Tech Briefs Magazine - April 2021 - 30

Optics
phonon (or a unit of vibrational energy)
scattering into a ground state, which then
serves as the injector of electrons into the
next step's upper level and the process
repeats. Such an arrangement of the electrons in the system is essential for lasing to
occur.
There are close to 15,000 interfaces
between quantum wells and barriers, half
of which are not even seven atomic layers
thick. The quality and reproducibility of
these interfaces are of critical importance
to the performance of terahertz lasers.

In a medical setting, the new portable
system - which includes a compact camera and detector and can operate anywhere with an electric outlet - could
provide real-time imaging during regular
skin cancer screenings or even during
surgical procedures to excise skin cancer
tissues. The cancer cells show up dramatically in terahertz because they have
higher water and blood concentrations
than normal cells.
The technology could also be applied
in many industries where the detection

of foreign objects within a product is
necessary to assure its safety and quality.
Detection of gases, drugs, and explosives
could become especially sophisticated
with the use of terahertz radiation. Compounds such as hydroxide, an ozonedestruction agent, have a special spectral
" fingerprint " within the terahertz frequency range, as do drugs including
methamphetamines and heroin, and
explosives including TNT.
For more information, contact Abby Abazorius at abbya@mit.edu; 617-253-2709.

Optical Phased Array Technology On-Chip at Near Infrared
and Blue Wavelength
This compact beam steering technology has applications in autonomous navigation,
AR, and neuroscience.
Columbia University, New York, New York

hile beam steering systems have
been used for years for applications such as imaging, display, and
optical trapping, they require bulky
mechanical mirrors and are overly sensitive to vibrations. Compact optical
phased arrays (OPAs), which change the
angle of an optical beam by changing
the beam's phase profile, are a promising new technology for many emerging
applications. These include ultra-small
solid-state LiDAR on autonomous vehicles, much smaller and lighter AR/VR
displays, large-scale trapped-ion quantum computers to address ion qubits,
and optogenetics, an emerging research
field that uses light and genetic engineering to study the brain.
Long-range, high-performance OPAs
require a large beam emission area
densely packed with thousands of actively phase-controlled, power-hungry, lightemitting elements. To date, such largescale phased arrays for LiDAR have been
impractical since the technologies in
current use would have to operate at
untenable electrical power levels.
Researchers have developed a lowpower beam steering platform that is a
non-mechanical, robust, and scalable
approach to beam steering. The team
demonstrated low-power, large-scale optical phased array at near infrared and
on-chip at blue wavelength for autonomous navigation and augmented reality, respectively. They also developed an
implantable photonic chip based on an
optical switch array at blue wavelengths

Fiber Input
Wire Bonds

Grating Emitters

Phase Shifters
Packaged large-scale optical phased array for solid-state LiDAR. (Credit: Steven Miller/Columbia
Engineering)

for precise optogenetic neural stimulation.
The team designed a multi-pass platform that reduces the power consumption of an optical phase shifter while
maintaining both its operation speed
and broadband low loss for enabling
scalable optical systems. The light signal
recycles through the same phase shifter
multiple times so that the total power
consumption is reduced by the same factor it recycles. They demonstrated a silicon photonic phased array containing
512 actively controlled phase shifters

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and optical antenna, consuming very
low power while performing 2D beam
steering over a wide field of view. The
results are a significant advance towards
building scalable phased arrays containing thousands of active elements.
Phased array devices were initially
developed at larger electromagnetic wavelengths. By applying different phases at
each antenna, researchers can form a
very directional beam by designing constructive interference in one direction
and destructive in other directions. In
order to steer or turn the beam's direcTech Briefs, April 2021

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Tech Briefs Magazine - April 2021

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