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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.