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Thin films of Ge–As–Se chalcogenide glasses have been deposited by thermal evaporation from bulk material and submitted to thermal treatments. The linear refractive index and optical band-gap for as-deposited and annealed films have been analyzed as function of the deposition parameters, chemical composition and mean coordination number (MCN). The chemical composition of the films was found to be directly affected by deposition rate, with low rates producing films with elevated Ge and reduced As content, whilst at high rates the Ge content was generally reduced and As levels increased compared with the bulk starting material. As a result films with close to the same stoichiometry as the bulk glass could be obtained by choosing appropriate deposition conditions. As-deposited films with MCN in between 2.44 and 2.55 showed refractive indices and optical band-gaps very close to those of the bulk glass whereas outside this range the film indices were higher and the optical gaps lower than those of the bulk glass. Upon annealing at close to their glass transition temperature, high MCN films evolved such that their indices and band-gaps approached the bulk glass values whereas at low MCN films resulted in no changes to the film properties.

Ge x As y Se100−x−y (33 ≤ x ≤ 39 and 12 ≤ y ≤16) glasses were prepared, and their structure and optical properties were studied by Raman and UV–Vis-IR spectroscopic techniques. Ge-tetrahedrons [GeSe4] dominated in the structural units, and ‘defect’ bonds, such as Ge–Ge, Ge–As and As–As bonds, also occurred in the glasses. A structural model for calculation of the optical band gap energy (E g ) of Ge–As–Se glasses was proposed, and the calculated values are consistent with experimental results. Increasing germanium and decreasing selenium content can reduce both the mean bond energies and optical band gap energies, enhancing the photo-sensitivity of the glasses.

I discuss our work to optimize of the properties of highly nonlinear Ge x As y Se 1-x-y chalcogenide glasses for all-optical signal processing.

Chalcogenide glasses, which contain the chalcogen elements S, Se and Te covalently bonded with network forming elements such as Ge, As, Sb, etc, possess a higher third order (Kerr) optical nonlinearity at telecommunications wavelengths than any other known glass. Their high linear index and low optical absorption also makes it practical to use them to fabricate nanowire waveguides. In particular the third order nonlinear response of these materials displays a pure refractive nonlinearity with negligible two-photon absorption and a complete absence of free carrier effects. As a result we have been able to demonstrate all optical signal processing of telecommunications signals at speeds up to 640Gb/s [1] and RF spectral analysis with ≈3THz bandwidth [2] using waveguides made from As 2 S 3 chalcogenide glass with nonlinear parameters up to ≈10,000W−1km−1. However, in order to reduce power requirements higher values of the nonlinear parameter are desirable. Here we describe our first results using a new waveguide material: Ge 11 As 22 Se 67 whose nonlinearity is about 4 times larger than As 2 S 3 [3] and which has allowed us to achieve nonlinear parameters in air-clad rib waveguides in excess of 26000W−1km−1. Rib waveguides were fabricated by dry etching 340nm deep into 680nm thick glass films deposited by thermal evaporation onto an oxidized silicon wafer. Waveguides 3µm and 4µm wide were used in these experiments and these had nonlinear parameters (γ=2πn 2 /A eff γ) of 33000W−1km−1 and 26000W−1km−1 respectively - record values for a glass waveguide. This enhanced nonlinear response along with dispersion control leads to strong effects such as supercontinuum generation (Fig. 1(a)) and broad-band four wave mixing with large gain (Fig. 1(b)) using pulses with peak powers of 10–30W. The nonlinear response is also sufficient to allow nonlinear processing using CW powers in the 100mW range. This talk will describe the properties of Ge 11 As 22 Se 67 waveguides and their nonlinear properties at telecommunications wavelengths.

Chalcogenide glasses are an important class or amorphous materials with applications that include phase-change optical memories, solar cells, and optical waveguides. Particularly interesting for optical applications is their good transparency in the mid-infrared combined with their high linear and nonlinear refractive indices. This last property has motivated interest in the use of chalcogenide waveguides for all-optical processing of high-speed telecommunications signals [1].

We present a systematic study of Ge(x)As(y)Se(1-x-y) bulk chalcogenide glasses to determine the best composition for fabricating all-optical devices. The dependence of physical parameters such as the band-gap, glass transition temperature and third order optical nonlinearity (n(2)) on composition has been studied and a relation between the bond-structure and elevated linear loss levels in high Germanium glasses has been identified. It is found that glasses with 11

This research focuses on several aspects of chalcogenide all-optical processors. This study has chosen glasses in the Ge-As-Se system with the aim of optimising glass composition to obtain low loss, high nonlinearity and glass stability, whilst complementary efforts are focussed on the production, optimisation and application of chalcogenide waveguide devices to all-optical of high-speed telecommunication signals. Devices have been characterised in realistic telecommunications conditions with the eventual aim being to validate performance at rates up to 640 Gb/s.

GexAsySe100-x-y glasses with 0les xles40 and 12lesyles40 have been characterized for properties of bulk material as well as thermally deposited films. The effect of phase separation on film properties is studied.

Chalcogenide glasses, which contain S, Se or Te atoms combined with network forming elements such as Ge, As, Sb have the largest third order optical nonlinearity of any inorganic glass. As a result they are attractive candidates for fibre and waveguide devices for all-optical signal processing in the telecommunications bands. In this talk I will review our recent progress in all-optical devices such as regenerators, wavelength converters and other devices in chalcogenide glasses.

Optical properties of chalcogenide glasses, GexAsySe100-x-y (33les x les39 and 12les y les16) were studied by using Raman, UV-vis-IR and PDS spectroscopic techniques, and the relationships between structure, composition and optical property were discussed.

We review the fabrication processes and properties of waveguides that have been made from chalcogenide glasses including highly nonlinear waveguides developed for all-optical processing.

Chalcogenide glasses are important amorphous semiconductors used for phase-change memories, solar cells and in photonics. Here I will review their photonic applications with an emphasis on new glasses for high speed all-optical signal processing.