Five Wavelength DFB Fiber Laser Source

Stable single mode laser sources with narrow linewidth are key components in high capacity wavelength division multiplexed (WDM) optical communication systems. Distributed feedback (DFB) [1,2,3] and distributed Bragg reflection (DBR) [4] fiber lasers are compact devices which are able to provide stable single mode operation. They are inherently fiber compatible and cascadable [2]. We present a multiwavelength laser source consisting of 5 fiber DFB lasers spliced together and pumped by a single 60 mW 1480 nm semiconductor laser.Each laser is fabricated individually using 5 cm erbium doped fiber spliced to dispersion shifted fiber and equipped with standard pigtails using angled connectors. The erbium doped fiber has a dopant concentration of 1.5x1025 m-3, core diameter of 4 mm and a numerical aperture of 0.27. It is kindly supplied by Lycom A/S. The Bragg gratings are photoinduced using a KrF excimer laser illuminating a 5 cm long phasemask (fabricated by QPS) with 248 nm light. The fluence on the fiber is around 0.4 J/cm2 per pulse. After around 3000 pulses the 4.2 cm long gratings had a peak reflectivity of 99% corresponding to a grating strength kL of around three. A phase shift was then induced in the central part of the grating by additional UV exposure. The lasers show high temperature stability. Longitudinal and polarization single mode operation without mode hopping has been verified continuously from room temperature up to 200BC as well as at -196BC. After UV writing the lasers, the angled pigtails are cut off and the lasers are spliced together and pumped with the same 60 mW semiconductor laser operating at 1480 nm.