CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Taiwanese Application Serial No. 107138611, filed on Oct. 31, 2018. The entirety of the application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

1. Technical Field

The present disclosure relates to light shielding sheets, and, more particularly, to a light shielding sheet for a lens.

2. Description of the Prior Art

In recent years, with the rapid development of portable electronic devices, cameras, mobile phones or tablets have emphasized the camera function. The optical lens module is configured to receive incident light from a target object and direct the incident light through a lens set including a plurality of optical lenses. The lens set is optimized to eliminate various aberrations, resulting in the best quality of the final image of the image sensing element.

Ideally, the incident light should contain only the surface light of the subject. However, due to the surrounding environment, the light incident on the optical lens module also contains the stray light from the non-target object. In order to avoid such unnecessary stray light affecting the image quality, a light shielding sheet is generally disposed at the front end of the optical lens module. The light shielding sheet absorbs the stray light incident near the edge of the lens, and thus reduces flares and ghosts formed by the stray light interfering with each other after multiple reflections in the optical lens module.

Due to the convenience of production, the current light shielding sheets are mostly made of a plastic material, and black ink is coated on the surface of the light shielding sheet as a light absorbing material. However, such a structure still does not completely block the light. In addition, since the light through hole of the light shielding sheet has right-angled edges, it cannot effectively block the harmful light incident obliquely.

Therefore, how to improve the light shielding effect of a light shielding sheet is becoming an urgent issue in the art.

SUMMARY

In view of the problems of the prior art, the present disclosure provides a light shielding sheet for a lens, comprising: a metal substrate, including: a first surface; a second surface opposing the first surface; a first through light hole being in communication with the first surface and having hole radiuses gradually decreasing in a direction from the first surface to the second surface, a ratio of a depth of the first through light hole to a difference between two of the hole radiuses at two ends of the first through light hole being less than or equal to 0.5; and a second through light hole being in communication with the first through light hole and the second surface; and a light extinction film covering the first surface, the second surface, a hole wall of the first through light hole and a portion of a hole wall of the second through light hole of the metal substrate.

In an embodiment, the metal substrate is made of one selected from the group consisting of iron, copper, aluminum, silver and gold.

In an embodiment, an exposed portion of the hole wall of the second through light hole exposed from the light extinction film has a width less than 5 μm in a direction extending from an axis of the second through light hole. In another embodiment, the width of the exposed portion of the hole wall of the second through light hole in the direction extending from the axis of the second through light hole is less than 3 μm.

In an embodiment, the hole wall of the first through hole is an annular inclined plane. In another embodiment, the hole wall of the first through hole is an annular concave plane.

In an embodiment, the light extinction film includes an anti-reflection film and a light absorption film disposed between the anti-reflection film and the metal substrate. In another embodiment, the light absorption film and the anti-reflection film are made of at least one selected from the group consisting of metal, metal nitride, metal hydrogen, metal oxide, a semiconductor element, semiconductor element nitride, semiconductor element hydrogen and semiconductor element hydroxide.

In an embodiment, each of the light absorption film and the anti-reflection film has a plurality of layers having different refractive indexes and stacked on one another in a high refractive index-low refractive index interaction.

In an embodiment, the metal is Ti or Cr.

In an embodiment, the light absorption film includes a Ti layer and has a refractive index of 1.7 to 2.5 for a wavelength of 400 to 700 nm and an absorption index less than 3.6.

In an embodiment, the semiconductor element is Si or Ge.

In an embodiment, each of the light absorption film and the anti-reflection film includes a Ti layer and a Si: H layer that has a total thickness less than a half of a total thickness of the Ti layer.

In an embodiment, each of the light absorption film and the anti-reflection film includes a SiO2layer and a Si: H layer that has a total thickness less than a half of a total thickness of the SiO2layer.

In an embodiment, the anti-reflection film includes a Si: H layer, a SiO2layer and a Ti layer having different refractive indexes and stacked on one another in a high refractive index-low refractive index interaction. In another embodiment, the Si: H layer has a refractive index of 4.7 to 5.2 for a wavelength of 400 to 700 nm and an absorption index less than 2, the SiO2layer has a refractive index of 1.46 to 1.51 and an absorption index less than 2, and the Ti layer has a refractive index of 1.85 to 4.1 and an absorption index less than 3.4.

In an embodiment, the light extinction film has an average reflective index less than 0.15% for a wavelength of 400 to 700 nm.

In an embodiment, the light extinction film total thickness less than 500 nm.

In an embodiment, the light extinction film has a chromaticity coordinate, in which 0<L*<1.4, |a*|<1, and −2.5<b*<0.

In the light shielding sheet according to the present disclosure, the light extinction film covers the first and second surfaces of the metal substrate, and the hole radiuses gradually decrease in a direction from the first surface to the second surface. Therefore, the light absorption is increased, the reflective index is reduced, and the problem of the prior art that the light shielding sheet cannot effectively shield ambient stray light is solved.

