About this Research Topic
Silicon-based photonics technology, which has the DNA of Si electronics technology, promises to provide a compact photonic integration platform with high integration density, mass-producibility, and excellent cost performance. This technology has been used to develop various photonic devices based on silicon, such as waveguides, filters, and modulators. In addition, germanium photodetectors have been built on a silicon photonic platform. These photonic devices have already been monolithically integrated on silicon chips. Moreover, photonics-electronics convergence based on silicon photonics is now being pursued. These emerging compact photonics-electronics convergent modules will have the potential to be used in the construction of energy-efficient cost-effective apparatuses for various applications, such as communications, information processing, and sensing. Hence, we have decided that the short/middle term research topics of this journal will cover silicon-(and germanium)-based photonic devices, their integration, and convergence with electronics.
As mentioned above, the silicon photonic platform has the potential for compact and energy efficient photonics-electronics convergence. Considering the material characteristics of silicon and difficulties in silicon microfabrication technology, however, silicon by itself is not necessarily an ideal material for the ultracompact, ultrahigh-density, ultralow-energy photonics-electronics convergent platform of the future. For example, silicon is not suitable for light emitting devices because it is an indirect transition material. In addition, the operation speed of silicon-based optical modulators is limited by the carrier mobility of silicon, which is significantly lower than that of III-V semiconductors. Moreover, the size reduction of the modulators is limited by a weak photon-carrier interaction in silicon. For similar reasons, germanium photodetectors also have some performance limitations. The resolution and dynamic range of silicon-based interference devices, such as wavelength filters, are significantly limited by fabrication errors in microfabrication processes.
For further performance improvement, various assisting technologies should be implemented on the silicon photonic platform. These technologies are categorized intointelligence assists and material assists. Intelligence assists are aimed at compensating for performance deficiencies, such as bandwidth limitations in modulators and detectors, by using the electronic circuits that are now being developed for digital coherent transmission systems. Material assists are designed to improve performance by introducing the right materials for the right functions. The materials to be implemented are III-V materials such as indium-phosphide and gallium-arsenide, group-IV materials such as carbon (including graphene) and tin, and various metallic materials for plasmonic effects. Fortunately, silicon-based photonic devices and silicon substrates are very robust physically, chemically, and mechanically; therefore, these heterogeneous material integrations can be achieved on this platform. Hence, we have decided that the middle/long term research topics of this journal will cover heterogeneous material integrations on the silicon photonic platform and their novel functionalities.
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