Abstract
A stimulated thermal Rayleigh scattering (STRS)-based self-injection locking technique is proposed and utilized in fiber laser to improve its spectral purity. Both theoretical and experimental analyses of the STRS-based filter and the interaction mechanism between the STRS-based filter and self-injection locking are demonstrated in detail. These analyses verify effects of the proposed method on single-longitudinal-mode (SLM) selection and linewidth compression. A fiber laser employing STRS-based self-injection locking configuration is designed, and a significant improvement of spectral purity comparing to commercially available lasers is achieved. Experimental results indicate that this fiber laser operates at SLM regime and has a linewidth of 45 Hz, and can be widely applied in distributed sensing, optical communication, and high-resolution optical spectrum analysis.
Highlights
The spectral purity of fiber laser is of considerable interest for those focusing on extending the maximum measurable range of distributed sensing systems
Where, ωin is the angular frequency of the injected light, which is equal to the central frequency of the frequency selecting element; ω0 is the angular frequency of free-running mode in main ring cavity (MRC); the injection locking region ωin is dependent on Pin, P0 and τ, where Pin and P0 are the optical powers in injected branch and MRC, τ is the cavity decay time which is ∼10 μs in this work [15]
A 980 nm pump laser, wavelength division multiplex (WDM) and Erbium-doped fiber (EDF) were worked as an Erbium-doped fiber amplifier (EDFA) and supplied the laser output; the variable optical attenuator (VOA) involved in MRC was used to adjust the ratio between Pin and P0
Summary
The spectral purity of fiber laser is of considerable interest for those focusing on extending the maximum measurable range of distributed sensing systems. In order to further compress the linewidth of these SLM lasers, researchers added frequency selecting elements such as fiber Bragg gratings (FBGs), dispersion gratings, arrayed waveguide gratings, thin-film dielectric interference filters, Fabry–Perot (FP) filters, and Mach–Zehnder interferometers (MZI) into the laser resonant cavities to suppress the sidebands from the major peak [5] Those filters can barely achieve laser linewidths in the order of ∼MHz. In recent years, spontaneous and stimulated scattering in optical fibers was reported as an effective tool to construct frequency selecting elements. By means of the narrow intrinsic linewidth, tiny frequency shift and exponential-rising response of multi-peak STRS in optical fiber, the combination of the STRSbased filter and self-injection locking would promote both the performances of SLM selection and linewidth compression, which corresponds to a significant improvement of the spectral purity in fiber lasers. A high spectral purity fiber laser employing STRS-based self-injection locking technique is proposed which experimentally verified the validity of the proposed method
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