Narrow-Linewidth Tunable Lasers With Retro-Reflective External Cavity

This letter presents the development of a fiber-pigtailed narrow-linewidth tunable laser that utilizes a retro-reflective optical system to construct the external cavity. For wavelength selection, a fixed etalon is employed to provide the International Telecommunication Union (ITU) grid with the 50-GHz spacing and a lead zirconate titanate-actuated tunable filter to select one ITU mode to resonate. The laser device measures a linewidth of 7 kHz, an output power of 14 dBm, a sidemode suppression ratio (SMSR)
${>}{\rm 55}~{\rm dB}$
, a tuning range
${>}{\rm 40}~{\rm nm}$
, and a response speed
${\sim}{\rm 2}~{\rm ms}$
. The superior performance well demonstrates the advantages of external cavity construction for the narrow-linewidth tunable lasers and may find applications in the emerging digital coherent communications.