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E N G A G E .

© 2013 Excelitas Technologies

E N A B L E . E X C E L .

Next generation IR imaging

component requirements

Dr Andy Wood

VP Technology – Optical Systems

November 2017

11

Some background

QIOPTIQ St. Asaph– a long history in

optics

• Optical design

• Mechanical design

• Electronic design

• Development engineering

• Test engineering

• Manufacturing engineering

• Optical component manufacture

• Thin film coating

• Holography

• Metalwork manufacture

• Assembly

• Optical & environmental test

• Qualification

Integrated Project Teams

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Product Range: Visible to Long-Wave Infrared

A huge diversity of requirements & technologies

1 10 20 µm0.4 0.7 2 3 5 70.1 0.4 0.7 1 2 3 5 7 10 20 µm1 10 20 µm0.4 0.7 2 3 5 70.1 0.4 0.7 1 2 3 5 7 10 20 µm

Visible NIR LWIRMWIR

Multi-spectral

SWIR

33

Product drivers

44

Infrared materials v Glass

• IR materials (generally) have significantly higher refractive indices• Visible glass: n = 1.45 – 2.0.

• IR Materials: n = 1.38 – 4.0.

• Dispersion can be significantly lower• Visible glass: V-value = 20 – 80.

• IR materials: V-value = 20 – 1000.

• 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.

55

A “typical” IR objective lens for an uncooled sensor

IR Petzval lens(8 – 12 µm)

Focal length : 100 mm

F-number : F/1.4

Field-of-view : 10°

GeGe

25.00 MM

#

# Hybrid refractive-diffractive surface

-1+3 +2 +1 Zero

Spurious diffraction orders impact image quality

Diamond-turned aspheric and diffractive surfaces are routinely employed

*

66

Sub-wavelength diffractive optics (Metasurface)

Ideal

………………………

échelette

aspect ratio ~1:8

aspect ratio ~1:140

• Blazed-Binary Sub-Wavelength Structures can

provide high broadband efficiency.

• 'Effective Index' is wavelength dependent.

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Athermalisation

Plastic spacer

Passive Mechanical Athermalisation• Simplified optics.

• No electronics / power.

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.KRS5

Ge

ZnSe

KRS5

Complex IR telescope

Focus & mag compensation

Compensation for temperature induced degradation of image quality is often essential

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• 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 (Y2O3).

• 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.

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.

Freeform reflectors

Catadioptric (Wiedemann)

Refractive

Wiedemann catadioptric

systems

99

Radial GRIN in chalcogenide

Temperature-induced diffusion(Naval Research Labs)

Based on a process developed successfully for polymer GRIN lenses

Does not lend itself to radial GRIN profiles – a new process is required.

GRIN lens(Avoids ghost

images)

Hybrid refractive-diffractive lens

Unwanted diffraction orders

Diamond turned L-GRIN lens for magnifier

1010

• 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.

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.

1111

Computational imaging

Detected image Processed image

Wide FOV IR objective possible with 2 thin ‘lenses’

Complex image

formation

model and

processing

Discontinuous

optical surfaces

Compact multi-aperture IR objective

3x shorter than conventional optics

Freeform

optics

Super-resolution

processing

Lens

arrays

Conventional System Wavefront Coding (Wiener) Wavefront Coding (CLS)

Man at 30 m

Man at 125 m

Simplified athermal

seeker lens

NoiseBespoke novel design software

– developed with Heriot-

Watt University

Freeform

surface

1212

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.

Optics in the dewar

• Locating lenses in the dewar of cooled thermal imaging cameras (@77K) 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.

Lens in the dewar

IR micro-camera(seeker optics)

Current IR fisheye lens technology

1313

• 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.

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

Alvarez platesNodal aberrations & phase space

Freeform reflector

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Summary

• Low cost manufacturing

- Automated manufacture & metrology.

- Moulded optics.

• Materials

- Multi-spectral optics (YAG, GGG, Yttria,

KRS6)

- Radial GRIN.

- Diamond lenses.

• Geometry

- Freeform optics.

- Lenslet array & discontinuous surfaces.

- Conformal optics.

• Metamaterials

- Motheye structures.

- Diffractive surfaces.

- Metalenses.

• Metrology

- Refractive index (n), dn/dT.

- GRIN lenses.

- Freeform optics.

• Thin-film coatings

- Multi-spectral.

- Improved robustness.

- Improved transmission.

- Uniform over highly curved surfaces.

Next generation component requirements ……..