Tech Briefs Magazine - November 2021 - PIT-18

Designing Advanced IR Optical Assemblies for UAVs
T
he UAV industry has significantly
evolved and grown in recent years.
Alongside this growth, we have seen the
development of UAVs and drones with
increasingly advanced infrared imaging
systems, containing detectors that are
larger in size and smaller in pixel size,
which present challenges for UAV optics.
Lens quality must increase in order to
maximize imaging performance in line
with detector capabilities, allowing for
high-resolution vision. Three crucial factors
should always be considered to
ensure the optical assembly is suitable
for UAVs and drones; these are known as
SWaP - Size, Weight, and Power consumption.
In other words, the optics
must be compact, lightweight, and with
reduced power consumption, in order
to enable maximum flight time.
The challenge falls on optical manufacturers
to design and produce optics
with a crisp, clean image over the entire
zoom range, and an MTF (modulation
transfer function) close to the diffraction
limit, while meeting strict SWaP
requirements. Optics must also be able
to withstand the harsh environmental
conditions associated with various UAV
and drone applications, such as in the
defense industry.
Background
The unmanned aerial vehicle (UAV)
industry is growing rapidly, with Teal
Group analysts estimating that worldwide
UAV production will total $135 billion
in the next ten years. When equip -
ped with high performance EO/IR camera
payloads, UAVs and drones lend
themselves to a wide range of imaging
applications.
The drone market consists of defense,
government, and commercial applications.
In the area of defense and govern(a)
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Frequency in cycles per mm
When equipped with high performance EO/IR camera payloads, UAVs and drones, lend themselves to
a wide range of imaging applications.
ment, drones are used for military and
police surveillance, border control, security,
and search and rescue operations.
Between 2009 and early 2017, at least 347
law enforcement and emergency responder
agencies in the U.S. acquired drones.
In the commercial drone market,
demands have been growing. Commercial
drones with thermal imaging capabilities
are playing a prominent role in inspecting
electrical power lines, oil pipelines, forest
fire detection, and other infrastructures.
Such capabilities are also used to assist in
firefighting operations by locating and
assessing fires, even when visibility is poor.
As UAV technology is applied in an
increasing variety of sophisticated tasks,
we see a growing need to maximize imaging
performance. Specific optical needs
are presented by the aforementioned
increase in detector resolution and size,
(b)
NFOV (275mm EFL) MTF, 3800-4200nm
TS 0.000, 0.0000 mm
TS 0.000, 2.4000 mm
TS 0.000, 4.8000 mm
TS 0.000, 6.1500 mm
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with its accompanying decrease in pixel
size. The production of smaller drones for
commercial use also increases the challenges
faced by optical manufacturers.
The Solution
High-quality lenses are essential to
leverage the advances in detector performance.
An inferior lens will produce
an inferior image, even with the best
detector. In order to match high-performance,
small pixel detectors, lower F#s
and tighter tolerances are required,
forming lenses with minimal aberrations.
To answer these requirements, lenses
must also have a long focal length, to
capture images from large distances. The
newest solutions are based on advanced
folded-optics and lightweight zoom lenses,
optimized for the next generation
infrared thermal imaging systems.
WFOV (20mm EFL) MTF, 3800-4200nm
TS 0.000, 0.0000 mm
TS Diff. Limit
TS 0.000, 2.4000 mm
TS 0.000, 3.6000 mm
TS 0.000, 4.8000 mm
TS 0.0000, 6.1500 mm
0 48 12 16 20 24 28 32 36 40
Spatial Frequency in cycles per mm
Figure 1. (a) Opto-mechanical layout and picture, (b) MTF characteristics.
18
Cov
ToC
Photonics & Imaging Technology, November 2021
Ø58±0.02
2.44°
*50.2°
38.3°
Modulus of the OTF
Modulus of the OTF

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Tech Briefs Magazine - November 2021

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