Communications: Fiber-coupled external cavity semiconductor laser

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 and the external cavity has lased in a single spectral line whose width was less than the 1.7 x 10 to the -5-nm resolution of the scanning Fabry-Perot interferometer used. 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 to select a desired mode of operation. The addition of elements inside the external cavity (including the optical fiber) introduces loss which increases both the threshold current for laser operation and the ratio of power at the gain element facet to cavity output power. With optimized design the long mean life of the semiconductor laser can be maintained by reducing the output power per gain element by less than 33 percent. In terms of the overall goal of this program, The Fiber-Coupled External Cavity Semiconductor Laser, the results obtained are extremely encouraging.