Sergio Tsuda

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.

10-Gb/s error-free transmission under optical reflection using isolator-free 1.3- /spl mu/m InP-based vertical-cavity surface-emitting lasers

Error-free transmission through 10-km single-mode fiber at 10 Gb/s under -13-dB optical reflections has been demonstrated for the first time using a directly modulated 1.3-/spl mu/m InP-based VCSEL without any optical isolator. The 13-GHz relaxation oscillation frequency and stable polarization suppresses relative intensity noise degradation under optical reflection. Only 1-dB error-free power penalty has been observed with optical reflection set with the worst polarization direction.

Semiconductor optical amplifier for amplification and switching applications

This paper presents recent progress on SOAs with dilute optical mode. The SOA optical mode is designed to be large to achieve high saturation power and low coupling losses of 1.16 and 0.89 dB for TE and TM polarizations with a lens fiber. A 2-mm long SOA has high saturation power (16.3 dBm), low PDG (<1 dB), low noise figure (<7.2 dB) and medium gain (>19.5 dB) across C-band. A 1.5mm-long SOA was successfully used as a 10 Gbit/s booster amplifier for 100km transmission. The dynamic properties of the SOA were characterized to support application as optical gate switch in sub GHz speed.

Transmission of 80/spl times/10 Gbit/s WDM channels with 50 GHz spacing over 500 km of LEAF/sup R/ fiber

We demonstrate transmission of 80/spl times/10 Gbit/s channels over 5/spl times/100 km of LEAF fiber. The impact of optical nonlinearities for 50 GHz channel spacing is evaluated by comparing the results of different interleaved channel polarization experiments.

High optical reflection resistance of 1.3-&#956;m InP-based isolator-free VCSELs: 10-Gbps error-free transmission under reflection

1.3-μm InP-based VCSELs with high optical reflection resistance for optical isolator-free 10-Gbps operation have been demonstrated. The 13-GHz relaxation frequency increased the critical feedback level of those VCSELs and allowed 10-km, 10-Gbps error free transmission without isolator, even with -13dB optical reflection.

Raman noise-figure improvement and multipath interference mitigation in effective-area-optimized dispersion-managed cable

We have experimentally demonstrated that dispersion-managed cable designed such that the inverse-dispersion-fiber (-D) section is sandwiched between two positive-dispersion-fiber (+D) sections has many advantages over existing transmission fibers and other dispersion-managed configurations. The symmetric configuration where the -D fiber section is centered in the middle of the span is the most interesting case for cable deployment.

Stimulated Brillouin scattering in Raman-amplified dispersion compensating fibers

In conclusion we performed experiments to study SBS in Raman amplified dispersion compensating fibres (DCFs) of different lengths. We developed a theory which estimates the SBS thresholds for unpumped, forward and backward Raman pumped DCFs of short length as a function of pump powers and fiber parameters. Theory and experiments both indicate significant alteration of SBS thresholds if Raman amplification is present inside a DCF depending on the power of the Raman pump. The results also imply that forward pumping of the DCF can be more detrimental to the transmission than backward pumping since it brings down the SBS threshold much faster than backward pumping does for the same length of the fiber.

320 Gbit/s WDM transmission over 450 km of LEAF/sup R/ optical fiber

We demonstrate transmission of 32/spl times/10 Gbit/s over 450 km of LEAF/sup R/ fiber with BER /spl sim/10/sup -13/, using the same dispersion compensation for all channels. The large effective area fiber strongly reduces all nonlinear effects, limiting the fiber-induced penalty to <1.3 dB.

Optimum pre-emphasis in ultra-long-haul networks

We investigate experimentally and theoretically the shape of the optimum spectral pre-emphasis for ultra-long-haul networks and systems in the presence of optical nonlinearities. In a 40×10 Gbits/s×2240 km system, we experimentally show the advantages of a pre-emphasis scheme that ensures minimum variations of path-averaged power among the wavelength-division-multiplexing channels between the cleanups performed by dynamic gain-flattening filters. This is achieved by enforcing a straight-line spectrum near the middle of the link between two consecutive gain-flattening nodes. We explain these results by a simple model, in which we derive the conditions for optimum pre-emphasis in the presence of either distortionlike (e.g., self-phase modulation) or noiselike (e.g., four-wave mixing) nonlinearities. We show that, for relatively small gain ripple, both of these optimum pre-emphasis techniques are equivalent to equalizing the optical signal-to-noise ratio for all channels and producing a flat power spectrum near the middle of the link. Hence, enforcing the straight-line spectrum in the middle of the link is the closest practical approximation to the optimum pre-emphasis.