JP2003109243A - Optical pickup device and optical pickup drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device that employs a light source mounting semiconductor laser chips with different emission light wavelengths into one package, can excellently detect a signal of each wavelength even when position accuracy of a light emitting section is deteriorated and effectively reduce deterioration in the detected signal due to the effect of double refraction of a substrate when information is reproduced from an optical recording medium with a high substrate double refraction. SOLUTION: A plurality of holograms 4, 5 placed on substrates are placed between a light source and an optical recording medium, the luminous flux is led to the optical recording medium 8 through each hologram, the holograms diffract the return luminous flux reflected in the recording face, the diffracted luminous flux is led to a light receiving element 9, a non-polarization hologram whose diffraction efficiency is nearly the same independently of a polarization direction of an incident light is adopted at least one (hologram 5) of the holograms, a polarization hologram whose diffraction efficiency differs from the polarization direction of the incident light is adopted for the other hologram 4, and a wavelength plate 10 for rotating a polarization direction of the returned luminous flux diffracted by the polarization hologram 4 and guided to the light receiving element 9 from the initial polarization direction is placed toward the optical recording medium nearer than the polarization hologram 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device and an optical disc drive device.

[0002]

2. Description of the Related Art Light used in common for a DVD type optical recording medium (digital video disc, etc.) having a wavelength of λ ₁ = 650 nm and a CD optical recording medium (compact disc, etc.) having a wavelength of λ ₂ = 780 nm. A pickup device has been put to practical use. In such an optical pickup device, when the optical system on the optical path from the light source to the optical recording medium is shared, a semiconductor laser chip that emits a light flux of each used wavelength is manufactured as a "monolithic chip" as a light source. (Hereinafter referred to as “two-wavelength monolithic chip”) or a semiconductor laser chip that emits a light flux of each used wavelength is mounted in one package.

In the above-mentioned two-wavelength monolithic chip, the positional relationship between the light emitting portions can be made close to each other, but it is not always easy to accurately set the positional relationship between the light emitting portions, and it is easy to increase the production yield. Not. Further, when the light source and the "light receiving element that receives the returning light flux" are housed in one package, if the interval between the light emitting portions is made small, there is a problem that "high-speed operation of the light receiving element becomes difficult" due to heat from the two-wavelength monolithic chip. It is difficult to apply to recording on an optical recording medium and high-speed reproduction.

On the other hand, when semiconductor laser chips having different emission wavelengths are mounted in one package, a semiconductor laser chip having a desired output for each wavelength can be used, and a semiconductor that is optimum for the specifications of the optical disk drive device can be used. Since a laser chip can be used, high speed and low cost can be achieved.

On the other hand, however, in this type of light source, since the semiconductor laser chips are individually mounted, an error occurs at the time of mounting, and the accuracy of the distance between the two light emitting portions is likely to decrease.
If such a decrease in the interval accuracy occurs, the accuracy of signal detection by the light receiving element tends to decrease.

An important problem in using an optical pickup device in common with a plurality of types of optical recording media having different wavelengths is that "the birefringence of the substrate is large" depending on the type of the optical recording medium. When recording or reproducing information on an optical recording medium with a large substrate birefringence, the detection signal (reproduction signal, focus signal, track signal) fluctuates due to the influence of the substrate birefringence. "
I have a problem.

[0007]

In view of the above-mentioned circumstances, the present invention uses a light source for mounting semiconductor laser chips having different emission wavelengths in one package, and even if the positional accuracy between the light emitting parts is poor, To realize good signal detection, effectively reduce detection signal deterioration due to the influence of birefringence of the substrate, and realize an optical pickup device with high light utilization efficiency and high speed operation, and an optical disc drive device using the same. It is an issue.

[0008]

The optical pickup device of the present invention records "a light beam selectively emitted from a light source having a plurality of semiconductor lasers having different emission wavelengths on an optical recording medium according to the wavelength of the light beam. Optical pickup device that irradiates the surface and receives the return light flux reflected by the recording surface by the light receiving means while performing at least one of recording, reproduction, and erasing of information "
And has the following features (claim 1).

That is, holograms provided on a plurality of substrates are arranged between the light source and the optical recording medium, and light beams from the light source are transmitted through the holograms provided on the plurality of substrates (regardless of wavelength). Leads to an optical recording medium. The plurality of holograms are individually provided on different substrates.

The return light beam reflected by the recording surface is diffracted by the hologram, and the diffracted light beam is guided to the light receiving element and received. As the return light flux, diffracted light by a hologram determined according to each return light flux is guided to the light receiving element.

At least one of the holograms provided on the plurality of substrates is a "non-polarization hologram whose diffraction efficiency is substantially the same regardless of the polarization direction of the incident light", and the other holograms are "the polarization direction of the incident light. Polarization hologram having different diffraction efficiency depending on ".

That is, if the total number of holograms is N (≧ 2) and m (≧ 1) of them are non-polarization holograms, the number of polarization holograms is N−m. When the total number of holograms is 2, as in the embodiment described later, one of them is a non-polarization hologram and the other one is a polarization hologram.

A "wave plate" for rotating the polarization direction of the "returned light flux diffracted by the polarization hologram and guided to the light receiving element" from the original polarization direction (the polarization direction when the light is emitted from the semiconductor laser chip) , Is arranged closer to the optical recording medium than the polarization hologram. That is, when the return light flux enters the polarization hologram, it has a polarization direction different from the original polarization direction emitted from the semiconductor laser.

In the optical pickup device according to the first aspect, "diffracted light by the hologram determined according to each return light beam" is guided to the light receiving element. The light receiving element that receives the diffracted return light flux can be provided separately for each return light flux, but among the diffracted light fluxes from the holograms provided on the plurality of substrates, “diffraction light fluxes with different wavelengths diffracted by different holograms” Can be received by the same light receiving element (claim 2).

For example, the luminous fluxes emitted from the light source are A, B
, They have different wavelengths from each other. Assuming that a plurality of holograms are holograms HA and HB, the return light flux A is diffracted by the hologram HA and is incident on the light receiving element PDA, and the return light flux B is diffracted by the hologram HB and is incident on the light receiving element PDA. , PDB can be separated from each other, but the light receiving elements PDA and PD
It is also possible that B is the same element and the return light beam A diffracted by the hologram HA and the return light beam B diffracted by the hologram HB are made incident on the same light receiving element.

In the optical pickup device of claim 1 or 2, the "plurality of substrates on which holograms are formed" is
Needless to say, these substrates can be separated from each other, but these substrates can be “integrated with each other” (Claim 3), and in this case, the hologram-transmitted substrates can be “passed through the light”. Integrated so that the surfaces to be closed have a gap "
It is possible (Claim 4).

The polarization hologram in the optical pickup device according to any one of claims 1 to 4 is described as follows: "For polarized light in two directions orthogonal to each other in the plane of the substrate, one direction shows a periodic lattice-like refractive index change. And the other direction has a substantially uniform refractive index "(claim 5).

The polarization hologram in the optical pickup device according to any one of claims 1 to 5 can be formed as "the surface structure of a film obtained by obliquely depositing an inorganic substance" (claim 6) or "organic stretching". It can also be formed by a "film" (claim 7).

Further, the non-polarization hologram in the optical pickup device according to any one of claims 1 to 7 may be "a transparent substrate on which concave and convex gratings are formed" (claim 8).

The non-polarization hologram in the optical pickup device according to any one of claims 1 to 8 is configured to "substantially totally transmit an incident light beam of a specific wavelength among a plurality of wavelengths and to diffract light of a first order with respect to light beams of other wavelengths. (Claim 9), in which case the wavelength of the light beam that substantially totally transmits the non-polarization hologram is set to about 660 nm for DVD, and the wavelength of the light beam that generates the first-order diffracted light is set to CD. About 780 nm
(Claim 10).

In the optical pickup device according to any one of claims 1 to 10, the polarization hologram is arranged such that "substantially all incident light in a specific polarization direction is transmitted and return light beams having a polarization direction orthogonal to this are substantially all transmitted. The polarization direction of each light flux of a plurality of wavelengths that is incident on the polarization hologram from the light source can be set to a direction in which the polarization hologram is almost completely transmitted (claim 11).

The arrangement of holograms in the optical pickup device according to any one of claims 1 to 11 is such that, on the optical path from the light source to the optical recording medium, the polarization hologram is on the light source side and the non-polarization hologram is on the optical recording medium side. It is preferably arranged (claim 12).

In the optical pickup device according to any one of claims 1 to 12, "the wave plate can be integrated with one of a plurality of substrates provided with holograms" (claim 13). In the optical pickup device according to any one of claims 1 to 13, the wave plate is basically a light beam diffracted by a polarization hologram and guided to a light receiving element (light beam a).
It is ideal to give a phase difference so that the polarization directions are orthogonal to each other when going (when incident on the optical recording medium) and returning (when returning light flux). From the viewpoint of suppressing the generation of "light emission noise of the laser chip", it is preferable to give the same phase difference to the light flux (light flux other than the light flux a) received by the light receiving element by diffraction by the non-polarization hologram. As described above, it is possible to give a phase difference of 90 degrees to each of the light fluxes of two wavelengths, but it is costly to realize it.

Therefore, as a suboptimal measure, it is conceivable to give a phase difference as close as possible to 90 degrees to the light flux a and other light fluxes. In this case, it is preferable that the phase difference given to the wavelength for detecting the polarization (wavelength of the light flux a) is in the “range of 90 ± 19 degrees” (claim 14).

The optical disk drive device of the present invention is "using an optical pickup device, the wavelengths used are different from each other.
15. An optical disc drive device for selectively performing one or more of information recording / reproducing / erasing with respect to one or more types of disc-shaped optical recording media, which is an optical pickup device according to any one of claims 1 to 14. The device according to claim 15 is mounted (Claim 15).

A plurality of optical recording media having different wavelengths are used as C
The invention of each of the above claims will be described more concretely as a D-type optical recording medium (hereinafter referred to as “CD type disc”) and a DVD type optical recording medium (hereinafter referred to as “DVD type disc”). Is a semiconductor laser chip with a wavelength of 780 nm (for CD discs) and a wavelength of 660 n.
m semiconductor laser chips (for DVD discs) are individually mounted, and one non-polarization hologram and one polarization hologram are used as holograms.

The position accuracy of the light emitting portion of each semiconductor laser chip in the light source may be inferior to the position accuracy of the two-wavelength monolithic chip, but by adjusting the two holograms separately, ""Focus and track adjustment" can be performed so that "a good signal with a small offset" can be detected.

Further, by making one hologram a "non-polarization hologram" and the other a "polarization hologram", the return light beam is diffracted by the non-polarization hologram with respect to the operating wavelength of the disk having a large birefringence of the substrate. "Detection signal fluctuation due to birefringence of the disk substrate" is reduced by detecting by doing, and for optical disks of other used wavelengths,
By diffracting the return light beam with a polarization hologram to detect it, it is possible to improve the optical power of the optical disc on the way from the light source to the optical recording medium and the amount of the return light beam received by the light-receiving element to enable high-speed recording / playback. Becomes

In the optical pickup device, the hologram arranged between the light source and the optical recording medium transmits the light from the light source and diffracts the return light beam.
It is ideal that 0% is transmitted and the returned light beam is diffracted by 100%. " In a normal hologram, in order to effectively increase the irradiation energy to the optical recording medium, if the light flux directed from the light source to the optical recording medium is transmitted by, for example, 95%, the diffraction efficiency will be about 2.5% at best. It only happens.

When a polarization plate is made to have polarization directions orthogonal to each other by using a wave plate and a hologram is a polarization hologram, about 95% or more of the hologram is transmitted on the outward path, and about 40% of the return light beam is transmitted.
Can be diffracted as + 1st order diffracted light.

According to the optical pickup device of the second aspect, the return light flux having a wavelength of 780 nm from the CD disk and the return light flux having a wavelength of 660 nm from the DVD disk are detected by the "common light receiving element". By doing so, the number of light receiving elements can be reduced, the circuit system can be simplified, and the cost can be reduced. In this case, each hologram
By optimizing each of the light fluxes of wavelengths: 780 nm and 660 nm, the track signal and the focus signal can be optimized for each wavelength.

As in the optical pickup device according to the third aspect, by integrating the two holograms, the optical pickup device can be downsized, and the optical pickup device can be made light-sensitive with respect to a change with time or the influence of heat. The pickup function can be stabilized.

As in the optical pickup device according to the fourth aspect, by integrating the two holograms so that the surfaces thereof do not come into contact with each other, "miniaturization / stability against aging and heat" can be realized, and It is possible to improve the yield by preventing the previously assembled hologram from moving or being damaged during the assembly adjustment of the hologram to be assembled from.

According to the optical pickup device of the fifth aspect, as the polarization hologram, "there is a lattice-like change in the refractive index with respect to polarized light in two directions orthogonal to each other in the plane of the substrate, and the other has a substantially uniform refractive index. By using the one that has the property of "is", it is possible to have characteristics of substantially total transmission and substantially total diffraction depending on the polarization direction, and it is possible to improve light utilization efficiency.

As in the optical pickup device according to the sixth aspect, by using a film formed by oblique vapor deposition of an inorganic substance as the material of the polarization hologram, it is possible to reduce the cost and thickness of the polarization hologram. As in the optical pickup device described above, by using an organic stretched film formed by orienting an organic substance as the material of the polarization hologram, cost reduction of the polarization hologram can be realized. In any of these cases, the optical pickup device The cost can be reduced.

As in the optical pickup device according to the eighth aspect, the cost of the non-polarization hologram is reduced by using the non-polarization hologram having the structure in which the concave-convex grid is formed on the transparent substrate. The cost of the optical pickup device / optical disc drive device can be reduced.

As in the optical pickup device according to the ninth aspect, a wavelength which is not diffracted by the non-polarization hologram is set so that "a loss of light amount when passing through the non-polarization hologram" does not occur at this wavelength, and the disc is irradiated. The amount of light and the amount of light received by the light receiving element can be improved, and high-speed recording / reproduction can be supported. Further, it is possible to detect the used wavelength that is diffracted without depending on polarization, and it is possible to suppress the fluctuation of the detection signal due to the birefringence of the disk substrate.

As in the optical pickup device according to the tenth aspect, the non-polarization hologram diffracts the return light beam having a wavelength of about 780 nm so that the return light beam can be detected for a CD disc without polarization dependency. By C
It is possible to avoid the influence of the birefringence of the substrate in the D-system disc.

Further, for a DVD type disk which requires recording power for high density and requires a wide band for signal detection, a light beam having a wavelength of about 660 nm is transmitted almost completely through a non-polarization hologram. Increasing the optical efficiency of the forward path to increase the optical disk irradiation power, allowing the return light flux to be completely transmitted without "loss in a non-polarization hologram" and diffracting it with a highly efficient polarization hologram to improve the amount of light received by the light receiving element. Therefore, it is easy to realize high-speed recording / reproducing.

According to the optical pickup device of the eleventh aspect, the polarization hologram is provided with "a characteristic of substantially totally transmitting incident light of a specific polarization direction and of substantially totally diffracting a return light beam having a polarization direction orthogonal to the incident light". By setting the polarization direction of each light flux of a plurality of wavelengths, which is given and is incident on the polarization hologram from the light source, to the direction in which the polarization hologram is almost totally transmitted, the most efficient state can be obtained.

According to the optical pickup device of the twelfth aspect, by disposing the polarization hologram on the light source side and the non-polarization hologram on the optical recording medium side,
It is possible to improve the efficiency in the forward and backward passes and enable high-speed recording / playback.

According to the optical pickup device of the thirteenth aspect, by integrating the wavelength plate into one of the holograms, the optical pickup device can be downsized.

Further, by constructing the optical pickup device according to the fourteenth aspect, it is possible to increase the light utilization efficiency in the forward path and the backward path with respect to the polarization hologram, and with the "semiconductor laser chip" with respect to the non-polarization hologram. By making the polarization direction of the return light beam to the
It is possible to reduce light emission noise caused by the luminous flux returning to the semiconductor laser chip.

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a diagram schematically showing an essential part of an embodiment of an optical pickup device in which a CD disc and a DVD disc can be used as two types of optical recording media having different wavelengths.

The semiconductor laser chip 1 having an emission wavelength of 780 nm and the semiconductor laser chip 3 having an emission wavelength of 660 nm are individually mounted on the light source. When a CD disk is used as the optical recording medium denoted by reference numeral 8, the semiconductor laser chip 1 is driven and emitted wavelength: 78
The 0 nm light flux passes through the first hologram 4, the second hologram 5, and the wave plate 10, is converted into a parallel light flux by the collimator lens 6, and is reflected by the objective lens 7 on the recording surface of the optical recording medium (CD disc) 8. It is illuminated as a light spot.

The light reflected by the recording surface is a "returning light beam".
Then, it returns to the optical path at the time of irradiation, is diffracted by the second hologram 5, and is received by the light receiving element 9.

When a DVD type disc is used as the optical recording medium 8, the semiconductor laser chip 3 is driven and the emitted light beam having a wavelength of 660 nm passes through the first hologram 4, the second hologram 5 and the wave plate 10. The light is transmitted and converted into a parallel light flux by the collimator lens 6, and is irradiated as a light spot on the recording surface of the optical recording medium (DVD disc) 8 by the objective lens 7. The light reflected by the recording surface becomes a “return light flux”, returns on the optical path at the time of irradiation, is diffracted by the first hologram 4, and is received by the light receiving element 9.

In this way, if "the signals are detected by using the holograms 4 and 5 which are different for each wavelength", it is much more accurate than adjusting the detection state for the return light flux of two wavelengths with one hologram. It can be adjusted. Further, the mounting accuracy of the semiconductor laser chips 1 and 3 and the chip of the light receiving element 9 (the accuracy of the relative positional relationship between these).
Since the mounting tolerance can be relaxed and the assembly tolerance is relaxed, the assembly yield of the optical pickup device is improved.

In FIGS. 2A and 2B, the first hologram 4 is shown.
And a specific configuration of the second hologram 5. Here, a case where the focus signal detection method is the knife edge method will be described.

The first hologram 4 is a "hologram that diffracts a light flux having a wavelength of 660 nm toward the light receiving element 9." As shown in FIG. 2A, the first hologram 4 has three
It is composed of parts. The hologram portion 10 is a "focusing hologram", and the hologram portion 12-
Reference numerals 1 and 12-2 are “track holograms”. The boundary line between the hologram portions 12-1 and 12-2 and the hologram portion 10 is a “knife edge”. Hologram part 1
0 diffracts a part of the return light flux (indicated by a solid circle in FIG. 2A) having a wavelength of 660 nm toward the light receiving element 9.

The light receiving element 9 is, as shown in FIG.
Divided light receiving surface 9-1 / 2 and single light receiving surface 9 on both sides
-3 and 9-4. The two-divided light receiving surface 9-1 / 2 is for generating a focus signal, and the light receiving surfaces 9-3 and 9-4 are for generating a track signal.

When the first hologram 4 is rotated around the optical axis, the diffracted return light beam is displaced like a precession movement about the optical axis, and this rotation causes a wavelength of 660.
The position of the “returned light beam spot” formed by the diffracted light of the returned light beam of nm can be located at the boundary of the two-divided light receiving surface 9-1 / 2 as shown in FIG. It is possible to obtain a good focus signal without any noise.

The first hologram 4 has a wavelength of 780 nm.
2 is also incident on the semiconductor laser chip 1 as it emits light.
Diffraction of return light beam by hologram 4 occurs, wavelength: 7
Since the diffraction angle of the first hologram 4 for the return light flux of 80 nm is larger than the diffraction angle of the return light flux of the wavelength: 660 nm, as shown in FIG.
Since it does not enter −1/2 and collects light at a position farther from the lens optical axis than the light receiving element 9, it has no effect on focus signal detection.

The second hologram 5 is a hologram for diffracting a return light beam having a wavelength of 780 nm, and is composed of three hologram portions as shown in FIG. 2 (b). The hologram portion 11 is a focus hologram, and the hologram portions 13-1 and 13-2 are track holograms.

The boundary line between the hologram portions 13-1 and 13-2 and the hologram portion 11 is the "knife edge".
The hologram portion 11 diffracts a part of the return light flux (shown by a broken line circle in FIG. 2A) having a wavelength of 780 nm toward the light receiving element 9.

When the second hologram 5 is rotated around the optical axis, the diffracted return light beam is displaced like a precession movement about the optical axis, and this rotation causes a wavelength of 780.
The position of the “returned light beam spot” formed by the diffracted light of the returned light beam of nm can be located at the boundary of the two-divided light receiving surface 9-1 / 2 as shown in FIG. It is possible to obtain a good focus signal without any noise.

The second hologram 5 has a wavelength of 660 nm.
2 (shown by a solid circle in FIG. 2B) is also incident, so that when the semiconductor laser chip 3 is caused to emit light,
Diffraction of the return light beam by the hologram 4, wavelength: 6
Since the diffraction angle by the second hologram 5 for the return light flux of 60 nm is smaller than the diffraction angle of the return light flux of wavelength: 780 nm, as shown in FIG.
Since it does not enter −1/2 and collects light at a position closer to the lens optical axis than the light receiving element 9, it does not affect the focus signal detection.

The same applies to the diffraction by the track hologram. The return light beam having a wavelength of 660 nm is diffracted by the first hologram 4, and the return light beam having a wavelength of 780 nm is diffracted by the second hologram 5, as shown in FIG. As shown in FIG. 6, the light beam is incident on the light receiving surfaces 9-3 and 9-4 for detecting the track signal to form a return light spot. Similar to the focus signal detection, the wavelength diffracted by the first hologram is 78.
The 0 nm return light beam and the wavelength 660 nm return light beam diffracted by the second hologram 5 are not incident on the light receiving surfaces 9-3 and 9-4 due to the difference in diffraction angle.

2C and 2D, the spots of the return light flux formed by the return light flux of each wavelength are drawn "shifted vertically on the light receiving surface", but as shown in FIG. In addition, since the light receiving element 9 is arranged at a portion where the diffracted light beams by the first and second holograms 4 and 5 intersect, the return light flux of each wavelength is actually formed on each light receiving surface of the light receiving element 9. The positions of the spots of the returning light fluxes are the same as each other.

Thus, different wavelengths: 660 nm, 7
If two holograms 4 and 5 having knife edges are individually arranged for a return light flux of 80 nm, focus adjustment and track adjustment can be performed independently for each wavelength, and a return light flux other than the desired wavelength enters each hologram. However, since the diffraction angle differs depending on the wavelength difference and does not enter the light receiving element 9, flare does not occur. The "diffracted light flux that does not enter the light receiving element" shown here is provided with a separate light receiving element to detect light,
If it is used as a part of the focus signal, the track signal, or the reproduction signal, the light utilization efficiency can be further improved, and the signal can be detected at higher speed.

When the diffracted light from the second hologram 5 is incident on the hologram forming area of the first hologram 4, the return light beam having a wavelength of 780 nm is diffracted by the second hologram 5 and then again by the first hologram 4. Since the light may be diffracted and may not be incident on the light receiving element 9, the diffracted light of the wavelength of 780 nm by the second hologram is changed to the first hologram 4.
Care must be taken not to enter the hologram forming area of.

In order to prevent the diffracted light from the second hologram 5 from entering the first hologram 4, the first hologram 4 and the second hologram 5 may be arranged appropriately apart from each other in the optical axis direction. In the first embodiment, the first hologram 4 and the second hologram 5 are spatially separated in the optical axis direction.

In a recordable optical pickup device, a "collimator lens having a shorter focal length" than that of a reproduction-only optical pickup device is used in order to improve light utilization efficiency.
Is used, the semiconductor laser chip 1 (wavelength: 78
0 nm) and semiconductor laser chip 3 (wavelength: 660 nm)
It is necessary to set the interval between the light emitting portions of about 100 μm.

If the light emitting section is not on the optical axis of the collimator lens, the light beam emitted from the collimator lens will not be parallel to the optical axis. However, if the focal length of the collimator lens is short, the light beam after collimation is inclined with respect to the optical axis. Becomes large, and the light enters the objective lens obliquely to generate coma, so that it becomes impossible to form a “small narrowed light spot” on the recording surface of the optical recording medium.

In order to set the distance between the light emitting portions of the semiconductor laser chips 1 and 3 to 100 μm, a semiconductor laser chip whose light emitting portion position is deviated from the center of the chip may be used. As shown in FIG. 3A, a normal semiconductor laser chip T
In 1 and T2, the light emitting portion is located at the center of the chip and the outer shape of the chip is about 300 μm. Therefore, when such chips are arranged close to each other, the light emitting portion spacing is also about 300 μm.

Recently, as shown in FIG. 3B, a semiconductor laser chip T having a light emitting portion positioned at the end of the chip.
3, T4 has been developed. With such chips, the distance between the light emitting points can be shortened to about 100 μm simply by arranging the chips. By mounting the semiconductor laser chips T3 and T4 whose light emitting points are at the ends of the chips in parallel in this way, it is possible to narrow the distance between the light emitting portions and make the light incident on the objective lens at an “angle closer to the optical axis”. Like

Another example in which the interval between the light emitting portions can be reduced is shown in FIG.
It shows in (c). A semiconductor laser chip 3 having an emission wavelength of 660 nm and a semiconductor laser chip 1 having an emission wavelength of 780 nm are arranged so as to face each other, and the emitted beams are respectively reflected by the adjacent surfaces of the synthetic mirror 2, and the light flux intervals are parallel to each other. (Gap between principal rays): Proximity light fluxes of approximately 100 μm. In this way, even if an ordinary semiconductor laser chip having a light emitting portion in the center of the chip is used,
A light flux close to about μm can be easily realized.

As described above, when the wavelength plate is used so that "the polarization directions of the forward and backward paths are orthogonal to each other" and the hologram is a polarization hologram, about 95% or more of the light fluxes of wavelengths: 660 nm and 780 nm are transmitted in the forward path. After passing through the optical recording medium and irradiating the optical recording medium, approximately 40% of the return light beam can be diffracted as + 1st-order diffracted light in the return path, and the light utilization efficiency can be effectively increased as compared with the case of using a normal hologram.

Therefore, by using the polarization hologram, the transmittance of the forward path can be increased to increase the recording speed, and the diffraction efficiency can be increased to detect the returning light flux with a "high S / N ratio", so that the reproduction speed can be increased. That is, the use of the polarization hologram is effective for improving the recording / reproducing speed in the optical disk drive device.

From the above viewpoints, it is effective to use both the first hologram 4 and the second hologram 5 in the embodiment of FIG. 1 as polarization holograms in order to improve the recording / reproducing speed. However, in the embodiment of FIG. 1, the target optical recording medium is a CD type disc and a DVD type disc, and in this "combination of optical recording mediums", if both the first and second holograms are polarization holograms, Such a problem occurs.

That is, a CD disc generally has a relatively large birefringence of the disc substrate, and when a polarization hologram is used as the second hologram 5 when recording or reproducing on such an optical recording medium, the return light flux is , "The phase difference received by the birefringence of the disk substrate" is added to the phase difference given by the wave plate, and the return light flux does not become "linear polarization orthogonal to the linear polarization direction of the outward light flux". It becomes elliptically polarized light and enters the second hologram.

Since the polarization hologram diffracts only the polarized component vibrating in the grating direction, the “polarized component in the direction orthogonal to the grating direction” in the return light beam in the elliptically polarized state is not diffracted and is not received by the light receiving element 9. .

As described above, depending on the type of the optical recording medium or the position in the radial direction within the same optical disc,
Since the amount of birefringence fluctuates, when the return light beam is diffracted by the polarization hologram to be detected, the detection signal level fluctuates depending on the amount of birefringence of the disk substrate, degrading the operational reliability of the optical pickup device.

In order to avoid such a "level fluctuation of the detection signal due to the birefringence of the disc substrate", when recording / reproducing / erasing the optical recording medium of the disc substrate having a large birefringence, the optical recording is performed. A “non-polarization hologram whose transmittance / diffraction efficiency does not depend on the polarization direction” may be used as a hologram that diffracts the return light beam from the medium toward the light receiving element.

In the embodiment of FIG. 1, since the optical recording medium 8 is a CD type disc and a DVD type disc, the returning light flux from the CD type disc having a large birefringence amount of the disc substrate is directed to the light receiving element 9. Diffractive second hologram 5
Is a "non-polarization hologram", while the first hologram 4 that diffracts the return light beam from the DVD disc toward the light receiving element 9 is a "polarization hologram".

Generally, one of the first and second holograms is a non-polarization hologram, and the other is a polarization hologram. When recording / reproducing / erasing an optical recording medium having a disk substrate having a large birefringence, the non-polarization hologram is used as the non-polarization hologram. In recording / reproducing / erasing an optical recording medium which has a relatively small birefringence and requires high efficiency, the returning light beam may be diffracted by a polarization hologram.

Although the detection of the focus signal has been described above, the track signal is detected on the light receiving surface 9- shown in FIG.
Known "push-pull method" using the outputs of 3 and 9-4
Can be generated by The first and second holograms 4, 5
Of the hologram portions 10, 12-1, 12-2, 11,
Reference numerals 13-1 and 13-2 denote light receiving surfaces 9-1 / 9 of the light receiving element 9.
It is designed so that the return light flux of each wavelength is “focused without aberration” on 2, 9-3 and 9-4 to form a spot of the return light flux.

FIG. 4 is a diagram showing another embodiment of the optical pickup device. In addition, in order to avoid complication, the same reference numerals as those in FIG.

In the optical pickup device of this embodiment, two substrates provided with holograms are integrated to reduce the size and improve the reliability of the optical pickup device.
Furthermore, it is integrated with the light source / light receiving element unit. A method of assembling the light source / light receiving element unit and the two holograms into a “hologram unit” will be described below.

In FIG. 4A, reference numeral 20 indicates a light source / light receiving element unit. The light source / light receiving element unit 20 includes the semiconductor laser chip 1 (emission wavelength: 780n
m), semiconductor laser chip 3 (emission wavelength: 660 nm)
And the light receiving element 9 are provided in the same package 21.

As shown in FIG. 4A, first, the semiconductor laser chip 3 having an emission wavelength of 660 nm is caused to emit light, and the first hologram 4 is placed on the cap of the package 21.
The position and orientation on the cap surface are adjusted so that the focus signal / track signal offset is zero. After the adjustment, the first hologram 4 is fixed to the cap with the adhesive 41. The process up to this point is exactly the same as the method of assembling a general hologram unit.

Next, as shown in FIG. 4B, the semiconductor laser chip 1 having an emission wavelength of 780 nm is caused to emit light, the second hologram 5 is placed on the first hologram 4, and the position and orientation are adjusted. , The focus signal / track signal offset is adjusted to 0, and the first hologram 4 is fixed with an adhesive 41 (additional to the one used for adhering the first hologram 4). Thus, the first and second holograms 4 and 5 are integrated with the light source / light receiving element unit 20 to be assembled as a "hologram unit".

In this way, the first and second holograms 4, 5
By sequentially bonding and integrating the two, the size is smaller than the case where the first hologram and the second hologram are provided separately, and it is stable against changes with time. If only the hologram unit is completed, the optical pickup device The adjustment of the hologram is not required at the time of assembling, and the assembling of the optical pickup device is greatly simplified, and the mass productivity is improved.

In the optical pickup device of FIG. 4B, the substrate thickness of the second hologram 5 is increased in order to prevent "diffracted light by the second hologram 5 from entering the hologram formation region of the first hologram 4." Thus, a necessary space is secured between the first and second holograms.

In the embodiment shown in FIG. 4, the first and second holograms 4 and 5 are in close contact with each other and integrated, but as in the embodiment shown in FIG. 5, the first hologram 4 and the second hologram 4 are integrated. 5, the separator 12 is interposed between the first and the
It is also possible to "unify the two substrates on which the holograms are formed so that the surfaces through which light passes may have a gap" without bringing the second holograms into close contact with each other.

As in the embodiment shown in FIG. 4,
After bonding the first hologram 4 to the cap of the package 21 of the light source / light receiving element unit 20, the second hologram 5 is attached.
When is placed on the first hologram 4, the glass surfaces of the two holograms come into close contact with each other. If the accuracy of the glass surface is good, the adhesion is strong. Therefore, if the second hologram 5 is moved when the second hologram 5 is aligned, a force that moves the second hologram 5 and the first hologram 4 that are in close contact with the second hologram 5 is also generated. As a result, the first hologram 4 fixedly bonded and fixed may move and peel off from the cap, or the position may be misaligned, resulting in a defective product, which may reduce the yield of the hologram unit.

In the embodiment of FIG. 5, the separator 12 having an opening is integrated with the first hologram 4, and after adjusting the position and the direction on the cap of the package 21 of the light source / light receiving element unit 20, the separator 12 is removed. It is fixed to the cap with the adhesive 41. Then, separator 1
The second hologram 5 is arranged via 2. Separator 1
Due to the interposition of 2, the glass surfaces of the hologram do not come into contact with each other, and the hologram is integrated with the air layer 45. When the second hologram 5 is aligned, the second hologram 5 is moved on the separator 12, so that the first hologram 4 that has been previously bonded does not move together.
It is possible to improve the yield of the hologram unit without peeling off of the film. After the adjustment, the second hologram 5 is adhered and fixed to the separator 12 with the adhesive 42, and the whole is integrated into a hologram unit.

In each of the embodiments described above, the first
Although the hologram 4 is a polarization hologram and the second hologram 5 is a non-polarization hologram, the polarization hologram states that "of the polarization directions of the incident light beam orthogonal to each other, substantially one diffraction is performed in one polarization direction, and almost all diffraction is performed in the other polarization direction. Characteristic that becomes transparent "
Can have To impart such characteristics to the polarization hologram, a birefringent material may be processed into a concavo-convex grid pattern, and an isotropic material may be embedded in the birefringent material to form a polarization hologram.

That is, of polarized light in two directions orthogonal to each other in the plane of the substrate, one polarized light has a periodic refractive index change in the lattice array direction, and polarized light in a direction orthogonal to this has a refractive index change. The configuration is such that the rate does not change and is substantially uniform. By doing so, it is possible to substantially totally diffract polarized light that oscillates in a direction in which there is a periodic change in refractive index, and substantially totally transmit polarized light in a direction orthogonal to this.

Such a polarization hologram can be realized by appropriately setting the birefringence direction of the birefringent material, the direction in which the concave-convex lattice is formed, and the refractive index of the isotropic material.

The birefringent material forming the polarization hologram will now be described. Conventionally, birefringent crystal materials such as LiNbO ₃ and CaCO ₃ are well known, but these materials are high in cost. It's a drawback. As a "birefringent film" that can be realized at low cost, there is a so-called "oblique vapor deposition film".

As shown in FIG. 6, the obliquely vapor-deposited film can be obtained by vacuum vapor-depositing a dielectric material with the substrate 60 to be formed inclined with respect to the evaporation source 61. As described in the paper “Retardation film” by Dr. Toyanaka, Ken, published in “Surface Technology Vol. 46, No. 7, 1995”, a dielectric material such as Ta ₂ O ₅ or SiO ₂ is used as an evaporation source, When the substrate is obliquely deposited, the birefringence: Δn (= n
A film having a p-ns) of about 0.08 can be formed.

This obliquely vapor-deposited film has a birefringence of "LiNbO.
_Although it is equivalent to the birefringence of the ₃ crystal: Δn ”, since it can be manufactured in a large area by a simple vacuum vapor deposition method, it can be manufactured at a much lower cost as compared with the case of using a LiNbO ₃ crystal.
Since it is a vapor-deposited film, it is very thin (less than 10 μm, LiNbO ₃
The thickness of the crystal is about 500 to 1000 μm), and the amount of aberration generated can be suppressed to a very small level even when placed in a divergent light beam. Since the obliquely deposited film is a retardation film, it can be used as a wave plate.

Another method for easily obtaining the "birefringent film" is to use an "organic highly oriented film". For example,
A film obtained by obliquely depositing SiO or the like on a transparent substrate such as glass,
An organic film such as polyethylene terephthalate (PET) is rubbed with a cloth to rub it, and a polydiacetylene monomer is vacuum-deposited on the alignment film to align it, and then ultraviolet rays are irradiated to polymerize it to form an anisotropic film. Method (J. Appl. Phys. Vol. 72. No3.P.
938 1992). By this method, a birefringent film made of an organic material can be produced at low cost.

As another processing method for obtaining a birefringent film, as shown in FIG. 7, polyimide, polycarbonate, PET,
There is also a method in which the molecular chains of the film 70 such as polyethylene are oriented uniaxially by stretching to generate "in-plane birefringence". In-plane birefringence: Δn can be changed by stretching temperature and applied force, and it is a cheap and mass-producible method (development of polyimide optical wave plate and its characteristics NTT
Sawada et al. IEICE Tech. 1994-08).

The birefringent film obtained by the above method is subjected to hologram processing for forming irregularities by etching or the like, and its surface is filled with a substance having an isotropic refractive index to make it flat, thereby reducing costs. It is possible to realize a highly efficient polarization hologram. The organic film can also be used as a wave plate.

In each of the embodiments described above, the second hologram 5 is a "non-polarization hologram". As shown in FIG. 8, the non-polarization hologram 5 has a structure in which a “hologram having an uneven grid shape” is formed on a transparent substrate such as glass or plastic. By changing the "depth of irregularities" in the grating, the 0th-order light transmittance and the 1st-order diffracted light diffraction efficiency can be controlled, and the efficiency does not change depending on the polarization direction of the incident light flux.

Such a non-polarization hologram 5 can be produced by forming a hologram pattern on a glass substrate by photolithography and transferring it to the substrate by etching. It can also be manufactured by injection molding of plastic. Either method can be mass-produced at low cost.

Second hologram 5 which is a non-polarization hologram
Has a large birefringence of the disk substrate, and the luminous flux of "wavelength to be detected without polarization (wavelength in the example being explained: 780 nm)" is 1
Diffracted the next time, and other wavelengths (660n in the example described)
It is desirable that the light flux of m) has a characteristic that does not generate first-order diffracted light. By doing so, it is possible to prevent loss of the light flux of the wavelength (660 nm) which is not detected as non-polarized light.

In order to realize a non-polarization hologram having such characteristics, the grating depth of the uneven non-polarization hologram shown in FIG. 8 may be adjusted. FIG. 9 shows “relationship between grating depth (horizontal axis) and diffraction efficiency (vertical axis)” when glass (BK7) is used as a substrate for forming a hologram grating. In this case, the width of the concave portion is equal to the width of the convex portion in the grid formed by the irregularities.

In order to generate the + 1st order diffracted light in the light beam having the wavelength of 780 nm and prevent the light beam having the wavelength of 660 nm from being substantially diffracted, the grating depth is set to 1.3 μm as shown in FIG. Just set it. At this time, wavelength: 660
The 0th-order light transmittance for a light beam of nm is 99.8%, which is almost the total transmission. The 0th-order light transmittance for a light having a wavelength of 780 nm is 79.8%, and the + 1st-order diffraction efficiency is 8.2%. Therefore, it becomes a non-polarization hologram that diffracts only the light flux of wavelength: 780 nm.

As the first hologram 4 (polarization hologram), the wavelength from the light source side: about 660 nm (660 ± 10 n)
(about m), the light beam emitted from the semiconductor laser chip 3 and having a wavelength of about 660 nm emits the first hologram 4 without substantial loss.
Since the light is transmitted through, the use efficiency of the light with which the DVD disc is irradiated is increased.

At this time, when a "wavelength: a light beam having a wavelength of about 660 nm is almost completely transmitted" is used as the second hologram 5 (non-polarization hologram), a light beam having this wavelength passes through the first and second holograms 4 and 5. Permeate without substantial loss, D
Since the VD type disc is irradiated, the efficiency of the irradiation light for the DVD type disc can be maximized.

Further, the wavelength of light returning to the first hologram 4 is approximately 660 nm. The polarization direction of the return light beam is made orthogonal to the polarization direction of the outward path, and the return light beam of the above wavelength incident on the first hologram 4 is substantially diffracted. Thus, the return light flux can be detected with maximum efficiency. The birefringence standard value range of DVD discs is relatively narrow, and there are almost no poor discs in the market that exceed the standard value.

In the DVD type disc, since the recording power is high due to the high density and the reproduced signal is in a wide band, it is necessary to detect the signal with a high SN ratio, and the forward transmittance and the first-order diffraction efficiency of the backward path are high. However, by configuring the first and second holograms as described above, the loss of the light amount at the time of transmitting the first and second holograms is minimized, and the return light flux from the DVD disc depends on the first hologram 4. Signals can be detected with a high SN ratio by maximizing the diffraction efficiency.

On the other hand, in the case of the CD type disc, the standard value of the birefringence of the disc substrate is wide and the CD-RO which is on the market.
Some M discs and the like have a large birefringence that is out of the standard value of the above-mentioned birefringence, but as described above, since the second hologram 5 is a non-polarization hologram, the wavelength reflected by the CD disc is large. : Since the return light flux of about 780 nm is diffracted by the second hologram 5 and detected by the light receiving element regardless of the polarization state, the detection signal is not affected by the birefringence of the disk substrate.

When the relationship between the polarization direction and the transmission / diffraction by the hologram described above is summarized with reference to FIG. 4B, the luminous fluxes emitted from the semiconductor laser chips 1 and 3 in FIG. 4B. The polarization direction (the vibration direction of the electric field vector) is parallel to the drawing, as indicated by arrows f1 and f2 in the drawing.

The first hologram 4 (polarization hologram) is
The orientation of the hologram is adjusted so that substantially all the light of each wavelength having such a polarization direction is transmitted. Such a polarization hologram can be realized by optimizing the birefringence directions (the fast axis and the slow axis) of the birefringent material and the refractive index of the isotropic substance to be filled.

Subsequently, the second hologram 5 (non-polarization hologram) transmits substantially all the light flux having a wavelength of approximately 660 nm and transmits approximately 80% of the light flux having a wavelength of approximately 780 nm. When the return light flux from the optical recording medium enters the second hologram 7, the light flux having a wavelength of about 660 nm is substantially completely transmitted, and 8.2% of the light flux having a wavelength of about 780 nm is +.
The light becomes first-order diffracted light and enters the light-receiving element 9, and about 80% of it is transmitted to the light source side.

The return light beam then enters the first hologram 4. At this time, since the return light beam having a wavelength of about 660 nm is turned by the wave plate 10 by 90 degrees from the direction in the forward path, The light is substantially totally diffracted by the first hologram 4 and enters the light receiving element 9 with high light intensity.

On the other hand, the return light flux having a wavelength of about 780 nm is
Although being affected by the wave plate 10, the polarization direction is not always orthogonal to the outward polarization direction. Therefore, a part of the return light flux having a wavelength of about 780 nm passes through the first hologram and a part is diffracted. The diffraction angle at this time is the wavelength:
Unlike the diffraction angle of the return light flux of about 660 nm,
As described above, the return light beam having a wavelength of about 780 nm diffracted by the first hologram 4 does not enter the light receiving element 9.

A wavelength plate that gives a phase difference of 90 degrees to a linearly polarized light beam having a wavelength of approximately 660 nm and a linearly polarized light beam having a wavelength of approximately 780 nm is technically possible.
If such a wave plate is used, the return light beam having a wavelength of 780 nm that is incident on the first hologram 4 can be almost totally diffracted. However, the use of a wave plate having such characteristics is not necessarily a good cost measure.

By the way, as is well known, the semiconductor laser chip has a problem that "emission noise is generated by the return light beam". That is, when the light flux emitted from the semiconductor laser chip is reflected and enters the light emitting portion of the chip,
The intensity of the original luminous flux emitted from the chip is changed.

The occurrence of the emission noise depends on the relationship between the polarization direction of the light beam emitted from the semiconductor laser chip and the polarization direction of the return light beam returning to the chip. The return light beams have the same polarization direction. "
Is most significant, and the least occurs when the polarization directions are orthogonal to each other.

From this point of view, the function of the wave plate 10 in each of the above-described embodiments is that the polarization direction of the return light beam is changed with respect to any of the light beams emitted from the semiconductor laser chips 1 and 3. It is preferable that each light beam is provided with a phase difference of 90 degrees so as to be orthogonal to the polarization direction of the outward path, but as described above, use of such a wave plate is not necessarily a cost effective measure.

Then, as a suboptimal measure, "a wavelength plate which gives a phase difference to light flux of any wavelength not 90 degrees, but gives a phase difference close to 90 degree to any wavelength to some extent. (Hereinafter referred to as “two-wavelength common wave plate”) ”, and it is possible to deal with it by" allowing in the form of a decrease in the amount of signal light "for the amount of the phase difference given from 90 degrees.

The two-wavelength common wave plate can be constructed as the above-mentioned "inorganic oblique vapor deposition film or organic stretched film". A crystal plate can be used, but since it is as thick as about 1 mm, aberration will occur if it is placed in the divergent optical path. Since the inorganic obliquely vapor-deposited film and the organic stretched film have a small thickness (within several tens of μm), even if they are arranged in the divergent optical path, the amount of aberration generated can be suppressed small.

The amount by which the phase difference due to the wave plate deviates from 90 degrees appears as a reduction in the amount of signal light due to the diffracted light from the polarization hologram. FIG. 10 shows “relationship between phase difference and signal strength”. A decrease in the amount of signal light means "a decrease in the amount of light returning to the light receiving element 9," which means that the reproduction speed decreases when information is reproduced.

In the detection by the polarization hologram, if the reduction of the signal light amount is allowed to be, for example, 10%, the allowable limit of the phase difference is 109 degrees (FIG. 10 (a)) for the light flux of wavelength: about 660 nm, wavelength: about 780 nm. Is 71 degrees (FIG. 10B). Therefore, "a phase shift of 90 degrees to ± 19 degrees" is allowed, and a wavelength plate having a phase difference within a range of ± 19 degrees centering on the ideal 90 degrees with respect to the wavelength for detecting polarization is used. Can be used. By using such a wavelength plate, it is possible to achieve both an effective deadline for the emission noise of the semiconductor laser chip and signal detection at a high S / N ratio.

The position of the "wave plate" may basically be a position between the hologram and the objective lens. In particular,
In the case of a thin plate such as the above-mentioned wave plate made of the birefringent film, which does not cause aberration even when arranged in the divergent light beam, as shown in FIGS. 1, 4 and 5, the second hologram 5 is used.
And the collimator lens 6 may be arranged between the lens and the collimator lens 6.

As described above, when the wave plate is provided between the hologram and the collimator lens, the wave plate can be integrated with one of the plurality of substrates provided with the hologram. One embodiment of such a case is shown in FIG.

In this embodiment, the two-wavelength common wave plate 1
3 is an example in which the third hologram 5 is integrated on the collimating lens 6 side of the second hologram 5. In this embodiment, since the first and second holograms 4 and 5 are integrated with the cap of the package 21 of the light source / light receiving element unit 20, the size of the optical pickup device can be reduced. That is, in this embodiment, the light source / light receiving element unit 20 and the first,
The second holograms 4 and 5 and the two-wavelength common wavelength plate 13 are integrated to form a "hologram unit".

Although the wave plate 13 is integrated with the second hologram 5 which is a non-polarization hologram in FIG. 11, the wavelength plate 13 is not limited to this and is integrated with the objective lens side of the first hologram 4 which is a polarization hologram. Alternatively, it may be integrated with the light source side of the second hologram 5.

It should be noted that arranging the wave plate as "close to the objective lens" as possible has the advantage that it is unlikely to be affected by the phase difference of the optical components from the light source to the wave plate.

In the optical pickup device shown in FIGS. 1, 4, 5, and 11, the first hologram 4 is a polarization hologram arranged on the light source side, and the second hologram 5 is a non-polarization hologram for optical recording. It is located on the medium side. When the order of this arrangement is reversed and the first hologram 4 is arranged closer to the optical recording medium than the second hologram 5, the return light flux of the wavelength desired to be detected by the non-polarization hologram (second hologram 5) is
Since it will be partly diffracted by the polarization hologram (first hologram 4) before entering the non-polarization hologram,
There is a problem that the amount of diffracted light in a non-polarization hologram decreases.

If the polarization hologram (first hologram 4) is arranged closer to the light source side than the non-polarization hologram (second hologram 5) as in each of the above-mentioned embodiments, the above problem does not occur and the efficiency is high. Detection can be performed.

In the optical pickup device described in each of the above embodiments, a light beam selectively emitted from a light source having a plurality of semiconductor lasers having different emission wavelengths is recorded on an optical recording medium corresponding to the wavelength of this light beam. In an optical pickup device that irradiates a surface and receives a return light beam reflected by a recording surface by a light receiving unit, and performs one or more of recording, reproduction, and erasing of information, a plurality of light sources are provided between a light source and an optical recording medium. The holograms 4 and 5 provided on the substrate are arranged, and the light flux from the light source is
The holograms 4 and 5 provided on the plurality of substrates are transmitted and guided to the optical recording medium 8, the return light flux reflected by the recording surface is diffracted by the hologram, and the diffracted light flux is guided to the light receiving element 9 to be received. Thus, at least one of the holograms provided on the plurality of substrates is the non-polarization hologram 5 whose diffraction efficiency is substantially the same regardless of the polarization direction of the incident light,
Another hologram is used as the polarization hologram 4 having different diffraction efficiency depending on the polarization direction of the incident light, and the polarization direction of the return light beam diffracted by the polarization hologram 4 and guided to the light receiving element 9 is swung from the original polarization direction. Wave plate 1
0 and 13 are arranged closer to the optical recording medium 8 than the polarization hologram 4 (claim 1).

In these optical pickup devices, the diffracted lights of different wavelengths among the diffracted lights from the holograms 4 and 5 provided on the plurality of substrates are received by the same light receiving element 9 (claim 2). Further, in the optical pickups of FIGS. 4, 5 and 11, a plurality of substrates on which holograms 4 and 5 are formed are integrated with each other (claim 3), and in the optical pickup device of FIG. The plurality of substrates on which the light is formed are integrated so that the surface through which light passes has a gap 45 (claim 5).

Further, in the optical pickup device of each of the above embodiments, the polarization hologram 4 has a periodic lattice-like refractive index change in one direction with respect to polarized light in two directions orthogonal to each other in the plane of the substrate, and the other direction. Has a substantially uniform refractive index (claim 5). And, as described above, such a polarization hologram can be formed as a surface structure of a film obtained by obliquely depositing an inorganic substance (FIG. 6) (Claim 6), or by an “organic stretched film (FIG. 7)”. It is also possible (Claim 7).

Further, the non-polarization hologram 5 can be constructed as a transparent substrate on which an uneven grid is formed (FIG. 8) (claim 8), and by adjusting the addition of the unevenness in the uneven grid. The incident light of a specific wavelength can be almost totally transmitted, and the first-order diffracted light can be generated with respect to other wavelengths (Claim 9). Approximately 660 nm for a DVD, a wavelength of light for generating first-order diffracted light is approximately 780 for a CD-based disc.
can be nm (claim 10).

In the optical pickup device shown in FIG. 4, the polarization hologram 4 is made to "substantially totally transmit incident light in a specific polarization direction,
It has a characteristic of substantially totally diffracting a return light beam having a polarization direction orthogonal to this. "
The polarization directions f1 and f2 of the light fluxes of a plurality of wavelengths incident on
The polarization hologram 4 is set in the "direction in which almost all the light is transmitted" (claim 11).

In each of the above optical pickup devices, the polarization hologram 4 is arranged on the light source side and the non-polarization hologram 5 is arranged on the optical recording medium 8 side on the optical path from the light source to the optical recording medium (claim 12). In the optical pickup device of FIG. 11, the wave plate 13 is integrated with one of a plurality of substrates provided with holograms (claim 13).

When a "two-wavelength common wave plate" is used as the wave plate 13 as in the optical pickup device of FIG. 11, the phase difference imparted by the wave plate is within a range of 90 ± 19 degrees with respect to the wavelength for polarization detection. By doing so, it is possible to effectively reduce the emission noise of the semiconductor laser chip due to the return light flux (claim 14).

FIG. 12 is a diagram showing an embodiment of an optical disk drive device. This optical disk drive device is a device that selectively records / reproduces / erases information by using an optical pickup device for two or more types of disc-shaped optical recording media having different wavelengths used. , An optical recording medium 50 (for example, the above-mentioned DVD disc,
Holding unit 51 to which a CD disc is selectively set
With respect to the set optical recording medium 50, a motor M as a "driving unit" for rotationally driving the optical recording medium 50 set in the holding unit 51, and a light having a wavelength peculiar to this optical recording medium is selected. An optical pickup device 52 for performing one or more of recording, reproduction, and erasing by means of a recording medium, and a displacement driving means 53 for displacing and driving the optical pickup device 52 in the radial direction of the optical recording medium 50.

As the optical pickup device 52, the optical pickup device according to any one of claims 1 to 14 which has been described in the above embodiment is an embodiment of the optical disk drive device according to claim 15. . The control unit 54 in FIG. 12 is configured by a microcomputer or the like, and controls each unit of the optical disk drive device.

When the optical pickup device 52 of the present invention is used, for example, as shown in the embodiment,
Since two semiconductor laser chips are contained in one package and a high-power semiconductor laser chip can be mounted, it is possible to realize a compact optical disk drive device capable of recording / reproducing both DVD-based disks and CD-based disks. .

In recent years, a "rewritable optical disk" has been mounted also in a notebook type personal computer, and there is a strong demand for thinning and power saving of the optical pickup device. The optical pickup device according to any one of claims 1 to 14 is small in size because two semiconductor laser chips are contained in one package, and in addition, the polarization hologram is used to improve the light utilization efficiency, and thus the driving amount is small. Recording and reproduction can be performed with an electric current.

Further, since a disc substrate having a large birefringence has a non-polarized detection system, stable reproduction is possible. It is possible to realize an optical disk drive device suitable for carrying a portable external drive or a drive device with a built-in notebook computer or for using for a longer time with limited power such as a battery.

In each of the embodiments described above, light fluxes of approximately 660 nm and approximately 780 nm have been described as a plurality of wavelengths, but the present invention is not limited to these wavelengths. For example, various wavelength combinations such as a combination of wavelength: 405 nm and a wavelength: 660 nm or a combination of wavelength: 405 nm and 780 nm are possible.

[0140]

As described above, according to the present invention, a novel optical pickup device and optical disc drive device can be realized. The optical pickup device of the present invention corrects the detection state of the returning light flux by using the hologram designed for each wavelength even if the light emitting unit position accuracy is poor due to the individual mounting of the plurality of semiconductor laser chips. It is easier to obtain the accuracy of returning light flux detection than in the case of using one hologram.

Since desired semiconductor laser chips can be individually selected and used according to the specifications of the optical pickup device, the semiconductor laser chips can be optimized according to the optical disk drive device, resulting in poor yield.
Cost reduction can be realized as compared with the case of using a wavelength monolithic chip.

Further, since detection with a non-polarized characteristic with respect to a specific wavelength is possible, stable reproduction can be performed without causing fluctuations in the detection signal due to birefringence of the disk substrate, and recording / recording can be performed with high efficiency. This can be realized by the polarization detection system for the wavelength to be reproduced.

Therefore, the optical disc drive apparatus of the present invention uses the optical pickup apparatus as described above,
It can be realized as an inexpensive, small-sized, and energy-saving device.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of an optical pickup device.

FIG. 2 is a diagram for explaining first and second holograms and a light receiving element.

FIG. 3 is a diagram for explaining a method of reducing a light emitting unit interval.

FIG. 4 is a diagram for explaining another embodiment of the optical pickup device.

FIG. 5 is a diagram for explaining another embodiment of the optical pickup device.

FIG. 6 is a diagram for explaining formation of a birefringent film by oblique vapor deposition.

FIG. 7 is a diagram for explaining an organic stretched film.

FIG. 8 is a diagram for explaining a non-polarization hologram.

FIG. 9 is a diagram for explaining diffraction characteristics of a non-polarization hologram.

FIG. 10 is a diagram showing a relationship between a phase difference given by a wave plate and signal intensity.

FIG. 11 is a diagram for explaining another embodiment of the optical pickup device.

FIG. 12 is a diagram for explaining an embodiment of an optical disc drive device.

[Explanation of symbols]

1 Semiconductor laser chip (emission wavelength: 780 nm) 3 Semiconductor laser chip (emission wavelength: 660 nm) 4 First hologram (polarization hologram) 5 Second hologram (non-polarization hologram) 6 Collimating lens 7 Objective lens 8 Optical recording medium 10 Wave plate

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Claims (15)

[Claims] 1. A light flux selectively emitted from a light source having a plurality of semiconductor laser chips having different emission wavelengths is applied to a recording surface of an optical recording medium according to the wavelength of the light flux and reflected by the recording surface. In the optical pickup device which receives / reproduces / erases information while receiving the returned light flux by the light receiving means, holograms provided on a plurality of substrates are arranged between the light source and the optical recording medium, The light flux from the light source is guided to the optical recording medium through each hologram provided on the plurality of substrates, the return light flux reflected by the recording surface is diffracted by the hologram, and the diffracted light flux is received by the light receiving element. Light is guided and received, and at least one of the holograms provided on the plurality of substrates is a non-polarization hologram whose diffraction efficiency is substantially the same regardless of the polarization direction of the incident light. The program is a polarization hologram whose diffraction efficiency is different depending on the polarization direction of the incident light, and a wavelength plate for rotating the polarization direction of the return light beam diffracted by the polarization hologram and guided to the light receiving element from the original polarization direction. An optical pickup device, which is arranged closer to the optical recording medium than the polarization hologram. 2. The optical pickup device according to claim 1, wherein diffracted light beams having different wavelengths which are diffracted by different holograms among diffracted light beams by the holograms provided on the plurality of substrates are received by the same light receiving element. An optical pickup device characterized by the above. 3. The optical pickup device according to claim 1 or 2, wherein a plurality of substrates on which holograms are formed are integrated with each other. 4. The optical pickup device according to claim 3, wherein a plurality of substrates on which holograms are formed are integrated so that surfaces through which light passes have a gap. 5. The optical pickup device according to any one of claims 1 to 4, wherein the polarization hologram has a refractive index of a periodic lattice in one direction with respect to polarized light in two directions orthogonal to each other in the plane of the substrate. An optical pickup device characterized by having a change and a substantially uniform refractive index in other directions. 6. The optical pickup device according to any one of claims 1 to 5, wherein the polarization hologram is formed as a surface structure of a film obtained by obliquely depositing an inorganic substance. 7. The optical pickup device according to claim 1, wherein the polarization hologram is formed of an organic stretched film. 8. The optical pickup device according to any one of claims 1 to 7, wherein the non-polarization hologram is a transparent substrate on which concave and convex gratings are formed. 9. The optical pickup device according to any one of claims 1 to 8, wherein the non-polarization hologram substantially totally transmits a light beam of a specific wavelength among a plurality of wavelengths and sets the light beam of another wavelength to one. An optical pickup device characterized in that it produces second-order diffracted light. 10. The optical pickup device according to claim 9, wherein the wavelength of the light flux that substantially totally transmits the non-polarization hologram is about 660 nm for DVD, and the wavelength of the light flux for producing the first-order diffracted light is about 780 nm for CD. An optical pickup device characterized in that 11. The optical pickup device according to any one of claims 1 to 10, wherein the polarization hologram substantially totally transmits an incident light beam of a specific polarization direction, and returns a return light beam having a polarization direction orthogonal to the incident light beam. An optical pickup device, which has a characteristic of causing substantially total diffraction, and sets a polarization direction of each light flux of a plurality of wavelengths that is incident on the polarization hologram from a light source so that the polarization hologram is substantially completely transmitted. 12. The optical pickup device according to any one of claims 1 to 11, wherein a polarization hologram is arranged on the light source side and a non-polarization hologram is arranged on the optical recording medium side on the optical path from the light source to the optical recording medium. An optical pickup device characterized in that 13. The optical pickup device according to any one of claims 1 to 12, wherein a wavelength plate is integrated with one of a plurality of substrates provided with holograms. . 14. The optical pickup device according to any one of claims 1 to 13, wherein the phase difference imparted by the wave plate is in the range of 90 ± 19 degrees with respect to the wavelength for polarization detection. Optical pickup device. 15. An optical disc drive device for selectively performing one or more of information recording / reproducing / erasing on / from two or more disc-shaped optical recording media having different wavelengths using an optical pickup device. As an optical pickup device, any one of claims 1 to 14
An optical disk drive device equipped with the one described in 1.