Low-loss plasmon-assisted electro-optic modulator

Abstract

For nearly two decades, the field of plasmonics1 - which studies the coupling of electromagnetic waves to the motion of free electrons in a metal2 - has sought to realize subwavelength optical devices for information technology3–6, sensing7,8, nonlinear optics9,10, optical nanotweezers11 and biomedical applications12. Although the heat generated by ohmic losses is desired for some applications (e.g. photo-thermal therapy), plasmonic devices for sensing and information technology have largely suffered from these losses inherent to metals13. This has led to a widespread stereotype that plasmonics is simply too lossy to be practical. Here, we demonstrate that these losses can be bypassed by employing “resonant switching”. In the proposed approach, light is only coupled to the lossy surface plasmon polaritons in the device’s off-state (in resonance) where attenuation is desired to ensure large extinction ratios and facilitate sub-ps switching. In the on state (out of resonance), light is prevented from coupling to the lossy plasmonic section by destructive interference. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses (2.5 dB), high-speed operation (>>100 GHz), good energy efficiency (12 fJ/bit), low thermal drift (4‰ K-1), and a compact footprint (sub-λ radius of 1 μm) can be realized within a single device. Our result illustrates the potential of plasmonics to render fast and compact on-chip sensing and communications technologies.

Fundamental limits of hot carrier injection from metal in nanoplasmonics

“…Fermi velocity, which for Au and Ag is about 8 1.4 10 / cm s × . These spectral components provide necessary momentum matching which allow absorption of SPP without assistance from the phonons or defects.…”

“…The salient feature of metallic structures is their ability to concentrate optical fields into the small volumes that are not limited by diffraction. A large number of plasmonic devices with enhanced performance in various regions of electro-magnetic spectra has been conceived [4] and to a certain degree demonstrated since the turn of the millennium, including sources [5], detectors [6,7] and modulators [8,9] of radiation, as well as wide range of sensors. Yet, with exception of sensors [10,11], plasmonic devices have failed to enter the mainstream for one reason -very high loss inherent to all metals.…”

Large-Scale Optical Neural Networks Based on Photoelectric Multiplication

“…This figure is out of reach with current technology, but research into fJ/bit on-chip interconnects may enable it in the future [61,26]. A range of modulator designs support few-fJ/bit operation [62,63,64,65]. On-chip interconnects also require photodetectors with ultra-low (fF) capacitance, so that a femtojoule of light produces a detectable signal without amplification [61,26]; such detectors have been realized with photonic crystals [66], plasmon antennas [67,68], and nanowires [69].…”

Plasmonic nanogap enhanced phase-change devices with dual electrical-optical functionality

“…Combining plasmonics with PCMs is a particularly promising approach for satisfying such stringent requirements, since the dimensions of such devices can be reduced to tens of nanometres and smaller-significantly below the diffraction limit of traditional optical devices (11,12). The combination of high electrical conductivity and strong plasmonic resonance at optical wavelengths in silver and gold has led to extremely compact electrooptic nanogap devices such as integrated light sources (13), photodetectors (14,15), and modulators (16,17). Additionally, the extremely high field-enhancement possible with sub-wavelength nanogaps enables very high-sensitivity spectral measurements for applications such as label-free detection of biomolecules (18)(19)(20).…”