"Research Is to See What Everybody Else Has Seen, and to Think What Nobody Else Has Thought."
(A. S. Gyrogyi)
Description of the published research will be updated soon. Description of the works under review/in progress will be added after publicaiton. For the time being, please visit to KhanLab@USC to know our ongoing efforts in developing wearables for precision health and pyschiatry.
Researchers are making continuous efforts to fabricate nanoscopic machines with added benefits (such as concise shape, high performance, and elegant design) to satisfy current technological demands. Metals lie at the core of developing such applications. New facts regarding the performance of the metal are being discovered from time to time. These freshly developed insights play a significant role in varying the metal’s different structural parameters for tuning light-metal interaction to construct enhanced subwavelength scale photonic devices [1,2]. The theory of Surface Plasmon Polariton (SPP) precisely describes this light-metal synergy. MIM waveguide-based SPP
sensors are being widely investigated in recent years due to their deep subwavelength light confinement, high integration, and fast manufacturing capability. Maneuvering the high susceptibility to the ambient medium, refractive index-based MIM sensors are playing a pivotal role in detecting biomaterials
Surface Plasmon Polaritons:
Surface Plasmon Polariton (SPP) is a groundbreaking development in metallic nanoplasmonics. When incident photons are coupled with oscillatory surface electrons of metal, an electromagnetic
surface wave propagates along with the metaldielectric interface at the resonant frequency. This light-matter interaction between the metal (“r < 0) and dielectric (“r > 0) is known as SPP , shown in Figure 1.1a.The amplitude of this surface wave decays exponentially with the increasing distance into each medium from the interface. The wave’s penetration depth is more extensive in the dielectric medium, as shown in Figure 1.1b. In some literature this penetration depth (skin depth) for metal is approximated to 10 nm while for dielectric it typically more than 100 nm. With such strong EM filed localization along with the interface, SPP has assured the nanoscale integration of photonic devices without altering the bandwidth, circumventing the limitations instigated by diffraction .
Due to strong light-matter interaction at the vicinity of the metal-dielectric interface, MIM waveguide-based plasmonic refractive index sensors are highly susceptible to the structural parameters and
ambient media. Hence, detection of any unknown material with these sensors opens up the opportunity in nanoscale sensing. As shown in Figure 1.2a, when sensing media is excited with a light source, SPP produces at the interface. In Figure 1.2c an associated dip in the transmittance curve is presented. When a sample to be sensed is brought to the sensing media, neff of the MIM waveguide changes (Figure 1.2b). This shift in neff results in shifts in the λres, shown in Figure 1.2c. By measuring the shift in λres, refractive index so as the unknown material is sensed by the plasmonic refractive index sensor. For MIM structure this unknown material can be gaseous molecules, chemical, bio-materials, etc.
Using supreme features of surface plasmon polaritons different metal-dielectric-metal (MDM) waveguides based plasmonic device has been designed over the years which confine the light in nano-scale region. However, MDM waveguides suffer from smalle propagating length due to longer interference of the EM field in metalic layer.
On the other hand, in dielectric waveguide nanoscale confinement is not possible. However, dielectric waveguide offers propagating length much higher than plasmonic waveguides. In view of this situation, efficient coupling method has been extensively studied by the researchers between dielectric waveguide and plasmonic waveguide in the same chip where first one will be used as a medium of transportation of the signal and the latter one will be used to address the subwavelength scale issue.
Finite Difference Time Domain Algorithm:
FDTD is a time domain numerical approach to solve partial differential form of maxwell’s equations. It is useful to model nano-scale optical devices for wide range of frequencies. Following approaches have been incorporated in the research lab to prepare the basic FDTD engine capitalizing the Matlab Software.
- 1D FDTD;
- 2D FDTD with PML;
- Polarization for different materials;
- Generation of pumping profile.
- Inject pumping profile in metal-dielectric interface.
Focus of this research was to calculate the transmittance of the nanoscale devices using the designed FDTD engine and compare the result with the CST Microwave studio and COMSOL Multiphysics softwares.
Selected Figures form Publications
Public Health Research:
The aims of the research was to evaluate the awareness level and associating factors of that awareness among the adult women of Dhaka city who face the persecution most of the time because of their socio-economic status in the society. The whole research was divided into following steps.
- Problem Identification;
- Literature Review;
- Questionnaire Preparation;
- Pilot Testing;
- Sample Size Selection;
- Data Collection;
- Data Editing and Cleaning;
- Data Analysis in SPSS;
- Report Writing.
This research aimed to gauge the emergence of mass malnutrition in women of Dhaka city due to long term pandemic and to find out the probable solution.
 W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” nature, vol. 424, no. 6950, pp. 824–830, 2003.
 V. V. Temnov, G. Armelles, U. Woggon, D. Guzatov, A. Cebollada, A. GarciaMartin, J.-M. Garcia-Martin, T. Thomay, A. Leitenstorfer, and R. Bratschitsch, “Active magneto-plasmonics in hybrid metal–ferromagnet structures,” Nature Photonics, vol. 4, no. 2, pp. 107–111, 2010
 D. K. Gramotnev and S. I. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nature photonics, vol. 4, no. 2, pp. 83–91, 2010.
 N. Kazanskiy, S. Khonina, and M. Butt, “Plasmonic sensors based on metalinsulator-metal waveguides for refractive index sensing applications: A brief review,” Physica E: Low-dimensional Systems and Nanostructures, vol. 117, p. 113798, 2020.