Semiconductor Optical Amplifier Device Research Articles

Polarization-insensitive fiber-to-fiber gain of semiconductor optical amplifier using closely stacked InAs/GaAs quantum dots

The gain characteristics of a semiconductor optical amplifier (SOA) that contains forty layers of closely stacked InAs/GaAs quantum dots (QDs) were studied by employing a fiber-to-fiber measurement system. The fiber-to-fiber gain values obtained for transverse-electric (TE)- and transverse-magnetic (TM)-polarized optical input signals exhibited their maxima at a wavelength of 1100 nm, which corresponds to the excited-state of the closely stacked QDs. In the wavelength range from 1060 to 1170 nm, the gain obtained for TE-polarized input signal was slightly higher than that for TM-polarized input signal and the absolute gain difference was less than 1 dB for an injection current of 80 mA. The small but non-zero difference of the gain reflects the polarization anisotropy of the optical gain provided by the closely stacked QDs. Our results suggest that closely stacked QDs are suitable for realizing polarization-insensitive SOA device with operation bandwidths of more than 100 nm.

Influence of co- and counter-propagating light on the phase-mismatch effect in semiconductor optical amplifiers

The phase-mismatch effect, caused by the difference in confinement factor between transverse electric (TE) and transverse magnetic (TM) modes, has not been observed in semiconductor optical amplifiers (SOAs) and is not typically accounted for. In this work, we investigate the characteristics of the phase-mismatch four wave mixing (FWM) effect, which occurs in SOA devices. Our results reveal a sinc-like response in the intensity of co- and counter-FWM conjugates as a function of the detuning shift between interacting beams. It is demonstrated that the coherence lengths between the phase match/mismatch cycles differ between co- and counter-propagating nondegenerate FWM experiments and depend on the amplified TE/TM polarizations of interacting waves aligned with respect to the birefringent axes of SOAs. The coherence lengths between each phase match/mismatch cycle in co-propagation experiments are found to be 1600 and infinite GHz, respectively, compared to 800 and 400 GHz found in counter-propagation experiments.

Experimental Characterization of Nonlinear Distortions of Semiconductor Optical Amplifiers in the WDM Regime

This article presents an experimental characterization of the impact of nonlinear impairments induced by semiconductor optical amplifiers (SOA) in a wavelength division multiplexed (WDM) coherent communication system. Motivated by a ceaseless traffic growth in optical transport systems, extending the bandwidth of the fiber link is a promising way to increase the throughput in optical networks. Using specific design, SOA can provide ultra-wideband (UWB) and continuous amplification spreading from S to L bands. For both off-the-shelf C-band SOA and UWB SOA devices, we show that SOA nonlinear impairments are not critical in the WDM regime. We report on the impact of the WDM channel count on the nonlinear distortions induced by an UWB SOA. We also demonstrate that besides having a wider bandwidth, our custom UWB SOA devices have superior performance compared to off-the shelf components even for C-band only transmission, and are well suited for wideband WDM signal amplification.

Phase-mismatch dependence of the four-wave mixing effect in semiconductor optical amplifiers.

The phase-mismatch effect due to polarization-dependent mode confinement factor has been shown to be not a crucial problem in semiconductor optical amplifiers (SOAs) and is usually not accounted for. The phase-mismatch four-wave mixing (FWM) process in SOA devices is experimentally reported. The results reveal a sinc-like behavior in the intensity of FWM conjugate as a function of wavelength separation between transverse electric (TE)/transverse magnetic (TM) pumps due to induced confinement factors difference. Efficient FWM occurred for a detuning shift of about 500 GHz, limited by phase-mismatch conditions and determined by coherence length required for low and high frequencies to complete a full phase-match cycle. Phase-match FWM with an infinity coherence length can be fulfilled by proper alignments of co-polarized TE/TM modes of input waves with respect to the birefringent axes of the device structure.

Scaling Capacity Growth of Fiber-Optic Transmission Systems Using 100+nm Ultra-Wideband Semiconductor Optical Amplifiers

We report on the use of semiconductor optical amplifiers (SOAs) to extend the optical bandwidth of next generation optical systems. After discussing the technological progress and the motivation for rekindling the interest in SOAs for line amplification, we point out that the nonlinear gain dynamics of SOA is not a limiting factor for employing SOA as line amplifier. We show that the passage to high wavelength division multiplexed (WDM) channel count tends to substantially reduce nonlinear impairments, both through numerical analysis and experimental investigations based on standard off the shelf SOA devices. We then present the characteristics of our novel ultrawideband SOA-based packaged devices exhibiting high gain over 100+nm optical bandwidth, high output saturation power and low noise figure. We finally review the recent demonstration of the first >100+Tb/s transmission based on such novel 100+ nm wide semiconductor optical amplifiers over 100 km distance.

Design and performance analysis of all-optical cascaded adder using SOA-based MZI

With the performance enhancements in all-optical signal processing and switching schemes in terms of data rate and processing speed, various devices enabled with all-optical operation are becoming primary requirements for current and future telecommunications and data networks. All-optical logic gates represent the best solution to realize both combinational as well as sequential devices in the optical domain, representing the basic building blocks for optical computing circuits. We propose herein an all-optical cascaded adder whose elementary blocks are a half-adder and full-adder, designed using semiconductor optical amplifier (SOA)-based Mach–Zehnder interferometer (MZI) gate configurations. They have high thermal stability and require low power. The nonlinear effects in the SOA device are used to implement different logic operations. The proposed cascaded adder was simulated in OptiSystem. The optical signal-to-noise ratio, bit error rate (BER), and Q-factor values were evaluated for different data rates. The design showed good performance up to 60 Gbps. The proposed design could find application in implementation of multistage arithmetic logic units.

Radar signal transmission and switching over optical networks

In this paper, we experimentally demonstrate a radar signal distribution over optical networks. The use of fiber enables us to distribute radar signals to distant sites with a low power loss. Moreover, fiber networks can reduce the radar system cost, by sharing precise and expensive radar signal generation and processing equipment. In order to overcome the bandwidth challenges in electrical switches, a semiconductor optical amplifier (SOA) is used as an all-optical device for wavelength conversion to the desired port (or channel) of a wavelength division multiplexing (WDM) network. Moreover, the effect of chromatic dispersion in double sideband (DSB) signals is combated by generating optical single sideband (OSSB) signals. The optimal values of the SOA device parameters required to generate an OSSB with a high sideband suppression ratio (SSR) are determined. We considered various parameters such as injection current, pump power, and probe power. In addition, the effect of signal wavelength conversion and transmission over fiber are studied in terms of signal dynamic range.

Overcoming the maximum amplification limit of coherent optical pulses in semiconductor optical amplifiers with time-polarization multiplexing

We present a time-polarization multiplexing setup that overcomes the maximum amplification limit of semiconductor optical amplifiers (SOAs) in the pulsed regime. A coherent optical pulse at the input is equally divided into two, which are independently amplified, and coherently recombined to compose an oversaturation amplified optical pulse at the output. This simple topology, containing an SOA and few extra devices, offers 1.96-dB oversaturation gain in comparison with a single SOA. Furthermore, little experimental complexity and, thus, cost, are required by the proposed topology.

Integral gain in quantum dot semiconductor optical amplifiers

In this paper, a new formula of integral gain in quantum dot (QD) semiconductor optical amplifiers (SOAs) depending on the QD states has been derived instead of conventional bulk relation. This formula will pave the way to develop all information in regard to SOA devices. Wetting layer (WL), excited state (ES), and ground state (GS) of SOAs have been employed to study the effects of important parameters in such these devices. Good results were obtained, since the effective capture time in QD is controlled. In addition, a suitable effective capture time must give a high integrated gain that required for all-optical applications. For the bulk model, the capture time to GS is not formulated well in previous studies therefore, it underestimates QD model.

Harmonic Distortion in Microwave Photonic Phase Shifters Based on Coherent Population Oscillations in SOAs

We present a theoretical and experimental evaluation of any general order harmonic distortion in a slow and fast light propagation phase shifter based on coherent population oscillations in a semiconductor optical amplifier device. Different optical filtering implementations are proposed for enhancing the performance of microwave photonic phase shifters.

Polarization-Dependent Gain in SOA-Based Optical Multistage Interconnection Networks

The small polarization dependence (< 1 dB) of optical components becomes significant in optical multistage interconnection networks. The cumulative effect can ultimately limit physical layer scalability by changing the maximum number of internal nodes that optical packets can traverse error free. It is shown that for nodes based on commercial semiconductor optical amplifier (SOA) switches with polarization-dependent gains of less than 0.35 dB, the maximum number of cascaded nodes changes by as much as 20 nodes, depending on both the packet wavelength and its state of polarization. This deviation in the number of nodes could correspond to a 100-fold decrease in the number of interconnected ports of an optical interconnection network such as the data vortex. This dramatic effect is explained in terms of optical signal-to-noise ratio degradation due to accumulated amplified spontaneous emission noise originating from the SOA device in the node

Polarization-Insensitive SOAs Using Strained Bulk Active Regions

The polarization dependent gain (PDG) and its control is a key issue for semiconductor optical amplifier devices. For the case of a strained bulk active region with lateral tapers, an analysis of the parameters that affect PDG is performed, and the magnitude of its variation is calculated. The critical design parameters are thus identified, and the expected PDG variance is discussed in the context of typical fabrication tolerances

Experiments on 40 Gb/s Transmission with Wavelength Conversion: Results from the IST ATLAS Project

In this article we report the main experimental results obtained in the framework of the IST ATLAS project regarding the transmission at 40 Gb/s over long terrestrial links, including the frequency conversion of a signal. We report the single-channel 40 Gb/s transmission over a link 500 km long with an amplifier spacing of 100 km, both with G.652 fibers and G.653 fibers by periodically compensating the chromatic dispersion with dispersion-compensating fibers. We report the single-channel transmission at 40 Gb/s, also, after the wavelength conversion of a channel with both PPLN and semiconductor optical amplifier devices. In particular, 500 km distances are obtained with PPLN wavelength conversion and 300 km distances with semiconductor optical amplifiers. Some results have been reported for electronic devices operating at 40 Gb/s.

Practical scheme for polarization-insensitive and frequency-conversion interval–independent four-wave mixing in semiconductor optical amplifiers

A practical scheme for polarization-insensitive and frequency-conversion interval-independent four-wave mixing in an optical loop configuration is proposed that uses one conventional semiconductor optical amplifier device and two perpendicular polarized pump sources. The significant advantages of this technique are simplicity of configuration, efficient conjugate power generation, effective suppression of the signal and one pump wave at the output port, and reduction in noise.

New electrolytes for n-type InP and electrochemical C - V profiling of a semiconductor optical amplifier device structure

New electrolyte systems for profiling n-type indium phosphide (InP) have been reported and are compared with the conventional HCl electrolyte. Among the new electrolytes, the electrolyte comprising HNO3-HF-H2O has better characteristics and is best suited for profiling InP material. Both epitaxial layers and substrate materials have been subjected to electrochemical carrier concentration profiling using the new electrolyte and the estimated concentration values are compared with that of Hall effect measurements. Barrier heights of the new electrolytes have been calculated. For the first time, the dopant profiling of a complete device structure grown by the chemical beam epitaxy technique for the realization of laser and semiconductor optical amplifier structures has been presented.

High-power mode-locked external cavity semiconductor laser using inverse bow-tie semiconductor optical amplifiers

This paper presents experimental results of using an inverse bow-tie gain guided semiconductor optical amplifier (SOA) as the optical gain element in a high-power external cavity semiconductor laser. An average output power of 700 mW is demonstrated in continuous-wave (CW) operation while 400 mW of average power is obtained in both passive and hybrid mode-locked operation, with subsequent optical amplification in an identical SOA. The mode-locked laser operates at a repetition rate of 1.062 GHz, owing to the interplay between the gain and saturable absorber dynamics. Optical pulses are generated with a temporal duration of 5 ps, which implies a pulse energy of 376 pJ, and a peak power of 60 W. Further reduction of the optical pulsewidth to 1.3 ps is also achieved by using dispersion compensation techniques. These results show the promise of novel SOA devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from mode-locked operation is sufficient for use in novel three-dimensional data storage applications, and in large-scale commercial printing and marking applications.

Imaging of the optical mode of waveguiding devices by scanning near-field optical microscopy

Scanning optical microscopy with uncoated dielectric silica probe is used in the near field to investigate the propagation of optical modes along tapered integrated semiconductor optical amplifier devices and at larger working distances to study the electromagnetic intensity profile in the focal plane of various microlensed fibers. We show how this technique provides images of the mode structure of optoelectronic devices and profiled optical fibers with typical sizes in the range 2–10 μm, with an accuracy of 0.2 μm in beamwaist measurements.

Monolithic integration of an amplifier and a phase modulator fabricated in a GRINSCH-SQW structure by placing the junction below the quantum well

We present results of a novel semiconductor optical amplifier device in which an amplifier and a phase modulator are integrated into a fundamental transverse-mode ridge waveguide. By placing the p-n junction below the quantum well (QW) during epitaxial growth and utilizing the effect of the electric field on the depletion width, the phase of the light from an integrated optical amplifier-modulator is varied. For a modulation reverse bias voltage range of 0.4 V, we have demonstrated a 360 degrees /mm phase shift with less than 1.2 dB of amplitude modulation. >