The measurement of chromatic dispersion in single-mode fibers byinterferometric loop

A method for chromatic dispersion measurement in long-length fibers (1-10 km) based on the application of an interferometric loop (IL) with phase modulation and lamp/monochromator light source is described. The wavelength region of the measurement is 1.1-1.6 μm and the dynamic range is >15 dB. The reproducibility error of the measured group delay and chromatic dispersion is 40 ps/km and 0.1 ps/km-nm respectively. The results obtained by the IL method and Nd-YAG/Raman laser technique are compared. The measured dispersion agrees with the theoretical results calculated from the refractive index profile of the preform. The influence of the type of phase modulation and the length source spectral width on the accuracy of chromatic dispersion measurements by IL technique is analyzed theoretically     

Optical PSK synchronous heterodyne detection transmissionexperiment using fiber chromatic dispersion equalization

This letter demonstrates an 8-Gb/s optical PSK (phase shift keying) synchronous detection transmission experiment using external cavity laser diodes. A 188-km 1.3-μm zero-dispersion fiber is used as the transmission medium at the wavelength of 1.55 μm. Fiber chromatic dispersion is successfully compensated with a microstrip-line delay equalizer     

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     

Statistical approach to end-to-end dispersion budgeting in single-mode fiber links using multilongitudinal-mode lasers

This paper presents a statistical analysis to the end-to-end chromatic dispersion budgeting in single-mode fiber links which employ multilongitudinal-mode laser transmitters around 1.3 or 1.55 μm regions. This is a novel approach which is relevant for upgrading the "bit rate × distance" of those already installed 400- and 565-Mbit/s fiber links.     

Phase-mismatch dependence of efficiency of wave generation through four-wave mixing in a single-mode optical fiber

The generation wave efficiency with respect to phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength. The generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector. The calculated efficiency as a function of the equivalent frequency separation can well explain and reflect the results obtained experimentally. Furthermore, the efficiency at zero chromatic dispersion wavelengths of 1.3 and 1.55 μm is also discussed considering chromatic dispersion slope against wavelength.     

Analysis of dynamic spectral width of dynamic-single-mode (DSM) lasers and related transmission bandwidth of single-mode fibers

A simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser, and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given. The dynamic spectral width of a DSM laser is determined by the modulated optical shape and the linewidth enhancement factor α. The spectral width caused by the dynamic wavelength shift is shown to be larger by (1 + alpha^{2})^1/2than that caused by the sideband of the signal of the intensity modulation. Furthermore, the maximum transmission bandwidth of a conventional single-mode fiber with a DSM laser is expressed by using the parameter α and the chromatic dispersion of the fiber. The product of the maximum bit rate and the square root of the fiber length at the wavelength of 1.55 μm is estimated to be about 25 Gbit/s . km^1/2.     

Guided-wave optical equalizer with α-power chirped grating

A theoretical investigation of a guided-wave optical equalizer with an α-power chirped grating is presented. A group delay dispersion of 3700 ps/nm can be obtained at λ=1.55 μm by a chirped grating with α=0.3. It is shown that the chromatic dispersion of 200 km of a fiber whose zero-dispersion wavelength is located at 1.3 μm can be compensated at 1.55 μm to achieve up to 10 GHz signal bandwidth     

Fiber fuse phenomenon in triangular-profile single-mode optical fibers

The unsteady-state thermal conduction processes in triangular-profile (TP) optical fibers, which exhibited zero chromatic dispersion near 1.55 /spl mu/m, were studied theoretically with the explicit finite-difference method (FDM). It was estimated that these fibers would exhibit a high-temperature optical absorption on the basis of the high-temperature loss-increase mechanism proposed for step-index (SI) optical fibers. The core-center temperature of the TP fibers changed suddenly and reached over 7/spl times/10/sup 5/ K when a 1.064-/spl mu/m laser power of 1 W was inputted into the core layer heated at 2608 K. This rapid heating of the core initiated the "fiber fuse" phenomenon. The propagation rates of the fiber fuse, estimated at 1.064 /spl mu/m, were in fairly good agreement with the experimentally determined values. It was found that the threshold powers for initiating the fiber fuse are linearly proportional to the roots of the effective core areas of both the SI and the TP optical fibers. This coincides the experimental result reported by Seo et al.     

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     

Compensation of 202 km single-mode fibre chromatic dispersion in 4Gbit/s optical CPFSK transmission experiment

Compensation for fibre chromatic dispersion in a coherent transmission system is demonstrated. A 4 Gbit/s optical CPFSK signal at 1.55 μm is transmitted through a 202 km conventional single-mode fibre. There is 1.8 dB degradation in transmission caused by fibre chromatic dispersion. This degradation has been completely compensated for using a delay equaliser with optical heterodyne detection     

The Design and Fabrication of Monomode Optical Fiber

The design of monomode fibers is discussed in the context of optimizing fiber loss and dispersion simultaneously, with reference to the materials choices and limitations to preform and fiber fabrication by the MCVD technique. Two classes of monomode structure-matched cladding and depressed cladding-are considered. Ultralow attenuation has been achieved reproducibly in both classes of fiber. The control of fiber geometry and dispersion is also discussed. Matched cladding fiber suitable for systems operating at both 1.3 and 1.55 µm has been studied and mean losses of 0.45 dB/km at 1.3 µm and 0.28 dB/km at 1.55 µm have been achieved for a total of 130 km. The behavior of depressed cladding fiber is compared with predictions from the theory of propagation in W fibers. Depressed cladding fiber with stable guidance has been demonstrated with attenuation of 0.37 dB/km at 1.3 µm and 0.21 dB/km at 1.55 µm.     

Modulated single-longitudinal mode semiconductor laser and fiber transmission characteristics at 1.55 µm

A laser light injection technique was studied to realize a semiconductor laser transmitter oscillating in a 1.55 μm single-longitudinal mode. When -15 dBm optical power was injected into the directly modulated laser, no dispersion degradation was observed in the error rate characteristics after transmitting through 44.3 km single-mode fibers at 100 Mbits/s. Effective gain coefficientg-alpha, measured by the light injection method, was 45 cm^-1near threshold. As this gain was sufficiently saturated at the -15 dBm injection power, undesired longitudinal modes in the modulated laser were suppressed.     

Large dispersion in photonic crystal waveguide resonator

Group delay and chromatic dispersion of a Fabry-Perot resonator embedded in a photonic crystal waveguide have been directly measured at 1.55 /spl mu/m wavelength using the phase-shift technique. The photonic crystal waveguide resonator was fabricated in an InGaAsP/InP heterostructure and was designed to show a channel spacing of 100 GHz. Group velocity dispersion up to 250 ps/nm was observed.     

Comparison of optical millimetre-wave system concepts with regardto chromatic dispersion

The author reports the impact of chromatic dispersion in optical millimetre-wave systems operating in the 1.55 μm wavelength window. Experimental and theoretical results confirm the dramatical millimetre-power degradation in conventional amplitude modulated systems using for example, external optical modulators. In comparison, by use of a similar setup a self-heterodyne-based system concept has been investigated showing negligible dependence on the chromatic dispersion     

Dispersion Measurement in Optical Fibers Using Supercontinuum Pulses

The chromatic dispersion of an optical fiber is measured using a time-of-flight technique, based on temporally and spectrally resolving a dispersed broadband pulse, on which a spectral fringe pattern has been imposed using an etalon. The technique employs broadband supercontinuum radiation, generated by launching picosecond pulses from a fiber laser into a photonic- crystal fiber. It allows the dispersion of highly dispersive optical fibers and components to be measured with a high spectral resolution over a wide wavelength region. The technique is demonstrated by measuring the dispersion of a dispersion-compensating module over its entire 400-nm transmission band with a subnanometer spectral resolution.     

High Power Highly Nonlinear Holey Fiber with Low Confinement Loss for Supercontinuum Light Sources

The high power holey fiber is an efficient supercontinuum light source by using picosecond pulse, which is a less expensive laser source compared with low power and expensive femtosecond laser sources. In this paper, a high power highly nonlinear holey fiber (HN-HF) with a low confinement loss is proposed for supercontinuum light sources. The finite difference method is used to calculate the different properties of the proposed HN-HF. High nonlinear coefficients are obtained at 1.06 μm, 1.31 μm, and 1.55 μm wavelengths with flattened chromatic dispersion and low confinement losses simultaneously. Moreover, numerical simulation results show that high power broad supercontinuum spectra with very short length of the proposed photonic crystal fiber are achieved.     

Chromatic dispersion limitations in coherent lightwave transmissionsystems

Computer simulation is used to evaluate the chromatic dispersion limitations for both various coherent lightwave transmission systems and direct-detection on-off keying (OOK) systems. The results show that for a 2-dB dispersion penalty the maximum modulation rate ranges from 5 to 9 Gb/s for systems operating at 1.55 μm with 15 ps/km-nm of chromatic dispersion and 100 km of fiber. The effect is less severe for OOK systems and most severe in coherent detection systems. Simulation results are in agreement with a available experimental data     

Enhanced performance of WDM systems using directly modulated lasers on positive dispersion fibers

Cost-effective directly modulated distributed feedback lasers (DML) have attracted much attention recently for operation at the 1.55 μm wavelength band applications in metropolitan area networks. In this paper, we show by simulation that the effect of directly modulated laser chirp can be compensated by a negative dispersion fiber, but this only occurs in a specific range of DML output power, and that a pulse broadened by the positive dispersion fiber can be equalized using self-phase-modulation (SPM) in optical fiber. The majority of metro and access networks are made up of conventional single-mode fibers (SMF) which are positive dispersion fibers. We demonstrated that optimum compensation is always feasible for such fibers, since the magnitude of the SPM can be controlled by changing the optical power in the fiber. Furthermore, simulation suggests that this technique will enable directly modulated wavelength division multiplexed systems to enhance their performance if the power of each channel is appropriate.     

Highly accurate long-span chromatic dispersion measurement system by a new phase-shift technique

A highly accurate long span chromatic dispersion measurement system, which is based on a wavelength-division-multiplexing phase-shift technique and utilizes six laser diodes in1.2 sim 1.6 mum spectral region, has been developed. It is intrinsically free from error due to the fiber length variation caused by temperature changes under the measurement. The measurement accuracies of dispersion and Zero-dispersion wavelength are extremely good and within ±0.02 ps/km . nm and ±0.1 nm in 1250 ∼ 1450 nm spectral region in the case of a 10.5-km single-mode fiber measurement. The dynamic range is over 50 dB excluding system theS/Nmargin of 5 dB. Using this system, chromatic dispersion measurements of a 101.9-km pure-silica-core single-mode fiber and a 100.7 km concatenated dispersion-shifted single-mode fiber have been successfully carried out. The measured result has coincided with the arithmetical mean of those of constituent fibers.     

Low-dispersion single-mode silica fibre with undoped core and three F-doped claddings

The refractive-index profile of an ideal single-mode silica fibre with undoped core and three F-doped claddings was optimised by calculation to realise two zeros of the chromatic dispersion at 1.30 and 1.55 ?m where the spectral loss has its local and absolute minima, respectively. The sensitivity of the chromatic dispersion due to different scale factors for the radial co-ordinate of the refractive-index profile is considered.