Random projections are used in applications such as compressive sensing, speckle spectroscopy, and recurrent neural networks. Most prior work has used speckle in free-space systems. Here we report results using laser speckle in planar and cylindrical waveguides with the goal of integrating the whole system in a photonic integrated circuit. We demonstrate a compressive sensing RF receiver over the 2-19 GHz band that recovers the amplitude, phase and frequency of one or two RF sinusoids in a 4.5-ns time window. The RF signal is modulated on a wavelength-chirped optical field, derived from a dispersed mode-locked laser pulse, that propagates through a 5-m, 105-micron fiber. The output of the fiber is imaged onto a fiber bundle such that 32 independent measurements of the speckle pattern are made, and differential outputs of pairs of photodiodes are then digitized to give 16 compressive measurements. The frequency resolution in a single pulse is about 100 MHz, but the resolution can be improved to about 20 KHz by using 100 pulses at a 35 MHz rate. A simpler system uses a stable single-frequency laser diode and speckle in a planar waveguide to determine RF frequency to about 100 MHz. Finally, speckle in a multimode waveguide is used as the reservoir in a recurrent neural network to predict an RF time series.
We propose and simulate integrated optical devices for accelerating numerical linear algebra (NLA) calculations. Data is modulated on chirped optical pulses and these propagate through a multimode waveguide where speckle provides the random projections needed for NLA dimensionality reduction.
The end performance of semiconductor optoelectronic devices is largely determined by the carrier dynamics of the constituent base materials. When combined with full-scale numerical models, optical spectroscopy is capable of providing detailed information about carrier generation and dynamics that is essential to accurate analysis of empirical test structure studies, and to translating those results into predictions for device performance. We have applied time-resolved and steady-state luminescence techniques to a variety of III-V materials and reference structures in order to investigate the mechanisms controlling carrier dynamics and to develop diagnostic tools to provide actionable feedback to R and D efforts for improvement and optimization of material/device performance.
We use steady-state and time-resolved spectroscopy to evaluate optoelectronic material quality and obtain detailed information about carrier generation, transport, and relaxation in semiconductor devices and test structures. This report focuses on time-resolved and steady-state photoluminescence of III-V reference heterostructures at temperatures between 4K and 300K in order to investigate the mechanisms limiting carrier lifetime and to develop the capability to provide actionable feedback to research-and-development efforts for improvement and optimization of material properties and/or device performance. We combine the results of photoluminescence experiments with model-based analyses and simulations of carrier relaxation to assess the impacts of defects and interface quality on the relaxation dynamics of photo-generated carriers in double heterostructure test vehicles grown by MOCVD and MBE.
In this work, the optical properties and emission dynamics of core-shell InGaAs/GaAs nanopillars (NPs) have been in-
vestigated using low-temperature photoluminescence (PL) and time-resolved photoluminescence (TRPL). These novel
structures have recently attracted much interest within the silicon photonics scientific community due to their potential
employment as gain medium for monolithically integrated lasers on silicon substrates. The optimization of the emission
properties of these heterostructures is essential to obtain full compatibility with silicon photonics and requires an accurate
tailoring of the pillar geometry (i.e. size, pitch) and composition. Therefore it is critical to gain deeper insight into the
optical and dynamical properties of different NP designs if optimal device performance is to be achieved. The experimental
characterization, carried out on a number of different NP structures with different geometries and compositions, shows that
the time evolution of the emission peak exhibits a strong excitation-dependent blue-shift which can be attributed to the
band-filling effect. Measured emission decay times were strongly geometry-dependent and varied from nanoseconds to
tens of picoseconds. In addition, a dramatic reduction of the decay time was observed for the highest indium concentration
due to the dominant contribution of the strain-induced non-radiative recombination processes.