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High sensitivity mapping of refractive index across a surface using a dual beam differential reflectance technique

High sensitivity mapping of refractive index across a surface using a dual beam differential reflectance technique
High sensitivity mapping of refractive index across a surface using a dual beam differential reflectance technique
With any waveguide device accurate knowledge of the optical characteristics is necessary for device design and specification; hence it is important from a practical and theoretical point of view to establish an efficient and precise method for measuring the refractive index profile of optical waveguides. For the majority of waveguide applications accurate knowledge of the absolute refractive index is rarely required but in contrast the difference between two adjacent regions is essential. The technique presented here addresses this second requirement. Measurements can be performed at any wavelength on the basis of intensity measurements of reflected signals from two adjacent points on the surface of a material and, since it is a non-contact measurement, it is also possible to record reflectance changes in situ. Samples can be heated, illuminated or processed in other ways, with a constant record of the refractive index changes which occur or are being made, mapped across an entire surface to an accuracy in Δn of 8 x 10-5. The spatial mapping of Δn is limited only by the focused spot diameters and the need for a separation between them, the surface quality and the noise associated with the combined detector and PSD electrical noise. We used CaF2 and ZnSe at various temperatures to calibrate and measure small refractive index changes.
0957-0233
86-94
Rivers, P.E.
c2edc418-b6ff-4dc2-a9d6-e7556014f14c
Rutt, H.N.
e09fa327-0c01-467a-9898-4e7f0cd715fc
Asal, R.
490148c2-6ad7-4a75-8221-2d15090d88b2
Rivers, P.E.
c2edc418-b6ff-4dc2-a9d6-e7556014f14c
Rutt, H.N.
e09fa327-0c01-467a-9898-4e7f0cd715fc
Asal, R.
490148c2-6ad7-4a75-8221-2d15090d88b2

Rivers, P.E., Rutt, H.N. and Asal, R. (1998) High sensitivity mapping of refractive index across a surface using a dual beam differential reflectance technique. Measurement Science and Technology, 9 (1), 86-94. (doi:10.1088/0957-0233/9/1/011).

Record type: Article

Abstract

With any waveguide device accurate knowledge of the optical characteristics is necessary for device design and specification; hence it is important from a practical and theoretical point of view to establish an efficient and precise method for measuring the refractive index profile of optical waveguides. For the majority of waveguide applications accurate knowledge of the absolute refractive index is rarely required but in contrast the difference between two adjacent regions is essential. The technique presented here addresses this second requirement. Measurements can be performed at any wavelength on the basis of intensity measurements of reflected signals from two adjacent points on the surface of a material and, since it is a non-contact measurement, it is also possible to record reflectance changes in situ. Samples can be heated, illuminated or processed in other ways, with a constant record of the refractive index changes which occur or are being made, mapped across an entire surface to an accuracy in Δn of 8 x 10-5. The spatial mapping of Δn is limited only by the focused spot diameters and the need for a separation between them, the surface quality and the noise associated with the combined detector and PSD electrical noise. We used CaF2 and ZnSe at various temperatures to calibrate and measure small refractive index changes.

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Published date: January 1998
Organisations: Optoelectronics Research Centre

Identifiers

Local EPrints ID: 77757
URI: https://eprints.soton.ac.uk/id/eprint/77757
ISSN: 0957-0233
PURE UUID: 6600f301-37fa-4cbe-82e0-c976520af0e5

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Date deposited: 11 Mar 2010
Last modified: 25 Jul 2018 16:32

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Contributors

Author: P.E. Rivers
Author: H.N. Rutt
Author: R. Asal

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