WO2003073141A1

WO2003073141A1 - Athermal resin optical waveguide device

Info

Publication number: WO2003073141A1
Application number: PCT/JP2003/001921
Authority: WO
Inventors: Yoshihiro Moroi; Hidehisa Nanai; Yuji Yamamoto; Shigeki Sakaguchi
Original assignee: Central Glass Company, Limited
Priority date: 2002-02-26
Filing date: 2003-02-21
Publication date: 2003-09-04
Also published as: JP2003322738A

Abstract

An athermal resin optical waveguide device comprising an optical waveguide formed on a substrate of fluorinated polyimide characterized by exhibiting a substantial non-dependence on temperature over a temperature range of 0 to 150ºC.

Description

Description Asamaru resin optical waveguide device Background of the invention

The present invention relates to an asamaru resin optical waveguide device which eliminates the need for external temperature control by eliminating the temperature dependence of the optical waveguide itself by using a polyimide substrate for the optical waveguide.

Dense Wavelength Division Multiplexing (DWDM) is being actively studied as a means to increase transmission capacity. In this DWDM, a wavelength multiplexer / demultiplexer that multiplexes or demultiplexes light of different wavelengths is an extremely important device. However, there is a problem that the center wavelength of the device changes due to a change in ambient temperature. One way to stabilize and improve such temperature characteristics is to incorporate a high-accuracy external temperature control device into the element as a correction component. However, this method hindered cost reduction and miniaturization of the device, and had a problem in practical use.

On the other hand, the change in the center wavelength of the device is due to the temperature dependence of the optical path length of the optical circuit that constitutes the device, and the temperature dependence of the optical path length is expressed by the following equation.

l / LX d S / dT = dn / dT + n a

Here, each symbol indicates the following.

L: waveguide length, S: optical path length (n X L), T: temperature

n: equivalent refractive index of the optical waveguide, α: linear thermal expansion coefficient of the substrate

d S / dT: Coefficient indicating the temperature dependence of the optical path length

d n / dT: thermo-optic constant

In this equation, lZLXd S / dT is zero, that is,

d n / dT + n = 0 (Equation 1)

In an optical waveguide that satisfies the condition, the temperature dependence of the optical path length of the optical circuit becomes zero, the change in the center wavelength of the device due to the temperature change in the surrounding environment is eliminated, and the temperature-independent optical waveguide (a (Referred to as a thermal optical waveguide).

In a quartz optical waveguide, a substrate having a negative linear thermal expansion coefficient is used, and an optical waveguide that is assimilated by controlling the linear thermal expansion coefficient is disclosed.

(See Japanese Patent Application Laid-Open No. 2000-352633). However, the applicable range of quartz optical waveguides is limited due to the fabrication temperature being close to 100 ° C. and the high fabrication cost, and there is a major problem in the spread of optical waveguide devices.

On the other hand, the thermo-optic constant (dn / dT) of the resin is negative in a resin optical waveguide whose fabrication temperature is low and cost reduction can be expected. From this, an asamaru optical waveguide can be manufactured by controlling the linear thermal expansion coefficient of the substrate. An as-made optical waveguide using a fluorinated acrylic resin as the optical waveguide material and a resin material as the substrate has been reported (see 2001 Optical Fiber Communication Conference and Exhibit, Postdeadline Papers, PD7-1).

However, the heat resistance temperature of this asamaru optical waveguide is as low as about 85 ° C., and there is a temperature problem when used in combination with an active element such as VOA. Another problem is that the propagation loss at 1.5 zm, which is a commonly used optical communication wavelength band, is as large as 0.8 dB / cm. Therefore, there has been a long-awaited need for a resin optical waveguide that is heat-resistant, has low propagation loss, and has long-term reliability in a resin waveguide expected to be reduced in cost.

Summary of the Invention

An object of the present invention is to solve the above-mentioned problems in the conventional asamaru optical waveguide and to provide an asamaru optical waveguide having low cost, easy manufacturing, heat resistance, low propagation loss, and long-term reliability. It is to provide.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and found that a fluorinated polyimide having high heat resistance and excellent light transmittance in an optical waveguide manufacturing process was used as a substrate material, and a waveguide material was used. By controlling the thermo-optic constant (dnZdT) of the substrate and the linear thermal expansion coefficient of the substrate, it was found that an asamal resin optical waveguide having low cost, heat resistance, low propagation loss, and long-term reliability can be manufactured. Has been reached. That is, according to the present invention, an optical waveguide formed on a fluorinated polyimide substrate, which has substantially temperature independence in a temperature range of 0 to 150 ° C. A waveguide device is provided.

Description of the preferred embodiment

In order to improve the heat resistance of the Asamaru resin waveguide device, a heat-resistant material such as fluorinated epoxy or deuterated polysiloxane may be used as the waveguide material. Although the light transmittance is good in the 85 m wavelength band, the propagation loss in the 1.5 m band, which is a normal optical communication wavelength band, is as large as 1 dB / cm, and the deuterated polysiloxane is 1.5 im. Although the propagation loss is about 0.4 dBZcm, the manufacturing cost is high, and it cannot be used practically as a general optical waveguide material.

Fluorinated polyimide has a high heat-resistant temperature of 300 ° C or higher and a small propagation loss of 0.3 dB / cm in the 1.5-m band, and is suitable as a resin-assembled optical waveguide material.

That is, using fluorinated polyimide as the optical waveguide material,

By controlling the linear thermal expansion coefficient of the fluorinated polyimide substrate so that the left side of dn / dT + n α = 0 (Equation 1) becomes substantially zero, heat-resistant and light-propagating Asamaru A resin optical waveguide can be provided.

Furthermore, by using fluorinated polyimide as the waveguide material, the substrate material and the waveguide material become the same material, which increases the compatibility, improves the adhesion between the substrate and the waveguide, and reduces and avoids the residual stress of the fabricated device. It is possible to improve the long-term reliability under high temperature and high humidity.

In other words, by using fluorinated polyimide for the substrate and controlling its linear thermal expansion coefficient, it has low cost, easy manufacturing, heat resistance, low propagation loss, long-term reliability, and eliminates temperature dependence. To provide an asamal resin optical waveguide device.

Hereinafter, the present invention will be described in more detail.

The present inventors have studied heat-resistant low-light-propagation-loss optical waveguides. As a result, the fluorinated polyimide substrate is prepared from a polyimide solution or a polyamic acid solution, or a mixture thereof.However, depending on the method of preparing the solution and the method of preparing the substrate, the coefficient of linear thermal expansion is from 40 pm / K to 120 ppm. It has been found that it can be set arbitrarily within the range of / K, and that it has a glass transition temperature of 300 ° C or higher and can be manufactured with high transparency, so that it is suitable as an optical waveguide substrate. In other words, by using a fluorinated polyimide substrate that has a linear thermal expansion coefficient of 40 to 120 ppm / K and a glass transition temperature of 300 ° C or higher, and has good light transmittance, the temperature of the transmission refractive index of the optical waveguide can be increased. An asamal resin optical waveguide device with no dependency can be formed.

Thermo-optical constants of the material used as an optical waveguide material (d NZDT) will depend on the material compositions being used, approximately - in the range of 0. 6 X 10- ⁴ ~ one 1. 8 X 10- ⁴ ZK Since the refractive index n is about 1.5, substituting these values into Equation 1 yields a coefficient of linear thermal expansion α of the substrate satisfying the assimilation condition in the range of 40 to 120 ppm / K. It is desired that the control can be performed arbitrarily.

Further, the optical waveguide may be used in combination with an active element such as VOA on the substrate, and since these elements generate heat, the heat resistance temperature is preferably about 150 ° C. or more.

In general, resin materials have high reliability up to about half the glass transition temperature (° C) and can ensure heat resistance. It is suitable as a material for an optical waveguide element having heat resistance. Next, from the viewpoint of light transmission, not only is the material of the optical waveguide highly transparent, but also the substrate for the optical waveguide needs to have high light transmission in order to obtain an optical waveguide with low light propagation loss. A fluorinated polyimide having a small propagation loss of 0.3 dBZ cm in the 1.5 ^ m band, which is a wavelength normally used for optical communication, is suitable as a material for an optical waveguide device.

Further, from the viewpoint of device reliability, it is preferable that characteristics do not change in a high-temperature and high-humidity test of Telcordia standard. By using fluorinated polyimide for the waveguide material, the substrate material and the waveguide material are the same, so that compatibility is high. In other words, it is possible to improve the adhesion between the substrate and the waveguide, to reduce and avoid the residual stress of the manufactured device. This can improve the reliability of the test. For this reason, fluorinated polyimide is suitable as a material for the optical waveguide device.

It is preferable to use a fluorinated polyimide having the above characteristics as an asamaru resin optical waveguide material.

The following are specific examples of tetrapyruonic acid and its derivatives used in the production of fluorinated polyimide constituting the substrate. Here, an example of tetracarboxylic acid will be given. 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane (hereinafter referred to as 6 FDA), 3,3 ', 4,4,1-tetracarboxydiphenyl ether, 3,3 ', 4,4'-benzophenone tetracarboxylic acid, 3,3', 4,4'-tetra-potoxydiphenylsulfone, pyromellitic acid and the like. These tetracarboxylic acids and their derivatives may be used alone or as a mixture.

As the diamine component, for example, the following diamine or its diisocyanate derivative is used. 2,2'-bis (trifluoromethyl) _4,4'-diaminobiphenyl (hereinafter referred to as TFDB), 2,2'-bis (p-aminophenol) hexafluoropropane, 2,2 ' -Dimethylbenzidine, 3,3,1-dimethylpentidine, 4,4'-oxydianiline (hereinafter referred to as ODA), etc., which may be used alone or in combination. No.

Using these, a polyimide substrate having high surface smoothness without bubble swelling or warpage due to stress generation can be manufactured.

As a specific composition, a suitable one can be selected by measuring the linear thermal expansion coefficient and the glass transition temperature of the obtained fluorinated polyimide.

An example of the asamaru resin optical waveguide device according to the present invention is a device that resonates, reflects, transmits, or branches a specific wavelength by interfering or resonating light propagating in the optical waveguide. Coupler, Matsu eighteenda interferometer, A resonator, a Fabry-Believe resonator, an arrayed waveguide diffraction grating, and the like. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Preparation Example 1)

88.8 g (0.2mo 1) of 6 FDA, 64.0 g (0.2mo 1) of TFDB, and 3.56.5 g of raphatone rattatone were added to a three-necked flask. The mixture was stirred in an oil bath at 170 ° C. for 6 hours under a nitrogen atmosphere to obtain a polyimide solution having a concentration of 30% and a viscosity of 50 boise (hereinafter, referred to as 6 FDAZTFDB polyimide solution).

(Preparation Example 2)

In a flask, 88.8 g (0.2 mol) of TFDB, 64.0 g (0.2 mol) of TFDB and 696 of N, N-dimethylacetamide (hereinafter referred to as DMAc) were added. .0 g was added. This mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain a polyamic acid solution having a concentration of 15% and a viscosity of 180 boise (hereinafter referred to as 6 FDA / TFDB polyamic acid solution).

(Preparation Example 3)

608.8 in 88.8 g (0.2 mol), TFDB in 44.8 g (0.14 mol), ODA in 12.0 g (0.06 mol) and DM 825.6 g of Ac was added. This mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain a polyamic acid solution having a concentration of 15% and a viscosity of 160 boise (hereinafter referred to as 6 FDA / TFDB / ODA polyamic acid solution).

(Example 1)

A polyimide optical waveguide core was prepared from the solution of Preparation Example 3, and the lower and upper clads were prepared with the solution of Preparation Example 2.

d n / dT + n = 0 (Equation 1)

It is known that d nZdT is — 1.17 X l O— ⁴ / K, and since the equivalent refractive index of the optical waveguide is 1.5, the coefficient of linear thermal expansion of the substrate is 78 p pmZ

If K, the optical waveguide becomes temperature independent. Therefore, the solution of Preparation Example 1 was prepared so that the linear thermal expansion coefficient of the polyimide substrate was 78 ppmZK, and 50 g of this solution was placed on a 20 cm square glass plate on which a release agent had been applied in advance. Cast using an applicator. After casting, heat treatment was performed in an oven at 70 ° C for 2 hours and at 150 ° C for 2 hours to partially remove the solvent. Thereafter, the solvent-containing plate was peeled from the support. Subsequently, the obtained solvent-containing plate was fixed to a frame, heated in an oven at 200 ° C. for 2 hours, and then heated at 380 ° C. for 2 hours to substantially completely remove the solvent. At this time, the heating rate to the heating temperature was set at 3 ° C / min. This polyimide substrate had a thickness of 550 m, a Young's modulus of 4.5 GPa, a glass transition temperature of 325 ° C, and a surface roughness of 4 nm. A coefficient of linear thermal expansion of 78 ppmZK was obtained. No foaming or warpage was observed on the polyimide substrate.

A linear optical waveguide and an arrayed waveguide diffraction grating were fabricated using the obtained polyimide substrate.

First, a 6 FDAZTFDB polyamic acid solution (the solution of Preparation Example 2) was spin-coated on this polyimide substrate, and heated at 70 ° C for 2 hours, at 160 ° C for 1 hour, at 250 ° C for 30 minutes, and at 350 ° C for 1 hour. Thermal imidization was performed to form an under clad with a thickness of 15 m. Next, a 6 FDAZTFDB / QDA polyamic acid solution (the solution of Preparation Example 3) was spin-coated on this substrate, and heated under the same conditions as above to form a core layer. This core layer was formed into a linear core pattern having a length of 7 Omm, a width of 8 mm, and a height of 8 zm by photolithography and dry etching. Next, an overcladding having a thickness of 15 m was formed on the substrate under the same conditions as those for forming a 6 FDAZTFDB polyamic acid solution (the solution of Preparation Example 2) undercladding. When the propagation loss was measured by a cutback method using 1.55 Aim light through the fabricated waveguide, it was 0.3 dBZcm, and the polarization dependent loss was less than 0.3 IdB / cm, making it suitable as an optical waveguide. Was obtained.

Array waveguide grating (AWG) with a core size of 8 m in width, 8 m in height, 8 x 8 channels, center wavelength of 1.5525 m, and a wavelength interval of 200 GHz is the same process as the fabrication of the above linear optical waveguide It was produced using. Array waveguide fabricated When the temperature characteristics of the diffraction grating were measured, the change in the center wavelength of the device was less than 0.01 nm / ° C in the range of 0 ° C to 150 ° C. The fabricated resin optical waveguide device had low optical loss, no polarization dependence, and was substantially temperature independent. The fabricated linear waveguide and AWG were left in an atmosphere at a temperature of 85 ° C and a humidity of 85% for 2,000 hours. However, there was no change in characteristics before and after the storage, and they had long-term reliability.

(Example 2)

A directional coupler having a waveguide length of 2 cm, a waveguide interval of a coupling portion of 3 m, and a coupling length of 1.2 mm was manufactured by the same material and the same process as in Example 1. The core size was 8 m wide and 8 m high. The incident light was measured using a 1.55 m laser in the range of 0 ° C to 150 ° C, and the branching ratio was determined by measuring the amount of light emitted from each port. At any temperature, the crossport showed a branching ratio of 99.1% or more, and was virtually independent of temperature. In addition, the insertion loss of the directional coupler was 1.0 dB, and the polarization dependent loss was 0.2 dB / cm or less. Thus, a suitable optical waveguide was obtained.

The fabricated directional coupler was left in an atmosphere at a temperature of 85 ° C and a humidity of 85% for 2000 hours. However, there was no change in characteristics before and after the exposure, and it had long-term reliability.

(Comparative Example 1)

A linear optical waveguide and an arrayed waveguide diffraction grating (AWG) were fabricated under the same conditions as in Example 1 'except that a silicon substrate was used as the substrate.

The light propagation loss was measured by the cutback method by passing 1.55 light through the fabricated linear optical waveguide.The measured loss was 0.6 dB / cm, and the polarization dependent loss was 0.7 dBZcm. Both dependency losses have worsened. When the temperature characteristics of the arrayed waveguide diffraction grating were measured, the change in the central wavelength of the device from 0 ° C to 150 ° C was −0.15 nm / ° C, which was unsuitable for AWG. there were. When the fabricated linear waveguide and AWG were left in an atmosphere at a temperature of 85 ° C and a humidity of 85% for 2,000 hours, separation occurred between the silicon substrate and the optical waveguide. In addition, the optical propagation loss has deteriorated to 0.8 dBZcm, and the long-term reliability is insufficient. there were.

According to the method of the present invention, it is possible to manufacture an asamaru resin optical waveguide device having low cost, easy production, heat resistance, low propagation loss, and long-term reliability.

Claims

The scope of the claims

1. An optical waveguide device formed on a fluorinated polyimide substrate, which is substantially temperature-independent in a temperature range of 0 to 150 ° C. .

2. The ASA according to claim 1, wherein the fluorinated polyimide substrate according to claim 1 has a linear thermal expansion coefficient of 40 to 120 pp mZK: and a glass transition temperature of 300 ° C. or more. One resin optical waveguide device.

3. The asamal resin optical waveguide according to claim 1, wherein the waveguide material is fluorinated polyimide, and all the constituent materials of the device are fluorinated polyimide.

4. The asamal resin optical waveguide according to claim 2, wherein the waveguide material is fluorinated polyimide, and all the constituent materials of the device are fluorinated polyimide.