All-Optical Sampling Using Nonlinear Polarization Rotation in a Single Semiconductor Optical Amplifier

We propose a novel all-optical sampling method using nonlinear polarization rotation in a semiconductor optical amplifier. A rate-equation model capable of describing the all-optical sampling mechanism is presented in this paper. Based on this model, we investigate the optimized operating parameters of the proposed system by simulating the output intensity of the probe light as functions of the input polarization angle, the phase induced by the polarization controller, and the ori- entation of the polarization beam splitter. The simulated results show that we can obtain a good linear slope and a large linear dynamic range,which is suitable for all-optical sampling. The operating power of the pump light can be less than lmW. The presented all-optical sampling method can potentially operate at a sampling rate up to hundreds GS/s and needs low optical power.

An Electroabsorption Modulator Monolithically Integrated with a Semiconductor Optical Amplifier and a Dual-Waveguide Spot-Size Converter

A semiconductor optical amplifier and electroabsorption modulator monolithically integrated with a spotsize converter input and output is fabricated by means of selective area growth,quantum well intermixing,and asymmetric twin waveguide technology. A 1550-1600nm lossless operation with a high DC extinction ratio of 25dB and more than 10GHz 3dB bandwidth are successfully achieved. The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3°× 18.0°, respectively, resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.

Design of Tensile Strained InGaAsP/InGaAsP MQW for 1.55μm Polarization Independent Semiconductor Optical Amplifier

The theoretical optimization of tensile strained InGaAsP/InGaAsP MQW for 1.55μm windows polarization-independent semiconductor optical amplifier is reported.The valence-band structure of the MQW is calculated by using k·p method,in which 6×6 Luttinger effective-mass Hamiltonian is taken into account.The polarization dependent optical gain is calculated with various well width,strain,and carrier density.

Wide-Band Polarization-Independent Semiconductor Optical Amplifier Gate with Tensile-Strained Quasi-Bulk InGaAs

A semiconductor optical amplifier gate based on tensile strained quasi bulk InGaAs is developed.At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band filling effect.Moreover,the most important is that very low polarization dependence of gain (<0 7dB),fiber to fiber lossless operation current (70～90mA) and a high extinction ratio (>50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm) and the whole L band (1570～1610nm).The gating time is also improved by decreasing carrier lifetime.The wide band polarization insensitive SOA gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.

Towards 640 Gbit/s wavelength conversion based on nonlinear polarization rotation in a semiconductor optical amplifier

Taking into account ultra-fast carrier dynamics, this paper models 640 Gbit/s wavelength conversion scheme based on nonlinear polarization rotation （NPR） in a single semiconductor optical amplifier （SOA） and investigates the performance of this kind of wavelength conversion scheme in detail. In this model, two carrier temperature equations are introduced to substitute two energy density equations, which reduce the complexity of calculation in comparison with the previous model. The temporary gain and phase shift dynamics induced by ultra-short optical pulses are numerically simulated and the simulated results are qualitatively in good agreement with reported experimental results. Simulated results show that non-inverted and inverted 640 Gbit/s wavelength conversions based on NPR are achieved with clear open eye diagrams. To further investigate the performance of the non-inverted wavelength conversion scheme, the dependence of output extinction ratio （ER） on some key parameters used in simulation is illustrated. Furthermore, simulated analyses show that high performance non-inverted wavelength conversion based on NPR can be achieved by using a red-shifted filtering scheme.

Photonic multi-shape UWB pulse generation using a semiconductor optical amplifier-based nonlinear optical loop mirror

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband（UWB） signal generation using a semiconductor optical amplifier（SOA） based nonlinear optical loop mirror（NOLM）.By employing the cross phase modulation（XPM） effect,cross gain modulation（XGM）,or both,multi-shape UWB waveforms are generated including monocycle,doublet,triplet,and quadruplet pulses.Both the shapes and polarities of the generated pulses are flexible to adjust,which may be very useful in UWB pulse shape modulation and pulse polarity modulation.

Photonic generation of power-efficient FCC-compliant ultra-wideband waveforms using semiconductor optical amplifier (SOA):theoretical analysis and experiment verification

We theoretically design a power-efficient ultra-wideband pulse generator by combining three monocycle pulses with different weights. We also experimentally demonstrate a feasible scheme to generate such power-efficient ultra-wideband waveforms using cross-phase modulation in a single semiconductor optical amplifier. The designed ultra-wideband pulse fully satisfies the requirements for the spectral mask specified by the Federal Communications Commission with high power efficiency. In the experiment, a power-efficient ultra-wideband waveform with a pulse duration of 310 ps is achieved, and the power efficiency is greatly improved compared with that of a single nlonocycle pulse or a mixture of two monoeycles.

Quantum-dot Semiconductor Optical Amplifiers in State Space Model

A state space model(SSM) is derived for quantum-dot semiconductor optical amplifiers(QD-SOAs).Rate equations of QD-SOA are formulated in the form of state update equations,where average occupation probabilities along QD-SOA cavity are considered as state variables of the system.Simulations show that SSM calculates QD-SOA′s static and dynamic characteristics with high accuracy.

Semiconductor Optical Amplifier and Gain Chip Used in Wavelength Tunable Lasers

The design concept of semiconductor optical amplifier(SOA)and gain chip used in wavelength tunable lasers(TL)is discussed in this paper.The design concept is similar to that of a conventional SOA or a laser;however,there are a few different points.An SOA in front of the tunable laser should be polarization dependent and has low optical confinement factor.To obtain wide gain bandwidth at the threshold current,the gain chip used in the tunable laser cavity should be something between SOA and fixed-wavelength laser design,while the fixed-wavelength laser has high optical confinement factor.Detailed discussion is given with basic equations and some simulation results on saturation power of the SOA and gain bandwidth of gain chip are shown.

All-optical XNOR and AND gates simultaneously realized in a single semiconductor optical amplifier with improved dynamics

All-optical XNOR and AND logic gates using four-wave mixing （FWM） and cross-gain modulation （XGM） in a single semiconductor optical amplifier （SOA） with improved dynamics are simultaneously realized. By numerical simulation, the effects of the input optical wave powers and injection current on the critical factors of the logic gate performances, such as the ON-OFF contrast ratio, the power-output level of the logic ＇1＇, and the difference between power outputs of the logic ＇1＇, are investigated in detail. In addition, the effect of the counter-propagating CW pump on the gain recovery is analysed.

Semiconductor optical amplifier used as regenerator for degraded differential phase-shift keying signals

Phase and amplitude regeneration are necessary for degraded differential phase-shift keying communication sys- tems. This paper proposes a regenerator based on semiconductor optical amplifier for differential phase-shift keying signals. The key regeneration mechanism is theoretically analysed. The effectiveness of semiconductor optical amplifier based regenerator is demonstrated by comparing the bit error rate and eye diagrams before and after regeneration for 40-Cbit/s differential phase-shift keying 1080-km transmission systems. The results show that regeneration effects are very well. Bit error rate is tess than 10-12 with the regenerator.

Optimization of regenerator based on semiconductor optical amplifier for degraded differential phase shift keying signal

Real time phase regeneration is necessary for degraded phase modulation format optical communication systems. A regenerator based on the discrimitive gain effect of a semiconductor optical amplifier was proposed in recent years. In this paper, for this type of regenerator, its optimal working condition is found by solving the dynamic equations which describe the variance of the optical field and carrier density in the semiconductor optical amplifier by the finite difference method. The results show that the optimal improvement of signal Q factor can reach more than 2.2 dB.

All-optical error-bit amplitude monitor based on NOT and AND gates in cascaded semiconductor optical amplifiers

This paper proposes and simulates a novel all-optical error-bit amplitude monitor based on cross-gain modulation and four-wave mixing in cascaded semiconductor optical amplifiers （SOAs）, which function as logic NOT and logic AND, respectively. The proposed scheme is successfully simulated for 40 Gb/s return-to-zero （RZ） signal with different duty cycles. In the first stage, the SOA is followed by a detuning filter to accelerate the gain recovery as well as improve the extinction ratio. A clock probe signal is used to avoid the edge pulse-pairs in the output waveform. Among these RZ formats, 33% RZ format is preferred to obtain the largest eye opening. The normalized error amplitude, defined as error bit amplitude over the standard mark amplitude, has a dynamic range from 0.1 to 0.65 for all RZ formats. The simulations show small input power dynamic range because of the nonlinear gain variation in the first stage. This scheme is competent for nonreturn-to-zero format at 10Gb/s as well.

Reconfigurable all-optical dual-directional half-subtractor for high-speed differential phase shift keying signal based on semiconductor optical amplifiers

All-optical digital logic elementary circuits are the building blocks of many important computational operations in future high-speed all-optical networks and computing systems. Multifunetional and reconfigurable logic units are essential in this respect. Employing the demodulation properties of delay interferometers for input differential phase shift keying signals and the gain saturation effect in two parallel semiconductor optical amplifiers, a novel design of 40 Cbit/s reconfigurable all-optical dual-directional half-subtractor is proposed and demonstrated. All output logic results show that the scheme achieves over 11=dB extinction ratio, clear and wide open eye diagram, as well as low polarization dependence （〈 1 dB）, without using any additional input light beam. The scheme may provide a promising candidate for future ultrafast all-optical signal processing applications.

1550nm Polarization-Insensitive Semiconductor Optical Amplifier Based on AlGaInAs-InP

Polarization insensitive AlGaInAs InP semiconductor optical amplifier is realized at a wavelength of 1550nm.The active layer consists of three tensile strained wells with strain 0 40%.The amplifiers are fabricated to ridge waveguide structure with 7° tilted cavity.The two facets are coated with two layers of anti reflection Ti 3O 5/Al 2O 3 films.Residual facet reflectivity is found to be less than 0 03%.The semiconductor optical amplifer exhibits 20dB of signal gain and 7 2dBm of saturation output power with an excellent polarization insensitivity (less than 0 8dB) at 200mA and 1540nm window.

Photonic ultra-wideband monocycle pulses generation using semiconductor optical amplifier and electro-absorber in parallel

A scheme for photonic generation of ultra-wideband （UWB） pulses using a semiconductor optical amplifier （SOA） and an electro-absorber （EA） in parallel is proposed and numerically demonstrated. By adjusting the time delay between two pump signals incident into the SOA and the EA, we can obtain monocycle pulses with reversed polarities and different bandwidths. The proposed method is flexible in pulse shaping and easy in practical optimization.

Multi-wavelength fiber ring laser based on a chirped moiré fiber grating and a semiconductor optical amplifier

A simple and cost-effective multi-wavelength fiber ring laser based on a chirped Moire fiber grating （CMFG） and a semiconductor optical amplifier （SOA） is proposed. Stable triple-wavelength lasing oscillations at room temperature are experimentally demonstrated. The measured optical signal-to-noise ratio （SNR） reaches the highest value of 50 dB and the power fluctuation of each wavelength is less than 0.2 dB within a 1-h period. To serve as a wavelength selective element, the CMFG possesses excellent comb-like filtering characteristics including stable wavelength interval and ultra-narrow passband, and its fabrication method is easy and flexible. The lasing oscillation shows a narrower bandwidth than SOA-based multi-wavelength fiber lasers utilizing some other kinds of wavelength selective components. Methods to optimize the laser performance are also discussed.

Optical Nonlinearity in a Novel Optical Signal Regeneration System Based on Cross-Gain Modulation Using Cascaded Semiconductor Optical Amplifiers

We propose a novel optical signal regeneration system based on wavelength converters by use of cross gain modulation in cascaded semiconductor optical amplifiers. The nonlinearity in optical input/output characteristics and eye opening using NRZ signal were archived.

Spectral Properties of Fabry-Pérot Laser Diodes and Conventional Semiconductor Optical Amplifiers

This paper presents an unified comprehensive model for the analysis of the spectral properties of Fabry-Perot laser diodes and conventional semiconductor optical amplifiers. We develop the model by considering the wide-band amplified spontaneous emission fields and the input optical signal fields in a general frame. Specifically, this paper discusses theoretical aspects of the model in details, which are based upon the spectra of material gain and spontaneous emission power, nonlinear gain suppression, and longitudinal spatial hole burning. This paper also presents simulation results of the model for the case of conventional semiconductor optical amplifier and the case of Fabry-Perot laser diode to demonstrate its capabilities.

Multi-Wavelength Conversion Using FP-LD with Linear Optical Amplifier

We propose and demonstrate a multi-wavelength converter using FP-LD with linear optical amplifier (LOA) which based on cross-gain modulation can convert an input signal to many wavelengths simultaneously for reconfigurable wavelength conversion in OXC and broadcasting in WDM systems.