A serial time-division multiplexing optical fiber sensing network with a large multiplexing capacity, which is based on identical ultraweak fiber Bragg gratings (FBGs) and self-heterodyne detection technique, is proposed. An experimental system, which has 10 identical ultraweak FBGs with the same Bragg wavelength of 1550 nm, reflectivity of −36 dB, and bandwidth of 0.1 nm, is set up to investigate the performance of the proposed scheme. The spectra of 10 ultraweak FBGs are resolved with a high accuracy, and the wavelength–temperature sensitivity and temperature resolution of the system are 10.5 pm/°C, 0.09°C, respectively. A self-heterodyne detection technique is adopted to increase the sensitivity of the receiver, which makes it possible to multiplex over 1000 FBGs along a single optical fiber. Theoretical analyses demonstrate that this sensing scheme can effectively increase the multiplexing capacity and measurement accuracy.
This paper presents theoretical analysis and experiment results of four different fibers transmitting 10MW peak power Nd:YAG laser pulse. The main factors limiting to optical fiber transmission of high power laser pulse is pointed, including air breakdown at focus area and surface damage of optical fiber. The theory of air breakdown and the fiber coupling conditions is described briefly. The results of study to the transmission properties and damage conditions are presented on the basis of four different types of optical fibers. The results of the experiments are further analyzed in the aspects of transmitting efficiency, air breakdown and surface damage. The local and foreign optical fibers, with plastic-cladding and silica-cladding, and step- index and graded- index fibers are tested separately in the experiments. The experiments showed that the imported fibers are able to transmit up to 10MW peak power laser pulse with no any visible damage, while energy density at the fiber output end surface is 3.54GW/cm2. For local fibers, damage on the input surface of both plastic-cladding and silica-cladding, step-index fibers was found obviously. The column damage to the graded index fiber was also found and investigated in the research. Damage mechanisms of fiber at high peak power laser pulses are summarized. High quality finishing of fiber end surface will improve damage threshold tremendously. The conclusion of the study is that transmitting Q-switched Nd:YAG pulses of 10MW peak power is feasible for the domestically made fibers if their end surfaces are properly processed.
Photonic crystal polarization maintaining optical fibers(PC-PMFs) could offer much higher birefringence than conventional PMFs and have many remarkable properties. In this article, the localized function was orthogonalized with another function for the PC-PMFs, so the orthogonal localized functions were got, and the mathematical model of modal birefringence for PC-PMFs was brought forward. What’s more, a mathematical formula of attenuation for PC-PMFs was made, the effecting factors on the attenuation of PC-PMFs were analyzed and the process technologies to decrease the loss of PC-PMFs were also proposed.