Highly sensitive squaring circuit for coherent optical communications

A squaring circuit with wide dynamic range and very high sensitivity is presented. The circuit is based on a commercial Gilbert-cell multiplier manufactured in submicron self-aligned bipolar silicon technology. In a 155-Mb/s frequency-shift keying (FSK) experiment, a dynamic range of more than 25 dB was obtained, and error rates well below 10/sup -9/ were demonstrated with an electrical input power of -45 dBm to the squaring circuit.<
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