CN113359226A

CN113359226A - Local heat treatment method for high-power laser fiber grating

Info

Publication number: CN113359226A
Application number: CN202110612584.8A
Authority: CN
Inventors: 刘广柏; 李文涛; 李骁军; 白云娜; 严超
Original assignee: Shanghai Feibo Laser Technologies Co ltd
Current assignee: Shanghai Feibo Laser Technologies Co ltd
Priority date: 2021-06-02
Filing date: 2021-06-02
Publication date: 2021-09-07

Abstract

A local heat treatment method for high-power laser optical fiber grating features that after the optical fiber grating is etched, it is put in a constant-temp box for low-temp annealing and special heat treatment. The local heat treatment method for the high-power laser fiber grating greatly improves the tolerance power of the fiber grating of the high-power fiber laser.

Description

Local heat treatment method for high-power laser fiber grating

Technical Field

The invention relates to a fiber grating, in particular to a local heat treatment method of a high-power laser fiber grating.

Technical Field

With the development of fiber lasers, the requirement on the tolerance power of a core device, namely a fiber grating, of the fiber laser is higher and higher, and the traditional fiber grating preparation method is that after the fiber grating is completely written, the fiber grating is placed in a thermostat and is annealed at low temperature for 6-16 days at 70-120 ℃; subsequent processes such as packaging and the like are started. The fiber grating produced in this way has low withstand power and is difficult to meet the increasing high-power requirements of fiber lasers. When the heating temperature of the optical fiber coating layer is more than 120 ℃, yellowing and aging phenomena and even complete failure can occur, the optical fiber coating layer cannot be reliably applied to a high-power optical fiber laser for a long time, the optical fiber temperature can be changed too violently by further increasing the optical fiber heat treatment temperature, the grating reflection spectrum distortion is caused by the generated thermal stress, and the laser output efficiency is greatly reduced when the optical fiber coating layer is applied to the optical fiber laser.

Disclosure of Invention

The invention aims to provide a local heat treatment method for a high-power laser fiber grating writing area.

The technical solution of the invention is as follows:

a local heat treatment method for a high-power laser fiber grating writing area is characterized by comprising the following steps:

1) after the fiber grating is completely written, placing the fiber grating in a thermostat, and performing low-temperature annealing at 70-120 ℃ for 6-16 days;

2) placing an engraving area of the fiber bragg grating in a high-temperature cavity, placing the tail fiber without stripping the coating in a normal-temperature environment, placing the engraving area on the bare fiber with the coating stripped, and enabling the distance between the left edge and the right edge of the engraving area and the girdling point of the tail fiber without stripping the coating to be more than or equal to 2 mm;

3) slowly heating the writing area from normal temperature to the highest temperature, wherein the variation range of the highest temperature is 300-800 ℃, the variation range of the heating rate is 2-15 ℃/min, and the temperature variation control point is not less than 6 or uniformly heating;

4) after the writing area is heated to the highest temperature, high-temperature maintenance is carried out, the high-temperature maintenance time is more than or equal to 30min, and the temperature change in the heat preservation stage is less than or equal to 5 ℃;

5) after the high temperature is kept, the temperature of the writing area 1 is slowly reduced to the room temperature, the temperature reduction rate is between 2 ℃/min and 15 ℃/min, and the temperature change control point is more than or equal to 6 or is reduced at a constant speed.

Preferably, when the laser power is less than or equal to 1500W, the variation range of the highest temperature is between 350 and 400 ℃, and when the laser power is more than 1500W, the variation range of the highest temperature is between 400 and 600 ℃.

Preferably, the high-temperature holding time is 40-90 min, and the temperature change in the heat preservation stage is less than or equal to 1-3 ℃.

Preferably, the variation range of the temperature rise/reduction rate is between 5 ℃/min and 10 ℃/min, and the temperature change control point is more than or equal to 8 or the temperature rise/reduction is carried out at a constant speed.

Generally, after the first step of the conventional fiber grating is completed, subsequent processes such as packaging and the like are performed, and the low-temperature annealing described in the first step is to remove residual hydrogen molecules in the optical fiber. The special processes of the second step to the fifth step are added in the invention, aiming at the special heat treatment of the fiber grating used for the high-power fiber laser, so as to improve the laser tolerance power of the fiber grating.

The principle is as follows:

the oxygen-deficient germanium defect of the fiber core of the hydrogen-carrying optical fiber is subjected to chemical reaction with hydrogen under the ultraviolet irradiation condition (grating writing), and the fiber core is denatured, so that the fiber core absorbs and scatters light energy and the like to generate heat when laser is introduced. After the second step to the fifth step of special local thermal process treatment are added, the defect of generating heat can be reduced, so that the laser tolerance power of the fiber grating is greatly improved.

The invention has the technical effects that:

by adopting the local heat treatment method of the high-power laser fiber grating, the tolerance power of the fiber grating of the high-power fiber laser is greatly improved.

Drawings

FIG. 1 is a partial schematic view of a fiber grating.

Fig. 2 is a time curve of the heat treatment temperature in the first embodiment of the local heat treatment of the fiber grating writing region of the kilowatt-level high-power fiber laser of the present invention (when the temperature is raised, the temperature change control points are 6, and the temperature is lowered at a constant speed).

FIG. 3 shows the variation of the gate temperature with the transmitted laser power according to one embodiment.

Fig. 4 is a time curve of the heat treatment temperature in example two of the present invention (10 temperature-raising temperature change control points and 10 temperature-lowering temperature change control points).

FIG. 5 is a time curve of the heat treatment temperature (constant temperature rise and constant temperature fall) in example two of the present invention.

Fig. 6 shows the variation relationship between the gate temperature and the transmitted laser power in the second embodiment of the present invention.

FIG. 7 shows the relationship between the temperature of the grating region of the fiber grating and the power of the transmitted laser in the case of a comparative example, where the grating writing region is not produced by the special heat treatment method of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereto.

The first embodiment is as follows:

1) the length of the writing area 1 is 2.5cm, the length of the bare fiber 2 with the coating layer stripped is 3.5cm, and the writing area 1 is located in the middle of the bare fiber 2 with the coating layer stripped.

2) The writing area 1 is slowly heated to the highest temperature of 300 ℃, the average heating temperature change rate is 2.1 ℃/min, and the temperature change control points are 6.

3) The temperature holding time is 30min at the maximum temperature of 300 ℃.

4) And slowly cooling the writing area 1 to room temperature, wherein the average cooling rate is 2.58 ℃/min, and the temperature is uniformly cooled. See fig. 2.

Referring to fig. 3, in the embodiment, the variation relationship between the temperature of the suspended test gate region and the transmitted laser power is determined without any heat dissipation treatment of the produced fiber grating. It can be seen that the gate temperature was 61 ℃ when 1500W laser was applied.

Example two:

2) The writing area 1 is slowly heated to the highest temperature of 500 ℃, the heating temperature change rate is 3.4 ℃/min, and the temperature change control points are 10. Or the heating temperature change rate is 3.4 ℃/min, and the temperature is raised at a constant speed.

3) The maximum temperature was 500 ℃ and the temperature holding time was 30 min.

4) And slowly cooling the writing area 1 to room temperature, wherein the temperature change rate of cooling is 3.4 ℃/min, and the temperature change control points are 10. Or the temperature change rate of the cooling is 3.4 ℃/min, and the temperature is cooled at a constant speed. (see fig. 4, 5).

Referring to fig. 6, the fiber grating produced in the second embodiment has no heat dissipation treatment, and the change relationship between the temperature of the suspended test gate region and the transmitted laser power is determined. As can be seen, the gate temperature was 51 ℃ when 1500W of laser was applied.

Comparative example:

the fiber grating produced by the special heat treatment method of the grating writing area does not adopt the invention, and the change relation between the temperature of the suspended test grid area and the transmission laser power is not carried out under the condition of any heat dissipation treatment. Referring to FIG. 7, it can be seen that the gate temperature has reached 65 ℃ when 600W laser is applied without the special heat treatment described in the present invention, whereas the long-term reliable operating temperature of the fiber is typically below 70 ℃.

Experiments show that the high-power laser fiber grating local heat treatment method greatly improves the tolerance power of the fiber grating of the high-power fiber laser.

Claims

1. A local heat treatment method for a high-power laser fiber grating writing area is characterized by comprising the following steps:

1) after the fiber grating is completely written, placing the fiber grating in a thermostat, and performing low-temperature annealing at the temperature of 70-120 ℃ for 6-16 days;

2) placing an engraving area (1) of the fiber bragg grating in a high-temperature cavity, placing a tail fiber (3) without stripping a coating layer in a normal-temperature environment, wherein the engraving area (1) is positioned on a bare fiber (2) without stripping the coating layer, and the distance between the left edge and the right edge of the engraving area (1) and the girdling point of the tail fiber (3) without stripping the coating layer is more than or equal to 2 mm;

3) slowly heating the writing area (1) from normal temperature to the highest temperature, wherein the variation range of the highest temperature is 300-800 ℃, the variation range of the heating rate is 2-15 ℃/min, and the temperature variation control point is not less than 6 or heats at a constant speed;

4) after the writing area (1) is heated to the highest temperature, high-temperature maintenance is carried out, the high-temperature maintenance time is more than or equal to 30min, and the temperature change in the heat preservation stage is less than or equal to 5 ℃;

5) after the high temperature is kept, the temperature of the writing area (1) is slowly reduced to room temperature, the temperature reduction rate is between 2 ℃/min and 15 ℃/min, and the temperature change control point is not less than 6 or is reduced at a constant speed.

2. The method for locally heat-treating the writing area of a high-power laser fiber grating according to claim 1, wherein the variation range of the highest temperature is between 350 ℃ and 400 ℃ when the laser power is less than or equal to 1500W, and the variation range of the highest temperature is between 400 ℃ and 600 ℃ when the laser power is more than 1500W.

3. The local heat treatment method for the writing area of the high-power laser fiber grating according to claim 1, wherein the high-temperature retention time is 40-90 min, and the temperature change in the heat preservation stage is less than or equal to 1-3 ℃.

4. The local heat treatment method for the writing area of the high-power laser fiber grating according to claim 1, wherein the variation range of the temperature rise/decrease rate is between 5 ℃/min and 10 ℃/min, and the temperature change control points are not less than 8 or the temperature rise/decrease is uniform.