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Residual speckles due to aberrations arising from optical errors after the split between the wavefront sensor and the science camera path are the most significant barriers to imaging extrasolar planets. While speckles can be suppressed using the science camera in conjunction with the deformable mirror, this requires knowledge of the phase of the electric field in the focal plane. We describe a method which combines a coronagraph with a simple phase-shifting interferometer to measure and correct speckles in the full focal plane. We demonstrate its initial use on the Stellar Double Coronagraph at the Palomar Observatory. We also describe how the same hardware can be used to distinguish speckles from true companions by measuring the coherence of the optical field in the focal plane. We present results observing the brown dwarf HD 49197b with this technique, demonstrating the ability to detect the presence of a companion even when it is buried in the speckle noise, without the use of any standard "calibration" techniques. We believe this is the first detection of a substellar companion using the coherence properties of light., Comment: 32 pages, 11 figures. Accepted for publication in MNRAS

This study assessed the solute permeability of a family of UV and moisture cured acrylates-based adhesives during in vitro ageing in pH 7.4 buffer. Acrylates have a potential role in bone fracture fixation, but their inability to allow microsolute exchange between the fractured bone surfaces may contribute to ineffective healing. Cyclic voltammetry and chronoamperometry were used to determine the diffusion coefficients for various electrochemically active probe molecules (O2, H2O2, acetaminophen, catechol, uric acid and ascorbic acid) at proprietary acrylic, urethane – acrylate and cyanoacrylate adhesives. All adhesives proved to be impermeable for up to 9 days ageing, following which a near-exponential increase in permeability resulted for all solutes. At 18 days, the diffusion coefficients were in the range of 10−5 cm2s−1 for O2 and H2O2 and 10−6 cm2s−1 for the organic solutes; no transport selectivity was seen between the latter. Adhesive joint strength showed a direct, inverse, correlation with permeability, with the more hydrophilic cyanoacrylates showing the greatest loss of strength. Adhesive permeabilisation does not appear to be compatible with the retention of bonding strength, but it serves as a new non-destructive predictor of adhesion strength change during ageing and practical use., Graphical abstract Image 1

A common clinical strategy for relief of pressure sores is theuse of pressure redistributing beds, mattresses and overlays. Alarge-scale mattress replacement was scheduled for 1998 andthis led to a multi-professional review of the pressure-relievingproperties of a range of foam mattresses. Mattresses weresubjected to 48 h indentor testing. Attention was paid to theabsolute peak pressures and the percentage change relative tothe initial readings. Having achieved a high ranking in indentortesting, selected mattresses were placed in the clinical settingfor a one-week period. A purchasing decision was made basedupon indentor testing, clinical evaluation and by examining price.For confirmation, a number of other major users were consulted.The 13 mattresses provided variable pressure relievingproperties. A process of exclusion was adopted in order to finda subset suitable for clinical evaluation. The standard NHSmattress performed poorly. One type was dual-function wherebythe mattress was intended to be matched for patient weight,having a "heavy" and a "light" side (deemed to be impractical).Some generated high initial pressures and were removed. Wediscarded mattresses that produced an increase in pressure overthe 24 h loading or that responded poorly after the rest period.The remaining mattresses were deemed suitable, on an equalbasis, for further testing. Three mattresses were placed on clinicaltrial for a one-week period, all performing satisfactorily. Pricewas examined in the context of manufacturers' guarantee usedas an indication of mattress life. On the basis of these findings,the team of nurses and engineers were able to make a purchasingrecommendation. We are confident that this will lead to fewerpressure sores, improved care and better patient outcome.

Metal press-fit cups and shells are widely used in hip resurfacing and total hip replacement procedures. These acetabular components are inserted into a reamed acetabula cavity by either impacting their inner polar surface (shells) or outer rim (cups). Two-dimensional explicit dynamics axisymmetric finite element models were developed to simulate these impaction methods. Greater impact velocities were needed to insert the components when the interference fit was increased; a minimum velocity of 2 m/s was required to fully seat a component with a 2 mm interference between the bone and outer diameter. Changing the component material from cobalt-chromium to titanium alloy resulted in a reduction in the number of impacts on the pole to seat it from 14 to nine. Of greatest significance, it was found that locking a rigid cap to the cup or shell rim resulted in up to nine fewer impactions being necessary to seat it than impacting directly on the polar surface or using a cap free from the rim of the component, as is the case with many commercial resurfacing cup impaction devices currently used. This is important to impactor design and could make insertion easier and also reduce acetabula bone damage.

Low-loss (1.4-cm(-1)) single-mode rib waveguides in Al(x)Ga(1-x)As heterostructures are fabricated by liquid phase epitaxy, double anodization, and photolithographic techniques. Switching of optical channels between adjacent waveguides is accomplished with directional coupler switches controlled with electrodes laid over an isolating dielectric, making a metal-oxide-semiconductor (MOS) configuration. Complete switching is achieved with20 V applied to a stepped Deltabetareversal electrode configuration. A 2 x 4 switching matrix with low-loss lateral offsets of the waveguides is demonstrated. By laying out several optical switching and guiding experiments within a 128-mum stripe, we show that independent optical circuits can be packed with adequate optical isolation using centerline separations approximately 10 microm.

This paper reports the effects of a synthetic bone substitute and bone allograft on cortical bone repair in an experimental model. To test the hypothesis that bovine trabecular bone matrix, BBM, can enhance the repair rate of cortical bone, osteotomies were created in the rabbit fibula and filled with either allograft or BBM particulates or left empty as controls. At five weeks post-surgery, mechanical tests and histological evaluations were performed. No significant differences were observed in the mechanical properties of the healing bone in the three animal groups (n=6). Histologically, the medullary cavity was obstructed and the cross-sectional area ratio of the osteotomies to intact bone was approximately 3 : 1. Highly significant area differences were observed between the intact bone group and both the BBM and the allograft groups (p0.001). At the junction between the original bone and the newly formed bone, both woven and lamellar bone microstructures were prevalent. However, in the BBM filled defects, the woven bone microstructure was not ostentatious. It is concluded that failure to demonstrate significantly differences between the treatments were due to the small sample sizes and or the efficacy of the tensile analysis.

Titanium-zirconium based alloys containing a small amount of niobium were investigated in order to evaluate their possible use as biomedical materials. Zirconium, which belongs to the IVa group, is known to have good corrosion resistance and biocompatibility similar to titanium. As the titanium-zirconium system shows a complete solid solution, a wide variation of alloy design is available and large quantities of solid-solution hardening must be possible. Niobium, having a beta-phase stabilizing effect, was chosen as a ternary element in order to control desirably the microstructure. There have been no reports which suggest its harm to a living body. The alloys containing 2% or 3% niobium showed the highest hardness value after aging heat treatment at 773 K. In contrast to this, no alteration of hardness was seen in specimens aged at 1073 K. Through conventional X-ray diffractometry and in situ X-ray analysis using a hot stage, beta-phase precipitation in the A matrix was identified. From the above results, it is concluded that alloys containing 2%-3% niobium are hopeful candidates for new kinds of biomedical alloys, when they are heat treated under suitable conditions.

Breaking gravity waves are studied in a wave tank at small grazing angles (4.5/spl deg/-11/spl deg/) where all four polarization elements (HH, VV, HV, VH) are simultaneously measured. Temporally averaged Doppler spectra are obtained for mechanically-generated 4 m breaking waves of various energies. The authors describe the dependence on breaking-wave energy of the parameters describing the backscatter. The results of grazing angle dependence of the backscatter are also shown and discussed.

Tenocytes detect mechanical stimuli in vivo, and respond through mechanotransduction pathways to initiate matrix remodelling in tendons. Due to the crimped nature of tendon fascicles, the strain field throughout is non-homogeneous. The present study has developed a means to quantify the local strain fields within a fascicle by monitoring the relative movement and deformation of fluorescently labelled tenocyte nuclei. A stage mounted test rig was designed to apply tensile strain to fascicles. Rat tail and bovine extensor tendons were harvested for analysis, and the cell nuclei stained and visualised using an inverted confocal microscope. As the fascicles were subjected to gross strains of up to 5%, the movement of selected tenocyte nuclei were recorded. Results from a series of cell nuclei from both tendon sources revealed that local strains were significantly less than the applied strain. The nuclei length to width ratio, an indicator of cell deformation, also increased with applied strain, most significantly between 2 and 3% applied strain.

Fibroblasts within tissues are exposed to a dynamic mechanical environment, which influences the structural integrity of both healthy and healing soft tissues. Various systems have been proposed to subject such cells to mechanical stimulation in culture. However the diverse nature of the studies, in terms of the strain profiles and the cell types, makes direct comparisons almost impossible. The present study addresses this issue by examining the metabolic response of two cell types subjected to three well defined strain profiles.A young fibroblast cell population, represented by HuFFs, showed both greater cell proliferation and collagen production than adult dermal fibroblasts under unstrained conditions. The three strain profiles produced differing effects on both cell types. Uniaxial strains enhanced [(3)H]-thymidine incorporation for both cell types, whilst biaxial strains either inhibited or had no effect on its incorporation. In contrast, [(3)H]-proline incorporation was inhibited under biaxial and uniaxial strains for the adult fibroblasts, whilst the HuFF cells showed a small increase in proline incorporation under non-uniform and uniaxial strains.

We utilized AO to discover a moon around asteroid 45 Eugenia by use of the PUEO AO facility at CFHT. With PUEO we performed a search for asteroidal satellites among two dozen asteroids, achieving moderate Strehl ratios (35%) and FWHM of about 0.12' at H band. During this survey, we detected a faint close companion to 45 Eugenia. The satellite was 6.14 magnitudes (at 1.65 micrometer) fainter and located at most 0.75' from Eugenia. Without the ability of AO to sharpen the contrast and increase the resolution to 0.1', the detection of this companion would have been impossible with ground-based telescopes. The companion was found to be in a 1200 km circular orbit with a period of 4.7 days. We discovered that the bulk density of the large (215 km) asteroid 45 Eugenia is a surprisingly low 1.2 g/cm3. This has lead to the exciting possibilities that either this main belt asteroid is a burned out comet or has a hollow 'rubble-pile' structure.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The IRTF is a 3.0 meter, f/38, infrared optimized, cassegrain telescope operated under contract from NASA with the primary mission of providing ground-based support for NASA's planetary missions. We are currently in the design and construction phase of a 36 element, curvature-based, natural guide star, adaptive optics facility installation for the IRTF. System architecture will be modeled on the highly successful AO systems developed at the University of Hawaii. The system should achieve an AO efficiency, q >= 0.4. The Strehl ratio is expected to exceed 0.8 in the K band. We estimate a limiting guide star magnitude for full correction of mR equals 14.4.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The non-circular shape of the Keck telescopes primary mirror, combined with the fact that the telescope is on an alt/az mount with the adaptive optics system on the left Nasmyth platform, means that as the telescope tracks a star field the hexagonal pupil image rotates on the wavefront sensor camera and on the deformable mirror. This creates a need for a dynamic control strategy. The control matrix, the list of which subapertures are sufficiently illuminated and the list of which actuators are active and which are slaved, all must change on the fly, with the loops closed and without perturbing a science observation in progress. This control strategy must also be robust in the presence of modest pupil translation. These needs are met in the Keck AO system by the Pupil Rotation Compensation (PRC) software tool. The PRC software is responsible for maintaining system parameters that are functions of the pupil position and orientation. This paper will present the details of the PRC software design including algorithms used for selecting active subapertures, dealing with variable subaperture illumination, calculating control matrices, and slaving actuators outside the pupil illuminated area on the deformable mirror.

The wavefront controller for the Keck Observatory AO system consists of two separate real-time control loops: a tip-tilt control loop to remove tilt from the incoming wavefront, and a deformable mirror control loop to remove higher-order aberrations. In this paper, we describe these control loops and analyze their performance using diagnostic data acquired during the integration and testing of the AO system on the telescope. Disturbance rejection curves for the controllers are calculated from the experimental data and compared to theory. The residual wavefront errors due to control loop bandwidth are also calculated from the data, and possible improvements to the controller performance are discussed.

For CCD wavefront sensor pixel input and processing the Adoptics software in use at the Mt. Wilson 100-inch Hooker telescope utilizes hand-crafted assembly code to maximize use of the Texas Instruments C40 DSP processor's bandwidth. For flexibility the software is built around a conceptual framework that allows compact implementation of wavefront sensor-specific operations as well as adaptability to different CCD architectures. Designed for use in multi-DSP systems, such as those used at Mt. Wilson, the software framework will support many different DSP network topologies and facilitates distributing pixel-processing operations across the network.

The Adoptics software used with the Hooker telescope's ADOPT adaptive optics system implements real-time control on a network of eight Texas Instruments C40 40Mhz DSP processors. System inputs and outputs consist of a 32 port 4 fiber wavefront sensor CCD with 32 X 32 pixels, a tilt mirror and a deformable mirror of which 241 elements are actively controlled. The network os eight DSP processors is configured as two cross-connected rings of four processors each. Four input sites perform intensity and gradient calculations immediately on incoming pixels as well as passing pixels on to adjacent sites for parallel calculations.

This paper describes the construction and testing of the Shack-Hartmann wavefront sensor camera for the new MMT adaptive optics system. Construction and use of the sensor is greatly simplified by having the 12 X 12 lenslet array permanently glued to the detector array, obviating the need for any further realignment. The detector is a frame transfer CCD made by EEV with 80 by 80 pixels, each 24 microns square, and 4 output amplifiers operated simultaneously. 3 by 3 pixel binning is used to create in effect an array of quad-cells, each centered on a spot formed by a lenslet. Centration of the lenslet images is measured to have an accuracy of 1 micrometers rms. The maximum frame rate in the binned mode is 625 Hz, when the rms noise is 4.5-5 electrons. In use at the telescope, the guide star entering the wavefront sensor passes through a 2.4 arcsec squares field stop matched to the quall-cell size, and each lenslet samples a 54 cm square segment of the atmospherically aberrated wavefront to form a guide star image at a plate scale of 60 micrometers /arcsec. Charge diffusion between adjacent detector pixels is small: the signal modulation in 0.7 arcsec seeing is reduced by only 10 percent compared to an ideal quad-cell with perfectly sharp boundaries.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Keck AO system is nearing completion and is nearly ready for system integration in the optics laboratory at Keck Headquarters. because of the ambitious scientific objectives of this project, the AO system is quite complex in design. The optics bench alone has 33 motion control axes, and potentially 6 image planes. Calibration will play a major role in making the AO system function as planned. We have identified approximately 35 separate calibration procedures that will be needed to be performed during the integration phase in the laboratory. Many of these procedures are quite straightforward. Other calibrations are quite involved and are mini 'research projects' in themselves. It is this last category that will be discussed in this paper.

The Multiple Mirror Telescope on Mt. Hopkins will soon be upgraded to a single 6.5 m primary mirror.An adaptive- optical system, featuring a thin-shell, adaptive-secondary mirror with 330 voice-coil actuators is being developed for this new telescope. The thin-shell mirror is supported by a thick, concave aluminum substrate which also holds the actuator control and monitoring electronics and serves as the reference surface. With the actuator electronics dissipating heat into the substrate, the thermal behavior of the aluminum reference plate becomes as important issue. This paper presents results form tow experiments designed to determine the thermal behavior of the reference plate.

The cassegrain adaptive optics system (ADOPT) on the Mount Wilson 100-inch telescope has been in operation now since June of 1995. This report chronicles the ongoing performance improvements, the drive towards unassisted use by visiting observers, and some significant science results of this system. The last includes: observations Mira with its companion and other red giants, many observations of asteroids, and the satellites of Jupiter and Saturn, the planets Uranus and Neptune, and of course, double stars. Objects with magnitudes from V=0.0 to V=13.7 have served as natural guide stars, with no change in optics or filters needed over this range. Resolution of 0.07 arcsec is routine on a bright object in good seeing, with 0.058 arcsec at B band as the best performance to date. Coronagraphic and spectroscopic additions are planned for the system.

The strength of knots tied at laparoscopy was compared with that of hand-tied knots.The force needed to undo or break eight types of knots that were tied in fresh postmortem human stomachs was measured. The knotting performance of nylon, polyglactin 910, braided silk, polytetrafluoroethylene, braided polyester fiber, braided polyester suture, polyamide 66, and polydiaxone was also compared.Measurements of knot strength of two to six half hitches (hand tied) showed that four half hitches were necessary to tie a secure nonslipping knot with most monofilament threads (nylon, polytetrafluoroethylene, braided polyester suture, and polyamide 66), while three half hitches were adequate to secure a knot when polyglactin 910, braided polyester fiber, silk, and polydiaxone were used. Additional throws did not increase knot strength once the knot no longer slipped (p = NS). Some commonly tied knots, three half hitches and surgical knots at laparoscopy were weaker than the same hand-tied knots (p0.05) but an additional throw increased knot security (p0.01). Differences between laparoscopic and hand-tied knot strengths were greater for monofilament than multifilament threads. There was a wider distribution of strengths for laparoscopically tied than hand-tied knots. Four half hitches were the most secure configuration for laparoscopically tied knots and were significantly stronger than three half hitches and surgical knots (p0.01). The extracorporeally tied slipknot (Roeder loop) was significantly less secure than four half hitches (p0.05).This study demonstrates that laparoscopically formed knots may be weaker than those tied by hand and shows that improvements in knot strength at laparoscopy can be achieved by choice of optimal knot configuration for different suture materials.

Since June of 1994 we have been operating and improving a natural-guide-star adaptive optics system on the Mount Wilson 100-inch telescope.1,3 The system is routinely operated by one person plus a telescope operator. First astronomical observations have achieved image profiles with a full-width-at-half-max (FWHM) of 0.068 arcsec, using a silicon CCD with no wavelength discrimination (Fig. 1).

In January 1994, we began construction of a modern adaptive optics system for the newly refurbished 100-inch telescope. The design philosophy of the adaptive optics system is to achieve a working system in the visible in a short time at relatively low cost. This means wavefront sensing with natural guide stars and implementation at the bent Cassegrain focus of the telescope. The system has an integrated wavefront sensor and finder camera, and is automated for one-person operation. It uses off-the-shelf components where possible. The deformable mirror, which has 241 actuators, is on loan from the U.S. Air Force. The use of an existing mirror imposes constraints that have driven some of the design considerations. The system is operating at the telescope, with early results described below.

Urinary stones exhibit a variable response to extracorporeal Shockwave lithotripsy (ESWL) and endoscopic lithotripsy. Although fragmentation is affected by the patient’s size, the type of Shockwave generating system, mode of localisation etc, it is also known that the physico-chemical characteristics of calculi affect treatment outcome. However it is still unclear why some stones break more readily than others. Although chemical composition has been proposed as an important factor, a literature review revealed conflicting results.

We have mounted an early adaptive optics system, the Atmospheric Compensation Experiment (ACE), on the 60-inch telescope at Mount Wilson Observatory in California in a program designed to investigate the performance of ACE at an astronomical site and to evaluate the usefulness of adaptive optics for astronomy. Despite its development as a non-astronomical instrument, ACE has produced positive results, including the obtaining of images of single and double stars with a resolution (full-width half-maximum) of 117 milliarcseconds at 700 nm. Improvement of image quality is obtained for guide objects with a B magnitude brighter than 5.9. To deepen this limiting magnitude, we have embarked on a low-noise high-speed CCD fabrication project jointly with JPL. First devices have been fabricated. We have applied post- processing techniques borrowed from speckle methodology to the adaptive optics images, and find that the pre- and post-processing techniques complement each other powerfully. We conclude that an adaptive optics system designed specifically for visible-wavelength astronomy would be a low-order system with good site thermal control, combined with post-processing. Such a system could be effective, robust and relatively low cost.

In this paper, we describe TRW's latest version of the scanning laser slope gauge (SLSG) which was used to characterize the sea surface in a recent ocean experiment. The SLSG, capable of measuring the spatial distribution and temporal evolution of the surface slopes of a patch of ocean, provides ground truth data which form a quantitative basis for the understanding of ocean wind-wave interactions and the development and validation of radar scattering models relevant to ocean remote sensing.

A three-color IR photometer suitable for speckle imaging or for traditional fast or slit-scan photometry is described, with special attention given to the photometer's scanning and relay optics, the dewar, the electronics, and the data acquisition and reduction hardware and software. The system is able to acquire sets of object and sky scans on three colors simultaneously, while concurrently performing a Knox-Thompson speckle analysis on the incoming data. The slit-scan photometry operation mode allows observations of objects too faint for speckle imaging. To date, the system was used to observe more than 20 T Tauri stars, several evolved stars, numerous binaries, and G29-38, with good agreement with published and known results for binary observations and those of NML Cyg and IRC + 10216.

Analysis of recent small-grazing-angle microwave backscattering data indicate that the Bragg mechanism alone cannot explain the experimental results. The authors investigate the issue of scattering mechanisms by studying the lineshapes of the backscattered microwave power spectra. It is found that spectral lineshapes can be decomposed into physically meaningful basis functions which are Gaussian, Lorentzian or Voigtian. Generally, the spectral component corresponding to the lower frequency peak in the power spectral density (PSD) of the vertical polarisation is well described by a Gaussian profile, while the spectral component due to the higher frequency peak in the horizontal polarisation PSD is well described by either a Lorentzian or a Voigtian profile, depending on the size of the radar footprint. These quantitative results provide compelling evidence that several entirely different mechanisms, corresponding to different surface features of the dynamic sea surface, are active in contributing to microwave backscattering returns. These mechanisms comprise: first, scattering from free Bragg waves, characterised by a Gaussian distribution in scatterer speeds and a Gaussian component in the PSD; secondly, scattering from sporadically appearing, fast moving, short lifetime, facet-like scatterers, characterised by an exponential distribution in scatterer lifetime and a Lorentzian component in the PSD; and finally, scattering from fast-to-intermediate speed bound-Bragg waves, or not-so-fast facets, characterised by a convolution of the Gaussian and Lorentzian processes, resulting in a Voigtian component in the PSD.

Backscattering experiments at microwave frequencies were conducted off the west coast of Scotland in the summer of 1991. Using a dual-polarization, eight-frequency, X band, coherent scatterometer mounted on the bow of a boat, we measured time-resolved backscattering from ocean waves at a range of grazing angles from 10° to 70°. From the grazing-angle-dependent signals and their Doppler spectra, we are able to differentiate Bragg scattering from non-Bragg scattering and resolve “peak separation” between the vertical and horizontal polarizations. We observe instances of “super” events, i.e., instances when the horizontal polarization return power equals or exceeds the vertical polarization power at particular frequencies. We find that “super” events occur not only at low grazing angles but at any grazing angle for upwind viewing directions and obtain statistics for such occurrences as a function of grazing angle. We study the coherence properties of scatterers and find strong evidence that at low grazing angles, lifetime-dominated, non-Bragg scattering contributes noticeably to returns of both polarizations, but is dominant in providing returns for the horizontal polarization. We examine “spiking” events and find that they can be related to, but need not be limited to, breaking wave events. By comparing the data of upwind runs with cross-wind and circle runs, we obtain wind direction dependence of Doppler spectra, which further assists in the identification of scattering mechanisms.

The transmission properties of single‐heterostructure GaAs‐AlxGa1−xAs rib waveguides (RWG) clad with thin anodized oxides (0–200 A) covered by gold (MOS structures) are investigated both theoretically and experimentally. Efficient polarizers having extinction ratios of 35 dB and insertion losses

Amorphous (vitreous) Y3Fe5O12 has been prepared using the twin‐roller quenching technique. The material is antiferromagnetic with a Neel temperature of approximately 40 K. The Mossbauer spectra indicate that the iron environment in the amorphous material is different from that in crystalline Y3Fe5O12 (YIG).

We have studied the properties of isolated and coupled optical rib waveguides (RWG) as a function of rib height and width in GaAs layers on AlGaAs for TE‐like and TM‐like polarizations. We compare mode shape parameters for isolated RWG to the coupling constant, K, obtained from distributed couplers. The effective index model accurately describes the mode distributions and the coupling constant for single‐mode RWG. The model also gives an accurate estimate for anodic oxide loaded strip waveguides. In this model, the relative lateral difference in the effective dielectric constant, Δx, is determined by the depth characteristics (the rib height, layer thicknesses, and compositions) and the free‐space wavelength. The lateral confinement of guided modes and K are then determined by Δx, the effective dielectric constant, the waveguide width, the waveguide spacing, and the free‐space wavelength. At λ?1.06 μm, ribs of height h?0.05 μm on GaAs waveguiding layers of thickness t?0.75 μm with underlying Al0.1Ga0.9As ...

We have illuminated a liquid-helium cooled, Hg-doped, Ge photoconductor with 10.6-\ensuremath{\mu}m radiation at power levels varying by a factor of 2000. The noise temperature was constant at 35\ifmmode^\circ\else\textdegree\fi{}K over this range, in spite of a resistance inversely proportional to power. This temperature has been used to infer a value of 0.135 for the ratio of free-carrier energy-loss time to recombination time.

Rib waveguides (RWG) formed on single heterostructure Al y Ga1− y As−Al x Ga1− x As slab waveguides1 provide a simple and powerful means to achieve the routing requirements of monolithic integrated circuits. The design, fabrication and use of single mode RWG is discussed here in the context of uniquely high lateral packing density and the use of efficient electrooptically controlled phase modulators for switching applications. The RWG are conveniently formed as an added processing step after epitaxial layer growth, requiring only layer thicknesses and compositions suitable for single slab waveguide modes. Doping levels of either type is only required to be ≲ 1017cm−3 and is compatible with future monolithic integration with cw operated lasers. The RWG are electrooptically modulated by applying voltages between metal electrodes overlaying a buffering oxide layer and the substrate.2 The RWG are modulated by the depletion layer field of the semiconductor which does not require a particular doping type. Close overlapping of the depletion layer field with the optical electric field leads to very efficient modulation. The profile of the high index waveguide layer and the respective effective indices for fundamental TE modes at 1.06 μm are shown in Fig. 1. This simple step waveguide model serves as a design guide for the RWG modes. Fig. 1 represents a coupled pair of RWG that serves as the basis of a switch. The effective refractive indices for a step height of 700 Å differ by 0.004. This provides sufficient lateral guiding and permits up to 3.5 μm wide ribs that can carry only one mode per polarization.