We demonstrate three microfluidic chip based microfiber/nanofiber sensors for ultra-sensitive absorption, fluorescence, and femtoliter-scale sensing, respectively. The sensors shown here may open up new opportunities for ultra-sensitive biosensing and single molecule analysis.
We reported a simple, robust, and highly sensitive temperature sensor using intrinsic Mach-Zehnder interferometer formed by means of bending a tapered microfiber, embedded in polydimethylsiloxane. The outer temperature perturbations modulate the refractive index of the polymer through thermo-optic and thermal expansion effects of the polymer. This leads to a phase difference between interfering guided modes through the bent-microfiber, which ultimately results prominent wavelength shift in the transmission spectrum. The sensor exhibits a linear temperature response with a sensitivity as high as -6.25nm/°C over the temperature range from 24° to 40 °C. The sensitivity of the sensor increases as wavelength increases.
We demonstrate surface plasmon (SP) excitation in Ag nanowires directly coupled with a microfiber in the presence of a
MgF<sub>2</sub> substrate. With scanning near-field optical microscopy, evident light output from the Ag nanowire and the
evanescent field of the coupling structure are observed in the near-field optical image. The tip enhancement of a Ag
nanowire is also analyzed from the optical intensity graph. Results presented in this work suggest a simple SP excitation
approach for plasmonic and photonic circuits with high compactness.
We experimentally demonstrate silver nanowire based plasmonic devices at optical communication wavelength 1.55 μm.
The plasmon propagation loss in a 300 nm diameter silver nanowire is measured to be 0.3 dB/μm. Two types of
plasmonic functional devices based on the coupling between two silver nanowires, nano-couplers and nano-splitters, are
Optical silica nanowires fabricated using a taper-drawing approach exhibit extraordinary uniformity, making them suitable for low-loss optical wave guiding. Air-clad optical nanowires can be used as subwavelength-diameter single-mode waveguides from the ultraviolet to the near-infrared spectral range. Using these nanowires as building blocks we assembled photonic devices that are much smaller than comparable existing devices, indicating the great potential for developing micro- and nanoscale photonic devices for future applications in a variety of fields such as optical communication, optical sensing and high-density optical integration.
Subwavelength-diameter silica wires fabricated using a taper-drawing approach exhibit excellent diameter uniformity and atomic-level smoothness, making them suitable for low-loss optical wave guiding from the UV to the near-infrared. Such air-clad silica wires can be used as single-mode waveguides; depending on wavelength and wire diameter, they either tightly confine the optical fields or leave a certain amount of guided energy outside the wire in the form of evanescent waves. Using these wire waveguides as building blocks we assembled microscale optical components such as linear waveguides, waveguide bends and branch couplers on a low-index, non-dissipative silica aerogel substrate. These components are much smaller than comparable existing devices and have low optical loss, indicating that the wire-assembly technique presented here has great potential for developing microphotonics devices for future applications in a variety of fields such as optical communication, optical sensing and high-density optical integration.
Based on the exact solution of Maxwell’s equations and numerical calculations, we have investigated the basic theoretical properties of metal-coated silica nanowires. Modal profile, field and power distributions, and conditions for surface plasmon excitation are studied. It shows that a thin layer of metal coat can influence the distribution of the electromagnetic field and enhance confinement ability of light power inside silica core due to its negative dielectric function, which may be favorable for reducing the size of wire waveguide for microphotonic applications.
We propose to use bent silica wires with nanometric diameters to guide light as optical waveguide bend. We bend silica wires with scanning tunneling microscope probes under an optical microscope, and wire bends with bending radius smaller than 5 μm are obtained. Light from a He-Ne laser is launched into and guided through the wire bends, measured bending loss of a single bend is on the order of 1 dB. Brief introductions to the optical wave guiding and elastic bending properties of silica wires are also provided. Comparing with waveguide bends based on photonic bandgap structures, the waveguide bends from silica nanometric wires show advantages of simple structure, small overall size, easy fabrication and wide useful spectral range, which make them potentially useful in the miniaturization of photonic devices.