Long-Wavelength Photonic Circuits

Abstract

Microresonators ..................................................................................................... 168 4.4.2 FSR Expansion Using Vernier Effect ................................................................... 1734.5 Interferometer-Coupled Microring Resonators ............................................................. 175 4.5.1 Principles of Interferometer-Coupled Microring Resonators: FanoResonances .............................................................................................................. 176 4.5.2 Optical Interleavers Using Microring Resonator-Based Interferometers ..... 1794.5.2.1 Microring-Assisted MZI Interleavers ................................................... 180 4.5.2.2 Microring Resonator MZI Interleavers ................................................ 1834.6 Summary and Future Outlook ........................................................................................ 190 Acknowledgments ...................................................................................................................... 191 References ..................................................................................................................................... 191Over the past decade, academic and industrial researchers worldwide have feverishly explored silicon (Si) photonics as a possible technology toward next-generation multichannel optical communications and optical interconnects for computercom [1-3]. Thanks to the mature silicon complementary metal-oxide semiconductor (CMOS) fabrication processes and foundry services [4, 5], various microscale and nanoscale photonic structures can now be fabricated with high precision and repeatability on silicon and silicon-oninsulator (SOI) wafers. As reviewed in various chapters of this handbook, silicon, as one of the most well-understood materials and the most abundant semiconductor, offers the key advantages of mature fabrication process, low cost, transparency to the telecommunication wavelength range (1300-1600 nm) due to the silicon band gap of 1.12 eV, along with a relatively high refractive index of ~3.5 for optical waveguiding and connement. Silicon refractive index is also tunable via thermal-optic effect (10−4/K) [2] and free-carrier plasma dispersion effect [6], though linear electro-optic Pockels effect is absent due to the inversion symmetry of bulk silicon crystal lattice. It is based on the above merits of silicon that various compact, passive photonic devices with recongurable multichannel processing capabilities have been demonstrated including devices based on Mach-Zehnder interferometers (MZIs) [7-11], arrayed waveguide gratings (AWGs) [12-17], and all sorts of microresonators [3, 18-20].