Heterogeneous integrated chip

Abstract

The disclosure provides a heterogeneous integrated chip, and relates to the technical field of quantum communication. The heterogeneous integrated chip comprises an input unit, a first waveguide conversion unit, a first phase modulation unit, a second waveguide conversion unit and a second phase modulation unit connected in sequence; the waveguide of the input unit is a silicon waveguide; the first waveguide conversion unit comprises a silicon waveguide and a silicon nitride waveguide, and is used for coupling the optical signal output by the silicon waveguide in the first waveguide conversion unit into the silicon nitride waveguide; the waveguide of the first phase modulation unit is a silicon nitride waveguide, is connected with the silicon nitride waveguide in the first waveguide conversion unit, and is used for inhibiting the introduction of phase noise of the input optical signal; the second waveguide conversion unit comprises a silicon nitride waveguide and a silicon waveguide, and is used for coupling the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit; and the waveguide of the second phase modulation unit is a silicon waveguide.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum communication technology, and more particularly, to heterogeneous integrated chips. Background Art

[0002] In recent years, driven by the increasing demand for secure communications, quantum communication technology, particularly quantum secure communication based on quantum key distribution (QKD), has rapidly developed and become a hot topic in research and commercialization. Quantum key distribution (QKD) utilizes the principles of quantum mechanics to securely transmit keys. By encoding information in quantum states (such as photon polarization or phase), QKD can detect any eavesdropping attempts on either side of the communication, thereby ensuring the security of information transmission. With the advancement of silicon photonics research, quantum key distribution systems are gradually moving from optical devices to chip-based systems, further improving their stability and practicality.

[0003] Currently, silicon waveguides are mostly used for phase modulation during optical signal transmission. However, silicon waveguides have poor thermal stability and can cause refractive index fluctuations when the temperature changes. This can lead to quantum state misalignment or signal distortion, making quantum coding unstable and affecting the reliability and security of key distribution. Summary of the Invention

[0004] In view of this, the present disclosure provides a heterogeneous integrated chip, comprising: an input unit, a first waveguide conversion unit, a first phase modulation unit, a second waveguide conversion unit, and a second phase modulation unit connected in sequence; wherein the waveguide of the input unit is a silicon waveguide, configured with different quantum key distribution protocols, for inputting an optical signal; the first waveguide conversion unit comprises a silicon waveguide and a silicon nitride waveguide, for coupling the optical signal output by the silicon waveguide in the first waveguide conversion unit into the silicon nitride waveguide, wherein the silicon waveguide in the first waveguide conversion unit is connected to the silicon waveguide of the input unit; the waveguide of the first phase modulation unit is a nitride waveguide. The silicon waveguide is connected to the silicon nitride waveguide in the first waveguide conversion unit and is used to suppress the introduction of phase noise of the input optical signal and adjust the phase of the input optical signal. The second waveguide conversion unit includes a silicon nitride waveguide and a silicon waveguide, and is used to couple the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit. The silicon nitride waveguide in the second waveguide conversion unit is connected to the silicon nitride waveguide of the first phase modulation unit. The waveguide of the second phase modulation unit is a silicon waveguide, which is connected to the silicon waveguide in the second waveguide conversion unit and is used to adjust the phase of the input optical signal.

[0005] According to an embodiment of the present disclosure, coupling an optical signal output from a silicon waveguide in a first waveguide conversion unit into a silicon nitride waveguide includes: adjusting the cumulative phase of the optical signal output from the silicon waveguide in the first waveguide conversion unit from a first phase to a second phase, coupling the optical signal output from the silicon waveguide in the first waveguide conversion unit into the silicon nitride waveguide, wherein the second phase is the cumulative phase of the optical signal output from the silicon nitride waveguide in the first waveguide conversion unit; coupling the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit includes adjusting the cumulative phase of the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit from a third phase to a fourth phase, coupling the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit, wherein the fourth phase is the cumulative phase of the optical signal output from the silicon waveguide in the second waveguide conversion unit.

[0006] According to an embodiment of the present disclosure, the first waveguide conversion unit includes: a first silicon-silicon nitride interlayer converter and a second silicon-silicon nitride interlayer converter connected in parallel; wherein the output end of the first silicon-silicon nitride interlayer converter and the output end of the second silicon-silicon nitride interlayer converter are both connected to the output end of the first phase modulation unit; the second waveguide conversion unit includes: a first silicon nitride-silicon interlayer converter and a second silicon nitride-silicon interlayer converter connected in parallel; wherein the output end of the first silicon nitride-silicon interlayer converter and the output end of the second silicon nitride-silicon interlayer converter are coupled to the input end of the second phase modulation unit.

[0007] According to an embodiment of the present disclosure, the first phase modulation unit includes: a thermo-optical modulation unit, which is used to split the input optical signal; and an optical delay unit, which is arranged to be connected to the output end of the thermo-optical modulation unit, and is used to delay the input optical signal and phase modulate the input optical signal.

[0008] According to an embodiment of the present disclosure, the thermo-optical phase modulation unit includes: a first thermo-optical modulator and a second thermo-optical modulator connected in parallel; wherein the input end of the first thermo-optical modulator is connected to the output end of the first silicon-silicon nitride interlayer converter; the input end of the second thermo-optical modulator is connected to the output end of the second silicon-silicon nitride interlayer converter; the output end of the first thermo-optical modulator and the output end of the second thermo-optical modulator are coupled and connected to the input end of the optical delay unit.

[0009] According to an embodiment of the present disclosure, the optical delay unit includes: a delay line and a waveguide connected in parallel; wherein the output end of the delay line is connected to a first silicon nitride-silicon interlayer converter; and the output end of the waveguide is connected to a second silicon nitride-silicon interlayer converter.

[0010] According to an embodiment of the present disclosure, the length difference between the delay line and the waveguide is ΔL, which is expressed as: ΔL=cΔt / n, where c is the speed of light in a vacuum, n is the waveguide refractive index, and Δt is the delay time.

[0011] According to an embodiment of the present disclosure, the second phase modulation unit includes: a third thermo-optic modulator and a first carrier depletion modulator connected in series; a fourth thermo-optic modulator and a second carrier depletion modulator connected in series; wherein the input end of the third thermo-optic modulator and the input end of the fourth thermo-optic modulator are connected to the output end of the second waveguide conversion unit; the output end of the first carrier depletion modulator and the output end of the second carrier depletion modulator are coupled to output a phase-modulated optical signal.

[0012] According to an embodiment of the present disclosure, the heterogeneous integrated chip further includes: a third phase modulation unit connected to the output end of the input unit, for adjusting the phase of the input optical signal; an intensity modulation unit, whose input end is connected to the output end of the second phase modulation unit and the output end of the third phase modulation unit, for modulating the light intensity and the entrapped state of the input optical signal; and a light intensity attenuation unit, whose input end is connected to the output end of the intensity modulation unit, for attenuating the input optical signal to the single-photon level.

[0013] According to an embodiment of the present disclosure, the light intensity attenuation unit includes: a first attenuator and a second attenuator, and the attenuation range of the first attenuator and the second attenuator is 0-60 dB.

[0014] According to an embodiment of the present disclosure, the present invention further includes: a substrate, wherein the material of the substrate includes silicon-on-insulator material or lithium niobate material.

[0015] According to an embodiment of the present disclosure, by setting the waveguide of the first phase modulation unit to a silicon nitride waveguide and utilizing the low thermo-optical coefficient of silicon nitride, the introduction of phase noise during the transmission of the optical signal is effectively suppressed, thereby avoiding signal distortion or instability. At the same time, a first waveguide conversion unit and a second waveguide conversion unit are provided, and the silicon waveguide and the silicon nitride waveguide are connected through the conversion units, so that the cumulative phase of the optical signal on different waveguides is matched, thereby realizing the coupled transmission of the optical signal on different waveguides and reducing the loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0017] Figure 1 The structure diagram of the heterogeneous integrated chip according to the embodiment of the present disclosure is schematically shown;

[0018] Figure 2 Schematically shows a schematic diagram of the BB84 polarization phase protocol and BB84 timestamp-phase protocol encoding process according to an embodiment of the present disclosure;

[0019] Figure 3 The following schematically illustrates a schematic diagram of the encoding process of the differential phase shift protocol and the coherent state single-path protocol according to an embodiment of the present disclosure;

[0020] Description of reference numerals:

[0021] 1. Input unit; 2. Modulation unit; 3. Third phase modulation unit; 4. Intensity modulation unit; 5. Attenuation unit; 101. Fifth thermo-optical modulator; 102. Third carrier depletion modulator; 103. Sixth thermo-optical modulator; 104. Fourth carrier depletion modulator; 210. First waveguide conversion unit; 211. First silicon-silicon nitride interlayer converter; 212. Second silicon-silicon nitride interlayer converter; 220. Thermo-optical modulation unit; 221. First thermo-optical modulator; 222. Second thermo-optical modulator; 230. Optical delay unit; 231. Optical delay Line; 232, waveguide; 240, second waveguide conversion unit; 241, first silicon nitride-silicon interlayer converter; 242, second silicon nitride-silicon interlayer converter; 250, second phase modulation unit; 251, third thermo-optical modulator; 252, fourth thermo-optical modulator; 301, seventh thermo-optical modulator; 302, fifth carrier depletion modulator; 401, seventh thermo-optical modulator; 402, fifth carrier depletion modulator; 403, eighth thermo-optical modulator; 404, sixth carrier depletion modulator; 501, first attenuator; 502, second attenuator. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may be implemented without these specific details. In addition, in the following description, descriptions of well-known systems and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0023] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0024] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0025] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0026] Figure 1 The schematic diagram of the structure of the heterogeneous integrated chip according to the embodiment of the present disclosure is shown schematically.

[0027] like Figure 1 As shown, the present disclosure provides a heterogeneous integrated chip, comprising: an input unit 1, a first waveguide conversion unit 210, a first phase modulation unit, a second waveguide conversion unit 240, and a second phase modulation unit 250 connected in sequence;

[0028] The waveguide of the input unit 1 is a silicon waveguide, which is configured with different quantum key distribution protocols and is used to input optical signals;

[0029] The first waveguide conversion unit 210 includes a silicon waveguide and a silicon nitride waveguide, and is used to couple the optical signal output by the silicon waveguide in the first waveguide conversion unit into the silicon nitride waveguide, wherein the silicon waveguide in the first waveguide conversion unit is connected to the silicon waveguide of the input unit.

[0030] The waveguide of the first phase modulation unit is a silicon nitride waveguide, which is connected to the silicon nitride waveguide in the first waveguide conversion unit and is used to suppress the introduction of phase noise of the input optical signal and adjust the phase of the input optical signal;

[0031] The second waveguide conversion unit includes a silicon nitride waveguide and a silicon waveguide, and is used to couple the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit to the silicon waveguide in the second waveguide conversion unit; wherein the silicon nitride waveguide in the second waveguide conversion unit is connected to the silicon nitride waveguide in the first phase modulation unit.

[0032] The silicon nitride waveguide in the second waveguide conversion unit 240 is connected to the silicon nitride waveguide in the first phase modulation unit. The waveguide in the second phase modulation unit 250 is a silicon waveguide, connected to the silicon waveguide in the second waveguide conversion unit, for adjusting the phase of the input optical signal.

[0033] In an embodiment of the present disclosure, the input unit can be configured with four coding protocols: BB84 polarization coding, BB84 timestamp-phase coding (time-bin), coherent time coding (COW), and differential phase coding (DPS) to meet different application scenarios and security requirements.

[0034] In photonic chips or quantum interference devices, quantum information is typically encoded in the phase or intensity of light. If the refractive index varies dramatically with temperature, phase noise can be introduced, causing interference fringes to drift and even destroying quantum coherence. Existing on-chip waveguides are typically silicon waveguides. However, due to silicon's poor thermal stability, its refractive index fluctuates significantly with temperature changes, introducing phase noise and leading to signal distortion or loss.

[0035] Based on this, the embodiment of the present disclosure sets the waveguide of the first phase modulation unit which plays the main phase modulation role to be a silicon nitride waveguide, wherein the first phase modulation unit is composed of Figure 1 The optical delay unit 230 is composed of a thermo-optical modulation unit 220. Utilizing the low thermo-optical coefficient of silicon nitride, when the system ambient temperature fluctuates, the refractive index of silicon nitride remains relatively stable, thereby reducing optical phase changes and suppressing the introduction of phase noise.

[0036] However, since the input unit and the second phase modulation unit are both silicon waveguides, and the first phase modulation unit is a silicon nitride waveguide, and the silicon waveguide is usually prepared on a silicon substrate, while the silicon nitride waveguide requires a layer of silicon nitride material to be deposited on the silicon waveguide, the two have different preparation processes, resulting in a certain distance at the physical level. In addition, the refractive index of the two is also different, which will cause the phase of the optical signal in different waveguides to be mismatched. As a result, it is difficult to directly couple the optical signal from one waveguide material into another waveguide material, and the coupling efficiency is extremely low. Based on this, a waveguide conversion unit is set to achieve the coupling output of the optical signal between different waveguides.

[0037] According to an embodiment of the present disclosure, coupling an optical signal output from a silicon waveguide in a first waveguide conversion unit into a silicon nitride waveguide includes: adjusting the cumulative phase of the optical signal output from the silicon waveguide in the first waveguide conversion unit from a first phase to a second phase, coupling the optical signal output from the silicon waveguide in the first waveguide conversion unit into the silicon nitride waveguide, wherein the second phase is the cumulative phase of the optical signal output from the silicon nitride waveguide in the first waveguide conversion unit; coupling the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit includes adjusting the cumulative phase of the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit from a third phase to a fourth phase, coupling the optical signal output from the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit, wherein the fourth phase is the cumulative phase of the optical signal output from the silicon waveguide in the second waveguide conversion unit.

[0038] In the embodiments disclosed herein, silicon waveguides and silicon nitride waveguides are often phase-mismatched for light of the same wavelength. This phase mismatch makes it difficult for light signals of the same wavelength to couple from one waveguide material to another, resulting in extremely low coupling efficiency. Specifically, the accumulated phase of the light signal is determined by the effective refractive index and optical path length of the waveguide. Since silicon waveguides and silicon nitride waveguides have different refractive indices, direct connection will result in discontinuous phases of the light, interference, signal distortion, or even complete failure. The expression for the accumulated phase is:

[0039] .

[0040] in, is the effective refractive index of the waveguide, is the wavelength of the optical signal, and L is the optical path length.

[0041] Based on this, it is necessary to make the cumulative phase modulation of the silicon waveguide and the silicon nitride waveguide in the waveguide conversion unit the same to form phase matching, so as to facilitate the coupling of the optical signal from one waveguide material into another waveguide material.

[0042] In the embodiments disclosed herein, a transition zone can be designed to gradually change the waveguide geometry for a smooth transition, avoiding sudden changes in the phase accumulation rate. Alternatively, optical path compensation can be implemented by adjusting the waveguide length or adding additional phase compensation components to the system to ensure overall phase consistency.

[0043] According to an embodiment of the present disclosure, the first waveguide conversion unit 210 includes: a first silicon-silicon nitride interlayer converter 211 and a second silicon-silicon nitride interlayer converter 212 connected in parallel; wherein the output end of the first silicon-silicon nitride interlayer converter 211 and the output end of the second silicon-silicon nitride interlayer converter 212 are both connected to the output end of the first phase modulation unit; the second waveguide conversion unit 240 includes: a first silicon nitride-silicon interlayer converter 241 and a second silicon nitride-silicon interlayer converter 242 connected in parallel; wherein the output end of the first silicon nitride-silicon interlayer converter 241 and the output end of the second silicon nitride-silicon interlayer converter 242 are coupled and connected to the input end of the second phase modulation unit.

[0044] In an embodiment of the present disclosure, the optical signal output by the input unit is divided into two paths by a 2×2 MMI (Multi-Mode Interferometer) and input into the first silicon-silicon nitride interlayer converter 211 and the second silicon-silicon nitride interlayer converter 212 respectively. Phase matching of optical signals between different waveguides is achieved by setting up the two interlayer converters.

[0045] According to an embodiment of the present disclosure, the first phase modulation unit includes: a thermo-optical modulation unit 220, which is used to split the input optical signal; and an optical delay unit 230, which is arranged to be connected to the output end of the thermo-optical modulation unit, and is used to delay the input optical signal and phase modulate the input optical signal.

[0046] In the disclosed embodiments, a thermo-optical modulation unit is provided to adjust and split the input optical signal, thereby balancing the power passing through the upper and lower arms of the optical delay unit, thereby achieving high interference visibility and reducing the quantum error rate. The split optical signals are then input into the optical delay unit. By configuring the optical delay unit as an unequal-arm Mach-Zehnder interferometer, one optical signal is delayed and phase-modulated between the two optical signals.

[0047] According to an embodiment of the present disclosure, the thermo-optical modulation unit 220 includes: a first thermo-optical modulator 221 and a second thermo-optical modulator 222 connected in parallel; wherein, the input end of the first thermo-optical modulator 221 is connected to the output end of the first silicon-silicon nitride interlayer converter 211; the input end of the second thermo-optical modulator 222 is connected to the output end of the second silicon-silicon nitride interlayer converter 212; the output end of the first thermo-optical modulator 221 and the output end of the second thermo-optical modulator 222 are coupled and connected to the input end of the optical delay unit 230.

[0048] In the embodiment of the present disclosure, the thermo-optical modulation unit is composed of parallel thermo-optical modulators to adjust and split the optical signal. The structure is simple and the volume of the chip can be effectively reduced.

[0049] According to an embodiment of the present disclosure, the optical delay unit 230 includes: a delay line 231 and a waveguide 232 connected in parallel; wherein the output end of the delay line is connected to the first silicon nitride-silicon interlayer converter; and the output end of the waveguide is connected to the second silicon nitride-silicon interlayer converter.

[0050] According to an embodiment of the present disclosure, the length difference between the delay line 231 and the waveguide 232 is ΔL, which is expressed as: ΔL=cΔt / n, where c is the speed of light in vacuum, n is the waveguide refractive index, and Δt is the delay time.

[0051] In an embodiment of the present disclosure, the voltage of a heating electrode disposed on an optical delay line is controlled, and the thermo-optical effect of a silicon nitride waveguide is utilized to change the refractive index of the optical waveguide, thereby adjusting the phase of the optical signal.

[0052] According to an embodiment of the present disclosure, the second phase modulation unit 250 includes: a third thermo-optical modulator 251 and a first carrier depletion modulator 252 connected in series; a fourth thermo-optical modulator 253 and a second carrier depletion modulator 254 connected in series; wherein the input end of the third thermo-optical modulator 251 and the input end of the fourth thermo-optical modulator 253 are connected to the output end of the second waveguide conversion unit 240; the output end of the first carrier depletion modulator 252 and the output end of the second carrier depletion modulator 254 are coupled to output two phase-modulated optical signals.

[0053] In the embodiment of the present disclosure, a thermo-optical modulator is used to ensure that the optical signal achieves π phase modulation, and a carrier depletion modulator is used to further assist in phase modulation; and the second phase modulation unit is set as a two-arm Mach-Zehnder interferometer, which can increase the modulation range and avoid the insufficient modulation range when only single-arm modulation is used, which cannot reach 3π / 2 and affects the encoding of the phase protocol.

[0054] According to an embodiment of the present disclosure, the heterogeneous integrated chip further includes: a third phase modulation unit 3, connected to the output end of the input unit, for adjusting the phase of the input optical signal; an intensity modulation unit 4, whose input end is connected to the output end of the second optical phase modulation unit and the output end of the third phase unit, for modulating the optical intensity and the decoy state of the input optical signal; and an optical intensity attenuation unit 5, whose input end is connected to the output end of the intensity modulation unit, for attenuating the input optical signal to the single-photon level.

[0055] According to an embodiment of the present disclosure, the input unit includes: a fifth thermo-optical modulator 101 and a third carrier depletion modulator 102 connected in series; a sixth thermo-optical modulator 103 and a fourth carrier depletion modulator 104 connected in series, and the output end of the third carrier depletion modulator 102 is coupled with the output end of the fourth carrier depletion modulator 104 to output an optical signal.

[0056] According to an embodiment of the present disclosure, the third phase modulation unit 3 includes a seventh thermo-optical modulator 301 and a fifth carrier depletion modulator 302 connected in series. The optical signal output by the input unit 1 is phase-modulated by the third phase modulation unit and then input into the 2×2MMI to be divided into two light beams. These two light beams are phase-modulated and entangled-state modulated in the intensity modulation unit 4 and then coupled again to output two light signals. One of the light signals is attenuated by the light intensity attenuation unit to output the quantum state.

[0057] According to an embodiment of the present disclosure, the forcing unit 4 includes: a seventh thermo-optical modulator 401 and a fifth carrier depletion modulator 402 connected in series; an eighth thermo-optical modulator 403 and a sixth carrier depletion modulator 404 connected in series, and the output end of the third carrier depletion modulator 402 is coupled to the output end of the fourth carrier depletion modulator 404.

[0058] In the embodiment of the present disclosure, one of the light signals output by the modulation unit 2 is input into the upper and lower arms of the forcing unit 4 after being split for phase modulation, or the light signal output by the third phase modulation unit 3 is input into the upper and lower arms of the forcing unit 4 after being split for phase modulation.

[0059] According to the embodiment of the present disclosure, the light intensity attenuation unit 5 comprises a first attenuator 501 and a second attenuator 502, and the attenuation ranges of the first attenuator and the second attenuator are 0-60dB.

[0060] In the embodiment of the present disclosure, the light signal modulated by the forcing unit 4 is again split by the 2*2 MMI, and one of the light signals is input into the light intensity attenuation unit 5 for signal attenuation.

[0061] According to the embodiment of the present disclosure, the substrate is made of silicon-on-insulator material or lithium niobate material.

[0062] In the embodiment of the present disclosure, if the substrate is silicon-on-insulator material, the silicon layer is on an insulating substrate (usually silicon oxide), and the thermal effect is low, which helps to reduce the power consumption of the chip. The silicon nitride is used as the waveguide, and the thermo-optic coefficient of the SiN waveguide is small, which has better temperature stability and can maintain stable performance in a wider temperature range. This feature is particularly important for quantum key distribution and sensing applications that are significantly affected by temperature changes. Therefore, the integration of SOI and SiN heterostructures has high integration, low loss, low power consumption, and temperature stability, which can significantly improve the performance of photonic integrated circuits.

[0063] If the substrate is lithium niobate material (LNOI for short), it has a very high nonlinear optical coefficient and a thermo-optic coefficient, which can realize efficient generation, control, frequency conversion, storage, and hetero-integrated single-photon detection of photonic states. Moreover, the combination of the nonlinear optical properties of LNOI and the low-loss transmission properties of SiN enables efficient generation and transmission of quantum photon pairs in quantum key distribution systems, reduces optical loss, improves optical performance, and all optical functions can be completed on the same chip, greatly reducing the size of the system and the complexity of the equipment. At the same time, the QKD system of LNOI and SiN hetero-integration has stronger adaptability to environmental factors such as temperature fluctuations and electromagnetic interference, which can improve the resistance of the system to external interference and enhance the security and reliability of quantum communication.

[0064] Therefore, in the embodiment of the present disclosure, by setting the waveguide of the first phase modulation unit to be made of silicon nitride material, the integration on silicon-on-insulator material or lithium niobate material is facilitated, the integration density is improved, and the stability during the transmission of the light signal is improved.

[0065] According to an embodiment of the present disclosure, the material of the heating electrode includes titanium, tungsten or titanium-tungsten alloy; the material of the lead electrodes of the thermo-optical modulator and the carrier depletion modulator is aluminum.

[0066] Figure 2 The figure schematically shows a BB84 phase protocol encoding process according to an embodiment of the present disclosure.

[0067] like Figure 2 As shown, a possible embodiment of the present disclosure provides a BB84 phase protocol encoding process, as shown below:

[0068] The pulsed optical signal enters the encoding chip through the input port A, and enters the input unit 1 after waveguide transmission. By applying a certain voltage to the heating electrodes of the upper and lower arm thermo-optical phase shifters of the input unit 1, the phase difference of the upper and lower arm light beams is controlled to be π, so that the optical signal is output only through the upper output port of the input unit 1 to the first waveguide conversion unit 210.

[0069] A Si-SiN interlayer converter is used to realize the input of the optical signal from the Si waveguide to the SiN waveguide terminal. The optical signal enters the thermo-optical modulation unit 220 through the SiN waveguide. By applying a certain voltage to the upper and lower arm modulators of the thermo-optical modulation unit 220 to generate unequal-ratio light beams, the loss difference generated by the two optical signals entering the optical delay unit 230 and the second phase modulation unit 250 with a ΔL path difference can be balanced, ensuring the power balance of the two output optical signals. The unequal-ratio light beams output from the output port of the thermo-optical modulation unit 220 enter the optical delay unit 230 to delay the input optical signal and modulate the phase of the optical signal.

[0070] After phase modulation at 230°, the optical beam enters the second waveguide conversion unit 240. A SiN-Si interlayer converter is used to transfer the optical signal from the SiN waveguide to the Si waveguide. The optical signal then enters the second phase modulation unit 250 through the Si waveguide. Different voltages are applied to the modulation arm of the second phase modulation unit 250 for dynamic modulation. This randomly generates phase differences of π / 2, 3π / 2, 0, and π between the two optical signals, and then outputs two optical signals. One optical signal is output from port B to monitor the generation of double pulses.

[0071] After being split, the other light signal enters the upper and lower arms of the intensity modulation unit 4 respectively. By applying a certain voltage to the upper and lower arm modulators, light intensity modulation and entrapped state modulation are performed, so that the two light signals are split in equal proportions, and one of the light beams is input into the light intensity attenuation unit 5.

[0072] Finally, appropriate voltages are applied to the optical attenuators 501 and 502. The optical signal is attenuated to 0.1 / pulse through the optical attenuation units 501 and 502 and output to the optical fiber through the output port C, realizing four quantum states. 、 、 、 Port D can detect four unattenuated quantum states.

[0073] like Figure 2 As shown, a possible embodiment of the present disclosure provides a BB84 timestamp-phase protocol encoding process, as shown below:

[0074] The pulsed optical signal enters the encoding chip through the input port A, and enters the input unit 1 after waveguide transmission. By applying a certain voltage to the heating electrodes of the upper and lower arm thermo-optical phase shifters of the input unit 1, the phase difference of the upper and lower arm light beams is controlled to be π, so that the optical signal is output only through the upper output port of the input unit 1 to the first waveguide conversion unit 210.

[0075] A Si-SiN interlayer converter is used to realize the input of the optical signal from the Si waveguide to the SiN waveguide terminal. The optical signal enters the thermo-optical modulation unit 220 through the SiN waveguide. By applying a certain voltage to the upper and lower arm modulators of the thermo-optical modulation unit 220 to generate unequal-ratio light beams, the loss difference generated by the two optical signals entering the optical delay unit 230 and the second phase modulation unit 250 with a ΔL path difference can be balanced to ensure the power balance of the two output optical signals. The unequal-ratio light beams output from the output port of the thermo-optical phase modulation unit 220 enter the optical delay unit 230 to delay the input optical signal and modulate the phase of the optical signal.

[0076] After phase modulation at 230°, the optical beam enters the second waveguide conversion unit 240. A SiN-Si interlayer converter is used to transfer the optical signal from the SiN waveguide to the Si waveguide. The optical signal then enters the second phase modulation unit 250 through the Si waveguide. Different voltages are applied to the modulation arm of the second phase modulation unit 250 for dynamic modulation, randomly generating a phase difference of 0 and π between the two optical signals. The two optical signals are then output. One optical signal is output from port B to monitor the generation of double pulses.

[0077] After being split, the other optical signal enters the upper and lower arms of the intensity modulation unit 4 respectively. By applying a certain voltage to the upper and lower arm modulators, light intensity modulation and entrapment modulation are performed, so that the two optical signals enter the light intensity attenuation unit 5 in an equal-proportional split manner.

[0078] Finally, appropriate voltages are applied to the optical attenuators 501 and 502. The optical signal is attenuated to 0.1 / pulse through the optical attenuation units 501 and 502 and output to the optical fiber through the output port C, realizing four quantum states. 、 、 、 Port D can detect four unattenuated quantum states.

[0079] According to an embodiment of the present disclosure, the modulation unit 2 includes: a first waveguide conversion unit 210 , a first phase modulation unit, a second waveguide conversion unit 240 and a second phase modulation unit 250 .

[0080] Depend on Figure 2 It can be seen that the encoding paths of both the BB84 polarization encoding and BB84 timestamp-phase encoding (time-bin) encoding protocols are as follows: the input optical pulse signal is transmitted through input unit 1 to modulation unit 2, where phase modulation and beam splitting are performed, outputting two light beams. One of the light beams is split through 2×2 MMI and then enters intensity modulation unit 4 for decoy state modulation, and finally output to optical attenuation unit 5 for output.

[0081] Figure 3 The following schematically shows a differential phase shift protocol encoding process according to an embodiment of the present disclosure.

[0082] like Figure 3 As shown, a possible embodiment of the present disclosure provides a differential phase shift protocol encoding process, as shown below:

[0083] The pulsed optical signal enters the encoder chip through input port A, travels through the waveguide, and enters input unit 1. By applying a specific voltage to the heating electrodes of the upper and lower arm thermo-optical modulators of input unit 1, the optical pulse is output only through the lower port of input unit 1 to the third phase modulation unit 3. Applying a specific voltage to the third phase modulation unit 3 dynamically modulates the pulse pairs, randomly generating phase differences of 0 and π between them, which then enter the intensity modulation unit 4.

[0084] Finally, by applying a certain voltage to the upper and lower arm modulators of the intensity modulation unit 4, light intensity modulation and decoy state modulation are performed, so that the light pulse enters the light intensity attenuation unit 5 in a proportional manner. Finally, by applying appropriate voltage to the optical attenuators 501 and 502, the light pulse pair is attenuated to 0.1 / pulse through the optical attenuation units 501 and 502, and is output to the optical fiber through the output port C, realizing four quantum states. 、 、 Preparation of (decoy state).

[0085] like Figure 3 As shown, a possible embodiment of the present disclosure provides a coherent state single-path protocol encoding process, as shown below:

[0086] The pulsed optical signal enters the encoder chip through input port A, travels through the waveguide, and then enters input unit 1. By applying a certain voltage to the heating electrodes of the upper and lower arm thermo-optical modulators of input unit 1, the optical pulse is output only through the lower port of input unit 1 to the third phase modulation unit 3. A certain voltage is applied to the third phase modulation unit 3 for dynamic modulation, resulting in zero phase difference between the pulse pairs before entering the intensity modulation unit 4.

[0087] Finally, by applying a certain voltage to the upper and lower arm modulators of the intensity modulation unit 4, light intensity modulation and decoy state modulation are performed, so that the light pulse enters the light intensity attenuation unit 5 in a proportional manner. Finally, by applying appropriate voltage to the optical attenuators 501 and 502, the light pulse pair is attenuated to 0.1 / pulse through the optical attenuation units 501 and 502, and is output to the optical fiber through the output port C, realizing four quantum states. 、 、 Preparation of (decoy state).

[0088] Depend on Figure 3 It can be seen that the encoding paths of the differential phase shift protocol and the coherent state single-channel protocol are both: the input optical pulse signal is transmitted to the third phase modulation unit 3 through the input unit 1, the phase is modulated in the third phase modulation unit 3, and the optical signal is output. The output optical signal is then split into 2×2 MMI beams and enters the intensity modulation unit 4 for decoy state modulation, and finally output to the optical attenuation unit 5 for output.

[0089] Therefore, the heterogeneous integrated chip disclosed in the present invention can perform rapid functional configuration of multiple QKD coding schemes on the chip, realizes the compatibility of multiple protocols on a single chip, improves the integration of the system, simplifies the device structure, and has the potential for low-cost promotion in practical applications; using SiN material for the waveguide of the first phase modulation unit can effectively reduce losses, and SiN has a small thermo-optical coefficient and better thermal stability than Si, which reduces quantum state misalignment or signal distortion, stabilizes quantum coding, and thus increases the reliability and security of quantum key distribution.

[0090] Those skilled in the art will appreciate that various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, even if such combinations or combinations are not explicitly described in this disclosure. In particular, various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0091] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A heterogeneous integrated chip, characterized in that: include: An input unit, a first waveguide conversion unit, a first phase modulation unit, a second waveguide conversion unit, and a second phase modulation unit connected in sequence; The waveguide of the input unit is a silicon waveguide, configured with different quantum key distribution protocols, for inputting optical signals; The first waveguide conversion unit includes a silicon waveguide and a silicon nitride waveguide, and is used to couple the optical signal output by the silicon waveguide in the first waveguide conversion unit to the silicon nitride waveguide, wherein the silicon waveguide in the first waveguide conversion unit is connected to the silicon waveguide of the input unit; The waveguide of the first phase modulation unit is a silicon nitride waveguide, which is connected to the silicon nitride waveguide in the first waveguide conversion unit, and is used to suppress the introduction of phase noise of the input optical signal and adjust the phase of the input optical signal; The second waveguide conversion unit includes a silicon nitride waveguide and a silicon waveguide, and is used to couple the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit to the silicon waveguide in the second waveguide conversion unit; wherein the silicon nitride waveguide in the second waveguide conversion unit is connected to the silicon nitride waveguide of the first phase modulation unit; The waveguide of the second phase modulation unit is a silicon waveguide, which is connected to the silicon waveguide in the second waveguide conversion unit and is used to adjust the phase of the input optical signal.

2. The heterogeneous integrated chip according to claim 1, characterized in that: The step of coupling the optical signal output from the silicon waveguide in the first waveguide conversion unit to the silicon nitride waveguide comprises: adjusting the accumulated phase of the optical signal output by the silicon waveguide in the first waveguide conversion unit from a first phase to a second phase, and coupling the optical signal output by the silicon waveguide in the first waveguide conversion unit to the silicon nitride waveguide, wherein the second phase is the accumulated phase of the optical signal output by the silicon nitride waveguide in the first waveguide conversion unit; The step of coupling the optical signal outputted from the silicon nitride waveguide in the second waveguide conversion unit to the silicon waveguide in the second waveguide conversion unit comprises: The accumulated phase of the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit is adjusted from the third phase to the fourth phase, so as to couple the optical signal output by the silicon nitride waveguide in the second waveguide conversion unit into the silicon waveguide in the second waveguide conversion unit, wherein the fourth phase is the accumulated phase of the optical signal output by the silicon waveguide in the second waveguide conversion unit.

3. The heterogeneous integrated chip according to claim 1, characterized in that: The first waveguide conversion unit includes: a first silicon-silicon nitride interlayer converter and a second silicon-silicon nitride interlayer converter connected in parallel; Wherein, the output end of the first silicon-silicon nitride interlayer converter and the output end of the second silicon-silicon nitride interlayer converter are both connected to the output end of the first phase modulation unit; The second waveguide conversion unit includes: a first silicon nitride-to-silicon interlayer converter and a second silicon nitride-to-silicon interlayer converter connected in parallel; The output end of the first silicon nitride-silicon interlayer converter and the output end of the second silicon nitride-silicon interlayer converter are coupled and connected to the input end of the second phase modulation unit.

4. The heterogeneous integrated chip according to claim 3, characterized in that: The first phase adjustment unit includes: a thermo-optical modulation unit, configured to split an input optical signal; and The optical delay unit is connected to the output end of the thermo-optical modulation unit and is used for delaying the input optical signal and performing phase modulation on the input optical signal.

5. The heterogeneous integrated chip according to claim 4, characterized in that: The thermo-optical modulation unit comprises: a first thermo-optical modulator and a second thermo-optical modulator connected in parallel; Wherein, the input end of the first thermo-optical modulator is connected to the output end of the first silicon-silicon nitride interlayer converter; The input end of the second thermo-optical modulator is connected to the output end of the second silicon-silicon nitride interlayer converter; The output end of the first thermo-optical modulator and the output end of the second thermo-optical modulator are coupled and then connected to the input end of the optical delay unit.

6. The heterogeneous integrated chip according to claim 4, characterized in that: The optical delay unit comprises: Delay lines and waveguides in parallel; Wherein, the output end of the delay line is connected to the first silicon nitride-silicon interlayer converter; An output end of the waveguide is connected to the second silicon nitride-silicon interlayer converter.

7. The heterogeneous integrated chip according to claim 6, characterized in that: The length difference between the delay line and the waveguide is ΔL, which is expressed as: ΔL=cΔt / n Where c is the speed of light in vacuum, n is the waveguide refractive index, and Δt is the delay time.

8. The heterogeneous integrated chip according to claim 6, characterized in that: The second phase modulation unit includes: a third thermo-optical modulator and a first carrier depletion modulator connected in series; a fourth thermo-optical modulator and a second carrier depletion modulator connected in series; Wherein, the input end of the third thermo-optical modulator and the input end of the fourth thermo-optical modulator are connected to the output end of the second waveguide conversion unit; The output end of the first carrier depletion modulator and the output end of the second carrier depletion modulator are coupled to output a phase-modulated optical signal.

9. The heterogeneous integrated chip according to claim 1, characterized in that: Also includes: a third phase adjustment unit, connected to the output end of the input unit, and configured to adjust the phase of the input optical signal; an intensity modulation unit, whose input end is connected to the output end of the second phase modulation unit and the output end of the third phase modulation unit, and is used to modulate the light intensity and the decoy state of the input optical signal; The light intensity attenuation unit has an input end connected to the output end of the intensity modulation unit and is used to attenuate the input light signal to the single photon level.

10. The heterogeneous integrated chip according to claim 1, characterized in that: Also includes: The substrate is made of silicon-on-insulator material or lithium niobate material.

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