Three-dimensional micro-Fresnel optical elements fabricated by micromachining technique - Electronics Letters

There are two figures of merit used to assess the suitability of a nonlinear material for all-optical switching devices [8]. If the loss is dominated by linear absorption, W = A n l a must be larger than unity. In PTS, W > 1 for I > 20MW/cm2, based on attenuation coefficients estimated from those reported by Thakur, Frye and Greene [9]. In the case where two-photon absorption dominates the loss, we need T = 2a,hlnzl to be less than unity. For PTS, the value of this parameter may vary with both intensity and pulse width. For the value of the nonlinear refractive index and the upper limit of the two-photon absorption coefficient reported in this Letter, the T-parameter has a maximum value of 0.04, but may, in fact, approach 0. It has been previously shown that, with increasing T, the switching power increases and the switching tends to become incomplete in a nonlinear directional coupler [IO]. With as small a T parameter as given here, we conclude that PTS is highly suitable for all optical applications at 1600nm. Furthermore, by extrapolating from measurements performed at 158Onm we find that the T-parameter is less than unity for at least part of the gain bandwidth of erbiumdoped fibre amplifiers [7]. In conclusion, we have measured the complex nonlinear refractive index of PTS at 1600nm. The nonlinear refractive index n2 was found to vary linearly with intensity. The two-photon absorption coefficient could not be measured before the damage threshold was reached, which resulted in our ability only to establish an upper l i i i t for az. At this wavelength, the values of the complex nonlinear refractive index, through the figures of merit, indicate that PTS is a good candidate for all-optical switching, and has potential for use in telecommunications.