Narrowband-Stop Reflector Using Guided-Mode Resonance in Waveguide Cavity for WDM Optical Interconnects

A guided-mode resonance (GMR) filter consists of a sub-wavelength grating in a thin film waveguide on a transparent substrate and shows a narrowband-stop filtering for an incident wave from air. A cavity-resonator-integrated GMR filter (CRIGF) provides GMR filtering with a miniaturized aperture by integrating a waveguide cavity formed by a pair of distributed Bragg reflectors. A combination of a CRIGF with a high reflection substrate can provide a new type of device of band-stop reflector. A concept of a future integrated-optic wavelength-selective modulator using the reflector is proposed. A theoretical model based on coupled-mode theories is discussed to provide analytical expression of a reflection coefficient of the reflector. It was quantitatively shown that reflection spectra depended on optical-buffer-layer thickness. Excess loss in the waveguide cavity should be suppressed to provide narrow bandwidth. It was also found that lower excess loss resulted in smaller fabrication tolerance. The reflector of 10-μm aperture was fabricated and characterized. The extinction ratio in reflectance was measured to be lower than -- 20 dB at a resonance wavelength. The bandwidth at -- 10 dB was narrower than 0.04 nm. Thus a narrowband-stop reflector was theoretically predicted and experimentally demonstrated.