Peyman Sarrafi

Tuneable four-wave mixing in AlGaAs nanowires.

We have experimentally demonstrated broadband tuneable four-wave mixing in AlGaAs nanowires with the widths ranging between 400 and 650 nm and lengths from 0 to 2 mm. We performed a detailed experimental study of the parameters influencing the FWM performance in these devices (experimental conditions and nanowire dimensions). The maximum signal-to-idler conversion range was 100 nm, limited by the tuning range of the pump source. The maximum conversion efficiency, defined as the ratio of the output idler power to the output signal power, was -38 dB. In support of our explanation of the experimentally observed trends, we present modal analysis and group velocity dispersion numerical analysis. This study is what we believe to be a step forward towards realization of all-optical signal processing devices.

High-visibility two-photon interference of frequency–time entangled photons generated in a quasi-phase-matched AlGaAs waveguide

We demonstrate experimentally the frequency-time entanglement of photon pairs produced in a CW-pumped quasi-phased-matched AlGaAs superlattice waveguide. A visibility of 96.0±0.7% without background subtraction has been achieved, which corresponds to the violation of the Bell inequality by 52 standard deviations.

Continuous-wave quasi-phase-matched waveguide correlated photon pair source on a III–V chip

We report on the demonstration of correlated photon pair generation in a quasi-phase-matched superlattice GaAs/AlGaAs waveguide using a continuous-wave pump. Our photon pair source has a low noise level and achieves a high coincidence-to-accidental ratio greater than 100, which is the highest value reported in III–V chips so far. This correlated photon pair source has the potential to be monolithically integrated with on-chip pump laser sources fabricated on the same superlattice wafer structure, enabling direct correlated/entangled photon pair production from a compact electrically powered chip.

Modeling of Pulse Propagation in Layered Structures With Resonant Nonlinearities Using a Generalized Time-Domain Transfer Matrix Method

We introduce a generalized time-domain transfer- matrix (TDTM) method, the only method to our knowledge that is capable of modeling high-index-contrast layered structures with dispersion and slow resonant nonlinearities. In this method transfer matrix is implemented in the time domain, either by switching between time and frequency domains using Fourier transform and its inverse operation, or by replacing the frequency variable (ω) with its temporal operator (-i (d/dt)). This approach allows us to implement the transfer matrix method (which can easily incorporate dispersion, is analytical in nature, and requires less computation time) in the time domain, where we can incorporate nonlinearity of various kinds, instantaneous (such as Kerr nonlinearity), or slow resonant nonlinearity (such as carrier-induced nonlinearity). This generalized TDTM method is capable of incorporate non-analytical forms of dispersion and of nonlinearity, making it a versatile tool for modeling optical devices where dispersion and nonlinearities are obtained phenomenologically. We also provide a few numerical examples to compare our method with the standard finite-difference time- domain (FDTD) method, as well as to examine the range of validity of our method. For pico-second and longer pulses, our results agree with the FDTD simulation results to within 1% and the computation time of our method is more than 100 fold reduced compared to that of FDTD for the longest pulse we used.

Rainbow-trapping by adiabatic tuning of intragroove plasmon coupling

Trapping broadband electromagnetic radiation over a subwavelength grating, provides new opportunities for hyperspectral light-matter interaction on a nanometer scale. Previous efforts have shown rainbow-trapping is possible on functionally graded structures. Here, we propose groove width as a new gradient parameter for designing rainbow-trapping gratings and define the range of its validity. We articulate the correlation between the width of narrow grooves and the overlap or the coupling of the evanescent surface plasmon fields within the grooves. In the suitable range (≲150 nm), this width parameter becomes as important as other known parameters such as groove depth and materials composition, but tailoring groove widths is remarkably more feasible in practice. Using groove width as a design parameter, we investigate rainbow-trapping gratings and derive an analytical formula by treating each nano-groove as a plasmonic waveguide resonator. These results closely agree with numerical simulations.