Patent ID: 9696207
Date: 2017-07-04
CPC Classifications: G01J,G01L,G01N

Claim:
1. A method of measuring waveguide mode spectra, the method comprising: forming a coupling interface between a coupling surface of a prism and a surface of a waveguide, the waveguide having a surface region of decreasing index with normalized slope where n=n(z) is a refractive index profile of the waveguide as a function of a distance z into the waveguide from the waveguide surface and λ is a measurement wavelength of a light beam from a light source, the surface region extending from a surface into the waveguide sample, and the prism having an input surface and an output surface; disposing an opaque light-blocking element spaced apart from both the input surface and the output surface in a portion of a path of the light beam emanating from the light source, the portion being closest to a plane of contact between the coupling surface and the waveguide sample; at least one of: allowing a second portion of light reflected from the coupling interface to reach the detector; and detecting the second portion with the detector at a position corresponding to as lowest-order mode, and is less than or equal to 7 times the maximum possible effective coupling length of the lowest-order mode or 7 mm, whichever is less.