Quantum key distribution system with low-loss dispersion-limited fiber

Abstract

A quantum communication system includes a quantum key generation system having a photon qubit generator, a low-loss dispersion-limited optical fiber having a length L (e.g., greater than 200 km) and a photon detector unit, and a communication network having a signal generator, a signal channel and a signal receiver. The low-loss dispersion-limited optical fiber extends between the photon qubit generator and the photon detector unit and optically couples the photon qubit generator and the photon detector unit. In addition, the low-loss dispersion-limited optical fiber is structurally configured to limit dispersion with an absolute dispersion rate of about 9 ps / (nm)km or less (and preferably 0.5 ps / (nm)km or less) and induce attenuation with an attenuation rate of about 0.175 dB / km or less, so that quantum key bit information of a plurality of photons output by the photon qubit generator can be received at a bit rate of at least 10 Gbit / sec at the photon detector unit.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Serial No. 62 / 771,711, filed on November 27, 2018, the contents of which are based on and are incorporated herein by reference in their entirety. Background Art

[0003] The present disclosure relates to a quantum communication system having a low-loss dispersion-limited optical fiber. More specifically, the present disclosure relates to a quantum communication system including a quantum key generation system having components optically coupled using a low-loss dispersion-limited optical fiber for providing an increased quantum key bit rate. Summary of the invention

[0004] According to some embodiments of the present disclosure, a quantum system includes:

[0005] A quantum key system comprising a photon qubit generator, a low-loss dispersion-limited optical fiber, and a photon detector unit; and

[0006] A signal receiver; wherein:

[0007] the low-loss dispersion-limited optical fiber extending between and optically coupling the photon qubit generator and the photon detector unit, the low-loss dispersion-limited optical fiber having a length L (e.g., L is between 100 km and 2000 km, or between 200 km and 1000 km);

[0008] The photonic qubit generator is structurally configured to output a plurality of photons, each photon of the plurality of photons comprising quantum key bit information;

[0009] The photon detector unit is structurally configured to receive the quantum key bit information of the plurality of photons;

[0010] The signal receiver is communicatively coupled to the photon detector unit and is structurally configured to compare the one or more signal bits with the quantum key bit information upon receiving the signal; and

[0011] The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of about 1550 nm at an absolute dispersion rate of about 9 ps / (nm)km or less, and induce attenuation of photons having the wavelength of about 1550 nm at an attenuation rate of about 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least 10 Gbit / sec.

[0012] According to some embodiments of the present disclosure, a quantum communication system includes: a quantum key generation system, the quantum key generation system having a photon qubit generator, a low-loss dispersion-limited optical fiber, and a photon detector unit, and a communication network, the communication network having a signal generator, a signal channel, and a signal receiver. The low-loss dispersion-limited optical fiber extends between the photon qubit generator and the photon detector unit, and optically couples the photon qubit generator and the photon detector unit. The photon qubit generator is structurally configured to output a plurality of photons, each of the plurality of photons including quantum key bit information. The photon detector unit is structurally configured to receive the quantum key bit information of the plurality of photons. The signal channel extends between the signal generator and the signal receiver and communicatively couples the signal generator and the signal receiver. The signal generator is structurally configured to output a signal including one or more signal bits. The signal receiver is communicatively coupled to the photon detector unit, and is structurally configured to compare the one or more signal bits with the quantum key bit information when receiving the signal. In addition, the low-loss dispersion-limited optical fiber has a length L>200km, and includes a core and a cladding surrounding the core. The low-loss dispersion-limited optical fiber is structurally configured to limit the dispersion of photons including a wavelength of about 1550nm at an absolute dispersion rate of about 9ps / (nm)km or less, and induce the attenuation of the photon pulse having the wavelength of about 1550nm at an attenuation rate of about 0.175dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least about 10Gbit / sec. According to some embodiments, the key rate of the rate of the quantum key generation system is at least 10kbit / sec.

[0013] According to some embodiments, the low-loss dispersion-limited optical fiber is structurally configured to limit the dispersion of photons including a wavelength of about 1550 nm with an absolute dispersion rate of about 9 ps / (nm)km (i.e., 9 ps / nm·km or 9 picoseconds / nm / km) or less, and induce attenuation of photons including a wavelength of about 1550 nm with an attenuation rate between 0.12 dB / km and 0.175 dB / km.

[0014] According to one embodiment of the present disclosure, the quantum communication system further includes a laser and a spectral filter optically coupled to the laser, the spectral filter being a bandpass filter having a bandpass width of 0.2 nm to 0.5 nm.

[0015] According to one embodiment, a low-loss dispersion-limited optical fiber has a core and a cladding surrounding the core and is structurally configured to limit the dispersion of photons having a wavelength including about 1550 nm to an absolute dispersion rate of about 5 ps / (nm)km (also referred to as 5 ps / nm·km) or less.

[0016] According to one embodiment, a low-loss dispersion-limited optical fiber has a core and a cladding surrounding the core and is structurally configured to limit the dispersion of photons having a wavelength of about 1550 nm to an absolute dispersion rate of about 5 ps / (nm)km (also referred to as 5 ps / nm·km) or less, and the quantum communication system does not include a spectral filter optically coupled to the laser or photon generator. According to some embodiments, the quantum communication system does not include a spectral filter located within the photonic qubit generator.

[0017] According to one embodiment, there is no optical transmission fiber between the photon qubit generator and the photon detector unit coupled to the low-loss optical low-dispersion fiber. According to one embodiment, the quantum communication system further comprises an intensity modulator and a beam splitter such that there is no optical transmission between the intensity modulator and the beam splitter.

[0018] According to one embodiment of the present disclosure, a quantum key generation system includes a low-loss dispersion-limited optical fiber extending between a photon qubit generator and a photon detector unit and optically coupling the photon qubit generator and the photon detector unit. The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of photons including a wavelength of about 1550 nm at an absolute dispersion rate of about 9 ps / (nm)km or less, and induce the attenuation of photons including the wavelength of about 1550 nm at an attenuation rate of about 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least about 10 Gbit / sec.

[0019] According to one embodiment of the present disclosure, a quantum key generation system includes a low-loss dispersion-limited optical fiber extending between a photon qubit generator and a photon detector unit and optically coupling the photon qubit generator and the photon detector unit. The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of photons including a wavelength of about 1550 nm at an absolute dispersion rate of about 10 ps / (nm)km or less, and induce the attenuation of photons including the wavelength of about 1550 nm at an attenuation rate of about 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least about 10 Gbit / sec.

[0020] According to some embodiments, a low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of photons including a wavelength of about 1550 nm at an absolute dispersion rate of about 5 ps / (nm)km (i.e., 5 ps / nm·km) or less, and induce attenuation of photons including the wavelength of about 1550 nm at an attenuation rate of about 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photonic qubit generator can be received at the photonic detector unit at a bit rate of at least about 10 Gbit / sec (e.g., at least 25 Gbit / sec or 50 Gbit / sec). According to some embodiments, the low-loss dispersion-limited optical fiber is structurally configured to limit the dispersion of photons including a wavelength of about 1550 nm to an absolute dispersion rate of about 5 ps / (nm)km or less, and to induce attenuation of photons including a wavelength of about 1550 nm at an attenuation rate between 0.12 dB / km and 0.175 dB / km. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following detailed description of certain embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, in which like structures are designated with like reference numerals, and in which:

[0022] Figure 1 schematically depicts a quantum communication system including a quantum key generation system and a communication network according to one or more embodiments shown and described herein;

[0023] Figure 2 schematically depicts a photon pulse pair according to one or more embodiments shown and described herein;

[0024] Figure 3A Schematically depicts a schematic diagram of a device according to one or more embodiments shown and described herein. Figure 1A cross-sectional view of an embodiment of a low-loss dispersion-limited optical fiber;

[0025] Figure 3B Diagrammatically depicts an example of a device according to one or more embodiments shown and described herein. Figure 3A The refractive index of a low-loss dispersion-limited optical fiber as a function of its radius;

[0026] Figure 4A Schematically depicts a schematic diagram of a device according to one or more embodiments shown and described herein. Figure 1 A cross-sectional view of another embodiment of a low-loss dispersion-limited optical fiber;

[0027] Figure 4B Diagrammatically depicts an example of a device according to one or more embodiments shown and described herein. Figure 4A The refractive index of a low-loss dispersion-limited optical fiber as a function of its radius; DETAILED DESCRIPTION

[0028] Reference now Figure 1 , schematically depicts a quantum communication system 100 including a quantum key generation system 101 and a communication network 190. The quantum key generation system 101 includes a photon qubit generator 120, a photon detector unit 140, and a dispersion-limited optical fiber 151 extending between and optically coupling the photon qubit generator 120 and the photon detector unit 140. The photon qubit generator 120 can be structurally configured to provide photons having any wavelength λ (e.g., between about 800 nm and about 1800 nm, such as about 1550 nm). Similarly, the detector unit 140 can be structurally configured to detect photons provided by the photon qubit generator 120, such as photons having a wavelength λ (between about 800 nm and about 1800 nm, such as about 1550 nm).

[0029] The communication network 190 includes a signal generator 192, a signal receiver 194, and a signal channel 195 extending between and communicatively coupling the signal generator 192 and the signal receiver 194. In addition, the signal receiver 194 is communicatively coupled to the photon detector unit 140, thereby communicatively coupling the quantum key generation system 101 to the communication network 190.

[0030] Still reference Figure 1, the photon qubit generator 120 of the quantum key generation system 101 is structurally configured to output a plurality of photons, each photon including a quantum key bit, and the photon detector unit 140 is structurally configured to determine quantum key bit information upon receiving at least one of the plurality of photons provided by the photon qubit generator 120. The quantum key bit information may include a cryptographic key that may be used to decode an encrypted message transmitted using the communication network 190. In addition, the signal generator 192 of the communication network 190 is structurally configured to output a signal including one or more signal bits, the one or more signal bits may include a portion of the encrypted message, and the signal receiver 194 is structurally configured to compare the one or more signal bits with the quantum key bit information upon receiving the signal, for example, to decode the encrypted message using the cryptographic key including the quantum key bit information. Figure 1 The protocol utilized in the embodiments of the invention is based on "time-bin" encoding with a decoy state method. Other protocols (e.g., twin-field QKD) may also be utilized. Exemplary quantum key distribution (QKD) implementations may utilize 3 or more quantum states. For example, many quantum key distribution (QKD) implementations utilize 4 BB84 (quantum) states. Other implementations may also be utilized.

[0031] In operation, the plurality of photons including the quantum key bits may pass through a low-loss dispersion-limited optical fiber 151 located between the photon qubit generator 120 and the photon detector unit 140. The low-loss dispersion-limited optical fiber 151 is structurally configured to control the dispersion of the plurality of photons passing through the low-loss dispersion-limited optical fiber 151 so that the temporal pulse width of each of the plurality of photons passing through the low-loss dispersion-limited optical fiber 151 is less than the pulse spacing distance between adjacent photons. As used herein, "temporal pulse width" is the full width at half maximum (FWHM) of the peak intensity of each photon pulse. Additionally, as used herein, "pulse spacing distance" is the distance between the pulse centers of adjacent photon pulses, where the pulse center corresponds to the peak intensity of each photon pulse. For example, in some embodiments, the low-loss dispersion-limited optical fiber 151 may be structurally configured to minimize the widening of the temporal pulse width of each photon pulse to prevent overlapping adjacent photon pulses.

[0032] Reference now Figure 2 , schematically depicts the temporal pulse width W of the first photon pulse 102 P1 and the temporal pulse width W of the second photon pulse 104 P2The first photon pulse 102 and the second photon pulse 104 are example photons output by the photon qubit generator 120, and the first photon pulse 102 and the second photon pulse 104 are adjacently positioned and propagated along the low-loss dispersion-limited optical fiber 151. The first photon pulse 102 includes a pulse center 103 corresponding to the peak intensity of the first photon pulse 102, and the second photon pulse 104 includes a pulse center 105 corresponding to the peak intensity of the second photon pulse 104. In addition, the pulse center 103 of the first photon pulse 102 is separated from the pulse center 105 of the second photon pulse 104 by a pulse spacing distance D. P .like Figure 2 As shown, the pulse spacing distance between the first photon pulse 102 and the second photon pulse 104 is greater than the sum of the temporal pulse half widths of each photon pulse 102 and 104 (ie, D P >(W P1 +W P2 ) / 2), so that the first and second photon pulses 102, 104 do not overlap. Figure 2 As shown, the pulse spacing distance between the first photon pulse 102 and the second photon pulse 104 is greater than the temporal pulse width W of each photon pulse 102, 104. P1 , W P2 , so that the first and second photon pulses 102, 104 do not overlap. As a non-limiting example, the temporal pulse width can be from about 20 ps to about 200 ps, ​​for example, about 30 ps, ​​40 ps, ​​50 ps, ​​60 ps, ​​70 ps, ​​80 ps, ​​90 ps, ​​100 ps, ​​110 ps, ​​120 ps, ​​125 ps, 130 ps, ​​140 ps, ​​150 ps, ​​160 ps, ​​170 ps, ​​180 ps, ​​190 ps, ​​etc.

[0033] Reference now Figures 3A-4B , depicting low-loss dispersion-limited optical fiber 151 in more detail. Figure 3A and Figure 4A Depicted separately Figure 1 A cross section of an embodiment of a low-loss dispersion-limited optical fiber 151 along line AA. In particular, Figure 3A A low-loss dispersion-limited optical fiber 151 ′ is depicted and includes a core 152 and a cladding 154 surrounding the core 152 . Figure 4A A low-loss dispersion-limited optical fiber 151″ is depicted. The low-loss dispersion-limited optical fiber 151″ also includes a core 152 and a cladding 154 surrounding the core 152, and further includes a cladding ring 155 disposed within the cladding 154, the cladding ring 155 separating the cladding 154 into a first cladding portion 154a and a second cladding portion 154b, the first cladding portion 154a being located between the cladding ring 155 and the core 152. In addition, Figure 3B and Figure 4B Depicted as Figure 3A and Figure 3B Graph of the refractive index as a function of radius of low-loss dispersion-limited optical fibers 151' and 151".

[0034] Reference again Figure 3A and Figure 4A , the fiber core 152 may include silica glass, polymers, etc., and may be doped with potassium (K), chlorine (Cl), fluorine (F), or a combination thereof. Although not intended to be limited by theory, doping the core 152 may reduce the viscosity and fictive temperature of the core 152. The fiber cladding 154 includes an outer cladding surface 156 and may include pure silica, F-doped silica, F (fluorine) / B (boron) co-doped silica, a low refractive index polymer, etc. Doping the cladding 154 with F may reduce the refractive index of the cladding 154. In addition, the cladding 154 includes a lower refractive index than the core 152 to promote total internal reflection of multiple photons propagating through the low-loss dispersion-limited optical fiber 151.

[0035] exist Figure 3A and Figure 4A In the depicted embodiment, the low-loss dispersion-limited optical fiber 151', 151" includes a single core 152, however in other embodiments, the low-loss dispersion-limited optical fiber 151', 151" may include multiple cores. In embodiments including multiple cores, the multiple cores may be spun, and the low-loss dispersion-limited optical fiber 151 may include any spin configuration, such as a unidirectional spin configuration, a bidirectional spin configuration, etc. In addition, in some embodiments, the low-loss dispersion-limited optical fiber 151', 151" may include a step refractive index profile, a parabolic refractive index profile, a graded refractive index profile, a triangular refractive index profile, etc.

[0036] Reference again Figure 3A and Figure 3B The core 152 of the low-loss dispersion-limited optical fiber 151' may include a radius R from about 1.5 μm to about 5 μm (eg, 2 μm to about 4 μm, 2.2 μm to about 3 μm, etc.). 芯 For example, 2.23 μm, 2.28 μm, 2.3 μm, 2.35 μm, 2.4 μm, 2.45 μm, 2.5 μm, 2.55 μm, 2.58 μm, 2.6 μm, 2.65 μm, 2.7 μm, 2.75 μm, 2.8 μm, 2.85 μm, 2.9 μm, 2.95 μm, etc. The core 152 of the low-loss dispersion-limited optical fiber 151 ′ includes a refractive index n1 and a relative refractive index Δ1 (which is relative to the refractive index n1 of pure silica). s and indicates the refractive index change between pure silica and core 152). The relative refractive index Δ1 includes (n1-ns ) / n s . As described above, the core 152 can be pure silica glass or glass doped with Cl, or K, or F to reduce loss. As a non-limiting example, the relative refractive index Δ1 can be from about -0.1 to about 0.2, etc., for example, -0.1, -0.05, 0, 0.05, 0.1, 0.15, etc. The cladding 154 includes a refractive index n2 and a relative refractive index Δ2 (which is relative to the refractive index n of pure silica s and indicates the refractive index change between pure silica and the core 152). The relative refractive index Δ2 includes (n2 - n s ) / n s . In addition, n2 < n1 and Δ2 < Δ1. As a non-limiting example, the relative refractive index Δ2 can be from about -0.4 to about -0.7, etc., for example, -0.45, -0.5, -0.55, -0.6, -0.65, etc.

[0037] In addition, the low-loss dispersion-limited optical fiber 151' includes a relative refractive index Δ between the core 152 and the cladding 154, and the relative refractive index Δ ranges from about 0.3 to about 0.8, where Δ = Δ1 - Δ2. As a non-limiting example, the relative refractive index Δ can be from about 0.4 to about 0.7, from 0.5 to about 0.65, etc., for example, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, etc. In addition, including dopants (e.g., upper dopants or lower dopants) in the core 152, the cladding 154, or both can change the relative refractive index between the core 152 and the cladding 154, that is, change the refractive index change Δ. As used herein, an "upper dopant" is a dopant that has a tendency to increase the refractive index relative to pure undoped SiO2, and a "lower dopant" is a dopant that has a tendency to decrease the refractive index relative to pure undoped SiO2.

[0038] Still referring to Figure 3A and Figure 3B, the low-loss dispersion-limited fiber 151' may include a cutoff wavelength of about 1200 nm or less, such as 1151 nm, 1100 nm, 1050 nm, 1031 nm, 1025 nm, 1000 nm, 975 nm, 973 nm, 950 nm, 929 nm, 925 nm, 915 nm, 911 nm, 909 nm, 905 nm, 900 nm, 875 nm, 850 nm, 825 nm, 800 nm, etc. While not intending to be limited by theory, the cutoff wavelength is a wavelength above which guided higher order modes are no longer supported within the core 152 and the core 152 becomes a single-mode core supporting only the fundamental mode. In operation, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151 ′, the low-loss dispersion-limited optical fiber 151 ′ induces a mode field diameter MFD of from about 6.5 μm to about 10 μm, for example, about 7 μm to about 9.5 μm, 7.5 μm to about 9.0 μm, 7 μm to about 8.5 μm, etc., such as 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, etc. While not intending to be limited by theory, the mode field diameter MFD is the lateral extent of the optical intensity distribution of the fundamental mode of the core 152 of the low-loss dispersion-limited optical fiber 151 ′.

[0039] Furthermore, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151', the low-loss dispersion-limited optical fiber 151' induces an effective area of ​​about 30 μm 2 To about 70μm 2 , for example, about 35 μm 2 To about 60μm 2 , about 40μm 2 To about 55μm 2 , about 45μm 2 To about 50μm 2 etc., such as 30μm 2 、35μm 2 , 40μm 2 , 45μm 2 , 50μm 2 、55μm 2 、60μm 2 、65μm 2 、70μm 2 、75μm 2 、80μm 2While not intending to be limited by theory, the effective area is the cross-sectional area over which the electric field energy of the fundamental mode of light propagating along the low-loss dispersion-limited optical fiber 151' is distributed within the core 152. For example, the effective area of ​​a single-mode optical fiber is related to the maximum energy that the core 152 can carry without inducing nonlinear type signal losses.

[0040] Still reference Figure 3A and Figure 3B When one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151', the low-loss dispersion-limited optical fiber 151' limits the dispersion of the one or more photons to an absolute dispersion rate of no more than 9 ps / (nm)km, for example, about 8.6 ps / (nm)km or less, 8.5 ps / (nm)km or less, 8 ps / (nm)km or less, 7.5 ps / (nm)km or less, 7 ps / (nm)km or less, 6.5 ps / (nm)km or less, 6 ps / (nm)km or less, 5.7 ps / (nm)km or less, 5.5 ps / (nm)km or less, , 5 ps / (nm)km or less, 4.5 ps / (nm)km or less, 4.5 ps / (nm)km or less, 4 ps / (nm)km or less, 3.6 ps / (nm)km or less, 3.5 ps / (nm)km or less, 3 ps / (nm)km or less, 2.5 ps / (nm)km or less, 2 ps / (nm)km or less, 1.5 ps / (nm)km or less, 1.1 ps / (nm)km, 1 ps / (nm)km or less, 0.5 ps / (nm)km or less, 0.1 ps / (nm)km or less, etc. While not intending to be limited by theory, the absolute dispersion rate is the distance of a photon pulse from the center of the pulse 103 ( Figure 2 )The rate at which a photon diffuses outward, for example, the rate at which the temporal pulse width of a photon pulse increases.

[0041] In addition, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151', the low-loss dispersion-limited optical fiber 151' induces a dispersion slope of about 0.05 ps / (nm 2 )km(i.e., 0.05ps / nm 2。 km) to about 0.055 ps / (nm 2 )km, for example, about 0.051ps / (nm 2 )km to about 0.054ps / (nm 2 )km, such as about 0.0515ps / (nm 2 )km、0.0516ps / (nm 2 )km、0.0518ps / (nm 2)km、0.052ps / (nm 2 )km、0.0521ps / (nm 2 )km、0.0525ps / (nm 2 )km、0.053ps / (nm 2 )km、0.0535ps / (nm 2 )km、0.0538ps / (nm 2 )km, etc. Although not intended to be limited by theory, the dispersion slope is the rate at which the absolute dispersion rate changes with wavelength. For flat dispersion over a wide wavelength window, a smaller dispersion slope may be desired. In addition, when one or more photons including a wavelength of about 1550nm propagate along the low-loss dispersion-limited optical fiber 151', the low-loss dispersion-limited optical fiber 151' induces an attenuation rate of about 0.175 dB / km or less, for example, about 0.17 dB / km or less, about 0.165 dB / km or less, such as about 0.16 dB / km, 0.155 dB / km, 0.15 dB / km, 0.14 dB / km, 0.13 dB / km, 0.12 dB / km, etc. Although not intended to be limited by theory, the attenuation rate is the rate of intensity loss (e.g., photon loss) of multiple photons propagating along the low-loss dispersion-limited optical fiber 151'.

[0042] Tables 1 and 2 below list Figure 3A and Figure 3B Properties of an example of a low-loss dispersion-limited optical fiber 151'.

[0043] Table 1:

[0044]

[0045]

[0046] Table 2:

[0047]

[0048] Reference now Figure 4A and Figure 4B , schematically depicts ( Figure 4A ) and graphically depicts ( Figure 4B ) The low-loss dispersion-limited optical fiber 151'' includes a cladding ring 155 disposed within the cladding 154, the cladding ring 155 being located between the first cladding portion 154a and the second cladding portion 154b. The core 152 of the low-loss dispersion-limited optical fiber 151'' may include a radius R 芯The first cladding portion 154a of the low-loss dispersion-limited optical fiber 151″ includes a radius R measured from the interface between the first cladding portion 154a and the cladding ring 155. 包层 , radius R 包层 From about 3 μm to about 12 μm, for example, about 4 μm to about 10 μm, 4.5 μm to 8.8 μm, etc., such as 3 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 8.8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc. Still referring to Figure 4A and Figure 4B The cladding ring 155 of the low-loss dispersion-limited optical fiber 151" includes a radius R measured from the interface between the cladding ring 155 and the second cladding portion 154b. 环 , radius R 环 From about 7μm to about 13μm, for example, 8μm to about 12μm, and about 9μm to about 11.5μm, etc., such as, 7μm, 7.5um, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.4μm, 11.5μm, 12μm, 12.5μm, 13μm, etc.

[0049] Still reference Figure 4A and Figure 4B The core 152 of the low-loss dispersion-limited optical fiber 151" includes a refractive index n1 and a relative refractive index Δ1 (which is relative to the refractive index n of pure silica). s and indicates the refractive index change between pure silica and core 152). The relative refractive index Δ1 includes (n1-n s ) / n s The first cladding portion 154a includes a refractive index n2 and a relative refractive index Δ2 (which is relative to the refractive index n of pure silica). s and indicates the refractive index change between pure silica and the first cladding portion 154a). The relative refractive index Δ2 includes (n2-n s ) / n s The cladding ring 155 includes a refractive index n3 and a relative refractive index Δ3 (which is relative to the refractive index n of pure silica). s and indicates the refractive index change between pure silica and the cladding ring 155). The relative refractive index Δ3 includes (n3-ns ) / n s The second cladding portion 154b includes a refractive index n4 and a relative refractive index Δ4 (which is relative to the refractive index n of pure silica). s and indicates the refractive index change between pure silica and the second cladding portion 154a). The relative refractive index Δ4 includes (n4-n s ) / n s .

[0050] In addition, n1>n3>n4>n2 and Δ1>Δ3>Δ4>Δ2. As described above, the core 152 can be pure silica glass or glass doped with Cl, or K or F to reduce losses. As a non-limiting example, the relative refractive index Δ1 can be from about -0.1 to about 0.2, for example, -0.1, -0.05, 0, 0.05, 0.1, 0.15, etc. The first cladding portion 154a, the cladding ring 155, and the second cladding portion 154b can each include glass doped with F (e.g., silica glass) for reducing their respective refractive indices. As a non-limiting example, the relative refractive index Δ2 can be from about -0.2 to about -0.7, for example, -0.25, 0.3, 0.35, -0.45, -0.5, -0.55, -0.6, -0.65, etc. As a non-limiting example, the relative refractive index Δ3 can be from about -0.1 to about -0.5, for example, -0.15, -0.2, -0.25, -0.3, -0.35, -0.4, -0.45, etc. As a non-limiting example, the relative refractive index Δ4 can be from about -0.2 to about -0.6, for example, -0.25, 0.3, 0.35, -0.45, -0.5, -0.55, -0.6, etc.

[0051] The low-loss dispersion-limited optical fiber 151″ includes a refractive index change Δ' between the core 152 and the first cladding portion 154a, and the refractive index change Δ' is from about 0.2 to about 0.6, where Δ'=Δ1-Δ2. In some embodiments, the refractive index change Δ' can be from about 0.4 to about 0.5, for example, 0.25, 0.3, 0.35, 0.4, 0.41, 0.43, 0.45, 0.47, 0.49, 5, 5.5, etc. The low-loss dispersion-limited optical fiber 151" also includes a refractive index change Δ" between the first cladding portion 154a and the cladding ring 155, and the refractive index change Δ" is from about 0 to about 0.2 (i.e., the refractive index of the cladding ring 155 can be higher than the refractive index of the first cladding portion 154a), where Δ"=Δ3-Δ2. In some embodiments, the refractive index change Δ" can be about 0.02, 0.05, 0.1, 0.12, 0.15, 0.18, etc. In addition, the low-loss dispersion-limited optical fiber 151" includes a refractive index change Δ"' between the first cladding portion 154a and the second cladding portion 154b, and the refractive index change Δ"' is from about 0 to about 0.1 (i.e., the refractive index of the second cladding portion 154b can be higher than the refractive index of the first cladding portion 154a), where Δ"'=Δ4-Δ2. In some embodiments, the refractive index change Δ'" may be approximately -0.02, -0.04, -0.05, -0.1, etc.

[0052] The low-loss dispersion-limited optical fiber 151" may include a cutoff wavelength of about 1600 nm or less, 1500 nm or less, 1350 nm or less, etc., for example, 1550 nm, 1516 nm, 1500 nm, 1464 nm, 1450 nm, 1403 nm, 1400 nm, 1384 nm, 1350 nm, 1300 nm, 1250 nm, 1200 nm, 11150 nm, 1100 nm, 1050 nm, 1000 nm, 950 nm, 900 nm, 850 nm, 800 nm Etc. In addition, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151 ″, the low-loss dispersion-limited optical fiber 151 ″ induces a mode field diameter of photons including a wavelength of about 1550 nm to be from about 8 μm to about 12 μm, for example, from about 9 μm to about 11 μm, 9.5 μm to about 10.5 μm, etc., such as 8 μm, 8.5 μm, 9 μm, 9.5 μm, 9.9 μm, 10 μm, 10.1 μm, 10.2 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, etc.

[0053] Furthermore, in some embodiments, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151 ″, the low-loss dispersion-limited optical fiber 151 ″ induces an effective area from about 50 μm 2To about 100 μm 2 、60μm 2 To about 90μm 2 、70μm 2 To about 80μm 2 etc., such as 50μm 2 、55μm 2 、60μm 2 、65μm 2 、70μm 2 、73.5μm 2 、74.3μm 2 、75μm 2 、76.8μm 2 、78.7μm 2 、80μm 2 、85μm 2 、90μm 2 、95μm 2 , 100μm 2 Etc. In addition, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151″, the low-loss dispersion-limited optical fiber 151″ induces a dispersion having an absolute dispersion rate of about 9 ps / (nm)km or less, for example, about 8.6 ps / (nm)km or less, 8.5 ps / (nm)km or less, 8 ps / (nm)km or less, 7.5 ps / (nm)km or less, 7 ps / (nm)km or less, 6.5 ps / (nm)km or less, 6 ps / (nm)km or less, 5.7 ps / (nm)km or less, 5.5 ps / (nm)km or less, 5.5 ps / (nm)km or less. s / (nm)km or less, 4.5ps / (nm)km or less, 4.5ps / (nm)km or less, 4ps / (nm)km or less, 3.8ps / (nm)km or less, 3.6ps / (nm)km or less, 3.5ps / (nm)km or less, 3ps / (nm)km or less, 2.5ps / (nm)km or less, 2ps / (nm)km or less, 1.5ps / (nm)km or less, 1.1ps / (nm)km, 1ps / (nm)km or less, 0.5ps / (nm)km or less, 0.1ps / (nm)km or less, etc.

[0054] In some embodiments, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151 ″, the low-loss dispersion-limited optical fiber 151 ″ induces a dispersion slope of about 0.05 ps / (nm 2 )km to about 0.1ps / (nm 2 )km、0.055ps / (nm 2)km to about 0.085ps / (nm 2 )km, such as about 0.0525ps / (nm 2 )km、0.055ps / (nm 2 )km、0.0564ps / (nm 2 )km、0.0575ps / (nm 2 )km、0.06ps / (nm 2 )km、0.0625ps / (nm 2 )km、0.0645ps / (nm 2 )km、0.065ps / (nm 2 )km、0.0675ps / (nm 2 )km、0.0676ps / (nm 2 )km、0.07ps / (nm 2 )km、0.0725ps / (nm 2 )km、0.075ps / (nm 2 )km、0.0775ps / (nm 2 )km、0.08ps / (nm 2 )km、0.0825ps / (nm 2 )km、0.0834ps / (nm 2 )km、0.085ps / (nm 2 )km, etc.

[0055] In addition, when one or more photons including a wavelength of about 1550 nm propagate along the low-loss dispersion-limited optical fiber 151", the low-loss dispersion-limited optical fiber 151" induces an attenuation rate of about 0.175 dB / km or less, for example, about 0.17 dB / km or less, about 0.165 dB / km or less, such as about 0.16 dB / km, 0.155 dB / km, 0.15 dB / km, 0.14 dB / km, 0.13 dB / km, 0.12 dB / km, etc.

[0056] Table 3 below lists the properties of an example low-loss dispersion-limited optical fiber 151".

[0057] Table 3:

[0058]

[0059]

[0060] refer to Figure 1, the quantum key generation system 101 of the quantum communication system 100 is configured to propagate quantum key bit information without photon entanglement, and includes a photon qubit generator 120 optically coupled to a photon detector unit 140 using one or more of the low-loss dispersion-limited optical fibers 151 as described above. Incorporating the low-loss dispersion-limited optical fibers 151 can increase the quantum key bit rate of the quantum key generation system 101 because the low-loss dispersion-limited optical fibers 151 induce a low absolute dispersion rate and a low attenuation rate of photons propagating through the low-loss dispersion-limited optical fibers 151.

[0061] The low-loss dispersion-limited fiber(s) 151 do not require dispersion compensation. According to one embodiment, there is no dispersion compensating fiber between the photon qubit generator and the photon detector unit (e.g., there is no dispersion compensating fiber coupled to the low-loss dispersion-limited fiber). According to one embodiment, there is no dispersion compensating fiber between the intensity modulator (IM) 124, 124' and the beam splitter 174.

[0062] In addition, if Figure 1 As shown, in this embodiment, there is no single-mode optical transmission fiber (such as available from Corning Incorporated in Corning, New York) between the photon qubit generator 120 and the photon detector unit 140. Fiber Optic or Therefore, the (multiple) low-loss dispersion-limited fibers 151 are not coupled to typical single-mode transmission fibers and therefore do not pre-compensate for the dispersion introduced into the quantum channel by such transmission fibers. Figure 1 The lossy dispersion limited optical fiber(s) 151 shown in the illustrated embodiment need not be coupled to a single mode optical transmission optical fiber and are not used to provide dispersion compensation for such optical transmission optical fiber. Figure 1 Embodiment(s) of the low-loss dispersion-limited optical fiber 151 for use with typical single-mode transmission optical fibers such as ) in the leu, a very low dispersion level is introduced into the quantum key generation system, so there is no need to couple to a dispersion compensating fiber in order to compensate for the dispersion losses induced by (multiple) optical fibers 151.

[0063] For example, Figure 1 As shown, there is no optical transmission fiber (such as, Fiber Optic or Ultra-fiber). Similarly, for example, Figure 1 As shown, there is no optical transmission fiber (eg, Fiber Optic or Ultra-fiber). According to one embodiment, there is no light transmission fiber between the photon qubit generator 120 and the photon detector unit 140 coupled to the low-loss optical low-dispersion fiber. According to one embodiment, the quantum communication system further comprises an intensity modulator and a beam splitter, such that there is no light transmission fiber between the intensity modulator and the beam splitter.

[0064] Typical optical transmission single-mode optical fibers have (or produce) a dispersion of at least 18 ps / (nm)km near a wavelength of 1550 nm. Typical low-loss single-mode transmission optical fibers have even greater dispersion. According to one embodiment, the low-loss dispersion-limited optical fiber 151 is not coupled to:

[0065] (i) a single-mode optical transmission fiber (via VA 158) having a dispersion of at least 18 ps / (nm)km; and / or

[0066] (ii) A single-mode light transmission optical fiber inducing an attenuation of 0.185 dB / km or more at a wavelength of about 1550 nm.

[0067] The photon qubit generator 120 of the quantum key generation system 101 may include a photon generator 122, which includes a laser 122A optically coupled to an intensity modulator (IM) 124. The laser 122A of the photon qubit generator 120 may be configured to output a large number of photons at a high (raw data) bit rate. The photon generator 122 may include a laser 122A optically coupled to an optional nonlinear crystal 122B. In addition, the photon generator 122 may be structurally configured to provide photons having an arbitrary wavelength λ (e.g., between about 800 nm and about 1800 nm, such as between about 1530 nm and about 1565 nm, about 1545 nm and about 1555 nm, or about 1550 nm). The photon detector unit 140 of the quantum key generation system 101 may include one or more single photon detectors 140A, 140B, such as, for example, one or more single photon detectors SPDD (e.g., (multiple) superconducting nanowire single photon detectors), carbon nanowire detectors, etc. In operation, the quantum key generation system 101 may execute any known or yet to be developed non-entanglement-based quantum communication protocol, such as the BB84 protocol, the E91 protocol, etc.

[0068] Still reference Figure 1, the quantum key generation system 101 may further include an attenuator 158 optically coupled to the photonic bit generator 120, for example, located between and optically coupled to the photonic quantum key bit generator 120 and the photonic detector unit 140. The attenuator 158 is structurally configured to attenuate a subset of the plurality of photons (i.e., photonic pulses) output by the photonic qubit generator 120.

[0069] like Figure 1 As shown, the quantum key generation system 101 can further include an optional spectral filter 180 optically coupled to the laser 122A. The optional spectral filter 180 reduces the spectral width of the photon pulse generated by the laser 122A before coupling to the low-loss dispersion-limited optical fiber 151, making the quantum communication system 100 less sensitive to dispersion (pulse broadening and / or overlap between pulses) when propagating in the low-loss dispersion-limited optical fiber 151. The spectral filter 180 can be, for example, a bandpass filter with a narrow bandpass (spectral) width of 0.2nm to 0.5nm. For example, the spectral filter 180 can be a 0.2nm, 0.25nm, 0.275nm, 0.3nm, 0.4nm or 0.5nm bandpass filter. The photon quantum key generator 120 can also include an interferometer, for example, a Michelsen interferometer 132. The Michelson interferometer 132 includes two Faraday mirrors (FM) 132A, 132B, and splits each input photon pulse provided by the laser 122A into two adjacent photon pulses (each adjacent photon pulse contains a plurality of photons). In some embodiments, the Michelson interferometer can split each photon pulse provided by the laser 122A into a pair of photon pulses separated by a time domain (time) difference of 25ps to 1000ps, such as 50ps to 500ps, 30ps to 100ps, 50ps to 500ps, 100ps to 500ps, 50ps to 250ps, 50ps to 150ps (e.g., 30ps, 40ps, 50ps, 60ps, 70ps, 75ps, 100ps or 150ps, or 200ps, 250ps, or 300ps, or 400ps, or 500ps, or between the two). In some embodiments, the photon pulse pairs provided by the Michelson interferometer are separated by a temporal (time) difference of 50 ps to 100 ps.

[0070] According to one embodiment, the low-loss dispersion-limited optical fiber has a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of about 1550 nm at an absolute dispersion rate of about 5 ps / (nm)km (i.e., 5 ps / nm·km) or less (e.g., 1 ps / (nm)km-5 ps / (nm)km), and the quantum communication system 100 does not include the optional spectral filter 180. For example, according to one embodiment, the low-loss dispersion-limited optical fiber is structurally configured to limit the dispersion of a photon pulse having a wavelength of about 1550 nm at an absolute dispersion rate of about 5 ps / (nm)km (also referred to as 5 ps / nm·km) or less, and the quantum communication system does not include a spectral filter optically coupled to a laser or a photon generator. For another example, according to some embodiments, the quantum communication system does not include a spectral filter located within a photonic qubit generator.

[0071] exist Figure 1 In the embodiment of the quantum communication system 100 shown, in order to provide secure communication and to invalidate potential coherent attacks, all photon pulses have random relative phases. This can be achieved, for example, by using a phase randomized laser. For example, in this embodiment, laser 122A is a phase randomized laser with 2.5GHz pulses. For example, phase randomization can be achieved by switching the laser current between pulses. However, the laser pulse rate can be, for example, between 1.5GHz and 25GHz (for example, between 1.5GHz and 10GHz, or between 2GHz and 10GHz, or between 2GHz and 5GHz). Other techniques for randomizing the relative pulse rate can also be used. Other methods for providing pulse phase randomization can also be used.

[0072] One method of encoding multiple quantum states of a photon pulse is to use an intensity modulator IM 124. In some embodiments, the qubit state (i.e., the qubit state or quantum state of the photon pulse) and the pulse amplitude are randomly selected by FPGA 202 (field programmable gate array or similar device), for example by using a pseudo-random number generator. Alternatively, ASIC, PSoC (programmable system on chip) or other similar devices can be used instead of FPGA 202. Therefore, in such embodiments, IM 124 is controlled by FPGA, ASIC, PSoC or other similar devices. Therefore, the FPGA or similar device controls the amplitude variation generated by IM 124. The FPGA ASIC, PSoC or other similar device can be located, for example, in the service channel 200.

[0073] For example, FPGA 202 provides a very high speed (very fast rate) output to a digital-to-analog converter DAC 203. Multiple outputs (e.g., three or four) from FPGA 202 are linked to DAC 203, which generates pulses (e.g., radio frequency) that drive intensity modulator IM 124. An optional amplifier 201 (e.g., an RF signal amplifier) ​​is located between intensity modulator 124 and DAC 203 and amplifies the pulses provided by the DAC to IM 124. For example, a DAC 202 may be used. Figure 1 The illustrated intensity modulator(s) IM 124 encode the three states. Other implementations of phase encoding, such as having decoy states(s), may require a phase modulator (not shown) in addition to the intensity modulator. The intensity modulator IM 124, such as a lithium niobate (LiNbO3) intensity modulator, modulates the intensity of the pulses leaving the interferometer and then provides the modulated pulses to an optical attenuator 158 (e.g., a variable attenuator VA).

[0074] The intensity modulator IM 124 receives the separated photon pulses 102, 104 provided by the Michelson interferometer, attenuates their intensity according to the signal received from the DAC 203, and then couples the attenuated separated photon pulses 102', 104' to the low-loss dispersion-limited optical fiber 151 via the optical attenuator 158. When the intensity modulator 124 controls the intensity of the pulses so as to provide the required pulse amplitude to the variable attenuator 158, the power of each pulse leaving the IM 124 corresponds to the pulse power provided by multiple photons (i.e., hundreds or even thousands of photons). The optical attenuator 158 then limits the power of the photon pulses to a desired mean photon number (e.g., to a single photon level).

[0075] More specifically, the photon pulse provided to the laser 122a is transmitted through an optional spectral filter and then through a Michelson interferometer 132. The Michelson interferometer 132 can be an unbalanced fiber Michelson interferometer (e.g., an interferometer having two arms A, B, which have unequal path lengths) that splits each photon pulse into two adjacent photon pulses P1, P2 that are coherent with each other and introduces a delay (time interval) between the two adjacent photon pulses. (The Michelson interferometer generates a pair of pulses 102, 104 separated in time by the optical path difference between the two arms divided by the speed of light from a single input pulse). The time interval between pulses 102, 104 depends on the length difference between the two arms A, B of the interferometer 132. In Figure 1In the illustrated embodiment, one of the interferometer arms is equipped with a piezoelectric fiber stretcher 135, which is structurally used to adjust the interferometer phase. This adjustment helps to improve the stability of the quantum key distribution system by compensating for environmental fluctuations (such as temperature changes, etc.). For example, the piezoelectric fiber stretcher 135 can be coupled to a controller (not shown) that senses temperature fluctuations, etc. within the quantum key generation system 101 and sends a signal to the piezoelectric fiber stretcher to adjust the fiber length of arm B of the fiber Michelson interferometer 132.

[0076] An attenuator 158 (e.g., a variable attenuator VA 158') coupled to the intensity modulator 124 attenuates the signal (i.e., the photon pulses 102, 104) so ​​as to set the mean average number of photons of the output signal (photon pulses 102', 104'). The attenuator 158 is located between the photonic quantum key bit generator 120 and the photon detector unit 140 and optically coupled to the photonic quantum key bit generator 120 and the photon detector unit 140. The attenuator 158 is structurally configured to attenuate a subset of the plurality of photons (i.e., photon pulses) output by the photonic qubit generator 120. The quantum key generation system 101 may also include other components, each located between the attenuator 158 and the photon detector unit 140 and optically coupled to the attenuator 158 and the photon detector unit 140. Each of these components may be optically coupled to adjacently positioned optical components and thereby optically coupled to the photonic key bit generator 120 and the photonic detector unit 140 using the low-loss dispersion limited optical fiber 151 described above.

[0077] As above relative to Figure 2 As described above, the low-loss dispersion-limited optical fiber 151 can be configured to optimize the temporal pulse width of the photon pulses propagating along the low-loss dispersion-limited optical fiber 151. Referring again to Figure 1 , the temporal pulse width of the photons propagating along the low-loss dispersion-limited optical fiber 151 is such that the two photons received by the photon detector unit 140 include the same or similar temporal pulse width. In some embodiments, the low-loss dispersion-limited optical fiber 151 has a core length L, where L<2000 km. In some embodiments, the low-loss dispersion-limited optical fiber 151 has a core length L, where L>100 km, or L>150 km, or L>200 km (e.g., 100 km to 1000 km, or 200 km to 1000 km, or 300 km to 1000 km, or 300 km to 600 km, or 400 km to 700 km). In particular, the low-loss dispersion-limited optical fiber 151 (e.g., Figure 3A and Figure 3B The low-loss dispersion-limited optical fiber 151' and Figure 4A and Figure 4BThe low-loss dispersion-limited optical fiber 151″) is configured so that the quantum key bit information of the plurality of photons output by the one or more photon qubit generators 120 can be received at the one or more photon detector units 140 at a bit rate (i.e., raw data bit rate) of at least 10 Gbit / sec (Gbit / sec), for example, 20 Gbit / sec, 30 Gbit / sec, 40 Gbit / sec, 50 Gbit / sec, 75 Gbit / sec, 100 Gbit / sec, 150 Gbit / sec, 200 Gbit / sec, 250 Gbit / sec or 500 Gbit / sec, etc. The raw data bit rate corresponds to a key rate of a quantum key generation system of at least 10 Kbit / sec.

[0078] Still reference Figure 1 , the quantum key generation system 101 further includes a beam splitter (BS) 174 optically coupled to the photodetector unit 140 and the low-loss dispersion-limited optical fiber 151, such that the low-loss dispersion-limited optical fiber 151 is located between the photon qubit generator 120 and the photon detector unit 140 along the optical path 172. In operation, a plurality of photon pulses including quantum key bits pass through the low-loss dispersion-limited optical fiber 151, such that the photon pulses are incident on the beam splitter 174 before being routed to the photon detector unit 140. That is, the photons propagating through the low-loss dispersion-limited optical fiber 151 pass through the beam splitter 174 before being detected by the photon detector 140. Figure 1 In the illustrated embodiment, the photodetector unit 140 includes a pair of photon detectors, namely a first photon detector 140A and a second photon detector 140B, which are optically coupled to an interferometer 142 (e.g., an unbalanced Michelson interferometer 142') with the same delay as the interferometer 132. An automatic feedback loop stabilizes the relative phase between the two interferometers 132, 142.

[0079] Beam splitter 174 splits optical path 172 into a plurality of optical paths, such as optical paths 172A and 172B. Figure 1 In the illustrated embodiment, SPD (single photon detector) 140A detects photons propagating along optical path 272A, while photons propagating through another optical path 172B are provided to interferometer 142. Still referring to Figure 1 , the first and second photon detectors 140A, 140B are structurally configured to receive the measurable particles (i.e., photon pulses) generated by the photon qubit generator 120. More specifically, each photon detector unit 140A, 140B measures a particle property of the measurable particles (the phase of the photon pulse or the time interval between pulses).

[0080] In the present embodiment, the unbalanced Michelson interferometer 142' splits each photon pulse into two pulses, each of which is provided to a separate Faraday reflector (FM) 142A, 142B. The reflected pulses are then combined by the interferometer 142 and provided to a single photon detector 140B for detection. The photon detectors 140A, 140B may include one or more low-noise photodiodes and / or one or more single-photon detectors, for example, one or more superconducting nanowire single-photon detectors. However, any combination of detectors arranged in the quantum key generation system 101 is contemplated.

[0081] In this embodiment, the particle property is phase. However, in other embodiments, the particle property may include any quantum information. For example, in other embodiments, the particle property may include any measurable quantum property particle, linear polarization, circular polarization, spin, translational momentum, orbital angular momentum, etc. The particle properties measured by each photon detector 140A, 140B can be converted into a quantum key bit. Each quantum key bit may include a binary bit, for example, a "1" bit or a "0" bit. In some embodiments, the particle properties measured by each photon detector 140A, 140b may include particle properties so that each quantum key bit generated at each photon detector includes a matching binary bit. For example, when the photon detector unit 140A measures a property including a "0" bit, the photon detector 140B may also measure a property including a "0" bit. In other embodiments, the particle properties measured by each photon detector unit 140A, 140b include orthogonal particle properties so that each quantum key bit generated at each photon detector includes an opposite binary bit. For example, when photon detector 140A measures an orthogonal characteristic including a "0" bit, photon detector 140b also measures an orthogonal characteristic including a "1" bit.

[0082] Furthermore, in operation, a plurality of iteratively converted quantum key bits may form a quantum key at each photon detector 140A, 140b. For example, each photon detector 140A, 140b may iteratively convert the received quantum key bits into a set of binary bits, such that each photon detector 140A, 140b may receive a quantum key related to the quantum key received by the other photon detectors 140A, 140b. This allows the quantum key to be used as a cryptographic key, enabling communication between a sender and a receiver over a classical communication channel (e.g., Figure 1Communications over the signal channels 195 of the communication network 190 may utilize quantum key encryption. Additionally, some embodiments may include an electronic storage device that is communicatively coupled to the photon detector units 140A, 140B and is structurally configured to electronically store the quantum key bits. In other embodiments, the photon detector unit 140 may be structurally configured to electronically store the quantum key.

[0083] The primary application of the technology disclosed herein is the communication of quantum key bit information due, at least in part, to the nature and mechanisms of quantum communication. However, it is well understood from the above disclosure that other and / or additional information may well be communicated via the technology disclosed herein, and the claims and disclosures herein regarding the communication of quantum key bit information may be generalized to the communication of information and quantum information.

[0084] For purposes of describing and defining the present technology, it is noted that reference herein to a variable as a "function" of a parameter or another variable is not intended to mean that the variable is a function of only the listed parameter or variable. Rather, reference herein to a variable as a "function" of the listed parameters is intended to be open ended, such that the variable may be a function of a single parameter or multiple parameters.

[0085] It should also be noted that reference herein to "at least one" of a component, element, etc. should not be used to infer that the alternative use of the article "a" or "an" should be limited to a single component, element, etc.

[0086] Note that statements herein that components of the present disclosure are "configured" in a particular way to embody a particular characteristic, or to function in a particular manner, are structural statements, as opposed to statements of intended use. More specifically, references herein to the manner in which a component is "configured" refer to the physical conditions of existence of the component, and as such are taken as explicit statements of the structural characteristics of the component.

[0087] For the purposes of describing and defining the present technology, it is noted that the terms "substantially" and "approximately" are employed herein to represent the inherent degree of uncertainty that can be attributed to any quantitative comparison, value, measurement, or other representation. The terms "substantially" and "approximately" are also used herein to represent the degree to which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0088] Where the subject matter of the present disclosure has been described in detail and with reference to specific embodiments thereof, it should also be noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even where specific elements are shown in each of the figures of the drawings of this specification. Furthermore, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure including, but not limited to, the embodiments defined by the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0089] Note that one or more of the appended claims use the term "characterized by / wherein" as a transitional phrase. For the purpose of defining the present invention, it should be noted that this term is introduced into the appended claims as an open transitional phrase that is used to introduce a recitation of a series of characteristics of the described structure and should be interpreted in a manner similar to the more commonly used open-ended preamble term "comprising".

Claims

1. A quantum communication system, comprising: A quantum key generation system comprising a photon qubit generator, a low-loss dispersion-limited optical fiber, and a photon detector unit; as well as A communication network, comprising a signal generator, a signal channel and a signal receiver; wherein: The low-loss dispersion-limited optical fiber extends between and optically couples the photon qubit generator and the photon detector unit, the low-loss dispersion-limited optical fiber having a length L between 100 km and 2000 km; The photon qubit generator is structurally configured to output a plurality of photons, each of the plurality of photons comprising quantum key bit information; The photon detector unit is structurally configured to receive the quantum key bit information of the plurality of photons; The signal channel extends between and communicatively couples the signal generator and the signal receiver; The signal generator is structurally configured to output a signal including one or more signal bits; The signal receiver is communicatively coupled to the photon detector unit and is structurally configured to compare the one or more signal bits with the quantum key bit information upon receiving the signal; as well as The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of 1550 nm at an absolute dispersion rate of 9 ps / (nm)km or less, and induce attenuation of photons having the wavelength of 1550 nm at an attenuation rate of 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least 10 Gbit / sec.

2. The quantum communication system according to claim 1, characterized in that The core comprises a silica based glass.

3. The quantum communication system according to claim 2, characterized in that: The silica glass of the core is doped with K, Cl, F or a combination thereof.

4. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes a step-index refractive profile.

5. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes a parabolic refractive index profile.

6. A quantum communication system as claimed in claim 1 or 2, characterized in that the core comprises a radius from 2.2 μm to 3 μm.

7. The quantum communication system according to claim 1 or 2, characterized in that: The core of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ1 ranging from -0.1 to 0.2, wherein: Δ1 includes (n1-n s ) / n s ; n1 comprises the refractive index of the core; and n s Includes the refractive index of pure silica.

8. The quantum communication system according to claim 1 or 2, characterized in that: The cladding of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ2 ranging from -0.4 to -0.7, wherein: Δ2 includes (n2-n s ) / n s ; n2 comprises the refractive index of the cladding; and n s Includes the refractive index of pure silica.

9. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes a cutoff wavelength of 1200 nm or less.

10. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes a mode field diameter from 7.5 μm to 9.0 μm.

11. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes 40 μm 2 To 55μm 2 effective area.

12. The quantum communication system according to claim 1, characterized in that: The low-loss dispersion-limited optical fiber includes 0.051ps / (nm 2 )km to 0.054ps / (nm 2 )km dispersion slope.

13. The quantum communication system according to claim 1 or 2, characterized in that: The cladding includes a first cladding portion, a second cladding portion, and a cladding ring disposed between the first cladding portion and the second cladding portion.

14. The quantum communication system according to claim 13, characterized in that: The core comprises a radius from 2.2 μm to 2.8 μm.

15. The quantum communication system according to claim 13, characterized in that: The core of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ1 ranging from -0.1 to 0.2, wherein: Δ1 includes (n1-n s ) / n s ; n1 comprises the refractive index of the core; and n s Includes the refractive index of pure silica.

16. The quantum communication system according to claim 13, characterized in that: The first cladding portion of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ2 ranging from -0.2 to -0.7, wherein: Δ2 includes (n2-n s ) / n s ; n2 comprises the refractive index of the first cladding portion; and n s Includes the refractive index of pure silica.

17. The quantum communication system according to claim 13, characterized in that: The cladding ring of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ3 ranging from -0.1 to -0.5, wherein: Δ3 includes (n3-n s ) / n s ; n3 comprises the refractive index of the cladding ring; and n s Includes the refractive index of pure silica.

18. The quantum communication system according to claim 13, characterized in that: The second cladding portion of the low-loss dispersion-limited optical fiber comprises a relative refractive index Δ4 ranging from -0.2 to -0.6, wherein: Δ4 includes (n4-n s ) / n s ; n4 comprises the refractive index of the second cladding portion; and n s Includes the refractive index of pure silica.

19. The quantum communication system according to claim 13, characterized in that: The low-loss dispersion-limited optical fiber includes a cutoff wavelength of 1500 nm or less.

20. The quantum communication system according to claim 13, characterized in that: The low-loss dispersion-limited optical fiber includes a mode field diameter from 9.5 μm to 10.5 μm.

21. The quantum communication system according to claim 13, characterized in that: The low-loss dispersion-limited optical fiber includes 70 μm 2 To 80μm 2 effective area.

22. The quantum communication system according to claim 13, characterized in that: The low-loss dispersion-limited optical fiber includes 0.055ps / (nm 2 )km to 0.085ps / (nm 2 )km dispersion slope.

23. The quantum communication system according to claim 1, characterized in that: The quantum key generation system further includes an attenuator optically coupled to the photonic qubit generator and structurally configured to attenuate a subset of the plurality of photons output by the photonic qubit generator.

24. The quantum communication system according to claim 1 or 2, characterized in that: The photon detector unit 140 includes a single photon detector.

25. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber is structurally configured to enable the quantum key bit information of the plurality of photons output by the photonic qubit generator to be received at the photonic detector unit at a bit rate of at least 50 Gbit / sec.

26. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber is structurally configured so that the quantum key bit information of the plurality of photons output by the photonic qubit generator can be received at the photonic detector unit at a bit rate of 100 Gbit / sec.

27. The quantum communication system according to claim 1 or 2, characterized in that: The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of 1550 nm at an absolute dispersion rate of 5 ps / (nm)km or less.

28. The quantum communication system of claim 26, further comprising an intensity modulator and a beam splitter, such that there is no light transmission fiber located between the intensity modulator and the beam splitter.

29. The quantum communication system according to claim 26, characterized in that: There is no light transmission fiber coupled to the low-loss dispersion-limited fiber between the photon qubit generator and the photon detector unit.

30. The quantum communication system according to claim 21, characterized in that: There is no dispersion compensating fiber coupled to the low-loss dispersion limited fiber between the photonic qubit generator and the photonic detector unit.

31. The quantum communication system of claim 1 or 2, further comprising a laser and a spectral filter optically coupled to the laser, the spectral filter being a bandpass filter having a bandpass width of 0.2 nm to 0.5 nm.

32. A quantum key generation system, comprising: a low-loss dispersion-limited optical fiber extending between and optically coupling a photon qubit generator and a photon detector unit, wherein: The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, has a length of at least 200 km, and is structurally configured to limit the dispersion of photons having a wavelength of 1550 nm at an absolute dispersion rate of 9 ps / (nm)km or less, and induce attenuation of photon pulses having the wavelength of 1550 nm at an attenuation rate of 0.175 dB / km or less, so that quantum key bit information of a plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least 10 Gbit / sec.

33. A quantum communication system, comprising: A quantum key generation system comprising a photon qubit generator, a low-loss dispersion-limited optical fiber, and a photon detector unit; as well as A communication network, comprising a signal generator, a signal channel and a signal receiver; wherein: The low-loss dispersion-limited optical fiber extends between and optically couples the photon qubit generator and the photon detector unit, the low-loss dispersion-limited optical fiber having a length L between 200 km and 1000 km; The photonic qubit generator is structurally configured to output a plurality of photons, each photon of the plurality of photons comprising quantum key bit information; The photon detector unit is structurally configured to receive the quantum key bit information of the plurality of photons; The signal path extends between and communicatively couples the signal generator and the signal receiver; The signal generator is structurally configured to output a signal including one or more signal bits; The signal receiver is communicatively coupled to the photon detector unit and is structurally configured to compare the one or more signal bits with the quantum key bit information upon receiving the signal; as well as The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of 1550 nm at an absolute dispersion rate of 9 ps / (nm)km or less, and induce attenuation of photons having the wavelength of 1550 nm at an attenuation rate of 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least 10 Gbit / sec.

34. A quantum system comprising: A quantum key system comprising a photon qubit generator, a low-loss dispersion-limited optical fiber, and a photon detector unit; as well as A signal receiver; wherein: The low-loss dispersion-limited optical fiber extends between and optically couples the photon qubit generator and the photon detector unit, the low-loss dispersion-limited optical fiber having a length L between 100 km and 1000 km; The photonic qubit generator is structurally configured to output a plurality of photons, each photon of the plurality of photons comprising quantum key bit information; The photon detector unit is structurally configured to receive the quantum key bit information of the plurality of photons; The signal receiver is communicatively coupled to the photon detector unit and is structurally configured to compare the one or more signal bits with the quantum key bit information upon receiving the signal; as well as The low-loss dispersion-limited optical fiber includes a core and a cladding surrounding the core, and is structurally configured to limit the dispersion of a photon pulse having a wavelength of 1550 nm at an absolute dispersion rate of 9 ps / (nm)km or less, and induce attenuation of photons having the wavelength of 1550 nm at an attenuation rate of 0.175 dB / km or less, so that the quantum key bit information of the plurality of photons output by the photon qubit generator can be received at the photon detector unit at a bit rate of at least 10 Gbit / sec.

35. A quantum system as claimed in claim 34, characterized in that The length L is between 100 km and 2000 km.

36. The quantum system of claim 34, wherein: The length L is between 200 km and 1000 km.

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