Few-mode fiber Bragg grating and laser system capable of suppressing high-order mode reflection

By setting a concentric circular refractive index modulation region in the Bragg grating of the small-mode fiber, the mutual coupling between the LP01 mode and the LP11 mode in the high-power fiber laser oscillator is suppressed, the problem of mode instability effect is solved, and the high-power output and beam quality are improved.

CN111856647BActive Publication Date: 2025-04-22NAT UNIV OF DEFENSE TECH
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Patent Information

Application Number
CN202010844385.5
Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
Filing Date
2020-08-20
Publication Date
2025-04-22
Estimated Expiration
2040-08-20

AI Technical Summary

Technical Problem

The mode instability effect in high-power fiber laser oscillators limits the improvement of output power, and the prior art methods to suppress mode instability are limited.

Method used

A small-mode optical fiber Bragg grating is designed, which is a concentric circular refractive index modulation region in the core. The radius of the modulation region is smaller than the core radius and is circularly symmetrical with the optical fiber vector mode, which suppresses the mutual coupling between the LP01 mode and the LP11 mode, and reduces the autocoupling coefficient and reflectivity of the LP11 mode.

Benefits of technology

The mutual coupling between LP01 mode and LP11 mode is completely suppressed, which significantly reduces the autocoupling coefficient and reflectivity of LP11 mode, realizes filtering of higher-order modes, and improves the threshold of mode instability and the power of output signal light.

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Abstract

The present invention proposes a few-mode fiber Bragg grating and a laser system that can suppress high-order mode reflection. A circular refractive index modulation zone concentric with the core is arranged in the core of the few-mode fiber. The radius of the refractive index modulation zone is smaller than the radius of the core. The refractive index modulation zone and the optical fiber vector mode are both circularly symmetrical. 01 Module and LP 11 The two modes will not be mutually coupled, and no energy exchange will occur between the two modes. 11 The self-coupling coefficient of the mode is lower than that of LP 01 Mode self-coupling coefficient, LP 11 The reflectivity of the mode is lower than that of LP 01 mode reflectivity, achieving LP 11 The few-mode fiber Bragg grating of the present invention can be used as a cavity mirror in a high-power fiber laser oscillator, which can realize both light reflection and mode control.
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