QTTH SYSTEM BASED ON MULTICORE OPTICAL FIBER MODE DIVISION MULTIPLEXING AND TRANSMISSION METHOD THEREOF

Abstract

A QTTH system based on multicore optical fiber mode division multiplexing, wherein comprising: an OLT end, a MDM-ODN and an ONU end, wherein the OLT end, the MDM-ODN and the ONU end are sequentially connected by an optical fiber; the MDM-ODN comprising a mode multiplexer and a mode demultiplexer, and the mode multiplexer and the mode demultiplexer are connected with each other through MCF, the OLT end comprising a classical signal transmitter, N DV-QKD units and N+1 mode convertors of the OLT end; the ONU end comprising N DV-QKD receivers, a classical signal receiver, N+1 mode convertors of the OLT end, 2N+1 PDs and one OC of the ONU end; the N DV-QKD receivers are respectively connected with the mode demultiplexer through PDs; the N+1 mode convertors of the OLT end are connected with the demultiplexer.

Claims

1. A QTTH system based on multicore optical fiber mode division multiplexing, wherein comprising: an OLT end (Optical Line Terminal), a MDM-ODN (Mode Division Multiplexing-Optical Distribution Network) and an ONU end (Optical Network Unit), wherein the OLT end, the MDM-ODN and the ONU end are sequentially connected by an optical fiber; the MDM-ODN comprising a mode multiplexer and a mode demultiplexer, and the mode multiplexer and the mode demultiplexer are connected with each other through MCF, wherein the MCF is a heterogeneous groove-type auxiliary seven-core fiber; the OLT end comprising a classical signal transmitter, N DV-QKD units and N+1 mode convertors of the OLT end, wherein one end of the N+1 mode convertors is connected with the classical signal transmitter, and the other end of the N+1 mode convertors is connected with a mode multiplexer of the MDM-ODN; the ONU end comprising N DV-QKD receivers, a classical signal receiver, N+1 mode convertors of the OLT end, 2N+1 PDs and one OC of the ONU end; the N DV-QKD receivers are respectively connected with the mode demultiplexer through PDs; the N+1 mode convertors of the OLT end are connected with the demultiplexer, wherein the mode convertors of the N ONU end are respectively connected with the classical signal receivers through PDs, and the remaining one mode convertor of the ONU end is respectively connected with each classical signal receiver through one PD and an OC of the ONU end; when the N+1 classical signals sent by the classical signal transmitter are converted from a basic mode to different mutually orthogonal modes through the mode convertor, the mutually orthogonal modes enter the mode multiplexer with the N quantum signals sent by the N DV-QKD units to be converted into a mode suitable for MCF transmission, and are sent to the mode demultiplexer through the MCF to be decomposed into independent N+1 classical signals and N quantum signals; each decomposed classical signal is converted into a mode of a basic mode through a mode convertor and is sent to a classical signal receiver through a connected PD; the quantum signal is sent through the connected PD to the DV-QKD receiver.

2. The system according to claim 1, wherein: the classical signal transmitter comprising a laser diode, an optical circulator and N intensity modulators, wherein the mode convertors of the N OLT ends are respectively connected with the optical circulator through the intensity modulators, and the remaining one mode convertor of the OLT end is directly connected with the optical circulator; the N+1 classical signals comprise one pilot signal and N OOK (On-Off Keying) signals.

3. The system according to claim 2, wherein the PD uses an InGaAs avalanche photodiode operating in a Geiger mode.

4. The system according to claim 3, wherein: when MCF is used for transmission, a 1550 nm wavelength channel is used for a quantum signal; an upstream 1490 nm wavelength channel or a downstream 1310 nm wavelength channel is used for the classical signal.

5. The system according to claim 4, wherein the mode multiplexer and the mode demultiplexer are composed of cascaded mode select couplers.

6. The system according to claim 1, wherein: the DV-QKD unit is a DV-QKD unit for generating a quantum signal based on a decoy state asymmetric BB84 protocol.

7. The system according to claim 6, wherein: the radius of the fiber core of the MCF is 5 mu m, and a refractive index groove is arranged on the outer side of the fiber core of the MCF; the thickness of the refractive index grooves is 3 μm, and the core pitch of the MCF is 42 μm.

8. The system according to claim 7, wherein: the core refractive index of the MCF is 1.4457; the refractive index difference between the core of the MCF and the cladding of the MCF is 0.003, and the refractive index difference between the refractive index grooves and the cladding of the MCF is 0.003.

9. A transmission method of multi-core fiber mode division multiplexing QTTH according to claim 1, wherein comprising the following steps: S1, system noise test: testing system noise under the condition that the OLT end emits the laser pulse train, and judging whether the signal-to-noise ratio is higher than the preset value of a set signal-to-noise ratio, if the signal-to-noise ratio is higher than the preset value of a set signal-to-noise ratio, entering steps S2 and S2′, and if the signal-to-noise ratio is lower than the preset value of a set signal-to-noise ratio, generating prompt information; S2, quantum state preparation: the DV-QKD unit preparing a quantum state according to a decoy state asymmetric BB84 protocol to generate a quantum signal; S2′, OOK modulation: the classical signal transmitter divides a classical signal into N+1 signals through an optical circulator, wherein one signal serves as a pilot signal, and the other N signals are modulated into N OOK signals through an intensity modulator; meanwhile, the classical signal comprises a pilot signal and N OOK signals; S2′.1, mode conversion: performing mode conversion on each classical signal obtained in the step ST through a mode convertor; S3, mode multiplexing transmission: the signals obtained through S2 and S2′.1 enter MCF through a mode multiplexer for multiplexing transmission and then reach a mode demultiplexer to be decomposed into multiple signals; S4, mode conversion: each classical signal is converted into a basic mode signal through a mode convertor; S5, self-homodyne detection: performing self-homodyne detection on each OOK signal; S6, error rate detection: the ONU end randomly selects a part of DV-QKD screening codes to detect the error rate; and if the measured error code rate value is greater than or equal to the theoretical calculation value of the decoy state, returning to the steps S2 and S2′; and if the measured error code rate value is less than the theoretical calculation value of the decoy state, then establishing safe communication.

10. The transmission method according to claim 9, wherein: the preset value of the signal-to-noise ratio is 20 dB, and the theoretical calculation value of the decoy state is 11%.

11. The system according to claim 2, wherein: the DV-QKD unit is a DV-QKD unit for generating a quantum signal based on a decoy state asymmetric BB84 protocol.

12. The system according to claim 4, wherein: the DV-QKD unit is a DV-QKD unit for generating a quantum signal based on a decoy state asymmetric BB84 protocol.

13. The system according to claim 5, wherein: the DV-QKD unit is a DV-QKD unit for generating a quantum signal based on a decoy state asymmetric BB84 protocol.

14. A transmission method of multi-core fiber mode division multiplexing QTTH according to claim 2, wherein comprising the following steps: S1, system noise test: testing system noise under the condition that the OLT end emits the laser pulse train, and judging whether the signal-to-noise ratio is higher than the preset value of a set signal-to-noise ratio, if the signal-to-noise ratio is higher than the preset value of a set signal-to-noise ratio, entering steps S2 and S2′, and if the signal-to-noise ratio is lower than the preset value of a set signal-to-noise ratio, generating prompt information; S2, quantum state preparation: the DV-QKD unit preparing a quantum state according to a decoy state asymmetric BB84 protocol to generate a quantum signal; S2′, OOK modulation: the classical signal transmitter divides a classical signal into N+1 signals through an optical circulator, wherein one signal serves as a pilot signal, and the other N signals are modulated into N OOK signals through an intensity modulator; meanwhile, the classical signal comprises a pilot signal and N OOK signals; S2′.1, mode conversion: performing mode conversion on each classical signal obtained in the step ST through a mode convertor; S3, mode multiplexing transmission: the signals obtained through S2 and S2′.1 enter MCF through a mode multiplexer for multiplexing transmission and then reach a mode demultiplexer to be decomposed into multiple signals; S4, mode conversion: each classical signal is converted into a basic mode signal through a mode convertor; S5, self-homodyne detection: performing self-homodyne detection on each OOK signal; S6, error rate detection: the ONU end randomly selects a part of DV-QKD screening codes to detect the error rate; and if the measured error code rate value is greater than or equal to the theoretical calculation value of the decoy state, returning to the steps S2 and S2′; and if the measured error code rate value is less than the theoretical calculation value of the decoy state, then establishing safe communication.

15. The transmission method according to claim 14, wherein: the PD uses an InGaAs avalanche photodiode operating in a Geiger mode.

16. The transmission method according to claim 15, wherein: when MCF is used for transmission, a 1550 nm wavelength channel is used for a quantum signal; an upstream 1490 nm wavelength channel or a downstream 1310 nm wavelength channel is used for the classical signal.

17. The transmission method according to claim 16, wherein: the mode multiplexer and the mode demultiplexer are composed of cascaded mode select couplers.

18. The transmission method according to claim 11, wherein: the DV-QKD unit is a DV-QKD unit for generating a quantum signal based on a decoy state asymmetric BB84 protocol.

19. The transmission method according to claim 18, wherein: the radius of the fiber core of the MCF is 5 mu m, and a refractive index groove is arranged on the outer side of the fiber core of the MCF; the thickness of the refractive index grooves is 3 μm, and the core pitch of the MCF is 42 μm.

20. The transmission method according to claim 18, wherein: the core refractive index of the MCF is 1.4457; the refractive index difference between the core of the MCF and the cladding of the MCF is 0.003, and the refractive index difference between the refractive index grooves and the cladding of the MCF is 0.003.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a whole structure frame diagram of the QTTH system based on multi-core fiber mode division multiplexing of the disclosure;

[0041] FIG. 2 is a cross-sectional view of a heterogeneous groove-type auxiliary seven-core fiber of the multi-core fiber mode division multiplexing-based QTTH system of the present disclosure;

[0042] FIG. 3 is a refractive index profile of a heterogeneous groove-type auxiliary seven-core fiber of the QTTH system based on multi-core fiber mode division multiplexing of the disclosure;

[0043] FIG. 4 is a signal distribution diagram of the QTTH system based on multi-core fiber mode division multiplexing of the disclosure;

[0044] FIG. 5 is a flow chart of the transmission method of the QTTH system based on multi-core fiber mode division multiplexing of the disclosure;

DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure, and it is obvious that the described embodiments are only a part of the embodiments of the present disclosure, but not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art based on the embodiments of the present disclosure without creative work, are within the scope of the present disclosure.

Embodiment 1

[0046] A QTTH system based on multicore optical fiber mode division multiplexing, as shown in FIG. 1, comprising: an OLT end, an MDM-ODN end and an ONU end sequentially connected through optical fibers.

[0047] The MDM-ODN comprises a mode multiplexer and a mode demultiplexer, wherein the mode multiplexer and the mode demultiplexer are both composed of cascade mode select couplers and are connected with each other through MCF (micro channel fiber), and the MCF is a heterogeneous groove-type auxiliary seven-core optical fiber and has the advantages of low crosstalk and large mode field area. In addition, the cascade mode select coupler is based on the phase matching principle, evanescent-field coupling occurs when the basic mode and the high-order mode reach phase matching, which can output the mode separation function of different modes at different ports, so that the cascade mode select coupler can be effectively used as a mode multiplexer and a mode demultiplexer, and has the advantages of easiness in manufacturing, high compatibility with optical fibers, low mode crosstalk and the like.

[0048] the OLT end comprising a classical signal transmitter, N DV-QKD (Discrete Variable-Quantum Key Distribution) units and N+1 mode convertors of the OLT end, wherein one end of the N+1 mode convertors is connected with the classical signal transmitter, and the other end of the N+1 mode convertors is connected with a mode multiplexer of the MDM-ODN;

[0049] the ONU end comprising N DV-QKD receivers, a classical signal receiver, N+1 mode convertors of the OLT end, 2N+1 PDs (light detectors) and one OC of the ONU end; the N DV-QKD receivers are respectively connected with the mode demultiplexer through PDs (light detectors); N+1 mode convertors of the OLT end are connected with the demultiplexer, wherein the mode convertors of the N ONU end are respectively connected with the classical signal receivers through PDs, and the remaining one mode convertor of the ONU end is respectively connected with each classical signal receiver through one PD and an OC (Optical Circulator) of the ONU end;

[0050] when the N+1 classical signals sent by the classical signal transmitter are converted from a basic mode to different mutually orthogonal modes through the mode convertor, the mutually orthogonal modes enter the mode multiplexer with the N quantum signals sent by the N DV-QKD units to be converted into a mode suitable for MCF transmission, and are sent to the mode demultiplexer through the MCF to be decomposed into independent N+1 classical signals and N quantum signals; each decomposed classical signal is converted into a mode of a basic mode through a mode convertor and is sent to a classical signal receiver through a connected PD; the quantum signal is sent through the connected PD to the DV-QKD receiver.

[0051] Wherein the PD uses an InGaAs avalanche photodiode operating in a Geiger mode.

[0052] Specifically, the classical signal transmitter comprises a laser diode, an optical circulator and N intensity modulators, wherein the mode convertors of the N OLT ends are respectively connected with the optical circulator through the intensity modulators, and the remaining one mode convertor of the OLT end is directly connected with the optical circulator; and the N+1 classical signals comprise one pilot signal and N OOK (On-Off Keying) signals. The classical signal generator generates a pilot signal, and has the advantages that coherent detection can be used at a receiving end to improve the spectrum efficiency and the network coverage, the related cost caused by using a narrow-band Local Oscillator (LO) on the ONU is reduced, and an OOK signal can be independently received through automatic detection.

[0053] Specifically, the DV-QKD unit generates quantum signals for key distribution based on a decoy state asymmetric BB84 protocol, and the protocol utilizes the space dimension of MCF instead of polarization as a degree of freedom. The working principle of the system is that quantum signals transmitted in any two fiber cores of the MCF are utilized to generate two mutually unbiased basis, and for the core A and the core B, the basis X is defined as (|A; |B) and the basis Y is defined as (|A+B, |A−B)) and a final secret key rate is R≥I.sub.AB−min (I.sub.AE/I.sub.BE), wherein I.sub.AB represents the classical mutual information I.sub.XY=H(X)−H(X|Y) between Alice (DV-QKD unit at OLT end) and Bob (DV-QKD receiver at ONU end) and min (I.sub.AE/I.sub.BE) relates to Alice and Eve or quantum mutual information between Alice and Eve. The asymmetry is realized by that the basis X and the basis Y are selected with different probabilities, the basis with the higher probability is selected for key generation, and the basis with the lower probability is selected for security detection, so that the mode can realize higher final key rate. Meanwhile, the disclosure further introduces a decoy state for effectively resisting PNS (Photon Number Splitting).

[0054] Furthermore, since the multi-core fiber inevitably has intermodal coupling, a power coupling equation is required to analyze the transmission characteristics of the multi-core fiber to determine whether the multi-core fiber meets the requirement of mode division multiplexing. The power coupling mode theory is that a system average value is introduced into the mode coupling theory, and the power is directly used as a coupling parameter, so that the problem of crosstalk between cores in the multi-core optical fiber can be effectively analyzed. When only the power coupling of the adjacent cores is taken into account, the power P.sub.i in the i.sup.th core can be expressed as:

[00001]$\frac{d{P}_i\left(z\right)}{dz}=\underset{i}{.Math.}{h}_{\mathrm{ij}}\left[P_j\left(z\right)-P_i\left(z\right)\right]$

[0055] the summation sign represents the sum of the coupling power of adjacent fiber cores, and h.sub.ij represents the power coupling coefficient between the i.sup.th fiber core and the j.sup.th fiber core. Assuming that the power coupling coefficients between the central core and the surrounding cores are equal to each other, i.e., h, and the power coupling coefficients between the surrounding cores are also equal to each other, i.e., g, the formula can be specifically expressed as follows:

[00002]$\frac{d{P}_1}{dz}=h\left(P_2-P_1\right)+h\left(P_3-P_1\right)+h\left(P_4-P_1\right)+h\left(P_5-P_1\right)+h\left(P_6-P_1\right)+h\left(P_7-P_1\right)\frac{d{P}_2}{dz}=h\left(P_1-P_2\right)+g\left(P_3-P_2\right)+g\left(P_4-P_2\right)+g\left(P_5-P_2\right)+g\left(P_6-P_2\right)+g\left(P_7-P_2\right)\frac{d{P}_3}{dz}=h\left(P_1-P_3\right)+g\left(P_2-P_3\right)+g\left(P_4-P_3\right)+g\left(P_5-P_3\right)+g\left(P_6-P_3\right)+g\left(P_7-P_3\right)\frac{d{P}_4}{dz}=h\left(P_1-P_4\right)+g\left(P_2-P_4\right)+g\left(P_3-P_4\right)+g\left(P_5-P_4\right)+g\left(P_6-P_4\right)+g\left(P_7-P_4\right)\frac{d{P}_5}{dz}=h\left(P_1-P_5\right)+g\left(P_2-P_5\right)+g\left(P_3-P_5\right)+g\left(P_4-P_5\right)+g\left(P_6-P_5\right)+g\left(P_7-P_5\right)\frac{d{P}_6}{dz}=h\left(P_1-P_6\right)+g\left(P_2-P_6\right)+g\left(P_3-P_6\right)+g\left(P_4-P_6\right)+g\left(P_5-P_6\right)+g\left(P_7-P_6\right)$

[0056] adding all the above formulas to obtain:

[00003]$\frac{d{P}_1}{dz}=hP-6h{P}_1\frac{dP}{dz}=6h{P}_1-hP$

[0057] in the formula, P=Σ.sub.k=2.sup.7 P.sub.k, the power of the central fiber core at the point z=0 is defined as P.sub.1(0), and the normalized power of the central fiber core and the surrounding fiber core in the seven-core optical fiber are obtained according to the two formulas:

[00004]$\begin{array}{cc}\frac{P_1\left(z\right)}{P_1\left(0\right)}=\frac{1+6\exp -\left(7hz\right)}{7}\frac{P_k\left(z\right)}{P_1\left(0\right)}=\frac{1+\exp -\left(7hz\right)}{7}& \left(0\right)\end{array}$

[0058] where P.sub.k(z) (k=2, 3, . . . , 7) is the optical power of the k.sup.th core, then the crosstalk of the surrounding cores under the condition that the middle core is excited is as follows:

[00005]$X_P\left(z\right)=\frac{1-\exp -\left(7hz\right)}{1+\exp -\left(7hz\right)}$

[0059] it can be seen that the power coupling coefficient has a large influence on the crosstalk of the multi-core fiber. The crosstalk conditions under different random errors in the multi-core fiber are calculated by utilizing a power coupling mode theory, and the fact that the crosstalk is reduced when the diameter difference between fiber cores is increased is found, so that the fact that the heterogeneous multi-core fiber effectively inhibits the intermodal crosstalk is proved. Compared with a non-groove structure, the crosstalk is integrally reduced by about 20-30 dB by providing a groove structure, so that the mode field area is increased by increasing the inner diameter of the groove, reducing the outer diameter of the groove and reducing the refractive index difference between the groove and the cladding, and the nonlinear damage is further reduced. Therefore, the heterogeneous groove-type structure seven-core optical fiber can enable light waves to be transmitted in respective fiber cores, greatly reduces coupling between the fiber cores, and can be used for mode division multiplexing.

[0060] More specifically, as shown in FIG. 2, for a groove-type structure core, the structure at the upper right corner in the figure has a core in the middle, and a cladding and t groove-type are provided outside the core, A represents the core pitch, and is set to 42 μm. Due to the refractive index groove structure around the fiber core, the electric field far away from the fiber core is restrained, so that the overlapping integral between the electric fields of the adjacent fiber cores is reduced, and the crosstalk is restrained to a certain degree.

[0061] More specifically, as shown in FIG. 3, refractive index grooves are provided outside the core of the MCF, and the refractive index of the core of the MCF is n.sub.1=1.4457, the refractive index difference between the core of the MCF and the cladding of the MCF is Δ1=0.003, and the refractive index difference between the grooves of the MCF and the cladding is Δ2=0.003. The core radius of the MCF is r.sub.1=5 μm, the distance between the core center of the MCF and the grooves is r.sub.2=10 μm, and the groove width of the MCF is r.sub.3=3 μm. Through comprehensive analysis, the parameter setting can effectively reduce the modal dispersion and increase the effective mode field area of the optical fiber.

[0062] More specifically, as shown in FIG. 4, in the heterogeneous groove-type auxiliary seven-core fiber of MCF, the 1.sup.th core and the 3.sup.th transmit DV-QKD signals, the 2.sup.th core transmits a pilot signal, the 4.sup.th core and the 5.sup.th core transmit upstream signals, and the 6.sup.th core and the 7.sup.th core transmit downstream signals.

[0063] Preferably, when MCF is used for transmission, a wavelength channel of 1550 nm is provided for the quantum signal; either an upstream 1490 nm wavelength channel or a downstream 1310 nm wavelength channel is provided for the classical signal to attenuate the effect of raman scattering noise.

[0064] S1, system noise test: checking whether the equipment at an OLT end, an MDM-ODN end and an ONU end being normally operated, and setting initial conditions; under the condition that the OLT end emits laser pulse trains, testing system noise, and judging whether the signal-to-noise ratio is higher than the preset value of a set signal-to-noise ratio; if the signal-to-noise ratio is higher than the preset value of the set signal-to-noise ratio, entering steps S2 and S2′, while if the signal-to-noise ratio is lower than the preset value of the set signal-to-noise ratio, generating prompt information; wherein, the signal-to-noise ratio of the test system is provided by the following formula: SNR=10 lg (P.sub.S/P.sub.N), P.sub.S represents a signal power and P.sub.N represents a noise power, and the preset value of the signal-to-noise ratio is 20 dB;

[0065] S2, OOK modulation: the classical signal transmitter divides a classical signal into N+1 signals through an optical circulator, wherein one signal serves as a pilot signal, and the other N signals are modulated into N OOK signals through an intensity modulator; meanwhile, the classical signal comprises a pilot signal and N OOK signals;

[0066] S2.1, mode conversion: each classical signal obtained in the step ST is subjected to mode conversion through a mode convertor, so that the classical signals in the basic mode are converted into different and mutually orthogonal modes through the mode convertor, and the quantum signals are transmitted in the basic mode without any mode;

[0067] S2′, quantum state preparation: the DV-QKD unit prepares a quantum state according to a decoy state asymmetric BB84 protocol to generate a quantum signal, and the specific steps comprise:

[0068] S2′. 1: in each pulse sending cycle, Alice randomly prepares and sends a signal state or decoy state to receiver Bob, there are different in average photon number between Alice and Bob. The initial state prepared at Alice |φ=|μ is converted into two state |φ.sub.1=e.sup.iθ.sup.1|μ and |φ.sub.2=e.sup.iθ.sup.2|μ of different phases through different ports of the Mach-Zehnder interferometer; after the state |φ.sub.1 and |φ.sub.2 is transmitted to the MCF, the MCF transforms the state by using different space dimensions of any two fiber cores (such as a core A and a core B); the |φ.sub.1 is converted into Quantum State|)=e.sup.iθ.sup.1k.sub.1|μ after it passing through the core A, the |φ.sub.1 is converted into Quantum State|B)=e.sup.iθ.sup.1 k.sub.2|μ after it passing through the core B; in the same way, the |φ.sub.2 is converted into |A+B=e.sup.iθ.sup.2 k.sub.1|μ and |A−B=e.sup.iθ.sup.2k.sub.2|μ after it passing through different fiber cores; the four states constitute two mutually unbiased basis, the basis X being defined as (|A, |B), the basis Y being defined as (|A+B, |A−B);

[0069] S2′. 2: Alice tells Bob which of these states are signal states and which are decoy states by using classical channels (there are independent classical channels between Alice and Bob for communication);

[0070] S3, mode multiplexing transmission: each signal obtained by S2.1 and S2′.1 enter MCF through a mode multiplexer for multiplexing transmission and then reach a mode demultiplexer to be decomposed into multiple signals;

[0071] S4, mode conversion: each classical signal is converted into a basic mode signal through a mode convertor, and a quantum signal does not need to be converted; meanwhile, the classical signal and the quantum signal are in a basic mode and can be transmitted through a single-mode optical fiber;

[0072] S5, detecting signal: each signal is detected by a photoelectric detector; the detector uses an InGaAs avalanche photodiode operated in a Geiger mode, the working mode of the avalanche diode is divided into a linear mode and a Geiger mode, the avalanche diode working in the linear mode can only respond to classical strong light signals but not respond to weak single photon signals of quanta, and the avalanche diode working in the Geiger mode can respond to both signals;

[0073] S6, self-homodyne detection: all signals respectively reach a receiver to complete information transmission, and the pilot frequency replaces the local oscillation to perform self-homodyne detection on each OOK signal, there is no complex DSPs needed;

[0074] S7, error rate detection: the ONU end randomly selects a part of DV-QKD screening codes to detect the error rate; and if the measured error code rate value is greater than or equal to the theoretical calculation value of the decoy state, returning to the steps S2 and S2′, and if the measured error code rate value is less than the theoretical calculation value of the decoy state, then establishing safe communication; wherein, the theoretical calculation value of the decoy state is 11%, and the specific steps comprising:

[0075] S7.1: Bob randomly selects a measuring basis to measure, and declares the measuring basis provided by the Bob and the received quantum state in which cycle;

[0076] S7.2: both Alice and Bob keep the correct part of the basis vector comparison as screening codes, and respectively calculate the counting rate and the error rate of the signal state and the decoy state, wherein only one part of the signal state is extracted for error rate estimation;

[0077] S7.3: both Alice and Bob determine whether there is wiretapping by carrying out error rate detection of the data, if wiretapping exists, then abandoning secret key and stopping communication, and if wiretapping does not exist, then proceeding with operations such as error correction, confidentiality amplification and the like.

[0078] The above embodiments are only intended to illustrate but not to limit the technical solution of the present disclosure; although the present disclosure has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present disclosure.