578results about "Reflectometers detecting back-scattered light in time-domain" patented technology

The present invention relates to a system and method to determine chromatic dispersion in short lengths of waveguides using a two wave interference pattern and a common path interferometer. Specifically the invention comprises a radiation source operable to emit radiation connected to a means for separating incident and reflected waves; the means for separating incident and reflected waves possessing an output arm adjacent to a first end of the waveguide; and the means for separating incident and reflected waves further connected to an optical detector operable to record an interference pattern generated by a reflected test emission from the radiation source. The interference pattern consists of two waves: one reflected from a first facet of a waveguide and the second reflected from a second facet of the same waveguide.

A wavelength dispersion probing system for determining a value of wavelength dispersion and its sign and reducing the trouble and time required for this determination. This wavelength dispersion probing system comprises light sources 10, 12, light attenuators 14, 16, optical multiplexer 18, phase modulator 20, optical amplifiers 22, 26, acoustooptical modulator 24, optical receiver 30. The intensity ratio of two wavelengths is set at 1 to 2 to detect Stokes light or anti-Stokes light included in the return light of an optical fiber 100 by the optical receiver 30, so that wavelength dispersion is probed. The wavelength dispersion is probed by changing the intensity ratio of the two wavelengths to observe the state of the change of the wavelength dispersion, so that the sign of wavelength dispersion is determined by the optical receiver 30.

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 provides automated systems and methods for measuring ORL of fibers under test. A computer-based test instrument using OTDR tests fibers with the help of a STFM having predefined characteristics that are recorded in a machine-readable memory. The information recorded in the memory is accessible to the computer-based instrument and is used to calibrate a power level of an illumination source in real time using the reflectance response of the STFM. The calibrated illumination power allows the instrument to automatically determine the ORL of the fiber being tested with precision, and without requiring the intervention of an operator. The instrument also has the capability to automatically sense the presence of a test fiber, and to automatically attenuate the reflectance signal to remove a saturation condition by controlling at least one of the illumination, the detector gain, an amplifier gain, and an optional in-line optical attenuator.

An optical time domain reflectometry apparatus has a laser and light modulator for producing coherent light pulses, each having two sections of higher intensity separated by a gap of lower or substantially zero intensity. As the light pulses propagate along the optical fibre, light is continuously Rayleigh backscattered by inhomogeneities of the optical fibre. A photodetector generates backscatter signals representing the intensity of light Rayleigh backscattered in the optical fibre as each light pulse travels along the optical fibre. The PC uses these backscatter signals to derive a difference signal representing a change dI in intensity between signals generated from two successive pulses. The PC then calculates the Root Mean Square (RMS) of the difference signal averaged over the interval between the two sections of the light pulses. Next, the PC averages the backscatter signal generated from the first of the pulses over the same interval and normalises the RMS difference signal using the averaged signal to obtain a compensated difference signal that depends only on differences in the rate of change of phase of light of the light pulses as they travelled along the waveguide. This is repeated at different wavelengths to allow the compensated difference signal to be adjusted to represent the magnitude of the differences.