Dylan F. Logan

Wavelength Locking and Thermally Stabilizing Microring Resonators Using Dithering Signals

The bandwidth bottleneck looming for traditional electronic interconnects has driven the consideration of optical communications technologies as realized through the complementary metal-oxide-semiconductor-compatible silicon nanophotonic platform. Within the silicon photonics platform, silicon microring resonators have received a great deal of attention for their ability to implement the critical functionalities of an on-chip optical network while offering superior energy-efficiency and small footprint characteristics. However, silicon microring-based structures have a large susceptibility to fabrication errors and changes in temperature. Integrated heaters that provide local heating of individual microrings offer a method to correct for these effects, but no large-scale solution has been achieved to automate their tuning process. In this context, we present the use of dithering signals as a broad method for automatic wavelength tuning and thermal stabilization of microring resonators. We show that this technique can be manifested in low-speed analog and digital circuitry, lending credence to its ability to be scaled to a complete photonic interconnection network.

Integrated thermal stabilization of a microring modulator

An integrated silicon photodiode and heater are used to thermally stabilize a microring modulator, interfacing with external feedback circuitry to provide error-free microring modulator operation under thermal fluctuations that would normally render it inoperable.

Defect-Enhanced Silicon-on-Insulator Waveguide Resonant Photodetector With High Sensitivity at 1.55

We describe the fabrication and characterization of a silicon waveguide resonant photodetector compatible with the optical-to-electrical conversion of wavelengths at, or around, 1550 nm. Sub-band responsivity is provided through the introduction of defects via inert self-implantation and subsequent annealing. The detector is located within a 20- m radius silicon microring resonator. An 18-dB resonant enhancement in absorption coefficient and 12-dB enhancement in photocurrent were measured, leading to a resonant responsivity of approximately 39 mA/W at 20-V reverse bias.

\mu

Recent attention has been attracted by photo-detectors integrated onto silicon-on-insulator (SOI) waveguides that exploit the enhanced sensitivity to subbandgap wavelengths resulting from absorption via point defects introduced by ion implantation. In this paper, we present the first model to describe the carrier generation process of such detectors, based upon modified Shockley-Read-Hall generation/recombination, and, thus, determine the influence of the device design on detection efficiency. We further describe how the model may be incorporated into commercial software, which then simulates the performance of previously reported devices by assuming a single midgap defect level (with properties commensurate with the single negatively charged divacancy). We describe the ability of the model to highlight the major limitations to responsivity, and thus suggest improvements which diminish the impact of such limitations.

m

We report on the application of defect-enhanced silicon waveguide photodiodes operating at 1550 nm as power monitors for use in photonic integrated circuits. In-line monitors of 250-μm length provide an efficiency of 97 mA/W by absorbing only 8% of the optical mode. The monitors were integrated onto micro-ring waveguide ports to provide measures of optical resonance characteristics and a feedback to a thermal resonance tuner. The suitability of these photodetectors for control of micro-ring resonators is demonstrated.

Modeling Defect Enhanced Detection at 1550 nm in Integrated Silicon Waveguide Photodetectors

We have devised and fabricated high-speed silicon-on-insulator resonant microring photodiodes. The detectors comprise a p-i-n junction across a silicon rib waveguide microring resonator. Light absorption at 1550 nm is enhanced by implanting the diode intrinsic region with boron ions at 350 keV with a dosage of 1 × 10 13 cm −2 . We have measured 3-dB band- widths of 2.4 and 3.5 GHz at 5 and 15 V reverse bias, respectively, and observed an open-eye diagram at 5 gigabit/s with 5 V bias. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Monitoring and Tuning Micro-Ring Properties Using Defect-Enhanced Silicon Photodiodes at 1550 nm

We design and demonstrate for the first time an end-to-end binary phase-shift keying (BPSK) link based on silicon microring resonators, with an operational bit-rate at 10 Gb/s. The obtained bit-error-rate is below the forward error correction limit, validating the practical application of the demonstrated technique. Performance comparisons to conventional BPSK modulation and demodulation techniques are also made. The microring-based BPSK link promises a compact, energy efficient, and low-cost interconnect solution for high-capacity transceivers.

Silicon-on-insulator microring resonator defect-based photodetector with 3.5-GHz bandwidth

We present a study on the effects of inert ion implantation of Silicon-On-Insulator (SOI) racetrack resonators. Selective ion implantation was used to create deep-level defects within a portion of the resonator. The resonant wavelength and round-trip loss were deduced for a range of sequential post-implantation annealing temperatures from 100 to 300 °C. As the devices were annealed there was a concomitant change in the resonance wavelength, consistent with an increase in refractive index following implantation and recovery toward the pre-implanted value. A total shift in resonance wavelength of ~2.9 nm was achieved, equivalent to a 0.02 increase in refractive index. The excess loss upon implantation increased to 301 dB/cm and was reduced to 35 dB/cm following thermal annealing. In addition to providing valuable data for those incorporating defects within resonant structures, we suggest that these results present a method for permanent tuning (or trimming) of ring resonator characteristics.

A 10-Gb/s Silicon Microring Resonator-Based BPSK Link

We present the novel mechanism of thermal dithering for breaking the symmetry of a microring resonance, and experimentally show it can be utilized to thermally stabilize a silicon microring resonator experiencing fluctuations of 3 K.

Defect-mediated resonance shift of silicon-on-insulator racetrack resonators

We demonstrate a novel in-band OSNR monitor with full optical components integration. The OSNR monitor is shown to have a working range of 17 dB for 40-Gb/s OOK and DPSK signals, and is insensitive to chromatic dispersion of 0-250 ps/nm.