JPS6295504A - Optical waveguide circuit - Google Patents

Abstract

PURPOSE:To improve operation efficiency by slanting optical waveguide end surfaces so that they cross each other in the prolongation direction on the substrate, and reflecting totally a light wave propagated in the optical waveguide by the slanting and surfaces. CONSTITUTION:Both end surfaces of the optical waveguide circuit are so slanted as to have a side crossing the top surface of the waveguide on the top surface and cross each other in the prolongation direction on the substrate side. Further, those slanting surfaces should reflect the propagated light to the other end part totally, so they are formed at 45 deg. to the waveguide. Light emitted at the light emission position 6 of a light emitting element 4 is incident on the waveguide 2 at right angles, reflected totally by slanting surface 3a in a direction L1, and then re-reflected totally by the other slanting surface 3b after being propagated in the waveguide 2 to reach the photodetection position 7 of a photodetecting element 5 provided at the other upper end part of the waveguide 2. Consequently, an optical fiber and the light emitting and photodetecting elements are coupled optically with easy and their positioning is also facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical waveguide circuits. More specifically, optical fibers, light emitting and
The present invention relates to an optical waveguide circuit for optically coupling with a light receiving element.

BACKGROUND OF THE INVENTION Recent developments in optical communication systems using optical fibers have been remarkable. In order to configure this optical communication system, in addition to light emitting and light receiving elements, various optical components such as optical modulators, optical switches, optical branching/coupling devices, optical multiplexers/demultiplexers, and optical filters are required. Optical coupling between optical components and optical fibers is required.

In early optical communication systems, the above-mentioned optical components were used as lenses,
It was composed of a combination of mirrors, prisms, etc. Optical coupling between such optical components and optical fibers is relatively easy, but optical devices constructed from conventional optical components such as lenses, mirrors, and prisms are large and
Furthermore, it is expensive, difficult to miniaturize, and furthermore difficult to provide sufficient mechanical stability and high reliability required for optical communication devices.

For example, it is often necessary to align the optical axis, and the optical axis tends to be distorted due to the influence of external forces such as vibrations, so it is necessary to re-align each time.

Therefore, an optical waveguide circuit was developed as a new optical system in which an optical waveguide is formed on a substrate. In this optical waveguide circuit, an optical waveguide made of a material with low optical loss and a high refractive index is provided on a substrate by, for example, a diffusion method or a deposition method, and light is propagated within the optical waveguide. In addition, this device can be used to construct a lens or prism by changing the thickness of a part of the optical waveguide, or to construct an optical modulator by applying an electric field to the optical waveguide by providing an electrode. Since it can be formed on a substrate, it has the possibility of multifunctionality.

Furthermore, in the optical waveguide circuit, it is possible to realize a so-called optical integrated circuit in which several optical elements are integrated in a hybrid or monolithic manner. For this reason, expectations have arisen for optical circuits to be smaller, lower in price, higher in performance, higher in reliability, etc., and research and development of optical waveguide circuits are being actively conducted in various fields.

Problems to be Solved by the Invention In order to introduce or extract light into or out of the optical waveguide of such an optical waveguide circuit, it is necessary to optically couple the optical waveguide to an external optical transmission line or a light emitting/light receiving element. . Optical fibers are most commonly used as external optical transmission lines. Usually, these optical couplings are performed by abutting the polished end face of the optical fiber against the end face of the optical waveguide. Furthermore, coupling with light emitting and light receiving elements is similarly achieved by abutting these elements against the end face of the optical waveguide.

However, the size of the optical waveguide is generally extremely small, and for example, when using single mode light with a wavelength of 1 μm, it is necessary to make the size of the optical waveguide about 10 μm or less. Therefore, it is necessary to align the end faces of the optical waveguide and the optical fiber or the light emitting/receiving element with high precision. That is, if this alignment is insufficient and axis misalignment occurs, the degree of coupling will decrease, resulting in a large coupling loss.

By using optical waveguide circuits in this way, it is possible to achieve miniaturization of optical devices such as optical integrated circuits, but on the other hand,
There is a problem in that an operator must perform extremely high-precision positioning, which requires a great deal of effort, in order to connect the optical fiber as an optical transmission path and the light-emitting/light-receiving element. Such alignment becomes necessary each time an axis misalignment occurs due to the action of an external force, and the burden on the operator becomes even heavier.

Therefore, it is necessary to develop a method that can relatively easily perform highly accurate positioning and maintain stable coupling even against external forces. Conventionally, the methods shown in the attached Figures 3 and 4 have been proposed for this purpose (Confucian-type wave light, 1985,
(See Nα1007 and No. 1008).

That is, as can be understood from FIG. 3, the first method is to integrally form a silica-based waveguide 11 and a reflector guide 12 on a silicon (Sl) substrate 10. The system waveguide 11 and the receiving/emitting element 13 are coupled using a reflecting mirror 14. In addition, the second method
As is clear from the figure, a quartz-based waveguide 11 and a laser diode (LD) guide 15 are similarly formed integrally on a Si substrate 10, and a quartz-based waveguide 11 and a laser diode (LD) as a light emitting element, for example, are integrated. ) 16 are combined as shown in the figure.

However, although these conventional methods improve the alignment accuracy and miniaturization to some extent, they cannot be applied to embedded waveguides, and have problems with waveguides. The versatility is extremely low, and in such a case, optical coupling must still be performed by end-face butting, as shown in the attached FIG. 5. That is, when using a buried waveguide 2 formed on a substrate 1, a light emitting element 4 having a light emitting position at position 6 and a light receiving element 5 having a light receiving position at position 7 are placed at their respective positions. , and are coupled by abutting against the end face of the buried waveguide.

With this type of end face coupling method, there is a high possibility that axis misalignment will occur when fixing the light receiving/emitting element, and it is also easy to cause axis misalignment due to external forces such as vibration, so alignment (alignment) must be performed each time. Therefore, workability becomes extremely poor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical waveguide circuit that has a low possibility of axis misalignment even when an embedded waveguide is used, and can therefore improve work efficiency. It is also an object of the present invention to provide a method for producing the same.

Means for Solving the Problems In view of the current state of conventional methods as described above regarding coupling between optical waveguides, optical transmission lines, and light-receiving/emitting elements, the present inventors have proposed the following.
As a result of various studies in order to realize an optical waveguide circuit structure useful for solving problems such as axis misalignment and connectivity with embedded waveguides, we found that the ends of the optical waveguide are tilted at a predetermined angle. The present invention was completed based on the discovery that it is advantageous to make the inclined surface capable of total reflection.

That is, the present invention relates to an improvement in the structure of an optical waveguide circuit, particularly an embedded type waveguide circuit, and the cough waveguide circuit has a substrate and a waveguide provided on the substrate, and both end surfaces of the waveguide are provided. is characterized in that it is composed of inclined surfaces that intersect with each other in the direction of extension on the substrate side.

The optical waveguide circuit of the present invention has, for example, a configuration as shown in the attached FIG. Each of the waveguides has a side perpendicular to the upper surface of the waveguide, and is an inclined surface that intersects in the direction of extension on the substrate side. Most preferably, these are inclined at an angle of 45° to the top surface of the waveguide. In other words, this corresponds to forming a right-angled prism on each end face of the waveguide.

In the present invention, the substrate and waveguide materials are not particularly limited, and any of various conventionally known materials can be used.

For example, as the substrate material, LiNb0=, quartz, silicon, or sapphire, or even a polymer resin, etc. are used, and as the waveguide material, when the substrate is formed of a 5iO7-based material, a refractive index increasing dopant, For example, P,
It may be SiC2-based glass containing Ge, Ti5Ta, Sb, etc., or if the substrate is plastic, it may be glass (that is, so-called plastic clad type). Furthermore, it may be a plastic waveguide circuit in which both the substrate and the waveguide are made of plastic, such as PMMA (polymethyl methacrylate) and tetrafluoroethylene vinyldene fluoride, polystyrene resin and PMMA, heavy water poisoned PMMA and fluoroalkyl methacrylate, etc. Various combinations of (#J is the waveguide material and the latter is the substrate material) can be used.

The waveguide circuit of the present invention is made of these materials, for example, when the substrate is a 5102-based material, a predetermined waveguide pattern is formed on the surface of the substrate using a resist using IJ sogelaf, and then a refractive index increasing agent is applied. After depositing by evaporation, etc., and thermally diffusing the deposit, the end face is polished at a 45° angle using a sharpener.
It can be obtained by doing diagonal research. In addition, a predetermined waveguide pattern is obtained using a resist on the substrate surface by photo-etching, then etching is performed to form a groove for the waveguide, a high refractive index material is deposited there by a vapor deposition method, and then a lift-off method is performed. A method such as forming a waveguide and forming an inclined surface using the Kensho method, or in the case of a plastic clad type, by forming the waveguide material into a predetermined shape in advance and molding it with the desired mold. You can also get it.

The optical waveguide circuit of the present invention may have various shapes, and in particular, it may be an embedded two-dimensional waveguide (planar waveguide) or a three-dimensional waveguide, and the general form of its transmission may also be a single waveguide. It may be either mode type or multimode type.

As the polishing method for forming the inclined surface, which is characteristic of the method of the present invention, for example, mechanical stability using alumina powder or diamond powder can be used, and various etching methods can also be used in combination. It is.

The optical waveguide circuit of the present invention is assembled with a light emitting element 4 and a light receiving element 5 or an optical fiber as an optical transmission line as shown in FIG. Used in contact. Although FIG. 2 shows an example of a light emitting/light receiving element, optical coupling can also be realized by using an optical fiber instead of these and bringing the end face of this optical fiber into contact with the upper end face of the waveguide 2.

As described in detail above, there are problems in classical optical waveguide circuits: (i) requirements for alignment accuracy between end faces of optical waveguides and optical fibers, or light emitting and light receiving elements (axis misalignment); (ii) Mechanical stability of the coupling part, for example, axis misalignment due to vibration, readjustment of the optical axis, (City) Requirements for miniaturization of optical circuit components, etc. can all be achieved using the optical waveguide circuit of the present invention. By doing so, it is possible to improve.

By the way, the above problem could be solved by adopting the configurations shown in Figures 3 and 4, but in these cases, it is difficult to apply the configurations to waveguides of different shapes, especially embedded waveguides. When doing so, each of the above-mentioned problems became apparent and the results were not satisfactory.

However, by using a waveguide circuit having a specific end face shape according to the present invention, all of the above problems could be advantageously solved. That is, in the optical waveguide circuit of the present invention, both end faces are formed by sloped faces having sides perpendicular to the top surface of the waveguide and intersecting with each other in the direction of extension on the substrate side.

Furthermore, since this inclined surface must be able to totally reflect the propagating light toward the other end, the inclined surface is formed at an angle of 45° with respect to the waveguide.

When using an optical waveguide with such a configuration, as shown in FIG. 2, highly accurate positioning can be achieved simply by abutting the end face of the optical fiber or the light emitting/receiving element against the end of the top surface of the waveguide. Furthermore, even if axis misalignment occurs due to vibration or the like, readjustment can be carried out extremely easily. Incidentally, the axis misalignment caused by this external force can be completely avoided by bonding the waveguide and the end face of the optical fiber or the light emitting/receiving element with a suitable adhesive or the like.

When such a waveguide circuit is used, for example, light emitted from the light emitting position 6 of the light emitting element 4 enters the waveguide 2 at right angles, and is totally reflected by the inclined surface 3a in the direction of After propagating through the waveguide 2, it is totally reflected again on the other inclined surface 3b, and reaches the light receiving position 7 of the light receiving element 5 provided at the other upper end of the waveguide 2. This is exactly the same in the case of coupling with optical fiber.

Although the buried waveguide has been explained above, the conventional third waveguide
The same effect can be achieved by forming the end faces of three-dimensional waveguides as shown in Figures 1 and 2 with inclined surfaces as shown in Figures 1 and 2. There is no need to form a reflective mirror guide or LD guide with a specific shape, which simplifies the manufacturing process and is advantageous in terms of cost.

EXAMPLES Hereinafter, the optical waveguide circuit of the present invention will be explained in more detail based on Examples (manufacturing examples), but the scope of the present invention is not limited by the following examples.

Production Example Using Z-cut LiNbO3 as a substrate, Ti was deposited as a contact ratio increasing agent in a predetermined waveguide pattern on the substrate according to a vapor deposition method, and thermally diffused to form a buried optical waveguide. The side surfaces of the substrate including both end surfaces of the waveguide were polished obliquely at an angle of 45° to the top surface of the waveguide using a polisher.

In the thus produced optical waveguide circuit, 0In was added as a light emitting element.
InGaA as GaAs P LD and photodetector
Optical coupling was carried out as shown in FIG. 2 using PIN-type photodiodes of 3.5 mm. When coupling loss was measured for such an optical coupling system, the loss was 0.5 dB.

Effects of the Invention As explained in detail above, the optical waveguide circuit of the present invention solves various problems of conventional products based on the unique feature that both end faces of the waveguide are composed of inclined surfaces capable of total reflection. It became possible to do so.

First, optical coupling with optical fibers and light-emitting/light-receiving elements is extremely easy, and alignment is also simplified.

That is, in the conventional device, it was necessary to take the trouble to provide an LD guide, a reflector guide, etc., which not only complicated the manufacturing process but also was disadvantageous in terms of cost.

In addition, it can be easily readjusted even if the axis is misaligned due to external force, and if the waveguide, optical fiber, and light emitting/receiving element are bonded together, it is completely stable even under the action of external force such as vibration. High reliability of coupling can be maintained.

Furthermore, in the configurations and combinations shown in FIGS. 3 and 4, it was necessary to use an end face connection method for embedded waveguides as in the case of classical optical couplers, but the present invention The optical waveguide circuit is highly versatile and can achieve constant and highly reliable optical coupling regardless of the shape of the waveguide.

Therefore, according to the present invention, it is possible to provide a low-cost, versatile, and easily aligned optical waveguide circuit, which can fully meet the demands for miniaturization.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a preferred example of the optical waveguide circuit of the present invention, and FIG. 2 is a diagram of the optical waveguide circuit of the present invention shown in FIG. 1 with the light emitting and light receiving elements fixed. FIG. 3 is a cross-sectional view taken along the waveguide, FIGS. 3 and 4 are perspective views for explaining conventional optical waveguide circuits, and FIG. 5 is a conventional optical coupling in a buried waveguide. FIG. 2 is a schematic cross-sectional view for explaining. (Main reference numbers) 1...Substrate, 2...Embedded waveguide, 3a, 3b...Slanted surface, 4...Light emitting element, 5...Light receiving element, 6...Light emitting position,

Claims (3)

[Claims] (1) In an optical waveguide circuit comprising a substrate and an optical waveguide formed on the substrate and optically coupled to an external optical fiber or a light emitting/light receiving element, the end surfaces of the optical waveguide are mutually disposed in the extending direction on the substrate side. The optical waveguide circuit is inclined so as to intersect with the optical waveguide, and the inclined end face totally reflects a light wave propagating through the optical waveguide. (2) The optical waveguide circuit according to claim 1, wherein the optical waveguide is a buried waveguide. (3) The optical waveguide circuit according to claim 1, wherein the optical waveguide is a three-dimensional optical waveguide.