Method for the local incorporation of Er into LiNbO3 guided wave optic devices by Ti co-diffusion

Abstract

Co-diffusion of Er with Ti into LiNbOs produces more than an order of magnitude enhancement in Er diffusivity over that achieved by ion implanting and thermal diffusion. The enhancement is dependent on the amount of Ti present. Er doped channel waveguide fabrication is completely compatible with standard Ti:LiNbOs technology. Fluorescence measurements from co-diffused and bulk grown Er doped LiNbOs show that the co-diffused Er3 + is in the LiNbO, phase.LiNbOs guided wave optics has produced the most sophisticated integrated optic structures to date, but the technology lacks the ability to produce or amplify light. Guided wave lasing and amplification have been reported in channel waveguides fabricated in bulk-grown Nd: LiNbOS.'.2 Bulk-doped materials are, however, not the optimal solution for guided wave integrated optics since absorption will occur in every section of the waveguide which is not optically pumped to transparency. Lateral confinement of the gain medium is also necessary to avoid absorption of the evanescent field. From a telecommunications perspective, Er is a more interesting rare-earth dopant due to its long lived -1.5 ,um radiative transition. Previous attempts to develop techniques which could be used to locally dope LiiOs with Er have met with limited success. Ion implanting ( lOI cm '-' dose of 200 keV Er ions) followed by a thermal annealing at 1050 "C for 45 h produced a l/e depth of 1.8 pm.3 A modest optical gain (0.75 dB) has been recently reported4 from similarly prepared channel waveguides. Guided wave stimulated emission at 1.53 ,um has also been observed5 after extended heating (80 h at 1060 "C) of an Er coated LiNb03 substrate. In this letter we demonstrate that the diffusivity of Er in LiNb03 can be dramatically enhanced by co-diffusing Ti with Er. Fluorescence spectra from co-diffused Er:Ti:LiNb03 and bulk doped Er:LiNbOs are nearly identical.Channel waveguides were photolithographically defined on z-cut LiNb03. Er and Ti/Er thin films were deposited by ion beam sputtering onto a photoresist patterned substrate or directly onto LiNbO, (planar diffusions). Er features could not be produced with this (liftoff) technique due to the poor sticking coefficient of Er on LiNb03. However, the films were easily processed if the Er was over-coated with Ti. Diffusions were carried out at 1050 "C under a flowing oxygen atmosphere containing water vapor. To characterize diffusion profiles, samples were mechanically milled at an angle with a rise-to-run of -1:30 (Fig. 1). Two-dimensional Er concentration depth profiles were made by electron microprobe (EMP) scans of the milled region (inset, Fig. 1). One-dimensional profiles were made by averaging successive scans (Fig. 2). Due to secondary x-ray excitations the EMP results represent the average Er content within the volume of the x-ray plume ( -1 ,um diam). An underestimation of the Er penetration is expected because of the plume effects.One-dimensional depth profiles from four Er diffusion experiments are shown in Fig. 2. In each case the Er f...

Spectroscopic properties and exicted-state relaxation dynamics of Er3+ in LiNbO3

“…4 The 4113/2 lifetime has been measured in one study [4] to be 7200 gs, and 7000 gs has been reported in another work [6]. These values are in agreement with our calculated radiative lifetime of 6450 gs within an uncurtainty of 10% which is typical for the Judd-Ofelt method.…”

“…In the limit of weak excitation an ion in an excited state decays with a measured lifetime zm given by: l/rm = Ar+Aph+Atr, (6) where Ar is the radiative transition rate, Aph is the nonradiative transition rate due to multiphonon emission and Atr is the rate of nonradiative energy transfer. When the concentration of active ions is sufficiently low, the last term in (6) becomes small and the decay is governed by radiative transitions and multiphonon relaxation.…”

“…As in previous published works, we investigate bulk-doped crystals which are not the optimal solution for guided-wave optics, but they can furnish reliable information useful for characterization of locally doped materials. It has been shown recently [6], that the bulk-grown Er 3 +-doped LiNbO3 and locally doped LiNbO3 by diffusion of Er 3+ have essentially the same structural and emission properties. …”

Selective co-doped erbium Ti:LiNbO 3 waveguide amplifiers

“…Although, optical net gain has been demonstrated by the diffusion of Er in LiNbO 3 at a temperature of 1100°C for 100 hours [3], selective diffusion is difficult to complete because of the lack of visibility in photolithographic mask alignments. In contrast, the Er and Ti co-diffusion process not only enhances the diffusivity of Er in LiNbO 3 [4], thus leading to shorter diffusion times, but also improves the visibility for the mask alignments. Therefore, the aim of this work was the demonstration of the fabrication of optical waveguide amplifiers in X-cut Y-propagating LiNbO 3 by Er and Ti co-diffusion.…”

Red, green and blue photoluminescence of erbium doped potassium tantalate niobate polycrystalline

“…After this period, basic research on optical spectroscopy of rare-earth ions in perovskite-type oxides was faded out except some, namely LiNbO 3 crystals [8,9]. Attention from a practical point of view was not paid either to most of these materials, because observed luminescence efficiency was low.…”