Spun fiber Raman amplifiers with reduced polarization impairments

Abstract

We report a novel vector model of Raman amplification in a fiber with randomly varying birefringence and unidirectional spin profile. Applying the model, we demonstrate for the first time simultaneous mitigation of polarization mode dispersion and polarization dependence of the Raman gain.

Virtually Isotropic Transmission Media With Fiber Raman Amplifier

“…As a result, the Raman gain depends only on the relative orientation between the input signal and the pump SOPs, which is not changing along the length of the isotropic fiber: co-polarized pump and signal waves give the upper limit of maximum Raman gain and cross-polarized waves result in the lower limit of minimum gain as a function of the PMD value. Finally, maximum and minimum PDGs converge and approach the upper limit of PDG which can exceed 20 dB [13].…”

“…For a fiber with random birefringence (SM fiber), the input and output PSPs are different. In view of this, we demonstrated experimentally and theoretically in our previous publications that, similar to PM fibers, PDG in SM fibers takes on its maximum value if the pump SOP is oriented along a PSP, and a small minimum one (different from zero) if the pump SOP is equally shared initially between the PSPs [12][13][14][15]. However, a SM fiber with PMD suppressed by periodic spinning becomes isotropic, i.e., without absolute anisotropy axis with reference to the whole fiber.…”

“…Hence, there is no difference in the Raman gain values and the PDG takes on the minimum value which equals zero [11]. Unlike a PM fiber, the random birefringence in a single mode fiber can be represented in terms of a fixed modulus model (FMM), where the length of the birefringence vector is fixed and its orientation is driven by a white-noise process, and a more complex random modulus model (RMM), in which both Virtually Isotropic Transmission Media with Fiber Raman Amplifier Sergey Sergeyev, Sergei Popov, Ari T. Friberg P the orientation and the length of the birefringence vector change randomly [13]. Poole and Wagner [3] have shown that the so-called principal states of polarization (PSPs) are a key concept in analyzing PMD in fibers with randomly varying birefringence.…”

“…Sergeyev et al [13] have recently put forward such a model, which takes the form of ordinary differential equations for the gain of the fiber Raman amplifier as a function of pump and signal states of polarization (SOP), PMD parameter, and the parameters of fiber spinning. Using this model, it was shown that it is possible to mitigate both PDG and PMD by adopting a fiber with a particular spin profile or, more specifically, a two-section fiber ("two-section approach") in which the first section has no spin and the second one is periodically spun [13]. As a result, PDG and PMD in 10 km of dispersion compensation fiber (DCF) can be suppressed to 0.13 dB and 0.032 ps/km 1/2 , respectively [13].…”

“…Using this model, it was shown that it is possible to mitigate both PDG and PMD by adopting a fiber with a particular spin profile or, more specifically, a two-section fiber ("two-section approach") in which the first section has no spin and the second one is periodically spun [13]. As a result, PDG and PMD in 10 km of dispersion compensation fiber (DCF) can be suppressed to 0.13 dB and 0.032 ps/km 1/2 , respectively [13]. To suppress PMD and PDG further, and thus to develop quasi-isotropic transmission media of 50 km length, we report herein on a novel approach to optimize the parameters of the first section of the fiber, viz., its correlation length and PMD.…”