Loss Measurements of Stoichiometric Ti and O Implanted LiNbO 3 Waveguides
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"[he optically polished x-cut crystals were purchased from Crystal Technology, Inc. The implantation was carried out using the Surface Modification and Characterization Facility at Oak Ridge National Laboratory. Following the process established by Poker and Xia [7], stoichiometric Ti and 0 implants of 2.5 and 7.5 x 10 17/cm2 were performed at 500°C. Titanium was implanted at 320 keV followed by an oxygen implantion at 120 keV. The ratio of Ti to 0 energy was computed using TRIM92 [81 to give equal ranges of 180 nm. The width of the waveguide is determined by the thickness of the implanted Ti layer and can be approximated by the straggling value given by TRIM as 65 nm Implantation at a temperature slightly above the recrystallization temperature reduces amorphization of the crystal by the implanted ions[7]. The fluences were based upon previous Ti implantation research which found that a high Ti dose is necessary to replicate the low loss guides that are produced by Ti indiffusion[3]. The combination of high temperature and 0 implant stabilizes the position of the Ti implant and prevents the formation of an oxide layer on the surface[7]. Transmission electron microscopic analysis[9] indicates that the implanted Ti layer remains below the crystal surface, suggesting that the guiding region is completely buried. 361
Mat. Res. Soc. Symp. Proc. Vol. 396 © 1996 Materials Research Society
The implanted crystals were dark after the Ti implantation but were a light grey after the oxygen implant. The crystals were annealed at 1000TC for 4 h in 02 bubbled through de-ionized water. After annealing the crystals return to a clear state. The waveguides were tested and characterized at 632.8 nm with a Metricon 2010 automated prism coupler equipped with a rutile prism. Analysis of the number, intensity and angular spacing of the modes yields information on the index and thickness of the guide. Due to the limitations of the prism coupler only TE modes could be investigated in LiNbO3 . After implantation the ends of the crystal were polished and end-fire coupling, using 40x microscope objectives, TE polarized 672 nm laser light and an Electrim 753 x 244 element CCD camera were used to estimate the losses in the guides. The public domain NIH Image program (available on the Internet by anonymous ftp from zippy nimh nih-gov) for Macintosh computers was used to analyze the digital images from the CCD camera. Attentuation Several techniques are available to measure attenuation of optical waveguides: sliding prism, cut-back and scattering are three of the most common. In this work we report loss measurements made using the scattering technique[10]. The edge of the 1 cm x 1.5 cm crystals wvere blacked out with a permanent marker to reduce scattering from the edges. As illustrated in Figure 1, screens were used to reduce stray light reflected from the input and output microscope objectives A macro lens was used that resulted in each column of 115 gm wide pixels in the digital image corresponding to a distance of 42 prm along the length of
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