No abstract

Interaction of spin and intrinsic orbital angular momentum of light is observed, as evidenced by length-dependent rotations of both spatial patterns and optical polarization in a cylindricallysymmetric isotropic optical fiber. Such rotations occur in straight few-mode fiber when superpositions of two modes with parallel and anti-parallel orientation of spin and intrinsic orbital angular momentum (IOAM=2 ) are excited, resulting from a degeneracy splitting of the propagation constants of the modes.

In September this year, the Government issued its draft Regulations on Food Safety (General Food Hygiene) 1995, which acknowledges for the first time the importance of a programme to make food handlers, their supervisors and managers, properly aware of the importance of food hygiene for the protection of the consumer and what they can do to prepare food safely. However, the regulation is specific neither about how training should best be implemented nor on the most important aspect of the policy, its end result. The standards of food hygiene awareness to be achieved through training have not been specified. The Department of Health, and the Ministry of Agriculture, Fisheries and Food (MAFF) cannot delegate their responsibility to protect the public health. Therefore, levels of food hygiene awareness, regardless of industrial sector, should be their prime concern. If the departments could set their minimum required standard of food hygiene awareness, the national framework of training which has evolved could naturally regulate the quality of training itself.

We present an experimental method for creating and verifying photon-number states created by non-degenerate, third-order nonlinear-optical photon-pair sources. By using spatially multiplexed, thresholding single-photon detectors and inverting a conditional probability matrix, we determine the photon-number probabilities created through heralded spontaneous four-wave-mixing. The deleterious effects of noise photons on reliable heralding are investigated and shown to degrade the conditional preparation of two-photon number states more than they degrade conditional single-photon states. We derive the equivalence between the presence of unwanted noise in the herald channel and loss in the signal channel of heralded experiments. A procedure for characterizing the noise-photon contributions, and a means of estimating the herald noise-free photon-number distribution is demonstrated.