Frequency routing device having a wide and substantially flat passband

Abstract

We describe a technique for producing a flat passband in a wavelength multiplexer. We obtain this by combining two output waveguides, and by optimizing their parameters so as to produce a maximally flat passband with minimal loss. The optimum parameters are obtained, to a good approximation, by choosing each output waveguide so that its mode approximately matches the input waveguide mode (see page 9 on) and by choosing the spacing of the two waveguides so that the multiplexer transmission coefficient at the edges of the passband is approximately equal to the value at the center of the passband. We also include, in the multiplexer, additional waveguides that allow the center wavelength of the passband to be varied in steps of S/Q, where S is the channel spacing and .delta. is an integer exceeding the number of channels (multiple control input waveguides). As a result, we obtain a unique arrangement, suitable for realization in integrated form using waveguide arrays. The arrangement is characterized by flat passbands, by high levels of rejection in the stopbands, and it has additional waveguides that allow multiple choices for the wavelengths of the various channels, without affecting the spacing and width of the channels. By properly selected the input and output waveguides,any desired channel wavelength can be selected., with errors less than S/(2.delta.). This is expected to be an important feature because current technologies cannot control the channel wavelength with the accuracy (of less than a nanometer) that is typically required for long haul and local area networks.

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