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All-optical signal processing based on semiconductor optical amplifiers
Yong LIU, Ligong CHEN, Tianxiang XU, Jinglei MAO, Shangjian ZHANG, Yongzhi LIU
Front Optoelec Chin. 2011, 4 (3): 231-242.
https://doi.org/10.1007/s12200-011-0141-1
In this paper, we review the recent progress in the optical signal processing based on the nonlinearity of semiconductor optical amplifiers (SOAs). The four important optical signal processing functional blocks in optical switching are presented, i.e., optical wavelength conversion, optical regeneration, optical logic, and optical format conversion. We present a brief overview of optical wavelength conversion, and focus on various schemes to suppress the slow gain recovery of the SOA and improve the operating speed of the SOA-based optical switches. Optical regeneration including re-amplification, re-shaping and re-timing is also presented. Optical clock recovery that is essential for optical regeneration is reviewed. We also report the recent advances in optical logic and optical format conversion, respectively. After reviewing the four important optical signal processing functional blocks, the review concludes with the future research directions and photonic integration.
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Silicon slow light photonic crystals structures: present achievements and future trends
Eric CASSAN, Xavier LE ROUX, Charles CAER, Ran HAO, Damien BERNIER, Delphine MARRIS-MORINI, Laurent VIVIEN
Front Optoelec Chin. 2011, 4 (3): 243-253.
https://doi.org/10.1007/s12200-011-0144-y
Slow light in planar photonic structures has attracted for some years an increasing interest due to amazing physical effects it allows or reinforces and to the degrees of freedom it raises for designing new optical functions. Controlling light group velocity is achieved through the use of periodical optical media obtained by nano-structuration of semiconductor wafers at the scale of light wavelength: the so-called photonic crystals. This article reviews present achievements realized in the field of slow light photonic bandgap structures, including the physical principles of slow light to the description of the most advanced integrated optical devices relying on it. Challenges and current hot topics related to slow light are discussed to highlight the balance between the advantages and drawbacks of using slow waves in integrated photonic structures. Then, future trends are described, which is focused on the use of slow wave slot waveguides for non-linear optics and bio-photonic applications.
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Compensation of quadrature imbalance in an optical coherent OQPSK receiver in presence of frequency offset
Xinying LI, Bo HUANG, Yufeng SHAO, Junwen ZHANG, Shumin ZOU, Wuliang FANG, Li TAO, Jiangbo ZHU, Chi NAN
Front Optoelec Chin. 2011, 4 (3): 288-291.
https://doi.org/10.1007/s12200-011-0140-2
In this paper, we describe the impact of quadrature imbalance (QI) in the presence of frequency offset in an optical coherent offset quadrature phase shift keying (OQPSK) receiver. Arbitrary conjugate misalignment was realized in a 2×4 90° optical hybrid, and the ellipse correction (EC) method of quadrature imbalance was applied in our simulation. In the case of transmission, the EC method can significantly improve the system performance.
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Generation of 40 GHz phase stable optical short pulses using intensity modulator and two cascaded phase modulators
Yu JI, Yan LI, Wei LI, Xiaobing HONG, Hongxiang GUO, Yong ZUO, Kun XU, Jian WU, Jintong LIN
Front Optoelec Chin. 2011, 4 (3): 292-297.
https://doi.org/10.1007/s12200-011-0142-0
Pulse sources based on lithium niobate modulators are very attractive for optical time division multiplexing (OTDM) transmission systems because the modulators are now commercially available, qualified for system use, and can operate up to very high speeds and over a wide wavelength range. In this paper, we describe the principles of operation and performance of the pulse source based on lithium niobate modulators. The pulse source is based on a Mach-Zehnder intensity modulator (IM) and two phase modulators (PMs). The continuous-wave (CW) light is modulated in an IM and then strongly phase modulated in two cascaded PMs. The chirped pulses are subsequently compressed to desired width using dispersion compensation technology. This method has the advantage of acquiring larger chirp using normal PM rather than that special designed PM of very low Vπ. It can also generate shorter pulses than conventional methods incorporating only one PM driving by a radio frequency (RF) signal with the power larger than 1 W which may damage the device. Generation of 40 GHz optical pulses shorter than 2 ps is theoretically illustrated, simulated and experimentally verified. Experimental results show that 40 GHz phase stable optical pulses with pulse-width of 1.88 ps, extinction ratio (ER) larger than 20 dB, the timing jitter of 57 fs and signal-to-noise ratio (SNR) of 32.8 dB can be achieved. This is also a cavity-less pulse source whose timing jitter is determined only by the RF source rather than by the actively controlled cavity. In the experiment, the phase noise of the RF source we used is as low as -98.13 dBc/Hz at a 10 kHz offset frequency which resulting very low timing jitter of generated pulses. The pulses are then modulated at 40 Gbaud/s with an inphase/quadrature (I/Q) modulator and multiplexed to 160 Gbaud/s with less interference between each other. After back-to-back demultiplexing by an electro-absorption modulator (EAM) to 40 Gbaud/s and demodulation by a delay interferometer (DI), clear and opened eye diagrams of 40 Gbaud/s I and Q tributary signals are obtained which verify the good performance of generated pulses in the 160 Gbaud/s differential quadrature phase shift keying (DQPSK) OTDM system and further prove the phase stability and high quality of generated pulses.
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Impacts of mismatched intrinsic parameter on leader-laggard synchronization between two mutually coupled VCSELs
Lingbo ZENG, Tao DENG, Zhengmao WU, Jiagui WU, Guangqiong XIA
Front Optoelec Chin. 2011, 4 (3): 298-307.
https://doi.org/10.1007/s12200-011-0139-8
Based on spin-flip model (SFM), the impacts of mismatched intrinsic parameter on leader-laggard chaos synchronization between two mutually coupled vertical-cavity surface-emitting lasers (VCSELs) have been investigated numerically. Results show that, for two VCSELs with identical intrinsic parameter, the switching point of leader-laggard caused by continually varying frequency detuning or injection rate detuning is located at zero frequency detuning or zero injection rate detuning, which indicates that the VCSEL with higher frequency or subject to lower injection level plays a leader role. However, for two VCSELs with mismatched intrinsic parameter, the switched point of leader-laggard will deviate from zero frequency detuning or zero injection rate. Therefore, compared with the results obtained under matched intrinsic parameter, the opposite results have been observed in the range between zero detuning and switching point. Additionally, the offsets of switching point induced by different intrinsic parameters are different, and the influence of line-width enhancement factor is found to be the most significant.
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High accuracy numerical solutions for band structures in strained quantum well semiconductor optical amplifiers
Xi HUANG, Cui QIN, Xinliang ZHANG
Front Optoelec Chin. 2011, 4 (3): 330-337.
https://doi.org/10.1007/s12200-011-0220-3
In this paper, we have calculated the band structure of strained quantum well (QW) semiconductor optical amplifiers (SOAs) by using plane wave expansion method (PWEM) and finite difference method (FDM), respectively. The difference between these two numerical methods is presented. First, the solution of Schr?dinger’s equation in a conduction band for parabolic potential well is used to check the validity and accuracy of these two numerical methods. For the PWEM, its stability and computational speed are investigated as a function of the number of plane waves and the period of QW. For FDM, effects of mesh size and QW width on its accuracy and calculation time are discussed. Finally, we find that the computational speed of FDM generally is faster than that of PWEM. However, the PWEM is more efficient than the FDM when wider SOAs are needed to be calculated. Therefore, to obtain high accuracy and efficient numerical solutions for band structures, numerical methods should be selected depending on required accuracy, device structure and further applications.
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16 articles
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