High-speed intensity modulation device, method and quantum communication system

Abstract

The application provides a high-speed intensity modulation device, method and quantum communication system. The device comprises an optical coupler, a transmission light path, a first phase modulator and a first high-speed driver. The first high-speed driver is connected with the first phase modulator and used for applying a high-frequency modulation signal with a frequency higher than a specified threshold to the first phase modulator. The optical coupler receives an optical pulse through an input port, splits the optical pulse into a first sub-optical pulse and a second sub-optical pulse. The first phase modulator is used for phase modulating the first sub-optical pulse and the second sub-optical pulse with different modulation efficiencies based on the high-frequency modulation signal. The optical coupler is further used for combining the first sub-optical pulse and the second sub-optical pulse after the first phase modulator, obtaining a combined optical pulse and outputting the combined optical pulse through an output port. In this way, the purpose of high-stable intensity modulation of a quantum light source with a speed of 10GHz or more is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical quantum intensity modulation, and in particular to a high-speed intensity modulation device, a method and a quantum communication system. BACKGROUND

[0002] In order to solve the problem of splitting photon number attack, the decoy state quantum communication protocol is generally used in the quantum communication system based on a weak coherent light source, and stable random modulation of the intensity of the quantum light source is generally required. At present, the quantum communication system in practical application is mainly at the level of 100 megahertz (MHz) and 1 gigahertz (GHz). In order to increase the safe transmission distance of quantum communication and improve the quantum key generation rate or information transmission rate, it is necessary to further break through the quantum communication system with a higher repetition frequency of 10 GHz, which requires a corresponding quantum light source intensity modulation device. At present, a phase modulator is arranged in a Sagnac interferometer, and the two light pulses transmitted clockwise and counterclockwise are modulated by time division or only one of them is modulated, so as to realize intensity modulation, which can meet the intensity modulation requirements of quantum light sources with a pulse repetition frequency of 100 MHz and about 1 GHz.

[0003] However, for the problem of intensity modulation of quantum light sources with a speed of 10 GHz or higher, the phase modulator itself has a certain length, which will cause multiple forward and reverse light pulses to be transmitted at the same time when modulating high-speed quantum states, and it is difficult to modulate the two light pulses by time division or only modulate one light pulse by time division, which limits the application of time division in high-speed modulation.

[0004] Therefore, it is difficult to implement the modulation of the two light pulses by time division or the modulation of only one light pulse at such a high speed by using the traditional time division method.

[0005] Therefore, how to realize intensity modulation of quantum light sources with a speed of 10 GHz or higher has become a key problem to be solved in quantum communication applications. SUMMARY

[0006] Therefore, the present application provides a high-speed intensity modulation device, a method and a quantum communication system to solve the technical problems in the background art.

[0007] According to a first aspect of the present application, a high-speed intensity modulation device is provided, comprising: an optical coupler, a transmission light path, a first phase modulator and a first high-speed driver.

[0008] The first high-speed driver is connected to the first phase modulator, and is used to apply a high-frequency modulation signal with a frequency higher than a specified threshold to the first phase modulator.

[0009] The optical coupler comprises a first port, a second port, a third port and a fourth port, receives an optical pulse through the first port, splits the optical pulse into a first sub-optical pulse and a second sub-optical pulse, and the first sub-optical pulse and the second sub-optical pulse have the same polarization state;

[0010] The second port and the third port of the optical coupler are connected through the transmission optical path, the first phase modulator is arranged in the transmission optical path, the first sub-optical pulse is output from the second port of the optical coupler and transmitted along the clockwise direction of the transmission optical path to the forward input optical port of the first phase modulator, and after passing through the first phase modulator, is transmitted along the clockwise direction of the transmission optical path to the third port of the optical coupler, the second sub-optical pulse is output from the third port of the optical coupler and transmitted along the counterclockwise direction of the transmission optical path to the reverse input optical port of the first phase modulator, and after passing through the first phase modulator, is transmitted along the counterclockwise direction of the transmission optical path to the second port of the optical coupler.

[0011] The first phase modulator is used for phase modulating the first sub-optical pulse and the second sub-optical pulse with different modulation efficiencies based on the high-frequency modulation signal; wherein the ratio of the modulation efficiency of the first sub-optical pulse to the modulation efficiency of the second sub-optical pulse is not less than a preset threshold, so that there is a phase difference between the phase-modulated first sub-optical pulse and the phase-modulated second sub-optical pulse.

[0012] The optical coupler is also used for combining the first sub-optical pulse and the second sub-optical pulse after passing through the first phase modulator to obtain a combined optical pulse and output the combined optical pulse through the fourth port.

[0013] In some embodiments, the first phase modulator comprises a fast axis and a slow axis.

[0014] The first sub-optical pulse and the second sub-optical pulse are both transmitted to the first phase modulator by the fast axis of the first phase modulator, or both are transmitted to the first phase modulator by the slow axis of the first phase modulator.

[0015] In some embodiments, the transmission optical path is a polarization maintaining optical fiber or a free space optical path.

[0016] In some embodiments, the second port and the third port of the optical coupler are both coupled with the slow axis of the polarization maintaining optical fiber, or both are coupled with the fast axis of the polarization maintaining optical fiber.

[0017] In some embodiments, the optical coupler is a polarization maintaining optical fiber coupler, and the first port, the second port, the third port and the fourth port are polarization maintaining optical fiber ports.

[0018] In some embodiments, the device further comprises a second phase modulator and a second high-speed driver,

[0019] The second phase modulator is arranged in the transmission optical path in series with the first phase modulator, for cooperating with the first phase modulator to modulate the first and second sub-optical pulses in phase.

[0020] The second high-speed driver is connected to the second phase modulator, for applying a high-frequency modulation signal with a frequency higher than a specified threshold to the second phase modulator.

[0021] In some embodiments, the phases modulated by the first and second phase modulators on the first and second sub-optical pulses are determined according to the intensity requirement of the output optical pulse.

[0022] In some embodiments, the first and second sub-optical pulses are transmitted through the first phase modulator at the same time, or the first and second sub-optical pulses are transmitted through the second phase modulator at the same time.

[0023] In some embodiments, the polarization state of the optical pulse is linear polarization.

[0024] In some embodiments, the high-speed intensity modulation device further comprises an optical polarizer,

[0025] The optical polarizer is arranged at the front end of the optical coupler, and the optical polarizer is used to linearly polarize the input optical pulse.

[0026] According to the second aspect of the present application, a high-speed intensity modulation method is provided, which is applied to the high-speed intensity modulation device described above.

[0027] According to the third aspect of the present application, a quantum communication system is provided, which comprises the high-speed intensity modulation device described above.

[0028] In summary, the high-speed intensity modulation device, method and quantum communication system provided by the embodiments of the present application have at least the following beneficial effects:

[0029] The application adopts an optical coupler to split a received optical pulse into a first sub-optical pulse transmitted in a clockwise direction along a transmission optical path and a second sub-optical pulse transmitted in an anticlockwise direction along the transmission optical path. The first sub-optical pulse and the second sub-optical pulse output by the optical coupler are respectively phase-modulated with different modulation efficiencies by a first phase modulator to which a high-frequency modulation signal is applied, so that the modulation efficiency of the first sub-optical pulse is much higher than that of the second sub-optical pulse, i.e., the first sub-optical pulse can be effectively phase-modulated and the second sub-optical pulse can be ineffective phase-modulated, so that the phase-modulated first sub-optical pulse and the phase-modulated second sub-optical pulse have a phase difference. The optical coupler combines the two high-speed modulated sub-optical pulses and outputs a combined optical pulse, thereby realizing high-speed modulation of the intensity of the output optical pulse. In this way, the two sub-optical pulses of the optical coupler transmitted along the same optical path before being combined have the same optical path, thereby having a self-compensation function to environmental interference, having the advantages of anti-interference and high stability, and achieving the purpose of high-stable intensity modulation of a 10GHz or higher rate quantum light source. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the present application, the specific embodiments or prior art technical solutions will be described below. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] Figure 1 A structure schematic diagram of a high-speed intensity modulation device provided by an embodiment of the present application is shown.

[0032] Figure 2 A structure schematic diagram of another high-speed intensity modulation device provided by an embodiment of the present application is shown.

[0033] Figure 3 A flowchart of a high-speed intensity modulation method provided by an embodiment of the present application is shown.

[0034] Figure 4 A structure schematic diagram of a quantum communication system provided by an embodiment of the present application is shown. DETAILED DESCRIPTION

[0035] In order to make the above and other features and advantages of the present application clearer, the present application will be further described below with reference to the drawings. It should be understood that the specific embodiments given herein are for the purpose of explanation and are only exemplary, but are not limiting.

[0036] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details. In other instances, well-known steps or procedures are not described in detail in order to avoid obscuring the present application.

[0037] The embodiment of the present application provides a high-speed intensity modulation device. Figure 1 The embodiment of the present application provides a high-speed intensity modulation device. Figure 1 As shown in the figure, the high-speed intensity modulation device can include an optical coupler 101, a transmission optical path 102, a first phase modulator 103 and a first high-speed driver 104. The optical coupler 101 and the transmission optical path 102 can constitute a Sagnac interferometer.

[0038] As shown in the figure, the first high-speed driver 104 is connected to the first phase modulator 103. The first high-speed driver 104 is used to apply a high-frequency modulation signal with a frequency higher than a specified threshold to the first phase modulator 103. Figure 1

[0039] In an embodiment, the high-frequency modulation signal with a frequency higher than a specified threshold can be a high-frequency modulation voltage signal or a modulation current signal with a frequency not less than 10 GHz.

[0040] In an embodiment, the optical pulse is a high-speed optical pulse, which refers to a high-repetition-frequency pulse light, for example, a pulse repetition frequency of 10 GHz or higher.

[0041] In an embodiment, the optical coupler 101 includes four ports, namely a first port A, a second port B, a third port C and a fourth port D. The first port A of the optical coupler 101 is an input port of the high-speed intensity modulation device, and the fourth port D of the optical coupler 101 is an output port of the high-speed intensity modulation device. The optical coupler 101 receives an optical pulse through the first port A, and divides the optical pulse into a first sub-optical pulse and a second sub-optical pulse. The polarization states of the first sub-optical pulse and the second sub-optical pulse are the same, and the intensities of the first sub-optical pulse and the second sub-optical pulse can be the same or different.

[0042] The optical coupler 101 is connected to the transmission optical path 102. Specifically, the second port B of the optical coupler 101 is connected to one end of the transmission optical path 102, and the third port C of the optical coupler 101 is connected to the other end of the transmission optical path 102. In this way, the first sub-optical pulse output from the second port B is coupled into the transmission optical path 102, and the second sub-optical pulse output from the third port C is coupled into the transmission optical path 102. In other words, the second port B and the third port C of the optical coupler 101 are connected through the transmission optical path 102.

[0043] As​Figure 1 As shown, the first phase modulator 103 includes three ports, which are a fifth port E, a sixth port F and a seventh port G. Among them, the fifth port E and the sixth port F are forward input optical ports and reverse input optical ports of the first phase modulator 103 respectively, and the seventh port G is an electrical port. The first phase modulator 103 is arranged in the transmission light path 102, that is, the first phase modulator 103 is coupled with the transmission light path 102 through the fifth port E and the sixth port F.

[0044] For example, the first phase modulator 103 is arranged in the transmission light path 102, the first route of sub-light pulses is output from the second port B of the optical coupler 101 and transmitted along the clockwise direction of the transmission light path 102 to the forward input optical port of the first phase modulator 103, that is, the fifth port E, and after passing through the first phase modulator 103, continues to be transmitted along the clockwise direction of the transmission light path 102 to the third port C of the optical coupler 101. The second route of sub-light pulses is output from the third port C of the optical coupler 101 and transmitted along the counterclockwise direction of the transmission light path 102 to the reverse input optical port of the first phase modulator 103, that is, the sixth port F, and after passing through the first phase modulator 103, continues to be transmitted along the counterclockwise direction of the transmission light path 102 to the second port B of the optical coupler 101.

[0045] That is, in the above embodiment of the present application, the first route of sub-light pulses output from the second port B of the optical coupler 101 is transmitted along the clockwise direction of the transmission light path 102, and coupled into the first phase modulator 103 through the fifth port E of the first phase modulator 103, and after passing through the first phase modulator 103, the first route of sub-light pulses is coupled into the transmission light path 102 through the sixth port F, and continues to be transmitted along the clockwise direction of the transmission light path 102 to the third port C of the optical coupler 101. In addition, the second route of sub-light pulses output from the third port C of the optical coupler 101 is transmitted along the counterclockwise direction of the transmission light path 102, and coupled into the first phase modulator 103 through the sixth port F of the first phase modulator 103, and after passing through the first phase modulator 103, the second route of sub-light pulses is coupled into the transmission light path 102 through the fifth port E, and continues to be transmitted along the counterclockwise direction of the transmission light path 102 to the second port B of the optical coupler 101.

[0046] The seventh port G of the first phase modulator 103 is connected with the first high-speed driver 104. The first phase modulator 103 receives the high-frequency modulation signal applied by the first high-speed driver 104 through the seventh port G. The first phase modulator 103 is configured to phase modulate the first route of sub-light pulses and the second route of sub-light pulses with different modulation efficiencies based on the high-frequency modulation signal.

[0047] The ratio of the modulation efficiency of the first sub-light pulse to the modulation efficiency of the second sub-light pulse is not less than a preset threshold. The phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference.

[0048] In an embodiment, the preset threshold can be not less than 10 decibels (dB). That is, the modulation efficiency of the first phase modulator 103 on the first sub-light pulse is much greater than the modulation efficiency of the first phase modulator 103 on the second sub-light pulse.

[0049] In the embodiment of the present application, the first phase modulator 103 can be made of a lithium niobate crystal, and can be a single-polarization phase modulator or a birefringent phase modulator. The first phase modulator 103 can accurately control the refractive index of the crystal by applying an electric field, thereby realizing the modulation of the phase of the light wave. For example, when a high-frequency modulation signal of 10 GHz or more is applied, the first phase modulator 103 is in a non-reciprocal state, and the efficiency of modulating the phase of the light pulse input from the forward input light port (for example, the first sub-light pulse) and the light pulse input from the reverse input light port (for example, the second sub-light pulse) is greatly different, at least 10 times or more than 100. When a high-frequency modulation signal with a frequency higher than a specified threshold is applied to the first phase modulator 103, there can be multiple sub-light pulses input from the forward input light port and sub-light pulses input from the reverse input light port at the same time.

[0050] That is, the modulation efficiency of the first phase modulator 103 on the first sub-light pulse is greatly different from the modulation efficiency of the first phase modulator 103 on the second sub-light pulse. Therefore, it can be considered that the first phase modulator 103 can effectively modulate the first sub-light pulse input from the fifth port E and transmitted forward through the first phase modulator 103, and cannot effectively modulate the second sub-light pulse input from the sixth port F and transmitted backward through the first phase modulator 103.

[0051] In the embodiment of the present application, when the two sub-light pulses pass through the first phase modulator 103 modulated at a high speed, the same high-frequency modulation signal is applied to the first sub-light pulse and the second sub-light pulse once, so that the required phase difference between the first sub-light pulse and the second sub-light pulse is formed. And by applying high-frequency modulation signals of different sizes, the phase difference between the first sub-light pulse and the second sub-light pulse after being modulated by the first phase modulator 103 is also different, so that the first sub-light pulse and the second sub-light pulse produce high-speed modulated light pulses of different intensities when they are combined and output by the optical coupler 101.

[0052] The optical coupler 101 is also configured to combine the first sub light pulse after the first phase modulator 103 with the second sub light pulse to obtain a combined light pulse and output the combined light pulse through the fourth port D.

[0053] In an embodiment, the first sub light pulse and the second sub light pulse after the phase modulation by the first phase modulator 103 are at different phases. The optical coupler 101 can combine the first sub light pulse after the first phase modulator 103 input from the third port C with the second sub light pulse after the first phase modulator 103 input from the second port B. In the process of combination, the optical coupler 101 can combine the two sub light pulses into a single combined light pulse while ensuring that the two sub light pulses maintain a specific phase difference.

[0054] In the above embodiment, the optical coupler 101 is used to split the received light pulse into the first sub light pulse transmitted in the clockwise direction along the transmission optical path 102 and the second sub light pulse transmitted in the counterclockwise direction along the transmission optical path 102. The first sub light pulse and the second sub light pulse output by the optical coupler 101 are respectively phase-modulated by the first phase modulator 103 with different modulation efficiencies by applying a high-frequency modulation signal, so that the modulation efficiency of the first sub light pulse is much higher than that of the second sub light pulse, that is, the first sub light pulse can be effectively phase-modulated, and the second sub light pulse can be ineffective phase-modulated, so that the first sub light pulse after high-speed phase modulation and the second sub light pulse after high-speed phase modulation have a phase difference. The optical coupler 101 combines the two sub light pulses after high-speed modulation and outputs a combined light pulse, thereby achieving high-speed modulation of the intensity of the output light pulse. In this way, the two sub light pulses of the optical coupler 101 have the same optical path before being combined, thereby having the advantages of self-compensation to environmental interference and high stability against interference, and achieving the purpose of high-stable intensity modulation of a quantum light source at a rate of 10 GHz or higher.

[0055] In some embodiments, the polarization state of the light pulse input to the optical coupler is linear polarization.

[0056] In some embodiments, the first phase modulator 103 can include a fast axis and a slow axis. The transmission speed of the two sub light pulses in the fast axis is higher than that in the slow axis.

[0057] In an embodiment, the first sub light pulse and the second sub light pulse can be transmitted through the fast axis of the first phase modulator 103.

[0058] Specifically, the first sub light pulse output from the second port B of the optical coupler 101 passes through the transmission optical path 102, is coupled to the fast axis of the first phase modulator 103 from the forward input optical port (i.e., the fifth port E) of the first phase modulator 103, and is output along the reverse input optical port (i.e., the sixth port F) of the first phase modulator 103 after being phase modulated by the fast axis of the first phase modulator 103. The second sub light pulse output from the third port C of the optical coupler 101 passes through the transmission optical path 102, is coupled to the fast axis of the first phase modulator 103 from the reverse input optical port (i.e., the sixth port F) of the first phase modulator 103, and is output along the forward input optical port (i.e., the fifth port E) of the first phase modulator 103 after being phase modulated by the fast axis of the first phase modulator 103.

[0059] In another embodiment, the first sub light pulse and the second sub light pulse are both transmitted by the slow axis of the first phase modulator 103 through the first phase modulator 103.

[0060] Specifically, the first sub light pulse output from the second port B of the optical coupler 101 passes through the transmission optical path 102, is coupled to the slow axis of the first phase modulator 103 from the forward input optical port (i.e., the fifth port E) of the first phase modulator 103, and is output along the reverse input optical port (i.e., the sixth port F) of the first phase modulator 103 after being phase modulated by the slow axis of the first phase modulator 103. The second sub light pulse output from the third port C of the optical coupler 101 passes through the transmission optical path 102, is coupled to the slow axis of the first phase modulator 103 from the reverse input optical port (i.e., the sixth port F) of the first phase modulator 103, and is output along the forward input optical port (i.e., the fifth port E) of the first phase modulator 103 after being phase modulated by the slow axis of the first phase modulator 103.

[0061] In the above embodiments, the transmission paths of the first sub light pulse and the second sub light pulse in the transmission optical path 102 and the first phase modulator 103 are consistent, which can ensure that the phase drifts caused by environmental interference of the two sub light pulses when passing through the transmission optical path 102 and the first phase modulator 103 are the same, so that the phase difference between them can be accurately controlled by modulating the first phase modulator 103.

[0062] In some embodiments, the first sub light pulse and the second sub light pulse are transmitted through the first phase modulator 103 at the same time. That is, at a certain time point, both sub light pulses enter the first phase modulator 103 and are simultaneously affected by the high-frequency modulation signal.

[0063] Thus, since the first sub light pulse and the second sub light pulse pass through the same modulation environment at the same time, the phase difference between the two sub light pulses can be precisely controlled.

[0064] In some embodiments, the transmission light path 102 can include a wired channel and a wireless channel. The wired channel can include a polarization maintaining optical fiber. The wireless channel can include a free space light path.

[0065] The polarization maintaining optical fiber is a special optical fiber that can keep the polarization direction of light unchanged during transmission along the slow axis or the fast axis of the polarization maintaining optical fiber. The free space light path can refer to a path of light propagation in free space, independent of optical fibers or other physical media.

[0066] In some embodiments, when the transmission light path 102 is a polarization maintaining optical fiber, the two sub light pulses output by the second port B and the third port C of the optical coupler 101 can be coupled to the slow axis of the polarization maintaining optical fiber or to the fast axis of the polarization maintaining optical fiber.

[0067] In some embodiments, the optical coupler 101 is a polarization maintaining optical fiber coupler, and the first port A, the second port B, the third port C, and the fourth port D are polarization maintaining optical fiber ports.

[0068] When the transmission light path 102 is a free space light path, the two sub light pulses output by the second port B and the third port C of the optical coupler 101 can be coupled to the same axis of the first phase modulator 103 through the free space light path.

[0069] In some embodiments, in order to enable the first phase modulator 103 to effectively modulate the second sub light pulse transmitted counterclockwise without effectively modulating the first sub light pulse transmitted clockwise, the first phase modulator 103 can be arranged in the transmission light path 102 in the opposite direction, i.e., the sixth port F of the first phase modulator 103 is connected to the second port B of the optical coupler 101 through the transmission light path 102, and the fifth port E of the first phase modulator 103 is connected to the third port C of the optical coupler 101 through the transmission light path 102.

[0070] In some embodiments, the phase modulated by the first phase modulator 103 can be determined according to the requirements of intensity modulation of the quantum communication protocol. For example, the requirements of intensity modulation in the quantum communication decoy state BB84 protocol are three intensities, and the first phase modulator 103 randomly modulates three phases to achieve modulation of three intensities.

[0071] In an embodiment, the type of phase modulated by the first phase modulator 103 can be considered as the phase difference between the first sub light pulse and the second sub light pulse after phase modulation. That is, the phase of the sub light pulse effectively modulated by the first phase modulator 103.

[0072] In some embodiments, in order to reduce the types of phases modulated by a single phase modulator, multiple phase modulators may be used for combined modulation to achieve intensity modulation control.

[0073] Figure 2 A schematic structural diagram of another high-speed intensity modulation device provided in an embodiment of the present application is shown. Figure 2 As shown, the high-speed intensity modulation device may include an optical coupler 201 , a transmission optical path 202 , a first phase modulator 203 , a first high-speed driver 204 , a second phase modulator 205 and a second high-speed driver 206 .

[0074] compared to Figure 1 The high-speed intensity modulation device shown, Figure 2 The high-speed intensity modulation apparatus shown is further provided with a second phase modulator 205 and a second high-speed driver 206 .

[0075] Figure 2 The optical coupler 201 in Figure 1 The optical coupler 201 is similar to the optical coupler 101 in FIG. The optical coupler 201 includes a first port A, a second port B, a third port C, and a fourth port D. The first port A is the input port of the high-speed intensity modulation device, and the fourth port D is the output port of the high-speed intensity modulation device. The optical coupler 201 receives an optical pulse through the first port A and splits the optical pulse into a first optical pulse and a second optical pulse. The first optical pulse and the second optical pulse have the same polarization state.

[0076] The second phase modulator 205 may be a phase modulator identical to the first phase modulator 203. The second phase modulator 205 may include three ports, namely, an eighth port M, a ninth port N, and a tenth port L. The eighth port M and the ninth port N are a forward input optical port and a reverse input optical port, respectively, and the tenth port L is an electrical port.

[0077] The second phase modulator 205 may be connected in series with the first phase modulator 203 in the transmission optical path 202 , that is, the second phase modulator 205 may be connected to the first phase modulator 203 in a forward direction or in a reverse direction.

[0078] That is, the sixth port F of the first phase modulator 203 is connected with the eighth port M of the second phase modulator 205 through the transmission light path 202, and the ninth port N of the second phase modulator 205 is connected with the third port C of the optical coupler 201 through the transmission light path 202. Alternatively, the sixth port F of the first phase modulator 203 is connected with the ninth port N of the second phase modulator 205 through the transmission light path 202, and the eighth port M of the second phase modulator 205 is connected with the third port C of the optical coupler 201 through the transmission light path 202.

[0079] The second phase modulator 205 can be used to cooperate with the first phase modulator 203 to perform phase modulation on the first and second sub light pulses.

[0080] That is, the second phase modulator 205 has two functions. One is to work as a backup phase modulator, that is, in the case that the first phase modulator 203 cannot work due to failure, the second phase modulator 205 works to perform phase modulation on the first and second sub light pulses with different modulation efficiencies based on the high-frequency modulation signal applied by the second high-speed driver 206 alone. The other is to work as a cooperative phase modulator, that is, in the case that the first phase modulator 203 works, the second phase modulator also works to perform phase modulation on the first and second sub light pulses based on the high-frequency modulation signal applied by the second high-speed driver 206 respectively.

[0081] In an embodiment, the modulation modes of the first phase modulator 203 and the second phase modulator 205 can include a separate modulation mode and a combined modulation mode. The separate modulation mode can mean that the first phase modulator 203 or the second phase modulator 205 performs phase modulation alone. The combined modulation mode can mean that the first phase modulator 203 and the second phase modulator 205 perform phase modulation cooperatively.

[0082] The second high-speed driver 206 is connected with the second phase modulator 205, that is, the second phase modulator 205 is connected with the second high-speed driver 206 through the tenth port L. The second high-speed driver 206 is used to apply a high-frequency modulation signal to the second phase modulator. It should be noted that the type and role of the second high-speed driver 206 can be the same as those of the first high-speed driver 204. When the second phase modulator 205 is applied with a high-frequency modulation signal with a frequency higher than a specified threshold, there can be multiple sub light pulses input by the forward input optical port and the reverse input optical port of the second phase modulator 205 at the same time.

[0083] In an embodiment, the first sub-light pulse is transmitted from the second port B of the optical coupler 201 along the clockwise direction of the transmission light path 202 through the first phase modulator 203 and the second phase modulator 205, and is transmitted to the third port C of the optical coupler 201 along the clockwise direction of the transmission light path 202 after being modulated by the first phase modulator 203 and / or the second phase modulator 205. The second sub-light pulse is transmitted from the third port C of the optical coupler 201 along the counterclockwise direction of the transmission light path 202 through the first phase modulator 203 and the second phase modulator 205, and is transmitted to the second port B of the optical coupler 201 along the counterclockwise direction of the transmission light path 202 after being modulated by the first phase modulator 203 and / or the second phase modulator 205.

[0084] In the above embodiment, by adding the second phase modulator 205, the redundancy of the device can be increased, and by the first phase modulator 203 and the second phase modulator 205 cooperatively modulating the two sub-light pulses, a more flexible phase modulation mode can be achieved, and the precision and speed of phase control can be improved. When the first phase modulator 203 fails to work, the second phase modulator 205 is enabled for phase modulation, so that the phase modulation process can be ensured to proceed normally and the device can avoid interruption.

[0085] In addition, by configuring two phase modulators in the transmission light path 202, the combination of modulation by the two phase modulators applied with high-frequency modulation signals can enable the first high-speed driver and the second high-speed driver to generate different modulation intensities through digital high-speed modulation.

[0086] In some embodiments, the random phase modulation of the second phase modulator 205 can be determined according to the demand of intensity modulation of the quantum communication protocol. For example, the demand of intensity modulation in the quantum communication decoy state BB84 protocol is three intensities, and the second phase modulator 205 randomly modulates three phases to achieve modulation of three intensities.

[0087] In some embodiments, the phase modulation of the first phase modulator and the second phase modulator to the first sub-light pulse and the second sub-light pulse is determined according to the demand of intensity modulation of the quantum communication protocol.

[0088] That is, whether in the separate modulation mode or in the combined mode, the phase difference between the first sub-light pulse and the second sub-light pulse after being modulated by the first phase modulator and / or the second phase modulator meets the demand of intensity modulation in the quantum communication protocol. In this way, high-precision implementation of the quantum communication protocol can be ensured, and by setting two phase modulators, the number of modulation states of a single phase modulator can be reduced, and the flexibility and adaptability of the device can be improved.

[0089] In some embodiments, in the high-speed modulation scenario, the phase difference between the phase-modulated first sub-light pulses and the second sub-light pulses is equal to the sum or difference of the phase modulated by the first phase modulator 203 and the phase modulated by the second phase modulator 205 when the first phase modulator 203 and the second phase modulator 205 are connected in series in the forward direction or in the reverse direction.

[0090] That is, when the first phase modulator 203 and the second phase modulator 205 are connected in series in the forward direction, the phase difference between the phase-modulated first sub-light pulses and the second sub-light pulses is equal to the sum of the phase modulated by the first phase modulator 203 and the phase modulated by the second phase modulator 205.

[0091] When the first phase modulator 203 and the second phase modulator 205 are connected in series in the reverse direction, the phase difference between the phase-modulated first sub-light pulses and the second sub-light pulses is equal to the difference of the phase modulated by the first phase modulator 203 and the phase modulated by the second phase modulator 205.

[0092] The phases modulated by the first phase modulator 203 and the second phase modulator 205 on the first sub-light pulses and the second sub-light pulses can be determined according to the requirements of intensity modulation in the quantum communication protocol.

[0093] Based on this, in the combined modulation mode, the types of the phases modulated by the first phase modulator 203 can be less than the required phases in the quantum communication protocol. The types of the phases modulated by the second phase modulator 205 can be less than the required phases in the quantum communication protocol.

[0094] In an embodiment, the phases modulated by the first phase modulator 203 and the second phase modulator 205 are determined by the peak value of the high-frequency modulation signal applied by the respective high-speed driver.

[0095] In this way, by combining the modulation of the first phase modulator 203 and / or the second phase modulator 205, not only can the phase be accurately controlled, but also the number of states modulated by a single phase modulator can be reduced, thereby reducing the difficulty of implementing the phase modulator driver.

[0096] In some embodiments, the first sub-light pulses and the second sub-light pulses are transmitted through the first phase modulator 203 at the same time, or the first sub-light pulses and the second sub-light pulses are transmitted through the second phase modulator 205 at the same time. In this way, by passing through the same phase modulator at the same time, it can be ensured that the two sub-light pulses can be modulated by the same high-frequency modulation signal, thereby helping to reduce the phase drift caused by environmental interference and improving the accuracy and reliability of the device.

[0097] In some embodiments, the high-speed intensity modulation device of the present application further comprises: an optical polarizer, which is arranged at the front end of the optical coupler 101, and is configured to linearly polarize the input light pulse.

[0098] In another aspect, the present application provides a high-speed intensity modulation method, which is applied to any one of the high-speed intensity modulation devices of the present application. Figure 3 In the illustrated embodiments, the method is applied to the high-speed intensity modulation device shown in Figure 1 In the illustrated embodiments, the method is applied to the high-speed intensity modulation device shown in Figure 3 FIG. 1 shows a flow diagram of a high-speed intensity modulation method according to an embodiment of the present application. Figure 3 The high-speed intensity modulation method can include the following steps.

[0099] S31, receiving a light pulse through the first port A of the optical coupler 101.

[0100] S32, splitting the received light pulse into a first sub-light pulse and a second sub-light pulse through the optical coupler 101.

[0101] S33, outputting the first sub-light pulse from the second port B of the optical coupler 101 and transmitting it to the forward input optical port of the first phase modulator 103 in the clockwise direction of the transmission optical path 102, and outputting the second sub-light pulse from the third port C of the optical coupler 101 and transmitting it to the reverse input optical port of the first phase modulator 103 in the counterclockwise direction of the transmission optical path 102.

[0102] S34, using the first phase modulator 103 receiving a high-frequency modulation signal with a frequency higher than a specified threshold to phase modulate the first sub-light pulse and the second sub-light pulse with different modulation efficiencies based on the high-frequency modulation signal, and transmitting the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse in the clockwise direction and the counterclockwise direction, respectively, to the transmission optical path 102.

[0103] The ratio of the modulation efficiency of the first phase modulator 103 on the first sub-light pulse to the modulation efficiency on the second sub-light pulse is not less than a preset threshold. The phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse have a phase difference.

[0104] S35, combining the first sub-light pulse and the second sub-light pulse after the first phase modulator 103 through the optical coupler 101 to obtain a combined light pulse and output it through the fourth port D.

[0105] In the above embodiment, the optical coupler 101 divides the received light pulse into a first sub-light pulse transmitted along the clockwise direction of the transmission optical path 102 and a second sub-light pulse transmitted along the counterclockwise direction of the transmission optical path 102. The first phase modulator 103 modulates the first sub-light pulse and the second sub-light pulse output by the optical coupler 101 with different modulation efficiencies by applying a high-frequency modulation signal, so that the modulation efficiency of the first sub-light pulse is much higher than that of the second sub-light pulse, that is, the first sub-light pulse can be effectively phase modulated, and the second sub-light pulse can be ineffective phase modulated, so that there is a phase difference between the phase-modulated first sub-light pulse and the phase-modulated second sub-light pulse. The optical coupler 101 combines the two high-speed modulated sub-light pulses and outputs a combined light pulse, realizing high-speed modulation of the intensity of the output light pulse. In this way, the two sub-light pulses of the optical coupler 101 have the same transmission path when combined, thereby having the advantages of self-compensation to environmental interference and high stability against interference, achieving the purpose of high-stable intensity modulation of a 10GHz or higher rate quantum light source.

[0106] In some embodiments, the method can further include that the first sub-light pulse and the second sub-light pulse are transmitted to the first phase modulator 103 by the fast axis of the first phase modulator 103, or are transmitted to the first phase modulator 103 by the slow axis of the first phase modulator 103.

[0107] In some embodiments, the method can further include that the first sub-light pulse and the second sub-light pulse are phase modulated by the second phase modulator 205 in cooperation with the first phase modulator 203.

[0108] In some embodiments, the method can further include that the phase modulated by the first phase modulator 203 and the second phase modulator 205 on the first sub-light pulse and the second sub-light pulse is determined according to the requirement of intensity modulation of the quantum communication protocol.

[0109] In some embodiments, the polarization state of the light pulse is linear polarization.

[0110] In some embodiments, the light pulse is input along the slow axis or the fast axis of the polarization maintaining optical fiber of the first port of the polarization maintaining optical fiber coupler.

[0111] In another aspect, the embodiments of the present application provide a quantum communication system, Figure 4 Fig. 4 shows a structure schematic diagram of a quantum communication system provided by the embodiments of the present application. Figure 4 As shown in the figure, the quantum communication system 400 can include the high-speed intensity modulation device 401 described in any of the embodiments of the present application.

[0112] The quantum communication system can be a discrete variable quantum communication system or a continuous variable quantum communication system.

[0113] It should be understood that the specific features, operations and details described above in relation to the device of the application can be similarly applied to the method and system of the application, or vice versa. In addition, each step of the method of the application can be performed by the corresponding component or unit of the device or system of the application.

[0114] The technical features described above can be combined arbitrarily. Although all possible combinations of the technical features are not described, any combination of the technical features should be considered as covered by the present specification, as long as there is no contradiction in such a combination.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-speed intensity modulation device, characterized in that: include: An optical coupler, a transmission optical path, a first phase modulator, and a first high-speed driver; The first high-speed driver is connected to the first phase modulator and is used to apply a high-frequency modulation signal having a frequency higher than a specified threshold to the first phase modulator; The optical coupler includes a first port, a second port, a third port, and a fourth port. The optical coupler receives a light pulse through the first port and splits the light pulse into a first light pulse and a second light pulse. The first light pulse and the second light pulse have the same polarization state. The second port and the third port of the optical coupler are connected via the transmission optical path. The first phase modulator is disposed in the transmission optical path. The first path optical pulse is output from the second port of the optical coupler and transmitted along the clockwise direction of the transmission optical path to the forward input optical port of the first phase modulator. After passing through the first phase modulator, the first path optical pulse is transmitted along the clockwise direction of the transmission optical path to the third port of the optical coupler. The second path optical pulse is output from the third port of the optical coupler and transmitted along the counterclockwise direction of the transmission optical path to the reverse input optical port of the first phase modulator. After passing through the first phase modulator, the second path optical pulse is transmitted along the counterclockwise direction of the transmission optical path to the second port of the optical coupler. The first phase modulator is configured to perform phase modulation on the first optical pulse and the second optical pulse at different modulation efficiencies based on the high-frequency modulation signal; wherein a ratio of the modulation efficiency of the first optical pulse to the modulation efficiency of the second optical pulse is not less than a preset threshold, so that a phase difference exists between the phase-modulated first optical pulse and the phase-modulated second optical pulse; The optical coupler is further configured to combine the first optical pulse and the second optical pulse after passing through the first phase modulator to obtain a combined optical pulse and output the combined optical pulse through the fourth port.

2. The device according to claim 1, characterized in that The first phase modulator includes a fast axis and a slow axis; The first path optical pulse and the second path optical pulse are both transmitted to the first phase modulator through the fast axis of the first phase modulator, or are both transmitted to the first phase modulator through the slow axis of the first phase modulator.

3. The device according to claim 1, characterized in that The transmission optical path is a polarization-maintaining optical fiber or a free-space optical path.

4. The device according to claim 3, characterized in that The second port and the third port of the optical coupler are both coupled to the slow axis of the polarization-maintaining optical fiber, or are both coupled to the fast axis of the polarization-maintaining optical fiber.

5. The device according to claim 1 or 3, characterized in that The optical coupler is a polarization-maintaining fiber coupler, and the first port, the second port, the third port and the fourth port are polarization-maintaining fiber ports.

6. The device according to claim 1, characterized in that The apparatus further includes a second phase modulator and a second high-speed driver, The second phase modulator is arranged in series with the first phase modulator in the transmission optical path, and is used to cooperate with the first phase modulator to phase modulate the first path optical pulse and the second path optical pulse; The second high-speed driver is connected to the second phase modulator and is configured to apply a high-frequency modulation signal having a frequency higher than a specified threshold to the second phase modulator.

7. The device according to claim 6, characterized in that Phases modulated by the first phase modulator and the second phase modulator on the first path optical pulse and the second path optical pulse are determined according to output optical pulse intensity requirements.

8. The device according to claim 6, characterized in that The first path optical pulse and the second path optical pulse are transmitted through the first phase modulator at the same time, or the first path optical pulse and the second path optical pulse are transmitted through the second phase modulator at the same time.

9. The device according to claim 1, characterized in that The polarization state of the optical pulse is linear polarization.

10. The device according to claim 1, characterized in that The high-speed intensity modulation device further comprises: an optical polarizer, The optical polarizer is arranged at the front end of the optical coupler, and is used for linearly polarizing the input optical pulse.

11. A high-speed intensity modulation method, characterized in that: Applicable to the high-speed intensity modulation device according to any one of claims 1 to 10.

12. A quantum communication system, characterized in that: The device comprises a high-speed intensity modulation device as claimed in any one of claims 1 to 10.

Images