Electro-optic modulation in integrated photonics

Abstract

Electro-optic modulators are an indispensable part of photonic communication systems, largely dictating the achievable transmission rate. Recent advances in materials and fabrication/processing techniques have brought new elements and a renewed dynamic to research on optical modulation. Motivated by the new opportunities, this Perspective reviews the state of the art in integrated electro-optic modulators, covering a broad range of contemporary materials and integrated platforms. To provide a better overview of the status of current modulators, an assessment of the different material platforms is conducted on the basis of common performance metrics: extinction ratio, insertion loss, electro-optic bandwidth, driving voltage, and footprint. The main physical phenomena exploited for electro-optic modulation are first introduced, aiming to provide a self-contained reference to researchers in physics and engineering. Additionally, we take care to highlight topics that can be overlooked and require attention, such as the accurate calculation of carrier density distribution and energy consumption, the correct modeling of thin and two-dimensional materials, and the nature of contact electrodes. Finally, a future outlook for the different electro-optic materials is provided, anticipating the research and performance trends in the years to come.

ℏω versus ℏk: dispersion and energy constraints on time-varying photonic materials and time crystals [Invited]

“…Getting into the specifics, different mechanisms can be conceivably used to change the refractive index, but most of them, such as electro-optic, acousto-optic, let alone thermo-optic, are limited in speed, so no photonic time crystals at optical frequencies can arguably be realized using them, as they require modulation frequencies on the order of the propagating wave frequency (instead, the first two of these mechanisms may be used in applications such as time-modulated optical isolators, which require modulation frequencies significantly smaller than the operational frequency, just enough to couple different modes [13]). Neither electro-optic nor acousto-optic modulation can change the refractive index by more than a fraction of a percent, and the speed of electro-optic modulators can reach 100's of GHz at best [77].…”

Optical Interconnects Finally Seeing the Light in Silicon Photonics: Past the Hype

“…Only those built on the silicon photonic platform and derived by free carriers are shown. A general overview of the other types of modulators known to be incompatible with the CMOS fabrication process can be found in [178].…”

“…Several approaches were utilized for enhancing the light-matter interaction in micro-resonators and reaching an ultra-compact device footprint, while maintaining high speed and low energy consumption. Namely, micro-disks [151,161,172,173], photonic crystal (PC) nanocavities [150,[174][175][176][177], and micro rings [147,148,[178][179][180][181].…”

Electro-optic metasurface-based free-space modulators

“…[13][14][15] However, most metasurface configurations are static, meaning that their optical responses are determined at the design stage by selecting geometrical and material parameters and remain constant once the metasurface is fabricated. Recent years has seen increasing efforts in trying to realize dynamic (tunable) optical metasurfaces, [16][17][18] a development that promises even more current and emerging applications available for metasurfaces, for example, in light detection and ranging (LIDAR), 19,20 spatial light modulators (SLMs), 21,22 computational imaging and sensing, 23 and virtual and augmented reality systems. 24 The fundamentally thin nature of metasurfaces poses daunt-ing challenges to the realization of dynamic metasurfaces, because the interaction length is severely limited.…”