Huang Yidong

Crystal-field analysis of the energy levels and spectroscopic characteristics of Nd3+ in YVO4

Based on the method previously proposed by the authors, the crystal-field analysis and investigation of the polarization and relative intensities of transitions between the sublevels 4F3/2 to 4I13/2, 4I11/2 and 4I9/2 in Nd3+:YVO4 crystals have been performed, in which the Nd3+ ions occupy positions with point symmetry D2d. The predicted polarization characteristics of all the emission lines under discussion are in complete agreement with those observed in experiments by other authors, and the emission lines with highest or comparatively high calculated intensities correspond to the laser emission lines that have been realized. In these calculations, the effect of seventh-order odd crystal field on the emission intensities was first omitted and then estimated by the method suggested by Judd in 1962. It turned out that this effect should be taken into account explicitly and cannot be completely made up only by multiplying a factor suggested by Judd. However, the simple method introduced can be seen as useful in the study of new laser crystals.

Slow Light by Two-Dimensional Photonic Crystal Waveguides

A simple and effective way to measure the group velocity of photonic crystal waveguides (PCWGs) is developed by using a fiber Mach–Zehnder interferometer. A PCWG with perfect air-bridge structure is fabricated and slow light with group velocity slower than c/80 is demonstrated.

Modelling of the Self Sum-Frequency-Mixing Laser

A theoretical model of the self sum-frequency-mixing (SFM) laser generated by a single crystal is proposed, in which spatial distribution of the pump and circulating fundamental lasers with arbitrary beam waists are taken into account. The model is then applied to two kinds of crystals of current interest, Nd:YAl3(BO3)4 and Nd:Ca4GdO(BO3)3. Numerical analyses of the self-SFM laser properties predict and confirm some experimental results. The model proposed is not limited to self-SFM lasers and may be applied to general analyses of the fundamental or nonlinear laser generation with Gaussian beams.

Group chain scheme analysis of the energy levels in laser crystals

A method for crystal-field energy level analysis was proposed which used the group chain scheme introduced by Butler. The ratios of crystal-field parameter calculated by a simple point charge model was used as a constraint condition, which turned out to be the same or essentially the same as those obtained by a superposition model or other models and the absolute values of these ratios can be seen as a measure of the degree of symmetry distortion of the system. As an example, the situation of D3 symmetry was studied. By using this fitting technique to obtain values for the parameters, only one minimum was found for each of the cases studied. The eigenfunctions obtained have obvious symmetry properties and the low-symmetry distortion of the system can easily be seen from the ratios Cmu k/C0k. Therefore, the crystal-field analysis is not only a formalism but also a real physical insight. The crystal field for Nd3+:YAl3(BO3)4 and NdAl3(BO3)4 crystals was analysed in detail.

Horizontally slotted photonic crystal nanobeam cavity with embedded active nanopillars for ultrafast direct modulation

A horizontally slotted photonic crystal nanobeam cavity with an embedded active nanopillar structure is proposed for ultrafast direct modulation. By designing the thicknesses of both the nanobeam and the horizontal slot layer, the quality factor (Q factor) and the mode volume (Vn) of the proposed cavity can be engineered independently. As a result, the spontaneous emission (SpE) rate is enhanced with a small Vn of 2.4 while the SpE rate and the cavity photon lifetime have an optimal Q factor of ~ 1000. In our simulation, the modulation bandwidth could be enhanced up to 170 GHz with different emission linewidths of the active nanopillar.

Discrete Frequency Entangled Photon Pair Generation Based on Silicon Micro-ring Cavities

In this paper, we propose and demonstrate a scheme to generate discrete frequency entangled photon pairs based on a silicon micro-ring resonator. The resonator is placed in a Sagnac fiber loop. Stimulated by two pump lights at two different resonance wavelengths of the resonator, photon pairs at another two resonance wavelengths are generated along two opposite directions in the fiber loop, by the nondegenerate spontaneous four wave mixing in the resonator. Their states are superposed and interfered at the output ports of the fiber loop to generate frequency entangled photon pairs. On the other hand, since the pump lights come from two continuous wave lasers, energy-time entanglement is an intrinsic property of the generated photon pairs. The entanglements on frequency and energy-time are demonstrated experimentally by the experiments of spatial quantum beating and Franson-type interference, respectively, showing that the silicon micro-ring resonators are ideal candidates to realize complex photonic quant...

The effect of mass difference between host ions on the thermal shift and broadening of the spectral lines of the active ions in crystals

It is shown in this letter that the mass difference between ions of the host crystals has an effect on the thermal broadening and shift of the spectral lines of active ions in the crystals. The effect is expressed as a multiplication factor D2 for the thermal broadening and shift caused by the one-phonon absorption and emission mechanism, and a multiplication factor D4 for the thermal broadening caused by the Raman scattering process. The expressions for the D-factor are given for crystals constituted of two and three kinds of ion respectively.

A study of the relative emission intensity and polarization for Nd3+ ions in an NdAl3(BO3)4 crystal

On the basis of both the crystal-field theory and the Judd-Ofelt method, the relative intensities and polarization characteristics of the individual transitions between the manifolds 4F3/2 to 4I11/2 and 4F3/2 to 4I9/2 for Nd3+ ions in an NdAl3(BO3)4 crystal were studied by experimental fluorescence spectroscopy and branching ratios. The theoretical results are in agreement with those of laser and fluorescence experiments. In this study, the crystal-field wavefunctions were obtained by fitting the Stark energy sublevels with a constraint condition imposed on the electrostatic ratios of the crystal-field parameter belonging to the same order of k, in a similar manner to that proposed by the present authors previously and referred to as the quasi-three-parameter method. It was shown that the minimum obtained in this way was the only solution corresponding to physical reality.

Theoretical analysis of the coupling between 4T2 and 2E states of the Cr3+ ion in tunable laser material

The effective matrix element of the spin-orbit coupling between the 2E and 4T2 states of the Cr3+ ion was calculated according to the C3i point symmetry that the Cr3+ ion occupies in garnets and the Huang-Rhys S factor and phonon energy h(cross) omega , which were estimated using the room-temperature absorption and emission spectra by means of a special multi-mode model. Based on the parameters obtained, the ratios of lifetimes tau (2E)/ tau (4T2) for Cr3+ in crystals of the garnets GSGG. YSGG, GGG and YGG were calculated by the models proposed by Donnelly et al. (1988) and Wojtowicz et al. (1991). The results turned out to be satisfactory. All the theoretical models describing the coupling of 2E and 4T2 states were compared and evaluated.

End-Output Coupling Efficiency Measurement of Silicon Wire Waveguides Based on Correlated Photon Pair Generation

A method to measure the end-output coupling efficiencies between silicon wire waveguides (SWWs) and optical fibers is proposed and demonstrated. The end-output coupling efficiency is calculated through four measured counting rates based on the correlated photon pair generation in the SWW. It provides a way to investigate and optimize the coupling processes at the input and output end of the optical waveguides separately.