| 摘要 |
PROBLEM TO BE SOLVED: To moderate position accuracy when a long pass filter and a short pass filter are placed one on top of another and maintain good permeability at any position in one direction in which the film thickness changes.SOLUTION: Each of the long pass filter LP, short pass filter SP, and band pass filter BP of a spectral filter 10 is placed one on top of another in such a way that the film thickness monotonously increases as it goes in one direction, the cutoff wavelength is monotonously extended as the film thickness increases, and the one direction matches each other. The film thickness gradient GL of the long pass filter LP is larger than the film thickness gradient GB of the band pass filter BP. At each position in the one direction, the cutoff wavelength WL of the long pass filter LP is shorter than the cutoff wavelength WBon short wavelength side of the band pass filter BP, and the cutoff wavelength WS of the short pass filter SP is longer than the cutoff wavelength WBon long wavelength side of the band pass filter BP, thereby allowing light in a wavelength region between the cutoff wavelength WBand the cutoff wavelength WBto pass through.SELECTED DRAWING: Figure 1 |
