Abstract-The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device.

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Acousto-optic tunable filters (AOTF) have been investigated as a potential basis for multiwavelength cross-connects in optical networks. In this paper, we discuss crosstalk issues, some of which are common to other cross-connect technologies, and some of which are unique to the AOTF, which will determine the suitability of the AOTF technology for this application. In particular we show how the interactions between wavelength channels make the AOTF sensitive to switch architectures. We conclude that significant performance improvements will be required to diminish crosstalk if the AOTF is to be useful in any but small-size cross-connects, even when space and wavelength dilation are used.

Abstrucf-Low temperature hydrogen diffusion in annealed proton-exchanged (APEm) waveguides has the potential of degrading device performance over a period of several years. An accelerated aging study was performed in order to determine its impact on device performance. The effect of aging was modeled as a second anneal. Both planar waveguides and Yfed Balanced-Bridge Modulator (YBBM) devices were aged at elevated temperatures. The hydrogen concentration profde of the planar waveguides was measured after aging with Secondary Ion Mass Spectrometry (SIMS) and compared to the profile from a control sample. The YBBM characteristics were measured as a function of aging time as well. Measured activation energies indicate that hydrogen diffusion is the dominant aging mechanism in the YBBM. Extrapolations indicate that device degradation is negligible at temperatures of 95" C or below. An operatinglstorage temperature as high as 125°C can be sustained for 13 years with little effect. A method for determining the effect of aging on any device is outlined.

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