Mechanisms of fast self pulsations in two-section DFB lasers

• Published in: IEEE journal of quantum electronics Vol. 32; no. 1; pp. 69 - 78
• Main Authors: Wenzel, H., Bandelow, U., Wunsche, H.-J., Rehberg, J.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.1996; Institute of Electrical and Electronics Engineers
• Subjects: Dispersion; Distributed feedback devices; Equations; Exact sciences and technology; Fundamental areas of phenomenology (including applications); High speed optical techniques; Laser modes; Laser theory; Lasers; Optical feedback; Optical modulation; Optical pumping; Optics; Physics; Pump lasers; Semiconductor lasers; laser diodes; Self-pulsing; Eigenmode; Theoretical study; Coupled mode theory; Spontaneous emission; Single mode laser; Semiconductor lasers; Numerical solution; Rate equation; Resonance; Q switched laser; Gain; Distributed feedback lasers
• ISSN: 0018-9197; 1558-1713
• DOI: 10.1109/3.481922

We show theoretically, that the detuning between the resonance frequencies of differently pumped DFB sections gives rise to two different pulsation mechanisms, 1) dispersive self Q-switching of a single-mode and 2) beating oscillations between two modes of nearly equal threshold gain. Our analysis is based on the dynamic coupled wave equations accomplished with carrier rate equations. We demonstrate the existence of certain isolated values of the detuning between both sections, at which two longitudinal eigenmodes become degenerate. In the degeneration point, the longitudinal excess factor of spontaneous emission has a singularity and the system of eigenmodes becomes incomplete. We derive reduced equations governing the dynamics in the vicinity of degeneration points. For an example device, the numerical integration of these equations clearly demonstrates the two different self pulsations with repetition rates of more than 100 GHz.