Fig. 2.
μ-spectrometer measurements. a, b A photocurrent spectrum of the fundamental antisymmetric (symmetric) mode of the three missing holes cavity (L3) modified for high Q factor in double membrane, with a linewidth of 132 pm (76 pm) and a Q factor of Q As~9900 (Q S~17,000) is shown in blue (red). Data was taken by measuring the photocurrent while a tuneable laser (P in = 125 μW) was swept across the cavity mode. c Color-coded photocurrent spectra (P in = 25 μW) showing the fundamental antisymmetric optical modes of an optimized H0 cavity spectrally tuned over 30 nm (x axis) by increasing the reverse tuning bias V T from 0 to 5.6 V (y axis) without reaching pull-in. The tuning range is approximately equal to one free spectral range in this case. d Data traces of photocurrent collected by voltage-tuning the optical mode (fundamental antisymmetric mode of the L3 cavity) over a fixed laser wavelength, then changing the laser wavelength by 1 nm and continuing the voltage tuning. The laser power was coupled into the cavity from top through a 0.45 NA objective, with the power incident on the sample being 12.5 μW. The scale on the bottom axis in the figure is obtained from a piecewise linear fit of the voltages at the maximum photocurrent versus wavelength. The cavity linewidth provides a spectral resolution of ~200 pm, and the FSR of ~13 nm is limited by the crossing with another cavity mode. The decrease in responsivity with decreasing inter-membrane distance (decreasing wavelength) is attributed to an asymmetry in membrane thickness, the upper membrane being 15 nm thicker46