1. An optical fiber comprising
a core area having a diameter of at least 10 \u03bcm; and
a cladding layer disposed to surround the core area, wherein the core area is doped in predetermined regions to create an acoustic refractive index profile that excludes thermal phonons from areas occupied by the optical mode and exhibits a negative lens structure that refracts acoustic electrostrictively-generated wave away from the core area occupied by said optical mode and reduces phonon-photon interaction time andor length.
2. The optical fiber as defined in claim 1 wherein the acoustic refractive index profile is a monotonic profile generated by decreasing dopant concentration toward the center of the core area, the slope of the acoustic refractive index profile sufficient to create the negative acoustic lens structure.
3. The optical fiber as defined in claim 2, wherein the slope of the monotonic acoustic refractive index profile is greater than 0.005\u03bcm.
4. The optical fiber as defined in claim 2, wherein the acoustic index contrast is greater than 0.05.
5. The optical fiber as defined in claim 1 wherein a large acoustic index contrast value is achieved with a pedestal optical index profile.
6. The optical fiber as defined in claim 1 wherein the core area exhibits a diameter greater than approximately 20 \u03bcm.
7. The optical fiber as defined in claim 1 wherein the doping profile of the optical and acoustic refractive indices are configured to minimize an overlap integral between a forward-directed optical field (photon) and retreating acoustic field (phonon), defined as photon-phonon overlap integral.
8. The optical fiber as defined in claim 1 wherein the fiber comprises a large mode area (LMA) fiber.
9. The optical fiber as defined in claim 1 wherein the fiber comprises a higher-order mode (HOM) fiber.
10. The optical fiber as defined in claim 9 wherein the core area is configured to exhibit a profile comprising a central area doped with a first combination of dopant species and at least one ring area doped with a second combination of dopant species, the spacing of the at least one ring controlled to refract the acoustic energy away from the optical mode field.
11. The optical fiber as defined in claim 10 wherein the core area is configured to have a central area doped with the first combination of dopant species and a plurality of ring areas doped with the second combination of dopant species.
12. The optical fiber as defined in claim 1 wherein the core area comprises
a central core portion; and
a ring core portion surrounding the central core portion and including a dopant species able to simultaneously increase the optical refractive index and decrease the acoustic refractive index.
13. The optical fiber as defined in claim 12 wherein the ring core portion is doped with aluminum.
14. The optical fiber as defined in claim 12 where the width of the ring core portion is selected to remain less than the lifetime of the phonons to refract the acoustic energy out of the optical field.
15. The optical fiber as defined in claim 1 wherein the core area is doped to exhibit a pedestal-like refractive index profile.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process for producing a conjugated diene copolymer rubber which comprises: initiating a copolymerization reaction in a reaction system comprising a first conjugated diene compound and a first aromatic vinyl compound, optionally adding a second conjugated diene compound and optionally adding a second aromatic vinyl compound to the reaction system during the copolymerization reaction, and completing the copolymerization reaction, and then adding a modifier to the reaction system, wherein a first polyfunctional monomer is added to the reaction system in the course of the reaction at a time when the polymerization conversion rate is 30% -70%.
2. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein the first polyfunctional monomer is continuously added to the reaction system.
3. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein the reaction system futher comprises a second polyfunctional monomer when the copolymerization reaction is initiated.
4. The process for producing a conjugated diene copolymer rubber according to claim 3, wherein the first polyfunctional monomer andor the second polyfunctional monomer is divinylbenzene.
5. The process for producing a conjugated diene copolymer rubber according to claim 4, wherein the first polyfunctional monomer is divinylbenzene and the amount of divinylbenzene added to the reaction system as the first polyfunctional monomer is is 0.001 to 1 part by mass with respect to 100 parts by mass of the total amount of the first conjugated diene compound, second conjugated diene compound, first aromatic vinyl compound, and second aromatic vinyl compound.
6. The process for producing a conjugated diene copolymer rubber according to claim 4, wherein the second polyfunctional monomer is divinylbenzene and the amount of divinylbenzene present in the reaction system is greater than 0 to 1 part by mass with respect to 100 parts by mass of the total amount of the first conjugated diene compound and first aromatic vinyl compound.
7. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein the modifier is a compound which can react with silica or a mixture of a tin compound and a compound which can react with silica.
8. The process for producing a conjugated diene copolymer rubber according to claim 7, wherein the compound which can react with silica is at least one compound selected from the group consisting of dibutyldichlorosilicon, methyltrichlorosilicon, methyldichlorosilicon, tetrachlorosilicon, triethoxymethylsiliane, triphenoxymethylsilane, trimethoxysilane, methyltriethoxysilane, 4,5-epoxyheptylmethyldimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane.
9. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein the first conjugated diene compound andor the second conjugated diene compound is 1,3-butadiene.
10. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein the first aromatic vinyl compound andor the second aromatic vinyl compound is styrene.
11. A conjugated diene copolymer rubber produced by the process according to claim 1.
12. The process for producing a conjugated diene copolymer rubber according to claim 6, the second polyfunctional monomer is divinylbenzene and wherein the amount of divinylbenzene present in the reaction system is greater than 0 to 1 part by mass with respect to 100 parts by mass of the total amount of the first conjugated diene compound and first aromatic vinyl compound.
13. The process for producing a conjugated diene copolymer rubber according to claim 8, wherein the compound which can react with silica is N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane.
14. The process for producing a conjugated diene copolymer rubber according to claim 1, which comprises: initiating a copolymerization reaction in a reaction system comprising a first conjugated diene compound and a first aromatic vinyl compound, adding a second conjugated diene compound and optionally adding a second aromatic vinyl compound to the reaction system during the copolymerization reaction, and completing the copolymerization reaction, and then adding a modifier to the reaction system, wherein a first polyfunctional monomer is added to the reaction system in the course of the reaction at a time when the polymerization conversion rate is 30% or more, but less than 70%.
15. The process for producing a conjugated diene copolymer rubber according to claim 1, which comprises: initiating a copolymerization reaction in a reaction system comprising a first conjugated diene compound and a first aromatic vinyl compound, optionally adding a second conjugated diene compound and adding a second aromatic vinyl compound to the reaction system during the copolymerization reaction, and completing the copolymerization reaction, and then adding a modifier to the reaction system, wherein a first polyfunctional monomer is added to the reaction system in the course of the reaction at a time when the polymerization conversion rate is 30% or more, but less than 70%.
16. The process for producing a conjugated diene copolymer rubber according to claim 1, which comprises: initiating a copolymerization reaction in a reaction system comprising a first conjugated diene compound and a first aromatic vinyl compound, adding a second conjugated diene compound and adding a second aromatic vinyl compound to the reaction system during the copolymerization reaction, and completing the copolymerization reaction, and then adding a modifier to the reaction system, wherein a first polyfunctional monomer is added to the reaction system in the course of the reaction at a time when the polymerization conversion rate is 30% or more, but less than 70%.
17. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein said first conjugated diene compound is selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3 -butadiene, 2-chloro-1,3-butadiene, and 1,3-pentadiene.
18. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein said first aromatic vinyl compound is selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, .alpha.-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethyl aminoethyl ether, N,N-dimethylaminoethylstyrene, vinylpyridine.
19. The process for producing a conjugated diene copolymer rubber according to claim 17, wherein said first aromatic vinyl compound is selected from the group consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, .alpha.-methyistyrene, 2,4-dimethyistyrene, 2,4-diisopropylstyrene, 4-tert-butyistyrene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethyl ether, N,N-dimethylaminoethylstyrene, vinylpyridine.
20. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein said first conjugated diene compound is 1,3-butadiene and said first aromatic vinyl compound is styrene, and said first polyfunctional monomer is divinylbenzene.
21. The process for producing a conjugated diene copolymer rubber according to claim 1, wherein said first polyfunctional monomer is added to the reaction system in the course of the reaction at a time when the polymerization conversion rate is 35% -60%.