Strong influence of hole shape on extraordinary transmission through periodic arrays of subwavelength holes

We show that extraordinary light transmission of periodic subwavelength hole arrays, generally attributed to surface-plasmon resonances, is strongly influenced by the hole shape. Both experiments and calculations, based on a Fourier modal method, demonstrate that a shape change from circular to rectangular increases the normalized transmission by an order of magnitude while the hole area decreases. Moreover, the spectra exhibit large redshifts (approximately 2500 cm(-1)). A comparison with the transmission of isolated holes shows that shape resonances of the rectangular holes play a dominant role.     

Novel integrated optic intensity modulator based on mode coupling

The analysis, design, realization, and measurements of a novel intensity modulator are reported. The operating principle is based on mode coupling between a passive low-loss SiON waveguide and an electro-optic high-loss polymer waveguiding structure. Matching the waveguides is critical and results in severe demands for the technology. Extended simulations by the Coupled Mode Theory, the Leaky Wave Model, and Finite Difference Beam Propagation Method resulted in the design of several modulator structures. After realization, modulation could be demonstrated at 632 nm and at 1523 nm using lossy waveguiding modes and surface plasmon modes.     

Contaminant detection in treated water using Optiqua’s MiniLab™ biosensing system: a case study for Bisphenol A

An inhibition assay for detection of Bisphenol A (BPA) in treated water has been developed and validated for the MiniLab? system from Optiqua Technologies. This biosensor-based analytical system can be used for detection of specific contaminants in solution. The system uses an integrated optic Mach-Zehnder interferometer chip that is functionalised with a biochemical interface layer. The sensor chip surface was first coated with aminodextran which formed a hydrophilic layer suitable for further modification. 4,4-bis(4-hydroxyphenyl) valeric acid (BVA), which is a structural analogue of BPA, was then successfully coupled to the aminodextran layer. This surface chemistry was used in a qualitative inhibition assay format for the selective detection of the presence of BPA. The assay was developed and optimised using a polyclonal anti-BPA antibody. Samples from 12 different water matrices of Singapore were spiked with known amounts of BPA and tested with the MiniLab? system. The working range of the BPA inhibition assay is from 0.5 to 5 µg/L. Intra- and inter-assay variations were measured, with calculated relative standard deviation averaging of about 15%. BPA concentrations of the spiked samples were also verified and confirmed with LC-MS. Such functionalised biosensor chip can be reused for more than 200 sample injections over a period longer than 6 months. Developed as a robust, user-friendly and cost-effective system that can be field deployed, the MiniLab? system enables target-specific assays currently only available in the lab to become available in the field.     

Antimicrobial silver nanoparticles generated on cellulose nanocrystals

We describe a new approach to the formation of silver nanoparticles (Ag NPs) using cellulose nanocrystals. The process involves periodate oxidation of cellulose nanocrystals, generating aldehyde functions which, in turn, are used to reduce Ag⁺ into Ag⁰ in mild alkaline conditions. The nanoparticles were characterized using transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy. From the microscope studies (TEM) we observed that Ag NPs have spherical shape with a size distribution comprise between 20 and 45 nm. The antibacterial activity was assessed using the minimum inhibitory concentration. The antibacterial assays compare favourably with most of other experiments conducted with the same species.     

Novel integrated optic intensity modulator based on mode coupling

Abstract

The analysis, design, realization, and measurements of a novel intensity modulator are reported. The operating principle is based on mode coupling between a passive low-loss SiON waveguide and an electro-optic high-loss polymer waveguiding structure. Matching the waveguides is critical and results in severe demands for the technology. Extended simulations by the Coupled Mode Theory, the Leaky Wave Model, and Finite Difference Beam Propagation Method resulted in the design of several modulator structures. After realization, modulation could be demonstrated at 632 nm and at 1523 nm using lossy waveguiding modes and surface plasmon modes.