Polarization dependent loss in III-nitride optical waveguides for telecommunication devices

Abstract

Excess polarization dependent loss (PDL) was investigated for GaN waveguide devices grown by molecular beam epitaxy (MBE). The loss for transverse magnetic polarization strongly depended on the edge dislocation density in the crystal, because the dislocations capture electrons and act like a wire-grid polarizer. By means of MBE regrowth on GaN grown with metal-organic chemical vapor deposition (MOCVD), the PDL was reduced to 1∼2dB∕mm with an edge dislocation density of 3×109cm−2, whereas it was approximately 10dB∕mm for an all-MBE-grown sample. An ultrafast all-optical switch utilizing the intersubband transition was fabricated with a multiple quantum well structure that was regrown with MBE on MOCVD-grown GaN. An extinction ratio of as high as 11.5dB was achieved with a control pulse energy of 150pJ, which is attributable to the reduction of the excess PDL.