ess of optical backplane emerge: the availability of optical connectors with the same reliability of the electronic connectors used in the backplanes and ability to operate in the same conditions, and the overall cost of an optical transmission system at 10 Gbit/s. As far as the cost is concerned, there is a strong push to reduce the cost of 10 Gbit/s trans- mitters and receivers also coming from other applications like the next generation gigabit passive optical network (GPON) at 10 Gbit/s (see Chapter 10). In this field the use of vertical cavity surface emitting laser (VCSEL; see Chapter 5) seems to be very promising [45], because, differently from other applications, here there is no need to use a wavelength around 1.5 um, but also shorter wavelengths can be used, in the second and even in the first fiber transmission window. As far as the transmission medium is concerned, at least three options are at the designed disposal: standard single-mode glass fibers [46], multimode glass fibers [46], and plastic fibers [45]. The choice of the optical transmission medium is a critical step in designing an optical backplane, due to the fact that a lot of elements depend on it. Naturally, standard single-mode glass fibers, used in the second transmission window, are very attractive due to the very good transmission performances (low loss, low disper- sion) and also due to the experience accumulated in all the equipment designing groups in designing systems based on this kind of fibers. Switching Systems: Architecture and Performances This choice has however its own weaknesses: the process to incorporate in a standard PCB-based backplane a glass transmission fiber is complex, resulting in a lower yield with respect to normal PCB production and a quite high cost of the final product. Quite complex are also the processes that are needed to interface transmitters and receiv- ers with a SO small core fiber, bringing further cost increase. The difficulties related to single-mode fibers can be relieved by using multimode fiber