G&H - Ruggedising G&H’ s hi-res SWIR lens systems

One arena that presents particularly interesting opportunities for us to go above and beyond in accommodating our customers’ special requirements is SWIR – Short-Wave Infrared.

One arena that presents particularly interesting opportunities for us to go above and beyond in accommodating our customers’ special requirements is SWIR –short-wave Infrared.

SWIR is favoured for many applications because it delivers a number of benefits over other wavelengths. At long ranges and in low visibility conditions, for example, the signal-to-noise ratio and image quality in the SWIR band are significantly better than in other bands such as NIR and the visible spectrum.

This tends also to result in more stable, error-tolerant imaging, delivering an extended range of coverage and better image interpretability, and making SWIR a good fit for many ground, air, maritime, and space deployments.

SWIR: where the challenges begin

Of course, these benefits are ultimately dependent on both the quality and resilience of the lenses and opto-mechanical lens systems used to capture the image – and this is where some challenges arise that G&H is particularly practiced in solving for our customers.

In short, this is about reconciling two apparently conflicting requirements: the need for super-sensitive, highly accurate SWIR optical solutions, but in a form that resists the extremes of temperature, shock, humidity, vibration, and even radiation inherent in many of the harsh environments (A&D, space) in which those solutions are often deployed.

At the same time, it is about delivering solutions with the low SWAP-C (size, weight, power, and cost) characteristics that render them operationally deployable and economically viable to produce.

Here’s how we design this “ruggedisation” into every feature and behaviour optical, electro-mechanical, spatial, structural – of our SWIR and other products and developments, and ensure that the process is agile, adaptive, and customercentric.

From the lens backwards: a catalogue of harsh conditions

First, let’s take a closer look at our customers’ challenges, and then we’ll move on to how our facility in Keene, New Hampshire – which specialises in custom optical and opto-mechanical analysis and design for lightweight, ruggedised solutions –has developed responses to address them.

At the fore in any imaging system is the lens, and harsh environments bring some testing challenges for these precision optics.

Vibration and shock, for example, can play havoc with the stability of lens mountings, causing lens displacement that results in tip, tilt, and de-centre issues, and significantly degrades optical performance.

Adequately constraining the lens is therefore critical – but temperature can also cause expansion and contraction, which, if the constraint is too tight, can subject the surface to stress and strain, causing similar degradation.

After the lens, the opto-mechanical elements are also susceptible to harsh environments. Expansion and contraction in these systems in response to temperature changes, if not coordinated with the behaviour of the optics, can once again cause stresses and strains on the lens that impair its performance.

Finally, the electronic elements – control boards, motors, and encoders – are also affected by harsh conditions, with PCBs, connectors, and wiring all being particularly susceptible to damage by temperature, shock, and vibration. in particular, in terms of performance, cost, and (in A&D and other applications in which imaging systems are often gimbal-mounted) space and weight. How does G&H achieve this?

All in-house – from expertise to materials

The answer lies not solely in the technical detail, but also in how G&H as an organisation operates, combining multi-disciplinary expertise hubs with highestquality materials sourced or produced mainly within the G&H network.

This in-house “virtuous circle” drives innovation not only in system design, but in adapting and reengineering existing solutions to create specific variants – e.g. ruggedised - based on customer feedback. Our ruggedisation expertise derives, in turn, from our many years’ experience of developing radiation-hard optical systems used in used in Earth observation, planetary exploration missions, and autonomous docking systems in space. The best way to illustrate how we tackle the challenges of SWIR system ruggedisation whilst incorporating optimal SWAP-C (size, weight, power, and cost) characteristics is probably to focus on one particular SWIR solution we produce: the 40-400 mm lens system. SWIR 40-400 mm: a case study in light, cost-effective ruggedisation

Developed in response to a market need for a CZ (continuous zoom) SWIR solution that would couple out-of-the-box integration capability with ruggedised performance, the FireAnt 40-400 mm SWIR is an agile reworking of an existing CZ SWIR solution that has delivered proven high performance to many of our customers.

However, it’s important to note that many of the approaches and benefits we explore below apply across our lens system solutions for other bands, too. Size, weight, power, and cost: an optimum balance

On the SWAP-C front, the FireAnt 40-400 mm system’s unique single aperture design, coupled with its folded geometry, deliver a much shorter track length and smaller physical footprint, enabling (for example) one gimbal window to accommodate multiple sensors, and SWIR imaging to be combined with other bands in one package. This reduction in size and bulk of course also helps to optimise weight, whilst power efficiency is enabled through an electronic control board that closely controls power consumption. Cost optimisation is achieved by standardisation of the core design and components, and by automated testing routines. Some of these functions include automatic focal length measurement, automatic distortion measurement where the field of view is mapped to the image diagonal, and automatic metric zoom table generation where measured focal lengths are mapped to specific encoder positions in zoom lenses. Taken in combination, G&H engineers accelerate the journey from proof of concept to production run, enabling a lower overall unit cost for a higher-quality output.

Standing up to the harshest conditions

On the ruggedisation front, the FireAnt 400-400 mm lens system, as with the other variants G&H develops, is the product of extensive design, engineering, and testing processes. Using a combination of tools including Zemax, Fred Optical Engineering Software (FRED), SolidWorks 2020 and SolidWorks Simulation 2020, G&H’s engineers went through a rigorous FEA (finite element analysis) process to model the effect of harsh environments on both the optics and associated systems. They then used these outputs to design, apply, and test the ruggedisation from the lens backwards.

Glass selection (Schott or Ohara for example), shaping, and lens edge thickness were all optimised, for mountings that would constrain adequately for resistance to shock, vibration, and deformation, but not become overtight with temperaturedriven expansion and contraction.

The G&H team at Keene, New Hampshire

The effect of temperature on the relationship between optics and opto-mechanics was also closely modelled, and adjustments made to the motor focus to prevent poor interplay between these elements that could cause optical degradation.

All individual PCB components were tested for resistance to temperature, shock, and vibration, military-specification connectors were specified throughout (as these meet the requirements of harsh conditions), and wiring was strain-relief tested to ensure resistance to shock and vibration.

Finally, as-built tolerances were engineered to safely accommodate vibration and gravitational forces and remain stable, yet deliver a fit that would enable optimum manufacturability.

Combined with active and passive athermalisation, AR coatings that strike an optimum balance between performance and durability, and IP67+ sealing for protection against ingress of dust and sand, the SWIR 40-400 mm solution is proof that resilience need not necessarily come at the cost of performance.

In fact, FireAnt 40-400 mm delivers exactly the same level of SWIR imaging performance and the same technical and market differentiators to our customers as its predecessor – continuous zoom, continuous focal length, constant light throughout F# stops, exact object distances with no drift or lag, and more – but in a significantly more robust package.

Ruggedisation expertise as a service

At G&H, we don’t just pride ourselves on the engineering expertise that goes into our products - we put that expertise at the service of our customers directly, to help support their own downstream product development.

This is as true of ruggedisation as of any other optical engineering process we can deliver, across any imaging band - as we say, “Any wavelength, any sensor, any application.

Indeed, our recently opened Optical Systems Innovation Hub demonstrates the emphasis we place on this customer-centricity, and the investment we have made in it, whilst our new and extensive cleanroom facility ensures we have the cuttingedge manufacturing and assembly capability to consistently deliver on the exacting standards of quality that our customers demand and deserve. Here, again, the FireAnt SWIR 40-400 mm has proven its worth. Approached by a customer to investigate whether a change to the mounting bolts to gain space in a gimbal environment would render their lens system susceptible to harsh environment impacts, we were able to comprehensively model the proposed design change and confirm that their proposal was still a viable ruggedised product.

Doubtless, this saved the customer considerable time and expense as reworking the gimbal design was avoided.

Ruggedisation in the real world

In summary, then, SWIR imaging solutions, including SWIR 40-400 mm, are particularly suited to applications and platforms that now see them in daily use in everything from laser targeting visualisation, to maritime fog/haze penetration, to mid to long-range surveillance – and often in space-constrained deployments such as gimbals.

At the same time, expectation of these systems’ performance is spiralling. With the sensor market moving rapidly towards moving towards 1280 x 1024 array the days of an optical lens system simply being a VGA camera are gone forever.

However, whilst performance, size, weight, and compactness are all critical factors in these environments, the most critical factor of all is whether the device will actually work properly when it’s in situ – or deliver disappointing results.

The difference between those two outcomes is ruggedisation. Quite simply, ruggedisation is now an inseparable requirement from the use of SWIR itself for many applications.

Watch the webinar, learn more

This article was based on our September 2021 webinar Designing and Manufacturing Hi-Res SWIR Lens Systems for Harsh Environments.

Watch it HERE.

To learn more about how our ruggedisation expertise can enable you to respond quickly to the demands of challenging infrared imaging markets, get in touch: info@gandh.com

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Explore our case studies for more information about the bene ts of using server racks.

Contact us today to talk about your requirements and our friendly team will be glad to hear from you.

Our products are available in a wide range of standard sizes, and our UK-based design team can create a custom solution to meet (almost) any application your product requires.

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