Observation of forbidden exciton transitions mediated by Coulomb interactions in photoexcited semiconductor quantum wells.

We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.

Slow light based on stimulated Raman scattering in an integrated liquid-core optical fiber filled with CS2.

We demonstrate a fiber-based slow light system using a carbon disulfide (CS2)) filled integrated liquid-core optical fiber (i-LCOF). Using 1 meter of i-LCOF we were able to delay 18ps pulses up to 34ps; a delay of 188% of the pulse width. This experimental setup serves as a foundation for slow-light experiments in other nonlinear liquids. Numerical simulations of pulse-propagation equations confirmed the observed delay and a simplified method is presented that can be applied to calculate induced delay for non-cw Stokes pulses. The system is all-fiber and compact with delays greater than a pulse width, indicating potential application as an ultrafast controllable delay line for time division multiplexing in multiGb/s telecommunication systems.

Brillouin lasing in integrated liquid-core optical fibers.

We report Brillouin lasing in an integrated liquid-core optical fiber filled with neat CS2. This is the first observation of Brillouin lasing in an optical fiber filled with a liquid, to the best of our knowledge. The linewidth of the single frequency liquid-based Brillouin laser was estimated to be <1 kHz by beating two similar but independent lasers against one another.

All-optical switching based on inverse Raman scattering in liquid-core optical fibers.

We report on a new platform for all-optical switching based on inverse Raman scattering in liquids. Narrowband switching, which could be suitable for wavelength-division-multiplexed applications, is demonstrated using integrated liquid-core optical fiber infiltrated with both neat liquids (CCl(4) and CS(2)) as well as an organic chromophore (ß-carotene) dissolved in CCl(4). Compared to standard glass optical fibers, these liquids have much larger Raman loss coefficients, which help reduce the pump power by at least an order of magnitude. Further improvements can be expected with the development of highly soluble organic compounds possessing large Raman cross sections.

Integrated liquid-core optical fibers for ultra-efficient nonlinear liquid photonics.

We have developed a novel integrated platform for liquid photonics based on liquid core optical fiber (LCOF). The platform is created by fusion splicing liquid core optical fiber to standard single-mode optical fiber making it fully integrated and practical - a major challenge that has greatly hindered progress in liquid-photonic applications. As an example, we report here the realization of ultralow threshold Raman generation using an integrated CS2 filled LCOF pumped with sub-nanosecond pulses at 532 nm and 1064 nm. The measured energy threshold for the Stokes generation is 1nJ, about three orders of magnitude lower than previously reported values in the literature for hydrogen gas, a popular Raman medium. The integrated LCOF platform opens up new possibilities for ultralow power nonlinear optics such as efficient white light generation for displays, mid-IR generation, slow light generation, parametric amplification, all-optical switching and wavelength conversion using liquids that have orders of magnitude larger optical nonlinearities compared with silica glass.

Demonstration of Zeno switching through inverse Raman scattering in an optical fiber.

We report the observation of Zeno switching through an inverse Raman scattering (IRS) process in an optical fiber. In IRS, light at the anti-Stokes frequency is strongly attenuated in the presence of a pump field, allowing it to be used for all-optical switching and modulation. Our observed level of induced absorption via IRS in the optical fiber is > 20 dB in a time scale of less than 5 ps. The full Raman response spectrum was extracted experimentally and excellent agreement was found between the experimental data and theoretical modeling of IRS.

Characterization of strong light-matter coupling in semiconductor quantum-dot microcavities via photon-statistics spectroscopy.

It is shown that spectrally resolved photon-statistics measurements of the resonance fluorescence from realistic semiconductor quantum-dot systems allow for high contrast identification of the two-photon strong-coupling states. Using a microscopic theory, the second-rung resonance of Jaynes-Cummings ladder is analyzed and optimum excitation conditions are determined. The computed photon-statistics spectrum displays gigantic, experimentally robust resonances at the energetic positions of the second-rung emission.