A distributed optical fiber sensor capable of measuring strain and/or temperature with high accuracy and high spatial resolution without requiring any manual adjustment. The distributed optical fiber sensor utilizing the Brillouin scattering phenomenon comprises a stepwise optical pulse light source generating an optical pulse having a stepwise distribution of light intensity increasing toward the center, a CW light source generating a continuous light, a sensing optical fiber which receives an optical pulse as a probe light and the continuous light as a pumping light and in which a Brillouin scattering phenomenon occurs between the probe light and the pump light, and a Brillouin time domain detector for determining the Brillouin loss or the gain spectrum from the light emerging from the sensing optical fiber and attributed to the Brillouin scattering phenomenon, and determining the distribution of strain caused in the sensing optical fiber in the longitudinal direction thereof and/or the distribution of temperature from the Brillouin loss or gain spectrum.

Distributed optical fiber sensor

The present invention relates to an optical fiber filter provided with a portion which selectively reflects or transmits light of a specific wavelength, this portion comprised of a multimode optical fiber in which the refractive index of the core changes periodically along the longitudinal direction thereof. Furthermore, this multimode optical fiber has an input end and an output end, with at least the input end of the multimode optical fiber being connected to a single mode optical fiber. As a result of forming an optical fiber filter in this way, it is possible to realize an optical fiber filter that exhibits no transmission loss at wavelengths other than the center wavelength.

optical fiber filter

Coherent light emitted from a coherent light source 1 is sent as a probe beam through a connector 31 into an optical fiber being measured. A portion of this beam is sent to an optical frequency converter 100 to form an optical pulse train having a frequency which is frequency-swept in steps of a designated frequency at a designated periodicity, and an optical pulse having a designated frequency is extracted from the optical pulse train by an electro-optic switch 18 and sent to the optical fiber being measured. Then, a signal beam exiting the optical fiber being measured is heterodyne-received by means of a local beam passing through either a connecting optical fiber 6 side or a frequency shifter 7 side according to the selection of optical switches 4 and 5. Consequently, it is possible to measure the characteristics of the optical fiber by means of a BOTDR, BOTDA or a COTDR.

Optical fiber characteristic measuring device

An improved backward Brillouin scattering optical time domain reflectometry (OTDR) device is provided which is capable of detecting the deterioration of or anticipating the fracture in an optical cable or optical fiber and measuring the position of the failure part with high resolution. To accomplish this, the OTDR constantly or periodically supplies an optical pulse having a power level of +8 dBm or higher from an optical pulse generator 20 to an optical cable, monitors a power ratio between the optical pulse supplied to the optical cable and a reflected pulse by an optical power comparator 40, detects correlation between the supplied optical pulse and the reflected pulse by a correlation detector 27 while switching the supplied optical pulse to a pseudo random optical pulse, and calculates the failure position of the optical cable when the factor of correlation shows the maximum value.

Backward brillouin scattering optical time domain reflectometry

An apparatus for measuring the characteristics of an optical fiber is provided. An optical pulse generator generates, from a coherent light, first and second optical pulses having a time interval which is equal to or shorter tan a life time of an acoustic wave in the optical fiber. A detector couples the coherent light with a Brillouin backscattered light which includes first and second Brillouin backscattered lights belonging to the first and second optical pulses respectively, thereby generating an optical signal. The detector further converts the optical signal into an electrical signal. A signal processor takes the sum of the electrical signal and a delay electrical signal which is delayed from the electrical signal by a delay time corresponding to the time interval, thereby generating an interference signal, and finds the characteristics of the optical fiber based on the interference signal.

Apparatus for measuring the characteristics of an optical fiber

PURPOSE:To enhance operability by performing adjustment only once, by subjecting an amplifying optical fiber provided other than an optical fiber to be measured to a light amplifying state wherein Brillouin light amplification is made possible. CONSTITUTION:An amplifying optical fiber 6 provided other than an optical fiber 9 to be measured is set to a light amplifying state making Brillouin amplification possible to optically amplifying the back Rayleigh's scattering light from the optical fiber 9 to be measured to detect the same. Therefore, the adjustment for allowing the difference between the frequency of an exciting light source, which is necessary for realizing a Brillouin light amplification state, and that of a searching light source to coincide with the frequency of the acoustic wave inherent to a medium may be once performed and operability is enhanced. By using a polarized wave holding optical fiber as the amplifying optical fiber, a constant mu-factor is obtained.

Apparatus for measuring back scattering light

PURPOSE: To take a measurement with high accuracy even if there is variance in the constituent material by correcting variance in the parameter of the optical waveguide by utilizing the relation between variation of the constituent material of the optical waveguide and variation in the reflection coefficient of back Rayleigh scattered light. CONSTITUTION: A reference optical fiber (s) and a test optical fiber (t) are connected to each other and an OTDR measuring instrument 1 is connected to the side of the fiber (s). A step of the signal (light) intensity in a measured waveform at a connection point (× mark) shows even a difference in back Rayleigh scattered light intensity due to the difference in structural parameter between both fibers (s) and (t). The intensity ratio Rs/Rt of signal light beams returning from before and behind the connection point is measured by a device 1 to find the specific refractive index difference Dt of the fiber (t). The Brillouin frequency shift f b0 (Dt) of the fiber (t) when strain is zero from the difference Dt is obtained. The strain (e) of the fiber (t) is found by specific arithmetic from the shift f b0 (Dt) and the measured Brillouin frequency shift f b (D,e) of the fiber (t). Thus, the variation of the Brillouin frequency shift of the fiber (t) can be corrected and the measurement is taken with high accuracy. COPYRIGHT: (C)1991,JPO&Japio

Method and device for measuring strain or temperature of optical waveguide

PURPOSE:To effectively evaluate an optical fiber characteristic by allowing a probing light from a probing light source to be made incident on an optical fiber to be measured, taking out selectively a generated back Brillouin scattered light and detecting it by a photodetector. CONSTITUTION:A probing light emitted from a probing light source 1 is sent to an optical fiber to be measured and generates a Brillouin scattered light. Subsequently, a back Brillouin scattered light which is scattered in the rear in the optical fiber to be measured 4 is taken out selectively by a selecting and taking out device 6. In this state, an optical demultiplexer 2 couples the probing light from the probing light source 1 to the optical fiber to be measured 4, and also, couples the back Brillouin scattered light generated in the optical fiber to be measured 4 by its probing light to the selecting and taking out device 6. The back Brillouin scattered light which has been fetched by this selecting and taking out device 6 is detected by a photodetector 7, and an electric signal which has been brought to photoelectric conversion is brought to signal processing 8. In such a way, an optical fiber network containing not only a cascaded optical fiber line but also a branch fiber line can be measured and evaluated by separating each optical fiber loss or fault position.

Optical fiber characteristic evaluating device

PURPOSE: To measure the characteristic distribution of an optical fiber with high accuracy by utilizing the amplification of Brillouin light between 1st and 2nd signal light which opposingly propagates in the optical fiber and analyzing the waveform of the 2nd signal light which receives the effect of said amplification. CONSTITUTION: The pulse-like signal light S1 (light frequency f 1 ) projected from a light source 1 is connected to the terminal 3-1 of the optical fiber to be measured 3 through a multiplexer/demultiplexer 4. The signal light S2 (light frequency f 2 ) projected from a light source 2 for CW oscillation is connected to the terminal 3-2. At such a time, the amplification of Brillouin light is performed with the light S2 and S1 by controlling 7 so as to obtain f 1 -f 2 =fB (fB is a Brillouin shift frequency peculiar to the optical fiber 3). A signal processor 6 receives the electrical signal of the light S2 detected by a photodetector 5 and analyzes the temporal waveform of said signal to obtain the light loss of the fiber 3 from the attenuation factor of the component amplified with the light amplification or the level difference of light receiving signal on an optional point. If the light power of the light source 2 is increased, the level of the light receiving signal can be increased. COPYRIGHT: (C)1990,JPO&Japio

Method and device for estimating characteristic of optical fiber

PURPOSE: To accomplish optical coupling with low loss by optically coupling a fiber Fabry-Perot interference element and 1st and 2nd optical connector ferrules by the aligning action the of a split sleeve. CONSTITUTION: The diameter of the ferrule of the ferrule of the fiber Fabry- Perot interference element 6 is made the same as those of the 1st and the 2nd optical connector ferrules 4-1 and 4-2 which are attached to light incident and exiting optical fibers 5-1 and 5-2. Then, the incident optical fiber connector ferrule 4-1, the fiber Fabry-Perot interference element 6, and the exiting optical fiber connector ferrule 4-2 are inserted in the same split sleeve 3 in this order. By using the same split sleeve 3, the aligning effect of the fiber in the ferrule by the split sleeve 3 is utilized over two steps. Thus, the filter which is small- sized and easy to attach and whose coupling loss is low is obtained. COPYRIGHT: (C)1991,JPO&Japio

Mitsuhiro Tatsuta

Papers

Apparatus for measuring back scattering light

Method and device for measuring strain or temperature of optical waveguide

Optical fiber characteristic evaluating device

Method and device for estimating characteristic of optical fiber

Optical frequency filter