VIAVI Solutions
White Paper
Optical Filters for LiDAR Systems
The Growing Importance of LiDAR for Automotive Applications
LiDAR systems have been used for several decades in satellites, surveying equipment and in specialized photography. In the
future, it’s expected that LiDAR systems will be an integral part of automotive sensor suites for enhanced safety and driver
assistance and in some limited roll outs of autonomous vehicles.
As a leading provider of patented optical filter technology for LiDAR systems, VIAVI Solutions has provided similar applications
to the government and aerospace markets for several decades. In 2010, VIAVI began offering its optical filters to the consumer
electronics market for gaming and computing, due to its ability to produce the filters at scale and with the highest precision
and durability required for large-scale implementations. Because of the proven quality of its filters, VIAVI is now enabling the
evolution of automotive safety.
How Time of Flight based LiDAR Works
LiDAR systems calculate the distance of objects
in the environment by emitting a pulsed laser
beam from a LiDAR camera. The beam of light
reflects off of an object, and the time it takes
for the light to travel back to the camera is
captured by the optical filter. By measuring the
returning light, the system can calculate the
distance of objects. This approach is known as
“time-of-flight” or ToF technology.
Optical Filter Requirements
Essential for LiDAR Systems
The hurdles are high for vendors that want to
provide optical filter technology for LiDAR
systems, and criteria is particularly stringent for
automotive applications. Three key optical filter
requirements are critical for LiDAR systems to
work most effectively in cars:
Must operate in high ambient light
conditions. Changing light conditions and reflections from other car headlights can impact the accurate detection and
measurement of surrounding objects by LiDAR systems. In order to gather the right data from the desired wavelength of light,
the optical filter must effectively block out unwanted information that also travels back to the camera. To ensure accuracy, the
As technology companies and auto makers add new functionality to make cars more
automated, LiDAR (Light Detection and Ranging) systems play an important role in
ensuring that cars accurately sense and react to the environment around them.
The Expanding Role and Requirements of Optical Filter
Technology for Automotive Applications and other
Sensing Systems
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optical filter must be able to reliably function across a wide
variety of changing light conditions.
Returning light emitted from the light source is low,
so it’s critical that it be captured efficiently. Because
the emitted light is spread out over long distances in the
environment and the reflective capabilities of surfaces vary
widely, typically only a few particles of light containing the
needed information return to the original light source. LiDAR
systems are dependent on high-quality filter technology
that can isolate the signal from just a few photons.
Must meet stringent durability requirements for
automotive applications. Automotive requirements are
very strict in terms of durability, in order to avoid safety
recalls. All LiDAR components, including filters, must
withstand severe temperature ranges between -40 and +125
degrees Celsius during testing and qualification. Equally as
important, the ability to manufacture hundreds of millions
of filters at scale and have them all operate consistently is
critical.
Key Differentiators of VIAVI Optical
Filter Technology
VIAVI optical filters address two major issues for LiDAR
systems in self-driving car designs: enabling a light signal to
travel further and the ability for the optical filter to operate
at a high level of reliability in the brightest levels of
sunlight. In LiDAR systems for automotive applications, every
nanometer of bandwidth counts to avoid accidents or recalls.
VIAVI optical technology filters light so that the signal-to-
noise ratio can be improved by as much as 150 percent, to
ensure the most accurate measurements.
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Transmittance [%]
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Comparison between 'standard' and LAS 940nm BP filter for AOI=0° - 35°
VCEL
standard_AOI=0°
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LA S_AOI=0°
LA S_AOI=35°
Key product features include:
Optical precision for volume manufacturing. VIAVI
provides Central Wavelength (CW) Control Specifications at
+/-0.4 percent that are optimum for manufacturing filters in
large volumes for cars. For example, a wavelength emitted
at 905nm has a tolerance of +/-4 nm.
Superior optical performance with high accuracy.
The passband capability of VIAVI filters operate at more
than 95 percent transmission, on a scale where 0 percent
equals no transmission of light and 100 percent represents
transmission of all light. Out-of-band blocking, or light
traveling outside of the desired transmission path, is more
than OD4, or less than .01 percent, and can be more than
OD6, or less than .001 percent, if required. VIAVI filters also
provide steep transitions for cut-on, the point where the
filter starts to transmit light and cutoff, where the filter
starts to block light, with a square bandpass essential for
ensuring accuracy in autonomous cars.
Extensive reliability testing that complies to multiple
industry standards. VIAVI optical filters pass rigorous
testing for heat soaking (testing filters at high levels
of humidity), temperature cycling (testing how filters
withstand wide temperatures between a range -40 degrees
and +125 degrees Celsius), manufacturability (testing
electronics in a reflow oven to ensure they can withstand
soldering temperatures required on electronic circuit boards),
and MIL-C hardness and adhesion tests (typical quality tests
performed on optical coatings).
VIAVI Optical Filters Move into a Variety
of New and Demanding Applications
In parallel with LiDAR systems for external measurement,
VIAVI is currently developing optical filter technology for
in-cabin systems that measure the biometrics of the driver.
In addition, the same VIAVI filter technology is moving into a
variety of other areas as electronics become more intelligent,
automatically recognizing and adapting to a variety of
internal and external conditions. The proven quality, precision,
durability and scale of VIAVI optical filters will help propel
various phases of automated vehicles and other sophisticated
sensing applications over the next decade.