| Popis: |
Electro-optically active resonant cavities are among the most fundamental building blocks of photonic integrated circuits and are integral in applications such as sensing, modulation, and light emission. In this thesis, active degenerate band edge (DBE) resonant cavities are proposed and demonstrated as an attractive topology for silicon photonic electro-optical devices. DBE resonators are a class of band edge photonic crystal resonators which feature large, distributed electric fields on resonance which enable interaction with dispersed analytes or distributed gain media. In addition, DBE resonators are notable for quality factor (Q) scaling of N5 where N is the number of periodic elements which make up the resonant cavity. This Q scaling is significantly larger than the N3 Q scaling for regular band edge cavities, leading to miniaturization of devices based on DBE resonators. Q scaling is not directly observed in other integrated optical topologies such as ring resonators or photonic crystal defect mode cavities. Electro-optically active devices based on DBE resonances are formed by the fabrication of p-i-n diodes around the optical cavity for the injection of carriers which modulate the refractive index through the plasma dispersion effect. The active DBE devices operate as optical switches with record-high DC tunability of 7 nm/V and low AC switching energy of 90 aJ/bit.The Q scaling in DBE resonators is limited by (1) propagation loss due to scattering from waveguide sidewalls and (2) disorder induced by variations in the size, shape and position of the periodic elements which make up the cavity. A study of the electron beam lithography processes used to expose the resonant cavities was carried out to reduce propagation losses and enable the measurement of N5 Q scaling. Waveguides produced with this optimized process demonstrated losses less than 3 dB/cm, compared to 10 dB/cm propagation loss for waveguides without the optimized process. Fiber-to-chip coupling losses, another significant source of passive losses in Si photonic circuits, are also reduced through the design of compact cantilever couplers. Cantilever couplers combine the bandwidth and polarization insensitivity of edge couplers with the small footprint of grating couplers. Measured compact cantilever couplers have a length of 7.5 µm and losses of less than 0.5 dB/connection for both TE and TM modes. Combining these low loss fiber-to-chip couplers with the optimized waveguides results in a total fiber-to-fiber insertion loss of less than 5 dB over a 100 nm bandwidth.A fundamental and long standing challenge in silicon photonics is the demonstration of a CMOS-compatible integrated optical light source. Ring resonators composed of hydrogenated amorphous Si (aSi:H) deposited at low temperatures show broadband photoluminescence across the 1300 – 1600 nm telecommunication window with periodic peaks in the spectrum corresponding to the resonant modes of the ring. aSi:H can be deposited with a variety of techniques and has a thermal budget within the constraints of back-end of line CMOS processing. These results indicate that aSi:H is a promising material for on-chip light emission. Electro-optically active DBE cavities composed of aSi:H are proposed and analyzed as CMOS-compatible integrated optical light sources. |
