In this paper, the refractive-index profile (RIP) of single-mode fiber is reconstructed from the measured transmitted near-field (NF) intensity combined with an inverse algorithm method, which can improve the conventional NF method to avoid the troubles introduced by multiple measurements and iteration smoothing in the processing of measuring the RIP without influencing the accuracy of the results. The method used here has the advantages of convenient operation and accurate results for the characterization of single-mode optical fiber; it can also be applied to the RIP measurement of graded index fibers, single-mode planar waveguides, and channel waveguides.
We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic <sup>87</sup>Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5<i>P</i><sub>1/2</sub> state to two hyperfine levels (the lower levels) of the 5<i>S</i><sub>1/2</sub> state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.
We present a scheme to realize entangled states, swap gate and quantum-information transfer for two atoms in cavity QED. The scheme does not require the transfer of quantum information between the atoms and cavity and that the cavity field is only virtually excited, thus the requirement on the quality factor of the cavity is greatly loosened.
We examine the gain property of a probe field interacting with two different three-level Lambda-type atomic systems with an open loop or a close loop. In the atomic system with an open loop, there exists quantum interference resulting from spontaneous emissions to two near-degenerate lower levels from a common upper level, and the weak probe field can be greatly amplified due to the spontaneously generated coherence. Moreover, the probe gain becomes sensitive to the relative phase between the probe and coupling fields, so we can realize phase control of the probe gain in principle. In the atomic system with a close loop, we use a microwave field to couple the two well-spaced lower levels so that quantum coherence similar to SGC can be generated. In this atomic system, we also can achieve the phase-sensitive probe gain due to the quantum interference between two different absorption channels for the probe field. Note, only in the case of three-photon resonance, this close-loop atomic system can reach a steady state. While in the case of three-photon off-resonance, the probe gain without inversion always oscillates periodically versus time, thus no steady-state probe gain can be achieved.
Two schemes for ultrabroad-band wavelength converters based on four-wave mixing in a semiconductor optical amplifier are proposed, both utilizing a conventional semiconductor optical amplifier (SOA) and two orthogonal-pump waves. In scheme I, the efficiency of wavelength conversion is measured for the wavelength shifts from 1500 nm to 1640 nm. The variation of conversion efficiency is < 0.9 dB over the wavelength range from 1530 nm to 1560 nm (C-band), and is < 4.5 dB over the wavelength range from 1560 nm to 1610 nm (L-band). The maximum conversion efficiency is about -8.7 dB. In scheme II, wavelength conversion with the polarization sensitivity less than 1.3 dB is obtained over a range from 1510 nm to 1620 nm.
Optical linear and nonlinear properties of AgGaGe<sub>x</sub>S<sub>2(1+x)</sub>, Hg<sub>(1-x)</sub>Cd<sub>x</sub>Ga<sub>2</sub>S<sub>4</sub>, LiInSe<sub>2</sub>, and LiInS<sub>2</sub> non-linear crystals are investigated in details so as their potential in frequency conversion of femtosecond pulses for lidar applications.
We applied a pumping field to couple the middle level of two- photon absorption with the fourth level. Two-photon absorption minimum was observed. This is the first observation and experimental analysis of such phenomenon after it was predicted four years ago. In sodium vapor, two-photon absorption strength of 3S<SUB>1/2</SUB>(Fequals2)-3P<SUB>3/2</SUB>-4D<SUB>3/2</SUB> was measured by detecting the fluorescence at 568.3 nm (4D<SUB>3/2</SUB>-3P<SUB>1/2</SUB>). Levels 3P<SUB>3/2</SUB> and 5S<SUB>1/2</SUB> were connected by pumping field. Experimental data of two-photon absorption strength vs detuning from middle level (TADM) shows that the two-photon absorption was reduced by 60% at line center in the presence of resonant pumping field. In rubidium vapor, two-photon absorption of 5S<SUB>1/2</SUB>(Fequals3)-5P<SUB>3/2</SUB>-8S<SUB>1/2</SUB>(Fequals3) was measured by detecting the fluorescence at 607 nm (8S<SUB>1/2</SUB>-5P<SUB>1/2</SUB>). Levels 5P<SUB>3/2</SUB> and 5D<SUB>5/2</SUB>(Fequals5) were connected by pumping field. The TADM profiles under different experimental condition indicate that the maximum reduction of two-photon absorption can be 80%. And the reduction effect reduced with lower strength, higher detuning frequency and wider line width of pumping field. At the same time, the position of minimum absorption depends on the detuning of pumping field. All the experimental profiles were fitted well with theoretical calculation results.
In this paper, we demonstrate a weak photon switch by Fano interference in a double quantum well structure. GaAs/AlGaAs and InGaAs/AlAs heterostructures are taken as switch media to show that the weak switch can work at different wavelength by choosing materials and structures. We also estimate the order of the switch power and show that this photon switch by Fano interference in coupled double quantum well structures is a weak optical switch that can be used to realize one optical beam control another beam.
An experimental study of electromagnetically induced two- photon transparency (EITT) in rubidium atomic vapor at room temperature is presented. A four level system is considered, involving the two-photon absorption process 5S<SUB>1/2</SUB> to 8S<SUB>1/2</SUB> via an intermediate state 5P<SUB>3/2</SUB>, and the single- photon control process 5P<SUB>3/2</SUB> to 5D<SUB>5/2</SUB>. A controlling pump laser beam is employed to coherently couple the 5P<SUB>3/2</SUB> and 5D<SUB>5/2</SUB> states, thus producing two dressed intermediate states, which give rise to destructive interference in the two-photon transition. Fluorescence from 8S<SUB>1/2</SUB> to 5P<SUB>1/2</SUB> is used to monitor the 5S<SUB>1/2</SUB>(Fequals3) to 8S<SUB>1/2</SUB>(Fequals3) two-photon absorption. An induced two-photon transparency of about 80% has been obtained at resonance; the experimental results are in good agreement with the general theory of Agarwal, when the appropriate spectroscopic parameters are employed.
We report the dynamic memory function of a hybrid bistable system with long-delayed feedback. Up to 51-bit binary data written to and read from an electro-optical bistable system pumped by a He-Ne laser have been demonstrated.