A method for reducing the channel spacing in a coherent optical heterodyne system

A method of channel allocation for the reduction of the channel spacings in a heterodyne optical transmission system is proposed and analyzed for the specific case of frequency shift keying (FSK). This technique makes it possible to reduce the average optical interchannel spacing by an amount approximately equal to the intermediate frequency. This can increase the number of channels that can be accommodated within the generally limited continuous tuning range of commercial lasers employed as local oscillators by as much as 100% without the need for auxiliary equipment.<
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