A quantum chip based on silicon photonics integration

Abstract

The present invention discloses a quantum chip based on silicon photonics integration, comprising a substrate, on which an intensity modulator, a phase modulator, a variable optical attenuator, a polarization modulator, a polarization multiplexer, a polarization demultiplexer and a polarization demodulator are integrated; the intensity modulator, the phase modulator, the variable optical attenuator and the polarization modulator are sequentially connected by electrical signals; the lower port of the output end of the variable optical attenuator is connected to a single photon detector for monitoring the attenuation level; the upper port of the output end of the attenuator is connected to the polarization modulator for preparing the polarization state; the polarization modulator is connected to the polarization demultiplexer through an optical fiber, and a polarization controller is also provided between the polarization modulator and the polarization demultiplexer; the polarization demultiplexer is further connected to the polarization demodulator. Integrating various electronic components on the substrate improves the integration degree of the system, enhances the flexibility of the system, reduces the number of components used, and lowers the manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optoelectronics and quantum communication technologies, and particularly to a quantum chip based on silicon photonics integration. Background Art

[0002] As an important part of quantum communication, QKD technology is mainly used for the generation and distribution of encryption keys. In theory, QKD can achieve absolutely secure confidential communication, and its security is guaranteed by physical laws such as the uncertainty principle and the principle of non-copyability of quantum states.

[0003] QKD technology can use entangled quantum states for key distribution: a set of entangled quantum states are sent to two trusted terminals respectively, so that the two communication parties share the entangled state; subsequently, at the terminals, both parties randomly select different basis vectors for measurement; both parties inform each other of the basis vectors used for measurement through a classical channel and synchronize, and retain the part measured simultaneously by both. Further, the communication parties can divide the data into two parts. One part publicly discloses the corresponding measurement results through the classical channel for Bell inequality testing, and the amount of information obtained by the eavesdropper can be detected according to the degree of violation of the Bell inequality; the other part retains the bits with the same measurement basis vectors as the original key.

[0004] Since the research on high-rate entangled state preparation technology and long-distance entangled state transmission technology is still in its infancy, QKD technology more often uses single-photon superposition states for key distribution: the two communication parties pre-select mutually unbiased bases, the preparation end randomly selects a set of mutually unbiased bases to prepare the corresponding quantum states, and the transmitting end sequentially records the selected unbiased bases; subsequently, the quantum states are sent to the receiving end through a quantum channel, and the receiving end randomly selects a set of mutually unbiased bases for measurement, and the receiving end records the measurement results and the bases used for measurement; both parties inform each other of the basis vectors used for measurement through the classical channel, and the bits with the same measurement basis vectors can be retained as the original key. At this time, the key has been generated and distributed to the two communication parties. The transmitting end can use the key to encrypt the classical communication signal and send it to the receiving end through the classical channel; the receiving end can also use the key to decrypt the classical communication signal and obtain the information content. If the eavesdropper intercepts the encrypted classical communication signal, it cannot be decrypted to obtain specific information because it does not have the key; if the eavesdropper eavesdrops on the quantum channel, it cannot obtain information without being detected by the legitimate communication parties because it cannot measure the transmitted quantum state without disturbing the original state (the principle of non-copyability of quantum states); when the communication parties detect that the transmitted quantum state has been eavesdropped and the bit error rate is abnormal, this group of keys can be discarded and a secure key can be regenerated.

[0005] In the actually used QKD system, the preparation end and the receiving end are mostly built with discrete optical elements, which will occupy a huge volume and put forward high requirements for the alignment of the optical path. In addition, it also has the disadvantages of complex structure, poor stability and high cost, which is not conducive to the popularization and application of QKD technology.

[0006] The QKD system based on polarization coding uses polarized photons as the carriers for encoding and transmitting quantum bits, which has the advantages of mature manipulation and simple structure. The polarized photons can be polarized entangled photon pairs generated by a nonlinear process or the polarization state of single photons. For example, the polarization coding BB84 protocol uses two sets of mutually unbiased bases to encode the 0 state and the 1 state. Therefore, it is required that the transmitting end prepares each polarization state with a high extinction ratio. However, due to reasons such as the imperfect roundness of the optical fiber and residual stress, the birefringence effect will occur in the optical fiber, making it difficult to maintain the stability of the polarization state during transmission in the optical fiber.

[0007] Therefore, it is necessary to further improve the existing QKD system to overcome the problems of large volume, complex structure, poor stability, high cost and unstable transmission of the polarization state in the optical fiber. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a quantum chip based on silicon photonics integration, which is small in volume, simple in structure, good in stability and low in cost.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows: A quantum chip based on silicon photonics integration includes a substrate, on which an intensity modulator, a phase modulator, an adjustable attenuator, a polarization modulator, a polarization multiplexer, a polarization demultiplexer and a polarization demodulator are integrated;

[0010] The intensity modulator, the phase modulator, the adjustable attenuator and the polarization modulator are sequentially connected by electrical signals;

[0011] The lower port of the output end of the adjustable attenuator is connected to a single photon detector for monitoring the attenuation level; the upper port of the output end of the attenuator is connected to the polarization modulator for preparing the polarization state;

[0012] The polarization modulator is connected to the polarization demultiplexer through an optical fiber, and a polarization controller is also provided between the polarization modulator and the polarization demultiplexer; the polarization demultiplexer is connected to the polarization demodulator;

[0013] The direct current light is coupled to the straight waveguide end face of the intensity modulator, modulated into optical pulses by the intensity modulator, and then enters the phase modulator for phase randomization. The average photon number of the randomized optical pulses is attenuated to the single photon level at the adjustable attenuator 140 and enters the polarization modulator, and the power and phase of the polarization state basis vectors are modulated by the polarization modulator;

[0014] The modulated optical pulse is converted into the corresponding polarization state in a straight waveguide by a polarization multiplexer, and then enters a single-mode fiber through end-face coupling. After the polarization state is transmitted through the single-mode fiber, it is coupled to a polarization demultiplexer through end-face coupling and is converted into the intensity and phase information in two straight waveguides by the polarization demultiplexer;

[0015] The polarization demodulator demodulates the power and phase of the polarization state basis vectors to achieve projection measurement; finally, the photons enter the fiber through end-face coupling and are transmitted through the fiber to two single-photon detectors, where photon counting is generated at the single-photon detectors.

[0016] Preferably, the polarization modulator includes an MMI optical coupler and an MZI. The MZI includes a TOPM and an EOPM. After the attenuated photons enter the polarization modulator, the TOPM inside the MZI compensates for the phase difference between the two arms, and the power and phase of the polarization state basis vectors are modulated by the EOPM inside the MZI and the external EOPM respectively.

[0017] Preferably, the polarization demodulator includes an MMI optical coupler and an MZI. The MZI includes a TOPM and an EOPM. The optical quantum information converted by the polarization demultiplexer compensates for the phase difference between the two arms through the TOPM inside the MZI, and the power and phase of the polarization state basis vectors are demodulated by the EOPM inside the MZI and the external EOPM respectively.

[0018] Preferably, the substrate is made of SiO2 material in the SOI system.

[0019] Preferably, the two output ports of the polarization demodulator are sequentially connected to a polarization controller and a single-photon detector through optical fibers respectively.

[0020] Preferably, the polarization multiplexer, the polarization demultiplexer, and the polarization demodulator all adopt an on-chip MZI structure.

[0021] Preferably, the MMI optical coupler, the TOPM, and the EOPM are all made of silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide, or silicon nitride materials.

[0022] Preferably, both the polarization multiplexer and the polarization demultiplexer include a Bi Level tapered structure and an adiabatic coupling structure connected in sequence.

[0023] Advantageous technical effects of the present invention:

[0024] 1. In the present invention, each electronic component is integrated on a substrate, which improves the integration degree of the system, enhances the flexibility of the system, reduces the number of components used, and reduces the manufacturing cost.

[0025] 2. The modulation mechanism of the present invention is based on an on-chip MZI, and an EOPM is used to regulate the phases of the two arms of the interferometer. The EOPM realized by the carrier effect can achieve a high modulation rate of 1.25 GHz, which is beneficial to realizing a high-speed polarization state preparation process and improving the rate of QKD.

[0026] 3. The present invention adds a TOPM to the MZI containing an EOPM to compensate for the phase difference between the two arms, achieving a high extinction ratio of 30 dB and improving the fidelity of polarization state preparation. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of a quantum chip based on silicon photonics integration of the present invention. Detailed Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail with reference to embodiments, but the scope of protection required by the present invention is not limited to the following specific embodiments.

[0029] As Figure 1 shown, a quantum chip based on silicon photonics integration includes a substrate, and the substrate includes a first substrate 110 and a second substrate 210. An intensity modulator 120, a phase modulator 130, an adjustable attenuator 140, a polarization modulator 150 and a polarization multiplexer 160 are integrated on the first substrate 110.

[0030] A polarization demultiplexer 220 and a polarization demodulator 230 are integrated on the second substrate 210;

[0031] The connection modes of each electronic component are as follows:

[0032] The intensity modulator 120, the phase modulator 130, the adjustable attenuator 140 and the polarization modulator 150 are sequentially connected through electrical signals;

[0033] The lower port of the output end of the adjustable attenuator 140 is connected to a single photon detector (not shown in the figure) for monitoring the attenuation level; the upper port of the output end of the attenuator 140 is connected to the polarization modulator 150 for preparing the polarization state;

[0034] The polarization modulator 150 is sequentially connected to the polarization demultiplexer 220 through a single-mode optical fiber 170 and a first polarization controller 180, and the polarization demultiplexer 220 is further connected to the polarization demodulator 230;

[0035] The DC light of the external laser is coupled to the end face of the straight waveguide of the intensity modulator 120, modulated into optical pulses by the intensity modulator 120, and then enters the phase modulator 130 for phase randomization. The average photon number of the randomized optical pulses is attenuated to the single-photon level at the adjustable attenuator 140 and enters the polarization modulator 150, and the power and phase of the polarization state basis are modulated by the polarization modulator 150;

[0036] Specifically, the polarization modulator 150 includes an MMI (multi-mode interference) optical coupler 151 and an MZI (Mach-Zehnder interferometer). The MZI includes a TOPM 152 (thermo-optic phase modulator) and an EOPM 153 (electro-optic phase modulator). After the attenuated photons enter the polarization modulator 150, the TOPM 152 inside the MZI compensates for the phase difference between the two arms, and the power and phase of the polarization state basis are modulated by the EOPM 153 inside the MZI and the external EOPM 153 respectively.

[0037] The modulated optical pulses are converted into corresponding polarization states in a straight waveguide by the polarization multiplexer 160, and then enter the single-mode fiber 170 through end-face coupling. After the polarization state is transmitted through the single-mode fiber 170, it is coupled to the polarization demultiplexer 220 through the end face, and the polarization demultiplexer 220 converts it into the intensity and phase information in two straight waveguides;

[0038] The polarization demodulator 230 demodulates the power and phase of the polarization state basis to achieve projective measurement;

[0039] The polarization demodulator 230 includes an MMI optical coupler and an MZI. The MZI also includes a TOPM and an EOPM. The optical quantum information converted by the polarization demultiplexer compensates for the phase difference between the two arms through the TOPM inside the MZI, and the power and phase of the polarization state basis are demodulated by the EOPM inside the MZI and the external EOPM respectively.

[0040] Finally, the photons enter the optical fiber through end-face coupling and are transmitted through the optical fiber to two single-photon detectors, where photon counting is generated at the single-photon detectors.

[0041] Specifically, the substrate uses SiO2 material in the SOI system.

[0042] The two output ports of the polarization demodulator are respectively connected to polarization controllers (240, 250) and single-photon detectors (260, 270) in sequence through optical fibers.

[0043] The polarization multiplexer 160, polarization demultiplexer 220, and polarization demodulator 230 all adopt an on-chip MZI structure. The MMI optical coupler 151, TOPM 152, and EOPM 153 components all adopt materials such as silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide, or silicon nitride. The polarization multiplexer 160 and polarization demultiplexer 230 both include a Bi Level tapered structure 162 and an adiabatic coupling structure 161 connected in sequence.

[0044] The polarization controllers 180, 240, and 250 are used to calibrate the polarization before the system runs. The polarization controller 180 can be used to control the fiber transmission crosstalk and improve the system performance. Since the single-photon detectors 260 and 270 used are polarization-related devices, the polarization controllers 240 and 250 are required to ensure their normal operation.

[0045] The present invention integrates each electronic component on a substrate, improving the integration degree of the system, enhancing the flexibility of the system, reducing the number of components used, and lowering the manufacturing cost.

[0046] Based on the modulation mechanism of the on-chip MZI, the present invention can use the EOPM to regulate the phase of the two arms of the interferometer. The EOPM realized by the carrier effect can achieve a high modulation rate of 1.25 GHz, which is beneficial to realizing the high-speed preparation process of the polarization state, thereby improving the rate of QKD.

[0047] The present invention adds a TOPM to the MZI containing an EOPM to compensate for the phase difference between the two arms, enabling a high extinction ratio of 30 dB and improving the fidelity of the polarization state preparation.

[0048] The structures such as the MZI, phase shifter, and polarization rotator adopted by the present invention are all based on mature silicon-based processes and are compatible with mature microelectronic CMOS processes.

[0049] A QKD method with polarization compensation provided by the present invention reduces the bit error rate of the system and increases the transmission distance of the system.

[0050] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the invention.

Claims

1. A quantum chip based on silicon photonics integration, characterized in that, It includes a substrate, on which an intensity modulator, a phase modulator, a tunable attenuator, a polarization modulator, a polarization multiplexer, a polarization demultiplexer and a polarization demodulator are integrated; The intensity modulator, the phase modulator, the tunable attenuator and the polarization modulator are sequentially connected by electrical signals; The lower port of the output end of the tunable attenuator is connected to a single-photon detector for monitoring the attenuation level; the upper port of the output end of the tunable attenuator is connected to the polarization modulator for preparing the polarization state; The polarization modulator is connected to the polarization demultiplexer through an optical fiber, and a polarization controller is also provided between the polarization modulator and the polarization demultiplexer; the polarization demultiplexer is further connected to the polarization demodulator; DC light is coupled to the straight waveguide end face of the intensity modulator and modulated into optical pulses by the intensity modulator, and then enters the phase modulator for phase randomization. The average photon number of the randomized optical pulses is attenuated to the single-photon level at the tunable attenuator and enters the polarization modulator, and the power and phase of the polarization state basis vectors are modulated by the polarization modulator; The modulated optical pulses are converted into corresponding polarization states in a straight waveguide by the polarization multiplexer, and then enter a single-mode optical fiber through end face coupling. After the polarization state is transmitted through the single-mode optical fiber, it is coupled to the polarization demultiplexer through end face coupling, and the polarization demultiplexer converts it into the intensity and phase information in two straight waveguides; The polarization demodulator demodulates the power and phase of the polarization state basis vectors to achieve projection measurement; finally, the photons are coupled into the optical fiber through the end face and transmitted to 2 single-photon detectors through the optical fiber, and photon counting is generated at the single-photon detectors.

2. The quantum chip based on silicon photonics integration according to claim 1, wherein The polarization modulator includes an MMI optical coupler and an MZI. The MZI includes a TOPM and an EOPM. After the attenuated photons enter the polarization modulator, the TOPM inside the MZI compensates for the phase difference between the two arms, and the power and phase of the polarization state basis vectors are modulated by the EOPM inside the MZI and the external EOPM respectively.

3. A quantum chip based on silicon photonics integration as claimed in claim 1, wherein, The polarization demodulator includes an MMI optical coupler and an MZI. The MZI includes a TOPM and an EOPM. The optical quantum information converted by the polarization demultiplexer compensates for the phase difference between the two arms through the TOPM inside the MZI, and the power and phase of the polarization state basis vectors are demodulated by the EOPM inside the MZI and the external EOPM respectively.

4. A quantum chip based on silicon photonics integration as claimed in claim 1, wherein, The substrate uses SiO2 material in the SOI system.

5. A quantum chip based on silicon photonics integration as claimed in claim 1, characterized in that, The two output ports of the polarization demodulator are sequentially connected to a polarization controller and a single-photon detector through optical fibers respectively.

6. The quantum chip based on silicon photonics integration according to claim 1, wherein The polarization multiplexer, the polarization demultiplexer and the polarization demodulator all adopt an on-chip MZI structure.

7. A quantum chip based on silicon photonics integration according to any one of claims 2 or 3, characterized in that The MMI optical coupler, the TOPM and the EOPM all use materials such as silicon, indium phosphide, indium gallium arsenide phosphide, silicon dioxide or silicon nitride.

8. A quantum chip based on silicon photonics integration as described in claim 1, characterized in that, The polarization multiplexer and the polarization demultiplexer both include a Bi Level tapered structure and an adiabatic coupling structure connected in sequence.

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