Photonic circuits made reprogrammable
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.
“Most importantly, in comparison to current methods, the time to prototype is much shorter and much more accurate”, says Raz who anticipates the method could be improved to further reduce prototyping times.
Next, the researchers designed a reconfigurable optical switch based on a micro-ring resonator (MRR) which they subjected to cycles of light soaking and heating treatments to exploit the metastable refractive index property a‐Si:H. Through multiple light soaking and heating steps, they reported the repeatable and reversible switching of the device’s resonance wavelength by 0.3nm. Further experiments show that the reversible refractive index changes were correlated to the metastable volumetric expansion (and strain) of the structure of the a‐Si:H membrane used.
Eindhoven University of Technology – www.tue.nl
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