Figure 3. Voltage sensitivity and temporal bandwidth.

(a) Optical detection of an applied modulating voltage. A periodic rectangular waveform is applied with peak-to-peak voltages of 500 μV_pp (green), 200 μV_pp (purple) and 100 μV_pp (orange) with a 10 Hz–10 kHz bandpass filter. The optical response from the 100 μV applied modulation demonstrates a SNR of 6.5 corresponding to an experimental detection limit of 15 μV. (b) Frequency dependence of the optical signal demonstrating sensitivity to high-speed fluctuations up to 10 kHz. A 1 mV_pp sinusoidal waveform with frequencies spanning 20 Hz–50 kHz is applied. Shown here for a device with large-area (80,000 μm²) graphene. The frequency bandwidth will increase inversely with graphene area as a consequence of graphene's high conductivity. The results provided by an RC equivalent circuit, accounting for the double-layer capacitance and graphene resistance, is plotted as the grey dashed line.