Improved Uncertainty of Optical Frequency Domain Reflectometry Based Length Measurement by Linearizing the Frequency Chirping of a Laser Diode

Length resolution of optical-frequency-domain-reflectometry (OFDR) is improved by reducing the chirping fluctuation of a laser diode. The fluctuation is detected as the frequency deviation of a beat signal from a reference interferometer, which is used as the control signal for servo-control of the laser diode (LD) drive current. As a result of the effective chirping stabilization, chirping span limited-resolution is achieved. In addition, use of a block gauge as the path difference of the reference interferometer enables the OFDR system to improve accuracy of the length as well as the resolution.