Narrow Linewidth Half-Open-Cavity Random Laser Assisted by a Three-Grating Ring Resonator for Strain Detection

Abstract

A stabilized narrow-linewidth random fiber laser for strain detection, based on a three-grating ring (TGR) resonator and half-open-cavity structure, is proposed and investigated experimentally. The half-open-cavity structure proved to provide double optical gain of erbium-doped fiber, which was beneficial to increase the photon lifetime as well as further narrow the linewidth. Meanwhile, the stability and frequency noise of narrow lasing output was improved by suppressing the competition-induced undesired residual random lasing modes with the TGR resonator. The TGR resonator is composed of a double-cavity fiber Bragg grating Fabry–Perot (FBG-FP) interferometer, a section of single-mode fiber, and a circulator. The specially designed double-cavity FBG-FP interferometer embedded in the TGR resonator acted as the strain-sensing element and improved the resolution of the dynamic strain. A stable ultra-narrow linewidth of about 205 Hz was obtained. The frequency noise was reduced to about 2 Hz/√Hz. A high dynamic strain measuring resolution of 35 femto-strain (fε)/√Hz was achieved.

Review of Random Fiber Lasers for Optical Fiber Sensors

“…When the π-FBG was used as an acoustic emission detection element [92], the resolution reached 280 fε/Hz 1/2 @ 1 kHz, which could already meet most high-precision measurement needs. Similar results were obtained by replacing the π-FBG with a dual-cavity fiber grating Fabry-Perot interferometer [93][94][95], as shown in Figure 20. The Fabry-Perot cavity interferometer suppressed multipeak laser modes and frequency jitter, reducing frequency noise to 3 Hz/Hz 1/2 , as shown in Figure 21a.…”

Partial Discharge Wideband Full-Band High-Gain Resonant Cavity UHF Sensor Research

“…Under certain conditions, the light rays in the resonant cavity can form a series of beams that interfere with each other [ 17 ]. This principle can be used in optical sensors to improve filtering performance and increase gain [ 18 ].…”

“…The general partial reflection cladding with the feed antenna has a narrow bandwidth, which is because the reflection coefficient of the partial reflection layer becomes smaller in phase as the frequency increases and is a negative reflection phase gradient [ 18 ]. For this defect, a partially reflective cladding with a positive reflective phase gradient is designed in this paper.…”

“…The gain directional map is a parameter used to describe the directionality of the antenna and the antenna efficiency, measuring the degree of concentration of the radiant energy of the antenna in free space and the degree of effectiveness of the antenna in converting wave energy into high-frequency current or energy [ 18 , 35 , 36 ]. The higher the gain, the better the directionality, the more concentrated the energy, and the higher the efficiency.…”