JPH08212584A - Optical head - Google Patents

Abstract

PURPOSE: To obtain a small sized optical head with a light weight, especially with a thin profile having high stability. CONSTITUTION: The optical head adopts a folding optical system having two reflecting faces 32, 33 recording or reproducing signal information by means of light. A 3rd reflecting face 36 is provided on the optical head and a servo signal magneto-optical signal generating means is provided on the 3rd reflecting face 36. Thus, the optical head with high signal quantity without being affected by a direct incident light from a semiconductor laser 31 is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording or reproducing information with light.

[0002]

2. Description of the Related Art In recent years, the technology for recording and reproducing information by using light has made remarkable progress. This is a so-called compact disc, which is a read-only optical device for reading out pre-recorded voice, characters, and image data, and has been greatly developed in terms of basic technology and market.

Further, a write-once filing device used for recording a large amount of data such as images and many text articles, that is, an optical disk device which can be written once and can be repeatedly read, However, optical recording devices such as a rewritable filing device capable of recording and erasing have been increasingly used in recent years.

As erasable and rewritable filing, a magneto-optical disk device and a phase-change disk device are now in the stage of full-scale start up in the market and technical aspects.

What supports the development of these devices are:
Although there are market needs, it can be said that the development of many peripheral technologies such as semiconductor laser technology, optical technology, medium technology, precision machine technology, and signal processing technology will contribute greatly. It is considered that the optical disc device will establish its position as a data storage device with the development of the technology and the expansion of the market size.

As one of the recent optical system element technologies,
Attempts have been made to construct a small and lightweight optical pickup using a hologram element. If the optical pickup becomes smaller and lighter, it will be advantageous not only in downsizing the entire device, but also in increasing the access speed, lowering the power consumption, reducing the total cost, and improving the device embedding property. The hologram element is a diffraction grating that records and reproduces images by utilizing light interference and diffraction phenomena.
It is used for research such as three-dimensional image recording and reproduction. It is generally much smaller and lighter than optical prisms and the like, and it is considered that it can be used as an optical component having a composite function, and some products have already been put into practical use.

A read-only optical disk device and a rewritable optical disk device using hologram elements will be described with reference to FIGS. 11 and 12, respectively. In FIG. 11, a light beam emitted from a semiconductor laser 1 which is a light source passes through a grating 2, is reflected by a reflection hologram 3 and is repelled, and then enters an objective lens 4 and is condensed by the objective lens 4. An image is formed on the recording surface 5 by the action. A pit signal previously recorded on the recording surface 5 is picked up by the imaged spot 6. Recording surface 5
The reflected return light including the previous signal component from the objective lens 4 again
It picks up and leads to the detector 7 side.

On the front surface of the semiconductor laser 1, a reflection hologram element 3 for guiding the return light containing the signal component from the recording surface 5 to the detector 7 side is arranged. A part of the return light is diffracted by the reflection hologram element 3 and is condensed on the detector 7 side. Based on the focused spot, a detector 7 extracts a servo signal for reproducing the recording signal and for tracking and focusing the spot 6 on the recording surface 5.

In the figure, the reproduction of the recording signal is performed by electrically converting the total intensity change of the returning light to the four-division sensor 8 which is a detector and binarizing it into 1 and 0 with a certain threshold value. Do this. Tracking is grating 2
The recording pit is irradiated with the ± 1st-order diffracted light generated in 2
The so-called three-beam method, which adjusts the balance of one beam with respect to the recording pit by the two detectors 9, is the focus adjustment.
The hologram surface is divided into two, the diffracted light is divided into two half moons, and the change of the image formation pattern due to the defocus at the focal position is detected by the four-division sensor. Further, the objective signal 4 is driven up and down and left and right by the actuator 10 composed of a permanent magnet and an electromagnetic coil by an error signal obtained by these, so that the signal of the recording surface 5 can be stably read out. Control.

Next, a rewritable optical disk device of the magneto-optical system will be described with reference to FIG. In the figure, a semiconductor laser 1 which is a light source as in FIG.
The light flux from 1 passes through a collimator lens 12, a prism anamorphic 13, a PBS prism 14, a flip-up prism 15, etc., and is focused on a recording medium 17 surface by an objective lens 16 to record and reproduce information.

In this case, the servo system such as tracking and focusing is basically the same as the former, but the recording and reproducing methods are different. In addition, although the recording material and the format of the recording medium surface are different, the detailed description of each optical component will be omitted here.

First, regarding the recording method, a bias magnetic field is applied in the opposite direction to the surface 17 of the perpendicular magnetic recording medium which is initialized and has a uniform magnetization direction, and the beam is condensed from above, which is called the Curie point of the magnetic material. Recording is performed by heating to a temperature, reducing the coercive force, and reversing the magnetization direction.

The reproducing method is performed photoelectrically by applying the magnetic Faraday effect or Kerr effect. In the case of medium reflection, which is called the Kerr effect, when the recording medium surface 17 is irradiated with laser light having linear polarization, the plane of polarization of the reflected light rotates according to the degree of magnetization. The rotation of this plane of polarization is analyzed by the analyzer 2.
The magnetic signal can be optically detected by converting the intensity into the intensity by 2.

In this case, the hologram element 20 is in the return optical path separated from the main optical axis by the PBS prism 14, and the polarization direction is 90 degrees by the half-wave plate 18 so that the Kerr signal polarization becomes the TM wave. It is rotated and is incident on the hologra element 20 at the Bragg angle while being condensed by the lens 19. The first-order diffracted light diffracted and divided by the hologram element 20 is imaged on the six-division sensor 21 and used for detecting error signals for tracking and focusing. The 0th-order diffracted light is made incident on the two-divided detector 23 through the analyzer 22 and used for reading the magnetic signal.

Further, there has been proposed a device which can be further reduced in size and weight by utilizing the holograms of these read-only and rewritable optical heads. Next, the configuration and operation of this device will be described with reference to FIG. In the figure, the light flux emitted from the semiconductor laser 24, which is a light source, is
Due to its characteristic, the first reflecting surface 25 spreads in an elliptical cross section.
Then, the second reflection surface 26 is irradiated with the light. The semiconductor laser 24 and the photodetector 29 described later are installed on the second reflecting surface 26. Further, the light flux reflected by the second reflecting surface 26 is the objective lens 2
After passing through 7, the light is focused on the recording surface 28. Recording surface 28
After picking up the recorded information by (1), it passes through the objective lens 27 again, is reflected by the second reflecting surface 26, and the return light is irradiated on the first reflecting surface 25. A hologram element is formed on the first reflecting surface 25, and a part of the returning light is separated to the detector 29 side to reproduce, track, and record the recorded information.
Detect each focusing servo signal.

As described above, the hologram element can be used for both a read-only optical disk device and a rewritable optical disk device, which contributes to the reduction in size and weight of the device.

[0017]

However, in the optical disk device using the hologram element as described above, the photodetector 29 for detecting the return light containing information is formed on the second reflecting surface 26 in a large size. The light beam incident on the objective lens 27 is largely shielded, and further, the reflected light from the first reflecting surface 25 is directly incident, which may cause deterioration of the output signal quality from the photodetector 29. It was

The present invention solves the above problems, and provides an optical head having a stable signal quality such as reproduction, focusing, and tracking, which has not been available in the past, by modifying the optical arrangement of the optical head using a hologram element. To aim.

[0019]

In order to achieve the above object, the present invention provides a semiconductor laser, a first reflecting surface formed of an ellipsoidal surface for reflecting a light beam emitted from the semiconductor laser, and the reflecting surface. From the recording surface to a second reflecting surface formed of a paraboloidal surface for further reflecting the light flux from the second reflecting surface, an objective lens for condensing the light flux from the second reflecting surface onto the recording surface, and returning to the objective lens from the recording surface. Reflective surface and first
In order to guide the light flux reflected by the first reflecting surface to a photodetector, in an optical head including a photodetector for photoelectrically detecting return light reflected and diffracted by the action of a hologram formed on the reflecting surface of A configuration in which a third reflecting surface is arranged substantially on the same plane as the first reflecting surface, and the third reflecting surface has astigmatism generating means, and the astigmatism generating means is a convex or concave cylinder. A structure in which the surface is a reflection surface, or a structure in which the third reflection surface or the plane mirror is provided, and a so-called knife edge for blocking a part of incident light is provided in a part of the plane mirror,
Further, the photodetector is arranged outside the light flux emitted from the semiconductor laser and on the side surface of the light flux connecting the second reflecting surface and the objective lens, and the number of the photodetectors is two or four.
The third reflecting surface has two reflecting portions, and the respective reflected lights are separated in a direction substantially perpendicular to the optical axis of the objective lens. The third reflection surface having the two reflection portions is provided on the second reflection surface so as to face the semiconductor laser, and the third reflection surface having the two reflection surfaces. Each of the two reflected light beams reflected by the surface is divided into polarized lights that vibrate in the directions perpendicular to each other, and the means for generating the polarized lights that vibrate in the directions perpendicular to each other is the third reflection having the two reflecting surfaces. It is configured by a polarization selection film provided on the surface.

[0020]

As described above, according to the present invention, the third reflecting surface is provided, and the third reflecting surface generates the error signal necessary for the focusing operation, and the orthogonal vibrating surface necessary for detecting the magneto-optical signal is provided. The two polarized light fluxes that it has are generated.

[0021]

Embodiments of the present invention will be described below with reference to FIGS.
Description will be given with reference to 0. FIG. 1 shows a first embodiment of the present invention. In the figure, a light beam emitted from a semiconductor laser 31 which is a light source is reflected by a first reflecting surface 32 and a second reflecting surface. It reaches 33, is further reflected, and enters the objective lens 34. The first reflecting surface 32 has an arbitrary convex hyperboloidal surface, and has a function of further expanding the emission angle of the reflected light as compared with the incident light. The second reflecting surface 3
Reference numeral 3 denotes a concave parabolic surface, which converts the light flux from the first reflecting surface 32 into a substantially parallel light flux and makes it enter the objective lens 34. The incident light beam is focused on the recording surface 35 as a light spot having a diameter of about 1 μm by the converging action of the objective lens 34. The objective lens 34 is a so-called micro Fresnel lens that utilizes diffraction of light having a concentric circular lattice pattern, and is formed as an integral structure directly or in contact with the optical head substrate. The data recorded on the recording surface 35 is picked up or recorded by the spot formed by the micro Fresnel lens.
Write data to. Recording surface 3
In order to make the imaging spot follow 5 with the required accuracy, it is necessary to operate the focus servo in the optical axis direction and the tracking servo in the direction perpendicular to the recording pit row or the tracking track (not shown). Generates light information.

The return light flux including the above-mentioned optical information reflected by the recording surface 35 is again incident on the objective lens 34, transmitted / diffracted, and then reflected by the second reflecting surface 33, and then the first reflecting surface 3
Reach 2. On the first reflecting surface 32, a hologram is formed on the convex surface thereof, which has a function of separating the returning light into a light detecting portion described later. This hologram is designed in consideration of the effect on the returning light flux, and the recording surface 3
Diffracted light of the return light flux from 5 can be separated from the forward optical axis at an arbitrary angle. The hologram shown in the figure is formed of a phase control type in which an arbitrary minute uneven shape is formed on the reflecting surface. In addition, a coating process using a metal thin film or the like is performed so as to increase the reflectance on the whole. Further, the light beam reflected / diffracted by this hologram reaches a third reflecting surface 36 formed on the second reflecting surface 33 so as to be substantially on the same plane while being condensed, and after being reflected here. It is incident on the photodetector 37.

The third reflecting surface 36 has a convex or concave cylindrical surface, and has an action of giving astigmatism to the reflected / diffracted light from the hologram. When the irradiation spot is narrowed to the target size on the recording surface 35 (during focusing), an optical system is formed so that a circular irradiation pattern called a circle of least confusion is formed on the surface of the photodetector 37. Are arranged.

FIG. 2 shows a plan view of a photodetector 37 for detecting the light flux separated by the hologram portion on the first reflecting surface 32 and further reflected by the third reflecting surface 36. In the same figure, the reflected light from the third reflecting surface 36 is condensed at approximately the center of the photodetector 37. The photodetector 37 is composed of a functional element having a photoelectric conversion function, such as a PIN photodiode, which is divided into four in the shape of a square as shown in the figure. Each output is taken out as described below, Necessary information can be obtained by calculation.

Assuming that the four photodiodes shown in FIG. 2 are S1, S2, S3, and S4 for convenience, and the signals output from them are P1, P2, P3, and P4, astigmatism is detected for focus error signal detection. Method, the push-pull method is used for tracking error signal detection. First, focus error detection will be described. Photodiodes S1 and S
By taking a differential signal between the sum signal P1 + P3 of the output from P.3 and the sum signal P2 + P4 of the outputs from the photodiodes S2 and S4, the condensing pattern changes due to the deviation of the light spot on the recording surface 35 in the optical axis direction. That is, the amount of deviation and the direction can be detected by the action of astigmatism associated with the defocusing of the spot.

The defocusing of the spot on the recording surface 35 changes the spot shape as shown in FIG. As described above, it can be realized by providing the photodetector 37 at the position of the circle of least confusion in the case of the recording surface 35 at the time of focusing, and the defocus direction can also be detected depending on the degree of spot change. it can. In FIG. 2, the sum of the light intensities incident on the photodiodes S1 and S3, and S2,
It is adjusted so that the sum of the intensities of light incident on S4 coincides, that is, the differential signal output (P1 + P3)-(P2 + P4) becomes zero. When the objective lens 34 and the recording surface 35 are defocused in a direction away from each other, the spot on the photodetector 37 is elongated in the photodiode S1 and S3 directions from the above-described minimum circle of confusion, and this causes the S1 and S3 parts. Intensity of light increases. Therefore, the output of the differential signal is changed to positive. On the other hand, in the opposite case, the direction of negative defocus can be known.

FIG. 4 shows the defocus amount of the spot on the recording surface 35 and the output characteristics of the differential signal. Further, based on the information on the output amount and the polarity, that is, the defocus direction, a drive actuator (not shown) provided in the optical system main body can be moved to execute the focus direction servo operation.

Next, the tracking operation by the push-pull method will be described. The incident light generated in the recording pit or tracking track (not shown) formed on the recording surface 35 shown in FIG.
The second-order diffracted light is projected on the photodetector 37 while partially overlapping each other. The overlapping parts interfere with each other,
A tracking error signal is obtained by balancing the respective intensities of the interference portions. The light intensity distribution state on the photodetector 37 is as shown in FIG.
The 0th-order diffracted light is incident on the center, and the ± 1st-order diffracted light is incident on both sides thereof, and a part of them overlaps with each other, causing interference, resulting in a decrease in light intensity. The rate of decrease of the light intensity is proportional to the incident intensity of the diffracted light, and the image formation spot on the recording surface 35 is displaced from the target recording pit row or tracking track in the direction perpendicular to the scanning direction. Photodetectors 37 for ± first-order diffracted lights
The incident intensity on is changed. That is, the intensity balance of the interference portion changes, and the deviation direction and amount of the light spot described above can be detected by monitoring this balance. In the photodetector 37, the sum of the intensities of the photodiodes S1 and S2, P1 + P2, and S3 and S4.
Sum of intensity, difference from P3 + P4, (P1 + P2)-(P3
+ P4), a tracking error signal can be obtained. However, as shown in the figure, the two interference portions have respective areas S1 and S where differential signals are taken.
It is projected on the photodetector 37 while straddling between 2 and S3 and S4.

FIG. 5 shows a tracking error signal when a light spot crosses a pit row or a tracking track. Furthermore, the recording surface 35 may have unevenness or shading.
The reproduction of the recording signal recorded in 1 can be obtained by taking the total output P1 + P2 + P3 + P4 of the photodiodes S1 to S4. Since the optical system including the light source, the objective lens, and the photodetector, which constitute the optical head described above, is extremely lightweight and thin, the entire system can be directly driven by the tracking and focus actuator (not shown). Moreover, since it is extremely lightweight, high-speed access operation can be realized. The first reflection surface 32 further widens the emission angle of the light beam from the semiconductor laser 31, and the second reflection surface 33 converts the light beam into a substantially parallel light beam, which is then incident on the objective lens 34. Therefore, the magnification of the optical system, that is, the objective lens An optical system called a teletype that can make the distance on the object side determined by the ratio between the optical conjugate position on the detection system side and that on the image side from the principal plane of 34 smaller than the actual one By combining with an optical system, an extremely thin object side optical system is formed. Further, the area of the first reflecting surface 32 can be made smaller than that in the case where the first reflecting surface 32 is made of a flat surface, the light intensity contributing to the image formation on the recording surface 35 can be increased, and the utilization efficiency can be improved. In addition, it is possible to further reduce the side lobes of the image forming spot, which is caused by the aperture of the objective lens 34 having a ring shape, that is, unnecessary light that spreads around the central light.

Next, a second embodiment of the present invention will be described with reference to FIG. As compared with the first embodiment, the basic structure of the optical system in FIG.
4 and then through the second and first reflecting surfaces 32 and 33 to the third
The structure and operation up to the reflecting surface 36 of the are similar,
The third reflecting surface 36 and its action are different from those of the first embodiment. The third reflecting surface 36 is composed of two planes, and is provided at substantially opposite positions on the second reflecting surface 33 with the semiconductor laser 31 interposed therebetween, as shown in the figure, and one reflected light is used to detect a focusing error signal. In addition, the other is used for tracking error signal detection and reproduction signal detection.

Assuming that the two portions of the third reflecting surface 36 are the a-face and the b-face, respectively, the light beam reflected by the a-face reaches the photodetector 38 provided on the side surface of the optical system as shown in the figure. .
The a-plane is provided at a position conjugate with the focal position of the objective lens 34, and as shown in FIG. 7, it is divided into two areas by a straight line passing through the center of the irradiation spot to this, The area is a mirror surface, and the other surface is a light-shielding surface that is an absorption or diffusion surface. Along with this reflecting surface, the photodetector 38 is also composed of two detecting surfaces as shown in FIG. 8, and the dividing line is the third reflecting surface 3 described above.
6 is formed in parallel with the divided surface of the a surface. Further, the light flux reflected on the b-side is provided at a position where the optical system faces the previous photodetector 38 and is incident on the photodetector 39 which is also composed of two divided areas. The line is in the same direction as the projection direction of the tracking track or pit row as shown in FIG. The tracking error signal detection method is based on the first embodiment described above.
The reproduction signal detection similarly takes the sum signal of the outputs of the two areas.

According to the structures of the first and second embodiments of the present invention described above, the photodetection section is arranged on the side surface of the optical system, and the third reflection for guiding the returning light to the photodetection section. By giving each surface an error signal generating action, it is possible to significantly reduce the influence of the light directly incident from the semiconductor laser on the photodetector.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, a reproducing function of a magneto-optical signal is added to the optical head optical system described above, and in the figure, the forward optical system from the semiconductor laser 31 to the recording surface 35 and the recording surface. The structure and operation of a part of the backward optical system from 35 to the first reflecting surface 32 are the same, but as described in the second embodiment, the first reflecting surface 3
In the case where the diffracted light incident on the photodetector in 2 is the + 1st-order diffracted light, the -1st-order diffracted light is used, and an optical head of a magneto-optical recording system capable of recording and erasing using this light flux is used. It is a thing. The magneto-optical recording, reproducing, and erasing methods are basically as described in the above-mentioned conventional example, but magneto-optical signal reproduction is performed on polarized light in two areas of the third reflecting surface 36. It depends on the action.

The details will be described below. In the figure, the ± 1st order diffracted light generated by the diffracting action of the first reflecting surface 32 is
A magneto-optical signal can be obtained by reflecting the light on each of the two reflection areas c and d, guiding the light to each of the photo detectors 40 and 41, and taking the differential signal. The operation of the two reflection areas c and d for this purpose will be described. As shown in the figure, the reflection areas c and d are functions of reflecting incident light with respect to the incident optical axis and in a direction substantially perpendicular to each other. And photodetectors 40 and 41 face each other. Further, the reflection area is composed of a polarization selection film having a vibration direction in one direction with respect to the incident light, and has the same action as c and d, but acts in the directions at right angles to each other, and consequently selects the polarization state in two directions. By taking each differential signal, the rotation of the polarization oscillation plane due to the Kerr effect,
That is, it is possible to reproduce the magneto-optical signal. An external magnetic field (not shown) for recording and erasing magneto-optical signals
According to the conventional method performed by modulating the output of the semiconductor laser 31.

[0035]

As is apparent from the above-described embodiments, according to the present invention, an optical system in which a semiconductor laser, an objective lens, and a photodetector are integrated, which employs a bending optical system having a plurality of internal reflection surfaces, is provided. In the head, as described above, by providing the third reflecting surface with the function of generating the focusing and tracking error signals, the photodetector can be arranged in the peripheral portion of the optical system. As a result, it is possible to significantly reduce the incident light on the photodetection unit directly from the semiconductor laser or due to the reflected light, to detect a high-quality optical signal, and to contribute to stable head operation.

[Brief description of drawings]

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

FIG. 2 is a plan view of a photodetector according to the first embodiment.

FIG. 3 is an explanatory view of the operation of the photodetector.

FIG. 4 is an explanatory diagram of an operation of the first embodiment.

FIG. 5 is an explanatory diagram of an operation of the first embodiment.

FIG. 6 is a configuration diagram of an optical head according to a second embodiment of the present invention.

FIG. 7 is a plan view of a third reflecting surface in the second embodiment.

FIG. 8 is an operation explanatory diagram of the photodetector according to the second embodiment.

FIG. 9 is an operation explanatory diagram of another photodetector in the second embodiment.

FIG. 10 is a configuration diagram of an optical head according to a third embodiment of the present invention.

FIG. 11 is a block diagram of a reproduction-only optical head using a conventional hologram element.

FIG. 12 is a block diagram of a rewritable magneto-optical head using a conventional hologram element.

FIG. 13 is a block diagram of a compact optical head using a conventional hologram and a micro Fresnel lens.

[Explanation of symbols]

 31 Semiconductor Laser 32 First Reflective Surface (Reflective Hologram) 33 Second Reflective Surface 34 Objective Lens (Micro Fresnel Lens) 35 Recording Surface 36 Third Reflective Surface 37 Photodetector

Claims (10)

[Claims] 1. A first semiconductor laser and an ellipsoidal surface for reflecting a light beam emitted from the semiconductor laser.
From the reflecting surface, a second reflecting surface formed of a paraboloidal surface that further reflects the light flux from the reflecting surface, an objective lens that focuses the light flux from the second reflecting surface onto the recording surface, and the recording surface. In an optical head comprising a photodetector for returning to the objective lens and photoelectrically detecting the return light reflected by the second reflecting surface and the first reflecting surface, the light is reflected by the action of the hologram formed on the first reflecting surface. An optical head characterized in that a third reflecting surface for guiding the diffracted light beam to the photodetector is arranged on substantially the same plane as the second reflecting surface. 2. The optical head according to claim 1, wherein the third reflecting surface has astigmatism generating means. 3. The optical head according to claim 2, wherein the astigmatism generating means is composed of a reflecting surface formed of a convex or concave cylindrical surface. 4. The optical head according to claim 1, wherein the third reflecting surface comprises a plane mirror, and a knife edge for blocking a part of incident light is provided on a part of the plane mirror. 5. The light according to claim 1, wherein the photodetector is arranged outside the light flux emitted from the semiconductor laser and on the side surface of the light flux connecting the second reflecting surface and the objective lens. head. 6. The optical head according to claim 5, wherein the photodetector comprises a photodiode having a light receiving portion divided into two or four parts. 7. The third reflecting surface has two reflecting portions,
2. The optical head according to claim 1, wherein the respective reflected lights are separated from each other with respect to the optical axis of the objective lens and in a substantially right angle direction. 8. A third reflecting surface having two reflecting portions,
8. The optical head according to claim 7, wherein the optical head is provided on the second reflecting surface so as to face the semiconductor laser. 9. The optical head according to claim 7, wherein the third reflecting surface having two reflecting surfaces divides each of the reflected two reflected light beams into polarized light beams vibrating in directions perpendicular to each other. 10. The optical head according to claim 7, wherein the means for generating polarized light vibrating in directions perpendicular to each other comprises a polarization selection film provided on the third reflecting surface having the two reflecting surfaces. .