| 摘要 |
PURPOSE:To improve the light utilization efficiency by providing unidirectional converging operation to a double diffraction grating which performs the spectral wavelength diffraction of incident light. CONSTITUTION:A condenser lens 7 is provided on the optical path of luminous flux which is emitted by an output optical fiber 6 and has wavelengths lambda1 and lambda2. Further, the double diffraction grating 8 is arranged on the optical path of the light which is converged by the lens 7 slantingly at a Bragg angle to the optical axis of the incident light. This grating 8 has diffraction gratings 8a and 8b formed on both the top and reverse surfaces of a parallel flat plate while equal in grating direction and slightly different in pitch. Input fibers 9 are provided in accordance with the number of light beams which are obtained by diffracting the light spectrally by the gratings 8a and 8b and differ in wavelength. In this constitution, the grating 8b on the reverse surface side is made capable of the unidirectional converging operation to cancel and remove astigmatism caused by incidence on the grating 8. Consequently, the quantity of the light incident on the input fiber is made large and the light loss can be reduced. |
