Acousto-optic interaction in polyimide coated optical fibers with flexural waves.

Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-optic coupling can be produced with a reasonably good efficiency. To our knowledge, it is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.

Tunable narrowband fiber laser with feedback based on whispering gallery mode resonances of a cylindrical microresonator.

Narrowband filtering based on whispering gallery modes of a slightly tapered cylindrical optical microresonator was used to implement a tunable narrowband erbium-doped fiber laser. The laser can be set to emit a single longitudinal cavity mode (single frequency), although the laser cavity is a few meters long. In the single-frequency regime the laser can emit a maximum power of 0.380 mW with a linewidth <35 kHz and a signal-to-noise ratio exceeding 50 dB. Tunability is achieved by sliding the excitation point along the microcylinder. A tuning range of 1.16 nm is demonstrated.

Concrete enclosure for shielding a neutron source.

In the aim to design a shielding for a 0.185 TBq (239)PuBe isotopic neutron source several Monte Carlo calculations were carried out using MCNP5 code. First, a point-like source was modeled in vacuum and the neutron spectrum and ambient dose equivalent were calculated at several distances ranging from 5 cm up to 150 cm, these calculations were repeated modeling a real source, including air, and a 1×1×1 m(3) enclosure with 5, 15, 20, 25, 30, 50 and 80 cm-thick Portland type concrete walls. At all the points located inside the enclosure neutron spectra from 10(-8) up to 0.5 MeV were the same regardless the distance from the source showing the room-return effect in the enclosure, for energies larger than 0.5 MeV neutron spectra are diminished as the distance increases. Outside the enclosure it was noticed that neutron spectra becomes "softer" as the concrete thickness increases due to reduction of mean neutron energy. With the ambient dose values the attenuation curve in terms of concrete thickness was calculated.