Experimental Study on the Role of Chromatic Dispersion in Continuous-Wave Supercontinuum Generation

The influence of chromatic dispersion on continuous-wave (CW)-pumped supercontinuum (SC) generation in kilometer-long standard fibers is experimentally investigated. We perform our study by means of a tunable, high-power fiber ring laser pumping a dispersion-shifted fiber in the wavelength range of small and medium anomalous dispersion. Our results show that, at low input powers, chromatic dispersion plays a dominant role on nonlinear pump spectral broadening, giving rise to a broader spectrum when pumping just above the zero-dispersion wavelength of the fiber. At higher input powers, however, the width of the generated SC spectrum is mostly due to the Raman effect, hence more independent of the value of the chromatic dispersion coefficient. We show that, in this case, the optimum pumping wavelengths for SC generation are not so close to the zero-dispersion wavelength of the fiber as in the previous case. In these conditions, as the chromatic dispersion grows, we can obtain square-shaped and high-power density spectra, which seem extremely promising for applications in optical coherence tomography.      

Experimental study on channel crosstalk due to fiber four-wavemixing around the zero-dispersion wavelength

Channel crosstalk due to fiber four-wave mixing (FWM) in multichannel systems operated around the zero-dispersion wavelength is experimentally studied. After determining the wavelength at which FWM light is most efficiently generated, the FWM efficiency is measured for possible frequency combinations which generate FWM light at that wavelength. Using these data, FWM crosstalk in multiwavelength systems is evaluated. The results show that actual crosstalk, is less than the value estimated by the theoretical model assuming the uniformly distributed chromatic dispersion for 80-km-long fibers. It is concluded that the theoretical model can be applied to system design dealing with the worst condition     

Chromatic-dispersion compensator using virtually imaged phasedarray

A new method for chromatic-dispersion compensation is proposed and demonstrated. This method can produce a chromatic dispersion practically in a wide range from -2000 to +2000 ps/nm and can compensate simultaneously for the dispersion of over 60 wavelength channels with 100-GHz spacing in a wavelength-division multiplexed (WDM) system that has a total bandwidth of over 50 nm. This method has further attractive features such as very small polarization-state dependence, mechanically variable chromatic dispersion, and potential for small packaging. It was experimentally confirmed that this method compensated for the chromatic dispersion accumulated through 110 km standard single-mode fiber (SMF) at 1.55-μm wavelength and that 10-Gb/s signal quality was clearly recovered after the 110-km transmission     

Low-dispersion fluoride glass single-mode fibres operating in twospectral ranges

Chromatic dispersion characteristics of fluoride glass single-mode fibres are investigated experimentally and theoretically. It is proposed that the quasi-single-mode operation at zero material dispersion wavelength is effective in extending the low dispersive spectral range. It is shown that total chromatic dispersion is suppressed within ±1 ps/km/nm in the two spectral ranges of 1.57-1.71 μm and 2.4-3.35 μm     

Compensation of fibre chromatic dispersion in optical heterodynedetection

Compensation of fibre chromatic dispersion in coherent optical fibre transmission is demonstrated. The chromatic dispersion of a 70 km single-mode fibre with 1.3 μm zero dispersion wavelength is compensated for using a microstrip line equaliser in the intermediate frequency band. Amplitude distortion due to fibre chromatic dispersion at 1.55 μm wave-length is reduced to below 2.5 % with the equaliser     

Four-wave-mixing suppression effect of dispersion varying fiber

This letter describes the four-wave-mixing (FWM) suppression effect of dispersion varying fiber (DVF) whose chromatic dispersion increases (or decreases) along its length. The FWM suppression performance is investigated for the dispersion variation rate and its cycle number in the DVF. Moreover, it is clarified experimentally that the DVF functions efficiently in wavelength division multiplexing (WDM) systems with an input power of more than 10 dBm/ch     

Over 1000 km FSK heterodyne transmission system experiment usingerbium-doped optical fiber amplifiers and conventional single-modefibers

The influence of spontaneous emission noise on coherent transmission systems using multistage erbium-doped optical fiber amplifiers is experimentally examined. A frequency-shift keying (FSK) heterodyne transmission experiment was successfully performed at 560 Mb/s through 1028 km of fiber using ten cascaded fiber amplifiers and conventional single-mode fibers with a zero dispersion wavelength of around 1.3 μm. In the experiment, no transmission penalty due to accumulated spontaneous emission noise or to fiber chromatic dispersion was observed     

Simple approximations for chromatic dispersion in single- mode fibers with various index profiles

Simple approximate formulas of chromatic dispersion and zero-chromatic dispersion wavelength are empirically derived for single-mode fibers with various index profiles having the deformations such as a central dip, hump, and/or tailing at a core cladding interface. These profiles are typical which are commonly obtained in current single-mode fibers. The approximation is based on the exact solution of vector-wave equation. These accuracies are better than 0.3 and 0.03 percent for the chromatic dispersion and zero-chromatic dispersion wavelength, respectively. With the aid of the simple approximations, the properties of chromaric dispersion and zero-chromatic dispersion wavelength for practical single-mode fibers are discussed. The relation between the chromatic dispersion and basic fiber parameters of single-mode fibers, effective cutoff wavelength of the LP11mode, and the spot-size of the LP01mode, are clarified.     

Fiber chromatic dispersion equalization at the receiving terminalof IM-DD ultra-long distance optical communication systems

We have evaluated the effect of fiber chromatic dispersion equalization at the receiving terminal for transoceanic optical communication systems. We used a 1000-km fiber loop with 31 Er-doped fiber amplifiers for the experiments, and measured the bit-error-rate characteristics after 9000-km transmission. Accumulated chromatic dispersion originating from the discrepancy between the signal wavelength and the system zero dispersion wavelength was equalized by the equalization fiber at the receiving terminal. We used both normal and anomalous dispersion fibers at the receiving end. The results have shown that the equalization method of the fiber chromatic dispersion at the receiving terminal is useful with some limitations for ultra-long distance optical communication systems     

Experimental evaluation of chromatic dispersion distortion inoptical CPFSK transmission systems

Receiver sensitivity degradations due to fiber chromatic dispersion without chromatic dispersion compensation in multigigabit optical continuous-phase frequency-shift-keying (CPFSK) transmission systems are evaluated experimentally and theoretically. Transmission distance limited by the chromatic dispersion of 15 ps/nm/km is estimated to be 130 km at 5 Gb/s and 33 km at 10 Gb/s     

Cross-phase modulation in dispersive fibers: theoretical andexperimental investigation of the impact of modulation frequency

We investigated, theoretically and experimentally, the impact of modulation frequency on cross-phase modulation (XPM) in dispersive fibers. A simple expression for the XPM index has been derived and verified by experiment. The XPM index is found to depend on fiber length, fiber chromatic dispersion, wavelength separation between the signal and the pump, and the intensity modulation frequency. At high modulation frequencies, the XPM index is inversely proportional to the product of the modulation frequency and wavelength separation     

Effects of water absorption peaks on transmission characteristics of LED-based lightwave systems operating near 1.3 µm wavelength

Chromatic dispersion effects on LED-based optical fiber systems are calculated as a function of transmission length and the LED central wavelength. The computer analysis includes the filtering effects of water absorption which reduces the spectral width of LED signal pulses. We show that the basebandwidth of multimode fiber systems can be significantly increased by offsetting the LED central wavelength above the wavelength at which minimum chromatic dispersion occurs in the fiber medium. Additional bandwidth degradation due to modal dispersion effects are not considered. However, the combined effects of optical loss and chromatic dispersion are used to calculate upper limits for repeater spacings in possible multimode wideband systems.     

Generation of Flat Supercontinuum in a Single-mode Optical Fiber with a Convex Chromatic Dispersion Profile

A single-mode optical fiber with a convex chromatic dispersion profile is proposed for generating a flat supercontinuum(SC).The fiber has normal dispersion and the dispersion parameter D(λ,z) is a convex function of wavelengths.It is shown from the numerical results that the chromatic dispersion,the flatness of the dispersion curve and the pump conditions have significant effect on SC generation.A flat and broad SC without strong residual pump component can be obtained when the pump wavelength is set in the...     

Chromatic dispersion measurement over a 120 km dispersion-shifted single-mode fibre in the 1.5 ?m wavelength region

Chromatic dispersion in the 1.47?1.60 ?m wavelength region is measured successfully for a dispersion-shifted fibre over 120 km by the LD phase-shift method. The measured value of a 123 km spliced fibre agrees well with the sum of chromatic dispersion values of its constituent fibres. This confirms the additive rule of chromatic dispersion for long dispersion shifted fibre in the 1.5 ?m wavelength region.     

Four-wave mixing suppression effect of dispersion distributedfibers

The four-wave mixing (FWM) suppression effect of dispersion distributed fibers (DDF's), which have a nonuniform chromatic dispersion along their length, has been investigated experimentally and theoretically. We fabricated two different kinds of DDF by the vapor-phase axial deposition (VAD) method to clarify the FWM suppression effect. Moreover, we investigated experimentally the effect of our fabricated DDF's on the transmission characteristics of 4×10 Gb/s wavelength division multiplexing (WDM) systems. We confirmed that the proposed DDF's can not only suppress PWM but also improve the input power limitation for WDM systems     

Near-IR comparative characterization of optical second-order nonlinearities in Te-based semiconductors

We have systematically characterized the second harmonic generation efficiency of Te-based binary and ternary II–VI compounds in the near-IR spectral region, namely at=1.5 m and=1.9 m. A phase mismatched technique has been employed, as a translation into the spectral domain of the Maker fringes method. By using sub-picosecond optical pulses, reliable results for the value of non second-order linear coefficientd and of chromatic dispersion have been obtained. We have performed a comparative evaluation of nonlinear wavelength conversion efficiency of Te-based semiconductors and GaAs. The ternary alloys Cd_0.5Zn_0.5Te and Cd_0.78Mn_0.22Te can be considered as the best performing basic materials for optical wavelength converters working in the third communication window, since they possess at the same time a highd coefficient, good transparency, and low chromatic dispersion.     

Technique for direct measurement of single-mode fiber chromatic dispersion

A technique for the direct measurement of single-mode fiber chromatic dispersion is presented. The technique uses wavelength modulation to provide a differential fiber chromatic delay signal from which chromatic dispersion is obtained directly. The system is described in detail and practical measurement results shown to illustrate the high accuracy of the technique and its versatility in use with all fiber types.     

Dispersion penalty reduction using an optical modulator with adjustable chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value.<>     

Chromatic Dispersion Compensation via Mid‐span Spectral Inversion with Periodically Poled LiNbO3 Wavelength Converter at Low Pump Power

Mid‐span spectral inversion (MSSI) has to utilize high optical pump power, for its operation principle is based on a nonlinear optical wavelength conversion. In this paper, a low pump‐power operation of MSSI‐based chromatic dispersion compensation (CDC) has been achieved successfully, for the first time to our knowledge, by introducing a noise pre‐reduction scheme in cascaded wavelength conversions with periodically poled LiNbO₃ waveguides at a relatively low operation temperature. As preliminary studies, phase‐matching properties and operation‐temperature dependence of the wavelength converter (WC) were characterized. The WC pumped at 1549 nm exhibited a wide conversion bandwidth of 59 nm covering the entire C‐band and a conversion efficiency of –23.6 dB at 11 dBm pump power. CDC experiments were implemented with 2.5 and 10 Gb/s transmission systems over 100 km single‐mode fiber. Although it is well‐known that the signal distortion due to chromatic dispersion is not critical at a 2.5 Gb/s transmission, the clear recovery of eye patterns was identified. At 10 Gb/s transmission experiments, eye patterns were retrieved distinctly from seriously distorted ones, and notable improvements in bit‐error rates were acquired at a low pump power of 14 dBm.     

Determination of Achievable Information Rates (AIRs) of IM/DD Systems and AIR Loss Due to Chromatic Dispersion and Quantization

The achievable information rates (AIRs) of a nonreturn-to-zero optical transmission system operating at 10Gb/s are determined based on experimentally obtained conditional probability density functions for an amplified spontaneous emission noise-dominated system in the presence of chromatic dispersion (with and without optical dispersion compensation). Specifically, we concentrate on the AIR loss due to the accumulation of chromatic dispersion, as well as the practical constraint of the analog-to-digital conversion and quantization of log-likelihood ratios