# Integrated Plasmo-Photonic Sensor with Voltage-Controlled Detection

## TL;DR

A new sensor uses plasmonic modes and voltage control to detect ions in liquids with high sensitivity.

## Contribution

The novel sensor design integrates plasmonic waveguides and voltage-controlled ion separation for enhanced detection.

## Key findings

- The sensor achieves a sensitivity of over 12460 nm/RIU at 1550 nm telecom wavelengths.
- Ion distribution changes in response to applied voltage affect interferometer transmission.
- Higher sensitivity is expected at mid-infrared wavelengths due to stronger absorption by chemicals and biomolecules.

## Abstract

In this paper, we propose and analyze a waveguide-integrated
interferometric
sensor in which interference occurs between two plasmonic modes propagating
in a single plasmonic waveguide. For the purpose of sensing, the vertical
plasmonic slot waveguide was rearranged by increasing the distance
between the metal electrodes. Consequently, the plasmonic modes associated
with each metal electrode have been separated, enabling them to propagate
independently on opposing edges of metal electrodes, which allows
for the implementation of a Mach–Zehnder interferometer. The
metal electrodes that support the plasmonic modes can also function
as electrical contacts. By applying a direct current (DC) voltage
between them, it is possible to efficiently separate ions that drift
to one of the metal electrodes. Consequently, any change in transmission
from the interferometer refers only to the amount of ions in a liquid,
as the output signal from the interferometer is normalized to a liquid
by the reference arm, which is in direct contact with the examined
liquid solution. The total amount of ions in the examined liquid remains
constant; however, what changes is their distribution in the gap as
the ions drift toward one of the metal electrodes when a voltage is
applied. The proposed configuration is highly sensitive to variations
in transmission between the two arms of the interferometer, enabling
a record sensitivity of over 12460 nm/RIU, even at the telecom wavelength
of 1550 nm. A further enhancement in sensitivity is expected in the
mid-infrared wavelengths, which correspond to the maximum absorption
peaks of most chemical and biological compounds.