Broad‐band guided‐wave light intensity modulator

Abstract

Abstract With a view to realizing a broadband guided‐wave light intensity modulator, we fabricated a traveling‐wave type guided‐wave light intensity modulator. We succeeded in experiments of light intensity modulation over 18 GHz. In this paper, the traveling wave operation is shown to be superior almost always to the conventional lumped element operation in terms of bandwidth and efficiency. As an electric circuit appropriate for the traveling wave operation, the effectiveness of nonsymmetric electrodes is described. Analytical results are shown for the transmission line constants and modulation frequency characteristics. Next, the push‐pull optical modulation which is useful to obtain an efficient optical intensity modulator with good optical characteristics is considered. The configuration for the optical circuit is studied and the possibility of obtaining a traveling wave operation is discussed. Further, the result of the prototype development and modulation experiment using a Ti diffused LiNbO 3 optical waveguide (c plate) is reported. The device consists of two branches made of a single transverse mode waveguide 5 μm wide, and a differential modulation portion with parallel waveguides. The electrodes are nonsymmetric transmission lines with separation 32 μm, width 20 μm and length 6 mm. The half wavelength voltage was 8.8 V, extinction ratio 98%, 1/√2 bandwidth 11.2 GHz and the modulation input power 130 mW for 88% intensity modulation. The modulation sensitivity was 11.3 μW/MHz, and the frequency characteristics were found to be excellent.