HK1222961B - Method of manufacturing the achromatic doublet prism array - Google Patents

Description

Method for manufacturing an achromatic bi-prism array

Technical Field

The present disclosure relates to a wide-angle camera using an achromatic dual-prism array and a method for manufacturing the same.

Background Art

There are many ways to capture wide-angle images; one approach is based on an N x N lens array system, which provides a compact and smaller camera module compared to more traditional camera modules that employ a single lens. This lens array technology uses prisms and other optical components to form an optical system that increases the viewing angle. However, the use of prisms introduces chromatic aberration, significantly reducing the modulation transfer function (MTF) of the optical system and, consequently, degrading the resulting image quality.

Summary of the Invention

An optical system and method for manufacturing the same disclose a prism-based optical system that reduces chromatic aberration. Based on wafer-level manufacturing, a novel achromatic dual-prism array features two asymmetric prisms that improve optical resolution without unduly complicating the wafer-level fabrication process. As used herein, the term "two asymmetric prisms" means that the shape of the first prism is asymmetric relative to the second prism. That is, the two prisms are inversely coupled to each other. The concept of asymmetry is discussed in more detail below.

In one embodiment, a wide-angle camera has a sensor having a plurality of pixel sub-arrays and an array of optical elements disposed on a first side of a substrate, wherein each of the optical elements is capable of forming an image from a field of view onto a different pixel sub-array. The wide-angle camera also includes an array of achromatic bi-prisms on a second side of the substrate, wherein each of the achromatic bi-prisms is aligned to provide a viewing angle using a different optical element, enabling the sensor to capture a wide-angle field of view while maintaining a compact form factor.

In another embodiment, in a miniaturized wide-angle camera of the type having an optical component array and a corresponding single prism array that can cooperate to capture a wide field of view, wherein the optical component array is formed on a first side of a substrate and the single prism array is formed on a second side of the substrate, and each of the single prisms is aligned with a different optical component to cause chromatic aberration, the improvement includes implementing the single prism array as an achromatic dual prism array formed using a wafer-level manufacturing method on the second side of the substrate, so that each achromatic dual prism is aligned with a different optical component, and the achromatic dual prism array and the optical component array cooperate to capture the wide field of view in a manner that reduces chromatic aberration.

In another embodiment, a method of fabricating an achromatic dual-prism array having N x N segments includes forming a first prism array on a substrate, each first prism being disposed within one of the N x M segments and composed of a first material; and forming a second prism array on the first prism array, each second prism being disposed within one of the N x M segments and composed of a second material different from the first material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary wide-angle camera using an achromatic dual-prism array in one embodiment.

FIG. 2 shows a front view of the camera of FIG. 1 , illustrating an embodiment in which the achromatic bi-prism array has nine elements arranged in a three-by-three array.

3 is a side cross-sectional view through line AA of the camera of FIG. 1 and FIG. 2 , illustrating three exemplary sub-cameras in one embodiment.

FIG. 4 shows further illustrative details of the sub-camera of FIG. 3 in one embodiment.

FIG5 shows an MTF full field of view graph of the optical performance of the exemplary sub-cameras of FIG3 and FIG4 in one embodiment.

FIG. 6 shows a point diagram generated by simulating the sub-cameras of FIG. 3 and FIG. 4 configured as described in FIG. 5 in one embodiment.

FIG. 7 shows a prior art wafer-level lens having three substrates and five surfaces for forming an image on a sensor array.

FIG. 8 is a graph illustrating the full-field MTF curve of the conventional wafer-level lens of FIG. 7 .

FIG. 9 is a point graph illustrating the optical performance of the wafer-level lens of FIG. 7 .

FIG. 10 shows another prior art wafer-level lens similar to the wafer-level lens of FIG. 7 but including a single prism.

FIG. 11 is a graph illustrating the MTF full field of view curve of the conventional optical performance of the wafer-level lens of FIG. 10 .

FIG. 12 is a point graph illustrating the optical performance of the wafer-level lens of FIG. 10 .

13 is a flow chart illustrating an exemplary method for fabricating a wide-angle camera with an achromatic dual-prism array.

FIG. 14 is a schematic diagram illustrating the appearance of an exemplary camera assembly in one embodiment, which includes an achromatic dual prism array stacked on a lens array assembly, an imaging sensor array, and an imaging substrate.

15A-C are schematic cross-sectional views illustrating steps of the method of FIG. 13 .

FIG. 16 is a schematic cross-sectional view illustrating an exemplary camera having a 2×2 achromatic bi-prism array formed by the method of FIG. 13 .

Description of reference numerals:

100: Camera; 102: Achromatic biprism array; 104: Lens array; 106: Sensor array; 108: Device; 110: Wide angle; 111: Field of view; 202(1)-(9): Achromatic biprism; 302(2), 302(5), 302(8): Optical components; 304(2), 304(5), 304(8): Pixel sub-array; 306, 306(2), 306(5), 306(8): Sub-camera; 402: First prism; 403: Bonding surface; 404: Second prism; 406: First substrate; 408: First lens; 410: Second substrate; 412: Second lens; 414: Third lens; 416: Third substrate; 418: Fourth lens; 420: Fifth lens; 500: MTF full field of view curve; 600: point plot; 700: wafer-level lens; 702(1)-(3): substrate; 704(1)-(5): surface; 706: sensor array; 1000: wafer-level lens; 1002: single prism; 1300: method; 1301, 1302, 1304, 1306, 1308, 1310, 1312, 1314, 1316, 1317, 1318, 1320: steps; 1400: camera assembly; 1402: achromatic dual prism array; 1408: imaging substrate; 1500: first mold; 1502 (1)-(4), 1510: area; 1506: substrate; 1508: second mold; 1514: lens array assembly; 1516: image sensor; 1600: camera; 1602: achromatic bi-prism array; 1604: first prism; 1606: second prism; 1614: lens array; 1616: sensor array.

DETAILED DESCRIPTION

FIG1 shows a side cross-sectional view of an exemplary wide-angle camera 100 using an achromatic biprism array 102. FIG2 shows a front view of the camera 100 illustrating the achromatic biprism array 102 having nine achromatic biprisms 202 (1)-(9) arranged in a three-by-three array. The camera 100 is shown in a device 108 selected from the group consisting of a smartphone, a personal camera, a wearable camera, etc. The camera 100 is suitable for use in any application requiring a compact image capture device with a wide-angle field of view. The camera 100 also includes a lens array 104 and a sensor array 106. The lens array 104 and the achromatic biprism array 102 enable the camera 100 to capture a wide-angle 110 field of view 111.

FIG3 is a side cross-sectional view through line AA of camera 100 illustrating three exemplary achromatic biprisms (202(2), 202(5), and 202(8)), corresponding optical components (302(2), 302(5), and 302(8)), and corresponding pixel sub-arrays (304(2), 304(5), and 304(8)). Each achromatic biprism 202, corresponding optical component 302, and corresponding pixel sub-array 304 form a sub-camera 306, where camera 100 has nine such sub-cameras. In the example of FIG3, sub-camera 306 includes achromatic biprism 202(2), corresponding optical component 302(2), and corresponding pixel sub-array 304(2).

FIG4 shows further exemplary details of the sub-camera of FIG3. Optical assembly 302(2) is a five-surface wafer-level lens structure having a first substrate 406 with a first lens 408, a second substrate 410 with a second lens 412 and a third lens 414, and a third substrate 416 with a fourth lens 418 and a fifth lens 420. Substrates 406, 410, and 416 are, for example, glass. Although lenses 408, 412, 414, 418, and 420 are shown in this embodiment, other optical assemblies with more or fewer lenses, or with different types of lenses, may be used without departing from the scope of the present invention.

Each achromatic biprism 202 is formed with two asymmetric prisms. The achromatic biprism 202 (2) has a first prism 402 and a second prism 404, the first prism 402 having a low Abbe number (V1) and a high refractive index (n1), and the second prism 404 having a high Abbe number (V2) and a low refractive index (n2). For example, in FIG4 , the first prism 402 has an angle of 13.6 degrees, a refractive index (n1) of 1.6, and an Abbe number (V1) of 30, while the first prism has an angle of -17.2 degrees, a refractive index (n2) of 1.5, and an Abbe number (V2) of 57. It should be understood that these values can be changed without departing from the scope of the present application. The achromatic biprism 202 (2) is used to change the viewing angle of the optical component 302 (2) and the sub-camera 306. The configuration of each achromatic biprism 202 is selected to change the viewing angle of the corresponding sub-camera 306 so that the camera 100 captures a wide angle 110 field of view 111. As will be discussed in further detail below, the achromatic biprism 202(2) is formed directly on a surface of the first substrate 406 (opposite the lens 408), thereby reducing manufacturing time and cost. Furthermore, the use of the achromatic biprism 202 significantly improves the optical resolution of the camera 100, so that the camera 100 is comparable in quality to cameras without prisms.

To achieve a compact camera with wide-angle performance, the present invention utilizes an achromatic biprism having two asymmetric prisms made from two different optical materials with different Abbe numbers. The first prism has a lower Abbe number than the second prism. The prisms are bonded together on a first substrate using wafer-level fabrication methods (e.g., method 1300 discussed in further detail below). The geometry of each achromatic biprism is based on its position within the array.

Assuming that the Abbe number of the first prism is V1 and the Abbe number of the second prism is V2, the refractive index of the first prism is n1, and the refractive index of the second prism is n2, high optical performance can be achieved in each sub-camera 306 (i.e., the achromatic biprism 202(2) and the optical element 302(2)) if the following two constraints are met.

Constraint 1: V2>V1, V2>50 and V1<35 (d-line, wavelength is 587 nm).

Constraint 2: n2<n1, n2<1.52 and n1>1.58 (d-line, wavelength is 587 nm).

The angle of the bonding surface 403 between the first prism 402 and the second prism 404 is determined by the refractive index matching of the different materials of the first prism 402 and the second prism 404. For example, the angles of the first prism 402 and the second prism 404 may differ from 13.6 and -17.2 degrees, respectively, as shown in FIG4 , but the angle of the first prism 402 is preferably negative compared to the angle of the second prism 404.

FIG5 shows an MTF full field curve graph 500 illustrating the optical performance of the exemplary sub-camera 306 (i.e., the achromatic bi-prism 202(2) and the optical component 302(2)) of FIG3 and FIG4. The Abbe number (V1) of the first prism 402 is 30, and the refractive index (n1) of the material of the first prism 402 is 1.6 (d-line, at 587 nm). The Abbe number (V2) of the second prism 404 is 57 and is made of a material with a refractive index (n2) of 1.51 (d-line, at 587 nm). FIG6 shows a point graph 600 generated by simulating the sub-camera 306 (i.e., the achromatic bi-prism 202(2) and the optical component 302(2)) of FIG3 and FIG4 configured as described in FIG5.

For comparison, several exemplary prior art optical configurations were tested and compared to the MTF full field curve graphs 500 and point graphs 600 of the achromatic biprism 202(2) and optical assembly 302(2) in Figures 3 and 4.

FIG7 shows a prior art wafer-level lens 700 having three substrates 702(1)-(3) and five surfaces 704(1)-(5) for forming an image on a sensor array 706. Wafer-level lens 700 is similar to optical element 302(2) of FIG3. It is worth noting that wafer-level lens 700 does not include any prisms and therefore does not have wide field of view capabilities.

Figure 8 is a graph 800 of MTF over full field of view illustrating prior art optical performance of wafer-level lens 700 of Figure 7. Figure 9 is a plot 900 illustrating optical performance of wafer-level lens 700 of Figure 7. MTF graph 800 and plot 900 illustrate typical performance of wafer-level lens 700.

FIG10 shows another prior art wafer-level lens 1000 similar to the wafer-level lens 700 of FIG7 , but having an additional single prism 1002 disposed on a surface of the substrate 702(1) opposite to the surface 704(1). The single prism 1002 has an Abbe number (V _D ) of 62.6 and is made of a material having a refractive index (n) of 1.5168 (d-line at 587 nm). Notably, the single prism 1002 provides wide-angle performance to the wafer-level lens 1000.

FIG11 is a graph 1100 of MTF over field of view illustrating the prior art optical performance of the wafer-level lens 1000 of FIG10 . FIG12 is a plot 1200 illustrating the optical performance of the wafer-level lens 1000 of FIG10 . The MTF over field of view graph 800 and the plot 900 illustrate the typical performance of the wafer-level lens 700. As shown in graph 1100 and the plot 1200, the addition of the single prism 1002 results in severe chromatic aberration, significantly degrading the optical resolution performance of the wafer-level lens 1000, as shown when FIG11 and FIG12 are compared with FIG8 and FIG9 . Therefore, using a single prism as shown in the wafer-level lens 1000 results in poor image quality.

However, when the MTF full field curve graph 500 of FIG. 5 and the spot diagram 600 of FIG. 6 are compared with the MTF full field curve graph 800 ( FIG. 8 ) and the spot diagram 900 ( FIG. 9 ) of the prior art, it is shown that the use of the achromatic biprism 202 in the sub-camera 306 of FIG. 3 results in a significant improvement in optical performance over the prior art wafer-level lens 1000 of FIG. 10 .

FIG13 is a flow chart illustrating an exemplary method 1300 for fabricating a wide-angle camera having an achromatic dual-prism array. FIG14 depicts a schematic diagram of the camera 100 of FIG1 , including the achromatic dual-prism array 102 superimposed on the lens array 104 and the imaging sensor array 106, and illustratively shown formed on an imaging substrate 1408, in one embodiment. FIG15A-C are cross-sectional diagrams illustrating the steps of the method 1300 of FIG13 for forming a plurality of cameras 100 on a wafer. In particular, FIG15A illustrates an exemplary use of molds 1500 and 1508 for forming first and second prisms on a substrate 1506, while FIG15B shows the substrate 1506, combined with a lens array assembly 1514 and an imaging sensor 1516, being diced to form individual camera assemblies 1400. FIG13-15B are best viewed in conjunction with the following description.

13-15B, the camera assembly 1400 has been drawn in a three-by-three array with reference to the above. However, it should be understood that the method 1300 is applicable to any array of N x M camera assemblies, where N and M are positive integers.

In step 1302, method 1300 generates a first mold corresponding to a first prism array. In one example of step 1302, a first mold 1500 is generated for forming the first prism array 402. The first mold 1500 is configured with a plurality of regions 1502 corresponding to the desired configurations of a plurality of first prisms 402. FIG15A shows that the first mold 1500 can form two achromatic dual prism arrays 1402, each corresponding to section line B-B in FIG14. Furthermore, while each region 1502 is associated with a given portion of the achromatic dual prism, each region 1502 can have a different configuration based on the desired configuration of the first prisms in that portion. In the example illustrated in FIG. 15 , a cross-section of a first mold 1500 is associated with first prisms 402 of achromatic biprisms 202 ( 2 ), 202 ( 5 ), and 202 ( 8 ) of the achromatic biprism array 102 of FIGs. 1 and 14 , wherein region 1502 is shaped and resized to form each of the first prisms 402 therein.

In step 1304, method 1300 forms a first prism array made of a first material on a first substrate using the first mold. In one embodiment of step 1304, the first material is disposed in a plurality of regions 1502(1)-(4) to form first prisms 404(1)-(4) on substrate 406, respectively. The first material can be an ultraviolet (UV) curable material. Substrate 406 can be glass, plastic, silicone, or other optically transparent material.

In optional step 1306 , the first material is cured to complete the formation of the first prism 1504 .

At step 1308 , method 1300 removes the first mold. In one example of step 1308 , first mold 1500 is removed to leave first prisms 402 on substrate 406 .

At optional step 1310, method 1300 generates a second mold corresponding to the second prism array. In one example of step 1310, a second mold 1508 is generated for forming the second prism array 404. Second mold 1508 includes at least one region 1510 corresponding to the desired configuration of a plurality of second prisms 404. Second mold 1508 corresponds to first mold 1500 and forms a plurality of cameras 100, for example, on a wafer. Each portion of region 1510 is associated with a given portion of the achromatic dual-prism array 102, wherein each portion of region 1510 may have a different shape and size based on the shape and size of the corresponding second prisms 404 of the achromatic dual-prism array 102. In the example illustrated in FIG15A, a cross-section of a second mold 1510 associated with sub-cameras 306(2), 306(5), and 306(8) of camera 100 of FIG1, 2, and 3 includes an area 1510 for forming second prisms 404 therein. For example, if section line B-B were to pass through portions 202(1)-202(3), the surface of the second mold 1510 would be different to match the intended configuration of the second prisms 404 of these sub-cameras 306.

In step 1312, method 1300 uses the second mold to form a second prism array composed of a second material different from the first material on the first prisms. In one embodiment of step 1312, the second material is disposed in region 1510 to form second prisms 404 (1)-(6) on the first prisms. In the embodiment shown in FIG15A for a three-by-three array, the center of the array corresponding to sub-camera 306 (5) contains only the second material and no first prisms. Therefore, the second material is formed on substrate 406 in this portion. The second material can be an ultraviolet (UV) curable material.

In optional step 1314 , the second material is cured to complete the formation of the second prism 404 .

At step 1316 , method 1300 removes the second mold. In one example of step 1316 , second mold 1508 is removed, leaving second prisms 404 on first prisms 402 and substrate 406 .

In optional step 1318, method 1300 laminates the first and second prism arrays formed in steps 1302-1316 onto a lens array assembly. In one example of step 1318, substrate 406 having first prism 402 and second prism 404 thereon is laminated onto lens array assembly 104 and image sensor array 106. In the example of FIG15B, an additional lens (e.g., lens 408 of FIG4) is formed on a second side of substrate 406 prior to lamination.

In optional step 1320, method 1300 dices the stacked array into blocks to form individual cameras. In one example of step 1320, achromatic prism array 102, substrate 406, lens array 104, and image sensor array 106 are diced into blocks (e.g., along cut lines 1518) to form individual cameras 100, as shown in FIG15C.

Steps 1301 and 1317 are optional. If step 1301 is included, then step 1317 is not included. If step 1317 is included, then step 1301 is not included. In each of the optional steps 1301 and 1317, an optional lens array is fabricated on a second side of the substrate. In one example of steps 1301 and 1317, lens 408 is fabricated on a second side of substrate 406. That is, if included, lens 408 can be fabricated on a second side of substrate 406 before or after fabrication of achromatic biprism array 102.

In the examples of Figures 1 to 15, the first prism 402 is not included in the sub-camera 306 (5) because the sub-camera 306 (5) does not need to modify its corresponding field of view. In other words, assuming that the camera 100 is formed by a symmetrical N x N array of sub-cameras 306, when N is an odd number, the central achromatic bi-prism of the achromatic bi-prism array 102 may not include the first prism 402 but may include materials corresponding to the other second prisms. When N is an even number, the central sub-camera may optionally include a first prism. For example, in a 4 x 4 array, the four central sub-cameras of the camera 100 may include only the second material. Alternatively, in a 4 x 4 array, the four central sub-cameras may include both the first and second prisms. Figure 16 is a cross-sectional schematic diagram illustrating an exemplary camera 1600 having a 2 x 2 achromatic bi-prism array 1602 formed by the method 1300 of Figure 13. Camera 1600 has an achromatic dual prism array 1602, a lens array 1614, and a sensor array 1616. In the example of FIG16 , camera 1600 is formed as a 2 x 2 sub-camera array, and thus has no central sub-camera, where each sub-camera includes both first and second prisms 1604, 1606.

15A-C , the second material forming the second prisms 404 can be fabricated from a single contiguous layer of material that encapsulates each of the first prisms 402. Advantageously, this saves time in aligning the second prisms 404 with the first prisms 402. Advantageously, the second mold 1508 can be configured so that only the top surfaces of the first prisms 402 are covered with the second material of the respective second prisms 404 in a manner similar to that of FIGURES 3 and 4. Advantageously, this saves money on the amount of material used to form the second prism array.

Changes may be made to the above methods and systems without departing from the scope of the present invention. It should be noted that the above description or the contents shown in the accompanying drawings are to be interpreted in an illustrative sense and not in a restrictive sense. The following claims are intended to cover all generic and specific features described herein, and for language constraints, the statements of the scope of the present methods and systems should fall within these claims.

Claims (11)

1. A method for manufacturing an achromatic biprism array having N x M sections, the method comprising: A first prism array is formed on the surface of a substrate, each first prism being disposed within one of the N x M portions and composed of a first material; and A second prism array is formed on the first prism array by arranging a connecting layer of a second material, different from the first material, covering each first prism on the substrate surface. Each second prism is disposed within one of the N x M portions, and each second prism corresponds to the region of the connecting layer above the corresponding first prism. Furthermore, each second prism is bonded to each other in opposite directions to its corresponding first prism. The Abbe number of the first material is lower than that of the second material, and the refractive index of the first material is higher than that of the second material. The step of forming the second prism array includes molding the adjoining layer using a second mold, the second prism array having (i) a single second region extending beyond the region of the first prism array on a plane parallel to the surface of the substrate and (ii) a plurality of regions corresponding to the corresponding first prisms. 2. The method according to claim 1, wherein the step of forming the first prism array comprises depositing and curing a UV-curable resin in a first mold. 3. The method of claim 1, further comprising: between the step of forming the first prism array and the step of forming the second prism array, removing the first mold used during the steps of forming the first prism array and depositing the second material in the second mold. 4. The method according to claim 1, wherein the step of forming the second prism array comprises depositing and curing a UV-curable resin in a second mold. 5. The method according to claim 1, further comprising stacking the formed first prism array and the second prism array on the lens array assembly along with the substrate. 6. The method of claim 5, further comprising dicing the stacked components to form a separate camera component array. 7. The method of claim 1, further comprising generating a first mold configured according to the intended structure of the first prism array. 8. The method of claim 1, further comprising generating a second mold configured according to the intended structure of the second prism array. 9. The method of claim 1, wherein the step of forming the first prism array is performed using a first mold having a first region corresponding to the construction of the first prism, the first region appearing only in a portion of the N x M portions of the achromatic biprism. 10. The method of claim 9, wherein the first region appears only in the outer portion of the achromatic biprism, such that no first prism is formed in the middle portion. 11. The method of claim 1, wherein in the step of forming the second prism array, each second prism in the second prism array is aligned with a corresponding first prism in the first prism array, the first prism having a thickness that increases in a first direction, and the second prism having a thickness that increases in a second direction, the second direction being 180 degrees opposite to the first direction.