CN210143015U - Time phase decoding device and quantum key distribution system including the same - Google Patents
Time phase decoding device and quantum key distribution system including the same Download PDFInfo
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- CN210143015U CN210143015U CN201920923419.2U CN201920923419U CN210143015U CN 210143015 U CN210143015 U CN 210143015U CN 201920923419 U CN201920923419 U CN 201920923419U CN 210143015 U CN210143015 U CN 210143015U
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Abstract
The utility model provides a time phase decoding device and including its quantum key distribution system. The time phase decoding apparatus includes: the device comprises a beam splitter, two reflecting devices which are optically coupled with the beam splitter through two arms respectively, a phase modulator arranged at the front end of the beam splitter or on at least one of the two arms, and a single photon detector. Each of the reflecting devices is a polarization orthogonal rotation reflecting device, each of the reflecting devices is a quarter-wave plate reflecting mirror, and the quarter-wave plate reflecting mirror is formed by integrally forming a quarter-wave plate and the reflecting mirror. The single photon detector is coupled to one of the ports of the beam splitter which are not coupled to the two arms and is used for detecting signals of the first time slot, the second time slot and the third time slot which are continuous in one pulse period. The utility model discloses a time phase place coding quantum key distribution decoding scheme can anti polarization induction decline, and helps eliminating or reducing the security problem that many detectors produced.
Description
Technical Field
The utility model relates to a secret communication technology field of optical transmission especially relates to a time phase decoding device and quantum key distribution system.
Background
The quantum secret communication technology is a leading-edge hotspot field combining quantum physics and information science. Based on quantum key distribution technology and one-time pad cipher principle, quantum secret communication can realize the safe transmission of information in public channel. The quantum key distribution is based on the physical principles of quantum mechanics Heisebauer uncertain relation, quantum unclonable theorem and the like, the secret key can be safely shared among users, potential eavesdropping behavior can be detected, and the quantum key distribution method can be applied to the fields of high-safety information transmission requirements of national defense, government affairs, finance, electric power and the like.
The ground quantum key distribution is mainly based on optical fiber channel transmission, and because phase encoding adopts the phase difference of front and back optical pulses to encode information and can be stably maintained in the long-distance optical fiber channel transmission process, a time phase encoding scheme which adopts an unequal arm interferometer to carry out phase encoding or comprises a group of phase encoding is the main encoding scheme for quantum key distribution application. However, the manufacturing of the optical fiber has non-ideal conditions such as non-circular symmetry of the cross section, nonuniform distribution of the refractive index of the fiber core along the radial direction, and the like, and the optical fiber is influenced by temperature, strain, bending, and the like in the actual environment, and can generate random birefringence effect. Therefore, after the optical pulse is transmitted by the long-distance optical fiber and transmitted by the two-arm optical fiber of the unequal-arm interferometer, the problem of polarization-induced fading exists when the unequal-arm interferometer is used for phase decoding interference, so that the decoding interference is unstable, and the error rate is increased. If use the equipment of rectifying, can increase system complexity and cost, and to strong interference condition such as aerial fiber cable, road bridge optical cable difficult to realize stable application. In addition, decoding of the time-phase encoding quantum key distribution system generally includes a time-based decoding optical path and a phase-based decoding optical path to perform base selection decoding detection on a time base and a phase base respectively, which requires four detectors, and the system is high in cost, and potential attack holes exist due to inconsistent performances of the four detectors.
For time-phase encoding schemes, how to stably and efficiently perform interferometric decoding is a hotspot and challenge for quantum secure communication applications based on existing optical cable infrastructure.
SUMMERY OF THE UTILITY MODEL
The utility model discloses a main aim at provides a time phase decoding device and quantum key distribution system based on this decoding device to solve the unstable difficult problem of phase place decoding interference that polarization induction fading arouses in time phase coding quantum key distribution is used. And, the utility model discloses make can use the detector of reduction quantity, eliminate or reduce the security problem that many detectors produced thereby to reduce manufacturing cost and system complexity appreciably.
The utility model provides an at least following technical scheme:
1. a time phase decoding apparatus, comprising: a beam splitter, two reflecting means optically coupled to the beam splitter via two arms, respectively, a phase modulator arranged at the front end of the beam splitter or on at least one of the two arms, a single photon detector, wherein,
each of the reflecting devices is a polarization orthogonal rotation reflecting device, one of the two reflecting devices or each of the two reflecting devices is a quarter-wave plate reflecting mirror, and the quarter-wave plate reflecting mirror is formed by integrally forming a quarter-wave plate and a reflecting mirror;
the single photon detector is coupled to one of the ports of the beam splitter which are not coupled to the two arms, and is used for detecting signals of a first time slot, a second time slot and a third time slot which are continuous in one pulse cycle, wherein the one pulse cycle comprises the first time slot, the second time slot and the third time slot.
2. The time phase decoding apparatus according to claim 1, wherein the phase modulator randomly modulates a phase of 0 degree or 180 degrees.
3. The time-phase decoding apparatus according to claim 1, wherein the one port is a non-input port.
4. The time phase decoding apparatus according to claim 1, further comprising an optical circulator disposed between the single photon detector and the one port of the beam splitter, the optical circulator including a first port, a second port, and a third port, the optical circulator being coupled to the one port of the beam splitter via the second port and being coupled to the single photon detector via the third port, wherein the first port is an input port of the time phase decoding apparatus, an optical pulse input from the first port is output from the second port to the beam splitter, and an optical pulse input from the second port is output from the third port.
5. A time phase decoding apparatus, comprising: an optical circulator, a beam splitter, two reflecting devices optically coupled with the beam splitter via two arms, a first single-photon detector and a second single-photon detector,
each of the reflecting devices is a polarization orthogonal rotation reflecting device, one of the two reflecting devices or each of the two reflecting devices is a quarter-wave plate reflecting mirror, and the quarter-wave plate reflecting mirror is formed by integrally forming a quarter-wave plate and a reflecting mirror;
the optical circulator comprises a first port, a second port and a third port and is coupled to one of the ports of the beam splitter which are not coupled to the two arms through the second port, the first port of the optical circulator is an input port of the time phase decoding device, optical pulses input by the first port of the optical circulator are output to the beam splitter through the second port of the optical circulator, and optical pulses output by the beam splitter to the second port of the optical circulator are output through the third port of the optical circulator;
the first single-photon detector is coupled to the other of the ports of the beam splitter that are not coupled to the two arms for detecting optical pulses output from the other port;
the second single-photon detector is coupled to the third port of the optical circulator and is used for detecting the optical pulse output from the third port of the optical circulator,
one of the first single-photon detector and the second single-photon detector detects signals of at least a first time slot and a second time slot which are continuous in a pulse cycle, and the other one of the first single-photon detector and the second single-photon detector detects signals of at least a second time slot and a third time slot which are continuous in a pulse cycle, wherein the pulse cycle comprises the first time slot, the second time slot and the third time slot.
6. The time phase decoding apparatus according to claim 5, wherein the apparatus further comprises a dc phase modulator provided on at least one of the two arms.
7. The time phase decoding apparatus according to claim 1 or 5, wherein the two arms are polarization maintaining fiber optical paths, and for any one of the quarter-wave plate mirrors: the included angle between the slow axis of the polarization-maintaining fiber of the arm coupled with the polarization-maintaining fiber and the slow axis or the fast axis of the quarter-wave plate of the polarization-maintaining fiber is 45 degrees.
8. The time phase decoding apparatus according to claim 1 or 5, wherein the beam splitter is a polarization maintaining coupler.
9. The time-phase decoding apparatus of claim 8, wherein the beam splitter is a 2 × 2 polarization maintaining coupler.
10. A quantum key distribution system, comprising:
the time phase decoding apparatus according to any one of claims 1 to 9, which is provided at a receiving end of the quantum key distribution system and used for decoding.
The utility model discloses a creative structure for can encode and decode the interference to the input light pulse of arbitrary polarization state steadily, realized unexpected beneficial effect from this. Utilize the utility model discloses a scheme can realize the stable interference output of locating at phase place base decoding interferometer to the input light pulse of arbitrary polarization state, has solved the induced decline of polarization in time phase coding quantum key distribution is used and has caused the problem that the system can't stabilize work. Also, the present invention makes it possible to employ a reduced number of detectors (one or two single photon detectors), thereby eliminating or reducing the safety problems that arise with multiple detectors and appreciably reducing manufacturing costs and system complexity. The utility model provides an easily realize and the time phase place code quantum key distribution decoding scheme of the induced decay of anti polarization of using.
Drawings
Fig. 1 is a schematic structural diagram of a time phase decoding apparatus according to a preferred embodiment of the present invention;
fig. 2 is a schematic structural diagram of a time phase decoding apparatus according to another preferred embodiment of the present invention;
fig. 3 is a diagram schematically showing a first time slot, a second time slot, and a third time slot within one pulse period.
Detailed Description
The following detailed description of the preferred embodiments of the invention, which is to be read in connection with the accompanying drawings, forms a part of this application, and together with the embodiments of the invention, serve to explain the principles of the invention. For the purposes of clarity and simplicity, a detailed description of known functions and configurations of devices described herein will be omitted when it may obscure the subject matter of the present invention.
The time phase decoding apparatus of a preferred embodiment of the present invention is shown in fig. 1, and includes the following components: a beam splitter 102, a phase modulator 103, quarter wave plate mirrors 104 and 105, a single photon detector 106.
The quarter wave plate mirror includes a quarter wave plate and a mirror integrally formed with the quarter wave plate at a rear end of the quarter wave plate. The quarter-wave plate reflector can be realized by plating a reflector on the surface of a quarter-wave plate crystal, and can also be realized by plating a reflector on the end face of a polarization-maintaining optical fiber with the phase difference of 90 degrees in transmission of a fast axis and a slow axis.
The quarter- wave plate mirrors 104 and 105 are polarization orthogonal rotation reflecting devices.
Here, the polarization orthogonal rotation reflection device is a reflection device capable of polarization orthogonal rotation reflection of two orthogonal polarization states of a reflected optical pulse, that is, converting each orthogonal polarization state of the optical pulse into a polarization state orthogonal thereto when reflecting an incident optical pulse. For example, it is assumed that the two orthogonal polarization states are an x polarization state and a y polarization state, respectively, the x polarization state transmitted to one polarization orthogonal rotation reflection device along the optical path is converted into a polarization state orthogonal thereto, i.e., a y polarization state, after being reflected by the polarization orthogonal rotation reflection device, and the y polarization state transmitted to the reflection device along the optical path is converted into a polarization state orthogonal thereto, i.e., an x polarization state, after being reflected by the polarization orthogonal rotation reflection device.
One port 101 on the side of the splitter 102 is the input port of the device. Quarter wave plate mirrors 104 and 105 are optically coupled to beam splitter 102 via two arms (upper and lower arms in fig. 1), respectively. The two arms can be polarization maintaining fiber optical paths; in this case, the slow axis of the polarization maintaining fiber of each arm makes an angle of 45 degrees with the slow or fast axis of the quarter-wave plate in the corresponding quarter-wave plate mirror. Beam splitter 102 and quarter wave plate mirrors 104 and 105 form an unequal arm michelson interferometer. The phase modulator 103 is located on either arm (in fig. 1, the upper arm) of the two arms.
The beam splitter 102 is configured to split one incoming optical pulse of any polarization state into two optical pulses to be transmitted along the two arms, respectively.
The two arms are used for respectively transmitting the two paths of light pulses.
The phase modulator 103 is configured to perform phase modulation on the optical pulse (i.e., one of the two optical pulses) transmitted by the arm in which the phase modulator is located according to a quantum key distribution protocol. The phase modulation by the phase modulator 103 is determined by the quantum key distribution protocol.
The temporal phase decoding means may comprise only one single-photon detector, such as the single-photon detector 106 shown in figure 1. The single photon detector 106 receives the optical pulse signal output from the other port on the beam splitter 102 side. The signal output to the single photon detector 106 during one pulse period comprises three time slots, namely a first time slot, a second time slot and a third time slot. The single photon detector 106 is configured to detect signals in the first time slot, the second time slot and the third time slot within one pulse period. At this time, the phase modulator may randomly modulate a 0 degree phase or a 180 degree phase.
It is possible that the time phase decoding device comprises two single photon detectors, in which case the device further comprises an optical circulator. The optical circulator includes a first port, a second port, and a third port. As illustrated with reference to fig. 1, one of the two single photon detectors, such as single photon detector 106 shown in fig. 1, is coupled to another port on one side of beam splitter 102 for detecting optical pulses output from the other port. The optical circulator may be located in front of beam splitter 102 with its second port coupled to port 101 on that side of beam splitter 102. The optical pulse input from the first port of the optical circulator is output from the second port thereof to the beam splitter 102, and the optical pulse input from the second port of the optical circulator is output from the third port thereof. And the other of the two single-photon detectors is coupled to the third port of the optical circulator and is used for detecting the optical pulse output by the third port of the optical circulator. One of the two single-photon detectors detects signals of at least a first time slot and a second time slot in a pulse period, and the other of the two single-photon detectors detects signals of at least the second time slot and a third time slot in the pulse period. At this time, the phase modulator may be a direct current phase modulator.
The time phase encoded light pulse includes four encoded light pulse states, two time bit encoded light pulse states and two phase encoded light pulse states. As shown in fig. 3, two time-bit encoded light pulse states correspond to a first time-slot light pulse and a second time-slot light pulse, respectively; the two phase-encoded optical pulse states correspond to states in which the phase difference between the first and second time slot optical pulses is 0 degrees and the phase difference between the first and second time slot optical pulses is 180 degrees, respectively. The corresponding states after decoding four encoded light pulses of time phase encoding are as follows: time bit coding first time slot light pulse is decoded and then changed into a first time slot and a second time slot front and back sub light pulse; time bit coding second time slot optical pulse is decoded and then changed into a second time slot and a front sub-two optical pulses and a rear sub-two optical pulses of a third time slot; the phase code is decoded into three sub-optical pulses of a first time slot, a second time slot and a third time slot corresponding to the state that the phase difference between a first time slot optical pulse and a second time slot optical pulse is 0 degrees, wherein the second time slot is a sub-optical pulse formed by interference of two optical pulses and is output by coherent constructive interference from one of two ports of a beam splitter; the phase code is converted into three sub-optical pulses of a first time slot, a second time slot and a third time slot after being decoded in a state that the phase difference between the first time slot optical pulse and the second time slot optical pulse is 180 degrees, wherein the second time slot is a sub-optical pulse formed by interference of two optical pulses, and the sub-optical pulse is output from the other port of the two ports of the beam splitter in an interference coherent and constructive manner.
In one possible application, the device comprises only one single-photon detector which detects the signals of three time slots within one pulse period. When the transmitting terminal adopts time base coding, if the single-photon detector only responds in the first time slot or only responds in the third time slot, generating a secret key according to a detection result; and if the single-photon detector only responds in the second time slot or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting end adopts phase base coding, if the single-photon detector only has response in the second time slot, generating a secret key according to the detection result and the phase modulated by the phase modulator; and if the single-photon detector only responds in the first time slot or the third time slot, or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm.
In another possible application, the device comprises two single-photon detectors, namely a first single-photon detector and a second single-photon detector; the first single-photon detector detects signals of a first time slot and a second time slot in a pulse period, and the second single-photon detector detects signals of the second time slot and a third time slot in the pulse period. When the transmitting terminal adopts time base coding, if the first single-photon detector only responds in the first time slot, a secret key is generated according to the detection result; and if the first single-photon detector only responds in the second time slot or responds in the two time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting terminal adopts time base coding, if the second single-photon detector only responds in the third time slot, a secret key is generated according to the detection result; and if the second single-photon detector only responds in the second time slot or responds in the two time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting end adopts phase-based coding, if the first single-photon detector only responds in the second time slot, a secret key is generated according to the detection result; and if the first single-photon detector only responds in the first time slot or the two time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting end adopts phase-based coding, if the second single-photon detector only responds in the second time slot, a secret key is generated according to the detection result; and if the second single-photon detector only responds in the third time slot or the two time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm.
In yet another possible application, the apparatus comprises two single-photon detectors, respectively a first single-photon detector and a second single-photon detector; each of the first and second single-photon detectors detects signals of three time slots within one pulse period. When the transmitting terminal adopts time base coding, if the first single-photon detector only responds in the first time slot or only responds in the third time slot, generating a secret key according to a detection result; and if the first single-photon detector only responds in the second time slot or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting terminal adopts time base coding, if the second single-photon detector only responds in the first time slot or only responds in the third time slot, generating a secret key according to a detection result; and if the second single-photon detector only responds in the second time slot or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting end adopts phase-based coding, if the first single-photon detector only responds in the second time slot, a secret key is generated according to the detection result; and if the first single-photon detector only responds in the first time slot or the third time slot or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm. When the transmitting end adopts phase-based coding, if the second single-photon detector only responds in the second time slot, a secret key is generated according to the detection result; and if the second single-photon detector only responds in the first time slot or the third time slot or responds in two or three time slots, discarding the detection result or generating a decoding result according to a quantum key distribution post-processing algorithm.
In operation, a light pulse enters the beam splitter 102 through the port 101 of the beam splitter 102 and is split into two light pulses by the beam splitter 102. One path of light pulse from the beam splitter 102 is subjected to phase modulation by the phase modulator 103 and then reflected back by the quarter wave plate mirror 104, and the other path of light pulse from the beam splitter 102 is directly transmitted to the quarter wave plate mirror 105 through the polarization maintaining fiber and reflected back by the quarter wave plate mirror 105. The two paths of reflected optical pulses with relative delays are combined by the beam splitter 102 to obtain output optical pulses, and the output optical pulses are output to the single photon detector 106 from another port. The signal output to the single photon detector 106 during a pulse period comprises three time slots. The single photon detector 106 detects the signals of three time slots within one pulse period.
The phase modulator 103 may be a birefringent phase modulator. The birefringent phase modulator is adapted to apply different adjustable phase modulations to two orthogonal polarization states passing therethrough. For example, the birefringent phase modulator may be a lithium niobate phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulation experienced by each of the two orthogonal polarization states passing through the lithium niobate phase modulator may be controlled and adjusted.
Although in fig. 1 only one phase modulator 103 is shown arranged on one of the two arms, it is also possible to arrange one phase modulator on each of the two arms. In the case where two phase modulators are thus provided, the difference between the phases modulated by the two phase modulators is determined by the quantum key distribution protocol, depending on the particular application. In addition, instead of providing a phase modulator on one or both of the two arms, a phase modulator may be provided before the beam splitter 102 for phase modulating the input optical pulses before splitting in accordance with a quantum key distribution protocol.
Since both reflecting devices 104 and 105 are polarization orthogonal rotating reflecting devices, for each of the two optical pulses: when the path of optical pulse is reflected by a corresponding reflection device of the two reflection devices, two orthogonal polarization states of the path of optical pulse are subjected to polarization orthogonal rotation reflection, so that after the path of optical pulse is reflected by the corresponding reflection device, each orthogonal polarization state of the path of optical pulse is converted into a polarization state orthogonal to the orthogonal polarization state. Thus, for the phase codec of fig. 1, by means of polarization orthogonal rotation reflection at the polarization orthogonal rotation reflection means, the phase difference transmitted through the two arms in the process of splitting by the beam splitter to the beam splitter and combining by the x-polarization state of the input optical pulse is exactly equal to the phase difference transmitted through the two arms in the process of splitting by the beam splitter to the beam splitter and combining by the y-polarization state of the optical pulse.
Although both the two reflection devices 104 and 105 are described above as polarization orthogonal rotation reflection devices in the form of quarter-wave plate mirrors, one of the two reflection devices may be other forms of polarization orthogonal rotation reflection devices, as the case may be, such as the polarization orthogonal rotation reflection devices of configuration 1, configuration 2, or configuration 3 described below.
According to configuration 1, the polarization orthogonal rotation reflection apparatus includes a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter being optically coupled to each other via a transmission optical path on which a half-wave plate is disposed, a polarization direction of an optical pulse input to the half-wave plate making an angle of 45 degrees with a fast axis or a slow axis of the half-wave plate. The transmission optical path may be formed by a polarization-maintaining fiber; in this case, the optical pulse is split by the polarization beam splitter and transmitted along the polarization maintaining fiber, and an included angle between the slow axis of the polarization maintaining fiber forming the transmission optical path and the fast axis or the slow axis of the half-wave plate is 45 degrees. Polarization quadrature rotating reflective device having configuration 1 when used in a decoding device of the present invention, the reflective device can be coupled to one arm of the decoding device by coupling the input port of its polarizing beam splitter to the arm.
According to configuration 2, the polarization orthogonal rotation reflection apparatus includes a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter are optically coupled to each other via a transmission optical path, the transmission optical path is formed by a polarization maintaining fiber, a slow axis and a fast axis of the polarization maintaining fiber respectively maintain two orthogonal polarization states of the optical pulse input to the polarization maintaining fiber to be stably transmitted, that is, polarization states are unchanged, and the two output ports of the polarization beam splitter and the polarization maintaining fiber are configured such that the optical pulses output from the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization maintaining fiber for transmission or are both coupled to the fast axis of the polarization maintaining fiber for transmission. Here, the optical pulses output from the two output ports of the polarization beam splitter are both coupled to the slow axis of the polarization maintaining fiber for transmission or are both coupled to the fast axis of the polarization maintaining fiber for transmission by twisting the polarization maintaining fiber by 90 degrees or by twisting (90+ n × 180) degrees, where n is an integer. Whether the polarization maintaining fiber is twisted or untwisted, the light pulse input from the slow axis of the polarization maintaining fiber is always transmitted along the slow axis (stably transmitted along the slow axis), and the light pulse input from the fast axis of the polarization maintaining fiber is always transmitted along the fast axis (stably transmitted along the fast axis). Polarization quadrature rotating reflective device having configuration 2 when used in a decoding device of the present invention, the reflective device can be coupled to one arm of the decoding device by coupling the input port of its polarizing beam splitter to the arm.
According to configuration 3, the polarization orthogonal rotation reflection apparatus includes a polarization beam splitter having an input port and two output ports, the two output ports of the polarization beam splitter being optically coupled to each other via a transmission optical path, the transmission optical path being formed by a polarization maintaining optical fiber including an odd number of 90-degree fusion splices, each 90-degree fusion splice being formed by fusion splicing of a slow axis of the polarization maintaining optical fiber in alignment with a fast axis of the polarization maintaining optical fiber. Polarization orthogonal rotating reflective device with configuration 3 when used in a decoding device of the present invention, the reflective device can be coupled to one arm of the decoding device by coupling the input port of its polarizing beam splitter to the arm.
Furthermore, the beam splitter 102 in fig. 1 may be a polarization maintaining beam splitter, such as a 2 × 2 polarization maintaining coupler.
The time phase decoding apparatus of another preferred embodiment of the present invention is shown in fig. 2, and includes the following components: an optical circulator 202, a polarization-maintaining beam splitter 203, a DC phase modulator 204, quarter-wave plate mirrors 205 and 206, and single photon detectors 207 and 208.
The quarter wave plate reflector includes a quarter wave plate and a reflector integrally formed with the quarter wave plate at a rear end of the quarter wave plate. The quarter-wave plate reflector can be realized by plating a reflector on the surface of a quarter-wave plate crystal, and can also be realized by plating a reflector on the end face of a polarization-maintaining optical fiber with the phase difference of 90 degrees in transmission of a fast axis and a slow axis.
Quarter-wave plate mirrors 205 and 206 are polarization quadrature rotating reflective devices.
The optical circulator 202 includes three ports, port a, port B, and port C, respectively. The optical pulse input from port a of the optical circulator 202 is output from port B of the optical circulator 202, and the optical pulse input from port B of the optical circulator 202 is output from port C of the optical circulator 202. Port a of optical circulator 202, i.e., port 201, is the input port of the device. Quarter wave plate mirrors 205 and 206 are optically coupled to polarization maintaining beam splitter 203 via two arms (upper and lower arms in fig. 2), respectively. The two arms are polarization-maintaining optical fiber light paths, and the included angle between the slow axis of the polarization-maintaining optical fiber of each arm and the slow axis or the fast axis of the quarter-wave plate in the corresponding quarter-wave plate reflector is 45 degrees. The polarization maintaining beam splitter 203 and the quarter wave plate mirrors 205 and 206 constitute an unequal arm michelson interferometer. The dc phase modulator 204 is located on either arm (in fig. 2, the upper arm) of the two arms. The single-photon detector 208 receives an optical pulse signal output from one port on the polarization-maintaining beam splitter 203 side to the port B of the optical circulator 202 and from the port C of the optical circulator 202 to the single-photon detector 208, and the single-photon detector 207 receives an optical pulse signal output from the other port on the polarization-maintaining beam splitter 203 side. The output signal of the unequal-arm Michelson interferometer in a pulse period comprises three time slots, namely a first time slot, a second time slot and a third time slot. One of the single photon detectors 207 and 208 detects signals of at least a first time slot and a second time slot in a pulse period, and the other of the single photon detectors 207 and 208 detects signals of at least a second time slot and a third time slot in a pulse period.
During operation, the optical pulse is input to the optical circulator 202 through the port a of the optical circulator 202, that is, the port 201, and the optical pulse input to the optical circulator 202 through the port a of the optical circulator 202 is output to the polarization-maintaining beam splitter 203 through the port B of the optical circulator 202 and split into two optical pulses by the polarization-maintaining beam splitter 203. One path of light pulse from the polarization-maintaining beam splitter 203 is subjected to direct current phase modulation by the direct current phase modulator 204 and then reflected back by the quarter wave plate reflector 205, and the other path of light pulse from the polarization-maintaining beam splitter 203 is directly transmitted to the quarter wave plate reflector 206 through the polarization-maintaining optical fiber and reflected back by the quarter wave plate reflector 206. The two paths of optical pulses reflected back after the relative delay are combined by the polarization-maintaining beam splitter 203 and then output to the single-photon detector 207 through the other port of the polarization-maintaining beam splitter 203, or output to the port B of the optical circulator 202 through the one port of the polarization-maintaining beam splitter 203 and output to the single-photon detector 208 through the port C of the optical circulator 202. The single-photon detector 207 detects signals of at least a first time slot and a second time slot, and the single-photon detector 208 detects signals of at least a second time slot and a third time slot; alternatively, the single photon detector 207 detects signals of at least the second time slot and the third time slot, and the single photon detector 208 detects signals of at least the first time slot and the second time slot. The phase modulator 204 may be a birefringent phase modulator.
Herein, the terms "beam splitter" and "beam combiner" are used interchangeably, and a beam splitter may also be referred to and used as a beam combiner, and vice versa. Herein, the term "polarization maintaining fiber optical path" refers to an optical path formed by connecting polarization maintaining fibers or an optical path formed by transmitting optical pulses by using polarization maintaining fibers.
The time phase decoding apparatus of the present invention as described above may be configured at the receiving end of the quantum key distribution system for decoding.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments, as illustrated in the accompanying drawings.
Claims (13)
1. A time phase decoding apparatus, characterized in that the time phase decoding apparatus comprises: a beam splitter, two reflecting means optically coupled to the beam splitter via two arms, respectively, a phase modulator arranged at the front end of the beam splitter or on at least one of the two arms, a single photon detector, wherein,
each of the reflecting devices is a polarization orthogonal rotation reflecting device, one of the two reflecting devices or each of the two reflecting devices is a quarter-wave plate reflecting mirror, and the quarter-wave plate reflecting mirror is formed by integrally forming a quarter-wave plate and a reflecting mirror;
the single photon detector is coupled to one of the ports of the beam splitter which are not coupled to the two arms, and is used for detecting signals of a first time slot, a second time slot and a third time slot which are continuous in one pulse cycle, wherein the one pulse cycle comprises the first time slot, the second time slot and the third time slot.
2. The time phase decoding device of claim 1, wherein the phase modulator randomly modulates a phase of 0 degree or 180 degrees.
3. The time-phase decoding apparatus of claim 1, wherein the one port is a non-input port.
4. The temporal phase decoding apparatus according to claim 1, further comprising an optical circulator disposed between the single-photon detector and the one port of the beam splitter, the optical circulator including a first port, a second port, and a third port, the optical circulator being coupled to the one port of the beam splitter via the second port and to the single-photon detector via the third port, wherein the first port is an input port of the temporal phase decoding apparatus, an optical pulse input from the first port is output to the beam splitter via the second port, and an optical pulse input from the second port is output from the third port.
5. The time-phase decoding device of claim 1, wherein the two arms are polarization-maintaining fiber optic paths, and for any quarter-wave plate mirror: the included angle between the slow axis of the polarization-maintaining fiber of the arm coupled with the polarization-maintaining fiber and the slow axis or the fast axis of the quarter-wave plate of the polarization-maintaining fiber is 45 degrees.
6. The time-phase decoding apparatus of claim 1, wherein the beam splitter is a polarization maintaining coupler.
7. The time-phase decoding apparatus of claim 6, wherein the beam splitter is a 2 x 2 polarization maintaining coupler.
8. A time phase decoding apparatus, characterized in that the time phase decoding apparatus comprises: an optical circulator, a beam splitter, two reflecting devices optically coupled with the beam splitter via two arms, a first single-photon detector and a second single-photon detector,
each of the reflecting devices is a polarization orthogonal rotation reflecting device, one of the two reflecting devices or each of the two reflecting devices is a quarter-wave plate reflecting mirror, and the quarter-wave plate reflecting mirror is formed by integrally forming a quarter-wave plate and a reflecting mirror;
the optical circulator comprises a first port, a second port and a third port and is coupled to one of the ports of the beam splitter which are not coupled to the two arms through the second port, the first port of the optical circulator is an input port of the time phase decoding device, optical pulses input by the first port of the optical circulator are output to the beam splitter through the second port of the optical circulator, and optical pulses output by the beam splitter to the second port of the optical circulator are output through the third port of the optical circulator;
the first single-photon detector is coupled to the other of the ports of the beam splitter that are not coupled to the two arms for detecting optical pulses output from the other port;
the second single-photon detector is coupled to the third port of the optical circulator and is used for detecting the optical pulse output from the third port of the optical circulator,
one of the first single-photon detector and the second single-photon detector detects signals of at least a first time slot and a second time slot which are continuous in a pulse cycle, and the other one of the first single-photon detector and the second single-photon detector detects signals of at least a second time slot and a third time slot which are continuous in a pulse cycle, wherein the pulse cycle comprises the first time slot, the second time slot and the third time slot.
9. The time phase decoding apparatus of claim 8, further comprising a dc phase modulator disposed on at least one of the two arms.
10. The time-phase decoding device of claim 8, wherein the two arms are polarization-maintaining fiber optic paths, and for any quarter-wave plate mirror: the included angle between the slow axis of the polarization-maintaining fiber of the arm coupled with the polarization-maintaining fiber and the slow axis or the fast axis of the quarter-wave plate of the polarization-maintaining fiber is 45 degrees.
11. The time-phase decoding apparatus of claim 8, wherein the beam splitter is a polarization maintaining coupler.
12. The time-phase decoding apparatus of claim 11, wherein the beam splitter is a 2 x 2 polarization maintaining coupler.
13. A quantum key distribution system, comprising:
a time phase decoding device according to any one of claims 1 to 12, provided at a receiving end of the quantum key distribution system for decoding.
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| CN110460433A (en) * | 2019-06-18 | 2019-11-15 | 中国电子科技集团公司电子科学研究院 | Time phase decoding apparatus and quantum key distribution system including it |
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| CN110460433A (en) * | 2019-06-18 | 2019-11-15 | 中国电子科技集团公司电子科学研究院 | Time phase decoding apparatus and quantum key distribution system including it |
| CN110460433B (en) * | 2019-06-18 | 2024-06-25 | 中国电子科技集团公司电子科学研究院 | Time phase decoding device and quantum key distribution system comprising same |
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