A quantum key encoding chip

Abstract

The application discloses a quantum key coding chip, comprising a pulse separation module, a first intensity modulator, a phase modulation module and a second intensity modulator connected in sequence. The phase modulation module comprises a first straight waveguide, a cross waveguide, a second straight waveguide and a first ground electrode, a first voltage electrode, a second ground electrode, a second voltage electrode and a third ground electrode arranged in parallel and in sequence. The first straight waveguide is located between the first ground electrode and the first voltage electrode, and the second straight waveguide is located between the second ground electrode and the second voltage electrode. The application integrates the required photoelectric devices for time phase coding in the same chip, and designs the phase modulation module as a structure of multiple waveguides and multiple electrodes, thereby realizing the chippification and low cost of the quantum key coding system, further reducing the area occupied by the phase modulation module in the chip, improving the integration of the chip, and reducing the required driving voltage and driving power consumption.

Description

Technical Field

[0001] This application belongs to the field of quantum information, and specifically relates to a quantum key distribution chip. Background Technology

[0002] Quantum key distribution (QKD) is a technology that uses the principles of quantum mechanics to securely share keys between communicating parties. Its core lies in the no-cloning theorem of quantum states, which states that an unknown quantum state cannot be precisely copied. Any measurement or eavesdropping of a quantum state will inevitably introduce interference, which can then be detected by the communicating parties.

[0003] A quantum key distribution (QKD) system mainly consists of a quantum key encoding part (transmitter), a quantum channel, and a quantum key decoding part (receiver). Common quantum key encoding methods include polarization encoding, phase encoding, and time-phase encoding. Polarization encoding uses the polarization state of photons to encode information, measuring the polarization state of photons through polarizers with different orientations to achieve key transmission. However, some problems exist in practical applications. For example, the polarization mode dispersion of optical fibers can cause distortion of the photon polarization state during transmission, affecting the accuracy of decoding. Simultaneously, the stability requirements of devices such as polarization controllers are high, and polarization encoding is sensitive to environmental factors (such as temperature and pressure), easily subject to external interference that can degrade system performance. Phase encoding encodes information by modulating the phase of photons, with common examples including differential phase shift keying (DPSK) protocols. Compared to polarization encoding, phase encoding is less dependent on the polarization state and less affected by optical fiber polarization mode dispersion. However, high-precision phase control technology is required during phase modulation and measurement, and the phase is easily affected by external environmental disturbances, such as temperature changes and fiber micro-bending, which can cause phase drift and affect the accuracy of key generation. Time-phase coding combines the features of time coding and phase coding, utilizing the position and phase information of photons in time for encoding. This method can fully utilize both time and phase degrees of freedom, improving the capacity and security of information encoding, while at the same time reducing the stringent requirements on a single degree of freedom to some extent, thus enhancing the system's anti-interference capability.

[0004] Currently, most commonly used time-phase coding systems employ discrete optical components. These components are relatively large, making it difficult to miniaturize the overall QKD system and hindering deployment and integration. Furthermore, the high cost of discrete optical components increases the overall cost of the QKD system, and their complex manufacturing process limits large-scale production and commercial applications. Currently, the half-wave voltage of commercial phase modulators is generally around 5V. In QKD systems, to achieve higher-precision phase shift modulation, such as 3π / 2 phase shift, higher phase shift modulation operations are typically required. This necessitates the system supporting higher RF drive voltage outputs. Increasing the drive voltage not only increases system power consumption but also complicates circuit design and drive control, reducing system stability and reliability.

[0005] In conclusion, there is an urgent need to develop a novel QKD encoding system or device. This system or device should effectively address the aforementioned problems, achieving miniaturized, low-cost, low-drive-voltage, and low-power QKD encoding. This would improve the practicality and commercial value of QKD technology, enabling its wider application in various real-world scenarios and promoting the further development and popularization of quantum communication technology. Utility Model Content

[0006] In view of the many problems of traditional QKD encoding systems in terms of size, cost, driving voltage, and complexity, this application proposes a quantum key encoding chip, the specific scheme of which is as follows: The quantum key encoding chip proposed in this application includes a pulse separation module, a first intensity modulator, a phase modulation module, and a second intensity modulator connected in sequence. The pulse separation module includes an input terminal and an output terminal, used to separate the initial optical pulse into two consecutive optical pulses; The first intensity modulator includes an input terminal and an output terminal, used to perform initial intensity modulation on two consecutive optical pulses respectively; The phase modulation module includes a first straight waveguide, a cross waveguide, a second straight waveguide, and a first ground electrode, a first voltage electrode, a second ground electrode, a second voltage electrode, and a third ground electrode arranged in parallel and sequentially. The first straight waveguide is located between the first zero electrode and the first voltage electrode, and the second straight waveguide is located between the second ground electrode and the second voltage electrode. The cross waveguide includes a horizontal channel and a vertical channel that are perpendicular to each other. The output end of the first straight waveguide is connected to the input end of the second straight waveguide through the vertical channel of the cross waveguide, and the output end of the second straight waveguide is connected to the second intensity modulator through the horizontal channel of the cross waveguide. The input ends of the first straight waveguide and the second straight waveguide are located on the same side of the phase modulation module. The second intensity modulator includes an input terminal and an output terminal, which is used to attenuate and modulate the optical pulse output by the phase modulation module and output it as a quantum key signal. The output terminal of the second intensity modulator is connected to an external quantum key receiver through a spatial channel or an optical fiber channel.

[0007] Optionally, the quantum key encoding chip further includes a first curved waveguide and a second curved waveguide, wherein the first curved waveguide is connected between the output end of the first straight waveguide and the input end of the vertical channel, and the second curved waveguide is connected between the output end of the vertical channel and the input end of the second straight waveguide.

[0008] Optionally, the pulse separation module is an unequal-arm interferometer, including a first waveguide beam splitter, a first interferometric arm waveguide, a second interferometric arm waveguide, and a second waveguide beam splitter. The first waveguide beam splitter is used to receive the input optical pulse and split it into the first interferometric arm waveguide and the second interferometric arm waveguide. The second waveguide beam splitter is used to receive the optical pulses from the first interferometric arm waveguide and the second interferometric arm waveguide and combine them into the same port for output. The lengths of the upper and lower interferometric arms have an optical path difference (ΔL).

[0009] Optionally, the first intensity modulator is an equal-arm interferometer, including a first control electrode group, which is used to control the phase difference between the optical pulses of the upper and lower arms of the interference after passing through the first intensity modulator.

[0010] Optionally, the second intensity modulator is an equal-arm interferometer, including a second control electrode group, which is used to control the phase difference between the optical pulses of the upper and lower arms of the interference after passing through the second intensity modulator.

[0011] Optionally, the first zero electrode, the first voltage electrode, the second ground electrode, the second voltage electrode, and the third ground electrode are all traveling wave electrodes, with their signal input terminals located on the same side and their signal output terminals located on the same side.

[0012] Optionally, the signal output terminals of the first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, and the second voltage electrode are provided with an integrated radio frequency matching resistor to eliminate radio frequency signal reflection.

[0013] Optionally, the first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, and the second voltage electrode are located on the same layer of the chip as the first straight waveguide and the second straight waveguide.

[0014] Optionally, the cross waveguide includes a multimode interference coupler at the center and four multi-stage tapered waveguides. The multimode interference coupler is used to constrain the optical pulse to propagate in a straight line from the horizontal or vertical channel. The multi-stage tapered waveguides are used as transition regions to connect the multimode interference coupler to the waveguides outside the cross waveguide.

[0015] Optionally, the edge distance between the first ground electrode, the second ground electrode, the third ground electrode and the first voltage electrode, the second voltage electrode is 2 to 10 μm.

[0016] In summary, compared with the prior art, the above-conceived technical solution of this application can achieve the following beneficial effects: This application provides a quantum key encoding chip, including a pulse separation module, a first intensity modulator, a phase modulation module, and a second intensity modulator connected in sequence. The phase modulation module includes a first straight waveguide, a cross waveguide, a second straight waveguide, and a first ground electrode, a first voltage electrode, a second ground electrode, a second voltage electrode, and a third ground electrode arranged in parallel and sequentially. The first straight waveguide is located between the first zero electrode and the first voltage electrode, and the second straight waveguide is located between the second ground electrode and the second voltage electrode. Based on the above solution, it can be seen that by integrating all the optoelectronic devices required for time phase encoding into the same chip and designing the phase modulation module as a structure of multiple waveguides and multiple electrodes, this application achieves chip-based and low-cost quantum key encoding system, while further reducing the area occupied by the phase modulation module in the chip, improving the chip integration. In addition, it reduces the required driving voltage and driving power consumption under the same chip area, thereby reducing the system complexity and cost of the driving circuit. Based on the above advantages, the quantum key encoding chip provided in this application achieves miniaturized, low-cost, low-driving-voltage, and low-power QKD encoding, which helps to improve the practicality and application value of QKD technology, enabling it to be more widely used in various practical scenarios. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a quantum key encoding chip provided in an embodiment of this application; Figure 2 This is a schematic diagram of the phase modulation module in the quantum key encoding chip of this application; Figure 3 This is a schematic diagram of the pulse separation module in the quantum key encoding chip of this application; Figure 4 This is a schematic diagram of the first intensity modulator in the quantum key encoding chip of this application; Figure 5 This is a cross-sectional schematic diagram of the quantum key encoding chip of this application; Figure 6This is a cross-sectional schematic diagram of a quantum key encoding chip in another embodiment of this application; Figure 7 This is a schematic diagram of a cross waveguide provided in an embodiment of this application. Detailed Implementation

[0019] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0021] This application proposes a quantum key encoding chip, such as Figure 1 As shown, the chip includes a pulse separation module, a first intensity modulator, a phase modulation module, and a second intensity modulator connected in sequence. An initial optical pulse enters the chip from its input port, and after being sequentially modulated by the pulse separation module, the first intensity modulator, the phase modulation module, and the second intensity modulator, it is encoded and output as a single-photon-level pulse from the chip's output port.

[0022] The pulse separation module includes an input and an output, used to separate the initial optical pulse into two consecutive optical pulses. This step is also known as time encoding in the time-phase encoding of the initial optical pulse. Time encoding mainly utilizes the difference in photon arrival times at the detector to distinguish different quantum states. In the time-phase encoding scheme, the transmitter controls the propagation time of photons in different paths, causing a significant difference in their arrival times at the receiver, thereby encoding the quantum state. The transmitter divides the optical pulse into multiple sub-pulses and introduces time differences through different paths or delay lines (in this application, different paths are unequal-ratio interferometers), assigning a specific time slot to each sub-pulse to represent a different quantum state. The receiver uses precise time measurement equipment, such as a single-photon detector and a time-to-digital converter, to measure the photon arrival time and reconstruct the transmitter's encoded information based on the time slots.

[0023] The first intensity modulator includes an input and an output, used to perform initial intensity modulation on two consecutive optical pulses. This step is also known as decoy state modulation in time-phase encoding of the initial optical pulses. The purpose of decoy state modulation is to improve system security by introducing additional pulse intensity and statistical analysis to detect eavesdropper behavior. One of the two optical pulses is the signal state, and the other is the decoy state. The light intensity of the signal state is greater than that of the decoy state, and the intensity ratio of different pulses is fixed, for example, a 3:1 ratio. When transmitting quantum signals, the signal state and decoy state pulses are randomly alternated, making it difficult for the receiver to distinguish the pulse types.

[0024] The second intensity modulator includes an input and an output. It is used to attenuate and modulate the optical pulses output from the phase modulation module to produce a quantum key signal. The output of the second intensity modulator is connected to an external quantum key receiver via a spatial channel or optical fiber channel. In a quantum key distribution system, the second intensity modulator also functions as an attenuator. The quantum key encoding chip, acting as the transmitter, needs to attenuate the modulated optical pulse signal to the single-photon level using the second intensity modulator (attenuator) to meet the requirements for quantum key decoding and pairing.

[0025] The phase modulation module includes a first straight waveguide, a cross waveguide, a second straight waveguide, and a first ground electrode, a first voltage electrode, a second ground electrode, a second voltage electrode, and a third ground electrode arranged parallel to each other in sequence. The first straight waveguide is located between the first zero electrode and the first voltage electrode, and the second straight waveguide is located between the second ground electrode and the second voltage electrode. The cross waveguide includes mutually perpendicular horizontal and vertical channels. The output end of the first straight waveguide is connected to the input end of the second straight waveguide through the vertical channel of the cross waveguide, and the output end of the second straight waveguide is connected to the second intensity modulator through the horizontal channel of the cross waveguide. The input ends of the first straight waveguide and the second straight waveguide are located on the same side of the phase modulation module. Figure 2 As shown. Thus, with the same width, the phase modulator can perform double-superimposed modulation on the passing light pulse, thereby achieving a larger range of phase modulation with the same width or chip area, without increasing the driving voltage and reducing power consumption requirements. Reference Figure 2 In both the first and second straight waveguides, the light propagates from left to right, and the electric field direction, as shown by the dashed arrow in the figure, passes through the waveguides from top to bottom. This arrangement ensures precise double-layer modulation.

[0026] Continue to refer to Figure 2The cross-shaped waveguide is connected to the first and second straight waveguides via a curved waveguide. After the optical pulse exits from the first straight waveguide, it travels through the cross-shaped waveguide and loops back to the input side of the first straight waveguide, thus ensuring that the input ends of the first and second straight waveguides are on the same side of the phase modulation module. Specifically, the vertical channel input end of the cross-shaped waveguide is connected to the output end of the first straight waveguide via a first curved waveguide, and the input end of the second straight waveguide is connected to the vertical channel output end of the cross-shaped waveguide via a second curved waveguide. The light's propagation direction changes by 90° in the first curved waveguide, and the light undergoes three 90° turns in the second curved waveguide before entering the second straight waveguide.

[0027] In other embodiments of this application, the pulse separation module is an on-chip unequal-arm interferometer, such as... Figure 3 As shown, the on-chip unequal-arm interferometer includes a first waveguide beamsplitter, a first interferometric arm waveguide, a second interferometric arm waveguide, and a second waveguide beamsplitter. The first waveguide beamsplitter receives the input optical pulse and splits it into the first and second interferometric arm waveguides. The second waveguide beamsplitter receives the optical pulses from the first and second interferometric arm waveguides and combines them into the same output port. The lengths of the upper and lower interferometric arms have an optical path difference (ΔL). The optical path difference ΔL results in a time difference Δt between the optical pulses in the first and second interferometric arm waveguides, where ΔL = Δt * c, and c is the speed of light.

[0028] In other embodiments of this application, the first intensity modulator is an equal-arm interferometer, which generally consists of two beam splitters and an upper and lower interference arm between the two beam splitters. The first intensity modulator also includes a first control electrode group, which is used to control the phase difference between the optical pulses passing through the upper and lower interference arms of the first intensity modulator. Figure 4 Similarly, the second intensity modulator can also be an equal-arm interferometer, including a second control electrode group. This second control electrode group is used to control the phase difference between the light pulses in the upper and lower arms of the interference device after passing through the first intensity modulator. The equal-arm interferometer controls the phase of the light in the interference arms through the electric field between the electrodes. The phase difference between the two interference arms affects the interference result, thereby controlling the intensity of the final output light. When the control electric field is strong enough or the length of the interference arms is long enough so that the phase difference between the two interference arms is large enough, the second intensity modulator can attenuate the light pulse to the single-photon level.

[0029] In other embodiments of this application, the first zero electrode, the first voltage electrode, the second ground electrode, the second voltage electrode, and the third ground electrode are all traveling wave electrodes, with their electrical signal input terminals located on the same side and their electrical signal output terminals located on the same side, such as when the signal input terminals are all located on the side of the light input. Figure 2(Input side of the circuit). A traveling-wave electrode is a radio frequency (RF) electrode structure used in high-speed electro-optic modulators. The RF signal (radio wave) in the traveling-wave electrode maintains velocity matching with the light wave during propagation, thereby achieving ultra-wideband, high-efficiency optical field modulation. The RF signal originates from the electrode's starting end (…). Figure 2 The input (from the input side) propagates along the electrode in the form of electromagnetic waves, rather than forming a static electric field locally.

[0030] Furthermore, the signal output terminals of the first ground electrode, second ground electrode, third ground electrode, first voltage electrode, and second voltage electrode are equipped with an integrated radio frequency matching resistor, such as... Figure 2 As shown, it is used to eliminate radio frequency signal reflection. The radio frequency matching resistor is the "terminal absorber" of the traveling wave electrode modulator, which ensures efficient and stable electro-optic interaction over a wide bandwidth by eliminating signal reflection.

[0031] In other embodiments of this application, the first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, and the second voltage electrode are located on the same layer of the chip as the first straight waveguide and the second straight waveguide. For example... Figure 5 As shown, the chip includes a substrate layer, an electrode layer, a waveguide layer, and a SiO2 dielectric layer. The electrode layer includes a first ground electrode, a second ground electrode, a third ground electrode, a first voltage electrode, and a second voltage electrode. The waveguide layer includes a first straight waveguide and a second straight waveguide. The SiO2 dielectric layer covers the electrode layer and the waveguide layer. The electrode layer is made of metal, and the waveguide layer is a single-crystal silicon waveguide, a Si3N4 waveguide, or a lithium niobate waveguide. Their patterns are formed through whole-layer deposition and photomask etching processes, forming an alternating arrangement. The electric field direction between the metal electrodes is parallel to the surfaces of the substrate layer and the dielectric layer. The preferred edge distance between the first ground electrode, the second ground electrode, the third ground electrode, and the first voltage electrode and the second voltage electrode is 2–10 μm. When the distance is less than 2 μm, fabrication becomes difficult, and the internal electric field uniformity does not meet requirements. When the distance is greater than 10 μm, the electric field strength within the waveguide is insufficient, requiring a larger driving voltage and higher power consumption for phase modulation. Therefore, it is preferable to control the distance range within 2–10 μm.

[0032] In another embodiment, the first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, the second voltage electrode, and the first straight waveguide and the second straight waveguide are located in adjacent layers (upper and lower layers) of the chip, such as... Figure 6As shown, the waveguide layer is covered by a SiO2 dielectric, and the electrode layer is covered by a passivation layer. This design is mainly due to the difficulty in fabricating the electrode layer and waveguide layer on the same layer. Etching residues can easily remain between electrodes, between waveguides, and between electrodes and waveguides, affecting electrical and optical performance. By placing the electrode layer and waveguide layer on top of each other, when the thickness of the electrode layer and waveguide layer is much smaller than the distance between them, the electric field direction between the electrodes can be considered parallel to the electrode surface or the substrate surface, and the photoelectric control function can still be achieved normally.

[0033] In other embodiments of this application, the cross-shaped waveguide includes a centrally located multimode interference coupler and four multi-stage tapered waveguides, such as... Figure 7 As shown, a multimode interference coupler is used to confine optical pulses to a straight path from a horizontal or vertical channel. A multi-stage tapered waveguide serves as a transition region connecting the multimode interference coupler to the waveguide outside the cross-shaped waveguide. The multi-stage tapered waveguide is constructed by cascading multiple tapered waveguide segments. Using multi-stage tapered waveguides (also known as tapered waveguides) allows a transition from a single-mode waveguide to the cross-shaped region, resulting in a slow change in the effective refractive index of the waveguide.

[0034] The various embodiments in this specification are described in a progressive, parallel, or combined manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum key encoding chip, characterized in that, It includes a pulse separation module, a first intensity modulator, a phase modulation module, and a second intensity modulator connected in sequence; The pulse separation module includes an input terminal and an output terminal, used to separate the initial optical pulse into two optical pulses, one preceding and one following. The first intensity modulator includes an input terminal and an output terminal, used to perform initial intensity modulation on two consecutive optical pulses respectively; The phase modulation module includes a first straight waveguide, a cross waveguide, a second straight waveguide, and a first ground electrode, a first voltage electrode, a second ground electrode, a second voltage electrode, and a third ground electrode arranged in parallel and sequentially. The first straight waveguide is located between the first zero electrode and the first voltage electrode, and the second straight waveguide is located between the second ground electrode and the second voltage electrode. The cross waveguide includes a horizontal channel and a vertical channel that are perpendicular to each other. The output end of the first straight waveguide is connected to the input end of the second straight waveguide through the vertical channel of the cross waveguide, and the output end of the second straight waveguide is connected to the second intensity modulator through the horizontal channel of the cross waveguide. The input ends of the first straight waveguide and the second straight waveguide are located on the same side of the phase modulation module. The second intensity modulator includes an input terminal and an output terminal, which is used to attenuate and modulate the optical pulse output by the phase modulation module and output it as a quantum key signal. The output terminal of the second intensity modulator is connected to an external quantum key receiver through a space channel or an optical fiber channel.

2. The quantum key encoding chip according to claim 1, characterized in that, It also includes a first curved waveguide and a second curved waveguide. The first curved waveguide is connected between the output end of the first straight waveguide and the input end of the vertical channel, and the second curved waveguide is connected between the output end of the vertical channel and the input end of the second straight waveguide.

3. The quantum key encoding chip according to claim 1, characterized in that, The pulse separation module is an unequal-arm interferometer, including a first waveguide beam splitter, a first interferometric arm waveguide, a second interferometric arm waveguide, and a second waveguide beam splitter. The first waveguide beam splitter is used to receive the input optical pulse and split it into the first interferometric arm waveguide and the second interferometric arm waveguide. The second waveguide beam splitter is used to receive the optical pulses from the first interferometric arm waveguide and the second interferometric arm waveguide and combine them into the same port for output. The lengths of the upper and lower interferometric arms have an optical path difference (ΔL).

4. The quantum key encoding chip according to claim 1, characterized in that, The first intensity modulator is an equal-arm interferometer, including a first control electrode group, which is used to control the phase difference between the optical pulses of the upper and lower arms of the interference after passing through the first intensity modulator.

5. The quantum key encoding chip according to claim 1, characterized in that, The second intensity modulator is an equal-arm interferometer, including a second control electrode group, which is used to control the phase difference between the optical pulses of the upper and lower arms of the interference after passing through the second intensity modulator.

6. The quantum key encoding chip according to claim 1, characterized in that, The first zero electrode, the first voltage electrode, the second ground electrode, the second voltage electrode, and the third ground electrode are all traveling wave electrodes, with their signal input terminals located on the same side and their signal output terminals located on the same side.

7. The quantum key encoding chip according to claim 6, characterized in that, The signal output terminals of the first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, and the second voltage electrode are provided with an integrated radio frequency matching resistor to eliminate radio frequency signal reflection.

8. The quantum key encoding chip according to claim 7, characterized in that, The first ground electrode, the second ground electrode, the third ground electrode, the first voltage electrode, and the second voltage electrode are located on the same layer of the chip as the first straight waveguide and the second straight waveguide.

9. The quantum key encoding chip according to claim 1, characterized in that, The cross-shaped waveguide includes a multimode interference coupler at the center and four multi-stage tapered waveguides. The multimode interference coupler is used to constrain the optical pulse to propagate in a straight line from a horizontal or vertical channel. The multi-stage tapered waveguides serve as transition regions connecting the multimode interference coupler to the waveguides outside the cross-shaped waveguide.

10. The quantum key encoding chip according to claim 1, characterized in that, The edge distance between the first ground electrode, the second ground electrode, the third ground electrode and the first voltage electrode, the second voltage electrode is 2 to 10 μm.

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