Chaos synchronization and chaotic signal masking in semiconductor lasers with optical feedback

Theoretical and experimental investigations of chaos synchronization and its application to chaotic data transmissions in semiconductor lasers with optical feedback are presented. Two schemes of chaos synchronization-complete and generalized synchronization-are discussed in the delay differential systems. The conditions for chaos synchronization in the systems and the robustness for the parameter mismatches are studied. The possibility of secure communications based on the chaos masking technique in semiconductor lasers with optical feedback is also discussed, and message transmission of a 1.5-GHz sinusoidal signal is demonstrated. The method of bandwidth enhancement of chaotic carriers is proposed for broad-band chaos communications.     

All-optical signal processing based on semiconductor optical amplifiers

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.     

光纤电压传感的DSP实现

光纤电压传感可以用于电网电压的监测和保护.本文在体调制型电压传感器的原理基础上,提出信息处理单元采用DSP技术,讨论了整个系统的构成、信息处理单元的硬件和软件结构.     

基于半导体光放大器的全光信号处理研究进展

本文介绍了基于半导体光放大器非线性光学特性的全光信号处理研究进展。探讨基于半导体光放大器的光波长转换,光信号再生、光逻辑门以及光信号的码型转换等全光信号处理单元。分析国内外各种全光信号处理方案,总结其特色,并对未来发展趋势以及光子集成提出了展望。     

Mode partition in semiconductor lasers with optical feedback

The authors point out that random noise processes induce mode partition fluctuations in semiconductor lasers. Mode partition depends on laser parameters and modulation current. However, external optical feedback can also increase mode partition noise. Here, a numerical solution of multimode noise-driven rate equations with time-delayed terms is utilized to investigate mode partition in semiconductor lasers with reflecting feedback. Photon statistics of the main and side modes in semiconductor lasers under both CW operation and dynamic operation are considered. Probability-density curves for the main and side modes are shown. The feedback-induced change of photon statistics of the main and side modes is clearly seen. Numerical results indicate that, if the laser used is exposed to reflections, a more stringent mode discrimination requirement for suppressing the buildup of laser-cavity longitudinal side modes may result. If mode discrimination is insufficient for avoiding the excitation of side modes, the feedback-induced power penalty depends on the fiber dispersion     

Spectral characteristics of semiconductor lasers with optical feedback

Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.     

Internal optical loss in semiconductor lasers

Internal optical loss in high-power semiconductor lasers based on quantum-well separate-confinement heterostructures was studied. Calculations show that the major portion of the internal optical loss occurs in the active region and emitters. Making the laser waveguide thicker and the cavity longer reduces the internal optical loss. Two possible approaches to the design of laser heterostructures are considered, and optimal solutions are suggested. The difference in the internal optical loss between lasers on InP and those on GaAs substrates is attributed to the larger cross section of photon absorption by holes in InP. Good agreement between the calculated and experimental values of the internal optical loss in lasers on InP and GaAs substrates is obtained.     

Coherent optical pumping of semiconductor lasers

The influence of coherent optical pumping in semiconductor lasers is investigated theoretically. In particular the mathematical conditions under which an optically pumped system behaves like an electrically (incoherently) pumped system are derived. We show that it is practically impossible to reach the interesting regime where coherent effects are important because of the inherent constraints to absorb photons at the pump frequency and to reach threshold gain at the lasing frequency. The effects of changing the temperature and of reduced dimensionality are discussed     

Millimetre-wave signal generation using pulsed semiconductor lasers

A novel technique for millimetre-wave signal generation using a pulsed semiconductor laser is proposed and demonstrated. Optical filtering is used to select only two modes and suppress all other modes in the optical spectrum of the laser. The two selected modes beat together in a photodiode to generate a millimetre-wave signal with 100% modulation depth     

Subharmonic modulation distortions in semiconductor lasers with optical feedback

Experimental studies of subharmonic modulation distortions of semiconductor lasers with optical feedback are described. These distortions were found to exhibit almost resonant frequency characteristics and threshold behaviour against the modulation frequency and its depth, respectively. It was inferred that they would be excited by parametric interactions caused by some laser diode parameter changes due to modulation.     

Analysis of DFB semiconductor lasers with external optical feedback

A theoretical analysis of the sensitivity of DFB semiconductor lasers to external optical feedback is presented. Numerical simulations allow the authors to determine the optimum facet reflectivity, for a given κL value, to minimise the sensitivity to external optical feedback     

Noise characteristics in line-narrowed semiconductor lasers with optical feedback

Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15?20 dB reduction in low-frequency wavelength instability, or phase noise.     

Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications

Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.     

Digital signal processing

Markets have always influenced the central thrust of the semiconductor industry. Beginning in the early eighties, the personal computer (PC) market has been the dominant market influencing the semiconductor industry. Single-chip microprocessors (MPUs) enabled what became the huge PC market, which ultimately overshadowed the earlier minicomputer and mainframe computer markets. The popularity of PCs led to investments in increasingly more powerful MPUs and memory chips of ever-growing capacity. MPUs and DRAMs became the semiconductor industry technology drivers for the data processing needs of the PC. But now, DSP, as opposed to conventional data processing, has become the major technology driver for the semiconductor industry as evidenced by its market growth and the fervour of chip vendors to provide new products based on DSP technology. The increasing need to digitally process analog information signals, like audio and video, is causing a major shift in the semiconductor business. Since DSP is the mathematical manipulation of those digitized information signals, specialized math circuitry is required for efficient signal processing-circuitry that was previously confined to classical DSP chips     

Optical signal processing based on semiconductor optical amplifier and tunable delay interferometer

In this paper,several applications in all-optical signal processing based on a semiconductor optical amplifier (SOA) and variable delayed interferometers (DIs) have been experimentally demonstrated.Wavelength converter based on a nonlinear polarization switch (NPS) and a DI is proposed and presented for the wavelength conversion of nonretum-to-zero (NRZ) signals.An alloptical nonretum-to-zero to return-to-zero (NRZ-to-RZ)format converter with tunable duty cycles is achieved by the DI with variable delays.The 40 Gb/s reconfigurable optical OR/NOR gate in a single SOA,followed a tunable optical bandpass filter (OBF) and a DI,optical 2R regeneration using an SOA-DI are investigated.It is found that this combinative realization of filters has been endowed with great flexibility and quality for 40 Gb/s optical logic and 2R regeneration.     

光纤耦合光双稳半导体激光器的研究

介绍一种紧凑的、能以较低输入光功率工作的光学双稳器件,由光电检测器、光纤定向耦合器和半导体激光二极管组合而成的。描述了工作原理,解释所观测到的一些效应,例如滞后回线、微分增益以及记忆功能。     

Multiwavelength lasers based on semiconductor optical amplifiers

Stable multiwavelength lasing is demonstrated with a novel laser, in which a semiconductor optical amplifier offers optical gain and cascaded sampled fiber gratings serve as a comb filter. Five lasing lines are obtained with a fixed wavelength spacing of 0.8 nm. Optical power fluctuations among the lasing lines are improved by adjusting the reflectivity profile through the cascade of two sampled gratings     

Chaos in semiconductor lasers with optical feedback: theory andexperiment

The authors present a detailed theoretical and experimental investigation of the nonlinear dynamics of a semiconductor laser with optical feedback. The results show that the coherence collapsed state is a chaotic attractor and that chaos is reached for increasing feedback level through a quasi-periodic route interrupted by frequency locking. Furthermore, the coexistence of two attractors, associated with the same external cavity mode, but having different relaxation oscillation frequencies, is demonstrated and explained     

Optical signal processing based on self-induced polarization rotation in a semiconductor optical amplifier

We demonstrate novel optical signal processing functions based on self-induced nonlinear polarization rotation in a semiconductor optical amplifier (SOA). Numerical and experimental results are presented, which demonstrate that a nonlinear polarization switch can be employed to achieve all-optical logic. We demonstrate an all-optical header processing system, an all-optical seed pulse generator for packet synchronization, and an all-optical arbiter that can be employed for optical buffering at a bit rate of 10 Gb/s. Experimental results indicate that optical signal processing functions based on self-polarization rotation have a higher extinction ratio and a lower power operation compared with similar functions based on self-phase modulation.