Understanding VCSEL-Based Gain Switching Optical Frequency Combs: Experimental Study of Polarization Dynamics

Abstract

This is a postprint version of the following published document:Prior, E.; Dios, C. de; Ortsiefer, M.; Meissner, P. and Acedo, P. (2015). Understanding VCSEL-based gain switching optical frequency combs: experimental study of polarization dynamics. Abstract-In this paper, we carry out an experimental study on the polarization properties of a vertical-cavity surface-emitting laser (VCSEL) working under gain switching (GS) regime and the characteristics of the resulting optical frequency comb signal. We have observed that each of the two polarization modes presented in the VCSEL continuous wave emission spectrum generate a separate optical frequency comb (OFC) whose modes are phase correlated thanks to the GS regime. We study how these combs associated with the main and orthogonal polarization modes, respectively, vary depending on the input parameters to the VCSEL (bias current and radio-frequency power and frequency). The correlation between both OFCs in the best operation point as defined by the OFC characteristics is also evaluated. Therefore, this study demonstrates that two orthogonally polarized combs are generated that exhibit a high correlation between each other that combine to produce a wider overall optical comb. Hence, we can predict the feasibility of dual-polarization VCSEL-based OFC generators in the few gigahertz repetition frequency rates, with highly correlated modes and continuously tunable distance between them, in a compact and energy-and cost-efficient system that can find application in ultrafast laser dynamics studies and or in polarization-division multiplexing optical communications.Index Terms-Energy efficiency, gain switching (GS), laser diodes (LDs), optical frequency comb generator (OFCG), orthogonal mode, polarization switching, vertical-cavity surface-emitting laser (VCSEL).

Expansion of VCSEL-Based Optical Frequency Combs in the Sub-THz Span: Comparison of Non-Linear Techniques

“…The most complicated set-up to change the comb spacing is the EO-OFC: it needs optical adjustment of the polarization in the PC placed before the first PM but also RF readjustment in both Phase Shifters. Regarding the VCSEL-OFC, a change in the frequency spacing slightly affects the optical span and the flatness as long as it remains within the VCSEL electronic modulation bandwidth (more details in [33]). …”

VCSEL-Based Optical Frequency Combs Expansion Induced by Polarized Optical Injection

“…to generate a regular pulse train. GS of single-mode semiconductor lasers offer combs with good tunability characteristics, and high efficiency and correlation between optical modes [9], [10]. OFCs using different types of commercial single-mode semiconductor lasers have been generated.…”

“…OFCs using different types of commercial single-mode semiconductor lasers have been generated. Edgeemitting lasers like Distributed feedback (DFB) or Discrete Mode Lasers (DML) [9], [11] and Vertical-Cavity Surface-Emitting Lasers (VCSEL) [10], [12], [13] have been used.…”

“…VCSELs are single-longitudinal mode semiconductor lasers with several advantages over edge-emitters like on-wafer testing capability, lower energy consumption, reduced manufacturing costs, and circular output beam [14], [15]. These properties make them appropriate for mass production and for OFC generation [10]. Single-transverse mode VCSELs can emit in two linear polarization modes with orthogonal directions [15].…”

“…Due to the special polarization properties of these devices dual-polarization VCSEL based OFCs can be generated, opening perspectives for polarization-sensitive sensing and multicarrier optical sources for polarization-division multiplexing optical communications. A simple way to obtain these OFCs is by gain-switching VCSELs: it has been experimentally [10] and theoretically shown [13] that two orthogonally polarized OFCs are generated in such a way that combine to produce a wider overall optical comb, although one of the OFCs has smaller power than the other. Optical injection has also been used experimentally to improve the characteristics of VCSEL-based gain switching OFCs [24].…”