Time division multiplexing optical fiber hydrophone array optical path structure

Abstract

The invention discloses a time division multiplexing optical fiber hydrophone array optical path structure, which comprises a downlink optical path, an optical fiber hydrophone array and an uplink optical path, the time division multiplexing optical fiber hydrophone array optical path structure adopts a 2 * 4 time division multiplexing mode, two 4 time divisions are connected in parallel, the downlink optical path comprises a first coupler and two downlink channels corresponding to 4 time division; the uplink optical path comprises two uplink channels corresponding to four time divisions and a second coupler, the four time divisions are formed by combining a third coupler, a delay optical fiber and an optical fiber hydrophone, and the delay optical fiber is located in the uplink channels of the four time divisions. According to the time division multiplexing optical fiber hydrophone array optical path structure, under the condition that the distance between the optical fiber hydrophones is not large, the time delay optical fiber is arranged in a four-time-division uplink channel, optical signals received by the optical fiber hydrophones are light sources which are emitted at the same time and then transmitted back to a detection end through the time delay optical fiber, and therefore positioning of a dry end target signal is better facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of communication systems, and more particularly to a time division multiplexing optical fiber hydrophone array optical path structure. BACKGROUND

[0002] In recent years, research on optical fiber hydrophones has gradually focused on how to use the characteristics of low transmission loss and large transmission bandwidth of optical fibers for signal transmission. Multi-channel signal transmission using one optical fiber or one pair of optical fibers can significantly reduce system cost, and this method is widely used in the field of optical fiber sensing. Common optical multiplexing methods mainly include: space division multiplexing, wavelength division multiplexing, time division multiplexing, etc.

[0003] Among them, the time division multiplexing method is currently relatively mature. It transmits optical pulses at different times back to the detection end by strictly controlling the delay and optical pulse interval, so that signals from optical fiber hydrophone probes at different positions are obtained.

[0004] One of the existing time division multiplexing methods is an 8-time division multiplexing method. It places a delay optical fiber on the downlink optical path, as shown in Figure 1 The pulse light emitted by the light source is split by the coupler, and the input pulse light is divided into 8 equal parts by controlling the delay optical fiber and the optical fiber beam splitter, and then a beam of light is synthesized by the beam splitter to return. The returning light is composed of multiple pulses, each pulse corresponding to a sensor signal. The pulse light of the 8-time division multiplexing method first passes through the delay optical fiber to reach the sensor, and the sensor transmits the signal back after receiving the signal, which will cause the time of the pulse signal reaching the sensor to be different, resulting in certain errors in the processing of the dry end underwater acoustic signal. Among them, the functions of each component are as follows: OC and oc are 1x2 couplers that balance the light intensity of each channel; D represents a delay optical fiber, different serial numbers correspond to different time division channels, and plays a role in controlling the uniformity of the delay of each channel; h is an optical fiber hydrophone, which is marked as h1, h2, …, h8 according to the serial number of the optical fiber hydrophone, and is used to receive underwater acoustic signals.

[0005] Therefore, it is urgent to propose a time division multiplexing optical fiber hydrophone array optical path structure to solve the problems. SUMMARY

[0006] (1) Technical problem to be solved

[0007] Therefore, the present application provides a time division multiplexing optical fiber hydrophone array optical path structure for signal positioning at the dry end.

[0008] (2) Technical scheme

[0009] To solve the above technical problems, the application provides a time division multiplexing optical fiber hydrophone array optical path structure, which comprises a downlink optical path, an optical fiber hydrophone array and an uplink optical path, and adopts a 2*4 time division multiplexing mode, and two 4 time divisions are connected in parallel, wherein the downlink optical path comprises a first coupler and two 4 time division corresponding downlink channels; the uplink optical path comprises two 4 time division corresponding uplink channels and a second coupler, and the optical fiber hydrophone array comprises optical fiber hydrophones arranged in the two 4 time divisions.

[0010] In one of the embodiments, the 4 time division is composed of a third coupler, a first delay optical fiber and an optical fiber hydrophone, each 4 time division is split by the third coupler in sequence, the first delay optical fiber is arranged in the uplink channel of the 4 time division, the first coupler is used for being connected with an acousto-optic modulator, the second coupler is used for being connected with an optical-electricity converter, the downlink channels of the two 4 time divisions are connected to the first coupler at the same time, and the uplink channels of the two 4 time divisions are connected to the second coupler at the same time.

[0011] In one of the embodiments, the first coupler and the second coupler are 1*2 couplers.

[0012] In one of the embodiments, the light emitted by the light source is split into a first light beam and a second light beam by the first coupler after being opened by the acousto-optic modulator, the first light beam is divided into four equal parts by one of the 4 time divisions, the second light beam is divided into four equal parts by the other of the 4 time divisions, the pulse light of the 2*4 time division multiplexing mode can transmit the signals received by the optical fiber hydrophones in the 4 time divisions to the optical-electricity converter at the same time, and the signals received by the optical fiber hydrophones in the 4 time divisions at the same time are continuous pulse signals.

[0013] In one of the embodiments, the time of each pulse cycle is T, the delay time generated by the first delay optical fiber between each of the 4 time divisions is not more than the quotient of the pulse cycle time T and the 4 time division multiplexing number, and the actual length of the first delay optical fiber is the theoretical length minus the coupler tail fiber length, the element spacing and the optical fiber allowance, wherein the theoretical length L = ct / n, c is the speed of light, t is the delay time between the optical fiber hydrophones, and n is the refractive index of the optical fiber.

[0014] In one of the embodiments, a second delay optical fiber is arranged between the uplink channel of one of the 4 time divisions and the second coupler.

[0015] In one of the embodiments, the method for calculating the light splitting ratio of the third coupler in the 4 time division comprises the following steps:

[0016] The light splitting ratio of the Nth coupler is obtained:

[0017] 10log10 C N = a P + a f , wherein C N is the splitting ratio of the Nth coupler, a p is the splice loss (dB), a f is the fiber loss (dB);

[0018] Obtain the splitting ratio of the N-1th coupler:

[0019] 10log 10 C N-1 = 2a P + a f + a c + 10log 10 [C N + 1], wherein a c is the additional loss of the Nth coupler, C N-1 is the splitting ratio of the N-1th coupler;

[0020] The splitting ratios of the third coupler in the four time divisions are 23%, 32%, 49%, respectively.

[0021] In one of the embodiments, the fiber hydrophone array includes a total of 8 fiber hydrophones arranged in two 4-time divisions, each of which includes 4 fiber hydrophones.

[0022] In one of the embodiments, the downlink optical path further includes a light source and an acousto-optic modulator, and the first coupler is connected with the acousto-optic modulator, and the light emitted by the light source is turned on by the acousto-optic modulator.

[0023] In one of the embodiments, the uplink optical path further includes a photoelectric converter, and the second coupler is connected with the photoelectric converter.

[0024] (III) Beneficial effects

[0025] The application is compared with the prior art, and the application is a time division multiplexing optical fiber hydrophone array optical path structure including a downlink optical path, an optical fiber hydrophone array and an uplink optical path, the time division multiplexing optical fiber hydrophone array optical path structure adopts a 2*4 time division multiplexing mode, two 4 time divisions are connected in parallel, wherein the downlink optical path includes a first coupler and two 4 time division corresponding downlink channels; the uplink optical path includes two 4 time division corresponding uplink channels and a second coupler, and the optical fiber hydrophone array includes optical fiber hydrophones arranged in the two 4 time divisions, the 4 time division is composed of a third coupler, a first delay optical fiber and an optical fiber hydrophone, and the first delay optical fiber is in the uplink channel of the 4 time division; by placing the first delay optical fiber in the uplink channel of the 4 time division, in the case that the spacing of the optical fiber hydrophones is small, the optical signal received by the optical fiber hydrophone is emitted by the light source at the same time, and then transmitted back to the detection end through the first delay optical fiber, which is more conducive to dry end target signal positioning; in addition, the 2*4 time division multiplexing mode is adopted, the optical power distribution is more uniform, and the coupler precision can be reduced to ±1.5%, thereby providing more reliable data for the rear-end signal processing; in addition, the 2*4 time division multiplexing mode reduces the type of coupler and improves the replaceability of optical devices, thereby reducing the production cost of the time division multiplexing optical fiber hydrophone array to a certain extent. BRIEF DESCRIPTION OF DRAWINGS

[0026] The features and advantages of the present application will be more clearly understood through the following detailed description taken in conjunction with the accompanying drawings, which are shown by way of illustration and not by way of limitation, in which:

[0027] Figure 1 is a corresponding 8 time division optical path diagram of the prior art time division multiplexing optical fiber hydrophone array optical path structure of the application;

[0028] Figure 2 is a corresponding 8 time division optical path diagram of the time division multiplexing optical fiber hydrophone array optical path structure provided by the embodiment of the application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0030] It should be noted that the terms "first", "second", "third", "fourth" and the like in the description and claims of the application are used for distinguishing between similar elements and not necessarily for describing a specific sequential or chronological order. The terms "comprising", "having", "including" and "containing" and any variations thereof are intended to cover a non-exclusive inclusion such that processes, methods, articles, or apparatuses that comprise, have, include or contain a list of elements are not required to comprise, have, include, or contain only those elements recited.

[0031] Figure 2 is an 8-time division optical path structure corresponding to the time division multiplexed fiber hydrophone array optical path structure provided by the embodiment of the application, as shown in Figure 2 The time division multiplexed fiber hydrophone array optical path structure is an 8-time division optical path structure, which comprises a downlink optical path, a fiber hydrophone array, and an uplink optical path. Specifically, the downlink optical path comprises a light source (LASER), an acousto-optic modulator (AOM), and a plurality of couplers. The uplink optical path comprises a photoelectric converter (Detector), a delay optical fiber, and a plurality of couplers. The fiber hydrophone array comprises a plurality of fiber hydrophones.

[0032] The time division multiplexed fiber hydrophone array optical path structure adopts a 2x4 time division multiplexing mode, and two 4-time divisions are connected in parallel. The downlink optical path comprises a light source, an acousto-optic modulator, a first coupler A, and two 4-time division corresponding downlink channels. The uplink optical path comprises two 4-time division corresponding uplink channels, a photoelectric converter, and a second coupler B. The fiber hydrophone array comprises a total of 8 fiber hydrophones arranged in two 4-time divisions. Each 4-time division comprises 4 fiber hydrophones, which are numbered as S1, S2, S3, and S4 according to the sequence of the fiber hydrophones, and are used to receive underwater acoustic signals.

[0033] Each 4-time division is combined by a third coupler C, a first delay optical fiber D and an optical hydrophone, each 4-time division is split by the third coupler C in turn, the first delay optical fiber D is in the uplink channel of the 4-time division, the acousto-optic modulator is connected with the first coupler A, the photoelectric converter is connected with the second coupler B, the downlink channels of the two 4-time divisions are connected to the first coupler A at the same time, and the uplink channels of the two 4-time divisions are connected to the second coupler B at the same time; the light emitted by the light source is split into a first beam and a second beam by the first coupler A after the light is turned on by the acousto-optic modulator, the first beam is divided into 4 equal parts by one of the 4-time divisions, and the second beam is divided into 4 equal parts by the other one of the 4-time divisions, the pulse light of the 2*4-time division multiplexing mode can transmit the signals received by the optical hydrophones in the 4-time divisions to the detection end, i.e. the photoelectric converter, at the same time, which is more conducive to signal positioning of the dry end; that is, in the case that the spacing of the optical hydrophones is small, the first delay optical fiber D is arranged in the uplink channel of the 4-time division, and the optical signals received by the optical hydrophones are emitted by the light source at the same time and then transmitted to the detection end through the first delay optical fiber D respectively, which is more conducive to signal positioning of the dry end; and the traditional delay optical fiber is arranged in the downlink optical path, the optical signals received by the optical hydrophones have a delay error when the signals are positioned at the rear end, therefore, the traditional delay optical fiber design method has a certain influence on the accuracy, and the present application effectively overcomes this problem.

[0034] In one embodiment, a second delay optical fiber E is arranged between the uplink channel of one of the 4-time divisions and the second coupler B, through the arrangement of the delay optical fiber E and the delay optical fiber D, in the case that the spacing of the optical hydrophones is small, the optical signals received by the optical hydrophones in the two 4-time divisions are emitted by the light source at the same time and then transmitted to the detection end through the delay optical fiber D respectively, which is more conducive to signal positioning of the dry end; and the traditional delay optical fiber is arranged in the downlink optical path, the optical signals received by the optical hydrophones have a delay error when the signals are positioned at the rear end, therefore, the traditional delay optical fiber design method has a certain influence on the accuracy, and the present application effectively overcomes this problem.

[0035] In one embodiment, the first coupler A and the second coupler B are 1*2 couplers, which are used to balance the light intensity of the corresponding channels.

[0036] In one embodiment, the third coupler C is a 1*2 coupler, which is used to balance the light intensity of the corresponding channels.

[0037] In one embodiment, the signals received by the fiber optic hydrophones in the 4-hour intervals at the same time are all continuous pulse signals. With the pulse period time as T, the delay time generated between each time interval in the 4-hour intervals through the first delay fiber D is no greater than the quotient of the pulse period time T and the number of multiplexing in the 4-hour intervals. The actual length of the first delay fiber D is the theoretical length minus the length of the coupler pigtail, the element spacing, and the fiber margin. Wherein, the theoretical length L = ct / n, c is the speed of light, t is the delay time between the fiber optic hydrophones, n is the refractive index of the fiber, the element is the fiber optic hydrophone, and the fiber margin is 3% of the element spacing.

[0038] like Figure 1 The traditional fiber optic hydrophone array optical path structure shown in the diagram has an 8-way split optical path. It uses two uplink and downlink optical fibers to detect 8 signals. The input signal corresponding to the light source is split by a coupler. The uplink and downlink optical paths each require 7 different types of couplers. This results in a small difference in the splitting ratio between the couplers, which requires high precision of the couplers. Furthermore, the returned signal becomes weaker and the optical power consistency becomes worse as the signal progresses.

[0039] By employing a 2×4 time-division multiplexing method for the 8-time-division optical path structure, the high precision requirements of the couplers can be reduced. Two parallel 4-time-division optical path structures are used to detect 8 signals. Specifically, the light emitted from the light source is switched on by the acousto-optic modulator and then split into a first beam and a second beam by the first coupler A. The first and second beams are then detected via two 4-time-division structures, achieving the detection of 8 signals. Each 4-time-division optical path structure uses uplink and downlink optical fibers to detect 4 signals. Each 4-time-division uplink and downlink optical path requires only 3 couplers of each type, making... The splitting ratio difference between the couplers in each 4-time division can be set to a larger value, which reduces the precision requirements of the couplers and solves the problem of high beam splitter precision requirements in conventional 8-time division multiplexing. In addition, since only 3 types of couplers are needed for each 4-time division, the optical signal returned by the fiber optic hydrophone is stronger. The parallel connection of two 4-time division couplers effectively improves the consistency of optical power. Moreover, the fact that only 3 types of couplers are needed for each 4-time division effectively reduces the types of couplers, improves the replaceability of optical components, and reduces the production cost of time-division multiplexed fiber optic hydrophone arrays to a certain extent.

[0040] To further explain the advantages of using a 2×4 time-division multiplexing method for the 8-time-division optical path structure in this invention, the splitting ratio of the coupler in the 8-time-division multiplexing system is further explained as follows:

[0041] An 8-time division multiplexing system needs to consider the consistency of optical power from each path. Therefore, considering splice loss and device loss, the calculation process for the splitting ratio of each coupler is as follows:

[0042] The splitting ratio of the Nth coupler:

[0043] 10log 10 C N =α P +α f , where C N Let α be the splitting ratio of the Nth coupler. p For the weld point loss (dB), α f This represents fiber loss (dB).

[0044] The splitting ratio of the (N-1)th coupler:

[0045] 10log 10 C N-1 =2α P +α f +α c +10log 10 [C N +1], where α c Adding loss to the Nth coupler, C N-1 The splitting ratio of the (N-1)th coupler.

[0046] Therefore, it can be calculated that, Figure 1 The traditional 8-time splitter couplers shown have splitting ratios of 10%, 12%, 14%, 18%, 23%, 32%, and 49%, with a coupler accuracy deviation of ±1% and additional loss <0.2dB. It is evident that the splitting ratio difference between the first four splitters in a traditional 8-time coupler is only 2%–4%. Currently, low-split-ratio couplers can only achieve an accuracy of ±1%, and this deviation may lead to uneven optical power distribution in the first four time periods of a traditional 8-time coupler.

[0047] In summary, the calculations yielded the following results: Figure 2 The splitting ratios of the four time-division couplers shown in this invention are 23%, 32%, and 49%, respectively. By adopting a 2×4 time-division multiplexing method, the optical power distribution is more uniform, and the coupler accuracy can be reduced to ±1.5%, providing more reliable data for back-end signal processing. In addition, the 2×4 time-division multiplexing method of this invention reduces the types of couplers, improves the replaceability of optical components, and reduces the production cost of time-division multiplexed fiber optic hydrophone arrays to a certain extent.

[0048] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A time division multiplexed fiber-optic hydrophone array optical path structure, characterized by, The time division multiplexed fiber hydrophone array optical path structure adopts a 2*4 time division multiplexing mode, and two 4 time divisions are connected in parallel, wherein the downlink optical path comprises a first coupler and two 4 time division corresponding downlink channels; the uplink optical path comprises two 4 time division corresponding uplink channels and a second coupler, and the fiber hydrophone array comprises fiber hydrophones arranged in the two 4 time divisions, the 4 time division is composed of a third coupler, a first delay optical fiber and a fiber hydrophone, and the first delay optical fiber is in the uplink channel of the 4 time division.

2. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1, wherein, The 4 time divisions are sequentially connected in series by the third coupler for light splitting, the first coupler is used for connecting with the acousto-optic modulator, and the second coupler is used for connecting with the photoelectric converter, the downlink channels of the two 4 time divisions are connected to the first coupler at the same time, and the uplink channels of the two 4 time divisions are connected to the second coupler at the same time.

3. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1 or 2, wherein, The first coupler and the second coupler are 1*2 couplers.

4. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 2, wherein, The light emitted by the light source is turned on by the acousto-optic modulator, and then divided into a first beam and a second beam by the first coupler, the first beam is divided into four equal parts by one of the 4 time divisions, and the second beam is divided into four equal parts by the other of the 4 time divisions, the pulse light of the 2*4 time division multiplexing mode transmits the signals received by the fiber hydrophones in the 4 time divisions to the photoelectric converter at the same time; wherein the signals received by the fiber hydrophones in the 4 time divisions at the same time are continuous pulse signals.

5. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 4, wherein, With each pulse period time as T, the delay time generated by the first delay optical fiber between each of the 4 time divisions is not greater than the quotient of the pulse period time T and the 4 time division multiplexing number, and the actual length of the first delay optical fiber is the theoretical length minus the coupler tail fiber length, the element spacing and the fiber allowance, wherein the theoretical length L=ct / n, c is the speed of light, t is the delay time between the fiber hydrophones, and n is the refractive index of the optical fiber, the element is the fiber hydrophone, and the fiber allowance is 3% of the element spacing.

6. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 2, wherein, A second delay optical fiber is arranged between the uplink channel of one of the 4 time divisions and the second coupler.

7. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1 or 2, wherein, The light splitting ratio calculation method of the third coupler in the 4 time division comprises the following steps: Obtain the light splitting ratio of the Nth coupler: 10 log 10 C N = a P + a f where C N is the splitting ratio of the Nth coupler, a p is the splice loss (dB), and a f is the fiber loss (dB). Obtain the light splitting ratio of the N-1th coupler: 10log 10 C N-1 = 2a P + a f + a c + 10log 10 [ C N + 1 ], where a c is the Nth coupler additional loss, C N-1 is the N-1st coupler splitting ratio; The light splitting ratios of the third couplers in the 4 time divisions are 23%, 32% and 49% respectively.

8. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1 or 2, wherein, The fiber hydrophone array comprises a total of 8 fiber hydrophones arranged in the two 4 time divisions, and each 4 time division comprises 4 fiber hydrophones.

9. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1, wherein, The downlink optical path further comprises a light source and an acousto-optic modulator, and the first coupler is used for connecting with the acousto-optic modulator, and the light emitted by the light source is turned on by the acousto-optic modulator.

10. The time division multiplexed fiber-optic hydrophone array optical path structure of claim 1, wherein, The uplink optical path further comprises a photoelectric converter, and the second coupler is connected with the photoelectric converter. The light emitted by the light source is turned on by the acousto-optic modulator, and then divided into a first beam and a second beam by the first coupler, the first beam is divided into four equal parts by one of the 4 time divisions, and the second beam is divided into four equal parts by the other of the 4 time divisions, the pulse light of the 2*4 time division multiplexing mode transmits the signals received by the fiber hydrophones in the 4 time divisions to the photoelectric converter at the same time; wherein the signals received by the fiber hydrophones in the 4 time divisions at the same time are continuous pulse signals. With each pulse period time as T, the delay time generated by the first delay optical fiber between each of the 4 time divisions is not greater than the quotient of the pulse period time T and the 4 time division multiplexing number, and the actual length of the first delay optical fiber is the theoretical length minus the coupler tail fiber length, the element spacing and the fiber allowance, wherein the theoretical length L=ct / n, c is the speed of light, t is the delay time between the fiber hydrophones, and n is the refractive index of the optical fiber, the element is the fiber hydrophone, and the fiber allowance is 3% of the element spacing. A second delay optical fiber is arranged between the uplink channel of one of the 4 time divisions and the second coupler.

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