JP4108014B2 - Inspection method for optical pickup - Google Patents

Description

  The present invention relates to an optical pickup inspection method, and more particularly, to an optical pickup inspection method for inspecting an optical head that reads and writes information on an information storage medium such as a DVD (Digital Versatile Disk).

  As one of methods for inspecting the performance of an optical pickup head for reading information from an optical disk type high density information storage medium and storing information in the high density information storage medium, an output signal evaluation method using a disk is known. is there. The inspection by the conventional output signal evaluation method will be briefly described with reference to FIG. The light emitted from the optical pickup head 2 becomes a condensing spot on the recording surface of the disk 1, and the reflected light from the disk 1 is received by the optical pickup head 2 again. Convert. The electric signal 4 is evaluated by an electric signal detection device 3 such as an oscilloscope. The electric signal 4 becomes a wave-like signal that repeats the strength with the signal recorded on the recording surface of the disk 1. Depending on the magnitude of the amplitude Δh of this signal and the magnitude of variation in the period Δt, The characteristics of the pickup head 2 are evaluated. Such an evaluation method is described in Patent Document 1, for example.

As another conventional inspection method for the optical pickup head, there is a method for evaluating the size of the spot diameter produced by the optical pickup head. This method will be briefly described with reference to FIG. In FIG. 8, a condensing spot 5 formed by condensing light emitted from the optical pickup head 2 is enlarged by an optical microscope 6, received by an image sensor 7, and processed by an image processing device 8. The image processing apparatus 8 measures and evaluates the spot diameter P when, for example, 50% of the maximum value of the light amount is set as a threshold value. This evaluation method is a generally well-known method, and is described in Non-Patent Document 1, for example.
JP 2002-216388 A Noboru Murayama et al., “Optical Disc Technology”, Radio Technology Inc.

  In the output signal evaluation method described in Patent Document 1, when the evaluation result is bad, the following three factors can be considered as factors. That is, “Laser output in the optical pickup fluctuates with time”, “Inappropriate position when irradiating a light spot on the disk” or “Reception in the optical pickup” It is not properly converted when converting the amount of light received by the unit into an electrical signal.

However, the output signal evaluation method described in Patent Document 1 has a problem that even if the evaluation result is bad, it cannot be divided into the above three possible factors.
That is, the recording surface of the optical disc 1 in FIG. 7 is generally formed with a groove called a guide groove, and it is necessary to accurately irradiate the center of this groove. Whether or not the light is accurately applied to the center of the groove is measured as a tracking error signal and a focus error signal in the optical pickup from the reflected light characteristics from the disk 1. Based on this signal, the optical pickup head 2 performs control so as to perform alignment so that the spot is accurately irradiated to the center of the groove of the disk 1. Such position control of the optical pickup head 2 is described in detail in, for example, Patent Document 1.

  Also, as a method for evaluating whether the laser output changes with time, a method of measuring the output change by installing a light receiving element at the exit of the optical pickup is conceivable. The output fluctuation occurs when the emitted light returns to its own laser. For this reason, the method of installing the light receiving element at the emission port is clearly different from the case of irradiating the disk 1 and therefore cannot be evaluated correctly.

  If the evaluation result in the output signal evaluation method is bad, the optical pickup head 2 cannot be repaired unless these factors can be specified. Further, it takes time to specify which process of the optical pickup process should be improved.

  In the spot diameter evaluation method described in Non-Patent Document 1 described above, high accuracy is required for focus adjustment of the optical microscope 6 in FIG. 8, and there is a problem that time is required for rough adjustment. Furthermore, since the optical aberration in the optical microscope 6 directly affects the spot image, there is a problem that the measurement accuracy is lowered.

  Accordingly, an object of the present invention is to make it possible to individually evaluate the time characteristics of laser light emission, the spatial characteristics of irradiation, and the light receiving characteristics of a light receiving unit installed in an optical pickup head.

In order to achieve the above object, an inspection method for an optical pickup according to the present invention is a method for evaluating an optical pickup head evaluation device that outputs emitted light from the optical pickup and transmitted through a diffraction grating while modulating a control signal of a light source in the optical pickup. and received by the optical detection unit, a first step of evaluating the time characteristic of the output of the optical pickup and a receiving optical signals in the control signal and the light detection part, in the diffraction grating is emitted from the optical pickup A second step of receiving the reflected light by the light receiving unit in the optical pickup and evaluating the light receiving characteristic of the light receiving unit based on the time characteristic of the output and the light reception signal in the light receiving unit; It is characterized by.
According to the present invention, in the above, it is preferable that the control signal of the light source in the optical pickup is a rectangular wave control signal .

  As described above, according to the inspection method for an optical pickup according to the present invention, the time characteristics of laser light emission, the spatial characteristics of irradiation, and the light reception characteristics of the light receiving unit installed in the optical pickup head are individually set. Can be evaluated.

A specific embodiment of the present invention will be described.
(1) First Embodiment FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1, 2 is an optical pickup head, 9 is a semi-transmissive diffraction grating, 10 is a condenser lens, 11 is an imaging lens, 12 is an image receiving element, 13 is an image analysis device, 14 is a half mirror, and 15 is a condenser. A lens, 16 is a light detection element, 17 is a light detection element in the optical pickup head 2, 3 is an electric signal detection device such as an oscilloscope, 18 is a laser in the optical pickup head 2, and 19 is a controller that drives the laser 18. .

  The light emitted from the optical pickup head 2 is collected on the groove surface of the diffraction grating 9. The light incident on the diffraction grating 9 is divided into zero-order diffracted light, ± first-order diffracted light, and so on. By making the pitch of the diffraction grating 9 appropriate, an image received by the imaging element 12 by the condenser lens 10 and the imaging lens 11 has an outline of + 1st order diffracted light and −1st order diffracted light as shown in FIG. In a contact state, interference fringes of 0th-order diffracted light and + 1st-order diffracted light can be generated, and simultaneously, interference fringes of 0th-order diffracted light and −1st-order diffracted light can be generated. Note that the generation of the interference fringes itself is as described in, for example, Japanese Patent Application Laid-Open No. 2002-090262, and is not an essential matter for the present invention, and thus detailed description thereof is omitted.

  As is well known, the pattern of the interference fringes changes depending on the aberration included in the light emitted from the optical pickup head 2. Defocusing occurs when the spot position on the diffraction grating 9 deviates from the groove surface of the grating, and this also changes the pattern of interference fringes, as described in JP-A-2002-090262. It is possible to detect the defocus from the interference fringe pattern and align the spot and the grating 9 in the optical axis direction. For example, the alignment is performed so that the defocus is zero. If the focus error signal of the optical pickup head 2 at this time is evaluated, the accuracy of focus on the actual disk can be evaluated.

  That is, it is well known that the image received by the image sensor 12 of FIG. 1 changes as shown in FIG. 3 depending on the positional relationship between the diffraction grating 9 and the focused spot. When there is a spot at the center of the convex portion of the diffraction grating 9 or the center of the concave portion as shown in FIGS. 3 (i) and (iii), the + 1st order diffracted light and the −1st order diffracted light have the same phase, The intensities of the interference fringes L or R generated as a result of the interference are equal. On the other hand, as shown in FIGS. 3 (ii) and (iv), when there is a spot on the boundary from the convex part to the concave part or the boundary from the concave part to the convex part, the + 1st order diffracted light and the −1st order diffracted light are used. A difference occurs in the intensity of the interference fringes L or R which are different from each other and are a result of the interference with the zero-order diffracted light.

  Based on the above, when the intensities of the interference fringes L and R coincide with each other, the position of the condensing spot is at the center of the groove or the valley. By adjusting the position of the focused spot, for example, by evaluating the characteristics of the tracking signal obtained by the optical pickup head 2 when the focused spot is positioned at the center of the convex part or the concave part of the grating 9, You can evaluate the tracking accuracy of the disc.

  Then, the position of the spot and the diffraction grating 9 is controlled based on the intensity ratio of the interference fringes L and R and the interference fringe pattern, and then the laser 18 is modulated by the controller 19 shown in FIG. An example of the modulation signal at this time, that is, the laser transmission control signal is shown in FIG. Here, as shown in the figure, modulation is performed so that a rectangular wave laser output is obtained at certain time intervals. In addition, FIG. 2A shows an example of a light reception signal received by the light detection element 16 as a light reception element by the half mirror 14 and the condenser lens 15 at this time. From the comparison between the control signal of the controller 19 and the light reception signal of the light detection element 16, the time change of the output of the laser 18 is evaluated. For example, the difference t1 between the rise time of the control signal of the controller 19 and the rise time of the light reception signal of the light detection element 16, the difference t2 between the fall time of the control signal and the fall time of the light reception signal, or the magnitude of the light reception signal Evaluate u. Further, the light reception signal at the light receiving element 17 at this time is similarly evaluated, and thereby the characteristics of the light receiving element 17 are evaluated.

As described above, the light emission time characteristics of the laser 18 installed in the optical pickup head 2, the spatial characteristics of the irradiation from the optical pickup head 2, and the light reception characteristics of the light receiving element 17 are simply and individually evaluated. be able to.
(2) Second Embodiment FIG. 4 is a diagram showing a second embodiment of the present invention. Here, as shown in FIG. 4, the light from the optical pickup head 2 is collected on the substrate 20 on which the diffraction grating pattern G is partially formed, and is collected by the condenser lens 10. The substrate 20 can be moved by the switching mechanism 21, and the position irradiated with the focused spot from the optical pickup head 2 can be switched between the lattice pattern G and the non-patterned portion N. The light passing through the condenser lens 10 is imaged on the image receiving element 12 by the imaging lens 11, whereby an image of the pupil plane of the condenser lens 10 is obtained.

  When spot light is irradiated onto the grating pattern G, the interference fringes L and R of 0th-order diffracted light and ± 1st-order diffracted light are analyzed in the analyzer 13 in the same manner as described in the first embodiment. Is obtained. From the interference fringes L and R, the aberration included in the light emitted from the optical pickup head 2 is analyzed. The analysis of the aberration is performed by a method as described in, for example, the above-mentioned JP-A-2002-090262. However, the analysis of the aberration itself is not an essential matter for the present invention, and a detailed description thereof will be omitted.

  At this time, as shown in FIG. 5, the coordinates A (xa, ya), C (xc, yc) of the two end points A and C of the interference region by the 0th order diffracted light and the + 1st order diffracted light, and the 0th order light and the −1st order The coordinates B (xb, yb) and D (xd, yd) of the two end points B and D of the interference area by light are calculated, and the numerical aperture is calculated from the relative position of these coordinates. For example, assuming that the wavelength used is λ and the grating pitch of the diffraction grating pattern G is p, when the numerical aperture NA satisfies the following formula, as shown in FIG. The outline of touches. Details of this point are as disclosed in JP-A-2002-090262.

p = λ / NA (1)
When the focal length of the condenser lens 10 in FIG. 4 is f, the radius r of the light beam formed on the pupil plane of the condenser lens 10 is expressed as follows from the definition of the numerical aperture.

r = f * NA / √ (1-NA ² ) (2)
Using this r, the coordinates of A to D are expressed as follows using the magnification g of the pupil plane of the lens 10 and the image sensor 12.

xa = xc = −r / 2 × g (3)
xb = xd = r / 2 × g (4)
ya = yb = √ (r ² − (r / 2) ² ) × g (5)
yc = yd = −√ (r ² − (r / 2) ² ) × g (6)
When the numerical aperture NA is changed to NA ′, the radius of the light beam is r ′ represented by the following equation.

r ′ = f × NA ′ / √ (1−NA ′ ² ) (7)
FIG. 5B shows a case where the radius r ′ of the light beam is larger than that in FIG. 5A, and FIG. At this time, the coordinates A to D are as follows, and the x coordinate does not change, but the y coordinate changes.

xa = xc = −r / 2 × g (8)
xb = xd = r / 2 × g (9)
ya = yb = √ (r ′ ² − (r / 2) ² ) × g (10)
yc = yd = −√ (r ′ ² − (r / 2) ² ) × g (11)
Using the equations (1) to (11), the numerical aperture of the light emitted from the optical pickup head 2 in FIG. 4 is determined.

  In addition, when spot light is irradiated onto the non-patterned portion N of the substrate 20 in FIG. 4, the light intensity distribution formed on the pupil plane of the condenser lens 10 is obtained in the analyzer 13 as shown. Since the intensity distribution formed on the pupil surface of the condenser lens 10 is substantially equal to the intensity distribution of the exit of the optical pickup head 2, the intensity distribution obtained by the analysis device 13 at this time is the intensity distribution of the aperture of the optical pickup head 2. To express. An example of the opening intensity distribution is shown in FIG. FIG. 6 also shows how the pupil plane of the condenser lens 10 is imaged on the image receiving element 12.

  As described above, the wavefront aberration, aperture intensity distribution, and numerical aperture of the light beam emitted from the optical pickup head 2 are obtained. These are subjected to Fourier transform to obtain intensity information on the focal plane, that is, the spot shape. In other words, as described in detail in “Light and Fourier Transform” written by Tanaka Kaihiko (Asakura Shoten, May 1992), if the input is in the front focal plane of the lens, the back focal plane of this lens is completely Fourier transform is obtained, and the scale is converted as follows, assuming that the scale at the front focus is δ1, the scale at the back focus is δ2, the wavelength is λ, and the focal length of the lens is f1.

δ2 = λ × f1 / δ1 (12)
Therefore, if the phase information determined from the light wavefront aberration and the amplitude information determined from the aperture intensity distribution are Fourier-transformed, the characteristics of the focused spot can be obtained with a scale determined by λ × f1.

A change in numerical aperture is treated as a change in f1.
This is expressed by the following equation. Here, Io (x1, y1) is the light intensity distribution on the lens surface, and the lens aperture is treated as a unit circle. φ (x1, y1) is a phase distribution due to the wavefront aberration of the emitted light beam on the lens surface, and similarly treats the lens aperture as a unit circle. Is (x2, y2) is the intensity distribution of the focused spot.

(F [Io (x1, y1) × φ (x1, y1)]) ²
= Is (λ · f1 / x2, λ · f1 / y2) (13)
f1 = √ (1 · NA ² −1) (14)
As described above, since the image of the focused spot is not directly evaluated, it is possible to perform measurement with high accuracy without requiring fine focus adjustment of the microscope during observation. When the diffraction grating surface and the focused spot position are displaced in the optical axis direction, a wavefront aberration called a defocus component occurs in the interference fringes. Therefore, by removing the defocus component from the wavefront phase distribution φ (x1, y1) at the time of Fourier transform, it is possible to evaluate the characteristics of the focused spot without defocus. In this way, it is not necessary to perform focus adjustment with high accuracy, so that evaluation can be performed quickly. That is, the size of the condensing spot formed by the optical pickup head can be evaluated quickly and with high accuracy.

Schematic which shows the apparatus for enforcing the inspection method of the optical pick-up of the 1st Embodiment of this invention The figure which shows an example of the light reception signal and laser transmission control signal in the photon detection element in the apparatus of FIG. The figure which shows the position of the spot in the inspection apparatus of FIG. 1, and the change of an interference pattern Schematic which shows the apparatus for enforcing the inspection method of the optical pick-up of the 2nd Embodiment of this invention The figure for demonstrating the relationship between the numerical aperture and the edge coordinate of an interference fringe in the inspection apparatus of FIG. The figure for demonstrating the measuring method of opening intensity distribution in the inspection apparatus of FIG. A diagram showing a method for evaluating characteristics of a conventional optical pickup head The figure which shows the spot diameter evaluation method of the conventional optical pick-up head

Explanation of symbols

2 Optical Pickup Head 3 Electric Signal Detection Device 9 Transflective Grating 12 Image Receiver 16 Photodetector 17 Photodetector 18 Laser 19 Controller

Claims (2)

The light output from the optical pickup and transmitted through the diffraction grating while modulating the control signal of the light source in the optical pickup is received by the light detection unit of the optical pickup head evaluation device, and the control signal and the light detection unit a first step of from the the receiving optical signals for evaluating the time characteristic of the output of the optical pickup,
The light emitted from the optical pickup and reflected by the diffraction grating is received by the light receiving unit in the optical pickup, and the light receiving characteristic of the light receiving unit is determined based on the time characteristic of the output and the light reception signal in the light receiving unit. A second step to evaluate;
An inspection method for an optical pickup comprising: 2. The optical pickup inspection method according to claim 1, wherein the control signal of the light source in the optical pickup is a rectangular wave control signal .

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