Low power telescopes such as those used in pairs in binoculars do not have a reticle at the intermediate, real, image plane. Therefore there is no need to correct aberrations of the intermediate images as it is in pointing devices. Generally, in order to keep the telescope simple and short the Petzval sum is not corrected. In most cases the solution is to introduce astigmatism in the eyepiece. If it is permissible to use the accommodation of the eye as a degree of freedom then it is possible to remove the astigmatism over the entire field of view and yet to obtain ever better imagery. The final virtual anastigmatic images presented to the eye by the telescope are formed on a curved surface convex towards the observer's eye. The eye will be focused at a close distance for axial images and relaxed for the extreme off-axis images. Then the telescope is to be designed for different conjugate positions at different field angles. Furthermore the telescope is to be designed for different exit pupil locations at different field angles in order to minimize vignetting when the exit pupil is not sufficiently large. Designing for different conjugate and pupil position at different field angles is almost always possible with most optical design codes using multiple configuration mode.
The full optimization process includes definition and maintenance of the merit function, selection of optimization strategy, the actual automatic improvement of the system, designer intervention and review of the final results. Well optimized systems are almost always achieved, not by a single run, but by repeated backtracking and re-optimization. A number of improvements to the whole process are presented, both to the damped lest squares algorithm itself and to the 'handling.' The enhancements include extensions to the classical damped least squares. These enhancements have been implemented in the widely used WinLens software package.
Hybrid optics offer a valuable aberration correction tool for the lens designer. However, careful consideration must be given to the calculation of the optical performance during the design process, and to the practical implementation of the elements if the potential benefits are to be realized in practice. Optical performance can be accurately assessed by tracing multiple diffraction orders. It may be particularly important to utilize such a technique if, for example, the image-forming bundles sample a small number of diffractive zones. This situation is examined in detail.
Over the years much time has been dedicated to improving lens optimization routines. Most of the work has been upon the damped least squares (DLS) method. In this paper a number of theoretical and practical enhancements are presented. Some are new, others have already been published but never transposed into commercial software. These enhancements combine to allow the user to make more informed choices at every stage of an optimization, and have now been incorporated into the widely used WinLens software package.
We discuss the requirements on design and production regarding geometric and chromatic aberrations for objectives used in 4Pi confocal microscopy. We show that even the selection of a category 1/1 glass will not automatically assure that these requirements are met, due to residual variations in the Abbe number v within the manufacturer's tolerances. Consequently, the optical design has to take into consideration the possibility of balancing chromatic aberrations by varying selected air spacings in the final assembly of each individual objective. We also demonstrate, that for analyzing the influence of aberrations on the intensity distribution along the optical axis, a scalar diffraction theory is still applicable and very useful.
In order to produce an instrument or sensor design in the face of demanding environmental constraints of a spaceborne system, an integrated approach to sensor design has been developed that incorporates design tools for: optical design, mechanical design, structural, stray light and thermal analysis. This integrated approach can be extended to the entire payload design and its increased constraints.
There are some unique optical design considerations in the design of a distributed aperture telescope array consisting of a number of individual afocal collector telescopes and a single combining telescope. As might be expected, diffraction limited imagery over the field of view requires the correction of spherical aberration, coma, astigmatism and field curvature. However, there is an additional requirement on the design of the collectors. Coherent addition of the light from the collectors requires that the ratio of the sine of the input and output chief ray angles be essentially constant over the field of view. This output angle restriction is equivalent to requiring the collector telescopes to have a specific variation in angular magnification with field. Variation of magnification with field is, by definition, image distortion. With simple two and three mirror afocal collector telescope designs, there are insufficient design degrees of freedom to control distortion in addition to the other aberrations. In this paper, we present a modification to a three-mirror collector design that permits the image distortion to be adjusted in a controlled manner without influencing the other third order, Seidel aberrations. This modification permits a large distributed aperture telescope array to be designed that has both a simple optical form and a much larger phased (i.e. corrected) field of view. As a design example, we investigate the effect of the distortion correcting element on the size of the achievable field of view for a 45 meter diameter distributed aperture telescope array populated with 8 meter diameter collectors.
A cryogenic mechanism has been built to correct for the blurring effects of atmospheric dispersion in adaptive-optics images from large aperture telescopes. Steward Observatory's 6.5 m telescope features a deformable Cassegrain secondary mirror compensating for atmospheric turbulence at wavelengths from 1 - 5 microns. At 1 micron, smearing caused by atmospheric dispersion equals the diffraction-limited image width (0.04 arcseconds FWHM). In order to correct for this effect and to maintain the low thermal background provided by the adaptive secondary, we have designed and built a cryogenic (77 K) atmospheric dispersion corrector. Operating over a spectral range of 1 - 5 microns, two pairs of counter-rotating calcium/lithium-fluoride prisms provide diffraction-limited imaging over a field of 1.7 arcminutes at a zenith angle up to 45 degrees.
Multi-beam scanning is the effective method for high speed and high definition in Laser Printing, and there are three systems for this method as follows: (1) Laser Diode (LD) Array system, (2) System for dividing a single light source, (3) System for combining beams of multiple LDs by optical devices. Each of these systems has both advantage and disadvantage, and which one to use among these three depends on application requirements. The third system above allows for the use of conventional LDs and therefore it is low cost and offers a large degree of freedom in selecting light sources. We have already developed a Two LD Prism-based Light Source Unit that uses a prism to combine the beams emitted by two LDs. This system achieves stable optical characteristics with any conventional scanning optical elements. We have further enhanced this system. We have determined an optimum design that includes scanning lens and have developed the Two LD Beam-crossing Light Source Unit which performs multi-beam scanning using two LDs without a prism. In this paper, we report on recent multi-beam-scanning technologies and introduce our newly developed the Two LD Beam-crossing Light Source Unit.
Generally, a spectrometer uses a diffraction grating to spread the spectral components of a light incident on the diffraction grating on a one-dimensional detector. The detector is composed of pixels linearly distributed along a line. However, the diffracted light is not spread linearly on the detector which means that the wavelength on pixel 1 is not linearly correlated with the wavelength on pixel 2. The resolution is therefore not constant for all the spectral range of the spectrometer. To know which pixel corresponds to which wavelength, a nonlinear calibration process must be applied to get a linear relation between the diffracted light position and the wavelength of this light. The new spectrometer that we present uses a special lens configuration name F-sin(theta) lens to provide a linear relation in the image plane between the pixel position and the wavelength of the light. The f- sin(theta) characteristic is defined as the difference in percent between the design position of the wavelength in the image plane and its ideal position, if the lens is perfect. The characteristic of the lens used in the spectrometer is better than 0.1%. The concept can also be used for WDM and DWDM applications.
Introducing the desired amount of distortion in an optical system is possible and relatively straight forward for optical designer. Known f-theta lenses used in laser scanner system is one of the most popular lenses of this type. With the development of DWDM system, compact spectrometer and various grating based devices, the interest in solving optical problems with innovative optical design has been a revival. On the other hand, it is possible to simplify considerably the task of the software by designing more sophisticated optical element. The F-sin(theta) lens is such a device which can be used in various grating based devices to improve the performance. This optical device is intended to provide a new lens or lens group which can be used with a diffraction grating to provide a linear output plane with the wavelength (lambda), but also with the order of diffraction (m), or with the grating spatial frequency, or with the inverse of the index of refraction (1/n). Based on theoretical consideration, we calculated which amount of distortion is desired to get linear output plane for a grating based device. We present singlet, achromatic doublet and mirror having this characteristic. These F-sin(theta) lenses present satisfactory distortion characteristic and have an improved correction for the curvature of image plane. F-sin(theta) lens will be also name F-lambda lens.
We present a design and tolerancing approach that permits the achievement of a high degree of spatial and spectral uniformity of response from a pushbroom imaging spectrometer. Such uniformity of response is crucial for the extraction of accurate spectroscopic information from remotely sensed data. The spectrometer system example comprises two independent spectrometer modules covering the 400 - 2500 nm range, separated through a dichroic mirror. The relative merits of alternative approaches are briefly reviewed before concentrating on the problem of building a flight-worthy system that can approximate its design performance. The tolerancing approach requires simultaneous monitoring of many parameters, and specifically: overall image quality, spectral distortion, spectral MTF variation with field, spatial distortion, spatial MTF variation with wavelength, and slit magnification to within a small fraction of a pixel. It is shown that the wavefront error alone or even supplemented by distortion figures is insufficient for characterizing a system with high response uniformity. Tolerance values on the components and their positioning are primarily guided by the need to achieve the same magnification between the two spectrometer modules, as well as by the interferometric alignment method.
In 2003, NASA is planning to send two robotic rover vehicles to explore the surface of Mars. The spacecraft will land on airbags in different, carefully chosen locations. The search for evidence indicating conditions favorable for past or present life will be a high priority. Each rover will carry a total of ten cameras of five various types. There will be a stereo pair of color panoramic cameras, a stereo pair of wide- field navigation cameras, one close-up camera on a movable arm, two stereo pairs of fisheye cameras for hazard avoidance, and one Sun sensor camera. This paper discusses the lenses for these cameras. Included are the specifications, design approaches, expected optical performances, prescriptions, and tolerances.
When a polarized polychromatic beam passes through birefringent medium, the constituent spectral components suffer different change of state of polarization. As a result when the beam passes through an analyzer, the color of the resultant beam changes depending on the orientation of the analyzer, state of polarization of the input beam, spectral intensity distribution of the source and the polarizing properties of the birefringent medium. In the present article the variation of trichromatic color coordinates of the resulting beam is observed both theoretically and experimentally with the variation of the azimuthal angle of the analyzer. A comparative study is carried out between a quarter-wave plate and an achromatic quarter-wave prism. This study is envisaged to be useful for the performance analysis of achromatic wave plates.
The Wide Field Camera 3 (WFC3) is a panchromatic imager that will be deployed in the Hubble Space Telescope (HST) in 2004. The mission of the WFC3 is to enhance HST's imaging capability in the ultraviolet, visible and near-infrared spectral regions. Together with a wavelength coverage spanning 2000A to 1.7 microns, the WFC3 high sensitivity, high spatial resolution, and large field-of-view provide the astronomer with an unprecedented set of tools for exploring all types of exciting astrophysical terrain and for addressing many key questions is astronomy today. The filter compliment, which includes broad, medium, and narrow band filters, naturally reflects the diversity of astronomical programs to be targeted with WFC3. The WFC3 holds 61 UVIS filters elements, 14 IR filters, and 3 dispersive elements. Accurate and comprehensive knowledge of the optical performance of these components including its pass-band and out-of-band rejection behavior are necessary to verify that the instrument will meet its scientific objectives. The measured throughput curves are essential components in instrument performance models used to plan observations, and in calibration algorithms for removing the instrument signature from in-flight data. We will report on the normal incidence in-band and out-of-band transmittance of the IR filters measured near the operating temperature of -30 degree(s)C and additional tests used to characterizes the filter's performance. Details of the characterization apparatus, that include an optical cryostat, and a grating spectrometer are discussed.
Design variants of a recently developed optical imaging system have been computed for the thermal infrared spectral bands, which offer some advantages for long-range surveillance and astronomy. Only the spherical primary mirror has the full pupil diameter, all other components being sub-diameter, so scaling is possible up to relatively large pupils. Low-cost fabrication is enabled by the prevalence of spherical optical surfaces. Both MWIR and LWIR spectral transmissions are enabled by the choice of corrector materials, the examples given employing germanium and sapphire for 3.5 - 5.5 micrometers and germanium and zinc selenide for 3.5 - 5.5 micrometers and 8 - 12 micrometers passbands. Diffraction at these wavelengths is the main contributor to resolution constraints, so high numerical aperture values are preferred to enable a better match of blur spot diameter to generally available pixel dimensions. The systems described can routinely be designed to have speeds of f/0.8 or faster, while maintaining diffraction-limited performance over useful angular fields. Because the new design system employs a relayed catadioptric, it is possible to make the aperture stop of the system coincident with the window of the detector cryostat, enabling precise radiometric geometry. The central obscuration provides a convenient location for a calibration source, and both this and a mask for secondary spider supports can be included within the detector cold screen structure. Dual-band operation could be enabled by inclusion of a spectral beam splitter prior to a dual relay/imager system.
Although relatively unaffected by rain and snow, free space infrared laser optical communication systems are affected by fog and atmospheric turbulence. We have calculated the signal loss from scintillation to predict bit error rates by varying the amount of scintillation, the link distance, and system details. Increasing the number of transmitters and the effective area was predicted to improve scintillation in earlier work in this field. We found that increasing both the number of transmitters and the effective receiver area greatly improved the signal loss caused by scintillation and thus, the bit error rate. For example, under high scintillation (Cn2 equals 10-13 m-2/3), the four transmitter/receiver system at a link distance of 1 km should experience a bit error rate of better than 10-10 for a 4.0 dB loss. Under the same conditions, an identical system with only one transmitter and receiver should experience a bit error rate of 10-1.5 (0.032 bits per second) for the same 4.0 dB loss. Increasing just the number of transmitters or the number of receivers improved the signal, but increasing both improved the signal even more than expected. In general, single beam systems should be limited to link distances less than about 600 m.
Laboratory-on-a-chip has been interested widely in recent years, where the sample preparation, bio-chemical reaction, separation, detection and analysis, are performed in a small biochip which is only a fingernall dimension. In order to obtain a high detection sensitivity 1 fluors/micrometers 2 (one fluorescence molecular per square micrometer) in biochip scanning system, it is required that the scanning objective lens is a big numerical aperture (> 0.5), very small focal spot (< 5 micrometers ) and long back focal length (> 3 mm). In this paper, a combined lens is designed for the scanning objective lens, which is with big numerical aperture NA > 0.7, very small focal spot (< 2 micrometers ) and long back focal length (> 3 mm). The phase aberrations of combined lens, including the aspherical aberration and the chromatic aberration corresponding to wavelength 532 nm, 570 nm, 635 nm, 670 nm, are corrected very well. The encircled energy diagram of the lens is good to the diffraction limit. The focal spot diagram, the optical path difference diagram, the transverse ray fan plot and the modulation transfer function, are studied also. A novel confocal scanning system of biochip with the designed combined lens as the objective lens is developed, some experiment results in a multi-channel biochip are obtained.