JPS603601A - Joined optical element - Google Patents

Abstract

PURPOSE:To eliminate a process for polishing surfaces to be joined together and to reduce the cost of an optical element by adhering light transmitting surfaces having prescribed surface roughness to each other. CONSTITUTION:The surfaces 1b, 2b, of transparent materials 1, 2 to be joined together for a lens, a prism or the like are ground with diamond pellets #1,500 to regulate the surface roughness to 0.02-0.2mu average roughness along the center line, and the resulting optical surfaces are joined together with an adhesive 3. Since the adhesive fills well the recesses of the surfces 1b, 2b, satisfactory light transmittance is provided, and a polishing process can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bonding element for optical technology, and more particularly to the degree of surface roughness of a bonding surface of an optical element.

As is well known, today optical glasses and plastics are molded using a molding method called Mositolens.
Lens manufacturing methods that omit polishing are widely adopted. However, since these lenses are processed by heating the material, so-called hot processing, the surface precision deteriorates due to shrinkage of the material after it returns to room temperature. It was necessary to polish it properly. Therefore, as a manufacturing method for optical elements such as lenses and prisms that require high precision, a material cut from a hot stamping material called a pressing material or a glass block material is roughly shaped using a diamond tool, etc. A grinding method using an abrasive slurry called sand kage is generally used, in which the surface is finished by using a coarse abrasive, then a fine abrasive, and finally polishing with an abrasive. In the process, the particle size of the abrasive material t is e#,
The angle ranges from 8° to ≠2000, and in the polishing process, a desired smooth surface is obtained by polishing with an abrasive such as chromium oxide or cerium oxide. However, in the above process, the working time required for the polishing process is longer than the sanding process, which has good grinding properties.
They tend to be extremely long, which increases manufacturing costs. Therefore, as a way to shorten the polishing time, polishing methods using fixed abrasive grains made by mixing abrasives into metals, resins, etc. are being used, but at present, polishing and processing methods using the above abrasives are the most common. It becomes.

On the other hand, optical elements such as lenses and prisms can not only be used alone, but also be used as a beam splitter by combining two or six lenses together to have the function of removing aberrations, or by combining multiple prisms. It is not uncommon for them to be used together as shown in the figure. In this case, the adhesive is present between the bonding surfaces and fills the irregularities on the surface of the optical element, so the high surface precision described above is not necessarily required. It is possible that this is not the case.

The purpose of the present invention is to focus on the above points, and to improve the surface roughness of the joint surface to such an extent that the polishing process can be omitted.
By verifying that there is no problem in actual use, the present invention aims to provide an optical bonding element that greatly reduces the cost by omitting the polishing process as far as the bonding surface is concerned.

Next, the results of an experiment to demonstrate that there is no problem in actual use even if the surface accuracy of the joint surface is such that the polishing step can be omitted will be explained. Hereinafter, the diamond pellet will be referred to as a fixed abrasive diamond pellet for the abrasive slurry.

According to a stylus type surface roughness measuring device, the centerline average roughness (hereinafter referred to as Ra) of the polished surface of optical glass using a conventional cerium oxide abrasive is 0.004 μm. In addition, the Ra of the surface ground by 41soo diamond pellets is 0.02 μm, and the grinding time is short, which is convenient as a pre-process to grinding by the above-mentioned abrasive.
Generally used.

Furthermore, Wf /! using a diamond pellet finer than +15oo! If fU processing is performed, the surface roughness will gradually become finer, and it is natural that the above-mentioned polishing time can be shortened accordingly, but the total processing time between polishing processing time and polishing processing time will hardly change, and the number of steps will increase. However, processing becomes complicated and workability deteriorates. Therefore, as a pre-process to the polishing process, the grinding process using the above-mentioned 41500 diamond pellet, which has a high grinding efficiency of 1gu, is 1&;iii fx
'tD h fx°'''-・4・CJ: 5 K li
f 'f'J'J @ The amount of transmitted light on the joint surface when the joint surface is ground with +1500 diamond beret with the best F-M ratio and is joined with adhesive without lif + rubbing, Furthermore, the amount of transmitted light at the bonded surface when the bonded surface polished using an abrasive material is bonded using an adhesive will be compared. In FIG. 1, (A) shows that the joint surfaces of the optical glass plates 1.2 to be joined are both polished with an abrasive material, and the respective polished surfaces ja and 2a are coated with adhesive 3.
When bonded by In surface 2a, these surfaces 1b.

If 2a is joined by adhesive 3, (C) is
The joint surfaces of the lath plates 1 and 2 are both ground surfaces 1b as they have been ground with the above-mentioned -$1500 diamond pellet.

2b are bonded with adhesive 3. Figure 2 shows (A), (B), (
Transmittance of the amount of light transmitted through the joint surface in C) (respectively AI
,B/.

(C'), and (D') is the transmittance of the amount of light in the case of (C) above, without using the adhesive 3 and simply abutting both the ground surfaces 1b and 2b before joining. Each is graphed with wavelength plotted on the horizontal axis. As is clear from the figure, at the wavelength of the laser diode of 800 nm,
The transmittance of the light amount in the above cases (A), CB), and (C) is 91%, 90%, and 88%, respectively, hardly changing, but in the above case (D') before adhesion, it is 60%. and is low. This means that the bonding surface is above −//p1500
Even on a ground surface that has been ground with diamond pellets, the adhesive fills the uneven parts of the bonded surface appropriately, so that the transmittance that was 60 cm without adhesive has increased to 88 cm. This shows that there has been a huge improvement. That is, both the case (A) in which the bonding surfaces are both polished surfaces and the case (C) in which both the bonding surfaces are ground surfaces ground with the above-mentioned 41500 diamond pellet after bonding by the intervention of adhesive. The difference in transmittance for the amount of light is only 3
It's nothing more than a chi. This decrease in transmittance becomes scattered light and dissipates; however, when applied to the joint surface of a prism for a beam splitter in the optical system of an optical digital disc reading section, for example, most of the optical path is Since it is configured as a so-called relay optical system with parallel light beams, the light flux passes through a large joint surface, so the adverse effects of scattered light caused by surface roughness are relatively insignificant. . Furthermore, due to the function of processing the increase or decrease in the amount of reflected light from the disk as an electrical signal, the harmful effects of scattered light are far less compared to the observation optical system with the naked eye.In the case of (C) above, only the ground surface It is clear that there is no problem in practical use with the bonding. From the above, it has been demonstrated that the surfaces of lenses, prisms, etc. that are bonded with adhesives as described above are not necessarily polished surfaces, and that there is no problem with the grinding surfaces of +1500 diamond berets, etc.

Next, as an example of a device having a cemented surface such as a lens or a prism as described above, an optical digital disk reading head will be considered. FIG. 3 is a perspective view showing a schematic configuration of the optical digital disc reading head 10. As shown in FIG. In the figure, reference numeral 11 is a laser diode, 12 is a collector lens, 13 and 14 are beam splitters, 115 is a critical angle prism, 16 is an optical path switching prism, 17 is an air-liquid plate, 18 and 19 are objective lenses, and 20 is an optical path switching prism. Signal reading elements 21, 22, 23, and 24 are bonding surfaces of adjacent optical elements, and 25 is a disk, respectively.

Then, the laser beam emitted from the laser diode 11 becomes parallel light beam by the collector lens 12,
It passes through the beam splitters 13 and 14, passes through the optical path switching prism 16 and the h-wavelength plate 17, and then passes through the objective lens 18.
The light beam is focused by the beam splitter 19 and reflected onto the digital signal bits recorded on the disk 25, and then returns along the same path again and is bent by 90 degrees by the 45 degree reflection surfaces of the beam splitters 13 and 14 to reach the critical angle. The signal passes through the prism 15 and reaches the signal reading element 20°, where it follows the signal track on the disk 25 and controls focus adjustment. In the optical system of the optical digital disc reading head 10 configured in this way, the beam splitter
Since the bonding surfaces 21 of 13° and 14 are interposed with a polarizing film that requires a high area density, these bonding surfaces have a high area density.

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14 and the critical angle prism 15, and the bonding surface 230 of the optical path switching prism 16 with the /4 wavelength plate 17, a total of 6 surfaces are also ground by the above-mentioned 41soo diamond pellet. There is no functional difference between the polishing surface and the polishing surface, and normal operation can be achieved. Also, both sides of the bonding surfaces 24 of the objective lenses 18 and 19! #15o.

It can also function satisfactorily as a grinding surface for diamond pellets. Next, in order to determine the limit of the surface roughness of the ground surface as described above, we conducted a functional test using a rougher diamond pellet to grind it and used it as a joint surface. The average roughness RaO of 2 μm was almost the limit. However, there is no big difference in machining time between -II-600 diamond beret and ≠1500 diamond beret, so +1500 which is closer to the polished surface
Of course, processing using a diamond beret is advantageous.1 As explained above, according to the present invention, in an optical element constructed by bonding optical surfaces that transmit light with adhesive, As far as the bonded surfaces bonded together using the above adhesive are concerned, it has been demonstrated that even if the polishing step is omitted, the optical performance required for practical use can be reliably maintained due to the action of the adhesive, and these bonded surfaces By completely omitting the polishing step, it is possible to greatly reduce the cost of the optical element, and also to obtain great effects such as shortening the #1 processing period and reducing the number of polishing equipment.

[Brief explanation of drawings]

FIGS. 1(A), (B), and (C) are cross-sectional views showing samples for measuring transmitted light on the bonding surface of an optical bonding element, respectively, and FIG. ), (C
Figure 3 is a schematic perspective view showing the configuration of an optical digital disc reading head. 1.2...・Optical junction element 1allbj
2a12b---Jointing surface 6・・・・・・・・・Adhesive patent applicant Olympus Optical Industry Co., Ltd. Embedded
Fujikawa 7 Department %2 Liquid length (nm) 2-43-2 Hatagaya, Shibuya-ku, Tokyo Lymphus Optical Industry Co., Ltd. 0 Inventors Akimi Matsuzawa 2-43-2 Hatagaya, Shibuya-ku, Tokyo Lymphus Optical Industry Co., Ltd. 4

Claims (1)

[Claims] An optical element constructed by bonding optical surfaces that transmit light to each other with an adhesive, wherein the surface roughness of the bonded surfaces ranges from 0.02 μm to 0.02 μm in center line average roughness. An optical bonding element characterized by bonding an optical surface in a range of up to 2 μm.