Recent advances in photonic integrated circuits

Abstract

Some recent advances in photonic integrated circuits are presented, including an InP-based monolithically integrated optical channel monitor, an arrayed waveguide grating (AWG) triplexer and a novel design of polarization insensitive AWGs. The optical channel monitor comprises a flat-field echelle grating and a slab photodetector array. The channel passband is flattened and widened without loss penalty. The shape of the slab waveguide detectors and the layer structure are optimized to obtain low crosstalk and low polarization dependence. It also has a smaller size due to the elimination of output waveguides. For triplexers in fiber access networks, a cross-order AWG design is proposed to overcome the device layout difficulty due to the wide spectral range of the wavelength channels. The spectral periodicity of the grating is utilized to reduce the free spectral range requirement. Consequently, the AWG can operate at a higher diffraction order with a smaller overall size. Finally, a novel design of a polarization insensitive arrayed waveguide grating is presented. Unlike conventional AWGs where the optical path length difference is obtained only in the arrayed channel waveguides, we design the star coupler regions according to Rowland circle construction with an oblique incidence/diffraction angle. As a result, the optical path length difference is produced in both the channel waveguides and the slab waveguide regions. By using the birefringence difference between the channel waveguide and the slab waveguide, a polarization dispersion compensated AWG is realized without any additional fabrication step.