KR100282101B1 - Magneto-optical scanning device comprising a polarization-sensitive beam splitter, a manufacturing method thereof and a beam splitter - Google Patents

Abstract

PURPOSE: To provide a splitter which is small in size and is light in weight by providing a wedgelike element formed of a unidirectionally oriented polymer material composed of a setting liquid crystal monomer composition. CONSTITUTION: The beam splitter is formed of the wedgelike element 1 composed of the unidirectionally oriented polymer material. Namely, the orientation of molecules of the wedgelike element 1 in a direction 2 is so selected that it is perpendicular to the optical axis of the element and parallel to the narrow end of the wedge, and an incident unpolarized beam 3 is split into an extraordinary light beam 4 and an ordinary light beam 5 which have mutually different polarizing directions. The angle value between the two output beams is proportional to the wedge angle and its birefringence value. Since the birefringence of the polymer material in use is relatively large, a relatively small wedge angle may be selected so as to actualize a given output beam angle. The wedge angle is determinative to the thickness of the beam splitter, so this beam splitter can be made thinner than a quartz beam splitter.

Description

A magneto-optical scanning device comprising a polarization sensitive beam splitter, a method of manufacturing the same, and a beam splitter

1 shows a monomer suitable for forming a wedge-shaped device according to the invention.

2 shows an example of an X group.

3 shows an example of an M group.

4 shows the structural formula of a suitable liquid crystal monomer composition.

5 shows a wedge-shaped element for use in a polarization sensitive beam splitter.

6 and 7 illustrate two different embodiments of a polarization sensitive beam splitter comprising two wedge shaped elements.

8 illustrates a polarization sensitive beam splitter comprising three wedge shaped elements.

9 shows an apparatus for scanning a magneto-optical record carrier.

10 shows an apparatus for scanning a magneto-optical record carrier.

11a and 11b show two orientations of the beam splitter and detection system of the apparatus of FIG.

12A and 12B show two embodiments of an integrated PPBS cube and a wedge element.

Figure 12c illustrates one embodiment of an integrated PPBS plate and wedge element.

Fig. 13A shows an apparatus for scanning a magneto-optical record carrier.

13B, 13C and 13D show an embodiment of an integrated mirror and wedge element.

The present invention relates to a polarization-sensitive beam splitter comprising at least one transparent wedge-shaped element of birefringent material and a device for scanning a magneto-optical record carrier comprising the beam splitter. It is about.

The invention also relates to a method of manufacturing a polarization sensitive beam splitter comprising at least one transparent wedge-shaped element made of birefringent material and to an apparatus for scanning a magneto optical record carrier.

This type of flatness sensitive beam splitter for use as a pick-up element of a magneto-optical recording system is described in US Pat. No. 4,951,274. In such a beam splitter, two transparent wedge-shaped devices are used, which are made of crystalline quartz and are fixed relative to each other in such a way that the optical axes of the devices extend from each other at an angle of 45 to 135 degrees. Such beam splitters (eg Wallaston prism) occupy a relatively large space in the pick-up element of the magneto-optical recording system. In addition, quartz devices must be precision machined and molded accurately.

It is an object of the present invention to provide a polarization sensitive beam splitter which is particularly compact and lightweight. It is an object of the present invention to provide a beam splitter that can be located in a light path simply and accurately in a desired manner. It is desirable to provide a beam splitter where the light components polarized at right angles in transmission are separated from each other and then the polarized light beams diverge from each other. Another object of the present invention is to provide a simple manufacturing method of such a polarization sensitive beam splitter.

As described earlier, the above and other objects can be achieved using a polarization sensitive beam splitter, wherein the beam splitter according to the present invention is a uniaxially oriented polymer consisting of a liquid crystal monomer composition in which a wedge-shaped device is cured. It characterized in that it comprises a substance.

According to a very suitable embodiment of the polarization sensitive beam splitter according to the invention, the beam splitter comprises two or three wedge shaped elements which differ in the direction of orientation of the polymeric material.

A particular embodiment of the beam splitter according to the invention comprises an antireflective grating made of a polymeric material on the beam splitter surface on which the light beams respectively enter and exit separately.

The apparatus for scanning a magneto-optical record carrier according to the present invention includes a beam splitter comprising a wedge-shaped element made of a uniaxially oriented polymer material. Since the beam splitter is compact, the optical path of the device can be highly integrated.

In order to obtain a beam splitter having a small total thickness, a plurality of small wedge-shaped devices having a sawtooth structure can be arranged in parallel. Two wedge-shaped elements with different orientation directions of the polymeric material can be used in pairs.

According to the present invention, an object of the present invention is to provide an alignment layer on two substrates, form a wedge-shaped inner space while arranging the substrates so that the alignment layers face each other, and then It is achieved by a method of forming a wedge-shaped device while filling the internal space with the liquid crystal monomer composition to be cured.

Thereafter, the substrate may be removed as necessary. For example, if one or both substrates are not removed because of protection of the outside of the beam splitter, it is preferable to use a substrate having a thickness of 0.1 to 1 mm.

U. S. Patent No. 5,042, 925 describes a polarization sensitive beam splitter having a polarizing layer comprising a cured liquid crystal monomer composition, but the polarizing layer is not wedge shaped. Known beam splitters are relatively large, some transmitting and some reflecting. The exact position and orientation in the light path is important for satisfactory manipulation of known beam splitters.

These and other features will be apparent from and elucidated with reference to the examples described below.

1 shows a plurality of suitable monomers from which a wedge shaped device can be manufactured for use in a polarization sensitive beam splitter according to the present invention. Suitable monomers include, in particular, acrylate compounds (group R is a hydrogen atom), methacrylate compounds (group R is a methyl group), chloroacrylates and fluoroacrylate compounds (group R is a chlorine atom or a fluorine atom). ), Epoxy compounds and vinyl ether compounds. An example of group X is shown in FIG. 2, where p can be from 1 to approximately 12. An example of a group M is shown in FIG. In the curing reaction of the monomer composition by the photopolymerization reaction, the properties of the photosensitive initiator that can be used can be applied to the properties of the monomers by known methods. Aromatic carbonyl compounds are suitable as photoinitiators for curing di (meth) acrylate compounds, while diaryliodonium compounds such as diphenyliodonium hexafluoroarsenide are used to cure epoxy and vinyl ether compounds. Can be used.

Example 1

The monomer composition comprises 2% by weight of the photosensitive initiator 2,2-dimethoxy-2-phenyl-acetophenone (commercially available from Ciba-Geigy) and the structural formula shown in FIG. For example, a liquid crystal diacrylate compound prepared by the method disclosed in EP 261 712 is prepared by mixing.

Two square glass plates are coated with a nylon alignment layer and rubbed with an anti-fluff cloth in a direction parallel to one of the edges of each glass plate. Subsequently, the glass plates are arranged to face each other in parallel with the friction direction while leaving the wedge-shaped space between the glass plates. The spacer is placed between the glass plates at one edge so that the angle between the glass plates, that is, the wedge angle, is 4 °. The above-described monomer composition is filled in the space between the glass plates, and then a solid wedge-shaped element is formed by activating radiation, that is, ultraviolet irradiation according to the embodiment, and the glass plate is removed.

5 shows a wedge shaped device 1 made such that the molecular orientation direction 2 is selected perpendicular to the optical axis of the device and parallel to the narrow edge of the wedge. The normal non-polarized incident light beam 3 is separated into a special light beam 4 and a general light beam 5 having different polarization directions. The angle between the two emission beams is proportional to the wedge angle and the birefringence value. Since the birefringence of the polymeric material used is relatively large, relatively small wedge angles can be taken to achieve a given angle between the exit beams. For example, for beam splitters made of crystalline quartz, the wedge angle should be approximately 15 times greater for the same angle between the exit beams, for example, with significantly lower birefringence than the polymeric material. Since the wedge angle is determined by the thickness of the beam splitter, it becomes clear that the beam splitter according to the present invention can be made significantly thinner than the quartz beam splitter.

Instead of the nylon alignment layer, other known alignment layers may be used, such as polyimide or polyethylene friction layers or silicon oxide layers sputtered at right angles. If desired, different orientations can be achieved, for example, by applying a magnetic field of 15 kGauss intensity.

Suitable materials and alternative methods usable for making polarization sensitive beam splitters according to the present invention are also described in R. A. M. Hikmet and D. J. Broer; Polymer 32 (9), pp. 1627-1632 (1991). The document also describes the manufacture of freestanding planar elements suitable for kinetic measurements.

Example 2

Two wedge shaped devices as described in Example 1 are prepared, one of which is made in the friction direction and the orientation of the molecules is chosen to be at an angle of 45 ° to the narrow wedge edge.

FIG. 6 shows a polarization sensitive beam splitter comprising two wedge shaped elements 11 and 12 whose orientation directions 13 and 14 are perpendicular to the optical axis of the beam splitter and are at an angle of 45 ° to each other.

In principle, the double beam splitter, also called a modified wallastone prism, separates the unpolarized incident light beam 15 into four sub-beams, two of which are b _{o, o} and b _{e. , e} matches, while the other two subbeams, b _{e, o} and b _{o, e} , extend at opposite angles with the previous subbeam in between. The first and second subscripts of these subbeams indicate that the associated wedge subbeams for the first and second wedge elements are ordinary (o) and extraordinary (e) beams, respectively. For simplicity _, the non-polarization propagation beams formed by sub-beams b _{o, o} and b _{e, e} are indicated by reference numeral 16, and the deflected sub-beams b _{e, o} and b _{o, e} polarized mutually perpendicular to 17 and 18. Such a beam splitter can be very usefully used in a scanning device for a magneto-optical record carrier.

The ratio between the intensity of the traveling beam 16 and the sum of the intensities of the deflected beams 17, 18 depends on the angle between the orientation direction 13 and the orientation direction 14. If the angle is 0 °, the ratio is infinite. That is, only the traveling beam 16 is present. If the angle is 45 °, the ratio is one. If the angle is 90 °, the ratio is zero. That is, there is no traveling beam 16, and the beam splitter functions as a wallastone prism that is not deformed. The ratio of the intensity of the three beams when polarizing the incident light beam 15 also depends on the polarization state of the incident light beam. Cutting losses are very large when manufacturing a quartz beam splitter at an angle not equal to 45 ° or 90 °, for example, whereas manufacturing a beam splitter from a polymeric material is essentially the same as that of the beam splitter shown in FIG. Same as Here, one of the friction directions must be chosen differently.

Example 3

Except for fabricating one device in the frictional direction, two wedge-shaped devices as described in Example 1 were fabricated to select the orientation of the molecules to be 90 ° with the narrow wedge edges. Optically neutral adhesive is used to bond the two wedge shaped devices.

7 shows a polarization sensitive beam splitter comprising two wedge shaped elements 21, 22 in which the orientation direction 23 and the orientation direction 24 are perpendicular to the optical axis. If necessary, the anti-reflective grating layers 25, 26 are anti-reflective using a glass plate attached to the beam splitter with the necessary gratings that are simulated on the entrance and exit surfaces of the beam splitter. -reflection grating layer. Here, the incident surface is a surface into which the beam enters the beam splitter, and the exit surface refers to a surface where the beam exits the beam splitter. The lattice helps to determine the orientation direction for the liquid crystal monomer composition and birefringent polymer molecules obtained by curing. Suitable gratings are formed by ridges with a height of 0.2 μm and an interval of 0.48 μm for light having a wavelength of 800 nm. If it is desired to produce the beam splitter with a very smooth side, this can be realized, for example, by providing a thin glass layer.

Example 4

Three wedge-shaped elements as described in Example 1 can be manufactured, wherein the wedge angles of the first element 28 and the third element 11 are the same and the wedge angle of the second element 27 is It is twice the wedge angle of the first element. Three wedge-shaped elements are continuously coupled to the beam splitter as shown in FIG. The friction directions 29 and 13 of the first and third elements are the same, respectively, while the friction direction 30 of the second element forms an angle of 90 ° with the friction direction 13. Due to this symmetrical structure, the prism, called double wallastone, only reduces the perturbation of wavefront of the transmitted light beams 4, 5. The 90 ° angle between the friction direction 13 and the friction direction 30 divides the incident non-polarization beam 15 into two polarized beams 4, 5. When taking another angle between 0 ° and 90 ° instead of 90 °, the incident beam is split into two polarized beams and one non-polarized beam, according to the division by the wallastone prism shown in FIG. Double wallastones made of quartz are inadequately large in many applications. However, double wallastones made of polymeric material can be made in very small sizes.

The polarization sensitive beam splitter according to the present invention is small and light. It is easy to provide the present polarization-sensitive beam splitter to the optical device, and it is particularly easy to position in the optical path because its orientation angle (angle with respect to the optical beam or optical axis) is not very important, and the optical characteristic is wedge-shaped It is determined by the choice of the angle between the glass plates during the manufacture of the device.

9 shows one embodiment of a scanning device of a magneto-optical device according to the present invention. Such a device comprises a light source 31 in the form of a semiconductor laser for supplying a scanning beam 32. An objective system 34 for concentrating the scanning beam generated by the light source is placed in the path of the scanning beam. The system includes a collimating lens 33 and an objective lens 34 for concentrating the scanning beam to form the scanning point 35 on the information carrier 36 of the record carrier. Arrange the partially polarized beam splitter 37 (PPBS) in the optical path. The structure and function of such a PPBS is described, for example, in EP 0 078 673. The apparatus preferably comprises a grating 38 for dividing the beam 32 into three sub-beams, for example for a tracking servosystem, such that the mirror 39 overlaps the light path as needed. ).

The scanning beam is reflected at the record carrier and passed through the objective system and mirror 39, which may be included if necessary, to the PPBS. The light passed by the PPBS is subsequently split by the polarization sensitive beam splitter 40 into two propagating beams and two deflecting beams that are polarized perpendicular to each other as shown in FIG. According to the invention, the beam splitter comprises two wedge shaped elements consisting of a birefringent material, ie a polymer oriented in a uniaxial direction formed from the cured liquid crystal monomer composition, wherein the orientations of the two wedge shaped elements are different.

The beam splitter 40 may be relatively thin because the required wedge angle is small. If the beam diameter is 5 mm, the beam divider thickness of 0.5 mm or less is sufficient to satisfactorily separate the exit beam. This thin beam splitter can be simply attached to the beam splitter 37 to reduce the number of components in the optical path. Simulation techniques can further reduce the provision of a grating 38 on the beam splitter 37.

The traveling beam formed by the beam splitter 40 can be used to generate servosignals that define the scan point at the correct location in the record carrier, while the two deflected beams that are tilted and mutually polarized vertically It is used to generate an information signal representing information stored in 36). The distribution of the light intensity from the record carrier for the two polarizing beams and the traveling beams on the other hand can be applied to the band widths of the information signal and the servo signal. In general, the intensity at the beam should be larger as the bandwidth is larger. The ratio of the intensity of light between the polarizing beam and the traveling beam is the orientation direction 13 and orientation direction 14 in FIG. 6 in the wedge-shaped element of the beam splitter 40 and the orientation direction 23 and orientation in FIG. By the angle α between the directions 24. This angle is preferably at least 45 ° to have sufficient light useful in a deflected polarization beam that generates a wide band information signal. The present invention offers the possibility of providing the angle between the orientation directions to any value between 0 ° and 90 °. The choice of angle depends on the conditions where the beam splitter should be used.

10 shows another embodiment of the magneto-optical record carrier scanning apparatus according to the present invention. While the embodiment of FIG. 9 uses a beam splitter comprising two wedge elements, this embodiment uses a polarization sensitive beam splitter 45 comprising one wedge element made of a birefringent material according to the present invention. do. The device is equipped with two detection systems. One of these detection systems 46 is installed in the beam path through the beam splitter 45 and used to generate the information signal. The other detection system 47 is installed in the beam returning from the record carrier and used to generate the servo signal by deflecting the beam direction using the coupling grating 48. 11A is a perspective view of the beam splitter 45 and the detection system 46. The beam splitter splits the incident beam 49 into two passing beams 50, 51, each of which is incident on either side of the dividing line 52 between the bisected split detection systems. Four spots 53 alongside the detection system are due to the beams generated by the three beam gratings 38. The desired orientation and polarization of the pass beams 50, 51 can be achieved by making the orientation direction 54 of the wedges of the beam splitter form an angle of 45 ° with the two plane intersections 55 forming the wedges. Another orientation of the beam splitter and detection system is shown in FIG. 11B.

In the apparatus of FIG. 10, the PPBS 37 'and the wedge 45 of the beam splitter can be integrated into one unit to make it more compact. Figure 12a shows a unit in which the wedge 45 is optically connected to one side of the cube that forms the PPBS 37 '. The wedges may also be arranged on the oblique side of the cube in contact with the PPBS coating 56 as shown in FIG. 12B. If the PPBS is in the form of a flat parallel plate 37 '', the PPBS coating 56 may be arranged on one side of the plate, as shown in Figure 12c, while the wedge 45 on the other side. Can be arranged.

FIG. 13A shows another embodiment of a magneto-optical record carrier scanning apparatus equipped with a mirror 57 to change the optical path of the apparatus. The mirror may be advantageously integrated with the beam splitter wedge 45. Wedges may be installed on one side of the flat parallel plate 58, while a reflective coating 57 may be provided on the other side of the wedges. FIG. 13B shows an integrated mirror and wedge with a reflective-coated axis of the wedge mounted on a plate. The integrated mirrors and wedges shown in FIGS. 13C and 13D both use internal reflections to deflect light. The wedge 45 can be arranged on the oblique side of the prism 59 as shown in FIG. 13C or on the prism face on which the incident beam is irradiated as shown in FIG. 13D.

In addition to the use of the beam splitter in the magneto-optical record carrier scanning apparatus, the beam splitter according to the present invention may also be used in other apparatuses for splitting the light beam into different polarizations to determine the polarization state of the light beam. It is sometimes desirable to couple out only a portion of the intensity in the light beam to determine the polarization state, ie the intensity of the traveling light beam can be used for other purposes. The above object can be satisfactorily realized by using the beam splitter according to the present invention. For example, when the orientation direction angle of the beam splitter shown in FIG. 6 is 45 ° or less, the intensity of the traveling beam 16 is greater than the sum of the intensities of the polarizing beam 17 and the polarizing beam 18. The polarization state of the light beam may be determined by determining its intensity, and may optionally be combined with the intensity of the traveling beam. The beam splitter according to the invention has the advantage that only one optical component is arranged in the light beam and that the intensity ratio of the required light beam can be easily obtained. The device is described, for example, in magazine Funkschau vol. 18, 1991, pp. 79-85, may be a receiver in an optical delivery system that finds information in an optical beam by a heterodyne device.

Claims (8)

In a polarization sensitive beam splitter for separating components of a light beam that are polarized at right angles in transmission, comprising one or more transparent wedge-shaped elements made of a birefringent uniaxially oriented liquid crystal material, wherein the material is cured A polarizing-sensitive beam splitter characterized in that it is a polymer formed of a liquid crystal monomer composition. The polarization-sensitive beam splitter of claim 1, wherein the two wedge-shaped elements comprise a polymeric material that is different in orientation. The device of claim 1, wherein the three wedge-shaped elements are arranged with two external elements on either side of the internal element, the two external elements having a polymer material having the same orientation direction, and the orientation direction of the external element being an internal element. And a direction different from the orientation direction of the polarization-sensitive beam splitter. 4. A polarization-sensitive beam splitter according to any one of claims 1 to 3, wherein at least one of an entrance surface and an exit surface is provided with an antireflective grating. 4. A polarization sensitive beam splitter according to claim 2 or 3, wherein the angle between the two orientation directions of the polymeric material in the wedge-shaped device is at least 45 degrees. A light source for supplying the scanning beam, an optical system for guiding the scanning beam onto the information plane of the recording carrier, a photosensitive detection system arranged in the path of the scanning beam from the recording carrier, and a path in front of the detection system. Apparatus for scanning a magneto-optical record carrier comprising the polarization sensitive beam splitter according to any one of claims 1 to 3 arranged. In a method of manufacturing a polarization-sensitive beam splitter comprising at least one transparent wedge-shaped element made of a birefringent material, the two substrates are each provided with an alignment layer, and the substrates then form a wedge-shaped inner space and the alignment layers are mutually different. After being arranged to face, the inner space is filled with a liquid crystal monomer composition which is continuously cured to form a wedge-shaped device, and if necessary, the substrate is removed, characterized in that the manufacturing method of the polarization-sensitive beam splitter. 8. The polarization of claim 7, wherein the second transparent wedge shaped elements of uniaxially oriented polymeric material having different orientation directions are formed in a similar manner, and the two wedge shaped elements are joined by an optically neutral adhesive. Method of manufacturing a detectable beam splitter.