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EP-4518196-B1 - MINIATURIZED TIME PHASE DECODER AND QKD RECEIVER

EP4518196B1EP 4518196 B1EP4518196 B1EP 4518196B1EP-4518196-B1

Inventors

  • TAO, JUN
  • LIU, Rende
  • TANG, YANLIN
  • TANG, Shibiao
  • YING, Yong

Dates

Publication Date
20260506
Application Date
20230411

Claims (10)

  1. A miniaturized time phase decoder, comprising a decoding chip implemented based on planar lightwave circuit technology, a first reflection unit (402) and a second reflection unit (401); wherein the decoding chip comprises a first beam splitter (201) and a second beam splitter (202), wherein the decoding chip is provided with an input port, a time basis signal output port, a first phase basis signal output port, a second phase basis signal output port, a first reflection port and a second reflection port; the first beam splitter (201) is provided with a first port, a second port, a third port and a fourth port, wherein a light input from the first port is output from the second port and the third port, and a light input from the third port is output from the first port and the fourth port; the second beam splitter (202) is provided with a fifth port, a sixth port, a seventh port and an eighth port, wherein a light input from the fifth port is output from the sixth port and the seventh port, and a light input from the seventh port is output from the fifth port and the eighth port; the input port is connected to the first port through a first waveguide (103); the second port is connected to the time basis signal output port through a second waveguide (105); the third port is connected to the fifth port through a third waveguide (104); the sixth port is connected to the first reflection port through a fourth waveguide (106); the seventh port is connected to the second reflection port through a fifth waveguide (300), wherein the fifth waveguide (300) has an optical path length different from an optical path length of the fourth waveguide (106); the eighth port is connected to the first phase basis signal output port through a sixth waveguide (101); the fourth port is connected to the second phase basis signal output port through a seventh waveguide (102); the first reflection unit (402) is arranged at the first reflection port, and the first reflection unit (402) is configured to reflect a light signal and deflect a polarization state of the light signal by 90 degrees; and the second reflection unit (401) is arranged at the second reflection port, and the second reflection unit (401) is configured to reflect a light signal and deflect a polarization state of the light signal by 90 degrees.
  2. The time phase decoder according to claim 1, wherein the first beam splitter (201) is configured to implement, for a light input from the first port, a beam splitting ratio of A2:A3 between the second port and the third port, wherein A2 is not equal to A3; and the second beam splitter (202) is configured to implement equal splitting.
  3. The time phase decoder according to claim 2, further comprising a third beam splitter (203), wherein the third beam splitter (203) comprises a ninth port, a tenth port, an eleventh port and a twelfth port, wherein a light input from the ninth port is output from the tenth port and the eleventh port, and a light input from the eleventh port is output from the ninth port and the twelfth port; for the light input from the ninth port, a beam splitting ratio between the tenth port and the eleventh port is A2:A3; and the sixth waveguide (101) comprises a first waveguide section and a second waveguide section, the eleventh port is connected to the eighth port through the first waveguide section, and the twelfth port is connected to the first phase basis signal output port through the second waveguide section.
  4. The time phase decoder according to any one of claims 1 to 3, wherein the reflection units (401, 402) are 45-degree Faraday rotator mirrors.
  5. The time phase decoder according to claim 2 or claim 3, wherein A2:A3=70:30.
  6. The time phase decoder according to any one of claims 1 to 3, wherein the waveguides (101, 102, 103, 104, 105, 106, 300) are fabricated from silicon dioxide materials, and the beam splitters are fabricated from silicon dioxide materials.
  7. The time phase decoder according to any one of claims 1 to 3, wherein an optical path length difference between the fifth waveguide (300) and the fourth waveguide (106) is 1/2 of a time interval between two light pulses under the phase basis.
  8. A QKD receiver used in a time phase encoding scheme, comprising a first photoelectric detection unit, a second photoelectric detection unit and the time phase decoder according to any one of claims 1 to 7; wherein the first photoelectric detection unit is configured to detect a light signal output from the time basis signal output port; and the second photoelectric detection unit is configured to detect light signals output from the first phase basis signal output port and the second phase basis signal output port.
  9. The QKD receiver according to claim 8, wherein the first photoelectric detection unit comprises a third single-photon detector arranged at the time basis signal output port.
  10. The QKD receiver according to claim 8, wherein the second photoelectric detection unit comprises a first single-photon detector and a second single-photon detector, the first single-photon detector is arranged at the first phase basis signal output port, and the second single-photon detector is arranged at the second phase basis signal output port.

Description

This application claims priority to Chinese Patent Application No. 202210443737.5, titled "MINIATURIZED TIME PHASE DECODER AND QKD RECEIVER", filed on April 24, 2022 with the China National Intellectual Property Administration. FIELD The present disclosure relates to the field of quantum information technology, and in particular to a miniaturized time-phase decoder and a QKD receiver that are implemented based on a planar lightwave circuit chip. BACKGROUND Quantum secure communication is a secure communication method different from classical communication, is capable to identically generate unconditionally secure keys between both sides of the communication, support encryption of classical information in a "one-time pad" manner, and ensure a high security of information transmission. Therefore, the quantum secure communication obtains wide attention. A quantum secure communication system in the prior art is implemented mainly based on quantum key distribution (QKD) technology. A QKD system includes a sender and a receiver. The sender realizes encoding and transmission of a quantum state using an encoder, and the receiver realizes decoding and detection of the quantum state using a decoder. The decoder is one of core devices of the receiver, determining system indicators such as the key rate and the error rate of the QKD system. In the QKD system based on a phase scheme or a time-phase scheme, interference demodulation is performed on a pulse photon pair with phase encoded information sent by the sender, so as to implement single photon detection. In the time phase encoding and decoding scheme based on the BB84 protocol, there are a phase basis and a time basis. A photon pair, formed by two pulses one after the other with a certain phase difference, can be generated by encoding for the phase basis, to form phase-encoded light pulses. Pulse photons distributed one after another in the time domain can be generated by encoding for the time basis, to form time-encoded light pulses. In a case of decoding, basis selection is performed using a basis selection unit, and then quantum states under different bases are respectively detected by different detectors. The phase-encoded light pulses are mainly interference demodulated by an unbalanced interferometer before the phase state detection. The on-chip time-phase decoder in the prior art, mainly applies the chip fabricated by silicon-based technique and the like to implement time-phase quantum state decoding. Figure 1 shows a prior art high-speed silicon-based on-chip QKD encoding and decoding system, which uses a chip for decoding in the time phase decoder, where the chip is reciprocal with the one of the sender. To be specific, a balanced interferometer and an unbalanced interferometer are included. The balanced interferometer is configured to measure states |0> and |1>, the unbalanced interferometer is configured to measure states [+> and |->. The interfered light pulses are ultimately detected by the off-chip single-photon detectors. Patent No. CN111934868A discloses a decoding chip and decoding method for quantum key distribution, which is mainly used in a QKD system based on a time phase encoding protocol. As shown in Figure 2, the decoding chip includes an input waveguide, a directional coupler, a phase modulator, a delay line, an output waveguide and the like. The decoding chip can implement an adjustable splitting ratio, balance the power of the double time-bin pulse light, so as to optimize an interference visibility and reduce a bit error rate. The interference visibility of the decoding chip is not sensitive to temperature variation, that is, the bit error rate caused by the optical device is not sensitive to temperature variation. Patent No. CN109343173A discloses a hybrid waveguide integrated interferometer, which is configured to implement the encoding and decoding function of the QKD system based on the phase encoding protocol. As shown in Figure 3, the interferometer includes a fiber, a waveguide coupler, an optical waveguide chip (including a delay line), a phase waveguide modulator, a reflection module and the like. In the interferometer, a difference between lengths of arms is readily controllable, thereby facilitating reducing the production cost of the unbalanced interferometer. The interferometer formed by using the optical waveguide chip is relatively stable and insensitive to external temperature variation and vibration. The interferometer has reduced size and convenient packaging. The decoders shown in Figure 1 and Figure 2 are each integrated with a phase modulator, and mainly use chips made from silicon, silicon nitrogen oxide or like materials. The waveguide chip mainly operates in a TE mode or a TM mode, and the polarization state is random before being coupled into the chip through the optical fiber transmission link, resulting in direct loss of photons in a non-operating mode after entering the waveguide chip, and causing problems suc