Ali W. Elshaari

Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides.

We demonstrate broadband all-optical modulation in low loss hydrogenated-amorphous silicon (a-Si:H) waveguides. Significant modulation (approximately 3 dB) occurs with a device of only 15 microm without the need for cavity interference effects in stark contrast to an identical crystalline silicon waveguide. We attribute the enhanced modulation to the significantly larger free-carrier absorption effect of a-Si:H, estimated here to be alpha = 1.6310(-16)N cm(-1). In addition, we measured the modulation time to be only tau(c) approximately 400 ps, which is comparable to the recombination rate measured in sub-micron crystalline silicon waveguides, illustrating the strong dominance of surface recombination in similar sized (460 nm x 250 nm) a-Si:H waveguides. Consequently, a-Si:H could serve as a high performance platform for backend integrated CMOS photonics.

Controlled storage of light in silicon cavities.

We experimentally demonstrate a tunable delay element that is inherently insensitive to free-carrier loss and achieves up to 300ps of delay. It is capable of arbitrarily storing and releasing a pulse of light through dynamic tuning of a system of microcavities. The inherent storage time is more than 32 times the duration of the stored pulse.

Optical time division multiplexer on silicon chip.

In this work, we experimentally demonstrate a novel broadband optical time division multiplexer (OTDM) on a silicon chip. The fabricated devices generate 20 Gb/s and 40 Gb/s signals starting from a 5 Gb/s input signal. The proposed design has a small footprint of 1mm x 1mm. The system is inherently broadband with a bandwidth of over 100nm making it suitable for high-speed optical networks on chip.

A passively mode-locked quantum-dot laser operating over a broad temperature range

Broad temperature operation is demonstrated from 20 to 110 °C in a 5-GHz monolithic two-section InAs/GaAs quantum dot passively mode-locked laser with an optimized absorber to gain section length ratio of 0.11. Stable pulses of less than 19 ps full-width-half-maximum are measured over this entire temperature range. For a grounded absorber, mode-locking from the ground-state occurred over the range 20–92 °C, dual-mode lasing involving both ground and excited states from 93 to 98 °C and exclusively from the excited-state from 99 to 110 °C. The observed broad temperature operation agrees with theoretical analysis based on measured gain and absorption data that predicted improved temperature performance for a short absorber. The results are promising for the development of temperature-insensitive pulsed sources for uncooled applications such as data multiplexing and optical clocking.

Single photon adiabatic wavelength conversion

Adiabatic wavelength conversion is experimentally demonstrated at a single photon power-level using an integrated silicon ring resonator. This approach allows conversion of a photon to arbitrary wavelengths with no energy or phase matching constraints. The conversion is inherently low-noise and efficient with greater than 10% conversion efficiencies for wavelength changes up to 0.5 nm, more than twenty times the resonators line-width. The observed wavelength change and efficiency agrees well with theory and bright coherent light demonstrations. These results will enable integrated quantum optical wavelength conversion for application ranging from wavelength-multiplexed quantum networks to frequency bin entanglement.

Scalable Hong-Ou-Mandel manifolds in quantum-optical ring resonators

Quantum Information Processing, from cryptography to computation, based upon linear quantum optical circuit elements relies heavily on the ability offered by the Hong-Ou-Mandel (HOM) Effect to route photons from separate input modes into one of two common output modes. Specifically, the HOM Effect accomplishes the path entanglement of two photons at a time such that no coincidences are observed in the output modes of a system exhibiting the effect. In this paper, we prove in principle that a significant increase in the robustness of the HOM Effect can be accomplished in a scalable, readily manufactured nanophotonic system comprised of two waveguides coupled, on chip, to a ring resonator. We show that by operating such a device properly, one can conditionally bunch coincident input photons in a way that is far more robust and controllable than possible with an ordinary balanced beam splitter.

Hybrid OTDM and WDM for multicore optical communication

In this work we propose a high-speed hybrid optical-time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) system that seamlessly generates high bit-rate data (>;200Gbit/s) from a low speed (5Gbit/s) quantum-dot mode locked laser pulse train. The high-speed output data can be generated using electro-optical micro-ring modulators that operate as low as (5Gbit/s). By utilizing time and wavelength domains, the proposed design is a promising solution for high-speed, compact and low-power consumption optical networks on chip.

Nanosecond Tunable Optical Delay Using Silicon Cavities

We present a tunable delay element that is inherently insensitive to free-carrier loss and achieves up to nanosecond delays even when tuned slowly. This will enable electrically tunable buffers on a silicon chip.

Design of uncooled high-bandwidth ultra-low energy per bit quantum dot laser transmitters for chip to chip optical interconnects

In this paper, we discuss our approach to developing uncooled, ultra low energy/bit QD MLL transmitters capable of providing high quality optical pulse trains suitable for multiplexing up to the 100 s of Gbps level. Up until now an analytical method to guide the design of temperature resistant MLLs based on convenient, measureable material parameters has not existed.

110 °C operation of monolithic quantum dot passively mode-locked lasers

Record performance over temperature is reported in a two-section InAs/GaAs quantum dot passively mode-locked laser. Stable pulses with less than 18 ps full-width-half-max are observed from 20-110 °C.