Application of repumping laser in optical switching

•We conducted coherent spectroscopy in a Ξ type atomic system.•DROP and EIT signals are observed.•Bi-modal all optical switching is demonstrated under DROP–EIT combination.•Repumping laser restores ‘radiation trapped’ atoms into the Ξ level coupling.•Intensity modulation depth is increased under the action of repumping laser.

The application of electromagnetically induced transparency (EIT) in high speed optical switching has remained as a key topic in research related to all optical switching. Demonstration of optical switching through EIT realized under ladder (Ξ) level coupling has been reported earlier. Due to narrow linewidth (ГEIT) and low coherent dephasing rate (γ) the EIT needs to be prepared only once to demonstrate such switching action. However, in a Ξ system the EIT is accompanied with double resonance optical pumping (DROP) signal, which is limited by spontaneous decay (Г) rates. It has been shown by our group that the simultaneous presence of DROP–EIT combination paves the way for executing a kind of slow–fast switching action. However the focus always remain on improving the modulation depth in such type of coherence assisted switch. Here we report a possible way to improve modulation depth by using an additional (named ‘repumping’ after convention used in laser cooling experiments) laser in the Ξ system. The 5S1/2→5P3/2→5D5/2 level coupling scheme of 87Rb atom is used in the current experiment.