Photonics Driving Economic Growth in Europe - Photonics21

2. Photonics Research and Innovation Challenges
EIR sources
As a consequence of the low concentration of
many critical analytes, there is a huge need of cost-
effective, narrow-band, medium-power (1–100
mW) light sources, allowing the measurement
process to be done quickly and with the required
resolution. Of particular interest are solid-state
lasers, such as QCLs (Quantum Cascade Lasers),
VECSELs (Vertical External Cavity Surface Emitting
Lasers), VCSELs (Vertical Cavity Surface Emitting
Lasers), and fibre lasers. Since many technologies
utilise electronic lock-in methods, it must be possible
to modulate the lasers electrically. For stable,
efficient operation in the MIR/FIR, the lasers must
be cooled and temperature-controlled, and care
must be taken that these cooling requirements
do not dominate the production cost of the complete
laser sub-system. For low-cost laser systems,
electrical emission wavelength tuning capability is
desirable, with tuning ranges of several 10 nm or
up to a few 100 nm.
A specific goal is the development of a family of tunable
EIR light emitters. Complete laser system costs,
including cooling, modulation control, and electrical
power supply, should reduce to a few €100.
Additionally, NIR/MIR light-emitting diodes (LEDs)
may be of interest as an alternative source in
sensing systems that do not require narrow-band
illumination. New and more powerful sources for
wide-band IR spectroscopy are also needed, such
as those based on fibre supercontinuum effects,
offering convenient coupling to optical fibres. Here
the goal is the development of NIR/MIR broadband
light sources offering emission powers ≥1 mW,
with ≤ €1 cost in large volumes.
EIR photodetectors (0D, 1D, 2D)
A large number of materials and detector types
are currently employed for point, linear and
image sensor devices for the NIR/MIR spectral
range, including pyroelectric detectors, thermo-
piles, microbolometers, narrow-bandgap photo-
voltaic detectors, Schottky barrier detectors, ex-
trinsic photoconductors, multi-quantum-well semi-
conductor heterostructures for QCDs and homo/
heterojunction internal photoemitters (HIP). The
challenge is to detect as many incoming photons as
possible, while reducing the effects of dark current.
This corresponds to the primary task of maximis-
ing the sensor’s detectivity, which is equivalent
to minimising its noise equivalent power. At the
same time, material and packaging costs must be
reduced to increasingly lower values, and cooling
requirements kept to a minimum.
The primary goal is to develop novel types of highly
cost-effective solid-state NIR/MIR sensors, based
on new or optimised material systems, and ideally
produced using well-established microelectronic
fabrication techniques. It must be straightforward
to produce these sensors as point detectors, line
sensors or image sensors, and they must have a
performance close to the ideal detector limit. Point
detectors should cost no more than €10, whilst
line or image sensors should cost less than €100,
including the cooling devices.
CMOS-based single-photon NIR image sensing
It has been demonstrated recently that novel
types of CMOS-based image sensors are capable
of detecting individual incident photons at room
temperature. Accepting the need for cooling, it
should also be physically possible to extend the
cut-off wavelength from silicon’s 1.1 µm to higher
values in the NIR, while still being sensitive to each
incident photon. This requires scientific progress
in two domains. Firstly, novel CMOS-based charge
detection circuits with sub-electron readout noise
performance are needed. Secondly, it will be necessary
to combine these charge detector circuits with
semiconducting materials exhibiting a cut-off wavelength
above silicon’s 1.1 µm. Promising candidates
include nanostructured (black) silicon, inorganic
narrow-bandgap crystalline semiconductors (such
as InGaAs), or novel types of organic semiconductors
sensitive in the NIR spectral domain.
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