CN110224819B - An On-Chip Decoder for Temporal BB84 Protocol - Google Patents

Abstract

An on-chip decoder for time BB84 protocol and a decoding method, the decoder comprises: an input waveguide (100); a 1×2 optical beam splitter (200) for dividing received signal light into two beams of equal intensity signal light; the optical delay line (300) is used to delay the signal light; the adjustable optical attenuator (400) is used to make the light intensity of the signal light and the signal delayed by the optical delay line (300) The light intensity is consistent; the phase offset modulator (500) is used to adjust the phase of the received signal light; the 2×2 interference coupler (600) is used to perform Hermitian operation on the received signal light; output The waveguide (700) is used for outputting the signal light. The decoder and decoding method can passively demodulate any four quantum state signal light satisfying the time BB84 protocol, and for the phase drift in the fiber channel and interference loop, the device can achieve precise compensation through on-chip regulation.

Description

An On-Chip Decoder for Temporal BB84 Protocol

technical field

The invention relates to the technical field of quantum communication and integrated optics, in particular to an on-chip decoder and a decoding method for time BB84 protocol.

Background technique

Currently recognized quantum key distribution devices are mainly based on traditional discrete optical prisms or optical fiber devices, which are bulky, difficult to integrate, and high cost, which is not conducive to large-scale commercialization. With the development of silicon-based photonics, the functions of discrete optical devices can gradually be realized on-chip, which facilitates integration. At the same time, large-scale and low-cost mass production can be achieved by using mature silicon device processing platforms. So people began to try to integrate the devices and subsystems required for quantum key distribution devices on a chip. For the quantum key distribution of the time BB84 protocol, the setting of the demodulation end generally corresponds to the quantum state prepared by the transmitter end, that is, the detection base of the demodulation end is consistent with the preparation base of the transmitter end, and the BB84 protocol with different preparation bases cannot be demodulated At the same time, due to the effects of dispersion, temperature jitter, and interference ring instability in the general system, phase drift will inevitably be caused. Therefore, the traditional scheme needs to add constant temperature and shock absorption measures to the quantum key distribution system and make real-time system parameters. Monitoring to reduce phase drift, which results in additional cost and rate sacrifice.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

Based on the above technical problems, the present invention provides an on-chip decoder and a decoding method for the time BB84 protocol, which are used to solve the problem of the large volume and high cost of discrete components in the traditional solution, and the inability of the existing technology to prepare time BB84 based on different bases. Protocol demodulation, unable to achieve on-chip phase compensation and other issues.

(2) Technical solutions

In a first aspect, the present invention provides an on-chip decoder for temporal BB84 protocol, including: an input waveguide 100 for inputting signal light to be decoded;

The 1×2 optical beam splitter 200 includes a first optical beam splitter 201 , a second optical beam splitter 202 and a third optical beam splitter 203 , wherein the first optical beam splitter 201 divides the signal light to be decoded into equal The two beams of intensity are sent to the second optical beam splitter 202 and the third optical beam splitter 203 respectively, and then the second optical beam splitter 202 and the third optical beam splitter 203 further divide the received signal light into equal parts respectively. Intensity of two beams of signal light;

The optical delay line 300 is arranged between the first optical beam splitter 201 and the second optical beam splitter 202, and is used for delaying the signal light sent from the first optical beam splitter 201 to the second optical beam splitter 202 ;

The adjustable optical attenuator 400 is arranged between the first optical beam splitter 201 and the third optical beam splitter 203 , and is used to transmit the signal light from the first optical beam splitter 201 to the third optical beam splitter 203 The intensity is consistent with the light intensity of the signal light after the delay of the optical delay line 300;

The phase offset modulator 500 includes a first phase offset modulator 501, a second phase offset modulator 502, a third phase offset modulator 503 and a fourth phase offset modulator 504, and is used to adjust the input signal light phase;

The 2×2 interference coupler 600 includes a first interference coupler 601 , a second interference coupler 602 , a third interference coupler 603 and a fourth interference coupler 604 , which are respectively used to perform Hermitian operation on the received signal light. , wherein the first interference coupler 601 and the second interference coupler 602 are respectively arranged after the second optical beam splitter 202 and the third optical beam splitter 203 , in the two beams of signal light emitted by the second optical beam splitter 202 One of the beams is sent to the first interference coupler 601 through the first phase offset modulator 501, the other beam is sent to the second interference coupler 602, and one of the two beams of signal light emitted by the third optical beam splitter 203 The second interferometric coupler 602 is sent to the second interferometric coupler 602 through the second phase offset modulator 502, and the other beam is sent to the first interferometric coupler 601; Two beams of signal light sent by an interferometric coupler 601, one of which is modulated by the third phase offset modulator 503 and sent to the third interferometric coupler 603, and the fourth interferometric coupler 604 is arranged in the second interferometric coupler After 602, it is used to receive two beams of signal light sent by the second interference coupler 602, wherein one beam of signal light is modulated by the fourth phase offset modulator 504 and then sent to the fourth interference coupler 604;

The output waveguide 700 includes a first output waveguide 701, a second output waveguide 702, a third output waveguide 703 and a fourth output waveguide 704, wherein the first output waveguide 701 and the second output waveguide 702 are used to output a third interference coupler 603 The signal light after the Hermitian operation, the third output waveguide 703 and the fourth output waveguide 704 are used for outputting the signal light after the Hermitian operation by the fourth interference coupler 604 .

Optionally, the materials of the input waveguide 100 , the 1×2 optical beam splitter 200 , the optical delay line 300 , the tunable optical attenuator 400 , the phase bias modulator 500 , the 2×2 interference coupler 600 and the output waveguide 700 It is a silicon material and is processed by a process compatible with microelectronics.

Optionally, the input waveguide 100 and the output waveguide 700 are transmitted in the fundamental mode of the transverse electric field mode.

Optionally, the 1×2 optical beam splitter 200 adopts a 1×2 multimode interference coupler (1×2MMI); the 2×2 interference coupler 600 adopts a 2×2 multimode interference coupler (2×2MMI).

Optionally, the phase bias modulator 500 employs a thermo-optically tuned phase modulator.

Optionally, the optical delay line 300 adopts a waveguide surround structure to delay the signal light by extending the length of the waveguide.

Optionally, the time delay of the optical delay line 300 is the same as the time delay of two pulses in the quantum state encoded by the encoder of the time BB84 protocol.

Optionally, the tunable optical attenuator 400 adopts a thermo-optically tuned Mach-Zehnder interference structure.

Another aspect of the present invention provides a decoding method, comprising:

S1, input the signal light to be decoded through the input waveguide 100, wherein the signal light to be decoded is the quantum state signal light encoded by the time BB84 protocol, and it is a double pulse state with a certain time interval;

S2, the first optical beam splitter 201 receives the signal light to be decoded and divides it into two signal beams of equal intensity, which are respectively sent to the second optical beam splitter 202 and the third optical beam through the optical delay line 300 and the adjustable optical attenuator 400 The beam splitter 203, the optical delay line 300 makes the first pulse of the signal light sent to the second optical beam splitter 202 and the second one of the other signal light sent to the third optical beam splitter 203 The pulses realize the overlap of coherence time, and the adjustable optical attenuator 400 makes the intensity of the two beams of signal light consistent before reaching the second optical beam splitter 202 and the third optical beam splitter 203;

S3 , adjust the phase of the phase offset modulator 500 and use the 2×2 interference coupler 600 to perform Hermitian operation on the received signal light to obtain the signal light that meets the decoding requirements of the time BB84 protocol, and output the signal light through the output waveguide 700 .

(3) Beneficial effects

The invention provides an on-chip decoder and a decoding method for the time BB84 protocol. The whole device is processed by a process compatible with the microelectronic process, which can realize integrated and low-cost mass production. The thermo-optic effect of silicon material is used inside the device to realize a wide range of on-chip phase bias regulation. On this basis, combined with other logic devices, through phase adjustment, the time BB84 quantum key distribution protocol under different preparation bases is realized. At the same time, for the phase shift of the quantum state signal light in the fiber channel and the interference loop, the decoder can perform on-chip compensation through corresponding regulation to achieve accurate passive demodulation, reducing the extra cost caused by off-chip compensation measures. Cost and bitrate sacrifice.

Description of drawings

FIG. 1 schematically shows a schematic diagram of an on-chip decoder structure and an external detector used for the temporal BB84 protocol according to an embodiment of the present disclosure;

FIG. 2 schematically shows a flowchart of a decoding method for the temporal BB84 protocol according to an embodiment of the present disclosure;

3 schematically shows a schematic diagram of the composition of a quantum state of the time BB84 protocol according to an embodiment of the present disclosure and a schematic diagram of its orientation in a two-dimensional Hilbert space;

FIG. 4 schematically shows a schematic diagram of the orientation of four quantum states in the two-dimensional Hilbert space and three typical quantum state schematic diagrams of the BB84 protocol according to an embodiment of the present disclosure;

FIG. 5 schematically shows a quantum state signal optical evolution diagram of the on-chip decoder for the time BB84 protocol in the working state according to an embodiment of the present disclosure;

FIG. 6 schematically shows a decoded signal light diagram at the output waveguide under the decoding method for the temporal BB84 protocol according to the embodiment of the present disclosure.

[reference number]

100-input waveguide

200—1×2 beam splitter

201-first beam splitter 202-second beam splitter

203-Third beam splitter

300-optical delay line

400 - Adjustable Optical Attenuator

500-Phase Offset Modulator

501 - First Phase Offset Modulator 502 - Second Phase Offset Modulator

503 - Third Phase Offset Modulator 504 - Fourth Phase Offset Modulator

600-2×2 Interference Coupler

601-first interference coupler 602-second interference coupler

603-third interference coupler 604-fourth interference coupler

700 - Output Waveguide

701-First output waveguide 702-Second output waveguide

703 - Third output waveguide 704 - Fourth output waveguide

800-Detector

801-First external detector 802-Second external detector

803-Third external detector 804-Fourth external detector

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

In a first aspect, the present invention provides an on-chip decoder for the temporal BB84 protocol, see FIG. 1 , including:

The input waveguide 100 is used to input the signal light to be decoded.

Specifically, the input waveguide 100 is used to input the signal light to be decoded. In the embodiment of the present invention, the signal light is the quantum state signal light sent by the time BB84 protocol.

The 1×2 optical beam splitter 200 includes a first optical beam splitter 201, a second optical beam splitter 202 and a third optical beam splitter 203, and is used to split the input signal light into two signals of equal intensity Light.

Specifically, in the decoder of the embodiment of the present invention, the first optical beam splitter 201, the second optical beam splitter 202, and the third optical beam splitter 203 use 1×2 multi-mode interference couplers (1×2 MMI), The first optical beam splitter 201 divides the signal light to be decoded into two beams of equal intensity and sends them to the second optical beam splitter 202 and the third optical beam splitter 203 respectively, and then the second optical beam splitter 202 and the third optical beam splitter The beam splitter 203 further divides the received signal light into two signal lights of equal intensity respectively.

The optical delay line 300 is arranged between the first optical beam splitter 201 and the second optical beam splitter 202, and is used for delaying the signal light sent from the first optical beam splitter 201 to the second optical beam splitter 202 .

Specifically, in the decoder of the embodiment of the present invention, the optical delay line 300 adopts a waveguide surround structure. By extending the length of the waveguide, the signal light is delayed, and the time delay is the same as the time delay in the quantum state encoded by the encoder of the time BB84 protocol. The time delays of the two pulses are the same, so that the first pulse in the signal light sent to the second optical beam splitter 202 and the second pulse in the other signal light sent to the third optical beam splitter 203 The overlap of coherence times is achieved.

The adjustable optical attenuator 400 is used to attenuate the intensity of the input signal light.

Specifically, in the decoder of the embodiment of the present invention, the adjustable optical attenuator 400 adopts a thermal-optical tuning Mach-Zehnder interference structure, and is disposed between the first optical beam splitter 201 and the third optical beam splitter 203, so that The light intensity of the signal light sent by the first optical beam splitter 201 to the third optical beam splitter 203 is consistent with the light intensity of the signal light delayed by the optical delay line 300 .

The phase offset modulator 500 includes a first phase offset modulator 501, a second phase offset modulator 502, a third phase offset modulator 503 and a fourth phase offset modulator 504, and is used to adjust the input signal light phase.

Specifically, in the decoder of the embodiment of the present invention, the first phase offset modulator 501, the second phase offset modulator 502, the third phase offset modulator 503, and the fourth phase offset modulator 504 use thermo-optical Tuning the phase modulator, the first phase offset modulator 501 is used to adjust the phase of one of the two signal beams split by the second optical beam splitter 202, and the second phase offset modulator 502 Phase adjustment is performed on one of the two signal beams split by the two-beam splitter 203 , and the third phase offset modulator 503 is used to adjust one of the two signal beams output by the 2×2 interference coupler 601 The signal light beams are phase-adjusted, and the fourth phase offset modulator 504 performs phase adjustment on one of the two signal beams output by the 2×2 interference coupler 602 .

The 2×2 interference coupler 600 includes a first interference coupler 601 , a second interference coupler 602 , a third interference coupler 603 and a fourth interference coupler 604 , which are respectively used to perform Hermitian operation on the received signal light. .

Specifically, in the decoder of the embodiment of the present invention, the first interference coupler 601 , the second interference coupler 602 , the third interference coupler 603 , and the fourth interference coupler 604 use 2×2 multi-mode interference couplers (2 ×2MMI), the first interference coupler 601 and the second interference coupler 602 are respectively arranged after the second optical beam splitter 202 and the third optical beam splitter 203, and the two beams of signal light emitted by the second optical beam splitter 202 One of the beams is sent to the first interference coupler 601 through the first phase offset modulator 501, the other beam is sent to the second interference coupler 602, and one of the two beams of signal light emitted by the third optical beam splitter 203 The beam is sent to the second interferometric coupler 602 through the second phase offset modulator 502, and the other beam is sent to the first interferometric coupler 601; the third interferometric coupler 603 is arranged behind the first interferometric coupler 601 for receiving The two beams of signal light sent by the first interferometric coupler 601, one of which is modulated by the third phase offset modulator 503 and sent to the third interferometric coupler 603, and the fourth interferometric coupler 604 is provided in the second interferometric coupling After the second interferometric coupler 602 , it is used to receive two beams of signal light sent by the second interference coupler 602 , wherein one beam of signal light is modulated by the fourth phase offset modulator 504 and then sent to the fourth interference coupler 604 .

The output waveguide 700 includes a first output waveguide 701 , a second output waveguide 702 , a third output waveguide 703 and a fourth output waveguide 704 .

Specifically, the first output waveguide 701 and the second output waveguide 702 are used to output the signal light after the Hermitian operation of the third interference coupler 603 , and the third output waveguide 703 and the fourth output waveguide 704 are used to output the fourth interference coupler Signal light after 604 Hermitian operation.

In the decoder of the embodiment of the present invention, the input waveguide 100 , the 1×2 optical beam splitter 200 , the optical delay line 300 , the adjustable optical attenuator 400 , the phase offset modulator 500 , and the 2×2 interference coupler 600 And the material of the output waveguide 700 is silicon material, that is, the decoder is fabricated on a silicon substrate using a process compatible with general microelectronic processes. Both the input waveguide 100 and the output waveguide 700 adopt the fundamental mode transmission of the transverse electric field mode.

The output waveguide 700 is followed by an external detector 800. Specifically, the first output waveguide 701 is followed by a first external detector 801, the second output waveguide 702 is followed by a second external detector 802, and the third output waveguide 703 is followed by a third external detector. The detector 803, the fourth output waveguide 704 is followed by a fourth external detector 804.

In the second aspect, the embodiment of the present invention also provides a decoding method for the time BB84 protocol, which can passively demodulate the time BB84 protocol under different preparation bases. The following is to passively decode the time BB84 protocol under different preparation bases. The demodulation method is described in detail by taking the demodulation as an example. Referring to Figure 2, the method includes:

S1, input the signal light to be decoded into the waveguide 100, wherein the signal light to be decoded is the quantum state signal light sent by the time BB84 protocol;

其代表第一个脉冲强度为 cos²(θ/2)、第二个脉冲强度为sin²(θ/2)，且第二个脉冲相对于第一个脉冲的相位差为φ，使用量子力学算符表示如下：Specifically, the quantum state signal light sent by the time BB84 protocol consists of two adjacent pulses, and its basic structure and its orientation in the two-dimensional Hilbert space are shown in Figure 3. For the two-dimensional Hilbert space A quantum state with coordinates (θ, φ) in special space

It represents that the first pulse intensity is cos ² (θ/2), the second pulse intensity is sin ² (θ/2), and the phase difference of the second pulse relative to the first pulse is φ, using quantum mechanics The operator is represented as follows:

表示如下：The quantum state orthogonal to the (θ, φ) quantum state in a two-dimensional Hilbert space is its symmetry point (π-θ, φ+π) about the center of the sphere, using quantum mechanical operators

It is expressed as follows:

与

正交、

与

正交，两组量子态之间不正交。在二维希尔伯特空间中这四个量子态信号光显示为过球心圆上的四等分点，因此对应本发明实施例所公开的解码器，输入波导100的四种量子态信号光可以表示为：For the time BB84 protocol, it requires the encoding end to prepare two sets of different quantum state signal lights, as shown in Figure 4, the two quantum states in each set are orthogonal to each other, that is

and

orthogonal,

and

Orthogonal, the two sets of quantum states are not orthogonal. In the two-dimensional Hilbert space, the four quantum state signal lights are shown as passing through the quarter points on the central circle, so corresponding to the decoder disclosed in the embodiment of the present invention, the four quantum state signals input to the waveguide 100 Light can be expressed as:

S2, the first optical beam splitter 201 receives the signal light to be decoded and divides it into two signal beams of equal intensity, which are respectively sent to the second optical beam splitter 202 and the third optical beam through the optical delay line 300 and the adjustable optical attenuator 400 The beam splitter 203, the optical delay line 300 makes the first pulse of the signal light sent to the second optical beam splitter 202 and the second one of the other signal light sent to the third optical beam splitter 203 The pulses realize the overlap of coherence time, and the adjustable optical attenuator 400 makes the intensity of the two beams of signal light consistent before reaching the second optical beam splitter 202 and the third optical beam splitter 203;

Specifically, as shown in FIG. 5 , the first optical beam splitter 201 receives the quantum state signal light input from the input waveguide 100, and divides it into two equal-intensity signal lights, which respectively pass through the optical delay line 300 and the adjustable optical attenuator. 400 is sent to the second optical beam splitter 202 and the third optical beam splitter 203 . Set the attenuation of the adjustable optical attenuator 400 to be consistent with the attenuation brought by the optical delay line 300, so that the intensity of the two beams of signal light before reaching the second optical beam splitter 202 and the third optical beam splitter 203 is the same; The time delay of the optical delay line 300 is set to be the same as the time delay of the two pulses in the quantum state encoded by the encoder of the time BB84 protocol, so that the first one of the signal lights sent to the second optical beam splitter 202 The pulse and the second pulse in the other beam of signal light sent to the third optical beam splitter 203 achieve overlap in coherence time. So far, at the detection time point, the information of the first pulse of the quantum state signal light in the input waveguide 100 is transferred to the input end of the optical beam splitter 202 , and the information of the second pulse is transferred to the input of the optical beam splitter 203 . end;

S3 , adjust the phase of the phase offset modulator 500 and use the 2×2 interference coupler 600 to perform Hermitian operation on the received signal light to obtain the signal light that meets the time BB84 protocol decoding requirements, and output it through the output waveguide 700 .

For the time BB84 protocol, its passive decoder needs to realize two different demodulations with equal probability. The first demodulation can accurately respond to the first set of quantum state signals prepared by the encoder, and the second set of quantum state signals can respond accurately. The light responds randomly; the second kind of demodulation can respond accurately to the second group of quantum state signal light prepared by the coding end, and respond randomly to the first group of quantum state signal light. However, the decoder disclosed in the embodiment of the present invention can passively demodulate any four quantum state signal lights (as described in step S1) that satisfy the time BB84 protocol.

Specifically, in the decoder disclosed in the embodiment of the present invention, the first optical beam splitter 201 receives the quantum state signal light input from the input waveguide 100 and divides it into two equal-intensity signal lights, which pass through the optical delay line 300 and the signal light respectively. The adjustable optical attenuator 400 is sent to the second optical beam splitter 202 and the third optical beam splitter 203, and further divided into four equal-intensity signal lights (as shown in FIG. 5 ). Both the second optical beam splitter 202 and the third optical beam splitter 203 include an upper output terminal and a lower output terminal. The light enters the first group of demodulation components A (as shown by the solid line box in FIG. 1 ), and the signal light from the lower output end of the second optical beam splitter 202 and the lower output end of the third optical beam splitter 203 jointly enter The second group of demodulation components B (as shown by the solid line box in FIG. 1 ), since the second optical beam splitter 202 and the third optical beam splitter 203 both divide the input signal light into two beams of signal light with equal intensities , so the demodulation probability of two different demodulation components is the same. The first set of demodulation components A and the second set of demodulation components B both include two phase offset modulators 500 and two 2×2 interference couplers 600 .

和

其组件内各元件的等效厄米运算及联合厄米运算L1为：For the first group of demodulation components A, as shown in FIG. 1 and FIG. 5 , at the detection time point, the information of the first pulse and the second pulse of the quantum state signal light are respectively transferred to the two terminals of the first coupler 601 . input terminals, and the phases of the first modulator 501 and the third modulator 503 are set to be

and

The equivalent Hermitian operation and joint Hermitian operation L1 of each element in the component are:

Under the operation of L1, it is obtained:

会在如图1所示的第一外部探测器801处准确响应，量子态

会在第二外部探测器802处准确响应，同时由于四种量子态

以及

为过球心圆上的四等分点，因此第一外部探测器801以及第二外部探测器802对于量子态

和

的响应是随机的。From the above, the signal light at the output waveguides 701 and 702 is shown in FIG. 6 , that is, at the detection time point, the quantum state

will respond accurately at the first external detector 801 as shown in Figure 1, the quantum state

will respond accurately at the second external detector 802, while due to the four quantum states

as well as

is the quarter point on the center circle, so the first external detector 801 and the second external detector 802 are very sensitive to the quantum state

and

The response is random.

和

时，输出波导703、704处的信号光如图6所示，可使得在探测时间点上，量子态

在第三外部探测器803处准确响应，量子态

在第四外部探测器 804处准确响应，并且第三外部探测器803和第四外部探测器804对于量子态

和

的响应是随机的。Similarly, for the second group of demodulation components B, at the detection time point, the information of the first pulse and the second pulse of the quantum state signal light are respectively transferred to the two input ends of the first coupler 602, and set The phases of the second modulator 502 and the fourth modulator 504 are respectively

and

, the signal light at the output waveguides 703 and 704 is shown in FIG. 6 , so that at the detection time point, the quantum state

Accurate response at third external detector 803, quantum state

responds accurately at the fourth outer detector 804, and the third outer detector 803 and the fourth outer detector 804 are very sensitive to the quantum state

and

The response is random.

To sum up, the results of the four detectors under the above settings fully meet the decoding needs of the current time BB84 protocol, that is, the function of passively demodulating any four quantum states that meet the time BB84 protocol is realized.

More generally, the quantum states of three typical temporal BB84 protocols are shown in Fig. 4, which include:

Time BB84 protocol 1: The encoding terminal prepares four quantum states |0>, |1>, |+> and |->;

Time BB84 protocol 2: The coding end prepares four quantum states |0>, |1>, |+i> and |—i>;

Time BB84 protocol 3: The coding side prepares four quantum states |+>, |->, |+i> and |—i>;

The decoding settings of the decoder disclosed in the embodiment of the present invention to the above-mentioned three typical time BB84 protocols are shown in Table 1 below:

Table 1

In addition, when the quantum state signal has a phase shift due to channel transmission or interference loop deviation (that is, when the phase between the two pulses before and after changes), the decoder disclosed in the embodiment of the present invention can perform on-chip compensation through corresponding regulation. to achieve accurate passive demodulation.

以及

产生相位偏移时：when the quantum state

as well as

When a phase shift is generated:

It is only necessary to make corresponding adjustments to the first modulator 501 and the second modulator 502:

On-chip phase compensation of the quantum state can be performed to re-implement accurate passive demodulation, reducing the additional cost and code rate sacrifice caused by off-chip compensation measures.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. An on-chip decoder for a time BB84 protocol, comprising:

an input waveguide (100) for inputting signal light to be decoded;

a 1 × 2 optical splitter (200) including a first optical splitter (201), a second optical splitter (202), and a third optical splitter (203), wherein the first optical splitter (201) splits the signal light to be decoded into two beams of equal intensity and sends the two beams of equal intensity to the second optical splitter (202) and the third optical splitter (203), and then the second optical splitter (202) and the third optical splitter (203) further split the received signal light into two beams of equal intensity;

the optical delay line (300) is arranged between the first optical beam splitter (201) and the second optical beam splitter (202) and is used for delaying the signal light transmitted by the first optical beam splitter (201) to the second optical beam splitter (202);

the variable optical attenuator (400) is arranged between the first optical beam splitter (201) and the third optical beam splitter (203) and is used for enabling the light intensity of the signal light sent to the third optical beam splitter (203) by the first optical beam splitter (201) to be consistent with the light intensity of the signal light delayed by the optical delay line (300);

a phase offset modulator (500) including a first phase offset modulator (501), a second phase offset modulator (502), a third phase offset modulator (503), and a fourth phase offset modulator (504) for adjusting a phase of the input signal light;

a2 x 2 interference coupler (600) comprises a first interference coupler (601), a second interference coupler (602), a third interference coupler (603) and a fourth interference coupler (604) for respectively performing Hermitian operation on received signal light, wherein the first interference coupler (601) and the second interference coupler (602) are respectively arranged behind the second optical beam splitter (202) and the third optical beam splitter (203), one of the two signal lights emitted by the second optical beam splitter (202) is sent to a first interference coupler (601) through a first phase offset modulator (501), the other signal light is sent to a second interference coupler (602), one of the two signal lights emitted by the third optical beam splitter (203) is sent to the second interference coupler (602) through a second phase offset modulator (502), and the other signal light is sent to the first interference coupler (601); the third interference coupler (603) is arranged behind the first interference coupler (601) and is used for receiving two beams of signal light sent by the first interference coupler (601), wherein one beam of signal light is sent to the third interference coupler (603) after being modulated by the third phase offset modulator (503), the fourth interference coupler (604) is arranged behind the second interference coupler (602) and is used for receiving two beams of signal light sent by the second interference coupler (602), and one beam of signal light is sent to the fourth interference coupler (604) after being modulated by the fourth phase offset modulator (504);

an output waveguide (700) comprising a first output waveguide (701), a second output waveguide (702), a third output waveguide (703) and a fourth output waveguide (704), wherein the first output waveguide (701) and the second output waveguide (702) are used for outputting the signal light after Hermite operation of the third interference coupler (603), and the third output waveguide (703) and the fourth output waveguide (704) are used for outputting the signal light after Hermite operation of the fourth interference coupler (604);

the input waveguide (100), the 1 x 2 optical beam splitter (200), the optical delay line (300), the adjustable optical attenuator (400), the phase bias modulator (500), the 2 x 2 interference coupler (600) and the output waveguide (700) are made of silicon materials and are processed by adopting a process compatible with a microelectronic process;

the input waveguide (100) and the output waveguide (700) adopt fundamental mode transmission of transverse electric field modes.

2. The decoder of claim 1, said 1 x 2 optical splitter (200) employing a 1 x 2 multimode interference coupler; the 2 x 2 interference coupler (600) employs a 2 x 2 multimode interference coupler.

3. Decoder according to claim 1, the phase offset modulator (500) employing a thermo-optically tuned phase modulator.

4. The decoder of claim 1, wherein the optical delay line (300) is configured as a waveguide loop to delay the signal light by extending the waveguide length.

5. Decoder according to claim 1 or 4, the optical delay line (300) having a time delay identical to the time delay of two pulses in a quantum state encoded by an encoder of the time BB84 protocol.

6. The decoder of claim 1, the variable optical attenuator (400) employing a thermo-optically tuned mach-zehnder interference structure.

Images