An optical pulse test apparatus according to the present disclosure includes a light generation unit configured to generate an optical pulse for generating backscattered light beams in an optical fiber under test and generate first light having an optical frequency for amplifying backscattered light in an LP11 mode out of the backscattered light beams in two LP modes through stimulated Brillouin scattering, and second light having an optical frequency for attenuating backscattered light in an LP01 mode out of the backscattered light beams in the two LP modes through stimulated Brillouin scattering, a mode demultiplexing unit configured to input the optical pulse, the first light, and the second light generated by the light generation unit into the optical fiber under test in the LP01 mode and separate, out of the backscattered light beams generated by the optical pulse, the backscattered light in the LP11 mode, a local oscillation light generation unit configured to generate local oscillation light by which the backscattered light separated by the mode demultiplexing unit is heterodyne-detected, a light reception unit configured to multiplex the backscattered light in the LP11 mode separated by the mode demultiplexing unit and the local oscillation light generated by the local oscillation light generation unit and photoelectrically convert the multiplexed light into an electrical signal, and an arithmetic processing unit configured to calculate a time-intensity distribution of the electrical signal obtained by the light reception unit photoelectrically converting the backscattered light in the LP11 mode.

An object of the present invention is to provide an optical pulse test apparatus and an optical pulse test method that are capable of determining a change in state of an optical fiber connection portion without the need for reference and without being affected by changes in gap interval before and after the change in state. The optical pulse test apparatus according to the present invention is configured to perform an OTDR measurement by using test optical pulses having spectral widths of from several nm to several hundred nm arranged at intervals of several ten nm to several hundred nm, calculate a reflection peak value caused by the Fresnel reflection at the connection portion from the obtained OTDR waveform, and determine a state such as water immersion of the optical fiber connection portion based on the value.

In some examples, a tunable dense wavelength division multiplexing (DWDM) optical time-domain reflectometer (OTDR) may include a fiber optic link analyzer, executed by at least one hardware processor, to determine, based on a user input, for a fiber optic link of a plurality of fiber optic links of a fiber optic cable, whether the fiber optic link is active or not active. The DWDM OTDR may specify, based on a determination that the fiber optic link is active, a test wavelength that is different from a data transmission wavelength of data transmitted by the fiber optic link. A DWDM multiplexer may be collocated with the DWDM OTDR to selectively connect, based on the specified test wavelength, the DWDM OTDR to the fiber optic link of the plurality of fiber optic links for testing of the fiber optic link.

An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, the beat signal may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.

According to examples, a Brillouin and Rayleigh distributed sensor may include a first laser source to emit a first laser beam, and a second laser source to emit a second laser beam. A photodiode may acquire a beat frequency between the two laser beams. The beat frequency may be used to maintain a predetermined offset frequency shift between the two laser beams. A modulator may modulate the first laser beam. The modulated first laser beam is to be injected into a device under test (DUT). A coherent receiver may acquire a backscattered signal from the DUT. The backscattered signal results from the modulated first laser beam injected into the DUT. The coherent receiver may use the second laser beam as a local oscillator to determine Brillouin and Rayleigh traces with respect to the DUT based on the predetermined offset frequency shift.

An object is to provide a light intensity distribution measurement method and a light intensity distribution measurement apparatus that are capable of accurately measuring the intensity of light in each mode at each position of an optical fiber through which light is propagated in a plurality of modes. With a light intensity distribution measurement apparatus according to the present invention, a gain coefficient matrix is acquired in advance, which is constituted by Brillouin gain coefficients of propagation modes with predetermined optical frequency differences measured using a reference optical fiber that exhibits the same properties as a measurement-target optical fiber and that does not cause mode coupling, and the intensity distribution of light in each propagation mode in a lengthwise direction of the measurement-target optical fiber is calculated based on the gain coefficient matrix and a difference in light intensity before and after Brillouin amplification of the probe light emitted in a predetermined propagation mode at a predetermined optical frequency difference measured using the measurement-target optical fiber.

An Optical Time Domain Reflectomeler (OTDR) tests an optical fiber by generating, transmitting, and receiving light signals from an optical fiber. The OTDR generates light signals having different characteristics and stitches these light signals into an OTDR trace. Backscatter and properties such as dynamic range effect the quality of the OTDR trace.

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.

The deep penetration of optical transmission from the very edges of the network with optical access networks to the very core with routing data within data centers before transmission has resulted in competing demands for increased functionality, reduced cost, enhanced manufacturability, and reduced footprint. At the same time monitoring and fault detection with prior art optical time domain reflectometry systems have not kept up to the demands of these networks and systems as they are expensive test equipment based solutions. It would be beneficial to provide embedded OTDR functionality within each transmitter, receiver or transceiver deployed within the network allowing every link to be monitored continuously. It would be further beneficial for such embedded OTDRs to meet the demands for lower cost, high volumes, and smaller footprints with enhanced manufacturability.

In some examples, a tunable dense wavelength division multiplexing (DWDM) optical time-domain reflectometer (OTDR) may include a fiber optic link analyzer, executed by at least one hardware processor, to determine, based on a user input, for a fiber optic link of a plurality of fiber optic links of a fiber optic cable, whether the fiber optic link is active or not active. The DWDM OTDR may specify, based on a determination that the fiber optic link is active, a test wavelength that is different from a data transmission wavelength of data transmitted by the fiber optic link. A DWDM multiplexer may be collocated with the DWDM OTDR to selectively connect, based on the specified test wavelength, the DWDM OTDR to the fiber optic link of the plurality of fiber optic links for testing of the fiber optic link.