All-optical control of light on a silicon chip

Abstract

Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components. Furthermore, it is highly desirable to use silicon--the dominant material in the microelectronic industry--as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon, but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III-V compound semiconductors, but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction of efficient optical switching in silicon using resonant structures.

Ring-Resonator-Based Wavelength Filters

“…• Thermo-optic effect: by applying heat to the ring the refractive index of the material changes [35] • Electro-optic effect: an electrical field causes the change in refractive index [36] • Carrier injection: optical pumping creates free carriers (single photonor two-photon absorption), which change the loss parameter and the refractive index of the material [37,38] • Changing the material (sensor) [39,40] • Opto-optical effect: the light itself causes a change in index via nonlinear effects [11] A change in effective index shifts the total wavelength response by an amount of ∆λ . This shift can be used in filter applications to tune the passband to the a desired wavelength.…”

“…Recently, GHz modulation in silicon-on-insulator (SOI) MRs based on this effect has been shown [38].…”

“…All-optical switching has been performed in GaAs/AlGaAs [91] and more recently in SOI micro rings [38] as well. The device structure under investigation has been a single micro ring coupled to a straight waveguide using either horizontal [91] or vertical [38] coupling.…”

“…The device structure under investigation has been a single micro ring coupled to a straight waveguide using either horizontal [91] or vertical [38] coupling. According to the considerations in Sect.…”

“…In the recently reported all-optical switching in SOI microrings [38] detuning is achieved by optical means, i. e. optically created free carriers modify the effective refractive index and provide a detuning of the MR resonances, which is equivalent to switching. These experiments have aroused a lot of speculation about the prospects and the potential of semiconductor/silicon-based all-optical signal processing.…”