B. Clesca

Experimental investigation of the gain flatness characteristics for 1.55 /spl mu/m erbium-doped fluoride fiber amplifiers

The flat gain over a broad spectral width offered by fluoride-based Erbium-Doped Fiber Amplifiers (EDFA) appears very attractive for wavelength-multiplex systems operating near 1550 nm. The relevant parameters (input pump and signal powers, fiber length) that determine the gain flatness characteristics of fluoride-based EDFA have been experimentally investigated. It is found that hat gain operation requires an optimal, though not critical, population inversion within the doped fiber, which is somewhat lower than the maximum population inversion achievable with 1.48 /spl mu/m-pumping. Implications on the design and operating conditions of fluoride-based EDFA are discussed.<<ETX>>

Gain flatness comparison between erbium-doped fluoride and silica fiber amplifiers with wavelength-multiplexed signals

With the ever growing interest in wavelength division multiplexing transmission systems, the need for an optical amplifier with a large bandwidth is more and more necessary. Unlike the standard erbium-doped silica fiber amplifiers, the fluoride-based fiber amplifiers display more uniform gain spectra. The benefit expected from fluoride amplifiers with multiwavelength signals has been experimentally assessed through comparisons in single- and cascaded-amplifiers configurations. Four db gain flatness was achieved with four wavelength-multiplexed signals extending over 23 nm after three fluoride amplifiers while 15 dB gain unbalance was observed after three silica amplifiers. This result shows that fluoride amplifiers may be of the utmost relevance for multiwavelength transport systems.<<ETX>>

Second-order distortion improvements or degradations brought by erbium-doped fiber amplifiers in analog links using directly modulated lasers

Within lightwave analog amplitude-modulated (AM) CATV systems using directly modulated lasers, erbium-doped fiber amplifiers (EDFAs) act upon the signal distortion because of the interaction between the laser chirp and the EDFA wavelength-dependent gain. This interaction is theoretically investigated in order to predict the EDFA-induced distortion. The relevant gain tilt characteristic for analog applications and the way to measure it are described. Expected and measured distortions at the EDFA output are in excellent agreement. Fiber amplifiers are found to decrease the signal distortion level when the gain tilt is negative, i.e., for wavelength above the gain maximum.<<ETX>>

1480-nm pumped erbium-doped fiber amplifiers with optimized noise performance for AM-VSB distribution systems

Within analog video transmission systems, optical amplifiers have to display simultaneously good noise and output power performance because of the very stringent carrier-to-noise ratio requirements imposed by the AM-VSB modulation format. We show, theoretically and experimentally, that properly designed forward 1480-nm pumped erbium-doped fiber amplifiers can deliver +16 dBm saturated output power with noise parameter (n/sub sp//C/sub x/) as low as 3.5dB. These amplifiers do not exhibit significant degradation of their noise performance when the input powers are as large as +3 dBm. These characteristics make 1480-nm pumped amplifiers suitable for AM-VSB transmission systems.<<ETX>>

Highly sensitive 565 Mb/s DPSK heterodyne transmission experiment using direct current modulation of a DFB laser transmitter

A comparison between external phase modulation and phase modulation obtained through direct current modulation of a multiquantum-well distributed feedback (DFB) transmitter is reported for a sensitive 565 Mb/s differential-phase-shift-keying (DPSK) heterodyne transmission experiment. A limited sensitivity penalty for direct phase modulation is expected from the driving current pulse shape, the transmitter FM response and the receiver characteristics. The experimentally observed 0.5 dB penalty is in agreement with theory and highlights the potential of direct DPSK modulation as compared to both standard DPSK and continuous-phase frequency shift keying (CPFSK) schemes.<<ETX>>

The WDM answer to line-rate increase within the terrestrial fiber-based networks

The line-rate, supported by a single optical fiber, is likely to be extended in the near future beyond 2.5 Gbit/s. Considerable attention is being paid to the wavelength division multiplexed (WDM) approach. This is due to the fact that the terrestrial optical backbones predominantly contain standard, 1310-nm optimized, G.652 fibers, while signal wavelength near 1550 nm is preferentially used in order to take advantage of both the lowest fiber attenuation and the only one mature optical amplification technology (erbium-doped fiber amplification). This paper examines high-capacity line systems relying on a single optical channel. We discuss the limitation caused by chromatic dispersion for achieving long nonregenerated fiber spans at 10 Gbit/s over standard G.652 fibers. We also describe another source of capacity-dependent limitation, the polarization mode dispersion. The paper also deals with the wavelength division multiplexing alternative, using a channel rate of 2.5 Gbit/s. Among the new technical issues raised by the use of several wavelength-multiplexed channels (such as transmitters wavelength selection and stabilization, propagation through the line fiber, demultiplexing on the receiver side), we particularly stress on the WDM amplification topic which is seen to date as the most limiting and challenging issue.