Optical blanks

Abstract

This invention provides an optical blank that is not prone to cracking even after reliability testing. The optical blank has a square planar shape and has a first main surface and a second main surface opposite to the first main surface. The optical blank includes: C-surface machined portions formed at the four corners; and R-surface machined portions formed at the intersections of the C-surface machined portions and the side surfaces connecting the first and second main surfaces. Preferably, all or part of the side surfaces are machined using either the C-surface or the R-surface.

Description

Technical Field

[0006]

[0001] The present invention relates to an optical blank for an electro-optical machine or the like, including an optical filter or the like containing a crystal or optical glass, and particularly to a chamfered optical blank. Prior Art

[0002] For optical parts such as optical filters, chamfering operations are usually performed to prevent the corners from being damaged. The chamfering operations usually include a C-chamfering operation in which the corners are cut into a straight line shape and an R-chamfering operation in which the corners are cut into an arc shape. From the viewpoints of cost and operation processes, the R-chamfering operation is not performed on all corners (four corners) of the optical blank. When grinding the main surface of the optical blank, C-chamfering is performed in advance to reduce the possibility of corner breakage.

[0003] However, if a thermal shock (heat shock) test is performed after grinding the main surface of the optical blank to further improve the quality of the optical blank, cracks may sometimes occur in the optical blank. The optical blank with such cracks becomes a defective product, resulting in a high cost. Therefore, it is required to achieve the following situation: even if a reliability test such as a thermal shock test is performed on the ground optical blank, cracks are not easily generated. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-27923 Summary of the Invention Problems to be Solved by the Invention

[0005] The problem to be solved by the present embodiment is to provide an optical blank that is not easily cracked even after a reliability test. Means for Solving the Problems

[0006] The present embodiment is an optical blank having a square planar shape and having a first main surface and a second main surface opposite to the first main surface. The optical blank includes: a C-surface processing portion formed at four corners; and an R-surface processing portion formed at a portion where the C-surface processing portion intersects with a side surface connecting the first main surface and the second main surface.

[0007] Moreover, it is preferable that the ratio L:R of the radius of curvature R of the R-surface processing portion to the length L of the C-surface processing portion is in the range of 1:0.05 to 1:0.15.

[0008] Moreover, it is preferable that the surface roughness of the side surface of the optical blank is 2.7 μm or less.

[0009] More preferably, all or a part of the side surface is subjected to C-plane processing or R-plane processing. Advantages of the Invention

[0010] Based on the above, the optical blank of the present embodiment has an advantage that cracks are not easily generated even after a reliability test. Brief Explanation of Drawings

[0011] (a) of FIG. 1 is a side view of the optical blank 10, and (b) of FIG. 1 is a front view of the optical blank 10.

[0012] (a1) and (a2) of FIG. 2 are partial enlarged views of the side surface of the optical blank 10, and (b) of FIG. 2 is a partial enlarged view of the front surface of the optical blank 10.

[0013] FIG. 3 is a flowchart showing the process from the manufacture of the optical blank to the reliability test.

[0014] (a) of FIG. 4 is a graph showing the breakage rate related to the ratio of C chamfer and R chamfer. (b) of FIG. 4 is a graph showing the breakage rate related to the surface roughness of the side surface. Embodiment

[0015] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In addition, the scope of the present invention is not limited to the embodiments described below. In each of the drawings, wirings, mounting pads, etc. are drawn thicker than actual for easier understanding.

[0016] <Structure of Optical Blank>

[0017] In the present embodiment, the long side direction of the rectangular optical blank 10 is set as the X-axis direction, the short side direction is set as the Y-axis direction, and the thickness direction perpendicular to the X-axis direction and the Y-axis direction is set as the Z-axis direction for explanation. At this time, the optical blank 10 described in the present embodiment has a rectangular shape, but may also be square.

[0018] The optical blanks 10 shown in Figure 1(a) and Figure 1(b) are, for example, AT-cut crystal plates, optical glass plates, LT (lithium tantalate) plates, and LN (lithium niobate) plates. The optical blanks 10 are typically used as products or parts for purposes such as wavelength-selective optical filters, light-polarizing plates, and heat dissipation plates that release heat.

[0019] The size or thickness of the optical blank 10 is not particularly limited. For example, the optical blanks shown in Figures 1(a) and 1(b) have a length of 30 mm in the X-axis direction, 20 mm in the Y-axis direction, and a thickness of 0.4 mm (Z-axis direction). As shown in Figure 1(a), the optical blank 10 has a first main surface 11a and a second main surface 11b. Furthermore, as shown in Figure 1(b), there are side surfaces 15a (with the long side of the optical blank 10), 15d (with the long side of the optical blank 10), 15b (with the short side of the optical blank 10), and 15c (with the short side of the optical blank 10). The first main surface 11a and the second main surface 11b undergo necessary grinding treatment to achieve a specified surface roughness, depending on the application. In the following description, they are sometimes referred to as side surfaces 15a, 15b, 15c, and 15d connecting the first main surface 11a and the second main surface 11b.

[0020] The optical blank 10 has a C-beveled portion 13a at the corner where the side surface 15a with the long side of the optical blank 10 intersects with the side surface 15b with the short side of the optical blank 10; a C-beveled portion 13b at the corner where the side surface 15a with the long side of the optical blank 10 intersects with the side surface 15c with the short side of the optical blank 10; a C-beveled portion 13c at the corner where the side surface 15d with the long side of the optical blank 10 intersects with the side surface 15b with the short side of the optical blank 10; and a C-beveled portion 13d at the corner where the side surface 15d with the long side of the optical blank 10 intersects with the side surface 15c with the short side of the optical blank 10. The C-beveled portion 13a is a smaller chamfer than the other C-beveled portions 13b to 13d, for example, a C1 chamfer with 1 mm removed. C-beveling sections 13b to 13d are C2 beveling sections with a 2mm reduction. C-beveling section 13a is provided to determine the orientation of the optical blank 10, which has characteristics in the cutting direction, such as AT-cut crystal plates.

[0021] Figures 2(a1) and 2(a2) are enlarged views of the area enclosed by the dotted line in Figure 1(a). As shown in Figure 2(a1), the sides 15a, 15b, 15c, and 15d of the optical blank 10 can be chamfered with radius R (RA) between the first main surface 11a and the second main surface 11b. Furthermore, as shown in Figure 2(a2), the sides 15a, 15b, 15c, and 15d of the optical blank 10 can also be chamfered with radius C (CA) between the first main surface 11a and the second main surface 11b. The chamfer R (RA) or chamfer C (CA) can be applied to all sides 15a, 15b, 15c, and 15d, or only sides 15a and 15d can be applied. Furthermore, as described later, side surfaces 15a, 15b, 15c and 15d or a portion thereof are preferably ground to achieve a surface roughness Ra value of 2.7 μm or less.

[0022] Figure 2(b) is an enlarged view of the area enclosed by the dotted line in Figure 1(b). As shown in Figure 2(b), regarding the C-beveled portion 13d of the optical blank 10, an R-beveled portion 13r is provided at the intersection of the C-beveled portion 13d and the side surface 15c having the short side of the optical blank 10, and an R-beveled portion 13r is also provided at the intersection of the C-beveled portion 13d and the side surface 15d having the long side of the optical blank 10. The relationship between the length L of the C-beveled portion 13d and the radius of curvature R of the R-beveled portion 13r will be explained using Figure 4.

[0023] <Manufacturing and Testing of Optical Blanks>

[0024] Figure 3 is a flowchart illustrating the process from manufacturing the optical blank to reliability testing. An optical plate (not shown) of a size large enough to manufacture hundreds or more optical blanks 10 is prepared. The optical plate is then cut to prepare rectangular optical blanks (step S31). The thickness t1 of the optical blank 10 is, for example, 0.5 mm.

[0025] As shown in FIG1(b), the rectangular optical blanks are processed by C-beveling portions 13a, 13b, 13c, and 13d. Next, as shown in FIG2(b), the C-beveling portions 13a, 13b, 13c, and 13d are processed by R-beveling portions 13r (step S32). Furthermore, as shown in FIG2(a1) and FIG2(a2), R-beveling RA or C-beveling CA can also be performed. In addition, in order to form these C-beveling portions 13a, 13b, 13c, and 13d and R-beveling portions 13r, the main surfaces of multiple rectangular optical blanks are bonded together to form a block. Next, the sides of the block are ground using an abrasive of a specified grit size. The C-beveled parts 13a, 13b, 13c, 13d, and 13r are formed by the grinding process, and the surface roughness Ra of the C-beveled parts 13a, 13b, 13c, 13d, and 13r is set to the desired surface roughness.

[0026] The optical blank after C-beveling and R-beveling is ground in such a way that the first main surface 11a and the second main surface 11b have a specified surface roughness and the thickness t2 is, for example, 0.4 mm (step S33).

[0027] For the optical preform, at least one of the first main surface 11a or the second main surface 11b is coated (step S34). The coating process is, for example, coating of a reflective film or coating of infrared cutoff, and there is no particular limitation on the type of coating. The optical preform 10 is thus completed. In addition, depending on the application of the optical preform 10, coating may sometimes be omitted.

[0028] Then, a reliability test is performed on the optical blank 10 (step S35). In this embodiment, the reliability test is a thermal shock test. The thermal shock test is a test that applies destructive stress to the optical blank 10 and measures the temperature difference that causes damage. It can be presumed that the optical blank 10 that does not break in the thermal shock test is a product that can withstand long-term changes over time. The optical blank 10 that does not show cracks or other damage in the thermal shock test is shipped as a product.

[0029] Furthermore, the thermal shock test conditions were as follows: the optical blank was placed on a heater (hot plate), heated to 178°C~180°C within 1 minute from room temperature and held for 2 minutes, and then the optical blank was instantly immersed in pure water at 20°C. Although these test conditions are quite stringent and would not be encountered by actual products, they were adopted for rigorous evaluation.

[0030] <Fragmentation rate due to thermal shock testing>

[0031] As explained in step S35 of Figure 3, thermal shock testing caused some optical blanks 10 to suffer damage such as cracking. This cracking and damage occurred on side surfaces 15a, 15b, 15c, or 15d, or on the C-beveled portions 13a, 13b, 13c, or 13d. The inventors changed the ratio of the C-beveled portions 13 (13a~13d) to the R-beveled portions 13r and investigated the breakage rate after thermal shock testing caused by this change. Furthermore, the inventors changed the surface roughness of side surfaces 15a, 15b, 15c, and 15d and investigated the breakage rate after thermal shock testing caused by this change. The graphs shown in Figures 4(a) and 4(b) below illustrate experimental examples when the optical blank 10 is made of glass.

[0032] Figure 4(a) is a graph showing the ratio of the C-beveled part 13 to the R-beveled part 13r. The vertical axis of the graph represents the breakage rate, and the horizontal axis represents the ratio of the length L of the C-beveled part 13 to the radius of curvature R of the R-beveled part 13r. The number of optical blanks (samples) for each ratio is 20. For example, if the C-beveled part 13d shown in Figure 2(b) is a C2 bevel, i.e., the length L = 2 mm, and the radius of curvature R of the R-beveled part 13r is 0.2 mm, then the R / C ratio is 0.10 (L:R = 1:0.10).

[0033] As shown in the graph of Figure 4(a), the breakage rate is 37% if only C-beveling is performed, and the breakage rate decreases if R-beveling is performed. The breakage rate is 32% when the R / C ratio is greater than 0.00 and less than 0.05 (L:R=1: greater than 0.00 and less than 0.05), and 26% when the R / C ratio is greater than 0.05 and less than 0.10 (L:R=1: greater than 0.05 and less than 0.10). Furthermore, the breakage rate is 19% when the R / C ratio is greater than 0.10 and less than 0.15 (L:R=1: greater than 0.10 and less than 0.15), and 11% when the R / C ratio is greater than 0.15 and less than 0.20 (L:R=1: greater than 0.15 and less than 0.20). Here, the larger the R-surface machining portion 13r is, the lower the breakage rate becomes, but this incurs the cost of prior chamfering. On the other hand, according to Figure 4(a), if the R / C ratio is 0.10 to 0.15, the breakage rate is halved compared to the case where only C machining is performed. The thermal shock test used in this experiment employs harsh conditions that are unlikely to occur with actual products. Therefore, if the breakage rate is halved under these harsh test conditions, the actual product will not experience breakage problems and will be considered a good product. Thus, in this embodiment, the preferred range for the R / C ratio is 0.10 to 0.15. Furthermore, according to Figure 4(a), the further preferred range for the R / C ratio is 0.15 to 0.20, but even if this range is not reached, the effects of this embodiment can still be achieved.

[0034] Figure 4(b) is a graph showing the changes in the surface roughness Ra (hereinafter sometimes simply referred to as surface roughness) of sides 15a, 15b, 15c, and 15d. The vertical axis of the graph represents the breakage rate, and the horizontal axis represents the surface roughness. Furthermore, the surface roughness ranges from left to right as follows: 1.2 μm to 3.0 μm, 0.9 μm to 2.7 μm, 0.6 μm to 1.8 μm, 0.5 μm to 1.0 μm, 0.3 μm to 0.5 μm, 0.2 μm to 0.4 μm, and 0.1 μm to 0.3 μm. This is because these were manufactured with surface roughness targets of 2.0 μm, 1.5 μm, 1.0 μm, 0.7 μm, 0.4 μm, 0.3 μm, 0.3 μm, and 0.2 μm, respectively, but the surface roughness of the actual manufactured optical blanks deviates from these targets. There are 20 optical blanks (samples) for each ratio.

[0035] As shown in Figure 4(b), the breakage rate decreases as the surface roughness of sides 15a, 15b, 15c, and 15d decreases. For optical blanks manufactured with a surface roughness of 1.2μm to 3.0μm with a target of 2.0μm, the breakage rate is 23%. For optical blanks manufactured with a surface roughness of 0.9μm to 2.7μm with a target of 1.5μm, the breakage rate is 7%. Furthermore, the breakage rate of optical blanks manufactured with a surface roughness of 1.0μm or less is less than 10%. Therefore, it can be confirmed that the breakage rate of optical blanks manufactured with a surface roughness of 2.7μm or less with a target of 1.5μm decreases dramatically.

[0036] Here, the smaller the surface roughness Ra, the lower the breakage rate, but this incurs processing costs associated with prior chamfering and grinding. On the other hand, according to Figure 4(b), if the surface roughness Ra is 0.9 μm to 2.7 μm, the breakage rate is reduced to about one-third compared to the case where the surface roughness Ra is 1.2 μm to 3.0 μm. The thermal shock test used in this study employs harsh conditions that are unlikely to occur with actual products. Therefore, it can be assumed that if the breakage rate is reduced to one-third under these harsh test conditions, the actual product will not experience breakage problems and will be considered a good product. Therefore, in this embodiment, the surface roughness Ra of the C-chamfered portion and the R-chamfered portion is preferably 2.7 μm or less. More specifically, according to Figure 4(b), the breakage rate is approximately 6 until the surface roughness Ra reaches 0.3 μm to 0.5 μm; therefore, the surface roughness Ra of the C-chamfered portion and the R-chamfered portion can also be 2.7 μm to 0.3 μm or less. Furthermore, according to Figure 4(b), if the surface roughness Ra is 0.4 μm or less, the breakage rate is reduced to about one-tenth compared to the case where the surface roughness Ra is 1.2 μm to 3.0 μm. Therefore, the preferred range for the surface roughness Ra of the C-beveled part and the R-beveled part is 0.4 μm or less. However, even if this level is not reached, the effect of this embodiment can still be obtained.

[0037] 10: Optical blanks

[0038] 11a: First Main Face

[0039] 11b: Second Main Face

[0040] 13(13a~13d): C-face chamfering section (C-surface machining section)

[0041] 13r: R-shaped chamfering section (R-surface machining section)

[0042] 15 (15a~15d): Side view

[0043] CA:C chamfer

[0044] L: Length

[0045] RA:R Chamfer

[0046] R: Radius of curvature

[0047] S31~S35: Steps

Claims

1. An optical blank, characterized in that its planar shape is square, having a first main surface and a second main surface opposite to the first main surface, and comprising: C-surface machining portions are formed at the four corners of the optical blank; And an R-surface processing portion is formed at the intersection of the C-surface processing portion and the side connecting the first main surface and the second main surface. The first main surface and the second main surface are arranged along the thickness direction of the optical blank. When the four corners are viewed from the first main surface or the second main surface, the radius of curvature R of the R-surface processing portion relative to the length L of the C-surface processing portion has a ratio of L:R of 1:0.05 to 1:0.

15.

2. The optical blank according to claim 1, wherein, The surface roughness of the side surface of the optical blank is less than 2.7 μm.

3. The optical blank according to claim 1 or 2, wherein, All or part of the side surface is machined using the C-surface or the R-surface.

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