High power, low threshold, Raman DFB fibre lasers

Abstract

Abstract:We demonstrate highly efficient Raman gain based distributed-feedback fibrelasers at ~1.11µm with up to 2W CW output-power with <0.01nm linewidth. The lasers are 30cm long and UV-written directly into two types of passive germanosilicate fibres. IntroductionAll-fibre rare-earth doped distributed feedback (DFB) lasers have attracted a lot of interest in recent years [1]. In addition to providing inherent fibre compatibility thereby ensuring low insertion loss, they exhibit numerous excellent optical properties. These include, outstanding beam quality, very low noise characteristics and extremely narrow linewidth, making them very useful sources in a number of applications in telecommunications, range-finding and LIDAR, and sensing [2][3][4]. It is a prerequisite of these sources to have high-concentration of rare-earth ions doping in the core of the fibre to facilitate high efficiency. High concentration of rare-earth ions can lead to problems with output power stability due to pair-ion quenching leading to inefficient pump energy transfer and excessive thermal loading. The operating wavelengths are also limited to regions characteristic to the specific rare-earth material used. A Raman gain based DFB fibre laser could overcome these limitations whilst maintaining all the attractive optical properties. This would therefore open up the prospect of generating high-power narrow linewidth low-noise oscillation at any desired wavelength ranging from the visible to the infrared region, pending only the availability of a suitable pump source [5][6]. Theoretical studies suggest that Raman DFB fibre lasers could be made comparatively efficient by employing π phase-shifted fibre Bragg gratings of only a few tens of centimetres of passive germanium doped silica fibres, and also that these should exhibit only watt-level threshold [7][8]. Only recently an experimental demonstration of Raman DFB fibre laser operating at 1.58µm was reported [9]. The threshold power required for laser oscillation in that case was extremely high at ~40W @1480nm, and only 65mW of output power was obtained at a pump power of 80W, corresponding to a conversion efficiency of only 0.08%.In this work, we experimentally demonstrate 30cm long Raman DFB (R-DFB) lasers in high-NA (0.35) and standard-NA (0.12) passive germanosilica (Ge/Si) fibres with threshold powers in the low watt regime. Up to 2W of CW output power is obtained for a pump power of only 13.7W with a threshold power of only ~1W. In addition to being the highest efficiency R-DFB laser demonstrated to date, it is also the highest ever reported output power from any DFB fibre laser, incl. rare-earth doped DFB fibre lasers, to the best of our knowledge. The highest achieved output power corresponds to a conversion efficiency of 14.6% which is ~182 times higher than the R-DFB reported in [9] The slope efficiencies with respect to the absorbed pump power are ~92% for the high-NA fibre, and ~74% for the low-NA fibre, respectively. The R-DFB fibre lasers oscillate with a linewidth of <0.0...

Highly efficient Raman distributed feedback fibre lasers

“…The maximum output they reported was 350mW with the incident pump power of 34W. Instead, we have demonstrated low threshold (~1W) and high power (with up to 2W) R-DFB fibre lasers at ~1.1µm [15].…”

Single-frequency Raman Distributed-feedback Fiber Laser

“…Fig.1 (b) shows the transmission spectrum of the grating. The index modulation is measured to be ~10 -5 and the grating inscription-induced loss has previously been found to be negligible [8]. The NA, mode field diameter (MFD), cut-off wavelength and background loss of the fiber is 0.35, 2.6 ± 0.3 µm (@1100nm), 1050 ± 50 nm and ~5dB/km, respectively.…”

“…However, the lasing wavelength region of RE-doped lasers is naturally limited by the specific RE ions used. Instead, a Raman gain-based DFB fiber laser is of considerable interest for overcoming not just the limitations in wavelength coverage from its rare-earth doped counterparts, but also because it opens up the prospect of generating high-power narrow linewidth low-noise oscillation at, in principle, any desired wavelength ranging from the visible to the infrared region [6][7][8].…”

“…The linewidth in that particular work was reported to be in the MHz region. Previously, we have demonstrated R-DFB fiber lasers at 1.1 µm with a threshold value as low as ~1W, high efficiency (up to 92%) and high output power (up to 2W) in 30cms long centre π phase-shifted DFB gratings in commercial Ge/Si fibers [8]. The pump used in that work was an unpolarized 1.06 µm Yb-doped fibre MOPA laser system.…”

Ultra-Wide Range Wavelength Conversion Using FWM in a Raman DFB Fiber Laser

“…However, so far, no FWM-related wavelength conversion has been observed in DFB fiber lasers. Recently, Raman DFB (R-DFB) fiber lasers with watt-level threshold and high output power have been experimentally demonstrated [5]. In that particular design, the phase-shifted DFB grating forms a high reflectivity resonating cavity for the R-DFB signal, whilst being mostly transparent to the pump wave.…”