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Mid-infrared silicon photonics emerge as the dominant technology to bridge photonics and electronics in multifunctional
high-speed integrated chips. The transmission and processing of optical signals lying at the mid-infrared
wavelength region is ideal for sensing, absorption-spectroscopy and free-space communications and the use of group IV
materials becomes principally promising as the vehicle towards their realization. In parallel, optical forces originating
from modes and cavities can reach to outstandingly large values when sizes drop into the nanoscale.
In this work, we propose the exploitation of large gradient optical forces generated between suspended silicon beams and
optomechanical transduction as a means of converting signals from the mid-infrared to the near-infrared region. A midinfrared
signal is injected into the waveguide system so as to excite the fundamental symmetric mode. In the 2-5μm
wavelength range, separation gaps in the 100nm order and waveguide widths ranging from 300–600nm, the mode is
mostly guided in the air slot between the waveguides which maximizes the optomechanical coupling coefficient and
optical force. The resulting attractive force deflects the waveguides and the deflection is linearly dependent on the midinfrared
optical power.
A simple read-out technique using 1.55μm signals with conventional waveguiding in the directional coupler formed by
the two beams is analyzed. A positive conversion efficiency (<0dB) is foreseen for waveguides with suspending lengths
up to 150μm. The converter could be ideal for use in sensing and spectroscopy rendering the inefficient mid-infrared
detectors obsolete. The low-index unconventional guiding in mid-infrared could be a key component towards
multifunctional lab-on-a-chip devices.
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