All-optical switching

Winter, Underhill, and co-workers have published extensively on the cubic NLO properties of complexes of DT and related ligands,411 22 particularly those containing formally Ni11 centers. For example, time-resolved 1,064 nm DFWM was used to obtain resonantly enhanced values for group 10 complexes such as (157).411 15 The smaller of (157) compared with (156) is largely due to resonance effects since the absorption maximum of (157) is somewhat removed from the laser fundamental. However, figures of merit derived from measurements of 2 and linear and two-photon absorption (TPA) coefficients show that low optical losses render complexes such as (157) superior to (156)413 for potential all-optical switching applications.411 14... 

Blom, F.C., vanDijk, D.R., Hoekstra, H.J.W.M., Driessen, A., and Popma, T.J.A., 1997, Experimental study of integrated-optics microcavity resonators Toward an all-optical switching device., Appl. Phys. Lett. 71(6) 747-749. 

Experimental work and theoretical investigation show an important role of spatial chaos in optical fibers, directional couplers, and generally in all-optical switching devices [96/97]. 

The spin properties of charge-separated ion pairs can also be exploited for the purposes of all optical switching. Radical pair intersystem crossing (RP-ISC) of the form [D+ -A- ] D+ -A- ] to yield the spin-correlated triplet state is observed in... 

V 1 three-photon figure of merit for all-optical switching... 

Large nonlinearities based on saturated absorption or bandfilling effects are reported for semiconductors. The response of these nonlinearities is fast but recovers only slowly due to the created excited state population. Decay times of the excited states on the order of some hundred picoseconds to nanoseconds are detrimental for all-optical switching with large repetition rates. 

To implement an all-optical switch based on the nonlinear refractive index n(I)= n0+n2-I a nonlinear phase (f>MI shift of 2 n or a multiple of 27ris required, depending on the geometry of the switch [1]. As the absorption of the material attenuates the intensity and consequently diminishes the nonlinear phase shift, low absorption is advantageous. To determine the net nonlinear phase shift over the propagation distance the signal depletion by absorption has to be included. 

For the continuous-wave semiconductor (AlGaAs) distributed feed back lasers (DFB) used in telecommunication technology today a nonlinear refractive index n2=S cm2/GW would be necessary for all-optical switching, which is presumably impossible to reach. Including an Erbium doped fiber amplifier (EDFA) the needed nonlinearity drops only by a factor of ten. 

An extremely useful feature of the third-order nonlinear optical response is the intensity-dependent refractive index, where the refractive index of the medium changes due to the interaction with a light beam. This optically-induced change in the refractive index is essential for all-optical switching applications. 

Niziol et al. review the linear and NLO properties of some catenanes and rotaxanes studied in solutions or tliln films. Techniques like UV-Vis spectrometry, second and tlilrd harmonic generation in thin films and electro-optic Kerr effects in solution have been employed. They review the synthesis and material processing of tlrese derivatives. Niziol et al. describe how the rotation rate of the macrocycle in catenane solutions is more than an order of magnitude larger than in rotaxanes. They comment on the factors on which the rate of rotation depends. This new class of molecules, with mobile subparts, is very likely to have useful applications including tire construction of synthetic molecular machines and all-optical switching elements. 

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