Bruce Gardiner Aitken

Highly nonlinear Ge-As-Se and Ge-As-S-Se glasses for all-optical switching

We have synthesized Ge-As-Se and Ge-As-S-Se chalcogenide glasses designed to have large optical nonlinearities. Measurements reveal that these glasses offer optical Kerr nonlinearities greater than 500 times that of fused silica and figures of merit for all-optical switching >5 at 1.25 and 1.55 /spl mu/m.

Third order cascaded Raman wavelength shifting in chalcogenide fibers and determination of Raman gain coefficient

Third order cascaded Raman shifting is used to generate light to 1867 nm in sulfide fibers, and the nonlinearity is measured to be ~5.7 times 10-12 (m/W). Damage at ~1 GW/cm2 limits the wavelength shift range.

Resonant and non-resonant effects in photonic glasses

Abstract Over the past ten years, a large amount of research has been done investigating materials, both glasses and polymers, which exhibit large non-linear susceptibilities, χ 3 . The measured χ 3 for a wide range of inorganic glasses are presented and discussed in terms of chemical composition. The experimental results from a single mode fiber with a large non-resonant χ 3 are presented. An argument is made for the choice of the non-resonant non-linear effect in cylindrical optical waveguides as the most practical route toward the realization of devices utilizing non-linear interactions. The argument takes into account various aspects that influence device performance other than the magnitude of χ 3 alone. A brief discussion of the resonant non-linear phenomena derived from band-filling in semiconductor doped glasses and the photorefractive effect in SiO 2 GeO 2 waveguide materials is included for comparison.

Studies of optical non-linearities of chalcogenide and heavy-metal oxide glasses

Abstract We present measurements of third order optical non-linearities in heavy-metal oxide and sulfide glasses, using the z-scan, time-resolved z-scan, and spectrally resolved two-beam coupling techniques. The non-linear index of refraction is found to increase with heavy-metal and sulfide content, and the nuclear contribution to the non-linearity is found to be approximately constant at (15±3)%. The largest non-resonant non-linear index of refraction occurs in 35La2S3·65Ga2S3. It is 30 times larger than the non-linear index of refraction in fused silica.

Excitation of rare earth emission in chalcogenide glasses by broadband Urbach edge absorption

Abstract Studies of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy in rare earth (RE)-doped chalcogenide glasses have shown that there are interactions between the fundamental optical absorption and emission processes of the chalcogenide host glasses such as Ge33As12Se55 and the spectrally overlapping intra 4f-shell transitions of Er, Pr and Dy dopants. A broad (∼0.5 eV fwhm), near-band edge PLE band is observed in the excitation spectra of RE emission bands in chalcogenide glasses, superimposed on the expected 4f-RE PLE peaks. The results reviewed here demonstrate that the broad band PLE of the RE emission is due to the absorption of light in the Urbach edge of the host glass followed by non-radiative transfer of the excitation energy to the RE emitters. On the basis of several unique properties of the broad band PLE, we suggest a model for the energy transfer process from the host glass to the REs mediated by intrinsic defect states in the glass.

Physical properties and Raman spectroscopy of GeAs sulphide glasses

Ternary GeAsS glasses have been investigated to determine the compositional dependence of selected physical properties. Although the latter show a linear variation with Ge:As ratio at a constant S content, many exhibit a non-linear dependence on the S content at a fixed Ge:As ratio. The trend of optical properties tracks the increasing formation of metal-metal bonds as the S concentration of these glasses is reduced below stoichiometry. Molar volume and thermal expansion coefficient display maxima near an average coordination number of 2.6 for which there is no apparent indication in the Raman spectra. The spectra of stoichiometric and S-excess glasses are dominated by a band at 345 cm -1 due to the symmetric stretching of both AsS 3 and GeS 4 groups; those of S-deficient glasses display bands associated with metal-metal bonds between 210 and 240 cm -1 whose intensity increase with increasing S deficiency.

Broad-band excitation mechanism for photoluminescence in Er-doped Ge25Ga1.7As8.3S65 glasses

Abstract Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been carried out at both room temperature and at 5 K on a series of Er-doped GeGaAsS glasses with varying doping concentrations, ranging from 200 to 7400 ppm Er. It is found that increased Er doping concentration results in an increase in the strength of the broad band excitation of the Er 3+ atoms. In addition, at low temperatures, a direct link between the broad band excitation process and the host glass luminescence is observed. The increased strength of the broad band excitation of the Er 3+ dopants corresponds with a decrease in the intensity of the host glass luminescence in the more heavily doped samples. This is interpreted as a quenching of the host glass luminescence through an increase in the non-radiative transfer of energy from defect states in the glass to the Er dopants. This supports a previous hypothesis that the same native defect states in the glass are involved in both the host glass PL and the broad band PLE of the rare earth dopants. The implications of the current results for the understanding of luminescence properties in undoped chalcogenide glasses are discussed briefly.

Property extrema in GeAs sulphide glasses

Abstract GeAsS glasses with Ge:As ratios of 2.5:1, 1:1 and 1:2 with S concentrations ranging from 35% to 80%, corresponding to an average coordination number (〈r〉) ranging from 2.35 to 2.98 were synthesized. For glasses with fixed Ge:As ratio, the absorption edge and the glass transition temperature vary monotonically with S content. The thermal expansion coefficient and molar volume, however, attain maxima at 〈r〉 near 2.6, which extrema correspond to a maximum in the relative intensity of a narrow polarized Raman band at 275 cm−1 and a minimum in the frequency of the boson peak. These features shift to smaller 〈r〉 with decreasing Ge:As ratio and are attributed to the development of molecular As4S3-like species in GeAsS glasses with intermediate S deficits.

Self-calibrating quantum efficiency measurement technique and application to Pr 3+ -doped sulfide glass

A measurement technique is described in which the radiative quantum efficiency of certain transitions in rare-earth-doped glasses can be determined based only on relative fluorescence measurements. We calibrate the emission from the level of interest by measuring emission into that level from a higher excited level. Application of the technique to Pr(3+)-doped sulfide glasses yields quantum efficiencies for the (1)G(4) ? (3)H(5) transition as high as 60%, in good agreement with measurements using the integrating sphere technique. Calculated efficiency values based on the Judd-Ofelt technique are shown to be subject to inherent uncertainties.

Multiphonon energy gap law in rare-earth doped chalcogenide glass

The parameters for multiphonon relaxation of rare earth (RE) ions in the sulfide glass Ge25As8.33Ga1.67S65 have been re-evaluated using the temperature dependence of the fluorescence lifetime to separate out true multiphonon decay from other non-radiative processes. It is found that for energy gaps to the next lowest level greater than 2500 cm−1, other non-radiative processes become dominant over multiphonon decay. The most likely process for this additional non-radiative decay is energy transfer to vibrational impurities such as OH and SH. The newly derived parameters lead to an electron–phonon coupling parameter ϵ=0.058, which is more in line with other glass types than the previously accepted value of ϵ=0.36. These new multiphonon relaxation parameters and the existence of additional non-radiative decay mechanisms has implications for the modeling of chalcogenide-based active devices.