Refractive index contrast
Refractive index contrast, in an optical waveguide, such as an optical fiber, is a measure of the relative difference in refractive index of the core and cladding. The refractive index contrast, Δ, is often given by Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Delta={n_1^2-n_2^2 \over 2 n_1^2}} , where n1 is the maximum refractive index in the core (or simply the core index for a step-index profile) and n2 is the refractive index of the cladding.[1] The criterion n2 < n1 must be satisfied in order to sustain a guided mode by total internal reflection. Alternative formulations include Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Delta=\sqrt{n_1^2-n_2^2}} [2] and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Delta = {n_1-n_2 \over n_1}} .[3][4] Normal optical fibers, constructed of different glasses, have very low refractive index contrast (Δ<<1) and hence are weakly-guiding. The weak guiding will cause a greater portion of the cross-sectional Electric field profile to reside within the cladding (as evanescent tails of the guided mode) as compared to strongly-guided waveguides.[5] Integrated optics can make use of higher core index to obtain Δ>1 [6] allowing light to be efficiently guided around corners on the micro-scale, where popular high-Δ material platform is silicon-on-insulator.[7] High-Δ allows sub-wavelength core dimensions and so greater control over the size of the evanescent tails. The most efficient low-loss optical fibers require low Δ to minimise losses to light scattered outwards.[7][8]
References
- Public Domain This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C". (in support of MIL-STD-188)
- ↑ "Definition: refractive index contrast". www.its.bldrdoc.gov.
- ↑ Snyder, A.W. (1981). "Understanding monomode optical fibers". Proceedings of the IEEE. 69 (1): 6–13. doi:10.1109/PROC.1981.11917. ISSN 0018-9219. S2CID 29679745.
- ↑ Okamoto, Katsunari (2006-01-01). "Wave theory of optical waveguides". Fundamentals of Optical Waveguides. Academic Press. pp. 1–12. doi:10.1016/b978-012525096-2/50002-7. ISBN 978-0-12-525096-2. S2CID 123835110.
- ↑ Zhou, J; Ngo, N Q; Ho, C; Petti, L; Mormile, P (2007-07-01). "Design of low-loss and low crosstalk arrayed waveguide grating through Fraunhofer diffraction analysis and beam propagation method". Journal of Optics A: Pure and Applied Optics. 9 (7): 709–715. Bibcode:2007JOptA...9..709Z. doi:10.1088/1464-4258/9/7/024. ISSN 1464-4258.
- ↑ Marcuse, Dietrich (1982). Light transmission optics (2nd ed.). New York: Van Nostrand Reinhold. ISBN 0-442-26309-0. OCLC 7998201.
- ↑ Melloni, A.; Costa, R.; Cusmai, G.; Morichetti, F.; Martinelli, M. (2005). "Waveguide index contrast: Implications for passive integrated optical components". Proceedings of 2005 IEEE/LEOS Workshop on Fibres and Optical Passive Components, 2005. Mondello, Italy: IEEE. pp. 246–253. doi:10.1109/WFOPC.2005.1462134. ISBN 978-0-7803-8949-6. S2CID 25058825.
- ↑ 7.0 7.1 Melati, Daniele; Melloni, Andrea; Morichetti, Francesco (2014-06-30). "Real photonic waveguides: guiding light through imperfections". Advances in Optics and Photonics. 6 (2): 156. Bibcode:2014AdOP....6..156M. doi:10.1364/AOP.6.000156. hdl:11311/863356. ISSN 1943-8206.
- ↑ Snyder, Allan W.; J. D. Love (1983). Optical waveguide theory. London: Chapman and Hall. ISBN 0-412-09950-0. OCLC 9557214.