This PDF file contains the front matter associated with SPIE Proceedings Volume 10743, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

Variations of Monte Carlo ray tracing are the most popular techniques for computing stray light in optical systems. The simplest and easiest to implement version doesn’t require ray splitting so what an incident ray becomes at each interaction is determined by the probabilities of the possible physical processes there. Unfortunately, for a low probability process such as polished surface scatter (including particulate contamination), it requires a prohibitively large number of initial rays to get a sufficient ray density at a typical focal plane area. The details of several simple modifications that require far fewer rays for the same or better accuracy will be presented. These include universal techniques applicable also to illumination patterns such as smart binning (also called ‘pixel interpolation’) and the use of quasi-random instead of pseudo-random number generators. In addition, there is the ‘tweaked’ Monte Carlo method developed specifically for veiling glare (light from bright regions in an image bleeding into dark regions and thus reducing contrast). However, most available software for computing out-of-field stray light in general optical systems use importance sampling in the form of preferred scattering towards predetermined ‘importance areas’ limited by the usual approximations to modest solid angles. For nearly all optical surfaces, micro-roughness scatter (and particulate forward scatter) in direction-cosine space is rotationally symmetric about the specular direction. In this case, an efficient and accurate (even for large solid angles) version called an ‘Importance Sector’ is proposed as a replacement.

The bidirectional reflectance distribution function (BRDF) plays a fundamental role in the optical characterization of a surface. The BRDF is a measure of the amount of light incident from one direction which is scattered by a surface in another direction. Integrating the BRDF over specified incidence and reflected solid angles defines the bihemispherical reflectance, which can be related to the absorptance and emissivity of a surface. We have designed and fabricated a high-accuracy bidirectional reflectometer and used it to measure the bidirectional reflectance of a smooth silicon substrate coated with the black absorber Aeroglaze Z302®. Two different coating thicknesses displaying different degrees of surface roughness were studied. A BRDF model consisting of diffuse, glossy, and specular components was then fitted to the experimental results. Finally, the Monte Carlo ray-trace (MCRT) method was used to split an incident beam into a group of reflected rays whose power and direction were determined by the BRDF model. The combined model is capable of simulating the performance of any optical instrument which has Z302 coated on its active surfaces. As a demonstration, the combined model is used to simulate the performance of the bidirectional reflectometer experiment used to obtain the original data.

Stray light, any unwanted radiation that reaches a focal plane, presents a significant challenge for both airborne and satellite remote sensing systems by reducing image contrast, creating false signals or obscuring faint ones, and ultimately degrading radiometric accuracy. These detrimental effects can have a profound impact on the usability of collected data, which must be radiometrically calibrated to be useful for scientific applications. Understanding the full impact of stray light on data scientific utility is of particular concern for lower cost, more compact satellite systems which inherently provide fewer opportunities for stray light control. To address these concerns, we present a general methodology for integrating an optomechanical system model with the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model. The results reported in this paper describe the collection of necessary raytrace data from an optomechanical system model (in this case, using FRED Optical Engineering Software), and also include the initial demonstration of the integration method by imaging DIRSIG test scenes. By integrating a high-fidelity optomechanical system model with a physics-driven, synthetic image generation model like DIRSIG, we are now able to explore system trade studies and conduct sensitivity analyses on parameters of interest, including those that influence stray light, by analyzing their effects on realistic test scenes. This new capability further aids in demonstrating the quantitative linkage between system trade studies and impact to scientific users, which will enhance the writing of system requirements.

In optical thin-films and surfaces, geometric phase is utilized to control the phase beyond that possible through optical path differences. Geometric-phase lenses, which are significantly thinner than refractive lenses for the same numerical aperture (NA), most commonly use a spherical phase profile. This is especially effective for normally incident light, but like other thin lenses, the performance degrades noticeably for off-axis incidence and wider fields-of-view. In this study, we investigate whether or not various aspheric designs provide better off-axis performance. We simulate aspheric singlet and doublet liquid crystal geometric-phase lenses (24.5 mm diameter, 40 mm back focal length at 633 nm), aiming to optimize spot size performance at 0, 3, and 7 degrees field angles, using Zemax OpticStudio 16.5. By using Zernike fringe phase expansions, we find conditions which provide improved off-axis performance. We demonstrate improved performance of a compact lens system utilizing these polarization-dependent optics.

Anisotropic materials can comprise multilayer stacks, where each anisotropic layer is, in turn, made from uniaxial-uniaxial or uniaxial-isotropic materials. Each uniaxial layer can be made from two dissimilar isotropic materials, e.g., a metal and a dielectric. Similar to usual metallo-dielectric structures, these multilayer structures can be used to achieve unique optical filters, and can be modeled as a bulk structure using effective medium theory. The optical properties of these anisotropic media can be described in terms of effective parameters such as permittivity and permeability tensors. In this work, optical propagation through such layered media is analyzed using Berreman 4 × 4 matrix along with appropriate boundary conditions. Reflection and transmission are investigated as functions of the incident angle and wavelength. Results are compared with those obtained using the transfer matrix approach. This analysis can be extended to Gaussian beam propagation through such anisotropic materials using angular plane wave approach.

Assessing and optimizing polarization performance in the context of ray-based optical design can be challenging. We describe an approach to this problem that decouples polarization effects from optical system geometry for reflective systems. Each surface's polarization properties are parameterized in terms of their impact on retardance and diattenuation in the small angle-of-incidence limit, separating polarization assessment from the task of coating design. A low-resolution ray trace of the system is adequate to determine ray geometry at each interface, which can then be interpolated to rapidly evaluate net Jones Matrix pupil functions. Coating behavior can be easily varied using the ellipsometric parameters to investigate impacts and compensation. Desired values of these parameters can then be specified as constraints in coating design. Investigation with candidate telescope optical designs for LUVOIR show baseline root-mean-square wavefront errors in the nm range for the on-diagonal Jones matrix component, and throughputs of tens of parts per million. Promising possibilities for compensation using a purpose-designed coating on the secondary mirror are discussed, which reduce the on-diagonal wavefront error by a factor ~ 20, with accompanying but more modest reductions in coupling into off-diagonal terms.

The light field describes the radiance at a given point from a ray coming from a particular direction. Total irradiance comes from all rays passing the point. For a static scene, the light field is unique. Cameras integrate the light field. Each camera pixel sees the integration of the light field over the entrance pupil for ray directions associated with lens aberrations. Images of this scene for any lens can then be simulated if the light field is known at its entrance pupil. Freeware rendering software was used to create a scene’s light field and images for real camera lenses with different aberrations are simulated.

There is a strong desire to reduce size and weight of single and multiband IR imaging systems in ISR operations on hand-held, helmet mounted or airborne platforms. NRL is developing new IR glasses that transmit from 0.9 to < 12 µm in wavelength, with refractive index ranging from 2.38 to 3.17, to expand the glass map and provide compact solutions to multispectral imaging systems. These glasses were specifically designed to have comparable glass molding temperatures and thermal properties so that they can be laminated and co-molded into optics with reduced number of air-glass interfaces (lower Fresnel reflection losses). These new NRL glasses also have negative or very low dn/dT, making it easier to athermalize the optical system. Our multispectral optics designs using these new materials demonstrate reduced size, complexity and improved performance. The glass database is now available for distribution. Some of the NRL glasses are also available commercially. This presentation will cover discussions on the new optical materials, multispectral designs, as well fabrication and characterization of new optics.

Marshall Space Flight Center’s (MSFC) X-ray and Cryogenic Test Facility (XRCF) has tested the optothermal stability of two low-CTE, large-aperture mirrors in a thermal vacuum chamber. The mirrors deformed from several causes such as: thermal gradients, thermal soaks, coefficient of thermal expansion (CTE) gradients, CTE mismatch, and stiction. This paper focuses on how the aforementioned conditions affected the surface figure of the large optics while in vacuum at temperatures ranging from 230 to 310 K (-43 to 37 ˚C). The presented data, conclusions, and taxonomy are useful for designing mirrors and support structures for telescopes. The data is particularly useful for telescopes that require extreme dimensional stability or telescopes that operate at a temperature far from ambient.

The Habitable Exoplanet Observatory (HabEx) mission has unique optical performance requirements which drive the mirror design process beyond the traditional criteria. While mass and stiffness are still important, the response to inertia loading (expressed in terms of Zernike coefficients) to omni-directional excitation dominates the effort. While a Zerodur mirror is the current baseline, as mass budgets change, a ULE design is being studied as a potential alternative. This trade study looked at over 264 design variations using the Arnold Mirror Modeler and ANSYS^© to investigate the influence of various design elements, including: substrate thickness, core cell size, hexapod geometry and local reinforcement. Design ‘goodness’ was evaluated based on the mirror’s inertial deformation response to omni-directional input. This response was calculated via RSSing Zernike polynomial responses to (XYZ) accelerations.

The thermal transfer issue is an important problem associated with the synchrotron radiation optical system. During projection x-ray microscopy (PXM), x-ray light comes from the wiggler insert parts. The vertical collimating mirror (VCM) absorbs 40 W of energy on the mirror surface. The mirror length is 1000 mm, and its width is 87 mm. Here we apply an x-ray optical simulation software, named SHADOW, as well as the finite element method (FEM) software, ANSYS®, to calculate the surface thermal deformation at various thicknesses of VCM. The FEM software calculates the mirror surface deformation from heat absorption, and the surface deformation can be fit by the B-spline curve. The thermal deformation fitting results can be fed back to the SHADOW software and be used to evaluate how mirror thermal deformation affects the optical system performance.

Effective transfer of beamed optical energy to a spacecraft requires that the source have a sufficiently small angular divergence to contain the beam within the area of the spacecraft collector. Such a directed energy system could be achieved by coherently combining many small optical sources distributed throughout a large-scale array. The fundamental unit of such a system is a master oscillator power amplifier (MOPA) which consists of a frequency stabilized laser source distributed to amplifier trees in the array. A fundamental challenge in long baseline coherent beam combination is that each source be combined with sub-wavelength accuracy over the entire array. In addition to perturbations due to mechanical and atmospheric disturbances, phase noise introduced by the amplifiers and the seed distribution network must also be accounted for in order to achieve the necessary accuracy. This work investigates the excess phase noise introduced by the amplifier stages and fiber optic links. Locking schemes that could be used to synchronize such an array are presented. The test bed used to interrogate phase noise is based on an all polarization maintaining fiber Mach-Zehnder interferometer (MZI), controlled by an FPGA based digital quadrature detection at a sampling rate of 1 MS/s yielding direct measurement of amplitude and phase with servo control for phase locking. Results for various MOPA and fiber link configurations based on Yb-doped fiber amplifiers operating at 1064 nm and kilometer scale link lengths are presented.

Practical details are recommended for the design of opto-mechanical products for use in space.

The Habitable Exoplanet Observatory Mission (HabEx) is one of four missions under study for the 2020 Astrophysics Decadal Survey. Its goal is to directly image and spectroscopically characterize planetary systems in the habitable zone around nearby sun-like. Additionally, HabEx will perform a broad range of general astrophysics science enabled by 100 to 2500 nm spectral range and 3 x 3 arc-minute FOV. To achieve its exoplanet science goals, HabEx is baselining both an internal coronagraph and a star-shade. But, an internal coronagraph requires an ultra-stable wavefront. Achieving this stability imposes never before required performance specifications upon the telescope and requires a new approach systems engineering. The telescope and coronagraph must be specified and designed as an integrated system. This paper describes a two-step systems engineering process that can be applied to any potential telescope/coronagraph combination. The first step is to determine the coronagraph’s performance metrics of core throughput, raw contrast and stability of raw contrast. The second step is to calculate the sensitivity of the coronagraph’s performance metric to its telescope’s optical performance (e.g. wavefront stability). To illustrate the process, four representative architectures are evaluated: two vectorvortex and a hybrid Lyot coronagraph in combination with an off-axis monolithic telescope; and, an apodized pupil Lyot coronagraph with an on-axis hexagonal segment telescope (similar to the Webb Telescope aperture or the potential Large UV/Optical/IR Surveyor (LUVOIR) decadal mission).

PROBA-3 is a European Space Agency (ESA) mission due to launch in 2020. The aim of the mission is two-fold: to study the solar corona, and to demonstrate formation flying technology. Two satellites will fly in formation, 150 m apart, to form a coronagraph instrument. The relative displacement between the two satellites must be known to within 300 μm to produce accurate coronagraph data. The instrument that will provide this high-accuracy measurement is FLLS – the Fine Lateral and Longitudinal Sensor.

Built by Neptec UK and Neptec Design Group, FLLS uses a retro-reflected laser beam to monitor the position of one satellite with respect to the other. Phase measurements of the reflected signal are used to compute the longitudinal displacement between the two satellites. The lateral displacement is measured from the position of the returning beam on a CMOS sensor.

FLLS is currently in preliminary testing, in collaboration with Surrey Space Centre. To support the testing, the performance of the lateral system of FLLS has been modelled. A computational model of the full optical system has been produced, and several calibration routines have been tested on the modelled beam images. The results of these routines have enabled predicted preliminary performance analysis of the FLLS instrument.

The paper and presentation will provide an overview of the method, model, and results of the preliminary performance modelling of FLLS.

In missile applications, there are many parameters to be optimized. One of these is diameter of seeker and the other one is counter-countermeasures. To decrease diameter of the seeker, there are some methods. One of them is light transfer to stable detector. In this technique, detector and objective stay stable out of gimbal mechanism and light is focused in front of the objective. Later virtual image is created at the detector. By this way, diameter of the objective and detector don’t affect diameter of the seeker and give more free space to put another detector for dual wavelength into system to be immune to countermeasures. In this study, dual mode system’s optical and mechanical designs have been made for mid-wave infra-red imaging and long-wave infra-red imaging. Optical designs performances have been illustrated in simulation results. Finally, conceptual design of dual mode seeker will be summarized.

The raised cosine is a bandwidth efficient pulse shaping waveform with relatively high peak to average power ratio (PAPR) for smaller excess bandwidths. Reducing the PAPR while maintaining the shaped waveform integrity and bandwidth efficiency increases the transmission rate by utilizing the spectrum more effectively. In this paper, we modify the raised cosine by reducing the adjacent symbol contribution to the PAPR with small increase in the Error Vector Magnitude (EVM) and the required bandwidth over the raised cosine waveform. The attained PAPR reduction is on the order of 1.5 dB for the smaller excess bandwidth.

Due to the complex and inhomogeneous structure of biological tissues, the analysis of imaging data collected with various optical biopsy methods is often complicated and time consuming. The major challenge here is to understand the peculiarities of light propagation and link it with advanced image/data classification pipelines. This presentation considers the application of the novel Artificial Intelligence (AI) based methods to the inverse problem of light transport in scattering media such as human skin. A spectral image classification pipeline based on Artificial Neural Networks (ANNs) has been developed by implementing and training several configurations of ANNs classifiers that fit for the scattering and absorption properties of the tissues. The training of the ANNs has been performed by the further developed unified Monte Carlo-based computational framework for light transport in scattering media. The hyperspectral data is acquired at each pixel as a function of time, by varying the illumination/detection wavelength and polarization of light. The results of nearly real-time chromophore mappings for parameters such as distributions of melanin, blood vessels, oxygenation, simulation of BSSRDFs, reflectance spectra of human tissues, corresponding colours and 3D rendering examples of human skin appearance will be presented and compared with the exact analytical solutions, phantom studies, traditional diffuse reflectance spectroscopic point measurements and advanced Spatial Frequency Domain Imaging (SFDI) technique. Computer simulation and training are accelerated by parallel computing on Graphics Processing Units (GPUs) using Compute Unified Device Architecture (CUDA) and Cloud-based environment. Open-source machine learning frameworks (e.g. Tensorflow) are used to measure and validate each ANN’s performance.

We propose and demonstrate compact on-chip optical filters with ultra-high efficiencies, which are designed via the recently-emerged objective-first inverse design algorithm. The all-dielectric high-pass, low-pass and all-pass filters presented in this study operate within the telecommunication wavelength spectrum of 1260 - 1625 nm. The high-pass filter shows an outstanding performance for the transmission efficiency higher than the frequency of 210 THz and an effective suppression of the other spectral region. Also, the proposed low-pass filter exhibits high transmission and significant blocking at the ranges of 170 Thz-205 Thz and 205 Thz-240 Thz, respectively. Furthermore, the designed allpass filter possesses notable spectral transmissivity and blocking characteristics. The promising features of the structures were also verified via the finite-difference time-domain method. Such manufacturable optical filters with great device performances are favorable candidates for next-generation photonic applications.

Silicon photonics is rapidly emerging as a promising technology to enable higher bandwidth, lower energy, and lower latency communication and information processing, and other applications. In silicon photonics, existing CMOS manufacturing infrastructure and techniques are leveraged. However, a key challenge for silicon photonics is the lack of mature models that take into account known CMOS process variations and their effect on photonic component behavior. A key factor for the adoption of silicon photonics into high-yield manufacturing is to extend process design kits (PDKs) to include photonic process variability models that are aware of variations that may occur during the fabrication process.

We study the effect of a well-known random process variation, line edge roughness (LER), present in the lithography and etch process, on the performance of a fundamental component, the Y-branch, through virtual fabrication simulations. Ideally, the Y-branch transmits the input power equally to its two output ports. However, imbalanced transmission between the two output ports is observed when LER is imposed on the Y-branch, depending on the statistical nature (amplitude and correlation length) of the LER. The imbalance can be as low as 1% for small LER amplitudes, and reach up to 15% for large LER amplitudes. In addition, LER increases the excess loss compared to the nominal (smooth) case. Ensemble statistical virtual fabrication and FDTD photonic simulations across a range of LER amplitude and correlation lengths are reported. These results can be captured as worst-case corner models and included in variation-aware photonic compact models.

Imaging system design is not limited to circular aperture shapes. However, non-circular apertures require a different set of polynomials, because broadly used Zernike polynomials are not orthogonal over non-circular shapes. Applying the Gram-Schmidt orthogonalization process provide the adopted set of orthogonal polynomials over selected non-circular aperture shape. However, when the aperture shape is complicated, non-symmetrical, the resulting set of polynomials can be very complex. In the case of odd-sided polygons is the analytical form of the polynomials inappropriate due to their complexity and these polynomials have to be expressed in their numerical form. Concerning the laborious complexity of some non-circular polynomials, we analyze the desired accuracy of such polynomials and their performance of the wavefront modeling according to classical circular Zernike polynomials.

Birefringence can be a crucial problem for many optical instruments operating with laser beams. Even for birefringence free optical elements, birefringence can be introduced due to mounting forces and torques. Highly sensitive polarimeters need to be used to reveal the limit values of linear or circular retardance introduced into the optical system. The correct assessment of polarimeter’s performance needs to be done with an appropriate test sample. We propose a birefringence test sample based on a basic load case of a circular plate loaded with torsion stress. Such a test sample has many advantages for a birefringence measurement testing. There is always present a zero level of stress in the middle of the circular sample. The stress level linearly increases towards the perimeter and its slope can be set arbitrarily. There is no change of either the sample volume or its shape under torsion stress. In the paper we evaluate the birefringence of a sample under torsion stress with Jones matrix calculus. We used a torsion stressed sample to verify reliability of our proposed setup for birefringence measurement based on polarizing Mach-Zehnder interferometer.

Dust defect is always a critical issue to degrade image qualities in kinds of imaging capturing modules, such as compact camera modules (CCMs) and digital single lens cameras (DSLRs). Dust particle may be deposited on the surface of lens or sensor in the step of assembly and even in the step of changing lens module by users. There have been lots of studies about image defects produced by dust particles on the surface of lens or sensor and the image compensation for dust defect on images, but the studies about the direct analysis of dust defects are still deficient. In this study, geometrical optics was used to analyze the image defects due to dust in the imaging capturing module. A defocused optical system with a planar light source with Lambertian emission was developed to analyze dust defect with image process and the concept of just noticeable difference (JND) of human vision. The proposed defocused optical system provides a way to help manufacturers to improve their production line efficiently.

Laser Doppler vibrometry (LDV) is a developing and potential vibration measurement technology. This paper gives a review on the fundamental principles and the essential techniques of LDV, put emphasis on comparing and analyzing between scanning laser Doppler vibrometry (SLDV) and continuous scanning laser Doppler vibrometry (CSLDV). Then some crucial issues including the analysis on vibration errors and the required solutions are proposed and commented. Finally, some typical examples applied in the fields of industry, agriculture, medicine, construction and aerospace are introduced to demonstrate the research progress as well as development trend of LDV.

Investigating photonic components as refractive index sensors requires reliable numerical models. Performing 3D simulations of large or complex components requires powerful hardware. Alternatives to time-consuming 3D simulations are approximations such as the effective refractive index method. We propose our improved method that more closely follows 3D results, named the inverse effective index method. The accuracy of our approximation method is verified by comparing experimental results with simulations. Ring resonators with 40μm radius are simulated and fabricated. Their qualities as refractive index sensors are assessed by probing their response in DI-water and in various saline solutions. The fabricated resonators are fitted with a microfluidic channel for sample delivery. A tunable laser is used to induce resonance in the ring resonators and the resonance frequencies are measured for all solutions. The accuracy between simulation and experimental data is found to rely heavily on the approximation technique being used. The differences vary from 300% to 6% depending on the approximation method. The fabrication and characterization of the ring resonator-based refractive index sensor took approximately two days, whereas the 2D simulations took under an hour to perform. This demonstrates the usefulness of a proper simulation tool to conduct accurate performance estimations in a short amount of time.

Modern development of aircraft engineering and consequently of the piloting process itself leads to an increase the volume of information that the pilot has to control. This makes necessary to improve the comfort of displaying flight information for the pilot. One of the main methods is the using of a Helmet-mounted display (HMD) in which the image is formed specifically in such way that the pilot’s eyes are not required to re-accommodate when reading output information. This allows increasing the concentration of the pilot on the outboard situation, reducing the fatigability of pilot’s eyes and improving the overall comfort of the flight.

Today many HMD systems are implemented in monocular design but for more comfort and informative work system should be binocular (or binocular), however not all optical schemes allow this to be done.

The work presents the analysis of modern solutions of Head-mounted optical systems design and an assessment of the feasibility of using certain systems in the form of binocular or biocular helmet displays.

This paper presents a passive target tracking method based on the vision information feedback from a variable boresight imaging system. Firstly, the variable boresight imaging system is modelled to demonstrate the adjustment of a camera boresight by Risley prisms. The passive tracking method is then introduced to determine the relative position of dynamic target without any prior information, which can serve as the feedback to steer the camera boresight towards the target of interest. Moreover, an experiment setup is designed with both hardware and software in order to evaluate the feasibility and accuracy of the proposed target tracking method.

Tactical missiles have seeker capability to detect and tract targets. Because of the seekers’ field of view, detonation range of the missiles has a limit. Mostly this limit is far away from the desired distance since seeker’s blind spot. To increase missile’s effectiveness against target, laser proximity sensor is used. Where the seeker’s blind spot distance is arrived, the proximity sensor will be used until its minimum distance limits. In this study, missile parameters are assumed and minimum detonation distance for seeker will be found. Effectiveness of warhead at this distance will be calculated. Later parameters of proximity sensor are determined. Optical design and modeling of the proximity sensor will be conducted and minimum distance of it will be determined. Warhead effectiveness of this minimum distance will be given. Finally, both results will be compared with each other.

The light filed modulated imaging spectrometer (LFMIS) can obtain a multispectral data cube in a single shot. The spatial sampling is effected by the design of spectral filters, because the diffraction limit increases as the sizes of the filters decrease. The spatial and spectral sampling characters of the system are determined by the system parameters, specially the parameters of the filters. This research presents the models of the system and the linear-variable optical filters (LVFs). The spatial sampling character is analyzed theoretically and confirmed by simulation results. Simulation experiments are performed to analyzed the characters of LVFs that effect the spectral sampling character. The results provide the parameter requirements of LVFs when designing an LFMIS system based on LVFs.