CN116418493A - Polarization coding chip and coding method for quantum key distribution - Google Patents
Polarization coding chip and coding method for quantum key distribution Download PDFInfo
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Abstract
The invention discloses a polarization coding chip and a coding method for quantum key distribution. The three phase modulators are arranged in the polarization coding unit, so that polarization coding can be realized at low driving voltage and fewer levels, monitoring and compensation devices are not needed, and the chip is easier to realize and has better high-low temperature stability. In addition, by arranging the pre-compensation unit realized by the phase modulator outside the polarization coding unit, the attenuation change introduced by the phase modulator in the polarization coding process can be compensated, so that the total attenuation generated by the polarization coding module on the optical signal is a fixed value, the power balance of different polarization states is effectively ensured, the quantum key distribution requirement is met, the correction of power imbalance is not needed, and the safe code rate is improved.
Description
Technical Field
The invention relates to the field of quantum secret communication, in particular to a polarization coding chip and a coding method for quantum key distribution.
Background
Quantum Key Distribution (QKD) is based on quantum mechanics principles, which is a key distribution system that can prove unconditionally secure by theory due to quantum unclonable and mismeasurable principles.
Quantum key distribution often involves complex optical signal encoding and decoding processes, and currently often implements the required encoder and decoder based on a combination of conventional fiber optics, which is bulky and costly.
The polarization encoding scheme is one of the mainstream quantum key distribution schemes, which is mainly implemented by means of a polarization encoding process based on phase modulation, namely: for two component lights with polarization states of |H > and |V >, respectively, a phase difference is formed between the two component lights by phase modulation
The two components will form a polarization state of +.>
Is provided. It follows that the phase difference between the two components of the input optical signal can be adjusted by the phase modulator +.>
The desired polarization encoding is achieved on the optical signal.
Currently, the mainstream polarization encoder is realized by means of a combination of an optical fiber device and a polarization-preserving phase modulator, and the polarization encoder is generally large in size and high in cost. For this reason, solutions for implementing optical signal encoding and decoding on optical chips are proposed in the prior art, thereby providing an important solution idea for implementing a small-volume, low-cost and highly stable quantum key distribution device.
Fig. 1 shows a prior art polarization encoding QKD system based on a silicon-based integrated chip that constructs a polarization encoder from a beam splitter, a polarization rotating combiner, and a silicon-based phase shifter.
In QKD systems, silicon-based phase modulators based on the principle of plasma dispersion effect have the common problem of modulation-related losses, i.e. the attenuation of the phase-change phase is correspondingly different when it is modulated out. Therefore, when the QKD system modulates different polarization states, there will be a difference in attenuation of the input optical signal, which ultimately results in unbalanced power of the output polarized optical signal. However, in quantum key distribution, it is theoretically necessary that the remaining dimensions other than the polarization state are indistinguishable. Thus, the prior art proposes to solve this problem by sacrificing a certain safe bitrate, but such a reduction of the bitrate is also disadvantageous for quantum key distribution.
In addition, polarization modulation in QKD systems is achieved based on phase adjustment, and the output light polarization state can be written as
Which is related to the modulated phase difference. The half-wave voltage (the driving voltage required to achieve pi phase shift) of current silicon-based phase modulators is typically large. For quantum key distribution it is generally at least necessary to encode with 4 polarization states, e.g.>
When the encoder outputs |+ >; />
When the encoder outputs |R >; />
When the encoder outputs >;
when the encoder outputs |L >. For this reason, the maximum driving voltage often needs to reach 1.5 times the half-wave voltage, and it is also necessary that high-speed switching between 4 different levels (0, 0.5 times the half-wave voltage, and 1.5 times the half-wave voltage) can be achieved. As such, high demands are placed on the driving circuitry, requiring the use of complex schemes and expensive devices, and even being impractical. Further, as the driving voltage increases, devices such as a power amplifier are often required. When a level 4 is required in quantum key distribution, the power amplifier works at different working points, and finally the output driving voltage is influenced by environmental factors such as temperature, so that a large coding error can be introduced, which often requires a monitoring and compensating unit to be designed for compensation, but the monitoring and compensating unit has high technical complexity and cost.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a polarization coding chip and a coding method for quantum key distribution. The polarization encoding unit is provided with three phase modulators, so that polarization encoding can be realized at lower driving voltage and fewer different levels, and a complex monitoring and compensating device is not required to be introduced on a chip, so that the polarization encoding chip is easier to realize and has better high-low temperature stability. In addition, by arranging the precompensation unit realized by the phase modulator outside the polarization coding unit, when the attenuation change phenomenon is generated when the optical signal is subjected to different polarization coding, the additional modulation phase is loaded on the optical signal corresponding to the modulation phase of the phase modulator in the polarization coding unit, and additional attenuation is introduced, so that the total attenuation generated by the polarization coding module on the optical signal is ensured to be a preset fixed value, the power balance of different polarization states is effectively ensured, the quantum key distribution requirement is more met, the correction of power imbalance is not needed, and the safe code rate is improved.
A first aspect of the present invention relates to an on-chip polarization encoding method for quantum key distribution, comprising a decoy state encoding step, an intensity modulation step, and a polarization encoding step;
the decoy state encoding step is used for performing decoy state encoding on the optical signal;
the intensity modulation step is used for modulating the intensity of the optical signal;
the polarization encoding step is used for polarization encoding the optical signal and comprises an encoding sub-step;
in the encoding substep, splitting the optical signal into first and second components; performing two-time phase modulation on the first component, wherein the modulation phases are respectively the first phase
And second phase->
On the second componentLine one-time phase modulation with a modulation phase of third phase +>
And polarization combining the phase modulated first and second components, j=1.
Further, in the encoding sub-step, the first phase
Second phase->
And a third phase
Is arranged to form a phase difference between said first and second components>
Said phase difference->
Selected from a predetermined first set of phases.
Further, the polarization encoding step further includes a pre-compensation sub-step for performing phase modulation on the optical signal, wherein the modulation phase is a fourth phase
The fourth phase
Is set such that the total attenuation value IL of the optical signal in the polarization encoding step is a fixed value.
Still further, the polarization encoding step further includes a fixed value setting sub-step in which the fourth phase is caused to be
At zero, record the phase difference +.>
And setting the maximum value of the total attenuation values IL (j) at the time of taking the values in the first phase set as the fixed value.
Optionally, the first set of phases includes 0, pi/2, pi, and 3 pi/2. Wherein the phase combination formed by the first phase, the second phase and the third phase
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
A second aspect of the invention relates to a polarization encoding chip for quantum key distribution, comprising a decoy-state encoding module, an intensity modulation module, and a polarization encoding module;
the decoy state encoding module is configured to decoy state encode the optical signal;
the intensity modulation module is configured to intensity modulate the optical signal;
the polarization coding module is used for polarization coding of the optical signal and comprises a polarization coding unit;
the polarization encoding unit comprises a first optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator and a polarization beam combiner; wherein,,
the first optical splitter is arranged to split the optical signal into first and second components;
the first, second and third phase modulators are disposed between the first optical splitter and the polarization beam combiner, wherein the first phase modulator is configured to modulate a first phase on the first component
Said second phase modulator for modulating a second phase +.>
Said third phase modulator for modulating a third phase +.>
The polarization beam combiner is arranged to combine the first and second components.
Further, the first phase
Second phase->
And a third phase->
Is arranged to form a phase difference between said first and second components>
Said phase difference->
Selected from a predetermined first set of phases.
Further, the polarization encoding module further comprises a pre-compensation unit;
the precompensation unit comprises a fourth phase modulator for modulating the optical signal with a fourth phase
The fourth phase
Is set such that the total attenuation value IL of the optical signal in the polarization encoding module is a fixed value.
Further, the fixed value is at the fourth phase
When zero, the phase difference ∈>
The maximum of the total attenuation values IL (j) at the time of the values in the first phase set.
Optionally, the first set of phases includes 0, pi/2, pi, and 3 pi/2. Wherein the phase combination formed by the first phase, the second phase and the third phase
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
Further, the decoy-state encoding module includes a mach-zehnder interferometer having a second optical splitter, a fifth phase modulator, a sixth phase modulator, and a third optical splitter;
the second optical splitter is arranged to split the optical signal into two components;
the fifth phase modulator is arranged for phase modulating one of the two components;
the sixth phase modulator is arranged for phase modulating the other of the two components;
the third beam splitter is arranged to interfere the two components.
Preferably, the first output end of the third optical beam splitter is connected with a tunable optical attenuator; and/or the second output end of the third optical beam splitter is connected with a photodiode.
Optionally, the tunable optical attenuator is implemented based on a carrier injection principle or is implemented based on a mach-zehnder interferometer; and/or the photodiode is a germanium photodiode formed by epitaxial growth on a silicon material.
Further, the intensity modulation module includes a fourth optical splitter, a seventh phase modulator, and the first optical splitter.
Preferably, the optical beam splitter is a multimode interferometer or a directional coupler; and/or the polarization beam combiner is a two-dimensional grating; and/or the phase modulator is a high-speed phase modulator formed based on the principle of plasma dispersion effect; and/or, the sixth and seventh phase modulators are low-speed phase modulators implemented based on thermo-optical effect; and/or the polarization coding chip is made of silicon.
Drawings
The following describes the embodiments of the present invention in further detail with reference to the drawings.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 illustrates a prior art polarization encoded QKD system based on a silicon-based integrated chip;
fig. 2 shows an example of a polarization encoding chip for quantum key distribution according to the present invention.
Detailed Description
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are provided by way of illustration to fully convey the spirit of the invention to those skilled in the art to which the invention pertains. Thus, the present invention is not limited to the embodiments disclosed herein.
Fig. 2 shows an example of a polarization encoding chip for quantum key distribution according to the present invention.
As shown in fig. 2, the polarization encoding chip according to the present invention may include a decoy state encoding module, an intensity modulation module, and a polarization encoding module for decoy state encoding, intensity modulation, and polarization encoding of an optical signal, respectively. Wherein the polarization encoding chip receives an input optical signal via the input waveguide 100 and outputs a polarization encoded optical signal outwards through the output waveguide 800.
In the present invention, the polarization encoding module includes a polarization encoding unit for implementing polarization encoding on the optical signal. As shown in fig. 2, the polarization encoding unit may include a first beam splitter 204, a polarization beam combiner 700, and first, second, and third phase modulators 303, 304, and 305 disposed between the first beam splitter 204 and the polarization beam combiner 700.
In the polarization encoding unit, the first optical beam splitter 204 splits an optical signal into first and second components, and outputs the first and second components via first and second beam splitting ends thereof, respectively.
The first beam splitting end of the first beam splitter 204 is connected to a first input of the polarization beam combiner 700 by a first waveguide and the second beam splitting end is connected to a second input of the polarization beam combiner 700 by a second waveguide, thereby allowing the first and second components to be transmitted to the polarization beam combiner 700.
At polarization combiner 700, the first and second components are polarization combined to form a polarization encoded optical signal and output out through output waveguide 800.
The first waveguide has formed thereon first and second phase modulators 303, 304 to allow the first component to be phase modulated twice before it reaches the polarization beam combiner 700, wherein the first phase modulator 303 modulates the first phase on the first component
The second phase modulator 304 is atModulating the second phase on the first component>
At the same time, a third phase modulator 305 is formed on the second waveguide for modulating a third phase thereon before the second component reaches the polarization beam combiner 700
Where j=1,..and N, N are natural numbers.
Thus, during polarization encoding, the first phase can be allowed to be set reasonably
Second phase->
And a third phase->
Is a combination of the first and second components, a phase difference corresponding to the polarization encoding is formed between the first and second components>
Wherein (1)>
The first set of phases may be selected which corresponds to the polarization states to be encoded in the employed polarization encoding scheme.
For example, for a conventional four-polarization coding scheme, it is desirable to code between four polarization states, |++ >, R >, |- > and L >. Accordingly, it is necessary to form a phase difference of 0, pi/2, pi and 3 pi/2 in size between the first and second components
At this time, the first phase set is [0, pi/2, pi, 3 pi/2]Wherein n=4.
As previously described, with the aid of the polarization braiding of the present inventionCode elements, which can utilize a first phase
Second phase->
And a third phase->
Is to achieve this phase difference +.>
The first phase is shown in
Second phase->
And a third phase->
By means of which phase difference +_in the first phase set required for polarization encoding can be achieved>
(Table I)
It can be seen that with the polarization encoding unit of the present invention, a maximum of pi/2 modulation phase is provided by the phase modulator when the four polarization states required for the polarization encoding scheme are implemented. Namely, the maximum driving voltage required by the polarization encoding unit is only 0.5 times of half-wave voltage, which is reduced to 1/3 of the maximum driving voltage required by the prior art, so that the driving voltage of the polarization encoding unit can be obviously reduced, and the requirement on a driving circuit is reduced. Meanwhile, it is also noted that in the polarization encoding unit of the present invention, the modulation phase of each phase modulator only needs to be switched between 0 and pi/2, in other words, the driving signal for the phase modulator only needs to be switched between two different levels, which is only half of four level signals required by the existing scheme in number, which significantly reduces the complexity of the driving circuit control process and improves the usability and stability thereof. Therefore, the polarization coding chip adopting the polarization coding unit can adopt lower driving voltage, is easier to realize, has good high-low temperature stability, does not need to carry out complex monitoring and compensation, and does not remarkably increase the cost and the volume.
Further, it is considered that the attenuation imbalance of the existing polarization encoding process is caused by that it introduces different attenuation on the optical signal when different polarization encoding is performed. Therefore, as shown in fig. 2, the invention also introduces a pre-compensation unit in the polarization encoding module, which is used for adding a link for carrying out attenuation pre-compensation on the optical signal based on the original polarization encoding process, compensating the attenuation difference in the polarization encoding process, and ensuring that the total attenuation value generated by the polarization encoding module on the optical signal is a fixed value when encoding different polarization states, namely, different polarized optical signals output by the polarization encoding module have the same power (light intensity).
Furthermore, as shown in fig. 2, the precompensation unit of the present invention does not use a conventional intensity modulation device or a functional structure, such as an intensity modulator, but is proposed to implement the precompensation unit by means of a fourth phase modulator 302 for a special application scenario of a polarization encoding chip. Conventional devices such as intensity modulators, while having power conditioning functionality, are not well suited to solving the problem of attenuation imbalance of polarization encoding chips. In the existing encoding chip, the difference in attenuation values of the phase modulator corresponding to different modulation phases is relatively small, and thus high power adjustment accuracy is required in compensating for such difference. In contrast, conventional power conditioning devices, such as intensity modulators, have excessive tuning ranges that require complex control procedures to achieve such attenuation compensation; meanwhile, the structure of the power regulating device is relatively complex, the complexity of the chip preparation process is unnecessarily increased, and the miniaturization of the power regulating device is also not facilitated.
In the precompensation unit of the present invention, the passive variation in one phase modulator is compensated for by the active variation in the attenuation of the other phase modulator, thereby overcoming the problem of attenuation imbalance caused by such undesired variation in attenuation values. Furthermore, the pre-compensation unit of the present invention may have the same characteristics as the phase modulator in the polarization encoding unit, thus allowing the required attenuation compensation to be provided in a very simple manner, and with a compensation accuracy consistent with the attenuation variation accuracy in the polarization encoding unit, enabling the required attenuation compensation to be achieved very accurately; and both have consistent environmental stability, thus allowing a stable compensation effect to be provided. At the same time, the precompensation unit implemented with the aid of the phase modulator requires a relatively simple manufacturing process and a relatively small size, which is very advantageous for the chip.
Specifically, in the precompensation unit of the present invention, the fourth phase modulator 302 may perform phase modulation on the optical signal, where the modulation phase is the fourth phase
Thereby realizing a fourth phase +.>
The corresponding attenuation is used as attenuation precompensation.
In the present invention, by properly setting the fourth phase in the precompensation unit
The total attenuation value IL of the optical signal in the polarization encoding module is always kept at a fixed value.
For this purpose, this fixed value may be set in advance by means of a fixed value setting step. As an example, in the fixed value setting step, the fourth phase may be caused to be
Each phase value in the first phase set is set as a phase difference
And recording the total attenuation value IL (j) generated by the polarization encoding module on the optical signal. Therefore, the maximum value of the total attenuation values IL (j) can be set to a fixed value.
Thereafter, a plurality of fourth phases for making the total attenuation value IL of the encoding coding module a fixed value may also be acquired in advance
And phase difference->
Is a phase combination of (a) and (b). Therefore, in performing polarization encoding, it is possible to easily perform the +.>
Determining the fourth phase +.>
Thus, a phase difference +_can be formed between the first and second components at the polarization encoding unit>
The fourth phase modulator 302 in the precompensation unit is used to apply a fourth phase to the optical signal>
The phase modulation of the polarization encoding module ensures that the total attenuation value IL generated on the optical signal when the polarization encoding module performs polarization encoding is a preset fixed value. Thus, the polarization encoding module can be allowed to stably output optical signals having different polarization states but the same power.
As shown in fig. 2, the decoy state encoding module may be implemented by means of a mach-zehnder interferometer having, as an example, a second optical splitter 201, a fifth phase modulator 301, a sixth phase modulator 401 and a third optical splitter 202.
In the decoy-state encoding module, the second optical beam splitter 201 is used to split the optical signal into two components, and the fifth phase modulator 301 and the sixth phase modulator 401 each phase modulate one of the two components, and the modulated two components finally interfere at the third optical beam splitter 202. Thus, by adjusting the amount of modulation phase provided by the fifth phase modulator 301, decoy-state encoding of the optical signal (e.g., generating signal states and decoy states) may be achieved. Wherein the sixth phase modulator 401 may be adjusted prior to the decoy encoding so that the mach-zehnder interferometer is at the correct operating point.
Preferably, an adjustable optical attenuator 500 and a photodiode 600 may also be connected at both outputs of the third optical splitter 202, respectively, thereby allowing the power of the input optical signal to be monitored by means of the photodiode 600, the optical signal being attenuated to a single photon level by means of the adjustable optical attenuator 500.
As an example, the tunable optical attenuator 500 may be implemented based on carrier injection principles or based on a mach-zehnder interferometer.
As an example, the photodiode 600 may be a germanium photodiode formed epitaxially on a silicon material.
With continued reference to fig. 2, the intensity modulation module may be implemented by way of example with a fourth optical splitter 203, a seventh phase modulator 402, and a first optical splitter 204. It will be appreciated by those skilled in the art that in the intensity modulation module, the optical signal may be intensity modulated by adjusting the modulation phase of the seventh phase modulator 402.
In a preferred example, the polarization encoding chip may be formed of a silicon material. For example, the first to seventh phase modulators, the first to fourth optical splitters, the polarization beam combiner 700, and the corresponding waveguides may be implemented with silicon materials.
Preferably, the first to fourth optical splitters may be multimode interferometers or directional couplers.
Preferably, the polarization beam combiner 700 may be a polarization rotating beam combiner, such as a two-dimensional grating.
Preferably, the first to seventh phase modulators may be high-speed phase modulators formed based on the principle of the plasma dispersion effect, which may be, for example, a carrier deposition type, a carrier injection type, or a carrier depletion type.
In addition, the sixth and seventh phase modulators may also be low-speed phase modulators implemented based on thermo-optic effects.
In conclusion, by means of the polarization encoding chip, power balance of different polarization states can be effectively guaranteed, the quantum key distribution requirement is met, correction of power imbalance is not needed, and therefore the safe code rate is improved. In addition, polarization state encoding can be realized with lower driving voltage and fewer different levels, so that complex monitoring and compensation processes are not required to be introduced on a chip, and the polarization encoding chip is easier to realize and has better high-low temperature stability.
Meanwhile, the invention also discloses an on-chip polarization coding method for quantum key distribution, which comprises a decoy state coding step, an intensity modulation step and a polarization coding step. The optical signal is encoded in a decoy state, the intensity modulation step is used for modulating the intensity of the optical signal, and the polarization encoding step is used for encoding the polarization of the optical signal.
The polarization encoding step of the invention may comprise a coding sub-step, wherein: splitting the optical signal into first and second components; performing two phase modulations on the first component, wherein the modulation phases are respectively the first phase
And a second phase
And performing a phase modulation on the second component with a modulation phase of a third phase +.>
Then, the process is carried out,the phase modulated first and second components are polarization combined to produce a polarization encoded optical signal.
In the encoding step, the first phase
Second phase->
And a third phase->
Is arranged to form a phase difference between the first and second components>
Wherein the phase difference delta->
Selected from a predetermined first set of phases.
For a first phase set comprising phases 0, pi/2, pi and 3 pi/2, etc., one can correspondingly select from the phase set sets [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]Is selected from the phase combinations formed by the first phase, the second phase and the third phase
Thereby allowing the polarization encoding required for the polarization encoding scheme to be achieved at lower driving voltages.
Further, the polarization encoding step of the present invention may further comprise a pre-compensation sub-step for performing a fourth phase on the optical signal
Is used for the phase modulation of the (a). Therefore, the fourth phase can be properly configured by encoding according to polarization
So that the optical signal is subjected to a polarization encoding stepThe total attenuation value IL in (a) is a fixed value.
To determine the fixed value, the polarization encoding step may further comprise a fixed value setting sub-step in which the fourth phase is caused to be
Zero, record phase difference +.>
The total attenuation value IL (j) at the time of the value in the first phase set is set to the maximum value of the total attenuation values IL (j). Therefore, attenuation changes introduced on the optical signal during different polarization state encoding in the polarization encoding process can be compensated, and the optical signal is ensured to have a fixed total attenuation value in the polarization encoding step, so that the polarization encoding more conforming to quantum key distribution is obtained.
While the invention has been described in connection with the specific embodiments illustrated in the drawings, it will be readily appreciated by those skilled in the art that the above embodiments are merely illustrative of the principles of the invention, which are not intended to limit the scope of the invention, and various combinations, modifications and equivalents of the above embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (17)
1. An on-chip polarization encoding method for quantum key distribution, comprising a decoy state encoding step, an intensity modulation step, and a polarization encoding step;
the decoy state encoding step is used for performing decoy state encoding on the optical signal;
the intensity modulation step is used for modulating the intensity of the optical signal;
the polarization encoding step is used for polarization encoding the optical signal and comprises an encoding sub-step;
in the encoding substep, splitting the optical signal into first and second components; performing two-time phase modulation on the first component, wherein the modulation phases are respectively the first phase
And second phase->
Performing a phase modulation on said second component with a modulation phase of a third phase +.>
And polarization combining the phase modulated first and second components, j=1, N being a natural number.
2. The on-chip polarization encoding method of claim 1, wherein in the encoding sub-step, the first phase
Second phase->
And a third phase->
Is arranged to form a phase difference between the first and second components
Said phase difference->
Selected from a predetermined first set of phases.
3. The on-chip polarization encoding method of claim 2, wherein the polarization encoding step further comprises a pre-compensation sub-step for phase modulating the optical signal with a modulation phase of a fourth phase
The fourth phase
Is set such that the total attenuation value IL of the optical signal in the polarization encoding step is a fixed value.
4. The on-chip polarization encoding method of claim 3, wherein the polarization encoding step further comprises a fixed value setting sub-step in which the fourth phase is caused to be
At zero, record the phase difference +.>
And setting the maximum value of the total attenuation values IL (j) at the time of taking the values in the first phase set as the fixed value.
5. An on-chip polarization encoding method according to any one of claims 2 to 4, wherein the first phase set comprises 0, pi/2, pi and 3 pi/2.
6. An on-chip polarization encoding method as claimed in claim 5, wherein a phase combination formed by the first phase, the second phase and the third phase
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
7. A polarization encoding chip for quantum key distribution, comprising a decoy state encoding module, an intensity modulation module and a polarization encoding module;
the decoy state encoding module is configured to decoy state encode the optical signal;
the intensity modulation module is configured to intensity modulate the optical signal;
the polarization coding module is used for polarization coding of the optical signal and comprises a polarization coding unit;
the polarization encoding unit comprises a first optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator and a polarization beam combiner; wherein,,
the first optical splitter is arranged to split the optical signal into first and second components;
the first, second and third phase modulators are disposed between the first optical splitter and the polarization beam combiner, wherein the first phase modulator is configured to modulate a first phase on the first component
Said second phase modulator for modulating a second phase +.>
Said third phase modulator for modulating a third phase +.>
The polarization beam combiner is arranged to combine the first and second components.
8. The polarization encoding chip of claim 7, wherein the first phase
Second phase->
And a third phase->
Is arranged to form a phase difference between said first and second components>
Said phase difference->
Selected from a predetermined first set of phases.
9. The polarization encoding chip of claim 8, wherein the polarization encoding module further comprises a pre-compensation unit;
the precompensation unit comprises a fourth phase modulator for modulating the optical signal with a fourth phase
The fourth phase
Is set such that the total attenuation value IL of the optical signal in the polarization encoding module is a fixed value.
10. The polarization encoding chip of claim 9, wherein the fixed value is at the fourth phase
When zero, the phase difference ∈>
The maximum of the total attenuation values IL (j) at the time of the values in the first phase set.
11. The polarization encoding chip of claim 8, wherein the first set of phases comprises 0, pi/2, pi, and 3 pi/2.
12. The polarization-encoding chip of claim 11, wherein a phase combination formed by the first, second, and third phases
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
13. The polarization encoding chip of any one of claims 7 to 12, wherein the decoy-state encoding module comprises a mach-zehnder interferometer having a second optical splitter, a fifth phase modulator, a sixth phase modulator, and a third optical splitter;
the second optical splitter is arranged to split the optical signal into two components;
the fifth phase modulator is arranged for phase modulating one of the two components;
the sixth phase modulator is arranged for phase modulating the other of the two components;
the third beam splitter is arranged to interfere the two components.
14. The polarization encoding chip of claim 13, wherein the first output end of the third optical beam splitter is connected with a tunable optical attenuator; and/or the second output end of the third optical beam splitter is connected with a photodiode.
15. The polarization-encoding chip of claim 14, wherein the tunable optical attenuator is implemented based on carrier injection principles or on a mach-zehnder interferometer; and/or the photodiode is a germanium photodiode formed by epitaxial growth on a silicon material.
16. The polarization-encoding chip of claim 13, wherein the intensity modulation module comprises a fourth optical splitter, a seventh phase modulator, and the first optical splitter.
17. The polarization encoding chip of claim 16, wherein:
the optical beam splitter is a multimode interferometer or a directional coupler; and/or the number of the groups of groups,
the polarization beam combiner is a two-dimensional grating; and/or the number of the groups of groups,
the phase modulator is a high-speed phase modulator formed based on the principle of plasma dispersion effect; and/or the number of the groups of groups,
the sixth and seventh phase modulators are low-speed phase modulators realized based on thermo-optical effect; and/or the number of the groups of groups,
the polarization coding chip is made of silicon.
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