Abstract:
An optical image device, having a lens module, an IR cut coating and an image sensor. The lens module has a molded glass aspheric lens and aspheric lens. The molded glass aspheric lens is disposed at one end near an object of which the image is to be captured, the IR cut coating is formed on the molded glass aspheric lens, and the image sensor is located behind the lens module to capture the image of the object. In addition to the lens module, the IR cut coating and the image sensor, the optical image device may further include a protective glass disposed on the image sensor.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates in general to an optical image device, and more particularly, to an optical image device that directly integrates an infrared (IR) cut filter into a molded glass aspheric lens.  
         [0003]     2. Related Art of the Invention  
         [0004]     Electronic products are continuously developed to be lighter, thinner, shorter, smaller and multi-functional. In addition to the digital still camera, the personal camera, the network camera, the cellular phone and the personal digital assistant all have had image devices integrated therein. To be portable and personalized, the image device requires good display quality, small volume and low cost. As the human eye is sensitive to the wavelength range from about 400 nm to about 700 nm, an IR cut filter is typically disposed in front of the charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) in the optical image device to capture an image similar to those captured by the human eye.  
         [0005]      FIG. 1  shows the spectrum of an IR cut filter in a conventional optical image device. As shown in  FIG. 1 , the transmittance of the IR cut filter for different wavelength affects the color performance of the image. Typically, the transmittance of the IR cut filter is about less than 3% for the wavelength between 700 nm and 1000 nm, about 50% for the wavelength between 650 nm and 390 nm, and larger than 85% for the wavelength between 410 nm to 630 nm. Normally, the IR cut filter requires 20-40 layers of optical thin film coated on a glass substrate to obtain the proper transmittance requirement.  
         [0006]      FIG. 2  shows a cross sectional view of a conventional optical image device. Referring to  FIG. 2 , a typical optical image device  100  includes a lens module  102 , an image sensor  104  and an IR cut filter  106 . The light from object sequentially travels through the lens module  102  and the IR cut filter  106  to form image on the image sensor  104  to achieve the image capture. The lens module  102  is normally composed of multiple lenses since a single lens can hardly resolve the problem of chromatic aberration. Therefore, the lens module  102  used in the high performance optical image device is normally a composite of lenses. The image sensor  104  is normally selected from either a charged-coupled device or CMOS. A cover glass  108  is typically implemented on the image sensor  104 , and the IR cut filter  106  can be directly coated on the cover glass  108  of the image sensor  104  or on another glass substrate.  
         [0007]     When the IR cut filter  106  is coated on the cover glass  108  of the image sensor  104 , the specification of dust, scratch and dig etc. will become more severe because cover glass  108  is very close to senor  104 . Any dust drops from cover glass to sensor can block several pixels&#39; image. If the IR cut filter  106  is coated on a separate substrate, it will cause a negative effect on the volume, weight and cost of the optical image device  100 . Because of the above problems, there is a huge demand to coat IR cut filter on lens element itself.  
         [0008]     Since the technology to make polished glass spherical lens is mature and there are a variety of materials available for making polished glass spherical lens, the polished glass spherical lens has been broadly applied in optical industry. However, the polished glass spherical lens has a difficulty in correcting the spherical aberration and astigmatism aberration for large aperture or big field of view applications. To improve on the drawbacks, the aspheric plastic lens can be used to correct spherical aberration. However, the tolerable operation and storage temperature of plastic lens are far inferior to the lens made of glass material, so the application of plastic lens is limited. In addition, the plastic lens is easily scratched so that a planar glass is required for protection. This causes an increase in size and cost.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an optical image device using a molded glass aspheric lens to solve the problems of polished glass spherical lens and aspheric plastic lens.  
         [0010]     The present invention provides an optical image device on which an IR cut filter is formed on a molding glass aspheric lens to reduce volume, weight and cost thereof.  
         [0011]     The optical image device includes a lens module, an IR cut coating and an image sensor. The lens module includes a molded glass aspheric lens and one aspheric lens. The molded glass aspheric lens is the first element of lens module and disposed at one side near the object. The IR cut coating is formed on the molded glass aspheric lens. The image sensor is disposed at the back of the lens module to capture the image of the object. In addition to the lens module, the IR cut coating and the image sensor, the optical image device may further include a cover glass disposed on the image sensor.  
         [0012]     In the present invention, the glass-molding aspheric lens includes a meniscus lens. The meniscus lens has a convex surface and a concave surface. The convex surface is facing the object and the concave surface is facing the image sensor. One of the convex and concave surfaces is coated with the IR cut filter.  
         [0013]     The second element in the lens module can be a molded glass aspheric lens or an aspheric plastic lens. The aspheric lens is a meniscus lens has a positive focal power. The stop of the lens module is located between the molded glass aspheric lens and second element, or between the molded glass aspheric lens and the object.  
         [0014]     In the present invention, the first element is a molded glass aspheric lens and second element is an aspheric lens, for example. The aspheric lens includes a plastic lens or a molded glass lens with a positive focal power. In addition, the stop is located between the first element and the second element or between the first element and the object.  
         [0015]     In one embodiment of the present invention, the optical image device includes a lens module, an IR cut coating and an image sensor. The lens module includes at least one molded glass aspheric lens as first element. The IR cut coating is formed on the first molded glass aspheric lens. The image sensor is disposed at back of the lens module to capture the image of an object. In addition to the lens module, the IR cut coating and the image sensor, the optical image device further comprises a cover glass on the image sensor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     These, as well as other features of the present invention, will become more apparent upon reference to the drawings.  
         [0017]      FIG. 1  shows the spectrum of an IR cut filter in a conventional optical image device.  
         [0018]      FIG. 2  shows the cross sectional view of a conventional optical image device.  
         [0019]      FIG. 3  shows the cross sectional view of an optical image device in a first embodiment of the present invention.  
         [0020]      FIG. 4  shows the cross sectional view of an optical image device in a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]      FIG. 3  shows the cross sectional view of an optical image device in a first embodiment of the present invention. As shown in  FIG. 3 , the optical image device  200  comprises a lens module  206 , an IR cut coating  208  coated on the lens module  206 , and an image sensor  212 .  
         [0022]     The lens module  206  usually comprises of multiple aspheric lenses, for example. In this embodiment, the lens module  206  includes at least one molded glass aspheric lens  202  and an aspheric lens  204 . The aspheric glass-molding lens  202  includes, for example, a meniscus lens with a convex surface A facing to an object and a concave surface B facing to the image sensor  212 . The aspheric lens  204  includes, for example, a meniscus lens. In the example of a meniscus lens, the aspheric lens  204  has a convex surface C facing to the image sensor  212  and a concave lens D facing to the object. The aspheric lens  204  has a positive power.  
         [0023]     The aspheric lens  204  is made of a plastic lens or a molded glass lens, for example. The IR cut coating  208  includes, for example, a multi-layer coating coated on molded glass aspheric lens. As shown in  FIG. 3 , the IR cut coating  208  is preferably coated on the concave surface B of the molded glass aspheric lens  202 . However, when the aspheric lens  204  is also a molded glass lens, the IR cut coating  208  can also be coated on the convex surface C or the concave surface D of the molded glass lens  204 .  
         [0024]     The stop of the lens module  206  is located between the aspheric glass-molding lens  202  and the aspheric lens  204 . The image sensor  212  includes CCD or CMOS, for example. A cover glass  210  is optionally disposed on the image sensor  212 .  
         [0025]     According to the above, in the lens module  206  of the current embodiment, including a molded glass aspheric lens  202  and an aspheric lens  204 , which can be a meniscus lens made of plastic or molded glass. The lens module  206  has to satisfy the following conditions:  
         [0026]     (a) The molded glass aspheric lens  202  includes a meniscus lens with a convex surface A facing to the object.  
         [0027]     (b) The aspheric lens  204  includes a meniscus lens with the convex surface C facing to the image sensor. The focal length of the aspheric lens  204  is positive.  
         [0028]     The stop of the lens module  206  is located between the aspheric glass-molding lens  202  and the aspheric lens  204 .  
         [0029]     When the stop is located between the molded glass aspheric lens  202  and the aspheric lens  204 , the system is more symmetric so coma aberration, distortion aberration and transverse chromatic aberration is lower. The lens parameters of the optical image device  200  is shown as Table 1  
                                                     TABLE 1                                   Radius of                   Curvature   Thickness   Refractive Index                                        Object   ∞   ∞               1   1.91207   0.544152   Nd = 1.806100,                       V = 40.9           2   2.05045   0.050712           Stop (STO)   ∞   0.169324           4   −5.082443   1.411840   Nd = 1.806100,                       Vd = 40.9           5   −1.90768   0.763565           6   ∞   0.500000   BK7           7   ∞   0.600000           Image   ∞   0.000000           (IMG)                      
 
         [0030]     Table 2 shows the coefficients of the aspheric lens.  
                                                         TABLE 2                                   S1   S2   S4   S5                                    K   0.102844   −11.980803   19.357042   −0.709569       A   0.324435E−2   0.262093   −0.301406E−1   0.241326E−3       B   0.196235E−2   0.262129   0.531035E−1   0.246487E−1       C   0.519398E−3   0.108598E−1   0.295892   0.322935E−2       D   0.700962E−3   0.240398E+1   −0.251002   −0.118364E−2                  
 
         [0031]     Z=ch 2 /{1+[1−(1+K)c 2 h 2 ] 1/2 }+Ah 4 +Bh 6 +Ch 8 +Dh 10  is the aspheric formula, where c is the radius of curvature and Z is the sag value.  
         [0032]      FIG. 4  shows a second embodiment of an optical image device according to the present invention. In  FIG. 5 , the structure of the current embodiment is similar to that of the first embodiment. In this embodiment, similarly, the optical image device  400  includes a lens module  406 , an IR cut coating  408  coated on the lens module  406 , and an image sensor  412 .  
         [0033]     The lens module  406  comprises one molded glass aspheric lens  402  and an aspheric lens  404 . The molded glass aspheric lens  402  includes a meniscus lens with a convex surface A facing to an object and a concave surface B facing to an image sensor  412 , for example. The aspheric lens  404  includes, for example, a meniscus lens with a positive focal power.  
         [0034]     The aspheric lens  404  includes a plastic lens or a molded glass lens, for example. The IR cut coating  408  includes a multi-layer coating coated on a glass material. As shown in  FIG. 4 , preferably, the IR cut coating  408  is formed on the concave surface B of the molded glass aspheric lens  402 . However, when the aspheric lens  404  is also made of molded glass lens, the IR cut coating  408  can also be coated on the aspheric lens  404 .  
         [0035]     In this embodiment, the stop of the lens module  406  is located between the molded glass aspheric lens  402  and the object. The image sensor  412  includes, for example, a charge-coupled device or a CMOS sensor. A cover glass  410  can be optionally disposed on the image sensor  412 .  
         [0036]     According to the above descriptions, in the lens module  406  of the invention, the aspheric glass-molding lens  402  includes at least one molded glass aspheric lens, and the aspheric lens  404  is made of one aspheric plastic or molded glass lens. The lens module  406  has to satisfy the following conditions:  
         [0037]     (a) The aspheric glass-molding lens  402  includes a meniscus lens with a convex surface A facing to the object.  
         [0038]     (b) The aspheric lens  404  includes a meniscus lens with a positive focal length.  
         [0039]     (c) The stop of the lens module  406  is located between the aspheric glass-molding lens  402  and the object.  
         [0040]     In the lens module  406  of the current embodiment, since the stop is located between the aspheric glass-molding lens  402  and the object, the system distortion aberration is relatively large compared to the first embodiment. However, as the stop is located between the aspheric glass-molding lens  402  and the object, the distance between the exit pupil position and the image sensor  412  is longer, such that the incident angle of the edge chief ray incident onto the image sensor  412  is smaller. Consequently, the relative illumination at the edge is better than previous embodiment.  
         [0041]     Accordingly, the present invention has at least the following advantages:  
         [0042]     1. The lens module in the optical image device provided by the present invention includes a molded glass aspheric lens and one aspheric lens. The IR cut coating can be directly coated on the molded glass aspheric lens to save the cost of fabricating the IR cut coating in a separate glass. Further, the size of the optical image device is greatly reduced.  
         [0043]     2. In the optical image device provided by the present invention, the molded glass aspheric lens and the aspheric lens are made of glass material, such that the position for coating the IR cut filter is more flexible.  
         [0044]     3. In the optical image device provided by the present invention, the molded glass aspheric lens is more rugged and can withstand scratching. Therefore, the first lens made of molded glass is more advantageous.  
         [0045]     4. In the optical image device of the present invention, the IR cut coating can be directly coated on the molded glass aspheric lens to save the fabrication of the cover glass on the image sensor. Therefore, the size and the cost of the optical image device can be further reduced.  
         [0046]     5. In the optical image device of the present invention, the IR cut coating can be directly coated on the molded glass aspheric lens, such that the fabrication of an additional glass substrate is saved. The size and cost of the optical image device is further reduced.  
         [0047]     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.