JPH04209339A - Light pickup device - Google Patents

Abstract

PURPOSE:To simply detect information included in amplitude distribution of laser beam returned from an optical disk based on a new theory by detecting an edge of an information bit of the optical disk utilizing an interference between an even and odd numbered mode through a waveguide for a double mode channel. CONSTITUTION:The beam emitted by a laser beam source 1, and passed through a half mirror 2, a collimator lens 3 and an objective lens 4, forms a spot on the optical disk 5. A reflected beam, retrograding and transmitting through the half mirror 2, forms a spot at a light incident edge 8 of the waveguide for the double mode channel 7 formed on a base 6. The even numbered mode and the odd numbered mode excited by the waveguide 7 propagate while interfering with each other branched at a branch 9, and propagate on waveguides 10, 11, then, are detected independently by a photodetector 12, 13 fixed on the base 6. The edge of the information bit on the optical disk can be detected by detecting a differential signal 15 of outputted signal of detectors 12 and 13 by a differential detector 14.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device. [0002]

[Prior Art] A conventional optical disc pickup device is
Many devices detect changes in the intensity of light reflected from an optical disk, and magneto-optical disk pickup devices that use polarization detection also detect changes in the polarization state as changes in light intensity. [0003]

[Problem to be solved by the invention] In general, optically, reflected light from a disk has information in the form of amplitude distribution and phase distribution, but it is extremely difficult to understand these as changes in light intensity. there were. An object of the present invention is to detect disc information contained in the amplitude distribution (including phase distribution) of laser light returned from an optical disc using a simple and compact device based on a new principle. [0004]

[Means for Solving the Problems] To achieve the above object, the present invention applies interference of both even and odd modes in a double-mode channel waveguide, thereby causing the amplitude distribution of the laser spot returned from the optical disk to be reduced. It reproduces all information. That is, a laser light source, an illumination optical system that guides the light emitted from the laser light source onto an optical disk medium and forms a light spot on the surface of the medium, a condensing optical system that condenses the light reflected by the medium, and a condensing optical system that condenses the light reflected by the medium. In an optical pickup device having a light detection means for detecting light focused by an optical system, the light detection means has a channel waveguide formed on a substrate, and the light reflected from the optical disk medium is incident on the waveguide. The condensing optical system is configured to form a light spot again at the end face, and the waveguide is in double mode at the incident end face of the waveguide where the light spot is formed, and two channels follow the double mode waveguide. It has a branch that distributes optical power to the waveguide. The photodetecting means has a photodetecting element that detects the optical power propagating in each of the two branched channel waveguides, and reads information on the optical disk medium based on the output signal of the photodetecting element. be. [0005] In addition, a waveguide branch is provided at the other end of the double mode channel waveguide in which the optical spot image is formed at one end, and the waveguide branch is provided to branch into three single mode waveguides, and the center of the three single mode waveguides is One of the three single mode waveguides guides the illumination light beam from the laser light source onto the optical disk medium through the objective lens, and the outer two of the three single mode waveguides.
It is also possible to use a configuration in which the guiding waveguide device is used for both illumination and detection, with a configuration having photodetecting elements that each detect light propagating through a single mode waveguide. [0006]

[Operation] The laser spot returned from the optical disc has information about the disc surface, but for simplicity we will consider it in one dimension, and the laser spot amplitude distribution U (x) to be detected is the amplitude of the laser spot incident on the disc. Distribution Uo(x)
and the amplitude distribution of the disk surface 0(x). Namely. U (x) = Uo (x) O (x) (1
). Although equation (1) is not strictly correct because it ignores diffraction in the return optical system, it does not pose any problem in explaining the present invention in detail. [0007] Now, take the center of the laser spot as the origin*
*For example, Uo(x) is clearly an even function. On the other hand, O(
x) is generally expressed as the sum of an even function and an odd function (it can be intuitively understood that the odd function component becomes particularly large when the laser spot is located at the edge of the information bit). [0008] Now, even and odd modes exist in the double mode waveguide, and their eigenfield distribution functions are expressed as fe (x
), fo (x), these are even and odd functions, respectively. Laser spot U returned from the disk (
x) excites guided mode light in the double mode waveguide, and the excitation efficiency η4 and η0 of even and odd modes are [0009], respectively.

[Equation 1] (00101.Then, the even and odd two modes interfere in the double mode waveguide, and as a result, in the subsequent waveguide branch, the optical power distributed to the two waveguides is In this case, no and T)o are generally complex numbers, but their phase difference is approximately n= (n=0
, ±1, ...), the length of the double mode region is an integral multiple of the complete coupling length Lc of both even and odd modes (the length at which the phase difference between even and odd modes is 180°), and the position is The phase difference is π
(2m+1)/2, (m=0. ±1...), when the length of the double mode region is multiplied by an odd number of Lc/2, the relative optical power distributed to the two waveguides is The difference will be the greatest. Now, if we detect the power of the light propagating through these two waveguides and take their differential output, we get
Odd function components included in O(x) in equation (1) can be detected. This indicates that it is possible to detect the edge portions of information bits on the disk as described above. Generally η. When the phase difference between
It is preferable that Δ=m(π-α), (m=0.±1...), so the length of the double mode region is L
=mLc (1-α/yr) (m=1.2.
−) is desirable.

Embodiment FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention, in which the optical disc is a phase modulation type such as a compact disc or an intensity (reflectance) modulation type disc such as a phase change type. thinking. Emit laser light source 1*
*The laser beam is reflected by a half mirror 2 and turned into a parallel beam by a collimator lens 3, and then an objective lens 4 forms a laser spot with a diffraction limit size on an optical disk 5. The light reflected by the optical disk 5 is returned to the objective lens 4.
The light then passes through the collimator lens 3, passes through the half mirror 2, and is focused on the input end 8 of the double mode channel waveguide 7 formed on the substrate 6, where the laser spot is again imaged. The even and odd mode lights excited in the double mode channel waveguide 7 by this laser spot propagate while interfering with each other and eventually reach the branch 9. The lights branched at branch 9 propagate through waveguides 10.11, and are independently detected by photodetectors 12.13 fixed to substrate 6. If the differential signal 15 of the output signals of the photodetectors 12 and 13 is obtained by the differential detector 14, the edges of the information bits on the disk can be detected. [00111 FIG. 2 is a schematic diagram of a second embodiment of the present invention. In this example, the present invention is applied to signal reading of a magneto-optical disk, and furthermore, a double mode waveguide is used for three
It branches into two single-mode waveguides, the central waveguide of which is used as the illumination light waveguide. That is, the laser light source 21 is fixed to the waveguide substrate 22 and excites guided light into the single mode channel waveguide 23. The light propagated through the single mode channel waveguide 23 eventually reaches the branch 24 and enters the double mode channel waveguide 25 . At this time, the center line of the single mode channel waveguide 23 and the center line of the double mode channel waveguide 25
If the center lines of the waveguides are made to coincide with each other, only the even mode will be excited in the double mode channel waveguide 25, and will actually propagate in a single mode state to reach the output end 26. For this reason,
The output end 26 is effectively considered a laser light source. Output end 2
The linearly polarized laser beam emitted from the collimator lens 27 passes through the polarizing prism 28 and the λ/4 plate 29 bonded to the polarizing prism 28, and becomes circularly polarized light.
0 and is focused on the disk 31 to form a diffraction-limited spot there. As is well known, magneto-optical pits can be considered substantially the same as phase modulation pits for circularly polarized light. The light reflected by the disk 31 is again λ/
It passes through the fourth plate 29, is reflected by the polarizing prism 28, and becomes the second λ
The light enters the /4 plate 32, is reflected by the reflective film on the surface 33, passes through 28 again, enters the third λ/4 plate 34, is reflected by the reflective film on the surface 35, is reflected again by 28, and is emitted. The light becomes linearly polarized light orthogonal to the time, passes through the collimator lens 27, and is again focused on the end face 26 of the double mode waveguide, where a spot is formed. [0012] The even and odd modes of light excited into the double mode channel waveguide 25 by this laser spot are as follows:
The signals propagate while interfering with each other and eventually reach the branch 24. Branch 24
The branched lights propagate through waveguides 41 and 42, respectively, and are independently detected by photodetectors 43 and 44 fixed to the substrate 6. Then, as in the first embodiment shown in FIG. 1, the differential detector 45 detects the direction of the magnetic field for each magnetic domain on the magneto-optical disk using the differential signal 46 of the output signals of the photodetectors 43 and 44. I can do it. [0013] The second embodiment is a pickup device for a magneto-optical disk, and in order to detect information on the disk by polarized light, the above members 28, 29, 3 are used.
2, 33, 34, and 35, and it goes without saying that these members are not necessary if the disk is not a magneto-optical disk. In each of the above embodiments, if a semiconductor such as silicon is used as the waveguide substrate, the photodetector can be monolithically formed on the same substrate as the waveguide. Furthermore, if a compound semiconductor such as gallium arsenide or indium phosphide is used as the waveguide substrate, both the photodetector and the laser diode can be monolithically formed on the same substrate as the waveguide, resulting in miniaturization and savings in layers. Adjustment can be achieved. Furthermore, it goes without saying that the double mode waveguide can be replaced by two adjacent single mode waveguides. [0014] As the optical disk medium, it is possible not only to use a phase modulation type disk having uneven pits, but also to use a phase change type disk in which pits are formed by changes in reflectance. In magneto-optical disks, it is necessary to arrange a wavelength plate in the illumination optical system to make the polarization state of light on the medium circularly polarized. Furthermore, the present invention can be applied not only to information on an optical disk that is originally to be read, but also to guide grooves for tracking servo. [0015]

As described above, according to the present invention, there is provided a new ultra-compact optical pickup that can detect the edges of information pits on an optical disk by utilizing the interference of both even and odd modes in a double-mode channel waveguide. Can configure devices. Further, this detection method is effective for any type of optical disc, and the optical system can be significantly downsized and simplified. Furthermore, if a semiconductor such as Si is used as the waveguide substrate, the photodetector can be monolithically formed on the same substrate as the waveguide. Furthermore, if a compound semiconductor such as GaAs is used as the waveguide substrate, a photodetector,
Both the laser diode and the waveguide can be monolithically formed on the same substrate, and the size of the layer can be reduced and adjustments can be reduced. [0016]

[Brief explanation of the drawing]

[0017]

FIG. 1 is a schematic configuration diagram of a first embodiment. [0018]

FIG. 2 is a schematic configuration diagram of a second embodiment. [0019]

[Explanation of symbols]

1.21 Laser light source 6.22 Waveguide substrate 327 Collimator lens 430 Objective lens 725 Double mode channel waveguide 10, 11.2
3.41.42 Single mode channel waveguide 12
, 13.43.44 Photodetection element

[Figure 1]

Claims (6)

[Claims] 1. A laser light source, an illumination optical system that guides the light emitted from the laser light source onto an optical disk medium and forms a light spot on the surface of the medium, and a condensing optical system that condenses the light reflected by the medium. and a light detection means for detecting light focused by the light focusing optical system, wherein the light detection means has a channel waveguide formed on a substrate, and the light detection means has a channel waveguide formed on a substrate, and the light detection means has a channel waveguide formed on a substrate. The condensing optical system is configured so that the reflected light forms a light spot again at the incident end face of the waveguide, and the waveguide is in a double mode at the incident end face of the waveguide where the light spot is formed. , the double mode waveguide subsequently has a branch for distributing optical power to two channel waveguides, and the optical detection means detects the optical power propagating in the two branched channel waveguides. An optical pickup device comprising a photodetecting element for each detection, and reading information on the optical disc medium based on an output signal of the photodetecting element. 2. A laser light source, an illumination optical system that guides the light emitted from the laser light source onto an optical disk medium and forms a light spot on the surface of the medium, and a condensing optical system that condenses the light reflected by the medium. In the optical pickup device, the illumination optical system and the light collection optical system share the same objective lens, and the light detection means detects the light collected by the light collection optical system. The means has a channel waveguide formed on a substrate, the condensing optical system is configured so that the reflected light from the optical disk medium forms a light spot again at the end face of the waveguide, and the channel waveguide has a double mode waveguide region at the end face where a light spot is formed by the condensing optical system, and following the double mode waveguide, there are three
It has a waveguide branch that branches into a single mode waveguide, and the illumination light beam from the laser light source is guided to the central one of the three single mode waveguides, and the illumination light beam is guided through the objective lens to the optical disk medium. Further, the detection means has a configuration including a photodetection element for respectively detecting the light propagating in the outer two single mode waveguides among the three single mode waveguides, and the photodetection means An optical pickup device characterized in that information on the optical disk medium is read by a detection signal of an element. 3. The optical pickup device according to claim 1, wherein a silicon semiconductor is used as the waveguide substrate, and the photodetector is monolithically formed on the substrate. 4. The optical pickup device according to claim 1, wherein a compound semiconductor is used for the waveguide substrate, and the photodetector and the laser light source are monolithically formed on the same substrate. 5. The optical pickup device according to claim 1, wherein the double mode waveguide is formed by two adjacent single mode waveguides. 6. A wavelength plate is disposed in the illumination optical system so that the polarization state of light on the medium becomes circularly polarized light, and a magneto-optical disk is used as the optical disk medium. 6. The optical pickup device according to 5.