Abstract
Despite the promise of an orders-of-magnitude increase in transmission capacity, practical implementation of mode-division multiplexing faces a number of challenges. The most important among them is the complexity of digital signal processing (DSP) for compensating mode crosstalk and modal dispersion. The most promising method proposed so far for reducing this DSP complexity is strong mode coupling. We propose and demonstrate, for the first time, a method of inducing strong mode coupling and reducing group delay spread using uniform long-period gratings (LPGs). Even though the LPGs have a fixed grating period, mode coupling is effective among all mode groups and over a broad wavelength range. Both insertion loss and mode-dependent loss can be significantly reduced by optimizing the index profile of and the number of modes supported by the fiber in which the LPG is applied.
Highlights
As single-mode fiber-optic communication systems approach their capacity limit, space-division multiplexing (SDM) has attracted significant attention in recent years[1,2]
Channel and even 0.01 dB/km of loss reduction is being sought for single-mode fibers (SMFs), the long-period gratings (LPGs) used to induce strong mode coupling must introduce extremely low losses, preferably below 0.1 dB, to ensure that the transmission capacity of an mode-division multiplexed (MDM) system is competitive with parallel SMF transmission systems
Through simulations, we demonstrate the reduction of intrinsic loss and mode-dependent loss (MDL) by optimizing the index profile of and the number of modes supported by the fiber in which the LPG is applied
Summary
We first demonstrate enhanced mode coupling among all 9 LP modes using a uniform single-period LPG. The differences in the powers of each mode group in the impulse responses of the GRIN FMF with and without pressure on the LPG can be used to characterize mode coupling mediated by the LPG. For each waveform measured under different pressure/mode-coupling efficiency, the RMS pulse width representing the GDS of the FMF was calculated using the following formula[13] σ = t2 − t 2. The fluctuations in RMS width and loss are due to environmental changes such as temperature and fiber deformation
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