JP2001116915A - Light beam separator for polarized-light separation of monochromatic light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a relatively small-sized light beam splitter for monochromatic polarized-light separation which is composed of a small number of constituent elements, can be manufactured in a single manufacturing process, and low in manufacture cost. SOLUTION: An element which changes the polarized state of monochromatic light is arranged in the course of a transmission body passing light beam or its partial light beam behind a grating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam splitter for separating a single light beam into polarized light. Such a beam separator is used, for example, in an optical pickup in which reading and writing of an information layer in a storage element are problematic.

[0002]

2. Description of the Related Art In the current state of the art, a number of solutions are known with integrated pickup systems which are implemented with refractive or diffractive optics and which can realize various functions. The central part of the system often consists of a combination of individual optical elements provided with a reflective layer, for example a prism, a flat plate or the like. Optical elements are often configured as integrated optical glass blocks to maintain subtle measurement accuracy and increase fault resistance, such as those sold by the Matsushita group, for example.

Another example is US Pat. No. 5,682,682.
373. It states that a polarizer as a central element separates a monochromatic ray into a vertical component and a horizontal component. According to this apparatus, reading and writing with an optical storage element are of various scales (CD, DVD).
Can be done.

[0004]

However, the polarizing optical element is made relatively complicated, and the adjustment work is complicated. In addition, the individual components must go through a number of technical steps during manufacture, resulting in high costs. Another pickup concept using diffractive optics is Spie No. 1663
Volume "Storing Optical Data" (1992), pp. 46-57. According to this, a volume grating made based on holography is arranged alongside a relief grating in a dense recording medium. Since these gratings placed on the translucent member are made by different manufacturing techniques, they must be coordinated with each other and assembled.
Therefore, to achieve high accuracy, this adjustment requires a great deal of effort.

[0005] From such a state of the prior art, the present invention provides a relatively small monochromatic light beam separator for monochromatic light polarization separation which has a small number of constituent elements, can be manufactured in one manufacturing process, and is inexpensive in manufacturing cost. The task is to provide.

[0006]

SUMMARY OF THE INVENTION This problem in the beam splitter for monochromatic polarization separation is achieved according to the invention by
The element that changes the polarization state of the monochromatic light is eliminated by arranging it in the path of the light beam passing through the light transmitting member or its partial light beam, also at a position subsequent to the grating. The grating is arranged on a translucent body, through which light rays pass.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention,
The grating and / or the polarization switching element may be arranged directly on the light-transmitting body or via the at least one light-transmitting intermediate on the light-transmitting body, or in each case immediately without contacting the light-transmitting body. In another preferred embodiment of the invention, the polarization switching element is arranged on the light-transmitting surface opposite the grating.
Advantageously, the grating and the polarization switching element each comprise a surface relief grating. Further advantageous embodiments are described in the dependent claims.

The light beam splitter constructed as described above for the purpose of polarization separation of monochromatic light has various alterations, so that a plurality of information layers can be read out in parallel or read and written simultaneously. It is possible to construct an optical pickup that can also be used.

Hereinafter, the present invention will be described in more detail based on a principle diagram. FIG. 1 shows a principle diagram of a light beam separator according to the present invention. A grating 2 is arranged on the light transmitting body 1. The monochromatic light incident on the grating 2 is polarized so that all the rays x pass through the grating 2 without diffracting as much as possible. The monochromatic beam is then preferably polarized such that the electric field strength vector of the beam oscillates perpendicular to the grating grooves. The monochromatic light beam passes through the light transmitting body 1 and reaches the element 3 that switches the polarization of the monochromatic light, and passes straight through the element 3. The grating 2 is preferably a phase grating having a high transmission for the used light beam.

The polarization switching element 3 has | ψ | = 70 ° -11
A phase shift is realized within the range of 0 °. The element 3 consists of a phase grating with a lattice constant that is not the first in the wavelength used during transmission and reflection, that is, allows a higher order. The light transmitting body 1 is formed of, for example, a glass plate having a parallel surface with a thickness of several mm.

To achieve a phase shift, the grating structures of grating 2 and element 3 must be arranged within a defined angular range of each other, preferably at an angle of 45 °. The grating 2 and the element 3 are either based on holographic / lithographic structuring techniques commonly used in electronics or are copies of a master element manufactured by said techniques. The element 3 can also be constituted by a birefringent crystal, foil, or the like.

FIG. 2 shows the principle of the beam splitter according to the present invention used in a simple pickup system. Light from a monochromatic light source 9, for example a laser diode, reaches a grating 21 arranged on the light transmitting body 1. The component (x) of the monochromatic light having an electric field intensity vibration plane perpendicular to the grating groove is not turned by the structure of the grating 21 and passes through, for example, the plate-shaped light transmitting body 1 having parallel surfaces without change in direction. Then, the light reaches the monochromatic light polarization switching element 3. At the exit of the element 3, it is preferably circularly polarized, the light passing through the optical lens system 5 and reaching the object 7,
Reflected by The focal plane 6 may be made of any material suitable for reflecting incident light, such as an optical disk, and may be made of various materials.

[0013] Such a circularly polarized light rotation sensor rotates the light in the opposite direction and passes the light through the optical lens system 5 and the element 3 again. After passing through the element 3, linearly polarized light rotated by 90 ° with respect to the light of the laser diode is generated. As a result, the light is diffracted with high efficiency by the grating 21, is totally reflected on the back surface of the light transmitting body 1, reaches the grating 22, is diffracted by the grating 22 to the first diffraction (light transmitting) device, and is used for evaluation processing. Detector 10
To reach.

Preferably, the lattice constants of the laser diodes 21 and 22 are the same so that the vertically incident laser diode light and the light rays emerging from the lattice 22 follow parallel lines as much as possible. However, it is precisely the grating 2 installed on the translucent body 1 that is parallel.
It is limited to the case where the surfaces of the light transmitting bodies in the elements 1, 22 and the element 3 maintain the parallelism with each other, and the degree of skew is negligible to a negligible degree. The grid 21 depicted in FIG.
And 22 are in a perpendicular relationship to the drawing plane.

FIG. 3 shows a movable focus position type beam splitter for parallel reading or simultaneous reading / writing having one or two overlapping focal planes used in the pickup system. In that case, the light of the light source 9 reaches the grating 21 where it is split into split beams y and z depending on the direction of the grating field position with respect to the ray field intensity vector. The separated light beam y is, as in the case of FIG.
The light passes through the element 31, the optical lens system 52, and the focal plane 6 and reaches the storage element 7.

The other separated light beam z is transmitted through the grid 2
The light is reflected by a plane opposite to the installation side plane 1 and reaches the grating 22, and then reaches the detector 11 via the elements 32 and 51 and the focal plane 12 by reciprocation described in FIG. After splitting at the grating 21, the split beam z is polarized mainly so that the electric field strength vector oscillates parallel to the grooves of the grating 21.

Preferably, the gratings 21, 22, and 23 have the same lattice constant, and the grating grooves are also in the same direction. In FIG. 3, the lattice grooves have a positional relationship perpendicular to the drawing. The corresponding focal plane is adjusted by the optical lens system 51. Like the elements 31 and 32, each of the gratings 21 and
2 and 23 are similarly configured.

The elements 31 and 32 also have | ψ | = 70 ° −
A phase shift is realized within a range of 110 °. Thereby, for example, a λ / 4 function is achieved. The result is a circularly polarized light beam with a different rotational direction, which travels in the illustrated reflected light path and reaches the separate detectors 10 and 11 via the focal planes 6 and 12, respectively.

The rotation of the polarization path in the directions of the focal planes 6 and 12 and vice versa is due to the function of the elements 31 and 32 described in FIG. In that case, the detector 10
Has a vibration plane of the electric field strength vector parallel to the groove of the grating 23, and the polarized light at the detector 11 has a vibration plane of the electric field strength vector perpendicular to the groove of the grating 22. Other polarization direction components at the detector can be neglected.

According to this device, the overlapping storage layers represented by the planes 6 and 12 can be read out in parallel or read and written simultaneously. In addition, the apparatus can be advantageously applied to a disc having a focal plane. In that case, data efficiency can be increased.

FIG. 4 is a diagrammatic view of the principle of a beam splitter according to the invention used in a pickup system for parallel reading or simultaneous reading and writing in two overlapping storage layers, in which case the optical lens system 5 has a vertical focus. The lines are arranged in the direction of the optical axis.

The monochromatic light of the light source 9 reaches the grating 21 through a collimator system 13 composed of, for example, a hybrid collimator, a beam generator and a rotating λ / 2 plate.
The grating 21 splits the light beam into split beams y and z depending on the incident polarization, as shown in FIG. The separated ray y is shown in FIG.
Pass through the element 31 having the polarization-influencing effect described in (1).
The grating 24 arranged in the translucent intermediate 4 efficiently diffracts a ray component whose electric field intensity vector oscillates in parallel with the groove of the grating 24, and the entirety of the light component in a plane opposite to the plane of incidence of the grating 24. The light is reflected and diffracted by another grating 25 again.

This diffracted light beam reaches the liquid crystal lens 8.
In addition, the separated light beam z having the electric field intensity component that mainly oscillates perpendicularly to the groove of the grating 25 also reaches the liquid crystal lens 8. This ray is diffracted by the grating 22 in the same way and totally reflected,
The light reaches the liquid crystal lens 8 through the polarization switching element 32 and the grating 25. Grids 21, 22, 23, 24 and 25
4 has a positional relationship perpendicular to the drawing in FIG.

As described above, in the liquid crystal lens 8, two substantially linearly polarized light beams having vibration planes perpendicular to each other are combined.
This type of liquid crystal lens has an imaging function only on the vibrating surface side, and the other vibrating surface passes without being affected. In the optical lens system 5, two light waves having different branching paths meet in this manner, and the focal planes 6 and 1 of the storage element 71 are combined.
2 is formed. The focal planes 6 and 12 are formed so as to be suitable for storing information in the photosensitive layer or reading out the information in the reflective layer.

The liquid crystal lens 8 is filled with liquid crystal as usual, and its azimuth varies with the set voltage.
This will also change the refractive index of the system. The electrodes are made transparent and are placed in a mold that forms the surroundings of the liquid. This surface may include constant bends, such as a microstructured surface.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a light beam separator according to the present invention.

FIG. 2 is a principle diagram of a beam splitter according to the present invention used in a pickup system.

FIG. 3 is a principle diagram of a beam splitter according to the present invention used in a pickup system for parallel reading or simultaneous reading and writing.

FIG. 4 is a principle diagram of a lens focal point overlapping beam splitter according to the present invention used in a pickup system for parallel reading or simultaneous reading and writing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Translucent body 2,21,22,23,24,25 Lattice 3,31,32 Light switching element 4 Translucent intermediate x light y, z Separated light 5,52,52,53 Optical lens system 6,12 Focal plane 7 Objective lens 71 Storage element 8 Liquid crystal lens 9 Light source 10, 11 Detector 13 Collimator system

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Lingley Wang (Original notation) Lingli Wang Netherlands NL-5709 CD Hermont Wedelhoff 6 (72) Inventor Reinhard Steiner (Original notation) Reinhard Steiner Germany D-07646 Stats Rhoda Homberger Ring 11a (72) Inventor Klaus Rudolf (Original notation) Klaus Rudolf Germany D-07749 Jena Maderweg 9 (72) Inventor Hans Jürgen Dofshall (Original notation) Hans-Juergen Dobschal German D- 99510 Kleinlomstedt-Keschauerweg 26a (72) Inventor Oliver Falkens Strand (original language notation) Oliver Falkenst oerfer Germany D-07749 Jena Maderu Veku 15

Claims (12)

[Claims] An element (3, 31, 32) for changing the polarization state of monochromatic light comprises a light transmitting body (1), a passing light beam and / or
Alternatively, in the course of the separated light beam (y, z), it is also arranged at a position subsequent to the grating (2, 21), and the monochromatic light beam (x) is at least placed on the translucent body (1). Either the light passes through the grating (2, 21) with no change in direction due to the polarization of the grating (2, 21), or separates light (y,
a beam splitter for splitting monochromatic light into polarized light, characterized by being split into z). 2. The grating (2, 21) and / or the polarization switching element (3, 31, 32) are directly on the translucent body (1) or via at least one translucent intermediate (4). 2. The beam splitter according to claim 1, wherein the beam splitter is arranged in the immediate vicinity of the translucent body. 3. The polarization switching element (3, 31, 32) is provided on the plane of the light transmitting body (1) opposite to the surface on which the grating (2, 21) is provided. A beam splitter according to claim 2. 4. The beam splitter according to claim 1, wherein the grating (2, 21) and the polarization switching element (3, 31, 32) each comprise a surface relief grating. vessel. 5. The polarization switching element (3, 31, 32) is | ψ |
The beam splitter according to one of claims 1 to 4, wherein a phase shift is realized in the range of = 70 ° -110 °. 6. The polarization switching element (3, 31, 32) is configured as a foil or a small plate.
Beam splitter according to one of claims 1 to 5. 7. A polarization switching element (3, 31, 32) comprising:
7. A beam splitter according to claim 1, wherein the beam splitter has a four-type structure. 8. An optical plate, a compact disc (C
D) or digital versatile disc (DV
A beam separator according to one of claims 1 to 7 for use in a device for reading and writing of D). 9. The light beam (x) or the separated light beam (y, z) emerging from the element (31, 32) is applied to the focal plane (6) and / or (12) or the storage element (7, 71).
8. An optical lens system (5, 53) for focusing is arranged in the optical path.
Ray separator based on one of the above. 10. An optical lens system (53) comprising a liquid crystal lens (8) and an optical lens (5).
A beam splitter according to claim 8. 11. A beam splitter according to claim 8, wherein the liquid crystal lens (8) comprises electrodes of a transparent material arranged in a mold forming the periphery of the liquid. 12. An optical plate, a compact disc (CD) or a digital versatile disc (D
10. A beam splitter according to claim 9 for use in a VD) read / write device.