JP2005321733A - Optical device with built-in saturable absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device using saturable absorption characteristics by hardly having an optical loss setting a saturable absorption region having uniform optical quality between minute grooves provided on an optical path of a planar optical waveguide. <P>SOLUTION: The optical device forms a carbon nanotube dispersion polymer region 7 by filling and drying carbon nanotube dispersion polymer solution in a very narrow groove 6 on a path of signal light of the plarnar optical waveguide 4. Then, when using solution mixing polymer mixing solvent with a solvent comprising a carbon nanotube, an amid based polarity organic solvent, non-ionic surfactant, and/or polyvinyl pyrrolidone (PVP), as the carbon nanotube dispersion polymer solution, the saturable absorption region uniformly dispersing the carbon nanotube is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical device with a saturable absorber for controlling light in a communication wavelength region using a saturable absorption function of a carbon nanotube dispersed polymer in a near infrared wavelength region.

  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 synchronization method is widely used, and a method using a saturable absorbing material is frequently used as a simple method for realizing mode synchronization. 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 light path of the planar optical waveguide in a very narrow space, for example, a gap of about 1 to 50 μm, and can be continuously formed as a part of the light path. Therefore, it is possible to provide a device that does not require light collection by a lens and that has little optical loss.

  Therefore, the object of the present invention is to provide a saturable absorption characteristic with a small optical loss by setting a saturable absorption region having a uniform optical quality between fine grooves provided on the light path of a planar optical waveguide. It is to provide an optical device to be used.

  In order to solve the above-mentioned problems, the present invention fills a carbon nanotube in the groove by filling a polymer solution in which carbon nanotubes are dispersed between very narrow grooves provided on the light path of the planar optical waveguide, and drying the polymer solution. It forms a dispersed polymer region. 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 comprising 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, a polymer solution in which the carbon nanotubes are uniformly dispersed can be obtained. Since the carbon nanotube content polymer obtained in this way is uniformly dispersed in the polymer base material, the saturable absorption function of the carbon nanotube can be sufficiently exhibited.

  In the present invention, in the path of the signal light of the planar optical waveguide, a groove provided in the path is filled with a carbon nanotube-dispersed polymer solution and dried, so that the carbon nanotubes are uniformly dispersed in the groove. The saturable absorption region can be manufactured very easily.

The specific configuration of the present invention is as follows.
(1) In a planar optical waveguide having a carbon nanotube dispersed polymer region in the middle of a signal light path, the carbon nanotube dispersed polymer region is formed in a groove formed in the middle of the optical signal path. An optical device characterized by being formed by filling and drying and utilizing its saturable absorption function.
(2) The optical device according to (1), wherein the groove has a width of 1 to 50 μm.
(3) 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 polyvinylpyrrolidone (PVP) solvent in a polymer mixed solvent (1 Or the optical device according to (2).
(4) The optical device according to (3), wherein the carbon nanotube is a single-walled carbon nanotube (SWNT).
(5) The optical device according to (3) or (4), wherein the polymer mixed solvent is a polyimide mixed solvent.
(6) The planar optical waveguide according to any one of (1) to (5), wherein a plurality of the carbon nanotube-dispersed polymer regions are provided close to each other in the light passage.
(7) In the path of the signal light of the planar optical waveguide, a groove is provided in the path, and the single-walled carbon nanotube (SWNT), the amide polar organic solvent, the nonionic surfactant, and / or polyvinylpyrrolidone are provided in the groove. (PVP) A method of manufacturing an optical device in which a minute region in which carbon nanotubes are uniformly dispersed is provided in a signal light path by filling and drying a carbon nanotube dispersion solution made of a polymer.

  A planar optical waveguide is a component that confines an optical signal in a specific region and guides it from an incident end to an output end, and has a structure in which a core having a high refractive index is surrounded by a cladding having a low refractive index. In the present invention, an optical device having a saturable absorption characteristic with low optical loss is provided by providing a saturable absorption region in the middle of the light path of such a planar optical waveguide.

As the planar optical waveguide material, glass, organic polymer, semiconductor, or the like can be used. As the substrate, in addition to the Si material, a ceramic substrate, a quartz substrate, a compound semiconductor substrate, or the like can be used. For example, a linear core can be sandwiched between a SiO ₂ undercladding layer and an overcladding layer on a substrate. The core may be made of SiO ₂ doped with impurities that increase the refractive index, for example, Ge. Light propagates through the core with a high refractive index.

  In the present invention, at least one groove that is orthogonal to and traverses the light path of the planar optical waveguide is formed by a combination of photolithography and dry etching, or is formed by a dicing saw. The groove is formed with a width of 1 to 50 μm. In order to form a region having saturable absorption characteristics in a minute region of a part of the core using this groove, a saturable absorbing material that can be embedded in the groove is required. The inventor of the present invention has found that a polymer 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, the inventor of the present invention can convert SWNTs into NMP (N-methylpyrrolidone) solvent, nonionic surfactant mixed solvent and / or polyvinylpyrrolidone (PVP) mixed solvent. It has been found that it is effective to use a mixed SWNT dispersion solvent. This solution 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.

  The carbon nanotube-dispersed polymer thus obtained can sufficiently exhibit the saturable absorption function of the carbon nanotubes because the carbon nanotubes are uniformly dispersed in the polymer base material.

  In the present invention, such a carbon nanotube-dispersed polymer solution is filled in a groove of about 1 to 50 μm provided in the middle of the light path of the planar optical waveguide, and dried, so that it is very simply saturable with low light loss. An optical device having absorption characteristics can be obtained.

  Carbon nanotubes are known to have a high saturable absorption function. In the present invention, single-walled carbon nanotubes (SWNT) are 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 organics (except lower hydrocarbons), inorganics, polar gases, natural and polymeric 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.

  A glass fiber filter, a membrane filter, etc. are used for the filter used by this invention. At that time, the retained particle diameter can be appropriately determined according to the purpose. The reserved particle diameter is obtained from the leaked particle diameter 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.

  Polyvinyl pyrrolidone (PVP) may be mixed in the solvent used in the present invention with a small loss of light dispersed in carbon nanotubes. 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 polyvinylpyrrolidone 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 relates to an optical device that uses a saturable absorption function such as waveform shaping, noise reduction, and mode locking of a pulse of an optical signal propagating in a light path of a planar optical waveguide, in a very small region in the middle of the light path. The saturable 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.

  A method for producing the optical device of the present invention will be described below as an example. The present invention is not limited to this.

Embodiments of the present invention will be described below in detail with reference to the drawings.
(Production of carbon nanotube-dispersed polyimide)
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)
A commercially available linear optical waveguide chip (manufactured by Nihon Hojo) was used as the quartz glass planar optical waveguide. As shown in FIG. 2, a groove 6 having a width of 30 μm and a depth of 150 μm was formed in this waveguide so as to be perpendicular to the light path 4 in the core portion. The optical waveguide chip was fixed to the pedestal, and a commercially available dicing saw was used to form the grooves.

  By filling the grooves formed in the planar optical waveguide chip thus obtained with the carbon nanotube-dispersed polyimide solution obtained above and drying, carbon nanotube-dispersed polyimide regions 7, 7 'are formed in the grooves. It was. The carbon nanotube-dispersed polyimide regions 7 and 7 'have extremely excellent saturable absorption characteristics because the carbon nanotubes are uniformly dispersed in the polyimide base material.

It is a figure which shows the concept of the conventional apparatus. It is the top view and side view of the optical apparatus of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Lens 3 Saturable absorber 4, 4 'Waveguide core part 5, 5' Waveguide clad part 6 Groove 7, 7 'Carbon nanotube dispersion | distribution polyimide 8 Board | substrate

Claims (7)

  In a planar optical waveguide having a carbon nanotube dispersed polymer region in the middle of a signal light path, the carbon nanotube dispersed polymer region is filled with a carbon nanotube dispersed polymer solution in a groove formed in the middle of the optical signal path, and dried. An optical device that is formed by using the saturable absorption function.   The optical device according to claim 1, wherein the groove has a width of 1 to 50 μm.   The carbon nanotube-dispersed polymer solution is a solution prepared 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. The optical device described.   The optical device according to claim 3, wherein the carbon nanotube is a single-walled carbon nanotube (SWNT).   The optical device according to claim 3, wherein the polymer mixed solvent is a polyimide mixed solvent.   The planar optical waveguide according to any one of 1 to 5, wherein a plurality of the carbon nanotube-dispersed polymer regions are provided close to each other in the light passage. In the signal light path of the planar optical waveguide, a groove is provided in the path, and the single-walled carbon nanotube (SWNT), the amide polar organic solvent and the nonionic surfactant and / or polyvinylpyrrolidone (PVP) are provided in the groove. In addition, a method of manufacturing an optical device in which a minute region in which carbon nanotubes are uniformly dispersed is provided in a signal light path by filling and drying a carbon nanotube dispersion solution made of a polymer.