M.Sc Thesis

M.Sc StudentZhurahov Michael
SubjectThermalization, Bistability and Classical Laser Light
Codensation in Erbium-Doped Fiber Cavities
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROFESSOR EMERITUS Baruch Fischer
DR. Refael Weill
Full Thesis textFull thesis text - English Version


This works deals with various physical phenomena that can occur in simple systems including erbium doped fibers cavities and spectral filters:  thermalization, bistability and classical laser light condensation.

In the first part we present a first experimental demonstration of classical cw laser condensation (LC) in the frequency (mode) domain. LC is based on weighting the modes in a noisy environment in a loss-gain measure compared to an energy (frequency) scale in quantum Bose-Einstein condensation (BEC). It is characterized by a sharp transition from multi- to single-mode oscillation. The condensation occurs when the spectral-filtering (loss-trap) has near the lowest-loss mode (“ground-state”) a power law dependence with an exponent smaller than 1. An added meaning of this LC mode system stems from its relation to regular lasing and photon-BEC.

In the second part we demonstrate thermalization and Bose-Einstein (BE) distribution of photons in standard erbium-doped fibers (edf) in a broad spectral range up to ~200nm at the 1550nm wavelength regime. Our measurements were done at a room temperature ~300K and 77K. It is a special demonstration of thermalization of photons in fiber cavities and even in open fibers. They are one-dimensional (1D), meters-long, with low finesse, high loss and small capture fraction of the spontaneous emission. Moreover, we find in the edf cavities coexistence of thermal-equilibrium (TE) and thermal lasing without an overall inversion (T-LWI). The experimental results are supported by a theoretical analysis based on the rate equations.

In the third part we show in an experimental and theoretical study bistability and hysteresis that depend on backward amplified spontaneous emission (ASE) in a unidirectional ring erbium doped fiber (edf) laser. It results from the interplay between the signal and the backward propagating amplified spontaneous emission (ASE) in the gain medium that is ejected from the fiber loop by an isolator. Another important factor is the strong wavelength dependence of the absorption and emission coefficients and their ratio.