Bulk Semiconductor Optical Amplifier Research Articles

Performance analysis of a cross-gain modulation (XGM) utilization in bulk-semiconductor optical amplifiers (SOAs) based all-optical 2R regeneration scheme

Performance analysis of a cross-gain modulation (XGM) utilization in bulk-semiconductor optical amplifiers (SOAs) based all-optical 2R regeneration scheme

Design and Analysis of Novel O-Band Low Polarization Sensitive SOA Co-Integrated With Passive Waveguides for Optical Systems

Low polarization-dependent semiconductor optical amplifiers (SOAs) with an easy fabrication process and the capability to be co-integrated with passive elements are crucial in photonic integrated circuits. In this work, we design, simulate, and optimize a low polarization-dependent bulk SOA based on a novel layerstack with an unstrained bulk active layer with a robust and easy fabrication process that allows the co-integration with passive waveguides. The designed layerstack shows that the reflection between SOA and the passive waveguide is less than 1.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> . Furthermore, by designing the ridge waveguide and layerstack (thickness of the core and cladding layers), the confinement factor of TE- and TM- modes (Г <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE</sub> / <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sub> ) are engineered to be approximately the same. This results in a low polarization-dependent SOA (since for the active bulk layer, the material gain of TE-mode is very close to the material gain of TM-mode). Numerical assessment of different length SOAs in terms of gain, polarization-dependent gain (PDG), noise figure are extensively investigated. Moreover, a booster SOA (1100 μm) with higher output saturation power has been investigated by widening the width of SOA from 1 μm to 3 μm. The output saturation power at 10 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> increases from +7.6 dBm to +13.9 dBm, when the width of the SOA waveguide increases from 1 μm to 3 μm. Finally, we discuss the fabrication tolerance on SOA characteristics. We show that the PDG strongly depends on the cladding layer thickness tolerance and decreases from 2.3 dB to 1.3 dB as it changes from 135 nm to 175 nm.

Design and Fabrication of Low Polarization Dependent Bulk SOA Co-Integrated With Passive Waveguides for Optical Network Systems

Low polarization-dependent semiconductor optical amplifiers (SOA) co-integrated with passive circuits via an easy fabrication process are highly demanded in optical communication systems. However, despite several SOAs have been reported, co-integration of polarization-independent bulk SOA with passive waveguides in the InP platform to generate complex systems remains an issue. In this work, we design, simulate, fabricate and characterize a low polarization-dependent SOA based on a bulk active layer that is co-integrated with passive waveguides and exhibits its potential application to realize photonic integrated circuits. Simulation results are in good agreement with the experimental results. Based on the simulation results, the designed SOAs with the length of 300 &#x03BC;m, 750 &#x03BC;m, and 1500 &#x03BC;m cover broadband with 3-dB bandwidth of around 65 nm, 40 nm, and 37 nm, respectively. Characterization of SOAs with different lengths between 300 &#x03BC;m and 1500 &#x03BC;m co-integrated with passive waveguide has been performed. Broadband gain and polarization-dependent gain (PDG) less than 2 dB is measured for 300 &#x03BC;m SOA. Also, at 1550 nm, output saturation power of 12.8 dBm is achieved at the current density of 11.6 kA&#x002F;cm². For the longest SOA with 1500 &#x03BC;m length, the higher gain of 16 dB with PDG lower than 2.5 dB and saturation power of 7.4 dBm at the wavelength of 1588 nm and current density of 4.1 kA&#x002F;cm² are achievable. Thus, one could design SOA based photonic circuits with higher gain and saturation power and low PDG by exploiting different SOA lengths and design at the wavelength of interest, opening to potential application in photonic integrated circuits like low-loss and polarization-insensitive switches.

Dynamics and its Effects on Saturation Region in Semiconductor Optical Amplifiers

We focus on studying the dynamics of bulk semiconductor optical amplifiers and their effects on the saturation region for short pulse that differ, however there is the same unsaturated gain for both dynamics. Parameters like current injection, fast dynamics present by carrier heating (CH), and spectra hole burning (SHB) are studied for regions that occur a response to certain dynamics. The behavior of the saturation region is found to be responsible for phenomena such as recovery time and chirp for the pulse under study.

Execution of all-optical Boolean OR logic using carrier reservoir semiconductor optical amplifier-assisted delayed interferometer

It is known that the conventional bulk semiconductor optical amplifier (SOA) faces the problem of the slow gain recovery time, which limits its application as a nonlinear element at higher data rates. Therefore, our goal is to find an alternative that works at higher rates with acceptable performance. In this paper, we employ, for the first time to our knowledge, a carrier reservoir SOA (CR-SOA) followed by a delayed interferometer (DI) to execute all-optically the Boolean OR operation at a data rate of 100 Gb/s. A performance comparison between the CR-SOA- and the conventional bulk SOA-based DI is made by studying the variation of the quality factor (Q-factor) against various key operating parameters, which include the transition time from the carrier reservoir to the active region, the population inversion factor, the injection current, the equivalent pseudorandom binary sequence length, the alpha-factor, the optical confinement factor, the operating data rate, the input pulse energy, and the continuous wave power in the presence of amplified spontaneous emission noise. The obtained results demonstrate that owing to the CR-SOA faster gain and phase recovery, the CR-SOA-DI is more suitable for realizing the OR logic gate at 100 Gb/s as it manages to achieve a more than acceptable Q-factor value of 9, compared to the unacceptable value of 3 when using the conventional SOA-DI.

Ultrafast carrier reservoir semiconductor optical amplifiers-based all-optical AND logic gate

It has become an imperative reality to find an alternative for the conventional bulk semiconductor optical amplifier (SOA), which suffers from the slow dynamic response, in light of the increased need for higher speeds. In this research, the carrier reservoir SOA (CR-SOA) is employed as a suitable alternative to investigate the all-optical AND logic gate for the first time at an operating speed of 100 Gb / s. For the reliability of the results, the CR-SOAs- and the conventional SOAs-based Mach–Zehnder interferometer are compared in the same operating conditions that include the effects of the amplified spontaneous emission noise and the operating temperature to obtain more realistic simulation results. The results of Wolfram Mathematica proved that the considered Boolean function is executed at 100 Gb / s with a higher quality factor when using CR-SOAs compared to SOAs, i.e., 14 versus 4.7.

Numerical study of carrier reservoir semiconductor optical amplifier-based all-optical XOR logic gate

The long carrier lifetime of the semiconductor optical amplifier (SOA) limits its operation speed and exploitation as ultrafast nonlinear switching element. Therefore, an alternative SOA with a faster carrier lifetime is desired for high speed photonic applications. In this paper, we employ the carrier reservoir SOA (CR-SOA) for the first time to demonstrate through simulations the feasibility of all-optical exclusive-OR (XOR) logic gate at 100 Gb/s. For this purpose, a pair of CR-SOAs are incorporated in a Mach-Zehnder Interferometer. The variation of the quality factor (QF) against the key operating parameters is examined for both CR-SOAs- and conventional SOAs-based XOR gate at 100 Gb/s, including the effect of amplified spontaneous emission. The results show that not only higher but also acceptable QF is obtained at 100 Gb/s only when using CR-SOAscompared to conventional bulk SOAs, i.e. QF = 18.5 versus 3.3, respectively.

640 Gb/s all-optical AND gate and wavelength converter using bulk SOA turbo–switched Mach–Zehnder interferometer with improved differential scheme

An enhanced version of the conventional differential scheme, employed to decouple the switching speed of an active Mach-Zehnder interferometer from the recovery time of its main nonlinear element (a bulk semiconductor optical amplifier, or SOA), is presented and numerically analyzed. A turbo-switch is also included within the scheme for speed boost and performance improvement. Through the use of the novel architecture and following a parameter optimization process, an all-optical AND Boolean gate operating error-free at 640 Gb/s is numerically demonstrated, thus becoming the fastest AND gate based on bulk SOAs. Additionally, the role of key design parameters in the switching-window formation process is investigated. It is shown that the delay and attenuation applied to the waveform traveling in the opposite interferometer arm play an appreciable role in decreasing data-patterning effects and thus improving the quality-factor and performance of the overall subsystem. An empirical linear relation between performance and operation speed for the proposed scheme is put forward. Finally, it is demonstrated that the proposed structure can also operate error-free at 640 Gb/s as an all-optical wavelength converter. Our simulation work represents a step forward to leverage the use of SOA-based interferometric structures for all-optical signal processing.

Picosecond and femtosecond asymmetric switching using a semiconductor optical amplifier-based Mach-Zehnder interferometer.

In this paper, we numerically analyze nonlinear asymmetric switching using a semiconductor optical amplifier (SOA) phase-shifter-based Mach-Zehnder interferometer (MZI), for the first time, to the best of our knowledge. The self-phase modulation (SPM) effect and nonlinear phase shift in each MZI arm are investigated for different input pulse intensities and linear gains in both picosecond and femtosecond regimes. The input light signal is split unequally over the two arms, where SOAs are placed and act as nonlinear phase shifters in each arm. The finite difference beam propagation method is used to solve the modified nonlinear Schrodinger equation to analyze the wave propagation. In this work, the main nonlinear effects in SOA, such as group velocity dispersion, Kerr effect, two-photon absorption, carrier heating, and spectral hole burning, are considered. Furthermore, the effect of SPM on distortion of the pulse shape and its spectrum, which can be used for pulse shaping in a picosecond-switching scheme, is studied. We depicted red and blue shifts that each pulse experiences in the process of switching in picosecond and femtosecond regimes, respectively. Based on the results for sub-picosecond input pulses, by controlling the bias current level in the MZI arms, the pulse distortion due to nonlinear effects of SOAs can be decreased at the switch output port, and symmetric pulse can be obtained. Switching with higher speed is possible in bulk SOAs in the femtosecond regime using asymmetric MZI-switching structure.

40 Gb/s NRZ-DQPSK data wavelength conversion with amplitude regeneration using four-wave mixing in a quantum dash semiconductor optical amplifier

Differential quadrature phase shift keying (DQPSK) modulation is attractive in high-speed optical communications because of its resistance to fiber nonlinearities and more efficient use of fiber bandwidth compared to conventional intensity modulation schemes. Because of its wavelength conversion ability and phase preservation, semiconductor optical amplifier (SOA) fourwave mixing (FWM) has attracted much attention. We experimentally study wavelength conversion of 40 Gbit/s (20 Gbaud) non-return-to-zero (NRZ)-DQPSK data using FWM in a quantum dash SOA with 20 dB gain and 5 dBm output saturation power. Q factor improvement and eye diagram reshaping is shown for up to 3 nm pump-probe detuning and is superior to that reported for a higher gain bulk SOA.

QPSK wavelength multicasting based on four-wave mixing in semiconductor optical amplifier

We experimentally demonstrate one-to-five quadrature phase-shift keying (QPSK) wavelength multicasting based on four-wave mixing in bulk semiconductor optical amplifier. The input 25 Gb/s nonreturn-to-zero QPSK signal is successfully multicast to five new wavelengths with all information preserved. All the multicast channels are with a power penalty less than 1.1 dB at a bit error rate (BER) of 10-3. A characterization of the conversion efficiency in terms of pump and signal powers using the BER as figure of merit is also presented, the results indicate that the pump and signal powers should be optimized to eliminate the introduced deleterious nonlinear components.

40 Gb/s NRZ-DQPSK Data All-Optical Wavelength Conversion Using Four Wave Mixing in a Bulk SOA

Differential quadrature phase shift keying (DQPSK) modulation has become particularly attractive in high-speed optical communications because of its resistance to fiber nonlinearities and its more efficient use of fiber bandwidth. Because of its wavelength conversion ability, semiconductor optical amplifier (SOA) four wave mixing effect has attracted much attention. We experimentally study the FWM wavelength conversion of 40 Gb/s (20 GBd) NRZ-DQPSK data. A bulk SOA with 21 dB gain and 10 dBm output saturation power is used. The Q-factors of the input and wavelength converted signal are measured. Some signal regeneration properties are shown. A Q-factor improvement up to 1.7 dB is observed.

Effect of input signal and filter parameters on patterning effect in a semiconductor optical amplifier

A numerical investigation is presented to show the dependence of patterning effect (PE) of an amplified signal in a bulk semiconductor optical amplifier (SOA) and an optical bandpass filter based amplifier on various input signal and filter parameters considering both the cases of including and excluding intraband effects in the SOA model. The simulation shows that the variation of PE with input energy has a characteristic nature which is similar for both the cases. However the variation of PE with pulse width is quite different for the two cases, PE being independent of the pulse width when intraband effects are neglected in the model. We find a simple relationship between the PE and the signal pulse width. Using a simple treatment we study the effect of the amplified spontaneous emission (ASE) on PE and find that the ASE has almost no effect on the PE in the range of energy considered here. The optimum filter parameters are determined to obtain an acceptable extinction ratio greater than 10dB and a PE less than 1dB for the amplified signal over a wide range of input signal energy and bit-rate.

Method to improve the noise figure and saturation power in multi-contact semiconductor optical amplifiers: simulation and experiment

The consequences of tailoring the longitudinal carrier density along the active layer of a multi-contact bulk semiconductor optical amplifier (SOA) are investigated using a rate equation model. It is shown that both the noise figure and output power saturation can be optimized for a fixed total injected bias current. The simulation results are validated by comparison with experiment using a multi-contact SOA. The inter-contact resistance is increased using a focused ion beam in order to optimize the carrier density control. A chip noise figure of 3.8 dB and a saturation output power of 9 dBm are measured experimentally for a total bias current of 150 mA.

All-optical high speed logic gates using SOA

In this paper a novel and simple structure of a high speed optical logic gate based on bulk semiconductor optical amplifier (SOA) is presented. The gain dynamic and phase response of bulk SOA using rate equations including the dynamics of carrier heating (CH) and spectral-hole burning (SHB) is investigated numerically. The operation of NOR gate is analyzed by using the presented numerical method, and a NOR gate that can operate up to 1 Tbps is designed. By using the proposed structure, high speed logic gates based on bulk SOA can be realized.

Theoretical and Experimental Study of the Frequency Response of the Nonlinear Polarization Rotation in a Bulk Semiconductor Optical Amplifier

To characterize and predict the dynamics of the nonlinear polarization rotation in SOAs, an experimental method based on the frequency response technique and a model based on the density matrix and effective index formalisms are presented. Both determine the angular displacement, at the Poincare Sphere, that produces the evolution of the polarization of the output signal.

COMPARISON BETWEEN ULTRAFAST GAIN AND PHASE DYNAMICS IN SEMICONDUCTOR OPTICAL AMPLIFIERS

The ultrafast dynamics of gain and phase in bulk semiconductor optical amplifiers are numerically investigated over a broad band of about 200 nm based on the semiclassical method of density matrix equations. The gain dynamics and phase dynamics are compared in four different bands for 200 fs Gaussian pump pulse. It is predicted that the recovery time of phase may be longer or shorter than that of gain depending on probe wavelengths. Furthermore, phase recovery overshoot may appear at wavelengths shorter than the pump wavelength. These interesting features result from the competition between spectral-hole burning and carrier heating over the whole band.

All-Optical Wavelength Conversion With Extinction Ratio Improvement of 100 Gb/s RZ-Signals in Ultralong Bulk Semiconductor Optical Amplifiers

All-optical wavelength conversion in ultralong semiconductor optical amplifier (UL-SOA) is presented. Opposite to other SOA based single path wavelength converters the UL-SOA's property as an extinction ratio (ER) regenerator can be used additionally to the wavelength conversion. When converting to lower wavelengths, cross-gain modulation as well as four-wave mixing (FWM) can be used as wavelength conversion mechanism. For the conversion to higher wavelengths only FWM has the ability for an ER improvement. Furthermore, the high-speed capability for the wavelength conversion with ER improvement in bulk UL-SOAs is analysed for 100 Gb/s RZ-signals. The degradation due to bit pattern effects is investigated for RZ-50% PRBS of different lengths. No significant influence could be observed for PRBS orders up to 25.

Widely Tunable Short-Pulse Generation With Ultralong Semiconductor Optical Amplifiers

Ultralong bulk semiconductor optical amplifiers (bulk UL-SOAs) have tremendous four-wave mixing (FWM) efficiencies so that due to two continuous wave (CW) input signals, a broad mode comb at the output of the UL-SOA can be obtained. When using tunable single mode lasers as input signals, the generated FWM mode comb is tunable in the mode spacing and the wavelength. As a result in time domain, widely tunable pulses in the repetition rate and the carrier frequency are obtained. Since the phase signature of the FWM modes is not linear over the whole mode comb, different filtering techniques can be applied for filtering modes with linear phase in order to efficiently generate short pulses. With the optimal filtering technique, pulses with full width at half maximum of less than 2 ps and a pulse repetition rate of 20 GHz can be obtained.

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.