KR930008935B1 - Optic polarization splitter - Google Patents

Abstract

The device divides the polarized light into the even mode of cosine type and the odd mode of sine type. The device includes: the input waveguides W1,W2 and the output waveguides W3,W4 on an optical crystal base plate; the middle waveguide W0 for dividing the polarized light; the electrode E1 for inducing the electric field perpendicularly; the electrode E2 for inducing the electric field horizontally, the width of the input waveguides W1,W2 and the output waveguides W3,W4 is 5 m, and the width of the middle waveguide is 8 m.

Description

Polarizer and its manufacturing method

1 and 2 show the configuration of a polarization separator according to the present invention, and FIG. 1 is a schematic diagram of a waveguide formed by depositing and thermally diffusing titanium on a crystal of lithium niobate (LiNbO ₃ ).

2 is a schematic view of the state attached to the electrode on the waveguide of the in-phase.

* Explanation of symbols for main parts of the drawings

E ₁ , E ₂ : electrode W ₀ : middle waveguide

W ₁ , W ₂ : Input waveguide W ₃ , W ₄ : Output waveguide

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separator and a method for manufacturing the same, in particular two modes, that is, an even mode in which the magnitude of the electric field of light is symmetric about the axis of the optical waveguide and has a cosine-shaped electromagnetic wave distribution. And a polarizing separator for attaching a pair of electrodes to an optical waveguide in which an odd mode having an asymmetrical and sine shape electromagnetic wave distribution interferes to separate two polarizations, and a method of manufacturing the same.

Here, polarization refers to two kinds of light states in which the vibration directions of the light electric fields are perpendicular to each other. Hereinafter, the polarization directions of the electric fields are parallel to the plane of the specimen, and the vertical polarization is used for the vertical cases. It is called (TM polarization).

Recently, many polarizers in the form of optical integrated devices have been proposed for use in optical communication, optical inertial systems, and laser Doppler speed gauges. For example, polarizers such as waveguides, X-crosses, Mach-Zehnder-type and reverse phase directional couplers covering metal thin films have been proposed. However, in order to divide the two polarizations, the output of the two polarizations must be arbitrarily adjusted, and in order to do so, there must be two polarization adjustment amounts. However, the polarization splitter in the previous example does not have the ability to control two polarizations externally, such as the X-crossing or the Mach-Zehnder, or (M. Masuda and GLYip, Appl. Phys Lett. 37, 20 (1980). See Yosi Shani, Charless H. Henry, Rodney C. Kistler and Kenneth. J. Orlovsky, Appl. Opt. 29, 337 (1980)). Only one quantity makes it difficult to separate two polarizations with high separation (RCAlferness and LLBuhl, Opt. Lett. 10, 140 (1984) and K. Habara, Electron. Lett. 23, 614 (1987) and O See Mikami, Appl. Phys, Lett 36, 494 (1980).

The present invention has been made to solve the above-mentioned conventional defects, and forms an anisotropic electro-optical optical waveguide and attaches a pair of electrodes to the optical waveguide so that two polarizations can regulate the output and its manufacture It is to provide a method.

The polarizing separator of the present invention has a configuration in which a pair Y-shaped waveguide is formed on a crystal surface of a base plate such as lithium niobate having anisotropic electric effect and a pair of electrodes are formed in the pair Y-shaped waveguide. Each of the waveguides has two separate input waveguides and an output waveguide connected to a single middle waveguide, so as to connect the Y-shaped waves.

More specifically, for example, the base plate is used by cutting lithium niobate perpendicularly to the Y-axis or Z-axis, and forms a twin-Y waveguide by depositing titanium on the lithium niobate base plate, and heating and diffusing it. The pair of electrodes is formed by depositing a conductor such as indium tin oxide on the middle waveguide of the pair Y-shaped waveguide.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view of an optical waveguide made by thermally diffusing 32 nm titanium on a Z surface of a lithium niobate (LiNbO ₃ ) crystal at 1000 ° C., where the input and output waveguides W ₁ , W ₂ and W ₃ , W ₄ Only one even mode can be maintained each, and the middle waveguide W ₀ made parallel to the X-axis direction has two modes, namely, right mode and device because the width of the optical waveguide is wider than the input and output portions. Even mode (even, odd mode) can be maintained. This waveguide is referred to as a two mode interference wav-eguide (TMI).

2 is a schematic view of the electrode attached to the fabricated waveguide, the electrode length; L ₁ = 3 mm, L ₂ = 9 mm, electrode E ₂ induces an electric field from top to bottom of the figure, and electrode E ₂ induces an electric field in a direction parallel to the figure.

In preparing the polarization separator of the present invention, after depositing titanium at a thickness of 32 nm on lithium niobate cut perpendicularly to the Z axis of the crystal as in the first degree, the titanium was diffused into lithium niobate at 1000 ° C. for 5 hours, thereby providing a width. In this 8 μm W ₀ waveguide, two modes can be guided, and in each of the two V-shape, 2 ° divided, W ₁ , W ₂ , W ₃ , W ₄ waveguides, Only the mode can be guided.

For example, when light is incident on the input side W ₁ optical waveguide of FIG. 1, the distribution of light does not change in the waveguide according to the progress of light in the W ₁ optical waveguide, but in the W ₀ optical waveguide part of the intermediate waveguide, As a result, the distribution of light oscillates from side to side. The vibrating light is divided into an output waveguide W ₃ optical waveguide and a W ₄ optical waveguide at the end of the W ₀ optical waveguide.

At this time, the light intensity divided into the two waveguides is not the same. 10 × log (I ₃ / (I ₃ + I ₄ )), or -10 × log (I ₄ / (I ₃ + I ₄ ), when the light intensity of the two output waveguides is I ₃ , I ₄ ) Is defined as the degree of separation, and the unit is decibels (dB). This value is different for both polarizations within the same device. This is because the refractive index of the lithium niobate waveguide for the two polarizations is different for the two polarizations. However, when the lithium niobate is formed on the Z-axis in the X-axis direction and the electrode is made as in the second degree, the refractive index of the vertically polarized light is changed by the electrode E ₁ , and the refractive index of the transversely polarized light is changed by the electrode E ₂ .

Therefore, when horizontal polarization and vertical polarization are incident simultaneously on the first waveguide and the voltages of the two electrodes are adjusted, the horizontal polarization (TE) comes out of the W ₃ waveguide and the vertical polarization (TM) comes out of the W ₄ waveguide only.

The length of the electrode may vary slightly depending on the fabrication method of the device, but in this embodiment, L ₁ = 3 mm and L ₂ = 9 mm, as shown in FIG. The relationship between the externally applied voltage and the refractive index change for both polarizations is given by

Δn (TE) = (r22 V ₂ + r23 V ₁ ) n ³ / 2d

△ n (TE) = r33 V 1 n 3/2 / d

Where r22, r23, and r33 are refractive index change coefficients according to the applied voltage in the optical waveguide having the photoelectric effect, n is the refractive index of the optical waveguide, d is the distance between the anode and the cathode of the electrode, and V ₁ and V ₂ are respectively The voltages applied to the electrodes E ₁ and E ₂ .

The material of the electrode may be used by depositing indium tin oxide in a thickness of 100-200 nm, or alternatively, by depositing an aluminum thin film having a thickness of 100 nm on silicon oxide (SiO ₂ ) having a thickness of 100-200 nm.

Output side W _3, W _4, but in order to increase the separation of the waveguide should be appropriate adjustment of the applied voltage, and, W _3, W ₄ and be as close to as possible the refractive index and the width of the waveguide symmetry, the larger each sayi W ₃ and W ₄ The degree of separation is high. However, if the angle is too large, the light loss is increased, so the device is made 2 °. In this way, a polarization separator having a separation of less than -20 dB was made. The applied voltage was a a _{V 1 = 12V, V 2 =} 20V.

Of course, the applied voltage to obtain the best separation is slightly different depending on the fabrication conditions of the device.

As described above, the polarization separator of the present invention has the advantage of individually controlling the outputs of the two polarizations by adjusting the voltage applied to the electrode.

Claims (4)

Input Y waveguides W ₁ , W ₂ and output waveguides W ₃ , W ₄ , and an intermediate waveguide W ₀ where the polarization is separated by the right mode and the odd mode interfere with the photonic crystal base plate having anisotropic electro-optic effect. On both sides of the intermediate waveguide W ₀ , electrodes E ₁ for inducing an electric field from the top of the base plate to the bottom of the base plate and an electrode E ₂ for inducing an electric field in a direction parallel to the base plate are provided. Polarization separator, characterized in that formed. The method of claim 1 wherein the input waveguide W _1, ryeolbu output waveguide and W ₂ W _3, W ₄ are 5㎛ width, each (θ) is divided is formed such that the 2 °, said intermediate waveguide section W ₀ is It is formed to have a width of 8㎛ so that one mode passes through the input waveguide W ₁ , W ₂ and output waveguides W ₂ , W ₄ , and _two modes pass through the middle waveguide W ₀ Separator. The intermediate waveguide W _{0 to} be manufactured is deposited on the lithium niobate transferred perpendicularly to the X or Z axis of the crystal so that the direction of the waveguide W ₀ is parallel to the X axis of the crystal, and then diffused into the input waveguides W ₁ and W _2. Forming a paired Y-shaped waveguide provided with secondary waveguides W ₃ , W ₄ and the middle waveguide W ₀ , and formed by depositing electrodes E ₁ and E ₂ on the intermediate waveguide W ₀ of the titanium waveguide. Polarizing separator manufacturing method. 4. The method of claim 3, wherein the titanium is deposited at 32nm in the titanium deposition step, and the titanium diffusion step is heat diffusion at 1000 ℃ for 5 hours to the input waveguide and the output waveguide W ₁ , W ₂ , W ₃ , W ₄ The width is 5㎛, the intermediate waveguide W ₀ is a polarization separator manufacturing method characterized in that it is formed so that the width is 8㎛.

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