Error-free soliton transmission at 20 Gbit/s over 7150 km throughall-optical synchronous phase modulation

All-optical soliton synchronous phase modulation through transmission fibre is shown to enable error-free propagation of 20 Gbit/s signals up to 7150 km without the need for dispersion management. Tolerance to imperfect clock-signal synchronisation is characterised experimentally     

An analytical model for the determination of optimal outputreflectivity and fiber length in erbium-doped fiber lasers

An analysis relating the output power of erbium-doped fiber lasers to the output mirror reflectivity r_out is performed, and a closed-form expression valid for r_out<0.95 is obtained. It shows that the laser output power is nearly independent of the output reflectivity when 0.5<r_out<0.95. The closed-form expression is used to study the dependence of the output power with laser wavelength and confirms the large tuning range (60 nm) already reported. However, it is shown that the tuning range is greatly increased (up to more than 100 nm) if r_out is chosen near 0.9. Finally, an approximate expression for the optimal fiber length needed to achieve maximum laser output is derived     

Analysis of transient gain saturation and recovery in erbium-dopedfiber amplifiers

An analysis of transient gain dynamics in erbium-doped fiber amplifiers is presented to provide a qualitative explanation of its time constants. The theory yields analytical solutions at the fiber amplifier input end, making it convenient to study the time dependence of gain saturation and recovery under changing input signal conditions. It is shown that, independently of the pump wavelength, gain saturation and recovery effects have long characteristic times (0.2-10.0 ms) which advantageously reduce saturation-induced crosstalk in the amplifier. The effect of saturation-induced gain modulation is found to vanish at signal frequencies above F=1 kHz, which is in good agreement with observed experimental results     

Theory and implementation of a Raman active fiber delay line

In an optical delay line made of a single-mode reentrant fiber loop, Raman amplification is used to compensate for recirculating signal losses. Concurrent Stokes noise amplification limits the system performances. A theoretical model shows that the signal-to-noise ratio decays as the reciprocal of the number of signal recirculations. Experimental results obtained with a 760-m-long fiber loop operated atlambda = 1.12 mum are presented. A new pump modulation technique resulting in improved output signal stability is reported whereupon optical delays up to 3 ms were achieved.     

1 GHz GaInAs:Fe photoconductive optical AND gate with approximately 100 fJ switching energy for time-division access fibre networks

A high-speed, three-port optical AND gate based on GaInAs:Fe photoconductive switches operating at lambda =1.3 mu m is demonstrated. An electrical power contrast ratio of 12 dB is obtained in optical-to-electrical time-division demultiplexing of a 1 GHz signal bit sequence by a 333.3 MHz clock with optical pulse energies of 100 fJ.<>     

Capacity Demand and Technology Challenges for Lightwave Systems in the Next Two Decades

Ten to 20 years from now, optical networks will have to carry vastly increased amounts of Internet traffic. Today's knowledge (2006) already points to ultimate technology limits in the physical layer, foretelling the end of the so-called "Optical Moore's Law." Such an observation is discordant with the generic and optimistic view of a "virtually infinite" optical bandwidth combined with unlimited Internet-traffic growth. In order to meet long-term needs and challenges, therefore, basic research in wideband optical components and subsystems must be urgently revived today     

Design optimization for efficient erbium-doped fiber amplifiers

The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFAs) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λ _p=980 nm and λ_p=1.47 μm. Three designs of fiber-amplifier waveguides are considered: one with the same mode size as standard 1.5-μm communication fibers (type 1); one with the same mode size as standard 1.5-μm dispersion-shifted fibers (type 2); and one with mode size smaller than those of communication fibers (type 3). For the 1.47-μm pump, fundamental LP₀₁ mode excitation is assumed, while for the λ_p=980-nm pump, concurrent excitation of LP₁₁ modes is considered. It is shown that excitation of higher-order pump modes at 980 nm does not significantly affect the amplifier gain performance. The effect of concentrating the Er³⁺ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2     

Modeling erbium-doped fiber amplifiers

Erbium-doped fiber amplifiers are modeled using the propagation and rate equations of a homogeneous two-level laser medium. Numerical methods are used to analyze the effects of optical modes and erbium confinement on amplifier performance, and to calculate both the gain and amplified spontaneous emission (ASE) spectra. Fibers with confined erbium doping are completely characterized from easily measured parameters: the ratio of the linear ion density to fluorescence lifetime, and the absorption of gain spectra. Analytical techniques then allow accurate evaluation of gain, saturation, and noise in low-gain amplifiers (G≲20 dB)     

Low-threshold synchronously pumped all-fiber ring Raman laser

Experimental results on a synchronously pumped, all single-mode fiber Raman laser with a low threshold of 740 mW are reported. Suppression of gain fluctuations due to pump phase noise has been achieved by implementing a fiber coupler of high multiplexing effect. Multistokes generation of low-noise optical pulse trains atlambda = 1.12 mum andlambda = 1.18 mum has also been obtained with a subwatt pump threshold.     

Spectral gain hole-burning at 1.53 μm in erbium-doped fiberamplifiers

Spectral gain hole-burning at λ₀=1.53 μm was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K. The hole width was found to broaden with temperature for T ⩾20 K according to a T^1.73 law. From the data, the room-temperature homogeneous linewidth associated with the 1.531-μm transition in the ⁴I_13/2-⁴I_15/2 laser system was determined to be Δλ_h=11.5 nm for aluminosilicate fibers