阅读说明：本技术 一种基于带内泵浦的高效率单频掺铥光纤激光器 (High-efficiency single-frequency thulium-doped fiber laser based on in-band pumping ) 是由 史伟 史朝督 �田�浩 邓勋 盛泉 姚建铨 于 2021-08-05 设计创作，主要内容包括：本发明公开了一种基于带内泵浦的高效率单频掺铥光纤激光器。采用波长为1650nm的激光作为泵浦掺铥光纤激光器,该泵浦波长对应于掺铥光纤带内泵浦吸收谱的峰值附近,不仅有着较高吸收截面,并且还有较小的量子亏损,可以极大提高激光器的效率,改善激光器的噪声和线宽特性。本发明通过受激拉曼散射的方式可以获取高效率和高功率的1650nm激光输出,为获取高功率的单频光纤激光器奠定了基础。(The invention discloses a high-efficiency single-frequency thulium-doped fiber laser based on an in-band pump. Adopt the wavelength to be 1650 nm's laser as the pumping thulium-doped fiber laser, this pumping wavelength is near corresponding to the peak value of the thulium-doped fiber in-band pumping absorption spectrum, not only has higher absorption cross section to there is less quantum loss in addition, can greatly improve the efficiency of laser, improves the noise and the linewidth characteristic of laser. The invention can obtain 1650nm laser output with high efficiency and high power by the mode of stimulated Raman scattering, and lays a foundation for obtaining single-frequency fiber laser with high power.)

1. The utility model provides a thulium fiber laser is mixed to high efficiency single-frequency based on in-band pumping which characterized in that, the laser includes: the device comprises a pumping source, a pumping coupling device, a high-reflectivity fiber grating, a thulium-doped active fiber and an output fiber grating;

the pump source is a 1650nm laser, the wavelength corresponds to the absorption peak value of the pump in the thulium-doped optical fiber ribbon, the absorption efficiency of the thulium-doped optical fiber to pump light is improved, and the efficiency and the output power of the laser are further improved;

the pumping source realizes 1650nm laser emission in a stimulated Raman scattering mode in the form of a Raman fiber oscillator or a Raman fiber amplifier;

1650nm laser of pump source output, through pump coupling device injects into the high reflection of light fiber grating the active optical fiber of thulium of doping in the single-frequency that output fiber grating constitutes mixes the thulium fiber resonator, mix thulium fiber to the very high absorption coefficient of 1650nm pump laser for produce sufficient laser gain in the thulium fiber of doping of shorter length, and then produce laser oscillation, through output fiber grating output target wavelength's single-frequency laser.

2. The high-efficiency single-frequency thulium-doped fiber laser based on in-band pumping according to claim 1, wherein the pumping source is a 1650nm laser, and the pumping mode is in-band pumping, thereby improving the gain in the thulium-doped fiber resonant cavity and reducing the quantum loss.

3. The high-efficiency single-frequency thulium-doped fiber laser device based on in-band pumping according to claim 1, characterized in that 1650nm laser is used as the pumping source, which shortens the length of the active fiber, further shortens the effective cavity length of the resonant cavity, and improves the power range of single longitudinal mode stable operation.

4. The high-efficiency single-frequency thulium-doped fiber laser device according to claim 1, wherein the pump coupling device is a wavelength division multiplexer or a signal pump combiner, and adopts a direct fusion coupling mode, and selects a corresponding coupling mode and device according to the form and transverse mode of the pump source, so as to realize a full-fiber system structure.

5. The high-efficiency single-frequency thulium-doped fiber laser based on in-band pumping according to claim 1, wherein the thulium-doped active fiber is a quartz fiber, or a germanate, silicate and other host material fiber.

Technical Field

The invention relates to the field of fiber lasers, in particular to a high-efficiency single-frequency thulium-doped fiber laser based on in-band pumping, and particularly relates to a novel pumping mode of the thulium-doped fiber laser.

Background

The thulium-doped fiber laser is an effective technical means for obtaining 2 μm fiber laser, and in recent years, research on the thulium-doped fiber laser is deepened gradually, and the currently mainstream fiber resonant cavity structure is a Distributed Bragg Reflector (DBR) short cavity type structure, so that high-efficiency laser output is difficult to obtain due to the short active fiber length (<2 cm). In the last 10 years, the mainstream approach has been to use highly doped rare earth doped soft glass fiber as the gain medium in the resonator to improve the output efficiency of the laser. The thulium-doped fiber laser based on germanate and silicate glass matrix is reported successively, the efficiency of the thulium-doped fiber laser is remarkably improved compared with that of the thulium-doped fiber laser adopting a common quartz fiber, but the concentration clustering phenomenon exists, so that the doping concentration of the active fiber has an upper limit, and further improvement of the laser skew efficiency needs to consider the optimization of the pumping wavelength.

Common pump wavelengths of the thulium-doped fiber laser are three, 793nm, 1210nm and 1570 nm. The three wavelengths correspond to three absorption bands, respectively. 793nm corresponds to³H₆→³H₄The absorption band of energy level transition is the pumping wavelength of the most mainstream thulium-doped fiber laser at present, the pumping mode is of a three-energy-level structure, the quantum efficiency of the pumping mode can reach 200% theoretically due to the existence of a cross relaxation phenomenon, the efficiency of laser can be greatly improved, but the influence of concentration cluster extinction effect is serious when 793nm laser pumping is adopted, the ideal 200% quantum efficiency is difficult to achieve, and no high-power 793nm single-mode laser diode can be used as a laser pumping source at present, so that the pumping mode is greatly limited in practical application; 1210nm corresponds to³H₆→³H₅Although the peak value of the absorption band of the energy level transition has an absorption cross section almost the same as that of 793nm, the laser efficiency is difficult to be greatly improved due to the fact that a cross relaxation process is lacked, so that large quantum loss exists in the pumping process; 1570nm corresponds to³H₆→³F₄The pumping mode is a two-level structure, belongs to in-band pumping, has low efficiency in reported work, and is mainly limited by the 1570nm laser of thulium-doped fiber pairLower absorption cross section. In that³H₆→³F₄In a transition stimulated absorption band, an absorption peak is located at about 1650nm, the absorption cross section of the laser is about twice of 1570nm, if the laser with the wavelength pumping thulium-doped fiber laser can greatly improve the skew efficiency of the laser, but the laser with the wavelength is difficult to obtain and is not in the emission bandwidth of Er ions, the reported pump light closest to the wavelength is 1610nm, the absorption cross section of the laser still has a large difference compared with 1650nm, so that the laser with the wavelength is urgently required to be obtained through a special method to provide efficient pumping for the thulium-doped fiber laser, and therefore high-efficiency 2-micrometer laser output is achieved.

Disclosure of Invention

The invention provides a high-efficiency single-frequency thulium-doped fiber laser based on in-band pumping, which adopts pumping wavelength of 1650nm and thulium ions³H₆→³F₄The stimulated absorption peaks of the transition are matched; the thulium-doped optical fiber in the resonant cavity has a higher pumping absorption coefficient to the pumping light with the wavelength, so that the invention not only ensures that the pumping intensity required by operation is met under the condition of a shorter thulium-doped optical fiber, but also can realize high-efficiency output of the thulium-doped optical fiber laser, and the details are described as follows:

a high efficiency single frequency thulium doped fiber laser based on in-band pumping, the laser includes: the device comprises a pumping source, a pumping coupling device, a high-reflectivity fiber grating, a thulium-doped active fiber and an output fiber grating;

the pump source is a 1650nm laser, the wavelength corresponds to the absorption peak value of the pump in the thulium-doped optical fiber ribbon, the absorption efficiency of the thulium-doped optical fiber to pump light is improved, and the output power of the laser is further improved;

the pumping source realizes 1650nm laser emission in a stimulated Raman scattering mode in the form of a Raman fiber oscillator or a Raman fiber amplifier;

1650nm laser of pump source output, through pump coupling device injects into the high reflection of light fiber grating mix the thulium active optical fiber in the single-frequency that output fiber grating constitutes mixes thulium fiber resonator, through the pumping mix thulium fiber and realize the particle number reversal, and then produce laser oscillation, through output fiber grating exports target wavelength single-frequency laser.

Further, 1650nm corresponds to thulium ions³H₆→³F₄The peak of the energy level transition stimulated absorption band is near, and the thulium ion has a higher absorption cross section of about 4.7 x 10 for the laser with the wavelength^-21cm²It is more than twice of the commonly used thulium-doped fiber laser pump wavelength 1570 nm. The gain in the thulium-doped fiber resonant cavity can be greatly improved, and especially for a short-cavity single-frequency thulium-doped fiber laser, the oblique efficiency and the output power of the laser can be greatly improved due to the characteristics.

Furthermore, due to the relatively high absorption cross section of the thulium ion pair 1650nm, enough gain can be achieved in a relatively short optical fiber length (about 1cm), the effective length of the resonant cavity is further shortened, and the power range of the single longitudinal mode stable operation of the laser is improved.

Wherein, the pumping source is preferably a 1650nm Raman fiber laser. The method for obtaining 1650nm laser radiation by adopting the stimulated Raman scattering mode is a high-efficiency method. Firstly, the Raman efficiency is high and can reach more than 85 percent, so that the energy loss is avoided; the system is flexible in configuration, has lower requirements on the type of the optical fiber and the structure of the Raman fiber laser, greatly facilitates the use environment of the system by adopting the optical fiber system, and is suitable for being used as a pumping source of the fiber laser. Furthermore, the pump coupling device is a wavelength division multiplexer or a signal pump beam combiner, a direct fusion coupling method is adopted, and a corresponding coupling mode and device are selected according to the form and the transverse mode of a pump source.

The thulium-doped active optical fiber is a quartz optical fiber or an optical fiber of germanate, silicate and other host materials.

The technical scheme provided by the invention has the beneficial effects that:

1) according to the invention, the preferred output laser wavelength of the pumping source is about 1650nm, which corresponds to the peak value of the pumping absorption band in the thulium ion band, so that extremely high absorption coefficient can be realized, and the tilting efficiency of the thulium-doped laser is greatly improved;

2) because the thulium-doped active optical fiber has a very high absorption coefficient to 1650nm laser, shorter thulium-doped active optical fiber can be adopted, which is beneficial to reducing the length of a resonant cavity, increasing the interval of longitudinal modes and realizing the output of single longitudinal mode laser with higher power;

3) due to smaller quantum loss between the 1650nm pumping wavelength and the target laser wavelength, the generation of thermal deposition and noise can be effectively reduced, the noise characteristic of output laser is improved, and the effect of line width compression is realized;

4) according to the technical scheme, the non-linear effect of stimulated Raman scattering is adopted to achieve the acquisition of 1650nm laser, the Raman process can achieve extremely high oblique efficiency, and the loss in the energy conversion process is reduced;

5) the invention adopts 1650nm Raman laser as pumping source, can be single mode laser output or multi-mode laser output, has flexible configuration, and is suitable for thulium-doped fiber laser with different pumping modes;

6) the method adopts a stimulated Raman scattering mode to obtain high-power 1650nm laser, is relatively convenient to realize, can obtain first-order Raman laser through 1.5 mu m laser, and can also obtain the first-order Raman laser through 1 mu m laser cascade Raman, and the output power of the laser can reach hundreds of watts to thousands of watts;

7) the method of using 1650nm laser as the pumping source of the thulium-doped fiber laser is applicable to thulium-doped fiber lasers and thulium-doped fiber amplifiers with different cavity structures.

Drawings

FIG. 1 is a schematic diagram of a high-efficiency single-frequency thulium-doped fiber laser based on in-band pumping;

FIG. 2 is a schematic diagram of a 1650nm Raman fiber oscillator;

FIG. 3 is a schematic diagram of a 1650nm Raman fiber amplifier;

fig. 4 is a schematic diagram of an increase curve of output power of a high-efficiency single-frequency thulium-doped fiber laser along with pump power based on in-band pumping.

In the drawings, the components represented by the respective reference numerals are listed below:

1: a highly reflective fiber grating; 2: a thulium doped active optical fiber;

3: outputting the fiber bragg grating; 4: a pump coupling device;

5: a pump laser; 6: a Raman pump source;

7: 1650nm high reflective fiber grating; 8: a first Raman fiber;

9: 1650nm output fiber grating; 10: a 1650nm semiconductor laser;

11: a Raman pump source; 12: a pump coupling device;

13: a second Raman fiber.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.

A 1650nm laser-based high efficiency thulium doped fiber laser, see fig. 1, comprising: the high-reflectivity fiber bragg grating structure comprises a high-reflectivity fiber bragg grating 1, a thulium-doped active optical fiber 2, an output fiber bragg grating 3, a pumping coupling device 4 and a pumping laser 5.

Wherein, the highly reflective fiber grating 1, the thulium-doped active fiber 2 and the output fiber grating 3 are connected in sequence to form a thulium-doped fiber resonant cavity; pump laser 5 links to each other with pumping coupling device 4, and pumping coupling device 4 links to each other with high reflection of light fiber grating 1, and pump laser 5 passes through pumping coupling device 4 and pours into the thulium-doped fiber resonator with the pump light, for thulium-doped active optical fiber 2 provides the gain, and the laser that produces is exported through output fiber grating 3 in thulium-doped fiber resonance.

The preferred pump coupling device 4 is a light splitting 1650/1950nm wavelength division multiplexer; the high-reflectivity fiber grating 1 is written on the SMF-28 fiber, the central wavelength is 1950nm, the bandwidth is 0.3nm, and the reflectivity is more than 99.99 percent; the thulium-doped active optical fiber 2 is a germanate optical fiber with a single cladding and thulium-doped ion concentration of 5 wt%, the size of a fiber core/cladding is 9/125, and the length is 0.8 cm; the output fiber grating 3 is inscribed on the PM1550 fiber, the central wavelength is 1950nm, the bandwidth is less than 0.05nm, and the reflectivity is 50%.

The preferred pump laser 5 is a 1650nm raman oscillator, see fig. 2, comprising: a Raman pump source 6 and a 1650nm high-reflectivity fiber grating 7; the first raman fiber 8, 1650nm output fiber grating 9.

The Raman pump source 6 is connected with the 1650nm high-reflection fiber grating 7, the Raman pump light is directly injected into the Raman oscillator, a Raman nonlinear effect is generated in the first Raman fiber 8 and is oscillated for multiple times in the Raman oscillator to form 1650nm laser lasing, and the 1650nm laser lasing is output by the 1650nm output fiber grating 9.

The preferable Raman pump source 6 is a 1570nm single-mode fiber laser, the highest output power is 5W, and the output fiber is an SMF-28 fiber; 1650nm high-reflectivity fiber grating 7 is written on SMF-28 fiber, with center wavelength of 1650nm and reflectivity of 99.99%; the Raman fiber 8 is a 300m common passive fiber with the model number of SMF-28; 1650nm output fiber grating 9 is written on SMF-28 fiber with center wavelength of 1650nm and reflectivity of 50%.

The output fiber grating 5 is inscribed on the PM1550 polarization maintaining fiber, two reflection bands are generated under the fast and slow axis effect, and only one reflection band can be superposed with the reflection band of the highly reflective fiber grating 3, so that single-polarization laser output is realized.

Further, the pump laser 5 can generate 1W laser output under the highest output power of the raman pump source 6, and inject the laser output into the thulium-doped active optical fiber 2 in a fiber core pumping manner, because the thulium-doped active optical fiber 2 is a highly thulium-doped germanate optical fiber, the doping concentration is 7.6 × 10²⁰ions/cm³Therefore, compared with a quartz optical fiber, the thulium-doped active optical fiber has higher absorption efficiency for 1650nm pump laser, the thulium-doped active optical fiber 2 has a length of 1.2cm, the reflectivity of the output fiber grating 5 is 50%, the highest slope efficiency can be realized, the output power curve is shown in fig. 4, the highest 464mW 1950nm laser output can be realized under 1W 1650nm pump power, and the slope efficiency can be as high as 53.6%.

Example 2

In the above embodiment 1, the pump laser 5 is a raman laser amplifier, as shown in fig. 3, and includes a 1650nm single-mode semiconductor laser 10, a raman pump source 11, a pump coupling device 12, and a second raman optical fiber 13.

The center wavelength of the preferable 1650nm single-mode semiconductor laser 10 is 1650nm, and the output power is 10 mW; the Raman pump source 11 is a 1570nm optical fiber laser and a tail fiber SMF-28 optical fiber, and the center wavelength is 1570nm and the highest output power is 10W; the pump coupling device 12 is an 1650/1570nm wavelength division multiplexer, the highest bearing power is 5W, the tail fiber model is SMF-28, and the insertion loss is less than 0.5 dB; the second raman fiber 13 is an SMF-28 ordinary single mode fiber, and has a length of 2 km.

Further, the 1650nm single-mode semiconductor laser 10 outputs laser light and injects the laser light into the second raman fiber 13 to provide laser seeds required by raman amplification; the pumping light output by the raman pumping source 11 is injected into the second raman fiber 13 through the pumping coupling device 12, and the second raman fiber 13 provides raman gain, so that the pumping light output by the raman pumping source 11 is converted into laser with a center wavelength of 1650 nm.

In the above embodiment 1, the pump coupling device 2 may be adjusted according to a change of the pumping mode, and the pump combiner is used for cladding pumping and the WDM is used for core pumping.

In the above embodiment 1, the highly reflective fiber grating 3 may be inscribed on a single-clad fiber, or may be inscribed on a double-clad fiber or a triple-clad fiber, and the reflection bandwidth may cover the reflection band of the output fiber grating 5, which is not limited in this embodiment of the present invention.

In the above embodiment 1, the thulium-doped active optical fiber 2 may be a highly thulium-doped germanate optical fiber, a thulium-doped silicate optical fiber, a thulium-doped phosphate optical fiber, or a commercially available thulium-doped optical fiber, which is not limited in this embodiment of the present invention.

In the above embodiment 1, the length of the thulium-doped active optical fiber 2 may be optimized according to the doping concentration of the optical fiber, as long as the single longitudinal mode output can be realized, which is not limited in the embodiment of the present invention.

In the embodiment of the present invention, except for the specific description of the model of each device, the model and specification of other devices, including the size, the numerical aperture, the length, the doping concentration, and the like of the optical fiber, are not particularly limited, as long as the device can perform the above functions.

Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.