Optical element control

#This application is a national phase filing under 37 U.S.C. § 371 based on International Application No. PCT/EP2017/070577, filed Aug. 14, 2017, and claims the benefit of priority of that International Application. The contents of the International Application are incorporated by reference herein.

#The present invention relates to optical systems and, more particularly, to the control of an optical property of an optical element.

#Optical imaging systems are used in a variety of different fields, such as ophthalmic imaging. Ophthalmic imaging relates to the imaging of parts of the eye, such as the retina, which can allow early signs of disease or pathology to be detected.

#Embodiments of the invention will now be explained in detail, by way of example only, with reference to the accompanying figures, in which:

#FIG. 1 is a schematic illustration of an optical system according to embodiments of the present invention;

#FIG. 2 is a schematic illustrating an implementation of the controller shown in FIG. 1 in programmable signal processing hardware;

#An optical system 100 according to an embodiment of the present invention is shown schematically in FIG. 1. The optical system 100 comprises an optical element 10, and a controller 20 having a memory 30. These components of the optical system 100 are described in more detail below. Other well-known components of the optical system 100 that are not necessary for understanding the present invention (such as a beam delivery pre-focussing optical system and a post-processing optics, control systems therefor, etc.) are not illustrated or described herein, for sake of clarity. The optical system 100 implements a dynamic focusing mechanism that can be used to compensate for systematic and target-related focus changes to ensure that an optical imaging system remains in focus with respect to a target, and may be used for correcting optical power change of a ellipsoidal mirror of an ophthalmoscope, for example. The control techniques described herein may be applicable for an imaging system where light is delivered and collected through the same beam delivery mechanism, or where light is only collected or delivered to a target.

#The optical element 10 may, as in the present embodiment, be provided in the exemplary form of a liquid lens. The optical element 10 is responsive to a control signal SC applied thereto by the controller 20 to vary, as an example of an optical property of the optical element 10 that can be varied by the applied control signal SC, the focal length of the optical element 10. As will be described in more detail below, the variation of the optical property with an applied signal shows hysteresis in a first range of values of the signal, and no hysteresis in at least one second range of values of the signal. It should be noted, however, that hysteretic behaviour is not specific to liquid lenses, and may also be observed in a variety of other optical components.

#For example, some types of thin-film membranes show hysteresis in transmitted light intensity as incident light intensity is increased and decreased (and vice versa) over a common range of values.