Scan distance (µm)
Optical path length (nm)
60
40
20 0
160
120
80
40
0
Scan distance (µm)
Optical path length (nm)
0 5 10 15
Unetched area
Bowl
bottom
SubstrateSubstrate
1L
2L
3L
4L
20
25
250
200
150
100
50
0
Imaging array
Sample and hold
Top chip
Imaging array
65 nm–0.18 µm
CIS process
Custom processor
I/O
ADC
Bottom chip
Analog/digital processor
9 Laser Focus World www.laserfocusworld.com January 2015
newsbreaks
Multiple diamond defects provide
subpicotesla magnetometer sensitivity
A single nitrogen-vacancy defect cen-
ter in a diamond can, when its op-
tical properties and spin properties
are queried by laser readout (for ex-
ample, measuring the resulting po-
larization), serve as a magnetometer
with a room-temperature sensitivity
of around 10 n T/Hz0.5. Researchers
at the University of Stuttgart (Ger-
many) and the University of Tsukuba
(Japan) have demonstrated that this
limited sensitivity can be boosted by
using multiple defect centers simul-
taneously to measure magnetic field;
in fact, the sensitivity scales as N0.5,
where N is the number of defects. To
do this, they reduced noise from the
green excitation and readout laser
and other sources, achieving a room-
temperature
‘World’s thinnest lens’ made from layers
of molybdenum disulfide
A group of researchers from the Australian National Universi-
ty (Canberra) and the University of Wisconsin (Madison) has
discovered that a single molecular layer L of molybdenum di-
sulfide (MoS2) has a giant optical path length (OPL); in com-
parison to another monolayer material, graphene, the OPL
of MoS2 is about 10 times greater. Although this may seem
like an esoteric result, it has a very practical consequence
for photonics: as the researchers have demonstrated, just
a few monolayers of MoS2 can be used to create what the
researchers call the “world’s thinnest optical lens,” only 6. 3
nm thick. With a diameter of about 20 µm, the concave MoS2
lens the researchers fabricated has a calculated focal length of
−248 µm at a 535 nm wavelength.
For experimentation, the researchers transferred single- or
few-layer MoS2 flakes onto a silicon wafer (under a microscope,
regions of differing colors corresponded to layers of different
thickness). To create the lens, they used a focused ion beam to
mill a concave bowl shape, producing a continuous, curved OPL
profile. The giant OPL arises from a corresponding giant elastic photon scattering efficiency. The researchers discovered that
the strength of the elastic interaction in the thin 2D MoS2 increases greatly with a growing refractive index as a result of the
ultrathin-film geometry. For every layer thickness increase of 1
nm, the OPL increases by more than 50 nm. The researchers
say that other high-index ultrathin-film transition-metal dichal-cogenide 2D semiconductors (of which MoS2 is an example) are
particularly well-suited for this approach. Reference: Jiong Yang
et al., arXiv:1411.6200 [ cond-mat.mtrl-sci] (2014).
Filter
Detection
Nitrogen-vacancy ensemble
Nitrogen-vacancy
fuorescence
Laser
Microwaves
Stacked image sensor
enables ‘Internet of
Things’ fire sensing
As the number of devices connected to
the Internet is expected to grow to more
than 50 billion devices by 2020, this interconnected network of sensors—
described as the Internet of Things (Io T)—
has become the focus of a number of
leading technology companies. Recognizing the growing continued on p. 10
continued on p. 10
