Optical Intensity Modulation in an LiNbO3 Slab-Coupled Waveguide

Yalin Lu,Kitt Reinhardt

doi:10.1155/2008/373259

Abstract

Optical intensity modulation has been demonstrated through switching the optical beam between the main core waveguide and a closely attached leaky slab waveguide by applying a low-voltage electrical field. Theory for simulating such an LiNb slab-coupled waveguide structure was suggested, and the result indicates the possibility of making the spatial guiding mode large, circular and symmetric, which further allows the potential to significantly reduce the coupling losses with adjacent lasers and optical networks. Optical intensity modulation using electro-optic effect was experimentally demonstrated in a 5 cm long waveguide fabricated by using a procedure of soft proton exchange and then an overgrowth of thin LN film on top of a c-cut LiNb wafer.

Highlights

High-speedoptical modulation by microwave and millimeter-wave signals is useful in many optoelectronics and microwave photonics applications, including long-haul optical communication systems, radio frequency-over-fiber (ROF) for transferring mobile RF signals, optical measurement, and high-resolution coherence spectroscopy
For simplicity and by a few times of fitting with LiNbO3’s refractive indices and the slabcoupled waveguide (SCW)’s structural parameters, in Figure 3 we show a preliminary single-spatial-mode simulated at the telecommunication wavelength of 1.55 μm in the
Fabrication of such LN SCOWs follows a procedure of a soft proton exchange (SPE) on c-cut LN crystal and an overgrowth of thin LN film on top of the wafer, and it was introduced with details in a previous publication [10]

Summary

Introduction

High-speedoptical modulation by microwave and millimeter-wave signals is useful in many optoelectronics and microwave photonics applications, including long-haul optical communication systems, radio frequency-over-fiber (ROF) for transferring mobile RF signals, optical measurement, and high-resolution coherence spectroscopy. High insertion loss is a “hard-to-avoid” issue, which is almost intrinsic to currently used waveguide designs and those associated fabrications Usually both titanium-indiffusion and proton exchange create a relatively large index difference (δn ∼ 0.02), which will confine the fundamental mode in a small core size of only about a few microns. A new intensity modulation mechanism, which has the potential to use a very low driving electrical voltage, was investigated This modulation principle involves leaking the light from the main guiding core to an attached leaky slab waveguide through slightly changing the beam’s polarization orientation by the applied electrical field. Realization of this function will rely on designing such a slabcoupled waveguide (SCW) structure. Of this paper, preliminary SCW design/simulation, initial fabrication of such SCW on LiNbO3 crystals, and experimental demonstration of the optical intensity modulation will be introduced

The SCW Design Using LN Crystal

Intensity Modulation Using the Leaky Mode

Experimental Demonstration

Conclusion