A Current-Mode Analog Front-End for Capacitive Length Transducers in Pneumatic Muscle Actuators.

This paper reports on the design, implementation, and characterization of a current-mode analog-front-end circuit for capacitance-to-voltage conversion that can be used in connection with a large variety of sensors and actuators in industrial and rehabilitation medicine applications. The circuit is composed by: (i) an oscillator generating a square wave signal whose frequency and pulse width is a function of the value of input capacitance; (ii) a passive low-pass filter that extracts the DC average component of the square wave signal; (iii) a DC-DC amplifier with variable gain ranging from 1 to 1000. The circuit has been designed in the current-mode approach by employing the second-generation current conveyor circuit, and has been implemented by using commercial discrete components as the basic blocks. The circuit allows for gain and sensitivity tunability, offset compensation and regulation, and the capability to manage various ranges of variations of the input capacitance. For a circuit gain of 1000, the measured circuit sensitivity is equal to 167.34 mV/pF with a resolution in terms of capacitance of 5 fF. The implemented circuit has been employed to measure the variations of the capacitance of a McKibben pneumatic muscle associated with the variations of its length that linearly depend on the circuit output voltage. Under step-to-step conditions of movement of the pneumatic muscle, the overall system sensitivity is equal to 70 mV/mm with a standard deviation error of the muscle length variation of 0.008 mm.

A Multilevel Synchronized Optical Pulsed Modulation for High Efficiency Biotelemetry.

The paper describes the design, implementation, and characterization of a novel multilevel synchronized pulse position modulation paradigm for high efficiency optical biotelemetry links. The entire optoelectronic architecture has been designed with the aim to improve the efficiency of the data transmission and decrease the overall power consumption that are key factors for the fabrication of implantable and wearable medical devices. By employing specially designed digital architectures, the proposed modulation technique automatically transmits more than one bit per symbol together with the reference clock signal enabling the decoding process of the received coded data. In the present case, the paper demonstrates the capability of the modulation technique to transmit symbols composed by 3 and 4 bits. This has been achieved by developing a prototype of an optical biotelemetry system implemented on an FPGA board that, making use of 500 ps laser pulses, operates under the following two working conditions: (i) 40 MHz clock signal corresponding to a baud rate of 40 Mega symbol per second for symbols composed by 3 bits; (ii) 30 MHz clock signal corresponding to a baud rate of 30 Mega symbol per second for symbols composed by 4 bits. Thus, for both these two configurations the transmission data rate is 120 Mbps and the measured BER was lower than 10-10. Finally, the power consumption was found to be 1.95 and 1.8 mW and the resulting energy efficiencies were 16.25 and 15 pJ/bit for transmitted symbols composed by 3 and 4 bits/symbol, respectively.

Laser Transmission Spectroscopy Based on Tunable-Gain Dual-Channel Dual-Phase LIA for Biological Nanoparticles Characterization.

Size and absolute concentration of suspensions of nanoparticles are important information for the study and development of new materials and products in different industrial applications spanning from biotechnology and pharmaceutics to food preparation and conservation. Laser Transmission Spectroscopy (LTS) is the only methodology able to measure nanoparticle size and concentration by performing a single measurement. In this paper we report on a new variable gain calibration procedure for LTS-based instruments allowing to decrease of an order of magnitude the experimental indetermination of the particle size respect to the conventional LTS based on the double ratio technique. The variable gain calibration procedure makes use of a specifically designed tunable-gain, dual-channel, dual-phase Lock-In Amplifier (LIA) whose input voltage signals are those ones generated by two Si photodiodes that measure the laser beam intensities passing through the sample containing the nanoparticles and a reference optical path. The LTS variable gain calibration procedure has been validated by firstly using a suspension of NIST standard polystyrene nanoparticles even 36 hours after the calibration procedure was accomplished. The paper reports in detail the LIA implementation describing the design methodologies and the electronic circuits. As a case example of the characterization of biological nanostructures, we demonstrate that a single LTS measurement allowed to determine size density distribution of a population of extracellular vesicles extracted from orange juice (25 nm in size) with the presence of their aggregates having a size of 340 nm and a concentration smaller than 3 orders of magnitude.

A 300 Mbps 37 pJ/bit Pulsed Optical Biotelemetry.

This article reports an implantable transcutaneous telemetry for a brain machine interface that uses a novel optical communication system to achieve a highly energy-efficient link. Based on an pulse-based coding scheme, the system uses sub-nanosecond laser pulses to achieve data rates up to 300 Mbps with relatively low power levels when compared to other methods of wireless communication. This has been implemented using a combination of discrete components (semiconductor laser and driver, fast-response Si photodiode and interface) integrated at board level together with reconfigurable logic (encoder, decoder and processing circuits implemented using Xilinx KCU105 board with Kintex UltraScale FPGA). Experimental validation has been performed using a tissue sample that achieves representative level of attenuation/scattering (porcine skin) in the optical path. Results reveal that the system can operate at data rates up to 300 Mbps with a bit error rate (BER) of less than 10 -10, and an energy efficiency of 37 pJ/bit. This can communicate, for example, 1,024 channels of broadband neural data sampled at 18 kHz, 16-bit with only 11 mW power consumption.

Transverse and soliton instabilities due to counterpropagation through a reflection grating in Kerr media.

Transverse instabilities are shown to accompany counterpropagation of optical beams through reflection gratings in Kerr media. The instability threshold of continuous waves is analytically derived, and it is shown that the presence of the grating broadens and narrows the stability region of plane waves in focusing and defocusing media, respectively. Furthermore, counterpropagating soliton stability is numerically investigated and compared with the transverse modulation instability analysis, revealing an underlying physical link.

Photorefractive solitons embedded in gratings in centrosymmetric crystals.

We investigate (1+1D) spatial optical solitons embedded in a fixed-volume grating in centrosymmetric photorefractive crystals. We numerically identify a two-parameter soliton family and deduce both its existence surface and soliton profiles. For shallow gratings, the soliton Fourier spectrum exhibits three lobes located at the reciprocal lattice points -K, 0, and K. Soliton trapping is a consequence of both the self-induced nonlinear waveguide and the grating reflectivity, which prevents the breakaway of the lateral components. To provide a preliminary evaluation of soliton stability, we also investigate the propagation of slightly perturbed soliton profiles.

Counterpropagating spatial Kerr soliton in reflection gratings.

We analytically predict the existence of both spatial bright and dark counterpropagating solitons in a reflection grating in the presence of the Kerr nonlinearity. The basic trapping mechanism consists of a twofold balance where diffraction is compensated by self-focusing and reflection is altered by the nonlinear-induced interferometric grating. We find that, whenever the spectral soliton profile lies within the grating stop band, bright and dark solitons exist only if the mutual phase of the counterpropagating solitons is pi or 0, respectively.

Mechanisms supporting long propagation regimes of photorefractive solitons.

We extend investigation of one-dimensional solitons in biased photorefractive crystals to long propagation regimes, where self-trapping over a large number of linear diffraction lengths combines with the progressive growth of generally distortive spatially nonlocal components. Results indicate that saturation halts the radiative misshaping of the soliton, which follows that specific bending trajectory along which its evolution is governed by the same local screening nonlinearity that intervenes in short propagation conditions, where spatial nonlocality has a negligible effect. This finding not only allows the prediction of the curvature and of the relative role of charge displacement and diffusion, but implies a set of interesting observable effects, such as boomerangs, counterpropagating and cavity geometries, quasirectilinear and anomalous collisions, along with specific consequences on soliton arrays and on coupling to bulk gratings.

Molding and stretched evolution of optical solitons in cumulative nonlinearities.

The observation of initial time dynamics of self-trapping in photorefractive media indicates that optical spatial solitons supported by intense cumulative nonlinearities manifest temporally nonlocal signatures in the form of stretched exponential behavior. This general result, supported also by numerical predictions, is triggered by wave shaping in a time-constant buildup map, a consequence of the spatially resolved inertial response intrinsic to the geometrical transition from a diffracting to a self-focused beam, inherent to soliton appearance.

Electro-optic beam manipulation through photorefractive needles.

We demonstrate electro-optic spatial two-dimensional mode switching in a bulk sample of potassium lithium tantalate niobate. Spatial confinement, mode coupling, and electro-optic functionality are mediated by two photorefractive needle solitons of opposite electroholographic charges embedded together in their anisotropic lobular structure.