A phase modulator that is only 29 µm long and operates at 65 GHz is demonstrated using plasmonics and the Pockels effect in a nonlinear polymer. The device operates across a 120-nm-wide wavelength range centred on 1,550 nm and at temperatures up to 85 °C.

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High-speed plasmonic phase modulators

We experimentally demonstrate an ultracompact PlasMOStor, a plasmon slot waveguide field-effect modulator based on a transparent conducting oxide active region. By electrically modulating the conducting oxide material deposited into the gaps of highly confined plasmonic slot waveguides, we demonstrate field-effect dynamics giving rise to modulation with high dynamic range (2.71 dB/μm) and low waveguide loss (∼0.45 dB/μm). The large modulation strength is due to the large change in complex dielectric function when the signal wavelength approaches the surface plasmon resonance in the voltage-tuned conducting oxide accumulation layer. The results provide insight about the design of ultracompact, nanoscale modulators for future integrated nanophotonic circuits.

Nanoscale conducting oxide PlasMOStor.

A novel ultrafast all-optical switching based on metal-insulator-metal nanoplasmonic waveguide with a Kerr nonlinear resonator is proposed and investigated numerically. With the finite-difference time-domain simulations, it is demonstrated that an obvious optical bistability of the signal light appears by varying the control-light intensity, and an excellent switching effect is achieved. This bistability originates from the intensity-dependent change induced in the dielectric constant of Kerr nonlinear material filled in the nanodisk resonator. It is found that the proposed all-optical switching exhibits femtosecond-scale feedback time.

Ultrafast all-optical switching in nanoplasmonic waveguide with Kerr nonlinear resonator

A novel and simple plasmonic filter based on metal-insulator-metal plasmonic waveguides with a nanodisk resonator is proposed and investigated numerically. By the resonant theory of disk-shaped nanocavity, we find that the resonance wavelengths can be easily manipulated by adjusting the radius and refractive index of the nanocavity, which is in good agreement with the results obtained by finite-difference time-domain (FDTD) simulations. In addition, the bandwidths of resonance spectra are tunable by changing the coupling distance between the nanocavity and waveguides. This result achieved by FDTD simulations can be accurately analyzed by temporal coupled mode theory. Our filters have important potential applications in high-density plasmonic integration circuits.

Tunable band-pass plasmonic waveguide filters with nanodisk resonators

Plasmonics provides a possible route to overcome both the speed limitations of electronics and the critical dimensions of photonics. We present an all-plasmonic 116–gigabits per second electro-optical modulator in which all the elements—the vertical grating couplers, splitters, polarization rotators, and active section with phase shifters—are included in a single metal layer. The device can be realized on any smooth substrate surface and operates with low energy consumption. Our results show that plasmonics is indeed a viable path to an ultracompact, highest-speed, and low-cost technology that might find many applications in a wide range of fields of sensing and communications because it is compatible with and can be placed on a wide variety of materials.

High-speed plasmonic modulator in a single metal layer

The ability of gratings made of dielectric ridges placed on top of flat metal layers to open gaps in the dispersion relation of surface plasmon polaritons (SPPs) is studied, both experimentally and theoretically. The gap position can be approximately predicted by the same relation as for standard optical Bragg stacks. The properties of the gap as a function of the grating parameters is numerically analyzed by using the Fourier modal method, and the presence of the gap is experimentally confirmed by leakage radiation microscopy. We also explore the performance of these dielectric gratings as SPP Bragg mirrors. The results show very good reflecting properties of these mirrors for a propagating SPP whose wavelength is inside the gap.

Design and properties of dielectric surface plasmon Bragg mirrors.

In this work we report on the characteristics of an electro-optical dielectric-loaded surface plasmon polariton waveguide ring resonator. By doping the dielectric host matrix with an electro-optical material and designing an appropriate set of planar electrodes, we measured a 16% relative change of transmission upon application of a controlled electric field. We have analyzed the temporal response of the device and conclude that electrostriction of the host matrix is playing a dominating role in the transmission response.

Performance of electro-optical plasmonic ring resonators at telecom wavelengths

Dielectric-loaded plasmonic waveguide disk resonators (WDRs) operating at telecom wavelengths are fabricated and investigated. Disks resonators of various radii coupled to a straight waveguide are studied both numerically and experimentally. For each disk radius, the gap between the disk and the waveguide is varied from 0 to 300 nm. Performance of the fabricated WDRs is characterized in the wavelength range of 1500–1620 nm using near-field optical microscopy. Wavelength selectivity and efficiency of the WDRs are evaluated and are in good agreement with numerical results.

http://www.nano-optics.org.uk/materials/pdfs/APL_98_161102.pdf

Experimental demonstration of dielectric-loaded plasmonic waveguide disk resonators at telecom wavelengths

We demonstrate both experimentally and numerically a compact and efficient, optically tuneable plasmonic component utilizing a surface plasmon polariton ring resonator with nonlinearity based on trans-cis isomerization in a polymer material. We observe more than 3-fold change between high and low transmission states of the device at milliwatt control powers (∼100 W/cm2 by intensity), with the performance limited by switching speed of the material. Such plasmonic components can be employed in optically programmable and reconfigurable integrated photonic circuitry.

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Optically-programmable nonlinear photonic component for dielectric-loaded plasmonic circuitry.

In-season crop yield estimation has various applications such as the farmer taking corrective measures to increase the yield, optimizing the supply-demand chain of fertilizers, pesticides and agricultural commodities, price prediction and determining the risk levels in agriculture insurance. Crop yield estimation models based on remote sensed satellite data and weather data have been widely adopted as do not require specific information about the crop and farming practices and hence are scalable across crops, growing locations and conditions. In this paper, we present a case study of weather and soil data based yield estimation modeling for paddy crop at different spatial resolution (SR) levels, namely, at the district (coarser SR) and taluk (finer SR) levels in India. We provide a detailed analysis of accuracy of the yield estimation models across varied sets of features and different machine learning (ML) techniques. Further, we perform dis-aggregation of district yield data by applying the machine learning models trained using district level data to predict yields at taluk level. Taluk level yield prediction by dis-aggregation of district level data has average error of 6% and maximum error of 25%.

Sukanya Randhawa

Papers

Design and properties of dielectric surface plasmon Bragg mirrors.

Performance of electro-optical plasmonic ring resonators at telecom wavelengths

Experimental demonstration of dielectric-loaded plasmonic waveguide disk resonators at telecom wavelengths

Optically-programmable nonlinear photonic component for dielectric-loaded plasmonic circuitry.

Machine Learning Methodologies for Paddy Yield Estimation in India: a Case Study