RU2046389C1 - Optical modes wave-guide controlled converter - Google Patents

Abstract

FIELD: data optical processing; integral optics; fiber-optic communication lines. SUBSTANCE: optical substrate with optical wave-guide is used in the device. There are two pairs of metal electrodes, which have interelectrode spaces be aligned with optical input and optical output. Electro-optic transparent layer has refractivity being higher than refractivity of optical waveguide. The layer is disposed onto the surface of optical waveguide above the first and the second metal electrodes under cover layer. The transparent layer has to be rectangular parallelepiped, which is truncated by the plane, which forms straight line when crossing with top plane of optical waveguide. The straight line is perpendicular to the direction of propagation of optical coherent radiation. EFFECT: improved efficiency of operation; improved reliability. 2 cl, 10 dwg

Description

 The invention relates to optical information processing, in particular to integrated optics devices, and can be used as an optical radiation mode converter, as well as an amplitude optical modulator for fiber-optic communication lines.

 The aim of the invention is to expand the functionality, increase speed and minimize the device.

 The goal is achieved in that the waveguide converter of the optical modes contains an optical substrate with an optical waveguide and metal electrodes. A coating layer is located above the optical waveguide, as well as second metal electrodes, the interelectrode region of which is coaxial with the interelectrode region of the first metal electrodes and is coaxial with the optical input and optical output. An electro-optical transparent layer with a refractive index greater than the refractive index of the optical waveguide is located on the surface of the optical waveguide above the first and second metal electrodes under the coating layer, and its thickness increases monotonically from the first to the second pair of metal electrodes.

 The electro-optical transparent layer can have a constant thickness, and its refractive index increases from the first to the second pair of metal electrodes.

 In FIG. 1 shows a diagram of a waveguide optical mode converter; in FIG. 2 shows the distribution of the refractive index of a three-layer waveguide structure; in FIG. 3 shows a graphical solution of the characteristic equation for the optical waveguide modes of TM and TE types of a three-layer waveguide structure; in FIG. 4 shows the distribution of refractive indices of a four-layer waveguide structure; in FIG. 5 shows a graphical solution of the characteristic equation for the optical waveguide modes of TM and TE types of a four-layer waveguide structure; in FIG. 6 together depicts graphical solutions of the characteristic equations of the optical waveguide modes of TM and TE types of three-layer and four-layer waveguide structures; in FIG. 7 and 8 depict graphical solutions of the characteristic equations of the optical waveguide modes of TM and TE types of three-layer and four-layer waveguide structures when control voltages are applied to metal electrodes; in FIG. Figures 9 and 10 depict graphical solutions of the characteristic equations of the optical waveguide modes of TM and TE types of three-layer and four-layer waveguide structures when control voltages are applied to metal electrodes.

 The waveguide optical mode converter comprises an optical substrate 1, an optical waveguide 2, an electro-optical transparent layer 3, a coating layer 4, metal electrodes 5, metal electrodes 6, an optical input 7, an optical output 8. The electro-optical transparent layer 3 is a rectangular parallelepiped truncated by a plane, moreover, the secant plane at the intersection with the upper plane of the optical waveguide 2 forms a straight line perpendicular to the propagation direction of the optical radiation. The optical input 7 and the optical output 8 are aligned with the interelectrode regions of the metal electrodes 5 and the metal electrodes 6. The electro-optical transparent layer 3 is located on the surface of the optical waveguide 2 above the metal electrodes 5 and the metal electrodes 6.

-Ф₂₄-Ф₂₃= πN (1) при N 0, 1, 2, где Ф₂₄ arctg{[(β/k)² n₄ ²] ^1/2/n₄ ²[n₂ ² (β/k)²]^1/2} (2) Ф₂₃ arctg{[(β/k)² n₃ ²]^1/2/n₂ ²[n₂ ² (β/k)²]^1/2} (3) для оптической волны ТМ-типа, где Ф₂₄ arctg{n₂ ²[(β/k)² n₄ ²]^1/2/n₄ ²[n₂ ² -(β/k)²]^1/2} (4)
Ф₂₃ arctg{n₂ ²[(β/k)² n₃ ²]^1/2/n₃ ²[n₂ ² (β/k)²]^1/2} (5) для оптической волны ТЕ-типа, где Ф_ij набег фазы оптического когерентного излучения на границе раздела i и j слоев; N порядковый номер моды; n₁ показатель преломления электрооптического прозрачного слоя 3; n₂ показатель преломления оптического волновода 2; n₃ показатель преломления оптической подложки 1; n₄ показатель преломления покровного слоя 4; β- постоянная распространения оптического излучения; W глубина оптического волновода 2; K волновое число (K 2 π / λ); λ длина волны оптического излучения в свободном пространстве.Consider the operation of the waveguide converter of the optical modes (Fig. 1). We apply to the optical input 7 optical coherent radiation; it will propagate along the optical waveguide 2. To facilitate consideration, we divide the optical waveguide 2 into three regions I, II, III (Fig. 1), where in I and III regions the optical waveguide 2 is a three-layer waveguide structure (Fig. 2), and the characteristic equation of which can be represented as:
Wk

-F ₂₄ -F ₂₃ = πN (1) at N 0, 1, 2, where Ф ₂₄ arctan {[(β / k) ² n ₄ ² ] ^1/2 / n ₄ ² [n ₂ ² (β / k ) ² ] ^1/2 } (2) Ф ₂₃ arctan {[(β / k) ² n ₃ ² ] ^1/2 / n ₂ ² [n ₂ ² (β / k) ² ] ^1/2 } (3) for a TM-type optical wave, where Ф ₂₄ arctan {n ₂ ² [(β / k) ² n ₄ ² ] ^1/2 / n ₄ ² [n ₂ ² - (β / k) ² ] ^1/2 } ( 4)
Ф ₂₃ arctan {n ₂ ² [(β / k) ² n ₃ ² ] ^1/2 / n ₃ ² [n ₂ ² (β / k) ² ] ^1/2 } (5) for a TE-type optical wave, where f _ij phase incidence of the optical coherent radiation at the interface of i and j layers; N fashion serial number; n ₁ refractive index of the electro-optical transparent layer 3; n _{2 is} the refractive index of the optical waveguide 2; n ₃ refractive index of the optical substrate 1; n ₄ refractive index of the coating layer 4; β is the propagation constant of optical radiation; W is the depth of the optical waveguide 2; K is the wave number (K 2 π / λ); λ wavelength of optical radiation in free space.

The solution of the characteristic equation (1) for the TM and TE types of optical waveguide modes (at N 0) is presented graphically in FIG. 3; the graphic solution shows that for a fixed thickness W of the optical waveguide 2 and for fixed values of the refractive indices n ₂ , n ₃ , n ₄ in regions I and III, optical waves of the TM and TE type with propagation constants β can propagate along the optical waveguide 2 ₁ and β _2, respectively.

 In region II (Fig. 1), the optical waveguide 2 is covered with an electro-optical transparent layer 3, which is a rectangular parallelepiped truncated by the ABCD plane, and the secant plane when crossing with the upper plane of the optical waveguide 2 forms a straight line perpendicular to the direction of propagation of optical radiation. In region II, the optical waveguide 2 is a four-layer waveguide structure, and the height of the electro-optical transparent layer 3 changes with the coordinate along the Y axis (Fig. 1).

 The distribution of the refractive index of a four-layer waveguide structure (region II) in a fixed cross section is shown in FIG. 4.

(6) и в области II для четырехслойной волноводной структуры характеристическое уравнение при условии, что
kn₂ ≥ β ≥ kn₃ (7) имеет вид:
Hh₁ N π + arctg (I₁₄h₄/h₁) +
+arctg{ I₁₂(h₂/h₁) tg [arctg(I₂₃h₃/h₂) Wh₂] (8) при N 0, 1, 2, где h₁ ² k²n₁ β²;
h₂ ² k²n₂ β²;
h₃ ² -k²n₃ ² + β²;
h₄ β² k²n₄ ²;
I_ij=

где Н толщина оптического прозрачного слоя 3.Obviously, the propagation constants β ₁ and β _{2 of the} optical waves of TM and TE types, respectively, must satisfy the inequality:

(6) and in region II, for the four-layer waveguide structure, the characteristic equation, provided that
kn ₂ ≥ β ≥ kn ₃ (7) has the form:
Hh ₁ N π + arctg (I ₁₄ h ₄ / h ₁ ) +
+ arctan {I ₁₂ (h ₂ / h ₁ ) tg [arctan (I ₂₃ h ₃ / h ₂ ) Wh ₂ ] (8) at N 0, 1, 2, where h ₁ ² k ² n ₁ β ² ;
h ₂ ² k ² n ₂ β ² ;
h ₃ ² -k ² n ₃ ² + β ² ;
h ₄ β ² k ² n ₄ ² ;
I _ij =

where H is the thickness of the optical transparent layer 3.

 The solution of the characteristic equation (8) at N 0 and the thickness of the optical waveguide 2 equal to W in regions I and III is shown graphically in FIG. 5.

In FIG. 6 together shows graphical solutions of the characteristic equations (1) and (8) for the three-layer and four-layer waveguide structures, respectively. From the graphical solutions of the characteristic equations (1) and (8) for the three-layer and four-layer waveguide structures (Fig. 6), the thickness H _{1 of the} electro-optical transparent layer 3 is determined, in which an optical waveguide TM with an optical waveguide 2 (region II) exists the propagation constant β ₁ * equal to the propagation constant β _{1 of the} TM type optical waveguide mode of a three-layer waveguide structure (regions I and III). If the matching conditions for the propagation constants of the optical waveguide modes of the three-layer waveguide structure β ₁ and the four-layer water-structure β ₁ * (i.e., when β ₁ * β ₁ ) are met, the TM-type optical waveguide mode of the three-layer waveguide structure (region I) is converted into an optical waveguide TM mode of a four-layer waveguide structure (at the boundary of regions I and II, Fig. 1) without energy loss.

From the graphical solutions of the characteristic equations (1) and (8) for a three-layer and four-layer waveguide structures (Fig. 6), it follows that for a selected thickness H _{1 of an} electro-optical transparent layer 3, an TE-type optical waveguide mode of a three-layer waveguide structure (region I) upon transition into a four-layer waveguide structure (region II, Fig. 1) is converted into an optical radiative mode, since for a fixed thickness H _{1 of the} electro-optical transparent layer 3 and a propagation constant β _{2 of the} TE-type optical waveguide mode For a four-layer waveguide structure, characteristic equation (8) for a four-layer waveguide structure does not have a solution, because the optical waveguide modes of the TE types of the three-layer and four-layer waveguide structures are not consistent with the propagation constants (i.e., β ₁ * ≠ β ₂ ).

With the propagation of the TM-type optical waveguide mode of a four-layer waveguide structure from the boundary of regions I, II to the boundary of regions II, III (Fig. 1) with an increase in the thickness of the electro-optical transparent layer 3, the propagation constant of this mode also increases at the boundary of regions II, III when the value propagation constant β ₂ * TM waveguide mode of the optical-waveguide-type four-layer structure, equal to the propagation constant β ₂ of the optical waveguide mode TE-type three-layer waveguide structure of the solutions ha akteristicheskih equations (1) and (8) is determined by the thickness H ₂ of the electrooptical transparent layer 3 (Fig. 6). Moreover, since the condition for matching the propagation constants β ₂ * of the TM optical waveguide mode of the four-layer waveguide structure and β ₂ TE-type optical waveguide mode of the three-layer waveguide structure (i.e., β ₂ * β ₂ ) is fulfilled, the TM optical waveguide mode -type of a four-layer waveguide structure (region II) is converted into an optical TE waveguide mode of a three-layer waveguide structure (region III) at the boundary of regions II, III without energy loss. Thus, the optical output 8 will be recorded optical coherent radiation of TE polarization.

r_ijn $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$ E (9) где Е напряженность электрического поля в межэлектродной области;
r_ij компонента электрооптического тензора.We apply a control voltage of such polarity to the metal electrodes 5 so that the refractive index of the electro-optical transparent layer changes upwards due to the electro-optical effect according to the law:
Δn _e.o =

r _ij n $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$ E (9) where E is the electric field strength in the interelectrode region;
r _ij component of the electro-optical tensor.

As a result, the propagation constant of the TM-type optical waveguide mode of the four-layer waveguide structure increases by Δ β, which is determined from the solution of characteristic equation (8) by substituting n ₁ n ₁ + + n _e.o. in this equation. The magnitude of the applied control voltage U ₁ is determined from equations (8), (9) and must satisfy the condition that the change in the propagation constant β ₁ ^{* of the} TM type optical waveguide mode of the four-layer waveguide structure should occur by Δ β ₁ equal to
Δ β ^' / β ₂ ^* β ₁ ^* / (10)
In this case, the TE optical type waveguide mode of the three-layer waveguide structure at the boundary of regions I and II (Fig. 1) is converted to the TM type optical waveguide mode of the four-layer waveguide structure, since the condition for matching the propagation constants of the optical waveguide modes is fulfilled (Fig. 7 ), i.e.

(β ₁ + Δ β ') β ₂ * (11)
Thus, in the region II (Fig. 1) of the four-layer waveguide structure, an TM-type optical waveguide mode will propagate from the boundary of regions I and II.

An optical TM waveguide mode of a three-layer waveguide structure at a given applied control voltage U ₁ to the metal electrodes 5 has a propagation constant β ₁ at the interface between regions I and II and, when going into a four-layer waveguide structure (region II, Fig. 1), it will be transformed into optical radiative mode, since the matching condition for the propagation constants of the TM-type optical waveguide mode of the three-layer waveguide structure and the four-type TM waveguide optical mode is not satisfied a waveguide structure with a fixed thickness H _{1 of the} electro-optical transparent layer 3 (Fig. 7), i.e.

r_ijn $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$ E (13)
В результате уменьшается постоянная распространения β₁ оптической волноводной моды ТМ-типа четырехслойной волноводной структуры на величину

, определяемую из (8), (13). В связи с этим происходят преобразования как оптической волноводной моды ТМ-типа, так и ТЕ-типа трехслойной волноводной структуры (область I, фиг. 1) в оптические излучательные моды четырехслойной волноводной структуры (область II, фиг. 1) на границе областей I, II, так как не выполняются условия согласования по постоянным распространения оптических волноводных мод ТМ- и ТЕ-типов трехслойной волноводной структуры (область I) и оптической волноводной моды ТМ-типа четырехслойной волноводной структуры при фиксированной толщине Н электрооптического прозрачного слоя 3 (фиг. 8), т.е.β ₁ ^* + Δ β '≠ β ₁ (12)
Consider the case of applying to the metal electrodes 5 a control voltage U _{2 of} such a polarity that the electro-optical transparent layer 3 changes the refractive index downward due to the electro-optical effect according to the law:
Δn

r _ij n $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$ E (13)
As a result, the propagation constant β _{1 of the} TM-type optical waveguide mode of the four-layer waveguide structure decreases by

determined from (8), (13). In this connection, both the TM-type optical waveguide mode and the TE-type transformations of the three-layer waveguide structure (region I, Fig. 1) are converted into optical radiative modes of the four-layer waveguide structure (region II, Fig. 1) at the boundary of regions I, II, since the matching conditions for the propagation constants of the optical waveguide modes of TM and TE types of the three-layer waveguide structure (region I) and the optical waveguide mode of the TM type of the four-layer waveguide structure with a fixed thickness H are electro-optic, th transparent layer 3 (Fig. 8), i.e.

≠ β₁; β $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ -

≠ β₂
Таким образом, прикладывая к металлическим электродам 5 управляющее напряжение необходимой полярности и величины, возможно оптические волноводные моды ТМ- и ТЕ-типов трехслойной волноводной структуры на границе областей I и II преобразовать либо в оптическую волноводную моду ТМ-типа, либо в оптические излучательные моды четырехслойной волноводной структуры (область II, фиг. 1), что говорит не только о возможности конверсии мод, но и о возможности амплитудной модуляции.β $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ -

≠ β ₁ ; β $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ -

≠ β ₂
Thus, by applying a control voltage of the required polarity and magnitude to the metal electrodes 5, it is possible to convert the optical waveguide modes of TM and TE types of a three-layer waveguide structure at the boundary of regions I and II into either a TM type optical waveguide mode or four-layer optical radiation modes waveguide structure (region II, Fig. 1), which indicates not only the possibility of mode conversion, but also the possibility of amplitude modulation.

Therefore, with a fixed thickness H _{1 of the} electro-optical transparent layer 3 (Fig. 1), a TM-type optical waveguide mode will propagate in the four-layer waveguide structure (region II), and the propagation constant of this optical mode will increase with increasing thickness of the electro-optical transparent layer 3, and with a thickness H _{2 of the} electro-optical transparent layer 3, the propagation constant of this optical mode will be β ₂ *.

We apply a control voltage of such polarity to the metal electrodes 6 so that the refractive index of the electro-optical transparent layer 3 changes downward due to the electro-optical effect according to the law (9). As a result, the propagation constant of the TM-type optical waveguide mode of the four-layer waveguide structure decreases by Δ β, which is determined from the solution of characteristic equation (8) by substituting n ₁ n ₁ + Δ n _e.o. in this equation.

(под действием электрооптического эффекта), равную

-

(14)
В этом случае оптическая волноводная мода ТМ-типа четырехслойной волноводной структуры (область II, фиг. 1) на границе областей II и III преобразуется в оптическую волноводную моду ТМ-типа трехслойной волноводной структуры (область III), так как выполняется условие согласования постоянных распространения данных оптических волноводных мод (фиг. 10), т.е.The value of the applied control voltage U ₃ is determined from equations (8) and (9) and must satisfy the condition that the propagation constant β ₁ * of the TM type optical waveguide mode of the four-layer waveguide structure should decrease by

(under the influence of the electro-optical effect) equal to

-

(fourteen)
In this case, the optical waveguide mode of the TM type of the four-layer waveguide structure (region II, Fig. 1) at the boundary of regions II and III is converted to the optical waveguide mode of the TM type of the three-layer waveguide structure (region III), since the condition for matching the propagation constants of the data is satisfied optical waveguide modes (Fig. 10), i.e.

) β₁ (15)
Таким образом, в области III трехслойной волноводной структуры будет распространяться оптическая волноводная мода ТМ-типа.(β $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ -

) β ₁ (15)
Thus, in region III of a three-layer waveguide structure, an TM-type optical waveguide mode will propagate.

We apply to the metal electrodes 6 a control voltage U _{4 of} such polarity that the refractive index of the electro-optical transparent layer 3 increases due to the electro-optical effect according to the law (9). As a result, the propagation constant of the TM-type optical waveguide mode of the four-layer waveguide structure increases by Δ β, which is determined from the solution of characteristic equation (8) by substituting n ₁ n ₁ + Δ n _e.o. in this equation.

≠ β₁ и β $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ +

≠ β₂.In this regard, the TM-type optical waveguide mode of the four-layer waveguide structure (region II) at the boundary of regions II, III is converted to the optical radiative modes of the three-layer waveguide structure (region III), since the conditions for matching the propagation constants of the TM-type optical waveguide are not satisfied of a four-layer waveguide structure and optical waveguide modes of TM and TE types of a three-layer waveguide structure (Fig. 9), i.e. β $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ +

≠ β ₁ and β $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ +

≠ β ₂ .

 Based on the foregoing, it is easy to consider the operation of the proposed device while supplying control voltages to the metal electrodes 5 and metal electrodes 6.

 The functionality of the waveguide optical mode converter with the simultaneous supply of control voltages to the metal electrodes 5 and metal electrodes 6 for various combinations of the polarization state of the optical coherent radiation at the optical input 7 are presented in table. 1.

 From the theory considered above it follows that when applying optical coherent radiation of various combinations of the polarization state to the optical output 8, the proposed device, while supplying control voltages to the metal electrodes 5 and metal electrodes 6, will function, as shown in Table. 2.

, удовлетворяющего условию
U₁≅

≅ U₂, (16) и при одновременной подаче на металлические электроды 6 управляющего напряжения

, удовлетворяющего условию
U₃≅

≅ U₄ (17) предлагаемое устройство будет функционировать либо как аналоговый амплитудный модулятор, либо как аналоговый поляризационный модулятор оптического излучения, в зависимости от комбинации приложенных управляющих напряжений к металлическим электродам 5 и металлическим электродам 6.From the above it follows that when applying to the metal electrodes 5 of the control voltage

satisfying the condition
U ₁ ≅

≅ U ₂ , (16) and with a simultaneous supply of control voltage to the metal electrodes 6

satisfying the condition
U ₃ ≅

≅ U ₄ (17), the proposed device will function either as an analog amplitude modulator or as an analog polarizing optical radiation modulator, depending on the combination of applied control voltages to the metal electrodes 5 and metal electrodes 6.

 A particular case of the proposed device is a device in which the electro-optical transparent layer 3 is made in the form of a rectangular parallelepiped with a refractive index that increases monotonically from the first to the second pair of metal electrodes, and the lowest refractive index of this layer should be greater than the refractive index of the optical waveguide 2. Obviously, the values of the refractive indices of the electro-optical transparent layer 3, necessary for the effective functioning of the inventive device, are determined from the solutions of the characteristic equations of the three-layer and four-layer waveguide structures.

 From the above theory it follows that the efficiency of the proposed device, i.e. the conversion efficiency of optical waveguide modes does not depend on the length of the metal electrodes 5 and 6, nor on the length L of the electro-optical transparent layer 3, which is due to the fact that intermode interactions occur at distances of the order of the wavelengths of optical coherent radiation.

 Consideration of the operation of the proposed device as an example was carried out for a planar optical waveguide. Obviously, when replacing the characteristic equations (1) and (8) with the characteristic equations corresponding to the parameters of optical waveguides of any type, this theory will be valid.

As an optical substrate 1, K-8 glass can be used, in which an optical waveguide 2 is formed by potassium thermal diffusion, the manufacturing conditions of which satisfy the condition for the existence of one TM and one TE optical waveguide in optical waveguide 2 at a given value of the optical coherent radiation wavelength ( wavelength of optical coherent radiation λ 0.85 μm; diffusion temperature T 350 ^о С; diffusion time t 1 h). On the surface of the optical waveguide 2 there are metal electrodes 5 and 6 of aluminum made by liquid photolithography (electrode width 20 μm, gap between electrodes 7 μm, electrode length 500 μm, thickness 0.2 μm). An electro-optical transparent layer 3 made of ZnO and having the following parameters is located on the surface of the optical waveguide 2: n ₁ 2.015, L 1500 μm, H ₁ 0.06 μm, H ₂ 0.08 μm). As the coating layer 4, any optically transparent medium with a refractive index lower than the refractive index of the optical waveguide 2 can be used, in our case air (n ₄ 1).

Claims (2)

 1. A WAVEGUIDE CONTROLLED OPTICAL MODE CONVERTER containing an optical substrate with an optical waveguide, radiation input-output devices and a pair of metal electrodes, over which a coating layer is located, characterized in that, in order to expand functionality, increase speed and reduce dimensions, it is additionally contains a second pair of metal electrodes, the interelectrode region of which is aligned with the interelectrode region of the first pair of metal electrodes, as well as with input devices radiation output, over the pairs of electrodes on the surface of the waveguide layer there is an electro-optically transparent layer of the length necessary to establish the waveguide mode under the electro-optically transparent layer, with a refractive index greater than the refractive index of the optical waveguide, and the electro-optically transparent layer is not waveguide at a given wavelength of optical radiation, and its thickness monotonically increases from the first to the second pair of metal electrodes.  2. The Converter according to claim 1, characterized in that the electro-optically transparent layer has a constant thickness, and its refractive index monotonically increases from the first to the second pair of metal electrodes.

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