Strong optomechanical interaction in a bilayer photonic crystal

We fabricated bilayer photonic crystal (PhC) as large as $20\times 30\mu \text{m}$ possessing 200-nm-thick slabs and a 200-nm-thick air gap. Input power dependence of reflectance spectra indicates air gap reduction by 3.6 nm. Combining it with finite element method calculation we estimate optomechanically generated force per unit stored energy as $0.4\mu \text{N}/\text{pJ}$, exhibiting strong optomechanical coupling. RF spectrum of reflected light reveals intensity modulation by thermal vibration of bilayer PhC, which also shows strong interaction of optical resonance mode and mechanical mode of bilayer PhC

Figure 1

(Color online) (a) Schematics of experiment. The structure is fully clamped (all-side clamped) (b) Top-view scanning electron microscope image, (c) Bird’s-eye view (upper) and cross section (lower) of bilayer PhC. Period is 750 nm and hole radius at the center is 270 nm. (d) 2D photonic band structure of TE mode with $n=2.8$ (effective index for TE mode). Inset is the lateral plot of ${\left|Hz\right|}^2$ at the $\Gamma$ point indicated by red dot (e) Vertical mode profiles of ${\left|Hz\right|}^2$ in the double slab at the $\Gamma$ point indicated in (d).

Figure 2

(Color online) (a) Resonant wavelength of band-edge modes as a function of air gap width. Band-edge modes for the lattice constant of 750 nm hole radius of 270 nm were calculated using plane-wave expansion method and exponentially fitted. (b) force per unit stored energy as a function of air gap width. Positive value means attractive one. (c) Reflectance spectrum of the bilayer PhC with $20\times 30\mu \text{m}$. Insets show the zoom-in of each resonance curve and fitted to Lorentzian.

Figure 3

(Color online) (a) Reflectance obtained by wavelength scanning with varying the input power. Dotted line indicates the initial resonance position $\lambda =1567.1\text{nm}$ Wavelength scan is always done from short to long wavelength. Resonance shift is defined from initial wavelength to the abrupt kink on the spectra. Inset shows the linearity between input power and redshift of resonance. (b) Reflectance spectra by wavelength sweeping across S-mode and (c) AS mode. In (b), input powers were 0.1 mW (thick black curve) and 13 mW (thin red curve). (c) was taken with low power (thick black curve) while irradiating cw pump beam at $\lambda =1568.0\text{nm}$ with input power of 13 mW (thin blue curve)

Figure 4

(Color online) (a) Fundamental vibration modes with even $\left(f=1.79\text{MHz}\right)$ and odd parity $\left(f=1.81\text{MHz}\right)$. (b) Radio frequency (RF) spectra of reflected light at $\lambda =1566.5\text{nm}$ (thick black curve) and $\lambda =1568.2\text{nm}$ (thin red curve). (c) Relative peak power in RF spectrum as a function of wavelength. Reference value was taken to the peak power at $\lambda =1566.5\text{nm}$.