An inexpensive, easily integrated, 40 Gbps photoreceiver operating in the communications band would revolutionize the telecommunications industry. While generation of 40 Gbps data is not difficult, its reception and decoding require specific technologies. We present a 40 Gbps photoreceiver that exceeds the capabilities of current devices. This photoreceiver is based on a technology we call "nanodust." This new technology enables nanoscale photodetectors to be embedded in matrices made from a different semiconductor, or directly integrated into a CMOS amplification circuit. Photoreceivers based on quantum dust technology can be designed to operate in any spectral region, including the telecommunications bands near 1.31 and 1.55 micrometers. This technology also lends itself to normal-incidence detection, enabling a large detector size with its associated increase in sensitivity, even at high speeds and reception wavelengths beyond the capability of silicon.
True 3D displays, whether generated by volume holography, merged stereopsis (requiring glasses), or autostereoscopic methods (stereopsis without the need for special glasses), are useful in a great number of applications, ranging from training through product visualization to computer gaming. Holography provides an excellent 3D image but cannot yet be produced in real time, merged stereopsis results in accommodation-convergence conflict (where distance cues generated by the 3D appearance of the image conflict with those obtained from the angular position of the eyes) and lacks parallax cues, and autostereoscopy produces a 3D image visible only from a small region of space. Physical Optics Corporation is developing the next step in real-time 3D displays, the automultiscopic system, which eliminates accommodation-convergence conflict, produces 3D imagery from any position around the display, and includes true image parallax. Theory of automultiscopic display systems is presented, together with results from our prototype display, which produces 3D video imagery with full parallax cues from any viewing direction.
Head-mounted or helmet-mounted displays (HMDs) have long proven invaluable for many military applications. Integrated with head position, orientation, and/or eye-tracking sensors, HMDs can be powerful tools for training. For such training applications as flight simulation, HMDs need to be lightweight and compact with good center-of-gravity characteristics, and must display realistic full-color imagery with eye-limited resolution and large field-of-view (FOV) so that the pilot sees a truly realistic out-the-window scene. Under bright illumination, the resolution of the eye is ~300 μr (1 arc-min), setting the minimum HMD resolution. There are several methods of achieving this resolution, including increasing the number of individual pixels on a CRT or LCD display, thereby increasing the size, weight, and complexity of the HMD; dithering the image to provide an apparent resolution increase at the cost of reduced frame rate; and tiling normal resolution subimages into a single, larger high-resolution image. Physical Optics Corporation (POC) is developing a 5120 × 4096 pixel HMD covering 1500 × 1200 mr with resolution of 300 μr by tiling 20 subimages, each of which has a resolution of 1024 × 1024 pixels, in a 5 × 4 array. We present theory and results of our preliminary development of this HMD, resulting in a 4k × 1k image tiled from 16 subimages, each with resolution 512 × 512, in an 8 × 2 array.
Advances in the development of imaging sensors depend upon (among other things) the testing capabilities of research laboratories. Sensors and sensor suites need to be rigorously tested under laboratory and field conditions before being put to use. Real-time dynamic simulation of real targets is a key component of such testing, as actual full-scale tests with real targets are extremely expensive and time consuming and are not suitable for early stages of development. Dynamic projectors simulate tactical images and scenes. Several technologies exist for projecting IR and visible scenes to simulate tactical battlefield patterns - large format resistor arrays, liquid crystal light valves, Eidophor type projecting systems, and micromirror arrays, for example. These technologies are slow, or are restricted either in the modulator array size or in spectral bandwidth. In addition, many operate only in specific bandwidth regions. Physical Optics Corporation is developing an alternative to current scene projectors. This projector is designed to operate over the visible, near-IR, MWIR, and LWIR spectra simultaneously, from 300 nm to 20 μm. The resolution is 2 megapixels, and the designed frame rate is 120 Hz (40 Hz in color). To ensure high-resolution visible imagery and pixel-to-pixel apparent temperature difference of 100°C, the contrast between adjacent pixels is >100:1 in the visible to near-IR, MWIR, and LWIR. This scene projector is designed to produce a flickerless analog signal, suitable for staring and scanning arrays, and to be capable of operation in a hardware-in-the-loop test system. Tests performed on an initial prototype demonstrated contrast of 250:1 in the visible with non-optimized hardware.
Modern synchrotron radiation sources of the 3rd generation like BESSY II, Spring-8 and others with their high brilliance beam characteristics need very high quality optics to exploit the full power of this radiation. For the grazing incidence reflecting type of that optics (flat, spherical or aspherical) besides roughness the slope deviation error is the most important spec, which has to be improved to meet the present and future performance requirements. Together with partners from industry we investigate and develop on the one hand surface figuring and polishing techniques for final finishing by using mainly ion beam milling technology and on the other hand we improve and make use of the combination of the surface shape measurements by means of interferometry, long trace and auto-collimation profilometry. We aim to achieve the following slope deviation errors on silicon optical elements: flat surface 310 mm long 0.03 arcsec rms, flat surface 100 mm long 0.02 arcsec rms and elliptical cylinder surface 210 mm long 0.1 arcsec rms. This is a five to ten-fold improvement compared to the present state of the art in production. To achieve the demanding specification it is necessary to measure and to deterministically machine the surface over a wide range of spatial wavelength down to the sub-millimeter range. In depth scale the sub-nanometer shape error level has to be achieved. The roughness of about 0.2 nm rms has not to be increased during the shape finishing.
Diffraction gratings can be manufactured in a large variety of ways depending on the required grating characteristics. In this work we have concentrated on surface relief gratings etched into large blocks of silicon with a polished surface. The applications for this kind of gratings are for mirrors and monochromators in the beam-line of a synchrotron. This application requires gratings with sub 100 nm etching depths -- in some cases even sub 10 nm -- with a very high control of the grating period and etching depth over the entire gratings ranging from 90 mm x 30 mm to 200 mm x 30 mm with useful areas from 80 mm x 10 mm to 190 mm x 10 mm. In some cases there are two grating tracks with different structure design on the same Si substrate. In this work we have shown that a combination of holographic exposure in a standard photo-resist and ion beam etching with a dwell time mode using a sub-aperture gaussian shaped removal function is an excellent fabrication procedure to meet the tight tolerances for this special type of gratings. We fabricate gratings for spectral ranges from 10 - 20 eV to 1000 - 2000 eV with etching depths ranging from 100 nm to a few nm and characterize them thoroughly by Atomic Force Microscopy.
Calcium Fluoride roughness evolution caused by ion beam milling has been studied in dependence on the ion milling parameters and different optically polished surfaces, respectively. For polished surfaces with high crystal damage, the roughness is dominated by the uncovering of the sub-surface damage due to the ion beam milling. For smooth surfaces with low damage the roughness is an intrinsic one and the creation of self-organized nanoscale structures can be obtained. Ion milling parameters influence more the intrinsic roughness than the extrinsic. Generally, high ion energies and sputter gases with low atom mass produce rough surfaces. Low ion energies and gases with high mass result in smooth surfaces. Ion bombardment induces a decomposition of CaF2 in the near surface layer. Surface analytical measurements show that ion sputtering to some extent decompose the CaF2 surface layer in contrast to the combined action of ion sputtering and low energy electron irradiation. The measured higher VUV absorption after ion milling is caused by the modified sub-surface layer mainly and not by the increased surface roughness.
We develop a Plasma Jet Chemical Etching (PJCE) technique for high rate precision machining of optical materials aiming in a technology mature for precision asphere and free-form surface topology fabrication. The present contribution summarizes the achievements after about twelve months experience with a prototype production tool facility. PJCE is performed with the help of a microwave driven reactive plasma-jet working in a broad pressure range (10-600 mbar). We developed a moveable lightweight microwave plasma jet source for dwell time techniques performed in a roughly pumped process chamber equipped with a six axis system for precision workpiece and plasma source movement. Volume etch rates of some 10 mm3/min have been achieved for fused silica and silicon, respectively, using reactive (CF4,SF6,O2) and inert (Ar,He) gas mixtures and applying a microwave (2.45 GHz) power in the 100-200 W range. Large quartz plates (80-160 mm) have been figured using dwell time methods to achieve aspheric deformations of some 10 micrometers . The figured surfaces show shape errors of 1-2 micrometers and a microroughness of 50-100 nm RMS but no sub-surface damage enabling a small tool shape conserving post polishing up to the sub-nanometer roughness level. Thus, surface shaping to the nanometer error range can be done by ion beam finishing.
Sub-aperture stitching interferometry (SASI) is an appropriate method to measure either large optical plane surface topologies or aspheres with strong deviation from the flatness with standard interferometers. Using SASI the surface shape is measured with a higher lateral resolution by multiple adjacent sub-aperture measurements with a sufficient overlap of the neighboring areas. In a second step, the total surface shape is composed with the help of a computer code by stitching the sub-aperture areas together. The overlap areas allow fitting. By means of a regression analysis, tilt and vertical displacement of adjacent areas are calculated and minimized. A confidence band calculated using a MATLAB based code describes the accuracy of the composition. The variance of this estimation is inverse proportional to the peak to valley value (PV) of the measured area and decreases with a 10-3 scaling of the width of the overlapping area. A statistical experimental design method is used to minimize the number of sub-apertures to be measured. The accuracy of the stitched total surface measurement can be increased with the help of model calculations by optimizing (i) the position of the sub-aperture, which was regarded as a standard, and (ii) the sequence of the stitched adjacent areas.
Atomic force microscopy (AFM) is usually the instrument of choice for the investigation of the surface roughness of thin films. Often a detailed image and roughness analysis is hindered by tip artifacts. Many of these artifacts arise from a spatial convolution or dilation of the actual tip and the shape of the surface features imaged. Therefore a careful tip evaluation and calibration is important for a reliable roughness evaluation. In this study about a process for the fabrication of self- assembled nanometer-sized surface structures using low- energy ion sputtering of semiconductor surfaces is reported. The dimension of these structures (typically between 10 and 100 nm), the distance between them and their shape can be tuned by the parameters of the sputter process. With the help of surfaces prepared by this way the influence of the actual AFM tip quality on the measured surface topography was evaluated. Furthermore, it is shown that the tip quality has a strong influence on the parameters extracted from first- and second-order statistics of the surface roughness. This applies particularly with regard to surfaces characterized by a low surface roughness (approximately 1 nm) as generally obtained by means of thin film technologies.
Ion beam figuring (IBF) using inert gas (e.g. Ar) and (Reactive) ion beam etching [(R)IBE] gain growing interest in precision optical surface processing, RIBE mainly for proportional transfer of 3D-resist masks structures in hard optical materials and IBF for finishing and nanometer precision surface figuring in high performance optics technology. Ion beam and plasma jet etching techniques related to different optical surface figuring requirements have been developed at IOM during the last decade. Some of these techniques have been proven to be mature for application in industrial production. The developmental work include material related process tuning with respect to enhance the processing speed and to improve surface roughness and waviness, further various processing algorithms related to different surface figure requirements and processing related equipment modification. Plasma jet assisted chemical etching is under development with respect to efficient machining techniques for precision asphere fabrication. The paper gives an overview of precision engineering techniques for optical surface processing focusing on the status of ion beam and plasma techniques. The status of the proportional transfer of 3D micro-optical resist structures (e.g. micro-lens arrays, blazed fresnel lens structures) into hard optical and optoelectronic materials by (reactive) ion beam etching will be summarized.
For EUV lithography mask blank substrates of the 6025 type will be made from Near Zero Thermal Expansion (NZTE) materials. The low thermal expansion of EUV substrates shall provide for the required better thermal stability during mask-writing and lithography exposure. The manufacturing of such NZTE mask blank substrates requires modified finishing processes in comparison to standard mask blanks. Super polishing takes place to provide high spatial frequency roughness of less than 2 Angstroms RMS. To improve the flatness and the roughness at the mid spatial frequencies another correction step is required. Such step can be Ion Beam Figuring for example. We evaluate the results for the different spatial frequencies by interferometry and atomic force microscopy. We have a closer look how the additional finishing steps improve the flatness and mid spatial frequency roughness. The impact of these newly introduced finishing steps for the high spatial frequency roughness is studied. We examine the processes for two different substrate materials with near zero thermal expansion (ZERODUR and ULE).
Calcium Fluoride microlens arrays have been produced with the help of an ion milling transfer of photoresist lenses which have been fabricated by two different techniques (i) by a melting resist technique and (ii) gray scale lithography. Major technical problems connected with the ion milling transfer of the photoresist lenses in the CaF2 material are surface roughness enhancement and variation of the lens shape. We studied the ion-induced decomposition of CaF2 and the surface roughness equatio in dependence on different milling conditions. For the microlens patter transfer the ratio of etching rates of the photoresist and the CaF2 have been adjusted by gas admixture of nitrogen to the Ar sputtering gas. The angle dependence of the etching rates leads also to a changing of the lens profile. The effect of ion beam induced surface roughness and the accuracy of the transfer process is discussed.
Matra Marconi Space (MMS) has designed, manufactured and tested a (Phi) 200 mm aspherical mirror to (lambda) /100 rms WFE for the purpose of a telescope demonstrator which both structure and mirrors are made from sintered Silicon Carbide. This outstanding performance has been achieved through a coordinated R and D program with the Insitut fuer Oberflaechen Modifizierung for the mastering of all the figuring aspects of any sintered Silicon Carbide telescope mirrors based on Ion Beam Figuring.
Reactive ion beam etching (RIBE) has been demonstrated to be an efficient figuring process for the fabrication of optical aspheric elements with high asphericities as they are needed for high performance EUV - or x-ray optics and satellite communications optics respectively. Using specially designed broad and medium beam size ion sources a RIBE process based on fluor containing etching gases was developed resulting in high removal rates and very smooth surfaces. In two applications the RIBE figuring was applied for the fabrication of fused silica aspheric surfaces with nanometer accuracy at a figuring depth of some ten micrometers. A setup with a computer controlled two-axis shutter system for shaping of the ion beam was applied for etching of a linear parabolic aspheric surface. In a second application a medium diameter high current source with a fixed beam profile was scanned across the surface with the dwell time being proportional to the desired material removal.
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