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  1. In recent years, organic dye molecules as photosensitizers have played a significant role in the field of dye-sensitized solar cells. In this context, two primary dihydroindolocarbazole-based organic dyes (sk201 and sk202), which were synthesized recently by Song et al., and three further designed dyes (DMZ1-3) were theoretically investigated based on density functional theory and time-dependent density functional theory. Molecular geometries, absorption spectra, charge transfer, molecular electrostatic potential and nonlinear optical properties were quantificationally studied and visually presented to reveal the relationships between the molecular structures and performances of dyes. The effects of joining the isolated dyes and TiO2 on themore »molecular absorption spectra and energy levels were analyzed. Moreover, several parameters, such as efficiency of light-harvesting, driving forces of electron regeneration and injection, excited-state lifetime and vertical dipole moment, were calculated to give the multi-angle demonstrations of the photovoltaic performances for these dyes.« less
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  3. Parity-time (PT) symmetry in non-Hermitian optical systems promises distinct optical effects and applications not found in conservative optics. Its counterpart, anti-PT symmetry, subscribes another class of intriguing optical phenomena and implies complementary techniques for exotic light manipulation. Despite exciting progress, so far, anti-PT symmetry has only been realized in bulky systems or with optical gain. Here, we report an on-chip realization of non-Hermitian optics with anti-PT symmetry by using a fully passive, nanophotonic platform consisting of three evanescently coupled waveguides. By depositing a metal film on the center waveguide to introduce strong loss, an anti-PT system is realized. Using microheatersmore »to tune the waveguides’ refractive indices, striking behaviors are observed such as equal power splitting, synchronized amplitude modulation, phase-controlled dissipation, and transition from anti-PT symmetry to its broken phase. Our results highlight exotic anti-Hermitian nanophotonics to be consolidated with conventional circuits on the same chip, whereby valuable chip devices can be created for quantum optics studies and scalable information processing.« less
  4. Weak measurement (WM) with state pre- and post-selection can amplify otherwise undetectable small signals and thus has potential in precision measurement applications. Although frequency measurements offer the hitherto highest precision due to the stable narrow atomic transitions, it remains a long-standing interest to develop new schemes to further escalate their performance. Here, we demonstrate a WM-enhanced correlation spectroscopy technique capable of narrowing the resonance linewidth down to 0.1 Hz in a room-temperature atomic vapour cell. The potential of this technique for precision measurement is demonstrated through weak magnetic-field sensing. By judiciously pre- and post-selecting frequency-modulated input and output optical states inmore »a nearly orthogonal manner, a sensitivity of 7 fT Hz^(−1/2) at a low frequency near DC is achieved using only one laser beam with 15 µW of power. Additionally, our results extend the WM framework to a non-Hermitian Hamiltonian and shed new light on metrology and bio-magnetic field sensing.« less
  5. Realization of chip‐scale nonreciprocal optics such as isolators and circulators is highly demanding for all‐optical signal routing and protection with standard photonics foundry process. Owing to the significant challenge for incorporating magneto‐optical materials on chip, the exploration of magnetic‐free alternatives has become exceedingly imperative in integrated photonics. Here, a chip‐based, tunable all‐optical isolator at the telecommunication band is demonstrated, which is based upon bulk stimulated Brillouin scattering (SBS) in a high‐Q silica microtoroid resonator. This device exhibits remarkable characteristics over most state‐of‐the‐art implements, including high isolation ratio, no insertion loss, and large working power range. Thanks to the guided acousticmore »wave and accompanying momentum‐conservation condition, bulk SBS also assist in realizing the nonreciprocal parity‐time symmetry in two directly coupled microresonators. The breach of time‐reversal symmetry further makes the design a versatile arena for developing many formidable ultra‐compact devices such as unidirectional single‐mode Brillouin lasers and supersensitive photonic sensors.« less
  6. Whispering-gallery-mode optical microresonators have found impactful applications in various areas due to their remarkable properties such as ultra-high quality factor (Q-factor), small mode volume, and strong evanescent field. Among these applications, controllable tuning of the optical Q-factor is vital for on-chip optical modulation and various opto-electronic devices. Here, we report an experimental demonstration with a hybrid structure formed by an ultra-high-Q microtoroid cavity and a graphene monolayer. Thanks to the strong interaction of the evanescent wave with the graphene, the structure allows the Q-factor to be controllably varied in the range of 3.9 × 105 ∼ 6.2 × 107 bymore »engineering optical absorption via changing the gap distance in between. At the same time, a resonant wavelength shift of 32 pm was also observed. Besides, the scheme enables us to approach the critical coupling with a coupling depth of 99.6%. As potential applications in integrated opto-electronic devices, we further use the system to realize a tunable optical filter with tunable bandwidth from 116.5 MHz to 2.2 GHz as well as an optical switch with a maximal extinction ratio of 31 dB and response time of 21 ms.« less