Integrated Optical Linear Edge Filters Using Apodized Sub-Wavelength Grating Waveguides in SOI

An integrated optical apodized sub-wavelength grating waveguide is designed and demonstrated exhibiting high-extinction edge-filter characteristics with a linear roll-off in the dB scale. For a given waveguide cross-sectional geometry with fixed grating duty cycle and period, it has been shown that the apodized device length L
_g
and width Wm are the two important parameters deciding the band-edge position, roll-off and broadband extinction around the Bragg wavelength. The experimental results from fabricated devices (L
_g
= 70 μm and W
_m
= 2.5 μm) in silicon-on-insulator substrates (device layer ~ 220 nm and buried oxide layer ~ 2 μm) show a smooth band-edge roll-off of 3.5 dB/nm (λ
_edge
~ 1550 nm) with a stopband (Δλ
_sb
50 nm) extinction of 40 dB and a nearly flat-top passband (Δλ
_pb
100 nm) with negligible insertion loss of ~ 0.5 dB.