Junpeng Guo

Wideband perfect light absorber at midwave infrared using multiplexed metal structures

We experimentally demonstrate a wideband near-perfect light absorber in the midwave IR region using a multiplexed plasmonic metal structure. The wideband near-perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on top of a thick metal layer in each unit cell. We also fabricate regular nonmultiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs more than 98% of the incident light over a much wider spectral band than regular nonmultiplexed structure perfect light absorbers in the midwave IR region.

E-Beam Patterned Gold Nanodot Arrays on Optical Fiber Tips for Localized Surface Plasmon Resonance Biochemical Sensing

Electron beam lithography (EBL) was used to directly pattern periodic gold nanodot arrays on optical fiber tips. Localized surface plasmon resonance of the E-beam patterned gold nanodot arrays on optical fiber tips was utilized for biochemical sensing. The advantage of the optical fiber based localized surface plasmon resonance (LSPR) sensors is the convenience to work with and work in harsh environments. An optical fiber tip LSPR refractive index sensor of 196 nm per refractive index unit (RIU) sensitivity has been demonstrated. The affinity sensing property of the fiber tip sensor was demonstrated using biotin/streptavidin as the receptor/analyte. The detection limit for streptavidin was determined to be 6 pM.

Extended long range plasmon waves in finite thickness metal film and layered dielectric materials

In this paper, we show that the propagation distance of the long range plasmon wave mode guided by a finite thickness gold metal film can be extended several orders of magnitude longer if we place intermediate dielectric layers on both sides of the metal film and choose the layer thickness properly. The propagation distance goes to infinite if the intermediate layer thickness approaches a critical thickness.

Fabrication of thin-film micropolarizer arrays for visible imaging polarimetry

We describe a microfabrication process for fabricating micropolarizer devices with polarization thin film. The polarization film is less than a 0.5 microm thick and can have a polarization extinction ratio of approximately 330 in the visible wavelength range. A single-state micropolarizer array with polarizing pixels as small as 5 microm x 5 microm has been fabricated. A multilayer spatially multiplexed three-state micropolarizer line array with a 14.4-microm resolution has also been fabricated for visible imaging polarimetry application.

Mie resonance-enhanced light absorption in periodic silicon nanopillar arrays.

Mie-resonances in vertical, small aspect-ratio and subwavelength silicon nanopillars are investigated using visible bright-field µ-reflection measurements and Raman scattering. Pillar-to-pillar interactions were examined by comparing randomly to periodically arranged arrays with systematic variations in nanopillar diameter and array pitch. First- and second-order Mie resonances are observed in reflectance spectra as pronounced dips with minimum reflectances of several percent, suggesting an alternative approach to fabricating a perfect absorber. The resonant wavelengths shift approximately linearly with nanopillar diameter, which enables a simple empirical description of the resonance condition. In addition, resonances are also significantly affected by array density, with an overall oscillating blue shift as the pitch is reduced. Finite-element method and finite-difference time-domain simulations agree closely with experimental results and provide valuable insight into the nature of the dielectric resonance modes, including a surprisingly small influence of the substrate on resonance wavelength. To probe local fields within the Si nanopillars, µ-Raman scattering measurements were also conducted that confirm enhanced optical fields in the pillars when excited on-resonance.

Characteristics of ultra-long range surface plasmon waves at optical frequencies

It has been reported earlier that ultra-long range surface plasmon waves can be supported if dielectric layers with lower index of refraction than that of the dielectric cladding are placed on either side of the thin metal film. In this paper, we report a further investigation of the ultra-long range surface plasmon modes and the condition to support such ultra-long propagation distances at optical frequencies. We studied the effects of the index of refraction contrast between the inner layer and the cladding dielectrics, the metal film thickness, and the dispersion with wavelength. We present a condition which must be satisfied by the waveguide structure to support the bound ultra-long range surface plasmon mode.

Femtosecond laser-pulse-induced birefringence in optically isotropic glass

We used a regeneratively amplified Ti:sapphire femtosecond laser to create optical birefringence in an isotropic glass medium. Between two crossed polarizers, regions modified by the femtosecond laser show bright transmission with respect to the dark background of the isotropic glass. This observation immediately suggests that these regions possess optical birefringence. The angular dependence of transmission through the laser-modified region is consistent with that of an optically birefringent material. Laser-induced birefringence is demonstrated in different glasses, including fused silica and borosilicate glass. Experimental results indicate that the optical axes of laser-induced birefringence can be controlled by the polarization direction of the femtosecond laser. The amount of laser-induced birefringence depends on the pulse energy level and number of accumulated pulses.

Control of 2D plasmon-polariton mode with dielectric nanolayers

We introduce two nanoscale thickness dielectric layers on the top and bottom sides of a finite width and finite thickness metal microstrip and have calculated the fundamental symmetric plasmon-polariton mode of the 2D metal-dielectric layer waveguide. The dielectric nanolayers provide an additional degree of freedom to control the plasmon-polariton mode. When the dielectric constant of the nanolayers is smaller than that of the cladding dielectric, the travel range of the fundamental symmetric plasmon-polariton mode is extended with the trade-off of the mode confinement. The figure of merit of the mode increases as the travel range extends.

Fabrication techniques for low loss silicon nitride waveguides

Optical waveguide propagation loss due to sidewall roughness, material impurity and inhomogeneity has been the focus of many studies in fabricating planar lightwave circuits (PLCs) In this work, experiments were carried out to identify the best fabrication process for reducing propagation loss in single mode waveguides comprised of silicon nitride core and silicon dioxide cladding material. Sidewall roughness measurements were taken during the fabrication of waveguide devices for various processing conditions. Several fabrication techniques were explored to reduce the sidewall roughness and absorption in the waveguides. Improvements in waveguide quality were established by direct measurement of waveguide propagation loss. The lowest linear waveguide loss measured in these buried channel waveguides was 0.1 dB/cm at a wavelength of 1550 nm. This low propagation loss along with the large refractive index contrast between silicon nitride and silicon dioxide enables high density integration of photonic devices and small PLCs for a variety of applications in photonic sensing and communications.

Fabrication of high-resolution micropolarizer arrays

Procedures for creating high-resolution polarization filter ar- rays using multilayer polyvinyl alcohol (PVA) films are described. Two state polarization filter arrays with 25mm resolution and three state po- larization filter arrays with 48 mm resolution are demonstrated.