| 摘要 |
A first alternating period layer (5) consisting of low-refractive-index laye rs (2) and high-refractive-index layers (3), a second alternating period layer (6) consisting of low-refractive-index layers (2) or high-refractive-index layers (3) and intermediate-refractive-index layers (4), and a third alternating period layer (7) consisting of low-refractive-index layers (2) a nd high-refractive-index layers (3) are provided on a transparent substrate in the order mentioned. The refractive index of the intermediate-refractive-ind ex layers (4) is higher than that of the low-refractive-index layers (2) and lower than that of the high-refractive index layers (3). In addition, the intermediate-refractive-index layers (4) contain the materials of the low- refractive-index layers (2) and the high-refractive-index layers (3). A dichroic mirror configured in this way has a narrow color separating band between a transmission wavelength band and a reflection wavelength band and therefore has a good color separating efficiency. Accordingly, a projection type display unit using this mirror provides a good color reproducibility while retaining a high spectrum utilization efficiency. |
