CN113804283A - System and method for testing phase noise of interference type optical fiber hydrophone - Google Patents
System and method for testing phase noise of interference type optical fiber hydrophone Download PDFInfo
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Abstract
The invention discloses a phase noise test system and method for an interference type optical fiber hydrophone, and designs a time division multiplexing array noise test optical system and a photoelectric signal processing system which comprise an optical fiber phase controller, wherein the phase controller is driven to enable an initial phase of an array interference signal to sweep by 0-2 pi, phase noise at a corresponding initial phase is synchronously tested and averaged for a short time, and a conversion result from intensity noise to phase noise of a remote system to be tested in a full state is obtained through a phase noise test result of an initial phase change period. The method can effectively eliminate noise test errors caused by initial phase change, shorten test time, synchronously obtain the light intensity noise and noise conversion characteristics of the system to be tested, and is particularly suitable for phase background noise test and performance evaluation of a low-signal-to-noise-ratio remote large-scale optical fiber hydrophone multiplexing array system.
Description
Technical Field
The invention relates to the technical field of phase noise testing, in particular to a system and a method for testing phase noise of an interference type optical fiber hydrophone.
Background
The optical fiber hydrophone is a hydroacoustic sensor using optical fibers as optical sensing and transmission media, can be used for detection of ocean sound fields and seismic fields, and is of an optical fiber interference type structure at present. By combining with the existing optical fiber communication technology, the optical fiber hydrophone can conveniently establish various underwater optical fiber sensing and transmission networks, effectively improves the array scale and the remote transmission distance, and provides an ideal technical approach for solving the large-scale application problems of ocean underwater sound detection, submarine energy exploration and the like.
With the continuous expansion of the scale of the optical fiber hydrophone array, the number of elements rises from hundreds to tens of thousands, the transmission distance is gradually expanded to hundreds or even thousands of kilometers, the optical loss of the system is increased rapidly, and different types of optical amplifiers, such as an optical power amplifier, an optical on-line amplifier, an optical preamplifier and the like, need to be added at different positions to compensate the system loss. Meanwhile, the addition of the multistage optical amplifier can also bring amplified spontaneous emission noise, and the noise is the random disturbance of the broadband light intensity, so that the optical signal-to-noise ratio of the hydrophone is reduced, and finally the integral lifting of the phase noise background of the hydrophone system is caused.
In a fiber optic hydrophone system, the signal optical power is assumed to be PpThe optical power of the intensity noise introduced by the optical amplification is PnThe optical signal-to-noise ratio of interference light intensity of the hydrophone is as follows:
let the phase signal take into account only the hydrophone system noise
The interference signal containing the light intensity noise is photoelectrically converted into:
in the above formula, V is the visibility of the interferometer, and the value is 1 under an ideal condition, and R is the photoelectric conversion responsivity;
system intrinsic phase noise associated with laser frequency dithering, photo detectors, a/D quantization and the like,
the initial phase of the two arms of the interferometer.
Influenced by factors such as external extremely low frequency temperature drift and environmental disturbance, the drift is slowly and randomly drifted between 0 pi and 2 pi, and the slow drift time and amplitude have larger uncertainty.
In a typical fiber optic hydrophone short-range noise test system, PnExtremely low and usually negligible, and
not in the detection frequency band of the hydrophone signal, can also be eliminated by high-pass filtering
Influence of slow drift on signal detection, namely actually measured phase noise which is system intrinsic noise
But in PnIn a large-scale long-distance optical fiber hydrophone test system with high occupation ratio, because the intensity noise has large amplitude and is white noise with broadband, the intensity noise cannot be directly filtered out, and the intensity noise is high in amplitude and is white noise with broadband, the intensity noise cannot be directly filtered outAfter phase demodulation and high-pass filtering, the final phase noise floor
Comprises the following steps:
in the above formula
Is a conversion term of intensity to phase noise, and
f is a nonlinear noise transfer function which is related to the initial phase
The values, the phase demodulation method of the optical fiber hydrophone and the OSNR and other parameters of the system are closely related. Under the general condition of
And k is an integer, and when k is an integer,
maximum;
when the temperature of the water is higher than the set temperature,
minimum; when in use
Random variation within a period of 0-2 pi,
with consequent fluctuations. Especially in fiber optic hydrophones where the OSNR is low and
under the conditions of (a) under (b),
will result in
A large amplitude change. FIG. 1 shows the measured phase noise floor (0 dB-1 rad/sqrt (Hz)) of a fiber optic hydrophone system with an OSNR below 18dB as a function of the initial phase
Results of the changes:
in fig. 1, during the process of the initial phase rising straight, the phase noise changes from-87 dB to-94 dB, and the fluctuation amplitude is about 7 dB. The results show that the conversion of intensity to phase noise is non-linear and closely related to the initial phase of the hydrophone system. Therefore, the special rule that the conversion from intensity to phase noise changes along with the initial phase brings difficulty to the accurate test of the phase noise of the optical fiber hydrophone system under the condition of low signal to noise ratio.
The background noise test schemes of the existing optical fiber hydrophones are not considered
The method adopts a direct test and averaging test method, and is suitable for the optical fiber hydrophone system with short distance, small scale and high OSNR. However, the above analysis shows that, when the direct test method is used for testing a large-scale remote transmission optical fiber hydrophone system, due to the introduction of the multistage optical amplification equipment,
relatively large, measured
Followed by
Large amplitude fluctuations occur, which will have a great influence on
The test accuracy of (2). In addition, when performing a phase noise test, it is usually necessary to perform a good external environment sound/vibration shielding for the hydrophone to be tested,
the phase noise test method is slightly influenced by the outside and slowly changes, and a long initial phase random drift and average time are always required to wait for obtaining a relatively comprehensive phase noise average result, so that uncertainty is brought to the test time and the test result of the phase noise of the optical fiber hydrophone.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a system and a method for testing the phase noise of an interference type optical fiber hydrophone, which can effectively eliminate the noise test error caused by initial phase change, shorten the test time, synchronously obtain the light intensity noise and the noise conversion characteristic of a system to be tested, and are particularly suitable for the phase background noise test and the performance evaluation of a remote large-scale optical fiber hydrophone multiplexing array system with low signal-to-noise ratio.
In order to achieve the above object, the present invention provides a phase noise testing system for an interferometric fiber optic hydrophone, comprising:
the signal transmitting unit is used for outputting a single pulse signal of the system to be tested;
the remote transmission unit comprises a downlink transmission optical fiber, an uplink transmission optical fiber and an optical amplifier, wherein the incident end of the downlink transmission optical fiber is connected with the signal transmitting unit and is used for remotely transmitting the single-pulse signal;
the interference unit comprises an input end, an output end and a phase controller, wherein the input end of the interference unit is connected with the emergent end of the downlink transmission optical fiber and is used for converting the single-pulse signal into a single-pulse interference signal and outputting the single-pulse interference signal;
the time division multiplexing unit comprises an input end and an output end, the input end of the time division multiplexing unit is connected with the output end of the interference unit, and the output end of the time division multiplexing unit is connected with the incident end of the uplink transmission optical fiber and used for converting the single-pulse interference signal into a time division multiplexing interference pulse signal and outputting the time division multiplexing interference pulse signal;
the signal receiving unit is connected with the emergent end of the uplink transmission optical fiber and used for receiving the time division multiplexing interference pulse signal and demodulating the time division multiplexing interference pulse signal to obtain the phase noise of the system to be detected;
and the control unit is electrically connected with the phase controller and is used for actively controlling the initial phase of the single-pulse interference signal.
In one embodiment, the interference unit is a michelson interference structure and comprises a fiber coupler, a first single-mode fiber, a second single-mode fiber, a first faraday mirror, a second faraday mirror and the phase controller;
the optical fiber coupler is provided with an input port, a first output port, a second output port and a third output port, the input port of the optical fiber coupler is the input end of the interference unit, and the third output port of the optical fiber coupler is the output end of the interference unit;
a first output port of the optical fiber coupler is connected with the first Faraday mirror through the first single-mode optical fiber, and a second output port of the optical fiber coupler is connected with the second Faraday mirror through the second single-mode optical fiber;
the phase controller is arranged on the first single-mode fiber.
In one embodiment, the phase controller is a piezoelectric ceramic ring with a cylindrical structure, and the piezoelectric ceramic ring is electrically connected with the control unit so that the piezoelectric ceramic ring stretches under the action of a voltage signal;
part of the first single mode fibers are tightly wound along the circumferential direction and are regularly arranged on the piezoelectric ceramic ring, so that the first single mode fibers wound on the piezoelectric ceramic ring are changed in length along with the expansion of the piezoelectric ceramic ring, and the phase difference of the single pulse interference signals is changed.
In one embodiment, the time division multiplexing unit comprises N-1 beam splitting couplers and N-1 beam combining couplers, wherein N is a time division multiplexing number and is a natural number greater than 1, and the beam splitting couplers and the beam combining couplers are provided with a common port, a port with a small coupling ratio and a port with a large coupling ratio;
the common port of the a-th beam splitting coupler is connected with the large coupling ratio port of the a-1 th beam splitting coupler through a delay optical fiber, and the common port of the a-th beam combining coupler is connected with the large coupling ratio port of the a-1 th beam combining coupler, wherein a is 2-N-1;
the large coupling ratio port of the (N-1) th beam splitting coupler is connected with the large coupling ratio port of the (N-1) th beam combining coupler through a delay optical fiber, the common port of the 1 st beam splitting coupler is the input end of the time division multiplexing unit, and the common port of the 1 st beam combining coupler is the output end of the time division multiplexing unit;
and the small coupling ratio port of the b-th splitting coupler is connected with the small coupling ratio port of the b-th combining coupler through a connecting optical fiber, wherein b is 1-N-1.
In one embodiment, the system further comprises a vacuum isolation tank, and the interference unit and the time division multiplexing unit are arranged in the vacuum isolation tank.
In one embodiment, the signal receiving unit includes:
the photoelectric detector comprises an input end and an output end, wherein an input port of the photoelectric detector is connected with an emergent end of the uplink transmission optical fiber and is used for converting the time division multiplexing interference pulse signal into a time division multiplexing interference electric signal;
the analog-to-digital converter comprises an input end and an output end, wherein the input end of the analog-to-digital converter is connected with the output end of the photoelectric detector and is used for converting the time division multiplexing interference electric signal from an analog signal to a digital signal;
and the phase noise demodulator comprises an input end and an output end, wherein the input end of the phase noise demodulator is connected with the output end of the analog-to-digital converter and is used for demodulating the digital signal to obtain the phase noise of the system to be detected.
In one embodiment, the control unit includes:
an analog-to-digital converter electrically coupled to the phase controller for applying a voltage signal to the phase controller;
and the control display module is electrically connected with the digital-to-analog converter and the phase noise demodulator and is used for controlling the output voltage of the digital-to-analog converter to obtain the phase noise level of the system to be tested in the initial phase full-change process.
In order to achieve the above object, the present invention further provides a phase noise test system for an interference type optical fiber hydrophone, which includes the following steps:
Vπp＝|Vomax-Vomin|
in the formula, VπpIs the half-wave voltage of the phase controller;
at every change of voltage VoiAnd waits for the phase controller to stabilize for a time taumAnd then, acquiring the time division multiplexing interference pulse signal, demodulating the phase noise of the system to be tested, storing K-second noise data, wherein one group per second and K groups in total are recorded as
Wherein, i is 1 to M, and j is 1 to K;
after M times of noise acquisition is completed, averaging the noise data of M multiplied by K seconds to obtain the phase noise level of the system to be measured in the initial phase full-variation process:
in the formula (I), the compound is shown in the specification,
the phase noise level of the system to be measured in the initial phase full-change process is obtained.
Aiming at the problems of the testing method in the prior art, the invention provides a system and a method for testing the phase noise of an interference type optical fiber hydrophone, which designs a time division multiplexing array noise testing optical system containing an optical fiber phase controller and a photoelectric signal processing system, and the system and the method have the following beneficial technical effects:
(1) adopt
Actively controlled noise test scheme, by controlling
1 or N periods are changed, and phase noise test is carried out in the complete period, so that the maximum and minimum conversion from the strength noise of the system to be tested to the phase noise, the average value and other comprehensive noise test results can be obtained, and the accuracy of the test results is improved;
(2)
controlled by the D/A signal of the control unit, the variation amplitude and time are driven by a program,
the time of the full-period change and phase noise test is efficient and controllable;
(3) the time division multiplexing noise test array with interference and multiplexing optical path separation is designed, and only 1 phase controller wound by piezoelectric ceramics is needed to realize time division multiplexing array signals
Control and phase noise comprehensive test, simple system structure and low cost.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a schematic diagram of phase noise of an optical fiber hydrophone varying with an initial phase in the prior art;
FIG. 2 is a schematic structural diagram of a phase noise testing system of an interferometric fiber optic hydrophone according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of an interference unit and a time division multiplexing unit according to an embodiment of the present invention;
fig. 4 is a schematic flow chart of a phase noise testing method for an interferometric fiber optic hydrophone in an embodiment of the invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that all the directional indicators (such as up, down, left, right, front, and rear … …) in the embodiment of the present invention are only used to explain the relative position relationship between the components, the movement situation, etc. in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indicator is changed accordingly.
In addition, the descriptions related to "first", "second", etc. in the present invention are only for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "connected," "secured," and the like are to be construed broadly, and for example, "secured" may be a fixed connection, a removable connection, or an integral part; the connection can be mechanical connection, electrical connection, physical connection or wireless communication connection; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.
The system for testing the phase noise of the interference type optical fiber hydrophone, disclosed by the embodiment, is applied to comprehensively testing the conversion characteristic from light intensity to phase noise of a remote large-scale optical fiber hydrophone array and the system phase background noise under the condition of low signal-to-noise ratio, and comprises a signal transmitting unit, a remote transmission unit, an interference unit, a time division multiplexing unit, a signal receiving unit and a control unit. The signal transmitting unit is used for outputting a single pulse signal of the system to be tested; the remote transmission unit comprises an incident end of a downlink transmission optical fiber, is connected with the signal transmitting unit and is used for remotely transmitting the single-pulse signal; the interference unit comprises an input end, an output end and a phase controller, wherein the input end of the interference unit is connected with the emergent end of the downlink transmission optical fiber and is used for converting the monopulse signals into monopulse interference signals and outputting the monopulse interference signals; the time division multiplexing unit comprises an input end and an output end, the input end of the time division multiplexing unit is connected with the output end of the interference unit, and the output end of the time division multiplexing unit is connected with the incident end of the uplink transmission optical fiber and used for converting the single pulse interference signal into the time division multiplexing interference pulse signal and outputting the time division multiplexing interference pulse signal; the signal receiving unit is connected with the emergent end of the uplink transmission optical fiber and used for receiving the time division multiplexing interference pulse signal and demodulating the time division multiplexing interference pulse signal to obtain the phase noise of the system to be tested; the control unit is electrically connected with the phase controller and is used for actively controlling the initial phase of the single-pulse interference signal.
In this embodiment, the signal transmitting unit includes a narrow linewidth laser and an AOM as a light source. The remote transmission unit consists of a downlink transmission fiber and an uplink transmission fiber, the downlink transmission fiber is provided with an erbium-doped fiber power amplifier EDFA-BA and an erbium-doped fiber line amplifier EDFA-LA, and the uplink transmission fiber is provided with an erbium-doped fiber line amplifier EDFA-LA and an erbium-doped fiber preamplifier EDFA-PA. The signal receiving unit includes a photodetector (D), an analog-to-digital converter (a/D), and a phase noise demodulator, and the control unit includes a digital-to-analog converter (D/a) and a control display module. The photoelectric detector comprises an input end and an output end, wherein the input end of the photoelectric detector is connected with the emergent end of the uplink transmission optical fiber and is used for converting the time division multiplexing interference pulse signal into a time division multiplexing interference electric signal; the analog-to-digital converter comprises an input end and an output end, wherein the input end of the analog-to-digital converter is connected with the output end of the photoelectric detector and is used for converting the time division multiplexing interference electric signal from an analog signal into a digital signal; the phase noise demodulator comprises an input end and an output end, wherein the input end of the phase noise demodulator is connected with the output end of the analog-to-digital converter and used for demodulating the digital signal to obtain the phase noise of the system to be tested. The digital-to-analog converter is electrically connected with the phase controller and is used for applying a voltage signal to the phase controller; and the control display module, the acousto-optic modulator and the analog-to-digital converter. And the digital-to-analog converter and the phase noise demodulator are electrically connected and used for controlling the output voltage of the analog-to-digital converter to obtain the phase noise level of the system to be tested in the initial phase full-change process.
Referring to fig. 2, the interference type optical fiber hydrophone phase noise test system is composed of three parts:
(1) the active initial phase control time division multiplexing noise test array unit specifically comprises an interference unit and a time division multiplexing unit in the embodiment;
(2) the active initial phase control time division multiplexing array noise test photoelectric signal processing unit specifically comprises a signal transmitting unit, a signal receiving unit and a control unit in the embodiment;
(3) the remote transmission and optical amplification unit to be tested is specifically a remote transmission unit in this embodiment.
Referring to fig. 3, a schematic structural diagram of the active initial phase control time division multiplexing noise test array unit, i.e., the interference unit and the time division multiplexing unit, is shown.
In this embodiment, the interference unit is a michelson interference structure, and includes a first single-mode fiber isolator ISO13dB single mode fiber coupler C with bending resistance0First bending-resistant single-mode fiber L1Second bend-resistant single mode fiber L2First Faraday mirror FRM with 45-degree rotation angle1Second Faraday mirror FRM with 45-degree rotation angle2And an all-fiber phase controller F-PK.
The optical fiber coupler is provided with an input port, a first output port, a second output port and a third output port, the input port of the optical fiber coupler is the input end of the interference unit, and the input port of the optical fiber coupler passes through the first single-mode optical fiber isolator ISO1The optical fiber is connected with the emergent end of the downlink transmission optical fiber; the third output port of the optical fiber coupler is the output end of the interference unit, and is connected with the input end of the time division multiplexing unit through a connecting optical fiber. The first output port of the optical fiber coupler is connected with the first Faraday mirror through a first single mode fiber, and the second output port of the optical fiber coupler is connected with the second Faraday mirror through a second single mode fiberThe mode fiber is connected with the second Faraday mirror, and the tail fiber among the devices is connected in a fusion mode.
Specifically, the phase controller is provided on the first single-mode optical fiber. In this embodiment, the main body of the phase controller is a piezoelectric ceramic ring PZT with a cylindrical structure with a diameter of about 20mm and a height of about 5 mm. The piezoelectric ceramic ring PZT adopts an axial voltage adding mode, and electric wires are respectively welded on the positive electrode (+), and the negative electrode (-) of the piezoelectric ceramic ring PZT and are led out to an interface of the input end of a control electric signal, namely a digital-to-analog converter D/A. Second single mode fiber L2The 1-2 m bending-resistant optical fibers are tightly wound and regularly arranged along the circumferential direction of the piezoelectric ceramic ring PZT, and fiber inlet and outlet ports on the piezoelectric ceramic ring PZT are fixed by glue to prevent the optical fibers from being separated from the piezoelectric ceramic ring PZT. Voltage signal V is loaded on piezoelectric ceramic ring PZT through digital-to-analog converter D/AoThe stretching state of the piezoelectric ceramic ring PZT can be changed, the piezoelectric ceramic ring PZT stretches to drive the length of the optical fiber wound on the piezoelectric ceramic ring PZT to change delta L, and therefore, the phase difference is generated at the output end of the interferometer
Wherein k is0The interferometer is input with light wave vector, n is the refractive index of the optical fiber, so the addition of the phase controller enables the interference unit to have the function of realizing active initial phase control.
In this embodiment, the time division multiplexing unit includes N-1 beam-splitting couplers Ca1～CaN-1N-1 beam combining couplers Cb1～CbN-1N-1 single-mode delay fibers D1～DN-1Wherein N is a natural number greater than 1, and D1～DN-1Are equal in length and meet the time division multiplexing channel spacing requirement, Ca1～CaN-1And Cb1～CbN-1The coupling ratio of the optical fiber is sequentially increased, and the optical power balance requirement of the time division multiplexing channel is met. Wherein, the beam splitting coupler and the beam combining coupler both have a common port (1 port in fig. 3), a port with small coupling ratio (2 ports in fig. 3) and a port with large coupling ratio (3 ports in fig. 3). The common port of the a-th beam splitting coupler is connected with the large coupling ratio port of the a-1 th beam splitting coupler through a delay optical fiberThe common port of each beam combiner is connected with the large coupling ratio port of the a-1 th beam combiner through a delay optical fiber, wherein a is 2-N-1; the large coupling ratio port of the (N-1) th beam splitting coupler is connected with the large coupling ratio port of the (N-1) th beam combining coupler through a delay optical fiber, the common port of the 1 st beam splitting coupler is the input end of the time division multiplexing unit, and the common port of the 1 st beam combining coupler is the output end of the time division multiplexing unit; and the small coupling ratio port of the b-th splitting coupler is connected with the small coupling ratio port of the b-th combining coupler through a connecting optical fiber, wherein b is 1-N-1. The connections of the devices in the time division multiplexing unit are mainly divided into three groups:
(1)Ca1～CaN-1and Cb1～CbN-1The ports with small coupling ratio are directly welded one by one to form N-1 time division multiplexing optical circuits, DN-1And CbN-1The ports with large coupling ratio are welded to form an Nth time division multiplexing optical loop;
(2)Ca2～CaN-1a common port, Ca1～CaN-1Large coupling ratio port and D1～DN-1The serial connection and the fusion are connected into a time division multiplexing beam splitting delay branch circuit;
(3)Cb1～CbN-2port with large coupling ratio, Cb2～CbN-1The public ports are connected in series and welded into a time division multiplexing beam combining branch circuit;
wherein, Ca1The common end of the optical fiber coupler is an input end of the time division multiplexing unit and is welded with a third output port of the optical fiber coupler through a connecting optical fiber; cb1The common end of the optical fiber isolator is the output end of the time division multiplexing unit and is connected with the optical fiber isolator ISO2And outputting the time division multiplexing interference optical signal with controllable initial phase. Through the design, the initial phase control of the N paths of time division multiplexing interference signals can be completed only by 1 phase controller.
It should be noted that, as described above, the interference unit and the time division multiplexing unit are both disposed in the vacuum isolation tank. The outside of the vacuum isolation tank is provided with 1 optical fiber bin penetrating sealing element (containing 2 optical fibers as an optical interface), 1 electric bin penetrating sealing element (containing 2 electric wires as an electric interface) and 1 vacuum extraction valve. The vacuum isolation tank is vacuumized to-0.075 Mpa to-0.085 Mpa to achieve a good sound/vibration shielding effect, and phase background noise measured by the testing system under the condition is mainly introduced by self noise of the optical fiber hydrophone system.
The working process of the interference type optical fiber hydrophone phase noise testing system is as follows:
the continuous light output by the narrow linewidth laser for the optical fiber hydrophone is chopped into pulse width tau through the AOM0Repetition frequency fAOMAnd the pulse duty ratio T is 1/N, the pulse light signal is connected to the interference unit and the time division multiplexing unit after passing through the downlink transmission and amplification unit, and then the interference light output signal passes through the uplink transmission and amplification unit, and then is sent to the control and display unit after passing through a series of processes such as a photoelectric detector (D), an analog-to-digital conversion (A/D) and a phase noise demodulation unit to obtain the phase background noise level of the time division multiplexing array of the system to be tested. The control and display unit has the functions of driving AOM pulse and A/D synchronous acquisition, and also generates a digital control signal, converts the digital control signal into a voltage signal through D/A, and accesses the control electric signal input end of the F-PK to realize the initial phase active control of the test system.
Based on the above system for testing phase noise of an interference-type optical fiber hydrophone, this embodiment also discloses a method for testing phase noise of an interference-type optical fiber hydrophone, which specifically includes the following steps with reference to fig. 4:
Vπp＝|Vomax-Vomin|
in the formula, VπpIs the half-wave voltage of the phase controller;
at every change of voltage VoiAnd waits for the phase controller F-PK to settle for a time τmAnd then, acquiring the time division multiplexing interference pulse signal, demodulating the phase noise of the system to be tested, storing K-second noise data, wherein one group per second and K groups in total are recorded as
Wherein, i is 1 to M, and j is 1 to K;
after M times of noise acquisition is completed, averaging the noise data of M multiplied by K seconds to obtain the phase noise level of the system to be measured in the initial phase full-variation process:
in the formula (I), the compound is shown in the specification,
the phase noise level of the system to be measured in the initial phase full-change process is obtained.
Considering that the time for outputting the control voltage and waiting for the stabilization of the F-PK is very short, the time for completing one test in the above steps 1-3 is about equal to M times K seconds.
In summary, the present embodiment provides a time division multiplexing test array structure of an optical fiber hydrophone including an initial phase controller and a phase noise test method. The initial phase of the test interferometer is changed between 0 and 2 pi by actively controlling and changing the voltage of the initial phase controller, and the phase noise of the hydrophone system to be tested corresponding to each initial phase is synchronously acquired and demodulated. After one period of test is finished, the phase noise and the average noise level of the system to be tested under the condition of full initial phase change can be obtained. The testing method can effectively eliminate noise testing errors caused by initial phase change, shorten testing time and synchronously obtain the light intensity noise and the noise conversion characteristic of the system to be tested. The method is particularly suitable for phase noise floor test and performance evaluation of a low-signal-to-noise-ratio remote large-scale optical fiber hydrophone multiplexing array system.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (8)
1. An interference type optical fiber hydrophone phase noise test system, comprising:
the signal transmitting unit is used for outputting a single pulse signal of the system to be tested;
the remote transmission unit comprises a downlink transmission optical fiber, an uplink transmission optical fiber and an optical amplifier, wherein the incident end of the downlink transmission optical fiber is connected with the signal transmitting unit and is used for remotely transmitting the single-pulse signal;
the interference unit comprises an input end, an output end and a phase controller, wherein the input end of the interference unit is connected with the emergent end of the downlink transmission optical fiber and is used for converting the single-pulse signal into a single-pulse interference signal and outputting the single-pulse interference signal;
the time division multiplexing unit comprises an input end and an output end, the input end of the time division multiplexing unit is connected with the output end of the interference unit, and the output end of the time division multiplexing unit is connected with the incident end of the uplink transmission optical fiber and used for converting the single-pulse interference signal into a time division multiplexing interference pulse signal and outputting the time division multiplexing interference pulse signal;
the signal receiving unit is connected with the emergent end of the uplink transmission optical fiber and used for receiving the time division multiplexing interference pulse signal and demodulating the time division multiplexing interference pulse signal to obtain the phase noise of the system to be detected;
and the control unit is electrically connected with the phase controller and is used for actively controlling the initial phase of the single-pulse interference signal.
2. The system according to claim 1, wherein the interference unit is a michelson interference structure, and includes a fiber coupler, a first single-mode fiber, a second single-mode fiber, a first faraday mirror, a second faraday mirror, and the phase controller;
the optical fiber coupler is provided with an input port, a first output port, a second output port and a third output port, the input port of the optical fiber coupler is the input end of the interference unit, and the third output port of the optical fiber coupler is the output end of the interference unit;
a first output port of the optical fiber coupler is connected with the first Faraday mirror through the first single-mode optical fiber, and a second output port of the optical fiber coupler is connected with the second Faraday mirror through the second single-mode optical fiber;
the phase controller is arranged on the first single-mode fiber.
3. The system according to claim 2, wherein the phase controller is a piezoelectric ceramic ring with a cylindrical structure, and the piezoelectric ceramic ring is electrically connected to the control unit, so that the piezoelectric ceramic ring expands and contracts under the action of the voltage signal;
part of the first single mode fibers are tightly wound along the circumferential direction and are regularly arranged on the piezoelectric ceramic ring, so that the first single mode fibers wound on the piezoelectric ceramic ring are changed in length along with the expansion of the piezoelectric ceramic ring, and the phase difference of the single pulse interference signals is changed.
4. The system for testing the phase noise of the interferometric optical fiber hydrophone according to claim 1, 2 or 3, wherein the time division multiplexing unit comprises N-1 beam splitting couplers and N-1 beam combining couplers, wherein N is a time division multiplexing number and is a natural number greater than 1, and each of the beam splitting couplers and the beam combining couplers has a common port, a port with a small coupling ratio and a port with a large coupling ratio;
the common port of the a-th beam splitting coupler is connected with the large coupling ratio port of the a-1 th beam splitting coupler through a delay optical fiber, and the common port of the a-th beam combining coupler is connected with the large coupling ratio port of the a-1 th beam combining coupler, wherein a is 2-N-1;
the large coupling ratio port of the (N-1) th beam splitting coupler is connected with the large coupling ratio port of the (N-1) th beam combining coupler through a delay optical fiber, the common port of the 1 st beam splitting coupler is the input end of the time division multiplexing unit, and the common port of the 1 st beam combining coupler is the output end of the time division multiplexing unit;
and the small coupling ratio port of the b-th splitting coupler is connected with the small coupling ratio port of the b-th combining coupler through a connecting optical fiber, wherein b is 1-N-1.
5. The system for testing the phase noise of the interference type optical fiber hydrophone according to claim 1, 2 or 3, further comprising a vacuum isolation tank, wherein the interference unit and the time division multiplexing unit are both arranged in the vacuum isolation tank.
6. The system for testing phase noise of an interferometric fiber optic hydrophone of claims 1, 2 or 3, wherein the signal receiving unit comprises:
the photoelectric detector comprises an input end and an output end, wherein an input port of the photoelectric detector is connected with an emergent end of the uplink transmission optical fiber and is used for converting the time division multiplexing interference pulse signal into a time division multiplexing interference electric signal;
the analog-to-digital converter comprises an input end and an output end, wherein the input end of the analog-to-digital converter is connected with the output end of the photoelectric detector and is used for converting the time division multiplexing interference electric signal from an analog signal to a digital signal;
and the phase noise demodulator comprises an input end and an output end, wherein the input end of the phase noise demodulator is connected with the output end of the analog-to-digital converter and is used for demodulating the digital signal to obtain the phase noise of the system to be detected.
7. The interferometric fiber optic hydrophone phase noise testing system of claim 6, wherein the control unit comprises:
a digital-to-analog converter electrically coupled to the phase controller for applying a voltage signal to the phase controller;
and the control display module is electrically connected with the digital-to-analog converter and the phase noise demodulator and is used for controlling the output voltage of the digital-to-analog converter to obtain the phase noise level of the system to be tested in the initial phase full-change process.
8. An interference type optical fiber hydrophone phase noise test system is characterized in that the interference type optical fiber hydrophone phase noise test system of any one of claims 1 to 7 is adopted, and the system specifically comprises the following steps:
step 1, changing the voltage applied by a phase controller from small to large, and acquiring the interference light intensity I (t) of a time division multiplexing interference pulse signal point by point;
step 2, obtaining the maximum value I (t) of interference light intensity I (t) in a change periodmaxAnd a minimum value IminAnd a corresponding voltage VomaxAnd VominAnd obtaining the half-wave voltage of the phase controller as follows:
Vπp＝|Vomax-Vomin|
in the formula, VπpIs the half-wave voltage of the phase controller;
step 3, gradually changing the voltage V applied by the phase controlleroIn the range of 0-2VπpStep size VmpThe number of changes M is 2Vπp/VmpAnd by setting the step length VmpLet M be an integer:
at every change of voltage VoiAnd waits for the phase controller to stabilize for a time taumAnd then, acquiring the time division multiplexing interference pulse signal, demodulating the phase noise of the system to be tested, storing K-second noise data, wherein one group per second and K groups in total are recorded as
Wherein, i is 1 to M, and j is 1 to K;
after M times of noise acquisition is completed, averaging the noise data of M multiplied by K seconds to obtain the phase noise level of the system to be measured in the initial phase full-variation process:
in the formula (I), the compound is shown in the specification,
the phase noise level of the system to be measured in the initial phase full-change process is obtained.
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