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Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

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Frequency-resolved adaptive probabilistic shaping for DMT-modulated IM-DD optical interconnects.

Lin Sun, Jiangbing Du, Chang Wang

|May 5, 2019

Summary

Probabilistically shaped discrete multi-tone (PS-DMT) modulation enhances optical interconnects by adapting signal entropy to channel response. This method boosts achievable information rates (AIR) for short-reach systems.

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Area of Science:

Optical Communications
Signal Processing
Information Theory

Background:

Advanced modulation techniques are crucial for increasing capacity in intensity-modulation and direct-detection (IM-DD) optical fiber systems.
Discrete multi-tone (DMT) modulation utilizes frequency-resolved constellations to optimize signal-to-noise ratio (SNR) distribution across the channel's frequency response.
Conventional DMT employs equiprobable constellations, limiting capacity gains.

Purpose of the Study:

To propose and investigate a probabilistically shaped DMT (PS-DMT) modulation scheme with adaptively loaded entropies for short-reach optical interconnects.
To evaluate the achievable information rate (AIR) improvements offered by PS-DMT using Maxwell-Boltzmann and dyadic distributions.
To experimentally validate the PS-DMT performance in a practical optical link.

Main Methods:

Development of PS-DMT by adaptively adjusting constellation entropies based on channel frequency response.
Theoretical analysis of AIR using generalized mutual information (GMI) for different PS-DMT distributions.
Experimental demonstration of PS-DMT over a 100-m multimode fiber link using vertical-cavity surface-emitting lasers (VCSELs).

Main Results:

PS-DMT achieves significant improvements in achievable information rate (AIR) compared to conventional DMT.
The proposed method leverages both the shaping gain of probabilistic shaping at limited SNR and frequency-resolved continuous entropy loading.
Experimental validation confirms the capacity enhancement in a real-world multimode optical link.

Conclusions:

PS-DMT offers a significant capacity improvement for short-reach optical interconnects by optimizing entropy loading to the channel's frequency response.
The combined benefits of shaping gain and adaptive entropy loading make PS-DMT a powerful technique for enhancing optical communication systems.
This approach has potential for broad application in both multimode and single-mode IM-DD fiber-optic communications.