Radek Chlebus

Differential group refractive index dispersion of glasses of optical fibres measured by a white-light spectral interferometric technique

We report on a white-light interferometric technique employing a low-resolution spectrometer to measure the differential group refractive index of glasses of optical fibres over a wide wavelength range. 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 to measure the equalization wavelength as a function of the path length difference, or equivalently the group dispersion. Subtracting the group dispersion of the optical components present in the interferometer along with the fibre, we measure the wavelength dependence of differential group refractive index for pure silica and SK222 glasses. We confirm that the differential group dispersion measured for pure silica glass agrees well with that described by the dispersion equation.

Direct measurement of group dispersion of optical components using white-light spectral interferometry

We present a simple white-light spectral interferometric technique employing a low-resolution spectrometer for a direct measurement of the group dispersion of optical components over a wide wavelength range. The technique utilizes an unbalanced Mach-Zehnder interferometer with a component under test inserted in one arm and the other arm with adjustable path length. We record a series of spectral interferograms to measure the equalization wavelength as a function of the path length difference. We measure the absolute group refractive index as a function of wavelength for a quartz crystal of known thickness and the relative one for optical fiber. In the latter case we use a microscope objective in front and a lens behind the fiber and subtract their group dispersion, which is measured by a technique of tandem interferometry including also a Michelson interferometer.

Dispersion error of a beam splitter cube in white-light spectral interferometry

We revealed that the phase function of a thin-film structure measured by a white-light spectral interferometric technique depends on the path length difference adjusted in a Michelson interferometer. This phenomenon is due to a dispersion error of a beam splitter cube, the effective thickness of which varies with the adjusted path length difference. A technique for eliminating the effect in measurement of the phase function is described. In a first step, the Michelson interferometer with same metallic mirrors is used to measure the effective thickness of the beam splitter cube as a function of the path length difference. In a second step, one of the mirrors of the interferometer is replaced by a thin-film structure and its phase function is measured for the same path length differences as those adjusted in the first step. In both steps, the phase is retrieved from the recorded spectral interferograms by using a windowed Fourier transform applied in the wavelength domain.

Group dispersion measurement of a holey fiber by white-light spectral interferometry

We present a white-light interferometric method for measuring the wavelength dependence of the group index of a pure silica holey fiber. The method is based on the recording of a series of the spectral interferograms in a 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 measure the equalization wavelength as a function of the path length difference, or equivalently the group index dispersion. Subtracting the group dispersion of the optical components present in the interferometer along with the fiber, first we measure the wavelength dependence of the differential group index of the pure silica glass provided that that the light is guided by the outer cladding of the fiber. Second, we measure the wavelength dependence of the group effective index of the fundamental mode supported by the fiber provided that some of the recorded interferograms are also due to the mode.

Spectral-domain interferometric technique used to measure group index dispersion of holey fibers

A new spectral-domain interferometric technique used for measuring the group index of holey fibers over a wide wavelength range is presented. The technique utilizes an unbalanced Mach-Zehnder interferometer with a fiber under test of known length placed in one of the interferometer arms and the other arm with adjustable path length. First, the differential group index of the fiber is measured. Second, the fiber excitation is changed to guide light in the fiber cladding or the fiber is replaced by the reference sample of known thickness and known group dispersion to determine precisely the group index of the fiber at one specific wavelength. The group index as a function of wavelength is measured for two different holey fibers, one of them made of pure silica glass.

Differential Group Index Dispersion of a Holey Fiber Measured by White-Light Spectral Interferometry

We present a new white-light interferometric method to measure the differential group index dispersion of a pure-silica holey fiber. The method is based on the recording a series of the spectral interferograms in 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 measure the equalization wavelength as a function of the path length difference, or equivalently the group index dispersion. Subtracting the group dispersion of the optical components present in the interferometer along with the fiber, we measure the wavelength dependence of the differential group index of both the pure-silica fiber glass and fundamental mode supported by the holey fiber.

White-light spectral interferometric techniques used to measure the group dispersion of isotropic and anisotropic optical elements

We present two di.erent white-light spectral interferometric techniques employing a low-resolution spectrometer for a direct measurement of the group dispersion of isotropic and anisotropic optical elements. First, the dispersion of the group refractive index for glass plate is measured in a Michelson interferometer with the plate of known thickness inserted in one of the interferometer arms. The technique utilizes the spectrometer to record a series of spectral interferograms for measuring the equalization wavelength as a function of the displacement of the interferometer mirror from the reference position, which corresponds to a balanced Michelson interferometer. The use of the technique is extended for measuring the dispersion of the group refractive indices for the ordinary and extraordinary polarizations in a quartz crystal. We con.rm that the measured group dispersions agree well with those resulting from the semiempirical dispersion equations. We also show that the measured mirror displacement depends, in accordance with the theory, linearly on the theoretical group refractive index and that the slope of the corresponding straight line gives precisely the thickness of the quartz crystal. Second, the group dispersion of the quartz crystal is measured in an unbalanced Mach-Zehnder interferometer with the adjustable path length when the crystal is inserted in the test arm. The use of the second technique is extended for measuring the di.erential group dispersion of a glass of a holey optical fiber.