Current-Based High-Sensitivity Differential Detection of Light Power Using Si Photodiodes in Bridge Configuration for Chemical/Biological Optical Sensing☆

Abstract We present a new optoelectronic technique based on the differential measurement of currents for the detection of the variations of low concentrations of chemical and biological substances by measuring light power absorption through two Si-photodiodes (SiPD) in a bridge configuration. The solution exhibits high sensitivity, linear response and allows the compensation of the initial bridge unbalance without changing its elements so optimising signal amplification gain and detection resolution. The technique shows unique performances with respect to voltage amplitude measurements performed by lock-in amplifiers. Moreover, the experimental apparatus is simple and suitable for portable integrated sensor systems. Its main performances have been evaluated through a prototype PCB demonstrating the capability to detect light power variations with a settable maximum sensitivity of 30mV/nW and a resolution of 33pW

Highly nonparaxial (1+1)-D subwavelength optical fields.

A general approach for describing (1 + 1)-D subwavelength optical field whose waist is much smaller than the wavelength is presented. Exploiting the vectorial Rayleigh-Sommerfeld diffraction theory, a suitable expansion in the ratio between the beam waist and the wavelength allows us to prove the a (1+1)D highly nonparaxial field is generally the product of a cylindrical wave carrier and an envelope which is angularly slowly varying. We apply our general approach to the case of highly nonparaxial Hermite-Gaussian beams whose description is fully analytical

Optical Measurements by Phase Shift Based Technique for High Sensitivity and High Resolution Detection of Chemical/Biological Substances

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Reconfigurable photoinduced metamaterials in the microwave regime

We investigate optically reconfigurable dielectric metamaterials at gigahertz frequencies. More precisely, we study the microwave response of a subwavelength grating optically imprinted into a semiconductor slab. In the homogenized regime, we analytically evaluate the ordinary and extraordinary component of the effective permittivity tensor by taking into account the photo-carrier dynamics described by the ambipolar diffusion equation. We analyze the impact of semiconductor parameters on the gigahertz metamaterial response which turns out to be highly reconfigurable by varying the photogenerated grating and which can show a marked anisotropic behavior.Comment: 6 figures, 7 page

Low-cost Discrete Off-the-shelf Components 1MHz Analogue Lock-in Amplifier for Fast Detection of Organic Compounds through Pulsed Lasers

Abstract We report on a low-cost analogue Lock-In Amplifier (LIA) designed to measure amplitude variations of 100 ns pulsed signals at operating frequencies f 0 up to 1MHz. The fabricated prototype PCB, implemented through discrete off-the-shelf components, allowed to validate the solution and to perform circuit testing and characterisations. The LIA architecture is simple and based on the classic phase-sensitive synchronous demodulation technique including two different amplification stages together with suitable filtering blocks that allow setting the instrument gain, sensitivity and resolution. With respect to conventional LIAs typically working at lower operating frequencies, the reported solution provides also high-speed DC output of about 1ms. By employing short voltage pulses, the LIA is capable to detect fast and small variations of the signal amplitude envisaging its use in sensor applications to measure reduced variations of chemical and physical phenomena through high-speed systems with very small time constants