JPH0677334B2 - Optical information reader - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical information reading device used for reading information recorded on an optical disc.

[Conventional technology]

An optical information reading device that reads information from an optical disc on which various information is recorded at high density, reproduces information by irradiating a narrow recording track with narrowed laser light and detecting the reflected light. Is to do.

FIG. 7 shows an example of such an optical information reader, in which the laser light emitted from the laser emission source 1 passes through a diffraction grating 2 for forming a light spot for tracking, and a beam splitter. After being reflected by 3,
The optical disk 6 is irradiated with light through the collimator 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 collimator lens 4, and further passes through the plano-concave lens 7 to the photodetector 8
The reflected light is converted into an electric signal.

Further, FIG. 8 shows a conventional example using a diffraction element 9 having a holographic grating (hologram grating) formed in place of the beam splitter 3. In this case, the laser emission source 1 and the diffraction grating 2 include a collimator lens 4 and the like. Is arranged on the same straight line as the photodetector 8 while the photodetector 8 is a laser emission source 1
Is arranged on the side of, and the reflected light from the optical disk 6 is diffracted by the diffraction element 9 and guided to the photodetector 8.

In the optical information reader as shown in FIG. 7 or FIG. 8, as shown by S in FIG. 6, the laser beam on the optical disk 6 is almost at the width of the recording track 6a (hatched for convenience). Thus, 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 with an extremely narrow width of about 1 to 2 μm, it is necessary to converge the laser light to be emitted into a small spot by the objective lens 5 having a high numerical aperture (NA). It is also required to increase the light intensity in the spot. However, as is well known, due to the second-order maximum component in the converged laser light, airy ring shown by S ₁ in FIG. 6 is generated, and this airy ring is adjacent to the recording track 6a.
There is a problem that crosstalk occurs at the time of reading information on the optical disk 6 due to spreading to 6a.

Therefore, as shown in FIG. 9 (a), on the surface 2b opposite to the grating surface 2a of the diffraction grating 2 in FIGS. 7 and 8, as shown in FIG. 9 (a), a light transmitting portion 10a narrower than the beam width of the transmitted laser light. Attach the filter 10 (hatched for convenience) with
As shown in FIG. 9B, the filter 10 suppresses the transmittance of the 0th-order diffracted light in the vicinity of both ends of the diffraction grating 2 in the direction corresponding to the radial direction of the optical disc 6, so that the recording track 6a is formed. It is known to reduce crosstalk when reading information.

[Problems to be Solved by the Invention]

However, the filter 10 as described above is usually formed by a metal vapor deposition technique, but the formation of the filter by this vapor deposition has a problem that the process is complicated and the cost is increased.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, an optical information reading device according to the present invention converges a light beam from a light source onto an optical disc, and receives reflected light from the optical disc by a light receiving element, thereby recording information on the optical disc. In an optical information reading device for reading, a 0th-order diffracted light beam for reading information on the optical disc, a pair of 1's for reading a tracking error, is provided between a light source and an optical disc. A diffraction grating that divides the light into a second-order diffracted light and a diffractive 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 diffractive element is such that the regions located at both ends in the radial direction of the optical disc have a transmittance of 0th-order diffracted light smaller than that in the central region in the radial direction. It is characterized by being divided into a plurality of areas.

[Action]

In the above structure, the light flux from the light source is split by the diffraction grating into 0th-order diffracted light and a pair of 1st-order diffracted light, and is converged on the optical disc. The reflected light from the optical disk enters the holographic grating on the diffraction element and
The second-order diffracted light is guided to the light receiving element and the information on the optical disk is converted into an electric signal.

In the present invention, the holographic grating on the diffractive element is divided into a plurality of regions in the direction corresponding to the radial direction of the optical disc, and the transmittance of 0th-order diffracted light in the regions at both ends in the direction corresponding to the radial direction is divided. Is set to be lower than the transmittance of the 0th-order diffracted light in the region located in the central portion in the direction corresponding to the radial direction, so that the holographic grating itself can suppress the above-mentioned second-order maximum component. Since the filter function is added, it is not necessary to form the conventional filter, so that it is possible to reduce the number of steps and the cost.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

As shown in FIG. 3, the optical information reader according to the present invention includes a laser emission source 11 as a light source, and a laser beam flux emitted from a chip 11a of the laser emission source 11 (see FIG. 1). Is an optical disc 16 through a diffraction grating 12, a diffraction element 13 having a holographic grating (hologram grating), a collimator lens 14 and an objective lens 15.
Converged on.

Then, the reflected light from the optical disc 16 enters the diffraction element 13 through the objective lens 15 and the collimator lens 14, and is guided to the photodetector 17 as a light receiving element by the holographic grating of the diffraction element 13, where tracking is performed. An error is detected, a focus error is detected, and information on the optical disc 16 is read. The third
In the figure, arrow A-A 'is the focus direction, and arrow B-
B'denotes a radial direction, and arrows CC 'indicate a tangential direction which is a direction in which pit rows are arranged on the optical disc 16.

As shown in FIGS. 1 and 2 (a), the photodetector 17 has five photodetection sections 17a to 17e which are divided from each other.
On the other hand, the diffractive element 13 has a holographic grating near the collimator lens 14, and the holographic grating has a dividing line L ₁ extending in a direction corresponding to the radial direction of the optical disc 16 and an optical disc.
Two dividing lines extending in the direction corresponding to the 16 pit row direction
By and L _2, L ₃ is divided into six areas 13a to 13f.
The diffractive element 13 including these six regions 13a to 13f is integrally formed of plastic or glass. In addition, P in FIG. 2 (a) indicates the outermost position of the light beam that passes through the diffraction element 13.

As shown in FIG. 2B, the transmittance of the 0th-order diffracted light in the holographic gratings of the 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 disc 16 is , Optical disc 16
Area located in the center of the direction corresponding to the radial direction of
0 in holographic gratings 13a and 13b
Each region 13 so that it is much smaller than the transmittance of the next-order diffracted light.
Holographic gratings of a to 13f are designed. The transmittance can be adjusted by changing the depth of the holographic grating.

The function of the holographic grating in each of the regions 13a to 13f of the diffractive element 13 will be described below. The holographic grating is emitted from the laser emission source 11 and divided by the diffraction grating 12.
Of the light flux composed of the second-order diffracted light and the pair of first-order diffracted light, the light flux that has passed through the holographic grating in the regions 13a, 13c, and 13e that is one side divided by the dividing line L ₁ is the collimator lens 14 and the objective lens 15. Optical disc through
The pit on 16 is irradiated with the reflected light thereof, after passing through the objective lens 15 and the collimator lens 14, according to the law of reflection, the regions 13b, 13d, which are the other side divided by the dividing line L ₁ in the diffraction element 13. Reach the surface of the 13f holographic grating.

The 0th-order diffracted light therein is diffracted by the regions 13b, 13d, and 13f and reaches the dividing line 1 between the regions 17b and 17c in the photodetector 17, and based on this, a focus servo system (not shown) drives the optical disk. The optical disc 16
The information recorded on the optical disc 16 is detected while following the spot of the laser beam.

On the other hand, the pair of first-order diffracted lights that are reflected from the optical disk 16 and reach the regions 13b, 13d, and 13f in the diffraction element 13 are diffracted by the regions 13b, 13d, and 13f and are detected by the photodetectors 17d and 17e of the photodetector 17. And is guided to the photodetectors 17d and 17e from the regions 13a, 13c, and 13e of the diffractive element 13 and is used for detection of a tracking error, as will be described later.

Further, the light flux emitted from the laser emission source 11, split into 0th-order diffracted light and 1st-order diffracted light by the diffractive element 12, and then passed through the holographic grating of the regions 13b, 13d, and 13f of the diffractive element 13 is the optical disc 16 Is reflected by the regions 13a, 13c and 13e of the diffractive element 13 and the 0th-order diffracted light therein is guided by the holographic grating of the regions 13a, 13c and 13e to the photodetection section 17a of the photodetector 17, and Based on the above, the information on the optical disc 16 is detected.

On the other hand, the area 13a of the diffraction element 13 reflected by the optical disk 16
・ The pair of 1st-order diffracted lights that have reached 13c ・ 13e are in the region 13a ・ 1
It is guided to the photodetectors 17d and 17e of the photodetector 17 by the holographic grating 3c and 13e. And the area
On the optical disc 16 by a tracking servo system (not shown) based on the light fluxes reaching the photodetection units 17d and 17e from 13a, 13c, and 13e and the light fluxes reaching the photodetection units 17d and 17e from the regions 13b, 13d, and 13f as described above. The spot of the laser light of is made to follow the recording track. As described above, the regions 13c, 13d and 13e, 13f located at both ends in the direction corresponding to the radial direction of the optical disc 16 are described.
The transmittance of the 0th-order diffracted light in the holographic grating is set to be considerably smaller than the transmittance of the 0th-order diffracted light in the holographic grating in the regions 13a and 13b located in the central portion in the direction corresponding to the radial direction. When reading information on the optical disc 16, crosstalk due to reading information on tracks other than the target track is sufficiently suppressed.

Next, FIG. 4 shows a modification.

As shown in FIG. 4 (a), the diffractive element 18 in this modified example uses a holographic grating as an optical disc.
Two dividing lines L ₁ and L ₂ in the direction corresponding to the 16 radial directions
And by two dividing lines L _3, L ₄ in the direction corresponding to the pit row direction of the optical disk 16 is divided into nine regions 18A～18i,
And, as shown in FIG. 4 (b), the regions 18d to 18f and the regions located at both ends in the direction corresponding to the radial direction.
Holographic gratings of the respective regions 18a to 18i so that the transmittance of the 0th-order diffracted light in 18g to 18i is considerably smaller than the transmittance of the 0th-order diffracted light in the regions 18a to 18c located in the central portion in the direction corresponding to the radial direction. 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, the holographic grating 20a having the above-mentioned filter function is formed on the upper surface of the diffraction member 20, and the diffraction grating 20b is formed on the lower surface of the diffraction member 20.
Are formed. The same members as those in the above embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the above embodiment, the laser emission source 11 and the photodetector 17 are separately configured, but the laser emission source 11 and the photodetector 17 are configured as a single element to reduce the size of the optical information. The present invention can also be applied to a reading device.

〔The invention's effect〕

As described above, the optical information reader according to the present invention reads the information on the optical disc by converging the light flux from the light source on the optical disc and receiving the reflected light from the optical disc by the light receiving element. In the optical information reading device described above, a light flux from the light source is divided between a light source and an optical disc into a 0th-order diffracted light for reading information on the optical disc and a pair of 1st-order diffracted light for reading a tracking error. It is provided with a diffraction grating for dividing and a diffraction element in which a holographic grating for guiding the reflected light from the optical disk to the light receiving element is formed, and the holographic grating on the diffraction element has a direction corresponding to the radial direction of the optical disk. The 0th-order diffracted light is transmitted from the regions located at both ends of the center of the region corresponding to the radial direction. A structure which is divided into a plurality of regions so decreases.

As a result, the holographic grating on the diffractive element is divided into a plurality of regions in the direction corresponding to the radial direction of the optical disc, and the transmittance of the 0th-order diffracted light in the regions at both ends in the direction corresponding to the radial direction is the radial direction. Since it is set to be lower than the transmittance of the 0th-order diffracted light in the region located in the central portion in the direction corresponding to the direction, the holographic grating itself has a filter function for suppressing crosstalk. As a result, the conventional separately provided filter is not required, so that the number of steps and the cost can be reduced.

[Brief description of drawings]

1 to 5 show an embodiment of the present invention, in which FIG. 1 is a perspective view showing a diffraction element and a photodetector, and FIG.
FIG. 2A is a plan view of the diffractive element, FIG. 2B is a graph showing the transmittance distribution of the 0th-order diffracted light in the diffractive element, and FIG.
FIG. 4A is a perspective view of the optical information reading device, FIG. 4A is a plan view of a diffractive element in the modification, and FIG. 4B is a distribution of transmittance of 0th-order diffracted light in the diffractive element in the modification. FIG. 5 is a perspective view showing another modification of the optical information reading device, FIG. 6 is a bottom view showing recording tracks on the optical disc and spots of laser light, and FIG. 7 is a conventional optical information reading device. FIG. 8 is a schematic front view showing the apparatus, FIG. 8 is a schematic front view showing another conventional optical information reading apparatus, and FIG.
FIG. 9 is a front view showing a diffraction grating in the optical information reading apparatus of FIG. 8 and FIG. 9B is a graph showing a distribution of transmittance of 0th-order diffracted light in the diffraction grating of FIG. 9A. Reference numeral 11 is a laser emission source (light source), 13 is a diffraction element, 16 is an optical disk, and 17 is a photodetector (light receiving element).

Claims (1)

[Claims] 1. An optical information reading apparatus for reading information on an optical disc by converging a light flux from a light source onto the optical disc and receiving reflected light from the optical disc by a light receiving element. A diffraction grating that divides a light beam from a light source into a 0th-order diffracted light for reading information on the optical disc and a pair of 1st-order diffracted light for reading a tracking error, and reflected light from the disc A diffractive element formed with a holographic grating that guides the light to the light receiving element, and the holographic grating on the diffractive element has regions located at both ends in the direction corresponding to the radial direction of the optical disc in the radial direction. Is divided into a plurality of regions so that the transmittance of 0th-order diffracted light is smaller than that of the region located in the center in the direction corresponding to An optical information reading device characterized by being provided.