CN114006693B - Polarization coding QKD system and method based on silicon optical integrated chip - Google Patents
Polarization coding QKD system and method based on silicon optical integrated chip Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
- H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/5161—Combination of different modulation schemes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/532—Polarisation modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/564—Power control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/615—Arrangements affecting the optical part of the receiver
- H04B10/6151—Arrangements affecting the optical part of the receiver comprising a polarization controller at the receiver's input stage
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
- H04L2209/12—Details relating to cryptographic hardware or logic circuitry
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention discloses a polarization coding QKD system based on a silicon optical integrated chip, which comprises a transmitting end and a receiving end, wherein the transmitting end and the receiving end both comprise a random number generator, an FPGA (field programmable gate array) and a quantum chip, and the FPGA is used for controlling the quantum chip and communicating through a classical channel; the random number generator is used for generating a modulation signal; in a transmitting end, the FPGA generates a pulse signal to drive the intensity modulator to generate a direct-current bias voltage to drive the adjustable attenuator, and drives the phase modulator and the polarization modulator to carry out phase randomization and polarization state preparation according to the generated modulation signal, and then the receiving end carries out demultiplexing through the polarization demultiplexer; in the receiving end, the FPGA drives a polarization demodulator according to a modulation signal generated by a random number generator, a measuring base is randomly selected to measure the received polarization state, and photon counting is carried out through a single photon detector and recorded as a measuring result. The invention reduces the error rate of the system and improves the transmission distance of the system.
Description
Technical Field
The invention relates to the technical field of micro-nano photoelectrons and quantum communication, in particular to a polarization coding QKD system and method based on a silicon optical integrated chip.
Background
QKD technology is an important component of quantum communications, primarily for the generation and distribution of encryption keys. QKD theoretically enables absolutely secure secret communications, the security of which is guaranteed by physical laws such as uncertainty principle and quantum state unclonable principle.
QKD techniques can utilize entangled quantum states for key distribution: respectively transmitting a group of entangled quantum states to two trusted terminals, so that both communication parties share the entangled states; then at the terminal, the two parties randomly select different basic vectors for measurement respectively; the two parties inform each other of the basic vector used for measurement through classical channels, and synchronize, and the part measured by the two parties at the same time is reserved. Further, the communication parties can divide the data into two parts, one part of the data is used for testing the Bell inequality through the corresponding measurement result disclosed by the classical channel, and the information quantity acquired by an eavesdropper can be detected according to the damage degree of the Bell inequality; the other part of data is reserved with the same bits of the measuring base vector as the original key.
Because the research of high-speed entangled state preparation technology and long-distance entangled state transmission technology is still in the beginning stage, QKD technology uses single photon superposition state for key distribution more: the communication parties select mutual unbiased bases in advance, the preparation end randomly selects one group of the mutual unbiased bases to prepare corresponding quantum states, and the emission end records the selected unbiased bases in sequence; then the quantum state is sent to a receiving end through a quantum channel, the receiving end randomly selects one group of mutually unbiased bases to measure, and the receiving end records a measuring result and the base used for measurement; the two parties inform the opposite party of the basic vector used for measurement through a classical channel, and the same bit of the basic vector is reserved for measurement and can be used as an original key. At this time, the secret key is generated and distributed to both communication parties, and the transmitting end can encrypt the classical communication signal by using the secret key and transmit the signal to the receiving end through a classical channel; the receiving end can also decrypt the classical communication signal with the key and obtain the information content. If the eavesdropper intercepts the encrypted classical communication signal, decryption cannot be performed to obtain specific information because the secret key is not mastered; if an eavesdropper eavesdrops on a quantum channel, the transmitted quantum state cannot be measured without disturbing the original state (quantum state unclonable principle), so that information cannot be acquired without being perceived by both legal communication parties; when both communication parties perceive that the transmitted quantum state is intercepted and the error rate is abnormal, the group key can be abandoned to regenerate the safe key.
In a QKD system in practical use, the preparation end and the receiving end are mostly built by using split-stereoscopic optical elements, which occupies huge volume and puts high demands on alignment of optical paths. In addition, the method has the defects of complex structure, poor stability, high cost and the like, and is not beneficial to popularization and application of QKD technology.
The QKD system based on polarization coding uses polarized photons as a carrier for coding and transmitting qubits, and has the advantages of mature control and simple structure. The polarized photons can be polarization entangled photon pairs generated by a nonlinear process, and can also be single photon polarization states, for example, the polarization encoding BB84 protocol utilizes two groups of mutually unbiased bases to encode 0 state and 1 state, so that the emitting end is required to prepare each polarization state with high extinction ratio. However, due to the reasons of non-ideal roundness, residual stress and the like of the optical fiber, a double refraction effect can be generated in the optical fiber, so that the polarization state is difficult to maintain stable in transmission in the optical fiber.
Therefore, there is a need for further improvements in existing QKD-based systems to overcome the large volume, complex structure, poor stability, high cost, and unstable polarization state transmission in optical fibers.
Disclosure of Invention
In order to solve the technical problems, the invention provides a system and a method based on polarization coding QKD of a silicon optical integrated chip, which have the advantages of small volume, simple structure, good stability, low cost and good stability.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: the polarization coding QKD system based on the silicon optical integrated chip comprises a sending end Alice and a receiving end Bob, wherein the sending end Alice and the receiving end Bob comprise a random number generator, an FPGA and a quantum chip, and the FPGA is used for controlling the quantum chip and communicating through a classical channel; the random number generator is used for generating a modulation signal;
the quantum chip comprises a substrate, wherein an intensity modulator, a phase modulator, an adjustable attenuator, a polarization modulator, a polarization multiplexer, a polarization demultiplexer and a polarization demodulator are integrated on the substrate;
the intensity modulator, the phase modulator, the adjustable attenuator and the polarization modulator are sequentially connected through electric signals;
the lower port of the emergent end of the adjustable attenuator is connected to a single photon detector for monitoring the attenuation level; the upper port of the emergent end of the attenuator is connected to the polarization modulator for preparing the polarization state;
the polarization modulator is connected with the polarization demultiplexer through an optical fiber, and the polarization modulator and the polarization demultiplexer are also provided with a polarization controller; the polarization demultiplexer is connected with the polarization demodulator;
in a sending end Alice, the FPGA generates a pulse signal to drive the intensity modulator to generate a direct-current bias voltage to drive the adjustable attenuator, and drives the phase modulator and the polarization modulator according to a modulation signal generated by the random number generator to perform phase randomization and polarization state preparation, and simultaneously records a randomly selected preparation base; multiplexing the prepared polarization state into a single-mode fiber through a polarization multiplexer for transmission, and then demultiplexing the polarization state through a polarization demultiplexer at a receiving end so as to execute the polarization measurement of the next step;
in the receiving end Bob, the FPGA drives the polarization demodulator according to the modulation signal generated by the random number generator, randomly selects a measurement base to measure the received polarization state, records the randomly selected measurement base, counts the photon number by the single photon detector, and records the photon count as a measurement result.
Preferably, in the quantum chip, the direct current light is coupled to the straight waveguide end face of the intensity modulator, modulated into light pulses by the intensity modulator, enters the phase modulator for phase randomization, the average photon number of the randomized light pulses is attenuated to a single photon level at the adjustable attenuator and enters the polarization modulator, and the power and the phase of the polarization state basic vector are modulated by the polarization modulator;
the modulated light pulse is converted into a corresponding polarization state in one straight waveguide by the polarization multiplexer, then enters a single-mode fiber through end surface coupling, and after the polarization state is transmitted through the single-mode fiber, the polarization state is coupled to the polarization demultiplexer through the end surface and is converted into intensity and phase information in two straight waveguides by the polarization demultiplexer;
the polarization demodulator demodulates the power and the phase of the polarization state basic vector to realize projection measurement;
finally, photons are coupled into the optical fiber through the end face and are transmitted to 2 single photon detectors through the optical fiber, and photon counting is generated at the single photon detectors.
Preferably, the polarization modulator comprises an MMI optical coupler and an MZI, the MZI comprises a TOPM and an EOPM, the attenuated photons enter the polarization modulator to compensate the phase difference of the two arms by the TOPM inside the MZI, and the power and the phase of the polarization state ground vector are modulated by the EOPM inside the MZI and the EOPM outside the MZI respectively.
Preferably, the polarization demodulator comprises an MMI optical coupler and an MZI, the MZI comprises a TOPM and an EOPM, the light quantum information converted by the polarization demultiplexer compensates phase difference of two arms through the TOPM inside the MZI, and the power and the phase of the polarization state ground vector are respectively demodulated through the EOPM inside the MZI and the EOPM outside the MZI.
Preferably, the substrate is SiO in SOI system 2 A material.
Preferably, two output ports of the polarization demodulator are respectively connected with the polarization controller and the single photon detector in sequence through optical fibers.
Preferably, the polarization multiplexer, the polarization demultiplexer and the polarization demodulator all employ on-chip MZI structures.
Preferably, the MMI optocoupler, TOPM and EOPM are all silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide or silicon nitride materials.
Preferably, the polarization multiplexer and the polarization demultiplexer each comprise a Bi Level tapered structure and an adiabatic coupling structure which are sequentially connected.
A polarization-compensated QKD method employing the above system, the method comprising the steps of:
step 1: a transmitting end Alice prepares polarization states H, V, A and D, and is coupled to an optical fiber line through a polarization multiplexer to be transmitted to a receiving end Bob;
step 2: the receiving end Bob measures deflection angles of the received polarization states, marks the deflection angles as rH, rV, rA and rD respectively, and sends the results to Alice through a classical channel;
step 3: the transmitting end Alice adds a corresponding rotation angle to the original polarization base to prepare a new state, and then randomly transmits the newly prepared H-r H ,V-r V ,A-r A ,D-r D The polarized photon sequence is coupled to the optical fiber through a polarization multiplexer and sent to a receiving end Bob;
step 4: the receiving terminal Bob randomly selects a right-angle base or an oblique base for measurement, and transmits the base used for measurement to Alice through a classical channel;
step 5: alice determines to use the correct measurement basis and sends it to Bob over the classical channel, both sides keeping the bits that the measurement basis is consistent with as the original key.
The beneficial technical effects of the invention are as follows:
the invention integrates all electronic components on the substrate, improves the integration level of the system, enhances the flexibility of the system, reduces the number of elements adopted and reduces the manufacturing cost.
The invention is based on the modulation mechanism of the on-chip MZI, and can adopt EOPM to regulate and control the phases of two arms of the interferometer. The EOPM realized by utilizing the carrier effect can reach a high modulation rate of 1.25GHz, which is beneficial to realizing a high-speed polarization state preparation process, thereby improving the rate of QKD.
According to the invention, TOPM is added into the MZI containing EOPM to compensate the phase difference of the two arms, so that 30dB high extinction ratio can be realized, and the fidelity of polarization state preparation is improved.
The structures such as the MZI, the phase shifter, the polarization rotator and the like adopted by the invention are all based on a silicon-based maturation process and are compatible with a mature microelectronic CMOS process.
The QKD method for polarization compensation reduces the error rate of the system and improves the transmission distance of the system.
Drawings
Fig. 1 is a schematic block diagram of a polarization encoded QKD system based on a silicon optical integrated chip according to the present invention.
Fig. 2 is a schematic structural diagram of a quantum chip according to the present invention.
Fig. 3 is a flow chart of a QKD method of polarization compensation of the present invention.
Detailed Description
The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.
As shown in fig. 1, a polarization coding QKD system based on a silicon optical integrated chip includes a transmitting end Alice and a receiving end Bob, where the transmitting end and the receiving end both include a random number generator, an FPGA and a quantum chip, where the FPGA is used to control the quantum chip and communicate through a classical channel; the random number generator is used for generating a modulation signal;
as shown in fig. 2, the quantum chip includes a substrate including a first substrate 110 and a second substrate 210, and an intensity modulator 120, a phase modulator 130, an adjustable attenuator 140, a polarization modulator 150, and a polarization multiplexer 160 are integrated on the first substrate 110.
The second substrate 210 has a polarization demultiplexer 220 and a polarization demodulator 230 integrated thereon;
the connection mode of each electronic component is as follows:
the intensity modulator 120, the phase modulator 130, the adjustable attenuator 140 and the polarization modulator 150 are sequentially connected through electrical signals;
the lower port of the output end of the adjustable attenuator 140 is connected to a single photon detector (not shown) for monitoring the attenuation level; the upper port of the exit end of the attenuator 140 is connected to the polarization modulator 150 for preparing the polarization state;
the polarization modulator 150 is connected to the polarization demultiplexer 220 through the single mode fiber 170 and the first polarization controller 180 in sequence, and the polarization demultiplexer 220 is connected to the polarization demodulator 230.
The direct current light of the external laser is coupled to the straight waveguide end face of the intensity modulator 120, modulated into light pulses by the intensity modulator 120, enters the phase modulator 130 for phase randomization, the average photon number of the randomized light pulses is attenuated to a single photon level at the adjustable attenuator 140 and enters the polarization modulator 150, and the power and the phase of the polarization state basic vector are modulated by the polarization modulator 150;
specifically, the polarization modulator 150 includes an MMI (multi-mode interference, multimode interference) optical coupler 151 and an MZI (Mach-Zehnder interferometer ) including a TOPM152 (thermo-optic phase modulator, thermo-optic phase modulator) and an EOPM 153 (electro-optic phase modulator ), and the attenuated photons enter the polarization modulator 150 to compensate for the phase difference of the two arms through the TOPM152 inside the MZI and modulate the power and phase of the polarization state basis vector through the EOPM 153 inside the MZI and the EOPM 153 outside the MZI, respectively.
The modulated light pulse is converted into a corresponding polarization state in one straight waveguide by the polarization multiplexer 160, then enters the single-mode fiber 170 through end surface coupling, and the polarization state is transmitted through the single-mode fiber 170, then is coupled to the polarization demultiplexer 220 through the end surface and is converted into intensity and phase information in two straight waveguides by the polarization demultiplexer 220;
the polarization demodulator 230 demodulates the power and the phase of the polarization state ground vector to realize projection measurement;
the polarization demodulator 230 comprises an MMI optical coupler and an MZI, wherein the MZI comprises a TOPM and an EOPM, the optical quantum information converted by the polarization demultiplexer compensates the phase difference of the two arms through the TOPM inside the MZI, and the power and the phase of the polarization state ground vector are respectively demodulated through the EOPM inside the MZI and the EOPM outside the MZI.
Finally, photons are coupled into the optical fiber through the end face and are transmitted to 2 single photon detectors through the optical fiber, and photon counting is generated at the single photon detectors.
Specifically, the substrate adopts SiO in SOI system 2 A material.
The two output ports of the polarization demodulator are respectively connected with a polarization controller (240, 250) and a single photon detector (260, 270) in sequence through optical fibers.
The polarization multiplexer 160, polarization demultiplexer 220, and polarization demodulator 230 all employ on-chip MZI structures. The MMI optocoupler 151, TOPM152 and EOPM 153 elements are all made of silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide or silicon nitride materials. The polarization multiplexer 160 and the polarization demultiplexer 230 each include a Bi Level cone structure 162 and an adiabatic coupling structure 161 connected in sequence.
Polarization controllers 180, 240,250 are used to calibrate polarization prior to system operation, and polarization controller 180 may be used to control fiber transmission crosstalk to improve system performance; since the single photon detectors 260,270 used are polarization dependent devices, their proper operation needs to be ensured by the polarization controllers 240, 250.
The working principle of the system is as follows: the FPGA1 at the transmitting end and the FPGA2 at the receiving end are respectively responsible for controlling the transmitting end and the receiving end chips and are communicated through an optical module serving as a classical channel, the FPGA1 at the transmitting end generates pulse signals to drive an intensity modulator, generates direct-current bias voltages to drive an adjustable attenuator, generates corresponding modulation signals to drive a phase modulator and a polarization modulator according to the generated random number 1 so as to carry out the processes of phase randomization and polarization state preparation, and simultaneously records randomly selected preparation bases. The prepared polarization state is multiplexed into a single-mode fiber through a polarization multiplexer for transmission, and then demultiplexed through a polarization demultiplexer at a receiving end so as to execute the next polarization measurement. At the receiving end, the FPGA2 generates a corresponding modulation signal according to the generated random number 2 to drive the polarization demodulator, a measurement base is randomly selected to measure the received polarization state, and the randomly selected measurement base is recorded. The single photon counting module comprises a single photon detecting and counting function, and the FPGA2 simultaneously records photon counting as a measuring result. The FPGA1 and the FPGA2 inform each other of the selected base through classical channels so as to carry out subsequent operations such as base vector comparison, confidentiality enhancement and the like.
In addition, the invention also provides a polarization compensation QKD method, as shown in FIG. 3, by taking the BB84 protocol of polarization coding as an example, alice first preparesPreparing all possible polarization states (H, V, A, D) and coupling into the fiber line through a polarization multiplexer for transmission to Bob; the deflection angles of Bob's measured received polarization states are respectively denoted as (r H ,r V ,r A ,r D ) And sends the result to Alice via classical channel; alice adds a corresponding rotation angle to the original polarization base to prepare a new state, and then randomly transmits the newly prepared H-r H ,V-r V ,A-r A ,D-r D A polarized photon sequence coupled to the fiber through a polarization multiplexer for transmission to Bob; bob randomly selects a right-angle base or an oblique base for measurement, and transmits the base used for measurement to Alice through a classical channel; alice determines to use the correct measurement basis and sends it to Bob over the classical channel, both sides keeping the bits that the measurement basis is consistent with as the original key.
The invention integrates all electronic components on the substrate, improves the integration level of the system, enhances the flexibility of the system, reduces the number of elements adopted and reduces the manufacturing cost.
The invention is based on the modulation mechanism of the on-chip MZI, and can adopt EOPM to regulate and control the phases of two arms of the interferometer. The EOPM realized by utilizing the carrier effect can reach a high modulation rate of 1.25GHz, which is beneficial to realizing a high-speed polarization state preparation process, thereby improving the rate of QKD.
According to the invention, TOPM is added into the MZI containing EOPM to compensate the phase difference of the two arms, so that 30dB high extinction ratio can be realized, and the fidelity of polarization state preparation is improved.
The structures such as the MZI, the phase shifter, the polarization rotator and the like adopted by the invention are all based on a silicon-based maturation process and are compatible with a mature microelectronic CMOS process.
The QKD method for polarization compensation reduces the error rate of the system and improves the transmission distance of the system.
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.
Claims (10)
1. The polarization coding QKD system based on the silicon optical integrated chip is characterized by comprising a sending end Alice and a receiving end Bob, wherein the sending end Alice and the receiving end Bob comprise a random number generator, an FPGA and a quantum chip, and the FPGA is used for controlling the quantum chip and communicating through a classical channel; the random number generator is used for generating a modulation signal;
the quantum chip comprises a substrate, wherein an intensity modulator, a phase modulator, an adjustable attenuator, a polarization modulator, a polarization multiplexer, a polarization demultiplexer and a polarization demodulator are integrated on the substrate;
the intensity modulator, the phase modulator, the adjustable attenuator and the polarization modulator are sequentially connected through electric signals;
the lower port of the emergent end of the adjustable attenuator is connected to a single photon detector for monitoring the attenuation level; the upper port of the emergent end of the attenuator is connected to the polarization modulator for preparing the polarization state;
the polarization modulator is connected with the polarization demultiplexer through an optical fiber, and the polarization modulator and the polarization demultiplexer are also provided with a polarization controller; the polarization demultiplexer is connected with the polarization demodulator;
in a sending end Alice, the FPGA generates a pulse signal to drive the intensity modulator to generate a direct-current bias voltage to drive the adjustable attenuator, and drives the phase modulator and the polarization modulator according to a modulation signal generated by the random number generator to perform phase randomization and polarization state preparation, and simultaneously records a randomly selected preparation base; multiplexing the prepared polarization state into a single-mode fiber through a polarization multiplexer for transmission, then demultiplexing the polarization state through a polarization demultiplexer at a receiving end, and then executing the next polarization measurement;
in the receiving end Bob, the FPGA drives the polarization demodulator according to the modulation signal generated by the random number generator, randomly selects a measurement base to measure the received polarization state, records the randomly selected measurement base, counts the photon number by the single photon detector, and records the photon count as a measurement result.
2. The silicon-optical integrated-chip-based polarization-encoded QKD system of claim 1, wherein in the quantum chip, direct-current light is coupled at a straight waveguide end face of the intensity modulator, modulated into optical pulses by the intensity modulator, and then enters the phase modulator for phase randomization, wherein the average photon number of the randomized optical pulses is attenuated to a single photon level at the adjustable attenuator and enters the polarization modulator, and the power and phase of the polarization state ground-vector are modulated by the polarization modulator;
the modulated light pulse is converted into a corresponding polarization state in one straight waveguide by the polarization multiplexer, then enters a single-mode fiber through end surface coupling, and after the polarization state is transmitted through the single-mode fiber, the polarization state is coupled to the polarization demultiplexer through the end surface and is converted into intensity and phase information in two straight waveguides by the polarization demultiplexer;
the polarization demodulator demodulates the power and the phase of the polarization state basic vector to realize projection measurement;
finally, photons are coupled into the optical fiber through the end face and are transmitted to 2 single photon detectors through the optical fiber, and photon counting is generated at the single photon detectors.
3. A silicon-optically integrated-chip-based polarization-encoded QKD system according to claim 1, wherein the polarization modulator comprises an MMI optical coupler and an MZI, the MZI comprising a TOPM and an EOPM, the attenuated photons entering the polarization modulator compensating for the phase difference of the two arms by the TOPM inside the MZI and modulating the power and phase of the polarization state basis vector by the EOPM inside the MZI and the EOPM outside the MZI, respectively.
4. The polarization-encoded QKD system of claim 1, wherein the polarization demodulator comprises an MMI optical coupler and an MZI, the MZI comprising a TOPM and an EOPM, the polarization-demultiplexed light quantum information being compensated for the two-arm phase difference by the TOPM inside the MZI, and the power and phase of the polarization state basis vector being demodulated by the EOPM inside the MZI and the EOPM outside the MZI, respectively.
5. The polarization-encoded QKD system of claim 1, wherein the substrate is SiO in SOI systems 2 A material.
6. The silicon-optical integrated-chip-based polarization-encoded QKD system of claim 1, wherein the two output ports of the polarization demodulator are sequentially coupled to a polarization controller and a single-photon detector, respectively, via optical fibers.
7. The silicon-optically integrated-chip-based polarization-encoded QKD system of claim 1, wherein the polarization multiplexer, polarization demultiplexer, and polarization demodulator each employ an on-chip MZI structure.
8. A silicon-optically integrated-chip-based polarization-encoded QKD system according to claim 3 or 4, wherein the MMI optocoupler, TOPM, and EOPM are each of silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide, or silicon nitride materials.
9. The silicon-optically integrated-chip-based polarization-encoded QKD system of claim 1, wherein the polarization multiplexer and the polarization demultiplexer each comprise a sequentially connected BiLevel taper and adiabatic coupling.
10. A polarization-compensated QKD method, wherein a system as claimed in any one of claims 1 to 9 is applied, the method comprising the steps of:
step 1: a transmitting end Alice prepares polarization states H, V, A and D, and is coupled to an optical fiber line through a polarization multiplexer to be transmitted to a receiving end Bob;
step 2: the deflection angles of the polarization states received by the receiving end Bob are respectively recorded as r H ,r V ,r A ,r D And sends the result to Alice via classical channel;
step 3: the transmitting end Alice adds a corresponding rotation angle to the original polarization base to prepare a new state, and then randomly transmits the newly prepared H-r H ,V-r V ,A-r A ,D-r D The polarized photon sequence is coupled to the optical fiber through a polarization multiplexer and sent to a receiving end Bob;
step 4: the receiving terminal Bob randomly selects a right-angle base or an oblique base for measurement, and transmits the base used for measurement to Alice through a classical channel;
step 5: alice determines to use the correct measurement basis and sends it to Bob over the classical channel, both sides keeping the bits that the measurement basis is consistent with as the original key.
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