Optical System Alignment, Tolerancing, and Verification XV

This work explores quick predictive methods for calculating potentially risky stresses and deflections in cemented doublets experiencing temperature change that agree well with finite element analysis. Adhesive theory, confirmed by finite element analysis, predicts stress singularities that complicate interpretation of the stress calculations. The presence of a stress singularity indicates the breakdown of linear elastic assumptions, but damage initiation and stress singularities are related. The authors find that geometry details near a bond edge can exacerbate or minimize damage initiation and stress concentrations. Because the interpretation of the stress results is complicated, the authors investigated predicted stresses in doublets that have been successfully tested between -40 and 85 °C. This study found that the thermal strain (∆T ∙ ∆α) should be less than 189 ppm, where ∆T is the temperature excursion and ∆α is the difference in the two glass coefficients of thermal expansion.

Real hardware lens assemblies have unique as-built optical axes. We discuss the definition of this axis and show how to find it in real hardware using the propagation of a Bessel beam through the assembly with no need for a rotary table. We show how a Bessel beam aids the initial assembly of the lens in an optimum manner and then how to use the Bessel beam to find any remaining centering error after the lens is assembled. The advantage of the method is not just better centering but the centering is faster and more amenable to automation.

White balance calibration of a colorimeter ensures measurement accuracy when probing a display, but the adjustment of display luminance can introduce spectral drift, drifting away from where the colorimeter was calibrated. Mimicking a uniform micro-LED or OLED panel with an integrating sphere, and using an imaging colorimeter, we compare error sources that contributes to colorimeter reading error, finding that spectral drifts are a major contributor to the inaccuracies in the colorimeter measurement. This finding highlights the need for colorimeter recalibration to account for the spectral drifts, especially the need for high-speed recalibration in mass production.

Separating robotic movement errors from measurement results requires a careful mapping of robotic movements. Comparing programmed movements to a known precision surface provides a method for quantifying movement errors through a measurement’s scan. We measured the airgap between a low coherence interferometry (LCI) probe mounted to the robotic arm and a precision optical flat. We programmed different movement paths of a 6-axis 946 mm reach robotic arm. The movements ranged from linear to a smooth arcing curvature at near, mid, and far reach locations. Deviations ranged from sub-micron to micron levels from the ideal motion paths. Mapping the places with minimal positioning errors is essential for our goal of accurate metrology results.

An innovated approach to mounting off-axis parabolas (OAPs) led to the successful alignment of five OAPs to span a 57-foot optical path distance. This confocal mount technique can also be broadened to allow alignment of other conics (ellipses and hyperbolas), and with extra thought, free-form mirrors. Examples will be given detailing the process for these other mirrors.

New radiographic imaging needs require large 270 mm x 270 mm square LYSO scintillators and the capability to use either 92 x 92 mm or 62 x 62 mm image sizes on different CCD cameras. A new telecentric zoom lens has been designed to meet these requirements. A two-color laser alignment system that enables the best possible system resolution will be discussed. Monitoring the retro-reflections at two different wavelengths simplify the optical alignment.

Precise alignment of fiber-arrays-to-chips is vital for next-generation optical interconnects to provide high bandwidth density with low energy cost for data centers. Utilizing two-photon lithography with sub-micron level resolution, the fiber-insertion ferrule will not only position the fiber-array vertically, but will also improve the coupling efficiency to grating couplers in the photonic integrated circuit. A free-form prism is 3D-printed together with the ferrule and is positioned under the ferrule, between fiber tip and the grating coupler. Presentation title: Fiber-array-to-chip alignment and coupling via 3D-printed lensed-ferrule. Author list: Shengtao Yu, Tristan E. Thrall, Thomas K. Gaylord, Muhannad S. Bakir.

Flat-field correction (FFC) is essential for addressing illuminance roll-off in optical imaging systems, a process that requires capturing an image of a uniform light source. In systems with switchable cylindrical lenses and variable focus, such as those used for eye prescriptions, the number of images required to collect for FFC increases with each lens adjustment. We propose a numerical method that uses a few core images to synthesize FFC images for various configurations, reducing data requirements substantially. This method was validated on two imaging systems with differing optical alignments, achieving illuminance uniformity deviations of less than 2% with just 4% of the original data.

An experimental prototype of an interposer-to-PIC evanescent coupler between silicon nitride and silicon was passively assembled using high speed pick and place technology with machine vision only. Optical testing of the packaged device revealed an average coupling loss upper limit of -2.16 dB (with a minimum of -0.93 dB) and an average 1 dB lateral alignment tolerance of +/- 1.14 um in the 1480-1640 nm wavelength range. The average loss upper limit varied by less than +/- 0.357 dB and the tolerance varied by less than +/- 30 nm from 23-60 degrees C. Likewise, the coupling loss had a total range of less than 1.5 dB when measured across four different packages, demonstrating repeatability. Results show the viability of this coupler to help achieve Pb/s co-packaged optics switch performance by eliminating active fiber-to-chip alignment and scaling down optical input/output pitch at the PIC level.

The adoption of freeform optics by designers and manufacturers has increased in recent years. With the increase of flexibility, a freeform surface can bring a system, it also brings more sensitivities. To effectively control these sensitivities during integration, the tolerancing needs to incorporate the limits of the metrology device for the tolerance operand under test. Understanding a vendor’s manufacturing and metrology capabilities is critical to designing and tolerancing a freeform surface that uses its physical features to aid in integration. Interfacing with a vendor early in the design process may improve manufacturing timelines due to the alignment of the freeform definition with the available metrology. Favorable freeform definitions will be reviewed along with tolerancing and specification recommendations.

Recent advances in a unique, pattern-recognition, electronic autocollimator engineered at Leviton Metrology Solutions in Boulder, CO are presented. A measurement system using this autocollimator called the Inter-target Differential Electronic Autocollimator (IDEA) is capable of making differential angular measurements between a target flat and a flat base reference mirror with 30 nrad accuracy. This measurement approach largely nullifies environmental influences on angle measurements and makes it possible to test payloads at extreme temperatures in thermal vacuum environments with exquisite accuracy. For shorter focal length versions of UWFOREA, the system can measure over an astounding and unprecedented +/-10° angular range with sub- 5 µrad calibrated accuracy. The internal stability of UWFOREA has been demonstrated to be as low as 5 nrad rms with only modest temperature control of about 1 C. Select UWFOREA and IDEA data for critical calibrations for a number of space-flight missions and ground support metrology systems are presented.

The Atmospheric Waves Experiment (AWE) Advanced Mesospheric Temperature Mapper (AMTM) is a widefield of view (WFOV) infrared imaging radiometer designed for use in measuring the P1(2) and P1(4) emission lines of the earth's OH layer to produce images of gravity waves. Designed, built, and characterized by Utah State University (USU) Space Dynamics Laboratory (SDL), the sensor is externally mounted to the International Space Station (ISS) looking nadir. This paper will present an overview of the optical design, tolerance analysis, detector focusing, and image quality verification testing in vacuum of the Opto-Mechanical Assembly (OMA).

This paper will present the newly developed high-power laser calibration system and alignment at NIMT. The system is composed of a high stability, high-power fiber laser with a wavelength of 1080 nm, as a laser source for calibration. Due to this wavelength is not visible to human eyes, the laser is equipped with a built-in red alignment laser and an automatic shutter that can be used for the routine alignment of the whole optical path. The method of calibration is in-direct comparison using 2 beam samplers and 2 monitor power meters, for better accuracy. Two beam expanders are used to adjust the laser beam diameter. The reference power meter for calibration is a thermopile sensor. The optical characterization results of the reference power meter such as power nonlinearity and detector surface non-uniformity, to be performed at the National Metrology Institute of Germany (PTB), will also be present.

As a CubeSat mission, the development of the TBIRD payload was focused on low SWaP and a “rapid prototyping” approach which accepted higher risks to accelerate the schedule and reduce costs. The optomechanical design process followed standard in-house processes to develop a system that would be robust to LEO environmental loads, with a focus on the stability of the transmit (Tx) and receive (Rx) channel performance metrics. TBIRD successfully met and exceeded the total downlink requirements, with a bandwidth of 200Gbps and a total downlink of 4.8TB of information in a single pass. DISTRIBUTION STATEMENT A. Approved for public release. Distribution is unlimited. This material is based upon work supported by the National Aeronautics and Space Administration under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.

POET is a proposed Canadian Microsatellite mission to detect new, potentially habitable, rocky planets transiting low-mass stars, and to characterize the atmospheres of known transitioning extrasolar planets. The all-reflective telescope offers simultaneous imaging in the u-band (300-400 nm), VNIR (400-900 nm) and SWIR (900-1700 nm) through a 20 cm aperture. The optical telescope assembly (OTA) has been designed and build with support from the Space Technology Development Program (STDP) of the Canadian Space Agency. The prototype underwent complete integration, optical properties testing, and performance verification in a thermal-vacuum chamber. POET is a collaboration between Bishop’s University, Western University, ABB and SFL-UTIAS.

The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite is a strategic climate continuity mission that will answer new and emerging advanced science questions related to Earth’s changing climate. These science goals are accomplished via PACE’s main optical instrument, a sophisticated spectrograph, the Ocean Color Instrument (OCI) consisting of UVVIS and VISNIR channels each complete with a dichroic, grating, and detector. We will overview the characterization methods used for each component, with respect to its metrology targets, and further discuss how baseline characterization served as a proxy when lines of sight to the optical components normal were lost in later integration steps.

Compared to the traditional optical design, the short wavelength infrared hyperspectrometer installed on the GaoFen-5 has a rectangular wide field-of-view (60 mm × 16 mm) with a spatial dimension of 2000 pixels, which is challenging for alignment and testing. This paper proposes an efficient method to align this wide-field hyperspectrometer. The experimental results demonstrate that the residual root mean square (RMS) of the system is less than 0.25λ@ 632.8nm, and the smile shifts are less than 1 nm. Furthermore, the on-orbit performance of the GF-5 illustrates that our method can meet the high requirements for high-precision alignment of hyperspectrometers.

Multi-aperture optical imagers intrigue attention for high-resolution Earth observation optics. One of the crucial technologies in establishing such optical systems is an on-orbit alignment method of piston-tip-tilt modes between each sub-aperture. Here, we propose using an image-based alignment approach based on the stochastic parallel gradient descent (SPGD) algorithm. We developed an efficient alignment algorithm as well as a tabletop multi-aperture imaging setup. The Experimental results showed the successful aperture synthesis of 37 mirror segments with the present approach.

This talk will consider the future of metal halide perovskite (MHP) photovoltaic (PV) technologies as photovoltaic deployment reaches the terawatt scale. The requirements for significantly increasing PV deployment beyond current rates and what the implications are for technologies attempting to meet this challenge will be addressed. In particular how issues of CO2 impacts and sustainability inform near and longer-term research development and deployment goals for MHP enabled PV will be discussed. To facilitate this, an overview of current state of the art results for MHP based single junction, and multi-junctions in all-perovskite or hybrid configurations with other PV technologies will be presented. This will also include examination of performance of MHP-PVs along both efficiency and reliability axes for not only cells but also modules placed in context of the success of technologies that are currently widely deployed.

The recent advent of robust, refractory (having a high melting point and chemical stability at temperatures above 2000°C) photonic materials such as plasmonic ceramics, specifically, transition metal nitrides (TMNs), MXenes and transparent conducting oxides (TCOs) is currently driving the development of durable, compact, chip-compatible devices for sustainable energy, harsh-environment sensing, defense and intelligence, information technology, aerospace, chemical and oil & gas industries. These materials offer high-temperature and chemical stability, great tailorability of their optical properties, strong plasmonic behavior, optical nonlinearities, and high photothermal conversion efficiencies. This lecture will discuss advanced machine-learning-assisted photonic designs, materials optimization, and fabrication approaches for the development of efficient thermophotovoltaic (TPV) systems, lightsail spacecrafts, and high-T sensors utilizing TMN metasurfaces. We also explore the potential of TMNs (titanium nitride, zirconium nitride) and TCOs for switchable photonics, high-harmonic-based XUV generation, refractory metasurfaces for energy conversion, high-power applications, photodynamic therapy and photochemistry/photocatalysis. The development of environmentally-friendly, large-scale fabrication techniques will be discussed, and the emphasis will be put on novel machine-learning-driven design frameworks that leverage the emerging quantum solvers for meta-device optimization and bridge the areas of materials engineering, photonic design, and quantum technologies.

Achieving precise alignment in Korsch telescopes involves intricate challenges, especially when determining the optical axis with the complex aspheric primary mirror. Traditional methods face limitations when obscured by secondary components like the telescope tube, folding mirror, and additional optical surfaces. These limitations can potentially result in the inability to find a solution or local optima. However, this study introduces a methodology employing laser radar to measure the three-dimensional aspheric primary mirror surface. Additionally, multiple laser radars positioned at various locations and the Korsch telescope share a common reference coordinate system, ensuring uniform management. Secondary components undergo measurement by additional laser trackers and autocollimators. Furthermore, all constituent parts of the Korsch telescope are digitized as CAD models, enabling the management of actual measured positions relative to nominal positions. This research streamlines the initial alignment of Korsch telescopes, easing the discovery of optical alignment solutions conducive to achieving global alignment solutions and maximizing the system's optical performance.

In this paper, we proposed a method for rapid calibration of long effective focal length collimators by the Ronchi test. In the paper, we would use the module to verify the alignment of an optical system with a focal length of 10,500mm and a f-number of approximately 14.3. By measuring changes in focal plane position, collimation could be quickly confirmed and adjusted. According to experiment results, the measurement error of the focal plane of this module is approximately ± 10 um. It means that the error in the distance between the primary mirror and the secondary mirror can be less than ± 0.2 um. The collimator of emission angle error less than 1.745E-5 mrad. Form the above experiment results, the module could perform collimation verification at lower cost and faster speed.

This paper introduces an innovative calibration technique based on the Vernier caliper principle for spatial frequency analysis, aimed at significantly improving the accuracy of collimator calibration. By using a lens with an effective focal length of 1000mm and a camera with a pixel size of 1.85μm, periodic patterns fixed on the focal plane of a collimator with a focal length of 10500mm are photographed. After capturing and comparing the periodic patterns at various light emission positions of the collimator, spatial frequency analysis calculations enable us to achieve sub-pixel level positioning accuracy. This accuracy allows for the precise determination of whether the collimator's target pattern is correctly positioned on its own focal plane, ensuring the collimator can produce highly parallel collimated light. This method has increased the measurement accuracy of the collimator tenfold, enhancing the defocus resolution range of the collimator from ±0.508mm to ±0.051mm, providing an efficient and reliable solution for collimator calibration.

The design verification phase of the FORMOSAT-8 remote sensing satellites program's telescope proto-flight model has been successfully passed the green light, paving the way for the implementation of the telescope as the payload for the multi-satellite remote sensing constellation of FORMOSAT-8, comprising FORMOSAT-8A, FORMOSAT-8B, FORMOSAT-8C, FORMOSAT-8D, FORMOSAT-8E, and FORMOSAT-8F (collectively referred to as FORMOSAT-8X) satellites. This paper presents a comprehensive report on the optical design methodology and the lens centering alignment performance of the corrector lens within the FORMOSAT-8 remote sensing satellites program.