CN110224819B - On-chip decoder for time BB84 protocol - Google Patents
On-chip decoder for time BB84 protocol Download PDFInfo
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- CN110224819B CN110224819B CN201910483830.7A CN201910483830A CN110224819B CN 110224819 B CN110224819 B CN 110224819B CN 201910483830 A CN201910483830 A CN 201910483830A CN 110224819 B CN110224819 B CN 110224819B
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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Abstract
An on-chip decoder and decoding method for a time BB84 protocol, the decoder comprising: an input waveguide (100); a 1 × 2 optical splitter (200) for splitting the received signal light into two signal lights of equal intensity; a light delay line (300) for delaying the signal light; a variable optical attenuator (400) for making the light intensity of the signal light consistent with the light intensity of the signal light delayed by the light delay line (300); a phase offset modulator (500) for adjusting the phase of the received signal light; a 2 × 2 interference coupler (600) for performing hermitian operations on the received signal light; an output waveguide (700) for outputting the signal light. The decoder and the decoding method can passively demodulate any four quantum state signal lights meeting the time BB84 protocol, and for phase drift in an optical fiber channel and an interference loop, the device can realize accurate compensation through on-chip regulation.
Description
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 a time BB84 protocol.
Background
The quantum key distribution device generally recognized at present is based on the traditional discrete optical prism or optical fiber device, and has the advantages of large volume, difficult integration, high cost and no contribution to large-scale commercialization. With the development of silicon-based photonics, the functions of discrete optical devices can be gradually realized on chip, so that integration is convenient, and meanwhile, large-scale low-cost mass production can be realized by utilizing a mature silicon device processing platform. Attempts have then been made to integrate the components and subsystems required for quantum key distribution devices on-chip. For time BB84 protocol quantum key distribution, the setting of the demodulation end generally corresponds to the quantum state prepared by the emission end, i.e. the detection base of the demodulation end is consistent with the preparation base of the emission end, and the BB84 protocols of different preparation bases cannot be demodulated; meanwhile, as the effects of dispersion, temperature jitter, unstable interference ring and the like in a general system can inevitably cause phase drift, the traditional scheme needs to add constant temperature and shock absorption measures in a quantum key distribution system and monitor system parameters in real time to reduce the phase drift, which can cause extra cost and code rate sacrifice.
Disclosure of Invention
Technical problem to be solved
Based on the technical problems, the invention provides an on-chip decoder and a decoding method for a time BB84 protocol, which are used for solving the problems that discrete elements in the traditional scheme are large in size and high in cost, and the time BB84 protocol under different preparation bases cannot be demodulated and on-chip phase compensation cannot be realized in the prior art.
(II) technical scheme
In a first aspect, the present invention provides 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 a signal light to be decoded into two beams with equal intensity and sends the two beams 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 with equal intensity;
a light delay line 300, disposed between the first optical splitter 201 and the second optical splitter 202, for delaying the signal light sent from the first optical splitter 201 to the second optical 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 for enabling the light intensity of the signal light transmitted 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 light 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 the phase of the input signal light;
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 configured to perform hermitian operations on received signal light, where the first interference coupler 601 and the second interference coupler 602 are respectively disposed behind the second optical beam splitter 202 and the third optical beam splitter 203, one of two beams of signal light emitted by the second optical beam splitter 202 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, one of two beams of signal light emitted by the third optical beam splitter 203 is sent to the second interference coupler 602 through the second phase offset modulator 502, and the other beam is sent to the first interference coupler 601; the third interference coupler 603 is arranged behind the first interference coupler 601 and is configured to receive two signal lights sent by the first interference coupler 601, wherein one signal light is modulated by the third phase offset modulator 503 and then sent to the third interference coupler 603, the fourth interference coupler 604 is arranged behind the second interference coupler 602 and is configured to receive two signal lights sent by the second interference coupler 602, and one 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, where the first output waveguide 701 and the second output waveguide 702 are used to output the signal light after hermitian operation by the third interference coupler 603, and the third output waveguide 703 and the fourth output waveguide 704 are used to output the signal light after hermitian operation by the fourth interference coupler 604.
Optionally, the input waveguide 100, the 1 × 2 optical splitter 200, the optical delay line 300, the adjustable optical attenuator 400, the phase offset modulator 500, the 2 × 2 interference coupler 600, and the output waveguide 700 are made of silicon materials and are processed by a process compatible with a microelectronic process.
Alternatively, the input waveguide 100 and the output waveguide 700 employ transverse electric field mode fundamental mode transmission.
Alternatively, the 1 × 2 optical splitter 200 employs a 1 × 2 multimode interference coupler (1 × 2 MMI); the 2 × 2 interference coupler 600 employs a 2 × 2 multimode interference coupler (2 × 2 MMI).
Alternatively, the phase offset modulator 500 employs a thermo-optically tuned phase modulator.
Alternatively, the light delay line 300 employs a waveguide surrounding structure to delay the signal light by extending the waveguide length.
Optionally, the time delay of the optical delay line 300 is the same as the time delay of two pulses in a quantum state encoded by an encoder of the time BB84 protocol.
Optionally, the tunable optical attenuator 400 employs a thermo-optically tuned Mach-Zehnder interference structure.
Another aspect of the present invention provides a decoding method, including:
s1, inputting signal light to be decoded through the input waveguide 100, wherein the signal light to be decoded is quantum state signal light encoded by the time BB84 protocol, which is a double-pulse state with a certain time interval;
s2, the first optical splitter 201 receives the signal light to be decoded and splits it into two signal lights with equal intensity, which are sent to the second optical splitter 202 and the third optical splitter 203 through the optical delay line 300 and the adjustable optical attenuator 400, the optical delay line 300 makes the first pulse in the signal light sent to the second optical splitter 202 and the second pulse in the other signal light sent to the third optical splitter 203 realize the overlapping of coherence time, the adjustable optical attenuator 400 makes the intensities of the two signal lights before reaching the second optical splitter 202 and the third optical splitter 203 consistent;
and S3, adjusting the phase of the phase offset modulator 500, performing Hermitian operation on the received signal light by using the 2 x 2 interference coupler 600 to obtain the signal light meeting the decoding requirement of the time BB84 protocol, and outputting the signal light through the output waveguide 700.
(III) advantageous effects
The invention provides an on-chip decoder and a decoding method for a time BB84 protocol, wherein the whole device is processed by adopting a process compatible with a microelectronic process, and large-scale mass production with integration and low cost can be realized. The phase offset regulation and control on a large scale on a chip are realized by utilizing the thermo-optic effect of a silicon material in the device, and on the basis, the demodulation function of a time BB84 quantum key distribution protocol under different preparation bases is realized by combining other logic devices and phase debugging; meanwhile, for the phase drift of quantum state signal light in an optical fiber channel and an interference loop, the decoder can carry out on-chip compensation through corresponding regulation and control to realize accurate passive demodulation, and the extra cost and code rate sacrifice caused by off-chip compensation measures are reduced.
Drawings
FIG. 1 schematically illustrates a schematic diagram of an on-chip decoder structure and an external probe for the time BB84 protocol according to an embodiment of the present disclosure;
fig. 2 schematically illustrates a flow chart of a decoding method for the time BB84 protocol of an embodiment of the present disclosure;
FIG. 3 schematically illustrates a composition diagram of quantum states of the temporal BB84 protocol and an orientation diagram thereof in a two-dimensional Hilbert space, in accordance with an embodiment of the present disclosure;
fig. 4 schematically shows an orientation schematic diagram of four quantum states in a two-dimensional hilbert space and quantum state schematic diagrams of three typical BB84 protocols, which satisfy the BB84 protocol according to an embodiment of the disclosure;
fig. 5 schematically shows a quantum state signal light evolution diagram of an on-chip decoder for the time BB84 protocol in an operating 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 time BB84 protocol according to an embodiment of the present disclosure.
[ reference numerals ]
100-input waveguide
200-1X 2 optical beam splitter
201-first optical splitter 202-second optical splitter
203-third optical splitter
300-light delay line
400-adjustable optical attenuator
500-phase offset modulator
501-first phase offset modulator 502-second phase offset modulator
503-third phase bias modulator 504-fourth phase bias modulator
600-2 x 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 probe 802-second external probe
803-third external probe 804-fourth external probe
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
In a first aspect, the present invention provides an on-chip decoder for the time BB84 protocol, see fig. 1, comprising:
an input waveguide 100 for inputting signal light to be decoded.
Specifically, the input waveguide 100 is used for inputting signal light to be decoded, and in the embodiment of the present invention, the signal light is quantum-state signal light sent by a time BB84 protocol.
The 1 × 2 optical splitter 200 includes a first optical splitter 201, a second optical splitter 202, and a third optical splitter 203, and splits an input signal light into two signal lights having equal intensities.
Specifically, in the decoder according to the embodiment of the present invention, a 1 × 2 multimode interference coupler (1 × 2MMI) is used as the first optical splitter 201, the second optical splitter 202, and the third optical splitter 203, the first optical splitter 201 splits the signal light to be decoded into two beams with equal intensity and sends the two beams 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 with equal intensity.
The optical delay line 300 is disposed between the first optical splitter 201 and the second optical splitter 202, and is configured to delay the signal light sent from the first optical splitter 201 to the second optical splitter 202.
Specifically, in the decoder according to the embodiment of the present invention, the optical delay line 300 adopts a waveguide surrounding structure, and the length of the waveguide is extended to delay the signal light, and the time delay is the same as the time delay of two pulses in the quantum state encoded by the encoder according to the BB84 protocol, so that the first pulse in the signal light sent to the second optical splitter 202 and the second pulse in the other signal light sent to the third optical splitter 203 realize the overlapping of the coherence time.
The variable optical attenuator 400 is used to attenuate the intensity of the input signal light.
Specifically, in the decoder according to the embodiment of the present invention, the variable optical attenuator 400 adopts a thermo-optic tuning mach-zehnder interference structure, and is disposed between the first optical splitter 201 and the third optical splitter 203, so that the light intensity of the signal light sent by the first optical splitter 201 to the third optical 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 configured to adjust a phase of the input signal light.
Specifically, in the decoder according to the embodiment of the present invention, the first phase bias modulator 501, the second phase bias modulator 502, the third phase bias modulator 503, and the fourth phase bias modulator 504 are thermo-optical tuning phase modulators, the first phase bias modulator 501 is configured to perform phase adjustment on one of the two signal lights split by the second optical splitter 202, the second phase bias modulator 502 is configured to perform phase adjustment on one of the two signal lights split by the second optical splitter 203, the third phase bias modulator 503 is configured to perform phase adjustment on one of the two signal lights output by the 2 × 2 interference coupler 601, and the fourth phase bias modulator 504 is configured to perform phase adjustment on one of the two signal lights 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 for hermitian calculation of received signal light.
Specifically, in the decoder according to the embodiment of the present invention, a 2 × 2 multimode interference coupler (2 × 2MMI) is adopted as the first interference coupler 601, the second interference coupler 602, the third interference coupler 603, and the fourth interference coupler 604, the first interference coupler 601 and the second interference coupler 602 are respectively disposed behind the second optical beam splitter 202 and the third optical beam splitter 203, one of the two beams of signal light emitted by the second optical beam splitter 202 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, one of the two beams of signal light emitted by the third optical beam splitter 203 is sent to the second interference coupler 602 through the second phase offset modulator 502, and the other beam is sent to the first interference coupler 601; the third interference coupler 603 is disposed behind the first interference coupler 601 and configured to receive two signal lights sent by the first interference coupler 601, wherein one signal light is modulated by the third phase shift modulator 503 and sent to the third interference coupler 603, the fourth interference coupler 604 is disposed behind the second interference coupler 602 and configured to receive two signal lights sent by the second interference coupler 602, and one signal light is modulated by the fourth phase shift modulator 504 and 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 for outputting the signal light after hermitian operation by 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 hermitian operation by the fourth interference coupler 604.
In the decoder according to the embodiment of the present invention, the input waveguide 100, the 1 × 2 optical splitter 200, the optical delay line 300, the adjustable optical attenuator 400, the phase offset modulator 500, the 2 × 2 interference coupler 600, and the output waveguide 700 are made of silicon materials, that is, the decoder is manufactured on a silicon substrate by a process compatible with a general microelectronic process. The input waveguide 100 and the output waveguide 700 both use fundamental mode transmission of the transverse electric field mode.
The output waveguide 700 is connected with the external detector 800, specifically, the first output waveguide 701 is connected with the first external detector 801, the second output waveguide 702 is connected with the second external detector 802, the third output waveguide 703 is connected with the third external detector 803, and the fourth output waveguide 704 is connected with the fourth external detector 804.
In a second aspect, an embodiment of the present invention further provides a decoding method for a time BB84 protocol, which can perform passive demodulation on a time BB84 protocol under different preparation bases, and the following describes the demodulation method in detail by taking the passive demodulation on a time BB84 protocol under different preparation bases as an example. Referring to fig. 2, the method includes:
s1, inputting the signal light to be decoded into the waveguide 100, wherein the signal light to be decoded is the quantum state signal light transmitted by the time BB84 protocol;
specifically, the quantum state signal light transmitted by the time BB84 protocol is composed of two adjacent pulses, the basic structure and the orientation thereof in the two-dimensional hilbert space are shown in fig. 3, and for the quantum state with coordinates (θ, Φ) in the two-dimensional hilbert space
Which represents the intensity of the first pulse as cos2(theta/2) and the second pulse intensity is sin2(θ/2), and the phase difference of the second pulse with respect to the first pulse is φ, using a quantum mechanical operator as follows:
the quantum state orthogonal to the (theta, phi) quantum state in the two-dimensional Hilbert space is its point of symmetry (pi-theta, phi + pi) about the center of the sphere, using quantum mechanical operators
Is represented as follows:
for the time BB84 protocol, it requires the encoding end to prepare two different sets of quantum state signal lights, as shown in FIG. 4, where the two quantum states in each set are orthogonal to each other, i.e. the two quantum states are orthogonal to each other
And
is 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 displayed as the quartering points on the circle passing through the center of sphere, so that the four quantum state signal lights input to the waveguide 100 can be represented as:
s2, the first optical splitter 201 receives the signal light to be decoded and splits it into two signal lights with equal intensity, which are sent to the second optical splitter 202 and the third optical splitter 203 through the optical delay line 300 and the adjustable optical attenuator 400, the optical delay line 300 makes the first pulse in the signal light sent to the second optical splitter 202 and the second pulse in the other signal light sent to the third optical splitter 203 realize the overlapping of coherence time, the adjustable optical attenuator 400 makes the intensities of the two signal lights before reaching the second optical splitter 202 and the third optical splitter 203 consistent;
specifically, as shown in fig. 5, the first optical splitter 201 receives the quantum-state signal light input by the input waveguide 100, and splits the quantum-state signal light into two equal-intensity signal lights, which are respectively transmitted to the second optical splitter 202 and the third optical splitter 203 through the optical delay line 300 and the adjustable optical attenuator 400. The attenuation of the adjustable optical attenuator 400 is set to be consistent with that of the optical delay line 300, so that the intensities of the two signal lights are consistent before the two signal lights reach the second optical beam splitter 202 and the third optical beam splitter 203; the time delay of the optical delay line 300 is set to be the same as the time delay of two pulses in the quantum state encoded by the encoder of the time BB84 protocol, so that the first pulse in the signal light sent to the second optical splitter 202 and the second pulse in the other signal light sent to the third optical splitter 203 achieve overlapping of the coherence time. At this point in time, 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 information of the second pulse is transferred to the input end of the optical beam splitter 203;
and S3, adjusting the phase of the phase offset modulator 500, performing Hermitian operation on the received signal light by using the 2 x 2 interference coupler 600 to obtain signal light meeting the decoding requirement of the time BB84 protocol, and outputting the signal light through the output waveguide 700.
For the time BB84 protocol, a passive decoder needs to realize two kinds of equal probability different demodulation, wherein the first demodulation can accurately respond to a first group of quantum state signal light prepared by an encoding end and randomly respond to a second group of quantum state signal light; the second demodulation can respond to the second group of quantum state signal light prepared by the encoding end accurately and respond to the first group of quantum state signal light randomly. 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 splitter 201 receives the quantum state signal light input by the input waveguide 100, splits the quantum state signal light into two beams of equal-intensity signal light, sends the two beams of equal-intensity signal light to the second optical splitter 202 and the third optical splitter 203 through the optical delay line 300 and the adjustable optical attenuator 400, and further splits the two beams of equal-intensity signal light into four beams (as shown in fig. 5). The second optical beam splitter 202 and the third optical beam splitter 203 each include an upper output end and a lower output end, the signal lights at the upper output end of the second optical beam splitter 202 and the upper output end of the third optical beam splitter 203 jointly enter the first group of demodulation components a (as shown by a solid line box in fig. 1), the signal lights at 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 a solid line box in fig. 1), and since the second optical beam splitter 202 and the third optical beam splitter 203 each split the input signal light into two signal lights with equal intensity, the demodulation probabilities of two different groups of demodulation components are the same. Wherein the first and second demodulation elements a and B each comprise two phase offset modulators 500 and two 2 x 2 interferometric couplers 600.
For the first group of demodulation components a, as shown in fig. 1 and 5, at the detection time point, the information of the first pulse and the second pulse of the quantum state signal light is transferred to the two input ends of the first coupler 601, and the phases of the first modulator 501 and the third modulator 503 are set as
And
the equivalent Hermite operation and the combined Hermite operation L1 of each element in the component are as follows:
under operation of L1:
the above results show that the output waveguide701. The signal light at 702 is shown in FIG. 6, i.e., the quantum state at the detection time point
Will respond accurately to, the quantum state at the first external detector 801 as shown in figure 1
Will respond accurately at the second external detector 802 due to the four quantum states
And
is a quartering point on a circle passing through the center of the sphere, and thus first external detector 801 and second external detector 802 are for quantum states
And
the response of (a) is random.
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 is transferred to the two input ends of the first coupler 602, and the phases of the second modulator 502 and the fourth modulator 504 are set to be
And
then, the signal light at the output waveguides 703 and 704 can be made to be quantum state at the detection time point as shown in fig. 6
Accurate response, quantum state, at a third external detector 803
Accurate response at fourth external detector 804, and third external detector 803 and fourth external detector 804 for quantum states
And
the response of (a) is random.
In summary, the results of the four detectors in the above arrangement completely satisfy the decoding requirement of the current time BB84 protocol, that is, the function of passively demodulating any four quantum states satisfying the time BB84 protocol is realized.
More generally, the quantum states of three typical time BB84 protocols are shown in fig. 4, which include:
time BB84 protocol 1: preparing |0>, |1>, | + > and | - > four quantum states at the encoding end;
time BB84 protocol 2: the encoding end prepares |0>, |1>, | + i > and | -i > four quantum states;
time BB84 protocol 3: the encoding end prepares four quantum states of | + >, | - >, | + i > and | -i >;
the decoder disclosed in the embodiment of the present invention sets the decoding settings for the above 3 typical time BB84 protocols as shown in table 1 below:
TABLE 1
In addition, when the phase shift of the quantum state signal is generated due to channel transmission or interference loop deviation (namely, when the phase between the two front and back pulses is changed), the decoder disclosed by the embodiment of the invention can carry out on-chip compensation through corresponding regulation and control to realize accurate passive demodulation.
When quantum state
And
when the phase offset is generated:
only the first modulator 501 and the second modulator 502 need to be adjusted accordingly:
on-chip phase compensation can be carried out on the quantum state, accurate passive demodulation is realized again, and extra cost and code rate sacrifice caused by off-chip compensation measures are reduced.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in 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.
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| EP4062580B1 (en) * | 2019-11-18 | 2023-10-11 | Telefonaktiebolaget LM Ericsson (publ) | Quantum bit decoding apparatus, system and method |
| CN111585755B (en) * | 2020-04-29 | 2021-02-23 | 中国科学院半导体研究所 | Multi-protocol compatible quantum key distribution decoding integrated chip with configurable on-chip unit |
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