Zoom imaging is of great importance in optical system to realize imaging to objects on different distances. Zoom imaging without moving elements is attracting more and more attention. The variable curvature mirror (VCM) is the key element to achieve zoom imaging without moving elements through applying external force on it, such as air pressure, piezoelectric actuators, etc. This type of zooming method is attractive as it can greatly reduce the volume and weight of the optical system compared with traditional zoom system.
A team led by Prof. ZHAO Hui from the Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) had reported that they've done studies on VCM that can realize changing of the curvature radius of the reflective mirror with high surface figure accuracy maintenance simultaneously.
Recently, the team announced that they designed and manufactured a new variable curvature mirror using the material of ultralumin, which shows good performance when actuated by air pressure. Their result was published on Journal Optics Express.
In their previous study, the researchers gave an analytical solution of the VCM with a thickness distribution of exponential shape using small parameters method. By comparing the results of finite element analysis with the same structural parameters, the two showed good consistency.
Based on this, they used the same approximation method to find an analytical solution for elastic thin plates with a cycloid-like thickness distribution. A VCM with such distribution was also designed, manufactured, processed and experimented.
Compared with VCM actuated by other means, VCM actuated by air pressure has the advantages of uniform force distribution and better contact. It can realize a good surface shape which could not be easy to achieve by mechanical movement due to the contact problem between the mechanical structures.
Moreover, on the base of systematical theoretical and experimental analysis, the team figured out what it could be when a VCM with cycloid-like thickness distribution is actuated by uniform pressure, the main aberration it has after actuation, also the analytical solution of the elastic plate with this shape.
These new results provide guides for further improving the structure design and optimization in the future.
With good surface performance, VCM has the potential to be used in visible imaging systems, such as space imaging cameras and earth-based telescopes.
This work was supported by the West Light Foundation of CAS, the Research Fund for Young Star of Science and Technology in Shaanxi Province of the China Scholarship Council.
