The optical device 1, wherein the peripheral portion is covered by {TAIL ~ the dielectric film} which has {HEAD ~ an optical thickness} of an odd multiple of λ/4, wherein λ is an oscillation wavelength 
The optical device 1 , wherein the peripheral portion is covered by { TAIL ~ the dielectric film } which has { HEAD ~ an optical thickness } of an odd multiple of λ/4 , wherein λ is an oscillation wavelength
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH