23.12.14

You are invited to attend a lecture

by

Omer Shlomovits

(MSc. student under the supervision of Prof. Moshe Tur)

School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel

Depletion and noise issues in fiber-optic Brillouin amplification

In the Stimulated Brillouin Scattering (SBS) effect, two frequency-shifted counter-propagating lightwaves, called signal and pump, interact to induce an acoustic wave, which later functions as a light scatterer, thus coupling the optical fields to each other. Provided that the frequency offset between the two lightwaves matches a particular resonance frequency, characteristic of the fiber, called the Brillouin Frequency Shift, amplification of the lower frequency lightwave, the signal, occurs as it propagates.

SBS has been a favorable mechanism for its robustness, simplicity of implementation and low pump power in standard fibers at room temperature. For this reasons the effect is widely used for numerous applications, including distributed sensing of temperature and strain, fiber lasers, optical memories and more. This work spans two topics, aiming at a common purpose of getting a better insight into the Brillouin amplification process while adjusting the existing models one step closer to the physical world.

In the first part of the talk, we will discuss the impact of laser phase noise on the Brillouin gain. It is shown that insufficient coherence of laser sources used in Stimulated Brillouin amplification setups not only leads to reduced gain but also to source-induced gain fluctuations (noise), which may affect performance. We will show that under commonly encountered conditions, even a relatively coherent source, having a linewidth of a 1 MHz, has enough phase noise to become the dominant contributor to the observed Brillouin gain fluctuations.

In the second part, we will focus on gain and polarization vector-properties of the SBS interaction in the presence of birefringence for the case of a strong enough signal to cause pump depletion. We determine that maximum and minimum gains are achieved for the same input states of polarization as in the undepleted case. Under normal conditions, the signal and pump power distributions along the fiber of the two input polarizations, which exhibit maximum and minimum gains, can be approximately deduced from a much simpler scalar formulation.

Tuesday, December 23, 2014, at 11:00

Room 011, EE- KITOT building