JP2792267B2 - Light head - Google Patents

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 or reproducing information by light.

[0002]

2. Description of the Related Art In recent years, technology for recording and reproducing information using light has made remarkable progress. A read-only optical device for reading music, characters, and image data recorded in advance is a so-called compact disc, CD-RO.
It is called M, and the basic technology and market are maturing. In recent years, rewritable disk devices such as magneto-optical disk devices and phase-change disk devices, which have been increasingly used in secondary storage devices of computers, rewritable filing devices, and the like, are now technically improved and market scale is increasing. We are approaching a full-fledged start with the aim of expansion. To support these technological developments, many peripheral technologies such as semiconductor laser technology, optical technology, media technology, and signal processing technology contribute greatly. In the future, with the development of technology and the expansion of the market scale, it is expected that the optical disk device will build its position as a data storage device.

In recent years, attempts have been made to construct a small and lightweight optical pickup using a hologram element as one of the optical element technologies. If the optical pickup becomes smaller and lighter, it will be advantageous not only in reducing the size of the entire device but also in increasing the access speed, reducing power consumption, reducing the total cost, and improving the incorporation. A hologram element is a diffraction grating that records and reproduces an image by using light interference and diffraction phenomena, and is used for research on three-dimensional image recording and reproduction. It is generally considered that it can be used as an optical component that is extremely small and light in comparison with an optical prism or the like, and some products have already been put into practical use.

A conventional read-only optical disk device and a rewritable optical disk device using a hologram element will be described with reference to FIGS. 9 and 10. FIG. In FIG.
A light beam emitted from a semiconductor laser 1 as a light source passes through a grating 21, is reflected by a reflection type hologram 22, is jumped up, enters the objective lens 4, and is condensed on the recording surface 5 a by the condensing action of the objective lens 4. Image. A pit signal previously recorded on the recording surface 5a is picked up by the formed spot. Further, the recording surface 5a
Then, the reflected return light including the signal component is again incident on the objective lens 4 and guided to the detector 23 side. A reflection hologram element 22 for guiding return light including a signal component from the recording surface 5a to the detector 23 side is disposed on the front surface of the semiconductor laser 1. A part of the return light is diffracted by the hologram element 22 and condensed on the detector 23 side. A recording signal is reproduced by the detector 23 based on the focused spot, and a servo signal for tracking and focusing of the recording surface spot is extracted. In the figure, reproduction of the recorded signal is performed by electrically converting the total intensity change of the return light to the four-divided sensor 24 and binarizing it into 1 and 0 with a certain threshold value. Tracking was generated by grating 21 ±
The so-called three-beam method in which the first-order diffracted light is applied to the recording pits and the two beams are balanced with respect to the recording pits by the two detectors 25. Focus adjustment is performed by dividing the hologram surface into two parts, dividing the diffracted light into two half-moons, and setting the focal position. Is performed by a method in which the change of the image formation pattern due to the focus in the above is detected by the four-division sensor 24. Further, the objective lens 4 is driven up, down, left and right by an actuator 26 composed of a permanent magnet and an electromagnetic coil based on the error signal obtained by these, and control is performed so that the signal on the recording surface can be stably read.

Next, a rewritable optical disk device based on the magneto-optical method will be described with reference to FIG. 9, a light beam from the semiconductor laser 1, which is a light source, is a collimator lens 27, a prism anamorphic 28, a PBS prism 29, and a flip-up prism 30 as in FIG.
The information is condensed on the recording medium surface 31 by the objective lens 4 via the above-mentioned elements, and information is recorded and reproduced. In this case, the servo method such as tracking and focus is basically the same as the example in FIG. 9, but the recording and reproducing methods are different. Although the recording material and the format of the recording medium surface 31 are also different, the detailed description including the functions of the optical components is omitted here. First, in the recording method, a bias magnetic field is applied in the opposite direction to the surface of the perpendicular magnetic recording medium 31 which has been initialized and the magnetization direction is uniform, and the beam is condensed from above and heated to the Curie point of the magnetic material to reduce the coercive force. Recording is performed by lowering and reversing the magnetization direction. The reproduction is performed photoelectrically by applying the magnetic Faraday effect or the Kerr effect. In the case of medium-pair reflection, the Kerr effect is called, and when a laser beam having linear polarization is applied to the recording medium surface, the polarization plane of the reflected light rotates according to the degree of magnetization. By converting the rotation of the polarization plane into an intensity by the analyzer 34, a magnetic signal can be optically detected. In this case, the hologram element 2
Numeral 2 is in the return optical path separated by the PBS prism 29 out of the main optical axis, and the polarization direction is rotated by 90 degrees by the half-wave plate 32 so that the Kerr signal polarization becomes a TM wave, and the hologram element 22 is Bragg angle. , While being condensed by the lens 33. The first-order diffracted light that has been diffracted and divided by the hologram element 22 is focused on a six-division sensor 24 and used for error signal detection for tracking and focusing. The 0th-order diffracted light passes through an analyzer 34 and a detector 35
Used for reading magneto-optical signals.

As described above, the hologram element 22
It can be used for both a read-only optical disk device and a rewritable optical disk device, and contributes to reducing the size and weight of the device.

[0007]

However, in the optical disk device using the hologram element as described above, although a reduction in size and weight has been realized to some extent, it is merely a replacement of a conventional optical component. In the read-only optical disk device, the role of the hologram element only serves as a beam splitter and an error detection optical system, and the overall size as viewed from the optical path length is the same as that of the conventional one. The same can be said for a rewritable optical disk device. It is necessary to make full use of the performance of holograms in order to promote high-speed access, small size and light weight more effectively.

An object of the present invention is to solve the above-mentioned problems, and to provide an optical pickup using a hologram element as a compact and lightweight one which has never been used before, by making full use of its hologram performance.

[0009]

To achieve the above object, an optical head according to the present invention comprises a semiconductor laser, a first reflecting surface for reflecting light emitted from the semiconductor laser, and a first reflecting surface for reflecting light emitted from the first reflecting surface. A second reflecting surface for reflecting the light beam, and an objective lens for condensing the light beam from the second reflecting surface, wherein the first reflecting surface is formed substantially along the incident surface of the objective lens; At least one of the reflection surface or the second reflection surface is constituted by a reflection hologram.

[0010]

According to the above-described structure of the present invention, the light emitted from the semiconductor laser and the reflected light from the recording surface are folded inside the optical system, so that a small and lightweight optical head can be constructed. Can be.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a sectional structure of an optical head according to a first embodiment of the present invention. In FIG. 1, a laser beam emitted from a semiconductor laser 1 as a light source is an incident surface of an objective lens 4, that is, a semiconductor laser. The light is applied to the surface on one side. A reflection hologram 2 is provided on a portion of the incident surface where the laser beam is irradiated.
, And reflects a laser beam. However, in this case, since only the 0th-order diffracted light passes through the objective lens 4 and is used for reproducing information from the recording medium 5, it can be considered as normal reflection. The light beam reflected here enters the second reflection surface 3 while expanding as it is. The second reflection surface 3 is a total reflection surface that is formed at or near the emission position of the semiconductor laser 1 and that is perpendicular to the optical axis of the objective lens 4. The semiconductor laser 1 and the multi-segmented photosensor 6 are integrally formed or attached to a part of the reflecting surface 3 on or near the surface.
The light beam reflected by the second reflecting surface 3 enters the objective lens 4 while spreading further. The light beam forms an image on the recording surface 5a as a spot of a predetermined size by the objective lens 4, and picks up information recorded as pits. The recording pit is formed with a size of about 1 μm, and therefore, in order to pick up this pit information, the spot diameter must be equal to or smaller than that. The reflected light beam including the information on the recording surface 5a returns to the objective lens 4 again and travels toward the second reflecting surface 3 while being further condensed. The light is further totally reflected on the same surface and is incident on the hologram surface. A part of the return light, that is, the first-order diffracted light, is diffracted by the reflection type diffraction grating formed on the hologram surface to the multi-division sensor 6. In FIG. 1, 3a is a glass substrate, and 8 is an external metal lens barrel.

FIG. 2 shows a surface of the objective lens 4 including the reflection type hologram 2 on the semiconductor laser 1 side. In the figure, a circular area at the center is a reflection type hologram 2 formed integrally with the objective lens 4 or a flat or curved surface with a UV curable resin or the like.
It is manufactured so that the next light forms an image on the sensor surface as a predetermined pattern. On the outside, the outgoing light or return light is transmitted by the glass surface of the objective lens 4. The periphery is the collar 7 of the objective lens 4. Further, as described above, about 15% of the amount of the first-order diffracted light generated here reflected on the hologram surface is condensed on the detector, that is, the multi-segment sensor 6. The zero-order diffracted light and other first-order diffracted lights are not used for the detection of the reproduction signal or the detection of the servo signal.

Next, members constituting a plane including the semiconductor laser, the multi-segment sensor and the second reflection surface will be described with reference to FIGS.

In FIG. 3, (a) is a plan view of the member, and (b) is a partial sectional front view in which the member is installed in the external metal barrel 8. A semiconductor laser 1, which is a light source, is located substantially at the center on a circular plane. The surrounding flat surface 3 is a total reflection mirror provided on a thermally stable glass substrate 3a coated with a metal film, on which a multi-segment sensor 6 is formed. The semiconductor laser 1 is thermally and spatially separated from the glass substrate 3a, penetrates the glass substrate 3a, and is further connected to an external metal barrel 8 thereunder. The glass substrate 3a is fixedly in contact with the metal lens barrel 8 via a coupling spacer 9. The mounting portion of the semiconductor laser 1 and its lower portion are cut in a half-moon shape as shown in the figure, and an output monitor photodiode 10 is provided below the semiconductor laser 1.

FIG. 4 shows an enlarged view and connection of the multi-segment sensor 6 for signal detection installed on the reflecting surface. In the drawing, the multi-segment sensor 6 is formed by four sensor groups 6a, 6b, 6c and 6d having long and narrow rectangular areas and arranged in contact with each other in the long side direction. These sensors 6a-
6d enables the detection of the reproduction signal, the detection of the servo signal for focusing and the detection of the tracking servo signal. 4
The outputs of the two sensors 6a to 6d are P1, P2, P3, P4
In this case, the total output of all the sensors 6a to 6d, that is, P1 + P2 + P3 + P4 is used for detecting the reproduction signal. Further, as the focus error signal FE among the servo signals, a difference signal (P1 + P4)-() between the sum of the outputs of the sensors 6a and 6d arranged on both sides and the sum of the outputs of the sensors 6b and 6c arranged inside. P2 + P3) is used.
That is, it is based on a beam size method for comparing the size of a condensed spot on a sensor due to focusing. Next, as the tracking error signal TE, a differential signal (P1 + P2)-(P3 + P4) of the sum of the outputs of the sensors 6a and 6b and the sum of the outputs of the sensors 6c and 6d is used. That is, it is based on a one-beam push-pull method for comparing the balance of ± first-order diffracted lights generated by recording pits. As described above, the optical processing is performed to reproduce the recording signal. This optical head has a lens barrel height of about 5 mm and a diameter of about 6 mm as a whole. An actuator for focusing and tracking is mounted on the outside of the head, and each servo drive is performed by feeding back an error signal obtained by the sensor. I do.

Next, the second embodiment of the present invention will be described with reference to FIGS.
An example will be described. FIG. 5 shows the entire cross section of the optical head. The light beam emitted from the semiconductor laser 1, which is a light source, passes through the first reflecting surface 11 and the second reflecting surface 12, further passes through the objective lens 4, and is focused on the recording surface 5a. The light beam whose pit information has been picked up on the recording surface 5a passes through the objective lens 4 again and reaches the second reflection surface 12. On the second reflection surface 12, a reflection hologram similar to that used for the first reflection surface of the first embodiment is formed. On this surface, the light beam is separated by the same operation as in the first embodiment and guided to the multi-segment sensor 6.

FIG. 6 shows a plan view and a front view of the second reflecting surface 12. It is made of a reflection type hologram surface except for the semiconductor laser 1 emission port and the surface of the sensor 6. Here, a light beam to be focused on the sensor 6 is generated, and the first reflection surface 11 is formed.
After the light is totally reflected, the light is condensed on the surface of the sensor 6. 9 is FIG.
It is a spesa as in (b). Thereafter, detection, tracking, and detection of recording / reproduction signals are performed by the same processing as in the first embodiment.
Each servo signal for focusing is detected and used for controlling the optical head.

Further, a third embodiment of the present invention will be described with reference to FIGS. FIG. 7 shows an overall cross section of a rewritable optical head of the magneto-optical type. In the figure, a light beam emitted from a semiconductor laser 1 as a light source is 2
The light is condensed on the recording surface 5a through the two reflecting surfaces 11, 12 and the objective lens 4 to record and reproduce information. Information is recorded on the recording surface 5a by applying a bias magnetic field by an external electromagnet in the opposite direction to the recording surface 5a of the perpendicular magnetic recording medium 5 in which the magnetization direction is initialized and the magnetic material is condensed. The recording is carried out by heating to the Curie point of, decreasing the coercive force and reversing the magnetization direction. The written recording is reproduced by photoelectrically applying the magnetic Kerr effect. When the recording surface 5a is irradiated with a laser beam having linear polarization, the polarization plane of the reflected light rotates according to the degree of magnetization. By converting the rotation of the polarization plane into an intensity by the analyzer 13, a magnetic signal can be optically detected. The reflection surface 12 is formed by a hologram surface, and the return light is separated out of the principal ray and guided to the detector side. In FIG. 7, 14 is a half-wave plate, and 16 is a detector.

FIG. 8 shows a plan view and a front view of an enlarged view of a main part including a detector. In both figures, the return light from the recording medium due to the light beam emitted from the semiconductor laser 1 is separated to the detector side as described above, and the second reflection surface 1
2, transmitted through the half-wave plate 14 and further separated by the polarizing prism 15 into two orthogonal linearly polarized lights. The transmitted light out of the separated light is condensed on the multi-segment sensor 6 and used for detecting servo signals for focusing and tracking. The magneto-optical reproduction signal is obtained by the differential output of the separated light. For this purpose, the detector 16 is provided on the reflected light side of the polarizing prism 15.

[0021]

As is apparent from the above embodiments, according to the present invention, the light path of the semiconductor laser is folded by having at least two or more reflecting surfaces including a part of the objective lens. It is possible to realize a small and light optical head, improve access speed,
This can contribute to lower power consumption, improvement in device incorporation, and cost reduction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the configuration of an embodiment of an optical head according to the present invention.

FIG. 2 is a partial view of the optical head according to the embodiment.

FIG. 3A is a plan view showing a part of the optical head of the embodiment; FIG. 3B is a partial cross-sectional front view showing a part of the optical head of the embodiment;

FIG. 4 is an enlarged plan view and a circuit diagram of a multi-split sensor for signal detection in the optical head of the embodiment.

FIG. 5 is a sectional view illustrating the configuration of a second embodiment of the optical head according to the present invention;

FIG. 6A is a plan view showing a part of the optical head of the embodiment; FIG. 6B is a partial cross-sectional front view showing a part of the optical head of the embodiment;

FIG. 7 is a sectional view illustrating the configuration of an optical head according to a third embodiment of the present invention;

FIG. 8A is a plan view showing a part of the optical head of the embodiment; FIG. 8B is a front view showing a part of the optical head of the embodiment;

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

FIG. 10 is a perspective view showing a configuration of a rewritable magneto-optical head using a conventional hologram element.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 reflection type hologram element (first reflection surface) 3 second reflection surface 4 objective lens

Claims (3)

(57) [Claims] 1. A semiconductor laser, a first reflecting surface that reflects light emitted from the semiconductor laser, a second reflecting surface that reflects a light beam from the first reflecting surface, and a second reflecting surface that reflects light emitted from the second reflecting surface. An optical head, comprising: an objective lens for condensing a light beam, wherein the first reflecting surface is formed along substantially the incident surface of the objective lens. 2. The optical head according to claim 1, wherein the first reflection surface is constituted by a reflection hologram or a total reflection surface. 3. A reflection hologram or total reflection comprising a plane or curved surface whose second reflecting surface is perpendicular to the optical axis of the objective lens and includes a semiconductor laser emission port, or a plane or curved surface located in the vicinity thereof. 2. The optical head according to claim 1, wherein the optical head comprises a surface.