Christopher Kang

Photonic crystal slab sensor with enhanced surface area

In this work, we demonstrate improved molecular detection sensitivity for silicon slab photonic crystal cavities by introducing multiple-hole defects (MHDs), which increase the surface area available for label-free detection without degrading the quality factor. Compared to photonic crystals with L3 defects, adding MHDs into photonic crystal cavities enabled a 44% increase in detection sensitivity towards small refractive index perturbations due to surface monolayer attachment of a small aminosilane molecule. Also, photonic crystals with MHDs exhibited 18% higher detection sensitivity for bulk refractive index changes.

Grating couplers on porous silicon planar waveguides for sensing applications

We study the use of polymer gratings as light couplers into porous silicon planar waveguides for sensing applications. Experimental evidence of a guided mode in a grating-coupled porous silicon structure is presented, along with a study of its detuning due to waveguide infiltration with a chemical linker. All the measurements are in good agreement with simulations obtained by means of a Fourier modal method, where the porous silicon birefringence is considered. These results demonstrate that this system is potentially useful for chemical and biological sensing applications.

Photonic crystal with multiple-hole defect for sensor applications

A photonic crystal defect consisting of several subwavelength holes was investigated as a means to increase the surface area of the defect region without compromising the quality factor of the structure. Finite-difference time-domain calculations were performed to determine the relationships between the size of the multi-hole defect (MHD) region, resonance frequency, quality factor, and refractive index of the defect holes. The advantage of using the MHD for sensing applications is demonstrated through a comparison with a single hole defect (SHD) photonic crystal structure. Assuming the same monolayer thickness of biomaterial coats the defect hole walls of the MHD and SHD, the MHD has a three times larger change in resonance frequency and two times larger quality factor.

Optimized light–matter interaction and defect hole placement in photonic crystal cavity sensors

Photonic crystal slab cavities were investigated for increased light-matter interaction based on selective placement of sublattice hole sized defect holes inside L3 cavities. A multiple-hole defect (MHD) consisting of three defect holes placed in the regions of highest cavity mode field intensity were demonstrated through finite-difference time-domain simulations and experiments to exhibit the strongest light-matter interaction without introducing significant scattering losses. Compared to an L3 cavity without defect holes, these strategically designed three-hole MHD cavities presented higher quality factor and more than double the resonance wavelength shift upon exposure to a thin oxide and two small chemical molecules.

Photonic crystal defect tuning for optimized light-matter interaction

Photonic crystal microcavities with multi-hole defects were simulated using finite difference time domain (FDTD) analysis. Subwavelength, multi-hole defects (MHD) offer a significant increase in defect surface area without compromising the quality factor of the photonic crystal. Calculations of the increase in surface area compared to a traditional, single hole defect are performed for MHD structures with varying subwavelength defect hole size, subwavelength defect hole spacing, and effective defect radius. For active photonic crystal applications, the resonance wavelength and quality factor of several different MHD photonic crystal structures was calculated as a function of the dielectric constant of the defect. MHD photonic crystals can be designed to enable large changes in resonance wavelength for small changes in defect dielectric constant. These structures would be advantageous for applications in biosensing and optical switching.

Nanoscale porous silicon waveguides for biosensing applications

Nanoscale porous silicon waveguides, both on silicon substrates and free-standing membranes, are explored for biosensing applications. Measured detection limits in the nanomolar range are reported for DNA sensing.