JPS6155612A - Three-dimensional light branching device - Google Patents

Abstract

PURPOSE:To obtain a three-dimensional light branching device low in branching loss and able to make branching angle large by connecting two branch waveguides having the same section and the same refractive index with a main waveguide to the main waveguide path in Y-form through a transitional area having a rectangular section and a specified refractive index, and providing a cladding of low refractive index enclosing it. CONSTITUTION:Branch waveguide paths 2, 3 having the same section and refractive index with the main waveguide 1 are connected to the main waveguide having sectional form of 2Tx in width, 2Ty in height and its refractive index is n2 in Y-form making an opening angle to 2theta through a transitional area 4 having a rectangular section and a refractive index n3, and a cladding 6 that encloses it and having a refractive index n1 lower than n2 is provided. By satisfying n3=n2[Sin<2>psi+cfs<2>(theta+psi)]<1/2> where psi is an angle made by a ray for waveguide mode transmitted in the main waveguide 1 and a transmission axis, a three-dimensional light branching device low in branching loss and capable of making branching angle 2 large can be obtained.

Description

Detailed Description of the Invention (7) Technical Field The present invention relates to a three-dimensional optical splitter. In planar optical waveguides, branch waveguides are important structures as power dividers and switches.

A problem with branched waveguides is that branching loss increases as the branching angle increases.

When the difference in refractive index between the core and the cladding is large, the power of the waveguide mode can be divided into each branch waveguide with relatively low loss. However, between the core and the kratzding,
If there is an extremely large difference in refractive index, the coupling efficiency with elements such as optical fibers will decrease, and it will often be difficult to manufacture.

B) Summary This is a three-dimensional optical splitter that combines waveguides with a rectangular cross section.

To reduce radiation loss, a region with a lower refractive index than the cladding is provided at the branching point. More preferably, this low refractive index region has an extra protruding portion above and below the height of the waveguide in the perpendicular direction with respect to the plane including the Y-shaped branch.

This is particularly effective when the branching angle is large, and the branching loss is reduced to about 1710 nm compared to the conventional branching waveguide structure.

(1) Prior Art FIG. 7 is a plan view showing a general two-dimensional Y-branch. 2
Dimension means that the same structure continues indefinitely in the direction perpendicular to the page. It is a type of slab railway.

The main waveguide 50 branches into two branch waveguides 51 and 52. The three waveguides 50, 51, 52 are in the transition region 53
are interconnected in the waveguide 50.51.52,
Since the transition region 53 has a refractive index greater than the refractive index of the surrounding cladding 54, light is confined within these waveguides.

The waveguide 50, etc. are sometimes called a core.

The refractive index of the core is n2, and the refractive index of the cladding is nl.

``2 > nl(1).Anderson and 5Asaki et al. approximately calculated the radiation loss in such a two-dimensional Y-branch (H9Sasaki and 1. Anderso
n, IEEE J, Quantun Elec
tron.

QE-14,883 (1978)).

According to their calculations, when the difference in refractive index between the core and cladding is large, the power of the waveguide mode can be divided into branch waveguides with relatively low loss. However, an extremely large refractive index difference deteriorates the coupling efficiency with other waveguides and is difficult to manufacture.

Figure 8 is coupled - multiple - wa
FIG. 3 is a plan view of a vequide type branch. -1Fons
It was proposed by tad, Orr et al.
H, A, ) hus and C, G, Fonsta
d. Jr.

IEEE J,-Jiao [Cictron, QE-17,
2821 (1981), .

HlA, Haus and L, P/! alter
-Orr, IIJE J, Quantun E
electron.

QE-19,840 (1983), ).

The main waveguide 50 is interrupted at a transition region 53, and intermediate core portions 55, 56 are formed in parallel on both sides of the transition region 53.

Parallel branch waveguides 51.52 are formed further outside the intermediate core portion 55.56.

This structure has the characteristic that the wavefront does not tilt even after branching. As the waveguide spacing increases, the coupling efficiency decreases. Therefore, in order to obtain a wide spacing between branch waveguides, it is necessary to increase the coupling length. This cannot be said to be an efficient branch waveguide spacing.

An efficient branching waveguide has the following characteristics: (1) small branching loss, (2) short coupling length, and (3) wide-angle guidance to match the spot size with other optical elements. It should meet the requirements such as being a wave path.

The present inventor has already invented a branching waveguide with low radiation loss for a two-dimensional planar type Y branch (1988 Electronics and Technology Society Comprehensive National Conference No. 1089 Proceedings 4-1
43).

FIG. 9 is a plan view thereof. The main waveguide 50 and branch waveguides 51 and 52 are coupled in a transition region 53, where a low refractive index portion 60 is provided. This is its characteristic. This refractive index n is the refractive index n2 of the core and cladding,
lower than nl.

nl ) nl) n, (2). The width of the main waveguide 50 and the branch waveguides 51 and 52 is 2T, and the included angle of the branch waveguide is 2θ.

It is assumed that the low refractive index section 60 has a rectangular shape having the same width as the waveguide and intersects with the branch waveguides 51 and 52 at the end.

Therefore, the low refractive index section 60 has a width of 2T and a length of 2Ta.
It becomes mθ. The structure of such a waveguide has an excellent feature that the radiation loss is reduced compared to the conventional structure, especially when the branching angle 2θ is large.

The main conventional techniques have been explained above. Conventionally, all Y-shaped optical branches have been treated two-dimensionally.

Even when a Y-shaped waveguide is fabricated on a plane, the depth of the waveguide remains unchanged, and therefore two-dimensional calculations are possible.

The inventor of the present invention has realized that a waveguide having a three-dimensional structure is suitable for further reducing branching loss.

In actual production, two-dimensional branches are difficult to create, and three-dimensional branches are sometimes more realistic. It is easy to create a waveguide with a finite depth, but it is difficult to create a waveguide with a substantially infinite depth.

Figure io shows the structure of a three-dimensional Y-branch. Waveguide 60.6
1.62 has a rectangular cross section with a width of 2Tx and a height of 2TyO. These form a core whose refractive index n2 is higher than the refractive index n1 of the cladding 64.

Cladding 64 is not shown, but waveguide 60 .
61 and 62 are surrounded from the left and right sides and from the bottom.

However, it is structurally the same as a conventional two-dimensional waveguide. This is because there is no change in the dimension in the depth direction. Also,
When θ is large, the loss is large.

sha) Structure of the present invention The present invention provides a Y-branch with a three-dimensional structure that has not been handled at all in the past.

FIG. 1 is a perspective view of a three-dimensional optical splitter according to the present invention.

The main waveguide 1 is a waveguide with a width of 2Tx and a height of 2T. The branch waveguide 2.3 is also a waveguide with a width of 2TX and a height of 2Ty, and is connected obliquely to the end of the main waveguide 1 so as to form an angle θ. Main waveguide 1, branch waveguide 2.
The refractive index of 3 is n2. The material surrounding these is called the cladding 6, and the refractive index n2 of the cladding 6 is larger than nI. Therefore, the waveguide 1.2.3 is sometimes called a core.

Now, the transition region 4 is provided with a low refractive index portion 5 having a lower refractive index than the core and cladding 6.

This point differs from the three-dimensional branch shown in FIG. This refractive index n
3 is lower than n1 and n2 and is similar to that shown in FIG.

The difference from the two-dimensional branch shown in FIG. 9 is that it is a three-dimensional branch, and the depth of each waveguide 1, 2, and 3 is finite. In the example shown in this figure, the low refractive index portion 5 protrudes from the upper surface of the waveguide 1.2.3 by ΔTy, and from the lower surface by ΔTy.

The low refractive index portion 5 has a width of 2TX and a length of 2TX (Inc.) θ.

The height is 2Ty + 2ΔTy. ΔTy may be 0. However, it is desirable that ΔTy have a certain degree of magnitude.

The relationship among the refractive indices n1, n2, and n3 follows equation (2).

FIG. 2 is an explanatory diagram showing the light rays traveling in the waveguide within the cross section at this branch.

The traveling direction of the main waveguide 1 is the two axes, the direction perpendicular to the plane containing the waveguides 1.2.3 is the y-axis, and the direction within the plane containing the waveguide and perpendicular to the main waveguide 1 is the y-axis. .

The reason why the refractive index n3 of the low refractive index portion 5 is made lower than nl is to suppress radiation within the waveguide plane (xz plane).

The reason why the protrusion ΔTy of the low refractive index portion 5 is provided is to suppress radiation in the y direction.

In order to determine the refractive index n3 of the low refractive index portion 5, a geometrical optics model within the slab line is considered in FIG. Here, it is treated as having a uniform refractive index in the y direction.

The terminal end of the main waveguide 1 and the starting end of the low refractive index section 5 are set at x@.

In other words, z=O. The terminal end QW of the low refractive index section 5 is Z =
It is given by 2Tx-θ.

The low refractive index portion 5 is an area partitioned by a rectangle P'/WQ. The branch waveguide 2.3 is a high refractive index line partitioned by half straight lines PR and QS forming an angle θ with respect to PQK, or partitioned by a half straight line WNSVU forming a diagonal angle θ with Wv.

Consider a light ray m corresponding to waveguide mode.

Let ψ be the angle that this light 111m makes with the propagation axis (two axes).

1i m 7jZ Suppose that the boundary Pv is passed at point A.

The incident angle at the low refractive index portion is assumed to be 01. From Snell's law, n2sinψ = n3sinθ1 (3). Assume that the light ray m further enters the branch waveguide 2 from the low refractive index section 5 at the boundary PQLvB point. Ray and P after incidence
If the angle formed by Q is 02, then from Snell's law, n3cosθ,=i12CO5θ2(4).

Here, it is assumed that the waveguide mode maintains the same mode even if it enters the branch waveguide. In this case, the angle between the propagation axis of the branch waveguide and the light beam must be ψ.

Then, if it is reflected at the 0 point inside the branch waveguide 2, /PCB becomes ψ.

In ΔPBC, θ + ψ = 02(5). From (3), (4), and (5), by eliminating θ1 and θ2, we get n3:= n, (s+nψ+ cos (θ
+ψ)) (6).

This formula is the equation that determines n3. Core refractive index n
2. When the branching angle 20 is given, n3 is uniquely calculated as a function of the angle ψ formed with the propagation axis of the light beam.

Geometrical optics calculations determine n3 as a function of ψ, which means that the light 1j1m whose angle with the propagation axis is ψ
Only the following can be obtained as satisfying the condition (5). In reality, not only ψ rays propagate in the waveguide.

Here, we will move from geometric considerations to wave optical considerations.

Here, the angle ψ that the light ray m corresponding to the waveguide makes with the propagation axis is
is given by ψ =, 7 < / ) (7) βTχ. Here, ux/Tx is a phase constant in the X direction within the core, and β is a phase constant in two directions within the core.

u x /T x and β can be determined as follows. Hz and Ey are the main components of the electromagnetic field, p in the X direction. At this time, Hz can be expressed as. The other main components are expressed using Hx.

Ey at X=±Tx (lyl <Ty), Hz
The characteristic equation uy is obtained from the continuous side of % Formula % (1) to obtain uy from the continuous side of .β can be obtained from x using - and 17. Here, VxSVy are the normalized frequencies in the X direction and the X direction, respectively. In this way, β
Since and uX are determined, ψ can be obtained from equation (7), and n3 is determined from this.

Next, a method for determining the vertical protrusion ΔTy of the low refractive index portion will be described.

When Δ'r,=0, the structure is leaky because the refractive index near the branch point is lowered, and the light beam in the yz plane exits to the cladding at a small angle with the y axis. This causes radiation loss.

Therefore, it is thought that this radiation will be suppressed if there are ΔTs above and below that are large enough to sufficiently cover the protrusion of the field to the cluttering.

That is, ΔTy >>Ty (Vy2- uy2)″″1/2(
17) is sufficient.

Next, we will discuss the limits of loss reduction in the three-dimensional branch structure designed in this way. In FIG. 2, when the guided wave reflected on PR is on QS, it travels through the branch waveguide while being reflected. However, when the light beam reflected on PR comes on PQ, it enters the low refractive index region again, resulting in a loss.

Such a loss occurs when θ and ψ. Therefore, the applicable range for the branching angle θ is θ 〉 ψ
(18).

Usually, a branched waveguide requires a structure with a large branching angle, so the scope of application of equation (18) does not pose a major problem.

B) Calculation of branch loss In order to calculate branch loss, it is necessary to find the mode function of the waveguide. Several methods have been proposed for this purpose.

Here, P B M (Propegating
B6amMethod) was employed to calculate the mode function of Zoo. In addition to this, the eigenfunction φ(
x, y), the energy transmitted to the branch waveguide can be determined.

The PBM method is an approximation method that is suitable for cases where the refractive index changes slowly in the direction in which light travels. For light propagating in two directions, Hx or Ey is simply written as ε). Now, t (XlyIZ) = E <x, yrz)exp
(-jkz) (20) Substituting a ~ into equation (19) and setting -kko10, we obtain. However, . (22) From E(X, y, z) to E(X
+ yr z + Δ2) is the recurrence formula % formula % (24). In this way, by sequentially applying the operators of equation (25), E(x+y+z) in the entire space can be determined in a near-unique manner by numerical calculation.

The electric field (or magnetic field) is E (X+ y+ z), and the eigenfunction of the branch waveguide is φ. Let it be (X, y).

The power transmittance η is 77=161J J E(x, y, z)φo(x-xc
,y)exp(jkon2xsinθ)dxdy1. XC is the X coordinate of the center of the branch waveguide. aX'P (・・−・・−・) is E(x+y+z)
andφ. (X-Xc.

This is a factor due to the fact that the wavefront with respect to y) is tilted by θ.

Branch loss is given by -10log η.

Compare the losses of the conventional branch and the branch of the present invention.

n3 is determined by equation (6). This is uniquely determined when ψ is given. In the case of a multimode waveguide, there are many ψ. However, there is only one option for n3.

Therefore, the present invention is most effective when ψ is one.

Therefore, a single mode waveguide is used. To make it even easier,
Assume a core with equal vertical and horizontal cross sections (Tx = Ty). 12. Since the E21 mode is the cutoff, the normalized frequency V only needs to be 2.2 or less.

■ is here ■" (n2-n12) k2T2 (28).

T is the length of Tx and Ty. The constant is the wavelength of light λ =
1 μm Waveguide width depth T = 5 μm Cladding refractive index n1 = 1.5 Normalized frequency V = 1.81 Upper and lower protrusion ΔTy =
It is set to 20 μm. Figure 3 shows the branching angle 2θ of the three-dimensional branch.
It is a graph which shows the calculation result of (-10#og(eta)) of the branch loss with respect to FIG.

As the branching angle Δθ increases, branching losses rapidly increase in the conventional branching (as shown in FIG. 10).

What is shown by the broken line is the branching loss of the three-dimensional branched structure included in the present invention but without vertical protrusion (ΔTy = 0).

The one with ΔTy=20 μm is shown by the lower solid line. The arrow is the point of θ=ψ. Inequality (18) corresponds to the region to the right of the arrow.

The one with ΔTy=20 μm has the least loss.

If the allowable f@ range of branching loss is 1 dB, then in the conventional structure, the branching angle can only be set to 4 degrees.

However, in the case of the present invention in which ΔTy = 20 μm, the angle can be expanded to 10 degrees.

It can be seen that the structure of the present invention is particularly suitable for wide-angle branching.

Figure 4 shows the same parameters (ΔTy = 20 μm),
In the present invention, it is a graph showing the ratio of difference between the refractive index n3 of the low refractive index portion and the cladding refractive index n1 with respect to the branching angle 2θ. The horizontal axis is 2θ, and the vertical axis is Δn3n1−n3 = (29) ln1. This is calculated by finding ψ using equation (7) from the single mode condition and substituting it together with the value of θ into equation (6).

The arrow is the point of ψ=θ. Due to the single mode condition, one curve can be drawn.

In the case of a multimode waveguide, ψ differs for each mode, so curves corresponding to the number of modes are generated. Since n3 takes one value, in this case, the branch has mode selectivity.

Next, for an example of a waveguide with a smaller normalized frequency,
Similar calculation results are shown in FIGS. 5 and 6.

The constants are the wavelength of light λ = 1 μm Waveguide width depth 'l' = 5 μm Cladding refractive index n1 = 1.5 Normalized frequency V = 1.22 Upper and lower protrusion ΔTy = 28 μm The broken line is ΔTy in the present invention = O, the lower solid line is ΔTy
=28 μm.

Since the core and cladding refractive index difference is smaller than in the previous example, the angle ψ that the ray makes with the axis is smaller.

In the case of the conventional example, as the branching angle 2θ increases, the loss increases rapidly. This is because ψ is smaller than the previous example.

In the case of the present invention, even if the branch angle is 10 degrees, the loss is 2 d
It is below B.

FIG. 6 shows the value obtained by dividing the deviation of the refractive index n3 of the low refractive index portion from the cladding refractive index n1 by nl in the present invention. It is determined from equations (6) and (7).

In order to show in more detail the difference in the mechanism of mode function change between the present invention and the conventional structure, a graph showing how the electric field distribution (magnetic field distribution) changes from the beginning to the end of the branch is shown. .

The field distribution of the conventional example is given in FIGS. 11-16.

Field distributions of the present invention are given in FIGS. 17-22.

In both examples, the constants are the same, branching angle 2θ = 8°, cluttering refractive index n, = 1.5 light wave.
Length λ = 1 μm Waveguide width Depth
2T = 5μm normalized frequency v = 1・
81 (protrusion ΔT7 of the present invention = 20 μm). Figure 11 shows the conventional example l E (0, y, Z) 1, IE (x
, Q, z) 1 at 220 to 200 μm. The y-axis is the vertical axis. It can be seen that there are many parts radiating to the line x=Q, y=0.

Figures 12 to 16 show the same conventional example with z"O, 50%
It shows the field distribution on the xy plane at 100, 150, and 200 μm. When Z=Q, the energy of light that was concentrated at
I can see it dispersing to both sides. However, z = 200
Even in μm, on the extension of the y-axis (x=0.7=0)
There is still a lot of light energy left. This results in radiation loss. Also, the energy entering the branch waveguide is small.

171st Nl'i: Field spectroscopy IE of the present invention (0, y, z)
kIE(x, 0.z)1 is shown along two axes. 2θ=8°0, n1=1.5, λ=1 μm, 2
T = 5 ttmSV = 1.81, Δτy = 20
It is μm.

It can be seen that most of the light energy enters the branch waveguide. Almost no light energy exists in the extension of the y-axis (x=o, y=O). In other words, radiation loss is small.

FIGS. 18 to 22 show that in the present invention, z = O, 5o
5100. It is a diagram showing the field strength in the xy plane of 150.200 μm. At z = 150, the optical energy separates and enters the branch waveguide, and at z = 200,
On the extension of the y-axis (x=0, 7=0), there is almost no light. In other words, there is no radiation loss and the radiation efficiently enters the branch waveguide.

Effects (1) Three-dimensional light branching. It is a structure that is realistic and easy to make.

(2) Although the difference in refractive index between the core and cladding is small, it is possible to provide optical branching with low branching loss.

Due to its low loss, it is used in optical integrated circuits, optical devices, etc.
A powerful branching structure can be provided.

(3) Compared to conventional branching, the loss is significantly lower, and even if the branching angle is increased, the loss does not increase significantly. Therefore, wide-angle branching can be realized.

(4) Since the difference in refractive index is small, it is easy to match with other optical elements.

(5) In the present invention, ΔTy = 0 is a relatively leaky structure. ΔTy (17
) formula), the leakage will be reduced. This point was explained using the calculation results, but I will explain it more intuitively.

FIG. 23 shows a cross-sectional view taken along the yz plane of the low refractive index portion (hatched). ) has no protrusion Δ
This is the case when Ty=Q. It is assumed that a ray whose angle with the xz plane is ψ' passes through to the cluttering at point M. Let the angle formed with the boundary surface be Φ1.

According to Snell's law, n3ccsg=n, cosΦr (30). It is incident almost squarely on the boundary surface.

(bJ corresponds to the configuration of the present invention and is the case where there is protrusion (ΔTy>O). It is assumed that a ray with an inclination of ψ′ is refracted at point N and exits at a refraction angle of Φ2. Boundary surface From Snell's law, n35inq)' = n l sinΦ2
(31).

Φ is the angle that a light ray makes with the optical axis when passing through the low refractive index region. When leaving the low refractive index, it is in any case refracted more in the y-axis direction, and this refraction angle is (Φ-ψ').

ψl is originally a small angle. (3o), (31)
From this, it can be seen that Φ1 〉 Φ2 (32). Since Φ1 is larger, the light wave will escape in the y direction when ΔTy=Q.

In the case of the present invention, the refraction angle is approximately Φ2-ψl=-γψ' (33). However, r is. The value shown on the vertical axis in FIGS. 4 and 6 is extremely small.

However, the refraction angle (Φ1−
ψ/) is approximately ψ′. It is 1/ψ' times more than the case of Δ+, Ty 4 Q.

Since ψI is an extremely small value, its reciprocal is much larger than 1. Therefore, 4TyK0 can more effectively suppress the radiation loss due to the escape of light rays in the y direction than when ΔTy==Q. Moreover, as in equation (, 33), this is a negative value, so Φ2 is smaller than g.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a three-dimensional branch of the present invention. FIG. 2 is a geometrical optical explanatory diagram showing catadioptric refraction of light rays in the cross section of the Y branch of the present invention. Figure 3 shows a Y branch with Δ'ry) set to 0 in the present invention,
7 is a graph showing calculation results of branching loss (aB) with respect to branching angle 2θ of the Y branch with Δ7y==Q in the present invention and the conventional Y branch. The lower solid line is the present invention, the upper broken line is the one with ΔTy=O, and the upper diagonal line is the conventional example (n3
core n1). n1=1.5, λ=1 itm, V=1.81
．． 2T = 5 μm. These are common to all three. n3 is 2θ
is given by equations (6) to (23) as a function of . Also shown in FIG. In the present invention, ΔTy=20 μm. The vertical arrow is the point where θ=ψ, and the present invention is based on this point.
It is effective in a large area. FIG. 4 is a graph showing the results of calculating the refractive index n3 of the low refractive index portion as a function of the branching angle 2θ in the present invention. The horizontal axis shows the branching angle 2θ, and the vertical axis shows the value obtained by dividing nl−n3=Δn3 by nl in %. The vertical arrow is the point where 0=ψ. The constants are the same as those in FIG.゛ Figure 5 shows the Y branch of the present invention with ΔTy > O, the Y branch of the present invention with ΔTy = 0, and the conventional Y branch.
A graph showing calculation results of branch loss (dB) with respect to branch angle 2θ. The lower solid line is the present invention, and the upper dashed line is ΔT.
The diagonal line above is the conventional example (n3=:n
According to 2). n1=1.5, λ=1μm, V=1
．． 22.2T=5μm, and the collerano value is common for the three branches. n3 is given as a function of 2θ and is represented in FIG. In the present invention, in this example,
Δ7y:=28 μm. FIG. 6 is a graph showing the results of calculating the refractive index n of the low refractive index portion as a function of the branching angle 2θ in the branched structure of the present invention. The horizontal axis is 2θ (branching angle), and the M axis is Δn3/n□. The constants are the same as those in FIG. FIG. 7 is a plan view of a very common two-dimensional light branch (conventional example). Figure 8 is coupled - multiple = wa
FIG. 2 is a plan view of a veguide type two-dimensional branch (known). FIG. 9 is a plan view of a two-dimensional Y-branch having a low refractive index portion in the transition region, which was previously invented by the present inventor. FIG. 10 is a perspective view showing a general shape that can be considered as a three-dimensional branch. FIG. 11 is a graph diagram showing the field distribution in the transition region in the conventional Y-branch (shown in FIG. 10). 2θ=8minn1=
1.5, λ = 1 μm, 2T = 5 μm, V
= 1.81. The horizontal axis indicates the propagation direction 2. The upper half shows IE(0,y.Z)l. The lower half is lli: (x, 0.Z) l
shows. FIG. 12 is a graph that two-dimensionally expresses the field strength on the xy plane at z=0 in the conventional Y-branch whose field distribution is graphically expressed in FIG. 11. The vertical and horizontal scales are at intervals of 1 μm. The height is the strength of the field and is on an arbitrary scale. FIG. 13 is a graph showing the field distribution in the xy plane of a conventional Y branch: cz = 50 μm. FIG. 14 is a graph showing the field distribution in the xy plane at z = 100 μm in a conventional Y branch. FIG. 15 is a graph showing the field distribution in the xy plane at Z = 150 μm in the conventional Y branch. FIG. 16 is a graph showing the field distribution in the xy plane at z = 200 μm in a conventional Y branch. FIG. 17 is a graph diagram showing the field distribution in the transition region of the Y-branch (shown in FIG. 1) of the present invention. 2θ=8°, 1l
l=1.5, λ=1μm12T=5μm1v=1.8
1, Δ'ry=2oμm. The horizontal axis indicates the propagation direction 2. Field distribution of z=Q~200 μm in the transition region. The upper half is IE(0,y,z)l. The bottom half is IE
(X, 0.Z)l. FIG. 18 is a graph diagram two-dimensionally showing the field distribution on the xy plane where z=Q in the Y branch of the present invention. The solid line is drawn in the X1y direction every 1 μm. The height represents the field strength. FIG. 19 is a graph diagram two-dimensionally showing the field distribution on the xy plane at Z = 50 μm in the Y branch of the present invention. FIG. 20 shows z = too μm in the Y branch of the present invention.
FIG. 2 is a graph diagram two-dimensionally showing the field distribution on the xy plane. FIG. 21 shows Z = 150 μm in the Y branch of the present invention.
FIG. 2 is a graph diagram two-dimensionally showing the field distribution on the xy plane. FIG. 22 shows Z = 200 μm in the Y branch of the present invention.
FIG. 2 is a graph diagram two-dimensionally showing the field distribution on the xy plane. FIG. 23 is a geometrical optical explanatory diagram showing the path of a ray on the yz plane of the Y branch. In (a), ΔTy=0. Φ) indicates the case of the present invention and ΔTy>O. 1 ・・・・・・・・・ Main waveguide 2
．． 3...Branch waveguide 4...Transition region 5
......Low refractive index section 6 ...... Cladding n1 ...
・・・・・・ Krutsding's refractive index n2 ・・・
・・・・・・ Core refractive index n3 ・・・・・・・・・
・・・Refractive index 2θ of low refractive index part ・・・・・・・・・
Opening angle of branch waveguide 2TX...Waveguide width 2T, ......Waveguide height ΔTy
・・・・・・・・・ Protrusion length of the low refractive index section from the top and bottom surfaces of the waveguide Inventor: Kawakami, Shojibe, Miyagi Hikaru, Nobuka, Izumi Patent applicant: Kawakami, Shojibe, Sumitomo Electric Industries, Ltd. Figure 10 Figure 1 Figure 3 (dB) Figure 4 (%) Figure 5 (dB) C-- Figure 6 n=1.5i=l/1m V = 1.222T= 5 //l11 (%) Δ
Ty=2811m Branch angle 20 Fig. 7 Fig. 8 Fig. 14 Conventional example Z = 150 μm Fig. 16 Conventional example Z = 200 μm Fig. 20 Fig. 21 Z = 150 μm Fig. 22 Z = 200 μm Present invention Fig. 23 (a ) There is no protrusion of n3 in the y direction ΔT y = On. (b)

Claims (4)

[Claims] (1) It has a cross section with a width of 2Tx and a height of 2Ty and a refractive index of n_
The main waveguide 1 is 2, and the refractive index coupled to the end of the main waveguide 1 in a Y shape with an opening angle 2θ is n_2 and the width is 2Tx.
, branch waveguides 2 and 3 having a cross section with a height of 2Ty, a cladding 6 surrounding the waveguides 1, 2, and 3 and having a refractive index n_1 lower than n_2, the main waveguide 1 and the branch waveguides 2 and 3.
A low refractive index portion 5 is provided in the transition region 4 coupled to the main waveguide 1 and has a substantially rectangular cross section PQWV in the plane containing the waveguide, and has a refractive index n_3 lower than n_1 and n_2. If ψ is the angle that the light ray corresponding to the elementary wave of wave mode light makes with the propagation axis, then n_3=n_2 [sin^2ψ+cos^2 (θ+ψ)
] A three-dimensional optical splitter characterized by ^1^/^2. (2) The three-dimensional optical splitter according to claim (1), in which the low refractive index portion 5 of the transition region 4 has a portion ΔTy that protrudes from the upper and lower surfaces of the main waveguide 1 and branch waveguides 2 and 3. (3) The three-dimensional optical branching device according to claim (1) or (2), wherein the main waveguide 1 and the branch waveguides 2 and 3 are single mode waveguides. (4) The upper and lower protrusion ΔTy of the low refractive index portion 5 is ΔTy
>>Ty(v_y^2-u_y^2)^-^1^/^2 The three-dimensional optical splitter according to claim (2) or (3).