JPH0743484B2 - Waveguide optical switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a waveguide type optical switch suitable for use in the field of optical communication and the like, and more specifically, it has little wavelength dependence and a wide wavelength range. The present invention relates to a waveguide type optical switch capable of simultaneously switching the signal lights in the region.

[Conventional technology]

For the further spread of optical fiber communication, in addition to high performance and low cost of optical fibers and light receiving / emitting devices, various optical circuit components such as optical branching / coupling devices, optical multiplexers / demultiplexers, and optical switches will be used. Development is at an indispensable stage. Among them, the optical switch will be able to switch the optical fiber line freely according to the demand, and in the near future, in order to secure the detour in case of line failure.
It is considered to play an important role.

Conventionally, 1) bulk type and 2) waveguide type have been proposed as the configuration form of the optical switch, but each has problems. The bulk type is assembled by using a movable prism, a lens, etc. as constituent elements, and has the advantages of less wavelength dependence and relatively low loss, but the assembly adjustment process is complicated and is not suitable for mass production, and it is expensive. It has drawbacks and has not yet spread widely. The waveguide type is a mass production of so-called integrated type optical switches in bulk, using photolithography and microfabrication technology, based on an optical waveguide on a planar substrate. Is expected as.

FIG. 7 is a plan view showing a configuration example of a conventional waveguide type optical switch. Here, the 3 dB optical couplers 2 and 3 formed on the substrate 1 constitute a directional coupler together with the two optical waveguides 4 and 5 which are close to each other, and the coupling rate thereof is 50% (completely at the signal light wavelength). It is set to be 1/2 of the bond length. The optical path lengths of the two optical waveguides 4 and 5 connecting between the 3 dB optical couplers 2 and 3 are the same in the state where the phase shifters 4a and 5a arranged on the way of these two optical waveguides are not operated ( Symmetric) is set.

The signal light incident from the input port 1a is emitted from the output port 2b and is not emitted from the output port 1b in the above state. However, 180 ° (π
Radian) When at least one of the phase shifters 4a and 5a is operated so that the optical path length difference near 1/2 wavelength corresponding to the optical phase is generated, the signal light is switched to be output from the output port 1b and serves as an optical switch. Is achieved. This type of waveguide type optical switch is also called a Mach-Zehnder interferometer circuit type and can realize a switching action by a relatively simple phase shifter, so that it can be used in various optical waveguide material systems including glass optical waveguides. Although it has been tried, the following problems have been encountered so far.

[Problems to be Solved by the Invention]

FIG. 8 is a wavelength characteristic diagram showing the coupling rate from the input port 1a to the output port 2b of the optical switch designed and manufactured for 1.3 μm wavelength. Curve (a) shows the phase shifter 4a and
5a is the coupling characteristic when the phase shifter is off, and curve (b) is the coupling characteristic when one of the phase shifters is on. For reference, the curve (c) shows the coupling ratio wavelength characteristic of the 3 dB optical coupler as a constituent element.

When one phase shifter is on (curve (b)), 1.
In a relatively wide wavelength range of about ± 0.2 μm with 3 μm as the center, the coupling ratio (1a → 2b) is almost zero (5% or less), and the signal light passes through the route (1a → 1b) with little wavelength dependence. It is possible to

On the other hand, in the off state (curve (a)), the coupling ratio of 90% or more (1a → 2b) is limited to a narrow region of about 1.3 μm ± 0.1 μm. For example, at a wavelength of 1.55 μm, the coupling ratio is 50%. There was a big problem that the switching state reached halfway because it reached only about%.

Thus, the largest cause of the large wavelength dependence of the conventional waveguide type optical switch shown in FIG.
The optical coupler (directional coupler) has a large wavelength dependency as shown in the curve (c) of FIG. 8, and the 50% coupling rate is obtained at the wavelength of 1.3 μm as shown in the curve (c). When set as above, at a wavelength of 1.55 μm, there was a large deviation from 50%, and there was a point that it did not function as a 3 dB optical coupler.

When an optical switch is used in fields such as optical fiber line switching, there are many situations in which 1.3 μm wavelength light and 1.55 μm wavelength light are simultaneously passing through the line. Having a property was a big problem in practical use.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks and provide a waveguide type Mach-Zehnder optical interferometer circuit type optical switch that operates with less wavelength dependence in a desired wavelength range, for example, 1.3 μm to 1.55 μm. To do.

[Means for Solving the Problems]

In the present invention, the two 3 dB optical couplers themselves, which are the constituent elements of the Mach-Zehnder type optical switch, are configured in the form of a Mach-Zehnder optical interferometer circuit, and the optical path length difference of this Mach-Zehnder optical interferometer circuit is used to reduce the use wavelength range. Slightly shorter than the wavelength end (1
(near μm). That is, the 3 dB optical coupler itself is configured by connecting two directional couplers with two optical waveguides, and the optical path length difference of about 1 μm is given to these coupling waveguides, and these 3 dB optical couplers are connected. 2 with combiner and phase shifter
The two optical waveguides are connected to each other to form a desired optical switch configuration as a whole.

That is, the present invention is directed to a substrate, two optical waveguides arranged on the substrate, two 3dB optical coupling portions for coupling the two optical waveguides at different positions of these optical waveguides, and two 3dB optical coupling portions. In a waveguide type optical switch having an optical phase shifter unit for finely adjusting the optical path length of the optical waveguide provided between the optical coupling units, each of the two 3 dB optical coupling units includes two optical waveguides. The optical waveguide includes two directional couplers arranged on the substrate so as to couple at different positions of the optical waveguide, and the difference in optical path length between the two optical waveguides connecting the two directional couplers to each other in the operating wavelength range. Set a little smaller than the wavelength at the short wavelength end, and set the optical waveguide with the longer optical path length out of the two optical waveguides in each of the two 3dB optical coupling sections between the two 3dB optical coupling sections. It is characterized in that they are arranged on opposite sides of each other.

Here, the operating wavelength range includes the range of 1.3 μm to 1.55 μm,
Set the optical path length difference within the dB optical coupler to approximately 1 μm and
It is preferable that the wavelength dependence of the coupling rate of the optical coupler is relaxed in the 1.3 μm to 1.55 μm region.

The optical waveguide can be composed of a glass optical waveguide, and the optical phase shifter can be composed of a thermo-optical effect phase shifter composed of a thin film heater arranged on the glass optical waveguide.

[Action]

Here, assuming that the coupling lengths of the directional couplers forming the 3 dB optical coupling Mach-Zehnder interferometer circuit are L1 and L2,
The optical path length difference between the coupling waveguides is λ ₀ . If λ ₀ = 0.0μ
In the case of m, the coupling rate characteristic of the 3 dB optical coupler is equivalent to that of the unidirectional coupler with the coupling length (L1 + L2), and as the wavelength λ increases, it becomes similar to the curve (c) in FIG. From 0%
It only monotonically increases towards 100%, which
There is no improvement effect.

Next, the operation of the present invention for setting the optical path length difference λ ₀ to around 1 μm will be described. In this case, when the wavelength λ is near λ ₀ , the optical path length difference λ ₀ is the same as the wavelength of the signal light, so that the Mach-Zehnder optical interferometer despite the optical path length difference between the directional couplers. The coupling ratio of the 3 dB optical coupler as a whole is
It is equivalent to a directional coupler with a coupling length (L1 + L2). This is based on the principle of interference of light waves that the difference in the optical path length of the Mach-Zehnder interferometer circuit is an integer multiple of the wavelength, which is indistinguishable from the case where the difference in the optical path length is zero.

When the signal light wavelength exceeds λ ₀ and reaches 1.3 μm, or even 1.55 μm, the optical path length difference gradually shifts from the relationship of an integral multiple (here, 1) of the wavelength, and becomes a fractional multiple. That is, in this state, a significant phase difference, that is, a phase difference deviated from an integral multiple of 2π, appears between the two directional couplers forming the 3 dB optical coupler in the form of the Mach-Zehnder interferometer. Due to this phase difference, the equivalent coupling length of the entire 3 dB optical coupler is L1 and L2.
It deviates from the simple sum of and gradually decreases. Here, in order to suppress the increase in the coupling rate of the simple directional coupler (coupling length = L1 + L2) due to the increase in wavelength due to the decrease in the equivalent coupling length due to the above-mentioned phase difference, the optical path length difference λ ₀ and the individual directionality If the coupling lengths L1 and L2 of the coupler are properly set, the 3dB optical coupler will
50% in the desired wavelength range, eg 1.3 to 1.55 μm
It is possible to maintain the coupling ratio in the vicinity, and by combining this Mach-Zehnder interferometer type 3 dB optical coupler, it is possible to provide an optical switch that can operate simultaneously in the entire desired wavelength range as a whole.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. In the following examples, the silica single mode optical waveguide formed on the silicon substrate is used as the optical waveguide, and the thermo-optical effect phase shifter mounted on the silica optical waveguide is used as the phase shifter. This is because this combination can provide an optical switch having excellent connectivity with a single-mode optical fiber and no polarization dependence, and the present invention is not limited to these combinations. Absent.

Example 1 FIG. 1 (A) is a plan view showing a configuration of an optical switch designed to be simultaneously operable in a wavelength range of 1.3 μm and a wavelength range of 1.55 μm as a first embodiment of the optical switch of the present invention. 1 (B), (C) and (D) are enlarged cross-sectional views of the cross-sections along the line segments AA ', BB' and CC 'of FIG. 1 (A), respectively. is there.

Here, 21 is a silicon substrate, 22 and 23 are 3 dB optical couplers, 24 and 25 are two silica single mode optical waveguides formed on the silicon substrate 21, and 24a and 25a are optical waveguides 24, respectively. And 25 are thermo-optic effect phase shifters (phase shifters). 1a and 1b are entrance ports, and 1b and 2b are exit ports. In this embodiment, unlike the conventional example shown in FIG. 7, the 3 dB optical couplers 22 and 23 of the Mach-Zehnder optical interferometer circuit are respectively composed of two directional couplers 22a and 22b and 23a and 23b. It is configured in the form. In each Mach-Zehnder interferometer circuit that constitutes the 3 dB optical couplers 22 and 23, an optical path length difference λ ₀ is set between the optical waveguides 22c and 22d and 23c and 23d. Here, the optical waveguides 22c and 23d having the longer optical path lengths are arranged on the opposite sides of the optical couplers 22 and 23.

As shown in FIGS. 1 (B), (C) and (D), the optical waveguides 24 and 25 have a core portion size of about 8 μm × 8 μm and a clad layer having a thickness of about 50 μm arranged on the substrate 1.
It is buried in 21b. Directional couplers 22a, 22b, 23a, 23b
Is the two optical waveguides 22 as illustrated in FIG. 1 (B).
It is constituted by arranging c (25) and 22d (24) in parallel at intervals of several μm over a length of several 100 μm.
In the line segment BB ′ shown in FIG. 1 (C), in order to set the optical path length difference of λ ₀ between the directional couplers 22a and 22b,
The optical waveguide 22c (25) is made longer than the optical waveguide 22d (24) so that the optical waveguide 22c draws a gentle arc,
On the contrary, between the directional couplers 23a and 23b, the optical waveguide 23d (24) is made longer than the optical waveguide 23c (25) so that the optical waveguide 23d draws an arc.

Two optical waveguides 2 in the part that connects the 3 dB optical couplers 22 and 23
The optical path lengths of 4 and 25 are set equally with an accuracy of 0.1 μm or less, and on the cladding layer 21b, as shown in FIG. 1 (D), thin film heaters (thermo-optical effect phase shifters 24a and 25a) are provided. A chromium metal film) is formed with a width of 50 μm and a length of about 5 mm.

The radius of curvature of the arc portion of the optical waveguide in this example was designed to be 50 mm. The chip size of the optical switch was 40 mm x 2.5 mm. The fabrication was performed by a known combination of a glass film deposition technique by flame hydrolysis reaction and a fine processing technique by reactive ion etching.

In the present invention, it is important to accurately set the optical path length difference λ ₀ between the two directional couplers forming the 3 dB optical couplers 22 and 23, respectively. As a result of fabrication experiments and simulations, it was found that it is desirable to suppress the setting error of λ ₀ within ± 0.1 μm, but this is a range that can be easily achieved by using photolithography technology.

Prior to describing the characteristics of the actually manufactured optical switch of this embodiment, the more detailed structure and coupling characteristics of the 3 dB optical couplers 22 and 23 will be described.

FIG. 2A is a coupling ratio vs. wavelength characteristic diagram of the Mach-Zehnder optical interferometer circuit type 3 dB optical couplers 22 and 23 which are constituent elements of the present invention. As shown in FIG. 2 (B), this coupling rate characteristic is for a test in which directional couplers 22a and 22b are separately formed by the optical waveguides 22c and 22d on the silicon substrate.
This is the result of actual measurement of the 3 dB optical coupler 22.

The curve (a) shown in FIG. 2 is the wavelength dependence of the coupling ratio of the directional couplers 22a and 22b, and the optical waveguide spacing of the coupling portion is 4
μm and the effective length of the coupling portion is L1 = L2 = 0.3 mm, which is realized. In this embodiment, the directional coupler
22a and 22b are designed equally.

The curve (b) shows the wavelength dependence characteristic of the coupling rate of the entire optical coupler 22 when the optical path length difference between the directional couplers 22a and 22b is set to λ ₀ = 1.15 μm. The point to be noted here is that the optical path length difference of λ ₀ = 1.15 μm is (1.15 μm / 1.45 μm), considering that the refractive index of the silica optical waveguides 24 and 25 is about 1.45. ) = 0.79 μm.

Curve (c) is 2 when λ ₀ = 0.0 μm is intentionally set.
The coupling ratio of the entire series of directional couplers 22a and 22b shows wavelength dependence, and the coupling characteristic in this case is comparable to that of the directional coupler of coupling length (L1 ++ L2), as discussed in the section "Action". ing. Curve (b) shows that the optical path length difference should be set appropriately (λ
₀ = 1.15 μm), the wavelength range of the entire optical coupler 22 is
From 1.22 to 1.60 μm, it is shown that the binding rate is within the error range of almost 50% ± 10%. This fact contrasts with the characteristic of the optical coupler in the conventional optical switch shown in the curve (c) of FIG. 8 that the region of the coupling rate of 50% ± 10% was limited to the narrow wavelength range of 1.24 to 1.37 μm. Target.

FIG. 3 shows an optical coupler having the characteristics shown in the curve (b) of FIG. 2A as the 3 dB optical couplers 22 and 23. It shows the measurement result of the coupling ratio (1a → 2b) vs. wavelength characteristic of the optical switch when the switch is manufactured.

The point to keep in mind when constructing this optical switch is the optical coupler.
In the inside of 22, the optical waveguide 22c has a longer optical path length by λ ₀ = 1.15 μm than in the optical waveguide 22d, on the contrary, inside the optical coupler 23, the optical waveguide 23d This is the point where the optical path length is set longer by λ ₀ = 1.15 μm than that of the waveguide 23c (this point will be discussed further later).

A curve (a) in FIG. 3 shows the wavelength dependence characteristic of the optical coupling rate (1a → 2b) when the optical switch is off, that is, when the phase shifters 24a and 25a are off. In the conventional example, that is, in FIG. 8 (a), the wavelength range in which the coupling rate is 90% or more is limited to 1.20 to 1.40 μm, whereas in FIG. 3 (a), the coupling rate is 90%. The wavelength range above is as wide as 1.20 to 1.61 μm, not only 1.3 μm band but 1.5
It also includes the 5 μm band.

The curve (b) in FIG. 3 corresponds to a 0.71 μm optical path length change by energizing one of the phase shifters (thin film heaters) and utilizing the change in the refractive index due to the thermo-optic effect. Coupling rate (1a → 2b) in the state caused in the optical waveguide of the device (ON state: thin film heater power consumption is about 0.5 watt)
Shows the wavelength-dependent characteristics of. The wavelength range in which the coupling rate is 5% or less is 1.24 to 1.70 μm. In this state, the signal light passes through the route (1a → 1b). That is, the optical switch of this embodiment has a 1.3 μm band and a 1.55 μm band.
In any of the wavelength bands, it is possible to simultaneously switch between the state where the coupling rate is 90% or more and the state where the coupling rate is 5% or less, which solves the drawbacks of the conventional optical switch.

In the state of the curve (b) in FIG. 3, the coupling ratio is about 2% (1a → 2b) at the wavelength of 1.3 μm, but by further lowering the coupling ratio, almost 100% of the light (1a → 1b) ) In order to propagate along the path, the optical path length change by the phase shifter is optimized at the wavelength of 1.3 μm.
It should be adjusted to 0.65 μm. This state corresponds to the curve (c) in FIG. However, in this case, there is a sacrifice that the coupling rate at the wavelength of 1.55 μm increases to about 6%.

The curve (d) in FIG. 3 shows the change in optical path length (1.55 μm / 2) =
Adjust to 0.775 μm, prioritize 1.55 μm wavelength band, 1.3 μm
This is an example in which the m wavelength band is sacrificed. The curve (b) is an intermediate state between the curve (c) and the curve (d), that is, the wavelength is 1.42μ.
The change in optical path length difference is (1.42 μm / 2) =
It can be said that this corresponds to the case where the thickness is adjusted to 0.71 μm and the 1.3 μm band and the 1.55 μm band are compatible with each other. Of course, the curves (b), (c) and (d) can be used properly according to the purpose.

Embodiment 2 FIG. 4 (A) is an explanatory diagram of the coupling rate vs. wavelength characteristic of the 3 dB optical coupler 22 used to construct the optical switch of the second embodiment of the present invention. The difference from the optical coupler in the first embodiment is that in the second embodiment, the directional couplers 22a and 22b are not equivalent, and as shown in FIG. 4 (B), the directional coupler 22a is
Has a coupling length L1 = 0.6 mm, and the directional coupler 22b has a coupling length L2 =
It is set to twice the 0.3 mm. Also, the important optical path length difference between the directional couplers 22a and 22b is λ ₀ = 0.95μ.
It is set to m. In FIG. 4 (A), the curve (a)
Shows the coupling characteristic of the directional coupler 22a, the curve (b) shows the coupling characteristic of the directional coupler 22b, and the curve (c) shows the coupling characteristic of the 3 dB optical coupler 22 as a whole. The wavelength dependence of the coupling rate of the 3 dB optical coupler 22 is more relaxed than the curve (b) of FIG. 2 (A) for the first embodiment, and the coupling rate is 50% ± 5%.
Has a wavelength range of 1.17 μm to 1.66 μm.

FIG. 5 shows the 3 dB optical coupler described in FIG.
FIG. 5 is an explanatory diagram of wavelength characteristics in the optical switch of the second embodiment, which is manufactured by arranging the same as in FIG. 1. The point to be pointed out here is the internal configuration of the 3 dB optical coupler 23. 3 dB
The coupling length of the directional coupler 23a constituting the optical coupler 23 is selected to be the same as that of the directional coupler 22b, and the coupling length of the directional coupler 23b is selected to be the same as that of the directional coupler 22a. It should also be mentioned that the optical path length difference between the directional couplers 23a and 23b is set so that the optical waveguide 24 becomes long.

In FIG. 5, the curve (a) is the coupling rate (1a → 2b) characteristic when the phase shifter of the optical switch is off. First
Compared with the case of the example, the wavelength region with a coupling rate of 90% or more is
It is further expanded to 1.11 μm to 1.75 μm. Curves (b), (c), and (d) have one phase shifter
(B) 0.71 μm, (c) 0.65 μm, and (d) 0.
It is a coupling rate characteristic when an optical path length difference change of 775 μm is applied and the optical switch is turned on, and almost the same state as the first embodiment is achieved, and the operation as a wide wavelength range optical switch was confirmed. .

Although the configuration and operation of the present invention have been described above with respect to two examples, the present invention is not limited to these configurations.

6 (A) to 6 (D) are explanatory views for considering a modification of the optical switch of the present invention. Here, two types of result lengths L1 and L2 used in the second embodiment are used as the directional coupler, and the optical path length difference between the directional couplers is set to λ ₀ = 0.95 μm. To do.

FIG. 6 (A) shows the configuration itself of the second embodiment, which operates as desired as the optical switch of the present invention.

FIG. 6B shows the optical path length difference in the 3 dB optical coupler 23 as
Contrary to the case of FIG. 3A, this is an example in which the side of the optical waveguide 23c is set longer, but with such an arrangement, switching operation with little wavelength dependence could not be obtained.

FIG. 6C shows a directional coupler 23a, 2 in the 3dB optical coupler 23.
This is an example in which the bond lengths L1 and L2 of 3b are replaced with those in the case of FIG. 6 (A), and this configuration was also unsuitable.

FIG. 6 (D) shows the coupling lengths L1 and L2 of the directional couplers 22a, 22b and 23a, 23b for both the 3 dB optical coupler 22 and the 3 dB optical coupler 23.
In this example, the optical waveguides 22d and 23c are set to be longer by replacing each other and reversing the respective optical path length differences in the 3 dB optical couplers 22 and 23 from the case of FIG. 6 (A). In this case, the same proper operation as in the case of FIG. 6 (A) was obtained.

From the above experiments, it is assumed that the optical switch of the present invention needs to have the constituent elements arranged so as to be substantially point symmetrical with respect to the center point. For details, it is necessary to make a judgment by individually simulating according to the wave coupling theory.

In the above embodiments, the optical path length between the two 3 dB optical couplers was the same when the phase shifter was off, but in some cases, an optical path length difference of about 0.71 μm was set beforehand. It is also possible to reverse the optical path length difference by turning on the phase shifter and reversely set the on / off state in FIGS. 3 and 5, and such an optical switch is also within the scope of the present invention. It should be pointed out that it is included in.

Although the optical path switching function of the switch of the present invention has been described above, the operation of the optical switch of the present invention is not necessarily limited to only the switch function, and an optical path length change of, for example, about 0.2 μm is given by the phase shifter. The inventive optical switch can also be operated as a variable optical coupler.

The configuration and operation of the present invention have been described above by taking the case of a silica-based optical waveguide provided on a silicon substrate as an example.
As mentioned earlier, the present invention is not limited to these material systems, but can be applied to other material systems as long as a directional coupler and a phase shifter can be configured, and is included in the scope of the present invention. For example, a LiNbO ₃ optical waveguide can be used as the optical waveguide, and an electro-optic effect phase shifter can be used as the phase shifter.

Further, since the coupling lengths of the individual directional couplers described in the above embodiments slightly change depending on the "habit" of the manufacturing process, the curve (a) of FIG. It is important for the manufacturer to make appropriate adjustments so as to obtain a wavelength dependent directional coupler similar to the curves (a) and (b) of FIG. 4 (A).

〔The invention's effect〕

As described above, in the present invention, the Mach-Zehnder optical interferometer circuit type 3 dB optical coupler configured by connecting two directional couplers with optical waveguides having slightly different lengths is used as a component together with the phase shifter. By configuring the Mach-Zehnder interferometer circuit type optical switch, it is possible to provide a waveguide type optical switch with extremely little wavelength dependence. The optical switch of the present invention is expected to make a great contribution to the construction of an optical fiber communication network in which signal lights of a plurality of wavelengths are multiplexed and propagated.

[Brief description of drawings]

FIG. 1 (A) is a plan view showing the configuration of the first embodiment of the optical waveguide type optical switch of the present invention, FIGS. 1 (B), (C) and (D) are sectional views of respective parts thereof, and FIG. A) is 3d which constitutes the switch according to the first embodiment of the present invention.
FIG. 2 (B) is an explanatory view of the 3 dB optical coupler, FIG. 3 is a coupling ratio characteristic diagram of the optical switch of the first embodiment of the present invention, and FIG. 4 (A). 3d which constitutes the second embodiment switch of the present invention
FIG. 4 (B) is an explanatory view of the 3 dB optical coupler, FIG. 5 is a coupling ratio characteristic diagram of the optical switch of the second embodiment of the present invention, and FIG. 6 is the present invention. FIG. 7 is a plan view showing a configuration example of a conventional waveguide type optical switch, and FIG. 8 is a wavelength characteristic diagram of a conventional waveguide type optical switch. . 1 …… Substrate, 2,3 …… 3dB optical coupler, 4,5 …… Optical waveguide, 4
a, 5a …… Phase shifter, 1a, 2a, 1b, 2b …… Input / output port, 2
1 ... Silicon substrate, 21b ... Quartz-based clad layer, 22,23
...... Mach-Zehnder optical interferometer circuit configuration 3 dB optical coupler, 22
a, 22b, 23a, 23b …… Directional coupler, 22c, 22d, 23c, 23d ……
Optical waveguide, 24,25 ... Quartz optical waveguide, 24a, 25a ... Thermo-optic effect phase shifter (thin film heater).

Claims (3)

[Claims] 1. A substrate, two optical waveguides arranged on the substrate, two 3 dB optical coupling portions for coupling the two optical waveguides at different positions of the optical waveguides, respectively. In the waveguide type optical switch, which is provided between the three 3 dB optical coupling sections and has an optical phase shifter section for finely adjusting the optical path length of the optical waveguide, each of the two 3 dB optical coupling sections is The two optical waveguides are provided with two directional couplers arranged on the substrate so as to couple the two optical waveguides at different positions of the optical waveguides. The optical path length difference is set to be slightly smaller than the wavelength at the short wavelength end of the operating wavelength range, and the optical waveguide with the longer optical path length among the two optical waveguides in each of the two 3 dB optical coupling sections is set. , The two 3dB optical coupling sections are mutually opposite. Waveguide-type optical switch, characterized in that arranged on the side. 2. The operating wavelength range includes a range of 1.3 .mu.m to 1.55 .mu.m, and the optical path length difference in the 3 dB optical coupler is approximately 1.
2. The waveguide type optical switch according to claim 1, wherein the wavelength dependence of the coupling rate of the 3 dB optical coupler is relaxed in the 1.3 .mu.m to 1.55 .mu.m range by setting the wavelength to .mu.m. 3. The optical waveguide comprises a glass optical waveguide,
3. The waveguide type optical switch according to claim 1, wherein the optical phase shifter is a thermo-optical effect phase shifter including a thin film heater arranged on the glass optical waveguide.