Optical head, optical information recording and reproducing device, and optical information system device

An optical head for use in an optical information recording and reproducing device for recording or reproducing information with respect to an information recording medium using laser light, the optical head comprising:

• an optical element made of a silicon resin cured material obtained by subjecting a silicon resin composition containing a caged-silsesquioxane compound to a curing treatment, wherein
• the caged-silsesquioxane compound contains at least one kind selected from the group consisting of silsesquioxane compounds expressed by the general formulas (1) through (3), and partially polymerized products thereof:
• (AR1R2SiOSiO1.5)n(R3R4HSiSiO1.5)p(BR5R6SiOSiO1.5)(HOSiO1.5)m-n-p-q (1)
• (AR1R2SiOSiO1.5)r(B1R5R6SiOSiO1.5)s(HOSiO1.5)t-r-s (2)
• (R3R4HSiOSiO1.5)r(B1R5R6SiOSiO1.5)s(HOSiO1.5)t-r-s (3)
• where, in the formulas (1) through (3), A is a group having a carbon-carbon unsaturated bond, B is a substituted or non-substituted saturated alkyl group or hydroxyl group, B1 is a substituted or non-substituted saturated alkyl group or hydroxyl group, or a hydrogen atom, R1 to R6 are each individually a functional group selected from a lower alkyl group, a phenyl group, and a lower arylalkyl group, m and t are each a number selected from 6, 8, 10, and 12, n is an integer from 1 to (m−1), p is an integer from 1 to (m-n), q is an integer from 0 to (m-n-p), r is an integer from 2 to t, and s is an integer from 0 to (t-r).