Oki Electric Industry Co., Ltd.

Kengo Koizumi

Hitoshi Murai

Hideyuki Iwamura

Tokuo Yamaguchi

To reduce costs by adopting a direct modulation system in which a semiconductor laser is directly modulated. An optical fiber sensor includes a light source configured to generate an optical pulse as probe light by a direct modulation system, an optical bandpass filter configured to extract anti-Stokes light that is a component on an anti-Stokes side of Brillouin scattered light from backscattered light generated by the probe light in an optical fiber to be measured, an interference signal acquisition unit configured to generate an interference signal by self-delayed heterodyne interference from the anti-Stokes light extracted at the optical bandpass filter and input to the interference signal acquisition unit and a Brillouin frequency shift acquisition unit configured to acquire a Brillouin frequency shift amount from the interference signal.

Optical fiber sensor and Brillouin frequency shift measurement method

To expand a measurement range with regard to SDH-BOTDR. A BFS1 and a BFS2, which is obtained by inverting the BFS1, are acquired on the basis of a first measurement signal and a first local oscillation signal that is a cosine wave, a BFS3 is acquired on the basis of a second measurement signal and a second local oscillation signal that is a sine wave, and a Brillouin frequency shift waveform is synthesized from the BFS1 to BFS3. In the case where an optical fiber is not strained or in the case where temperature of the optical fiber is not changed, a phase rotation number N, which is a phase difference between a measurement signal and a local oscillation signal, is calculated on the basis of intensity of the measurement signal, and an offset corresponding to the phase rotation number N is given to the synthesized Brillouin frequency shift waveform.

Optical fiber strain and temperature measurement apparatus and optical fiber strain and temperature measurement method

To uniquely determine a Brillouin frequency shift (BFS) even if a relation between phase and intensity of an intensity signal corresponding to a phase difference between the two optical paths in an interferometer varies. An optical fiber sensor includes a reference section average value calculation unitconfigured to acquire average intensity in a reference section, a phase control unitconfigured to control a delay unit in such a manner that a phase difference between two optical paths is swept from 0 to 2&#x3c0;, a Brillouin scattering coefficient elimination unitconfigured to eliminate a Brillouin scattering coefficient from an interference signal by using an intensity signal, a phase/amplitude calculation unitconfigured to acquire an initial phase &#x3c6;and amplitude of the interference signal by using a relation between average intensity Iand the phase obtained through the phase sweep from 0 to 2&#x3c0;, a normalization unitconfigured to use the amplitude of the interference signal to normalize the interference signal from which the Brillouin scattering coefficient is eliminated, and a BFS computation unitconfigured to compute a BFS by using the normalized interference signal.

Optical fiber sensor and brillouin frequency shift measurement method

A self-delayed homodyne interferometer includes light source unit, a splitting unit, an interference signal acquisition unit, a scattered light intensity acquisition unit, and a signal processing unit. The light source unit generates probe light. The splitting unit splits into two branches, Brillouin backscattered light occurring in an optical fiber to be measured with the probe light. The acquisition unit receives scattered light of one branch, and uses a self-delayed homodyne interferometer to generate an interference signal. The acquisition unit receives scattered light of the other branch, and acquires intensity of the scattered light. The signal processing unit separates and acquires a frequency shift amount from the intensity of the interference signal, and strain and temperature change from the intensity of the scattered light. The acquisition unit can change a phase of the scattered light of the one of the two branches.

The light source unit generates probe light. The splitting unit splits Brillouin backscattered light, which arise in the optical fiber under test owing to the probe light, into two branches of a first light path and a second light path. The delay unit gives a delay between light propagating through the first light path and the second light path. The multiplexer unit multiplexes light propagating through the first light path and the second light path to generate multiplexed light. The coherent detection unit performs heterodyne detection on the multiplexed light to output a difference frequency as a first electrical signal. The frequency shift amount obtaining unit performs homodyne detection on one of the two branches split from the first electrical signal and the second electrical signal having the same frequency as the frequency of the first electrical signal to obtain a frequency shift amount. The signal intensity obtaining unit generates intensity information of the first electrical signal as an intensity signal. The signal processing unit obtains strain &#x3b4;&#x3b5; and a temperature change &#x3b4;T separately from the frequency shift amount and the intensity.

Measurement apparatus and measurement method

By removing remaining components of Rayleigh scattered light, control is sufficiently performed of polarization states even when the wavelength of scattered light has changed. A light source unit configured to generate probe light, a wavelength control unit configured to receive backscattered light emitted from an optical fiber to be tested by the probe light and to output Brillouin backscattered light included in the backscattered light, and a self-delayed heterodyne interferometer to which the Brillouin backscattered light is input are included. The wavelength control unit includes a wavelength separation filter, a variable wavelength filter, an optical intensity measurement unit, and a control unit. The wavelength separation filter has two output ports, outputs and transmits, from one of the two output ports, the Brillouin backscattered light to the variable wavelength filter, and outputs and transmits, from the other output port, Rayleigh scattered light to the optical intensity measurement unit. The optical intensity measurement unit measures a center wavelength and a peak intensity of the Rayleigh scattered light. The control unit controls a cutoff wavelength of the variable wavelength filter in accordance with a direction and amount of change of the center wavelength.

Optical fiber strain and temperature measurement apparatus

A measuring apparatus includes a light source unit configured to generate probe light, a bifurcating unit configured to cause Brillouin backscattered light occurring from the probe light to bifurcate into first light, which propagates through a first optical path, and second light, which propagates through a second optical path, a delay unit configured to delay one of the first light and the second light, an optical multiplexer configured to multiplex the first light and the second light to generate multiplexed light, and a coherent detector configured to perform homodyne detection of the multiplexed light and to output a difference frequency obtained as a result of the detection as a phase-difference signal.

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Tokyo, Japan

Kengo Koizumi