Gbit / s Lithium Niobate Modulator

As 10 Gbit/s long-distance optical communication systems become more and more pervasive, requirements rise relating to increased levels of performance, as well as the miniaturization of key devices that configure such systems. Lithium niobate (LN) modulators are used primarily as optical modulators that change high-speed electrical signals at 10 Gbit/s to optical signals for long-distance communication systems. Driver ICs intended for driving such LN modulators are becoming key devices that impact the performance of a system as much as LN modulators. High quality output waveforms with little noise are required of LN modulator drivers, since signal waveforms output by LN modulator drivers extensively impact optical waveforms output by LN modulators, as well as their optical transmission characteristics. Furthermore, not only are waveform characteristics vital but miniaturization is also essential for long-distance transmission systems, since wavelength division multiplexing is often incorporated in longdistance transmission systems. At OKI we have thus far developed electro-absorption (EA) modulator drivers and commercialized them using a Gallium Arsenide (GaAs) Pseudomorphic High Electron Mobility Transistor (PHEMT) structure, which offer superior high speed and waveform characteristics1). Using the PHEMT structure, we have also been developing a driver amplifier that operates at 40 Gbit/s2). LN modulator drivers, however, are required to have not only such high speed characteristics but also a high output amplitude of 6Vpp, more than double of EA drivers, making it difficult to satisfy both operationg speed and output amplitude, because they are in a trade-off relasionship. Our report on the configuration, circuit and device design is provided, as well as operating characteristics of the LN modulator driver, as we were able to realize highspeed operations at 11.3 Gbit/s and high output amplitude characteristics with the 6 Vpp output amplitude through our development of LN modulator driver by applying our device structure and circuit design technologies that have been nurtured over the years during our development efforts.