Showing papers by "Lan Yang published in 2009"

High- Q surface-plasmon-polariton whispering-gallery microcavity

Abstract: Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials (1). Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales (2-9). In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10, 11). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths (12-16). Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high-Q SPP whispering-gallery microcavity that is made by coating the surface of a high-Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 ± 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide (17, 18). This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.

Fabrication of high-Q polydimethylsiloxane optical microspheres for thermal sensing

Abstract: Polydimethylsiloxane (PDMS) optical microspheres are fabricated and whispering gallery modes with quality factors of 106 in the 1480 nm band are demonstrated. The dependence of the resonance shifts on the input power is investigated in both the transient (blueshift) and the steady-state (redshift) regimes. Moreover, we demonstrate that such high-Q PDMS optical resonators can be used as highly sensitive thermal sensors with temperature sensitivity of 0.245 nm/°C, which is one order of magnitude higher than conventional silica microsphere resonators. The estimated thermal resolution of the sensor is 2×10−4 °C.

Electromagnetically induced transparency-like effect in a single polydimethylsiloxane-coated silica microtoroid

Abstract: We study both experimentally and theoretically the coupling between a fiber taper and two whispering-gallery modes, which are simultaneously excited in a single pilydimethyl-siloxane-coated silica microtoroid system. The transmission spectrum of the fiber-coupled two-mode microresonator shows a sharp electromagnetically induced transparency-like window within the resonant absorption region. This line shape results from destructive interference between two optical pathways associated with two distinct coexisting modes in a single resonator. The sharp transparency peak has great potential applications in light modulation and highly sensitive biochemical sensors.

Oscillatory thermal dynamics in high-Q PDMS-coated silica toroidal microresonators

Abstract: We study the oscillatory thermal dynamics of a high-Q PDMS-coated silica microtoroid both experimentally and theoretically. We demonstrate that the competing thermo-optic effects in silica and PDMS lead to thermally-induced self-modulation in the transmission spectra. A dynamical model is built using thermal dynamics and coupled-mode theory to analyze the oscillation behaviors. Effects of input power, taper-cavity air gap and wavelength scanning speed on the oscillation behaviors are investigated with a detailed comparison between theory and experiments.

On-chip green silica upconversion microlaser

Abstract: We demonstrate an erbium-doped silica toroidal microcavity upconversion laser on a silicon chip lasing in the visible spectral range (510-580 nm). The microcavity is pumped at 1458 nm by a tapered optical fiber coupled to the cavity and the lasing threshold is 690 µW. Lasing is observed at room temperature despite the high nonradiative relaxation rates of Er in pure silica that usually precludes upconversion. lasing from higher excited states. This is attributed to the very high circulating pump power in the high-Q microcavity (Q > 10^7).

Low-threshold microlaser in a high-Q asymmetrical microcavity.

Abstract: We experimentally report an asymmetrical spherical microcavity with thermal-induced deformation, in which five-bounce whispering-gallery modes possess not only ultrahigh quality factors (Q) but also remarkably directional escape emission from the microsphere boundary. With efficient free-space excitation and collection, a low-threshold microlaser is demonstrated and exhibits a highly directional emission. Our measurement agrees well with the theoretical predictions by corrected Fresnel law.

Frequency noise of a microchip Raman laser

Abstract: We report measurement of the fundamental component of frequency noise in a micro-Raman laser fabricated on a silicon chip. A frequency noise spectral component that is equivalent to a Schawlow-Townes linewidth of 3-Hz is measured.

High-Q surface-plasmon whispering-gallery microcavity

Abstract: We demonstrate a high-Q surface-plasmon-polariton (SPP) whispering-gallery microcavity with SPP Q factors up to 1,376 ± 65 in the near infrared. The SPP eigenmodes are accessed evanescently using a tapered optical waveguide.

Single nanoparticle detection by mode splitting in ultra-high-Q microtoroid

Abstract: We experimentally demonstrate that a single nanoparticle can induce mode splitting of MHz in an ultra-high-Q microtoroid resonator, which can be used to extract information of the nanoparticle. Analytical model matches well with the experiments.

Compensation of thermal effect in high-Q toroidal microresonators by PDMS coating

Abstract: We theoretically and experimentally demonstrate that thermal effect in ultra-high-Q silica toroidal microresonators can be compensated by applying a layer of polydimethylsiloxane (PDMS). The observed Q factor is 1.5×106 for coating thickness of 0.52 µm.

Observation of EIT-like effect in a single high-Q microcavity

Abstract: We study the coupling between a fiber-taper and two whispering-gallery modes simultaneously excited in a single PDMS-coated silica microtoroid theoretically and experimentally. The transmission spectrum of the fiber coupled two-mode resonator shows a sharp electromagnetically-induced-transparency-like window.

Level Crossing in toroidal on-chip microcavities

Abstract: Level crossing between optical whispering-gallery modes is studied in toroidal microcavities We photograph azimuthal and radial envelope patterns of crossed optical modes We also investigate anti-crossing between modes and polarization evolution