1. Technical Field
The present disclosure relates to infrared-cut (IR-cut) filters, and particularly, to an IR-cut filter and a lens module including the IR-cut filter.
2. Description of Related Art
Sapphires have excellent hardness and wear-resistance, and are used in optics and machinery. The sapphire can be used as a cover to protect lenses received in a lens module. However, quality of images captured by the lens module may be affected by infrared light as the sapphire allows the transmission of infrared light.
Therefore, it is desirable to provide an IR-cut filter and a lens module, which can overcome the limitations described.
Embodiments of the disclosure will be described with reference to the drawings.
Referring to
The substrate 10 is plate shaped and is made of sapphire. Sapphire is a gemstone variety of the mineral corundum, and has a hexagonal crystal structure. The main chemical component of sapphire is aluminum oxide, and the refraction index of the sapphire is from about 1.747 to about 1.760. The growth direction of the sapphire is a-axis (11
The infrared filtering film 20 increases the reflectivity of the substrate 10 in relation to infrared light, and is coated on the first surface 11 of the substrate 10 by a sputter method or an evaporation deposition method. The infrared filtering film 20 includes a number of first high refraction index layers and a number of first low refraction index layers alternately stacked on the substrate 10.
The film structure of the infrared filtering film 20 is represented by (xHyL)η, 30≦η≦80, 1<x<2, 1<y<2; where η is a positive integer. H represents a quarter of optical thickness of a central wavelength of the first high refraction index layers, L represents a quarter of optical thickness of the central wavelength of the first low refraction index layers. xH represents x times a quarter of optical thickness of the central wavelength of the first high refraction index layers, yL represents y times a quarter of optical thickness of the central wavelength of the first low refraction index layers, and η represents a number of cycles of the first low refraction index layer and the first high refraction index layer. In this embodiment, 40≦η≦70, the central wavelength is a middle of a wavelength range which is filtered or reflected by the infrared filtering film 20.
The material of the high refraction index layers is titanium dioxide (TiO2), and the refraction index of the first high refraction index layer is about 2.705. The material of the first low refraction index layers is silicon dioxide (SiO2), and the refraction index of the first low refraction index layers is about 1.499. The materials of the high and first low refraction index layers can be other materials.
The transmissivity of the IR-cut filter 100 at infrared wavelength from about 825 nm to about 1300 nm is lower than about 2%. The infrared lights are filtered after the lights passing through the IR-cut filter 100.
Referring to
The anti-reflection film 30 is configured to increase the transmissivity of the substrate 10 within the visible light spectrum and the reflectivity of the substrate 10 within the infrared light range. The anti-reflection film 30 is coated on the second surface 12 of the substrate 10 by a sputter method or an evaporation deposition method. The anti-reflection film 30 includes a number of second high refraction index layers and a number of second low refraction index layers stacked alternately on the second surface 12 of the substrate 10.
The film structure of the anti-reflection film 30 is represented by (mHnL)δ, 4≦δ≦8, 1<m<2, 1<n<2; where δ is a positive integer. H represents a quarter of optical thickness of a central wavelength of the second high refraction index layers, and L represents a quarter of optical thickness of the central wavelength of the second low refraction index layers. mH represents m times a quarter of optical thickness of the central wavelength of the second high refraction index layers, nL represents n times a quarter of optical thickness of the central wavelength of the second low refraction index layers, and δ represents as a number of cycles of the second low refraction index layers and the second high refraction index layers. In this embodiment, 5≦η≦6, the central wavelength is a middle of a wavelength range filtered or reflected by the anti-reflection film 30.
The material of the second high refraction index layers is titanium dioxide (TiO2), and the refraction index of the second high refraction index layer is about 2.705. The material of the second low refraction index layers is silicon dioxide (SiO2), and the refraction index of the second low refraction index layers is about 1.499. The materials of both layers may be other materials.
The transmissivity of the IR-cut filter 100a at infrared wavelengths, from about 825 nm to about 1300 nm, is lower than about 1%. The transmissivity of the IR-cut filter 100a at infrared wavelengths from about 390 nm to about 760 nm is greater than about 99%. The infrared is filtered from all the light passing through the IR-cut filter 100a.
Referring to
In other embodiments, the IR-cut filter 100 or 100a can be received in the receiving room 113 or can be positioned on the image side 112 for filtering infrared light.
Particular embodiments are shown and described by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiments thereof without departing from the scope of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.
Number | Date | Country | Kind |
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101118892 | May 2012 | TW | national |