Fabrication of TE/TM Mode Splitter Using Completely Buried GaAs/GaAlAs Waveguide

Abstract

A GaAs/GaAlAs-system TE/TM mode splitter using the mode interference principle is described. Single- and double-mode waveguides are patterned by reactive ion etching after the first molecular beam epitaxy. They are then completely buried by liquid-phase epitaxy, which enables low loss propagation due to side-wall smoothness, because of the thermal deformation effect. For achieving low loss characteristics in this mode splitter, the surface treatment process before crystal growth and S-bend waveguide mask formation procedure are also optimized. Propagation loss of the single-mode waveguide is less than 1.0 dB/cm. In order to secure birefringence of the waveguide for mode splitting, upper and lower GaAlAs-cladding mol fractions are different. Finally, the fabricated device achieves the TE/TM mode splitting ratio of 8.2 dB for both polarizations.

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“…INTRODUCTION P OLARIZATION splitters find applications in optical systems where polarization states of light are important. Some of these systems are used in communications, sensing, data storage, imaging, and signal processing [1], [2]. For many birefringent optical devices, separation of orthogonal polarization states is a straightforward solution where polarization splitters can be used.…”