JPH0963099A - Optical information read-out device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering in an S/N ratio due to diffracted light beams used for no signal detection. SOLUTION: The diffracted light beams 103, 104 unnecessary for signal detection are made incident respectively on the surfaces 14, 15 different from the reflection surface 11 on which the diffracted light beam 102 used for signal detection is made incident. By working the surfaces 14, 15 to a coarse surface, or respectively providing reflection preventing films 14a, 15a on the surfaces 14, 15, the diffracted light beams 103, 104 are led to the outside of a light transmissivity block 3 while preventing the diffracted light beams 103, 104 from being reflected to the inside of the transmissivity block 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detecting means such as a multi-divided light receiving element, in which a laser beam is focused on a fine light spot and is incident on a recording surface of an information recording medium such as an optical disk, and reflected light from the recording surface is detected. The present invention relates to an optical information reading device which is used to read signal information written on an optical disk or the like by detecting the optical information.

[0002]

2. Description of the Related Art An optical pickup for reading signal information recorded on an optical disk is equipped with a servo function for focusing and tracking, and by this servo function, mechanical fluctuations such as surface wobbling and eccentricity associated with rotation of the optical disk are generated. The optical pickup accurately follows the fluctuations.

By the way, in order to improve the followability of the optical pickup and increase its reliability, it is necessary to reduce the size and weight of the optical pickup. A conventional example of a compact and lightweight optical pickup that meets such a demand will be described below.

FIG. 6 shows an optical pickup disclosed in Japanese Patent Laid-Open No. 62-117150. A light emitting element 1001 made of, for example, a semiconductor laser element is attached to the upper surface of a transparent substrate 1000 having a rectangular parallelepiped shape. The laser diffused light emitted from the light emitting element 1001 toward the inside of the transparent substrate 1000 has its optical path changed in a direction corresponding to the right side of FIG. 6 by the diffraction grating 1002 formed on the upper surface of the transparent substrate 1000.

Subsequently, the laser diffused light is transmitted to the transparent substrate 100.
0 are sequentially reflected by the reflection surfaces (total reflection surfaces) 1003, 1004, and 1005 formed on both front and back surfaces (upper and lower sides in FIG. 6) of 0, and are transmitted in a zigzag shape inside the transparent substrate 1000. Then, the diffraction grating 1006 formed on the upper surface of the transparent substrate 1000 converts the light into parallel rays, and the diffraction grating 10
It is focused on the recording surface of the optical disk 1110 by an objective lens 1007 provided at a position just above 06 at a predetermined distance. As a result, a light spot is formed on the recording surface of the optical disk 1110.

The reflected light from the optical disk 1110 is transmitted in the direction corresponding to the left side in FIG. 6 in the transparent substrate 1000 by following the path opposite to the above, and the concave lens 1008 formed on the back surface of the transparent substrate 1000 and the upper surface. After being reflected by each reflecting surface of the cylindrical lens 1009 formed on the above, it is finally detected by the photodetector 1010. As a result, the signal information recorded on the recording surface of the optical disc is read. Further, focusing servo and tracking servo are performed by using the detection result of the photodetector 1010 including the multi-divided light receiving element.

As another conventional example of a compact and lightweight optical pickup, the applicant of the present invention has disclosed in Japanese Patent Laid-Open No. 6-314.
There is an optical information reader previously proposed in Japanese Patent No. 437. FIG. 8 is a diagram schematically showing the configuration of this optical information reading device. This optical information reading device has a light transmissive block 2001, and an upper surface 2013 thereof has
Si substrate 2006, submount 2003 on which semiconductor laser 2002 is mounted, and objective lens 2007
Is installed. On the lower surface of the Si substrate 2006, a photodetector 2004 including a multi-divided light receiving element and a reflection hologram beam splitter 2005 are formed. The light emitted downward from the semiconductor laser 2002 is vertically incident on the light transmissive block 2001, and the oblique reflection surface 20
After repeating reflection in order of 11, the reflection hologram beam splitter 2005, and the vertical reflection surface 2012, it is guided to the objective lens 2007, and is condensed by the objective lens 2007 as a light spot on the recording surface of the optical disc 2008 above.

On the other hand, the light reflected by the optical disk 2008 travels in the opposite direction to enter the reflection hologram beam splitter 2005, is deflected by the reflection hologram beam splitter 2005, and is collected on the photodetector 2004. Be illuminated. The information signal written on the optical disc 2008 is detected by the electric signal photoelectrically converted by the photodetector 2004. Further, a focus error signal and a tracking error signal are also detected at the same time, and a servo mechanism (not shown) is driven by these signals, thereby performing focusing servo and tracking servo.

[0009]

In the conventional optical pickup shown in FIG. 6, a diffraction grating 1002 is provided in order to propagate the laser light emitted from the light emitting element 1001 inside the transparent substrate 1000 as shown in the figure. Further, a diffraction grating 1006 is used to collimate the laser beam between the transparent substrate 1000 and the objective lens 1007. Therefore, when the laser beam is diffracted by the diffraction grating 1002 in the forward path (the optical path from the light emitting element 1001 to the optical disk 1110), and when the laser light is diffracted by the diffraction grating 1006 in the return path (the optical path between the optical disk 1110 and the photodetector 1010). When the reflected light from 1110 is diffracted, diffracted light 1210 and 1220 unnecessary for signal detection are generated.
These lights are repeatedly reflected inside the transparent substrate 1000 as shown in FIG. 7, and become stray light. However, FIG. 7 illustrates only part of the optical path of stray light. Part of the stray light is detected by the photodetector 1010, and the S / N at the time of signal detection is detected.
It had the drawback of reducing the ratio.

Further, since the reflection type hologram beam splitter 2005 which is a diffractive optical element is used in the optical information reading apparatus shown in FIG. 8, in the return type reflection hologram beam splitter 2005 as shown in FIG. Folded light 2101, + 1st-order diffracted light 2102 used for signal detection, + 2nd-order and higher-order diffracted light 2103,
Negative order diffracted light 2104 is generated. Then, stray light is generated due to the diffracted light 2103 of the + 2nd order or more and the diffracted light 2104 of the negative order which are unnecessary for signal detection. More specifically, the diffracted light 210 of + second order or more generated in the reflection hologram beam splitter 2005 is generated.
3 is reflected by the lower surface 2014 and the inclined reflection surface 2011 of the light transmissive block 2001,
Stray light is generated by repeating reflection many times within 1. The negative-order diffracted light 2104 generated by the reflective hologram beam splitter 2005 is reflected by the slanted reflection surface 2011 and the side surface 2015 of the light transmissive block 2001, and is repeatedly reflected in the light transmissive block 2001 a number of times. Stray light.

A part of the stray light thus detected is detected by the photodetector 2004. Therefore, noise is generated due to stray light, and the S / N ratio at the time of signal detection is reduced.

The present invention has been made in view of the above circumstances, and an object thereof is to read an optical information which can prevent a decrease in S / N ratio due to stray light and can significantly improve reliability. It is to provide a device.

[0013]

The optical information reading device of the present invention is an optical information reading device for irradiating an optical disc with light and detecting the information recorded on the optical disc from the light reflected by the optical disc. A light emitting means for emitting the light, an objective lens for irradiating the light onto the optical disk, a light receiving means for receiving the light reflected by the optical disk, and a light for propagating the light emitted from the light emitting means. A light-transmitting block that guides the light reflected by the optical disk to the light-receiving means, the light-transmitting block being provided on a main surface on which a diffractive means is provided and on the main surface. A first surface and a second surface which are inclined and opposed to each other, and the first surface guides the light reflected by the optical disc to the diffractive means, and the diffractive means diffracts the diffractive means. Detect the information in the light Diffracted light so that unnecessary diffracted light does not enter the second surface, and the second surface guides the diffracted light necessary for detecting the information to the light receiving means, By doing so, the above object is achieved.

The light-transmitting block has a plurality of surfaces including the main surface and the first and second surfaces, and the diffracting means separates the unnecessary diffracted light from the plurality of surfaces. The light may be incident on a surface different from the main surface and the first and second surfaces.

The main surface of the light-transmitting block and the surface different from the first and second surfaces may be processed to prevent reflection of the unnecessary diffracted light.

The diffracting means may diffract the light from the first surface so as not to generate at least a part of the unnecessary diffracted light.

The light-transmitting block has a plurality of surfaces including the main surface and the first and second surfaces, and the diffracting means does not generate a part of the unnecessary diffracted light. And the remaining portion is the main surface of the plurality of surfaces,
The light may be diffracted so as to be incident on a surface different from the first and second surfaces.

The light emitting means, the light receiving means, and the objective lens may be provided on the main surface of the light transmissive block.

Another optical information reading device of the present invention is an optical information reading device which irradiates an optical disc with light and detects the information recorded on the optical disc from the light reflected by the optical disc. A substrate having a main surface on which a light emitting means for emitting light, a light receiving means for receiving the light reflected by the optical disc, and a first and a second diffracting means are formed, and the light is irradiated onto the optical disc. Light transmissive, which has an objective lens and the substrate therein, propagates the light emitted from the light emitting means, guides the light to the objective lens, and guides the light reflected by the optical disk to the light receiving means. A block, the light-transmissive block has a main surface facing the main surface of the substrate, the main surface of the light-transmissive block is partially processed into a reflection portion, The first and second diffractive means , The unnecessary diffracted light for detecting the information of 該回 diffracted diffract light so as not to be incident on the reflection surface, to achieve the above object by its.

The first diffracting means may cause the unnecessary diffracted light to be incident on a portion of the main surface of the light transmissive block different from the reflecting portion.

A portion of the main surface of the light transmissive block, which is different from the reflection portion, may be processed so as to prevent reflection of the unnecessary diffracted light.

The first and second diffracting means may diffract the light so as not to generate at least a part of the unnecessary diffracted light.

The light transmissive block has a plurality of surfaces including the main surface, and the first and second diffracting means do not generate a part of the unnecessary diffracted light, and The light may be diffracted so that the remaining portion is incident on a portion of the main surface of the light transmissive block that is different from the reflection portion or a surface that is different from the main surface.

The objective lens may be disposed above the second diffracting means and may be provided on the main surface of the light transmissive block.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of the configuration of the optical information reading apparatus of the present invention. This optical information reader is
It has a light-transmissive block 1 and Si
A substrate 6, a submount 3 on which the semiconductor laser 2 is mounted, and an objective lens 7 are mounted. Further, on the lower surface of the Si substrate 6, a photodetector 4 including a multi-divided light receiving element and a reflection hologram beam splitter 5 are formed.

The light-transmitting block 1 is produced by molding resin or glass. Light-transmissive block 1
The inclined reflection surfaces 11, 1 are provided on both ends of the lower surface 14 of the
2 is formed. The inclined reflection surfaces 11 and 12 have the same inclination angle with respect to the upper surface 13 of the light transmissive block. In FIG. 1, the longitudinal direction of the light transmissive block 1 is indicated by Y and the width direction thereof is indicated by X. Si substrate 6
Is mounted in the central portion of the light transmissive block 1 in the longitudinal direction, and the submount 3 is mounted on one of the end portions (the left end portion in FIG. 1) of the Si substrate 6. Si substrate 6
A photodetector 4 is formed in the vicinity of the submount 3, and a reflection hologram beam splitter 5 is formed at the end opposite to the end where the submount 3 is mounted on the lower surface of the submount 3.
The objective lens 7 is arranged at one of the longitudinal end portions (the right end portion in FIG. 1) of the upper surface 13 of the light transmissive block 1, and is fixed to the upper surface 13. An optical disk 8 is arranged above the objective lens 7.

The operation of this optical information reader will be described below with reference to FIG.

The light emitted downward from the semiconductor laser 2 is vertically incident on the light transmissive block 1 and is reflected by the inclined reflection surface 11, the reflection hologram beam splitter 5, and the inclined reflection surface 12 in this order. After repeating, the light enters the objective lens 7. The objective lens 7 irradiates the recording surface of the optical disc 8 with light, thereby forming a light spot on the recording surface. On the other hand, the light reflected by the optical disk 8 is
The light beam is deflected by the reflection hologram beam splitter 5 following the above-mentioned path in reverse, and is condensed on the photodetector 4. A focus error signal and a tracking error signal, which are servo signals, are detected by the beam size method and the push-pull method from the electric signal photoelectrically converted by the photodetector 4. A servo mechanism (not shown) is driven according to these servo signals, and focusing servo and tracking servo are performed. Further, the information signal written on the recording surface of the optical disk 8 is detected by the electric signal photoelectrically converted by the photodetector 4.

In this embodiment, out of the diffracted light generated by the reflection hologram beam splitter 5, diffracted light not used for signal detection is guided to the outside of the light transmissive block 1. Here, the + 1st-order diffracted light 102 is used for signal detection, and the diffracted light 103 of the + 2nd-order or higher order shown in FIG.
The case of leading outside will be described as an example. Diffracted light 103 of the + 2nd order or more goes downward in FIG. Therefore, if the + 2nd order diffracted light is made incident on the lower surface 14, higher order diffracted light will also be made incident on the lower surface 14. At this time, if the light reflection on the lower surface 14 is prevented, it is possible to prevent the diffracted light of the + 2nd order or more from being repeatedly reflected inside the light transmissive block 1. The reflection of light on the lower surface 14 is
This can be prevented by making the lower surface 14 rough. Alternatively, it is possible to prevent reflection on the lower surface 14 by providing an antireflection film 14a on the lower surface 14 as shown in FIG. In this embodiment, this allows the light incident on the lower surface 14 to be guided to the outside of the light transmissive block 1 without being reflected, and as a result, stray light due to reflection inside the light transmissive block 1 can be prevented. be able to.

Here, of the light rays in the light beam entering the reflection-type hologram beam splitter 5, a light ray 100 enters the reflection-type hologram beam splitter 5 at an incident angle α,
Consider a case where diffracted light of order m exits at a diffraction angle β. At this time, the following expression (1) is established.

Sin α-sin β = m × (λ / nd) (1) However, m = 0, ± 1, ± 2, ... Further, λ is the wavelength of the light ray 100, n is the refractive index of the medium through which the light ray 100 passes, and d is the pitch of the hologram of the portion where the light ray 100 is incident. By substituting the incident angle α determined based on the specifications relating to the dimensions of the optical system shown in FIG. 1 into the above formula (1), the diffraction angle β _{(2) of} the + 2nd-order diffracted light, that is, the + 2nd-order diffracted light is emitted. You can find the direction to do. In this way, the range of the direction in which the + 2nd-order diffracted light is emitted is obtained in consideration of the variation of the mounting position of each optical element provided in the light-transmitting block 1, and the + 2nd-order diffracted light is used as the inclined reflection surface 11 based on the obtained range. Β ₍₂₎
To reduce. As a result, all the diffracted light 103 of the + 2nd order or higher can be guided to the lower surface 14 of the light transmissive block 1.

Alternatively, if the range of the direction in which the + 2nd order diffracted light is emitted is obtained as described above, the thickness in the direction perpendicular to the upper surface 13 of the light transmissive block 1 is reduced in consideration of the range. The lower surface 14 may be widened. Also in this case, similarly to the case where the diffraction angle β ₍₂₎ is reduced, the diffracted light 103 of the + _2nd order or more can be guided to the lower surface 14.

In the above description, an example in which the diffracted light 103 of + 2nd order or more is guided to the outside of the light transmissive block 1 has been considered.
Similarly for the negative order diffracted light 104, by guiding these diffracted lights to the side surface 15 of the light transmissive block 1 and processing the surface 15 into a rough surface, or by providing the antireflection film 15a on the surface 15, The diffracted light 104 of negative order can be guided to the outside of the light transmissive block 1 while being prevented from being reflected inside the light transmissive block 1.

In the above example, the + 1st order diffracted light 102
Is used for signal detection, but when −1st order diffracted light is used for signal detection, unnecessary diffracted light such as positive diffracted light and negative diffracted light of 2nd or higher order are transmitted by the same procedure. It is possible to prevent stray light from being repeatedly reflected in the block 1.

Although the 0th-order diffracted light 101 finally returns to the semiconductor laser 2, the noise due to this return light can be suppressed by oscillating the semiconductor laser 2 while superposing a high frequency.

Instead of guiding unnecessary diffracted light that is not used for signal detection to the outside of the light transmissive block 1, it is possible to prevent it from being generated from the beginning. Here, a case where only the + 1st order diffracted light 102 is used for signal detection and the unnecessary diffracted light 104 of the negative order is not generated will be described as an example. In FIG. 3, the diffracted light of negative order 1
Of the 04, only the −1st order diffracted light 105 is shown. The negative-order diffracted light 104 is generated toward the left in FIG. If the -1st order diffracted light is not generated, the diffracted light of a negative order higher than the -1st order is not generated.

Firstly, from the above equation (1), the diffraction angle beta ₍₁₎ of the + 1st-order diffracted light 102 used for signal detection, the diffraction angle beta _(-1) and satisfies the formula (2) of the -1st-order diffracted light 105 and (3) is introduced.

[0039] _{sinα-sinβ (1) = λ} / nd (2) sinα-sinβ (-1) = -λ / nd (3) These equations (2) and from _{(3), sinβ (-1)} = 2sinα −sin β ₍₁₎ (4) −1 When the _first-order diffracted light 105 exists, the following equation (5)
The condition expressed by is satisfied.

0 ≦ sin β ₍₋₁₎ ≦ 1 (5) From this, 0 ≦ 2 sin α−sin β ₍₁₎ ≦ 1 On the contrary, when the following condition (6) is satisfied, the −1st order diffracted light 105 does not exist. 2sinα-sinβ ₍₁₎ > 1 (6) From this, the condition where the negative order diffracted light does not exist is as in the following formula (7). β ₍₁₎ <Sin ⁻¹ (2sin α ⁻¹ ) (7) Therefore, for all the rays incident on the reflection hologram beam splitter 5, +1 is used for signal detection.
If the hologram pitch of the reflection hologram beam splitter 5 is set so that the diffraction angle β ₍₁₎ of the secondary diffracted light 102 satisfies the condition (7), it is possible to prevent the diffracted light 104 of the negative order from being generated. . That is, it is possible to prevent stray light from being generated due to the diffracted light 104 having a negative order.

In the above description, the case where the + 1st-order diffracted light 102 is necessary for signal detection and the negative-order diffracted light 104 is not generated has been described. However, the -1st-order diffracted light 105 is required and the positive-order diffracted light 105 is required. The same can be considered when the diffracted light is not generated. That is, when the condition (8) is satisfied,
There is no positive order diffracted light.

Β _(-1) <Sin ^-1 (2sin α-1) (8) An example of a specific method of setting the hologram pitch of the reflection hologram beam splitter 5 will be described below. First, the incident angle α to the reflection hologram beam splitter 5 is determined based on the specifications relating to the dimensions of the optical system in the forward path of the optical path shown in FIG. 1. Next, negative diffracted light 1
The range of the diffraction angle β ₍₁₎ of the + _{1st order} diffracted light such that 04 does not occur is obtained from the above equation (7). One value that allows the photodetector 4 to be arranged is determined from the obtained range, and the hologram pitch is calculated from the above equation (2) using this value. Next, it is confirmed whether or not the calculated pitch is an actually manufacturable pitch, and if the pitch cannot be manufactured, if possible, the diffraction angle β of the + 1st order diffracted light β ₍₁₎ Or select again or start again from the determination of the incident angle α. If the pitch is manufacturable, the optical path of the diffracted light of the + 2nd or higher order of the reflection hologram beam splitter 5 having the pitch is obtained,
It is confirmed whether or not the diffracted light of the second or higher order is incident on the surface of the light transmissive block which is the propagation path of the + 1st order diffracted light.
When it is incident, the selection of the value of β ₍₁₎ is performed again.

As described above, the diffracted light of the + 2nd order or more that is incident on the surface serving as the propagation path of the + 1st order diffracted light has a rough surface as the surface on which the diffracted light of the + 2nd order or more enters. By providing an antireflection film on this surface, the light can be guided to the outside of the light transmissive block 1 without being reflected.

For example, when the incident angle α of the light beam on the reflection type hologram beam splitter 5 is 70 deg, the condition of the diffraction angle β ₍₁₎ of the + _1st order diffracted light so that the diffracted light of the negative order is not generated is as follows. From (7), β ₍₁₎ <Sin ⁻¹ (2sin α−1) = 61.6 deg. That is, the diffraction angle β ₍₁₎ of the + 1st order diffracted light needs to be smaller than 61.6 deg. From this range, the value of β ₍₁₎ is 5
If 0 deg is defined, the wavelength λ = 0.78 μm, the refractive index n of the medium
= 1.454, the hologram pitch is d = λ / {n · (sinα-sinβ ₍₁₎ )} = 3.09 μm from the above equation (2) Therefore, if the pitch of the reflection hologram beam splitter 5 is 3.09 μm, It is possible to prevent generation of diffracted light of negative order.

When the above condition (7) cannot be completely satisfied, the negative order diffracted light 104 is emitted in a direction substantially parallel to the reflection surface of the reflection hologram beam splitter 5, and the + 1st order diffracted light is propagated. It is possible to lead to the outside of the light transmissive block 1 from the side surface 15 which is not. Also in this case, by processing the side surface 15 to be rough or providing the side surface 15 with the antireflection film 15a, the diffracted light 104 can be guided to the outside of the light transmissive block 1 without being reflected,
Stray light can be prevented from being generated due to the reflection of light inside the light transmissive block 1. In this case, both the unnecessary negative diffracted light 104 and the diffracted light of + 2nd order or higher are guided to the outside of the light transmissive block 1 as described above.

In the above embodiment, the optical information reading device using the light transmissive block in which the inclined reflection surface has the same inclination angle with respect to the upper surface has been described. The arrangement of each optical component is not limited to that described in the above embodiment. Below, FIG. 4 and FIG.
Another example of the configuration of the optical information reading device of the present invention will be described with reference to FIG.

The optical information reader 1 shown in FIGS. 4 and 5 is mounted on the light-transmissive block 3 and the light-transmissive block 3 molded with a light-transmissive resin so as to take the optoelectronic integrated substrate 2 therein. The objective lens 8 is included.

As the optoelectronic integrated substrate 2, GaAs / G is used.
A compound semiconductor substrate such as an aAlAs-based substrate or an InP / InGaAsP-based substrate is used. A light emitting element 4, a light receiving element 5, an electronic device such as an electronic integrated circuit (not shown), a reflection hologram beam splitter 6, and a reflection hologram 7 having a deflection function are arranged on one surface of the substrate 2. There is.

The light emitting element 4 is formed on one end of the optoelectronic integrated substrate 2 in the longitudinal direction, and the light receiving element 5 is formed on the central portion in the longitudinal direction.
And the light emitting element 4. The reflection hologram 7 having a deflection function is formed on the other end of the optoelectronic integrated substrate 2 in the longitudinal direction. In FIG. 4, the longitudinal direction is indicated by Y and the width direction is indicated by X.

The light transmissive block 3 is, for example, a PMM.
It is formed by pouring a light-transmissive resin such as A or PC into a mold and molding so that the optoelectronic integrated substrate 2 is taken inside. At this time, the surfaces 9 and 10 are formed on the surface of the light transmissive block 3 so as to face the optoelectronic integrated substrate 2. The portions 9a and 9b of the surface 9 and the surface 10 are made reflective surfaces by vapor deposition of an Al film or the like.

The objective lens 8 is arranged on the surface 9 of the light transmissive block 3 so as to be located directly above the reflection hologram 7.

The operation of the optical information reading device 1 will be described below. The light emitted from the light emitting element 4 is reflected by the reflecting surface 10.
After being reflected by the reflective hologram beam splitter 6
After that, the light is reflected by the reflection surface 9b, is deflected by the reflection hologram 7, and goes upward. The deflected light is condensed by the objective lens 8 and condensed as a light spot on the recording surface of the optical disc 20.

The light reflected by the optical disk 20 is
The light beam travels in the opposite direction, is deflected by the reflection hologram beam splitter 6, is reflected by the reflection surface 9a, and then enters the light receiving element 5. The light receiving element 5 is the optical disc 2
The reflected light from 0 is detected, and this is photoelectrically converted and given to an electronic integrated circuit (not shown). The electronic integrated circuit outputs the focus error signal, the tracking error signal, and the signal information recorded on the optical disc, which is obtained by performing the signal processing.

Unnecessary diffracted light generated in the reflection type beam splitter 6 and the reflection type hologram 7 is guided to the outside of the light transmissive block 3. First, on the return trip, surface 9
Diffracted light generated when the light from the portion 9b enters the reflection hologram beam splitter 6 will be described.
Here, the + 1st order diffracted light 102 is used for signal detection, and +2
It is assumed that the diffracted light 103 of the order higher than the order is unnecessary.
Similarly to the + 1st-order diffracted light 102 directed to the portion 9a of the surface 9, the diffracted light 103 of the + 2nd order or higher also goes to the surface 9 as shown in FIG. Therefore, in this embodiment, the diffracted light 1 is formed by roughening the portion 9c on which the diffracted light 103 is incident or by attaching an antireflection film to the portion 9c.
03 is guided to the outside of the block 3 while being prevented from being reflected inside the light transmissive block 3. On the other hand, the negative-order diffracted light 104 enters the side surface 11 of the light transmissive block 3. Therefore, by processing the side surface 11 into a rough surface or providing an antireflection film on the side surface 11, the diffracted light 10
4 is not reflected inside the light transmissive block 3,
It is guided to the outside of the block 3 from the side surface 11. The 0th-order diffracted light 101 finally returns to the light emitting element 4.

Next, the diffracted light generated when the light from the portion 9b of the surface 9 is incident on the reflection hologram 7 on the outward path will be described. Here, it is assumed that the + 1st-order diffracted light 202 is converged on the optical disk 20 by the objective lens 8 and the 0th-order diffracted light 201 and the diffracted light 203 of the + 2nd order or higher are unnecessary. In this case, the objective lens 8 has +1
The outward optical system is set so that only the second-order diffracted light 202 enters, and the 0th-order diffracted light 201 is transmitted through the light-transmitting block 3.
Diffracted light 203 of + 2nd order or more on the side surface 12 of
The light enters the portion other than the position where the objective lens 8 is provided. The side surface 12 is processed into a rough surface, or an antireflection film is attached to the side surface 12.
Is guided from the side surface 12 to the outside of the block 3 without being reflected inside the light transmissive block 3. The portion of the surface 9 on which the diffracted light 203 of the + 2nd order or more is incident is also processed in the same manner, and the diffracted light 203 is also guided to the outside of the light transmissive block 3.

Alternatively, instead of guiding the diffracted light, which is unnecessary for signal detection, to the outside of the light transmissive block 3, it may not be generated. The specific method for preventing generation of unnecessary diffracted light is the same as that described in the above embodiment, and therefore the description thereof is omitted.

In this way, in this embodiment, all the diffracted light unnecessary for signal detection is made incident on the surface (portion) different from the propagation path of the diffracted light used for signal detection, and from there, the light-transmitting block. The generation of stray light is prevented by directing the light outside the light-transmitting block or by guiding the rest of the diffracted light outside the light-transmitting block.

[0058]

As described above, the optical information reading device of the present invention prevents unnecessary diffracted light from entering the surface of the light transmissive block which is the propagation path of the diffracted light used for signal detection. There is. As a result, it is possible to prevent diffracted light that is unnecessary for signal detection from becoming stray light that is repeatedly reflected inside the light transmissive block. As a result, it is possible to prevent a decrease in the S / N ratio due to stray light, and it is possible to significantly improve the reliability of information reading.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of an optical information reading device of the present invention.

FIG. 2 is a diagram showing an optical path of diffracted light in the optical system shown in FIG.

FIG. 3 is a diagram showing incident light and ± first-order diffracted light in a reflection hologram beam splitter.

FIG. 4 is a side sectional view showing another embodiment of the optical information reading device of the present invention.

5 is a diagram showing an optical path of unnecessary diffracted light in the optical system shown in FIG.

FIG. 6 is a side sectional view showing a conventional example of an optical pickup.

7 is a diagram showing an optical path of unnecessary diffracted light in the optical system shown in FIG.

FIG. 8 is a side sectional view showing a conventional example of an optical information reading device.

9 is a diagram showing diffracted light generated by a reflective hologram beam splitter in the optical system shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light-transmitting block 2 Semiconductor laser 3 Submount 4 Photodetector 5 Reflective hologram beam splitter 6 Si substrate 7 Objective lens 8 Optical disc 100 Incident light 101 0th-order diffracted light 102 + 1st-order diffracted light 103 + 2nd-order and higher-order diffracted light 104 Negative order diffracted light 105 −1st order diffracted light

Claims (12)

[Claims] 1. An optical information reader for irradiating an optical disk with light and detecting information recorded on the optical disk from the light reflected by the optical disk, the light emitting means emitting the light, and the light. An objective lens for irradiating the optical disc onto the optical disc, a light receiving means for receiving the light reflected by the optical disc, a light emitted from the light emitting means, guided to the objective lens, and reflected by the optical disc. A light-transmissive block for guiding the light to the light-receiving means, the light-transmissive block having a main surface provided with a diffractive means;
A first surface and a second surface which are inclined and opposed to the main surface, and the first surface guides the light reflected by the optical disk to the diffractive means, and the diffractive means. Diffracts the diffracted light so that unnecessary diffracted light for detecting the information does not enter the second surface, and the second surface is necessary for detecting the information. Information reading device for guiding various diffracted light to the light receiving means. 2. The light transmissive block has a plurality of surfaces including the main surface and the first and second surfaces,
The optical information reading device according to claim 1, wherein the diffractive unit causes the unnecessary diffracted light to be incident on a surface different from the main surface and the first and second surfaces of the plurality of surfaces. 3. The main surface of the light transmissive block, and a surface different from the first and second surfaces are processed so as to prevent reflection of the unnecessary diffracted light. The optical information reading device described. 4. The optical information reading device according to claim 1, wherein the diffracting means diffracts the light from the first surface so as not to generate at least a part of the unnecessary diffracted light. 5. The light transmissive block has a plurality of surfaces including the main surface and the first and second surfaces,
The diffracting means does not generate a part of the unnecessary diffracted light, and causes the remaining part of the diffracted light to enter a surface different from the main surface and the first and second surfaces of the plurality of surfaces. The optical information reading device according to claim 1, which diffracts the light as described above. 6. The main surface of the light transmissive block has:
The optical information reading device according to claim 1, further comprising the light emitting unit, the light receiving unit, and the objective lens. 7. An optical information reading device for irradiating an optical disk with light and detecting information recorded on the optical disk from the light reflected by the optical disk, the light emitting means emitting the light, and the optical disk. A light receiving means for receiving the light reflected by the optical disk, a substrate having a main surface on which first and second diffracting means are formed, an objective lens for irradiating the light onto the optical disc, and the substrate inside. A light-transmitting block that propagates the light emitted from the light-emitting means, guides the light to the objective lens, and guides the light reflected by the optical disk to the light-receiving means. The block has a main surface facing the main surface of the substrate, and the main surface of the light transmissive block is partially processed into a reflecting portion, and the first and second diffractive means are provided. Detects the information in the diffracted light Optical information reading device for diffracting the light so as not to be incident on the reflecting surface unnecessary diffracted light to that. 8. The optical information reading device according to claim 7, wherein the first diffracting means makes the unnecessary diffracted light incident on a portion of the main surface of the light transmissive block different from the reflecting portion. . 9. The optical information reading device according to claim 8, wherein a portion of the main surface of the light transmissive block different from the reflection portion is processed to prevent reflection of the unnecessary diffracted light. apparatus. 10. The optical information reading device according to claim 7, wherein the first and second diffracting means diffracts the light so as not to generate at least a part of the unnecessary diffracted light. 11. The light-transmissive block has a plurality of surfaces including the main surface, and the first and second diffractive means prevent generation of a part of the unnecessary diffracted light. The optical information according to claim 7, wherein the light is diffracted so that the remaining portion is incident on a portion of the main surface of the light transmissive block different from the reflection portion or a surface different from the main surface. Reader. 12. The objective lens according to claim 7, wherein the objective lens is arranged above the second diffractive means and is provided on the main surface of the light transmissive block. Optical information reader.