Liquid crystal lens element and optical head device

A liquid crystal lens element comprising:

• a first substrate;
• a second substrate disposed so as to be opposed to the first substrate;
• and
• a liquid crystal layer sandwiched between the first and the second substrates and configured to change focal point of light transmitted through the liquid crystal layer according to a magnitude of applied voltage to the liquid crystal layer,
• wherein on one of the surfaces of the first substrate, a first transparent electrode is formed and a concave-convex portion made of a transparent material and having a cross section of a saw-tooth shape or a saw-tooth shape approximated by steps is formed so as to form a plurality of annular shapes concentric around an optical axis of incident light, and on one of the surfaces of the second substrate, a second transparent electrode is formed, and at least one of the first and second transparent electrodes is divided into annular electrode segments, a dividing position of the at least one of the first and second transparent electrodes into the annular electrode segments agrees with dividing positions of the concave-convex portion of the first substrate into the annular shapes, and based on a resistance between each of the annular electrode segments and a respective one of the annular electrode segments adjacently outside of each of the annular electrode segments, a resistance between each of the annular electrode segments and a respective one of the electrode segments adjacently inside of each of the electrode segments is twice as large.

A liquid crystal lens element for changing focal point of light transmitted through the liquid crystal layer according to the magnitude of voltage applied to the liquid crystal layer, which comprises a first Fresnel lens portion, a second Fresnel lens portion and an electrode lens portion;

• wherein the first Fresnel lens portion comprises a pair of transparent substrates, a first liquid crystal layer sandwiched between the transparent substrates, a pair of electrodes formed on surfaces of the respective transparent substrates so as to be opposed to each other to apply voltage to the first liquid crystal layer, and a first concave-convex portion having a rotational symmetry about an optical axis of light and having a cross section of saw-tooth shape or a cross section of saw-tooth shape approximated by steps, the first concave-convex portion being made of a transparent material and formed on an upper surface of at least one of the pair of electrodes opposed to each other;
• the second Fresnel lens portion comprises a pair of transparent substrates, a second liquid crystal layer sandwiched between the transparent substrates, a pair of electrodes formed on surfaces of the respective transparent substrates so as to be opposed to each other to apply voltage to the second liquid crystal layer, and a second concave-convex portion having a rotational symmetry about the optical axis of light and having a cross section of saw-tooth shape or a cross section of saw-tooth shape approximated by steps, the second concave-convex portion being made of a transparent material and formed on an upper surface of at least one of the pair of electrodes opposed to each other;
• the electrode lens portion comprises a pair of transparent substrates, a third liquid crystal layer sandwiched between the transparent substrates, and a pair of electrodes for applying voltage to the third liquid crystal layer, and disposed on surfaces of the transparent substrates so as to be opposed to each other, wherein at least one of the electrodes is a complex electrode constituted by a low resistant electrode and a high resistant plane electrode;
• wherein the first, the second and the third liquid crystal layers are made of a nematic liquid crystal having a parallel alignment at a time of no voltage application or at a time of voltage application, an ordinary refractive index direction of the first liquid crystal layer and an extraordinary refractive index directions of the second liquid crystal layer and the third liquid crystal layer agree with each other.