PERFORMANCE OF A ZERO-CROSSING OPTICAL-SPECTRUM ANALYZER

The performance of a zero-crossing-based optical spectrum analyzer is presented. With the use of only a single comparator, the analyzer circuit detects one zero crossing per Nyquist interval with a location accuracy of 1 part in 256. The dynamic range of sampling is limited only by the supply voltages of the comparator and the noise arising from truncation errors associated with computation. The 512-component spectra of various interferogram inputs are directly computed by Newton's formula from the measured crossings. The single-channel spectrum analyzer with a preselectable Nyquist sampling interval setting is constructed with discrete transistor-transistor logic and analog components. The ultimate performance characteristics of the analyzer are set by the response capabilities of the electronic components used.