Combined Optical Signal Research Articles

A Secure Optical Body Area Network Based on Free Space Optics and Time-Delayed 2D-Spectral/Spatial Optical CDMA

Free space optics (FSO)-based optical body area networks (OBANs) are receiving massive attention as an opportunity to address the limitations of their radio frequency (RF)-based counterparts. This boom in research interests is primarily due to multitude of benefits, including high capacity, immunity to electromagnetic interference (EMI), rapid installation, cost efficiency, and license-free use of spectrum. Securing the transmission of patient health data against interception in OBANs using insecure FSO channels is a challenging task. Therefore, we propose a low-cost, flexible, and secure OBAN based on FSO technology and a time-delayed two dimensional (2D) spectral/spatial optical code-division multiple access (OCDMA) system. The proposed architecture consists of eight sensors attached to the bodies of patients. The sensors operate at a rate of 50 kbps. Electrical data generated from each sensor are used to modulate an optical carrier and then encoded using 2D-spectral/spatial double weight–zero cross correlation (DW-ZCC) code. The 2D encoded optical signals are then time delayed to eliminate the multiple parallel FSO channels between the transmitter and medical center. The combined optical signal consists of eight 2D-encoded time-delayed optical signals transmitted towards a remote medical center over an FSO channel with a range of 1 km. The received signal is decoded and the data from each sensor are recovered after photodetection at the medical center for further analysis. The overall performance of the sensors is analyzed using bit-error rate (BER) and quality factor (Q-factor) plots for different weather conditions and lengths of the FSO channel, considering the log-normal channel model. The capital expenditure (CAPEX) of the proposed architecture is analyzed and compared with the conventional 2D-spectral/spatial FSO system to determine the overall impact of introducing time delay units on the cost of implementation.

Microwave photonic frequency down-conversion with self-interference cancellation and SSBI mitigation

In this paper, we proposed a microwave photonic frequency down-conversion scheme with the functions of self-interference cancellation (SIC) and signal–signal beat interference (SSBI) mitigation. The scheme is based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. One of the dual-parallel Mach–Zehnder modulator (DP-MZM) which is located in the upper part of the DP-QPSK modulator is used to achieve SIC by properly biasing the modulator. A local oscillator signal is loaded on the other DP-MZM which is located in the lower part of the DP-QPSK modulator. After photoelectric conversion of the combined optical signal by a photo-detector (PD), the signal of interest (SOI) is down-converted to an intermediate frequency (IF) signal. The SSBI is mitigated by Kramers–Kronig (KK) detection to achieve lower IF down-conversion. Experimental results show that the SIC for a single-tone interference signal is around 53 dB, and for an interference signal with a bandwidth of 100 MHz, the SIC achieved at least 29 dB. A simulation verifies the effect which the least mean square (LMS) algorithm mitigated on the influence of multipath After SIC, we used KK algorithm to reduce error vector magnitude (EVM) of the down-converted 16-QAM signal from 17.54% to 9.07%, which indicates a remarkable SSBI mitigation effect.

Photonic-Enabled Doppler Frequency Shift Measurement for Weak Echo Signals Based on Optical Single-Sideband Mixing Using a Fixed Low-Frequency Reference

A simplified photonic-enabled Doppler frequency shift (DFS) measurement approach is proposed based on a single dual-polarization binary phase-shift keying (DP-BPSK) modulator with the help of a fixed low-frequency reference. The low-frequency reference and the transmitted signal are combined and then single-sideband mixed in the upper dual-drive Mach-Zehnder modulator (DD-MZM) in the DP-BPSK modulator to generate an optical sideband of the transmitted signal and a mixed optical sideband of the two signals, which is combined with the optical sideband of the echo signal from the other DD-MZM. The combined optical signal is detected in a low-speed photodetector. Both the direction and the value of the DFS can be measured by analyzing the frequency of the generated photocurrent. An experiment is performed. DFS from -100 to 100 kHz is measured for microwave signals from 6.9 to 16.1 GHz with a measurement error of less than ±0.04 Hz. The stability of the system is also studied, and the change of the measurement error is less than ±0.04 Hz in 30 minutes.

MUX/DEMUX SiC receiver for visible light communications

In this paper we present a MUX/DEMUX device based on a multilayer a-SiC:H optical filter that requires near-ultraviolet steady state optical switches to select desired wavelengths in the visible range. The selector filter is realized by using a two terminal double pi’n/pin a-SiC:H photodetector. Five visible communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the photocurrent, under near-UV front steady state background. Data shows that 25 current levels are detected and corresponds to the thirty-two on/off possible states. The proximity of the magnitude of consecutive levels causes occasional errors in the decoded information. To minimize the errors, four parity bit are generated and stored along with the data word. The parity of the word is checked after reading the word to detect and correct the transmitted data. Results showed that the background works as a selector in the visible range, shifting the sensor sensitivity and together with the parity check bits allows the identification and decoding of the different input channels. A transmission capability of 60 kbps using the generated codeword was achieved.

Application of combined optical signal processing methods to compensate for nonlinear effects in fibre-optic communication links

We report on the use of complex quadrature amplitude signal processing methods based on a combination of static neural networks and special modulation techniques. The conditions are found that allow one to construct the most effective combination of signal processing methods for transmitting signals with considerable power (in the nonlinear regime). Using analytical methods, it is shown how the statistical properties of a signal affect the efficiency of combined processing methods.

Probing of quantum energy levels in nanoscale body SOI-MOSFET: Experimental and simulation results

In the efforts to address the need for developing ultra-fast computers based on combined electronic and optical signal processing using silicon-based nanoscale devices, new types of transistors have been developed. Ultra-Thin Body and Nano-Scale Body (NSB) Silicon-On-Insulator Metal–Oxide-Semiconductor Field-Effect-Transistor devices, sharing a similar W/L but with a channel thickness of, respectively, 46 nm and down to 1.6 nm, have been fabricated using a selective Gate-Recessed Channel process on the same silicon wafer, and electrically tested at room (300 K) and low (77 K and 4.7 K) temperatures. In addition to the observed drain current values, which were found to be different by three orders of magnitude, quantum steps have been identified in the NSB transfer curves when measured at low temperatures. Since the NSB device's channel is part of a quantum well structure, the steps can point to discrete levels of energy. Such an approach can lead the way to some opportunities toward inter-subband emitting devices. Location of discrete steps is evidence of indirect-to-direct transition in ultra-thin silicon.

Simultaneous wideband radio-frequency self-interference cancellation and frequency downconversion for in-band full-duplex radio-over-fiber systems.

A photonic approach for simultaneous wideband radio-frequency (RF) self-interference cancellation and frequency downconversion in an in-band full-duplex radio-over-fiber system is proposed based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) in the DP-QPSK modulator is used to cancel the self-interference directly in the optical domain and generate two sidebands of the desired RF signal, whereas the lower DP-MZM generates two sidebands of the local oscillator. After detecting the combined optical signal at a photodetector, the desired RF signal is downconverted to an intermediate frequency (IF) signal with the self-interference cancelled. The proposed approach can overcome the reappearance of the interference signal and the power fading effect of the received signal caused by fiber dispersion. An experiment is performed. The cancellation depth for single frequency interference cancellation is around 58dB, whereas that for the wideband interference cancellation is larger than 25dB. The fading effect of the proposed IF transmission system is also evaluated compared with the traditional RF transmission system.

VIS/NIR wavelength selector based on a multilayer pi'n/pin a‐SiC:H optical filter

AbstractIn this paper, we present a tandem visible/nearinfrared (VIS/NIR) wavelength selector based on a multilayer a‐SiC:H optical filter that requires appropriate near‐ultraviolet steady states optical switches to select the desired wavelengths in the VIS/NIR ranges. Spectral response measurements are presented and show the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. The selector filter is realized by using a two terminal double pi'n/pin a‐SiC:H photodetector. Five visible/infrared communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analysed by reading out the photocurrent, under near‐UV steady state background. Results show that the background side and intensity works as a selector in the infrared/visible regions, shifting the sensor sensitivity. This nonlinearity allows the identification and decoding of the different input channels in the visible/infrared ranges. This concept is extended to implement a 1 by 5 wavelength division multiplexer with channel separation in the VIS/NIR range and a transmission capability of 30 Kbps. The relationship between the optical inputs and the output signal is established and an algorithm to decode the Multiplexed (MUX) signal presented. An optoeletronic model gives insight on the system physics. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Error control on spectral data of four‐wave mixing based on a‐SiC technology

AbstractIn this paper we exploit the nonlinear property of the SiC multilayer devices to design an optical processor for error detection that enables reliable delivery of spectral data of four‐wave mixing over unreliable communication channels. The SiC optical processor is realized by using double pin/pin a‐SiC:H photodetector with front and back biased optical gating elements. Visible pulsed signals are transmitted together at different bit sequences. The combined optical signal is analyzed. Data show that the background acts as selector that picks one or more states by splitting portions of the input multi optical signals across the front and back photodiodes.Boolean operations such as EXOR and three bit addition are demonstrated optically, showing that when one or all of the inputs are present, the system will behave as an XOR gate representing the SUM. When two or three inputs are on, the system acts as AND gate indicating the present of the CARRY bit. Additional parity logic operations are performed using four incoming pulsed communication channels that are transmitted and checked for errors together. As a simple example of this approach, we describe an all‐optical processor for error detection and then provide an experimental demonstration of this idea. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

SiC pinpin photonic filters for linking the visible spectrum to the telecom gap

Expanding far beyond traditional applications at telecommunications wavelengths, the SiC photonic devices has recently proven its merits for working with visible range optical signals. Reconfigurable wavelength selectors are essential sub-systems for implementing reconfigurable WDM networks and optical signal processing. Visible range to telecom band spectral translation in SiC/Si can be accomplished using wavelength selector under appropriated optical bias, acting as reconfigurable active filters. In this paper we present a monolithically integrated wavelength selector based on a multilayer SiC/Si integrated optical filters that requires optical switches to select wavelengths. The selector filter is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Red, green, blue and violet communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the generated photocurrent, under different background wavelengths applied either from the front or the back side. The backgrounds acts as channel selectors that selects one or more channels by splitting portions of the input multi-channel optical signals across the front and back photodiodes. The transfer characteristics effects due to changes in steady state light, irradiation side and frequency are presented. The relationship between the optical inputs and the digital output levels is established.

Bridging the Visible Spectrum to Telecom Gap with SiC Nanophotonic Spectral Translation

Abstract Visible range to telecom band spectral translation in SiC/Si can be accomplished using wavelength selector under appropriate optical bias, acting as reconfigurable active filters. In this paper we present a monolithically integrated wavelength selector based on a multilayer SiC/Si integrated optical filters that requires optical switches to select wavelengths. The selector filter is realized by using a double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Red, green, blue and violet communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the generated photocurrent, under different background wavelengths applied either from the front or the back side. The backgrounds acts as channel selectors that chooses one or more channels by splitting portions of the input multi-channel optical signals across the front and back photodiodes. The transfer characteristics effects due to changes in steady state light, irradiation side and frequency are presented. The relationship between the optical inputs and the digital output levels is established.

Design of an optical transmission WDM link using plastic optical fibers

ABSTRACTIn this paper we present the design of an optical transmission system, using plastic optical fiber (POF), which operates in the visible range of the electromagnetic spectrum. The optical signals are generated by modulated visible LEDs, transmitted through POF and at the reception end a pin-pin photodetector is implemented. A computer simulation tool dedicated to the analysis of optical circuits was used for preliminary analysis of the optical system. The performance of the optical link was analyzed by BER prediction variation on the transmission rate. The tested optical system was assembled using high efficiency LEDs of the same wavelengths, a commercial POF and a pin-pin photodetector based on a-SiC:H/a-SI:H. This detector behaves as an optical filter with controlled wavelength sensitivity. Different optical signals, obtained by adequate modulation of LED optical sources, were coupled into the POF and the combined optical signal at the fiber termination was directed onto the photodetector active area. The output photocurrent was measured with and without optical bias. Results compare the use of a pin-pin transducer device in free space and in a POF transmission link.

SiC monolithically integrated wavelength selector with 4 channels

ABSTRACTIn this paper we present a monolithically integrated wavelength selector based on a double pin/pin a-SiC:H integrated optical active filter that requires optical switches to select visible wavelengths. Red, green, blue and violet pulsed communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analyzed by reading out the generated photocurrent, under violet (400 nm) background applied either from the front or the back side of the device. The front and back backgrounds acts as channel selectors that selects one or more channels by splitting portions of the input multi-channel optical signals across the front and the back photodiodes. The transfer characteristics effects due to changes irradiation side are presented. The relationship between the optical inputs and the corresponding digital output levels is established through a 16-element look-up table to perform the optoelectronic conversion.Results show that the wavelength selector acts as a reconfigurable active filter that enhances the spectral sensitivity in a specific wavelength range and quenched it in the others, tuning a specific band. A binary weighted RGBV code that takes into account the specific weights assigned to each bit position is presented and establishes the optoelectronic functions.

Electrochemical plasmonic sensors

The enormous progress of nanotechnology during the last decade has made it possible to fabricate a great variety of nanostructures. On the nanoscale, metals exhibit special electrical and optical properties, which can be utilized for novel applications. In particular, plasmonic sensors including both the established technique of surface plasmon resonance and more recent nanoplasmonic sensors, have recently attracted much attention. However, some of the simplest and most successful sensors, such as the glucose biosensor, are based on electrical readout. In this review we describe the implementation of electrochemistry with plasmonic nanostructures for combined electrical and optical signal transduction. We highlight results from different types of metallic nanostructures such as nanoparticles, nanowires, nanoholes or simply films of nanoscale thickness. We briefly give an overview of their optical properties and discuss implementation of electrochemical methods. In particular, we review studies on how electrochemical potentials influence the plasmon resonances in different nanostructures, as this type of fundamental understanding is necessary for successful combination of the methods. Although several combined platforms exist, many are not yet in use as sensors partly because of the complicated effects from electrochemical potentials on plasmon resonances. Yet, there are clearly promising aspects of these sensor combinations and we conclude this review by discussing the advantages of synchronized electrical and optical readout, illustrating the versatility of these technologies.

Optical processing devices based on a‐SiC:H multilayer architectures

AbstractRed, green and blue optical signals were directed to an a‐SiC:H multilayered device, each one with a specific transmission rate. The combined optical signal was analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that when a chromatic time dependent wavelength combination with different transmission rates irradiates the multilayered structure, the device operates as a tunable wavelength filter and can be used in wavelength division multiplexing systems for short range communications. An application to fluorescent proteins detection is presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Light-triggered Silicon-carbon Pi'npin Devices for Optical Communications: Theoretical and Electrical Approaches

AbstractIn this paper a light-activated multiplexer/demultiplexer silicon-carbon device is analysed. An electrical model for the device operation is presented and used to compare output signals with experimental data. An algorithm that takes into accounts the voltage and the optical bias controlled sensitivities is developed. The device is a double pi'n/pin a-SiC:H heterostructure with two optical gate connections for light triggering in different spectral regions. Multiple monochromatic pulsed communication channels were transmitted together, each one with a specific bit sequence. The combined optical signal was analyzed by reading out, under different applied voltages and optical bias, the generated photocurrent across the device. Experimental and simulated results show that the output multiplexed signal has a strong nonlinear dependence on the light absorption profile, i.e. on the incident light wavelength, bit rate and intensity under unbalanced light generation of carriers. By switching between positive and negative voltages the input channels can be recovered or removed from the output signal.

Large area double p–i–n heterostructure for signal multiplexing and demultiplexing in the visible range

Results on the use of a double a-SiC:H p–i–n heterostructure for signal multiplexing and demultiplexing applications in the visible range, are presented. Modulated monochromatic beams together (multiplexing mode), or a single polychromatic beam (demultiplexing mode) impinge in the device and are absorbed, accordingly to their wavelength, giving rise to a time and wavelength dependent electrical field modulation. Red, green and blue pulsed input channels are transmitted together, each one with a specific transmission rate. The combined optical signal is analyzed by reading out, under different applied voltages, the generated photocurrent. Results show that in the multiplexing mode the output signal is balanced by the wavelength and transmission rate of each input channel, keeping the memory of the incoming optical carriers. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing regaining the transmitted information. An electrical model gives insight into the device operation.

Optical Processing Devices for Optical Communications: Multilayered a-SiC:H Architectures

AbstractIn this paper three multilayered architectures based on a-SiC:H with voltage controlled spectral selectivity in the visible spectrum range are analyzed. Multiple simultaneous modulated communication channels (red, green and blue or their polychromatic mixtures) were transmitted together at different frequencies. The combined optical signal was analyzed by reading out the photocurrent signal generated by the devices, under different applied voltages. Results show that the multiplexed signal depends on the device architecture and is balanced by the wavelength and transmission speed of each input channel, keeping the memory of the incoming optical carriers. In the single graded p-i’i-n configuration the device acts mainly as an optical switch while in two stacked p-i’-n-(ITO)-p-i-n configurations, the input channels are selectively tuned by shifting between forward and reverse bias. An electrical model, supported by a numerical simulation gives insight into the device operation.