JPH03100927A - Optical pickup device - Google Patents

Abstract

PURPOSE:To enable signal detection only by one optical system, to reduce cost and size of an optical pickup device by arranging a dual grating, which is equipped with a polarized light separating diffraction grating and a beam splitting diffraction grating, on an optical path between a semiconductor laser and a recording medium. CONSTITUTION:Since a light beam emitted from a semiconductor laser 12 is passed through a collimator lens 13 and vertically made incident on a polarized light separating diffraction grating 14a of a dual grating 14, the incident light is made incident on a beam dividing diffraction grating 14b on an opposite side almost without being diffracted. A magneto-optical disk 16 is irradiated through an objective lens 15 with the light diffracted by the diffraction grating 14b. The reflected light from the disk 16 is passed through the objective lens 15, transmitted through the diffraction grating 14b and generates + or -1st order diffracted light. The diffracted light is made incident on the diffraction grating 14a and Bragg diffraction is executed to the light. Then, polarized separation into S and P polarized waves is executed and the light is made incident through the collimator lens 13 on 4-division photodetectors 17b and 17c and 2-division photodetectors 17a and 17d. Then, a focus error signal and a track error signal are respectively detected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical pickup device that records and reproduces information and detects focus error signals, track error signals, etc. using an optical information recording medium such as a magneto-optical disk. Regarding.

2. Description of the Related Art An example of a conventional optical pickup device will be described with reference to FIG. The light emitted from the semiconductor laser 1 is collimated by a collimating lens 2, beam-shaped by two beam shaping prisms 3, reflected by a beam splitter 4, and condensed by an objective lens 5 to be directed onto an optical disk 6. The light is irradiated onto the surface, thereby recording information and the like.

Further, the reflected light from the optical disk 6 passes through the beam splitter 4, is condensed by the condenser lens 7, and enters the diffraction grating 8a of the dual grating 8. The incident light exits from the diffraction grating 8b formed on the opposite surface and is separated into transmitted light T and diffracted light.

The transmitted light T is received by the 4-split light receiving element 9a, so that a focus error signal can be detected using the astigmatism method, and the diffracted light is received by the 2-split light receiving element 9b, so that a focus error signal can be detected using the bush-pull method. Track error signals can be detected using Further, by determining the intensity difference between the diffracted light and the transmitted light T, it is also possible to reproduce the magneto-optical signal.

Problems to be Solved by the Invention In the conventional device as described above, the semiconductor laser l
An irradiation optical system 10 for irradiating the light emitted from the optical disk 6 onto the optical disk 6 and a signal detection optical system 11 for the signal detection after the reflected light from the optical disk 6 passes through the beam splitter 4 are separated. It is provided. For this reason, these two optical systems occupy a large proportion of the area, making it impossible to make the device more compact.In addition, in devices equipped with a magneto-optical head, this becomes an obstacle to making the head more compact. There's a problem.

Means for Solving the Problems Therefore, in order to solve such problems, the present invention collimates the light emitted from a laser light source using a collimating lens, and condenses the parallel light using an objective lens to generate light. In an optical pickup device that records information by illuminating an information recording medium, and also reproduces information and detects a focus error signal and a track error signal using reflected light from the optical information recording medium, the laser beam emitted from the laser light source On the optical path between the collimating lens and the objective lens, the polarized light is directed towards the optical information recording medium, and a polarization splitting grating having a high density pitch is formed on the surface located on the laser light source side. A dual grating formed with a beam splitting diffraction grating having a pitch different from that of the polarization splitting diffraction grating is provided on a surface located on the recording medium side,
The photodetector for detecting the polarized light that passed through the dual grating was disposed on the optical path on the semiconductor laser side.

As a result, the light emitted from the semiconductor laser is diffracted by passing through the polarization splitting grating and the beam splitting grating of the dual grating via the collimating lens, and is focused by the objective lens to the optical information recording medium. At the same time, the reflected light from the optical information recording medium becomes diffracted light by passing through the beam splitting diffraction grating again, and furthermore, the diffracted light passes through the polarized Jlii diffraction grating. The polarized light is separated by passing through the light, and the polarized light is detected by a photodetector, thereby making it possible to reproduce information and detect a focus error signal and a track error signal.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 4. On the optical path of the light emitted from the semiconductor laser 12 as a laser light source, via a collimating lens 13,
A dual grating 14 is provided. In this dual grating 14, a polarization separation grating 14a having a high density pitch is formed on the surface located on the semiconductor laser 12 side, and a polarization separation grating 14a having a pitch different from that of the polarization separation grating 14a on the opposite surface. A beam splitting diffraction grating 14b is formed. On the optical path behind this dual grating 14, a magneto-optical disk 16 as an optical 5 information recording medium is disposed via an objective lens 15. Furthermore, light receiving elements 17a to 17d as photodetectors are provided around the semiconductor laser 12.

FIG. 4 shows the arrangement of the light receiving elements 17a to 17d as viewed from the optical axis A side of the semiconductor laser 12.
On both sides of the semiconductor laser 12 are four-divided light receiving elements 17.
b, 17 c are arranged, and furthermore, 2
Divided light receiving elements 17a and 17d are provided. Therefore, in this embodiment, the collimating lens 13, the dual grating 14, the objective lens 1
5 is arranged.

In such a configuration, the function of the dual grating 14 will first be explained based on FIGS. 2 and 3.

The polarization separation diffraction grating 14a has a high density pitch (the pitch is about the same as the wavelength or less than the wavelength). Therefore, as shown in FIG. 2, when light enters the polarization separation grating 14a of the dual grating 14 at a substantially right angle, no diffracted light is generated due to the high density pitch. The reason for this will now be explained based on FIG. In the case of high-density pitch, the diffraction mechanism is black diffraction, so the incident light propagation vector Va, the output light propagation vector vb, and the grating vector Vc are
Form a closed isosceles triangle. Therefore, as the incident angle decreases, the diffraction angle increases so that the phase matching condition (see equation (1)) in the Z direction (direction parallel to the grating vector) is satisfied.

λ sinθi+sinθo=-- (1) 1 θi: Incident angle θ0: Output angle λ: Wavelength Δ1: Polarization separation grating pitch In this case, the phase matching in the Z direction is not satisfied as the incident angle becomes further smaller. and no diffraction occurs.

Therefore, in this case, by making the light P incident perpendicularly as shown in FIG. 2, the incident light on the polarization splitting grating 14a is hardly diffracted and reaches the beam splitting grating 14b on the opposite surface. do.

The pitch of the beam splitting grating 14b is formed to cause diffraction, and the pitch is set coarser than the pitch of the polarization splitting grating 14a. In this case, the diffraction angle θ is expressed as follows.

λ θ, = sin-' (-) ... (2) A
.

Δ,: Pitch of beam splitting diffraction grating. However, Δ3 is set so that θ is approximately 30″ to 50″ (the reason for this will be described later).

The light that has now passed through the beam splitting grating 14b is irradiated onto the magneto-optical disk 16, and the light reflected thereby enters the beam splitting grating 14b again. In the beam splitting grating 14b, the utilization efficiency (P,) of light used for signal detection is
If we use all the diffracted light of the light reflected by the magneto-optical disk 16 and do not consider the reflectance on the magneto-optical disk 16, it is expressed as P, = 2 (1-2η,)η, ...(3) . In this case, η is the diffraction efficiency at the beam splitting diffraction grating 14b, and when η,=0.25, P has a maximum value of 0.25. Note that the value of η can be obtained by appropriately setting the depth of the diffraction grating.

In this way, it is reflected by the magneto-optical disk 16,
The ±1st order diffracted lights generated by passing through the beam splitting diffraction grating 14b are respectively incident on the polarization splitting diffraction grating 14a. Now, the following relationship exists between the incident angle θ of incidence on the polarization separation grating 14a and θ.

sin θ, xnsin θ, (4) n: refractive index of the substrate Here, θ, as described above, was set to = 30" to 50" (
45'' is the best point) The reason is that the angle (however, Therefore, as shown in 2, the ±1st-order light incident on the polarization separation grating 14a from the beam diffraction grating 14b is black-diffracted, and the S and P This means that the light is polarized into polarized waves.

Next, the flow of the overall configuration of this embodiment will be explained based on FIG. 1 using the dual grating 14 having the functions described above. First, the light emitted from the semiconductor laser 12 is collimated by the collimating lens 13 (beam shaping and collimation are performed at the same time), and then enters the polarization separation grating 14a of the dual grating 14 in a substantially perpendicular state. The light is diffracted by passing through the beam splitting grating 14b, focused by the objective lens 15, and irradiated onto the surface of the magneto-optical disk 16, thereby recording information. In addition, the reflected light from the magneto-optical disk 16 is guided to the dual grating 14 again, and is separated into the first-order light and the eleventh-order light by the beam splitting grating 14b. The light is separated into S-polarized light and P-polarized light by the polarization separation grating 14a (at this time, 1st-order P-polarized light a, 1st-order S-polarized light S, -1st-order S polarized light c, and -1st-order P polarized light d). In this way, the light separated into four types is transmitted to the four-divided light receiving elements 17b, 17c and the two-divided light receiving elements 17a, 17 as shown in FIG.
The light is received at d.

Then, if the output polarized light of the semiconductor laser 12 is tilted at about 45 degrees with respect to the grating direction of the polarization separation grating 14a, the intensity ratio of the S-polarized light and the P-polarized light becomes almost the same, and from the difference in intensity, the magneto-optical signal can be detected. In addition,
The magneto-optical signal may be detected using any of the following polarized waves: 1st-order P polarized light a, 1st-order S polarized light b, -1st-order S polarized light C1 - 1st-order P polarized light d-, or all polarized waves Detection may also be performed using Further, the focus error signal can be detected from first-order S polarized light or -first-order S polarized light using diffracted light. In this case, the diffracted light causes astigmatism so that the astigmatism method can be applied. The method is to modulate the polarization splitting grating 14a, the beam splitting grating 14b, or both gratings with a modulation pitch. Furthermore, the track error signal can be obtained by applying the bush-pull method to any of the four lights mentioned above.

A state of the signal detection optical system that performs such signal detection Pencil case 4
The two diffracted lights (a) and (c) shown in FIGS. (a) and (b) are guided to four-split light receiving elements 17b and 170, and a focus error signal is detected, and the transmitted light beams (a) and (d) of the polarization splitting grating 14a are split into two. Track error signals are detected using elements 17a and 17d.

A magneto-optical signal is detected from the difference in the amount of light between the diffracted lights S and C and the transmitted lights A and D.

Further, in FIGS. 4(a) and 4(b), the directions of the dividing lines of the two-split light receiving elements 17a and 17d may be such that the two of them face directions perpendicular to each other at the same time.

In this embodiment, the light receiving elements include two four-part light receiving elements 17b and 17c and two two-part light receiving elements 17a and 17.
Two d's, a total of four, are used, but as another example, 1
For example, signal detection may be performed using one each of a 4-split photodetector and a 2-split photodetector.Also, in addition to detecting using the bush-pull method described above, when detecting using a sample servo method, The two-split light receiving element may be configured as an undivided light receiving element.

Effects of the Invention The present invention provides a method in which a dual grating comprising a polarization separation grating having a polarization separation function and a beam splitting grating having a diffraction function is simply disposed on an optical path between a semiconductor laser and an optical information recording medium. Since signal detection can be easily performed by simply using the optical Since the number of parts in the system can be significantly reduced, an inexpensive, compact, and lightweight device can be obtained.

FIG. 5 is a configuration diagram showing a conventional example.

12... Laser light source, 13... Collimating lens,
14... Dual grating, 14a... Polarization splitting diffraction grating, 14b... Beam splitting diffraction grating, 15
...Objective lens, 16...Optical information recording medium, 17a
~17d...Photodetector applicant Rico Co., Ltd. -

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a side view showing the configuration of a dual grating, FIG. Figure 4 shows the traveling path of light diffracted by the dual grating.35Figure 6

Claims (1)

[Claims] The light emitted from the laser light source is collimated by a collimating lens, and the collimated light is focused by an objective lens and irradiated onto an optical information recording medium to record information, and the reflected light from the optical information recording medium is In an optical pickup device that reproduces information and detects focus error signals and track error signals by detecting them with a detector,
A polarization separation diffraction grating having a high density pitch on a surface located on the laser light source side is provided on an optical path between the collimating lens and the objective lens, on which light emitted from the laser light source is directed toward the optical information recording medium. A dual grating formed with a beam splitting diffraction grating having a pitch different from that of the polarization splitting diffraction grating is provided on a surface located on the optical information recording medium side, and the polarized light passing through the dual grating is detected. An optical pickup device characterized in that the photodetector is disposed on an optical path on the semiconductor laser side.