JPH09293260A - Optical crystalline element and optical pickup using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a practical light quantity by providing one ridge line at the boundary plane of plural translucent parts to simplify the structure. SOLUTION: An optical crystalline element is constituted of a translucent part 1 made of a translucent uniaxial crystal and a translucent part 2 having refractive indexes substantially equal to the ordinary ray refractive index or the extraordinary ray refractive index and respective translucent parts 1, 2 are joined with boundary planes 3 and the element has one ridge line 4 at the boundary planes 3. Then, the translucent part 2 having a refractive index equal to the ordinary ray refractive index is selected by properly selecting the angle formed by the optical crystalline axis of the uniaxial crystal of the translucent part 1 with respect to the optical axis of an incident light beam and the ordinary ray refractive index. Thus, the element whose functions are different according to the polarized states of a light beam passing through an optical crystalline element is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization optical crystal element, and more particularly to an optical system of an optical pickup in an optical information reader.

[0002]

2. Description of the Related Art Optical information readers include so-called CD (compact disk) and SD (super densi) optical recording media.
ty disk) and other compatible optical video disc players that can read recorded information from optical discs,
The optical pickup has an optical system that irradiates the optical disc through the quarter wavelength plate and the objective lens and reads the return light from the optical disc through the objective lens and the quarter wavelength plate. A phase difference method, a push-pull method, and the like are used as a tracking servo control method for the optical pickup. In the optical pickup, during reproduction, the objective lens is deviated due to the eccentricity of the optical disc, which causes the returning light spot to move on the returning light receiving element. In tracking servo control, a method for highly accurate optical pickup position control is always required. In the prior art,
In general, the pickup uses a 4-division DET using the astigmatism method for the focus servo, so that the beam moves due to the movement of the objective lens and the division line shifts.

Further, in an integrated drive type push-pull method optical pickup, a return hologram is divided by diffraction using a polarization hologram having a diffraction grating having unevenness or a refractive index distribution, and a low-order diffracted light spot is formed on a light receiving element. It has also been attempted to form. Since this polarization hologram uses diffraction, the incident beam can be split into several beams.

However, in the method using the polarization hologram, it is difficult to produce a hologram having a high diffraction efficiency, high-order diffracted light is lost, and the amount of light that can be actually used is small. Further, since the hologram has a strong wavelength dependence,
There are drawbacks such as weak sensitivity to changes in the wavelength of the semiconductor laser of the light source.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical crystal element for an optical pickup and an optical pickup optical system using the same, which can obtain a practically usable light amount with a very simple structure.

[0006]

The optical crystal element of the present invention comprises a first light-transmitting portion made of a light-transmitting uniaxial crystal and a refractive index substantially equal to the ordinary or extraordinary ray refractive index of the uniaxial crystal. And a second light-transmitting portion that is bonded to the first light-transmitting portion via an interface, and has at least one ridge line at the interface.

The optical pickup of the present invention outputs a light beam of 1
An optical pickup which irradiates an optical recording medium through a / 4 wavelength plate and an objective lens, and reads return light from the optical recording medium through the objective lens and a ¼ wavelength plate, which is a translucent uniaxial A first light-transmitting portion made of a crystal and a second light-transmitting portion having a refractive index substantially equal to the ordinary or extraordinary ray refractive index of the uniaxial crystal and joined to the first light-transmitting portion via an interface. At least 1 at the interface.
An optical crystal element having two ridges is arranged on the light beam incident side.

According to the present invention, the birefringence of a uniaxial crystal is used to separate the polarization of an ordinary ray and an extraordinary ray having oscillating planes orthogonal to each other as a forward light beam and a return light beam, respectively. Since the return light spot on the light receiving element is obtained, the optical pickup optical system configuration can be simplified. The setting of the optical crystal axis and the setting of the optical axis of the incident light beam are simplified. The optical crystal element, wherein the optical material is an optically isotropic material,
Optically isotropic materials are often cheaper than uniaxial crystals, and since the manufacturing process can be further simplified, downsizing and cost reduction can be achieved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Optical Crystal Element) As shown in FIG. 1, the optical crystal element of the present embodiment has a first translucent portion 1 made of a translucent uniaxial crystal.
And a second light transmissive portion 2 having a refractive index substantially equal to the ordinary or extraordinary light refractive index of the uniaxial crystal, and the first and second light transmissive portions have an interface 3 therebetween. Joined together,
It has at least one ridge 4 at the interface.

The uniaxial crystal exhibits birefringence having different refractive indexes for two orthogonal polarized lights, that is, an ordinary ray refractive index and an extraordinary ray refractive index. The behavior of light waves in this optical crystal can be described by an index ellipsoid. The line of intersection between the index ellipsoid and the plane is generally an ellipse, and the light waves polarized in the directions of the two principal axes orthogonal to each other (the optical field has a vibration direction) have two different values corresponding to the length of the principal axis of the index ellipsoid. It propagates through the crystal with a refractive index. x _i is called an optical principal axis, n _i is called a principal refractive index, and optical crystals are classified into the following three types.

1) If n ₁ = n ₂ = n _3, an isotropic crystal that does not exhibit birefringence (isotropic crystal system) 2) If n ₁ = n ₂ ≠ n ₃ , a uniaxial crystal (tetragonal crystal) System, trigonal system, hexagonal system) 3) In the case of n ₁ ≠ n ₂ ≠ n ₃ , biaxial crystal (triclinic system, monoclinic system, orthorhombic system) z axis in uniaxial crystal An ordinary ray having a polarization direction perpendicular to a plane (main cross section) formed in the light wave propagation direction has a constant refractive index n ₁ = n ₂ = n ₀ (ordinary ray refractive index) regardless of its propagation direction. Propagate inside. On the other hand, the extraordinary ray having the polarization direction in the main cross section is
When the angle formed by the axes is θ, the light propagates in the crystal with a refractive index given by n (θ) in the following equation.

[0012]

[Equation 1]

Here, n (θ) is the propagation of extraordinary rays in the crystal.
N depending on the direction, at θ = 0 to 90 degrees _o(Ordinary ray refractive index)
~ N_e(Refractive index of extraordinary rays). For uniaxial crystals, n
(Θ) = n_o(Z-axis direction corresponding to θ = 0
There is only one optical axis or optical crystal axis). n_e> N_oPlace
Quartz (quartz) is a positive crystal, n_o> N_eCalcite in case of
Etc. are called negative crystals.

Therefore, if the optical crystal axis of the uniaxial crystal is not parallel to the optical axis of the incident light ray, it is possible to separate the two polarizations of the extraordinary ray and the ordinary ray on the planes of oscillation perpendicular to each other. That is, the angle formed by the optical crystal axis of the uniaxial crystal of the first light-transmitting portion 1 and the ordinary ray refractive index with respect to the optical axis of the incident light ray is appropriately selected, and the second refractive index equal to the ordinary ray refractive index is selected. By selecting the translucent part 2, an element having a different function depending on the polarization state of the light beam passing through the optical crystal element can be obtained.

Specifically, as shown in FIG.
The function of the optical crystal element in the optical pickup having the quarter wave plate 9 and the optical crystal element 10 as the axis will be described.
The first light-transmitting portion 1 made of a negative uniaxial optical crystal with no> ne, and the second light-transmitting portion made of the same material as the first light-transmitting portion and having a crystal axis in the traveling direction of the light ray (optical axis). It is a parallel plate composed of the part 2. The first and second light-transmitting portions have a plane interface 3
And the two interfaces form one ridgeline 4 by being joined together. A light beam having a vibrating surface parallel to the paper surface is irradiated from the light source side to the optical disc side (solid line right arrow), and the return light reflected from the optical disc (broken line left arrow) is detected.

The optical axis of the first transparent portion 1 is not parallel to the optical axis,
For example, if it is perpendicular to the paper surface, the light beam that oscillates parallel to the paper surface becomes an ordinary ray and has a refractive index of no. Since the refractive index of the second light transmissive portion 2 is also no, the optical crystal element 10
Acts as a transparent parallel plate having a refractive index of no as a whole. On the other hand, considering the return light on the return path, since it passes through the quarter-wave plate 9 twice, the vibration direction of the light is perpendicular to the paper surface.
In the second translucent portion 2, it becomes an ordinary ray as in the outward path and no
However, the first translucent portion 1 behaves as an extraordinary ray, so that the refractive index is ne. Therefore, the optical crystal element 10 acts as a prism with respect to the returning light, and makes the ridge line a boundary.

The second light transmitting portion 2 does not have to have the same crystal as the first light transmitting portion 1, and the ordinary ray refractive index n of the first light transmitting portion 1 is n.
It may be formed from an optically isotropic material such as optical glass having a refractive index ng equal to o. In this case, no = ng, so
It acts as a transparent parallel plate having a refractive index of no in the outward path. Since the two concavo-convex optical crystal bodies are bonded so that the optical crystal axes of the first and second translucent portions are perpendicular to each other, the deflection angle of the return light can be maximized. The deflection angle of the return light can be adjusted by changing the angle of the interface 3 of the element arranged perpendicular to the optical axis with respect to the optical axis.

Further, not only when the refractive index of the second light transmitting portion is approximately equal to the ordinary ray refractive index of the first light transmitting portion of the uniaxial crystal, but as shown in FIGS. 2 (b) and 2 (c). Even when the refractive index of the second light transmitting portion is approximately equal to the extraordinary ray refractive index of the first light transmitting portion of the uniaxial crystal, the optical crystal element 10 functions as a parallel plate and a prism in the light reciprocating path. Although the second and first optical crystal element bodies are made of the same uniaxial crystal in the above, they may be selected from various uniaxial crystals.

Specifically, LiN is formed in the first and second transparent portions.
An example of an optical crystal element using bO ₃ is shown in FIG. Also,
In FIG. 4, a crystal is first shown as a positive uniaxial crystal (no <ne).
An example of the optical crystal element used for the second transparent crystal part will be shown. In FIGS. 3 and 4, (a) is a forward path, (b) is a return path, no and ne are crystal axis directions, double-headed arrows are light beam oscillation directions, and polarization is return light oscillation directions. Show.

Even when a positive uniaxial crystal is used for the first translucent crystal part, an optical glass (ng = no) having a refractive index ng equal to the ordinary ray refractive index no of the positive uniaxial crystal is used as the second translucent material. It can also be used as a part. Also in this case, as in FIG. 4, the ridge line projects to the opposite side of the case of the negative uniaxial crystal. (Manufacturing Method of Optical Crystal Element) 1) Both sides of a plurality of uniaxial crystal flat plate members A and B are polished.

2) As shown in FIG. 5, flat plate members A and B
Alternately stick together to form blocks. 3) As shown by the alternate long and short dash line in FIG. 5, the block is cut in parallel to the required bias angle to form a plurality of flat plates C composed of alternating uniaxial crystal stripes. 4) Polish the cut surface of each striped flat plate.

5) As shown in FIG. 6, the striped flat plates C are alternately laminated to form a block. 6) As shown by the solid line perpendicular to the paper surface of FIG. 6, the block is cut in parallel along the ridgeline of each element to form a plurality of flat plates to which the elements are connected. Cut vertically.

7) Polish both sides of the flat plate to which the elements are connected. 8) An optical crystal element is obtained by cutting into the required element size. Examples of uniaxial crystal materials are shown in the table below.

[0024]

[Table 1] (Optical Pickup Using Optical Crystal Element) FIG. 7 schematically shows an optical pickup of the recording / reproducing apparatus of this embodiment. In the irradiation optical system, the laser beam light (solid line) from the laser light source 21 passes through the optical crystal element 10 and the quarter-wave plate 9 as parallel light by the collimator lens 22, and is rounded by the objective lens 26 to have a minute diameter. It is focused on the recording surface pit row of the optical disc 27 as a spot. In the same detection optical system as the return optical system, the optical disc 2
The reflected light from 7 again passes through the objective lens 26 and becomes 1 /
The four-wave plate 5 polarizes the vibrating surface with an inclination of 90 degrees, passes through the optical crystal element 10 again, and is divided and deflected by the optical crystal element 10. The deflected return light is condensed by the collimator lens 22 and guided to the divided light receiving surface of the photodetector 29. The optical crystal element 10 is arranged so that the ridge line 4 is perpendicular to the optical axis, and the divided light-receiving surfaces are arranged symmetrically with respect to the ridge line 4.

Here, as shown in FIG.
The output signal from the divided light-receiving surface is processed and the recorded information is reproduced by the RF signal. Focusing and tracking servo are also performed from the output signal. Since the return light can be separated along the ridgeline of the optical element as shown in FIG. 8, the beam movement on the light receiving surface due to the movement of the actuator can be ignored with respect to the ridgeline. When a push-pull signal is used for tracking, it is possible to eliminate the adverse effect of beam movement.

Further, as shown in FIG. 9, the output signals A to G from the divided surfaces A to G obtained by dividing the light receiving surface of the photodetector 29 into four parts.
An RF signal, a focus signal, a push-pull signal, and a phase difference method signal can be obtained from G by a circuit that executes the equation shown in FIG. Law (DV
D-ROM) can also be output, so reproduction from optical disks with different pit depths is possible.

In this way, in the pickup device, the objective lens 26, the optical crystal element 10 and the quarter-wave plate 9 can be controlled as an integrated driving body as shown by the broken line in FIG. 10, and an infinite specification type pickup is achieved. Since it can be done and the structure is simple, complicated adjustment is not necessary. further,
As shown in FIG. 11, a finite-specification type pickup in which the optical crystal element 10 and the quarter-wave plate 9 are arranged between the objective lens 26 and the light source side collimator convex lens 28 and can be controlled together with the photodetector 29 as an integrated driving body. Can also be achieved. (Other Embodiments) Another pickup optical system is shown in FIG.
As shown in FIG. 2, a dielectric mirror 31 is arranged between the optical crystal element 10 and the collimator lens 22 of FIG.
2 and the laser light source 21 between the polarization beam splitter 32
There is a device that protects the laser light source.

In such a pickup optical system, as shown in FIG. 13, the photodetector 29 is used as a 4 × 2 division element, and the equation shown in FIG. 13 is executed from the output signals D1-8 from the division elements D1-8. The RF signal, the focus signal, the push-pull signal, and the phase difference method signal can be obtained by the circuit for performing the phase difference method (DVD-RAM) as the tracking signal.
D-ROM) can also be output, so reproduction from optical disks with different pit depths is possible.

Similarly, a cylindrical lens is provided between the polarization beam splitter and the photodetector shown in FIG. 12, and the 4 × 2 splitting element of the photodetector 29 shown in FIG.
Even the push-pull method (DVD-RAM), the phase difference method (DV
D-ROM) can also be output, so reproduction from optical disks with different pit depths is possible. On the other hand, as the optical crystal element 10, as shown in FIG. 15, (a), (b)
And (d) in which the plane interface from the ridge is inclined symmetrically with respect to the pickup optical axis, (c) and (e) in which the plane interface from the ridge is biased to the pickup optical axis, The prism shape of the optical crystal element can be variously combined according to the pickup optical system, such as (f) in which alternating-stage three-division type plane interfaces are formed. Further, in the optical crystal used for the pickup, the interface with the glass is a flat surface in the embodiment, but even if it is a curved surface, the same effect can be obtained. Another possibility is that only one surface of the interface is curved. The three-division type shown in FIG. 15D is effective in dealing with crosstalk (a signal jumps from an adjacent track).

Further, although the return beam is divided into two by one ridge line in the above-mentioned embodiment, this can be divided into four when the optical crystal is a quadrangular pyramid. It is effective for applications such as detection, and it is also effective for inclination and deviation in the time axis direction. That is,
The position can be controlled so that the scanning direction coincides with the tangential direction (track extension direction) of the pit train so that the pit train, which is the information recording portion of the optical disc, is moved by scanning.

[0031]

According to the present invention, the first light-transmissive portion made of a light-transmissive uniaxial crystal and a refractive index substantially equal to the ordinary or extraordinary light refractive index of the uniaxial crystal are provided. The second light-transmissive portion is joined to the light-transmissive portion through the interface and has at least one ridgeline at the interface, so that the polarization of the extraordinary ray and the ordinary ray can be separated. Therefore, it is possible to obtain an optical crystal element which can obtain a practical amount of light and is strong against a change in the wavelength of the laser.

Further, according to the present invention, a light beam is applied to an optical recording medium through a quarter wavelength plate and an objective lens, and return light from the optical recording medium is read through the objective lens and the quarter wavelength plate. A pickup having a first light-transmitting portion made of a light-transmitting uniaxial crystal and an interface having a refractive index substantially equal to an ordinary ray index or an extraordinary ray refractive index of the uniaxial crystal and having an interface with the first light transmitting portion. For a DVD and a DVD-RAM, since the optical crystal element, which is composed of the second light-transmitting portion that is joined via the optical crystal element and has at least one ridgeline at the interface, is an optical pickup optical system arranged on the light beam incident side. The structure of the compatible player can be extremely simplified, and miniaturization and cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical crystal element of an example.

FIG. 2 is a cross-sectional view of an optical crystal element of an example.

FIG. 3 is a cross-sectional view of an optical crystal element of an example.

FIG. 4 is a cross-sectional view of an optical crystal element of another example.

FIG. 5 is a perspective view of an optical crystal plate block in a method for manufacturing an optical crystal element of an example.

FIG. 6 is a cross-sectional view of an optical crystal plate block in an optical crystal element manufacturing method of an example.

FIG. 7 is a schematic perspective view of an optical pickup optical system using the optical crystal element of the example.

FIG. 8 is a schematic plan view of a light receiving element of an optical pickup optical system using the optical crystal element of the example.

FIG. 9 is a schematic plan view of a light receiving element of an optical pickup optical system using an optical crystal element of another example.

FIG. 10 is a schematic cross-sectional view of an optical pickup optical system using the optical crystal element of the example.

FIG. 11 is a schematic cross-sectional view of an optical pickup optical system using an optical crystal element of another example.

FIG. 12 is a schematic cross-sectional view of an optical pickup optical system using an optical crystal element of another example.

FIG. 13 is a schematic plan view of a light receiving element of an optical pickup optical system using an optical crystal element of another example.

FIG. 14 is a schematic plan view of a light receiving element of an optical pickup optical system using an optical crystal element of another example.

FIG. 15 is a cross-sectional view of an optical crystal element of another example.

[Explanation of symbols for main parts]

 1 1st translucent part 2 2nd translucent part 3 Interface 4 Ridge line 9 Quarter wave plate 10 Optical crystal element 21 Laser light source 22 Collimator lens 26 Objective lens 27 Optical disk 29 Photodetector

Claims (21)

[Claims] 1. A first light-transmitting portion made of a light-transmitting uniaxial crystal, and a refractive index substantially equal to an ordinary ray index or an extraordinary ray refractive index of the uniaxial crystal, and the first light transmitting portion. An optical crystal element, comprising: a second light-transmitting portion that is bonded to the substrate through an interface, and has at least one ridgeline at the interface. 2. The optical crystal element according to claim 1, wherein the surfaces of the incident side and the emitting side are parallel planes. 3. The optical crystal element according to claim 1, wherein the interface is a flat surface. 4. The optical crystal element according to claim 3, wherein the interface includes a spherical surface or an aspherical surface. 5. The optical crystal element according to claim 1, wherein an optical crystal axis of the first light transmissive portion is substantially parallel or perpendicular to the ridge line. 6. The optical crystal element according to claim 1, wherein the first and second translucent portions are made of the same material. 7. The optical crystal element according to claim 1, wherein an optical crystal axis of the second light transmissive portion is substantially perpendicular or parallel to the ridge line. 8. The optical crystal element according to claim 7, wherein the optical crystal axes of the first and second translucent portions are arranged to intersect with each other. 9. The optical crystal element according to claim 8, wherein the optical crystal axes of the first and second translucent portions are arranged at an angle of 90 degrees with respect to each other. 10. The optical crystal element according to claim 1, wherein the second light transmissive portion is made of an optically isotropic material. 11. An optical pickup which irradiates an optical recording medium with a light beam through a quarter wavelength plate and an objective lens, and reads return light from the optical recording medium through the objective lens and the quarter wavelength plate. And a first light-transmitting portion made of a light-transmitting uniaxial crystal, and a refractive index substantially equal to the ordinary ray refractive index or extraordinary ray refractive index of the uniaxial crystal, and the first light transmitting portion An optical pickup comprising: an optical crystal element having a second light-transmissive portion bonded through an interface and having at least one ridgeline at the interface, the optical crystal element being disposed on a light beam incident side. 12. The optical pickup according to claim 11, wherein the optical crystal element is arranged such that the uniaxial crystal is substantially perpendicular to an optical axis of an incident light beam and a vibration surface. 13. The optical crystal element according to claim 11, wherein the surface on the incident side and the surface on the output side are parallel planes. 14. The optical crystal element according to claim 11, wherein the interface is a flat surface. 15. The optical crystal element according to claim 14, wherein the interface includes a spherical surface or an aspherical surface. 16. The optical crystal axis of the first light-transmissive portion is substantially parallel or perpendicular to the ridgeline.
1. The optical crystal element according to 1. 17. The optical crystal element according to claim 11, wherein the first and second translucent portions are made of the same material. 18. The optical crystal axis of the second light-transmissive portion is substantially perpendicular or parallel to the ridgeline.
1. The optical crystal element according to 1. 19. The optical crystal element according to claim 18, wherein the optical crystal axes of the first and second light transmissive portions are arranged so as to intersect with each other. 20. The optical crystal element according to claim 19, wherein the optical crystal axes of the first and second translucent portions are arranged at an angle of 90 degrees with respect to each other. 21. The optical crystal element according to claim 11, wherein the second light transmissive portion is made of an optically isotropic material.