Fabrication of high-mesa waveguides based on wide-band-gap II-VI semiconductors for telecom wavelength applications

We fabricated high-mesa waveguides for application to inter-subband transition (ISBT) all-optical switches based on (CdS/ ZnSe)/BeTe multiple-quantum well (MQW). These waveguides comprised a (CdS/ZnSe)/BeTe MQW core layer sandwiched between two ZnMgBeSe cladding layers and were fabricated by dry etching in an inductively coupled plasma (ICP). As a result of the optimization of etching conditions using BCl3 Cl-2, and Ar as process gases, we found that BCl3/Ar is effective for etching these II-VI waveguide materials. We studied transmissivity at an optical communication wavelength of 1.55 mu m in the fabricated waveguides. The insertion losses of the waveguides at transverse electric (TE) polarization were as low as 2.8 to 3.0 dB, which did not depend on waveguide length up to 0.95 mm. This indicates that a coupling loss between a waveguide and a fiber is a major contributor of TE insertion loss. On the other hand, transverse magnetic (TM) polarization insertion loss due to inter-subband absorption was observed, in which the extinction ratio of TM to TE polarization was 19 dB/mm.