An optical fiber key distribution system based on the phase noise of a semiconductor light source

Abstract

The present invention relates to the technical field of optical information security, and in particular to an optical fiber key distribution system based on the phase noise of a semiconductor light source, which includes a light source, a first beam splitting device, a second beam splitting device, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, a first optical fiber link, a second optical fiber link, a third optical fiber link, and a fourth optical fiber link. The present invention eliminates the intensity noise term by using the difference method, and ensures that the restored signal has high consistency while extracting the phase noise; the present invention is ingeniously and novelly designed, so that the optical signals sent from both communication parties experience the same path, and the phase noise of the light source is extracted after beat frequency subtraction, and the finally formed key is only related to the light source itself and the key distribution path, with stronger anti-interference ability, realizing high-speed key distribution between the two communication parties.

Description

Technical Field

[0001] The present invention relates to the technical field of optical information security, and in particular to an optical fiber key distribution system based on the phase noise of a semiconductor light source. Background Art

[0002] Cryptography, as an important technology for ensuring information security, has received increasing attention due to its potential applications in alleviating the increasingly serious security threats brought about by the development of communication and computer systems. In an encryption system, key distribution, which provides shared keys for legitimate users, is one of the most critical issues and has also been a hot topic in recent years.

[0003] Currently, the mainstream key distribution schemes are mainly divided into two categories according to their security sources. The security of the former key distribution is called computational security, and its security mainly comes from mathematical algorithms. The purpose is to make it impossible for attackers to crack the encryption algorithm and obtain the key within a short time with limited computing power. The representatives are the currently widely used RSA algorithm and DES algorithm. The security of the latter key distribution scheme based on physical principles is called information-theoretic security, and its security is mainly guaranteed by the uncertainty of physical processes or phenomena. Therefore, it is called a key distribution scheme at the physical layer. Quantum key distribution is the most well-known key distribution scheme at the physical layer. Theoretically, a key distribution scheme completely based on the physical layer remains secure against infinite computing power. However, the currently proposed key distribution schemes at the physical layer are difficult to achieve a high transmission rate over long distances (usually below 1 Mbit / s). Therefore, how to achieve high-speed and anti-interference key distribution over long distances is an important issue restricting the development of physical layer secure key distribution technology. Summary of the Invention

[0004] The present invention provides an optical fiber key distribution system based on the phase noise of a semiconductor light source for the problems of the prior art. By using the difference method, the intensity noise term is eliminated, and while extracting the phase noise, it is ensured that the restored signal has high consistency. The present invention is ingeniously and novelly designed, enabling the optical signals sent from both communication parties to pass through the same path, extracting the phase noise of the light source after beat frequency subtraction, and finally the formed key is only related to the light source itself and the key distribution path, with stronger anti-interference ability, realizing high-speed key distribution between both communication parties.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides an optical fiber key distribution system based on the phase noise of a semiconductor light source, including a light source, a first beam splitting device, a second beam splitting device, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, a first optical fiber link, a second optical fiber link, a third optical fiber link, and a fourth optical fiber link;

[0007] The light source emits an optical signal, which is split by a first beam splitter device to a first optical fiber link and a second optical fiber link respectively;

[0008] The first optical fiber link is connected to a second beam splitter device; the first photodetector and the second photodetector are respectively connected to the second beam splitter device;

[0009] The second optical fiber link is connected to a third beam splitter device; the third photodetector and the fourth photodetector are respectively connected to the third beam splitter device.

[0010] Wherein, the first optical fiber link, the second optical fiber link, the third optical fiber link and the fourth optical fiber link are all standard single-mode optical fibers.

[0011] Wherein, the optical path difference between the third optical fiber link and the fourth optical fiber link is greater than the interference length of the light source.

[0012] Wherein, the second beam splitter device and the third beam splitter device are both 3×3 fiber couplers.

[0013] Wherein, the bandwidths of the first photodetector, the second photodetector, the third photodetector and the fourth photodetector are the same.

[0014] Advantages of the present invention:

[0015] The optical signal emitted from a semiconductor laser with stable operation in the present invention is split by a first beam splitter device and then reaches the two legitimate parties of communication respectively. After passing through a 3×3 coupler, it reaches the other end of communication through two optical fiber links and then enters the 3×3 coupler to complete beat frequency. Finally, it is received by the photodetectors of the two communication parties respectively. The signal received by the photodetector is subtracted from the signal received by another detector locally. After subtracting the intensity noise term, the phase noise term related to the light source itself can be obtained as the basis for generating the key; the present invention eliminates the intensity noise term by using the difference method, and ensures high consistency of the restored signal while extracting the phase noise; the present invention is ingeniously and novelly designed, so that the optical signals emitted from the two communication parties experience the same path, and the phase noise of the light source is extracted after beat frequency subtraction. Finally, the formed key is only related to the light source itself and the key distribution path. Due to the high-speed and physically random characteristics of the phase noise of the semiconductor light source, the generated key can reach a high generation rate and randomness. Under the above settings, the anti-interference ability is stronger, and high-speed key distribution between the two communication parties is realized. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of an optical fiber key distribution system based on the phase noise of a semiconductor light source of the present invention.

[0017] Figure 2 Schematic diagram of the difference signal received by both communication parties in the fiber optic key distribution system based on the phase noise of a semiconductor light source according to this embodiment under two 40-kilometer external fiber lengths.

[0018] In Figures 1 to 2 the reference numerals include:

[0019] 1. Light source; 2. First beam splitter device; 3. First optical fiber link; 4. Second optical fiber link; 5. Second beam splitter device; 6. Third beam splitter device; 7. First photodetector; 8. Second photodetector; 9. Third photodetector; 10. Fourth photodetector; 11. Third optical fiber link; 12. Fourth optical fiber link. Detailed implementation manners

[0020] For the convenience of understanding by those skilled in the art, the present invention will be further described below in conjunction with embodiments and the accompanying drawings. The content mentioned in the implementation manners does not limit the present invention. The present invention will be described in detail below with reference to the accompanying drawings.

[0021] A fiber optic key distribution system based on the phase noise of a semiconductor light source, as Figure 1 shown, includes a light source 1, a first beam splitter device 2, a second beam splitter device 5, a first photodetector 7, a second photodetector 8, a third photodetector 9, a fourth photodetector 10, a first optical fiber link 3, a second optical fiber link 4, a third optical fiber link 11, and a fourth optical fiber link 12;

[0022] The light source 1 emits an optical signal, which is split by the first beam splitter device 2 to the first optical fiber link 3 and the second optical fiber link 4 respectively;

[0023] The first optical fiber link 3 is connected to the second beam splitter device 5; the first photodetector 7 and the second photodetector 8 are respectively connected to the second beam splitter device 5;

[0024] The second optical fiber link 4 is connected to the third beam splitter device 6; the third photodetector 9 and the fourth photodetector 10 are respectively connected to the third beam splitter device 6.

[0025] Specifically, the light source 1 and the first beam splitter device 2 can be located at any one of the communication parties locally, or can be remote from both communication parties; the first beam splitter device 2 is used to receive the optical signal from the light source 1 and transmit it to the first optical fiber link 3 and the second optical fiber link 4;

[0026] The second beam splitter device 5 is configured to receive the optical signal from the first optical fiber link 3 and transmit it to the third beam splitter device 6; and to receive the optical signal from the third beam splitter device 6 and transmit it to the first photodetector 7 and the second photodetector 8;

[0027] The third beam splitter device 6 is configured to receive the optical signal from the second optical fiber link 4 and transmit it to the second beam splitter device 5; and to receive the optical signal from the second beam splitter device 5 and transmit it to the third photodetector 9 and the fourth photodetector 10;

[0028] The first optical fiber link 3, the second optical fiber link 4, the third optical fiber link 11, and the fourth optical fiber link 12 are all configured to transmit optical signals;

[0029] The first photodetector 7, the second photodetector 8, the third photodetector 9, and the fourth photodetector 10 are all configured to convert the optical signal into an electrical signal to obtain the corresponding secret key;

[0030] The second beam splitter device 5, the first photodetector 7, and the second photodetector 8 are located at the local side of one of the two communicating parties, and the third beam splitter device 6, the third photodetector 9, and the fourth photodetector 10 are located at the local side of the other of the two communicating parties.

[0031] In the present invention, the optical signal emitted from the stable semiconductor laser is split by the first beam splitter device 2 and then reaches the two legitimate parties of the communication respectively. After passing through the 3×3 coupler, it reaches the other end of the communication through two optical fiber links, enters the 3×3 coupler to complete beat frequency, and finally is received by the photodetectors of the two communicating parties respectively. After the signal received by the photodetector is subtracted from the signal received by another detector at the local side to subtract the intensity noise term, the phase noise term related to the light source 1 itself can be obtained as the basis for generating the secret key; the present invention eliminates the intensity noise term by using the difference method, and ensures high consistency of the restored signal while extracting the phase noise; the two communicating parties can directly quantify the restored phase noise as the basis for generating the secret key sequence to form a generated key, or form a ciphertext by means of exclusive OR with the plaintext.

[0032] The phase noise in the stable semiconductor laser comes from the spontaneous emission of photons. Different from the pseudo-randomness of statistics, due to the uncertainty principle of quantum mechanics, it has physical true randomness, and the random bit generation rate is ultimately only limited by the laser linewidth, which means that the digital secret key extracted from the phase noise of the laser also has true randomness. However, in addition to the phase noise, there is also intrinsic intensity noise in the laser during operation.

[0033] Among them, the design of the present invention is ingenious and novel, so that the optical signals sent from both communication parties experience the same path, and the phase noise of the light source 1 is extracted after beat frequency subtraction. Finally, the formed secret key is only related to the light source 1 itself and the secret key distribution path. Due to the high-speed and physically random characteristics of the phase noise of the semiconductor light source 1, the extracted secret key can achieve a relatively high generation rate and randomness. Under the above settings, the anti-interference ability is stronger, and high-speed secret key distribution between both communication parties is realized.

[0034] In this embodiment, the first optical fiber link 3, the second optical fiber link 4, the third optical fiber link 11, and the fourth optical fiber link 12 are all standard single-mode optical fibers. Among them, the optical path difference between the third optical fiber link 11 and the fourth optical fiber link 12 is greater than the interference length of the light source 1. Among them, the second beam splitter device 5 and the third beam splitter device 6 are both 3×3 fiber couplers. Among them, the bandwidths of the first photodetector 7, the second photodetector 8, the third photodetector 9, and the fourth photodetector 10 are the same.

[0035] In this embodiment, as Figure 1 shown, the light source is a broad-spectrum superluminescent light-emitting diode. In order to obtain a sufficiently large noise variance, the noise signal is filtered by an optical filter with a bandwidth of 100 GHz and a central wavelength of 1542.32 nm, and then split into two single-mode 3×3 couplers through a single-mode 3 dB coupler (the first beam splitter device), and then enters two 40-kilometer external optical fiber links. After reaching the other end 3×3 coupler, beat frequency is completed and then received by a high-speed photodetector. The length difference between the two external optical fiber links is 160.3 meters, which is much greater than the interference length of the filtered light wave. When the optical powers of the light reaching the coupler from the two external optical fiber links are equal, the optical signals received by the two local detectors can be expressed as:

[0036]

[0037]

[0038] Here, T represents the time delay generated due to the length difference between the two external optical fiber links, ψ j and ψ 2 are the additional phase delays of the 3×3 coupler. Here, the additional phase delay can be expressed as

[0039]

[0040] According to the expression of the laser composite radiation field

[0041]

[0042] Here, the constant E 0is the mean - field amplitude, the functions δ(t) and φ(t) are the relative intensity fluctuation and relative phase fluctuation respectively, and are a series of zero - mean generalized stationary real numbers related to time, which are related to the relative intensity noise and relative phase noise respectively. ω 0 corresponds to the emission frequency at the center spectrum of the SLD light source.

[0043] Combining equations (1), (2) and (4) gives the light intensities received by the two detectors as

[0044]

[0045] Here represents the time - varying phase fluctuation of light, can be regarded as Gaussian white noise, and its mean - square phase deviation is Here T C is the coherence time of light after passing through the filter. As the relative delay T increases, the phase - difference fluctuation and the phase - noise amplitude also increase. When T >> T, the phase noise approaches the asymptotic level, which is the case in this example, while the intensity fluctuations δ(t) and δ(t + T) can be neglected in comparison, that is

[0046]

[0047]

[0048] At this time, subtracting the amplitudes of the two local receivers, the difference signal can be expressed as

[0049]

[0050] It can be found that only the phase - noise term is included in the difference signal here. It is worth noting that due to the existence of the additional phase delay, to ensure that the difference signals obtained by the two communication parties have good consistency, the additional phase delays of the two corresponding detectors should be the same.

[0051] Such as Figure 2 is the waveform comparison within 30 ns of the difference signal after subtracting the original signals received by both parties. Here, 4 photodetectors with a bandwidth of 3.5 GHz are used, and the oscilloscope sampling rate is 5 GSample / s. Through the Pearson correlation - coefficient formula

[0052]

[0053] The correlation coefficient of the two difference signals calculated is 0.94, indicating that they have a very high similarity. Then, the method of double - threshold quantization is used to convert the analog signal into a digital - signal sequence, and the conversion rule is

[0054]

[0055] q+ and q are respectively the high and low quantization thresholds, and ε is a scalar determining the final threshold. Under the above conditions, by adjusting the value of ε, the generation rate of the final secret key can reach 2.3 Gbit / s, while the bit error rate of the secret key sequences of both parties is only 0.0001% at this time.

[0056] As described above, it is only a preferred embodiment of the present invention, and there is no limitation in any form to the present invention. Although the present invention is disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, when making some changes or modifications using the above-disclosed technical content into equivalent embodiments of equivalent changes, but as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical means of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A fiber optic key distribution system based on the phase noise of a semiconductor light source, characterized in that: it includes a light source, a first beam splitter device, a second beam splitter device, a first photodetector, a second photodetector, a third photodetector, a fourth photodetector, a first optical fiber link, a second optical fiber link, a third optical fiber link and a fourth optical fiber link; the light source emits an optical signal, which is split by the first beam splitter device to the first optical fiber link and the second optical fiber link respectively; the first optical fiber link is connected to the second beam splitter device; the first photodetector and the second photodetector are respectively connected to the second beam splitter device; the second optical fiber link is connected to the third beam splitter device; the third photodetector and the fourth photodetector are respectively connected to the third beam splitter device; the optical path difference between the third optical fiber link and the fourth optical fiber link is greater than the interference length of the light source; both the second beam splitter device and the third beam splitter device are 3×3 fiber couplers; the bandwidths of the first photodetector, the second photodetector, the third photodetector and the fourth photodetector are the same; the first beam splitter device is used to receive the optical signal from the light source and transmit it to the first optical fiber link and the second optical fiber link; the second beam splitter device is used to receive the optical signal from the first optical fiber link and transmit it to the third beam splitter device; and is used to receive the optical signal from the third beam splitter device and transmit it to the first photodetector and the second photodetector; the third beam splitter device is used to receive the optical signal from the second optical fiber link and transmit it to the second beam splitter device; and is used to receive the optical signal from the second beam splitter device and transmit it to the third photodetector and the fourth photodetector; the first optical fiber link, the second optical fiber link, the third optical fiber link and the fourth optical fiber link are all used to transmit optical signals; the first photodetector, the second photodetector, the third photodetector and the fourth photodetector are all used to convert optical signals into electrical signals to obtain corresponding keys; the second beam splitter device and the first photodetector and the second photodetector are located at one of the two communicating parties locally, and the third beam splitter device and the third photodetector 9 and the fourth photodetector are located at the other of the two communicating parties locally; the optical signal emitted from a stable working semiconductor laser is split by the first beam splitter device and then reaches the two legitimate parties of the communication respectively. After passing through the 3×3 coupler, it passes through two optical fiber links and reaches the other end of the communication and then enters the 3×3 coupler to complete the beat frequency. Finally, it is respectively received by the photodetectors of the two communicating parties. After the signal received by the photodetector is subtracted from the signal received by another detector locally and the intensity noise term is subtracted, the phase noise term related to the light source itself can be obtained as the basis for generating the key; The light source is a wide-spectrum superluminescent light-emitting diode. In order to obtain a sufficiently large noise variance, the noise signal is filtered by an optical filter with a bandwidth of 100 GHz and a center wavelength of 1542.32 nm, and then split into two single-mode 3×3 couplers through a single-mode 3 dB coupler, and then enters two 40-kilometer external optical fiber links. After reaching the 3×3 coupler at the other end, beat frequency is completed and then received by a high-speed photodetector; the length difference between the two external optical fiber links is 160.3 meters, which is much larger than the interference length of the filtered light wave; when the optical power reaching the coupler from the two external optical fiber links is equal, the optical signals received by the two local detectors can be expressed as: Here, τ represents the time delay caused by the length difference between two external optical fiber links, ψ 1 and ψ 2 are the additional phase delays of the 3×3 coupler. The additional phase delay can be expressed as: According to the expression of the laser composite radiation field: Here, the constant E 0 is the mean-field amplitude. The functions δ(t) and φ(t) are the relative intensity fluctuation and the relative phase fluctuation respectively, which are a series of zero-mean generalized stationary real numbers related to time, and are respectively related to the relative intensity noise and the relative phase noise; ω 0 The emission frequency corresponding to the center spectrum of the SLD light source; Combining equations (1), (2) and (4) gives the optical intensities received by the two detectors as: Here represents the time-varying phase fluctuations of light, which can be regarded as Gaussian white noise with a mean-square phase deviation of where τ c is the coherence time of the light after passing through the filter; as the relative delay τ increases, the phase difference fluctuations and the phase noise amplitude also increase; when τ >> τ c the phase noise approaches the asymptotic level, and the relative intensity fluctuations δ(t) and δ(t + τ) are negligible by comparison, that is: At this time, subtracting the amplitudes of the two local receivers, the difference signal can be expressed as Four photodetectors with a bandwidth of 3.5 GHz are used, and the oscilloscope sampling rate is 5 GSample / s; through the Pearson correlation coefficient formula: The correlation coefficient of the two difference signals calculated is 0.94, indicating that they have a very high similarity; then the analog signal is converted into a digital signal sequence using the method of double-threshold quantization, and the conversion rule is: q+ and q- are the high and low thresholds of quantization respectively, and ε is a scalar that determines the final threshold.

2. A fiber optic key distribution system based on the phase noise of a semiconductor light source according to claim 1, characterized in that: The first optical fiber link, the second optical fiber link, the third optical fiber link, and the fourth optical fiber link are all standard single-mode optical fibers.

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