In this paper, we will review the state-of-the-art of LiNbO3 based integrated electro-optic modulators and will show how micro-structuring techniques such as etching, domain inversion and thin film processing can be used to realize new configurations which can take the performance to unprecedented levels. In particular, we will review recent results on the use of domain inversion on a micron scale and we report on the fabrication of a chirp-free modulator having ∼ 2 V switching voltage and bandwidth of 15 GHz designed by placing the waveguide arms of the Mach-Zehnder interferometer in opposite domain oriented regions. We also review some of the new modulation formats (e.g. DQPSK) that can represent an application development of the presented micro-structured devices. Finally, we address the issue of the integration of the modulator chip in a transmitter board comprising tunable laser, bias-control electronics and RF driver. The requirements of integration can even push further the reduction in size of modulator chips, thus making more crucial the use of micro-and nano-structuring techniques.Mach-Zehnder modulator exploiting domain inversion for ultralow voltage operation.

Fabrication, characterization and application of periodical ferroelectric domains in ridges and Ti in-diffused ridge waveguides on X- and Y-cut Lithium Niobate (LN) are reported. The ridge waveguides of 3.5 microm height and 9 microm width were fabricated by inductively coupled plasma (ICP) etching followed by Ti in-diffusion into the ridges only. Appropriate electrodes on their side walls enabled domain inversion restricted to the ridge. The domain structure was investigated by selective chemical etching. Second harmonic generation in a 1.4 cm long ridge waveguide on an X-cut substrate was demonstrated at 1548 nm fundamental wavelength with an efficiency of 17% W(-1).

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