JP2864702B2 - Optical integrated pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical pickup for reproducing information from an optical recording medium by using a laser beam, and more specifically, to an interference optical system configured using an optical waveguide. The present invention relates to an integrated optical pickup provided.

[Prior Art] Conventionally, in an optical recording medium on which information is recorded and reproduced by a laser beam, information is recorded by the length of a pit.
In order to realize a higher density optical recording medium, information is recorded not only by the pit length but also by the pit depth.
It is necessary to regenerate. In such a high-density optical recording medium, a heterodyne interferometer using laser light interference is used to detect the depth of a pit. Conventionally, a heterodyne interferometer for measuring position, displacement and velocity with high accuracy is a light source He-Ne laser 100, a half mirror 102, a λ / 2 plate 104, a mirror 105, a Bragg cell 106, as shown in FIG. It comprises a half mirror 107, a polarizing beam splitter 108, a λ / 4 plate 109, and a photodetector 110. The laser light emitted from the He-Ne laser 100 is linearly polarized light polarized in a direction parallel to the paper surface,
Into two beams. The first of the two split beams is a polarizing beam splitter 10.
8, the surface of the optical recording medium 112 is irradiated through the λ / 4 plate 109. Pits 113 of the laser-irradiated portion of this optical recording medium 112
The depth reflected light or signal light received Doppler shift f _S due to a change in polarization plane is rotated 90 ° by passing through the lambda / 4 plate 109 again, polarized become beam polarized in a direction perpendicular to the paper surface beam The light is reflected by the splitter 108.
On the other hand, the second beam of the two divided beams is rotated by 90 ° by the λ / 2 plate 104 to be in a direction perpendicular to the paper surface, reflected by the mirror 105, and incident on the Bragg cell 106. Bragg cell 106 is an optical modulator using an acousto-optic effect, first-order light diffracted by an acoustic wave of a frequency f _R, which is excited by the drive circuit 114 as a reference beam is given by the frequency shift f _R. When heterodyne detection is performed by multiplexing and interfering the signal light and the reference light with the half mirror 107, a signal oscillating at the Doppler beat frequency f _R ± f _S is detected by the photodetector 110. This signal is amplified by an amplifier 116, and the Doppler beat frequency f _R ± f _S is measured by a spectrum analyzer 118 to detect the speed of the pit 113 simultaneously with the direction of the change in the depth of the pit 113 due to the rotation of the optical recording medium 112. it can. That is, pit 113
Change or velocity v of the depth, when the wavelength of the laser light is lambda, using Doppler shift f _S, can be determined by _{v = f S λ / 2 (} 1). Further, the pit depth of the optical recording medium 112 can be detected by integrating the speed with time. That is, the pit depth Δz is as follows: Δz = λ / 2 · λf _S dt = λ / (4π) · ∫ (δφ / δt) dt = λ / (4π) · (φ _D −φ _O ) (2) Given by However, phi represents the phase, phi _D is the detected phase, phi _O represents the initial phase.

[Problems to be Solved by the Invention] However, this heterodyne interference optical system is usually configured by arranging and fixing necessary optical components on an anti-vibration table such as an optical bench, and a delicate optical axis between the components. There is a problem that adjustment is necessary, reliability and productivity are low, and the optical system is large and heavy, so that it is not practical for use in an optical pickup in an optical recording apparatus.

The present invention has been made in order to solve the above-described problems, and an object of the present invention is to integrate a main part of an interference optical system on a single substrate by using a thin film wave technique, An object of the present invention is to provide a compact, stable and highly reliable optical integrated type pickup that does not require optical axis adjustment.

[Means for Solving the Problems] To achieve this object, an integrated optical pickup according to the present invention includes a plurality of light sources and a light source for splitting light from the first light source into first and second lights. 1 optical waveguide for demultiplexing, a mode converter for rotating the polarization plane of the demultiplexed first light by approximately 90 °, and applying a constant frequency shift to the first light whose polarization plane is rotated by approximately 90 °. The frequency shifter and the refractive index of the optical waveguide change non-linearly with respect to the propagation direction of the light, irradiating the device under test with the light radiated out of the optical waveguide, and reflecting the light from the device under test on the optical waveguide. A plurality of graded-index optical waveguides, means for transmitting the second light to the first graded-index optical waveguide, and an optical recording medium transmitted from the first graded-index optical waveguide A multiplexing optical waveguide for multiplexing and interfering reflected light from the optical disc with output light from the frequency shifter; A photodetector for detecting output light from the optical waveguide, a second optical waveguide for demultiplexing light from the second light source into third and fourth light, and a second optical waveguide for demultiplexing the third light. Means for transmitting the second graded-index optical waveguide, means for transmitting the fourth light to the third graded-index optical waveguide, and means for transmitting the fourth light from the second and third graded-index optical waveguides. And a plurality of photodetectors that respectively detect reflected light from the optical recording medium.

Preferably, the frequency shifter comprises an optical waveguide having a magneto-optical effect, and means for applying a sawtooth-shaped magnetic field to the optical waveguide.

Furthermore, a mode splitter that separates the light whose polarization plane and the rotation plane of the light source rotate by approximately 90 ° between the light source and the gradient index optical waveguide and guides the light to the photodetector, and a mode conversion efficiency of approximately 50
%, A mode filter that attenuates the light whose polarization plane and the polarization plane of the light source are rotated by approximately 90 ° between the light source and the refractive index distribution type optical waveguide, and a mode conversion efficiency of approximately 50%. % Mode converter.

In addition, a single light source may be used, and the light from the light source may be split into two and transmitted to the first and second demultiplexing optical waveguides. Using
Means may be provided for transmitting light from the light source to the first, second and third graded index optical waveguides, respectively.

[Operation] In the integrated optical pickup of the present invention having the above configuration, the frequency emitted from the semiconductor laser as the first light source is used.
The laser light of f _O becomes TE mode in which the direction of the electric field oscillation is parallel to the thin film surface, and propagates through the optical waveguide.
Split into two lights. The demultiplexed first light is converted into a TM mode by a mode converter and modulated by a modulator using a phase shift due to a magneto-optical effect, that is, by a frequency shifter, so that the frequency is shifted by a fixed amount f _R , The reference light has a frequency of f _O + f _R. The demultiplexed second light is radiated out of the optical waveguide by the gradient index optical waveguide in which the refractive index of the optical waveguide changes nonlinearly with respect to the propagation direction of the light, and irradiates the surface of the optical recording medium. Is done. Reflected from the optical recording medium, the frequency receiving only the Doppler shift f _S
The signal light of f _O + f _S is guided again into the optical waveguide by the gradient index optical waveguide, and is multiplexed by the optical multiplexing optical waveguide together with the reference light which is the output light from the frequency shifter. When this is detected by the light detector, the light detector measurement signal that oscillates at a Doppler beat frequency f _R -f _S by the interference of the reference light and the signal light is detected. By comparing the reference signal from the measurement signal and the frequency shifter, the Doppler shift f _S is determined, the direction and varying the rate of change in the depth of the pits caused by the rotation of the optical recording medium can be detected, the speed Is integrated over time to detect the depth of the pit. At this time, a mode converter having a mode conversion efficiency of 50% provided in front of the gradient index optical waveguide is used as the second mode converter.
Since the light travels back and forth, the TE mode is almost 100% converted to the TM mode whose polarization plane differs from that of the light source by 90 °. Since the TM mode is attenuated by the mode filter or separated by the mode splitter and guided to the photodetector, it does not reach the light source. Further, the light emitted from the second light source is split into third and fourth lights by the second splitting optical waveguide, and transmitted to the second and third refractive index distribution type optical waveguides, respectively. Irradiates the optical recording medium. Then, by detecting the reflected light from the optical recording medium with the photodetector, tracking control similar to the well-known three-beam method can be performed.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

The integrated optical pickup is, for example, as shown in FIG.
Bi: YIG (Bix _x Y) formed on a substrate 11 such as (Gd ₃ Ga ₅ O ₁₂ )
_3-x Fe ₅ O ₁₂ ), magnetic thin film 12 having a magneto-optical effect such as Bi: GdIG (BI _x Gd _3-x Fe ₅ O ₁₂ ), semiconductor lasers 13 and 14, Si
It comprises photodetectors 16, 17, 18 such as photodiodes.

The magnetic thin film 12 is provided with a ridge portion 21 whose film thickness is larger than other portions, forming a ridge-type waveguide 21. The laser light propagates along the ridge waveguide 21. The ridge-type waveguide 21 is manufactured using well-known photolithography. That is, the substrate 11
A magnetic thin film 12 is formed thereon by a thin film forming means such as a liquid phase growth method or a sputtering method, and a photoresist is applied thereon. Then, after patterning into a predetermined waveguide shape, portions other than the portion to be the ridge 21 are etched by a predetermined thickness by plasma etching, sputter etching, wet etching using hot phosphoric acid, or the like. Finally,
Ridge type waveguide by removing photoresist
21 is formed.

The laser light emitted from the semiconductor laser 13 enters the ridge waveguide 21. At this time, the laser light propagating through the ridge-type waveguide 21 emits TE light whose vibration direction of the electric field is parallel to the film surface.
The semiconductor laser 13 is mounted so as to be in the mode. The laser light that has propagated through the ridge-type waveguide 21 is composed of a ridge-type waveguide having one end divided into two branch waveguides.
The light is split into two by the branch 23, and the branch waveguide 24,
Propagate 25.

On the branch waveguide 24, a buffer layer 27 made of SiO ₂ or the like is provided.
Further, electrodes 28 and 30 made of a metal such as Al are provided, and constitute a mode converter 32 and a frequency shifter 33, respectively.

When a direct current is applied to the electrode 28 in a direction perpendicular to the propagation direction of the laser light, a magnetic field parallel to the propagation direction of the laser light is generated, and the magnetic field magnetizes the branch waveguide 24 immediately below the electrode 28, so that the Faraday effect is generated. Causes mode conversion. By this mode conversion, the TE mode is converted into a TM mode in which the vibration direction of the magnetic field is parallel to the thin film surface. Here, the branch waveguide 24 uses the birefringence generated in the magnetic thin film 12 to generate TE and TE.
Since the TM mode is made to have the same propagation constant, 100% mode conversion can be obtained with a magnetic field applied in a certain direction.

By flowing a current from an oscillator (not shown) to the electrode 30 of the frequency shifter 33, the branch waveguide 24 immediately below the electrode 30 has:
A magnetic field perpendicular to the propagation direction of the laser light and parallel to the thin film surface is applied. This magnetic field magnetizes the branch waveguide 24 and causes a phase shift due to the magneto-optical effect in the TM mode. That is, assuming that the propagation constant of the TM mode when no magnetic field is applied is β _O and the propagation constant when a magnetic field is applied is β, β = β _O + γ (3) Here, γ is the amount of phase shift due to the magneto-optical effect. As shown in FIG. 1, the z-axis in the propagation direction of the laser light, taking the x-axis in the direction perpendicular to the thin film plane _{γ, γ = 2ω O ε O} ∫Re [ε xz e z * e z] dx ( 4) given by Where ω _O is the angular frequency of the laser light,
epsilon _O is the vacuum permittivity, e _x and e _z are the electric field of the TM mode x
Component and z component, ε _xz is one of the off-diagonal components of the relative permittivity tensor of the magnetic thin film 12, * is a complex conjugate, and Re is a real part of a complex number. ε _xz has a relationship with the Faraday rotation coefficient θ _F and ε _xz = j (2n ₁ / k) θ _F (5). Here, n ₁ is the refractive index of the magnetic thin film 12, k is the wave number of the laser light in a vacuum, and is given by k = 2π / λ (6) where λ is the wavelength of the laser light. Further, in a range in which the magnetization of the magnetic thin film 12 is not saturated, the magnetization of the magnetic thin film 12 is proportional to the applied magnetic field H, that is, the current I flowing through the electrode 30. Therefore, when this proportionality constant is V, θ _F = VI (7 ).

(5) Substituting expression (4) below, γ = 2ω _O ε _O become _{(2n 1 / k) θ F} ∫Re [je x * e z] dx = Aθ F (8). Here, A is a constant.

Assuming that the length of the portion where the magnetic field is applied by the electrode 30 in the branch waveguide 24 is l, the phase-shifted TM
Field _{mode, e x = E x sin [} ω O t + (β O + γ) 1] = E x sin [ω O t + Aθ F 1 + β O 1] becomes (9). _{Here, θ F = ω R t /} (A1) (10) i.e., (7) _{than, I = ω R t / (} AlV) (11) become as when the electrode 30 supplying a current I e _{x = E x sin [(ω O} + ω R) t + β1] (12) , and the angular frequency of the laser light ω _O = 2πf _O from omega _O +
to _{ω R = 2π (f O +} f R), i.e., the frequency of the laser light is shifted from f _O by f _R, a f _O + f _R. However, the electrode
The current of the reference signal flowing through 30 has an amplitude of 2π / as shown in FIG.
(A1V), similar frequency shift can be obtained as a sawtooth wave of period 2π / ω _R. The laser beam having the frequency f _O as shown in FIG. 3A incident on the branch waveguide 24 in this manner has a frequency as shown in FIG.
shifted by f _R, the frequency becomes the reference light of f _O + f _R.

On the other hand, the laser light propagating in the branch waveguide 25 is transmitted through the mode splitter 34a, and the TE mode is converted into the TM mode by 50% by the mode converter 36a. This mode converter
Like the mode converter 32, the buffer layer 36a includes a buffer layer 38 and an electrode 39a provided on the ridge waveguide 37a.
However, since the length is half of the mode converter 32,
The mode conversion efficiency is also 50%, which is half. The light incident on the gradient index optical waveguide 41a from the mode converter 36a becomes a laser beam 42a condensed to an appropriate beam diameter from the gradient index optical waveguide 41a to the optical recording medium 44 on which the pits 43 are formed. Irradiated.

The graded index optical waveguide 41a is made of Y ₃ Fe using well-known thin film forming means, photolithography, heat diffusion, or the like.
It can be formed by diffusing an element that increases the refractive index such as Bi or an element that decreases the refractive index such as A1 from the surface into ₅ O ₁₂ (YIG) or the like. At this time, the refractive index distribution has a substantially Gaussian distribution in the depth direction and the lateral direction, and in the propagation direction of the laser light, as shown in FIG. It is divided into a decreasing area. In a region where the surface refractive index is substantially constant, the laser light that has been diffused and emitted from the ridge waveguide 37a by diffraction becomes substantially parallel light. Further, in the region where the surface refractive index decreases in a non-linear manner, as described in Suzuki, Miyazaki, Proceedings of the IEICE Spring National Convention, SC-6-6 (1989), laser light is applied to the substrate. It radiates in one direction and at the same time focuses on one point.

The laser light reflected from the optical recording medium 44 is
Receiving only the Doppler shift frequency f _S in accordance with the rate of change of depth of the pits 43 of the irradiated portion of the laser light on the surface of, the frequency becomes f _O + f _S as of FIG. 3 (c). The signal light, which is the reflected light that has undergone the Doppler shift, is guided into the ridge-type waveguide 37a by the gradient index optical waveguide 41a, and passes through the mode converter 36a again.
% Mode conversion occurs, and the remaining TE mode is also completely converted to TM mode.

The mode splitter 34a includes two parallel optical waveguides 45a and 46a, and a buffer layer 47 made of SiO ₂ or the like and a metal clad 48a made of a metal such as A1. However, the buffer layer 47 is made thinner than the other buffer layers 27 and 38. The two optical waveguides 45a and 46a are manufactured so that the TE mode propagation constants are substantially equal to each other, and operate as a directional coupler. Here, since the metal cladding 48a hardly affects the propagation constant of the TE mode, the TE mode incident on the optical waveguide 45a is
Then, the light enters the mode converter 36a. Buffer layer 47
Is thin, the metal cladding 48a has a large effect on the TM mode propagation constant, and the TM mode propagation constant in the optical waveguide 45a loaded with the metal cladding 48a is smaller than the TM mode propagation constant in the optical waveguide 46a. . That is, since the propagation constants of the TM mode are different from each other in the optical waveguides 45a and 46a, no light wave transition occurs in the TM mode, and as a result, the TM mode does not operate as a directional coupler. Therefore, the TM mode incident on the optical waveguide 46a from the mode converter 36a does not shift to the optical waveguide 45a, but propagates through the optical waveguide 46a and the branch waveguide 49. As a result, the signal light that has undergone the Doppler shift does not return to the semiconductor laser 13 that is the light source, so that the semiconductor laser 13 does not generate noise induced by the return light, and can perform good S / N reproduction. .

Further, the frequency shifter 33 receives a frequency shift by f _R ,
The reference light propagating through the branch waveguide 24 is combined with the signal light propagating through the branch waveguide 49 by the Y branch 50.
The combined laser beam, the amplitude due to interference has vibrated in Doppler beat frequency f _R -f _S, heterodyne detection is performed by detecting this by the photodetector 16, Figure 3 (d ) As in the Doppler beat frequency f _R −
A signal oscillating at f _S is obtained.

The output signal of the photodetector 16 is compared with the fundamental frequency f _{R of the} current applied to the electrode 30 of the frequency shifter 33, and the Doppler shift is performed.
By obtaining _fS , it is possible to detect the direction of the change in the depth of the pit 43 of the optical recording medium 44 and the speed of the change at the same time. When the direction of the displacement of the depth of the pit 43 of the optical recording medium 44 is reversed, a Doppler beat occurs at a position of f _R + f _S with respect to the frequency shift f _R of the reference light as shown in FIG. . Furthermore, the optical recording medium obtained from the Doppler shift f _S
The depth of the pit 43 can be detected by integrating the change speed of the depth of the 44 pits 43 with time.

The laser light emitted from the semiconductor laser 14 propagates through the ridge-shaped waveguide 52, and the two branch waveguides 54 and 55
Is divided into two parts. Branch waveguide 54 and
The laser light that has propagated through 55
Propagate through 34b and 34c, mode converters 36b and 36c,
The optical recording medium 44 is provided by the gradient index optical waveguides 41b and 41c.
Are irradiated as laser beams 42b and 42c. At this time, each of the mode splitters 34b and 34c includes two optical waveguides 45b, 46b and 45c, 46c, a buffer layer 47, and metal clads 48b and 48c, and has the same function as the above-described mode splitter 34a. Mode converters 36b and 36c
Are ridge-type waveguides 37b and 37c, buffer layer 38, electrode 39
b and 39c, and has the same function as the mode converter 36a described above. The gradient index optical waveguides 41b and 41c also have the same function as the above-described gradient index optical waveguide 41a. Accordingly, the laser light reflected from the optical recording medium 43 is transmitted through the optical waveguides 37b and 3c by the gradient index optical waveguides 41b and 41c, respectively.
It is led to 7c, and is converted to the TM mode by the mode converters 36b and 36c. And the mode splitters 34b and 34c
Guided to the ridge waveguides 56 and 57 through the photodetector
Detected at 17 and 18, respectively.

Here, the laser beam 42 applied to the optical recording medium 44
As shown in the top view of FIG. 5, a, 42b and 42c are provided with a laser beam 42a for reproducing information is arranged at the center of the pit 43. Laser beams 42b and 4 for performing tracking control
2c is arranged such that the center of the beam is on the opposite side of the pit 43, and half of the laser beams 42b and 42c are present in the pit. Generally, the pit
When the laser beams 42b and 42c are irradiated to 43, the amount of reflected light decreases due to interference between reflected light from pits and other than pits.
In FIG. 5, when the laser beams 42a, 42b, and 42c are entirely shifted downward from the plane of the drawing, the portion of the laser beam 42b that irradiates the pit becomes large, so that the amount of reflected light decreases, and the laser beam 42c Since the portion irradiated to the outside increases, the amount of reflected light increases. The reverse is true when the paper is shifted above the plane of the paper. Therefore, the tracking control is performed in the same manner as the well-known three-beam method by moving the integrated optical pickup so that the reflected light amounts of the laser beams 42b and 42c, that is, the difference between the outputs of the photodetectors 17 and 18 are always zero. It can be performed. As shown in the cross-sectional view of FIG. 6, information is recorded not only on the length of the pit 43 but also on the pit 43 on the optical recording medium 44. The information recorded at high density on the optical recording medium 44 can be reproduced by performing accurate detection by the heterodyne interference method using the beam 42a. In addition, by performing encoding so that the average of the depths of the pits 43 is constant in the optical recording medium, it is possible to perform stable tracking without being affected by a change in the depth of the pits.

As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and various modifications can be made.

That is, the materials of the substrate, the magnetic thin film, the buffer layer, and the electrode are not particularly limited. For example, sapphire, glass, etc. are used for the substrate, rare-earth iron garnet is used for the magnetic thin film, a dilute magnetic semiconductor such as CdMnTe, a paramagnetic material such as Faraday rotating glass, and TAG (Tb ₃ Al ₅ O ₁₂ ) are buffered. An oxide or a nitride such as ZnO or AlN may be used for the layer, and gold or the like may be used for the electrode. Further, a buffer layer may be provided on the entire surface of the magnetic thin film.

Further, the optical waveguide does not need to be of a ridge type, and may be, for example, a rectangular waveguide, a buried waveguide, a dielectric loaded waveguide, a diffusion waveguide, or the like. The shape is not particularly limited as long as it can be confined in the lateral direction.

Alternatively, a magnetic thin film may be used only for the frequency shifter and the mode converter, and a dielectric material having no magneto-optical effect may be used for other portions. Further, the shape of the electrode for applying a magnetic field to the frequency shifter and the mode converter is not particularly limited. Furthermore, a magnetic field may be applied by providing an external electromagnet, coil, or the like. Further, when the branch waveguide 24 and the ridge-type waveguides 37a, 37b, 37c are formed so that the propagation constants of the TE mode and the TM mode are different from each other, 100% mode is applied when a magnetic field in a certain direction is applied. No conversion is available. However, since the mode conversion can be added by periodically inverting the direction of application of the magnetic field, for example, as shown in FIG. In vessel 32
A 100% mode conversion and a 50% mode conversion are obtained in the mode converters 36a, b, c.

Further, the splitting of the laser light is performed not by the Y-branch waveguide but by the eighth
As shown in the top view of the figure, this may be performed by directional couplers 62 and 63 in which two optical waveguides are formed in parallel. At this time, the wavelength division ratio can be changed by adjusting the length of the parallel portion of the two optical waveguides. Furthermore, as shown in the figure, a laser beam from the reference light and the light source subjected to frequency shift by f _R by the frequency shifter multiplexing may detect the frequency f _R of the reference signals to interfere. That is, a part of the TE mode emitted from the semiconductor laser 13 and propagating through the optical waveguide 64 is split by the directional coupler 62 into the optical waveguide 65. The laser light that has propagated through the optical waveguide 65 enters the gradient index optical waveguide 41a via the mode splitter 34a and the mode converter 36a as described above in detail, and is irradiated on the optical recording medium 44. Receiving only the Doppler shift frequency f _S according to the speed of the depth of the change in the pit 43 of the surface of the optical recording medium 44, the reflected light from the optical recording medium 44 the frequency becomes f _O + f _S is the refractive index distribution After being guided to the ridge-type optical waveguide 37a by the type optical waveguide 41a and converted into the TM mode by the mode converter 36a, it is guided to the optical waveguide 46a by the mode splitter 34a and propagates through the branch waveguide 49. Propagating through the optical waveguide 64
The TE mode is further provided by an optical waveguide 67
Is demultiplexed. The remaining TE mode propagating through the optical waveguide 64 is converted to the TM mode by the mode converter 32 as described above in detail, and the frequency is shifted to f _R by the frequency shifter 33.
And the reference light has a frequency of f _O + f _R. The reference light is split into two by the Y branch 68 and propagates through the branch waveguides 69 and 70, respectively. The reference light propagating in the branch waveguide 70 and the signal light propagating in the branch waveguide 49 are Y-branched 71
Are combined. The combined laser beam, the amplitude due to interference has vibrated in Doppler beat frequency f _R -f _S, heterodyne detection is carried out by this is detected by the photodetector 72, the Doppler beat frequency f _R A signal oscillating at −f _S is obtained. On the other hand, when the reference light that has propagated through the branch waveguide 69 and the laser light that has not undergone the frequency shift that has propagated through the optical waveguide 67 are multiplexed by the Y-branch 74, the amplitude of the multiplexed laser light becomes larger due to interference. Is the frequency f _R
In which oscillates a signal that oscillates at a frequency f _R is obtained by detecting this in the photodetector 76. By determining the Doppler shift f _S by comparing the output signal of the photodetector 72 and 76, it is possible to detect the direction and the speed at the same time the depth of the change in the pit of the optical recording medium 44. At this time,
Even if the frequency shift f _R of the reference light fluctuates due to fluctuations in the temperature or the like of the frequency shifter 33, the Doppler beat frequency f _R −f _S of the output of the photodetector 72 and the frequency f f of the reference signal of the output of the photo detector 76 the difference f _S and _R is constant, it is possible to accurately obtain the Doppler shift f _S.

Also, as shown in FIG. 9, the laser beam emitted from the semiconductor laser 13 and propagated through the ridge-type waveguide 21 is
Laser light propagating through the two branch waveguides 81 and 82,
For reproducing the laser beam propagating through the branch waveguide 81, the branch waveguide
The laser light propagating through 82 may be used for tracking. That is, the laser light that has propagated through the branch waveguide 81 is further divided into two laser lights by the Y branch 23, and is used for detecting the pit depth due to interference as described in detail. The laser light propagating through the branch waveguide 82 is further divided into two by a Y branch 84, guided to the branch waveguides 54 and 55, and used for tracking control as described in detail above. Accordingly, only one semiconductor laser needs to be used as the light source, and the cost of the optical integrated pickup can be reduced.

As shown in FIG. 10, a Y-branch 86 is used instead of the mode splitter 34a, and the Y-branch 86 and a semiconductor laser as a light source are used.
13, for example, a buffer layer 88 on the ridge waveguide 21.
And a mode filter 92 comprising a metal clad 90. The mode filter 92 allows only the TE mode to pass by the function of the metal clad 90 and attenuates the TM mode.
In other words, the laser light reflected from the optical recording medium 44 enters the TM mode by the mode converter 36a, is branched by the Y branch 86, and propagates through the branch waveguides 25 and 49. Here, since the TM mode propagating through the ridge-shaped waveguide 21 through the branch waveguide 25 is attenuated by the mode filter 92, the semiconductor laser
Does not reach 13. Therefore, S / N is not affected by return light.
Good reproduction can be performed. On the other hand, the semiconductor laser 13
The TE mode emitted from the ridge waveguide is not affected by the metal cladding 90 and propagates through the ridge waveguide 21 without attenuation.

As shown in FIG. 10, two semiconductor lasers 94 and 95 may be used for tracking. That is, the laser beams emitted from the semiconductor lasers 94 and 95 propagate through the ridge waveguides 96 and 97, respectively, and the mode splitter 34b
And 34c, and the tracking control is performed as already described in detail. However, the arrangement of the laser beams 42a, 42b and 42c on the optical recording medium 44 may be the same as the tracking control by the well-known three-beam method as shown in FIG.

A region where the refractive index in the refractive index distribution type optical waveguide decreases nonlinearly may be manufactured by using oblique polishing. First, as shown in FIG. 12 (a), a magnetic thin film 12 whose refractive index in the depth direction is changed is manufactured by a thin film forming means such as a liquid phase growth method. At this time, by changing the growth temperature during liquid phase growth, the composition of the magnetic thin film 12 changes,
Accordingly, the refractive index also changes. Therefore, the magnetic thin film 12 may be grown while gradually changing the growth temperature so that the refractive index decreases in the depth direction. Next, the surface is obliquely polished as shown in FIG. This makes it possible to produce an optical waveguide in which the refractive index of the polished surface decreases nonlinearly. Further, the shape of the refractive index distribution in the refractive index distribution type optical waveguide is not particularly limited. The size of the light spot irradiated on the object to be measured can be controlled by the distribution of the refractive index.

[Effects of the Invention] As is clear from the above description, according to the present invention, the main components of the interference optical system such as a laser beam splitter, a multiplexer, and a frequency shifter using the thin-film waveguide technology. Since the units are integrated on one substrate, optical axis adjustment is unnecessary, and a small, stable, and highly reliable optical integrated pickup can be manufactured with high productivity. In addition, the mode converter and the mode splitter, or the Y-branch waveguide and the mode filter are combined to prevent the reflected light from the optical recording medium from returning to the light source. And reproduction with good S / N can be performed.

[Brief description of the drawings]

FIGS. 1 to 12 show an embodiment embodying the present invention. FIG. 1 is a configuration diagram of an optical integrated pickup according to an embodiment of the present invention, and FIG. FIG. 3 is a diagram showing a waveform of a current applied to an electrode of a shifter. FIG. 3 is an explanatory diagram showing a relationship between frequencies of laser light in an optical integrated pickup according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram showing the relationship between the surface refractive index and the propagation direction in the gradient index optical waveguide. FIG. 5 is an explanatory diagram showing the arrangement of laser beams on the optical recording medium.
FIG. 7 is a sectional view of an essential part of an optical recording medium, FIG. 7 is a partial view showing another embodiment of a mode converter in an optical integrated pickup, and FIGS. 8 to 10 are optical integrated pickups. FIG. 11 is a top view showing another embodiment of the present invention, FIG. 11 is an explanatory view showing another example of the arrangement of the laser beam on the optical recording medium, and FIG. 12 shows a method for producing a gradient index optical waveguide. FIG. 13 is a cross-sectional view of an essential part to be described, and FIG. 13 is a block diagram showing an optical system of a conventional heterodyne pickup. In the figure, 11 is a substrate, 12 is a magnetic thin film, 13 and 14 are semiconductor lasers,
16, 17, 18 are photodetectors, 21, 56, 57 are ridged waveguides,
23, 50, 53, 68 are Y-branches, 24, 25, 49, 54, 55 are branch waveguides, 32 is a mode converter, 33 is a frequency shifter, 34a, 34
b and 34c are mode splitters, 36a, 36b and 36c are mode converters, 41a, 41b and 41c are gradient index optical waveguides, and 92 is a mode filter.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/135

Claims (6)

(57) [Claims] A plurality of light sources; a first optical waveguide for demultiplexing light from the first light source into first and second light; and a first light waveguide for demultiplexing the first light. A mode converter for rotating the polarization plane by approximately 90 °, a frequency shifter for giving a constant frequency shift to the first light whose polarization plane is rotated by approximately 90 °, and a refractive index of the optical waveguide that is not relative to the light propagation direction. A plurality of refractive index distribution type optical waveguides that change linearly, radiate light out of the optical waveguide, irradiate the optical recording medium, and guide reflected light from the optical recording medium into the optical waveguide; Means for transmitting the second light to the first graded-index optical waveguide, reflected light from the optical recording medium transmitted from the first graded-index optical waveguide, and output from the frequency shifter A multiplexing optical waveguide for multiplexing and interfering with light and an output light from the multiplexing optical waveguide are detected. An output light detector, a second optical waveguide for splitting light from the second light source into third and fourth lights, and a second refractive index distribution for converting the third light into the second refractive index distribution. Means for transmitting the fourth light to the third graded-index optical waveguide, and means for transmitting the fourth light to the third graded-index optical waveguide. An integrated optical pickup, comprising: a plurality of photodetectors for respectively detecting reflected light from a recording medium. 2. The optical integrated pickup according to claim 1, wherein the frequency shifter applies an optical waveguide having a magneto-optical effect and a magnetic field whose amplitude changes in a sawtooth shape to the optical waveguide having the magneto-optical effect. And an integrated optical pickup. 3. The integrated optical pickup according to claim 1, wherein the light whose polarization plane and substantially 90 ° polarization plane are rotated between the light source and the refractive index distribution type optical waveguide is separated. An integrated optical pickup comprising: a mode splitter for leading to the photodetector; and a mode converter having a mode conversion efficiency of about 50%. 4. The integrated optical pickup according to claim 1, wherein the mode filter attenuates the light whose polarization plane and the polarization plane of the light source are rotated by about 90 ° between the light source and the light irradiation means. An integrated optical pickup comprising: a mode converter having a mode conversion efficiency of about 50%. 5. The integrated optical pickup according to claim 1, wherein a single light source and light from said light source are split into two and transmitted to said first and second splitting optical waveguides. 1. An optical integrated pickup, comprising: 6. An integrated optical pickup according to claim 1, further comprising: a plurality of light sources; and means for transmitting light from said light sources to said first, second and third graded index optical waveguides, respectively. An integrated optical pickup, comprising: