Tech Briefs Magazine - September 2024 - PIT-12
TECHNOLOGY LEADERS Optics
Ultra-Narrowband Optical Filters
Pushing Boundaries from the UV to the LWIR
Developments in ultra-narrow manufacturing capabilities enable
transformative, world-changing, technology.
A
dvances in optical sensors and
imaging technologies are ever
more rapidly assimilated into
how humans interact, understand
themselves, and explore the world
around them. The scope of inquiry for
optical devices is broad and they enable
technologies within, such as implanted
transdermal bioMEMS devices, and beyond,
or as space-flight surveyors deployed
as near and deep space instruments.
Central to the functionality of
modern optical devices, ultra-narrow
bandpass (UNBP) thin-film optical filters
enable discrimination of sub-nanometer
bands inside broad spectra.
These filters, pioneered as NIR DWDM
filters for the telecommunications industry,
are now essential in extracting
meaningful signal from imaging and
sensing devices operating anywhere between
the deep ultraviolet and the mid
infra-red bands.
Novel deposition techniques, such as
SIRRUS™, developed at Alluxa, have
transformed the fabrication of UNBP filters
from a low throughput, high-cost enterprise
into a highly deterministic manufacturing
process. Critical filter attributes
such as form factor, spatial uniformity,
and spectral resolution have exceeded capability/performance
thresholds of recent
years. The following examples highlight
some of the latest applications of
UNBP's.
Heliophysics, as a subject matter, has
come to the forefront as a social curiosity
and as a venue for study of a broad range
of sun-earth interactions. Research into
magnetic field/plasma phenomena,
such as coronal mass ejections (CMEs),
is a subject of great interest.2 Investigations
over the last two decades range
from high atmospheric flights to instrumentation
aboard numerous space-flight
missions. These solar surveyors have
used multi-wavelength UNBP filters for
high spatial and temporal resolution
scans of the low, mid, and high segments
12
Figure 1. Interface Region Imaging Spectrograph (IRIS) explorer visualization with windowed SJI imagery. (Image:
Alluxa)
of the heliosphere. As the next generation
instrumentation is being developed,
the requirement for finer resolution imaging
of plasma velocity (i.e., temperature
profiling of the heliosphere) have
increased. To address this need, Alluxa is
building high finesse multi-cavity
UNBP's in the UV.
Filters with >500 layers have been produced
for imaging spectrographs and
other sensing applications. Using an array
of instrumentation developed internally,
Alluxa filters are shown to exhibit
FWHM < 0.5 nm and peak transmittance
of 0.10-0.50 (10-50 percent), while blocking
200-1200 nm at OD6-12 as seen in
Figure 2. This impressive spectral profile
is attributed to deposition system configuration
and process methodologies for
minimizing losses (scatter + absorption)
in high interface-count filters, a capability
critical to high performing UV filters.
Atmospheric observation and modeling
are a principal concern for everyone
catching a ride on this blue-bubble. It
could significantly alter individual lives
and geo-economic constructs such as the
green-house emissions global mercantile
system. Specifically, filters at 532 nm and
1064 nm will be significant in upgrading
our ability to measure backscatter and
volume depolarization for diurnal cloud
and aerosol profiles in the troposphere.
Figures 3 and 4 demonstrate the performance
of a 532-0.127 and 1064-0.25 OD6
Ultra-Narrow Bandpass filter, respectively,
closely matching the intended theoretical
simulation. The filters will be implemented
in a flight mission for
practical use in atmospheric Lidar remote
sensing.3,4
Another area of experimentation
and growth is that of gas monitoring
and analysis, particularly at wavelengths
in the LWIR. Laser applications
in this wavelength regime range
from experimental tattoo removal procedures
to manufacturing medical
Photonics & Imaging Technology, September 2024
Tech Briefs Magazine - September 2024
Table of Contents for the Digital Edition of Tech Briefs Magazine - September 2024
Tech Briefs Magazine - September 2024 - Intro
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