Electrical Engineering-Systems Dept.

סמינר מחלקתי

You are invited to attend a lecture by

Eado Meron

(Ph.D. student under the supervision of Prof. Meir Feder and Prof. Mark Shtaif, TAU)

on the subject:

Communications in the optical fiber channel

Novel methods for the optical fiber channel have increased the achievable data rates considerably. From the original On-Off Keying (OOK) signaling schemes, optical communications have evolved and now use, in addition to wave-division multiplexing (WDM), polarization multiplexed and coherent communications. This raised the profound question: what is the ultimate limit for optical data rate? What is the information theoretical capacity of the optical channel?

Due to the Kerr effect, the optical channel is described by a nonlinear differential equation. Hence, the methods used to evaluate this capacity differ considerably from these used for linear channels. Moreover, the desire to avoid channel nonlinearities limits the spectral efficiency of current state-of-the-art systems. In this talk we address several topics, proposing modulation schemes and signals spaces that may help in evaluating the achievable data rates in the optical fiber channel.

We first show that when a narrow-band (relative to the overall bandwidth, e.g. 40 GHZ) channel is used, the nonlinearity induces out-of-band power which can be exploited beneficially to increase the achievable data rate. However, when the entire bandwidth of the optical channel is modulated, we show that unlike linear channels, this out-of-band power yields a finite rate limit for a Gaussian input signal independently of the input power.

We then argue that the inverse scattering transform (IST) induces the most natural signal space for evaluating information theoretic quantities since it contains discrete degrees of freedom invariant under signal evolution. We use the scattered domain to characterize the data rates in restricted scenarios. We also analyze a unique problem of communicating with sets (not sequences) of discrete values, inherent to communication via the IST,. Finally, we analyze the performance of space time codes and equalization methods when used in polarization dependent loss (PDL) impaired channels. We show that these codes enhance the performance of typical optical systems by approximately 2dB. Furthermore, equalization of strong polarization mode dispersion can by itself act as a space-time code, reducing the harmful effects of PDL.