AU2020103313A4 - A distributed optical fiber Fizeau interferometer based on the principle of optical time domain reflection (OTDR) - Google Patents
A distributed optical fiber Fizeau interferometer based on the principle of optical time domain reflection (OTDR) Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
- G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/212—Mach-Zehnder type
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- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Instruments For Measurement Of Length By Optical Means (AREA)
Abstract
The invention proposes a distributed optical fiber Fizeau interferometer based on optical time
domain reflection, for distributed optical fiber sensing and measurement. The system consists of:
a broad spectrum light source (1), a three-port fiber circulator (2), a Mach-Zehnder
Interferometer (5) comprising 2 x 2 fiber couplers (3) and (4), a sensing fiber (6), a photodetector
(9), a photodetector (10), and a differential signal amplifying processing circuit (11). In this
system, optical time domain reflection allows for distribution measurements; interferometric
characteristics allow for small disturbance measurements; differential signal detection can cancel
out the average strength signal, multiplying the interference signal. The two light pulse signals
are in the same fiber with the same ambient temperature variation, eliminating the effects of
temperature. Thus, the use of this distributed Fizeau interferometer can be widely applied to the
distributed disturbance measurement and the safety monitoring of ambient environment.
1/3
DRAWINGS
1 2 3 5 4 8 9
Iz
PD, PD 12
9 10
11
S(zt)A[S2(z,t)-S(z,t)J
FIG. 1
(a) (b) (c)
FIG. 2
FI G.
6 r
9 Z
PD, PD2 12
13 A 10
S(zt)=-A[S2(zI)-S (z,t)]
FIG. 3
Description
1/3 DRAWINGS
1 2 3 5 4 89
Iz
PD, PD 12 9 10 11
S(zt)A[S2(z,t)-S(z,t)J
FIG. 1
(a) (b) (c) FIG. 2
6 r 9 Z PD, PD2 12
13 A 10
S(zt)=-A[S2(zI)-S (z,t)]
FIG. 3
A distributed optical fiber Fizeau interferometer based on the principle of optical time domain
reflection (OTDR)
[0001] The invention proposes a distributed optical fiber Fizeau interferometer based on the
principle of optical time domain reflection (OTDR), which can be used for the sensing and
measuring of distribute optical fibers, belongs to the optical fiber sensing technology field.
[0002] Take advantage of the fact that the backscattered Rayleigh light in the transmission fiber
carries information about the fiber's position and external disturbances, using the white light
interference technique and the spectroscopic method of optical-path separation of a single optical
pulse to produce two pulses before and after an unbalanced Mach-Zehnder interferometer, a
distributed optical fiber Fizeau interferometer based on the principle of OTDR can be
constructed, which offers the possibility of sensing and measuring the distributed interference.
[0003] The OTDR invented in 1976 by M.K. Barnoski and S.M. Jensen, allows the distribution
measurement of optical fiber losses by detecting the backscattered light in the optical fiber.
When a narrow pulse of light is injected into the fiber under test, the system can check the
continuity in the fiber and measure its attenuation by measuring the change of the backscattered
light intensity with time, thus determining the length of the fiber under test and the distribution
of losses along the line. The non-destructive, one-end-only, intuitive and fast advantages of
OTDR test methods make them indispensable in the production, construction and maintenance of
optical fiber cables. However, the traditional OTDR techniques only measure the backscattered
intensity signal, hence they are only sensitive to end faces, breakpoints, or large fixed bending
losses, and are less sensitive to small disturbances in the fiber over time, such as vibration
signals. To this end, the disclosed invention technology patent CN101290235A gives an
interference-type OTDR, on the basis of the original OTDR, it uses a 2 x 2 coupler, and adds a
reference fiber, so as to achieve that on the basis of the backscattered intensity signal,
superimpose the distributed interference information. However, due to the separation of the
detection optical fiber and the reference optical fiber, the temperature effect is difficult to
overcome. On the other hand, a smaller interference signal is superimposed on a larger intensity
signal, resulting in a low detection sensitivity of the system. In order to solve the shortcomings
of the separation of the detection optical fiber and the reference optical fiber, the invention
technology patent number CN102809421A uses a polarized light beam splitter on the basis of the
traditional OTDR, which uses the polarized orthogonal separation on the backscattering light and
amplifies it in a differential manner. On the one hand, this loses the characteristics of
interferometry; on the other hand, it also degrades the positioning accuracy of vibration detection
due to the effect of ambient temperature changes on optical fiber birefringence.
[0004] In order to overcome the above-mentioned drawbacks and shortcomings, a distributed
optical fiber Fizeau interferometer based on the principle of OTDR is proposed. The light source
used is a white light source, and a single light pulse is optical-path-separated by an unbalanced
Mach-Zehnder interferometer in the same optical fiber to form two backscattered Rayleigh
signals, the optical paths of the two pulses of light are compensated by the same unbalanced
Mach-Zehnder interferometer, and a distributed Fizeau interferometer is formed for the
distributed measurement. At the same time, differential detection and amplification of the two
signals is performed by taking advantage of the inverse interference signal characteristic of the two detection ports of the 2x2 fiber coupler. On the one hand, this automatically eliminates the intensity backscattering signal, which does not cause interference, and on the other hand, it also eliminates the backscattering intensity signal background in the coherent signal. In addition, the interference signal is multiplied. Due to the advantages of optical interferometry, such as high sensitivity, large dynamic range, fast response, long transmission distance, etc., and the fact that the back and forward pulses in the same optical fiber are in a common optical path, the temperature change has the same effect on the optical path of both pulses, which makes it possible to automatically compensate for the temperature effect. Therefore, this new optical time-domain scattering Fizeau interferometer is expected to be able to detect and locate long distance distributed small disturbances.
[0005] To overcome the drawbacks of existing technology, the invention proposes a distributed optical fiber Fizeau interferometer based on the principle of OTDR, that can be used for the sensing and measuring of distributed optical fibers, as shown in FIG. 1. It is characterized by: the system consists of a broad spectrum light source (1), a three-port fiber circulator (2), an unbalanced Mach-Zehnder Interferometer (5) comprising 2 x 2 fiber couplers (3) and (4), a sensing fiber (6), a photodetector (9), a photodetector (10), and a differential signal amplifying processing circuit (11). The light emitted by the broad spectrum light source (1) is fed into the system by the three-port fiber circulator (2), the other two ports of the three-port fiber circulator are connected to the fiber coupler (3) and the photodetector (9), respectively, and the other port of the fiber coupler (3) is connected to the photodetector (10). The photodetector (9) and the photodetector (10) are then connected to the differential signal amplifying circuit (11), and the output of the fiber coupler (4) is connected to the sensing fiber (6).
[0006] The light pulses emitted by the broad spectrum light source (1) are passed through a three-port fiber circulator (2) and arrive at an unbalanced Mach-Zehnder interferometer (5) consisting of two 2 x 2 fiber couplers (3) and (4) with an optical range difference of nAL. The light pulses are uniformly divided into two pulses (7) and (8) in front of and behind, and form an optical range difference of nAL. The two light pulses transmitted forward along the optical fiber are Rayleigh scattered along the way, and the resulting two backscattering Rayleigh light are transmitted back along the same optical fiber. The optical paths of the reflected back and forward scattered light signals are compensated for by an unbalanced Mach-Zehnder interferometer (5).
Since the two pulses of incident light are of equal light amplitudes and have the same frequency
as the incident light, the Rayleigh scattering light is generated by the same mechanism, and if the
phase matching condition is satisfied, there will be an interference, and the coherent signals will
be received by two photodetectors (9) and (10) respectively. Since the two coherent signals
received by the two detectors are output from the two ports of the 2 x 2 fiber coupler, the phases
are reversed, and after passing the differential signal amplifying processing circuit (11), it
automatically cancels out the backscattered signals and the DC portion of the coherent signal
which are irrelevant to the interferometry, while the measured coherent signal is differentially
enhanced. In addition, since the two interference signals are in a common optical path, this
constitutes a distributed backscattered Fizeau interferometer and automatically eliminates the
influences of ambient temperature.
[0007] The system can use a standard single-mode telecommunication optical fiber, or any
polarization maintaining optical fibers, as shown in FIG. 2. When a polarization maintaining
fiber is used for the sensing system, it helps to improve the interference performance of the
system. The two transmission fibers receiving optical signals should be of equal length to ensure
that the two backscattered light signals are received simultaneously. In order to equalize the
intensity of the two optical signals to achieve a large dynamic range and high detection
sensitivity, one of the optical signals requires the addition of an optical attenuator (12) to adjust
the intensity of the backscattered light signal, as shown in FIG. 3. In order to improve the signal
to-noise ratio of the system, the present invention may also use a method of coding modulation
to the light source or the electro-optical signal modulator to achieve this purpose. In addition,
without violating the spirit of the present invention, a modulation signal generator (13) can be
added to the system to directly modulate the broad spectrum light source superluminescent diode
(SLD). Or to use an amplified spontaneous emission (ASE) broad spectrum light source with a
higher power, and add an electro-optical signal modulator (14), the modulation signal generator
(13) modulates the optical signal of the electro-optical signal modulator (14) to improve the
signal-to-noise ratio of the system, as shown in FIG. 4. In order to improve the system's ability to
recognize and determine the disturbance signal, the present invention can also add a fiber end
reflector (15), as shown in FIG. 6, to reflect back the two separated back and forward optical
pulse signals in turn at the fiber end, forming a long-arm Fizeau interferometer with a common
fiber path. First, the signal is afiber-end-reflected signal, which has a large signal amplitude for
the backscattered light, and can be used to distinguish whether the system has completed a full
process dynamic interferometric scan of the tag signal; second, the disturbance information of
the signal is contained in a group of backscattered interference signals preceding the signal, and
thus the signal can be used as a judgment signal of confirmation check to identify whether a
disturbance event has occurred in the system.
[0008] The objective of the invention is achieved as follows:
[0009] The working principle of the distributed Fizeau interferometer based on the principle of
OTDR is shown in FIG. 1. The light emitted from the pulsed light source is divided into two
coherent light of equal power by a 2 x 2 coupler with a spectral ratio of 1:1, and they pass
through an unbalanced Mach-Zehnder interferometer, resulting in an optical path difference nAL.
The two light pulses transmitted forward along the optical fiber are scattered by Rayleigh along
the way, and the resulting two backscattering Rayleigh light will be transmitted back along the
same optical fiber. The reflected back and forward scattered light signals are passed through an
unbalanced Mach-Zehnder interferometer, and the photodetectors should detect three groups of
backscattering signal pulses, as shown in FIG. 5. The two light pulses whose optical path is
compensated interfere with each other, while the two light pulses which are not compensated by
optical path are backscattered intensity signals, the timing diagram of the received optical signals
is shown in FIG. 5.
[0010] The two backscattering Rayleigh signals of the back and forward pulsed light along the same fiber are optical-path-compensated, then after passing the coupler, since both of them have the same frequency as the incident light and the power of both incident light is equal, the mechanism of Rayleigh scattering is the same. Assuming that the phase difference change of the two Rayleigh scattering light is much lower than the frequency of light wave electric field, the phase difference change is relatively slow. Therefore, they will be equivalent to a Fizeau interferometer and form an interference signal at each of the two ports of the coupler, so that the light signals arriving at the light detectors PD i and PD 2 will be Si(z, t) and S2(z, t), respectively. The distributed dynamic interference signal after differential amplification is S(z, t)= A[S2(z, t) Si(z, t)], where A is the signal amplification factor.
[0011] Compared to the prior art, the disclosed distributed optical fiber Fizeau interferometer based on the principle of OTDR has the following distinctive features: (1) OTDR characteristic enables distributed measurement; (2) interferometric characteristic - enables measurement of small disturbances; (3) differential signal detection characteristic - cancels out the mean intensity signal while multiplying the interference signal; (4) automatic temperature compensation characteristic - since two optical pulse signals are located in the same optical fiber, the ambient temperature change is considered to be the same, which automatically eliminates the effect of temperature.
[0012] FIG. 1 is a schematic representation of the structure of a distributed optical fiber Fizeau interferometer based on the principle of OTDR.
[0013] FIG. 2 (a) is a cross-section of a typical standard single-mode telecommunication optical fiber, (b) is a cross-section of a panda polarization maintaining optical fiber, and (c) is a cross- section of a bowtie polarization maintaining optical fiber.
[0014] FIG. 3 is a schematic diagram of the architecture of a distributed Fizeau interferometer
system with the addition of a direct signal coding modulator for the light source.
[0015] FIG. 4 is a schematic diagram of the structure of a distributed Fizeau interferometer
system with the addition of a high-power ASE light source, along with the addition of an electro
optical modulator and a signal coding modulator that encode and modulate the light pulses.
[0016] FIG. 5 is a timing diagram of the distributed optical fiber Fizeau interferometer based on
the principle of OTDR when receiving signals.
[0017] FIG. 6(a) shows a distributed Fizeau interferometer system with a fiber end reflector; (b)
shows a schematic diagram of the interference signal corresponding to the reflector.
[0018] The invention is described in more detail below in connection with the drawings:
[0019] Embodiment 1:
[0020] In conjunction with FIG. 1, the present embodiment is, a light pulse emitted by a broad nL spectrum light source has a pulse width of Tand a pulse periodof - , to ensure that a second interrogation light pulse is sent after the backscattered light signal generated by the first light pulse has been received in an optical fiber of a length L. The light pulses from the light source pass through a three-port fiber circulator and are divided into two light signals of approximately equal optical power by a 3dB fiber coupler with a spectral ratio of 1:1, which are passed through an unbalanced Mach-Zehnder interferometer, and the optical path of n A L is formed. Since both pulses of light transmitted forward along thefiber will be Rayleigh scattered, the backscattering Rayleigh light from the two pulses will be transmitted along the fiber back to the unbalanced Mach-Zehnder interferometer. The two backscattering light pulses with optical path compensation have the same light amplitude, the frequency is same as the incident light, and the Rayleigh scattering light will be generated by the same mechanism, which will result in interference if the phase match condition is satisfied. One of the path is received by the photodetector PD after passing the three-port fiber circulator (loss at about l dB), at the same time, the other one is received directly by the photodetector PD 2 after attenuated by the optical attenuator. As the two coherent signals are received by the two detectors are output by the two ports of the 2 x 2 fiber coupler, so the phase is just opposite, adjust the attenuator, so that the two optical signal sizes can reach a balance. In this case, after passing the differential signal amplifier, the average intensity signal, which is not related to interferometry, is cancelled, and the two interference signals are multiplied differentially. At the same time, since the two pulsed optical signals share the same optical fiber, the change in optical path caused by the change in ambient temperature is almost identical, and the resulting phase difference remains unchanged. This automatically eliminates the influence of ambient temperature.
[0021] Embodiment 2:
[0022] In conjunction with FIG. 2, the second embodiment of the present invention differs from the first embodiment in that, in order to improve the signal-to-noise ratio, a modulation signal generator (13) is added to the first embodiment to directly encode and modulate the broad spectrum light source SLD. For example, using complementary code light pulses as detection pulses to improve the detection performance of this OTDR-based distributed Fizeau interferometer, and this can increase the effective measurement distance and reduce the time required for measurement without affecting the distance resolution.
[0023] Embodiment 3:
[0024] In conjunction of FIG. 3, the third embodiment of the present invention differs from the first embodiment in that, in order to further extend the detection distance and improve the signal to-noise ratio, a higher-power ASE broad spectrum light source is adopted on the basis of the first embodiment, and an electro-optical signal modulator (14) is added to encode the pulsed optical signal, and the modulation signal generator (13) performs the optical signal modulation on the fiber signal modulator (14). For example, pseudo-random codes are used to encode and decode the pulsed optical signals to improve the signal's rejection of noise.
Claims (3)
1. A distributed optical fiber Fizeau interferometer based on the principle of optical time
domain reflection (OTDR), which is characterized by: the system consists of a broad spectrum
light source (1), a three-port fiber circulator (2), an unbalanced Mach-Zehnder Interferometer (5)
comprising 2 x 2 fiber couplers (3) and (4), a sensing fiber (6), a photodetector (9), a
photodetector (10), and a differential signal amplifying processing circuit (11). The light emitted
by the broad spectrum light source (1) is fed into the system by the three-portfiber circulator (2),
the other two ports of the three-port fiber circulator are connected to the fiber coupler (3) and the
photodetector (9), respectively, and the other port of the fiber coupler (3) is connected to the
photodetector (10). The photodetector (9) and the photodetector (10) are then connected to the
differential signal amplifying circuit (11), and the output of the fiber coupler (4) is connected to
the sensing fiber (6).
2. As claimed in claim 1, a distributed optical fiber Fizeau interferometer based on the
principle of OTDR, its characteristics also include: 1) The system can use a standard single
mode telecommunication optical fiber, or any polarization maintaining optical fiber. 2) The two
transmission fibers receiving optical signals of the system are equal in length.
3) Add an optical
attenuator (12) in front of the photodetector (9) or the photodetector (10) for pre-adjustments. 4)
Add a modulation signal generator (13) for direct modulation of the broad spectrum light source
superluminescent diode (SLD). 5) Adopt a higher power amplified spontaneous emission (ASE)
broad spectrum light source. 6) Add an electro-optical signal modulator (14) to the broad
spectrum light source (1) and the three-port fiber circulator (2). 7) Modulate the signal generator
(13) to modulate the optical signal to the electro-optical signal modulator (14). 8) Add a reflector
(15) to the sensing fiber (6) end.
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| AU2020103313A AU2020103313A4 (en) | 2020-11-09 | 2020-11-09 | A distributed optical fiber Fizeau interferometer based on the principle of optical time domain reflection (OTDR) |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113340421A (en) * | 2021-07-05 | 2021-09-03 | 西安交通大学 | All-fiber micro spectrometer based on fiber end face Fizeau interference |
| CN113532539A (en) * | 2021-07-27 | 2021-10-22 | 安徽理工大学 | Optical fiber sensing system, method and device for simultaneously measuring temperature, strain and pressure |
| CN113607261A (en) * | 2021-07-19 | 2021-11-05 | 复旦大学 | Optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion |
-
2020
- 2020-11-09 AU AU2020103313A patent/AU2020103313A4/en not_active Ceased
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113340421A (en) * | 2021-07-05 | 2021-09-03 | 西安交通大学 | All-fiber micro spectrometer based on fiber end face Fizeau interference |
| CN113340421B (en) * | 2021-07-05 | 2023-02-28 | 西安交通大学 | All-fiber micro spectrometer based on fiber end face Fizeau interference |
| CN113607261A (en) * | 2021-07-19 | 2021-11-05 | 复旦大学 | Optical fiber sensing system with phase-sensitive optical time domain reflection and optical fiber interference fusion |
| CN113532539A (en) * | 2021-07-27 | 2021-10-22 | 安徽理工大学 | Optical fiber sensing system, method and device for simultaneously measuring temperature, strain and pressure |
| CN113532539B (en) * | 2021-07-27 | 2024-01-26 | 安徽理工大学 | Optical fiber sensing system, method and device for simultaneously measuring temperature, strain and pressure |
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