Achieving ever higher performance levels in optical design does not always require going to more cost and/or complexity in the designs. Often it is possible to make major performance improvements by (1) looking for alternate solutions with the same (or fewer) number of elements while (2) questioning assumptions that have crept in at the very beginning of the design process, and by utilizing little-known exceptions to general rules and principles.
Emission microscopy involves post-mortem analysis of integrated circuits. By applying an electric signal to faulty chips, infra-red emission occurs at sites of potential failure. The ability to examine entire chips has not been fully incorporated into the objective design of emission microscopes. This ability allows faster identification of trouble points. After failure-sites have been identified, they are more closely investigated by using higher power microscope objectives. A 0.8X lens having an numerical aperture of the object of 0.32 is discussed. This lens covers an object full field of view of 18.0 X 18.0 mm (diagonal of 25.5 mm) at 50% vignetting, reaching 25 X 25 mm (diagonal 35 mm) at 100% vignetting. Unique features include a 20 mm working distance for the insertion of analytic probes, a 100 mm gap between objective and decollimating lens groups for mounting issues, and a back focal length of 50 mm for introduction of filters, beam splitters and/or other auxiliary optics.
We first examine how a video camera lens acts in concert with a CCD sensor array to produce an optical image that is limited by both spatial and temporal bandwidth with regard to its ability to represent a set of points in object space. We then relate these factors to human visual perception and discuss three video camera operating regimes distinguished by four separate types of intended camera usage. Next we suggest three lens designs to meet minimum imaging requirements imposed by each of these different situations. Our designs are based upon the use of injection molded plastics and incorporate aspheric surfaces to minimize the number of lens elements while providing integral mechanical mounting features to facilitate automated lens assembly. In all, we have attempted to reduce lens production costs while meeting the imaging criteria established for each type of video camera application.
Many imaging applications, such as machine vision, parts inspection, and gauging, make us of telecentric lens configurations to improve measurement accuracy and reduce alignment sensitivity. CCD cameras are frequently chosen to record the final image. Although lenses can be designed to work as standalone telecentric devices, it is sometimes desireable to use a modular approach, in which a telecentric `attachment' is mated to a primary or `base' lens. This allows one to vary the object field coverage by changing attachment lenses, keeping the same primary lens. A simple attachment could consist of an achromat mounted one focal length away from the entrance pupil of the primary lens. Such arrangements can become lengthy for large fields and magnifications. Stock achromats may not meet size requirements, nor provide optimum image quality. A more complex arrangement that reduces the lens length and improves imaging can be obtained by using a telephoto lens (front-vertex-to-image/efl < 1.0) as an attachment. This paper will outline the development of a modular telecentric system and a first-order method for evaluating the suitability of lenses for use as telecentric attachments.
The Virtual Retinal Display (VRD) is a unique approach to developing a high-resolution head- mounted display currently under development at the University of Washington's Human Interface Technology (HIT) Laboratory. Rather than looking at a screen though a magnifier or optical relay system, the viewer of the VRD has a scanned beam of light enter the pupil of the eye and focused to a spot on the retina. This type of optical system is subject to different design constraints than a typical HMD. With the VRD it may be possible to realize higher resolution, greater color saturation, higher brightness and larger field-of-view than a traditional LCD or CRT screen-based system. In this paper the author will present the VRD approach and how it can provide these advantages. Issues to be resolved for the VRD to reach its full potential and some of the solutions developed at the HIT lab will also be discussed.
With the advent of small format LCD display panels, a new level of performance and miniaturization is now possible for head mounted displays used in virtual reality systems. Recent work at the University of North Carolina has led to a rugged, compact and light weight display system well suited for glasses mounted, moderate field of view monocular displays (30 degree(s) H MUL 21 degree(s) V) as well as tiled wide field of view display systems. The optical design uses a plastic broadband polarizing beam splitter coupled with quarter wave plates and mirrors to extend the optical path length between the LCD panel and the imaging lens. This not only relaxes the performance requirements on the imaging lens but also reduces the overall depth to equal the smallest dimension of the LCD display. The cost engineered optical system is expected to weight <EQ 5 g and cost approximately $DOL15 to produce. A description of the optical design, including photographs of a plastic broadband polarizing beam splitter, is presented along with performance results of the product prototype.
In a previous paper by the authors, a High-Resolution Insert Head-Mounted Display (HRI- HMD) that uses only fixed electronic devices was proposed and designed. The design concept is innovative and it is the first and only known such design to implement a high-resolution insert for HMDs. The high resolution insert system consists of three stages: an objective to collimate the image of the display, a duplicator to produce insert images, and an eyepiece to view the insert and background images. In this paper, a detailed description of the HRI-HMD is given, which includes detailed analysis of the performance and a discussion of physical constraints. Analysis is conducted for each stage as well as for the entire system. The potential benefits of individually optimizing each channel of the duplicator and balancing aberrations from different stages are discussed. The benefits of employing binary optics at the duplicator are also discussed. The geometry of a folded model is described as well. From this analysis, the achievable performance of the HRI-HMD can be estimated against its size and cost.
Polarization aberrations due to varying polarization state across the field of view (FOV) are investigated for crossed folding mirrors. We define crossed mirrors as oriented in space such that s-polarized light incident on the first mirror is p-polarized at the second mirror. This completely compensates for polarization state changes at one point in the field of view. The resulting polarization aberrations are explored across the FOV using the example of aluminum mirrors overcoated with a 12 layer, highly reflective, dielectric stack. The polarization aberration is very low along a band across the field of view. For arbitrary points in the FOV, the retardance and diattenuation are slightly elliptical.
This theoretical discussion deals with obliquely projected images on the surface of curved viewing screens. Resulting perspective and geometrical distortions are usually precorrected with computer software in nearly real time, or by optical printing methods in the case of film. Owing to the significant technical and cost overhead of these methods, there is an interest in producing real-time passive correction using optics supplemental to the normal projection lens. Several concepts to this end are described.
Many electronic fingerprinting devices are required to have a distortion-free high-contrast imaging capability, with diffraction-limited resolution. That is, no software correction of image distortion is allowed, and all fingerprint scaling correction must be accomplished with optical components. For such systems, a minimum of four key requirements must be satisfied simultaneously in the optical design: (1) Total internal reflection (TIR) at the fingerprinting surface; (2) Optical compensation for producing zero distortion; (3) Variable anamorphic scaling capability in two axes for producing correct image sizing; (4) Diffraction-limited imagery across the entire field of view. In the mechanical design for manufacture and assembly of the imaging system, generally a number of mechanical implementations are needed to provide for each of alignment. Thus a strong interaction between the optical designer, the mechanical engineer, and the marketing company which dictates the system specification is essential all throughout the design process. In this paper we present several optical design principles involved with electronic fingerprinting. A discussion of the Scheimpflug condition, its attendant keystone distortion, tilted object and image planes to assist the correction of distortion, tilted lens elements to assist in the correction of defocus, and variable anamorphic prism pairs (or cylinders) will illustrate how a unified design solution is arrived at for a complex imaging system. Illumination concepts involving TIR and non-TIR approaches are also discussed.
We present the design for an echelle spectrograph for 6.5 m telescopes: i.e. the converted MMT and Magellan. We incorporate fused silica prism cross dispersion for higher transmission, and use a single camera that records simultaneously full 300 - 1100 nm wavelength range of CCD detectors. The broad wavelength coverage in a single exposure will make this a powerful instrument for many scientific problems: i.e. the study of the metallicity, evolution and clustering of the primordial Lyman alpha forest, tracing the nucleosynthetic history and element depletion pattern in the ISM of high redshift galaxies, determining if dark- matter halos are ubiquitous, and studying metal abundance analyses of stars. Six detectors are placed tangent to the focal sphere of a Schmidt camera. Each has its own thin field flattener. In this way excellent image quality is maintained while the obscuration by the detector array is minimal, even though it is big enough to cover the entire cross dispersed spectrum. Each back-illuminated CCD is dedicated to a limited spectral range, and can be given appropriately optimized coatings for highest efficiency. Designs for 20 and 30 cm beams have been produced, both using 60 cm Schmidt plates and achieve resolving power slit width products of 50,000 arcseconds. The 2048 square CCDs yield spectral resolution sampling of 200,000/pixel. The `point and shoot' character of the spectrograph should result in simplified controls and software.
This paper presents the results of a camera feasibility study for the High Resolution Optical/UV Spectrograph. We develop the concept of a sub-aperture long focus camera for this instrument,. This paper additionally illustrates the advantages of a new interactive optimization technique as applied to this study.
Following a brief definition, it has been explored that a roof Dove prism is a typical circular beam deflector used in a transmitted parallel beam. The importance attached to this prism is apparent for its multifunction. However, the unfavorable value of the length-aperture ratio of the roof Dove for most popular optical glass has imposed restrictions on extending its application to many cases. To overcome the difficulty, a new type of roof Dove, i.e., a square-sectional roof Dove prism and its equivalent are suggested, and on this basis have been built up two kinds of prism array to greatly reduce the length-aperture ratio. The potential of these new types of reflecting prism and reflecting prism array will rely on the development of the fabrication technique as well as on the further researches.
A comprehensive database of essentially all of the world's lens patents has been compiled, and an interface written, to permit a lens designer to quickly scan all of the lenses suitable for a stated purpose or constructed in accordance with stated rules. These data can easily be imported into a commercial optical design program, yielding immediate starting points for many optimization problems.
Optical interconnects relying on holographic optical elements commonly suffer from strong chromatic aberrations. These aberrations limit the coupling efficiency of optical links if the laser wavelength varies with time or from sample to sample. Semiconductor lasers are the only candidates for optical links because of their efficiency and compactness. Unfortunately, these lasers show a strong tendency to wavelength drifts. Therefore, the flexibility of holographic interconnects can only be saved if the chromatic aberrations are reduced. Here, 4 different achromatized optical interconnecting schemes are discussed which have been under investigation for the last few years in our department. This report summarizes the achromatization efforts for space-invariant as well as for space-variant interconnects.
A single hybrid refractive/diffractive lens element is designed to replace the multiple refractive cylindrical lenses in the motionless-head parallel readout optical disk system. The new system has less elements, simplified alignment, and significantly reduced aberrations. Experimental results are presented. In addition, a design for the disk illumination element based on diffractive optics technology is introduced.
The optical transpose interconnection system (OTIS) provides a good interconnection using only a pair of lenslet arrays. We have designed and optimized various OTIS systems based on refractive, spherical diffractive, and aspheric diffractive lenslets. The optimization goal is to maximize power coupling into the elements of a detector array. The various design approaches are compared and the optimal design is extracted; the parameters of the model are then to be used for the fabrication of the lenslet array. We also address system geometry, symmetry, and illumination issues relevant to the system design.
Several optical systems, based on a combination of lenslet arrays and computer-generated holograms (CGH), are described. They provide full or neighborhood connectivity between arrays of electronic processors, each processor containing one transmitter and N detectors. Some of the system are symmetrical, and therefore bi-directional. Specific designs include a system utilizing reflection-mode modulators that provides reciprocal connections between two planes of processors, and a system requiring sources or transmissive modulators that provides the connections required by a back-propagation neural network with an arbitrary number of layers. We derive expressions governing the lengths of the lenslet-based system and of a previous design based on bulk optics and CGH. The proposed systems require fewer components, less volume, and less alignment than the bulk optics system.
Free-space digital optics is a new technology that exploits the ability of optics to handle thousands of light beams or information channels at once. This and other features of optics complement the strengths and weaknesses of purely electronic systems. A compact free-space optical system that uses array of microlens for chip-to-chip and board-to-board interconnections is proposed. Here the weakly diffracted Gaussian beam and wavelength division architecture are utilized to improve the channel density and reduce the crosstalk in a microlens interconnection system. Based on the simulation, we improve the channel capacity by 3.47 times (or reduce the crosstalk by 93.1 dB) while maintaining the same crosstalk (or channel density) compared with the conventional microlens interconnection system. As for the nonperfect filtering effect of different wavelengths at the detector plane, it is also studied to fully investigate the properties of the proposed scheme. The parameter sensitivity of the proposed system is studied for completeness. From the simulations, the relationship between the interconnection distance and spot size at the detector plane is wavelength-independent. In addition, the spot size is the most sensitive to the change of the microlens diameter compared with the other system parameters.
Two basic architectures are deduced from 1D multistage architectures with nearest-neighbor (NN) interconnection of switches and extended into 2D architectures by a mathematical transformation. These two architectures are the Spanke-Benes (SB) network and the NN multistage interconnection network of switches (NN-MIN). The properties and applications of the two 2D architectures are described.
The paper presents the results of experimental studies in modelling and realization of some elements of optical binary logic and of a switch of 2 X 2 type. In the devices, as gates there are employed structures in which optical modulation of light flux is performed at the expense of the effect of photoinduced spatial redistribution of electric field. Pockel's transverse electrooptical effect is used in them to read off information. The optical schemes of elements of binary logic are given, the ways of realization of logical functions are described.
The assignment of wavelengths to the paths of wavelength division multiplexing/optical frequency division multiplexing networks (wavelength allocation) is analyzed and the applicability of mathematical methods (optimization) is discussed.
Lenses whose material is represented by a line on the glass map (nd equals f((upsilon) d)), as opposed by a point, like homogeneous glass, open the door to a wide variety of optical design applications incorporating entire lenses of axial gradient refractive material (GRADIUM). This material essentially gives bi-aspheric performance to lenses with spherical surfaces and exhibits a controlled gradient in both index and dispersion. Thus, the applications for this material range from the simple singlet lens used for laser applications, in which spherical aberration is eliminated, to complex multi-element lens systems where improved overall performance is desired. The fusion/diffusion process that produces this material, is surprisingly simple, repeatable, and applicable to mass production. The advantage of GRADIUM and its accessibility in commercially available lens design programs, (ZEMAX, CODE V and OSLO), provides optical designers with the opportunity to push performance further than with conventional optics.
Recent advances in macro axial gradient material fabrication, via the diffusion of glass plates, has opened the door to a wide variety of optical design applications incorporating entire lens elements of gradient refractive material. Optical elements, which are made out of macro gradient refractive material, are represented by lines, as opposed to points, of the glass map (nd vs. vd diagram) and thus are of considerable interest to optical designers. Eastman Kodak Co. and Lightpath Technologies entered into a joint venture to redesign and build several prototypes of a commercially available zoom slide projector lens. The goal of this redesign was to keep physical packaging and optical performance the same, while simultaneously removing as many elements as possible. The seven element production lens was redesigned to a five element lens with a single axial gradient meniscus element whose overall index change is 0.15. This paper describes the design, fabrication, and results of this endeavor.
An F/1.27 objective lens suitable for night vision applications employing lanthanum axial gradient-index (GRIN) materials is described. Although two GRIN elements were used, the number of elements was not substantially reduced relative to that of conventional homogeneous systems with equivalent performance. Tolerances and fabrication issues are discussed.
We provide experimental verification of the performance of an optical-digital imaging system that delivers near diffraction limited imaging over a wide depth of field. A custom aspheric optical element is used to modify an incoherent optical system so that the generated optical image is nearly independent of misfocus-induced blur. The resulting image, called an intermediate image, is not spatially diffraction limited. Digital processing of the intermediate image produces a final image that forms a close approximation to the diffraction limited image. The combined effect of the optical-digital system is to image objects independently of focus or range, that is, the system has an extended depth of field.
A new interferometric method for measuring refractive index distribution in GRIN blanks with shapes deviating from plane-parallel ones is described. It uses a standard double-pass interferometric scheme modified to provide single passing of the beam through the investigated GRIN sample. Four interferograms recorded with one preliminary adjustment of the sample allow to restore the distribution of refractive index in the sample, eliminating errors introduced by imperfectness of the interferometer and of sample surfaces, and wedge shape of the sample. The method does not need information about the thickness and the wedge angle of a blank. Two-dimensional dependence of refractive index in transverse dimensions along the sample surface can be measured with the accuracy better than 1(DOT)10-4.
The development ofmodem optical instruments has evolved into a complex multi-disciplinary activity with the explosion of sophisticated applications. For specialized optical systems, the development ofeven a prototype has become a costly exercise. This paper presents a new concept of virtual prototyping for optical systems to minimize the development time, cost and risk. This process employs the computer-aided design and modeling tools to address the broad issues of system layout, optical and optomechanical design, structural and thermal analysis for the real operating environment, tolerance budgeting and optimization procedures. The Center for Applied Optics (CAO) at the University of Alabama in Huntsville (UAH) has developed the necessary computer interfaces between the various stages of optical system design, development and evaluation. As a common thtabase is used for the optical and mechanical design and analyses, the possibility ofa human error is eliminated while minimizing the time and effort required to accomplish these critical tasks. The virtual prototyping concept works in an iterative fashion to achieve the desired system performance at a minimum cost. This technique has been successfully employed in the design and development of several optical instruments for space, military and commercial applications, covering a broad spectrum from Uv to JR The performance specifications and the results of virtual prototyping for some typical systems are also presented.
Keywords: Virtualprototyping, computer-aided design andmodeling, optomechanical design, tolerance analysis, optimization
An interesting optical design problem is to design a laser cavity which will couple an astigmatic waist to a TEMoo output. The astigmatic waist is used to reduce the thermal effects introduced in a dye laser when pumped at high power levels. The use of components which are inexpensive and readily available was one of the requirements in the design. We looked at the problem from an aberration stand point. We present two designs for a dye laser cavity which couples an astigmatic waist to a TEMoo output. Each design uses a tilted spherical mirror to introduce the astigmatism needed to produce the astigmatic waist. A second mirror tilted in an orthogonal direction is used to remove the astigmatism. The tilted mirrors also introduce coma into the system. One design uses symmetry to remove the coma. The second design uses an asymmetric design which removes the coma and requires fewer elements.
In the case of a simple, one-piece optical imaging element the possibility of aplanatic correction is important. Such a correction can be obtained for a single holo-lens recorded on spherical surface. This needs, however, relatively high spatial frequency to be recorded. From the technological point of view the combination of classic spherical lens with a diffractive structure of relatively low spatial frequency seems much more convenient. Such hybrid lens is a single element consisting of diffractive and refractive parts. Even if one of the lens surfaces is flat (and on this surface the diffractive structure is deposited) it is possible to obtain the aplanatic correction for selected locations of the object point.
In an earlier paper the author proposed a new image quality measure and a new definition of a center of a point spread. Determination of the value of this measure is equivalent to simultaneous optimalization of the reference sphere. This measure resolves itself into a mean square of the wave aberration in the case of small aberration. In the present paper, the parameters of the optimal reference sphere are calculated for the circular, annular and rectangular exit pupils.
Here we put forward the idea of getting superresolution in confocal setup with apodization film. By this configuration we can suppress the background noise aroused by apodization film, and further avoid problem owing to non-axial points when modified lens is used solely. Also we introduce a new model based on the confocal setup to explain superior resolution mechanism in near field optical microscope. Theoretical development and skeptical comments are given in this paper.
The development of modern optical instruments has evolved into a complex multi-disciplinary activity with the explosion of sophisticated applications. For specialized optical systems, the development of even a prototype has become a costly exercise. This paper presents a new concept of virtual prototyping for optical systems to minimize the development time, cost and risk. This process employs the computer-aided design and modeling tools to address the broad issues of system layout, optical and optomechanical design, structural and thermal analysis for the real operating environment, tolerance budgeting and optimization procedures. The Center for Applied Optics at the University of Alabama in Huntsville has developed the necessary computer interfaces between the various stages of optical system design, development and evaluation. As a common database is used for the optical and mechanical design and analyses, the possibility of a human error is eliminated while minimizing the time and effort required to accomplish these critical tasks. The virtual prototyping concept works in an iterative fashion to achieve the desired system performance at a minimum cost. This technique has been successfully employed in the design and development of several optical instruments for space, military and commercial applications, covering a broad spectrum from UV to IR. The performance specifications and the results of virtual prototyping for some typical systems are also presented.
In this paper, deflection and scanning of a HeNe beam by a programmable phase Fresnel lens written on a LCTV has been demonstrated. Translation and tilt aberration respectively produces coarse and fine deflection of the beam. The rapid translation of the lens function, time dependent variation of the magnitude of the tilt aberration, and a combination of these two methods are used to demonstrate laser beam scanning. In our experiments, using the wavefront tilt aberration a measurable scan deflection accuracy of less than 8 (mu) rad is achieved. Using the lens translation scheme the beam is scanned over a 0.8 cm X 0.8 cm area at a distance of 50 cm. The scan time of the current system is limited by the standard video frame rate of the existing LCTV drive electronics. The performance limits of the LCTV-based deflection and scanning system are compared with those of acousto-optic deflectors and scanners.