Abstract

The series combination of a semiconductor-diode gain element (a diode laser whose end facets have been antireflection coated) and an optical fiber has been placed inside an external cavity as illustrated in Fig. 1. The external cavity operated with an output at a single wavelength whose width was less than the 1.7 × 10^–5-nm resolution of the scanning Fabry-Perot interferometer used. The spectrum illustrated in Fig. 2 is for a multimode optical fiber inside the cavity. When a grating in the Littrow configuration is used as one of the cavity end reflectors, the spectral line can be tuned. Other elements such as a polarizer can also be placed inside the cavity at the fiber output to select the polarization of this output. With proper alignment of the elements inside the cavity, temporally stable operation of the external cavity output is obtained— there are no spikes or fluctuations within the 225 MHz bandwidth of the detection circuit, there is negligible modal noise as measured on a sprectrum analyzer, and the drift in output which occurs over the order of several minutes is consistent with thermal variations expected in the experiment.

© 1982 Optical Society of America