Ibrahim Abdulhalim

Surface Plasmon Resonance for Biosensing: A Mini-Review

Abstract A variety of configurations and formats have been devised to exploit the phenomenon of surface plasmon on metal dielectric interfaces for sensing a variety of significant analytes, such as pesticides and explosives, pathogens and toxins, and diseased tissue. Researchers continue to aim at detecting lower concentrations in smaller volumes of samples in real time. A new research field, called nanoplasmnonics, has emerged in this regard.

Sensitivity enhancement of guided-wave surface-plasmon resonance sensors

It is demonstrated theoretically and experimentally that, by using the guided-wave surface-plasmon sensor configuration with a top layer of dielectric thin film (10-15 nm) having a high value of the real part of the dielectric function, it is possible to improve the sensitivity of the sensor up to 1 order of magnitude. The stability is improved because the thin nanolayer acts as a protection layer for the metal. The enhancement is due to the increase in the interaction volume and the evanescent field enhancement near the top layer-analyte interface.

Omnidirectional reflection from Fibonacci quasi-periodic one-dimensional photonic crystal

It is shown that omnidirectional reflection (ODR) is possible from quasi-periodic isotropic dielectric stacks following a Fibonacci sequence (FS). The transition from truly periodic to fully quasi-periodic structure is investigated by building periodic structures having unit cells made of FS of order j. The number of periods required to achieve ODR decreases as j increases until only a single period is required at which the structure is fully quasi-periodic. As compared to the periodic case, for the quasi-periodic structure the spectral range is wider, the thickness of the single layers is smaller and the tolerance on the layer thicknesses is smaller.

Analytic propagation matrix method for linear optics of arbitrary biaxial layered media

We present an analytic simplified form for the 4 × 4 propagation matrix of a general homogeneous biaxial layer. The expression is applicable to any linear homogeneous, absorbing, biaxial, gyrotropic, magneto-optic, arbitrarily oriented anisotropic structure. Its simple form speeds up the calculation of the optical properties of inhomogeneous anisotropic media and allows real-time analysis of ellipsometric experimental data. A simplified analytic expression for the propagation matrix is also derived for the case of mode degeneration such as for propagation at certain angles and for the isotropic case. Using this analytic method it is found that the time required for calculating the propagation matrix is shorter by a factor of two than that using direct numerical calculation.

Figure-of-merit enhancement of surface plasmon resonance sensors in the spectral interrogation

We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann-Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range.

Surface-enhanced fluorescence from metal sculptured thin films with application to biosensing in water

Surface-enhanced fluorescence from porous, metallic sculptured thin films (STFs) was demonstrated for sensing of bacteria in water. Enhancement factors larger than 15 were observed using STFs made of silver, aluminum, gold, and copper with respect to their dense film counterparts. The STFs used are assemblies of tilted, shaped, parallel nanowires prepared with several variants of the oblique-angle-deposition technique. Comparison between the different films indicates that the enhancement factor is higher when the tilt is either small ( 80 deg); thus, the enhancement is higher when only a single resonance in the nanowires is excited.

Liquid crystal Lyot tunable filter with extended free spectral range

Extension of the dynamic range of liquid crystal tunable Lyot filter is demonstrated by incorporating with it a liquid crystal variable retarder as an eliminator for the third and fourth order peaks. The filter is continuously tunable in the range 500 nm to 900 nm with a nominal width in the range 50nm-100nm. Design procedure is described including the exact solution to the LC director profile and the suitability for biomedical optical imaging applications. Flexibility in the design is proposed by applying different voltages to the different liquid crystal retarders thus compensating for small thickness deviations from the nominal values and obtaining the high dynamic range.

Electrically and Optically Controlled Light Modulation and Color Switching Using Helix Distortion of Ferroelectric Liquid Crystals

Abstract The electro-optic effect associated with the helix distortion of chiral smectic C (SmC*) liquid crystals and its application to light modulation are investigated. Optically and electrically addressed spatial light modulators based on this effect are demonstrated. They exhibit an analog response, response times as short as 100 μs, good contrast ratio and resolution, and color switching capability. The analog response is shown to be a result of the gradual distortion of the helix at low voltages. Optically this corresponds to a linear rotation of the average optic axis and change of the average effective birefringence. From measurements of the wavelength of the maximum transmission the birefringence has been found to change as a function of dc voltage and frequency of ac voltage and magnitude. The agreement between theory and experiment suggests that color changes are due solely to birefringence changes associated with changes in the geometry of the helix. We derive expressions for the angle of rot...

Analytic propagation matrix method for anisotropic magneto-optic layered media

Simplified analytic expressions are derived for the optical propagation matrix of magnetic anisotropic Kerr media using the Lagrange-Sylvester interpolation polynomial. This expression is used to investigate magnetic Kerr films in Fabry-Perot configurations, magneto-optic recording quadrilayers and alternating periodic stacks. It is found that the magneto-optic reflection coefficients are enhanced by a few orders of magnitude due to multiple reflections. Bragg-type reflection peaks from periodic structure appear solely due to the gyrotropy and it is shown that omnidirectional reflection is possible under certain conditions. This analytic approach is faster than using direct numerical calculation.

Competence between spatial and temporal coherence in full field optical coherence tomography and interference microscopy

Distinction between spatial and temporal coherence characteristics of the interferogram from low-coherence microscopic systems is investigated. It is shown that the coherence region is determined by the temporal coherence only when the path length difference is scanned in a region where the reference and sample beams are collimated, that is, containing a single spatial frequency. Spatial coherence has an effect when the path length scan is performed with a non-collimated beam, such as a defocus scan of a lens where the focal depth of the lens mainly determines the coherence region. In the latter case, the fringe size for a monochromatic light is smaller than half the wavelength by a factor determined by the spatial coherence. A new analytic relation is derived for the fringe size showing that it has better validity than the Ingelstam relation in the high NA region.