Design of omnidirectional reflector air-waveguide

In this paper, we study the structure of air-waveguide surrounded by omnidirectional reflectors for both vertical and horizontal confinements. The structure is designed for the fabrication processes using GaAs-based materials and their oxides with which the omnidirectional reflectors have been demonstrated elsewhere. The vertical and horizontal confinements are achieved by the omnidirectional reflectors consisting of AlGaAs/AlGaAs -oxide multilayers and AlGaAs/air multilayers, respectively. Due to large index difference between GaAs (n=3.53) and AlAs-oxide (n=1.56), large photonic band gap can be obtained. In our design, AlGaAs (n=3.2) and AlGaAs-oxide (n=2.2) are used as the materials for growth of multilayers. The band structure of the omnidirectional reflector is calculated by transfer matrix method. For the AlGaAs/air multilayers, with the thickness ratio of the AlGaAs/air multilayers to be 40%/60%, the normalized band gap that is in the range between 0.18 to 0.34 and 0.45 to 0.62 exists only for the TE mode. With a pulsed input light of the wavelength at 1.55 μm launched at the position of z=0, the entrance of the air-waveguide, the propagation loss is calculated. The minimum propagation loss is 0.23 dB/μm for the wavelength at 1.596 μm. By tuning the structure of the omnidirectional reflector and the air-waveguide, for example by increasing the period of the multilayers, the propagation loss can still be decreased.