Inter-signal time delay compensation method based on discrete signal time sequence translation

Abstract

The invention discloses an inter-signal time delay compensation method based on discrete signal time sequence translation, and relates to the field of optical signal processing and time delay influence suppression. In an optical interference sensing technology, time delay exists between two paths of signals of a common mode due to different transmission paths of the two paths of signals. The inter-signal time delay compensation method comprises the following steps: converting two paths of signals into two paths of discrete digital signals, measuring inter-signal time delay, determining a time sequence difference point number of the two paths of signals, and realizing inter-signal time delay compensation by translating the time sequence point number of the signals; and the compensation residue is reduced by finely adjusting the length of the signal transmission optical fiber or the sampling rate, and the time delay compensation effect is improved. By means of the method, efficient time delay compensation is achieved, synchronism between optical signals is enhanced, and signal noise suppression and information extraction effects can be optimized.

Description

Technical Field

[0001] The present invention belongs to the field of optical signal processing and delay influence suppression, and specifically relates to a method for compensating inter-signal delay based on discrete signal timing shift. Background Art

[0002] Compared with electrical sensing technology, fiber optic interferometry sensing technology has higher detection resolution and wider measurement frequency band, and shows great advantages in measuring weak signals. In addition, since the sensing front end is passive, it is not easily affected by external electromagnetic interference and detection, and the optical signal can be transmitted over long distances with low loss through optical fiber, forming a good array deployment capability, forming a fiber optic sensor array, which has been increasingly widely used in fields such as underwater acoustic detection and earthquake monitoring. When optical signals are transmitted in a fiber optic interferometry (array) system, channel delays will be generated due to different paths. The delay will cause demodulation distortion during the demodulation of the optical phase signal, affect the noise common mode suppression effect, and cause errors when extracting the "time and space strength" information of the signal to be measured through multiple demodulated signals. In order to avoid the above problems, it is necessary to reduce the delay between signals and suppress the influence of the delay.

[0003] Delays also exist in other fields, and corresponding delay measurement research has been carried out. In view of the random delays existing in network control systems in the communication field, delay evaluation prediction methods and corresponding compensation methods have been proposed, but their complex algorithm operations are not suitable for optical fiber sensing systems with fixed delays. In electronic sensing measurement systems, the measurement methods of inter-channel delays, measurement accuracy evaluation, and delay generation factors have been studied, providing technical references for delay measurement in sensing systems, but have not yet been applied in optical fiber sensing systems. In optical fiber communication systems, in order to measure the length of optical fiber for optical signal transmission, a variety of measurement technologies such as optical time domain reflection technology based on optical pulses, optical frequency domain emission technology, and frequency measurement have been proposed, and research has been carried out on issues such as measurement accuracy and measurement blind spots. However, the above methods can measure the delay or the length of the optical fiber that causes the delay, and methods to suppress the influence of delay on signal demodulation, noise suppression, and information extraction in the signal still need further research and development. In addition, in the combined analysis of multiple signals, the sampling delay of the acquisition card is an influencing factor, and it is often necessary to improve the synchronization performance of the acquisition card, resulting in a surge in the price of the acquisition card, and even the current acquisition card products cannot meet the required synchronization performance.

[0004] Therefore, it is a problem that technicians in this field need to solve to propose a new method to suppress the impact of delay based on the new physical imagination and laws generated by the time delay between signals and to achieve high-precision delay suppression. Summary of the invention

[0005] The object of the present invention is to provide a method for compensating inter-signal delay based on discrete signal timing shift, so as to achieve the effect of suppressing the influence of inter-signal delay.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for compensating signal delay based on discrete signal timing shift, comprising the following steps:

[0008] Step 1: convert the two signals into two discrete digital signals, wherein the two signals are common-mode signals of the same source;

[0009] Step 2: Measure the delay τ between signals and determine the number of delay bits of the two signal sequences, where the number of delay bits is the number of misalignment bits expressed by the delay in the discrete digital signal sequence;

[0010] Step 3: Shift one channel of data in the corresponding direction in timing by the number of delay bits in step 2 to align the signals in timing.

[0011] As a further solution of the present invention, the signal includes a light source phase signal, an intensity signal and a phase modulation signal, which are converted into discrete digital signals after sampling with the same sampling parameters; the sampling parameters include sampling rate, sampling time and sampling amplitude resolution.

[0012] As a further solution of the present invention, the inter-signal delay τ=nl / c, n is the refractive index of light in the optical fiber, c is the speed of light in a vacuum, and l is the length of the delay optical fiber.

[0013] As a further solution of the present invention, after step three, the compensation residual is reduced by adjusting the sampling rate or the delay optical fiber length l.

[0014] As a further solution of the present invention, a method for reducing the compensation residual by adjusting the length difference l between the delayed optical fiber and the short optical fiber is:

[0015] From Δτ*c / n=Δl, the required adjusted optical fiber length Δl is obtained, so that the delay corresponding to the adjusted delayed optical fiber length l±Δl matches the delay bit number, reducing the compensation residual Δτ.

[0016] As a further solution of the present invention, a method for reducing the compensation residual by adjusting the sampling rate is:

[0017] Change the acquisition card sampling rate f so that the timing bit interval Δt is a divisor of the delay τ, so that the delay τ matches the number of delay bits and the compensation residual Δτ is reduced.

[0018] Beneficial effects of the present invention:

[0019] 1. The present invention achieves compensation for the delay caused by transmission optical fiber, data acquisition and other hardware through discrete digital signal timing shift, which effectively suppresses the influence of delay.

[0020] 2. The limitation of compensation accuracy determined by sampling rate is broken through by selecting optical fiber length and sampling rate, which effectively improves the suppression effect of delay influence. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] Figure 1 It is a schematic diagram of the structure of the optical fiber sensing system with time delay that the present invention is directed to;

[0023] Figure 2 Schematic diagram of output signal spectrum corresponding to 0km delay optical fiber and 2km delay optical fiber in an embodiment of the present invention;

[0024] Figure 3 This is a flow chart of delay compensation in an embodiment of the present invention;

[0025] Figure 4 Schematic diagram of a delay residue reduction method based on delay optical fiber length adjustment in an embodiment of the present invention;

[0026] Figure 5 Schematic diagram of the relationship between the delay bit number and the sampling rate corresponding to a 2km delay optical fiber in an embodiment of the present invention;

[0027] Figure 6 Schematic diagram of the relationship between the compensation residual and the sampling rate corresponding to a 2 km delayed optical fiber in an embodiment of the present invention.

[0028] In the figure: 1. Laser; 2. Coupler 1; 3. Interferometer 1; 4. Interferometer 2; 5. Delay fiber; 6. Data processing module; 7. Coupler 2; 8. Coupler 3; 9. Faraday rotator; 10. Short optical fiber; 11. Delay fiber. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, the optical fiber sensing system structure with time delay provided by the present invention includes a laser 1, an interferometer 1 3, an interferometer 2 4, a delay optical fiber 5, and a data processing module 6;

[0031] The interferometer 1 3 and the interferometer 2 4 are both fiber Michelson interferometers, and are both composed of a coupler connected to a Faraday rotator 9, wherein the interferometer 1 3 is a coupler 2 7, and the interferometer 2 4 is a coupler 3 8; the function of the fiber Michelson interferometer is to generate an optical phase noise spectrum;

[0032] The delay fiber 5 is the length difference between the long fiber 11 and the short fiber 10. The light output by the laser 1 and the light source frequency noise are distributed through the coupler 2 and then input into the interferometer 2 4 and the interferometer 1 3 through the short fiber 10 and the long fiber 11 respectively.

[0033] The data processing module 6 can convert the interference optical signal into an electrical signal, realize data collection and optical phase demodulation, and obtain two discrete digital light source phase noise signals. The signal comes from the frequency noise of the same light source, so it is common mode. In addition, due to the difference in distance of the transmission path of the light carrying the light source frequency noise, there is a time delay in the two discrete digital light source phase noise signals; for example, when the transmission distance difference between the long optical fiber 11 and the short optical fiber 10, that is, the length of the delay optical fiber 5 is 2km, when the two signals are subtracted, the following will appear: Figure 2 The corresponding result of the "2km delayed optical fiber" shown in the figure is: When there is no difference in the transmission path of the light, that is, there is no delay, when the two signals are subtracted, the following result will appear: Figure 2 The corresponding results of "0km delayed optical fiber" are shown. Compared with the corresponding results of "0km delayed optical fiber", the corresponding signal noise floor of "2km delayed optical fiber" caused by delay is significantly raised, resulting in the degradation of the performance of the sensing system. Therefore, in order to suppress the influence of delay, the present invention proposes the following method.

[0034] A method for compensating signal delay between signals based on discrete signal timing shift, such as Figure 3 As shown, the following steps are included:

[0035] S1, converting the two signals into two discrete digital signals through the same data acquisition card, setting the sampling rate of the data acquisition card of the data processing module 6 to f, and obtaining two discrete digital light source phase noise signals after demodulation, the discrete data timing interval Δt of the signal is 1 / f seconds;

[0036] The two signals are common-mode signals of the same origin, which are mainly light source phase signals, intensity signals and phase modulation signals in optical interferometry sensing technology, and are converted into discrete digital signals after sampling with the same sampling parameters (sampling rate, sampling time and sampling amplitude resolution).

[0037] S2. The delay τ = nl / c is calculated from the length l of the delay optical fiber 5, where n is the refractive index of light in the optical fiber and c is the speed of light in a vacuum. Then, τ / Δt≈N, the delay τ is expressed as a misalignment of the delay bit N in the timing of the two discrete signals.

[0038] The inter-signal delay τ is generated by different optical signal transmission paths (transmission optical fiber length l), τ = nl / c, and the delay τ can be measured by a variety of technologies and is a fixed value;

[0039] The delay bit number N is the number of offset bits represented by the delay in the discrete digital signal timing.

[0040] S3, shifting one channel of data by the number of bits N in a certain direction in time sequence, so that the signals are aligned in time sequence;

[0041] The number of bits for shifting the timing sequence of the signal is to shift one channel of data in a certain direction in timing by the number of delay bits mentioned above so as to align the signals in timing.

[0042] S4. After compensation, there is a certain difference between the delay τ and the delay compensation amount N*Δt, which is the compensation residual Δτ, which can be reduced by the following methods:

[0043] Method 1: From the compensation residual Δτ, Δτ*c / n=Δl, the required adjusted fiber length Δl is obtained, Δl is a small amount relative to l, and the required adjusted fiber length Δl is added or subtracted from the delay fiber 5 length l, so that the delay corresponding to l±Δl matches the delay bit number, reducing the compensation residual Δτ, such as Figure 4 shown.

[0044] Method 2: Change the acquisition card sampling rate f, so that the time sequence bit interval Δt is a divisor of the delay τ, so that the delay τ matches the delay bit number, and the compensation residual Δτ is reduced. Figure 5 , 6 As shown, for the 2km delay optical fiber 5, the 9.81*10 -6 s delay, by adjusting the sampling rate (0-10 6 Hz), the compensation residual Δτ has 9 minimum points, that is, the compensation residual Δτ can be reduced at its corresponding sampling rate.

[0045] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for compensating signal delay based on discrete signal timing shift, characterized in that: The steps include: Step 1: convert the two signals into two discrete digital signals, wherein the two signals are common-mode signals of the same source; Step 2: Measure the delay τ between signals and determine the number of delay bits of the two signal sequences, where the number of delay bits is the number of misaligned bits expressed by the delay in the discrete digital signal sequence; Step 3: Shift one channel of data in the corresponding direction in timing by the number of delay bits in step 2 to align the signals in timing.

2. According to claim 1, a method for compensating signal delay between signals based on discrete signal timing shift, characterized in that: The signal includes a light source phase signal, an intensity signal and a phase modulation signal, which are converted into a discrete digital signal after being sampled with the same sampling parameters; the sampling parameters include a sampling rate, a sampling time and a sampling amplitude resolution.

3. The method for compensating signal delay between signals based on discrete signal timing shift according to claim 2, characterized in that: The inter-signal delay τ=nl / c, where n is the refractive index of light in the optical fiber, c is the speed of light in a vacuum, and l is the length of the delay optical fiber, which is the difference between the long optical fiber and the short optical fiber.

4. The method for compensating signal delay between signals based on discrete signal timing shift according to claim 3, characterized in that: After step 3, the compensation residual is further reduced by adjusting the sampling rate or the delay optical fiber length l.

5. The method for compensating signal delay between signals based on discrete signal timing shift according to claim 4, characterized in that: The method of reducing the compensation residual by adjusting the delay fiber length l is: From Δτ*c / n=Δl, the required adjusted optical fiber length Δl is obtained, so that the delay corresponding to the adjusted delayed optical fiber length l±Δl matches the delay bit number, reducing the compensation residual Δτ.

6. The method for compensating signal delay between signals based on discrete signal timing shift according to claim 4, characterized in that: The method to reduce the compensation residual by adjusting the sampling rate is: Change the acquisition card sampling rate f so that the timing bit interval Δt is a divisor of the delay τ, so that the delay τ matches the number of delay bits and the compensation residual Δτ is reduced.

Images