Research Index / Ultrafast Technology / Electro-Optic Imaging

In order to to determine the electric-field distributions above devices such as microwave integrated circuits and passive and active antennas and arrays, an external electro-optic field-mapping system has been developed.  Using this setup, we have measured the amplitude and phase of all three field components in three dimensions.  Both guided waves and radiated fields from complex microwave circuits have been mapped.

Electro-optic Probe Station

Experimental Setup:

The electro-optic measurement setup is sketched in the figure above.  For sensing the tangential field components, Lithium Tantalate (LiTaO₃) is used, while the normal field component was measured with a Bismuth Silicate (BSO) crystal.  The electro-optic signal is measured in a harmonic-mixing scheme at an intermediate frequency of several MHz using an RF lock-in amplifier.  The phase-locked-loop electronics of the laser system allows synchronization of the cw signal from a microwave source to the laser pulse train so that measurements in amplitude and phase can be performed.  The device under test (DUT) is raster-scanned under the electro-optic probe using two translation stages.  

An advantage of the electro-optic measurement technique is its high bandwidth from MHz up to the sub-mm wave regime resulting from the fast response time of the linear electro-optic effect and the ultrashort-duration laser pulses used as sampling gates.  Moreover, due to tight focusing of the laser beam, high spatial resolution of a few mm can be obtained.  A strict avoidance of metallized parts (especially electrical interconnects) and the miniaturization of the probe crystal allows it to operate near conducting and dielectric objects with minimal distortion of the field to be measured.

Electric Near-Field Distributions of a Microwave Patch Antenna:

The measurements yield amplitude A(x,y) and phase - information of the electric field in a plane above the device under test.  The distance to the antenna can be varied to investigate the field distribution in three dimensions.  To illustrate these results, these (frequency-domain) data are transformed to the time domain according to the equation:  

E(x,y,t) is displayed as an animation in the following examples.

Examples:

1. x-, y-, and z-component of the patch antenna.

2. Normal component of a microwave distribution network.

Copyright © Center for Ultrafast Optical Science, University of Michigan

Maintained by: cuos-webmaster@umich.edu