Hirotoshi Nagata

Materials reliability for high-speed lithium niobate modulators

As demand for lithium niobate optical modulators for use in high-speed optical communication systems has increased, their device performance and reliability have been vigorously improved, and some devices have found practical applications in systems. However, there are few reports, yet, about the quality and reliability of the lithium niobate material itself, although such information is necessary for improving further the device reliability and the fabrication yield. Here is presented data concerning material reliability for z-cut lithium niobate wafers commercially supplied in Japan. A variation is detected sometimes in the device performance such as dc-drift and optical insertion loss, and it seems to be caused mainly by an unpredictable fluctuation in the performance of individual wafers.

Application of microsandblast machining to LiNbO3 wafer surface for broadband modulators

Machining technology for LiNbO3 (LN) wafer surface aiming a mass-production of broadband LN modulators is investigated. Although several manufacturers commercially supply 40G LN modulators, there are many difficulties in mass-production of such broadband LN modulators. For instance, in order to realize sufficiently broadened bandwidth performance, machining of LN wafer surfaces is necessary as demonstrated by ridge-waveguide modulators and devices using very-thin substrates. We focus the study on the machining technology of LN wafers applicable to mass- production based on micro-sandblast techniques. In order to demonstrate effectiveness of the micro-sandblast, 40G LN modulators designed to have a partially thinned substrate along RF-electrodes are experimentally fabricated.