POLARISATION DIVISION

Suzuki, K., Kubota, H., Kawanishi, S. et al., High-speed bi-directional polarisation division multiplexed optical transmission in ultra low-loss (1.3 dB/km) polarisation-maintaining photonic crystal fibre, Electron. Lett., 37, 1399, 2001. 

We shall present, in the following sections, two complementary measurement strategies which allow the value of this variance to be minimised. The first concerns the technique by which the measuring time is divided between the two polarisation states, and the second minimises the variance by determining an optimal division of the counting times. 

Unfortunately QM/MM potentials are not devoid of problems. The most severe ones are probably the division of covalent bonds across the QM and MM regions and the lack of explicit polarisation of the MM approach. The first of these two difficulties has been looked at by several groups who have proposed different schemes to deal with the problem Warshel and Levitt [299] have used a single hybrid orbital on the MM atom in the QM/MM region a similar approach has been proposed subsequently by Rivail and co-workers [312, 355, 373] with their frozen orbital (or excluded orbital) in which the continuity between the two critical regions is assured by a strictly localised bond orbital (SLBO) obtained from model compounds. Another popular approach introduces link atoms [300, 310, 315] between QM and MM covalently bonded atoms to cap the valency of the QM atoms the link atoms, usually hydrogen, do not interact with the MM atoms. These are not, by any means, the only ways of dealing with this problem. However, so far it does not seem to have an obvious solution. 

---