JPS63183636A - Thin film optical waveguide type optical head - Google Patents

Abstract

PURPOSE:To make an optical head miniature and light-weight by providing an optical system, etc. on a plane waveguide for generating a refractive index compression by a surface acoustic wave. CONSTITUTION:A laser light from a semiconductor laser 13 passes through a collimating lens 14 formed in a recessed part of an optical waveguide 2 of a lithium niobate substrate 11, a groove-like beam splitter 3, a surface acoustic wave device 18, and an objective lens 15 provided with a 45 deg. inclined surface for executing a complete reflection, and irradiates an optical disk 6. A reflected light thereby passes through a counter-optical sensor lens 17 in the same way and made incident on an optical sensor 10 and detected. On the other hand, a refractive index distribution of the waveguide 12 by an electro-acoustic transducer 18a and an ultrasonic reflecting body 18b of the device 18 functions as a diffraction grating the laser light is separated into a '0'-order diffracted light and a primary diffracted light of a desired frequency, and by using the primary diffracted light, a tracking control is executed. By this constitution in which an optical system, etc. are formed as one body with an optical waveguide, it becomes unnecessary to adjust focusing, etc. of every part, and an optical head can be made light in weight and miniature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head for recording, reproducing, and erasing used in an optical disk memory system, and particularly relates to an optical head using a thin film optical waveguide.

[Conventional technology]

As the information society progresses, the amount of information handled in society is steadily increasing. For this reason, there is an increasing demand for increasing the storage capacity of information recording devices that store this information. Systems that use magnetic or optical methods to record or reproduce various types of information have been put into practical use. Among these, optical disk systems that use optical disks as memory media are different from conventional magnetic methods. It has the excellent feature of being able to record at a density 100 times higher than that of systems using media, and also being able to obtain high-quality playback signals without contact. Memory systems using such optical recording media include video discs and digital audio discs.

FIG. 13 shows the basic configuration of the optical head used in these systems. In the figure, a laser beam emitted from a semiconductor laser 1 is converted into a parallel beam by a collimating lens 2, passes straight through a beam splitter 3, and is further converted into a parallel beam by a collimating lens 2.
/4 wavelength plate 4. A light spot 7 is formed by focusing on an optical disk 6 through an objective lens 5. This light spot 7 is reflected from the optical disk 6 and returns to the objective lens 5.1/4.
After passing through the wave plate 4 and being reflected in the right angle direction by the beam splitter 3, which is a half mirror, the cylindrical lens 8
, 9 and is imaged on the optical sensor 10. The sensor 10 then detects the focus and tracking information of the objective lens 5 and the presence or absence of a recording signal on the disk.

In such an optical system, it is necessary to adjust the position of each optical component so that the spot light is focused on the optical disk 6 and the optical sensor 10, so there is a problem that the adjustment takes a lot of time.

Additionally, this optical head has a problem in that there is a limit to the overall size reduction.

Since miniaturization of the optical head greatly contributes to miniaturization and higher reliability of the entire optical disk system 11, research and development thereof is currently being widely promoted. One of the proposals for reducing the size and weight of an optical head is disclosed in Japanese Patent Application Laid-Open No. 60-202553. This proposal is the 14th
As shown in the figure, a waveguide 12 is formed by diffusing titanium to a thickness of several microns on a substrate 1 made of lithium niobate (LiNbOs). A light spot 16 is formed by inputting the light from the semiconductor laser 13 and focusing the light spot 16 on the end face of the waveguide 12 on the other side using gradient index lenses 35 and 36.

This type of technology is summarized in the following document. Chee Suhara et al., ``Ingrated Optics Components and Devices
of Quantum Electronics, No. 845-867
Page, 1986 ('I', S U l! A R
^etaR,σIntegrated Optic
sComponents and Devices
Using Periodic Structure
es” IEEE J, of Quantun+E
electronics.

pp845 867.1986) - [Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into consideration optical spot actuating technology, that is, autofocus and autotracking, and in order to realize these functions,
Place the entire optical head on a coil actuator, etc.
I had no choice but to use a method of moving it forward, backward, left and right. For this reason, there was a problem that the structure was complicated and the reliability for autofocus and autotracking was low.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical head using a thin film optical waveguide that is small and lightweight and capable of reliably focusing and auto-tracking a light spot.

[Means for solving problems]

In order to achieve the above object, the present invention provides a collimating lens formed on a planar optical waveguide.

It consists of an optical system consisting of a beam splitter and an objective lens, and a laser light source that inputs laser light into this optical system,
In a thin-film optical waveguide type optical head that records, reexamines, and erases information by irradiating and focusing the laser beam onto an optical recording medium via the optical system, an external light source is provided near the objective lens. It is equipped with a lens whose focal length is variable depending on the signal.

[Effect]

According to the above configuration, the refractive index of the lens mounted near the objective lens is changed by an external signal, and the focal position of the optical system is changed by changing the magnitude of the refractive index in the optical waveguide. Furthermore, since the refractive index distribution can be changed, focusing and 1-racking of the optical beam 11 can be performed without involving mechanical operations.

〔Example〕

Embodiments of the optical head according to the present invention will be described below with reference to the drawings. However, the present invention is not limited to these examples.

FIG. 1 shows an embodiment of the present invention. In these figures, parts that are the same as or equivalent to those of the conventional example shown in FIGS. 13 and 14 are denoted by the same reference numerals.

In FIG. 1, an optical waveguide 12 is formed by diffusing titanium to a thickness of several microns on a substrate 11 made of lithium niobate or the like.

Note that there are various types of optical waveguides in addition to these, and the materials used for them can be broadly divided into inorganic and organic types. A typical example of an inorganic type is lithium niobate (LiN
bOa), glass, etc.

Waveguides are created by doping these materials with ions (Table 1).

There are various organic types, each of which is created by spin code, sputtering, etc. on glass, 5iOz, etc. (Table 2
).

On the other hand, collimating lens 14. The objective lens 15 and the light sensor lens 17 are typically a geodesic lens provided in four circular parts on the optical waveguide 12, a gradient index lens that has a distribution of refractive index by implanting an ion beam, etc. Mode index lenses, Fresnel lenses that utilize diffraction phenomena, grating lenses, etc. can be used. In this example.

A geodesic lens with a focal length of 665 mm is formed by a depression with a diameter of 7.6 mm and a depth of approximately 0.2 mm.

For geodesic lenses, see below, for example. Nis, Soteini et al., ``Geodesic Optics 2221 Components'' (S, 5ottinia)
Q, “Geodesic optics:
new components,”)J, Opt,
Soc, Am, pp. 1230-12'34, l! 18
0 years.

Next, the beam splitter 3 is placed shallowly on the waveguide surface)
(ridge), and the light from the waveguide is partially reflected and partially transmitted. The ratio can be changed depending on the height of the ridge.

Regarding the beam splitter 3, see below, for example. ″
Thin Film Beam Splitter and Reflector Four Optical Guided Waves Applied Physics Letters (Thin-f)
ilm beam 5plitter andrefl
director for optical guided
waves,” Applied Physics Le
), pp. 588-590, 1975.

V, T, Tsang, et a Q.

On the other hand, a semiconductor laser (GaAs) 13 and an optical sensor (semiconductor sensor) 10 are provided on two orthogonal end surfaces of the optical waveguide 12. Furthermore, the end face of the optical waveguide 12 on the side where the objective lens 15 is provided is a slope forming an angle of about 45 degrees with respect to the surface, and the beam light from the objective lens 15 is completely reflected here. (Same principle as a prism) As shown in FIG. 1, it faces toward the optical disk 6.

Beam splitter 3 and objective lens 15 on optical waveguide 12
A surface acoustic wave device 18, which is a feature of this embodiment, is formed between the two ends, with an electroacoustic transducer (<square-shaped electrode) 18a on one end face and an ultrasonic reflector on the other end. Alternatively, the reflective electrode 18b is embedded and bonded.

In this embodiment, since the optical waveguide 12 is made of lithium niobate (L i N b O3) which has a piezoelectric effect, the electroacoustic transducer 18a only needs to be a comb-shaped electrode. However, if the optical waveguide 12 itself does not have a piezoelectric effect, for example, it is made of glass, As25a, etc., electric sound! ! ! The lI+- transducer 18a is a combination of a comb-shaped electrode and a thin film of ZnO, etc., which itself has a piezoelectric effect.

Further, in this embodiment, the ultrasonic reflector 18b is 1
Although a conventional reflector is used, one similar to electroacoustic transducer 18a can be used. However, in that case, it is necessary to appropriately adjust the phase of the voltages applied to both transducers.

Next, the operation and effect of this embodiment will be explained. The light emitted from the semiconductor laser 13 becomes parallel light by the collimating lens 14, passes through the beam splitter 3, the focal position and beam position are controlled by the surface acoustic wave device 18 and the objective lens 15, and is reflected by the inclined end face of the optical waveguide 12. As a result, a light spot 16 is formed on the optical disk 6. moreover,
The light reflected from the optical disc 6 passes through the objective lens 15 again.
, through the surface acoustic wave device 18, and the beam splitter 3.
The light is reflected in a substantially perpendicular direction, passes through a lens 17, and forms an image on the optical sensor 10. This optical sensor 10 detects the focus state and tracking state of the light spot 6 and the presence or absence of information.

Next, referring to FIGS. 2 to 5, description will be given of how the single surface acoustic wave device 18 can adjust the position of the optical spot 6, that is, how to perform tracking and adjust the focal length FA.

First, with reference to FIG. 2, points that can be adjusted for tracking will be explained. A signal (frequency Fl) is applied from a signal source, for example, an ultrasonic voltage source 19-1, to a surface acoustic wave device 18 provided with an ultrasonic transducer 18c of an electric 'fI acoustic transducer and an ultrasonic reflector 18d at both ends. Then, an ultrasonic standing wave is generated within the surface acoustic wave device 18. At this time, the refractive index distribution in the crystal becomes as shown in FIG. 3 when viewed as a cross section taken along the line ■--■ in FIG. 2, and this series of refractive index distributions acts in the same way as a diffraction grating. When a laser beam 20 is incident on this crystal, the laser beam 20 is separated into a 0th-order diffracted beam 21 that travels straight and a 1st-order diffracted beam 22 that is refracted. At this time, since the refraction angle of the primary light 22 can be changed by changing the frequency of the signal applied to the crystal, tracking adjustment of the optical spot 16 is possible using this primary light 22.

Note that the refraction angle actually used is less than the bottom.

Furthermore, the intensity of the primary light 22 can be changed by changing the amplitude of one surface acoustic wave. These operations are reliable and quick to respond because there are no mechanical movements.

Next, referring to FIGS. 4 and 5, the points in which the focal length can be adjusted will be explained. In this case, one surface acoustic wave device 18 is applied with an ultrasonic wave having a frequency F2 such that its half cycle is exactly the same as the total length of two surface acoustic wave devices 18.

Then, in the surface acoustic wave device 18, a standing wave with a waveform corresponding to a half period of the sine curve as shown in FIGS. 4 and 5 is generated, and therefore, its refractive index distribution also corresponds to the waveform of this standing wave. Become something. Therefore, a surface acoustic wave device having such a refractive index distribution acts like a convex lens on the light beam passing through it, and the amplitude of the applied voltage is
When the lens is small as shown in the figure, it acts as a lens with a long focal length, and when it is large as shown in Figure 5, it acts as a lens with a short focal length. In this way, by using the apparatus described above, the focal length can be adjusted without any mechanical operation by changing the amplitude of the applied ultrasonic voltage.

Therefore, as shown in FIG. 6, a surface acoustic wave device 18-1 (see FIGS. 2 and 3) whose refraction angle of the light beam passing through it can be changed depending on the frequency F1, and a surface acoustic wave device 18-1 (see FIGS. By providing a surface acoustic wave device 18-2 (see Figures 4 and 5) that can change the focal length of the light beam, tracking and focus adjustment of the light spot can be performed without requiring any mechanical operation. . In addition.

Since the first-order diffracted light is used for tracking adjustment, 1
The incident angle and exit angle of the light beam with respect to the surface acoustic wave device actually vary to some extent.

In addition, the sound velocity in lithium niobate L i N b 03 is 6.57 x l O"M/S1?Alkara, Fl is an ultrasonic wave of about several 100 MHz, and F2 is a surface acoustic wave device 18 When considering that the total length of is lommR degrees, ultrasonic waves of about 300 to 400H7 are used.

Next, FIG. 7 shows the operation of the embodiment of FIG. 6.

First, the ultrasonic transducer 1 of the surface acoustic wave device 18-1
A signal (frequency Fs) from a signal source 19-1 is applied between 8c and the ultrasonic reflector 18d to form the surface acoustic wave device 1.
8-1, a lattice-like standing wave, and hence a lattice-like refractive index distribution, as shown in the figure is generated. Now the frequency F1
By changing the angle, the refraction angle of the first-order diffracted light of the light beam 20 can be changed, and the tracking adjustment R of the light spot 16 can be adjusted.

On the other hand, to the other surface acoustic wave device 18-2, a signal (frequency Fz) from the ultrasonic wave @19-2 is applied between the ultrasonic transducer 18e and the ultrasonic reflector 18f, and the surface acoustic wave device 18-2 In the elastic wave device 18-2, a standing wave having a half period of the frequency F2 as shown in the figure is not generated, but a refractive index distribution having the same waveform as the standing wave on the right is generated. By changing the amplitude of the ultrasonic wave g19-2, the refractive index of the lens for the light beam 20 can be changed, and the focus of the light spot 16 can be adjusted.

Note that the lattice-like refractive index distribution generated in the surface acoustic wave device 18-1 may be a traveling wave of the same ultrasonic wave as well as a standing wave. In this case, the ultrasonic reflector 18b becomes an ultrasonic absorber.

A surface acoustic wave device performs tracking and a surface acoustic wave device performs focus adjustment.

It is not necessarily necessary to provide them separately as shown in FIGS. 6 and 7, and one can be used for both purposes as shown in FIG. A general view of this is shown previously in FIG. 1 as an example. In this case, the waveform of the standing wave generated within the surface acoustic wave device 18 has one frequency F2 as shown in FIG.
A lattice-shaped wave of frequency F2 is superimposed on a half-period wave of .

Note that since the standing wave changes from moment to moment, the ultrasonic wave F2 for focus adjustment is applied only during the period when a predetermined focus state is achieved, as shown in FIGS. 9(a) and 9(b). You can use it even more effectively if you use it. In other words, due to the synchronization circuit, as shown in FIG. 9(b), tl
, L2..., the semiconductor laser is driven only during the periods. In addition, as a focus adjustment signal, Fig. 9 (
As shown in c), a rectangular wave or a trapezoidal wave may be used, and the semiconductor laser may be driven by a flat portion of the waveform.

FIG. 10 shows an optical system for focus detection by the optical sensor 1o. When using the optical waveguide 12,
It is difficult to arrange a three-dimensional optical system, and an astigmatic focus detection method often used in optical disk systems cannot be configured. The optical system shown in FIG. 10 employs this detection method in a planar arrangement. The parallel laser beam 20 passes through the objective lens 15 and forms a light spot 16 on the optical disk 6 . Further, the reflected light from the optical disk 6 passes through the objective lens 15 again, is reflected in the right angle direction by the beam splitter 3a, and is split in half by the beam splitter 3b, one of which travels straight and the other reflected in the right angle direction. The divided lights pass through lenses 17a and 17b having the same focal length, respectively, and are imaged onto optical sensors 10a and 10b.

At this time, the respective optical sensors 10a and 10b are set at the respective focal positions 26a of the lenses 17a and 17b.

26b, one is placed at the front position d1 and the other is placed at the rear position ds, and each optical sensor IOa.

The focus position can be detected from changes in the amount of light applied to the job.

FIG. 11 shows a signal processing circuit for the optical sensors 10a and 10b. No. 48 from the optical sensors 10a and 10b is amplified by amplifiers 27a and 27b, respectively, and then subtracted by an operational amplifier 28 to obtain a differential signal f+-f-. FIG. 12 shows the voltage of each signal and the optical sensor 10a.
, 10. This is a graph showing the relationship between the position and the position of b. As can be seen from this figure, one in-focus position can be found by setting the differential signal f+-f- to 0 volts.

〔Effect of the invention〕

As described above, according to the present invention, an optical head using a thin film optical waveguide is equipped with a lens whose focal length can be changed by an external signal, so that focusing and tracking of laser light can be performed without involving mechanical operation. The actuator can be configured, and the optical head can be made small, lightweight, and reliable.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the optical head according to the present invention, FIG. 2 is a plan view showing the surface acoustic wave device shown in FIG. 1, and FIG. , FIG. 4 and FIG. 5 are plan views showing the operation of this embodiment, FIG. 6 is a schematic plan view showing another embodiment of the present invention, and FIG. 7 is an explanatory diagram showing the operation of FIG. 6. FIG. 8 is an explanatory diagram showing the effect of FIG. 1,
9(a) is a perspective view showing another embodiment of the present invention, FIGS. 9(b) and 9(Q) are explanatory views showing the effect of FIG. 9(a), and FIG. 11 is a circuit diagram showing the focus error detection means, FIG. 12 is a graph showing changes in signal voltage, and FIG. 13 is a configuration diagram showing a conventional optical head. 1st
FIG. 4 is a perspective view showing a conventional waveguide type optical head. 3... Beam splitter, 6... Optical disk, 10
... Optical sensor, 12 ... Optical waveguide, 13 ... Semiconductor laser, 14 ... Collimator lens, 15 ... Objective lens, 18 ... Surface acoustic wave device, 18a ...
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Claims (1)

[Scope of Claims] 1. In an optical head that records, reproduces, and erases information by irradiating and focusing a laser beam onto an optical recording medium, a planar head made of a material that produces a density of refractive index due to surface acoustic waves. It consists of an optical waveguide with a collimating lens on the waveguide,
An optical system consisting of a beam splitter, an electroacoustic transducer that generates a refractive index distribution on a waveguide using surface acoustic waves, and an objective lens, and a beam splitter that guides the light reflected from the optical recording medium, a sensor lens, and an optical sensor. A thin film optical waveguide type optical head characterized by having an optical system. 2. The thin-film optical waveguide type optical head according to claim 1, wherein a semiconductor laser is used as the laser light source, and is bonded to or embedded in one end surface of the waveguide. 3. The thin film optical waveguide type optical head according to claim 1, wherein the electroacoustic transducer is driven by the output of the optical sensor. 4. In claim 1, the optical waveguide generating the refractive index distribution is made of a material having a piezoelectric effect,
A thin film optical waveguide type optical head, wherein the electroacoustic transducer is a comb-shaped electrode. 5. The thin-film optical waveguide type optical head according to claim 1, wherein the electroacoustic transducer is made of a material that vibrates by itself. 6. In claim 1, a circuit is provided for synchronizing the surface acoustic waves of the electroacoustic transducer and the light emitted by the laser light source, and the circuit is configured to synchronize the refractive index of the waveguide with a predetermined density. A thin film optical waveguide type optical head characterized in that a laser light source functions to emit light only when the laser light source is activated. 7. An optical head that records, reproduces, and erases information by irradiating and focusing a laser beam onto an optical recording medium, which is composed of a planar optical waveguide made of a material that produces a density of refractive index by surface acoustic waves. , a collimating lens on the waveguide,
The optical system includes an electroacoustic transducer that generates a refractive index distribution on the waveguide using surface acoustic waves, and an objective lens. The resulting waveguide is cut to produce a half-period surface acoustic wave, and the resulting unevenness of the refractive index on the waveguide gives a lens effect to the light beam passing through it, and by changing the amplitude of the surface acoustic wave, the above lens effect is achieved. 1. A thin-film optical waveguide type optical head characterized in that the focal position provided by the optical head is variable. 8. In claim 7, a circuit is provided for synchronizing the surface acoustic wave of the electroacoustic transducer and the light emitted by the laser light source, and the circuit is arranged such that the refractive index of the waveguide has a predetermined density. A thin film optical waveguide type optical head characterized in that it functions so as to emit laser light only when . 9. In claim 7, the optical waveguide generating the refractive index distribution is made of a material having a piezoelectric effect,
A thin film optical waveguide type optical head characterized in that an electroacoustic transducer is a comb-shaped electrode. 10. The thin-film optical waveguide type optical head according to claim 7, wherein the electroacoustic transducer is made of a material that vibrates by itself. 11. In an optical head that records, reproduces, and erases information by irradiating and focusing a laser beam onto an optical recording medium, the optical head is composed of a planar optical waveguide made of a material that produces a density of refractive index by surface acoustic waves. , has an optical system consisting of a collimating lens on the waveguide, two electroacoustic transducers that generate a refractive index distribution on the waveguide by surface acoustic waves, and an objective lens, and one of the electroacoustic transducers The signal causes a half-period surface acoustic wave to cross the light beam passing through the waveguide, and the resulting density and density of the refractive index on the waveguide lens the light beam passing through it, causing the above-mentioned By varying the amplitude of the surface acoustic wave, the focal position provided by the lens action is variable, and another drive of the electroacoustic transducer causes a surface acoustic wave across the light beam; As a result, the periodic density and density of the refractive index of the waveguide imparts a diffraction effect to the light beam passing therethrough, and by changing the frequency of the surface acoustic wave based on the other electroacoustic transducer, the optical A thin-film optical waveguide type optical head characterized by making the traveling direction of the beam variable. 12. The thin-film optical waveguide type optical head according to claim 11, wherein the lattice-like spacing and density of the refractive index is caused by a standing wave of a surface acoustic wave. 13. The thin-film optical waveguide type optical head according to claim 11, wherein the lattice-like spacing and density of the refractive index is caused by traveling waves of surface acoustic waves. 14. In claim 11, there is provided a circuit that synchronizes the driving of the electroacoustic transducer by ultrasonic elastic waves and the light emitted from the laser light source, and the circuit synchronizes the refractive index of the waveguide. A thin film optical waveguide type optical head characterized in that it functions to emit laser light only when the density is a predetermined value. 15. A thin film optical waveguide type according to claim 11, wherein the optical waveguide that produces a refractive index distribution is made of a material having a piezoelectric effect, and the electroacoustic transducer is a comb-shaped electrode. light head. 16. The thin film optical waveguide type optical head according to claim 11, wherein the electroacoustic transducer is made of a material that vibrates by itself. 17. An optical head that records, reproduces, and erases information by irradiating and focusing a laser beam onto an optical recording medium, which is composed of a planar optical waveguide made of a material that produces a density of refractive index by surface acoustic waves. , an optical system including a collimating lens on the waveguide, an electroacoustic transducer that generates a refractive index distribution on the waveguide by surface acoustic waves, and an objective lens, and the electroacoustic transducer is configured to generate the refractive index distribution on the waveguide by an external signal. A first half-period surface acoustic wave is generated across the light beam passing through the waveguide, and the resulting density of the refractive index on the waveguide imparts a lensing effect to the light beam passing therethrough, the focal position provided by the lens action is variable by varying the amplitude of the elastic wave; and further generating a second surface acoustic wave across the light beam by the electroacoustic transducer;
As a result, the periodic density and density of the refractive index of the waveguide gives a diffraction effect to the light beam passing therethrough, and the second
A thin film optical waveguide type optical head characterized in that the traveling direction of a light beam can be varied by changing the frequency of a surface acoustic wave. 18. A thin film optical waveguide type according to claim 17, wherein the optical waveguide that produces a refractive index distribution is made of a material having a piezoelectric effect, and the electroacoustic transducer is a comb-shaped electrode. light head. 19. The thin-film optical waveguide type optical head according to claim 17, wherein the electroacoustic transducer is made of a material that vibrates by itself. 20. In claim 17, a circuit is provided for synchronizing the surface acoustic wave of the electroacoustic transducer and the light emitted by the laser light source, and the circuit is configured to synchronize the refractive index of the waveguide with a predetermined density. A thin-film optical waveguide type optical head characterized in that a laser light source functions to emit light only in the case of.