JPH03201225A - Waveguide element - Google Patents

Abstract

PURPOSE:To relieve position accuracy by bisecting a guided luminous flux by a pair of mirror surfaces formed on an optical waveguide layer and focusing these fluxes individually to photodetector pairs, thereby making focus detection. CONSTITUTION:A buffer layer 6 and the optical waveguide layer 7 are formed on a semiconductor plate 5 and a pair of the mirror parts 13a, 13b formed by perpendicularly notching the surface of the optical waveguide layer down to a grating coupler 8 and the buffer layer 6 are formed on the waveguide layer 7. A part of the section parts of these mirrors are formed as the mirror surfaces 13a1 and 13b1 of hollow surfaces. The luminous flux from a light source 1 is condensed onto an information recording medium 12, by which recording and reproducing are executed. The reflected luminous flux from the recording surface is optically coupled to the optical waveguide layer 7 and the optically coupled luminous flux is split into two parts within the optical waveguide layer and is focused to the photodetector pairs 10a to 10d, by which the focus detection is made. The degree of freedom of the position accuracy of a waveguide element 3 is increased in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide element. The present invention can be used in optical information recording and reproducing devices such as optical pickups.

[Prior Art] Optical information recording and reproducing devices using waveguide elements are known. For example, Japanese Patent Laid-Open No. 63-61430 discloses an optical pickup using a waveguide element.

[Problems to be Solved by the Invention] The waveguide device disclosed in the above publication has the following problems.

That is, in this waveguide element, a light beam reflected from the recording surface of an optical information recording medium and returned to a substantially parallel light beam by an objective lens is optically coupled to an optical waveguide layer using a pair of focusing type grating couplers. 2 with a tendency to converge
Divide into luminous flux. Then, focus detection is performed by focusing these two beams onto each of a pair of photodetectors.

In such a waveguide device, the position of each focusing type grating coupler and the position of the photodetector pair are precisely determined on the premise that the light beam incident on the grating in the focused state is a parallel light beam. ing. Therefore, in order to obtain the desired accuracy in focus detection, the positional accuracy of the waveguide element with respect to the optical element at the same level as the objective lens must be set with sufficient precision, making assembly of the optical information recording/reproducing device troublesome. Therefore, it is difficult to improve the yield of the same device.

The present invention was made in view of the above-mentioned circumstances, and
The purpose is to provide a waveguide element with a large degree of freedom regarding positional accuracy.

[Means to solve the problem] The present invention will be explained below.

The waveguide element of the present invention records and/or reproduces optical information by condensing a light flux from a light source onto the recording surface of an optical information recording medium, and directs the reflected light flux from the recording surface into an optical waveguide layer. A focus detection method that performs focus detection by dividing the optically coupled light beam into two within the optical waveguide layer, and focusing each of the two divided light beams on a pair of photodetectors integrated with the optical waveguide layer. This is a waveguide element used in ``.'', and is characterized by the following points.

That is, a pair of tiger surfaces are integrally formed in the optical waveguide layer.

This "pair of Schiller surfaces""divides the light beam guided by the optical waveguide layer into two along the principal ray" and reflects each of the divided light beams toward each of the photodetector pairs,
Further, they are arranged so that the directions of the chief rays in each of the divided light beams are substantially parallel to each other.

"Dividing into two along the principal ray" means that the light beams reflected by a pair of mirror surfaces are "separated from each other at the principal ray portion of the previous light beam." Therefore, the light ray forming one side edge of the two separated light beams is the principal ray of the light beam before separation. Therefore, among the above-mentioned "rays forming the side edges of the luminous fluxes in the two luminous fluxes", the one that was the principal ray in the luminous flux before separation is referred to as the "principal ray in each divided luminous flux".

[Function] In the waveguide element of the present invention, when the degree of convergence or the degree of divergence of the light beam optically coupled to the optical waveguide layer changes, the focusing position of each light beam divided into two by a pair of Schiller surfaces changes to "divided". However, since the principal rays in each divided light beam are substantially parallel to each other, the interval between the focal points of each light beam hardly changes.

[Examples] Hereinafter, specific examples will be described with reference to the drawings.

FIG. 1 is a diagram for explaining one embodiment of the waveguide element of the present invention.

FIG. 1(a) shows a waveguide element 3. FIG.

As shown in the cross-sectional view in FIG. 1(b), the waveguide element 3 has a structure in which a buffer layer 6 is provided on a semiconductor substrate 5, and an optical waveguide layer 7 is further formed on the buffer layer 6. The semiconductor substrate 5 is made of Si, GaAs, etc., but the substrate is not limited to a semiconductor substrate, and may be made of glass, ceramics, other dielectrics, or plastics.

Buffer layer 6. The optical waveguide layer 7 is formed by forming a film of a material transparent to the wavelength used, such as glass, dielectric, or plastic, by methods such as vapor deposition, sputtering, CVD, coating, oxidation, and diffusion. Of course, the optical waveguide layer 7 is the buffer layer 6.
It is configured to have a higher refractive index.

As shown in FIGS. 1(a) and 1(b), a grating coupler 8 is formed on the waveguide layer 7, and a pair of mirror portions 13a and 13b are formed on the waveguide layer 7. There is. These sill parts 13a and 13b are shown in FIG.
), the optical waveguide layer 7 is formed by cutting out the optical waveguide layer 7 perpendicularly to the surface of the optical waveguide layer up to the buffer layer 6 by a method such as etching or cutting. Schiller surface 1 where a part of each is concave
3al and 13b1.

In this example, the mirror surface is a total reflection surface that is in contact with the air, but it is also possible to coat the cross section with a metal film to make it a mirror surface, or the part created by the notch has a refractive index lower than that of the optical waveguide layer. It may be filled with material. Also, Schiller surface 13al,
Although 13bl is perpendicular to the surface of the optical waveguide layer in this example, it may be inclined with respect to the surface of the optical waveguide layer.

In this example, the grating coupler 8 is of a linear type with equal intervals, but a curved type with unequal intervals can be used instead, and a volume phase type or a blaze type can also be used. Furthermore, it is also possible to use a prism coupler instead of the grating coupler 8.

Reference numerals 10a, 10b, 10c, and 10d indicate photodetectors.

Among these photodetectors, photodetectors 10a and 10b constitute one photodetector pair, and photodetectors 10c and 10d constitute another photodetector pair.

In this example, the photodetectors 10a to 10d are made by diffusing impurities into the semiconductor substrate 5 to form photodiodes, as shown by reference numeral 10 in FIG. 1(b), but Schottky type photodiodes may be used. You can also do it.

FIG. 1(c) shows how the waveguide element 3 is used.

Reference numeral 1 indicates a light source. The light source 1 is preferably one with good coherence, such as a laser light source or a semiconductor laser, but an LED can also be used.

A light beam from a light source 1 is collimated by a collimating lens 2, passes through a half mirror 14, and is focused onto a recording surface of an optical information recording medium 12 by an objective lens 4. The reflected light beam from the recording surface enters the half mirror 14 via the objective lens 4, and the component reflected by the half mirror 14 is optically coupled to the optical waveguide layer 7 by the grating coupler 8.

Collimating lens 2. The objective lens 4 is not limited to a single lens as shown in the figure, but may be a combination of lenses, and a Fresnel lens, a distributed refractive index lens, or the like may be used in addition to a normal lens. Furthermore, instead of the half-shiller 14, a combination of a polarizing beam splitter and a quarter-wave plate may be used.

The light beam optically coupled to the optical waveguide layer 7 is guided within the optical waveguide layer 7, a portion of which is reflected by the mirror surface 13a1, and the remainder of which is reflected by the mirror surface 13bl.

The light beam reflected by the mirror surface 13a1 is reflected by the mirror surface 1
Due to the action of 3Aal as a concave mirror, it becomes a convergent light beam sandwiched between light rays A and B, and is focused toward the photodetectors 10a and 1Ob.

The light beam reflected by the mirror surface 13b1 becomes a convergent light beam sandwiched between the light beams C2D and is transmitted to the photodetector 10C910d.
The light is focused towards the photodetector.

The light beam guided through the optical waveguide layer 7 is guided by the mirror surface 13al,
Before being reflected by 13bl, it is a single beam having a principal ray, but by being reflected by a pair of mirror surfaces 13al and 13bl, it is separated into two convergent beams. At this time, the separation is performed along the principal ray, and after being reflected by the mirror surface 13a1, the principal ray becomes a ray A, and after being reflected by the mirror surface 13b1, it becomes a ray A. That is, ray A,
D is the above-mentioned "principal ray in each divided luminous flux".

The photodetectors 10a and 10b detect when the light flux irradiating the optical information recording medium is correctly "focused" on the recording surface.
“The light flux reflected on the mirror surface 13a1” is detected by the photodetector 10
The deployment position is determined so as to converge at an intermediate position between a and 10b. At this time, the light beam optically coupled to the optical waveguide layer 7 is a parallel light beam.

Similarly, the photodetectors 10a and 10b are positioned so that the light beam reflected on the mirror surface 13b1 in the "focused" state is focused at an intermediate position between the photodetectors 10c and 10d. There is. Photodetectors 10a, 10b, 10
The outputs from c, 10d are a, b, c, respectively.
Let it be d.

When the distance between the recording surface and the objective lens 4 becomes smaller than the "focusing distance", the light beam optically coupled to the optical waveguide layer 7 is slightly divergent, and the convergent light beam reflected by the Schiller surfaces 13al and 13bl is converged. The position is displaced in a direction away from each mirror surface from the focusing position in the "in-focus state", and as shown in FIG. It becomes larger than the amount of light received. On the other hand, when the distance between the recording surface and the objective lens 4 is larger than the "focusing distance", the light beam coupled to the optical waveguide layer 7 is slightly convergent, and the focus position of the light beam reflected by the mirror surfaces 13al and 13bl is is displaced in a direction closer to each Schiller surface than the focusing position in the "in-focus state", and as shown in FIG. 2(b), the amount of light received by the photodetectors 10b and 10c is
The amount of light received at a and 10d is smaller.

Therefore, the focus detection signal (a+
d) - (b + c), this focus detection signal will be O when the distance between the recording surface and the objective lens 4 is smaller (-) than the "focusing distance", when it is larger (+), and in the focused state. Become. Therefore, focus control can be performed by servo driving the objective lens 4 so that this focus detection signal becomes O.

FIG. 3(a) is an enlarged view of the vicinity of the photodetectors 10a to 10d. As described above, the "principal ray in the divided beam" that is focused toward the photodetector pair by the photodetectors 10a and 10b is the ray A. Photodetector 10c
, 10d, the "principal ray in the split beam" focused toward the photodetector pair is a ray as described above. These principal rays A and D do not change whether the light beam optically coupled to the optical waveguide layer 7 is a parallel light beam, a convergent light beam, or a diverging light beam.

The edge of the light beam converged toward the pair of photodetectors by the photodetectors 10a, 10b is formed with the principal ray A.Light ray B1 is the edge of the beam focused toward the pair of photodetectors by the photodetectors 10c, 10d. The light ray C formed with the above-mentioned principal ray changes as shown in (1), (2), and (2) depending on whether the state of the light beam when optically coupled to the optical waveguide layer 7 is convergent, parallel, or divergent. Accordingly, the focusing position of the light beam is the above-mentioned chief ray A.
, D, but since the chief rays A and D are substantially parallel, the distance between the focusing positions of each light beam hardly changes.

Therefore, even if the position of the waveguide element 3 is slightly tilted with respect to the light beam incident on the waveguide element 3, the change in the interval between the focusing positions of each light beam converging toward each photodetector pair is small, and the waveguide element 3 3 has a large tolerance for "tilt" errors, and the grating coupler 8, mirror surfaces 13al, 13b
l. It is also easy to correct mutual placement errors among the photodetectors 10a to 10d.

On the other hand, as shown in FIG. 3(b), if the chief rays A and D in each divided beam are at a constant angle, the beam converging towards each photodetector pair will be Since the distance between the focusing positions changes depending on the state of the light beam optically coupled to the optical waveguide layer (focusing, divergence, parallelism), the tolerance for the "tilt" error of the waveguide element 3 becomes extremely strict, and the grating coupler 8 , mirror surfaces 13al, 13bl
, it becomes almost impossible to correct mutual arrangement errors among the photodetectors 10a to 10d.

In order to make the chief rays JA and D in each divided light beam substantially parallel to each other by being reflected by a pair of mirror surfaces, the mirror surfaces 13al and 13bl for the principal rays of the mirror surfaces 13al and 13bl are used. It is sufficient if the reflection angles at are substantially equal to each other.

Note that signals (
a+b)-(c+d), this signal can be used as a track control signal in the well-known bush-pull method.

Furthermore, the signal (a+b+c+d) may be used as the RF signal.

FIG. 4 shows another embodiment. In order to avoid complexity, the same reference numerals as in FIG. 1 are used for items that are not likely to be confused with each other.

In this embodiment, the left half of the light beam optically coupled to the optical waveguide layer 7 of the waveguide element 3A is reflected by the mirror surface 13:1 and is directed toward a pair of photodetectors 10a and 10b. The right half is reflected by the mirror surface 13° and focused toward a pair of photodetectors 10c and 10d. The principal rays in each beam divided by l pairs of mirror surfaces are rays B1 and C1,
Mirror surfaces 13°, 1
．． 13't, the attitude of 1 is set.

In this example, the aforementioned focus detection signal and track control signal have opposite signs to those in the embodiment shown in FIG.

Fifth, another embodiment is shown.

In this embodiment as well, the same reference numerals as in FIG. 1 are used for parts that are unlikely to be confused with each other.

In this embodiment, the entire waveguide element 3B is optically transparent, at least in the portion where the grating coupler 8 is provided. The light beam from the light source 1 passes through the waveguide element 3A while remaining diverging, and is transferred to the optical information recording medium 1 by the objective lens 4A.
The light is focused on the recording surface of No. 2. The reflected light beam from the recording surface becomes a convergent light beam by the objective lens 4A, and is optically coupled to the optical waveguide layer 7 by the grating coupler 8.

The optically coupled light beam is split into two by a pair of mirror surfaces, and the principal rays of each split light beam are reflected so that they are approximately parallel to each other, and are transmitted to two photodetector pairs 10' (by α-3i etc.). Although the photodiode is a photodiode, it may be an impurity-diffused photodiode similar to the embodiment shown in FIG. 1).

In this example, the light beam optically coupled to the optical waveguide layer 7 is already convergent at the time of optical coupling, so the mirror surface does not necessarily have to be concave, but the mirror surface shape can be a planar shape. Also good.

The planar configurations of the waveguide elements shown in FIGS. 1, 4, and 6, which will be described later, can also be used in the manner shown in FIG. 5 if the portion where the grating coupler is provided is made light-transmissive.

FIG. 6 shows two other embodiments.

The feature of the example shown in FIG. 6 is that the mirror surface 13 of a part of the mirror
al', 13bl', 13al'', 13b
1" is a metal reflective surface loaded with a metal film. Regarding the arrangement of a part of the mirror, the arrangement of FIG. 6(a) is the same as the example of FIG. 4, and the example of FIG. 6(b) is the same. This corresponds to the example in Figure 1.

In the example of FIG. 6(a), the principal rays in each divided luminous flux are rays B2. C2, and in the example of FIG. 6(b), ray A3
゜D3, and the mirror surface 1 is adjusted so that these are approximately parallel.
3al', 13bl', 13al'', 13
bl'' attitude is set.

When the mirror surface is made of a metal reflective surface as in these examples, the reflection angle can be made smaller than when the mirror surface is made of a total reflection surface, so there is a greater degree of freedom in arranging the optical elements.

Furthermore, the two examples of waveguide elements shown in FIG. 6 can be used in the same side view arrangement as in FIG. 1(b), and the portion where the grating coupler is formed is optically transparent in the thickness direction. With this configuration, it can also be used in a side view arrangement as shown in FIG.

In addition, the arrangement of the two photodetectors constituting the photodetector pair was changed to
As shown in the figure, one photodetector 10AI may block the light ray A0 directed toward the other photodetector 10BI.

In this way, when two photodetectors are arranged in parallel to form a photodetector pair as in the example shown in FIG. 1, the influence of the gap between the photodetectors can be eliminated, so that even higher sensitivity can be achieved. Such a photodetector arrangement is applicable to all the embodiments described above.

[Effects of invention As described above, according to the present invention, a novel waveguide element can be provided.

Since this waveguide element has the above configuration,
It is easy to correct the inclination of the waveguide element with respect to the incident light beam, and the positional accuracy of the optical elements within the waveguide element can be made looser than in conventional elements.

Further, when the mirror surface is given the effect of a concave mirror, the focal length of the mirror surface does not change depending on the wavelength, so that stable focus detection is possible even with wavelength fluctuations in the light source.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining one embodiment of the present invention, FIG. 4 is a diagram for explaining another embodiment, and FIG. 5 is a diagram for explaining another embodiment, FIG. 6 is a diagram for explaining another embodiment, and FIG. 7 is a diagram for explaining still another embodiment. 380. Waveguide element, 13al, 13b1. ,, Mira part, A, D. Figure 2 Figure 3 (a) Figure Figure 3

Claims (1)

[Claims] A light beam from a light source is focused on a recording surface of an optical information recording medium to record and/or reproduce optical information, and a reflected light beam from the recording surface is optically coupled to an optical waveguide layer. , a focus detection method in which the optically coupled light beam is divided into two within the optical waveguide layer, and each of the two divided light beams is focused on a pair of photodetectors integrated with the optical waveguide layer to perform focus detection. The waveguide element used has a pair of mirror surfaces integrally formed in the optical waveguide layer, and the pair of mirror surfaces divides the light beam guided into the optical waveguide layer into two along the principal ray. At the same time, each of the divided luminous fluxes is reflected toward each of the photodetector pairs, and the directions of the principal rays in each of the divided luminous fluxes are arranged so as to be substantially parallel to each other. waveguide element.