| 摘要 |
PURPOSE:To prevent the deterioration of the S/N of signal light due to light reflection by facing the other surface, which does not form the diffraction grating of a grating lens, to a light source. CONSTITUTION:Emitting light 4 from the light source 2 made of a semiconductor laser transmits a beam splitter 6 and makes incident on a collimator lens 12 composed of the grating lens 10, which is formed for instance with acrylic resin. On its one surface 9, coaxial circular fine pitch diffraction gratings 8 with rectangular or saw-toothed sections are formed at different intervals. The other surface of the lens 10 is flat and another surface 11 not forming the diffraction grating 8 is faced the light source 2. Since the light incident on the other surface not forming the diffraction grating of the grating lens 10 becomes divergent, the reflected light also becomes divergent. Accordingly the quantity of reflected light led to a photodetector 24 can be substantially reduced to improve the S/N. |
