A Stable Zn-indiffused LiNbOA Stable Zn-indiffused LiNbO33 Mode Converter Mode Converter

at 0.632-at 0.632-μμm Wavelengthm Wavelength

STUT

Hsuan-Hsien Lee2, Ruey-Ching Twu1, Hao-Yang Hong 1, and Chin-Yau Yang 1

1. Department of Electro-Optical Engineering,1. Department of Electro-Optical Engineering,2. Department of Electrical Engineering, 2. Department of Electrical Engineering,

Southern Taiwan University of Technology Tainan 710, Taiwan, R.O.C.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.

AbstractAbstract

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.

IntroductionIntroduction

Similar to the device structure as proposed in [1], the outer electrodes through the EO coefficients of r12 and r22 (r12=-r22) 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 35nmNi film 6nm

thermal diffusion850°C-150 min

Al electrode 300nm

patterned (lift-off)

patterned (lift-off)

output beamCCD camera

Si photodetector

SiO2 buffer layer300 nm

substrate end faces polished

He-Ne laser coupled into

Fig.2. Conversion characteristics of input TM-polarized mode versus VC voltages under different phase matching voltages V1. (a) V1 = 0 V, (b) V1 = 8 V, (c) V1 = 12 V, and (d) V1 = 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 V1 = 12 V (V2 = 0 V) as seen in Fig.2(c). The conversion efficiency ofabout 99.5%is obtained at VC = +6 V, VC = −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 V1 = 12 V, the maximum conversion is gradually reduced as an increase of illuminating time at

Results and Discussions

the applied

voltage of VC = +6 V. However, the maximum conversion is stable at the applied voltage of VC = −5 V.

ConclusionsIn 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