Optical device, photonic integrated circuit and optical quantum computer

Abstract

The application provides an optical device, a photonic integrated circuit and an optical quantum computer, and relates to the field of integrated optics. The optical device comprises a first waveguide and a second waveguide arranged at intervals. The first waveguide is a straight-through waveguide, and the second waveguide is provided with a plurality of polarization conversion sections and matches the effective refractive index of the first waveguide to convert a first polarization mode into a second polarization mode through twice coupling between the first waveguide and the second waveguide. Thus, the application realizes selective processing of the first polarization mode through the effective refractive index matching between the waveguides during mode conversion, allows the input optical signal to contain the second polarization mode component, and avoids the intensity loss caused by filtering the second polarization. After the light beam is coupled to the second waveguide, the hybrid noise generated in the processing process remains in the second waveguide and cannot be mixed with the first waveguide, so that the optical signal in the first waveguide does not need to be filtered and processed by using a multimode interference structure or the like, and the intensity loss is further reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated optics, in particular to an optical device, a photonic integrated circuit and an optical quantum computer. BACKGROUND

[0002] In the field of integrated optics (i.e. optical integrated circuit), polarization state is a main parameter of optical signal. Among them, the polarization state of integrated optics mainly includes transverse electric mode (TE) and transverse magnetic mode (TM), and in a specific optical integrated circuit, the optical device often has certain requirements for the polarization state. For example, the input end of a fiber-optic gyroscope (FOG) often needs to process transverse electric fundamental mode optical signal (i.e. TE0), and the components of other modes need to be filtered or converted before entering the fiber-optic gyroscope.

[0003] Therefore, how to convert the mode of the optical signal in the waveguide to meet the requirements of the optical device is a technical problem to be solved by those skilled in the art. SUMMARY

[0004] Therefore, the embodiments of the present application provide an optical device, a photonic integrated circuit and an optical quantum computer, which convert the first polarization into the second polarization through the effective refractive index matching between the first waveguide and the second waveguide.

[0005] In a first aspect, the present application provides an optical device. The optical device comprises a first waveguide and a second waveguide, the first waveguide and the second waveguide are formed in a waveguide layer and are spaced apart, the first waveguide is at least used for passing through an optical signal in a second polarization fundamental mode, the second waveguide comprises a first polarization conversion section arranged close to an input end of the first waveguide, a second polarization conversion section arranged close to an output end of the first waveguide, and an isolation reset section arranged between the first polarization conversion section and the second polarization conversion section. Among them, at least part of the isolation reset section is away from the first waveguide. The effective refractive index of the first polarization conversion section based on an intermediate target order mode matches the effective refractive index of the first waveguide based on a first polarization fundamental mode, so that the first polarization fundamental mode optical signal in the first waveguide is coupled to the first polarization conversion section through the first waveguide and converted into the intermediate target order mode; the effective refractive index of the second polarization conversion section based on the intermediate target order mode matches the effective refractive index of the first waveguide based on a second polarization fundamental mode, so that the intermediate target order mode optical signal in the second waveguide is coupled to the first waveguide through the second polarization conversion section and converted into the second polarization fundamental mode.

[0006] In a second aspect, the present application provides a photonic integrated circuit, which comprises the optical device of the first aspect and a fiber-optic gyroscope based on a transverse magnetic mode, wherein the fiber-optic gyroscope is connected to the output end of the first waveguide of the optical device, the first polarization configuration of the optical device is a transverse magnetic mode, the second polarization configuration is a transverse electric mode, and the target order configuration is a first order.

[0007] In a third aspect, the present application provides an optical quantum computer, which comprises a single-photon source, an optical quantum chip, and a single-photon detector, one or more of the single-photon source, the optical quantum chip, and the single-photon detector comprising the optical device of the first aspect.

[0008] Based on the optical device, the photonic integrated circuit, and the optical quantum computer provided by the present application, the optical device comprises a first waveguide and a second waveguide arranged at intervals. The first waveguide is a straight-through waveguide, and the second waveguide is provided with a plurality of polarization conversion sections and is matched with the effective refractive index of the first waveguide to convert a first polarization mode into a second polarization mode through two couplings between the first waveguide and the second waveguide. In this way, the present application realizes selective processing of the first polarization mode through the effective refractive index matching between the waveguides when the mode is converted, and allows the input optical signal to contain the second polarization mode component, thereby avoiding the intensity loss caused by filtering the second polarization. In addition, the hybrid noise generated in the processing process will remain in the second waveguide and cannot be mixed with the first waveguide, so that the optical signal in the first waveguide does not need to be filtered and processed by using a multi-mode interference structure or the like, further reducing the intensity loss. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present 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.

[0010] Figure 1 FIG. 1 is a schematic structural diagram of a photonic integrated circuit provided by some embodiments of the present application.

[0011] Figure 2 FIG. 2 is a waveguide cross-sectional schematic diagram of an optical device provided by some embodiments of the present application.

[0012] Figure 3 FIG. 3 is a structural schematic diagram of an optical device provided by some embodiments of the present application.

[0013] Figure 4 FIG. 4 is a schematic diagram of the relationship between the waveguide width and the effective refractive index.

[0014] Figure 5 is another structural schematic diagram of an optical device provided by some embodiments of the present application.

[0015] Figure 6 is still another structural schematic diagram of an optical device provided by some embodiments of the present application.

[0016] Figure 7 is another structural schematic diagram of an optical device provided by some embodiments of the present application.

[0017] In the formula, 100 is a photonic integrated circuit; 110 is a light source to be measured; 120 is an optical device; 121 is a waveguide layer; 122 is a cladding layer; 123 is a substrate; 130 is a fiber-optic gyroscope; 310 is a first waveguide; 320 is a second waveguide; 321 is a first polarization conversion section; 322 is a second polarization conversion section; 323 is an isolation reset section; 3231 is a lifting structure; 3232 is a reset structure; 3233 is a width gradient structure; 324 is a scattering section; 3241 is a turning structure; and 3242 is a mode mismatch structure. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0019] It should be noted that the diagrams provided in the embodiments only schematically illustrate the basic concept of the present application, and therefore, in the diagrams, only the components related to the present application are shown, but not the components number, shape and size when actually implemented. The shape, number and proportion of each component when actually implemented can be randomly changed, and the component layout form can also be more complex.

[0020] In the present application, it should be noted that, if the terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like appear, the indicated orientation or position relationship is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first" and "second" appear, they are only for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0021] SUMMARY

[0022] As mentioned in the background, in the field of integrated optics, the polarization state of a light beam often presents two orthogonal polarization states, namely the TE mode (transverse electric mode) and the TM mode (transverse magnetic mode). Among them, the TE mode refers to the polarization state in which the electric field direction is perpendicular to the incident plane, while the TM mode refers to the polarization state in which the magnetic field direction is perpendicular to the incident plane.

[0023] In practical optical integrated circuits, light (i.e., optical signals) is often transmitted based on the fundamental mode in single-mode optical fibers or waveguides to ensure a relatively stable phase relationship during transmission. Therefore, optical devices requiring polarization states often need to remove unwanted polarized fundamental mode components from the beam.

[0024] Taking fiber optic gyroscopes as an example, they often rely on transverse electric fundamental mode for testing. This means that before the optical signal enters the gyroscope, other polarization components (i.e., transverse magnetic fundamental mode) in the optical signal need to be removed. In practice, this "removal" of the transverse magnetic fundamental mode can be achieved by converting it into a transverse electric fundamental mode or by filtering it. This removal process is often implemented using an optical device.

[0025] To further illustrate this process, this application also provides a schematic structural diagram of a photonic integrated circuit including optical devices and a fiber optic gyroscope. Figure 1 ).

[0026] like Figure 1 As shown, the photonic integrated circuit 100 may include a light source under test 110, an optical device 120, and a fiber optic gyroscope 130. The light source under test 110 can provide an optical signal for measurement, which is then fed into the fiber optic gyroscope 130 via the optical device 120 for measurement. The optical device 120 can be used to convert or filter the transverse magnetic fundamental mode component in the optical signal.

[0027] In practical implementation, the aforementioned optical device 120 can generally be formed based on modulation structures such as waveguide mode conversion structures. A waveguide is a dielectric structure used to guide light along a specific path. It is a fundamental component in integrated optical systems, similar to a wire in an integrated circuit, responsible for transmitting optical signals from one optical component to another. By restricting the propagation path of light, waveguides ensure efficient light transmission within a specific area, thereby enabling the processing and transmission of optical information.

[0028] A waveguide-based mode conversion structure is a device for realizing the conversion between different modes in an optical waveguide (such as a tapered waveguide). Its core goal is to efficiently convert the fundamental mode (such as the TE0 mode) into other modes (such as the TE1 mode, the TE2 mode, etc.). However, in the mode conversion process of the waveguide, the conversion between the fundamental modes often needs to pass through multiple mode conversion structures, and other noise (such as hybrid noise in the mode conversion process) may be introduced in the processing of the mode conversion structure. This case will seriously affect the power of the optical signal, and in some cases (such as the TE0 component in the optical beam may generate noise in the TM0 conversion process), additional filtering processing (such as removing the TE0 component before processing and removing other components except TE0 after processing) may be required, further reducing the power of the optical signal.

[0029] To solve the foregoing technical problems, the present application provides an optical device, a photonic integrated circuit and an optical quantum computer. The optical device comprises a first waveguide and a second waveguide arranged at intervals. The first waveguide is a straight-through waveguide, and the second waveguide is provided with a plurality of polarization conversion sections and matches the effective refractive index with the first waveguide to convert the first polarization basis mode into the second polarization basis mode through two couplings between the first waveguide and the second waveguide. Thus, the present application realizes selective processing of the first polarization basis mode through effective refractive index matching between the waveguides in the mode conversion, allows the input optical signal to contain the second polarization basis mode component, avoids the intensity loss caused by filtering the second polarization, and further reduces the intensity loss by not filtering the optical signal in the first waveguide using a multi-mode interference structure or the like.

[0030] Before further describing the optical device provided by the present application, the actual form of the waveguide structure is described. That is, the present application provides a schematic diagram of the waveguide cross section of the optical device Figure 2 .

[0031] As shown in Figure 2 , the core structure in the cross section of the optical device 120 is a waveguide layer 121, and the waveguide structure is formed in the waveguide layer 121. Above and below (or around the waveguide layer 121) is often provided with a cladding layer 122 (or buffer layer, generally configured as silicon oxide) to realize optical isolation and optimize mode matching. Then, a substrate 123 (generally a silicon substrate / silicon base) is often provided below the cladding layer 122 to provide mechanical support, and an electrode layer (not shown in the figure) can be provided above the cladding layer 122 to apply a modulation electric field.

[0032] In the present application, in order to avoid energy loss caused by doping, the aforementioned waveguide layer 121 can be configured as a thin film lithium niobate material. The waveguide structure (specifically the first waveguide and the second waveguide) provided in the present application is configured as a ridge waveguide. For the causes, effects and formation of the waveguide layer topography (the cross-section in the figure is a stack of trapezoidal and rectangular shapes), please refer to the description of the related art, which will not be repeated here.

[0033] In addition to the optical device, the present application provides a photonic integrated circuit and an optical device related to the optical device of the present application. Among them, the photonic integrated circuit / optical device is provided with the optical device provided in the present application based on actual needs. For example, the photonic integrated circuit provided in the present application can include the optical device provided in the present application and a fiber-optic gyroscope based on a transverse magnetic mode, wherein the fiber-optic gyroscope is connected to the output end of the first waveguide of the optical device, the first polarization configuration of the optical device is a transverse magnetic mode, the second polarization configuration is a transverse electric mode, and the target order configuration is a first order (the intermediate target order configuration is TE1). In addition, other photonic integrated circuits or optical devices related to the optical device provided in the present application are also within the protection scope of the present application. Figure 1 For example, the photonic integrated circuit provided in the present application can include the optical device provided in the present application and a fiber-optic gyroscope based on a transverse magnetic mode, wherein the fiber-optic gyroscope is connected to the output end of the first waveguide of the optical device, the first polarization configuration of the optical device is a transverse magnetic mode, the second polarization configuration is a transverse electric mode, and the target order configuration is a first order (the intermediate target order configuration is TE1). In addition, other photonic integrated circuits or optical devices related to the optical device provided in the present application are also within the protection scope of the present application.

[0034] The following will be described in detail Figures 3-7 The optical device for converting the polarization state provided in the present application will be described in detail.

[0035] Exemplary optical devices

[0036] As described above, in order to overcome the aforementioned technical problems, the present application provides an optical device based on a waveguide structure, which is different from the mode converter of the conventional waveguide structure. The present application performs mode conversion through effective refractive index matching.

[0037] The actual principle of mode conversion based on effective refractive index matching is phase-matched energy coupling, that is, when the effective refractive indices of two waveguides are consistent, the phase-matching condition is met, thereby triggering energy exchange between modes, so that the energy is completely transferred from the input mode to the target mode, and mode conversion is realized.

[0038] For example, when the effective refractive index of TM0 based on one waveguide matches the effective refractive index of TE1 based on the adjacent waveguide, the light beam of TM0 will be coupled into another waveguide and converted into TE1 mode.

[0039] In practical applications, the aforementioned effective refractive index matching is asymmetric, that is, the matching process of the aforementioned TM0 and TE1 cannot be simply understood as N TM0 =N TE1 , but should be understood as N TM0 (the effective refractive index of the reaction polarization state TM0) = N TM0→TE1(Effective refractive index for the change of polarization state from TM0 to TE1). In practical applications, the effective refractive index from TE1 to TM0 is different from the effective refractive index from TE0 to TE1, thus ensuring that energy is unidirectionally converted to a specific mode and does not return.

[0040] Based on the aforementioned phase-matched energy coupling, the waveguide structure provided in this application can have two waveguides and form at least two segments through the aforementioned effective refractive index matching to realize the conversion from the first polarization fundamental mode (such as TM0) to the second polarization fundamental mode (TE0).

[0041] To further illustrate this point, this application provides a schematic diagram of the structure of an optical device. Figure 3 To distinguish it from the aforementioned Figure 2 The structure shown, Figure 3 In the following figures, the optical device will still be referred to as 120 to reflect the improved optical device of this application.

[0042] like Figure 3 As shown, the optical device 120 may include a first waveguide 310 and a second waveguide 320. The first waveguide 310 and the second waveguide 320 are spaced apart (the specific gap is called gap, which needs to ensure that crosstalk is avoided and the aforementioned energy coupling can occur. The specific gap can be determined experimentally, and it can generally be 0.2um~0.7um, preferably 0.6um).

[0043] The first waveguide 310 can at least be used to directly transmit optical signals in the second polarization fundamental mode, so as to prevent the optical signals in the second polarization fundamental mode from being unable to enter the second waveguide 320 for processing, thus reducing the intensity of the output optical signal. The specific shape of the first waveguide 310 can be determined based on actual process limitations. For example, when the waveguide layer is configured as a thin-film lithium niobate material, the waveguide layer may be anisotropic, then the aforementioned first waveguide 310 can be configured as a linear waveguide (also referred to as a through waveguide). Specifically, it can be presented as follows: Figure 3 The waveguide shown is a straight line without planar bends and has the same width everywhere.

[0044] Based on other isotropic waveguide materials (such as isotropic hybrid waveguide materials formed by heterogeneous integration of lithium niobate thin films with high refractive index materials such as silicon nitride (SiN), tantalum pentoxide (Ta2O5), or chalcogenide glasses), the first waveguide 310 can be a channel with the same waveguide width everywhere, and it can have a bent shape. See details in [link to relevant documentation]. Figure 7 And its related descriptions.

[0045] To realize the conversion of polarization state, the second waveguide 320 at least comprises a first polarization conversion section 321 and a second polarization conversion section 322. The first polarization conversion section 321 and the second polarization conversion section 322 can be coupled with the first waveguide 310 by effective refractive index, so that the light beam is converted between different waveguides. In the conversion process, the light beam first passes through the first polarization conversion section 321, and then passes through the second polarization conversion section 322. That is, the first polarization conversion section 321 is arranged close to the input end (in) of the first waveguide 310, and the second polarization conversion section 322 is arranged close to the output end (out) of the first waveguide 310.

[0046] The arrangement of the first polarization conversion section 321 and the second polarization conversion section 322 can be adjusted based on the requirements of mode conversion to realize the coupling with the first waveguide 310. Preferably, to realize the coupling of the two conversion sections with the corresponding sections in the first waveguide 310, the conversion sections and the sections in the first waveguide 310 should be parallel (i.e. the same extension direction). That is, the first polarization conversion section 321 is parallel to the input end of the first waveguide 310 (the same extension direction), and the second polarization conversion section 322 is parallel to the output end of the first waveguide 310 (the same extension direction). The spacing between the two and the first waveguide can be adjusted according to actual needs, and in general cases, the spacing between the two and the first waveguide 310 is the same. In addition, the aforementioned parallel (or the same extension direction) can be understood as approximately parallel within the range allowed by process error, so as to realize the coupling of the first waveguide 310 and the second waveguide 320.

[0047] Considering that the above structure can realize the mutual conversion between TM0 and TE0 by controlling parameters, for the convenience of description, the polarization state to be converted is recorded as the first polarization, and the polarization state of the conversion result is recorded as the second polarization. Considering the difficulty and noise of direct conversion, an intermediate non-zero order mode (recorded as an intermediate target order mode) can also be introduced in the above conversion process. The intermediate target order mode can be a non-zero order mode of the first polarization or a non-zero order mode of the second polarization (preferably TM1, TE1, etc. low order state to improve stability).

[0048] Therefore, the polarization conversion process based on the first polarization conversion section 321 and the second polarization conversion section 322 can be understood as the mode conversion of the first polarization base mode to the intermediate target order mode in the first polarization conversion section 321, and the mode conversion of the intermediate target order mode to the second polarization base mode in the second polarization conversion section 322, so as to realize the conversion of the first polarization base mode to the second polarization base mode.

[0049] For the convenience of describing the actual matching situation, the m order mode of the nth polarization can be recorded as T(n,m) (also as the aforementioned intermediate target order), and the corresponding effective refractive index can be recorded as NT(n,m). (n,m) .

[0050] The effective refractive index matching relationship involved in the process from the first polarization base mode to the intermediate target order mode to the second polarization base mode in the present application can be analyzed as follows: in the first polarization conversion section 321, NT (1,0) = NT T(1,0)→T(n,m) of the second waveguide 320. In the second polarization conversion section 322, NT (n,m) = NT (n,m)→T(2,0) of the first waveguide 310. Thus, the transfer of the polarization state is realized.

[0051] Thus, the first polarization conversion section 321 matches the effective refractive index based on the intermediate target order mode with the effective refractive index based on the first polarization base mode of the first waveguide 310 (N T(1,0) = N T(1,0)→T(n,m) of the second waveguide), so that the second polarization base mode optical signal T(1, 0) in the first waveguide 310 is coupled to the first polarization conversion section 321 through the first waveguide 310 and converted into the intermediate target order mode T(n, m). The second polarization conversion section 322 matches the effective refractive index based on the intermediate target order mode with the effective refractive index based on the second polarization base mode of the first waveguide 310 (N T(n,m) = N T(n,m)→T(2,0) of the first waveguide), so that the intermediate target order mode optical signal T(n, m) in the second waveguide 320 is coupled to the first waveguide 310 through the second polarization conversion section 322 and converted into the second polarization base mode T(2, 0).

[0052] In particular, based on the foregoing non-linear / irreversible correlation discussion, NT (n,m) = NT (n,m)→T(2,0) of the second waveguide 320 is not equivalent to NT (2,0)→T(n,m) = NT (2,0) of the first waveguide 310, i.e., the aforementioned second polarization base mode T(2, 0) inherent in the first waveguide 310 does not enter the second waveguide 320 at the second polarization conversion section 322 of the second waveguide 320.

[0053] Exemplarily, for the aforementioned conversion process from TM0 to TE0, the aforementioned intermediate target order mode can be TE1, i.e., when the TM0 component in the light beam reaches the region in the first waveguide 310 corresponding to the first polarization conversion section 321, based on the effective refractive index N TM0 = N TE1The TM0 component here can be converted into a TE1 component and enter the second waveguide 320. When the TE1 component reaches the second polarization conversion section 322, the effective refractive index N TE0 = the effective refractive index N' of the second polarization conversion section 322 in the second waveguide 320 for the TE1 component TE1 . The TE1 component here is converted into a TE0 component and returns to the first waveguide 310. The TE0 component in the first waveguide 310 can be directly output from the output end of the first waveguide 310.

[0054] In some embodiments, to ensure the normal execution of the aforementioned mode conversion, the aforementioned two coupling processes need to be isolated to ensure that the intermediate target mode is not disturbed during transmission. Therefore, the aforementioned second waveguide 320 further includes an isolation reset section 323 arranged between the first polarization conversion section 321 and the second polarization conversion section 322.

[0055] The isolation reset section 323 needs to be away from the first waveguide 310 in structure to ensure that the intermediate target mode is not disturbed during transmission and to block the coupling range of the two coupling areas. That is, at least part of the aforementioned isolation reset section 323 (presented as an arc-shaped middle area in the figure) is away from the first waveguide 310. The isolation reset section 323 can be away from the gap by a distance h, that is, the distance between the isolation reset section 323 and the first waveguide 310 can be gap+h. The selection of the related parameters of the aforementioned isolation reset section 323 is similar to the aforementioned gap, as long as the disturbance can be reduced, and the optimal data can be determined through multiple tests.

[0056] Specifically, the isolation reset section 323 can include a first interface connected with the first polarization conversion section 321 and a second interface connected with the second polarization conversion section 322. The tangent direction of the first interface is consistent with the extension direction of the input end of the first waveguide 310, and the tangent direction of the second interface is consistent with the extension direction of the output end of the first waveguide 310. In the isolation reset section 323, it is away from the first waveguide 310, so that the distance between the middle part of the isolation reset section 323 and the first waveguide 310 is h+gap, which is greater than the distance gap between the two end interfaces of the isolation reset section 323 and the first waveguide 310.

[0057] Therefore, based on the aforementioned settings, the second polarization basis mode component in the optical signal entering the first waveguide from the input end of the first waveguide is output from the output end of the first waveguide, the first polarization basis mode component is coupled from the first waveguide to the second waveguide based on the first polarization conversion section and converted into an intermediate target mode, and then coupled from the second waveguide to the first waveguide based on the second polarization conversion section and converted into a second polarization basis mode to be output from the output end of the first waveguide.

[0058] In summary, based on the foregoing provided optical device, the optical device comprises a first waveguide and a second waveguide arranged at intervals. Among them, the first waveguide is a straight-through waveguide, and the second waveguide is provided with a plurality of polarization conversion sections and matches the effective refractive index with the first waveguide to convert the first polarization mode into the second polarization mode through twice coupling between the first waveguide and the second waveguide. Thus, the present application realizes the selective processing of the first polarization mode through the effective refractive index matching between the waveguides during mode conversion, and allows the input optical signal to contain the second polarization component, avoiding the intensity loss caused by filtering the second polarization. In addition, after the light beam is coupled into the second waveguide, the hybrid noise generated in the processing process will remain in the second waveguide and cannot be mixed with the first waveguide, so there is no need to filter the optical signal in the first waveguide by using a multi-mode interference structure and the like, further reducing the intensity loss.

[0059] At the processing level of the subsequent optical signal, other optical devices (such as a fiber-optic gyroscope based on a transverse magnetic mode) can be coupled at the output end of the first waveguide 310, so that the processed optical signal is subjected to subsequent processing and analysis in the corresponding optical device. In addition, the output end of the first waveguide 310 can also be coupled with other waveguides (denoted as a third waveguide), so that the mode-converted optical signal enters the third waveguide, thereby performing subsequent optical signal transmission and processing (such as quantum gate processing in the third waveguide as a single-mode light source).

[0060] At the actual preparation level, the parameters of the waveguide only need to meet the matching requirement of the effective refractive index to realize the optical device provided by the present application. To further simplify the preparation of the optical device, the adjustment of the effective refractive index can be realized by adjusting the waveguide width. That is, the first polarization conversion section, the second polarization conversion section, and the first waveguide realize the effective refractive index matching based on the waveguide width.

[0061] At the corresponding actual preparation link, the relationship between the waveguide width and the effective refractive index under different polarization states in the waveguide layer can be collected and determined, and then a suitable waveguide width is configured based on the relationship to realize the optical device provided by the present application.

[0062] To further illustrate the process, the present application provides a relationship diagram of the waveguide width and the effective refractive index Figure 4 . Among them, Figure 4 The relationship diagram of the waveguide width and the effective refractive index under different polarization states (i.e. polarization state transition) is shown. Taking the middle target bit TE1 as an example, in the data graph shown in Figure 4 , from top to bottom, six curves of TE0, TE0→TE1, TM0, TM0→TE1, TE1→TE0, and TE1 are presented. The vertical coordinate is the effective refractive index, and the horizontal coordinate is the waveguide width. The specific data can be determined by experiment / test / theoretical calculation. Figure 4The data in this example is merely to illustrate the waveguide determination process; the actual data curves presented are not identical. Figure 4 They are generally different.

[0063] In the actual fabrication process, the width of the first waveguide 310 is constant and denoted as w0, while the first polarization conversion section 321 and the second polarization conversion section 322 of the second waveguide 320 are constant and denoted as w1 and w2, respectively.

[0064] Considering the influence of width on the effective refractive index, the aforementioned effective refractive index can be analyzed based on the width w and T(n,m), i.e., it can be denoted as N(w, T(n,m)). Therefore, the effective refractive index of the first waveguide 310 based on TM0 can be denoted as N(w0, TM0), the effective refractive index based on TE0 can be denoted as N(w0, TE0), and the effective refractive index based on TE1→TE0 can be denoted as N(w0, TE1→TE0). For the second waveguide 320, the effective refractive index based on TM0→TE1 in the first polarization conversion section 321 can be denoted as N(w1, TM0→TE1), the effective refractive index based on TE1 in the second polarization conversion section 322 can be denoted as N(w2, TE0→TE1).

[0065] The aforementioned conditions for effective refractive index matching can be characterized as: N(w0, TM0) = N(w1, TM0→TE1), N(w0, TE1→TE0) = N(w2, TE1). Therefore, combined with... Figure 4 The data shown only needs to specify one width (e.g., w0), and other widths can be based on... Figure 4 The data shown is directly determined. The general process for determining the parameters is similar to the previous conversion process. For a known w0, the effective refractive index based on the first polarization fundamental mode can be determined (e.g., N(w0, TM0)). Then, the width value corresponding to the aforementioned value is determined from the curve from the first polarization fundamental mode to the intermediate target mode, which is w1. Then, N(w1, TM0→TE1) is determined from the known w0, and w2, which has the same value, is determined from the curve of the intermediate target mode.

[0066] In addition, it can be seen from Figure 4 As can be seen from this, when N(w0, TE1→TE0) = N(w2, TE1), N(w2, TE0→TE1) ≠ N(w0, TE0). That is, TE0 (i.e. the second polarization fundamental mode) remaining in the first waveguide 310 will not couple back to the second waveguide 320 in the second polarization conversion section 322.

[0067] Based on the foregoing arrangement, the foregoing optical device can be implemented by configuring the waveguide widths, and the respective waveguide widths w0, w1, w2 thus determined are often different, i.e., the foregoing first polarization conversion section and second polarization conversion section have different waveguide widths. Figure 3 In the foregoing, the sizes of w0, w1, and w2 are not shown to be different.

[0068] To avoid the optical performance hardening (generally manifested as phase change) caused by the sudden change of the waveguide width in the second waveguide, the foregoing different waveguide widths can be adjusted by the foregoing isolation reset section.

[0069] Please continue to refer to Figure 3 The isolation reset section 323 in the optical device 120 shown in the foregoing can include a lifting structure 3231 and a reset structure 3232. The lifting structure 3231 is connected to the first polarization conversion section 321 and matches the width (w1) of the first polarization conversion section 321, and the reset structure 3232 is connected to the second polarization conversion section 322 and matches the width (w2) of the second polarization conversion section 322.

[0070] Considering that the lifting structure 3231 and the reset structure 3232 are directly connected to the first polarization conversion section 321 and the second polarization conversion section 322, the foregoing width matching can at least include that the waveguide width at the contact with the polarization conversion section is consistent with the corresponding polarization conversion section.

[0071] Considering the difference in waveguide width between the foregoing first polarization conversion section 321 and second polarization conversion section 322, the width of the foregoing lifting structure 3231 and reset structure 3232 can be changed to adapt to the different waveguide widths at both ends. That is, the width of the lifting structure 3231 and the reset structure 3232 changes in the direction from the first polarization conversion section 321 to the second polarization conversion section 322 (not shown in the figure), so that the width at the connection between the lifting structure 3231 and the first polarization conversion section 321 is the same as the width of the first polarization conversion section 321 (i.e., w1), and the width at the connection between the reset structure 3232 and the second polarization conversion section 322 is the same as the width of the second polarization conversion section 322 (i.e., w2).

[0072] In addition, the waveguide width of the lifting structure 3231 and the reset structure 3232 itself can remain unchanged and the change in waveguide width can be achieved by external structures. To further illustrate this case, the present application also provides a structural schematic diagram of an optical device in this case (FIG. 6). Figure 5

[0073] As Figure 5 ​As shown, the isolation reset section 323 further comprises a width tapering structure 3233 connected between the lifting structure 3231 and the reset structure 3232. At this time, the lifting structure 3231 can be configured as a width-fixed S-shaped rising bend (i.e. the width of the bend is constant as w1 within the tolerance range, and the S-shaped bend is also called Sbend) based on the width (w1) of the first polarization conversion section 321, and the reset structure 3232 is configured as a width-fixed S-shaped falling bend (i.e. the width of the bend is constant as w2 within the tolerance range) based on the width (w2) of the second polarization conversion section 322. The width tapering structure 3233 (also called taper) has a width of w1 at the connection with the lifting structure 3231 and a width of w2 at the connection with the reset structure 3232, and the waveguide width gradually changes from w1 to w2. Specifically, the waveguide width of the width tapering structure 3233 monotonically changes from w1 to w2, and the specific change form can be adjusted according to actual needs. The application preferably linearly changes, and the width tapering structure 3233 presents a trapezoidal structure.

[0074] In addition, in order to ensure that the partial area of the isolation reset section 323 is away from the first waveguide 310, the distance (h+gap, h is the lifting height of the lifting structure 3231) between the end of the lifting structure 3231 away from the first polarization conversion section 321 and the first waveguide 310 is greater than the distance (i.e. the gap gap) between the first waveguide 310 and the first polarization conversion section 321. Correspondingly, the reset structure 3232 gradually eliminates the aforementioned h, so that the distance between the connection with the second polarization conversion section 322 and the first waveguide 310 returns to gap.

[0075] The selection of the internal parameters (such as lifting height h, total length, etc.) of the aforementioned isolation reset section 323 generally needs to select parameters with less interference, which can be tested by experiments.

[0076] Therefore, based on the foregoing setting, the optical device can be realized by the waveguide width, and the influence of the sudden change of the waveguide width can be avoided by the width tapering design of the isolation reset section at the second waveguide.

[0077] Based on the foregoing, in order to further illustrate the optical device in actual application. The application also designs for the O-band (Original Band) commonly used in the field of optical fiber communication to realize the conversion between the transverse magnetic mode and the transverse electric mode of the O-band. That is, in the design, the first polarization of the optical device is configured as the transverse magnetic mode (i.e. TM0), the second polarization is configured as the transverse electric mode (i.e. TE0), and the target order is configured as the first order (i.e. TE1).

[0078] Specifically, the first polarization conversion section 321 is configured as a transverse magnetic mode (TM0), the second polarization conversion section 322 is configured as a transverse electric mode (TE0), and the target order is configured as the first order (TE1). Figure 5The optical device shown is an example, wherein the device-related dimensions are: w0=1um, w1=2.1um, w2=2.6um, gap=0.6um, h=3um. In addition, the length of the first polarization conversion section 321 is 163um, the length of the second polarization conversion section 322 is 197um, the length of the lifting structure 3231 is 50um, the length of the width-gradual-change structure 3233 is 20um, and the length of the reset structure 3232 is 50um.

[0079] It should be noted that, considering that the optical device under the aforementioned device parameters is difficult to clearly reflect the dimensions and changes of each structure if strictly drawn in the drawings according to the scale. In order to clearly reflect the device structure, the size of the optical device in the drawings of the present application may be different from the actual scale. That is, the drawings of the present application are only an exemplary description of the device structure, and do not strictly reflect the actual size.

[0080] In addition, in order to match the aforementioned optical device, Figure 2 In the optical device 120 shown, the substrate 123 can be silicon-based, the aforementioned waveguide layer 121 can be a 500nm-thick thin-film lithium niobate material, the aforementioned waveguide structure can be a ridge waveguide with an etching depth of 200nm, and the aforementioned cladding layer 122 can be silicon oxide.

[0081] In some embodiments, considering that there can be hybrid noise in the actual application process of mode matching, especially in the area of width change (such as the width-gradual-change structure 3233), hybridization is prone to occur and light beam components outside the intermediate target mode remain in the second waveguide 320. In order to avoid the influence of the component on the converted first polarization basis mode light beam in the first waveguide 310 when it exits from the second waveguide 320.

[0082] A processing structure such as a filter can be added at the tail end of the aforementioned second waveguide 320 (i.e., the end of the second polarization conversion section 322). However, considering that there is no other available light beam in the second waveguide 320, the light beam in the second waveguide 320 can be directly scattered out. That is, the aforementioned processing structure can be a scattering section. In order to avoid the influence of the light beam remaining in the second waveguide 320 on the first waveguide 310, the end of the aforementioned scattering section is oriented differently from the extension direction of the first waveguide, so that the hybrid noise in the second waveguide is scattered based on the end orientation, so as to avoid its influence on the light beam in the first waveguide.

[0083] In order to further illustrate the end scattering structure, the present application also provides a structural schematic diagram of an optical device with an end scattering structure Figure 6 .

[0084] As Figure 6As shown, the second waveguide 320 of the optical device 120 may further include a scattering section 324 to scatter noise remaining in the second waveguide 320. Further, the scattering section 324 may generally be based on an arc-shaped bend waveguide (denoted as arc-shaped steering structure 3241) so that its end is not parallel to or intersects with the direction of the first waveguide 310. Its end is generally located on the side away from the direction of the first waveguide.

[0085] Preferably, the aforementioned arc-shaped steering structure 3241 can be presented as at least a partial arc located on the side away from the direction of the first waveguide. That is, the arc-shaped steering structure 3241 is connected to the end of the second polarization conversion section 322, and the extension direction of the second polarization conversion section 322 is the tangent direction at the connection between the arc-shaped steering structure 3241 and the second polarization conversion section 322 (i.e., the radius R of the arc-shaped steering structure 3241 in the figure is perpendicular to the second polarization conversion section 322). Preferably, the aforementioned arc-shaped steering structure 3241 can be a quarter circle.

[0086] Furthermore, considering that the first polarization fundamental mode and other difficult-to-handle beams may reappear during the aforementioned hybridization process, a mode mismatch structure 3242 can be further configured at the rear end of the aforementioned arc-shaped steering structure 3241. The mode mismatch structure 3242 is connected to the end of the arc-shaped steering structure and is used to adjust the effective refractive index of the residual beam within the second waveguide 320, so that the residual beam is mismatched with the mode supported by the second waveguide 320 and scattered from the end of the mode mismatch structure 3242.

[0087] Preferably, the aforementioned mode mismatch structure 3242 can also be achieved by varying the width of the waveguide, such as by presenting a width-gradient structure, and the width at the connection between the mode mismatch structure 3242 and the arc-shaped steering structure is consistent with the width of the second polarization conversion section 322 (i.e., w2). In practical design, the end width of the mode mismatch structure 3242 can be w3, which is generally smaller than the widths of the aforementioned waveguides (i.e., w0, w1, w2).

[0088] Furthermore, to illustrate the influence of other forms of the first waveguide 310 on the aforementioned second waveguide 320, this application also provides a first waveguide 310 in a non-straight-through waveguide configuration. In this case, the waveguide layer material is generally an isotropic waveguide material, so that the first waveguide 310 can pass through the optical signal of the second polarization fundamental mode after bending.

[0089] like Figure 7 As shown, there is a certain angle bend between the input and output ends of the first waveguide 310, causing the extension directions of the input and output ends to be inconsistent. Correspondingly, the first polarization conversion section 321 of the second waveguide 320 is parallel to the input end of the first waveguide 310, and the second polarization conversion section 322 is parallel to the output end of the first waveguide 310.

[0090] The intermediate isolation reset section 323 is adaptively adjusted based on the bending of the first waveguide 310, so that the tangent direction of the first interface of the isolation reset section 323 in contact with the first polarization conversion section 321 is the extension direction of the input end and away from the first waveguide 310 in the subsequent waveguide, and then reset so that the tangent direction of the second interface of the isolation reset section 323 is the extension direction of the output end and in communication with the second polarization conversion section 322. Other structures (such as scattering sections 324, fiber-optic gyroscopes, etc.) can be adaptively adjusted according to the shape of the first waveguide 310, which is not shown in the figure.

[0091] In practical applications, the optical device and the photonic integrated circuit provided by the present application can be realized based on basic materials such as lithium niobate (LiNbO3), and integrated in a photonic quantum computer. The photonic quantum computer is a quantum computing device that uses photons (light particles) as qubits (quantum bits) for information processing.

[0092] In the photonic quantum computer, it mainly includes a single photon source, a photonic quantum chip, and a single photon detector. The single photon source generates high-quality single photons as qubit carriers by laser excitation of quantum dots or spontaneous parametric down conversion (SPDC). The photonic quantum processor is composed of optical elements such as optical fibers, waveguides, beam splitters, phase modulators, and mirrors to realize optical transmission and logic operations (such as Hadamard gate and CNOT gate). The single photon detector can measure the final state of the photon (such as polarization or path) and output the calculation result. The specific processing process of the photonic quantum computer can be referred to the specific description of the related art, which is not described here.

[0093] In practical applications, the optical device and the photonic integrated circuit provided by the present application can involve various components of the aforementioned photonic quantum computer. That is, one or more of the single photon source, the photonic quantum chip, and the single photon detector in the photonic quantum computer includes the optical device provided by the present application.

[0094] For example, the single photon source can be modulated by the optical device to make the output light beam a single-mode light signal. The photonic quantum chip can select a specific mode by the aforementioned optical device to realize high-fidelity transmission of qubits (such as polarization-encoded photons). The single photon detector can perform phase difference detection through the photonic integrated circuit.

[0095] Therefore, the photonic quantum computer involving the aforementioned optical device is also within the protection scope of the present application.

[0096] The above disclosed embodiments of the present application are only used to help explain the present application. The embodiments do not describe all of the details of the present application, and the present application is not limited to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. An optical device, characterized in that, The optical device includes a first waveguide and a second waveguide, the first waveguide and the second waveguide being formed within a waveguide layer and spaced apart, the first waveguide being used at least for direct transmission of an optical signal in a second polarization fundamental mode, and the second waveguide including: A first polarization conversion section is set near the input end of the first waveguide; A second polarization conversion section is positioned near the output end of the first waveguide; and An isolation reset section is provided between the first polarization conversion section and the second polarization conversion section, wherein at least a portion of the isolation reset section is far from the first waveguide; The first polarization conversion section matches the effective refractive index of the intermediate target mode with the effective refractive index of the first waveguide based on the first polarization fundamental mode, so that the optical signal of the first polarization fundamental mode in the first waveguide is coupled to the first polarization conversion section through the first waveguide and converted into the intermediate target mode; the second polarization conversion section matches the effective refractive index of the intermediate target mode with the effective refractive index of the first waveguide based on the second polarization fundamental mode, so that the optical signal of the intermediate target mode in the second waveguide is coupled to the first waveguide through the second polarization conversion section and converted into the second polarization fundamental mode.

2. The optical device according to claim 1, characterized in that, Effective refractive index matching is achieved by the different waveguide widths of the first polarization conversion section, the second polarization conversion section, and the first waveguide; the isolation reset section includes: A lifting structure, wherein the lifting structure is connected to and matches the width of the first polarization conversion segment, and the distance between the end of the lifting structure away from the first polarization conversion segment and the first waveguide is greater than the distance between the first waveguide and the first polarization conversion segment; and A reset structure, wherein the reset structure is connected to the second polarization conversion segment and matches the width of the second polarization conversion segment.

3. The optical device according to claim 2, characterized in that, The lifting structure is configured as a fixed-width S-shaped upward curve based on the width of the first polarization conversion section, and the reset structure is configured as a fixed-width S-shaped downward curve based on the width of the second polarization conversion section. The isolation reset section also includes a width gradient structure connecting the lifting structure and the reset structure.

4. The optical device according to claim 2, characterized in that, The widths of the lifting structure and the reset structure vary along the direction from the first polarization conversion segment to the second polarization conversion segment, so that the width at the connection between the lifting structure and the first polarization conversion segment is the same as the width of the first polarization conversion segment, and the width at the connection between the reset structure and the second polarization conversion segment is the same as the width of the second polarization conversion segment.

5. The optical device according to claim 1, characterized in that, The second waveguide further includes a scattering section disposed at the end of the second polarization conversion section, wherein the end orientation of the scattering section is different from the extension direction of the first waveguide, so that the hybrid noise in the second waveguide is scattered based on the end orientation.

6. The optical device according to claim 5, characterized in that, The scattering region includes: An arc-shaped steering structure, wherein the arc-shaped steering structure is connected to the end of the second polarization conversion segment, and the extending direction of the second polarization conversion segment is the tangential direction at the connection point between the arc-shaped steering structure and the second polarization conversion segment; and A mode mismatch structure, wherein the mode mismatch structure is connected to the end of the arc-shaped steering structure and is used to adjust the effective refractive index of the residual beam in the second waveguide so that the residual beam is mismatched with the mode supported by the second waveguide and is scattered from the end of the mode mismatch structure.

7. The optical device according to claim 6, characterized in that, The arc-shaped steering structure is configured to be bent at 90° and the width of the arc-shaped steering structure is the same as the width of the second polarization conversion segment. The mode mismatch structure is configured to be a width-gradient structure and the width at the connection between the mode mismatch structure and the arc-shaped steering structure is the same as the width of the second polarization conversion segment.

8. The optical device according to any one of claims 1-7, characterized in that, The waveguide layer is configured as a thin-film lithium niobate material, and both the first waveguide and the second waveguide are configured as ridge waveguides; The first polarization configuration is a transverse magnetic mode, the second polarization configuration is a transverse electric mode, and the target order configuration is first order.

9. A photonic integrated circuit, characterized in that, The photonic integrated circuit includes: The optical device according to any one of claims 1 to 8; and A fiber optic gyroscope based on a transverse magnetic fundamental mode, wherein the fiber optic gyroscope is connected to the output end of the first waveguide of the optical device, the first polarization configuration of the optical device is a transverse magnetic mode, the second polarization configuration is a transverse electric mode, and the target order is configured as first order.

10. An optical quantum computer, characterized in that, The optical quantum computer includes a single-photon source, an optical quantum chip, and a single-photon detector, wherein one or more of the single-photon source, the optical quantum chip, and the single-photon detector include the optical device as described in any one of claims 1-8.

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