JP3018621B2 - Waveguide type light controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical controller, and more particularly to a TE / TM using a Z-cut LiNbO ₃ substrate.
The present invention relates to a waveguide type light controller suitable for use as a mode light splitter.

[0002]

2. Description of the Related Art As a conventional waveguide type optical controller, for example, a polarization splitter, a configuration in which a metal film is added to a waveguide on one side of a directional coupler type, a configuration using a branched or crossed waveguide, There has been proposed a configuration in which an electrode is divided in the length direction in a directional coupler type and an electric field is inverted (inverted Δβ type). Each of these polarization splitters changes the propagation constant for TE polarized light or TM polarized light in each method.

Now, an inverted Δβ type structure will be described with reference to FIGS. 6 and 7. FIG. As shown in FIG. 6, the control electrode 2 provided on the waveguide 1 is divided into two, and has a configuration in which electric fields having phases opposite to each other are applied. FIG. 7 is a switching diagram in this configuration. The vertical axis is the coupling length normalized by the complete coupling length of both TE and TM polarizations, and the horizontal axis is the difference ΔβL / π between the propagation constants of adjacent waveguides proportional to the electric field, L / L _TM ≒ 2, L / L _This is an example in which _TE = 2 + α is set. At this time, when the voltage V ₀ is applied, the TM polarized light indicated by the broken line is in a straight traveling state (indicated by (=) in the figure), whereas the TE polarized light indicated by the solid line is in a cross state (indicated by (x) in the figure). ), And the light incident from the input terminal 3 is emitted from the output terminal 4 and the output terminal 5 as shown in FIG.

[0004]

However, in the conventional example of the conventional inverted .DELTA..beta. Type structure, there is a problem that a high operating voltage is required when shifting from the cross state to the straight state. Further, in the conventional example of the other configuration, a portion that causes a phase change (for example, a portion to which a metal film is added) has a different manufacturing process from other regions, and requires a high manufacturing accuracy, so that the manufacturing process is complicated. was there.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type light controller which does not require a high operating voltage and has a simplified manufacturing process.

[0006]

Means for Solving the Problems The invention according to claim 1so
Is the substrate with perfect coupling length for TE polarized light and TM polarized light.versus
DoWaveguide is formed with Ti diffusion amount with perfect coupling length matching
In the waveguide type optical controller, the
A first control electrode for applying a vertical electric field, and the first control electrode
Formed in the middle and both sides of the electrode and laterally
Second control electrode for applying an electric fieldAnd maximum transmission with TE polarized light
The voltage of the second control electrode for obtaining light is the minimum transmitted light with TM polarization.
Control voltage application to match the voltage of the first control electrode
Means are provided in the waveguide light controller.

[0007]

[0008]

As described above, according to the present invention , in addition to the first control electrode for applying a vertical electric field, a second control electrode for applying a lateral electric field is provided as an electrode.
In order to change the voltage at which the transmitted light of the TE polarized light is maximized by intentionally causing a DC drift with respect to the polarized light,
The voltage of the 2nd control electrode which obtains the maximum transmitted light by TM polarization
The voltage is made equal to the voltage of the first control electrode for obtaining the minimum transmitted light.
Therefore, high manufacturing accuracy is not required at the manufacturing process stage, so that the manufacturing process can be simplified. Also, the present invention does not require a high operating voltage because it is not an inverted Δβ structure.

[0009]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic plan view showing an embodiment of a waveguide type light controller according to the present invention, and FIGS. 2 and 3 are explanatory diagrams of the operation of the waveguide type light controller. In this embodiment, the substrate 10 has a Z-cut crystal cut surface and LiNbO ₃
The substrate 10 is provided with a pair of waveguides 11 and 12 formed by diffusing Ti. An insulating film 1 is formed on the directional couplers 11A and 12A of the waveguides 11 and 12 which are close to each other.
As shown in FIG. 3, first control electrodes 14 and 15 for applying a vertical electric field in the Z direction to the waveguides 11 and 12 through the third control electrode 3 are formed between the first control electrodes 14 and 15. On both sides, second control electrodes 16 to 18 for applying a horizontal electric field to the waveguides 11 and 12 are formed as shown in FIG. By setting the diffused Ti film thickness to a certain value, the waveguides 11 and 12 have the same perfect coupling length for TE polarized light and TM polarized light. In this embodiment, the input light is 1.55 μm and the Ti film thickness is about 470 A.
° and Ti diffusion at 1050 ° C for 8 hours.

At this time, the relationship between the voltage and the optical output seen at the second output terminal 19 is as shown in FIG.
The polarization-independent state in which the light output of the polarized light (solid line) and the light output of the TM polarized light (dashed line) are both maximized. After this, the second control electrode 1
As shown in FIG. 2, a lateral electric field is applied to the substrate 10 for a long time at 6 to 18. Then, this lateral electric field causes T
A change in the refractive index contributing only to the E-polarized light occurs, and further, as shown in FIG. 5, a DC drift phenomenon occurs in which the voltage-light output characteristic changes with respect to the TE-polarized light. If the amount of DC drift is adjusted according to the voltage application time, the voltage (V _SW (TM)) at which the TM polarized light is turned off and the voltage V _P (TE) at which the optical output of the TE polarized light becomes maximum can be matched. It becomes possible. FIG. 5 shows a state where V _P (TE) and V _SW (TM) match. In this state, voltage (V) = V _P (TE) = V
_{When SW} (TM) is applied, the first input terminal 20 shown in FIG.
The TE polarization component of the input light from
And TM polarized light components can be output separately from the first output terminal 21.

[0012]

As described above, the invention according to claim 1 is described above.
According to the first aspect, a first control electrode for applying a vertical electric field in the Z direction to the waveguide, and a second control electrode formed on the middle and both sides of the first control electrode and applying a horizontal electric field to the waveguide Electrodes, and a DC drift with respect to the TE polarized light is intentionally caused by the lateral electric field so that the voltage at which the transmitted light of the TE polarized light is maximized can be changed. Therefore, the manufacturing process can be simplified as compared with a conventional structure in which a high operating voltage is not required and a metal film is added . Also, billing
In the invention described in Item 1, the control voltage applying means performs the maximum for the TE polarized light.
The voltage of the second control electrode for obtaining large transmitted light is the minimum in TM polarized light.
To match the voltage of the first control electrode to obtain the transmitted light
did. Therefore, the TE polarization component and the TM polarization component
It is possible to output separately from different terminals.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing one embodiment of a waveguide type light controller according to the present invention.

FIG. 2 is an explanatory diagram of an operation of the waveguide type light controller.

FIG. 3 is an explanatory diagram of an operation of the waveguide type light controller.

FIG. 4 is a diagram showing the relationship between voltage and light output according to the present invention.

FIG. 5 is a diagram showing the relationship between voltage and light output according to the present invention.

FIG. 6 is a schematic plan view showing an example of a conventional waveguide light controller.

FIG. 7 is an operation principle diagram of a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 11, 12 Waveguide 13 Insulating film 14, 15 First control electrode 16-18 Second control electrode

Claims (1)

(57) [Claims] 1. The substrate has a perfect coupling length for TE polarized light and T
In M polarization in waveguide type optical controller comprising a waveguide is formed by Ti diffusion quantity coupling length match against, a first control electrode for applying the vertical electric field in the Z-direction in the waveguide, the first T and a second control electrode for applying an electric field in the lateral direction in the middle and both sides are formed and the waveguide of the control electrode, the voltage of the second control electrode for obtaining the maximum transmitted light in the TE polarization
Match the voltage of the first control electrode to obtain the minimum transmitted light with M polarization
And a control voltage applying means for causing the waveguide to be controlled.