Design and Fabrication of LiNbO₃ Modulator for Radio over Fiber System

Radio over fiber (ROF) techniques could achieve ultra-wide wireless access and wired-line transmission of RF signal with high-capacity and low cost. The millimeter-wave modulator with wide bandwidth is the most important device in ROF system. This paper describes the design and manufacture process of the dual-parallel Mach-Zehnder modulator (DPMZM). To reduce the direct current (DC) shift and thermal drift, a particular electrode structure has been chosen, which applies selective corrosion to strip off most part of SiO₂ buffer except the SiO₂ just under the hot electrode. The tested parameters of sample DPMZM are as follows. The characteristic impedance is 35 Ω, the insert loss is 7.2 dB, the extinction ratio is 26 dB, the half-wave voltage is 3.0 V when single arm is driving or 1.5 V when two arms are driving, and the modulate bandwidth is about 20 GHz. It is obvious that, except for the bandwidth, the performance of fabricated modulator has the same (or higher) level as the high quality products manufactured in the international market. The fabrication of LiNbO₃ DPMZM has not been reported by the domestic organization so far.