G. Wylangowski

Quantum-efficiency of praseodymium doped Ga:La:S glass for 1.3 /spl mu/m optical fibre amplifiers

The gain of Pr/sup 3+/-doped ZBLAN fibre amplifiers is hindered by a poor quantum efficiency due mainly to a high rate of multiphonon decay. Sulphide-based glasses ameliorate this problem through a higher radiative rate and lower nonradiative rate. In this letter, Pr/sup 3+/-doped Ga:La:S glass has been evaluated spectroscopically in bulk and fibre form for its quantum-efficiency at 1.3 microns. Measurements reveal that absorption bands are broadened and the effective separation between the /sup 1/G/sub 4/ and /sup 3/F/sub 4/ level is reduced compared to ZBLAN glass. Judd-Ofelt analysis and the theory of multiphonon-decay now predict efficiencies of 80%, while 58% is measured. Oxide impurities are shown to play a key role in quenching of the radiative emission.<<ETX>>

High performance acousto-optic chalcogenide glass based on Ga2S3-La2S3 systems

Chalcogenide glass systems based on Ga2S3-La2S3 (GLS glass), have been found to exhibit relatively high acousto-optic figures of merit. low acoustic loss and high acoustic velocity. These properties of the GLS glass combined with its transparency both in the visible and the infrared (0.5-10 µm), nontoxity, high softening temperature (Tg = 561 °C), ease of fabrication, optical quality, chemical stability, and isotropic properties, make it attractive for acousto-optic device applications.

Acousto‐optic modulation using a new chlorotellurite glass

Results of initial tests on an acousto‐optic modulator using a new chlorotellurite glass with a composition of 3TeO2‐2ZnCl2 are reported. This glass exhibits a wider transparency range (0.42–5.7 μm) than other tellurite glasses, with approximately the same figures of merit. We obtained an 80% diffraction loss and a 65% diffraction efficiency at a 633 nm wavelength, using an 80 MHz 15×1 mm piezoelectric transducer with 1.5 W of rf power. This glass is able to convert to fiber form, thus allowing efficient in‐fiber acousto‐optic modulators to be built.

Spectroscopy of Pr3+-doped low-phonon-energy glasses based on halides and sulfides

The optical properties of praseodymium-doped glasses have attracted considerable attention recently for their potential application as a 1.3 micron optical amplifier. We report here on our spectroscopic evaluation of a series of low-phonon-energy glasses based on halides and sulphides. These results, though driven by the desire for a practical amplifier, provide insight into the application of these glasses not only for telecommunications applications, but also an understanding of the overall optical properties of a low-phonon-energy glass. Using Raman spectroscopy, the vibrational characteristics of the glass host are determined. Absorption measurements across the visible and infrared allow evaluation of the intrinsic loss of these glasses when in fiber form, as well as providing an indication of glass purity. Fluorescence of Pr3+-doped glasses, through excitation of the 3P0, 1D2 and 1G4 levels, is measured along with the fluorescence lifetimes. These radiative properties are compared to those predicted by a Judd-Ofelt analysis, which has been performed on all glasses. In this way, this work provides an overall spectroscopic evaluation of the optical properties of low-phonon-energy glasses, leading the way towards a practical device.

Application of low-phonon energy glasses for optical amplification at 1.3 μm

We report on recent progress towards the application of both mixed cadmium halides and sulphide-based glasses as host materials for a Pr3+-doped 1.3 micron optical fiber amplifier. Both of these materials offer the potential for higher gains than can be currently achieved in a Pr3+-doped ZBLAN fiber. Fundamental glass properties, including optical and thermal characteristics, are compared. Losses of these glasses in fiber form have been estimated and spectroscopic measurements are summarized. From these studies we show that quantum efficiencies over an order of magnitude higher than those demonstrated with Pr3+-doped ZBLAN amplifiers are in principle obtainable. Measured efficiencies of 11% and 52% for the Cd halide and Ga sulphide, respectively, are achieved, while 25% and 80% are predicted. Numerical modelling allows comparison of the expected amplifier performance. Thermal analysis has identified the challenges which remain for the drawing of single mode fibers and the results of preliminary fiber drawing trials are described. The relative merits of each of the various glasses are considered and the challenges before a practical amplifier is achieved are outlined.

Low-cost metal/glass fibre polarisers produced in continuous lengths

Fibre polarisers are essential devices in optical fibre communication and sensor systems whenever the control of polarisation is needed. They are particularly important in fibre-gyro systems where low insertion-loss and high extinction-ratio polarisers are required, A wide polarising spectral-window is another important requirement, since in many practical fibre systems broad-spectrum LEDs are used as the light source. Wide-bandwidth polarisers are also needed in wavelength-multiplexing systems. In the last few years several approaches for fabricating optical-fibre polarisers have been proposed and demonstrated. Most have been based on polishing the fibre to expose the optical field. Amongst these, high extinction ratios have been demonstrated using an overlay of a birefringent crystal or a metal film. However, the exposed-field polishing technique is time consuming and requires considerable skill. Moreover, a high extinction ratio in combination with a wide spectral-range has not been reported. We report here a new approach which yields continuous lengths of polariser fibre and provides a practical low-cost solution. The technique is based on a fibre fabrication process which allows continuous access to the core optical field, as well as providing an extremely-smooth, low-scatter surface at which interactions can be obtained. The design has been used to make metal/glass fibre polarisers in which a metal is incorporated directly into the fibre close to the core, as shown in Figure 1. The result is a high-performance metal/glass fibre polariser which can be produced in continuous lengths and whose extinction ratio can be adjusted to requirements by cutting to a given length