JP2793706B2 - Optical head for magneto-optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding an optical head for a magneto-optical disk, an object of the present invention is to reduce the number of parts and to reduce the size and weight of the optical head. In a magneto-optical disk optical head for reading out information of the optical disk by polarization-separating the beam, a prism made of optical glass having one inclined surface, and a surface including a reflected laser beam and a normal line of the one inclined surface are provided. A prism made of quartz having an optical axis in the direction of 45 degrees is bonded to the slopes, and one prism having a beam splitter film in a bonded portion is formed.The laser beam from the laser diode is formed of the optical glass. And then reflected by the beam splitter film toward the magneto-optical disk, where the magneto-optical The reflected laser beam from the prism is perpendicularly incident on one surface of the optical glass prism among the prisms, and a predetermined component of the reflected laser beam passes through the beam splitter film, and the quartz prism Is configured to be polarized and separated into two light beams.

[Industrial applications]

 The present invention relates to an optical head for a magneto-optical disk.

In a magneto-optical disk device, an increase in access speed is desired.

In order to increase the access speed, it is necessary to reduce the weight of the optical head.

[Conventional technology]

FIG. 4 shows a conventional optical head 1 for a magneto-optical disk.

The optical head 1 has a prism 4 having a beam splitter film 3, a half-wave plate 5, a polarizing beam splitter 6, a laser diode 7, a collimating lens 8, an objective lens 9, a lens 10 on a movable base 2. 11 and the photodiodes 12 and 13 are assembled. The difference between the outputs of the photodiodes 12 and 13 is differentially amplified and output as a reproduction signal.

The optical head 1 is moved in the radial direction of the magneto-optical disk 15 and accessed as indicated by an arrow 16.

[Problems to be solved by the invention]

As described above, the optical head 1 has a configuration including many components, and it is difficult to reduce the size and weight.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head for a magneto-optical disk capable of reducing the number of parts and reducing the size and weight.

[Means for solving the problem]

The present invention relates to an optical head for a magneto-optical disk for reading out information of a magnetic disk by polarization-separating a reflected laser beam emitted from a laser diode and reflected by the magneto-optical disk, wherein a prism made of optical glass having one inclined surface; A prism made of quartz whose optical axis is in a direction of 45 degrees with respect to a plane including the reflected laser beam and the normal of one slope is bonded to each other with the above slopes, and a beam splitter film is attached to the bonded portion. The laser beam from the laser diode is incident on the optical glass prism, is reflected by the beam splitter film and travels toward the magneto-optical disk, and the reflected laser beam from the magneto-optical disk is One of the above prisms is perpendicularly incident on one surface of an optical glass prism, and Predetermined component of the beam transmitted through the beam splitter film is configured to be polarization split into two beams by the quartz prism.

[Action]

According to the first aspect of the present invention, the one prism reduces the number of components and enables the optical head to be reduced in size and weight.

〔Example〕

FIG. 1 shows an optical head 20 for a magneto-optical disk according to an embodiment of the present invention. In the figure, parts corresponding to those shown in FIG. 4 are denoted by the same reference numerals.

The optical head 20 is provided with a laser diode 7, a collimating lens 8, an objective lens 9, a prism 22, a lens 23, and a divided photodiode 24 composed of two photodiode auto units 24a and 24b on a base 21. It is a configuration provided in the arrangement of FIG.

As shown in FIG. 2 and FIG. 3, the prism 22 includes a right-angled triangular prism 25 made of optical glass and a right-angled triangular prism made of quartz.
It is a structure in which 26 is laminated.

The optical glass that is the material of the prism 25 is BK7 (refractive index n
= 1.51).

 The angle α is 64.5 degrees.

The slopes 27 _-1, the beam splitter film (half mirror film) 28 is formed.

The surface _27-2 is a surface on which the laser beam 29 emitted from the laser diode 7 is incident.

The surface _27-3 is a laser beam reflected from the magneto-optical disk 15.
30 is the incident surface.

Looking at the prism 26, the direction of the optical axis 31 is inclined
The direction is inclined 45 degrees with respect to a plane S (corresponding to the paper surface in FIG. 2) including the normal line 32 perpendicular to 27 _-1 and the reflected laser beam 30. This eliminates the need for a half-wave plate.

 The angle β is 64.5 degrees.

Crystal, ordinary refractive index n ₀ is 1.5419, extraordinary refractive index n _e
Is 1.5509.

33 _-1 is the slope. 33 _-2 exit faces of the laser beam, 33 _-3 is the mounting surface.

The prisms 25 and 26 are integrated by bonding the slopes _27-1 and _33-1 with a transparent adhesive.

The prism 22 having the above structure is adjusted in position so that the optical axis 31 forms a 45-degree direction with respect to the polarization direction of the reflected laser beam 30 and the surface _27-3 is perpendicular to the reflected laser beam 30. Installed on 21.

Laser diode 7 and have the collimating lens 8, the incident angle γ with respect to the surface 27 _-2 laser beam 29 is arranged so as to be 72 degrees.

The lens 23 is _disposed to face the surface 33-2.

The split photodiode 24 is disposed behind the lens 23.

In the prism 22, right-angle triangular prisms 25 made of optical glass lowers the relative refractive index with respect to the glass of the quartz performs beam shaping effect on the laser beam 29, reflected laser beam 30 will be reflected by the inclined surface 33 _-1 It acts to suppress that.

 Next, the operation of the optical head 20 will be described.

The laser beam emitted from the laser diode 7, the angle of incidence on the surface 27 _-2 prism 25 of the prism 22 gamma (gamma =
At a beam shaping ratio of about 2.5, and enters the prism 25.

The laser beam incident on the prism 25, the predetermined component by the beam splitter film 28 is reflected and emitted from the surface 27 _-3.

The laser beam is converged on the surface of the magneto-optical disk 15 by the objective lens 9 and is reflected and rotated by the polarization plane according to the information recorded on the magneto-optical disk 15.

Reflected laser beam 30 containing information of magneto-optical disk 15
Is incident at an angle perpendicular to the plane 27 _-3 prism 25 (2
2) Get in.

The reflected laser beam 30 that has entered the glass prism 25 (22) first reaches the beam splitter film 28, where a predetermined component is transmitted and the remaining components are reflected.

The laser beam 30 _-1 transmitted enters from the inclined surface 33 _-1 crystal prism 26, and birefringence extraordinary ray and the ordinary ray 30 _-1-0 30
_-1-e . Refraction angle δ of ordinary ray _30-1-0 is 2.382
Every time, the refractive surfaces of the extraordinary ray 30 _-1-e epsilon is 3.004 degrees, both the separation angle theta ₁ is 0.622 degrees.

The ordinary ray _30-1-0 and the extraordinary ray _{30-1 -e} are
Ray 30 is refracted when the surface 33 _-2 emitted into the air
_Divided into _-1-0-1 and ray _{30-1 -e-1} and spread further.

The refraction angle _の of the ray _30-1-0-1 is 3.684 degrees, the refraction angle η of the ray 30-1 _-e-1 is 4.662 degrees, and the separation angle θ2 between the _two is 0.99 degrees.

The light beams _30-1-0-1 and _{30-1 -e-1} are condensed on the split photodiode 24 through the lens 23, respectively.

The dimension l between the points to be converged is represented by l = f × tan θ ₂ . Focal length at thisゝf lens 23, theta ₂ is the light beam lens 30 _-1-0-1, a separation angle of 30 _-1-e-1.

f is 15 mm, theta ₂ is 0.99 °, the separation distance l is 262μm
Becomes

This separation distance l (l = 262 μm) is a distance that can be sufficiently divided by the current division photodiode, and
_-1-0-1 is focused on one photodiode portion 24a of the split photodiode 24, and the light beam _{30-1 -e-1} is focused on another photodiode portion 24b.

The outputs of the photodiode units 24a and 24b are differentially amplified by the differential amplifier 14 and output as a reproduced signal.

The optical head 20 includes a prism 2, a half-wave plate 5, a polarizing beam splitter 6, two lenses 10, 11 and two photodiodes 1 constituting the optical head 1 shown in FIG.
Since the seven parts 2 and 13 are composed of three parts, one prism 22, one lens 23 and one split photodiode 24, the size and weight are considerably smaller than in the past.

Thus, the access operation of the optical head 20 is performed at a higher speed than in the related art.

In addition, since the number of the photodiodes 24 is one, the position adjustment of the photodiodes, which had conventionally been separately adjusted, can be performed only once, and the adjustment is simplified.

The _{focal points of} the light beams _30-1-0-1 and _{30-1 -e-1} are determined by the birefringence of the quartz prism 26 and the angle β of the quartz prism 26, which are physical constants. For this reason, the distance l between the light-convergent points can be expected to be constant at the time of manufacture, which helps to simplify the adjustment.

Since the quartz prism 26 is used, the degree of polarization separation is 100 times or more higher than when a multilayer film is used, and there is no change with time and no dependence on the incident angle.

Calcite is mechanically weak, has a slight deliquescence, and is weak to heat, so it is difficult to process and coat it as compared with glass. Also, since the thermal expansion coefficient is larger than glass, it is necessary to pay attention to bonding. Quartz is easy to process, chemically stable, and inexpensive because it is already artificially mass-produced.

〔The invention's effect〕

As described above, according to the first aspect of the invention, since the polarization separation of the reflected laser beam is performed by one prism, the number of parts can be significantly reduced.
Thereby, downsizing and weight reduction can be achieved. This can speed up access.

According to the invention of claim 2, the laser beam can be shaped.

According to the third aspect of the present invention, it is possible to reduce the adverse effect of the bonding adhesive layer.

[Brief description of the drawings]

FIG. 1 is a view showing an optical head for a magneto-optical disk according to an embodiment of the present invention, FIG. 2 is a view showing the configuration and function of a prism in FIG. 1, and FIG. 3 is a prism in FIG. FIG. 4 is a diagram showing a conventional example. In the figure, 7 is a laser diode, 14 is a differential amplifier, 15 is a magneto-optical disk, 20 is an optical head for a magneto-optical disk, 21 is a base, 22 is a prism, 23 is a lens, 24 is a split photodiode, 24a, 24b is a photodiode part, 25 is a right-angled triangular prism made of optical glass, 26 is a right-angled triangular prism made of quartz, _27-1 is a slope, _27-2 and _27-3 are planes, 28 is a beam splitter film, and 29 is a laser. Beam, 30 is a reflected laser beam, 30 _-1 is a laser beam transmitted through a beam splitter film, 30 _-1-0 is an ordinary ray, 30 _-1-e is an extraordinary ray, 30 _-1-0-1 , 30 _{-1 -e-1} is the separated light beam, 31 is the optical axis, 32 is the normal, 33 _-1 is the slope, 33 _-2 , 33 _-2 is the surface, and S is the normal of the reflected laser beam and the slope of the quartz prism. Include the surface.

Claims (3)

(57) [Claims] A reflected laser beam (3) emitted from a laser diode (1) and reflected by a magneto-optical disk (5).
In the optical head for a magneto-optical disk for reading the information of the magneto-optical disk by polarization-separating the optical glass ( ₀ ), a prism (2) made of an optical glass having one slope (27 _-1 ) is used.
5) and the reflected laser beam (30) and its one slope (33
_-1 ) and a prism (26) made of quartz having an optical axis (31) at a direction of 45 degrees with respect to the plane (S) including the normal (32) of the slope ( _27-1 , _33-1). ) And a prism (22) having a beam splitter film (28) at the bonding portion. The laser beam (2a) from the laser diode (7) is incident on the optical glass prism. The reflected laser beam (30) from the magneto-optical disk (15) is reflected by the beam splitter film (26) toward the magneto-optical disk (15). Incident on one surface of the prism (25) perpendicular to (27 _-3 ),
A predetermined component of the reflected laser beam passes through the beam splitter film (28), and the quartz prism (26)
An optical head for a magneto-optical disk characterized in that it is configured to be polarized and separated into two light beams (30 _-1-0 , 30 _-1-e ). 2. A reflected laser beam (3) emitted from a laser diode (1) and reflected by a magneto-optical disk (5).
In the optical head for a magneto-optical disk for reading out the information of the magneto-optical disk by polarization-separating the light beam of 0), one inclined surface (27 _-1 ) and a surface for shaping the laser beam (27 _-2 )
A prism (25) made of optical glass having a reflection laser beam (30) and a normal ( _32-1 ) to one slope thereof (33 _-1 )
Doo containing surface (S) in the direction of 45 degrees the optical axis with respect to (31) to quartz prism (26) and the slope (27 _-1, 3
3 _-1 ) is composed of one prism (22) having a beam splitter film (28) at the bonded part, and the laser beam (2a) from the laser diode (7) is made of the optical glass. The light enters the prism surface ( _27-2 ) at an angle, is beam-shaped, is reflected by the beam splitter film (26), travels toward the magneto-optical disk (15), and reflects from the magneto-optical disk (15). A laser beam (30) is incident on one surface of the optical glass prism (25) of the prism (22) perpendicularly to (27 _-3 ), and a predetermined component of the reflected laser beam is The two light beams (30 _-1-0 , 30 _-1-e ) are transmitted through the splitter film (28) and are transmitted by the quartz prism (26).
An optical head for a magneto-optical disk, wherein the optical head is configured to be polarized and separated. 3. A prism (22) formed by bonding the prism (25) made of optical glass and the prism (26) made of quartz, wherein the beam splitter film (28) is a part of the bonded part. 3. An optical head for a magneto-optical disk according to claim 1, wherein said optical head is provided on a side of said optical glass prism.