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 b e directly connected to digital oscilloscopes, spectrum analyzers, and othe r widely used instruments. The probe incorporates a balanced optical receiv er with two high-speed InGaAs p-i-n photodetectors (PDs) to reduce noise, a nd optical isolators to decrease the light reflected from the optics back t o the laser diode (LD). To increase sensitivity, we employ cadmium tellurid e (CdTe), which has a large EO coefficient, and a high-power 1.3-mum distri buted-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 oscillos cope. In addition, when connected to a spectrum analyzer, the probe signifi cantly simplifies frequency-domain analysis. We demonstrate the measurement of electric nearfield distribution radiating from a two-layer printed circ uit board (PCB) and a cellular phone. The result shows that the probe syste m is a potential candidate for electromagnetic interference (EMI) instrumen ts.