Next generation IR imaging component requirements

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Tracey Haynes
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1 Next generation IR imaging component requirements Dr Andy Wood VP Technology Optical Systems November Excelitas Technologies E N G A G E. E N A B L E. E X C E L. 0

2 Some background Optical design Mechanical design Electronic design Development engineering Integrated Project Teams Optical component manufacture QIOPTIQ St. Asaph a long history in optics Test engineering Manufacturing engineering Thin film coating Holography Metalwork manufacture Assembly Optical & environmental test Qualification 1 1

3 Product Range: Visible to Long-Wave Infrared Multi-spectral Visible NIR SWIR MWIR LWIR µm A huge diversity of requirements & technologies 2 2

4 Product drivers 3 3

5 Infrared materials v Glass IR materials (generally) have significantly higher refractive indices Visible glass: n = IR Materials: n = Dispersion can be significantly lower Visible glass: V-value = IR materials: V-value = Many IR materials are opaque in the visible and often reflective Most visible materials are opaque in the IR (beyond 2 µm). IR materials are heavier than visible glasses. IR materials can be significantly more expensive than visible glasses. IR materials have very large dn/dt values. Significantly fewer practical IR materials to choose from. 4 4

$A typical IR objective lens for an uncooled sensor IR Petzval lens (8 12 µm) Diamond-turned aspheric and diffractive surfaces are routinely employed # Ge Ge * 25.$

6 A typical IR objective lens for an uncooled sensor IR Petzval lens (8 12 µm) Diamond-turned aspheric and diffractive surfaces are routinely employed # Ge Ge * MM # Hybrid refractive-diffractive surface Focal length : 100 mm F-number : F/1.4 Field-of-view : Zero Spurious diffraction orders impact image quality

$Sub-wavelength diffractive optics (Metasurface) aspect ratio ~1:140 échelette Ideal aspect ratio ~1:8$

7 Sub-wavelength diffractive optics (Metasurface) aspect ratio ~1:140 échelette Ideal aspect ratio ~1:8 Blazed-Binary Sub-Wavelength Structures can provide high broadband efficiency. 'Effective Index' is wavelength dependent. 6 6

Athermalisation Compensation for temperature induced degradation of

Complex mechanisms. Less complex optics.

Passive Optical Athermalisation Simplified or no mechanisms.

Chalcogenide materials are beneficial and can be moulded.

8 Athermalisation Compensation for temperature induced degradation of image quality is often essential Active Mechanical Athermalisation Complex mechanisms. Less complex optics. Electronics & power, temp sensors. Passive Optical Athermalisation Simplified or no mechanisms. More complex optics, exotic materials. Chalcogenide materials are beneficial and can be moulded. No electronics / power. Passive Mechanical Athermalisation Simplified optics. No electronics / power. Ge Plastic spacer KRS5 KRS5 ZnSe Complex IR telescope Focus & mag compensation 7 7

Multi-spectral imaging Multi-spectral imaging greatly enhances discrimination within the scene.

Graphene based sensor development underway for Visible LWIR.

$Wiedemann catadioptric systems Freeform reflectors Catadioptric (Wiedemann) Refractive Compact optical design solutions$ $Lenses in some unusual materials give useful refractive solutions in addition to alkali halides - e.g. Gadolinium Gallium Garnet (GGG), Yttrium Aluminium Garnet (YAG) & Yttria (Y 2 O 3 ).$

9 Multi-spectral imaging Multi-spectral imaging greatly enhances discrimination within the scene. Dual waveband detectors demonstrated in the laboratory (e.g. LWIR & SWIR). Graphene based sensor development underway for Visible LWIR. Single aperture multi-spectral lenses required for low Size and Weight. Wiedemann catadioptric systems Freeform reflectors Catadioptric (Wiedemann) Refractive Compact optical design solutions include freeform reflectors, refractive and catadioptric constructions. Lenses in some unusual materials give useful refractive solutions in addition to alkali halides - e.g. Gadolinium Gallium Garnet (GGG), Yttrium Aluminium Garnet (YAG) & Yttria (Y 2 O 3 ). Synthetic diamond lenses provide the most compact and lightweight solutions. Multi-spectral anti-reflection and mirror coatings required with good environmental properties. Surfaces required with very low roughness (<2 nm RMS) particularly for visible-ir new challenge for diamond turning. 8 8

Radial GRIN in chalcogenide Based on a process developed

$ghost images) Hybrid refractivediffractive lens Unwanted$ Research Labs) Diamond turned L-GRIN lens for magnifier

10 Radial GRIN in chalcogenide Based on a process developed successfully for polymer GRIN lenses GRIN lens (Avoids ghost images) Hybrid refractivediffractive lens Unwanted diffraction orders Temperature-induced diffusion (Naval Research Labs) Diamond turned L-GRIN lens for magnifier Does not lend itself to radial GRIN profiles a new process is required. 9 9

Computational imaging Combines novel optics and image processing to generate unique product differentiation.

Technology takes advantage of the rapid advances in electronics processing power.

New challenges for the optical designer needs holistic approach to optimise optics, sensor and image processing as an integrated system.

11 Computational imaging Combines novel optics and image processing to generate unique product differentiation. Benefits include reduced length & mass, fewer optical elements, removal of moving parts (e.g. for focus and FOV change) and novel functions such as foveated imaging and post-focusing. Technology takes advantage of the rapid advances in electronics processing power. Can break some of the fundamental scaling rules associated with conventional optics. New challenges for the optical designer needs holistic approach to optimise optics, sensor and image processing as an integrated system. Wavefront coding, multi-aperture and multi-scale imaging are of particular interest. Requires manufacture of freeform surfaces in IR materials including cubic forms, lenslet arrays and discontinuous surfaces

12 Computational imaging Lens arrays Freeform optics Bespoke novel design software developed with Heriot- Watt University Noise Compact multi-aperture IR objective Complex image formation model and processing Super-resolution processing 3x shorter than conventional optics Wide FOV IR objective possible with 2 thin lenses Freeform surface Simplified athermal seeker lens Conventional System Wavefront Coding (Wiener) Wavefront Coding (CLS) Man at 30 m Discontinuous optical surfaces Man at 125 m Detected image Processed image 11 11

Optics in the dewar Locating lenses in the dewar of

technology Lens in the dewar IR micro-camera Novel lens

extreme thermal shock and remain aligned.

different at room temperature metrology and build

13 Optics in the dewar Locating lenses in the dewar of cooled thermal imaging cameras significantly reduces camera size and mass. Technology demonstrated by ONERA/SOFRADIR and SCD product developments are starting. Multi-aperture computational imaging solutions proposed for some applications. IR micro-camera (seeker optics) Current IR fisheye lens technology Lens in the dewar IR micro-camera Novel lens mounting solutions required lenses need to survive extreme thermal shock and remain aligned. Lens profiles and optical performance significantly different at room temperature metrology and build complexity. Coatings required to adhere at -196 C and survive thermal shock. Silicon and germanium are preferred lens materials. Multi-aperture solutions proposed to keep all optics within the dewar

Significant activity in USA ( ) and Germany ( ); Optimax and Asphericon are leading suppliers.

14 Freeform optics The current hot topic in classical optics - reduces element count and enables novel geometries with folded optics. Optical design methodology (modelling, aberrations, optimisation, tolerancing), manufacturing processes and metrology are developing rapidly. Significant activity in USA ( ) and Germany ( ); Optimax and Asphericon are leading suppliers. Freeform prism near-to-eye display Nodal aberrations & phase space Freeform reflector Alvarez-based focus and zoom concept of potential interest for infrared systems. Freeform optics required for folded systems, computational imaging and conformal optics. No equivalent of Seidel aberration theory used for rotationally symmetric systems diagnostic tools in development based on nodal aberration theory and phase space techniques. Manufacturing techniques include deterministic grinding & polishing, diamond turning with slow & fast tool-servo and diamond milling. Metrology remains the most significant challenge particularly in production. Alvarez plates 13 13

15 Summary Next generation component requirements.. Low cost manufacturing - Automated manufacture & metrology. - Moulded optics. Metamaterials - Motheye structures. - Diffractive surfaces. - Metalenses. Materials - Multi-spectral optics (YAG, GGG, Yttria, KRS6) - Radial GRIN. - Diamond lenses. Geometry - Freeform optics. - Lenslet array & discontinuous surfaces. - Conformal optics. Metrology - Refractive index (n), dn/dt. - GRIN lenses. - Freeform optics. Thin-film coatings - Multi-spectral. - Improved robustness. - Improved transmission. - Uniform over highly curved surfaces

PRECISION LENS MOLDING OF CHALCOGENIDE OPTICS. Jayson J. Nelson 22 Apr 2015

PRECISION LENS MOLDING OF CHALCOGENIDE OPTICS Jayson J. Nelson 22 Apr 2015 PRECISION LENS MOLDING OF CHALCOGENIDE OPTICS 2 Global markets are looking for low cost materials that satisfy infrared imaging