Bahareh Haji-saeed

Photoconductive optically driven deformable membrane under high-frequency bias: fabrication, characterization, and modeling

The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator are described. Device operation utilizes an electrostatically driven pixelated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 mum thick grid of patterned photoresist supports the 2 mum thick aluminized Mylar membrane. A conductive ZnO layer is placed on the backside of the GaAs wafer. Similar devices were also fabricated with InP. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. The device operates as an impedance distribution between two cascaded impedances of deformable membrane substrate, substrate, and electrode. An analysis of devices operation under several bias conditions, which relates membrane deformation to operating parameters, is presented.

Electrically Tunable Surface Plasmon Source for THz Applications

In this paper, we propose a design for a widely tunable solid-state optically and electrically pumped terahertz source based on the Smith-Purcell free-electron laser. Our design consists of a thin dielectric layer sandwiched between an upper corrugated structure and a lower layer of thin metal, semiconductor, or high-electron-mobility material. The lower layer is for current streaming, which replaces the electron beam in the Smith-Purcell free-electron laser design. The upper layer consists of two microgratings for optical pumping, and a nanograting to couple with electrical pumping in the lower layer. The optically generated surface plasmon waves from the upper layer and the electrically induced surface plasmon waves from the lower layer are then coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

An all optically driven integrated deformable mirror device

We demonstrate a technique for actuating micromirrors vertically cascaded on wafer fused GaAs-GaP photodiodes. Unlike traditional actuation schemes, the electrostatic drive of the individual capacitive actuators is addressed optically in this device. Vertical mirror displacements of up to 500 nm were observed using interferometry while addressing the photodetectors with a 5 mW optical signal. Microlenses were used to address a 900 pixel device with patterned conductive pillars and thin film load resistors for each actuator-detector element. This approach can enable realization of faster and denser adaptive optics wave front corrector arrays.

Adaptive filtering with organic photorefractive materials via four-wave mixing

In prior work, we exploited the nonlinearity inherent in four-wave mixing in organic photorefractive materials for adaptive filtering. In this paper, we extend our work further and demonstrate new applications which involve: dislocation, scratches and defect enhancement. With the availability of the organic photorefractive materials with large space-bandwidth product, it should open the possibility of using the adaptive filtering techniques in quality control systems.

Characterization of optical correlation via dynamic range compression using organic photorefractive materials

In prior work, we demonstrate optical correlation via dynamic range compression in two-beam coupling using thin-film organic materials. In this paper, we continue the effort; characterize the performance of this correlator for variety of input. We successfully demonstrated correlation results almost free of cross- correlation and noise for extremely complicated noisy image were the signal image consist of several targets and reference image superposed of many templates.

All optically driven MEMS deformable mirrors via direct cascading with wafer bonded GaAs/GaP PIN photodetectors

Significant progress has been made to realize optically controlled phase correction micro-mirror arrays. The devices consist of silicon nitride spring plate mirrors optically actuated by integrated GaAs P-I-N photodetectors wafer bonded on a GaP platform.

All optically-driven MEMS deformable device via an array of photodetectors

We are in the process of developing an all optically driven, deformable mirror device through the integration of an array of photodetectors with an array of MEMS deformable mirror devices. In this paper we demonstrate the optical actuation of a single-pixel, deformable-mirror MEMS device through a direct cascade with a photodetector. Deformation is quasilinear at low light intensities, and saturates at higher intensities. We also describe the fabrication of an integrated device consisting of an all optically addressed deformable-mirror MEMS suspended over a p-i-n photodetector. Initial demonstration of optical actuation of the deformable mirror using the newly integrated device is also presented. We have fabricated several membrane materials, membrane structures, and photodetector arrays.

Optically Actuated MEMS Deformable Mirror Device

We propose a new design, fabrication procedures and the operating theory for a very low-power optically actuated deformable mirror device. The deformable mirror consists of an array of AlGaAs PIN photo detectors bonded onto a transparent substrate, a thin film resistor, and a suspended membrane

Current injection effects on surface plasmons for a tunable THz source

In this paper, we present simulation results pertaining to our broadband solid-state optically and electrically pumped THz source design. Our design consists of a thin layer of dielectric sandwiched between a nano-grating and a thin film, such as metal, semiconductor, or high electron mobility material. By passing a DC current through the lower layer, a THz emission will be radiated from the nano-grating. We demonstrate preliminary current injection effects on surface plasmons propagating on this device utilizing known analytical surface plasmon formulas and COMSOL Multiphysics finite element analysis software.

Optical correlation via dynamic range compression using organic photorefractive materials

In this paper, we demonstrate optical correlation via dynamic range compression in two-beam coupling using thin-film organic materials. In contrast to the first demonstration, in which it was not possible to demonstrate correlation with complicated input, here we demonstrate correlation with extremely challenging cases involving finger prints, images in clutter, and SAR images. Our correlation results outperform many correlation results, including ones based on optimal filters.