A traveling -wave, electro

A traveling-wave, electro-optic phase modulator using bulk LiNbO^ was designed and con­ structed for efficient wideband operation. A second design which uses total internal re­ flection to couple the KF and optical fields was also constructed. This design is tunable over the efficiency-bandwidth curve and is thus quite versatile in many optical modulation applications. In recent years research on electro-optic modulators has strongly emphasized the development of integrated-optic devices because of their apparent potential for greater per­ formance and suitability to fiber optic systems.1 For some applications, however, bulk devices may be more suitable because of lower optical insertion loss and simpler and more developed technologies required to fabricate such devices. In this paper we report the demonstration of two bulk electro-optic modulators which improve various characteristics of performance of previous bulk designs. The first is based on the traveling-wave modulator described by White and Chin2 with significant modifications to the strip line and the method of inserting the electro-optic crystal into that strip line (figure 1). Coplanar strip line designed for 50 ohms was etched on a dielectric board. In the center section, one of the conductors was removed to allow insertion of the crystal. LiNbO^ was chosen and cut and polished to 0.2 x 0.2 x 8.0 mm along the X, Z and Y axes, respectively. In order to utilize the r^o E-O coefficient electrodes were deposited on the Z faces of the crystal, thus forming a 50 ohm transmission line. The crystal was attached to the strip line by flowing solder on the conductor in the center section and placing the crystal on it, Z face down. This provided a good electrical and acoustic bond. The other electrode was connected by wire bonding. Because the strip line gap and crystal thickness were so small, the wires could be kept very short, resulting in very small impedance discontinuities between the different transmission lines and good tuning over a very wide band.