Waveguide Formation in Silica by Implantation with Si, P and Geions
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ABSTRACT Low loss channel waveguides have been formed in substrates of fused silica and silica-onsilicon by the implantation of 5 MeV Si, P and Ge ions. The silica-on-silicon substrates comprised an upper core layer which was doped with either 3 or 7% Ge. Annealing of the implanted silica-on-silicon waveguides has defined a narrow range of temperature (500 - 600'C) over which the loss coefficient, (x,was at a minimum of 0.10 - 0.20 dB/cm at wavelengths of X = 1300 and 1550 nm. For the fused silica substrates, a similar minimum loss ( 0.10 - 0.20 dB/cm) was measured at 1300 nm. However, at X = 1550 nm the value of x was significantly increased because of an absorption edge in the fused silica (Suprasil-2) at -1500 nm. The results show that the optical loss characteristics of the waveguides were essentially independent of the ion species.
INTRODUCTION Silica waveguides have formed the basis of many recent developments in optical devices and circuits [1]. A major technology used in the fabrication of waveguides in these circuits has been the buried channel process in which an etched core was embedded beneath a thick overcladding layer by flame hydrolysis deposition (FDH) or chemical vapor deposition (CVD). However, sequential steps of etching and re-deposition have been required in the fabrication of
buried channel waveguides. As an alternative process, the formation of low loss channel waveguides has recently been demonstrated using Ge ion implantation [2,3]. Townsend has shown that the ion implantation of silica glass produced a buried layer with an increase in refractive index of -1-2% [4,5] which formed the core region of a waveguide. The planar structure formed by this process was simpler than the steps associated with buried channel waveguides while providing superior control of the introduced species compared with an ion exchange process. Studies of the implantation of fused silica with Si and Ge ions have also demonstrated the photobleaching of the ion-induced optical absorption with 249 nm laser light, thereby allowing the direct writing of gratings in a waveguide [6,7]. As a result, the potential exists for the fabrication of planar waveguides with the incorporation of grating devices directly in the core. In the present paper, we compare for the first time the characteristics of channel waveguides formed by Si, P and Ge ion implantation into substrates of i) fused silica and ii) Ge-doped silica-onsilicon. For these experiments, the P and Ge ions were selected as dopant species in silica glass, while Si was chosen as a non-dopant ion having a similar atomic mass to P. The ions were implanted into substrates of fused silica and flame hydrolysis deposited silica-on-silicon to evaluate the effects of fabrication method of the glass on the characteristics of the waveguides. In addition, the use of substrates with differing levels of Ge doping has allowed assessment of any compositional effects on the properties of the waveguides. 417 Mat. Res. Soc. Symp. Proc. Vol. 396 © 1996 Materials Research Society
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