**7. All optical signal processing functionalities survey**

Many efforts have been put in the past years to design and implement the entire collection of subsystems required for enabling high speed all-optical routing and switching by all-optical signal processing exploiting a variety of nonlinear media [124]. Significant examples are, format conversion by cross phase modulation at 40 Gb/s based on single SOAs [125] and 160 Gb/s all-optical OOK to DPSK format converter based on HNLF [126]. Both the schemes require high input power, i.e. high clock power in the first case and high input power, 20 dBm for the HNLF, making their operation expensive in terms of energy consumption. Coupling loss of 8 dB between the lensed fiber and the waveguide is reported in [127], as reverse biased silicon-onisolator p-i-n rib waveguides is wavelength converted via FWM. In [128], demonstration of FC NRZ-DPSK-to-RZ-DPSK, NRZ-DPSK-to-RZ-DPSK and NRZ-to-RZ in a PPLN waveguide by using SHG/DFG, while all-optical wavelength MC based on combination of XGM and XPM in a QD-SOA is presented in [129]. Here the detrimental effect of FWM coherent cross talk on the conversion is identified as the major drawback, responsible for degradation when using four equally spaced channels. Recently, T-H Cheng et al. demonstrated the multicasting in a HNLF loop mirror using FWM at 10 Gbit/s, but using three-pump lasers. In [130], demonstration of Grooming Switch for an OTDM Meshed Networking was reported, however OTDM-to-WDM would need thermally stabilized packaging and the light-paths in the WDM-to-OTDM must preferably be made of waveguides rather than fiber. Each of the demonstration could not support simultaneous MC, FC and WC of multiple modulation format signals to groom OTDM signals in a gridless elastic communication [7]. **Table 2** summarizes the devices used in all optical processing functionalities to date.

The suitability of optical wavelength converters for future networks will be judged on specific criteria that these must fulfill [56, 60]. In particular, modules will ideally have to simultaneously present the following characteristics: compactness (can be integrated in a single substrate with the other switch modules), operation at low optical/electrical powers with high dynamic range, polarization insensitivity, complete transparency to bit-rate (>100 Gb/s) and format or easily adjustable, induce minimal transmission power penalty (small chirp, amplitude distortion and extinction ratio reduction, and large OSNR) to a signal and thus can be cascaded, provision of amplification and (ideally) regeneration and wide conversion bandwidth (tunability) without the need of filtering.

The fundamental idea, common for all technologies discussed here, is the exploitation of the physical properties of a nonlinear element to perform optical processing. The main nonlinear elements are: SOA-MZI, PPLN and HNLF. SOA based devices have the added advantages of compactness and low energy requirements to trigger nonlinearities. Fibers have an instantaneous response to pulses but on the other hand have limited nonlinearity, even in specially designed photonic crystal fibers, hence long lengths and high injected powers are required for efficient operation [74].

*DOI: http://dx.doi.org/10.5772/intechopen.88354 All Optical Signal Processing Technologies in Optical Fiber Communication*

**Table 2.**

*Major technologies devices for all-optical processing reported to date.*
