Waveguide grating filters for dispersion compensation and pulsecompression

Dispersion compensation and pulse compression are theoretically demonstrated using aperiodic waveguide gratings. The gratings are designed to have both a flat amplitude and a quadratic phase response over the pulse bandwidth. This results in nearly transform-limited compressed pulses. The appropriate waveguide grating parameters are obtained by applying the Gel'fand-Levitan-Marchenko inverse scattering method to the coupled mode equations which describe propagation. The technique is illustrated by designing an aperiodic grating which compresses a 60-ps pulse by a factor of three. Limitations and possible extensions of the general method are discussed     

Model for analyzing manufacturing-induced internal stresses in 50-GHz DWDM multilayer thin-film filters and evaluation of their effects on optical performances

The manufacture of a high-quality reliable thin-film filter (TFF) requires a detailed understanding of the stresses created within the device during fabrication. The ability to systematically approximate the internal stress effect on optical performance is of crucial importance to provide fabrication guidance and improve manufacturing yield. This paper analyzes the internal stress distributions in the substrate and thin-film layers of a 50-GHz TFF and examines the relation of these stresses to the filter's optical characteristics. A linear model along the thickness direction is introduced based upon Townsend's theory of multilayer structures. The analytical results for the key optical parameters are in good agreement with measurements on fabricated filters. This model analyzes the effects of process parameters, such as the substrate type, its coefficient of thermal expansion, and the final substrate thickness on the optical performance of the transmission spectrum center wavelength, transmission passband ripple and isolation, the chromatic dispersion, and polarization-mode dispersion.     

Entirely thin-film allpass coupled-cavity filters in a parallelconfiguration for adjustable dispersion-slope compensation

Conventional dispersion-slope compensation filters suffer from a fundamental tradeoff between the amount of dispersion-slope compensation and the compensation bandwidth. A novel multireflection device, composed of two coupled cavity filters in a parallel configuration is proposed that has an adjustable dispersion-slope independent of the compensation bandwidth. The device provides an adjustable dispersion-slope value between -6.7 and -35.7 ps³ over a bandwidth of 3 nm. The center wavelength is adjustable over a 10-nm range     

Experimental demonstration of nonlinearity and dispersion compensation in an embedded link by optical phase conjugation

We report in this letter, the experimental demonstration of simultaneous dispersion and nonlinearity compensation in an embedded link characterized by strongly asymmetrical power profiles. This result is obtained by using a highly efficient optical phase conjugator based on a periodically poled lithium-niobate waveguide, combined with two small dispersion-compensating elements properly inserted in the link.     

Experimental demonstration of fibre-optic delay line filters withnegative coefficients

The authors present the implementation and experimental demonstration of two fibre-optic delay line filters with negative coefficients using differential detection. These filters have characteristics that cannot be obtained using purely positive recirculating delay lines     

A compact thin-film-based all-pass device for the compensation of the in-band dispersion in FBG filters

Fiber Bragg grating (FBG)-based bandpass filters, while possessing close to ideal sharp rolloff characteristics, can suffer from a significant amount of in-band dispersion. Results concerning the compensation of the in-band dispersion of a typical 100-GHz FBG using two thin-film all-pass filters, each composed of two coupled-cavities packaged in a compact configuration, are presented. The total peak insertion loss of the compensation package is less than 2.5 dB.     

Experimental demonstration of the maximum likelihood-based chromatic dispersion estimator for coherent receivers

We perform an experimental investigation of a maximum likelihood-based (ML-based) algorithm for bulk chromatic dispersion estimation for digital coherent receivers operating in uncompensated optical networks. We demonstrate the robustness of the method at low optical signal-to-noise ratio (OSNR) and against differential group delay (DGD) in an experiment involving 112 Gbit/s polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (16 QAM) and quaternary phase-shift keying (QPSK).     

Experimental demonstration of postnonlinearity compensation in a multispan DPSK transmission

We demonstrate significant performance improvement in 10-Gb/s multispan differential phase-shift keying transmissions by employing postnonlinearity compensation (PNC) for both dispersion-managed soliton and quasi-linear transmission. Measurements of timing misalignment tolerance as well as bandwidth requirement of the PNC unit show that the PNC technique is robust and practical, and can be easily extended to higher bit-rate transmissions.     

Dielectric multilayer thin-film filters for WDM transmission systems

Dielectric multilayer thin-film (DMF) filters for a wavelength-division-multiplexing (WDM) system are discussed. It was found that a 23-layer 3-cavity bandpass-type DMF-filter made of TiO2and SiO2is most suitable for this type of system. An optical multi/demultiplexer employing this type of bandpass DMF-filter is applicable to a two-way WDM transmission system.     

Experimental demonstration of long-distance dispersion-managedsoliton propagation at zero average dispersion

We observed for the first time stable propagation of dispersion-managed solitons with zero or slightly below normal average dispersion over 28000 km in a recirculating fiber loop. Comparison between theory and experiment provides a highly sensitive estimate of the average dispersion     

A novel ultra-compact resonator for Superconducting thin-film filters

This paper proposes a novel thin-film resonator structure, which combines the microstrip resonator and the coplanar resonator to form an integrated resonator. This resonator structure has an extremely compact size, as compared to the thin-film resonator structures from the literature, and its resonant frequency was shown theoretically to be less sensitive to, or even insensitive to, the thickness of the substrate. An eight-pole quasi-elliptic filter based on this novel resonator was designed. The exact filter layout was simulated and optimized by full-wave electromagnetic simulation using IE3D software. The full-wave simulated filter response was in good agreement with the theoretical filter response. A filter was fabricated on a double-sided YBa/sub 2/Cu/sub 3/O/sub 7/ thin film epitaxially grown on a 2-in-diameter MgO wafer. The measured filter response showed a bandwidth of 1.5 MHz and a center frequency of 850.3 MHz at 78 K. The insertion loss at the passband center was 1 dB, corresponding to a filter Q of 28 000. Steep rejection slopes were obtained at the band edges and rejections reached over 70 dB in approximately 300 kHz from the passband edges. No pronounced changes were observed for input power levels between -20-0 dBm, indicating a relatively high power-handling capability of the filter.     

Adaptive algorithms for a two-channel structure employing allpass filters, with applications to polarization mode dispersion compensation

A two-channel structure consisting of multiple cascades of allpass filters and directional couplers has certain desirable attributes. This paper considers adaptive algorithms for adjusting the parameters of such systems. The exemplary algorithms are motivated by an application to the compensation of polarization mode dispersion, which is a key problem in fiber optic systems. Gradient algorithms are shown to exhibit extremely slow convergence. This problem is solved by deriving a Newton-type algorithm. However, possible convergence to a local minimum emerges as a more fundamental problem. One of the conditions for local minima is specifically identified in terms of problematic parameter states.     

Experimental demonstration of step-like dispersion profiling inoptical fibre for soliton pulse generation and compression

Generation of 100 GHz trains of 500-700 fs pulses using dual-frequency beat conversion in a step-like dispersion profiled fibre is reported. The authors believe that this is the first time the generation and compression of soliton pulses using such a fibre has been demonstrated. The fabrication of such fibre assemblies does not require any special facilities and relies only on conventional optical fibre technology. They believe that the use of profiling the fibre dispersion by fibre segments instead of continuously dispersion-decreasing fibre is not only possible but preferable in many applications     

Birefringence compensation for polarization-independent directionalcoupler wavelength filters

We show how polarization-independent optical wavelength filters can be achieved using asymmetric directional couplers with birefringence-compensation. Simulations demonstrate that excellent polarization behavior can be achieved with practical tolerances and without sacrificing filter bandwidth or insertion loss     

Experimental demonstration of pattern effect compensation using anasymmetrical Mach-Zehnder interferometer with SOAs

We propose an asymmetrical interferometer to compensate the pattern effect in semiconductor optical amplifier (SOA) as an inline amplifier in dense wavelength-division-multiplexing (DWDM) system. Experiments are demonstrated with a commercial integrated Mach-Zehnder interferometer (MZI)-SOA. The experiments showed that in a 16×10-Gb/s DWDM system, the power penalty induced by the SOA decreased from 6.8 to 0.9 dB by the interference at 1 mW input power, and the input power dynamic range of the SOA was efficiently extended     

Bi-end dispersion compensation for ultralong optical communicationsystem

Bi-end dispersion compensation (DC) for ultralong nonreturn-to-zero (NRZ) optical transmission system is studied. Both the loss and dispersion of the transmission fiber are periodically compensated. Two dispersive elements are placed at the input and output ends of a compensation period, respectively, to compensate for fiber dispersion. The pulse compression owing to self-phase modulation (SPM) can be adjusted by the compensation ratios of the dispersive elements at the two ends of a compensation period. Therefore, the pulse compression can be optimized and the system performance can be improved to compare with the system with either pre- or postdispersion compensation. The rules to design the system are considered. The transmission system of 10-Gb/s bit rate, 9000-km transmission distance, and 100-km compensation period is taken as an example. The second-order fiber dispersion is assumed to be completely compensated. Wave equation is numerically solved to study the system performance which is represented by Q factor. The relations of several system parameters and Q factor are studied. The system parameters include the compensation ratios of the dispersive elements at the two ends of a compensation period, dispersion of transmission fiber, signal power, and the compensation ratios of third-order fiber dispersion. If the third-order fiber dispersion cannot be completely compensated, it is found that one can use a higher signal power to improve the system performance     

高速光通信系统中的色散补偿技术

高速光纤通信系统中，色散补偿和极化模色散补偿是提高信噪比、改善系统性能的必要手段。本文介绍了几种常用商用传输光纤及其色散特性，分析了相应的色散补偿技术，重点分析了其中普遍采用的色散补偿光纤技术。     

色散与色散斜率同时进行补偿的方法

在参考大量国外文献的基础上,介绍了三类对光纤传输线路中色散与色散斜率同时进行补偿的方法,并将每类补偿方法又细分成几种.     

An adaptive approach for designing phase compensation filters

The objective of this communication is to introduce an adaptive method for designing filters to compensate for nonlinear phase shift introduced into a data stream by fixed (i.e., nonadaptive) recursive digital filters, e.g., those obtained via the bilinear transform.     

A novel active compensation scheme for active-RC filters

A novel scheme using two internally compensated operational amplifiers with unmatched gain-bandwidth products is suggested as a replacement for the conventional single-amplifier integrators, inverters or summers. The scheme, while providing exact phase compensation, contributes to magnitude compensation as well. Filters realized using such a scheme have an extended range of frequency of operation with reduced error in pole frequency and in Q.