Controlling slow and fast light and dynamic pulse-splitting with tunable optical gain in a whispering-gallery-mode microcavity

TL;DR

This paper demonstrates how tunable optical gain in a WGM microcavity enables dynamic control of slow and fast light, including pulse splitting, with potential applications in optical communication and signal processing.

Contribution

It introduces a method to control light speed and pulse splitting in a microresonator using optical gain, a novel approach for dynamic optical signal manipulation.

Findings

Transition from undercoupling to overcoupling by increasing pump power.

Two-fold delay enhancement in slow light regime.

Dynamic pulse splitting controlled by optical gain.

Abstract

We report controllable manipulation of slow and fast light in a whispering-gallery-mode (WGM) microtoroid resonator fabricated from Erbium (Er3+) doped silica. We observe continuous transition of the coupling between the fiber-taper waveguide and the microresonator from undercoupling to critical coupling and then to overcoupling regimes by increasing the pump power even though the spatial distance between the resonator and the waveguide was kept fixed. This, in turn, enables switching from fast to slow light and vice versa just by increasing the optical gain. An enhancement of delay of two-fold over the passive silica resonator (no optical gain) was observed in the slow light regime. Moreover, we show dynamic pulse splitting and its control in slow/fast light systems using optical gain.