A fiber-optic relative-humidity sensor composed of two silver coating and a thick porous silicon film is proposed and
demonstrated for relative humidity sensing. The two Ag coatings are magnetically sputtered, with porous silicon
membrane sandwiched in between, which constructs a low-fineness Fabry-Perot sensing head. Experimental results show
that the interference fringe of the proposed porous silicon Fabry-Perot sensor shifts by 10.3 nm when relative humidity
increases from 11% to 97%. The linearity of interference fringe shift to relative humidity is averagely 0.9764 below 85%
RH. The proposed sensor is suitable for relative humidity sensing in the ambient environment.
In this work, we theoretically and experimentally demonstrate a highly sensitive porous silicon membrane
waveguide biosensor in the Kretschmann configuration, and show how the cladding material directly impacts
the waveguide sensor detection sensitivity and resonance width. Dielectric and metal-clad porous waveguides in
the Kretchmann configuration have the potential to achieve significantly enhanced performance for small
molecule detection compared to planar waveguide and surface plasmon resonance sensors due to increased
surface area and strong field confinement in the porous waveguide layer. First order perturbation theory
calculations predict that the quality factors of polymer-cladded porous silicon waveguides with porous silicon
losses less than ~500 dB/cm are at least two times larger than the quality factors of gold-cladded porous silicon
waveguides and traditional surface plasmon resonance sensors.
Porous silicon is an excellent material for biosensing because of its large surface area and ability to filter out large
contaminant species. In order to characterize the sensitivity of porous silicon based biosensors for biomolecules of
different sizes, a mesoporous silicon waveguide with average pore diameter of 20 nm is used to detect single strand
DNA oligos with different numbers of base pairs at different concentrations. Experimental results indicate that 16-mer
DNA is detected most sensitively with the mesoporous silicon waveguide.
Porous silicon is a suitable host material for biosensing applications due to its high surface area to volume ratio, which
enables substantial infiltration of biomolecules. Resonant waveguides can be fabricated from porous silicon based on a
two layer porous silicon structure. Light is coupled into the waveguide only at a particular angle of incidence.
Biomolecular binding inside the pores induces an increase in the effective porous silicon refractive index and causes a
change in the angle at which light is coupled into the waveguide. A biosensor for DNA detection based on a porous
silicon waveguide has been fabricated. Detection of DNA at concentrations on the level of ~μM is reported. Simulations
suggest significantly lower detection levels are possible.
In this paper we introduce and analyze a multiple-RF-beam beamformer in receive mode utilizing the principle of space-time delta-sigma modulation. This principle is based on sampling input signals in both time and space and converting the sampled signals into a digital format by delta-sigma conversion. Noise shaping is achieved in 2D frequency domain. We show that the modulator can receive signals of narrow and wide bandwidths with steering capability, can receive multiple beams, and establish tradeoffs between sampling in time and in space. The ability of the modulator to trade off between time and space provides an effective way to sample high frequency RF signals without down conversion. In addition, a space-time delta-sigma modulator has better performance than a solely temporal delta-sigma modulator (for the same filter order), as is typically used in communication systems to digitize the down-converted analog signals.