Narrow-Linewidth Er-Doped Fiber Lasers With Random Distributed Feedback Provided By Artificial Rayleigh Scattering

Abstract

A compact random fiber laser based on a short artificial Rayleigh reflector and heavily-doped Er fibers (custommade and commercial as a reference) has been proposed, characterized and optimized in terms of efficiency, linewidth and noise level. A 10-cm artificial Rayleigh reflector with mean scattering level of +41.3 dB/mm relative to the natural Rayleigh scattering of the host fiber and low insertion loss level (~0.05 dB/cm at 1535 nm) was fabricated using a femtosecond direct writing technique. Its implementation as a distributed output mirror in a half-open cavity of a 980-nm diode pumped Er-doped fiber laser results in random lasing at 1535 nm in single-and fewmode regimes with power up to 100 mW, slope efficiency up to 16.5%, and signal-to-noise ratio up to 60 dB. A single-frequency regime with ~10 KHz linewidth was observed at output power up to 2.5 mW. Tunability potential of such random lasers is also demonstrated.

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

“…A narrow linewidth is beneficial to suppress frequency noise levels of fiber lasers and can further improve resolution in optical dynamic strain-sensing systems [ 1 , 2 , 3 ]. Random fiber lasers (RFLs) have a simple cavity configuration, low threshold, and good temporal coherence, and they are a promising alternative for narrow linewidth and low frequency noise fiber lasers [ 4 , 5 , 6 ]. Recently, RFLs have attracted considerable interest due to their unique emission characteristic and potential sensing application prospects [ 4 , 7 ].…”

“…Compared with backward RS inside SMF, a random weak grating array (RWGA) can provide strong random feedback, so that RWGA-based RFLs have superior performances, such as a narrow linewidth, compact structure, and high optical signal-to-noise ratio (OSNR) [ 10 , 11 ]. Differing from the feedback mechanism of backward RS, RWGA has wavelength dependence and can strongly improve random feedback efficiency by introducing refractive index modulation, which results in a low lasing threshold combining with the high-efficiency gain provided by erbium-doped fiber (EDF) [ 6 , 12 , 13 , 14 ]. RWGA can be regarded as the superposition of many Fabry–Perot interferometers which introduced by weak FBGs.…”

Femtosecond laser writing of random distributed reflectors in single- and multi-mode fiber optical fibers

“…The presence of frozen inhomogeneities in the light-guiding core of an optical fiber leads to weak backscattering of modes propagating along the fiber, which is widely used in distributed sensor systems [1] and fiber lasers with distributed feedback [2,3]. For standard telecommunication optical fibers (for example, SMF-28) the natural Rayleigh backscattering level is -100-105 dB/mm in the spectral region of 1.55 µm.…”

“…In fiber lasers with distributed feedback, low backscattering forces the use of relatively long fiber segments (~1-100 km) to achieve an acceptable integral reflection coefficient. A controlled increase in the backscattering level in optical fibers paves the way to the development of improved distributed sensors [4], as well as compact lasers with random distributed feedback [3].…”

“…One of the most promising methods of amplifying the backscattering signal in an optical fiber is the method of femtosecond laser writing [3,4]. The method allows to create both point (Fresnel reflection) and continuous (Mie and Rayleigh scattering) random refractive index structures by writing them with femtosecond visible/IR laser pulses through a protective fiber coating (for example, polyimide or acrylate), which is especially important for practical applications.…”