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This PDF file contains the front matter associated with SPIE Proceedings Volume 8844, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
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Optical tolerancing simulation has improved so that the modeling of optomechanical accuracy can better predict as-built
performance. A key refinement being proposed within this paper is monitoring formal interference fits and checking lens
elements within their mechanical housings. Without proper checks, simulations may become physically unrealizable and
pessimistic, thereby resulting in lower simulated yields. An improved simulation method has been defined and
demonstrated in this paper with systems that do not have barrel constraints. The demonstration cases clearly show the
trend of the beneficial impact with yield results, as a yield increase of 36.3% to 39.2% is garnered by one example.
Considerations in simulating the realistic optomechanical system will assist in controlling cost and providing more
accurate simulation results.
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The Hobby-Eberly Telescope (HET) Wide Field Corrector (WFC) is a four-mirror optical system which corrects for aberrations from the 10-m segmented spherical primary mirror. The WFC mirror alignments must meet particularly tight tolerances for the system to meet performance requirements. The system uses 1-m class highly aspheric mirrors, which precludes conventional alignment methods. For the WFC system alignment a “center reference fixture” has been used as the reference for each mirror’s vertex and optical axis. The center reference fixtures have both a CGH and sphere mounted retroreflector (SMR) nests. The CGH is aligned to the mirror’s optical axis to provide a reference for mirror decenter and tilt. The vertex of each mirror is registered to the SMR nests on the center reference fixtures using a laser tracker. The spacing between the mirror vertices is measured during the system alignment using these SMR nest locations to determine the vertex locations. In this paper we present the procedures and results from creating and characterizing these center reference fixtures. As a verification of our alignment methods we also present results from their application in the WFC system alignment are also presented.
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As many authors have documented, it is possible to correct secondary color without using special glasses, if there are
substantial separations between lenses or groups that are chromatically uncorrected. The trick is to use the separations to
“induce” secondary color by allowing the rays of different colors to separate from each other before being refracted by
the group that follows. This approach works, but the use of separated and uncorrected groups that correct each other
raises the question of tolerance sensitivity, because misalignments between the groups causes imperfect correction of the
aberrations. It is generally good practice to correct aberrations within groups, rather than allow the groups to “crosscorrect”
each other. On the other hand, the use of special glass types to control secondary color directly is often either
discouraged for cost reasons, or simply not allowed because of thermal shock sensitivity. Moreover, some optical
systems (particularly projector applications) require extremely good secondary color correction – often to a small
fraction of a pixel. The important question is how much secondary color can be induced before the increased tolerance
sensitivity negates the advantage of the color correction. In this paper, we examine the as-designed and as-built
performance of several sample systems that rely on separated groups for the correction of secondary color, and compare
the performance to that of systems designed without regard to secondary color correction.
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The optical alignment of the star trackers on the Global Precipitation Measurement (GPM) core spacecraft at NASA
Goddard Space Flight Center (GSFC) was challenging due to the layout and structural design of the GPM Lower Bus
Structure (LBS) in which the star trackers are mounted as well as the presence of the star tracker shades that blocked
line-of-sight to the primary star tracker optical references. The initial solution was to negotiate minor changes in the
original LBS design to allow for the installation of a removable item of ground support equipment (GSE) that could be
installed whenever measurements of the star tracker optical references were needed. However, this GSE could only be
used to measure secondary optical reference cube faces not used by the star tracker vendor to obtain the relationship
information and matrix transformations necessary to determine star tracker alignment. Unfortunately, due to
unexpectedly large orthogonality errors between the measured secondary adjacent cube faces and the lack of cube
calibration data, we required a method that could be used to measure the same reference cube faces as originally
measured by the vendor. We describe an alternative technique to theodolite autocollimation for measurement of an
optical reference mirror pointing direction when normal incidence measurements are not possible. This technique was
used to successfully align the GPM star trackers and has been used on a number of other NASA flight projects. We also
discuss alignment theory as well as a GSFC-developed theodolite data analysis package used to analyze angular
metrology data.
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In a lens system a temperature change has the effect of changing the index of refraction and the geometry of the lens
elements. In addition, after a temperature change the lens takes some time to stabilize. As a consequence the optical
properties of the nominal lens system change. We review the concepts of the opto-thermal coefficient and of the thermal
diffusivity, and provide a method for their rapid calculation in lens design software. We also provide tables of these
coefficients that are needed in a lens tolerancing analysis.
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The ATLAS Instrument for the ICESat-2 mission at NASA's Goddard Space Flight Center required a test-bed to prove
out new concepts before the mission launches in 2016. The Optical Development System (ODS) laboratory was created
to use breadboard, prototype, and engineering-model levels of hardware and software to model and evaluate the ATLAS
alignment system. A one meter parabolic mirror was used to create a collimated light beam to align prototype and
engineering model transmitter and receiver optics and test closed-loop alignment algorithms. To achieve an error of less
than two micro-radians, an active deformable mirror was used to correct the wave front to subtract out the collimator
mount error.
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For many years parabolic mirrors have been used as the primary focusing optics of short pulse high power lasers.
Pushing the boundaries of the highest focused intensities requires not only increases in peak laser power but also
exploring the limits of focal spot size. Modelling has been performed at the Central Laser Facility to evaluate the
performance and tolerance of the alignment of a variety of off-axis parabolic mirrors and their limitations in correcting
beam aberrations. Practical considerations such as debris shields and optic mounting have also been assessed for their
effects on the focal spots.
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Cygnus is a high-energy radiographic x-ray source. Three large zoom lenses have been assembled to collect images from
large scintillators. A large elliptical pellicle (394 × 280 mm) deflects the scintillator light out of the x-ray path into an
eleven-element zoom lens coupled to a CCD camera. The zoom lens and CCD must be as close as possible to the
scintillator to maximize light collection. A telecentric lens design minimizes image blur from a volume source. To
maximize the resolution of objects of different sizes, the scintillator and zoom lens are translated along the x-ray axis,
and the zoom lens magnification changes. Zoom magnification is also changed when different-sized recording cameras
are used (50 or 62 mm square format). The LYSO scintillator measures 200 × 200 mm and is 5 mm thick. The
scintillator produces blue light peaking at 435 nm, so special lens materials are required. By swapping out one doublet
and allowing all other lenses to be repositioned, the zoom lens can also use a CsI(Tl) scintillator that produces green
light centered at 540 nm (for future operations). All lenses have an anti-reflective coating for both wavelength bands.
Two sets of doublets, the stop, the scintillator, and the CCD camera move during zoom operations. One doublet has x-y
compensation. Alignment of the optical elements was accomplished using counter propagating laser beams and
monitoring the retro-reflections and steering collections of laser spots. Each zoom lens uses 60 lb of glass inside the 425
lb mechanical structure, and can be used in either vertical or horizontal orientation.
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Most of the practical optical systems have circular shape lens pupil and rectangular shape image field. This paper
proposes a four dimensional polynomial to describe the full-field wavefront with orthogonal polynomials set in both
circular pupil and rectangular field. The basic functions of both the pupil wavefront and the field wavefront are Zernike
circle polynomials, multiplying each other to a four dimensional double Zernike polynomial (DZP) function. The double
Zernike polynomial coefficients of the full-field wavefront represent the global optical aberration of the image system.
The misalignment perturbation changes the corresponding least squares fitted DZP coefficients. The changed DZP
coefficients shows both linear and nonlinear response to the misalignment status when the misalignment is large. The
Tri-Mirror Anastigmatic Telescope is used as one of the implemented example showing the changed DZP due to
perturbation.
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We present Finite-Difference Time-Domain (FDTD) simulations to explore feasibility of chip-to-chip waveguide
coupling via Optical Quilt Packaging (OQP). OQP is a newly proposed scheme for wide-bandwidth, highly-efficient
waveguide coupling and is suitable for direct optical interconnect between semiconductor optical sources, optical
waveguides, and detectors via waveguides. This approach leverages advances in quilt packaging (QP), an electronic
packaging technique wherein contacts formed along the vertical faces are joined to form electrically-conductive and
mechanically-stable chip-to-chip contacts. In OQP, waveguides of separate substrates are aligned with sub-micron
accuracy by protruding lithographically-defined copper nodules on the side of a chip. With OQP, high efficiency chip-to-chip
optical coupling can be achieved by aligning waveguides of separate chips with sub-micron accuracy and reducing
chip-to-chip distance. We used MEEP (MIT Electromagnetic Equation Propagation) to investigate the feasibility of OQP
by calculating the optical coupling loss between butt coupled waveguides. Transmission between a typical QCL ridge
waveguide and a single-mode Ge-on-Si waveguide was calculated to exceed 65% when an interchip gap of 0.5 μm and
to be no worse than 20% for a gap of less than 4 μm. These results compare favorably to conventional off-chip coupling.
To further increase the coupling efficiency and reduce sensitivity to alignment, we used a horn-shaped Ge-on-Si
waveguide and found a 13% increase in coupling efficiency when the horn is 1.5 times wider than the wavelength and 2
times longer than the wavelength. Also when the horizontal misalignment increases, coupling loss of the horn-shaped
waveguide increases at a slower rate than a ridge waveguide.
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The main goal of this work is to show the principles, design and performance of a modified point diffraction
interferometer to evaluate the local higher order aberrations of progressive addition lenses in order to analyze the
tolerances in the design of these ophthalmic components for a reasonable level of comfort by the different users. We also
present a detailed analysis of high order aberrations in circular regions within the four most relevant regions of interest of
this kind of lenses.
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Lenses with high numerical apertures can be optimized and manufactured to produce diffraction-limited performance
across an entire field-of-view while having significant pupil aberration. Optimization is generally based on root-meansquare
(RMS) wavefront error. Most modern optical software correctly takes into account the need for chief-ray aiming
but can still model such systems differently from one another, including the reporting of RMS values. These differences
can affect the nominal performance, both on- and off-axis, and can therefore complicate technical discussions and have
an effect on the design and tolerancing of the lens. Understanding the functions of the lens in the application is
important. Test results from an interferometer can lead to further discrepancies compared to the actual system function.
These differences are explored in the case of a high numerical aperture objective lens. Some reasons for these differences
are examined.
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In the assembly of multi-component optical systems the precise positioning of every single lens element respectively lens surface is key to reach an optical performance that corresponds to the optical design. Here, in addition to lateral decentering of single elements – such as shift and tilt – the accurate positioning of the optical surfaces along the optical axis is an essential requirement. In this contribution we present the highly accurate determination of lens center thicknesses and air gaps of optical assemblies in a non-contact manner. The measurement technique is based on time-domain low coherent interferometry (also known as A-scan optical coherence tomography). Here, a low coherent interferometer signal is recorded in a Michelson-type setup as a function of a variable optical delay in the reference arm. Whenever the variable optical path length matches the path length to a lens surface, a coherence peak occurs. Thus, relative surface distances can be derived from the optical delay between two peaks. For a highly-accurate measurement a precise determination of the optical delay length with minimized Abbe-errors is required. Here, a precise long-coherent reference interferometer is superimposed to the short-coherent signal in the optical delay line. Both signals are recorded simultaneously; subsequently, the data is transferred to a PC system for the analysis. With the presented technique lens thicknesses and air spacings of up to 800 mm can be measured with a resulting accuracy significantly below 0.5 μm. The obtained results can be used for the compensation of potential deviations/errors in the manufacturing process or for quality control using a pass/fail-evaluation.
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Optical systems are increasingly used in microsystems, telecommunication, aerospace and laser industry. Due to the complexity and sensitivity of optical systems, their verification poses many challenges to engineers. Traditionally, the analysis of such systems has been carried out by paper-and-pencil based proofs and numerical computations. However, these techniques cannot provide perfectly accurate results due to the risk of human error and inherent approximations of numerical algorithms. In order to overcome these limitations, we propose to use theorem proving (i.e., a computer-based technique that allows to express mathematical expressions and reason about them by taking into account all the details of mathematical reasoning) as an alternative to computational and numerical approaches to improve optical system analysis in a comprehensive framework. In particular, this paper provides a higher-order logic (a language used to express mathematical theories) formalization of ray optics in the HOL Light theorem prover. Based on the multivariate analysis library of HOL Light, we formalize the notion of light ray and optical system (by defining medium interfaces, mirrors, lenses, etc.), i.e., we express these notions mathematically in the software. This allows us to derive general theorems about the behavior of light in such optical systems. In order to demonstrate the practical effectiveness, we present the stability analysis of a Fabry-Perot resonator.
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Structural Health Monitoring (SHM) is an all-embracing process of implementing a damage detection and
characterization strategy for critical infrastructures. Its data acquisition portion relies on a multi-disciplinary approach
that combines a variety of sensing technologies to capture, log and analyze data of various types. Engineering surveying
science and practice is a key element in SHM that contributes to the detailed characterization of structures’ geometry in
space and time. Optical and digital imagery systems and methods form an integral part of surveying techniques, and
therefore, their evolution has a profound effect in SHM applications. This paper attempts a summary classification and a
critical discussion of conventional and emerging engineering surveying techniques related to optical systems for SHM.
More specifically, optical sensors are categorized and cross-compared using various criteria, such as their principle of
operation, their accuracy characteristics, their limitations due to atmospheric and other effects and their potential to
monitor low or high dynamic phenomena. Also, practical issues of interest are examined including their ability to
provide simultaneously measurements at a single- /multi-point locations and their capacity to operate remotely and /or
integrated within a sensors network. Finally, examples and summary results from various sources are included to further
enhance discussion.
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Development of an imaging telescope having a large mirror generally requires a sound infrastructure including expensive
devices such as collimators and interferometers. In this paper we investigate the development and characterization of a
medium size telescope (140 mm aperture) using simple techniques. Alignment was done with a mechanical measurement
device. Detector was placed using an image of a ruled outside building. Radiometric calibration was done with open-sky
images. And finally MTF was measured using stellar images. We found that MTF of our telescope is greater than %15
all along the detector at 20 lp/mm, which is the Nyquist frequency of 25 μm pixel size. This shows that alignment and
focus adjustments work well enough in the telescope. These simple techniques can be used for the development and
characterization of a medium-size and medium-resolution imaging telescopes.
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