Spectra of Structures Based on Thin-Core Optical Fibers with Film Overlays
- PDF / 1,103,182 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 164 Views
TRODYNAMICS AND WAVE PROPAGATION
Spectra of Structures Based on Thin-Core Optical Fibers with Film Overlays O. V. Ivanova, b, c, *, L. I. Yusupovaa, c, and A. M. Nizametdinova aKotelnikov
Institute of Radio Engineering and Electronics (Ulyanovsk Branch), Russian Academy of Sciences, Ulyanovsk, 432071 Russia b Ulyanovsk State University, Ulyanovsk, 432017 Russia cUlyanovsk State Technical University, Ulyanovsk, 432027 Russia *e-mail: [email protected] Received April 18, 2019; revised August 8, 2019; accepted August 9, 2019
Abstract—Transmission spectra of fiber-optic structures in which transformation of modes occurs in a segment of the thin-core SM450 fiber and a thin-film coating deposited on the cladding are studied. The modes and the corresponding dispersion relations are calculated for the SM450 cladding in the absence and presence of the overlay. It is shown that the dips in the transmission spectrum are caused by interference effects. A setup is constructed for deposition of polyvinyl-alcohol films on a segment of an optical fiber with a length of up to 20 cm with the aid of pulling from solution at a pulling rate of 0.1–1.7 mm/s. Transmission spectra of the structure are measured after deposition of overlays. Spectral shifts result from deposition of thin films. Wavelength shift is determined versus the pulling rate that determines the overlay thickness. DOI: 10.1134/S1064226920070049
INTRODUCTION Recent interest in fiber-optic structures the spectral characteristics of which are determined by interaction and transformation of several fiber modes has been driven mainly by simplicity, compactness, and prospects for measurement of environmental parameters (refractive index, chemical composition, humidity, etc.). The following structures can be used for such purposes: long-period fiber gratings [1], tapers [2, 3], misaligned splicing points [4], and inserts of special fibers. Multimode [5] and few-mode fibers [6], thincore fibers [7–10], coreless fibers [11], depressedcladding fibers [12, 13] and alternative fibers [14–16] may serve as inserts. Fiber structures with inserts made from nonstandard fibers exhibit coupling of core modes to modes of inserts (including cladding modes) the field of which propagates to the outer surface of the fiber cladding. Such modes are sensitive to various physical parameters of the external medium. Fiber structures with such properties are used as sensors that make it possible to determine humidity [15], temperature [7], refractive index of external medium [10, 16], and level of liquid [17–19]. Thin-core fiber inserts are unable to hold a mode, so that the mode passes to the cladding. Interference of several modes excited at the first splice of the insert and modes that reach the second splice leads to complicated spectra with nonmonotonic intensity distri-
bution with respect to wavelength [17]. Positions of spectral peaks are sensitive to the refractive index of the external medium. The sensitivity of structures with excitation of cladding modes can be substantially enhanc
Data Loading...
