可调谐窄带宽的负系数微波光子滤波器

针对负系数微波光子滤波器很难用正系数的光学抽头来实现,提出了一款基于色散器件级联的可调谐、窄带宽、负系数微波光子滤波器。利用整形后的多波长光纤激光器的输出信号作为滤波器的抽头光源,将单模光纤与F-P光纤环级联作为延迟单元,实现滤波器的频率选择性。利用相位调制器和级联的色散器件共同作用,实现负系数的微波光子滤波器。实验得到了波长间隔为0.34 nm的多达37个激光信号的稳定输出,进而基于此实验结果仿真研究了F-P光纤环中C2、C3的耦合系数r、不同长度的可调谐光纤延迟线（TODL）和延迟单元中不同长度的单模光纤等参数对微波光子滤波器性能的影响。     

Dispersion slope equalizer for dispersion shifted fiber using alattice-form programmable optical filter on a planar lightwave circuit

This paper reports an integrated-optic dispersion slope (third-order dispersion) equalizer for dispersion shifted fiber which employs a lattice-form programmable optical filter on a planar lightwave circuit (PLC). This dispersion slope equalizer consists of nine symmetrical interferometers interleaved with eight asymmetrical interferometers. The performance of the equalizer is evaluated numerically. We confirm experimentally that this equalizer is effective in reducing the pulse waveform deterioration caused by the dispersion slope. In addition, the equalizer improves the power penalty of a 200-Gb/s, 100-km, time-division multiplexed optical transmission experiment     

Unrepeated transmission of 20-Gb/s optical quadrature phase-shift-keying signal over 200-km standard single-mode fiber based on digital processing of homodyne-detected signal for Group-velocity dispersion compensation

We demonstrate unrepeated optical transmission of 20-Gb/s quadrature phase-shift-keying (QPSK) signals over a 200-km-long standard single-mode fiber (SMF) without using any optical dispersion compensator. By employing optical homodyne detection, which can restore the entire information of the complex amplitude of the transmitted signal, group-velocity dispersion (GVD) of the SMF can be compensated electrically by a linear equalizer at the receiver. From off-line bit-error-rate measurements, we find that a simple transversal filter implemented in digital signal processing circuits after homodyne detection can effectively cancel the fiber GVD of up to 4000 ps/nm, enabling successful 20-Gb/s QPSK transmission.     

Cascaded Mach–Zehnder Interferometers Assembled by Submicrometer PTT Wires

A single bow-shaped Mach–Zehnder interferometer (MZI) and two-cascaded MZIs were assembled by flexible submicrometer polymer wires, which were directly drawn from poly(trimethylene terephthalate) melt. The size of the cascaded MZIs is tens to hundreds of micrometers and their path-length differences can be dynamically adjusted by micromanipulation under an optical microscope. Experimental results show that the cascaded MZIs have a large extinction ratio (25 dB) with a flat-top transmission over a wavelength range of 1.3–1.6 $mu$m. The insertion losses of the cascaded MZIs with two and three bow-shaped MZIs are 1.1–1.8 and 1.5–2.3 dB, respectively.      

Electrical Mitigation of Penalties Caused by Group Delay Ripples for Different Modulation Formats

Electrical equalizers are proposed to mitigate the distortions caused by group delay ripples (GDRs) of cascaded optical filters (e.g., fiber Bragg gratings for chromatic dispersion (CD) compensation). Different electrical equalizers including feedforward equalizer (FFE), decision-feedback equalizer (DFE), nonlinear FFE-DFE, and maximum-likelihood sequence estimator are investigated and compared comprehensively for four different modulation formats: ON-OFF keying, optical duobinary, optical single sideband, and differential phase-shift keying. Especially, we find that the relationship of electrical equalization performance on the modulation format is very similar for the mitigation of GDR and CD.     

A band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter（MPF）based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated.In the experiment,a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source（BOS）with a Lyot-Sagnac filter.A standard single-mode fiber（SMF）and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio（MSSR）and Q-factor of the filter.The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator.The results have significant guidance for MPF design by choosing appropriate devices and parameters.Based on the analyses,a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of0.01,the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.     

Planar lightwave circuit dispersion equalizer

The authors report an integrated-optic dispersion equalizer fabricated on a planar lightwave circuit (PLC). This PLC dispersion equalizer is composed of several asymmetrical Mach-Zehnder interferometers cascaded in series. The dispersion equalizer has a high degree of design flexibility and can compensate for both normal and anomalous fiber dispersions at any center wavelength. Moreover, the equalizer can be applied to WDM transmission systems. This equalizer employing five asymmetrical interferometers is fabricated and its measured dispersion values are +834 and -1006 ps/nm. The effectiveness of the equalizer is demonstrated in a 2.5 Gb/s transmission experiment with a 1.3 μm zero-dispersion fiber at 1.55 μm. Also, its performance is evaluated theoretically     

Compensation for chromatic dispersion and nonlinear effect in highdispersive coherent optical repeater transmission system

A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible     

Electronic Dispersion Compensation

The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization.     

常规DSF光纤参变放大器的带宽拓宽研究

为了拓宽常规色散位移光纤(DSF)型双抽运光纤参变放大器(FOPA)的放大带宽,提出了用DSF和单模光纤(SMF)级联来构造周期色散补偿双抽运FOPA的思想。利用SMF正的二阶色散以减小DSF负的四阶色散引起的相位失配,从而达到有效拓宽FOPA放大带宽的目的。结合四波混频耦合方程对该双抽运FOPA进行仿真研究,得到拓宽为69nm的放大带宽的结果。结果表明,光纤长度一定时,采用给出的最佳补偿光纤长度进行色散补偿,可有效减小因DSF四阶色散引起的相位偏移,进而拓宽放大带宽;分多段级联进行色散补偿时,可进一步拓展放大带宽。     

Fourth-order dispersion compensation for 250-fs pulse transmissionover 139-km optical fiber

Record distance transmission of 250-fs pulses over 139-km optical fiber at 6-GHz repetition is realized by compensating chromatic dispersion up to fourth-order using a novel approach. The link is designed combining 108.5-km standard single-mode fiber (SMF), 17.5-km dispersion-shifted fiber, and 13-km negative-slope dispersion-compensating fiber to achieve both zero total chromatic dispersion and slope at the 1.55-μm carrier. Fourth-order pulse dispersion caused by the fiber dispersion curvature around 1.55 μm is then suppressed by adding the quadratic phase of opposite sign from excess SMF to produce 503-fs output. However, both higher quality and shorter 390-fs output is achieved after applying 6-GHz electrooptic phase modulation (3.5 π O-peak) to prestretched pulses and adding a further 50-m SMF to the link     

Comparison of nonlinear pulse interactions in 160-Gb/s quasi-linear and dispersion managed soliton systems

The understanding and development of 160-Gb/s transmission systems requires the study of the impact of different dispersion compensation schemes on pulse propagation in nonlinear fiber. In this paper, we present an investigation of 160-Gb/s optical transmission systems, focusing on optimal propagation regimes, and in particular, we analyze different transmission limitations and dominant nonlinear effects by comparing quasi-linear and dispersion managed soliton systems. Two quasi-linear systems, one using nonzero dispersion-shifted fiber (NZDSF) and the other single-mode fiber (SMF), and one short-period (1 km) dispersion managed soliton (DMS) system are studied, both for single-channel and wavelength-division-multiplexed (WDM) transmission. First, the performance of the two quasi-linear systems in single-channel transmission are compared and it is shown that the NZDSF and SMF systems allow similar error-free transmission distances with only small differences in the intrachannel four-wave mixing (IFWM) induced amplitude jitter. The effect of pulsewidth on transmission performance in this regime was investigated and the use of shorter pulses was found to result in lower amplitude jitter. We analyzed the behavior of the DMS system and showed that the reduced pulse broadening during transmission allowed a significantly longer single-channel transmission distance with a smaller impact of nonlinearities compared to quasi-linear propagation. The sensitivity of the DMS system performance to statistical fluctuations in the fiber dispersion was studied and the results show the level of accuracy in the dispersion management map which must be ensured in these systems. Finally, the performance of the DMS in WDM transmission was investigated and it was found that it was subject to very large penalties increasing the minimum channel spacing possible because of the strong impact of interchannel cross-phase modulation (XPM).     

Reconfigurable Dispersion Equalizer Based on Phase-Apodized Fiber Bragg Gratings

We present a novel dispersion equalizer design for the compensation of chromatic dispersion and chromatic dispersion slope in WDM systems. The device is based on a cascade of complex quasi-periodic chirped fiber Bragg gratings. We show that the use of a low chirp results in the distribution of the resonating cavities along the optical fiber length, which allows reconfiguration of the spectral characteristics by the application of a temperature profile. This paper exposes in detail the numerical techniques used in the optimization of the fiber Bragg grating filters taking into account fabrication imperfections. We present a specific design for a 32-channel dispersion equalizer for 10 Gbit/s and a 50-GHz channel spacing. We examine the spectral characterization of a device fabricated using a phase-apodized mask for various settings of the chromatic dispersion profile. We demonstrate a tuning range of $pm {800}~{rm ps}/{rm nm}$ over a bandwidth of 30 GHz. On average, the standard deviation of the phase ripple was below 0.1 rad. Finally, we evaluate the performance of this device by bit error rate measurements.      

一种新型的全光纤超短光脉冲压缩方案

文章提出了一种基于正常色散递减光纤（ND—DDF）、单模光纤（SMF）和非线性环镜（NOLM）组成的全光纤超短脉冲压缩方案。利用光脉冲在正常色散区的色散递减光纤（ND-DDF）中传输时,在脉冲的中心部分将带上较大线性正啁啾（和普通光纤相比）,当脉冲在SMF中传输时色散致啁啾对其进行补偿从而有一个脉冲压缩的过程,最后利用NOLM对压缩后的脉冲进行进一步的压缩和消基座处理。数值模拟的结果表明：半峰全宽为10ps、能量为74pJ的高斯脉冲经过1km的DDF、79m的SMF和20m的NOLM后,可以获得峰值功率为210W,半峰全宽为120fs且几乎无基座的超短脉冲。     

光纤技术的进展与应用

本文介绍了光纤的传输特性，简述了常规单模光纤和色散位移单模光纤的特点和应用，重点阐述了非零色散位移光纤的性能及光纤色散补偿技术，分析了各种光纤的应用条件。     

Fiber transmission for sub-500-fs pulses using adispersion-compensating fiber

We report transmission of ~60-fs and ~245-fs pulses, respectively, over 42-m and 2.5-km fiber links which consist of standard single-mode fibers (SMF) concatenated with dispersion-compensating fibers (DCF). The experiments using very short pulses (~60 fs) over a short fiber length (~42 m) demonstrate the ability to achieve simultaneous dispersion and dispersion slope compensation using this technique. Femtosecond spectral interferometry measurements of this 42-m link show that its residual dispersion slope is approximately six times lower than that of the dispersion-shifted fiber. Finally, to demonstrate that the dispersion-limited propagation distance is proportional to the cube of the pulsewidth, we transmit ~245-fs pulses over a 2.5-km SMF-DCF link and achieve comparable pulse restoration as with the shorter fiber experiments     

MLSE Equalizers for Frequency Discrimination Receiver of MSK Optical Transmission System

We propose maximum-likelihood sequence estimator (MLSE) equalizers based on either Viterbi algorithm or template matching temple matching (TM) for the equalization of impairments imposed on the minimum shift keying (MSK) modulation formats in long haul transmission without optical dispersion compensation. The TM-MLSE equalizer is proposed as a simplified alternative for the Viterbi-MLSE equalizer. It is verified that the Viterbi-MLSE equalizer can operate optimally when noise approaches a Gaussian distribution. Simulation results of the performances of the two MLSE equalizers for optical frequency discrimination receiver-based optical MSK systems are described. The transmission performance is evaluated in terms of: (1) the chromatic dispersion (CD) tolerance for both Viterbi-MLSE and TM-MLSE equalizers; (2) transmission distance limits of Viterbi-MLSE equalizers with various number of states; (3)the robustness to fiber polarization mode dispersion (PMD) of Viterbi-MLSE equalizers; and (4) performance improvements for Viterbi-MLSE equalizers when utilizing sampling schemes with two and four samples per bit over the conventional single sample per bit. With a small number of states (64 states), the non-compensating optical link can equivalently reach up to approximately 928 km SSMF for 10 Gb/s transmission or 58 km SSMF for 40 Gb/s. The performance of 16-state Viterbi-MLSE equalizers for optical frequency discrimination receiver (OFDR)-based optical MSK transmission systems for PMD mitigation is also numerically investigated. The performance of Viterbi-MLSE equalizers can be further improved by using the sampling schemes with multiple samples per bit compared to the conventional single sample bit. The equalizer also offers high robustness to fiber PMD impairment.     

Performance comparison between DCF and RDF dispersion compensation in fiber optical CATV systems

An architecture of an externally modulated AM-VSB CATV 77-channel erbium-doped fiber amplifier (EDFA)-repeated system which use the combination of a single-mode fiber (SMF) and reverse dispersion fiber (RDF) as a dispersion compensation device is proposed and demonstrated. Compared to the conventional externally modulated fiber optical CATV systems with or without a dispersion compensation fiber (DCF), excellent performance of composite second order (CSO) /spl ges/ 78 dB accompanied by satisfied carrier-to-noise ratio (CNR) /spl ges/ 50 dB and composite triple beat (CTB) /spl ges/ 65 dB was obtained in the proposed system.     

基于OOC的WDM+OCDMA系统性能研究

基于光正交码,研究了WDM+OCDMA系统的性能。采用4个波长信道和3个码字的光正交码OOC(37,4,1),对12个用户的WDMA+OCDMA进行了系统仿真,用户数据速率为1Gbit/s,单模光纤长为50km,色散补偿光纤长为5km。如需增加WDMA+OCDMA的用户数,可以通过增加波长信道数或码字容量来实现。分析了色散效应对WDMA+OCDMA系统性能的影响,研究了用户之间相对延时对多址干扰和系统性能的影响。     

Dispersion Compensation Over All the Telecommunication Bands With Double-Cladding Photonic-Crystal Fiber

This paper numerically describes the design of double-cladding photonic-crystal fiber (DC-PCF) for ultrabroad- band compensation over all telecommunication bands (O to L), i.e., ranging from 1260 to 1625 nm. We show that an ultrabroad- band compensating DC-PCF can be designed simply by considering the zero-dispersion wavelength and the relative dispersion to the slope at a particular wavelength of a conventional single-mode fiber (SMF). As a result, we reveal that the proposed DC-PCF can successfully compensate for the dispersion of a conventional SMF with an effective dispersion range of plusmn0.4 ps/nm ldr km over all telecommunication bands as well as provide an effective area comparable to that of conventional dispersion-compensating fiber.