Changhun Lee

Blazed wire-grid polarizer for plasmon-enhanced polarization extinction: design and analysis

We explore plasmon-enhanced wire-gird polarizers (WGPs) to achieve improved polarimetric performance with more relaxed fabrication parameters compared to conventional WGP. A WGP designed with a blazed wire-grid profile was considered for plasmonic enhancement. The results show that a blazed WGP can achieve extremely high polarimetric extinction at a longer wire-grid period (Λ) compared to conventional WGP structure. Under the optimum geometrical parameters, a blazed WGP may attain an extinction ratio of over 40 dB at Λ = 800 nm, which may allow photolithography for fabrication. In contrast, conventional WGPs obtained comparable performance at Λ = 200 nm, requiring more difficult lithographic techniques. The study can therefore be of significant importance for WGPs to be more widely available for diverse applications.

Surface plasmon microscopy by spatial light switching for label-free imaging with enhanced resolution

In this Letter, we describe spatially switched surface plasmon microscopy (ssSPM) based on two-channel momentum sampling. The performance evaluated with periodic nanowires in comparison with conventional SPM and bright-field microscopy shows that the resolution of ssSPM is enhanced by almost 15 times over conventional SPM. ssSPM provides an extremely simple way to attain diffraction limit in SPM and to go beyond for super-resolution in label-free microscopy techniques.

Effect of Nanogap-Based Light-Matter Colocalization on the Surface Plasmon Resonance Detection

A nanoscale gap aperture has been used as a fundamental tool for diverse applications. In this paper, we investigate the effect of nanogap aperture parameters on optical sensors, primarily based on surface plasmon resonance. A simple 2-D model was used for DNA immobilization and hybridization, in which nanogap enables light-matter colocalization to amplify detection signatures, thereby enhancing performance characteristics. Interestingly, the optimum gap geometry that produces maximum light-matter overlap and the largest resonance shift was not associated with the smallest gap size. Highest sensitivity was observed to correlate with negative resonance shift due to increased damping as well as the excitation of higher order surface plasmon polariton modes. Zero-shift nanogap was also discussed. The results suggest that careful design of nanogap apertures should be carried out to make the most of what they can achieve.

Quantitative image analysis of angle scanning label-free surface plasmon resonance microscopy

In this report, we describe improvement of image resolution in surface plasmon resonance microscopy (SPRM) which suffers from poor quality due to severe surface plasmon (SP) propagation. Our approach takes two-channel momentum sampling by switched light incidence followed by minimum filtering to implement spatially switched SPRM (ssSPRM). The performance evaluated with periodic wires in comparison with conventional SPRM and bright-field microscopy shows that the effect of SP propagation can be circumvented and the effective decay length of SPRM is calculated to increase by only 7% compared to that of bright-field images.

Numerical analysis of blazed wire-grid polarizer for plasmonic enhancement

We analyze the characteristics of plasmonics-based enhancement of a wire-grid polarizer (WGP) by rigorous coupledwave analysis (RCWA). We consider blazed WGP (bWGP) for improvement of polarimetric performance based on plasmonic momentum-matching in the metal/dielectric interface. The analysis used a model of triangular wire-grids approximated with five graded layers of identical thickness. We have compared the performance to that of a conventional WGP (cWGP) with a corresponding lamellar grating shape profile. As a performance measure, we calculated transmittance (TR) and extinction ratio (ER). It was found that TR in both cases tends to decrease monotonically with a longer period (Λ). The maximum TR of bWGPs is lower than cWGPs. On the other hand, maximum ER of bWGPs is much higher than that of cWGPs, particularly at a longer period, with an extinction peak peaked at Λ = 800 nm. For cWGPs, an extinction peak is observed at Λ = 200 nm with comparable enhancement (~42 dB). We have also computed relative TR (RTR) and relative ER (RER) for assessment of performance relative to cWGP. RTR decreases slowly in a manner similar to TR, however, RER increases exponentially with a longer wire-grid period. The results suggest that strong localization of near-fields observed with bWGPs can be used to improve polarimetric performance of a WGP.

Theoretical analysis of optical conveyor belt with plasmonic nanodisk array

Plasmonic optical trapping allows trapping and manipulation of micro- and even nanometer-sized particles using localized and enhanced electric fields by plasmon resonance in metallic nanostructure. We consider an optical conveyor belt consisting of an array of nanodisks acting as optical tweezers with different sizes to implement a system to trap and manipulate particles through a laser-induced gradient force. An electric field induced and localized at each optical resonator is sensitive to the wavelength and polarization. The maximum electric field is enhanced at resonant wavelength depending on the shape and size of the plasmonic nanostructure used for light localization. By changing the light wavelength and polarization, the position of localized light induced in the disk can be determined and nanoparticles can be moved to a desired location through the variation of resonance conditions without any mechanical forces.