JP2009032360A - Pickup device, coma aberration correction method, or the like - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pickup device for optimally adjusting each of tilts of a plurality of objective lenses with a simpler configuration to correct each coma aberration, and to provide a coma aberration correction method, etc. <P>SOLUTION: The optical pickup 1 is equipped with an actuator 10 with a plurality of objective lenses 11a and 11b mounted thereon. At least one objective lens not satisfying a sine condition is contained in the plurality of objective lenses so that coma aberration occurs depending on the tilt of incidence light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present application relates to a technical field such as an optical pickup including an actuator equipped with a plurality of objective lenses.

  The objective lens used in the optical pickup provided in the information reproducing / recording apparatus for reproducing or recording an optical disc is usually sine condition so that the manufacturing and assembly errors of the mirror provided in the optical pickup do not adversely affect the performance. Designed to satisfy. For this reason, coma does not occur due to the inclination of the incident light to the objective lens. Therefore, it is only necessary to correct only the coma aberration caused by the inclination of the objective lens itself. The sine condition is expressed by the following equation.

nsinα / nsinα ′ = constant where n is the refractive index of the medium in the object space, n ′ is the refractive index of the medium in the image space, and α is the optical axis of the light beam coming from the object point on the optical axis in the object space. The inclination, α ′, means an angle conjugate to α in the image space.

  Incidentally, in recent years, an information reproducing / recording apparatus capable of reproducing or recording a plurality of optical discs having different recording densities of CD, DVD, and Blu-ray Disc is known. Such an information reproducing / recording apparatus includes an optical pickup having two objective lenses, an objective lens for CD and DVD and an objective lens for Blu-ray.

  Such two objective lenses are generally fixedly mounted on an actuator, and the tilt angle of the objective lens itself is adjusted by adjusting the tilt angle of the actuator. Therefore, when the direction and magnitude of the tilt of the two objective lenses are different, even if the tilt of one objective lens is best adjusted so as not to cause coma, the tilt of the other objective lens is the best. This causes a problem that it cannot be adjusted.

Regarding such a problem, in the technique disclosed in Patent Document 1, in an optical pickup including a plurality of objective lenses, the optical pickup includes a plurality of mounting holes for inserting the plurality of objective lenses. The mounting surface of at least one of the mounting holes is provided with a lens holder that is formed with a curved surface so that the inclination of the objective lens installed on the mounting surface can be adjusted. Tilt adjustment between a plurality of objective lenses is possible.
JP 2006-019001 A

  However, in the technique of Patent Document 1 as described above, a special lens holder formed with a curved surface is required so that the inclination of the objective lens can be adjusted, and the lens holder is attached when the objective lens is attached. Since it needs to be fixed, it is considered difficult to correct coma caused by the inclination of the objective lens itself in a state where information can be read from the optical disk by servo control.

  In view of this, the present application considers the elimination of such a point as one of the problems, and a pickup device and a coma capable of correcting the respective coma aberrations by adjusting the inclinations of a plurality of objective lenses with a simpler configuration. An object is to provide an aberration correction method and the like.

  In order to solve the above problem, the invention according to claim 1 is a pickup device including an actuator having a plurality of objective lenses mounted thereon, and coma aberration is generated in the plurality of objective lenses due to an inclination of incident light. As described above, at least one objective lens that does not satisfy the sine condition is included.

  According to a fourth aspect of the present invention, coma aberration is reduced by adjusting a tilt angle of incident light on the objective lens that does not satisfy the sine condition in the pickup device according to any one of the first to third aspects. A correction means for correcting is provided.

  The invention described in claim 7 is a coma aberration correcting method for correcting coma using the pickup device according to any one of claims 1 to 3, wherein the objective lens does not satisfy the sine condition. The coma aberration is corrected by adjusting the incident angle of the incident light to.

  Hereinafter, the best embodiment of the present application will be described with reference to the accompanying drawings. In addition, embodiment described below is embodiment at the time of applying this application with respect to adjustment apparatuses, such as a mirror inclination.

  First, with reference to FIG. 1 etc., the structure and function of a mirror tilt adjusting device according to this embodiment will be described.

  FIG. 1 is a diagram illustrating a schematic configuration example of a mirror tilt adjusting device according to the present embodiment.

  As shown in FIG. 1, the mirror tilt adjusting device S includes an optical pickup (pickup device) 1, a signal processing unit 2, a control unit 3, an actuator driving circuit 4, a jitter meter 5, and the like.

  In the example of FIG. 1, a spindle motor that rotates and drives an optical disk D as an example of an optical recording medium, a carriage that moves the optical pickup 1 to a predetermined reading position on the optical disk D, and laser light of a laser diode that will be described later. A laser drive circuit for controlling the intensity is not shown. In this embodiment, CD, DVD, and Blu-ray Disc (hereinafter referred to as BD) are assumed as examples of the optical disc D.

  The optical pickup 1 reads a signal by irradiating the optical disc D with laser light and receiving reflected light with respect to the irradiated light.

  More specifically, the optical pickup 1 has two wavelengths (for example, 780 nm) suitable for the actuator 10, CD, and DVD in which the first objective lens 11a and the second objective lens 11b are fixedly mounted via the lens holder 10a. And a first laser diode 12a that emits a first laser beam having a wavelength suitable for BD (for example, 405 nm), a second laser diode 12b that emits a second laser beam having a wavelength suitable for BD, a first beam splitter 13a, and a second beam. Splitter 13b, first collimator lens 14a, second collimator lens 14b, first mirror 15a, second mirror 15b, first multilens 16a, second multilens 16b, first light receiving element 17a, second light receiving element 17b, etc. It is configured with.

  The optical pickup 1 is configured so that the first objective lens 11a and the second objective lens 11b are mounted. However, the present invention is not limited to this, and three or more objective lenses are mounted. (For example, an objective lens is provided for each optical disc of CD, DVD, and BD).

  In such a configuration of the optical pickup 1, when the first laser light is emitted from the first laser diode 12 a, the light passes through the first beam splitter 13 a and is made substantially parallel light by the first collimator lens 14 a, The light is reflected by one mirror 15a and is incident on the first objective lens 11a. Then, the light incident on the first objective lens 11a is condensed on the recording surface of the optical disc D.

  On the other hand, when the second laser light is emitted from the second laser diode 12b, the light passes through the second beam splitter 13b, is made into substantially parallel light by the second collimator lens 14b, and is reflected by the second mirror 15b. The light enters the second objective lens 11b. Then, the light incident on the second objective lens 11 b is collected on the recording surface of the optical disc D.

  The reflected light reflected from the optical disk D is reflected by the first mirror 15a or the second mirror 15b, reflected by the first beam splitter 13a or the second beam splitter 13b, and the first multi lens 16a or the second multi lens. The light is received by the first light receiving element 17a or the second light receiving element 17b via 16b. Then, an RF (Radio Frequency) signal corresponding to the intensity of the received light is amplified to a predetermined level by an RF amplifier (not shown) and output to the signal processing unit 2.

  At the time of correcting coma aberration described later, the signal processing unit 2 outputs various error signals to the control unit 3, and the control unit 3 servo-controls the actuator 10 via the actuator drive circuit 4 based on these signals.

  Here, the first objective lens 11a is an objective lens for CD and DVD, and coma aberration is caused by the inclination of incident light (the inclination from the optical axis, and the incident angle represented by “θ” in FIG. 1). Is designed to occur (so that the sine condition is not satisfied). On the other hand, the second objective lens 11b is an objective lens for BD, and is designed so that coma aberration does not occur due to the inclination of incident light (sine condition is satisfied).

  FIG. 2 is a graph showing coma aberration characteristics when an objective lens satisfying the sine condition is used and when an objective lens not satisfying the sine condition is used.

  In an objective lens that satisfies the sine condition, as shown in FIG. 2A, the coma aberration hardly occurs due to the inclination of the incident light to the objective lens. Instead, the coma aberration largely occurs due to the inclination of the objective lens. It is supposed to be. On the other hand, in an objective lens that does not satisfy the sine condition, as shown in FIG. 2B, coma aberration is intentionally generated by the inclination of the incident light to the objective lens. The coma aberration generated by the inclination of is smaller than that of the objective lens satisfying the sine condition shown in FIG. By adjusting the tilt angle of the incident light to the objective lens that does not satisfy such a sine condition, the coma aberration can be corrected (coma aberration is canceled out later).

  From the viewpoint of canceling coma aberration, as shown in FIG. 2B, the ratio of coma aberration generated by the inclination of the incident light to the objective lens (that is, coma aberration when the inclination angle changes by a unit amount). It is preferable that the ratio of change) and the ratio of coma generated by the tilt of the objective lens be approximately the same (one to one), but strictly speaking, for example, incident light on the objective lens It is desirable to determine the ratio of coma generated due to the inclination of the objective lens in consideration of the residual coma aberration magnitude of the objective lens (that is, considering canceling the residual coma aberration).

  As the ratio of coma generated by the tilt of incident light to the objective lens increases, the range in which coma can be corrected by adjusting the tilt angle of incident light is expanded. It can be said that the range in which the coma aberration can be corrected becomes narrower by adjusting the inclination angle of the actuator 10.

  Here, the inclination angle of the incident light to the first objective lens 11a is adjusted by, for example, changing the angle of the first mirror 15a.

  In order to correct the coma aberration (that is, to eliminate the coma aberration), for example, an RF level or jitter as an example of a parameter value obtained from the signal read by the optical pickup 1 is the best (for example, in the case of the RF level, The mirror angle may be adjusted so that the value is an extreme value (for example, maximum), and in the case of jitter, the value is an extreme value (for example, minimum). For example, the signal processing unit 2 calculates jitter based on the signal read by the optical pickup 1 and outputs the value to the jitter meter 5. The jitter meter 5 displays the calculated value (or RF level). The adjuster changes the angle of the first mirror 15a while watching the value displayed on the jitter meter 5, and adjusts the angle at which the jitter becomes the best. After the adjustment, the angle of the first mirror 15a is fixed with a UV curing adhesive or the like. A mirror driving circuit that receives the jitter output from the jitter meter 5 and adjusts the angle of the first mirror 15a so that the jitter becomes the best may be provided.

  The inclination angle of the second objective lens 11b itself is adjusted by changing the inclination angle of the actuator 10 (for example, the inclination of the reference surface of the lens holder 10a). After the adjustment, the actuator 10 is fixed with a UV curable adhesive or the like.

  Next, a coma aberration correction method at the time of manufacturing the optical pickup 1 will be described with reference to FIG.

  FIG. 3 is a flowchart illustrating an example of a coma aberration correction process in manufacturing the optical pickup 1 and the like.

  In FIG. 3, when the coma aberration correction process is started, for example, the BD as the optical disk D is set in the mirror tilt adjusting device S (step S1), and the servo control of the BD is started (step S2). Next, as described above, the angle of the actuator 10 is adjusted so that the jitter and RF level are the best (step S3), and the actuator 10 is fixed with a UV curable adhesive or the like (step S4). Thus, the coma aberration on the second objective lens 11b side is corrected.

  Next, the DVD as the optical disk D is set in the mirror tilt adjusting device S (change of the optical disk D) (step S5), and servo control of the DVD is started (step S6).

  Next, as described above, the angle of the first mirror 15a is adjusted so that the jitter and RF level are the best (step S7), and the first mirror 15a is fixed with a UV curable adhesive or the like (step S8). Thus, the coma aberration on the first objective lens 11a side is corrected.

  Note that the required accuracy of the BD is stricter than that of the DVD or CD, and it is necessary to correct the coma aberration more strictly. Therefore, an objective lens that satisfies the sine condition is used on the BD side as usual. It is desirable to adjust the tilt angle of the objective lens itself, and it is desirable to adjust the tilt angle of the incident angle to the objective lens using an objective lens that does not satisfy the sine condition on the DVD or CD side.

  As described above, according to the above embodiment, the first objective lens 11a that does not satisfy the sine condition and the sine condition are satisfied so that the optical pickup 1 generates coma aberration due to the inclination of the incident light. The second objective lens 11b is provided with an actuator 10, and the coma aberration on the second objective lens 11b side is adjusted by adjusting the tilt angle of the second objective lens 11b itself (adjusting the tilt angle of the actuator 10). And the coma aberration on the first objective lens 11a side can be corrected by adjusting the tilt angle of the incident light on the first objective lens 11a. Therefore, the first objective lens 11a and the second objective lens 11b are corrected. Even when the actuator 10 is mounted on the actuator 10, the tilt of these two objective lenses can be adjusted optimally with a simpler configuration. It is possible to correct the Ma aberration.

  In the above-described embodiment, an objective lens that does not satisfy the sine condition is employed for both the first objective lens 11a and the second objective lens 11b so that coma aberration occurs due to the inclination of incident light. Also good. In this case, the tilt angle of the actuator 10 (for example, the tilt of the reference surface of the lens holder) is adjusted to “0”, and then each objective lens (the first objective lens 11a and the second objective lens 11b) is used. By reading the signal from each optical disk D and adjusting the tilt angle of the incident light to each objective lens so that the RF level, jitter, etc. are the same as above, and fixing it with UV adhesive etc. Aberrations will be corrected. In this case, the optical pickup 1 has a wide allowable range with respect to the change in the tilt of the lens holder, and can increase the allowable tilt value of the lens holder and improve the yield.

  In the above embodiment, the tilt angle of the incident light to the first objective lens 11a is adjusted by changing the angle of the first mirror 14a. However, the present invention is not limited to this. For example, The position of the first collimator lens 14a or the first laser diode 12a may be adjusted by moving the position vertically and horizontally to change and adjust the tilt angle of the incident light on the first objective lens 11a.

It is a figure which shows the example of a schematic structure of the mirror inclination etc. adjustment apparatus which concerns on this embodiment. It is a figure which shows the coma aberration characteristic at the time of using the objective lens which satisfies sine conditions, and the objective lens which does not satisfy sine conditions. It is a flowchart which shows an example of the correction process of the coma aberration at the time of manufacture of optical pick-up 1 grade | etc.,.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up 2 Signal processing part 3 Control part 4 Actuator drive circuit 5 Jitter meter 10 Actuator 11a 1st objective lens 11b 2nd objective lens 12a 1st laser diode 12b 2nd laser diode 13a 1st beam splitter 13b 2nd beam splitter 14a 1st collimator lens 14b 2nd collimator lens 15a 1st mirror 15b 2nd mirror 16a 1st multi lens 16b 2nd multi lens 17a 1st light receiving element 17b 2nd light receiving element S Mirror inclination etc. adjustment apparatus

Claims (7)

A pickup device including an actuator equipped with a plurality of objective lenses,
The plurality of objective lenses include at least one objective lens that does not satisfy the sine condition so that coma is generated due to the inclination of incident light. The pickup device according to claim 1,
The plurality of objective lenses include an objective lens that satisfies the sine condition together with an objective lens that does not satisfy the sine condition. The pickup device according to claim 1,
The objective lens that does not satisfy the sine condition is formed so that the coma aberration ratio generated by the inclination of the incident light and the coma aberration ratio generated by the inclination of the objective lens are approximately the same. Pickup device characterized by that.   The correction apparatus which correct | amends a coma aberration by adjusting the inclination angle of the incident light to the objective lens which does not satisfy the sine conditions in the pick-up apparatus as described in any one of Claims 1 thru | or 3 is provided. The adjustment device. The information processing apparatus according to claim 4,
The adjustment device adjusts an incident angle of the incident light so that a parameter value obtained from the read signal becomes the best. The information processing apparatus according to claim 5,
The correction means adjusts an incident angle of the incident light after adjusting an inclination angle of an actuator provided in the pickup device so that a parameter value obtained from the read signal becomes the best. Adjustment device. A coma aberration correcting method for correcting coma aberration using the pickup device according to claim 1,
A coma aberration correcting method, wherein coma aberration is corrected by adjusting an incident angle of incident light to an objective lens that does not satisfy the sine condition.

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