THE EFFECT OF STITCHING ERRORS ON THE SPECTRAL CHARACTERISTICS OF DFB LASERS FABRICATED USING ELECTRON-BEAM LITHOGRAPHY

We present the first comprehensive investigation on field stitching errors and their effect on the single-mode characteristics of DFB lasers fabricated using electron beam lithography. The stitching errors are associated with small-area, high-resolution electron beam exposure, which has the potential advantage of high-speed writing of laser gratings. Measurements show that the errors are composed of a systematic and a stochastic part. Their effect on the gain margin was simulated both for lambda/4 phase-shifted and optimized multiple-phase-shifted DFB lasers. Simulations show that the lasers are insensitive to the systematic part of the stitching errors if the number of errors is large enough. The stochastic part was found to give rise to a variation in gain margin of the DFB lasers. We have concluded that the field stitching accuracy in the high-resolution mode of a commercial system for electron beam lithography is sufficient to provide a high yield of single-mode lasers. However, it is essential that certain precautions are taken considering exposure conditions, and that a fault tolerant laser design is used.