At&t Bell Laboratories

Leonard J Ketelsen

David Alan Ackerman

Louis A Koszi

Philip J Anthony

Venkataraman Swaminathan

Charles B Roxlo

Edward J Flynn

Lasers for use in multichannel analog optical fiber communication systems (e.g., of the type contemplated for CATV) have to meet very stringent requirements, including high linearity. DFB lasers are advantageously used in such communication systems. Typically only a relatively small percentage of the nominally identical DFB lasers on a wafer meet the specifications. It has now been discovered that the likelihood that a given DFB laser will meet the requirements is substantially increased if the laser comprises means that are adapted for producing a non-uniform photon density in the laser cavity, with the density of photons being larger in the rear portion of the cavity than in the front portion, such that during operation of the laser the gain in the back portion is substantially independent of the laser current, whereas the gain in the front portion is a function of the laser current. A particular embodiment of the invention is a 'bare patch' DFB laser having a grating that extends only part way from the front facet towards the back facet, such that a portion of the laser cavity does not have the grating associated therewith. The design ensures that the proper photon density is established within the laser cavity with high probability, largely independent of the rear (HR) facet reflection phase.

Analog optical fiber communication system, and laser adapted for use in

A semiconductor distributed feedback laser having a grating with .lambda./4 phase shift which is produced by moving the left and right sections of the grating with respect to each other in a direction perpendicular to the longitudinal axis of the active region.

Phase shifted distributed feedback laser

Lasers for use in multichannel analog optical fiber communication systems (e.g., of the type contemplated for CATV) have to meet very stringent requirements, including high linearity. DFB lasers are advantageously used in such communication systems. Typically only a relatively small percentage of the nominally identical DFB lasers on a wafer meet the specifications. It has now been discovered that the likelihood that a given DFB laser will meet the requirements is substantially increased if the laser comprises means that are adapted for producing a non-uniform photon density in the laser cavity, with the density of photons being larger in the rear portion of the cavity than in the front portion, such that during operation of the laser the gain in the back portion is substantially independent of the laser current, whereas the gain in the front portion is a function of the laser current. Exemplarily, lasers according to the invention have power asymmetry less than about 5. Preferred embodiments are AR/HR lasers with KL in the range 1.6-2.5. Optionally lasers according to the invention have a phase shift located in the back portion of the grating, a split contact, and/or a non-constant mesa width.

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Fanwood, NJ, United States of America

Leonard J Ketelsen