| 摘要 |
At least one metal species g is selected from the metal group G consisting of Nb, Ta, Pb, Ti, Tl and Zr. At least one metal species f is selected from the metal group F1 consisting of La, In, Y, Zr and Ta. The metal species g and f are not simultaneously Ta or Zr. The metal species g and f have concentrations distributed in mutually reverse directions. The element exhibits a ratio of dCf/dCg, in which dCf and dCg represent concentration distribution gradients of metal species f and g, respectively, ranging from -4 to -0.2. Alternatively, at least one metal species f may be selected from the metal group F2 consisting of Ga, Sn, Ba, Sr and Ca, while causing the ratio of dCf/dCg to be in the range of from -7 to -0.5. Thus, a gradient index optical element is obtained, which exhibits less refractive index change and large Abbe number change and is hence superior to conventional elements in correction of chromatic aberration.
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