Highly efficient Raman distributed feedback fibre lasers

Abstract

We demonstrate highly efficient Raman distributed feedback (DFB) fibre lasers for the first time with up to 1.6 W of continuous wave (CW) output power. The DFB Bragg gratings are written directly into two types of commercially available passive germano-silica fibres. Two lasers of 30 cm length are pumped with up to 15 W of CW power at 1068 nm. The threshold power is ~2 W for a Raman-DFB (R-DFB) laser written in standard low-NA fibre, and only ~1 W for a laser written in a high-NA fibre, both of which oscillate in a narrow linewidth of <0.01 nm at ~1117 nm and ~1109 nm, respectively. The slope efficiencies are ~74% and ~93% with respect to absorbed pump power in the low-NA fibre and high-NA fibre respectively. Such high conversion efficiency suggests that very little energy is lost in the form of heat through inefficient energy transfer. Our results are supported by numerical simulations, and furthermore open up for the possibility of having narrow linewidth all-fibre laser sources in wavelength bands not traditionally covered by rare-earth doped silica fibres. Simulations also imply that this technology has the potential to produce even shorter R-DFB laser devices at the centimetre-level and with mW-level thresholds, if Bragg gratings formed in fibre materials with higher intrinsic Raman gain coefficient than silica are used. These materials include for example tellurite or chalcogenide glasses. Using glasses like these would also open up the possibility of having narrow linewidth fibre sources with DFB laser oscillating much further into the IR than what currently is possible with rare-earth doped silica glasses.

Detailed study of four-wave mixing in Raman DFB fiber lasers

“…The R-DFB grating is 30 cm long with a center π phase-shift [18,19]. It was fabricated directly into a standard single-mode fiber (SMF) (PS980 from Fibercore Ltd.) with UV light at 244 nm using our continuous grating writing technique [20].…”

“…It was fabricated directly into a standard single-mode fiber (SMF) (PS980 from Fibercore Ltd.) with UV light at 244 nm using our continuous grating writing technique [20]. The coupling coefficient of the grating is 37 m -1 [18]. A length L2 = 1.8 m of the same PS980 fiber was used as the pigtailing fiber of the R-DFB grating.…”

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

“…We used the same R-DFB grating sample (30cms long with center π phase shift formed in Nufern UHNA4 fiber) as used in our previous work [7]. The NA, propagation loss (α) at 1.1 µm and nonlinear coefficient (γ @ 1.1µm) are estimated to be 0.35, 5 dB/km and ~34 (Wkm) -1 , respectively.…”

Single-frequency Raman Distributed-feedback Fiber Laser

“…Thus, watt-level of pump powers and long lengths of (>10cms) DFB gratings have been highlighted as being required for efficient lasing [9]. R-DFB fiber lasers at 1.6µm have been demonstrated in commercial Raman fiber and highly nonlinear fiber with thresholds of 39W and 4.3W, respectively [7].…”