JP2005321483A - Optical device with built-in saturable absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device using saturable absorption characteristics without an optical loss forming a saturable absorption region having uniform optical quality between minute slits on an optical path of optical fibers. <P>SOLUTION: In the optical device having the saturable absorption region on the optical path of the optical fiber, the saturable absorption region is formed by filling and drying carbon nano-tube dispersion polymer solution in the slit formed between both end faces of the two optical fibers held on the same axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a saturable absorber built-in optical device for controlling light in the near-infrared wavelength region by utilizing a saturable absorption function of a carbon nanotube-dispersed polymer.

  Ultra-short-time pulse lasers that oscillate pulse light instantaneously for a very short time are expected to have a wide range of applications in the observation of ultra-high-speed physical and chemical phenomena, optoelectronics, processing technology, and medical fields. As a method for generating ultra-short-time pulsed light, a mode-locking method is widely used, and a method using a saturable absorbing material is frequently used as a simple method for realizing mode-locking. As a saturable absorbing material in the near-infrared wavelength region, there is a compound semiconductor multiple quantum well system which has been put into practical use since 1995, but there is a problem that the manufacturing cost is high and the optical damage resistance is weak.

  Therefore, it has been desired to develop a saturable absorbing material having a low manufacturing cost and an excellent optical damage property. Recently discovered carbon nanotubes are hexagonal mesh-like sheet-like structures with a diameter of 1 micron or smaller than carbon fibers, forming a tube parallel to the axis of the tube. Is known to have a saturable absorption function in the near-infrared wavelength region, and the application of SWNTs to optical elements operating in the near-infrared wavelength region has been proposed.

  For example, if the saturable absorption function of carbon nanotubes is used, a mode-locked short-time pulse laser light source that is currently popular can be provided inexpensively and compactly. As an apparatus that utilizes the saturable characteristics of such carbon nanotubes, it has been proposed to use a thin film in which SWNT is coated on glass (see Patent Document 1 below).

In addition to ultra-short-time pulse lasers, using the characteristics of carbon nanotube saturable absorbers that increase the transmittance as the optical power increases will reduce noise light relative to the signal light. Application as a noise reduction device for signal light has also been proposed (see Patent Document 2 below).
JP 2003-121892 A JP 2003-248251 A

  However, all of the devices using the saturable absorption characteristics of carbon nanotubes proposed above apply SWNTs on a substrate such as glass. When the SWNT thin film formed on such a glass substrate is incorporated into a device using an optical fiber, as shown in FIG. 1, the light that has once spread out of the passage must be collected by a lens, The entire apparatus becomes a large scale, and there is a problem that it takes time to adjust the optical axis and the cost is high. In addition, it is difficult to apply SWNT uniformly on a glass substrate by spraying a SWNT solution onto a glass substrate, and it is difficult to produce a reproducible device with variations in optical quality depending on the location. could not.

  On the other hand, if the saturable absorber is accommodated in a very small region, for example, a gap of about 1 to 50 μm in the optical path of the optical fiber, and can be continuously formed as a part of the optical path. Therefore, it is possible to provide a device that does not require light collection by a lens and that has little optical loss.

  Accordingly, an object of the present invention is to utilize a saturable absorption characteristic with a small optical loss in which a saturable absorption region having a uniform optical quality is formed between fine slits provided on a light path of an optical fiber. It is to provide an optical device.

  In order to solve the above-mentioned problems, the present invention forms a carbon nanotube-dispersed polymer region in a slit by filling a polymer solution in which carbon nanotubes are dispersed in a slit provided on the optical path of an optical fiber and drying the polymer solution. To do. In order to uniformly disperse the carbon nanotubes in the water-soluble polymer, it is known that it is effective to use an aqueous carbon nanotube dispersion containing water and a surfactant. By mixing this nanotube-dispersed aqueous solution with a water-soluble polymer solution, a polymer solution in which carbon nanotubes are uniformly dispersed can be obtained. In addition, in order to uniformly disperse carbon nanotubes in a polymer soluble in an amide polar solvent, the inventor of the present invention can use an amide polar organic solvent and a nonionic surfactant and / or polyvinylpyrrolidone (PVP). It has been found that it is effective to use a carbon nanotube dispersion solvent comprising By mixing this carbon nanotube dispersion solvent with a polymer solvent, it was confirmed that a polymer solution in which the carbon nanotubes were uniformly dispersed could be obtained, and that the obtained carbon nanotube dispersion polymer had a saturable absorption function.

  In the present invention, a minute saturable absorption in which carbon nanotubes are uniformly dispersed in the middle of an optical fiber by filling a carbon nanotube-dispersed polymer solution into a slit formed in an optical fiber held by a holding member or a capillary tube and drying the slit. The area can be manufactured very simply.

The specific configuration of the present invention is as follows.
(1) In an optical device having a saturable absorption region in an optical path of an optical fiber, the saturable absorption region is formed of a carbon nanotube-dispersed polymer in a slit formed between both end faces of two optical fibers held coaxially. An optical device formed by filling and drying a solution.
(2) The optical device according to (1), wherein the slit is formed by cutting an optical fiber held on a holding member.
(3) The apparatus according to (1) or (2) above, wherein the holding member is formed with a groove for holding the ferrule or coating portion of the optical fiber and / or a groove for forming the slit on the substrate. .
(4) The apparatus according to (1) above, wherein the slit is formed between two end faces by inserting two optical fibers into a capillary tube.
(5) The optical device according to any one of (1) to (4), wherein the slit is 1 to 50 μm.
(6) The carbon nanotube-dispersed polymer solution is a solution obtained by mixing a carbon nanotube, an amide-based polar organic solvent, a nonionic surfactant and / or a polyvinyl pyrrolidone (PVP) solvent in a polymer mixed solvent (1 The optical device according to any one of (5) to (5).
(7) The optical device according to (6), wherein the carbon nanotube is a single-walled carbon nanotube (SWNT).
(8) The optical device according to (7), wherein the polymer mixed solvent is a polyimide mixed solvent.
(9) The optical device according to any one of (1) to (7), wherein a plurality of the connection regions are formed in a portion adjacent to the optical fiber.
(10) A slit is formed by cutting the optical fiber held on or in the holding member, and the single-walled carbon nanotube (SWNT), the amide polar organic solvent, and the nonionic surfactant are formed in the slit. A method of manufacturing an optical device having a carbon nanotube-dispersed polymer region in the middle of an optical path of an optical fiber by filling and drying a carbon nanotube-dispersed solution composed of polyvinylpyrrolidone (PVP) and a polymer.
(11) Two optical fibers are inserted into a capillary tube, and a slit is formed between both end faces thereof. A single-walled carbon nanotube (SWNT), an amide polar organic solvent, a nonionic surfactant, and / or Alternatively, a method for producing an optical device having a carbon nanotube-dispersed polymer region in the middle of an optical path of an optical fiber by filling and drying a carbon nanotube-dispersed solution comprising polyvinylpyrrolidone (PVP) and a polymer.

  In one embodiment of the present invention, as shown in FIG. 2, an optical fiber is fixed by a support substrate, and a slit is formed by a blade or the like at the center of the fixed support substrate. Next, by filling the carbon nanotube-dispersed polymer solution between the slits and drying, an optical device having saturable absorption characteristics with low light loss can be obtained very simply.

  An optical fiber transmits and receives optical signals through long and thin lines of fused silica or other transparent material used to transmit light. The optical fiber can support the glass strand from which the coating is removed or the coated optical fiber with a holding member.

  In order to fix the optical fiber on the holding member, a V-shaped or U-shaped groove can be cut in the holding member, and the optical fiber can be embedded and fixed in this groove. Further, a groove perpendicular to the groove can be cut in the center of the holding member so that a slit can be easily formed later.

  As the holding member for fixing the optical fiber, a ferrule in which a hole aligned with the outer diameter of the optical fiber passes through the center can also be used. The optical fiber can be fixed through the through hole, and a groove can be cut from the side surface of the ferrule with a blade to form a slit. The side surface of the holding ferrule can be ground so that a slit can be easily formed later.

  As the holding member, glass, zirconia, or the like, which is a material having an expansion coefficient equal to or close to that of glass, is preferable. In addition to ceramics such as alumina and garnet, a holding member made of resin such as epoxy resin or liquid crystal polymer may be used. Good. As the resin, either a thermoplastic resin or a thermosetting resin can be used.

  An adhesive can be used to fix the optical fiber to the holding member. As the adhesive, an epoxy adhesive, an ultraviolet curable adhesive, or the like can be used.

  According to another aspect of the present invention, an optical fiber is formed by inserting two optical fibers into a capillary tube, forming a slit between both end faces, filling the slit with a carbon nanotube-dispersed polymer solution, and drying. A carbon nanotube-dispersed polymer region is formed in the middle of the light path.

As such a capillary tube, for example, a commercially available glass-made optical fiber connection capillary tube (splicer) can be used.
In order to form a microscopic region having saturable absorption in the middle of an optical fiber by holding the optical fiber on a holding member or a capillary tube, a material having a saturable absorption characteristic capable of embedding a minute gap is used. Necessary. The inventor of the present invention has found that a polymer solution in which carbon nanotubes are uniformly dispersed is extremely useful as a material satisfying such conditions.

  In general, when carbon nanotubes are dispersed in a material such as a polymer, it is extremely difficult to uniformly disperse the carbon nanotubes into bundles and ropes due to mutual cohesive force (van der Waals force). is there. In particular, the smooth surface at the atomic level of carbon nanotubes is a factor that reduces the affinity for the substrate. Due to such characteristics of the carbon nanotubes, it has been difficult to mix and disperse the carbon nanotubes in the polymer. In particular, it has been extremely difficult to form a polymer material with excellent optical quality in which carbon nanotubes are uniformly dispersed.

  In order to uniformly disperse SWNTs in a polymer, for example, SWNTs are mixed in NMP (N-methylpyrrolidone) solvent and nonionic surfactant mixed solvent and / or polyvinylpyrrolidone (PVP) mixed solvent. It has been found that it is effective to use a dispersion solvent. Next, this solvent is treated with ultrasonic waves, and then filtered with an ultracentrifuge or glass fiber filter paper to obtain a solvent in which only fine SWNTs are dispersed. By mixing this with a polymer solvent, a polymer solution in which carbon nanotubes are uniformly dispersed can be obtained. Filtration may be performed at the stage of the SWNT dispersion, or after mixing the dispersion with a polymer mixed organic solvent.

  Examples of the polymer used in the present invention include polyimide and polyvinyl alcohol, but it is required that the polymer is soluble in a solvent. Particularly preferably, a solvent-soluble polyimide is used. As a polyimide soluble in a solvent, a block copolymerized polyimide is known.

  Carbon nanotubes are known to have a high saturable absorption function. In the present invention, SWNT is preferably used. The production method of SWNT is not particularly limited, and a thermal decomposition method using a catalyst (a method similar to a vapor phase growth method), an arc discharge method, a laser evaporation method, a HiPco method (High-Presence carbon monoxide process). ) Etc., any known manufacturing method may be employed.

  As the amide polar organic solvent used in the present invention, specifically, any of dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) and the like can be used. Particularly preferably, N-methylpyrrolidone (NMP) and / or dimethylacetamide (DMAC) can be used. They can dissolve many natural and synthetic polymer resins.

  The nonionic surfactant used in the present invention may be any of polyoxyethylene-based, polyhydric alcohol and fatty acid ester-based, or a system having both of these, particularly preferably a polyoxyethylene-based surfactant. Things are used. Examples of polyoxyethylene surfactants include fatty acid polyoxyethylene ethers, higher alcohol polyoxyethylene ethers, alkyl phenols polyoxyethylene ethers, sorbitan ester polyoxyethylene ethers, castors Examples include oil polyoxyethylene ether, polyoxypropylene polyoxyethylene ether, and fatty acid alkylol amide. Examples of polyhydric alcohol and fatty acid ester surfactants include monoglycerite surfactants, sorbitol surfactants, saltabine surfactants, and sugar ester surfactants.

  The amount of these nonionic surfactants to be added can be appropriately determined depending on the amount of SWNT blended and the type of amide polar organic solvent to be blended, but generally 0.005 to 10% is sufficient for SWNT. A good dispersion effect. If it is 0.005% or less, the amount of the surfactant with respect to SWNT is insufficient, so that some of the nanotubes aggregate and precipitate. If it is 10% or more, the rotation of the surfactant molecules in the solvent becomes difficult, so that a sufficient amount of the hydrophobic portion of the surfactant cannot be adsorbed on the surface of the hydrophobic nanotube. It is inconvenient for dispersion of fine nanotubes. When the SWNT content is 0.005 to 0.05%, the nonionic surfactant content is preferably 0.01 to 5%.

  The amount of SWNT blended varies depending on the purpose of use, but is not particularly limited as long as dispersibility is obtained. When SWNT is used and dispersed in a mixed solution of NMP and polyoxyethylene surfactant, it can be dispersed to a maximum of 0.05%.

  The ultrasonic waves used in the present invention were 20 kHz, 150 W and 28 kHz, 140 W, and a good dispersion effect could be obtained by processing for about 1 hour, but the ultrasonic conditions of the present invention are limited to this. Is not to be done. It can be determined appropriately depending on the amount of carbon nanotubes to be blended, the type of amide polar organic, and the like.

  As the filter used in the present invention, a glass fiber filter, a membrane filter or the like is used. At that time, the retained particle diameter can be appropriately determined according to the purpose. The retained particle diameter is obtained from the diameter of the leaked particles when barium sulfate or the like specified in JIS 3801 is naturally filtered, and substantially corresponds to the average pore diameter of the filter. For example, when applied to an optical instrument using light scattering reduction, the smaller the retained particle diameter of the filter, the better, but generally the retained particle diameter is 0.1 to 2.0 μm, preferably 0.1 to 1.0 μm. Things can be used.

  Polyvinylpyrrolidone (PVP) may be mixed in the carbon nanotube dispersion solvent used in the present invention. Polyvinyl pyrrolidone is known to have a so-called wrapping effect that is adsorbed on the surface of the carbon nanotube and encapsulates the carbon nanotube. Therefore, it is considered that mixing with the carbon nanotube dispersion in the present invention has an effect of preventing aggregation and reaggregation of carbon nanotubes.

  The blending amount of polyvinyl pyrrolidone in the carbon nanotube dispersion solvent can be appropriately determined depending on the blending amount of the carbon nanotubes, but is preferably 0.1% to 10%.

  The present invention is an optical device that uses a saturable absorption function such as waveform shaping, noise reduction, and mode locking of an optical pulse propagating in the optical path of an optical fiber, and is saturable in a minute region in the optical path of the optical fiber. The absorption region can be formed very easily. Therefore, as a device using the saturable absorption function, an inexpensive device that is compact and has little optical loss can be manufactured in a short time.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

(Preparation of carbon nanotube-dispersed polyimide solution)
SWNT (3 mg) was mixed in a mixed solvent of NMP (N-methylpyrrolidone) solvent (30 g) and nonionic surfactant Triton X-100 (30 mg) and treated with ultrasonic waves (20 kHz) for 1 hour. . Next, this dispersion solution was filtered with a glass fiber filter paper (GC-50, retained particle diameter 0.5 μm) to obtain a carbon nanotube dispersion solvent.
When the carbon nanotube dispersion obtained above and an organic solvent mixed solution (30 g) of solvent-soluble polyimide were mixed and stirred, a uniform solution colored black was obtained.

(Production of optical device)
As shown in FIG. 3, a groove 5 on which the optical fiber is placed is formed on the upper surface of the holding member 4.
The polymer coating in the middle of the optical fiber is peeled off to expose the glass fiber 6 of the optical fiber. The element wire 6 is placed in a groove 5 formed on the holding member 4, and after being poured with an epoxy adhesive, it is cured and fixed. The strand 6 is cut with a dicing saw to process the slit 7. At that time, the slit 7 was made to have a width of 30 μm.
Next, an appropriate amount of the carbon nanotube-dispersed polyimide solution prepared as described above was filled between the slits 7. By drying this, the slit 7 is filled with polyimide in which carbon nanotubes are dispersed.
In this way, as shown in the cross-sectional view of FIG. 4, a carbon nanotube dispersed polymer region having a saturable absorption function could be formed very easily in a minute region in the middle of the optical path of the optical fiber.

(Production of optical device)
As the holding member, a commercially available optical fiber connecting capillary (microcapillary) shown in FIG. 5 was used. As shown in FIG. 6, an optical fiber from which two coatings have been removed is inserted into the optical fiber connecting capillary, and the width of the slit 13 formed by the distance between both end faces is set to 25 μm. It was fixed with an adhesive.
Next, an appropriate amount of the carbon nanotube-dispersed polyimide solution prepared in Example 1 was filled between the slits 13. By drying this, the slit 13 is filled with polyimide in which carbon nanotubes are dispersed.
In this way, a carbon nanotube-dispersed polymer region having a saturable absorption function could be very easily formed in a minute region in the optical path of the optical fiber held in the optical fiber connecting capillary of the holding member 14. .

It is a conceptual diagram of the optical apparatus using the conventional carbon nanotube thin film. It is a figure which shows the manufacturing method of the optical apparatus of this invention. It is a sketch of the slit of the Example of this invention. It is sectional drawing of the optical apparatus of the Example of this invention. It is a sketch of the holding member (capillary type for optical fiber connection) of the Example of this invention. It is a sketch of the slit of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Lens 3 Saturable absorber 4 Holding member 5 V groove 6 Optical fiber glass strand 7 Slit 8 Holding member 9 Optical fiber glass strand 10 Carbon nanotube dispersion polymer 11 Through hole 12 Optical fiber glass strand 13 Slit 14 Holding member

Claims (11)

In an optical device having a saturable absorption region in an optical path of an optical fiber, the saturable absorption region is filled with a carbon nanotube-dispersed polymer solution in a slit formed between both end surfaces of two optical fibers held coaxially. An optical device formed by drying. The optical apparatus according to claim 1, wherein the slit is formed by cutting an optical fiber held on a holding member. The apparatus according to claim 1 or 2, wherein the holding member is formed with a groove for holding the ferrule or covering portion of the optical fiber and / or a groove for forming a slit on the substrate. The apparatus according to claim 1, wherein the slit is formed by inserting two optical fibers into a capillary tube and between both end faces thereof. The optical device according to claim 1, wherein the slit is 1 to 50 μm. 6. The carbon nanotube-dispersed polymer solution is a solution obtained by mixing a carbon nanotube, an amide-based polar organic solvent, a nonionic surfactant and / or a polyvinyl pyrrolidone (PVP) solvent in a polymer mixed solvent. An optical device according to any one of the above. The optical device according to claim 6, wherein the carbon nanotube is a single-walled carbon nanotube (SWNT). The optical device according to claim 7, wherein the polymer mixed solvent is a polyimide mixed solvent. The optical device according to claim 1, wherein a plurality of the connection regions are formed in adjacent portions of the optical fiber. A slit is formed by cutting an optical fiber held on or in a holding member, and a single-walled carbon nanotube (SWNT), an amide-based polar organic solvent, a nonionic surfactant, and / or a slit are formed in the slit. A method for producing an optical device having a carbon nanotube-dispersed polymer region in the middle of an optical path of an optical fiber by filling a carbon nanotube-dispersed solution composed of polyvinylpyrrolidone (PVP) and a polymer and drying the solution. Two optical fibers are inserted into a capillary tube, and a slit is formed between both end faces thereof. A single-walled carbon nanotube (SWNT), an amide polar organic solvent, a nonionic surfactant and / or polyvinylpyrrolidone are formed in the slit. (PVP) A method of manufacturing an optical device having a carbon nanotube dispersed polymer region in the middle of an optical path of an optical fiber by filling and drying a carbon nanotube dispersed solution made of a polymer.