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- Front Matter: Volume 9822
- Materials
- Fabrication
- Optical Design and Analysis I
- Optical Design and Analysis II
- GRIN I
- GRIN II
- Coatings and Filters
- Optical Design and Analysis III
Front Matter: Volume 9822
Front Matter: Volume 9822
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9822, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
Materials
Evaluation of chalcogenide glasses for multispectral imaging in the visible, SWIR and LWIR spectral regions
A. Bréhault,
L. Calvez,
T. Pain,
et al.
Show abstract
In this paper, a first part will present the mechanical properties of the chalcohalide glass system GeS2-Ga2S3-CsCl. The hardness, Young’s modulus, shear modulus and toughness of a series of glasses (0.8 GeS2 - 0.2 Ga2S3)100-x CsClx with x = 0, 5, 10, 15 have been investigated and compared with other glasses. Two particular compositions 75 GeS2 - 15 Ga2S3 - 10 CsCl and 65 GeS2 - 20 Ga2S3 - 15 CsCl are compared with existing industrial chalcogenide glasses. In a second part, two multispectral antireflective coatings are presented. These coatings, developed for a multispectral application, enhanced the transmissions in specific bands.
Manufacturing of transparent ZnS ceramics by powders sintering
Show abstract
We report the use of the low cost hot-pressing technique to produce ZnS for multispectral operation, from visible up to
12 μm. Considerable progress has been obtained by developing efficient precipitation and combustion powders synthesis
procedures. The main emphasis has been on the elaboration of ZnS precursor powders with controlled
morphology/chemical composition to reduce extrinsic scattering and impurities. We were able to produce ZnS parts with
visible transparency and transmission in the 8-12 μm range that is comparable to that of CVD ZnS. The correlation of
processing variables with powders sinterability and optical transmission of the HPed ceramics is discussed.
Rugged spinel optics for space based imaging systems
Show abstract
Space environment is very harsh for optical systems. Currently available optical materials for space
applications are susceptible to surface and bulk damage due to high-speed impacts from dust and debris found
in the space environment. Impacts lead to surface pitting and fracturing that may compromise structural
integrity and degrade the optical performance of imaging systems. We are developing polycrystalline spinel
as a rugged optics material. With its 3x hardness and 5x strength, as compared to BK7 glass, spinel is a very
promising optical material for space imaging applications. Spinel’s broad transmission from 160 nm to 5000
nm will also enable multispectral imaging from ultraviolet to midwave infrared.
Engineering novel infrared glass ceramics for advanced optical solutions
Show abstract
Advanced photonic devices require novel optical materials that serve specified optical function but also possess
attributes which can be tailored to accommodate specific optical design, manufacturing or component/device
integration constraints. Multi-component chalcogenide glass (ChG) materials have been developed which exhibit
broad spectral transparency with a range of physical properties that can be tuned to vary with composition, material
microstructure and form. Specific tradeoffs that highlight the impact of material morphology and optical properties
including transmission, loss and refractive index, are presented. This paper reports property evolution in a
representative 20 GeSe2-60 As2Se3-20 PbSe glass material including a demonstration of a 1D GRIN profile through
the use of controlled crystallization.
Designing mid-wave infrared (MWIR) thermo-optic coefficient (dn/dT) in chalcogenide glasses
Show abstract
Seventeen infrared-transmitting GeAsSe chalcogenide glasses were fabricated to determine the role of chemistry and
structure on mid-wave infrared (MWIR) optical properties. The refractive index and thermoptic coefficients of
samples were measured at λ = 4.515 μm using an IR-modified Metricon prism coupler, located at University of
Central Florida. Thermo-optic coefficient (dn/dT) values were shown to range from approximately -40 ppm/°C to
+65 ppm/°C, and refractive index was shown to vary between approximately 2.5000 and 2.8000. Trends in
refractive index and dn/dT were found to be related to the atomic structures present within the glassy network, as
opposed to the atomic percentage of any individual constituent. A linear correlation was found between the quantity
(n-3•dn/dT) and the coefficient of thermal expansion (CTE) of the glass, suggesting the ability to compositionally
design chalcogenide glass compositions with zero dn/dT, regardless of refractive index or dispersion performance.
The tunability of these novel glasses offer increased thermal and mechanical stability as compared to the current
commercial zero dn/dT options such as AMTIR-5 from Amorphous Materials Inc. For IR imaging systems designed
to achieve passive athermalization, utilizing chalcogenide glasses with their tunable ranges of dn/dT (including zero)
can be key to addressing system size, weight, and power (SWaP) limitations.
High accuracy refractive index measurement system for germanium and silicon using the channelled spectrum method in the range of 3 to 15 μm
Hilmar Straube,
Christian Hell
Show abstract
The refractive index of germanium is known only up to the third decimal according to publicly available sources. This
data from various authors shows deviations in the order of several 10-3 not to be explained by experimental errors of the
refractive index measurement. This is a strong indication that there is optically relevant material property variation. We
present an interferometric method to measure the refractive index and its temperature dependency on etalon samples,
which are cheaper to prepare with high quality than prism samples needed for the classical method of index
measurement. Resolution and stability of our method is better than 10-4. The method can be used for both germanium
and silicon. Our goal is to be able to produce material with optically relevant specifications. This is in contrast to the
conventional method of specifying these important IR-optical materials in terms of electrical properties such as dopant
type and concentration.
Fabrication
Chalcogenide material strengthening through the lens molding process
Show abstract
The demand for infrared transmitting materials has grown steadily for several decades as markets realize new
applications for longer wavelength sensing and imaging. With this growth has come the demand for new and
challenging material requirements that cannot be satisfied with crystalline products alone. Chalcogenide materials,
with their unique physical, thermal, and optical properties, have found acceptance by designers and fabricators to
meet these demands.
No material is perfect in every regard, and chalcogenides are no exception. A cause for concern has been the
relatively low fracture toughness and the propensity of the bulk material to fracture. This condition is amplified
when traditional subtractive manufacturing processes are employed. This form of processing leaves behind micro
fractures and sub surface damage, which act as propagation points for both local and catastrophic failure of the
material.
Precision lens molding is not a subtractive process, and as a result, micro fractures and sub surface damage are not
created. This results in a stronger component than one produced by traditional methods. New processing methods
have also been identified that result in an even stronger surface that is more resistant to breakage, without the need
for post processing techniques that may compromise surface integrity.
This paper will discuss results achieved in the process of lens molding development at Edmund Optics that result in
measurably stronger chalcogenide components. Various metrics will be examined and data will be presented that
quantifies component strength for different manufacturing processes.
Applicability of an annealing coefficient for precision glass molding of As40Se60
Show abstract
Precision glass molding has a well-documented decrease in the index of refraction of the glass during the molding process. This index drop must be taken into account in the optical design in order to accurately determine the optical performance of the final lens. Knowing the annealing coefficient of the glass being molded allows the index to be fine-tuned by adjusting the cooling rate during the molding process. While annealing coefficients are available for visible glasses, the validity of using this method for chalcogenide gasses has not yet been investigated. This paper will determine the annealing coefficient for As40Se60 experimentally, and then verify the results by comparing calculated and experimental refractive index values for other cooling rates.
Molded, wafer level optics for long wave infra-red applications
Show abstract
For many years, the Thermal Imaging market has been driven by the high volume consumer market. The first signs of
this came with the launch of night vision systems for cars, first by Cadillac and Honda and then, more successfully by
BMW, Daimler and Audi. For the first time, simple thermal imaging systems were being manufactured at the rate of
more than 10,000 units a year. This step change in volumes enabled a step change in system costs, with thermal imaging
moving into the consumer’s price range.
Today we see that the consumer awareness and the consumer market continues to increase with the launch of a number
of consumer focused smart phone add-ons. This has brought a further step change in system costs, with the possibility to
turn your mobile phone into a thermal imager for under $250.
As the detector technology has matured, the pixel pitches have dropped from 50μm in 2002 to 12 μm or even 10μm in
today’s detectors. This dramatic shrinkage in size has had an equally dramatic effect on the optics required to produce
the image on the detector. A moderate field of view that would have required a focal length of 40mm in 2002 now
requires a focal length of 8mm. For wide field of view applications and small detector formats, focal lengths in the range
1mm to 5mm are becoming common.
For lenses, the quantity manufactured, quality and costs will require a new approach to high volume Infra-Red (IR)
manufacturing to meet customer expectations. This, taken with the SwaP-C requirements and the emerging requirement
for very small lenses driven by the new detectors, suggests that wafer scale optics are part of the solution. Umicore can
now present initial results from an intensive research and development program to mold and coat wafer level optics,
using its chalcogenide glass, GASIR®.
Optimum selection of high performance mirror substrates for diamond finishing
Show abstract
Due to advances in manufacturing processes, the substrate options for high performance diamond machined mirrors are
expanding. Fewer compromises have to be made to achieve the needed weight, stiffness and finish while maintaining
reasonable costs. In addition to the traditional mirror materials like aluminum and beryllium, there are some less
common materials that can now be included in the trade space that fill the cost and performance continuum between
wrought aluminum and beryllium mirrors. Aluminum and beryllium, respectively, had been the low cost/fair
performance and very high cost/very high performance bounds for substrate selection. These additional substrates
provide multiple near net shape blank options and processes, mostly within these bounds, that can be considered in a
mirror cost versus performance trade analysis.
This paper will include a summary of some advances in manufacturing processes that provide more substrate options for
diamond machined mirrors with some sample performance analysis and data. This is merged with the traditional
substrate options to illustrate the now larger mirror substrate trade space. Some benchmark structural analysis is
provided to back up a generic mirror design trade study.
Bubble formation in additive manufacturing of glass
Junjie Luo,
Luke J. Gilbert,
Daniel C. Peters,
et al.
Show abstract
Bubble formation is a common problem in glass manufacturing. The spatial density of bubbles in a piece of glass is a
key limiting factor to the optical quality of the glass. Bubble formation is also a common problem in additive
manufacturing, leading to anisotropic material properties. In glass Additive Manufacturing (AM) two separate types of
bubbles have been observed: a foam layer caused by the reboil of the glass melt and a periodic pattern of bubbles which
appears to be unique to glass additive manufacturing. This paper presents a series of studies to relate the periodicity of
bubble formation to part scan speed, laser power, and filament feed rate. These experiments suggest that bubbles are
formed by the reboil phenomena why periodic bubbles result from air being trapped between the glass filament and the
substrate. Reboil can be detected using spectroscopy and avoided by minimizing the laser power while periodic bubbles
can be avoided by a two-step laser melting process to first establish good contact between the filament and substrate
before reflowing the track with higher laser power.
Optical Design and Analysis I
Recent advances in joint optical-digital design for optronics applications
Show abstract
Increasing the capture volume of visible cameras while maintaining high image resolutions, low power consumption and
standard video-frame rate operation is of utmost importance for hand-free night vision goggles or embedded surveillance
systems. Since such imaging systems require to operate at high aperture, their optical design has become more complex
and critical. Therefore new design alternatives have to be considered. Among them, wavefront coding changes and
desensitizes the modulation transfer function (MTF) of the lens by inserting a phase mask in the vicinity of the aperture
stop. This smart filter is combined with an efficient image processing that ensures optimal image quality over a larger
depth of field. In this paper recent advances are discussed concerning design and integration of a compact imaging system
based on wavefront coding. We address the design, the integration and the characterization of a High Definition (HD)
camera of large aperture (F/1.2) operating in the visible and near infrared spectral ranges, endowed with wavefront coding.
Two types of phase masks (pyramidal and polynomial) have been jointly optimized with their deconvolution algorithm in
order to meet the best performance along an increased range of focus distances and manufactured. Real time deconvolution
processing is implemented on a Field Programmable Gate Array. It is shown that despite the high data throughput of an
HD imaging chain, the level of power consumption is far below the initial specifications. We have characterized the
performances with and without wavefront coding through MTF measurements and image quality assessments. A depth-of-
field increase up to x2.5 has been demonstrated in accordance with the theoretical predictions.
Phase mask for infrared lens athermalization: design considerations
Shay Elmalem,
Emanuel Marom
Show abstract
Design of Infra-red (IR) imaging systems requires solutions for overcoming thermal variations of IR lenses, in particular those fabricated out of Germanium. The known thermal dependence of the index of refraction of Germanium results in significant focal shift, which produces image blur. Known solutions to overcome the thermal fluctuations are reviewed. A solution based on an alloptical phase mask with no moving parts will be shown to provide improved imagery for broad band IR scenes in the presence of wide temperature variations. Phase mask design considerations and trade-offs are analyzed.
Evaluate depth of field limits of fixed focus lens arrangements in thermal infrared
Show abstract
More and more modern thermal imaging systems use uncooled detectors. High volume applications work with detectors
that have a reduced pixel count (typically between 200x150 and 640x480). This reduces the usefulness of modern image
treatment procedures such as wave front coding. On the other hand, uncooled detectors demand lenses with fast fnumbers,
near f/1.0, which reduces the expected Depth of Field (DoF).
What are the limits on resolution if the target changes distance to the camera system? The desire to implement lens
arrangements without a focusing mechanism demands a deeper quantification of the DoF problem.
A new approach avoids the classic “accepted image blur circle” and quantifies the expected DoF by the Through Focus
MTF of the lens. This function is defined for a certain spatial frequency that provides a straightforward relation to the
pixel pitch of imaging device.
A certain minimum MTF-level is necessary so that the complete thermal imaging system can realize its basic functions,
such as recognition or detection of specified targets. Very often, this technical tradeoff is approved with a certain lens.
But what is the impact of changing the lens for one with a different focal length? Narrow field lenses, which give more
details of targets in longer distances, tighten the DoF problem.
A first orientation is given by the hyperfocal distance. It depends in a square relation on the focal length and in a linear
relation on the through focus MTF of the lens. The analysis of these relations shows the contradicting requirements
between higher thermal and spatial resolution, faster f-number and desired DoF.
Furthermore, the hyperfocal distance defines the DoF-borders. Their relation between is such as the first order imaging
formulas.
A calculation methodology will be presented to transfer DoF-results from an approved combination lens and camera to
another lens in combination with the initial camera. Necessary input for this prediction is the accepted DoF of the initial
combination and the through focus MTFs of both lenses. The accepted DoF of the initial combination defines an
application and camera related MTF-level, which must be provided also by the new lens. Examples are provided.
The formula of the Diffraction-Limited-Through-Focus-MTF (DLTF) quantifies the physical limit and works without
any ray trace. This relation respects the pixel pitch, the waveband and the aperture based f-number, but is independent of
detector size. The DLTF has a steeper slope than the ray traced Through-Focus-MTF; its maximum is the diffraction
limit. The DLTF predicts the DoF-relations quite precisely. Differences to ray trace results are discussed.
Last calculations with modern detectors show that a static chosen MTF-level doesn’t reflect the reality for the DoFproblem.
The MTF-level to respect depends on application, pixel pitch, IR-camera and image treatment. A value of
0.250 at the detector Nyquist frequency seems to be a reasonable starting point for uncooled FPAs with 17μm pixel
pitch.
Characterization of the image quality of a wide angle MWIR f-theta objective lens by means of pixel contrast
Bertram Achtner
Show abstract
Objective lenses for missile warning systems have typically a wide field of view of about 120° to 180°. In order to get a
linear correlation between object angle w[rad] and image height y[mm] they have a f-theta correction, with the focal
length f[mm] as correlation factor. Usually the image quality criteria for optical systems are specified with MTF- or
Strehl-values. In this case the image quality is indicated as pixel contrast defined by the amount of energy from a point
source falling on one pixel compared to the amount of energy of the same source falling onto the neighboring pixels. The
image of a point source from infinity is the Airy disk, which has a circular shape provided that the pupil is also circular.
In order to get correct values for quadratic pixels the ensquared energy has to be taken. The size of the Airy disk is
correlated to the f/# of the optical system and the wavelength. There is an interconnection between dimension of the
optical system, f/#, Airy disk and achievable pixel contrast. These dependencies are discussed for a recently developed
168° field of view objective lens.
Experimental verification of the minimum number of diffractive zones for effective chromatic correction in the LWIR
Show abstract
With the move to smaller pixel sizes in the longwave IR region there has been a push for shorter focal length lenses that
are smaller, cheaper and lighter and that resolve lower spatial frequencies. As a result lenses must have better correction
for both chromatic and monochromatic aberrations. This leads to the increased use of aspheres and diffractive optical
elements (kinoforms). With recent developments in the molding of chalcogenide materials these aspheres and kinoforms
are more cost effective to manufacture. Without kinoforms the axial color can be on the order of 15 μm which degrades
the performance of the lens at the Nyquist frequency. The kinoforms are now on smaller elements and are correcting
chromatic aberration which is on the order of the design wavelength. This leads to kinoform structures that do not
require large phase changes and therefore have 1.5 to just over 2 zones. The question becomes how many zones are
required to correct small amounts of chromatic aberration in the system and are they functioning as predicted by the lens
design software? We investigate both the design performance and the as-built performance of two designs that
incorporate kinoforms for the correction of axial chromatic aberration.
Optical Design and Analysis II
Design method for a laser line beam shaper of a general 1D angular power distribution
E. Oved,
A. Oved
Show abstract
Laser line is a beam of laser, spanned in one direction using a beam shaper to form a fan of light. This illumination tool
is important in laser aided machine vision, 3D scanners, and remote sensing. For some applications the laser line should
have a specific angular power distribution. If the distribution is nonsymmetrical, the beam shaper is required to be
nonsymmetrical freeform, and its design process using optical design software is time consuming due to the long
optimization process which usually converges to some local minimum. In this paper we introduce a new design method
of a single element refractive beam shaper of any predefined general 1D angular power distribution. The method makes
use of a notion of "prism space", a geometrical representation of all double refraction prisms, and any 1D beam shaper
can be described by a continuous curve in this space. It is shown that infinitely many different designs are possible for
any given power distribution, and it is explained how an optimal design is selected among them, based on criteria such as
high transmission, low surface slopes, robustness to manufacturing errors etc. The method is non-parametric and hence
does not require initial guess of a functional form, and the resultant optical surfaces are described by a sequence of
points, rather than by an analytic function.
Electronic eyebox for weapon sights
Show abstract
We expand the effective size of the eyebox of a magnified telescopic weapon sight by following the movements of the
operator’s eye to create a larger, ‘electronic eyebox’. The original eyebox of the telescope is dynamically relocated in
space so that proper overlap between the pupil of the eye and the exit pupil of the device is maintained. Therefore, the
operator will perceive the entire field of view of the instrument in a much bigger spatial region than the one defined by
the original eyebox. Proof-of-the-concept results are presented with a more than 3.5X enlargement of the eyebox
volume along with recommendations for the next phase of development.
Time-resolved non-sequential ray-tracing modelling of non-line-of-sight picosecond pulse LIDAR
Show abstract
The ability to detect motion and to track a moving object that is hidden around a corner or behind a wall
provides a crucial advantage when physically going around the obstacle is impossible or dangerous. One recently
demonstrated approach to achieving this goal makes use of non-line-of-sight picosecond pulse laser ranging.
This approach has recently become interesting due to the availability of single-photon avalanche diode (SPAD)
receivers with picosecond time resolution. We present a time-resolved non-sequential ray-tracing model and its
application to indirect line-of-sight detection of moving targets. The model makes use of the Zemax optical
design programme's capabilities in stray light analysis where it traces large numbers of rays through multiple
random scattering events in a 3D non-sequential environment. Our model then reconstructs the generated
multi-segment ray paths and adds temporal analysis. Validation of this model against experimental results is
shown. We then exercise the model to explore the limits placed on system design by available laser sources and
detectors. In particular we detail the requirements on the laser's pulse energy, duration and repetition rate, and
on the receiver's temporal response and sensitivity. These are discussed in terms of the resulting implications
for achievable range, resolution and measurement time while retaining eye-safety with this technique. Finally,
the model is used to examine potential extensions to the experimental system that may allow for increased
localisation of the position of the detected moving object, such as the inclusion of multiple detectors and/or
multiple emitters.
Novel silicon lenses for long-wave infrared imaging
Show abstract
The design, fabrication and performance of a novel silicon lens for Long Wave Infrared (LWIR) imaging are presented.
The silicon lenses are planar in nature, and are created using standard wafer scale silicon micro-fabrication processes.
The silicon batch processes are used to generate subwavelength structures that introduce spatially varying phase shifts in
the incident light. We will show that the silicon lens designs can be extended to produce lenses of varying focal lengths
and diameters, thus enabling IR imaging at significantly lower cost and reduced weight and form factor. An optical
design program and a Finite-Difference Time-Domain (FDTD) simulation software tool are used to model the lens
performance. The effects of polarization anisotropy are computed for the resultant subwavelength structures. Test
samples with lenses with focal lengths in the range of 10 to 50 mm were fabricated. The test sample also included a
prism structure, which is characterized by measuring the deflection of a CO2 laser beam and compared to theoretical
beam deflection. The silicon lenses are used to produce an image on a VGA micro-bolometer array.
Expanded IR glass map for multispectral optics designs
Show abstract
This paper presents new multispectral IR glasses with transmission from 0.9 to > 14 μm in wavelength and refractive
index from 2.38 to 2.17. These new glasses are designed to have comparable glass softening temperatures and
compatible coefficients of thermal expansion to allow bonding and co-molding of multilayer optics. With large variation
in their Abbe numbers and negative to near-zero dn/dT, optics made from these new glasses can significantly reduce the
size/weight or complexity of the multispectral imaging systems for weight sensitive platforms.
Computing the PSF with high-resolution reconstruction technique
Show abstract
Point spread function (PSF) is a very important indicator of the imaging system; it can describe the filtering characteristics of the imaging system. The image is fuzzy when the PSF is not very well and vice versa. In the remote
sensing image process, the image could be restored by using the PSF of the image system to get a clearer picture. So, to measure the PSF of the system is very necessary. Usually we can use the knife edge method, line spread function (LSF) method and streak plate method to get the modulation transfer function (MTF), and then use the relationship of the
parameters to calculate the PSF of the system. In the knife edge method, the non-uniformity (NU) of the detector would
lead an unstable precision of the edge angle; using the streak plate could get a more stable MTF, but it is only at one
frequency point in one direction, so it is not very helpful to get a high-precision PSF. In this paper, we used the image of the point target directly and combined with the energy concentration to calculate the PSF. First we make a point matrix target board and make sure the point can image to a sub-pixel position at the detector array; then we use the center of
gravity to locate the point targets image to get the energy concentration; then we fusion the targets image together by
using the characteristics of sub-pixel and get a stable PSF of the system. Finally we use the simulation results to confirm
the accuracy of the method.
GRIN I
Advanced gradient-index lens design tools to maximize system performance and reduce SWaP
Show abstract
GRadient-INdex (GRIN) lenses have long been of interest due to their potential for providing levels of performance
unachievable with traditional homogeneous lenses. While historically limited by a lack of suitable materials, rapid
advancements in manufacturing techniques, including 3D printing, have recently kindled a renewed interest in GRIN
optics. Further increasing the desire for GRIN devices has been the advent of Transformation Optics (TO), which
provides the mathematical framework for representing the behavior of electromagnetic radiation in a given geometry by
“transforming” it to an alternative, usually more desirable, geometry through an appropriate mapping of the constituent
material parameters. Using TO, aspherical lenses can be transformed to simpler spherical and flat geometries or even
rotationally-asymmetric shapes which result in true 3D GRIN profiles. Meanwhile, there is a critical lack of suitable
design tools which can effectively evaluate the optical wave propagation through 3D GRIN profiles produced by TO.
Current modeling software packages for optical lens systems also lack advanced multi-objective global optimization
capability which allows the user to explicitly view the trade-offs between all design objectives such as focus quality,
FOV, ▵nand focal drift due to chromatic aberrations. When coupled with advanced design methodologies such as TO,
wavefront matching (WFM), and analytical achromatic GRIN theory, these tools provide a powerful framework for
maximizing SWaP (Size, Weight and Power) reduction in GRIN-enabled optical systems. We provide an overview of
our advanced GRIN design tools and examples which minimize the presence of mono- and polychromatic aberrations in
the context of reducing SWaP.
Materials figure of merit for achromatic gradient index (GRIN) optics
Show abstract
A new figure of merit is developed for ranking pairs of materials as candidates for gradient index (GRIN) optics capable
of good color correction. The approach leverages recent work which derives a connection in GRIN lenses between the
optical properties of constituent materials and the wavelength dependence of the lens power. We extend the analysis
here, the effectiveness of which is evidenced by a simulated f/3 GRIN lens with diffraction-limited performance over the
visible spectrum, using the top material pair selected out of a database of >60,000 possible candidates.
IR-GRIN optics for imaging
Show abstract
Infrared (IR) transmitting gradient index (GRIN) materials have been developed for broad-band IR imaging. This
material is derived from the diffusion of homogeneous chalcogenide glasses has good transmission for all IR wavebands.
The optical properties of the IR-GRIN materials are presented and the fabrication methodologies are discussed.
Modeling and optimization of the diffusion process is exploited to minimize the deviation of the index profile from the
design profile.
Athermal achromat lens enabled by polymer gradient index optics
Show abstract
An optical design is shown which provides simultaneous color correction over the visible spectrum and passive thermal
compensation, for an f/4 doublet made of a glass and a polymer gradient index (GRIN) element. The design is enabled
by a new optical model for the thermally varying GRIN element, which incorporates measured material properties from
20-40°C (limited only by the extent of the measured data set). The design is made possible because of the GRIN degrees
of freedom available to the material. A color-corrected doublet is most efficient when there is a large ratio of the
dispersion strength (Abbe number) between the two materials. To make that doublet athermal, however, there needs to
be an equally high ratio between the thermal coefficients. The large ratio of polymer to glass thermal coefficients
presents a unique advantage for GRIN: the effective GRIN dispersion coefficient can have just as large a ratio to the
glass as the thermal coefficients, making for a powerful athermal achromat. To our knowledge, this is the first example
of a polymer GRIN used for simultaneous chromatic and thermal correction.
GRIN II
Transformation optics relay lens design for imaging from a curved to a flat surface
Show abstract
Monocentric lenses are excellent candidates for compact, broadband, high resolution, wide-field imaging.
Traditional monocentric designs produce a curved image surface and have therefore found limited utility. The use of
an appropriately machined fiber bundle to relay the curved image plane onto a flat focal plane array (FPA) has
recently emerged as a potential solution. Unfortunately the spatial sampling that is intrinsic to the fiber bundle relay
can have a negative effect on image resolution, and vignetting has been identified as another potential shortcoming
of this solution. In this paper we describe a metamaterial optical element that avoids the deleterious effects of
sampling and can provide a high-quality image relay from the curved monocentric image surface to a flat FPA.
Using quasi-conformal transformation optics (TO) a classical Maxwell’s “fish-eye” lens is transformed into a shape
with a concave front surface and flat back surface. We quantify image quality metrics such as spot size, field of
view, and light efficiency along with manufacturing cost metrics such as index contrast and anisotropy. Based on
this analysis we identify and fully optimize a monocentric lens in combination with a TO-designed GRIN image
relay optic.
ALON GRIN optics for visible-MWIR applications
Show abstract
Surmet continuously strives to develop novel, advanced optical ceramics products for current and future defense and
commercial systems. Using conventional powder processing techniques, Surmet has made substantial progress in its ability
to manufacture large ALON® sensor windows, lenses, domes and transparent armor. In addition to transparency, Surmet
has demonstrated the ability to incorporate other capabilities into its optical ceramic components, including: EMI shielding,
heating, internal antennas and cooling channels.
Working closely with the University of Rochester, Surmet has developed gradient index (GRIN) optics in ALON for
use in the visible through the MWIR applications. Surmet has demonstrated the ability to tailor the refractive index of
ALON® Optical Ceramic by either varying its composition or through the addition of dopants. Smooth axial and radial
gradient profiles with ~0.055 change in refractive index, over depths of 1-8 mm (axial) and over 20 mm radius (radial)
have been demonstrated. Initial design studies have shown that such elements provide unique capabilities. Radial gradients
in particular, with their optical power contribution, provide additional degrees of freedom for color correction in broadband
imaging systems.
Surmet continues to mature ALON® GRIN technology along with the associated metrology. Surmet is committed to
the development of its ALON® GRIN capability as well as finding insertion opportunities in novel imaging solutions for
military and other commercial systems.
Raman and CT scan mapping of chalcogenide glass diffusion generated gradient index profiles
Show abstract
Metrology of a gradient index (GRIN) material is non-trivial, especially in the realm of infrared and large refractive index. Traditional methods rely on index matching fluids which are not available for indexes as high as those found in the chalcogenide glasses (2.4-3.2). By diffusing chalcogenide glasses of similar composition one can blend the properties in a continuous way. In an effort to measure this we will present data from both x-ray computed tomography scans (CT scans) and Raman mapping scans of the diffusion profiles. Proof of concept measurements on undiffused bonded sheets of chalcogenide glasses were presented previously. The profiles measured will be of axially stacked sheets of chalcogenide glasses diffused to create a linear GRIN profile and nested tubes of chalcogenide glasses diffused to create a radial parabolic GRIN profile. We will show that the x-ray absorption in the CT scan and the intensity of select Raman peaks spatially measured through the material are indicators of the concentration of the diffusion ions and correlate to the spatial change in refractive index. We will also present finite element modeling (FEM) results and compare them to post precision glass molded (PGM) elements that have undergone CT and Raman mapping.
An analytical study of thermal invariance of polymeric nanolayer gradient index optical components
Show abstract
Specially formulated Gradient-Index polymeric optical materials offer capabilities not possible in conventional GRIN or
homogenous optics. A novel technology that enables large scale processing of nanolayered polymer films into real,
performance-enhancing lenses and other optical components for Defense-related optical systems is currently being
employed.
Polymeric nanoLayer GRIN materials (LGRIN) offer the ability to design and fabricate optics with custom gradient
refractive index profiles in optical components up to 90 mm in diameter and approaching 5 cm thick. High performance
achromatic singlet lenses were designed using specially developed ZEMAX design tools and exceptionally high quality
lenses were fabricated from the LGRIN materials. Optical performance of LGRIN optics is shown to be significantly
better than with conventional monolithic optics while also significantly reducing optical system mass, volume, and
optical element count.
Understanding the thermal behavior of such optical components is essential to their operational capability. An
experimental study of the effects of elevated operational environments to validate the feasibility of deploying LGRIN
optics into real-world operational environments was carried out. Interferometric and physical measurements of structure
and optical performance of LGRIN lenses was completed over a 30° - 50°C temperature range. It is shown that
nanolayered LGRIN optics and components exhibit no significant variation in optical performance with temperature as
compared with commercial, homogenous acrylic optics in the designed operational thermal range.
Coatings and Filters
Low-loss crystalline coatings for the near- and mid-infrared
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Substrate-transferred crystalline coatings have recently emerged as a groundbreaking new concept in optical
interference coatings. Building upon our initial demonstration of this technology, we have recently realized significant
improvements in the limiting optical performance of these novel single-crystal GaAs/AlGaAs multilayers. In the nearinfrared
(NIR), for center wavelengths spanning 1064 to 1560 nm, we have reduced the excess optical losses (scatter +
absorption) to less than 5 ppm, enabling the realization of a cavity finesse exceeding 300,000 at the telecom-relevant
wavelength range near 1550 nm. Moreover, we demonstrate the direct measurement of sub-ppm optical absorption at
1064 nm. Concurrently, we investigate the mid-IR (MIR) properties of these coatings and observe exceptional
performance for first attempts in this important wavelength region. Specifically, we verify excess losses at the hundred
ppm level for wavelengths of 3300 and 3700 nm. Taken together, our NIR optical losses are now fully competitive with
ion beam sputtered films, while our first prototype MIR optics have already reached state-of-the-art performance levels
for reflectors covering the important fingerprint region for optical gas sensing. Thus, mirrors fabricated via this
technique exhibit the lowest mechanical loss (and thus Brownian noise), the highest thermal conductivity, and,
potentially, the widest spectral coverage of any “supermirror” technology, owing to state-of-the art levels of scatter and
absorption losses in both the near and mid IR, all in a single material platform. Looking ahead, we see a bright future for
crystalline coatings in applications requiring the ultimate levels of optical, thermal, and optomechanical performance.
HfO2/SiO2 multilayer based reflective and transmissive optics from the IR to the UV
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HfO2/SiO2 multilayer based reflective optics enable threat detection in the short-wave/middle-wave
infrared and high power laser targeting capability in the near infrared. On the other hand, HfO2/SiO2
multilayer based transmissive optics empower early missile warning by taking advantage of the extremely
low noise light detection in the deep-ultraviolet region where solar irradiation is strongly absorbed by the
ozone layer of the earth’s atmosphere. The former requires high laser damage resistance, whereas the
latter needs a solar-blind property, i.e., high transmission of the radiation below 290 nm and strong
suppression of the solar background from 300 nm above. The technical challenges in both cases are
revealed. The spectral limits associated with the HfO2 and SiO2 films are discussed and design concepts
are schematically illustrated. Spectral performances are realized for potential A and D and commercial
applications.
Ultra-narrow bandpass filters for infrared applications with improved angle of incidence performance
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Narrow band-pass optical interference filters are used for a variety of applications to improve signal
quality in laser based systems. Applications include LIDAR, sensor processing and free space
communications. A narrow band width optical filter allows for passage of the laser signal while rejecting
ambient light. The more narrow the bandwidth, the better the signal to noise. However, the bandwidth
of a design for a particular application is typically limited by a number of factors including spectral shift
over the operational angles of incidence, thermal shift over the range of operating temperature and, in
the case of laser communication, rejection of adjacent laser channels. The trade-off of these parameters
can significantly impact system design and performance. This paper presents design and material
approaches to maximize the performance of narrow bandpass filters in the infrared.
Acousto-optic tunable filter as a notch filter
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An acousto-optic tunable filter (AOTF) is an all solid-state robust device with no-moving parts that has been used in the
development of hyperspectral imagers from the ultraviolet to the longwave infrared. Such a device is developed by bonding
a piezoelectric transducer on a specially cut prism in a birefringent crystal. When broadband white light is incident on the
prism input facet, two orthogonally polarized diffracted beams at a wavelength with a narrowband bandpass are
transmitted. The transmitted wavelength can be tuned by varying the applied radio frequency (RF). This is what is done
in a hyperspectral imager. An AOTF can also be used with multiple RFs applied at the same time to diffract a number of
different wavelengths. This mode can be exploited to design a tunable optical notch filter where multiple RFs are applied
simultaneously such that all wavelength in a specific range can transmit except for a specific wavelength which is notched.
We designed an optical system using a TeO2 AOTF with telecentric confocal optics operating in the shortwave infrared
(SWIR) with a 16-channel RF driver where both the amplitude and frequency can be controlled independently for each
channel. We will discuss the optical system, its characterization and present results obtained.
New counter-countermeasure techniques for laser anti-dazzling spectacles
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Aviation, commercial and military, is new area in optics that is suffering from laser threats in the last years. Dazzling
and damage to pilot's eyes by laser pointers is a common threat lately. Under certain conditions, laser light, directed at
aircraft can be hazardous. The most likely scenario is when bright visible laser light causes distraction and/or temporary
flash blindness to the pilot, during a critical phase of flight like landing or takeoff. It is also possible, that a visible or
invisible beam could cause permanent damage to a pilot's eyes. This paper presents a novel technology for protection of
the human eye against laser threats in the visible range.
Optical Design and Analysis III
Exploring the imaging properties of thin lenses for cryogenic infrared cameras
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Designing a cryogenic camera is a good strategy to miniaturize and simplify an infrared camera using a cooled
detector. Indeed, the integration of optics inside the cold shield allows to simply athermalize the design,
guarantees a cold pupil and releases the constraint on having a high back focal length for small focal length
systems. By this way, cameras made of a single lens or two lenses are viable systems with good optical features
and a good stability in image correction. However it involves a relatively significant additional optical mass
inside the dewar and thus increases the cool down time of the camera. ONERA is currently exploring a
minimalist strategy consisting in giving an imaging function to thin optical plates that are found in conventional
dewars. By this way, we could make a cryogenic camera that has the same cool down time as a traditional dewar
without an imagery function. Two examples will be presented: the first one is a camera using a dual-band
infrared detector made of a lens outside the dewar and a lens inside the cold shield, the later having the main
optical power of the system. We were able to design a cold plano-convex lens with a thickness lower than 1mm.
The second example is an evolution of a former cryogenic camera called SOIE. We replaced the cold meniscus
by a plano-convex Fresnel lens with a decrease of the optical thermal mass of 66%. The performances of both
cameras will be compared.
The first order solutions for two configurations of discrete zoom lenses
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Discrete zoom systems are commonly used as laser beam expanders and infrared zoom lenses. The reason to design a
discrete zoom lens is that they are often a desirable compromise between fixed-focal length lenses and continuous zoom
lenses, offering many advantages to imaging systems of all types. They have the advantage over continuous zoom systems
for containing fewer elements, thus reducing the weight of the system, and having one mechanical motion instead of two.
In literature there is little information on the first order parameters and starting requirements for discrete systems. This
work derives the first order equations for two different discrete zoom systems. The equations are derived from the
requirements of first order parameters which define the starting group focal lengths. The two design configurations studied
are: one zoom group flipping in and out of the system; one zoom group moving laterally along the optical axis. This work
analyzes the first order equations for both configurations and discusses the starting point for the designs taking into
consideration system limitations. Final designs for both configurations are then compared over several parameters: group
focal lengths, lens diameters, overall length, number of elements, materials, and performance.
Foveated optics
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Foveated imaging can deliver two different resolutions on a single focal plane, which might inexpensively allow more
capability for military systems. The following design study results provide starting examples, lessons learned, and
helpful setup equations and pointers to aid the lens designer in any foveated lens design effort.
Our goal is to put robust sensor in a small package with no moving parts, but still be able to perform some of the
functions of a sensor in a moving gimbal. All of the elegant solutions are out (for various reasons). This study is an
attempt to see if lens designs can solve this problem and realize some gains in performance versus cost for airborne
sensors. We determined a series of design concepts to simultaneously deliver wide field of view and high foveal
resolution without scanning or gimbals.
Separate sensors for each field of view are easy and relatively inexpensive, but lead to bulky detectors and electronics.
Folding and beam-combining of separate optical channels reduces sensor footprint, but induces image inversions and
reduced transmission. Entirely common optics provide good resolution, but cannot provide a significant magnification
increase in the foveal region. Offsetting the foveal region from the wide field center may not be physically realizable, but
may be required for some applications.
The design study revealed good general guidance for foveated optics designs with a cold stop. Key lessons learned
involve managing distortion, telecentric imagers, matching image inversions and numerical apertures between channels,
reimaging lenses, and creating clean resolution zone splits near internal focal planes.