Research On Low Half-wave Voltage Of Lithium Niobate Modulator

Electro-optic modulator has great value in optical communication, optical sensor and optical information processing. Now, electro-optic modulator are usually fabricated on the LiNbO3 crystal due to its high electro-optic coefficient, good optical transparency from wavelength 450 nm to 4500 nm and mature waveguides processing. For LiNbO3electro-optic modulator, half-wave voltage(HWV) is an important parameter, lower HWV means lower power consumption of the electro-optic modulating system, which is advantageous to the device’s performance and the integration of the system. So diminishing half-wave voltage is an important research field. Increasing the length of electrode is a better way to lower the half-wave voltage, but it requires the device to be made long enough, which is disadvantageous to the fabrication and integration of the device. Making special waveguide structure like ridge structure waveguide that enhance the interaction between waveguide and electrode will lower the half-wave voltage as well. However, making ridge structure waveguide is very complicated.In this paper, we focus on the lowering the half-wave voltage of LiNbO3 modulators. The reflection type LiNbO3 modulator was studied and fabricated through annealed proton-exchanged process. x-cut LiNbO3 crystal was used in this paper. The outline of the work as follows:1. Studying the basic theory of reflection-type LiNbO3 modulatorFirstly, it is investigated to lower the half-wave voltage by studying the traditional LiNbO3 phase modulator, Mach-zehnder modulator, and analyzing the theory of reflection-type modulator. What’s more, LiNbO3 waveguide Fabry–Pérot(F-P) cavity was studied and its transmission characteristics was analyzed as well.2. Studying on annealed proton-exchanged techniques to making LiNbO3 optical waveguides and theory on making Li NbO3 waveguide.At first, analyzing the parameters to design the single-mode LiNbO3 waveguide by the effective refractive index method. After analyzing the annealed process and proton-exchanged process respectively, the parameters, such as temperature and time, to make the desire waveguides is investigated. In the process, much more attention was paid on the parameters of annealed process and proton-exchanged process which affect significantly the qualities of LiNbO3 waveguide. According to the test data, single-mode LiNbO3 waveguide with low loss was made successful.3. The design, making and test of LiNbO3 reflection type modulatorAccording to the theory of the LiNbO3 reflection type modulator, the structure of the device was designed and the mask was custom-made. Then the LiNbO3 reflection type phase modulator, intense modulator, and LiNbO3 waveguide F-P cavity were made respectively through the annealed and proton-exchanged processes, and the operation of the fabricated electric-optic modulator were characterized. In addition, the transmission of LiNbO3 waveguide F-P was also investigated.