Modulation frequency-shift technique for dispersion measurements in optical fibers
An improved technique for chromatic dispersion measurements in single-mode fibers using phase-shift measurements is presented. The conventional experimental setup using a modulated light-emitting diode filtered by a monochromator as a light source, a fast receiver, and a vector voltmeter for the phase measurements suffers from inherent drawbacks such as strong phase fluctuations due to poor SNR and RF interference providing biased measurements. The improved method eliminates these drawbacks with optical signal processing by shifting the modulation frequency down to the kilohertz range and maintaining the phase resolution due to high-frequency modulation. The advantages inherent in low-frequency detection and signal processing, such as stability, low noise, and strong filtering capability, and the resolution achieved by using a high modulation frequency result in reliable and accurate group delay measurements, giving a measured standard deviation of <0.5 nm for the zero chromatic dispersion wavelength.
Record created on 2010-04-07, modified on 2016-08-08