Although optical fiber is efficient for transmitting light, its functionality is limited by the dielectric material of the core and nonlinear-optical responses and has a dielectric diffraction limit. Therefore, the optical properties of the optical fiber cannot be altered after the fiber drawing fabrication, thus limiting the development of novel in-fiber devices. In this talk, I will present our recent development of “Meta”-optical fiber, an advanced optical fiber integrated with emerging nanophotonic concepts such as optical metasurfaces, plasmonic nanowires, and zero-index photonics. I will present the development of ultrathin optical metalens which is cascaded on the facet of a photonic crystal fiber that enables light focusing. I will also discuss the first experimental demonstration of zero-index resonance excitation in an optical fiber coated with AZO nanolayer and the excitation of plasmonic resonances on holey optical fiber for advanced optical sensing and tip-enhanced Raman spectroscopy. These advanced “meta”-optical fibers open a pathway to revolutionary in-fiber lasers/spectroscopies, optical imaging/sensing, and optical communication devices.
Discovery of novel active materials is fundamental for photonic applications. The epsilon-near-zero (ENZ) materials have been shown to be as one of the most promising optical materials in the recent years as the electromagnetic field inside media with near-zero permittivity has been shown to exhibit unique optical properties, including strong electromagnetic wave confinement, enhanced quantum emission near ENZ media, non-reciprocal magneto-optical effects, unique topological properties, and abnormally large optical nonlinearity. While ENZ optics have been investigated extensively in the last few years, the current commonly used ENZ materials suffer from limited optical enhancement because of the lack of precise control of ENZ frequency, loss, and thickness for efficient ENZ mode excitation. In addition, the active tunability and enhanced nonlinearity and emission properties in ENZ materials have yet been fully experimentally explored. This talk will review our recent studies on the active linear, nonlinear, and emission properties of conducting oxide and metallic nitride epsilon-near-zero materials in planar and optical fiber platforms [1-7]. I will present a method to engineer the field intensity enhancement of the Al-doped zinc oxide (AZO) ENZ thin films synthesized by atomic layer deposition (ALD) technique. I will then discuss the observation of abnormal nonlinear temporal dynamic of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using a degenerate pump-probe spectroscopy technique. I will present the first comprehensive study of photoluminescence from a 2D material placed near ENZ films and its dependence on the losses of materials, as well as the spectral response of such emitters with excitation wavelengths across the ENZ regime. Finally, I will also discuss the first experimental demonstration of optically confined ENZ resonance excitation in an optical fiber waveguide uniformly coated with AZO nanolayer. These studies enrich the fundamental understanding of emission and nonlinear properties on ENZ thin films and the integration of ENZ materials and optical fiber will open the path to revolutionary ultracompact in-fiber optical devices for optical communication, imaging, sensing/laser applications.
We report on our efforts to develop a whispering gallery mode resonator etalon as a tool for precision radial velocity observations to detect exoplanets. The crystalline MgF2 etalon will be referenced to a compact fiber laser frequency comb, and will serve as the wavelength calibration source for a stabilized, high resolution, visible band spectrograph. The extreme stability required for the detection and characterization of exo-Earths orbiting solar-type stars will be achieved by employing a composite resonator structure with a compensating material to balance the resonator’s coefficients of thermal expansion and thermal refractivity. Progress in modeling the etalon to achieve single mode-like performance, and experiments to demonstrate broad-band (octave-spanning) ling to a white light source, are described.
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