JPH06103542B2 - Waveguide type optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a waveguide type optical device formed by utilizing a tapered optical waveguide and applicable to an optical head for recording / reproducing signals to / from an optical disc. Regarding the head.

[Conventional technology]

There is known a tapered optical waveguide in which an end portion of a waveguide layer formed on a substrate is tapered (for example, Japanese Patent Laid-Open No. 60-7
8406 publication). In such a tapered optical waveguide, the guided light propagated in the waveguide layer having a constant layer thickness is extracted to the substrate side at the tapered portion, but it is known that the extracted light is divergent. Has been.

Therefore, if it becomes possible to form a minute focal point for the light extracted from the tapered optical waveguide to the substrate side by appropriately designing the tapered shape from the divergent type, this can be used, for example, for information on an optical disk. It is expected to be used as a recording / playback illumination spot.

By the way, as a structure in which a waveguide is used for an optical head used for recording / reproducing an optical disc signal, a structure in which a diffraction grating for optical coupling is formed on a flat plate type optical waveguide is known (special feature: (Kaisho 61-236037),
This type of head uses a diffraction grating to take out light to the outside or to introduce reflected light from the optical disk into the optical waveguide. For example, the guided light is diffracted to both sides of the diffraction grating. There is a problem that the efficiency of light utilization for irradiation of the light is low, and it is difficult to manufacture a diffraction grating for coupling.

On the other hand, in the tapered optical waveguide, the radiation characteristic of the light extracted to the substrate side is stable against the wavelength change of the light source,
Further, as described later, since substantially all the light can be extracted to the substrate side, it has a high applicability to the above optical head because it has high light utilization efficiency and is easy to manufacture.

[Problems to be Solved by the Invention]

However, even if it becomes possible to form a fine focus by properly designing the taper shape as described above, the focus is located in the vicinity of the interface between the substrate and the waveguide layer. In such a case, when it is actually taken out of the substrate, it becomes a divergent light beam, and the focus of the taken-out light cannot be directly used for illumination for recording / reproduction of the optical disk.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a taper capable of converging light extracted to the substrate side to a focal point of a minute point distant from the boundary surface. An object of the present invention is to provide a novel waveguide type optical head using a waveguide layer.

[Means for Solving the Problems]

In order to achieve the above object, a waveguide type optical head according to the present invention has a flat surface for forming a waveguide layer, has a lower refractive index than the waveguide layer, and is transparent to the guided light; Of the waveguide layer formed on the plane, the waveguide layer is connected to the uniform-thickness waveguide layer having a uniform layer thickness and the uniform-layer thickness waveguide layer, and the uniform layer is formed at the connection portion. A tapered waveguide having the same layer thickness as the thick waveguide layer, the layer thickness gradually decreasing with distance from the connecting portion, and radiating the guided light propagating through the uniform thickness waveguide layer to the substrate side. Layer, and the waveguide layer includes a lens having a light condensing function in the width direction of the waveguide layer, and the radiated light emitted toward the substrate side by the tapered waveguide layer is spot-shaped on the optical disc. It is characterized in that it is configured to focus.

Further, in the above-mentioned waveguide type optical head, the substrate is formed by connecting a propagation substrate and a radiation substrate sharing a plane for forming a waveguide layer in a waveguide direction in the waveguide layer, and the radiation substrate is more than the propagation substrate. Also has a large refractive index, and the connection portion between the propagation substrate and the radiation substrate is close to the radiation start position determined by the refractive index of the propagation substrate and the waveguide layer and the shape of the tapered waveguide layer, and this radiation start position Is set so as not to exceed in the waveguide direction.

As another configuration for achieving the above object, a waveguide type optical head according to the present invention has a flat surface for forming a waveguide layer, has a lower refractive index than the waveguide layer, and A transparent substrate, a waveguide layer formed on the plane of the substrate, and a clad layer embedded in the plane of the substrate, the waveguide layer having a uniform layer thickness. The wave layer and the uniform-thickness waveguide layer are connected to each other, and have the same layer thickness as the uniform-thickness waveguide layer at the connection portion, and the layer thickness gradually decreases as it goes away from the connection portion. And a tapered waveguide layer that radiates guided light propagating through the waveguide layer toward the substrate side, the cladding layer having a lower refractive index than the substrate, and the shape of the tapered waveguide layer and the waveguide layer. , The waveguide layer is provided so as to include the radiation start position to the substrate side which is determined by the refractive index of the substrate, and the waveguide layer is Comprising a lens having a condensing effect in a direction, characterized in that it is configured to focus a spot shape radiation emitted to the substrate side by the tapered waveguide layer on the optical disk.

[Work]

In the waveguide type optical head of the present invention, the lens formed in the waveguide layer is formed so as to collect the guided light in the width direction of the waveguide layer, and the tapered waveguide layer is formed in the waveguide layer. The propagated guided light is emitted to the substrate side, and the emitted light emitted to the substrate side is focused on the optical disc in a spot shape.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

First, a tapered optical waveguide applied to the waveguide type optical head of the present invention will be described.

FIG. 6 schematically shows an example of a tapered optical waveguide applied to the present invention.

In the figure, reference numeral 10 indicates a substrate and reference numeral 20 indicates a waveguide layer.

The waveguide layer 20 is composed of a uniform thickness waveguide layer 21 having a uniform thickness and a tapered waveguide layer 22.

The substrate 10 is configured by connecting the propagation substrate 11 and the radiation substrate 12 in a linked manner. Both the propagation substrate 11 and the radiation substrate 12 are transparent to the guided light and share the plane for forming the waveguide layer. Then
A waveguide layer 20 including a uniform thickness waveguide layer 21 and a tapered waveguide layer 22.
Are formed on the plane.

For the following description, the X and Z directions are defined as shown in the figure. Z
The direction corresponds to the plane of the substrate 10 and corresponds to the propagation direction of the guided light. That is, the guided light is guided and propagated in the uniform thickness waveguide layer 21 to the right in FIG. The X axis is orthogonal to the plane,
The position of the X axis is the uniform thickness waveguide layer 21 and the tapered waveguide layer 22.
Represents the connecting part of. Therefore, the tapered waveguide layer 22 is
This is the right part of the X axis in FIG.

The region TR in which the tapered waveguide layer 22 is formed is called a tapered region.

The area above the waveguiding layer 20 is the air area occupied by air. Regarding the relationship of the refractive index, for example, in this example, the refractive index of the substrate 10 is 1.51 for the propagation substrate 11, 1.515 for the radiation substrate 12, the refractive index of the waveguide layer 20 is 1.52, and the refractive index of air is 1. Therefore, the refractive index increases in the order of the air region, the propagation substrate 11, the radiation substrate 12, and the waveguide layer 20. Further, it is assumed that the thickness of the uniform waveguide layer 21 is 2.63 μm, the length of the taper region TR is 6000 μm, and the wavelength of the propagated light is 0.6328 μm (He-Ne laser light).

The shape of the free surface (boundary surface with the air region) of the tapered waveguide layer 22 has a uniform thickness with the uniform thickness waveguide layer 21 at the connecting portion with the uniform thickness waveguide layer 21 as shown in the figure. The taper is formed by decreasing the layer thickness with increasing distance from the connecting portion.

However, since the thickness of the uniform-thickness waveguide layer is extremely small as compared with the length of the tapered region as described above, even if it is called a taper, its inclination is extremely small.

In forming the taper region TR, various taper shapes can be easily realized by controlling the moving speed of the mask by performing sputtering while moving the mask in the Z direction by a shadow mask sputtering method.

Next, the operation of the tapered waveguide will be described.

In FIG. 6, the light wave propagating in the Z-direction through the uniform-thickness waveguide layer 21 has a wavelength of 0.6328 μm, and the guided mode is the fundamental wave.
It is in TE ₀ mode. Uniform layer thickness The thickness of the waveguide layer 21 is 2.63 μm.
Therefore, the effective refractive index in this mode is N =
It becomes 1.5107. In addition, we consider the propagation mode as a superposition of plane waves, and consider the elementary waves as asymptotic fields by quasi-geometric optics. That is, a plane wave, which is an elementary wave, is treated as a set of light rays propagating in the direction normal to the wavefront. Using the above effective refractive index, the incident TE ₀ mode has a propagation angle θi of 86.
Represented as a 42 degree ray group. In the following description, the angle will be expressed as an angle with the X axis unless otherwise specified.

Now, the light beam propagating through the uniform-thickness waveguide layer 21 propagates in a zigzag manner while repeating total reflection at the boundary surface with the substrate 10 and the boundary surface with the air region.

When such propagating light enters the tapered waveguide layer 22, as shown in FIG. 7, the tangent 2A of the free surface of the tapered waveguide layer 22, that is, the boundary surface with the air region is inclined with respect to the Z direction. Therefore, when the light is totally reflected on the free surface and re-incident on the boundary surface with the substrate 10, the incident angle θ is equal to the uniform thickness waveguide layer 21.
Is smaller than the propagation angle θi at. In this way, in the tapered waveguide layer 22, the propagation angle becomes gradually smaller as the reflection within the tapered region TR is repeated.

On the other hand, in the illustrated example, the critical angle of total reflection at the interface between the tapered waveguide layer 22 and the substrate 10 is 83.4 with respect to the propagation substrate 11.
2 degrees, 83.35 degrees with respect to the radiation substrate 12, and the critical angle of total reflection at the boundary surface between the tapered waveguide layer 22 and the air region is 41.14 degrees.

Here, for simplicity, assuming that the entire substrate is composed of the propagation substrate 11, the light incident on the tapered waveguide layer 22 propagates in a zigzag manner while repeating reflection, and
The angle of incidence on the boundary surface on the side of 10 and the air region, that is, the angle of incidence on the free surface is gradually reduced, but first, the angle of incidence on the side of the substrate 10 becomes smaller than the critical angle of 83.42 degrees, and a part of the power of light becomes , Leaks to the side of the substrate 10. The leak power ratio at this time depends on the refractive index of the waveguide layer 20, the refractive index of the substrate 10 and the incident angle of the light ray to the reflection point, and can be calculated by a relational expression known as the Fresnel power transmission coefficient. it can. As described above, the position where the power leakage starts is the radiation start position.

When the reflection angle is further repeated and the incident angle on the boundary surface on the air region side becomes smaller than the critical angle 41.14 degrees, the light leaks out to the air region as well. Since the difference in the critical angle of reflection is large, substantially all the light leaks to the substrate side after the light leaks to the substrate side and before the light leaks to the air region. Therefore, it is not necessary to consider leakage to the air region side.

The direction α of light leaking to the substrate 10 side can be known by Snell's law regarding refraction.

Now, assuming that the entire substrate is made of the propagation substrate as described above, the behavior of the light leaking to the substrate side as described above, that is, the radiated ray, was investigated as follows.

Referring again to FIG. 6, the light propagating in the uniform thickness waveguide layer 21 propagates uniformly with the propagation angle θi of 86.42 degrees as described above. Therefore, when such light enters the tapered waveguide layer 22 at the X axis of the connecting portion, all the incident light rays have an angle of θi with respect to the X axis. Therefore, first, considering the light that enters the tapered surface directly across the connecting portion diagonally to the upper right, the total of this light is the point O (connecting portion) in FIG. 6 at the boundary with the substrate 10. The light is reflected by the point P and enters the tapered waveguide layer 22, and the distance between the point O and the point P is
Using a layer thickness of 2.63 gives 2.63 tan (86.42 degrees) = 42.04 μm.

In the same way, the light is incident across the connecting part diagonally downward right and
The total ray that is reflected once at the interface with 10 and then is incident on the free surface of the tapered region is the ray that is incident between points O and Q in FIG. The distance between the O point and the Q point is 42.04 μm, which is the same as the above.

Therefore, considering that the light rays that pass through the connecting portion and enter the tapered waveguide layer 22 are those that are reflected from the region IP in FIG. become.

Therefore, tracing was performed on a large number of rays that are totally reflected at an angle of θi from the region IP to the right.

First, in order to see the effect of the free surface shape of the tapered waveguide layer on the above behavior, a concave surface 4-1, a linear shape 4-2, and a convex surface 4-as shown in FIG. I assumed 3. These shapes can be expressed as X = a {1- (b · Z) ^C } ... (1) where a = 2.63 μm, b = 1/6000 and the parameter is c The parameters c are 0.5, 1, and 2 for the shape 4-1, the linear shape 4-2, and the convex shape 4-3, respectively. Also, as described in the previous example, the thickness of the uniform thickness waveguide layer is
It is 2.63 μm and the length of the tapered region is 6000 μm.

When investigating the behavior of the radiant ray leaked to the substrate side, the degree of concentration of the radiant ray within the substrate is examined. This degree of concentration is defined as the ray density as follows. That is, consider a plane Zobs orthogonal to the Z axis as shown in FIG. 9, divide this plane Zobs into sections of 2 μm each in the X direction, count the number m of emitted rays passing through each section, and calculate the total number m of emitted rays m. The light density D is defined as the ratio (m / m) ≡ D with. The section having the maximum light density is called the maximum light density position, and the position of this maximum light density position on the substrate is determined by determining the position of the plane Zobs in the Z direction by 1 μm.
Find this by scanning in m steps.

When investigating the behavior of the radiated rays, the power balance between the waveguide layer and the substrate due to the radiation is not taken into consideration. Further, only the propagation in the positive direction of the Z axis, that is, the rightward direction in FIG. 9 is considered, and the tracing is terminated when the incident angle of the reflected light ray on the substrate side boundary surface becomes ≦ 0.

One ray totally reflected at the position of X = Z = 0 in the region IP of FIG. 6 is traced by the above-mentioned method, and the substrate 10 of a large number of radiation rays leaked from this one ray to the substrate side one after another. Figure 10 shows the results of an investigation of the state of propagation in the interior. This figure shows that the shape of the free surface of the tapered waveguide layer is the convex surface 4-3 (c) of FIG.
= 2), the radiation ray group that passes through the maximum ray density position (Fig. 10 (II)) and the radiation ray group that does not pass (I (I) and (III)) are shown separately. However, regardless of whether the free surface shape of the tapered waveguide layer is a convex surface, a concave surface, or a straight surface, it is qualitatively the same behavior. That is, regardless of the shape of the free surface, in general, radiation that emits light rays that do not pass the maximum ray density position with a radiation area that emits a ray group that passes the maximum ray density position (the area between AB in FIG. 10) sandwiched between them. Area exists.

However, when the incident position on the tapered waveguide layer 22 is moved within the region IP, the three types of surface shapes shown in FIG. (C = 0.5), straight line (c = 1), and convex surface (c = 2) were examined. If the shape of the free surface was concave or straight, the origin position of the tracing ray changed within the region IP. By doing so, the maximum ray density position fluctuates in both X and Z directions, but when the shape of the free surface is convex, it does not fluctuate at all, and it is found that the focusing property of rays is extremely stable.

FIG. 11 shows how the maximum ray density position fluctuates as the trace ray origin position changes. In (I) and (II) of the same figure, the vertical axis Zi represents the Z coordinate of the starting point, and the horizontal axis represents the fluctuation amounts of the maximum ray density position in the Z and X directions, respectively. The broken line is the case where the free surface is concave (c = 0.5), and the solid line is the case where it is linear (c = 1).

When the free surface shape is convex (c = 2), the maximum ray density position does not fluctuate at all with respect to the fluctuation of the origin of the tracing ray.
That is, the behavior of the emitted ray is extremely stable with respect to the fluctuation of the origin position of the traced ray. Upon examination, it was found that this tendency applies not only to the case of c = 2, but also to the case of c = 3, 4, ..., And the case of a convex surface represented by a trigonometric function or the like.

By the way, the above description does not consider the power balance in the tracing ray as described above. However, in actual radiation, the balance of power must be taken into consideration.
Considering this balance of power, there are the following problems.

That is, on the left side of the position indicated by the symbol A in FIG. 10, there is the radiation start position described above. This radiation start position is the substrate 1
0, determined by the refractive index of the waveguiding layer 20 and the shape of the tapered region, but if the entire substrate 10 is composed of the propagation substrate 11, the leakage of light from the radiation start position to the substrate side will occur. Although it starts, this leak amount is determined by the incident angle to the substrate and the reflectance. Therefore, when the power, that is, the light intensity, of each radiated ray due to this leakage is calculated by the Fresnel power transmission coefficient, it propagates through the uniform waveguide layer and is radiated from the tapered waveguide layer to the substrate side. All of the power of the emitted light is emitted to the substrate side while the reflection and emission are repeated only about 10 times from the emission start position. As a result, in such a case, the power in the waveguiding layer for each ray incident from the range of IP in FIG. The light rays are focused in a relatively narrow space. First
Figure 12 outlines this state.

However, as shown in the same figure, the refraction angle of the radiation ray from the vicinity of the radiation start position, that is, the radiation angle is close to 90 degrees, and therefore, the concentration of power due to the focusing of the radiation ray is the waveguide layer 20 inside the substrate 10.
It will occur at a position very close to the boundary surface of. Therefore, in such a case, it is extremely difficult to set the power concentration position outside the substrate, and eventually, it is a divergent light beam that can be extracted outside the substrate.

Therefore, in the present invention, the substrate 10 is composed of a propagation substrate 11 and a radiation substrate 12 having a larger refractive index than the propagation substrate 11, and the position of the connecting portion is close to the radiation start position, and this radiation start position is set in the waveguide direction. By setting so as not to exceed in, it is possible to set the power concentration position of the radiated light beam at a position away from the boundary surface between the substrate and the waveguide layer.

Referring again to FIG. 6, in this example the tapered waveguide layer 22
The free surface shape of is the same as the convex surface 4-3 in FIG.
When laser light having a wavelength of 0.6328 μm is guided in the TE ₀ waveguide mode in the waveguide layer 20, the radiation start position R toward the substrate side is Z
It is at a position of 4058 μm from the position of = 0.

Further, in the above example, the connecting portion between the propagation substrate 11 and the radiation substrate 12 is set at a position slightly displaced from the radiation start position R toward the X axis side, but the setting position of the connecting portion is as described above. Since the condition is that the position is close to the start position and does not exceed the emission start position in the waveguide direction, the position of the connecting portion can be set near the emission start position R with the position of the emission start position R being the limit.

Since the refractive index of the radiation substrate 12 is higher than the refractive index of the propagation substrate, the propagating light is reflected inside the tapered waveguide layer 22 and enters the radiation substrate 12, so that radiation is started into the radiation substrate 12.

If the entire substrate is composed of a propagation substrate, the direction of the radiation ray radiated at the radiation start position will be close to the interface between the substrate and the waveguide layer as described above, and the power concentration will be above the boundary. Although it occurs in the vicinity of the surface (see FIG. 12 (I)), the radiation substrate 12 has a larger refractive index than the propagation substrate, and therefore the difference in refractive index from the waveguide layer 20 is small. Therefore, the refraction angle, that is, the radiation angle of the radiation ray leaking into the radiation substrate 12 is smaller than that of the radiation ray emitted into the propagation substrate at the radiation start position, and as shown in FIG. The position where the power is concentrated due to the intersection of the radiated rays in the direction rising up with respect to the boundary surface is located at a position distant from the boundary surface, and therefore the power of the radiated light is actually concentrated outside the substrate. Will also be possible. Since the radiation into the radiation substrate 12 starts in the vicinity of the radiation start position, the distance between the radiation positions of the radiation rays adjacent to each other is relatively wide in this state, so that the radiation rays from a relatively wide area should be focused. You can

As described above, in the tapered optical waveguide applied to the present invention, as shown in FIG. 13, the propagation angle is changed in the region I and the radiation is started in the region II, at which time the radiation angle is reduced. For this reason, a radiation substrate having a small refractive index difference from the waveguide layer is used in the region II, and the power is extracted from the radiation rays rising to the substrate surface, so that the position of power concentration is moved away from the substrate surface.

In the above example, the shape of the free surface of the tapered waveguide layer is a convex shape, but the shape is not limited to this. But,
The use of a convex free surface improves the stability of the power concentration position.

Now, in the tapered optical waveguide described above, the substrate is composed of the propagation substrate and the radiation substrate having a larger refractive index than this, and the radiation beam with a small radiation angle is taken out into the radiation substrate. Can be located at a position distant from the boundary surface between the waveguide layer and the waveguide layer, and by making the free surface shape of the tapered waveguide layer convex, it is possible to enhance the stability of power concentration. Therefore, the applicability to the waveguide type optical head applicable to the information recording / reproducing optical head of the optical disk is improved.

Next, it has the same function as the above-mentioned tapered optical waveguide,
Another example of a tapered optical waveguide applicable to the waveguide type optical head according to the present invention will be shown.

FIGS. 15 (I) and 15 (II) schematically show another embodiment of the tapered optical waveguide.

In FIGS. 15 (I) and (II), this tapered optical waveguide has a substrate 10, a waveguide layer 20, and a cladding layer 30, and the substrate 10 has a plane for forming the waveguide layer. , Has a lower refractive index than the waveguide layer 20 and is transparent to the guided light.

The waveguide layer 20 is formed on the substrate 10 and includes a cladding layer.
30 is embedded in the plane of the substrate 10 for forming the waveguide layer. Further, the waveguide layer 20 is connected to the uniform thickness waveguide layer 21 having a uniform thickness and the uniform thickness waveguide layer 21, and has the same layer thickness as the uniform thickness waveguide layer 21 at the connection portion. However, the layer thickness gradually decreases as it goes away from the connecting portion, and the tapered waveguide layer 22 emits the guided light propagating through the uniform layer thickness waveguide layer 21 to the substrate side.

The cladding layer 30 is provided so as to include the radiation start position R toward the substrate side, which is determined by the shape of the tapered waveguide layer 22, the waveguide layer 20, and the refractive index of the substrate 10.

The clad layer 30 is provided to prevent light from leaking from the tapered waveguide layer 22 in this clad layer portion by total reflection, and its refractive index is lower than that of the substrate 10. .

Further, the free surface of the tapered waveguide layer 22 of the waveguide layer 20 can be formed in a convex shape so as to protrude from the substrate 10.

In the tapered optical waveguide having the above-described structure, the waveguide layer 20 has the same structure as the tapered optical waveguide shown in FIGS. It is similar. Here, the difference from the above-mentioned tapered optical waveguide is that the clad layer 30 is provided on the substrate 10 as a means for limiting the radiation start position of the radiation beam.

That is, if there is no cladding layer in this portion, light leakage starts from the radiation start position R. However, the cladding layer having a lower refractive index than the substrate 10 so as to include the radiation start position R
Since the 30 is provided, if the clad layer 30 does not exist, the ray that starts to radiate from the position R still repeats total reflection in the clad layer portion, and the substantial radiation starting point is as shown in FIG. 15 (II). It will move to the right edge of layer 30.
Therefore, when radiation is actually started at this position, the angle of incidence of the light rays that are incident on the substrate inside the tapered waveguide layer can be made sufficiently small, and as a result, the radiation angle is also small, and each radiation ray is emitted by the substrate. Since the radiated rays are close to each other and are parallel to each other, the position where the power is concentrated is located away from the boundary surface. It is also possible to actually concentrate the power of the emitted light outside the substrate.

Therefore, the essence of this tapered optical waveguide is that the propagation angle is changed in the region I of the tapered waveguide layer 22 as shown in FIGS. 15 (I) and (II), and the region where the cladding layer 30 is installed is changed.
In II, the emission of radiation rays along the surface of the substrate is effectively limited, and the power is extracted by the radiation rays rising to the surface of the substrate in the region III, whereby the position of power concentration is moved away from the surface of the substrate.

As described above, the tapered optical waveguide shown in FIGS. 15 (I) and (II) has the cladding layer 30, and the radiation start position of the emitted light beam can be adjusted by the cladding layer 30, so that the power of the guided light can be controlled by the substrate. The tapered waveguide layer 22 can be located at a position away from the boundary surface between the waveguide layer 20 and the waveguide layer 20, and the free surface shape of the tapered waveguide layer 22 can be convex to improve stability of power concentration. Become. Therefore, the applicability to a waveguide type optical head applicable to an optical head for recording / reproducing optical disk information is improved.

Next, FIG. 14 shows an example in which the tapered optical waveguide described with reference to FIGS. 6 to 13 is used in a waveguide type optical head, and FIG. An example of using the tapered optical waveguide described in FIG. 15 in a waveguide type optical head is shown.

As shown in FIGS. 14 and 16, no matter which tapered optical waveguide is used, the light extracted to the substrate 10 side does not have the focusing property in the width direction of the waveguide layer 20, In order to focus the light extracted to the substrate side in a spot shape on the optical disc 50, for example, the cylindrical lens 40 is used as an anamorphic optical system, and the cylindrical lens 40 can focus the waveguide layer in the width direction. Can have

Regarding the tapered optical waveguide described with reference to FIGS. 6 to 14 described above, the inventors of the present application refer to “Takeda
Miyazaki: Condensing Characteristics of Tapered Waveguide for Integrated Optical Disk Head: IEICE Transactions Vol.J71-C, No.11, P.1552〜
1558, November 1988 ”.

By the way, it is not preferable to mount the above lens on the outside of the waveguide because there are many inconveniences such as complicated optical axis alignment and management of the gap between the substrate and the lens.

Therefore, in the present invention, a lens portion (waveguide lens) having a condensing action in the width direction of the waveguide layer is provided in the waveguide layer of the above-mentioned tapered optical waveguide, and the lens portion and the tapered waveguide are provided. Radiation light radiated from the waveguiding layer to the substrate side by the wave layer is focused outside the substrate to be spot-shaped on the optical disk or the like.

Hereinafter, description will be given based on the illustrated embodiment.

FIG. 1 is a schematic perspective view of a tapered optical waveguide showing an embodiment of a waveguide type optical head according to the present invention.

In the figure, reference numeral 1 denotes a waveguiding layer, and the waveguiding layer is a uniform thickness waveguide layer and a tapered waveguiding layer similar to the tapered optical waveguide described with reference to FIGS. 6 to 13. It is composed of and. The layer thickness of the uniform thickness waveguide layer is about 2 μm.

Reference numerals 2 and 3 denote substrates, which are the propagation substrate 2 and the radiation substrate 3 which share the plane for forming the waveguide layer 1.
Are connected in the above-described order in the waveguide direction in the waveguide layer 1, and the radiation substrate 3 has a larger refractive index than the propagation substrate 2. Here, when the refractive index of the waveguide layer 1 is nf, the refractive index of the propagation substrate 2 is ns, and the refractive index of the radiation substrate 3 is nc, the relationship of nf>nc> ns is established.

Further, the connection portion between the propagation substrate 2 and the radiation substrate 3 is close to the radiation start position determined by the refractive indexes of the propagation substrate 2 and the waveguide layer 1 and the shape of the tapered waveguide layer, and this radiation start position is It is set so as not to exceed in the waveguide direction.

Further, in FIG. 1, reference numeral 7 indicates a waveguide lens which is a feature of the present invention. The waveguide lens 7 is a waveguide layer (either a uniform waveguide layer or a tapered waveguide layer before the radiation position). However, it is configured to have a focusing action in the width direction of the waveguide layer 1 (y direction in the drawing).
As the waveguide lens 7, a mode index lens shown in FIGS. 2 (a) and 3 (a), (b),
A waveguide lens such as a Luneburg lens shown in FIG. 2 (b), a geodesic lens shown in FIG. 2 (c), or a grating lens (Fresnel lens in the example shown) shown in FIG. 4 can be used.

Now, since the tapered optical waveguide having the above-mentioned configuration is configured in the same manner as the tapered optical waveguide described with reference to FIGS. 6 to 13 above except the waveguide lens 7,
It has the same function. Therefore, a feature of the present invention is that when a tapered optical waveguide is applied to an optical head, a lens having a function equivalent to an external lens such as a cylindrical lens is integrally formed on the waveguide layer 1 to form the waveguide layer 1.
This is because it also has a focusing property in the width direction.

Next, the function of the tapered optical waveguide shown in FIG. 1 will be described.

In FIG. 1, when laser light is incident on the waveguide layer 1 by Butt coupling (a method in which a semiconductor laser is directly adhered to the end face of the waveguide layer 1), the guided light 6 propagating in the waveguide layer 1 is guided. The TE ₀ mode which is the fundamental wave of the waveguide becomes TE ₀ mode, and the guided light 6 of this TE ₀ mode reaches the waveguide lens 7 while gradually expanding the beam width as it propagates in the waveguide layer 1 in the Z direction in the figure. . When a collimator lens is added, parallel light arrives.

The guided light 6 that has reached the waveguide lens 7 is
Due to the focusing action of, the light becomes focused light that is focused in the width direction of the waveguide layer 1, and becomes a beam that is focused on the focal point 8 in the air.
The focusing action of the waveguide lens 7 is only the component in the width direction of the waveguide layer, that is, the y direction in the figure.

Now, the guided light that has passed through the waveguide lens 7 reaches the tapered portion 4 of the tapered waveguide layer while gradually narrowing the beam width,
By the action of the taper portion 4, it is radiated as a leaky wave to the substrates 2 and 3, and radiated from the end face 5 of the radiation substrate 3 to the outside of the substrate. Due to the action of the taper portion 4 and the action of the substrate 2 and the substrate 3, the emitted light 9 has a focusing property of the component in the x direction in the figure, and becomes a beam that focuses on the focal point 8. Therefore, when the tapered optical waveguide according to the present invention is used, the radiation light 9 emitted to the outside is focused in the x and y directions in the figure by the action of the waveguide lens 7, the tapered waveguide layer and the substrate. The emitted light becomes the emitted light, and a minute light spot can be formed at the focal point 8 in the air.

Therefore, when the tapered optical waveguide shown in FIG. 1 is used as an optical head, the optical disk may be arranged at the position of the focal point 8 and the emitted light 9 can be focused in a spot shape on the optical disk. Further, the signal light reflected from the optical disk follows the above-mentioned path in the opposite direction, is propagated in the opposite direction through the waveguide layer 1 again, and the signal is detected. Incidentally, a photodetector or the like for detecting the signal light may be formed in the waveguide layer.

By the way, in the tapered optical waveguide shown in FIG. 1, an example in which a waveguide lens is provided in the waveguide layer of the tapered optical waveguide described in FIGS. 6 to 13 is shown. Even if a waveguide lens is provided in the waveguide layer of the tapered optical waveguide having the clad layer shown, the same effect can be obtained, and the same can be applied to the waveguide type optical head.

FIG. 5 is a schematic perspective view of a waveguide type optical head showing an embodiment thereof, which has a flat surface for forming a waveguide layer and has a lower refractive index than the waveguide layer. And a waveguide layer 1 formed on the plane of the substrate 2, and a clad layer 30 embedded in the plane of the substrate 2. The wave layer 1 is connected to the uniform-thickness waveguide layer having a uniform layer thickness and the uniform-thickness waveguide layer, and has the same layer thickness as the uniform-thickness waveguide layer at the connection portion. The layer thickness gradually decreases as the distance increases, and the waveguide layer 6 includes a tapered waveguide layer that radiates the guided light 6 propagating in the uniform-thickness waveguide layer to the substrate 2 side. It is provided with a low refractive index so as to include the radiation start position toward the substrate 2 side which is determined by the shape of the tapered waveguide layer and the refractive index of the waveguide layer 1 and the substrate 2. In addition, the waveguide layer 1 includes a waveguide lens 7 having a condensing action in the width direction of the waveguide layer 1, and the emitted light emitted to the substrate 2 side by the tapered waveguide layer 4 is emitted outside the substrate. It is configured so as to be focused in a spot shape on the optical disk surface.

That is, the waveguide type optical head having the configuration shown in FIG.
By adding the waveguide lens 7 shown in FIGS. 2 to 4 in the waveguide layer 1 of the tapered optical waveguide described with reference to FIG. 15, the width direction of the waveguide layer 1 is increased. Also has a converging property, and it is possible to obtain the same effect as the waveguide type optical head shown in FIG.

〔The invention's effect〕

As described above, according to the present invention, since the tapered optical waveguide forming the main part of the optical head can have the focusing property,
It is possible to form a minute light spot on the optical disc without using an external lens such as a cylindrical lens.

Therefore, in the waveguide type optical head according to the present invention, the condensing optical system can be configured only by the tapered optical waveguide, and the optical axis can be aligned by a thin film process such as photolithography when forming the tapered optical waveguide. ,
Adjustment work is greatly reduced. Moreover, since the number of optical components such as the cylindrical lens is significantly reduced, an inexpensive optical head can be provided.

Further, in the waveguide type optical head according to the present invention, since the condensing optical system can be constituted only by the tapered optical waveguide, the miniaturization and the weight saving can be easily achieved, and the high stability of the waveguide type optical head can be achieved. Also, the reliability can be improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of a tapered optical waveguide which constitutes a waveguide type optical head according to the present invention.
FIG. 4 to FIG. 4 are views each showing an example of a waveguide lens formed in the waveguide layer of the same tapered optical waveguide, and FIG. 5 is another view of the tapered optical waveguide constituting the waveguide type optical head according to the present invention. FIG. 6 is a schematic perspective view showing an embodiment of the present invention, FIG. 6 is an explanatory view showing an example of a tapered optical waveguide applicable to the waveguide type optical head of the present invention, and FIGS. 7 to 13 are the same. FIG. 14 is a diagram for explaining the action of the tapered optical waveguide, FIG. 14 is a diagram showing an example of an optical head using the tapered optical waveguide shown in FIG. 6, and FIG. 15 is a waveguide type optical head of the present invention. FIG. 16 is a diagram schematically illustrating another example of a tapered optical waveguide that can be applied, and FIG. 16 is a diagram illustrating an example of an optical head using the tapered optical waveguide shown in FIG. 1,20 ... Waveguide layer, 2,11 ... Propagation substrate, 3,12 ... Radiation substrate, 4 ... Tapered portion, 5 ... Emitting end face, 6 ... Guided light,
7 ... Waveguide lens, 8 ... Focus, 9 ... Synchrotron radiation,
10 ... Substrate, 21 ... Uniform thickness waveguide layer, 22 ... Tapered waveguide layer, 30 ... Clad layer, 50 ... Optical disk.

Claims (3)

[Claims] 1. A substrate having a flat surface for forming a waveguide layer, having a refractive index lower than that of the waveguide layer, and transparent to guided light, and a waveguide layer formed on the flat surface of the substrate. Consists of
The waveguide layer has a uniform thickness waveguide layer having a uniform layer thickness and is connected to the uniform thickness waveguide layer, and has the same layer thickness as the uniform thickness waveguide layer at the connection portion. And a tapered waveguide layer that radiates guided light propagating through the uniform-thickness waveguide layer to the substrate side, and
The waveguide layer is provided with a lens having a light collecting action in the width direction of the waveguide layer, and is configured to focus the emitted light emitted toward the substrate side by the tapered waveguide layer on the optical disc in a spot shape. A waveguide type optical head characterized in that 2. The waveguide type optical head according to claim 1, wherein the substrate is formed by connecting a propagation substrate and a radiation substrate, which share a plane for forming a waveguide layer, in the waveguide direction in the waveguide layer. The radiating substrate has a higher refractive index than the propagation substrate,
The connection portion between the propagation substrate and the radiation substrate is close to the radiation start position determined by the refractive index of the propagation substrate and the waveguide layer and the shape of the tapered waveguide layer, and does not exceed this radiation start position in the waveguide direction. A waveguide type optical head characterized by being set as follows. 3. A substrate having a flat surface for forming a waveguide layer, having a refractive index lower than that of the waveguide layer, and transparent to guided light, and a waveguide layer formed on the flat surface of the substrate. A clad layer embedded in the plane of the substrate, the waveguide layer being a uniform-thickness waveguide layer having a uniform layer thickness and being connected to the uniform-thickness waveguide layer. It has the same layer thickness as the one-layer waveguide layer, and the layer thickness gradually decreases as it goes away from the connecting portion, and the tapered waveguide that radiates the guided light propagating through the uniform-thickness waveguide layer to the substrate side. And a clad layer having a refractive index lower than that of the substrate, and provided so as to include a radiation start position to the substrate side which is determined by the shape of the tapered waveguide layer and the waveguide layer and the refractive index of the substrate. In addition, the waveguide layer is provided with a lens having a light collecting action in the width direction of the waveguide layer, and the tapered waveguide layer serves as a base. Waveguide type optical head is characterized in that it is configured radiation emitted to the side so as to converge into a spot shape on the optical disk.