Key biological issues in contact lens development

A contact lens is a medical device widely used as an alternative to spectacles in order to correct refractive vision problems. The evolution of polymeric biomaterials has heralded a continuous development in the materials used to produce contact lenses and maximize patient comfort and limit adverse events. Microbial keratitis (MK) is a relatively rare but potentially devastating condition associated with contact lens use, particularly with the extended wear of hydrogel lenses. It is the principal complication related to contact lens wear and the large population at risk make it a public health concern. Bacterial binding to the contact lens material is a precursor to the development of MK and is influenced by properties of the material and the bacteria. In order for bacteria to infiltrate the cornea there must be some degree of corneal damage, usually caused by trauma or hypoxia. The most recent materials available aim to allow the continuous wear of lenses while limiting corneal hypoxia, thus helping to prevent the development of MK. Limitations to the treatment of MK require that novel approaches may be necessary in order to limit bacterial adhesion to contact lens materials.

Curl antenna lens as angle of arrival sensor

A lens antenna consisting of a double-sided 3 x 3 array of curl antennas that can convert an incident LH/RHCP signal into a transmitted LH/RHCP signal is shown to have an additional property that allows the angle of incidence of an incoming linear or circularly polarised signal to be determined. Here the angle of arrival information is obtained via a simple boresight power measurement made at the lens receive side. It is shown that an unambiguous angle of arrival information for signals arriving at up to +/- 45 degrees can be obtained.

Imaging of dipole sources and transfer of modulated signals using phase conjugating lens techniques

The authors discuss the imaging properties and transfer of amplitude and phase-modulated signals through a phase conjugating lens (PCL). The authors outline the mechanisms of the near-field and far-field subwavelength imaging of Hertzian dipole sources using PCL, particularly the authors show that one-dimensional subwavelength resolution of multiple sources is possible in the far-field using a PCL augmented with specially designed scatterers located in both the adjacent vicinity of the sources and in the mirror symmetric positions in the image plane. These scatterers enable evanescent-to-propagating spectrum and its dual, propagating-to-evanescent, field conversion. Thus, the subwavelength information encoded into propagating waves on the source side can be extracted on the image side. Next, for the first time the transfer of amplitude and phase modulated signals through a PCL augmented with evanescent-to-propagating spectrum conversion is discussed and it has been demonstrated that multiple amplitude or phase modulated dipole sources can be distinguished in the far-field with subwavelength resolution without the necessity for numerical post-processing of the received data. From the study conducted here, it is concluded that a system of transmitters/receivers augmented with a PCL and appropriate scatterers operates without the need for any numerical processing of the receive data in order to separate channel information from very close proximity stations.

Active Phase Conjugating Lens With Sub-Wavelength Resolution Capability

Experimental results are presented for the focusing capability of an active phase conjugating lens for a single and a dipole source pair and these are compared with predictions. In addition for a single source we illustrate the ability of the lens to project a null at the lens focus instead of a peak. A scheme is also presented such that when a source or pair of sources is imaged through an identical pair of passive scatterers located symmetrically about the lens that imaging with sub-wavelength resolution is possible. The rationale for the operation of the lens and aberrations observed due to its finite array size is discussed and is supported throughout by means of numerical simulation.