Cascaded uncoupled dual-ring modulator

We demonstrate that by coherent driving two uncoupled rings in same direction, the effective photon circulating time in the dual ring modulator is reduced, with increased modulation quality. The inter-ring detuning dependent photon dynamics, Q-factor, extinction ratio and optical modulation amplitude of two cascaded silicon ring resonators are studied and compared with that of a single ring modulator. Experimentally measured eye diagrams, together with coupled mode theory simulations, demonstrate the enhancement of dual ring configuration at 20 Gbps with a Q ~ 20,000

Chip scale low dimensional materials: optoelectronics and nonlinear optics

The CMOS foundry infrastructure enables integration of high density, high performance optical transceivers. We developed integrated devices that assemble resonators, waveguide, tapered couplers, pn junction and electrodes. Not only the volume standard manufacture in silicon foundry is promising to low-lost optical components operating at IR and mid-IR range, it also provides a robust platform for revealing new physical phenomenon. The thesis starts from comparison between photonic crystal and micro-ring resonators based on chip routers, showing photonic crystal switches have small footprint, consume low operation power, but its higher linear loss may require extra energy for signal amplification. Different designs are employed in their implementation in optical signal routing on chip. The second part of chapter 2 reviews the graphene based optoelectronic devices, such as modulators, lasers, switches and detectors, potential for group IV optoelectronic integrated circuits (OEIC). In chapter 3, the highly efficient thermal optic control could act as on-chip switches and (transmittance) tunable filters. Local temperature tuning compensates the wavelength differences between two resonances, and separate electrode is used for fine tuning of optical pathways between two resonators. In frequency domain, the two cavity system also serves as an optical analogue of Autler-Towns splitting, where the cavity-cavity resonance detuning is controlled by the length of pathway (phase) between them. The high thermal sensitivity of cavity resonance also effectively reflects the heat distribution around the nanoheaters, and thus derives the thermal conductivity in the planar porous suspended silicon membrane. Chapter 4 and 5 analyze graphene-silicon photonic crystal cavities with high Q and small mode volume. With negligible nonlinear response to the milliwatt laser excitation, the monolithic silicon PhC turns into highly nonlinear after transferring the single layer graphene with microwatt excitation, reflected by giant two photon absorption induced optical bistability, low power dynamic switching and regenerative oscillation, and coherent four-wave-mixing from high Kerr coefficient. The single layer graphene lowers the operational power 20 times without enhancing the linear propagation loss. Chapter 6 moves onto high Q ring resonator made of plasma enhanced chemical vapor deposition grown silicon nitride (PECVD SiN). PECVD SiN grown at low temperature is compatible with CMOS processing. The resonator enhanced light-matter interaction leads to molecular absorption induced quality factor enhancement and thermal bistability, near the critical coupling region. In chapter 7, carrier transport and recombination in InAs quantum dots based GaAs solar cells are characterized by current-voltage curve. The parameters include voltage dependent ideality factor, series and shunt resistance. The device variance across the wafer is analyzed and compared. Quantum dots offers extra photocurrent by extending the absorption edge further into IR range, but the higher recombination rate increases the dark current as well. Different dots sized enabled by growth techniques are employed for comparison

Suppression of Edge Recombination in InAs/InGaAs DWELL Solar Cells

The InAs/InGaAs DWELL solar cell grown by MBE is a standard pin diode structure with six layers of InAs QDs embedded in InGaAs quantum wells placed within a 200-nm intrinsic GaAs region. The GaAs control wafer consists of the same pin configuration but without the DWELL structure. The typical DWELL solar cell exhibits higher short current density while maintaining nearly the same open-circuit voltage for different scales, and the advantage of higher short current density is more obvious in the smaller cells. In contrast, the smaller size cells, which have a higher perimeter to area ratio, make edge recombination current dominant in the GaAs control cells, and thus their open circuit voltage and efficiency severely degrade. The open-circuit voltage and efficiency under AM1.5G of the GaAs control cell decrease from 0.914V and 8.85% to 0.834V and 7.41%, respectively, as the size shrinks from 5*5mm2 to 2*2mm2, compared to the increase from 0.665V and 7.04% to 0.675V and 8.17%, respectively, in the DWELL solar cells

Spatially controlled electrostatic doping in graphene p-i-n junction for hybrid silicon photodiode

Sufficiently large depletion region for photocarrier generation and separation is a key factor for two-dimensional material optoelectronic devices, but few device configurations has been explored for a deterministic control of a space charge region area in graphene with convincing scalability. Here we investigate a graphene-silicon p-i-n photodiode defined in a foundry processed planar photonic crystal waveguide structure, achieving visible - near-infrared, zero-bias and ultrafast photodetection. Graphene is electrically contacting to the wide intrinsic region of silicon and extended to the p an n doped region, functioning as the primary photocarrier conducting channel for electronic gain. Graphene significantly improves the device speed through ultrafast out-of-plane interfacial carrier transfer and the following in-plane built-in electric field assisted carrier collection. More than 50 dB converted signal-to-noise ratio at 40 GHz has been demonstrated under zero bias voltage, with quantum efficiency could be further amplified by hot carrier gain on graphene-i Si interface and avalanche process on graphene-doped Si interface. With the device architecture fully defined by nanomanufactured substrate, this study is the first demonstration of post-fabrication-free two-dimensional material active silicon photonic devices.Comment: NPJ 2D materials and applications (2018

Cosmic Radiation Reduced Photo-Thermal Dispersion in Silicon Micro-Ring Resonators

We show post-spaceflight results for a silicon photonic integrated circuit micro-ring resonator. The free-carrier lifetime reduced by factor of 2 after radiation damage events in space

Performance Evaluation of Silicon Mach-Zehnder Modulator after Cosmic Radiation to Enable Small Satellite Laser Communication

To evaluate the performance change of Photonic integrated circuits after real cosmic radiation, silicon Mach-Zehnder Modulators were mounted on International Space Station on Low Earth Orbit for 6 months’ radiation harshness. Measured data of the device before and after radiation showed the permanent change of the effective index (around 10-3), the reduced carrier recombination lifetime, and the extended high speed bandwidth