IBM has created low-loss (0.3% loss over 10 microns) silicon waveguide could enable new photonic chip designs for applications that rely on visible light, and could lead to more efficient lasers and modulators used in telecoms.
Above – Illustration of a pair of silicon high contrast gratings that can be used to guide visible light on a chip with low losses despite large absorption by the silicon material.
Nanostructures were used to make high contrast gratings. Such a grating consists of nanometer-sized ‘posts’ lined up to form a ‘fence’ that prevents light from escaping. The posts are 150 nanometers in diameter and are spaced so that light passing through them interferes destructively with light passing between them. Destructive interference is a phenomenon where waves – including electromagnetic waves such as visible light – that oscillate out of sync cancel each other out. This way, no light can “leak” through the grating and most of it gets reflected back inside the waveguide.
The next step is to engineer the efficient coupling of the light out of the waveguides into other components. That’s a crucial step in our research, with the ultimate goal of integrating the all-optical transistors into integrated circuits that would be able to perform simple logic operations.
For guiding light on a chip, it has been pivotal to use materials and process flows that allow low absorption and scattering. Based on subwavelength gratings, here, we show that it is possible to create broadband, multimode waveguides with very low propagation losses despite using a strongly absorbing material. We perform rigorous coupled-wave analysis and finite-difference time-domain simulations of integrated waveguides that consist of pairs of integrated high-index-contrast gratings. To showcase this concept, we demonstrate guiding of visible light in the wavelength range of 550–650 nm with losses down to 6 dB/cm using silicon gratings that have a material absorption of 13,000 dB/cm at this wavelength and are fabricated with standard silicon photonics technology. This approach allows us to overcome traditional limits of the various established photonics technology platforms with respect to their suitable spectral range and, furthermore, to mitigate situations where absorbing materials, such as highly doped semiconductors, cannot be avoided because of the need for electrical driving, for example, for amplifiers, lasers and modulators.
SOURCES – IBM, Nature Light and Science Applications
Written by Brian Wang, Nextbigfuture.com
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