave quantum cascade laser fiber-coupled laser source. Background Technology

[0002] High-power mid-wave lasers have attracted significant attention in molecular spectroscopy, biomedical diagnostics, free-space optical communication, and defense industries, demonstrating immense economic and social value in areas such as trace gas detection, infrared countermeasures, laser surgery, and high-capacity communication. Quantum cascade lasers, with their advantages of flexible wavelength design via quantum well band structure, compact device structure, and high electro-optical conversion efficiency, have become one of the most important laser sources in the mid-infrared band. However, limitations in active region quantum well design, material epitaxial growth quality, and the low damage threshold of device cavity surface coatings restrict the output power of a single quantum cascade laser to a relatively limited level for long-term stable operation, making it difficult to meet the urgent demands for high-power mid-wave lasers in applications such as high-precision molecular detection, long-distance high-capacity communication, and infrared countermeasures.

[0003] To overcome the power limitations of single quantum cascade lasers, beam combining technology is currently mainly divided into two categories: coherent beam combining and incoherent beam combining. While coherent beam combining offers high beam quality, its system structure is complex, and it places extremely stringent requirements on optical path stability and device matching consistency, making it difficult to maintain stable operation over long periods. Therefore, incoherent beam combining has received more attention due to its relatively simple structure and lower engineering difficulty. Typical incoherent beam combining methods include polarization beam combining, spectral beam combining, and spatial beam combining. However, polarization and spectral beam combining have significant limitations in the number of beam paths, limiting the potential for power increases. Spatial beam combining, on the other hand, relies heavily on complex spatial optical path structures, placing extremely high demands on the beam pointing consistency and optical axis stability of each laser path. As the number of beam paths increases, the system complexity and assembly difficulty increase significantly, severely restricting its ability to extend to higher power levels.

[0004] In recent years, with the continuous maturation of mid-wave infrared fiber device fabrication processes and the ongoing development of low-loss chalcogenide fiber materials, fiber-based beam combining technology has gradually become an important research direction for high-power mid-wave infrared laser output. This technology not only enables efficient power superposition of multiple lasers but also naturally possesses the advantage of high output optical axis stability, balancing high power output with good system stability, and is considered one of the promising technical routes in the field of mid-wave infrared laser power combining. However, chalcogenide fibers have a high refractive index, and their end faces exhibit strong Fresnel reflection loss. This not only reduces the coupling efficiency of the system but also allows reflected laser light to potentially damage quantum cascade lasers, severely affecting the overall stability and reliability of the system. Due to this limitation, the output power level of current mid-wave infrared laser fiber beam combining has been limited for a long time, severely restricting the further development and engineering application of this technology. Therefore, how to effectively suppress the Fresnel reflection loss at the end face of chalcogenide fibers, improve the coupling efficiency and operational stability of the system, and achieve stable output of high-power mid-wave infrared lasers has become an important technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a high-power mid-wave quantum cascade laser fiber combining laser source that can still maintain high coupling efficiency even when the incident laser beam quality is poor. This effectively solves the problems of complex optical paths and poor optical axis stability in traditional spatial combining technology, and realizes efficient and stable power combining of multiple mid-wave infrared lasers.

[0006] The technical solution of the present invention is: this high-power mid-wave quantum cascade laser fiber bundler laser source includes N quantum cascade lasers, N focusing lenses, an N×1 fiber bundler (3), a collimating output mirror (4), and a heat sink (5), where N≥3; The output ends of N quantum cascade lasers are respectively aligned with the incident surfaces of N focusing lenses, the output surfaces of N focusing lenses are respectively aligned with the input fiber end faces of N×1 fiber combiner, and the output end face (9) of N×1 fiber combiner is aligned with the collimating output mirror to complete the beam combining of N quantum cascade lasers; N quantum cascade lasers, N focusing lenses and N fiber input end faces of N×1 fiber combiner are all integrated on the heat sink; The wavelengths of N quantum cascaded lasers are all located in the mid-infrared band. Their emitted lasers are focused by their respective focusing lenses and then coupled into the N fibers of an N×1 fiber combiner for power combining. The fiber bundler is based on chalcogenide fiber. Its input end consists of N chalcogenide fibers (8). The first infrared transparent window (6) is bonded to the chalcogenide fiber through the first liquid glass (7). The output end face is bonded to the chalcogenide end cap (11) through the second liquid glass (10). The chalcogenide end cap is bonded to the second infrared transparent window (13) through the third liquid glass (12). The refractive index is matched by the first, second and third liquid glasses.

[0007] This invention utilizes an N×1 fiber combiner based on chalcogenide fiber to power combine multiple mid-wave infrared quantum cascade lasers. Chalcogenide end caps are used to reduce the power density at the output end face, and liquid glass is employed for refractive index matching encapsulation of the fiber end face, effectively suppressing Fresnel reflection at the chalcogenide fiber end face. This solves the problems of complex spatial combining structures, poor optical axis stability, and limited number of combined paths in traditional methods. It also overcomes the technical bottleneck of low coupling efficiency in fiber combining. Compared to existing combining schemes, this invention features a compact structure, high optical axis stability, high combining efficiency, and high system integration, enabling the generation of high-power, high-stability mid-wave infrared laser output. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the structure of a high-power mid-wave quantum cascade laser fiber bundle combiner laser source according to the present invention.

[0009] Figure 2 This is a schematic diagram of the structure of the input end of a 7×1 fiber optic combiner provided in one embodiment of the present invention.

[0010] Figure 3 This is a schematic diagram of the output end of a 7×1 fiber optic combiner provided in one embodiment of the present invention.

[0011] Figure 4 The graph shows the variation of output power of a high-power mid-wave quantum cascade laser fiber combiner laser source with input power and the corresponding coupling efficiency data provided in one embodiment of the present invention. Detailed Implementation

[0012] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0013] It should be noted that the term "comprising" and any variations thereof in the specification, claims and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products or devices.

[0014] like Figure 1 As shown, this high-power mid-wave quantum cascade laser fiber combiner laser source includes N quantum cascade lasers, N focusing lenses, an N×1 fiber combiner 3, a collimating output mirror 4, and a heat sink 5, where N≥3; The output ends of N quantum cascade lasers are respectively aligned with the incident surfaces of N focusing lenses, the output surfaces of N focusing lenses are respectively aligned with the input fiber end faces of an N×1 fiber combiner, and the output end face 9 of the N×1 fiber combiner is aligned with a collimating output mirror, thus completing the beam combining of N quantum cascade lasers; the N quantum cascade lasers, N focusing lenses, and N fiber input end faces of the N×1 fiber combiner are all integrated on a heat sink. The wavelengths of N quantum cascade lasers are all located in the mid-infrared band. Their emitted lasers are focused by their respective focusing lenses and then coupled into the N fibers of an N×1 fiber combiner for power combining. The output power of each quantum cascade laser has good power consistency and spectral consistency to ensure that the combined laser has high monochromaticity. The fiber optic combiner is based on chalcogenide fiber. Its input end consists of N chalcogenide fibers 8. The first infrared transparent window 6 is bonded to the chalcogenide fiber through the first liquid glass 7. The output end face is bonded to the chalcogenide end cap 11 through the second liquid glass 10. The chalcogenide end cap is bonded to the second infrared transparent window 13 through the third liquid glass 12. The refractive index is matched by the first, second and third liquid glasses.

[0015] This invention utilizes an N×1 fiber combiner based on chalcogenide fiber to power combine multiple mid-wave infrared quantum cascade lasers. Chalcogenide end caps are used to reduce the power density at the output end face, and liquid glass is employed for refractive index matching encapsulation of the fiber end face, effectively suppressing Fresnel reflection at the chalcogenide fiber end face. This solves the problems of complex spatial combining structures, poor optical axis stability, and limited number of combined paths in traditional methods. It also overcomes the technical bottleneck of low coupling efficiency in fiber combining. Compared to existing combining schemes, this invention features a compact structure, high optical axis stability, high combining efficiency, and high system integration, enabling the generation of high-power, high-stability mid-wave infrared laser output.

[0016] The N quantum cascade lasers, the N focusing lenses, and the N input fiber end faces of the N×1 fiber combiner are all integrated and mounted on the same heat sink, and fixed by ultraviolet curing, achieving miniaturization and integration of the system. The heat sink is equipped with a temperature control system to stabilize the operating temperature of the quantum cascade lasers at a predetermined temperature, ensuring stable operation and output stability of the lasers under different output power conditions.

[0017] Preferably, the focusing lens is a high-transmittance optical lens in the mid-infrared band, which focuses the laser emitted from the quantum cascade laser into the core of the input fiber of the N×1 fiber combiner.

[0018] Preferably, the focusing lens is a silicon lens with a transmittance of more than 98.5% for mid-wave infrared laser.

[0019] Preferably, the chalcogenide optical fiber is arsenic sulfide optical fiber with a numerical aperture greater than 0.35 in the mid-infrared band. A larger numerical aperture ensures high coupling efficiency even when the incident laser beam quality is poor.

[0020] Preferably, the chalcogenide end cap is made of the same or matching matrix glass material as the N chalcogenide optical fibers. It has high transmittance in the mid-infrared band and its refractive index matches that of the chalcogenide optical fiber. It fills the optical interfaces between the chalcogenide optical fiber and the infrared transmission window, between the end cap and the output end face of the N optical fibers, and between the end cap and the infrared transmission window, thereby reducing Fresnel reflection loss at the interfaces. Due to the inherently high refractive index of chalcogenide glass, strong Fresnel reflection occurs when laser light is incident on the fiber end face in free space. This not only affects the overall coupling efficiency of the system but also damages the quantum cascade laser due to the laser light reflected from the end face, severely impacting the overall stability of the system. By introducing the liquid glass, Fresnel reflection can be effectively suppressed, improving the overall coupling efficiency and system stability.

[0021] Preferably, the heat sink is equipped with a circulating water cooling system to control the temperature.

[0022] Preferably, N=7, the center wavelength of the quantum cascade laser is located near 4.6μm, the operating temperature is controlled at 20℃, and the output power of the quantum cascade laser is 2.01W, 1.99W, 2.13W, 2.05W, 2.17W, 2.05W, and 1.97W, respectively.

[0023] Preferably, the focal length of the silicon lens is 50mm.

[0024] Preferably, the infrared light-transmitting window is made of calcium fluoride crystal sheet.

[0025] The present invention has the following beneficial technical effects:

[0026] 1. The high-power mid-wave quantum cascade laser fiber combining laser source provided in this embodiment uses an N×1 fiber combiner based on chalcogenide fiber to combine the power of multiple quantum cascade lasers. By utilizing the large numerical aperture characteristic of chalcogenide fiber, it can still ensure high coupling efficiency when the incident laser beam quality is poor. This effectively solves the problems of complex optical path and poor optical axis stability in traditional spatial beam combining technology, and realizes efficient and stable power combining of multiple mid-wave infrared lasers.

[0027] 2. The high-power mid-wave quantum cascade laser fiber combiner laser source provided in this embodiment integrates a chalcogenide end cap at the output end of the fiber combiner. The end cap is made of the same glass matrix material as the chalcogenide fiber. By increasing the effective area of ​​the output end face, the power density is reduced, which significantly improves the device's resistance to damage under high power conditions.

[0028] 3. The high-power mid-wave quantum cascade laser fiber-to-laser source provided in this embodiment uses self-developed liquid chalcogenide glass to bond and match the optical interface, effectively suppressing the inherent Fresnel reflection loss of the chalcogenide fiber end face, while avoiding damage to the quantum cascade laser by feedback light, thereby improving the overall coupling efficiency and system stability of the system.

[0029] 4. The high-power mid-wave quantum cascade laser fiber combiner laser source provided in this embodiment integrates N quantum cascade lasers, N focusing lenses, and the N input fiber end faces of an N×1 fiber combiner onto the same heat sink, is fixed by ultraviolet curing, and is equipped with a temperature control system to precisely control the temperature of the quantum cascade lasers, making the system more miniaturized and integrated, and ensuring the power stability of the system under long-term operating conditions.

[0030] A specific embodiment of the present invention will now be described in more detail.

[0031] like Figure 1 As shown, this high-power mid-wave quantum cascade laser fiber combiner laser source includes seven quantum cascade lasers 1-1 to 1-7, seven focusing lenses 2-1 to 2-7, a 7×1 fiber combiner 3, a collimating output mirror 4, and a temperature control system 5.

[0032] The seven quantum cascade lasers are mounted on the same water-cooled heat sink platform, and a focusing lens is placed at the output end of each quantum cascade laser. After being focused by the focusing lens, the mid-wave infrared laser is coupled into the seven input optical fibers of the 7×1 fiber combiner 3.

[0033] In this embodiment, the center wavelength of the quantum cascade laser is located near 4.6 μm, and the operating temperature is controlled at 20 °C. The output powers of each quantum cascade laser are 2.01 W, 1.99 W, 2.13 W, 2.05 W, 2.17 W, 2.05 W, and 1.97 W, respectively.

[0034] The focusing lens is a silicon lens with a focal length of 50mm and a transmittance of more than 98.5% in this band.

[0035] The 7×1 fiber combiner 3 is made of arsenic sulfide fiber. Its numerical aperture in the mid-infrared band is greater than 0.35, which can ensure efficient coupling and transmission of mid-infrared lasers and realize power combining of multiple mid-infrared lasers.

[0036] To reduce Fresnel reflection loss at the end face of the chalcogenide fiber, an infrared transmission window is integrated at the input end of the 7×1 fiber combiner 3. Liquid chalcogenide glass is filled between the input fiber end face and the infrared transmission window. This liquid chalcogenide glass serves both bonding and refractive index matching functions; its refractive index is between that of the infrared transmission window and the arsenic sulfide fiber, thereby reducing Fresnel reflection caused by abrupt changes in the interface refractive index.

[0037] Furthermore, a chalcogenide end cap and an infrared transmission window are integrated at the output end of the 7×1 fiber combiner 3. Liquid chalcogenide glass material is filled between the output fiber end face and the chalcogenide end cap, as well as between the chalcogenide end cap and the infrared transmission window, to reduce Fresnel reflection caused by abrupt changes in the interface refractive index.

[0038] In this embodiment, the infrared light-transmitting window is made of calcium fluoride crystal sheet, which has high transmittance in this wavelength band.

[0039] The chalcogenide end cap is made of the same matrix glass material as the output optical fiber. By increasing the effective area of ​​the output end face, the power density of the laser output end face is reduced, thereby improving the device's damage resistance.

[0040] During operation, the lasers emitted from the seven quantum cascade lasers are focused and coupled into the 7×1 fiber combiner 3 to achieve power superposition. The combined lasers are then output through the collimating output mirror 4.

[0041] The input optical fibers of the seven quantum cascade lasers, seven focusing lenses, and the 7×1 fiber combiner 3 are all integrated on the heat sink 5 by UV curing.

[0042] The input structure diagram of the 7×1 fiber combiner 3 is shown below. Figure 2 As shown, it includes a first infrared light-transmitting window 6, a first liquid glass 7, and an arsenic sulfide optical fiber 8.

[0043] The output structure diagram of the 7×1 fiber optic combiner 3 is shown below. Figure 3 As shown, it includes a bundle combiner output end face 9, a second liquid glass 10, a chalcogenide end cap 11, a third liquid glass 12, and a second infrared light-transmitting window 13.

[0044] When all seven quantum cascaded lasers operate at maximum output power, the total input power reaches 14.27W, and the system output is 10.36W, corresponding to an overall system transmission efficiency of 73%. During system operation, no significant power attenuation, fiber damage, or device failure was observed, indicating that the structure has good long-term operational stability.

[0045] Compared with existing technologies, this embodiment uses liquid glass to match the refractive index of the optical interface, which effectively reduces Fresnel reflection loss at the end face of the chalcogenide fiber, reduces the impact of feedback light on the quantum cascade laser, improves the coupling efficiency and operational stability of the system, and achieves mid-wave infrared laser output of more than 10W.

[0046] Figure 4 The output power and corresponding coupling efficiency of a high-power mid-wave quantum cascade laser fiber combiner laser source under different currents are shown.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A high-power mid-wave quantum cascade laser fiber-based laser source, characterized in that: It includes N quantum cascaded lasers, N focusing lenses, an N×1 fiber combiner (3), a collimating output mirror (4), and a heat sink (5), where N≥3; The output ends of N quantum cascade lasers are respectively aligned with the incident surfaces of N focusing lenses, the output surfaces of N focusing lenses are respectively aligned with the input fiber end face of N×1 fiber combiner, and the output end face (9) of N×1 fiber combiner is aligned with the collimating output mirror to complete the beam combining of N quantum cascade lasers. N quantum cascade lasers, N focusing lenses, and N fiber input end faces of an N×1 fiber combiner are all integrated on a heat sink; The wavelengths of N quantum cascaded lasers are all located in the mid-infrared band. Their emitted lasers are focused by their respective focusing lenses and then coupled into the N fibers of an N×1 fiber combiner for power combining. The fiber bundler is based on chalcogenide fiber. Its input end consists of N chalcogenide fibers (8). The first infrared transparent window (6) is bonded to the chalcogenide fiber through the first liquid glass (7). The output end face is bonded to the chalcogenide end cap (11) through the second liquid glass (10). The chalcogenide end cap is bonded to the second infrared transparent window (13) through the third liquid glass (12). The refractive index is matched by the first, second and third liquid glasses.

2. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 1, characterized in that: The focusing lens is a high-transmittance optical lens in the mid-infrared band, which focuses the laser emitted from the quantum cascade laser into the core of the input fiber of the N×1 fiber combiner.

3. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 2, characterized in that: The focusing lens is a silicon lens, which has a transmittance of more than 98.5% for mid-wave infrared laser.

4. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 3, characterized in that: The chalcogenide optical fiber is an arsenic sulfide optical fiber with a numerical aperture greater than 0.35 in the mid-infrared band.

5. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 4, characterized in that: The chalcogenide end cap is made of the same or matching matrix glass material as the N chalcogenide optical fibers.

6. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 5, characterized in that: The heat sink is equipped with a circulating water cooling system to control the temperature.

7. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 6, characterized in that: With N=7, the center wavelength of the quantum cascade laser is located near 4.6μm, the operating temperature is controlled at 20℃, and the output power of the quantum cascade laser is 2.01W, 1.99W, 2.13W, 2.05W, 2.17W, 2.05W, and 1.97W, respectively.

8. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 7, characterized in that: The focal length of the silicon lens is 50mm.

9. The high-power mid-wave quantum cascade laser fiber combiner laser source according to claim 8, characterized in that: The infrared light-transmitting window is made of calcium fluoride crystal sheet.

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