Brillouin single-longitudinal-mode frequency-shift fiber laser

Abstract

The invention provides a brillouin single-longitudinal-mode frequency-shift fiber laser comprising a light source module, an optical fiber circulator, an optical amplifier, an optical fiber isolator, a first optical fiber coupler, a first frequency-shift fiber, a second frequency-shift fiber, and a second optical fiber coupler. According to the invention, a unidirectional active annular resonate cavity is constructed. On the basis of a technical scheme of a fiber composite cavity, a mode selection characteristic of the composite cavity is utilized, so that thus the cavity longitudinal mode interval is larger than the brillouin gain spectrum width; and thus only one cavity longitudinal mode in the brillouin gain spectrum range is capable of carrying out oscillation starting and forming laser emission, thereby realizing brillouin single-longitudinal-mode running frequency-shift fiber laser outputting with high efficiency and low cost. The brillouin single-frequency laser frequency follows pump seed light all the time; and the broadband frequency shift effect is stable. Single-longitudinal-mode running is realized based on the composite cavity. The laser has a simple structure without any complicated control requirement; and a strict application requirement on the broadband frequency shift technology by a spontaneous Brillouin scattering type-based distributed fiber temperature strain sensing system can be met fully.

Description

technical field [0001] The invention relates to a broadband frequency shifting technology required by a distributed optical fiber sensing system based on spontaneous Brillouin scattering, in particular to a Brillouin single longitudinal mode frequency shifting fiber laser. Background technique [0002] In the distributed optical fiber sensing (BOTDR) system based on spontaneous Brillouin scattering, the frequency shift of Brillouin spontaneously scattered light relative to the incident light is affected by temperature and strain. For single-mode optical fibers in the communication band, Brillouin The frequency shift of the spontaneous scattered light relative to the incident light is about 11GHz, where the linear coefficient of the change in the frequency shift of the Brillouin scattered light caused by temperature is 1.09±0.08MHz / ℃, and the linear coefficient of the change in the frequency shift of the Brillouin scattered light caused by the strain The coefficient is 0.052±...

AI Technical Summary

Problems solved by technology

Since the Brillouin gain spectrum width is about 30MHz, and the cavity length of an active ring cavity Brillouin laser is generally on the order of tens of meters (corresponding to a cavity longitudinal mode interval of 2~10MHz), it is easy to appear multi-longitudinal mode operation Mode, resulting in large fluctuations in the frequency shift, which directly leads to the reduction of measurement accuracy in the BOTDR system

In order to avoid multi-longitudinal mode operation, some researchers locked the frequency of the injected pump seed light and the Brillouin laser operating frequency on two cavity longitudinal modes of the resonator at the same time through a laser frequency stabilization scheme, thereby realizing a single longitudinal mode. Brillouin laser output in mode operation (see Jihong Geng, et al., IEEE Photon. Technol. Lett. 18, 1813-1815 (2006)), but this scheme involves a complex feedback control system, and the stability is not easy Done well, under external disturbances, it is easy to lose the frequency stability lock, which will reduce the stability of the entire BOTDR system and increase the cost a lot

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