1998 Fiscal Year Final Research Report Summary
Twin beam in fibers ; its production with a wave-guide type nonlinear crystal
| Project/Area Number |
08554011
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
物理学一般
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KUGA Takahiro The Univ.of Tokyo, Graduate School of Arts and Sciences, Associate Professor, 大学院・総合文化研究科, 助教授 (60195419)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Optical fiber / Wave-guide type crystal / Quasi-phase matching / Twin beam / Quantum correlation / Coincidence |
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| Research Abstract |
Twin beam is a pair of optical beams that have the same statistical properties of light. Twin beam is described only by a Quantum theory and there is no classical analogue to it. In many years, twin beam has been utilized to clarify the Quantum nature of light, such as an intensity interference, photon entanglement, non-local correlation (EPR paradox) etc. Since twin beams were generated by a parametric down-conversion with bulk nonlinear crystals in most of the former works, there were unavoidable difficulties so called a geometrical problem. In the parametric down-conversion, pairs of photons are emitted in a fairly large solid angle as long as a phase match condition is satisfied. Therefore, it is almost impossible to collect all photons in pairs. On the other hand, if one uses a wave-guide type nonlinear crystal as the down-converter, pairs of photons are confined in the wave-guide and it is easy to couple them to optical fibers and detect all pairs of photons.
We utilized the wave-guide type crystal to generate the twin beam. First of all, we characterized the crystal by means of a second harmonics generation (SHG). We made a laser diode with an extended cavity oscillating in 1.55 mu m range. We measured SHG spectra and efficiency of the crystal by changing the frequency and power of the laser diode and compared them with theoretical calculations. We found a small discrepancy between experiments and calculations, but the discrepancy was acceptable if we took account of an inhomogeneity of the crystal.
Unfortunately, we can not complete our project within a given period for lack of efficient detectors in 1.55 mum region and the limitation of time to develop such detectors. However, we accumulated the basic information and data to realize twin beam in fibers. We will continue the project and complete it in the near future.
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