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We present a new lithographic technique based on a hybrid photothermal process to modulate the refractive index in commercial SU-8 photoresist. Owing to a difference in cross-linking, the refractive index of unexposed SU-8 cross-linked by thermally induced polymerization is 0.0072 higher than that of SU-8 cross-linked by UV exposure and postbaking. Making use of this property, we fabricated two thick, flat-topped index-modulated diffractive optical elements (DOEs) that contain different phase distributions and measured their wavefront reconstruction. The good experimental reconstructions of the index DOEs demonstrate the potential to extend the refractive-index modulation technique for the fabrication of three-dimensional optical elements without needing a development step.

We demonstrate an enhancement of fluorescence emission due to bimetallic silver-gold film-induced surface plasmon wave extension. Rhodamine B (RhB) dyes were excited by the evanescent wave field produced from surface plasmon polaritons excited on metal-deposited sections along an embedded strip waveguide. Various silver-gold combinations were used to quantify for the evanescent field enhancement. The underlying silver yields better evanescent field enhancement, while the overlying gold ensures that the stability of the sensing surface is not compromised. In comparison to the conventional single gold film surface plasmon resonance (SPR) configuration, the two-layered metallic structure is capable of enhancing the surface plasmon polariton (SPP) evanescent field considerably, as verified experimentally by the ca. 4.0 times improvement in the RhB fluorescence emission. The compact waveguide structure and improved electric field probing depth can potentially be exploited for on-chip SPR--fluorescence excitation of less concentrated fluorophore-labelled biological and chemical analytes, with a capability of massively parallel processing for high throughput screening.

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelengthmodulated waveguide SPR sensor with a bimetallic silver-gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of d =d n, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.