Schematic of a two-beam pumping experiment: Two beams are spatially detuned with a distance d < 2R, being shifted temporally with a delay time τ. (Source. HIT / AAAS)
Recently, the new principle of all-optical switch proposed by the research team of Song Qinghai of Harbin Institute of Technology, Shenzhen is expected to break the trade-off between ultra-short switching time and ultralow energy consumption.
All-optical switch is the fundamental building block of optical communications, optical computing, as well as quantum information. An innovative approach utilizing the far field characteristics of topologically protected bounded states in the continuum is able to break the long-standing trade-off between ultrashort switching time and ultralow energy consumption. The advance could lead to an efficient ultrafast all-optical switch, and eventually revolutionize the all-optical computing.
All-optical switch is a kind of device that controls light by light, which is the fundamental building block of modern optical communications and information processing. Creating an efficient, ultrafast, and compact all-optical switch has been recognized as the key step for the developments of next-generation optical and quantum computing. In principle, photons don’t interact one another directly in the low power linear regime, and a cavity is usually needed to resonantly enhance the field of control light and increase the interaction. In early works, the performances of all-optical switches have been improved rapidly by optimizing resonators such as microrings or photonic crystals. For further improvements, the research area reaches the limit – the trade-off between ultralow energy consumption and ultrashort switching time.
“Low energy consumption usually requires high Q factor of resonator, whereas the longer lifetime high-Q mode imposes an obstacle for improving the switching speed,” said Qinghai Song from Harbin Institute of Technology, China. “An alternative approach with plasmonic nanostructure has been recently exploited to break the trade-off. The inserting and propagating loss is as large as 19 dB and additional power consumption is required to amplify the signals.”
The lasing actions at the topologically protected bounded states in the continuum has the potential to eventually solve this long-standing challenge. The researchers from Harbin Institute of Technology, Australian National University and City University of New York detail their innovation of the switching mechanism at the topologically protected bounded states in the continuum (BICs), which offers an ultrafast transition of microlaser emission from a radially polarized donut beam to linearly polarized lobes and vice versa. The extremely high Q factor of the BICs can dramatically reduce the laser threshold and eventually break the above trade-off in conventional all-optical switches.
Next step of this research is to cascadedly integrate several such switchable microlasers with an integrated photonic chip and to perform optical logic operations. This is the prerequisite for the ultimate goal – the optical computing or quantum computing. (Source: HIT)
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