An ultracompact 3 dB coupler is designed and fabricated in silicon on insulator,based on 1×2 line tapered multimode interference (MMI) coupler.Comparing with the conventional straight MMI coupler,the device is ～40% shorter in length.The device exhibits uniformity of 1 3dB and excess loss of 2 5dB.
The band structure of 2D photonic crystals (PCs) and localized states resulting from defects are analyzed by finite-difference time-domain (FDTD) technique and Padé approximation.The effect of dielectric constant contrast and filling factor on photonic bandgap (PBG) for perfect PCs and localized states in PCs with point defects are investigated.The resonant frequencies and quality factors are calculated for PCs with different defects.The numerical results show that it is possible to modulate the location,width and number of PBGs and frequencies of the localized states only by changing the dielectric constant contrast and filling factor.
SOI waveguides fabricated by wet-etching method are demonstrated.The single mode waveguide and 1×2 3dB MMI splitter are analyzed and designed by three dimensional beam propagation method to correct the error of effective index method and guided mode method.The devices are fabricated.Excellent performances,such as low propagation loss of -1.37dB/cm,low excess loss of -2.2dB,and good uniformity of 0.3dB,are achieved.
