In-line Semiconductor Optical Amplifiers Research Articles

A pulse amplitude modulation scheme based on in-line semiconductor optical amplifiers (SOAs) for optical soliton systems

<p>The objective of this work is to simulate a pulse amplitude modulation (PAM) scheme based on in-line semiconductor optical amplifiers for optical soliton systems. The max. power for soliton systems, based on various bits/symbol PAM modulation schemes after a fiber length of 100 km, is simulated and clarified. In addition to the max. Q factor for soliton systems, PAM modulation schemes with various in-line SOA injection currents and a fiber length of 100 km are also simulated and demonstrated in the results. The total electrical power after photo-detectors for soliton systems, based on PAM modulation schemes with various in-line SOA injection currents and a fiber length of 100 km, is also simulated and clarified in the results. The study emphasizes that the higher the SOA injection current, the higher the electrical power and the lower the Q factor that can be achieved in the soliton system.</p>

Characterization of Wideband Semiconductor Optical Amplifiers based on OptiSystem and MATLAB

A study about different types of semiconductor optical amplifiers (SOA)s - linear, nonlinear and in-line SOAs modelling is carried out. The SOA key performance characteristics covered in this paper include optical gain, power, and amplified spontaneous emission (ASE) noise figure. These characteristics definition are included in this work together with the tabulation of each SOA specification parameter operating in the operational conventional (C-) band. The first modelling of SOA wideband travelling wave (TW) component is done through a simple configuration using OptiSystem software. Next, the second modelling method is simulated through numerical steady-state model using MATLAB software. Each graphical result is explained and discussed according to the operational characteristic theories of SOA along with the evaluation for the best performance among the types of SOAs. The contrasted result among them had shown that linear SOA has the most ideal and competitive characteristics, as compared to the nonlinear and in-line SOAs, especially a better choice as gain medium in the multiwavelength fiber laser (MWFL) application.

Improving the power efficiency of SOA-based UWB over fiber systems via pulse shape randomization

A simple pulse shape randomization scheme is considered in this paper for improving the performance of Ultra Wide band (UWB) communication systems using On Off Keying (OOK) or Pulse Position Modulation (PPM) formats. The advantage of the proposed scheme, which can be either employed for Impulse Radio (IR) or for carrier-based systems, is first theoretically studied based on closed-form derivations of power spectral densities. Then, we investigate an application to an IR-UWB over optical fiber system, by utilizing the 4-th and 5-th orders of Gaussian derivatives. Our approach proves to be effective for 1 Gbps-PPM and 2 Gbps-OOK transmissions, with an advantage in terms of power efficiency for short distances. We also examine the performance for a system employing an in-line Semiconductor Optical Amplifier (SOA) with the view to achieve a reach extension, while limiting the cost and system complexity.

Off-set Filtering Effect in SOA Based Optical Access Network

In-line and reflective semiconductor optical amplifiers (SOA and RSOA) can be effectively utilized as external optical intensity modulators. However the limited modulation bandwidth affects the application possibilities, because next generation access networks desire high trans- mission speed. Bandwidth enhancement can be achieved by means of optical equalization thanks to the chirping char- acteristics of semiconductor optical amplifier. The limited modulation transfer function can be combined with the converted phase modulation transfer function. Investiga- tion of optical filter with optimal slope is a crucial chal- lenge in this approach. The presented simulations describe the slope dependence of the modulation band. The model can take into account the different type of realizable opti- cal filters. However there is a trade-off between modula- tion efficiency and modulation bandwidth due to the extra insertion loss of the set-off optical filter. In the paper theo- retical and simulation investigations are presented with the result of improved modulation bandwidth.

Simple Uplink SOA Pattern Effects Compensation for Reach-Extended 10G-EPONs

A simple and effective technique enabling strong pattern effects mitigation in uplink in-line semiconductor optical amplifiers (SOAs) for reach-extended, high-speed, passive optical networks, is proposed and experimentally demonstrated. The technique relies in selectively injecting into the saturated amplifier a low-power CW assist light (AL) at shorter wavelength than the data signal. The presence of the AL, which is enabled when the power level of input data triggers pattern effects in the SOA, clamps the carrier density with almost negligible gain reduction at the 1.3 μm data wavelength. By injection of an AL signal at 1.27 μm with 1 mW power in the booster SOA of a two-SOA cascade reach-extender, an increase as large as 7 dB in the access span loss dynamic range for error-free transmission at 10 Gb/s is reported with a trunk span loss of 23 dB.

Flat gain, wide bandwidth of in-line semiconductor optical amplifier in CWDM Systems

Semiconductor optical amplifier (SOA) is one of the commonly used amplifiers in optical networks. This paper reviews the SOA implementation in coarse wavelength division multiplexing (CWDM) systems, which includes the explanation of the fundamental concepts such as the configuration, principle of operation as amplifiers, and the performance in different CWDM topologies. Simulation using OptiSystem software was carried out to determine the gain saturation at high input power and longer wavelengths. It shows that SOA implementation in CWDM networks is capable of providing flat gain for 40 nm wavelength span.

107 Gb/s uncompensated transmission over a 470 km hybrid fiber link with in-line SOAs using MLSE and duobinary signals

We experimentally demonstrate uncompensated 8-channel wavelength division multiplexing (WDM) and single channel transmission at 10.7 Gb/s over a 470 km hybrid fiber link with in-line semiconductor optical amplifiers (SOAs). Two different forms of the duobinary modulation format are investigated and compared. Maximum Likelihood Sequence Estimation (MLSE) receiver technology is found to significantly mitigate nonlinear effects from the SOAs and to enable the long transmission, especially for optical duobinary signals derived from differential phase shift keying (DPSK) signals directly detected after narrowband optical filter demodulation. The MLSE also helps to compensate for a non-optimal Fabry-Perot optical filter demodulator.

Semiconductor Optical Amplifier for Detection Function in Radio Over Fiber Systems

This paper demonstrates that in broadband networks in-line semiconductor optical amplifiers (SOAs) beside providing system gain can also be used as simultaneous transceivers. The SOA branching stages are studied and presented for bus configuration. Using a steady-state model, we have made a small-signal approximation applying an equivalent circuit for detection based on the rate equations. The theory enables us to explain the detection functionality, the optimal working state of the multifunctional SOA, and to analyze noise properties. The measurements support the calculations. So the SOA-transceivers are potentially useful in subcarrier multiplexed access systems.

Assessment of gain saturation in cascaded semiconductor optical amplifier for high-bit-rate wavelength-division-multiplexing signals over long transmission distance

In this paper, the investigation of 10 channels at 80-Gb/s wavelength-division-multiplexing (WDM) transmission over 910-km single-mode fiber and dispersion compensating fiber using cascaded in-line semiconductor optical amplifiers at a span of 70 km for soliton return zero differential phase-shift keying (RZ-DPSK) modulation format is achieved. With the narrow channel spacing (i.e., 200 GHz), the results of quality is more than 15 dB the received signals after covering 910-km transmission distance without any power drop. The semiconductor optical amplifier (SOA) structure parameters for in-line amplifier is optimized to obtain low cross talk in multichannel WDM systems at nil power penalty with sufficient gain. For the differential gain 200 atto cm 2 and length 750 mm of SOA has minimum SOA-induced cross talk is observed. The impact of optical power received and the Q factor at different differential gain, carrier lifetime, and length has been illustrated. It is found that for a transmission distance of 700 km, with decrease the channel spacing, there is an increase in cross talk among channels, hence the signal quality continues to decrease. A clear eye diagram and a good optical spectrum are observed at a transmission distance of 910 km in a soliton RZ-DPSK system.

Power budget improvement for long-haul WDM transmission with optimum placement of SOAs

Sufficient power margin is investigated for ten-channels WDM transmission over 68,908 km by using cascaded in-line semiconductor optical amplifier for the differential phase-shift keying (DPSK) modulation format for the first time. For this, we used the structural optimization and placement scheme of semiconductor optical amplifiers (SOAs) for long-haul WDM transmission. The SOA model for in-line amplifier has low crosstalk, ASE noise power and low noise figure with sufficient gain. The impact of noise figure, amplification factor, ASE noise power, optical gain and crosstalk with signal input power for the SOA model has been illustrated, which shows that 400 mA is the optimum bias current. We observed that the optimized optical filter bandwidth for the 100 GHz channel spacing is 0.4 nm. We observe that as we decrease the channel spacing, the quality of signal is degraded. We show that the optimum span scheme-1 is used up to a transmission distance of 68,908 km with good quality for power margin more than 24 dB. This placement scheme of SOAs shows good power budget for long transmission distance. We show the optical spectrum and clear eye diagram at the transmission distance of 68,908 km for optimum span schemes. Finally, we investigate the maximum transmission distance with decrease in channel spacing, i.e., 20 and 50 GHz.

Interleaved Bidirectional Transmission of 16 $\times$ 10-Gb/s DWDM Signals Using DPSK Modulation Format and In-line Semiconductor Optical Amplifiers

We have performed both experimental and numerical analyses of interleaved bidirectional transmission of 16 times 10-Gb/s dense-wavelength-division-multiplexed (DWDM) signals using differential-phase-shift-keying (DPSK) modulation format and in-line semiconductor optical amplifiers (SOAs). The constant intensity of DPSK-modulated DWDM signals enabled us to mitigate the crosstalk effects in the bidirectional SOA. We have demonstrated error-free bidirectional transmission of 16 channels over an 80-km single-mode fiber (SMF) with matching dispersion-compensating fiber and in-line amplification provided by an SOA. SOAs can be used for bidirectional transmission if the facet reflections can be controlled. In order to understand further the effect of the SOA facet reflectivity on transmission results, we developed a simulation model for our system. Based on the good agreement between our simulation and experimental results, we have found out that the system reflections can be minimized by careful optimization of the bias current and reflectivity of the SOA

Comparative Analysis of BER Estimation Methods in Numerical Simulation of 40-Gb/s RZ-DPSK Transmission With In-Line SOAs

Applying direct error counting, we compare the accuracy and evaluate the validity of different available numerical approaches to the estimation of the bit-error rate (BER) in 40-Gb/s return-to-zero differential phase-shift-keying transmission. As a particular example, we consider a system with in-line semiconductor optical amplifiers. We demonstrate that none of the existing models has an absolute superiority over the others. We also reveal the impact of the duty cycle on the accuracy of the BER estimates through the differently introduced Q-factors

RZ-DPSK transmission at 80 Gbit/s channel rate using in-line semiconductor optical amplifiers

We numerically demonstrate the feasibility of return-to-zero differential phase-shift keying transmission at 80Gbit/s channel rate using cascaded in-line semiconductor optical amplifiers.

Transmission performance of 20×10Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

Abstract We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on–off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor. The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems. The bit error rate (BER) for all channels observed is less than 10 −10 up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.

10 Gbps optical soliton transmission link using in-line SOA on standard SMF at 1.3 μm

In this paper, 10 Gbps optical soliton transmission link using in-line semiconductor optical amplifiers (SOAs) for already installed standard single mode fibers (SMF) at 1.3 μm wavelength has been reported. The pattern effect and the impact of chirp on pulse propagation after amplification have been investigated. The observations are based on modeling and simulation optical soliton transmission link. Optical soliton pulse transmission over distances of the order of several hundreds of kilometers has been shown with and without initial chirp.

Feasibility of soliton-like DPSK transmission at 40 Gb/s with in-line semiconductor optical amplifiers

We analyze a soliton-like phase-shift keying 40-Gb/s transmission system using cascaded in-line semiconductor optical amplifiers. Numerical optimization of the proposed soliton-like regime is presented

10 Gbps WDM transmission performance limits using in-line SOAs and an optical phase conjugator based on four-wave mixing in SOAs as a mid-span spectral inversion technique

We have theoretically investigated the transmission performance limits of all semiconductor optical amplifiers (SOA)-based 10 Gb/s wavelength division multiplexing (WDM) systems using in-line SOAs and an optical phase conjugator (OPC) based on four-wave mixing in SOAs as a mid-span spectral inversion technique. With a verified numerical model of SOAs, we have found that the crosstalk from SOAs in OPC is a dominant factor to limit the number of channels in WDM systems. In order to increase the available number of channels, we optimize the input optical power and the injection current to SOAs in OPC with using a reservoir channel in in-line SOAs. All SOA-based 10 Gb/s WDM systems using the OPC can transmit 16 channel signals up to 240 km distance with a 3 dB power penalty.

WDM Transmission of 16<tex>$,times,$</tex>10.709 Gb/s Over 640-km SSMF Using Cascaded Semiconductor Optical Amplifiers and DPSK Modulation Format

To extend transmission distance using cascaded in-line semiconductor optical amplifiers (SOAs) and differential phase-shift-keying modulation format, optimal operation conditions for SOAs, such as input power and operation current, are studied. 16/spl times/10.709-Gb/s wavelength-division-multiplexing transmission over 640-km SSMF with the optimal system design parameters is demonstrated. This is, to the best of our knowledge, the largest bit-rate distance product reported.

1050-km WDM Transmission of 8<tex>$,times,$</tex>10.709Gb/s DPSK Signal Using Cascaded In-Line Semiconductor Optical Amplifier

We have performed eight-channel wavelength-division-multiplexing transmission over 1050-km single-mode fiber using cascaded in-line semiconductor optical amplifier and differential phase-shift keying modulation format for the first time; more than 6 dB of power margin was achieved over forward-error correction threshold. Factors that affect the transmission performance were discussed. It was found that four-wave mixing is the main factor that limits the maximum transmission distance. Larger capacity distance product can be realized by further optimizing the configuration of transmission link.

Bi-directional transmission of 8x10Gb/s DPSK signals over 80km of SMF-28 Fiber using in-line semiconductor optical amplifier

We report the bi-directional transmission of 8x10Gb/s signals using an in-line SOA over 80km SMF-28 with matching DCF for the first time. Our results suggest very promising applications for bi-directional transmission in metro and access networks with simple configuration and low cost.