Waveguide produced by fiber on glass method using Er3+-doped tellurite glass

https://doi.org/10.1016/j.jnoncrysol.2006.12.003Get rights and content

Abstract

We report the fabrication of waveguides using the fiber on glass (FOG) method. Taking advantage of a Thermal Mechanical Analyzer (Shimadzu TMA-50), we were able to produce a new type of waveguide by coupling an erbium doped fiber core onto a planar glass substrate. Both optical fiber core and substrate were fabricated from tellurite glass. Important thermal characteristics of the substrate and fiber like the transition temperature Tg, the temperature for the crystallization onset Tx and the maximum crystallization temperature Tc were determined by Differential Thermal Analysis (DTA). The thermal expansion coefficient of the tellurite glass was determined by Thermal Mechanical Analysis (TMA).

Introduction

The integrated optics is a new branch in the field of optoelectronics, which has been progressing rapidly. Optical waveguides are one of the main components in circuits for optical communications. Several methods have been developed to produce optical waveguides in glasses. Among them ion exchange has been recognized as a valuable technique for the fabrication of active devices allowing high optical gain per length unit [1], [2]. This technique enables the realization of both passive and active integrated optical devices including the fabrication of waveguides in glass substrates [3], [4], [5], [6], [7]. The many benefits of ion exchange include low production and materials cost, low birefringence and propagation losses, and compatibility with single-mode fibers. However, the increasing complexity of functional devices usually requires waveguides of varying widths, often in close proximity to each other.

Glass integrated optics can offer excellent flexibility to accommodate more functions and it is suitable to cost effective mass production. Integrated optical lasers and amplifiers have been obtained using rare earth-doped glasses exploiting different technologies [8].

Moreover, the tellurite glasses have gained a wide attention because of their potential as hosts of rare-earth elements for the development of fiber and integrated optic amplifiers and lasers covering all the main telecommunication bands. In fact, Tm3+, Er3+ and Tm3+–Ho3+ doped glasses can be used for amplification in the S, C and L bands between 1.46 and 1.61 μm [9], [10], [11]. Tellurite glasses exhibit the lowest phonon energy (around 780 cm−1) when compared with the silicate or phosphate glasses and they also offer good stability and chemical durability. Furthermore, they exhibit high refractive index, a wide transmission range (0.35–5 μm), low process temperature and significant non-linear properties [12], [13], [14].

In this work, the fabrication and characterization of waveguides using the fiber on glass (FOG) concept proposed by Benson et al. [15] are reported. This method correlates the principal characteristics of fiber and substrate with the transition temperature Tg, the temperature for the crystallization onset Tx and the maximum crystallization temperature Tc. The fabricated waveguide device was obtained by thermally welding an optical fiber core onto an Er3+-doped glass. Both fiber core and glass substrate were produced from tellurite glasses, which enables the device to operate in the 1.5 μm telecommunications window.

Section snippets

Experimental

The glass samples were prepared by the conventional technique of melting and quenching. A platinum crucible containing the glass constituents was placed in a quartz tube, and heated in a resistance furnace from ambient temperature up to 750 °C, where it remained for 2 h. In order to drag vapor from the glass sample, a low oxygen flow was introduced during the melting. After melting, the glass is quenched and cooled to ambient temperature. Finally, to reduce internal stresses caused by the thermal

Results

Table 1 presents the basic thermal parameters of the glasses fabricated in the present work. With Na2O concentrations ranging from 10 to 12 mol%, we succeeded in the fabrication of glasses like TEGNAZO10 and TEGNAZO12 which exhibit similar values of both Tg and Tx. They also exhibit a reasonable Tg  Tx difference (110–120 °C) which favors the welding process. These are the reasons why these glasses were chosen to fabricate the optical fiber core and substrate, respectively.

Based on the Tg results

Discussion

The Tx  Tg difference was an important criterion to evaluate the glass stability and consequently its glass formation capability. This criterion was used to know if the glass was viscous enough to shape in the FOG concept.

To obtain good results during the welding process, it is desirable that both the fiber core and the glass substrate exhibit similar values for Tg. In order to prevent against possible crystallization, it is also desirable that both the substrate and the fiber core show a large

Conclusion

In this work, we have described the fabrication of a new class of active optical devices formed by an optical fiber thermally welded onto a glass substrate. Both the optical fiber and the substrate were fabricated from tellurite glass doped with high Er3+-ions concentrations. The device was produced through the FOG method. This technique is an alternative for the production of active optical devices in the form of channel waveguide differing from the classical waveguide fabrication methods as

Acknowledgements

The authors would like to thank the Brazilian agencies CNPq, FAPESP, PRONOE, CEPOF for the financial support.

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