CN111934868B - Decoding chip and decoding method for quantum key distribution - Google Patents
Decoding chip and decoding method for quantum key distribution Download PDFInfo
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- CN111934868B CN111934868B CN202010824987.4A CN202010824987A CN111934868B CN 111934868 B CN111934868 B CN 111934868B CN 202010824987 A CN202010824987 A CN 202010824987A CN 111934868 B CN111934868 B CN 111934868B
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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
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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
- H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
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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
Abstract
A decoding chip for quantum key distribution, comprising: an input waveguide for receiving and transmitting an optical signal to be decoded; the directional coupler comprises a first directional coupler, a second directional coupler and a third directional coupler, wherein the first directional coupler is used for dividing input light into two beams of light, and the second directional coupler and the third directional coupler are used for realizing optical quantum interference; the phase modulator comprises a first phase modulator and a second phase modulator and is used for modulating the phase of the optical signal; the delay line structure is used for delaying the optical signal and inhibiting the influence of temperature on the error rate; and the output waveguide is used for outputting the demodulated optical signal. The decoding chip can realize adjustable beam splitting ratio, and balance the power of double-time-gap pulse light, thereby optimizing interference visibility and reducing bit error rate. The interference visibility of the decoding chip is insensitive to temperature change, namely the error rate caused by an optical device is insensitive to temperature change.
Description
Technical Field
The invention relates to the technical field of quantum communication, in particular to a decoding chip and a decoding method for quantum key distribution.
Background
Quantum Key Distribution (QKD) is a technology based on quantum physics and communication principles to achieve unconditionally secure secret communication. QKD has developed rapidly in recent years and has gradually entered commercialization. At present, a commercialized quantum key system adopts phase-based and time-based quantum state coding, and quantum communication safety is realized by combining strong attenuation coherent state with decoy state preparation. However, the optical fiber is built by a split device or a part of optical fiber devices, so that the optical fiber has the defects of discrete devices, low integration level, large volume, poor long-range stability, serious phase and other quantum state drift phenomena and the like. The integrated photon has the characteristics of good stability, reconfigurability, expansibility and the like, and is expected to gradually replace a bulk optical device in a key system to realize system integration. However, the bit error rate of the current QKD chip is seriously affected by temperature, so that the requirement on the temperature of the chip is severe during operation.
Disclosure of Invention
In view of the above, the present invention provides a decoding chip and a decoding method for quantum key distribution, so as to solve at least one of the above technical problems in part.
To achieve the above object, as an aspect of the present invention, there is provided a decoding chip for quantum key distribution, including:
an input waveguide for receiving and transmitting an optical signal to be decoded;
the directional coupler comprises a first directional coupler, a second directional coupler and a third directional coupler, wherein the first directional coupler is used for dividing input light into two beams of light, and the second directional coupler and the third directional coupler are used for realizing optical quantum interference;
the phase modulator comprises a first phase modulator and a second phase modulator and is used for modulating the phase of the optical signal;
the delay line structure is used for delaying the optical signal and inhibiting the influence of temperature on the error rate;
an output waveguide for outputting the demodulated optical signal;
the input waveguide is connected with the input end of the first directional coupler, and two output ends of the first directional coupler are respectively connected with the two first phase modulators and then connected with the input end of the second directional coupler; two output ends of the second directional coupler are respectively connected with two input ends of the delay line structure; two output ends of the delay line structure are respectively connected with the two second phase modulators and then connected with the third directional coupler; and two output ends of the third directional coupler are respectively connected with the output waveguides.
The structure formed by the first directional coupler, the first phase modulator and the second directional coupler is used for realizing the function of adjusting the power ratio of time-slot pulse light.
The structure composed of the second directional coupler, the delay line structure, the second phase modulator and the third directional coupler is used for realizing resolution of time-based quantum states and setting of base-resolving phases of phase-based quantum states.
The delay line structure comprises two arms, each arm comprises a plurality of curved waveguides, straight waveguides and isolation grooves, wherein the curved waveguides are quarter circles with the radius of R, and R is not smaller than the minimum light passing radius; the difference between effective refractive indexes of TE and TM fundamental modes of the straight waveguides is close to zero through optimized design, and two sides of each straight waveguide are respectively provided with an isolation groove.
The arm length difference of the two arms is equal to the difference of the total lengths of the respective straight waveguides in the two arms, the total number of the bent waveguides in the two arms is the same, and the total lengths of the respective bent waveguides in the two arms are the same.
Wherein the directional coupler is a 3db directional coupler.
The decoding chip is made of silicon, silicon oxynitride or silicon dioxide.
Wherein, under the condition that the decoding chip material is silicon dioxide or silicon oxynitride, the phase modulator is a thermo-optic phase modulator;
and under the condition that the decoding chip material is silicon, the phase modulator is a thermo-optic phase modulator or an electro-optic phase modulator.
As another aspect of the present invention, there is provided a decoding method using the decoding chip as described above, including the steps of:
inputting signal light to be decoded through an input waveguide; the signal light to be decoded is quantum state signal light of a BB84 time base and a phase base.
Setting the phase of the first phase modulator to balance the power of the double-time-gap pulse light;
and setting the phase of the second phase modulator to enable the decoder chip to reach the base decoding phase of the BB84 phase base quantum state, so as to realize signal light decoding.
Wherein the signal light to be decoded in the step of inputting the signal light to be decoded through the input waveguide is quantum state signal light of a BB84 time base and a phase base.
Based on the above technical solution, the decoding chip and the decoding method for quantum key distribution according to the present invention have at least one or some of the following advantages over the prior art:
1. the decoding chip can realize the passive demodulation of the BB84 protocol time base quantum state and the phase base quantum state.
2. The decoding chip can realize adjustable beam splitting ratio, and balance the power of double-time-gap pulse light, thereby optimizing interference visibility and reducing bit error rate.
3. The interference visibility of the decoding chip is insensitive to temperature change, namely the error rate caused by an optical device is insensitive to temperature change.
4. The decoding chip provided by the invention is provided with the phase modulator, and can actively compensate the phase drift of the phase-based quantum state drift.
5. In the decoding chip, if a silicon dioxide material system is adopted, the additional loss of the chip is lower, and the code rate is higher.
Drawings
Fig. 1 schematically illustrates a QKD decoding chip structure and an external single-photon detector for implementing error code temperature insensitivity according to an embodiment of the present disclosure;
FIG. 2 schematically illustrates a schematic diagram of a delay line 400 according to an embodiment of the disclosure;
FIG. 3 schematically illustrates another structure of the delay line 400 according to an embodiment of the disclosure;
fig. 4 schematically illustrates a BB84 phase-based and time-based quantum state decoding schematic of an embodiment of the disclosure.
In the above drawings, the reference numerals have the following meanings:
100. an input waveguide;
200. a directional coupler; 201. a first directional coupler; 202. a second directional coupler;
203. a third directional coupler;
300. a phase modulator; 301. a first phase modulator; 302. a second phase modulator;
400. a delay line structure; 401. bending the waveguide; 402. a straight waveguide; 403. an isolation trench;
500. an output waveguide;
601. a first single photon detector; 602. a second single photon detector.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
As shown in fig. 1, an embodiment of the present invention provides a BB84 QKD decoding chip, including:
an input waveguide 100 for receiving and transmitting an optical signal to be decoded.
The directional coupler 200 specifically includes a first directional coupler 201, a second directional coupler 202, and a third directional coupler 203, where the first directional coupler 201 is configured to divide input light into two beams of light, and the second and third directional couplers 202 are configured to implement optical quantum interference.
The phase modulator 300 specifically includes a first phase modulator 301 and a second phase modulator 302, which are used for modulating the phase of the optical signal.
The delay line structure 400 is used to delay the optical signal and suppress the influence of temperature on the error rate.
And an output waveguide 500 for outputting the demodulated optical signal.
Wherein the input waveguide 100 is connected to the input of the first directional coupler 201, and two outputs of the first directional coupler 201 are respectively connected to the two first phase modulators 301, and then connected to two inputs of the second directional coupler 202. Two output terminals of the second directional coupler 202 are connected to two input terminals of the delay structure 400, respectively. The two outputs of the delay structure 400 are connected to the first phase modulator 301 and the second phase modulator 302, respectively, and subsequently to the third directional coupler 203. Two output ends of the third directional coupler 203 are respectively connected to the output waveguides 500. The two output waveguides 500 are connected to the first single-photon detector 601 and the second single-photon detector 602 through single-mode fibers, respectively.
The structure formed by the first directional coupler 201, the first phase modulator 301 and the second directional coupler 202 realizes the function of adjusting the power ratio of the time-slot pulse light. The structure formed by the second directional coupler 202, the delay line structure 400, the second phase modulator 302 and the third directional coupler 203 realizes the resolution of time-based quantum states and the setting of base-solving phases of phase-based quantum states.
The delay line structure 400 comprises two arms, each arm comprises a plurality of curved waveguides 401, straight waveguides 402 and isolation grooves 403, wherein the curved waveguides 401 are quarter circles with the radius of R, and R is not smaller than the minimum light passing radius; the straight waveguide 402 is designed to make the difference between the effective refractive indices of the TE and TM fundamental modes close to zero by optimization, wherein close to zero means that the difference between the effective refractive indices of the two modes is within 5%. Two isolation grooves 403 are respectively arranged on two sides of each straight waveguide 402. The arm length difference of the two arms is equal to the difference of the total lengths of the respective straight waveguides in the two arms, the total number of the bent waveguides in the two arms is the same, and the total lengths of the respective bent waveguides in the two arms are the same. Fig. 2 and 3 show two embodiments of this design feature.
Due to the presence of stress birefringence in the curved waveguide, the effective refractive index difference between the TE and TM modes is not zero, and this difference varies with temperature. Thus, the 'phase difference of TE and TM mode phase-based quantum states' caused by birefringence also varies with temperature, so that the visibility of the overall (sum of TE and TM modes) phase-based quantum state interference also varies with temperature. In order to suppress the temperature influence, the invention provides an congruent structure of the double-arm bent waveguide, so that the stress birefringence generated by the double-arm bent waveguide is the same, namely the phase difference value of 'TE and TM mode phase base quantum states' in the double arms caused by temperature change is the same so as to counteract the temperature influence. The delay line is completely generated by the optimized straight waveguide, on one hand, due to the optimized design, effective refractive indexes of TE and TM modes in the straight waveguide are approximately the same, on the other hand, isolation grooves are arranged on two sides of the straight waveguide, stress can be released, heat insulation can be achieved, and therefore stress birefringence in the straight waveguide is approximately zero, and the straight waveguide cannot be influenced by temperature change. By combining the design of the curved waveguide and the straight waveguide, the phase difference value' of the TE and TM mode phase base quantum state in the two arms does not change along with the temperature, so that the interference visibility V of the whole phase base quantum state does not change along with the temperature. The bit error rate QBER and the interference visibility relation are as follows: QBER = (1-V)/2. The bit error rate does not vary with temperature. Therefore, the structure can inhibit the influence of temperature on the bit error rate QBER and realize the effect that the bit error rate is insensitive to the temperature.
The directional couplers 200 are all 3db directional couplers.
Is a 3db directional coupler.
The decoding chip is made of silicon, silicon oxynitride or silicon dioxide.
In the case where the decoding chip material is silicon dioxide or silicon oxynitride, the phase modulator 300 is a thermo-optic phase modulator.
In the case where the decoding chip material is silicon, the phase modulator 300 is a thermo-optic phase modulator or an electro-optic phase modulator.
Silicon dioxide is specifically exemplified for the chip material system. The straight waveguide 402 is made of silica materials with different doping, the refractive index difference is 0.75%, the core layer is made of silica materials with germanium doping, the refractive index n1=1.4508, the upper and lower cladding layers are made of silica materials with boron and phosphorus doping, the refractive index n2=1.445, and the sectional dimension of the waveguide is 6 μm × 6 μm.
The embodiment of the invention also provides a decoding method for the time base and phase base BB84 protocol, which can be used for respectively passively demodulating the time base quantum state and the phase base quantum state. The method comprises
S1, inputting signal light to be decoded through an input waveguide 100, wherein the signal light to be decoded is quantum state signal light of a BB84 time base and a phase base.
As shown in FIG. 4 in particular, for the time base BB84 quantum state, quantum state |0> indicates a pulse in the first time gap; quantum state |1> is pulsed for the second time interval. For the phase base BB84 quantum state, | + > represents the superposition state of the first and second time gap pulses, and the relative phase difference between the first and second time gap pulses is 0; i-also represents the superposition of the first and second temporal gap pulses, with a relative phase difference of π. When the BB84 quantum state passes through the decoder chip, three time slots are output where a photon may be detected. The phase basis quantum state | + >, | - > can be measured by interference occurring in the second intermediate time gap. The time-based quantum states |1> and |0> are measured through the first and third time slots.
And S2, setting the phase of the phase modulator 301 to balance the power of the double-time-slot pulse light.
Specifically, the first directional coupler 201, the first phase modulator 301, and the second directional coupler 202 constitute an MZI structure, and by adjusting the phase value of the phase modulator 301, the power ratio of the two outputs of the second directional coupler 202 can be adjusted, so that the power loss difference caused by different paths can be compensated, and finally, the pulse power is balanced. As shown in FIG. 4, when quantum state |0> is input, single-photon detector 601 has the same probability of detecting a photon in the first and second time gaps; when quantum state |1> is input, single-photon detector 602 has the same probability of detecting a photon in the second and third time gaps. The bit error rate of time-based quantum state de-fundamentation can be reduced. Furthermore, for phase-based quantum states, their interference occurs in a second time gap, the intermediate time gap. Power balancing leads to improved interference visibility and also reduces bit error rate.
S3, setting the phase of the phase modulator 302 to enable the decoder chip to reach the base decoding phase of the BB84 phase base quantum state.
Specifically, the second directional coupler 202, the delay structure 400, the second phase modulator 302, and the third directional coupler 203 constitute an AMZI structure. The structure has two functions, one of which generates time delay to realize the resolution of time-based quantum states; the phase value of the phase modulator 302 is set to realize the resolution of the phase-based quantum state.
The quantum states |0> and |1> are determined by measurements of the first and third time gaps. Single photon detectors 601 and 602 detect a photon as |0> state in the first time interval and as |1> in the third time interval.
The quantum states | + > and | - >, are determined by measurement of the second time gap. By adjusting the phase modulator 302, 601 and 602 interfere constructively and destructively, respectively. The phase 302 is adjusted to maximize the visibility of the interference, and the corresponding relative extinction ratio of 601 to 602 is also maximized, where the bit error rate is minimized.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A decoding chip for quantum key distribution, comprising:
an input waveguide for receiving and transmitting an optical signal to be decoded;
the directional coupler comprises a first directional coupler, a second directional coupler and a third directional coupler, wherein the first directional coupler is used for dividing input light into two beams of light, and the second directional coupler and the third directional coupler are used for realizing optical quantum interference;
the phase modulator comprises a first phase modulator and a second phase modulator and is used for modulating the phase of the optical signal;
the delay line structure is used for delaying the optical signal and inhibiting the influence of temperature on the error rate;
an output waveguide for outputting the demodulated optical signal;
the input waveguide is connected with the input end of a first directional coupler, two output ends of the first directional coupler are respectively connected with two first phase modulators and then connected with the input end of a second directional coupler; two output ends of the second directional coupler are respectively connected with two input ends of the delay line structure; two output ends of the delay line structure are respectively connected with the two second phase modulators and then connected with the third directional coupler; and two output ends of the third directional coupler are respectively connected with the output waveguides.
2. The decoding chip according to claim 1, wherein the first directional coupler, the first phase modulator, and the second directional coupler are configured to implement a function of adjusting a ratio of pulsed light powers in a time slot.
3. The decoding chip according to claim 1, wherein the second directional coupler, the delay line structure, the second phase modulator, and the third directional coupler are configured to achieve resolution of time-based quantum states and setting of base phase of phase-based quantum states.
4. The decoding chip according to claim 1, wherein the delay line structure comprises two arms, each arm comprises a plurality of curved waveguides, straight waveguides and isolation grooves, wherein the curved waveguides are quarter circles with a radius R, and R is not less than a minimum clear light radius; the difference between effective refractive indexes of TE and TM fundamental modes of the straight waveguides is close to zero through an optimized design, and two sides of each straight waveguide are respectively provided with an isolation groove.
5. The decoding chip of claim 4, wherein the difference between the arm lengths of the two arms is equal to the difference between the total lengths of the straight waveguides in the two arms, the total number of the curved waveguides in the two arms is the same, and the total lengths of the curved waveguides in the two arms are the same.
6. The decoding chip of claim 1, wherein the directional coupler is a 3db directional coupler.
7. The decoding chip according to claim 1, wherein the material of the decoding chip is silicon, silicon oxynitride or silicon dioxide.
8. The decoding chip of claim 7,
under the condition that the decoding chip material is silicon dioxide or silicon oxynitride, the phase modulator is a thermo-optic phase modulator;
and in the case that the decoding chip material is silicon, the phase modulator is a thermo-optic phase modulator or an electro-optic phase modulator.
9. A decoding method using the decoding chip according to any one of claims 1 to 8, comprising the steps of:
inputting signal light to be decoded through an input waveguide; the signal light to be decoded is quantum state signal light of a BB84 time base and a phase base;
setting the phase of the first phase modulator to balance the pulse light power of the double time gaps;
and setting the phase of the second phase modulator to enable the decoder chip to reach the base-decoding phase of the BB84 phase base quantum state, thereby realizing signal light decoding.
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