Ultrafast Control of Microlasers

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)

Reference: C. Huang et al.: Ultrafast control of vortex microlasers, Science 367, 1018 (2020); DOI: 10.1126/science.aba4597

Link: State Key Laboratory on Tunable Laser Technology, Laboratory of Micro-Nano Optoelectronic Information System, Harbin Institute of Technology, Shenzhen, China

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