JPS59116705A - Optical mixing coupler and its production - Google Patents

Abstract

PURPOSE:To provide an optical mixing coupler which provides a high mixing effect of light with high accuracy although it is small in size by constituting the coupler of a mixing part consisting of a single path located at the center of a transparent base plate and branch parts branching to plurality from both ends thereof. CONSTITUTION:A waveguide 2 having roughly a circular sectional shape and consisting of a region having the larger refractive index than the refractive index in the base plate part is provided integrally in a transpreant base plate 1. The waveguide is constituted of a mixing part 2B of the final stage consisting of a single path at the center of the substrate and branch parts 2A branching to plurality from both ends toward both side faces 1A, 1B. The transmitted light from the path 4A is successively joined in the unit of the two paths and is finally mixed in the part 2B. The mixed light is successively divided in the pattern symmetrical to the above by the waveguides 6A, 5A, 4A and is connected to a prescribed number of optical fiber groups 3 in the branch path 4B in the final stage. The core diameter in the mixing part is approximately equal to the core diameter in the connecting fibers and therefore the uniform mixing of the light is surely accomplished in the short distance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coupler that connects two sets of optical fibers and mixes the light transmitted through one set of optical fibers before sending it to the other set of optical fibers.

Conventionally, optical mixing couplers have been used with fiber bundles (arrayed) connected to the input side and output side as shown in the figure.
/3. A mixing waveguide with a width of /lI and a thickness equivalent to the fiber core diameter/! ;'1-11 It is formed from a solid dielectric flat plate such as lath, and this is made of a side plate made of a polymer material.
/B has been reported to have been glued together. This method is not fully satisfactory in terms of reliability, accuracy, transmission loss performance at fiber connections, etc., and has many problems.

Furthermore, as shown in FIG. 2, it has been proposed that branched waveguides for input and output are provided at both ends of the mixing coupler 15 at intervals in the width direction; A mixing waveguide section with a width equal to n waveguides is required, and in order to mix the lights from these n waveguides so that they have equal intensities in the width direction, the mixing coupler must be quite long. Become.

There is also a method of creating a mixing section by bundling two or more fibers together, twisting them in a heated, softened state, and fusing them together.
This poses a problem in terms of reliability because the shape of the optical transmission section deforms into an unexpectedly complicated shape.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a high-precision optical mixing coupler that is small but has a high light mixing effect.

Another object of the present invention is to provide a method by which the above-mentioned mixing coupler can be mass-produced at low cost and with stable quality.

The optical mixing coupler of the present invention which achieves the above object integrally forms in a transparent substrate a waveguide consisting of an area having a substantially circular cross section with a refractive index higher than that of the surrounding area, and the waveguide is located at the center. It consists of a mixing section consisting of a single path and a plurality of branch sections each branching from this mixing coupler and reaching each of the opposite sides of the substrate, and the diameter thereof extends over the entire length of the waveguide and is equal to the core diameter of the optical fiber to be connected. are configured almost identically.

In the above configuration, in a preferred embodiment, the branching portion of the waveguide is such that the number of branches at all branching points of the waveguide is unified to three, and the number of branches at all branching points of the waveguide is unified to three, and Il[α Next, form two branches each.

As a result, the light entering the branch waveguide of the substrate from the optical fiber connected to the end of the substrate is sufficiently uniformly mixed with the light from the two sets of fibers in a single path approximately equal to the core diameter of the fiber, and then In this mixed transmission light, other 7
The mixed light from the pair of fibers is added sequentially as it progresses through the waveguide, and finally the light introduced through the three paths is mixed in the single-path mixing section. Furthermore, the light mixed in the mixing section branches into three paths at each branch point and reaches the other end, as described above, before branching into a group of fine lights connected to the other end surface of the substrate.

In the present invention, it is of course possible to configure the present invention so that three or more branching paths branch out from the seven branching points, in addition to the two described above.

However, if the number of branches from the seven branch points increases too much, the angle between the outermost branches will become large, and a relatively long waveguide will be required for uniform mixing. The former bifurcated unit structure is desirable for compactness.

According to the optical mixing coupler of the present invention, since the light introduced from the branching section is mixed in the mixing section having a diameter approximately equal to the core diameter of the connecting fiber, uniform mixing is reliably performed over a short distance.

Furthermore, since the branching section and the mixing section are integrally formed within a single substrate, the structure is very simple, and assembly work such as fiber connection is very easy and easy to handle.

Furthermore, as will be described later, a manufacturing method was used in which the surface of the substrate glass was masked leaving an opening for the waveguide pattern, and during this time, ions that increased the refractive index of the substrate glass were diffused and penetrated through L1 to form a waveguide. In this case, in the product of the present invention, the entire waveguide including the mixing section has a uniform diameter, so
Since the opening width of the mask for preventing ion transmission is uniform, the depth of ion diffusion and penetration is uniform over the entire length of the waveguide.

Therefore, almost no optical loss occurs at the connection point between the branching part and the mixing part, and the propagation loss can be kept very small over the entire length.

Next, the present invention will be described in detail with reference to the embodiments shown in the drawings.

FIG. 3 is a plan sectional view of the light mixing section (7) according to the present invention, and FIG. 1 is a side view. It is a region where the refractive index is higher than that of the other parts, for example, the refractive index at the center is maximum and it is provided in a para-integral manner toward the periphery.

The waveguide has a single-path final stage mixing section 2B in the center of the substrate, and branches from both ends of this mixing section 2B into a plurality of branches to reach /B on both opposing sides 7 of the substrate. It is composed of 2 parts and 2 parts.

The waveguides in our branch section located on one side of the mixing section 2B are an even number of inlet paths arranged parallel to each other at intervals with their ends exposed on both sides of the substrate /A and /B. A.
. . ., an O/stage merging path tA that merges the transmitted light from these introduction paths 5A in units of three paths, and further the transmission light from these merging paths 5A... It is composed of off-stage merging paths g that merge in three-way units, and in this way, the waveguides are sequentially merged in three-way units to form the final-stage merging path +A as three paths, and these two final-stage branch paths The transmitted light from A is finally mixed in a mixing section 2B.

This mixed light is then sequentially divided by waveguides arranged in a pattern symmetrical to that described above.

In other words, the mixed light from the mixing section 2B is divided equally by the three-way off-stage branch path B-6B, and the transmitted light from each off-stage branch path B-6B is divided into three paths by the first-stage branch path 5B. In this way, they are sequentially branched into three paths at one branch point 7, and connected to a predetermined number (even number) of optical fiber groups 3 at the final branch path <zB.

Here, as shown in Fig. 5, if the branching angle θ formed by the two branching paths at each of the seven branching points is too large, the mixing efficiency after merging will deteriorate and light loss will occur, so it is preferably 50. It is more preferable to set it to 70 or less. In addition, the shape of the waveguide after branching has a gentle curvature R.
It is desirable to provide.

In the present invention, the plane pattern of the branching road is not only a symmetrical 7-shaped pattern as shown in Fig. 5, but also a straight line running through one branching road from before the branch as shown in Fig. The other branch path may be formed into a branching shape.

The inventors' experiments have confirmed that when the branching angle θ is sufficiently small, there is almost no difference in the light mixing uniformity (light distribution within the cross section of the mixing path) regardless of the shape. .

Next, a preferred method for manufacturing the optical mixing coupler of the present invention will be explained using off-line diagrams.

First, a transparent substrate 3/ made of alkali-containing glass, such as alkali borosilicate glass, is prepared, and one side of this substrate is formed into a desired Gi waveguide pattern, for example, the pattern shown in FIG. The opening 33 is left and covered with a mask 32 for preventing ion transmission.

- As an example, the thickness of the substrate 3/ is 3 mm, the width of the pattern opening 33 is approximately S μm, the branch angle θ of all branch points 7 is 102, the radius of curvature R of the waveguide near the branch point is IIQ
Let it be mm.

In addition, the mask 32 is made of metal such as titanium using the high frequency spackle method! The film is formed to a thickness of about μm, and a part of this film is etched using a well-known photolithography technique to form a desired pattern opening 33. Next, mask 32
The surface side of the substrate is immersed in a bath of molten salt lI3 containing ions having a large electronic polarizability and contributing to an increase in the refractive index of the substrate glass.

As this salt II3, a nitrate or sulfate containing at least one of thallium (Tl) ions, cesium (Cs) ions, and silver (Ag) ions can be used.

Next, the electrode I1.2 is closely attached to the opposite side of the mask surface of the glass substrate 3 via a conductive paste layer made of a paste of clay and KNO3, for example. is connected to the cathode side of the DC power source 3, and the electrode 1/ provided in the molten salt 3 is connected to the anode of the power source 1 to apply a DC voltage. When the temperature of the molten salt 13° glass substrate 3/ is set to, for example, SSO''C, which is lower than the softening humidity of the substrate glass, and a DC voltage of, for example, 5 cm is applied for several minutes, a semicircular high refractive index is formed in a cross section perpendicular to the glass substrate surface. The layer / is obtained.

This high refractive index portion 5'/ is formed by replacing the seven-valent ions in the substrate glass with ions that contribute to increasing the refractive index of the glass, such as thallium ions in the molten salt 13, and It has a refractive index distribution such that the refractive index is maximum immediately below and gradually decreases in the radial direction around the above point.

The width of the high refractive index portion 51 formed as described above on the substrate surface is approximately jOμm in the numerical example described above.

In addition to promoting ion exchange by applying an electric field between both surfaces of the substrate, it is also possible to use an ion exchange method using natural diffusion without applying an electric field.

Next, the mask 3.2 on the glass substrate 3/surface is removed by etching, polishing, etc., and the substrate surface on the side of the high refractive index portion 1 is treated with an IJ that has a small electronic polarizability, that is, it has a small contribution to increasing the refractive index with respect to the substrate glass. When a DC voltage is applied at high speed and an ion exchange process is performed for about 100 minutes using SV, for example, to diffuse the ions S2 into the substrate, a substantially circular waveguide 53 is formed in a cross section perpendicular to the substrate surface. The diameter of this waveguide 53 is approximately 50 μm in the above numerical example.
It is.

Next, the glass substrate is taken out from the molten salt and cut into a predetermined size, and then the side surfaces are polished to a smooth surface.

In the manner described above, an optical mixing coupler having the waveguide pattern shown in FIG. 3 can be obtained.

According to the experimental results, a graded index fiber 3 with a core diameter of jOμ and a refractive index difference of 7% between the center and the outer periphery was placed on each side of the above mixing coupler /A,
/B, wavelength 0. The insertion loss of the coupler was investigated by measuring the emitted light of 3 μm in diameter.As a result, a low loss of approximately /dB and a nearly uniform light intensity was obtained in all g fibers.

According to the method described above, by using a large motherboard, it is possible to manufacture a large number of mixer coverrs at once in seven processing steps, resulting in extremely high productivity and less variation in quality between products. suitable for production.

[Brief explanation of drawings]

1 and 2 are plan sectional views showing a conventional optical mixing head; FIG. 3 is a plan sectional view showing an embodiment of the present invention; FIG. 1 is a side view of the same; and FIG. FIG. 6 is a plan view showing an example of a branch shape of a waveguide, and FIG. 6 is a plan view showing another example of a branch shape. Figure 7 is a side sectional view showing step-by-step an example of a method for manufacturing the optical mixing head of the present invention. Board.../, 3/, 2.33...
...Waveguide, 2A...Branch section 2B...
...Mixing section 3 ... Optical fiber 7 ... Branch point 32 ...
Mask 33......Opening/, 4', 2
...... Electrode '73... Molten salt 5
／・・・・・・・High refractive index part 3.2・・・・・・・
・Ion Figure 1 Figure 3 Figure 5 (A) (B) Figure 6 (D)

Claims (1)

[Claims] 1) A mixing device in which a waveguide consisting of a region having a refractive index higher than the surrounding area and having a substantially circular cross section is integrally formed in a transparent substrate, and the waveguide consists of a single path located at the center. The mixing part is composed of a plurality of branching parts each branching from both ends of the mixing part and reaching each of the opposite sides of the substrate, and the diameter thereof is made almost the same as the core diameter of the optical fiber to be connected over the entire length of the waveguide. An optical mixing coupler 02, characterized in that, in the claims, the number of branches at all branch points of the waveguide is unified to three, and the number of branches at all branch points of the waveguide is unified to three, and the interval is An optical mixing coupler configured to sequentially branch into two branches at a time. 3) Cover the surface of the glass substrate with an ion transmission prevention mask while leaving an opening in the predetermined optical path pattern, and cover the surface of the glass substrate with an ion transmission prevention mask that contributes to an increase in the refractive index of the substrate glass to a greater extent than the ions in the substrate, and contacting the mask surface with an ion source containing exchangeable ion gates and diffusing ions in the ion source into glass through the mask openings; and removing the mask; On-off ion exchange in which the substrate surface is brought into contact with an ion source containing ions that contribute less to the increase in the refractive index of the substrate glass than the ions in the ion source in the off-ion exchange step and that can be exchanged with the ions in the glass. A method for manufacturing an optical mixing coupler, comprising the steps of: