Negative Dispersion Fiber Research Articles

Directly modulated cable television transport systems using negative dispersion fiber

A directly modulated AM-VSB cable-television transport system using negative dispersion fiber (NDF) as the transmission medium is proposed and successfully demonstrated. Good performances of carrier-to-noise radio, composite second order, and composite triple beat were obtained over a 70-km NDF transport without optical amplification. The directly modulated laser has a positive chirp, while NDF has a negative dispersion property in the transmission fiber. This negative dispersion property compensates for the laser chirp and results in a system with better transmission performance.

Directly modulated CWDM/DWDM system using negative dispersion fiber for metro network application

We demonstrate the error-free transmission of directly modulated 2.5, 10, and 40-Gb/s coarse wavelength-division-multiplexing/dense wavelength-division-multiplexing signals over negative dispersion fiber (dispersion: −2.5 ps/km/nm @ 1550 nm) without dispersion compensation. The results indicate that the metro core/access network could be implemented cost-effectively by using the proposed negative dispersion fiber and directly modulated lasers.

Externally modulated lightwave CATV transport systems employing negative dispersion fiber

An externally modulated AM-VSB CATV transport system in the 1550nm region using negative dispersion fiber (NDF) as the transmission medium is proposed and successfully demonstrated. Good performances of carrier-to-noise radio (CNR), composite second order (CSO) and composite triple beat (CTB) were achieved over an-80km NDF transmission without dispersion compensation. Externally modulated transmitter has a positive residual Mach-Zehnder modulator (MZM) chirp; but, NDF has a negative dispersion property in the transmission fiber. This negative dispersion property overcomes the positive frequency chirp and results in system with better transmission performance.

Analysis of power-dependent phase-matched four-wave mixing in dispersion-managed transmission systems.

We investigate power-dependent phase-matched four-wave mixing (FWM) in wavelength division multiplexing transmission lines, in which positive and negative dispersion fibers are alternately arranged to manage the dispersion and the dispersion slope. The FWM effect shows power-independent phase matching when the channel power is low. However, it is power dependent at high power. The maximum FWM conversion efficiency is shifted away from the zero channel space in the case of power-dependent phase matching. Optimization of the dispersion system for suppression of the FWM effect is determined.

Directly modulated 10-gb/s signal transmission over 320 km of negative dispersion fiber for regional metro network

We demonstrate the transmission of directly modulated 10-Gb/s wavelength-division-multiplexing (WDM) signals over 320 km of negative dispersion fiber [(NDF) dispersion: -2.5ps/km/nm at 1550 nm] without dispersion compensation. The results indicate that a regional metro WDM network could be implemented cost-effectively by using the NDF and direct modulated lasers.

Directly modulated laser parameters optimization for metropolitan area networks utilizing negative dispersion fibers

The optimization of an uncooled directly modulated laser operated at 10 Gbit/s for metropolitan area networks utilizing negative dispersion fibers is presented. The laser optimization is performed in order to accomplish two goals: maximizing the back-to-back sensitivity and the dispersion tolerance of negative dispersion single-mode fiber. Extensive numerical simulations reveal that a significant improvement of system performance can be achieved by optimizing simultaneously four laser intrinsic parameters, namely linewidth enhancement factor, photon lifetime, gain parameter, and gain compression factor. The optimal laser parameters have been obtained at a temperature of 25/spl deg/C. The optimized laser shows a weak dependence of back-to-back sensitivity and dispersion tolerance on variations of laser intrinsic parameters as well as on laser temperature up to 85/spl deg/C. Nevertheless, the gain compression factor is the most stringent intrinsic parameter, because it controls the right balance between the transient and adiabatic chirps. The results show also that the impact of laser parasitics on system performance is only slightly altered with the temperature increase up to 85/spl deg/C. Back-to-back sensitivities of about -27.8 dBm and -29.1 dBm and 1 dB dispersion tolerances of about 1550 ps/nm and 1580 ps/nm have been achieved at 25/spl deg/C and 85/spl deg/C, respectively. The dispersion tolerance doubles the value of 750 ps/nm reported in a practical experiment.

40 Gbit/s direct modulation of distributed feedback laser for very-short-reach optical links

40 Gbit/s direct modulation of a 1.3 µm distributed feedback laser is reported for very-short-reach optical links. Error-free operation is accomplished by using a negative dispersion fibre.

FWM generation in higher order fiber dispersion managed transmission line

Describes, in terms of fiber parameters, four-wave-mixing generation in a higher order fiber dispersion managed transmission line in which positive and negative dispersion fibers are used to manage both second- and third-order fiber dispersion. An analysis shows that the full-width at half-maximum interaction in dense wavelength-division-multiplexing systems can be reduced by properly setting the channel spacing to suit the dispersion allocation in the transmission line.

Transport performance of an 80-Gb/s WDM regional area transparent ring network utilizing directly modulated lasers

The transport performance of a regional area wavelength division multiplexing (WDM) transparent optical network is studied. We present excellent performance results (Q factors for all received signals greater than 10 with small power penalties) for a ring network based on application-optimized cost-effective optical layer components and fiber. The network consists of six network nodes, interconnected with 86.5-km spans of uncompensated negative dispersion fiber, resulting in a maximum transmission distance around the ring of 519 km, and it supports 32 directly modulated channels operating at 2.5 Gb/s (80-Gb/s network capacity). The novel design of the network nodes ensures great flexibility in terms of scalability and transparency, as well as great performance. To our knowledge, the capacity-length product of this transparent network, using cost-effective directly modulated lasers (DMLs) and no dispersion compensation, is the highest ever reported.

Metro network utilizing 10 Gb/s directly modulated lasers and negative dispersion fiber

In this letter, we present the feasibility of metro area transparent wavelength-division-multiplexing networking with cost-effective 1550 nm 10 Gb/s directly modulated transmitters. We report excellent performance results (Q-factor>9 dB) for a transparent short-reach metropolitan area ring network based on application-optimized, optical layer components and fiber. The demonstration is based on a network consisting of four nodes interconnected with 25.5 km spans of uncompensated negative dispersion fiber. The network is designed to support 32 directly modulated channels operating at 10 Gb/s (320 Gb/s capacity).

Conception, Realization, and Characterization of a Very High Negative Chromatic Dispersion Fiber

After a brief presentation of many possible solutions usable to control or compensate the chromatic dispersion of optical links, we report the simulation, realization, and characterization of a dual asymmetric core dispersion compensating optical fiber. The simulation stage, using a cylindrical coordinates B.P.M., determines the optimized refractive index profile of the dispersion compensating fiber (DCF) including the optogeometrical tolerances, like the effect of the central index dip obtained by MCVD process. The realized fiber is characterized by phase shift method to measure its chromatic dispersion. The dispersion coefficient was measured to be −1800 ps/(nm·km) in the 1.55-μm low-loss window. A study of the propagation behavior and measurements of connection, propagation, and bending losses of this fiber are also presented.

10-Gb/s transmission of 1.55-μm directly modulated signal over 100 km of negative dispersion fiber

In this letter, the largest transmission distance (100 km) ever reported for a commercially available 10-Gb/s 1.55-/spl mu/m directly modulated signal over a single fiber link without using any dispersion compensation is demonstrated. The achieved dispersion-length product for a Q-factor greater than 9.4 dB (bit-error rate less than 10/sup -15/) was about 750 ps/nm. The fiber that enabled such long transmission distance with high dispersion tolerance is a nonzero dispersion-shifted fiber that has negative dispersion in the entire usable bandwidth (1280-1620 nm) and is optimized for operation with directly modulated lasers. The excellent single-channel transmission performance that we achieved can be expected also from wavelength-division-multiplexed systems with channels across the erbium-doped fiber amplifier bands.

Extraction of laser rate equations parameters for representative simulations of metropolitan-area transmission systems and networks

In this paper we present procedures for the extraction of laser rate equation parameters. The parameters are extracted using fitting of static and dynamic measurements with simple theoretical expressions. In particular, chirp related parameters are extracted directly through measured chirp and power waveforms. The extracted parameters are used in a large-signal rate equation laser model to calculate the power and chirp waveforms. The simulations are compared with experiments and the agreement is excellent. The procedures have been applied to directly modulated lasers having different chirp characteristics and designed for either 2.5 or 10 Gb/s operation. Using the rate equation laser model with the extracted parameters, we performed a simulation study to identify the value of employing a negative dispersion fiber in metro-area networks. It is shown that dispersion shifted fibers with negative dispersion across the entire usable fiber bandwidth (1280–1620 nm) advances the performance of directly modulated lasers used in wavelength division multiplexed metropolitan-area transmission systems and networks. At 2.5 Gb/s transmission over 300 km of negative dispersion fibers is possible for directly modulated lasers across the erbium doped fiber amplifier bandwidth, while at 10 Gb/s an impressive distance of 100 km can be achieved.

Demonstration of negative dispersion fibers for DWDM metropolitan area networks

We present a detailed experimental and theoretical study, showing that a novel nonzero dispersion-shifted fiber with negative dispersion enhances the capabilities of metropolitan area optical systems, while at the same time, reducing the system cost by eliminating the need of dispersion compensation. The performance of this dispersion-optimized fiber was studied using different types of optical transmitters for both 1310- and 1550-nm wavelength windows and for both 2.5-and 10-Gb/s bit rates. It is shown that this new fiber extends the nonregenerated distance up to 300 km when directly modulated distributed feedback (DFB) laser transmitters at 2.5 Gb/s are used. The negative dispersion characteristics of the fiber also enhance the transmission performance in metropolitan area networks with transmitters that use electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers, which are biased for positive chirp. In the case of 10 Gb/s, externally modulated signals (using either EA-DFBs or external modulated lasers using Mach-Zehnder modulators), we predict that the maximum reach that can be accomplished without dispersion compensation is more than 200 km for both 100- and 200-GHz channel spacing. To our knowledge, this is the first demonstration of the capabilities of a nonzero dispersion-shifted fiber with negative dispersion for metropolitan applications.

320-Gb/s WDM transmission with 50-GHz channel spacing over 564 km of short-period dispersion-managed fiber (perfect cable)

We propose a short-period dispersion-managed fiber that consisted of conventional single-mode fiber (17 ps/km/nm) and negative dispersion fiber (-15 ps/km/nm). Thus, the average dispersion of the proposed fiber was only 1 ps/km/nm. The lengths of the positive and negative fiber sections were only 4.5 km so that they can be accommodated within a single 9-km-long cable. We evaluated the performance of this fiber using a 320-Gb/s (32/spl times/10 Gb/s) WDM system with 50-GHz channel spacing. After 563-km transmission, the average Q-factor was measured to be better than 18 dB without any dispersion compensation.

High-power side-pumped passively mode-locked Er-Yb fiber laser

A side-pumped double-clad Er-Yb fiber laser passively mode-locked with a saturable absorber is demonstrated for the first time. Pumped with a power of 1 W from a broad-stripe diode laser, an environmentally stable cavity design produces positively chirped 3-ps pulses at a repetition rate of 30 MHz with an average output power of 50 mW. The pulses can be linearly compressed to 330 fs in a length of negative dispersion fiber, whereas nonlinear compression in standard telecom fibers yields 130-fs pulses with pulse energies of 1.2 nJ.

Ultrashort-pulse fiber ring lasers

This paper reviews recent progress on ultrashort pulse generation with erbium-doped fiber ring lasers. The passive mode-locking technique of polarization additive pulse mode-locking (P-APM) is used to generate stable, self- starting, sub-500 fs pulses at the fundamental repetition rate from a unidirectional fiber ring laser operating in the soliton regime. Saturation of the APM, spectral sideband genera- tion, and intracavity filtering are discussed. Harmonic mode- locking of fiber ring lasers with soliton pulse compression is addressed, and stability regions for the solitons are mapped and compared with theoretical predictions. The stretched- pulse laser, which incorporates segments of positive- and negative-dispersion fiber into the P-APM fiber ring, gen- erates shorter (sub-100 fs) pulses with broader bandwidths (> 65 nm) and higher pulse energies (up to 2: 7n J). We dis- cuss optimization of the net dispersion of the stretched-pulse laser, use of the APM rejection port as the laser output port, and frequency doubling for amplifier seed applications. We also review the analytical theory of the stretched-pulse laser as well as discuss the excellent noise characteristics of both the soliton and stretched-pulse lasers.

Impact of cross-phase modulation for WDM systemsover positive and negative dispersion NZ-DSF and methods for its suppression

The impact of cross-phase modulation (XPM) is measured on positive and negative dispersion fibre. The exponential build-up of XPM over positive dispersion fibre indicates amplification due to modulation instability. Methods for suppressing XPM crosstalk are also demonstrated.

Ultrashort Pulses from a Gain-Switched DFB Laser by Fiber Compensation of the Chirp and Thermal Tuning of the Cavity

Ultrashort pulses of -3.5 ps were obtained for the first time from a gain-switched DFB laser at λ = 1.55 μm through passive compression in a negative dispersion fiber. The corresponding length was optimized for a precise compensation of the quadratic laser chirp using a parabolic law which describes the evolution of the second-order central moment of the pulse while propagating along the fiber. This formula, together with the one which relates the second-order central moment of the pulse autocorrelation versus the same moment of the pulse intensity, holds for any kind of pulse regardless of its profile. A further improvement of the pulse width and shape was obtained through the thermal tuning of the DFB cavity in the operation range of 17-26°C.

Unrepeatered transmission of an OTDM 40 Gbit/s signalover110 km using a dispersion-adjustable PLC delay equaliser

Using a dispersion-adjustable PLC delay equaliser, unrepeatered 110 km transmission of a 40 Gbit/s PRBS signal over both positive and negative dispersion fibre has been successfully demonstrated for the first time.