Heterodyne based optical spectrum analysis with reduced data acquisition requirement

Heterodyne based optical spectrum analysis (OSA) involves mixing an input signal (402) with a swept local oscillator signal (406) to generate a heterodyne beat signal and then stretching the heterodyne beat signal before the signal is sampled. A system for optical spectrum analysis includes a local oscillator source (405), an optical coupler (410), a heterodyne receiver (412), and a processor (416). A circuit for stretching the heterodyne beat signal is included in the heterodyne receiver and may include a diode (674) in series with a capacitor (676) and a resistor (678) or a diode (874) in series with a capacitor (876) and a switch (880). Stretching the heterodyne beat signal involves extending the duration of the signal so that the signal can be detected with fewer samples per unit of time than an unstretched signal. Another embodiment of an OSA includes a first data acquisition unit for obtaining low resolution data and a second data acquisition unit for obtaining high resolution data.