Characterization of External Cavity Laser with Thin Film Narrow Bandpass Filter

An external cavity laser (ECL) with a thin film narrow bandpass filter was designed and characterized. The novel ECL structure utilized a narrow bandpass filter whose center wavelength and bandwidth were easily controlled. Moreover, it has an advantage of stable lasing wavelength due to the small variation of filter performance over temperature. The ECL was composed of one side anti-reflection coated laser diode (LD), bandpass filter, and a partial mirror. For single mode operation, the filter was tilted to prohibit reflected light at the filter surface entering the LD waveguide. In this paper, we varied the filter angle and measured performance of the ECL. When the filter was tilted, a single mode operation was observed while optical power decreased. The optimum performance was obtained when the filter angle was 2 degrees, where side mode suppression ratio was 45 dB and optical power was 1.8 mW at 30 mA.