CN101159365A - Multi-channel fiber laser coherent beaming device and coherent beaming method based on overlapping volume gratings - Google Patents

Abstract

The invention discloses a multi-channel fiber laser coherent beam combining device and a coherent beam combining method based on overlapping volume gratings. The device comprises that one side of the fiber grating is sequentially connected with a fiber coupler, a doped double-clad fiber, a lens, a dichromatic mirror, a reflection mirror, a polarization controller, a reflection mirror, an overlapping volume grating, and an output coupling mirror. This method can realize the coherent combination of multi-channel fiber laser beams without complex phase detection and control of each beam. By sharing the resonant cavity formed by the output coupling mirror and the fiber grating, the phases of the beams are interlocked. By overlapping volume gratings, each beam achieves coherent superposition in the near field and far field, achieving the purpose of greatly improving the output power and brightness of the fiber laser. The structure is simple, and the system complexity does not increase with the increase of the number of bundled fiber lasers. It can be widely used in fields that require high-power fiber laser as a light source, and can obtain high-power, high-beam quality, and compact high-energy laser systems.

Description

Multi-channel fiber laser coherent beaming device and coherent beaming method based on overlapping volume gratings

technical field

The invention relates to a laser technology, in particular to a multi-channel fiber laser coherent beam combining device and a coherent beam combining method based on overlapping volume gratings.

Background technique

Developing a high-power, high-beam-quality, efficient, and compact high-energy laser system to meet the needs of various applications, especially military, is the long-term research goal of countries all over the world. Fiber lasers have the characteristics of high efficiency, compactness, good beam quality, good heat dissipation characteristics and high output power stability, and the flexibility of optical fibers enables them to flexibly adapt to different installation environments by bending without affecting the output of the beam. Therefore, the competitiveness of fiber lasers far exceeds other lasers, has a huge market, and has broad application prospects in industry, medicine and military. In the industrial and medical fields, fiber lasers can be used in welding and cutting, weld seam cleaning, laser engraving, drilling, product marking, laser inspection and measurement, laser imaging, laser radar systems, laser medical treatment, medical device microprocessing, etc. . In the military, high-power (above 100kW) lasers can be used to build ground-based, space-based, star-based and ship-borne high-energy laser weapon systems to achieve effective strikes against enemy missiles, aircraft, satellites and other targets. Fields such as optoelectronic countermeasures have important strategic and tactical significance. In recent years, with the emergence of large mode area double-clad fibers and the development of high-power semiconductor laser pumping technology, the output power of fiber lasers has increased significantly, and the output power of a single fiber laser has exceeded kilowatts. However, due to the limitations of physical mechanisms such as nonlinear effects of doped fibers, optical damage, and thermal damage, the output power of the above-mentioned single fiber laser is difficult to meet the high power requirements of high-energy laser systems. It is difficult and expensive to significantly increase the output power of a single laser. At the same time, as the output power increases, a single fiber laser has defects such as poor beam quality.

Contents of the invention

The object of the present invention is to provide a multi-channel fiber laser coherent beam combining device based on overlapping volume gratings, which is simple in structure, easy to use, low in cost, and can greatly improve the output power and brightness of the laser.

Another object of the present invention is to provide a laser coherent beam combining method.

In order to overcome the deficiencies in the prior art, the technical solution to be solved by the present invention is achieved in this way: a multi-channel fiber laser coherent beaming device based on overlapping volume gratings, the invention has outstanding substantive features and remarkable progress in that an optical fiber The grating is connected to a fiber coupler, and the other side of the fiber coupler is respectively connected to at least two doped double-clad fibers. A lens is placed on one side of each doped double-clad fiber, and a lens is placed on one side of each lens. There is a dichromatic mirror, a polarization controller is arranged between the dichromatic mirror and the reflecting mirror, an overlapping volume grating is arranged on one side of the reflecting mirror, and an output coupling mirror is arranged on one side of the overlapping volume grating, and the output coupling mirror outputs group light. The superimposed volume grating refers to multiple gratings with a certain thickness obtained by holographic recording in the same area of the optical medium.

A coherent grouping method based on an overlapping volume grating multi-channel fiber laser coherent grouping device according to claim 1, characterized in that it comprises:

a. When one fiber grating constitutes one side of multiple fiber laser resonators, when the wavelength of each laser matches the working wavelength of the fiber grating, each fiber laser works at the same wavelength;

b. A fiber grating and an output coupling mirror form an optical resonant cavity;

c. A fiber grating and an output coupling mirror form a common resonant cavity for multiple fiber lasers. The output coupling mirror feeds back part of the energy of the bundled power to each fiber laser, and the optical oscillations of each fiber laser are mutually restrained, so that each fiber laser phase interlock;

d. An overlapping volume grating is a beam combiner and a beam splitter at the same time. It can not only diffract multiple incident fiber lasers satisfying the Bragg condition in the same direction according to the Bragg angle, but also reflect the output coupling mirror back The light beam is diffracted into multiple sub-beams;

e. The two-way multiplexing of an overlapping volume grating can not only realize the combination of multiple fiber lasers, but also make the laser reflected by the output coupling mirror diffract into multiple beams and feed back to each fiber laser to realize the phase of the output beam of each fiber laser. interlock;

f. A laser that is stimulated to emit in a doped double-clad fiber is coupled into a fiber grating through a fiber coupler;

g. An overlapping volume grating is a plurality of gratings with a certain thickness obtained by holographic recording in the same area of the optical medium, and the number of the gratings is equal to the number of fiber lasers that need to be bundled;

h, one when light beams k ₁ and k _i where i=1, 2,..., N are incident at Bragg angles α ₁ and α _i determined by volume gratings K _G1 and K _Gi respectively, their diffracted light exits in the same direction, volume There is an angle φ _i between the grating vectors K _G1 and K _Gi of the grating, which is determined by the Bragg condition cos(φ _i -β)=K _Gi /2k, where β is the angle between the diffracted light and the positive direction of the z-axis , namely the Bragg angle, K _Gi =2π/d _i , d _i is the grating constant of the i-th grating, k=2πn/λ is the transmission constant of the light beam in the optical medium, λ is the wavelength of the incident light, and n is the optical medium average refractive index.

Compared with the prior art, the present invention has the following technical effects:

1. By sharing a fiber grating, each fiber laser can work at the same optical wavelength;

2. By overlapping the volume grating, each fiber laser can achieve near-field and far-field coherent superposition, so as to greatly improve the output power and brightness of the fiber laser;

3. By sharing the resonant cavity composed of fiber grating and output coupling mirror, no complex phase detection and control is required, and the interlocking of the positions of each fiber laser can be realized to achieve the purpose of co-length interference output;

4. The structure is simple, and the system complexity does not increase with the increase of the number of bundled fiber lasers.

Description of drawings

Fig. 1 is the schematic diagram of device structure principle of the present invention;

Fig. 2 is a schematic diagram of overlapping volume grating beam assembly in Fig. 1;

Detailed ways

Accompanying drawing is embodiment of the present invention.

Below in conjunction with accompanying drawing, content of the present invention will be further described:

As shown in Figure 1, a multi-channel fiber laser coherent beam combining device based on overlapping volume gratings, one fiber grating 1 is connected to a fiber coupler 2, and the other side of the fiber coupler 2 is connected to at least two doped double Clad optical fiber 3, a lens 4 is arranged on one side of each doped double-clad optical fiber 3, a dichroic mirror 5 is arranged on one side of each lens 4, and a polarizer is arranged between the dichromatic mirror 5 and the reflecting mirror 7 A controller 6, an overlapping volume grating 8 is placed on one side of the reflecting mirror 7, and an output coupling mirror 9 is placed on one side of the overlapping volume grating 8, and the output coupling mirror 9 outputs the group light 10, and the output coupling mirror refers to a reflectivity of about 4% transmission/reflection mirrors, in addition, fiber couplers, output coupling mirrors, and polarization controllers are all mature commercially available products, which are products well known to those skilled in the art.

A method for coherent beaming of a multi-channel fiber laser coherent beaming device based on overlapping volume gratings according to claim 1, comprising:

a. When one fiber grating constitutes one side of multiple fiber laser resonators, when the wavelength of each laser matches the working wavelength of the fiber grating, each fiber laser works at the same wavelength;

b. A fiber grating and an output coupling mirror form an optical resonant cavity;

c. A fiber grating and output coupling mirror constitute a common resonant cavity for multiple fiber lasers. The output coupling mirror feeds back part of the energy of the bundled power to each fiber laser. The optical oscillations of each fiber laser are mutually restrained, and the phase of each fiber laser interlock;

d. An overlapping volume grating is a beam combiner and a beam splitter at the same time. It can not only diffract multiple incident fiber lasers satisfying the Bragg condition in the same direction according to the Bragg angle; at the same time, it can also reflect the output coupling mirror back The light beam is diffracted into multiple sub-beams;

e. The two-way multiplexing of an overlapping volume grating can not only realize the combination of multiple fiber lasers, but also make the laser reflected by the output coupling mirror diffract into multiple beams and feed back to each fiber laser to realize the phase of the output beam of each fiber laser. interlock;

f. A laser that is stimulated to emit in a doped double-clad fiber is coupled into a fiber grating through a fiber coupler;

g. An overlapping volume grating is a plurality of gratings with a certain thickness obtained by holographic recording in the same area of the optical medium, and the number of the gratings is equal to the number of fiber lasers that need to be bundled;

h, one when light beams k ₁ and k _i where i=1, 2,..., N are incident at Bragg angles α ₁ and α _i determined by volume gratings K _G1 and K _Gi respectively, their diffracted light exits in the same direction, volume There is an angle φ _i between the grating vectors K _G1 and K _Gi of the grating, which is determined by the Bragg condition cos(φ _i -β)=K _Gi /2k, where β is the angle between the diffracted light and the positive direction of the z-axis , namely the Bragg angle, K _Gi =2π/d _i , d _i is the grating constant of the i-th grating, k=2πn/λ is the transmission constant of the light beam in the optical medium, λ is the wavelength of the incident light, and n is the optical medium average refractive index.

As shown in Figure 1, in order to make each fiber laser work at the same wavelength, a 1 xN fiber coupler and a fiber grating are used in the scheme. The stimulated emission of laser light in each doped double-clad fiber is coupled into the fiber grating through the fiber coupler. Since the fiber grating has a narrow wavelength selectivity, only when the wavelength of the laser matches the working wavelength of the fiber grating can an effective beam feedback, thereby forcing each fiber laser to work at the same wavelength.

Coherent superposition of laser beams is achieved by overlapping volume gratings:

Overlapped volume gratings are multiple gratings with a certain thickness obtained by holographic recording in the same area of the optical medium, and the number of volume gratings is equal to the number of fiber lasers that need to be bundled. Due to the narrow spectral selectivity of the volume grating, the beam of a specific wavelength has a high diffraction efficiency only when it is incident at or close to the Bragg angle (the angle is determined by the volume grating), and when the incident beam does not meet the Bragg condition, it is diffracted The efficiency is very low or close to zero.

In order to introduce optical feedback, an output coupling mirror is added after the stacked volume grating, and the output coupling mirror and the fiber grating together form an optical resonant cavity. The output coupler mirror reflects a fraction of the combined optical power into the overlapping volume grating. Since a good beam combiner is also a good beam splitter, the bidirectional multiplexing of overlapping volume gratings can make the beam reflected by the output coupling mirror into the overlapping volume gratings be diffracted by each volume grating according to their respective Bragg angles, forming multiple beam of diffracted light. These diffracted lights are respectively coupled into each fiber laser to form optical feedback, so that part of the energy of different fiber lasers enters other fiber lasers, so that the optical oscillations of each fiber laser are mutually restrained to achieve the purpose of phase interlocking.

As shown in Fig. 2, light beams k ₁ and _ki (i=1, 2, ..., N) are incident at Bragg angles α ₁ and α _i determined by volume gratings K _g1 and K _Gi respectively, in order to make their diffracted light along the same The direction of output (i.e. to achieve beam combination), the volume grating is designed so that there is a specific angle φ _i between the grating vector K _G1 and K _Gi , which is determined by the Bragg condition cos(φ _i -β)=K _Gi /2k , where β is the angle between the diffracted light and the positive direction of the z-axis, that is, the Bragg angle, K _Gi =2π/d _i , d _i is the grating constant of the i-th grating, k=2πn/λ is the light beam in the optical medium The transmission constant, λ is the wavelength of the incident light, and n is the average refractive index of the optical medium. Since the polarization direction of the output laser light from each doped fiber may change randomly, a polarization controller is added to the optical path shown in Fig. Coherent conditions (ie same frequency, same polarization, constant phase difference).

The fiber grating and the output coupling mirror form a resonant cavity, which realizes the bit interlocking of each fiber laser:

In summary, the present invention first forces each fiber laser to work at the same wavelength by sharing the same fiber grating, and then through the resonant cavity formed by the output coupling mirror and the fiber grating, the phase of each beam can be locked, and finally through the overlapping volume grating, The coherent superposition of each beam can be realized in both the near field and the far field, so as to greatly improve the output power and brightness of the fiber laser. This solution does not require complex phase detection and control of each beam, and can realize coherent beam combining of multiple fiber lasers. It can be widely used in fields that require high-power fiber lasers as light sources. , Compact high-energy laser systems are of great significance.

Example 1

2-way fiber laser coherent bundle embodiment

The resonant wavelength of the fiber grating is 1550nm, and its reflectivity is about 95%; a 1×2 fiber coupler with a splitting ratio of 50:50 is used; the doped fiber is an erbium-ytterbium co-doped large mode area double-clad fiber, and the lengths are respectively It is about 1m; the focal length of the lens is about 1.5cm; the pump sources work around the wavelength of 980nm, and the maximum output power of each pump source is about 20W; the output laser power of the two doped fibers under the excitation of pump light They are 5.6W and 6.2W respectively; due to the spectral selectivity of fiber gratings, the wavelengths of the output lasers from the two doped fibers are both 1550nm; 100%; adjust the polarization controller so that the polarization directions of the output lasers of the two doped fibers are the same (perpendicular to the paper); the reflectivity of the two mirrors is about 98% when the 1550nm light wave is incident at an angle of 45°; Two volume gratings overlap in the same area of the dichromate crystal, the vector of volume grating 1 is parallel to the crystal surface, and the angle with the vector of volume grating 2 is about 3.6°; The output laser beams correspond to the incident volume grating 1 and volume grating 2 at the angles α ₁ =11.9271° and α ₂ =8.3271°, the output angle of the coherent beam laser is β = 11.9271°, the beam power is about 10.2W, and the beam efficiency is 86%; the reflectivity of the output coupling mirror to 1550nm light waves is about 4%, which reflects a part of the beam power into the overlapping volume grating to diffract into 2 beams of light, and these two beams of light enter the 2 channels of mixed light along the opposite direction of the original channel Optical feedback is formed in the doped fiber, so that the oscillations of the two doped fibers are mutually restrained to achieve phase interlocking.

The number of fiber couplers, doped fibers, pump light sources, lenses and mirrors needs to be changed only for the bundle of multi-channel fiber lasers, and the number of volume gratings also needs to be consistent with the number of laser beams that need to be bundled.

Example 2

For example, to realize 4 laser beams, only need to use 1×4 fiber coupler, 4 doped fibers with basically the same length, and 4 pump sources with corresponding wavelengths (if the erbium-ytterbium co-doped fiber, the wavelength of the pump source should be at Near 980nm), 4 lenses, 4 dichroic mirrors and 4 reflectors, at the same time, 4 individual gratings should be recorded in the optical medium in advance, and the angle between the grating vectors is determined by the Bragg condition, so that 4 fiber lasers can be realized coherent bundles.

Claims (2)

1. multi-channel optical fibre laser coherence beam combination device based on overlapping body grating, it is characterized in that a fiber grating (1) connects a fiber coupler (2), the opposite side of its fiber coupler (2) connects two doping double-cladding optical fibers (3) respectively at least, one side of every doping double-cladding optical fiber (3) all is equipped with lens (4), one side of each lens (4) has dichroic mirror (5), be equipped with Polarization Controller (6) between dichroic mirror (5) and the speculum (7), speculum (7) one sides have overlapping body grating (8), and overlapping body grating (8) one sides have output coupling mirror (9).

2. the coherent beam combination method of the described multi-channel optical fibre laser coherence beam combination device based on overlapping body grating of a claim 1 is characterized in that comprising:

A, when a fiber grating constitutes one side of a plurality of fiber laser resonant cavitys, when the operation wavelength of each Wavelength of Laser and fiber grating was complementary, each fiber laser worked in same wavelength;

B, fiber grating and output coupling mirror constitute optical resonator;

C, fiber grating and output coupling mirror constitute the common resonant chamber of multi-channel optical fibre laser, output coupling mirror feeds back to the part energy of beam combination power in each fiber laser, the optics vibration of each fiber laser checks and balance the phase place interlocking of each optical-fiber laser;

D, an overlapping body grating are beam combination devices, still beam splitter simultaneously, the incident optical laser that it both can satisfy multichannel the Bragg condition by the Bragg angle along same direction diffraction; Simultaneously, the beam diffraction that also output coupling mirror can be reflected becomes the multichannel beamlet;

E, an overlapping body grating two-way multiplexing both can have been realized the beam combination to multi-channel optical fibre laser, and also the laser diffraction that output coupling mirror is reflected becomes multi beam to feed back to the phase place interlocking that each fiber laser is realized each fiber laser output beam;

The laser of stimulated emission is coupled into fiber grating by fiber coupler in f, the doping double-cladding optical fiber;

G, an overlapping body grating are to write down the certain thickness a plurality of grating that has that obtains by holographic method in the same area of optical medium, and the number of its grating equates with the number that needs the beam combination optical-fiber laser;

H, one are as light beam k ₁And k _iI=1 wherein, 2 ..., N is respectively with body grating K _G1And K _GiThe Bragg angle α that determines ₁And α _iIncident, their diffraction light is along same direction outgoing, the grating vector K of body grating _G1And K _GiBetween an included angle is arranged _i, this angle is by Bragg condition cos (φ _i-β)=K _Gi/ 2k decision, wherein β is the angle of diffraction light and z axle positive direction, i.e. Bragg angle, K _Gi=2 π/d _i, d _iBe the grating constant of i grating, k=2 π n/ λ is the transmission of light beam in optical medium, and λ is the incident light wavelength, and n is the mean refractive index of optical medium.