JPH03111825A - Distribution coupling type optical switch and its manufacture - Google Patents

Abstract

PURPOSE:To realize the optical switch which can be shortened in coupling length and its manufacture by providing a coupling part which is made of a group II-VI compound and couples upper clad layers in two stripes on an optical guide layer between the upper clad layers. CONSTITUTION:On a substrate 10, a lower clad layer 12 and an optical guide layer 14 are provided in order and a 1st rib 24 and a 2nd rib 24 which consist of the upper clad layers 16a and 16b, cap layers 18a and 18b, and (n)-side electrodes 20a and 20b are formed thereupon in two stripes. Then, light is guided by optical waveguide parts 26a and 26b constituted below the 1st rib 24a and 2nd rib 24b of the optical waveguide layer 14. Further, the coupling part 31 is formed of the group II-VI compound on the part between the two upper clad layers 16a and 16b of the optical guide layer 14, so the coupling length can be shortened by increasing the film thickness, so that the optical switch can be reduced in size.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a distributed coupling type optical switch and a method for manufacturing the same.

(Prior Art) Distributed coupling type (also referred to as directional coupling type) optical switches using semiconductor waveguides are attracting attention as optical switches for optical exchangers because they are capable of high-speed operation and low driving voltage operation. ing. In particular, compound semiconductor materials are used in semiconductor waveguides.
For example, optical switches using GaAs-based and InP-based materials are the main focus.

FIG. 8(A) is a schematic perspective view showing the configuration of a typical example of a conventional distributed coupling type optical switch, and FIG. 8(B) is a sectional view thereof.

In these figures, 10 is an n◆-GaAs substrate, 12 is an n-AβGaAs lower cladding layer provided on this substrate 10, and 14 is a 1-G layer provided on the lower cladding layer 12.
This is an aAs light guide layer. 16a and +6b are striped p-AβGaAs upper cladding layers, which are arranged on the optical guide layer 14 at appropriate intervals. Roughly 18a and +8b are upper cladding layer 1
p-GaAs camp layers provided on 6a and +6b, respectively; 20a and 20b are p-GaAs
These are upper electrodes provided on the cap layers 18a and +sb, respectively.

On the other hand, an n-side electrode 22 is provided below the n''-GaAs substrate 10.
is formed. In addition, these upper cladding layers 16a
, the cap layer 18a and the electrode 20a are the first ribs 24a.
lF! :, and the upper cladding layer +6b, the cap layer 18b and the electrode 20b are the second ribs 24b! 1) It is a distributed coupling optical switch having a structure in which the -AuGaAs upper cladding layers 16a and +6b are removed by etching or the like, leaving two rib portions, the first rib 24a2 and the second rib 24b.

In this distributed coupling optical switch, portions 26a and 26b of the 1-GaAs optical guide layer 14 immediately below the first rib 24a and the second rib 24b serve as optical waveguide sections, respectively.

In addition, in FIG. 8(8), W is the upper cladding layer 16.
a and +6b Therefore, the width of the first rib 24a and the second rib 24b, S is the distance between the upper cladding layer 16a and +ab, therefore, the distance between the first rib 24a and the second rib 24b, t is the thickness of the light guide layer 14, H indicates the thickness of the upper cladding layer.

Figure 8 (A) and CB)! In the distributed coupling type optical switch having the structure described above, the smaller the rib width W and the smaller the rib spacing S, the smaller the first rib 24a and the second rib 24b.
It is known that the bond length L0 can be made small. It is also known that if the coupling length Lc can be shortened, the optical switch can be made smaller.

(Problem to be Solved by the Invention) However, in the conventional optical switch described above, the minimum width of W and S is determined for manufacturing reasons, so there is a limit to reducing the coupling length L0. .

This invention was made in view of the above-mentioned problem of shortening the coupling length, and therefore, an object of the present invention is to provide an optical switch capable of shortening the coupling length L6 and a method suitable for manufacturing the same. It is about providing.

(Means for Solving Problem 1) In order to achieve this object, the distributed coupling type optical switch of this application includes a substrate, a lower cladding layer and a light guide layer sequentially provided on the substrate. and two striped upper cladding layers juxtaposed on the light guide layer, and in a distributed coupling optical switch made of a compound semiconductor, a layer is formed directly or intermediately on the light guide layer between these upper cladding layers. It is characterized by comprising a bonding portion made of a II-VI group compound and bonding these upper cladding layers through the layers.

Further, according to the method of manufacturing a distributed coupling type optical switch of this application, at least a lower cladding layer, a light guide layer,
The step of forming the thin films for forming the upper cladding layer and the upper electrode in this order, and the step of forming the thin films for forming the upper electrode and the upper cladding layer in this order until the surface of the thin film for forming the light guide layer is exposed or as described above. a step of removing the thin film for forming the upper cladding layer until it remains as a thin layer, and so that the thin films for forming the upper electrode and the upper cladding layer remain as two striped structures; a step of forming a lower electrode on the lower side of the substrate to produce the optical switch intermediate; and the surface of the thin film for forming the light guide layer between the two striped structures or on the thin layer. The present invention is characterized in that it includes a step of depositing a thin film made of a U-VI group compound with a predetermined thickness corresponding to the characteristics of the optical switch intermediate described above.

(Function) Hereinafter, the distributed coupling type optical switch C of this application may be abbreviated as an optical switch. ), a joint made of If-VI group compound is provided between the two striped upper cladding layers, that is, between the first rib and the second rib. The electric field coupling between the two is strengthened.

As a result, the coupling length Lc can be shortened, and the optical switch can be made smaller.

Furthermore, as is clear from the experimental results described later (see Figure 5), the bond consisting of a II-VI group compound can: (1) increase the film thickness to shorten the bond length and C , ■...The change in bond length Lc with respect to the change in film thickness is
The bond is looser than when the bond is made of, for example, /1lGaAs, and the change in bond length with respect to change in film thickness is saturated. Unique effects such as the characteristic that the saturation value of the bond length changes with changes in thickness can be obtained. Therefore, for example, A
The bond length Lc can be controlled more easily than when constructed from QGaAs.

According to the method for manufacturing a distributed coupling type optical switch of this application, an optical switch intermediate is first produced and its characteristics are measured. Next, an appropriate coupling length Lc is obtained between the two striped upper cladding layers of this optical switch intermediate, and hence between the first rib and the second rib, which can give the optical switch the desired characteristics. A thin film consisting of a ■-■ group compound is deposited with a film thickness of: Here, as already explained, the change in the bond length of the optical switch with respect to the change in the thickness of the thin film made of the ■-■ group compound is easy, so the bond length can be easily controlled, making it easy to fabricate an optical switch with desired characteristics. become.

(Embodiments) Hereinafter, embodiments of the distributed coupling type optical switch of this application and its manufacturing method will be described with reference to the drawings.

1. Figure 1 is a perspective view showing an embodiment of the optical switch of the present invention, and Figure 2 shows the optical switch shown in Figure 1 along the Y-
It is a sectional view of the main part taken along the Y line. It should be noted that these figures are merely schematic illustrations to the extent that the present invention can be understood, and the shapes, dimensions, and arrangement relationships of each component are not limited to the embodiments described below.

Furthermore, in the following embodiments, the structure will be explained with reference to FIGS. 1 and 2, assuming that the optical switch is constructed of a GaAs/AβGaAs system as an example.

Further, the same constituent components as those shown in FIGS. 8(A) and (8) are indicated by the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, n-Aj is formed on the n''-GaAs substrate 10.
2GaAs lower cladding layer 12.1-GaAs light guide layer 14, p-Au fffied to each other in stripes
GaAs upper cladding layer 16a and +6b, p-GaA
s cap layers 18a and +8b are provided, and p-
An n-side electrode 20a is placed on the GaAs caps 18a and +8b.
and 20b, an n-side electrode 22 is provided on the n''-GaAs substrate 1o.
A bonding pad portion 20c connected to b is provided.

These upper cladding layers 16a and 16b, cap layer 1
8a and 18b, and the n-side electrodes 20a and 20b are the first rib 24a and the second rib 24b, respectively! It consists of

Optical waveguiding is performed in optical waveguide sections 26a and 26b (see FIG. 2) formed under the first rib 24a and second rib of the optical guide layer 14.

Roughly speaking, this optical switch consists of an H-- group compound on the portion of the light guide layer 14 between the two upper cladding layers lea and +6b, and these upper cladding layers 16a.

A connecting portion 31 is provided to connect between +6b and 6b.

The film thickness of this joint portion 31 is the same as that of the two upper cladding layers 16a.
The film thickness is set to be thinner than that of +6b and to a predetermined value depending on the design. Although the details will be described later, this bonding portion 31 can be formed by, for example, vapor-depositing a TI-VI group compound.

FIG. 3 is a diagram approximately representing the refractive index distribution in the optical switch shown in FIG. 2. Here, the 1-GaAs optical guide layer 14, the n-AffGaAs lower cladding layer 12
．． 1) -AβGaAS upper cladding layer 16a, +6b
, the refractive indices of the p-GaAs cap layers 18a, 18b, and the coupling portion 31 are n, , n2, n3, and n11, respectively.
% n 5. Further, in calculating the equivalent refractive index described below, the origin x=O and y=o of the xy coordinate system were taken as shown in FIG. That is, x=O is the midpoint between the first and second optical waveguides 26a and 26b, and y=o
is the surface of the light guide layer 14. And the light guide layer 1
4, the area of the optical waveguides 26a and 26b will be described as I, the area where the coupling part 31 is not provided as ■, and the area where the coupling part 31 is provided as ■.

Here, neql % new□ in Fig. 3 is the equivalent refractive index caused by the propagation constant βr β■ β■ when the regions I, II, and ■ in Fig. 3 are respectively considered as slab waveguides. become that way.

n 1m,” (n +2n I*ff2+ n 2*
ff2)"2...'(1)n 28M" (n +2n
2eff' + n 3*ff2)"'・"(2)
However, nl*ff, n2@ff, and n3sff are effective refractive indices, respectively.

Further, regarding the waveguide modes in the optical waveguide sections 26a and 26b, considering only the TE mode and assuming that the phase constants in the X direction and the y direction are respectively, k is determined by the following equation (3).

kxW=pit +tan - goose [(n+/n+s
,)2 to +*q/L]"tan-'[(n+/n2*J
2 to 2*q'A/kx] "" (3) However, in equation 3), W is the rib width, p is a positive integer, and A is A=[1 −exp(−2eq・s)]/[l+ex
p(-kze,-s)]-(4) In odd mode, A□[l”exp(-2e*・s)]/[1-ex
p(-kze9·S)] (5).

However, in equations 4) and 5, S is the distance between the first and second ribs 24a and 24b. Also, in formula (3), 70. , (4) and (5), 2. , is determined by the following equation (6).

L*q"[(n+2-nteq2)ko-L2]"2
"" (6) However, i in formula (6) is 1 or 2, and is a cane.

is determined by Equation (10) described later.

On the other hand, k is determined by the following equation (7).

kyt"QT["tan-'(k2/ky)+tan-
'[(k3/kyXk3"k4'B)/(k, -B+
)]...(7) However, in formula 7), q is a positive integer, and 8 is determined by formula (8) below.

B=[l4-exp(2 to 3H)]/[1-eXl
)(2 to 3·H)] -...(s) However, in formula 8), H is the upper cladding layer 16a.

The thickness is +6b, and k and 3 are determined by the following equation (9).

ka"[(n+2-n*2)ko'-ky2]"2
(9) However, in equation (9), j=2.3.4, and ko is determined by equation (10) below.

ko=2vt/λ −(10) However, λ in formula 10) is the wavelength of light in vacuum.

Note that in region (2), 03 in equation (9) is calculated as 08.

Next, according to equations (3) and (6) above, even
phase constant k for each mode and odd mode
ll@and, , j&, the propagation low numbers β and β of each mode. is determined by the following equations (11) and (12).

β@=[(nlkG)2-kV2-kX@2] −
(II) β. = [(nlkG)2- kv2- kxo
2] "" (12) Furthermore, 8. and β. More below (
13) The bond length Lc is determined according to the formula.

Lc=it/(β, -80) (13) Calculating the electric field distribution of the optical switch according to the above equations (1) to (13) results in the following.

FIG. 4 shows the electric field distribution h(
FIG. 3 is a diagram for explaining the film thickness dependence of the bonding portion 31;
The distribution of the electric field in the light guide layer 14 in the X direction is shown when the film thickness of the coupling portion 31 is set as a parameter hi.

In FIG. 4, the lower diagram is a sectional view of the optical switch of the embodiment, and the upper diagram is an electric field distribution curve diagram. Furthermore, in the electric field distribution curve diagram, the horizontal axis shows the X direction of the optical switch, and the vertical axis shows the electric field E of the even mode (x) and the electric field E of the odd mode. (x) and the sum E (x). Also,
Calculation of the electric field distribution curve is performed using the first and second ribs 24a and 24b.
Each width Wt is 2.5 um, the rib interval SII is 5 μm, the film thickness t of the light guide layer 14 is 0.5 m, the lower cladding layer 12 is roughly composed of n Ano, 3 Gao, and 7 As layers, and the upper Cladding layers 16a, 16b @pA R
O,3G a O,? A: We investigated an optical switch composed of three layers. In the electric field distribution curve diagram, ■ means h=o,
This is a characteristic diagram of an optical switch with lum
FIG. 3 is a characteristic diagram of an optical switch in which =oum (when there is no coupling part 31).

As is clear from Figure 4, compared to the case where h=o, h=o
, lum, the electric field coupling portion increases.

In this way, when the electric field coupling becomes stronger, light transfers from the first optical waveguide section 26a to the second optical waveguide section 26b over a shorter distance than before. This means that the coupling length of the optical switch can be reduced.

Moreover, FIG. 5 shows the coupling length for light having a wavelength of 1.3 layers m when the film thickness of the coupling portion 31 made of II-VI group is changed. FIG. Note that the optical switch used in the experiment was the same as that used for measuring the electric field strength distribution.

In addition, the parameter is the coupling part 31 consisting of II-VI group.
The refractive index is . Furthermore, as a comparative example, the joint '&
The relationship between the film thickness of the coupling portion and the coupling length is also shown for an optical switch composed of AAo, 3Gao, and 7As layers (refractive index n=3.25). In this example, the ■-■ group compound is 2nO (refractive index n = 2.0
), ZnS (n = 2.3), Cd5e (n = 2
．． 5), Zn5e (n=2.5), 2nTe
(n=2.7), CdTe (n=2.7)
@Used respectively.

As is clear from FIG. 5, regardless of the magnitude of the refractive index of the coupling portion 31, as the film thickness ha of the coupling portion 31 is increased, the coupling length Lc can be decreased. It can be seen that the film thickness of the bonding portion becomes saturated when it exceeds a certain film thickness. In addition, in the case of the bonding portion 31 consisting of the ■-■ group, A
It can be seen that the degree of change in bond length with respect to change in film thickness is weaker than in the bonding portion of the comparative example made of the llGaAs layer, making it easier to control the bond length. Furthermore, it can be seen that even if the bonding portion 31 is made of the II-VI group, the higher the refractive index of the bonding portion 31, the larger the change in the bond length Lc with respect to the change in the film thickness of the bonding portion 31. Such a tendency holds true even if the phosphor spacing S is other values. That is, even when the rib width W and the rib spacing S are constant (for example, when they are the minimum dimensions determined for manufacturing reasons), by increasing the film thickness hv of the coupling portion 31, an optical switch with a short coupling length L0 can be obtained. becomes possible.

The above is a description of the embodiment of the optical switch of this application. However, the optical switch of the present invention is not limited to the above-described embodiments, and various modifications as described below can be made.

The above-mentioned example is G a A s / A 11 G
The aAs-based optical switch has been explained. However, I
The same can be said of optical switches constructed of nP/InGaAsP and other compound semiconductor materials. The same thing can be said even if the conductivity type of the light guide layer 14 is set to n or p conductivity type, or the conductivity type of each layer is reversed.

Further, in the above-mentioned embodiment, the coupling portion 31 made of a group II-III material was directly provided on the optical guide layer 14.

However, an intermediate layer may be provided between the light guide layer 14 and the coupling portion 31. An example will be explained with reference to FIG.

FIG. 6 shows an upper cladding layer 16a as an intermediate layer.

FIG. 6 is a cross-sectional view of an optical switch comprising a thin layer 16c of the same material as +6b; This thin layer 16c can be formed by leaving a thin layer without etching up to the upper surface of the striped upper cladding layer 16a, 16b% light guide layer 14. According to the optical switch shown in FIG. 6, light confinement in the lateral direction (in the direction indicated by the width W of the ribs 24a and 24b) can be slightly reduced.

Further, the compound of the ■-■ group is not limited to the above-mentioned examples, and other suitable compounds may be used.

1 μI Tomo KuzuNext, an embodiment of the optical switch manufacturing method of this application will be explained using an example of manufacturing the optical switch described using FIG. 1. Figures 7 (A) to (C) are process diagrams for explaining the process, and are cross-sectional views showing the state of the optical switch in the main steps in the process, focusing mainly on one optical switch part. .

First, n-AflG was deposited on the n◆-GaAs substrate 10 as thin films for forming the lower cladding layer, the optical guide layer, the upper cladding layer, the cap layer, and the upper electrode in this embodiment.
aAS layer 12x, 1-GaAs layer 14x, p-AJG
aAs layer fax, p-GaAs layer 18x and thin film for p-side ohmic electrode (e.g. Ti/Pt/Au thin film)
20x are formed in this order (FIG. 7(A)). Note that each compound semiconductor layer 12x to 18x is formed by MOCVD method.
Further, the thin film 20x for the p side-mick electrode was formed by a vapor deposition method.

Next, the thin film 20× for the p-side electrode is processed into a predetermined shape (a stripe shape with a width W and a bonding pad portion of 20%) by well-known phosphorography technology and etching technology, and the upper electrodes 20a, 20b are formed. form.

Next, using the upper electrodes 20a and 20b as a mask, a p-GaAs layer 1 which is a thin film for forming a cap layer and an upper cladding layer is formed.
The 8x and p-Al2GaAs layers 16x are removed by a known etching technique until the surface of the 1-GaAs layer 14x, which is a thin film for forming a light guide layer, is exposed, and two stripe-shaped first and second ribs are formed. 24a.

24b (FIG. 7(B)'').

Next, a lower electrode 22 made of an n-side ohmic electrode (for example, Au/Ge/Ni) is formed on the lower side of the substrate 10 by a known film-forming technique, and then the substrate 10 is An intermediate body 41 of the optical switch of the example is prepared by dividing the optical switch into each optical switch part (see FIG. 7(C)).
)).

Next, the characteristics of this optical switch intermediate body 41 are measured. From this measurement result and the characteristic diagram shown in FIG. 5, it is known how thick the bonding portion 31 should be to obtain the optimum bonding length Lc.

Next, the two ribs 24a of the structure shown in FIG. 7(C)
, 24b A mask made of a 5iQ2 film, for example, which emits only tg of Wr, is formed by known phosphorography and etching techniques. After that, II-V of a predetermined film thickness
A thin film made of a group I material is formed by a suitable method such as a vapor deposition method to form a joint portion 31 made of a group II-VI material. After forming the thin film made of II-VI group, the characteristics of the optical switch are measured, and if satisfactory characteristics cannot be obtained due to insufficient thickness of the thin film, the thin film made of II-VI group is measured. Reapply. As a result, an optical switch having a coupling part 31 consisting of the ■-■ group is obtained (see Figure 2).
.

Incidentally, the thin film composed of the II-VI group may have one kind of composition, or depending on the design, a plurality of kinds of thin films having different compositions may be laminated.

(Effects of the Invention) As is clear from the above description, according to the optical switch of this application, there are two striped upper cladding layers between the first rib and the second rib. - A bonding portion made of a group compound is provided. The bonding portion made of this II-VI group compound has the following properties: (1)...Increasing the film thickness can shorten the bond length Lc, and (2)...The change in the bond length Lc with respect to the change in film thickness is as follows:
It is looser than when the joint is made of AtGaAs, for example.
However, it also shows the property that the bond length change with respect to film thickness changes is saturated, and it also shows the property that the saturation value of bond length with respect to film thickness change changes by changing the composition of the -n-VI group compound. .

Therefore, since the coupling length can be shortened, the optical switch can be made smaller. Furthermore, since the coupling length Lc can be more easily controlled than when the coupling portion is made of, for example, MLGaAs, the optical switch can be manufactured more easily.

According to the method for manufacturing a distributed coupling type optical switch of this application, an optical switch intermediate is first produced and its characteristics are measured. Next, an appropriate coupling length Lc is obtained between the two striped upper cladding layers of this optical switch intermediate, and hence between the first rib and the second rib, which can give the optical switch the desired characteristics. A thin film of a II-VI compound is deposited with a thickness such that: Here, as explained above, the change in the bond length of an optical switch with respect to a change in the thickness of a thin film made of a group II-VI compound is gradual, so the bond length can be easily controlled and an optical switch with desired characteristics can be easily manufactured. become.

[Brief explanation of drawings]

Fig. 1 is a perspective view for explaining the optical switch of the example, Fig. 2 is a sectional view for explaining the optical switch of the example, and Fig. 3 shows the refractive index distribution in the optical switch of the example. 4 is a diagram showing the dependence of the electric field distribution in the optical switch of the example on the film thickness of the coupling part. FIG. 5 is a diagram showing the relationship between the bond length and the film thickness of the coupling part. 6 is a cross-sectional view for explaining an optical switch of another embodiment, FIGS. 7(A) to (C) are process diagrams for explaining an embodiment of a manufacturing method, and FIGS. 8(A) and ( 8) is a perspective view and a sectional view showing an example of a conventional optical switch. DESCRIPTION OF SYMBOLS 10... Substrate, 12... Lower cladding layer 14... Light guide layer 16a, 16b - Upper cladding layer 18a, 18b - Cap layer 20a, 20b -p side electrode 20c... Bonding pad part 22...n-side electrode, 24a...first rib 2
4b...Second rib, 26a, 26b...Optical waveguide portion 31.-Coupling portion 16 made of -II-VT group compound
c... Intermediate layer (thin layer with upper cladding layer remaining) 12x... Thin film for forming lower cladding layer 14x... Thin film for forming light guide layer 16x... Thin film for forming upper cladding layer 18x. ... Thin film for forming cap layer 20x... Thin film for forming upper electrode 41... Intermediate of optical switch. Patent Applicant: Oki Electric Industry Co., Ltd. Figure 1: A perspective view for explaining the optical switch of the embodiment. Figure 1: A sectional view for explaining the optical switch of the embodiment. A diagram showing the refractive index distribution in the optical switch of the embodiment. A diagram showing the dependence of the electric field distribution in the switch on the film thickness of the coupling part. Figure 4+6c Intermediate layer (thin layer with the upper cladding layer remaining) Cross-sectional diagram for explaining the optical switch of another example , a process diagram illustrating an example of a method for producing an intermediate for an optical switch, FIG. 7(C), a process diagram illustrating an example of a manufacturing method

Claims (2)

[Claims] (1) Comprising a substrate, a lower cladding layer and a light guide layer sequentially provided on the substrate, and two striped upper cladding layers juxtaposed on the light guide layer, made of a compound semiconductor. A distributed coupling type optical switch comprising: a coupling portion made of a II-VI compound and coupling between the upper cladding layers, directly or via an intermediate layer on the light guide layer between the upper cladding layers; Distributed coupling type optical switch. (2) forming at least a thin film for forming a lower cladding layer, a light guide layer, an upper cladding layer, and an upper electrode on the substrate in this order, and forming a thin film for forming each of the upper electrode and upper cladding layer,
Until the surface of the thin film for forming the light guide layer is exposed or until the thin film for forming the upper cladding layer remains as a thin layer,
and a step of removing the thin films for forming each of the upper electrode and the upper cladding layer so that they remain as two striped structures, and forming a lower electrode on the lower side of the substrate and forming the optical switch intermediate. forming a II-VI group film of a predetermined thickness depending on the characteristics of the optical switch intermediate on the surface of the thin film for forming the optical guide layer between the two striped structures or on the thin layer. 1. A method for manufacturing a distributed coupling optical switch, comprising the step of depositing a thin film made of a compound.