A real-time electro-optic handy probe using a CW laser

This paper describes a real-time electro-optic (EO) probe system that can be directly connected to digital oscilloscopes, spectrum analyzers, and other widely used instruments. The probe incorporates a balanced optical receiver with two high-speed InGaAs p-i-n photodetectors to reduce noise, and optical isolators to decrease the light reflected from the optics back to the laser diode. To increase sensitivity, we employ CdTe, which has a large EO coefficient, and a high-power 1.3-μm distributed-feedback laser diode as a CW laser source. We used it to measure eye diagrams at 1 Gbps that were displayed on a digital oscilloscope. In addition, when connected to a spectrum analyzer, the probe significantly simplifies frequency domain analysis. We demonstrate the measurement of electric near-field distribution radiated from a two-layer printed circuit board and a cellular phone. The result shows that the probe system is a potential candidate for electromagnetic interference instruments