LC lenses have advantages that can much save the volume and weight of the conventional imaging systems with the electrical tunable focal lengths. The optical designs of LC lenses become more and more important in the future. The FCPM method can be utilized to observe the refractive index distribution of the LC lens, which the refractive index is necessary in the optical simulation tools since the LC lenses are usually considered as one kind of GRIN lenses.
Although the lens power and performance are not high enough at present, we can adjust a conventional zoom lens behind the LC lens to solve the aberration of the LC lenses, as shown in Fig. 6-1. The refractive index variation of LC lenses measured by FCPM method can help the optical designs of the conventional lens groups.
Furthermore, the optical designs of the LC lens-only system can be achieved by the simulation tools. Even the rotation and movement of LC molecules can also be observed by FCPM method, only if the laser scanning speed is improved under the order of 10−3sec
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Fig. 6-1 The simulation process that the aberration of LC lens can be solved by the conventional lens group.
Actually, the FCPM method can observe not only the stable state of LC lens, but also the rotation process of LC molecules driven with electric field. The temporal analysis of LC directors in the LC lens was possible with the 3D profile constructed by the FCPM method. For example, the phenomenon that LC lens will focus twice while applied with overload voltage cannot be easily illustrated with fringing patterns or simulation results. However, the LC directors variation measured by the FCPM method shows that phenomenon is a transition state which caused with the rotating speed difference of the LC molecules on the center or the border. With the temporal variation of the fluorescence intensity from LC layers, as shown in Fig. 6-2,we can more detail observe the movement of LC molecules driven with different electric fields, which much helps the LC lens designs.
Fig. 6-2 Temporal variation of the fluorescence intensity emitted from the cylindrical LC lens driven with 65Volt (Vrms).
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Fig. 6-3 The optical path length variation of the cylindrical LC lens driven with 65V at different time. The variation curve at the first focusing peak and the stable state were similar.
Fig. 6-4 The schematic of LC molecules orientation in the cylindrical LC lens driven with 65V, at different time during the focusing process.
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