Although rays form the basis of both our initiative thinking and our numerical modeling of optical systems, we must remember that they are no more than mathematical constructs with a relatively tenuous connection to the physical world. What's more, certain aspects of their link to wave-based models of optical systems have always been problematic. For example, the limit to what rays can tell us about the associated wave field remains unclear. The current state of the art is reviewed and a framework is then outlined that offers a more direct appreciation of these issues and promises extended capabilities for ray-based methods. The new approach involves modeling wave propagation by using--as an intermediate tool--a windowed Fourier transform of the field.

If the monochromatic error function of optical systems is computed analytically by means of aberration coefficients, certain intermediate results of this computation can be used for the investigation of the aberration balance. For the analysis of local minima resulting from optimization, a new automatic technique has been developed that groups together monochromatic aberrations having a large mutual compensation of their effect on the error function. Criteria are proposed to evaluate the quality of aberration balance. Present experience suggests the existence of a correlation between the quality of the pattern of aberration balance and the value of the error function.

Air index induced focal plane movements of optical systems can be avoided by suitable optical design. The design theory for `thin' optical systems and a paraxial approach for arbitrary systems are presented. Applications are e.g. test optics for space applications.

No abstract available.

Conformal dome surfaces may enhance the overall performance of missile systems employing optical sensors by providing a more aerodynamically shaped airframe, however realistic implementation of these highly aspheric surfaces is currently limited by the severe image aberrations they introduce to the transmitted wavefront. This paper proposes an optical correction technique designed to combat the large magnitude and varying nature of third order astigmatism introduced by conformal missile domes. The newly developed technique utilizes axial translation of crossed cylindrical elements to provide variable astigmatism correction as a function of sensor gimbal angle. Theoretical motivation for the optical correction technique is provided, and its performance is assessed in a sample conformal dome and optical sensor systems.

We present calculation schemes for the attainment of isoplanatic imaging on the optical axis using aspherical surfaces. The consequences of the isoplanatic condition for the illumination over the cross-section of an imaging beam are considered. The variation of the useful image volume as a function of the isoplanatic prescription is illustrated by a few examples. Finally, we present a calculation scheme to attain stigmatic imaging over a ring field area.

A method is presented for determining effective approximations to the initial directions of rays that eventually pass through given points on some internal surface of a non-axially symmetric system.

Use of a solid modeler and ray topology information allows logical decisions to replace fuzzy numerical comparisons when determining the correct ray path in a non-sequential ray trace.

No abstract available.

No abstract available.

This paper introduces the group theory and the isomorphism concept in order to demonstrate how to bypass and simplify scientific difficulties using these tools. The isomorphism relationship which is being investigated by this paper is the one existing between the Wigner distribution function and the canonical ABCD integral transformation.

No abstract available.

This paper presents new lens optimization methods based on real-coded genetic algorithms (GAs). We take advantage of GA's capability of global optimization and multi-objective optimization against two serious problems in conventional lens optimization techniques: (1) choosing a starting point by trial and error, and (2) combining plural criteria to a single criterion. In this paper, two criteria for lenses, the resolution and the distortion, are considered. First, we propose a real-coded GA that optimizes a single criterion, a weighted sum of the resolution and the distortion. To overcome a problem of the difficulty in generating feasible lenses especially in large-scale problems, we introduce an enforcement operator to modify an infeasible solution into a feasible one. By applying the proposed method to some small- scale problems, we show that the proposed method can find empirically optimal and suboptimal lenses. We also apply the proposed method to some relatively large-scale problems and show that the proposed method can effectively work under large-scale problems. Next, regarding the lens design problem as a multi-objective optimization problem, we propose a real-coded multi-objective GA that explicitly optimizes the two criteria. We show that effectiveness of the proposed method in multi-objective lens optimization by applying it to a three-element lens design problem.

Global optimization with escape function was applied to a zoom lens with aspherical surfaces. Good solutions of various types were found within a short time.

Method of generalized simulated annealing with constrained random walk is used for global optimization of the structural design of cemented/broken contact doublet lenses in accordance with prespecified paraxial characteristics and primary aberration targets.

No abstract available.

We present here briefly the scientific objectives, the mechanical design as well as the main components and observing modes of the new Thermal Infrared Multi Mode Instrument (TIMMI 2) for the 3.6-m telescope of European Southern Observatory (ESO) at La Silla, Chile. At greater detail we describe the optical design of the instrument.

A spectrograph design was needed for an application in medial optics. Requirements for resolution were modest, cost was to be minimized, and every photon was precious. The initial design used a concave, aberration-corrected, holographically-recorded, diffraction grating. This design cost too much and collected too few of the precious photons. Several design forms, which use refractive optics with a planar diffraction grating, were investigated. The design that was chosen and built uses two aspheric glass lenses, one for collimating and one for focusing, together with a planar diffraction grating.

Designing an imaging spectrometer using an AOTF can be a difficult task since there is no software that can simulate the bulk diffraction that takes place in the AOTF material. In this paper we will describe the method used to simulate the effects of the AOTF using a refractive grating halfway along the crystal. Apart from the zero order we also collect the +1 and -1 orthogonally polarized orders produced by the AOTF, gaining additional information that may be used in certain applications. The +1 and -1 order are imaged into the same focal plane, eliminating the need of a separate focal plane for each order and resulting in considerable savings in cost and mass. The whole system is achromatized from 1.2 - 2.4 microns using only two types of glass, one of which is BK7. The system has been designed, built, and tested.

Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, ideally suited for space-based remote sensing of earth resources. An optical system composed of dual spectrographs and a common fore-optic has been designed for the visible-near infrared (VNIR) and shortwave bands with 10-nm spectral resolution, providing 30-meter ground resolution from an altitude of 605 km. The spectrograph designs are based on a modified Offner 1-X relay with spherical mirrors and a convex spherical holographic grating for the secondary mirror. The fore-optic is a three-mirror anastigmatic telescope with a 360-mm focal length to match the pixel pitch of the respective 1024 X 1024 visible silicon CCD and SWIR HgCdTe FPAs. The primary advantages of this design are the relatively low f-number (f/3), large flat field (18 mm), and low distortion. Preliminary performance results of a VNIR testbed grating and spectrograph are presented and compared to the design predictions.

The interface between optical design and fine-mechanical design is a creatively fertile stage in the design of an optical system. The optical designer learns `What the system is all about' and the fine-mechanical engineer is liberated creatively by finding out what the priorities are. On the other hand, optical tolerancing as a discipline, which is an attractive mix of optical physics at one end and hard-nosed mechanical pragmatism at the other, has a relatively fragmented literature. It is the purpose of this paper to (1) Point out some cultural contrasts between optical engineers, mechanical engineers and physicists in this context, (2) To present a new method of displaying the optical surface sensitivities so that one may identify datum surfaces in an intuitive way and (3) To summarize some useful formulae which provide a key to the mounting of optical components. Together these three aspects illustrate the scenery of this fertile terrain.

Today's compact, high-zoom-ratio lenses for camera are made possible by design analysis, modern design method and manufacturing technologies, and the incorporation of aspheric elements.

The optical design of a visible waveband, high performance zoom lens objective system, which utilizes aspherical surfaces and a zoom group internal stop, is described.

An all-spherical negative-positive-positive telecentric zoom lens suitable for DMD projection is described. The zoom range is 2:1 and the aperture is f/3.

Some ideas of design zoom lenses with removed forward entrance pupils (pinhole zoom lenses) are presented. The methodology and current status will be discussed in this paper. Number of examples illustrate approaches proposed: optical extension adapter which allows to use together a pinhole lens with fixed focal length and video-camera zoom lens to form a zoom pinhole lens; three positive components, including linearly moving collective lens to provide variable focal length.

Recently, in the field of still cameras, AE(auto exposure) and AF(auto focus) became popular enough. But camera shake often become a cause of blurred photograph. In the field of video cameras, comprising an image stabilizing function becomes a must today, then it is expected in the field of still cameras now. In this paper I will introduce the optical design of EF74-300/4-5.6 IS put on the market in 1995 by Canon, which comprise an image stabilizing function.

While computer graphics play a significant component in the development of virtual environments, optics and its interface to the computer graphics software play an essential role as well because they are both required for the effective visualization of virtual environments. Moreover, optical technology is often a component in satisfying stringent tracking requirements. We shall focus in this paper on aspects of virtual environments where optics play a part, describe the development of the VRDA tool for visualization of anatomy, and summarize recent investigations of visual optics for improved head-mounted displays.

Many objective lenses designed for very high volume production now typically contain aspherical surfaces. One such example is an aspherized version of the traditional Cooke triplet. While these aspherical designs are better than their antecedents, the basic design limitations, astigmatism and manufacturing sensitivities, remain. An inverse triplet having a negative, positive, negative configuration and aspherical surfaces has no all-spherical counterparts, but instead depends on the aspheres to correct the primary aberrations. If a sufficient number of surfaces are aspherical, there are more degrees of freedom than required for aberration correction, so the lens can be optimized to reduce the manufacturing sensitivities by reducing the amount of aberration correction contribution by an individual element.

A compact, wide angle projection lens suitable for use with large format LCDs is presented. Plastic aspheric elements are used extensively to help simplify the design and minimize aberrations.

The design of a 90 x 30 degrees FOV anamorphic fisheye lens is presented. The F/4.5 lens maps the FOV on a 60 mm square array detector.

A nearly diffraction limited catadioptric relay system is described which enables the use of very compact projection lenses with dual DMD projectors.

A uniquely packaged three-mirror anastigmat (TMA) is discussed. The telescope has 5 major parts, including the optics. This compact TMA exhibits diffraction-limited performance in the MWIR and LWIR wavelength regions and operates at fast F-numbers and relatively wide fields of view. Optical surfaces and critical mechanical interfaces are single-point diamond-turned, allowing for drop-together assembly and alignment. This paper discusses the evolution of the optical/mechanical design, developed under the auspices of the Standard Missile Company and NAVSEA PMS422.

No abstract available.

Optical chromatism or dispersion, the variation of optical properties with radiation wavelength was discovered by Isaac Newton, who pursued the reflective route to avoid it, whereas Chester Moor Hall and John Dollond, discovered how to overcome it by means of balancing or correction. Chromatic correction implies the use of multiple optical elements of multiple materials in combination, such that their dispersive effects cancel each other.

This paper reviews the methods of selecting optical materials for designing apochromatic and superachromatic lenses. The application of these glass combinations to the design of photographic lenses and microscope objectives is reported.

Most frequently, discussion of low-order primary and secondary axial chromatic aberrations is based on finite spectral band definitions of V-number (V) and relative partial dispersion (P), typically the band between lines F-C, of optical glass types Yet, because of the wavelength variation of refractive index, discussion of V and P at wavelengths other than the visible may bring more questions than answers.

A statistical methodology used to judge optical material interpolation models is presented in this paper. A quality- of-fit criterion related to probable performance impact in lens design is used. This treatment was developed as a way to judge the acceptability in lens design of low and medium precision data so that material model developed from this type of data could be used to some level of confidence in a wide assortment of lens designs--in other words, judging whether the material model is universally applicable. The results will show that a universal acceptability criterion is very demanding on the statistics of the data. However, the method developed lends itself to a wider use in judging material models for less demanding lens designs, too. Therefore, the initial criteria goal may rule out some fit models for universal utility in lens design, but the same material models may be usable for less demanding lens design performance situations.

No abstract available.

With the improvement of the linear-variable-filter (LVF), it is possible to design a cooled field stop using a miniature LVF. The principle, structure and characteristics of this cooled field stop are described in this paper.

For the earth observation system, most newly-designed optical imaging systems are generally based on the principle of pushbroom imaging. With the rapid development of infrared array detectors, this technology, which gives consideration to both spatial resolution and radiative sensitivity, is extended to instruments with thermal infrared wavebands. Comparing with separate detectors system, the pushbroom imaging system using array detectors possesses a wide field of view (FOV) which reduces the off-axis image quality and is harmful to the resolution of the system. The structure using array aperture in synthesized manner makes it possible to enhance both image quality and radiative sensitivity.

Stereo microscopes have many applications in the surgical operations such as opthamaic operations. Stereo zoom microscopes have also been in widespread use because of their versatility. The zoom lens in them are critical for whole optics. This paper describes the method and process of desiging stereo zoom microscope, especially its zoom part, and also gives parts of the MACRO sequences for optimizing its configuration and its cam.

During a few years the microporous polymeric films are widely used in the various practical purposes, such as a filtration and a separation of liquid mixes as well as the separation material in chemical power supply. As a result of the our experimental researches the dependence between the parameters of the technological process of manufactures of these films and their light scattering properties was found. Knowledge of this dependence make it possible to construct the systems of a dynamic control of technological process of manufacture of the microporous polymeric films.

A new configuration of two-mirror optical system with a small fold mirror is presented in this paper. Consisting of a concave (positive power) primary mirror followed by a small flat mirror, a concave (positive power) secondary mirror, four lenses and a beam splitter, it gives the excellent image quality. A 1.5-m EFL, F/10 system of the upper configuration is designed over the 4° field angle and 0.50 ~ 0.70 μm wavelength range. The aberrations have been highly corrected and the distortion is less than 0.3% over the field. The obscuration could be minimized by reducing primary radius of curvature and avoiding the spider that holds the small fold mirror.

The optical design of telecentric optical systems is not a well known or published area of the optical design field. This paper is intended as a partial remedy for these deficiencies. The property of telecentricity will be defined and the use of telecentric optical systems will be discussed. This paper will recommend a standard method of telecentric lens description, quantification, specification, and terminology. Telecentric optical design challenges, difficulties, and recommendations will be discussed. Finally, a complete telecentric optical system design specifications will be presented.

Conventional refractive or reflection-refractive objectives for Night Vision Goggles (NVG) are more complicated because they require larger relative aperture and better correction of aberrations in broadband spectral response. However, further improvement of this objective is limited by conventional optics. Diffractive optics has some unique features, which can improve the imaging quality of the conventional optics system. First, effective dispersion of diffractive optics is opposite in sign to that of refractive elements, the monochromatic aberrations are easier to be corrected. Second, diffractive optics does not contribute Petzval field curvature. Third, another advantages of diffractive optics applied to the objective design are to reduce number of optical elements, overall weight and system cost. Finally, optical imaging quality of NVG that compares with the conventional optics is improved significantly. The paper will describe two hybrid diffractive-refractive objective design configurations of NVG and show comparable or improved imaging quality compared with conventional six- element objective.

Commercial optical design software routinely contains a programming language which can be used to augment and/or extend the optimization control and/or the analytical capabilities of the basic software package. In particular, we extensively use CODE V and its macro language in the design and analysis of optical systems. One example describes a method to calculate and remove or reduce the aspheric departure of a surface during the optimization process. A second example enables the designer to evaluate the dispersion characteristics of several materials over a given spectral band as an aid in selecting refractive lens materials which offer the best chance of achieving a chromatic correction solution in a wide spectral band lens system.

Deviation should be induced in the result of the spectral calibration of a optical remote sensor with large aperture and large field of view (FOV) because of the optical system of the calibration facility can not have a large aperture and a large FOV simultaneously. Detail analysis of the possible deviation were given for a multichannel imager and a imaging spectrometer respectively. For a imaging spectrometer, a modified method of test and data process is proposed.

An interferometer system scheme is proposed. This system consists of two Michelson interferometers and two laser sources and requires no use of modulation technique. Within a displacement range of about 10 microns, it is expected that the absolute displacement can be measured with a very high speed without the phase ambiguity problem. The possibility is demonstrated by numerical analysis.

Most optical systems are generally used in normal conditions, that means, in normal temperature and pressure. but some optical systems,f or example, those specially used in remote satellite or in aerospace, may be affected by the thermal effects caused by the environmental temperature variation. Some deviations will take place in the refractive indices, curvatures, element thicknesses and airspaces of these systems due to the great variation and difference in temperature, pressure and radiation, and certainly the image quality of the systems will be also not as good as that before. Therefore, when we design these systems, the most important thing is to eliminate the thermal effects caused by the environmental temperature. Most of the previous research involved description of the uniform temperature fields, and some researchers studied the theory of radial distribution of temperature gradients in optical glass lenses. Only in recent years the athermalisation techniquies are proposed and some special examples are reported. Several famous optical design corporations have adopted the techniques and used in their optical design software, for example CODE V of O.R.A. and OSLO Six of Sinclair, however these achievements are only initiatory.

This work describes the application of matrices to the modeling and optimization of optical systems under third order approximation. Although third order would require matrices of dimension 24, only 16 different coefficients need be considered for axis symmetric systems. A careful choice of coordinates allows the exact solution of Snell's law at a spherical interface and the determination of all the coefficients for spherical systems. As an application example the model is used to minimize either distortion or coma for a system composed of two thin lenses.

The basic principles and detailed description of the controllable optical laboratory of a new type are reported. The laboratory is based on a modular principle and enabled to mount and adjust any optical scheme (geometrical or wave) in short time. The scheme not only linear, but also ramified, practically of any grade of complexity. The laboratory training works can be carried out in several modes: from usual hand-operated with readout of distances and angles on scales and limbs up to completely controlled IBM PC with digital processing of received one-coordinate distributions (received with photo diodes) or digital optical images (by means CCD-camera). The set of equipment comprises optical component manufacturing with use of photolithography technology (such as slits, apertures, disks, one-dimensional and two-dimensional, regular and chaotic structures, zone plates, etc.) and compactly placed on a common photo pattern. The laboratory equipment is supplied with the software including the guide - programs realizating the laboratory training works, test programs of the control of knowledge and simulating programs allowing to expand an opportunity of real physical experiment. The software is made as the original WINDOWS-applications.

Firstly, various technical aspects of ArF optics are surveyed. At present, the ArF excimer laser is regarded as one of the most promising candidates as a next-generation light source for optical lithography. Discussions are ranging over some critical issues of ArF optics. The lifetime of ArF optics supposedly limited by the radiation compaction of silica glass is estimated in comparison with KrF optics. Availability of calcium fluoride (CaF₂) is also discussed. As a designing issue, a comparative study is made about the optical configuration, dioptric or catadioptric. In the end, our resist-based performance is shown. Secondly, estimated are the future trend regarding minimum geometry and the optical parameters, such as numerical aperture and wavelength. For the estimation, simulations based on aerial images are performed, where in the resolution limit is defined as a minimum feature size which retains practical depth of focus. Pattern geometry is classified into two categories, which are dense lines and isolated lines. Available wavelengths are assumed to be KrF excimer laser ((λ =248 nm), ArF excimer laser (λ =193 nm) and F₂ excimer laser (λ =157 nm). Based upon the simulation results, the resolution limit is estimated for each geometry and each wavelength.

Offner's ring-field all-reflecting triplet was the first successful projection system used in microlithography. It evolved over several generations, increasing NA and field size, reducing the feature sizes printed from three down to one micron. Because of its relative simplicity, large field size and broad spectral bandwidth it became the dominant optical design used in microlithography until the early 1980's, when the demise of optical lithography was predicted. Rumours of the death of optics turned out to be exaggerated; what happened instead was a metamorphosis to more complex optical designs. A reduction ring-field system was developed, but the inevitable loss of concentricity led to a dramatic increase in complexity. Higher NA reduction projection optics have therefore been full-field, either all-refracting or catadioptric using a beamsplitter and a single mirror. At the present time, the terminal illness of optical lithography is once again being prognosed, but now at 0.1 micro feature sizes early in the next millenium. If optics has a future beyond that, it lies at wavelengths below the practical transmission cut-off of all refracting materials. Scanning all-reflecting ring-field systems are therefore poised for a resurgence, based on their well-established advantage of rotational symmetry and consequent small aberration variations over a small, annular field. This paper explores some such designs that potentially could take optical lithography down to the region of 0.025 micron features.

The lighting industry, like many others, has experienced a tremendous amount of change over the last three decades. This change has been, to a large part, driven by significant advancements in technology outside of its own realm. In particular, the increased availability of raw computing power to a wider range of users has had an extensive effect on how this industry designs the optical components of their products. The purpose of this paper is to take a look back at some of hte evolution that has occurred and then to examine where the lighting industry may be going.

The differential geometry of surfaces describes both intrinsic and extrinsic properties: the intrinsic ones, such as the metric, are inherent, whereas extrinsic ones describe shape relative to 3D space, such as the distribution of surface normal vectors. This paper describes how the surface normals of a non-rotationally-symmetric illumination lens are generated, via Snell's law in vector form, from (1) the distribution of light from a sources, and (2) a desired directional distribution of light exiting the lens. These two distributions are expressed as grids with cells of variable size but constant photometric flux, on the Gaussian sphere of directions. The grids must be sufficiently fine so as to generate enough surface normal vectors for accurate numerical generation of the requisite surface. The grids must have the same number of cells, and the same topology (i.e., rectangular vs. polar). The source-intensity grid must be adjusted to account for Fresnel reflection losses. For an unfaceted (smooth-surfaced) lens, the array of surface normal vectors must be adjusted for equality of the crossed partial derivatives. This class of lenses has only recently become producible due to the advent of electric- discharge machining for the shaping of non-rotationally symmetric injection molds for plastic lenses.

The goal of this paper is to construct an irradiance simulation at an image. We will demonstrate a software method written by Al Greynolds for passing bitmap images through a lens system and directly viewing the changes to the image caused by the lens itself, sources outside the field of view, or defects in manufacture. The routine calls the emitting data command and is a new feature in ASAP 6.0 from Breault Research Organization. It is another way to evaluate a lens system and see the effects of irradiance modeling and more. The dynamic range covered by this simulation is not limited to 1 bit, 8 bit or 24 bit images. The distribution file is based on the full floating point precision of the computer and accurate to 7 significant digits. The method will accommodate any dynamic range the user wishes.

In document imaging systems, integrating cavity effect (ICE) is defined as the increase in perceived reflectance of the imaged portion of a document done due to the reflectance of the surrounding portion of that document. The illuminator kernel function, or one trip spread function (OTSF), characterizes the ICE present during an imaging operation. Insight into the functional form of the OTSF of a complex system can be gained from an analysis of the OTSF of simpler, related systems. Closed form expressions for the OTSF of a simple strip illumination system are derived. These expressions are shown to be a good approximation to the exact OTSF of this system by comparison to Monte Carlo- based illumination ray tracing results. Using the closed form expressions one can easily calculate the approximate magnitude of ICE present in similar systems.

Marshall Space Flight Center has been developing a space deployable, lightweight membrane concentrator to focus energy from the sun into a solar engine while remaining aligned to the sun. For an inner surface, this engine has a cylindrical heat exchanger cavity coaligned to the optical axis; the engine warms gas to propel the spacecraft. The membrane concentrator is a 1727 mm (68.00 in.) diameter, F/1.7 Fresnel lens. This large membrane is made from polyimide and is 0.076 mm (0.0030 in.) thick; it has the Fresnel grooves cast into it. The solar concentrator system has a super fast paraboloid reflector near the lens focus and immediately adjacent to the cylindrical exchanger cavity. The paraboloid collects the wide bandwidth and some of the solar energy scattered by the Fresnel lens. Finally, the paraboloid feeds the light into the cylinder. The Fresnel lens also possesses a narrow annular zone that focuses a reference beam toward four detectors that keep the optical system aligned to the sun; thus, occurs a refracting lens that focuses two places summarized as a composite Fresnel lens for solar concentration and alignment.

In microgravitation experiments the shadow profile of molten and undercooled metallic alloy spheres of 7 - 8 mm diam. are imaged by means of LED illumination and backlight reflectors made from thin tantalum foil, with rolled grooves in oblique orientation. In spite of their macroscopic structure the reflectors permit measuring the contours of the oscillating spheres for viscosity and surface tension calculations.

The ability to accurately model the performance of faceted reflectors using software can significantly reduce reliance on prototypes and reduce design costs. This paper discusses the use of software to design and analyze these common reflectors. Simulation results from lamps in reflectors are presented as well as simulation results from selected portions of the faceted reflectors to illustrate the important design principles.

This paper deals with diffractive surfaces used in optical designs: fabricated devices operating over the infrared wavebands are detailed, and the means of manufacture within the Thomson Optronic Group are described.

We review the relatively short history of the ring-toric lenslet. We discuss ring-toric lenslet design and elements that we have fabricated. We illustrate how a focus-error signal (FES) is measured with a ring-toric lens. We have found that the FES slope. a measure of sensitivity to defocus, is higher for the ring-toric lenslets described in this paper than for other techniques, such as the astigmatic and obscuration methods. We measured an FES slope of 0.63 per micron of defocus. The theoretical FES slope is 1.4 micrometers ^-1. Finally, we describe a multi-level DOE fabricated in a single etch using grayscale-photomask technology.

The optical system of the spatially modulated imaging interferometer spectrometer based on the solid dihedral- corner Michelson interferometer is introduced. The model of high throughput imaging interferometer, the modified sampling theorem, the main factors influencing the interferogram modulation, and the beam splitters are discussed. Some experimental results are presented.