Tellurite And Fluorotellurite Glasses For Active And Passive

1. Introduction; MDO 4
Infrared transmission is useful for spectroscopic sensing of chemicals / organic
groups, whose fundamental absorption bands occur in the mid-IR region. Bandwidth, and
hence information carrying capacity is maximaised at zero dispersion (d 2 n/dλ 2 =0,
occurring at 1.3 µm for silica, and at longer wavelengths for infrared transmitting
materials), and intrinsic scattering losses fall with increasing wavelength [10].
A high linear refractive index generally results in higher non-linearity than silica, with
the possibility for use in high-speed switching and high power delivery devices. Glasses
with an induced second-order non-linearity can be used for second harmonic generation.
The third-order non-linearity can be utilised in devices to boost the transmitted signal
with solitons, and the bandwidth increased with all-optical processing [12]. Raman
amplification is another way of amplifying the signal carried by the fibre, and is an
intrinsic non-linear property of the material. Novel glasses have been shown to exhibit
Raman gain much higher than silica [13].
1.3. Aims and objectives of this study
The glasses studied here, tellurite and fluorotellurite (TeO2-based), exhibit many of the
desirable properties listed in section 1.2, and therefore show potential in a number of
devices and applications. However, there is not much published work to date, particularly
on fluorotellurite glasses. Useful properties include transmission from the visible (400
nm) to the mid-IR (6 µm) [11], high refractive index (≈ 2, compared to ≈ 1.5 of silica
[14]), large non-linearity (non-linear refractive index two orders of magnitude greater
than silica [12]), with broad, long erbium (III) lifetimes [15], and Raman gain around 30