JPH07141685A - Optical integrated pickup - Google Patents

Abstract

PURPOSE:To separate a recording mark signal from an other phase substance signal and to improve an S/N by using both left and right circularly polarized light for reproducing beams. CONSTITUTION:A light beam reflected from a disk surface 13 is converged on a waveguide end surface 9 through a 1/4 wavelength plate 10, and waveguided beams of TE, TM modes are excited in a double mode waveguide 8 at nearly equal quantity. At this time, the waveguide 8 whose essential length is set for both TE, TM modes so that a phase difference of even-odd modes in respective polarization modes becomes odd times of 90 deg.C. The waveguide 8 is distributed to two pieces of channel wavelength 6, 7 by a wavelength branch 5. The single mode waveguides 6, 7 are branched by TE-TM mode splitters 15, 20 respectively, and the polarization distinguished beams are detected by photodetectors 18, 19, 23, 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical integrated pickup used in a reproducing apparatus such as an optical disk.

[0002]

2. Description of the Related Art In recent years, waveguides have been drawing attention in various fields. The reason is that the use of the waveguide has the advantages that the optical system can be made smaller and lighter, and the adjustment of the optical axis becomes unnecessary. The waveguide is a single mode waveguide in which only the 0th mode light is excited due to the difference in the refractive index between the waveguide (core portion) and the substrate (clad portion), the width of the waveguide or the refractive index distribution.
It is classified into a double-mode waveguide in which two modes of the next and first modes are excited, and a multi-mode waveguide in which three or more modes of zero-order, first-order, and second-order and above are excited.

A method for detecting a minute phase change of an object using mode interference of a waveguide has already been announced by the present inventors (H. Ooki and J. Iwasaki, Opt.
Commun. 85 (1991) 177). Further, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 4-252444 that the technique for detecting a minute phase change is applied to reproduction of a magneto-optical disk.

In general, the magnetization of the tracks of the magneto-optical disk is aligned in one direction (for example, upward) by applying a strong external magnetic field before recording. Then, a recording mark (a mark for recording information on the magneto-optical disk) having magnetization in the opposite direction (for example, downward) is formed on the track. That is, the recording on the magneto-optical disk depends on the direction of magnetization.

Such a recording mark behaves as an object having a different phase depending on the direction of magnetization when irradiated with circularly polarized light. Therefore, assuming reproduction of circularly polarized light, a minute phase change detection due to mode interference is used to detect a magneto-optical disk. It can be played back.

[0006]

However, since information such as a sector number is pre-formatted as pits (pre-pits) on a magneto-optical disk in general, there is a problem that the pre-pits and the recording marks cannot be distinguished from each other. It was In addition, there is a problem that if the disk surface has fine roughness, all of them are detected.

The present invention has been made in view of the above problems, and it is possible to reproduce recorded information on a magneto-optical disk by a mode interference method, and phase information such as prepits and surface roughness of a disk and phase information of a recorded mark. It is an object of the present invention to provide an optical integrated pickup capable of distinguishing between and.

[0008]

As a result of earnest research, the inventors of the present invention have found that the unevenness of the phase information when magnetized with right-handed circularly polarized light and with left-handed circularly polarized light is magnetized ( I noticed that the phase information such as the prepits and the surface roughness of the disc did not change while the recording mark part) was reversed.

That is, it has been realized that only the information of the recording mark can be reproduced by irradiating the disc with left and right circularly polarized light and obtaining the signal difference due to the respective polarization components. Therefore, the optical integrated pickup of the present invention comprises, firstly, a "laser light source, an optical system for converging a laser spot on a recording medium and forming an image of reflected light from the recording medium on the end face of the double mode waveguide. A double-mode waveguide, and a waveguide substrate in which first and second single-mode waveguides connected to the double-mode waveguide by a first waveguide branch are formed, In an optical integrated pickup for detecting information recorded on the recording medium by using mode interference of guided light propagating in a waveguide, right and left circularly polarized light is irradiated on the recording medium with substantially equal amplitude, and the double mode Polarization conversion means arranged between the laser light source and the recording medium such that the reflected light imaged on the end face of the waveguide is excited with substantially equal intensities in the TE and TM modes; First and second polarization discriminating means for discriminating the guided light guided through the second single mode waveguide into TE mode light and TM mode light, and separating them by the first and second polarization discriminating means. The information on the recording medium is reproduced by using the generated two TE mode lights and two TM mode lights (Claim 1).

Preferably, secondly, "the first and second polarization discriminating means are formed on a waveguide.
TE-TM mode splitter, wherein the first and second TE-TM mode splitters are used as second and third waveguide branches, respectively, and third and fourth waveguides are respectively provided in the second and third waveguide branches. And the fifth and sixth single-mode waveguides are connected (claim 2).

Preferably, thirdly, "the light from the laser light source is incident on a seventh single mode waveguide formed on the waveguide substrate, and the seventh single mode waveguide is the first Is connected to the double-mode waveguide through a waveguide branch of (3). Further, preferably, it is fourthly constituted by "arranging a TE-TM mode converter in the seventh single mode waveguide (claim 4)".

[0012]

As described above, the recording mark has the function of rotating its plane of polarization when linearly polarized light is incident,
When circularly polarized light enters, the polarization state does not change, and only its phase undergoes modulation. Therefore, in this case, the recording mark has the same meaning as a phase pit having an extremely low height. When it is attempted to detect this phase information with high sensitivity by using the mode interference of the waveguide, it is naturally greatly affected by other phase objects existing on the disk such as surface roughness of the disk. However, the recording mark causes opposite phase modulation for left and right circularly polarized lights, but a general phase object has the same phase modulation direction regardless of the rotation direction of circularly polarized light. Therefore, by using the left and right circularly polarized light, it is possible to distinguish the recording mark from other phase objects.

[0013]

1 is a schematic diagram showing an optical integrated pickup according to an embodiment of the present invention. The light that has entered the single mode waveguide 3 from the laser light source 2 mounted on the waveguide substrate 1 is a T beam that is installed on the single mode waveguide 3.
It passes through the E-TM mode converter 4. The mode converter 4 propagates the TE and TM mode lights in the waveguide 3 after passing through the mode converter 4 in substantially equal amounts. The single mode waveguide 3 joins the double mode waveguide 8 together with the other single mode waveguides 6 and 7 at the waveguide branch 5. Since the center of the waveguide 3 and the center of the double mode waveguide 8 are aligned with each other, only the 0th (even) mode is excited in the double mode waveguide 8. The 0th-order mode light is emitted from the end face 9, passes through the quarter-wave plate 10 and forms a minute laser spot 12 on the magneto-optical disk surface 13 by the objective lens 11. 1
The / 4 wave plate 10 is arranged such that the TE and TM mode lights emitted from the end face of the double mode waveguide 8 are circularly polarized lights to the left and right (or right and left), respectively, and both have substantially the same amplitude. ing. Here, since the emitted lights of the TE and TM modes originally have almost the same amplitude, these left and right circularly polarized lights are combined to result in a substantially linearly polarized state. The polarization direction of this linearly polarized light depends on the phase difference between the TE and TM modes, but it may be any direction. The polarization direction of this linearly polarized light rotates due to the polar Kerr effect of the recording mark, which means that the phase of the combined left and right circularly polarized light changes. The light reflected by the disk surface 13 passes through the objective lens 11 and the quarter-wave plate 10 again, and is condensed on the end face 9 of the waveguide, and the TE and TM mode guided lights are approximately equal in the double mode waveguide 8. Excite. Here, the double-mode waveguide 8 is set so that its substantial length L for both TE and TM modes is such that the phase difference between the even and odd modes in each polarization mode is an odd multiple of 90 degrees. As described above, Japanese Patent Laid-Open No. 4-252444 discloses that the phase information contained in the reflected light from the disk 13 focused on the end face 9 of the waveguide can be taken out as an intensity change. Double mode waveguide 8
When the branch angle of the single mode waveguides 6 and 7 after the branch 5 is small, the substantial length L of may operate like a double mode waveguide. Therefore, the length of L is equal to the length of the double mode waveguide 8 plus the length of light propagation in the double mode.

The double mode waveguide 8 eventually reaches the waveguide branch 5, where the guided light is two channel waveguides 6, 7.
Will be distributed to. At this time, part of the guided light is also distributed to the waveguide 3, but since the center of the waveguide 3 and the center of the waveguide 8 coincide with each other as described above, only the 0th-order mode light is emitted from the waveguide 8. It is distributed to the waveguide 3. Generally, when the phase modulation of the disk surface is small, most of the guided light excited in the double-mode waveguide 8 is the 0th-order mode, and it is direct that the 0th-order mode is selectively distributed to the waveguide 3. It does not cause signal loss, and is rather preferable in terms of S / N. The intensity of the light distributed to the single mode waveguides 6 and 7 is asymmetric as a result of mode interference in the double mode waveguide 8. What is important here is that in the case of information by recording marks, the amounts of light distributed to the single mode waveguides 6 and 7 are opposite in TE mode light and TM mode light, and other phases such as surface roughness of the disk are generated. In the case of information, it is always in phase. Utilizing this, the single mode waveguides 6 and 7 are branched by the TE-TM mode splitters 15 and 20, respectively, in order to extract only the signal due to the recording mark, and the light thus polarized and discriminated is single mode waveguides 16 and 17. , 22 and 24 through photodetector 1
It is detected at 8, 19, 23 and 24.

The method of discriminating between the TE mode light and the TM mode light as described above is performed by the TE-TM provided on the waveguide substrate.
Not only the method of using the mode splitter, but also the method of discriminating the guided light emitted from the single mode waveguides 6 and 7 by the polarization mode splitter may be used. In FIG. 1, the TE mode light is emitted from the single mode waveguides 16 and 21, and the TM mode light is emitted from the single mode waveguides 17 and 22. At this time, as shown in FIG. 1, the photodetectors 18 and 23 and the photodetectors 19 and 24 are differentiated, and if the difference signal between them is taken, the signals other than the recording mark signal are canceled.

However, the substantial length L of the double-mode waveguide 8 is set so that the phase difference between the even and odd modes is an odd multiple of 90 degrees, but by this alone, the signal of the recording mark happens to be TE, There is a possibility of becoming in phase in both TM modes. In order to avoid this, assuming that the substantial length L of the double mode waveguide 8 in the TE mode is M times 90 degrees as the phase difference between the even and odd modes, and the same as N times in the TM mode, M− It is preferable that N be an even multiple of 2.

In the present embodiment, the mode converter 4 is provided so that light propagates in the polarization directions of the TE and TM modes in substantially equal amounts, but this is determined by previously determining the polarization direction of the laser light source. Alternatively, light may be propagated in amounts substantially equal to the polarization directions of the TM and TM modes. In this case, the mode converter 4 may be omitted.

[0018]

[Effect] In the optical integrated pickup of the present invention, by using both left and right circularly polarized light as the reproduction light, the signal of the recording mark can be transmitted to other phase objects (for example, prepits and surface roughness of the disk) even though it is a mode interference method. It becomes possible to separate from the signal, and the S / N can be greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an optical integrated pickup according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Waveguide substrate 2 ... Laser light source 3, 6, 7, 16, 17, 21, 22 ... Single mode waveguide 4 ... TE-TM mode converter 5 ... Waveguide branch 8 ... Double-mode waveguide 9 ... End face 10 ... Quarter wave plate 11 ... Objective lens 12 ... Laser spot 13 ... Photomagnetic disk 14 ... Electrodes 15, 20 ... -TE-TM mode splitter 18, 19, 23, 24 ... Photodetector

Claims (4)

[Claims] 1. A laser light source, an optical system for converging a laser spot on a recording medium and imaging reflected light from the recording medium on an end face of the double mode waveguide, the double mode waveguide and the double mode waveguide. A waveguide substrate in which first and second single-mode waveguides connected to the mode waveguide by a first waveguide branch are formed, and guided light propagating in the double-mode waveguide In an integrated optical pickup for detecting information recorded on the recording medium by using the mode interference of (1), left and right circularly polarized light is irradiated on the recording medium with substantially equal amplitude and is imaged on the end face of the double mode waveguide. The polarization conversion means is arranged between the laser light source and the recording medium so that the reflected light is excited in the TE and TM modes with substantially equal intensities, and the first and second single mode waveguides are guided. The first and the second polarization discrimination means, has two T separated by the first and second polarization discrimination means for discriminating the guided light to light of TE mode and TM mode
An optical integrated pickup characterized by reproducing information on the recording medium by using E mode light and two TM mode lights. 2. The first and second polarization discriminating means are first and second TE-TM mode splitters formed on a waveguide, and the first and second TE-TM mode splitters are provided. The second and third waveguide branches as the second and third waveguide branches, respectively.
3. The integrated optical pickup according to claim 1, wherein the third and fourth single-mode waveguides and the fifth and sixth single-mode waveguides are connected to the waveguide branches, respectively. 3. The light from the laser light source is incident on a seventh single mode waveguide formed on the waveguide substrate, and the seventh single mode waveguide passes through a first waveguide branch. 2. The integrated optical pickup according to claim 1, wherein the optical integrated pickup is connected to the double mode waveguide. 4. The seventh single mode waveguide is provided with a T
The integrated optical pickup according to claim 3, further comprising an E-TM mode converter.