Abstract
We examine the near-IR light-matter interaction for graphene integrated cavity ring resonators based on silicon-on-insulator (SOI) race-track waveguides. Fitting of the cavity resonances from quasi-TE mode transmission spectra reveal the real part of the effective refractive index for graphene, n(eff) = 2.23 ± 0.02 and linear absorption coefficient, α(gTE) = 0.11 ± 0.01dBμm(-1). The evanescent nature of the guided mode coupling to graphene at resonance depends strongly on the height of the graphene above the cavity, which places limits on the cavity length for optical sensing applications.
Highlights
The disruptive technological potential of graphene is extremely wide ranging [1], with the emergence of the first commercial devices anticipated as early as 2015
For Lg = 150μm, the cavity signal is reduced to half its original value for a graphene height, h ~120nm and for this length of graphene deposited at the surface (h = 0), a cavity resonance with ER(0) ~17dB would be all but quenched
We have deposited chemical vapour deposition (CVD) graphene on racetrack type silicon cavity resonators as a route to improving the surface reactivity for bio-molecular and/or gas sensing applications
Summary
The disruptive technological potential of graphene is extremely wide ranging [1], with the emergence of the first commercial devices anticipated as early as 2015. The transmission spectrum (of a tuneable laser or broadband source) at the wire-guide output reveals these cavity resonances, the spectral position of which is a strong function of the local (near surface) refractive index, which depends on the concentration of the bound target molecule. By monitoring this transmitted light intensity it is possible to detect extremely small changes in the refractive index of the near surface region as molecules attach themselves to the primed silicon cavity surface. As a first step in this process, in this contribution we report measurement of the optical response of graphene coated cavities and in so doing determine both the real part of the effective refractive index and the quasi-TE (in-plane) linear absorption coefficient for single layer graphene
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