JP2002090605A - Lens-adjusting device and lens-adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens-adjusting device with which dust or the like is prevented from adhering to a diffraction grating, and a lens-adjusting method utilizing such a device. SOLUTION: This lens-adjusting device 10 is provided with a diffraction device 22 diffracting the light transmitted through a lens 12 to zero-th order diffracted light and first-order diffracted light differently and making the diffracted light interfere, a moving device 36 for moving the device 22, and an aberration measuring device 44 for obtaining the aberration of the lens from the interference image by the zero-th order diffracted light and the first- order diffracted light. Then, the device 22 is equipped with the diffraction grating 24, having a diffraction surface 26 where plural grooves 28 are formed, a conductive film 30 covering over the diffraction surface, in a state where a recessed part 60 corresponding to a groove is left and an electrical wire 32 which grounds the conductive film to ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information storage medium of an optical disk system, for example, a DVD (Digita1 VersatileDisable).
The present invention relates to an apparatus and method for adjusting an optical lens for reading and writing information, or an optical lens for forming a light spot by combining light in a laser processing machine, a laser microscope, or the like.

[0002]

BACKGROUND OF THE INVENTION In order to read information from an optical disk type high-density information storage medium and to store information on the high-density information storage medium, light emitted from a light source can be accurately irradiated to a target place. Optical system is required. for that reason,
In particular, the objective lens of the optical system not only requires strict optical characteristics per se, but also must be accurately fixed to a target place.

As a method of inspecting or adjusting an objective lens, as shown in FIG. 1, light (eg, laser light) 2 emitted through an objective lens 1 is used as a reference 3 for lens inspection (eg, an optical disk). ), The reflected light from the reference reference 3 is detected, the reproduction signal 4 obtained from this detection is compared with the reference signal 5, and the phase difference 6 between the reproduction signal 4 and the reference signal 5 is minimized. It is conceivable to adjust the inclination or the like of the objective lens 1 so that the phase difference falls within a predetermined allowable value (jitter method).

However, the characteristics of the objective lens 1 generally differ from each other, and there is no fixed relationship between the amount of tilt of the objective lens 1 and the like and the phase difference 6, and as shown in FIG. The other objective lens 1B may exhibit significantly different characteristics (lens tilt angle-phase characteristics). Also,
The tilt adjustment of the objective lens and the comparison of signals must be repeatedly performed, and it is difficult to objectively determine at which stage the adjustment is completed. Further, the inclination of the objective lens 1 and the like cannot be sufficiently grasped from the reproduction signal 4. Therefore, the present invention
It is an object of the present invention to provide a new lens adjusting device that replaces the above-described jitter method.

[0005]

SUMMARY OF THE INVENTION A first embodiment of a lens adjusting apparatus according to the present invention is to obtain diffracted lights of different orders from light transmitted through the lens, and to obtain diffracted lights of these different orders (for example, 0th-order diffracted light and ± 1st-order diffracted light). ), A diffracting means for obtaining an interference image by causing interference, a moving means for moving the diffraction device, and an aberration measuring means for obtaining aberration of the lens from the interference image. Further, the diffraction means includes a diffraction grating having a diffraction surface in which a plurality of grooves are formed, a conductive film covering the diffraction surface while leaving a concave portion corresponding to the groove, and grounding the conductive film to ground. Grounding means. Note that the thickness of the conductive film is preferably about 40% or less of the width of the groove.

A lens adjusting device according to a second embodiment of the present invention comprises:
The diffraction means has a diffraction grating having a diffraction surface on which a plurality of grooves are formed, and forms a smooth surface on the opposite side of the diffraction surface by filling each groove of the diffraction surface, and has a different refractive index from the diffraction grating. And a coating layer made of a material having the following.

A lens adjusting device according to a third embodiment of the present invention comprises:
The diffraction means includes a diffraction grating having a diffraction surface in which a plurality of grooves are formed, and a covering plate disposed on the diffraction surface at a predetermined distance from the diffraction surface. .

The lens adjusting devices of the first to third embodiments further include a tilt adjusting means for adjusting the tilt of the lens, and a control for operating the tilt adjusting means in accordance with the aberration obtained by the aberration measuring means. Means are preferably provided.

A lens adjusting method according to a first embodiment of the present invention is as follows.
A diffraction grating having a diffraction grating having a diffraction surface with a plurality of grooves formed thereon, a conductive film covering the diffraction surface while leaving a concave portion corresponding to the groove, and grounding means for grounding the conductive film to ground. Providing a means, providing light transmitted through the lens to the diffraction grating, causing the diffracted lights of different orders obtained from the diffraction grating to interfere with each other, moving the diffraction device; and A step of obtaining the aberration of the lens from an image; and a step of adjusting the inclination of the lens according to the aberration. Note that the thickness of the conductive film is preferably about 40% or less of the width of the groove.

A lens adjusting method according to a second embodiment of the present invention includes:
Diffraction means, a diffraction grating having a diffraction surface in which a plurality of grooves are formed, fills each groove of the diffraction surface and forms a smooth surface on the opposite side of the diffraction surface, and has a different refractive index from the diffraction grating. And a coating layer made of a material having the same.

A lens adjusting method according to a second embodiment of the present invention comprises:
The diffraction means includes a diffraction grating having a diffraction surface on which a plurality of grooves are formed, and a covering plate disposed on the diffraction surface at a predetermined distance from the diffraction surface.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments of the present invention will be described below with reference to the accompanying drawings. First, FIG. 3 shows an optical storage medium such as a DVD (Digita1 Versa).
1 shows an optical lens adjustment system (adjustment device) 10 for reading and writing information on a tile disk, or an optical lens for forming a light spot by combining light in a laser processing machine, a laser microscope, or the like.

A lens to be adjusted by the adjustment system 10 (hereinafter, referred to as an “objective lens”) 12 is provided on an optical pickup 14. The objective lens 12 is supported by a tilt adjusting device 16, and by operating the tilt adjusting device 16, the tilt of the objective lens 12 (in two directions, a left-right direction and a direction perpendicular to the drawing) can be adjusted. It is. When reading the tilt of the objective lens 12, the objective lens 12 and the optical pickup 14 are held with the optical axis of the objective lens 12 substantially aligned with the optical axis 20 of an evaluation device 18 described later. In the present embodiment, only the objective lens 12 is used alone and the tilt adjustment device 1 is used.
6, the optical pickup 14 is supported by the tilt adjusting device 16, and the optical pickup 1 is supported by the tilt adjusting device 16.
By changing the inclination of 4, the inclination of the objective lens 12 may be adjusted. Also, the tilt adjusting device 16
May be a simple manual adjustment screw or a device driven by a motor.

The evaluation device 18 for evaluating the inclination of the objective lens 12 has a diffraction device 22. The diffraction device 22 has a plate-like diffraction grating 24. The diffraction grating 24 is made of acrylic resin,
As shown in FIG. 4A, a plurality of grooves 28 are formed on one surface (diffraction surface) 26 at a predetermined pitch and arranged in parallel with each other. I have. When the optical lens to be adjusted is, for example, an objective lens for reading and writing information on an optical disk, the pitch of the grooves 28 is preferably equal to the distance between tracks on the optical disk. The diffraction surface 26 on which the groove 28 is formed, or both the diffraction surface 26 and the surface on the opposite side, are covered with a conductive film 30 made of a conductive material. In addition, the conductive film 30 includes an electric wire 32 serving as a grounding means.
Is grounded to the ground 34 via the.

The diffraction grating 24 is arranged perpendicular to the optical axis 20 so that the diffraction surface 26 substantially coincides with the focal point of the objective lens 12. The diffraction grating 24 is also connected to a moving device 36 that moves the diffraction grating 24 in a direction perpendicular to the optical axis 20 (the left-right direction in FIG. 3). Note that, as the moving device 36, a linear stage having a piezo element, a DC motor, or a stepping motor with high resolution, which can move the diffraction grating 24 by a small amount can be suitably used. On the opposite side of the objective lens 12 with the diffraction grating 24 interposed therebetween, a collimating lens 38 for demodulating light transmitted through the objective lens 12 and the diffraction grating 24 into parallel light, and a collimating lens 38
An imaging lens 40 that re-images the parallel light transmitted through the imaging lens 40 and an imaging element (for example, a charge-coupled device) 42 that receives the light transmitted through the imaging lens 40 are arranged.

The image pickup device 42 is electrically connected to an aberration measuring device 44. The aberration measurement device 44 includes the imaging device 4
The display device 46 for displaying the image received by the display device 2 and the display device 4
An aberration calculator 48 for measuring the aberration of the objective lens 12 based on the image displayed in 6 is provided. The aberration measuring device 44
It is electrically connected to the control device 50 for controlling the driving of the tilt adjusting device 16 and the moving device 36 described above.

The tilt adjustment of the objective lens 12 by the adjustment system 10 having the above configuration will be specifically described. At the time of adjusting the tilt, as shown in FIG. 3, the objective lens 12 is fixed with its optical axis substantially aligned with the optical axis 20. Next, a light source (not shown) arranged on the opposite side of the diffraction grating 24 with the objective lens 12 therebetween is turned on, and parallel light (for example, laser light) is incident on the objective lens 12. The light transmitted through the objective lens 12 is focused on the diffraction grating 24, particularly on the surface where the groove 28 is formed. Also, the diffraction grating 24
Are the 0th-order diffracted light, ± 1st-order diffracted light,.
The light is split into nth-order diffracted light, and is projected on an image sensor 42 via a collimator lens 38 and an imaging lens 40. Here, the diffraction grating 24 is the zero-order diffracted light 5 on the projection surface of the image sensor 42.
The 2nd and + 1st-order diffracted lights 54 are designed to partially interfere with each other, and the 0th-order diffracted light 52 and the -1st-order diffracted light 56 are designed to interfere with each other. Therefore, as shown in FIGS. 5A and 5B, the display device 46 for reproducing the image projected on the image sensor 42 has an interference image (interference fringe) of the 0th-order diffracted light 52 and the + 1st-order diffracted light 54. , An interference image (interference fringe) of the 0th-order diffracted light 52 and the -1st-order diffracted light 56 is projected.

The shape of the interference fringes differs depending on the tilt direction of the objective lens 12. Now, the objective lens 12 is
5 is parallel to the longitudinal direction of the groove 28 but inclined in a direction perpendicular to the groove 28 (transverse direction of the groove).
The interference pattern shown in FIG. When the objective lens 12 is parallel to the transverse direction of the groove 28 of the diffraction grating 24 but is inclined in the longitudinal direction of the groove 28, interference fringes shown in FIG. 5B appear.

At this time, when the moving device 36 is driven based on a signal from the control device 50 to move the diffraction grating 24 in the left-right direction (the direction transverse to the groove) in FIG. 3, the change in the phase of the 0th-order diffracted light and +1 A shift occurs between the change in the phase of the first-order diffracted light and the change in the phase of the minus first-order diffracted light, and the light intensity at each point of the interference fringes changes. For example, the light intensity change at point a in FIG. 5A draws a waveform (sine wave) Ia shown in FIG. 6, and the light intensity change at point b in FIG. 5A shows the waveform (sine wave) shown in FIG. (Wave) Ib, and a phase difference φ is observed between both waveforms Ia and Ib. Therefore, for example, when the difference between the phase of the point a and the phases of a plurality of other points on the X-axis in FIG. 5A is plotted on a graph based on the phase of the point a, a quadratic curve shown in FIG. 7 is obtained. And the quadratic coefficient of this quadratic curve represents the tilt of the objective lens 12 in the transverse direction. As shown, the X axis is the center point of the interference fringes (corresponding to point a) on the line (center line) connecting the center of the 0th-order diffracted light and the center of the ± 1st-order diffracted light.
, And a line orthogonal to the center line.

Similarly, on the basis of the phase of the point a, the difference between the phase of the point a and the phases of a plurality of other points on the Y and Y 'axes shown in FIG. FIG.
Are obtained, and the quadratic coefficient of the quadratic curve represents the inclination of the objective lens 12 with respect to the longitudinal direction. It should be noted that the Y and Y ′ axes are points a
And a line in a direction making an angle of, for example, 45 ° with the center line.

The calculation for obtaining the inclination of the objective lens 12 as described above can be automatically performed by the aberration calculator 48.

The inclination of the objective lens 12 calculated by the aberration calculator 48 is output to the controller 50. Control device 5
In the case of 0, the tilt adjusting device 16 is driven based on the tilt of the objective lens 12 obtained from the aberration calculator 48 to correct the tilt of the objective lens 12. If necessary, the above-described processing is performed again on the corrected objective lens 12 to verify whether or not the inclination of the objective lens 12 has been corrected. Tilt can also be corrected.

The result of the tilt adjustment of the objective lens performed in this way depends on the optical distortion (that is, disturbance of interference fringes) of the interference image projected on the image sensor 42.
Most of the disturbance of the interference fringes is caused by dust or dirt attached to the surface of the diffraction grating 24. In particular, if dust or dirt adheres to the groove 28 at the focal position of the objective lens 12, the intensity or direction of the diffracted light changes depending on the location, and the interference fringes are more disturbed, which adversely affects the result of the tilt adjustment. Exert.

The diffraction grating 24 can be easily formed by resin molding or the like. However, since the resin is easily charged with static electricity, there is a problem that dust is particularly easily adhered and the adhered dust cannot be easily removed. On the other hand, since the depth and width of the grooves of the diffraction grating are generally about several μm or less, particularly in the case of a diffraction grating made of a relatively soft resin, if an attempt is made to physically contact an object with the diffraction grating to remove dust and the like. In addition, the groove may be broken. Further, since the diffraction grating is a reference surface for adjusting the inclination of the objective lens, in order to replace a diffraction grating with a broken groove, the inclination, position, and the like of the diffraction grating must be adjusted again.

To cope with this problem, in the adjustment system 10 of the present embodiment, the surface of the diffraction grating 24 is covered with the conductive film 30 as described above, and the electric charge held in the diffraction grating 24 is transferred to the ground 34 via the electric wire 32. To the diffraction grating 2
No electric charge is stored in 4. Therefore,
Dust having electric charge is hard to adhere to the diffraction grating 24, and the attached dust can be removed only by lightly contacting a cleaning member such as a lens paper with the diffraction grating 24. Therefore, even when the diffraction grating 24 is formed of a relatively soft resin, the grooves formed in the diffraction grating are not broken.

The thickness of the conductive film 30 will be described with reference to FIG. In order to obtain clear interference fringes between a bright part and a dark part, the ratio of the light quantity of the ± 1st-order diffracted light to the light quantity of the 0th-order diffracted light (hereinafter referred to as “light quantity ratio”) is 0.2 to 5,
Preferably, it is 0.5 to 2. On the other hand, 0
The ratio of the light quantity of the ± 1st-order diffracted light to the light quantity of the second-order diffracted light varies depending on the dimensions of the groove surface, and more specifically, the dimensions of the concave portion 60 drawn by the surface of the conductive film that comes into contact with the atmosphere and the convex portion 62 between adjacent concave portions. More specifically, when the thickness of the conductive film 30 is constant at all places,
Is equal to the depth of the groove 28, so that there is no difference in the optical path length in the depth direction between the case without the conductive film 30 and the case with the conductive film 30, and does not affect the light amount ratio. However, since the conductive film 30 is also formed on the side surface (side wall) of the groove 28, in the diffraction grating 24 where the conductive film 30 is formed, the concave portion 6 is formed.
A difference occurs between the width B1 of 0 and the width B2 of the convex portion 62, which affects the light amount ratio. Specifically, when the width B1 of the concave portion 60 is equal to the width B2 of the convex portion 62, the light amount ratio is 1, and when the concave portion 60 is completely filled with the conductive film 30, the light amount ratio is 0. Therefore, in the present embodiment, the thickness of the conductive film 30 is set to about 40% or less of the width B1 ′ of the groove 28 so that a light amount ratio equal to or more than the above-described lower limit (0.2) is obtained. In order to obtain a clearer interference fringe, the conductive film 3
It is preferable that the thickness of 0 is about 20% or less of the width B1 'of the groove 28.

In the above description, the conductive film 30 only needs to have conductivity for the purpose of removing charges. Also,
The conductive film 30 is preferably transparent because it needs to transmit light. However, even if it is a non-transparent conductive film, if the film thickness is small, it can sufficiently transmit light, and the sensitivity can be increased by increasing the sensitivity of the image sensor 42 for measurement. An interference fringe having a necessary contrast can be obtained. Therefore, various conductive materials (for example, chromium, gold, platinum, and silver) are used as a material for forming the conductive film 30.
Is available.

In the above description, in the diffraction device 22, the surface of the diffraction grating 24 is covered with the thin conductive film 30, but as shown in FIG.
6 may be covered with a covering layer 70 made of a material having a different refractive index from the material constituting the diffraction grating 24. In this case, as shown, the coating layer 70 completely fills the groove 28 of the diffraction grating 24, and the surface on the side opposite to the groove 28 is a smooth surface 72. In the case of this diffraction device, dust and the like adhering to the smooth surface 72 can be removed only by lightly bringing a cleaning member such as a lens paper into contact with the diffraction grating 24.

Further, as shown in FIG. 4C, the diffraction surface 26 of the diffraction grating 24 is covered with a coating plate 80 arranged at a predetermined interval on the diffraction surface 26, and these diffraction gratings 24 and the coating plate are covered. The distance between them may be precisely defined by the spacers 82 disposed therebetween. In the case of this diffractometer,
The diffraction surface 26 is protected from dust and the like by the cover plate 80. Further, dust and the like adhering to the cover plate 80 can be removed only by lightly bringing a cleaning member such as a lens paper into contact with the diffraction grating 24.

Further, the diffraction device 22 to the image pickup device 4
The configuration of the optical system arranged in the optical path up to 2 (that is, the type and number of lenses) is not limited to the above embodiment.

[0031]

As described above, according to the lens adjusting apparatus and the lens adjusting method of the present invention, the inclination of the objective lens can be adjusted easily and in a short time. Further, since the diffraction surface of the diffraction grating can be maintained in a clean state, it can be used for a long time without replacing the same diffraction grating, and as a result, the adjustment yield can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of lens adjustment of a conventional jitter type optical pickup.

FIG. 2 is an explanatory view of a conventional example.

FIG. 3 is a schematic configuration diagram of a lens adjustment device according to the present invention.

FIG. 4A is a partial cross-sectional view of the diffraction device according to the first embodiment;
(B) Partial sectional view of the diffraction device of the second embodiment, (c) third
FIG. 2 is a partial cross-sectional view of the diffraction device according to the embodiment.

FIG. 5 is a diagram showing interference fringes generated by a diffraction grating.

FIG. 6 is a diagram showing a change in light intensity due to a minute displacement of a diffraction grating.

FIG. 7 is a diagram showing a phase distribution of interference fringes.

[Explanation of symbols]

 10: Optical lens adjustment system 12: Objective lens 14: Optical pickup 16: Inclination adjustment device 18: Evaluation device 20: Optical axis 22: Diffraction device 24: Diffraction grating 26: Diffraction surface 28: Groove 30: Conductive film 34: Ground 36: moving device 38: collimating lens 40: imaging lens 42: imaging device 44: aberration measuring device 46: display device 48: aberration calculating device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G086 HH06 2H044 AC01 2H049 AA03 AA13 AA43 AA50 AA55 AA57 AA70 5D117 AA02 CC07 KK15 KK16 KK17 5D119 AA38 BA01 NA02 PA05

Claims (9)

[Claims] 1. A lens adjusting device for adjusting a lens, comprising: diffracting means for obtaining diffracted lights of different orders from light transmitted through the lens, and interfering the diffracted lights of the different orders to obtain an interference image; Moving means for moving the diffraction device; and aberration measuring means for obtaining the aberration of the lens from the interference image, wherein the diffraction means corresponds to a diffraction grating having a diffraction surface on which a plurality of grooves are formed, and the grooves. A lens adjusting device comprising: a conductive film that covers the diffraction surface while leaving a concave portion; and a grounding unit that grounds the conductive film to ground. 2. The method according to claim 1, wherein the thickness of the conductive film is about 4 times the width of the groove.
2. The lens adjusting device according to claim 1, wherein the value is set to 0% or less. 3. A lens adjusting device for adjusting a lens, comprising: diffracting means for obtaining diffracted lights of different orders from light transmitted through the lens, and interfering the diffracted lights of the different orders to obtain an interference image; A moving means for moving the diffraction device; and an aberration measuring means for obtaining the aberration of the lens from the interference image, wherein the diffraction means comprises: a diffraction grating having a diffraction surface formed with a plurality of grooves; A lens adjusting device comprising: a filling layer formed of a material having a different refractive index from the diffraction grating, wherein each lens groove is filled and a smooth surface is formed on a side opposite to the diffraction surface. 4. A lens adjusting device for adjusting a lens, comprising: diffracting means for obtaining diffracted lights of different orders from light transmitted through the lens, and interfering the diffracted lights of the different orders to obtain an interference image; A moving means for moving the diffraction device; and an aberration measuring means for obtaining aberration of the lens from the interference image, wherein the diffracting means comprises: a diffraction grating having a diffraction surface on which a plurality of grooves are formed; And a cover plate disposed at a predetermined distance from the diffraction surface. 5. The apparatus according to claim 1, further comprising: tilt adjusting means for adjusting the tilt of the lens; and control means for operating the tilt adjusting means in accordance with the aberration obtained by the aberration measuring means. 5. The lens adjustment device according to any one of 4. 6. A lens adjusting method for adjusting a lens, comprising: a diffraction grating having a diffraction surface with a plurality of grooves formed therein; and a conductive film covering the diffraction surface with a concave portion corresponding to the groove remaining. Preparing a diffracting means having grounding means for grounding the conductive film to ground; and impinging light transmitted through the lens on the diffraction grating and diffracted light of different orders obtained from the diffraction grating. A lens comprising: a step of causing interference; a step of moving the diffraction device; a step of determining the aberration of the lens from the interference image; and a step of adjusting the tilt of the lens according to the aberration. Adjustment method. 7. The thickness of the conductive film is set to about 4 times the width of the groove.
7. The lens adjusting method according to claim 6, wherein the value is set to 0% or less. 8. A lens adjusting method for adjusting a lens, comprising: a diffraction grating having a diffraction surface having a plurality of grooves formed thereon; and a smooth surface filling each groove of the diffraction surface and being opposite to the diffraction surface. Forming a diffraction means comprising a coating layer made of a material having a different refractive index from the diffraction grating; anda step of providing light transmitted through the lens to the diffraction grating, and obtaining the light from the diffraction grating. Interfering diffracted lights of different orders, moving the diffraction device, obtaining aberration of the lens from the interference image, and adjusting a tilt of the lens according to the aberration. A lens adjustment method characterized by that: 9. A lens adjusting method for adjusting a lens, comprising: a diffraction grating having a diffraction surface on which a plurality of grooves are formed; and a coating disposed on the diffraction surface at a predetermined distance from the diffraction surface. A step of preparing a diffractive means including a plate; a step of irradiating the light transmitted through the lens onto the diffraction grating to interfere with diffracted lights of different orders obtained from the diffraction grating; and moving the diffraction device. A lens adjustment method, comprising: a step of determining the aberration of the lens from the interference image; and a step of adjusting a tilt of the lens according to the aberration.