NOVELTY - An optical element (5) comprises optical components (2,4) both having light transmittance, and a joining film (3) for joining optical components. The joining film has silicon structure having random atomic structure including siloxane bonding (Si-O), and leaving group coupled with silicon structure, and is formed by plasma polymerization method. The difference of refractive index of joining film with respect to refractive index of optical components (2,4) is made into 0.01 or more by adjusting film forming conditions during plasma polymerization.    USE - Optical element. Uses include but are not limited to solar cell, optical lens, diffraction grating, optical filter, guard plate, optical disk, liquid crystal display element, organic electroluminescent element, electrophoretic display element, etc.    ADVANTAGE - The optical element has excellent light resistance and optical characteristics, and is easily manufactured with favorable dimensional accuracy.    DETAILED DESCRIPTION - An optical element comprises optical components (2,4) both having light transmittance, and a joining film for joining optical components. The joining film has silicon structure having random atomic structure including siloxane bonding (Si-O), and leaving group coupled with silicon structure, and is formed by plasma polymerization method. Energy is applied to at least one portion of joining film, and optical components are joined with adhesiveness of joining film when leaving group existing in surface of joining film is desorbed from silicon structure. The difference of refractive index of joining film with respect to refractive index of optical components (2,4) is made into 0.01 or more by adjusting film forming conditions during plasma polymerization. An INDEPENDENT CLAIM is included for manufacture of optical element.    DESCRIPTION OF DRAWING(S) - The drawing shows the longitudinal cross-sectional view illustrating manufacture of optical element. (Drawing includes non-English language text)    Optical components (2,4)    Joining film (3)    Optical element (5)