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Nanowires in thin-film: a toolbox for ultra-fast and quantum optics

Leah Poffenberger, Corporate Communications Manager, Optica

At the 2022 Laser Congress, Optica Fellow and Stanford University Dean of Applied Optics Martin Fejer presented a plenary on new directions in guided wave nonlinear optics (NLO) to advance an already dynamic field.

Since the 1980s, guided wave NLO has focused on using materials like silicon nitride and silica to move technology forward, but more recent advances have leveraged other materials like lithium niobite toward an ultimate goal of room temperature few photon nonlinear optical interactions in solid-state media. Fejer began his talk with background on the developments that led to thin-film lithium niobate systems, some of which took place 50 years ago at Bell Labs.

Lithium niobate, first demonstrated by Kurt Nassau and Gabriel Loiacono, is an ideal material for a number of optics applications thanks to its transparency range from the near ultraviolet to the mid-infrared, a large Chi 2 non-linearity and ferroelectric properties that allow patterning of its non-linearity. This ferroelectric property allows lithium niobate to be engineered to quasi-phase match nonlinear interactions, another idea first proposed at Bell Labs. About 30 years ago, lithium niobate quasi-phasematching wave guides were introduced as a platform, which are now routine for classical and quantum applications and commercially available. However, a key development in the last few years—nanowire waveguides—has opened up new avenues for improving this technology for new applications.

 Nanowire waveguides, fabricated in commercially available thin-film lithium niobate wafers have enabled development of NLO waveguides with efficiencies an order and a half larger than traditional devices. Other developments, like an alternative method for creating thin-film lithium niobate wafers using sapphire cladding instead of silica, continue to build the toolbox for the field. Researchers around the world are just beginning to experiment with some of the applications for these NLO waveguides, with a particular interest in the quantum optics application.

“Nanowires in thin-film offer a toolbox for ultra-fast and quantum optics with strong coupling, patterned non-linearity, dispersion engineering, and dense photonic integration,” said Fejer. “We have many interesting opportunities, both to revisit old ideas but with a greatly expanded parameter range, as well as to try out new concepts that are enabled by the engineering flexibility of the platform.”

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