JP2007042246A - Lens measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens measuring device for an optical pickup, configured so as to easily maintain the accuracy of the device, and to reduce time necessary for manufacturing the device and detecting characteristics of an objective lens. <P>SOLUTION: A light transmitted through an objective lens 6 is emitted from an optical pickup 1, the transmitted light is diffracted by a diffraction grating 11 to be a diffracted light whose phase is modulated for each wavelength, then the diffracted light is received as an interference image by reducing its center area quantity by a semitransmissive optical element 15, and the objective lens 6 is inspected based on the change of optical intensity in the interference image. Thus, the inspection is carried out within a short time by the simplified device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup lens measuring device for recording, reproducing, erasing, etc., information signals such as data, images, and sounds on an information recording medium such as an optical disk.

  An optical pickup is used as one of means for recording or reproducing information on an information recording medium such as an optical disk. This optical pickup requires an optical system capable of accurately irradiating a target location with light emitted from a light source in order to read information from the information recording medium and record information on the information recording medium. A typical optical pickup includes a light source such as a semiconductor laser element and a light receiving element, a collimating lens, an optical element such as a beam splitter or an objective lens.

  As a conventional example, an apparatus for irradiating an optical disk with a laser using an optical pickup will be described with reference to the block diagram of the optical disk apparatus in FIG.

  In FIG. 6, the light emitted from the light source 2 in the optical pickup 1 passes through the beam splitter 3 and becomes parallel light by the collimating lens 4. The parallel light is reflected by the rising mirror 5, then collected by the objective lens 6 and irradiated onto the optical disk 7 as a light spot. Grooves 8 are formed on the information recording surface of the optical disc 7 at regular intervals, and information is reproduced by irradiating light onto a convex portion 9 (track) located between the groove 8 and the adjacent groove. And recording and erasing are possible.

  The reflected light reflected by the optical disk 7 travels in the opposite direction to the optical path of the emitted light up to the beam splitter 3, is separated into an optical path different from the optical path of the emitted light by the beam splitter 3, and enters the light receiving element 10. . In the light receiving element 10, for example, a focus signal is detected by an astigmatism method, or a tracking signal is detected by a push-pull method.

  The objective lens 6 in the optical pickup 1 is moved in two axial directions, ie, an optical axis direction (focusing direction) and a direction orthogonal to the optical axis direction (tracking direction) by an electromagnetic driving force by an objective lens driving device (actuator) (not shown). The displacement is changed. As a result, the light spot accurately scans the track while focusing on the recording surface of the optical disc 7. During recording, information is recorded along a track on the recording surface of the optical disk 7 by a light spot. During reproduction, the light beam reflected by the recording surface is detected by the light receiving element 10 to reproduce information on the recording surface. .

  In order to read / write information from / to a high-density information recording medium such as a high-density and large-capacity DVD (Digital Versatile Disk) that has been used in recent years, light from a light source accurately irradiates a predetermined position. Must be configured. Therefore, the objective lens in the optical pickup is required to have strict optical characteristics in the objective lens itself, and it is necessary to accurately adjust the attachment position and angle.

  In order to solve these problems, the light transmitted through the objective lens in the optical pickup is diffracted to generate diffracted lights of different orders, and the diffracted lights of the respective orders are interfered to form a sharing interference image, A diffraction interferometry method has been proposed in which various aberrations (defocus, coma, astigmatism, spherical aberration) are evaluated using the phase differences of the light intensity measured at multiple points in this interference image, and the objective lens is adjusted. (For example, refer to Patent Document 1).

  FIG. 7 shows a schematic diagram of a lens measuring device using the diffraction interferometry.

  In FIG. 7, a diffraction grating 11 is disposed at the position of the light spot where the light beam emitted from the optical pickup 1 is collected, and the light incident on the diffraction grating 11 is in the 0th order, ± 1st order, ± It is decomposed into diffracted light of the order of the second order. At this time, when sharing interference light due to diffracted light is received as diffuse light (spherical wave), the central portion is bright and the peripheral portion is dark as shown in the light amount distribution diagram of the sharing interference image in FIG. An interference image with a bias is obtained. Therefore, in FIG. 7, the shearing interference image is once converted into parallel light by the condenser lens 12 and then imaged on the light receiving surface of the image sensor 14 by the imaging lens 13. In the image formed on the image sensor 14, the interference region of 0th-order diffracted light and ± 1st-order diffracted light includes interference fringes due to defocus, coma aberration, astigmatism, and spherical aberration.

  Here, since each point in the interference fringe has a unique phase, the diffraction grating 11 is moved at a constant speed in a direction perpendicular to the optical axis, and the light intensity change at a certain point in the interference region of the diffracted light is different from that. It is possible to obtain the phase difference of the light intensity change at the point, analyze the phase difference to evaluate each aberration, and inspect and adjust the objective lens 6.

In order to improve the measurement accuracy of coma, astigmatism, spherical aberration, etc., the phase of the diffracted light is changed using a diffraction grating having a plurality of regions where the grating grooves of the diffraction grating are different, and two diffracted lights of different orders are There has been further proposed an aberration detection method and apparatus for forming a shearing interference image by causing interference (see, for example, Patent Document 2).
JP 2000-329648 A JP 2002-202223 A

  However, in the conventional lens measuring device described above, it is necessary to accurately match the optical axis of the objective lens that emits the light beam from the optical pickup with the optical axis of the condensing lens on the device side that collects the light beam. This requires a long time for proper alignment and requires the use of a plurality of optical elements such as a condensing lens and an imaging lens, which complicates the configuration of the optical system on the device side and tends to cause a decrease in accuracy. Had problems.

  SUMMARY OF THE INVENTION An object of the present invention is to simplify the optical system of these devices so as to make it easy to maintain the accuracy of the devices, and to shorten the time required for device manufacture and characteristic detection.

  In order to achieve the above object, in the lens measurement device of the present invention, a diffraction grating that forms diffracted light of different orders from the light emitted from the lens, an imaging device that captures the diffracted light as an interference image, the diffraction grating, and the And a transmissive optical element that is disposed between the imaging elements and has a higher transmittance as the distance from the intersection with the optical axis of the zeroth-order diffracted light increases.

  Also, a diffraction grating that forms diffracted light of different orders from the light emitted from the lens, an image sensor that captures the diffracted light as an interference image, and a zero-order diffracted light that is disposed between the diffraction grating and the image sensor. And a transmission optical element whose transmittance increases stepwise as the distance from the intersection with the optical axis increases.

  As described above, according to the present invention, it is possible to simplify the configuration of the optical system of the apparatus, eliminate the need for precisely aligning the optical axes between lenses, and reduce the time required for lens measurement.

  Further, since there is no condensing lens or imaging lens on the apparatus side, the same effects as those of the conventional apparatus can be obtained with a simpler apparatus.

  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 device according to Embodiment 1 of the present invention.

  In FIG. 1, an optical pickup 1 is fixed by an optical pickup holding mechanism (not shown). A semiconductor laser light source, a collimator lens, a beam splitter and an objective lens 6 (not shown) are mounted in the optical pickup 1, and light from the semiconductor laser light source in the optical pickup 1 passes through the collimator lens and the beam splitter. The light is emitted from the objective lens 6.

  The light emitted from the objective lens 6 is incident on the diffraction grating 11 at the imaging position, and is diffracted into 0th-order diffracted light, ± 1st-order diffracted light, ± 2nd-order diffracted light,. The diffracted light passes through the transflective optical element 15 and is projected onto the screen 16. A projection image of the diffracted light projected on the screen 16 is captured by the image sensor 14 through the imaging lens 17. Thereby, on the light receiving surface on the image sensor 14, the 0th-order diffracted light and the + 1st-order diffracted light, and the 0th-order diffracted light and the −1st-order diffracted light overlap to form a shearing interference image. The interference fringes received on the light receiving surface of the image sensor 14 are analyzed by the analysis device 18 and the analysis results are displayed on the display device 19. Here, the transflective optical element 15 has a characteristic that the transmittance increases from the central region 20 including the portion intersecting the optical axis of the 0th-order diffracted light toward the outer peripheral region 21. Here, when a transmission optical element whose transmittance gradually increases as it moves away from the central region 20 is used, it can be changed with high accuracy because it changes uniformly with respect to light with less disturbance, and the transmittance increases stepwise. The resulting transmissive optical element is easier to manufacture.

  FIG. 2 shows a characteristic diagram of the transflective optical element according to Embodiment 1 of the present invention. The transflective optical element 15 can have a simple structure when a static optical element such as an ND filter is used, and the transmission characteristics can be controlled when a dynamic optical element such as a liquid crystal element is used. Can do. An opal diffuser is suitable for the screen 16 in consideration of spatial resolution and linearity between the projection light quantity and the photographing light quantity.

  Although the installation position of the screen 16 varies depending on the imaging magnification of the sharing interference image, the aperture diameter of the objective lens 6 of the optical pickup 1 is slightly smaller than the light receiving surface of the image sensor 14, and the imaging magnification of the sharing interference image is large. Assuming that the magnification is equal, the optimal distance between the screen 16 and the imaging lens 17 and between the imaging lens 17 and the light receiving surface of the light receiving element 14 is twice the focal length f2 of the imaging lens 17. .

  The diffraction grating 11 used here is a phase modulation element that is manufactured by, for example, etching using quartz glass as a mask and partially modulates the phase of transmitted light. The diffraction grating 11 has a plurality of grating grooves formed at predetermined intervals on one surface of a substrate having a constant thickness. FIG. 3 shows a configuration diagram of the diffraction grating according to the first embodiment of the present invention. Here, a diffraction grating having three types of grating groove regions is illustrated. In the first grating groove region 22, a plurality of grating grooves formed in a direction orthogonal to the moving direction of the diffraction grating are extended with a constant interval. In the second grating groove region 23, a plurality of grating grooves formed in parallel with the first grating groove region 22 in a direction having an angle of 45 ° are extended at a constant interval. Further, in the third grating groove region 24, a plurality of grating grooves formed in parallel with the grating grooves of the second grating groove region 23 in a direction having an angle of 90 ° are extended with a certain interval. Has been. Therefore, the light transmitted through the objective lens 6 of the optical pickup 1 is moved by moving the diffraction grating 11 having three types of grating groove regions in a direction perpendicular to the first grating groove region 22. To the second grating groove region 23 and the third grating groove region 24 sequentially, and the diffraction direction of the light can be converted.

  Examples of interference fringe patterns caused by sharing interference generated on the light receiving surface of the image sensor 14 include an interference pattern caused by defocusing, an interference pattern caused by coma aberration, an interference pattern caused by astigmatism, and an interference pattern caused by spherical aberration. Generally, these aberrations do not appear alone, but are formed by combining a plurality of aberrations.

  Since diffraction grating 11 in the first embodiment has three types of grating groove regions, it is obtained from light incident on each of first grating groove region 22, second grating groove region 23, and third grating groove region 24. The aberration is analyzed from the obtained sharing interference pattern. Aberration analysis in the analysis device 18 is performed using a phase shift method in which the phase distribution of light intensity at a plurality of points in the interference region is obtained and each aberration is evaluated.

  Although FIG. 1 shows an example in which the transflective optical element 15 is provided between the diffraction grating 11 and the screen 16, as shown in FIG. 4 as a schematic diagram of another configuration of the lens measuring device, the diffraction grating 11 and the objective When it is provided between the lenses 6, it is easy to replace the transflective optical element 15 according to the application, and by fixing the transflective optical element 15 to the diffraction grating 11 or the like, the time required for aligning the transflective optical element 15 alone with the optical axis. Can also reduce the loss.

  If the transflective optical element 15 is provided between the diffraction grating 11 and the screen 16 or between the imaging lens 17 and the image sensor 14, a lens measuring device including the transflective optical element 15 in the apparatus may be obtained. it can.

(Embodiment 2)
FIG. 5 shows a schematic diagram of a lens measuring apparatus according to Embodiment 2 of the present invention.

  The lens measurement device according to the second embodiment of the present invention is different from the lens measurement device according to the first embodiment of the present invention in that the screen 16 and the imaging lens 17 are not installed. In Embodiment 2 of the present invention, the light diffracted by the diffraction grating 11 passes through the semi-transmissive optical element 15 and forms an image on the light receiving surface of the imaging element 14.

  By directly capturing an image with the image sensor 14, the image sensor 14 can be brought closer to the diffraction grating 11 than in the first embodiment of the present invention. Conversely, if the distance between the image sensor 14 and the diffraction grating 11 is too long, the diffraction grating The diffracted light from 11 is diffused and inspection cannot be performed. Moreover, a simpler lens measurement device can be provided by the configuration of the second embodiment of the present invention.

  The lens measuring method and apparatus of the present invention can simplify the optical system of the lens measuring apparatus, and it is not necessary to align the optical axis of the objective lens and the optical axis of the condenser lens with high accuracy. Recording of information signals such as data, images, and audio on an optical disc type high-density information recording medium (for example, BD, HD-DVD, etc.) having the effect of shortening the recording capacity and speed. It can also be applied to an optical pickup inspection and adjustment device that performs reproduction, erasure, and the like.

Schematic of the lens measuring device in Embodiment 1 of the present invention Characteristics diagram of transflective optical element according to Embodiment 1 of the present invention Schematic diagram of diffraction grating in Embodiment 1 of the present invention Schematic of another structure of the lens measuring device in Embodiment 1 of this invention Schematic of the lens measuring device in Embodiment 2 of the present invention Configuration diagram of optical disc apparatus in conventional example Schematic diagram of a conventional lens measurement device Light intensity distribution diagram of sharing interference image in conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up 6 Objective lens 11 Diffraction grating 14 Image pick-up element 15 Semi-transmissive optical element 16 Screen 17 Imaging lens 18 Analyzing device 19 Display device

Claims (5)

A diffraction grating that forms diffracted light of different orders from the light emitted from the lens, an image sensor that captures the diffracted light as an interference image, and an optical axis of the diffracted light that is disposed between the diffraction grating and the image sensor. A lens measuring device comprising: a transmissive optical element whose transmittance increases as the distance from the crossing portion increases. The lens measuring apparatus according to claim 1, further comprising a screen disposed between the transmissive optical element and the imaging element. The lens measuring device according to claim 1, wherein the transmission optical element is an ND filter. The lens measuring device according to claim 1, wherein the transmissive optical element is a liquid crystal element. The lens measuring device according to claim 2, wherein the screen is an opal diffuser.

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