JP2552202Y2 - Hologram optical head - Google Patents

Description

[Detailed description of the invention]

[0001]

[Industrial application] This invention is based on
The photodetector and hologram element are integrated and
The present invention relates to a hologram optical head having a margin for movement of return light due to the hologram optical head.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a conventional optical head. The laser light emitted from the laser diode 1 is split into three light beams by a diffraction grating 2, reflected in a right angle direction by a half mirror 3, converted into parallel light by a collimator lens 4, and directed to a disk 7 by a rising mirror 5. The light is reflected at a right angle, collected by the objective lens 6 and focused on the signal surface of the disk 7.
The return light reflected by the disk 7 passes through the effect lens 6 along the same path, is reflected by the rising mirror 5 in a right angle direction,
The light is condensed by the collimator lens 4, passes through the half mirror 3, and further passes through the glass plate 8 for restoring the optical axis shift caused by passing through the half mirror 3, which is a flat glass plate. After passing through the concave lens 9, the light detector 10
Is irradiated. Although not shown, the photodetector 10 is a six-segment optical sensor having elements on both sides of the four-segment optical sensor. Focusing error detection is caused by transmission through the flat half mirror 3 and the glass plate 8. The astigmatism method using astigmatism is used, and tracking error detection is performed using two of the three beams.

[0003]

The above-mentioned conventional optical head has a large number of components and is arranged independently, so that it is not easy to miniaturize the optical head and requires a lot of man-hours for assembling each optical component. And a large number of adjustment steps are required. In addition, each optical component is often fixed with an adhesive, but the adhesive is easily affected by the temperature, so that there is a possibility that the optical component may be displaced due to temperature fluctuation. Since the number of locations to be used increases, there is a problem that the reliability of signal detection is reduced. In addition,
1-1177504 "Reflection type grating lens and optical head"
The `` device '' consists of multiple areas composed of hologram elements.
Detection with a grating substrate and a plurality of divided light receiving surfaces
An optical head device including a device is disclosed. But
However, this is a laser beam emitted from a laser diode.
Laser beam reaching the photodetector with respect to the irradiation optical axis of the laser beam.
With the configuration that the optical axis of the road is branched on the way by the beam splitter
is there. For this reason, laser diodes, hologram elements,
All optical elements that can be unitized, such as photodetectors,
Has a branch optical axis when compared to a coaxial arrangement
The unit configuration is enlarged around the laser beam irradiation optical axis
Equipment based on its structural characteristics based on the photodetection principle
Have a certain limit to the compactness of
Was something. In addition, the hologram element is
Into four regions, and different diffraction grating patterns
A lattice lens with a pattern is disclosed.
The four regions that define the diffraction grating pattern are a pair of obtuse angles.
Region and a pair of acute angle regions, especially in the acute angle region
For patterns, the wavelength of laser light caused by temperature changes
The tolerance range for the change of the diffraction angle due to fluctuation is obtuse
Issues such as limited allowable temperature change
was there. In addition, Japanese Patent Application Laid-open No.
-253678 "Optical semiconductor device" and JP-A-3-760
No. 35 "Hologram type optical pickup device" or JP
No. 3-269835 “Optical Pickup Device”
Hologram element on laser beam irradiation optical axis of laser diode
And a laser beam diffracted by the hologram element and returned
Is received by a photodetector in which the light receiving elements are linearly arranged.
A hologram laser unit is disclosed. But
However, both hologram laser units use photodetectors.
Are arranged in a straight line,
Of diffraction angle due to wavelength fluctuation of laser light due to power change
The fluctuation of the light receiving point on the light receiving element due to the
The setting of the light receiving area that allows the fluctuation of the light receiving point
It is not easy to design the photodetector because it differs depending on the child
Had the problem of.

The present invention has been made in view of the above circumstances, reduces the number of components of an optical head, integrates each optical component to reduce the size, reduces the number of assembling steps and adjustment steps, and further reduces temperature fluctuations. It is an object of the present invention to provide a hologram optical head which is less affected by the hologram.

[0005]

Means for Solving the Problems To achieve the above object,
The hologram optical head of the present invention
A laser diode for irradiating a laser beam, and the laser die
Coaxially arranged on the irradiation optical axis of the Aether and orthogonal to the irradiation optical axis
Two orthogonal axes that intersect on the irradiation optical axis
Diffraction gratings with different patterns for each of the four regions
The provided four-division hologram element and the laser diode
Are distributed around the periphery of the disk and reflected by the disk.
The laser light passes through each area of the four-division hologram element.
The laser light diffracted when returning to the
A set of four light receiving elements that receive light every time
And a photodetector in which the light receiving element is divided into two.
It is characterized by the following .

Further , the four-division hologram element is
One of the two orthogonal axes that divide the four regions is the jitter direction
Parallel to the jitter direction, and the photodetector is coupled in the jitter direction.
Then, the first light receiving element is disposed at a position rotated by 45 °, and
90 ° sequentially different from the first light receiving element
That the second, third and fourth light receiving elements are disposed
It is a feature .

[0007]

In the hologram optical head described above, the return light reflected by the disk is diffracted by the four regions of the hologram element and separated into four light beams, and individually irradiates the four light receiving elements of the photodetector. . In this case, the tracking error can be detected by the difference between the outputs of the light receiving elements respectively corresponding to the two areas of the hologram element composed of four areas and the other two areas, that is, by the push-pull method. Focusing error detection can be performed by the so-called double knife edge method based on the outputs of the two divided light receiving elements respectively corresponding to the two regions.

According to the hologram optical head of the second aspect ,
Return light that has passed through each area of the quadrant hologram element is determined.
In the normal state, approximately each of the first to fourth light receiving elements
In the center, so that, for example,
The wavelength of the laser beam fluctuates,
The fold angle changes and the first to fourth light receiving elements receive light.
Even if the light receiving point moves in the circumferential direction, the quadrant hologram
The four regions constituting the element evenly and uniformly move the light receiving point
Each can absorb as much as possible .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows one embodiment of the hologram optical head of the present invention.
FIG. 2 is an optical system configuration diagram showing an embodiment, and FIG.
FIG. 3 is an enlarged sectional view of the gram laser unit, and FIG.
FIG. 4 shows a grid pattern of a program element, and FIG.
FIG. 5 is a plan view of the light receiving element of the photodetector shown in FIG.
FIG. 6 shows a reference example of another lattice pattern of the
The case with grid pattern of holograms surface shown in FIG. 5
It is a top view of a light receiving element. Used in FIGS. 4 and 6
The suffixes attached to the symbols B and D are one-byte characters in the following description.
It is marked with a symbol. In FIG. 1, reference numeral 11 denotes a hologram laser unit which emits laser light and receives return light, which will be described in detail later . Reference numeral 12 denotes a laser beam emitted from the hologram laser unit 11 which rises toward the disk 14 and returns. A rising mirror for reflecting light toward the hologram laser unit 11, and reference numeral 13 denotes a disk 14.
Is an objective lens that converges a laser beam on the signal surface of (1).

FIG. 2 shows the details of the hologram laser unit 11. This hologram laser unit 11
A laser diode 17 is connected to a base 15 via a stem 16.
And a photodetector 18 attached thereto, accommodated in a case 19, and a cover glass 21 having a hologram surface, that is, a hologram element 20 formed on the inner surface side, is fixed to a laser light emission window 19 a opened in the case 19.

As shown in FIG. 3, the hologram element 20 is composed of four regions a, b, c and d in which a circle is equally divided into four and different grating patterns are formed. In the illustrated example of the grid pattern, a and d are equal pitches for the grid pitch, b and c are equal pitches wider than the above a and d, and a and c are the same direction for the grid direction, and b and d are the same. It is perpendicular to the directions a and d and in the same direction. The light detector 18 includes:
As shown in FIG. 4, the first to fourth light receiving elements A, B,
C and D are provided. The light receiving elements A, B, C, and D receive light beams transmitted through the four regions a, b, c, and d of the hologram element 20, respectively.
Is a light receiving element composed of a single element, and light receiving elements B and D are two-divided light receiving elements composed of two elements B1, B2 or D1, D2, respectively. Further, the light receiving elements A and D are the narrow equal pitch areas a of the hologram element 20;
The light receiving elements B and C are located at the same distance from the optical axis Z corresponding to d, and the light receiving elements B and C are closer to the optical axis Z than the positions of the light receiving elements A and D corresponding to the wide equal pitch regions b and c. In the position.

Next, signal detection by the hologram optical head will be described. The laser light emitted from the laser diode 17 in the hologram laser unit 11 passes through the hologram element 20, is reflected at right angles by the rising mirror 12, is converged by the objective lens 17, and focuses on the signal surface of the disk 14, The return light reflected by the disk 14 follows the same path, passes through the objective lens 13, is reflected again at right angles by the rising mirror 12, and passes through the cover glass 21 of the hologram laser unit 11. When passing through the hologram element 20, the four hologram elements 20 pass through four regions a, b, c, and d having different grating patterns, thereby obtaining four diffracted lights (for example, using only + 1st-order diffracted light). . The light beams that have passed through the regions a, b, c, and d of the hologram element 20, respectively, receive the light receiving elements A,
Each of B, C, and D is irradiated. Now, assuming that the jitter direction (disc tangent direction) is the Y axis, the reproduced RF signal (R
F), the tracking error detection signal (TE), and the focusing error detection signal (FE) are respectively obtained from the following equations . RF = A + B1 + B2 + C + D1 + D2 ... [1] TE = (A + D1 + D2)-(B1 + B2 + C) ... [2] FE = (B1 + D2)-(B2 + D1) ... [3] tracking error detection region a of the hologram element 20, the semi-circular portion and the region b of d, receiving the difference between amount of light passing through each other semi-circular portion of c elements a and D
It is used to detect the output difference between the B and C, the so-called push-pull method. The focusing error detection is a so-called double knife edge method.

When the jitter direction is the X axis, the reproduction R
The F signal (RF) and the focusing error detection signal (FE) are the same as described above, but the tracking error detection signal (TE) is given by the following equation: TE = (A + B1 + B2)-(C + D1 + D2) [4] ] . The principle of this detection is the same as in the above equation [2] .

In the above hologram optical head, when the hologram laser unit 11 is mounted on a base (not shown) of the optical head, an adjustment point comes every 90 ° by rotating the hologram laser unit about the Z axis. Therefore, only the adjustment of one axis in the Z-axis direction (focus direction) is required to adjust the mounting position. On the other hand, in the conventional optical head shown in FIG. 7, it is necessary to adjust three axes of a focus direction and two directions perpendicular to the focus direction, and the adjustment is greatly simplified. When the wavelength of the laser beam emitted from the laser diode 17 changes, the diffraction angle in the hologram element 20 changes. According to the present invention, the optical element can be made longer in the direction of 45 ° with respect to the XY axis. Therefore, it is easy to absorb the influence of the fluctuation of the diffraction angle, that is, the wavelength fluctuation of the laser light emitted from the laser diode 17.

As described above, according to the hologram optical head,
A laser die that irradiates the disk with laser light
A plane orthogonal to the irradiation optical axis on the irradiation optical axis of the arm 17
Are divided into four regions by two orthogonal axes intersecting on the irradiation optical axis.
For a, b, c, and d, the number of times the pattern differs for each region
Coaxially arranged 4-division hologram element 20 with folded grating
And a pair facing the periphery of the laser diode 17.
Dispersion of the four light receiving elements A, B, C, and D divided into two
The four-divided hologram element 20 is provided by the photodetector 18 provided.
Laser beam
Mode 17, a hologram element 20, and a photodetector 18.
All optical elements that can be unitized are coaxially arranged.
The laser light of the laser diode 17
Hologram divided into four parts inside a virtual cylinder whose axis is the irradiation optical axis of
Since the ram element 20 and the photodetector 18 can be arranged, the unit
Highest density arrangement is possible to increase the compactness of
And the laser diode 17 and the hologram
The element 20 and the photodetector 18 are configured as one unit,
High degree of integration can be achieved and miniaturization can be achieved.
Further, four regions constituting the four-division hologram element 20
a, b, c, d have the same area, so they are caused by temperature change
Of the diffraction angle due to the wavelength fluctuation of the rotating laser light
Each area can share the tolerance range equally,
The maximum allowable temperature change can be assured. Ma
The four-division hologram element 20 divides the four regions.
One of the two orthogonal axes is parallel to the jitter direction.
The photodetector 18 is rotated 45 ° with respect to the jitter direction.
A first light receiving element A is disposed at a position
A and A at positions 90 ° different from A
3. Is the fourth light receiving element B, C, D arranged and configured?
Return after passing through each area of the quadrant hologram element 20
Light is supplied to the first to fourth light receiving elements in a steady state, respectively.
A light can be received substantially at the center of A to D.
If the temperature of the laser beam changes with temperature, the hologram
The diffraction angle at the element 20 changes, and the first to fourth light receiving
The light receiving point of the return light received by the elements A to D moves in the circumferential direction
However, four regions constituting the four-division hologram element 20
a, b, c, d evenly move the light receiving point and
Maximum absorption, which is a fatal
You can avoid inviolability and promise stable reproduction
You . In the present invention, grid patterns other than those shown in the figures are used as grid patterns of the four regions of the hologram element 20.
Can also be used. However, for example, as shown in FIG.
As shown in the figure, the lattice direction is composed of four regions a, b, c, and d.
In this case, four light receiving elements A, as shown in FIG.
B, C, and D must be arranged in one row,
The present invention is characterized in that it is disposed around the optical axis of irradiation of laser light.
It would fall outside the scope of the plan. For your information,
When the optical elements B and C are two-divided optical sensors, the reproduction RF
Signal (RF), tracking error detection signal (TE),
Regarding the focusing error detection signal (FE),
Equations [1], [2], and [3] can be applied.

The hologram laser unit 11 may be fixed to the base of the optical head and the objective lens actuator for controlling the objective lens 13 may be separately provided. It is also possible to adopt a configuration in which the components are provided integrally. In this case, the integration of the components is more highly realized.

[0017]

[Effect of the Invention] According to the present invention,
The laser beam is irradiated on the irradiation optical axis of the laser diode.
Two orthogonal planes intersecting a plane orthogonal to the emission axis on the irradiation optical axis
Different patterns for each of the four regions divided by the axis
Coaxial hologram element with four diffraction gratings
And a pair facing the periphery of the laser diode is 2
In a photodetector with four divided light receiving elements arranged in conformal distribution
To receive the diffracted light by the quadrant hologram element
The laser diode, the hologram element and the optical detector
All the optical elements that can be unitized, such as
Can be configured to be axially arranged,
4 minutes inside a virtual cylinder about the irradiation optical axis of the laser beam
Since the split hologram element and photodetector can be
The highest density arrangement is possible to increase the compactness of the
This allows the laser diode, hologram element, and light
The detector and the detector are configured in one unit to achieve highly integrated
It is possible to achieve miniaturization and
Since the four regions constituting the system element have the same area,
Of diffraction angle due to wavelength fluctuation of laser light due to power change
Each area can equally share the tolerance for change
The maximum allowable temperature change
It has excellent effects such as being able to.

Further , the present invention provides a four-division hologram element.
Is one of the two orthogonal axes that divide the four regions
Parallel to the jitter direction, wherein the photodetector is
The first light receiving element is arranged at a position rotated by 45 ° with respect to the direction.
If the first light receiving element is sequentially different by 90 °,
The second, third, and fourth light receiving elements are disposed at the closed positions.
Passed through each area of the quadrant hologram element
Return light is received in first to fourth light receptions in a steady state, respectively.
The light can be received almost at the center of the element, so that, for example,
The wavelength of the laser beam fluctuates with the temperature change,
The diffraction angle at the element changes, and the first to fourth light receiving elements
4 minutes even if the light receiving point of the received return light moves in the circumferential direction
The four regions constituting the split hologram element evenly move the light receiving point.
Etc. and each absorbs as much as possible, so that the optical head
Avoids fatal unrecoverable playback for stable playback
It has effects such as being able to be bundled.

[Brief description of the drawings]

FIG. 1 is an optical system configuration diagram showing an embodiment of a hologram optical head according to the present invention .

FIG. 2 is an enlarged sectional view of the hologram laser unit shown in FIG.

FIG. 3 is a view showing a lattice pattern of the hologram element of FIG. 2;

FIG. 4 is a plan view of a light receiving element of the photodetector shown in FIG.

FIG. 5 is a diagram showing a reference example of another grating pattern of the hologram element .

6 is a plan view of the light receiving element when due to the lattice pattern of the hologram element shown in FIG.

FIG. 7 is an optical system configuration diagram showing an example of a conventional optical head.

[Explanation of symbols]

11 the hologram laser unit 17 laser diode 18 light detectors A, B (B1, B2) , C, D (D1, D2) receiving element 19 casing 19a the laser light emitting window 20 hologram element a, b, c, and d hologram element 4 areas 21 cover glass

Claims (2)

(57) [Scope of request for utility model registration] 1. A laser for irradiating a disk with laser light.
Laser diode and on the irradiation optical axis of the laser diode.
A plane that is coaxially arranged and that is orthogonal to the irradiation optical axis is the irradiation optical axis.
For each of the four areas divided by the two orthogonal axes that intersect,
Divided hologram with diffraction gratings of different patterns
And equiangular dispersion around the laser diode
Out of the laser light reflected by the disk
Diffraction when returning through each area of the split hologram element
Four laser beams are received for each area.
It consists of a light receiving element, and a pair of opposing light receiving elements is divided into two.
A hologram optical head , comprising: a photodetector. 2. The four-division hologram element includes:
One of the two orthogonal axes that divide the region
Parallel and the photodetector is 4
A first light receiving element is provided at a position rotated by 5 °, and the first light receiving element is provided.
At 90 ° position sequentially
2. The hologram optical head according to claim 1 , wherein second, third, and fourth light receiving elements are provided.