Tech to help autonomous vehicles better scan for nearby fast-moving
objects
Mechanical control and modulation of light on a silicon chip could
enhance lidar

Date:
July 15, 2020
Source:
Purdue University
Summary:
Researchers have built a way that lidar could achieve
higher-resolution detection of nearby fast-moving objects through
mechanical control and modulation of light on a silicon chip.



FULL STORY ==========================================================================
A self-driving car has a hard time recognizing the difference between
a toddler and a brown bag that suddenly appears into view because of limitations in how it senses objects using lidar.


==========================================================================
The autonomous vehicle industry is exploring "frequency modulated
continuous wave" (FMCW) lidar to solve this problem. Researchers have
built a way that this type of lidar could achieve higher-resolution
detection of nearby fast- moving objects through mechanical control and modulation of light on a silicon chip.

The work, published in Nature, was conducted by the OxideMEMS lab
at Purdue University and the Laboratory of Photonics and Quantum
Measurements at E'cole polytechnique fe'de'rale de Lausanne (EPFL),
a research institute and university in Lausanne, Switzerland.

FMCW lidar detects objects by scanning laser light from the top of
an autonomous vehicle. A single laser beam splits into a comb of other wavelengths, called a microcomb, to scan an area. Light bounces off of an object and goes to the detector through an optical isolator or circulator, which ensures all reflected light ends up at the detector array.

What Purdue and EPFL researchers developed uses acoustic waves to enable
faster tuning of these components, which could bring higher-resolution
FMCW lidar detection of nearby objects.

The technology integrates microelectromechanical systems (MEMS)
transducers made of aluminum nitride to modulate the microcomb at high frequencies ranging from megahertz to gigahertz. The optical isolator
that the team developed as part of this process is further described in
a paper published in Nature Communications.



==========================================================================
An array of phased MEMS transducers, also used in cellphones to discern cellular bands, stirs light at gigahertz frequencies by launching a
corkscrew- like stress wave into a silicon chip.

"The stirring motion modulates light such that it can only travel in
one direction," said Sunil Bhave, a Purdue professor of electrical and
computer engineering.

Hao Tian, a Purdue Ph.D. candidate in electrical and computer engineering, built the MEMS transducers at the Scifres Nanofabrication Facility of
Purdue's Birck Nanotechnology Center in Discovery Park. He integrated
the transducers with a silicon nitride photonics wafer developed at EPFL.

"The tight vertical confinement of the bulk acoustic waves prevents
cross-talk and allows for close placement of the actuators," Tian said.

Other transducers in the same technology excite an acoustic wave that
shakes the chip at megahertz frequencies, demonstrating sub-microsecond
control and tuning of the laser pulse microcomb or soliton.



========================================================================== "This achievement, bridging integrated photonics, MEMS engineering and nonlinear optics, represents a new milestone for the emerging chip-based microcomb technology," said Junqiu Liu, the first author on the Nature
paper who leads the fabrication of silicon nitride photonics chips at
the EPFL Center of MicroNanoTechnology.

This light modulation technique not only integrates mechanics with optics,
but also the fabrication processes involved, making the technology more commercially viable, the researchers said. The MEMS transducers are
simply fabricated on top of the silicon nitride photonics wafer with
minimal processing.

"As yet unforeseen applications will follow up across multiple
communities," said Tobias Kippenberg, a professor of physics at
EPFL. "It's been shown time and again that hybrid systems can obtain
advantages and functionality beyond those attained with individual constituents." According to the researchers, the new technology could
provide the impetus for microcomb applications in power-critical systems
such as in space, data centers and portable atomic clocks, or in extreme environments such as those with cryogenic temperatures.

"Our results would not have been possible without this multidisciplinary
and intercontinental collaboration," Bhave said.


========================================================================== Story Source: Materials provided by Purdue_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Junqiu Liu, Hao Tian, Erwan Lucas, Arslan S. Raja, Grigory
Lihachev, Rui
Ning Wang, Jijun He, Tianyi Liu, Miles H. Anderson, Wenle Weng,
Sunil A.

Bhave, Tobias J. Kippenberg. Monolithic piezoelectric control
of soliton microcombs. Nature, 2020; 583 (7816): 385 DOI:
10.1038/s41586-020-2465-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200715131251.htm

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