Tech Briefs Magazine - June 2021 - 47

Both were placed together on top of a
silicon wafer. The resulting camera performs
extremely well and is much easier
to produce. The process involves injecting
two solutions into a beaker and waiting
5 to 10 minutes. The resulting solution
can be easily fabricated into a functional
device.
There are many potential uses for
inexpensive infrared cameras including
autonomous vehicles that rely on sensors
to scan the road and surroundings.
Infrared can detect heat signatures from
living beings and see through fog or
haze, so car engineers would include
them if the cost was not prohibitive.
For more information, contact Louise
Ler ner at louise@uchicago.edu; 773-702-8366.
Tiny Light Detectors Record the Incoming Angle of Light
These tiny detectors could record characteristics of light such as color, polarity, and angle.
Stanford University, Palo Alto, California
G
eckos and many other animals have
heads that are too small to triangulate
the location of noises the way hu -
mans do: with widely spaced ears. In -
stead, they have a tiny tunnel through
their heads that measures the way incoming
sound waves bounce around to figure
out which direction they came from.
A similar system for detecting the
angle of incoming light was developed
that could let tiny cameras detect where
light is coming from but without the
bulk of a large lens, which is the typical
way to determine the direction of light.
These tiny detectors could record characteristics
of light such as color, polarity,
and angle of light. More detailed
light detection could support advances
in lens-less cameras, augmented reality,
and robotic vision, which is important
for autonomous cars.
If a sound isn't coming from directly
over a gecko's head, one eardrum
essentially steals some of the sound
wave energy that would otherwise tunnel
through to the other. This inference
helps the gecko understand where
a sound is coming from. This structure
was mimicked in the photodetector by
having two silicon nanowires - each
about 100 nano meters in diameter -
lined up next to each other like the
gecko's eardrums. They are positioned
so closely that when a light wave comes
in at an angle, the wire closest to the
light source interferes with the waves,
hitting its neighbor and basically casting
a shadow. The first wire to detect
the light would then send the strongest
current. By comparing the current in
both wires, the researchers can map the
angle of incoming light waves.
For more information, contact Taylor
Kubota at tkubota@stanford.edu; 650-7247707.
Optical
Device Fine-Tunes the Color of Light
The new photonic architecture could transform digital communications, artificial
intelligence, and quantum computing.
Stanford University, Stanford, California
hite light is not white at all but
rather a composite of many photons
- droplets of energy that make up
light from every color of the rainbow.
Researchers have developed an optical
device that allows engineers to change
and fine-tune the frequencies of each
individual photon in a stream of light to
virtually any mixture of colors.
The structure consists of a low-loss
wire for light carrying a stream of photons
that passes by like cars on a busy
throughway. The photons then enter a
series of rings like the off-ramps in a
highway cloverleaf. Each ring has a modulator
that transforms the frequency of
the passing photons - frequencies that
our eyes see as color. There can be as
many rings as necessary and engineers
can finely control the modulators to dial
in the desired frequency transformation.
Among the applications are optical
neural networks for artificial intelligence
that perform neural computations using
W
Tech Briefs, June 2021
Cov
light instead of electrons. Existing methods
that accomplish optical neural networks
do not actually change the frequencies
of the photons but simply reroute
photons of a single frequency. Performing
such neural computations through frequency
manipulation could lead to much
more compact devices.
The color of a photon is determined by
the frequency at which the photon resonates,
which in turn is a factor of its
wavelength. A red photon has a relatively
slow frequency and a wavelength of about
650 nanometers. At the other end of the
spectrum, blue light has a much faster
frequency with a wavelength of about 450
nanometers.
A simple transformation may involve
shifting a photon from a frequency of
500 nanometers to 510 nanometers or,
as the human eye would register it, a
change from cyan to green. The new
architecture can perform these simple
transformations with fine control.
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ToC
For an example, an incoming light
stream is comprised of 20 percent photons
in the 500-namometer range and
80 percent at 510 nanometers. Using
the new device, an engineer could finetune
that ratio to 73 percent at 500
nanometers and 27 percent at 510
nanometers, all while preserving the
total number of photons. In the quantum
world, a single photon can have
multiple colors. In that circumstance,
the new device actually allows changing
of the ratio of different colors for a single
photon.
The device allows for " arbitrary "
transformation but that does not mean
random. Instead, it means that it can
achieve any linear transformation that
the engineer requires. The engineer
can control the frequencies and proportions
very accurately and a wide variety
of transformations are possible.
For more information, contact Tom Abate
at tabate@stanford.edu; 650-736-2245.
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Tech Briefs Magazine - June 2021

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