Alan F. Evans

Dramatically improved transmission of ultrashort solitons through 40 km of dispersion-decreasing fiber.

A 40-km length of optical fiber whose group-velocity dispersion decreases exponentially along its length has been fabricated. We experimentally compare the propagation of picosecond solitons through the dispersion-decreasing fiber with that through a constant-dispersion fiber of the same path-averaged dispersion. For a wide range of input powers, the output pulse widths of the dispersion-decreasing fiber are found to be as short as the input pulse widths, whereas the output pulse widths of the constant-dispersion fiber are significantly larger. Numerical simulations of the experiment are performed and are in good agreement with the experimental results.

Stimulated Brillouin scattering in Raman-pumped fibers: a theoretical approach

We develop a theoretical approach to describe stimulated Brillouin scattering (SBS) in Raman-pumped optical fibers. We derive the condition for the SBS threshold as a function of fiber parameters and the input power of forward and/or backward pump. A particular emphasis is given to the effect of the fiber length and unequal absorption coefficients for pump and signal wavelengths on the SBS threshold. Simple, yet accurate, analytical expressions for the SBS threshold in pumped fibers are also obtained. We show that in pumped fibers, the SBS threshold power is inversely proportional to the path-average integral of Raman gain. Validity ranges of derived formulas are considered in detail. The theoretical predictions are verified experimentally. The calculated values of the SBS threshold powers are in a good agreement with the measured threshold power in Raman-pumped dispersion-compensated fibers.

Fiber design considerations for 40 Gb/s systems

In this paper, we review the fundamental advantages and drawbacks of 40-Gb/s systems from a fiber manufacturers perspective. Based on modeling, experimental results, and fundamental understanding, we correlate the fiber design parameters with the expected performance of long-haul systems operating at 40 Gb/s. Nonlinear penalties, dispersion tolerances, modulation formats, polarization-mode dispersion, and Raman amplification are covered. We also present the fiber features required for both metro and submarine networks at this specific data rate.

Synchronization of passively mode-locked erbium-doped fiber lasers and its application to optical communication networks

We synchronized two passively mode-locked erbium-doped fiber lasers using a phase lock loop with a large dynamic range and bandwidth, which is realized by using a novel acoustooptic-modulator-grating scheme. Cross-correlation of the two lasers shows the interlaser jitter is under 2 ps (same as the laser pulse width) for period as long as hours. To prove the quality of phase locking, we apply synchronized lasers in two all-optical network applications, one of which requires the lasers to have the same wavelength and the second requires the lasers to be at different wavelengths. In the single wavelength application, the synchronized lasers drive a cascade of two low-birefringence, polarization maintaining, optical logic gates with switching timing window of 4 and 5 ps, respectively. We obtain nonlinear transmission of /spl sim/50% at a switching energy of 8 pJ and contrast ratio of 16 dB, which are comparable performance as that obtained using a single laser. In the different wavelength application, we use 0.8 ps pulses to switch 2 ps pulses in a two-wavelength nonlinear optical loop mirror demultiplexer with timing window of 5.5 ps. Stable switching is reached at a efficiency as high as 90% at switching energy of 0.8 pJ, and a contrast ratio of 20 dB. Excellent agreement is found between the experimental data and the simulated results, which exclude the timing jitter.

Raman amplification in broadband WDM systems

After comparing Raman and erbium amplification, this talk focuses on why distributed Raman amplification has become a catalyzing technology to ultra-long 10 Gb/s and future 40 Gb/s transmission. A review of how Raman systems work and recent transmission results underscores its potential.

80 Gb/s to 10 Gb/s polarization-insensitive demultiplexing with circularly polarized spun fiber in a two-wavelength nonlinear optical loop mirror

We demonstrate the first polarization insensitive demultiplexing of 10-Gb/s channels from 80-Gb/s pseudorandom bit streams using a two-wavelength nonlinear optical loop mirror with circularly polarized spun fiber. The polarization sensitivity of the device is reduced to <1 dB for >90% transmission, and bit-error-rate measurements show that the remaining polarization sensitivity leads to a power penalty difference of 1.5 dB. The nonlinear transmission is 91% for a switching energy of 4 pJ/pulse, and the full-width at half-maximum timing window is 9.6 ps. The circularly polarized spun fiber has a /spl lambda//sub 0/ of 1541 nm, a length of /spl sim/1 km, and /spl sim/4.1 times higher nonlinearity than that of conventional dispersion-shifted fiber. The spin rate is 16 turns/m and the birefringence is /spl Delta/n/spl sim/1/spl times/10/sup -6/, corresponding to 25 turns/beat length.

Distributed amplification: how Raman gain impacts other fiber nonlinearities

The gain and noise figure of distributed amplifiers can be integrated and lumped at the end of each fiber span. This paper investigates whether this convenient simplification is valid in the presence of fiber nonlinearities. Distributed Raman amplification affects other fiber nonlinearities by changing the evolution of signal power along the fiber. Depending on system parameters can impact on self phase modulation and four wave mixing when gain is greater than -15 dB and increases the signal-to-signal Raman power transfer for all system at much lower gain values.

Effects of lateral load and external twist on polarization-mode dispersion of spun and unspun fibers.

Using the coupled-mode theory, we have developed a theoretical model to analyze the effects of lateral load and external twist on polarization-mode dispersion (PMD) of spun and unspun fibers. Modeling results show that spun and unspun fibers have very different PMD responses to lateral load and external twist. Experimental results show good agreement with the theory.

Novel fibers for dispersion-managed high-bit-rate systems

Summary form only given. Novel dispersion-managed fibers that minimize four-wave mixing (FWM) and other nonlinear effects with built-in dispersion compensation, large effective areas, and low dispersion slopes have been developed. These fibers are also expected to be flexible enough to allow upgrades in both wavelength-division multiplexing and time-division multiplexing approaches. Propagation and FWM efficiency models have been used to optimize the designs and evaluate the system advantages of these fibers.

Constraints on the design of single-channel, high-capacity (>10 Gb/s) soliton systems

We have examined the design constraints of single-channel soliton systems operating at high data rates (>10 Gb/s). While Gordon-Haus timing jitter is the most important effect for 10 Gb/s transoceanic systems, it is fiber perturbations arising from discrete in-line amplification that severely limit the transmission distance and amplifier spacing at higher data rates. Dispersion-decreasing fiber or distributed optical amplification, both of which locally balance dispersion and fiber nonlinearities, could eliminate this constraint and extend the regime of stable soliton transmission.<<ETX>>