Disperzno spremenjena vlakna
All-optical, thermo-optical path length modulation based on the vanadium-doped fibers

This paper presents an all-fiber, fully-optically controlled, optical-path length modulator based on highly absorbing optical fiber. The modulator utilizes a high-power 980 nm pump diode and a short section of vanadium-co-doped single mode fiber that is heated through absorption and a non-radiative relaxation process. The achievable path length modulation range primarily depends on the pumps power and the convective heat-transfer coefficient of the surrounding gas, while the time response primarily depends on the heated fibers diameter. An absolute optical length change in excess of 500 m and a time-constant as short as 11 ms, were demonstrated experimentally. The all-fiber design allows for an electrically-passive and remote operation of the modulator. The presented modulator could find use within various fiber-optics systems that require optical (remote) path length control or modulation.

Opportunities to Enhance Multimode Fiber Links by Application of Overfilled Launch

This paper investigates possibilities for the practical design of high-performance multimode fibers (MMFs) that can provide bandwidths in excess of 10 GHz ...km in an overfilled regime of operation. Analysis of standard MMF in an overfilled launch demonstrates that the theoretical bandwidth limitations arise from the influence of cladding on the propagation of the highest order modes. Practical MMF profile designs that overcome this problem are investigated. The standard 50-and 62.5- m fiber profiles are redesigned first to allow for the performance in an overfilled launch with the differential mode delays (DMDs) below 0.055 and 0.250 ns/km, respectively. It is shown that such fibers can exhibit the same or better theoretical bandwidth in an overfilled launch when compared to standard fiber under restricted launch. Elimination of the need for the restricted mode launch in high-performance multimode transmission systems can improve reliability issues and can relax the range of tolerance requirements imposed on terminal equipment, optical components, and link installation. Furthermore, MMFs that can be operated in an overfilled launched are compatible with emerging vertical cavity surface emitting laser (VCSEL) wavelength division multiplexing (WDM) array technologies. A successfully controlled higher order mode DMD also allows for the reduction of MMF core size and mit Delta that can be beneficial for low-cost high-performance single-channel links. It is demonstrated that properly designed reduced core fibers can achieve theoretical DMDs in the range of 0.005-0.02 ns/km. The bend loss properties of redesigned fibers are investigated in detail, showing that the proposed modifications do not lead to significant degradation of bend loss performance. Moreover, they can be manufactured at considerably lower cost while utilizing commercially readily available low-cost VCSELs. Even where the theoretical limit is not achieved by practical fiber making, the reduced core size and mit Delta MMF can provide higher production yield, lower cost, and higher average bandwidth.

Optical fiber for dispersion addressing

This letter presents a fully distributed forward propagating system, suitable for use with microbend sensors. The principle relies on selected mode launch in specially designed multimode fiber where a short pulse is launched into the fundamental mode. In the presence of microbend disturbance located down the sensing fiber, light couples from the fundamental to higher-order modes that propagate at different group velocity than the fundamental mode. The position of the disturbance is determined by the time delay between the pulse carried by the fundamental mode and by the pulse carried by higher-order modes. The group velocity difference is maximized by proper construction of the refractive index profile of the proposed fiber. Experimentally produced fibers exhibited difference of group velocities in ranges over 1%. This allows for easy reconstruction of position and amplitude of microbend deformations located down the sensing fiber. 2000 American Institute of Physics.