On-chip quantum light source

Abstract

The application provides an on-chip quantum light source, comprising: a laser suitable for generating pump laser; a quantum chip comprising: a support layer; an edge coupler located at the edge of the quantum chip and suitable for coupling the pump laser transmitted by an external optical fiber to the quantum chip; a coupling component formed on the support layer and distributing the pump laser transmitted to the quantum chip into two parts with a specific power splitting ratio; a connecting component which is a connecting waveguide and has two ends connected with the input and output ports of the coupling component respectively; the coupling component is configured to couple a part of the pump laser into the cavity of a ring resonator; the pump laser coupled into the ring resonator resonates in the resonator and generates correlated photon pairs through spontaneous four-wave mixing effect. The coupling component is also suitable for outputting the pump laser not coupled into the cavity, the correlated photon pairs, and the residual part of the pump laser after being coupled into the ring cavity and resonating.

Description

Technical Field

[0001] This invention relates to the field of quantum technology, and more specifically, to an on-chip quantum light source. Background Technology

[0002] Quantum light sources are one of the core resources of quantum technology, and the generation of high-quality quantum light sources is a current research hotspot in academia and industry. Quantum light sources can be generated through optical nonlinear transformation processes in materials, such as spontaneous parametric down-conversion (SPDC) and spontaneous four-wave mixing (SFWM) effects. In nonlinear optical crystals, correlated photon pairs can be generated through SPDC, but this implementation requires the construction of a free-space optical system and precise spatial optical alignment. Furthermore, due to the large wavelength gap between the pump laser and signal light during SPDC, complex phase-matching designs are needed to improve the efficiency of correlated photon pair generation. Therefore, quantum light source systems based on nonlinear crystals suffer from drawbacks such as system complexity, poor stability, and difficulty in integration. SFWM is another technical solution for generating correlated photon pairs; compared to SPDC-based quantum light sources, SFWM-based quantum light sources are easier to meet phase-matching requirements. In particular, fiber-based SFWM quantum light sources exhibit high nonlinear conversion efficiency due to their long coherence length within a small mode area. However, noise generated by spontaneous Raman scattering (SpRS) in the fiber reduces the signal-to-noise ratio of correlated photon pairs. While reducing the fiber temperature can suppress SpRS noise, it increases system complexity and significantly raises costs. Summary of the Invention

[0003] In view of this, the present invention provides an on-chip quantum light source, comprising:

[0004] Lasers suitable for generating pump lasers;

[0005] Quantum chips, including:

[0006] Support layer, including substrate and lower cladding layer;

[0007] An edge coupler, formed on the support layer and located at the edge of the quantum chip, is suitable for coupling pump laser from a laser to the quantum chip via an external optical fiber and transmitting it to the coupling component via an input waveguide.

[0008] The coupling component, a multimode waveguide, is formed on the support layer and is suitable for redistributing the pump laser transmitted to the quantum chip into two parts with a specific power split ratio.

[0009] The connecting component, which connects the waveguide, is connected to the coupling component to form a ring resonant cavity;

[0010] The coupling component is configured to couple a portion of the pump laser into the ring resonant cavity by causing a self-image effect in the pump laser; the pump laser coupled into the ring resonant cavity resonates in the resonant cavity and undergoes a spontaneous four-wave mixing effect to generate correlated photon pairs; the coupling component is also suitable for outputting the pump laser that is not coupled into the cavity, the correlated photon pairs, and the residual portion of the pump laser after it is coupled into the cavity and resonates.

[0011] According to an embodiment of the present invention, the length of the coupling component along a first direction of incident pump laser and the width in a second direction perpendicular to the first direction are configured to determine the power splitting ratio of the coupling component.

[0012] According to an embodiment of the present invention, a first output port, a first input port, and a second output port are formed on the coupling component;

[0013] The pump laser undergoes a self-image effect within the coupling component to split the pump laser into two parts with a specific power splitting ratio. The first output port is suitable for transmitting the pump laser coupled into the cavity to the ring resonant cavity through a connecting waveguide.

[0014] The second output port is suitable for outputting correlated photon pairs, pump lasers not coupled into the cavity, and residual portions of pump lasers after they have been coupled into the ring cavity and resonated.

[0015] According to an embodiment of the present invention, a second input port is formed on the coupling component, which is suitable for transmitting pump laser from the edge coupler to the cavity of the ring resonant cavity. The first input port, the first output port, the second input port, the second output port, the coupling component, and the connecting waveguide constitute the ring resonant cavity.

[0016] According to an embodiment of the present invention, the on-chip quantum light source further includes a phase shifter.

[0017] Phase shifters are used to adjust the resonant wavelength of a ring resonant cavity.

[0018] According to an embodiment of the present invention, the quantum chip further includes:

[0019] An input waveguide, connected to an edge coupler and a second input port, is formed on a support layer and is suitable for receiving pump laser input to the quantum chip via the edge coupler and transmitting the pump laser to the second input port.

[0020] The output waveguide, formed on the support layer, is suitable for outputting correlated photon pairs, pump lasers not coupled into the cavity, and residual portions of pump lasers after they have been coupled into the ring cavity and resonated.

[0021] Cladding is used to confine the optical field to propagate within the waveguide and protect the core layer.

[0022] According to an embodiment of the present invention, the on-chip quantum light source further includes:

[0023] Beam splitting assembly, suitable for splitting the laser output from a ring coupler into a first sub-laser and a second sub-laser;

[0024] A power meter suitable for detecting the power of the pump laser based on the first sub-laser.

[0025] According to an embodiment of the present invention, the on-chip quantum light source further includes:

[0026] The first filtering component is used to filter out unconverted pump light, ensuring that only the generated correlated photon pairs enter the subsequent experimental setup.

[0027] According to an embodiment of the present invention, the on-chip quantum light source further includes:

[0028] The second filtering component is suitable for separating the signal photon and the idler photon in a correlated photon pair;

[0029] The detection assembly includes two single-photon detectors, a time analyzer, and a computer. The two single-photon detectors are used to detect the signal photon and idler photon output from the second filter assembly, respectively. The electrical signal pulses triggered by the signal photon and idler photon received by the two single-photon detectors are transmitted to the time analyzer. The time analyzer is connected to the computer and transmits the photon arrival time analysis results to the computer to complete the measurement of single-photon count rate and coincidence count rate.

[0030] According to embodiments of the present invention, there is no need to construct a free-space optical system or to design complex phase matching. The design of the ring resonator avoids the drawbacks of on-chip quantum light source systems based on nonlinear crystals, such as complexity, poor stability, and low integration. Simultaneously, by utilizing the resonance enhancement effect of the ring resonator, the optical field confinement capability can be enhanced within a small size, increasing the optical power density. This design effectively improves the nonlinear conversion efficiency of the spontaneous four-wave mixing (SFWM) process of the ring resonator.

[0031] The ring resonant cavity formed by the coupling component and the connecting waveguide can extend the nonlinear coherence length within a small size of tens of micrometers. This design achieves high nonlinear conversion efficiency without relying on long waveguides, compensating for the low integration density of long waveguides, and avoiding the dispersion and phase mismatch problems caused by excessive light-matter interaction in long waveguides. The coupling component has a large tolerance to manufacturing processes and achieves optical power distribution based on the self-image effect, overcoming the drawback of the waveguide gap in the coupling region of micro-ring resonators based on directional couplers being subject to strict process requirements. In addition, the coupling component is much less sensitive to temperature changes than directional couplers, and temperature fluctuations do not significantly affect coupling performance and power splitting ratio. At the same time, the power coupling ratio of the coupling component is not sensitive to wavelength changes, so the ring resonant cavity based on the 2×2 multimode interference coupler has a uniform extinction ratio and stable Q value over a long wavelength range. Furthermore, adjusting the power coupling ratio at the output port of the coupling component does not introduce additional insertion loss. Therefore, the design of the coupling component can effectively improve the stability of the on-chip quantum light source generation process and the nonlinear conversion efficiency of the generated photon pairs. Attached Figure Description

[0032] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0033] Figure 1 A schematic diagram of an on-chip quantum light source provided according to an embodiment of the present invention is shown.

[0034] Figure 2 A partial structural schematic diagram of a ring resonant cavity based on a 2×2 multimode interference coupler provided according to an embodiment of the present invention is shown.

[0035] Figure 3 A cross-sectional view of a quantum chip provided according to an embodiment of the present invention is shown.

[0036] Figure 4 shows the transmission curve and electric field distribution of a 2×2 multimode interference coupler achieving an approximately 50:50 power splitting ratio according to an embodiment of the present invention.

[0037] Figure 5 This is a transmission curve diagram of a racetrack-type ring resonator in the prior art.

[0038] Figure 6 The transmission curve of the ring resonator based on the 2×2 multimode interference coupler according to an embodiment of the present invention is shown.

[0039] Figure 7 The electric field distribution diagram of the ring resonator based on the 2×2 multimode interference coupler is shown in the embodiment of the present invention.

[0040] Explanation of reference numerals in the attached figures

[0041] 1: Laser; 2: Quantum chip; 21: Support layer; 211: Substrate; 212: Lower cladding; 22: Coupling component; 221: First output port; 222: First input port; 223: Second output port; 224: Second input port; 23: Connection component; 24: Input waveguide; 25: Output waveguide; 26: Cladding; 27: Phase shifter; 28: Ring resonator based on 2×2 multimode interference coupler; 3: Tunable optical attenuator; 4: First dense wavelength division multiplexer; 5: Second dense wavelength division multiplexer; 6: Polarization controller; 7: Edge coupler; 8: Beam splitter; 9: Power meter; 10: First filter component; 11: Second filter component; 12: Detector component. Detailed Implementation

[0042] In the process of realizing this invention, it was discovered that in an integrated photonics platform, based on second- or third-order nonlinear effects (such as SPDC, SFWM), waveguides and microring resonators on a quantum chip can be used as nonlinear optical media to generate correlated photon pairs, thereby improving the system integration.

[0043] Taking the four-wave mixing process in a silicon wire waveguide as an example, the conversion efficiency of nonlinear effects in the waveguide is related to the waveguide length. The relationship between the coherence length and phase mismatch in the waveguide is expressed as Equation (1) to Equation (2).

[0044] (1);

[0045] (2).

[0046] Coherence length This is the maximum tolerable wave vector mismatch. It is the group refractive index of the waveguide. It is the angular frequency difference between the pump laser and the idler light, and c is the speed of light.

[0047] Long waveguides offer high nonlinear conversion efficiency, but as the waveguide length increases, the design integration decreases. Furthermore, long waveguides have a long interaction length between light and matter, resulting in severe waveguide dispersion and phase mismatch during transmission.

[0048] Microring resonators (MRRs) based on directional couplers offer another approach to on-chip generation of correlated photon pairs. Compared to waveguides, MRRs, through resonance enhancement, can improve the confinement of the optical field, increase optical power density, and enhance nonlinear conversion efficiency within a smaller size. The high integration density of the ring cavity allows for the extension of the nonlinear coherence length within a diameter as small as tens of micrometers, enabling highly efficient generation of correlated photon pairs. On silicon, silicon nitride, and lithium niobate-based material platforms, researchers have successfully achieved on-chip quantum light source generation using MRRs based on directional couplers.

[0049] The photon generation rate of a microring resonator is related to its quality factor. The quality factor (Q-factor, Q) of a single-mode cavity is expressed by equation (3).

[0050] (3);

[0051] in It is the resonant wavelength of a single-mode cavity. It is the full width at half maximum (FWHM) at the resonant wavelength, i.e., the linewidth of the single-mode cavity.

[0052] The generation rate of correlated photon pairs generated via the SFWM process within a single-mode cavity based on third-order nonlinear effects. It is represented by equation (4).

[0053] (4);

[0054] For group velocity, It is a third-order nonlinear optical coefficient. Q is the pump laser power, and Q is the total mass factor. It is the resonant angular frequency, and L is the annular cavity circumference of the single-mode cavity. It is the external quality factor of the single-mode cavity. It's a phase mismatch.

[0055] From equation (4), we can obtain that When the round-trip loss between the pump light and the generated photon pair is ignored, the above relationship becomes At this point, a high Q value means a higher photon pair generation rate, but as shown in equation (3), a high Q value means a narrow bandwidth. When the wavelength range spanned by the resonance becomes narrower, the number of photon pairs generated at that resonant wavelength may be less. Structurally, commonly used microring resonators are designed based on directional couplers. The power splitting ratio of directional couplers is wavelength-sensitive and highly dependent on the waveguide size of the coupling region and the gap between the coupling region ring waveguide and the bus waveguide. For a directional coupler of a certain size, a small change in the gap of the coupling region will cause a large shift in the resonant wavelength. Small-sized photonic waveguides are extremely sensitive to manufacturing tolerances, and the coupling coefficient of the coupling region is difficult to control precisely, making the Q value at a specific wavelength easily affected. In addition, microring resonators based on directional couplers are very sensitive to temperature and polarization changes, and this drawback seriously affects the stability of photon pair generation.

[0056] Therefore, both long waveguide-based and micro-ring resonator-based schemes have shortcomings and challenges in achieving high-quality on-chip light source fabrication.

[0057] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0058] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as 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.

[0059] 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 are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0060] Figure 1 A schematic diagram of an on-chip quantum light source provided according to an embodiment of the present invention is shown.

[0061] Figure 2 A partial structural schematic diagram of a ring resonant cavity based on a 2×2 multimode interference coupler provided according to an embodiment of the present invention is shown.

[0062] Figure 3A cross-sectional view of a quantum chip provided according to an embodiment of the present invention is shown.

[0063] like Figures 1-3 As shown, the on-chip quantum light source includes: a laser 1 and a quantum chip 2. Laser 1 is used to generate pump laser. Quantum chip 2 includes: a support layer 21, an edge coupler 7, a coupling component 22, and a connection component 23. The coupling component 22, formed on the support layer 21, is a multimode waveguide, suitable for redistributing the pump laser coupled to the chip into two parts with a specific power splitting ratio through self-image effect. The connection component 23 is a connection waveguide. The connection waveguide is connected to the coupling component 22 to form a ring resonant cavity.

[0064] In this context, as the coupling region structure of the ring resonant cavity based on a 2×2 multimode interference coupler, the coupling component 22 is configured to couple a portion of the pump laser into the ring resonant cavity by causing the pump laser to undergo a self-image effect. The pump laser coupled into the ring resonant cavity resonates in the resonant cavity and undergoes a spontaneous four-wave mixing effect to generate correlated photon pairs (including signal photons and idler photons). The coupling component is also suitable for outputting the pump laser that is not coupled into the cavity, the correlated photon pairs, and the residual part of the pump laser after it is coupled into the ring cavity and resonates.

[0065] According to embodiments of the present invention, there is no need to construct a free-space optical system or to design complex phase matching. The design of the ring resonator 28 based on a 2×2 multimode interference coupler avoids the drawbacks of quantum light source systems based on nonlinear crystals, such as complexity, poor stability, and low integration. Simultaneously, by utilizing the resonance enhancement effect of the ring resonator, the optical field confinement capability can be enhanced within a small-size structure, increasing the optical power density. This design effectively improves the nonlinear conversion efficiency of spontaneous four-wave mixing (SFWM).

[0066] The coupling component 22, in conjunction with the connecting waveguide, forms a ring resonant cavity. This structure can extend the nonlinear coherence length within a small size of tens of micrometers. This design overcomes the low integration density of long waveguides, achieving high nonlinear conversion efficiency within a small size, while avoiding dispersion and phase mismatch problems caused by excessive light-matter interaction in long waveguides. The coupling component 22 has a large tolerance to manufacturing processes, overcoming the drawback of the waveguide gap in the coupling region of micro-ring resonators based on directional couplers being heavily dependent on the manufacturing process. Furthermore, the coupling component 22 is far less sensitive to temperature changes than directional couplers; temperature fluctuations do not significantly affect coupling performance and power splitting ratio. Simultaneously, the power coupling ratio of the coupling component 22 is insensitive to wavelength changes; therefore, the ring resonant cavity 28 based on a 2×2 multimode interference coupler exhibits a uniform extinction ratio and stable Q value over a longer wavelength range. Moreover, adjusting the power coupling ratio at the output port of the coupling component 22 does not introduce additional insertion loss. Therefore, the design of the coupling component 22 can effectively improve the stability of the on-chip quantum light source generation process and the nonlinear conversion efficiency of the generated photon pairs.

[0067] According to an embodiment of the present invention, the support layer 21 includes a substrate 211 and a lower cladding layer 212. The substrate material of the substrate 100 can be silicon, which provides support for the overall structure. The material of the lower cladding layer 212 is silicon dioxide with a refractive index of 1.44. The coupling component 22 can be a multimode interference coupler, and its fabrication material can be, for example, silicon, silicon nitride, lithium niobate, etc. When silicon is used as the material, the waveguide size in this invention is designed to be 220 nm × 500 nm in thickness and width to ensure single-mode transmission of the input light field. The length and width of the multimode waveguide region are set to 31 μm × 3 μm to achieve a 50:50 power splitting ratio.

[0068] According to an embodiment of the present invention, the length of the multimode waveguide in the multimode interference coupling region of the coupling component 22 along the first direction of optical transmission and the width along the second direction perpendicular to the first direction are configured to determine the power splitting ratio of the coupling component. In this embodiment, the coupling component 22 is designed to achieve a 50:50 power splitting ratio. By designing the length and width parameters of the coupling component, the coupling component 22 can be designed with other power splitting ratios to achieve precise control of the ring resonator 28 to an undercoupled or overcoupled state by adjusting the coupling coefficient of the coupling region, thereby achieving precise control of the transmission spectrum bandwidth. The power splitting ratio is determined by the length and width structural parameters of the coupling component itself, improving the stringent requirements of the manufacturing process on the coupling region gap of the micro-ring resonator based on the directional coupler. The power splitting ratio of the coupling component 22, determined based on the length and width parameters, is insensitive to wavelength over a relatively long wavelength range (e.g., around 25 nm) and is minimally affected by environmental factors such as temperature. Therefore, this design can achieve stable and efficient generation of correlated photon pairs.

[0069] According to an embodiment of the present invention, a first output port 221, a first input port 222, a second output port 223, and a second input port 224 are formed on the coupling component 22.

[0070] According to an embodiment of the present invention, the two ends of the waveguide are respectively connected to the first input port 222 and the first output port 221 of the coupling component 22, and together with the coupling component 22, form a ring resonant cavity.

[0071] After the pump laser is input into the coupling component 22 through the second input port 224, it excites multiple waveguide modes. Since different waveguide modes propagate at different speeds in the medium, interference occurs at different locations within the multimode waveguide, ultimately forming a specific optical field distribution at the output port. By configuring the length of the coupling component 22 along the optical transmission direction and its width perpendicular to the direction of light, the output power splitting ratio of the optical field at the first output port 221 and the second output port 223 of 222 can be precisely controlled. The first output port 221 is used to input a portion of the pump laser into the resonant cavity via a connecting waveguide. The second output port 223 is used to output the generated photon pair, the uncoupled pump laser, and the residual portion of the pump laser after resonance within the ring cavity to subsequent experimental devices.

[0072] According to an embodiment of the present invention, the on-chip quantum light source further includes a phase shifter 27. The phase shifter 27 is adapted to adjust the resonant wavelength of the ring resonant cavity 28 based on a 2×2 multimode interference coupler.

[0073] According to an embodiment of the present invention, the quantum chip 2 further includes an input waveguide 24, an output waveguide 25, and a cladding 26. The cladding 26 is a low-refractive-index layer made of silicon dioxide. The input waveguide 24 is formed on the support layer 21 and connected to the second input port 224, and is adapted to transmit the pump laser coupled to the quantum chip 2 by the edge coupler 7 to the second input port 224, and further to the coupling component 22. The output waveguide 25 is formed on the support layer 21 and connected to the second output port 223, and is adapted to output the generated correlated photon pairs, the pump laser not coupled into the resonant cavity, and the residual portion of the pump laser after resonance in the ring cavity. The cladding 26 is adapted to constrain the propagation of the light field within the waveguide and protect the core layer containing the ring resonant cavity 28 based on the 2×2 multimode interference coupler.

[0074] According to an embodiment of the present invention, the coupling component 22 described above can be, for example, a multimode interference coupler including two input ports and two output ports. The present invention takes a 2×2 multimode interference coupler (abbreviated as 2×2 MMI) as an example. By designing the length and width of the multimode waveguide in the multimode interference coupling region of the 2×2 MMI, and the positions of each input port and output port, the optical power coupled into the ring resonant cavity 28 based on the 2×2 multimode interference coupler through the first output port 221 can be controlled. The splitting ratio of the first output port 221 is the square of the cross-coupling coefficient k of the ring resonant cavity 28 based on the 2×2 multimode interference coupler. The splitting ratio of the second output port 223 is the square of the self-coupling coefficient t of the ring resonant cavity 28 based on the 2×2 multimode interference coupler. The amplitude transmission coefficient a within the ring resonant cavity 28 based on the 2×2 multimode interference coupler includes the transmission loss and coupling loss of the ring resonant cavity 28 based on the 2×2 multimode interference coupler. When intrinsic loss is considered and the self-coupling coefficient t < amplitude transmission coefficient a, the ring resonator 28 is in an overcoupled state, exhibiting a wider bandwidth and a higher probability of generating photon pairs. Furthermore, the phase shifter 27 can modulate the resonant wavelength of the ring resonator 28 based on a 2×2 multimode interference coupler. This device generates correlated photon pairs within the resonator based on a spontaneous four-wave mixing effect. Its advantages of easily adjustable bandwidth and low environmental (temperature) sensitivity enhance the stability of the photon pair generation process and the nonlinear conversion efficiency of the generated photon pairs.

[0075] According to an embodiment of the present invention, the pump laser from laser 1 is coupled to quantum chip 2 via edge coupler 7, and then transmitted into coupling component 22 through input waveguide 24 and second input port 224. By designing coupling component 22, a 2×2 MMI with different power splitting ratios can be achieved between first output port 221 and second output port 223. A portion of the pump light is input into the ring resonant cavity 28 based on the 2×2 multimode interference coupler through first output port 221 to resonate and undergo spontaneous four-wave mixing, generating correlated photon pairs. The newly generated correlated photon pairs, the pump laser not coupled into the cavity, and the residual portion of the pump laser after resonance in the ring cavity are transmitted to subsequent devices through second output port 223 to further complete the filtering and photon correlation characteristic measurement process. In addition, phase shifter 27 can adjust the resonant wavelength of the device.

[0076] The present invention proposes to use a ring resonator based on a 2×2 multimode interference coupler to replace the micro-ring resonator based on a directional coupler in order to solve the problems of low environmental (temperature) tolerance, small manufacturing tolerance, and difficulty in controlling the coupling state of the micro-ring resonator based on the directional coupler in the process of realizing on-chip quantum light source generation.

[0077] In this embodiment of the invention, the ring resonant cavity 28 based on a 2×2 multimode interference coupler is composed of a 2×2 multimode interference coupler and a connecting waveguide. Spontaneous four-wave mixing occurs within this ring resonant cavity to generate photon pairs, achieving on-chip correlated photon pair generation. Simultaneously, the resonant wavelength of the device can be tuned using a phase shifter.

[0078] The power transfer in the bus waveguide of a ring resonant cavity based on a 2×2 multimode interference coupler can be expressed as:

[0079] (5);

[0080] The quality factor Q of a ring resonator based on a 2×2 multimode interference coupler can be expressed as:

[0081] (6);

[0082] in, The full width at half maximum (FWHM) of the ring resonant cavity at the resonant wavelength in this invention is... The self-coupling coefficient is... It is the power loss factor, and , For phase accumulation around the circumference, The wavelength in vacuum is given by λ, and L is the circumference of the annular cavity. Let be the group refractive index of the waveguide.

[0083] Figure 4A This is a transmission curve diagram of a 2×2 multimode interference coupler according to an embodiment of the present invention.

[0084] like Figure 4A As shown, the horizontal axis represents the operating wavelength of the 2×2 multimode interference coupler set in the simulation process, and the vertical axis represents the transmittance of the 2×2 multimode interference coupler. It can be seen that within a wavelength range of approximately 25 nm from 1500 nm to 1525 nm, the first and second output ports of the 2×2 multimode interference coupler stably achieve a uniform beam splitting ratio of approximately 50:50.

[0085] Figure 4B This is an electric field distribution diagram of a 2×2 multimode interference coupler according to an embodiment of the present invention at a wavelength of approximately 1500 nm.

[0086] like Figure 4B As shown, the horizontal axis represents the length of the 2×2 multimode interference coupler in the simulation setting, and the vertical axis represents the width of the 2×2 multimode interference coupler in the simulation setting. This demonstrates that the 2×2 multimode interference coupler can achieve a uniform power splitting ratio over a relatively long wavelength range.

[0087] Figure 5 This is a transmission curve diagram of a racetrack-shaped microring resonator in the prior art.

[0088] like Figure 5 As shown, the racetrack-shaped microring resonator in the prior art is a microring resonator based on directional coupling. The perimeter of this microring resonator is the same as the perimeter of the ring resonator 28 based on a 2×2 multimode interference coupler in this embodiment of the invention. The horizontal axis is the operating wavelength of the microring resonator in the simulation settings, and the vertical axis is the transmittance. According to Figure 5 It can be concluded that the extinction ratio of this micro-ring resonator is strongly correlated with wavelength and has an extremely narrow bandwidth.

[0089] Figure 6 The transmission curve of the ring resonator based on the 2×2 multimode interference coupler according to an embodiment of the present invention is shown.

[0090] like Figure 6 As shown, the horizontal axis represents the operating wavelength of the ring resonator based on a 2×2 multimode interference coupler in the simulation setup, and the vertical axis represents the transmittance.

[0091] The transmission curves show that the ring resonator 28 based on the 2×2 multimode interference coupler exhibits a uniform extinction ratio in the wavelength range of 1500-1525 nm. Compared to Figure 5 The transmission curve of the racetrack-shaped microring resonator based on the directional coupler shows that the extinction ratio of the ring resonator 28 based on the 2×2 multimode interference coupler does not fluctuate much with wavelength, which can be used to stably realize the generation of correlated photon pairs. Meanwhile, due to the 50:50 power splitting ratio of the 2×2 multimode interference coupler, the ring resonator 28 based on the 2×2 multimode interference coupler is in an overcoupled state compared to... Figure 5 Compared to microring resonators based on directional couplers, ring resonators based on 2×2 multimode interference couplers have a wider bandwidth.

[0092] Figure 7 The diagram shows the total electric field distribution of the ring resonator based on a 2×2 multimode interference coupler according to an embodiment of the present invention.

[0093] like Figure 7 As shown, the horizontal axis represents the length of the 2×2 multimode interference coupler, and the vertical axis represents the width of the 2×2 multimode interference coupler. It can be seen that after achieving a 50:50 power split ratio through the 2×2 multimode interference coupler, approximately half of the input pump light enters the ring resonant cavity 28 based on the 2×2 multimode interference coupler for transmission.

[0094] The embodiments of the present invention propose based on The ring resonator 28 of the MMI replaces the micro-ring resonator based on the directional coupler for on-chip correlated photon pair generation. The invention proposes a ring resonator based on... The MMI's ring resonator 28 combines the advantages of high integration and high nonlinear conversion efficiency of micro-ring resonators based on directional couplers, while improving the disadvantages of high temperature sensitivity and low manufacturing tolerance of micro-ring resonators based on directional couplers. Furthermore, due to... The power splitting ratio of the MMI structure is easy to control. During the design process, it is easier to ensure that the ring resonator 28 based on the 2×2 multimode interference coupler is in an undercoupled / overcoupled state, so as to realize the wide and narrow control of the transmission spectrum bandwidth of the device.

[0095] According to an embodiment of the present invention, the above-mentioned on-chip quantum light source further includes: the output end of the laser 1 is connected to the input end of the tunable light attenuator 3, and the other end of the tunable light attenuator 3 is sequentially connected to the first dense wavelength division multiplexer 4, the second dense wavelength division multiplexer 5, and the polarization controller 6.

[0096] The adjustable optical attenuator 3 is used to adjust the pump light power, avoiding nonlinear damage to the device caused by excessive pump light power. It can also adjust the power as needed to adapt to the photon pair generation requirements of the ring resonator 28 based on the 2×2 multimode interference coupler under different coupling states. The first dense wavelength division multiplexer 4 and the second dense wavelength division multiplexer 5 are connected in series to filter and select the frequency of the input pump light, removing stray wavelength noise and selecting the target wavelength of the pump laser required for the spontaneous four-wave mixing effect. The polarization controller 6 is used to adjust the polarization state of the pump light, ensuring polarization matching between the pump light polarization state and the coupling component 22, maximizing the coupling efficiency of the pump light input to the ring resonator 28 based on the 2×2 multimode interference coupler, and ensuring the stable occurrence of the spontaneous four-wave mixing effect.

[0097] According to an embodiment of the present invention, the on-chip quantum light source further includes: a beam splitter 8, a power meter 9, and a first filter 10. The beam splitter 8 is adapted to split the laser output from the ring coupler into a first sub-laser and a second sub-laser, and the power meter 9 is adapted to detect the power of the pump laser based on the first sub-laser. The first filter 10 is adapted to filter out residual pump light in the second sub-laser, ensuring that only correlated photon pairs enter the subsequent experimental setup.

[0098] The aforementioned on-chip quantum light source also includes: a second filtering component 11 (e.g., a dense wavelength division multiplexer) and a detection component 12. The second filtering component 11 is suitable for separating the signal photon and the idler photon in a correlated photon pair, and transmitting the signal photon and the idler photon to single-photon detectors 121 and 122, respectively. The detection component 12 includes single-photon detectors 121 and 122, a time analyzer 123, and a computer 124. The two single-photon detectors are respectively suitable for detecting the two photons from the second filtering component 11, namely the signal photon and the idler photon, and transmitting the electrical signal pulse triggered after receiving the photon to the time analyzer 123. The time analyzer 123 is connected to the computer 124 and transmits the photon arrival time analysis results to the PC (i.e., computer 124) to complete the measurement of the single-photon count rate and coincidence count rate.

[0099] The ring resonator 28 based on a 2×2 MMI design according to an embodiment of the present invention combines the advantages of high integration and high nonlinear efficiency of micro-ring resonators designed with directional couplers. The ring resonator 28 based on a 2×2 MMI can be adjusted to be in an overcoupled / undercoupled state by controlling the power splitting ratio of the MMI structure, thus achieving precise control of the spectral bandwidth. Different power splitting ratios such as 50:50, 72:28, 85:15, and 92:8 can be achieved by controlling the length and width of the MMI structure and the design of the input and output waveguides. Furthermore, by selecting a butterfly design for the main body of the MMI, the MMI can achieve a continuous and uniform splitting ratio. Compared to adjusting the coupling coefficient by designing the coupling length, waveguide width, or coupling gap of the directional coupler, the ring resonator 28 based on a 2×2 MMI is easier to control precisely in terms of the resonator's coupling coefficient and has lower requirements for manufacturing processes. Furthermore, leveraging its easily adjustable bandwidth, the ring resonator 28 based on 2×2 MMI can theoretically be designed in an overcoupled state to achieve a wide bandwidth, thereby increasing the number of correlated photon pairs generated. Microring resonators based on directional couplers have coupling coefficients that are highly sensitive to environmental conditions (temperature), and even small changes in the coupling gap can cause significant fluctuations in the coupling coefficient, resulting in high environmental sensitivity and low process tolerance. In contrast, MMI structures themselves have low manufacturing requirements and low environmental (temperature) sensitivity. Therefore, the ring resonator 28 based on 2×2 MMI can reduce environmental (temperature) sensitivity, and the coupling coefficient does not fluctuate much with temperature, improving the stability of the correlated photon pair generation experiment and potentially achieving high nonlinear conversion efficiency in the spontaneous four-wave mixing process.

[0100] According to embodiments of the present invention, unlike micro-ring resonators based on directional couplers, the power splitting ratio of a 2×2 MMI is insensitive to wavelength variations compared to directional couplers. Therefore, the ring resonator 28 based on a 2×2 MMI has a wavelength-independent extinction ratio and uniform bandwidth over a wide wavelength range. The ring resonator based on a 2×2 MMI can achieve uniform bandwidth and a suitable Q value. In this invention, the ring resonator based on a 2×2 multimode interference coupler provides a novel method for on-chip quantum light sources. This method can effectively improve the stability of the quantum light source generation experiment process and enhance the nonlinear conversion efficiency.

[0101] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. An on-chip quantum light source, characterized in that, include: Lasers suitable for generating pump lasers; Quantum chips, including: Support layer, including substrate and lower cladding layer; An edge coupler, formed on the support layer and located at the edge of the quantum chip, is suitable for coupling pump laser from a laser to the quantum chip via an external optical fiber and transmitting it to the coupling component via an input waveguide. The coupling component, a multimode waveguide, is formed on the support layer and is suitable for distributing the received pump laser into two parts with a specific power splitting ratio through the self-image effect. The connecting component is a connecting waveguide that is connected to the coupling component to form a ring resonant cavity; The coupling component is configured to couple a portion of the pump laser into the ring resonant cavity by causing a self-image effect in the pump laser; the pump laser coupled into the ring resonant cavity resonates in the resonant cavity and undergoes a spontaneous four-wave mixing effect to generate correlated photon pairs; the coupling component is also adapted to output the pump laser that is not coupled into the cavity, the correlated photon pairs, and the residual portion of the pump laser after it is coupled into the cavity and resonates.

2. The on-chip quantum light source according to claim 1, characterized in that, The length of the coupling component along a first direction of incident pump laser and the width along a second direction perpendicular to the first direction are configured to determine the power splitting ratio of the coupling component.

3. The on-chip quantum light source according to claim 1, characterized in that, The coupling component has a first output port, a first input port, and a second output port. The pump laser undergoes a self-image effect within the coupling assembly to split the pump laser into two parts with a specific power splitting ratio. The first output port is adapted to input the pump laser coupled into the cavity into the cavity through the connecting waveguide. The second output port is used to output the associated photon pair, the pump laser that was not coupled into the cavity, and the residual portion of the pump laser after it was coupled into the annular cavity and resonated.

4. The on-chip quantum light source according to claim 3, characterized in that, The coupling component has a second input port, which is connected to the input waveguide and the coupling component, and is suitable for transmitting the pump laser received from the edge coupler by the input waveguide to the coupling component; The first input port, the first output port, the second input port, the second output port, the coupling component, and the connecting waveguide constitute the ring resonant cavity.

5. The on-chip quantum light source according to claim 1, characterized in that, The on-chip quantum light source also includes: A phase shifter is used to adjust the resonant wavelength of the ring resonator.

6. The on-chip quantum light source according to claim 4, characterized in that, The quantum chip also includes: The input waveguide, connected to the edge coupler and the second input port, is formed on the support layer and is suitable for receiving pump laser coupled to the quantum chip via the edge coupler and transmitting the pump laser to the second input port through the input waveguide. An output waveguide, formed on the support layer, is suitable for outputting the associated photon pair, the pump laser not coupled into the cavity, and the residual portion of the pump laser after it is coupled into the annular cavity and resonates. The upper cladding is suitable for confining the optical field to propagate within the waveguide and protecting the core layer.

7. The on-chip quantum light source according to claim 1, characterized in that, The on-chip quantum light source also includes: The beam splitting assembly is suitable for splitting the laser output from the ring coupler into a first sub-laser and a second sub-laser; A power meter suitable for detecting the power of the pump laser based on the first sub-laser.

8. The on-chip quantum light source according to claim 1, characterized in that, The on-chip quantum light source also includes: The first filtering component is used to filter out unconverted pump laser light, ensuring that only the generated correlated photon pairs enter the subsequent experimental setup.

9. The on-chip quantum light source according to claim 1, characterized in that, The on-chip quantum light source also includes: The second filtering component is suitable for separating the signal photon and the idler photon in a correlated photon pair.

10. The on-chip quantum light source according to claim 1, characterized in that, The on-chip quantum light source also includes: The detection assembly includes two single-photon detectors, a time analyzer, and a computer. The two single-photon detectors are used to detect the signal photon and idler photon output from the second filter assembly, respectively. The electrical signal pulses triggered by the signal photon and idler photon received by the two single-photon detectors are transmitted to the time analyzer. The time analyzer is connected to the computer and transmits the photon arrival time analysis results to the computer to complete the measurement of single-photon count rate and coincidence count rate.

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