JPH0973017A - Transmission type hologram element and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram element capable of efficiently utilize short wavelength light and to provide an optical pickup device capable of detecting the short wavelength light. SOLUTION: This device is provided with a first light source 1 which outputs light for reproducing a first information recording medium having a first wavelength, a second light source 2 which outputs light for reproducing a second information recording medium having a wavelength longer than the first wavelength, and a transmission type hologram element 4 which is provided in the outward light paths from the first and second light sources 1, 2 and is common to the first and the second light sources 1, 2 to obtain separate diffracted light fluxes separated from the outward paths corresponding to the returning fluxes from the first and second information media. The hologram 4 has a characteristic that the light for reproducing the first information recording medium has a larger product of diffraction efficiency related to the transmitting light flux through the hologram element 4 in its outward light path and the diffraction efficiency concerning the separately diffracted light flux, compared with the light for reproducing the second information recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission 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 shows Japanese Patent Laid-Open No. 3-76035 (G1).
1B 7/135) is a configuration diagram of an optical pickup device which performs a focus servo by an astigmatism method and a tracking servo by a three-beam method, which are described in JP 1B 7/135).

In FIG. 10, 101 is an information recording medium (optical disk), 102 is a semiconductor laser which outputs a laser beam (light flux) in an upward direction, and 103 is a diffraction for three divisions for dividing the light flux into three light fluxes. A grating 104 is a return light flux (reflected light flux) that transmits the above three light fluxes and is from the disc 101.
A hologram element for diffracting the light beam and giving astigmatism corresponding to the focus state to the light beam, and 105 for converging the three light beams transmitted through the hologram element 104 as three spots on the disc 101. Condenser lens, 1
Reference numeral 06 denotes the disk 10 diffracted by the hologram element 104.
1 is a photodetector for detecting the return light flux from

[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), information recording media of other standards having different recording densities such as track density (track pitch), for example, DVD (digital video disc)
There is a problem that can not be played.

To solve this problem, by using a light source for outputting a short wavelength light corresponding to an information recording medium having a high recording density and adding an optical system in part, an information recording medium having a high recording density and a small recording density can be obtained. It has been proposed to be able to reproduce both of the information recording media.

However, the life of a light source generally becomes shorter as the oscillation wavelength thereof becomes smaller. Therefore, when the light source for outputting a short wavelength light is used for an information recording medium having a small recording density as described above, 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 inventor of the present application paid attention to an optical pickup device provided with two light sources according to the recording density of the information recording medium. However, in order to reproduce a high-density information recording medium, in an optical pickup device further provided with a semiconductor laser that outputs a light of a short wavelength that can reduce a focused spot, a Si semiconductor that is generally used as shown in FIG. Since the light-receiving sensitivity of the photodetector consisting of 1 becomes worse as the wavelength becomes shorter, there is a possibility that the light having a short wavelength cannot be detected with high sensitivity.

The present invention has been made in view of the above problems, and it is possible to provide a hologram element capable of efficiently utilizing light of a short wavelength and an optical pickup device capable of sensitively detecting light of a short wavelength. Is the purpose.

[0010]

A hologram element of the present invention is a transmission type hologram element as a separating means for obtaining a separated diffracted light beam of a first diffraction order which is obtained by separating an incident light beam. The element has 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 second diffracted light beam of the different diffraction order of the separated diffracted light beam. It is characterized by

Further, the hologram element of the present invention is a transmission type hologram element as a separating means for obtaining a separated diffracted light beam of a first diffraction order obtained by separating the incident light beam, and the hologram element has a wavelength of Compared with the product of the diffraction efficiency of the separated diffracted light flux in the light of 765 to 800 nm and the diffraction efficiency of the diffracted light flux of the second diffraction order having a different order in the light, the wavelengths of 620 to 6
It is characterized in that the product of the diffraction efficiency of the separated diffracted light flux of 60 nm light and the diffraction efficiency of the diffracted light flux of the second diffraction order of the light is large.

In particular, the separated diffracted light flux of the first diffraction order is the first-order or -1st-order diffracted light, and the second diffraction order light flux is the zero-order diffracted light. .

The optical pickup device of the present invention is provided with a plurality of light sources for outputting light having wavelengths corresponding to information recording media having a plurality of different recording densities, and is capable of reproducing the plurality of different information recording media. Is provided in the forward light path from the plurality of light sources, and is common to the plurality of light sources for obtaining a separated diffracted light flux separated from the corresponding forward light path from the return light flux from the information recording medium. A hologram element of a transmission type is provided, and the hologram element has a property that the shorter the wavelength is, the larger the product of the diffraction efficiency of the light beam passing through the hologram element in the forward optical path and the diffraction efficiency of the separated diffracted light beam is. It is characterized by having.

Further, the optical pickup device of 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 a light flux of the light output from the plurality of light sources, respectively. A condensing means for condensing on the corresponding information recording medium, and a separation provided in the forward light path from the plurality of light sources and separated from the corresponding forward light path from the return light flux from the information recording medium. And a transmission type hologram element common to the plurality of light sources for obtaining a diffracted light beam, wherein the hologram element has a diffraction efficiency relating to a light beam transmitted through the hologram element in the forward light path as the wavelength is shorter. It is characterized by having a large product with the diffraction efficiency of the separated diffracted light flux.

In the optical pickup device of the present invention, the first light source for outputting the light for reproducing the first information recording medium having the first wavelength and the second light source having a wavelength longer than the first wavelength are provided. A second light source that outputs a light for reproducing a second information recording medium having a wavelength, and a first light source that is provided in a forward light path from the first and second light sources. A transmission type hologram element common to the first and second light sources for obtaining a separated diffracted light flux obtained by separating the return light flux from the corresponding forward light path, and the hologram element includes a second
Of the information recording medium reproducing light, the first information recording medium reproducing light has a diffraction efficiency related to the light beam passing through the hologram element in the forward light path and a diffraction efficiency related to the separated diffracted light beam. Is characterized by having a large product of

Particularly, the first light source has wavelengths of 620 to 6
A semiconductor laser that outputs light of 60 nm,
The light source is a semiconductor laser that outputs light having a wavelength of 765 to 800 nm.

In particular, the luminous flux transmitted in the forward light path is a 0th-order diffracted light, and the separated diffracted luminous flux is a 1st-order diffracted light or a -1st-order diffracted light.

Further, in the hologram element, the groove depth of the grating on the hologram surface is set such that the value of the product increases as the wavelength becomes shorter. In the hologram element, it is preferable to set the groove depth of the grating so that the light utilization efficiency for the first wavelength is at or near the first maximum value.

In particular, it is characterized in that a three-division diffraction grating is provided in the forward optical path leading to the hologram element. 3 above
The division diffraction grating may be a transmission-type three-division diffraction grating or a reflection-type three-division 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-division diffraction grating surface on the other surface facing the one surface. .

The diffraction grating for three divisions is
The main light flux generated by division and the sub-light fluxes on both sides of the main light flux are generated. It is preferable that the shorter the wavelength of the incident light flux, the smaller the diffraction efficiency of the main light flux and the higher the diffraction efficiency of the sub-light flux. Particularly, it is preferable that the main light flux is a 0th-order diffracted light and the two sub-light fluxes are a 1st-order diffracted light and a -1st-order diffracted light. In this three-division diffraction grating, for example, the groove 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. The three-division diffraction grating is composed of three light beams condensed on the information recording medium. As the wavelength of the light flux becomes shorter, the intensity of the focused light spot (sub spot) of the sub light flux becomes higher than that of the focused light spot (main spot) of the main light flux.

Therefore, since the information recording medium having a high track density has a small track pitch, the area in which the sub-spots extend over the tracks is small. However, the information recording medium having a high track density divides a light beam having a short wavelength into the above three divisions. Tracking servo can be performed by using a sub-spot generated by passing through the diffraction grating and having a high intensity. As a result, the ratio of the noise component contained in the tracking error signal can be reduced, and good tracking servo can be performed even on an information recording medium having a high track density.

On the other hand, an information recording medium having a low track density performs tracking servo by using a light flux having a long wavelength. The intensity of the sub-spot is reduced by passing the light flux having a long wavelength through the three-division diffraction grating, but since the medium has a large track pitch (track width), the sub-spot has a large area and extends over the tracks. Therefore, good tracking servo can be performed on an information recording medium having a low track density.

In the above optical pickup device, an information recording medium having a high recording density is reproduced by reproducing light having a shorter wavelength than that of an information recording medium having a small recording density.

Further, the photodetector for detecting the return light flux is Si
It may be composed of a photodiode composed of a system semiconductor.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An optical pickup device according to an embodiment of the present invention for performing focus servo by an astigmatism method and tracking servo by a three-beam method will be described with reference to the schematic configuration diagram of FIG.

In this embodiment, the information recording medium is a CD having a distance of 1.2 mm from the transparent substrate surface (incident surface) on the reproducing light incident side to the recording surface (reflecting surface) at a wavelength of 780 n.
When reproducing with m laser light, the distance from the transparent substrate surface (incident surface) on the reproduction light incident side to the recording surface (reflection surface) is 0.6 m.
The track pitch is CD (pitch = 1.6μ
m), which is about half of the high density information recording medium (DVD)
The case of reproducing with light of wavelength 635 nm is shown. Focus and NA (numerical aperture) for these light sources and light of wavelength 780 nm are shown.
The optical elements other than the correction lens for correction are common.

In FIG. 1, 1 is a semiconductor laser (first light source) that outputs a laser beam (first light flux) having a wavelength of 635 nm, and 2 is a wavelength 780 n that is arranged in proximity to the first light source 1.
This is a semiconductor laser (second light source) that outputs m laser light (second light flux).

Reference numeral 3 denotes at least the 0th-order diffracted light (main light flux) of the first and second light fluxes, and ± 1 for tracking servo.
This is a so-called transmission type three-division diffraction grating made of optical glass or optical resin that divides into three light beams (not shown) made of secondary diffracted light (sub-light beams). In the present embodiment, the three-division diffraction grating 3 is made of quartz glass, and has three-division diffraction grating surfaces formed of linear gratings with an equal interval of 20 μm.

As shown in FIG. 2, the diffracted light such as the 0th-order diffracted light and the ± 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. Occurrence rate) changes periodically, and the period of these periodic fluctuations varies depending on the wavelength. In FIG. 2, η ₀ ,
η ₁ is the 0th-order diffracted light at a wavelength of 635 nm, ±
The diffraction efficiency of the first-order diffracted light is shown, and ξ ₀ and ξ ₁ show the diffraction efficiency of the 0th-order diffracted light and the ± 1st-order diffracted light with respect to the wavelength of 780 nm, respectively.

The three-division diffraction grating 3 is designed so that the shorter the wavelength, the smaller the diffraction efficiency of the main light beam and the greater the diffraction efficiency of the sub-light beam. In the case of this 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 with respect to 35 nm is about 0.48,
The diffraction efficiency of the ± 1st order diffracted light is about 0.22, and the wavelength 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 is emitted from the diffraction grating 3 for three divisions.
Of the three light fluxes (main light flux and sub light flux) and reflected light flux (return light flux) from the information recording medium relating to the three light fluxes, spatial variation corresponding to the focus state on the information recording medium (this embodiment). Then, it is a transmission hologram element (separation means) made of optical glass or optical resin or the like for obtaining a separated diffracted light beam that is 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 composed of curved gratings having different widths and pitches between 2 and 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 the ± 1st-order diffracted light generated by the transmission hologram element 4 is diffracted with respect to the groove depth T of the grating (that is, the diffracted light Occurrence rate) changes periodically, and the period of these periodic fluctuations differs depending on the wavelength. In addition, in FIG.
₀ and φ ₁ are the 0th-order diffracted light with respect to the wavelength of 635 nm,
The diffraction efficiencies of the ± first-order diffracted light are shown, and ψ ₀ and ψ ₁ show the diffraction efficiencies of the 0th-order diffracted light and the ± 1st-order diffracted light with respect to the wavelength of 780 nm, respectively.

In the optical pickup device of this embodiment, the light source 1
The laser beam having a wavelength of 635 nm (or a wavelength of 780 nm) output from (or the light source 2) passes through the transmission hologram element 4 in the 0th diffraction order, is then reflected by the information recording medium, and is transmitted by the transmission hologram element 4 in the 1st order. This is a configuration for detecting the return light that is transmitted and diffracted.

Therefore, the utilization efficiency for the light of wavelength 635 nm and the light of wavelength 780 nm in the transmission hologram element 4 is the diffraction efficiency of the 0th order diffracted light and the diffraction efficiency of the 1st order diffracted light (separated diffracted light beam) shown in FIG. Product φ ₀ × φ ₁ , ψ ₀ × ψ ₁
And is as shown in FIG.

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

Specifically, in the case of this embodiment, the grating 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 (outgoing light) for 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 (outgoing light) is about 0.64, and the diffraction efficiency of the ± 1st-order diffracted light (returned light) is about 780 nm. It is about 0.14. That is, as can be seen from FIG.
The use efficiency of the 635 nm wavelength light in the hologram element 4 is about 0.10 (maximum use efficiency: first maximum value),
The utilization efficiency of light having a wavelength of 780 nm is about 0.09.

Denoted at 5 is a drivable support corresponding to the servo, and the above three light beams (main and sub light beams) transmitted (0th order) through the transmission hologram element 4 are focused spots on the information recording medium. Lens (light collecting means) for collecting light as
It is.

6 is a wavelength of 63 in the case of light having a wavelength of 780 nm.
Compared with the light of 5 nm, it is condensed at a position that is 0.6 mm longer and N
Correction lens (condensing means) for correcting A so as to be small
In the case of reproducing the high-density recording medium DVD, it is deviated from the optical path by a driving device (not shown), and in the case of reproducing the CD, it is arranged in the optical path.

Here, as shown in FIG. 6, the focused spot (main spot) of the main light beam scans the track on which information is recorded, and the focused spots (sub-spots) of both sub-light beams are recorded on the track. Scan so that it slightly straddles both sides of. Since the reflectance outside the track is set to be higher than that of the track, when the main spot is displaced from the track, a difference occurs in the reflection intensity from both sub-spots.

Reference numeral 7 is used when reproducing a high density information recording medium for detecting a reflected light flux (returned light flux) from the information recording medium which is transmitted and diffracted in the first order by the transmission hologram element 4 through the condenser lens 5. It is a 6-division photodetector.

As shown in FIG. 7, this 6-division photodetector 7
Is a four-division photodetector 7a for detecting the reflected light beam related to the main spot and outputting a focus signal and a reproduction signal by the conventionally known astigmatism method, and the conventional reflected light beam related to the sub-spot. The above-mentioned 4 for outputting a tracking error signal by the well-known three-beam tracking method
It has photodetection sections 7b, 7b located on both sides of the divided photodetection section. The photodetectors 7b and 7b independently detect the reflected light fluxes related to the sub-spots, and a tracking error signal corresponding to the difference in the amount of light received between the photodetectors 7b and 7b that occurs according to the track shift of the main spot. Is output.

As shown in FIG. 8, this 6-division photodetector 7
Is 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 divided photodetection section. The p ⁺ type semiconductor region 23 is provided, and the p ⁺ type semiconductor regions 23, n ^{− are provided.}
It has a PIN photodiode corresponding to each of the divided photodetection portions formed by the type semiconductor layer 22 and the n ⁺ type Si substrate 21.

Reference numeral 8 denotes a CD which passes through the condenser lens 5 and the correction lens 6 and detects the reflected light flux (returned light flux) from the information recording medium which is first-order transmitted and diffracted by the transmission hologram element 4.
This is a 6-division photodetector having the same configuration as the 6-division photodetector 7 used for reproducing.

In such an optical pickup device, the hologram element 4 is set so that the utilization efficiency of the light having the wavelength of 635 nm is higher than that of the light having the wavelength of 780 nm. It is possible to suppress a decrease in the strength of

Therefore, as in this embodiment, the 6-division photodetector 7 is used.
Even if it consists of a Si-based photodiode whose sensitivity deteriorates as the wavelength becomes shorter, which is conventionally used,
Since the intensity of the feedback light of 35 nm can be sufficiently secured, the feedback light of the wavelength of 635 nm can be detected with high sensitivity by the 6-division photodetector 7.

On the other hand, the light having a wavelength of 780 nm has a wavelength of 635.
Although the attenuation factor of the hologram element 4 is larger than that of the light of wavelength nm, the 6-division 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 greater the diffraction efficiency of the sub-light beam. As shown in FIG. 9, the light intensity of the focused spot (sub-spot) related to the sub-beam on the information recording medium is greater at the wavelength of 635 nm than at the wavelength of 780 nm. In the case of this embodiment, the intensity of the main spot / the intensity of the sub-spot is about 2 at the wavelength of 635 nm, and the wavelength of 7
At 80 nm, the intensity of the main spot / intensity of the sub-spot is about 4.

In this device, since light having a wavelength of 635 nm is used for the high-density information recording medium DVD having a large track density, that is, a small track pitch, the intensity of the sub-spot becomes large due to the characteristics of the three-division diffraction grating 3. , The S / N of the tracking signal becomes good. Therefore, the high density information recording medium can be reproduced while performing good tracking.

On the other hand, since the CD has a large track width, it is possible to extend the sub-spot over the track over a large area even when using light with a wavelength of 780 nm, and it is possible to perform reproduction while performing good tracking.

The wavelengths of the above-mentioned first and second light sources can be appropriately changed, but the wavelength λ ₁ = 620 to 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 ˜800 nm, both CD and an information recording medium having a track density of about 1.5 to 3 times that of CD can be reproduced 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.

Furthermore, although the optical pickup device using the transmission type three-division diffraction grating has been described above, it is of course applicable 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, but one light detecting means may be commonly used for information recording media having a plurality of recording densities.

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

Further, in this embodiment, the distance between the transparent substrate surface (incident surface) on the reproducing light incident side and the recording surface (reflection surface) is 1.2 mm, and the transparent substrate surface on the reproducing light incident side. The distance from the (incident surface) to the recording surface (reflection surface) is 0.
The track pitch is CD (pitch = 1.
High density information recording medium (DVD) which is about half of 6 μm)
However, the present invention can also reproduce a high-density information recording medium in which the distance from the incident surface to the recording surface is 1.2 mm. Of course, it can be applied to an optical recording medium different from the above.

The present invention can also be applied to tracking servo methods other than the tracking servo method by the three-beam method using a diffraction grating for three divisions, and focus servo methods other than the focus servo method by the 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 favorably reproduce a plurality of information recording media having different recording densities (for example, both CD and DVD).

In the optical pickup device of the present invention,
Since the reproduction light of short wavelength has a smaller attenuation rate in the hologram element, it is possible to suppress the reduction of the intensity of the return light from the information recording medium due to the reproduction light of short wavelength. Therefore, even if the Si-based photodetector is used, it is possible to favorably reproduce the information recording medium having a high recording density which is reproduced by the reproduction light having the short wavelength. Further, the return light from the information recording medium due to the reproduction light of the long wavelength has a larger attenuation rate than the reproduction light of the short wavelength, but since the photodetector has a good sensitivity on the long wavelength side, the reproduction light of the long wavelength is used. An information recording medium having a small recording density to be reproduced can be reproduced well.

As described above, in the optical pickup device of the present invention, a plurality of information recording media having different recording densities (eg CD
Both DVD and DVD) can be reproduced well.

[Brief description of 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 the light of 80 nm, and the light of wavelength 635 nm.

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

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

FIG. 5 is a diagram showing a relationship between a grating depth T of the hologram element and 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 and main spots and sub spots in the optical pickup device of the present 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 6-division photodetector used in this 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 and a sub-spot in the case of m and a wavelength of 635 nm.

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

FIG. 11 is a diagram showing a relationship of relative photosensitivity with respect to wavelength of a conventional Si-based photodetector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st light source 2 2nd light source 3 Transmission type diffraction grating for 3 divisions 4 Transmission type hologram element 5 Condensing lens (condensing means) 6 Correction lens (condensing means) 7, 8 Photodetector

Claims (11)

[Claims] 1. A transmission hologram element as a separating means for obtaining a separated diffracted light beam of a first diffraction order, which is separated from an incident light beam, wherein the hologram element is A transmissive hologram element having a large product of a diffraction efficiency of a separated diffracted light beam and a diffraction efficiency of a second diffracted light beam of a different diffraction order of the separated diffracted light beam. 2. A transmission type hologram element as a separating means for obtaining a separated diffracted light beam of a first diffraction order formed by separating an incident light beam, wherein the hologram element has a wavelength of 7
Compared to the product of the diffraction efficiency of the separated diffracted light flux in the light of 65 to 800 nm and the diffraction efficiency of the diffracted light flux of the second diffraction order having a different order in the light, the wavelengths of 620 to 660 nm The transmission hologram element is characterized in that the product of the diffraction efficiency of the separated diffracted light flux of the light and the diffraction efficiency of the diffracted light flux of the second diffraction order in the light is large. 3. The separated diffracted light beam of the first diffraction order is 1
The transmissive hologram element according to claim 1 or 2, wherein the second-order or -1st-order diffracted light and the second-order diffracted light flux is a 0th-order diffracted light. 4. A plurality of light sources for outputting light of wavelengths corresponding to a plurality of information recording media having different recording densities,
An optical pickup device capable of reproducing the plurality of different information recording media, which is provided in a forward light path from the plurality of light sources, and is separated from the corresponding forward light path from a return light flux from the information recording medium. The hologram element of the transmission type common to the plurality of light sources for obtaining the separated diffracted light flux is provided, and the hologram element has a diffraction efficiency related to a light flux transmitted through the hologram element in the outward optical path as the wavelength is shorter, and An optical pickup device characterized by having a large product with a diffraction efficiency related to a separated diffracted light beam. 5. A plurality of light sources that output light having wavelengths corresponding to a plurality of information recording media having different recording densities, and light fluxes of light output from the plurality of light sources are collected on the corresponding information recording media. Condensing means for emitting light, and the plurality of light sources provided in the forward light path from the plurality of light sources, for obtaining the separated diffracted light flux obtained by separating the return light flux from the information recording medium from the corresponding forward light flux. A transmission-type hologram element common to the light sources, the hologram element having a shorter wavelength has a diffraction efficiency related to a light beam passing through the hologram element in the forward light path and a diffraction efficiency related to the separated diffracted light beam. An optical pickup device characterized by having a large product of 6. A first light source for outputting a 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 which outputs light for reproducing the medium and a forward light path provided from the first and second light sources, which is provided in the forward light path, and the corresponding forward light from the return light flux 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 the optical path, and the hologram element serves as light for reproducing a second information recording medium. In comparison, the light for reproducing the first information recording medium has a property that the product of the diffraction efficiency related to the light beam passing through the hologram element in the forward light path and the diffraction efficiency related to the separated diffracted light beam is large. Optical pickup device. 7. The first light source has wavelengths of 620 to 660.
7. The optical pickup device according to claim 6, wherein the second light source is a semiconductor laser which outputs a light of wavelength nm of 765 to 800 nm. 8. The light flux transmitted in the forward light path is a 0th-order diffracted light, and the separated diffracted light flux is a 1st-order diffracted light or a -1st-order diffracted light.
6. The optical pickup device as described in 6 or 7. 9. The hologram element has a shorter wavelength,
The groove depth of the grating on the hologram surface is set so that the value of the product becomes large.
The optical pickup device according to 6, 7, or 8. 10. A diffraction grating for three divisions is provided in a forward optical path leading 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, further comprising a three-division diffraction grating surface on the other surface facing the one surface.