A tunable single-mode source is obtained using a coaxially packaged Fabry-Perot laser diode with a built-in external cavity. The facet of the coupling fiber becomes an optical reflector and forms an external cavity with a laser facet. The single-mode oscillation condition is controlled and stabilized by tuning the operating temperature. The tuning range is about 10 nut with the side mode suppression ratio of more than 27 dB when the temperature changes from 11.5 degrees C to 25 degrees C. (C) 2006 Wiley Periodicals, Inc.