Wavelength coding confidential optical fiber communication system

Abstract

The invention discloses a wavelength-coded confidential optical fiber communication system. A receiving end is composed of a broadband light source, a 2 * 2 optical fiber coupler, a 1 * n wavelength wave separator, n photoelectric detectors and an n * 1 coding restorer; the signal transmitting end is composed of an optical fiber delay line, a 1 * n wavelength splitter, n phase modulators, an n * 1 wavelength combiner and a 1 * n code splitter. An original signal needing to be transmitted is decomposed into n modulation signals by a 1 * n code divider, the n modulation signals act on n phase modulators, and phase modulation is carried out on n wide-spectrum light with different wavelengths; at a receiving end, a wavelength wave separator is adopted to decompose the interference signals into n different interference signals, the interference signals are converted into electric signals through n photoelectric detectors, and the n electric signals are restored into original signals through a coding restorer. As n phase-modulated '0' and '1' binary signals instead of intensity signals are adopted, and meanwhile, the optical path lengths of n wavelengths are different, and a decomposition-recovery method is adopted for the original signals, the eavesdropping difficulty is greatly increased.

Description

Technical Field

[0001] The present invention relates to a secure wired communication system, and in particular to a wavelength-coded secure optical fiber communication system based on the Sagnac effect. Background Art

[0002] Traditional wired communication systems, including optical fiber communication, are not physically confidential. The so-called confidentiality is only the encryption and decryption process of the transmission signal. There is a physically confidential optical fiber communication system based on the Sagnac interference effect, such as Figure 2 As shown, the signal receiving end is composed of a broadband light source 13, a 2*2 single-mode fiber coupler 2 and a photodetector 14. The broadband light source 1 emits a short coherent length light beam with a constant light intensity, which is incident on the 2*2 single-mode fiber coupler 2. The fiber coupler 2 splits the incident light into two. The upper output port and the lower output port of the coupler 2 output two beams of light, which are respectively coupled into the 6-1 end of the single-mode fiber cable 6 and the 7-1 end of the single-mode fiber cable 7, which are tens to hundreds of kilometers long. The lengths are equal, and the two beams of light reach the 6-2 end and the 7-2 end at the other end respectively via the single-mode optical fiber cable 6 and the single-mode optical fiber cable 7. The signal transmitting end is composed of a light delay line 8 and a signal phase modulator 15. The light output from the 6-2 end of the single-mode optical fiber cable 6 is input to the 7-2 port of the single-mode optical fiber cable 7 via the optical fiber delay line 8 and the signal phase modulator 15; the light output from the 7-2 end of the aforementioned single-mode optical fiber cable 7 is input to the 6-2 port of the single-mode optical fiber cable 6 via the signal phase modulator 15 and the optical fiber delay line 8. The two beams of light input from the 7-2 port of the single-mode optical fiber cable 7 and the 6-2 port of the single-mode optical fiber cable 6 are returned to the 7-1 port and the 6-1 port respectively through the long-distance single-mode optical fiber cable 7 and the single-mode optical fiber cable 6. The two beams of light output from the 7-1 port and the 6-1 port are coupled to the lower port and the upper port of the 2*2 single-mode optical fiber coupler 2. The two beams of light from the upper port and the lower port are synthesized by the single-mode optical fiber coupler 2 to form an interference signal, which is output from the left port of the single-mode optical fiber coupler 2 and then converted into an electrical signal output by the photodetector 14. The electrical signal to be transmitted is loaded on the electrode of the signal phase modulator 13, and the optical phase changes of 0 and π are generated to represent the digital signals "0" and "1" respectively. Due to the existence of the optical fiber delay line 8, this phase change is not simultaneous for the two paths of light traveling in opposite directions. By using a burst period of twice the time it takes for the light to pass through the delay line 8, the double transmission signal can be restored at the electrical output end of the photodetector 14. Note that what is transmitted in the optical fiber is the optical phase signal, not the optical intensity signal. Therefore, if a single optical signal is stolen in the middle of the optical cable, it cannot be restored to the intensity-type "0" and "1" signals. If a dual optical signal is stolen in the middle of the optical cable, since the coherence length of the wide-spectrum light source 1 is only on the order of 100μm, the stolen dual optical signals must be adjusted to an equidistant range of less than 100μm between the two light beams, which is very difficult.

[0003] but, Figure 2 The optical fiber communication system based on the Sagnac effect shown still has the possibility of being eavesdropped, for example, by using a Michelson interferometer with an automatic control and adjustment function. In order to solve this problem, we propose the following invention. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the existing optical fiber communication system based on the Sagnac effect is still subject to eavesdropping, and to provide a wavelength division multiplexing method, using a wide spectrum light source, phase modulating n different wavelengths in the same optical path, and the optical path lengths of these n wavelengths are also different. At the same time, these n modulated signals are realized by the decomposition-restoration device of the original signal. The eavesdropper can only take out a small amount of light energy in the middle of the optical path, and needs to decompose it into n different wavelengths, adjust the matching of n different optical paths, and synthesize and decrypt the original signal, making eavesdropping extremely difficult.

[0005] To solve the above problems, the technical solution adopted by the present invention is:

[0006] A wavelength-coded secure optical fiber communication system, comprising a receiving end consisting of a wide-spectrum light source, a 2*2 optical fiber coupler, a first 1*n wavelength splitter, n photoelectric detector groups 4 and an n*1 code restorer; the communication optical cable is two single-mode optical fiber cables of equal length of tens to hundreds of kilometers; the signal transmitting end consists of an optical fiber delay line, a second 1*n wavelength splitter, n phase modulator groups, an n*1 wavelength combiner and a 1*n code divider;

[0007] The wide spectrum light source 1 is connected to one end of a 2*2 optical fiber coupler, and the input end of the first 1*n wavelength splitter is connected to the other end of the same side of the 2*2 optical fiber coupler; the two ends of the other side of the 2*2 optical fiber coupler are respectively connected to the two ends of two digital communication single-mode optical fiber cables; the n output ends of the first 1*n wavelength splitter are respectively connected to n photoelectric detector groups; the n signals output by the n photoelectric detector groups are connected to the n input ends of the n*1 code restorer, and the output of the n*1 code restorer is the restored original signal;

[0008] Two ends of two communication single-mode optical fiber cables at the transmitting end, one end is connected in series with the optical fiber delay line, the second 1*n wavelength splitter, n phase modulator groups, and n*1 wavelength combiner to the other end.

[0009] Furthermore, the n phase modulator groups are all lithium niobate waveguide devices.

[0010] Furthermore, the broadband light source is an ASE fiber light source with broadband and short coherence length.

[0011] Furthermore, it is characterized in that the n photodetector groups are PIN detectors or APD detectors.

[0012] Furthermore, the two single-mode optical fiber cables with a length of tens to hundreds of kilometers are two multi-core optical fiber cables of equal length.

[0013] Furthermore, the first 1*n wavelength splitter, the second 1*n wavelength splitter, and the n*1 wavelength combiner are wavelength division multiplexing devices.

[0014] The beneficial effects achieved by the present invention are:

[0015] Due to the use of the first 1*n wavelength splitter, n photoelectric detector groups, the second 1*n wavelength splitter, n phase modulator groups, and n*1 wavelength combiner, the present invention is actually an interference system synthesized by n Sagnac fiber interferometers of different wavelengths, and the original signal is further simply encrypted and decrypted using 1*n partial encoders and n*1 code restorers. Since the n interference systems can be artificially set to different optical path lengths, some channels are even set with false modulation signals. For eavesdropping on signals in the middle, the stolen light energy cannot be too large, otherwise it will be discovered. The eavesdropper must complete the optical path matching of n interferometers, obtain the analytical coding method, and eliminate false signals, making the originally very difficult theft almost impossible. The present invention is a physical confidential optical fiber communication system, which only has a simple encryption-decryption process and realizes high-speed communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a wavelength-coded secure optical fiber communication system invented based on Sagnac interferometry;

[0017] Figure 2 It is a schematic diagram of the existing secure optical fiber communication system based on Sagnac interferometry;

[0018] ·Reference symbols: broadband light source: 1; 2*2 optical fiber coupler: 1; 1*n wavelength splitter: 3; n photodetector groups: 4; n*1 code restorer: 5; communication single-mode optical fiber cable: 6; communication single-mode optical fiber cable: 7; optical fiber delay line: 8; 1*n wavelength splitter: 9; n phase modulator groups: 10; n*1 wavelength combiner: 11; 1*n code divider: 12; broadband light source: 13; photodetector: 14; phase modulator: 15. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings and embodiments.

[0020] The present invention is a wavelength-coded secure optical fiber communication system based on the Sagnac effect. Figure 1 As shown, the signal receiving end is composed of a wide-spectrum light source 1, a 2*2 optical fiber coupler 2, a 1*n wavelength splitter 3, n photodetector groups 4, and an n*1 code restorer 5. The short coherent length light beam with constant light intensity emitted by the wide-spectrum light source 1 is incident on the 2-1 end of the 2*2 optical fiber coupler 2, and is emitted from the 2-2 end and the 2-3 end of the optical fiber coupler 2. The emitted light from the 2-2 end is coupled into the 6-1 end of the single-mode optical fiber cable 6 with a length of tens to hundreds of kilometers, and the emitted light from the 2-3 end is coupled into the 7-1 end of the single-mode optical fiber cable 7 with a length of tens to hundreds of kilometers. The lengths of the single-mode optical fiber cable 6 and the single-mode optical fiber cable 7 are the same. The two beams of light reach the 6-2 end and the 7-2 end at the other end via the single-mode optical fiber cable 6 and the single-mode optical fiber cable 7 respectively. The signal transmitting end is composed of an optical fiber delay line 8, a 1*n wavelength splitter 9, n phase modulator groups 10, an n*1 wavelength combiner 11 and a 1*n code divider 12. The light output from the 6-2 end of the single-mode optical fiber cable 6 is input to the 7-2 port of the single-mode optical fiber cable 7 via the optical fiber delay line 8, the 1*n wavelength splitter 9, the n phase modulator groups 10 and the n*1 wavelength combiner 11; the light output from the 7-2 end of the single-mode optical fiber cable 7 is input to the 6-2 port of the single-mode optical fiber cable 6 via the n*1 wavelength combiner 11, the n phase modulator groups 10, the 1*n wavelength splitter 9 and the optical fiber delay line 8. The light input from port 7-2 of the single-mode optical fiber cable 7 is returned to port 7-1 via the long-distance single-mode optical fiber cable 7, and the light input from port 6-2 of the aforementioned single-mode optical fiber cable 6 is returned to port 6-1 via the long-distance single-mode optical fiber cable 6. The light returned from port 7-1 and port 7-1 are synthesized by the 2*2 optical fiber coupler 2 to form an interference signal, and half of the light energy is output by port 2-4 of the coupler 2, and then decomposed into n lights of different wavelengths by the 1*n wavelength splitter 3, and converted into electrical signals by the photoelectric detector group 4 composed of n photoelectric detectors, and then synthesized and restored to the original signal by the n*1 code restorer.

[0021] The eavesdropper needs to steal dual-path optical signals in the middle of the optical cable, and it is impossible to steal too much optical energy. At the same time, to correctly separate n different optical wavelengths, interference matching of n wavelengths is required, that is, adjusting the two light beams to an equal distance within a range of less than about 100μm. This is an almost impossible task. Furthermore, it must be restored to the original code in the correct encoding method, and the encoding decomposition method of the original signal is unknown to the eavesdropper.

[0022] Example

[0023] The present embodiment is a wavelength-coded secure optical fiber communication system, wherein the wide-spectrum light source 1 adopts an ASE light source, the 2*2 optical fiber coupler 2 is made by a single-mode optical fiber taper process, the 1*n wavelength splitter 3 adopts a wavelength division multiplexing device; n photoelectric detector groups 4 adopt APDs or PIN tubes, the n*1 coding restorer 5 is an electrical hardware digital circuit, the communication single-mode optical fiber cable 6 and the communication single-mode optical fiber cable 7 are two of the multi-core single-mode optical fiber cables of equal length of tens to hundreds of kilometers, the optical fiber delay line 8 is composed of several kilometers of single-mode optical fiber, the 1*n wavelength splitter 9 and the n*1 wavelength combiner 11 adopt wavelength division multiplexing devices of the same band as the 1*n wavelength splitter 3, the n phase modulator groups adopt n dual-port lithium niobate phase modulators, and the 1*n code divider 12 is a digital circuit that electrically distributes the original electrical signal to n modulated signals.

[0024] Specifically, taking the scheme of Example 1 as an example, the broadband light source 1 adopts a semi-conductor laser of 980nm to pump the erbium-doped optical fiber to generate 10mW ASE superradiation, generating two peaks of 1530nm and 1560nm with bandwidths of 7nm and 10nm, and the 1*n wavelength splitter 9, the n*1 wavelength combiner 11, and the 1*n wavelength splitter 3 all adopt 1530 / 1560WDM couplers; the single-mode optical fiber cable 6 and the single-mode optical fiber cable 7 are 100 kilometers in length, the optical fiber delay line 8 adopts 5 kilometers of single-mode bare optical fiber, and the photodetector group 4 adopts two PIN tubes, and the original signal is decomposed and synthesized into 2 groups of signals, that is, n is 2.

[0025] Specifically, taking the scheme of Example 2 as an example, the broadband light source 1 adopts a semi-conductor laser of 980nm to pump the erbium-doped optical fiber to generate 10mW ASE superradiation, which is then filtered into a broadband light source with a bandwidth of 40nm by a flat filter. The 1*n wavelength splitter 9, the n*1 wavelength combiner 11, and the 1*n wavelength splitter 3 all adopt AGW devices and are divided into 8 groups, that is, n is 8; the single-mode optical fiber cable 6 and the single-mode optical fiber cable 7 are 100 kilometers in length, the optical fiber delay line 8 adopts 5 kilometers of single-mode bare optical fiber, and the photodetector group 4 adopts 8 APD tubes, and the original signal is decomposed and synthesized into 8 groups of signals.

[0026] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A wavelength-coded secure optical fiber communication system, characterized in that: The receiving end is composed of a wide-spectrum light source, a 2*2 optical fiber coupler, a first 1*n wavelength splitter, n photodetectors and an n*1 code restorer; the communication optical cable is two single-mode optical fiber cables of equal length ranging from tens to hundreds of kilometers; the signal transmitting end is composed of an optical fiber delay line, a second 1*n wavelength splitter, n phase modulators, an n*1 wavelength combiner and a 1*n code divider; A wide-spectrum light source is connected to one end of a 2*2 optical fiber coupler, and an input end of a first 1*n wavelength splitter is connected to the other end of the same side of the 2*2 optical fiber coupler; two ends of the other side of the 2*2 optical fiber coupler are respectively connected to two ends of two digital communication single-mode optical fiber cables; n output ends of the first 1*n wavelength splitter are respectively connected to n photoelectric detectors; n signals output by the n photoelectric detectors are connected to n input ends of an n*1 code restorer, and the output of the n*1 code restorer is the restored original signal; Two ends of two digital communication single-mode optical fiber cables at the transmitting end, one end is connected in series with an optical fiber delay line, a second 1*n wavelength splitter, n phase modulators, and an n*1 wavelength combiner to the other end.

2. A wavelength-coded secure optical fiber communication system according to claim 1, characterized in that: The n phase modulators are all lithium niobate waveguide devices.

3. A wavelength-coded secure optical fiber communication system according to claim 1, characterized in that: The broadband light source is an ASE optical fiber light source with broadband and short coherence length.

4. A wavelength-coded secure optical fiber communication system according to claim 1, characterized in that: It is characterized in that The n photodetectors are PIN detectors or APD detectors.

5. A wavelength-coded secure optical fiber communication system according to claim 1, characterized in that: The two single-mode optical fiber cables with a length of tens to hundreds of kilometers are two multi-core optical fiber cables with equal length.

6. A wavelength-coded secure optical fiber communication system according to claim 1, characterized in that: The first 1*n wavelength splitter, the second 1*n wavelength splitter, and the n*1 wavelength combiner are wavelength division multiplexing devices.

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