JP3119547B2 - Equivalent Wollaston prism and optical pickup head using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equivalent Wollaston prism for an optical pickup head and an optical pickup head using the same. The present invention relates to an optical pickup head using a Wollaston prism.

[0002]

BACKGROUND OF THE INVENTION Typically, an optical pickup head for a magneto-optical disk system consists essentially of a collimator lens, several beam splitters, and other lenses to detect RF, focusing and tracking signals. I have. Thereafter, such signals are transmitted forward for further processing, and data is extracted from the optical disk. Typically, a pickup head is composed of ten or more parts that are difficult to assemble and align. Consequently, U.S. Patent Nos. 4,771,414 and 4,951,274
A Wollaston prism as disclosed in US Pat.

Referring to US Pat. No. 4,771,414 as an example, FIG. 1 shows the configuration of a pickup head using a Wollaston prism. The pickup head 10 mainly includes a semiconductor laser 11 and
Collimator lens 12 and first polarized beam splitter 13
, Objective lens 14 and second polarizing beam splitter 15
A first light receiving lens 16, a first light detector 17,
It comprises a phase compensator 18, a half-wave plate 19, a Wollaston prism 20, a second light receiving lens 21, and a second light detector 22. The laser light beam L emitted from the semiconductor laser 11 is collimated by the collimator lens 12. The first polarization beam splitter 13 polarizes the laser light beam L toward the objective lens 14 and then focuses the light beam L on the optical disk 30. The reflected laser beam L is focused by the objective lens 14 and then
The light is polarized by the first polarization beam splitter 13 and directed to the second splitter 15. The laser beam L is split into a first laser beam L1 and a second laser beam L2. The first laser beam L1 is directed to the photodetector 17 through the first light receiving lens 16. The photodetector 17 receives the laser beam L1 and generates a detection output signal. The error signal generator 31 receives the detection output signal of the photodetector 17, and outputs the focusing error signal Sf and the tracking error signal St for the focus servo control and the tracking servo control, respectively.
To produce The second laser beam L2 is supplied to the phase compensator 18
Through the half-wave plate 19 to the Wollaston prism 20, where the P-polarized component LP and the S-polarized component LS
And focused on the second photodetector 22 through the second light receiving lens 21. The information signal generator 32 receives the P-polarized component LP and the S-polarized component LS and generates a reproduced information signal Si.

[0004]

However, in the conventional optical pickup device described above, the information signal S
Since i, the focusing error signal Sf and the tracking error signal St are detected separately, the structure for this device is bulky, complicated and expensive. Furthermore, the Wollaston prism in such a device is made up of two birefringent prisms, which requires a large space, is very expensive, and is difficult to align. In most cases, this type of Wollaston prism guides the laser beam directly, requiring the entire system to be arranged in a straight line, limiting the miniaturization of the structure.

The main object of the present invention is to convert an incident light beam to S
And to provide an equivalent Wollaston prism for splitting into two adjacent beams, both rotated about 90 °, with P and P polarization. A second object of the present invention is to provide an optical pickup head that can be optimally designed with very few parts that are easily manufactured at low cost.

[0006]

According to the present invention, an equivalent Wollaston prism for polarizing and splitting an incident light beam includes first and second prisms, the first prism comprising an incident light beam. Surface, a polarization splitter at a first predetermined angle with respect to the incident surface, and a developing surface at a second predetermined angle with respect to the polarization splitter. And the polarizing splitter splits the incident light beam into a reflected beam and the remaining components. Also, the second prism reflects the remaining component of the incident light beam toward the expression surface at a third predetermined angle with the boundary surface of the first prism attached to the polarization splitter. It has a reflective surface to make it work.

According to the present invention, an optical pick-up head for picking up information on an optical disk includes a laser beam generator for emitting a light beam; guiding the light beam onto the disk; A light beam guiding device for splitting the reflected light beam; including a first and a second prism, wherein the first prism receives the light beam; A polarizing splitter at one predetermined angle, and a manifestation surface at a second predetermined angle with respect to the polarizing splitter, wherein the polarizing splitter reflects the light beam. Splitting the beam into a first polarized beam and a second polarized beam, wherein the second prism has an interface attached to a polarization splitting plate of the first prism; and 3 pre-determined An equivalent Wollaston prism having a reflective surface for reflecting the second polarized beam toward the manifestation surface at an inclined angle; and the first and second polarized waves. A light detection unit for receiving the beam and generating a detection signal according to the first and second polarized beams.

[0008]

Referring to FIG. 2, there is shown a schematic diagram of two preferred embodiments of the equivalent Wollaston prism of the present invention. The equivalent Wollaston prism 6 includes a first prism 62 and a second prism 64. The first prism 62 has an entrance surface 622, a polarization splitting surface 624, and an expression surface 626. Incident light beam L
I is the equivalent Wollaston prism 6 through the entrance surface 622
, The prism 6 itself has an optical axis oriented toward the polarization splitting surface 624. The polarization splitting surface 624 is provided at a first predetermined angle with respect to the incident surface 622, and converts the light beam LI into a first reflected beam LP (beam L
I), and the remaining component LS (beam L
I having an S-polarized component of I). The manifestation plane has a second predetermined angle θ with respect to the polarization splitting plane 624, and from the manifestation plane:
A first reflected beam LP comes out. The second prism 64 has a boundary surface 642 and a reflection surface 644. Boundary surface 6
Reference numeral 42 denotes a boundary between the first prism 62 and the second prism 64, where the second prism 64 is attached to the polarization splitting surface 624. Reflective surface 644
Of the light beam LI, also referred to as a second reflected beam LS, which is provided at a third predetermined angle φ with respect to the manifestation surface 626 of the first prism 62 and includes the S polarization component of the light beam LI Reflect the rest. The second reflected beam LS exits the equivalent Wollaston prism 6 through the manifestation surface 626 of the first prism 62.

In the present invention, the preferred values of the first predetermined angle and the second predetermined angle θ are 45
°, the incident light beam LI becomes the first reflected beam L
At right angles to P to facilitate design and assembly of the entire system. In order to achieve total reflection, it is necessary to determine the value of the angle φ according to the following equation: φ <90 ° −sin ⁻¹ (1 / n), where n is the first and second angles. Is the refractive index of the material of the prisms 62 and 64 of FIG. FIG.
In the path of the second reflected beam LS shown in FIG.
In the following case, the path of the second reflected beam LS shown in FIG. 2B is a case where φ is 45 ° or more. The refraction angle γ of the second beam LS is determined by the following equation: γ = sin ⁻¹ [n ^* sin (90 ° −2φ)]. As can be seen from the above equation, the value of φ must be carefully designed to ensure that the first and second reflected beams LP and LS are projected at the correct position for later processing.

Referring to FIG. 3, there is shown a schematic diagram of an optical pickup head system using the equivalent Wollaston prism in FIG. The optical pickup head 5 according to the present invention includes a laser beam generator 51 (ie, a semiconductor laser) and a collimator lens 5.
2, a beam splitter 53, an objective lens 54, a half-wave plate 55, an equivalent Wollaston prism 6 (as shown in FIG. 2), a light receiving lens 67, and a light detection unit 7
And a signal generator 8.

A laser beam LI emitted from a laser beam generator 51 is collimated by a collimator lens 52, projected through a splitter 53, and thereafter,
It is focused on the optical disk 30 by the objective lens 54. The reflected laser beam LI is converged by the objective lens 54 and then deflected by the splitter 53 through the half-wave plate 55 toward the equivalent Wollaston prism 6. The reflected laser beam LI is split by the equivalent Wollaston prism 6 into a P polarization component LP and an S polarization component LS. The P-polarization component LP and the S-polarization component LS are projected onto the light detection unit 7 after passing through the light receiving lens 67.

Referring to FIG. 4, there is shown in accordance with the present invention.
Of the circuit of the light detection unit 7 and the signal generator 8
The figure is shown. The light detection unit 7 is a reflection laser
The polarization component LP and the S polarization component LS of the beam LI are detected.
Have five photodetectors A, B, C, D and E for
I have. Detection signals generated by those photodetectors
R _A, R_B, R_C, R_DAnd R_EIs sent to the signal generator 8.
Can be The signal generator 8 comprises adders 81, 82 and 83
And subtracters 84, 85 and 86.
The signal generator 8 outputs the detection signal R_A, R_B, R_C, R_Das well as
R_EReceived and the tracking error signal St (= R_A-R
_B) And the information signal Si (= (R_A+ R_B)-(R_C+ R
_D+ R_E)) And the focusing error signal Sf (= (R_C+
R_E) -R_D) And produce.

Since the first prism 62 is rectangular and the second prism 64 is thin, the equivalent Wollaston prism 6 according to the present invention can be made compact in size.
In such a configuration, when the reflected laser beam LI is split into an S-polarized component and a P-polarized component, it is rotated by about 90 °.

[0014]

Therefore, the overall structure of the pickup head does not need to be straight, reducing the volume of the entire system and the complexity of assembly, leaving more room for pickup head design. The configuration according to the present invention reduces the total number of elements and the cost because the information signal, the focusing error signal and the tracking error signal are detected by only one signal generator and a photodetector having five photodetectors. Achieved.
Therefore, the entire configuration is simpler and smaller than the pickup head produced by the conventional technique, and is advantageous in cost.

Although the invention has been described in accordance with what is considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but falls within the spirit and scope of the appended claims. It is intended to cover many modifications and similar sequences, the scope of which is consistent with the broadest interpretation so as to encompass all such modifications and similar structures.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conventional optical pickup head using a conventional Wollaston prism.

FIG. 2 (a) shows a preferred embodiment of a Wollaston prism according to the present invention; FIG. 2 (b) shows another preferred embodiment of a Wollaston prism according to the present invention.

FIG. 3 is a diagram showing an optical pickup head using an equivalent Wollaston prism according to the present invention.

FIG. 4 is a diagram showing a circuit of a light detection unit and a signal generation device according to a preferred embodiment.

[Explanation of symbols]

 Reference Signs List 5 pickup head 6 equivalent Wollaston prism 7 light detection unit 8 signal generator 30 optical disk 51 laser beam generator 52 collimator lens 53 beam splitter 54 objective lens 55 half wave plate 62 first prism 64 second prism 67 light receiving Lens 622 Incident surface 624 Polarization dividing surface 626 Expression surface 642 Boundary surface 644 Reflecting surface

Continuation of the front page (51) Int.Cl. ⁷ identification code FI G11B7 / 135 G11B7 / 135Z (56) References JP-A-2-168205 (JP, A) JP-A-64-48019 (JP, A (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 5/04 G02B 5/32 G11B 7/135

Claims (4)

(57) [Claims] 1. An equivalent Wollaston prism for polarizing and splitting an incident light beam: an incident surface for receiving an incident light beam, a polarization splitting surface at a first predetermined angle with respect to said surface, And a manifestation plane at a second predetermined angle with respect to the polarization splitting plane, wherein the polarization splitting plane splits the incident light beam into a reflected beam and the remaining components. A first prism; a boundary surface attached to the polarization splitting surface of the first prism; and a third predetermined angle at which the remaining component of the incident light beam is directed toward the expression surface. A second prism having a reflecting surface for reflecting light , wherein the third predetermined angle φ is such that n is equal to the first and second angles.
An equivalent Wollaston prism, wherein the refractive index of the material of the second prism is determined by the following equation: φ <90 ° −sin ⁻¹ (1 / n) . Wherein said first and second equivalent Wollaston prism according to claim 1, characterized in that the predetermined angle is 45 degrees. 3. An optical pickup head for picking up information on an optical disk, comprising: a laser beam generator for emitting a light beam; and a light beam guide device for guiding the light beam onto the disk. A light beam guide device for splitting the light beam, and an equivalent Wollaston prism including a first prism and a second prism, wherein the first prism has an incident surface for receiving the light beam; A polarization splitting surface at a first predetermined angle with respect to the incident surface, and a manifestation surface at a second predetermined angle with respect to the polarization splitting surface, wherein the The polarization splitting surface acts to split the light beam into a reflected first polarization beam and a second polarization beam, and the second prism comprises a polarization of the first prism. A boundary surface attached to the dividing surface, and a reflecting surface at a third predetermined angle for reflecting the second polarized beam toward the manifestation surface; A light detection unit for receiving the first and second polarized beams and generating a detection signal according to the first and second polarized beams , wherein the third predetermined angle φ is n To the first and
An optical pickup head characterized in that the refractive index of the material of the second prism is determined by the following equation: φ <90 ° −sin ⁻¹ (1 / n) . 4. The optical pickup head according to claim 3, wherein the first and second predetermined angles are 45 degrees.