JPS6269211A - Optical branching device - Google Patents

Abstract

PURPOSE:To reduce crosstalk by arranging a reflector on a specific diagonal of the crossing area of a main waveguide part and branch waveguide parts. CONSTITUTION:A branch waveguide part 12 crosses the main waveguide part 11 and the crossing area 13 of those main waveguide part 11 and branch waveguide part 12 form a parallelogram optical branching device. The reflector composed of an interference film filter 14 is arranged on a short diagonal of the parallelogram crossing area 13. Consequently, when light beams L1 and L2 having some wavelength are reflected from the branch waveguide 12 to the main waveguide part 11, both beams L1 and L2 are reflected to pass through specific optical paths, so that there is no crosstalk generated.

Description

DETAILED DESCRIPTION OF THE INVENTION r Industrial Field of Application J The present invention relates to an optical branching device for branching and multiplexing a plurality of light waves.

1 Conventional technology, I As a technical paper on optical splitters,
Paper at the National Conference of the Communication Society, "Formation of quartz-based movable surface-first circuits" (Reference 1), Paper at the National Conference of the Optical and Radio Division of the Institute of Electronics and Communication Engineers in 1981, "Unfinished silica-based waveguide optical demultiplexing" (Reference 1) 2) etc.

1-The optical branching device of writing ai has a Y-shaped waveguide part i, and has a 3 dB
Used for branching.

On the other hand, as a subscriber-based optical communication system, a four-wave multiplier system is being considered, and as an optical multiplexer/demultiplexer for such a system, for example, Create a wave path.

It has been proposed that an interference film filter is disposed at a predetermined portion of the waveguide.

The basic optical branching structure of the optical multiplexer/demultiplexer is as shown in Fig. 8 (a) and (b).
intersect at a crossing angle of 0, and these waveguides l.

The intersecting region 3 of the two shapes is a parallelogram (ABCD).

- Crossing membrane filter 4 Located in the crossing area 3 and crossing angle θ
is placed perpendicular to the bisector of.

In addition, when this optical multiplexer/demultiplexer is used as a 4-wave Higashikawa,
3 dB: Unlike the 1,1 type, 100% optical transmission from waveguide 1 to waveguide 1, IOH optical transmission from branch waveguide 2 to l-, waveguide 1, or -L guide. It is necessary to transmit 10Q$ of light from the wave section 1 to the branch waveguide section 2.

Problem 1 to be Solved by the Invention Incidentally, in the case of the optical multiplexer/demultiplexer described in , the interference film filter 4 is disposed in the intersection area 3 to provide the optical multiplexer/demultiplexer tt. Crosstalk, insertion loss, etc. were occurring because the configuration of the first branch was not optimized.

For example, in Figure PI3 (A) 1 port), when light beams Ll, L, + of a certain wavelength are reflected from the branch waveguide section 2 side to the L liquid guide section l, the light beam L1 passes through a predetermined optical path, but the light beam L2 returns to the original branch waveguide al12, causing a problem.

In view of the above problems, the present invention aims to provide an optical branching device with low crosstalk and insertion loss.

One stage for solving the problem, the present invention provides branch waveguide for the i-i wave section 11 as in the first IN. In the optical splitter where IA+2 intersects and the intersection region 13 of the L waveguide section 11 and the branching four-wave section 12 forms a W-shaped quadrilateral shape,! , the quadrilateral intersection area 13 in rows f is characterized in that a reflector +4 is disposed 5 on its short diagonal line 1-.

1 Effect A As is clear from FIG. 1, the optical splitter of the present invention has the following effects:
A reflector consisting of an F' decoupling film filter 14 is provided with an intersection of 1. Yes, because it is placed on a short diagonal of area 13, for example,
A light beam L1 of a certain wavelength. L2 from the branch waveguide 12 side
Waveguide? When reflected to Bll, both light beams L1 and L2 are reflected and pass through a predetermined optical path as shown in FIG. 1, so that no crosstalk occurs.

Embodiment 1 Hereinafter, an embodiment of the optical branching device of the present invention will be described with reference to the drawings.

In FIG. 1, L waveguide section 11. Each branch waveguide section 12 consists of a core 15 and a cladding 16 covering the core 15.

The branch waveguide section 12 is the L waveguide section l! The intersection region 13 intersects with the intersection angle θ, and the descending quadrilateral (original ABCΩ) portion is the intersection region 13.

The intersection area 13 is cut by νJ along the short diagonal line BD of the descending quadrilateral (OABCD), and a reflector made of an interference film filter 14 is placed on the diagonal line BD.

Note that when the thickness of the P# membrane filter 14 is so large that it cannot be ignored compared to the width of the waveguide, the effective reflection surface (usually the filter center plane) of the f membrane removal filter 14 is defined by the diagonal line BD.
).

These F waveguide sections 11. Branch waveguide section 12. As is known, the F membrane removal filter 14 is provided on a silicon substrate, and the main waveguide section 11, the branch waveguide section 12, and the silicon substrate are connected to each other.
A buffer layer is interposed in 11.

Further, an optical fiber, or a main wave section or a branch waveguide section of another optical splitter is optically connected to each end of the main branch section 111 and the branch waveguide section 12.

Figure 2 is a schematic diagram of the 4-wave east system, and El
o is electric/light change! ! ! ! 07E is an optical/electrical converter, and 07E is a 4-wave optical multiplexer/demultiplexer.

FIG. 3 is a schematic illustration of a four-wave optical multiplexer/demultiplexer in a two-legged system constructed of the optical branching device of the present invention, and the characteristics of each interfering membrane filter 14a, 14b, and 14e are as shown in Table 3. be.

Generally, in the case of a multimode F-type waveguide, one waveguide section 11
．． 111 of the branch waveguide section 12 has a diameter of 40 to 50 mm, and if it is manufactured using the technology as described in Keki Document 2, it will have a diameter of about 3°11 l.
Although a precision of less than or equal to B is required, it is possible to manufacture a product that satisfies this precision in one aspect of the present invention.

By the way, inside the main waveguide section 11 and the branch waveguide section 12,
In addition to the light beam components parallel to the waveguide as described above, there are higher-order modes having a travel angle α as shown in FIG.

Also, for this α, the maximum value (maximum propagation angle) for NA
αSaW exists, and α satisfies 0≦α≦α−■.

In the case of such a high-order mode, even if the interference film filter 14 is placed at a predetermined position as shown in FIG. 5, satisfying the conditions of the present invention, there is a risk that crosstalk will occur.
If it is set so that ≧α■ax, higher-order modes will not be guided and crosstalk will not occur.

For all α (O≦α≦αmat), the condition for satisfying the above inequality is 0≧αzen aX.

When this condition is satisfied, even if the T-#8 filter 14 deviates from the optimum position, the light beam will not enter the waveguide mode, and therefore, although the insertion loss will increase, no crosstalk will occur.

In FIG. 6, -L waveguide section 11. Branch waveguide f! 112
The width of is -, and in the intersection area 13 the line segment X-X is 1 horizontal
When the width of the λ° region 13 is W', W
゛ becomes as follows.

! 1nα"=W◆-□-s+n(α10) Among these, the -Ill light ray is incident on the 1゛ interfering film filter 14, but its residual is not incident, and this becomes the insertion loss. .

Therefore, in the range of 0≦π/2−α, the larger 0 is, the smaller the insertion loss due to this cause is.

・Force 51: The wavelength transmission (reflection) characteristics of the interfering film filter 14 are that of a one-immersion filter! For the incident angle O1n of 4, cas θ
depends on it in the form of a function containing.

Such r· is shown in FIG. 7, and as is clear from the figure, within the range O≦O1n≦π/2, the characteristic variation with respect to the variation in Oin is the smallest in the vicinity of OinmO.

-1- The incident angle of 17 inches of the membrane removal filter 14 is centered at the angle 0/2 of the intersection angle 0, and ±α around it.
IHi is within the range of rmax.

Therefore, in order to reduce wavelength characteristic fluctuations for each mode, the smaller θ is, the better.

Taking the above into consideration, the crossing angle 0 is desirably larger than the α layer aX and approximately equal to its α−aX, as a condition for reducing not only crosstalk but also insertion loss.

As a specific example of the present invention, Δ=1z, αax “8°, 0
= IO" optical splitter.

In this case, since each waveguide section 11.12 consists of a core and a cladding, the diagonal line 80-L of the intersection area 13 by the core,
When arranging the membrane removal filter 14 with a thickness of 20 μm,
Part 1: The center line that divides the thickness of the membrane removal filter 14 into two halves was made to coincide with the diagonal mBD.

In the above-described embodiment, the interference film filter 14, which is a multiplexing/demultiplexing section, is used as the reflector, but a half mirror may be used as the reflector, and in this case, it is only a branch.

Effect of invention 1 As explained in IJ1, the optical splitter according to the present invention is as follows.

Since the reflector is disposed in the intersection region of the main waveguide section and the branch waveguide section and on a predetermined diagonal line 1 of the intersection region, the distance can be reduced.

Also, as in implementation jE, if the intersection angle of the branch waveguide with respect to the -L waveguide is θ, and the maximum propagation angle in the waveguide is α-d, then θ is larger than α By being large and approximately equal to αWaX, insertion loss can also be reduced.

[Brief explanation of drawings]

11i4 is an f-plane view of an optical splitter showing an embodiment of the present invention, FIG. 2 is a schematic diagram of a 4-wave multilayer system, and FIG. 3 is a schematic diagram of 4 Shibukawa optical multiplexers/demultiplexers in the same system. , Fig. 4 is an explanatory diagram showing the higher-order modes of the optical splitter, Fig. 5 is an explanatory diagram to explain the crosstalk of higher-order modes in the optical splitter, and Fig. 6 is an explanatory diagram showing the insertion loss in the optical splitter. Theory I to explain
JJri4, FIG. 7 is an explanatory IJI diagram showing the relationship between the crossing angle 0 and insertion loss, and FIGS. 8(a) and 8(b) are explanatory diagrams showing a conventional optical splitter. U... Main waveguide section 12...Fist branch waveguide section 13 Fist/intersection area 14/φe "Demembrane filter 151IlI11 Core 16...-Clad 0...Fist intersection angle BD Slightly diagonal agent Patent attorney Yoshio Saito Figure 1 Figure 2 Figure 3E Figure 4 I Figure 6 b (a) Figure 5 7E

Claims (4)

[Claims] (1) In an optical splitter in which a branch waveguide intersects with a main waveguide, and the intersection region of the main waveguide and the branch waveguide has a parallelogram shape, the above-mentioned parallelogram intersection region is an optical splitter characterized by a reflector arranged on a short diagonal line. (2) The intersection angle of the branch waveguide with respect to the main waveguide is 0,
When the maximum propagation angle in the waveguide is αmax, θ
The optical splitter according to claim 1, wherein is larger than αmax and approximately equal to αmax. (3) The optical splitter according to claim 1, wherein the reflector is an interference film filter. (4) The optical splitter according to claim 1, wherein the reflector is a half mirror.