GaAs/AlGaAs first-order gratings fabricated with electron beam lithography and very-narrow-linewidth long-cavity DBR laser diodes

A technique for fabricating GaAs/AlGaAs first-order gratings using electron beam (EB) lithography and its application to long-cavity distributed-Bragg-reflector (DBR) laser diodes are presented. The field stitching error, which limits the application of EB lithography to optical devices, was reduced to 5 nm by deflection amplitude calibration using marks on the samples. A technique for controlling the coupling coefficient using partially corrugated gratings is also proposed. These techniques were applied to fabrication of GaAs/AlGaAs first-order gratings of graded-index, separate-confinement-heterostructure, single-quantum-well (GRIN-SCH-SQW) distributed-Bragg-reflector (DBR) laser diodes. The resulting stitching error did not influence the single-mode lasing characteristics, and a very narrow linewidth of 237 kHz was achieved. The results show that EB lithography using the above techniques is useful in the fabrication of various optical devices with gratings