A group at the Optoelectronics Research Centre (Southampton, England) has created an all-fiber, 2-μm-emitting laser that can be tuned between 1820 and 2075 nm (a range of 255 nm) with an optical signal-to-noise ratio of greater than 40 dB over the whole tuning range and a 3 dB power flatness of 200 nm. The thulium-doped fiber (TDF) laser has an output power of 30 mW at the center of its tuning range.
The TDF itself has a mode-field diameter of 6.2 μm at 2000 nm and is pumped with two singlemode laser diodes (LD-1 and LD-2), each emitting 210 mW at 1550 nm and coupled in via a wavelength-division multiplexer (WDM). The fiber laser has a ring configuration with isolators (ISOs) on each end of the gain-fiber section, a fiberized grating-based tunable filter with a 3 dB bandwidth of 3 nm for tuning the wavelength, a polarization controller (PC), and a 3 dB (50%) coupler (TAP) to remove half the recirculating light as laser output. Because the tunability at the short-wavelength end was limited by insertion loss of the WDMs, the researchers expect to extend the tuning range down to around 1700 nm with better WDMs. One promising use for this laser is in hollow-core photonic-bandgap fiber (HC-PBGF) communications systems, which are in the research stage and have a predicted low-loss window at around 2 μm. Contact Zhihong Li at [email protected].
