Semiconductor gain medium with multimode and single mode regions

Abstract

A semiconductor gain medium has an optical cavity comprising a multimode region permitting propagation of light with a diverging phase front and a single mode region. An optical cavity is formed by optical feedback within the medium. Preferably, the feedback comprises a combination of a cleaved facet and a grating. The gain medium may be an amplifier or, in addition to the amplifier, may include a resonator cavity, or operate as an unstable resonator.

Description

BACKGROUND OF THE INVENTION1. Technical FieldThe present invention relates to semiconductor gain media, especially to those devices that include an integrated multimode region and single mode region and more particularly to laser devices with single spatial mode, diffraction-limited emission with flared gain regions.2. Background ArtExternal-cavity semiconductor lasers, including lasers with frequency selective tuning elements in the cavity, are well known and have been extensively studied. For example, T. Fujita, et al., in Applied Physics Letters 51(6), pages 392-394 (1987), describe a laser having a buried heterostructure laser that has been antireflection (AR) coated on the intracavity facet, a collimating lens, a polarization beamsplitter, external cavity mirrors in each of the TE and TM polarization light paths, and an electro-optic modulator in the TE polarization path between the beamsplitter and cavity mirror. The configuration allows selection of either the TE or TM mode o...

AI Technical Summary

Benefits of technology

The above objects are met with a semiconductor active medium comprising an, at most, marginally stable resonant cavity with a single-spatial-mode filter therein. The semiconductor active medium is preferably an electrically pumped light amplifying diode heterostructure or "amplifier chip" that has a flared gain region with a narrow, single mode, optical aperture end and a broad light output end. The flared gain region permits the light to freely diverge as it propagates in the gain region, so the light has a diverging phase front. Only the central-most light rays of backward propagating light can pass through the narrow aperture end of the flared gain region to reach an external rear reflector of the resonant cavity. Rear reflectors integral with the diode heterostructure could also be used. The rear reflector can be a mirror surface or a frequency selective grating reflector. Orientation of the grating reflector determines which wavelength of light will couple back through the narrow aperture in the amplifier chip into the flared gain region. The flared gain region ensures high power amplification of forward propagating light while maintaining a single spatial mode of oscillation.

Problems solved by technology

A problem with previously available external-cavity semiconductor lasers is their generally low output power (on the order of 10 mW cw and 200-300 mW pulsed).

Further, higher output powers are associated with unstable output intensity and frequency and less than good modal quality.

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