Modulation In Semiconductor Optical Amplifier Research Articles

Study of recombination's effect oncharacteristic and self -phase modulation in semiconductor optical amplifier

This paper presents a detailed simulation study of the spontaneous and auger recombination on amplification characteristic and self -phase modulation in travelling- wave (TW) semiconductor optical amplifier (SOAs). The effect is studied on the gain, output signal power, nonlinear phase shift spectrum, and shape of amplified pulse at a range of drive currents. For small value of recombination, gain and output signal power were large, and the peak spectrum shifts more to longer wavelengths.

Performance optimization of RSOA based mm-wave radio-over-fibre access network

In this paper, a Reflective Semiconductor Optical Amplifier based, Radio-over-Fibre access network configuration has been proposed to feed future millimeter-wave radio systems. The system architecture combines several approaches to overcome the challenges of millimeter-wave signal transmission. Reflective semiconductor optical amplifier modulator realizes a colorless and relatively cost-effective Remote Antenna Unit. The same optical carrier is used for both downlink and uplink. Optical single-sideband modulation is used at the downlink, which is robust against chromatic dispersion, but the complex realization of this modulation format is not possible at the Remote Antenna Unit. Optical intermediate frequency transmission is applied at the uplink direction, and the required local oscillator signal originates from the central station. The critical element is the reflective optical amplifier, as it compensates for the optical loss and works as an external intensity modulator. The operation of the reflective optical amplifier is modeled by multisection rate and wave equation-based description. The amplification and modulation behaviors of an available reflective optical amplifier are also measured. The experimental work validated the colorless operation and the quality of the modulation versus bias current and input optical power. Finally, system simulation was realized. The uplink and downlink power budgets were balanced, and optimal values for the optical coupling rate and RSOA bias current have been selected.

Reflective Semiconductor Optical Amplifier Direct Modulation Capability Enhancement Using Birefringent Fiber Loop

The feasibility of employing a birefringent fiber loop to enhance the performance of a directly modulated reflective semiconductor optical amplifier is experimentally demonstrated for the first time. The birefringent fiber loop acts as an optical filter of opposite slope than that of the reflective semiconductor optical amplifier electro-optical response and counteracts the finite reflective semiconductor optical amplifier modulation bandwidth of only 0.89 GHz. By proper adjustment of its detuning, the birefringent fiber loop tailors the spectral components that physically manifest due to the reflective semiconductor optical amplifier dynamic perturbation subject to direct modulation in the saturated gain regime, and suppresses the pattern-dependent distortions in the time domain. In this manner, the birefringent fiber loop manages to significantly improve the quality characteristics of the encoded signal at higher data rates than those enabled by the reflective semiconductor optical amplifier limited modulation capability. Owing to the birefringent fiber loop, the reflective semiconductor optical amplifier modulation range is extended to 4 Gb/s at the raw bit error rate of 1.0×10−9, and to 11 Gb/s at the forward error correction limit of 3.8×10−3. These results, which are unique against the evaluation criterion adopted in the first case, and the modulation speed achieved with post-filtering schemes in the second, highlight the beneficial role that the birefringent fiber loop can play in supporting reflective semiconductor optical amplifier operation for intensity amplification and modulation purposes.

Hybrid electronically addressable random fiber laser.

We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obtained by synchronizing the SOA driver to the returning amplified Rayleigh back-scattered light from a selected short section of the EDF. By tuning the SOA pulse rate, random lasing was achieved by addressing selected meter-long sections of the 81-m long EDF, which was open-ended. Laser oscillation can be potentially obtained with SOA modulation frequencies from several kHz to the MHz regime. We discuss the mechanism leading to the hybrid random laser emission, connecting with phase sensitive optical time domain reflectometry and envision potential applications of this electronically addressable random laser.

SOA fiber laser mode-locked by gain modulation

This work reports, for the first time to our knowledge, on an experimental and theoretical study of mode locking via synchronous pumping of a semiconductor optical amplifier (SOA) used as the active medium of a fiber laser. SOA modulation with injection current pulses having duration of 1.2 μs and repetition rate equal to that of the fundamental intermode frequency spacing of the cavity (84.9 kHz) led to generation of mode-locked pulses with duration of 650 ns at a wavelength of 1.54 μm. The feasibility of the proposed method and the basic parameters of the generated pulses are corroborated by numerical modeling. The key advantages of the proposed laser are simplicity of implementation, comparatively high efficiency, spectral universality, and possibility of pulse shape control.

Width-tunable pulse laser via optical injection induced gain modulation of semiconductor optical amplifiers

A width-tunable pulse laser via an optical injection induced gain modulation of a semiconductor optical amplifier (SOA) is demonstrated. When the pump current of the SOA is 330 mA or 400 mA and a continuous wave is injected into the laser cavity with different powers, bright or dark pulses with different pulse widths and frequency repetition rates are obtained. The bright and dark pulses are formed by the effect of gain dispersion and cross-gain modulation of the SOA.

Dark Pulse Laser With Tunable Width Based on SOA and Feedback

We demonstrate a dark pulse optical fiber laser with tunable widths based on semiconductor optical amplifier and feedback. In the case of different feedback lengths, by adjusting the polarization controller, dark pulses with a frequency repetition of 13.3 MHz and widths vary from 4.29 to 15.15 ns are generated. Dark pulses are produced by the interaction of birefringence, large normal dispersion, cross-phase modulation, and cross-gain modulation in semiconductor optical amplifier.

A study of 100 Gb/s 2R regeneration for return-to-zero code signal

Quality of optical signal can be severely degraded after a long distance optical fiber transmission, therefore all-optical 2R (re-amplification, re-shaping) regeneration is required for its low power consumption and good potential of high-speed operation. Semiconductor optical amplifier (SOA) is a very promising candidate for regeneration due to its relatively low nonlinear switching power threshold and possibility of integration. However, speeds of the existing 2R schemes based on SOAs are limited by pattern effects introduced by the long carrier recovery time. So far, most of experimental results for SOA-based regeneration schemes have been limited to 40 Gb/s, only a few demonstrations at 80 Gb/s are available. An effective method to cope with the pattern effects in the SOA is to employ cross gain compression (XGC) effect. Simultaneously injecting two signals of different wavelengths with complementary logics and balanced powers into the SOA leads to an almost constant ability to make the XGC effect intrinsically immune to the pattern effects. Previously, 2R experimental results were demonstrated at 10 Gb/s and 40 Gb/s with XGC respectively, but no further results of higher speed have been presented to date. In this study, we improve the previous two-stage configuration for XGC-based regeneration by introducing a transient cross phase modulation (T-XPM) in the first SOA for generating the high-quality logic-inverted signal, which, as we find, is essential to facilitating the high-speed XGC operation in the next SOA. Firstly, a numerical model of the photon-electron dynamics in an SOA is built with considering the ultrafast intra-band processes, amplified spontaneous emission (ASE) noise at multiple wavelengths, and device segmentation along propagation direction. The quality of the logic-inverted signal with different offsets of the filter wavelength for T-XPM is studied with the model. It is found that the appropriate blue-shift detuning of the filter wavelength greatly helps to improve the quality of the logic-inverted signal. In experiment, the influence of the filter offset on the quality of the logic-inverted signal is also investigated systematically and the best quality and the largest eye-opening of the logic-inverted signal are achieved with a blue-shift of 0.72 nm, which are consistent with the simulation result. With the best logic-inverted signal, XGC effect is deployed in the second SOA. Effective reduction of the amplitude fluctuation can be observed by comparing the eye diagrams of the input degraded with output regenerative signals. Bit error rates (BERs) are also measured for all four tributaries of the degraded and the regenerated signals and the receiving sensitivity at a BER of 10-9 is improved by 1.7-2 dB. Such results show that the XGC-based 2R regeneration scheme is effective even at a speed of as high as 100 Gb/s with the help of high-quality logic-inverted signal. Degraded signals at different wavelengths (from 1535 nm to 1555 nm) are successfully regenerated with Q-factor improvement, demonstrating the wavelength-independent regeneration capability of the XGC-based 2R regenerator.

25 Gbit/s differential phase-shift-keying signal generation using directly modulated quantum-dot semiconductor optical amplifiers

Error-free generation of 25-Gbit/s differential phase-shift keying (DPSK) signals via direct modulation of InAs quantum-dot (QD) based semiconductor optical amplifiers (SOAs) is experimentally demonstrated with an input power level of −5 dBm. The QD SOAs emit in the 1.3-μm wavelength range and provide a small-signal fiber-to-fiber gain of 8 dB. Furthermore, error-free DPSK modulation is achieved for constant optical input power levels from 3 dBm down to only −11 dBm for a bit rate of 20 Gbit/s. Direct phase modulation of QD SOAs via current changes is thus demonstrated to be much faster than direct gain modulation.

Design and analysis of all-optical AND, XOR and OR gates based on SOA–MZI configuration

The novel designs of all-optical logic gates using cross-gain modulation and cross phase modulation in semiconductor optical amplifiers, have been suggested and demonstrated successfully at 10 Gb/s. Mach–Zehnder configuration with two 3 dB couplers is used to introduce phase modulation on the saturated inverted output of SOA. No additional input beam such as clock signal or continuous light wave is used as in several other designs. In the designs, one data act as a pump and another act as a probe signal. Therefore, while passing through SOA, one data acting as a pump, saturates another data which is a probe signal. Different arrangements of input part of SOA–MZI, create three gates such as AND, XOR and OR. Gates are analyzed according to the extinction ratio, wavelength spectrum, frequency chirping and bit error rate. Very high extinction ratio is found i.e. 54.5, 36.32 and 37.5 at 1550.5 nm for AND, XOR and OR gates respectively. The wavelength spectrum, of all the three gates, lies within 1554.8 nm to 1555.2 nm which is near the central wavelength of probe pulse at 1550 nm. Negative frequency chirp are found for all the three gates with bit error rate 7.1×10−30, 1×10−31 and 2.1×10−12 for AND, XOR and OR respectively.

Group Velocity Manipulation of 10 Gb/s Signal by Mutually-Modulated Cross-Gain Modulation in Semiconductor Optical Amplifiers

We propose and experimentally demonstrate the propagation of slow/fast-light via mutually modulated cross-gain modulation in a semiconductor optical amplifier (SOA). Owing to very short recovery time in SOAs, the group velocity of 10-Gb/s signal light can be controlled by manipulating the saturating light. The maximum controlled time of one pulse period has been observed, whereas the signal light is modulated by either the sinusoidal signal or the real telecom signal.

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This article is a study of the non-linear phenomena, XPM (cross phase modulation) and XGM (cross gain modulation) in SOAs (semiconductor optical amplifiers). The analysis of the nonlinear effects allows us to design a wavelength converter based on Mach-Zehnder interferometer with SOA in its arms (SOA-MZI). This type of system is important in all-optical signal processing due to it can produce the inverse signal and the non-inverse signal at the desired wavelength. This device has been simulated to analyse its performance and made by discrete components showing it is viable and improvable through integration.

All Optical Wavelength Conversion Based on Cross Polarization Modulation in Semiconductor Optical Amplifier

The paper presents a novel inherent polarization sensitivity technique using SOA to perform cross polarization modulation. The wavelength conversion takes place due to nonlinear rotation in state of polarization at the output of the SOA. Nonlinear polarization rotation is enhanced by optimizing the various parameters of SOA. The conversion is achieved with wavelength separation of 1 nm for up and down conversion with non-return to zero input signals at bit rate of 10 Gb/s. It is predicted that conversion efficiency becomes almost same for both up and down conversions at high value of pump signal power. Improved extinction ratio is observed for all optical wavelength conversion.

All-Optical Canonical Logic Units-Based Programmable Logic Array (CLUs-PLA) Using Semiconductor Optical Amplifiers

All-optical programmable logic arrays (PLAs) based on canonical logic units (CLUs), i.e., minterms and maxterms, are presented. We experimentally demonstrated the full set of two-input and three-input minterms as well as maxterms using the cross-gain modulation in semiconductor optical amplifiers (SOAs). Maxterms can be easily obtained based on minterms. The reconfigurability and scalability of the system are largely enhanced compared to our previous work. Correct and clear temporal waveforms are achieved for all the canonical logic units. The measured extinction ratios of two-input and three-input CLUs are ~ 15 dB and ~ 11 dB, respectively. Based on the CLUs, both sum-of-products and product-of-sums typed PLAs are exhibited. Six important logic functions, including full-adder, full-subtractor, multiplier, multiplexer, demultiplexer and decoder, are presented as examples to show that the canonical logic units-based programmable logic array (CLUs-PLA) can be reconfigured to perform different logic functions. The features of simple architectures, integration ability of SOA and programmable filter enable the great integration potential for CLUs-PLA.

40-Gb/s all-optical digital 4-bit priority encoder employing cross-gain modulation in semiconductor optical amplifiers

High-speed all-optical logic circuits have attracted much attention because of their important roles in signal processing in next-generation optical networks. The digital encoder is widely used in binary calculation, multiplexing, demultiplexing, address recognition and data encryption. A priority encoder allows the existence of multiple valid inputs simultaneously, identifies the priority of the request signals and encodes the priority. We propose and experimentally demonstrate an all-optical 4-bit priority encoder for return-to-zero signals at 40 Gbit/s based on cross-gain modulation in semiconductor optical amplifiers. Detuning filters after semiconductor optical amplifiers are employed to improve the output performance. Correct logic bit sequences and clear open eye patterns with extinction ratios exceeding 10 dB are achieved.

Optical transient waveform monitoring based on cross-gain modulation in semiconductor optical amplifier

An all-optical transient waveform equivalent time sampling system based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) is presented. A noisy SOA dynamic model and PIN equivalent circuit function are employed for system evaluating. The results show this SOA-XGM sampler with subtracting postprocessing can achieve picosecond sampling window. The shape of sampling window can be adjusted by SOA bias current and amplitude of control pulse. Compared with amplified spontaneous emission (ASE) noise of SOA and thermal noise in PIN, the jitter of sampling control pulse causes most sampling error. Simulations show that this SOA-XGM sampler can be a capable candidate for transient waveform sampling.

Self-Phase Modulation in Semiconductor Optical Amplifiers: Impact of Amplified Spontaneous Emission

This paper presents a detailed theoretical and experimental study of the impact of amplified spontaneous emission (ASE) on self-phase modulation in semiconductor optical amplifiers (SOAs). A theoretical model of pulse propagation in SOAs is developed that includes the ASE power and its effect on gain-saturation and gain-recovery. We study the impact of ASE on the nonlinear phase shift, frequency chirp, spectrum, and shape of amplified picosecond pulses at a range of drive currents. We verify our predictions experimentally by launching gain-switched picosecond pulses with 3-mW peak power into a commercial SOA exhibiting 9-ps gain-recovery time at a current of 500 mA. Understanding the impact of ASE on SOAs is important for applications that employs SOAs for all-optical signal processing and as data-network amplifiers.

High-speed, all-optical XOR gates using semiconductor optical amplifiers in ultrafast nonlinear interferometers

We will review three recently-proposed high-speed, all-optical Exclusive OR (XOR) gates operating at 40 and 85 Gb/s, which were demonstrated using ultrafast nonlinear interferometers (UNIs) incorporating semiconductor optical amplifiers (SOAs). The first 40-Gb/s XOR gate was obtained using a dual UNI configuration. The second is a 40-Gb/s XOR gate without additional probe beam required, where the only inputs launched into the setup were data A and B. The XOR logic of data A and B is the sum of two components \( \bar A \)B and A\( \bar B \), each of which was obtained from the output of UNI via cross-phase modulation (XPM) in SOAs. Furthermore, an 85-Gb/s XOR gate is, by far, the fastest XOR gate realized by SOAs, which was also demonstrated using a dual UNI structure. The operating speed of the XOR gate was enhanced by incorporating the recently proposed turbo-switch configuration. In addition, the SOA switching pulse energies of these XOR gates were lower than 100 fJ.

All-Optical OR/NOR Bi-Functional Logic Gate by using Cross-Gain Modulation in Semiconductor Optical Amplifiers

All-Optical OR/NOR Bi-Functional Logic Gate by using Cross-Gain Modulation in Semiconductor Optical Amplifiers

Regenerative Amplification by Using Self-Phase Modulation in a Quantum-Dot SOA

We experimentally demonstrate regenerative amplification of 10-, 20-, and 40-Gb/s return-to-zero signals exploiting a simple scheme based on self-phase modulation (SPM) in a columnar quantum-dot (CQD) semiconductor optical amplifier (SOA) and the use of a red-shifted off-set filter. We study the signal Q 2-factor improvement as a function of the input power to the amplifier. We also report results using a quantum-well (QW) SOA for comparison. We find that the SPM-based regenerative amplification is only possible in the quantum-dot amplifier.