Fiber laser amplifier

Abstract

The invention belongs to the technical field of lasers, and discloses an optical fiber laser amplifier, which sequentially comprises a circulator, a positive coupler, a negative coupler and a negative coupler along the direction of an optical path, and is characterized in that the circulator is used for receiving signal light and outputting the signal light to the positive coupler; the forward coupler is used for coupling the signal light and the forward pump light and outputting forward coupled light; the erbium-doped gain optical fiber is used for pre-amplifying the forward coupling light and outputting pre-amplified laser; the erbium-ytterbium co-doped gain optical fiber is used for carrying out main amplification on the pre-amplified laser and outputting main amplified laser; the reverse coupler is used for coupling the reverse pump light into the erbium-ytterbium co-doped gain fiber; and the chirp fiber bragg grating CFBG is used for reflecting the main amplified laser back to the original path, and the laser is output from the circulator after being amplified for the second time. According to the invention, the problems of low laser energy conversion efficiency, low output power and poor pulse output quality are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to a fiber laser amplifier. Background Art

[0002] 1.5μm band lasers are located in the low-loss window of optical fiber communication. They not only occupy an important position in the field of optical communication, but also show strong application potential and commercial value in many fields such as precision processing, spectroscopy, and medical treatment. Erbium-doped gain fiber is the main way to achieve 1.5μm band laser output, but erbium ions are prone to concentration quenching effect when doped at high concentrations, resulting in reduced pump efficiency. Studies have shown that adding ytterbium ions as activators to erbium-doped fibers can solve this problem. Erbium-ytterbium co-doped fibers can have higher laser conversion efficiency, but at high power, Yb-ASE (Yb-band amplified spontaneous emission) is very obvious and easy to form parasitic oscillations, affecting system stability. High conversion efficiency has high requirements for the power of the input signal light. In addition, when pumping at high power, strong absorption will lead to high heat load on the fiber, thereby affecting the pump light power and laser conversion efficiency.

[0003] At present, the problem of low laser conversion efficiency is mainly solved by using erbium-ytterbium co-doped gain fiber. However, erbium-ytterbium co-doped gain fiber has high requirements for input signal light, and high energy conversion efficiency can only be obtained when the input signal is high power (W level). At present, a combination of erbium-doped gain fiber and erbium-ytterbium co-doped gain fiber is used to achieve high laser energy conversion efficiency at low output power, but it uses unidirectional pumping, and strong absorption will cause high heat load on the fiber, thereby limiting the pump light power and its conversion efficiency. In addition, when the power of erbium-ytterbium co-doped fiber is high, Yb-ASE is very obvious and parasitic oscillation is easy to form, affecting the stability of the system. In addition, high-power laser output laser amplifiers generally use large mode field gain fiber, but the output laser beam quality is generally poor. Summary of the invention

[0004] Based on this, the present invention proposes a fiber laser amplifier to solve the problems of low laser energy conversion efficiency, low output power and poor pulse output quality.

[0005] The optical fiber laser amplifier provided by the present invention comprises, in order along the optical path direction:

[0006] A circulator, used for receiving the signal light and outputting the signal light to the forward coupler;

[0007] A forward coupler, used for coupling the signal light and the forward pump light, and outputting the forward coupled light;

[0008] An erbium-doped gain optical fiber, used for pre-amplifying the forward coupled light and outputting pre-amplified laser light;

[0009] Erbium-ytterbium co-doped gain optical fiber, used for performing main amplification on the pre-amplified laser and outputting main amplified laser;

[0010] A reverse coupler, used for coupling reverse pump light into the Erbium-Ytterbium co-doped gain fiber;

[0011] The chirped fiber grating CFBG is used to reflect the main amplified laser back to the original path, and the laser is output from the circulator after secondary amplification.

[0012] Furthermore, the erbium-doped gain fiber and the erbium-ytterbium co-doped gain fiber are connected via a mode field adapter.

[0013] Furthermore, the fiber laser amplifier also includes two fiber high-reflection mirrors arranged before and after the erbium-ytterbium co-doped gain fiber along the optical path direction.

[0014] Furthermore, the circulator includes a first end, a second end and a third end, the first end of the circulator is used to connect to the signal light fiber, the second end of the circulator is used to output the signal light, and the third end of the circulator is used to output the laser after secondary amplification.

[0015] Furthermore, the fiber laser amplifier also includes a single-mode optical fiber connected to the circulator, which is used to optimize the beam quality of the output laser after secondary amplification.

[0016] Furthermore, the fiber laser amplifier also includes a fiber end cap connected to the single-mode optical fiber to prevent Fresnel reflection from occurring at the fiber end.

[0017] Furthermore, the chirped fiber grating CFBG is a 1560nm high-reflection CFBG.

[0018] Furthermore, the optical fiber high reflective mirror is a 1010nm-1060nm optical fiber high reflective mirror.

[0019] Furthermore, the fiber laser amplifier includes a first pump source and a second pump source, wherein the first pump source is used to generate forward pump light, and the second pump source is used to generate reverse pump light.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention adopts a combination of bidirectional pumping of erbium-doped gain fiber and erbium-ytterbium co-doped gain fiber, which can obtain high laser conversion power and high-power output laser under low-power input laser. The bidirectional pumping method has higher slope efficiency and signal-to-noise ratio, can reduce thermal effects, and effectively improve the pump light power that the amplification system can withstand.

[0022] 2. Direct connection of erbium-doped gain fiber and erbium-ytterbium co-doped gain fiber has high requirements on the core diameter matching of the optical fiber. The present invention uses a mode adapter for connection to increase the types of gain fibers that can be used.

[0023] 3. The present invention uses a fiber reflector to form an auxiliary resonant cavity. A 10××nm fiber high reflector is inserted before and after the erbium-ytterbium co-doped gain fiber to form an auxiliary resonant cavity. The auxiliary resonant cavity can effectively suppress the Yb-ASE effect, and the Yb band oscillation in the auxiliary resonant cavity can be pumped twice to improve the pump conversion efficiency (Pump Conversion Efficiency, PCE for short).

[0024] 4. After the single-pass amplification is completed in the present invention, the laser is transmitted to the 1560nm high-reflection CFBG, and the laser is reflected back to the original path, and is output from the circulator after the second amplification (completing the two-pass amplification); the double-pass amplification can improve the amplification efficiency, and the 1560nm high-reflection CFBG can also compensate for the high-order dispersion and further filter out the Yb-ASE, thereby improving the output optical signal-to-noise ratio and the output laser performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A schematic structural diagram of a fiber laser amplifier provided in an embodiment of the present invention.

[0027] The meanings of the symbols in the accompanying drawings are:

[0028] 1-signal light, 2-circulator, 3-forward pump light, 4-forward coupler, 5-erbium-doped gain fiber, 6-mode field adapter, 7-first 1040nm high reflective mirror, 8-erbium-ytterbium co-doped gain fiber, 9-second 1040nm high reflective mirror, 10-reverse coupler, 11-reverse pump light, 12-1560nm high reflective CFBG, 13-single mode fiber, 14-fiber end cap. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] See also Figure 1 The fiber laser amplifier provided in the embodiment of the present invention includes a circulator 2, a forward coupler 4, an erbium-doped gain fiber 5, a mode field adapter 6, an erbium-ytterbium co-doped gain fiber 8, a reverse coupler 10, and a 1560nm high-reflection CFBG 12 in sequence along the optical path direction, and requires a signal light 1, a forward pump light 3, and a reverse pump light 11.

[0031] The circulator 2 comprises a first end 21, a second end 22 and a third end 23; wherein the first end 21 of the circulator is connected to the signal light fiber for receiving the signal light; the second end 22 of the circulator outputs the signal light to the forward coupler; and the third end 23 of the circulator outputs the laser after secondary amplification. The signal light is the laser to be amplified. As an example, a 1.5μm pulse laser with a power of about 100mW is selected as the signal light to be amplified.

[0032] The main function of the circulator in the optical path is to complete the separation of forward and reverse transmission light and realize bidirectional optical signal transmission on a single optical fiber. The circulator has non-reciprocity, that is, the transmission direction of the signal is irreversible, and the optical signal can only be guided from one port to another in one direction at a time.

[0033] The forward pump light 3 and the reverse pump light 11 are both generated by a pump source, which can be integrated inside the fiber laser amplifier, including a first pump source and a second pump source, wherein the first pump source is used to generate the forward pump light, and the second pump source is used to generate the reverse pump light. Bidirectional pumping has a high slope efficiency and signal-to-noise ratio, and can reduce thermal effects, effectively increasing the pump light power that the amplification system can withstand.

[0034] The forward coupler 4 is used to couple the signal light 1 and the forward pump light 3 and output the forward coupled light.

[0035] The reverse coupler 10 is used to couple the reverse pump light 11 into the Er / Yb co-doped gain fiber 8 .

[0036] The present invention adopts a combination of "erbium-doped gain fiber EDF + erbium-ytterbium co-doped gain fiber EYDF" gain fibers, which can improve PCE at low input, reduce the number of amplifier stages, and obtain high energy conversion efficiency at low input power. The erbium-doped gain fiber EDF is used to pre-amplify the forward coupled light and output pre-amplified laser. The erbium-ytterbium co-doped gain fiber EYDF is used to perform main amplification on the pre-amplified laser and output the main amplified laser.

[0037] In this embodiment, the erbium-doped gain fiber 5 and the erbium-ytterbium co-doped gain fiber 8 are connected via a mode field adapter 6. If the size difference between the two sections of the erbium-doped gain fiber 5 and the erbium-ytterbium co-doped gain fiber 8 is not large, the two sections of the optical fiber can be directly connected without the need for a mode field adapter 6.

[0038] Preferably, an auxiliary resonant cavity is formed by inserting a fiber reflector before and after the erbium-ytterbium co-doped gain fiber 8 along the optical path direction. The present invention uses a 1010nm-1060nm fiber high reflector as a fiber reflector. This embodiment uses a 1040nm fiber high reflector as an example, which are a first 1040nm high reflector 7 and a second 1040nm high reflector 9 located before and after the erbium-ytterbium co-doped gain fiber 8 along the optical path direction. The auxiliary resonant cavity can effectively suppress the Yb-ASE effect, and the Yb band oscillation in the auxiliary resonant cavity can be pumped twice to improve the PCE (pump conversion efficiency).

[0039] It should be noted that the high-reflection mirror mentioned in the embodiment of the present invention refers to a reflector with a reflectivity exceeding 99%.

[0040] After completing the single-pass amplification, it reaches the 1560nm high-reflection CFBG 12. The 1560nm high-reflection CFBG is used to reflect the laser back to the original path. After the second amplification, it is output from the third end 23 of the circulator (completing the two-pass amplification).

[0041] High reflectivity CFBG (High Reflectivity Chirped Fiber Bragg Grating) refers to a chirped fiber grating (CFBG) with high reflectivity and ultra-flat reflection spectrum written in an optical fiber. In the embodiment of the present invention, a chirped fiber grating with a reflectivity exceeding 99% can be called a high reflectivity CFBG, and the present embodiment preferably uses a 1560nm high reflectivity CFBG.

[0042] By realizing double-pass amplification through high-reflection CFBG, the amplification efficiency can be improved and the length of the gain fiber can be reduced; the optical path structure designed by the present invention can achieve high integration. In addition, the high-reflection CFBG can also compensate for high-order dispersion and further filter out Yb-ASE, thereby improving the output light signal-to-noise ratio and improving the output laser performance.

[0043] Furthermore, the fiber laser amplifier also includes a single-mode optical fiber 13 connected to the third end 23 of the circulator, which is used to optimize the beam quality of the output laser after secondary amplification.

[0044] Furthermore, the fiber laser amplifier also includes a fiber end cap 14 connected to the single-mode optical fiber 13, which is used to reduce the output optical power density and prevent Fresnel reflection from occurring at the output optical fiber end.

[0045] When the fiber laser amplifier is working, the erbium-doped gain fiber 5 and the erbium-ytterbium co-doped gain fiber 8 are both placed on a water-cooled plate for heat dissipation.

[0046] In a preferred embodiment of the present invention, the fiber laser amplifier adopts a combined gain fiber of "erbium-doped gain fiber EDF + erbium-ytterbium co-doped gain fiber EYDF", combined with auxiliary resonant cavity pumping to suppress Yb-ASE, and uses a high-reflection CFBG to reflect the light beam back to the original path for double-pass amplification; it can improve PCE at low input, reduce the number of amplifier stages, improve amplification efficiency, reduce the length of the gain fiber, compensate for high-order dispersion and improve the output light signal-to-noise ratio; ultimately achieve high energy conversion efficiency, high output power, and high-quality laser pulse output.

[0047] High-reflection CFBG can achieve double-pass amplification to improve amplification efficiency, compensate for high-order dispersion caused by the amplification process, and further filter out Yb-ASE, thereby improving the output light signal-to-noise ratio and output laser performance.

[0048] The fiber laser amplifier disclosed in the embodiment of the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A fiber laser amplifier, characterized in that: The fiber laser amplifier includes, in sequence along the optical path direction: A circulator, used for receiving the signal light and outputting the signal light to the forward coupler; A forward coupler, used for coupling the signal light and the forward pump light, and outputting the forward coupled light; An erbium-doped gain optical fiber, used for pre-amplifying the forward coupled light and outputting pre-amplified laser light; Erbium-ytterbium co-doped gain optical fiber, used for performing main amplification on the pre-amplified laser and outputting main amplified laser; A reverse coupler, used for coupling reverse pump light into the Erbium-Ytterbium co-doped gain fiber; The chirped fiber grating CFBG is used to reflect the main amplified laser back to the original path, and the laser is output from the circulator after secondary amplification.

2. The fiber laser amplifier according to claim 1, characterized in that: The erbium-doped gain optical fiber and the erbium-ytterbium co-doped gain optical fiber are connected via a mode field adapter.

3. The fiber laser amplifier according to claim 2, characterized in that: The fiber laser amplifier also includes two fiber high-reflection mirrors arranged before and after the erbium-ytterbium co-doped gain fiber along the optical path direction.

4. The fiber laser amplifier according to claim 1, characterized in that: The circulator comprises a first end, a second end and a third end. The first end of the circulator is used to connect to a signal light optical fiber, the second end of the circulator is used to output signal light, and the third end of the circulator is used to output laser light after secondary amplification.

5. The fiber laser amplifier according to claim 1, characterized in that: The fiber laser amplifier also includes a single-mode optical fiber connected to the circulator, which is used to optimize the beam quality of the output laser after secondary amplification.

6. The optical fiber laser amplifier according to claim 5, characterized in that: The fiber laser amplifier also includes a fiber end cap connected to the single-mode optical fiber to prevent Fresnel reflection from occurring at the fiber end.

7. The optical fiber laser amplifier according to claim 1, characterized in that: The chirped fiber grating CFBG is a 1560nm high-reflection CFBG.

8. The fiber laser amplifier according to claim 3, characterized in that: The optical fiber high reflective mirror is a 1010nm-1060nm optical fiber high reflective mirror.

9. The fiber laser amplifier according to claim 1, characterized in that: The fiber laser amplifier comprises a first pump source and a second pump source, wherein the first pump source is used to generate forward pump light, and the second pump source is used to generate reverse pump light.

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