This paper addresses the intriguing possibilities offered by the combination of superconductor and optical technologies. We review theoretical and experimental studies of superconductor-light interactions which, as a part of the field of nonequilibrium superconductivity witnessed a considerable development over the last fifteen years.
Integrated optoelectronic circuits consists of monolithically integrating high speed electronics with photonic devices such as light emitters and photodetectors on a common substrate. Requirements for optoelectronic integration are being driven by the needs of optical interconnects, optical communication, and optical computing and signal processing. During the past few years significant progress in this technology has been realized due to improvements in material growth, device processing and digital GaAs integrated circuit development. This paper will present a state-of-the-art review of this technology, its application to high speed systems and make projections for future developments.
Very high quality GaxInl_xAsyPl_y-InP heterojunctions, quantum wells and superlattices have been grown by LP-MOCVD. The InP epilayer with a residual doping levels as low as 3x1013cm-3, with Hall mobility as high as 6000 cm2V-1s- 1 300 K and 200.000 cm2V-1s-1 at 50Ã‚Â° K have been grown. Photoluminescence at 2 K showed that it is the purest InP epilayer has been reported in the litterature, with zero compensation ratio. GaInAs-InP hetero-junction with electron mobility as high as 12000 cm2V-1s-1 at 300Ã‚Â°K and 260.000 cm2V-1s-1 at 2Ã‚Â°K with a carrier concentration of 3x1014cm-3 have been measured. The successful mono-layer epitaxy of Ga0.5In0 5As/InP heterostructures by alternating the growth of n(GaAs) and n(InAs) atomic layers. Such structures are designed as (GaAs) (InAs) . The influence of parameters such as n or the introduction of a purging time between the InAs-GaAs monolayers have been investigated. Low temperature photoluminescence experiments showed that (GaAs)n(InAs)n/InP multiquantum wells had a better uniformity in composition and thickness than the conventional Ga0.47In 0.53 As/InP system.
Image data compression is one of the oldest but still very active area of research in image processing. The digital representation of an image requires a very large number of bits. The goal of image data compression is to reduce this number, as much as possible, and reconstruct a faithful duplicate of the original picture. Early efforts in image coding, solely guided by information theory, led to a plethora of methods. The compression ratio reached a plateau around 10:1 a couple of years ago. Recent progress in the study of the brain mechanism of vision and scene analysis has opened new vistas in picture coding. Directional sensitivity of the neurones in the visual pathway combined with the separate processing of contours and textures has led to a new class of coding methods capable of achieving compression ratios as high as 100:1.
The increasing needs for long links high bit rate telecommunications systems and for sophisticated guided wave arrangements for fiber sensors led to a rapid evolution of the Integrated Optic technology. Briefly speaking, many progresses have been reported in two main directions. In the first, LiNb03 based waveguides by Ti in diffusion were used to demonstrate various components from low loss high speed modulators or matrix switch arrays to specific chips for fiber sensors like the fiber gyroscope. As a matter of fact, several of these devices begin to be commercially available from different companies. In the second, waveguides are fabricated in semiconductor materials and rapid progresses in the growth techniques led to high quality devices in both GaAs and InP systems leading to realistic previsions for complete monolithic integration. The range of devices already demonstrated is quite impressive as it comprises broadband modulators and switches, multiplexers/demultiplexers, tunable filters, frequency shifters, polarization controllers, switching matrices, multifunction chips for sensors and even some first try of real optoelectronic integration. As a matter of fact, many materials have been used and considered for integrated optics applications. If some kind of active device has to be realized, in general, it is necessary to employ basic materials with the desired properties unless "active" overlayers are used (such as non linear organic materials...). In that paper, the basic properties of integrated optic devices will outlined by giving typical examples in the two main present technologies : LiNb03 and semiconductors.
This paper reviews the progress in the development of infrared image sensors with Schottky-barrier detectors. Schottky-barrier focal plane arrays (FPAs) are the only infrared imagers that are fabricated by the well established silicon VLSI process. Therefore, at the present time they represent the most mature technology for large-area high-density focal plane arrays for many SWIR (1 to 3 μm) and MWIR (3 to 5 μm) applications. Infrared line sensing arrays with up to 4096 x 4 elements and area sensing arrays with up to 512 x 512 elements have been reported. PtSi Schottky-barrier detectors (SBDs) represent the most established SBD technology for applications in the SWIR and MWIR bands at an operating temperature of about 80K. These SBDs can be designed for operation at 77K with a dark current density in the range of 1.0 to 20 nA/cm2. Pd2Si SBDs were developed for operation with passive cooling at 120K in the SWIR band. IrSi SBDs have also been investigated to extend the application of Schottky-barrier focal plane arrays (FPAs) into the LWIR (8 to 10 μm) spectral range. Because of very low readout noise, the IR-CCD imagers with PtSi SBDs which have quantum efficiency of .5 to 1% at 4.0 gm are capable of 300K thermal imaging with a noise equivalent temperature (NEAT) of less than 0.1K for operation at 30 frames/s and f/1.5 to f/3.0 optics.
The III -V compound semiconductors comprise an important class of materials for optoelectronic device applications. Despite this, it has not as yet proven possible to form insulators on any of these materials with a quality comparable to what can be achieved on Silicon using thermal Si02. This in turn has resulted in severe restrictions in device and integrated circuit development due to the reduced design flexibility imposed by this more limited technology base.
Layered synthetic microstructures (LSMs), a subset of multilayer coatings, are coming into widespread use in the soft x-ray region because of the favorable optical properties of materials at those wavelengths. In addition to the simple multilayered structures, Fabry-Perot etalons are also being designed and constructed. The design possibilities are not so favorable at the longer wavelengths (VUV) because of the increased absorptance of the spacer materials. A small number of elements are potentially useful as spacer materials in the VUV. Magnesium, with its critical wavelength at about 1200 Å may be useful in designing LSMs for wavelengths somewhat shorter. It is a difficult material to evaporate in vacuum, however, and its tendency for interdiffusion with materials used for nodal layers has yet to be determined. Aluminum, germanium, and silicon have their critical wavelengths grouped around 800 Å so that the choice between them might depend heavily on their tendency to interdiffuse with the nodal layer material rather than their optical properties. Beryllium could be used for LSMs to wavelengths as long as about 500 Å but the difficulties and dangers in using that element, plus the availability of other elements that can be used to even longer wavelengths, militates against it. This paper will review the principles of LSMs, discuss the possible materials for use in LSMs in the VUV, and will show some of the design efforts currently being carried out.
The recent progress in semiconductor heterostructure devices is reviewed. The field of electronic devices, while relying on rather mature concepts, is evidencing progress towards the intrinsic materials and structure performance. This is due to progress in technological manufacturing steps allowing device miniaturization and optimization. The field of optoelectronic devices relies on newer, more fundamental concepts modifications and witnesses the emergence of materials with unsurpassed performances. These are fundamentally based on low-dimensional physical concepts.