MC-en

Due to distinct modal distribution, different modes in an optical nanocircuit are competent for various different circuit functions. For example, the guided transverse electric modes on a plasmonic two-wire transmission line (TWTL) exhibit reduced group velocity, enhanced intensity and small modal volume that are competent for enhancing the nanoscale light-matter interaction. On the other hand, the transverse magnetic modes process higher group velocity, lower loss and diverse modal profile that are suitable for power delivery and surface plasmon amplification. To facilitate multiple functions in complex nanocircuits, it is therefore of critical importance to have the ability to control the guided mode at will, such that its optical impedance matches to that of other circuit elements and the field strongly interacts with nearby quantum systems. In this work, we propose three efficient mode converters for the control of propagation properties of the guided modes in a TWTL. The guided modes on a TWTL are uniquely interpreted as results of near-field coupling of guided surface plasmons on solitary wires. We demonstrate successful control over the emission of a nanoantenna and discussed applications in index sensing and manipulation of nanoscale light-matter interaction. Practical and realizable fabrication strategies are discussed as well. Our mode converter provides simple and promising solutions to achieve the required control of optical impedance and is of great potential for the manipulation of light-nanomatter interaction at nanoscale.

Related Publication:

Optics Express 2012, 20, 20342-20355. (selected for the "Virtual Journal for Biomedical Optics")

Plasmonics offer unique opportunity to realize optical-frequency integrated circuits with sub-wavelength footprint at nanoscale. Being able to manipulate and convert the guided optical modes not only enables multiple circuit functions but also provides an access to the control of nanoscale light-matter interaction. To prove the concept of local plasmonic mode conversion, we present in this work the design and fabrication of a high-definition prototype integrated plasmonic gold nanocircuit with an optimally designed mode converter for optical signals at 194 THz. We experimentally demonstrate selective excitation and successful local conversion between the symmetric and the anti-symmetric modes of a plasmonic two-wire transmission line, as shown in the figure on the left. The efficient mode conversion is achieved by differentiating the wire length in the converter and the explicit mode identification is done by observing the position and the polarization of the scattering signal. This is the first experimental demonstration of deterministic mode conversion in a complex integrated plasmonic nanocircuit at 194 THz. Our design can be combined with index tunable materials and serve as an active element for plasmonic nanocircuits. Applications of nanoscale light-matter interaction are anticipated.

Related Publication:

Nano Letters 2014, 14, 3881-3886. (selected for the "Virtual Journal for Biomedical Optics")