Suhrawardi Ilyas

Organic modification of mesoporous silicon rugate filters: the influence of nanoarchitecture on optical behaviour

The internal nanostructure and optical properties of mesoporous silicon rugate filters prepared on different p+ type silicon substrates are compared for applications in biosensing. Chemical derivatisation of the internal surface by undecenoic acid hydrosilylation results in red-shifting of the resonant wavelength of the filter, whereby the magnitude of the red shift is found to be a function of the pore morphology. The pore structure was found to play a significant role during infiltration of protein into the photonic crystal.

Optimisation of Nanostructured Porous Silicon Surface Chemistry Towards Biophotonic Sensors

Narrow line-width porous silicon rugate filters, fabricated by electrochemical etching of crystalline silicon with sinusoidal variation in the current density, provide a class of optical material that may find utility in biosensing applications. Herein, we demonstrate the use of hydrosilylation chemistry to passivate the filters from oxidation, and to provide coupling points for attachment of biorecognition species. Porous silicon rugate filters were derivatised with two functional alkenes and were characterized using Fourier transform infrared spectroscopy (FTIR) concurrently with analysis of the reflectivity spectrum throughout organic derivatisation. The reproducible optical signals upon chemical and biological modification may provide a robust methodology for sensing of biological species and open the way for a new class of optical biosensor

Porous Silicon Based Rugate Filters

We report on the design and fabrication of porous silicon based rugate filters. We have achieved very narrow linewidth, high reflectivity optical filters made entirely from silicon by continuously varying of the refractive index of Si and apodizing the index profile of the structure

Single and multi-array GRIN lenses from porous silicon

Intensive research for more than a decade has demonstrated that porous silicon (PSi) can be an excellent alternative material for multilayer optical devices, such as Bragg mirrors, microcavities and filters. In this paper, we shall describe a new application of PSi. We have designed, fabricated and tested various types of PSi based graded refractive index (GRIN) lenses. These planar micro-lenses are embedded in the Si wafer and have made-to-order focal lengths. Our fabrication technique allows the manufacture of a single lens or an array of lenses with variable focal length. The design opens the possibility of integrating the GRIN lenses with existing Si based optical devices such as detectors and waveguides.

Nanoporous silicon GRIN lenses

We describe a novel application of nanoporous silicon as thin GRIN lenses. Positive and negative lenses can be made by achieving a continuous radial variation of the porosity during the fabrication of the layer. The gradient of refractive index in radial direction depends on resistivity of the silicon wafer and etching current density. The shape of the anode determines the type of lens. An electrode in the shape of a ring produces the positive lenses, while a point electrode produces the negative lens.

Graded refractive index devices from porous silicon

This paper discusses a number of optical devices that fabricated from mesoporous silicon to highlight the excellent device qualities and ease of fabrication which is achievable using PSi. Specifically, the paper discusses about the design and properties of devices with continuously varying refractive index profiles. The authors have made two types of index gradients: axial gradients, in which the index varies parallel to the optical axis, and radial gradients, in which the index varies perpendicular to the optical axis. As an example of axial gradient device, the authors discussed the design and fabrication of rugate filters with sinusoidally varying refractive indexes that act as single line reflection filters with narrow line-widths (< 10nm) and close to 100% reflectivity. The authors also talk about gradient refractive index (GRIN) lenses that we made for the first time from PSi. These planar lenses are embedded in the Si wafer and have, in theory, the ability to correct chromatic and some other aberrations that afflict conventional lenses.

High quality optical components from porous silicon

This paper concentrates on a small number of optical devices fabricated from mesoporous silicon to highlight the excellent device qualities and ease of fabrication which is achievable using porous silicon (PSi). Specifically, this study discusses the design and properties of PSi based laser mirrors, optical micro-cavities and single-line filters containing continuously varying refractive index profiles.

Functionalization of Porous Silicon Based Photonic Crystals with Organic Monolayers

Porous silicon photonic crystals were reacted with unsaturated molecules in thermal hydrosilylation reactions to form silicon-carbon linked monolayers with functional groups designed for biosensor preparation. The derivatization was followed by infrared, X-ray photoelectron and reflection spectroscopies. Monolayer formation on the internal surfaces of the porous silicon structures resulted in predictable changes of their optical properties. Long term stability studies showed that the monolayers did not prevent slow oxidation of the porous silicon matrix in air