Justin R. Burr

Degenerate band edge resonances in coupled periodic silicon optical waveguides

Using full three-dimensional analysis we show that coupled periodic optical waveguides can exhibit a giant slow light resonance associated with a degenerate photonic band edge. We consider the silicon-on-insulator material system for implementation in silicon photonics at optical telecommunications wavelengths. The coupling of the resonance mode with the input light can be controlled continuously by varying the input power ratio and the phase difference between the two input arms. Near unity transmission efficiency through the degenerate band edge structure can be achieved, enabling exploitation of the advantages of the giant slow wave resonance.

Optimization of electron beam patterned hydrogen silsesquioxane mask edge roughness for low-loss silicon waveguides

Abstract. We carried out a multiparameter fabrication study designed to reduce the line edge roughness (LER) of electron beam (e-beam) patterned hydrogen silsesquioxane resist for the purpose of producing low-loss silicon strip waveguides. Reduced mask roughness was achieved for 50°C pre-exposure baking, 5000  μC/cm2 dose with a beam spot size more than twice as large as the electron beam step size, development in 25% tetramethylammonium hydroxide and postdevelopment baking with rapid thermal annealing in an O2 ambient at 1000°C. The LER caused by pattern fracturing and stage stitches was reduced with multipass writing and per-pass linear and rotational offsets. Si strip waveguides patterned with the optimized mask have root-mean-square sidewall roughness of 2.1 nm with a correlation length of 94 nm, as measured by three-dimensional atomic force microscopy. Measured optical propagation losses of these waveguides across the telecommunications C-band were 2.5 and 2.8  dB/cm for the transverse magnetic and transverse electric modes, respectively. These reduced loss waveguides enable the fabrication of advanced planar lightwave circuit topologies.

Degenerate band edge resonances in periodic silicon ridge waveguides

We experimentally demonstrate degenerate band edge resonances in periodic Si ridge waveguides that are compatible with carrier injection modulation for active electro-optical devices. The resonant cavities are designed using a combination of the plane-wave expansion method and the finite difference time domain technique. Measured and simulated quality factors of the first band edge resonances scale to the fifth power of the number of periods. Quality factor scaling is determined to be limited by fabrication imperfections. Compared to resonators based on a regular transmission band edge, degenerate band edge devices can achieve significantly larger quality factors in the same number of periods. Applications include compact electro-optical switches, modulators, and sensors that benefit from high-quality factors and large distributed electric fields.

Zero-coupling-gap degenerate band edge resonators in silicon photonics.

Resonances near regular photonic band edges are limited by quality factors that scale only to the third power of the number of periods. In contrast, resonances near degenerate photonic band edges can scale to the fifth power of the number periods, yielding a route to significant device miniaturization. For applications in silicon integrated photonics, we present the design and analysis of zero-coupling-gap degenerate band edge resonators. Complex band diagrams are computed for the unit cell with periodic boundary conditions that convey characteristics of propagating and evanescent modes. Dispersion features of the band diagram are used to describe changes in resonance scaling in finite length resonators. Resonators with non-zero and zero coupling gap are compared. Analysis of quality factor and resonance frequency indicates significant reduction in the number of periods required to observe fifth power scaling when degenerate band edge resonators are realized with zero-coupling-gap. High transmission is achieved by optimizing the waveguide feed to the resonator. Compact band edge cavities with large optical field distribution are envisioned for light emitters, switches, and sensors.

7 nm/V DC tunability and millivolt scale switching in silicon carrier injection degenerate band edge resonators

We demonstrate electro-optical tuning of degenerate band edge resonances in Si photonic waveguides for applications including tunable filters, low voltage switches, and modulators. Carrier injection modulation is enabled by introducing periodic Si slabs to electrically connect the resonator to P and N dopants. Measured devices yield a large DC tunability of 7.1 nm/V and a peak switching slope of 206 dB/V. Digital data transmission measurements at 100 Mb/s show 3 dB of switching with a swing voltage of 6.8 mV, 91.4 aJ/bit switching energy, and 1.08 pJ/bit holding energy.

Experimental Verification of Degenerate Band Edge Dispersion in Silicon Photonic Integrated Circuits

On resonance, periodic dielectric media of finite length exhibit large and distributed internal electric field distributions. The large and distributed fields have been exploited for applications in light emission, optical switching, and nonlinear optics. Resonance quality factors scale as the number of periods cubed near a regular band edge with quadratic dispersion. For chip-scale integrated photonics, significant footprint reduction is possible by exploiting the quartic dispersion of a degenerate band edge with quality factors that scale to the fifth power of the number of periods. Band diagrams with quartic dispersion are extracted from transmission measurements of fabricated devices realized in silicon photonics. Transmission measurements show Fano resonances with a sharp transmission peak-to-bandgap extinction ratio of 20 dB and quality factors of 27 000.

Giant Slow Wave Resonances in Coupled Periodic Silicon Optical Waveguides

Using full three dimensional analysis, we show that the quality factor of finite length coupled periodic silicon waveguides can scale to the fifth power of the number of periods. Near unity transmission can be achieved.