Interferometric In-Phase and Quadrature Oscilloscope

A technique is presented for measuring the in-phase and quadrature components of a modulated optical signal, using standard electrical and optical components and a high-bandwidth equivalent-time sampling oscilloscope. The measurement setup consists of an interferometer, optical mixer, and sampling oscilloscope with two low-speed sampling modules (50 kHz) and two high-speed optical sampling modules (65 GHz). The simultaneous measurement of four de-skewed signals allows for the separate determination of the phase noise, amplitude modulation, and phase modulation. From these results, the complete trajectory in time of the complex signal is constructed.