A real-time electro-optic handy probe using a continuous-wave 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 (PDs) to reduce noise, and optical isolators to decrease the light reflected from the optics back to the laser diode (LD). To increase sensitivity, we employ cadmium telluride (CdTe), which has a large EO coefficient, and a high-power 1.3-mum distributed-feedback (DFB) LD as a continuous-wave (CW) laser source. We used it to measure eye diagrams at 1 Gb/s 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 nearfield distribution radiating from a two-layer printed circuit board (PCB) and a cellular phone. The result shows that the probe system is a potential candidate for electromagnetic interference (EMI) instruments.