JPH0445895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Field of the Invention>> The present invention relates to a pickup device for an optical information recording medium such as an optical disk, and particularly to one in which each element is integrally integrated.

<<Prior art and its problems>> Optical video disc systems and optical digital audio disc systems that have recently come into practical use basically consist of individual optical components as shown in Figure 1. A pick-up of the structure used is used.

A laser beam (wavelength: approximately 800 nm) emitted from a laser diode 1 travels straight through a polarizing prism splitter 2, passes through a quarter-wave plate 4, and is focused by an objective lens 3 onto the surface of a disk 5. The reflected light intensity of the laser beam changes depending on the presence or absence of pits on the disk 5, but the reflected light is condensed by the objective lens, travels through the optical system in the opposite direction, and passes through the quarter-wave plate 4. It passes through again and enters the polarizing 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 polarizing prism splitter 2, and the path of the reflected light is changed by the light receiving element 6 to the disk 5. Changes in reflected light intensity depending on the presence or absence of the upper bit are detected.

However, such conventional pickups have the following problems.

First of all, it is well known that the oscillation characteristics of a semiconductor laser can be changed by externally incident light, but in this type of pickup, changing the oscillation characteristics of the laser diode 1 means that the reproduction characteristics may deteriorate. This will result in a decrease in sound quality.
Therefore, as mentioned above, in the conventional pickup, the 1/4 wavelength plate 4 and the polarizing prism splitter 2 prevent the reflected light from the disk 5 from returning to the laser diode 1. to ensure stable operation. 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, it is difficult to make the disk 5 completely orthogonal due to the fact that the transparent substrate material (polycarbonate, acrylic, etc. is used) has a tendency to refract. The reality is that incidence is unavoidable.

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 costs rise, advanced component integration technology becomes necessary.

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

≪Object of the Invention≫ This invention 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 provides a light emitting and emitting part that generates laser light and a part that detects reflected light. It is an object of the present invention to provide a pickup device for an optical information recording medium that does not require assembly and adjustment and can be miniaturized by integrating the above on one substrate.

<<Configuration and Effects of the Invention>> In order to achieve the above object, the present invention provides a substrate having an optical waveguide formed on its surface; a light emitting section that propagates a light beam on the optical waveguide; and a light emitting section on the optical waveguide. a surface acoustic wave generator that propagates a surface acoustic wave and deflects the light beam within the plane of the optical waveguide using the surface acoustic wave; emits the light beam from the end face of the optical waveguide; an integrated lens unit that performs two-dimensional focusing and focal position adjustment; a light receiving unit in which a plurality of light receiving elements are combined that are arranged at appropriate intervals from the emission position of the light beam and receive reflected light of the light beam; By receiving the output of the light receiving section, processing the signal, and supplying the control signal to the surface acoustic wave generating section and the integrated lens section, the deflection angle of the light beam is controlled, the two-dimensional focusing of the output beam is performed, and the focal position is adjusted. It is characterized by integrally integrating a control unit that performs control and;

According to this invention, the paths of the incident light to the disk and the reflected light from the disk are completely different, and both the incident path and the reflection path can be realized with an extremely simple integrated optical system device, and the reflected light is directed to the light source side. There is no return at all, and it is possible to prevent a decrease in reliability due to a change in the oscillation characteristics of the laser diode due to return incidence, as in the conventional case.

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, which has the excellent effect of making it possible to downsize the entire device.

<<Description of Embodiment>> FIG. 2 shows a schematic configuration of a pickup according to an embodiment of the present invention. This pickup is constructed using a silicon substrate 21, and a LiNbO ₃ substrate 22 is placed on the silicon substrate 21 on the light emitting section side. A thin film optical waveguide 23 is formed on this LiNbO ₃ 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 propagates through the waveguide 23.

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 transmitted to an IDT (interdigitated ultrasonic oscillator) 26 created on a waveguide 23.
Surface acoustic waves (SAW) generated as described below from
and is incident on the wavefront of the surface acoustic wave at a Bragg angle θ ₀ . If the wavelength of the laser beam is λ, the wavelength of the surface acoustic wave is Λ ₀ , and the refractive index of the waveguide is n, then if the condition of sin θ ₀ = λ/2nΛ ₀ is satisfied, then the surface acoustic wave of an appropriate amplitude can be The laser beam is completely reflected by the wavefront,
The traveling direction of the laser beam changes by 2θ ₀ .

As shown in Figure 3, surface acoustic wave SAW
Since the area where the wavefront exists is limited by the intersecting width L of the electrodes of the IDT 26, the accompanying periodic structure of refractive index change is also limited to the same range of L. Therefore, unlike surface acoustic waves that spread infinitely, surface acoustic waves with a limited width cannot be represented by waves that propagate in only one direction, but can be represented by a superposition of countless plane waves with different propagation directions. . When the frequency applied to the IDT 26 is decreased from f ₀ to f ₁ , the period Λ ₁ of the generated surface acoustic wave becomes larger than Λ ₀ , and the laser beam 40 incident at an angle θ ₀ meets the black condition with respect to the period Λ ₁ . Not satisfied. However, as we saw earlier, surface acoustic waves with a limited width include surface acoustic waves with various propagation directions, so the Black diffraction condition sinθ ₁ = λ/2nΛ ₁ is satisfied for waves in a specific direction. As a result, the laser beam 40 is subjected to Bragg diffraction, and its traveling direction is
Changes by 2θ ₁ . Next, if the frequency of the high-frequency signal applied to the IDT 26 is set to _f2 , which is greater than _f0 , there will also be a wave in the direction that satisfies the Bragg diffraction condition _sinθ2 =λ/ _2nΛ2 , and the laser beam 40
is diffracted in a direction shifted by 2θ ₂ from the direction of travel.
In this way, the irradiation position of the laser beam can be controlled by optical deflection by Bragg diffraction. This is used to control the swinging of the heavy beam perpendicular to the track direction of the disk 5, as will be described later.

The light beam, which has been collimated by the collimating lens 25 and whose traveling direction has been appropriately changed by the surface acoustic wave, is then focused by the grating lens 27 formed on the waveguide 23. This Gouletaing lens 27 has electrodes 28, 28 provided on both sides.
By applying a voltage between them, the refractive index of the grating lens 27 is changed, thereby changing the phase constant of the guided light. With this grating lens 27, the focusing position of the light beam can be changed back and forth in the plane direction of the waveguide 23. At this time, the amount of change in the phase constant of the guided light is determined by the electrode 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 passing through the grating lens 27 is
Next, the light enters a waveguide type lens 29 for outputting the guided light, which is formed on the side end side of the waveguide 23, and this lens 2
9 , the light is emitted from the side end face of the waveguide 23 .

This lens 29 consists of a high refractive index region formed in a substantially hemispherical shape at an appropriate depth from the surface of the waveguide 23 by thermally diffusing titanium, and electrodes 30 formed on both sides,
The refractive index changes depending on the voltage applied between 30° and 30°. The electrodes 30, 30 are in the groove 3 parallel to the waveguide 23.
1 and 31 are bored, and aluminum is vapor-deposited on the opposing walls. Figure 4 a and b are electrodes 3
It shows focus control performed within a plane by a voltage applied between 0 and 30. Point B is the focal point when no voltage is applied, and by controlling the applied voltage, the lens 29
As the refractive index increases, the focal point moves to point A, and as the refractive index decreases, the focal point moves to point C. This lens 29 and the grating lens 27 enable two-dimensional fur cutting.

Therefore, the angle is changed appropriately by the surface acoustic wave SAW from the IDT 26, and the grating lens 27
The light beam focused at an appropriate position by the lens 29 is emitted from the side end face of the waveguide 23 at an appropriate angle of inclination toward a predetermined track of the disk 5. The irradiation position and focal position of this beam are controlled by the frequency applied to the IDT 26 and the electrodes 28, 28.
This is done by a combination of the voltage applied between the electrodes 30 and the voltage applied between the electrodes 30, 30.

Next, the reflected light beam from the disk 5 enters the light receiving section 32 provided on the side end surface of the same substrate 21.

The light receiving section 32 consists of photodiodes A1, A2, B1, B2, C1, and C2 divided into six as shown in FIG. To be more specific, in the radial direction of disk 5,
It is divided into two groups: A1, B1, C1 group and A2, B2, C2 group, and in the track direction of disk 5, it is divided into three groups: A1, A2 group, B1, B2 group, and C1, C2 group. has been done. Furthermore, among the six photodiodes, the two photodiodes B1 and B2 located at the center of the disk 5 in the track direction are smaller than the others. The output of the 6-divided 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 track error signal that indicates how far the center of the pit 17 and the center of the beam are shifted in the track direction.
An RF signal (data signal) that determines the beam intensity can be obtained.

The output level of each photodiode is also A1
When expressed as ~C2, the focus error signal output Vf
is given by Vf = (B1 + B2) - (A1 + A2 + C1 + C2). This output Vf is obtained from the differential amplifier DA1 shown in FIG.

The output characteristics of the focus error signal are as shown in FIG. 6, and the sizes of photodiodes B1 and B2 are smaller than the others so that the output becomes 0 at the in-focus position. When the focus of the beam is closer than the surface of the disk 5, the beam diameter expands on the light receiving section 32, so the outputs of photodiodes B1 and B2 are reduced, and the outputs of photodiodes A1, A2, C1, and C2 are increased. Therefore, the focus error signal Vf becomes negative. Conversely, if the focal point is farther away than the disk 5, the beam diameter on the light receiving section 32 decreases and the outputs of the photodiodes B1 and B2 increase, so the focus error signal Vf becomes positive.
This focus error signal Vf is obtained by the control circuit 33 shown in FIG. 2, and based on the error, the control voltages applied to the electrodes 28 and 30 are adjusted so that the beam is correctly focused on the disk 5 surface. controlled by. This is the so-called focus servo.

Also, the track error signal Vt is expressed as the following equation.

Vt=(A1+B1+C1)-(A2+B2+C2) This track error signal Vt is obtained from the differential amplifier DA2 in FIG. If the center of the beam on the light receiving section 32 is at the center of the group of photodiodes A1, B1, C1 and the group of A2, B2, C2, the signal output Vt will be 0, but if it shifts from the center to one of the groups , the output of that group increases and the output of the other group decreases. For example, if the beam center shifts upward in the direction of the group of photodiodes A1, B1, and C1, that is, in the radial direction of the disk in FIG. The error signal Vt has a positive value. If the beam center shifts in the opposite direction, the track error signal Vt becomes a negative value, and the distance of the shift can be determined from the magnitude of each signal. This track error signal Vt is also determined by the control circuit 33, and the frequency applied to the IDT 26 is controlled based on the error signal, thereby controlling the so-called track servo.

Note that the digital data signal represented by the pits of the disk 5 is detected as a change in the intensity of reflected light, and therefore the total value of the outputs of all the divided photodiodes of the light receiving section 32 is the RF signal (data signal). do.

The control circuit 33 is integrally formed on the silicon substrate 7, and includes a microcomputer, etc.
In addition to the above-mentioned focus servo, tracking servo, etc., various types of control and signal processing for correctly reading data from the disk 5 are performed.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the structure of a conventional digital disk pick-up, Fig. 2 is a perspective view of a pick-up according to an embodiment of the present invention, and Fig. 3 is one of the main parts of the pick-up according to the present invention. Diagram explaining Bragg diffraction of a light beam due to surface acoustic waves,
FIGS. 4a and 4b are a schematic plan view and a schematic side sectional view showing how a light beam is focused in a plane direction by a waveguide lens, which is also one of the main parts of the present invention, and FIG. 5 is a schematic side sectional view of the present invention. FIG. 6 is a diagram showing the configuration of the light receiving section in the pickup. FIG. 6 is a diagram showing the output characteristics of the focus error signal corresponding to the light receiving section 32. 5...Disk, 21...Silicon substrate, 22
...LiNbO ₃ substrate, 23 ... Waveguide, 24 ... Laser diode, 25 ... Collimating lens, 2
6...IDT, 27...Grating lens, 2
8... Electrode, 29... Waveguide lens, 30...
Electrode, 32... Light receiving section, 33... Control circuit.

Claims (1)

[Scope of Claims] 1. A substrate on which an optical waveguide is formed; a light emitting unit that propagates a light beam on the optical waveguide; a surface acoustic wave that propagates on the optical waveguide; a surface acoustic wave generation unit that deflects the light beam within the plane of the optical waveguide; an integrated lens that outputs the light beam from the end face on the side of the optical waveguide and performs two-dimensional focusing and focal position adjustment of the output beam; a light-receiving section which is arranged at an appropriate interval from the emission position of the light beam and is composed of a plurality of light-receiving elements that receive the reflected light of the light beam; , a control unit that controls the deflection angle of the light beam, two-dimensional focusing of the output beam, and the focal position by supplying the control signal to the surface acoustic wave generation unit and the integrated lens unit; A pick-up device for optical information recording media characterized by being integrated.