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We demonstrate a 1km long optical fiber with continuous grating enhanced back scattering and attenuation close to standard single mode fiber. Scattering was observed to be more than 10dB above the Rayleigh back scattering of the optical fiber over a 10nm bandwidth between 1542 and 1552nm. The fiber attenuation was estimated to be 0.4dB/km. Our result was enabled through the fabrication of a standard...
Forward phase-matched Brillouin optomechanical resonance, excited by a tapered fiber, in a graphene inner-deposited whispering-gallery-mode microfluidic cavity, is demonstrated for the first time. The generated Brillouin optomechanical modes with Q factor ∼ 47000 show extremely high sensitivity (200kHz/ppm) for absolute gas detection based on frequency variation, achieving a detection limit down to...
We demonstrate a novel distributed fiber sensing technique with a record broadband sensitivity of 10nε/VHz at a sampling rate of 1MHz. A standing acoustic wave is generated by all-optical excitation of two simultaneously counter-propagating Brillouin dynamic gratings. A dual-tone readout probe pulse is used for the distributed measurement of strain-induced nonlinear phase-shifts of the acoustic wave...
We have demonstrated enhancement of measurement function in Brillouin Optical Correlation Domain Reflectometry (BOCDR) by totally combining, for the first time, four performance improvement schemes, which are double modulation scheme, temporal gating scheme, intensity modulation scheme, and phase modulation scheme. We have achieved distributed strain measurement with 10.1cm spatial resolution, over...
A novel and simple analytical expression to describe the Brillouin gain spectral broadening as a function of the spatial resolution in time-domain Brillouin distributed fiber sensors is deduced. The proposed model is experimentally validated using a pump-probe Brillouin sensing setup and also compared with numerical and approximate results. In addition, a compact mathematical form is presented for...
In this work is discussed an effect of nanocoating long-period grating (LPG) with an aluminum oxide (Al2O3) on its refractive index (RI) and temperature (T) sensitivity. For comparison two LPGs, namely one before and after the nanocoating process were optimized towards working at dispersion turning point (DTP) of higher order cladding modes. The DTP was reached with two methods, i.e., by wet etching...
We have demonstrated a quasi-distributed sensor using an active mode-locking (AML) laser with multiple fiber Bragg grating (FBG) reflections of the same center wavelength. We found that variations in the multiple cavity segment lengths between FBGs can be measured by simply sweeping the modulation frequency, because the modulation frequency of the AML laser is proportionally affected by cavity length.
A novel BOTDA method based on differential π-phase-shift-pulse pair is proposed for narrowing the Brillouin gain spectrum. Theoretical analysis and experimental results demonstrate that the proposal could achieve 17 MHz Brillouin gain spectrum linewidth with a fixed spatial resolution of 2.5 m. The Brillouin gain spectrum linewidth is 3 times narrower than that obtained using conventional single-pulse...
This paper presents a novel optical fiber device based on a polymer suspended mirror on the end facet of an optical fiber. With an own-developed optical 3D micro-printing technology, SU-8 suspended-mirror devices (SMDs) were successfully fabricated on the top of a standard single-mode optical fiber. Optical reflection spectra of the fabricated SU-8 SMDs were measured and compared with theoretical...
Optical fibers have been successfully utilized for point sensors targeting physical quantities (stress, strain, rotation, acceleration), chemical compounds (humidity, oil, nitrates, alcohols, DNA) or radiation fields (X-rays, β particles, γ-rays). Similarly, bundles of fibers have been extremely successful in imaging visible wavelengths for medical endoscopy and industrial boroscopy. This work presents...
We propose an image reconstruction method of digital holography for getting more accurate reconstruction. Digital holography provides both the light amplitude and the phase of a specimen through recording the interferogram. Since the Fresenl diffraction can be efficiently implemented by the Fourier transform, zero padding technique can be applied to obtain more accurate information. In this work,...
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...
A 9.5-m continuous chirped fiber Bragg grating (CFBG) interrogated with an optical frequency domain reflectometer is used for strain and temperature measurements. The spatial resolution is 4 mm and the noise level is 0.1 K corresponding to 1 μstrain. The strain profile is also derived from the optical reflection spectrum alone, and the results are in good agreement with the profile obtained from the...
We propose an improved optical coherence domain polarimetry (OCDP) calibration scheme by using polarization mode crosstalk (PMC). The scheme can be used to calibrate the OCDP system's measurement result about intensity of PMC. The intensity of 1st order PMCs are measured by polarization extinction ratio (PER) meter as the scale to transfer the standard into OCDP system, and the higher order PMCs formed...
The frequency division multiplexing (FDM) technique is firstly introduced into a direct-detection phase-sensitive OTDR to improve the distributed fiber acoustic sensing performance by using a frequency step sweeping laser source and a dual probe pulse scheme. By using FDM technique, a 40 kHz sampling rate to vibration is realized with a 10 km measurement range, which implies the tradeoff between the...
A comparative analysis of two optical fiber sensing platforms is presented. The sensors are based on surface plasmon resonance (SPR) in a D-shaped plastic optical fiber (POF) with a photoresist buffer layer between the exposed POF core and the thin gold film. We show how the sensor's performances change when the photoresist layer changes. The photoresist layers proposed in this analysis are SU-8 3005...
We report a directional-coupler-based refractive index sensor and its cost-effective fabrication method using hydrofluoric acid droplet wet-etching and surface-tension-driven liquid flows. The proposed fiber sensor consists of a pair of twisted tapered optical fibers with low excess losses. The fiber cores in the etched microfiber region are exposed to the surrounding medium for efficient interaction...
We demonstrate a high accuracy demodulation platform with a tunable Fabry-Perot filter (TFF) for twin-grating based fiber optic sensing network with hybrid TDM/FDM. The hybrid TDM/FDM scheme can improve the spatial resolution to centimeter but increases the requirement of high spectrum resolution. To realize the demodulation of the complex twin-grating spectrum, we adopt the TFF demodulation method...
In this paper, Fresnel reflection based fiber-optic sensor for the real-time monitoring of cryogenic temperature is presented. The proposed sensor system utilizes a linear thermo-optic coefficient of polymer and Fresnel reflection of the fiber end. Epoxy resin and poly methyl metha acrylate (PMMA) are used as sensor head material. The designed sensor head measures the temperature ranging from −180°C...
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