1. A Stable Zn-indiffused LiNbO 3 Mode Converter at 0.632-μm Wavelength STUT Hsuan-Hsien Lee 2, Ruey-Ching Twu 1, Hao-Yang Hong 1, and Chin-Yau Yang 1 1. Department of Electro-Optical Engineering, 2. Department of Electrical Engineering, Southern Taiwan University of Technology Tainan 710, Taiwan, R.O.C. A novel Zn-indiffused mode converter has been proposed and experimentally studied in an -x-cut/z-propagation lithium niobate at a wavelength of 0.632 μm for the first time. The results also show that the proposed mode converter can operate with a stable conversion efficiency of about 99.5% between TM and TE polarizations. Abstract In the past decade, most of the commercial waveguide-type lithium niobate (LN) products operating in the infrared wavelengths (1.32−1.55 μm) were widely used in the fiber optical communications. In the optical sensor applications, a He-Ne laser of 0.632-μm wavelength is often used as a light source. In this paper, a metallic Zn-indiffused mode converter is successfully demonstrated on the −x-cut/z-propagation LN substrate for the first time. The optimized phase-matching and mode-conversion voltages for maximum conversion are 12 V and −5 V, respectively. The results also show that the proposed mode converter can operate with a stable conversion efficiency of about 99.5% between TM and TE polarizations at a throughput power of 25 μw in a period of 60 min. Introduction Similar to the device structure as proposed in [1], the outer electrodes through the EO coefficients of r 12 and r 22 ( r 12 =- r 22 ) while a voltage applied between the center and outer electrodes forces mode conversion through EO coefficient r61. Principles and Experiments Fig.1 Device structures for (a) top view, and (b) cross section view; (c) surface photography offabricated device. Zn film 35nm Ni film 6nm thermal diffusion 850°C-150 min Al electrode 300nm patterned (lift-off) patterned (lift-off) output beam CCD camera Si photodetector SiO2 buffer layer 300 nm substrate end faces polished He-Ne laser coupled into Fig.2. Conversion characteristics of input TM- polarized mode versus V C voltages under different phase matching voltages V 1. (a) V 1 = 0 V, (b) V 1 = 8 V, (c) V 1 = 12 V, and (d) V 1 = 16 V. Fig.3. Long-term stabilitymeasurements on the conversion performance at different measured times. (a) 20 min, (b) 40 min,(c) 50 min, and (d) 60 min. The phase matching between TM and TE modes can be achieved by using the optimized voltages at V 1 = 12 V (V 2 = 0 V) as seen in Fig.2(c). The conversion efficiency of about 99.5% is obtained at V C = +6 V, V C = −5 V, and the conversion characteristics are also similar to the results as reported in [2]. Under a throughput power of 25μw.At an applied constant voltage of V 1 = 12 V, the maximum conversion is gradually reduced as an increase of illuminating time at Results and Discussions the applied voltage of V C = +6 V. However, the maximum conversion is stable at the applied voltage of V C = −5 V. Conclusions In conclusion, we report on the first stable Zn-indiffused mode converter in an -x-cut/z-propagation lithium niobate here. This technique is very attractive to be using in the integrated waveguide sensors with stable power handling and polarization controlling, especially in the visible wavelength region. [1]. S. Thaniyavarn, “Wavelength independent, optical damage immune z-propagation LiNbO3 waveguide polarization converter,” Appl. Phys. Lett., 47, 674-677 (1985). [2]. T. Kawazoe, K. Satoh, I. Hayashi, and H. Mori, “Fabrication of integrated-optic polarization controller using z- propagating Ti-LiNbO3 waveguides,” J. Lightwave Technol. 10, 51-56 (1992). Reference