Propagation losses and gain measurements in erbium-doped fluoride glass channel waveguides by use of a double-pass technique.

We have studied Er3+, Yb3+, and Ce3+ codoped microchannel waveguides that were developed by two methods: ionic exchange for heavy metal fluoride glasses [ZrF4-BaF2-AlF3-CeF3 (ZBAC)] and vapor phase deposition for transition metal fluoride glasses [PbF2-ZnF2-GaF3 (PZG)] by using a double-pass technique. For the first time to our knowledge, the measurement of propagation losses and amplification tests were carried out by use of the same experimental setup, leading to complete characterization of the waveguides. Net gains higher than 1 dB/cm were achieved in ZBAC Er/Ce single-mode fluoride glass waveguides.

Scanning near-field optical microscopy as a tool for the characterization of multimode interference devices.

We report the scanning near-field optical microscopy (SNOM) characterization of a 4 x 4 multimode interference (MMI) device working at a wavelength of 1.55 microm and designed for astronomical signal recombination. A comprehensive analysis of the mapped propagating field is presented. We compare SNOM measurements with beam-propagation-method simulations and thus are able to determine the MMI structure's refractive-index contrast and show that the measured value is higher than the expected value. Further investigation allows us to demonstrate that good care must be taken with the refractive-index profile used in simulation when one deals with low-index contrast structures. We show evidence that a step-index contrast is not suitable for adequate simulation of our structure and present a model that permits good agreement between measured and simulated propagating fields.