Waveguide saturable absorbers at 1.55 µm based on intraband transitions in GaN/AlN QDs.

We report on the design, fabrication and optical characterization of GaN/AlN quantum-dot-based waveguides for all-optical switching via intraband absorption saturation at 1.55 µm. The transmittance of the TM-polarized light increases with the incident optical power due to the saturation of the s-p(z) intraband absorption in the QDs. Single-mode waveguides with a ridge width of 2 µm and a length of 1.5 mm display 10 dB absorption saturation of the TM-polarized light for an input pulse energy of 8 pJ and 150 fs.

Raman-assisted Brillouin optical time-domain analysis with sub-meter resolution over 100 km.

Sub-meter resolution in long-distance Brillouin Optical Time Domain Analysis (BOTDA) cannot be trivially achieved due to several issues including: resolution-uncertainty trade-offs, self-phase modulation, fiber attenuation, depletion, etc. In this paper we show that combining Raman assistance, differential pulse-width pair (DPP) measurements and a novel numerical de-noising procedure, we could obtain sub-meter resolution Brillouin optical time-domain analysis over a range of 100 km. We successfully demonstrate the detection of a 0.5 meter hot-spot in the position of worst contrast along the fiber.

Fibre optics wavemeters calibration using a self-referenced optical frequency comb.

Self-referenced optical frequency combs enable the measurement of optical frequencies with a very high accuracy, achieving uncertainties close to the atomic clock used as reference (<10(-13) s). In this paper, we present the technique for the measurement of laser frequencies for optical communications followed at IO-CSIC and its application to the calibration of two wavemeters in the 1.5 µm optical communication window. Calibration uncertainties down to 12 MHz and 59 MHz were obtained, respectively, for each of the devices. Furthermore, the long-term behaviour of the higher resolution wavemeter was studied during a 750 h period of sustained operation, exhibiting a dispersion in the measurements of 7.72 MHz. Temperature dependence of the device was analysed, enabling to further reduce dispersion down to a 2.15 MHz range, with no significant temporal deviations.

Experimental investigation of the effect of pump incoherence on nonlinear pump spectral broadening and continuous-wave supercontinuum generation.

The development of high-power cw fiber lasers has triggered a great interest in the phenomena of nonlinear pump spectral broadening and cw supercontinuum generation. These effects have very convenient applications in Raman amplification, optical fiber metrology, and fiber sensing. In particular, it was recently shown that pump incoherence has a strong impact in these processes. We study experimentally the effect of pump incoherence in nonlinear pump spectral broadening and cw supercontinuum generation in optical fibers. We show that under certain experimental conditions an optimum degree of pump incoherence yields the best performance in the broadening process. We qualitatively explain these results, and we point out that these results may have important implications in cw supercontinuum optimization.

Light collimation and focusing by a thin flat metallic slab.

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a point source. The effect is optimized when the radiation is around the bulk, not at the surface, plasma frequency. Also, the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of Al, whose imaginary part of permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.

Realization of an infrared spectroradiometer.

This paper describes a fully automatic spectroradiometer designed to measure the absolute spectral irradiance of light sources in the 800-2400-nm spectral range by direct comparison of radiation sources with a standard source, both placed the same distance away. The total estimated uncertainty in the comparison process is <1%, which, added to the standard source uncertainty, allows us to obtain the absolute spectral irradiance values of sources in this spectral range with an accuracy of better than 3%.

Absolute spectral irradiance scale in the 700-2400 nm spectral range.

An absolute spectral irradiance scale for the 700-2400 nm range has been developed. The scale is based on an absolute radiometer and a series of interference filters, which were used to determine the spectral irradiance of quartz halogen incandescent lamps at a number of discrete wavelengths. Values at intermediate wavelengths have been obtained by interpolation. This new scale was compared with NIST standards based on blackbody radiance. Both scales were found to agree within +/- 1%.