JPH04161905A - Te/tm mode light splitter - Google Patents

Abstract

PURPOSE:To monolithically form a semiconductor optical element by guiding both the TE mode light and the TM mode light in the upstream region from the branch point of the first wave guide path, guiding the TE mode light in the downstream region from the branch point of the first wave guide path, and guiding the TM mode light in the second wave guide path. CONSTITUTION:The first wave guide path 2 made of a mixed crystal semiconductor with the refraction factor smaller than the refraction factor of a substrate 1 is extended on a semiconductor substrate 1, and the second wave guide path 3 branched and stretched from the first wave guide path 2, made of a compound semiconductor super lattice containing the same component as the component of the mixed crystal, and having nearly the same height as the height of the first wave guide path 2 is extended. A clad layer 4 surrounding the second wave guide path 3 and the first wave guide path 2, made of the same super lattice as that of the second wave guide path 3 on the semiconductor substrate 1, and made of a layer lower than either the first wave guide path 2 or the second wave guide path 3 in height is extended. A semiconductor optical element can be monolithically formed.

Description

[Detailed description of the invention] [Summary] TE mode light and 7M used for coherent optical communication, etc.
Regarding the improvement of the TE-TM mode optical soot lifter that separates the mode light, we aim to provide a TE-TM mode optical soot printer that can be monolithically formed with semiconductor optical elements such as semiconductor light emitting elements and semiconductor light receiving elements. A waveguide made of a mixed crystal semiconductor having a diffraction index smaller than the refractive index of the semiconductor substrate, such as a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorus, extends on a semiconductor substrate such as indium phosphorus, A superlattice of a compound semiconductor that branches off and extends from this first waveguide and contains the same components as the above-mentioned mixed crystal, such as a superlattice of indium gallium arsenide and indium phosphide, or an indium gallium arsenide phosphide superlattice. A second waveguide is formed of a superlattice of indium phosphorus and indium phosphorus, and has a height that is approximately the same as that of the first waveguide. 1 waveguide, and is formed of the same superlattice as the second waveguide, and has a height equal to that of the first waveguide and the second waveguide. TE- with a structure in which a cladding layer consisting of a layer lower than either of the above extends.
It is constituted by a TM mode optical soot lifter or a TE-TM mode optical soot lifter having a structure in which the mixed crystal semiconductor end region and the superlattice N region are reversed.

[Industrial application field]

The present invention relates to improvements in a TE/TMM mode splitter that separates TE mode light and 7M mode light used in coherent optical communications and the like. In particular, it relates to an improvement that enables monolithic formation with semiconductor optical elements such as semiconductor light emitting elements and semiconductor light receiving elements.

[Conventional technology]

Since it is manufactured using conventional TE/TM mode optical soot lifters, lithium nitride, etc., it cannot be monolithically formed with semiconductor optical elements such as semiconductor light emitting elements and semiconductor light receiving elements.

[Problem to be solved by the invention]

However, it would be extremely convenient if it could be formed monolithically with a semiconductor optical element such as a TE-TM mode optical soot lifter, semiconductor light emitting element, semiconductor light receiving element, etc.

An object of the present invention is to meet this demand, and to provide a TE/TM mode optical soot lifter that can be formed monolithically with a semiconductor optical element such as a semiconductor light emitting element or a semiconductor light receiving element.

[Means for Solving the Problems] The above object can be achieved by any of the following means.

The first means is a semiconductor substrate (1) made of indinium phosphorus or the like.
A first waveguide ( 2
) extends from 0.05° to 2° with respect to this first waveguide (2).
The first waveguide (2
), branching and elongating from a superlattice of a compound semiconductor containing the same components as those of the above-mentioned mixed crystal, such as a superlattice of indium gallium arsenide and indinium phosphide or a superlattice of indium gallium arsenide phosphide and indinium phosphide. A second waveguide (3) consisting of a superlattice of phosphorus and having approximately the same height as the first waveguide (2) extends, and this second waveguide ( 3) and the first waveguide (2
) is formed on the semiconductor substrate (1) by the same superlattice as the second waveguide (3), and the height is the same as that of the first waveguide (2). There is a TE-TM mode optical splitter having a structure in which a cladding layer (4) consisting of a lower layer than either of the second waveguide (3) extends.

The second means is a semiconductor substrate (1) made of indinium phosphide or the like.
A superlattice having a refractive index smaller than that of the semiconductor substrate (1), for example, a superlattice of indium gallium arsenide and indium phosphide or a superlattice of indium gallium arsenide phosphide and indium phosphide, is formed on the top. 1 waveguide (2a) extends, and this first waveguide (2a) and 0
．． The first direction toward the direction forming an angle of 05° to 2°
The waveguide (2a) is branched and extended from the waveguide (2a) as a starting point, and is made of a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorus containing the same components as the superlattice component, and is made of a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorous, A second waveguide (3a) having approximately the same height as the waveguide (2a) extends, and this second waveguide (3a) and the first waveguide (2a) Surrounding the
The second waveguide (3) is formed on the semiconductor substrate (1).
It is made of a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorous containing the same components as in a), and has a height equal to that of the first waveguide (2) and the second waveguide (3). This is a TE-TMM mode splitter having a structure in which a cladding layer (4) consisting of a layer lower than either of the two extends.

[Effect]

The following relationship exists between the equivalent refractive index of a certain superlattice, for example, an indium gallium arsenide/indium phosphorus superlattice, and the refractive index of a mixed crystal made by mixing all the components of this superlattice. For TE mode light, the equivalent refractive index of the superlattice is larger than the refractive index of the mixed crystal, but for 7M mode light, the refractive index of the mixed crystal is larger than the equivalent refractive index of the superlattice. This is illustrated as follows. Figure 8(a)(b)(c) and Figure 9(a)(b)
) (C). In other words, in the case of Figure 8, since the superlattice is sandwiched between mixed crystals, the refractive index of TE mode light is high at the center where the superlattice is located, and the refractive index of 7M mode light is high at the center where the superlattice is located. It becomes low in the part.

In addition, in the case of Figure 9, the mixed crystal is sandwiched between superlattices, so the refractive index of TE mode light is lower at the center where the mixed crystal is, and the refractive index of 7M mode light is lower at the center where the mixed crystal is. It becomes high in some parts.

On the other hand, whether in TE mode light or 7M mode light, or in superlattice or mixed crystal, in the region where the height is increased to form a so-called ridge, the equivalent refractive index becomes larger.

The present invention was completed by skillfully combining these two properties, and the layer structure and T
The refractive index for E mode light and the refractive index for 7M mode light are shown in Fig. 5 (a) (b) (c), Fig. 6 (a) (b) (C), and Fig. 7 (a). (b) It will look like (c).

First, the A cross section is the same as in Figure 8(a), so if there is no ridge, the refractive index would be as in Figure 8(b).
It should look like (c), but since there is a ridge, T
The refractive index for E-mode light and the refractive index for 1M-mode light are both increased in the ridge portion, as shown in FIGS. 5(b) and 5(c).
It becomes as shown in .

Therefore, this region functions as a waveguide for both TE mode light and 1M mode light.

Next, since cross section B is a combination of FIG. 8(a) and FIG. 9(a), if there is no ridge,
b) It should look like (c).

However, since there is a ridge, for TE mode light,
It becomes especially large in the left half and becomes very large in the right half, and for 1M mode light, it becomes somewhat large in the left half and especially large in the right half, as shown in Fig. 6 (b) and (c). Therefore, the left half functions as a waveguide for TE mode light, and the right half functions as a waveguide for 1M mode light. The effect appears.

Thirdly, since the C section has a structure where FIG. 8(a) and FIG. 9(a) are juxtaposed, if there is no ridge, the T
The refractive index for E mode light is shown in Figures 8(b) and 9(b).
) are juxtaposed, and the refractive index for 1M mode light is supposed to be the juxtaposition of FIG. 8(c) and FIG. 9(C). However, since there is a ridge, the refractive index for TE mode light and the refractive index for 1M mode light are increased at the ridge portion, as shown in FIGS. 7(b) and 7(c). Therefore, the first waveguide 2 functions as a waveguide for 1M mode light, and the second waveguide 3 functions as a waveguide for TE mode light.

(Example) Hereinafter, with reference to the drawings, a TE-
The TM mode optical soot printer will be explained.

Refer to FIG. 2. Using the MOCVD method, a 30-layer thick Inc;
A superlattice layer 41 having a thickness of 1.2n is formed in which P layers and 30-layer InP layers are alternately laminated.

See Figures 3(a) and (b) Figure 3(a) is a plan view, and Figure 3(b) is its D-
It is a D sectional view.

Silicon nitride Wa21 is formed in a linear shape with a thickness of about 6n, and
The superlattice layer 41 is converted into a mixed crystal layer only in the region covered by the silicon nitride film 21 by heat treatment at about 0° C., so that the superlattice layer 41 is made of a mixed crystal semiconductor having the same composition as that contained in the superlattice layer 41. A first waveguide 2 is formed.

It is desirable that the first waveguide 2 be curved as shown in the figure, because it is easy to connect to a curved point to form a second waveguide. Note that although the curve is not drawn as a smooth curve in the figure, it is desirable that the curve is smooth.Then, the used silicon nitride film 21 is removed.

See Figures 4(a) and (b) Figure 4(a) is a plan view, and Figure 4(b) is its E-
It is an E sectional view.

Above the first waveguide 2 formed in the previous step and on the third waveguide
As shown in Figure (a), a belt-shaped region that starts from the curved part of the first waveguide 2 and branches from the first waveguide 2 at an angle of 0.05° to 2°, for example, 1°. A resist mask or the like 31 is formed on top of the superlattice layer 41, and the surface of the superlattice layer 41 is etched by 0.5n using reactive ion etching.
Etching is removed to form a step. After that, the used resist mask etc. 31 is removed.

See FIG. 1(a) As a result of the above steps, as shown in the perspective view of FIG. 1(a), the area covered by the resist mask etc. 31 becomes a ridge with a higher height than other areas. .

Then, starting from the curved part of the first waveguide 2, 0°05
The second waveguide 3 is formed by branching from the first waveguide 2 at an angle of 1° to 2°, for example, 1°, and is made of a superlattice layer, but has a ridge shape. The cladding layer 4 consists of a low-height region.

1(b) is a plan view of a TE-TM mode optical soot lifter according to an embodiment of the present invention shown in perspective view in FIG. 1(a). The first waveguide 2, which has a width of about 6n and is made of a mixed crystal semiconductor, is curved at the center and extends in the left-right direction in the figure, with an angle of 0.05° to 2° with respect to the first waveguide 2. For example, a second waveguide 3 made of a superlattice also extends in the left-right direction starting from the curved central portion in a direction forming an angle of 1°. The other region is a cladding layer 4 made of a superlattice, and this cladding layer 4 and the first and second waveguides 2
・The difference from 3 is that the height of the waveguides 2 and 3 is increased by about 0.5n compared to the height of the ground layer 4, and is formed into a ridge.

The reference figure in FIG. 1(c) is a sectional view taken along E-E of the plan view shown in FIG. 1b.
As shown in FIG. 5(a), FIG. 6(a), and FIG. 7(a), respectively. As described above in the [Function] section, the first waveguide 2 shown in FIG. 5(a) has a T
It functions as a waveguide for both E-mode light and 7M-mode light, and a mode drift function is expressed in the branching point region shown in FIG. 6(a), and the second waveguide shown in FIG. 7(a) The waveguide 3 functions as a waveguide for TE mode light.

Note that even if the superlattice region and the mixed crystal region in the above embodiment are reversed, it can function as a TE-7M mode optical splitter, and in that case, the TE-7M mode light waveguide region and the
The waveguide region for M-mode light is reversed.

〔Effect of the invention〕

As explained above, the TE-TM mode optical splinter according to the present invention is surrounded by a cladding layer made of a superlattice of indium gallium arsenide and indinium phosphide or a superlattice of indium gallium arsenide phosphide and indinium phosphide, for example. A ridge-shaped first waveguide made of a mixed crystal semiconductor containing, for example, indium, gallium, arsenic, and phosphorous extends, and branches off from this first waveguide to form, for example, indium gallium arsenide and indium. A structure in which a ridge-shaped second waveguide extends, consisting of a superlattice of indium gallium phosphide or an indium gallium phosphide superlattice, or a structure including, for example, indium, gallium, arsenic, and phosphorus. A ridge-shaped first waveguide is surrounded by a cladding layer made of a mixed crystal semiconductor and is made of a superlattice of, for example, indium gallium arsenide and indium phosphide or a superlattice of indium gallium arsenide phosphide and indium phosphide. The structure is such that a ridge-shaped second waveguide made of a mixed crystal semiconductor containing, for example, indium, gallium, arsenic, and phosphorus extends from the first waveguide. In the region downstream from the above branch point, both TE mode light and 7M mode light are guided, but the TE-TMM mode branching function is expressed at the above branch point,
In the region downstream from the above-mentioned branch point, each of the first waveguide and the second waveguide has a waveguide function for TE mode light and 7M mode light, and the semiconductor It can function as a TE-7M mode optical splitter that can be formed monolithically with semiconductor optical elements such as light emitting elements and semiconductor light receiving elements.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of a TE/TM mode optical soot lifter according to an embodiment of the present invention. FIG. 1(b) is a plan view of a TE/TM mode optical soot lifter according to an embodiment of the present invention. FIG. 1(c) is a side cross-sectional view of a TE/TM mode optical soot lifter (EE--E cross-sectional view of FIG. 1(b)) according to an embodiment of the present invention. These are a diagram, a plan view, a side view, a top view, and a side view. FIG. 5(a), FIG. 6(a), and FIG. 7(a) are cross sections AA and BB shown in side views of a TE-TM mode optical splitter according to an embodiment of the present invention. It is a layer structure diagram of a cross section and a CC cross section. Figure 5 (, b) (c), Figure 6 (b) (c), Figure 7
Figures (b) and (C) show the refractive index of TE mode light and TM mode light in the cross sections shown in Figures 5(a), 6(a), and 7(a), respectively. FIGS. 8 and 9 are diagrams explaining the natural laws on which the present invention is based. 1... Semiconductor substrate (indium phosphorus substrate), 2...
・First waveguide (ridge-shaped mixed crystal layer), 3... second waveguide (ring-shaped superlattice layer), 4... cladding layer (
5... Semiconductor substrate, 6... Superlattice, 7... Mixed crystal.

Claims (1)

[Scope of Claims] [1] A first layer made of a mixed crystal semiconductor having a refractive index smaller than that of the semiconductor substrate (1), on a semiconductor substrate (1).
A waveguide (2) extends and branches and extends from the first waveguide (2) as a starting point in a direction forming a predetermined angle with the first waveguide (2). A second waveguide (3) is formed of a superlattice of a compound semiconductor containing the same components as those of the crystal, and has a height roughly the same as that of the first waveguide (2). and the second waveguide (3) is placed on the semiconductor substrate (1) surrounding the second waveguide (3) and the first waveguide (2).
A cladding layer (4) consisting of the same superlattice as in 3) and having a height lower than either of the first waveguide (2) and the second waveguide (3) is extended. , an area upstream from the branching point of the first waveguide (2) guides both TE mode light and TM mode light, and a region upstream from the branching point of the first waveguide (2) guides both TE mode light and TM mode light. The downstream region guides the TE mode light, and the second waveguide (3) guides the T mode light.
A TE/TM mode optical splitter characterized by guiding M mode light. [2] The semiconductor substrate (1) is an indium phosphorous substrate, and the mixed crystal semiconductor forming the first waveguide (2) is a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorous; 2 waveguide (3) and the cladding layer (4)
TE/TM mode according to claim [1], characterized in that the superlattice forming the above is a superlattice of indium gallium arsenide and indium phosphide or a superlattice of indium gallium arsenide phosphide and indium phosphide. light splitter. [3] A first layer formed of a superlattice having an equivalent refractive index smaller than the refractive index of the semiconductor substrate (1) on the semiconductor substrate (1).
A waveguide (2a) extends, branches and extends from the first waveguide (2a) as a starting point in a direction forming a predetermined angle with the first waveguide (2a), and extends from the first waveguide (2a) as a starting point. A second waveguide (3a) made of a mixed crystal semiconductor containing the same components as the lattice components and having a height roughly the same as that of the first waveguide (2a) extends; Surrounding the second waveguide (3a) and the first waveguide (2a), a layer made of the same mixed crystal semiconductor as the second waveguide (3a) is disposed on the semiconductor substrate (1). , a cladding layer (4a) consisting of a layer whose height is lower than either of the first waveguide (2a) and the second waveguide (3a) extends, and the first waveguide (2a) ), the region upstream from the branching point guides both TM mode light and TE mode light,
A region downstream of the branching point of the first waveguide (2a) guides TM mode light, and a region downstream of the branching point of the first waveguide (2a) guides TM mode light.
) is a TE/TM mode optical splitter characterized by guiding TE mode light. [4] The semiconductor substrate (1) is an indium phosphorous substrate, the superlattice forming the first waveguide (2a) is a mixed crystal semiconductor containing indium, gallium, arsenic, and phosphorus, and the second waveguide (3a) and the cladding layer (4a)
), the TE/TM according to claim [3], wherein the mixed crystal is a superlattice of indium gallium arsenide and indium phosphorus or a superlattice of indium gallium arsenide phosphide and indium phosphorus. mode optical splitter.