Photonic circuits made reprogrammable

April 03, 2020 //By Julien Happich
Photonic circuits
Researchers at Eindhoven University of Technology have designed a novel type of photonic integrated circuits (PICs) whose switching properties (light routing states) can be reprogrammed via light-soaking and thermal annealing steps.

To do so, they used hydrogenated amorphous silicon (a-Si:H), a material broadly known for its use in thin-film silicon solar cells and the Staebler-Wronski effect (SWE) describing how the material’s refractive index can be altered via light exposure or heating.

Current programmable PIC concepts suffer from issues such as volatility and/or high optical signal losses, explain the authors in a paper titled “Metastable Refractive Index Manipulation in Hydrogenated Amorphous Silicon for Reconfigurable Photonics” published in the journal of Advanced Optical Materials. In a proof-of-concept experiment, they studied changes in the refractive index of a thin layer of a-Si:H on a silicon substrate. The authors submitted the material to cycles of heating (for four hours in the dark in a nitrogen atmosphere) and light soaking treatments (using a tunable laser in the near-infrared range). The experiment showed a reversible refractive index change of about 0.001 (0.3%), a key requirement for the fabrication of reconfigurable PICs.

"This is the world's first demonstration of a reconfigurable PIC, where the material chosen for making the integrated optical circuit is being programmed", said Oded Raz, Associate Professor at the Department of Electrical Engineering and research lead for this project.

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