Results 1 - 7 of 7
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[en] We investigated a multi-layer structure for a broadband coherent perfect absorber (CPA). The transfer matrix method (TMM) is useful for analyzing the optical properties of structures and optimizing multi-layer structures. The broadband CPA strongly depends on the phase of the light traveling in one direction and the light reflected within the structure. The TMM simulation shows that the absorption bandwidth is increased by 95% in a multi-layer CPA compared to that in a single-layer CPA.
[en] We have observed a quench of lasing at an exceptional point in an electronic circuit system by applying an asymmetric gain in coupled oscillators. Because of the analogy between an oscillation in a laser and an oscillation in an operational amplifier, the oscillation stops when the system hits an exceptional point. This phenomenon is also theoretically investigated.
[en] We report room temperature lasing in ZnO inverse opal photonic crystals in the near-ultraviolet (UV) frequency range. We observe random lasing due to disorder in the structures when the photonic pseudogaps are located away from the ZnO gain spectrum. Tuning the first ΓL-pseudogap to the gain peak leads to a five-fold reduction in lasing threshold and a frequency shift of the lasing modes due to the enhanced confinement of light
[en] We conduct a numerical study on the giant optical resonances near the split photonic band edges of two-dimensional square lattices. Their quality factors are 1 order of magnitude higher than those near the regular band edges. Such enhancement results from the efficient interference of multiple Bloch waves, which minimizes light leakage from the periodic pattern of finite size. The variation of the quality factor with the pattern size is nonmonotonic for the split band edge resonance, leading to an optimal size for the maximal quality factor.
[en] We systematically studied the lasing characteristics in photonic polycrystalline and amorphous structures. 2D arrays of air holes were fabricated in a GaAs membrane. InAs quantum dots embedded in the membrane provide gain for lasing under optical pumping. The lasing modes are spatially localized, and blue shift as the structural order becomes short ranged. Our three-dimensional numerical simulations reveal that the out-of-plane leakage of the lasing mode dominates over the in-plane leakage. The lasing modes in a photonic polycrystalline move away from the center frequency of the photonic band gap to reduce the out-of-plane leakage. In a photonic amorphous structure, the short-range order improves optical confinement and enhances the quality factor of resonances. Understanding the behavior of photonic polycrystalline laser and amorphous laser opens the possibility of controlling lasing characteristic by varying the degree of structural order.
[en] We study numerically the density of optical states (DOS) in two-dimensional photonic structures with short-range positional order and observe a transition from polycrystalline to amorphous photonic systems. In polycrystals, photonic band gaps (PBGs) are formed within individual domains, which leads to a depletion of the DOS similar to that in periodic structures. In amorphous photonic media, the domain sizes are too small to form PBGs, thus the depletion of the DOS is weakened significantly. The critical domain size that separates the polycrystalline and amorphous regimes is determined by the attenuation length of Bragg scattering, which depends not only on the degree of positional order but also the refractive-index contrast of the photonic material. Even with relatively low-refractive-index contrast, we find that modest short-range positional order in photonic structures enhances light confinement via collective scattering and interference.
[en] We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PASs) with short-range order. From calculations of the density of optical states (DOS) for PASs with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PASs, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PASs without long-range order.