Gain Saturation Of Semiconductor Optical Amplifier Research Articles

MEMS-SOA Spectrum-Sliced Auto-Equalized Source Enabling Uniformly Tunable Microwave Photonic Filter

In this work, we report a Micro-Electro-Mechanical System (MEMS)-Semiconductor Optical Amplifier (SOA) active interferometer as a low cost and miniaturized tunable broadband sliced source and optical loss auto-equalizer for single pass band microwave photonic filter (MPF). A low finesse Fabry-Perot MEMS interferometer is formed from a movable deeply etched micro-mirror in front of a cleaved fiber facet. The interferometer slices the amplified spontaneous emission (ASE) output of the SOA, while the output is feedback to the SOA again for amplification and optical loss auto-equalization through the SOA gain saturation effect. This configuration improved the uniformity of the MPF passband attenuation along the tuning range down to 3.72 dB only. The filter center frequency can be finely tuned electrically for ±241.6 MHz with a MEMS electrostatic comb actuator driving the mirror. The center frequency is controlled by the distance between fiber facet and micro-mirror. The operation of the proposed MEMS-SOA based MPF is experimentally verified as a proof of concept from 1.2 to 4.5 GHz and can be easily extended to higher frequencies. A tuning resolution of 6.04 MHz/ $\mu \text{m}$ is achieved with stopband attenuation larger than 20 dB and 3-dB bandwidth mean value of 141 MHz.

Further Investigation of Intensity Noise Reduction on an Incoherent Light Source using a Gain Saturated Semiconductor Optical Amplifier in a Spectrum-sliced Channel at 2.5 Gb\\s

The “spectrum-slicing” technique, employing incoherent light, has been shown to be a highly practical, cheap and hence very attractive proposal for future all-optical networks. In this study, the use of semiconductor optical amplifier gain saturation for intensity noise reduction on incoherent light is further studied in terms of the Relative-Intensity-Noise (RIN), with a view to obtaining the optimum SOA injection current and input power conditions to achieve the best possible intensity noise reduction, in conjunction with OSNR, BER and Q-factor results. The results reported herein give designers knowledge of the best SOA operating conditions to enhance overall system performance, whilst still obtaining signal gain from the SOA.

Low-Pattern-Dependence Prechirp Optical Modulation by Using Saturation Behaviors of SOA-Integrated EAM

Low-pattern-dependence and chirp-control optical modulation using a monolithic integration of devices is proposed and demonstrated in this study. The monolithic integration consisting of semiconductor optical amplifier (SOA) and electroabsorption modulator (EAM) is used. As high enough optical power is coupled into a device to reach saturation condition, the field driving operation in an EAM (reversed-bias diode) and the current injection operation in an SOA (forward-bias diode) will have mutually complementary optical properties because of the reversed carrier dynamics, enabling optical waveform and its phase control. A 100 μm long EAM integrated with a 700 μm long SOA is fabricated for the device under test. A 10 Gb/s non-return-to-zero pattern trains are used for examining time-evolution optical waveform. A distorted waveform by gain saturation of SOA can be corrected by reversely predistorted signal modulated by EAM, sending out a nondistorted optical waveform. An improved signal-to-noise ratio (SNR) of data pattern from 8.8 to 10.8 is obtained by adjusting bias points of EAM and SOA, confirming pattern waveform enhancement. Total negative chirp of 6.2 GHz is also obtained from EAM and SOA, where -2.6 GHz frequency shift from SOA is extracted. Setting EAM and SOA in a negative chirp regime, a successful 43 km (photoreceiver limit) error free data transmission is found, suggesting that such an integration chip can enable simultaneously amplitude, pattern and prechirp optical processing, and showing high potential in the application of metro-area optical network.

Regenerative Wavelength Conversion of DPSK Signals Through FWM in an SOA

We experimentally investigate broadband regenerative capability of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for nonreturn-to-zero differential phase-shift keying signals at 10 Gb/s. This scheme exploits the amplitude-limiting properties of the FWM process, when proper SOA gain saturation and α-factor depletion result in almost negligible additional phase noise for the converted signal after delay-interferometer demodulation. We report characterization in both the wavelength down- and up-conversion operations, demonstrating sound <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor improvement (through a factor comprised between 1.4 and 2.4) over a conversion range of about 50 nm.

Analytical approach of developing wavelength encoded AND, NAND and X-OR logic operations and implementation of the theory using semiconductor optical amplifiers

Frequency encoding technique is a very promising and faithful technology for very fast long-haul optical communication and super fast computation. Implementation of different logic gates based on the principle of frequency conversion is the key mechanism of frequency encoded data processing and networking. It is established that semiconductor optical amplifiers (SOA) have been used successfully for the purpose of frequency conversion. One of the important techniques of frequency conversion is the conjugate beam generation by four wave mixing (FWM) in SOA and ultimately conversion of it into desired frequency by means of reflecting semiconductor optical amplifier (RSOA). However the efficiency of conjugate beam generation is restricted by polarization dependent gain saturation of SOA. This dependency can be successfully removed using polarization diversity scheme. Another technique of the frequency conversion is based on nonlinear rotation of the state of polarization of the linearly polarized probe beam. An important advantage of using polarization rotation in SOA is that a small change in rotation of the state of polarization will lead to a large difference in output power. Here in our present communication we propose a method of developing wavelength encoded AND, NAND and X-OR logic operations exploiting the above mentioned functions of SOA. For this purpose we have developed an analytical treatment based on which above mentioned three logic gates are conducted. The satisfactory simulation result proves also the validity of the developed theory.

Patterning characteristics and its alleviation in high bit-rate amplification of bulk semiconductor optical amplifier

An investigation is carried out on high bit-rate pulse propagation through bulk semiconductor optical amplifier (SOA) and a tunable optical bandpass filter (OBPF) placed at the output of the SOA for the alleviation of patterning of the amplified signal due to gain saturation in SOA. The effect of the OBPF in terms of its central wavelength detuning and bandwidth on the quality of peak power equalization of the output signal is investigated for signal pulsewidth smaller and larger than the critical pulsewidth of the amplifier at bit-rates of 20 and 40 Gb/s, respectively. It is observed that the scheme is highly useful for the signal pulses with width greater than the critical width.

Semiconductor optical amplifier pattern effect suppression using Lyot filter

The feasibility of employing a Lyot filter to compensate for the pattern effect in a semiconductor optical amplifier (SOA) is experimentally demonstrated. The operation mechanism relies on the control of its comb-like transfer function by proper adjustment of the wavelength spacing and detuning to suppress the spectral components broadened owing to SOA gain saturation. The scheme is experimentally demonstrated on amplified 10 Gbit/s return to zero data.

Analysis of the Physical Impairments on Maximum Size and Throughput of SOA-Based Optical Burst Switching Nodes

In this paper, the physical limitations of semiconductor optical amplifier (SOA)-based switching nodes for optical burst switching (OBS) are investigated. The investigation covers two broadcast-and-select (BAS)-based architectures. Their maximum size and throughput are analyzed for nodes at different bit rates. As main impairments for signal degradation amplifier noise, crosstalk, SOA gain saturation and dynamics, and SOA chirp are evaluated by simulations. In conclusion, general rules for design burst switching nodes are established.

Amplitude Regenerative Characteristics of RZ-DPSK Wavelength Converter Based on Four-Wave Mixing in SOA

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero (RZ) differential-phase-shift-keying (DPSK) wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). The Q-factor and the optical signal-to-noise ratio (OSNR) before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of 10Gbit/s RZ-DPSK signal with OSNR lower than 19dB.

Complete theoretical analysis of actively mode-locked fiber ring laser with external optical modulation of a semiconductor optical amplifier

We present a complete and extensive study of an actively mode-locked ring laser that uses a semiconductor optical amplifier (SOA) acting both as gain medium and mode-locker controlled by an external optical signal, including self-phase modulation (SPM) due to the SOA gain saturation by the recirculating mode-locked pulses and the associated imposed chirp. The operation of the different cavity elements is separately modelled and combined to obtain the self-consistent equation of mode-locking. The role of the critical parameters on the formation of the mode-locked pulses, which include the SOA linewidth enhancement factor, small signal gain and carrier lifetime, the external driving pulse width and energy and the bandwidth of the filter, as well as the simultaneous effect of SPM and dispersion is thoroughly investigated in order to specify the conditions that are required to obtain output pulses of short width and high energy. The adopted theoretical approach and the outcome of the simulation can form the basis for analyzing, evaluating and improving the performance of more complex, non-trivial implementations that exploit this ring laser platform and which are expected to find application in all-optical networks.

The effect of carrier transport on the dynamic performance of gain-saturation wavelength conversion in MQW semiconductor optical amplifiers

This paper investigates the effect of carrier transport on the dynamic properties of wavelength conversion using gain-saturation in semiconductor optical amplifiers (SOAs). It is shown that the carrier transport slows the rise time of the probe optical power by about 10 ps, but the fall time of the probe power is not significantly slowed. However, the dynamics of the probe chirp are slowed by as much as 30-50 ps when operating at 5 Gb/s. The effect of the modified chirp dynamics due to transport is shown to give an additional dispersion penalty, but this is always less than 1 dB. Electrical feedforward of the optical signal input into the SOA is shown to improve extinction ratio of the conversion process. Carrier transport degrades performance of this scheme by up to 3 dB at high data rates. These results show that it is important to take the chirp performance of SOAs into account when designing them for long-haul communications.