1. Field of the Invention
The present invention relates to passive light-transmitting elements and methods for making the same, and particularly to a light-transmitting element for an imaging system and a method for making the light-transmitting element.
2. Related Art
With the ongoing development of optical technology, light-transmitting elements are now in widespread use in a variety of applications. Polymethyl methacrylate (PMMA) is a transparent thermoplastic resin which has a visible light transmittance higher than that of glass, excellent optical properties, and low birefringence. Therefore PMMA has long been used as a material for a wide variety of optical products such as optical lenses and optical discs.
In recent years, there has been an increasing demand for PMMA to be used as a light-transmitting element for the plastic lens of imaging systems. The light-transmitting element for the lens functions to propagate and diffuse light that enters from a certain direction, such that the light exits in the direction of imaging.
In a typical imaging system, the light-transmitting element is a light-transmitting plate. If the distance traveled by light through the light-transmitting plate is relatively long, the amount of light lost in the light-transmitting plate is correspondingly high. For preventing or minimizing loss of light, the material of the light-transmitting plate is required to have a high light transmittance. Thus PMMA has been routinely employed for use in light-transmitting plates.
However, a light-transmitting element made of PMMA still has relatively high light reflection at interfaces thereof. This reduces the overall light transmittance of the light-transmitting element. Even when a light-transmitting element is configured to be optically optimized, the light transmittance is generally only in a range up to 92 percent. That is, at least 8 percent of light is reflected. Thus the resolution of the image obtained in the imaging system is decreased, and the quality of the obtained image may not be satisfactory.
Therefore, a light-transmitting element and a method for making the light-transmitting element which overcome the above-described problems are desired.
An object of the present invention is to provide a light-transmitting element for an imaging system which has a high light transmittance.
Another object of the present invention is to provide a method for making a light-transmitting element for an imaging system which has a high light transmittance.
To achieve the first of the above objects, a light-transmitting element for imaging system includes a substrate made of polymethyl methacrylate, and at least one coating film. The substrate has a first surface, and a second surface opposite to the first surface. The coating is formed on at least one surface of the substrate. The coating film is selected from the group consisting of a single layer and a plurality of layers, and comprises a material selected from the group consisting of tantalum pentoxide, magnesium fluoride, silicon oxide, and any mixture or combination thereof.
To achieve the second of the above objects, a method for forming a light-transmitting element comprises the steps of: providing a substrate made of polymethyl methacrylate, the substrate having a first surface and a second surface opposite to the first surface; and depositing at least one coating film on at least one surface of the substrate. The coating film is selected from the group consisting of a single layer and a plurality of layers, and comprises a material selected from the group consisting of tantalum pentoxide, magnesium fluoride, silicon oxide, and any mixture or combination thereof.
A main advantage of the invention is that the light transmittance of the light-transmitting element is improved. Accordingly, the quality of images obtained by the imaging system is enhanced.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
The substrate 12 is made of polymethyl methacrylate (PMMA) and has a thickness of 0.85 mm. The coating film 14 is made of silicon oxide (SiO2), and has a thickness of 67.22 nm.
A method for making the light-transmitting element 10 comprises the steps of: providing a substrate 12 made of PMMA having a first surface 122 and a second surface 124 opposite to the first surface 122; and depositing a coating film 14 made of SiO2 on the first surface 122 of the substrate 12 by electron beam evaporation.
The coating film 14 can also be deposited on the substrate 12 in any conventional manner, such as by way of (but not limited to) magnetron sputter vapor deposition (MSVD), chemical vapor deposition (CVD), spray pyrolysis (i.e., pyrolytic deposition), atmospheric pressure CVD (APCVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PEVCD), plasma assisted CVD (PACVD), thermal or electron-beam evaporation, cathodic arc deposition, plasma spray deposition, and wet chemical deposition (e.g., sol-gel, mirror silvering etc.). It is noted that sputter deposited coatings are perceived by some to be less mechanically durable than coatings deposited by spray pyrolysis or CVD-type coating methods. Examples of suitable CVD coating apparatuses and methods are found, for example (but not limiting the present invention to), in U.S. Pat. Nos. 3,652,246, 4,351,861, 4,719,126, 4,853,257, 5,356,718 and 5,776,236.
When external light enters the coating film 14 of the light-transmitting element 10, travels through the substrate 12, and exits from the second surface 124, the light transmittance of the light-transmitting element 10 is increased. The average light transmittance of the light-transmitting element 10 at light wavelengths of 800 nm, 750 nm, and 350 nm can be seen from the following table 1:
When external light enters the coating film 22 of the light-transmitting element 20, travels through the substrate 12, and exits from the second surface 124 in the direction of the coating film 24, the light transmittance of the light-transmitting element 20 is increased. The average light transmittance of the light-transmitting element 20 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following table 2:
In alternative embodiments, a material with a special refractive index and/or a thickness of the coating film 22 and/or the coating film 24 can be varied according to particular requirements. The average light transmittance of various different embodiments of the light-transmitting element 10 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following tables 3 through 6:
A method for making the light-transmitting element 30 comprises the steps of: providing the substrate 12 made of PMMA having the first surface 122 and the second surface 124 opposite to the first surface 122; depositing the first inner layer 324 on the first surface 122 of the substrate 12; depositing the first outer layer 322 on the first inner layer 324 of the substrate 12 by electron beam evaporation; depositing the second inner layer 342 on the second surface 124 of the substrate 12 by electron beam evaporation; and depositing the second outer layer 344 on the second inner layer 342 of the substrate 12 by electron beam evaporation.
When external light enters the first hybrid coating film 32 of the light-transmitting element 30, travels through the substrate 12, and exits from the second surface 124 in the direction of the second hybrid coating film 34, the light transmittance of the light-transmitting element 30 is increased. The average light transmittance of the light-transmitting element 30 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following table 7:
In alternative embodiments, a material and/or a thickness of the first hybrid coating film 32 and/or the second hybrid coating film 34 can be varied according to particular requirements. For instance, the first outer layer 322 is made of SiO2, and has a thickness of 8.52 nm. The first inner layer 324 is made of MgF2, and has a thickness of 69.56 nm. The second inner layer 342 is made of SiO2, and has a thickness of 8.55 nm. The second outer layer 344 is made of MgF2, and has a thickness of 69.19 nm. The average light transmittance of the above-described alternative embodiment of the light-transmitting element 30 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following table 8:
In a further alternative embodiment, the first outer layer 322 is made of Ta2O5, and has a thickness of 5.59 nm. The first inner layer 324 is made of MgF2, and has a thickness of 90.46 nm. The second inner layer 342 is made of SiO2, and has a thickness of 57.69 nm. The second outer layer 344 is made of MgF2, and has a thickness of 91.36 nm. The average light transmittance of the above-described further alternative embodiment of the light-transmitting element 30 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following table 9:
In a still further alternative embodiment, the first outer layer 322 is made of SiO2, and has a thickness of 53.08 nm. The first inner layer 324 is made of Ta2O5, and has a thickness of 4.14 nm. The second inner layer 342 is made of SiO2, and has a thickness of 37.73 nm. The second outer layer 344 is made of MgF2, and has a thickness of 72.31 nm. The average light transmittance of the above-described still further alternative embodiment of the light-transmitting element 30 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following table 10:
In a yet further alternative embodiment, the first outer layer 322 is made of SiO2, and has a thickness of 51.00 nm. The first inner layer 324 is made of Ta2O5, and has a thickness of 3.20 nm. The second inner layer 342 is made of Ta2O5, and has a thickness of 3.21 nm. The second outer layer 344 is made of MgF2, and has a thickness of 97.14 nm. In addition, the first hybrid coating film 32 further includes an innermost layer, which is made of MgF2 and has a thickness of 56.19 nm. The second hybrid coating film 34 further includes an innermost layer, which is made of SiO2 and has a thickness of 50.95 nm. The average light transmittance of the above-described yet further alternative embodiment of the light-transmitting element 30 at light wavelengths of 800 nm, 750 nm, 550 nm and 350 nm can be seen from the following
It is can be seen that a material and/or a thickness of the substrate 12 can be varied according to a particular requirements. Also, a thickness of the coating films 22, 24, 32, 34 can be varied according to particular requirements.
It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
Number | Date | Country | Kind |
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200410026475.4 | Jun 2004 | CN | national |