JPH035566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film waveguide type head that utilizes a thin film waveguide and is used as a recording or reproducing head for a recording medium.

Conventionally, there are bright spot scanning devices that use laser beams, and they use polygon rotation boundaries to deflect the laser beam and f-θ to condense the deflected light flux and convert it into linear bright spot motion. It consists of lenses, etc. However, in these conventional devices, the assembly and precise adjustment of the device is very complicated because each operating part requires a certain distance between the optical paths and each other, and the assembled device becomes large. It had drawbacks.

On the other hand, the present applicant has filed an application for a new bright spot scanning device that solves the above-mentioned drawbacks as Japanese Patent Application No. 12939/1983, and the contents of the application are as follows: Thin film lenses and A/O deflectors are attached to the thin film waveguide formed on the substrate.
A bright spot scanning element is created by integrally forming an E/O modulator, etc., and a compact device that does not require assembly and adjustment is obtained, replacing the conventional large bright spot scanning device that requires precise adjustment. It is. Optical elements using such thin film waveguides have characteristics that have not been seen in the past, and in particular, the above-mentioned bright spot scanning element is compact and capable of high-speed scanning.

Therefore, optical elements using thin film waveguides are expected to have a variety of applications, and one example of such applications is application to heads for photothermal magnetic recording or reproduction of video signals and the like.

However, an element that forms a bright spot on the end face of a thin film waveguide is used as a head, and the end face is brought into contact with or close to the recording medium and moved relatively, and the intensity of the bright spot is modulated with the recording signal to generate the signal. When recording or, on the other hand, reproducing, the following inconveniences occur.

That is, in order to obtain high output efficiency, the output end faces of the waveguides of these heads are optically polished with sharp cuts, and the edges are extremely sharp.
When the end face of the same shape is brought into contact with a recording medium in the form of a tape or the like and moved relative to the recording medium for scanning, there is a risk that the sharp edges of the end face may damage the surface of the recording medium. On the other hand, when scanning a disc-shaped recording medium such as a floppy disk with the head slightly floating, there is no risk of damage to the recording body while the head is floating, but damage may occur when it descends before and after that. Furthermore, the shape of the waveguide end face as described above can be said to be a shape that hinders the floating of the head when air resistance is taken into account.

An object of the present invention is to solve the above-mentioned drawbacks and to provide a recording or reproducing head having a shape that does not damage the recording medium and can alleviate the air resistance that prevents the head from flying when used as a flying head. The objective is to provide a new head that utilizes a thin film waveguide.

Embodiments of the present invention will be described below with reference to the drawings.

First, a bright spot scanning element using a thin waveguide will be explained using FIGS. 1 and 2.

In this bright spot scanning element, a semiconductor laser 2 is bonded to a waveguide 2 formed on a substrate 1, and a toothed electrode 7 and thin film lenses 5, 6 are provided on the surface of the waveguide. A collimated laser beam 4 is now guided into the waveguide 2. The light beam 4 transmitted through the waveguide becomes a parallel light beam 5 by a thin film lens 5, and is generated by an ultrasonic surface acoustic wave 8 excited by a comb tooth-shaped electrode 7 provided in a part of the waveguide 2. It causes a diffraction effect and is deflected. Furthermore, this deflected light beam 15 passes through a thin film lens 9.
The light is focused to form a bright spot 11 on the end face 10 of the thin film waveguide. That is, the end surface 10 is formed at a position that substantially coincides with the focal plane of the thin film lens 9 having power in the x-y plane (shown in the figure), and the condensed light beam is focused at or near the end surface 10 in the x direction. , eject. Further, the z direction perpendicular to the xy plane is limited by the thickness d (usually several μm) of the waveguide.
In such a configuration, the bright spot scanning element of this embodiment changes the frequency of the high-frequency voltage applied to the comb tooth-shaped electrode 7 to change the wavelength of the ultrasonic surface acoustic wave on the waveguide, thereby deflecting the ultrasonic surface acoustic wave. The angle is controlled to scan the bright spot on the exit end face.

In this way, the bright spot scanning element shown in the first diagram is very compact because it has an optical deflector and a condenser lens on the same substrate, and scans by forming a bright spot at or near the exit end face of the waveguide. It also has the advantage of not requiring precise adjustment.

To explain each component of the bright spot scanning element in more detail, the substrate 1 is suitably made of a material that has a piezoelectric effect and allows high-frequency ultrasonic waves to propagate efficiently, such as LiNbO 3 , LiNbO ₃ ,
LiTaO ₃ , ZnO, etc. are preferable. Moreover, the waveguide 2 is
In the case of LiNbO ₃ substrate, Ti is heated at high temperature (approximately 1000℃).
It is formed in-diffuse on the substrate to a thickness of several micrometers. In addition, in the case of LiTaO ₃ substrate, Nb or Ti is injected.
- Obtained by diffusing. It is desirable that the waveguide be formed of a material that has a high refractive index and a large refractive index difference with the substrate, allowing light to propagate even if the waveguide is made thin.
Furthermore, since the refractive index of the waveguide is high, the bright spot formed by the condenser lens on the end face can have a very small diameter, that is, a sharp spot.

The deflector is preferably one that utilizes ultrasonic surface acoustic waves, and as shown in FIG. Excite ultrasound. The pitch a of the SAW electrode is set to 1/2 of the center wavelength of the ultrasonic wave to be excited. For example, if _three LiNbO units are distributed, the electrode pitch a=
If set to 16.5 μm, ultrasonic waves with a wavelength of 33 μm can be excited when a 200 MHz high frequency voltage is applied.
(The speed of ultrasonic waves is approximately 6.6 x 10 ⁶ mm/sec.) The band of the deflector obtained with this one electrode is determined by the angular selection width of the Bragg-type diffraction grating created by the excited ultrasonic waves and the piezoelectric It is limited by the band of the transducer itself, which consists of material and electrodes.

As shown in FIG. 2, the SAW electrode 7 has a parallel light beam 6
When a high frequency voltage of frequency f is applied to the SAW electrode 7, an ultrasonic surface acoustic wave 8 is excited, thereby forming a diffraction grating structure. As a result, the parallel light beam 6 undergoes black diffraction and becomes a diffracted light beam 15 and a zero-order diffracted light beam 16. At this time, the diffraction angle 2θ between the diffracted light beam 15 and the zero-order diffraction light beam 16 is given by the following equation.

2θ=2sin ^-1 (λf/2vn) (1) Here, v is the speed of the ultrasonic wave in the medium, and f is
The frequency applied to the SAW electrode 7, λ, is the wavelength of the incident light beam in vacuum, n is the refractive index of the medium. By changing the frequency f applied to the SAW voltage 7, the above
2θ can be changed, but the maximum deflection angle of this deflection angle 2θ is determined by the angle selection range of Bragg diffraction, and outside a certain frequency range, the coupling conditions of the diffraction grating structure are deviated from, and the diffraction efficiency decreases. The angle θ ₀ is generally taken to be equal to the Bragg angle corresponding to the center frequency f ₀ of the frequency range, and θ ₀ is given by θ ₀ = sin ^-1 (λf ₀ /2vn) (2) . In FIG. 1, the diffracted light beam 15 and the zero-order product light beam 16 are focused on the end surface 10 of the waveguide 2 as point images 11 and 14, respectively, by the action of the imaging lens 9. At this time, a light shielding material 17 is provided near the zero-order point image 14.

In this case, since the lens 9 has no imaging effect in the z-direction perpendicular to the waveguide, the spot size of the point image in the z-direction becomes approximately equal to the thickness of the waveguide. In this example, this thickness is approximately 2 μm. The ultrasonic surface acoustic wave 12 that has passed through the parallel light beam 6 is absorbed by the ultrasonic absorber 13 .

By using the chirp signal centered at the high frequency f ₀ as the high frequency signal applied to the SAW electrode 7, the dotted line 11 is moved and bright spot scanning is performed.

On the other hand, by changing the current applied to the semiconductor laser 3 in accordance with the recording signal, it is possible to modulate the brightness of the point image 11. Therefore, this bright spot scanning element can be used as it is as a one-dimensional scanning head for recording and reproduction. For example, when applied as a magnetic recording head, a photothermal magnetic recording medium 18 is attached to the waveguide exit end face 10 of this bright spot scanning element in the form of a tape.
High-speed scanning recording can be performed by moving the semiconductor laser 3 in the direction of the arrow while contacting the end face, and in synchronization with this, modulating the applied current of the semiconductor laser 3 with a video signal or the like.

However, in this case, as mentioned above, there is a good chance that the recording medium in contact with the output end face will be damaged by the sharp edges of the waveguide surface end face.

Furthermore, although the above description has been made regarding a bright spot scanning type element, the same applies to an element formed monolithically with a plurality of waveguides and used as a multichannel head.

Furthermore, although the case where the recording medium is tape-shaped has been described, if a disk-shaped recording medium is used, high-speed scanning recording can be similarly performed by moving the head from track to track to the next track. Note that the head is generally used slightly raised above the disk surface. In this case as well, there is a risk that the disk may be damaged before and after the head floats, especially by the traverse of the waveguide end face 10, as described above, and furthermore, the high air resistance caused by the traverse may impair the flying characteristics of the head.

A first embodiment of the present invention that eliminates the above-mentioned disadvantages is shown in FIG. This embodiment is applied to a recording head for a tape-shaped recording medium.

The principle of the bright spot scanning element is the same as the example shown in FIG.

In FIG. 3, a cover member 19 is provided on the surface of the thin film waveguide 2 via a spacer 20, and is preferably made of a material having approximately the same abrasion strength as the substrate 1. The spacer 20 is used to obtain a gap between the thin film waveguide 2 and the cover member 19 so that the cover layer 19 does not affect the light beam propagating through the ultrasonic elastic surface 8 and the thin film waveguide 2. , the thickness is, when geodigital lenses are used for the thin film lenses 5 and 9.
A cover layer 19 is placed at a position of several μm from the surface of the SAW electrode 7 or, if a Luneburg lens is used, from the top surface of the Luneburg lens.
The thickness is sufficient so that the back side of the

The spacer 20 having such a thickness is formed by vapor deposition of metal or dielectric material, or by adhering a very thin sheet-like object such as Mylar film, copper foil, or aluminum foil onto the thin film waveguide 2. .

The cover member 19 covers the entire surface of the thin film waveguide, and one end face thereof is substantially in the same plane as the output end face of the waveguide 2, and both form the head face of the recording head. This allows the waveguide 2
The sharp edges are not exposed.

At least a portion of the traverse of this head surface, that is, the traverse of the substrate 1 and the cover member 19 facing the recording medium 18 is chamfered or rounded as shown in FIG.

With the configuration described above, the bright spot scanning head of this embodiment can prevent damage to the recording medium 18 and prevent the bright spot scanning performance from being affected by rubber, dust, dirt, etc. on the surface of the thin film waveguide 2. Deterioration can be prevented.

The above is a case where it is applied to a fixed head for a tape-shaped recording medium, but when applied to a floating head for a disk-shaped recording medium, the air resistance when floating due to the twill is reduced by chamfering or rounding. This makes it possible to obtain good flying characteristics.

If it is not necessary to protect the entire waveguide from dirt, dust, etc., as shown in Figure 5,
The object of the present invention can also be achieved by providing a cover member 19' with a rounded twill, with the surface facing the recording medium coinciding with the output end surface of the waveguide.

FIG. 6 shows an embodiment in which the present invention is applied to a thin film waveguide type four-channel recording multihead for tape-shaped recording media constructed on the same substrate.

In FIG. 6, reference numeral 21 denotes a semiconductor substrate, on which four semiconductor lasers 22 to 25 are constructed. Reference numerals 26 to 29 are thin film waveguides through which the light beams from the semiconductor lasers 22 to 25 propagate, respectively, and these have a monolithic structure.

An example of monolithically configuring multiple semiconductor lasers and thin film waveguides on the same substrate in this way is
Literature IEEE Journal of Quantum Electronics vol.
QE-13, No. 4, pp220 “A Freguency-
Multiplexing Light Source With
Monolithically Integrated Distributed−
Feedback Diode Laser” by K. AiKi et al.

The emitted light from the semiconductor lasers 22 to 25 propagates through thin film waveguides 26 to 29, respectively, and reaches the output end face 3.
0, but at this time, the semiconductor laser 22~
The drive current of 25 is modulated by the recording signal, and the tape-shaped recording medium 31 is placed in contact with the element end face 30.
Signals can be recorded on the recording medium 31 by moving in the direction of the arrow in the figure.

32 is an adhesive layer having a lower refractive index than the thin film waveguides 26 to 29, and the cover member 33 is attached to the thin film waveguide 26.
~ 29, and the thin film waveguide 2
It also serves as a cover layer for layers 6 to 29.
The twills of the surfaces of the substrate 21 and cover member 33 that contact or are close to the recording medium 31 are chamfered or rounded.

With such a configuration, it is possible to prevent damage to the recording medium due to the twisting of the waveguide. In addition, since the thin film waveguide type head of this example is in a nearly completely sealed state, the effect of preventing property deterioration due to dirt, dust, dirt, etc. adhering to the waveguide surface is as shown in the third figure. It will be higher than the example.

Although the embodiments of the present invention have been described above with reference to the recording head, the present invention relates to the shape of the head, and it goes without saying that it is applicable not only to recording heads but also to reproducing heads.

As explained above, the present invention has the following advantages by providing a cover member directly or close to the surface of the thin film waveguide in a thin film waveguide type recording or reproducing head.

(1) In the case of a fixed head for a tape-shaped or disk-shaped recording medium, it is possible to prevent damage to the recording medium due to the twisting of the thin film waveguide facing the medium.

(2) In the case of a floating head for a disk-shaped recording medium, it has the advantages mentioned in (1) during ascent and descent, and by suppressing air resistance, it can provide good flying characteristics during ascent. .

Further, when the cover member is provided over the entire surface of the waveguide, there is an advantage that deterioration of device characteristics caused by dust, dirt, etc. adhering to the thin film waveguide can be prevented.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a recording head using a bright spot scanning element using a thin film waveguide type A/O deflector. 3 and 4 are diagrams showing a first embodiment in which the present invention is applied to a fixed recording head for a tape-shaped recording medium using a thin film waveguide type A/O deflector. Figure 5 shows the second
FIG. 3 is a sectional view of the head of the embodiment. FIG. 6 is a diagram showing a third embodiment in which the present invention is applied to a recording head in which thin film waveguides are monolithically constructed on the same substrate. In the figure, 2, 26, 27, 28, 29... thin film waveguide, 3, 22, 23, 24, 25... semiconductor laser, 5, 9... thin film lens, 7... SAW electrode, 15... diffraction Luminous flux, 16...0th order diffracted luminous flux,
18... Tape-shaped recording medium, 19... Cover member.

Claims (1)

[Scope of Claims] 1. Consisting of a thin film waveguide and a means for generating an elastic wave on the surface of the waveguide, the light beam propagating through the waveguide is deflected by the surface acoustic wave, and the deflected light beam is In a thin film waveguide type head that performs recording or reproduction by emitting light from an end face of a waveguide disposed opposite to a recording medium, a spacer is provided on the waveguide, and a spacer is provided on the waveguide so that the light beam is emitted from the end face of the waveguide disposed opposite to the recording medium. 1. A thin film waveguide type head, characterized in that a cover member having an end face is formed therein, and a gap is provided between the waveguide and the cover member.