JP2000056151A - Optical intersection waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the light loss at the part where linear waveguides cross each other. SOLUTION: A linear waveguide composed of an InP lower clad layer 2, an InGaAsP core layer 3 and an InP upper clad layer 4, is provided with an InGaAsP high-refractive-index imparting layer 5, the equivalent refractive index of the center part in the core of the linear waveguide is set higher than that nearby the clad at the peripheral part in the core to vary the electric field distribution of propagated light, and the light is made hard to spread at the intersection part, thereby reducing the light loss at the parts where linear waveguides cross each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross waveguide in which linear waveguides intersect in an optical waveguide circuit on a substrate.

[0002]

2. Description of the Related Art An optical waveguide comprising a core and a clad formed on a substrate has a function of transmitting an optical signal from one point on the substrate to another point, and is widely used in the field of optoelectronics. . By transmitting an optical signal between a branching element, a multiplexing element, a spectral element, a modulation element, a switching element, and the like in which an optical waveguide is formed on the same substrate, various functions can be exhibited. In an integrated optical device in which many such devices are integrated on the same substrate, optical signals must be exchanged between the devices in a complicated manner.
It is necessary to cross the optical waveguides.

[0003]

Conventionally, since the refractive index in the core of the linear optical waveguide is uniform, simply intersecting the linear waveguide of the conventional structure increases the light loss at the intersection. . For this reason, the number of intersections existing on one optical path cannot be increased unnecessarily, which has been an obstacle in improving the integration degree of the optical integrated device.

[0004] The present invention has been made in view of the above circumstances, and has as its object to provide a cross waveguide that can reduce light loss at a portion where a straight waveguide crosses.

[0005]

In order to achieve the above object, according to the structure of the present invention, in an optical waveguide circuit formed on a substrate, an equivalent refractive index of a center portion in a core of an intersecting linear waveguide is reduced. Along the central axis, the peripheral portion in the core is higher than the equivalent refractive index in the vicinity of the cladding.

[0006] A core layer having a predetermined width on the substrate and a high refractive index imparting layer located above the core layer and having a width smaller than the width of the core layer are provided. The equivalent refractive index when the point at the intersection belongs to one of the linear waveguides is A, and the equivalent refractive index when the point at the intersection belongs to the other linear waveguide is B. Where the point at the intersection is set to the larger equivalent refractive index of A and B.

By making the equivalent refractive index of the central portion of the core higher than that of the peripheral portion, the electric field distribution of the light in the core changes, the light is hardly spread even at the intersection, and the light loss due to the intersection is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. The crossing angle of the straight waveguide was a right angle.

FIG. 1 is a schematic perspective view of a cross waveguide according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of the cross waveguide.
FIG. 3 shows the distribution of the equivalent refractive index of the cross waveguide as viewed from the top surface of the substrate, FIG. 4 shows a graph showing the relationship between the cross loss and the width of the high refractive index providing layer, and FIG. The distribution of the absolute value of is shown.

1 and 2, 1 is an InP substrate, and 2 is
InP lower cladding layer (1.5μm thickness), 3 is InGaAsP
Core layer (InP substrate lattice matching, composition for absorption edge wavelength 1.53 μm, thickness 0.24 μm), 4 is InP upper cladding layer (thickness 0.01 μm), 5 is InGaAsP high refractive index imparting layer (InP substrate lattice Matching, composition for absorption edge wavelength 1.50 μm, thickness 0.5 μm). The wavelength of the signal light is 1.55
μm.

The equivalent refractive index of the core where the InGaAsP high refractive index imparting layer 5 was not provided was 3.2. The InGaAsP high refractive index imparting layer 5 increases the equivalent refractive index at the center of the InGaAsP core layer 3 with respect to the periphery. The equivalent refractive index of the core where the InGaAsP high refractive index providing layer 5 was present was 3.4. The width of the InP lower cladding layer 2, the width of the InGaAsP core layer 3, and the width of the InP upper cladding layer 4 were all 2.5 μm. InGaAsP
The relationship with the cross loss was examined by changing the width of the high refractive index providing layer 5 variously. The width of the high refractive index providing layer is 0 μm or 2.5
In the case of μm, the equivalent refractive index in the core is uniform, which corresponds to a conventional structure.

In FIG. 3, reference numeral 6 denotes a portion where the InGaAsP high refractive index imparting layer 5 is further provided among the portions where the core layer is provided.
The equivalent refractive index of the portion where the GaAsP high refractive index providing layer 5 is provided is 3.
4. Reference numeral 7 denotes a portion where the core layer is provided and where the InGaAsP high refractive index providing layer 5 is not provided.
The equivalent refractive index of the portion where there is no is 3.2. Reference numeral 8 denotes a clad portion (a portion having only the InP substrate 1) and an equivalent refractive index of 1.0.
It is.

Here, consider the point P in FIG. 3, which is the point of the intersection. When it is considered that the point P belongs to the first linear waveguide (the linear waveguide extending in the left-right direction in the drawing), the point P belongs to the portion 7 where the InGaAsP high refractive index providing layer 5 is not provided. When it is considered that the point P belongs to the second linear waveguide (the linear waveguide extending in the vertical direction in the figure), the point P is InGaAs.
P The high refractive index providing layer 5 belongs to the portion 6. The equivalent refractive index (A) of the part 7 is 3.2, the equivalent refractive index (B) of the part 6 is 3.4, and in the present invention, the equivalent refractive index at point P is one of A and B. Since it is set to the larger one, the equivalent refractive index at point P is set to 3.4 (B). At any point in the intersection, the equivalent refractive index is set in this relationship.

FIG. 4 shows the relationship between the width of the high refractive index providing layer and the crossing loss. As shown in FIG. 4, when the width of the InGaAsP high refractive index providing layer 5 is larger than 0 μm and smaller than 0.6 μm, the crossing loss is reduced as compared with the conventional structure, and the effect of the first embodiment is shown. I have. In particular, when the width of the InGaAsP high refractive index providing layer 5 is 0.2 μm, the crossing loss is about 1 / of the conventional structure (a structure in which the equivalent refractive index in the core is uniform).
3.

FIG. 5 shows the distribution of the absolute value of the electric field of the waveguide cross section obtained by the mode analysis method and the beam propagation method in the first section.
The comparison is made between the case of the waveguide structure of the embodiment and the case of the conventional structure (a structure in which the refractive index in the core is uniform).

FIG. 5A shows that the width of the high refractive index providing layer is 0.2 μm.
FIG. 5B shows the electric field distribution (eigenmode) of the linear waveguide in the case of m, and FIG. 5B shows the electric field distribution immediately after passing through the intersection when the width of the high refractive index providing layer is 0.2 μm. FIG. 5 (c)
FIG. 5 (d) shows the electric field distribution (eigenmode) of the linear waveguide of the conventional structure, and FIG. 5 (d) shows the electric field distribution immediately after passing through the intersection of the conventional structure.

The electric field distribution of the linear waveguide using the first embodiment shown in FIG. 5A is different from the electric field distribution of the conventional linear waveguide shown in FIG. The electric field distribution is changing, and the spread of light at the intersection is small. as a result,
The electric field distribution after passing through the intersection of the first embodiment shown in FIG. 5B hardly changes compared with the electric field distribution after passing through the intersection of the conventional structure shown in FIG. 5D. This results in a low cross-loss value.

It is also possible to use the linear waveguide of the optical cross waveguide of the first embodiment by connecting it to a normal linear waveguide having a uniform equivalent refractive index in the core. If the cross-sectional structure of the straight waveguide of the first embodiment changes smoothly and the equivalent refractive index in the core matches the cross-sectional structure of the uniform straight waveguide as the structure of the connection portion, No loss is caused by the connection.

A description will be given of a second embodiment of the present invention. FIG.
The cross section of the cross waveguide according to the second embodiment of the present invention,
FIG. 7 is a graph showing the distribution of the equivalent refractive index of the cross waveguide as viewed from the upper surface of the substrate, and FIG. 8 is a graph showing the relationship between the cross loss and the width of the high refractive index providing layer. The crossing angle of the straight waveguide was a right angle.

In FIG. 6, 13 is an InP substrate, and 14 is an InP substrate.
P Lower cladding layer (1.5 μm thick), 15 is InGaAsP
Core layer (InP substrate lattice matching, composition corresponding to absorption edge wavelength 1.42 μm, thickness 0.28 μm), 16: InP upper cladding layer (thickness: 0.01 μm), 17: InGaAsP high refractive index providing layer (InP substrate lattice) Matching, absorption edge wavelength 1.13 μm composition, thickness 0.5 μm). The wavelength of the signal light is 1.55
μm.

The equivalent refractive index of the core without the InGaAsP high refractive index providing layer 17 was 3.2. The equivalent refractive index of the core where the InGaAsP high refractive index imparting layer 17 was provided was 3.3. InP lower cladding layer 14 width, InGaAsP core layer 1
5 and the width of the InP upper cladding layer 16 are all 2.5 μm.
m. The width of the InGaAsP high refractive index providing layer 17 was variously changed, and the relationship with the cross loss was examined. When the width of the InGaAsP high refractive index providing layer 17 is 0 μm or 2.5 μm, the equivalent refractive index in the core is uniform, which corresponds to a conventional structure.

In FIG. 7, reference numeral 18 denotes a portion having the InGaAsP high refractive index providing layer 17 among the portions having the core layer, and an equivalent refractive index of the portion having the InGaAsP high refractive index providing layer 17 is 3.3. . 19 is the portion where the core layer is located.
The equivalent refractive index of the portion without the GaAsP high refractive index providing layer 17 and the portion without the InGaAsP high refractive index providing layer 17 is 3.2. Reference numeral 20 denotes a clad portion (a portion having only the InP substrate), and the equivalent refractive index is 1.0.

Here, the equivalent refractive index at the point of intersection is the first
And the point P corresponds to the second straight waveguide (the straight waveguide extending in the vertical direction in the figure) when the equivalent refractive index is considered to belong to the straight waveguide (the straight waveguide extending in the horizontal direction in the figure). It is set to the larger of the equivalent refractive index when it is considered to belong. That is, in the second embodiment, the equivalent refractive index at the intersection is 3.3.

FIG. 8 shows the relationship between the width of the high refractive index providing layer and the crossing loss. As shown in FIG. 8, when the width of the InGaAsP high refractive index providing layer 17 is larger than 0 μm and smaller than 2.3 μm, the cross loss is reduced as compared with the conventional structure.
This shows the effect of the second embodiment. In particular, when the width of the InGaAsP high refractive index providing layer 17 is 0.4 μm, the crossing loss is about 40 times that of the conventional structure (the structure having a uniform refractive index in the core).
%.

Next, a third embodiment of the present invention will be described. FIG.
The cross section of the cross waveguide according to the third embodiment of the present invention,
FIG. 10 is a graph showing the distribution of the equivalent refractive index of the cross waveguide as viewed from the upper surface of the substrate, and FIG. 11 is a graph showing the relationship between the cross loss and the width of the high refractive index providing layer. The crossing angle of the straight waveguide was a right angle.

In FIG. 9, reference numeral 21 denotes an InP substrate;
P Lower cladding layer (1.5 μm thickness), 23 is InGaAsP
Core layer (InP substrate lattice matching, composition corresponding to absorption edge wavelength 1.62 μm, thickness 0.26 μm), 24: InP upper cladding layer (thickness: 0.01 μm), 25: InP high refractive index providing layer (thickness: 0) .59 μm). The wavelength of the signal light is 1.65.
μm.

The equivalent refractive index of the core without the InP high refractive index providing layer 25 was 3.2. InP high refractive index imparting layer 2
The equivalent refractive index of the core in the portion where No. 5 was found was 3.28.
The width of the InP lower cladding layer 22, the width of the InGaAsP core layer 23, and the width of the InP upper cladding layer 24 were all 2.5 μm. The width of the InP high refractive index providing layer 25 was variously changed, and the relationship with the cross loss was examined. When the width of the InP high refractive index providing layer 25 is 0 μm or 2.5 μm, the refractive index in the core is uniform, which corresponds to a conventional structure.

In FIG. 10, reference numeral 26 denotes a portion where the InP high refractive index providing layer 25 is further provided among the portions where the core layer is provided.
The equivalent refractive index of the portion where the InP high refractive index providing layer 25 is provided is 3.
28. Reference numeral 27 denotes a portion where the core layer does not have the InP high refractive index providing layer 25,
The equivalent refractive index of the portion where there is no is 3.2. Reference numeral 28 denotes a clad portion (a portion having only an InP substrate) having an equivalent refractive index of 1.0.
It is.

Here, the equivalent refractive index at the point of intersection is the first
And the point P corresponds to the second straight waveguide (the straight waveguide extending in the vertical direction in the figure) when the equivalent refractive index is considered to belong to the straight waveguide (the straight waveguide extending in the horizontal direction in the figure). It is set to the larger of the equivalent refractive index when it is considered to belong. That is, in the third embodiment, the equivalent refractive index at the intersection is 3.3.

FIG. 11 shows the relationship between the width of the high refractive index providing layer and the crossing loss. As shown in FIG. 11, when the width of the InP high refractive index providing layer 25 is larger than 0 μm and smaller than 2.3 μm, the crossing loss is reduced as compared with the conventional structure.
The effect of the third embodiment is shown. In particular, when the width of the InP high refractive index providing layer 25 is 0.5 μm, the crossing loss is about 43% of the conventional structure (a structure in which the refractive index in the core is uniform).

Considering the above three embodiments, the width of the high refractive index imparting layer in which the effect of the present invention is remarkably exhibited is 0.1 mm.
It can be said that this is the case where the width is 1 μm or more and 1/3 or less of the width of the core layer.

Although the present invention has been specifically described based on the above three embodiments, the "structure in which the equivalent refractive index of the central portion in the core is higher than the equivalent refractive index of the peripheral portion in the core" of the present invention is as follows. The present invention can also be realized by using a layer structure not specifically described in the above-described embodiment.

For example, as shown in FIG.
9, an InP lower cladding layer 30 and an InGaAsP core layer 31 may be provided, and an InGaAsP high refractive index providing layer 32 may be provided on the InGaAsP core layer 31.

Further, as shown in FIG.
On top of this, an InP lower cladding layer 34, an InGaAsP lower guide layer 35, an InGaAsP core layer 36, and an InP upper cladding layer 3.
7 may be provided, and an InGaAsP high refractive index providing layer 38 may be provided on the InP upper cladding layer 37.

Further, as shown in FIG.
An InP lower cladding layer 40, an InGaAsP lower guide layer 41, and an InGaAsP core layer 42 may be provided thereon, and an InGaAsP high refractive index providing layer 43 may be provided on the InGaAsP core layer 42.

Further, as shown in FIG.
On top of this, the InP lower cladding layer 45 and the InGaAsP core layer 4
6 is provided, and the InGaAsP core layer 4 is formed on the InGaAsP core layer 46.
6 may be provided with an InGaAsP high refractive index providing layer 47 having the same composition.

12 to 15, it is possible to realize "a structure in which the equivalent refractive index of the central portion in the core is higher than the equivalent refractive index of the peripheral portion in the core", and obtain the effect of reducing the cross loss. Can be.

[0038]

As described above, according to the present invention,
Since the optical loss when the straight waveguides are crossed can be reduced, it is effective for improving the integration degree of the integrated optical device manufactured on the substrate.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a cross waveguide according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a cross waveguide.

FIG. 3 is a distribution diagram of an equivalent refractive index as viewed from the upper surface of the substrate of the cross waveguide.

FIG. 4 is a graph showing a relationship between crossing loss and a width of a high refractive index imparting layer.

FIG. 5 is a graph showing a distribution state of an absolute value of an electric field in a waveguide section.

FIG. 6 is a cross-sectional view of a cross waveguide according to a second embodiment of the present invention.

FIG. 7 is a distribution diagram of an equivalent refractive index as viewed from above the substrate of the cross waveguide.

FIG. 8 is a graph showing the relationship between crossing loss and the width of a high refractive index providing layer.

FIG. 9 is a cross-sectional view of a cross waveguide according to a third embodiment of the present invention.

FIG. 10 is a distribution diagram of an equivalent refractive index as viewed from above the substrate of the cross waveguide.

FIG. 11 is a graph showing the relationship between the crossing loss and the width of the high refractive index providing layer.

FIG. 12 is a cross-sectional view of a cross waveguide according to another embodiment of the present invention.

FIG. 13 is a cross-sectional view of a cross waveguide according to another embodiment of the present invention.

FIG. 14 is a cross-sectional view of a cross waveguide according to another embodiment of the present invention.

FIG. 15 is a cross-sectional view of a cross waveguide according to another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 InP substrate 2 InP lower cladding layer 3 InGaAsP core layer 4 InP upper cladding layer 5 InGaAsP high refractive index providing layer 13 InP substrate 14 InP lower cladding layer 15 InGaAsP core layer 16 InP upper cladding layer 17 InGaAsP high refractive index providing layer 21 InP Substrate 22 InP lower cladding layer 23 InGaAsP core layer 24 Upper cladding layer 25 InP high refractive index imparting layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shunji Seki 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 2H047 AA05 AB01 GG02 GG07

Claims (3)

[Claims] In an optical waveguide circuit formed on a substrate, an equivalent refractive index of a central portion in a core of an intersecting linear waveguide is changed along a central axis in a peripheral portion of the core near a clad. A cross waveguide characterized by having a higher refractive index than an equivalent refractive index. 2. The semiconductor device according to claim 1, further comprising: a core layer having a predetermined width on the substrate; and a high refractive index providing layer located above the core layer and having a width smaller than the width of the core layer. And a cross waveguide. 3. The method according to claim 1, wherein the equivalent refractive index is A when the point of the intersection belongs to one of the linear waveguides, and the point of the intersection is the other of the linear waveguides. A crossed waveguide characterized in that, when the equivalent refractive index is assumed to be B, the point of the intersection is set to the larger equivalent refractive index of A and B.