Wavefront aberrations of a liquid crystal lens with focal length variable from negative to positive values

We prepare a two-voltage-driven liquid crystal (LC) lens. The optimum condition mainly for the positive lens with a variable power range from +7.1 to -2.6 D is obtained when V, is constant higher than V-2 and the lens power changed by varying V2, and that mainly for the negative lens with a variable power range from -4.7 to + 1.0 D is obtained when V-2 is constant higher than V-1 and the lens power changed by varying V-1. In both cases, the root-mean-square (rms), astigmatism (As), coma (Com), and third-order spherical (SA) aberrations are measured for the first time using the Fizeau interferometer (Zygo DVD-400, wavelength is 405 mu m). Comparably small aberrations are observed for the LC lens fabricated in this study. Under the mainly positive lens conditions, the rms and Com aberrations are smaller than the tolerance values except for the highest lens power region. The As aberration monotonically decreases and SA decreases in negative value with increasing lens power and are almost within the tolerance values, but SA exceeds it in the highest positive power region. Under the mainly negative lens condition, the rms aberration is small and the tolerance value is satisfied. The As and Com aberrations are larger than those in the mainly positive LC lens, and decrease with increasing absolute value of lens power. SA is smaller than that under the mainly positive power condition and the tolerance value is satisfied in the entire power range.