969 results about "Rayleigh scattering" patented technology

A method for forming an optical fiber includes drawing the optical fiber from a glass supply and treating the fiber by maintaining the optical fiber within a treatment temperature range for a treatment time. Preferably also, the fiber is cooled at a specified cooling rate. The optical fiber treatment reduces the tendency of the optical fiber to increase in attenuation due to Rayleigh scattering, and/or over time following formation of the optical fiber due to heat aging. Apparatus are also provided.

A dispersion-shifted optical fiber (NZDSF) includes a central core (r₁, Dn₁), an inner cladding having at least three zones with a first intermediate cladding zone (r₂, Dn₂), a second ring zone (r₃, Dn₃) and a third buried trench zone (W_tr, Dn_t). The buried trench zone has an index difference (Dn_t) with the optical cladding between −5·10⁻³ and −15·10⁻³ and has a width (W_tr) between 2.5 μm and 5.5 μm. The present optical fiber, at a wavelength of 1550 nm, has reduced Rayleigh scattering losses of less than 0.164 dB/km, with limited bending losses.

A CW lightwave modulated by a continuously reiterated psuedorandom code sequence is launched into an end of a span of ordinary optical fiber cable. Portions of the launched lightwave back propagate to the launch end from a continuum of locations along the span because of innate fiber properties including Rayleigh scattering. This is picked off the launch end and heterodyned producing a r.f. beat signal. The r.f. beat signal is processed by a plurality (which can be thousands) of correlator type pseudonoise code sequence demodulation and phase demodulator units, operated in different time delay relationships to the timing base of the reiterated modulation sequences. These units provide outputs representative of phase variations in respective unique spectral components in the r.f. beat signal caused by acoustic, or other forms of, signals incident to virtual sensors at fiber positions corresponding to the various time delay relationships.

An optical power monitoring device includes a photodetector disposed in close proximity to the cladding of an optical fiber for measuring Rayleigh scattered light from the core of the optical fiber. To ensure only Rayleigh scattered light is measured, a cladding stripper is provided to remove any cladding light prior taking a reading with the photodetector.

A time correlated single photon counting system having a programmable delay generator triggered by a laser fire event detector. The system may be used for chemical agent detection based on Rayleigh scattering using optical time domain reflectometry techniques. The system may also be used for Raman detection using frequency to time transformations.

An optical fiber preform 2 having a viscosity ratio Reta=eta0/etat of 2.5 or less between the core average viscosity eta0 and the total average viscosity etat is prepared, and is drawn by a drawing furnace 11 so as to yield an optical fiber 3, which is then heated to a temperature within a predetermined range so as to be annealed by a heating furnace 21 disposed downstream the drawing furnace 11. Here, upon annealing in the heating furnace 21, the fictive temperature Tf within the optical fiber lowers, thereby reducing the Rayleigh scattering loss. At the same time, the viscosity ratio condition of Reta<=2.5 restrains the stress from being concentrated into the core, thereby lowering the occurrence of structural asymmetry loss and the like. Hence, anoptical fiber which can reduce the transmission loss caused by the Rayleigh scattering loss and the like as a whole, and a method of making the same can be obtained.

The invention discloses a sensing device of optical fiber distribution type temperature and stress and mainly comprises a light source module (1), a frequency discriminator module (2), and a thermo tank module (3), which are all connected with one another by polarization-preserving fiber. The invention is a direct detection method which is based on optical fiber Raman scattering used as a carrier wave of temperature information, brillouin scattering used as a carrier wave of stress, rayleigh scattering used for measuring relative frequency of a outgoing laser beam to a frequency discriminator and Fabry-Perot etalon used for discriminating frequency and distributing sensing temperature and stress. The invention has the advantages of simple structure, fine stability, avoidance of outgoing power of the light source during coherent detection, outgoing frequency of the light source. Instability of acoustic modulation or electro-optic modulation frequency is directly referred to measure errors and the direct detection technology of the frequency discrimination is not sensitive to frequency drift of the light source and fluctuation of signal intensity.

Scatter effects are reduced in a radiographic imaging device, such as a digital slot scan mammographic imaging device, by reducing detected scatter and processing detector information to compensate for scatter effects. Spatial intensity profile information together with other imaging signal and patient dependent parameters can be used in image processing to estimate and compensate for various scatter effects including single and multiple scatters and Compton and Rayleigh scatter.

A method of obtaining a distributed measurement comprises deploying an optical fibre in a measurement region of interest, and launching into it a first optical signal at a first wavelength λ₀ and a high power level, a second optical signal at a second wavelength λ₋₁, and a third optical signal at the first wavelength λ₀ and a low power level. These optical signals generate backscattered light at the second wavelength λ₋₁ arising from Raman scattering of the first optical signal which is indicative of a parameter to be measured, at the first wavelength λ₀ arising from Rayleigh scattering of the first optical signal, at the second wavelength λ₋₁ arising from Rayleigh scattering of the second optical signal, and at the first wavelength λ₀ arising from Rayleigh scattering of the third optical signal. The backscattered light is detected to generate four output signals, and a final output signal is derived by normalising the Raman scattering signal to a function derived from the three Rayleigh scattering signals, which removes the effects of wavelength-dependent and nonlinear loss.

The invention provides a method for simultaneously measuring distributed type temperatures and strain. A brillouin optical time domain reflectometer and a coherent light time domain reflectometer share the same optical path system and the same circuit system and serve as a sensing measurement system. The sensing measurement system works in a BOTDR mode and a COTDR mode in an alternate mode to measure a brillouin scattering spectrum and a Rayleigh scattering spectrum which are distributed along a single single-mode sensing optical fiber and detect the frequency shift of the brillouin scattering spectrum and the frequency shift of the Rayleigh scattering spectrum, a linear equation set in two unknowns about the temperature and the strain is set up according to the characteristic that the frequency shift of the two scattering spectra is in the linear relationship with the temperature and the strain, and the temperature and the strain of each position of the sensing optical fiber can be obtained by solving the equation set, and then the temperatures and the strain distributed along the whole sensing optical fiber can be obtained. According to the method, the complexity and the manufacturing cost of the system are greatly reduced, no special requirement for the brillouin frequency shift coefficient of the optical fiber exists, and the application range of the measurement system is enlarged.

The invention discloses a detection method suitable for a sensing device of optical fiber distribution type temperature and stress. The sensing device of the optical fiber distribution type temperature and stress mainly comprises a light source module (1), a frequency discriminator module (2), and a thermo tank module (3), which are all connected with one another by polarization-preserving fiber. The detection method of the invention is a direct detection method which is based on optical fiber Raman scattering used as a carrier wave of temperature information, brillouin scattering used as a carrier wave of stress, rayleigh scattering used for measuring the relative frequency of a outgoing laser beam to the frequency discriminator and Fabry-Perot etalon used for discriminating frequency and distributing sensing temperature and stress. The invention has the advantages of simple structure, fine stability, avoidance of outgoing power of the light source during coherent detection, and outgoing frequency of the light source. Instability of acoustic modulation or electro-optic modulation frequency is directly referred to measure errors and the direct detection technology of frequency discrimination is not sensitive to the frequency drift of the light source and the fluctuation of signal intensity.

The invention discloses a long-distance distributed optical fiber vibration sensing system and a method thereof. The system comprises an induction system for inducting outside vibration events and a detecting and controlling system for detecting and controlling vibration signals; the induction system is connected with the detecting and controlling system. The induction system comprises a light source, a pulse modulator, an optical fiber circulator, a first optical fiber amplifier, and a light switch of a first optical fiber filter. The detecting and controlling system comprises a plurality of optical-electrical converters and a system control unit; the system control unit collects output light of the converters, analyzing the collected signals and judges whether the alarm is needed according to the analysis result. The invention adopts the optical switch technology to adopt time-division processing on backward Rayleigh scattering light which is reflected back, the dynamic range of the system is large, and the sensible distance can be tens of kilometers as high as possible, even hundreds of kilometers; and the invention adopts phase detecting technology and optical time domain reflection technology and can greatly improve detecting sensibility of the system and positioning precision.

The invention relates to a demodulating method of a distributed disturbance sensor based on a Rayleigh scattering spectrum related coefficient. The distributed disturbance sensor adopts a technical method of optical frequency zone reflection and beat frequency interference of a laser source of a linear tuning ultra-narrow line width echo wall mold self-injecting locked mode. The distributed disturbance sensor comprises a main interferometer used for obtaining sensing signals and an auxiliary interferometer used for providing clock triggering signals for a collecting device. The demodulating method comprises the following steps: obtaining different beat frequency signals through a linear tuning light source and converting information of a wavelength zone to the information of distance zones of positions of corresponding cables by utilizing fast Fourier transform. Signals of the sensing optical cables are selected in the distance zones by a movable window, and then, are converted to the wavelength zone through plural fast Fourier inversion to form the Rayleigh scattering spectrums. The Rayleigh scattering spectrums disturbed by the outside world at different moments are compared, i.e., the disturbed Rayleigh scattering spectrums at the different moments are compared. The demodulating method is characterized in that information of whether the sensing optical cables is disturbed or not and the information of the disturbance intensity are obtained through related coefficients.

The invention relates to a temperature-measuring system of distributed fibers, aiming at the continuous monitoring of temperature parameters of underground electromechanical transport equipment. The temperature-measuring system of distributed fibers comprises a singlechip control board, a fiber temperature field information acquisition module, a photoelectric detector and a circuit signal post-processing module, wherein the fiber temperature field information acquisition module comprises a pulse fiber laser and a wavelength division multiplexer; the circuit signal post-processing module comprises an acquisition card and a personal computer (PC); the singlechip control board is connected with the pulse fiber laser and the acquisition card by leads; the wavelength division multiplexer is connected with the pulse fiber laser and the photoelectric detector by fibers; incident light emitted by the pulse fiber laser is output to the sensing fiber by the wavelength division multiplexer; the sensing fiber feeds backward scattered light with temperature variance information of mine equipment back to the wavelength division multiplexer; and the wavelength division multiplexer extracts two scattered light beams of anti-Stokes and Stokes from the backward scattered light to restrain Rayleigh scattered light and other non-linear scattered light; and the photoelectric detector is connected with the acquisition card by a lead.

A CW lightwave modulated by a continuously reiterated binary pseudorandom code sequence is launched into an end of a span of ordinary optical fiber cable. Portions of the launched lightwave back propagate to the launch end from a continuum of locations along the span because of innate fiber properties including Rayleigh scattering. This is picked off the launch end and heterodyned to produce a r.f. beat signal. The r.f. beat signal is processed by a plurality (which can be thousands) of correlator type binary pseudonoise code sequence demodulators respectively operated in different delay time relationships to the timing base of the reiterated modulation sequences. The outputs of the demodulators provide r.f. time-domain reflectometry outputs representative of signals (e.g., acoustic pressure waves) incident to virtual sensors along the fiber at positions corresponding to the various time delay relationships.

The invention relates to an optical fiber sensor. The invention discloses an optical fiber destabilization detecting method combining based on a phase sensitivity light time domain reflection and a polarization sensitivity light time domain reflection method and distributed optical fiber sensing system thereof to improve the detecting accuracy and reliability of the optical fiber destabilization. The method comprises: a. injecting an optical signal with determined polarization state into the optical fiber; b. receiving the back rayleigh scattering light in the optical fiber; c. diving the rayleigh scattering light into two bundles to perform the Phi-OTDR data acquisition and the POTDR data acquisition; d. determining the destabilization and position thereof based on the distortion points of the Phi-OTDR data and the POTDR data. The invention also discloses an optical fiber destabilization detecting device. The technical scheme of the invention is used for monitoring and protecting the optical cable lines, thereby greatly improving the precision and the sensitivity of the monitoring system and reducing the erroneous judgment rate and the missing report rate.

A method for forming an optical fiber includes drawing the optical fiber from a glass supply and treating the fiber by maintaining the optical fiber within a treatment temperature range for a treatment time. Preferably also, the fiber is cooled at a specified cooling rate. The optical fiber treatment reduces the tendency of the optical fiber to increase in attenuation due to Rayleigh scattering, and/or over time following formation of the optical fiber due to heat aging. Apparatus are also provided.

The invention discloses a distributed optical fiber sensing system and a detection method utilizing the same. The optical fiber sensing system comprises a light source unit, an optical circulator, and a detection unit, wherein the light source unit emits light which is suitable for detecting and processing; the optical circulator receives the light which comes from the light source unit, and transmits the received light into a sensing optical fiber used for the detection; and the detection unit receives backscattered light caused by the light which enters the sensing optical fiber from the optical circulator, interference light formed by Rayleigh scattering light and scattered light of one component of Brillouin in the backscattered light through heterodyne interference is obtained in the detection unit and is converted into an electrical signal, and the detection unit also detects the electrical signal to obtain the change of the temperature and strain in the sensing optical fiber.