Figure 1

Schematic of the asynchronous measurement technique. (a, b) Two individual probes (single-channel probe and reference probe) are used in the conventional technique. The reference probe placed on the measurement plane restricts the moveable area of the measurement probe. To increase the measurable area, the reference probe should be set at the edge of the measurement plane; however, this generally results in unacceptable signal-to-noise ratio (SNR) degradation of the reference probe. Therefore, a reference port is required on the source side. (c) One integrated multichannel electro-optic (EO) probe is used for the near-field measurements in the new technique, in which no fixed reference probe or reference port is needed.