JP4071175B2 - Method for producing polyimide optical element - Google Patents

Description

  The present invention relates to a method for manufacturing a polyimide optical element, and more particularly to a method for manufacturing an optical element such as an optical waveguide, a diffraction grating, and a wavelength filter formed from polyimide.

  2. Description of the Related Art Conventionally, optical elements such as optical waveguides, diffraction gratings, and wavelength filters, particularly optical waveguides used as optical communication devices, are well known that are formed from glass such as quartz.

  However, in recent years, it has been necessary to mass-produce various optical communication devices at low cost for the construction of optical fiber networks including WDM communication. Therefore, it is necessary to form optical waveguides from organic materials, especially solder reflow. For example, it has been studied to form from a polyimide having excellent heat resistance required.

For example, light that focuses pulsed laser light inside a matrix made of an organic material, moves the focal point inside the matrix, and forms a core area consisting of a continuous refractive index change area inside the matrix. A method for manufacturing a waveguide has been proposed (see, for example, Patent Document 1). In this proposal, a mother phase is formed by drying and curing liquid fluorinated polyimide, and this mother phase is placed on an XYZ stage. Then, by controlling the movement of the XYZ stage while condensing the pulse laser beam inside the matrix phase, a refractive index changing region where the refractive index is higher than the refractive index of other regions along the locus of the condensing point. It is considered to form continuously.
JP 2002-14246 A

  However, when the refractive index change region is formed in the matrix made of polyimide by the above method, the refractive index once changed in the refractive index change region returns to the original refractive index with time, and the optical waveguide disappears. This causes a malfunction.

  An object of the present invention is to provide a method for producing a polyimide optical element, which can form a stable refractive index change region and can reduce light propagation loss even when formed from polyimide having excellent heat resistance. It is in.

  In order to achieve the above object, a method for producing a polyimide optical element according to the present invention includes a step of preparing a polyimide precursor film, condensing a pulsed laser beam inside the polyimide precursor film, and a condensing point of the polyimide optical element. A step of forming a refractive index changing region having a changed refractive index by moving continuously or discontinuously inside the precursor coating, and a step of imidizing the polyimide precursor coating in which the refractive index changing region is formed. It is characterized by including.

In the present invention, it is preferable that the pulse width of the pulse laser beam is 10 ⁻¹² seconds or less.

  Further, in the present invention, the light transmittance at a thickness of 10 μm of the polyimide precursor film is 95% or more at the wavelength of the pulse laser beam, and a wavelength 1 / N (N is the wavelength of the pulse laser beam) And an integer selected from 2, 3, 4) is preferably 50% or less.

  In the present invention, it is preferable that the polyimide precursor film contains an imidization accelerator.

  According to the method for producing a polyimide optical element of the present invention, first, a refractive index changing region is formed on a polyimide precursor film by moving a condensing point of a pulse laser beam, and then the polyimide precursor film is imidized. Thus, polyimide is formed. For this reason, the refractive index once changed in the refractive index changing region is unlikely to return to the original refractive index with time, and as a result, a stable refractive index changing region can be formed and light propagation loss can be reduced. A polyimide optical element can be manufactured.

  In the method for producing a polyimide optical element of the present invention, first, a polyimide precursor film is prepared. The polyimide precursor film can be obtained, for example, by preparing a polyimide precursor solution, forming the solution into a film, and drying the solution.

  The polyimide precursor solution contains at least a polyimide precursor and a solvent.

  The polyimide precursor is a polyamic acid and can be obtained by reacting an organic tetracarboxylic dianhydride with a diamine.

  Examples of the organic tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 2,2-bis (2,3-dicarboxyphenyl). ) Propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, bis (3,4-di Carboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfonic acid dianhydride and the like.

  Preferably, for example, 2,2-bis (2,3-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 4,4 -Bis (3,4-dicarboxytrifluorophenoxy) tetrafluorobenzene dianhydride, 1,4-bis (3,4-dicarboxytrifluorophenoxy) tetrafluorobenzene dianhydride, (trifluoromethyl) pyromellit Fluorine-substituted tetracarboxylic dianhydrides containing fluorine atoms in the molecule, such as acid dianhydride, di (trifluoromethyl) pyromellitic dianhydride, di (heptafluoropropyl) pyromellitic dianhydride Can be mentioned.

  These organic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  Examples of the diamine include m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, and 3,3'-diaminodiphenyl. Sulfone, 2,2-bis (4-aminophenoxyphenyl) propane, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 2,4-diaminotoluene, 2 , 6-diaminotoluene, 4,4′-diaminodiphenylmethane, 4,4′-diamino-2,2′-dimethylbiphenyl, and the like.

  Preferably, for example, 2,2′-bis (trifluoromethoxy) -4,4′-diaminobiphenyl (TFMOB), 3,3′-diamino-5,5′-bis (trifluoromethyl) biphenyl, 2, 2-bis (4-aminophenyl) hexafluoropropane (BAAF), 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane (HFBAPP), 2,2′-bis (trifluoromethyl) -4,4'-diaminobiphenyl (TFMB), 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (BIS-AP-AF), 2,2-bis (3-amino-4- Methylphenyl) hexafluoropropane (BIS-AT-AF), 2,2′-difluorobenzidine (FBZ), 4,4′-bis (aminothio) Intramolecular such as Kutafluoro) biphenyl, 3,5-diaminobenzotrifluoride, 1,3-diamino-2,4,5,6-tetrafluorobenzene, 2,2′-bis (trifluoromethyl) benzidine (BTFB) And fluorine-substituted diamines containing fluorine atoms.

  These diamines may be used alone or in combination of two or more.

  And a polyimide precursor can be obtained by making organic tetracarboxylic dianhydride and diamine react according to a conventional method. That is, for example, an organic tetracarboxylic dianhydride and a diamine are mixed at a ratio of approximately equimolar in an inert gas atmosphere in a reaction solvent at a temperature of 250 ° C. or lower, preferably from room temperature (25 ° C.) to The polyimide precursor can be obtained as a viscous solution by stirring for about 5 to 20 hours in the range of 80 ° C.

  The reaction solvent is not particularly limited as long as it dissolves the organic tetracarboxylic dianhydride and diamine and can dissolve the resulting polyimide precursor. For example, N-methyl-2-pyrrolidone, N, Examples include polar solvents such as N-dimethylacetamide, N, N-diethylacetamide, and dimethyl sulfoxide. These polar solvents can be used alone or as a mixed solvent of two or more.

  The polyimide precursor thus obtained has a weight average molecular weight of, for example, about 5,000 to 500,000, preferably about 10,000 to 150,000, and is, for example, 1 to 50% by weight in the reaction solvent, preferably 5 to 30% by weight (solid content concentration).

  Moreover, an imidation promoter can be mix | blended with the solution of this polyimide precursor as needed. By blending an imidization accelerator, imidization of the polyimide precursor can be promoted, and light propagation loss of the polyimide optical element can be reduced.

  Examples of the imidization accelerator include polyethylene glycol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, polypropylene glycol, polypropylene glycol monomethyl ether, and polypropylene glycol dimethyl ether. These imidation accelerators may be used independently and may use 2 or more types together. Further, if such an imidization accelerator is used, it can be volatilized together with the residual solvent in imidization (curing) of the polyimide precursor, so that the residual in the finally obtained polyimide film can be reduced and transparent. It can prevent that the resin characteristic requested | required for optical uses, such as property, is inhibited.

  In addition, as the imidization accelerator, those having a weight average molecular weight in the range of usually 100 to 2000, and further 200 to 1000 are preferably used.

  The mixing ratio of the imidization accelerator is, for example, in the range of 5 to 50 parts by weight, preferably 10 to 40 parts by weight with respect to 100 parts by weight of the polyimide precursor.

  Moreover, a photosensitive agent can be mix | blended with the solution of this polyimide precursor as needed. By blending the photosensitizer, the change in the refractive index can be increased at the condensing point of the pulse laser beam.

  As the photosensitizer, for example, a 1,4-dihydropyridine derivative represented by the following general formula (1) is preferably used.

（式中、Ａｒは１，４−ジヒドロピリジン環への結合位置に対してオルソ位にニトロ基を有する芳香族基を示し、Ｒ１は水素原子または炭素原子数１〜３のアルキル基を示し、Ｒ２、Ｒ３、Ｒ４およびＲ５はそれぞれ独立に水素原子または炭素原子数１または２のアルキル基を示す。）
上記式（１）中、Ａｒで示されるオルソ位にニトロ基を有する芳香族基として、好ましくは、ｏ−ニトロフェニル基が挙げられ、また、Ｒ１、Ｒ２、Ｒ３、Ｒ４およびＲ５で示される炭素数１、２または３のアルキル基として、好ましくは、メチル基（Ｃ１）、エチル基（Ｃ２）、ｎ−プロピル基（Ｃ３）、ｉ−プロピル基（Ｃ３）が挙げられる。

(In the formula, Ar represents an aromatic group having a nitro group in the ortho position relative to the bonding position to the 1,4-dihydropyridine ring, R1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 , R3, R4 and R5 each independently represents a hydrogen atom or an alkyl group having 1 or 2 carbon atoms.)
In the above formula (1), the aromatic group having a nitro group at the ortho position represented by Ar is preferably an o-nitrophenyl group, and carbons represented by R1, R2, R3, R4 and R5. As the alkyl group of Formula 1, 2, or 3, preferably, a methyl group (C1), an ethyl group (C2), an n-propyl group (C3), or an i-propyl group (C3) is exemplified.

  More specifically, such 1,4-dihydropyridine derivatives include, for example, 1-ethyl-3,5-dimethoxycarbonyl-4- (2-nitrophenyl) -1,4-dihydropyridine, 1-methyl-3. , 5-Dimethoxycarbonyl-4- (2-nitrophenyl) -1,4-dihydropyridine, 1-propyl-3,5-dimethoxycarbonyl-4- (2-nitrophenyl) -1,4-dihydropyridine, 1-propyl -3,5-diethoxycarbonyl-4- (2-nitrophenyl) -1,4-dihydropyridine.

  The blending ratio of the photosensitive agent is, for example, in the range of 0.5 parts by weight or more and less than 10 parts by weight with respect to 100 parts by weight of the polyimide precursor.

  Next, in this method, a polyimide precursor film is obtained by forming a film of the polyimide precursor solution obtained above and then drying it.

  The film formation of the polyimide precursor solution is not particularly limited, and for example, a known film formation method such as a spin coating method or a casting method can be used.

  For example, a polyimide precursor film can be obtained by applying a polyimide precursor solution on the substrate by the film forming method described above and drying the solution.

  A board | substrate is not specifically limited, For example, a glass substrate, a silicon wafer, a metal film, a plastic film, a flexible circuit board etc. are used.

  Although the thickness of the polyimide precursor film | membrane obtained in this way is not specifically limited, From a viewpoint of facilitating formation of a refractive index change area | region, it is 3-2000 micrometers, Preferably, it is 10-100 micrometers.

  Further, the light transmittance at a thickness of 10 μm of the polyimide precursor film is 95% or more at the wavelength of the pulse laser beam described below, and the wavelength of 1 / N of the wavelength of the pulse laser beam (N is 2, 3 or more). And an integer selected from 4) is preferably 50% or less.

  In the method for producing a polyimide optical element of the present invention, as will be described later, pulse laser light is condensed inside the polyimide precursor film. However, in the processing via such a multiphoton absorption process, light absorption is excessive. If it is too large, the irradiation energy at the condensing point is insufficient, and it becomes difficult to process directly into the polyimide precursor film.

  When N photons are absorbed at the same time, the wavelength is 1 / N, and it is preferable that the light absorption is larger at the wavelength of 1 / N.

  And in the manufacturing method of the polyimide optical element of this invention, a pulse laser beam is then condensed inside the polyimide precursor film, and the condensing point is moved continuously or discontinuously inside the polyimide precursor film. Thus, a refractive index change region in which the refractive index is changed continuously or discontinuously is formed.

  For example, an apparatus shown in FIG. 1 is used to focus pulse laser light inside the polyimide precursor film and move the focused point continuously or discontinuously inside the polyimide precursor film.

  That is, in FIG. 1, the apparatus includes a light source 1 that emits pulsed laser light, a reflecting mirror 2, a condenser lens 3, and an XYZ stage 4.

  As the light source 1, a laser using a titanium / sapphire crystal as a medium, a pulse laser obtained by reproducing / amplifying a dye laser, or the like is used.

The pulse width is 10 ⁻¹² seconds or less, preferably 10 ⁻¹² to 10 ⁻¹⁵ seconds. When the pulse width exceeds 10 ⁻¹² seconds, the refractive index other than the condensing point of the laser light may change. The wavelength is preferably 400 nm to 1.2 μm in the visible light region. Moreover, although a repetition frequency is not specifically limited, Usually, it is preferable that they are 1 Hz-80 MHz. The irradiation energy of the pulse laser beam can be selected as appropriate, but is usually 0.01 nJ / pulse to 500 mJ / pulse, preferably 10 nJ / pulse to 100 mJ / pulse, and more preferably 0.01 to 100 μJ / pulse. is there.

  The reflecting mirror 2 reflects the pulsed laser light emitted from the light source 1 so as to go toward the condenser lens 3.

  The condensing lens 3 condenses the pulsed laser light reflected by the reflecting mirror 2 inside the polyimide precursor film 5 placed on the XYZ stage 4. The magnification of the condensing lens 3 is preferably 2.5 to 150 times, and more preferably 10 to 50 times, for example.

  The XYZ stage 4 has a polyimide precursor film 5 placed thereon and moves three-dimensionally in the X, Y, and Z directions indicated by arrows.

  In this method, for example, a substrate 6 on which a polyimide precursor 5 is formed is placed on the XYZ stage 4, and pulsed laser light is emitted continuously or discontinuously from the light source 1. Light is applied to the condensing lens 3 through the reflecting mirror 2, and is condensed from the condensing lens 3 into the polyimide precursor film 5. Inside the polyimide precursor film 5, a structural change occurs at the condensing point P of the pulse laser beam, and the refractive index at the condensing point P becomes higher than the refractive index of the other portions.

  Then, the XYZ stage 4 is moved three-dimensionally along with such irradiation of the pulse laser beam. Then, since the condensing point P of the pulsed laser light relatively moves inside the polyimide precursor film 5, the refractive index is continuously higher than other portions along the moving locus of the condensing point P. Alternatively, the refractive index changing region S is three-dimensionally formed as a discontinuous region.

  Note that the size, shape, and degree of refractive index change of the refractive index changing region S formed in this way are the irradiation time of the pulse laser beam, the moving direction and speed of the focal position, the size of the pulse width, It can be adjusted as appropriate depending on the magnitude of the irradiation energy or the numerical aperture or magnification of the condenser lens 3.

  And in the manufacturing method of the polyimide optical element of this invention, the polyimide precursor film | membrane in which the refractive index change area | region was formed by pulse laser beam is imidized after that. The imidization is cured by heating by a known method such as hot air circulation, radiant heating, induction heating or the like. Further, it is preferable to imidize in a vacuum or in an inert gas atmosphere in order to prevent the coating from being colored. Thereby, the polyimide precursor film is imidized, and a polyimide film in which the refractive index change region is formed three-dimensionally continuously or discontinuously can be obtained.

  According to such a method, after the refractive index change region is formed three-dimensionally continuously or discontinuously in the polyimide precursor film, this is imidized to obtain a polyimide film. , Manufacturing a polyimide optical element that once changed the refractive index is less likely to return to the original refractive index over time, and as a result, a stable refractive index change region can be formed and light propagation loss can be reduced. can do.

  In the polyimide optical element thus obtained, the refractive index of the refractive index changing region is higher than the refractive index of the other region inside the polyimide film. It can be widely used as an optical element.

  More specifically, as an optical element, it can be used for, for example, an optical waveguide, a diffraction grating, a wavelength filter, etc. More specifically, for example, an optical switching component, an optical multiplexing / demultiplexing component, a wavelength conversion filter, an optical It can be used for an isolator, an optical circulator, an optical connector, an optical external modulator, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples and comparative examples.

Example 1
16.0 g (0.05 mol) of 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl (TFMB) was dissolved in 152.8 g of N, N-dimethylacetamide (DMAc). While stirring, 22.2 g (0.05 mol) of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) was added to this solution and then stirred at room temperature for 24 hours. And reacted. Furthermore, 11.5 g of polyethylene glycol dimethyl ether having a weight average molecular weight of 500 (30 parts by weight of the polyamide precursor) was added to prepare a polyimide precursor solution.

  Then, the polyimide precursor solution was applied onto a substrate made of synthetic quartz glass having a thickness of 1.0 mm by spin coating, dried at 90 ° C. for about 15 minutes, and dried to a thickness of 30 μm on the substrate. A polyimide precursor film was formed.

  This polyimide precursor film is placed on an XYZ stage, and a titanium / sapphire / femtosecond pulse laser device having a wavelength of 780 nm, a pulse width of 150 femtoseconds, and a repetition frequency of 1 kHz at a depth of 10 μm inside the polyimide precursor film. Is used to continuously irradiate pulsed laser light under irradiation conditions of irradiation energy of 0.15 μJ / pulse and objective lens magnification of 10 times, and simultaneously move the polyimide precursor film in a direction perpendicular to the irradiation direction. As shown schematically in FIG. 2, a refractive index changing region S1 having a length of 20 mm continuous in the moving direction was formed by moving at a speed of about 100 μm / second.

  Then, it heated at 360 degreeC for 2 hours in a vacuum atmosphere, imidation was completed, and the optical waveguide which consists of a refractive index change area | region of 20 mm length was formed in the polyimide membrane | film | coat.

  After cutting a 1 mm portion from both ends of this optical waveguide with a dicing device and processing the end face, light is propagated in the optical waveguide by allowing light having a wavelength of 1550 nm to enter the optical waveguide through a single mode fiber. confirmed.

Example 2
The polyimide precursor film prepared in Example 1 was placed on an XYZ stage, and pulsed laser light was discontinuously irradiated under the same irradiation conditions by the same pulse laser apparatus as in Example 1, and at the same time with respect to the irradiation direction. In the vertical direction, the polyimide precursor film is moved at a moving speed of about 100 μm / sec. As shown schematically in FIG. 3, the refractive index is 5 μm, the line spacing is 5 μm, the number of lines is 50, and the line length is 3 mm. A change region S2 was formed.

  Thereafter, heating was performed at 360 ° C. for 2 hours in a vacuum atmosphere to complete imidization, and a diffraction grating composed of the above-described 50-line refractive index changing regions was formed in the polyimide film.

  This diffraction grating was irradiated with a 633 nm He—Ne color laser, and it was confirmed that diffracted light was emitted.

Comparative Example 1
A solution of a polyimide precursor was prepared in the same manner as in Example 1, applied to a substrate made of synthetic quartz glass having a thickness of 1.0 mm by spin coating, and dried at 90 ° C. for about 15 minutes. A polyimide precursor film having a thickness of 30 μm after drying was formed.

  Then, it heated at 360 degreeC for 2 hours in the vacuum atmosphere, and imidation was completed, and the polyimide membrane | film | coat was obtained. Next, an optical waveguide composed of a refractive index change region having a length of 20 mm was formed by the same operation as in Example 1.

  After cutting a 1 mm portion from both ends of this optical waveguide with a dicing device and processing the end face, light having a wavelength of 1550 nm was made incident on the optical waveguide through a single mode fiber. Initially, the light propagated in the optical waveguide. However, after leaving at room temperature for 90 days, light did not propagate in the optical waveguide.

Comparative Example 2
A polyimide precursor solution was prepared in the same manner as in Example 1, applied to a substrate made of synthetic quartz glass having a thickness of 1.0 mm by spin coating, and dried at 90 ° C. for about 15 minutes. A polyimide precursor film having a thickness of 30 μm after drying was formed.

  Then, it heated at 360 degreeC for 2 hours in the vacuum atmosphere, and imidation was completed, and the polyimide membrane | film | coat was obtained. Next, a diffraction grating composed of 50 line refractive index changing regions was formed by the same operation as in Example 2.

  When this diffractive grating was irradiated with a 633 nm He—Ne color laser, initially diffracted light was generated, but after standing at room temperature for 90 days, no diffracted light was generated.

It is a schematic perspective view which shows one Embodiment of the apparatus used for the manufacturing method of the polyimide optical element of this invention. It is a schematic perspective view which shows the aspect which forms the optical waveguide of Example 1 using the apparatus shown in FIG. It is a schematic perspective view which shows the aspect which forms the diffraction grating of Example 2 using the apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Reflecting mirror 3 Condensing lens 4 XYZ stage 5 Polyimide precursor film 6 Substrate

Claims (4)

Preparing a polyimide precursor film;
Condensing the pulsed laser beam inside the polyimide precursor film and moving the condensing point continuously or discontinuously inside the polyimide precursor film forms a refractive index change region where the refractive index has changed. The process of
A method for producing a polyimide optical element, comprising a step of imidizing the polyimide precursor film in which the refractive index changing region is formed. 2. The method for producing a polyimide optical element according to claim 1, wherein a pulse width of the pulsed laser light is 10 ⁻¹² seconds or less. The light transmittance at a thickness of 10 μm of the polyimide precursor film is 95% or more at the wavelength of the pulse laser beam, and a wavelength 1 / N of the pulse laser beam wavelength (N is 2, 3, 4). The method for producing a polyimide optical element according to claim 1, wherein the integer is selected from the group consisting of 50% or less. The said polyimide precursor membrane | film | coat contains the imidation promoter, The manufacturing method of the polyimide optical element in any one of Claims 1-3 characterized by the above-mentioned.

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