Equalization of modal dispersion in multimode fiber using spatial light modulators

Abstract

-Intersymbol interference (ISI) due to modal dispersion is the dominant limitation to the bit rate-distance product in multimode fiber-optic communication systems. If the light launched into the fiber excites only the desired principal modes, modal dispersion can be eliminated. We can achieve this by using spatial light modulators (SLMs) to perform adaptive spatial filtering on the electric fields of the light. In this paper, we develop an optimization framework for setting the SLMs to obtain an upper bound on the achievable performance and develop heuristics that nearly reach this upper bound. Using this framework, we show that both a sophisticated semidefinite programming-based algorithm and a simple adaptive algorithm achieve performance close to the upper bound. Performance and system complexity tradeoff curves are constructed, showing that a 20×20 array of SLM pixels with binary phase control performs within 15% of more complex implementations. Finally, we extend the framework and present preliminary results showing the promise of further increases in the capabilities of multimode fiber by using the fiber as a multiple-input, multiple-output (MIMO) transmission medium.

Algorithms for Compensation of Multimode Fiber Dispersion Using Adaptive Optics

“…3 clearly show that at optimum, the SLM reflectances do not have unit magnitude. This is contrary to what is stated in [6]. However, Fig.…”

“…1, and it was originally proposed in [6]. It consists of a transmitter, the MMF itself, and a receiver in which received light pulses are detected and decoded.…”

“…However, this can lead to noise enhancement, and, therefore, degradation of achievable bit-error ratio (BER) [5]. Instead, the use of adaptive optics was proposed in [6]. This involves shaping the spatial profile of the electric field at the input end of the fiber using a spatial light modulator (SLM) to excite only desired PMs.…”

“…Experiments [7] have shown that this approach is capable of realizing high bit rates. In [6], a basic theoretical framework was developed. This framework, however, did not model all physics of the system pertinent to the problem.…”

Device design and signal processing for multiple-input multiple-output multimode fiber links

“…The signal processing employed in this work 4 was simple and the data rates achieved somewhat modest, although it was successful in demonstrating the utility of MIMO communication over multimode fiber media. The use of spatial signal design by means of a spatial light modulator with a feedback link from the receiver to the transmitter has been shown to be a means of realizing similar benefits 5 . More recently, a coherent demodulation MIMO implementation for MMF links has been demonstrated 6, 7 as a means of utilizing MIMO over optical fibers.…”