Application of the Fractional Fourier Transform for dispersion compensation in signals from a fiber-based Fabry-Perot interferometer
Abstract
Optical methods of measurement do not require contact of a probe and the object under study, and thus have found use in a broad range of applications such as nondestructive testing (NDT), where noninvasive measurement is crucial. Measuring the refractive index of a material can give a valuable insight into its composition. Low‑coherence radiation sources enable measurement of the sample’s properties across a wide spectrum, while simultaneously measuring the absolute value of optical path difference between interfering waves, which is necessary to calculate the refractive index. The measurement setup used in this study consists of a fiber‑based Fabry‑Perot interferometer, illuminated by a low‑coherence infrared source. The samples under measurement are located in the cavity of the interferometer, and their transmission spectra are recorded using an optical spectrum analyzer. Additional reference measurements are performed with the cavity filled with air, in order to precisely measure the geometrical length of the cavity. The purpose of the study was to develop a digital signal processing algorithm to improve the resolution of analysis of the spectra of radiation measured at the output of the interferometer. This goal was achieved by decreasing the broadening of the signal in the Fourier domain caused by dispersion of the medium filling the cavity. The Fractional Fourier Transform is a generalization of the Fourier transform allowing arbitrary rotation of the signal in the time-frequency domain, allowing more precise analysis of signals with variable frequency. This property makes this transformation a valuable tool for the analysis of interferometric signals obtained from measurements of dispersive media, as the variable rate of change of the optical path length with respect to wavenumber in such media results in varying frequency of the modulation of measured spectra. The optical path difference inside the material under measurement is used together with the geometrical length obtained from the reference measurement in order to determine the refractive index. The parameters of the transformation are found by iterative adjustment to the signal under analysis. The developed algorithm was tested using both real measured spectra and simulated signals based on a theoretical model of the interferometric setup, and its effectiveness was compared to previously used methods of analysis. (...)
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- Category:
- Conference activity
- Type:
- materiały konferencyjne indeksowane w Web of Science
- Title of issue:
- Photonics Applications in Astronomy, Communications, Industry, and High Energy Physics Experiments 2017 strony 1 - 9
- ISSN:
- 0277-786X
- Language:
- English
- Publication year:
- 2017
- Bibliographic description:
- Mrotek M., Pluciński J..: Application of the Fractional Fourier Transform for dispersion compensation in signals from a fiber-based Fabry-Perot interferometer, W: Photonics Applications in Astronomy, Communications, Industry, and High Energy Physics Experiments 2017, 2017, ,.
- DOI:
- Digital Object Identifier (open in new tab) 10.1117/12.2281017
- Bibliography: test
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- Mrotek, M., Analiza sygnału pomiarowego z interferometru niskokoherencyjnego, master's thesis (2016).
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- Ozaktas, H. M., Arikan, O., Kutay, M. A., Bozdagi, G., Digital Computation of the Fractional Fourier Transform, IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 44, NO. 9 (SEPTEMBER 1996). open in new tab
- Pluciński, J., Karpienko, K., Fiber optic Fabry-Pérot sensors: modeling versus measurements results, Proc. SPIE 10034, 11th Conference on Integrated Optics: Sensors, Sensing Structures, and Methods, 100340H (September 2, 2016). open in new tab
- Pluciński, J., Karpienko, K., Response of a fiber-optic Fabry-Pérot interferometer to refractive index and absorption changes: modeling and experiments, Proc. SPIE 10161, 14th International Conference on Optical and Electronic Sensors, 101610F (10 November 2016). open in new tab
- Ciddor, P. E., Refractive index of air: new equations for the visible and near infrared, Appl. Optics 35, 1566-1573 (1996). open in new tab
- Hale, G. M., Querry, M. R., Optical constants of water in the 200-nm to 200-µm wavelength region, Appl. Opt. 12, 555-563 (1973). open in new tab
- Verified by:
- Gdańsk University of Technology
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