At&t Bell Laboratories

Paul M Nitzsche

David Alan Ackerman

Charles B Roxlo

Edward J Flynn

Carl J McGrath

Paul W Smith

We have discovered that the yield of DFB lasers suitable, e.g., for use in AM CATV systems can be substantially increased if the lasers have a back facet with a higher reflectivity (&gt;80%, preferably &gt;90%) HR coating thereon than is conventional (e.g., .about.65%). Exemplary currently preferred embodiments of the invention comprise a three-pair stack of .lambda./4 yttrium-stablized zirconia/Si having about 95% reflectivity.

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

An advantageous method of fabricating lasers adapted for use in a multichannel analog optical fiber communication system, e.g., a CATV system, is disclosed. A laser generally can be used in such a communication system only if it meets, inter alia, very stringent intermodulation specifications. To identify such lasers typically requires extensive testing. It has now been discovered that certain readily determinable parameters can be used to predict the intermodulation behavior of a given device. This discovery makes possible a simpler, and therefore less costly, process of identifying suitable lasers, resulting in a more economical method of making lasers for the stated application. The method comprises measuring the light versus current (L versus I) characteristic of a given laser, determining therefrom the first, second, and possibly higher, order derivatives of L with respect to I, and determining thereform a parameter that is a predictor of the distortion behavior of the laser. Exemplarily, the quantity is the normalized second order distortion (2HD/C), defined as 20 log (mL'/4L'.sup.2), where m is the modulation index, and L' and L' are the first and second derivatives, respectively, of L. 2HD/C has a pronounced minimum at I=I.sub.op , the current at which L'=0. Advantageously, lasers are selected that have 2HD/C less than a predetermined value (e.g., -70 dbc, with m=0.04) over a relatively wide current range (e.g., at least 4 mA).

Growing community of inventors

Plainfield, NJ, United States of America

Paul M Nitzsche