Live Electro-optic Imaging (LEI) for Real-time Analyses of Electric Near-flelds over Microwave Circuits

Live electro-optic imaging (LEI) system is described in this paper, which enables the real-time imaging functionality of electrical signals on up to 10GHz-class circuits in realtime on a screen at video frame rates as high as 30 frames per second. In the system, photonics provides important features of the system: its 100 £ 100-channel parallel detection and the low invasiveness of electrooptic crystal. With the LEI system, novel diagnostic methods are provided through instantaneous and intuitive analyses of RF signal distribution changes. As an example, LEI observation results for a coplanar waveguide with a moving metal plate are presented. 1. INTRODUCTION In this paper, we report instantaneous and continuous imaging of microwave electric near-flelds, which is named live electro-optic imaging (LEI). The concept of LEI is shown in Figure 1. By the LEI system, electric near-fleld distibuions over a microwave curcuit can be visualized as a motion picture. Wireless communications systems with higher performance and functionality will be essential in the highly networked information societies of the future. In development and production of such systems, a lot of prototypes are designed, built and tested in order to achieve desired speciflcations. If the performance of prototype is not enough, it is important to determine the cause of trouble promptly. It is expected that LEI is an innovative technology for this purpose. In the vicinitiy of microwave circuit, electric near-fleld distribution image beyond its difiraction limit can be obtained. Because there is a correlation between microwave electric near-flelds and the status of each circuit, observation of electro near-flelds will be important to deal with them. We have developed a LEI system on the basis of photonics technology. Figure 2 shows a photograph of the LEI system. In our LEI system, parallel detection (1,2) and real-time image processing (3) of electric flelds are realized. Its resolution is 100£100pixels and its frame rate is 30 frames per second. Electric fleld imaging with such a high resolution and high speed have not been achieved before, and motion pictures of electric near-fleld distribution were successfully acquired for the flrst time. In this paper, we describe the operation principle of the LEI system and some of the advanced microwave electric fleld measurements that can be done with it.