**10. Conclusion**

In this chapter the design of a singular device for use both in CWDM/DWDM systems has been studied. Applications such as, tunable optical filters, demultiplexers and wavelength routers, using holographic SLM technology, have been reviewed taking into account ITU-T G.694.1 and G.694.2 Recs. for central wavelengths allocation.

Application of Computed Generated Hologram design (CGH) to CWDM/DWDM systems has been studied and some comments about this hologram generation technique and its results have been made in order to highlight the phases of the process implementation and the issues related to the diffraction target misalignment and the use of 2-4 phase holograms, etc.

The novel idea in this work is the design of a compatible CWDM/DWDM device able to carry out different multiplexing functions. As we commented before, a better device performance as a tunable filter, demultiplexer or router could be implemented if only one of these functions is required.

The design of equalized holographic ROADM devices for applications in CWDM optical networks has been developed. By using a mixed hologram, corresponding to the combination of several input wavelengths, the tuning of a broad range of wavelengths has been obtained allowing the full routing of several channels from the input fiber to the outputs. As it is possible to change the active pixels in the SLM for each hologram, in order to maintain a fixed output power level, channel equalization has been reached. Intrinsic losses of the device have been optimized using 4-phases holograms whose diffraction efficiency, for the 1st order, is twice that of binary holograms.

Also, the ROADM size has been minimizing by using a "2f-folded" instead of a "linear-4f" for the optical structure. To reduce the total insertion losses of the holographic device a SOA has been added increasing the input power range for equalization. An example of use of these ROADM devices in CWDM Metro and Access Networks (PONs) has been reviewed.

Another example of application is dealing with the design of a holographic router with losses compensation and wavelength conversion, whose main application is in the interconnection nodes of Metro networks. This device uses a SOA (Semiconductor Optical Amplifier), in the non-linear region, to do the wavelength conversion and, in addition, to supply the gain in order to compensate for the intrinsic losses of the holographic router. Other applications in Metro networks like path protection between nodes or switch matrix for ring networks interconnection could be implemented showing the versatility of these devices (Tibuleac & Filer, 2010).

Laboratory experiments testing the capability of a phase FLC-SLM to be used in these devices have been carried out and results show that, for different types of holograms, the possibility of distributing several wavelengths depends on the diffracted angle and, therefore, enabling the building of filters, demultiplexers or wavelength routers.
