On-chip adjustable optical attenuation device based on MZ interference structure and CV-QKD system

Abstract

The application provides an on-chip adjustable optical attenuation device based on an MZ interference structure and a CV-QKD system, and comprises an optical beam splitting unit, a first interference arm, a second interference arm and an optical beam combining unit; the optical beam splitting unit is connected with the first interference arm and the second interference arm respectively, the first interference arm is provided with a first thermal phase shift unit, the second interference arm is provided with a second thermal phase shift unit, and the first thermal phase shift unit and the second thermal phase shift unit are connected with the optical beam combining unit respectively; the first interference arm and the second interference arm are unbalanced, the sensitivity of the optical attenuation coefficient of the adjustable optical attenuation device to temperature fluctuation is reduced by using the unbalanced adjustable optical attenuation device, and the adjustable optical attenuation module in the CV-QKD system comprises a plurality of unbalanced adjustable optical attenuation devices which are arranged in cascade. The over noise caused by temperature fluctuation can be reduced, the problem of high-precision on-chip adjustable optical attenuation control required by the integrated CV-QKD system can be solved, and the system security code rate can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of continuous variable quantum key distribution technology, and more specifically, to an on-chip tunable optical attenuation device and a CV-QKD system based on an MZ interference structure. Background Technology

[0002] With the development of quantum computing technology, classical cryptography based on computational complexity faces significant security vulnerabilities. Quantum key distribution (QKD), a key distribution system based on quantum physics principles, possesses unconditional security and has attracted widespread attention and research. Continuous variable quantum key distribution (CV-QKD) technology has advantages such as high code rate and good integration with classical fiber optic communication devices and networks, showing broad application prospects.

[0003] Existing CV-QKD systems typically employ discrete optoelectronic devices, resulting in drawbacks such as low integration density, large size, and high cost. To overcome these shortcomings, integrated optics methods can be used to improve the integration density of CV-QKD. A CV-QKD system consists of two parts: a transmitter and a receiver. The transmitter prepares the quantum states required for the CV-QKD protocol primarily through signal modulation and tunable optical attenuation. Specifically, the signal modulation module modulates the signal in the IQ phase space, while the tunable optical attenuation module accurately controls the signal variance. The modulation accuracy of the signal variance is a crucial indicator limiting system performance and security.

[0004] For CV-QKD systems based on discrete optoelectronic devices, tunable light attenuation modules typically employ mechanical methods to alter light transmittance, thereby achieving high controllability of light intensity attenuation. However, this method is not suitable for CV-QKD systems with integrated optical schemes. For CV-QKD systems, on the one hand, light intensity needs to be attenuated to the quantum level, requiring a very large attenuation coefficient; on the other hand, CV-QKD systems demand high attenuation precision and are highly sensitive to noise, requiring strict control over the impact of parameter fluctuations (such as temperature) on the tunable light attenuator. Summary of the Invention

[0005] This invention aims to address at least the existing problem that the intensity attenuation control method of the tunable light attenuation module in the existing discrete optoelectronic device CV-QKD system is not suitable for CV-QKD systems with integrated optical solutions; there is a need for a tunable light attenuator with high attenuation coefficient and high precision to achieve on-chip integration of CV-QKD systems; CV-QKD systems have high requirements for attenuation accuracy and are very sensitive to noise, requiring strict control of the impact of parameter fluctuations on the tunable light attenuator, and high-precision temperature control is one of the technical challenges.

[0006] To this end, the first aspect of the present invention provides an on-chip tunable optical attenuation device based on an MZ interference structure.

[0007] A second aspect of the present invention provides a CV-QKD system.

[0008] This invention provides an on-chip tunable optical attenuation device based on an MZ interference structure, comprising: an optical beam splitter, a first interference arm, a second interference arm, and an optical beam combiner. The optical beam splitting unit is connected to the first interferometer arm and the second interferometer arm respectively. The first interferometer arm is provided with a first thermal phase shifting unit, and the second interferometer arm is provided with a second thermal phase shifting unit. The first thermal phase shifting unit and the second thermal phase shifting unit are respectively connected to the optical beam combining unit. The optical beam splitter unit is used to split the incident light signal into two beams, and to make the two beams have different transmission coefficients. and The light enters the first and second interferometer arms; the first thermal phase-shifting unit is used to introduce a phase change into the light field passing through the first interferometer arm. The second thermal phase-shifting unit is used to introduce a phase change into the optical field passing through the second interferometer arm. The optical beam combining unit is used to combine the light fields that have passed through the first thermal phase shift unit and the second thermal phase shift unit to form an output light field. The tunable light attenuation device is used to attenuate the incident light signal to a weak quantum signal; the first and second interferometer arms are unbalanced, and the sensitivity of the light attenuation coefficient of the tunable light attenuation device to temperature fluctuations is reduced by using the tunable light attenuation device with unbalanced interferometer arms.

[0009] According to the above-described technical solution of the present invention, an on-chip tunable optical attenuation device based on an MZ interference structure may further have the following additional technical features: In the above technical solution, the output light field of the incident light signal after passing through the tunable light attenuation device is:

[0010] The light field of the incident light signal input to the tunable light attenuator is: , The transmittance coefficient of the optical signal after passing through the first thermal phase-shifting unit. The transmittance coefficient of the optical signal after passing through the second thermal phase-shifting unit.

[0011] In the above technical solution, the light intensity of the output light field after the incident light signal passes through the tunable light attenuation device can be characterized as:

[0012] in, To adjust the output light intensity of the light attenuation device, Input light intensity to the adjustable light attenuation device. The relative phase difference between the first and second interferometer arms is given.

[0013] In the above technical solution, adjustable optical attenuation is achieved by changing the relative phase difference between the first and second interferometer arms; the optical attenuation coefficient is: .

[0014] The present invention also provides a CV-QKD system, which is integrated on a chip using an integrated optical method and includes a light source generation module, a signal modulation module, and an adjustable light attenuation module; The light source generation module is connected to the signal modulation module and is used to generate an optical carrier signal and transmit the optical carrier signal to the signal modulation module. The signal modulation module is connected to the adjustable optical attenuation module and is used to modulate the IQ components of the optical signal according to the protocol adopted by the CV-QKD system, and send the modulated optical signal to the adjustable optical attenuation device.

[0015] The adjustable optical attenuation module is used to attenuate the optical signal according to the modulation variance requirements given by the system, and output the attenuated optical quantum signal to the channel. The tunable light attenuation module includes several cascaded on-chip tunable light attenuation devices based on the MZ interference structure, as described in any of the above technical solutions.

[0016] According to the above-described technical solution of the present invention, a CV-QKD system may further have the following additional technical features: In the above technical solution, the tunable light attenuation module includes at least two on-chip tunable light attenuation devices based on the MZ interference structure; Several on-chip tunable optical attenuation devices based on the MZ interference structure are cascaded together to reduce the sensitivity of the optical attenuation coefficient of the tunable optical attenuation module to temperature fluctuations.

[0017] In the above technical solution, the transmission coefficients of the two beams split by the optical beam splitting unit are unbalanced, which causes the first interference arm and the second interference arm in any adjustable optical attenuation device to be unbalanced.

[0018] In the above technical solution, after several on-chip tunable optical attenuation devices based on the MZ interference structure are cascaded, the phase fluctuation generated by the first thermal phase shift unit and the second thermal phase shift unit when the temperature fluctuates is as follows:

[0019] in, Let λ represent the phase fluctuation, and λ be the wavelength of the incident light signal. The length of the heat-shifting phase shifter along the direction of light transmission. Due to temperature fluctuations, is the thermo-optic coefficient, and n is the refractive index.

[0020] In summary, due to the adoption of the above-mentioned technical features, the beneficial effects of the present invention are: A Mach-Zehnder (MZ) interferometry scheme is employed to reduce the power balance between the two arms of the interference, thereby decreasing the sensitivity of the optical attenuation coefficient to temperature fluctuations and improving the controllability of optical intensity attenuation. Simultaneously, multiple cascaded on-chip tunable optical attenuation devices based on the MZ interferometry structure are used to achieve significant optical attenuation, solving the problem of high-precision on-chip tunable optical attenuation control required for integrated CV-QKD systems. Furthermore, the over-noise introduced by temperature fluctuations is reduced, effectively improving the system's secure bit rate.

[0021] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of an on-chip tunable optical attenuation device based on an MZ interference structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the module of the transmitter of a CV-QKD system according to an embodiment of the present invention; Figure 3 This is a schematic diagram of an adjustable light attenuation module in a CV-QKD system according to an embodiment of the present invention. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] The following reference Figures 1 to 3 This invention describes an on-chip tunable optical attenuation device and a CV-QKD system based on an MZ interference structure, provided by some embodiments of the present invention.

[0026] Some embodiments of this application provide an on-chip tunable optical attenuation device based on an MZ interference structure.

[0027] like Figure 1 As shown, the first embodiment of the present invention proposes an on-chip tunable optical attenuation device based on an MZ interference structure, comprising: an optical beam splitting unit, a first interferometer arm, a second interferometer arm, and an optical beam combining unit; The optical beam splitting unit is connected to the first interferometer arm and the second interferometer arm respectively. The first interferometer arm is provided with a first thermal phase shifting unit, and the second interferometer arm is provided with a second thermal phase shifting unit. The first thermal phase shifting unit and the second thermal phase shifting unit are respectively connected to the optical beam combining unit. The optical beam splitter unit is used to split the incident light signal into two beams, and to make the two beams have different transmission coefficients. and The light enters the first and second interferometer arms; the first thermal phase-shifting unit is used to introduce a phase change into the light field passing through the first interferometer arm. The second thermal phase-shifting unit is used to introduce a phase change into the optical field passing through the second interferometer arm. The optical beam combining unit is used to combine the light fields that have passed through the first thermal phase shift unit and the second thermal phase shift unit to form an output light field. The tunable light attenuation device is used to attenuate the incident light signal to a weak quantum signal; the first and second interferometer arms are unbalanced, and the sensitivity of the light attenuation coefficient of the tunable light attenuation device to temperature fluctuations is reduced by using the tunable light attenuation device with unbalanced interferometer arms.

[0028] Assuming the incident tunable light attenuation device has the following optical field: The output light field of the incident light signal after passing through the tunable light attenuation device is: (1); in, The transmittance coefficient of the optical signal after passing through the first thermal phase-shifting unit. The transmittance coefficient of the optical signal after passing through the second thermal phase-shifting unit.

[0029] The intensity of the output light field after the incident light signal passes through the tunable light attenuation device can be characterized as follows: (2); in, To adjust the output light intensity of the light attenuation device, Input light intensity to the adjustable light attenuation device. The relative phase difference between the first and second interferometer arms is given.

[0030] Adjustable optical attenuation is achieved by changing the relative phase difference between the first and second interferometer arms; the optical attenuation coefficient is: (3).

[0031] The second embodiment of the present invention proposes a CV-QKD system, and based on the first embodiment, as follows: Figures 1 to 3 As shown, for a thermal phase-shifting unit, temperature fluctuations will cause changes in the refractive index, affecting phase fluctuations, i.e., in formula (2) or (3). Δφ This will change, causing fluctuations in the optical attenuation coefficient.

[0032] Fluctuations in the optical attenuation coefficient introduce excess noise into the CV-QKD system, affecting its secure bit rate. Therefore, strict temperature control of the thermal phase-shifting unit is necessary, and the precision of temperature control determines the magnitude of the excess noise introduced by the thermal phase-shifting unit. For CV-QKD systems, higher temperature control precision increases the difficulty, cost, and size of the electronic control components; achieving exceptionally high temperature control precision is difficult with current technology.

[0033] Therefore, in the design of CV-QKD systems, the requirements for tunable optical attenuators need to take into account the following two factors: on the one hand, it is necessary to reduce the difficulty of temperature control, that is, to reduce the sensitivity of the optical attenuation coefficient to temperature fluctuations; on the other hand, it is necessary to meet the requirement of a large attenuation coefficient, so that classical strong light can be attenuated to a weak quantum signal.

[0034] To address the above issues, this embodiment proposes a CV-QKD system that cascades multiple unbalanced on-chip tunable optical attenuation devices based on the MZ interference structure. This reduces the sensitivity of the optical attenuation coefficient to temperature fluctuations and achieves a large attenuation coefficient.

[0035] In this embodiment, the CV-QKD system is integrated on-chip using an integrated optical method, including a light source generation module, a signal modulation module, and an adjustable light attenuation module; The light source generation module is connected to the signal modulation module and is used to generate an optical carrier signal and transmit the optical carrier signal to the signal modulation module. The signal modulation module is connected to the adjustable optical attenuation module and is used to modulate the IQ components of the optical signal according to the protocol adopted by the CV-QKD system, and send the modulated optical signal to the adjustable optical attenuation device.

[0036] The adjustable optical attenuation module is used to attenuate the optical signal according to the modulation variance requirements given by the system, and output the attenuated optical quantum signal to the channel. The tunable light attenuation module includes several cascaded on-chip tunable light attenuation devices based on the MZ interference structure as described in the first embodiment.

[0037] The tunable light attenuation module includes at least two on-chip tunable light attenuation devices based on the MZ interference structure; The sensitivity of the optical attenuation coefficient to temperature fluctuations is reduced by cascading several on-chip tunable optical attenuation devices based on the MZ interference structure.

[0038] The transmission coefficients of the two beams split by the optical beam splitter are unbalanced, thus causing an imbalance between the first and second interferometer arms within any adjustable optical attenuation device. That is, the transmission coefficient... and It does not approach 0.5.

[0039] In the above technical solution, after several on-chip tunable optical attenuation devices based on the MZ interference structure are cascaded, the phase fluctuation generated by the first thermal phase shift unit and the second thermal phase shift unit when the temperature fluctuates is as follows: (4); in, Let λ represent the phase fluctuation, and λ be the wavelength of the incident light signal. The length of the heat-shifting phase shifter along the direction of light transmission. Due to temperature fluctuations, is the thermo-optic coefficient, and n is the refractive index.

[0040] like Figure 3 As shown, the tunable light attenuation module of this CV-QKD system is composed of m unbalanced on-chip tunable light attenuation devices based on the MZ interference structure cascaded together. The incident light first enters unbalanced tunable light attenuation device 1, and the light output from unbalanced tunable light attenuation device 1 enters unbalanced tunable light attenuation device 2. This process continues, and finally, the light output from the m-th unbalanced tunable light attenuation device is the weak quantum signal required by the CV-QKD system. Transmission coefficients are shown in the diagram. It does not approach 0.5.

[0041] The third embodiment of the present invention proposes a CV-QKD system, and based on the second embodiment, as follows: Figures 1 to 3 As shown, the requirements for the tunable light attenuation module of a certain CV-QKD system are: the attenuation coefficient is close to -40dB and the output power fluctuation is less than 1% when the temperature changes by 0.1K.

[0042] The tunable optical attenuation module in this embodiment consists of two unbalanced on-chip tunable optical attenuation devices based on the MZ interference structure cascaded together, i.e., m=2; and by adjustment, the transmission coefficients of the optical beam splitter and optical beam combiner are made unbalanced. Without loss of generality, it is assumed that the parameters of the two cascaded unbalanced tunable optical attenuators are the same, let... , , For silicon oxide, the rate of change of its dielectric constant with temperature (thermo-optic coefficient) is taken as... ;wavelength The lengths of the first and second thermal phase-shifting units along the optical transmission direction The incident light intensity is 0.37mW. According to formulas (3) and (4), the attenuation coefficient of the tunable light attenuation module of the CV-QKD system in this embodiment is about -40dB; however, when the temperature changes by 0.1K, its output power fluctuates by 0.3%.

[0043] The first comparative example of this invention presents a CV-QKD system, and based on the first embodiment, as follows: Figures 1 to 2 As shown, the CV-QKD system is integrated on-chip using an integrated optical method, and its transmitting end includes a light source generation module, a signal modulation module, and an adjustable light attenuation module. The light source generation module is connected to the signal modulation module and is used to generate an optical carrier signal and transmit the optical carrier signal to the signal modulation module. The signal modulation module is connected to the adjustable optical attenuation module and is used to modulate the IQ components of the optical signal according to the protocol adopted by the CV-QKD system, and send the modulated optical signal to the adjustable optical attenuation device.

[0044] The adjustable optical attenuation module is used to attenuate the optical signal according to the modulation variance requirements given by the system, and output the attenuated optical quantum signal to the channel. The tunable light attenuation module includes an on-chip tunable light attenuation device based on an MZ interference structure as described in the above embodiments.

[0045] The difference between this comparative example and the first embodiment is that the first and second interference arms in the adjustable light attenuation device are balanced, that is, the transmission coefficients of the two beams of light split by the light beam splitting unit tend to be balanced. and Approaching 0.5; The transmittance coefficients of the optical signal passing through the first thermal phase-shifting unit and the second thermal phase-shifting unit tend to be in equilibrium; that is... and Approaching 0.5.

[0046] For on-chip tunable optical attenuation devices based on the MZ interference structure, the balance of the two arms is improved, that is, the balance of the two arms is maximized. Approaching 0.5 can significantly improve the attenuation rate of tunable optical attenuators. However, its optical attenuation coefficient is very sensitive to temperature fluctuations, resulting in higher over-noise.

[0047] Suppose that a certain CV-QKD system requires the following for the tunable light attenuation module: the attenuation coefficient is close to -40dB and the output power fluctuation is less than 1% when the temperature changes by 0.1K.

[0048] In this comparative example, the tunable light attenuation module of the CV-QKD system is composed of a single on-chip tunable light attenuation device based on the MZ interference structure. The transmission coefficients of the two beams split by the beam splitter unit are adjusted by adjusting the tunable light attenuation module. and To achieve a balance between the transmittance coefficients of the optical signal passing through the first thermal phase-shifting unit and the transmittance coefficients of the optical signal passing through the second thermal phase-shifting unit. and Strive for balance; without losing generality, it can make , , .

[0049] For silicon oxide, the rate of change of its dielectric constant with temperature (thermo-optic coefficient) is taken as... ;wavelength The lengths of the first and second thermal phase-shifting units along the optical transmission direction The incident light intensity is 0.37mW. According to formulas (3) and (4), the attenuation coefficient of the tunable light attenuation module of the CV-QKD system in this embodiment is about -40dB; however, when the temperature changes by 0.1K, its output power fluctuates by 16.4%.

[0050] As can be seen from the comparative example and the third embodiment, both schemes can achieve a decay of approximately 40 dB. However, the third embodiment is much less sensitive to temperature than the comparative example.

[0051] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A CV-QKD system, characterized in that, It includes a light source generation module, a signal modulation module, and an adjustable light attenuation module; The light source generation module is connected to the signal modulation module and is used to generate an optical carrier signal and transmit the optical carrier signal to the signal modulation module. The signal modulation module is connected to the adjustable optical attenuation module and is used to modulate the IQ components of the optical signal according to the protocol adopted by the CV-QKD system, and send the modulated optical signal to the adjustable optical attenuation device. The adjustable optical attenuation module is used to attenuate the optical signal according to the modulation variance requirements given by the system, and output the attenuated optical quantum signal to the channel. The tunable light attenuation module includes at least two cascaded on-chip tunable light attenuation devices based on the MZ interference structure; by cascading several on-chip tunable light attenuation devices based on the MZ interference structure, the sensitivity of the light attenuation coefficient of the tunable light attenuation module to temperature fluctuations is reduced. The on-chip tunable optical attenuation device based on the MZ interference structure includes: an optical beam splitter, a first interferometer arm, a second interferometer arm, and an optical beam combiner unit; The optical beam splitting unit is connected to the first interferometer arm and the second interferometer arm respectively. The first interferometer arm is provided with a first thermal phase shifting unit, and the second interferometer arm is provided with a second thermal phase shifting unit. The first thermal phase shifting unit and the second thermal phase shifting unit are respectively connected to the optical beam combining unit. The optical beam splitter unit is used to split the incident light signal into two beams, and to make the two beams have different transmission coefficients. and The light enters the first and second interferometer arms; the first thermal phase-shifting unit is used to introduce a phase change into the light field passing through the first interferometer arm. The second thermal phase-shifting unit is used to introduce a phase change into the optical field passing through the second interferometer arm. The optical beam combining unit is used to combine the light fields that have passed through the first thermal phase shift unit and the second thermal phase shift unit to form an output light field. The tunable light attenuation device is used to attenuate the incident light signal to a weak quantum signal; the first and second interferometer arms are unbalanced, and the sensitivity of the light attenuation coefficient of the tunable light attenuation device to temperature fluctuations is reduced by using the tunable light attenuation device with unbalanced interferometer arms. The transmission coefficients of the two beams split by the optical beam splitter are unbalanced, which causes the first and second interference arms in any adjustable optical attenuation device to be unbalanced.

2. The CV-QKD system according to claim 1, characterized in that, The output light field of the incident light signal after passing through the tunable light attenuation device is: in, The output light field of the tunable light attenuation device. The light field for the incident light signal input to the tunable light attenuator, The transmittance coefficient of the optical signal after passing through the first thermal phase-shifting unit. The transmittance coefficient of the optical signal after passing through the second thermal phase-shifting unit.

3. The CV-QKD system according to claim 2, characterized in that, The intensity of the output light field after the incident light signal passes through the tunable light attenuation device can be characterized as follows: in, To adjust the output light intensity of the light attenuation device, Input light intensity to the adjustable light attenuation device. The relative phase difference between the first and second interferometer arms is given.

4. The CV-QKD system according to claim 3, characterized in that, The adjustable light attenuation function is achieved by changing the relative phase difference between the first and second interferometer arms; the light attenuation coefficient of the adjustable light attenuation device is: 。 5. The CV-QKD system according to claim 1, characterized in that, After several on-chip tunable optical attenuation devices based on the MZ interference structure are cascaded, the phase fluctuation generated by the first thermal phase shift unit and the second thermal phase shift unit when the temperature fluctuates is as follows: in, Let λ represent the phase fluctuation, and λ be the wavelength of the incident light signal. The length of the heat-shifting phase shifter along the direction of light transmission. Due to temperature fluctuations, is the thermo-optic coefficient, and n is the refractive index.

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