A device includes a first-type liquid crystal (LC) lens configured to provide a first optical power that is variable in a first step resolution. The device also includes a second-type LC lens coupled with the first-type LC lens, and configured to provide a second optical power that is variable in a second step resolution. The first step resolution is smaller than the second step resolution. A total optical power of the device is a sum of the first optical power and the second optical power, and is variable in the first step resolution.