An innovative architecture for compact, integrated volume holographic memories is described. It is based on phase-conjugate readout and on a modulator -detector -memory array implemented in a silicon integrated circuit. The lensless memory module sustains dynamic read-write holograms by periodic refreshing. The integrated circuit is described and experimentally characterized. Holograms were stored in a prototype storage module that uses a 30 ± -cut BaTiO 3 crystal and the 90 ± recording geometry. As many as three angularly multiplexed holograms were periodically refreshed and subjected to .40% decay from exposure to the reference beam over 50 to 100 cycles. Experimental data are presented. © 1997 Optical Society of AmericaThe use of counterpropagating reference beams for recording and readout in volume holographic memories permits compact storage modules 1 -3 with lensless signal-beam paths. The reference beam for readout is the conjugate of the reference beam for recording. We refer to this technique as conjugate readout. Figure 1 shows a compact module that uses angular multiplexing. The module is composed of a photorefractive crystal in which holograms are stored, a pair of liquidcrystal beam steerers (one of which is hidden behind the crystal) that is responsible for angularly multiplexing holograms in the crystal, and an optoelectronic integrated circuit (OEIC) that merges the functions of a ref lective spatial light modulator (SLM ) for recording holograms and a detector array for readout. One writes holograms by letting the signal beam modulated by the OEIC interfere with the plane wave coming from the back of the crystal. Holograms are read out by illumination of the crystal from the front with a counterpropagating plane wave, which is the conjugate of the reference wave used to write holograms. The resulting conjugate reconstruction self-focuses back onto the OEIC. The conjugate reference can be produced by a phase-conjugate mirror, 2 or it can simply consist of a counterpropagating beam in the case of plane waves.

Besides high-power light-emitting diodes (LEDs) with dimensions in the range of mm, micro-LEDs (μLEDs) are increasingly gaining interest today, motivated by the future applications of μLEDs in augmented reality displays or for nanometrology and sensor technology. A key aspect of this miniaturization is the influence of the structure size on the electrical and optical properties of μLEDs. Thus, in this article, investigations of the size dependence of the electro-optical properties of μLEDs, with diameters in the range of 20 to 0.65 μm, by current–voltage and electroluminescence measurements are described. The measurements indicated that with decreasing size leakage currents in the forward direction decrease. To take advantage of these benefits, the surface has to be treated properly, as otherwise sidewall damages induced by dry etching will impair the optical properties. A possible countermeasure is surface treatment with a potassium hydroxide based solution that can reduce such defects.

We examine the present state of holographic random access memory (HRAM)

A new method for fabricating analog light modulators on VLSI devices is described. The process is fully compatible with devices fabricated by commercial VLSI foundries, and the assembly of the modulator structures requires a small number of simple processing steps. The modulators are capable of analog amplitude or phase modulation and can operate at video rates and at low voltages (2.2 V). The modulation mechanism and the process yielding the modulator structures are described. Experimental data are presented. © 1995 Optical Society of America The development of highly integrated spatial light modulators and smart pixel arrays based on VLSI circuitry and liquid-crystal devices has recently made signif icant progress.

We show that a reduction in the pulse distortion caused by chromatic dispersion can be achieved through pulse shaping. We argue that a simple binary phase mask in the Fourier plane of the laser spectrum can improve the transmission of short pulses in a dispersive channel through reduced broadening. The argument was tested experimentally, and a good agreement was found with the theory.Optically transmitted pulses in a single-mode channel can be severely distorted and broadened as the result of chromatic dispersion. Several methods have been used to overcome the distortion of the pulse envelope caused by group-velocity dispersion (GVD): a grating pair, 1 a Fabry -Perot interferometer, 2 a phase conjugator, 3 a laser modulated with a periodic injection current sweep, 4,5 and time lenses for Gaussian-shaped pulses. 6In soliton propagation self-phase modulation compensates the GVD of a hyperbolic secant pulse shape. 7With z denoted as the position along the dispersive channel, y g as the group velocity, and T t 2 z͞y g as the delayed time, the inf luence of GVD on the complex temporal pulse electric field u͑T , z͒ envelope is given bywhere U ͑v, 0͒ is the Fourier transform of u͑T , 0͒, v is the angular frequency (relative to the laser's center frequency v 0 ), Dv is the spectral width corresponding to the pulse, and b 2 ≠ 2 b͞≠v 2 j v0 is the GVD per unit length.Recently 9,10 the possibility of pulses that do not disperse by virtue of their unique shaping was introduced. Based on the time-space analogy Rosen et al.as the initial pulse envelope to reduce the effect of GVD. a, b, f , and p . 2 are real positive parameters of the pulse. This pulse ͑u u C , Dv `͒ propagates along a dispersive channel at a distance of Dz Ӎ 2 p 2p b 2 f 2 p͓4͑1 1 p͔͒ ͑22p͒/p ͞b 2 while maintaining a nearconstant peak value of ju C ͑0, z͒j.The spectrum of u C iswhere T b b 2 f ͞b, T a b 2 f ͞a, and the power p 4 has been chosen as an example.In what follows we describe an experimental investigation of the possibility of creating dispersion-resistant pulses through pulse shaping and show that it can be accomplished by use of a simple binary phase mask in the spectral plane. We find that using a binary approximation of the initial pulse spectrum [Eq. (3)], U B ͑v, 0͒ U C ͑v, 0͒͞jU C ͑v, 0͒j, still leads to a considerable reduction in pulse distortion. This approximation enables us to use a binary (0 or p) phase mask instead of a complicated amplitude and phase filter.The pulse field U B and its capability of maintaining its form without distortion when traveling through a dispersive channel depend on the ratio T b ͞T a . We find numerically that T b ͞T a p 8͞5 is suff icient in that the intensity I B ͑T 0, z͒ ju B ͑0, z͒j 2 of the center of the symmetric pulse and its shape remains at a nearly constant height over the interval Dz Ӎ 8T 2 b ͞b 2 near z 0. One may increase this interval by increasing the ratio T b ͞T a , yet increasing the interval spoils the constancy of I B ͑0, z͒ in the region of interest. At z 0 the pulse has a main lobe wid...