Evaluation of optical thickness and refractive index of a layered sample by low-coherence optical tomography

Pratima Sen; Shubhada Kumbhaj; Sanjay Gupta

doi:10.1117/12.444917

19 October 2001 Evaluation of optical thickness and refractive index of a layered sample by low-coherence optical tomography

Pratima Sen, Shubhada Kumbhaj, Sanjay Gupta

Author Affiliations +

Proceedings Volume 4579, Optical Fiber and Planar Waveguide Technology; (2001) https://doi.org/10.1117/12.444917
Event: Asia-Pacific Optical and Wireless Communications Conference and Exhibit, 2001, Beijing, China

Abstract

Following coupled mode approach, we report ab initio calculations of the signal intensity obtainable at the output end of a fiber optic coupler in a standard OCT technique and the results have been verified experimentally. The calculated intensity output varies periodically with respect to the path length difference between the sample and the reference arm and represent the interference signal, which sustains within the coherence length of the source. In the experimental setup, we have used 670-nm semiconductor diode laser possessing coherence length of 60 micron as a source. We have used a sample consisting of thin layer of glass plate and mirror. Reference mirror of 80% reflectivity was chosen. The output from the coupler was read on the Digital Storage Oscilloscope. A comparison of the theoretical plot of signal amplitude as a function of reference mirror position with the trace of the signal obtained on DSO exhibits good matching. The refractive index of the glass plate as calculated experimentally was 1.50 +/- .0125 which agrees well with the standard value. The experimental setup can enable one to determine the refractive index as well as optical thickness of any thin film simultaneously. The signal-to-noise ratio was found to be approximately 20 dB.

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Pratima Sen, Shubhada Kumbhaj, and Sanjay Gupta "Evaluation of optical thickness and refractive index of a layered sample by low-coherence optical tomography", Proc. SPIE 4579, Optical Fiber and Planar Waveguide Technology, (19 October 2001); https://doi.org/10.1117/12.444917

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KEYWORDS

Mirrors

Reflectivity

Refractive index

Optical coherence tomography

Fiber optics

Glasses

Optical tomography

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