Phase Correlation and Linewidth Reduction of 40 GHz Self-Pulsation in Distributed Bragg Reflector Semiconductor Lasers

In this paper, self-pulsation (SP) in a distributed Bragg reflector (DBR) semiconductor laser without a saturable absorber is experimentally and theoretically investigated. Detailed experimental characterizations of the SP DBR laser are reported in the optical and radio-frequency domains. Phase correlation between the longitudinal modes selected by the DBR mirror has been experimentally demonstrated. A theoretical model based on coupled rate equations for three modes has been developed to study the time evolution of phases and amplitudes of the modes. The carrier density modulation, resulting from the beating between adjacent longitudinal modes generates four-wave mixing (FWM) and is responsible for mutual injection locking, leading to passive mode-locking. The calculated power spectral density of the frequency noise derived from the model is in agreement with experimental results and proves that the phases of the longitudinal modes are identically correlated through the FWM process in this type of SP lasers

I. Introduction

In Order to improve transmission distance, transparency, capacity and speed of optical networks, much attention has been paid to investigating practical means for all-optical signal processing, for example all-optical digital logic functions and retiming, reshaping and reamplifying (3R) regenerators [1], [2]. All-optical clock recovery regeneration at 40 Gbit/s and beyond appears to be a crucial element for future transparent networks. One solution to achieve the regeneration is an all-optical clock recovery element combined with a Mach–Zehnder interferometer [2]. In this respect truly all-optical clock recovery is of very high interest as it would supersede the complicated optoelectronic schemes including: a high speed photo-receiver, a high- filter, a power amplifier, and a high speed laser or an integrated laser modulator. Among the different approaches investigated so far, we can mention in particular the one using self-pulsating (SP) lasers.