The availability of fiber combiners has been essential to the wide deployment of robust fiber lasers in the market. Some
standard parts have emerged in larger volume, but new designs involving both different processes and different fiber
configurations are being proposed to the market, offering novel or improved specifications. We will present some of
those new designs involving true signal fiber feed-throughs and better return loss and isolation properties. The new
fabrication process also allows more latitude in selecting the number of input pump fibers and is independent of the
signal fiber's internal structure.
In this paper we review the damage mechanisms that need to be considered when building high power fibre lasers. More specifically we look at thermal issues, optically induced coating damage, bulk and surface damage thresholds of the host glass. We also discuss the reliability of tapered fibre bundles and Bragg gratings at these power densities.
Fiber lasers have shown extraordinary progress in power level, reaching the kilowatt range. These results were achieved with large mode area fibers pumped with high power laser diodes coupled with bulk-optics. To enable the commercial development of these high power fiber lasers, we have demonstrated several All-Fiber components, which replace the bulk-optic interface in the present laser configurations. These components include multimode fused fiber bundle combiners with or without signal fiber feed-through, Bragg gratings and mode field adaptors. The multimode fibers are used to couple several fiber pigtailed pump diodes to a double-clad fiber. Such combiners may contain a signal fiber to provide an input or output for the core modes of the double-clad fiber. Mode field adaptors perform fundamental mode matching between different core fibers. Bragg gratings are used as reflectors for the laser cavity. These components exhibit low-loss and high power handling of 200 Watts has been demonstrated. They enable the design of true high power single-mode All-Fiber lasers that will be small, rugged and reliable.
The major use of tapered fibers is the in-line all-fiber spectral filters. Tapered filters are fabricated from a single piece of single-mode optical fiber that is heated and tapered until a given non-uniform longitudinal profile is obtained. This profile creates modes coupling with only forward propagating cladding modes. It is shown that tapered fibers induce low loss, low dispersion and low polarization dependence. The temperature sensitivity can be controlled by an appropriate packaging technique. Their main applications are the gain flattening filters, ASE noise suppression filters and spectrum correctors.
We present various fabrication techniques for 1 by 8 single- mode fiber couplers. Single-mode couplers are used for signal distribution in optical networks. Traditionally, for division of eight or more, several couplers are cascaded. This constraints increases the length as well as the production cost of the component. Our work demonstrates that the fusion/stretching process for making couplers can be applied to couplers containing up to eight fibers. Three different techniques have been studied to produce these couplers. Through one technique, uniformity of power was obtained at 1.55 micrometers . Typical losses are less than 1 dB. A theoretical analysis of the structure shows the coupling of eight supermodes. However, if transversal symmetry is respected, only two of these supermodes will interact in the power transfer between the fibers. The control of the interaction of these two supermodes permits a control of the wavelength dependence of the component. These phenomena are analyzed and experimental results are presented. The new 1 by 8 coupler is a compact component of less than 10 cm that integrates itself efficiently within the networks.
High isolation 1480-1550 nm WDM using fused fibers has been achieved. Several techniques have been tested but 2 by 2 fused couplers cascaded with filters give best results. Indeed, they demonstrate an isolation greater than 30 dB over 25 nm for the 1480-1550 nm WDM with a maximum insertion loss of 0.3 dB. Furthermore, the polarization dependence has been reduced to 0.1 dB. This device can therefore realize very efficient demultiplexing in EDFAs at low price.