Applications of FFT and digital filtering in reconstruction of refractive index profile of surface channel waveguides from near-field intensity pattern

Hery Susanto Djie; Henri P. Uranus; M Muljono; John E. Batubara

doi:10.1117/12.370365

12 November 1999 Applications of FFT and digital filtering in reconstruction of refractive index profile of surface channel waveguides from near-field intensity pattern

Hery Susanto Djie, Henri P. Uranus, M Muljono, John E. Batubara

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Proceedings Volume 3896, Design, Fabrication, and Characterization of Photonic Devices; (1999) https://doi.org/10.1117/12.370365
Event: International Symposium on Photonics and Applications, 1999, Singapore, Singapore

Abstract

Refractive index profile of surface channel waveguides can be determined by analyzing the near-field intensity pattern. A mathematical model, the inverse Helmholtz equation, is derived in order to use these data to reconstruct the refractive index profile under consideration. In this work, the measured near-field intensities are preprocessed by means of gamma correction, background noise subtraction, Fast Fourier Transform, and low pass finite impulse response (FIR) digital filter. Several types of FIR windows are chosen. The results are used to reconstruct the refractive index profile of the waveguide. The results show that the application of low pass FIR digital filter by using Hamming window reduces noises better than other windows. The application of this method in determination of refractive index profile of annealed proton exchange LiNbO₃ channel waveguides is demonstrated.

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Hery Susanto Djie, Henri P. Uranus, M Muljono, and John E. Batubara "Applications of FFT and digital filtering in reconstruction of refractive index profile of surface channel waveguides from near-field intensity pattern", Proc. SPIE 3896, Design, Fabrication, and Characterization of Photonic Devices, (12 November 1999); https://doi.org/10.1117/12.370365

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KEYWORDS

Refractive index

Near field

Waveguides

Digital filtering

Channel waveguides

Spatial frequencies

Linear filtering

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