MEMS + Lens = Compact LIDAR
If you see a car driving down the road and it looks as if there is a rotating ice bucket on the top, it’s likely a self-driving car, and the bucket is its LIDAR unit. The system
works, but is relatively bulky, slow, and may amass a layer
of bug splats over time. Fortunately, researchers at
Argonne National Laboratory ( www.anl.gov) and Harvard
University ( www.harvard.edu) have come up with a
technology that combines a microelectromechanical
system (MEMS) with newly crafted metasurface lenses to
produce a much more compact infrared light-focusing
Their device is based on a metasurface lens that
measures only 900 microns in diameter and 10 microns
in thickness (less than 0.04 by 0.0004 inches). As you
may know, metamaterials are synthetic structures that
exhibit properties not generally found in natural materials.
Hence, a metasurface is an artificial sheet material of
subwavelength thickness whose structure imposes
unusual phase shifts on transmitted or reflected light.
Interestingly, it can display a negative refractive index
within a particular frequency range (i.e., it causes the light
to travel faster than it would in a vacuum).
In the new optical system, MEMS mirrors reflect
scanned light, which is focused by the metalens without
the need for additional optical components such as a
focusing lens. The trick was to integrate the two
technologies without hurting their performance.
The eventual goal is to fabricate all components of an
optical system with the same technology used to
manufacture today’s electronics. According to Argonne’s
Daniel Lopez, “These devices are key today for many
technologies. They have become technologically
pervasive and have been adopted for everything from
activating automobile air bags to the global positioning
systems of smart phones ... In principle, optical systems
could be made as thin as credit cards.” ▲
Fusion is Coming! Again!
Every few years, someone announces a “breakthrough” in fusion technology that promises to provide the world
with clean, safe, cheap, inexhaustible power. In 2005, Bill
Gates assured us, “Two years from now, spam will be
solved.” So much for promises. However, if at first you don’t
succeed, raise a big wad of money and try, try again.
The latest to take the fusion pledge is a collaboration
between MIT ( web.mit.edu) and a new company called
Commonwealth Fusion Systems (CFS, www.cfs.energy). CFS
is basically an MIT spinoff, created by former Plasma
Science and Fusion Center staff and students who have
cleverly siphoned an initial $50 million from Eni — an Italian
multinational energy company founded in 1953.
The key to CFS’ plans is an effort to develop the world’s
most powerful large-bore superconducting electromagnets,
which are to be used to keep the hot plasma from escaping
the donut-shaped chamber and ruining everyone’s day. The
result will be a much more compact tokamak than, say, the
large-scale ITER currently under construction in France.
Whereas ITER is aiming for an output of 500 MW, the
CFS project — dubbed SPARC — has a more modest final
goal of 200 MW; this is comparable to most existing
commercial power plants.
According to CFS, it will go online within 15 years.
Maybe. Possibly. Nah. ▲
■ View of a metasurface-based flat lens (square piece)
integrated onto a MEMS scanner.
■ BY JEFF ECKERT TECHKNOWLEDGEY 2018
■ A visualization of MIT’s planned fusion experiment.
Credit: Ken Filar/MIT.
10 May/June 2018