Conventional SOA Research Articles

Design and analysis of all optical header recognition system employing combination of carrier reservoir SOA and conventional SOA

Design and analysis of all optical header recognition system employing combination of carrier reservoir SOA and conventional SOA

Computational study of wavelength conversion based on XGM by photonic crystal semiconductor optical amplifier

In this paper, a numerical study of wavelength conversion based on cross-gain modulation (XGM) has been conducted for the first time using the photonic crystal semiconductor optical amplifier (PC-SOA). A PC-SOA and an optical filter have been used in this design. Nonlinear effects, such as carrier depletion (CD), carrier heating (CH), and spectral hole burning (SHB), have been included in the PC-SOA. The rate and propagation equations have been solved using the finite difference method (FDM). The optimal wavelength conversion based on XGM has been obtained in the PC-SOA through the application of 3.2fJ and 1.0pJ energies for the input and the continuous wave (CW) signals, respectively, and a 15mA injection current for the biasing. The effects of the injection current and input signal energies on wavelength conversion have also been investigated for further examination of the impact of the XGM mechanism on wavelength conversion. It has finally been demonstrated that the PC-SOA exhibits better conditions and performance than the conventional bulk SOA in wavelength conversion based on XGM. Furthermore, the PC-SOA provides a far more appropriate alternative than the bulk SOA for all-optical integrated circuits due to the smaller length of the device and the lower value of injected current.

Design and simulation of the all-optical XOR logic gate by XPM mechanism using photonic crystal semiconductor optical amplifier based on Mach–Zehnder interferometer

In the presented structure, the performance of the all-optical XOR logic gate (AO-XOR-LG) is investigated. The XOR-LG is designed and simulated using a photonic crystal semiconductor optical amplifier (PC-SOA) based on Mach–Zehnder interferometer (MZI) and cross-phase modulation (XPM) nonlinear mechanism. The input optical pulse train used in this simulation is the type of RZ (Return-to-Zero). The finite difference method (FDM) has been used to solve the rate and propagation equations. The effect of input signal energy, bias current, and group refractive index on the output signal and gain of the XOR-LG is studied. The optimal mode is obtained for the XOR-LG with a bit rate of 80 Gbps. Furthermore, for the first time, the effects of quality factor (QF), conversion efficiency (CE), extinction ratio (ER), pattern effect (PE), and gain recovery are simultaneously analyzed in the simulation to increase PC-SOA performance. According to the results, PC-SOA has a more reasonable logic performance than conventional SOA, and due to its much shorter length than SOA, it can be a much better choice for integrated optical circuits.

Efficient Optically-Pumped Semiconductor Optical Amplifier in a Coupled-Waveguide Configuration: A Novel Proposal

We propose an efficient scheme of optical pumping and a compact design of an optically-pumped semiconductor optical amplifier (OP-SOA), with gain characteristics which are qualitatively similar to that of conventional (electrically-pumped) SOA. The optical pump is coupled into the ‘active waveguide’ from an adjacent channel waveguide, called ‘pump waveguide’; by suitably tailoring the coupling between the two waveguides, selective transfer of pump power all along the active waveguide can be achieved. We show that optical pumping through the coupled-waveguide configuration is efficient over the existing schemes of optical pumping in semiconductors. The optical pump can be coupled into the pump waveguide through a separate fiber-pigtail, just as the signal is coupled to the active waveguide in commercially available SOA. Thus, the OP-SOA would be a stand-alone 3-port integrated optical device, without any electrical connections. The proposed scheme enables optical-to-optical gain control, in place of the current-controlled gain in conventional SOA. Performance characteristics of the OP-SOA are simulated for an InGaAsP/InP heterostructure device using a well-established model. It is found that for an input optical pump power of 25 dBm at the wavelength of 1310 nm, a small signal gain >30 dB is achieved at the wavelength of 1550 nm.

Virtual Hand with Ambiguous Movement between the Self and Other Origin: Sense of Ownership and 'Other-Produced' Agency.

The feeling that a body part is one's own body (sense of ownership; SoO) and the feeling based on the causal relationship between one's will and action (sense of agency; SoA) have been recognized as the basis of our bodily self-consciousness. Previously, the illusory SoO over a fake body part (e.g., rubber hand) was introduced as the rubber hand illusion (RHI). Furthermore, it was determined that one could also evoke a SoA over an object with movements linked to the one's prior intention. On the other hand, the postdictivity of our spontaneity implies that it is essentially inseparable whether actions originate from self or others. In other words, our SoA or daily experiences are obtained in such as inseparable scenario. Previous research, however, has maintained the premise that self- and other-origin movements are perceptually distinguishable. Here, we implement a protocol to make these aspects ambiguous for the participants and to estimate whether they can feel SoO and/or SoA and how. To this end, we employ an experiment using virtual reality, under which participants observe virtual fingers moving very slowly (or quickly or not moving) while their own fingers do not move. For evaluation of the illusory SoO, measurements of skin conductance responses against a knife threat are adopted. Additionally, we introduce face-to-face interviews to determine whether the feelings regarding the slow movement match the conventional SoA definition. Our representative results suggest that the SoO is evoked over the hand, and various attitudes to accept its movement as the participant's own with awareness that they did not originate it are reported by the majority. As the results show, the novelty of this protocol is discovering that in such a situation, the SoO cooperates with an externally produced SoA to establish one's own bodily experience rather than the independence of the SoO and SoA.

Reflective semiconductor optical amplifiers-based all-optical NOR and XNOR logic gates at 120 Gb/s

In this paper, we reported a reflective semiconductor optical amplifier (RSOA), in which the input light propagates and reflects back to the input port after amplifying twice through its active region. The RSOA produces higher gain and lower noise figure at low drive currents with energy-efficient than the conventional SOAs. The RSOA’s features are employed herein to numerically analyze the ultrafast performance of the all-optical NOT-OR (NOR) and Exclusive-NOR (XNOR) logic gates using a dual-RSOAs-based scheme at 120 Gb/s. A comparison between RSOAs- and conventional SOAs-based AO NOR and XNOR gates is made by studying the quality factor (QF) against the critical operational parameters when the effects of the amplified spontaneous emission and the operating temperature are included to obtain more realistic results. Compared to conventional SOAs, the RSOAs allow to achieve more acceptable performance at 120 Gb/s and to render the implementation of the NOR and XNOR gates more feasible.

120 Gb/s all-optical NAND logic gate using reflective semiconductor optical amplifiers

In this paper, the unique features of the reflective semiconductor optical amplifiers (RSOAs) are exploited to numerically simulate the ultrafast performance of an all-optical NOT-AND (NAND) logic gate for the first time using a return-to-zero modulation format at a data rate of 120 Gb/s. A comparison is made between RSOAs and conventional SOAs through studying the dependence of the gate’s quality factor (QF) on the critical operational parameters, including the effects of both amplified spontaneous emission and operating temperature to get more realistic results. The results show that the all-optical NAND logic gate can be executed at 120 Gb/s using the RSOAs scheme with a higher QF than when using conventional SOAs.

Numerical analysis of four wave mixing in photonic crystal semiconductor optical amplifier

Abstract In this paper, we present a theoretical analysis of four-wave mixing (FWM) between short optical pulses in a photonic crystal semiconductor optical amplifier (PC-SOA). The proposed model is based on a nonlinear propagation equation by taking into account self-phase modulation (SPM), carrier density pulsations (CDP), carrier heating (CH), and spectral-hole burning (SHB). To analyse the FWM in a PC-SOA, pulse evolution in a temporal and spectral domain are investigated. Also, the optical fluid method is used in the photonic structure for design and engineering an appropriate bandwidth with constant group index to analyse the FWM mechanism. The bandwidth is designed in the L-Band region of telecommunication optical networks. Based on calculated results, it is depicted that for low energy short pulses, the conversion efficiency (CE) of PC-SOA is higher than conventional SOA. Furthermore, it is shown that, by increasing the injection current the CE is increased.

Computational study of pulse propagation in photonic crystal semiconductor optical amplifier

A theoretical analysis of photonic crystal semiconductor optical amplifier (PC-SOA) is presented. The proposed model is based on rate and propagation equations. The analysis is carried out using two input signal regimes of constant and Gaussian waves. To the best of the authors’ knowledge, temporal and spatial variation of picosecond pulses have not been previously investigated in active PC medium. The effect of injection current, group index, and amplifier length variation on the output signal and amplifier gain is investigated. Based on the results, temporal peak shift, chirp, and spectral width increased in low current regime compared to conventional SOAs. It is also demonstrated that short length PC-SOA can be used as a preamplifier in photonic integrated circuits.

Performance investigation of 120 Gb/s all-optical logic XOR gate using dual-reflective semiconductor optical amplifier-based scheme

Reflective semiconductor optical amplifiers (RSOAs) use an anti-reflective coating on the front facet and a high reflectivity coating on the rear facet to produce a higher gain than conventional SOAs. In this paper, this potential is exploited to numerically investigate the ultrafast performance of an all-optical logic XOR gate implemented using a dual-RSOA-based scheme at a data rate of 120 Gb/s. The simulation results demonstrate that the XOR gate is capable of operating at 120 Gb/s with better performance than when using conventional SOAs.

160 Gb/s photonic crystal semiconductor optical amplifier-based all-optical logic NAND gate

The performance of an ultra-fast all-optical logic NOT-AND gate using photonic crystal semiconductor optical amplifiers (PCSOA)-based Mach–Zehnder interferometers is numerically analysed and investigated. The dependence of the quality factor (Q-factor) on the input signals’ and PCSOA operating parameters is examined, with the impact of amplified spontaneous emission included so as to obtain realistic results. The achieved Q-factor is 18 at 160 Gb/s, which is higher than when using conventional SOAs.

Performance analysis of all-optical XOR gate with photonic crystal semiconductor optical amplifier-assisted Mach–Zehnder interferometer at 160 Gb/s

The photonic crystal (PC) can be used to prohibit, confine, or control the propagation of light in a photonic band-gap. The performance of an ultrafast exclusive disjunction (XOR) gate-implemented with a photonic crystal semiconductor optical amplifier (PC-SOA)-assisted Mach–Zehnder interferometer (MZI) is numerically investigated and analyzed at a data rate of 160 Gb/s. The impact of the data signals and PC-SOA’s critical parameters on the output quality factor (Q-factor) is examined and assessed. The simulation results demonstrate that the XOR gate which is based on the proposed scheme is capable of operating at the target data rate with logical correctness and high quality. This is achieved with better performance than when having conventional SOAs in the MZI, which justifies employing PC-SOAs as nonlinear elements.

Phase-Transparent Amplification of 16 QAM Signals in a QD-SOA

We study the nonlinear phase distortions in a columnar quantum dot semiconductor optical amplifier (QD-SOA) for coherent 16 quadrature amplitude modulation (QAM) signals. A few ps gain recovery in the QD-SOA enables suppression of the pattern dependent phase noise, which is a major performance limiting issue in conventional SOAs. A 25 dB phase and intensity transparent amplification of 40 Gb/s 16 QAM signals is experimentally demonstrated by error vector magnitude measurement.

OOK-to-QPSK modulation-format conversion based on two gain-transparent SOAs

In this paper, the system scheme of on–off keying (OOK) to quadrature phase-shift keying (QPSK) format conversion is proposed, which is based on two gain-transparent semiconductor optical amplifiers (GT-SOA). GT-SOA is used as a simple all-optical phase modulator, which is no effects of cross gain modulation and four-wave mixing existing in conventional SOA. The assistant light is used to speed up the SOA carrier recovery time. The principles of OOK to QPSK format conversion are expounded. The influences of the assistant light power and signal light power on the conversions are numerically analyzed. The OOK signal can still be exactly converted to the QPSK signal with the power of OOK signal being changed within a certain range.

Detailed theoretical investigation on relative intensity noise reduction enhancement based on reflective SOAs

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.

Saturated collision amplifier reach extender for XGPON1 and TDM/DWDM PON

Saturated Collision Amplifier (SCA) is a novel amplification scheme that uses SOA saturation in order to maximize the output power and minimize the ASE noise and the polarization sensitivity. We demonstrate the SCA reach extension in a commercial single-wavelength XGPON1 prototype system where bidirectional optical budget of up to 50 dB is obtained. The traffic performances are compared between the SCA and the conventional SOA extender. The novel extension scheme is demonstrated also for two- and four-wavelength 10 Gbit/s unidirectional downstream configurations with 45 km and 100 km transmission distances with 58-dB maximum total optical budget for each wavelength.

Analytical Investigation of an All-Optical T-Type Flip-Flop Using a Semiconductor Optical Amplifier Mach–Zehnder Interferometer with Push–Pull Configuration

To achieve an optical regenerator for a differential phase-shift keying signal based on a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI), we need an all-optical T-type flip-flop (T-FF) for encoding. We propose an all-optical T-FF consisting of an SOA-MZI with push–pull configuration and a feedback mirror to overcome the speed limitation of the previously proposed counter-faced configuration. Numerical simulation reveals its possibility of stable operation in 10 Gbps with a 27 - 1 pseudo random binary sequence (PRBS) signal even by using a conventional SOA with a slow carrier recovery of 100 ps, and the possibility of 40 Gbps operation is also investigated.

A novel approach to all-optical wavelength conversion by utilizing a reflective semiconductor optical amplifier in a co-propagation scheme

Nonlinear optical gain modulation in an InGaAsP/InP bulk reflective semiconductor optical amplifier (RSOA) is studied. The differences of the optical properties between RSOAs and conventional SOAs are initially investigated. All-optical wavelength conversion based on nonlinear gain modulation in RSOAs is demonstrated at a bit rate of 2.488Gbit/s. It is shown that a bit-error-rate of <10−9 can be achieved and an extinction ratio of >9dB can be obtained at a bit rate of 2.488Gbit/s with a 231–1 non-return-to-zero (NRZ) pseudorandom bit sequence (PRBS). In comparison with conventional SOAs, wavelength conversion by RSOAs shows much improved performances in high-speed all-optical wavelength conversions.

Time-domain simulation of channel crosstalk and inter-modulation distortion in gain-clamped semiconductor optical amplifiers

A time-domain model is implemented for gain-clamped semiconductor optical amplifiers (GC-SOAs) based on a combination of the separated traveling-wave equations and effective Bloch equations. The key feature of this model lies in its capability of handling the lasing–signal, signal–signal, and signal–noise interactions over a broad wavelength band. Therefore, various nonlinear phenomena such as the cross-gain saturation (XGS) and nondegenerate four-wave mixing (ND-FWM) can readily be captured. After being implemented and validated, this model is applied to the simulation of GC-SOA dynamic behaviors such as the channel crosstalk and intermodulation distortion (IMD). Simulation results show that the third-order IMD can be effectively suppressed by a gain-clamping lasing mode in GC-SOAs in comparison with that in conventional SOAs. The channel crosstalk can also be suppressed to some extent in GC-SOAs, but not as effectively. Other than a homogeneous reduction, the gain-clamping in GC-SOAs does not change the dependence of the channel crosstalk and IMD on the input signal power and channel spacing. It is also shown that the channel crosstalk, unlike the IMD, cannot be efficiently reduced by enlarging the channel spacing even in GC-SOAs.

Performance of a slow positron beam using a hybrid lens design

The University of Hong Kong positron beam employs conventional magnetic field transport to the target, but has a special hybrid lens design around the positron moderator that allows the beam to be focused to millimeter spot sizes at the target. The good focusing capabilities of the beam are made possible by extracting work-function positrons from the moderator in a magnetic field free region using a conventional Soa lens thus minimizing beam canonical angular momentum. An Einzel lens is used to focus the positrons into the magnetic funnel at the end of transportation magnetic field while at the same time bringing up the beam energy to the intermediate value of 7.5 keV. The beam is E × B filtered at this intermediate energy. The final beam energy is obtained by floating the Soa–Einzel system, E × B filter and flight tube, and accelerating the positrons just before the target. External beam steering saddle coils fine tune the position, and the magnetic field around the target chamber is adjusted so as to keep one of the beam foci always on the target. The system is fully computer controlled. Variable energy-Doppler broadened annihilation radiation (VEDBAR) data for a GaN sample are shown which demonstrate the performance of the positron beam system.