Quantum key distribution optical chip for time-phase encoding and unequal-arm interferometer optical chip

Abstract

The present invention proposes a quantum key distribution optical chip and an unequal-arm interferometer optical chip that are particularly suitable for a time-phase encoding scheme, to accurately and efficiently implement the time-phase encoding scheme of optical signals and its variants. Among them, an intensity-to-phase scheme implemented by combining an equal-arm interferometer and an unequal-arm interferometer in a time-phase modulation module is adopted, and it is proposed to set a delay optical path interface on the optical chip to access the external delay optical path to the optical arm of the unequal-arm interferometer, effectively avoiding the difficulty of etching a long arm length difference in chip manufacturing, enabling the simple and accurate implementation of a long arm length difference in the unequal-arm interferometer and allowing the adjustment of the arm length difference, greatly improving the working stability, performance accuracy and configuration flexibility of the optical chip.

Description

Technical Field

[0001] The present invention relates to the field of quantum secure communication, and particularly to a quantum key distribution optical chip for time-phase encoding, and an unequal-arm interferometer optical chip applicable to the quantum key distribution optical chip. Background Art

[0002] Quantum key distribution based on the quantum uncertainty principle is a practical quantum communication technology that has been theoretically proven to be unconditionally secure, and is the ultimate solution to the increasingly serious information security problems. With the in-depth development of quantum communication towards engineering, large-scale, and high-performance, the requirements for products put into practical applications are increasing day by day, including the stability, reliability, manufacturability, testability, acquisition cost, operation and maintenance cost, etc. of the equipment itself. Existing actual devices have various performance defects and imperfect factors, which will increasingly become factors hindering the rapid development process of the industrialization of quantum communication. The development and evolution directions of contemporary mainstream communication devices are nothing more than three aspects: 1) smaller size and lower cost; 2) lower power consumption and green communication; 3) better stability, reliability, and wide environmental adaptability. To solve the above problems, the generally applicable solution is to continuously improve the integration of products. By integrating electronics, optoelectronics, and optical units, the complexity of internal interconnections is reduced, the size is reduced, the power consumption is reduced, and the mechanical and climate environmental adaptability is improved through packaging technology. Therefore, the demand for the comprehensive integration of optical, optoelectronic, electronic functions, and data processing in quantum communication products has become increasingly urgent, and has attracted the attention and emphasis of domestic and foreign research institutions and industrial mainstream companies.

[0003] However, existing quantum key distribution schemes are usually designed based on non-optical chip implementation methods, and there may be some problems when directly implementing them in the form of optical chips. For example, in Figure 1 a traditional quantum key distribution system for time-phase encoding shown, a scheme combining an equal-arm interferometer and an unequal-arm interferometer is adopted. However, when directly applying this scheme to implement an optical chip, due to the great technical difficulty in etching a long arm length difference on the chip, it is difficult to perform the etching process of a long arm length difference on a small chip, difficult to layout, with poor etching consistency, large attenuation, and once etched, the set value of the arm length difference cannot be adjusted significantly, etc. Therefore, it is difficult to obtain a satisfactory optical chip for the quantum key distribution system for time-phase encoding. Summary of the Invention

[0004] To address this issue, the present invention proposes an optical chip for implementing an unequal-arm interferometer, and further designs a quantum key distribution optical chip particularly suitable for a time-phase encoding scheme to accurately and efficiently implement the time-phase encoding scheme of optical signals and its variants. At the same time, debugging and experimental functions are also provided, which is beneficial to the working stability and function expansion of the optical chip. More particularly, by adopting an intensity-to-phase scheme achieved by combining an equal-arm interferometer and an unequal-arm interferometer in the time-phase modulation module, and proposing to set a delay optical path interface on the optical chip to connect the external delay optical path to the arm of the unequal-arm interferometer, the difficulty of etching a large difference in long arm lengths in chip manufacturing is effectively avoided, enabling the simple and accurate implementation of the long arm length difference in the unequal-arm interferometer and allowing the adjustment of the arm length difference, greatly improving the working stability, performance accuracy, and configuration flexibility of the optical chip.

[0005] Specifically, the quantum key distribution optical chip for time-phase encoding of the present invention may include a time-phase modulation module for performing time-phase encoding on optical signals. The time-phase modulation module includes a cascaded first equal-arm interferometer and an unequal-arm interferometer, where:

[0006] The first equal-arm interferometer is configured to output an optical signal only at the first or second output end, or output optical signals at both the first and second output ends simultaneously and with a specific phase difference between the optical signals by modulating the phase difference between the two arms;

[0007] The unequal-arm interferometer is configured to make the optical signals output from different output ends of the first equal-arm interferometer appear at different time positions within a time period; and,

[0008] The quantum key distribution optical chip is provided with a delay optical path interface to allow an external delay optical path to be connected and access at least one of the two arms of the unequal-arm interferometer as a part of the arm.

[0009] Furthermore, the first equal-arm interferometer includes a first multimode interference coupler, a second multimode interference coupler, first and second arms formed between the first and second multimode interference couplers, and a first phase modulator disposed on the first and / or second arm;

[0010] The unequal-arm interferometer includes the second multimode interference coupler, a third multimode interference coupler, and first and second arms formed between the second and third multimode interference couplers; and,

[0011] At least one of the first and second arms of the unequal-arm interferometer includes an arm length adjustment component, which is configured to change the arm length of the arm by connecting the delay optical path to the arm through the delay optical path interface.

[0012] Further, the arm length adjustment component includes a fourth multimode interference coupler, one of the delay optical path interfaces, and the delay optical path; the fourth multimode interference coupler is configured to couple the optical signal transmitted along the first direction on the arm to the delay optical path interface, and couple the optical signal input through the delay optical path interface to the arm and transmit it along the first direction.

[0013] Wherein, the delay optical path includes an optical fiber and a reflection element connected to one end of the optical fiber; and / or, the fourth multimode interference coupler is a 2*2 multimode interference coupler to allow connecting a monitoring photodiode to monitor the optical intensity of the optical signal output by the first equal-arm interferometer.

[0014] Further, the arm length adjustment component includes two of the delay optical path interfaces and the delay optical path.

[0015] Further still, the delay optical path includes an optical fiber for connecting the two delay optical path interfaces.

[0016] Further, the first phase modulator is a carrier dispersion type phase modulator; and / or, adjustable attenuators are provided on the first and / or second arms of the first equal-arm interferometer.

[0017] Further, a first phase shifter is provided on the first and / or second arm of the first equal-arm interferometer for finding the optimal operating point of the first equal-arm interferometer; and / or, a fourth phase modulator is provided on the first and / or second arm of the unequal-arm interferometer.

[0018] Preferably, the first phase shifter is a thermally tunable phase shifter; and / or, the fourth phase modulator is a carrier dispersion type phase modulator.

[0019] Further, the quantum key distribution optical chip of the present invention may further include:

[0020] An intensity compensation module configured to adjust the optical intensity of the optical signal so that a preset optical intensity relationship is satisfied between optical signals of different quantum states; and / or,

[0021] A decoy state intensity modulation module configured to perform decoy state encoding on the optical signal; and / or,

[0022] A synchronous optical path configured to receive and output synchronous optical signals; and / or,

[0023] An attenuation monitoring module configured to allow obtaining the optical intensity information of the output optical signal of the quantum key distribution optical chip and / or the optical intensity information of the attack optical signal.

[0024] Further, the intensity compensation module includes a second balanced interferometer, which has a fifth multimode interference coupler, a sixth multimode interference coupler, first and second arms formed between the fifth and sixth multimode interference couplers, and a second phase modulator disposed on the first and / or second arm.

[0025] Preferably, a second phase shifter is provided on the first and / or second arm of the second balanced interferometer for finding the optimal operating point of the second balanced interferometer.

[0026] Preferably, the second phase modulator is a carrier dispersion type phase modulator; and / or, the second phase shifter is a thermal tuning type phase shifter.

[0027] Further, the decoy state intensity modulation module includes a third balanced interferometer, which has a seventh multimode interference coupler, an eighth multimode interference coupler, first and second arms formed between the seventh and eighth multimode interference couplers, and a third phase modulator disposed on the first and / or second arm.

[0028] Preferably, a third phase shifter is provided on the first and / or second arm of the third balanced interferometer for finding the optimal operating point of the third balanced interferometer.

[0029] Preferably, the third phase modulator is a carrier dispersion type phase modulator; and / or, the third phase shifter is a thermal tuning type phase shifter.

[0030] Further, the attenuation monitoring module includes a ninth multimode interference coupler, which is configured to split the optical signal output by the time phase modulation module to be respectively used as the output optical signal of the quantum key distribution optical chip and for optical intensity detection to obtain the optical intensity information of the output optical signal.

[0031] Preferably, the ninth multimode interference coupler is a 2*2 multimode interference coupler to allow connecting a monitoring photodiode to monitor the attack light injected into the quantum key distribution optical chip; and / or, the attenuation monitoring module further has an adjustable attenuator disposed before the ninth multimode interference coupler.

[0032] Further, the synchronization optical path includes an adjustable attenuator and a twelfth multimode interference coupler located after the adjustable attenuator;

[0033] The twelfth multimode interference coupler is configured to split the synchronization optical signal to obtain the optical intensity information of the output synchronization optical signal.

[0034] Furthermore, the quantum key distribution optical chip may further include a tenth multimode interference coupler and an eleventh multimode interference coupler, and is also provided with a first optical signal input interface, a second optical signal input interface, an optical signal output interface, an output optical intensity monitoring interface, a synchronous optical input interface, and a synchronous optical output interface, where:

[0035] The first and second optical signal input interfaces are configured to allow the input of optical signals;

[0036] The tenth multimode interference coupler is configured to split the optical signal input through the first optical signal input interface and transmit it respectively towards the intensity compensation module and the time-phase modulation module;

[0037] The eleventh multimode interference coupler is configured to couple the optical signal input through the second optical signal input interface and the optical signal output by the intensity compensation module to the decoy state intensity modulation module respectively;

[0038] The optical signal output interface is configured to output the output optical signal of the quantum key distribution optical chip;

[0039] The output optical intensity monitoring interface is configured to allow the acquisition of the optical intensity information of the output optical signal of the quantum key distribution optical chip;

[0040] The synchronous optical input interface and the synchronous optical output interface are respectively used for the input and output of the synchronous optical signal.

[0041] Preferably, an adjustable attenuator is further provided on the optical path between the tenth multimode interference coupler and the time-phase modulation module.

[0042] Furthermore, the first optical signal input interface is an FC / UPC or FC / APC interface and is used to connect to polarization-maintaining optical fiber; and / or, the second optical signal input interface is an FC / UPC or FC / APC interface and is used to connect to polarization-maintaining optical fiber; and / or, the delay optical path interface is used to connect to polarization-maintaining optical fiber; and / or, the optical signal output interface is an FC / UPC or FC / APC interface and is used to connect to polarization-maintaining optical fiber; and / or, the synchronous optical input interface and the synchronous optical output interface are FC / UPC interfaces and are used to connect to polarization-maintaining or single-mode optical fiber; and / or, the output optical intensity monitoring interface is an FC / UPC interface and is used to connect to polarization-maintaining or single-mode optical fiber.

[0043] Another aspect of the present invention relates to an optical chip for implementing an unequal-arm interferometer, which includes a second multimode interference coupler, a third multimode interference coupler, and first and second arms formed between the second and third multimode interference couplers. Among them, a delay optical path interface is provided on the optical chip; and at least one of the first and second arms includes an arm length adjustment component, which is configured to change the arm length of the arm by accessing an external delay optical path through the delay optical path interface into the arm.

[0044] Further, the arm length adjustment component includes a fourth multimode interference coupler, one of the delay optical path interfaces, and the delay optical path; the fourth multimode interference coupler is configured to couple the optical signal transmitted along the first direction on the arm to the delay optical path interface, and couple the optical signal input through the delay optical path interface to the arm and make it transmit along the first direction. Among them, the delay optical path may include an optical fiber and a reflection element connected to one end of the optical fiber.

[0045] Further, the arm length adjustment component includes two of the delay optical path interfaces, and the delay optical path. Among them, the delay optical path may include an optical fiber, which is used to connect the two delay optical path interfaces.

[0046] Further, one or more of an adjustable attenuator, a phase modulator, an intensity modulator, and a phase shifter may also be provided on the first and / or second arm. Description of the Drawings

[0047] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0049] Figure 1 The schematic diagram of a quantum key distribution system for time-phase encoding in the prior art is shown;

[0050] Figure 2 Schematically shows an embodiment of an unequal-arm interferometer optical chip and a quantum key distribution optical chip for time-phase encoding according to the present invention;

[0051] Figure 3 Schematically shows another embodiment of an unequal-arm interferometer optical chip and a quantum key distribution optical chip for time-phase encoding according to the present invention;

[0052] Figure 4 Schematically shows another embodiment of an unequal-arm interferometer optical chip according to the present invention and a quantum key distribution optical chip for time-phase encoding;

[0053] Figure 5 Schematically shows yet another embodiment of an unequal-arm interferometer optical chip according to the present invention and a quantum key distribution optical chip for time-phase encoding. Specific embodiments

[0054] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example to fully convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0055] Figure 2-5 Specific embodiments of a quantum key distribution optical chip for time-phase encoding according to the present invention (which includes an unequal-arm interferometer optical chip according to the present invention) are respectively schematically shown.

[0056] In the optical chip of the present invention, in order to implement the time-phase encoding function, a time-phase modulation module is provided, which may include a cascaded first equal-arm interferometer and an unequal-arm interferometer.

[0057] The first equal-arm interferometer is used to output an optical signal only at the first or second output end by modulating the phase difference between the two arms, or to output optical signals at both the first and second output ends simultaneously and with a specific phase difference between the two optical signals.

[0058] For example, by modulating a phase difference of 0 between the optical signals on the two arms of the first equal-arm interferometer, the first equal-arm interferometer will output an optical signal only at its first output end, and no optical signal will be output at the second output end; by forming a phase difference of π between the optical signals on the two arms, the first equal-arm interferometer will output an optical signal only at its second output end, and no optical signal will be output at the first output end; by forming a phase difference of π / 2 between the optical signals on the two arms, the first equal-arm interferometer will output optical signals at both the first and second output ends simultaneously, and the phase difference between the two optical signals is 0; by forming a phase difference of 3π / 2 between the optical signals on the two arms, the first equal-arm interferometer will output optical signals at both the first and second output ends simultaneously, and the phase difference between the two optical signals is π.

[0059] The unequal-arm interferometer is cascaded with the first equal-arm interferometer and is used to make the time positions at which the optical signals output from different output ends of the first equal-arm interferometer appear different within a time period. Thus, with the combined action of the first equal-arm interferometer and the unequal-arm interferometer, time-phase encoding of the optical signal is achieved.

[0060] Different from the prior art, instead of directly etching the two arms of the unequal-arm interferometer on the optical chip, the present invention provides a delay optical path interface on the optical chip to allow the external delay optical path to be connected to at least one of the two arms of the unequal-arm interferometer as a part of the connected arm, so that the required long arm length difference of the unequal-arm interferometer can be accurately realized. At the same time, it also enables the adjustment of the longer arm length difference of the unequal-arm interferometer to be conveniently and accurately achieved by simply changing the optical path of the external peripheral delay optical path. Therefore, the present invention can avoid a series of problems caused by the technical difficulty of etching a long arm length difference on the optical chip, so that the arm length difference of the unequal-arm interferometer can be easily and accurately configured, while obtaining the adjustment ability of the arm length difference, greatly improving the efficiency and applicability of the optical chip.

[0061] As a specific embodiment, the first equal-arm interferometer may include a first multimode interference coupler (MMI Coupler), a second multimode interference coupler, a first arm and a second arm formed between the first and second multimode interference couplers, and a first phase modulator disposed on the first and / or second arm. For example, see Figure 2-5 .

[0062] The first multimode interference coupler is used to split the optical signal 1:1 so that the optical signal enters the first and second arms respectively.

[0063] The first phase modulator is used to perform high-speed electro-optic phase modulation on the optical signal on the first and / or second arm to form the required phase difference between the optical signals on the two arms. Preferably, the first phase modulator may adopt a carrier dispersion type phase modulator RF3.

[0064] The second multimode interference coupler is used to combine the phase-modulated optical signals on the two arms and cause interference.

[0065] Furthermore, a first phase shifter may be disposed on the first and / or second arm of the first equal-arm interferometer to find the optimal working point of the first equal-arm interferometer. Preferably, the first phase shifter may adopt a thermal tuning type phase shifter PS3.

[0066] Furthermore, adjustable attenuators (such as VOA2, VOA3) may be disposed on the first and / or second arm of the first equal-arm interferometer to provide an optical intensity adjustment function.

[0067] In this specific embodiment, the unequal-arm interferometer may share the second multimode interference coupler with the first equal-arm interferometer. Therefore, it includes a second multimode interference coupler, a third multimode interference coupler, and a first arm and a second arm formed between the second and third multimode interference couplers.

[0068] In particular, at least one of the first and second arms of the unbalanced interferometer may further include an arm length adjustment component for adjusting the arm length by accessing an external delay optical path into the arm.

[0069] Figure 2 FIG. 3 shows an example of the arm length adjustment component.

[0070] As shown in Figure 2 FIG. 3, the arm length adjustment component may include a fourth multimode interference coupler, a single delay optical path interface, and an external delay optical path connected through the delay optical path interface, wherein the delay optical path interface is disposed on the optical chip.

[0071] The fourth multimode interference coupler is used to couple the optical signal transmitted along the first direction on the arm to the delay optical path interface, and to couple the optical signal input through the delay optical path interface to the same arm and the optical signal continues to be transmitted along the first direction. The delay optical path may include an optical fiber (e.g., an 8 cm optical fiber) and a reflection element (e.g., a mirror) connected to one end of the optical fiber. Therefore, the delay optical path can be simply accessed to the arm of the unbalanced interferometer by connecting the other end of the optical fiber in the delay optical path to the delay optical path interface, so as to obtain a desired arm length difference on the unbalanced interferometer.

[0072] As a preferred example, the fourth multimode interference coupler may employ a 2×2 multimode interference coupler to allow connection of a monitoring photodiode (e.g., MPD3) to monitor the optical intensity of the optical signal output by the first balanced interferometer.

[0073] In the present invention, the arm length adjustment component may be provided only on the first or second arm of the unbalanced interferometer, for example, see Figure 2 ; or the arm length adjustment component may also be provided on both the first and second arms of the unbalanced interferometer, for example, see Figure 3 .

[0074] As a preferred example, a tunable optical attenuator (e.g., VOA4) may also be provided on the first and / or second arm of the unbalanced interferometer for providing an optical intensity adjustment function to balance the optical power of the signal light in the two arms. For example, an arm length adjustment component may be provided on the long arm of the unbalanced interferometer, and at the same time, a tunable optical attenuator VOA4 may be provided on the short arm, for example, see Figure 2 ; or, arm length adjustment components may be provided on both the long arm and the short arm of the unbalanced interferometer, and at the same time, a tunable optical attenuator VOA4 may be provided on the short arm, for example, see Figure 3 .

[0075] Figure 4 FIG. 5 shows another example of the arm length adjustment component.

[0076] As shown in Figure 4As shown in FIGS. 4 or 5, the arm length adjustment component may include two optical delay path interfaces disposed on the optical chip and an optical delay path. Among them, the optical delay path may include an optical fiber (such as a 2*8 cm optical fiber). Therefore, the optical delay path can be simply connected to the arms of the unbalanced interferometer by connecting the two ends of the optical fiber in the optical delay path to the two optical delay path interfaces respectively, so as to obtain a desired arm length difference on the unbalanced interferometer.

[0077] As a preferred example, an adjustable optical attenuator (such as VOA4) may also be provided on the first and / or second arm of the unbalanced interferometer to provide an optical intensity adjustment function to balance the signal optical power of the two arms.

[0078] In the present invention, the arm length adjustment component may be provided only on the first or second arm of the unbalanced interferometer. For example, see Figure 4 ; or the arm length adjustment components may also be provided on the first and second arms of the unbalanced interferometer respectively. For example, see Figure 5 .

[0079] For example, the arm length adjustment component may be provided on the long arm of the unbalanced interferometer, and at the same time, the adjustable optical attenuator VOA4 may be provided on the short arm. For example, see Figure 4 ; or, the arm length adjustment components may be provided on both the long arm and the short arm of the unbalanced interferometer, and at the same time, the adjustable optical attenuator VOA4 may be provided on the short arm. For example, see Figure 5 . Continuing to refer to Figure 2-5 , an intensity compensation module may also be provided on the optical chip of the present invention to adjust the optical intensity of the optical signal to compensate for, for example, the different optical intensity attenuations introduced by the time phase modulation module when preparing different quantum states on the optical signal, and ensure that the optical signals of the different quantum states prepared satisfy a preset optical intensity relationship.

[0080] As a specific implementation manner, the intensity compensation module may include a second balanced interferometer, which has a fifth multimode interference coupler, a sixth multimode interference coupler, first and second arms formed between the fifth and sixth multimode interference couplers, and a second phase modulator disposed on the first and / or second arm. For example, see Figure 2-5 .

[0081] The fifth multimode interference coupler is used to split the optical signal 1:1 so that the optical signal enters the first and second arms respectively.

[0082] The second phase modulator is used to perform high-speed electro-optic phase modulation on the optical signal on the first and / or second arm to form a required phase difference between the optical signals on the two arms. Preferably, the second phase modulator may adopt a carrier dispersion type phase modulator RF1.

[0083] The sixth multimode interference coupler is used to merge the phase-modulated optical signals on the two arms and cause interference.

[0084] Furthermore, a second phase shifter may be disposed on the first and / or second arms of the second equal-arm interferometer to find the optimal operating point of the second equal-arm interferometer. Preferably, the second phase shifter may be a thermally tunable phase shifter PS1.

[0085] Continuing to refer to Figure 2-5 , a decoy state intensity modulation module may also be disposed on the optical chip of the present invention to perform decoy state encoding on the optical signal.

[0086] As a specific implementation, the decoy state intensity modulation module may include a third equal-arm interferometer having a seventh multimode interference coupler, an eighth multimode interference coupler, first and second arms formed between the seventh and eighth multimode interference couplers, and a third phase modulator disposed on the first and / or second arms. For example, refer to Figure 2-5 .

[0087] The seventh multimode interference coupler is used to split the optical signal 1:1 so that the optical signal enters the first and second arms respectively.

[0088] The third phase modulator is used to perform high-speed electro-optic phase modulation on the optical signal on the first and / or second arm to form a required phase difference between the optical signals on the two arms. Preferably, the third phase modulator may be a carrier dispersion type phase modulator RF2.

[0089] The eighth multimode interference coupler is used to combine the phase-modulated optical signals on the two arms and cause interference.

[0090] Furthermore, a third phase shifter may be disposed on the first and / or second arms of the third equal-arm interferometer to find the optimal operating point of the third equal-arm interferometer. Preferably, the third phase shifter may be a thermally tunable phase shifter PS2.

[0091] Continuing to refer to Figure 2-5 , an attenuation monitoring module may also be disposed on the optical chip of the present invention to allow obtaining the optical intensity information of the optical signal output from the optical chip to monitor the signal attenuation in the optical chip.

[0092] As a specific implementation, the attenuation monitoring module may include a ninth multimode interference coupler, which is used to split the optical signal output by the time phase modulation module (such as the time phase encoded optical signal) to be respectively used as the optical signal output from the optical chip and for optical intensity detection to obtain the optical intensity information of the output optical signal.

[0093] As a preferred example, the ninth multimode interference coupler may be a 2*2 multimode interference coupler to allow connecting a monitoring photodiode (such as MPD4) to monitor the attack light injected into the optical chip.

[0094] In addition, a synchronization optical path may be provided on the optical chip of the present invention for receiving and outputting synchronization optical signals.

[0095] To better understand the working principles of the various modules in the optical chip of the present invention, the following will describe the specific implementation manners of the optical chip in conjunction with Figure 2-5 to describe the specific implementation manners of the optical chip.

[0096] Figure 2 Fig. shows a specific implementation manner of the optical chip of the present invention. As Figure 2 shown, the optical chip includes functional modules such as an intensity compensation module, a decoy state intensity modulation module, a time phase modulation module, an attenuation monitoring module, and a synchronization optical path. Among them, only the first arm of the unequal-arm interferometer of the time phase modulation module includes an arm length adjustment component. For the sake of brevity, the structures and functions of the above functional modules will not be elaborated here.

[0097] In Figure 2 the specific implementation manner, a tenth multimode interference coupler and an eleventh multimode interference coupler are also formed on the optical chip, and the following optical interfaces are provided: a first optical signal input interface 1 (Sig-in1), a second optical signal input interface 2 (Sig-in2), a delay optical path interface 3, an optical signal output interface 4 (Sig-out), an output optical intensity monitoring interface 5 (Mon), a synchronization optical input interface 6 (Syn-in), and a synchronization optical output interface 7 (Syn-out).

[0098] Both the first and second optical signal input interfaces 1 and 2 are used to input optical signals, so as to obtain time phase encoding in the optical chip, for example.

[0099] The tenth multimode interference coupler is used to split the optical signal input through the first optical signal input interface 1 and transmit it to the intensity compensation module and the time phase modulation module respectively.

[0100] As a preferred example, a tunable optical attenuator (such as VOA1) may be provided on the optical path between the tenth multimode interference coupler and the time phase modulation module, and preferably two-stage tunable optical attenuators are provided.

[0101] The eleventh multimode interference coupler is used to couple the optical signal input through the second optical signal input interface 2 and the optical signal output by the intensity compensation module to the decoy state intensity modulation module respectively.

[0102] The time phase modulation module is configured to use the optical signal output by the decoy state intensity modulation module and the optical signal output by the tenth multimode interference coupler as inputs respectively.

[0103] The attenuation monitoring module is used to split the optical signal output by the time-phase modulation module and output it outward via the optical signal output interface 4 and the output optical intensity monitoring interface 5 respectively.

[0104] As a preferred example, a tunable optical attenuator (such as VOA5) can also be set before the ninth multimode interference coupler in the attenuation monitoring module, and preferably two-stage tunable optical attenuators are set.

[0105] The synchronization optical path is used to transmit the synchronization optical signal input through the synchronization optical input interface 6 to the synchronization optical output interface 7.

[0106] As a preferred example, a tunable optical attenuator (such as VOA6) can also be set on the synchronization optical path. Further, a twelfth multimode interference coupler can be set after the tunable optical attenuator on the synchronization optical path, which is used to split the synchronization optical signal for output through the synchronization optical output interface 7 respectively and for optical intensity detection to obtain the optical intensity information of the output synchronization optical signal.

[0107] In this specific embodiment, the first and second optical signal input interfaces 1 and 2 can be FC / UPC or FC / APC interfaces and are used to connect polarization-maintaining optical fibers; the delay optical path interface 3 is used to connect polarization-maintaining optical fibers; the optical signal output interface 4 can be FC / UPC or FC / APC interface and is used to connect polarization-maintaining optical fibers; the synchronization optical input interface 6 and the synchronization optical output interface 7 can be FC / UPC interfaces and are used to connect polarization-maintaining or single-mode optical fibers; the output optical intensity monitoring interface 5 can be FC / UPC interface and is used to connect polarization-maintaining or single-mode optical fibers.

[0108] Figure 3 Another specific embodiment of the optical chip of the present invention is shown, which is different from Figure 2 in that both the first and second arms of the unequal-arm interferometer of the time-phase modulation module include arm length adjustment components. Correspondingly, another delay optical path interface 8 is also provided on the optical chip, which is used to connect the delay optical path arranged outside the optical chip (body) and access it into the arm through a multimode interference coupler. Among them, the multimode interference coupler can adopt a 2*2 multimode interference coupler to access the monitoring photodiode (such as MPD5).

[0109] Figure 4 Another specific embodiment of the optical chip of the present invention is shown, which is different from Figure 2 in that the structure of the arm length adjustment component is different. Correspondingly, two delay optical path interfaces 3 and 8 for the same arm length adjustment component are provided on the optical chip.

[0110] Figure 5 Another specific embodiment of the optical chip of the present invention is shown, which is different from Figure 4The difference lies in that both the first and second arms of the unequal-arm interferometer of the time phase modulation module include arm length adjustment components. Correspondingly, another two optical delay path interfaces 9 and 10 for the other arm length adjustment components are also provided on the optical chip.

[0111] Based on the above description, it can be known that the present invention proposes a quantum key distribution optical chip applicable to a time phase encoding scheme, which not only allows for accurate and efficient implementation of time phase encoding of optical signals, but also allows for the implementation of various variants based on the time phase encoding scheme, and provides various debugging and experimental functions, which is beneficial to the working stability of the optical chip and expands the functionality of the optical chip. More particularly, the present invention realizes an intensity-to-phase scheme by combining an equal-arm interferometer and an unequal-arm interferometer in the time phase modulation module, and proposes to set optical delay path interfaces on the optical chip to access the external optical delay path to the arms of the unequal-arm interferometer, effectively avoiding the difficulty of etching a large arm length difference in chip manufacturing, enabling simple and accurate implementation of the large arm length difference in the unequal-arm interferometer, and at the same time enabling the optical chip to have the function of adjusting the arm length difference in the unequal-arm interferometer, greatly improving the working stability, performance accuracy and configuration flexibility of the optical chip.

[0112] Furthermore, as Figure 2-5 shown, in the quantum key distribution optical chip of the present invention, a beam splitter and a monitoring photodiode (such as MPD1) can also be provided on the optical path between the intensity compensation module and the decoy state intensity modulation module to obtain the optical intensity information of the optical signal on this optical path; and a beam splitter and a monitoring photodiode (such as MPD2) can be provided on the optical path between the decoy state intensity modulation module and the time phase modulation module to obtain the optical intensity information of the optical signal on this optical path.

[0113] In addition, it should also be noted that although in Figure 2-5 the diagrams related to the first, second and third equal-arm interferometers, the phase modulators RF1-3 and the phase shifters PS1-3 are shown to act on the first and second arms simultaneously, those skilled in the art can understand that Figure 2-5 the diagrams are only schematic, and the phase modulators RF1-3 and the phase shifters PS1-3 can be respectively formed on the first arm and / or the second arm to act on the optical signals on the first and second arms respectively.

[0114] Furthermore, a fourth phase modulator can also be provided on the first and / or second arm of the unequal-arm interferometer of the time phase modulation module, so as to be able to prepare, for example, two other quantum states, thereby being used to implement a 6-state protocol, etc. Preferably, the fourth phase modulator can be a carrier dispersion type phase modulator.

[0115] Furthermore, one or more of an adjustable attenuator, a phase modulator, an intensity modulator, and a phase shifter can be provided on the first and / or second arm of the unequal-arm interferometer, so that it can be used to implement the CVQKD protocol.

[0116] Although the present invention has been described above with reference to specific embodiments in conjunction with the accompanying drawings, it is readily appreciated by those skilled in the art that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention, which will not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications, and equivalent replacements to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A quantum key distribution optical chip for time-phase encoding, which includes a time-phase modulation module for performing time-phase encoding on an optical signal. The time-phase modulation module includes a cascaded first equal-arm interferometer and unequal-arm interferometer, where: The first equal-arm interferometer is configured to output an optical signal only at the first or second output terminal, or output optical signals at both the first and second output terminals simultaneously with a specific phase difference between the optical signals by modulating the phase difference between the two arms; The unequal-arm interferometer is configured to make the optical signals output from different output terminals of the first equal-arm interferometer appear at different time positions within a time period; And, A delay optical path interface is provided on the quantum key distribution optical chip to allow an external delay optical path to be connected and access at least one of the two arms of the unequal-arm interferometer as a part of the arm; The quantum key distribution optical chip further includes: An intensity compensation module, which is configured to adjust the optical intensity of the optical signal so that the optical signals in different quantum states satisfy a preset optical intensity relationship; A decoy state intensity modulation module, which is configured to perform decoy state encoding on the optical signal; A tenth multimode interference coupler, an eleventh multimode interference coupler, a first optical signal input interface, and a second optical signal input interface; The first and second optical signal input interfaces are configured to allow optical signals to be input; The tenth multimode interference coupler is configured to split the optical signal input through the first optical signal input interface and transmit it respectively towards the intensity compensation module and the time-phase modulation module; The eleventh multimode interference coupler is configured to couple the optical signal input through the second optical signal input interface and the optical signal output from the intensity compensation module to the decoy state intensity modulation module respectively; The time-phase modulation module is configured to be able to use the optical signal output from the decoy state intensity modulation module and the optical signal output from the tenth multimode interference coupler as inputs respectively.

2. The quantum key distribution optical chip according to claim 1, where: The first equal-arm interferometer includes a first multimode interference coupler, a second multimode interference coupler, first and second arms formed between the first and second multimode interference couplers, and a first phase modulator provided on the first and / or second arm; The unequal-arm interferometer includes the second multimode interference coupler, a third multimode interference coupler, and first and second arms formed between the second and third multimode interference couplers; and, At least one of the first and second arms of the unequal-arm interferometer includes an arm length adjustment component, which is configured to change the arm length of the arm by connecting the delay optical path to the arm through the delay optical path interface.

3. The quantum key distribution optical chip according to claim 2, wherein The arm length adjustment component includes a fourth multimode interference coupler, one of the delay optical path interfaces, and the delay optical path; The fourth multimode interference coupler is configured to couple the optical signal transmitted along the first direction on the arm to the delay optical path interface, and couple the optical signal input through the delay optical path interface to the arm and make it transmit along the first direction.

4. The quantum key distribution optical chip according to claim 3, wherein: The delay optical path includes an optical fiber and a reflection element connected to one end of the optical fiber; and / or, The fourth multimode interference coupler is a 2×2 multimode interference coupler to allow connecting a monitoring photodiode to monitor the optical intensity of the optical signal output from the first equal-arm interferometer.

5. The quantum key distribution optical chip according to claim 2, wherein, The arm length adjustment component includes two of the delay optical path interfaces and the delay optical path.

6. The quantum key distribution optical chip according to claim 5, wherein, The delay optical path includes an optical fiber for connecting the two delay optical path interfaces.

7. The quantum key distribution optical chip according to claim 2, wherein: The first phase modulator is a carrier dispersion type phase modulator; and / or, An adjustable attenuator is provided on the first and / or second arm of the first equal-arm interferometer.

8. The quantum key distribution optical chip according to claim 2, wherein, A first phase shifter is provided on the first and / or second arm of the first equal-arm interferometer for finding the optimal operating point of the first equal-arm interferometer; and / or, A fourth phase modulator is provided on the first and / or second arm of the unequal-arm interferometer.

9. The quantum key distribution optical chip according to claim 8, wherein, The first phase shifter is a thermally tunable phase shifter; and / or, the fourth phase modulator is a carrier dispersion type phase modulator.

10. The quantum key distribution optical chip according to claim 1, further comprising: A synchronization optical path configured to receive and output a synchronization optical signal; and / or, An attenuation monitoring module configured to allow obtaining the optical intensity information of the output optical signal of the quantum key distribution optical chip and / or the optical intensity information of the attack optical signal.

11. The quantum key distribution optical chip according to claim 1, wherein, The intensity compensation module includes a second equal-arm interferometer having a fifth multimode interference coupler, a sixth multimode interference coupler, first and second arms formed between the fifth and sixth multimode interference couplers, and a second phase modulator provided on the first and / or second arm.

12. The quantum key distribution optical chip according to claim 11, wherein, A second phase shifter is provided on the first and / or second arm of the second equal-arm interferometer for finding the optimal operating point of the second equal-arm interferometer.

13. The quantum key distribution optical chip according to claim 12, wherein, The second phase modulator is a carrier dispersion type phase modulator; and / or, the second phase shifter is a thermally tunable phase shifter.

14. The quantum key distribution optical chip according to claim 1, wherein, The decoy state intensity modulation module includes a third equal-arm interferometer having a seventh multimode interference coupler, an eighth multimode interference coupler, first and second arms formed between the seventh and eighth multimode interference couplers, and a third phase modulator provided on the first and / or second arm.

15. The quantum key distribution optical chip according to claim 14, wherein, A third phase shifter is provided on the first and / or second arm of the third equal-arm interferometer for finding the optimal operating point of the third equal-arm interferometer.

16. The quantum key distribution optical chip according to claim 15, wherein, The third phase modulator is a carrier dispersion type phase modulator; and / or, the third phase shifter is a thermally tunable phase shifter.

17. The quantum key distribution optical chip according to claim 10, wherein, The attenuation monitoring module includes a ninth multimode interference coupler configured to split the optical signal output from the time phase modulation module to be respectively used as the output optical signal of the quantum key distribution optical chip and for optical intensity detection to obtain the optical intensity information of the output optical signal.

18. The quantum key distribution optical chip according to claim 17, wherein: The ninth multimode interference coupler is a 2×2 multimode interference coupler, which allows connecting a monitoring photodiode to monitor the attacking light injected into the quantum key distribution optical chip; and / or, The attenuation monitoring module further includes an adjustable optical attenuator disposed before the ninth multimode interference coupler.

19. The quantum key distribution optical chip according to claim 10, wherein: The synchronization optical path includes an adjustable optical attenuator and a twelfth multimode interference coupler located after the adjustable optical attenuator; The twelfth multimode interference coupler is configured to split the synchronization optical signal, so as to obtain the optical intensity information of the output synchronization optical signal.

20. The quantum key distribution optical chip according to claim 10, further comprising an optical signal output interface, an output optical intensity monitoring interface, a synchronization optical input interface, and a synchronization optical output interface, wherein: The optical signal output interface is configured to output the output optical signal of the quantum key distribution optical chip; The output optical intensity monitoring interface is configured to allow obtaining the optical intensity information of the output optical signal of the quantum key distribution optical chip; The synchronization optical input interface and the synchronization optical output interface are respectively used for input and output of the synchronization optical signal.

21. The quantum key distribution optical chip according to claim 1, wherein, An adjustable optical attenuator is further disposed on the optical path between the tenth multimode interference coupler and the time phase modulation module.

22. The quantum key distribution optical chip according to claim 20, wherein: The first optical signal input interface is an FC / UPC or FC / APC interface and is used for connecting a polarization maintaining optical fiber; and / or, The second optical signal input interface is an FC / UPC or FC / APC interface and is used for connecting a polarization maintaining optical fiber; and / or, The delay optical path interface is used for connecting a polarization maintaining optical fiber; and / or, The optical signal output interface is an FC / UPC or FC / APC interface and is used for connecting a polarization maintaining optical fiber; and / or, The synchronization optical input interface and the synchronization optical output interface are FC / UPC interfaces and are used for connecting a polarization maintaining or single-mode optical fiber; and / or, The output optical intensity monitoring interface is an FC / UPC interface and is used for connecting a polarization maintaining or single-mode optical fiber.

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