Abstract
Polarization switching (PS) and polarization bistability (PB) characteristics of a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection (OOI) with time-varying injection power are experimentally investigated for the first time. To implement the optical injection, a Mach-Zehnder modulator (MZM) modulated by a triangular radio wave is adopted, and the influences of some typical parameters on the performances of PS and PB are analyzed. Under suitable operation conditions, PB in the VCSEL subject to OOI with time-varying injection power can be observed only for the input power P0 of MZM locating within a determined range, and the width of hysteresis loop gradually decreases with the increase of P0 from the minimum P0, min to the maximum P0, max. Under different frequency detuning Δ ν between the injection light and the X polarization mode of the VCSEL, the determined ranges of P0 required for PB are different. With the variation of Δ ν from a negative value to a positive value, both P0, min and P0, max present a trend of decrease first and then increase. Additionally, with the increase of the modulation frequency, the hysteresis loop width firstly increases rapidly and then gradually tends saturation.
Highlights
Vertical-cavity surface-emitting lasers (VCSELs) have received much attention due to their unique features, such as low threshold current, easy to integrate, high coupling efficiency with optical fibers, low manufacturing cost, etc. [1]
polarization bistability (PB) in the VCSEL subject to orthogonal optical injection (OOI) with time-varying injection power can be observed only for the input power P0 of Mach-Zehnder modulator (MZM) locating within a determined range, and the width of hysteresis loop gradually decreases with the increase of P0 from the minimum P0,min to the maximum P0,max
The results demonstrate that the sweep rate of the time-varying current affects the Polarization switching (PS) and PB characteristics of VCSELs, and rapidly scanning the current is helpful for increasing the width of the hysteresis loop [13], [14]
Summary
Vertical-cavity surface-emitting lasers (VCSELs) have received much attention due to their unique features, such as low threshold current, easy to integrate, high coupling efficiency with optical fibers, low manufacturing cost, etc. [1]. For VCSELs under optical feedback, through scanning the polarization direction and the feedback light strength, PS and PB can be observed, and the influences of the sweep rate have been analyzed [16]–[18]. According to the polarized direction of the injection light relative to the dominant mode in a free-running VCSEL, optical injection can be categorized into orthogonal optical injection (OOI), parallel optical injection (POI) and variable polarization optical injection (VPOI). Our group experimentally reported the influence of the polarization angle of optical injection on the PB characteristic in a VCSEL under VPOI [26]. Hurtado et al experimentally observed three different shapes of power-induced hysteresis cycles in VCSELs under OOI, and analyzed the effect of bias current on PB [27], [28]. The influences of the frequency detuning, injection power and bias current on PS and PB have been investigated [29]–[31]
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