Process for producing optical element

A process for producing an optical device, comprising the steps of:

• placing an adhesive composition prepared by hydrolyzing, dehydrating and condensing a starting solution containing:
• (A) 10 to 50 mol % of a silane compound represented by the following formula (1):
• SiX14 (1)
• wherein X1 is a hydrolyzable group, or a combination of this silane compound and a metal alkoxide represented by the following formula (7):
• M(OR4)n (7)
• wherein M is Ti, Al or Zr, R4 is an alkyl group or trialkoxysilyl group, and n is 4 when M is Ti or Zr and n is 3 when M is Al, with the proviso that only one of the three R4's can be a trialkoxysilyl group when M is Al, the amount of the metal alkoxide being 50 mol % or less based on 100 mol % of the total of the metal alkoxide and the silane compound represented by the above formula (1),
• (B) 25 to 65 mol % of a silane compound represented by the following formula (2):
• PhSiX23 (2)
• wherein Ph is a phenyl group or substituted phenyl group, and X2 is a hydrolyzable group, and
• (C) 25 to 65 mol % of a silane compound represented by the following formula (3):
• (CH3)2SiX32 (3)
• wherein X3 is a hydrolyzable group, between an optical part and another part;
• and
• heating it to bond the optical part to the another part.