N. Kagi

BROADBAND FIBER OPTICAL PARAMETRIC AMPLIFIERS

The bandwidth of a single-pump fiber optical parametric amplifier is governed by the even orders of fiber dispersion at the pump wavelength. The amplifier can exhibit gain over a wide wavelength range when operated near the fibers zero-dispersion wavelength. It can also be used for broadband wavelength conversion,with gain. We have experimentally obtained gain of 10-18 dB as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm.

Cross-phase modulation in fiber links with multiple optical amplifiers and dispersion compensators

We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical amplifiers and dispersion compensators. Our theory suggests that the XPM effect can be modeled as a phase modulator with inputs from the intensity of copropagating waves. The frequency response of the phase modulator corresponding to each copropagating wave depends on fiber dispersion, wavelength separation, and fiber length. The total XPM-induced phase shift is the integral of the phase shift contributions from all frequency components of copropagating waves. In nondispersive fibers, XPM is frequency-independent; in dispersive fibers, XPMs frequency response is approximately inversely proportional to the product of frequency, fiber dispersion, and wavelength separation. In an N-segment amplified link, the frequency response of XPM is increased N-fold, but only in very narrow frequency bands. In most other frequency bands, the amount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequency response of XPM is increased N-fold at all frequencies if the dispersion is compensated for within each fiber segment. Thus, the XPM-induced phase shift is smaller in systems employing lumped dispersion compensation than in systems employing distributed dispersion compensation.

Optimizing the location of dispersion compensators in periodically amplified fiber links in the presence of third-order nonlinear effects

In order to minimize third-order nonlinear effects while compensating dispersion in a periodically amplified link, it is more effective to place a single dispersion compensator at the end of the link than to individually compensate each segment. The improvement obtained by using the former approach instead of the latter one, defined as the ratio of the powers of the four-wave mixing products in the two cases, is (sin N u/N sin u)/sup 2/ where N is the number of segments, and u represents phase mismatch. We have experimentally verified this conclusion, by performing a cross-phase modulation experiment in a two-segment link.

Cancellation of third-order nonlinear effects in amplified fiber links by dispersion compensation, phase conjugation, and alternating dispersion.

We show that in principle it is possible to cancel third-order nonlinear effects in optical fiber links. The necessary conditions exist in two-segment links, with dispersion compensation, phase conjugation, and amplification between the two, as well as opposite chromatic dispersion coefficients in the segments. The cancellation is independent of loss, modulation format, and modulation frequency.

Cross phase modulation in fiber links with optical amplifiers

Summary form only given. In WDM optical communication systems, nonlinear effects in optical fibers can lead to crosstalk between channels . It has been reported that cross phase modulation (XPM) induced by residual intensity modulation causes penalty in multi-channel PSK and FSK systems. Previously we have shown that chromatic dispersion has a significant impact on the magnitude of XPM in a single segment of fiber. In this paper, we investigate experimentally and theoretically XPM in systems where multiple optical amplifiers are used as repeaters.

Compensation of cross-phase modulation in periodically amplified CPFSK optical communication systems

In long-distance periodically amplified systems, dispersion compensation is highly beneficial. In this paper, we show that compensating the dispersion in each segment (type-A systems) still leads to significant cross phase modulation (XPM) induced penalty even when high dispersion fiber is used, but the penalty is greatly reduced by concentrating the dispersion compensation at one place (type-B systems).