Optical acoustic interferometric fiber sensors are based on measuring the phase change in an optical wave that propagates through a fiber due to a strain induced by the acoustic signal. This phase change is measured by using an optical interferometry technique. Such sensors allow the detection of periodic length changes that can be on the order of few femtometers. However, the linear dynamic range in optical interferometers is limited since a change in the fiber length, on the order of the optical wavelength (∼ μm), results in deterioration of the measured signal. Changes in the phase of a radio frequency (RF) signal that is transmitted over a fiber can be used to detect environmental perturbations. Since the wavelength of the RF signal is on the order of few centimeters, large changes in the fiber may be detected without a distortion. However, since the induced phase changes in the fiber are proportional to the signal frequency, the use of an RF signal instead of an optical signal significantly decreases the sensor sensitivity. Therefore, there is a need to enhance the response and to decrease the noise in fiber sensors that are based on RF signals. Free-running oscillators can be used as sensors due to the dependence of their oscillation frequency on environmental conditions. In particular, optoelectronic oscillators (OEOs) can be used as fiber sensors. Such oscillators generate ultra-low phase noise RF signals due to the long fiber that is inserted into their cavity. The developed technology is a new acoustic sensor, that is based on the detection of small phase changes in an RF signal transmitted through an optical fiber.
- Accurate and sensitive signal detection from large distances
- Very large linear dynamic range due to the long wavelength of the microwave in relation to the optical wavelength
- Very large film width because no complex signal processing is required
- Possible integratation in any existing fiber whisper system
- Possibility of long distance whispering
Applications and Opportunities
- Optical fiber sensing