Photonic Seismometer Based on Whispering Gallery Modes

We present the concept of an all-optical seismometer based on the principle of optical whispering gallery modes (WGMs). The proposed sensor is compact, rugged, low power, and resistant to electromagnetic interference. A cantilever configuration of a fiber-pigtailed photonic integrated circuit with a ring resonator is employed as the sensing element. The measurement approach is based on the optical excitation of the WGMs of a ring resonator using a 1313 nm tunable diode laser. A digital signal processing system analyzes the recorded WGM scans. The base acceleration is calculated from the WGM shifts caused by the deformation of the optical ring resonator. A prototype seismometer is developed, calibrated, and tested. The frequency response of the seismometer is assessed by observing the free vibration of the sensor. The preliminary results are encouraging and suggest that a WGM-based optical seismometer is feasible.