Mixed-period multiphase shift long-period fiber grating and preparation method thereof

Abstract

The invention provides a mixed-period multi-phase shift long-period fiber grating and a preparation method thereof, aiming at spectrum broadening caused by self-phase modulation, four-wave mixing and stimulated Brillouin scattering. The mixed-period multi-phase shift long-period fiber bragg grating realizes a specific filtering function by controlling fiber bragg gratings with different periods and applying phase shift and etching domains. A transmission spectrum of the laser is provided with a narrow passband and two wide stop bands, the central wavelength of the narrow passband corresponds to the central wavelength of signal laser, the wide stop bands are located on the two sides of the narrow passband, and the wave band range of the wide stop bands corresponds to parasitic laser wave bands generated by self-phase modulation, four-wave mixing and stimulated Brillouin scattering. Light of a specific wave band can be coupled to a cladding mode from a fiber core mode, meanwhile, the situation that follow-up devices are damaged by returned light is avoided, and only signal laser is contained in a fiber core. Compared with an existing method, the method has the advantages of being good in effect, low in cost, wide in application range and the like.

Description

Technical field [0001] The present invention belongs to the field of high power fiber lasers, specifically relates to a mixing cycle multiphase shift long-period fiber grating and preparation method thereof. Background [0002] At present, the nonlinear effect of high-power laser excitation has seriously worsened the linewidness level of the output laser, and has become a problem in making single-mode fiber lasers with ultra-narrow linewidth and high power characteristics. Nonlinear effects include stimulated Raman scattering due to stimulated scattering, stimulated Brillouin scattering, and four-wave mixing, self-phase modulation, and cross-phase modulation due to nonlinear refractive index modulation. Stimulated Brillouin scattering produces several GHz Stokes signal light and anti-Stokes signal light near the signal light, while four-wave mixing and self-phase modulation are nonlinear effects that directly cause the laser spectral broadening of the fiber laser signal. When th...

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Problems solved by technology

[0003] Tilted fiber Bragg gratings have been used to suppress stimulated Brillouin scattering, which proves that it has a strong filtering effect on the backward transmitted Stokes light, but tilted fiber Bragg gratings will not only couple the core mode to the In the backward cladding mode, when this part of the return light is incident into the fiber laser under extremely high power, the system stability will be reduced, and even the subsequent devices of the fiber laser will be burned; Suppress the self-phase modulation effect and the four-wave mixing effect, but these will not only suppress the spurious laser, but also filter out most of the signal laser, which will cause a significant drop in the output laser power of the fiber laser

Using phase-shifted long-period fiber gratings to filter out the self-phase modulation effect and four-wave mixing effect, the effect is significant at lower power, and the self-phase modulation effect and four-wave mixing effect are intensified at higher power, which leads to laser spectrum The broadening is intensified, and the stop band of the phase-shifted long-period fiber grating cannot completely cover the broadened laser caused by the nonlinear refraction effect, so there will be residual nonlinear refraction effect spectral components near the main lobe of the output spectrum, which cannot achieve narrowing of the output laser spectral linewidth The goal

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