JPH09167374A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mass-produce high performance and highly reliable optical heads by making the optical film of the beam splitter of each optical head capable of dealing with an optical disk having different double refraction of a specified film material, a layer number and a substrate material. SOLUTION: A light emitted from a semiconductor laser 21 is reflected by a beam splitter 22, made a light beam 24 by a condenser lens 23, passed through an objective lens 7 and thereby, light spots 9a and 9b are formed in an optical disk 10a. A reflected light 27C is passed through the beam splitter 22 and received by a photodetector 29. The optical film surface 22a of the beam splitter 22 reflects an S polarized light with power efficiency E1, passes a P polarized light with power efficiency E2 and a TiO2 film is formed on a glass substrate with E27E1 and E170.5. This optical head is capable of dealing with optical disks having double refraction different from each other and mass-produced to have high performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of an optical disk device for optically recording or reproducing information on an optical disk.

[0002]

2. Description of the Related Art An objective lens used in an optical head is designed in consideration of the thickness of an optical disk. For an optical disk having a thickness different from the designed value, spherical aberration occurs and the focusing performance deteriorates, and recording is performed. It becomes difficult to reproduce. Conventionally, compact discs (CDs), video discs, magneto-optical discs for data, etc. all have a thickness of 1.2 mm. Therefore, it is possible to record / reproduce different types of optical disks with one optical head.

On the other hand, in recent years, in order to increase the density of optical discs, it has been considered to increase the numerical aperture of the objective lens. When the numerical aperture of the objective lens is increased, the optical resolution is improved and the frequency band for recording / reproducing can be widened, but there is a problem that coma aberration increases when the optical disc is tilted. Due to the warp of the optical disc and the inclination when the optical disc is mounted, the optical disc has an inclination with respect to the objective lens, and coma aberration occurs in the converged light spot. Even if the numerical aperture is increased due to the coma aberration, the convergence performance is not improved. Therefore, to prevent coma from increasing even if the numerical aperture of the objective lens is increased,
The thickness of the optical disk is reduced to 0.6 mm to increase the density. However, when the optical disc is made thin, the objective lens for recording and reproducing the optical disc cannot reproduce the conventional optical disc, and the compatibility with the conventional optical disc cannot be maintained.

Therefore, a bifocal optical head as shown in FIG. 20 has been proposed. In FIG. 20, the radiant light flux emitted from the semiconductor laser 41 is condensed by the condenser lens 42 to become a parallel light beam 43. This light beam 43
Is configured to enter the polarization beam splitter 44 as P-polarized light. Therefore, almost all of the light beam 43 incident on the polarization beam splitter 44 passes through here,
After being converted into substantially circularly polarized light by the quarter-wave plate 45, the optical path is bent by the reflection mirror 46 and the light enters the objective lens 7. A hologram 8 is formed on the inner peripheral surface of the incident surface of the objective lens 7. This hologram 8 is a blazed hologram so that high-order diffracted light is suppressed. Therefore, the light passing through the hologram 8 is mainly divided into first-order diffracted light diffracted by this hologram and zero-order diffracted light that is not affected by the diffraction. The 1st-order diffracted light is narrowed down by the objective lens 7 to form a light spot 9a, and the 0th-order diffracted light is narrowed down by the objective lens 7 together with the light passing through the outer peripheral portion where the hologram 8 is not formed to form a light spot 9b. Light spot 9a is 1.2 mm
The optical spot 10b is for reproducing the thick optical disk 10a, and the light spot 9b is for recording and reproducing the 0.6 mm thick optical disk 10b. FIG. 21A shows the optical disc 10.
21A shows a state where the light spot 9a is converged on the information recording medium surface, and FIG. 21B shows a state where the light spot 9b is converged on the information recording medium surface of the optical disc 10b. When reproducing an optical disk 10a having a thickness of 1.2 mm, the light spot 9a is controlled so as to be formed on the recording medium surface of the optical disk 10a, and when reproducing an optical disk 10b having a thickness of 0.6 mm, the By controlling the spots 9b to be formed on the recording medium surface of the optical disc 10b, the optical discs 10a, 10 having different thicknesses can be formed.
b can be recorded and reproduced with one objective lens. Note that FIG. 20 shows a state in which the light spot 9a is converged on the optical disc 10a. Next, the reflected light 47a reflected from the optical disk 10a or 10b
Alternatively, 47b (not shown) passes through the objective lens 7, the hologram 8, the reflection mirror 46, and the quarter-wave plate 45 again and enters the polarization beam splitter 44. If the optical disk has no birefringence, the reflected light 47a, 47b is 1/4
Since it becomes S-polarized light by the action of the wave plate 45, it is reflected by the polarization beam splitter 44, passes through the diaphragm lens 48 and the cylindrical lens 49, and is received by the photodetector 50. The photodetector 50 is configured to detect the reproduction signal, the focus control signal by the astigmatism method, and the tracking control signal by the phase difference method.

In the above structure, the optical disk 10b having a thickness of 0.6 mm is a high density optical disk and is manufactured so as to have a small birefringence. This high-density optical disc includes a two-layer disc that reproduces two faces from one side through a layer of several tens of μm, and the amount of reflected light is reduced, so that a larger amount of light is required than when reproducing CD on only one face. Further, it is difficult to reduce the light quantity in order to secure the SN ratio in the high frequency range. Therefore, in an optical head used for a high-density optical disc, a polarization beam splitter is usually used for separating reflected light and irradiation light to minimize the light amount loss due to the separation. On the other hand, the 1.2 mm-thick optical disc 10a is a CD or the like, and a disc having large nonstandard birefringence is on the market. In a CD that does not require the same amount of light as a high-density optical disc, the reflected light and the irradiation light are separated by a half mirror, and the light amount loss associated with the separation is large, but it is not affected by birefringence. The optical disc 10a can also be used. However, in a common optical head that reproduces a high-density optical disc and a CD with one optical head, there are conflicting problems of securing a sufficient amount of light for the high-density optical disc and dealing with a large birefringence for the CD. Need to respond. In such an optical head, when the optical disk 10a has a large birefringence, the reflected light 47a
Most of them pass through the polarization beam splitter 44, and the amount of light reaching the photodetector 50 decreases, which makes reproduction difficult.

On the other hand, in order to solve the above problems, by providing means for splitting the light flux from the light source, the light of the same polarization direction as the light of the light source is split at a fixed ratio, and the light of the light source is split. Most of the light in the polarization direction orthogonal to the light is transmitted to the photodetector, so that the photodetector can receive the light even when the birefringence of the optical disk is ½ wavelength. That is, due to the combination of the birefringence of the quarter-wave plate and the optical disk, the light beam splitting means transmits the light to the photodetector even if the light from the light source and the reflected light from the optical disk have the same polarization direction. be able to. Furthermore, when the birefringence is small as in a high density optical disc, most of the reflected light from the optical disc can be received by the photodetector, and the reflected light that reaches the photodetector as in the case of using a half mirror. It does not become half, and the light utilization efficiency can be improved. A specific example will be described below.

In FIG. 22, those having the same numbers as those in FIG. 20 perform the same operation. The emitted light beam emitted from the semiconductor laser 1 is condensed by the condenser lens 2 into a parallel light beam 3, which is incident on the beam splitter 4 which is a light beam splitting unit as P-polarized light. This beam splitter 4
Suppose that there is no power loss due to division, the P-polarized light transmits with a power efficiency of E1 and a power efficiency of (1-E
An optical film surface 4a is formed which is reflected by 1) but is reflected by the power efficiency E2 for S-polarized light. Therefore, in the P-polarized light beam 3 that has entered here, E1 passes through it,
The ordinary light and the extraordinary light pass through a quarter-wave plate 5 that converts the light into a substantially circularly polarized light with a quarter-wave phase difference, and the light path is bent by a reflection mirror 6 to enter the objective lens 7. This objective lens 7 has the same configuration as that of the conventional example, and a blazed hologram 8 is formed on the inner peripheral portion of the incident surface of the objective lens 7. The light passing through the hologram 8 is mainly divided into first-order diffracted light and zero-order diffracted light, and the first-order diffracted light is narrowed down by the objective lens 7 to form a light spot 9a.
The 0th-order diffracted light is narrowed down by the objective lens 7 together with the light on the outer peripheral portion of the lens on which the hologram is not formed to form a light spot 9b. The light spot 9a is for reproducing the 1.2 mm thick optical disk 10a.
b is for recording / reproducing an optical disc 10b (not shown) having a thickness of 0.6 mm. FIG. 22 shows the optical disk 10.
The state where the light spot 9a is converged on the information recording medium surface of a is shown. As shown in FIG. 21A, the thickness 1.2
When reproducing the optical disc 10a having a thickness of 10 mm, the light spot 9a is controlled so as to be formed on the surface of the recording medium of the optical disc 10a, and the optical disc 10b having a thickness of 0.6 mm is recorded and reproduced as shown in FIG. If the light spot 9
b is formed on the surface of the recording medium of the optical disc 10b, the optical discs 10 having different thicknesses are controlled.
It is possible to record and reproduce a and 10b with one objective lens.

Next, the reflected light 11a or 11b reflected from the optical disk 10a or 10b passes through the objective lens 7, the hologram 8, the reflection mirror 6 and the quarter-wave plate 5 again and enters the beam splitter 4. If the optical disk has no birefringence, the reflected light 11a, 11b is 1
It becomes S-polarized light by the action of the / 4 wavelength plate 5, is reflected by the beam splitter 4, passes through the diaphragm lens 12 and the cylindrical lens 13, and is received by the photodetector 14. The photodetector 14 is configured to detect a reproduction signal, a focus control signal by the astigmatism method, and a tracking control signal by the phase difference method.

As described above, the beam splitter 4 has a P
When the polarized light is transmitted with the power efficiency E1, there is almost no power loss due to the division on the optical film surface 4a formed of the dielectric multilayer film, so that the reflection of the P polarized light has the power efficiency (1
-E1). As the birefringence of the optical disc 10a, the phase difference between the fast axis and the slow axis is set to 2φ °, and the light transmission rate η of the beam splitter 4 is set as a ratio of transmitting light from the light source to the optical disc and reflecting light from the optical disc. Expressed as the product of the ratios transmitted to the detector, η = SQR ((E1 × E2 × cosφ) 2+ (E1 × (1-E1) × sin
φ) 2). However, SQR is the square root.

In this formula, φ = 0 when there is no birefringence as in a high density optical disk, so that the light transmittance η1 is E1 ×
E2, non-standard compact disc with 1 birefringence
At 80 °, φ = 90 °, so the optical transmissivity η2 is E1
X (1-E1). The maximum η1 is E1 and E2
Both are 1 and η 2 is maximum when E 2 is 0.5, so E 2 is 1 and E 1 is 0.5 or more and 1 or less.

That is, although some compact discs have a large birefringence outside the standard, E2> E1, E1>
By providing the beam splitter 4 satisfying the condition of 0.5, the reproduction output can be sufficiently secured, and the optical disc 10 made with a small birefringence like a high density optical disc.
In b, a sufficient amount of light can be obtained to secure the SN ratio. Therefore, it is possible to solve the problem of the decrease in the amount of light when the half mirror is used and the problem of birefringence when the polarization beam splitter is used.

Next, the second example is shown below. In FIG. 23, the light emitted from the semiconductor laser 21 is incident as S-polarized light on a flat plate-shaped beam splitter 22 which is a light beam splitting means. This beam splitter 22 has a power efficiency E for S-polarized light, assuming that there is no power loss due to division.
It is reflected at 1 and transmitted at power efficiency (1-E1), but P
The optical film surface 22 that transmits the polarized light with power efficiency E2
a is formed. Therefore, the light from the light source is reflected by E1 and condensed by the condenser lens 23 to become a light beam 24.
Others are the same as those in FIG. 22, and two spots 9a and 9b are formed through the quarter-wave plate 25, the reflection mirror 26, the hologram 8 and the objective lens 7. 21 (a) and FIG.
When reproducing an optical disk 10a having a thickness of 1.2 mm as in 1 (b), the light spot 9a is controlled so as to be on the recording medium surface of the optical disk 10a, and the optical disk 10b having a thickness of 0.6 mm is recorded and reproduced. In this case, the optical spots 9b are controlled so as to come to the recording medium surface of the optical disc 10b, so that the optical discs 10a and 10b having different thicknesses are formed.
Is recorded and reproduced with one objective lens. Optical disk 1
The reflected light 27a reflected from 0a is again reflected by the objective lens 7,
Hologram 8, reflection mirror 26 and quarter wave plate 25
And then enters the beam splitter 22. This reflected light 27a becomes P-polarized light by the action of the quarter-wave plate 25, passes through the beam splitter 22, and becomes a concave lens 28.
Then, the light is received by the detector 29. In this case, if the optical disk 10a has a birefringence of ½ wavelength,
The reflected light 27a becomes S-polarized light and the beam splitter 22
Although (1−E1) is transmitted to the photodetector 29, the photodetector 29 receives it and a sufficient reproduction signal can be obtained. Also,
If the optical disk 10b has no birefringence, the reflected light 27
b becomes P-polarized light and enters the beam splitter 22,
E2 is transmitted and received by the photodetector 29.

That is, in the optical head shown in FIG.
By providing the beam splitter 4 satisfying the conditions of 2> E1 and E1> 0.5, the reproduction output can be sufficiently ensured, and the SN ratio is improved in the optical disc 10b made with a small birefringence such as a high density optical disc. A sufficient amount of light can be obtained to secure Therefore, it is possible to solve the problem of the decrease in the amount of light when the half mirror is used and the problem of birefringence when the polarization beam splitter is used.

[0014]

However, in the common optical head for reproducing a high density optical disc and a CD with such one optical head, the key point is a key point.
Quite stringent specifications are required for the optical film of the splitter.

In terms of performance, since the semiconductor laser of the optical head has a wavelength variation of about ± 20 nm, it is necessary to have the same performance in a wide wavelength range. In particular, in the flat-type beam splitter shown in FIG. 23, since non-parallel light is incident, it becomes a condition in a wider wavelength range. In addition, it is necessary that the efficiency is as high as possible, that is, a large amount of light is returned to the photodetector. The higher the efficiency, the lower the output of the semiconductor laser and the longer the life of the laser.

Further, the reliability of the optical film must be such that its performance is maintained for a long period of time without deterioration. The film material and the substrate must be harmless because it is a film material that is stable in all environments, has sufficient film adhesion, and is an optical head that is particularly developed mainly for consumer use.

Further, for mass production, the structure should be simple, the number of layers of the film should be as small as possible, and the manufacturing should be easy.

It was indispensable to find an optical film for the beam splitter which satisfies the above-mentioned severe requirements.

[0019]

A beam splitter which is a key point in an optical head capable of supporting both a disc having a small birefringence such as a high-density optical disc and a compact disc having a large non-standard birefringence. By making the optical film a specific film material, number of layers, and substrate material,
It is possible to mass-produce optical heads with high performance and high reliability.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) As described above, since recording and reproduction of a high density optical disk requires a larger amount of light than a compact disk, it is indispensable to develop an optical component as a light beam splitting means in place of the Hafmirer. It was An optical head using the newly developed flat beam splitter will be described below.

First, a method of making a beam splitter will be described. Glass substrate (refractive index 1.5
1) is heated to 300 ℃, the degree of vacuum is 5 × 10 ^-6 torr
Then, oxygen gas was introduced into the device through a pressure controller to set the degree of vacuum to 1.5 × 10 ⁻⁴ torr,
TiO ₂ (refractive index 2.30) was vapor-deposited by an electron gun to an optical film thickness λ (λ is ¼ of a design wavelength of 662 nm). After that, the substrate is inverted while a vacuum is maintained to form an antireflection film (AR film) on the back surface, MgF ₂ (refractive index 1.38) is formed in the first layer, and then a pressure controller is used in the apparatus. Oxygen gas is introduced to adjust the degree of vacuum to 8 × 10 ⁻⁵ to
As rr, Al ₂ O ₃ (refractive index 1.62) of the second layer is
Further, a MgF ₂ film was formed on the third layer by vapor deposition. Each layer was set to the optical film thickness of (Table 1). After opening to the atmosphere, the substrate was taken out and cut to prepare a sample.

[0022]

[Table 1]

The transmission characteristics of the prepared sample are shown in FIG. This characteristic was measured at an incident angle of 55 °, and light was incident from the TiO ₂ film side and emitted from the AR film. TS, T
P represents the transmittance for S and P polarized light, respectively.

In this way, a beam splitter having flat characteristics with an S transmittance of 47% (reflectance of 53%) and a P transmittance of 90% in a wide wavelength range centered around the design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

FIG. 2 shows the transmittance of S-polarized light when the incident angle is changed by ± 8 ° around 55 ° for three wavelengths of 642 nm, 662 nm and 682 nm in the beam splitter of this embodiment. It shows the transmittance of polarized light. It can be seen from FIG. 2 that the characteristics are almost the same for any laser wavelength. The wavelength width of ± 20 nm is sufficient to allow variations in laser wavelength generated during laser manufacturing or variations in characteristics during film formation. Since the S-polarized light transmittance decreases (the reflectance increases) and the P-polarized light transmittance increases with the incident angle, even if the light incident from the laser is non-parallel light to the detector, the disk with a small birefringence is detected. The distribution of the light quantity of the arriving light beam is almost the same as the distribution before entering the beam splitter.

Using such a beam splitter, as shown in FIG.
When an optical head having the same structure as that of No. 3 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc having a small birefringence such as a high-density optical disc (ha-
Twice less than Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. The incident angle of the center of the light beam entering the beam splitter from the laser is also within the range of 40 °, which is appropriate for the construction of the optical head.
Satisfactory results were obtained at 60 °.

When the coating of the antireflection film on the back surface was omitted, the reproducing output was somewhat lowered, especially for a compact disc having a large birefringence outside the standard, but it did not affect the reproducing at all.

A heat shock test (80
℃, -40 ℃ each hold 1 hour, 10 cycles), high temperature and high humidity test (60 ℃, 90% RH, 1000 hours), low temperature test (-40 ℃, 1000 hours), various reliability such as tape peeling test When the optical characteristics and the surface of the surface were observed with an optical microscope before and after the test, no change was observed.

Thus, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment has a simple structure in which a single layer film is coated on an inexpensive glass substrate, and complicated processing such as a beam splitter using a prism, polishing, and bonding steps are also performed. It is unnecessary. Further, as shown in FIG. 1, since there is little change in transmission characteristics with respect to wavelength, there is no need to use highly accurate film thickness control during manufacturing, and time control can be sufficient to form equipment, and film formation can be simplified. Since the effective area is wide and mass production is possible at one time, a large cost reduction can be expected.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. Although vapor deposition is used in the present embodiment, the present invention is not limited to this, and for example, sputtering, CVD, or sol-gel method may be used.

(Embodiment 2) An embodiment of an optical head using another beam splitter will be described below.

First, a method of making a beam splitter will be described. Glass substrate (refractive index 1.5
1) is heated to 300 ℃, the degree of vacuum is 5 × 10 ^-6 torr
Then, oxygen gas was introduced into the device through a pressure controller to set the degree of vacuum to 1.5 × 10 ⁻⁴ torr,
A TiO ₂ film (refractive index 2.30) was formed by an electron gun, a SiO ₂ film (refractive index 1.46) was subsequently formed under the condition that the introduction of oxygen gas was stopped, and a TiO ₂ film was formed under the same conditions as above ( Deposition was performed to the optical film thickness shown in Table 2). afterwards,
The substrate was inverted while the vacuum was maintained, and the antireflection film (Table 1) was formed in the same manner as in Example 1. After opening to the atmosphere, the substrate was taken out and cut to prepare a sample.

[0033]

[Table 2]

The transmission characteristics of the prepared sample are shown in FIG. This characteristic was measured at an incident angle of 55 °, in which light was incident from the side of the three-layer film and emitted from the AR film. TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having flat characteristics with S transmittance of 31% (reflectance of 69%) and P transmittance of 80% in a wide wavelength range centering around the design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

FIG. 4 shows the transmittance of S-polarized light when the incident angle is changed by ± 8 ° around 55 ° for three wavelengths of 642 nm, 662 nm and 682 nm in the beam splitter of this embodiment, P It shows the transmittance of polarized light. It can be seen from FIG. 4 that the characteristics are almost the same for any laser wavelength. The wavelength width of ± 20 nm is sufficient to allow variations in laser wavelength generated during laser manufacturing or variations in characteristics during film formation. Since the S-polarized light transmittance decreases (the reflectance increases) and the P-polarized light transmittance increases with the incident angle, even if the light incident from the laser is non-parallel light to the detector, the disk with a small birefringence is detected. The distribution of the light quantity of the arriving light beam is almost the same as the distribution before entering the beam splitter.

Using such a beam splitter, as shown in FIG.
When an optical head having the same structure as that of No. 3 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc having a small birefringence such as a high-density optical disc (ha-
Twice as much as Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. The incident angle of the center of the light beam entering the beam splitter from the laser is also within the range of 40 °, which is appropriate for the construction of the optical head.
Satisfactory results were obtained at 60 °.

Further, if the antireflection film on the back surface was omitted from the coating, the reproduction output would be somewhat lowered, especially for a compact disc having a large birefringence outside the standard, but this did not affect the reproduction. .

Although the three-layer film of this embodiment is inferior to the beam splitter of the first embodiment in the transmittance of P-polarized light, it can increase the reflectance of S-polarized light by nearly 20%, so that it has a high density with little birefringence. A larger amount of light can be obtained for the optical disc.

A heat shock test (80
℃, -40 ℃ each hold 1 hour, 10 cycles), high temperature and high humidity test (60 ℃, 90% RH, 1000 hours), low temperature test (-40 ℃, 1000 hours), various reliability such as tape peeling test When the optical characteristics and the surface of the surface were observed with an optical microscope before and after the test, no change was observed.

Thus, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment uses the most proven film materials such as TiO ₂ and SiO ₂ as optical film materials, and has a simple structure in which these three-layer films are coated on an inexpensive glass substrate. Therefore, it is easy to mass-produce, and complicated processing such as a beam splitter using a prism, polishing, and a bonding step are not required, so that it is low cost and extremely useful.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. In addition, although the film structure as shown in Table 2 is shown in this embodiment, the number of layers and the film thickness of each layer are not limited to this.

Although vapor deposition is used in this embodiment, the present invention is not limited to this. For example, sputtering or CV is used.
D or the sol-gel method may be used.

As described above, by using the beam splitter in which at least one layer of TiO ₂ film is formed on the glass substrate according to Examples 1 and 2, an optical head that solves the above problems can be realized at low cost and is extremely useful. .

(Embodiment 3) An embodiment of an optical head using another beam splitter will be described below.

First, a method of making a beam splitter will be described. Glass substrate (refractive index 1.5
1) is heated to 300 ° C and the degree of vacuum is 5 × 10 ^-6 torr
Then, MgF ₂ (refractive index 1.38) of the first layer was vapor-deposited by an electron gun to an optical film thickness shown in (Table 3). Subsequently, oxygen gas was introduced into the apparatus through a pressure controller, the degree of vacuum was set to 8 × 10 ⁻⁵ torr, and Al ₂ O ₃ (refractive index 1.62) of the second layer was set (Table 3). ) Was vapor-deposited to the optical film thickness of. Similarly, MgF ₂ , Al ₂ O
_A total of 10 layers of ₃ films were deposited alternately. After that, the substrate was inverted while keeping the vacuum, and MgF ₂ , Al ₂ shown in (Table 1)
An antireflection film (AR film) made of an O ₃ film was formed under the same film forming conditions. After opening to the atmosphere, the glass substrate was taken out and cut to prepare a sample.

[0047]

[Table 3]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic was measured at an incident angle of 55 °, in which light was incident from the 10-layer film side and emitted from the AR film. T
S and TP represent transmittances for S and P polarized light, respectively.

In this way, a beam splitter having flat characteristics with an S transmittance of 31% (reflectance of 69%) and a P transmittance of 90% in a wide wavelength range centered around the design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

FIG. 6 shows the transmittance of S-polarized light when the incident angle is changed ± 8 ° about 55 ° in the beam splitter of this embodiment for three wavelengths of 642 nm, 662 nm and 682 nm. It shows the transmittance of polarized light. It can be seen from FIG. 6 that the characteristics are almost the same for any laser wavelength. The wavelength width of ± 20 nm is sufficient to allow variations in laser wavelength generated during laser manufacturing or variations in characteristics during film formation. Since the S-polarized light transmittance decreases (the reflectance increases) and the P-polarized light transmittance increases with the incident angle, even if the light incident from the laser is non-parallel light to the detector, the disk with a small birefringence is detected. The distribution of the light quantity of the arriving light beam is almost the same as the distribution before entering the beam splitter.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 3 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc having a small birefringence such as a high-density optical disc (ha-
About 2.5 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. The incident angle of the center of the light beam entering the beam splitter from the laser is also set to an appropriate angle of 40 in view of the construction of the optical head.
Satisfactory results were obtained for ° to 60 °.

Further, if the coating of the antireflection film on the back surface is omitted, the reproduction output will be somewhat lowered, especially for a compact disc having a large non-standard birefringence, but this will not affect the reproduction. .

A heat shock test (80
℃, -40 ℃ each hold 1 hour, 10 cycles), high temperature and high humidity test (60 ℃, 90% RH, 1000 hours), low temperature test (-40 ℃, 1000 hours), various reliability such as tape peeling test When the optical characteristics and the surface of the surface were observed with an optical microscope before and after the test, no change was observed.

Thus, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment is very useful for a disc having a small birefringence such as a high-density optical disc because it can obtain a larger amount of light than other flat beam splitters. For example,
Since the output of the laser can be suppressed to a lower level, the life of the laser can be extended. Further, since the optical film thickness is the same except for the second layer, the film thickness control becomes relatively easy during formation.

Similarly, Table 4 shows the examination results for three kinds of beam splitters having different film constitutions by alternate films of MgF ₂ film and Al ₂ O ₃ film.

[0056]

[Table 4]

By appropriately changing the film structure in this way, the transmittance (reflectance) of S-polarized light can be freely set while maintaining flat characteristics with respect to wavelength.

The beam splitter of this embodiment is made of Mg
The film materials widely used as optical film materials such as F ₂ and Al ₂ O ₃ are used, and since these multilayer coatings have a simple structure on an inexpensive glass substrate, mass production is easy, and Since it does not require complicated processing such as a beam splitter using a prism, polishing, and an adhesion process, it is low cost and extremely useful.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. Although the film configuration as shown in (Table 3) or (Table 4) is shown, the number of layers and the film thickness of each layer are not limited to this.

Further, although vapor deposition was used for film formation, the present invention is not limited to this. For example, sputtering, CVD, or sol-gel method may be used.

In addition to the film materials used in this example, MgF ₂ as a low refractive index film material and a film having a refractive index of 1.56 to 1.92 as a high refractive index film material are alternately used as main constituent thin films. It is calculated that by stacking layers, an extremely highly efficient beam splitter with an S-polarized reflectance of 70% and a P-polarized transmittance of 85% or more can be obtained in a wide wavelength range especially at an incident angle of 55 ° at the center of the light beam. As a result, I understand.

(Example 4) In Example 3, an example was shown in which a beam splitter was formed by alternating layers of an Al ₂ O ₃ film as a high refractive index film and a MgF ₂ film as a low refractive index film.

In this embodiment, a part of the MgF ₂ film is S
The effectiveness of the beam splitter replaced with the iO ₂ film will be described.

Preparation was carried out in the same manner as in Example 3 by using Mg
A total of 12 layers of F ₂ , SiO ₂ and Al ₂ O ₃ films were vapor-deposited with an optical film thickness as shown in (Table 5) and then inverted to form an AR film having the film configuration shown in (Table 1). No oxygen gas was introduced into the SiO ₂ film.

[0065]

[Table 5]

The transmission characteristics of the produced beam splitter are shown in FIG. The characteristics were measured at an incident angle of 55 °, and the light was incident from the 12-layer film side and emitted from the AR film side. T
S and TP represent transmittances for S and P polarized light, respectively.

Thus, the S transmittance is 30% in a wide wavelength range.
A flat plate type polarization haf mirror having flat characteristics (reflectance 70%) and P transmittance 89% was obtained. This is almost the same characteristic as the beam splitter which does not include the SiO ₂ film shown in the third embodiment. Moreover, it was confirmed that absorption can be ignored in the visible region.

FIG. 8 shows the transmittance of S-polarized light when the incident angle is changed by ± 8 ° around 55 ° for three wavelengths of 642 nm, 662 nm and 682 nm in the beam splitter of this embodiment, P It shows the transmittance of polarized light. It can be seen from FIG. 8 that the characteristics are almost the same for any laser wavelength. The wavelength width of ± 20 nm is sufficient to allow variations in laser wavelength generated during laser manufacturing or variations in characteristics during film formation. Since the S-polarized light transmittance decreases (the reflectance increases) and the P-polarized light transmittance increases with the incident angle, even if the light incident from the laser is non-parallel light to the detector, the disk with a small birefringence is detected. The distribution of the light quantity of the arriving light beam is almost the same as the distribution before entering the beam splitter.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 3 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc having a small birefringence such as a high-density optical disc (ha-
About 2.5 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. The incident angle of the center of the light beam entering the beam splitter from the laser is also set to an appropriate angle of 40 in view of the construction of the optical head.
Satisfactory results were obtained for ° to 60 °.

Further, if the coating of the antireflection film on the back surface is omitted, the reproduction output is somewhat lowered, especially for a compact disc having a large birefringence outside the standard, but this does not affect the reproduction. .

A heat shock test (80
℃, -40 ℃ each hold 1 hour, 10 cycles), high temperature and high humidity test (60 ℃, 90% RH, 1000 hours), low temperature test (-40 ℃, 1000 hours), various reliability such as tape peeling test When the optical characteristics and the surface of the surface were observed with an optical microscope before and after the test, no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment is very useful for a disc having a small birefringence such as a high-density optical disc because it can obtain a larger amount of light than other flat beam splitters. For example,
Since the output of the laser can be suppressed to a lower level, the life of the laser can be extended.

The feature of the beam splitter of this embodiment is that SiO ₂ which is the most widely used low refractive index optical film material.
Even if a part of the MgF ₂ film is replaced with a film, the performance as a beam splitter is hardly deteriorated. MgF
_{The two} films are extremely excellent low-refractive-index film materials, but the only drawback is that they have large internal stress and are easily peeled off when the film thickness is large. However, the SiO ₂ film is a material superior in chemical and mechanical stability to MgF ₂ . As a result of actual evaluation, the multilayer film of the present example shows that MgF ₂ , Al ₂ O of (Table 3)
It was confirmed that the mechanical strength against scratching was improved compared to the alternating film of ₃ films.

From this, according to the present embodiment, the reliability can be further improved and it is extremely useful. In this example, the first layer and the tenth layer among the MgF ₂ films shown in (Table 3) were used.
Although the layers and the twelfth layer are SiO ₂ films, the first layer, the third layer,
It has been found that even if the fifth layer is a SiO ₂ film and the optical film thickness is the same as in (Table 5), the same performance and reliability as a beam splitter can be obtained.

The beam splitter of this embodiment is made of Mg
_{F 2, Al 2 O 3,} SiO 2 and with a film material which is widely used as an optical film material that, these multilayer co inexpensive glass substrate - for a coating was a simple structure, and mass production Since it is easy, and complicated processes such as a beam splitter using a prism, polishing, and bonding steps are unnecessary, it is low cost and extremely useful.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. The film structure is not limited to the number of layers or the film thickness of each layer.

Further, although vapor deposition was used for film formation, the present invention is not limited to this. For example, sputtering, CVD, or sol-gel method may be used.

(Embodiment 5) An embodiment of an optical head using another beam splitter will be described below.

First, a method of making a beam splitter will be described. Glass substrate (refractive index 1.5
1) is heated to 300 ° C and the degree of vacuum is 5 × 10 ^-6 torr
After reaching, the first layer of SiO ₂ (refractive index 1.46) was vapor-deposited by an electron gun to an optical film thickness shown in (Table 6). Subsequently, oxygen gas was introduced into the apparatus through a pressure controller, the degree of vacuum was set to 1 × 10 ⁻⁴ torr, and Y ₂ O ₃ (refractive index 1.80) of the second layer was set (Table 6). ) Was vapor-deposited to the optical film thickness of. In the same manner, SiO ₂ and Y ₂ O ₃ films were alternately deposited to form a total of 8 layers. After that, the substrate was inverted while keeping the vacuum, and the antireflection film (AR film) made of the MgF ₂ and Al ₂ O ₃ films shown in (Table 1) was formed. After opening to the atmosphere, the glass substrate was taken out and cut to prepare a sample.

[0080]

[Table 6]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic was measured at an incident angle of 55 °, in which light was incident from the 8-layer film side and emitted from the AR film. TS,
TP represents the transmittance for S and P polarized light, respectively.

As described above, a beam splitter having flat characteristics with an S transmittance of 31% (reflectance of 69%) and a P transmittance of 85% in a wide wavelength range centered around the design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

FIG. 10 shows the transmittance of S-polarized light when the incident angle is changed by ± 8 ° around 55 ° for three wavelengths of 642 nm, 662 nm and 682 nm in the beam splitter of the present embodiment. It shows the transmittance of polarized light. It can be seen from FIG. 10 that the characteristics are almost the same for any laser wavelength. The wavelength width of ± 20 nm is sufficient to allow variations in laser wavelength generated during laser manufacturing or variations in characteristics during film formation. Since the S-polarized light transmittance decreases (the reflectance increases) and the P-polarized light transmittance increases with the incident angle, even if the light incident from the laser is non-parallel light to the detector, the disk with a small birefringence is detected. The distribution of the light quantity of the arriving light beam is almost the same as the distribution before entering the beam splitter.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 3 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc having a small birefringence such as a high-density optical disc (ha-
About 2.4 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. The incident angle of the center of the light beam entering the beam splitter from the laser is also set to an appropriate angle of 40 in view of the construction of the optical head.
Satisfactory results were obtained for ° to 60 °.

When the coating of the antireflection film on the back surface was omitted, the reproduction output was somewhat lowered, especially for a compact disc having a large birefringence outside the standard, but this did not affect the reproduction. .

A heat shock test (80
℃, -40 ℃ each hold 1 hour, 10 cycles), high temperature and high humidity test (60 ℃, 90% RH, 1000 hours), low temperature test (-40 ℃, 1000 hours), various reliability such as tape peeling test When the optical characteristics and the surface of the surface were observed with an optical microscope before and after the test, no change was observed.

Thus, a practical optical head having no problem in performance and reliability was realized. In the beam splitter of this embodiment, the MgF ₂ film is not used as the low refractive index film material,
It was confirmed by a scratch test that the mechanical strength was higher because it was composed of a SiO ₂ film having a mechanical performance superior to that of the F ₂ film.

Further, since the optical film thickness is the same except for the second layer, the film thickness control becomes relatively easy during formation.

Since the beam splitter of this embodiment has a simple structure in which these multilayer coatings are formed on an inexpensive glass substrate, it is easy to mass-produce, and a beam splitter using a prism is used. Since it does not require complicated processing, polishing and bonding steps, it is low cost and extremely useful.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. The film structure is not limited to the number of layers or the film thickness of each layer.

Further, although vapor deposition was used for film formation, the present invention is not limited to this. For example, sputtering, CVD, or sol-gel method may be used.

Besides the film materials used in this example, SiO ₂ as a low refractive index film material and a film having a refractive index of 1.62 to 1.85 as a high refractive index film material are alternately used as main constituent thin films. It is calculated that by stacking layers, an extremely highly efficient beam splitter with an S-polarized reflectance of 70% and a P-polarized transmittance of 85% or more can be obtained in a wide wavelength range especially at an incident angle of 55 ° at the center of the light beam. As a result, I understand.

The antireflection film used in each example will be described below with reference to conventional examples. In the optical head shown in FIG. 23, the beam splitter, which is a beam splitting means, transmits as much reflected light from the disc as possible,
It is required to lead to the photodetector. For that purpose, it is preferable to form an antireflection film on the back surface of the optical film surface 22a.

The light incident on the beam splitter from the disc side is P-polarized for a disc having a small birefringence such as a high density optical disc, and is S-polarized in the worst case for a non-standard compact disc. There is.

Therefore, the antireflection film is required to have a transmission characteristic close to 100% for both S and P polarized light. Furthermore, in order to allow non-parallel light or laser wavelength variation, the characteristics must be flat in a relatively wide wavelength range.

FIG. 11 is a simulation result of transmission characteristics when an MgF ₂ single layer film, which is widely used as an antireflection film for glass lenses, is coated on a glass substrate. The incident angle was 55 °, and it was hypothesized that the transmittance was 100% in the entire wavelength range for both S and P polarized light on the back surface. Note that TS and TP represent transmission characteristics of S and P polarized light, respectively.

As described above, the P-polarized light transmittance is almost 100% with flat characteristics, but the S-polarized light transmittance is about 93%. Although it is a MgF ₂ single-layer film having excellent performance at normal incidence, satisfactory results cannot be obtained for obliquely incident light as in the present invention.

Further, in FIG. 12, a TiO ₂ film (refractive index 2.30, optical film thickness 1.79) is formed as the first layer on the glass substrate.
λ), and a simulation result of transmission characteristics when a two-layer film of a SiO ₂ film (refractive index 1.46, optical film thickness 0.81λ) is coated on the second layer. Incident angle is 55
And hypothetically, on the back surface, the transmittances of both S and P polarized light were assumed to be 100% in all wavelength regions. Note that TS and TP represent transmission characteristics of S and P polarized light, respectively.

As described above, the transmittances of both S and P polarized lights are close to 100% at the maximum, but their wavelengths are deviated from each other, and the characteristics are not so flat with respect to the wavelength, so that it cannot be said to be a satisfactory result.

On the other hand, FIG. 13 is used in each of the previous embodiments.
MgF ₂ , Al ₂ having the film structure (Table 1) on a glass substrate
It is a simulation result of transmission characteristics when an antireflection film of an O ₃ film is formed. The incident angle was 55 °, and on the back surface, the transmittance was virtually 10 for both S and P polarized light.
It was assumed to be 0%. Note that TS and TP represent transmission characteristics of S and P polarized light, respectively.

As described above, a transmittance of about 99% is obtained for both S and P polarized light over a wavelength width of near 100 nm. This is a satisfactory result when used in the optical head of the present invention. As described in the above-mentioned examples, when this film structure was actually prepared, almost simulation results could be confirmed, and there was no problem in reliability.

The film constitution of the antireflection film is MgF ₂ , A
The number and thickness of the films in (Table 1) are not limited as long as the l ₂ O ₃ film is the main constituent thin film.

Further, other laser wavelengths can be dealt with by simply changing the film thickness. Further, although vapor deposition was used for forming the film, the present invention is not limited to this, and for example, sputtering,
CVD or a sol-gel method may be used.

(Embodiment 6) In the following embodiment, FIG.
A description will be given of an optical head using a beam splitter that has a function of splitting P-polarized incident light into reflected and transmitted light and S-polarized light almost reflected as in the case of the second beam splitting means.

First, a method of making a beam splitter will be described. The glass prism (refractive index 1.51) is heated to 300 ° C in a vacuum evaporation system, and the degree of vacuum is 5 × 10 ^-6 t.
After reaching the orr, oxygen gas was introduced into the device through a pressure controller to set the vacuum degree to 1.5 × 10 ⁻⁴ torr, and the TiO ₂ film (refractive index 2.30) was set by an electron gun.
Then, a SiO ₂ film (refractive index 1.46) was vapor-deposited under the condition that the introduction of oxygen gas was stopped. Similarly, each layer was set to the optical film thickness shown in Table 7 to form a dielectric multilayer film having a total of 7 layers. After cooling, the prism was taken out and joined to another prism having no film to form a beam splitter.

[0106]

[Table 7]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having characteristics of S transmittance of 2% (reflectance of 98%) and P transmittance of 59% at a design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 2.4 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

Further, in this embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of the present embodiment uses the most proven film material such as TiO ₂ and SiO _{2 as} an optical film material, and has no problem in reliability. Further, since the optical film thickness of each layer is the same, the film thickness control becomes very easy especially when an optical monitor is used.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. In addition, although the film structure as shown in Table 7 is shown in the present embodiment, the number of layers and the film thickness of each layer are not limited to this.

Although vapor deposition is used in this embodiment, the present invention is not limited to this. For example, sputtering, CV
D or the sol-gel method may be used.

(Embodiment 7) An embodiment of an optical head using another beam splitter will be described below.

The manufacturing method is the same as that of Example 6, a dielectric multilayer film having the structure of (Table 8) is formed, and after cooling, the prism is taken out and joined to another prism having no film to form a beam. Created a splitter.

[0117]

[Table 8]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

In this way, the S transmittance is 3% (reflectance 97%) and the P transmittance is 69% in a wide wavelength range at the design wavelength of 662 nm.
A beam splitter having a flat characteristic of is obtained.
Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 3 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

Further, in this embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of the present embodiment uses the most proven film material such as TiO ₂ and SiO _{2 as} an optical film material, and has no problem in reliability.

Further, other laser wavelengths can be dealt with by simply changing the film thickness. In this example, as shown in (Table 8), the seventh layer was 1.91λ and the ninth layer was 2.1.
7λ, the other layer was 1.19λ, but the first layer was 2.17.
Similar performance and reliability were obtained when λ, the third layer was 1.91λ, and the other layers were 1.19λ.

Although vapor deposition is used in this embodiment, the present invention is not limited to this. For example, sputtering or CV is used.
D or the sol-gel method may be used.

(Embodiment 8) An embodiment of an optical head using another beam splitter will be described below.

First, regarding the method of making the beam splitter,
Will be explained. Glass prism (refractive index
1.51) is heated to 300 ° C. and the degree of vacuum is 5 × 10^-6t
After reaching orr, the
Vacuum level is 1.0 × 10 by introducing elementary gas^-Fourset in torr
And Ta by electron gun_TwoO _FiveFilm (refractive index 2.10)
Under the condition that the introduction of oxygen gas is stopped._Twofilm
(Refractive index 1.46) was deposited. Similarly, for each layer (table
9) Dielectric multilayer consisting of a total of 9 layers set to the optical thickness of 9)
A film was formed. After cooling, remove the prism and attach the film.
To form a beam splitter by joining with other prisms that are not
Done.

[0128]

[Table 9]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having characteristics of S transmittance of 2% (reflectance of 98%) and P transmittance of 67% at a design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 3 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

In the present embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment uses Ta ₂ O ₅ and SiO ₂ which are the most proven film materials as optical film materials, and has no problem in reliability. Further, since the optical film thickness of each layer is the same, the film thickness control becomes very easy especially when an optical monitor is used.

In contrast to the sixth or seventh embodiment, the beam splitter of the present embodiment does not use TiO ₂ as a film material and therefore has a number of film layers, but has an advantage. An ultraviolet curable resin is often used to bond a prism with a film and a prism without a film, but the nature of TiO ₂ is that if ultraviolet rays are excessively irradiated under a sealed condition, reduction proceeds and light absorption is increased. Will occur. This is not a problem if you manage the time properly, but in case of emergency,
Yield may be reduced. The film material of this embodiment does not have this concern at all.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. In addition, although the film configuration as shown in Table 9 is shown in this embodiment, the number of layers and the film thickness of each layer are not limited to this.

Although vapor deposition is used in this embodiment, the present invention is not limited to this. For example, sputtering or CV is used.
D or the sol-gel method may be used.

(Embodiment 9) An embodiment of an optical head using another beam splitter will be described below.

The preparation method was the same as in Example 8 (see Table 1
A dielectric multilayer film having the structure of 0) was formed, and after cooling, the prism was taken out and joined to another prism having no film to form a beam splitter.

[0140]

[Table 10]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having flat characteristics of S transmittance 1% (reflectance 99%) and P transmittance 70% at a design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 3 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

Further, in this embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

Thus, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment uses Ta ₂ O ₅ and SiO ₂ which are the most proven film materials as optical film materials, and has no problem in reliability.

As in the previous embodiment, since TiO ₂ is not used, the number of film layers is slightly large, but there is an advantage that light absorption does not occur even if ultraviolet rays are excessively irradiated during prism adhesion.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. In addition, although the film configuration as shown in Table 10 is shown in this embodiment, the number of layers and the film thickness of each layer are not limited to this, and for example, as shown in Table 10 in this embodiment. Regarding Ta ₂ O ₅ , although the 11th and 13th layers were set to 1.97λ and the other layers were set to 1.06λ,
Similar performance and reliability were obtained when the first and third layers were set to 1.97λ and the other layers were set to 1.06λ.

Although vapor deposition is used in this embodiment, the present invention is not limited to this. For example, sputtering, CV
D or the sol-gel method may be used.

(Embodiment 10) An embodiment of an optical head using another beam splitter will be described below.

First, a method of making a beam splitter will be described. A glass prism (refractive index 1.51) was set in the vacuum evaporation system, and after the vacuum reached 5 × 10 ⁻⁵ torr, a ZnS film (refractive index 2.3 was obtained by an electron gun).
5), followed by vapor deposition of a MgF ₂ film (refractive index 1.38). Similarly, each layer was set to the optical film thickness shown in Table 11 to form a dielectric multilayer film having a total of 7 layers. After the film formation, the prism was taken out and joined to another prism having no film to form a beam splitter.

[0152]

[Table 11]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having characteristics of S transmittance of 1% (reflectance of 99%) and P transmittance of 59% at a design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 2.4 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

Further, in this embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment uses a film material such as ZnS and MgF _{2 which} has a proven track record as an optical film material, and has no problem in reliability. Further, since the optical film thickness of each layer is the same, the film thickness control becomes very easy especially when an optical monitor is used.

As in the previous embodiment, since TiO ₂ is not used, the number of film layers is slightly large, but there is an advantage that light absorption does not occur even if ultraviolet rays are excessively irradiated at the time of prism adhesion.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. Further, although vapor deposition is used in this embodiment, the present invention is not limited to this, and for example, sputtering, CVD, or sol-gel method may be used.

(Embodiment 11) An embodiment of an optical head using another beam splitter will be described below.

The manufacturing method was the same as in Example 10, except that a dielectric multilayer film having the structure shown in (Table 12) was formed, and after the film formation, the prism was taken out and joined to another prism having no film. -Created a Musplitter.

[0163]

[Table 12]

The transmission characteristics of the produced beam splitter are shown in FIG. This characteristic has an incident angle of 45 °, and TS and TP represent transmittances for S and P polarized light, respectively.

Thus, a beam splitter having characteristics of S transmittance 3% (reflectance 97%) and P transmittance 72% at a design wavelength of 662 nm was obtained. Moreover, it was confirmed that absorption can be ignored in the visible region.

Using the beam splitter of this embodiment, as shown in FIG.
When an optical head having the same structure as that of No. 2 was examined, a sufficient amount of light was obtained to secure the SN ratio for a disc made with a small birefringence such as a high-density optical disc (ha-
About 3 times that of Fumira). On the other hand, even for a compact disc having a large non-standard birefringence, a light amount equivalent to that of a half mirror was obtained, and a sufficient reproduction output could be secured. At this time, the incident angle of the light beam entering the beam splitter from the laser was 45 °. It was also found that variations in laser wavelength of about ± 20 nm that occur during laser manufacturing or variations in characteristics during film formation can be tolerated.

Further, in the present embodiment, the prism ray
The anti-reflection film is provided on the entrance / exit surface, but if the coating of this anti-reflection film is omitted, the output secured for both high density optical discs and non-standard compact discs will drop somewhat, but It wasn't something to give.

A heat shock test (80
C., -40.degree. C. for 1 hour each, 10 cycles), high temperature and high humidity test (60.degree. C., 90% RH, 1000 hours), low temperature test (-40.degree. C., 1000 hours) before and after various reliability tests. The optical characteristics were evaluated, but no change was observed.

In this way, a practical optical head having no problem in performance and reliability was realized. The beam splitter of this embodiment uses a film material such as ZnS and MgF _{2 which} has a proven track record as an optical film material, and has no problem in reliability. In addition, the number of layers is only 5, and the manufacture is simple.

As in the previous embodiment, since TiO ₂ is not used, the number of film layers is somewhat large, but there is an advantage that light absorption does not occur even if ultraviolet rays are excessively irradiated at the time of adhering the prism.

Also, other laser wavelengths can be dealt with by simply changing the film thickness. Further, although vapor deposition is used in this embodiment, the present invention is not limited to this, and for example, sputtering, CVD, or sol-gel method may be used.

[0172]

The optical film of the beam splitter, which is a key point in the optical head capable of supporting both a disc having a small birefringence such as a high-density optical disc and a compact disc having a large non-standard birefringence, By using a specific film material, number of layers, and substrate material, it becomes possible to mass-produce optical heads having high performance and high reliability.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing transmission characteristics of a beam splitter according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing transmission characteristics with respect to an incident angle of the beam splitter according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing transmission characteristics of a beam splitter according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram showing transmission characteristics with respect to an incident angle of a beam splitter according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing transmission characteristics of a beam splitter according to a third embodiment of the present invention.

FIG. 6 is a characteristic diagram showing transmission characteristics with respect to an incident angle of a beam splitter according to a third embodiment of the present invention.

FIG. 7 is a characteristic diagram showing transmission characteristics of a beam splitter according to a fourth embodiment of the present invention.

FIG. 8 is a characteristic diagram showing transmission characteristics with respect to an incident angle of a beam splitter according to a fourth embodiment of the present invention.

FIG. 9 is a characteristic diagram showing transmission characteristics of a beam splitter according to a fifth embodiment of the present invention.

FIG. 10 is a characteristic diagram showing transmission characteristics with respect to an incident angle of a beam splitter according to a fifth embodiment of the present invention.

FIG. 11 is a characteristic diagram (simulation) showing transmission characteristics of a conventional MgF ₂ single-layer antireflection film.

FIG. 12 is a characteristic diagram (simulation) showing the transmission characteristics of a conventional TiO ₂ and SiO ₂ antireflection film.

FIG. 13 is a characteristic diagram showing transmission characteristics of the antireflection film of the present invention.

FIG. 14 is a characteristic diagram showing transmission characteristics of a beam splitter according to a sixth embodiment of the present invention.

FIG. 15 is a characteristic diagram showing transmission characteristics of a beam splitter according to a seventh embodiment of the present invention.

FIG. 16 is a characteristic diagram showing transmission characteristics of a beam splitter according to an eighth embodiment of the present invention.

FIG. 17 is a characteristic diagram showing transmission characteristics of a beam splitter according to a ninth embodiment of the present invention.

FIG. 18 is a characteristic diagram showing transmission characteristics of a beam splitter according to example 10 of the present invention.

FIG. 19 is a characteristic diagram showing transmission characteristics of a beam splitter according to example 11 of the present invention.

FIG. 20 is a block diagram of an optical head using a conventional polarization beam splitter.

FIG. 21 is an explanatory diagram of optical disc thickness and light spots.

FIG. 22 is a configuration diagram of an optical head that reproduces both a high-density optical disc and a conventional optical disc with large birefringence (prism type beam splitter).

FIG. 23 is a block diagram of an optical head for reproducing both a high-density optical disc and a conventional optical disc having a large birefringence (a flat plate type beam).
Musplitter)

[Explanation of symbols]

 1 Semiconductor Laser 2 Condenser Lens 3 Light Beam 4 Beam Splitter 4a Optical Film Surface 5 1/4 Wave Plate 7 Objective Lens 8 Hologram 9a Light Spot 9b Light Spot 10a Optical Disc 10b Optical Disc 11a Reflected Light 11b Reflected Light 14 Photo Detector

Claims (10)

[Claims] 1. A light source, a light beam splitting means for splitting a linearly polarized radiated light flux emitted from the light source into a plurality of light fluxes without substantially changing the light flux diameter, and a light flux splitting means for splitting the light flux. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
5. An optical head satisfying the condition of 5, wherein a beam splitter having a structure in which at least one layer of TiO ₂ film is formed on a glass substrate is used as the light beam splitting means. 2. A light source, a light beam splitting means for splitting a linearly polarized radiated light beam emitted from the light source into a plurality of light beams without substantially changing the light beam diameter, and a light beam splitting means for splitting the light beam by the light beam splitting means. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
An optical head satisfying the condition of 5, wherein a beam splitter having a structure in which an MgF ₂ film and an Al ₂ O ₃ film are alternately laminated as a main constituent thin film on a glass substrate is used as the light beam splitting means. An optical head characterized by. 3. The glass substrate according to claim 2,
MgF in the odd numbered layers _TwoAl film as an even layer_TwoO_ThreeThe membrane
10 layers are alternately laminated with the same optical film thickness, and only the second layer is light
Beam with a structure in which the optical film thickness is set to about twice that of other layers
An optical head characterized by using a liter. 4. A light source, a light beam splitting means for splitting a linearly polarized radiated light flux emitted from the light source into a plurality of light fluxes without substantially changing the light flux diameter, and a light flux splitting means for splitting the light flux. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
An optical head satisfying the condition of 5, wherein a beam splitter having a structure in which an SiO ₂ film and a Y ₂ O ₃ film are alternately laminated as a main constituent thin film on a glass substrate is used as the light beam splitting means. An optical head characterized by. 5. The glass substrate according to claim 4,
SiO in the odd numbered layers _TwoMembrane, Y in even layers_TwoO_ThreeThe membrane
8 layers are alternately laminated with one optical thickness, and only the second layer is optically
Beam splitting with a film thickness set to about twice that of other layers
An optical head characterized by using a tape. 6. The method according to claim 1, 2, 3, 4 or 5.
An optical head having an antireflection film formed by alternately laminating three layers of MgF ₂ films and Al ₂ O ₃ films on one surface of the beam splitter. 7. A light source, a light beam splitting means for splitting a linearly polarized radiated light beam emitted from the light source into a plurality of light beams without substantially changing the light beam diameter, and a light beam splitting means for splitting the light beam by the light beam splitting means. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
In the optical head satisfying the condition of 5, a multilayer film in which a TiO ₂ film and a SiO ₂ film are alternately laminated as a main constituent thin film is provided on a glass prism as the light beam splitting means, and another multilayer film is provided on the multilayer film. A beam with a structure in which glass prisms are joined.
An optical head that uses a splitter. 8. The TiO ₂ film as an odd layer and the SiO ₂ film as an even layer, counting from the glass prism, according to claim 7.
Nine layers having the same optical film thickness are alternately laminated to form a first layer and a third layer.
An optical head using a beam splitter having a configuration in which the optical thickness of one of the layers, or any combination of the seventh layer and the ninth layer, is set to be thicker than the other layers. 9. A light source, a light beam splitting means for splitting a linearly polarized radiated light flux emitted from the light source into a plurality of light fluxes without substantially changing the light flux diameter, and a light flux splitting means for splitting the light flux. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
In the optical head satisfying the condition of 5, a multilayer film in which a Ta ₂ O ₅ film and a SiO ₂ film are alternately laminated as a main constituent thin film is provided on a glass prism as the light beam splitting means, and the multilayer film is provided on the multilayer film. An optical head using a beam splitter having a structure in which another glass prism is joined. 10. A light source, a light beam splitting means for splitting a linearly polarized radiated light flux emitted from the light source into a plurality of light fluxes without substantially changing the light flux diameter, and a light flux splitting means for splitting the light flux. A wavelength plate that polarizes at least one as an irradiation light beam into substantially circularly polarized light, an objective lens that converges the irradiation light beam that has passed through this wavelength plate onto an optical information medium and collects the reflected light, and an objective lens that collects the reflected light. And a photodetector for receiving the reflected luminous flux after passing through the wave plate and the luminous flux splitting means, the luminous flux splitting means having a power efficiency of E when splitting the emitted luminous flux from the emitted luminous flux.
1. E2> E1 and E1> 0.E1 where E2 is the power efficiency in transmitting a polarization component orthogonal to the polarization direction of the irradiation light flux in the reflected light flux to the photodetector.
In the optical head satisfying the condition of 5, a multilayer film in which a ZnS film and a MgF ₂ film are alternately laminated as a main constituent thin film is provided on a glass prism as the light beam splitting means, and another glass is provided on the multilayer film. A beam with a structure in which prisms are joined.
An optical head that uses a splitter.