The above schematic shows a photonic waveguide based on plasmonics on an Si photonic platform. The optical field is confined in a 100-nm-wide gap between two metallic plates. By filling this gap with electro-optic (EO) polymers and applying voltage to these metallic plates, we can change the refractive index of the EO polymer. Thus, we can construct a very compact optical phase shifter, which is a fundamental element of optical modulators.
Recently, such a plasmonic-polymer waveguide system has been used to develop Mach-Zhender interferometer optical modulators19. Since the gap is very narrow, the electric field in the gap is very strong and the modulation efficiency becomes extremely high. For example, the voltage-length product -- which is a measure of the efficiency of phase shifters -- reaches 0.006 V.cm, which is less than 1/100 of that of a typical silicon modulator. Thus, a device a few tens of micrometers long can function as a modulator with practical modulation depth, and such a small device can operate at very high frequencies of over 100 GHz. Such plasmonic devices would be a significant breakthrough in the post-Moore photonics technology.
Summary
Moore’s Law in data transmission systems is nearing its end, and we need post Moore-photonics technology. In the development of post-Moore photonics technology, we can apply the same approaches that have been established in electronics, and silicon photonics can provide immediate solutions for post-Moore photonics technology. However, we must note here that silicon photonics itself requires post-Moore technology because of the quantum limit in miniaturisation and poor material characteristics. Here again, the same approaches established in electronics are applicable to post-Moore silicon photonics with the help of backend photonics and plasmonics.
Biography
Koji Yamada is head of the Silicon Photonics Group at the Electronics and Photonics Research Institute - a division of Japan's National Institute for Advanced Industrial Science and Technology (AIST). Key themes of his group's work include the research and development of advanced silicon photonics devices.
Web - https://unit.aist.go.jp/esprit/en/research/5_si-photo/si-photo_en.html
References and further reading
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