JP2005062756A - Optical waveguide-coupler circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymeric optical waveguide circuit nearly independent of a change of polarized light and undesirable thickness and refractive index changes which occur particularly in formation of a core layer. <P>SOLUTION: The optical waveguide-coupler circuit device comprises a substrate, a polymeric lower cladding layer formed on the substrate, at least two polymeric optical waveguides formed on the polymeric lower cladding layer, a polymeric upper cladding layer which covers the polymeric optical waveguides, and a plurality of directional couplers fabricated by making two optical waveguides of the above at least two polymeric optical waveguides close to each other in a plurality of positions, wherein one end of each of the two polymeric optical waveguides is used as an input terminal and the other end as an output terminal. The two optical waveguides which connect adjacent arbitrary two directional couplers of the plurality of directional couplers are made different from each other in the effective optical path by ΔL and this effective optical path difference ΔL is set at 0.28-0.39 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer optical waveguide circuit device. The present invention relates to a polymer optical waveguide circuit that is resistant to changes in polarization and, particularly, undesirable film thickness changes and refractive index changes that occur when creating a core layer, which are applied to optical demultiplexers and multiplexers in optical communications, for example. .

In a high-density wavelength division multiplexing (DWDM) communication system using light in the S, C, and L wavelength bands, 80-100 nm band light centered at 1550 nm wavelength is distributed at a constant distribution ratio regardless of wavelength change. There is a wavelength-independent optical waveguide coupler as an optical device that is output so as to be divided into channels. A coupler with a distribution ratio of 1: 1 is called a 3dB coupler and is used in many situations.
The wavelength-independent optical waveguide coupler is composed of a Mach-Zehnder interferometer type optical circuit 17 as illustrated in FIG. 7, and two optical waveguide cores 13 formed on the surface of a substrate 20 made of quartz or a silicon wafer, 14 (for example, see Non-Patent Document 1 and Patent Document 1).

K.JINGUJI et al, “MACH-ZEHNDER INTERFEROMETER TYPE OPTICAL WAVEGUIDE COUPLER WITH WAVELENGTH-FLATTENED COUPLING RATIO”, Electron. Lett., 1990, Vol.26, No.17, pp.1326-1327 Japanese Patent Laid-Open No. 3-213829

The optical waveguide cores 13 and 14 are covered with a lower clad layer 18 and an upper clad layer 19 formed on the substrate 20. When the main component of the core and the clad is made of silicon dioxide (SiO ₂ ), it is called a quartz optical waveguide, whereas when it is made of a polymer material, it is called a polymer optical waveguide.
The Mach-Zehnder interferometer type optical circuit 17 includes two directional couplers 15 and 16 formed by bringing the optical waveguide cores 13 and 14 close to each other in parallel. The Mach-Zehnder interferometer type optical circuit 17 has an 80-100 nm wavelength band centered on the 1550 nm wavelength input to one end of the optical waveguide core 13 or 14, 13 a or 14 a of the optical waveguide cores 13 and 14. The power of the signal light is separated at a distribution ratio of 1: 1 and output to the other ends 13b and 14b of the optical waveguide cores 13 and 14 at 50% of the input, respectively.

One application example of the Mach-Zehnder interferometer type optical circuit 17 is a 2 × 2 N splitter as illustrated in FIG. This 2 × 2 N splitter is a waveguide branching circuit composed of a wavelength-independent 3 dB coupler 9 having waveguide wiring similar to that of the Mach-Zehnder interferometer type optical circuit 17 and two 1 × N splitters arranged side by side. 10 in the longitudinal direction. The 2 × 2 N splitter shown in FIG. 2 having such a characteristic wiring structure realizes an optical power splitter function while having a wavelength band required for DWDM.
For example, the 2 × 2 N splitter shown in FIG. 2 has a wavelength of 80-100 nm centered on the 1550 nm wavelength input to one of the input ports 9 a and 9 b of the wavelength-independent 3 dB coupler 9. The signal light λ having a band has a function of evenly distributing and outputting the input optical power from the respective output ports 10 ₁ , 10 ₂ ,..., 10 _{2N of the} waveguide branch circuit 10. Even if it is input to the input port 9b, the effect is exactly the same, but in a normal communication system, considering the safety of the communication circuit, one of the input ports 9a and 9b serves as a spare. It has become.

In order to manufacture a 2 × 2 N splitter using a polymer waveguide as shown in Fig. 2, a lower cladding layer is formed on a substrate by spin coating, and a waveguide core layer is formed thereon. Is made in a similar manner. Then, using the 2 × 2 N splitter shown in FIG. 2 as one cell and a mask having a pattern in which many cells of the same shape are arranged, the waveguide core is formed by photolithography technique and reactive ion etching technique. The layer is dry etched to form a waveguide circuit. An upper clad layer is further formed thereon by spin coating. Thereafter, each cell is cut and separated by dicing, and end face polishing is performed to obtain a 2 × 2 N splitter shown in FIG.
As described above, when the lower clad layer, the waveguide core layer, and the upper clad layer are formed by spin coating, the inertial force (or centrifugal force) in the radial direction from the center differs, and the film forming process In general, due to the action of the surface tension of the film, a change due to film thickness variation in the radial direction occurs on the substrate after fabrication. When the waveguide core thickness changes, the propagation constant of the waveguide mode also changes. Therefore, this variation in the core thickness affects the characteristics of the 2 × 2 N splitter guided light shown in FIG.
On the other hand, after the waveguide core layer is patterned by dry etching using reactive ion etching, the stress applied to the waveguide core changes, thereby changing the relative refractive index difference between the waveguide core and the surrounding cladding. It often happens. This change is not only related to the refractive indexes of the core and cladding raw materials, but also delicately related to the waveguide pattern, so that precise control becomes difficult. If the relative refractive index difference between the waveguide core and the surrounding cladding changes, the propagation constant of the waveguide mode also changes in this case, so the optical characteristics of the 2 × 2 N splitter shown in FIG. 2 change.
In addition, since the polymer material has birefringence and the change in characteristics increases as the polarization direction of the light used changes, the polarization dependent loss characteristic (PDL) of the 2 × 2 N splitter shown in Fig. 2 is poor. Become .
However, the waveguide branch circuit 10 constituting the latter half of the 2 × 2 N splitter shown in FIG. 2 has characteristics such as a change in the thickness of the core layer and a change in the relative refractive index even if a polymer optical waveguide is used. Since it is difficult to depend on the change in polarization, it is not significantly affected by the change in the thickness of the core layer, the change in relative refractive index difference, and the change in polarization (for example, see Patent Document 2).

Bao-Xue Chen et al, “Optical Coupler”, US Patent 5757995

   Therefore, the problem is the wavelength-independent 3 dB coupler 9 constituting the first half of the 2 × 2 N splitter shown in FIG.

   In general, this value is large for polymer materials compared to the fact that quartz is almost zero, such as the birefringence of fluorinated polyimide, which is a typical polymer material used in optical waveguides, is about 0.0082. . Regarding the change in film thickness, according to the result of measuring the thickness of the waveguide core layer actually created by the prism coupler method when trying to create an 8 μm waveguide core layer by the above method, the range is as follows: It had a fluctuation range of about 0.7 μm. At the same time, the change in the relative refractive index difference was about ± 10%. When the waveguide core thickness, relative refractive index difference or light polarization plane changes with this size, the propagation constant or effective refractive index of the waveguide mode propagating through the wavelength-independent 3 dB coupler 9 changes greatly. The balance of parameters will be lost and the characteristics will deviate from the design target.

   When analyzed using the Mach-Zehnder interferometer type optical circuit 17 illustrated in FIG. 7 having the same structure as the wavelength-independent 3 dB coupler 9, the thickness of the waveguide cores 13 and 14 or the thickness around the waveguide cores is analyzed. When the relative refractive index difference with the cladding changes, the propagation constant of the light propagating through the waveguide changes, and the characteristic deterioration caused by this is mainly due to two causes. The first cause is that the complete coupling length of the two directional couplers 15 and 16 changes, and the designed coupling rate cannot be achieved. The second is that the phase difference caused by the optical path length difference between the waveguide cores 13 and 14 changes, thereby changing the power distribution ratio. Further, when the polarization plane of the input signal light changes, the equivalent refractive index of the optical waveguide changes due to the influence of birefringence. As a result, the phase difference caused by the complete coupling length of the two directional couplers 15 and 16 and the optical path length difference between the waveguide cores 13 and 14 changes, and the power distribution ratio deviates from the design value. It will be.

   In order to solve the above-mentioned problems caused by the change in the thickness of the waveguide core layer, it is only necessary to precisely control the thickness of the core layer film in the center portion of the substrate and use only the center portion of the substrate and the vicinity thereof. However, the effective area of the substrate that can be used is reduced, which naturally increases the manufacturing cost.

   In addition, in order to suppress the change in the relative refractive index difference between the waveguide core and the surrounding cladding, it is necessary to precisely control the refractive index of each polymer raw material used to form the core and the cladding. It is. However, since it is influenced by various complex and many factors such as the manufacturing conditions of the polymer raw materials, the storage conditions and the accompanying aging, as well as the preparation conditions of the core layer and the waveguide pattern, in practice, Such precise control is very difficult.

   In order to solve the problem of polarization dependence, in order to solve this, a groove is dug in the waveguide cross section, and a thin film wave plate is inserted into the groove, thereby rotating the polarization plane in a right angle direction, and the influence before and after the rotation is affected. There is a method of canceling the polarization dependence by canceling. However, in order to achieve this effect, mirror-symmetric optical waveguide circuit wiring is required, so it is used for symmetric structures such as AWG. However, wavelength independence is realized by the asymmetry of the optical waveguide circuit. This method cannot be applied to such couplers. In addition, the conditions imposed on the manufacturing process, such as digging a groove in the waveguide and inserting a thin film wave plate into the groove, are complicated, and the yield is poor due to the need for microscopic work, resulting in high costs. There are also disadvantageous aspects such as.

   Therefore, in order to solve the above-mentioned problem of dependence on geometric parameters and physical parameters as described above, it is necessary to improve the overall waveguide circuit structure. The object of the present invention is to maintain the merit of low cost, which is the most important reason for adopting the polymer optical waveguide, while maintaining the advantage of polarization-independent on the silicon or quartz substrate with the existing technology. It is an object of the present invention to provide a polymer optical waveguide type Mach-Zehnder interferometer optical circuit having a wide wavelength band that is independent of changes in thickness and relative refractive index difference.

   In order to solve the above problems and achieve the object, the polymer optical waveguide coupler circuit 8 resistant to the change in polarization, the change in the thickness of the waveguide core layer and the change in the relative refractive index difference shown in FIG. It consists of two optical waveguide cores 2 and 3 formed on the surface of a substrate 1 made of a wafer or the like. The optical waveguide cores 2 and 3 are covered by a lower clad layer 6 and an upper clad layer 7 formed on the substrate 1, and two directional couplers are formed by bringing the optical waveguide cores 2 and 3 close to each other in parallel. 4 and 5, the factors related to the cross-sectional shape and circuit wiring of the optical waveguide cores 2 and 3 are constant even when the circuit characteristics change with wavelength, polarization, waveguide core thickness and relative refractive index difference. It is characterized by optimizing to be kept at

   As shown in FIG. 1, a directional coupler 4 having two optical waveguide cores 2 and 3 covered with cladding layers 6 and 7 and formed by bringing the two optical waveguide cores 2 and 3 close to each other, 5 is provided in the longitudinal direction of these optical waveguides, and the length of the two optical waveguide cores 2 and 3 is different from each other. The optical waveguide circuit is characterized in that each element optimized so as to be kept constant with respect to changes in core thickness and relative refractive index difference has the parameters described below.

ここで

のように表せる。ここにA_out とB_out はそれぞれ光導波路コア2 、3 の別端2b 、3b から出力する光の振幅、L_c1 とL_c2 はそれぞれ方向性結合器4 、5 の完全結合長、L₁ とL₂ はそれぞれ方向性結合器4 、5 の平行部の長さ、L_e1 とL_e2 はそれぞれ方向性結合器4 、5 の等価平行部増加長、βは光導波路コア2 、3 を伝播する導波モードの伝播定数およびΔL は光導波路コア2 と3 の長さの差である。但し、前記L_c1 、L_c2 とL_e1 、L_e2 およびβは偏光方向により異なる値を持っている。
前記のL_c1 、L_c2 とL_e1 、L_e2 は偏光のみに依存するのではなく、ともに波長λ、光導波路コア2 、3 の幅w と厚さt 、光導波路コア2 、3 の屈折率n_g 、クラッド6 、7 の屈折率n_c 、方向性結合器4 、5 の平行部間隔s₁ 、s₂ との関数

である。それらと同じく 、伝播定数βも波長λと、光導波路コア2 、3 の幅w と厚さt と、光導波路コア2 、3 の屈折率n_g と、クラッド6 、7 の屈折率n_c との関数

である。光導波路コア2 、3 の屈折率n_g とクラッド6 、7 の屈折率n_c はともに偏光モード（TE mode or TM mode ）と波長λとの関数

である。通常、比屈折率差Δを

で定義する。式4 から式9 を式1 に代入すると、パワー分配比 率ηは波長λ、比屈折率差Δ、導波路コアの厚さt と偏光モードとの関数

である。偏光モードを考慮して 、使用波長バンドと、想定する導波路コア厚さt と比屈折率差Δの変化範囲で、次の式11 から式15 までの連立方程式

を満足するように、光導波路コア2 、3 の幅w 、方向性結合器4 、5 の平行部間隔s₁ 、s₂ 、クラッド6 、7 の屈折率n_c 、方向性結合器4 、5 の平行部の長さL₁ 、L₂ および光導波路2 と3 の長さの差ΔL という各パラメータを最適化することにより、波長依存性、導波路コア厚さ依存性、比屈折率差依存性と偏光依存性をともに解消することが出来る。ここでδη≦2% となるようにσ_λ 、σ_Δ とσ_t を設定した。但し、 図１に示す光回路8 の出力特性は周期性を持つので、一つ偏光モードに対して波長、導波路コア厚さおよび 比屈折率差を 共に無依存化した最適化パラメータのセット数は多数存在する。これによりTE モードとTM モードをそれぞれ計算し得る最適化パラメータのセット数はその二倍となる。 This technique can be explained as follows.
Assuming that a TE-polarized or TM-polarized optical signal is input to one end 2a of the optical waveguide core 2 of the optical circuit 8 shown in FIG. 1, the other ends 2b and 3b of the optical waveguides 2 and 3 shown in FIG. The power distribution ratio η

here

It can be expressed as Where A _out and B _out are the amplitudes of the light output from the other ends 2b and 3b of the optical waveguide cores 2 and 3, respectively, L _c1 and L _c2 are the complete coupling lengths of the directional couplers 4 and 5, respectively, and L ₁ L ₂ is the length of the parallel parts of the directional couplers 4 and 5, respectively, _{Le 1} and Le ₂ are the equivalent parallel part increase lengths of the directional couplers 4 and 5, respectively, and β is propagated through the optical waveguide cores 2 and 3. The propagation constant and ΔL of the waveguide mode are the difference between the lengths of the optical waveguide cores 2 and 3. However, L _c1 , L _c2 and L _e1 , L _e2 and β have different values depending on the polarization direction.
The above-mentioned L _c1 , L _c2 and _{Le 1} , Le ₂ do not depend only on the polarization, but both the wavelength λ, the width w and the thickness t of the optical waveguide cores 2 and 3, the refractive index of the optical waveguide cores 2 and 3 n _g , refractive index n _c of clads 6 and 7, function of directional couplers 4 and 5, parallel spacing s ₁ and s ₂

It is. They Like, also the wavelength λ propagation constant beta, a width w and thickness t of the optical waveguide core 2, 3, and the refractive index n _g of the optical waveguide core 2, 3, and the refractive index n _c of the cladding 6, 7 Functions

It is. The optical waveguide core 2, 3 function of the refractive index n _c of the refractive index n _g and the cladding 6, 7 are both polarization mode (TE mode or TM mode) and the wavelength λ of

It is. Usually, the relative refractive index difference Δ

Defined in Substituting Equation 4 to Equation 9 into Equation 1, the power distribution ratio η is a function of wavelength λ, relative refractive index difference Δ, waveguide core thickness t and polarization mode.

It is. Considering the polarization mode, the following simultaneous equations (11) to (15) are used in the wavelength band to be used and the range of change of the assumed waveguide core thickness t and relative refractive index difference Δ.

The optical waveguide cores 2 and 3 have a width w, the directional couplers 4 and 5 have parallel portion spacing s ₁ and s ₂ , the claddings 6 and 7 have a refractive index n _c , and the directional couplers 4 and 5 to satisfy By optimizing parameters such as the lengths L ₁ and L ₂ of the parallel part and the difference ΔL between the lengths of the optical waveguides 2 and 3, wavelength dependence, waveguide core thickness dependence, and relative refractive index difference dependence And polarization dependency can be eliminated. Here, σ _λ , σ _Δ and σ _t were set so that δη ≦ 2%. However, since the output characteristics of the optical circuit 8 shown in FIG. 1 are periodic, the number of optimization parameter sets in which the wavelength, waveguide core thickness, and relative refractive index difference are all made independent for one polarization mode. There are many. As a result, the number of optimization parameter sets that can calculate the TE mode and the TM mode, respectively, is doubled.

として設定される 。ここに添字l=1,2 はそれぞれTE とTM モードを指し、m 、n とo はそれぞれ波長、導波路コア厚さと比屈折率差のサンプリング値を示す 。従って計算値と目標値との一致の程度 を統計的に表す評価関数δを

で表示することが出来る。数値計算法により 式17 のδを最小化することによって選ばれた 各パラメータを使った高分子光導波路カプラ回路は偏光依存性、導波路コア厚さ依存性、比屈折率差依存性それに波長依存性を共に解消することが出来る。 Next, a statistical optimization method was used to make the waveguide circuit parameters independence of the wavelength, the waveguide core thickness, and the relative refractive index difference obtained by the above calculation further polarization independent. . Where η _lmn is the power distribution ratio of the light obtained by the above calculation, Q is the design target value, and D _lmno is the difference between η _lmno and Q

Set as. Here, the subscripts l = 1 and 2 indicate the TE and TM modes, respectively, and m, n and o indicate the sampling values of the wavelength, the waveguide core thickness and the relative refractive index difference, respectively. Therefore, the evaluation function δ that statistically represents the degree of coincidence between the calculated value and the target value is

Can be displayed. The polymer optical waveguide coupler circuit using each parameter selected by minimizing δ in Equation 17 by numerical calculation is polarization dependent, waveguide core thickness dependent, relative refractive index difference dependent, and wavelength dependent Both sexes can be eliminated.

In the present invention, the factors relating to the core cross-sectional shape, refractive index and circuit wiring of the polymer optical waveguide coupler circuit 8 shown in FIG. Optimized to keep constant with respect to changes in refractive index difference, therefore, due to variations in waveguide core thickness caused by polymer optical waveguide manufacturing process, changes in relative refractive index difference and birefringence The effect of the power distribution ratio due to the polarization dependence caused is clearly reduced.
Therefore, the present invention manufactures a polymer optical waveguide coupler circuit that can be used without a polarization maintaining means for an input optical signal, while having a wavelength band of 120 nm centered on a 1550 nm wavelength used for high-density wavelength multiplex communication. Sometimes the process conditions can be greatly relaxed and the yield can be improved.

The polymer optical waveguide coupler circuit 8 which is resistant to changes in polarization, waveguide core thickness and relative refractive index difference of the present invention using the above-described method is characterized by optimizing each element as follows. That is, the material of the substrate 1 as shown in FIG. 1 is a quartz or silicon, or the like, the optical waveguide core 2, 3 of material 1550nm wavelength high a birefringent refractive index n _g and from 0.008 to 0.01 of from 1.508 to 1.568 is a molecule, the material of the lower cladding layer 6 and the upper cladding layer 7 covering the optical waveguide core 2, 3 is a 1550nm wavelength is a polymer having a birefringence of refractive index n _c and 0.008 to 0.01 of from 1.503 to 1.562. The cross-sectional shape of the optical waveguide cores 2 and 3 is a square having a width of 8 μm and a thickness of 7 to 8 μm, and the parallel part length L ₁ of the directional coupler 4 is 0.702 to 0.979 mm or 1.956 to 2.539. mm, parallel part length L ₂ of the directional coupler 5 is 1.956 ～2.539Mm or 0.702 ~0.979mm, parallel portion spacing s ₁ of the directional coupler 4 is 4.7 ~5.1 μm, parallel portion interval of the directional coupler 5 The characteristic feature is that s ₂ is 4.7 to 5.1 μm and the length difference ΔL between the optical waveguide cores 2 and 3 is 0.28 to 0.39 μm.

The present invention relates to an optical waveguide coupler circuit device, a substrate, a polymer lower cladding layer formed on the substrate, at least two polymer optical waveguides formed on the polymer lower cladding layer, A polymer upper cladding layer covering the polymer optical waveguide; and a plurality of directional couplers configured by bringing two of the at least two polymer optical waveguides close to each other at a plurality of locations. An optical waveguide coupler circuit device having one end of each of the two polymer optical waveguides as an input end and the other end as an output end, wherein the plurality of directional couplers are A difference ΔL is provided between the effective optical path lengths of the two optical waveguides connecting between any two adjacent directional couplers, and the effective optical path length difference ΔL is set to 0.28 to 0.39 μm. To do.
The present invention relates to an optical waveguide coupler circuit device, a substrate, a polymer lower cladding layer formed on the substrate, at least two polymer optical waveguides formed on the polymer lower cladding layer, A polymer upper cladding layer covering the polymer optical waveguide; and a plurality of directional couplers configured by bringing two of the at least two polymer optical waveguides close to each other at a plurality of locations. A difference ΔL is provided between the effective optical path lengths of the two optical waveguides connecting between any two adjacent directional couplers of the plurality of directional couplers. The difference ΔL is set to 0.28 to 0.39 μm, and each of the directional couplers includes a parallel portion of two optical waveguides.
The present invention is characterized in that in the optical waveguide coupler circuit device, the polymer optical waveguide is made of a polymer material having a refractive index of 1.508 to 1.568 at a wavelength of 1550 nm.
The present invention is characterized in that in the optical waveguide coupler circuit device, the polymer optical waveguide is composed of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.
In the optical waveguide coupler circuit device, the polymer optical waveguide is composed of a polymer material having a refractive index of 1.508 to 1.568 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. And
The present invention is characterized in that in the optical waveguide coupler circuit device, the polymer lower clad layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm.
The present invention is characterized in that in the optical waveguide coupler circuit device, the polymer upper clad layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm.
The present invention is characterized in that in the optical waveguide coupler circuit device, the polymer lower cladding layer is made of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.
According to the present invention, in the optical waveguide coupler circuit device, the polymer upper cladding layer is made of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.
The present invention is the optical waveguide coupler circuit device, wherein the polymer lower cladding layer is composed of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. And
According to the present invention, in the optical waveguide coupler circuit device, the polymer upper clad layer is composed of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. Features.
The present invention provides an optical waveguide coupler circuit device in which the polymer lower cladding layer and the polymer upper cladding layer have a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. It is composed of molecular materials.
In the optical waveguide coupler circuit device, the length of the parallel portion of the two optical waveguides in the one directional coupler is 0.702 to 0.979 mm, and the length of the parallel portion of the other directional coupler is It is characterized by being selected from 1.956 to 2.539mm respectively.
The present invention is characterized in that, in the optical waveguide coupler circuit device, the distance between the parallel portions of the two optical waveguides in each of the directional couplers is selected to be 4.7 to 5.1 μm.
The present invention is characterized in that, in an optical waveguide coupler circuit device, the cross-sectional shape of the optical waveguide is formed in a square shape having a width W and a thickness t.
The present invention is characterized in that, in the optical waveguide coupler circuit device, the cross-sectional shape of the optical waveguide is rectangular, and the length of one side thereof is 8 μm.
The present invention is characterized in that, in the optical waveguide coupler circuit device, the cross-sectional shape of the optical waveguide is a square, and the thickness t is 7 to 8 μm.
The present invention is characterized in that, in an optical waveguide coupler circuit device, the cross-sectional shape of the optical waveguide is rectangular, the width W is 8 μm, and the thickness t is 7 to 8 μm.
The present invention is characterized in that in the optical waveguide coupler circuit device, the substrate is made of a quartz plate.
According to the present invention, in the optical waveguide coupler circuit device, the substrate is formed of a silicon plate.
According to the present invention, in the optical waveguide coupler circuit device, the substrate is made of a polyimide resin plate.

As shown in FIG. 1, a polymer optical waveguide coupler circuit 8 which is resistant to changes in polarization, waveguide core thickness and relative refractive index difference according to the present invention is formed on the surface of a substrate 1 made of a quartz plate. The optical waveguide cores 2 and 3 are provided. Optical waveguide core 2 as shown in FIG, 3 is 1.508, a polymer material having a birefringence index of refraction n _g and 0.008 to 0.01 of ～1.568, width and 7-8 thickness of [mu] m of the cross section 8 [mu] m Created to be a square with The material of the lower cladding layer 6 and the upper cladding layer 7 covering the optical waveguide core 2, 3 is a polymer having a birefringence of refractive index n _c and from 0.008 to 0.01 of from 1.503 to 1.562.
The optical waveguide cores 2 and 3 are provided with two directional couplers 4 and 5 which are formed close to each other in parallel. The directional coupler 4 is formed so that the parallel part length L ₁ is 0.702 to 0.979 mm (or 1.956 to 2.539 mm) and the parallel part interval s ₁ is 4.7 to 5.1 μm. The directional coupler 5, the parallel portion length L ₂ is 1.956 ~2.539mm (or 0.702 ~0.979mm), is created as a parallel section spacing s ₂ is at 4.7 ~5.1 μm.
The length difference ΔL between the optical waveguide cores 2 and 3 is preferably formed in the range of 0.28 to 0.39 μm.

An example of a method for producing the polymer optical waveguide coupler circuit 8 according to the present invention will be described below.
A quartz plate is used as substrate 1 and a lower clad layer is formed on its surface. Polymer solution (4,4 '-(Hexafluoroisopropylidene) diphthalic anhydride) And 2,2'-bis (trifluoromethyl) 4,4'-diaminobiphenyl (2,2'-Bis (trifluoromethyl) -4,4'-diaminobiphenyl) in N, N, -dimethylacetamide ( N, N, -Dimethylacetamide), and a solution stirred at 25 ° C. for 24 hours under a nitrogen atmosphere is formed into a thin film by spin coating, and then about 20 μm thick is removed by solvent removal and heat treatment. A polymer lower cladding layer 6 is formed.
Then, on this lower clad layer 6, 2,2′-bis (trifluoromethyl) 4,4′-diaminobiphenyl (2,2 ′) of diamine used in preparing the polymer for forming the clad layer is formed. -Bis (trifluoromethyl) -4,4'-diaminobiphenyl) is replaced with 4,4'-Diaminodiphenyl ether, and the total amount of diamines is 4,4'- ( Hexafluoroisopropylidene) diphthalic anhydride (4,4 '-(Hexafluoroisopropylidene) diphthalic anhydride) was added in an equimolar amount, and the polymer lower clad layer was formed using the polymer solution prepared by the same means. A thin film is formed on top by spin coating, and then a 7-8 μm thick polymer core layer with a refractive index higher by 0.24% to 0.30% than the lower cladding layer 6 is formed by solvent removal and heat treatment. To do.
Then, after a predetermined optical waveguide pattern is formed with a photoresist on the surface of the core layer, the core layer is selectively etched by reactive ion etching in an oxygen gas atmosphere, whereby an optical waveguide core having the predetermined pattern is formed. 2 and 3 are formed. Thereafter, the optical waveguide cores 2 and 3 are embedded by spin coating using the same polymer solution as that used for forming the lower cladding, followed by methods such as solvent removal and heat treatment. A polymer upper cladding layer 7 is formed. The refractive index of the upper cladding layer 7 is lower than that of the core, but it is not necessarily equal to that of the lower cladding layer 6.

   In the above embodiment, a quartz plate is used as the substrate 1, but a silicon plate or a polyimide resin plate can also be used.

An experiment was conducted on the operation of the polymer optical waveguide coupler circuit 8 according to the present invention. The results are as follows.
First, the waveguide core thickness is changed to 7 μm and the relative refractive index difference is changed between 0.24% and 0.30% to change the polarization of the present invention shown in FIG. 1 and the change of the waveguide core thickness and the relative refractive index difference. Seven wavelengths, 1490 nm, 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm, and 1610 nm light are input as TE polarized light and TM polarized light to one end 2 a of the optical waveguide core 2 of the strong polymer optical waveguide coupler circuit 8. FIGS. 3 and 5 are graphs in which the ratio of the optical power coming out from the other ends 2b and 3b of the optical waveguide core, that is, the power distribution ratio, is plotted for each wavelength. The results show that the power distribution ratio due to the change in wavelength over the 120 nm bandwidth and the change in relative refractive index difference between 0.24% and 0.30% is in the range of 50 ± 1.91% and 50 ± 1.75%, respectively.

Next, the same experiment as described above was performed by changing the waveguide core thickness to 8 μm and the relative refractive index difference between 0.24% and 0.30%. Figures 4 and 6 show the power distribution ratio of TE and TM polarized light, respectively. The power distribution ratio due to the change in wavelength and the change in relative refractive index difference of 0.24% to 0.30% is in the range of 50 ± 1.91% and 50 ± 1.75%, respectively. Polarization, waveguide core thickness, relative refractive index difference And there is almost no influence by the change of wavelength.
Therefore, the polymer optical waveguide coupler circuit 8 that is resistant to changes in polarization, waveguide core thickness, and relative refractive index difference of the present invention is a signal light having a 120 nm band centered on a 1550 nm wavelength used for high-density wavelength multiplexing communications. Even if the waveguide core thickness and relative refractive index difference caused by process errors change in the range of 7 to 8 μm and 0.24% to 0.30%, respectively, they have very little effect on wavelength change and signal light polarization change. The characteristics remain the same. Therefore, the polymer optical waveguide coupler circuit 8 which is resistant to changes in polarization, waveguide core thickness and relative refractive index difference of the present invention constitutes a polymer optical waveguide 2 × 2 N splitter shown in FIG. 2 as an example. This makes the coupler 9 easy to manufacture because it makes the polarization independent while having a wide wavelength band, and is independent of the geometrical and physical changes that occur in the manufacturing process.

In the present invention, the dependence on the polarization change and the wavelength change is suppressed to almost zero by the above optimization method, so that the polarization of the polymer optical waveguide 2 × 2 N splitter is made independent as one application example. Can be used to
Since the present invention provides a method for optimization without changing the materials that have been used in the past, it is not necessary to change the polymer optical waveguide manufacturing process that has been developed so far. Therefore, polarization and wavelength independence in circuit characteristics can be achieved while maintaining the merit that the optical waveguide manufacturing cost is low when a polymer is used as a material.

The top view and side view of the coupler circuit which show one Embodiment of this invention. Top view of polymer optical waveguide 2 × 2N splitter. The figure which shows the change of the power distribution ratio with respect to the wavelength change of TE mode signal light in the optical waveguide coupler circuit device based on this invention, when core thickness is 7 micrometers and the fluctuation | variation range of a relative refractive index difference is 0.24-0.30%. The figure which shows the change of the power distribution ratio with respect to the wavelength change of TE mode signal light in the optical waveguide coupler circuit device based on this invention, when core thickness is 8 micrometers and the fluctuation | variation range of a relative refractive index difference is 0.24-0.30%. The figure which shows the change of the power distribution ratio with respect to the wavelength change of TM mode signal light in the optical waveguide coupler circuit device based on this invention, when core thickness is 7 micrometers and the fluctuation | variation range of a relative refractive index difference is 0.24-0.30%. The figure which shows the change of the power distribution ratio with respect to the wavelength change of TM mode signal light in the optical waveguide coupler circuit device based on this invention, when core thickness is 8 micrometers and the fluctuation | variation range of a relative refractive index difference is 0.24-0.30%. The top view and side view of the Mach-Zehnder interferometer type optical circuit 17.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide core 3 Optical waveguide core 4 Directional coupler 5 Directional coupler 6 Lower clad layer 7 Upper clad layer 9 Wavelength independent 3 dB coupler 10 Waveguide shunt circuit 13 Optical waveguide core 14 Optical waveguide core 15 direction Sexual coupler 16 Directional coupler 18 Lower clad 19 Upper clad

Claims (21)

A substrate,
A polymer lower cladding layer formed on the substrate;
At least two polymer optical waveguides formed on the polymer lower cladding layer;
A polymer upper cladding layer covering the polymer optical waveguide;
A plurality of directional couplers configured by bringing two optical waveguides out of the at least two polymer optical waveguides close to each other at a plurality of locations;
An optical waveguide coupler circuit device having one end of each of the two polymer optical waveguides as an input end and the other end as an output end,
A difference ΔL is provided in the effective optical path length of the two optical waveguides connecting between any two adjacent directional couplers of the plurality of directional couplers;
An optical waveguide coupler circuit device characterized in that the effective optical path length difference ΔL is set to 0.28 to 0.39 μm. A substrate,
A polymer lower cladding layer formed on the substrate;
At least two polymer optical waveguides formed on the polymer lower cladding layer;
A polymer upper cladding layer covering the polymer optical waveguide;
A plurality of directional couplers configured by bringing two optical waveguides out of the at least two polymer optical waveguides close to each other at a plurality of locations;
A difference ΔL is provided in the effective optical path length of the two optical waveguides connecting between any two adjacent directional couplers of the plurality of directional couplers, and the effective optical path length difference ΔL Is set to 0.28 to 0.39 μm,
Each of the directional couplers comprises a parallel portion of two optical waveguides, respectively.    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer optical waveguide is made of a polymer material having a refractive index of 1.508 to 1.568 at a wavelength of 1550 nm.    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer optical waveguide is made of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.    3. The optical waveguide according to claim 1, wherein the polymer optical waveguide is made of a polymer material having a refractive index of 1.508 to 1.568 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. Coupler circuit device    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer lower cladding layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm.    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer upper clad layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm.    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer lower cladding layer is made of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.    3. The optical waveguide coupler circuit device according to claim 1, wherein the polymer upper cladding layer is made of a polymer material having a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm.    3. The optical waveguide according to claim 1, wherein the polymer lower cladding layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. Coupler circuit device    3. The optical waveguide according to claim 1, wherein the polymer upper cladding layer is made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. Waveguide coupler circuit device    The polymer lower clad layer and the polymer upper clad layer are made of a polymer material having a refractive index of 1.503 to 1.562 at a wavelength of 1550 nm and a birefringence of 0.008 to 0.01 at a wavelength of 1550 nm. Item 1 or 2 optical waveguide coupler circuit device    The length of the parallel portion of the two optical waveguides in the one directional coupler is selected from 0.702 to 0.979 mm, and the length of the parallel portion in the other directional coupler is selected from 1.95 to 2.539 mm. The optical waveguide coupler circuit device according to any one of claims 1 to 12.    The optical waveguide coupler circuit device according to any one of claims 1 to 13, wherein an interval between parallel portions of two optical waveguides in each directional coupler is selected to be 4.7 to 5.1 µm.    15. The optical waveguide circuit device according to claim 1, wherein a cross-sectional shape of the optical waveguide is formed in a square shape having a width W and a thickness t.    16. The optical waveguide coupler circuit device according to claim 15, wherein the cross-sectional shape of the optical waveguide is a square, and the length of one side thereof is 8 μm.    16. The optical waveguide coupler circuit device according to claim 15, wherein the optical waveguide has a square cross section and a thickness t of 7 to 8 [mu] m.    16. The optical waveguide coupler circuit device according to claim 15, wherein the optical waveguide has a square cross section, a width W of 8 [mu] m, and a thickness t of 7 to 8 [mu] m.    19. The optical waveguide coupler circuit device according to claim 1, wherein the substrate is made of a quartz plate.    19. The optical waveguide coupler circuit device according to claim 1, wherein the substrate is made of a silicon plate.    The optical waveguide coupler circuit device according to claim 1, wherein the substrate is made of a polyimide resin plate.

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