Effects of beam length and vibration amplitude on measurement resolution in microresonator-based optical sensing

Microresonator-based optical sensing has been reported to achieve a high measurement resolution of near-infrared light intensity. The light intensity was measured from the resonant frequency shift with the thermal stress of a silicon doubly clamped beam. In this study, the beam length and vibration amplitude were considered as parameters for improving the measurement resolution. This study investigates the effect of these parameters on the sensitivity (resonant frequency shift per light intensity) and the quality factor (Q factor) to estimate the measurement resolution, considering the thermomechanical noise as the fundamental limitation. The result of the measurement indicated that the longer the resonator, the greater the shift in the resonant frequency. The Q factor is considered to be constant regardless of the resonator beam length. Although the vibration amplitude was increased until nonlinear vibration occurred, no change in the sensitivity and Q factor was observed. The light intensity measurement resolution was calculated using a theoretical equation based on the experimental tendencies. The device with the longest beam length of 800 µm and the gold nanostructured absorber had the highest resolution. The light intensity measurement resolution was improved with a longer beam length and larger vibration amplitude.