An optical device comprises an imaging element and a package accommodating the imaging element and having an opening the top view of which is square. An optical lowpass filter having a square major surface is adhered to the opening with an ultraviolet curing adhesive. The optical lowpass filter comprises a 45 DEG split birefringence plate so cut and machined as to split a beam of light to two beams the angle between which is 45 DEG and to form two split patterns. The optical lowpass filter also comprises a color correction filter and an antireflection filter. A cut or rectangular groove as a part for passing ultraviolet radiation to cure the ultraviolet curing adhesive is formed in the optical lowpass filter.
