Refractive-index profile measurement of highly multimode planar waveguides by guided-beam tracking

Abstract

A novel method of measuring the refractive-index profile of deep multimode planar waveguides is described. Unlike in mode spectroscopy, several modes are excited simultaneously by a prism coupler. Superposition of the modes forms a guided beam that refracts continuously inside the graded-index waveguide and reflects periodically from the waveguide surface. Measurement of the periodicity as a function of the excitation angle enables one to calculate the refractive-index profile of the waveguide.

Application of the Refracted Near-Field Technique to Multimode Planar and Channel Waveguides in Glass

“…5 the RNF profile of a waveguide, fabricated by thermal Na + -Tl + ion exchange process in KF 3, has been compared with the profile, obtained by the combination of mode spectroscopy and guided beam tracking [10]. 5 the RNF profile of a waveguide, fabricated by thermal Na + -Tl + ion exchange process in KF 3, has been compared with the profile, obtained by the combination of mode spectroscopy and guided beam tracking [10].…”

Prism Excitation of Highly Multimode Deep Planar Waveguides

“…Details of this so called guided-beam tracking method which is complementary to mode spectroscopy have been given in [12]. In this respect, the guided beams offer a substitution; the dependence of the period length 1 on the effective index of refraction yields the information about the refractive index profile of the waveguide as well.…”