JPS6147923A - Optical head - Google Patents

Abstract

PURPOSE:To make the whole optical system small in size and simple by synthesizing and separating a luminous flux generated from plural light sources having each different frequency, by the same dichroic mirror. CONSTITUTION:A laser beam 19 for reading and a preceding laser beam 20 generated from a laser light source 17 for reading, and a laser beam 14 for recording generated from a laser light source 11 for recording are synthesized in a light sending system by a dichroic mirror 45, focused by an objective lens 22, and plural condensing spots are irradiated on an information storage medium 23 at the same time. Also, this optical system is constituted so that the laser beam 19, the preceding laser beam 20 and the laser beam 14 reflected from the medium 23 are separated in a photodetecting system extending to a photodetector 33 by the same dichroic mirror 45. Therefore, one piece of dichroic mirror 45 is satisfactorily used, and the whole optical system can be made small in size and simple.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention is applicable to image files, still image files, CO
M (computer output memory), etc., and causes local state changes such as punching holes in the recording layer of information storage media or changing optical properties such as refractive index and reflectance using focused light. The present invention relates to an optical head that is capable of recording information and reproducing information therefrom.

[Technical background of the invention and its problems]

Conventionally, optical heads of the above type are known to be capable of recording information at high speed, and have a function of simultaneously reading the recording and confirming the recorded contents.

In this optical head, as shown in FIG. 6, a hole is made in the recording layer 2 of the information storage medium 1, or the optical characteristics such as refractive index and reflectance are changed to cause a local change in the state. In order to record information, a blinkable recording laser beam 3 is focused on the recording H2 of the information storage medium 1 to form a recording focused beam spot 4. This recording focused beam spot 4 is connected to a groove-shaped tracking guide 5.
move along. Then, when the recording laser beam 3 is turned on, a local state change occurs on the recording layer 2 of the information storage medium 1, and a new information signal bit 6 is recorded.
is formed. Immediately after recording, a reading laser beam 7 for checking the recorded content is focused to form a reading focused beam spot 8. The recording laser beam 3 and the reading laser beam 7 pass through the same objective lens 9 in order to be condensed, but in the state of parallel light before passing through the objective lens 9, the optical axis W of the recording laser beam 3 and the reading laser beam Since the optical axis r of the laser beam 7 is slightly tilted, the recording focused beam spot 4 and the reading focused beam spot 8 are located at separate positions on the recording layer 2 of the information storage medium 1.

However, with this optical head, when recording continuously, the real purpose is to reconfirm the recorded content and the area to be recorded, so check in advance (before recording) whether there is no problem with recording there No confirmation has been made. Since the reading focused beam spot 8 whose recording state is to be inspected is always behind the recording focused beam spot 4 in the traveling direction,
Even if an abnormality is detected during continuous recording of information, it means that erroneous recording has already been performed, and prior confirmation cannot be performed.

Therefore, as shown in FIG. 7, a preceding focused beam spot 1 is placed in front of the recording focused beam spot 4 in the traveling direction.
An optical head that forms 0@ has been developed.

In this optical head, at least three beam spots 10°4.8 are arranged approximately on the same line along the tracking guide 5 on the recording R2 of the information storage medium 1, that is,
A beam spot 10 capable of at least reading, a beam spot 4 used at least for recording information, and a beam spot 8 capable of at least reading information are arranged in order from the front in the traveling direction, and the leading beam spot 10 is arranged in order from the front in the traveling direction. Using beam spot 10, 1) confirm that no information has already been recorded in that part; 2) that the part is a fil area that does not have a high error rate due to dust, scratches, etc. 3) When the information storage medium 1 was created, the information storage medium 1 was already formed by reading the information on the uneven bits 6 partially formed along the tracking guide 5 (formed when the master was created). 1 position (track number, sector position)
4) Before recording, investigate from where on the surface of the recording layer 2 of the information storage medium 1 is an inappropriate recording area due to scratches, past recording errors, etc. It looks like this.

By the way, in the above optical head, before irradiating the laser beam onto the information storage medium 1, it is necessary to combine the recording laser beam 3 and the reading laser beam 7 in the middle of the optical path. Furthermore, if part of the recording laser beam 3 enters the information reading system, not only will the recording signal enter the read signal, but it will also have a negative effect on defocus correction and track deviation correction. The recording laser beam 3 must be separated and removed with great precision. Further, when the recording laser beam 3 and the reading laser beam 7 are combined, it is necessary to minimize the decrease in optical efficiency (loss of light amount) at that part.

For this reason, conventionally, 2! ! As a method of combining and separating these types of light, a method has been adopted in which the wavelengths of the recording laser beam 3 and the reading laser beam 7 are changed and a dichroic mirror is used. However, currently, separate dichroic mirrors are used to combine and separate the laser beams, and separate deflection beam splitters are used for isolation, making the optical system as a whole larger and more complex. .

[Purpose of the invention]

The present invention has been made based on the above circumstances, and an object thereof is to provide an optical head in which the entire optical system can be downsized and simplified.

[Summary of the invention]

In order to achieve the above object, the present invention combines light beams generated from a plurality of light sources having different oscillation frequencies using a dichroic mirror, and focuses the light beams on the information storage medium using an objective lens, so that a plurality of light beams can be focused at once. In an optical head that irradiates a light spot onto an information storage medium and divides the light flux emitted from the information storage medium by a dichroic mirror, at least a part of which is detected by a photodetector,
This device is characterized in that the above-mentioned light beams are combined and separated using the same dichroic mirror.

[Embodiments of the invention]

This figure shows a head, and numeral 11 in this figure is a recording laser light source. This disappears when reading information. When recording new information,
A signal having information to be recorded is sent to the recording information signal generator 1.
2 to the recording laser drive circuit 13, and the recording laser light source 11 blinks accordingly to form a recording laser beam 14 (see Fig. 3). The emitted light is received by the recording laser light amount monitor part 15, and is fed back to the recording laser drive circuit 13 so that the recording laser light amount when turned on is kept fairly constant. This is a reading multiple laser light source, which includes one reading laser light source 17 and a multiple laser light generating section 18 .

The light m generated from this reading laser light source 17 is always kept constant regardless of whether information is being recorded or read. Further, from this reading laser light source 17, a reading laser beam 19 and a leading laser beam 20 are formed by a multiplex laser beam generator 18. In addition, in the case of the reading multiplex laser light source 16, a part of the light emitted from the reading laser beam m monitor part 1
21, and negative feedback is provided to the reading laser drive circuit 122 to stabilize the amount of output light. The reading laser beam 19, the preceding laser beam 20, and the recording laser beam 14 are integrated in the multiplex laser beam processing unit 21, and are applied to the tracking guide 2 on the recording layer 24 of the information storage medium 23 through the objective lens 22.
The light is focused in a line along 5 (see Figure 3). and,
A leading beam spot 26, a recording beam spot 27, and a reading beam spot 28 are formed in this order on the tracking guide 25. Further, the light reflected on the information storage medium 23 passes through the objective lens 22 again and then passes through the multiple laser beam processing section 21 to two preceding laser beam reflected light amount detection sections, an information signal reading section 30, and a track deviation detection section 31. , and are distributed to the defocus detection section 32, respectively.

However, the information signal reading section 30 and the track deviation detection section 31
, the defocus detection section 32 is shared by the same photodetector 33. In addition, the outputs of the track deviation detection section 31 and the defocus detection section 32 are transmitted to the track deviation/defocus correction circuit 3.
4, the objective lens 22 is moved in two axial directions to correct the track deviation/defocus correction drive aperture r! It is now sent to i35.

Here, information signal detection, defocus detection, and track deviation detection are performed using the reading beam spot 28. Note that 36 in FIG. 3 is an information signal pit.

Next, the multiplex laser light generating section 18 will be explained in detail. First, to explain the principle, numeral 37 in FIG. 4 is a glass plate having a wedge-shaped cross section, and its upper surface 38 and lower surface 39 are non-parallel and optically flat. Moreover,
The lower surface 39 is inclined with respect to the upper surface 38 by an angle α. Further, the upper surface 38 and the lower surface 39 are coated to have appropriate light reflectance and light transmittance, respectively, depending on the light intensity ratio of each beam of multiplexed laser light to be obtained. For example, the upper surface 38 has a light reflectance of 38% and a light transmittance of 62%, and the lower surface 39 has a light reflectance of 100%.
%, and the light transmittance is 0%.

However, when the laser beam (laser beam) La enters from above the glass plate 37 created in this way,
38% of the light is reflected by the upper surface 38, and the 0th order reflected light 1
-b. In addition, 62% of the incident light La enters the inside of the glass plate 37, and a part of the pattern that is 100% reflected by the three lower surfaces passes through the upper surface 38 and proceeds to the outside of the glass plate 37, and the primary reflected light 1c becomes.

At this time, the light intensity of the primary reflected light LC is 3 with respect to the incident light a.
8% (0,62x O,62). Further, the direction in which this light flux travels has an angle of β with respect to the O-order reflected light Lb, and moreover, it is β-2α. The light flux that does not go outside the glass plate 37 but is reflected toward the inside of the glass plate 37 from the upper surface 38 is reflected again from the lower surface 39, and a part of it proceeds to the outside of the glass plate 37 as secondary reflected light 1-d.

At this time, the angle γ between the secondary reflected light 1-d and the 0th-order reflected light 1b becomes γ-4α. The amount of secondary reflected light 1d is 14.6% of the incident light La (0, f32X IX 1,3
8X i, OXo, 62-0.14 (3). Therefore, the O-order reflected light Lb (3.8%) and the first-order reflected light LC
(38%) are almost equal in light intensity, while the secondary reflected light 1-
Since the light intensity of d (14,6%) is significantly small, the O-order reflected light Lb serves as the reading laser beam 19 (optical axis r of the reading laser beam 19), and the primary reflected light LO serves as the preceding laser beam 20 ( Optical axis p of the preceding laser beam 20
) is used as

However, the structure shown in FIG. 4 used to explain the principle has a big problem in terms of implementation. The problem is the O-order reflected light Lb and the 1st-order reflected light L after being split into multiple laser beams.
c, the optical axis centers of the secondary reflected light Ld are shifted, and the incident light 1-a is incident along the direction from the narrower to the wider distance between the upper surface 38 and the lower surface 39; Since the light travels in the direction in which the distance between each reflected light beam Lb, LC, and 16 becomes wider, depending on the construction of the optical system, the zero-order reflected light beam b passes through the center of the objective lens 22. Then, the primary reflected light 1c may protrude outside the objective lens 22. Therefore, in order to eliminate this problem and implement it, as shown in Figure 5,
The structure is such that the incident light 1a from the light 1Ii17 is incident along the direction from the widest distance to the narrowest distance between the upper surface 38 and the lower surface 39. (In addition, 40 is a collimating lens.) That is, the reading laser beam 19 (Let) immediately after being reflected on the upper surface 38 or the lower surface 39
, preceding laser beam 20 (Lc), secondary reflected light 41
(Ld) The shift in the center of the optical axis of (Ld) can be reduced. Further, at the objective lens 22, the optical axis r of the reading laser beam 19 and the preceding laser beam 2
0 can be made to coincide with the optical axis p.

Next, the optical head will be explained in more detail, focusing on the multiple laser light processing section 21. That is, the recording laser light source 11 and the reading laser light source 17 have different oscillation frequencies, and the laser beam emitted from the reading laser light source 17 is converted into a parallel beam by the collimating lens 40, and then sent to the multiplex laser light generating section 1B. The laser beam is divided into a reading laser beam 19 and a leading laser beam 20, and is incident on a beam splitter 42. Further, the recording laser beam 14 generated from the recording laser light source 11 passes through a collimating lens 43, has its beam shape corrected by a beam shape correction prism 44, and enters the deflection beam splitter 42. The reading laser beam 19I3, the preceding laser beam 20, and the recording laser beam 14 are the same deflection beam splitter 4.
Pass through 2 different locations. The recording laser beam 14 passes sequentially through a dichroic mirror 45 and a quarter-wave plate 46 and is focused onto the recording layer 24 of the information storage medium 23 by the objective lens 22 . On the other hand, the reading laser beam 19 and the preceding laser beam 20 are
After being reflected by the total reflection prism 47, the recording laser beam 14 is reflected by the dichroic mirror 45.
The light passes through the quarter-wave plate 46 and is focused onto the recording layer 24 of the information storage medium 23 by the objective lens 22. Next, the reading laser beam 19, the preceding laser beam 20, and the recording laser beam 14 reflected by the information storage medium 23 pass through the objective lens 22j5 and the quarter-wave plate 46 again, and then are reflected by the same dichroic mirror 45. Separated. That is, the recording laser beam 14 passes through the dichroic mirror 45 and is returned to the deflection beam splitter 42. Also, a reading laser beam 19 and a preceding laser beam 20 are provided.
is reflected by the dichroic mirror 45 and returned to the deflection beam splitter 42 via the total reflection prism 47. These recording laser beam 14, reading laser beam 19, and preceding laser beam 20 are
By reciprocating through the four-wavelength plate 46, the plane of polarization is rotated by 90 degrees compared to when it passes through the polarization beam splitter 42, so it does not pass through the polarization beam splitter 42 and is reflected by this polarization beam splitter 42. .

The recording laser beam 14, the reading laser beam 19, and the preceding laser beam 20 are emitted from different locations on the deflection beam splitter 42. The emitted reading laser beam 19 and preceding laser beam 20 are focused in only one direction (direction along the plane of the paper) by a cylindrical lens 48 . Here, the reading laser beam 19 and the preceding laser beam 20 overlap each other in a parallel state, but the optical axis r of the reading laser beam 19 and the optical axis p of the preceding laser beam 2° are slightly inclined to each other. Therefore, the cylindrical lens 48 separates the light at or near the focal point. A light shielding plate 49 is arranged at this separated portion (at or near the condensing point), and this light shielding plate 49 allows
The preceding laser beam 20 is blocked and the reading laser beam 19 is extracted. A photodetector (not shown) is arranged at a position on the light shielding plate 49 that is irradiated with the preceding laser beam 20, and this photodetector constitutes the preceding laser beam reflected light amount detection section 29. Further, the reading laser beam 19 extracted by the light shielding plate 49 is focused by a spherical lens 50 and irradiated onto the photodetector 33. The photodetector 33 reads information, detects track deviation using the push-pull method, and at the same time detects defocus using the astigmatism method.

According to the above configuration, the same dichroic mirror 45
is used to transmit the reading laser beam 19 and the preceding laser beam 20 emitted from the reading multiple laser light source 16 and the recording laser beam 14 emitted from the recording laser light source 11 to the information storage medium 23. The optical system combines the reading laser beam 19 and the preceding laser beam 20 reflected from the information storage medium 23 and the recording laser beam 14 to a photodetector 33.
Since the configuration is such that the light receiving system is separated up to , only one dichroic mirror 45 is required, and the entire optical system can be made smaller and simpler.

In addition, since the reading laser beam 19, the preceding laser beam 20, and the recording laser beam 14 are configured to pass through the same deflection beam splitter 42 in the light transmitting system and the light receiving system, further miniaturization and simplicity can be achieved. This improves workability during manufacturing and lowers costs.

In the above embodiment, a method using the quarter-wave plate 46 and the polarizing beam splitter 42 was adopted as a light flux controller, but there is no problem even if the light flux reflected by the information storage medium 23 returns to the light source. In this case, 1/4 wavelength plate 4
It is also possible to adopt a method of using a half prism instead of the deflection beam splitter 42 without using the deflection beam splitter 42.

〔Effect of the invention〕

As explained above, according to the present invention, an optical head is capable of reading at least information from an information storage medium using focused light, and is also capable of irradiating a plurality of focused spots onto the information storage medium at once. , a plurality of light sources having different oscillation frequencies, an objective lens that focuses light beams generated from these light sources on the information storage medium, and a photodetector that detects at least a portion of the light beam emitted from the information storage medium. and a combining/separating means for combining and separating the light beams generated from the plurality of light sources, and the combining/separating means uses the same dichroic mirror,
The light beams generated from the plurality of light sources are combined in a light transmitting system leading to the information storage medium, and the light emitted from the information storage medium is separated in a light receiving system leading to the photodetector. Therefore, excellent effects such as miniaturization and simplification of the entire optical system can be achieved.

[Brief explanation of the drawing]

Figures 1 to 5 show one embodiment of the present invention.
2 is a block diagram showing the optical head, FIG. 3 is a perspective view showing the state of the laser beam directed onto the information storage medium, and FIG. FIG. 4 is a principle diagram showing a multiplexed laser beam generating section, FIG. 5 is a detailed diagram of the configuration, FIG. 6 is a perspective view showing the state of a laser beam directed onto an information storage medium in a conventional device, and FIG. FIG. 7 is a plan view showing the state of a beam spot formed on an information storage medium in another conventional device. DESCRIPTION OF SYMBOLS 11... Laser light source for recording, 17... Laser light source for reading, 22... Objective lens, 23... Information storage medium, 33... Photodetector, 42... Polarizing beam splitter, 45 ...Dichroic mirror. Applicant's representative Patent attorney Takehiko Suzue "-1 Figure 3 Figure 4 Figure 6 Figure 7

Claims (4)

[Claims] (1) In an optical head that can read at least information from an information storage medium using focused light and that can irradiate the information storage medium with multiple focused spots at once, multiple a plurality of light sources, an objective lens that focuses the light beams generated from these light sources on the information storage medium, a photodetector that detects at least a portion of the light beams emitted from the information storage medium, and light beams generated from the plurality of light sources. The combining/separating means uses the same dichroic mirror to send the light beams generated from the plurality of light sources to the information storage medium. An optical head characterized in that the optical head is configured to combine light in an optical system and separate light emitted from the information storage medium in a light receiving system up to the photodetector. (2) The combining/separating means has a configuration in which the light transmitting system and the light receiving system are equipped with a polarizing beam splitter or a half prism, and the dichroic mirror is placed closer to the objective lens than the polarizing beam splitter or half prism. Claim 1 characterized in that
Optical head described in section. (3) The combining/separating means is configured such that the light beam in the light transmitting system and the light beam in the light receiving system pass through the same deflection beam splitter or half prism. Optical head described in section. (4) The combining/separating means is configured such that the light beam in the light transmitting system and the light beam in the light receiving system pass through different locations of the same polarizing beam splitter or half prism. The optical head according to any one of items 1 to 3.