Ee Jin Teo

Low loss silicon waveguides for the mid-infrared

Silicon-on-insulator (SOI) has been used as a platform for near-infrared photonic devices for more than twenty years. Longer wavelengths, however, may be problematic for SOI due to higher absorption loss in silicon dioxide. In this paper we report propagation loss measurements for the longest wavelength used so far on SOI platform. We show that propagation losses of 0.6-0.7 dB/cm can be achieved at a wavelength of 3.39 µm. We also report propagation loss measurements for silicon on porous silicon (SiPSi) waveguides at the same wavelength.

Selective electroless silver plating of three dimensional SU-8 microstructures on silicon for metamaterials applications

We report a method for selective silver coating of SU-8 structures on Si substrates by treating the sample with radio frequency plasma prior to electroless plating. Silver films with high conductivity of 9 × 10−8Ω.m and low surface roughness of 9 nm have been obtained. When combined with two-photon lithography, this process can be utilized for three-dimensional metamaterials applications. Unlike previous work on selective coating, our process can coat directly on SU-8 photoresist that is widely used for two-photon lithography and does not require any resin modification.

Metal-assisted photonic mode for ultrasmall bending with long propagation length at visible wavelengths

In this work, we investigate the use of metal-assisted photonic guiding in a polymer-metal waveguide as an alternative approach for high density photonic integration at visible wavelengths. We demonstrate high confinement and long propagation length in sub-wavelength dimensions down to 300nm × 200nm using leakage radiation microscopy at a wavelength of 632.8 nm. Simulations using the finite element method (FEM) show that the optimum dimension that gives good confinement and propagation length is similar to that of the predicted plasmonic mode supported in the same waveguide. Under such optimum conditions, the metal-assisted photonic mode shows a five times longer propagation length and higher transmission efficiency for all 90° bending radius down to 1 μm compared to the plasmonic mode.

Radio frequency plasma pre-treatment for selective electroless Ag coating of three-dimensional SU-8 microstructures

Three dimensional metamaterials are fabricated using direct laser writing in SU-8 polymer followed by an electroless coating process. A method has been developed to allow for selective electroless plating of SU-8 microstructures with a smooth conformal coating of Ag. The process utilizes radio frequency plasma pretreatment to modify the SU-8 surface so that Ag ions can nucleate on the surface, leaving the substrate uncoated. An array of split ring resonators and other 3D microstructures are used to demonstrate how the technique can be applied to metamaterials applications.

Optical microcavities fabricated using direct proton beam writing

Proton beam writing (PBW) is a high-resolution direct write lithographic technique suitable for the fabrication of micro/nano optical components with smooth vertical sidewalls. In the present work PBW was used to fabricate smooth micro cavities in negative tone photoresist SU-8 and Rhodamine B doped SU-8. Two different laser cavities based on whispering gallery mode resonators were fabricated using PBW. The laser cavities in Rhodamine B doped SU-8 resist were optically pumped with a pulsed frequency doubled Nd: YAG laser, and emits light in the chip plane at 643 nm. The presented laser cavities showed pump threshold as low as 3 μJ/mm2, which is the lowest threshold reported in planar cavities fabricated in Rhodamine B dye based polymer laser cavities.

Mid-infrared silicon photonic devices

The mid-infrared spectral region is interesting for bio-chemical sensing, environmental monitoring, free space communications, or military applications. Silicon is relatively low-loss from 1.2 to 8 μm and from 24 to 100 μm, and therefore silicon photonic circuits can be used in mid- and far- infrared wavelength ranges. In this paper we investigate several silicon based waveguide structures for mid-infrared wavelength region.