| 摘要 |
<p>In a free-space optical communication system utilising infra-red wavelengths a lens (2) used for directing optical signal energy, for example onto a detector device, has one surface formed with a profile in one plane at least such that the beam width in that plane of the incident optical energy that is directed onto the detector device, over a predetermined range of angles of incidence, is greater than a predetermined minimum value. The lens may have different profiles in two orthogonal planes, such that optical energy is directed effectively onto the detector device from a wider range of angles of incidence in one of those two planes than in the other.</p> |
