JPS59107431A - Pickup for optical digital disk - Google Patents

Abstract

PURPOSE:To prevent the variation of oscillation characteristics of a laser diode which is due to the oblique input of the laser light to a disk and at the same time to omit the assembling control to attain a compact structure of the titled pickup, by integrating an emitting part of the laser light and a detecting part of the reflected light on a substrate. CONSTITUTION:The light beams emitted from a laser diode 24 to a waveguide path 23 are turned into parallel beams by a collimator lens 25 and receives a proper angle change with the surface acoustic wave sent from a comb-shaped electrode ultrasonic wave oscillator IDT26 produced on the path 23. Then the parallel beams are made incident to a prescribed track of a disk 5 with inclination of a proper angle from the side edge face of the path 23 by exercising control in combination over the applied voltage between electrodes 28 set at both ends of a grating lens 27 and the applied voltage between electrodes 30 set at both ends of the path 23. Then the irradiating position and the focal position are controlled. The reflected light beams sent from the disk 5 are made incident to a photodetecting part 32 formed at the side edge face of the same substrate 21. Thus a focus error signal is obtained.

Description

[Detailed Description of the Invention] ・Field of the Invention) This invention relates to a pickup for an optical digital disc that is put into practical use as a video disc or a digital audio disc, and particularly relates to a pickup for an optical digital disc that is put into practical use as a video disc or a digital audio disc. It is related to IC products that are becoming more and more popular.

(Prior art and its problems) In optical video disc systems and optical digital audio disc systems, which have recently come into practical use, basically individual optical discs as shown in Figure 1 are used. A pickup made using 4VJ parts is used.

Laser light emitted from laser diode 1 (wavelength is approximately 8
00nm) goes straight through the deflection prism splitter 2 and 1/
The light passes through a four-wavelength plate 4 and is focused and irradiated onto the surface of the disk 5 by the objective lens 3.

The reflected light intensity of the laser beam changes depending on the presence or absence of pits on the disk 5, and the reflected light is focused by the objective lens 3, travels through the optical system in the opposite direction, and passes through the quarter-wave plate 4. It passes through again and stumbles onto the deflection prism splitter 2. Since the polarization plane of the reflected light at this time has been rotated by 90 degrees with respect to the light emitted from the laser diode 1, the path of the reflected light is changed by the deflection prism splitter 2, and the reflected light is transmitted to the light receiving cable 6 by the °C disk 5. I"i' 7 in the upper pit
! 11 is detected.

However, conventional pickups like this have the following problems.

First, the oscillation characteristic of a semiconductor laser is that the input signal from β1 is 0.
It is well known that the oscillation characteristics of the laser diode 1 in this type of pickup are changed by the j-light, but in this type of pickup, a change in the oscillation characteristics of the laser diode 1 causes a deterioration in the reproduction characteristics and a deterioration in the sound quality.

Therefore, in conventional pickups, as mentioned above, 1
Due to the action of the /4 wavelength plate 4 and the deflection prism printer 2,
This prevents the reflected light from the disk 5 from returning to the laser diode 1 and causing the laser diode 1 to operate stably. However, this is an ideal case in which the plane of polarization of the reflected light that has passed through the quarter-wave plate is completely orthogonal to that of the light emitted from the laser diode 1.

In reality, due to the fact that the transparent substrate material 131 of the disk 5 (polycarbonate, acrylic, etc. is used) has a tendency to refract, the completely orthogonal V is a rotation, and the laser diode The reality is that the return incidence to 1 cannot be avoided.

In order to solve this problem, for example, it is possible to make the laser beam incident obliquely, but this increases the number of optical parts and requires high-density integration of optical parts. As the loss increases from 1 to 1 due to an increase in the number of components, advanced component integration technology becomes necessary.

Furthermore, since the optical system is constructed using individual lens systems and mirrors, assembly and adjustment are troublesome, and miniaturization is difficult.

(Object of the Invention) The present invention is a light emitting device that prevents the oscillation characteristics of a laser diode from changing due to oblique incidence of laser light on a disk, and at the same time generates radar light.

An object of the present invention is to provide an optical digital disk pickup that does not require assembly and adjustment and can be miniaturized by integrating an emitting part and a part for detecting reflected light on one substrate.

(Structure and Effects of the Invention) In order to achieve the above object, the present invention includes a substrate on which an optical waveguide is formed, a light emitting part that propagates a light beam to the optical waveguide, and an elastic member on the optical waveguide. a surface acoustic wave generator that propagates a surface wave and deflects the light beam within the plane of the optical waveguide according to the surface acoustic wave;
an integrated lens section that performs two-dimensional focusing and focal position adjustment of the emitted beam; and a plurality of light receiving water droplets that are arranged at appropriate intervals from the emitted position of the light beam and that receive reflected light of the light beam. a light-receiving section that is combined with
By receiving the output of the light receiving section, processing the signal, and supplying the control signal to the surface acoustic wave generating section J3 and the grading section, the deflection angle of the light beam is controlled, and the two-dimensional focusing a3 and the focal point of the output beam are controlled. A control section that controls the position is integrally integrated, the three light beams emitted from the integrated lens section are aimed obliquely at the disk, and the diagonal reflected light from the disk is made to enter the light receiving section. Characterize what you did.

According to this invention, the paths of the incident light to the disk and the paths of the reflected light from the disk can be realized using an optical system device in which the product ratio of μ and H is completely different, and the return of the reflected light to the light source side is completely eliminated, unlike the conventional method. It is possible to prevent a decrease in reliability due to a change in the oscillation characteristics of the laser diode due to the return incidence.

In addition, since the light beam output position and the reflected light reception position are formed on the same side of the substrate, the distance between the pickup and the disk can be narrowed, resulting in an excellent effect that the entire device can be made smaller.

(Description of Embodiment) FIG. 2 shows a schematic configuration of a pickup according to an embodiment of the present invention. This pickup is silicon long plate 21
The silicon substrate 2 on the light emitting part side is configured using J3.
A LiNb0a substrate 22 is mounted on the substrate 10. A thin film optical waveguide 23 is formed on this LiNbO3 substrate 22 by thermal diffusion of titanium (Ti). The laser diode 24 is connected to the end face of the waveguide 23, and the laser beam generated from the laser diode 24 is connected to the waveguide 23.
Propagate 3.

The light beam emitted from the laser diode 24 to the waveguide 23 is first collimated by the collimating lens 25. The collimated beam is created on the waveguide 23)
It intersects with a surface acoustic wave (SAW) generated from T (comb-shaped m-pole supercombining optical pendulum) 26, which will be described later, and is incident on the wavefront of this surface acoustic wave at a Bragg angle θ0.The wavelength of the Rede light is λ1. Taking the wavelength of the surface acoustic wave as 〇 and the refractive index of the wave path, sin θ0 = λ/211 Δ.

If the following conditions are met, the laser beam will be completely reflected by the wavefront of the surface acoustic wave with an appropriate amplitude, and the traveling direction of the laser beam will change by 20 alet=).

As shown in Figure vR3, the area where the surface acoustic wave SAW wavefront exists is limited by the intersection width of the electrodes of IDT 26, so the periodic structure of the accompanying refractive index change also follows the same L. limited to a range. Therefore, unlike a surface acoustic wave that spreads infinitely, this surface acoustic wave with a limited width cannot be expressed as a wave that propagates only in the 1h direction, but can be expressed as a superposition of 11 plane waves with different propagation directions. It will be done. ID
When the frequency applied to T 2 (3 is decreased from fo to fl, the period △1 of the generated surface acoustic wave becomes larger than △0, and the laser beam 40 incident at an angle θ0 has a period Δ
Bragg for 1! 1 is not satisfied. However, as we saw earlier, surface acoustic waves with a limited width include elastic Table 1Ilj waves with various propagation directions, so for waves in a specific direction, the Black diffraction condition s i nθ1=
Since λ/21) Δ1 is satisfied, the laser beam 40 undergoes Bragg diffraction, and the traveling direction changes by 2θ1. Next I D l
' If the frequency of the frequency signal applied to is diffracted in a direction shifted by 2θ2 from the traveling direction. This J:
In this way, the irradiation position of the laser beam can be controlled by optical deflection due to Bragg diffraction.

This is used to control the beam in a direction perpendicular to the track direction of the disk 5, as will be described later.

=1 The light beam, which has been collimated by the remetering lens 25 and whose traveling direction has been appropriately changed by the surface acoustic wave, is then focused by the grading lens 27 formed in the waveguide 23. This grating lens 27 is constructed by applying a voltage between stepped electrodes 28 and 28 on both sides.
The refractive index of the grating lens 27 is changed, thereby changing the phase constant of the guided light.The grating lens 27 allows the focusing position of the light beam to be changed back and forth in the plane direction of the waveguide 23. When,
The amount of change in the phase constant of the guided light is +4i 28 .

Since the voltage is proportional to the voltage applied between 28 and 28, the focusing position of the light beam is controlled in proportion to the applied voltage.

The light beam that has passed through the grating lens 27 is then incident on a waveguide shaped lens 29 for the waveguide 04 created on the side end side of the waveguide 23, and this lens 29 allows the waveguide 2
The light is emitted from the side end surface of 3.

It consists of a high refractive index region formed in a substantially hemispherical shape at an appropriate depth from the surface of the channel 23, and the refractive index is changed by a voltage applied between electrodes 30.degree. 30 formed on both sides.

The electrode 30.30 is formed by drilling a groove 31.31 parallel to the waveguide 23 and depositing aluminum on the opposite wall thereof. FIGS. 4(a) and 4(b) do not show the focus control performed in a plane by the voltage applied between the electrodes 30, 30. Point B is the focal point when no voltage is applied, and when the applied voltage is controlled and the refractive index of the lens 29 increases, the focal point moves to point A, and when the refractive index Iζ decreases, the focal point moves to point C. Move. Two-dimensional focus A-cashing is possible with this lens 29 and the grating lens 27.

Therefore, the light beam whose angle is appropriately changed by the surface acoustic wave SAW from the IDT 26 and focused at an appropriate position by the grating lens 27 is transferred to the waveguide 2 by the lens 29.
The disc 5 is ejected from the side end surface of the disc 5 by changing the angle appropriately and facing a predetermined track of the disc 5. Control of the beam irradiation position and focal position is determined by the combination of the frequency applied to the IDT 26, the voltage applied between the electrodes 28, and the voltage applied between the electrodes 30 and 30.

Next, the reflected light beam from the disk 5 is lrJ −g%
The light receiving section 32 provided on the side end surface of the plate 21 is covered.

The light receiving section 32 includes a photodiode A1. △2,81. B2. It consists of C1°C2. To be more specific, in the radial direction of the disk 5, there is Δ1,131.
．． Group c1 and A2. It is divided into two groups of B2°C2, and in the track direction of the disk 5 there are A1. A
It is divided into three groups: a set of phase 2, a set of phases Bl and +32, and a set of CI and C2. Furthermore, among the six small photodiodes A--the two photodiodes B1 and 82 located at the center of the disk 5 in the track direction are smaller than the others.

The output of this 6-segment photodiode produces a focus error signal that indicates the shift in focus of the light beam with respect to the disk 5 surface, and a rack error signal (1) that indicates the deviation of the beam center from the center of pitches 1 to 17 in the track direction. and,
An RF multiplied signal (data signal) is obtained that determines the intensity of the beam.

If the output level of each photodiode is also expressed as A1-C2, then the output V of the focus error signal is given by Vf = (B1+82>-(AI+A2-1-CI+G2)).This output Vf is expressed as shown in FIG. Differential amplifier DA
Obtained from I.

The output characteristics of the focus error signal are as shown in Figure 6.
The sizes of photodiodes B1 and B2 are smaller than the others so that the output becomes O at the focused position. When the focus of the beam is closer to the disk 5 surface, the beam diameter expands above the light receiving section 32. e1 Photodiode B
The output of diode A1. A2
．． C.I.

The output of C2 increases. Therefore, fornonos error ia 1
No. V[ becomes negative. Conversely, if the focal point becomes farther than the disk 5, the beam diameter J3I) on the light receiving section 32 decreases, and the diameter of the beam J3I) on the light receiving section 32 decreases. Since the output of B2 increases, the focus error signal V[ becomes positive. this)A
- A scrap error signal V" is determined by the control circuit 33 according to FIG. This is the so-called focus servo.

Further, the 1 to rack error signal Vt is expressed as in the following equation.

Vt = (AI +81 10 CI >-(A2 +
82 10G 2 ) This tracking error signal vt is applied to the differential amplifier DA2 in FIG.
obtained from. The center of the beam B3 on the light receiving section 32 is the photodiode A1.81. CI group and A'2
．． B2. If it is in the center of the croup of C2, the signal output v
t becomes 0, but if the center shifts to either group, the output of that group will increase, and the output of the other group will decrease.

For example, the beam center is photodiode A1. B1゜C1
If it shifts upward in the direction of the group, that is, in the radial direction of the disk in Fig. 5, the output of this group increases and becomes "2".
Since the output of the group is decreasing, the tracking error signal Vt
becomes a zu with a plus.

If the beam center shifts in the opposite direction, the tracking error signal becomes a negative value, and the distance of the shift can be determined from the magnitude of each signal. This h-rack error signal Vt is also obtained by the control circuit 33, and based on the error signal, the ID
The frequency applied to T26 is controlled, thereby controlling so-called track revolution.

Note that the digital data signal represented by the bits of the disk 5 is detected as a change in the intensity of the reflected light, and therefore the total ai value of the output of the divided small diodes A to the light receiving section 32 is Let R, F (U number (data signal)).

The control circuit 33 is integrated on the silicon substrate 7 and includes a microcomputer, etc., as described above.
771 - Performs various controls and signal processing for correctly reading data from the disk 5, in addition to cass servo, tracking → no-vo, etc.

[Brief explanation of the drawing]

Figure 1 shows the four parts of a conventional digital disc pickup amplifier.
FIG. 2 is a schematic view of a pickup according to an embodiment of the present invention, and FIG. 3 is a diagram showing Bragg diffraction of a light beam due to surface acoustic waves, which is also one of the main parts of the pickup of the present invention. The explanatory diagrams, FIGS. 4(a) and 4(b), are schematic plan views showing how a light beam is condensed in a plane direction by a waveguide lens, which is also one of the main parts of the present invention. 5 is a schematic side sectional view, FIG. 5 is a diagram showing the configuration of the light receiving section in the pickup of the present invention, and FIG. 6 is a dimensional diagram showing the output characteristics of the focus error signal corresponding to the light receiving section 32. 5... Disk 21... Silicon substrate 22... Li Nil 03 substrate 23... Waveguide 24... Laser diode 25... Lens to collimator 1 26... IDT 27...・Grating lens 28... Electrode 29... Waveguide lens 30... Electrode 32... Light receiving section 33... Control circuit Patent applicant Kazu Tateishi Co., Ltd. Patent attorney 1) 5 (zlFigure 1Figure 2Figure 3Figure 4

Claims (1)

[Claims] (1) A substrate on which an optical waveguide is formed; a light emitting unit that propagates a light beam to the optical waveguide; and a light emitting unit that propagates a surface acoustic wave on the leading waveguide, and uses the surface acoustic wave to transmit the light beam to the optical waveguide. A surface acoustic wave generator for deflecting within the plane of the optical waveguide; and an integrated unit for emitting the optical beam from the end face on the side of the optical waveguide, and adjusting the two-dimensional force adjustment and focal position of the output beam. a light-receiving part, which is arranged at an appropriate distance 1+x from the emission position of the light beam, and is combined with m number of light-receiving elements that receive the reflected light of the light beam; By receiving and processing signals, and supplying the control signals to the surface acoustic wave generator and the grating ink unit, the deflection angle of the light beam and the two-dimensional focusing and focal position of the emitted beam are controlled. An optical digital disc pickup characterized by integrally integrating a control section and a controller.