The focus of research of Aitchison Group is micro and nano fabrication for optical sensing and signal processing. This covers a broad range of research areas including nonlinear optics, plasmonics, silicon and III-V photonics.
Vertical integration approach in AlGaAsZhongfa Liao (Google scholar)
Many of the basic material properties of AlGaAs/GaAs are advantageous to designing photonic integrated circuits (PICs). All compositions of AlxGa1-xAs are lattice matched. The band gap energy can be varied from 1.42 eV (GaAs) to 2.17 eV (AlAs) and, similarly, the index of refraction at 850 nm can be varied from 3.68 (GaAs) to 2.99 (AlAs). These make epitaxy processes less restrictive and offer more design flexibility. The 785 - 850 nm spectral window has several potential applications. For non-invasive bio sensing, it is the wavelength range where hemoglobin has the lowest absorption. As current data center communication systems use 850 nm vertical cavity lasers, monolithic integration would enable efficient wavelength division multiplexing devices. AlGaAs/GaAs has also been identified as the promising material system for quantum optics. The integration of pump lasers, nonlinear optical elements and signal processing waveguides opens the possibility of a true quantum optics technology.
Nonlinear optics in semiconductor superlatticesPisek Kultavewuti
Our group works on nonlinear optics in semiconductors and superlattices, especially an AlGaAs system which possesses highly nonlinear property. Microscale AlGaAs optical circuits could provide a solution to on-chip frequency conversion devices. Based on third-order nonlinearity, an AlGaAs waveguide is a promising approach to providing an efficient tunable optical parametric oscillation light source when it is integrated with an optical resonator. The group also looks at enhancing nonlinearity by using nano-structured waveguides. In the quantum optics aspect of frequency conversion, the group is also interested in on-chip sources of entangled photons. The group successfully generated and characterized entangled photon pairs in quasi-phase matched AlGaAs superlattice waveguides using the second-order nonlinearity.
PlasmonicsXiao Sun, Farshid Bahrami
Surface plasmon (SP) is a surface wave which results from the coupling of an electromagnetic wave with the collective electronic oscillations at a metal-dielectric interface. SP has a number of unique features, and can be of great importance for practical applications. Unlike dielectric waveguides whose light confinement is limited by diffraction, plasmonic waveguides can “squeeze” light to a subwavelength scale. This offers the possibility of scaling down photonic devices to the size of transistors which may result in successful integration of photonics and electronics. Since metal is part of a plasmonic waveguide, it suffers from a large propagation loss. This is a major limitation that has prevented plasmonics from becoming a more useful technology.
We have proposed a hybrid plasmonic waveguide (HPWG) that consists of a metal plane seperated from a high index medium by a low index spacer. The guide provides a better compromise between loss and confinement compared to purely plasmonic waveguides. Its fabrication is compatible with silicon on insulator technology, and it offers the possibilty of integration of plasmonics and silicon photonics on the same platform. We have designed and experimentally demonstrated a range of devices including polarizers, polarization rotators, and directional couplers.
Optical hydrogen sensorNick Carriere, Muhammad Alam, Farshid Bahrami
Hydrogen has many applications including aerospace, oil refinary, semiconductor industry, and fuel cells. Being a very small molecule, hydrogen easily leaks out and forms an explosive mixture with air. A reliable sensing method is necessary for safe use of hydrogen. We have devleoped an integrated optic hydrogen sensor for detection of hydrogen. Currently we are working on integrating this device with other sensors on the same chip to implement an "optical nose" which will be able to detect concentrations of multiple gases.
Micro-structured surface for algal biofilm growthScott Genin
There is a potential to use algae as a feedstock for biofuels and biomaterials because of their high growth rates relative to terrestrial crops, their high concentrations of valuable biochemicals, and their ability to be used to treat waste streams. One barrier to commercialization of algae in is its high de-watering cost associated with low biomass conconcentration in suspended algal cultures. To reduce harvesting and de-watering costs, algae biomass can be grown as an immobilized film. Light is an important nutrient in algae biofilm growth, but current algal film photobireactor designs do not optimize light delivery to the algal biofilms. To improve light delivery in algae film bioreactors, we are buliding and testing new optical waveguides with microstructured patterns to opimize the light emission and thus improve algal film growth.
Bragg microcavity filter for optical sensingJames Dou
Optical microcavity filters play vital roles both in telecommunication and sensing applications. One very attractive optical microcavity is the bragg microcavity formed by a periodic dielectric slot waveguide. Strong light confinement in the low refractive index slot region formed by two silicon slabs on a silicon dioxide substrate makes this structure useful for optofluidic, sensing, and optical trapping applications. We have demonstrated that good sensitivity can be achieved using this structure.
Lossy optical materials for absorption based switchingArash Joushaghani
Optical absorption is usually undesirable in photonic integrated systems as it results in attenuation of signal power. However, from a design perspective, optical materials with large absorption can be a powerful tool in designing optical system. They not only allow us to properly do impedance matching between different photonic components, but also enable efficient detectors and absorption based switches. We are investigating novel and lossy optical materials to demonstrate optical switching. Emphasis is placed on using Vanadium Dioxide (VO2) in a hybrid plasmonic system to achieve optical switching.