We investigate the effect of thermal aging on the optical properties of multimode silica fibers. Samples were submitted to several heating-cooling cycles of 8 h each. Analyses were performed using an optical spectrum analyzer and an optical time-domain reflectometer to determine the signal loss. We proved that the attenuation coefficient is closely related to Rayleigh backscattering. Results show an increase of the attenuation coefficient with aging time. The obtained results show a degradation of the optical properties of fibers from 1680 h on, due to local variation of the refractive index induced by fluctuation of the material density.
We investigate the effect of thermal aging on the optical properties of multimode silica fibers. Samples are submitted to several heating-cooling cycles of 8 h each. Analysis is performed using the optical spectrum analyzer, the fixed analyzer method, and the polarization-dependent loss measurements to determine respectively the signal loss values, the differential mode delay, and the polarization-dependent loss. Results show an increase of the attenuation coefficient, the differential mode delay, and the polarization-dependent loss values with the increase of aging time. The obtained results show a degradation of the optical properties of fibers from 1680 h related to structural changes, and to the increase of the optical anisotropy of fibers.
Since new modulation schemes have become a great center of interest, Mach-Zehnder fiber fused interferometers (MZI) became necessary to ensure the direct detection (DD) from phase modulated signals, like DPSK (Differential Phase Shift Keying) or DQPSK. As these modulation schemes are very interesting in optical transmissions due to their capabilities, MZIs cannot be overlooked in the future optical links. In this paper, we review the base principles for using MZI as DPSK demodulators, and the major characteristics associated to these devices. In order to evaluate the minimal characteristics required for efficient modulation format conversion, we propose some numerical simulation results. Based on these results, we depicted a new fabrication process for the realization of MZIs by adiabatic stretching of one of the interferometer's arm. This is carried out by a CO2 laser, and the fabrication major points that must be respected are discussed. After review the MZI thermal dependency mechanism, the last part presents the experimental results obtained for the quantification of MZI temperature control accuracy needed for its utilization as an 43 Gbit/s PSBT (Phase Shaped Binary Transmission) encoder.
Optical components based on geometrical and refractive index variations could be studied by coupled mode theory. For that we introduce a new coupling coefficient which takes into account not only the geometrical variations, but also the core refractive index variations along the propagation axis for the coupled mode theory. The results show that the coupling coefficient between modes can be separated in a sum of two coefficients. The first one is the classic coefficient which takes into account the radius variation along axis. The second one is reported in order to study the index variation. We examine with more details the effect of the core dopants diffusion due to the heating during the fabrication process. The concatenation of a biconical tapers and long period grating is presented.