Bio-Inspired Sensors and Optoelectronics Laboratory
sensitivity in the infrared spectrum is a challenging task due to the
minute energy of each photon at less than one atto-Joule. Infared
imagers are used in many applications
including telecommunications, biophotonics, optical tomography,
explosives detection and non-destructive material evaluation. It
includes the fiber optic telecommunications wavelengths around
1.5 um, and can advance rapidly emerging technologies like
quantum key distribution and quantum computing. Furthermore, many
medical applications like optical tomography rely on short-wave
infrared since it has great penetration depth through the skin, and
therefore enables deeper non-invasive screening. Additionally, night
sky radiance offers significant spectral power in SWIR due to the
chemical reactions involving hydroxyl groups in the upper atmosphere.
This phenomenon makes SWIR uniquely attractive for military and
homeland security applications. BISOL has developed novel infared
imagers based on the nano-injection technology. The nano-injection
imagers can provide high-fidelity internal amplification with small
pixel sizes and a large number of pixels, which is currently a
difficult task with mainstream technologies, primarily due to noise
At a wavelength of 1550 nm, the pixels in the imager show
responsivity values reaching 2,500 A/W at room temperature and 250 A/W
-75 C, due to an internal charge amplification mechanism in the
detector. In the imager, the measured imager noise was 28 electrons
(e-) rms at a frame rate of 1,950 frames/sec. Additionally, compared to
a high-end short-wave infrared imager, the nano-injection camera shows
two orders of magnitude improved signal-to-noise ratio at
thermoelectric cooling temperatures, primarily due to the small excess
noise at high amplification.
Enhanced Infrared Detectors:
Infrared photodetectors and imagers have been widely applied in many
different areas including Medical, Industrial, Defense, and Research
application. One of the most important infrared photodetectors, Quantum
well infrared photodetectors (QWIPs), still have some intrinsic
weaknesses for infrared detection, such as being insensitive to normal
incident radiation and low detection efficiency. In BISOL, we have
proposed to use surface plasmonic structure to convert the normal
incident infrared electromagnetic waves to surface plasmonic waves,
which can be effectively absorbed by quantum wells.
Furthermore, with a careful design of the plasmonic structure the
electric field intensity in the quantum wells can be much enhanced,
which also leads to a much enhanced optical absorption and detection
Plasmonic structures with different designs and parameters have been
simulated using 3D Finite-difference Time-domain (FDTD)
methods. With the optimized structure, we fabricated the
plasmonic enhanced QWIP with thin quantum well active region.
Our testing results demonstrated a much improved sensitivity of the
detector at a normal incident radiation, and matched with the
simulation results very well.
The mid-infrared spectral region is of great importance in Biosensing
because of its specific sensitivity to so many of the building blocks
of life. However, the operating wavelength (3-30um) is orders of
magnitude larger than the probed molecules that are a few nanometer.
Therefore, the interaction between the molecule and light is too weak
to be detected. The current methods requires lab scale facility and are
not viable for a compact sensor. We propose a chip scale
mid-infrared biosensor operating in the mid-infrared region of the
principle of its operation is based on plasmonic quantum cascade laser
(QCL). We have developed composite optical antenna integrated with the
QCL, where the optical beam, instead of diverging in free space,
converges into a sub wavelength “hot spot” in the near field region
(within 50nm above the antenna surface). This way we overcome the
hurdle of low light-particle interaction mentioned previously. The next
challenge lies in integrating a passive component, which is capable of
delivering the bio-molecule within the “hot spot” region of the
antenna. In order to do so, we are working on an integrated
microfluidic device with the plasmonic QCL, where the input and output
channels are used for the control and delivery of biomolecules.
BISOL is investigating novel experimental and theoretical methods for
measuring and calculating the Casimir force. The Casimir
effect is caused by quantum mechanical fluctuations in the vacuum of
empty space. In the small space between objects, only a
finite number of states are allowed. Outside those objects,
an infinite number of states is allowed. The virtual
particles that pop into existence and fill these states create a
pressure that pushes the objects together. BISOL uses
computational research tools such as MATLAB, Mathematica, and COMSOL to
study the Casimir effect. Theoretically, electromagnetics,
quantum mechanics, and even quantum field theory are needed.
Finally, we use a variety of tools including an atomic force microscope
to verify our predictions experimentally.
Metamaterials and Plasmonics:
Many important bio-molecules have a unique patten of vibrational
resonances in the Terahertz (10^12) frequency band. By
exciting these signatures with a broad infrared source one can uniquely
identify single molecule types. However optical frequencies
in this range have a wavelength of microns. So how is it
possible to squeeze light into the volume of a single
molecule? We use a plasmonic metamaterial structure that
squeezes in the Ez direction with a metal-insulator-metal sandwich with
an insulator thickness on the order of 50 nanometers and cavity defect
photonic crystal to squeeze the light in the planar
Simulation results show that even though the mode is quite lossy,
because its confinement volume is so small, the Purcell constant
(interaction strength) remains quite high. And so we have
proposed a design that, by using surface plasmons can squeeze light
many orders of magnitude without sacrificing the cavity's interaction
strength. We hope that this device coupled with a broad
infrared source and detector will make tagless single
molecule detection and identification possible.
Plasmon Enhanced Quantum Cascade Lasers:
We integrate a plasmonic crystal structure over the facet of a
Mid-infrared quantum cascade laser, working at room temperature and can
squeeze optical mode orders of magnitude below the diffraction limit.
The unique combination of strong interaction and broad spectral
resonance allows for optical spectroscopy measurements down to the
sensitivity of a single molecule.
We simulate and fabricate novel Plasmon polariton crystal (PPC)
structures on the facet of QCL. Simulation results have shown an
extraordinary optical transmission at the mid infrared region.
The optical mode of the laser is studied using an
apertureless Near field scanning electron microscope.
Lens Lithography: A novel nanolithography technique for
fabrication of large areas of uniform nanohole and nanopillar arrays
arrays of nanopillars and nanoholes have been found a wide range of
applications in many devices such as solar cells, photodetectors,
surface plasmonics, photonic crystals, data storage, nanofiltration,
fuel cells and artificial kidneys. A low-cost and high-throughput
lithography technique of forming uniform nanoholes and nanopillars
would be extremely desirable. BISOL have developed a novel
nanolithography technique, Super Lens Lithography, to produce a large
area of highly uniform nanopillars and nanoholes in photoresist and
these nanopatterns can be transferred to other material layers. Our
technique is based on the super-lens effect of silica or polystyrene
(PS) micro-/nano-spheres under UV light region.
A large monolayer of hexagonally close packed (hcp) microspheres was
formed using our home-made setup. Both our simulation and experimental
results have shown that a large area of uniform nanoholes and
nanopillars in different materials can be generated.
Avalanche-free Single Photon Detector Arrays:
BISOL has been working to create a novel short-wave infrared single
photon detector, conceptually based on the detection in human visual
system. Currently, silicon avalanche photodiodes are the only devices
with acceptable performance. However, their wavelength is limited to
below ~1000 nm, and the maximum array size is limited to a few tens of
pixels per side.
Some of the applications of
such a single photon detector array are biophotonics, optical
tomography, homeland security, non-destructive material inspection,
astronomy, quantum key distribution, quantum imaging, and homeland
We have created the "nano-injection detector" operating at wavelengths
beyond the silicon limit. It is based on a nano-transistor, and unlike
avalanche detectors, does not produce any "excess noise" but actually
suppresses the noise to sub-Poissonian levels. The detector has
achieved internal amplification values exceeding 10,000 at bias
voltages of ~1 V at room temperature. Record breaking jitter values
less than 15 ps have also been measured on high-speed devices at room
Opto-Electro-Mechanical Single Photon Detectors:
BISOL has been working on expanding the original nano-injection
detector into an Opto-Electro-Mechanical (OEM) version which operates
based on tunneling current. In the OEM nano-injection detector, a
cantilever holds a tip a small distance above a photoconductive sample.
When the sample is activated, an electric field is generated that pulls
the tip closer to the surface of the device, and the sharpness of the
tip creates a very small region of focused charge and electric field
that acts as a multiplier of charge. The increasing proximity of the
tip to the surface increases the tunneling current between the tip and
Because of the charge focalization, a gain has already been achieved.
In the future BISOL would like to extend the work to research the
Casimir Effect, which has been identified as a dominant force in the
Quantum Cascade Lasers: Design and realization
Quantum cascade laser (QCL) is a unipolar semiconductor laser works
based on intersubband transition. We are involved in simulation of band
structure, fabrication of devices using micro fabrication techniques
and characterization. Our QCL research focuses primarily on improving
its thermal performance, tunability, collimation and novel designs.
Various designs like injectorless QCL, dot-contact QCL, phonon avoided
scalable cascade laser, plasmonic QCL devices are being
BISOL has designed and optimized a novel
phonon-avoided QC laser using a custom developed simulation model.
Essential parameters, such as band diagram, transition energy modal
loss, optical confinement have been calculated using FDTD based
simulations. Processing steps have been designed based on nano-sphere
lithography and Focused Ion Beam (FIB) techniques. An injectorless QCL
laser has been demonstrated with improved thermal performance. 2D FDTD
simulations have been performed to design plasmonic QC laser.
Infrared Detectors: Electrically
tunable quantum dot/ridge infrared photodetectors:
infrared photodetector, such as quantum dot infrared photodetector
(QDIP), and quantum ridge infrared photodetector (QRIP), promised much
more advantages both theoretically and experimentally compared with
quantum well infrared photodetector (QWIP) because of the unique
properties of low-dimensional system. Meanwhile, to be able to tune the
detection wavelength of photodetector at pixel levels are especially
exciting for scientists. We, BISOL group, developed an electrically
tunable quantum dot and quantum ridge infrared photodetector based on
the electrical confinement on quantum wells. The detection wavelength
of our detector can be tuned at a single pixel level by only changing
3D simulation results confirm the wavelength-tunability of our device
by changing the voltage. The energy state levels and wavefunctions in
the quantum dot generated by electrical confinement have also been
demonstrated. Further simulation results show our device can also
detect the electromagnetic wave in terahertz range using the
intersublevel spacing formed by electrical confinement. Fabrication and
characterization of the device are in progress.
Infrared Detectors: Infrared
Detectors based on Type-II Superlattices:
type-II superlattices provide a unique opportunity to produce highly
performance IR detector arrays in the long and very long wavelength IR
(LWIR, VLWIR). Also, higher operating temperature is expected due to
the low Auger recombination rate.
type-II superlattices with excellent structural, optical, and
electrical quality have been grown.
Some of the results shown
P-i-N photodiodes at a
cutoff wavelength of 15.5 um showed background limited performance
(BLIP) at nearly 60 K with a current responsivity of about 3.5 A/W.
Devices for room
temperature operation were designed. These devices showed a cutoff
wavelength of about 9 um and a detectivity of 1.3E9 (cm.Hz^0.5/W) at
A wide wavelength tuning
range was demonstrated by changing the layer thickness of the
superlattices. The longest cutoff wavelength is more than
Performance Phase Modulators based on Stepped QWs:
optical modulators are enabling technology for photonic systems.
Although semiconductor-base modulators can be integrated with other
photonic components, they have a low figure of merit due to the high
loss and low electrorefraction.
A novel quantum well was designed and
optimized to enhance material electrorefraction at a low loss. Measured
figure of merit is about one order of magnitude better than the best
Linear InP-based Phase Modulators:
high linearity is a key feature required for analog photonic systems,
such as analog RF photonics. Unlike lithium niobate, semiconductor
modulators have a poor linearity which limits their performance for
a novel linearization method is developed.This method is only based on
modification of the quantum wells and doping, and no feedback or feed
forward signal is involved. Therefore, the speed of the device is not
affected. Measured linearity is more than two orders of magnitude
higher than the best reported devices, while the device maintains a
very high efficiency.
surface-normal modulators are attractive for a wide range of
applications including optical computers, high density 2-D
interconnects, ultra-low power free-space communication for mobile
platforms, and optical tags.
novel stepped quantum wells are used to produce extremely efficient
surface-normal modulators around 1550 nm. These devices are 5-6 mm wide
and can be electrically tuned to operate over a 100C temperature range,
and with a +/-60 degree field of view. They show higher efficiency,
higher extinction ratio, and wider operating temperature than any
reported surface-normal devices.
Integrated Circuits and Nano-Photonics
similar to electronic devices, integration will provide the ultimate
functionality of the photonic systems. Integration is a mandatory step
for realization of ultra-high capacity photonics with a very small
footprint and low cost. High index contrast nano-photonics provide the
necessary platform to manipulate light in micron
range for a highly dense integration.
Photonic Integrated Circuits
and Nano-Photonics: Arrayed Waveguide Grating (AWG) Based
||Results: a novel integration method is
developed. Active and passive photonic components can be integrated without
regrowth. This reduces the cost significantly, as the
process is much simpler than regrowth and has a potentially higher
yield. As a proof of concept for this method, single-chip multi-channel
(wavelength) lasers based on AWGs and SOA has been demonstrated.
Integrated Circuits and Nano-Photonics: Chip-Scale
Wavelength Division Multiplexing (WDM):
etched submicron waveguides are used to produce integrated multi
ring-resonators that are individually tunable. Independent modulation
of each WDM channel was demonstrated.
Integrated Circuits and Nano-Photonics:
High Index Contrast Nano-Photonics:
loss deeply-etched waveguides with electrical contacts were
demonstrated. Nano-ring resonators with a very small diameter showed a
quality factor Q of ~100,000. A ring-resonator with such a high quality
factor provides an electrically tunable filter with FWHM of only a few
gigahertz, a very high tuning speed, and an extremely small footprint.
Many other interesting photonic components such as highly dispersive
waveguides, single-mode lasers, and high-order filters can be realized
with this deeply-etched semiconductor platform.