On broadening techniques for a high-resolution optical accelerometers

The paper discusses techniques for broadening the frequency bandwidth of a low natural frequency optical accelerometer to the [0.01 - 100] Hz band while preserving high resolution. The sensor mechanics is made of a leaf-spring suspended proof mass with a natural frequency of 2.8 Hz. The motion of the proof mass is read out with a custom design of a homodyne quadrature Michelson interferometer. The quadrature interferometer allows for precise measurement of the mass motion over several multiples of the laser wavelength (1550 nm) with a relative resolution measured at 2×10⁻¹³ m/Hz at 10 Hz. Two different strategies are employed for extending the corner frequency of the sensor bandwidth above the sensor mechanical frequency. They consist of a force feedback loop and an electronic filtering of the sensor's response. Both methods were experimentally applied and compared in terms of resolution. The sensor has a 10 × 10 × 10 cm³ compact design. The combination of the high-resolution readout and the large measurement bandwidth makes this sensor suitable for applications where high performance in the low-frequency regime is needed, namely active seismic isolation for ground-based scientific instruments (e.g. gravitational wave detectors) and ground compensation scheme in absolute quantum gravimeters.