R.M. Jopson

Polarization-Mode Dispersion

Publisher Summary Polarization mode dispersion (PMD) is a linear effect that can be compensated in principle. In an ideal circularly symmetric fiber, the two orthogonally polarized modes have the same group delay. However, in reality, fibers exhibit a certain amount of birefringence because of imperfections in the manufacturing process or mechanical stress on the fiber after manufacture. It is noted that fluctuations in the polarization mode and fiber birefringence produced by the environment lead to dispersion that varies statistically with time and frequency. PMD causes different delays for different polarizations and when the difference in the delays approaches a significant fraction of the bit period, it leads to pulse distortion and system penalties. Environmental changes— including temperature and stress—cause the fiber PMD to vary stochastically in time. PMD, illustrating the basic concepts, the measurement techniques, the PMD measurement, the PMD statistics for first- and higher orders, the PMD simulation and emulation, the system impairments, and the mitigation methods has been summarized in the chapter. Both the optical and the electrical PMD compensations are considered.

Measurement of second-order polarization-mode dispersion vectors in optical fibers

A polarization-mode dispersion (PMD) measurement technique is described that allows the determination of second- and higher order PMD vectors in optical fibers. The algorithm, based on Muller matrices, requires the launch of only two polarizations per wavelength and uses large rotation angles as well as interleaving to attain low-noise high-resolution PMD data. It has been applied to fibers ranging from 2 to 40 ps in mean PMD.

Modeling of gain in erbium-doped fiber amplifiers

An analytic method is described for fully characterizing the gain of an erbium-doped fiber amplifier (EDFA) that is based on easily measured monochromatic absorption data. The analytic expressions presented, which involve the solution of one transcendental equation, can predict signal gains and pump absorptions in an amplifier containing an arbitrary number of pumps and signals from arbitrary directions. The gain of an amplifier was measured over a range of more than 20 dB in both pump and signal powers. The measured theoretical results agreed to within 0.5 dB. Although the results described apply explicitly to EDFAs pumped in the 1480-nm region, they are also applicable to EDFAs pumped in the 980-nm region. The method is valid whenever the gain saturation by amplified spontaneous-emission noise can be neglected, which is typically the case for amplifiers with less than about 20 dB of gain.<<ETX>>

All-optical regeneration in one- and two-pump parametric amplifiers using highly nonlinear optical fiber

We describe the operation of a two-pump parametric optical regenerator. It is shown that higher order parametric coupling provides optical regeneration with a high extinction ratio. Excessive spectral broadening is studied in a two-pump architecture and compared with that of the one-pump parametric regenerator. We show that the spectral widths of the higher order terms can be controlled in amplifiers by using counterphased optical pumps.

Probability densities of second-order polarization mode dispersion including polarization dependent chromatic fiber dispersion

We describe experiments and simulation of second-order polarization mode dispersion (PMD) components in optical fibers with emphasis on polarization-dependent chromatic dispersion (PCD). Excellent agreement is found in comparisons of experimental, simulated, and theoretical probability densities. To our knowledge, these are the first such comparisons for the second-order PMD magnitude and the PCD.

1-Tb/s transmission experiment

A 1-Tb/s aggregate capacity (50 channels each at 20 Gb/s) was transmitted through 55 km of nonzero-dispersion fiber. Fifty channels were generated by polarization multiplexing 25 wavelengths.

1.5 mu m multiquantum-well semiconductor optical amplifier with tensile and compressively strained wells for polarization-independent gain

A multiquantum-well optical amplifier for 1.5- mu m wavelength operation using alternating tensile and compressively strained wells in the active region is described. For each bias level measured, the polarization sensitivity of the amplifier gain is 1 dB or less averaged over the gain bandwidth. This amplifier is suitable for integration with other optical devices in photonic integrated circuits which require polarization-independent gain.<<ETX>>

The statistics of PMD-induced chromatic fiber dispersion

This paper presents a statistical description of polarization dependent chromatic dispersion (PCD) in optical fibers due to second-order polarization mode dispersion (PMD). This chromatic dispersion is the cause of pulse broadening and compression of the signal components propagating in the principal states of polarization. We show here that, remarkably, the probability density function of PCD has the form of the energy density of a first-order optical soliton. We report measurements that are in agreement with the prediction of this soliton density. Moreover, since a large number of independent experimental samples are difficult to obtain, we also report simulations of the experimental process and these serve to underscore the agreement between theory and measurement. The probability density functions of first and second-order PMD vectors are spherically symmetric. However, these vectors are not statistically independent. The mean square depolarization with respect to wavelength of a launched pulse is revealed to be 33% stronger than expected for spherical symmetry in the absence of dependence, while the mean square PCD is weaker by 67%.

10-Gb/s 360-km transmission over dispersive fiber using midsystem spectral inversion

The use of multi-gigabit per second transmission speeds over the worlds embedded fiber plant (normal dispersion fiber) is severely limited by the chromatic dispersion in systems operating at wavelengths within the gain bandwidth of erbium-doped fiber amplifiers. A dispersion-compensation technique utilizing a midsystem spectral inversion was used to overcome this limit, resulting in 1.55- mu m 10-Gb/s transmission through 360 km of normal-dispersion fiber.<<ETX>>

Four-wave mixing in fibers with random birefringence.

Parametric amplification is made possible by four-wave mixing. In low-birefringence fibers the birefringence axes and strength vary randomly with distance. Light-wave propagation in such fibers is governed by the Manakov equation. In this paper the Manakov equation is used to study degenerate and nondegenerate four-wave mixing. The effects of linear and nonlinear wavenumber mismatches, and nonlinear polarization rotation, are included in the analysis. Formulas are derived for the initial quadratic growth of the idler power, and the subsequent exponential growth of the signal and idler powers (which continues until pump depletion occurs). These formulas are valid for arbitrary pump and signal polarizations.