JPS62231944A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To shorten the length of an element so that it can be made small in size, by constituting a waveguide so that each waveguide contents in both ends for constituting the element and its interval widens as it approaches the center, and also, each equivalent refractive index increases as the interval of the waveguides widens. CONSTITUTION:On a substrate 7, optical waveguides 8a, 8b are formed, and this optical waveguide 8a or 8b consists of an input use waveguide 9a or 9b, an output use waveguide 10a or 10b, and waveguides 11a, 12a or 11b, 12b which are placed between said waveguides. As he input use waveguides 9a, 9b advance from an input port, an interval between each of them narrows and they contact each other at a contact P. These input use waveguides 9a, 9b are connected to the waveguides 11a, 11b, respectively, and as the waveguides 11a, 11b advance from a contact P1, an interval between each of them widens, and also, each equivalent refractive index difference increases. That is to say, the equivalent refractive index increases together with width of the waveguide, therefore, as it advances from the contact P1, the width of the waveguide 11a is narrowed, and also, the width of the waveguide 11b is widened, therefore, the equivalent refractive index difference increases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical switch that electrically controls the traveling direction of light propagating in an optical waveguide.

[Conventional technology]

Conventionally, there is a balanced type optical switch as this type of optical switch. This type of optical switch is characterized by the fact that it is easy to reduce the operating voltage, and the requirements for precision in positioning the electrodes and the waveguide are relaxed.

Examples of this prior art include V., Ramaswamy, M., I.
ILDivino and R, D, 5tandley
“Applied physics LetLer”3
2i (IQ), 15 May 1978 (US)
There are those described in p-644 to p-646. Such a conventional example will be explained based on FIG. 2.

FIG. 2 is a configuration diagram of a conventional example. In FIG. 2, two optical waveguides 2a-2τ are provided on the substrate 1.

2b-21 are formed, and one element 5 is constituted by the 3 dB power plastic parts 3a, 3b and the interference part 4 provided therebetween.

The 3 dB power plastic parts 3a and 3b equally distribute the light input from one waveguide to the two optical waveguides 2a-2a, 2b-2 and output the same. In addition, the interference section 5 includes electrodes 6a and 6b on the central portions of the optical waveguides 2a-2 and 2b-21.
to control the phase of the light.

[Problem that the invention seeks to solve]

However, such a conventional example requires two parts, a 3 dB coupler part and an interference part, so the element length may be long, and the characteristics of the 3 dB coupler part change depending on the manufacturing conditions. There is a problem that there are restrictions on the creation conditions.

The present invention has been made to solve the above problem, and its purpose is to reduce the size and simplify manufacturing by eliminating the need for a 3 dB power plastic section.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a waveguide type optical switch that includes two waveguides whose mutual spacing is narrow at both ends constituting an element and wide at the center, in which the two waveguides are in contact at both ends constituting the element. a waveguide which widens as it approaches the center and whose mutual equivalent refractive index increases as the waveguide spacing increases, electrodes provided on each of the waveguides, and an input side and an output side of the two waveguides. and waveguides connected to each other.

[Effect]

In the present invention having the above characteristics, first, when light is input through the input waveguide, the light traveling to the waveguide is separated into a symmetric mode and an antisymmetric mode at the end thereof. Next, as the mode advances from the end of the waveguide to the center of the element, the symmetric mode transfers power to the waveguide with a wider waveguide width, and the antisymmetric mode s11 transfers power to the waveguide with a narrower waveguide width.

Furthermore, when proceeding from the midpoint of the element to the end, the power is equally distributed between the two waveguides.

At the end of the element described above, the phase difference between the symmetrical mode and the antisymmetrical mode determines which output waveguide these are outputted to.

Similarly, when a voltage is applied to the electrodes, the difference in equivalent refractive index between the two waveguides can be changed by an electro-optic effect. Therefore, the above-described waveguide type optical switch can perform a switching operation as an optical switch.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1, 3, and 4 (
The explanation will be based on a) and (b).

FIG. 1 is a configuration diagram showing an embodiment of a waveguide type optical switch according to the present invention.

In FIG. 1, an optical waveguide 8a is provided on the substrate 7.

8b is formed. This optical waveguide 8a or 8b is
Input waveguide 9a or 9b + output waveguide 10a or 10b and waveguides 11a and 12 arranged between them
It consists of a or 11b and 12b.

As the input waveguides 9a and 9b move toward the input boat, the distance between them becomes narrower, and the input waveguides 9a and 9b contact each other at a contact point P.

These input waveguides 9a and 9b are respectively waveguides 11
a, connect to 11b.

The waveguides 11a+11b are arranged such that the distance between them widens 9 as they proceed from the contact point P1, and the difference in their equivalent refractive indexes also increases. That is, since the equivalent refractive index increases with the waveguide width, the width of the waveguide 11a is made narrower and the width of the waveguide 11b is made wider as the waveguide goes beyond the contact point P1. This increases the equivalent refractive index difference.

Furthermore, as the distance between the two waveguides 11a and 11b increases, the coupling coefficient between the two waveguides 11a*11b decreases.

Next, at the midpoint (Z=t/2) of the element 13 constituting the waveguide optical switch, the waveguide 11a is inserted.

iib is connected to waveguides 12a and 12b, respectively.

As the waveguides 12a and 12b move toward the center of the element 13, the distance between them becomes narrower, and the difference in their equivalent refractive indexes becomes smaller. As a result, the waveguides 12a, 12b
The coupling coefficient between the two increases as one moves beyond the midpoint.

Furthermore, the widths of these waveguides are configured to become the same as they advance from the midpoint.

Next, at contact P2, the waveguide 12a.

12b are in contact with each other as shown in FIG. 1, and their waveguide widths are the same. Moreover, at the contact point P2, the waveguides 12a and 12b have output waveguides 10a and 12b, respectively.
IQb connects.

As shown in FIG. 1, electrodes 14a are provided on the outside of the waveguides 11a and 12a, 11b and 12b.

14b is provided. This configuration shows a case where a material whose refractive index changes largely with respect to an electric field in a direction perpendicular to the surface of the substrate 7 is used, such as an L 1Nb03-Z plate.

Moreover, from the midpoint (Z=t/2) of the element 13 to the contact PL,
As it moves closer to P2, the distance between the electrodes 14a and 14b increases, and the edges of the electrodes 14a and 14b (the part where the refractive index change is the largest) become closer to the waveguides 11a, 12a, 11
I try to stay away from b and i2b.

That is, when a voltage is applied to the electrodes i 4 a s 14 b, the waveguides 11a and 12a are formed due to the electro-optic effect.

The isolateral refractive index change at 11b and 12b is the contact point PL,
It becomes almost 0 at P2, and the midpoint of element 13 (Z
= 4/2).

FIG. 3 shows the starting point (2=0) of the element 13 and the ending point (2=t
) is a relational diagram showing an overview of changes in the coupling coefficient and equivalent refractive index while proceeding to ). Δβ is the waveguide 11a and 11
b, the maximum equivalent refractive index difference between 12a and 12b.

Next, the principle of operation will be explained based on FIGS. 4(a) and 4(b).

Figures 4(a) and 4(b) are explanatory diagrams of the operating principle.
In (a), the phase difference is 2nπ, and in (b), the phase difference is (2nπ).
The case of n+1)π is shown. However, n=o, 1,
It is 2°3...

First, when the light S is input from the input waveguide 9a (or 9b), the light S that has proceeded to the contact point P1 is in the symmetric mode S.
1 and antisymmetric mode S2. Next, contact P1
As the wave moves toward the center point (Z=t/2) of the multi-element 13, the symmetric mode S5 transfers its power to the waveguide 11a, and the antisymmetric mode S11 transfers its power to the waveguide 11b.

Further, proceeding from the midpoint of the element 13 (Z=t/2) to the contact P2, the symmetrical mode S5 or S7 and the antisymmetrical mode S6 or S8 are again the same as at the contact P1. Power is equally distributed in the waveguides 12a and 12b.

This phenomenon occurs because the two waveguides 12a and 1
This is because, in a system with 2b, the power distribution of the symmetric mode S3 and the antisymmetric mode S11 is determined by the ratio of the waveguide spacing to the waveguide width (or equivalent refractive index difference). In other words, the symmetric mode is the waveguide 11 with a wide waveguide width.
This is because the main power is present in bt12b, and the main power is present in the waveguides 11a and 12a having a narrow waveguide width in the antisymmetric mode.

At the contact point P2, the symmetrical mode S5 or S7
The phase difference between the antisymmetric mode S6 or Sg determines which output waveguide 1Qa, 10b these are output to.

For example, if the phase difference is 0.2π, 4π, etc., the output waveguide 10 is
a, and the phase differences are π, 3π, and 5π.

..., then the light is output to the output waveguide iob like light S10 in FIG. 4(b).

The phase difference at the contact point P2 is obtained by multiplying the difference in equivalent refractive index for the symmetric mode and the antisymmetric mode by the wave number of light, and then integrating this from Z20 to 2=1.

Similarly, when the difference in equivalent refractive index between the waveguides 11a and 12a and the waveguides 11b and 12b is increased, the difference in equivalent refractive index between the symmetric mode and the antisymmetric mode becomes larger.

Conversely, waveguides 11 ap 12a and waveguides iib and 12
When the equivalent refractive index difference between b is made smaller, the difference in equivalent refractive index between the symmetric mode and the antisymmetric mode becomes smaller.

Further, when a voltage is applied to the electrodes 14a and 14b, the equivalent refractive index difference between the waveguides 11a and 12a and the waveguides 11b and 12b can be changed by the electro-optic effect.

Therefore, in this way, the waveguides 11a, 11b.

It is possible to operate as a waveguide type optical switch only at the points t2a and i2b. Therefore, even though the electrode structure is close to that of a simple balance bridge type waveguide optical switch, the 3 dB power plug part is not required.

Next, Fig. 5 (al) r (a2) t (c),
In (a), the results of analyzing the operating characteristics of a waveguide optical switch element are shown.

FIG. 5 is an explanatory diagram of the operating characteristics of elements in a waveguide type optical switch. Note that the following equation (11) was used as the coupling equation. This is an essential equation set corresponding to the configuration of the waveguide type optical switch shown in FIG.

However, δ=Δβα−I Z/ CL/2) −11)
...(2) Equation a: Optical power b in waveguides 11a and 112a: Optical power ψ in waveguides 11b and 12b: Waveguides 11a and 1
Opening angle (rad) of waveguides 11a and 11b and 12a and 12b Δβ: Maximum equivalent refractive index difference between waveguides 11a and 11b and 12a and 12b 2: Propagation distance t: Element length Ko: Maximum difference between waveguides 11a and 11b and 12a and 12b The coupling coefficients are the coupling coefficients of the waveguides 11a and 11b and 12a and 12b at the contact points P1 and P2.

B: Two waveguides 11a and 12a and a waveguide 11b.

12b and a coefficient that relates the coupling coefficient. For example, wavelength of light = 0.63 μm 1 waveguide width 3 am
In the waveguide created by diffusing Ti with a thickness of 30 OA into LiNbO3 at 100°C, BzO,
There is an actual experimental value of 058.

Lo=(tc/2γKo Here, in FIG. 5, the value obtained by substituting the experimental value of tozO,25+w was used.

In addition, Fig. 5 (al), (a2), (b),
In (c), element length L = 5 tea, I-/
The case where to=20 and the opening angle ψ is set to three values is shown.

First, FIG. 5(al) is an explanatory diagram of the operating characteristics in the case of ψ=1/200. In the figure, the vertical axis indicates the relative optical output power, and the horizontal axis indicates the maximum equivalent refractive index difference Δβ, which is the normalized value Δβ/Ko divided by 1.

Here, when light is input to one input waveguide, for example 9a, the optical output power of the output waveguide 10a or 10b and the power of the input light are shown as 1.

When inputting to the input waveguide 9a, the output waveguide 1
The power of the light output to 0a is output in the Bar direction (○
and a solid line), and the power of light output to the output waveguide 10b is shown by a cross direction output (× and a broken line in the figure).

Therefore, in the output waveguide 10ay10b,
It can be seen that as Δβ increases, it switches periodically.

FIG. 5(a2) is an explanatory diagram in which the value of the relative output optical power on the vertical axis shown in FIG. 5(al) is expressed in dB.

From this Fig. 5 (a2), 20
It can be seen that an extinction ratio of dB or more can be obtained.

FIGS. 5(b) and 5(C) show the opening angle ψ=0.
0075 and ψ=0.0025. FIG. Note that the vertical axis indicates relative optical output power, and the horizontal axis indicates Δβ/Ko.

In these cases, the design differs from the case in FIG. 5(al). Further, eXp in the above equation (2) indicating the coupling coefficient K.

Similar to the case in Figure (al), even if only B is different, the effect is the same. This is because the waveguide creation conditions are as shown in Figure 5 (al
).

Also, in the case of Fig. 5(b) * (C), 2
It can be seen that an extinction ratio of 0 dB or more can be obtained.

By the way, FIG. 6 shows the relationship between relative optical output power and Δβ/Ko when the equivalent refractive index difference between waveguides 11a and 11b and 12a and 12b at contact points P1 and P2 is not O and has a value of Δβ0. FIG.

FIG. 7 is an explanatory diagram showing the relationship between the equivalent refractive index difference, the coupling coefficient, and the propagation distance Z in the case shown in FIG. This is Δβ0 for the isolateral refractive index in the case of FIG. 4(b).
It shows the state where the top is raised.

It can be seen that the characteristics shown in FIG. 6 described above, and in this case, the characteristics shown in FIG. 5 (al), are deteriorated. Therefore, it can be understood that it is desirable that Δβ0 be as small as possible.

FIG. 8 is an explanatory diagram showing the characteristics of the measurement results of the prototype device.

Here, the prototype device has an element length L=6ra, an average waveguide width of 3 μm, and waveguides 11a and 11b and 12a and 12b.
The maximum value of the waveguide width ratio is 0.85:1.15, ψ
= 0.005.

In addition, this element was created using a substrate 7 of an L:Nb05-Z plate.
A Ti film is deposited to a thickness of 300× and diffused at 1000° C. to form a waveguide pattern. On top of this, Si02 is sputter deposited to a thickness of 2000× and electrodes 14a and 1 are formed on the upper side.
4b was installed. This electrode 14a.

The maximum interval between 14b is 20μm1 and the minimum interval is 13μm
It becomes.

First, FIG. 8(a) is a diagram showing the relationship between applied voltage and relative optical output. Here, the horizontal axis indicates the magnitude of the voltage applied to the electrodes 14a, 14b, and the vertical axis indicates the output waveguides 10a, 1.
The relative optical output power from 0b is shown.

As can be seen from Fig. 8(a), Fig. 8(a) corresponds to Fig. 5(a1), and Δβ/Ko is approximately proportional to the applied voltage.Therefore, as expected from the analytical results, It can be seen that the output waveguides 10a and 10b operate in a manner that they are periodically switched.

Next, FIG. 8(b) is a diagram showing the relationship between the extinction ratio and the diffusion time of the element. The vertical axis shows the extinction ratio of the element, and the horizontal axis shows the diffusion time.

As can be seen from this figure, a relatively high extinction ratio can be obtained regardless of the diffusion time. Therefore, it can be seen that the restrictions on the creation conditions are lenient.

〔Effect of the invention〕

As described above, according to the waveguide type optical switch according to the present invention, the waveguides are in contact at both ends of the element, and widen as they approach the center, and their equivalent refractive indexes increase as the distance between the waveguides increases. By making it
It exhibits the following effects.

In other words, it is not necessary to connect the 3 dB coupler section as in the conventional example, so the device length can be shortened and the device can be made smaller. Also, the requirements for the manufacturing conditions are relaxed, but it still has the characteristics of the conventional balanced bridge type optical switch. However, this characteristic has the effect that it does not have much influence on the alignment accuracy between the electrode and the waveguide.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram of a conventional example, Fig. 3 is a diagram showing the relationship between the coupling coefficient and the equivalent refractive index, and Figs. 4 (a) and (b). is an explanatory diagram of the operating principle.v
(a) shows the case where the phase difference is 2nπ, and (b) shows the case where the phase difference is (2n+1)π. Figure 5 (al)
. (a2), (b) I (C) is an explanatory diagram of the operating characteristics of the element, and (al) is when ψ = 1/200, (
a2) is when the relative optical output power value is expressed in dB, (b) is when ψ=0.0075, and (C) is when ψ=0.
The case of 0025 is shown. Figure 6 shows the relative optical output power and Δ
FIG. 7 is an explanatory diagram showing the relationship between β/Ko, FIG. 7 is an explanatory diagram showing the relationship between the coupling coefficient and isolateral refractive index difference, and FIGS. 8(a) and 8(b) are explanatory diagrams showing the characteristics of the prototype element. (a) is a relationship diagram between applied voltage and relative optical output, and (b) is a relationship diagram between extinction ratio and diffusion time. 7... Substrate aa, sb... Optical waveguide 9a, 9b
...Input waveguide 10attOb...Output waveguide 11ay11b, 12a, 12b-waveguide 13...
・Device patent applicant Takashi Kanakura, patent attorney representing Oki Electric Industry Co., Ltd. 2. Block diagram showing one embodiment of the present invention 1 = Block diagram of conventional example 2-0 Propagation distance zZ Coupling coefficient and equipolarized refractive index Relationship diagram @ 3111a (al) (a2) Explanation diagram of the operating characteristics of the element Noodle 51 (,b) Explanation of the operating characteristic of the element O @ t=5″ Noodle 5 l Relative optical output power and ΔR Explanatory diagram axis showing relationships 6
Figure Relationship between coupling coefficient and equivalent refractive index difference Axis 7 Figure Applied voltage [v] (a) Explanatory diagram showing the characteristics of the prototype element Tsumugi 81 Procedural correction band (spontaneous) June 29, 1988 Patent Office Director Kunio Ogawa 1, Indication of the case 1986 Patent Application No. 074285 2, Title of the invention Waveguide type optical switch 3, Relationship with the person making the amendment Case Patent applicant Location 1-chome Toranomon, Minato-ku, Tokyo No. 7 No. 12 Name (029) Oki Electric Industry Co., Ltd. Representative Bridge
Hon Nankai 4, agent 7, amendment content 1, and scope of claims are revised as shown in the attached sheet. 2. In the 20th line of page 1 of the specification, the word "balanced type" is corrected to "balanced bridge type." 3. In the 17th to 18th lines of page 2 of the specification, the phrase ``the interference unit 5 is'' is corrected to ``the interference unit 4 is''. 4. In the 16th to 17th lines of page 3 of the specification, the phrase "refractive index" is corrected to "refractive index difference." 5. In the 6th line of page 4 of the specification, the phrase ``The symmetric mode is'' is corrected to ``The symmetric mode 53 is''. 6. In the 9th line of page 4 of the specification, insert ``the above two modes'' after ``proceeding from the midpoint of the element to the edge''. 7. On page 4, line 15 of the specification, the phrase "equivalent refractive index difference" is corrected to "equivalent refractive index difference." 8. On page 8, line 12 of the specification, "waveguide 11a" is corrected to "waveguide 11b." 9. On page 8, line 13 of the specification, "waveguide 11b" is corrected to "waveguide 11a." 10. On page 9, line 13 of the specification, the statement "The phase difference is 0.2π. 4π, . . ." is corrected to "The phase difference is 0, 2π, 4π. . . ." 11. On page 12, line 7 of the specification, rBzO, ossj is corrected to rB:o, 0012J. 12. On page 12, line 15 of the specification, “φ=1/200j
The statement “φ=l/1000 J is corrected. 13. On page 13, line 16 of the specification, “φ=0.0075
J is corrected to ``φ=O,0O15J. 14. On page 13, line 17 of the specification, [φ=0.0025
Correct the statement J to [φ=0.0005J. 15. On page 16, line 15 of the specification, the phrase "refractive index" is corrected to "refractive index difference." 16, Specification page 17, line 11 K “φ=1/200J
Correct the statement as ``φ=1/1000 J.In the 12th line of page 17 of the Oka Specification, it says ``φ= 0.0075.
j is corrected to ``φ= 0.0015 J. 18. In the specification, page 17, line 13, ``φ= 0.002
5 Correct J to φ=0.0005J. 19. Correct Figure 2 as shown in the attached drawing. Correct Figure 5 (al) as shown in the attached drawing. 21. 5th Figure (b) is corrected as shown in the attached drawing. 22. Figure 5 (c) is corrected as shown in the attached drawing. 23. Figure 6 is corrected as shown in the attached drawing. Spacing between claims In a waveguide type optical switch, the two waveguides are narrow at both ends of the element and wide at the center, and the two waveguides are in contact at both ends of the element and widen as they approach the center. comprises a waveguide which is amplified as the waveguide spacing increases, electrodes provided on each of the waveguides, and waveguides connected to the input side and output side of the two waveguides, respectively. A waveguide type optical switch with a conventional example.

Claims (1)

[Scope of Claims] In a waveguide type optical switch equipped with two waveguides whose mutual spacing is narrow at both ends constituting an element and wide at the center, the two ends constituting the element touch each other as they approach the center. a waveguide which spreads out and whose mutual equivalent refractive index amplifies as the distance between the waveguides increases; electrodes provided on each of the waveguides; and electrodes connected to the input and output sides of the two waveguides, respectively. What is claimed is: 1. A waveguide type optical switch comprising: