Spectral-domain measurement of phase modal birefringence in polarization-maintaining fiber

We report on a new and simple method for measuring the wavelength dependence of phase modal birefringence in a polarizationmaintaining fiber. The method is based on application of a lateral pointlike force on the fiber that causes strong coupling between polarization modes and utilizes their interference resolved as the channeled spectrum. The change of the phase retrieved from two recorded channeled spectra that are associated with the known displacement of coupling point is used to determine the phase modal birefringence as a function of wavelength. A windowed Fourier transform is applied to reconstruct precisely the phase change and the phase ambiguity is removed provided that we know the phase change of the spectral fringes at one specific wavelength. The measured wavelength dependence of phase modal birefringence is compared with that resulting from the group modal birefringence measurement

Surface plasmon resonance based measurement of the dielectric function of a thin metal film

A spectral method based on surface plasmon resonance (SPR) in air is used to measure the dielectric function of a thin metal film. The method utilizes the spectral dependence of the ratio of the reflectances of p- and s-polarized waves measured in the Kretschmann configuration at different angles of incidence. By processing these dependences in the vicinity of a dip, or equivalently near the resonance wavelength, and using the dispersion characteristics of a metal film according to a proposed physical model, the real and imaginary parts of the dielectric function of the metal can be determined. The corresponding dielectric function of the metal is obtained by a least squares method for such a thickness minimizing the difference between the measured and theoretical dependence of the resonance wavelength on the the angle of incidence. The feasibility of the method is demonstrated in measuring the dielectric function of a gold film of an SPR structure comprising an SF10 glass prism and a gold coated SF10 slide with an adhesion film of chromium. The dielectric function according to the Drude-Lorentz model with two additional Lorentzian terms was determined in a wavelength range from 534 to 908 nm, and the results show that the gold film is composed of homogenous and rough layers with thicknesses 42.8 nm and 2.0 nm, respectively. This method is particularly useful in measuring the thickness and dielectric function of a thin metal film of SPR structures, directly in the Kretschmann configuration.Web of Science1811art. no. 369

Spectral interferometry and reflectometry used for characterization of a multilayer mirror

A white-light spectral interferometric technique is used to retrieve a relative spectral phase and group delay of a multilayer mirror from the spectral interferograms recorded in a dispersive Michelson interferometer. The phase retrieval is based on the use of a windowed Fourier transform in the wavelength domain, and characterization of the multilayer mirror is completed by a three-step measurement of the reflectance spectrum of the mirror in the same interferometer

Phase sensitive measurement of the wavelength dependence of the complex permittivity of a thin gold film using surface plasmon resonance

We report on a new method for measuring the wavelength dependence of the complex permittivity of a thin gold film of a surface plasmon resonance (SPR) structure comprising a gold-coated SF10 slide with an adhesion film of chromium attached to an SF10 glass prism. The method is based on spectral interferometry and utilizes a setup with a birefringent crystal and the SPR structure in the Kretschmann configuration, in which channeled spectra are recorded and from them, the phase functions of the SPR for air at different angles of incidence are retrieved. The SPR phenomenon is manifested as an abrupt phase change with respect to the reference phase difference for the interference resolved with the SF10 glass prism alone. The phase changes for different angles of incidence are processed in the vicinity of the resonance wavelengths to obtain the real and imaginary parts of the complex permittivity in a wavelength range from 530 to 850 nm or equivalently, the parameters of a modified Drude-Lorentz model. This research, to the best of the authors' knowledge, is the first demonstration of spectral interferometry-based measurement of the complex permittivity function of a thin metal film, which is important from the point of view of material characterization directly performed in the Kretschmann configuration.Web of Science93100199

White-light spectral interferometric technique to measure a nonlinear phase function of a thin-film structure

We present a new two-step white-light spectral interferometric technique to measure a nonlinear phase function of a thin-film structure. The technique is based on recording of channeled spectra at the output of a Michelson interferometer and their processing by using a windowed Fourier transform to retrieve the phase functions. First, the phase function including the effect of a thin-film structure is retrieved. Second, the structure is replaced by a reference sample of known phase change on reflection and the corresponding phase function is retrieved. From the two functions, the nonlinear phase function of the thin-film structure is obtained. The feasibility of this simple method is confirmed in processing the experimental data for a SiO2 thin film on a Si wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. The thicknesses obtained are compared with those resulting from reflectometric measurements, and a good agreement is confirmed

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

Reflection-based fibre-optic refractive index sensor using surface plasmon resonance

A reflection-based fibre-optic refractive index sensor using surface plasmon resonance (SPR) in a thin metal film sputtered on a bare core of a multimode optical fibre is presented. The sensing element of the SPR fibre-optic sensor is the core of a step-index optical fibre made of fused silica with a gold film double-sided sputtered on the whole core surface, including the core end face. Consequently, a terminated reflection-based sensing scheme to measure the refractive indices of liquids is realized. The sensing scheme uses a wavelength interrogation method and the refractive index of a liquid is sensed by measuring the position of the dip in the reflected spectral intensity distribution. As an example, the aqueous solutions of ethanol with refractive indices in a range from 1.333 to 1.363 are measured. In addition, the increase in the sensitivity of the SPR fibre-optic refractive index sensor with the decrease of the fibre sensing length is demonstrated.Web of Science9art. no. 1403

Spectral interferometry and reflectometry used to measure thin films

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO2 thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements

Surface plasmon resonance based sensing of aqueous solutions using spectral interferometry

This paper deals with a polarimetric setup to measure the refractive index change of aqueous solutions. The experimental method is based on the surface plasmon resonance effect in the Kretschmann configuration combined with spectral interferometry. In order to retrieve surface plasmon resonance-induced differential phase change, a windowed Fourier transform was adopted to extract the phases from two spectral interferograms, one corresponding to the reference material (air) and the second to the analyte (NaCl aqueous solution). The shift of phase curve is related to the analyte refractive index change. The refractive index of the NaCl aqueous solutions (0, 2 and 5 percent) was measured by the Abbe refractometer at a wavelength of 589.3 nm and compared with theoretical one, calculated by the Lorentz–Lorenz equation. An excellent agreement between the values was confirmed. The resonance wavelengths as extremes of the surface plasmon resonance-induced differential phase changes retrieved from spectral interference signals were compared with the resonance wavelengths determined from spectral reflectance measurements. A good agreement between the values was confirmed.Web of Science1291272

Measurement of the group dispersion of the fundamental mode of holey fiber by white-light spectral interferometry

We present a new method for measuring the group dispersion of the fundamental mode of a holey fiber over a wide wavelength range by white-light interferometry employing a low-resolution spectrometer. The method utilizes an unbalanced Mach-Zehnder interferometer with a fiber under test placed in one arm and the other arm with adjustable path length. A series of spectral signals are recorded to measure the equalization wavelength as a function of the path length, or equivalently the group dispersion. We reveal that some of the spectral signals are due to the fundamental mode supported by the fiber and some are due to light guided by the outer cladding of the fiber. Knowing the group dispersion of the cladding made of pure silica, we measure the wavelength dependence of the group effective index of the fundamental mode of the holey fiber. Furthermore, using a full-vector finite element method, we model the group dispersion and demonstrate good agreement between experiment and theory