Sensitivity improvement of an electro-optic high-impedance probe

This paper describes techniques for improving sensitivity of an electro-optic (EO) high-impedance probe, which is a powerful tool for measuring multigigahertz signals of on-board circuits. Higher sensitivity is achieved by decreasing the half-wave voltage of the EO crystal in the probe head and by increasing the laser power. To decrease the half-wave voltage, we employ Bi₁₂TiO₂₀, a newly developed crystal with a larger EO coefficient, and a 1.3-μm laser diode instead of a 1.55-μm laser diode. To boost the laser output power, the sampling rate is increased by using a specially designed laser driver unit. These techniques improve the total voltage sensitivity of the probe system 3.6 times compared with our previous system. This directly leads to a more than one order reduction of signal acquisition time. Moreover these techniques make the probe system cost effective because they eliminate the need for expensive optical components