Laser Doppler Velocimetry (LDV) has been widely used for many years in fluid mechanics to measure particle velocity. However, the signal of LDV is weaker in most applications. One challenging issue is how to effectively discover the weak characteristics from the signal submerged in noise. To address the issue, a method based on Stochastic Resonance is proposed in this paper. Using the SR method, the noise may be weakened and weak characteristics highlighted, and therefore velocity can be is obtained. FFT and the method are adopted to process simulated laser Doppler signals in circumstance of MATLAB. The input and the output signal-to-noise ratios of the bistable system demonstrate the effectiveness of the SR method.
A novel quasi-distributed fiber temperature sensor based on the cascaded quantum dot fibers (QDFs) is proposed in this paper. The cascaded QDFs are fabricated by the 3D printing technology and can be divided into two parts QDF1 and QDF2. When the excitation light is coupled into the fiber, the QDF1 emits the 630nm fluorescence and the QDF2 emits the 530nm fluorescence. Because the fluorescence peaks will change with the temperature linearly, it can be used as the fiber temperature sensor. In the experiment, by controlling the temperature at each QDF, the sensor realizes the temperature measurement at different position. The sensitivity of the sensor at different position is 0.15nm/°C and 0.153nm/°C, respectively. The results verify the feasibility of the structure for distributed temperature sensing. The spatial resolution is 1.8mm, which is limited by the length of the printed QDF.
Based on the principle of Solc interferometer, an optical fiber sensor which can realize torsional direction and torsion angle measurement simultaneously is proposed in this paper. The sensor is consisted of a segment of single mode fiber (SMF), polarization maintaining fiber (PMF) and two polarizers. When the light of the broad band source is transmitted in the sensor, the interference spectra can be observed at the output of the sensor. The interference spectra of the sensor can be changed when the sensor is twisted clockwise or counter-clockwise. Because the peaks position and dips position in interference spectra are reversed when clockwise and counter-clockwise torsions are applied, the torsional direction can be judged conveniently. With the increase of the torsion angle, the extinction ratio (ER) of interference spectra will change significantly. By measuring the changes of the ER, torsion angle can be calculated easily. The highest sensitivity can reach to 0.79dB/° in the range of [-50,52°].
A printing method of quantum dots (QDs) optical fiber is presented in this paper. The printing ink with suitable viscosity is composed of the UV adhesive and the CdSe/ZnS quantum dot. By adjusting the pressure and waveform parameters of inkjet printer, a stable droplet is formed. A segment of QDs optical fiber is printed on the organic polymer material substrate subjected to viscous treatment by controlling the spacing between adjacent droplets. When the printed QDs optical fiber is aligned to multi-mode optical fiber which is used to transmit the excitation light, strong fluorescence of the QDs fiber is detected by the optical spectrum analyzer (OSA). Using the printed QDs optical fiber as the senor, the temperature measurement is realized. The sensitivity of the luminescent peak with the temperature is about 115.0pm/°C.
A compact high birefringence polarization maintaining fiber (PMF) sensor for simultaneous strain and temperature measurement is proposed. This sensor is a modal interferometer (MI) sensor which is composed of a segment of high birefringence polarization maintaining fiber. One side of the fiber is spliced to the pigtail of a polarization beam splitter (PBS) with core-offset and axes alignment, the other end is spliced to the standard single-mode fiber (SMF) with core alignment and forms a fiber bubble. In experiments, an optical switch and the PBS are used to generate two orthogonal linear polarized lights. When the two orthogonal linear polarized lights enter the sensing fiber respectively, two different interference spectra will be achieved and own different response to the strain and temperature. Using these properties, the sensor realizes the simultaneous strain and temperature measurement. For 0.01 nm wavelength resolution, the strain and temperature resolution of the sensor are 10 uε and 0.285°C, respectively.
A novel fiber relative humidity (RH) sensor is demonstrated in this paper. The sensor is composed of a fiber Michelson modal interferometer (MMI) and the ZnO nanorods which grown on the fiber to improve the sensitivity of the sensor. Two standard single mode fibers are spliced to form the MMI, misaligned splicing program is used at the spliced point. Relative humidity sensing experiment shows that the intensity of interference spectrum changes linearly with relative humidity. With the relative humidity increasing in the range from 30% to 85%, the intensity of the dip in the interference spectrum linearly increases higher than 50%. The relative humidity response of the sensor is induced by the interference between core mode and cladding mode. The ZnO nanorods with high surface to volume ratio grown outside of the fiber cladding enhance the sensitivity of the sensor.
A novel all-fiber Mach-Zehnder modal interferometer (MZMI) for temperature and strain measurements is demonstrated. The interference between the core and the cladding modes in the single mode fiber (SMF) is utilized. To excite the cladding modes, a microcavity is embedded in the SMF. After propagating a distance in the cladding, the cladding modes will couple back to the core mode at the other point fabricated by core-offset splicing. The MZMI exhibits a high temperature sensitivity (<0.1nm/ °C) in the range of 200-600 (°C). The strain response of the MZMI is also investigated. This compact, simple and cost-effective MZMI owns potential applications in temperature and strain measurements.
We demonstrate a tunable erbium-doped fiber ring laser based on an all-fiber filter. The filter consists of an optical
circulator, a fiber loop mirror(FLM) and a polarizer which is spliced to a segment of polarization maintaining fiber (PMF)
at the angle of 45° with respect to the fast axis of the PMF. The laser can be tuned by adjusting two polarization
controllers (PC) in the laser. The tuning range can reach to 6.08nm (1553.92-1560.1nm) with side mode suppression
ratio (SMSR) over 38 dB. The stability of the laser is verified at room temperature in one hour, and the power fluctuation of the laser is less than 0.5 dB.
In this paper, by utilizing two series connected Lyot-Sagnac filter, we propose a switchable erbium-doped fiber laser
(EDFL) which can be switched between single-wavelength and multi-wavelength in the experiment. The laser can
realize stable single-wavelength, dual-wavelength, triple-wavelength output at room temperature by adjusting
polarization orientations of two polarization controllers(PCs) in the two series connected Lyot-Sagnac filter. The optical
signal-to-noise ratio (OSNR) of the laser is over 30 dB, and the peak fluctuation over 30 minute is less than 0.5 dB at
room temperature.
A switchable dual-wavelength erbium-doped fiber laser is proposed. The proposed fiber laser, which utilizes a two-taper
Mach-Zehnder interferometer filter as the wavelength-selective component, realizes single-, dual-wavelength switching
by adjusting the curvature of two-taper. The side-mode suppression ratios (SMSRs) is over 36 dB and the power
variation for each wavelength is less than 0.5dB in one hour under room temperature.
In this paper, a simple and all-fiber frequency comb generator by stimulated Brillouin scattering (SBS) in highly
nonlinear fiber (HNLF) is demonstrated. The optical resonator is composed of a segment of highly nonlinear fiber and
two optical loop mirrors. Besides these, a segment of 6m-long erbium-doped fiber was placed in the resonator to
provided linear gain. A tunable laser and a 980-nm laser diode were used as the Brillouin pump and the EDF pump
respectively. When the wavelength and the power of pump lasers are adjusted correctly, dozens of comb lines with comb
spacing in 0.075 nm (9.37 GHz) are obtained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.