JPH0242649A - Optical information reader - Google Patents

Abstract

PURPOSE:To eliminate the need for a filter to be additionally provided and to reduce manhours by dividing a holographic grating on a diffraction element into plural areas so that the transmittance of the zero order diffraction light of the areas positioned at both edges in a direction corresponding to the radial direction of an optical disk can be made smaller than that of the area positioned in a central part in the direction. CONSTITUTION:The holographic grating on a diffraction element 13 is divided into plural areas 13a-13f in the direction corresponding to a radial direction B-B' of an optical disk 16, and the transmittance of the zero order diffraction light in the areas 13c-13f at both edges in the direction corresponding to the radial direction B-B' is set so as to be lower than the transmittance of the zero order diffraction light in the areas 13a and 13b positioned in the central part in the direction corresponding to the radial direction B-B'. Consequently, to the holographic grating itself, a filtering function for suppressing secondary maximum components is given. Thus, since the conventional filter does not need to be formed, the manhours can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information reading device used for reading information recorded on an optical disc.

[Conventional technology]

Optical information reading devices that read information from optical discs on which various types of information are recorded at high density reproduce information by emitting focused laser light onto narrow recording tracks and detecting the reflected light. This is what we do.

FIG. 7 shows an example of such an optical information reading device, in which laser light emitted from a laser light source 1 passes through a diffraction grating 2 for forming a tracking light spot, and then passes through a beam splitter. After being reflected by 3,
The light is irradiated onto the optical disc 6 via the collimating lens 4 and the objective lens 5. The reflected light from the optical disk 6 passes through the beam splitter 3 via the objective lens 5 and the collimating lens 4, and then passes through the plano-concave lens 7 to the photodetector 8.
The reflected light is then converted into an electrical signal.

Furthermore, FIG. 8 shows a conventional example in which a diffraction element 9 on which a holographic grating (hologram grating) is formed is used in place of the beam splitter 3. In this case, the laser emission source 1 and the diffraction grating 2 are replaced by a collimating lens 4, etc. On the - side, the photodetector 8 is placed on the same straight line as the laser emission source 1.
The light reflected from the optical disk 6 is diffracted by the diffraction element 9 and guided to the photodetector 8.

In the optical information reading device as shown in FIG. 7 or FIG. 8, as shown by S in FIG. The information on the recording track 6a is read based on the reflected light from the recording track 6a while tracking the recording track 6a by a tracking servo system (not shown).

By the way, since the recording track 6a is formed to have an extremely narrow width of about 1 to 2 μm, the irradiated laser beam also needs to be converged into a small spot by the objective lens 5 with a high numerical aperture (NA). It is also required to increase the light intensity within the spot. However, as is well known, a near ring indicated by S in FIG. 6 occurs in the focused laser beam due to the second maximum component, and this near ring causes the adjacent recording tracks 6a and 6a to appear. As a result, there is a problem in that crosstalk occurs when reading information on the optical disc 6.

Therefore, the grating surface 2a of the diffraction grating 2 in FIGS. 7 and 8
As shown in FIG. 9(a), a filter 10 (shown by hatching for convenience) in which a light-transmitting part 10a is formed is narrower than the beam width of the transmitted laser light is attached to the surface 2b opposite to the filter 10, as shown in FIG. 9(a). As shown in FIG. 9(b), the filter lO suppresses the transmittance of the O-th order light in the vicinity of both ends of the diffraction grating 2 in the direction corresponding to the radial direction of the optical disk 6. It is known to reduce crosstalk when reading information.

[Problem to be solved by the invention]

However, although the filter 10 as described above is usually formed by metal vapor deposition, forming the filter by vapor deposition has the problem of complicating the process and increasing costs.

[Means to solve the problem]

In order to solve the above-mentioned problems, an optical information reading device according to the present invention converges a luminous flux from a light source onto an optical disc and receives reflected light from the optical disc with a light-receiving element. In an optical information reading device that performs reading, between a light source and an optical disk,
The luminous flux from the light source is divided into two parts: one for reading the information on the optical disk, and one for reading the tracking error.
a diffraction grating that divides the optical disc into a pair of first-order diffraction lights, and a diffraction element formed with a holographic grating that guides the reflected light from the disc to the light receiving element, and the holographic grating on the diffraction element The area is divided into a plurality of areas such that the area located at both ends in the direction corresponding to the radial direction has a lower transmittance of zero-order diffracted light than the area located at the center in the direction corresponding to the radial direction. It is characterized by:

[For production]

In the above configuration, the light beam from the light source is split by the diffraction grating into an O-order pointing beam and a pair of first-order diffracted beams, and the beams are focused onto the optical disk. The reflected light from the optical disk enters the holographic grating on the diffraction element, and 1
The next diffracted light is guided to a light receiving element, and the information on the optical disc is converted into an electrical signal.

In the present invention, the holographic grating on the diffraction element is divided into a plurality of regions in a direction corresponding to the radial direction of the optical disk, and the transmittance of the zero-order diffracted light in the regions at both ends in the direction corresponding to the radial direction is is set to be lower than the transmittance of the 0th order diffracted light in the region located at the center in the direction corresponding to the radial direction, so that the second large component is suppressed in the holographic grating itself. As a result, there is no need to form a conventional filter, and it becomes possible to reduce the number of man-hours and costs.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 5.

As shown in FIG. 3, the optical information reading device according to the present invention includes a laser light source 11 as a light source, and the luminous flux of the laser light emitted from the chip 11a (see FIG. 1) of the laser light emitting a11 is , a diffraction grating 12 , a diffraction element 13 having a holographic ink grating (hologram grating), a collimating lens 14 , and an objective lens 15 .

Then, the reflected light from the optical disk 16 is reflected by the objective lens 15.
, enters the diffraction element 13 via the collimating lens 14, and is guided by the holographic grating of the diffraction element 13 to the photodetector 17 as a light receiving element, where:
Detection of tracking errors, detection of focus errors, and reading of information on the optical disc 16 are performed. In FIG. 3, arrow AA' indicates the focus direction, arrow BB' indicates the radial direction, and arrow c-c' indicates the tangential direction, which is the direction in which the focus rows are arranged on the optical disc 16.

As shown in FIGS. 1 and 2(a), the photodetector 17 has five photodetecting sections 17a to 17e that are divided from each other. On the other hand, the diffraction element 13 has its collimating lens 1
The holographic ink grating has a holographic grating at a portion closer to 4, and this holographic ink grating has a dividing line extending in a direction corresponding to the radial direction of the optical disc 16, and two division lines extending in a direction corresponding to the pit row direction of the optical disc 16. Six areas 13 are formed by lines L2 and L3.
It is divided into a-13f. These six areas 13a
The diffraction element 13 including .about.13f is integrally formed of plastic or glass. In addition, Fig. 2 (a
) indicates the outermost position of the light beam passing through the diffraction element 13.

As shown in FIG. 2(b), the transmittance of the O-order light in the holographic gratings in regions 13c, 13d and 13e, 13f located at both ends of the diffraction element 13 in the direction corresponding to the radial direction of the optical disk 16 The holographic ink gratings in each region 13a to 13f are designed to be considerably smaller than the transmittance of the O-th order light in the holographic gratings in the regions 13a and 13b located at the center in the direction corresponding to the radial direction of the optical disk 16. has been done. Note that the transmittance can be adjusted by changing the depth of the holographic grating.

The functions of the holographic grating in each region 13a to 13f of the diffraction element 13 will be described below.
Region 1, which is one side of the luminous flux consisting of a 0th-order diffracted light and a pair of 1st-order diffracted lights emitted from the laser emission source 11 and divided by the diffraction grating 12, divided by the dividing line L1.
The light beams that have passed through the holographic gratings 3a-13c and 13e are irradiated onto the pits on the optical disk 16 via the collimating lens 14 and the objective lens 15, and the reflected light is reflected from the objective lens 15 and the collimating lens 1.
4, according to the law of reflection, the other side of the diffraction element 13 divided by the dividing line 1, the region 13b.
- Reaches the surface of the holographic gratings 13d and 13f.

Of these, the 0th order diffracted light is diffracted by regions 13b, 13d, and 13[, and is then diffracted by regions 17b and 1 in the photodetector 17.
7c, and based on this, a focus servo system (not shown) causes the spot of the laser beam on the optical disk 16 to follow the surface wobbling of the optical disk 16, and the laser beam is recorded on the optical disk 16. Information is detected.

On the other hand, a pair of first-order diffracted lights that are reflected from the optical disk 16 and reach areas 13b, 13d, and 13f in the diffraction element 13 are diffracted by areas 13b-13d, and 13f, and are then diffracted by the photodetectors 17d and 17e of the photodetector 17. Guided by
As described later, the area 13a13cm1 of the diffraction element 13
3e is used for tracking error detection together with the light flux guided to the photodetectors 17d and 17e.

Further, the laser beam is emitted from the laser light source 11, and after being split into the O-order light and the 1st-order diffracted light by the diffraction grating 12, the diffraction element 1
The light flux that has passed through the holographic gratings in regions 13b, 13d, and 13f of No. 3 is reflected by the optical disk 16 and reaches the region L3a13cm13e of the diffraction element I3.
However, among these, the O-th instruction is for areas 13a, 13c,
The light is guided to the light detection section 17a of the photodetector 17 by the holographic grating 13e, and based on this,
Information on the optical disc 16 is detected.

On the other hand, the pair of first-order diffracted lights that are reflected by the optical disk 16 and reach the regions 13a, 13c, and 13e of the diffraction element 13 are transmitted to the photodetector section 17d of the photodetector 17 and 1
Guided by 7e. Then, a tracking servo system (not shown) is applied to the optical disc 16 based on the light beams that have reached the photodetectors 17d and 17e from the areas 13a13c13e and the light beams that have reached the photodetectors 17d and 17e from the areas 13b, 13d, and 13f as described above. The laser beam spoiler 1- is made to follow the recording track. Note that, as described above, the regions 13c and 13d located at both ends of the optical disc 16 in the direction corresponding to the radial direction
The transmittance of the O-order diffracted light in the holographic gratings 13e and 13f is set to be considerably smaller than the transmittance of the 0th-order diffracted light in the holographic gratings in the regions 13a and 13b located at the center in the direction corresponding to the radial direction. Therefore, when reading information on the optical disc 16, crosstalk caused by reading information on tracks other than the target track is sufficiently suppressed.

Next, a modified example is shown in FIG.

As shown in FIG. 4(a), the diffraction element 18 in this modification has a holographic grating arranged along two dividing lines in a direction corresponding to the radial direction of the optical disc 16, -L2 and in the pit row direction of the optical disc 16. Nine regions 18a are formed by two dividing lines L3 and L4 in corresponding directions.
18i, and as shown in FIG. 4(b), O in regions 18d to 18f and regions ILg to 18i located at both ends in the direction corresponding to the radial direction.
Each region 18a to 18C is arranged so that the transmittance of the next finger light is considerably smaller than the transmittance of the 0th order diffracted light in the regions 18a to 18C located at the center in the direction corresponding to the radial direction.
A 18i holographic grating is designed.

FIG. 5 shows another modification. In this modification, the diffraction grating and the diffraction element are integrated on the diffraction member 20. That is, on the upper surface of the diffraction member 20, the holographic grating 2 which also has the above-mentioned filter function is installed.
0a, and a diffraction grating 20b is also formed on the lower surface of the diffraction member 20. Note that the same reference numerals are given to the same members as those in the above embodiment, and the description thereof will be omitted.

In the second embodiment, a laser light source 11 and a photodetector 1 are used.
．． Although 7 is configured as a separate unit, the present invention is also applicable to an optical information reading device in which the laser emission source 11 and the photodetector 17 are configured as a single element to achieve miniaturization.

〔Effect of the invention〕

As described above, the optical information reading device according to the present invention reads information on the optical disc by converging the light beam from the light source onto the optical disc and receiving reflected light from the optical disc with the light receiving element. In the optical information reading device, the light beam from the light source is separated into a 0th-order diffracted light for reading information on the optical disc and a pair of 1st-order diffracted lights for reading tracking errors between the light source and the optical disc. It is equipped with a diffraction grating for dividing, and a diffraction element in which a holographic grating is formed to guide reflected light from the optical disc to the light receiving element, and the holographic ink grating on this diffraction element is arranged in a direction corresponding to the radial direction of the optical disc. The structure is divided into a plurality of regions such that the regions located at both ends have a lower transmittance of the 0th order light than the region located at the center in the direction corresponding to the radial direction.

As a result, the holographic grating on the diffraction element is divided into a plurality of regions in a direction corresponding to the radial direction of the optical disk, and the transmittance of the zero-order light in the regions at both ends in the direction corresponding to the radial direction is as described above. Since the transmittance is set to be lower than the transmittance of the zero-order light in the region located at the center in the direction corresponding to the radial direction, the holographic grating itself has a filter function to suppress crosstalk. As a result, the conventional separate filter is no longer necessary, resulting in the effect of reducing man-hours and costs.

[Brief explanation of the drawing]

1 to 5 show embodiments of the present invention, in which FIG. 1 is a perspective view showing a diffraction element and a photodetector, FIG. 2(a) is a plan view of the diffraction element, and FIG. Figure (b) is a graph showing the distribution of the transmittance of the O-order index light in the diffraction element, Figure 3 is a perspective view of the optical information reading device, Figure 4 (a) is a plan view of the diffraction element in a modified example, FIG. 4(b) is a graph showing the distribution of transmittance of zero-order index light in a modified diffraction element, FIG. 5 is a perspective view showing another modification of the optical information reading device, and FIG. 6 is an optical disc. FIG. 7 is a schematic front view showing a conventional optical information reading device; FIG. 8 is a schematic front view showing another conventional optical information reading device; FIG. 9(a) is a front view showing the diffraction grating in the optical information reading device of FIG. 7 or 8, and FIG. 9(b) is a front view of the 0th order light in the diffraction grating of FIG. 9(a). It is a graph showing the distribution of transmittance. 11 is a laser emission source (light 'rJ,), 13 is a diffraction element, 16 is an optical disk, and 17 is a photodetector (light receiving element). Tomizu (a) Tomizu Kazuzu Meizu Figure 9 (a) Kazuzu (b) Takanumaru

Claims (1)

[Scope of Claims] 1. In an optical information reading device that reads information on an optical disc by converging a light beam from a light source onto an optical disc and receiving reflected light from the optical disc with a light receiving element. , between the light source and the optical disk, a diffraction grating that splits the light beam from the light source into a 0th-order diffracted beam for reading information on the optical disk and a pair of 1st-order diffracted beams for reading tracking errors; a diffraction element on which a holographic grating is formed to guide the reflected light of the optical disc to the light receiving element, and the holographic grating on the diffraction element has regions located at both ends in a direction corresponding to the radial direction of the optical disc. An optical information reading device characterized in that the optical information reading device is divided into a plurality of regions such that the transmittance of zero-order diffracted light is smaller than that of a region located at the center in a direction corresponding to the radial direction.