Dispersion Slope Compensation Research Articles

Symmetric slope compensation in a long-haul WDM system using the CRZ format

We numerically compared symmetric and asymmetric dispersion slope compensation schemes in a long-haul, chirped-return-to-zero, wavelength-division-multiplexed system. Symmetric compensation has significant advantages over asymmetric compensation. We elucidate the physical reasons and the system implications.

Generation of negative third-order dispersion in coiled single-mode fibers

We describe the generation of negative third-order dispersion in coiled single-mode fibers that exhibited positive third-order dispersion before coiling. We observed these slope changes in DSFs and 1.3 μm zero-dispersion SMFs in the 1.5 μm region. The generated negative third order dispersion ranges over a broad band of about 8 nm for DSFs and over 20 nm for SMFs. We confirmed the effectiveness of coiled fibers as unique dispersion slope compensators for DSFs.

Adaptive dispersion equalization by monitoring relative phase shift between spacing-fixed WDM signals

This paper proposes a novel adaptive dispersion equalization system that equalizes the temperature-induced dispersion fluctuation in long-span ultra-high-speed optical transmission systems. The system monitors the dispersion fluctuation by measuring the relative delay between two wavelength division multiplexed (WDM) signals, and equalizes the dispersion fluctuation by wavelength tuning. A variable-dispersion equalizer can be used instead of wavelength tuning. Adaptive equalization is successfully demonstrated in 40-Gb/s (8-ps-RZ pulses) 400-km transmission. Furthermore, the proposed equalization system is shown to be applicable to WDM systems that use dispersion and dispersion slope compensation. Since the sensitivity to the dispersion fluctuation is improved by extending the wavelength spacing of the signal and monitor channels, the system is shown to operate even when polarization-mode dispersion (PMD) of the transmission fiber must be taken into account.

Experimental Investigations of a Stress-Gradient Sampled Bragg Grating with a Chirp in the Sampling Period

The spectrum response of a sampled Bragg grating (SBG) with a chirp in the sampling period (CSP) under stress-gradient is experimentally investigated for the first time. It is shown that unlike in a conventional SBG without CSP, the bandwidths of the multiple stopbands vary with the stress asymmetrically around the center Bragg wavelength. These results coincide with the theoretical predictions presented by us. The present experimental demonstration is useful for the application of the SBG with CSP in dispersion slope compensation of fiber in dense wavelength division multiplexing (DWDM) systems.

8 THz bandwidth dispersion-slope compensator module for multiband 40 Gbit/s WDM transmission systems using an AWG and spatial phase filter

The authors demonstrate a 2 × 40-channel dispersion-slope compensator for 40 Gbit/s wavelength-division multiplexing (WDM) transmission systems that employs an arrayed-waveguide grating (AWG) with a 4.0 THz bandwidth and a spatial phase filter. It can compensate for the dispersion slope of the entire bandwidth of C- and L-bands simultaneously.

Tunable compensation of the dispersion slope mismatch in dispersion-managed systems using a sampled nonlinearly chirped FBG

We demonstrate dispersion slope compensation for three 10-Gbit/s wavelength-division-multiplexing (WDM) channels using a sampled nonlinearly chirped fiber Bragg grating (FBG) in a dispersion-managed transmission system. The replicated wavelength bands of the sampled FBG have a different wavelength separation than the WDM channels, causing each channel to experience a different dispersion compensation that can be tuned upon stretching of the FBG. We achieve significant power penalty reduction for all three channels using our dispersion-slope-compensation method with a tunable amount of dispersion over 900 and 1200 km fiber links.

16 x 20-Gb/s, 400-km WDM transmission over NZDSF using a slope-compensating fiber-grating module

We demonstrate 16-channel wavelength-division multiplexing transmission over nonzero dispersion-shifted fiber at a per-channel rate of 20 Gb/s. A broad-band dispersion-compensating grating module is used for compensation of dispersion and dispersion slope.

Dispersion Compensating Fibers

The basic principles for use of dispersion compensating fibers (DCF) are reviewed, including definition of figure of merit and condition for dispersion slope compensation. The main design features of a triple-cladding index profile design are examined theoretically and experimentally. Production results are presented for three types of DCF. It is shown that polarization-mode dispersion can be reduced by introducing oscillatory twist into the fiber. The splice loss between DCF and standard fibers is shown to be reducible by use of a special intermediate fiber. Two methods for measuring the nonlinear effective area of DCF are compared and good agreement is found. Measurement results for the nonlinear refractive index n2 are reported. The nonlinear coefficient n2/Aeff of DCF is found to be a factor of 5 higher than that on standard single-made fibers. The macrobending resistance of DCF is examined and found to be comparable with that of standard fibers. The microbending resistance of DCF is found to be better than that of standard fibers. Finally, positive results from a cabling experiment with DCF are reported.

640-Gbit/s optical TDM transmission over 92 km through a dispersion-managed fiber consisting of single-mode fiber and "reverse dispersion fiber"

A 640-Gbit/s optical time division multiplexed signal was successfully transmitted over a 92-km zero-dispersion-flattened transmission line. The transmission line consisted of single-mode fiber, dispersion-shifted fiber, and reverse dispersion fiber. By using reverse dispersion fiber instead of dispersion slope compensation fiber, we were able to increase the transmission distance from 63 to 92 km because reverse dispersion fiber has less polarization mode dispersion and a flatter dispersion profile.

Unrepeatered 160 Gbit/s RZ single-channel transmission over 160 km of standard fibre at 1.55 [micro sign]m with hybrid MZI optical demultiplexer

The authors report on single-channel, single-polarisation, 160 Gbit/s, RZ, 1.55 µm transmission over 160 km of standard fibre without inline optical amplifiers, with passive compensation of dispersion and dispersion slope, and using an optical 160 to 10 Gbit/s demultiplexer based on a hybrid Mach-Zehnder interferometer.

640 Gbit/s (16 channel × 42.7 Gbit/s) WDM L-band DSF transmission experiment using 25 nm bandwidth AWG dispersion slope compensator

640 Gbit/s (16 channel × 42.7 Gbit/s) WDM L-band DSF transmission experiment using 25 nm bandwidth AWG dispersion slope compensator The authors report error-free 640 Gbit/s (16 channel × 42.7 Gbit/s) 100 km L-band dispersion-shifted fibre transmission of a carrier-suppressed return-to-zero (223 – 1) pseudo-random binary sequence by using a novel 25 nm bandwidth arrayed-waveguide grating dispersion slope compensator based on time-space conversion.

640 Gbit/s (40 Gbit/s × 16 channel) dispersion-managed DWDM soliton transmission over 1000 km with spectral efficiency of 0.4 bit/Hz

The results from a 640 Gbit/s (40 Gbit/s/spl times/16 channel) dense WDM soliton transmission experiment over 1000 km with the use of a dispersion-managed transmission line are reported. The spectral efficiency was as high as 0.4 bit/Hz. The transmission line comprised conventional 1.3 /spl mu/m singlemode fibres and dispersion compensating fibres with dispersion slope compensation and a repeater span of 50 km.

Layered optical thin-film allpass dispersion equaliser for compensation of dispersion slope of optical fibres

The authors propose and demonstrate novel coupled two-cavity allpass filters realised entirely as thin-film structures for dispersion slope compensation of optical fibres. The filters have centre wavelengths tunable over 15 nm. By cascading two such filters, the dispersion slope can be adjusted between –4.5 and –12.0 ps3 over a compensation bandwidth between 2.4 and 1.2 nm, respectively. A combination of two of the cascaded filters enables transmission of 1.6 ps pulse trains at 1550 nm through 60 km of dispersion-shifted fibre without waveform distortion.

Adjustable coupled two-cavity allpass filter for dispersion slope compensation of optical fibres

A novel adjustable coupled two-cavity allpass filter has been realised for the dispersion slope compensation of optical fibres. The filter gives variable compensation between –2.0 and –15.5 ps3 over a bandwidth between 3.6 and 1.2 nm, respectively. The filter performance agrees quite well with that predicted by existing theory.

Dispersion and dispersion-slope compensation of NZDSF over the entire C band using higher-order-mode fibre

The authors demonstrate simultaneous dispersion and dispersion-slope compensation of 240 km of NZDSF from 1530 to 1560 nm using a higher-order-mode-fibre compensator. With this compensator, 40 Gbits/s operation is achieved across the band, in contrast to a several-nanometre window using commercial DCF.

Integrated all-pass filters for tunable dispersion and dispersion slope compensation

New integrated optical all-pass filters are presented that can be used for tunable dispersion compensation, dispersion slope compensation, and as building blocks in tunable bandpass filters. The dispersion slope compensation capability is demonstrated using ring resonators in /spl Delta/=2% Ge-doped silica planar waveguides. In addition, a tunable four-stage filter with free-spectral range (FSR)=25 GHz, a passband width of 14 GHz (0.56/spl times/FSR), and D=1800 ps/nm is reported.

Sampled fiber grating based-dispersion slope compensator

We propose a novel design for a compact dispersion slope compensator based on sampled fiber Bragg gratings. By chirping the sample function in a sampled grating, we show that the dispersion slope can be controlled to match that of current transmission fibers. Interleaving several sampled gratings provides an effective technique to reduce UV-induced refractive index requirements to readily achievable levels.

Numerical and experimental investigation of power and wavelength margins for a 20-Gb/s dispersion-managed soliton transmission system on standard fiber

A good agreement has been found between numerical and experimental investigation of a 20-Gb/s dispersion-managed soliton transmission system on standard fiber. More than 6 dB of power margin over 30 nm has been obtained at 1100 km by improving the dispersion slope compensation and the prechirping.

16 x 10 Gb/s WDM transmission over 840-km SMF using eleven broad-band chirped fiber gratings

We demonstrate wavelength-division-multiplexed transmission of 16 10-Gb/s nonreturn-to-zero channels with 50-GHz spacing over 840 km of conventional single-mode fiber (SMF), or 14 times the 10-Gb/s dispersion limit, using a total of eleven chirped fiber gratings for dispersion compensation. Each grating has a nominal dispersion of -1330 ps/nm km for compensating 80 km of SMF and a bandwidth of 6.5 nm, and one grating has additional dispersion slope compensation of -35 ps/nm/sup 2/ equivalent to 480 km of SMF. The large number of closely spaced wavelengths and long transmission distance significantly stress the wavelength uniformity, bandwidth, and cascadability of the fiber gratings.

Long-haul soliton WDM transmission with periodic dispersion compensation and dispersion slope compensation

A 20 Gb/s-based soliton wavelength division multiplexed (WDM) transmission experiments using periodic dispersion compensation and dispersion slope compensation were demonstrated. Accumulated dispersion slope was compensated with two methods. The first method was periodical individual dispersion compensation. By using this technique, 60 Gb/s (20 Gb/s/spl times/3 WDM) transmission over 8000 km was demonstrated. The second method was the use of a dispersion-flattened transmission fiber. 160 Gb/s (20 Gb/s/spl times/8 WDM) transmission over 4000 km using periodically dispersion compensated dispersion-flattened fiber was also demonstrated.