JPH0242648A - Optical information reader - Google Patents

Abstract

PURPOSE:To reduce the number of components and to prevent a crosstalk by integrating a diffraction grating and a holographic grating on a diffraction element and suppressing the transmissivity of a zero order diffraction light in a specific method. CONSTITUTION:For a diffraction element 13, for example, six areas 13a-13f to be mutually divided are integrally formed, and to four areas 13a-13d among them, the holographic gratings are formed, and to the other two areas 13e and 13f, the diffraction gratings are formed. The transmissivity of the zero order diffraction light in the diffraction grating and/or holographic grating positioned in the vicinities of both edges in a direction corresponding to a radial direction B-B' of an optical disk 16 in the diffraction grating 13 is set so as to be smaller than the transmittance of the zero order diffraction light in the diffraction grating and/or holographic grating positioned in the vicinity of a central part in the direction corresponding to the radial direction B-B'. Thus, the number of components is reduced, and simultaneously, the crosstalk is prevented.

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 a laser beam emitted from a laser light source l passes through a diffraction grating 2 to form a tracking spot.
After passing through and being reflected by the beam splinter 3, it 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 objective lens 5 and the collimating lens 4, passes through the beam splitter 3, and then enters the photodetector 8 via the plano-concave lens 7, where the reflected light is converted into an electrical signal. It is set to be converted.

Moreover, FIG. 8 shows a conventional example in which a holographic grating element 9 on which a holographic 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 provided with a collimating lens. 4. The photodetector 8 is placed on the same straight line as the objective lens 5, etc., and the photodetector 8 is placed on the side of the laser emission source 1, so that the reflected light from the optical disk 6 is transmitted to the photodetector 8 by the holographic grating element 9. It is designed to be guided by.

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, in the focused laser beam, a near ring indicated by SI occurs due to the second maximum component, and this near ring causes the adjacent recording tracks 6a and 6a to
6a, 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 transparent part 10a is formed is narrower than the beam width of the transmitted laser light is attached to the filter 2b on the opposite side. In the filter 10, as shown in FIG. 9(b),
It is known that by suppressing the transmittance of the 000th order diffracted light near both ends of the diffraction grating 2 in the direction corresponding to the radial direction of the optical disk 6, crosstalk can be reduced when reading information on the recording track 6a. There is.

[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. Further, the optical information reading device has a large number of parts and a complicated structure.

[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 configured to perform reading, diffraction is used to divide a light beam from a light source into an O-order instruction beam for reading information on an optical disk and a pair of first-order diffracted beams for reading tracking errors. A diffraction element including a grating and a holographic grating that guides reflected light from the optical disc to the light receiving element are integrally formed, and is located near both ends of the diffraction element in a direction corresponding to the radial direction of the optical disc. The transmittance of the 0th order diffracted light in the diffraction grating and/or holographic grating is the transmittance of the 0th order diffracted light in the diffraction grating and/or holographic grating located near the center of the diffraction element in the direction corresponding to the radial direction. It is characterized by being set to be smaller.

[For production]

In the above configuration, a light beam such as a laser beam from a light source is split by a diffraction grating on a diffraction element into an O-order directed beam and a pair of first-order diffracted beams, and the beams are converged onto an optical disk. The reflected light from the optical disk enters the holographic grating on the diffraction element, and the first-order diffracted light reaches the light receiving element, where the information on the optical disk is converted into an electrical signal.

Further, in the present invention, since the diffraction element and the holographic grating are integrated on the diffraction element, the number of parts is reduced. In addition, as a measure to prevent crosstalk, the diffraction grating and/or the holographic grating itself is formed to have a filter function that suppresses the transmittance of the zero-order diffracted light at both ends in the direction corresponding to the radial direction of the optical disk. Therefore, it is no longer necessary to form a filter by vapor deposition as in the past.
It becomes possible to reduce 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 12 as a light source, and a beam of laser light emitted from a chip 12a (see FIG. 1) of the laser light source 12. is focused onto the optical disk 16 via the diffraction element I3, the collimating lens 14, and the objective lens 15.

The reflected light from the optical disk 16 is reflected by an objective lens 15.
, enters the diffraction element 13 via the collimating lens 14, and further passes from the diffraction element 13 to the photodetector 1 as a light receiving element.
7, where detection of tracking errors, detection of focus errors, and reading of information on the optical disc 16 are performed. In FIG. 3, arrow A-A' indicates the focus direction, arrow B-B' 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 is made of plastic or glass and has six regions 13a to 1 divided from each other.
3f, of which four areas 13a~
A holographic grating is formed in each of the regions 13d, and a diffraction grating is formed in each of the other two regions 13e and 13f. Each area 13a~
The holographic grating and diffraction grating 13f are formed near the surface of the diffraction element 13 near the collimator lens 14. Note that P in FIG. 2(a) indicates the outermost position of the light beam passing through the diffraction element 13. 6 The functions of each region 13a to 13f of the diffraction element 13 will be explained below. It becomes a parallel light beam, and the objective lens 15 directs it to the optical disk 1.
The bit above 6 is irradiated. The O-th order diffracted light that has passed through the area 13a has an inclination angle within a certain range with respect to the optical disk 16 after passing through the objective lens 15, as shown by the arrow in FIG. According to the law of reflection, it is reflected at the same angle as the incident light beam as shown by the arrow E, passes through the objective lens 15 and the collimating lens 14, and reaches the surface of the holographic grating formed in the region 131) of the diffraction element 13.

A holographic grating is formed in the region 13b to divide the reflected light beam from the optical disk 16 into 0th-order diffracted light that returns to the laser emission source 12 as it is and 1st-order diffracted light that enters the photodetector 17. 13
The first-order diffracted light split by the holographic grating b is divided into areas 17b and 1 in the photodetector 17.
The dividing line between 7c! A focus servo system (not shown) causes the spot of the laser beam on the optical disk 16 to follow the surface deflection of the optical disk 16, and the information recorded on the optical disk 16 is detected.

Further, the O-th order light emitted from the laser emission source 12 and passing through the holographic grating in the area 13b of the diffraction element 13 is similarly reflected by the optical disk 16 and returns to the area 13a of the diffraction element 13, and is reflected by the holographic grating in the area 13a. The first-order diffracted light reaches the photodetector 17a of the photodetector 17 by the graphic grating, and the photodetector 17a
The information on the optical disc 16 is detected.

Further, the light beam emitted from the laser emission source 12 and reaching the regions 13e and 13f of the diffraction element 13 is divided into 0th-order diffracted light and ±1st-order diffracted light for detecting tracking errors by the diffraction gratings formed in the regions 13e and 13f. The area 13
The first-order diffracted light reaches the photodetectors 17e and 17d of the photodetector 17 by the holographic gratings formed on the photodetectors 17e and 13d, respectively.
Based on the light beam reaching the optical disk 17d, a tracking servo system (not shown) causes the spot of the laser beam on the optical disk 16 to follow the recording track.

Further, the laser beam is emitted from the laser light source 12, and the diffraction element 13
The light flux reaching the regions 13c and 13d reaches the optical disk 16 after the intensity of the O-th order light is lowered by the holographic grating formed in these regions 13c and 13d. Most of the light beam reflected by the optical disk 16 reaches the diffraction gratings in regions 13e and 13f of the diffraction element 13, but is not branched to the photodetector 17.

In the above process, the proportion of the O-order light that passes through the diffraction element 13 among the light flux emitted from the laser emission source 12 corresponds to the radial direction of the optical disc 16, as shown in FIG. 3(b'). The holographic gratings in regions 13a and 13b located near the center in the direction corresponding to the radial direction of the optical disk 16 are high, and the holographic gratings in regions 13c and 13d and regions 13e and 13r located near both ends in the direction corresponding to the radial direction of the optical disk 16 are high.
In the diffraction grating, the holographic grating and diffraction grating in each region 13a to 13f are formed so as to be lower than the holographic grating in regions 1.3a and 13b.

As a result, the intensity distribution of the light beam at the time it passes through the diffraction element 13 becomes equivalent to the conventional intensity distribution using the filter 10. Therefore, when detecting information on the optical disc 16, crosstalk is sufficiently suppressed.

Here, in the diffraction gratings in the regions 13e and 13f, by changing the spectral ratio of the 0th-order diffracted light and the 1st-order diffracted light, an arbitrary filter effect can be obtained, and the 0-th order diffracted light and the 1st-order diffracted light are applied to the diffraction grating. It can serve both the division role and the filter function.

On the other hand, the holographic intergrating in regions 13c and 13d has the same function as the holographic grating in region 13b, but by changing only the depth of the holographic grating,
It is possible to control the spectral ratio of the 0th order diffracted light to an arbitrary value, thereby making it possible to control the spectral ratio of the 0th order diffracted light in the region 13b to
Since the proportion of the 0th order diffracted light passing through the holographic gratings C and 13d can be set low, the desired filter effect can also be obtained in the holographic gratings in the regions 13c and 13d.

Next, a modified example is shown in FIG.

The diffraction element 18 in this modification has five regions 18a to 18a.
A holographic grating is formed in each of four regions 18a to 18d, and a diffraction grating is formed in the other region 18e.

Similarly to the above embodiment, the light beam emitted from the laser light source 12 and passed through the holographic grating in the area 18a is reflected by the optical disk 16, and then reaches the holographic grating in the area 18b.
Focus servo is performed by the photodetector I7 based on this luminous flux. On the other hand, the light beam that has passed through the holographic grating in the 6-page area 18b is reflected by the optical disk 16 and then reaches the holographic grating in the area 18a.
Detection of the information above is performed.

Further, the light beam emitted from the laser emission source 12 and passed through the diffraction grating in the area 18e is reflected by the optical disk 16 and reaches the areas L3c and 13d of the diffraction element 13, and is detected by the photodetector 17 based on this light beam.・Linking servo is performed. Conversely, the light beams that have passed through the hollow rough quadrants in regions 18c and 18d reach the diffraction grating in region 18e after being reflected by the optical disk 16. Also in this modification, the proportion of the 0th-order diffracted light that passes through the diffraction element 18 is determined by the area 18c located at both ends of the direction 1iij corresponding to the radial direction of the optical disc 16.
-i8e, regions 18a and 18 located at the center of the optical disc 16 in a direction corresponding to the radial direction;
(i

In the above embodiment, each region 13a of the diffraction element 13
Although the holographic grating or diffraction grating of -13 was provided near the surface of the diffraction element 13 near the collimating lens 14, they may also be provided near the surface of the diffraction element 13 on the opposite side from the collimating lens 14. good.

Furthermore, in the above embodiment, the laser emitting source 12 and the photodetector 17 were configured separately, but the laser emission source 12 and the photodetector 17 are configured as a single element to achieve miniaturization. The present invention is also applicable to formula information reading devices.

〔Effect of the invention〕

As described above, the optical information reading and receiving 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 5 and receiving the reflected light from the optical disc with the light receiving element. In an optical information reading device designed to perform and a holographic grating that guides reflected light from the optical disc to the light receiving element are integrally formed, and near both ends of the diffraction element in a direction corresponding to the radial direction of the optical disc. The transmittance of the O-order diffraction light in the diffraction grating and/or holographic grating located in the center of the diffraction grating and/or holographic grating located near the center of the diffraction element in the direction corresponding to the radial direction is This configuration is set so that the transmittance is smaller than the transmittance.

As a result, the diffraction element and the holographic grating are integrated on the diffraction element, making it possible to reduce the number of parts. As a measure to prevent crosstalk, the transmittance of the O-th order light in the diffraction grating and/or the horizontal direction grating located near both ends in the direction corresponding to the radial direction of the optical disc is 7. a diffraction grating located near the center in a direction corresponding to the radial direction;・'or hol'
:J Since it is formed so that the transmittance of the O-th order light is smaller than that of the graphic grating, the diffraction element itself has a filter function, and as a result, there is no need for a separate filter like in the past. Therefore, it is possible to reduce the number of man-hours and the number of steps.

[Brief Description of the Drawings] Figures 1 to 5 show embodiments of the present invention, in which Figure 1 is a perspective view showing a diffraction element and a photodetector, and Figure 2 (a) is a perspective view of a diffraction element and a photodetector. A plan view of the diffraction element, Fig. 2(b) is a graph showing the transmittance distribution of 0th order diffracted light in the diffraction element, and Fig. 3 is an optical information reader JT! , ' A perspective view of the device, Figure 4 is a front view showing the objective lens and the optical disk, Figure 5 is a plan view showing the diffraction element in a modified example, and Figure 6 is a recording track on the optical disk and a laser beam spot. bottom view showing,
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 a diffraction grating in the optical information reading device of FIG. 7 or FIG. FIG. 9(b) is a graph showing the transmittance distribution of the O-order light in the diffraction grating of FIG. 9(a). 12 is a laser emission source (light source), 13 is a diffraction element, 16
1 is an optical disk, and 17 is a photodetector (light receiving element).

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. , The light flux from the light source is divided into 0th order diffracted light for reading information on the optical disk and 1st order diffracted light for reading tracking error.
a diffraction element that is integrally formed with a diffraction grating that divides the first-order diffraction light into a pair of first-order diffraction lights, and a holographic grating that guides the reflected light from the optical disc to the light receiving element, and the radial direction of the optical disc in this diffraction element. The transmittance of the 0th order diffracted light in the diffraction grating and/or holographic grating located near both ends in the direction corresponding to An optical information reading device characterized in that the transmittance is set to be smaller than the transmittance of zero-order diffracted light in a graphic grating.