Lightwave lattice filters for optically multiplexed communication systems

It has proven desirable to use multistage etalons and resonators in lightwave communication systems. The design of these linear structures, however, is made difficult by the manner in which their transfer functions are nonlinear with respect to their composite reflection coefficients. If we interpret the etalons as discrete-time lattice filters, then z-transform techniques may be used to recursively synthesize filters with desirable properties. An algorithm is developed which can be used to design the arbitrary all-pole transfer functions in transmission, and the restricted class of pole-zero transfer functions in reflection, which are possible to implement with this architecture. We present some design examples such as notch, or channel-blocking, filters and flat-top bandpass, or channel-passing, filters which are appropriate for frequency-division multiple access and wavelength-division multiplexed communications systems. The theory predicts, and we show experimentally, how these structures may be used to discriminate, or route, signals based on their modulated or coded characteristics