Abstract

While much of the GaAs integrated optic work has been directed at 1 um fiber optic applications, another exciting area is in laser system applications. In particular a wideband modulator operating as a frequency shifter for 10.6 um that has attractive bandwidth, efficiency and power handling is of much interest. Here we report on the design and development of advanced modulator structures of this type operating at microwave frequencies between 8 - 18 GHz. A previously reported device (Ref. ¹) consisted of a semiconductor thin film slab waveguide with metal electrodes applied directly on the top and bottom. The major short coming of this geometry was the high Insertion loss due to absorption by the metal layers. To avoid this problem it was necessary to place a low index buffer material between the waveguide and metal. While ideal geometry would consist of an epitaxially grown structure of GaAs and GaAlAs, difficulties in producing high quality epitaxial layers resulted in excessive free carrier loss. We alternatively considered the use of ThF₄ as the buffer material and have recently been successful in reducing the insertion loss of the device. As will be discussed, these layers also offer some added flexibility which we have exploited to improve the overall optical and microwave design of the device.

© 1988 Optical Society of America