Semiconductor or solid-state laser having an external fiber cavity

Abstract

A semiconductor laser having an external cavity including a single-mode optical fiber. A Bragg grating is written onto the fiber which defines the end of the optical cavity, selects the lasing wavelength, and discriminates against the lasing of higher-order transverse modes in the multi-mode gain region. In one embodiment, the semiconductor laser includes an optically active vertical-cavity semiconductor stack similar to a vertical-cavity surface emitting laser. The stack is optically pumped either from the front or the back over a relatively large area such a multi-mode beam is output. Optics couple the multi-mode beam to the single-mode input of the fiber. A partially transmissive mirror of reflectivity between 25 and 40% may be placed on the output surface of the semiconductor stack to form a coupled-cavity laser. A plurality of laser diodes can be angularly positioned around the area of the semiconductor stack being pumped to increase the total pump power. In a second embodiment, the semiconductor laser includes a broad-area diode laser/amplifier. Anamorphic optics couple the asymmetric output of the optical diode to the single-mode fiber. In a third embodiment, a laser diode pumps a solid-state rod composed of an optically active material such as YAG. One end of the rod is coated with a mirror, and the other end is optically coupled to the single-mode fiber having the Bragg grating written thereon. The invention can be advantageously used to optically pump an erbium-doped fiber amplifier.