JPH05101435A - Optical head - Google Patents

Abstract

PURPOSE:To provide the optical head featuring a small size, lightness in weight, high-speed access, low cost and excellent property to be assembled into apparatus. CONSTITUTION:The luminous flux emitted from a semiconductor laser 1 is reflected by a reflection type hologram element 2 formed on an objective lens surface and a total reflection mirror 3 and is further condensed by an objective lens 4 to a recording surface 5, by which recording pits are read out. The return light contg. recording signals is introduced by the hologram formed on the surface of the reflection type hologram element 2 to a multidivision photosensor 6, by which the signals are read. The semiconductor 1 and the multidivision photosensor 6 are disposed in the positions not hindering the respective reflected luminous fluxes according to this constitution and, therefore, the small and light optical head of the high access is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in an optical information recording / reproducing apparatus for recording / reproducing information by light.

[0002]

2. Description of the Related Art In recent years, techniques for recording and reproducing information by using light have made remarkable progress. A read-only optical device for reading out pre-recorded voice, characters, and image data, so-called compact disc, CD-RO
It is called M laser disk, and these basic technologies and markets are maturing. In addition, rewritable disk devices such as magneto-optical disk devices and phase change disk devices, which have been increasingly used in recent years as secondary storage devices for computers and rewritable filing devices, are currently undergoing technical improvements, Market expansion,
Aiming to gain market share, we are approaching a full-scale launch. Although there are market needs that support these technological developments, it can be said that many peripheral technology developments such as semiconductor laser technology, optical technology, medium technology, and signal processing technology contribute greatly. It is expected that the optical disc device will establish its position as a data storage device with the further development of technology and the expansion of the market size.

In recent years, attempts have been made to construct a compact and lightweight optical pickup by using a hologram element as one of optical system element technologies. If the optical pickup becomes smaller and lighter, it will be advantageous in terms of not only downsizing of the entire device but also of increasing access speed, lowering power consumption, reducing total cost, and improving assembling. The hologram element is composed of a diffraction grating that records and reproduces an image by utilizing light interference and diffraction phenomenon, and is also used for research such as three-dimensional image recording and reproduction. The hologram element can be used as an optical component that is much smaller and lighter than an optical prism, and some products have already been put to practical use.

A conventional optical disk recording / reproducing apparatus will be described below with reference to the drawings. 9 and 10 show configurations of a reproduction-only optical disc device and a rewritable optical disc device using a hologram element. As shown in FIG. 9, the light beam emitted from the semiconductor laser 71, which is a light source, passes through the grating 72, is reflected upward by the reflection hologram 73, enters the objective lens 74, and is condensed by the objective lens 74. An image is formed on the recording surface 75. A pit signal pre-recorded on the recording surface is picked up by the imaged spot 80. Further, the reflected return light including the signal component from the recording surface 75 is again returned to the objective lens 74.
Is picked up and led to the detector 76 side. Semiconductor laser 71
On the front surface of the reflective hologram element 73 for guiding the return light including the signal component from the recording surface 75 to the detector 76 side.
Has been placed. A part of the return light reflected by the hologram element 73 is diffracted and condensed on the detector 76 side. Based on the focused spot, the detector 76 retrieves a servo signal for reproducing the recording signal and for tracking and focusing the spot on the recording surface. In the configuration of FIG. 9, the reproduction of the recording signal electrically converts the total intensity change of the return light to the four-division sensor 77, and the threshold value is set to 1 or 0 at 2
This is done by digitizing. Tracking irradiates the recording pits with ± 1st order diffracted light generated by the grating 2,
In the so-called three-beam method in which two detectors 8 balance two recording pits with respect to two recording pits, focus adjustment is performed by dividing the hologram surface into two and dividing the diffracted light into two half moons, which is accompanied by defocusing at the focus position. This is performed by a method of detecting a change in the image formation pattern with a four-division sensor. Also,
An actuator 7 including a permanent magnet and an electromagnetic coil is used by using the error signal obtained by this configuration.
The objective lens 74 is driven up, down, left, and right by 9 to control so that the signal on the recording surface can be read out stably.

Next, FIG. 10 shows the structure of a rewritable optical disk device using the magneto-optical system. As shown in the figure, the light flux emitted from the semiconductor laser 81, which is a light source, passes through a collimator lens 82, a prism anamorphic 83, a PBS prism 84, a flip-up prism 85, etc., and is condensed on a recording medium surface 87 by an objective lens 86. Recording and playback of. In this case, the servo system such as tracking and focusing is basically the same as the configuration of FIG. 9, but the recording and reproducing methods are different. Although the recording material and the format of the recording medium surface are different, the detailed description of the functions of the optical components will be omitted here.

In the magneto-optical recording method, a bias magnetic field is applied in the opposite direction to the perpendicular magnetic recording medium surface 87 which is initialized and the magnetization direction is aligned, and the beam is condensed from above to the Curie point temperature of the magnetic material. Recording is performed by heating to lower the coercive force and reverse the magnetization direction. The reproducing method is performed photoelectrically by applying the magnetic Faraday effect or Kerr effect. In the case of medium reflection, it is called the Kerr effect,
The surface of the recording medium is irradiated with laser light having linear polarization, and the plane of polarization of the reflected light rotates according to the degree of magnetization. The magnetic signal is optically detected by converting the rotation of the polarization plane into light intensity by the analyzer 92. In this case, the hologram element 90 is in the return optical path separated by the PBS prism 84 out of the main optical axis, and the polarization direction is rotated by 90 degrees by the half-wave plate 88 so that the Kerr signal polarization becomes TM wave. Then, the light enters the hologram element 90 while being condensed by the lens 89. The first-order diffracted light diffracted by the hologram element 90 and divided is imaged on the six-division sensor 11 and used for detecting error signals for tracking and focusing. The 0th-order diffracted light is used for magnetic signal reading through the analyzer 92.

As described above, the hologram element can be used in 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.

[0008]

However, in the optical disk device using such a conventional hologram element, although it is small and lightweight to some extent, it must be said that it is merely a replacement of the conventional optical component. Absent. In the read-only optical disc device, the hologram element has only the role of the beam splitter and the error detection optical system, and the overall size seen from the optical path length is the same as the conventional one. The same applies to a rewritable optical disk device. In order to further improve high-speed access and reduce size and weight, it is necessary to fully utilize the performance of holograms and consider a completely new configuration, not simply replacing existing components.

The present invention solves such a problem, and an object of the present invention is to provide an optical pickup using a hologram element, by utilizing its hologram performance, to provide a compact and lightweight optical head which has never existed before. Is.

[0010]

In order to achieve this object, the present invention provides a semiconductor laser, a first reflecting surface for reflecting light emitted from the semiconductor laser, and a light flux reflected from the first reflecting surface. The first reflection unit includes a second reflecting surface that reflects light, an objective lens that condenses a light flux from the second reflecting surface onto a recording surface, and a detection unit that detects reflected light from the recording surface. A surface of the optical head disposed on the entrance surface of the objective lens, at a position not in contact with or included in the reflected light beam from the first reflection surface and the reflected light beam from the second reflection surface, Arranging the semiconductor laser and the detector,
At least one of the reflecting surfaces is constituted by a reflection hologram.

[0011]

According to the present invention, the light emitted from the semiconductor laser is bent inside the optical system, and the semiconductor laser and the detecting portion are not present in the optical path. It is possible to configure an optical head that minimizes the above.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical head according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an optical head according to the first embodiment of the present invention. As shown in the figure, the laser light flux emitted from the semiconductor laser 1 as a light source is applied to a part of the incident surface of the objective lens 4, that is, the surface of the recording medium 5 on the semiconductor laser 1 side. A flat surface or a curved surface is formed by the reflection hologram 2 on a portion of the incident surface of the objective lens 4 which is irradiated with the laser light flux, and reflects the laser light flux. In this case, since only the 0th-order diffracted light is transmitted through the objective lens 4 and reaches the recording medium 5 to be used for reproducing information, it is considered as normal reflection. The light flux reflected by the reflection hologram 2 enters the second reflecting surface 3 while spreading. The second reflection surface 3 is a total reflection surface which is arranged at or near the emission position of the semiconductor laser 1 and is provided substantially at right angles to the optical axis of the objective lens 4. The light flux reflected by the second reflecting surface enters the objective lens 4 while further spreading.
The light beam is imaged as a spot of a predetermined size on the recording surface by the objective lens 4, and the information recorded as a pit is read. The recording pit is formed to have a size of about 1 μm, and in order to read this pit information, the spot diameter must be equal to or smaller than that of the recording pit. The light flux containing information reflected on the recording surface returns to the objective lens 4 again, and further converges toward the second reflecting surface 3. The light is further totally reflected by the total reflection surface 3 and enters the hologram surface 2. A part of the return light, that is, the first-order diffracted light is diffracted to the multi-division sensor 6 by the reflection type diffraction grating formed on the hologram surface 2. All the information processing is performed by the diffracted light, that is, the light containing the reproduction information of the recording surface and the servo signal information.

2A and 2B, a reflection hologram 1 is shown.
The structure of the objective lens 11 provided with 2 is shown. As shown in the figure, the inclined circular area 12 at the center of the objective lens 11
Is a reflection type hologram that is formed integrally with the objective lens 11 or is formed on a flat surface or a curved surface with a UV curable resin or the like. The diffracted first-order light in the return light generated on the reflection surface of the reflection hologram 12 is formed as a predetermined pattern on the sensor surface. The outside of the reflection hologram 12 is the glass of the objective lens 11, through which emitted light or return light is transmitted. Further, the peripheral portion thereof is the flange 3 of the objective lens. The 1st diffraction order light generated by the reflection hologram 12 is about 1 of the amount of light reflected on the hologram surface.
5% or more is focused on the multi-segment sensor. 0
The second-order diffracted light and other first-order diffracted light are not used for reproducing signal detection or servo signal detection.

Further, as shown in FIG. 2B, the reflection hologram 12 is attached at an angle θ with respect to the optical axis of the objective lens. Therefore, the LD and the sensor section are arranged outside the bent optical path on the way. You can do it. That is, the light beam can be guided to the objective lens without being blocked by the LD and the sensor. However, the light flux that actually passes through the objective lens and contributes to the image formation on the recording surface is the light flux that has passed through the ring-shaped portion excluding the first reflecting surface.

The structures of the semiconductor laser and the multi-divided sensor are shown in FIGS. As shown in FIG. 3, a semiconductor laser 21, which is a light source, is provided substantially at the center of a substrate, and a multi-division sensor 23 is formed on the same surface thereof.
A return light including information such as a reproduction signal and a servo signal reflected by the recording surface and passed through the objective lens, the first and second reflecting surfaces and the hologram surface is detected. An output monitor photodiode 24 is installed immediately below the semiconductor laser 21. This member is attached to the inner surface of the CAN with a predetermined position and direction.

FIG. 4 shows the structure of a signal detecting multi-divided sensor installed on the same plane and its control circuit. As shown in FIG. 4, the multi-division sensor has an elongated rectangular area and is formed by four pin photodiode sensor S1 to S4 groups arranged in contact with each other in the long side direction.
The operation of this sensor is to detect a reproduction signal, focus, and tracking servo signal by S1 to S4, respectively. Assuming that the four sensors are S1, S2, S3, and S4, and the outputs are P1, P2, P3, and P4, the sum output of all areas, that is, P1 + P2, is used to detect the reproduction signal.
Use + P3 + P4. Further, the focus error signal among the servo signals is the area S1, which is arranged on both sides.
The sum of the outputs of S4 and the area S2 located inside
S3 output sum differential signal (P1 + P4)-(P2 + P
Take 3). That is, it is based on the beam size method for comparing the sizes of the focused spots on the sensor due to the defocus. Area S for tracking error signals
The differential signal (P1 + P2)-(P3 + P4) of the sum of the outputs of 1, and S2 and the sum of the outputs of the areas S3 and S4 is taken. That is, the one-beam push-pull method is used to compare the balance of the ± first-order diffracted lights generated by the recording pits. In this way, the optical processing is performed to reproduce the recorded signal. The optical head is composed of a lens barrel height of 5 mm and a diameter of 6 mm as a whole. Focusing and tracking actuators are attached to the outside of the optical head, and each servo is fed back by feeding back the error signal obtained by the sensor. Drive.

Next, an optical head according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 shows the configuration of the optical head of the second embodiment. Semiconductor laser 31 as a light source
Similarly to the first embodiment, the light flux emitted from the laser beam passes through the first reflecting surface 32 and the second reflecting surface 33, further passes through the objective lens 34, and is condensed on the recording surface 35. Recording surface 3
The light flux from which the pit information was read at 5 is again the objective lens 3
4 and reaches the second reflecting surface 33. The second reflection surface 33 is provided with a reflection hologram that has the same function as that used in the first reflection surface of the first embodiment. In this respect, the light beam is separated by the same operation as in the first embodiment, and the light beam is guided to the multi-division sensor 36. FIG. 6 (A),
The configuration of the second reflecting surface is shown in (B). A reflection hologram surface 42 is formed on almost the entire upper surface of a glass substrate 41 having a small coefficient of thermal expansion, and a light beam which is focused on the sensor portion is generated on this surface, and after the light is totally reflected by the first reflection surface, the sensor is formed. Focus on the surface. After this, servo signals for recording / reproducing signals, tracking, and focusing are detected by the same method as in the first embodiment to control the optical head.

Further, FIGS. 7 and 8 show the structure of an optical head according to a third embodiment of the present invention. FIG. 7 shows the overall structure of a magneto-optical rewritable optical head. As shown in the figure, the light beam emitted from the semiconductor laser 51, which is a light source, is focused on the recording medium surface 55 through the two reflecting surfaces 52 and 53 and the objective lens 54 as in the first and second embodiments. Record and play back information. To record information on the recording medium surface 55, a bias magnetic field is applied by an external magnetic field in the opposite direction to the initialized and aligned perpendicular magnetic recording medium surface 55,
Recording is performed by converging a light beam from above and heating it to the Curie point temperature of the magnetic material to lower the coercive force and reverse the magnetization direction. The written recording signal is reproduced photoelectrically by applying the Kerr effect. When the recording medium surface 55 is irradiated with laser light having linear polarization, the polarization plane of the reflected light rotates according to the degree of magnetization of the recording surface 55. The magnetic signal can be optically detected by converting the rotation of the polarization plane into the light intensity by the analyzer 56. Further, the reflection surface 52 is formed by a hologram surface, and the return light 62 is separated to the outside of the chief ray 59 and guided to the detector 57.

FIG. 8 shows the structure of the main part of the optical head including the detector. The light beam emitted from the semiconductor laser 61 reaches the recording medium through the objective lens 60, and the return light 62 from the recording medium is separated to the detector side, transmitted through the half-wave plate 63, and polarized by the polarization prism 64. It is further separated by the plane 65 into two orthogonal linearly polarized lights. The transmitted light of the separated light is focused on the multi-divided sensor 66 and used for focusing and tracking servo signal detection.
Further, the magneto-optical reproduction signal is obtained by the differential output of the separated lights, and one of the detectors 67 for that purpose is installed on the reflected light side.

The objective lens 60 is supported on the upper part of the CAN inner surface 69, the semiconductor laser and sensor mounting surface 70 is formed inside the object lens 60, and the semiconductor laser and the sensor are fixed.

[0021]

As is clear from the above description of the embodiments, according to the present invention, the semiconductor laser and the sensor are arranged outside the optical axis of the objective lens, and the objective is obtained without the semiconductor laser and the sensor blocking the light beam. By providing a compact and lightweight optical head that has at least two reflecting surfaces including a hologram surface while making it enter the lens, an inexpensive optical head with fast access speed, low power consumption, and excellent device embeddability can be provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an optical head according to a first embodiment of the present invention.

FIG. 2A is an enlarged plan view of an essential part of the same, and FIG. 2B is an enlarged cross-sectional view of an essential part of the same.

FIG. 3 is a plan view showing an arrangement of the semiconductor laser and a sensor.

FIG. 4 is a plan view showing a configuration of the multi-division sensor and its signal detection circuit.

FIG. 5 is a sectional view showing a schematic configuration of an optical head of the second embodiment.

FIG. 6A is a plan view of the reflective hologram surface, and FIG. 6B is a sectional view of the reflective plate.

FIG. 7 is a sectional view showing a schematic configuration of an optical head according to the third embodiment.

FIG. 8 is a configuration diagram of main parts of the optical head.

FIG. 9 is a perspective view showing the structure of a reproduction-only optical head using a conventional hologram element.

FIG. 10 is a perspective view showing the configuration of the rewritable magneto-optical head.

[Explanation of symbols]

 1 semiconductor laser 2 reflection hologram element 3 total reflection mirror 4 objective lens 5 recording surface 6 multi-segment photo sensor

Claims (3)

[Claims] 1. A semiconductor laser, a first reflecting surface for reflecting light emitted from the semiconductor laser, a second reflecting surface for reflecting a light beam from the first reflecting surface, and a second reflecting surface. An objective lens for condensing the reflected light flux from the recording surface onto the recording surface, and a detector for detecting the reflected light from the recording surface, wherein the first reflecting surface is disposed on the incident surface of the objective lens. An optical head, wherein the semiconductor laser and the detection unit are arranged at positions not in contact with or included in the reflected light flux from the first reflection surface and the reflected light flux from the second reflection surface. .. 2. The optical head according to claim 1, wherein the first reflection surface is a reflection hologram or a total reflection surface. 3. The optical head according to claim 1, wherein the second reflection surface is a total reflection surface or a reflection hologram.