An optical fiber interferometric system for non-contact measurement of atmospheric optical turbulence

Abstract

Optical turbulence degrades the quality of laser beam propagation and the quality of the image of optical system, limiting the spatial resolution that can be obtained. A novel single-air-gap fiber optical interferometric system useful for non-contact measurement of the fine structure of optical turbulence is presented. The main idea of this system is based on the application of a specially constructed optical fiber Mach-Zehnder interferometer to measure the phase fluctuations effected by the random fluctuations of refractive index in the turbulent atmosphere. The light source is a long coherence length infrared laser operating at the wavelength of 1.31μm and the optical path exposed to the atmosphere can be adjusted to a most suitable value according to the operational environment. Theoretical estimation illustrates that the system can measure the minimal atmospheric refractive index fluctuation up to 10^-10 during a 2cm propagation path. It is easy to have a calibration of the system and the result shows that the voltage refractive index sensitivity is about 2.1x10^-6 V^-1. The system is integrated and well fixed in a burly airproof box with only the sensing arm exposed to the air. It follows that the system is suitable for the measurement of atmospheric turbulence over land and ocean surfaces.