JPH01106343A - Optical beam device - Google Patents

Abstract

PURPOSE:To prevent the dislocation in the lapse of time of a two-light flux position from generating by providing a first optical surface to reflect the light of a first facing wavelength area and transmit or partially transmit the light of a second wavelength area and a second optical surface to reflect or transmit the light of the second wavelength area. CONSTITUTION:In an optical surface 106A for the light flux made incident on a light flux reflection prism mirror 105, the light flux of a wavelength lambda1 is totally reflected and the light flux of a wavelength lambda2 has a total transmission factor or a suitable transmission factor (reflection factor). The light flux of the wavelength lambda2 to transmit the optical surface 106A is totally reflected to an optical surface 106B. The light flux of the wavelength lambda1 transmitted by the incompletion of the polarization characteristic of the optical surface 106A transmits the 106B surface and does not become ghost light beams. The return light beams from a disk 109 follows a reverse light path, becomes a linear polarization orthogonal to the light inputting time by a lambda/4 plate 107, the light path is changed to a converging lens 112 side with a polarization beam splitter 104 and the light beams are detected by a sensor 113.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam device, and more particularly, to an objective lens that focuses light emitted from a light source onto an object, and an objective lens that focuses the light emitted from the light source onto an object. The present invention relates to a light beam device including an optical system for illuminating the objective lens.

[Conventional technology]

In recent years, optical information recording and reproducing devices capable of recording, reproducing, and erasing information at high density have been attracting attention, and one of them is a system that utilizes reversible density changes in an optical information recording medium.

This recording method is performed by irradiating a light spot narrowed down to the diffraction limit, thereby rapidly heating and cooling the optical information recording medium to transform it into a state with a specific reflectance. The erasing method is to irradiate a light spot with a low power density (hereinafter referred to as an "erasing spot"), and to heat and slowly cool the optical information recording medium from the state having the reflectance described above. Transferring to the original state is performed by K.

As mentioned above, such an optical information recording medium requires a light spot narrowed down to at least the diffraction limit (this light spot has low power during reproduction) and an erasing spot. An optical head for forming these light spots has a structure disclosed in Japanese Patent Laid-Open No. 199251/1983.

FIG. 8 is a schematic configuration diagram of the optical head.

As shown in the figure, K, 1 is a recording/reproducing semiconductor radar that oscillates at a wavelength λl, and emits radar light at high output during recording and low output during reproduction. Reference numeral 2 denotes an erasing semiconductor laser which oscillates at a wavelength λ3, and emits a high-output laser beam during erasing. Numerals 3 and 4 are condenser lenses that convert the light beams from the bidirectional conductor radars 1 and 2 into parallel light beams, respectively. 5
, 6 are a pair of cylindrical lenses, which correct the shape of the light beam for recording and reproduction into a substantially circular shape. Reference numeral 2o denotes an erasing beam forming element which splits the wavefront of the light beam and further deflects the optical path to form an erasing spot.

8 is a polarizing beam sinter, which reflects S-polarized light and P-polarized light.
Transmits polarized light. 9 and 1o each represent a quarter wavelength plate.

Reference numeral 11 denotes an optical filter, which transmits a light beam having a wavelength of λ and reflects a light beam having a wavelength of λ. Reference numeral 12 denotes an objective lens, which focuses a light beam onto the optical information recording medium 14.

Reference numeral 17 indicates a recording/reproducing spot narrowed down on the optical information recording medium, and reference numeral 18 indicates an erasing spot formed in a circular shape by the element 20.

13 is a condenser lens 1, 15 is a cylindrical lens for detecting a focus control signal by an astigmatism method, and 16 is a signal detector, which is a plurality of signal detectors for detecting a reproduction signal, a focus control signal, and a tracking control signal. It consists of a light-receiving element.

The operation of the conventional optical head constructed as described above will now be described. First, in recording or reproducing, the recording/reproducing semiconductor radar 1 emits a light beam of a predetermined power. This S-polarized light beam is reflected by the polarizing beam splitter 8, passes through the quarter-wave plate 9, and then
A recording/reproducing light spot 17 is irradiated onto the disk 14 by the objective lens e12. During recording, this light spot 17 increases its power, rapidly heats and cools the optical information recording medium of the disk 14, changes its state, and changes its reflectance. This creates recording pits. During reproduction, the beam intensity of the light beam is lowered to irradiate the light spot 17 without causing any change in the state of the optical information recording medium of the disk 14, and the reflected light from there is condensed by the lens e12. and returns it to the polarizing beam splitter 8. At this time, the returned light beam undergoes reflection on the disk 14 and I
The A wavelength plate 9 changes the S-polarized light to the P-polarized light.

Therefore, the polarized beam is transmitted through the polarization beam sinter 8, and the IA wave plate 1
0. After passing through the optical filter 11, the light is focused into the signal detector 16 by the condensing lens r13. The cylindrical lens e1.5 gives astigmatism to this aperture light and enables focus detection. It goes without saying that reflected light can also be detected in the light beam during recording as described above.

Next, in erasing, the erasing semiconductor radar 2 emits a predetermined /4 watt light beam. This S-polarized light beam is reflected by the polarizing beam splitter 8 and is then reflected by the IA wavelength plate 1.
Since it has a wavelength of λ2, it is reflected by the optical filter 11 and returns to the quarter-wave plate 10, and then passes through ζ to become P-polarized light, which is then transmitted through the polarizing beam splitter 8. Then, it passes through the quarter-wave plate 9 and the objective lens 12.
The beam is focused onto the disk 14 as an erasing light spot 18.

The spot 18 is a rapidly heated and gradually cooled spot by the erasing beam forming element 20. The function of the erasing beam forming element 20 will be explained below.

The erasing beam forming element 20 splits the wavefront of the light beam and polarizes the optical path using a polarizing prism in which one side is partially parallel and the other half is formed as one or more chip/cut sections. A rapid heating and slow cooling slit is formed by the two luminous fluxes.

The optical information recording medium, which has been rapidly heated and gradually cooled by this erasing spot, undergoes a gradual cooling effect, changes its state, and returns to its pre-recording reflectance, thereby performing erasing.

Note that the reflected light from the optical information recording medium of the erasing spot 23 is converted into a plane wave by the objective lens 12, and then converted into a plane wave again.
The light passes through the /4 wavelength plate and enters the polarizing beam splitter 8. At this time, the light beam has changed from P-polarized light to S-polarized light, so it is reflected by the polarization beam sinter 8 and reflected in the direction of the recording/reproducing semiconductor radar 1.

[Problem that the invention seeks to solve]

However, the conventional optical head having the above structure has the following problems in structure.

(1) Although it is surprising in ordinary practical optical systems,
Ideal optical characteristics cannot be obtained, and as the number of parts increases, assembly errors occur, costs increase, etc. For example, complete PBS, i.e. 100% S-polarized reflectance,
A PBS called P-polarized light transmittance OS is difficult to manufacture. The same applies to the optical characteristics of the optical filter 11.

(2) Practical semiconductor radars must allow for wavelength fluctuations of several 10 nm due to manufacturing variations, temperature dependence of wavelength, etc. Next, 1/1 of the conventional optical head
A four-wave plate does not function as a perfect quarter-wave plate in that wavelength range.

(3) Since the wavelengths of semiconductor radars are different (separated by optical filters), K at both wavelengths is 1/4
A combination that forms a wave plate is difficult to achieve.

(4) Since there are a large number of optical parts, assembly errors and variations in precision of each part cannot be avoided.

Due to the above-mentioned structural problems, the separation of the light beams from the two semiconductor lasers described in the conventional example is insufficient, and noise is superimposed on the focus control signal and the tracking control signal, resulting in a problem with the sensor. Problems have arisen in terms of characteristics, such as the system becoming unstable or difficult to adjust.

Furthermore, since there are a large number of optical parts, it is necessary to improve the accuracy of each part, and there are also operational problems such as difficulty in assembly and adjustment.

[Means for solving problems]

The above problem arises when the optical beam device has an objective lens that focuses light emitted from a light source onto an object, and an optical system that irradiates the objective lens with the light emitted from the light source. a first optical surface that reflects light in a first wavelength range and transmits or partially transmits light in a second wavelength range; and a first optical surface that reflects or transmits light in the second wavelength range; The problem is solved by the light beam device of the present invention, which is characterized by providing a first optical surface and a second optical surface facing each other.

[For production]

The light beam device of the present invention reflects light in a first wavelength range,
In addition, by providing a first optical surface that transmits or partially transmits light in the second wavelength range, and reflecting the light in the first wavelength range and irradiating it to the objective lens, the light in the first wavelength range can be transmitted. A second optical surface is provided that forms a light beam, and is opposite to the first optical surface and reflects light in a second wavelength range, so that out of the light that has passed through the first optical surface, , forming a light beam in the second wavelength range by reflecting at least the light in the second wavelength range, further transmitting the light through the first optical surface, and irradiating the objective lens; , by irradiating the second optical surface with light, transmitting the light through the second optical surface and the first optical surface, and irradiating the objective lens with the light, in the second wavelength range. It forms a light beam.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Since the light beam device of the present invention is suitably used in an optical head device for an optical information recording medium, the case where it is used in an optical head device will be described as an example.

FIG. 1 is a schematic diagram of a first embodiment of an optical head device according to the present invention.

In FIG. 1, reference numeral 101 is a semiconductor radar light source in which a recording/reproducing semiconductor radar that oscillates at a wavelength λ1 and an erasing semiconductor radar that oscillates at a wavelength λ2 are housed in one package. Reference numeral 102 denotes a collimator lens that converts the light beam from the semiconductor Rade light source 101 into a parallel light beam, and the light emitting points of the Rades of wavelength λ1 and wavelength λ2 are shifted from each other. here,
It goes without saying that the semiconductor laser light source described in the present invention may be constructed by superimposing the j4-cage light beams of the configuration shown in the conventional example. A beam shaping prism 103 corrects the shape of the recording/reproducing light beam into a substantially circular shape. 104
is a polarizing beam splitter, and 104A, 104B, and 104C represent optical surfaces of the polarizing beam splitter 104, respectively. The spectral characteristics of the optical surface 104 are as shown in Figure 2 (,).If the incident light is P polarized light, it will be completely transmitted, and if it is S polarized light, it will not be transmitted. The polarized light enters the optical surface 104A and is completely transmitted. Note that optical surface 1
04B completely transmits the wavelength λ1°λ snow regardless of whether it is P polarized light or S polarized light. Reference numeral 105 is a light beam reflecting prism mirror, which is shown in a simplified manner in FIG. The direction is S polarized light. 106 is an optical element for forming an extinguished beam, and the spectral characteristics of the optical surface 106A, which is the first optical surface, and the optical surface 106B, which is the second optical surface, are shown in FIGS. 3(,) and (b), respectively. . The light beam incident on the light beam reflecting prism mirror 105 is as shown in FIG. 3 6).
At the optical surface 106A, the light beam with the wavelength λ1 is totally reflected, and the light beam with the wavelength λ1 is completely transmitted or has an appropriate transmittance T (reflectance R). Figure 3) As shown, optical surface 106A
The light flux of wavelength λ3 that has passed through is totally reflected by the optical surface 106B. Due to the incompleteness of the polarization characteristics of the optical surface 106A, the transmitted light beam of wavelength λ1 is prevented from transmitting through the surface 106B and becoming ghost light. 107 is a λ/4 plate for the wavelength λ1, which converts directly spun polarized light into circularly polarized light.

108 is an objective lens, 109 is a disk, 110
A and IIIA are the luminous fluxes of wavelengths λ1 and λ, respectively, and ll
0B and IIIB indicate their light intensity distributions. The returning light from the disk 109 follows a reverse optical path,
The λ/4 plate 107 generates orthogonal polarized light that is orthogonal to the light emitted.
The optical path is changed to the side and detected by the sensor 113. Note that since information reproduction is performed with a light beam of wavelength λl, the sensor 113
It is necessary to cut out the ghost light of the light beam with wavelength λ2, but if the optical surface 104C is a surface with spectral characteristics as shown in FIG. 2(b), it is possible to transmit only the light beam with wavelength λ1. can.

Note that the spectral characteristics of the optical surface 104C are such that optical treatment is applied to the optical surface 106A and/or 106B so that the return light with a wavelength λl incident on the sensor 113 is not affected by the return light with a wavelength λ2. If so, the optical surface 104C
It is not necessary to perform optical treatment to exhibit the spectral characteristics shown in FIG. 2).

Next, the function of the extinction beam forming optical element 106 will be explained.

FIG. 4 is a schematic explanatory diagram of the function of the erasing beam forming optical element. Note that the reference numbers for the constituent members are the same as those used in FIG. 1.

First, a method of adjusting the light intensity distribution of the erase spot will be explained.

In the figure, an incident light beam 201 has a wavelength λ.

The optical surface 106A is for forming a spot for erasing.
A part of the luminous flux is reflected (reflectance R) and the objective lens, =
"108, and the other light beams have a transmittance T-(1-r
t). The transmitted light beam is totally reflected by the optical surface 106B, a part of the light beam passes through the 106-plane and is directed toward the objective lens 108, and the other beam is reflected at the 106-plane. Similarly, the light beams transmitted and reflected by the surfaces 106A and 1061 are superimposed on the medium surface to form an erasing light beam 111B.
form. At this time, if the light intensity of the incident light beam 201 is 1, the light intensity of the light beam that has passed through the optical element 106 m times! . can be written as follows.

lo-R, Im(40)-Rm-1(1-R)21, is a monotonically increasing function with respect to R, 11 is a monotonically decreasing function, and Im(>1) has an extreme value at (-i; TT). Since R is a convex function, by appropriately adjusting R, the intensity distribution of the combined erasing light beam can be changed. For example, if R-0,5, IO;0.5,! 1 rin0.2
5. 1! =0.125,... and as the distance of 1m increases, the strength can be weakened.

Also, for example, if R-0,25, I, -0,25,
l5-0.56, I," = 0.141.-... J)
A distribution can be created with mwml as the peak.

Therefore, by using this luminous flux, it is possible to appropriately adjust the reflectance R in accordance with the characteristics of the medium and control the heating and cooling rate. It goes without saying that only the light reflected once can be used as R-1.

Next, a method of adjusting the erase spot shape will be explained. Fourth
As shown in the figure, by making the optical surface 106B a cylindrical surface with curvature in the plane of the paper, the paraxial image plane is not shifted in the plane perpendicular to the plane of the paper, so that the first light beam (wavelength λ
1), and in a plane parallel to the plane of the paper, the image plane moves toward the objective lens 108 due to the action of the cylindrical surface, so that on the medium
As shown in 1B, the light beam becomes an oval shape. Adjustment in the length direction of this oval light beam is possible by adjusting the curvature as shown in FIG. 4 106B. Furthermore, by adjusting the inclination of the surface 106B in the paper, the relative position with respect to the spot of the first light beam can be adjusted.

The function of the optical element for forming an erase spot has been described above, but the same effect can be obtained by forming the surface 106B shown in FIG. 4 as a group of flat surfaces or a group of curved surfaces.

FIG. 5 is a schematic diagram showing a second embodiment of the optical head device according to the present invention. Note that the same reference numerals will be used for the same constituent members as in the first embodiment shown in FIG. 1, and duplicate explanations will be omitted.

As shown in the figure, this embodiment is an example in which the erasing spot forming optical element 106 is used as a transmissive element for a light beam having a wavelength of λ, and the two-wavelength light source shown in FIG. , Semiconductor laser 304.3 oscillates at λ2
01. Note that the behavior of the first wavelength λ1 is the same as that described in the explanation of FIG. 1, so a description thereof will be omitted. Semiconductor radar 301 that oscillates at a second wavelength λ
The luminous flux is irradiated onto the optical element 106 via the collimator lens 302 and the mirror 303. In this embodiment, the optical characteristics of the optical surface 106C are defined as the wavelength characteristics of the surface 106A of the optical element 106 shown in FIG. Utilizes transmitted light from Note that the optical element 106
The erasing beam forming process after guiding the light of wavelength λ2 into the laser beam is different from that described with reference to FIG. 4, so the explanation will be omitted.

FIG. 6 is a schematic diagram showing a third embodiment of the optical head device according to the present invention. Note that the same reference numerals are used for the same constituent members as in the first embodiment shown in FIG. 1, and redundant explanation will be omitted.

In the same figure, 406 is the optical element 106 shown in FIG.
However, as shown in FIG. 7(&), its optical surface 406A exhibits a polarization characteristic different from that of the optical surface 106A shown in FIG. 3(a).

As shown in FIG. 7(a), the optical surface 406B exhibits the same polarization characteristics as the optical surface 106B shown in FIG. 3(b).

The light flux of the first wavelength λ1 incident on the optical surface 406A of the optical element 406 is arranged to become S-polarized light, is totally reflected on the optical surface 406A, and is reproduced in the same manner as explained in FIG. 1 below. - Form a recording spot 110B. disc 1
The returning light from the λ/4 plate 107 passes through the optical surface 406A as 6p polarized light, and at this time, astigmatism occurs on the optical surface 406B, and the light is condensed at the λ/4 plate 107. The sensor 113 receives light and performs focusing using the well-known astigmatism method. Moreover, the luminous flux of the second wavelength λ3 is
After being completely or partially transmitted through the optical surface 406, it is totally reflected at the optical surface 406B and directed toward the medium surface. The subsequent functions are the same as those explained with reference to FIG. 1, so their description will be omitted.

〔Effect of the invention〕

As explained above in detail, according to the light beam equipment of the present invention, two light beams can be superimposed by simply inserting an optical surface.
Not only can the spot shape and intensity distribution be adjusted for one light beam, but also one optical element can be used for multiple functions, so there is an effect that no deviation in the position of two light beams occurs over time.

Furthermore, since the number of parts can be reduced, assembly errors are small and the parts are less susceptible to variations in accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a first embodiment of an optical head device according to the present invention. FIG. 2(a)), FIG. 3(,)(), and FIG. 7(a)) are characteristic diagrams showing the spectral characteristics of the optical element. FIG. 4 is a schematic explanatory diagram of the function of the erasing beam forming optical element. FIG. 5 is a schematic diagram showing a second embodiment of the optical head device according to the present invention. FIG. 6 is a schematic diagram showing a third embodiment of the optical head device according to the present invention. FIG. 8 is a schematic diagram of a conventional optical head. 101: Semiconductor Rade light source, 102: Collimator lens, 103: Beam shaping grism, 104: Polarizing beam splitter, 105: Luminous flux reflecting prism mirror, 106:
Optical element for forming extinction beam, 107: λ/4 plate, 108
: Objective lens, 110A. 111A: Luminous flux, ll0B, IIIB: Light intensity distribution, 1
09: Optical information recording medium, 112: Condensing lens, 11
3: Sensor, 104A, 104B. 1040.106A, 106B, 406A, 4061:
Optical surface, 301, 304: semiconductor radar, 302: collimator lens, 3o3: mirror, 4o6: optical element. Agent Patent Attorney Johei Yamashita Figure 1

Claims (5)

[Claims] (1) A light beam device including an objective lens that focuses light emitted from a light source onto an object, and an optical system that irradiates the objective lens with the light emitted from the light source, a first optical surface that reflects light in one wavelength range and transmits or partially transmits light in a second wavelength range;
A light beam device further comprising: a second optical surface facing the first optical surface. (2) The light beam device according to claim 1, wherein the first optical surface and the second optical surface are provided on a constituent surface of one optical element. (3) The light beam device according to claim 1 or 2, wherein the second optical surface is formed by a group of flat surfaces or a group of curved surfaces. (4) It has a detection means for irradiating an object with the light condensed by the objective lens and detecting the return light from the object, and the return light of the first wavelength range is detected on the light detection means. in,
Claim 1, wherein optical treatment is applied to the first optical surface and/or the second optical surface so as not to overlap with light in a wavelength range different from the first wavelength range. light beam device. (5) A detection means for irradiating an object with the light condensed by the objective lens and detecting the return light from the object, and the return light of the first wavelength range is detected on the light detection means. in,
The light beam according to claim 1, further comprising a third optical surface that transmits only light in the first wavelength range so as not to overlap with light in a wavelength range different from the first wavelength range. Device.