| 摘要 |
PROBLEM TO BE SOLVED: To materialize low reflectance independent of the dispersion in manu facture of silicon nitrides. SOLUTION: A reflection preventive film is composed of the silicon nitride 101 of the first layer where the refractive index is 1.82 to 2.00 and the thickness of an optical film is seventeen-hundredths to twenty three-hundredths as large as the oscillated wavelength and the silicon oxide 102 of the second layer where the thickness of the optical film is three-hundredths to fifteen-hundredths as large as the oscillated wavelength. Here, selecting the silicon nitride and the silicon oxide of such film thickness and refractive indexes that the reflectance becomes minimum to the laser oscillating wavelength will enable the reflectance to be under 0.6% even if the dispersion in manufacture of silicon nitrides and silicon oxides occurs. This way, a reflection preventive film which has stable low reflectance independent of the refractive index and the film thickness of the silicon nitride 101 is provided, and the yield in single vertical mode of a DFB (distributed feedback type) can be improved. |
