Abstract: Coupled fiber-optic, evanescent-wave biosensors are improved through the use of configurations which adjust certain optical characteristics for enhanced sensitivity. In the preferred embodiment, this is carried out by inputting light into the coupler at either a different wavelength or multiple wavelengths simultaneously. In alternative embodiments, different modulation schemes and/or interferometric schemes are utilized. For example, at each of the inputs, different carrier frequencies may be used and modulated at lower frequencies, including prime-number frequencies. As the refractive index is changed in the vicinity of the coupling, a shift in the wavelength will induce a phase shift in the baseline signal such that, during data collection, the sensor is able to detect more refined changes. In general, through appropriate choice of input wavelength, fewer operational points will fall in an inefficient local maximum or minimum, thereby affording much greater sensitivity.

Abstract: Coupled fiber-optic, evanescent-wave biosensors are improved through the use of configurations which detect changes in polarization for enhanced sensitivity. The inventive approach forms the necked-down region by heating and pulling the fibers without twisting them. As such, when polarized light is introduced, including randomly polarized light, the outputs will exhibit a split based upon polarization orientation as well. One or more bindings partners are then attached to the necked-down region and within the evanescent field for very specific and direct detection of minute concentrations of an analyte of interest. The invention is applicable to any type of organic/inorganic material, so long as the interaction of one component causes a change in any optical property detectable by the apparatus. The biomolecule may be linked to the surface of the fusion joint by means of a spacer molecule. Polarizing beam splitters are employed to detect the based upon polarization orientation.