CN117278215A - Optical quantum chip for quantum key distribution and optical communication and phase compensation method - Google Patents
Optical quantum chip for quantum key distribution and optical communication and phase compensation method Download PDFInfo
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Abstract
The invention belongs to the technical field of secret communication, and discloses an optical quantum chip and a phase compensation method for quantum key distribution and optical communication, wherein the chip comprises a transmitting end and a receiving end which are connected by an optical fiber channel, and the transmitting end comprises a light source, a first integrated optical chip containing 4 AMZIs, a 4X1 polarization-preserving beam combiner BC and an adjustable attenuator VOA; the receiving end comprises a depolarizer, a polarization beam splitter PBS, a second integrated optical chip containing 2 AMZIs and 4 single photon detector SPDs. Compared with the prior art, the invention adopts a passive momentum state preparation mode, does not need a complex high-speed voltage driving module, and effectively reduces the complexity and the manufacturing difficulty of the system by integrating the interferometer into the optical chip. In addition, the polarization disturbance of the immune channel can be immunized, the passive base selection can be realized, the polarization and wavelength attack of an eavesdropper can be resisted, the key distribution can be carried out uninterruptedly by adopting a real-time phase compensation method, and the stability and the safety of the system are improved.
Description
Technical Field
The invention relates to the technical field of secret communication, in particular to an optical quantum chip and a phase compensation method for quantum key distribution and optical communication.
Background
Quantum key distribution can provide unconditional secure key distribution for both remote communication parties, and the most mature is the BB84 quantum key distribution protocol. The optical fiber quantum key distribution system generally adopts a single-mode optical fiber as a transmission channel, but the polarization state of photons can be changed in the transmission process due to the inherent birefringence effect of the optical fiber channel, and the photons can be changed along with the change of the external environment. However, when the traditional Mach-Zehnder interference loop scheme based on the double unequal arms decodes interference at a receiving end, the polarization state is randomly changed due to disturbance of an optical fiber channel, and the polarization changes of long and short arms of the interferometer are different, so that the stability of the interference is affected, and therefore, the system is poor in stability and is easy to be disturbed by the environment. In addition, for a quantum key distribution system of phase coding, an active quantum state preparation mode is generally adopted, a phase modulator is added on one arm of the unequal-arm interferometer to carry out phase modulation, so that the manufacturing difficulty of the interferometer is increased, a complex ADC driving circuit is also needed to drive the phase modulator, and the complexity of the system is increased.
In the prior art, one scheme for solving the polarization disturbance is to use a Faraday-Michelson interferometer, so that the influence of the fiber birefringence effect and the environmental disturbance on the polarization state can be eliminated, the polarization change of the long and short arms can be automatically compensated, and the system is very stable. Yet another solution is an interferometer as disclosed in patent CN210041849U, employing a faraday rotator, which also automatically compensates for channel polarization disturbances and different polarization variations of the long and short arms based on the faraday effect. However, in these schemes, the interferometer built by the discrete optical elements has large volume, complex structure, poor stability, high cost, difficult mass production, and low manufacturing precision of the interferometer arm length difference, which may not only result in poor system stability, but also fail to meet the demands of system demand integration and miniaturization.
In order to improve the integration level of the interferometer, patent CN109391471B and the document Zhang G W, et al, polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit [ J ]. Photonics Research, 2021, 9 (11): 2176-2181 carry out hybrid integration on the Faraday-Michelson interferometer, and the scheme has a reflection module such as a reflector or a magneto-optical crystal such as a Faraday mirror, which results in lower integration level, larger volume and complex manufacture of the interferometer. Similarly, the solution of CN210041849U is also subject to the problem of increased integration difficulty due to the inclusion of magneto-optical crystals. In addition, the scheme adopts an active phase modulation mode to prepare the quantum state, a high-speed phase modulation structure is needed, and compared with a thermal phase modulation structure in an integrated optical circuit, the requirements on the speed and the complexity of a corresponding driving circuit are high.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a passive sub-key optical communication system based on an interferometer chip and a phase compensation method.
The technical scheme of the invention is realized as follows:
an optical quantum chip for quantum key distribution and optical communication comprises a transmitting end and a receiving end which are connected by a fiber channel,
the transmitting end comprises a light source, a first integrated optical chip comprising a first unequal arm Mach-Zehnder interferometer AMZI1, a second unequal arm Mach-Zehnder interferometer AMZI2, a third unequal arm Mach-Zehnder interferometer AMZI3, a fourth unequal arm Mach-Zehnder interferometer AMZI4, a 4X1 polarization-maintaining beam combiner BC and an adjustable attenuator VOA; each unequal arm Mach-Zehnder interferometer AMZI of the first integrated optical chip is at least provided with 1 input port and 1 output port; the 4 output ports of the light source are respectively connected with the 4 input ports of the first integrated optical chip; the 4 output ports of the first integrated optical chip are respectively connected with the 4 input ports of the 4X1 polarization-maintaining beam combiner BC; the output port of the 4X1 polarization-maintaining beam combiner BC is connected with an adjustable attenuator VOA; the output port of the adjustable attenuator VOA is used as the output port of the transmitting end; the light source outputs a path of optical signal from one output port of the light source in a random time sharing mode at a preset repetition frequency; the long and short arm phase differences of 4 unequal arm Mach-Zehnder interferometers AMZI in the first integrated optical chip are respectively 0, pi/2, pi and 3 pi/2;
the receiving end comprises a depolarizer, a polarization beam splitter PBS, a second integrated optical chip comprising a fifth unequal arm Mach-Zehnder interferometer AMZI5 and a sixth unequal arm Mach-Zehnder interferometer AMZI6, and 4 single photon detectors SPDs; each unequal arm Mach-Zehnder interferometer AMZI of the second integrated optical chip is provided with 1 input port and 2 output ports; the input port of the depolarizer is used as the input port of the receiving end; the output port of the depolarizer is connected with the input port of the polarization beam splitter PBS; two output ports of the polarization beam splitter PBS are respectively connected with 2 input ports of the second integrated optical chip; the 4 output ports of the second integrated optical chip are respectively connected with a single photon detector; the depolarizer is used for changing the optical signal transmitted by the optical fiber channel into a random polarization state, and combining with the polarization beam splitter PBS to realize the measurement basis vector selection of the equal probability; the long and short arm phase differences of 2 unequal arm Mach-Zehnder interferometers AMZI in the second integrated optical chip are respectively 0 and pi/2.
Preferably, one phase shifter is respectively arranged on the long arms of the 4 unequal arm Mach-Zehnder interferometers AMZI in the first integrated optical chip and the long arms of the 2 unequal arm Mach-Zehnder interferometers AMZI in the second integrated optical chip.
Preferably, the 4 different arm mach-zehnder interferometers AMZI in the first integrated optical chip are respectively provided with 2 input ports, and one photoelectric detector PD is connected to 1 input port of each different arm mach-zehnder interferometer AMZI; an circulator CIR is also arranged between the 4X1 polarization-maintaining beam combiner BC and the adjustable attenuator VOA; the first port, the second port and the third port of the circulator CIR are respectively connected with the output port of the continuous laser, the output port of the 4X1 polarization-maintaining beam combiner BC and the input port of the adjustable attenuator VOA.
Preferably, the light source comprises 1 pulse laser and 1X4 optical switch OS; the pulse laser is connected with the input port of the 1X4 optical switch OS, and the 4 output ports of the 1X4 optical switch OS are respectively used as the 4 output ports of the light source.
Preferably, the light source comprises 4 pulsed lasers.
Preferably, one fiber isolator is provided after each of the 4 pulse lasers.
The invention also discloses a phase compensation method, which comprises the following steps:
s1: the optical signal of the transmitting end only passes through a first unequal arm Mach-Zehnder interferometer AMZI1 of a first integrated optical chip, and an adjustable attenuator VOA attenuation value is set to enable the emergent light intensity to be strong compared with the quantum signal;
s2: the receiving end respectively adjusts the long and short arm phase differences of a fifth unequal arm Mach-Zehnder interferometer AMZI5 and a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip until the count value of a first single photon detector SPD1 corresponding to the output port of the fifth unequal arm Mach-Zehnder interferometer AMZI5 reaches the maximum, the count value of a second single photon detector SPD2 reaches the minimum, and the long and short arm phase differences of the fifth unequal arm Mach-Zehnder interferometer AMZI5 are 0; the count values of a third single photon detector SPD3 and a fourth single photon detector SPD4 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 are equal, and the long and short arm phase difference of the sixth unequal arm Mach-Zehnder interferometer AMZI6 is pi/2;
s3: the optical signal of the transmitting end only passes through a second unequal arm Mach-Zehnder interferometer AMZI2 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are equal; meanwhile, the count value of a third single photon detector SPD3 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is maximized, the count value of a fourth single photon detector SPD4 is minimized, and the long and short arm phase difference of the second unequal arm Mach-Zehnder interferometer AMZI2 is pi/2;
s4: the optical signal of the transmitting end only passes through a third unequal arm Mach-Zehnder interferometer AMZI3 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count value of a first single photon detector SPD1 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip is minimum, and the count value of a second single photon detector SPD2 is maximum; meanwhile, count values of a third single photon detector SPD3 and a fourth single photon detector SPD4 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip are equal, and a long and short arm phase difference of the third unequal arm Mach-Zehnder interferometer AMZI3 of the first integrated optical chip is pi;
s5: the optical signal of the transmitting end only passes through a fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are equal; meanwhile, the count value of a third single photon detector SPD3 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is minimum, the count value of a fourth single photon detector SPD4 reaches maximum, and the long and short arm phase difference of the fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip is 3 pi/2.
The invention also discloses another phase compensation method, which comprises the following steps:
s1: the continuous optical signals generated by the continuous laser at the transmitting end enter 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip through the circulator CIR at the same time, long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers AMZI are scanned at the same time, detection results of the 4 photoelectric detectors PD are recorded, and 4 phase scanning curves are obtained;
s2: the sending end sets the long and short arm phase differences of 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip to be 0, pi/2, pi and 3 pi/2 respectively according to the corresponding phase scanning curves, and takes the detection results of the corresponding 4 photoelectric detectors PD as reference values;
s3: when the system works normally, the sending end continuously adjusts the long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip by using a PID algorithm, so that the detection results of the 4 photoelectric detectors PD are stabilized at respective reference values;
s4: when the system works normally, the receiving end calculates the drift amount of the phase difference of each long and short arm of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 by using the data with the unmatched base and the bit error rateAnd->And performing real-time phase compensation.
Preferably, the method for calculating the drift amount of the long-short arm phase difference is as follows:
s1: counting the counts of the first single photon detector SPD1 and the second single photon detector SPD2 of the receiving end when the sending end prepares the quantum state phase difference pi/2And->And counting of the first single photon detector SPD1 and the second single photon detector SPD2 at the receiving end when preparing the quantum phase difference of 3 pi/2>And->The method comprises the steps of carrying out a first treatment on the surface of the Counting +.about.of third single photon detector SPD3 and fourth single photon detector SPD4 at receiving end when preparing quantum phase difference pi at transmitting end>And->And the count of the third single photon detector SPD3 and the fourth single photon detector SPD4 at the receiving end when preparing the quantum state phase difference 0 +.>And；
s2: according to the formulaAndrespectively calculating the fifth inequalityPhase difference drift amount of arm Mach-Zehnder interferometer AMZI5 and sixth unequal arm Mach-Zehnder interferometer AMZI6 +.>And->。
Compared with the prior art, the invention has the following beneficial effects:
the invention provides an optical quantum chip and a phase compensation method for quantum key distribution and optical communication, which adopt a passive quantum state preparation mode without a complex high-speed voltage driving module, and effectively reduce the complexity and the manufacturing difficulty of a system by integrating an interferometer into the optical chip. In addition, by adopting a depolarizer and combining a polarization beam splitter at a receiving end, the polarization disturbance of a channel can be immunized, meanwhile, the passive base selection can be realized, the polarization and wavelength attack of an eavesdropper can be resisted, and the key distribution can be carried out uninterruptedly by adopting a real-time phase compensation method, so that the stability and the safety of the system are improved.
Drawings
FIG. 1 is a schematic block diagram of an optical quantum chip for quantum key distribution and optical communication according to the present invention;
FIG. 2 is a schematic block diagram of an embodiment of an optical quantum chip for quantum key distribution and optical communication according to the present invention;
fig. 3 is a schematic block diagram of a second embodiment of an optical quantum chip for quantum key distribution and optical communication according to the present invention.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.
As shown in fig. 1, an optical quantum chip for quantum key distribution and optical communication includes a transmitting end and a receiving end connected by a fiber channel,
the transmitting end comprises a light source, a first integrated optical chip comprising 4 unequal arm Mach-Zehnder interferometers AMZI, a 4X1 polarization-preserving beam combiner BC and an adjustable attenuator VOA; each unequal arm Mach-Zehnder interferometer AMZI of the first integrated optical chip is at least provided with 1 input port and 1 output port; the 4 output ports of the light source are respectively connected with the 4 input ports of the first integrated optical chip; the 4 output ports of the first integrated optical chip are respectively connected with the 4 input ports of the 4X1 polarization-maintaining beam combiner BC; the output port of the 4X1 polarization-maintaining beam combiner BC is connected with an adjustable attenuator VOA; the output port of the adjustable attenuator VOA is used as the output port of the transmitting end; the light source outputs a path of optical signal from one output port of the light source in a random time sharing mode at a preset repetition frequency; the long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers in the first integrated optical chip are respectively 0, pi/2, pi and 3 pi/2;
the receiving end comprises a depolarizer, a polarization beam splitter PBS, a second integrated optical chip comprising 2 unequal arm Mach-Zehnder interferometers AMZIs and 4 single photon detector SPDs; each unequal arm Mach-Zehnder interferometer AMZI of the second integrated optical chip is provided with 1 input port and 2 output ports; the input port of the depolarizer is used as the input port of the receiving end; the output port of the depolarizer is connected with the input port of the polarization beam splitter PBS; two output ports of the polarization beam splitter PBS are respectively connected with 2 input ports of the second integrated optical chip; the 4 output ports of the second integrated optical chip are respectively connected with a single photon detector; the depolarizer is used for changing the optical signal transmitted by the optical fiber channel into a random polarization state, and combining with the polarization beam splitter PBS to realize the measurement basis vector selection of the equal probability; the long and short arm phase differences of the 2 unequal arm Mach-Zehnder interferometers in the second integrated optical chip are respectively 0 pi/2.
The specific working process is as follows:
the transmitting end emits light pulse from any output port of the light source, enters the unequal arm Mach-Zehnder interferometer corresponding to the first integrated optical chip, and after being emitted, the light pulse is changed into a phase coding quantum state through the 4X1 polarization-maintaining beam combiner BC and the adjustable attenuator VOA, and can be written as
，
Wherein temporal pattern |0>And |1>The polarization states of (a) are all horizontal polarization,is the long and short arm phase difference of the unequal arm Mach-Zehnder interferometer. The phase differences corresponding to the first unequal arm Mach-Zehnder interferometer AMZI1, the second unequal arm Mach-Zehnder interferometer AMZI2, the third unequal arm Mach-Zehnder interferometer AMZI3 and the fourth unequal arm Mach-Zehnder interferometer AMZI4 are respectively 0, pi/2, pi and 3 pi/2. After passing through a single-mode fiber channel, the phase encoding state becomes unpredictable polarization state when reaching the receiving end due to the birefringence effect and the disturbance of the environment where the channel is located.
The light pulse with arbitrary polarization enters the receiving end, is depolarized by the depolarizer, changes the polarization state into random polarization state, then enters the input port of the polarization beam splitter PBS, and exits from the two output ports with equal probability. Assuming that the optical signals emitted from the two output ports of the polarization beam splitter PBS are respectively a first signal optical component and a second signal optical component, the first signal optical component and the second signal optical component respectively enter the two input ports of the second integrated optical chip of the receiving end, and then respectively enter the fifth unequal arm mach-zehnder interferometer AMZI5 and the sixth unequal arm mach-zehnder interferometer AMZI6 for decoding, the normalized response results of the 4 single photon detector SPDs can be respectively obtained as follows
，
Different fromThe normalized light intensity of the corresponding single photon detector SPD is shown in Table 1:
table 1: normalized light intensity table of 4 SPDs of phase decoding integrated chip
And according to the detection result and the basic vector information corresponding to the modulation phase, obtaining an initial key, and then performing post-processing procedures such as error code estimation, error correction, secret amplification and the like to generate a safe quantum key between the sending end A and the receiving end B.
As shown in fig. 2, an optical quantum chip embodiment 1 of the present invention for quantum key distribution and optical communication:
the light source comprises 1 pulse laser and a 1X4 optical switch OS; the pulse laser is connected with the input port of the 1X4 optical switch OS, and the 4 output ports of the 1X4 optical switch OS are respectively used as the 4 output ports of the light source.
The long arms of the 4 unequal arm Mach-Zehnder interferometers in the first integrated optical chip and the long arms of the 2 unequal arm Mach-Zehnder interferometers in the second integrated optical chip are respectively provided with a phase shifter.
A specific working procedure of the embodiment is as follows:
LD1 emits light pulse with horizontal polarization, and enters into different arm Mach-Zehnder interferometer corresponding to the first integrated optical chip from any output port of 1X4 optical switch OS, and after exiting, becomes phase coding quantum state after passing through 4X1 polarization-preserving beam combiner BC and adjustable attenuator VOA, and can be written as
，
Wherein temporal pattern |0>And |1>The polarization states of (a) are all horizontal polarization,is the long and short arm phase difference of the unequal arm Mach-Zehnder interferometer. The long arms of the first unequal arm Mach-Zehnder interferometer AMZI1, the second unequal arm Mach-Zehnder interferometer AMZI2, the third unequal arm Mach-Zehnder interferometer AMZI3 and the fourth unequal arm Mach-Zehnder interferometer AMZI4 are respectively provided with phase shifters PSA1, PSA2, PSA3 and PSA4, and the phase differences are respectively adjusted to be 0, pi/2, pi and 3 pi/2. After passing through a single-mode fiber channel, the phase encoding state becomes unpredictable polarization state when reaching the receiving end due to the birefringence effect and the disturbance of the environment where the channel is located.
The light pulse with arbitrary polarization enters the receiving end, is depolarized by the depolarizer, changes the polarization state into random polarization state, then enters the input port of the polarization beam splitter PBS, and exits from the two output ports with equal probability. Assuming that optical signals emitted from two output ports of the polarization beam splitter PBS are a first signal optical component and a second signal optical component, the first signal optical component and the second signal optical component enter two input ports of a second integrated optical chip of a receiving end respectively, and then enter a fifth unequal arm mach-zehnder interferometer AMZI5 and a sixth unequal arm mach-zehnder interferometer AMZI6 respectively for decoding, long arms of the fifth unequal arm mach-zehnder interferometer AMZI5 and the sixth unequal arm mach-zehnder interferometer AMZI6 are respectively provided with phase shifters PSB1 and PSB2, and phase differences are respectively adjusted to be 0 pi/2. The normalized response results of the SPDs of the 4 single photon detectors can be respectively obtained as
，
Different fromThe normalized light intensity of the corresponding single photon detector SPD is shown in Table 2:
table 2: normalized light intensity table of 4 SPDs of phase decoding integrated chip
And according to the detection result and the basic vector information corresponding to the modulation phase, obtaining an initial key, and then performing post-processing procedures such as error code estimation, error correction, secret amplification and the like to generate a safe quantum key between the sending end A and the receiving end B.
The phase shift exists in the long and short arm phase differences of the unequal arm Mach-Zehnder interferometers AMZI in the interferometer chip due to temperature, vibration and the like, so that phase compensation is needed. The invention also provides a phase compensation method, which comprises the following steps:
s1: the optical signal of the transmitting end only passes through a first unequal arm Mach-Zehnder interferometer AMZI1 of a first integrated optical chip, and an adjustable attenuator VOA attenuation value is set to enable the emergent light intensity to be strong compared with the quantum signal;
s2: the receiving end respectively adjusts the long and short arm phase differences of a fifth unequal arm Mach-Zehnder interferometer AMZI5 and a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip until the count value of a first single photon detector SPD1 corresponding to the output port of the fifth unequal arm Mach-Zehnder interferometer AMZI5 reaches the maximum, and the count value of a second single photon detector SPD2 reaches the minimum, which is equivalent to the phase difference of 0; the count values of the third single photon detector SPD3 and the fourth single photon detector SPD4 corresponding to the two output ports of the sixth unequal arm Mach-Zehnder interferometer AMZI6 are close to or equal to each other, and the phase difference is pi/2;
s3: the optical signal of the transmitting end only passes through a second unequal arm Mach-Zehnder interferometer AMZI2 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are close to or equal to each other; meanwhile, the count value of a third single photon detector SPD3 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is maximized, the count value of a fourth single photon detector SPD4 is minimized, and the long and short arm phase difference of the second unequal arm Mach-Zehnder interferometer AMZI2 equivalent to the first integrated optical chip is pi/2;
s4: the optical signal of the transmitting end only passes through a third unequal arm Mach-Zehnder interferometer AMZI3 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count value of a first single photon detector SPD1 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip is minimum, and the count value of a second single photon detector SPD2 is maximum; meanwhile, count values of a third single photon detector SPD3 and a fourth single photon detector SPD4 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip are close to or equal to each other, and a long-short arm phase difference of the third unequal arm Mach-Zehnder interferometer AMZI3 equivalent to the first integrated optical chip is pi;
s5: the optical signal of the transmitting end only passes through a fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are close to or equal to each other; meanwhile, the count value of the third single photon detector SPD3 corresponding to two output ports of the sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is minimized, the count value of the fourth single photon detector SPD4 reaches the maximum, and the long and short arm phase difference of the fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip is 3 pi/2.
The specific working principle is as follows:
before key distribution, the light source is first set to a strong light mode for phase scanning. The optical pulse generated by the light source is controlled to only enter the first unequal arm Mach-Zehnder interferometer AMZI1, at the moment, the long and short arm phase differences of the first unequal arm Mach-Zehnder interferometer AMZI1 are 0, and the receiving end respectively adjusts the long and short arm phase differences of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chipAnd->The detection result of the SPDs of the 4 single photon detectors is that
，
When the count value of the first SPD1 reaches the maximum, the count value of the second SPD2 reaches the minimum, which is equivalent to the phase differenceIs 0; the count values of the third single photon detector SPD3 and the fourth single photon detector SPD4 corresponding to the two output ports of the sixth unequal arm Mach-Zehnder interferometer AMZI6 are close to or equal to each other, and the equal value is equal to pi/2 of the long-short arm phase difference of the first unequal arm Mach-Zehnder interferometer AMZI 1.
FixingAnd->The light pulse generated by the light source is controlled to only enter the second unequal arm Mach-Zehnder interferometer AMZI2, and the phase shifter on the long arm of the second unequal arm Mach-Zehnder interferometer AMZI2 is regulated to enable the phase difference to be +.>The detection result of the 4 SPDs is
，
When the count values of the first single photon detector SPD1 and the second single photon detector SPD2 are close to or equal to each other, the count value of the third single photon detector SPD3 reaches the maximum, the count value of the fourth single photon detector SPD4 reaches the minimum, which is equivalent to the long and short arm phase difference of the second unequal arm Mach-Zehnder interferometer AMZI2Pi/2.
FixingAnd->The light pulse generated by the light source is controlled to only enter the third unequal arm Mach-Zehnder interferometer AMZI3, and the phase shifter on the long arm of the third unequal arm Mach-Zehnder interferometer AMZI3 is regulated to enable the phase difference to be +.>The detection result of the SPDs of the 4 single photon detectors is that
，
When the count value of the SPD1 of the first single photon detector reaches the minimum, the count value of the SPD2 of the second single photon detector reaches the maximum; at the same time, third single photon detectionThe count values of the detector SPD3 and the fourth single photon detector SPD4 are close to or equal to each other, which is equivalent to the long and short arm phase difference of the third unequal arm Mach-Zehnder interferometer AMZI3Pi is the number;
fixingAnd->The light pulse generated by the light source is controlled to only enter the third unequal arm Mach-Zehnder interferometer AMZI3, and the phase shifter on the long arm of the third unequal arm Mach-Zehnder interferometer AMZI3 is regulated to enable the phase difference to be +.>The detection result of the SPDs of the 4 single photon detectors is that
，
When the count values of the first single photon detector SPD1 and the second single photon detector SPD2 are close to or equal to each other; meanwhile, the count value of the third single photon detector SPD3 reaches the minimum, the count value of the fourth single photon detector SPD4 reaches the maximum, and the count value is equivalent to the long and short arm phase difference of the fourth unequal arm Mach-Zehnder interferometer AMZI4Is 3 pi/2.
As shown in fig. 3, a second embodiment of an optical quantum chip for quantum key distribution and optical communication according to the present invention:
the light source comprises 4 pulse lasers, and an optical fiber isolator is arranged behind each of the 4 pulse lasers. The 4 unequal arm Mach-Zehnder interferometers in the first integrated optical chip are respectively provided with 2 input ports, and 1 input port of each unequal arm Mach-Zehnder interferometer is connected with one photoelectric detector PD; an circulator CIR is also arranged between the 4X1 polarization-maintaining beam combiner BC and the adjustable attenuator VOA; the first port, the second port and the third port of the circulator CIR are respectively connected with the output port of the continuous laser, the output port of the 4X1 polarization-maintaining beam combiner BC and the input port of the adjustable attenuator VOA.
The second specific working process of the embodiment comprises the following steps:
the transmitting end randomly selects one of LD1, LD2, LD3 and LD4 to transmit light pulse with horizontal polarization, enters the corresponding unequal arm Mach-Zehnder interferometer of the first integrated optical chip, and after being emitted, becomes phase coding quantum state after passing through a 4X1 polarization-preserving beam combiner BC and an adjustable attenuator VOA, and can be written as
，
Wherein temporal pattern |0>And |1>The polarization states of (a) are all horizontal polarization,is the long and short arm phase difference of the unequal arm Mach-Zehnder interferometer. The long arms of the first unequal arm Mach-Zehnder interferometer AMZI1, the second unequal arm Mach-Zehnder interferometer AMZI2, the third unequal arm Mach-Zehnder interferometer AMZI3 and the fourth unequal arm Mach-Zehnder interferometer AMZI4 are respectively provided with phase shifters PSA1, PSA2, PSA3 and PSA4, and the phase differences are respectively adjusted to be 0, pi/2, pi and 3 pi/2. After passing through a single-mode fiber channel, the phase encoding state becomes unpredictable polarization state when reaching the receiving end due to the birefringence effect and the disturbance of the environment where the channel is located.
The light pulse with arbitrary polarization enters the receiving end, is depolarized by the depolarizer, changes the polarization state into random polarization state, then enters the input port of the polarization beam splitter PBS, and exits from the two output ports with equal probability. Assuming that optical signals emitted from two output ports of the polarization beam splitter PBS are a first signal optical component and a second signal optical component, the first signal optical component and the second signal optical component enter two input ports of a second integrated optical chip of a receiving end respectively, and then enter a fifth unequal arm mach-zehnder interferometer AMZI5 and a sixth unequal arm mach-zehnder interferometer AMZI6 respectively for decoding, long arms of the fifth unequal arm mach-zehnder interferometer AMZI5 and the sixth unequal arm mach-zehnder interferometer AMZI6 are respectively provided with phase shifters PSB1 and PSB2, and phase differences are respectively adjusted to be 0 pi/2. The normalized response results of the SPDs of the 4 single photon detectors can be respectively obtained as
，
Different fromThe normalized light intensity of the corresponding single photon detector SPD is shown in Table 3:
table 3: normalized light intensity table of 4 SPDs of phase decoding integrated chip
And according to the detection result and the basic vector information corresponding to the modulation phase, obtaining an initial key, and then performing post-processing procedures such as error code estimation, error correction, secret amplification and the like to generate a safe quantum key between the sending end A and the receiving end B.
The phase shift exists in the long and short arm phase differences of the unequal arm Mach-Zehnder interferometers AMZI in the interferometer chip due to temperature, vibration and the like, so that phase compensation is needed. The invention also provides another phase compensation method, which comprises the following steps:
s1: the continuous optical signals generated by the continuous laser at the transmitting end enter 4 unequal arm Mach-Zehnder interferometers of the first integrated optical chip through the circulator CIR at the same time, long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers AMZI are scanned at the same time, detection results of the 4 photodetectors PD are recorded, and 4 phase scanning curves are obtained;
s2: the sending end sets the long and short arm phase differences of 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip to be 0, pi/2, pi and 3 pi/2 respectively according to the corresponding phase scanning curves, and takes the detection results of the corresponding 4 photoelectric detectors PD as reference values;
s3: when the system works normally, the sending end continuously adjusts the long and short arm phase differences of 4 AMZIs of the first integrated optical chip by using a PID algorithm, so that the detection results of the 4 photoelectric detectors PD are stabilized at respective reference values;
s4: when the system works normally, the receiving end calculates the drift amount of the phase difference of each long and short arm of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 by using the data with the unmatched base and the bit error rateAnd->And performing real-time phase compensation to keep the error rate of the system at the minimum level.
The method for calculating the phase difference drift amount comprises the following steps:
s1: counting the counts of the first single photon detector SPD1 and the second single photon detector SPD2 of the receiving end when the sending end prepares the quantum state phase difference pi/2And->And counting of the first single photon detector SPD1 and the second single photon detector SPD2 at the receiving end when preparing the quantum phase difference of 3 pi/2>And->The method comprises the steps of carrying out a first treatment on the surface of the Counting +.about.of third single photon detector SPD3 and fourth single photon detector SPD4 at receiving end when preparing quantum phase difference pi at transmitting end>And->And the count of the third single photon detector SPD3 and the fourth single photon detector SPD4 at the receiving end when preparing the quantum state phase difference 0 +.>And->；
S2: according to the formulaAndthe phase difference drift amount +_of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 are calculated respectively>。
The specific working principle is as follows:
the continuous optical signal generated by the continuous laser LD5 at the transmitting end enters the 4 unequal arm Mach-Zehnder interferometers of the first integrated optical chip through CIR at the same time, scans the long and short arm phase differences of 4 AMZIs and records the detection results of 4 photodetectors PD, and can be written as
，
Wherein,the phase adjusted for the 4 phase shifters. From 0 to 2 pi adjustment4 phase scanning curves with cosine functions can be obtained, voltages corresponding to phases of 0 or pi/2 or pi or 3 pi/2 can be found on each curve, and detection results of the corresponding 4 photodetectors PD are used as reference values.
The system starts to work normally, and the sending end continuously adjusts the long and short arm phase differences of 4 AMZIs of the first integrated optical chip by using a PID algorithm, so that the detection results of the 4 photoelectric detectors PD are stabilized at respective reference values.
Then the receiving end calculates the Mach-Zehnder of the fifth unequal arm by using the data with the unmatched base and the bit error rateThe drift amount of the long and short arm phase differences of the Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 is respectively 0 and pi/2, the ideal phase difference of the long and short arms of the receiving end fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 is respectively, and the actual phase drift is respectivelyAnd->. Firstly counting the count +.about.of the first single photon detector SPD1 and the second single photon detector SPD2 when the transmitting end prepares the quantum phase difference pi/2>And->Can be written as +.>
，
When preparing the quantum state phase difference 3 pi/2, the counts of the first single photon detector SPD1 and the second single photon detector SPD2And->Respectively is
，
Thus, the phase shift of the fifth unequal arm Mach-Zehnder interferometer AMZI5 can be calculated。
Simultaneously counting counts of a third single photon detector SPD3 and a fourth single photon detector SPD4 of the receiving end when the sending end prepares a quantum state phase difference piAnd->，
，
And when preparing quantum state phase difference 0, counting of third single photon detector SPD3 and fourth single photon detector SPD4 at receiving endAnd->，
，
Thus, the phase drift of the sixth unequal arm Mach-Zehnder interferometer AMZI6 can be calculated。
To calculate the phase drift valueAnd->The corresponding voltages are used for correcting the phase shifter voltages of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 respectively, and then real-time phase compensation can be achieved.
As can be seen from the various embodiments of the present invention, the present invention proposes an optical quantum chip for quantum key distribution and optical communication, which adopts a passive quantum state preparation method, and does not need a complex high-speed voltage driving module, and by integrating an interferometer into the optical chip, the complexity and the manufacturing difficulty of the system are effectively reduced. In addition, by adopting a depolarizer and combining a polarization beam splitter at a receiving end, the polarization disturbance of a channel can be immunized, meanwhile, the passive base selection can be realized, the polarization and wavelength attack of an eavesdropper can be resisted, and the key distribution can be carried out uninterruptedly by adopting a real-time phase compensation method, so that the stability and the safety of the system are improved.
Claims (9)
1. An optical quantum chip for quantum key distribution and optical communication is characterized by comprising a transmitting end and a receiving end which are connected by a fiber channel,
the transmitting end comprises a light source, a first integrated optical chip comprising a first unequal arm Mach-Zehnder interferometer AMZI1, a second unequal arm Mach-Zehnder interferometer AMZI2, a third unequal arm Mach-Zehnder interferometer AMZI3, a fourth unequal arm Mach-Zehnder interferometer AMZI4, a 4X1 polarization-maintaining beam combiner BC and an adjustable attenuator VOA; each unequal arm Mach-Zehnder interferometer AMZI of the first integrated optical chip is at least provided with 1 input port and 1 output port; the 4 output ports of the light source are respectively connected with the 4 input ports of the first integrated optical chip; the 4 output ports of the first integrated optical chip are respectively connected with the 4 input ports of the 4X1 polarization-maintaining beam combiner BC; the output port of the 4X1 polarization-maintaining beam combiner BC is connected with an adjustable attenuator VOA; the output port of the adjustable attenuator VOA is used as the output port of the transmitting end; the light source outputs a path of optical signal from one output port of the light source in a random time sharing mode at a preset repetition frequency; the long and short arm phase differences of 4 unequal arm Mach-Zehnder interferometers AMZI in the first integrated optical chip are respectively 0, pi/2, pi and 3 pi/2;
the receiving end comprises a depolarizer, a polarization beam splitter PBS, a second integrated optical chip comprising a fifth unequal arm Mach-Zehnder interferometer AMZI5 and a sixth unequal arm Mach-Zehnder interferometer AMZI6, and 4 single photon detectors SPDs; each unequal arm Mach-Zehnder interferometer AMZI of the second integrated optical chip is provided with 1 input port and 2 output ports; the input port of the depolarizer is used as the input port of the receiving end; the output port of the depolarizer is connected with the input port of the polarization beam splitter PBS; two output ports of the polarization beam splitter PBS are respectively connected with 2 input ports of the second integrated optical chip; the 4 output ports of the second integrated optical chip are respectively connected with a single photon detector; the depolarizer is used for changing the optical signal transmitted by the optical fiber channel into a random polarization state, and combining with the polarization beam splitter PBS to realize the measurement basis vector selection of the equal probability; the long and short arm phase differences of 2 unequal arm Mach-Zehnder interferometers AMZI in the second integrated optical chip are respectively 0 and pi/2.
2. The optical quantum chip for quantum key distribution and optical communication according to claim 1, wherein one phase shifter is provided on each of the long arms of the 4 unequal arm mach-zehnder interferometers AMZI in the first integrated optical chip and the long arms of the 2 unequal arm mach-zehnder interferometers AMZI in the second integrated optical chip.
3. The optical quantum chip for quantum key distribution and optical communication according to claim 1, wherein the 4 unequal arm mach-zehnder interferometers AMZI in the first integrated optical chip are respectively provided with 2 input ports, and one photodetector PD is connected to 1 input port of each unequal arm mach-zehnder interferometer AMZI; an circulator CIR is also arranged between the 4X1 polarization-maintaining beam combiner BC and the adjustable attenuator VOA; the first port, the second port and the third port of the circulator CIR are respectively connected with an output port of a continuous laser, an output port of the 4X1 polarization-maintaining beam combiner BC and an input port of the adjustable attenuator VOA.
4. A light quantum chip for quantum key distribution and optical communication according to claim 1 or 2 or 3, wherein the light source comprises 1 pulse laser and 1X4 optical switch OS; the pulse laser is connected with the input port of the 1X4 optical switch OS, and the 4 output ports of the 1X4 optical switch OS are respectively used as the 4 output ports of the light source.
5. An optical quantum chip for quantum key distribution and optical communication according to claim 1 or 2 or 3, wherein the light source comprises 4 pulsed lasers.
6. The optical quantum chip for quantum key distribution and optical communication of claim 5, wherein one optical fiber isolator is disposed after each of the 4 pulse lasers.
7. A phase compensation method using the optical quantum chip for quantum key distribution and optical communication according to any one of claims 1 or 2 or 4 or 5, comprising the steps of:
s1: the optical signal of the transmitting end only passes through a first unequal arm Mach-Zehnder interferometer AMZI1 of a first integrated optical chip, and an adjustable attenuator VOA attenuation value is set to enable the emergent light intensity to be strong compared with the quantum signal;
s2: the receiving end respectively adjusts the long and short arm phase differences of a fifth unequal arm Mach-Zehnder interferometer AMZI5 and a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip until the count value of a first single photon detector SPD1 corresponding to the output port of the fifth unequal arm Mach-Zehnder interferometer AMZI5 reaches the maximum, the count value of a second single photon detector SPD2 reaches the minimum, and the long and short arm phase differences of the fifth unequal arm Mach-Zehnder interferometer AMZI5 are 0; the count values of a third single photon detector SPD3 and a fourth single photon detector SPD4 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 are equal, and the long and short arm phase difference of the sixth unequal arm Mach-Zehnder interferometer AMZI6 is pi/2;
s3: the optical signal of the transmitting end only passes through a second unequal arm Mach-Zehnder interferometer AMZI2 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are equal; meanwhile, the count value of a third single photon detector SPD3 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is maximized, the count value of a fourth single photon detector SPD4 is minimized, and the long and short arm phase difference of the second unequal arm Mach-Zehnder interferometer AMZI2 is pi/2;
s4: the optical signal of the transmitting end only passes through a third unequal arm Mach-Zehnder interferometer AMZI3 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count value of a first single photon detector SPD1 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip is minimum, and the count value of a second single photon detector SPD2 is maximum; meanwhile, count values of a third single photon detector SPD3 and a fourth single photon detector SPD4 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip are equal, and a long and short arm phase difference of the third unequal arm Mach-Zehnder interferometer AMZI3 of the first integrated optical chip is pi;
s5: the optical signal of the transmitting end only passes through a fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip, and the corresponding long and short arm phase difference is regulated, so that the count values of a first single photon detector SPD1 and a second single photon detector SPD2 corresponding to two output ports of a fifth unequal arm Mach-Zehnder interferometer AMZI5 of the second integrated optical chip are equal; meanwhile, the count value of a third single photon detector SPD3 corresponding to two output ports of a sixth unequal arm Mach-Zehnder interferometer AMZI6 of the second integrated optical chip is minimum, the count value of a fourth single photon detector SPD4 reaches maximum, and the long and short arm phase difference of the fourth unequal arm Mach-Zehnder interferometer AMZI4 of the first integrated optical chip is 3 pi/2.
8. A phase compensation method using an optical quantum chip for quantum key distribution and optical communication according to any one of claims 3 to 5, comprising the steps of:
s1: the continuous optical signals generated by the continuous laser at the transmitting end enter 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip through the circulator CIR at the same time, long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers AMZI are scanned at the same time, detection results of the 4 photoelectric detectors PD are recorded, and 4 phase scanning curves are obtained;
s2: the sending end sets the long and short arm phase differences of 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip to be 0, pi/2, pi and 3 pi/2 respectively according to the corresponding phase scanning curves, and takes the detection results of the corresponding 4 photoelectric detectors PD as reference values;
s3: when the system works normally, the sending end continuously adjusts the long and short arm phase differences of the 4 unequal arm Mach-Zehnder interferometers AMZI of the first integrated optical chip by using a PID algorithm, so that the detection results of the 4 photoelectric detectors PD are stabilized at respective reference values;
s4: when the system works normally, the receiving end calculates the drift amount of the phase difference of each long and short arm of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 by using the data with the unmatched base and the bit error rateAndand performing real-time phase compensation.
9. The phase compensation method according to claim 8, wherein the method of calculating the drift amount of the long and short arm phase difference is:
s1: counting the counts of the first single photon detector SPD1 and the second single photon detector SPD2 of the receiving end when the sending end prepares the quantum state phase difference pi/2And->And counting of the first single photon detector SPD1 and the second single photon detector SPD2 at the receiving end when preparing the quantum phase difference of 3 pi/2>And->The method comprises the steps of carrying out a first treatment on the surface of the Counting +.about.of third single photon detector SPD3 and fourth single photon detector SPD4 at receiving end when preparing quantum phase difference pi at transmitting end>And->And the count of the third single photon detector SPD3 and the fourth single photon detector SPD4 at the receiving end when preparing the quantum state phase difference 0 +.>And->；
S2: according to the formulaAndthe phase difference drift amount +_of the fifth unequal arm Mach-Zehnder interferometer AMZI5 and the sixth unequal arm Mach-Zehnder interferometer AMZI6 are calculated respectively>And->。
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