JPH01279433A - Optical pickup - Google Patents

Abstract

PURPOSE:To attain small size and light weight for an optical pickup by adopting the constitution so that beam shaping and beam separation are implemented by one diffraction grating. CONSTITUTION:A light L1 radiated from a light source 1 is collimated into a collimated light L2 by a collimate lens 2. In this case, the intensity distribution of the collimated light L2 is elliptic. The collimated light L2 is made incident in a diffraction grating 8, the collimated light L2 is diffracted with a high efficiency and becomes an incident light L3 to an objective lens 6. The incident light L3 has a circular intensity distribution. The incident light L3 passes through a pi/4 plate 5 and the objective lens 6 and is focused on the optical disk 9. In this case, the incident light L3 is converted into a circularly polarized light L4. A reflected light L5 including the information from the disk 9 passes through the pi/4 plate 5 and is converted again into a linearly polarized light L6 and made incident in the grating 8. In this case, the diffraction efficiency of the incident light 6 at the grating 8 is low in the direction of polarization, the incident light L6 passes through the grating 8 without any modification and is led to a photodetector 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for recording or reproducing information from or to an information recording medium such as an optical disk.

[Conventional technology]

A conventional optical pickup used for recording and reproducing optical discs, as shown in FIG. /4 plate) 5, Objective lens 6
, a photodetector 7, etc.

The light emitted from the light source 1 and converted into parallel light by the collimating lens 2 exhibits an elliptical intensity distribution. 7' Rhythm 3 changes the intensity distribution of the elliptical light into a circular one due to the refraction of the light. Shape. The beam splitter 4 has the property of transmitting or reflecting almost 100% of the source depending on the state of polarization, and splits the light from the light source and the reflected light from the optical disk whose polarization state has been converted by the λ/4 plate. Perform the separation.

[Problem that the invention seeks to solve]

The conventional optical pick-up device 7'' described above has a plurality of glass-split prisms in order to shape the light intensity distribution from an oval to a circular shape and to separate the light from the semiconductor radar and the reflected light from the original disk. Moreover, it is necessary to arrange them in a space. Because of these multiple glass parts, it is difficult to make the device smaller and lighter, and the manufacturing process becomes longer and higher cost. Also, the mutual position of each part is difficult to make. There was a problem that the adjustment was complicated.

The present invention aims to solve all of the above-mentioned conventional problems and to provide an optical pick-up device 7'J that is small, lightweight, and easy to manufacture, in which beam shaping and beam separation are performed using a single diffraction grating. .

[Means for solving problems]

The present invention provides a light source, a collimating lens that converts diverging light from the light source into parallel light, and a collimating lens that shapes the intensity distribution of the light from the collimating lens from an oval to a circular shape and using a difference in the polarization state of the light. a diffraction grating that separates the light circulating from the information recording medium to the reflected light from the information recording medium, and the polarization state of the reflected light from the information recording medium to linearly polarized light whose polarization plane is rotated by 90 degrees from the time of incidence. Changing [Effect] If the period of a transmission type diffraction grating is appropriately selected, the diffraction efficiency can be increased depending on the state of polarization of the incident wave. This development is used for light separation.

When light from a light source is incident on a diffraction grating, diffraction is generated by selecting a polarization state that causes diffraction of the cylindrical index.
The direction of light travel is changed, thereby shaping the light intensity distribution from an oval to a circle. By selecting the period of the diffraction grating, the angle of incidence of light from the light source on the grating, and the output angle of the diffracted light, a circular intensity distribution of light can be created. High diffraction efficiency can also be obtained by selecting the depth of the grooves in the diffraction grating. Next, when the reflected light from the optical disk enters the diffraction grating, it becomes VC.
By selecting the polarization state, the light can be transmitted through the diffraction grating without causing any diffraction sound and without changing its direction. This makes it possible to separate the reflected light from the optical disc from the light from the light source and guide it to the photodetector.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, the main parts are a light @ 1, a collimating lens 2, a beam sinter 10, a λ/4 plate 5,
It is composed of an objective lens 6 and a photodetector 7.

The light source 1 is preferably a semiconductor radar or a He-Ne radar F,y gas ray. In particular, semiconductor lasers are smaller than gas lasers and are preferable for downsizing the entire optical pickup. As shown in FIG. 5, the output light of No. 7 has an oval intensity distribution, and its polarization direction is parallel to the bamboo ring direction of the oval of the intensity distribution.

The collimating lens 2 is a normal glass lens, a Western-style lens, or a hologram element.
By changing the distance l@total focal length from the light source 1 to the total focal length, the diverging light from the light source 1 is changed into parallel light. At that time, if the focal length fc of the collimating lens 2 and the spread angle of the beam of the light emitted from the light source 1 are expressed as θ↓ θ11, as shown in Figure 6, then the intensity distribution of the parallel light passing through the collimating lens 2ft is The upper and shorter axis diameters of the ellipse are I
The relationship J+-fc Htane to LH-fc ・tane 11 ・ is established.

The diffraction grating 8 shapes the intensity distribution of the light and separates the light from the light source 1 and the optical disk, and waits for a period of 1/2 to 1 times the wavelength of the LED light.
Those drawn on electron beam resist using an electron beam, those created on photoresist using holographic techniques,
Alternatively, a resist pattern prepared by the above method may be used as a mask and transferred onto a substrate by etching, or a multilayer structure may be used by injection molding using a diffraction grating prepared by the above method as a master. .

As shown in Figure 3, the relationship between the shaping rate of the intensity distribution is as follows:
It is determined by the incident angle of the light incident from the semiconductor radar and the exit angle of the light diffracted by the diffraction grating. When the period of the diffraction grating is constant, the relationship between the incident angle and the output angle can be determined from the diffraction relationship. Separately, since the oval light distribution determined by the characteristics of the light source is made circular, the necessary relationship between the incident angle and the output angle can be determined.

As shown in Fig. 4, when the direction of the grooves of the diffraction grating 8 matches the direction of polarization of the incident light (S polarization), high polarization efficiency is exhibited, and most of the incident light changes its direction. It emits light. At this time, the wavelength λ of the incident light, the pitch 41 of the diffraction grating, the incident angle θ1 of the human incident light, and the output angle θ of the emitted light. Then, sin θ1 + sin θ. = λ /
The relationship d holds true. Also, the beam diameter D1 at the time of incidence and the beam diameter D1 at the time of exit in the plane formed by the optical axis and the normal line of the diffraction grating. and 1-, cosσ0/Cogθj = Do/Dj.

The beam diameter in a plane perpendicular to the above-mentioned plane containing the optical axis does not change even after passing through the diffraction grating. Therefore, the direction of the grooves of the diffraction grating is made to match the polarization direction of the incident light, and the incident angle is θ0 and the output angle is θ. , cos tJ(3/cosθi −Do
/ Di -zll/LL By arranging all the diffraction gratings, efficient diffraction is achieved, the direction of the beam is changed,
Moreover, the intensity distribution can be shaped from an oval to a circle.

The ↓/4λ plate 5 is arranged between the diffraction grating 8 and the optical disk 9 with its principal axis direction shifted by 45 degrees from the polarization plane of the incident light, and converts the linearly polarized incident light into circularly polarized light, which is reflected from the optical disk 9. The polarization state of the light is returned from circular polarization to linear polarization, thereby rotating the polarization states t90' of the light entering from the light source side of the diffraction grating 8 and the light entering from the optical disk 9 side.

The objective lens 6 is located between the i/4λ plate 5 and the original disk 9,
It is arranged with the distance from the original disk 9 as its focal length.

The photodetector 7 that detects the reflected signal (RF multiplied signal and error signal) from the optical disk 9 is an optical I which is integrated with a grading coupler, an optical waveguide, and a photodiode.
Examples include those that utilize Ci, and those that utilize all of them, such as the Bushzol method, the critical angle method, and the Naifezi method, as two-detection methods. In particular, it is preferable to use il''lr or original IC in order to reduce the weight and size of the entire device.

To summarize the movement of light from the light source 1 to the photodetector 7, light L1 emitted from the light source 1 is converted into parallel light L2 by the collimating lens 2. At this time, due to the characteristics of the semiconductor radar, that is, the light source 1, the intensity distribution of the parallel light L2 has an oval shape. The parallel light L2 is incident on the diffraction grating 8, but at this time, since the direction of polarization of the parallel light L2 is parallel to the direction of the grooves of the diffraction grating 8, the parallel light L2 is diffracted with high efficiency, and the traveling direction changes and becomes incident light L6 to the objective lens 6. Since the traveling direction of the incident light L6 has changed, the circular intensity distribution has completely collapsed. The incident light L6 passes through the λ/4 plate 5 and the objective lens 6, and is focused on the optical disk 9.

At this time, the light L3 changes from linearly polarized light to circularly polarized light L4 by passing through the λ/44 plate 5t. optical disc 9
The reflected light L5 containing information from the ray L4 is the same circularly polarized light as L4, but by passing through λ/4ri14ffi, it is converted into linearly polarized light L6 again and enters the n diffraction grating 8. At that time, the polarization direction of the incident light L6 to the diffraction grating 8 is
Since the direction is important to the direction of the groove, the incident light L
The rotation efficiency of the diffraction grating 8 of 6 is low, and the incident light L6 passes through the diffraction grating 8 as it is and is guided to the photodetector 17.

〔Effect of the invention〕

As explained above, the function of shaping the light intensity distribution and separating the light from the semiconductor laser and the reflected light from the optical disk has been improved from the conventional optical pickup that uses multiple prisms. In the invention, since this was realized using a single diffraction grating, it became possible to make the optical pickup smaller and lighter, and the number of parts was reduced, resulting in lower costs and improved accuracy.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the basic construction of an embodiment of the present invention, Fig. 2 is a schematic sectional view of the above embodiment, and Fig. 3 is the relationship between the incident angle and the output angle determined by the period of the diffraction grating. , and a graph showing the beam shaping rate determined by the incident angle and the output angle. Figure 4 shows the relationship between the ratio of the wavelength of the incident light and the period of the diffraction grating and the diffraction efficiency. FIG. 5 is a perspective view showing the intensity distribution of emitted light from a μ semiconductor laser, and FIG. 6 is a schematic diagram showing an example of the optical system of a conventional optical pickup. 1. Light t Me 2...Collimating lens, 3...
Prism 4...Beam splitter 5...λ/4 plate 6...Objective lens 7...Photodetector 8...Diffraction grating 9...Original disk 10...Beam splitter patent applicant Asahi Kasei Kogyo Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 1-Year J-W Diffraction Go+ Period Figure 5 R1 □ Figure 6 Procedural Amendment (Spontaneous) August 17, 1988 Patent Director General Yoshi 1) Takeshi Moon 1, Indication of the case, Patent Application No. 107575, filed in 1988, Name of the invention 3, Person making the amendment Relationship in the case Patent applicant: 1-2-6 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture No. 5, "Splitter 4" in column 6 of "Detailed Description of the Invention" of the specification to be amended, content of amendment 1, line 8 of page 2 of the specification, is corrected to "splitter 10". 2. "Beam splitter 10" on page 5, lines 4-5 of the specification
Correct J to "diffraction grating 8". 3. Correct "Figure 6" in the third line from the bottom of No. 5 of the specification to "Figure 5". 4. In the specification, page 6, line 6, ``Separation from optical disc''
5. In the 4th line from the bottom of No. 8 of the specification, ``J to raise the force using an object'' is corrected to ``separation of reflected light from an optical disk.'' 6. Correct "14" in line 5 from the bottom of No. 9 of the specification to "5". 7. Correct "17" in the second line of page 10 of the specification to "7". Below 1

Claims (1)

[Scope of Claims] An optical pickup having a light source, an optical path system that guides light from the light source to an information recording medium and guides reflected light from the information recording medium to a photodetector, and the photodetector, comprising: a collimating lens that converts diverging light from a light source into parallel light; and a collimating lens that shapes the intensity distribution of the light from the collimating lens from an ellipse to a circular shape, and the light that travels from the collimating lens toward an information recording medium due to the difference in the polarization state of the light. a diffraction grating that separates the reflected light from the information recording medium; a 1/4λ plate that changes the polarization state of the reflected light from the information recording medium into linearly polarized light whose plane of polarization is rotated by 90 degrees from that at the time of incidence; and the information recording medium. An optical pickup characterized by being equipped with a photodetector that detects reflected light from a recording medium.