Wideband tunable laser sources with multiple gain elements

Abstract

This invention provides a tunable laser in which a plurality of gain elements (e.g., semiconductor diodes) with a plurality of gain spectra are optically coupled to a splitting-combining means (e.g., a wavelength router or fiber-optic coupler) in parallel, and the splitting-combining means is in optical communication with a wavelength-selecting means (e.g., a diffraction grating optically coupled to a movable mirror). The tunable laser of the present invention further comprising an optical fiber, optically coupling the splitting-combining means to the wavelength-selecting means. The use of a plurality of distinct gain spectra greatly enhances the tuning range of the tunable laser in the present invention. Moreover, by employing a long optical fiber as a substantial portion of an external cavity, the axial-mode spacing in the laser cavity is so small that mode-hops are effectively inconsequential for practical purposes, thereby rendering the wavelength tuning to be effectively continuous in the tunable laser of the present invention. Additionally, the availability of a plurality of the gain spectra can be further exploited, so as to provide additional capabilities in wavelength selecting/tuning. As such, the present invention provides a versatile and robust tunable laser in a simple and low cost construction.