End face coupler, optical chip and light quantum computer

Abstract

The invention provides an end face coupler, an optical chip and an optical quantum computer, and relates to the technical field of optical communication, the end face coupler comprises a first coupling waveguide and a second coupling waveguide located on a first waveguide layer, and a third coupling waveguide located on a second waveguide layer, and the first coupling waveguide, the second coupling waveguide and the third coupling waveguide extend in the same direction; the first coupling waveguide and the second coupling waveguide are respectively provided with a first tip and a second tip, the third coupling waveguide is provided with an adiabatic conical area, the adiabatic conical area is provided with a third tip, and an optical signal of the optical fiber enters the first coupling waveguide and the second coupling waveguide through the first tip and the second tip respectively. And the third coupling waveguide is coupled to the third coupling waveguide through the third tip. Due to the infinitely small arrangement of the third tip end of the adiabatic conical region, loss caused by conversion from a fundamental mode to a high-order mode and refractive index mismatch is not generated, the purpose of low loss of the end face coupler is achieved, and the broadband characteristic is obtained; the double tips are matched with 9-micron large mode spots, and the alignment process tolerance of the optical fiber and an end face mode field is larger.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical communication, in particular to an end-face coupler, an optical chip and an optical quantum computer. BACKGROUND

[0002] With the rapid development of thin-film lithium niobate photonic integration platform, on-chip optical communication systems have higher requirements for high-efficiency and wide-band fiber-chip coupling solutions. As a key interface for realizing efficient transmission of optical signals between optical fibers and waveguides, the performance of an end-face coupler directly affects the insertion loss, bandwidth capacity and polarization stability of the system. In high-speed coherent communication, data center interconnection and the next generation of optical networks (such as 5G front-end / middle-end transmission, AI computing cluster), low loss and wide spectrum coupling need to be realized in the C band (1530nm-1565nm) and L band (1565nm-1625nm) at the same time to meet the demand of large capacity and multi-wavelength multiplexing transmission.

[0003] However, traditional end-face couplers are easily affected by mode mismatch, polarization sensitivity and wavelength dependence in a wide band range, resulting in a decrease in coupling efficiency and an increase in polarization-dependent loss (PDL). Especially on high refractive index difference platforms such as thin-film lithium niobate, the significant difference in mode field size further aggravates the complexity of coupling design. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide an end-face coupler, an optical chip and an optical quantum computer, which can realize the functions of high bandwidth, large mode spot and high coupling efficiency.

[0005] In one aspect of the embodiments of the present application, an end-face coupler is provided, which comprises a first coupling waveguide and a second coupling waveguide located in a first waveguide layer, and a third coupling waveguide located in a second waveguide layer, the first coupling waveguide, the second coupling waveguide and the third coupling waveguide extend in the same direction; The first coupling waveguide and the second coupling waveguide have a first tip and a second tip respectively, the third coupling waveguide has an adiabatic taper region, the adiabatic taper region has a third tip, and the optical signal of the optical fiber enters the first coupling waveguide and the second coupling waveguide through the first tip and the second tip respectively, and is coupled to the third coupling waveguide through the third tip.

[0006] Optionally, the tip width of the first tip is 0.2um±100nm, the tip width of the second tip is 0.2um±100nm, and the tip width of the third tip is simultaneously smaller than the tip width of the first tip and the tip width of the second tip.

[0007] Optionally, the third coupling waveguide further comprises a second output region connected with the adiabatic taper region, for outputting the optical signal coupled into the third coupling waveguide.

[0008] Optionally, the first coupling waveguide comprises a first taper gradually changed transmission region, a first transition region and a first output region connected in sequence, the first tip is located at one end of the first taper gradually changed transmission region away from the first transition region, and the projection of the adiabatic taper region of the third coupling waveguide and the first output region is located within the projection of the first transition region and the first output region of the first coupling waveguide.

[0009] Optionally, the second coupling waveguide comprises a second taper gradually changed transmission region and a second transition region connected in sequence, the second tip is located at one end of the second taper gradually changed transmission region away from the second transition region, and the output end of the second transition region is connected with the input end of the adiabatic taper region of the third coupling waveguide.

[0010] Optionally, the second output region of the third coupling waveguide is a ridge waveguide output region, and the first output region of the first coupling waveguide is a flat plate waveguide output region.

[0011] Optionally, the application further comprises a substrate and a cladding region located on the substrate, the first waveguide layer and the second waveguide layer are located in the cladding region, and the substrate has a cavity. The cladding region has a channel in communication with the cavity of the substrate, the cladding region is divided into a central region and side edge regions located on both sides of the central region through the channel, the two side edge regions are connected with the central region through cantilever beams respectively, and the first waveguide layer and the second waveguide layer are located in the central region.

[0012] Optionally, the wave bands of the first coupling waveguide, the second coupling waveguide and the third coupling waveguide are between 1530 nm and 1565 nm and between 1565 nm and 1625 nm. The first coupling waveguide, the second coupling waveguide and the third coupling waveguide all comprise lithium niobate waveguides.

[0013] In another aspect of the embodiments of the application, an optical chip is provided, comprising the end face coupler.

[0014] In still another aspect of the embodiments of the application, an optical quantum computer is provided, comprising a quantum light source, an optical chip and a detector, and the optical chip comprises the end face coupler.

[0015] The end face coupler, the optical chip and the optical quantum computer provided by the embodiment of the application adopt the setting of the infinitely small third tip of the adiabatic tapered region, so that the mode transition from the third tip to the flat adiabatic tapered region is 100%, without mode transition from the fundamental mode to the high-order mode and the loss caused by the refractive index mismatch, thereby achieving the purpose of low loss of the end face coupler; the setting of the infinitely small third tip can be realized by twice etching in the process, and the broadband characteristics can be obtained; and the double-tip end face coupler of the first tip and the second tip can match the 9um large mode spot, and the alignment process tolerance of the optical fiber and the end face mode field is larger. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments of the application. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0017] Figure 1 is one of the end face coupler structure schematic diagrams provided by the embodiment of the application; Figure 2 is the second end face coupler structure schematic diagram provided by the embodiment of the application; Figure 3 is the third end face coupler structure schematic diagram provided by the embodiment of the application; Figure 4 is the FDTD TE transmission light field diagram of the end face coupler provided by the embodiment of the application; Figure 5 is the FDTD TE transmission efficiency diagram of the end face coupler provided by the embodiment of the application. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application.

[0019] In the description of the application, it should be explained that the directions or position relationships indicated by the terms "inner", "outer" and the like are based on the directions or position relationships shown in the drawings, or the directions or position relationships commonly used when the product of the application is placed, and are only for the convenience of describing the application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second" and the like are only used for differentiation and description, and cannot be understood as indicating or implying relative importance.

[0020] It also needs to be explained that unless otherwise explicitly specified and limited, the terms "set", "connected" should be broadly understood. For ordinary skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0021] In the prior art, to achieve the multiple goals of low loss, large mode field, low polarization sensitivity (i.e. low polarization dependent loss) and high process tolerance, there are inherent trade-offs and conflicts in physical principles and manufacturing processes, which are the core challenges faced by current technology.

[0022] Physical contradiction between large mode field and polarization sensitivity: the core technical path to expand the mode field size (such as to 9μm) is to weaken the light field restriction, usually using shallow etched sub-wavelength grating (SWG) or slowly varying taper (multi-layer taper) structure. However, this weak restriction effect makes the light field extremely sensitive to the microscopic asymmetry of the waveguide. The thin film lithium niobate platform itself has material anisotropy, and the mainstream dry / wet etching process will introduce significant sidewall tilt and roughness. The geometric asymmetry caused by these processes will directly lead to strong waveguide birefringence. A large size mode field will "perceive" these asymmetries in a larger range, thereby amplifying the effective refractive index difference and field distribution difference between TE mode (transverse electric mode) and TM mode (transverse magnetic mode), leading to a sharp increase in polarization dependent loss (PDL). Therefore, there is a conflict between the design concept of large mode field and the requirement of low polarization sensitivity.

[0023] Conflict between high performance and high tolerance process: high process tolerance requires that the device performance is not sensitive to nanoscale fluctuations of etching depth and critical dimension (CD). However, the advanced nanostructure (such as the period and duty cycle of SWG) used to achieve low loss and large mode field is extremely sensitive to manufacturing errors in its optical properties. For example, the effective refractive index of SWG is precisely determined by the geometric parameters of its nanostructure, and a few nanometer size deviation is enough to cause a significant change in the effective refractive index, leading to mode field mismatch, phase error and a sharp increase in scattering loss. Pursuing low loss and large mode field must rely on high-precision, low-error complex nanostructures, which is exactly contrary to the goal of high process tolerance, becoming an important constraint on production yield.

[0024] Trade-off between mode purity and loss: large mode field converters are prone to excite high-order modes or produce radiation modes when the design is improper, especially in the transition region of taper structure or grating. These non-ideal modes will translate into additional insertion loss or crosstalk, directly damaging the performance of low loss. Optimizing mode purity requires more complex and longer adiabatic design, which is contrary to the demand for compactness of chips and may introduce new process challenges.

[0025] To achieve uniform high-efficiency coupling in the super-wide C+L band (about 95nm bandwidth), it is essentially a confrontation with the dispersion effect, and the difficulty comes from the following aspects: Strong dispersion effect: This is the primary physical obstacle preventing broadband from being realized.

[0026] The challenges come from two aspects: Material dispersion: The refractive index of thin-film lithium niobate varies with wavelength, which is an inherent material property.

[0027] Waveguide dispersion: Nanostructures (such as SWGs) introduced to achieve large mode fields and mode matching exhibit extremely strong waveguide dispersion. Their equivalent refractive index is highly sensitive to wavelength. The peak coupling efficiency typically occurs at a specific phase-matched wavelength. Once the wavelength shifts, the phase-matching condition is broken, the equivalent refractive index distribution changes, leading to mode field deformation and mismatch, and a rapid decrease in coupling efficiency. Over the vast wavelength span from C to L bands, this mismatch effect is amplified, resulting in severe ripples and roll-off in the bandwidth response curve, making it difficult to maintain a flat surface.

[0028] Wavelength dependence of phase matching: Both grating couplers and end-face couplers rely on some form of phase matching for efficient coupling. While end-face couplers do not depend on Bragg diffraction, the underlying mode field transformation process still requires adiabatic or mode evolution conditions. These conditions are difficult to satisfy simultaneously over a wide wavelength range. For example, an apodized grating or tapered structure optimized for a 1550nm wavelength typically exhibits a decrease in mode overlap integral at 1580nm or 1620nm, leading to increased loss.

[0029] The complexity of multi-objective optimization: Broadband performance is not an independent design objective. In practical designs, large mode coverage, low polarization sensitivity, and high tolerance must be considered simultaneously. These performance indicators are interdependent, forming a complex multi-objective optimization problem. When an optimization algorithm adjusts parameters to improve polarization sensitivity for one wavelength range (such as the C-band), it may sacrifice performance in another wavelength range (such as the L-band). Therefore, the final design is often a compromise of global performance, and it is difficult to simultaneously optimize all performance indicators across the entire 95nm bandwidth.

[0030] In view of this, embodiments of this application provide an end-face coupler, please refer to... Figure 1 As shown, it includes: a first coupled waveguide 101 and a second coupled waveguide 102 located in the first waveguide layer, and a third coupled waveguide 103 located in the second waveguide layer, wherein the first coupled waveguide 101, the second coupled waveguide 102 and the third coupled waveguide 103 extend in the same direction; The first coupling waveguide 101 and the second coupling waveguide 102 have a first tip 1 and a second tip 2, respectively. The third coupling waveguide 103 has an adiabatic conical region 7. The adiabatic conical region 7 has a third tip 71 with an infinitely small tip width. The optical fiber enters the first coupling waveguide 101 and the second coupling waveguide 102 through the first tip 1 and the second tip 2, respectively, and is coupled to the third coupling waveguide 103 through the third tip 71.

[0031] The first coupling waveguide 101 and the second coupling waveguide 102 are located in the same layer, both in the first waveguide layer; the third coupling waveguide 103 is located in another second waveguide layer. The first coupling waveguide 101, the second coupling waveguide 102, and the third coupling waveguide 103 extend in the same direction. For example, all three coupling waveguides extend along... Figure 1 The extension direction F1 is extended, which means that the optical signal is transmitted in the same direction in the three coupled waveguides, all along the extension direction F1.

[0032] During optical signal transmission, the optical signal in the optical fiber enters the first coupling waveguide 101 through the first tip 1 and enters the second coupling waveguide 102 through the second tip 2. The optical signal is transmitted in the first coupling waveguide 101 and the second coupling waveguide 102 respectively. Finally, the optical signals in the first coupling waveguide 101 and the second coupling waveguide 102 are coupled to the third coupling waveguide 103 through the third tip 71 and transmitted by the third coupling waveguide 103.

[0033] The end-face coupler provided in this application embodiment adopts an infinitesimally small third tip 71 of the adiabatic conical region 7, so that the mode transition from the third tip 71 to the gentle adiabatic conical region 7 is 100%, without the transition from the fundamental mode to higher-order modes or the loss caused by refractive index mismatch, thereby achieving the purpose of low loss of the end-face coupler; the infinitesimally small third tip 71 can be achieved by two etching processes, which can obtain broadband characteristics; and the dual-tip type end-face coupler with first tip 1 and second tip 2 can play the role of matching the 9um large mode spot, while the alignment process tolerance between the optical fiber and the end-face mode field is larger.

[0034] It should be noted that the third tip 71 being infinitely small means that the width of the third tip 71 approaches zero infinitely. The width of the tip is the dimension of the width direction F2 of each coupled waveguide on its plane that is perpendicular to its extension direction F1. This definition also applies to the width of the first tip 1 and the second tip 2.

[0035] Furthermore, the structure of the adiabatic conical region 7 is a conical region, and the adiabatic nature of the optical waveguide refers to the gradual change of its structural parameters (such as width and refractive index) along the propagation direction, so that the optical field mode remains stable without reflection or mode conversion. By setting the adiabatic conical region 7 in a gradually changing conical shape and increasing the length of the conical region, the optical signal can be transmitted in the waveguide as much as possible, achieving low-loss mode transmission.

[0036] In some embodiments, the tip width w1 of the first tip 1 is 0.2um ± 100nm, and the tip width w2 of the second tip 2 is 0.2um ± 100nm.

[0037] The purpose of this configuration is to make the widths of the first tip 1 and the second tip 2 relatively small, so as to minimize the abrupt change in refractive index from the first tip 1 to its first tapered gradient transmission region 3 and the abrupt change in refractive index from the second tip 2 to its second tapered gradient transmission region 4. This will minimize return loss and achieve low loss of the end-face coupler.

[0038] Of course, the width of the third tip 71 is smaller than the width of the first tip 1 and the second tip 2, and can approach zero infinitely. Its purpose is also to achieve low loss of the end face coupler.

[0039] Furthermore, both the first tip 1 and the second tip 2 are located in the first waveguide layer, meaning that the first tip 1 and the second tip 2 are located in the same plane, and the planar spacing gap between the first tip 1 and the second tip 2 is 0.6um ± 100nm. The small planar spacing between the first tip 1 and the second tip 2 can reduce electromagnetic field leakage between them and avoid mutual interference of signals; it can also suppress external noise through the field blocking effect.

[0040] The interlayer distance between the second waveguide layer where the third coupling waveguide 103 is located and the first waveguide layer where the first coupling waveguide 101 and the second coupling waveguide 102 are located is very small and can be basically ignored. This can effectively reduce the signal transmission delay from the first coupling waveguide 101 and the second coupling waveguide 102 to the third coupling waveguide 103, suppress external electromagnetic interference, reduce the interlayer decoupling effect, and improve signal integrity and system stability.

[0041] Specifically, the third coupling waveguide 103 also includes a second output region 8 connected to the adiabatic conical region 7 for outputting optical signals coupled into the third coupling waveguide 103.

[0042] The optical signal that enters the third coupling waveguide 103 through the third tip 71 is transmitted sequentially through the adiabatic conical region 7 and the second output region 8, and after exiting through the second output region 8, it enters the single-mode waveguide for on-chip transmission.

[0043] The adiabatic conical region 7 of the third coupling waveguide 103 is mainly used to achieve efficient and low-loss coupling between different waveguides or modes, so that the optical energy in the first coupling waveguide 101 and the second coupling waveguide 102 can be coupled into the third coupling waveguide 103 for transmission with high efficiency and low loss. Its core function is to ensure that the optical field maintains mode matching during transmission through the tapered gradual change of the adiabatic conical region 7, thereby maximizing the coupling efficiency and reducing the loss caused by reflection and mode mismatch.

[0044] By setting an adiabatic conical region 7 with a gradually changing width, the optical field transitions gradually from the first coupled waveguide 101 and the second coupled waveguide 102 to the third coupled waveguide 103, avoiding mode mismatch and reflection caused by abrupt changes. The adiabatic conical region 7 can also optimize optical field overlap and improve the coupling efficiency between the coupled waveguides. Furthermore, the adiabatic conical region 7 has a high tolerance for manufacturing errors, making it suitable for challenges arising from differences in the refractive index of the coupled waveguide materials.

[0045] Depend on Figure 1 It can be seen that the third tip 71 of the insulating cone region is infinitely small, and the width of the insulating cone region towards the extension direction F1 gradually increases. After the width increases to a certain extent, the width of the insulating cone region remains unchanged and is consistent with the width of the second output region 8.

[0046] As for the first coupled waveguide 101 and the second coupled waveguide 102, the first coupled waveguide 101 includes a first tapered gradient transmission region 3, a first transition region 6 and a first output region 9 connected in sequence. The first tip 1 is located at the end of the first tapered gradient transmission region 3 away from the first transition region 6. The projections of the adiabatic tapered region 7 and the first output region 9 of the third coupled waveguide 103 are located within the projections of the first transition region 6 and the first output region 9 of the first coupled waveguide 101.

[0047] The first tip 1 is the input end of the first tapered gradient transmission region 3. The optical signal enters the first tapered gradient transmission region 3 through the first tip 1. The width of the first tapered gradient transmission region 3 gradually increases towards the extension direction F1. The optical signal enters the first transition region 6 connected to it. The first transition region 6 is the smooth transition region of the main optical path. A small portion of the optical signal enters the main optical path and smoothly transitions to the first output region 9 for output. Most of the optical signal is coupled into the third coupling waveguide 103 through the third tip 71 in the first transition region 6 for transmission and is output from the second output region 8 of the third coupling waveguide 103.

[0048] The projections of the adiabatic conical region 7 and the first output region 9 of the third coupling waveguide 103, that is, the overall projection of the third coupling waveguide 103 including the third tip 71, are all located within the projections of the first transition region 6 and the first output region 9 of the first coupling waveguide 101. In other words, the widths of the first transition region 6 and the first output region 9 are both greater than the widths of the first coupling waveguide 101 at various points.

[0049] The second coupled waveguide 102 includes a second tapered gradient transmission region 4 and a second transition region 5 connected in sequence. The second tip 2 is located at the end of the second tapered gradient transmission region 4 away from the second transition region 5. The output end of the second transition region 5 is connected to the input end of the adiabatic tapered region 7 of the third coupled waveguide 103 in the first transition region 6 of the first coupled waveguide 101.

[0050] The second tip 2 is the input end of the second tapered gradient transmission region 4. The optical signal enters the second tapered gradient transmission region 4 through the second tip 2. The width of the second tapered gradient transmission region 4 gradually increases in the extension direction F1. The optical signal enters the second transition region 5 connected to it. The output end of the second transition region 5 is connected to the input end of the adiabatic tapered region 7 of the third coupling waveguide 103 and to the first transition region 6 of the first coupling waveguide 101. This allows the optical signal of the second transition region 5 to be coupled into the third coupling waveguide 103 through the third tip 71 for transmission and output by the second output region 8 of the third coupling waveguide 103.

[0051] Furthermore, the output end of the second transition region 5 facing the extension direction F1 forms a conical region 51. The width of the conical region 51 gradually decreases towards the extension direction F1 until it also forms a tip. The output end of the second transition region 5 and the input end (insulated conical region 7) of the third coupling waveguide 103 are basically fully connected to completely couple the optical signal in the second coupling waveguide 102 into the third coupling waveguide 103, thereby improving the coupling efficiency of the optical signal.

[0052] The second output region 8 of the third coupled waveguide 103 is a ridge waveguide output region, and the first output region 9 of the first coupled waveguide 101 is a planar waveguide output region.

[0053] The main function of the output region of a ridge waveguide is to efficiently couple optical signals, that is, to couple the optical signals transmitted in the coupling waveguide to external devices (such as optical fibers, lasers or detectors), while reducing signal loss and improving coupling efficiency.

[0054] The second output region 8 of the third coupling waveguide 103 is a ridge waveguide output region. For example, the second output region 8 is a shallowly etched ridge waveguide. The ridge waveguide structure increases the waveguide's dimensions (such as ridge height and width), reducing diffraction when light waves exit from the end face of the second output region 8 and lowering the beam divergence angle. This increases the receiving area when light enters the end face of the second output region 8, thereby increasing the coupling area with other optoelectronic devices and significantly improving the coupling efficiency with external devices. Furthermore, the ridge waveguide has a larger dimensional tolerance, facilitating manufacturing processes, reducing processing difficulty, and contributing to stable optical signal output.

[0055] The first output region 9 of the first coupling waveguide 101 is a planar waveguide output region. The main function of the planar waveguide output region is to focus the optical signal and couple it into the single-mode waveguide at the back end for subsequent transmission or reception.

[0056] like Figure 2 As shown, for the first coupled waveguide 101, the width w3 at the output end of the first tapered gradient transmission region 3 and the first transition region 6 is 1µm ± 100nm; the width w5 at the output end of the first transition region 6 is 1.2µm ± 100nm; and the width w6 at the output end of the first output region 9 is 3µm ± 100nm.

[0057] For the second coupled waveguide 102, the width w4 at the junction of the second tapered gradient transmission region 4 and the second transition region 5, i.e., the output width w4 of the second tapered gradient transmission region 4, is 0.3um ± 100nm; the plane height H1 between the second tapered gradient transmission region 4 and the tapered region 51 is 1.5um ± 100nm.

[0058] For the third coupling waveguide 103, the second output region 8 is used to couple the single-mode waveguide at the back end, and the width wg_out of the second output region 8 is 0.9um + 200nm.

[0059] The width of each of the aforementioned zones primarily determines its cutoff frequency and operating frequency band. A wider width allows for the transmission of lower frequencies of electromagnetic waves and a longer transmission distance, but also results in faster attenuation. Therefore, low-frequency signals propagate more slowly in the waveguide, potentially leading to signal distortion.

[0060] As can be seen from the above widths, the width of the third coupling waveguide 103 is relatively small overall. It transmits electromagnetic waves at higher frequencies, with faster transmission speeds and higher signal fidelity, ensuring signal integrity and improving communication quality.

[0061] The length L1 of the second tapered gradient transmission region 4 is 400um ± 200um, the length L2 between the output end of the second tapered gradient transmission region 4 and the third tip 71 is 50um ± 20um, the length L3 of the first transition region 6 is 100um ± 50um, and the length L4 of the first output region 9 is 50um ± 10um.

[0062] Long-distance transmission requires consideration of signal attenuation. Therefore, this application sets the length of each zone within a suitable range, which also helps to improve signal integrity.

[0063] On the other hand, such as Figure 3As shown, the end face coupler also includes a substrate 13 and a cladding region located on the substrate 13. For example, the cladding region can be a silicon oxide cladding region. The first waveguide layer and the second waveguide layer are both located in the cladding region. That is, the first coupling waveguide 101, the second coupling waveguide 102 and the third coupling waveguide 103 are all located in the cladding region, while the substrate 13 has a cavity 130.

[0064] For example, the substrate 13 is generally silicon. A cavity 130 is formed in the substrate 13 by using silicon substrate hollowing technology, which can reduce the absorption loss of optical signals by the silicon substrate, thereby reducing the loss of the end coupler and achieving the purpose of low loss.

[0065] Furthermore, the cladding region has a channel 120 communicating with the cavity 130 of the substrate 13. The cladding region is divided into a central region 10 and side regions 12 located on both sides of the central region 10 through the channel 120. The two side regions 12 are connected to the central region 10 through cantilever beams 11. The first waveguide layer and the second waveguide layer are located in the central region 10, that is, the first coupling waveguide 101, the second coupling waveguide 102 and the third coupling waveguide 103 are all located in the central region 10.

[0066] The cantilever beam 11 provides mechanical support to the encapsulation area, making the end coupler more structurally stable, and thus more stable during optical signal transmission.

[0067] In addition, the first coupling waveguide 101, the second coupling waveguide 102, and the third coupling waveguide 103 of this application all have wavelengths between 1530nm and 1565nm and between 1565nm and 1625nm. The first coupling waveguide 101, the second coupling waveguide 102, and the third coupling waveguide 103 all include lithium niobate waveguides to be suitable for end-face couplers of lithium niobate C+L broadband large mode. They support 9μm large mode end-face couplers in ultrawide C+L bands (C band: 1530nm to 1565nm and L band: 1565nm to 1625nm), which not only effectively suppresses high-order mode excitation and improves bandwidth flatness, but also enhances the tolerance of the fabrication process, better meets the requirements of high-yield manufacturing, achieves uniform high-efficiency coupling, and significantly improves the mode field matching degree with optical fiber, thereby achieving lower coupling loss and polarization dependence in a wide spectral range.

[0068] In summary, in the end-face coupler provided in this application embodiment, the optical signal in the optical fiber is first coupled at the double tips formed by the first tip 1 and the second tip 2, and then enters the first tapered graded transmission region 3 and the second tapered graded transmission region 4 before reaching the gently sloping adiabatic tapered region 7. Due to the infinitely small width of the third tip 71, higher-order mode conversion is avoided. Finally, after exiting from the first output region 9 and the second output region 8, it enters the single-mode waveguide for on-chip transmission.

[0069] This application employs a dual-tip coupling, which can match a large 9µm pattern size and expands the alignment tolerance, which is beneficial for component applications such as packaging. At the same time, the cantilever beam 11 structure, combined with the infinitesimal setting of the third tip 71 of the gently sloping adiabatic conical region 7, minimizes the absorption loss of the substrate 13 and the loss caused by the transition of higher-order modes, thereby achieving the goal of low loss of the end-face coupler. Finally, through two etching processes, the infinitesimal setting of the third tip 71 of the gently sloping adiabatic conical region 7 is achieved, which can obtain broadband characteristics.

[0070] Figure 4 , Figure 5 The FDTD (Finite-Different Time Domain) TE (Transverse Electrical Mode) transmission optical field diagram and FDTD TE transmission efficiency diagram of the end-face coupler of this application are shown respectively. It can be seen that after adopting the end-face coupler of this application, the transmission efficiency is high and the transmission is stable, and it can achieve the functions of high bandwidth, large mode size and high coupling efficiency.

[0071] Based on this, this application embodiment also provides an optical chip, including the aforementioned end-face coupler.

[0072] An end-face coupler is the interface connecting an optical chip to an external optical fiber, achieving efficient optical signal transmission through mode field matching. Using the end-face coupler provided in any of the above embodiments, optical coupling can be achieved, effectively improving the coupling efficiency between the first coupling waveguide 101, the second coupling waveguide 102, and the third coupling waveguide 103, thus realizing stable optical transmission. When applied to an optical chip, it achieves mode field matching between the optical fiber and the optical chip, reducing coupling loss.

[0073] On the other hand, embodiments of this application also provide an optical quantum computer, including a quantum light source, an optical chip, and a detection device, wherein the optical chip includes the aforementioned end-face coupler.

[0074] In this system, the quantum light source generates photons, which are then transmitted through an optical chip. The detection device converts the optical signal from the optical chip into an electrical signal to achieve functions such as transmission or display.

[0075] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An end-face coupler, characterized in that, include: A first coupled waveguide and a second coupled waveguide located in the first waveguide layer, and a third coupled waveguide located in the second waveguide layer, wherein the first coupled waveguide, the second coupled waveguide and the third coupled waveguide extend in the same direction; The first and second coupled waveguides have a first tip and a second tip, respectively. The third coupled waveguide has an adiabatic tapered region with a third tip. The optical signal of the optical fiber enters the first and second coupled waveguides through the first and second tips, respectively, and is coupled to the third coupled waveguide through the third tip.

2. The end-face coupler according to claim 1, characterized in that, The first tip has a tip width of 0.2um ± 100nm, the second tip has a tip width of 0.2um ± 100nm, and the third tip has a tip width that is smaller than both the first tip width and the second tip width.

3. The end-face coupler according to claim 1 or 2, characterized in that, The third coupling waveguide also includes a second output region connected to the adiabatic conical region for outputting light coupled into the third coupling waveguide.

4. The end-face coupler according to claim 3, characterized in that, The first coupled waveguide includes a first tapered gradient transmission region, a first transition region, and a first output region connected in sequence. The first tip is located at the end of the first tapered gradient transmission region away from the first transition region. The projections of the adiabatic tapered region and the first output region of the third coupled waveguide are located within the projections of the first transition region and the first output region of the first coupled waveguide.

5. The end-face coupler according to claim 3, characterized in that, The second coupled waveguide includes a second tapered gradient transmission region and a second transition region connected in sequence. The second tip is located at the end of the second tapered gradient transmission region away from the second transition region. The output end of the second transition region is connected to the input end of the adiabatic tapered region of the third coupled waveguide in the first transition region of the first coupled waveguide.

6. The end-face coupler according to claim 4, characterized in that, The second output region of the third coupled waveguide is a ridge waveguide output region, and the first output region of the first coupled waveguide is a planar waveguide output region.

7. The end-face coupler according to claim 1 or 2, characterized in that, It also includes a substrate and a covering region located on the substrate, wherein the first waveguide layer and the second waveguide layer are both located in the covering region, and the substrate has a cavity; The cladding region has a channel communicating with the cavity of the substrate. The cladding region is divided into a central region and side regions located on both sides of the central region through the channel. The two side regions are respectively connected to the central region through cantilever beams. The first waveguide layer and the second waveguide layer are located in the central region.

8. The end-face coupler according to claim 1 or 2, characterized in that, The first coupled waveguide, the second coupled waveguide, and the third coupled waveguide all have wavelengths between 1530nm and 1565nm and between 1565nm and 1625nm. The first coupling waveguide, the second coupling waveguide, and the third coupling waveguide all include lithium niobate waveguides.

9. An optical chip, characterized in that, Includes the end face coupler as described in any one of claims 1 to 8.

10. An optical quantum computer, characterized in that, It includes a quantum light source, an optical chip, and a detector, wherein the optical chip includes the end-face coupler as described in any one of claims 1 to 8.

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