JP2000235124A - Optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide which is capable of suppressing the coupling and reverse traveling of the reflected return light generated at a joint surface between a light input part and a light exit part to the core in the light input part when the light propagates from the light input part to the light exit part. SOLUTION: This optical waveguide is joined with a first core 3 constituting the light input part 1 and a second core 4 constituting the light output part 11. The second core 4 varies in at least either of the material or composition from the first core 3. The refractive index of the second core 4 is made lower than the refractive index of the first core 3. The optical waveguide described above is so formed that at least either of the thickness D and width W of the second core 4 is larger than that of the first core 3. The joint surfaces of the first core 3 and the second core 4 may be made diagonal with the progressing direction of the light at this time. These points are applicable similarly to the case the light propagates conversely from the second core 4 to the first core 3, i.e., the case 11 is formed as the light input part and 1 as the light output part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a butt joint in which two different optical waveguides are joined, and more particularly, to the realization of a small optical waveguide having a small amount of reflected return light.

[0002]

2. Description of the Related Art The joining of two optical waveguides differing in at least one of the material or composition of a core is generally called a butt joint (butt joining method), and is widely used in waveguide type optical devices. FIG. 10 is a perspective view showing the vicinity of a joint surface in a conventional butt joint. here,
I is an optical input unit, and II is an optical output unit. 1 is an upper clad, 2 is a lower clad, and 3 is a first
And 4, a second core in the light output section II. FIG.
FIG. 11 is a vertical sectional view taken along line AA ′ in the vertical direction of 0.
FIG. 12 is a cross-sectional view taken along the line BB 'in the horizontal direction of FIG.
Shown in

In this conventional example, as shown in FIG. 11, the thickness D ₁ of the first core 3 in the light input section I is equal to the thickness D ₂ of the second core 4 in the light output section II. Further, as shown in FIG. 12, the width W ₁ of the first core 3 in the light input section I is equal to the thickness D ₂ of the second core 4 in the light output section II. That is, in this conventional example, the first core 3 and the second core 4
Although the material and the composition are different from those of, the shape is the same.

[0004]

However, the difference in the material and composition between the first core 3 and the second core 4 in the above-mentioned conventional example corresponds to the difference in the refractive index between the first and second cores 3 and 4. Therefore, when the light incident from the light input unit I propagates to the light emission unit II, reflected return light is generated due to Fresnel reflection at the joint surfaces thereof. For example, at a wavelength of 1.55 μm, the upper cladding 1 and the lower cladding 2 have a refractive index of 3.1.
7, the first core 3 of the optical input unit I is an active layer for a semiconductor laser with a refractive index of 3.5, and the second core 4 of the optical output unit II is an InGaAsP having a band gap wavelength of 1.3 μm.
(Hereinafter referred to as 1.3Q) and the refractive index is assumed to be 3.39. The thickness D ₁ of the first core 3 and the thickness D ₂ of the second core 4
Is 0.4 μm, reflection light of about −38 dB is generated according to the calculation for the TE mode. In this calculation, the width W ₁ of the _first core 3 and the width W ₁
The width W ₂ of the core 4 is kept assumed to be equal.

[0005] Even if the amount of reflected return light is as large as this, when the first core 3 is an active layer such as a semiconductor laser or an amplifier, it has a significant effect on element characteristics. Had been a problem until.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to reflect light generated at a joint surface between a light input part and a light emission part when light propagates from the light input part to the light emission part. It is an object of the present invention to provide an optical waveguide capable of suppressing return light from being coupled to a core of an optical input portion and traveling backward.

[0007]

According to a first aspect of the present invention, a first core forming an optical input section and a second core forming an optical output section are joined. In the optical waveguide, the second core is different from the first core in at least one of a material and a composition, and the refractive index of the second core is lower than that of the first core. At least one of the thickness and the width of the core is larger than that of the first core.

[0008] In order to achieve the above object, a second aspect of the present invention is provided.
In the invention, a first core constituting an optical output unit and a second core constituting an optical input unit are joined, and the second core has at least one of a material and a composition with the first core. And the refractive index of the second core is different from the first core.
In the optical waveguide configured to be higher than the first core, at least one of the thickness and the width of the second core is smaller than that of the first core.

Here, the joint surface between the first core and the second core may be inclined with respect to the traveling direction of light propagating through the first core.

[0010] In order to achieve the above object, a fourth aspect of the present invention is provided.
According to the invention, a first core constituting an optical input unit and a second core constituting an optical output unit are joined, and the second core is formed of the first core and at least one of a material and a composition. And the refractive index of the second core is different from the first core.
In an optical waveguide configured to be lower than the core, the transmission refractive index of light propagating through the first core is substantially equal to the transmission refractive index of light propagating through the second core.
At least one of the thickness and the width of the second core is the first core.
The core is larger than that of the core.

[0011] In order to achieve the above object, the present invention provides a semiconductor device comprising:
In the invention, a first core constituting an optical output unit and a second core constituting an optical input unit are joined, and the second core has at least one of a material and a composition with the first core. And the refractive index of the second core is different from the first core.
In the optical waveguide configured to be higher than the core, the transmission refractive index of light propagating through the first core is substantially equal to the transmission refractive index of light propagating through the second core.
At least one of the thickness and the width of the second core is the first core.
Characterized in that it is smaller than that of the core.

[0012]

According to the present invention, according to the present invention, when light propagates from a light input section to a light output section, reflected return light generated at a joint surface between the light input section and the light output section is transmitted to the core of the light input section. It is possible to suppress the combination and the backward movement.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a first embodiment of the present invention. Here, I is an optical input unit, and II is an optical output unit. Reference numeral 1 denotes an upper clad, 2 denotes a lower clad, 3 denotes a first core in the optical input section I, and 4 denotes an optical output section II.
In the second core. FIG. 2 is a vertical sectional view taken along the line AA 'in the vertical direction of FIG.

[0015] The thickness D ₂ of the conventional example and the thickness D ₁ of the first core 3 and the second core 4 shown in FIG. 11 was equal. On the other hand, in the present embodiment, as shown in FIG. 2, the thickness D ₁ of the _first core 3 and the thickness D ₂ of the second core 4 are made different, and The center of the second core is not aligned in the thickness direction.

The compositions and materials of the upper clad 1, the lower clad 2, the first core 3, the second core 4, and the like are, for example, the same as those of the above-described conventional example. That is, at a wavelength of 1.55 μm of the propagating light, the upper clad 1 and the lower clad 2 have InP of 3.17 in refractive index, the first core 3 of the optical input section I is an active layer for a semiconductor laser and has a refractive index of 3.
5. The second core 4 of the optical output section II is 1.3Q (InGaAsP having a band gap wavelength of 1.3 μm) and has a refractive index of 3.
Assume 39.

FIG. 3 shows that the thickness D ₁ of the first core 3 is 0.
When the thickness D ₂ of the second core 4 is a variable at 4 μm, the eigenmode of the first core 3 is reflected on the joint surface between the first core 3 and the second core 4, and The result of calculating the amount of reflected return light coupled to the core 3 and moving backward is shown.

In the analysis of reflected return light, as described below, Method of Lines (Kono et al., IEEE, Photonics Technology Letters, vol. 10, pp.
108-110, 1998).

When the wave equation is expressed in a matrix,

[0020]

(Equation 1)

## EQU2 ## Here, z is the light propagation direction. [A] is a matrix including a differential operator for coordinates in a direction perpendicular to the light propagation direction z.

When formula (1) is diagonalized,

[0023]

(Equation 2)

Is obtained. In addition,

[0025]

(Equation 3)

[0026]

(Equation 4)

Here, the matrix [T] is a unitary matrix for diagonalizing the matrix [A].

The solution of the equation (2) is obtained in each region of the optical input unit I including the first core 3 and the optical output unit II including the second core 4.

[0029]

(Equation 5)

Is represented in the form Here, F and G correspond to a forward wave and a backward wave, respectively.

By setting the boundary condition for the field component expressed by using the equation (5), the amount of reflected return light at the interface between the light input portion I and the light output portion II having different core materials can be obtained.

As can be seen from FIG. 3, the second refractive index is low.
Reflection return light quantity returns thickness D ₂ is increased in the core 4 when the first core 3 is reduced.

(Second Embodiment) FIG. 4 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a second embodiment of the present invention. FIG. 5 is a longitudinal sectional view taken along the line AA ′ in the vertical direction of FIG. In the present embodiment, unlike the first embodiment, the center of the first core 3 in the thickness direction coincides with the center of the second core 4 in the thickness direction. Again, in this case,
Similarly to the calculation result in the first embodiment shown in FIG. 3, when the thickness D2 of the _second core 4 having a low refractive index increases,
The amount of reflected return light that is coupled to the core 3 is reduced.

(Third Embodiment) FIG. 6 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a third embodiment of the present invention, and FIG. 7 is a horizontal BB ′ of FIG.
It is a cross-sectional view along a line. In the first and second embodiments, the thickness D ₂ of the second core 4 having a low refractive index is larger than the thickness D ₁ of the first core 3 having a high refractive index.
As shown in FIGS. 6 and 7, while keeping the thickness D ₂ of the second core 4 having a low refractive index equal to the thickness D ₁ of the first core 3 having a high refractive index, the width W of the second core 4 is kept equal. ₂ for the first core 3
By also wider than the width W ₁ of the first of the above,
The same effect as in the second embodiment can be obtained.

(Fourth Embodiment) FIG. 8 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a fourth embodiment of the present invention. As shown in FIG. 8, the thickness D2 of the _second core 4 having a low refractive index is made larger than the thickness D1 of the _first core 3 having a high refractive index, and the width W2 of the _second core 4 is made large. Even if the width is larger than the width W1 of the _first core 3, the same effect as in the first to third embodiments can be obtained.

(Fifth Embodiment) In the conventional example shown in FIG. 11, the joint surface between the first core 3 and the second core 4 is perpendicular to the traveling direction of light. 1 to 8
, The thickness D ₂ of the second core 4 having a low refractive index
Is thicker than the thickness D ₁ of the first core having a high refractive index,
Or the width W ₁ of the width W ₂ of the second core 4 first core 3
Or at least one of the first and second cores 3 and 4 may be inclined with respect to the traveling direction of light as shown in FIG. Needless to say.

(Other Embodiments) In the above description, it is assumed that light propagates from the first core 3 having a high refractive index to the second core 4 having a low refractive index. When light propagates from the core 4 to the first core 3, ie,
The present invention is also applicable to a case where II is a light input unit and I is a light output unit.

That is, the first core 3 forming the light output section I and the second core 4 forming the light input section II are joined, and the second core 4 is made of a material or In an optical waveguide in which at least one of the compositions is different and the refractive index of the second core 4 is higher than that of the first core 3, at least one of the thickness and the width of the second core 4 is the first core. By making it smaller than that of the third embodiment, the same effect as in the first to fourth embodiments can be obtained. Also, in this case, similarly to the fifth embodiment, the bonding surface between the first core 3 and the second core 4 may be inclined with respect to the traveling direction of light.

[0039]

As described above, according to the present invention,
Since at least one of the thickness and the width of the second core is larger or smaller than that of the first core according to the difference in the refractive index between the first and second cores, light is emitted from the light input unit. When the light propagates to the portion, the reflected return light generated at the joint surface between the light input portion and the light output portion can be prevented from being coupled to the core of the light input portion and going backward.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view taken along the line AA ′ in the vertical direction of FIG.

FIG. 3 shows a thickness D1 of the _first core 3 of FIG.
In the case where the thickness D ₂ of the second core 4 is a variable, the first
FIG. 6 is a characteristic diagram showing a calculation result of the amount of reflected return light reflected at the joint surface between the first core 3 and the second core 4, coupled to the first core 3, and traveling backward. .

FIG. 4 is a perspective view of the vicinity of a joint surface of a butt joint of an optical waveguide according to a second embodiment of the present invention.

5 is a vertical sectional view taken along the line AA 'in the vertical direction of FIG.

FIG. 6 is a perspective view of the vicinity of a joint surface of a butt joint of an optical waveguide according to a third embodiment of the present invention.

FIG. 7 is a cross-sectional view taken along the line BB 'in the horizontal direction of FIG.

FIG. 8 is a perspective view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a fourth embodiment of the present invention.

FIG. 9 is a longitudinal sectional view showing the vicinity of a joint surface of a butt joint of an optical waveguide according to a fifth embodiment of the present invention.

FIG. 10 is a perspective view of the vicinity of a joint surface in a conventional butt joint.

11 is a cross-sectional view taken along the line AA ′ of FIG. 10 shown as a conventional example.

FIG. 12 is a cross-sectional view taken along the line BB ′ of FIG. 10 shown as a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper clad 2 Lower clad 3 1st core 4 2nd core I Optical input part II Optical output part

Claims (5)

[Claims] 1. A first core constituting an optical input unit and a second core constituting an optical output unit are joined, and the second core is at least one of a material and a composition with the first core. And the refractive index of the second core is lower than that of the first core, wherein at least one of the thickness and the width of the second core is the first core.
An optical waveguide characterized by being larger than that of the core. 2. A first core constituting an optical output unit and a second core constituting an optical input unit are joined, and the second core is at least one of a material and a composition with the first core. And the refractive index of the second core is higher than that of the first core. At least one of the thickness and the width of the second core is the first core.
An optical waveguide characterized by being smaller than that of the core. 3. The optical waveguide according to claim 1, wherein a joining surface between the first core and the second core is inclined with respect to a traveling direction of light propagating through the first core. An optical waveguide, comprising: 4. A first core constituting an optical input section and a second core constituting an optical output section are joined, and the second core is at least one of a material and a composition with the first core. And the refractive index of the second core is lower than that of the first core. In the optical waveguide, the transmission refractive index of light propagating in the first core and the refractive index of light propagating in the second core An optical waveguide characterized in that at least one of the thickness and the width of the second core is larger than that of the first core so that the transmitted refractive index of the light is substantially equal. 5. A first core constituting an optical output unit and a second core constituting an optical input unit are joined, and the second core is at least one of a material and a composition with the first core. Are different from each other, and the refractive index of the second core is higher than that of the first core. In the optical waveguide, the transmission refractive index of light propagating through the first core and the refractive index of light propagating through the second core An optical waveguide, wherein at least one of the thickness and the width of the second core is smaller than that of the first core so that the transmitted light has substantially the same refractive index.