JPH11312330A - Beam splitter and composite optical element equipped with same, optical pickup device, and optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the beam splitter whose light absorption loss, incidence angle dependence, and polarized light separation difference are all small, to provide the composite optical element equipped with it, and to provide the optical pickup device and optical recording and reproducing device which have recording and reproducing characteristics of high quality and small power consumption and are small-sized and thin. SOLUTION: A beam splitter film (half-mirror film 2) has a 1st layer film 2a with a refractive index n1 (e.g. TiO2 film with n1 =2.28), a 2nd layer film 2b with a refractive index n2 less than n1 (e.g. Al2 O3 film with n2 =1.63) on the 1st layer film 2a, a 3rd layer film 2c with a refractive index n3 less than n2 (e.g. SiO2 film with n3 =1.46) on the 2nd layer film 2b, a 4th layer film 2d with a refractive index n4 nearly equal to n2 (e.g. Al2 O3 film with n4 =1.63) on the 3rd layer film 2c, a 5th layer film 2e with a refractive index n5 nearly equal to n4 (e.g. n5 =2.28) on the 4th layer film 2d, and a 6th layer film 2f with a refractive index n6 less than or equal to n3 (e.g. MgF2 film with n6 =1.38) on the 5th layer film 2e.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam splitter, a composite optical element having the same, and an optical pickup device and an optical recording / reproducing device. The present invention relates to a beam splitter formed with a beam splitter film that transmits a return light beam reflected by a recording medium and returns, a composite optical element including the same, an optical pickup device, and an optical recording / reproducing device.

[0002]

2. Description of the Related Art An optical recording / reproducing apparatus for reproducing information recorded on an optical recording medium such as a ROM (Read Only Memory) disk or a RAM (Random Access Memory) disk, or recording information on an optical recording medium, includes: An optical pickup device using a semiconductor laser as a light source is used. In recent years, along with the demand for smaller and thinner optical recording / reproducing devices, there has also been a demand for smaller and thinner optical pickup devices. From this viewpoint, a semiconductor laser as a light source and a return light beam returning from an optical recording medium are received. An optical pickup apparatus and an optical recording / reproducing apparatus using a composite optical element in which a light receiving element for performing photoelectric conversion on a single semiconductor substrate is integrally formed have attracted attention. An example of an optical pickup device and an optical recording / reproducing device using the composite optical element will be described with reference to FIG. 6 which is a schematic configuration diagram of the optical pickup device and FIG. 7 which is a schematic configuration diagram of the optical recording / reproducing device. Will be described.

[0003] As shown in FIG.
A pair of a first light receiving element 7a and a second light receiving element 7b formed on the semiconductor substrate 4, and fixed on the first light receiving element 7a and the second light receiving element 7b with an adhesive or the like;
A beam splitter 3 having a surface on which a first light receiving element 7a and a second light receiving element 7b are formed on a semiconductor substrate 4 and a high reflection surface 3b substantially parallel to a beam splitter film forming surface 3a inclined at approximately 45 degrees. And a semiconductor laser 6 fixed to the upper surface of the spacer 5 on the semiconductor substrate 4 on the side facing the beam splitter film forming surface 3a.

[0004] A servo actuator 9 such as a biaxial actuator is disposed on the composite optical element 8. For example, when the servo actuator 9 is a two-axis actuator, for example, as shown in FIG.
The movable portion 9b holding the objective lens 9a is supported by a pair of parallel springs 9c extending from the fixed portion 9d,
A focusing coil and a tracking coil (both not shown) are fixed to the movable portion 9b. The focusing coil and the tracking coil are fixed to the fixed portion 9d and are made of a magnetic material such as iron. Both are arranged in a gap of a magnetic circuit composed of a yoke (not shown) and a magnet fixed to the yoke. You. A current having a magnitude and direction based on a focusing error signal and a tracking error signal, which will be described later, is applied to the focusing coil and the tracking coil, and controls and drives the movable portion 9b holding the objective lens 9a in the focusing direction and the tracking direction. The optical pickup device is schematically configured such that the composite optical element 8 and the servo actuator 9 are fixed to the optical block 11 with an adhesive or a screw.

As shown in FIG. 7, for example, an optical recording / reproducing apparatus guides an optical block 11 having an optical pickup device in a tracking direction, and regulates both a focusing direction and a tracking direction. The axis 12a, the sub-guide axis 12b, which is substantially parallel to the main guide axis 12a, restricts only the focusing direction, drives the optical block 11 in the tracking direction, and includes a moving means constituted by a linear motor or the like. Although omitted, it is schematically constituted by a spindle motor for rotating the optical recording medium 10, circuits for signal processing and a system controller, and the like. FIG. 7 shows an example in which the moving means is constituted by a pair of linear motors. A magnetic circuit is constituted by an outer yoke 14 to which a magnet 13 is fixed and an inner yoke 15, and an inner part is provided inside a coil 16 fixed to the optical block 11. This is a case where the yoke 15 is inserted.

Hereinafter, the optical system will be described again with reference to FIG. The outward light beam (dashed-dotted line in the figure) emitted from the light emitting surface 6a of the semiconductor laser 6 is reflected by the beam splitter film forming surface 3a of the beam splitter 3, and provided to the servo actuator 9 such as a biaxial actuator. The light is focused on the signal recording surface of the optical recording medium 10 via the objective lens 9a. Then, the return light beam reflected on the signal recording surface again passes through the objective lens 9a, is guided from the beam splitter film forming surface 3a into the beam splitter 3, and
(A two-dot chain line in the figure). Further, the return light beam reflected on the surface of the beam splitter 3 facing the first light receiving element 7a is reflected on the high reflection surface 3b and irradiates the second light receiving element 7b. A focusing error signal, a tracking error signal, an RF signal, and the like are detected from the signals photoelectrically converted by the first light receiving element 7a and the second light receiving element 7b. For an example of the method of detecting the focusing error signal, the tracking error signal, and the RF signal, see FIG. 8 which is a schematic view of the first light receiving element 7a and the second light receiving element 7b viewed from the direction A in FIG. I will explain.

Each of the first light receiving element 7a and the second light receiving element 7b has a light receiving portion divided into four. The light receiving portions of the first light receiving element 7a are denoted by a, b, c,
d, and the light receiving portions of the second light receiving element 7b are e, f,
g, h, the focusing error signal is ((ad
-Bc)-(eh-fg)), and the tracking error signal is, for example, TPP (Top-hold and Push-
(Cdgh-abef) -Kt ((c
dgh (mirror level of dgh) − (mirror level of abef)) (where Kt is a coefficient for adjusting the offset amount of the tracking error signal), and the RF signal is abc
Defgh is detected.

The beam splitter film formed on the beam splitter film forming surface 3a reflects, for example, 20% of the outward light beam and guides it to the optical recording medium 10 via the objective lens 9a, and 80% transmits the light beam. Film is formed. Further, such a beam splitter film is also formed on the surface of the beam splitter 3 facing the first light receiving element 7a, and for example, 42% of the return light beam is reflected through the high reflection surface 3b. Thus, a film is formed which leads to the second light receiving element 7b and transmits 58% of the light to the first light receiving element 7a. These beam splitter films are required to have a small light absorption loss, and the characteristics of the beam splitter films formed at two locations of the beam splitter 3 are the optical characteristics of the composite optical element 8 and the optical pickup device. In addition, the recording / reproducing characteristics of the optical recording / reproducing apparatus are largely affected. In particular, high performance optical characteristics are required for the beam splitter film formed on the beam splitter film forming surface 3a that reflects the forward light beam and transmits the backward light beam.

An optical pickup device using the composite optical element 8 is generally constituted by a finite optical system that does not use a collimator lens. However, the optical pickup device which is configured by the finite optical system without using the collimator lens and uses the composite optical element 8 has the following problems. The first problem is that the reflectance and the transmittance in the beam splitter film largely depend on the incident angle of the incident light. Light incident on the beam splitter film forming surface 3a of the beam splitter 3 and the beam splitter film formed on the surface facing the first light receiving element 7a is divergent light and / or convergent light, and is incident on these beam splitter films. The angles of incidence vary. In particular, the beam splitter film formed on the beam splitter film forming surface 3a receives the incident light from the air medium and the objective lens 9a.
The return light beam, which is convergent light determined from the NA (Numerical Aperture), is directly incident, and for example, an angle of 45 degrees ± 8 degrees between the vertical axis of the beam splitter film forming surface 3a and the optical axis center of the return light beam. It is required that the reflectance is approximately constant 20% within the range. A second problem is that if the incident angle between the vertical axis of the beam splitter film forming surface 3a and the optical axis center of the outward light beam and the return light beam has a range of, for example, 45 degrees ± 8 degrees,
The difference is that the difference in optical characteristics between the P-polarized component and the S-polarized component is large. That is, in an optical pickup device constituted by a finite optical system, it is required that there is no polarization separation difference which is a characteristic difference between a P-polarized light component and an S-polarized light component. If there is no polarization separation difference, there is no danger that the recording / reproducing characteristics will be degraded due to variations in polarization due to the polarization ratio of the laser beam or the birefringence of the optical recording medium 10. Therefore, in the beam splitter film formed on the beam splitter film forming surface 3a, for example, the incident angle between the vertical axis of the beam splitter film forming surface 3a and the optical axis center of the forward light beam and the backward light beam is 45 degrees ± 8. When it is in the range of degrees, it is required that no polarization separation difference occurs when Rs = Rp = 20%, or that the difference is extremely small even if it occurs.

Hereinafter, the beam splitter film formed on the beam splitter film forming surface 3a of the beam splitter 3 will be described. Generally, an optical functional film such as a beam splitter film utilizes light interference generated by making the film thickness substantially equal to the wavelength of light used for recording and reproduction. For example, the condition for causing interference to light that is perpendicularly incident on a single-layer beam splitter film is n × d = m × 4 / λ (however,
n is the refractive index of the single-layer beam splitter film, d is the thickness of the single-layer beam splitter film, m is the interference order (also referred to as phase thickness or Quarter Wave Optical Thickness, hereinafter referred to as phase thickness m), λ Is the wavelength of light). The single-layer beam splitter film has two different refractive indices: a first interface between air and the single-layer beam splitter film and a second interface between the single-layer beam splitter film and the optical element. There is an interface. When the phase film thickness m is an odd number, the phase of the reflected wave from the first boundary surface and the phase of the reflected wave from the second boundary surface are shifted by π, and the effect of weakening the reflected light due to the interference effect is maximized. Conversely, when the number of the phase thin films m is even, the phases are aligned, and the effect of strengthening the reflected light is maximized.

[0011] The condition for causing the interference, n × d = m
As is clear from × 4 / λ, the effect of the interference condition can be controlled by the refractive index n of the optical function film and the film thickness d of the optical function film, and an arbitrary optical function can be obtained. However, the optical materials from which an arbitrary optical functional film can be obtained are limited, and in practice, a high-refractive-index thin film and a low-refractive-index thin film are alternately formed using an optical material capable of forming a stable optical functional film. It is common to form an optical function film having a laminated thin film structure by laminating. Therefore, the optical characteristics due to interference can be calculated by the matrix method using the optical impedance. Here, assuming that the refractive index of the single-layer beam splitter film is n, the thickness of the single-layer beam splitter film is d, and the incident angle to the single-layer beam splitter film is θ, the single-layer beam splitter film has Characteristic matrix M
Is represented by two rows and two columns in Equation 1 below.

[0012]

(Equation 1)

Further, the characteristic matrix M of the multilayer beam splitter film is the product of the matrices of the respective layers.
(M1) (M2)... (Mi). At this time, the reflectivity R of the multilayer beam splitter film can be calculated by the following equation 2 from the elements of the matrix product, the refractive index n _{0 of} the incident medium, and the refractive index n _s of the optical element.

[0014]

(Equation 2)

The characteristics of the beam splitter film formed on the beam splitter film forming surface 3a of the beam splitter 3 constituting the composite optical element 8 include the following. 1. Light absorption loss is small. 2. Small incident angle dependency. It was mentioned earlier that the three points of small polarization separation difference are required. Of these,
3. Regarding the small polarization separation difference, if the beam splitter film is made of a metal film, a beam splitter film with a small polarization separation difference can be obtained. However, since the metal film has a large light absorption loss in the visible or near-infrared region of the wavelength of the semiconductor laser 6, a large output is required for the emission power of the semiconductor laser 6 during recording and reproduction. Therefore, in the optical pickup device and the optical recording / reproducing device equipped with the composite optical element 8, the power consumption during recording / reproducing is large, and the power supply and the circuit and the peripheral devices attached to them take into account the size, This was one of the factors that hindered miniaturization.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide a beam splitter having a small light absorption loss, incident angle dependence and polarization separation difference, and to provide recording / reproducing by providing the beam splitter in a composite optical element. An object of the present invention is to provide an optical pickup device and an optical recording / reproducing device which can provide high-quality recording / reproducing characteristics at the time, consume less power, and can be further reduced in size and thickness.

[0017]

In order to solve the above-mentioned problems, a beam splitter according to the present invention has a beam splitter film on a beam splitter film forming surface which is at least approximately 45 degrees with respect to the optical axis of incident light. Is formed, for example, at a light wavelength of 780 nm
A first layer film having a refractive index of n ₁ , for example, a TiO ₂ film having a refractive index of 2.28;
A second layer film formed on the layer film and having a refractive index n _{2 in} a relationship of n ₂ <n _{1 with} respect to a refractive index n ₁ of the first layer film;
For example, an Al ₂ O ₃ film having a refractive index of 1.63 is formed on the second layer film, and the refractive index n ₃ has a relationship of n ₃ <n _{2 with} respect to the refractive index n ₂ of the second layer film. A third layer film, for example, an SiO ₂ film having a refractive index of 1.46 and a refractive index n ₄ formed on the third layer film, wherein n ₄ ≒ n is greater than the refractive index n ₂ of the second layer film. the fourth-layer film on the _second relationship, for example, and the Al ₂ O ₃ film having a refractive index of 1.63, while being formed on the fourth layer film, the refractive index n ₅ to the refractive index n ₁ of the first layer film For n
_Fifth layer film having a relationship of ₅ ≒ n ₁ , for example, a refractive index of 2.2
8 formed on the TiO ₂ film and the fifth layer film,
The refractive index n ₆ is n ₆ ≦ n _{3 with} respect to the refractive index n ₃ of the third layer film.
For example, Mg having a refractive index of 1.38.
And an F ₂ film.

The composite optical element of the present invention has at least a first light receiving element and a second light receiving element formed on a semiconductor substrate, and a light emitting surface formed on the semiconductor substrate and substantially perpendicular to the semiconductor substrate. A first light receiving device that is fixed on the semiconductor laser and the first light receiving element and the second light receiving element, reflects the forward light beam emitted from the light emitting surface of the semiconductor laser, and reflects and returns the first light beam; A beam formed with a beam splitter film forming surface on which a beam splitter film leading to an element is formed, and a high reflection surface reflecting a return light beam reflected on the upper surface of the first light receiving element and leading to the second light receiving element. in the composite optical element having a splitter, for example a beam splitter film with respect to the wavelength 780nm of light, the first layer film refractive index of n _1, such as TiO ₂ having a refractive index of 2.28 And a film formed on the first layer film, wherein the refractive index n ₂ is n with respect to the refractive index n ₁ of the first layer film.
_{A second} layer film having a relation of ₂ <n ₁ , for example, a refractive index of 1.6
3 formed on the Al ₂ O ₃ film and the second layer film, and the refractive index n ₃ is smaller than the refractive index n ₂ of the second layer film by n ₃ < _3.
A third layer film having a relationship of n ₂ , for example, an SiO ₂ film having a refractive index of 1.46, and a refractive index n ₄ formed on the third layer film with respect to the refractive index n ₂ of the second layer film. And n ₄膜 n ₂ , for example, Al ₂ O having a refractive index of 1.63.
And a refractive index n ₅ formed on the _third film and the fourth layer film.
There fifth layer film having a relationship of n ₅ ≒ n ₁ with respect to the refractive index n ₁ of the first layer film, for example, a TiO ₂ film having a refractive index 2.28,
A sixth layer film formed on the fifth layer film and having a refractive index n ₆ of n ₆ ≦ n _{3 with} respect to the refractive index n ₃ of the third layer film, for example, MgF having a refractive index of 1.38. _{And two} membranes.

The optical pickup device of the present invention has at least a first light receiving element and a second light receiving element formed on a semiconductor substrate, and a light emitting surface formed on the semiconductor substrate and substantially perpendicular to the semiconductor substrate. A first light receiving device that is fixed on the semiconductor laser and the first light receiving element and the second light receiving element, reflects the forward light beam emitted from the light emitting surface of the semiconductor laser, and reflects and returns the first light beam; A beam formed with a beam splitter film forming surface on which a beam splitter film leading to an element is formed, and a high reflection surface reflecting a return light beam reflected on the upper surface of the first light receiving element and leading to the second light receiving element. In an optical pickup device having a composite optical element having a splitter and an objective lens for condensing a forward light beam on an optical recording medium, for example, a light wavelength of 780 nm is used. Beam splitter film which is first-layer film refractive index of n _1, for example, refractive index 2.28 Ti
An O ₂ film and a refractive index n formed on the first layer film
₂ is a two-layer film having a relationship of n ₂ <n ₁ with respect to the refractive index n ₁ of the first layer film, for example, and the Al ₂ O ₃ film of refractive index 1.63, is formed on the second layer film And a _third layer film in which the refractive index n ₃ has a relationship of n ₃ <n ₂ with the refractive index n ₂ of the second layer film, for example, a SiO ₂ film having a refractive index of 1.46,
A _fourth layer film formed on the layer film and having a refractive index n ₄ of n ₄ ≒ n _{2 with} respect to the refractive index n ₂ of the second layer film;
For example, an Al ₂ O ₃ film having a refractive index of 1.63 is formed on the fourth layer film, and the refractive index n ₅ has a relationship of n ₅ ≒ n _{1 with} respect to the refractive index n ₁ of the first layer film. A fifth layer film, for example, a TiO ₂ film having a refractive index of 2.28 and a refractive index n ₆ formed on the fifth layer film, wherein n ₆ ≦ n with respect to the refractive index n ₃ of the third layer film. _It has a sixth layer film having a relation of ₃ , for example, an MgF ₂ film having a refractive index of 1.38.

In the optical recording / reproducing apparatus of the present invention, at least the first light receiving element and the second light receiving element formed on the semiconductor substrate, and the light emitting surface formed on the semiconductor substrate and substantially perpendicular to the semiconductor substrate. And a semiconductor laser having the semiconductor laser fixed on the first light receiving element and the second light receiving element.
A beam splitter film forming surface on which a beam splitter film is formed to reflect a forward light beam emitted from a light emitting surface of a semiconductor laser and guide a reflected return light beam to a first light receiving element; and a first light receiving element. A composite optical element having a beam splitter formed with a highly reflective surface for reflecting the return light beam reflected on the upper surface and guiding the reflected light beam to the second light receiving element; and an objective lens for converging the forward light beam on the optical recording medium. In an optical recording / reproducing apparatus having an optical pickup device having: and a moving means for controlling and driving the optical pickup device in a tracking direction, for example, a beam splitter film for a light wavelength of 780 nm is a first layer having a refractive index of n _1. film, for example, a TiO ₂ film having a refractive index 2.28, n ₂ is formed into the first layer film, the refractive index n ₂ with respect to the refractive index n ₁ of the first layer film The two-layer film having a relationship of n _1, for example, and the Al ₂ O ₃ film having a refractive index of 1.63, while being formed on the second layer film, the refractive index n ₃ is the refractive index n ₂ of the second layer film
A third layer film having a relationship of n ₃ <n ₂ , for example, an SiO ₂ film having a refractive index of 1.46 and a third layer film, and a refractive index n ₄ of the second layer film. the fourth-layer film having a relationship of n ₄ ≒ n ₂ with respect to the refractive index n _2, for example, the refractive index 1.
The film is formed on the Al ₂ O ₃ film of No. 63 and the fourth layer film, and has a refractive index n ₅ of n ₅に 対 し て with respect to the refractive index n ₁ of the first layer film.
A fifth layer film having a relationship of n ₁ , for example, a TiO ₂ film having a refractive index of 2.28 and a refractive index n ₆ formed on the fifth layer film with respect to a refractive index n ₃ of the third layer film. And a sixth layer film having a relationship of n ₆ ≦ n ₃ , for example, MgF ₂ having a refractive index of 1.38.
And a film. The optical recording / reproducing apparatus referred to here includes a reproduction-only apparatus that performs only reproduction, a recording-only apparatus that performs only recording, and a device that can perform both recording and reproduction.

According to the above-described means, it is possible to provide a beam splitter having a beam splitter film whose light absorption loss, incident angle dependence and polarization separation difference are all small. Therefore, if an optical pickup device and an optical recording / reproducing device are configured by using the composite optical element having the beam splitter, the emission power of the semiconductor laser at the time of recording / reproducing may be small, and the power supply, the circuit, and the peripherals attached thereto may be used. The components can be reduced in size and thickness, and as a result, the power consumption and the size and thickness of the optical pickup device and the optical recording / reproducing device can be reduced. In addition, since it is possible to provide a beam splitter having a small incident angle dependence, an optical pickup device and an optical pickup corresponding to an optical recording medium having a higher density by using an objective lens having a large NA are provided. It is possible to provide a recording / reproducing device.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a beam splitter in which a beam splitter film is formed on a beam splitter film forming surface which is at least approximately 45 degrees inclined with respect to the optical axis of incident light, this beam splitter, and a light receiving device. An optical pickup device having at least this composite optical element and an objective lens, a moving means for controlling and driving the optical pickup device in the tracking direction, It can be applied to an optical recording / reproducing apparatus having the same.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment to which the present invention is applied will be described below with reference to FIGS. Note that components in the figure that have the same structure as the conventional technology are denoted by the same reference numerals. The schematic configuration of a beam splitter, a composite optical element, an optical pickup device, and an optical recording / reproducing device to which the present invention is applied is as follows.
For example, this is the same as the case described with reference to FIGS. 6 and 7 in the related art, and a duplicate description will be omitted.

Example 1 In this example, a trapezoidal prism was manufactured using optical glass SF11 having a light wavelength of 780 nm and a refractive index of 1.76.
This is an example in which a half mirror film, which is an example of a beam splitter film, is formed on a slope of the prism, that is, on a surface on which the beam splitter film is formed, to produce a beam splitter. This will be described with reference to FIGS.

First, as shown in FIG. 1 which is a schematic sectional view of the beam splitter, the beam splitter film forming surface 3a
In addition, TiO having a refractive index of 2.28 and a film thickness of 90.0 nm (optical film thickness of 205.2 nm) is used as the first layer film 2a.
_Two films are formed. Next, on the first layer film 2a, the second layer film 2b has a refractive index of 1.63 and a thickness of 125.25 nm.
An Al ₂ O ₃ film having a thickness of 6 nm (optical thickness of 204.7 nm) is formed. Next, a third layer film 2c having a refractive index of 1.46 and a film thickness of 104.0 nm is formed on the second layer film 2b.
An SiO ₂ film having an optical thickness of 151.8 nm is formed.
Next, an Al ₂ O ₃ film having a refractive index of 1.63 and a film thickness of 183.3 nm (optical thickness of 298.8 nm) is formed on the third layer film 2c as the fourth layer film 2d. Next,
A refractive index of 2.28 is formed on the fourth layer film 2d as a fifth layer film 2e.
And a film thickness of 92.8 nm (optical film thickness of 211.6).
nm) of a TiO ₂ film. Next, the fifth layer film 2e
An M layer having a refractive index of 1.38 and a film thickness of 166.8 nm (optical film thickness of 230.2 nm) is formed thereon as the sixth layer film 2f.
By forming the gF ₂ film, the fabrication of the beam splitter 3 in which the half mirror film 2 having a thickness of 762.5 nm was formed on the slope of the trapezoidal prism 1 was completed.

Then, a laser beam having a wavelength of 450 nm to 850 nm was incident on the half mirror film 2 of the manufactured beam splitter 3 at an incident angle of 45 degrees, and the polarization separation difference of the half mirror film 2 was measured. The resulting graph is shown in FIG.
As is apparent from FIG. 2, in particular, the wavelength 780 of the laser light
nm, Rp = 19.8%, Rs = 20.
The polarization separation difference Rs-Rp was 0.9%, which was 1% or less. The laser wavelength fluctuates by about ± 20 nm due to manufacturing variations and changes in the use environment temperature. For example, the polarization separation difference at 760 nm of 780 nm-20 nm is 1.4%, and 800 nm of 780 nm + 20 nm.
When the polarization separation difference is observed, it is understood that the wavelength dependency is very small at 1.1%.

Further, a laser beam having a wavelength of 780 nm was incident on the half mirror film 2 of the manufactured beam splitter 3 while changing the incident angle from 35 to 55 degrees, and the incident angle dependence of the half mirror film 2 was measured. The resulting graph is shown in FIG. As is clear from FIG. 3, Rs is within 20.7 ± 0.5% in the range of the incident angle of 45 ° ± 8 °, and Rp is 19.9 ± in the range of the incident angle of 45 ° ± 8 °.
1.0% or less, and the polarization separation difference Rs-Rp =
It was 1.4%.

As described above, the beam splitter 3 according to the present embodiment in which the half mirror film 2 is formed by applying the present invention.
Since no metal film was used, the light absorption loss was small, and the incident angle dependence and the polarization separation difference could be made extremely small.

Embodiment 2 In this embodiment, a trapezoidal prism is manufactured using optical glass SF11 having a light wavelength of 655 nm and a refractive index of 1.78.
This is an example in which a half mirror film, which is an example of a beam splitter film, is formed on a slope of the prism, that is, on a surface on which the beam splitter film is formed, to produce a beam splitter. This will be described again with reference to FIG. 1 and FIGS.

First, as shown in FIG. 1, a refractive index of 2.3 is formed as a first layer film 2a on a beam splitter film forming surface 3a.
2 and a film thickness of 74.3 nm (an optical film thickness of 172.1 nm).
(4 nm) TiO ₂ film is formed. Next, the first layer film 2
A having a refractive index of 1.63 and a film thickness of 98.0 nm (an optical film thickness of 159.7 nm) is formed as a second layer film 2b on a.
An l ₂ O ₃ film is formed. Next, on the second layer film 2b, a third layer film 2c having a refractive index of 1.46 and a thickness of 1
An SiO ₂ film having a thickness of 57.4 nm (optical thickness of 229.8 nm) is formed. Next, a fourth layer film 2d is formed on the third layer film 2c.
Has a refractive index of 1.63 and a film thickness of 92.6 nm.
An Al ₂ O ₃ film having an optical thickness of 150.9 nm is formed. Next, a TiO ₂ film having a refractive index of 2.32 and a thickness of 74.2 nm (optical thickness of 172.1 nm) is formed as a fifth layer film 2 e on the fourth layer film 2 d. Next,
A refractive index of 1.38 is formed on the fifth layer film 2e as a sixth layer film 2f.
And a film thickness of 132.2 nm (optical film thickness of 182.2 nm).
The formation of the beam splitter 3 in which the half mirror film 2 having a thickness of 628.7 nm was formed on the slope of the trapezoidal prism 1 by forming an MgF ₂ film having a thickness of 4 nm) was completed.

Then, a laser beam having a wavelength of 450 nm to 850 nm was incident on the half mirror film 2 of the manufactured beam splitter 3 at an incident angle of 45 degrees, and the polarization separation difference of the half mirror film 2 was measured. The result is shown in FIG. Further, a laser beam having a wavelength of 655 nm was incident on the half mirror film 2 of the manufactured beam splitter 3 while changing the incident angle from 35 degrees to 55 degrees, and the incident angle dependence of the half mirror film 2 was measured. The result is shown in FIG. As is clear from FIGS. 4 and 5, also in this embodiment, the light absorption loss was small as in Embodiment 1, and the incident angle dependency and the polarization separation difference could be made extremely small.

In Embodiments 1 and 2 described above, the sixth layer film 2f
Is shown as an MgF ₂ film, but the present invention is not limited to this. For example, an SiO ₂ film may be used. In the first and second embodiments, the case where the second layer film 2b and the fourth layer film 2d are made of an Al ₂ O ₃ film has been described. However, the present invention is not limited to this.
For example, CeF ₃ , LaF ₃ , or a mixed film of ZrO ₂ and Al ₂ O ₃ may be used. Further, in the first and second embodiments described above,
FIG. 2 shows an example in which the third layer film 2c is formed of a SiO ₂ film, but the present invention is not limited to this, and may be, for example, an MgF ₂ film. Furthermore, in the above-described first and _second embodiments, the case where the first layer film 2a and the fifth layer film 2e are formed of a TiO ₂ film has been described, but the present invention is not limited to this. It is possible to form a dense film by assisted vapor deposition or sputtering, and to use a material having a refractive index equivalent to that of a TiO ₂ film.

The beam splitter 3 on which the half mirror film 2 of the first or second embodiment is formed can be used for the composite optical element 8, and an optical pickup device using this composite optical element 8. And an optical recording / reproducing apparatus can be constituted by using this optical pickup device.

[0034]

According to the beam splitter of the present invention, it is possible to provide a beam splitter having a small light absorption loss, incident angle dependency and polarization separation difference. The composite optical element equipped with the beam splitter can operate with low power because the emission power of the semiconductor laser during recording and reproduction can be small, and can extend the life of the semiconductor laser, that is, the length of the composite optical element itself. Life can be extended. Further, in the optical pickup device including the composite optical element and the optical recording / reproducing device including the optical pickup device, high-quality recording / reproducing characteristics are obtained, and power consumption during recording / reproducing is reduced. In addition, the size and thickness of the optical pickup device and the optical recording / reproducing device can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a beam splitter according to the present invention.

FIG. 2 is a graph of a reflectance characteristic of a half mirror film in Example 1.

FIG. 3 is a graph showing the incident angle dependence of a half mirror film in Example 1.

FIG. 4 is a graph showing a reflectance characteristic of a half mirror film in Example 2.

FIG. 5 is a graph showing the incident angle dependence of a half mirror film in Example 2.

FIG. 6 is a schematic configuration diagram of a conventional optical pickup device.

FIG. 7 is a schematic configuration diagram of a conventional optical recording / reproducing apparatus.

FIG. 8 is a schematic view taken in the direction of the arrow A as viewed from a direction A in FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Prism, 2 ... Half mirror film, 2a ... 1st layer film,
2b: second layer film, 2c: third layer film, 2d: fourth layer film, 2
e: Fifth layer film, 2f: Sixth layer film, 3: Beam splitter, 3a: Beam splitter film forming surface, 3b: High reflection surface, 4: Semiconductor substrate, 5: Spacer, 6: Semiconductor laser, 7a: 1 light receiving element, 7b ... second light receiving element, 8
.. Composite optical element, 9 servo actuator, 9a objective lens, 9b movable part, 9c parallel spring, 9d fixed part, 10 optical recording medium, 11 optical block, 12a
Main guide shaft, 12b Sub guide shaft, 13 Magnet, 14 Outer yoke, 15 Inner yoke, 16 Coil

Claims (8)

[Claims] 1. A beam splitter in which a beam splitter film is formed at least on a slope approximately 45 degrees with respect to the optical axis of incident light, wherein the beam splitter film has a first layer film having a refractive index of n _1. A second layer film formed on the first layer film and having a refractive index n _{2 in} a relationship of n ₂ <n _{1 with} respect to a refractive index n ₁ of the first layer film; A _third layer film formed on the layer film and having a refractive index n _{3 in} a relationship of n ₃ <n _{2 with} respect to the refractive index n ₂ of the second layer film; A _fourth layer film having a refractive index n ₄ of n ₄ ≒ n _{2 with} respect to a refractive index n _{2 of the second} layer film; a fifth layer film rate n ₅ is in a relationship of n ₅ ≒ n ₁ with respect to the refractive index n ₁ of the first layer film, while being formed on said fifth layer film, Beamsplitter refractive index n ₆ is characterized in that it comprises a sixth layer film having a relationship of n ₆ ≦ n ₃ relative refractive index n ₃ of the third layer film. 2. The beam splitter according to claim 1, wherein a thickness of the beam splitter film is substantially equal to a wavelength of the incident light. A first light receiving element and a second light receiving element formed on at least a semiconductor substrate; a semiconductor laser formed on the semiconductor substrate and having a light emitting surface substantially perpendicular to the semiconductor substrate; A beam splitter that is fixed on the first light receiving element and the second light receiving element, reflects the outward light beam emitted from the light emitting surface, and guides the reflected return light beam to the first light receiving element. A beam splitter formed with a film splitter film forming surface on which a film is formed, and a high reflection surface that reflects the return light beam reflected by the upper surface of the first light receiving element and guides the reflected light beam to the second light receiving element; in the composite optical element having a refraction of the beam splitter film, a first layer film having a refractive index of n _1, it is formed into the first layer film, the refractive index n ₂ of the first layer film a second layer film with respect to n ₁ that the relation of n ₂ <n _1, while being formed on the second layer film, the refractive index n ₃ relative refractive index n ₂ of the second layer film a third layer film having a relation of n ₃ <n ₂ , formed on the third layer film, and having a refractive index n ₄ of n ₄ ≒ n _{2 with} respect to a refractive index n ₂ of the second layer film. a fourth layer film in the relationship, while being formed on the fourth layer film, the refractive index n ₅ in the relation of n ₅ ≒ n ₁ with respect to the refractive index n ₁ of the first layer film A five-layer film, and a sixth-layer film formed on the fifth-layer film and having a refractive index n _{6 in} a relationship of n ₆ ≦ n _{3 with} respect to a refractive index n ₃ of the third-layer film. A composite optical element comprising: 4. The composite optical element according to claim 3, wherein the thickness of the beam splitter film is substantially equal to the wavelength of the outward light beam. 5. A semiconductor laser having at least a first light receiving element and a second light receiving element formed on a semiconductor substrate, a semiconductor laser formed on the semiconductor substrate and having a light emitting surface substantially perpendicular to the semiconductor substrate, A beam splitter that is fixed on the first light receiving element and the second light receiving element, reflects the outward light beam emitted from the light emitting surface, and guides the reflected return light beam to the first light receiving element. A beam splitter formed with a film splitter film forming surface on which a film is formed, and a high reflection surface that reflects the return light beam reflected by the upper surface of the first light receiving element and guides the reflected light beam to the second light receiving element; a composite optical element having, in an optical pickup apparatus having an objective lens for focusing the outgoing light beam to the optical recording medium, the beam splitter film, a refractive index at n ₁ That the first layer film, wherein is formed in a first layer film, the second layer film refractive index n ₂ which is in relation of n ₂ <n ₁ with respect to the refractive index n ₁ of the first layer film A third layer film formed on the second layer film and having a refractive index n _{3 in} a relationship of n ₃ <n _{2 with} respect to a refractive index n ₂ of the second layer film; A _fourth layer film formed on the layer film and having a refractive index n ₄ of n ₄ ≒ n _{2 with} respect to the refractive index n ₂ of the second layer film; And a _fifth layer film having a refractive index n _{5 in} a relationship of n ₅ ≒ n _{1 with} respect to the refractive index n _{1 of the first} layer film; the optical pickup apparatus rate n ₆ is characterized in that it comprises a sixth layer film having a relationship of n ₆ ≦ n ₃ relative refractive index n ₃ of the third layer film. 6. The optical pickup device according to claim 5, wherein a thickness of the beam splitter film is substantially equal to a wavelength of the outward light beam. 7. A semiconductor laser formed on at least a semiconductor substrate and having a light emitting surface substantially perpendicular to the semiconductor substrate, wherein the first and second light receiving elements are formed on at least a semiconductor substrate; A beam splitter that is fixed on the first light receiving element and the second light receiving element, reflects the outward light beam emitted from the light emitting surface, and guides the reflected return light beam to the first light receiving element. A beam splitter formed with a film splitter film forming surface on which a film is formed, and a high reflection surface that reflects the return light beam reflected by the upper surface of the first light receiving element and guides the reflected light beam to the second light receiving element; An optical pickup device having a composite optical element having an optical lens and an objective lens for condensing the outward light beam on an optical recording medium; and controlling the optical pickup device in a tracking direction. In the optical recording and reproducing apparatus and a moving means for driving said beam splitter film, a first layer film having a refractive index of n _1, it is formed into the first layer film, the refractive index n ₂ wherein a second layer film having a relationship of n ₂ <n ₁ with respect to the refractive index n ₁ of the first layer film, while being formed on the second layer film, the refractive index n ₃ of the second-layer film a third layer film with respect to the refractive index n ₂ which is in relation of n ₃ <n _2, while being formed on the third layer film, the refractive index n ₄ is the refractive index n ₂ of the second layer film A fourth layer film having a relationship of n ₄ ≒ n ₂ with respect to the fourth layer film, and having a refractive index n ₅ of n ₅に 対 し て with respect to a refractive index n ₁ of the first layer film. a fifth layer film having a relationship of n ₁ , and a refractive index n ₆ being formed on the fifth layer film and having a relationship of n ₆ ≦ n _{3 with} respect to a refractive index n ₃ of the third layer film. A certain sixth layer Optical recording and reproducing apparatus characterized in that it comprises and. 8. The optical recording / reproducing apparatus according to claim 7, wherein a thickness of the beam splitter film is substantially equal to a wavelength of the outward light beam.