Liquid droplets suspended by the tip of a thin wire, glass capillary, or needle form high-Q optical resonators, thanks to surface tension. Under gravity equilibrium conditions, maximum drop diameter is approximately 1.5 mm for paraffin oil (volume ∼ 0.5 μL) using, instance, silica fiber with 250 μm thickness. Whispering gallery modes are excited free-space near-infrared laser that frequency locked cavity resonance. The droplet serves as miniature laboratory sensing chemical species and...

This paper reports proof-of-principle of an optical fiber Bragg grating (FBG) operating as electric field sensor. The system is based on a semiconductor diode laser, emitting around 1577.5 nm that interrogates the sensor its maximum reflectivity point. application strong causes small variation path length waveguide due to electrostriction and thus perturbs peak wavelength. Calibration dynamic range tests are performed using parallel-plate capacitor create variable (1–100 kV/cm). A great...

An optical frequency synthesizer (OFS), based on difference- generation (DFG), is demonstrated at 3 µm. By mixing a near-infrared (IR) OFS and tunable continuous-wave (CW) laser in periodically poled lithium-niobate (PPLN) crystal, new comb created from 2.9 to 3.5 µm (in 180 nm wide spans) with 100 MHz mode spacing. phase-locking, the pump near-IR OFS, mid-IR directly linked Cs primary standard via global positioning system (GPS) time receiver. Then, compactness of our fibre-based set-up...

We report the theoretical description and experimental demonstration of an optical resonator formed by inserting a Fiber Bragg Grating (FBG) in closed fiber loop.The spectral characteristics such strongly depend on reflectivity FBG.In wavelength region where FBG R is negligible, system behaves like conventional ring resonator.On other hand, when not vanishing, split-mode structure can be observed, associated to degeneracy removal two counterpropagating resonant modes.The magnitude mode...

We propose a robust and reliable method of active mode locking mid-infrared quantum cascade lasers develop its theoretical description. Its key element is the use an external ring cavity, which circumvents fundamental issues undermining stability in lasers. show that can give rise to generation picosecond pulses phase-locked frequency combs containing thousands cavity modes.

A 3-microm continuous-wave difference-frequency source is directly referenced to a mid-infrared optical frequency comb synthesizer by measuring their beat-note signal fast HgCdTe detector. Absolute metrology of molecular vibration spectra demonstrated locking the coherent radiation nearest tooth and tuning mode spacing across Doppler-broadened absorption profile CH(4) ro-vibrational transition.

Abstract Liquid droplet whispering-gallery-mode microresonators open a new research frontier for sensing, optomechanics and photonic devices. At visible wavelengths, where most liquids are transparent, major contribution to optical quality factor is expected theoretically from thermal surface distortions capillary waves. Here, we investigate experimentally these predictions using transient cavity ring-down spectroscopy. With our scheme, the out-coupling intrinsic loss measured independently...

Liquid droplets are ubiquitous in nature wherein surface tension shapes them into perfect spheres with atomic-scale smooth surfaces. Here, we use stable that cohost equatorial acoustical and optical resonances phase matched to enable the exchange of energy momentum between sound light. Relying on free-space laser excitation multiple whispering-gallery modes, harness a triple-resonant forward Brillouin scattering stimulate optomechanical waves. Nonlinear amplification droplet vibrations 60-70...

We report on a method for surface plasmon resonance (SPR) refractive index sensing based direct time-domain measurements. An optical resonator is built around an SPR sensor, and its photon lifetime measured as function of loss induced by variations. The does not rely any spectroscopic analysis or intensity measurement. Time-domain measurements are practically immune to light fluctuations thus lead high resolution. A proof concept experiment carried out in which sensor response liquid samples...

In this paper we theoretically investigate a ring resonant cavity obtained by closing on itself π-shifted fiber Bragg grating, to be used for refractive index sensing applications. Differently from conventional the spectral structure of is characterized an asymmetric splitting doublet composed right side resonance having Fano profile and left symmetric Lorentzian profile. The shows narrower sharper peak than all other kinds achievable with both resonators gratings. A reduction linewidth...

In this paper, we report on theoretical investigation of split mode resonant sensors based fiber Bragg grating (FBG) ring resonators and π-shifted (π-FBG) resonators. By using a resonator (π-FBGRR) instead conventional (FBGRR), the symmetric antisymmetric resonance branches (i.e., eigen-modes perturbed system) show peculiar very important features that can be exploited to improve performance optic spectroscopic sensors. particular, π-FBGRR branch taylored have maximum splitting sensitivity...

We demonstrate a strain sensor with very high sensitivity in the static and low frequency regime based on fiber ring cavity that includes π phase-shifted Bragg grating. The grating acts as partial reflector couples two counter-propagating modes, generating splitting of resonant frequencies. presence sharp transition within grating's spectral transmittance makes this extremely sensitive to length, temperature, refractive index region where is written. variations caused by small mechanical...

The electric quadrupole fundamental (v=1←0) band of molecular deuterium around 3 μm is accessed by cavity ring-down spectroscopy using a difference-frequency-generation source linked to the Cs-clock primary standard via an optical frequency comb synthesizer. An absolute determination line position and strength reported for first two transitions (J=2←0 J=3←1) S branch. accuracy 6×10(-8) achieved line-center frequencies, which improves factor 20 previous experimental results [A. R. W. McKellar...

High-sensitivity spectroscopy of methane around 3 microm was carried out by means a 5.5-mW cw difference-frequency generator in conjunction with high finesse cavity off-axis alignment. By cavity-output integration minimum detectable absorption coefficient 5.7*10-9 cm-1Hz-1/2 achieved, which compares well results already reported the literature. Detection natural abundance also performed ambient air, for different values total pressure, allowing direct concentration measurements via...

An external ring-cavity quantum cascade laser (QCL) is demonstrated. Gain competition between the clockwise and anticlockwise modes results in a transition from bidirectional to directional emission as current increased. In regime, spatial hole burning (SHB) suppressed, spectrum evolves single longitudinal mode, contrast with multimode of comparable Fabry-Pérot QCL. The absence SHB long path-length cavity make this an excellent candidate for active mode-locking high-sensitivity spectroscopic...

In this Letter, we report the theoretical model and experimental evidence of a mode-splitting cloning effect due to resonant coupling between modes having different polarizations in weakly birefringent fiber Bragg grating (FBG) ring resonators. This modal depends on birefringence FBG reflectivity. ideal case absence birefringence, single split-mode structure can be observed resonator transmission spectrum degeneracy removal two counter-propagating modes. presence secondary split doublet...

A fiber Bragg grating (FBG)-coupled ring laser sensor is demonstrated. In the proposed configuration interrogating source, sensing head and readout instrument are integrated in a single fiber-optic device. An FBG inserted within bidirectional couples two counterpropagating modes of cavity, generating splitting resonant wavelengths proportional to reflectivity. When cavity gain brought beyond threshold, peaks split resonances simultaneously lase, leading beat note emission spectrum whose...

We present a simple and effective method for frequency locking laser source to free-space-coupled whispering-gallery-mode cavity. The scheme relies on the interference of spatial modes contained in light scattered by cavity, where low- high-order are simultaneously excited. A dispersion-shaped signal proportional imaginary component resonant optical field is simply generated filtering light. Locking diode equatorial liquid droplet resonator demonstrated using this scheme, its performance...