JPH0279231A - Hologram unit and optical pickup - Google Patents

Abstract

PURPOSE:To extremely simplify the construction at an optobase side and to facilitate miniaturizing and lightening by making respective optical parts in a unit as a hologram unit. CONSTITUTION:A laser diode chip 15 to generate a laser light, A diffraction grating 17 to divide a laser light emitted from the laser diode chip 15 into 3 optical beams, a hologram 18 to have at least 2 areas having a different a grating pattern and arranged in the forward direction of the diffraction grating 17 and a light detector 16 arranged at the position corresponding to the return light reflected by a disk 5 and diffracted by a hologram 18 are provided in a single body and a hologram unit is obtained. Thus, since the whole is unitted, for the construction at the optobase side, a very simple construction is sufficient and the optobase can be easily miniaturized and lightened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hologram unit used as an optical system in an optical pickup of an optical disk device, and an optical pickup using this hologram unit.

[Prior Art] In Figure 6 UA, which shows a conventional hologram optical pickup, laser light emitted from a laser diode chip (semiconductor part) when a laser diode 1 is shown is divided into three light beams by a diffraction grating 2. and passes through the hologram 3. This hologram 3 has two different lattice patterns.
It has two areas.

Three light beams (0-order light) transmitted through the hologram 3 are focused by an objective lens 4, and form light spots corresponding to the real light source ◯ and the two imaginary light sources X and Y on the signal surface of the optical disk 5. The light beam reflected by the disk 5, that is, the return light, is
The light returns to the hologram 31\ on the same optical path again, and the +1st order light (or -1st order light) diffracted by the hologram 3 heads towards the photodiode 6. This photodiode 6
As shown in FIG. 6, the four-division segment A
.

It is a 6-segment photodiode with two segments on both sides of B, C, and D)-E and F. It receives the returned light that has passed through the two areas of the hologram 3, and detects focusing errors and tracking errors. Detection and RF reproduction signal detection.

In a conventional optical pickup, the laser diode 1, the diffraction grating 2, the hologram 3, and the photodiode 6 are used.
were individually attached to the opto base in the illustrated path. Note that the diffraction grating 2 is attached to a diffraction grating holder, and this diffraction grating holder is attached to the optical base. Further, although not shown, the optical pickup includes an objective lens actuator that drives the objective lens 4 in two axes, that is, the focusing direction and the tracking direction.

[Problems to be Solved by the Invention] In a structure in which each optical system component is individually attached to an opto-base as in the conventional optical pickup described above, the structure of the opto-base becomes complicated. Furthermore, it is necessary to adjust the positions of the laser diode 1, the diffraction grating 2, the hologram 3, and the photodiode 6, which is complicated. Furthermore, the diffraction grating 2 is moved around the optical axis ( When the light spot on the photodiode 6 is rotated in the θ direction (in the θ direction in Fig. 6), the light spot on the photodiode 6 also moves in the θ direction, causing a shift, and therefore, the photodiode 6 must be readjusted to accommodate the shift. There was a problem.

The present invention was made to solve the above-mentioned conventional drawbacks, and it simplifies the opto-based structure of the optical pickup.
The purpose is also to reduce the number of man-hours required for adjusting optical system components.

[Means for Solving the Problems] In order to solve the above problems, the invention of claim 1 includes a laser diode chip that emits a laser beam, and a laser beam emitted from this laser diode chip that is divided into three light beams. a diffraction grating; a hologram having at least two regions with different grating patterns and disposed in front of the diffraction grating; and a photodetector disposed at a position corresponding to the return light reflected by the disk and diffracted by the hologram. were integrated into a hologram unit.

In the invention of claim 2, a hologram unit is formed by integrally providing a laser diode chip, a hologram grating formed by forming a diffraction grating surface and a hologram surface on the front and back sides of a single transparent plate, and a photodetector.

A third aspect of the invention is an optical pickup using the above hologram unit.

[Function] In the above configuration, the photodiode, diffraction grating, hologram, and photodetector in the optical pickup, or the photodiode, hologram grating, and photodetector are integrated into a unit, so the structure on the optobase side is extremely simple. It is possible to easily make the OPT5 base smaller and lighter.

In addition, since the optical system parts except the objective lens actuator are unitized, the assembly of the optical pickup is completed simply by aligning the optical axes of the objective lens actuator and this hologram unit, which greatly reduces assembly man-hours. reduced.

Furthermore, since the positional relationship between the diffraction grating and the photodetector is fixed, the hologram unit can be rotated around the optical axis (in the θ direction) relative to the opto base when adjusting the phase of the spot for tracking error detection. Phase adjustment is completed simply by moving the photodetector, and there is no need to readjust the position of the photodetector.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a hologram unit according to the first aspect of the invention, and FIG. 2 shows an optical pickup using this hologram unit.

This optical pickup is carried out by the objective lens actuator 10.
, an optical base 11, and a hologram unit 12.

The hologram unit 12, as shown in FIG.
6 is provided, and a diffraction grating 17 is housed in the heat sink 14. Further, a hologram 18 having two regions 18a and 18b with different lattice patterns is attached to the opening of one cap having an opening at the top. This one cap is attached to the stem 13. As shown in FIG. 3, the photodiode IG is a 6-segment photodiode that has four segments A, B, C, and D and two segments E and F on the left and right sides.
It's the same as here. In this manner, the laser diode depth 15, the diffraction grating 17, the hologram 18, and the photodiode 16 are integrated into the aforementioned hologram unit 11 in a predetermined and accurate mutual positional relationship. Printed wiring is formed on the lower surface of the stem 13, and leads 20
is connected. And this hologram unit 1
1 is a stem 13 that is rotatably attached to the opt base 10. 13a is a notch for adjusting the rotation.

The objective lens actuator 10 is a general two-axis actuator, and is shown as a model in FIG. Focusing control and tracking control are performed by driving the Tr in the tracking direction.

In the above configuration, the laser light emitted from the laser diode chip 15 is divided into three light beams by the diffraction grating 17 and transmitted through the hologram 18. The three light beams (0-order light) transmitted through the hologram 18 are focused by an objective lens 21 to form a light spot on the signal surface of the optical disc 5.

The light spot on the disk is similar to that shown in FIG. 7 when explaining the conventional example. The light beam reflected by the disk 5, that is, the return light, returns to the hologram 18 again along the same optical path, but it returns to the hologram 18 in two areas 18a and 1 of the hologram 18.
+1st order light (or -1st order light) each diffracted by 8b
goes toward the photodiode 16 and connects six spots on the photodiode 16 as shown in FIG. This photodiode 16 detects the returned light.
The focusing error signals (F, E), racking error signals (T, E), and RF reproduction signals (R, F) are as follows.

F, E= (A+C)-(B+D)...■T,
E=E−F ・・・■R,F=
A+B+C+D... ■Note that this signal detection method is the same as the conventional one.

Since the optical base 11 in the optical pickup described above only needs to be considered for attachment of the stem 13 portion of the hologram unit 12, it has an extremely simple structure, and the optical base can be easily made smaller and lighter.

Further, since the assembly of the optical pickup is completed simply by aligning the optical axes of the hologram unit 12 and the actuator 10, the number of assembly steps is significantly reduced.

Furthermore, the hologram 18 and the diffraction grating 1 are unitized.
Since the mutual positional relationship between the photodiode 7 and the photodiode 16 has been determined, the phase adjustment of the spot for tracking error detection (that is, the adjustment of the angle θ in the above-mentioned FIG. 7) is performed.
In this case, phase adjustment is completed simply by rotating the hologram unit 12 around the optical axis (in the θ direction in FIG. 2) with respect to the opto base 11, and the photodiode 1 as in the conventional example is
6 is not necessary.

FIG. 4 shows a hologram unit 31 according to a second aspect of the present invention, and FIG. 5 shows an optical pickup using this hologram unit 31. This optical pickup is also composed of three pieces, the two-axis actuator 10, the hologram unit 31, and the optical base 12, as described above.

The hologram unit 31 has a diffraction grating surface 32 on one surface (top surface in the embodiment) of a single transparent plate that divides the laser light emitted from the laser diode chip 15 into three light beams, and a diffraction grating surface 32 on the other surface. The structure includes a hologram grating 34 having a hologram surface 33 formed of at least two regions 33a and 33b with different grating patterns on the lower surface (in the embodiment), and this hologram grating 34 is attached to the cap 19.

Although the shape of the heat sink 14 is different from that in FIG. 1, the other stem 13, the laser diode chip 15 attached to the heat sink 14, and the laser diode chip 15
The photodiode 16 and the like adjacent to the photodiode 16 are substantially the same as those shown in FIG.

In the above optical pickup, the laser beam emitted from the laser diode chip 15 is transmitted to the hologram grating 34.
Transparent. At this time, the 0th order light diffracted by the hologram surface 33 of the hologram grating 34 is transmitted to the diffraction grating surface 32.
When the light beam passes through the diffraction grating surface 32, it is split into three light beams. The three light beams transmitted through the hologram grating 34 are focused by the objective lens 21,
A light spot is formed on the signal surface of the optical disc 5. The light beam reflected by the disk 5, that is, the return light, returns to the porogram surface 33 of the hologram grating 34 on the same optical path.
Return to. At that time, diffraction occurs again on the diffraction grating surface 32, but the returned light uses only the 0th order light of the diffraction on the diffraction grating surface 32, is diffracted at a predetermined angle on the hologram surface 33, and its +1st order light (or − primary light) is directed to the photodiode 16. The return light that has passed through the two regions 33a and 33b of the hologram surface 33 is
Similarly to what is shown in the figure, six spots are connected on the six-segment photodiode 16.

This photodiode 16 detects the returned light, but the focusing error signals (F, E), tracking error signals (T, E), and RF reproduction signals (R, F) are the same as those in the above ■, ■, and ■, respectively. It is.

As for the above-mentioned optical pickup and tube, unitization simplifies opto-based m construction, reduces size and weight, reduces the number of steps required to assemble the optical pickup, and allows the phase of the spot for tracking error detection to be reduced. Adjustment becomes easier.

Note that the specific structure of unitizing the photodiode, diffraction grating, hologram, and photodetector, or the photodiode, hologram grating, and photodetector, is not limited to the above embodiments, and various designs are possible. It is.

[Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

Since each optical system component is unitized as a hologram unit, the structure of the opto-base side can be extremely simple, and the opto-base can be easily made smaller and lighter.

Furthermore, the assembly of the optical pickup is completed simply by aligning the optical axes of the objective lens actuator and this hologram unit, which greatly reduces the number of assembly steps.

Furthermore, since the positional relationship between the diffraction grating and the photodetector is fixed, the hologram unit can be rotated around the optical axis (in the θ direction) relative to the opto base when adjusting the phase of the spot for tracking error detection. Phase adjustment is completed simply by moving the photodetector, and there is no need to readjust the position of the photodetector.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the invention according to claims 1 and 3, in which FIG. 1 is a perspective view of a hologram unit, FIG. 2 is a schematic sectional view of an optical pickup, and FIG. An explanatory diagram of a spot on a diode, FIGS. 4 and 5 show an embodiment of the invention according to claims 2 and 3, FIG. 4 is a perspective view of a hologram unit, and FIG. 5 is a schematic diagram of an optical pickup. A sectional view, FIG. 6 is a configuration diagram of an optical system showing a conventional optical pickup, and FIG. 7 is an explanatory diagram of a light spot on a disk. 10... Objective lens actuator, 11... Obtogesse, 12.31... Porogram unit, 13
...Stem, 15...Laser diode chip, 1
6... Photodiode (photodetector), 17... Diffraction grating, 18... Hologram, 1... Cap,
32... Diffraction grating surface, 33... Hologram surface, 34
...Hologram grating.

Claims (1)

[Claims] 1. A laser diode chip that emits laser light, a diffraction grating that divides the laser light emitted from the laser diode chip into three light beams, and at least two regions with different grating patterns. A hologram unit that integrally includes a hologram placed in front of a diffraction grating and a photodetector placed at a position corresponding to the return light reflected by a disk and diffracted by the hologram. 2. A laser diode chip that emits laser light, a transparent plate that has a diffraction grating surface on one side that divides the laser light emitted from the laser diode chip into three light beams, and a grating on the other side. A hologram unit integrally provided with a hologram grating having a hologram surface consisting of at least two regions with different patterns, and a photodetector disposed at a position corresponding to return light reflected by a disk and diffracted by the hologram surface. . 3. An optical pickup comprising the hologram unit according to claim 1 or 2, an optical base that holds the hologram unit, and an objective lens actuator that drives an objective lens in a focusing direction and a tracking direction.