JP2001060337A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device capable of executing stable optical detection without putting big restriction on the arrangement of an optical system even though an optical recording medium itself has double refractivity. SOLUTION: In an optical pickup device 1A having a phase difference plate 12 to convert polarized state with respect to an emitted light beam from a laser beam source 13 and a return Light beam from an optical recording medium 5 and having a diffraction type element 21 which separates a return light beam from an optical axis forwarding from a laser beam source 13 to an optical recording medium 5 by a difference of polarization state between an emitted light beam and an return Light beam and guides the same to an otical detector 14, a polarization bearing of an emitted light beam from the laser beam source 13 is arranged so as to face to the radial direction of the optical recording medium 5 (double refrection direction of the optical recording medium 5), and at the same time, a bearing of the phase difference plate 12 and an phase quantity are set so that a peak value of signal intensity detected by a detector 14 appears while the double refractive quantity changes from 0 to 1/4 wave length when the double refraction quantity of the optical recording medium 5 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device for reproducing an optical recording medium. More specifically, the present invention relates to an optical system for separating outgoing light from a light source and return light from an optical recording medium.

[0002]

2. Description of the Related Art An optical pickup device for reproducing an optical recording medium such as a compact disk (CD) includes:
A polarization system configured to be able to separate outgoing light and return light by passing outgoing light from a laser light source and return light from an optical recording medium through a 1/4 wavelength phase difference plate (1/4 wavelength plate). Optical pickup devices are known. For example, as shown in FIGS. 10 and 11, a polarizing beam splitter 11 (polarization splitting element), a quarter-wave retardation plate 12, and an objective lens 1 are provided at an intermediate position in an optical path from a laser light source to a photodetector.
6, the light emitted from the laser light source 13 composed of a laser diode passes through the polarizing beam splitter 11 and the quarter-wave retardation plate 12, and then forms a light spot on the recording surface of the optical recording medium 5. Irradiated and returned light from the optical recording medium 5 passes through the quarter-wave retardation plate 12 and the polarization beam splitter 11 again. When the return light from the optical recording medium 5 passes through the quarter-wave retardation plate 12, it is changed into a laser light having a polarization direction different from the polarization direction of the light emitted from the laser light source 13 by 90 °. Light source 13
The light is guided to the photodetector 14 installed in a direction different from the above.

As shown in FIGS. 1 and 2, a diffraction element 21 (hologram element) is disposed between a laser light source 13 and a quarter-wave retardation plate 12 as a polarization separation element. The return light from the optical recording medium 5 may be guided to the photodetector 14 by the pattern element 21 in some cases.

In any of these polarization type optical pickup devices 1A and 1B, as shown in the development views of the optical system and the polarization state of light in FIGS. The emitted linearly polarized light is converted into circularly polarized light by the quarter-wave retarder 12, and the return light (circularly polarized light) from the optical recording medium 5 is converted into the quarter-wave retarder 1.
2 changes the linearly polarized light emitted from the laser light source 13 into linearly polarized light having a polarization direction different from that of the laser light by 90 °, and guides the linearly polarized light to a photodetector 14 installed in a direction different from the laser light source 13.

Accordingly, in the optical pickup devices 1A and 1B of this type, the light emitted from the laser light source 13 can be effectively applied to the optical recording medium 5, and the return light from the optical recording medium 5 can be detected with high efficiency. There is an advantage that it can be guided to the vessel 14.

[0006]

However, in the above description, the effective light amount is 100% when the birefringence δ of the optical recording medium 5 is 0, and the optical recording medium 5 itself has In the case of having the refraction, the birefringence also causes a change in the polarization state of light, so that there is a problem that the effective light amount is lower than 100%.

For example, as shown in FIG. 12C, if the optical recording medium 5 itself has a birefringence δ equivalent to １ ／ wavelength in a reciprocating motion, the optical recording medium 5 may be reflected by the optical recording medium 5. Already becomes linearly polarized light. As a result, the return light reflected by the optical recording medium 5 is again transmitted to the quarter-wave retarder 1.
After passing through 2, the linearly polarized light becomes circularly polarized light, and the effective light amount is reduced to 50%. further,
As shown in FIG. 12D, if the optical recording medium 5 has a birefringence δ corresponding to λ / 2 (λ = wavelength) in a reciprocating manner, the return light is reduced to １ ／. Wavelength retardation plate 12
At this point, the light is changed to linearly polarized light having the same polarization direction as the linearly polarized light emitted from the laser light source 13 at this time. As a result, the return light and the light emitted from the laser light source 13 cannot be separated, and the effective light amount of the light reaching the photodetector 14 is 0%.
It will be.

[0008] The relationship between the birefringence amount δ of the optical recording medium 5 and the detected light amount is represented as a relationship shown by a dotted line L0 in FIG. That is, assuming that the amount of light detected by the photodetector 14 when the amount of birefringence δ of the optical recording medium 5 is 0 is 1, light is not changed until the amount of birefringence δ of the optical recording medium 5 becomes 0 to λ / 2. The signal intensity detected by the detector 14 decreases,
When the birefringence δ of the optical recording medium 5 becomes λ / 2, the signal intensity becomes zero.

Generally, the base of the optical recording medium 5 is manufactured by injection molding, and at this time, the resin flows from the center side of the optical recording medium 5 to the outside in the radial direction.
It is easy to have birefringence that the refractive index differs between the radial direction and the circumferential direction. In order to confirm the current state, when the signal intensity is measured from the center side to the outside in the radial direction of the optical recording medium 5, the characteristic shown in FIG. 13 is obtained as an example having extremely birefringence. There was something. According to the characteristics shown in FIG. 13, the signal intensity is very low at the center of the disk, and shows a minimum value when the signal intensity goes a little outward in the radial direction. Is getting higher. Considering from these results, in the case of the characteristic shown in FIG. 13, the birefringence amount δ is λ / 2 in a region slightly outside from the center in the radial direction, and the birefringence amount δ gradually increases outside in the radial direction from there. It can be seen that it has become smaller. Although this example is an extreme example, it can be assumed that disks manufactured by the same manufacturing method show a similar tendency, and are generally considered to have a certain amount of birefringence in the entire radial direction. Can be

On the other hand, the direction of the anisotropic axis of the retardation plate 12 (hereinafter, simply referred to as the azimuth) is directed to the birefringent direction of the optical recording medium 5 so that the optical recording medium 5 itself and the birefringent direction are oriented. The phase difference plate 12 is configured to act as one phase difference plate, and the phase difference plate 12
In place of the wavelength, it is conceivable to use a material having a phase difference whose phase difference is shifted from １ ／ wavelength by an amount corresponding to the birefringence of the optical recording medium 5 itself.

With this configuration, the phase difference plate 12 and the optical recording medium 5 together function as a quarter-wave phase difference plate, so that the light emitted from the laser light source 13 is Even if 5 has birefringence, after the return light has passed through the retardation plate 12,
Is changed to a linearly polarized light having a polarization direction different from that of the linearly polarized light emitted from by 90 °. Therefore, even if the optical recording medium 5 has birefringence, an optical pickup device with a high effective light amount can be configured.

When such a configuration is adopted, the polarization direction of the laser light emitted from the laser light source 13 and the axial direction of the phase difference plate 12 are usually set at an angle of 45 °. Such setting is generally performed by rotating the laser light source 13 around the emission optical axis and adjusting the angular position thereof. However, such an adjustment method uses the laser light source 13 as shown in FIGS.
When the light detector 14 and the light detector 14 are separate bodies, the laser light source 13
Can be independently rotated around the emission optical axis. However, as in the optical pickup device 1A shown in FIGS. 1 to 3, the laser light source 13 is formed integrally with the photodetector 14 as the light source unit 20. In such a case, there is a problem that the arrangement of the optical system is greatly restricted, for example, such an adjustment method cannot be adopted.

[0013] In view of the above problems, an object of the present invention is to provide:
It is an object of the present invention to provide an optical pickup device capable of performing stable light detection without greatly restricting the arrangement of the optical system even if the optical recording medium itself has birefringence.

[0014]

According to the present invention, there is provided a phase difference plate for converting a polarization state of light emitted from a laser light source and return light from an optical recording medium, and comprising: A polarization separating element that separates the return light from the optical axis toward the optical recording medium from the laser light source based on the polarization state of the return light and guides the return light to a photodetector, wherein the optical recording medium is When the relationship between the amount of birefringence and the signal intensity detected by the detector is measured, the position is determined so that the peak of the signal intensity appears while the amount of birefringence changes from 0 to 波長 wavelength. The phase difference of the phase difference plate and the direction of the anisotropic axis (hereinafter, referred to as the direction of the phase difference plate) are set.

According to the present invention, the retardation of the retardation plate is adjusted so as to absorb the birefringence of the optical recording medium according to the flow direction of the resin when the substrate of the optical recording medium is manufactured by injection molding. And direction. That is, unlike the prior art, regardless of which direction the optical recording medium actually has birefringence, first, the direction of the laser light source is fixed, and the polarization direction of the emitted light emitted from the light source is changed. Assuming that the optical recording medium is fixed, a phase difference plate is formed so that the peak of the signal intensity detected by the photodetector appears before the amount of birefringence of the optical recording medium changes from 0 to 波長 wavelength. Set the phase difference and azimuth of. Here, the amount of birefringence of the manufactured optical recording medium is at most equivalent to １ ／ wavelength. Therefore, in the present invention, if the amount of birefringence of the optical recording medium is between 0 and 波長 wavelength, the return light from the optical recording medium is transmitted regardless of the birefringence direction of the optical recording medium. Since detection can be performed with high intensity, an optical pickup device having a high effective light amount can be configured. Further, the laser light source can be arranged in an optimal state from the viewpoint of design, regardless of which direction the birefringence of the optical recording medium is actually directed. Therefore, even in the optical pickup device in which the laser light source and the detector are integrated, it is possible to perform stable signal detection from any optical recording medium and from any position in the radial direction of the optical recording medium. it can.

In the present invention, the polarized light separating element may convert the first and second linearly polarized light from return light including the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other. It is preferable that each of them has a partial polarization property to be emitted toward the photodetector at a fixed ratio.

According to this structure, the optical recording medium has an amount of birefringence, and the return light incident on the polarization separation element contains both the first linearly polarized light and the second linearly polarized light. However, a part of any linearly polarized light is detected by the photodetector. Therefore, even if all of the linearly polarized light included in the return light is the second linearly polarized light, the signal intensity level is suppressed to some extent, while the return light is reduced due to the birefringence of the optical recording medium. , Even if all the linearly polarized light included in is a first linearly polarized light, a signal is detected with a certain intensity. Here, in the optical pickup device, when detecting the return light, if the detected signal intensity is high to some extent, there is not much met even if the detected signal intensity is higher, and to what level when the detected signal intensity is low. Is more important. However, in the present invention, signal detection can be performed at a certain level due to the partial polarization of the polarization splitting element even under the condition where the signal intensity becomes zero conventionally. Therefore, no matter what birefringence the optical recording medium has, signal detection can be performed reliably. Further, a signal can be reliably detected from any location in the radial direction of the optical recording medium.

The present invention can also be defined as follows. That is, a phase difference plate that converts the polarization state of the emitted light from the laser light source and the return light from the optical recording medium, and travels from the laser light source to the optical recording medium based on the polarization state of the emitted light and the return light. A polarization splitting element for separating the return light from the optical axis and guiding the return light to a photodetector, wherein the phase difference plate has a angle of 50 degrees to 6 degrees with respect to the laser light emitted from the laser light source.
The azimuth is set to be 0 degrees.

In the present invention, the polarized light separating element converts the s-polarized light and the p-polarized light from the return light including the linearly polarized light of the s-polarized light and the p-polarized light whose polarization directions are orthogonal to each other at a fixed ratio. It is preferable to have a partial polarization that separates the light toward the photodetector.

In this case, when the transmittance and the diffractivity for the s-polarized light are Ts and Rs, respectively,
When both the transmittance Ts and the diffraction rate Rs for the s-polarized light are about 0.3 or more, and the transmittance and the diffraction rate for the p-polarized light are Tp and Rp, respectively, the transmission for the p-polarized light is It is preferable that both the rate Tp and the diffraction rate Rp be approximately 0.3 or more.

In the present invention, the ratio of the transmittance Ts to the s-polarized light and the diffraction rate Rs is set to about 0.5: 0.5, and the transmittance Tp and the diffraction rate R to the p-polarized light are set.
It is preferable that the ratio to p is approximately 0.5: 0.5.

In the present invention, it is preferable that the phase difference of the phase difference plate is set within a range of about 20 degrees around 90 degrees.

The present invention can be further defined as follows. That is, a phase difference plate that converts the polarization state of the emitted light from the laser light source and the return light from the optical recording medium, and travels from the laser light source to the optical recording medium based on the polarization state of the emitted light and the return light. A polarization separation element for separating the return light from the optical axis and guiding the return light to a photodetector, wherein the polarization direction of the light emitted from the laser light source is 45 degrees with respect to the radial direction of the optical recording medium. And the azimuth of the phase difference plate is shifted within a range of about 5 degrees to about 15 degrees with respect to 45 degrees.

In the present invention, the phase difference of the phase difference plate is set to approximately 90 degrees, and the azimuth of the phase difference plate is set to 5 degrees.
It is preferable to set within the range of 0 degrees to 60 degrees. For example, it is preferable that the direction of the phase difference plate is set to about 55 degrees.

In the present invention, the phase difference of the phase difference plate is set within a range of about 20 degrees around 90 degrees, and the azimuth of the phase difference plate is set within a range of 50 degrees to 60 degrees. Is preferred. For example, it is preferable to set the azimuth of the retardation plate to about 55 degrees. Also in such a case, the polarization separation element separates the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other toward the photodetector at a fixed ratio. It is preferable to have such partial polarization.

In the present invention, for example, a diffraction-type element can be used as the polarization splitting element. In this diffraction-type element, a diffraction grating may be formed by a polydiacetylene derivative film.

In the present invention, the retardation plate may be formed of a polydiacetylene derivative film or a dielectric film obliquely deposited on a substrate.

The present invention is effective when applied to an optical pickup device in which the polarization splitting element is formed integrally with the retardation plate and the laser light source and the photodetector are integrated as a light source unit. is there.

[0029]

Embodiments of the present invention will be described with reference to the drawings. In the following description, an example in which a diffractive element is used as a polarization splitting element will be described. Nevertheless, the optical pickup device of this embodiment is basically the same as the optical pickup device described with reference to FIGS. Since the configuration is common, the corresponding elements will be described with the same reference numerals.

[Overall Configuration] FIGS. 1 and 2
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing a plan view of a main part of an optical disk drive device to which the present invention is applied, and an explanatory diagram showing an arrangement of an optical system thereof.

As shown in FIGS. 1 and 2, the optical disk drive includes a motor 6 for rotating an optical recording medium 5 and an optical pickup 1A for reading information from the optical recording disk. In the optical pickup device 1A, the optical system includes a laser light source 13 composed of a laser diode and a recording surface 51 of the optical recording medium 5.
Are arranged in this order on the optical path leading to. The polarization type diffractive element 21 (hologram element / polarization splitting element), the phase difference plate 12, the rising mirror 17, and the objective lens 16. Further, in the vicinity of the laser light source 13, a photodetector 14 composed of a photodiode is arranged. For the objective lens 16, a lens actuator 7 for driving the objective lens 16 in the tracking direction and the focusing direction is formed as usual, and the lens actuator 7 and the optical system move in the radial direction of the optical recording medium 5. It is configured on a possible frame 8.

FIGS. 3A and 3B are a perspective view showing the appearance of the light source unit used in the optical pickup device shown in FIG. 2, and a plan view showing the internal structure thereof.

As shown in FIGS. 3A and 3B, the laser light source 13 is formed as a light source unit 20 on the same substrate as the photodetector 14. In this light source unit 20, a plurality of lead frames 22 protrude from a package 23, a laser light source 13 composed of a laser diode is provided on a substrate in the package 23, and a laser beam emitted from the laser light source 13 rises at 90 °. A mirror 24 and a photodetector 14 formed of a split type photodiode formed on the side of the laser light source 13 are formed.

Referring to FIG. 2, a diffraction element 21 has a diffraction grating 210 formed on one surface thereof.
0 diffracts only ordinary light and allows extraordinary light to pass through as it is.
As such a diffractive element 21, various elements to be described later can be used, but an element obtained by subjecting lithium niobate to proton exchange can also be used.

Since this type of diffractive element 21 is well known, a detailed description thereof will be omitted, but a diffraction grating 2 is provided on the surface of a lithium niobate crystal plate which is a birefringent crystal substrate.
10. In this diffraction grating 210, the surface of the lithium niobate crystal plate, which is a birefringent crystal plate,
The proton ion exchange region is formed in a lattice with a constant width and depth. A non-proton ion exchange region in which proton exchange has not been performed remains between adjacent proton ion exchange regions. A dielectric film having a certain thickness, for example, S
An iO ₂ film is formed, and the surface of the proton ion exchange region is exposed as it is. Here, on the surface of the lithium niobate crystal plate, proton ion exchange regions and non-proton ion exchange regions are formed alternately (periodically). The proton ion exchange region of the crystal plate has a refractive index ne for an extraordinary light of 0.
On the contrary, the refractive index no for ordinary light is 0.1.
It decreases by about 04.

Here, a dielectric film having a predetermined thickness is formed on the surface of the non-proton ion exchange region so that the extraordinary light is not affected by the diffraction effect. The phase difference generated when passing through the proton ion exchange region is canceled. The phase of ordinary light advances when passing through the proton ion exchange region. However, the phase is relatively delayed when passing through the non-proton ion exchange region, and further delayed by the dielectric film formed on the surface. Therefore, ordinary light undergoes a diffractive action due to the occurrence of a phase difference when passing through the diffraction element 21. On the other hand, the extraordinary light component, when passing through any of the regions, undergoes the same phase change, and therefore travels straight without passing through the diffraction effect.

The optical pickup device 1 configured as described above
In A, basically, after the laser light is emitted from the laser light source 13, the linearly polarized light that has passed through the diffractive element 21 is
The light is converted into circularly polarized light by the 波長 wavelength phase difference plate 12 and the return light (circularly polarized light) from the optical recording medium 5 is combined with the linearly polarized light emitted from the laser light source 13 by By changing the light into linearly polarized light having different polarization directions, the diffraction element 21 guides the return light to the photodetector 14 installed in a direction different from that of the laser light source 13.

[Structure of Retardation Plate] Such a principle can be established without any problem when the optical recording medium 5 has no birefringence. However, as described above, the optical recording medium used in the optical pickup device 1A is used. The optical recording medium 5 is indicated by an arrow D in FIG. 1 because the resin generally flows in the radial direction from the inner peripheral side when the base is manufactured by injection molding.
As shown by, it has birefringence in the radial direction. Therefore, in the present invention, in order to prevent the detection sensitivity from being lowered due to the birefringence, the following two measures are taken.

FIG. 4 shows the relationship between the amount of birefringence of the optical recording medium and the intensity of the signal detected by the photodetector when the phase difference of the phase difference plate and the azimuth are changed in the optical pickup device shown in FIG. It is a graph which shows a relationship. FIG. 5 shows the relationship between the amount of birefringence of the optical recording medium and the intensity of the signal detected by the photodetector, showing the effect when the first countermeasure described below is taken in the optical pickup device shown in FIG. It is a graph. FIG. 6 is a graph showing the birefringence of the optical recording medium and the signal detected by the photodetector in the optical pickup device shown in FIG. 2 showing the effect obtained when the first countermeasure and the second countermeasure described later are taken. It is a graph which shows the relationship with intensity.

First, the first measure is to design the optical recording medium 5 as having a radial birefringence even if it is not clear which direction the birefringence direction of the optical recording medium 5 is actually. The light source unit 20 is arranged with the posture as set. That is, the light source unit 20 is disposed such that the polarization direction of the laser light emitted from the optical laser light source 13 is oriented at 45 ° with respect to the radial direction of the optical recording medium 5. Further, the diffraction element 21 is provided on the light detector 1 disposed on the light source unit 20.
4 is arranged in a direction suitable for the light receiving position. Next, when the birefringence of the optical recording medium 5 is changed from 0 to 波長 wavelength, it is determined that the birefringence exists in the range of 0 to ０ wavelength. ), During which a peak of the signal intensity detected by the detector 14 appears.
The phase difference Φ and the azimuth θ of the phase difference plate 12 are set.

Under such conditions, the phase difference Φ of the phase difference plate 12
And the azimuth θ, each of the following samples: Sample 1 Phase difference Φ of the phase difference plate 12 = 90 °, azimuth θ = 45 ° Sample 2 Phase difference Φ of the phase difference plate 12 = 98.4 °, azimuth θ = 45 ° Sample 3 Phase difference Φ of phase difference plate 12 = 120 °, azimuth θ = 45 ° Sample 4 Phase difference Φ of phase difference plate 12 = 90 °, azimuth θ = 55.4 ° Sample 5 Phase difference plate 12 Sample 6 The phase difference Φ = 90 °, the azimuth θ = 70 ° Sample 6 The signal intensity was measured using the phase difference plate 12 of the phase difference plate 12 having the phase difference Φ = 98.4 ° and the azimuth θ = 55.4 °.

FIG. 4 shows the results of measuring the signal intensity when the birefringence of the optical recording medium 5 was changed from 0 to 3/4 wavelength using these samples. Here, each sample 1
4 are indicated by lines L1 to L6 in FIG.

As is apparent from the results shown in FIG.
When the phase difference Φ and the azimuth θ of the phase difference plate 12 are changed, the relationship between the amount of birefringence of the optical recording medium 5 and the signal intensity changes.

FIG. 4 shows the characteristics of samples 2 and 3 as indicated by line L2 and line L2, respectively.
As shown by L3, the phase difference plate 1 is set on the basis of the sample 1 corresponding to the conventional example (the characteristics thereof are indicated by a line L1 in FIG. 4).
When only the phase difference Φ of the phase difference plate 12 is changed from 90 ° to 98.4 ° and 120 ° while the azimuth θ of 2 is set to 45 °, the birefringence amount of the optical recording medium 5 becomes 0 to 1/4
It can be seen that no signal intensity peak appears during the change to the wavelength.

Further, as shown by the line L5 in FIG. 4, the phase difference plate 1
In the case where the azimuth θ of the phase difference plate 12 is changed to 70 ° while the phase difference Φ of 2 is set to 90 °, while the amount of birefringence of the optical recording medium 5 changes from 0 to 波長 wavelength, Although the peak of the signal strength appears, the signal strength decreases.

On the other hand, FIG.
As shown by reference numeral 4, when the azimuth θ of the phase difference plate 12 is set to 55.4 ° while the phase difference Φ of the phase difference plate 12 is set to 90 ° with respect to the sample 1 which is the conventional example. The peak of the signal strength appears while the amount of birefringence of the optical recording medium 5 changes from 0 to 波長 wavelength, and a high signal strength is obtained.

As shown by the line L6 in FIG. 4, the phase difference plate 1
2 is set to 55.4 ° and the phase difference Φ of the phase difference plate 12 is set to 98.4 °, the birefringence of the optical recording medium 5 is from 0 to １ ／ wavelength. The peak of the signal strength appears during the change, and the signal strength is also high. Moreover, in the sample 6, the birefringence, which is expected to be the most likely for the optical recording medium 5, shows a signal intensity peak at a position of 1/8 wavelength. Therefore, when the optical pickup device 1B is configured to correspond to the sample 6, FIG.
As shown by comparing the data of Sample 1 which is a conventional example and the data of Sample 6 which is an optimal embodiment of the present invention,
Since a peak appears in the signal intensity between the birefringence of the optical recording medium 5 and the wavelength of 0 to 波長 wavelength, the birefringence of the optical recording medium 5 is larger than the range of 0 to １ ／ wavelength. Within a narrow condition range, it is possible to prevent an error from occurring due to the optical recording medium 5 having birefringence.

As described above, the range in which the signal intensity peaks and the signal intensity is high while the amount of birefringence of the optical recording medium 5 changes from 0 to 波長 wavelength is the phase difference. The azimuth θ of the plate 12 is set in the range of 50 ° to 60 °, and the phase difference of the phase difference plate is about 2 degrees around 90 degrees.
This is the case where the angle is set to 0 degree.

However, even in the optical pickup device 1A thus configured, as shown in FIG.
There is a condition in which the signal intensity becomes 0 while the birefringence of changes from 波長 wavelength to ／ wavelength. Generally, it is considered that the birefringence of the optical recording medium 5 is in a range from 0 to 波長 wavelength, but the birefringence of the optical recording medium 5 is 1 /
The following countermeasures may be taken so as to be able to cope with the case where the wavelength is between 2 wavelengths and 3/4 wavelength.

The second countermeasure in the present invention is that the diffraction type element 21 used as the polarization splitting element is converted into s-polarized light (first linearly polarized light) and p-polarized light (first linearly polarized light) whose polarization directions are orthogonal to each other. (2 linearly polarized light), the s-polarized light and the p-polarized light are separated toward the photodetector 14 at a constant ratio from the return light including the linearly polarized light.

That is, in the diffractive element 21, when the transmittance and the diffraction rate for the s-polarized light are Ts and Rs, the ratio between the transmittance Ts and the diffraction rate Rs for the s-polarized light is 0: 1. Is the transmittance T for s-polarized light.
The ratio between s and the diffraction index Rs is set to 0.5: 0.5. Conversely, when the transmittance and the diffraction rate for the p-polarized light are Tp and Rp, the ratio of the transmittance Tp to the p-polarized light and the diffraction rate Rp of 1: 0 is changed to the p-polarized light. The ratio between the transmittance Tp and the diffraction rate Rp is set to 0.5: 0.5.

For example, as shown in FIGS. 10 and 11, when a polarization beam splitter 11 composed of a cubic prism is used as a polarization separation element of an optical pickup device, the transmittance and reflectance for s-polarized light are set to T.
s and Rs, the transmittance Ts for s-polarized light
And the ratio of the reflectance Rs to 0.5: 0.5. Conversely, when the transmittance and the reflectance for the p-polarized light are Tp and Rp, the ratio between the transmittance Tp and the reflectance Rp for the p-polarized light is 0.5: 0.5.

Note that the ratio of the transmittance T to the reflectance R is not more than 0.1.
Although it is preferable to make them equal, such as 5: 0.5,
Even if they are not the same, it is preferable to secure a certain ratio, that is, both of them are about 0.3 or more according to the necessity of design.

Accordingly, the optical pickup device 1A of the present embodiment
6, both s-polarized light and p-polarized light are included in the return light incident on the diffractive element 14 due to the birefringence of the optical recording medium 5, as indicated by the solid line L7 in FIG. Some of these polarized lights enter the photodetector 14, respectively. Therefore, when the polarized light included in the return light is, for example, all s-polarized light, the level of the signal intensity is suppressed to some extent, but instead of the return due to the birefringence of the optical recording medium 5. Even if the polarized light included in the light is all p-polarized light, the signal can be detected with a certain degree of intensity. Here, as for the optical pickup device 1A, when detecting the return light, there is no problem if the detected signal intensity is high to some extent.

Therefore, in the present embodiment, a signal can be detected at a somewhat high level even under the condition that the signal strength becomes zero in the related art. Therefore, even when only p-polarized light is included in the return light due to the birefringence of the optical recording medium 5, a certain level or more is obtained due to the partial polarization of the diffractive element 21. Can always be detected. Therefore, no matter what birefringence the optical recording medium 5 has, signal detection can be reliably performed.

[Other Embodiments] In the above embodiment, the diffraction element 21 as the polarization splitting element and the retardation plate 1
2 was used separately, but as shown in FIG. 7 (A), a diffraction element 21 or a cubic prism-shaped polarizing beam splitter 11 shown in FIGS. 10 and 11 was used.
For example, a composite optical element 25 integrated with the retardation plate 12 may be used as the polarization separating element. With this configuration, the diffraction element 21 or the cubic prism-shaped polarization beam splitter 11 and the retardation plate 12 may be handled as the composite optical element 25, so that the efficiency of the assembly work of the optical pickup device can be increased and the diffraction type element can be used. In forming such a composite optical element 25 capable of increasing the efficiency of adjusting the birefringence direction of the element 21 and the azimuth of the phase difference plate 12 and reducing the size of components, the diffraction optical element 21 and the like are used. There is a method in which the polarization separation element and the retardation plate 12 are formed separately, and then bonded with an adhesive.

Further, as described below, if the complex optical element 25 is formed by forming the retardation plate 12 on the diffraction element 21 or the polarizing beam splitter 11 in the form of a cubic prism, an optical pickup device can be assembled. In addition to increasing the efficiency of work, increasing the efficiency of adjusting the birefringence direction of the diffraction element 21 and the orientation of the phase difference plate 12, and reducing the size of parts,
Part costs can also be reduced.

In order to manufacture such a composite optical element 25, for example, as shown in FIGS. 7B and 7C, the side of the diffractive element 21 on which the diffraction grating 210 is formed. A dielectric film 121 is obliquely vapor-deposited on the surface 21b opposite to the above, and the phase difference plate 12 is formed by the dielectric film 121. In this case, an inorganic oxide such as tantalum pentoxide, tungsten oxide, bismuth trioxide, or titanium oxide is obliquely vapor-deposited from a direction indicated by an arrow A that forms a predetermined angle with respect to a normal direction H of the diffraction element 21. The birefringent film 121 made of a dielectric film formed as described above is formed, for example, in the normal direction H.
The angle formed between the birefringent film and the crystal axis of the birefringent film is set to, for example, 70 °, and the film thickness is adjusted so that the birefringent film 121 obliquely deposited has an optical function as the 波長 wavelength retardation plate 21. Fulfill. Further, by adjusting the angle between the normal direction H and the crystal axis of the birefringent film and the film thickness, various retardation plates 21 can be formed not only for the quarter-wave plate. In this case, the amount of phase difference can be controlled by the deposited film thickness, and the azimuth can be controlled by the deposition direction.

In order to form the retardation plate 12 on the diffraction element 21, a polydiacetylene derivative film may be used instead of oblique deposition of a dielectric film. In this case,
For example, as shown in FIG. 8A, for example, a PET film (polyethylene terephthalate film) 125 or a polyimide film is applied to the back surface side of the diffraction element 21 so as to have a predetermined thickness, and then a polyester or the like is applied. Rubbing treatment with the fibers of Next, a polydiacetylene derivative film 122 having birefringence is formed on the surface of the PET film 125 by a vacuum evaporation method. Here, as can be seen from FIG. 8A, the polydiacetylene derivative film 122 has a X direction according to the rubbing direction with respect to the PET film 125.
It is oriented in the −Y plane, and the main chain direction (orientation direction) is in the Y-axis direction as shown by the arrow YH. The polydiacetylene derivative film 122 formed in this manner has birefringence, and the refractive index (ne) in the orientation direction YH is different from the refractive index (no) in the direction YI perpendicular to the orientation direction YH. Here, the film thickness d of the polydiacetylene derivative film 5 is
For example, if it is determined to satisfy the following equation: 2πΔnd / λ = π / 2, the quarter-wave retarder 12 can be formed.

In the above equation, λ and Δn are the wavelength of light incident on the polydiacetylene derivative film 5, respectively.
It is a difference in refractive index (ne-no) between extraordinary light and ordinary light. The extraordinary light is a polarized light that vibrates in the orientation direction YH of the polydiacetylene derivative film 5, and the ordinary light is the polydiacetylene derivative film 5
Is a polarized light that oscillates in a direction YI perpendicular to the alignment direction YH.

Such a polydiacetylene derivative film 12
In FIG. 8, as shown in FIG. 8B, the orientation direction YH of the polydiacetylene derivative film 5 is X′-Y with respect to linearly polarized light traveling while vibrating in the Y′-axis direction in the Y′-Z ′ plane. '
When arranged so as to be inclined at 45 degrees with respect to the Y ′ axis in the plane, the linearly polarized light incident on the phase difference plate 12 is between the component of the orientation direction YH and the component perpendicular to the orientation direction YH. A quarter-wave phase difference is generated and the light is emitted as circularly polarized light. When this circularly polarized light is reflected by the optical recording medium and passes through the polydiacetylene derivative film 122 again, the circularly polarized light is emitted as linearly polarized light having a 90-degree vibration direction different from that of the firstly incident linearly polarized light. That is, the phase difference plate 12 of the present example functions as a 波長 wavelength plate. Also, by adjusting the film thickness,
Various retardation plates can also be formed. In the retardation plate 12 thus formed, the azimuth can be controlled by the rubbing direction, and the phase amount can be controlled by the film thickness.

In forming the diffraction element 15, a polydiacetylene derivative film may be used. In this case, first, as shown in FIG.
After a PET film (polyethylene terephthalate film) 212 or a polyimide film is applied to a predetermined thickness on the rear surface side of 2, a rubbing treatment is performed with a fiber such as polyester. Next, as shown in FIG. 9B, a polydiacetylene derivative film 213 is formed by vacuum-depositing a diacetylene monomer on the surface of the PET film 212 and then irradiating ultraviolet light to polymerize the monomer. At this time, the polydiacetylene derivative film 213
The ET film 212 is spontaneously aligned along the rubbing direction. Next, as shown in FIG. 9C, a light-shielding mask 214 is provided on the surface of the polydiacetylene derivative film 213. The light-shielding mask 214 is formed from a material having an ultraviolet blocking property such as chrome, and a fine periodic lattice pattern is formed as the ultraviolet transmitting portion 214a. After disposing the light-shielding mask 214, high-intensity ultraviolet rays 215 are irradiated from the surface side. As a result, the irradiated light
Since the light passes through the ultraviolet transmitting portion 214 a of the light-shielding mask 214, the surface of the polydiacetylene derivative film 213 is exposed to a region corresponding to the fine periodic lattice pattern formed on the light-shielding mask 214. Here, the polydiacetylene derivative film 213 was colored,
Is irradiated, the irradiated portion is decomposed and becomes transparent.
Further, the region irradiated with the ultraviolet rays 215 loses the birefringence and becomes isotropic having a refractive index substantially equal to the ordinary light refractive index in the colored portion. Therefore, if the film thickness of the transparent portion is equal to the film thickness of the colored portion, a diffraction grating having perfect polarization can be obtained.

Here, when the irradiation amount of the ultraviolet ray is adjusted, the transparent portion (the region irradiated with the ultraviolet ray) shrinks and becomes thinner than the colored portion (the region not irradiated with the ultraviolet ray). As a result, as shown in FIG.
3b forms a periodic grating. Therefore, even when ordinary light is incident, diffraction occurs due to the steps on the surface.
The diffraction element 21 does not have perfect polarization characteristics and has partial polarization.

In the diffraction element 21 thus formed,
By adjusting the irradiation amount of the ultraviolet light, it is possible to make the film completely polarized or partially polarized. Also, when changing the diffraction characteristic with respect to ordinary light, it can be handled by changing the process conditions. Furthermore, it is possible to form a very fine diffraction grating simply by changing the exposure pattern without using a process such as etching.
In addition, it is possible to manufacture the grating element 21 having a high degree of freedom in designing the layout of the optical system.

In the above embodiment, the optical pickup device 1A using the diffractive element 21 as the polarization splitting element has been described as an example. However, as shown in FIGS. 9 and 10, a cubic prism-shaped polarizing beam splitter 11 is used. The present invention may be applied to an optical pickup device 1B using as a polarization separation element.

[0066]

As described above, in the optical pickup device according to the present invention, the azimuth of the retardation plate does not always need to be set to the direction of the birefringence of the optical recording medium. The phase difference and azimuth of the phase difference plate are set so that the peak of the signal intensity at the photodetector appears while the amount of refraction changes from 0 to 波長 wavelength.

The optical recording medium is irradiated with the laser light emitted from the laser light source through a phase difference plate having an azimuth of 50 to 60 degrees.

Further, the polarization direction of the light emitted from the laser light source is arranged so as to be at 45 ° to the radial direction of the optical recording medium, and the azimuth of the phase difference plate is set at an azimuth of 45 °. To be shifted in the range of about 5 to 15 degrees.

Therefore, in the present invention, if the amount of birefringence of the optical recording medium is between 0 and 波長 wavelength, the direction of the retardation plate is oriented in the direction of birefringence of the optical recording medium. Even without this, the return light from the recording medium can be detected with a high intensity, so that an optical pickup device with a high effective light amount can be configured. Also, regardless of which direction the optical recording medium is actually oriented in birefringence, the light source can be arranged in an optimal state from the viewpoint of design and the like. Therefore,
Even in an optical pickup device or the like in which a light source and a detector are integrated, stable signal detection can be performed by absorbing the birefringence of the optical recording medium.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a planar arrangement of a main part of an optical disk drive using a diffraction element as a polarization splitting element of an optical pickup device.

FIG. 2 is an explanatory view schematically showing an arrangement of an optical system of an optical pickup device used in the optical disk drive shown in FIG.

FIGS. 3A and 3B are a perspective view showing an appearance of a light source unit used in the optical pickup device shown in FIG. 2 and a plan view showing an internal structure thereof, respectively.

4 shows the relationship between the amount of birefringence of an optical recording medium and the intensity of a signal detected by a photodetector when the phase difference amount and azimuth of a phase difference plate are changed in the optical pickup device shown in FIG. It is a graph.

FIG. 5 shows a first example of the optical pickup device shown in FIG.
5 is a graph showing the relationship between the amount of birefringence of an optical recording medium and the intensity of a signal detected by a photodetector, showing the effect of taking the above measure.

FIG. 6 shows a first example of the optical pickup device shown in FIG.
9 is a graph showing the relationship between the amount of birefringence of an optical recording medium and the intensity of a signal detected by a photodetector, showing the effects obtained when the above measures and the second measure are taken.

FIGS. 7A, 7B, and 7C are explanatory diagrams each showing a main part of an optical system of an optical pickup device using a composite optical element obtained by integrating a retardation plate and a diffraction element, FIG. 3 is an explanatory view showing a configuration of the composite optical element, and an explanatory view showing a state in which a dielectric film is obliquely deposited in order to manufacture the composite optical element.

FIGS. 8A and 8B are explanatory views showing the configuration of a composite optical element in which a retardation plate using a polydiacetylene attracting film and a diffraction element are integrated, and FIGS. It is explanatory drawing which shows a principle.

FIG. 9 (A), (B), (C), (D)
FIG. 7 is a process cross-sectional view for manufacturing a composite optical element by forming a partially polarizing diffractive element using a polydiacetylene derivative film on a retardation plate.

FIG. 10 is an explanatory diagram schematically showing a planar arrangement of a main part of an optical disc drive device using a cubic prism-shaped polarization beam splitter as a polarization separation element of the optical pickup device.

11 is an explanatory diagram schematically showing an arrangement of an optical system of an optical pickup device used in the optical disk drive shown in FIG.

12A is a development view of an optical system included in an optical pickup device, and FIGS. 12B to 12D schematically show a reciprocating birefringence amount and a polarization state of light of the optical recording medium itself. FIG.

FIG. 13 is a graph showing the relationship between the radial position of an optical recording medium and the intensity of a signal detected by a photodetector therefrom in a conventional optical pickup device.

[Explanation of symbols]

 Reference Signs List 1A, 1B optical pickup device 5 optical recording medium 11 polarization beam splitter polarization separation element) 12 retardation plate 13 laser light source 14 photodetector 16 objective lens 20 light source unit 21 diffractive element (polarization separation element) 25 composite optical element 121 oblique Evaporated birefringent film 122,213 Polydiacetylene inducer film

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01L 31/0232 H01L 31/12 G 31/12 H01S 5/022 H01S 5/022 H01L 31/02 D

Claims (16)

[Claims] 1. A phase difference plate for converting a polarization state of light emitted from a laser light source and return light from an optical recording medium, and optical recording from the laser light source based on polarization states of the emitted light and the return light. A polarization separating element for separating the return light from the optical axis toward the medium and guiding the return light to a photodetector, wherein a birefringence amount of the optical recording medium and a signal intensity detected by the detector are When the relationship is measured, the birefringence amount is 0
An optical pickup device, wherein the phase difference of the phase difference plate and the direction of the anisotropic axis are set so that the peak of the signal intensity appears while the wavelength changes from to 波長 wavelength. 2. The polarization separation element according to claim 1, wherein the polarization separation element converts the return light including the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other.
And an optical pickup device having partial polarization in which both the first and second linearly polarized lights are emitted toward the photodetector at a constant ratio. 3. A phase difference plate for converting polarization states of light emitted from a laser light source and return light from an optical recording medium, and optical recording from the laser light source based on polarization states of the emitted light and the return light. A polarization separation element that separates the return light from the optical axis toward the medium and guides the return light to a photodetector, wherein the phase difference plate is at an angle of 50 degrees with respect to the laser light emitted from the laser light source. An optical pickup device which is set to have an azimuth of 60 degrees. 4. The polarization separation element according to claim 3, wherein the polarization separation element converts the s-polarized light and the p-polarized light from return light including linearly-polarized light of s-polarized light and p-polarized light whose polarization directions are orthogonal to each other. An optical pickup device having a partial polarization property of separating light toward the photodetector at a constant rate. 5. In claim 4, when the transmittance and the diffraction rate for the s-polarized light are Ts and Rs, respectively, both the transmittance Ts and the diffraction rate Rs for the s-polarized light are about 0.3 or more. And the transmittance and the diffractivity for the p-polarized light are Tp and R, respectively.
An optical pickup device, wherein when p is set, both the transmittance Tp and the diffractivity Rp for the p-polarized light are set to about 0.3 or more. 6. The transmittance according to claim 5, wherein the ratio between the transmittance Ts for the s-polarized light and the diffraction rate Rs is approximately 0.5: 0.5, and the transmittance Tp and the diffraction rate Rp for the p-polarized light. An optical pickup device having a ratio of approximately 0.5: 0.5. 7. The method according to claim 3, wherein
An optical pickup device, wherein the phase difference of the phase difference plate is set within a range of about 20 degrees around 90 degrees. 8. A phase difference plate for converting polarization states of light emitted from a laser light source and return light from an optical recording medium, and the optical recording from the laser light source based on the polarization states of the emitted light and the return light. A polarization separation element that separates the return light from the optical axis toward the medium and guides the return light to a photodetector, wherein the polarization direction of the light emitted from the laser light source is set with respect to the radial direction of the optical recording medium. An optical pickup device wherein the azimuth of the phase difference plate is shifted within a range of about 5 degrees to about 15 degrees with respect to 45 degrees. 9. The light according to claim 8, wherein the phase difference of the phase difference plate is set to approximately 90 degrees, and the azimuth of the phase difference plate is set within a range of 50 degrees to 60 degrees. Pickup device. 10. The optical pickup device according to claim 9, wherein the azimuth of the phase difference plate is set to about 55 degrees. 11. The phase difference plate according to claim 8, wherein the phase difference of the phase difference plate is set within a range of about 20 degrees around 90 degrees, and the azimuth of the phase difference plate is set within a range of 50 degrees to 60 degrees. An optical pickup device characterized in that: 12. The optical pickup device according to claim 11, wherein the azimuth of the phase difference plate is set to about 55 degrees. 13. The polarization separation element according to claim 12, wherein the polarization separation element directs the first linearly polarized light and the second linearly polarized light having the polarization directions orthogonal to each other to the photodetector at a fixed ratio. An optical pickup device having partial polarization so as to be separated. 14. The light according to claim 1, wherein the polarization separation element is a diffraction element, and the diffraction grating of the diffraction element is formed of a polydiacetylene derivative film. Pickup device. 15. The optical pickup device according to claim 1, wherein the retardation plate is formed of one of a dielectric film and a polydiacetylene derivative film obliquely deposited. . 16. The polarization separation element according to claim 1, wherein the polarization separation element is formed integrally with the retardation plate, and the laser light source and the photodetector are integrated as a light source unit. An optical pickup device, characterized in that: