JPH02308125A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To allow the execution of a switching operation simply by lowering the refractive index of the output side branches of a Y-branch waveguide by forming a cut-off means for a waveguide mode in the above-mentioned output side branches. CONSTITUTION:The refractive indices of the output side branches 21a, 21b of the Y-branch waveguide are lowered to cut off the waveguide mode. The means thereof is a current implantation type electrode for implanting carriers to the output side branch branches and voltage impression type electrode which impresses a prescribed voltage. The light entering from the main path is emitted as the light of equally divided light outputs from the respective output side branches. The refractive index of the one output side branch is lowered by operating the cut-off means 18 formed in this output side branch, by which the propagation mode of the guided light is cut off at this time. Then, the state equiv. to the state that this output side branch does not substantially exist is attained and, therefore, the incident light is eventually totally emitted from the other output side branch. The light entering from the main path is emitted from the arbitrary one output side branch in this way if the cut-off means is operated.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a waveguide type optical switch, and more specifically, a waveguide type optical switch that is easy to manufacture and does not exhibit wavelength dependence or polarization dependence. Regarding switches.

(Prior Art) For example, a branching interferometric modulator is manufactured by combining the branches of two Y-branch waveguides. In this case, as shown in the perspective view of FIG. 6, each Y-branch waveguide is formed by forming a thin layer of a semiconductor of a predetermined composition on a semiconductor substrate 1 as a lower landing layer, a core layer, and an upper cladding layer. The waveguide 2 is formed by sequentially laminating layers. The waveguide 2 includes a main path 2a that is a manual path for light, and output side branches 2b and 2c that branch off and extend from the main path 2a at a predetermined branching angle θ.

Here, assuming that the cross-sectional structures of the branch 2a and the branch 2b are the same, the light incident from the main path 2a will be transmitted to the branch 2b and the branch 2c.
It is emitted as light with equal light output from. That is, the light with optical output 1 that has entered the main path 2a is transmitted to the branch 2b and the branch 2C.
The light is emitted equally as light with an optical output of 0.5.

A branching interferometric modulator that combines such Y-branching waveguides has a structure as shown in Part 5. That is, the output branches 2b and 2c of one Y-branch waveguide are connected to the input branches 2b' and 2c' of the other Y-branch waveguide, respectively, and the electrodes 3a and 3b are connected to the connection parts. It is formed.

In this modulator, the light incident from the main path 2a is split into a branch 2
The guided light that is divided into two parts b and 2c, and propagates from branch 2c to 2c', for example, undergoes a phase change due to a predetermined voltage applied from electrode 3a, so that the guided light propagates from branch 2b to 2b'. It will combine with and interfere with the guided light. As a result, the output of the light emitted from the main path 2al changes in accordance with the phase difference between the guided lights propagating through both branches.

(A Plot to be Solved by the Invention) In the case of the above-mentioned branching interferometric modulator, mode interference of light propagating through a waveguide is utilized. Therefore, the optical output of the emitted light must depend on the polarization and wavelength of the light to be propagated.

In the case of the Y-branch waveguide used in the combination, its switching characteristics have polarization dependence and wavelength dependence, so it operates only for guided light of one polarization and one wavelength. I can't.

The present invention solves the above-mentioned problems, does not develop polarization dependence or wavelength dependence in switching characteristics, and is applicable not only to the above-mentioned branching interferometric modulator but also to optical switches for various optical circuit components. The purpose of the present invention is to provide a waveguide type optical switch that has excellent functions as an optical switch.

(Means for Solving the Problem) In order to achieve the above-mentioned object, the present invention
A waveguide type optical switch is provided, which includes a Y-branch waveguide or an X-branch waveguide, and has a waveguide mode cutoff means formed at the output side branch.

Specifically, the waveguide mode cutoff means in the optical switch of the present invention is formed on the surface of an output side branch that branches off from the main path on the input side at a predetermined branching angle,
This is a means for reducing the refractive index of these output side branches and cutting off their waveguide modes, such as a current injection type electrode that injects carriers into the output side branch or a voltage application type electrode that applies a predetermined voltage.

(Function) For example, in the optical switch of the present invention in which the output side branches have the same cross-sectional structure, when the cutoff means of the output side branches is not activated, the light incident from the main path is equally distributed from each output side branch. It is emitted as light with a light output of Here, by activating the cutoff means formed in one output side branch, the refractive index of the output side branch is lowered and the propagation mode of the guided light is cut off, and this output side branch is effectively Since it is the same as not existing, all of the incident light will be emitted from the other output side branch. That is, by activating this cutoff means, the light incident from the main path can be made to exit from any one of the output side branches. This function is a switching function.

At this time, due to the effect of the branching angle θ, some output loss occurs when the light incident from the main path exits from one of the output branches, but the degree is small and can be ignored in practice. , the optical loss when guided light having a spot size of 4 μm and a wavelength of 1.55 #m is propagated through a branched waveguide whose constituent material is GaAs and whose branching angle θ is lo is 072. Since it is 0.5', 0.
It becomes 27dB.

(Embodiments of the Invention) Below, an embodiment of a symmetrical Y-branch waveguide type optical switch in which the waveguide mode cutoff means is a current injection type electrode will be described.
The explanation will be based on the attached drawings.

FIG. 1 is a schematic perspective view of the optical switch according to the embodiment, and FIG. 2 is a sectional view of the output side branch.

In the main path 20 of this optical switch, Au-Ge-N
A substrate 12 of n0GaAs is laminated on the lower electrode 11 made of i/Au, and n″A j!
Lower cladding layer 13 consisting of GaAs, n-C
; core N14 consisting of aAs; A ridge-shaped upper cladding layer 15 made of n-AlGaAs is sequentially laminated,
The entire structure is covered with an insulating thin film 19 of Sin.

In the output side branches 21a and 21b, a cap IJ16 made of n-GaAs is further laminated on the upper cladding layer 15 described above, and Zn is diffused from the cap N16 to a predetermined depth of the upper cladding layer 15. A diffusion region 17 is formed. And the whole is insulation thin 119
A window 19a is formed in the cap layer 16, and a current injection electrode 18 made of Cr/Au is formed in the window 19a. This electrode 18
is the waveguide mode cutoff means in the present invention.

In FIG. 1, the electrode 1st is the output side branch 21a.

However, these electrodes I8 may be formed on a portion of the upper surface of the output branches 21a, 21b instead of all of them. Further, the electrode 18 is connected to the output side branch 2]a
, 21b.

Branch angle θ: 2°, road width of output side branches 21a and 21b 5
In μm, the wavelength is 1.3 μm from the main path 20.

With the guided light of 1.55 μm incident, the electrode 18
The current value injected from the branch 21 at that time is changed.
The optical output of light emitted from a and 21b was measured. The results are shown in Figure 3. In the figure, the O mark represents the branch 21a, the e mark represents the branch 21b, and the solid line represents the wavelength of 1.3 μm.
The dotted line represents the case where the wavelength is 1.55 μm.

Furthermore, the polarization dependence of guided light of both wavelengths was investigated with the injection current set to 100 mA. The results are shown in FIG. In the figure, the mark 0 indicates a wavelength of 1.3μm, and the mark ・ indicates a wavelength of 1.55μm.
This represents the case of m.

As is clear from FIG. 3, in the Y-branch waveguide of the example, when the injection current from the electrode 18 is 0, the current is 1.3 to 1.
For waveguide light with a wavelength of 1.55 μm, branches 21a and 21
The light emitted from b is divided into equal parts, but when the injected current exceeds 250 mA, a switching characteristic of 0-1 appears. In other words, this Y branch waveguide has a wavelength of 1.3
For waveguide light in the range of ~1.55 μm, the injection current is 25 μm.
By setting the voltage to 0 mA or more, it becomes an optical switch. Also,
As is clear from FIG. 4, the switching characteristics of this Y-branch waveguide do not exhibit polarization dependence.

Although a symmetrical Y-branch waveguide has been shown as an example, the present invention is not limited to this type. A similar effect can be obtained by forming a waveguide mode cutoff means at the branch. Further, in the X-branch waveguide, if a similar means is formed on the output side branch, the same operation as in the embodiment can be performed.

(Effects of the Invention) As is clear from the above description, the waveguide type optical switch of the present invention includes a Y-branch waveguide or an X-branch waveguide, and at least one of the output branches has a waveguide mode cut Since the cut-off means is provided, a 0-1 switching operation can be performed simply by lowering the refractive index of one output branch by activating the cut-off means. This operation does not exhibit wavelength dependence or polarization dependence.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a symmetrical Y-branch waveguide type optical switch which is an embodiment of the present invention, FIG. 2 is a sectional view of the output side branch of the optical switch of FIG. 1, and FIG. 3 is a diagram of the optical switch of the embodiment. FIG. 4 is a relationship diagram showing the relationship between the injection current value and the optical output; FIG. 4 is a relationship diagram showing the relationship between the incident polarization direction angle and the branching ratio of the optical switch of the embodiment; FIG.
The figure is a schematic diagram of a conventional branching interferometric modulator, and FIG. 6 is a perspective view of a conventional Y branching waveguide. DESCRIPTION OF SYMBOLS 11... Lower electrode, 12... Substrate, 13... Lower cladding layer, 14... Core layer, 15... Upper cladding layer, 16... Cap layer, 17... Zn#A Loss area, 1st... Current injection electrode (waveguide mode cant-off means), 19... Insulating thin film, 19a... Window, 2o...
...Main road, 21a. 21b... Output side branch.

Claims (1)

[Claims] 1. A waveguide type optical switch comprising a Y-branch waveguide or an X-branch waveguide, and at least one of the output branches is provided with cutoff means for waveguide mode.