All-optical wavelength conversion by semiconductor opticalamplifiers

Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber     

Predicted performance of quantum-well GaAs-(GaAl)As opticalamplifiers

The gain, noise, and saturation performance of GaAs-(GaAl)As quantum-well laser amplifiers is calculated. A single-quantum-well amplifier with 100-mA injection should achieve similar gains to those of present devices with bulk active regions, but with improved saturation output powers and near-ideal noise performance. A low-current amplifier with a 2.5-mA injection current is investigated for varying well thickness and number of wells     

Design and analysis of vertical-cavity semiconductor opticalamplifiers

The authors present detailed, yet largely analytical, models for gain, optical bandwidth, and saturation power of vertical-cavity semiconductor optical amplifiers (VCSOAs) in reflection and transmission mode. Simple formulas for the gain-bandwidth product are derived. The saturation model considers a sublinear material gain, gain enhancement by the standing-wave effect, and all relevant carrier recombination mechanisms. Excellent agreement with measurements on novel 1.3-μm VCSOAs is obtained. The models are used to analyze device performance and to investigate optimization options. Parameter plots are given which allow for an easy exploration of the VCSOA design space, matching desired performance data with the required mirror reflectivity and pump current     

Gain optimization in switches based on semiconductor opticalamplifiers

The distribution of unsaturated gains that minimizes the noise figure of a three-stage optical switch based on semiconductor-optical-amplifier (SOA) gates is found. Gain saturation under both unidirectional (isolators inserted) and bidirectional (no isolators) propagation of spontaneous emission noise is analyzed, and a noise figure penalty associated with the absence of isolators is determined. Determination of the optimal set of pump currents is a nonlinear optimization problem, while determination of the optimum set of saturated gains is a linear optimization problem. The latter solution is found analytically, while the former solution requires a nonlinear optimization approach. The results are extended to the case of a sequence of N SOA's     

Wavelength conversion by four-wave mixing in semiconductor opticalamplifiers

Time-resolved spectral analysis is performed on 10 Gb/s signals wavelength converted by four-wave mixing (FWM) in semiconductor optical amplifiers. A pattern-dependent chirp resulting from parasitic gain modulation by the signal is measured and characterized as a function of the converter's pump-to-probe ratio. This chirp is found to be insignificant for pump-to-probe ratios exceeding 9 dB     

Polarization-insensitive semiconductor optical amplifier arraygrown by selective MOVPE

Polarization-insensitive 1.3 μm wavelength semiconductor optical amplifier (SOA) arrays are developed for the first time, by using a new fabrication process with selective MOVPE. In a four-channel array, the SOAs have uniform device characteristics of more than 20 dB signal gain and less than 1 dB polarization sensitivity     

Enhanced multiwave mixing interactions in semiconductor opticalamplifiers via pump modulation

It is demonstrated that, by modulating a semiconductor optical amplifier at a frequency determined by the detuning between the pump and probe in a collinear four wave mixing geometry, the enhancements in gain and reflectivity of two to three orders of magnitude are possible for remarkably small modulation depths (m=10^-2). The mechanism of frequency mixing using population pulsations in semiconductor laser amplifiers is summarized. In particular, the modification to the standard geometry to achieve enhancements is discussed. The appropriate four wave mixing equations including current modulation terms are solved analytically in the undepleted pump approximation. The analytic forms for transmission gain and phase conjugate reflectivity in several cases of interest are computed. In particular, the case in which four wave mixing is absent and energy transfer occurs solely as a result of the current modulation is examined     

Polarization-independent δ-strained semiconductor opticalamplifiers: a tight-binding study

We present a tight-binding analysis of the polarization dependence of GaAs δ-strained semiconductors optical amplifiers. Our approach allows us to account for band nonparabolicity, valence band mixing, as well as thin layer perturbations, overcoming the natural limitations of standard techniques based on the envelope function formalism. We explain how thin strained GaAs layers embedded in a lattice-matched InGaAsP-InGaAs quantum well can he used to achieve polarization-insensitive optical amplification. The theory is also applied to other structures providing optical amplification, showing how the concept of “virtual barriers” can lead to high polarization insensitivity     

4 Gb/s optical wavelength conversion using semiconductor opticalamplifiers

Semiconductor optical amplifiers used for efficient wavelength conversion up to 4 Gb/s are discussed. The rise and fall times as well as extinction ratio are experimentally analyzed. System performance at 4 Gb/s is evaluated showing a penalty of only 1.5 dB for the converted signal for conversion over 17 nm     

Comparison of conventional and gain-clamped semiconductor opticalamplifiers for wavelength-division-multiplexed transmission systems

We compare the output spectra and data streams of a conventional 1550-nm semiconductor optical amplifier (SOA) with its gain-clamped (GCSOA) counterpart, in order to assess the impact of gain clamping on cross-gain modulation (XGM) and difference frequency generation (DFG). Whereas the conventional SOA exhibits a large amount of crosstalk due to XGM, there is virtually no XGM present in the GCSOA. However, the XGM effect in the SOA shows evidence of diminished efficiency at moderate input levels. We observe much higher DFG levels from the GCSOA (roughly 10 dB greater than the SOA). These DFG levels are such that cascaded wavelength cross-connect devices, in-line amplifiers, and even optical gates could experience inhibited performance     

Noise study of low-dimensional quantum-well semiconductor laseramplifiers

Low noise characteristics of semiconductor laser amplifiers (SLAs) consisting of low-dimensional quantum-well structures are obtained theoretically using density matrix theory. Due to a sharper gain spectrum as well as a smaller population inversion parameter in quantum-wire and quantum-box structures, predominant two beat noises of traveling-wave SLAs were found to be reduced in the lower dimensional quantum-well structures, even in solitary devices without a narrow bandpass filter. The noise figure can be reduced to 3.3 dB in a quantum-box structure, which nears the theoretical limit of 3 dB     

Frequency-conversion efficiency independent of signal-polarizationand conversion-interval using four-wave mixing in semiconductor opticalamplifiers

In this letter, we demonstrate that four-wave mixing in semiconductor optical amplifiers, with the use of two orthogonal-polarized pumps in a polarization-diversity scheme, allows frequency conversion with efficiency independent of both signal polarization and conversion interval     

Static and dynamic characteristics analysis of all-opticalwavelength conversion using directionally coupled semiconductor opticalamplifiers

We analyze the wavelength-converting operation of directionally coupled semiconductor optical amplifiers (DCSOA's) with respect to their static and dynamic characteristics. A complete dynamic DCSOA model based on the modified time-dependent transfer-matrix method is developed. This model accurately considers longitudinal variations of carrier and photon densities, gain, refractive index, coupling coefficients, and lateral optical fields. The extinction ratio, modulation bandwidth, and frequency chirping of DCSOA-based wavelength converters are investigated. For most characteristics, the DCSOA scheme has advantages over cross-gain modulation. Furthermore, by optimizing the injection current into the DCSOA, even better performance can be attained     

An all-optical wavelength-converter with semiconductor opticalamplifiers monolithically integrated in an asymmetric passiveMach-Zehnder interferometer

An all-optical wavelength-converter based on monolithic integration of a Mach-Zehnder interferometer and integrated semiconductor optical amplifiers was demonstrated. This device exhibited high stability, penalty-free conversion at 5 Gbit/s (at a BER of 10⁹), no-excess penalty after a transmission over 60 km on standard fiber, and low signal-polarization dependency. The device operated in a 26-nm-wide optical window     

电子全息在自旋电子学及半导体多量子阱材料研究中的应用

随着现代信息科学技术的发展，自旋阀、磁隧道结等自旋电子学材料及半导体量子阱等光电材料日益受到人们的关注。由于电子显微学方法在衍射、成像及谱学方面具备综合优势，近来已被广泛用于自旋电子学和量子阱光电材料研究领域，以揭示其显微结构和优异物理性能之间的内在联系。其中，普通的电子显微学方法，如透射电子显微术，特别是高分辨电子显微学等是研究这类低维超薄膜晶体结构及其界面关系的有力工具。     

Stability analysis of quantum-well semiconductor lasers withcarrier transport effects

We have formulated a coupled-mode theory with the inclusion of carrier transport effects and used it to analyze dynamics of laser arrays. Special attention has been paid to high-frequency behavior and carrier transport limitations imposed on in-phase mode. General theory has been illustrated for two laterally coupled lasers. Stability analysis had been performed and it was found that the inclusion of the carrier transport effects modifies the stability diagram for &thetas;=π, where &thetas; is the difference between electric field phases of the two lasers     

Efficiency flattening and equalization of frequency up- anddown-conversion using four-wave mixing in semiconductor opticalamplifiers

We show that four-wave mixing in semiconductor optical amplifiers with the use of two orthogonally polarized pumps offers the possibility of frequency conversion with constant efficiency over several terahertz. The same two-pump configuration permits one to convert the signal to lower or higher frequencies with the same efficiency     

Equivalent circuit model for multi-electrode semiconductor opticalamplifiers and analysis of inline photodetection in bidirectionaltransmissions

A rate equation model for static and dynamic behavior for bidirectional transmission in a multisection semiconductor optical amplifier (SOA) is presented. The rate equations for each section have been implemented on an electrical simulator. Here, we have used the model to study the inline photodetection in presence of bidirectional transmission. Small signal photodetection response in presence of co- and contrapropagating signals is given. The photodetection crosstalk expression in bidirectional transmission has also been reported. Simultaneous bidirectional photodetection experiments using a three-electrode SOA show good agreement between measured crosstalk and simulated results obtained by harmonic balance method. A photodetection response nearly free of crosstalk has been obtained for certain operating conditions due to the cross gain modulation between contrapropagating signals     

Ultrafast gain dynamics in asymmetrical multiple quantum-well semiconductor optical amplifiers

A numerical model for the investigation of the ultrafast gain properties in asymmetrical multiple quantum-well semiconductor optical amplifiers has been developed considering propagation of ultrashort optical pulses with different wavelengths. The dynamics of the number of carriers and carrier temperature are investigated for each quantum well. The results agree with the experimental results of pump probe measurements with different wavelengths. It is shown that gain recovery is slower for higher energy wells for pump signals of all wavelengths.