Focus on sub-nanometer measurement accuracy: distortion and reconstruction of dynamic displacement in a fiber-optic microprobe sensor

Abstract

We established a complete model and relationship between laser source characteristics and measurement accuracy of high precision fiber microprobe sensor (FMS) based on phase generated carrier demodulation. The laser carried out high-bandwidth frequency modulation to improve the measurement speed. Meanwhile, the laser also carried out large-amplitude frequency modulation to eliminate tens of nanometers of nonlinear error, thus improving the measurement accuracy. Further, the laser center wavelength is required to be stabilized under the above modulation to achieve a high measurement stability. The conflict between laser frequency modulation and central stability is revealed and analyzed alongside the distortion of measurement accuracy. A modified frequency stabilization method for laser source under high-bandwidth and large-amplitude modulation is proposed for improving measurement accuracy to realize sub-nanometer precision. The experimental results showed that when the modulation bandwidth was 1 MHz and maximum modulation amplitude was 2.61 GHz, the distributed feedback laser central wavelength stability was 2.9 × 10−10 (τ = 1s) according to Allan variance. Additionally, the relative expanded uncertainty of the laser wavelength was demonstrated to be superior to 5 × 10−8 (k = 2) within 3 hr, which was at least one order of magnitude higher than that of the traditional method. The resolution and stability of FMS is better than 0.4 nm, and the nonlinear error is reduced from tens of nm to 0.8 nm, which meets the requirements of sub-nanometer measurements.

Keywords

• displacement measurement
• fiber microprobe sensor
• high-bandwidth and large-amplitude frequency modulation
• central wavelength stability
• sub-nanometer measurements