JP2008032588A - Lens-measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device for simplifying device composition by improving the mechanical strength of a diffraction grating, in a lens-measuring device, such as an optical pickup and DSC that use the diffraction grating. <P>SOLUTION: The mechanical strength of the diffraction grating 8 is improved, and aberration measurement accuracy is improved, by forming a protective layer 22 adjusting a refractive index and thickness on the diffractive grating 8; and furthermore, the device composition can be significantly simplified and stable lens measurements in with stabilized accuracy can be achieved by possessing spherical aberration correction mechanism using a refractive index difference of the protective layer 22. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc type information recording medium, for example, a lens for recording / reproducing information on a DVD (Digital Versatile Disc) or BD (Blu-ray Disc), or an imaging optical system of a DSC (Digital Still Camera). The present invention relates to a measuring device for optical components such as a lens to be mounted.

  There is an optical pickup as an optical device for reproducing information on an information recording medium of an optical disc system and recording information on the information recording medium. This optical pickup requires an optical system for accurately and accurately irradiating light emitted from a built-in light source to a predetermined position on the information recording medium. However, the characteristics of the manufactured optical pickup may not be within the required range due to the characteristics of the parts constituting the optical system and the variations in assembly.

  Among these optical systems, in particular, objective lenses require strict optical characteristics such as a wavefront aberration of about one-hundredth of the laser wavelength used (for example, λ = 660 nm for DVD). It must be prepared and fixed with high precision.

  Therefore, in the optical pickup manufacturing process, it is necessary to measure and adjust the state of the optical system. As a conventional method of adjusting an optical pickup, there is a lens evaluation method using a sharing interference image (see, for example, Patent Document 1).

  FIG. 5 is a diagram illustrating the lens measurement method disclosed in Patent Document 1. In FIG.

  In FIG. 5, the light emitted from the light source 2 in the optical pickup 1 is collimated by the lens 3, is reflected by the mirror 4, and enters the objective lens 6 supported by the holder 5. The light emitted from the objective lens 6, that is, the light emitted from the optical pickup 1, is adjusted by the diffraction grating adjustment mechanism 7 in the diffraction grating 8 whose horizontal, vertical, and tilt positions are adjusted with respect to the optical axis of the objective lens 6. Is incident on. The incident light generates diffracted light and is emitted from the diffraction grating 8. The emitted 0th-order light and ± 1st-order light are interfered by overlapping 0th-order light and + 1st-order light, and 0th-order light and −1st-order light, respectively. The emitted light passes through the cover glass 10 whose positions such as horizontal, vertical, and tilt are adjusted by the cover glass adjusting mechanism 9.

  Of the light transmitted through the cover glass 10, the zero-order light and the ± first-order light overlapping the zero-order light are captured by the condenser lens 11. Here, the condenser lens 11 has a numerical aperture larger than the numerical aperture (NA) of the objective lens 6 in order to capture all the zero-order light of the objective lens 6. Further, the condensing lens 11 is a lens that takes into account spherical aberration that occurs due to transmission through the cover glass 10, and for example, a biological microscope objective lens or an optical pickup objective lens is used. The light emitted from the condenser lens 11 is imaged on the image sensor 13 by the imaging lens 12. The processing device 14 analyzes the interference fringe pattern of the image formed on the image sensor 13 to detect aberrations that are optical characteristics of the optical pickup 1 and the objective lens 6, and displays them on the display device 15. Based on the detection result, the position of the objective lens 6 in the optical pickup 1 is adjusted by the objective lens adjusting mechanism 16.

  Since the accuracy of the diffraction grating decreases when dust or the like adheres to the diffraction surface, it is necessary to keep the diffraction surface clean. For this reason, some conventional diffraction gratings coat the diffraction surface of the diffraction grating (see, for example, Patent Document 2).

  FIG. 6 is a diagram showing a diffraction grating provided with the cover plate of Patent Document 2. As shown in FIG. In FIG. 6, the description of the same reference numerals as those in FIG. 5 is omitted.

  In FIG. 6, many coating plates 18 are arranged on the diffraction surface of the diffraction grating 17 at a predetermined interval, and the distance between the diffraction grating 17 and the coating plate 18 is defined by the spacer 19 arranged between them. To do.

  FIG. 7 is a view showing a diffraction grating provided with a coating layer of Patent Document 2. As shown in FIG. In FIG. 7, the description of the same reference numerals as those in FIGS.

  In FIG. 7, the diffraction surface of the diffraction grating 20 is covered with a coating layer 21 made of a material having a refractive index different from that of the material constituting the diffraction grating 20.

  Some conventional optical pickup devices have a wave plate attached to a diffraction grating in the device in order to reduce the size of the device (see, for example, Patent Document 3).

Further, in next-generation media such as BDs, the diffraction grating pitch is reduced and the thickness of the diffraction grating is 1 μm or less due to the high NA of the objective lens of the optical pickup accompanying the increase in the density of the optical disk. It is necessary to make it very thin, about 1/10 compared to. In addition, the distance between the objective lens and the diffraction grating, the diffraction grating and the cover glass, and the cover glass and the condensing lens is set to 300 μm or less, which is a very narrow distance of 1/10 or less compared with a device such as a CD.
JP 2000-329648 A JP 2002-090605 A JP 2003-217162 A

  However, the conventional lens measuring device has the following problems.

  In the conventional configuration, since the case where the diffraction grating is thin and mechanically fragile is not assumed, when the objective lens is adjusted, the diffraction grating and the objective lens may come into contact with each other and the diffraction grating may be damaged. Further, in the BD optical system and the DVD optical system, since the gap between the lens and the diffraction grating is small, it is difficult to newly insert a reinforcing plate.

  Also, when attaching the diffraction grating to the reinforcing plate or adjustment mechanism, it is pasted with an adhesive, etc., but due to the reduction in mechanical strength due to thinning of the diffraction grating, the diffraction grating is distorted and bent during bonding. However, the interference fringes generated by the diffraction grating may change, and the aberration detection accuracy of the optical pickup may deteriorate.

  As described above, in the conventional lens inspection apparatus, when the measurement is performed more than a certain number of times, the diffraction grating may be damaged or the diffraction surface may become dirty, and the diffraction grating may not perform its function and measurement may not be possible. is there. Therefore, when continuously measuring several hundred units of lenses, it is necessary to prepare a large number of diffraction gratings that require time loss due to replacement of the diffraction grating and fine diffraction surfaces.

  In order to achieve the above object, a lens measuring device of the present invention includes a light source that emits light to a lens, a diffraction grating that forms diffracted light of different orders from light emitted from the light source and transmitted through the lens, A protective layer formed on the diffraction surface of the diffraction grating opposite to the lens, a light receiving device that receives the different orders of diffracted light that interfered with each other, and a measuring device that measures aberration of the lens from the received interference image And on the optical axis of the lens, the surface of the protective layer opposite to the diffraction surface is flat, and the surface of the diffraction grating on the lens side and the surface on the measurement device side The optical distance is equal to the optical distance between the lens side surface of the protective layer and the measurement device side surface.

  As described above, according to the lens measuring device of the present invention, the protective layer formed on the diffraction surface of the diffraction grating prevents damage and contamination of the diffraction grating and prevents time loss when continuously performing the lens inspection. In addition, it is possible to provide a measuring apparatus that can accurately measure the lens. Therefore, the number of continuous operations of the lens inspection device can be increased.

  In addition, according to the lens measuring device of the present invention, since the probability of distortion occurring in the diffraction grating can be reduced, a lens measuring device with stable accuracy can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram of a lens measuring apparatus according to the first embodiment. In FIG. 1, the description of the same reference numerals as those in FIGS.

  In FIG. 1, reference numeral 22 denotes a protective layer formed on the groove surface of the diffraction grating 8.

  Hereinafter, the lens measurement method of the present embodiment will be described.

  The laser light emitted from the light source 2 inside the optical pickup 1 that is the measurement target is made substantially parallel light by the lens 3, then reflected by the mirror 4, and enters the objective lens 6 supported by the holder 5. . The light emitted from the objective lens 6, that is, the light emitted from the optical pickup 1 is incident on the diffraction grating 8 whose position such as horizontal, vertical, and tilt is adjusted by the diffraction grating adjusting mechanism 7. Here, in particular, the inclination is adjusted so as to be perpendicular to the optical axis of the optical pickup 1.

  The diffraction grating 8 has a structure having a flat surface planarized with high accuracy on the light incident surface from the optical pickup 1 and a diffraction surface in which a plurality of grooves are formed at a predetermined pitch on the opposite surface. ing.

  Light incident from the flat surface of the diffraction grating 8 generates diffracted light at a certain predetermined angle and is emitted from the diffraction grating 8 by the grooves on the diffraction surface.

  Of the emitted diffracted light, the 0th-order light and the + 1st-order light, and the 0th-order light and the −1st-order light are overlapped to cause interference. The light emitted in this way is incident on the protective layer 22 formed so as to cover all or part of the diffraction surface of the diffraction grating 8.

  The light transmitted through the protective layer 22 is emitted from an emission surface formed on a smooth surface opposite to the surface facing the diffraction surface. Of the light emitted from the emission surface, the zero-order light and the ± first-order light superimposed on the zero-order light are captured by the condenser lens 11.

  FIG. 2 is a schematic diagram of zero-order light and ± first-order light incident on the condenser lens in the first embodiment. In FIG. 2, the description of the same reference numerals as those in FIGS. 1 and 5 to 7 is omitted.

  In FIG. 2, 23 is 0th-order light, 24 is + 1st-order light, 25 is -1st-order light, and 26 is interference light when the light emitted from the condenser lens 11 is viewed from above the condenser lens. The condenser lens 11 has a numerical aperture larger than the numerical aperture (NA) of the objective lens 6 in order to capture all the zero-order light 23 of the objective lens 6.

  Further, as shown in FIG. 2, the size of the region of the protective layer 22 covering the diffractive surface is the size of the region where the interference light of the 0th order light and the ± first order light taken into the condenser lens 11 is transmitted through the protective layer 22. However, in order to increase the mechanical strength, it is preferable to cover the entire surface of the diffraction grating 8 to increase the thickness of the entire surface to obtain a uniform mechanical strength. The light emitted from the condenser lens 11 is imaged on the image sensor 13 by the imaging lens 12. The interference fringe pattern of the formed image is analyzed by the processing device 14 to detect aberrations that are optical characteristics of the optical pickup 1 and the objective lens 6 and display them on the display device 15. Based on the detection result, the position of the objective lens 6 in the optical pickup 1 is adjusted by the objective lens adjusting mechanism 16.

  FIG. 3 is a dimension diagram of the diffraction grating and the protective layer in the first embodiment. In FIG. 3, the description of the same reference numerals as those in FIGS. 1 to 2, 5 to 7 is omitted.

  In FIG. 3, the thickness of the diffraction grating 8 is a, the width of the convex part of the groove is b, the width of the concave part of the groove is c, the height of the groove is h, the pitch of the diffraction grating 8 is d, and the optical axis of the objective lens 6 The thickness of the protective layer 22 is e, the refractive index of the diffraction grating 8 is n1, the refractive index of the protective layer 22 is n2, the wavelength of the laser from the optical pickup is λ, and the numerical aperture of the objective lens of the optical pickup is NA. . Here, the pitch d of the diffraction grating 8 is d = b + c.

  The design of the diffraction grating 8 is most preferably performed under the conditions of the following formulas (1) to (3) from the viewpoint of improving analysis accuracy when analyzing interference fringes. This is because of the following two points. The first point is that the overlapping areas of the 0th-order light and the + 1st-order light, and the 0th-order light and the −1st-order light are the largest in order to perform highly accurate analysis by using interference fringes in a large area. This is to ensure that The second point is that by increasing the contrast of the interference fringes of the 0th order light, the + 1st order light, and the −1st order light transmitted through the protective layer 22, the 0th order light, the + 1st order light, and the −1st order light are slightly changed. This is because even with a slight phase shift, a clear brightness and darkness is generated by the interference fringes to increase sensitivity and perform highly accurate analysis.

  However, m is an integer of 0, 1, 2,.

  From the equation (1), it can be seen that the groove pitch d of the diffraction grating 8 decreases as the NA increases. For example, a DVD with NA of about 0.6 has a fine shape of d≈1 μm, and a BD with a NA of 0.85 has a fine shape of d≈0.470 μm.

  The groove height h of the diffraction grating 8 depends on the difference between the refractive index n1 of the diffraction grating 8 and the refractive index n2 of the protective layer 22 from the equation (2), and the groove depth h decreases as the difference increases. . BD has a very fine shape with a groove pitch of about 0.47 μm. Therefore, processing becomes difficult and processing accuracy is lowered by increasing the groove depth. Therefore, the refractive index is set so that the difference between n1 and n2 is as large as possible. Since spherical aberration correction of the protective layer 22 depends on the thickness e of the protective layer 22, in order to have the same function as the conventional cover glass, assuming that the refractive index of the conventional cover glass is n3 and the thickness is H, It is most preferable to satisfy the following conditions.

  For example, if quartz (refractive index≈1.456) is used for the diffraction grating 8 and a protective layer 22 having a refractive index of about 1.3 is used, the groove height is about 1.04 μm. When the constituent materials of the diffraction grating 8 and the protective layer 22 are different, on the optical axis of the objective lens 6, the optical distance between the surface of the diffraction grating 8 on the objective lens 6 side and the surface on the condenser lens 11 side, and the protective layer The protective layer 22 is formed so that the optical distance between the surface on the objective lens 6 side of 22 and the surface on the condenser lens 11 side becomes equal.

  The condensing lens 11 is designed so that the optical conditions are the best, such as the smallest spherical aberration, under the condition of being transmitted through the cover glass. Therefore, the thickness of the cover glass depends on the optical condition correction characteristics of the condenser lens 11. If an objective lens of a biological microscope is used as the condenser lens 11 and quartz having a thickness of 170 μm, which is generally used for a cover glass, is used, the thickness of the protective layer 22 is about 190.4 μm. The range of thickness depends on the spherical aberration correction optical characteristics of the condensing lens 11, but if this apparatus judges based on the point of inspection and adjustment of the aberration amount of about several mλ, the spherical aberration amount after exiting the condensing lens Is preferably set to be within several mλ.

  If the material used for the protective layer 22 is, for example, an optical adhesive that is also used in the optical disc manufacturing process, the refractive index is easily matched, the hardness after curing is high, and the thickness is easy to handle because it is easy to handle in the manufacturing process. Can be calculated.

  The protective layer 22 is formed on the diffraction grating 8 by applying an optical adhesive on the diffraction grating quartz wafer and rotating the diffraction grating wafer at a high speed of about 5000 to 8000 rpm to form a uniform liquid film. It is considered that this is sufficiently possible by using a so-called spin coating method in which this is cured to form a thin protective layer.

  As described above, according to the present embodiment, by forming the protective layer 22 with the refractive index adjusted on the groove surface of the diffraction grating 8, the diffraction grating portion in which the diffraction grating 8 and the protective layer 22 are combined is formed. It becomes possible to make the base material thickness about twice as thick. As a result, the mechanical strength of the diffraction grating portion is improved as compared with the mechanical strength possessed by the single diffraction grating, and the distortion and deflection of the diffraction grating 8 that occurs when the adhesive is attached to the diffraction grating adjusting mechanism 7 are prevented. This can prevent a decrease in aberration detection accuracy. At the same time, it is possible to prevent the diffraction grating 8 from being damaged by contact with other apparatus components and the objective lens 6. Further, by using the protective layer 22 with the refractive index and thickness of the protective layer adjusted, it is possible to perform spherical aberration correction equivalent to that of the cover glass, and the cover glass, position adjusting mechanism, etc. can be omitted, and the device configuration can be omitted. It can be greatly simplified.

  Further, the concave portion of the grating groove of the diffraction grating 8 is filled with the protective layer 22, and the distance between the convex surface of the diffraction grating 8 and the surface of the protective layer 22 facing the convex surface, and the concave surface of the diffraction grating 8 By making the distance between the surface of the concave portion and the surface of the protective layer 22 facing it equal, the diffraction surface which is the groove surface of the diffraction grating 8 is completely covered with the protective layer 22. As a result, foreign matter can be prevented from adhering to the micron-order grooves, and foreign matter on the exit surface of the protective layer 22 can be easily removed simply by lightly touching it with a wiping member such as a lens cleaner. It becomes possible.

  In addition, by using a material that has semi-transmission characteristics with respect to the light incident on the material used for the protective layer, it is possible to reflect a part of the light incident on the diffraction grating and detect the signal characteristics of the optical pickup. It is also possible to have

  FIG. 4 is a schematic diagram of the diffraction grating, the semi-reflective layer, and the protective layer in the first embodiment. 4, the description of the same reference numerals as those in FIGS. 1 to 3 and FIGS. 5 to 7 is omitted.

  In the present embodiment, the protective layer is written with a single material, but as shown in FIG. 4, a thin semi-reflective layer 27 having a semi-reflective property is formed between the diffraction grating 8 and the protective layer 22, A two-layer structure in which a protective layer with an adjusted refractive index is formed on top of it to improve the mechanical strength, correct spherical aberration, and detect the signal characteristics of the optical pickup by reflecting the light emitted from the optical pickup. It is also considered possible. Here, as the semi-reflective layer 27, for example, a material such as aluminum, gold, or platinum may be used.

  In the present embodiment, the material used for the protective layer 22 is an optical adhesive. However, the protective layer is formed using a transparent metal oxide thin film such as silicon dioxide having a low refractive index as well as the optical adhesive. You may do it. The protective layer can be formed satisfactorily by using a sol-gel method or the like, which is known as a manufacturing method for forming an optical thin film on the surface of an optical component such as a lens, and a high-quality metal oxide thin film can be obtained. When using a metal oxide thin film, the transmittance may decrease depending on its thickness, but it is sufficient if the decrease in the amount of transmitted light is corrected by adjusting the light emission amount of the optical pickup or the original laser light source. Is possible.

  The lens measuring apparatus of the present invention is a measuring apparatus for an objective lens of an optical pickup or a lens such as a DSC mounted on an optical information recording apparatus by forming a protective layer having an adjusted refractive index and thickness on a diffraction grating. Applicable.

Schematic diagram of lens measuring apparatus in Embodiment 1 Schematic diagram of 0th order light and ± 1st order light incident on condensing lens in Embodiment 1 Dimensional diagram of diffraction grating and protective layer in Embodiment 1 Schematic diagram of diffraction grating, semi-reflective layer, and protective layer in Embodiment 1 The figure which shows the lens measuring method of patent document 1 The figure which shows the diffraction grating provided with the coating plate of patent document 2 The figure which shows the diffraction grating provided with the coating layer of patent document 2

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up 2 Light source 3 Lens 4 Mirror 5 Holder 6 Objective lens 7 Diffraction grating adjustment mechanism 8 Diffraction grating 11 Condensing lens 12 Imaging lens 13 Imaging element 14 Processing apparatus 15 Display apparatus 16 Objective lens adjustment mechanism 22 Protective layer

Claims (3)

A light source that emits light to the lens;
A diffraction grating that forms diffracted light of different orders from light emitted from the light source and transmitted through the lens;
A protective layer formed on the diffraction surface of the diffraction grating opposite to the lens;
A light receiving device that receives the diffracted lights of different orders that interfere with each other;
A measuring device that measures the aberration of the lens from the received interference image,
On the optical axis of the lens, the surface of the protective layer opposite to the diffraction surface is flat, and the optical distance between the lens-side surface of the diffraction grating and the surface of the measurement device, and the protection An optical distance between the lens-side surface of the layer and the measuring device-side surface is equal. In the diffraction surface of the diffraction grating, the distance between the concave surface and the surface of the protective layer facing the concave surface is equal to the distance between the convex surface and the surface of the protective layer facing the convex surface. The lens measuring device according to claim 1. 3. The lens according to claim 1, wherein the refractive index of the protective layer is lower than the refractive index of the diffraction grating, and the thickness of the protective layer is thicker than the thickness of the diffraction grating on the optical axis of the lens. measuring device.

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