High-precision optical interference in Mach-Zehnder-type photonic crystal waveguide.

Excellent optical interference was experimentally demonstrated in the near infrared region using asymmetric Mach-Zehnder (MZ) type GaAs-based two-dimensional photonic crystal (2DPC) slab waveguides with directional couplers (DCs). As one of two MZ arm lengths changed in units of the lattice constant, the output intensities exhibited sinusoidal curves in excellent agreement with coupled-mode theory. In another experiment where the DCs were operated by two incident optical beams with externally controlled phase's difference, a sinusoidal change was observed also in output intensities according to the theory of the DC. These results were obtained by virtue of excellent nano-fabrication of the 2DPC structures and pave the way to successful operation of a PC-based ultra-small symmetrical MZ (SMZ) all-optical switch.