Nippon Telegraph and Telephone Corporation

Ntt Corporation

Yusuke Koshikiya

Nazuki Honda

Atsushi Nakamura

Daisuke Iida

Tetsuya Manabe

Tatsuya Okamoto

Tomokazu Oda

Hiroyuki Iida

Hidenobu Hirota

Takui Uematsu

Fumihiko Ito

Xinyu Fan

Hiroshi Takahashi

Kazutaka Noto

A cable test system, an analysis apparatus, a cable test method, and a program are capable of recognizing a sag section of an overhead cable without sending a worker to a site. In some implementations, the cable test system includes an optical fiber vibration distribution measurement apparatus that acquires a vibration distribution waveform of an overhead optical fiber cable to be tested. The vibration distribution waveform being represented in a time domain and a distance domain in a longitudinal direction. The analysis apparatus that calculates a propagation speed of vibrations propagating through the overhead optical fiber cable from the vibration distribution waveform and detects, as a cable sag section, a section of the overhead optical fiber cable in which the propagation speed is equal to or lower than a threshold value.

Overhead optical cable test system and method

An object is to provide an optical fiber test method and an optical fiber test device capable of acquiring a maximum loss of a higher-order mode at a connection point of an optical fiber transmission line through which a plurality of modes propagate. The optical fiber test device according to the present invention includes: a light source unitthat allows probe light L, which has a tunable wavelength and is continuous light, to enter one end Tof an optical fiber in a fundamental mode and allows pulsed pump light L, which is shifted to a high frequency side by a frequency at which a Brillouin interaction occurs with respect to the probe light L, to enter the other end Tof the optical fiber in a higher-order mode as a measurement target; and an analysis unitthat acquires, from a light intensity of the probe light Lamplified by the pump light L, a time waveform of an amplification component, calculates a connection loss of the pump light Lat a connection point from a ratio of the amplification components before and after the connection point, acquires a wavelength dependency of the connection loss, detects a maximum value of the connection loss from the wavelength dependency of the connection loss, and sets the maximum value as a maximum loss of the higher-order mode at the connection point.

Optical fiber test method and optical fiber test equipment

The present disclosure relates to a frequency modulation amount measuring device that measures an optical spectral shift of scattered light at a position in an optical transmission line, and calculates a frequency modulation amount at the position, using the measured optical spectral shift.

Devices and methods for measuring the amount of frequency modulation

An object of the present invention is to provide a Brillouin gain spectrum distribution measuring method and apparatus capable of measuring a BGS, having a line width narrower than usual, in a distributed manner in the longitudinal direction of an optical fiber under test. This measuring apparatus prepares pump light in which a pulse is added to continuous light and probe light of continuous light in which a frequency is shifted from the pump light, makes the probe light incident on one end of the FUT and the pump light incident on the other end, and obtains a time waveform of a component amplified by the pump light pulse of a probe light intensity amplified by the pump light. This measuring apparatus changes an optical frequency difference between the pump light and the probe light, and obtains a time waveform for each optical frequency difference. This measuring apparatus obtains a BGS distribution of the FUT from these time waveforms.

Brillouin gain spectrum distribution measurement method and equipment

The present invention has an object to provide a mode field diameter measurement method enabling easily measuring a mode field diameter in an optical fiber, which is capable of propagating a fundamental mode (LP01 mode) and a first higher order mode (LP11 mode), without using a mode multiplexer, and a measurement device of the mode field diameter measurement method. In a mode field diameter measurement method according to the present invention, an intensity ratio between an LP01 mode and an LP11 mode output from an optical fiber to be tested is changed, a mode field diameter is measured by a variable aperture (VA) method for each intensity ratio, and each mode field diameter is calculated.

Mode field diameter measuring method and mode field diameter measuring device

An optical fiber measurement system is presented. The optical fiber measurement system includes a light incident circuit which makes a probe light incident on one end of an optical fiber and makes a secondary probe light and a pump light as an optical pulse incident on the other end of the optical fiber; a light receiver which measures a light intensity of arbitrary one propagation mode in the probe light propagating through the optical fiber; and a control calculation device which sets a propagation mode of the probe light, the secondary probe light, and the pump light, an optical frequency difference of the secondary probe light, and an optical frequency difference of the pump light with respect to the light incident circuit, and calculates loss and crosstalk at each point in a longitudinal direction of the optical fiber from the light intensity measured by the light receiver.

Optical fiber measurement system, optical fiber measurement method, control arithmetic device, and program

The present disclosure generates an optical spectrogram, representing a temporal change in frequency characteristics, using a plurality of spectral data measured by an OFDR measurement instrument at different times, and filters the optical spectrogram in both a time direction and a frequency direction.

Technique for analyzing a spectrum of backscattered light in an optical fiber

An object of the present disclosure is to provide a frequency division multiplexing coherent OTDR, a test method, a signal processing apparatus, and a program that can maintain, even in a case where a DFB laser is used, a spatial resolution equivalent to a spatial resolution achieved when a fiber laser or an external resonant laser is used. An OTDR according to the present disclosure includes a light incidence unit configured to change an optical frequency of light from a light source by a predetermined frequency interval at a predetermined time interval to generate test light pulses and cause the test light pulses to sequentially enter a fiber under test, a light reception unit configured to use the light from the light source as local light to coherently detect backscattered light from the fiber under test to acquire a received signal, and a computation unit configured to separate the received signal into signals with frequencies obtained by changing the optical frequency by the predetermined frequency interval, square amplitudes of the signals resulting from frequency separation to generate square values, perform Wiener filter processing on the square values, compensate values resulting from the Wiener filter processing for delay time when the test light pulses are caused to enter the fiber under test, and calculate an arithmetic mean of the compensated values.

Optical frequency multiplexing coherent OTDR, testing method, signal processing device, and program

An object of the present invention is to provide an optical pulse test apparatus that can test an optical fiber cable at once in a short period of time. The optical pulse test apparatus according to the present invention includes: an optical pulse signal generation unitthat emits an optical pulse with a width that is n times as large as a pulse width T corresponding to desired spatial resolution; a light reception unitthat receives reflected light and back-scattered light from n FUTs; an optical path control unitthat switches paths connected to the n FUTs are connected at an interval T, inject the optical pulse, as a test optical pulse having the pulse width T, sequentially into the paths, then switches the paths at an interval ts that is shorter than the time period T, and emit the reflected light and the back-scattered light from the n FUTs sequentially onto the light reception unitat an interval n&#xd7;ts; and an arithmetic processing unitthat divides the electrical signal output from the light reception unit, with an interval equal to the interval ts at which switching the paths is performed, into discrete signals respectively corresponding to the FUTs, and calculates the reflectance distributions of the reflected light and the back-scattered light of the respective FUTs.

Optical pulse testing device and optical pulse testing method

An object of the present disclosure is to provide an optical fiber cable monitoring method and an optical fiber cable monitoring system capable of linking information obtained from a measurement result with information stored in a DB and accurately specifying a loss occurrence location on an optical fiber cable. The optical fiber cable monitoring method according to the present disclosure uses two types of optical fiber measurement techniques having different sensitivities. Each of closure locations on the optical fiber cable is acquired with a high-sensitivity measurement technique, and geographical location information and the closure locations on the optical fiber are linked in an arrangement order of the closures. Thus, an operator can recognize an actual location (geographical location information) of a closure that is linked to a location of a point of abnormality on the optical fiber cable when an abnormality in the closure is detected with a low-sensitivity measurement technique.

Optical fiber monitoring method, and optical fiber monitoring system

A test pulse is generated from a first and a second test light beam pulse with different wavelengths, with a predetermined time difference applied between the first and the second test light beam pulse. A circulator inputs the test pulse to a trunk fiber of a measurement target fiber line. A reflected light is extracted which is output from an input end of the trunk fiber. A filter extracts stimulated Brillouin backscattered light. A receiver receives and converts the scattered light into an electrical signal. A processing device carries out the signal to determine in which of N branched fibers the stimulated Brillouin scattered light is generated, while varying a time difference between the first and the second test pulse.

Optical fiber line characteristic analysis apparatus and analysis method thereof

An object of the invention is to provide an optical reflectometry and an optical reflectometer, in which accurate measurement can be performed irrespective of a measurement distance. In the optical reflectometry and optical reflectometer according to the invention, in which a distribution of backscattered light intensity from a measurement target in an optical propagation direction is measured using Optical Frequency Domain Reflectometry (OFDR), a coherence monitor unitthat monitors a coherence property of a frequency sweep light sourceis provided, and measurement result of a measuring unitis corrected based on the monitor result of the coherence monitor unit

Growing community of inventors

Musashino, Japan

Yusuke Koshikiya