A multi-band quantum cascade laser beam combining system

Abstract

The invention belongs to the field of laser technology, and proposes a multi-band quantum cascade laser beam combining system. The beam combining system includes, in the optical path, a plurality of quantum cascade laser tube cores with different lasing wavelengths, a shaping lens system, a fast and slow axis collimating optical system, a spatial beam combining reflector group, a coupling focusing lens group, a Bragg diffraction grating, and a quantum cascade laser beam combining output lens group; the wavelengths of the laser outputs from the plurality of quantum cascade laser tube cores with different lasing wavelengths are different, and the laser passes through the shaping lens system and the fast and slow axis collimating optical system to improve the output beam quality before entering the spatial beam combining reflector group, and after spatial beam combining, the beam performance is improved through the coupling focusing lens group and the Bragg diffraction grating, and finally an excellent combined beam is output through the quantum cascade laser beam combining output lens group.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, in particular to a beam combining system of a multi-band quantum cascade laser tube core combining a spatial beam combining technology and a spectral (grating) beam combining technology, and in particular to a multi-band quantum cascade laser beam combining system. Background Art

[0002] Quantum cascade lasers have the advantages of small size, light weight, direct modulation, high electro-optical conversion efficiency, and high reliability. They have important application prospects in environmental monitoring, lidar, medical diagnosis, space communications, and military defense. After years of research, the performance of mid-infrared quantum cascade lasers has been continuously improved, but due to the limitations of device structure and material properties, it has become very difficult to further increase the output power. At present, how to further increase the output power of mid-infrared quantum cascade lasers while maintaining high beam quality has become a pain point that restricts its application. The method of multi-band beam combining is an effective way to achieve high-power, high-performance laser output.

[0003] Beam combining is a key technology for quantum cascade lasers to achieve high-power, high-brightness laser output. It is based on the optical properties of lasers such as phase, light field distribution, polarization and spectrum. Through optical effects such as refraction, reflection and diffraction, multiple low-power unit beams are coupled into a high-power laser output, while maintaining a high beam quality, which greatly improves the brightness and power of the quantum cascade laser output beam. According to the coherence requirements and beam combining mechanism of the laser units involved in beam combining, laser beam combining technology can be divided into coherent beam combining and incoherent beam combining methods, among which typical incoherent beam combining methods include spatial beam combining, polarization beam combining, wavelength beam combining and spectral beam combining. The following compares the main features of coherent beam combining and incoherent beam combining.

[0004] (1) Laser coherent synthesis: The basic condition for laser coherent synthesis is that the laser wavelengths are the same. Phase control technology is required during synthesis. The maximum peak power of the coherent beam is N2 times the peak power of a single beam. N is the number of laser beams. However, through the research results of domestic and foreign scholars, it can be found that the synthesis efficiency decreases significantly with the increase of the number of laser beams during coherent synthesis.

[0005] (2) Incoherent laser beam combining: Compared with coherent beam combining, incoherent laser beam combining technology has higher reliability and practical significance. Incoherent laser beam combining does not require precise polarization state and phase synchronization. It can superimpose laser beams of different wavelengths or laser beams of the same wavelength.

[0006] Due to the limitations of optical components in the mid-infrared band and the stringent thermal management requirements, laser beam combining technology has been less studied in the field of mid- and long-wave infrared quantum cascade lasers. Since coherent beam combining has too high requirements for the phase control of the laser, it is not easy to achieve and is rarely used. In recent years, the most commonly used beam combining technologies for mid- and long-wave infrared quantum cascade lasers are spatial beam combining and spectral beam combining. Spatial beam combining superimposes multiple sub-beams in space to increase the power. Its beam combining efficiency is high, but the beam quality of the output beam is poor. Spectral beam combining uses the dispersion and feedback of the grating to achieve wavelength locking. The beam quality of the output beam is close to that of a single beam combining unit, but its installation is complex and the beam combining efficiency is low. Summary of the invention

[0007] In order to solve the above problems, the present invention proposes a multi-band quantum cascade laser beam combining system, which aims to realize a multi-wavelength beam combining system by combining the traditional lens spatial beam combining with the novel Bragg grating for wavelength spectral beam combining, and after spatial beam combining of multiple quantum cascade laser cores, further improve the beam quality through the dispersion element.

[0008] The technical solution adopted by the present invention is: a multi-band quantum cascade laser beam combining system, which comprises, in an optical path, a plurality of quantum cascade laser tube cores with different lasing wavelengths, a shaping lens system, a fast-slow axis collimating optical system, a spatial beam combining reflector group, a coupling focusing lens group, a Bragg diffraction grating, and a quantum cascade laser beam combining output lens group; the wavelengths of laser outputs from the plurality of quantum cascade laser tube cores with different lasing wavelengths are different, and the laser passes through the shaping lens system and the fast-slow axis collimating optical system to improve the output beam quality before entering the spatial beam combining reflector group, and after spatial beam combining, the beam performance is improved through the coupling focusing lens group and the Bragg diffraction grating, and finally an excellent combined beam is output through the quantum cascade laser beam combining output lens group.

[0009] Furthermore, the wavelength distribution range of the Bragg diffraction grating is 20 nm, the central wavelength is 4600 nm, the central wavelength of the tube core with the maximum wavelength is 4650 nm, and the wavelengths of the intermediate tube cores are selected according to their spatial positions and the principle of linear chirp.

[0010] Furthermore, the plurality of quantum cascade laser dies are separate dies or laser bars.

[0011] Furthermore, the central reflection wavelength of the Bragg diffraction grating varies linearly along the length direction, the central reflection wavelength is in the range of 4500 to 4700 nanometers, and the central reflectivity is 5% to 50%.

[0012] Furthermore, the plurality of quantum cascade laser tube cores with different lasing wavelengths are designed as a straight line, rectangular, circular or square array.

[0013] Furthermore, the beam combining system also includes a shell and a laser window. The laser window is arranged on the shell. The quantum cascade laser die, shaping lens system, fast and slow axis collimation optical system, spatial beam combining reflector group, coupled focusing lens group, Bragg diffraction grating, and quantum cascade laser beam combining output lens group are all placed inside the shell. The combined laser is output through the laser window.

[0014] Furthermore, the grating period of the Bragg diffraction grating can be designed to be a variable period, a "chirp" period.

[0015] Furthermore, each quantum cascade laser die passes through a heat sink and a cooling device below.

[0016] Furthermore, the quantum cascade laser core structure is composed of a surface metal electrode layer, a ridge waveguide layer, a p-type doped cladding layer, a p-type doped light confinement layer, a quantum well or quantum dot active region, a grating layer, an n-type doped light confinement layer, an isolation layer, and a substrate layer from top to bottom.

[0017] The present invention is a system that comprehensively uses laser spatial beam combining and spectral beam combining technology to perform spatial beam combining on multiple quantum cascade laser cores, and then further improves the beam quality through diffraction optical elements to achieve multi-band quantum cascade laser beam combining. It solves the pain point that a single medium- and long-wave infrared quantum cascade laser has low light output power and cannot meet certain application scenarios that require a high-power laser source. While maintaining high beam quality, it greatly improves its output power and solves the pain point that restricts its application. The proposed multi-band quantum cascade laser beam combining system consists of: multiple quantum cascade lasers with different lasing wavelengths, a shaping system, a fast and slow axis collimation optical system, a spatial beam combining reflector group, a coupled focusing lens group, a Bragg diffraction grating, and a quantum cascade laser beam combining output lens group. The proposed laser beam combining system has good scalability, and can be expanded in the later stage to achieve the beam combining of more than 8 multi-band quantum cascade lasers.

[0018] The working principle of the present invention is as follows: the wavelengths of the laser output by the multiple quantum cascade laser tube cores with different lasing wavelengths described in the present invention are different. The laser passes through a shaping lens system and a fast-slow axis collimation optical system to improve the output beam quality and then enters a spatial beam combining reflector group. After spatial beam combining, the beam performance is improved by a coupling focusing lens group and a Bragg diffraction grating. Finally, an excellent combined beam is output through a quantum cascade laser beam combining output lens group. The present invention adopts a fast-slow axis collimation optical system placed on the back of the Bragg diffraction grating, so that the laser beams from each laser tube core become parallel beams after passing through the fast-slow axis collimation optical system and are projected onto the diffraction grating. The grating period, rotation direction and spatial distance of the diffraction grating from the tube core are appropriately selected, so that the laser beams of different wavelengths from each tube core are diffracted to the same direction on the +1-order diffraction stripes, thereby realizing multi-tube core semiconductor laser beam combining.

[0019] Compared with the existing design solutions, the design scheme conceived by the present invention has the following advantages: (1) The Bragg grating has a strong wavelength locking effect on each quantum cascade laser die, which is not easily affected by environmental vibration during beam combining, achieving a good beam combining effect, improving beam combining quality, and simplifying the process.

[0020] (2) Compared with the multi-band spatial beam combining scheme composed of all lenses, the volume of this system is greatly reduced, the beam characteristics are improved, and the reliability and stability are enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the multi-band quantum cascade laser beam combining system of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] See also Figure 1A multi-band quantum cascade laser beam combining system, which includes, on an optical path, four quantum cascade laser tube cores 1, 2, 3, and 4 with different lasing wavelengths, a shaping lens system 5, a fast-slow axis collimating optical system 6, a spatial beam combining reflector group 7, a coupling focusing lens group 8, a Bragg diffraction grating 9, and a quantum cascade laser beam combining output lens group 10; the wavelengths of laser outputs from the four quantum cascade laser tube cores with different lasing wavelengths are different, and the laser passes through the shaping lens system 5 and the fast-slow axis collimating optical system 6 to improve the output beam quality before entering the spatial beam combining reflector group 7, and after spatial beam combining, the beam performance is improved through the coupling focusing lens group 8 and the Bragg diffraction grating 9, and finally an excellent combined beam is output through the quantum cascade laser beam combining output lens group 10.

[0024] Furthermore, the wavelength distribution range of the Bragg diffraction grating 9 is 20 nm, the central wavelength is 4600 nm, the central wavelength of the tube core with the maximum wavelength is 4650 nm, and the wavelengths of the tube cores in the middle are selected according to their spatial positions and the principle of linear chirp.

[0025] Furthermore, the quantum cascade laser tube core is a separate tube core or a laser bar.

[0026] Furthermore, the central reflection wavelength of the Bragg diffraction grating 9 varies linearly along the length direction, the central reflection wavelength is in the range of 4500 to 4700 nanometers, and the central reflectivity is 5% to 50%.

[0027] Furthermore, the plurality of quantum cascade laser tube cores with different lasing wavelengths are designed as a straight line, rectangular, circular or square array.

[0028] Furthermore, the beam combining system also includes a shell and a laser window. The laser window is arranged on the shell. The quantum cascade laser tube core, the shaping lens system 5, the fast and slow axis collimation optical system 6, the spatial beam combining reflector group 7, the coupled focusing lens group 8, the Bragg diffraction grating 9, and the quantum cascade laser beam combining output lens group 10 are all placed inside the shell, and the combined laser is output through the laser window.

[0029] Furthermore, the grating period of the Bragg diffraction grating 9 can be designed to be a variable period, a "chirped" period.

[0030] Furthermore, in terms of heat dissipation, each quantum cascade laser die passes through a heat sink and a cooling device below.

[0031] Furthermore, in terms of circuit, each quantum cascade laser die can be driven individually, or several can be grouped together for joint driving.

[0032] Furthermore, the quantum cascade laser tube core structure is composed of a surface metal electrode layer, a ridge waveguide layer, a p-type doped cladding layer, a p-type doped light confinement layer, a quantum well or quantum dot active region, a grating layer, an n-type doped light confinement layer, an isolation layer, and a substrate layer from top to bottom. The substrate is the substrate of the epitaxially grown laser. The quantum well or quantum dot active region is a layer where carriers recombine to generate laser light, and the light confinement layers located above and below it are used to confine the laser light in the vertical direction to prevent the laser light generated in the active region from leaking out of the laser. The light confinement layers greatly improve the light extraction efficiency of the laser.

[0033] The present invention has the following advantages: (1) The Bragg diffraction grating 9 performs strong wavelength locking on each quantum cascade laser die, which is not easily affected by environmental vibration during beam combining, thus achieving a good beam combining effect, improving beam combining quality, and simplifying the process.

[0034] (2) Compared with the multi-band spatial beam combining scheme composed of all lenses, the volume of this system is greatly reduced, the beam characteristics are improved, and the reliability and stability are enhanced.

[0035] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-band quantum cascade laser beam combining system, characterized by: The beam combining system comprises, in sequence, a plurality of quantum cascade laser tube cores with different lasing wavelengths, a shaping lens system, a fast and slow axis collimating optical system, a spatial beam combining reflector group, a coupling focusing lens group, a Bragg diffraction grating, and a quantum cascade laser beam combining output lens group on an optical path; the wavelengths of laser outputs from the plurality of quantum cascade laser tube cores with different lasing wavelengths are different, and the laser enters the spatial beam combining reflector group after passing through the shaping lens system and the fast and slow axis collimating optical system to improve the output beam quality, and after being spatially combined, the beam performance is improved through the coupling focusing lens group and the Bragg diffraction grating, and finally an excellent combined beam is output through the quantum cascade laser beam combining output lens group.

2. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The wavelength distribution range of the Bragg diffraction grating is 20nm, the central wavelength is 4600nm, the central wavelength of the tube core with the maximum wavelength is 4650nm, and the wavelengths of the tube cores in the middle are selected according to their spatial positions and the principle of linear chirp.

3. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The plurality of quantum cascade laser dies are separate dies or laser bars.

4. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The central reflection wavelength of the Bragg diffraction grating changes linearly along the length direction, the central reflection wavelength is within the range of 4500 to 4700 nanometers, and the central reflectivity is 5% to 50%.

5. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The multiple quantum cascade laser tube cores with different lasing wavelengths are designed to be a straight line, rectangular, circular or square array.

6. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The beam combining system also includes a shell and a laser window. The laser window is arranged on the shell. The quantum cascade laser tube core, the shaping lens system, the fast and slow axis collimation optical system, the spatial beam combining reflector group, the coupled focusing lens group, the Bragg diffraction grating, and the quantum cascade laser beam combining output lens group are all placed inside the shell. The combined laser is output through the laser window.

7. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The Bragg diffraction grating can be designed with a grating period of variable period, a "chirp" period.

8. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: Each quantum cascade laser die passes through a heat sink and cooling device below.

9. A multi-band quantum cascade laser beam combining system as claimed in claim 1, characterized in that: The quantum cascade laser core structure comprises, from top to bottom, a surface metal electrode layer, a ridge waveguide layer, a p-type doped cladding layer, a p-type doped light confinement layer, a quantum well or quantum dot active region, a grating layer, an n-type doped light confinement layer, an isolation layer, and a substrate layer.

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