A wavelength-tunable single-frequency fiber amplifier with seed light spatial coupling

Abstract

The present invention relates to a wavelength-tunable single-frequency fiber amplifier with seed light spatial coupling, belonging to the field of optics, and mainly solves the problem of narrow wavelength tuning bandwidth of high-power single-frequency lasers. The seed source uses a temperature-tunable Yb:YAG non-planar ring oscillator; in order to prevent the seed source device from being damaged by the backward spontaneous emission of the gain fiber, an optical isolator is added between the seed source and the fiber amplification system; in order to improve the coupling efficiency of the seed light to the fiber amplification system, the seed light coupling injection system uses a combination of a convex lens and an aspherical lens to inject the seed light into the signal input fiber of the pump combiner; in order to improve the pump coupling efficiency of the fiber amplification system and obtain high-power output, the gain fiber uses double-clad ytterbium-doped fiber. The laser implemented by the present invention can stably output continuous single-frequency laser of 1031 nm with a power of more than 10 W, the laser linewidth ≤ 20 kHz, the wavelength tuning bandwidth is 0.4 nm; the seed light coupling efficiency ≥ 60%, and the amplification gain of the fiber amplification system is 21 dB.

Description

Technical Field

[0001] The present invention belongs to the field of optics and laser design technology, and relates to a wavelength tunable single-frequency fiber amplifier with seed light spatial coupling. Background Art

[0002] With the continuous improvement of the combat capability requirements of the new generation of fighter jets, laser rangefinders and speedometers are also developing towards longer detection distances and higher speed measurement requirements. Therefore, higher requirements are also imposed on laser rangefinders and speedometers. The sensitivity of coherent detection can approach the quantum noise limit of the detector under certain conditions, enabling ultra-long-distance detection. It is expected to increase the laser detection distance of laser rangefinders and speedometers to the order of 100 kilometers, while achieving high-precision speed measurement.

[0003] The single-frequency laser is the core device of the coherent detection system. Solid-state lasers can obtain wavelength-tunable single-frequency lasers with narrow linewidths and large bandwidths, while fiber amplifiers have advantages in maintaining the single-frequency performance of the seed source. The present invention provides a design method for obtaining high-power, narrow-linewidth, and large-bandwidth wavelength-tunable lasers. Summary of the Invention

[0004] Technical Problems to be Solved

[0005] In order to avoid the deficiencies of the prior art, the present invention proposes a wavelength tunable single-frequency fiber amplifier with seed light spatial coupling.

[0006] Technical Solution

[0007] A wavelength tunable single-frequency fiber amplifier with seed light spatial coupling, characterized in that it includes a seed source, an optical isolator 8, a seed light coupling injection system, and a fiber amplification system in sequence along the optical path; the above-mentioned seed source includes a first semiconductor laser 1, a first convex lens 2, a second convex lens 3, a non-planar circulator 4, a permanent magnet 5, and a dichroic mirror 7; the laser of the first semiconductor laser 1 passes through the first convex lens 2 and the second convex lens 3 and is incident on the non-planar circulator 4 at 45°, and after reflection, it passes through the dichroic mirror 7 and then is injected into the optical isolator 8, wherein a permanent magnet 5 is provided on the non-planar circulator 4; the laser passing through the optical isolator 8 is injected into the fiber amplification system after passing through the seed light coupling injection system composed of a third convex lens 9 and an aspherical lens 10; the fiber amplification system includes two identical semiconductor lasers, a pump combinator 11, a double-clad ytterbium-doped fiber 14, and a dichroic mirror 15; the laser of the seed light coupling injection system is injected into the signal input fiber of the pump combinator 11, and the two semiconductor lasers are respectively connected to the pump input fibers of the pump combinator 11. The output fiber of the pump combinator 11 is connected to the double-clad ytterbium-doped fiber 14, and the output laser of the double-clad ytterbium-doped fiber 14 is incident on the dichroic mirror 15 at 45°, and after transmission through the dichroic mirror 15, a single-frequency laser with amplified power is obtained.

[0008] A temperature control device 6 is provided on the non-planar circulator 4.

[0009] When the seed source and the 1031nm single-frequency laser with output power amplified by the optical isolator 8, the seed light coupling injection system and the fiber amplifier system are arranged in sequence along the optical path, the parameter combinations of each device are: 945nm semiconductor laser 1, convex lens 2 with a focal length of 150mm, convex lens 3 with a focal length of 100mm, Yb:YAG non-planar circulator 4, 945 / 1031nm dichroic mirror 7, 1031nm optical isolator 8, convex lens 9 with a focal length of 50mm, aspherical lens 10 with a focal length of 6mm, pump combiner 11, 976nm semiconductor laser 12, 976nm semiconductor laser 13, double-clad ytterbium-doped fiber 14 and 976 / 1031nm dichroic mirror 15.

[0010] The laser linewidth of the 1031nm single-frequency laser is ≤20kHz, and the wavelength tuning bandwidth is 0.4nm.

[0011] The seed light coupling efficiency is ≥60%.

[0012] The amplification gain of the fiber amplifier system is 21dB.

[0013] Beneficial effects

[0014] A wavelength tunable single-frequency fiber amplifier with seed light spatial coupling proposed by the present invention mainly solves the problem of narrow wavelength tuning bandwidth of high-power single-frequency lasers. In order to obtain a tunable single-frequency seed light with narrow linewidth and large bandwidth, a temperature-tuned Yb:YAG non-planar circulator is used as the seed source; in order to prevent the seed source device from being damaged by the backward spontaneous emission of the gain fiber, an optical isolator is added between the seed source and the fiber amplifier system; in order to improve the coupling efficiency of the seed light to the fiber amplifier system, the seed light coupling injection system uses a combination of a convex lens and an aspherical lens to inject the seed light into the signal input fiber of the pump combiner; in order to improve the pump coupling efficiency of the fiber amplifier system and obtain high-power output, a double-clad ytterbium-doped fiber is used as the gain fiber.

[0015] The present invention provides a design method for fiber amplification using a solid single-frequency laser. Among them, in order to obtain a tunable single-frequency seed light with a narrow linewidth and a large bandwidth, the seed source uses a Yb:YAG non-planar ring oscillator pumped by a semiconductor laser with a central wavelength of 945 nm and temperature tuning; in order to prevent the seed source device from being damaged by the reverse spontaneous emission of the gain fiber, an optical isolator is added between the seed source and the fiber amplification system; in order to improve the coupling efficiency of the seed light to the amplification system, the seed light coupling injection system uses a combination of a convex lens and an aspherical lens. Among them, the aspherical lens has a higher numerical aperture and stronger light-gathering ability than an ordinary lens, which is the key to improving the coupling efficiency; in order to improve the pump coupling efficiency, the gain fiber uses a double-clad ytterbium-doped fiber, which can couple the pump light into the inner cladding with a much larger mode field diameter than the core, thereby greatly improving the pump coupling efficiency of the fiber.

[0016] The laser implemented by the present invention can stably output continuous single-frequency laser of 1031 nm above 10 W, the laser linewidth ≤ 20 kHz, and the wavelength tuning bandwidth is 0.4 nm; the seed light coupling efficiency ≥ 60%, and the amplification gain of the fiber amplification system is 21 dB. Brief Description of the Drawings

[0017] Figure 1 It is a schematic optical path diagram of a wavelength-tunable single-frequency fiber amplifier with spatial coupling of seed light involved in the present invention. 1, 2, 3, 4, 5, 6, 7 constitute the seed source; 9, 10 constitute the seed light coupling injection system; 11, 12, 13, 14, 15 constitute the fiber amplification system.

[0018] In the figure: 1 - 945 nm semiconductor laser; 2 - convex lens with a focal length of 150 mm, 3 - convex lens with a focal length of 100 mm; 4 - Yb:YAG non-planar ring oscillator; 5 - permanent magnet; 6 - temperature control device; 7 - 945 / 1031 nm dichroic mirror; 8 - 1031 nm optical isolator; 9 - convex lens with a focal length of 50 mm; 10 - aspherical lens with a focal length of 6 mm; 11 - pump combiner; 12, 13 - 976 nm semiconductor lasers; 14 - double-clad ytterbium-doped fiber; 15 - 976 / 1031 nm dichroic mirror. Detailed Embodiments

[0019] Now, the present invention will be further described in combination with the embodiments and the drawings:

[0020] The scheme of the wavelength-tunable single-frequency fiber amplifier with spatial coupling of seed light is as follows:

[0021] The single-frequency fiber amplifier is composed of a seed source, an optical isolator, a seed light coupling injection system, and a fiber amplification system.

[0022] The seed light is obtained by pumping a Yb:YAG non-planar ring oscillator with a 945 nm semiconductor laser. The pump light is injected onto the input / output coupling surface of the Yb:YAG non-planar ring oscillator using a 1.5:1 coupling lens group. The output laser is filtered by a 945 / 1031 nm dichroic mirror. The temperature of the Yb:YAG non-planar ring oscillator is precisely controlled by a temperature control device to achieve tunable single-frequency 1031 nm laser output.

[0023] An optical isolator is used to prevent the reverse spontaneous emission of the gain fiber from damaging the seed source device.

[0024] The fiber amplifier system consists of a pump combiner, a 976 nm semiconductor laser, a double-clad ytterbium-doped fiber, and a 976 / 1031 nm dichroic mirror.

[0025] The seed light coupling injection system consists of a convex lens and an aspheric lens, which efficiently injects the seed light into the signal input fiber of the pump combiner.

[0026] The output fiber of the 976 nm semiconductor laser is coupled to the pump input fiber of the pump combiner by fusion splicing, and the output fiber of the pump combiner is coupled to the ytterbium-doped fiber by fusion splicing.

[0027] The 1031 nm single-frequency amplified laser is filtered out using a 976 / 1031 nm dichroic mirror.

[0028] The installation implementation steps are as follows:

[0029] The implementation steps of the seed source system are as follows:

[0030] (1) Install the Yb:YAG non-planar ring oscillator 4 and the temperature control device 6, and power on the temperature control device 6 to achieve temperature control and adjustment of the non-planar ring oscillator 4.

[0031] (2) Install and adjust the orientation of the 945 nm semiconductor laser 1, and install a convex lens 2 with a focal length of 150 mm and a convex lens 3 with a focal length of 100 mm to collimate and focus the 945 nm pump light output by the 945 nm semiconductor laser 1, so that the pump light is incident on the input / output coupling surface of the Yb:YAG non-planar ring oscillator 4 at an incident angle of 45°.

[0032] (3) Install a permanent magnet 5 at the Nd:YAG non-planar ring oscillator, power on the 945 nm semiconductor laser 1, and 1031 nm single-frequency laser can be output; install the 945 / 1031 nm dichroic mirror 7 and adjust its orientation so that the output laser is incident on the 945 / 1031 nm dichroic mirror 7 at 45°, and 1031 nm single-frequency laser (i.e., seed light) is obtained.

[0033] 2. Install the 1031 nm optical isolator 8 and adjust its orientation so that the seed light passes perpendicularly through the 1031 nm optical isolator 8.

[0034] 3. Install the convex lens 9 with a focal length of 50 mm and the aspherical lens 10 with a focal length of 6 mm to collimate and focus the seed light laser.

[0035] 4. Install the pump combiner 11, adjust the position and orientation of the signal input fiber of the pump combiner 11, and inject the seed light into the signal input fiber of the pump combiner 11.

[0036] 5. Fuse the output fibers of the 976 nm semiconductor lasers 12 and 13 to the pump input fibers of the pump combiner 11, and fuse the output fiber of the pump combiner 11 to the double-clad ytterbium-doped fiber 14. Combining with step 4, realize the simultaneous coupling of the signal light and the pump light into the double-clad ytterbium-doped fiber 14.

[0037] 6. Install the 976 / 1031 nm dichroic mirror 15 and adjust its orientation so that the laser output from the fiber amplification system is incident on the 976 / 1031 nm dichroic mirror 15 at an angle of 45°, and finally obtain the power-amplified 1031 nm single-frequency laser.

Claims

1. A wavelength tunable single-frequency fiber amplifier with seed light spatial coupling, characterized in that it includes a seed source, a 1031 nm optical isolator (8), a seed light coupling injection system, and a fiber amplification system in sequence along the optical path; the above-mentioned seed source includes a 945 nm semiconductor laser (1), a convex lens (2) with a focal length of 150 mm, a convex lens (3) with a focal length of 100 mm, a Yb:YAG non-planar ring resonator (4), a permanent magnet (5), and a 945 / 1031 nm dichroic mirror (7); the laser of the 945 nm semiconductor laser (1) passes through the convex lens (2) with a focal length of 150 mm and the convex lens (3) with a focal length of 100 mm, and is incident on the Yb:YAG non-planar ring resonator (4) at 45°, and after reflection, it is injected into the 1031 nm optical isolator (8) through the dichroic mirror (7), and a permanent magnet (5) is provided on the Yb:YAG non-planar ring resonator (4); the laser passing through the 1031 nm optical isolator (8) is injected into the fiber amplification system through a seed light coupling injection system composed of a convex lens (9) with a focal length of 50 mm and an aspherical lens (10) with a focal length of 6 mm; the fiber amplification system includes two identical semiconductor lasers, a pump combiner (11), a double-clad ytterbium-doped fiber (14), and a 976 / 1031 nm dichroic mirror (15); the laser of the seed light coupling injection system is injected into the signal input fiber of the pump combiner (11), and the two semiconductor lasers are respectively connected to the pump input fibers of the pump combiner (11), the output fiber of the pump combiner (11) is connected to the double-clad ytterbium-doped fiber (14), and the output laser of the double-clad ytterbium-doped fiber (14) is incident on the dichroic mirror (15) at 45°, and after transmission by the dichroic mirror (15), a single-frequency laser with amplified power is obtained; a temperature control device (6) is provided on the Yb:YAG non-planar ring resonator (4); when the seed source, the 1031 nm optical isolator (8), the seed light coupling injection system, and the fiber amplification system output a 1031 nm single-frequency laser with amplified power along the optical path in sequence, the parameter combinations of each device are: 945 nm semiconductor laser (1), convex lens (2) with a focal length of 150 mm, convex lens (3) with a focal length of 100 mm, Yb:YAG non-planar ring resonator (4), 945 / 1031 nm dichroic mirror (7), 1031 nm optical isolator (8), convex lens (9) with a focal length of 50 mm, aspherical lens (10) with a focal length of 6 mm, pump combiner (11), first 976 nm semiconductor laser (12), second 976 nm semiconductor laser (13), double-clad ytterbium-doped fiber (14), and 976 / 1031 nm dichroic mirror (15).

2. The wavelength tunable single-frequency fiber amplifier with seed light spatial coupling according to claim 1, characterized in that: the laser linewidth of the 1031 nm single-frequency laser ≤ 20 kHz, and the wavelength tuning bandwidth is 0.4 nm.

3. The wavelength tunable single-frequency fiber amplifier with seed light spatial coupling according to claim 1, characterized in that: the seed light coupling efficiency ≥ 60%.

4. The wavelength-tunable single-frequency fiber amplifier for seed light spatial coupling according to claim 1, characterized in that: the amplification gain of the fiber amplification system is 21 dB.

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