Abstract: A spectral filter (10) is provided with a long-pass filter (12) and a short-pass filter (13). The long-pass filter (12) has a film thickness gradient GL wherein film thickness increases monotonically in a single direction, and transmits light of a wavelength region longer than a cut-off wavelength WL. The short-pass filter (13) has a film thickness gradient GS wherein film thickness increases monotonically in a single direction, and transmits light of a wavelength region shorter than a cut-off wavelength WS. The long-pass filter (12) and the short-pass filter (13) are overlapped such that the single directions match each other. At the positions in the single directions, a transmittance peak is formed by the cut-off wavelength WL being shorter than the cut-off wavelength WS. The film thickness gradient GL is greater than the film thickness gradient GS.

Abstract: In this optical filter, each side of a substrate that is at most 0.3 mm in thickness is coated with a multilayer film. Both of the multilayer films are under compressive stress, and the optical filter satisfies the relation F??1.25t+1.525 (where F represents the ratio of the strength of the optical filter to the strength of the substrate (the strength of the optical filter with the substrate coated divided by the strength of the uncoated substrate) and t represents the thickness of the substrate (in mm)).

Abstract: A spectral filter (10) is provided with a long-pass filter (12) and a short-pass filter (13). The long-pass filter (12) has a film thickness gradient GL wherein film thickness increases monotonically in a single direction, and transmits light of a wavelength region longer than a cut-off wavelength WL. The short-pass filter (13) has a film thickness gradient GS wherein film thickness increases monotonically in a single direction, and transmits light of a wavelength region shorter than a cut-off wavelength WS. The long-pass filter (12) and the short-pass filter (13) are overlapped such that the single directions match each other. At the positions in the single directions, a transmittance peak is formed by the cut-off wavelength WL being shorter than the cut-off wavelength WS. The film thickness gradient GL is greater than the film thickness gradient GS.

Abstract: In this optical filter, each side of a substrate that is at most 0.3 mm in thickness is coated with a multilayer film. Both of the multilayer films are under compressive stress, and the optical filter satisfies the relation F??1.25t+1.525 (where F represents the ratio of the strength of the optical filter to the strength of the substrate (the strength of the optical filter with the substrate coated divided by the strength of the uncoated substrate) and t represents the thickness of the substrate (in mm)).

Abstract: A multilayer film of an IR cut filter has the following characteristics. The multilayer film is formed by stacking a high refractive index layer 4 and a low refractive index layer 5 on a substrate 2 and average transmittance in a wavelength region of 450 nm to 600 nm is equal to or greater than 90%. A wavelength with transmittance of 50% at an incidence angle of 0° is in a range of 650±25 nm. 0.5%/nm<|DT|<7%/nm is satisfied. A difference in wavelength with transmittance of 50% between an incidence angle of 0° and an incidence angle of 30° is equal to or less than 8 nm. A difference in wavelength with transmittance of 75% between an incidence angle of 0° and an incidence angle of 30° is equal to or less than 20 nm. Here, |DT| is a value (%/nm) of |(T70%?T30%)/(?70%??30%)| at the incidence angle of 0°, T70% is a transmittance value of 70%, T30% is a transmittance value of 30%, ?70% is a wavelength (nm) with transmittance of 70%, and ?30% is a wavelength (nm) with transmittance of 30%.

Abstract: Provided is an optical pickup device which suppresses the decrease of light amount and performs conversion to circular polarization light, wherein the optical pickup device includes a beam splitter and a raising mirror on each of which a layered member is formed, and the optical pickup device satisfies conditional expressions relating to intensities of S-polarized light and P-polarized light with respect to the beam splitter of a laser beam emitted from a semiconductor laser element, reflectances of S-polarized light and P-polarized light on the beam splitter, a reflection phase difference obtained by subtracting a phase of S-polarized light from a phase of P-polarized light after the reflection, reflectances of S-polarized light and P-polarized light on the raising mirror, and a reflection phase difference obtained by subtracting a phase of S-polarized light from a phase of P-polarized light after the reflection.

Abstract: Provided is an optical pickup device which suppresses the decrease of light amount and performs conversion to circular polarization light, wherein the optical pickup device includes a beam splitter and a raising mirror on each of which a layered member is formed, and the optical pickup device satisfies conditional expressions relating to intensities of S-polarized light and P-polarized light with respect to the beam splitter of a laser beam emitted from a semiconductor laser element, reflecances of S-polarized light and P-polarized light on the beam splitter, a reflection phase difference obtained by subtracting a phase of S-polarized light from a phase of P-polarized light after the reflection, reflectances of S-polarized light and P-polarized light on the raising mirror, and a reflection phase difference obtained by subtracting a phase of S-polarized light from a phase of P-polarized light after the reflection.

Abstract: A non-polarizing beam splitter has a first prism; one or more ground layer(s) made of a dielectric material which is (are) formed on a slant face of the first right angle prism; an Au layer having thickness of 13 to 35 nm which is formed on the ground layer; one or more protective layer(s) made of a dielectric material which is (are) formed on the Au layer; and a second prism which is jointed to an outermost layer of the protective layer via adhesive. The non-polarizing beam splitter divides light at wavelength of 640 nm to 820 nm into transmission light and reflection light by a predetermined ratio.

Abstract: A non-polarizing beam splitter has a first prism; one or more ground layer(s) made of a dielectric material which is (are) formed on a slant face of the first right angle prism; an Au layer having thickness of 13 to 35 nm which is formed on the ground layer; one or more protective layer(s) made of a dielectric material which is (are) formed on the Au layer; and a second prism which is jointed to an outermost layer of the protective layer via adhesive. The non-polarizing beam splitter divides light at wavelength of 640 nm to 820 nm into transmission light and reflection light by a predetermined ratio.