Major Funding

Defense Advanced Research
Projects Agency

Microsystems Technology Office:
(DARPA-MTO)
DARPA MTO

1) Photon Counting Array (PCAR): Focalized Carrier Augmented Sensors (FOCUS)
2) Efficient Mid-Infrared Laser (EMIL): Phonon Avoided Scalable Quantum Cascade Laser (PASCAL)
3) Young Faculty Award: Electrically Tunable Quantum Dots for Adaptive Infrared Imaging
4) High-speed Nano-injection Single-Photon Detector Arrays and Imagers.
5) 4p-Steradian Curved And Lensless Imagers (4p-SCALE)

 

National Science Foundation (NSF): NSF

1) NSF Career Award: Avalanche-Free Single Photon Detectors Based on Type-II Heterojunctions and Nano-Switches

2) Tunable Quantum Well Infrared Detector

3) Highly Efficient Laser Cryo-cooler

4) Ultra-Broadband Plasmon-Polariton Crystals for Label-Free Single Molecule Detection

5) EAGER: Study of Casimir Force Engineering by Modeling and Implementing Novel Three-dimensional Structures

6) Photonic-Jet Coupled Optical Antenna

7) Highly Sensitive Eye-safe Flash LiDARs based on Nanoinjection Detectors

 

W.M. Keck Foundation: WMKECK

Ultra-sensitive NIR Camera for Astronomy

 

Argonne National Laboratory: Argonne

Cognitive Processing of Biometric Information

 

Air Force Office of Scientific Reseach (AFOSR):

NSF

Solid-state Quantum Refrigration

 

Army Research Office (ARO):

ARO

Ultra-Sensitive Infrared Imagers

 

The Initiative for Sustainability and Energy
at Northwestern University(ISEN):
NSF

Using Plasmonic Photonic Crystals As Thermal Emitter to Produce Highly Efficient Thermophotovoltaic Solar Cells

Bio-Inspired Sensors and Optoelectronics Laboratory

Research Interests

Infrared Imagers:

P-QWIP

Motivation: Improving 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 considerations.  

Results: 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.

 

Plasmonic Enhanced Infrared Detectors:

P-QWIP

Motivation:  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 efficiency.

Results: 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. 

 

Infrared Biosensors:

Casimir

Motivation: 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 optical spectrum.

Results: 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.

 

The Casimir Effect:

Casimir

Motivation: 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.

 

Novel Metamaterials and Plasmonics:

plasmonics

Motivation: 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 direction. 

Results: 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.

 

Surface Plasmon Enhanced Quantum Cascade Lasers:

plasmonic laser

Motivation: 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.

Results: 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.

 

Super Lens Lithography: A novel nanolithography technique for fabrication of large areas of uniform nanohole and nanopillar arrays

NSL

Motivation: Uniform 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.

Results: 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.

 

Single Photon Detectors: Avalanche-free Single Photon Detector Arrays:

Nano-injection detector

Motivation: 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 security.

Results: 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 temperature.

 

Single Photon Detectors: Opto-Electro-Mechanical Single Photon Detectors:

OEM FOCUS

Motivation: 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 the device.

Results: 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 experiments.

Novel Quantum Cascade Lasers: Design and realization

QDot laser

Motivation: 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 studied. 

Results:  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.

 

Novel Infrared Detectors: Electrically tunable quantum dot/ridge infrared photodetectors:

QRIP

Motivation: Low-dimensional 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 the voltage.

Results: 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.

 

Novel Infrared Detectors: Infrared Detectors based on Type-II Superlattices:

Type-II

Motivation: 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.

Results: type-II superlattices with excellent structural, optical, and electrical quality have been grown.

Some of the results shown here are:

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 room temperature.

A wide wavelength tuning range was demonstrated by changing the layer thickness of the superlattices. The longest cutoff wavelength is more than 30 um.

 

Electrooptical Modulators: High Performance Phase Modulators based on Stepped QWs:

Motivation: 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.

Results: 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 reported modulators.

 

 

Electrooptical Modulators: Highly Linear InP-based Phase Modulators:

Motivation: 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 integrated photonics.

Results: 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.

 

Electrooptical Modulators: High-performance Surface-normal Modulators:

Surface Normal Modulator
Modulator

Motivation: 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.

Results: 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.

 

Photonic Integrated Circuits and Nano-Photonics

Motivation: 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 Multi-wavelength Lasers:

AWG_laser 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.

 

Photonic Integrated Circuits and Nano-Photonics: Chip-Scale Wavelength Division Multiplexing (WDM):

CSWDM Results: deeply etched submicron waveguides are used to produce integrated multi ring-resonators that are individually tunable. Independent modulation of each WDM channel was demonstrated.

 

Photonic Integrated Circuits and Nano-Photonics: High Index Contrast Nano-Photonics:

Ring Resonator Results: ultra-low 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.