Abstract

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 As₂S₃ 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: Ge₁₁As₂₂Se₆₇ whose nonlinearity is about 4 times larger than AS₂S₃ [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=2πn₂/A_effλ) 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 Ge₁₁As₂₂Se₆₇ waveguides and their nonlinear properties at telecommunications wavelengths.

© 2009 IEEE