We show that, using index guidance within an isotropic all SiO<sub>2</sub> structure of only 4 layers, it possible to design an optical
fiber that supports just one mode of a single polarization: the azimuthally polarized TE<sub>01</sub> mode. In particular a ring guide
of appropriate index of doped SiO<sub>2</sub>, thickness and radius guides TE<sub>01</sub> as the fundamental mode. Then an outer layer can be used to cut off higher order modes. This design is in contrast to those that require Bragg guidance or anisotropic
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.
Dense all-fiber WDM's designed for telecommunication network applications around 1550 nm have been made from the all-fiber Mach-Zehnder interferometers' technology. They demonstrate isolation greater than 20 dB and loss smaller than 0.1 dB. Channel spacing of 0.7 nm has been achieved experimentally supporting a 20.5 dB isolation. A cascaded structure made of two interferometers has also been constructed highlighting the ease with which one can arrange several of them in series and thus increase the quantity of channels supported while maintaining high isolation.
Fused and tapered single-mode fiber couplers are used to make polarization insensitive Wavelength Division Multiplexers with a wavelength spacing of around 1 nm. Different structures are presented. As opposed to that of single highly elongated fused couplers, their responses are polarization independent.