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CN-122027151-A - Chip quantum key distribution system

CN122027151ACN 122027151 ACN122027151 ACN 122027151ACN-122027151-A

Abstract

The invention belongs to the technical field of secret communication and discloses a chip quantum key distribution system, wherein a transmitting end comprises an intensity modulation module and a coding chip of an adjustable attenuation module, the intensity modulation module is used for chopping an optical pulse signal into two sub-pulses with a time difference of T, the two sub-pulses are respectively subjected to intensity modulation to generate a signal state and a decoy state of a time phase coding quantum state, the adjustable attenuation module is used for attenuating the time phase coding quantum state to a single photon magnitude, a receiving end comprises a decoding chip, and the orthogonal polarization delay module included in the decoding chip is used for delaying the TM polarization mode and the TE polarization mode by T. Compared with the prior art, the invention can realize time phase encoding and reduce the complexity of a transmitting end by cutting the optical pulse into 2 sub-pulses and respectively modulating the intensities, and the decoding chip adopts a passive base selection and a symmetrical structure unequal arm interferometer, can realize polarization independent receiving and decoding, and improves the stability of a system.

Inventors

  • QU XIUXIU
  • FENG XIAOQING
  • WANG DONG
  • ZHAO YIBO
  • DING YAO
  • ZHAO ZHIYUAN

Assignees

  • 北京中科国光量子科技有限公司

Dates

Publication Date
20260512
Application Date
20260407

Claims (13)

  1. 1. A system for distributing a chip quantum key comprising a transmitting end and a receiving end connected by a fiber channel, wherein the transmitting end comprises: A laser LD for generating an optical pulse signal; the coding chip comprises an intensity modulation module and an adjustable attenuation module which are integrated on the same substrate; The intensity modulation module is used for chopping the optical pulse signal into two sub-pulses with the time difference of T, and respectively carrying out intensity modulation on the two sub-pulses to generate a signal state and a decoy state of a time phase coding quantum state; the time phase encoding quantum state comprises 2Z base quantum states and 1X base quantum state; the adjustable attenuation module is used for attenuating the time phase coding quantum state to a single photon magnitude and outputting the single photon magnitude to the optical fiber channel; the receiving end comprises a decoding chip, a first single photon detector SPD1 and a second single photon detector SPD2; the decoding chip is used for receiving the quantum state transmitted by the optical fiber channel and decoding the Z base and the X base, and comprises a first beam splitter BS1, a second beam splitter BS2, a first polarization beam splitter PBS1 and an orthogonal polarization delay module; the BS1 is used for splitting the received quantum state to realize passive base selection, the quantum state emitted from one output port of the BS1 enters the SPD1 to realize Z base decoding measurement, and the quantum state emitted from the other output port of the BS1 enters an unequal arm interferometer with a symmetrical structure formed by the BS2, the PBS1 and the orthogonal polarization delay module to realize polarization independent X base decoding; two output ports of the BS2 are connected with two input ports of the PBS1 through optical waveguides with equal length; two output ports of the PBS1 are connected with an orthogonal polarization delay module through optical waveguides with equal length to form a Sagnac ring; the delay time difference of the orthogonal polarization delay module for the TM polarization mode and the TE polarization mode is T; The interference result of the unequal arm interferometer enters the SPD2 for detection.
  2. 2. The system of claim 1, wherein the intensity modulation module modulates the intensity of the next or the previous sub-pulse to 0 to obtain the Z-based quantum states, respectively Or (b) The X-base quantum state is obtained when the intensity of the two sub-pulses is modulated into half at the same time 。
  3. 3. The system of claim 2, wherein the intensity modulation module is a first mach-zehnder modulator MZM1 comprising a third beam splitter BS3 and a fourth beam splitter BS4, wherein a first phase modulator PM1 is disposed on one arm of MZM 1.
  4. 4. A system for distributing a quantum key in accordance with claim 3, wherein the BS4 of the intensity modulation module is provided with an additional output port for power monitoring by connection to the photodetector PD.
  5. 5. The system of claim 2, wherein the intensity modulation module comprises a fifth beam splitter BS5 and a second phase modulator PM2, one input port of BS5 is connected to the laser LD, the other input port is connected to the tunable attenuation module, and two output ports of BS5 are directly connected by an optical waveguide, and PM2 is disposed on the optical waveguide.
  6. 6. The system of any of claims 1-5, wherein the tunable attenuation module is a second mach-zehnder modulator, MZM2, formed by a sixth beam splitter, BS6, and a seventh beam splitter, BS7, wherein a first phase shifter, PS1, is disposed on one arm of the MZM 2.
  7. 7. The system of any one of claims 1-5, wherein the orthogonal polarization delay module comprises a second polarization beam splitter PBS2, a first quarter wave plate QWP1, a second quarter wave plate QWP2, a second phase shifter PS2, and a reflective film; One input port and one output port of the PBS2 are respectively connected with two output ports of the PBS1 through optical waveguides with equal length, the other input port and the other output port of the PBS2 are respectively connected to the edge of the decoding chip through the optical waveguides with equal length, and the end surfaces of the corresponding positions of the waveguides are plated with reflecting films; QWP1 and QWP2 are respectively arranged on one waveguide and are used for rotating the polarization by 90 degrees when the optical signal passes back and forth; PS2 is disposed on one of the waveguides.
  8. 8. The system of claim 7, wherein QWP1 and QWP2 are each high birefringent waveguide sections having an asymmetric cross-sectional structure such that TE and TM modes of transmitted light produce an effective refractive index difference Δn; The length L of the high birefringent waveguide segment satisfies Δn×l=λ 0 /4, where λ 0 is the operating wavelength; the QWP1 and QWP2 enable the optical signals to pass back and forth, and then the total phase delay is lambda/2, so that the polarization is rotated by 90 degrees and returns along the original path of the incident optical path.
  9. 9. The system of claim 7, wherein QWP1, QWP2 each comprise a waveguide substrate, a waveguide core and a slot structure opening on the waveguide core; The waveguide core layer is made of high-refractive-index materials, the groove structure extends along the light transmission direction and penetrates through the width direction or the depth direction of the waveguide core layer, low-refractive-index media are filled in the groove, and the difference between the refractive index of the low-refractive-index media and the refractive index of the waveguide core layer is not smaller than 1.0; The groove structure and the waveguide core layer form an asymmetric transmission structure, so that the TE polarization mode and the TM polarization mode of transmitted light generate an effective refractive index difference delta n with preset sizes; The total length L of the waveguide core layer in the light transmission direction satisfies Δn×l=λ/4, where λ is the operating wavelength.
  10. 10. The system according to any one of claims 1-5, wherein the orthogonal polarization delay module comprises a second polarization beam splitter PBS2, a first sub-wavelength grating SWG1, a second sub-wavelength grating SWG2, a third phase shifter PS3; One input port and one output port of the PBS2 are respectively connected with two output ports of the PBS1 through optical waveguides with equal length, the other input port and the other output port of the PBS2 are respectively connected with the edge of the decoding chip through the optical waveguides with equal length, SWG1 and SWG2 are respectively arranged at the tail ends of the two waveguides, the period lambda of the grating is far smaller than the working wavelength lambda 0 , lambda < lambda 0 /(2 n), n is the refractive index, and only zero-order reflection and transmission are supported; the sub-wavelength grating forms a one-dimensional photonic band gap through periodic refractive index modulation, and strong coherent reflection is realized in a working band; The grating structure has double refraction characteristics, pi phase difference is generated on incident polarized light, and the polarization of the reflected light is rotated by 90 degrees; PS3 is disposed on one of the waveguides.
  11. 11. The system of any of claims 1-5, wherein the orthogonal polarization delay module comprises a third polarization beam splitter PBS3 and a fourth phase shifter PS4; one input port and one output port of the PBS3 are respectively connected with two output ports of the PBS1 through optical waveguides with equal length, the other input port and the other output port of the PBS3 are directly connected through the optical waveguides, and the PS4 is arranged on the optical waveguides.
  12. 12. The system of claim 1, wherein BS1 is further provided with an additional input port for outputting another interference result of the interferometer and with a third single photon detector SPD3 for detection.
  13. 13. The system of claim 1, wherein BS1 has a split ratio of 10:90.

Description

Chip quantum key distribution system Technical Field The invention relates to the technical field of optical communication and quantum key distribution, in particular to a chip quantum key distribution system. 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. However, the prior art has the following drawbacks: 1. the complexity of the transmitting end is high, the integration level is low, the traditional time phase coding system is built by adopting discrete optical elements, the intensity modulation, the phase modulation and the adjustable attenuation are mutually independent, the light path is complex, the volume is large, the cost is high, the consistency is poor, and the chip formation and the mass production are difficult to realize. 2. The polarization sensitivity and the stability of the receiving end are poor, the inherent birefringence effect exists in the optical fiber channel, the random change of photon polarization state can be caused by the environmental disturbance, the traditional unequal arm Mach-Zehnder interferometer is seriously affected by polarization, the interference stability is poor, and the system cannot stably work for a long time. 3. The interferometer structure is asymmetric and needs delay lines, the conventional unequal arm interferometer depends on physical delay lines to realize time difference, the consistency of arm length is poor, the loss is unbalanced, the interference visibility is low, and a circulator is needed, so that miniaturization and integration are further limited. Therefore, a full-chip quantum key distribution system with simplified transmitting end, irrelevant receiving end polarization and symmetrical interferometers without delay lines is needed to solve the pain point in the prior art. Disclosure of Invention Aiming at the defects in the prior art, the invention provides a chip quantum key distribution system. The technical scheme of the invention is realized as follows: A system for distributing a chip quantum key comprising a transmitting end and a receiving end connected by a fiber channel, wherein the transmitting end comprises: A laser LD for generating an optical pulse signal; The coding chip comprises an intensity modulation module and an adjustable attenuation module which are integrated on the same substrate; The intensity modulation module is used for chopping the optical pulse signal into two sub-pulses with the time difference of T, and respectively carrying out intensity modulation on the two sub-pulses to generate a signal state and a decoy state of a time phase coding quantum state; the time phase encoding quantum state comprises 2Z base quantum states and 1X base quantum state; the adjustable attenuation module is used for attenuating the time phase coding quantum state to a single photon magnitude and outputting the single photon magnitude to the optical fiber channel; the receiving end comprises a decoding chip, a first single photon detector SPD1 and a second single photon detector SPD2; the decoding chip is used for receiving the quantum state transmitted by the optical fiber channel and decoding the Z base and the X base, and comprises a first beam splitter BS1, a second beam splitter BS2, a first polarization beam splitter PBS1 and an orthogonal polarization delay module; the BS1 is used for splitting the received quantum state to realize passive base selection, the quantum state emitted from one output port of the BS1 enters the SPD1 to realize Z base decoding measurement, and the quantum state emitted from the other output port of the BS1 enters an unequal arm interferometer with a symmetrical structure formed by the BS2, the PBS1 and the orthogonal polarization delay module to realize polarization independent X base decoding; two output ports of the BS2 are connected with two input ports of the PBS1 through optical waveguides with equal length; two output ports of the PBS1 are connected with an orthogonal polarization delay module through optical waveguides with equal length to form a Sagnac ring; the delay time difference of the orthogonal polarization delay module for the TM polarization mode and the TE polarization mode is T; The interference result of the unequal arm interferometer enters the SPD2 for detection. Preferably, the intensity modulation module modulates the intensity of the next subpulse or the previous subpulse to 0 to obtain Z-base quantum states respectivelyOr (b)The X-base quantum state is obtained when the intensity of the two sub-pulses is modulated into half at the same time。 Preferably, the intensity modulation module is a first mach-zehnder modulator MZM1 formed by a third beam splitter BS3 and a fourth beam splitter BS4, wherein a first phase modulator PM1 is arranged on one arm of the MZM 1. Preferably, the BS4 of the intensity modulation module is provided with