Michael L. Cooper

Giant birefringence in multi-slotted silicon nanophotonic waveguides

We demonstrate record giant birefringence, nearly twice as large as has previously been achieved (Delta n(group) = 1.5 over more than 60 nm of bandwidth near lambda= 1550 nm) using a multi-slotted silicon nanophotonic waveguide. The birefringence is optimized by the use of materials with high refractive index contrast to create a compact single-mode waveguide, and the etching of deeply sub-wavelength channels within the waveguide, which are strongly coupled in the near field and separated by narrow air channels of optimum lateral width. When used as a polarization-selective delay element, the delay-bandwidth product per unit length is 46.6/mm over a bandwidth of 8.74 T Hz. We also design and demonstrate mode shaping of both the TE and TM polarizations to achieve near-identical coupling to a macroscopic external object, such as a lensed fiber or detector.

Statistics of light transport in 235-ring silicon coupled-resonator optical waveguides

In contrast to recent reports of localization-impaired transport in long slow-light waveguides, we demonstrate light transport in silicon coupled-resonator optical waveguides (CROWs) consisting of up to 235 coupled microrings without localization over frequency bands that are several hundred gigahertz wide. Furthermore, from the unique statistical signatures provided by time-domain propagation delay measurements, we demonstrate the spectrally correlated nature of light propagation in CROWs.

Waveguide dispersion effects in silicon-on-insulator coupled-resonator optical waveguides

The dispersion of the waveguides that constitute microring resonators can considerably affect the dispersion characteristics of coupled-resonator optical waveguides (CROWs). We derive expressions for CROW dispersion and group delay for silicon-on-insulator microring CROWs, showing both theoretically and experimentally the band-to-band dependence of the bandwidth and group delay on the dispersion properties of the constituent single-mode silicon waveguide.

Numerically-assisted coupled-mode theory for silicon waveguide couplers and arrayed waveguides

We investigate coupled-mode theory in designing high index contrast silicon-on-insulator waveguide couplers and arrayed waveguides. We develop and demonstrate a method of solution to the inverse problem of reconstructing the coupling matrix from the modal profiles obtained, in this case, from finite-difference frequency-domain field calculations. We show that whereas supermode theory provides a good approximation of the mode profiles, next-to-nearest-neighbor coupling becomes significant at small separation distances between arrayed waveguides. These distances are quantified for three different silicon-on-insulator material platforms. We also point out the phenomenon of field skewing and deformation at small separations.

Low-power continuous-wave four-wave mixing in silicon coupled-resonator optical waveguides

We demonstrate four-wave mixing in silicon-on-insulator coupled-resonator optical waveguides consisting of 35 and 65 microring resonators, using a cw pump with coupled power below 20 mW and observed parametric conversion across more than 10 THz. The conversion efficiency is enhanced by +16 dB relative to a silicon straight waveguide of equivalent length, due to the slowing factor of the coupled-resonator structure.

Quantitative infrared imaging of silicon-on-insulator microring resonators.

There is considerable research activity in multiresonator optical circuits in silicon photonics, e.g., for higher-order filters, advanced modulation format coding/decoding, or coupled-resonator optical waveguide delay lines. In diagnostics of such structures, it is usually not possible to measure each individual microring resonator without adding separate input and output waveguides to each resonator. We demonstrate a non-invasive diagnostic method of quantitative IR imaging, applied here to a series cascade of rings. The IR images contain information on the otherwise inaccessible individual through ports and the resonators themselves, providing an efficient means to obtain coupling, loss, and intensity-enhancement parameters for the individual rings.

Two-Pump Four-Wave Mixing in Silicon Waveguides

We report dual-pump four wave mixing in silicon waveguides and demonstrate generation of up to 10 sidebands with self-seeded higher order pumps. A conversion efficiency of −8.38dB was measured between the signal and phase-conjugated idler.

Correlations between light at spectrally distant wavelengths in coupled microring resonator waveguides

We demonstrate that propagation through a silicon microring coupled-resonator optical waveguide can introduce spectral correlations between two or more light sources separated by almost 1 THz over information bandwidths upto 40 GHz.

Statistics of photon transport in hundreds of coupled resonators

Intensity and group delay are measured with high spectral resolution in long silicon microring coupled-resonator optical waveguides (CROWs), with the first experimental evidence that coherent oscillations of the coupled resonators constitute the propagating eigenmodes.

Tuning of microring resonators

Structural imperfections in fabricated microring resonators make post-fabrication tuning of rings useful in order to obtain desired transmission, phase and delay characteristics. Optical trimming of polymer microrings has been demonstrated using photobleaching. Here we investigate post-fabrication tuning of silicon-on-insulator microrings and microring based devices, including aligning the resonant frequencies of rings, and tuning the coupling coefficients.