A nanonewton force sensor using a U-shape tapered microfiber interferometer.

Nanomechanical measurements, especially the detection of weak contact forces, play a vital role in many fields, such as material science, micromanipulation, and mechanobiology. However, it remains a challenging task to realize the measurement of ultraweak force levels as low as nanonewtons with a simple sensing configuration. In this work, an ultrasensitive all-fiber nanonewton force sensor structure based on a single-mode-tapered U-shape multimode-single-mode fiber probe is proposed and experimentally demonstrated with a limit of detection of ~5.4 nanonewtons. The use of the sensor is demonstrated by force measurement on a human hair sample to determine the spring constant of the hair. The results agree well with measurements using an atomic force microscope for the spring constant of the hair. Compared with other force sensors based on optical fiber in the literature, the proposed all-fiber force sensor provides a substantial advancement in the minimum detectable force possible, with the advantages of a simple configuration, ease of fabrication, and low cost.

Two-dimensional displacement estimation of one-dimensional laser speckle images for detection of acoustic vibration.

Detection and recovery of audio signals using optical methods is an appealing topic. Observing the movement of secondary speckle patterns is a convenient method for such a purpose. In order to have less computational cost and faster processing, one-dimensional laser speckle images are captured by an imaging device, while it sacrifices the ability to detect speckle movement along one axis. This paper proposes a laser microphone system to estimate the two-dimensional displacement from one-dimensional laser speckle images. Hence, we can regenerate audio signals in real time even as the sound source is rotating. Experimental results show that our system is capable of reconstructing audio signals under complex conditions.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus.

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 105, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 105 CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

[Detection of Atmospheric HONO and NO2 by Incoherent Broadband Cavity Enhanced Spectroscopy].

We report on the development of an optical instrument based on LED-IBBCEAS for simultaneous measurements of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air. The light emitting from the LED centered at 365 nm was directly focused into the cavity formed with two high reflectivity mirrors, separated by a distance of 1. 76 m. The light output of the cavity was received with a portable spectrometer. The mirror reflectivity was calibrated by absorption spectra of NO2 and O2-O2. In the spectral range of 353-376 nn, the maximum mirror reflectivity was found to be 0.999 17. Detection limits (1σ) of 0.6 ppbv for HONO and 1.8 ppbv for NO2 were achieved with an acquisition time of 120 s. In order to test the accuracy of measured results by present setup, concentrations of NO2 were recorded during continuous 56 hours and compared with data from a NOX analyzer equipped with a blue light converter. The least-square fit lines give gradients of 1. 09 and respective intercepts of 3.45, with a linear correction factor of 0.89. The concentrations of HONO and NO2 in indoor air were monitored, the concentrations of HONO varied from near 0 to 5.3 ppbv in 24 hours, the averaged concentration was 1. 8 ppbv, and the concentrations of NO2 varied from 5 to 51 ppbv at the same time, the averaged concentration was 21.9 ppbv.

Impact of phase on collision between vortex solitons in three-dimensional cubic-quintic complex Ginzburg-Landau equation.

We present a systematic analysis for three generic collisional outcomes between stable dissipative vortices with intrinsic vorticity S = 0, 1, or 2 upon variation of relative phase in the three-dimensional (3D) cubic-quintic complex Ginzburg-Landau equation. The first type outcome is merger of the vortices into a single one, of which velocity can be effectively controlled by relative phase. With the increase of the collision momentum, the following is creation of an extra vortex, and its velocity also increases with growth of relative phase. However, at largest collision momentum, the variety of relative phase cannot change the third type collisional outcomes, quasielastic interaction. In addition, the dynamic range of the outcome of creating an extra vortex decreases with the reduction of cubic-gain. The above features have potential applications in optical switching and logic gates based on interaction of optical solitons.

Continuous emission of fundamental solitons from vortices in dissipative media by a radial-azimuthal potential.

We report novel dynamical regimes of dissipative vortices supported by a radial-azimuthal potential (RAP) in the 2D complex Ginzburg-Landau (CGL) equation with the cubic-quintic nonlinearity. First, the stable solutions of vortices with intrinsic vorticity S = 1 and 2 are obtained in the CGL equation without potential. The RAP is a model of an active optical medium with respective expanding anti-waveguiding structures with m (integer) annularly periodic modulation. If the potential is strong enough, m jets fundamental of solitons are continuously emitted from the vortices. The influence of m, diffusivity term (viscosity) ß, and cubic-gain coefficient ε on the dynamic region is studied. For a weak potential, the shape of vortices are stretched into the polygon, such as square for m = 4. But for a stronger potential, the vortices will be broke into m fundamental solitons.

Phase controlling of collisions between solitons in the two-dimensional complex Ginzburg-Landau equation without viscosity.

We present a systematic analysis of the outcome of soliton collisions upon variation of the relative phase φ of the solitons, in the two-dimensional cubic-quintic complex Ginzburg-Landau equation in the absence of viscosity. Three generic outcomes are identified: merger of the solitons into a single one, creation of an extra soliton, and quasielastic interaction. The velocities of the merger soliton and the extra soliton can be effectively controlled by φ. In addition, the range of the outcome of creating an extra soliton decreases to zero with the reduction of gain or the increasing of loss. The above features have potential applications in optical switching and logic gates based on interaction of optical solitons.

Continuous generation of "light bullets" in dissipative media by an annularly periodic potential.

We report novel dynamical regimes of "light bullets" supported by an annularly periodic potential in the three-dimensional (3D) complex Ginzburg-Landau equation with the cubic-quintic nonlinearity. This is a model of an active optical medium with respective expanding anti-waveguiding structures with m≥2 (integer) annularly periodic modulation. If the potentials are strong enough, they give rise to continuous generation of m jets light bullet by an initial light bullet initially placed at the center. The influence of m and diffusivity term (viscosity) ß on the corresponding strength of potential is studied. In the case of m = 0 (conical geometry), these are concentric waves expanding in the radial direction.