Optical loss measurement of low-loss thin-film waveguides by photographic analysis

Photographic film was used to measure low intensities of guided light scattered from three different thin-film optical waveguides. The technique is shown to permit measurement of optical loss down to 0.07 dB/cm. The method involves the taking of a photograph of a guided light beam (λ = 632.8 nm) and the use of a microdensitometer to measure the two-dimensional scattered intensity profile. The sensitivity of the photographic film permits the measurement of low light levels, and the beam profile information permits the evaluation of the uniform scattering assumption. The technique can be adapted to channel waveguide loss by using high-definition photographic film. Additionally, the use of infrared-sensitive film can permit the technique to measure loss in the infrared.