An optical coherence-domain reflectometry system provides an interferometer driven by a broadband incoherent light source with the device under test connected to one arm of the interferometer and a movable scanning mirror in the other arm providing a reference signal. The mirror moves at a controlled velocity to produce a Doppler shift in the reference signal frequency. The reference signal arm also includes a piezoelectric transducer which modulates the phase of the reference signal at a given frequency, causing a further shift in the reference signal frequency. The interference signal is detected and measured by a polarization diversity receiver. A linear polarizer in the reference signal arm is adjusted to produce equal reference signal powers in each arm of the polarization diversity receiver in the absence of a reflection signal from the test arm. The measured reflectometry signal is substantially independent of the state of polarization of the reflected signal from the device under test.

Polarization independent optical coherence-domain reflectometry

Polarization mode dispersion (PMD) in short and long single-mode fibers was measured by a polarization-maintaining Michelson interferometer. A nonnegligible PMD was found in some standard fibers. The sensitivity enables PMD to measure the bend-induced PMD of a fiber rolled on a 28-cm diameter drum. A theoretical model for PMD with random mode coupling is developed, and an explicit equation for the time-of-flight distribution is presented. Comparison between measurements on short and long fibers with residual birefringence leads to an estimation of the coupling length on the order of 20-30 m. >

Polarization mode dispersion of short and long single-mode fibers

An interferometric technique for chromatic dispersion measurement of higher modes in short lengths of high order mode fibres is presented. The dispersion is measured using the wavelength dependence of the interference signal between the basic mode and the high order mode. Neither mode transformers nor RF circuitry are required.

Interferometric technique for measuring dispersion of high order modes in optical fibres

We report on a white-light interferometric technique for a broad spectral range measurement (e.g. 500–1600 nm) of chromatic dispersion of polarization modes in short-length optical fibres. The technique utilizes an unbalanced Mach–Zehnder interferometer with a fibre under test of known length inserted in one of the interferometer arms and the other arm with adjustable path length. We record a series of spectral interferograms by VIS–NIR and NIR fibre-optic spectrometers to measure the equalization wavelength as a function of the path length difference, or equivalently the differential group index dispersion of one polarization mode. The differential group dispersion of the other polarization mode is obtained from measurement of the group modal birefringence dispersion. We verify the applicability of the method by measuring the chromatic dispersion of polarization modes in a birefringent holey fibre. We apply a five-term power series fit to the measured data and confirm by its differentiation that the chromatic dispersion agrees well with that specified by the manufacturer. We also measure by this technique the chromatic dispersion of polarization modes in an elliptical-core fibre.

https://iopscience.iop.org/article/10.1088/0957-0233/21/4/045302/pdf

Measurement of chromatic dispersion of polarization modes in optical fibres using white-light spectral interferometry

We present a white-light spectral interferometric method for measuring the chromatic dispersion of microstructured
fibers made of polymethyl methacrylate (PMMA). The method uses an unbalanced Mach-Zehnder interferometer
with the fiber of known length placed in one of the interferometer arms and the other arm with adjustable
path length. We record the spectral interferograms to measure the equalization wavelength as a function of the
path length difference, or equivalently the differential group refractive index dispersion over a wide wavelength
range. First, we verify the applicability of the method by measuring the wavelength dependence of the differential
group refractive index of a pure silica fiber. We apply a five-term power series fit to the measured data and
confirm by its differentiation that the chromatic dispersion of pure silica glass agrees well with theory. Second, we
measure the chromatic dispersion for the fundamental mode supported by two different PMMA microstructured
fibers, the multimode fiber and the large-mode area one.

Measurement of chromatic dispersion of microstructured polymer fibers by white-light spectral interferometry

Chromatic dispersion characteristics around zero-dispersion wavelength have been measured in short samples of single-mode fibers by a spectral scanning of the interference signal in a Michelson interferometer. The propagative refractive index is directly obtained from the phase-difference variations with the wavelength between a light beam propagated through the fiber and a reference beam. The optimum operative conditions of the interferometer for obtaining the unequivocal analysis of experimental signals are discussed. The accuracy of the results obtained shows the reliability of the method for a complete dispersion characterization. >

J. Pelayo

Papers

Chromatic dispersion characterization in short single-mode fibers by spectral scanning of phase difference in a Michelson interferometer