Nonlinear Semiconductor Research Articles

Generation and Transmission of a Quasi-Optical Single Sideband Signal for Radio-Over-Fiber Systems

Generation of a quasi-optical single sideband (OSSB) signal for a radio-over-fiber system utilizing the coherent population oscillation effects in a nonlinear semiconductor optical amplifier and transmission over a single-mode fiber (SMF) are investigated. The quasi-OSSB signal generator consists of an electroabsorption modulator and a nonlinear semiconductor optical amplifier. Characteristics of generated quasi-OSSB signals having different radio-frequency (RF) waves (1-50 GHz) transmitted over SMFs of different lengths (4-21 km) were investigated. Bit-error-rate performance of quasi-OSSB signals having 155-Mb/s differential phase-shift keying (DPSK) data transmitted over 0- to 55-km-long SMFs was also evaluated.

Electromagnetic wave analogue of an electronic diode

An electronic diode is a nonlinear semiconductor circuit component that allows conduction of electrical current in one direction only. A component with similar functionality for electromagnetic waves, an electromagnetic isolator, is based on the Faraday effect of rotation of the polarization state and is also a key component in optical and microwave systems. Here we demonstrate a chiral electromagnetic diode, which is a direct analogue of an electronic diode: its functionality is underpinned by an extraordinarily strong nonlinear wave propagation effect in the same way as the electronic diode function is provided by the nonlinear current characteristic of a semiconductor junction. The effect exploited in this new electromagnetic diode is an intensity-dependent polarization change in an artificial chiral metamolecule. This microwave effect exceeds a similar optical effect previously observed in natural crystals by more than 12 orders of magnitude and a direction-dependent transmission that differs by a factor of 65.

Improvements to Long-Duration Low-Power Gain-Switching Diode Laser Pulses Using a Highly Nonlinear Optical Loop Mirror: Theory and Experiment

This work presents an experimental and theoretical study on the improvements to pulsed diode laser gain-switched (GS) optical sources. Simultaneous compression and reshaping of the limited quality pulses obtained with this technique are reported using a highly nonlinear optical loop mirror (HNOLM) directly coupled to the diode laser source, without any previous pulse conditioning. The HNOLM is based on the use of a microstructured optical fiber and a highly nonlinear semiconductor optical amplifier; it is compact and offers benefits in terms of reduced system complexity. The experimental observations are compared to a theoretical model of the system, and excellent agreement is observed.

A novel all optical method of implementing an n-bit wavelength encoded complete digital data comparator using nonlinear semiconductor optical amplifiers

Data comparator is the integral part of arithmetic and logical unit of any electronic or optical data processor. Due to some inherent limitations of electronics it cannot be possible to obtain a super fast operation (over terahertz limit) from electronic comparators. Again wavelength encoding technique has been established as an excellent one over other existing optical data encoding techniques. Semiconductor optical amplifier (SOA) technologies have shown their strong potentiality of realizing many all-optical systems. In this communication the authors have proposed a new scheme of developing all-optical wavelength encoded n bit binary comparator exploiting the four-wave mixing, wavelength filtering, wavelength conversion and nonlinear polarization rotation capabilities property of nonlinear semiconductor optical amplifiers. The scheme can be used for comparing signed and unsigned optical binary data of any bit wide numbers as well. The comparator is especially suitable for use as a building block in a larger optical circuit, such as in an all optical telecommunications switch.

Combined optical amplification and dispersion compensation in radio over fibre links

The study presents theoretical and experimental investigations on radio over fibre links concerning the effect of fibre dispersion. An approach is presented to overcome the radio-frequency suppression effect in optical links based on the joint effect of semiconductor optical amplifier chirp, chromatic dispersion and non-linearities of optical fibre. The results show that the frequency notches caused by the dispersion induced carrier suppression effect may be sharply alleviated and the performance of the transmitted signal can be improved.

Four-Wave-Mixing-Based Dual-Wavelength Conversion in a Semiconductor Optical Amplifier

The simultaneous wavelength conversion of two different formats or bit-rate optical signals, with low input power, is demonstrated in a highly nonlinear semiconductor optical amplifier with a single strong continuous-wave pump. For two amplitude-modulated signals of different bit rates, moderate penalties are obtained, and for the case of mixed amplitude and phase modulation at 10 Gb/s, practically penalty-free operation is achieved. In all cases, small difference (<; 1.1 dB) between single- and dual-channel operation is obtained, allowing asynchronous operation.

Theoretical modeling of an improved all-optical flip flop based on a nonlinear semiconductor distributed feedback laser structure

A new, improved design of an all-optical flip flop is proposed. The waveguiding layer of the device consists of a phase-shifted nonlinear grating. The grating layers of a high refractive index have a negative nonlinear coefficient. A phase-shift section exists at the middle of the waveguiding layer. The optical gain is provided by current injection into an active layer. Nonlinearity in the waveguiding layer is achieved by direct absorption at the edge of the absorption band (Urbach tail). In the "OFF" state, the waveguiding layer forms a weak grating with an optical feedback below the laser threshold. In the "ON" state, the device functions as a distributed feedback (DFB) laser due to an induced strong grating in the nonlinear waveguiding layer. The improvements of the device performance by reducing the set pulse energy and accelerating the switch-off process are discussed. Field simulations in the time domain were performed.

Context-kernel support vector machines (KSVM) based run-to-run control for nonlinear processes

Past studies on multi-tool and multi-product (MTMP) processes have focused on linear systems. In this paper, a novel run-to-run control (RtR) methodology designed for nonlinear semiconductor processes is presented. The proposed methodology utilizes kernel support vector machines (KSVM) to perform nonlinear modeling. In this method, the original variables are mapped using a kernel function into a feature space where linear regression is done. To eliminate the effects of unknown disturbances and drifts, the KSVM expression for the KSVM controller is modified to include constants that are updated in a manner similar to the weights used in double exponential weighting moving average method and the control law for KSVM controllers is derived. Illustrative examples are presented to demonstrate the effectiveness of KSVM and its method in process modeling and control of processes. Even if there is limited data in process modeling, KSVM still has the good capability of characterizing the nonlinear behavior. The performance of the proposed KSVM control algorithm is highly satisfactory and is superior to the other MTMP control algorithms in controlling MTMP processes.

Experimental investigation on the quality improvement of low-power gain-switching diode laser picosecond pulses using a compact highly nonlinear optical loop mirror

The experimental work presented in this paper investigates the quality improvement of gain-switched (GS) sources. GS is a straightforward technique to achieve short pulses from diode lasers; however, such pulses exhibit long duration (10-100 ps), low power (in the milliwatt range), are asymmetric and are often generated along with pedestals or subpulses. Simultaneous compression and reshaping of these low quality pulses has been observed experimentally for several input power values. These effects have been achieved using a highly nonlinear optical-loop mirror, based on a microstructured optical fiber and a nonlinear semiconductor optical amplifier. It is designed to be compact and to directly process these complex pulses thus eliminating the requirement for prepulse conditioning. This offers overall benefits in terms of reduced system complexity. The quality of the pulses is characterized by their temporal width, pedestal height, duration, and spectral components. A maximum overall compression factor of 6 for a 10-mW average input power is observed. Additionally, the pulses obtained are observed to have improved quality for the input power range considered (500 µW to 30 mW, GS typical operational range) and the experimental scheme used preserves the compactness, efficiency, and simplicity of GS light sources.

Method of developing an all optical wavelength encoded single bit comparator exploiting four wave mixing and wavelength filtering character of nonlinear semiconductor optical amplifiers

Data Comparator is the integral part of arithmetic and logical unit of any electronic or optical data processor. Due to some inherent limitations of electronics it is not possible to obtain super fast data processing (over Terahertz limit) from electronic comparator. Again frequency encoding technique has been established as an excellent one over the other optical data encoding techniques. Semiconductor optical amplifiers (SOA) technologies have shown its potentiality of realising many all-optical systems. In this communication the authors have proposed a new all-optical wavelength encoded single bit binary comparator exploiting the four wave mixing and wavelength filtering property of nonlinear semiconductor optical amplifier.

Compression and Reshaping of Gain-Switching Low-Quality Pulses Using a Highly Nonlinear Optical Loop Mirror

This work presents an experimental study on the improvement of pulsed diode laser gain-switched (GS) optical sources where simultaneous compression and reshaping of the low-quality pulses obtained with this technique are reported. These effects are achieved using a highly nonlinear optical loop mirror (HNOLM) directly coupled to the diode laser source without any previous pulse conditioning. The HNOLM is based on the use of a microstructured optical fiber and a highly nonlinear semiconductor optical amplifier. This system is compact and robust. The pulses have been characterized through the evaluation of their autocorrelation traces and a study using a temporal information via intensity algorithm. Results show that the loop improves the quality of complex GS pulses in several aspects: they are compressed, their symmetry is improved, and the width and height of the pedestals that commonly appear accompanying GS pulses are reduced. The system proposed offers overall benefits in terms of reduced system complexity.

Victim Alignment in Crosstalk-Aware Timing Analysis

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Modeling the effect of coupling-noise on circuit delay is a key issue in static timing analysis and involves the <emphasis emphasistype="italic">victim-aggressor alignment</emphasis> problem. As delay-noise strongly depends on the skew between the victim-aggressor driver input transitions, it is not possible <emphasis emphasistype="italic">a priori</emphasis> identify the victim-driver input transition that results in the worst-case delay-noise. Several approaches have been proposed in literature which heuristically search for the worst-case victim-aggressor alignment. This paper presents an analytical result that obviates the need to search for the <emphasis emphasistype="italic">optimal</emphasis> victim-driver input transition, thereby simplifying the victim-aggressor alignment problem significantly. Using the properties of standard nonlinear complementary metal-oxide semiconductor drivers, it is shown that for monotonic input transitions the worst-case victim-driver input transition is the one that switches at the <emphasis emphasistype="italic">latest</emphasis> point in its timing window. Similarly, the victim-driver input alignment at the earliest point in the timing window is optimal for early-mode analysis. Although this result has been empirically observed in the industry, to the best of our knowledge this is the first paper which provides a rigorous analysis and shows that the above result holds for both linear and nonlinear drivers. It is also shown that the latest alignment of the victim-driver input transition results in the latest victim <emphasis emphasistype="italic">receiver output</emphasis> arrival time even for the cases where the victim is coupled to <emphasis emphasistype="italic">multiple</emphasis> aggressors. Finally, experimental results show that limiting the alignment of the victim to only the latest victim-driver input transition can significantly reduce the runtime of existing approaches with no loss of accuracy. </para>

All optical Flip-Flop based on a nonlinear DFB semiconductor laser: Theoretical study

A new design of an all optical Flip-Flop is proposed. It consists of a nonlinear distributed feedback (DFB) laser. The wave guiding layer of the DFB laser consists of linear grating section followed by a nonlinear one, and both sections are separated by a phase shift section. In the OFF-state, the real part of the refractive index in the wave guiding layer forms a Bragg grating. In the ON-state, it forms a Bragg grating with a phase shift section. Optical gain is achieved by current injection in the semiconductor active layer. Nonlinearity in the nonlinear layers of the semiconductor grating was achieved by direct absorption at the edge of the absorption band (Urbach tail). Numerical simulation shows that the device switches in a nanosecond time scale.

Simplified theory of optical nonlinearities in spin-polarized semiconductors

The spin degree of freedom is largely disregarded in existing theories of the density-dependentoptical properties of an interacting electron–hole plasma in quasiequilibrium. Here, weextended the pair equation, which is applicable to a bulk semiconductor at elevatedtemperatures, to calculate optical nonlinearities due to a spin-polarized plasma. Weobtained agreement with recent circular dichroism data in laser-excited GaAs by using theplasma density alone as the fitting parameter. The simplicity of our theory, based on theanalytical pair-equation formula, makes it ideal for conveniently modelling absorption in acarrier spin-polarized semiconductor.

Using ANOVA in a Microwave Round-Robin Comparison

This paper describes a procedure for comparing calibrated nonlinear radio-frequency (RF) measurements performed on a nonlinear device by five different measurement laboratories. The device under test (DUT) is a nonlinear active semiconductor device that is designed to generate a maximum number of harmonic tones. The goal is to obtain a simple automated method that detects if some laboratory had measurement problems during the measurement campaign. The developed comparison method is based on the analysis of variance (ANOVA) technique.

On the choice of nonlinear optical and semiconductor converters of femtosecond laser pulses into terahertz range

We carried out an experimental study of the use of nonlinear crystals ZnTe, GaP, GaSe, DAST, and LiNbO3 and semiconductors GaAs and InAs for the rectification of femtosecond optical pulses. This conversion produces broadband terahertz pulses consisting of a single period of the field oscillation. Here, we discuss features of different types of the terahertz converters, their efficiency, and spectral range.

SOA Intensity Noise Suppression in Spectrum Sliced Systems: A Multicanonical Monte Carlo Simulator of Extremely Low BER

We present a thorough numerical study of intensity noise mitigation of spectrum sliced wavelength-division multiplexing (SS-WDM) systems employing a nonlinear semiconductor optical amplifier (SOA) before the modulator. Our simulator of the SS-WDM link, embedded inside a Multicanonical Monte Carlo (MMC) platform, estimates the tails of the probability density functions of the received signals down to probabilities smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> . We introduce a new, simple, and efficient technique to handle intersymbol interference (ISI) in MMC simulations. We address the impact of optical postfiltering on SOA noise suppression performance. While previous research experimentally observed the SOA-induced noise cleaning in SS-WDM systems, this is the first complete simulator able to correctly predict the ensuing BER improvement. We measure the BER at different bit-rates and validate predicted BERs with and without post filtering.

Method of implementing frequency encoded multiplexer and demultiplexer systems using nonlinear semiconductor optical amplifiers

Multiplexing and demultiplexing are the essential parts of any communication network. In case of optical multiplexing and demultiplexing the coding of the data as well as the coding of control signals are most important issues. Many encoding/decoding mechanisms have already been developed in optical communication technology. Recently frequency encoding technique has drawn some special interest to the scientific communities. The advantage of frequency encoding technique over any other techniques is that as the frequency is fundamental character of any signal so it remains unaltered in reflection, refraction, absorption, etc. during transmission of the signal and therefore the system will execute the operation with reliability. On the other hand, the switching speed of semiconductor optical amplifiers (SOA) is sufficiently high with property of best on/off contrast ratio. In our present communication we propose a method of implementing a ‘4-to-1’ multiplexer (MUX) and a ‘1-to-4’ demultiplexer (DEMUX) exploiting the switching character of nonlinear SOA with the use of frequency encoded control signals. To implement the ‘4-to-1’ MUX and ‘1-to-4’ DEMUX system, the frequency selection by multiquantum well (MQW)-grating filter-based SOA has been used for frequency routing purpose. At the same time, the polarization rotation character of SOA has also been exploited to get the desired purpose. Here the fast switching action of SOA with reliable frequency encoded control input signals, it is possible to achieve a faithful MUX/DEMUX service at tera-Hz operational speed.

Stabilization of complex spatio-temporal dynamics near a subcritical Hopf bifurcation by time-delayed feedback

We investigate complex spatio-temporal dynamics in the framework of a generic model describing nonlinear semiconductor or electrochemical systems with S-shaped current-voltage characteristics. Global time-delayed feedback control is applied to stabilize unstable spatio-temporal patterns which are created in a subcritical Hopf bifurcation. This demonstrates the invalidity of the alleged odd-number limitation of time-delayed feedback control in systems with spatial degrees of freedom.

On the Role of High-Order Coherent Population Oscillations in Slow and Fast Light Propagation Using Semiconductor Optical Amplifiers

In this paper, we present a numerical investigation of the phase shift experienced by the detected envelope of a sinusoidally modulated optical carrier propagating in a nonlinear semiconductor optical amplifier. The model we employed accounts for high-order coherent population oscillations. As such, it allows for large gain levels and arbitrary modulation indexes of the input field. We highlight the role of the fields that are generated by high-order nonlinearities and compare the results with those of more common small-signal nonlinear models. We find that conventional models suffice only for low powers, small modulation indexes, and moderate amplifier gain levels.