Saturated Semiconductor Optical Amplifier Research Articles

Placement of Semiconductor Optical Amplifiers in WDM Ring Topology Networks

In this paper, an analytical approach to evaluate the number of users supported by a typical WDM ring topology network has been given. To increase the number of supportable users, usage of semiconductor optical amplifiers (SOAs) have been explored. The network analysis is performed for three cases viz., without SOAs, with ideal SOAs and with gain saturated SOAs. In all the cases, the effect of extinction ratio is also considered. It has been observed that for zero extinction ratio, the network without SOAs supports 96 users. With ideal SOAs in the network, the number of users will increase to 608. When saturation effect in amplifier gain is considered, the number of supportable users will decrease to 320 only.

Wavelength channel data rewrite using saturated SOA modulator for WDM networks with centralized light sources

This paper describes a method for realizing the efficient utilization of wavelength resources in wavelength-division multiplexing networks with centralized light sources. Using a deeply saturated semiconductor optical amplifier (SOA) modulator located in a remote node (RN), we erase the data on a downstream signal with a low extinction ratio and modulate it with new data to generate an upstream signal. Thus, we use only one wavelength for bidirectional transmission between a center node and an RN, without placing lasers at the RN. In this paper, we analyze the data suppression characteristic of the SOA using a large signal model. We also estimate the bit error rate degradation in the presence of an unsuppressed downstream bit pattern in an upstream signal. We then report experimental results that confirm the basic characteristics of the wavelength channel data rewriter, which we constructed using a linear amplifier and an SOA. Finally, we provide the results of a data transmission experiment that we undertook using the data rewriter.

Suppression of cross-gain modulation in SOA using RZ-DPSK modulation format

Conventional ON-OFF keyed modulation format is susceptible to cross-gain modulation in saturated semiconductor optical amplifiers (SOAs) that leads to crosstalk penalty for dense wavelength-division-multiplexing (DWDM) input signals. Differential phase-shift keying of optical pulses has virtually no pulse-pattern effect and is robust to cross-gain modulation. We report experimental results that confirm reduction of crosstalk penalty in SOA with differential phase-shift-keyed DWDM input signals in comparison with ON-OFF keyed signals operating at 12.5 Gb/s with 25-GHz channel spacing.

Novel extended SOAs model for applications in very high-speed systems and its experimental validation

A novel model for current-induced gain saturated semiconductor optical amplifiers including the gain recovery dynamics is presented. An experimentally validation is also reported with practical application in an all-optical modulator for ultrafast transmission.

Analysis and optimization of intensity noise reduction in spectrum-sliced WDM systems using a saturated semiconductor optical amplifier

Theoretical and experimental results on the reduction of the intensity noise in spectrum-sliced wavelength-division-multiplexing systems using a saturated semiconductor optical amplifier (SOA) are presented. The influence of the injected current and the input power to the saturated SOA on the noise reduction and its bandwidth are studied. The optimum condition for a high noise suppression ratio and a large bandwidth is derived. For the optimum operation of the SOA, an increase of 13.5 dB in the intensity-noise-limited signal-to-noise ratio for a bitrate of 2.488 Gb/s and of 17.5 dB for a bitrate of 622 Mb/s are obtained experimentally in a single-stage SOA.

Optical preamplifier using inverted signal ofamplified spontaneous emission in saturatedsemiconductor optical amplifier

A novel optical preamplifier using the optical modulation of amplified spontaneous emission (ASE) in a semiconductor optical amplifier (SOA) is demonstrated. The input signal is converted to the modulation of the ASE due to saturation characteristic in an SOA. The receiver sensitivity was improved by 10 dB at 1 Gbit/s using the proposed preamplifier. The proposed device can not only amplify optical signal but also suppress the intensity noise of the input signal under saturation regime. The intensity noise of 1 Gbit/s spectrum-sliced light was significantly suppressed using the nonlinear characteristic of the preamplifier.

Modeling and measurement of longitudinal gain dynamics in saturated semiconductor optical amplifiers of different length

A new frequency-domain wave-propagation model that includes a position- and time-dependent carrier lifetime and the effect of amplified spontaneous emission is introduced and used to accurately simulate recovery time experiments in 0.5- and 1.0-mm long semiconductor optical amplifiers. It is compared to a constant lifetime model at different saturation levels, showing better performance and consistency. The role of the amplified spontaneous emission in saturated amplifiers is also discussed.

Interferometric method of suppressing the pattern effect in a semiconductor optical amplifier

A new idea of using change in index of refraction to suppress gain variation in a saturated semiconductor optical amplifier (SOA) is presented. This kind of gain compensation has the advantage of high speed because it involves two phenomena that always accompany each other. This compensation can be achieved with a nonsymmetrical Mach-Zehnder interferometer structure. Calculated results show that with this structure the input and output power of the SOA can be extended to nearly 10 dB from the former small-signal limit when less than 1-dB gain variation is permitted. Numerical simulations with an advanced dynamic model of the SOA agree with the calculated results.

Suppression of interferometric crosstalk and ASE noise using a polarization multiplexing technique and an SOA

Noise suppression at 10 Gbit/s and 20 Gbit/s is demonstrated using a gain saturated semiconductor optical amplifier (SOA) and a polarization multiplexing technique, where no impairments like waveform distortion and extinction ratio degradation caused by the gain saturation of the SOA appear. Moreover, the method is bit rate transparent and the input power dynamic range is very large. Furthermore, the SOA can provide a high gain.

A transfer function approach to the small-signal response of saturated semiconductor optical amplifiers

A theoretical analysis of the small-signal frequency response (SSFR) of a wavelength converter based on cross-gain modulation in a semiconductor optical amplifier with a finite waveguide loss is presented. We use a transfer function formalism to explain the resonant behavior of the frequency response. The limitations to the magnitude of the spectral overshoot are also accounted for. Operating with the data and CW signals in a co-propagating configuration, we find that the resonance only exists for a finite waveguide loss. In a counter-propagating scheme, a resonance can exist regardless of the presence of loss.

Spectral broadening of stochastic light intensity-smoothed by a saturated semiconductor optical amplifier

We present calculations of the intensity smoothing of stochastic light by a semiconductor optical amplifier (SOA). We predict spectral changes of the light that are due to amplitude-to-phase coupling in the gain medium. The intensity smoothing of noisy optical signals with an SOA carries a penalty of spectral broadening (increased phase noise) that increases with increasing alpha parameter (linewidth enhancement factor). The spectral broadening also increases with increasing strength of the intensity fluctuations being smoothed.

Noise properties of nonlinear semiconductor optical amplifiers

We demonstrate experimentally and describe analytically two important noise contributions in saturated semiconductor optical amplifiers. The first is spontaneous emission power enhancement that is due to the increased and spatially dependent inversion factor. The second is caused by a nonlinear interaction between the saturating signal and the amplifier noise that, in the optical domain, causes a distinct modification of the noise spectrum over a narrow bandwidth. This modification manifests itself as a noise power decrease in the detected electronic domain.

Photonics applications in switching: An ATM optical node

Abstract An ATM optical node architecture that carries out cell routing and buffering by photonic means, controlled by electronic circuits, is presented. An evolutionary approach, where cell aggregation and compression are introduced to achieve a large throughput, with a high performance, is also described. And we report experimental results that demonstrate the feasibility of all the relevant photonic functions, based on advanced optoelectronic devices, namely: fast wavelength reassignment, suitable for multigigabit operation, based on fast tunable lasers and semiconductor optical amplifiers; high bit rate packet storage in a multiwavelength fiber loop memory including fast optical gates; dynamic wavelength selection, based on distributed feedback (DFB) filters with nanosecond tuning response; and all optical demultiplexing of multigigabit/s time division multiplexing (TDM) signals by means of saturated semiconductor optical amplifiers.