We demonstrate a novel method that enables one to measure the structure of highly reflecting fiber Bragg gratings. The method is based on measuring both the transmission and reflection spectra of the grating and applying an inverse-scattering algorithm. The use of the transmission spectrum significantly reduces the sensitivity of the reconstruction to measurement noise, and therefore it significantly decreases the measurement duration. We experimentally demonstrate our method for reconstructing the structure of an apodized grating with a reflectivity of 99.91%.

We demonstrate a novel, versatile method for sensitive measurement of nonresonant third-order optical nonlinearities in waveguides. The measurement is referenced to a bulk sample with well-known nonlinear optical properties, thus ruling out the influence of laser pulse parameters like duration, contrast, and spectral phase or amplitude. Since the generated mixing product is heterodyne detected, extremely small third-order optical nonlinearities, e.g., from air-filled short waveguides, can be measured.

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