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Optical filters are crucial elements in optical communication networks. However, they seriously affect the signal quality, especially in the concatenation condition. In this paper, we study and simulate the signal penalties induced by five types of filters, including Butterworth, Gaussian, Bessel, Fiber Bragg Grating (FBG) and Fabry–Perot (F–P) filters, in order to optimize the optical network performance. Signal penalties, including both filter concatenation effect and filter induced in-band and out-band crosstalk, are analyzed by eye opening penalty (EOP) and Q-penalty. Simulation results show that the Butterworth filter performs best among these four types of filters. Total Q-penalty induced by a Butterworth filter-based demultiplexer/multiplexer pair, considering both filter concatenation effect and crosstalk, is lower than 0.5 dB, when the filter bandwidth is in the range of 42–46 GHz. Simulations done in a 100 Gbps PM-DQPSK optical network indicate that the permitted cascaded number is 14 and 10 with respect to the case of filters aligned and misaligned, respectively. Penalties induced by laser frequency shift are investigated and the performance of the 3rd-order Butterworth filter is compared to the 4th-order superGaussian filter. Finally, discussions of optical filter performances, including insertion loss, reconfigurability and programmability, are presented.

Possible switching architectures, with Optically Programmable Logic Cells - OPLCs - will be reported in this paper. These basic units, previously employed by us for some other applications mainly in optical computing, will be employed as main elements to switch optical communications signals. The main aspect to be considered is that because the nternal components of these cells have nonlinear behaviors, namely either pure bistable or SEED-like properties, several are the possibilities to be obtained. Moreover, because their properties are dependent, under certain condition, of the signal wavelength, they are apt to be employed in WDM systems and the final result will depend on the orresponding optical signal frequency. We will give special emphasis to the case where self-routing is achieved, namely to structures of the Batcher or Banyan type. In these cases, as it will be shown, there is the possibility to route any packet input to a certain direction according to its first bits. The number of possible outputs gives the number of bits needed to route signals. An advantage of this configuration is that a very versatile behavior may be allowed. The main one is the possibility to obtain configurations with different kinds of behavior, namely, Strictly Nonblocking, Wide-Sense Nonblocking or Rearrangeably Nonblocking as well as to eliminate switching conflicts at a certain intermediate stages.