High-speed joint-transform optical image correlator using GaAs/AlGaAs semi-insulating multiple quantum wells and diode lasers

Photorefractive two-beam coupling joint transform correlator: modeling and performance evaluation

The photorefractive two-beam coupling joint transform correlator combines two features. The first is embedded semi-adaptive optimality, which weighs the correlation against clutter and noise in the input, and the second is the intrinsic dynamic range compression nonlinearity, which improves several metrics simultaneously without metric trade-off. Although the two beam coupling correlator was invented many years ago, its outstanding performance was recognized on only relatively simple images. There was no study about the performance of this correlator on complicated images and using different figures of merit. In this paper, the study is extended to more complicated images. For the first time, to our knowledge, we demonstrate simultaneous improvement in metrics performance without metric trade-off. The performance was evaluated compared to the classical joint transform correlator. A typical experimental result to validate the simulation results was also shown in this work. The best performing operation parameters were identified to guide the experimental work and for future comparison with other well-known optimal correlation filters.

Real-time contrast-enhanced holographic imaging using phase coherent photorefractive quantum wells

We demonstrate wide-field real-time and depth-resolved contrast enhanced holographic imaging (CEHI) using the all-optical phase coherent photorefractive effect in ZnSe quantum wells. Moving objects are imaged at large depth-of-field by the local enhancement of a static reference hologram. The high refresh rate of the holographic films enables direct-to-video monitoring of floating glass beads and of living Paramecium and Euglena cells moving in water. Depth resolution is achieved by tilting the incident laser beam with respect to the normal of the cuvette. This creates double images of the objects, which are analyzed geometrically and with Fresnel diffraction theory. A two-color CEHI set-up further enables the visualization of a concealed 95 µm thick wire behind a thin layer of chicken skin.

Resonant photorefractive effect in InGaAs/GaAs multiple quantum wells

Semi-insulating InGaAs/GaAs multiple quantum wells are fabricated by metal-organic vapor-phase epitaxy and proton implantation. Two-wave mixing gain and four-wave mixing diffraction efficiency are measured at wavelengths of 0.91-0.94microm in the Franz-Keldysh geometry. We observe a large photorefractive effect caused by the excitonic electro-optic effect. The maximum diffraction efficiency reaches ~1.5x10(-4) .

Direct-to-video holographic 3-D imaging using photorefractive multiple quantum well devices

Customised photorefractive quantum well devices have been developed for real-time video acquisition of coherence-gated, three-dimensional images. Holographic imaging with direct video capture has been demonstrated. The technique has been applied to 3-D imaging through turbid media with 50 mm transverse and 60 mm depth resolution being achieved using near infrared light through a phantom of 13 mean free paths scattering depth. Spectrally-resolved holographic imaging has also been demonstrated.

Direct-to-video holographic readout in quantum wells for three-dimensional imaging through turbid media

Customized photorefractive quantum-well devices have been developed for real-time video acquisition of coherence-gated, three-dimensional images in turbid media. Large-field-of-view holographic imaging with direct video capture is now possible. We have evaluated the role of intensity-limited device performance in Fourier-plane and image-plane holography in such devices and, using near-infrared light, have imaged through turbid phantoms of 13 mean free paths' scattering depth with 50-microm transverse and 60-microm depth resolution.

Optical correlator that uses cesium vapor

We obtain the correlation pattern between two amplitude-modulated input images of 36 and 280 random black and white pixels, using the standard degenerate four-wave-mixing geometry of 852-nm optical beams in a 1-mm-thick cesium-vapor cell. The total optical input power is 3.2 mW to obtain 0.4 nW of power in the correlation pattern. We verified that the buildup time of the four-wave-mixing signal is ~30 ns. Using the random patterns, we analyze the performance of the cesium optical correlator in terms of the number of pixels that can be processed and the number of photons per pixel used. We show how to scale our experimental results for the efficiency of the cesium correlator to images containing a larger number of pixels.

Adaptive bacteriorhodopsin-based holographic correlator for speed measurement of randomly moving three-dimensional objects

An adaptive correlator system is presented that uses a bacteriorhodopsin film as the active holographic material. Because M-type holography with bacteriorhodopsin films is used, the TV frame rate is met at fairly low intensities. No limitations arising from the heterodyne operation of the dual-axis joint-Fourier-transform correlator were observed. The system's capability to monitor autonomously the speed of an object moving randomly in the whole viewing field of a video camera is demonstrated.

Time-to-space mapping of femtosecond pulses

We report time-to-space mapping of femtosecond light pulses in a temporal holography setup. By reading out a temporal hologram of a short optical pulse with a continuous-wave diode laser, we accurately convert temporal pulse-shape information into a spatial pattern that can be viewed with a camera. We demonstrate real-time acquisition of electric-field autocorrelation and cross correlation of femtosecond pulses with this technique.