CN103825190B - The method and device of high-energy basic mode laser is exported based on stimulated Brillouin scattering technology in large core fiber - Google Patents

Abstract

A method and device for outputting high-energy fundamental-mode laser in a large-core-diameter optical fiber based on stimulated Brillouin scattering technology, which belongs to the field of optics. The present invention solves the problem of pump utilization in the output of high-energy single-mode laser in a large-core-diameter optical fiber. Not a high question. The method of the invention is as follows: the space laser beam is split into pumping light and seed light; the pumping light is coupled into a fiber circulator and injected into a large-core-diameter optical fiber; the seed light is coupled into a single-mode optical fiber to perform phase modulation on the seed light , resulting in a Stokes frequency shift to form the modulated seed light; the center of the single-mode fiber and the large-core fiber are aligned and fused together, and the modulated seed light enters the large-core fiber from the single-mode fiber and is combined with the pump light In the large-core fiber, the stimulated Brillouin scattering amplification method is used to transfer the high energy of the pump light into the seed light in the form of the fundamental mode, and the high-energy fundamental mode laser is obtained after the stimulated Brillouin scattering Output from fiber optic circulator.

Description

Output of high energy fundamental mode excitation in large core diameter fiber based on stimulated Brillouin scattering technology Light method and device

technical field

The invention relates to a high-energy fundamental-mode laser output method, which belongs to the field of optics.

Background technique

Fiber lasers have many advantages that are incomparable to other lasers, such as: high output power, high pump conversion efficiency, broadband gain, good transverse mode stability and easy heat dissipation, etc., which can be described as hot in today's research. However, due to the extremely small aperture of the fiber, the damage threshold of the conventional fiber is very low, and nonlinear effects are prone to occur, which greatly limits the output power of the fiber. These problems can be effectively overcome by increasing the core diameter of the fiber, but increasing the core diameter of the fiber will make the output beam multi-mode and greatly reduce the beam quality.

In the past two decades, in order to obtain single-mode output light in large-core-diameter optical fibers, many schemes have been proposed, but each has its own defects. For example, at the end of last century, double-clad fiber has been widely researched and applied because it can increase the output energy and maintain a single fundamental mode output light. However, the signal light in double-clad fiber can only be transmitted in a small core, which has been It cannot meet the high power requirements of today's fiber lasers. There is a way to filter out the high-order modes in the large-core fiber by bending the fiber, so as to obtain a better output beam, but this method will bring a lot of optical loss, which is not only extremely inefficient, but also violates the high efficiency of fiber lasers. The main purpose of high power and energy is difficult to apply. There is also a way to selectively excite the desired transmission mode in a large-core fiber by using a long-period fiber grating, and at the same time, the transmitted light can be reduced to the fundamental mode light through the grating or holographic plate. Although this method effectively utilizes the field area of the large-core-diameter fiber, it has not yet provided amplification technology, and it is difficult to meet the demand for high-energy fiber lasers in the near future. The large mode area fiber (LMA) can output single-mode laser in a larger core diameter fiber, and it has also received extensive attention in recent years, but at present, this method can only be used for fibers with a core diameter of tens of microns. , the output energy is still limited to a certain extent. In addition, the University of Southampton accurately excited the fundamental mode light in a large-core-diameter optical fiber of the order of 100 microns by splicing the taper method, which is very eye-catching. However, no amplification mechanism is provided in their scheme, and the output beam energy is still only at the level of ordinary single-mode fiber.

Generally speaking, the previous methods for single-mode laser output in large-core fibers generally only increase the core diameter of the fiber to the order of tens of microns, the laser energy that can be tolerated is still very limited, and the pump utilization rate is not high. Not very high, generally no more than 80%.

Contents of the invention

The purpose of the present invention is to solve the problem of low pump utilization rate in outputting high-energy single fundamental mode laser in a large-core-diameter fiber, and provides a method based on stimulated Brillouin scattering technology to output high-energy fundamental-mode laser in a large-core-diameter fiber. Method and device for modulo laser.

The method for outputting high-energy fundamental-mode laser in a large-core-diameter optical fiber based on stimulated Brillouin scattering technology in the present invention, the method is:

The space laser is split into pump light and seed light;

The pump light is coupled and injected into the fiber circulator, and injected into the large core diameter fiber through the fiber circulator;

The seed light is coupled and injected into the single-mode fiber, and then the injected seed light is phase-modulated to generate a Stokes frequency shift to form the modulated seed light;

The single-mode fiber and the large-core fiber are centered and connected together by fusion splicing, or processed by tapering after fusion;

After modulation, the seed light enters the large-core fiber from the single-mode fiber and meets the pump light. In the large-core fiber, the high energy of the pump light is transferred into the fundamental mode by the method of stimulated Brillouin scattering amplification. In the seed light of the form, the beam after the stimulated Brillouin scattering is output by the fiber circulator, and the high-energy fundamental mode laser is obtained.

The device for realizing the method for outputting high-energy fundamental-mode laser in a large-core-diameter fiber based on stimulated Brillouin scattering technology includes a light source, a beam splitter, a first coupler, a second coupler, and a first large-core-diameter fiber , a first single-mode fiber, a fiber circulator, a second large core diameter fiber, a second single-mode fiber, a phase modulator and a mirror;

The spatial beam output by the light source is incident on the beam splitter, and the transmitted beam and reflected beam are formed by the beam splitter;

The transmitted light beam is coupled to the first large-core fiber by the first coupler to form pump light, the pump light output by the first large-core fiber is injected into the A port of the fiber circulator, and the pump light is sent from the B port of the fiber circulator port output and incident into the second largest core diameter fiber;

The reflected light beam is incident on the mirror, and the light beam reflected and output by the mirror is coupled to the first single-mode optical fiber through the second coupler to form seed light, and the seed light is output after being modulated by the phase modulator, and enters the second single-mode optical fiber. Optical fiber, the modulated seed light is injected into the second largest core diameter optical fiber;

The modulated seed light meets the pump light, is amplified by Brillouin scattering, and then injected into port B of the fiber optic circulator, and output from port C of the fiber optic circulator.

Advantages of the present invention: the present invention provides a method that can obtain fundamental mode output laser in optical fibers with a core diameter of hundreds of microns, and has a stable output structure, simple structure, high conversion efficiency, and theoretically, the pump utilization rate can reach 99%. It has a breakthrough significance for the high power of fiber laser. The method of the invention not only makes the output laser energy of the large-core-diameter optical fiber high, but also has stable excitation and output beams and high repeatability, and the output beams are guaranteed to be fundamental mode beams.

Description of drawings

Fig. 1 is a schematic diagram of the optical path structure of a high-energy fundamental-mode laser device output in a large-core-diameter fiber based on the stimulated Brillouin scattering technology of the present invention;

Figure 2 is a diagram of the connection between a large-core fiber and a single-mode fiber;

Fig. 3 is the light spot pattern of output high-energy fundamental mode laser;

Fig. 4 is the waveform diagram of the incident space light beam;

Fig. 5 is a waveform diagram of outputting high-energy fundamental mode laser light.

detailed description

Specific Embodiment 1: The present embodiment will be described below in conjunction with FIG. 1. The method for outputting high-energy fundamental-mode laser in a large-core-diameter fiber based on the stimulated Brillouin scattering technique described in this embodiment uses The high-energy pump light with frequency difference and reverse transmission performs stimulated Brillouin scattering amplification on the fundamental mode seed light; the method of exciting the fundamental mode seed light in the large-core fiber is as follows: the large-core fiber and the single-mode fiber Make a heart-to-heart connection; the specific method is:

The space laser is split into pump light and seed light;

The pump light is coupled and injected into the fiber circulator, and injected into the large core diameter fiber through the fiber circulator;

The seed light is coupled and injected into the single-mode fiber, and then the injected seed light is phase-modulated to generate a Stokes frequency shift to form the modulated seed light;

The single-mode fiber and the large-core fiber are centered and connected together by fusion splicing, or processed by tapering after fusion;

After modulation, the seed light enters the large-core fiber from the single-mode fiber and meets the pump light. In the large-core fiber, the high energy of the pump light is transferred into the fundamental mode by the method of stimulated Brillouin scattering amplification. In the seed light of the form, the beam after the stimulated Brillouin scattering is output by the fiber circulator, and the high-energy fundamental mode laser is obtained.

The large-core optical fiber is a graded-index fiber, for example, a graded-square-rate fiber can be used.

Specific embodiment 2: The present embodiment will be described below in conjunction with FIG. 2 . This embodiment will further explain Embodiment 1. The center of the single-mode optical fiber and the large-core-diameter optical fiber are aligned and connected together by fusion splicing; or after fusion splicing, tapered method for processing;

The large-core fiber is a multimode fiber, and the core diameter of the large-core fiber is greater than or equal to 100 μm. When the diameter of the cladding is the same as that of the single-mode fiber, it is butted by center fusion splicing, and the melting point 12 is formed at the joint; as shown in Figure 2, the diameter of the cladding of the two is the same, but the diameter of the core of the two is different.

A specific example is given: both cladding diameters are 125 μm, the core diameter of the large-core fiber is 105 μm, and the core diameter of the single-mode fiber is 8.3 μm. The single-mode fiber is centered with the large-core fiber and fused into one fiber.

If the cladding diameter of the multimode fiber is larger than that of the single-mode fiber, the two fibers are connected by fusion splicing and tapering.

Specific Embodiment Three: The present embodiment will be described below in conjunction with FIGS. 1 to 5. The device for implementing the method for outputting high-energy fundamental-mode laser in a large-core-diameter optical fiber based on the stimulated Brillouin scattering technology described in Embodiment 1 includes: Light source 1, beam splitter 2, first coupler 3, second coupler 4, first large-core fiber 5, first single-mode fiber 6, fiber circulator 7, second large-core fiber 8, second Single-mode optical fiber 9, phase modulator 10 and mirror 11;

The spatial beam output by the light source 1 is incident on the beam splitter 2, and the transmitted beam and the reflected beam are formed by the beam splitter 2;

The transmitted light beam is coupled to the first large-core fiber 5 by the first coupler 3 to form pumping light, and the pumping light output by the first large-core fiber 5 is injected into the A port of the optical fiber circulator 7, and the pumping light is transmitted from the optical fiber The B port output of the circulator 7 is incident into the second large core diameter optical fiber 8;

The reflected light beam is incident on the mirror 11, and the light beam reflected and output by the mirror 11 is coupled to the first single-mode fiber 6 through the second coupler 4 to form a seed light, and the seed light is output after being modulated by the phase modulator 10, and Entering the second single-mode fiber 9, the modulated seed light is injected into the second large core diameter fiber 8;

The modulated seed light and the pump light undergo Brillouin scattering and are injected into port B of the optical fiber circulator 7 and output from port C of the optical fiber circulator 7 .

The light source 1 is a space laser. Due to the limited energy that fiber lasers can achieve at present, space lasers can provide greater pumping energy, so space lasers are used as light sources. It is divided into two beams: the pump light and the seed light, and the ratio of the two is determined by the beam splitting ratio of the beam splitter 2.

The lengths of the first large-core-diameter optical fiber 5 and the first single-mode optical fiber 6 do not need to be too long, and only need to complete the coupling beam transmission. The second large core-diameter fiber 8 needs to be long enough to ensure that the seed light and the pump light can perform sufficient "stimulated Brillouin scattering amplification". At the same time, the optical paths of the two should be controlled so that the pump light meets the seed light as soon as possible after entering the large core diameter fiber, so as to prevent the pump light from being "produced by stimulated Brillouin scattering" and unable to transfer all the energy to the seed light. The scattered light beam enters from port B of the fiber optic circulator 7 and exits from port C. If the high-energy beam output from port C needs to be used as a space laser, it can be converted into a parallel beam by using a lens. If it is used as fiber optic light, it can be used directly.

The amplified single fundamental mode light can still maintain a good single fundamental mode state, and the output beam is shown in Figure 3. At the same time, the amplified laser maintains almost the same waveform as the seed light, as shown in Figure 4 and Figure 5 .

In the mechanism of stimulated Brillouin scattering, the greater the pump energy, the higher the conversion efficiency. Some people predict that when the pump energy reaches a certain level, the conversion efficiency can reach 99%. Therefore, under this scheme, the greater the energy demand, the higher the pump utilization rate. Generally speaking, in existing optical fiber amplifiers, the pump utilization rate is difficult to exceed 80%. In our existing experiments, the pump utilization rate has exceeded 90% only under the energy that a 100-micron fiber can bear. The output energy and pump utilization are improved to a great extent.

As shown in Figure 2, after the centers of the two are aligned, they are connected together by fusion splicing. The excitation principle has nothing to do with the size of the core diameter. In theory, fibers with a large core diameter can be used. We can at least expand to a core diameter fiber of several hundred microns, or even a few millimeters core diameter fiber, to withstand the powerful pump light energy. Therefore, the output beam energy and peak power we can get are very high. We expect that at least tens of millijoules of energy can be obtained under nanosecond pulses, and at least tens of megawatts of peak power can be obtained under picosecond pulses. In addition, the welding method we use, once the welding point is completed, the output beam will maintain the same state every time in the future. The output is stable and the operation is simple, which has great application value and prospect.

Claims (5)

1. A method for outputting a high-energy fundamental mode laser in a large core diameter fiber based on stimulated Brillouin scattering technology, characterized in that the method is: The space laser is split into pump light and seed light; The pump light is coupled and injected into the fiber circulator, and injected into the large core diameter fiber through the fiber circulator; The seed light is coupled and injected into the single-mode fiber, and then the injected seed light is phase-modulated to generate a Stokes frequency shift to form the modulated seed light; The single-mode fiber and the large-core fiber are centered and connected together by fusion splicing, or processed by tapering after fusion; After modulation, the seed light enters the large-core fiber from the single-mode fiber and meets the pump light. In the large-core fiber, the stimulated Brillouin scattering amplification method is used to transfer the high energy of the pump light into the fundamental mode. In the seed light, the beam after the stimulated Brillouin scattering is output by the fiber circulator, and the high-energy fundamental mode laser is obtained. 2. The method for outputting high-energy fundamental-mode laser in a large-core fiber based on stimulated Brillouin scattering technology according to claim 1, wherein the core diameter of the large-core fiber is greater than or equal to 100 μm. 3. The method for outputting high-energy fundamental-mode laser light in a large-core fiber based on stimulated Brillouin scattering technology according to claim 1, wherein the large-core fiber is a graded-index fiber. 4. realize the device of claim 1 based on the method for outputting high-energy fundamental mode laser in a large-core-diameter fiber based on stimulated Brillouin scattering technology, characterized in that it includes a light source (1), a beam splitter (2) , the first coupler (3), the second coupler (4), the first large-core fiber (5), the first single-mode fiber (6), the fiber circulator (7), the second large-core fiber ( 8), a second single-mode optical fiber (9), a phase modulator (10) and a mirror (11); The spatial beam output by the light source (1) is incident on the beam splitter (2), and the transmitted beam and the reflected beam are formed by the beam splitter (2); The transmitted light beam is coupled to the first large-core fiber (5) by the first coupler (3) to form pump light, and the pump light output by the first large-core fiber (5) is injected into the fiber circulator (7) A port, the pump light is output from the B port of the optical fiber circulator (7) and incident into the second largest core diameter optical fiber (8); The reflected light beam is incident on the mirror (11), and the light beam reflected by the mirror (11) is coupled to the first single-mode optical fiber (6) through the second coupler (4) to form a seed light, and the seed light is phased The modulator (10) outputs after modulation, and enters the second single-mode fiber (9), and the modulated seed light is injected into the second large-core-diameter fiber (8); The modulated seed light meets the pump light, is amplified by Brillouin scattering, and then injected into port B of the fiber optic circulator (7), and output from port C of the fiber optic circulator (7). 5. The device for outputting high-energy fundamental-mode laser in a large-core-diameter fiber based on stimulated Brillouin scattering technology according to claim 4, characterized in that the light source (1) is a space laser.