Random‐access distributed fiber sensing

Optical sensing offers an attractive solution to the societal concern for prevention of natural and human‐generated threats and for efficient use of natural resources. The unprecedented properties of optical fibers make them ideal for implementing a ‘nervous system’ in structural health monitoring: they are small, low‐cost and electrically and chemically inert. In particular, the nonlinear interaction of stimulated Brillouin scattering allows for the distributed measurement of strain and temperature with tens of km range. In this work, a novel, radar‐inspired technique for random‐access Brillouin scattering‐based sensors is shown, making a significant step towards a real optical sensing nerve. The method selectively addresses each fiber segment as a distinct sensing element in a synaptic neuronal system. The measurement principle relies on phase‐coding of both the Brillouin pump and signal waves by a high‐rate, pseudo‐random bit sequence. Temperature measurements with 1 cm resolution are reported. The measurement range is scalable to several km.     

Doppler effect's contribution to ultrasonic modulation of multiply scattered coherent light: Monte Carlo modeling

Modulation of light by ultrasound in turbid media is investigated by modified public domain software based on the Monte Carlo algorithm. Apart from the recognized modulation mechanisms, originating in scatterers' displacements and refractive index modulation, an additional mechanism, evolving from Doppler shift during photon scattering, is considered. Comparison of the relative contributions from all three mechanisms to light modulation by ultrasound is performed for different medium scattering properties and ultrasound frequencies. Refractive index modulation remains the strongest mechanism for light modulation by ultrasound, but for high ultrasound frequencies and for large scattering coefficients the Doppler effect can become dominant.     

An analytical expression for the electric field in MSM structures

In this work the conformal mapping is used to determine an analytical expression for the electric field in MSM structures. The expression simplifies the analysis of optically generated carriers transport, i.e. the determination of the response of the MSN photodetectors. It can also be useful in the analysis of MSM electrooptical modulators operation.