Brillouin scattering measurement method and brillouin scattering measurement system
AssigneeNeubrex Co., Ltd.
InventorTsuneo HORIGUCHI
Life of this patent
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Abstract
A Brillouin backscattered spectrum is obtained in such a way that two optical pulse pairs each composed of two pulses of different durations and of the same phase and n phase difference are launched into a sensing optical fiber; Brillouin backscattered lights produced by the optical pulse pairs are detected into signals for the respective optical pulse pairs; the signals are sampled with two window functions whose time widths are equal to respective pulse durations of the optical pulse pair and whose delay time is variable; each sampled signal is transformed with a predetermined transformation; products of the transformed signals are calculated; and subtraction between the products is performed.
Claims12
A Brillouin scattering measurement method for measuring a physical quantity from frequency shift variation of a Brillouin backscattered light, comprising:
- generating two types of optical pulse pairs each composed of two pulses of different durations, one of the pairs having pulses of the same phase and the other pair having pluses of different phases;
- detecting, with an optical heterodyne receiver, Brillouin backscattered lights respectively produced by launching the generated two types of optical pulse pairs into one end of an optical fiber;
- sampling the signals detected by the optical heterodyne receiver, with two window functions whose time widths are equal to respective pulse durations of the optical pulse pairs and whose delay time is variable;
- transforming the respective signals sampled with the two window functions, with a predetermined transformation;
- calculating products of the two signals, which respectively correspond to the two types of optical pulse pairs, transformed with the predetermined transformation;
- and
- subtracting the calculated products from each other, thereby to obtain a spectrum of the Brillouin scattered light.
A Brillouin scattering measurement system for measuring a physical quantity from frequency shift variation of a Brillouin backscattered light, comprising:
- a light source, or a first light source and a second light source different from the first light source;
- a pulse modulator for modulating a light emitted from the light source or any one of the two light sources to an optical pulse pair each composed of two pulses having different durations;
- a pulse phase modulator for modulating the optical pulse pairs modulated by the pulse modulator to two types of optical pulse pairs, one of the optical pulse pairs having the pulses of the same phase and the other pair having the pulses of different phases;
- a first optical coupler for receiving the two types of optical pulse pairs to launch the received optical pulse pairs into one end of an optical fiber through an input path of the coupler and for receiving Brillouin backscattered lights produced in the optical fiber, to output the backscattered lights through a path different from the input path;
- a second optical coupler for receiving the Brillouin backscattered lights output from the first optical fiber along with the light emitted from the light source or a light emitted from the other of the first or the second light sources, to output the two kinds of lights individually;
- a balanced photodiode for individually receiving the two kinds of lights output from the second optical coupler, to output one kind of signals after adjusting balance of the input signals;
- and
- a signal processor for processing the signal output from the balanced photodiode, wherein
- the signals of the Brillouin backscattered lights produced by the two types of optical pulse pairs are individually processed with the signal processor in such a way that the signals received by the balanced photodiode are sampled with two window functions whose time widths are equal to the respective durations of the pulses of the optical pulse pairs and whose delay time is variable;
- and the two windowed signals are transformed with a predetermined transformation;
- and the transformed signals, which respectively correspond to the two types of optical pulse pairs, are multiplied by each other;
- and then the calculated products are subtracted from each other, thereby to obtain a spectrum of the Brillouin backscattered light.
Dependencies are inferred from the claim text.