JP3338290B2 - Transmission hologram element and optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transmission type hologram element and an optical pickup device.

[0002]

2. Description of the Related Art In recent years, optical pickup devices corresponding to various information recording media have been researched and developed.

FIG. 10 is a diagram of Japanese Patent Application Laid-Open No. 3-76035 (G1).
FIG. 1B is a configuration diagram of an optical pickup device that performs focus servo by an astigmatism method and tracking servo by a three-beam method described in Japanese Patent Application Laid-Open No. 1B 7/135).

In FIG. 10, 101 is an information recording medium (optical disk), 102 is a semiconductor laser for outputting a laser beam (light beam) in an upward direction, and 103 is a three-division diffraction for dividing the light beam into three light beams. A grating 104 transmits the three light beams and returns a light beam (reflected light beam) from the disk 101.
A hologram element for diffracting the light beam and giving the light beam astigmatism corresponding to the focus state, and 105 for condensing the three light beams transmitted through the hologram element 104 as three spots on the disk 101. Condensing lens, 1
06 is the disk 10 diffracted by the hologram element 104
This is a photodetector that detects the return light beam from the light source 1.

[0005]

However, in such an optical pickup device, a specific information recording medium, for example,
Since various optical elements including a light source are set so as to reproduce a CD (compact disc), an information recording medium of another standard having a different recording density such as a track density (track pitch), for example, a DVD (digital video disc)
Cannot be played back.

To solve this problem, the use of a light source that outputs short-wavelength light corresponding to an information recording medium having a large recording density and the addition of a part of an optical system have resulted in an information recording medium having a large recording density and a small recording density. It has been proposed to be able to play both information recording media.

However, the light source generally has a shorter life as its oscillation wavelength becomes smaller. Therefore, when a light source that outputs short-wavelength light is also used for an information recording medium having a small recording density as described above, such a light source is required. The life of the light source is shortened. As a result, there arises a problem that the life of the optical pickup device is shortened.

Therefore, the present inventor paid attention to an optical pickup device having two light sources according to the recording density of an information recording medium. However, in order to reproduce a high-density information recording medium, an optical pickup device further provided with a semiconductor laser which outputs a short-wavelength light capable of reducing a converging spot, as shown in FIG. Since the light-receiving sensitivity of the photodetector composed of the above becomes worse as the wavelength becomes shorter, there is a possibility that short-wavelength light cannot be detected with high sensitivity.

The present invention has been made in view of the above-mentioned problems, and provides a hologram element capable of efficiently using short-wavelength light and an optical pickup device capable of detecting short-wavelength light with high sensitivity. Is the purpose.

[0010]

A hologram element according to the present invention is a transmission hologram element as a separating means for obtaining a separated diffracted light beam having a first diffraction order separated from an incident light beam. The element has such a property that the shorter the wavelength of the incident light beam, the larger the product of the diffraction efficiency of the separated diffracted light beam and the diffraction efficiency of the diffracted light beam of the second diffraction order having a different diffraction order from the diffraction order of the separated diffracted light beam. It is characterized by the following.

Further, the hologram element of the present invention is a transmission type hologram element as separation means for obtaining a separated diffracted light beam of the first diffraction order separated from an incident light beam, wherein the hologram element has a wavelength of Compared with the product of the diffraction efficiency related to the separated diffracted light beam in the light of 765 to 800 nm and the diffraction efficiency related to the diffracted light beam of the second diffraction order having a different order from the first diffraction order, the wavelength is 620 to 6
A characteristic is that the product of the diffraction efficiency of the separated diffracted light beam at 60 nm light and the diffraction efficiency of the diffracted light beam of the second diffraction order in the light is large.

Particularly, the separated diffracted light beam of the first diffraction order is a first-order or -1st-order diffracted light beam, and the light beam of the second diffraction order is a zero-order diffracted light beam. .

An optical pickup device according to the present invention includes a plurality of light sources for outputting light having wavelengths corresponding to a plurality of information recording media having different recording densities, and is capable of reproducing the plurality of different information recording media. It is provided in the outgoing light path from the plurality of light sources, and is common to the plurality of light sources for obtaining a separated diffracted light beam separated from the corresponding outgoing light path from the return light beam from the information recording medium. A transmission type hologram element, wherein the hologram element has such a property that, as the wavelength is shorter, the product of the diffraction efficiency of the light beam transmitted through the hologram element in the outward light path and the diffraction efficiency of the separated diffraction light beam is larger. It is characterized by having.

Further, the optical pickup device of the present invention comprises a plurality of light sources for outputting light having wavelengths corresponding to a plurality of information recording media having different recording densities, and a light flux of the light outputted from the plurality of light sources. Light-collecting means for condensing light on the corresponding information recording medium, and a separation provided in an outgoing light path from the plurality of light sources and separated from the corresponding outgoing light path from a return light beam from the information recording medium. A transmission-type hologram element common to the plurality of light sources for obtaining a diffracted light beam, and the hologram element has a diffraction efficiency of a light beam transmitted through the hologram element in the forward optical path as the wavelength is shorter. It is characterized in that the product has a large product of the diffraction efficiency of the separated diffracted light beam.

Further, the optical pickup device of the present invention comprises: a first light source for outputting light for reproducing a first information recording medium having a first wavelength; and a second light source having a longer wavelength than the first wavelength. A second light source that outputs light for reproducing a second information recording medium having a wavelength, and a second light source that is provided in an outgoing optical path from the first and second light sources and that is provided from the first and second information recording media. And a transmission-type hologram element common to the first and second light sources for obtaining a separated diffracted light beam separated from the corresponding forward light path from the returned light beam.
The light for reproducing the first information recording medium is more diffractive than the light for reproducing the information recording medium, and the diffraction efficiency for the light flux transmitted through the hologram element in the forward optical path and the diffraction efficiency for the separated diffracted light flux. Are characterized by having a large product of

In particular, the first light source has a wavelength of 620 to 6
A semiconductor laser that outputs 60 nm light;
Is a semiconductor laser that outputs light having a wavelength of 765 to 800 nm.

In particular, the light beam transmitted through the outward light path is a zero-order diffracted light beam, and the separated diffracted light beam is a first-order diffracted light beam or a -1st-order diffracted light beam.

Further, the hologram element is characterized in that the groove depth of the grating on the hologram surface is set such that the value of the product increases as the wavelength decreases. Preferably, the hologram element sets the groove depth of the grating such that the light use efficiency with respect to the first wavelength is at or near the first maximum value.

In particular, the invention is characterized in that a diffraction grating for three divisions is provided in a forward optical path leading to the hologram element. 3 above
The splitting diffraction grating may be a transmission-type three-segment diffraction grating or a reflection-type three-segment diffraction grating.

Further, the hologram element is made of a transparent member, and has a hologram surface on one surface of the member and a three-divided diffraction grating surface on the other surface opposite to the one surface. .

[0021] The three-division diffraction grating converts the incident light beam into
A split main light beam and sub-light beams on both sides are generated. It is preferable that the shorter the wavelength of the incident light beam, the smaller the diffraction efficiency of the main light beam and the larger the diffraction efficiency of the sub-light beam. In particular, it is preferable that the main light beam is a zero-order diffracted light, and the two sub-light beams are a first-order diffracted light and a -1st-order diffracted light. For example, the grating depth of the grating is set such that the smaller the wavelength of the light beam, the smaller the diffraction efficiency of the main light beam and the greater the diffraction efficiency of the sub light beam.

The shorter the wavelength of the incident light beam, the smaller the diffraction efficiency of the main light beam and the higher the diffraction efficiency of the sub light beam. As for the spot, the shorter the wavelength of the light beam, the greater the intensity of the condensed spot (sub spot) of the sub light beam relative to the condensed spot (main spot) of the main light beam.

Accordingly, an information recording medium having a high track density has a small track pitch, and therefore has a small area over which sub-spots cross tracks. However, an information recording medium having a high track density divides a light beam having a short wavelength into three light beams. Tracking servo can be performed using a sub spot having a large intensity generated by passing through the diffraction grating. As a result, the ratio of the noise component included in the tracking error signal can be reduced, so that good tracking servo can be performed even on an information recording medium having a high track density.

On the other hand, for an information recording medium having a low track density, tracking servo is performed using a light beam having a long wavelength. The intensity of the sub-spot is reduced by passing this long-wavelength light beam through the three-division diffraction grating. However, since the medium has a large track pitch (track width), the sub-spot straddles the track in a large area. Therefore, good tracking servo can be performed on an information recording medium having a low track density.

In the above-described optical pickup device, the information recording medium having a high recording density is reproduced with a reproduction light having a shorter wavelength than the reproduction light of the information recording medium having a low recording density.

The photodetector for detecting the return light beam is Si
It may be composed of a photodiode composed of a system semiconductor.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device for performing focus servo by an astigmatism method and tracking servo by a three-beam method according to an embodiment of the present invention will be described with reference to the schematic configuration diagram of FIG.

In this embodiment, the information recording medium is a CD having a thickness of 1.2 mm from the surface of the transparent substrate (incident surface) on the reproduction light incident side to the recording surface (reflective surface).
m, and the distance from the transparent substrate surface (incident surface) on the incident side of the reproducing light to the recording surface (reflective surface) is 0.6 m.
m, and the track pitch is CD (pitch = 1.6 μm).
m), a high-density information recording medium (DVD)
A case in which reproduction is performed using light having a wavelength of 635 nm is shown.
Optical elements other than the correction lens for performing the correction are common.

In FIG. 1, reference numeral 1 denotes a semiconductor laser (first light source) for outputting a laser beam (first light beam) having a wavelength of 635 nm, and reference numeral 2 denotes a wavelength of 780 n arranged close to the first light source 1.
A semiconductor laser (second light source) that outputs m laser light (second light flux).

Numeral 3 denotes at least the 0th-order diffracted light (main light beam) for the first and second light beams, and ± 1 for tracking servo.
This is a so-called transmission-type three-division grating made of optical glass or optical resin that divides the light into three light beams (not shown) composed of next-order diffracted light (sub-beams). In the present embodiment, the three-division grating 3 is made of quartz glass and has a three-division grating surface formed of linear gratings having a period of 20 μm and having equal intervals.

As shown in FIG. 2, the diffracted light such as the 0th-order diffracted light and ± 1st-order diffracted light generated by the three-division diffraction grating 3 has a diffraction efficiency (that is, diffracted light) with respect to the groove depth t of the grating. ), And the period of these periodic fluctuations differs depending on the wavelength. In FIG. 2, η ₀ ,
η ₁ is the 0th-order diffracted light for the wavelength of 635 nm, ±
The diffraction efficiency of the first-order diffracted light is shown, and ξ ₀ and ξ ₁ represent the diffraction efficiencies of the 0-order diffracted light and the ± 1st-order diffracted light with respect to the wavelength of 780 nm.

The three-division diffraction grating 3 is designed such that the shorter the wavelength, the lower the diffraction efficiency of the main light beam and the higher the diffraction efficiency of the sub light beam. In the case of the present embodiment, since the grating depth t is set to about 0.38 μm, the wavelength 6
The diffraction efficiency of the 0th-order diffracted light for 35 nm is about 0.48,
The diffraction efficiency of ± 1st-order diffracted light is about 0.22, and the wavelength is 78
The diffraction efficiency of the 0th-order diffracted light with respect to 0 nm is about 0.63, ±
The diffraction efficiency of the first-order diffracted light is about 0.15.

Reference numeral 4 denotes the above-mentioned 3 which has been emitted from the three-division diffraction grating 3.
Spatial variation corresponding to the focus state of the information recording medium (reflected light beam) from the information recording medium, which transmits the three light beams (main light beam and sub light beam) and reflects the three light beams. Is a transmission type hologram element (separation means) made of optical glass or optical resin for obtaining a separated diffracted light beam transmitted and diffracted in the first order while giving astigmatism.

As shown in FIG. 3, the hologram element of this embodiment is a transmission type made of quartz glass having a hologram surface having a curved grating having a width and a pitch different from 2 to 4 μm depending on the position in the hologram surface. It is a hologram element. The width and pitch of the curved grating are determined depending on the positional relationship between the light sources 1 and 2 and the corresponding photodetectors described below.

As shown in FIG. 4, the diffracted light such as the 0th-order diffracted light and ± 1st-order diffracted light generated by the transmission type hologram element 4 has a diffraction efficiency (that is, a diffracted light of the diffraction light) with respect to the groove depth T of the grating. The rate of occurrence varies periodically, and the cycle of these periodic variations differs depending on the wavelength. In FIG. 4, φ
₀ and φ ₁ are 0-order diffracted light with respect to a wavelength of 635 nm,
± 1 shows the diffraction efficiency of the diffracted light, ψ _{0, 0-order} diffracted light [psi ₁ is for each wavelength 780 nm, showing the diffraction efficiency of ± 1-order diffracted light.

In the optical pickup device of this embodiment, the light source 1
(Or 780 nm) laser light output from the light source 2 (or the light source 2) is transmitted through the transmission type hologram element 4 by zero-order diffraction, is reflected by the information recording medium, and is primary-ordered by the transmission type hologram element 4. This is a configuration for detecting return light that is transmitted and diffracted.

Accordingly, the utilization efficiency of the transmission type hologram element 4 with respect to light having a wavelength of 635 nm and light having a wavelength of 780 nm depends on the diffraction efficiency of the zero-order diffraction light and the diffraction efficiency of the first-order diffraction light (separated diffraction light beam) shown in FIG. Product φ ₀ × φ ₁ , ψ ₀ × ψ ₁
Is as shown in FIG.

The hologram element 4 of this embodiment is designed such that the shorter the wavelength, the higher the utilization efficiency.

Specifically, in the case of this embodiment, the lattice depth T is set to about 0.35 μm. Therefore, as can be seen from FIG. 4, the diffraction efficiency of the 0th-order diffracted light (forward light) with respect to the wavelength of 635 nm in the hologram element 4 is about 0.49,
The diffraction efficiency of the ± 1st-order diffracted light (return light) is about 0.21, the diffraction efficiency of the 0th-order diffracted light (forward light) at a wavelength of 780 nm is about 0.64, and the diffraction efficiency of the ± 1st-order diffracted light (return light) is It is about 0.14. That is, as can be seen from FIG.
The utilization efficiency of light having a wavelength of 635 nm in the hologram element 4 is about 0.10 (maximum utilization efficiency: first maximum value),
The utilization efficiency of light having a wavelength of 780 nm is about 0.09.

Numeral 5 is supported so as to be drivable in accordance with the servo, and transmits the three light beams (main and sub light beams) transmitted through the transmission type hologram element 4 (zero-order diffraction) onto each information recording medium on each information recording medium. Condensing lens (light collecting means) for collecting light
It is.

Reference numeral 6 denotes a wavelength of 780 nm and a wavelength of 63
It is focused at a position 0.6 mm longer than the light of 5 nm, and N
Correction lens (light collecting means) for correcting A to be small
When a high-density recording medium DVD is reproduced, the optical disk is deviated from the optical path by a driving device (not shown). When a CD is reproduced, the optical disk is arranged in the optical path.

Here, as shown in FIG. 6, the condensed spot (main spot) relating to the main light beam scans the track on which information is recorded, and the condensed spots (sub-spots) relating to both sub light beams correspond to the track. Is scanned so as to slightly straddle both sides of. Since the reflectance outside this track is set to be higher than that of the track, if the main spot is displaced from the track, a difference occurs in the reflection intensity from both sub-spots.

Numeral 7 is used for reproducing a high-density information recording medium for detecting a reflected light beam (return light beam) from the information recording medium which has been transmitted and diffracted by the transmission type hologram element 4 in the first order through the condenser lens 5. It is a six-segment photodetector.

As shown in FIG. 7, this six-segment photodetector 7
A four-divided light detector 7a for detecting a reflected light beam related to the main spot and outputting a focus signal and a reproduction signal by a conventionally known astigmatism method, and a reflected light beam related to the sub-spot. The above 4 for outputting a tracking error signal by a well-known three-beam tracking method.
It has photodetectors 7b, 7b located on both sides of the split photodetector. The light detectors 7b, 7b independently detect reflected light fluxes related to the sub-spots, and generate a tracking error signal corresponding to a difference in the amount of received light between the light detectors 7b, 7b generated according to a track shift of the main spot. Is output.

As shown in FIG. 8, this six-segment photodetector 7
Are formed selectively on the n ⁺ -type Si substrate 21, the n ⁻ -type semiconductor layer 22 formed on the surface thereof, and on the surface portion of the n ⁻ -type semiconductor layer 22 corresponding to each of the divided photodetectors. A p ⁺ type semiconductor region 23 is provided, and these p ⁺ type semiconductor regions 23 and n ⁻
It has a PIN photodiode corresponding to each of the divided light detection units constituted by the type semiconductor layer 22 and the n ⁺ type Si substrate 21.

A CD 8 passes through a condenser lens 5 and a correction lens 6, and detects a reflected light beam (return light beam) from an information recording medium that has been transmitted and diffracted by the transmission hologram element 4 in the first order.
Is a six-segment photodetector having the same configuration as the six-segment photodetector 7 used when reproducing the image.

In such an optical pickup device, the hologram element 4 is set so that the use efficiency of the light having the wavelength of 635 nm is higher than that of the light having the wavelength of 780 nm. Can be suppressed from decreasing in strength.

Therefore, as in this embodiment, the six-split photodetector 7
, The sensitivity is degraded as the wavelength becomes shorter, which has been conventionally used.
Since the intensity of the feedback light having a wavelength of 35 nm can be sufficiently ensured, the feedback light having a wavelength of 635 nm can be detected with high sensitivity by the six-divided photodetector 7.

On the other hand, the light having a wavelength of 780 nm has a wavelength of 635 nm.
Although the attenuation factor by the hologram element 4 is larger than that of light of nm, the six-split photodetector 8 composed of a Si-based photodiode has sufficient sensitivity to light of wavelength 780 nm. The split photodetector 8 can detect with high sensitivity.

Therefore, in such an optical pickup device, D
VD and CD can be reproduced well.

In this optical pickup device, the three-division diffraction grating 3 is set so that the shorter the wavelength, the smaller the diffraction efficiency of the main light beam and the larger the diffraction efficiency of the sub light beam. As shown in FIG. 9, the light intensity of the converging spot (sub-spot) relating to the sub-beam on the information recording medium is larger at a wavelength of 635 nm than at a wavelength of 780 nm. In the case of the present embodiment, at a wavelength of 635 nm, the intensity of the main spot / the intensity of the sub-spot is about 2, and the wavelength 7
At 80 nm, the intensity of the main spot / the intensity of the sub spot is about 4.

This device uses light having a wavelength of 635 nm for a high-density information recording medium DVD having a large track density, that is, a small track pitch. , The S / N of the tracking signal is improved. Therefore, it is possible to reproduce a high-density information recording medium while performing good tracking.

On the other hand, since the CD has a large track width, the sub-spot can be straddled over a large area of the track even if light having a wavelength of 780 nm is used, and reproduction can be performed while performing good tracking.

The wavelengths of the first and second light sources can be changed as appropriate, but the wavelength λ ₁ = 620-660n.
a semiconductor laser that outputs a luminous flux of m and a wavelength λ ₂ = 765
In the case of a semiconductor laser that outputs a light flux of up to 800 nm, reproduction can be performed on both a CD and an information recording medium having a track density of about 1.5 to 3 times that of a CD while performing good tracking servo. In this case, it is preferable strength of intensity / side spot of the main the wavelength lambda ₁ spot about 4-7, the intensity of the intensity / side spot of the main the wavelength lambda ₂ spot is about 2-3.

Further, in the above description, the optical pickup device using the transmission type three-division diffraction grating has been described. However, the present invention can of course be applied to the optical pickup device using the reflection type three-division diffraction grating. Of course, the optical path can be bent by interposing a reflecting means such as a mirror between the separating means and the information recording medium.

Further, in the above description, a plurality of light detecting means are used. However, it is of course possible to adopt a configuration in which one light detecting means is common to information recording media having a plurality of recording densities.

In addition, an optical element in which the transmission-type three-segment diffraction grating 3 and the transmission-type hologram element 4 are integrated may be used.

In this embodiment, a CD having a distance of 1.2 mm from the surface (incident surface) of the transparent substrate on the reproduction light incident side to the recording surface (reflection surface) is used. The distance from the (incident surface) to the recording surface (reflective surface) is 0.
6 mm thick and the track pitch is CD (pitch = 1.
High-density information recording medium (DVD)
Has been described, for example, it is also possible to reproduce a high-density information recording medium whose distance from the incident surface to the recording surface is 1.2 mm thick. Of course, the present invention can be applied to optical recording media different from the above.

The present invention can be applied to a tracking servo method other than a tracking servo method using a three-beam method using a three-division diffraction grating, and a focus servo method other than a focus servo method using an astigmatism method.

[0060]

The hologram element of the present invention can efficiently use light of a short wavelength. Therefore, when this hologram element is used in an optical pickup device, it is possible to satisfactorily reproduce a plurality of information recording media having different recording densities (for example, both CD and DVD).

Also, in the optical pickup device of the present invention,
Since the short-wavelength reproduction light has a smaller attenuation rate in the hologram element, it is possible to suppress a decrease in the intensity of the feedback light from the information recording medium due to the short-wavelength reproduction light. Therefore, even if an Si-based photodetector is used, it is possible to satisfactorily reproduce an information recording medium having a large recording density and reproducing with short-wavelength reproduction light. In addition, the return light from the information recording medium due to the long-wavelength reproduction light has a larger attenuation rate than the short-wavelength reproduction light, but the photodetector has good sensitivity on the long-wavelength side. An information recording medium with a low recording density to be reproduced can also be satisfactorily reproduced.

As described above, in the optical pickup device of the present invention, a plurality of information recording media (for example, CDs) having different recording densities are provided.
And DVD).

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram of an optical pickup device according to an embodiment of the present invention.

FIG. 2 shows a wavelength 7 with respect to a grating depth t of a diffraction grating for three divisions.
It is a figure which shows the relationship of the diffraction efficiency of 80 nm light and 635 nm wavelength light.

FIG. 3 is a top view showing a hologram surface of a hologram element used in the present embodiment.

FIG. 4 shows a wavelength 78 with respect to the grating depth T of the hologram element.
It is a figure which shows the relationship of the diffraction efficiency of 0 nm light and 635 nm wavelength light.

FIG. 5 is a diagram showing the relationship between the grating depth T of the hologram element and the utilization efficiency of light having a wavelength of 780 nm and light having a wavelength of 635 nm.

FIG. 6 is a schematic top view showing a positional relationship between a track, a main spot, and a sub spot in the optical pickup device of the embodiment.

FIG. 7 is a schematic top view of a photodetector of the optical pickup device.

FIG. 8 is a partial schematic cross-sectional view of a six-segment photodetector used in the present embodiment.

FIG. 9 shows a wavelength of 780n in the optical pickup device.
It is a schematic diagram which shows the relationship of the intensity | strength of a main spot at the time of m and wavelength 635nm, and a sub spot.

FIG. 10 is a schematic structural diagram of an optical pickup device according to a conventional example.

FIG. 11 is a diagram illustrating a relationship between relative light sensitivity and wavelength of a conventional Si-based photodetector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st light source 2 2nd light source 3 transmission-type 3 division | segmentation diffraction grating 4 transmission-type hologram element 5 condensing lens (condensing means) 6 correction lens (condensing means) 7, 8 Photodetector

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-92885 (JP, A) JP-A-2-224456 (JP, A) JP-A-2-103001 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02B 5/32 G02B 5/18 G03H 1/00 G11B 7/135

Claims (11)

(57) [Claims] 1. A transmission type hologram element as a separating means for obtaining a separated diffraction light beam of a first diffraction order separated from an incident light beam, wherein the hologram element is arranged such that as the wavelength of the incident light beam becomes shorter, A transmission hologram element having a property that a product of a diffraction efficiency of a separated diffracted light beam and a diffraction efficiency of a diffracted light beam of a second diffraction order different from the diffraction order of the separated diffraction light beam is large. 2. A transmission hologram element as a separation means for obtaining a separated diffraction light beam of a first diffraction order separated from an incident light beam, wherein the hologram element has a wavelength of 7.
Compared with the product of the diffraction efficiency of the separated diffracted light beam in the light of 65 to 800 nm and the diffraction efficiency of the diffracted light beam of the second diffraction order having a different order from the first diffraction order in the light, the wavelength is 620 to 660 nm. A transmission hologram element characterized by having a large product of the diffraction efficiency of the separated diffracted light beam in the light of (d) and the diffraction efficiency of the light of the second diffraction order in the light. 3. The separated diffracted light beam of the first diffraction order is 1
The transmission hologram element according to claim 1, wherein the light beam of the second diffraction order is a diffracted light beam of the 0th order, in addition to the diffracted light of the 1st or −1st order. 4. A light source for outputting light having a wavelength corresponding to information recording media having a plurality of different recording densities,
An optical pickup device capable of reproducing the plurality of different information recording media, provided in an outgoing optical path from the plurality of light sources, and separated from the corresponding outgoing optical path from a return light beam from the information recording medium. A transmission-type hologram element common to the plurality of light sources for obtaining the separated diffracted light flux is provided. The shorter the wavelength, the more the hologram element has a diffraction efficiency related to a light flux transmitted through the hologram element in the forward optical path and An optical pickup device having a property that a product of a diffraction efficiency and a diffraction efficiency of a separated diffracted light beam is large. 5. A plurality of light sources for outputting light of wavelengths corresponding to a plurality of information recording media having different recording densities, and luminous fluxes of light output from the plurality of light sources are collected on the corresponding information recording media, respectively. Focusing means for emitting light, and the plurality of light sources provided in an outgoing optical path from the plurality of light sources, for obtaining a separated diffracted light beam separated from the corresponding outgoing optical path from a return light beam from the information recording medium. A hologram element of a transmission type common to the light source, wherein the shorter the wavelength, the higher the diffraction efficiency of the light beam transmitted through the hologram element in the forward optical path and the higher the diffraction efficiency of the separated diffraction light beam. An optical pickup device characterized by having a property of having a large product with the following. 6. A first light source for outputting light for reproducing a first information recording medium having a first wavelength, and a second information recording having a second wavelength longer than the first wavelength. A second light source that outputs light for medium reproduction; and a second light source that is provided in an outgoing optical path from the first and second light sources, and that receives the corresponding outgoing light beam from the first and second information recording media. A transmission-type hologram element common to the first and second light sources for obtaining a separated diffracted light beam separated from an optical path, wherein the hologram element converts light for reproducing a second information recording medium into light. Compared with this, the light for reproducing the first information recording medium has a property that the product of the diffraction efficiency of the light beam transmitted through the hologram element in the forward optical path and the diffraction efficiency of the separated diffraction light beam is larger. Optical pickup device. 7. The first light source has a wavelength of 620 to 660.
7. The optical pickup device according to claim 6, wherein the second light source is a semiconductor laser that outputs light having a wavelength of 765 to 800 nm. 8. The light beam transmitted through the outward light path is a zero-order diffracted light beam, and the separated diffracted light beam is a first-order diffracted light beam or a −1st-order diffracted light beam.
8. The optical pickup device according to 6 or 7. 9. The hologram element, as the wavelength is shorter,
The groove depth of the grating on the hologram surface is set so that the value of the product is large.
9. The optical pickup device according to 6, 7, or 8. 10. The apparatus according to claim 4, wherein a diffraction grating for dividing into three is provided in a forward optical path to the hologram element.
The optical pickup device according to 5, 6, 7, 8, or 9. 11. The hologram element is made of a transparent member, and has a hologram surface on one surface of the member.
11. The optical pickup device according to claim 10, wherein the other surface facing the one surface has a three-divided diffraction grating surface.