CN104901149A - Spectral beam combining system based on three diffraction gratings - Google Patents

Abstract

The invention discloses a spectral beam combining system based on three diffraction gratings. The system comprises M seed resources with different wavelengths, M optical fiber amplifier arrays, M output collimators, a first diffraction grating, a second diffraction grating, a third diffraction grating, a plane reflector, a Fourier lens and a CCD (Charge Coupled Device) camera. The system combines multipath optical fiber laser beams into a beam of laser for outputting, so as to realize the output of high power and high beam quality. The spectral beam combining system solves the problems that the quality of a beam combined by the traditional spectral combining system is degraded seriously and the path spreading of single diffraction gratings is difficult, and is feasible for realizing higher power spreading of an optical fiber laser.

Description

Spectral Beam Combining System Based on Three Diffraction Gratings

technical field

The invention relates to a fiber laser spectrum combining system, in particular to a spectrum combining system based on three diffraction gratings.

Background technique

Due to the good characteristics of small size, high efficiency, good beam quality and easy thermal management, fiber lasers have achieved rapid development in recent years, and have been widely used in the fields of space communication, laser weapons, material processing, remote sensing and laser radar. application. With the development of technology, fiber lasers with high power and high beam quality have gradually become an urgent demand in various application fields. However, due to the limitations of nonlinear effects, thermal effects, and end-face damage, single-channel fiber lasers have a certain power limit. In this case, fiber laser beam combining technology came into being, including coherent beam combining and incoherent beam combining. Coherent beam combining has strict requirements on the linewidth and phase of the laser, and encountered certain bottlenecks on the way to achieve high-power combining. Non-coherent beam combining, also known as spectral beam combining, greatly reduces the requirements on the wavelength, phase and line width of the laser. This method uses a diffraction grating to emit lasers of different wavelengths incident at different angles at the same diffraction angle. , so as to obtain a beam combining laser with a common aperture output. The spectral beam combining technology is considered to be a very promising high-power beam combining technology, and has recently become a research hotspot.

The structure of the existing fiber laser spectrum beam combining system is shown in Figure 2, by N seed sources 201 of different wavelengths, N fiber amplifiers 202 and N collimator output devices 203, folding mirror group 204, and diffraction grating 205 , a flat mirror 206, a Fourier lens 207, and a CCD camera 208. The seed sources of N different wavelengths are amplified to a certain power by N fiber amplifiers, and emitted by N collimated output devices. Each outgoing laser beam is incident on the diffraction grating through a pair of refraction mirrors, and the diffraction grating is placed _at a Littrow angle with a wavelength of λ0. By adjusting the refraction mirrors, each beam can be incident on the diffraction grating at a suitable angle. Therefore, they emit at the same angle to achieve high-power common-aperture output of multiple lasers.

However, there are certain defects in the above-mentioned existing spectrum synthesis system. The laser sources used in the experiment all have a certain linewidth. According to the blazed grating equation 2d sinθ=λ, it can be deduced that the diffraction grating exists for a light source with a certain linewidth. Chromatic dispersion effect Δθ=Δλ/2d cosθ, since the beam quality directly depends on the far-field divergence angle and the beam waist radius, this dispersion effect will lead to a decline in the quality of the combined beam. In order to ensure that the quality of the combined beam will not be severely degraded, it is necessary to limit The linewidth Δλ of each sub-beam, according to the relevant literature analysis, shows that Δλ should be limited to GHz level, and for narrow linewidth fiber lasers, Δλ directly determines the scattering threshold of stimulated Brillouin scattering, which is smaller The Δλ limits the power of a single sub-beam, thereby limiting the power expansion of spectral synthesis.

Contents of the invention

The present invention aims at the above-mentioned existing fiber laser beam combining system with serious degradation of combined beam quality and inconvenient expansion of beam combining laser paths, and proposes a spectral beam combining system based on three diffraction gratings. The system can greatly reduce the degradation of beam quality through the dispersion compensation characteristics of parallel gratings, and realize more convenient channel number expansion through the spatial structure of three gratings.

Technical solution of the present invention is as follows:

A spectral beam combining system based on three diffraction gratings, including M seed sources of different wavelengths, M fiber amplifier arrays, M collimated output devices, the first diffraction grating, the second diffraction grating, and the third Diffraction grating, plane mirror, Fourier lens and CCD camera, the positional relationship of above-mentioned elements is as follows: the second diffraction grating is placed with the Littrow angle that wavelength is λ ₀ , and the first diffraction grating is in the second diffraction grating The upper right is placed parallel to it, and the third diffraction grating is placed parallel to it at the lower right of the second diffraction grating. The seed source, optical fiber amplifier and collimator output device are connected in series in sequence and arranged into M rows and columns of high-power In the fiber amplifier array, the laser output from the high-power fiber amplifier with a wavelength less than λ ₀ is incident parallel to the first diffraction grating, and the laser output from the high-power fiber amplifier with a wavelength greater than λ ₀ is incident parallel to the third diffraction grating. The diffracted light of the first diffraction grating and the diffracted light of the third diffraction grating are all diffracted by the second diffraction grating to form a common-aperture laser output through the described plane mirror. The Fourier lens and the CCD camera are in sequence, and the CCD camera is located at the focal plane of the Fourier lens.

The wavelength range of the seed sources with different wavelengths is 1040nm-1090nm, and the line width is tens of GHz.

The first diffraction grating, the second diffraction grating and the third diffraction grating are all polarization-independent multilayer electrolyte reflective diffraction gratings, and the groove density is 960 grooves per millimeter.

The front surface of the one piece of plane reflector is coated with a high transmittance film with a laser transmittance of 99%, and the rear surface is coated with an anti-reflection film.

Technical effect of the present invention:

The present invention uses three diffraction gratings to combine various laser beams, which can be regarded as two sets of upper and lower double grating structures. The double grating structure can achieve a certain dispersion compensation, which greatly reduces the distortion caused by the limited line width of the incident light source. The problem of beam quality degradation, which makes the double grating structure can reduce the requirements for the line width of the sub-beam, because we know that for narrow line width high power fiber lasers, the line width directly affects the scattering of stimulated Brillouin scattering Threshold, then the requirement for line width is relaxed, which means that the power of sub-beams can be made higher, which is very beneficial to beam combining technology. At the same time, limited by the grating manufacturing process, the size of a single grating cannot be made particularly large. In reality, it is impossible to have infinite parallel light beams incident on a diffraction grating at the same time, and the structure of three diffraction gratings can just solve this problem. We divide the sub-beams with different wavelengths into upper and lower parts, which are respectively incident on two diffraction gratings in parallel, and their diffracted light is jointly incident on the third grating, thus realizing the spectral combination of multiple beams.

The three diffraction gratings all use quartz substrates, which have good thermal stability and can withstand high-power-density laser irradiation without complex cooling systems.

Description of drawings

Fig. 1 is the schematic diagram of the spectral beam combining system based on three diffraction gratings of the present invention

Figure 2 is a schematic diagram of the existing spectral beam combining system

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Please refer to FIG. 1 first. FIG. 1 is a schematic diagram of a spectral beam combining system based on three diffraction gratings according to the present invention. It can be seen from the figure that the spectral beam combining system based on three diffraction gratings in the present invention includes M seed sources 101 of different wavelengths, M fiber amplifier arrays 102, M collimator output devices 103, a first diffraction grating 104, a second Two diffraction gratings 105, the third diffraction grating 106, plane mirror 107, Fourier lens 108 and CCD camera 109, the positional relationship of the above-mentioned elements is as follows: the second diffraction grating 105 is the Littrow angle pendulum of λ ₀ with wavelength Put, the first diffraction grating 104 is placed parallel to it on the upper right of the second diffraction grating 105, and the third diffraction grating 106 is placed parallel to it on the lower right of the second diffraction grating 105. The seed source 101, optical fiber Amplifier 102 and collimator output device 103 are connected in series successively and arranged into a high-power fiber amplifier array of M rows and one column according to wavelength, and the laser light output by the high-power fiber amplifier with wavelength less than λ ₀ is incident on the first diffraction grating 104 in parallel, and the wavelength is greater than The laser light output by the high-power optical fiber amplifier of λ ₀ is incident on the third diffraction grating 106 in parallel, and the diffracted light of the first diffraction grating 104 and the diffracted light of the third diffraction grating 106 are formed through the diffraction of the second diffraction grating 105 Common-aperture laser is exported through described plane mirror 107, and this plane mirror 107 forms 45 ° with optical path, and the reflected light beam direction of this plane mirror 107 is described Fourier lens 108 and CCD camera 109 successively, and this CCD camera 109 is positioned at described The focal plane of the Fourier lens.

The wavelength range of the seed sources 101 of different wavelengths is 1040nm-1090nm, and the line width is tens of GHz.

The first diffraction grating 104 , the second diffraction grating 105 and the third diffraction grating 106 are all polarization-independent multilayer electrolyte reflective diffraction gratings, and the groove density is 960 grooves per millimeter.

The front surface of the piece of flat mirror 107 is coated with a high transmittance film with a laser transmittance of 99%, and the rear surface is coated with an anti-reflection film.

The seed sources 101 of different wavelengths are divided into two groups according to the wavelengths, as shown in Figure 2, one group of wavelengths is less than λ ₀ , λ _n <...λ ₁ <λ ₀ , located in the upper part of Figure 2; the other group The wavelength is greater than λ ₀ , and λ _m >...λ _n+1 >λ ₀ , located in the lower half of Fig. 2 . A group of light beams with a wavelength smaller than λ ₀ are incident parallel to the first diffraction grating 104, emerge at different diffraction angles and are transmitted to the same point of the second diffraction grating 105, and a group of light beams with a wavelength greater than λ ₀ are incident parallel to the first diffraction grating 104. The third diffraction grating 106 emits at different diffraction angles and transmits to the second diffraction grating 105, acting on the same point as the first group of light beams. According to the grating equation, the second diffraction grating 105 diffracts all the light beams incident on it, thereby realizing the common-aperture output of all sub-beams, and the output combined light beam is transmitted to a plane mirror 107, and 99% of the light passes through the plane mirror 107,1 % of the light is reflected by the plane mirror 107, and is imaged by a Fourier lens 108 on the CCD camera 109 located at the focal plane, so as to detect the far-field synthetic light spot.

The following is an example of four-way fiber amplifier beam combining. The four-way seed sources 101 have wavelengths of 1060nm, 1064nm, 1072nm, and 1076nm respectively. First, the second diffraction grating 105 is placed at the Littrow angle of the 1068nm wavelength laser. The blazed grating equation 2d sinθ=λ, can draw that for a wavelength of 1064nm, a diffraction grating with 960 lines per millimeter has a Littrow angle of 30.84°; then place the first diffraction grating 104 and the third diffraction grating 106 at a certain distance Placed at the upper right and lower right of the second diffraction grating 105 respectively; the sub-beams of 1060nm and 1064nm are incident on the first diffraction grating 104, and the sub-beams of 1072nm and 1076nm are incident on the third diffraction grating; Source 101, turn on the four-way fiber amplifier 102, adjust the collimator 103 so that each laser beam is incident on the corresponding diffraction grating in parallel, finely adjust the positions of the three diffraction gratings, so that the 1060nm and 1064nm sub-beams pass through the first diffraction grating Diffraction light and 1072nm, 1076nm sub-beams pass through the diffraction light of the third diffraction grating and act on the same point of the second diffraction grating 105; the plane mirror 107 is placed at 45° to the optical axis, and the Fourier lens 108 and CCD are finely adjusted The position of the camera 109 makes it possible to monitor the far-field spot of the synthesized beam on the CCD camera. By adjusting the optical adjustment element in the optical path, the far-field spot of the synthesized beam in the CCD camera is completely common in aperture, thereby completing the spectrum synthesis of the four-way fiber laser. .

Claims (4)

1. A spectral beam combining system based on three diffraction gratings is characterized in that comprising M seed sources (101) of different wavelengths, M fiber amplifier arrays (102), M collimating output devices (103), the first Block diffraction grating (104), second block diffraction grating (105), third block diffraction grating (106), plane mirror (107), Fourier lens (108) and CCD camera (109), the positional relationship of above-mentioned elements is as follows : the second diffraction grating (105) is placed at the Littrow angle with a wavelength of λ ₀ , the first diffraction grating (104) is placed parallel to it on the upper right of the second diffraction grating (105), and the third diffraction grating The grating (106) is placed parallel to it at the bottom right of the second diffraction grating (105), and the described seed source (101), optical fiber amplifier (102) and collimator output device (103) are connected in series successively and arranged into M The high-power fiber amplifier array of a row, the laser light that the high-power fiber amplifier output of wavelength is less than λ ₀ is incident on the first diffraction grating (104) in parallel, and the laser light that the wavelength is greater than the high-power fiber amplifier output of λ ₀ is incident parallelly to The third diffraction grating (106), the diffracted light of the first diffraction grating (104) and the diffraction light of the third diffraction grating (106) are all diffracted by the second diffraction grating (105) to form a common aperture laser through the described The plane mirror (107) output, this plane mirror (107) becomes 45 ° with the optical path, and the reflected beam direction at this plane mirror (107) is successively described Fourier lens (108) and CCD camera (109), this CCD camera (109) is located at the focal plane of the Fourier lens. 2. The spectral beam combining system based on three diffraction gratings according to claim 1, characterized in that the wavelength range of the seed sources (101) of different wavelengths is 1040nm-1090nm, and the linewidth is tens of GHz. 3. The spectral beam combining system based on three diffraction gratings according to claim 1, characterized in that the first diffraction grating (104), the second diffraction grating (105) and the third diffraction grating ( 106) are all polarization-independent multilayer electrolyte reflective diffraction gratings, the groove density is 960 grooves per millimeter, and the diffraction efficiency is greater than 98%. 4. The spectral beam combining system based on three diffraction gratings according to claim 1, characterized in that the front surface of the plane mirror (107) is coated with a high transmittance film with a laser transmittance of 99%, and the rear surface is coated with With AR coating.