We present a theoretical analysis of the response of whispering gallery modes for biosensing applications, studied
numerically in microcylinders and semi-analytically in microspheres. The effect of single and multiple particles
is calculated, simulating biological analytes of different sizes and polarizabilities attached to the microresonator
surface. Besides whispering-gallery-mode frequency shifts, we find that also broadenings and splittings (from
lifted rotational symmetry) appear due to particles attachment and/or the vicinity to a planar coupler. For a
single analyte, both particle size and refractive index can be determined from the broadening and shift, opening
the perspective to a new biosensing modality.
We report on an array of atomic force microscopes (AFM) based on a simple optical set-up using heterodyne detection. The deflection of AFM cantilevers is given by the path differences between the reference and the measuring wave in a Michelson interferometer. A matrix of micro-lenses is placed just above the cantilevers, in such a way that the deflected light from each cantilever is collected by one micro-lens. Both the micro-lenses and the cantilever chips are previously glued to increase the robustness of the system. The interference between the light from each micro-lenses and the
reference light is selected by a diaphragm and subsequently detected by a photodetector. This procedure is repeated for each cantilever. In order to validate our instrument we measure the profile of a binary grating having a step height of 19.66 nm. By a piezoelectric platform a lateral range of 10 μm was scanned with a speed of 1 μm/s and an integration time of 10 ms, which leads to a lateral resolution of 10 nm. The profiles measured by the cantilevers are in good agreement with the profile of the sample grating.
The power spectrum density of the intensity of jittery but coherent trains of linearly chirped Gaussian pulses after a high-dispersion line with arbitrary first (β2) and second order(β3) dispersion is computed in the small-signal
approximation. Before the dispersive line the timing jitter of the input train causes noise sidebands around the harmonics of the train. The noise bandwidth of these jitter sidebands depends on the pulse-to-pulse correlation. The result of the propagation in a dispersive line is a multiplicative factor in the noise spectral density. This term depends on the dispersive characteristics of the line and the pulse parameters but not on the timing jitter's correlation. The structure of this new factor is peaked, resulting in narrowband noise patterns at specific locations of the spectrum. The bandwidth of the dispersion-induced noise patterns is in general broader than the timing jitter's bandwidth. When the lines are Talbot dispersive devices, i. e., are designed to multiply the repetition rate of the train), jitter noise around the harmonics of the output train is left untouched. Therefore the jitter structure of the multiplied train is inherited from the initial train. More general RF spectral patterns, depending on the pulse-to-pulse jitter correlation, are also analyzed.
There exists a well-known analogy between the paraxial or one-dimensional Fresnel diffraction and the propagation of pulses in linear dispersive medium with negligible attenuation. Under this analogy, the envelope of a pulse is equivalent to the distribution of complex amplitude of the light in diffraction. In this context, we study the propagation of a train of identical Gaussian chirped pulses arranged in time in the same way as the Fresnel zones of a phase zone plate, in a highly dispersive guiding medium. From this study we find that the input train focuses in an only pulse, for certain values of total dispersion. We establish the focusing condition and characterize the output signal through its width and peak intensity.