An optical filter, a wavelength division multiplexing device, and an optical quantum computer

Abstract

This application provides an optical filter, a wavelength division multiplexing (WDM) device, and an optical quantum computer, relating to the field of integrated optics. The optical filter provided in this application is configured based on the Mach-Zehnder interferometer principle and has two waveguides, each containing multiple phase shifters. To overcome manufacturing and temperature errors in the optical filter, the lengths of the aforementioned phase shifters are constrained so that the sum of the product of the effective refractive index fluctuations of the phase shifters on both sides under temperature changes and their lengths is equal, and the sum of the product of the effective refractive index fluctuations of the phase shifters under width changes and their lengths is also equal. This overcomes the influence of manufacturing and temperature fluctuations on the optical filter, improving its stability. Furthermore, considering the solvability of the aforementioned constraints, the aforementioned phase shifters can have at least three waveguide widths (preferably four) to ensure that the aforementioned constraints can be practically achieved.

Description

Technical Field

[0001] This application relates to integrated optical technology, specifically to an optical filter, a wavelength division multiplexing device, and an optical quantum computer. Background Technology

[0002] Optical filters are important components in the field of integrated optics (i.e., optical integrated circuits). A commonly used optical filter is the Mach-Zehnder interferometer (MZI), which primarily relies on two phase-shifting arms of unequal length to achieve filtering. That is, the light beam forms a phase difference after passing through the two phase-shifting arms, resulting in interference and thus initial filtering.

[0003] Given that the aforementioned devices are mainly based on phase-shifting arms of unequal length, how to design the phase-shifting arms and their length more reasonably in practical applications is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, embodiments of this application provide an optical filter, a wavelength division multiplexing device, and an optical quantum computer, which improve the rationality of phase shifter design by introducing temperature constraints and process constraints.

[0005] In a first aspect, this application provides an optical filter. The optical filter includes a first waveguide and a second waveguide, wherein the first waveguide and the second waveguide form a Mach-Zehnder interference structure. The first waveguide includes a first phase shifter group composed of at least one phase shifter with different widths, and the second waveguide includes a second phase shifter group composed of at least one phase shifter with different widths. Each phase shifter in the first and second phase shifter groups has at least three different waveguide widths. The sum of the products of a first fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase shifter arm length of the corresponding phase shifter is equal to the sum of the products of the first fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase shifter arm length of the corresponding phase shifter. The sum of the products of a second fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase shifter arm length of the corresponding phase shifter is equal to the sum of the products of the second fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase shifter arm length of the corresponding phase shifter. The first fluctuation factor reflects the numerical fluctuation of the effective refractive index under temperature changes, and the second fluctuation factor reflects the numerical fluctuation of the effective refractive index under changes in the waveguide width of the phase shifter.

[0006] Secondly, this application provides a wavelength division multiplexing device, which includes at least a plurality of optical filters as described in the first aspect, wherein the plurality of optical filters are cascaded based on different center wavelengths to separate different wavelength signals of the input beam.

[0007] Thirdly, this application provides an optical quantum computer, which includes 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 include an optical filter wavelength division multiplexing device as described in the first aspect.

[0008] Therefore, this application provides an optical filter, a wavelength division multiplexing device, and an optical quantum computer. The optical filter is configured based on the Mach-Zehnder interferometer principle and has two waveguides, each containing multiple phase shifters. To overcome manufacturing and temperature errors in the optical filter, the lengths of the aforementioned phase shifters are constrained so that the sum of the product of the effective refractive index fluctuations of the phase shifters on both sides under temperature changes and their lengths is equal, and the sum of the product of the effective refractive index fluctuations of the phase shifters under width changes and their lengths is also equal. This overcomes the influence of manufacturing and temperature fluctuations on the optical filter, improving its stability. Furthermore, considering the solvability of the aforementioned constraints, the aforementioned phase shifters can have at least three waveguide widths (preferably four) to ensure that the aforementioned constraints can be practically achieved. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the first structure of an optical filter provided in some embodiments of this application.

[0011] Figure 2 This is a schematic diagram of a second structure of an optical filter provided in some embodiments of this application.

[0012] Figure 3 This is a schematic diagram of a third structure of an optical filter provided in some embodiments of this application.

[0013] Figure 4 This is a schematic diagram of the fourth structure of the optical filter provided in some embodiments of this application.

[0014] Figure 5 This is a schematic diagram of the fifth structure of an optical filter provided in some embodiments of this application.

[0015] Figure 6 This is an example block diagram of a wavelength division multiplexing device provided in some embodiments of this application.

[0016] Among them, 100 is an optical filter; 110 is a first waveguide; 120 is a second waveguide; 131 is a first phase shifter; 132 is a second phase shifter; 133 is a third phase shifter; 134 is a fourth phase shifter; 140 is a width transition structure; 151 is a first phase shift arm pair; 152 is a second phase shift arm pair; 153 is a third phase shift arm pair; 154 is a fourth phase shift arm pair; 111 is a first upstream phase shifting section; 112 is a first connecting section; 113 is a first downstream phase shifting section; 121 is a second upstream phase shifting section; 122 is a second connecting section; 123 is a second downstream phase shifting section; 161 is a first upstream component of phase shifting; 162 is a first downstream component of phase shifting; 163 is a third upstream component of phase shifting; 164 is a third downstream component of phase shifting; and 600 is a wavelength division multiplexing structure. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0019] In this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0020] Application Overview:

[0021] The Mach-Zehnder Interferometer (MZI) is an optical device based on the principle of amplitude-splitting two-beam interference. Its core function is to achieve high-precision optical measurement by measuring the relative phase shift of two beams of light after they have traveled through different paths.

[0022] In practical applications, Mach-Zehnder interferometers are often used as optical filters. Specifically, after multiplexing the optical signal input, different wavelengths undergo constructive / destructive phase changes at the output port due to the difference in Δφ.

[0023] In integrated optics, the aforementioned optical filters based on the Mach-Zehnder interferometer principle are often composed of two 3dB directional couplers (beam splitters) and two waveguides. The waveguides are used to phase-adjust the internal beam, creating a phase difference between the two waveguides. 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 the wires in integrated circuits, 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.

[0024] In practical phase adjustment, the phase shifter within the waveguide component / waveguide can generally be based on the length difference between two waveguides. That is, phase adjustment is mainly achieved by using different lengths of the same wavelength. The phase adjustment formula for the aforementioned process is Δφ*λ=2π*ΔL*n. eff Where ΔL is the phase difference between the two waveguides, and λ is the wavelength. eff The effective refractive index.

[0025] However, in actual use and fabrication, the Mach-Zehnder interferometer may introduce errors, thereby compromising the designed optical constraints. Specifically, during device fabrication, the waveguide width of the actual fabricated phase-shifting arm often deviates from the design value, affecting the effective refractive index and consequently causing the filter's center wavelength to drift. During operation, significant changes in external temperature can also affect the material's refractive index, leading to further center wavelength drift in the filter.

[0026] To address the aforementioned technical problems, this application finds that they can be overcome by cascading multiple phase shifters and introducing temperature and width constraints. Specifically, the optical filter provided in this application is configured based on the Mach-Zehnder interferometer principle and has two waveguides, each containing multiple phase shifters. To overcome manufacturing and temperature errors in the optical filter, the length of the aforementioned phase shifters is constrained so that the sum of the product of the effective refractive index fluctuations of the phase shifters on both sides under temperature changes and their lengths is equal, and the sum of the product of the effective refractive index fluctuations of the phase shifters under waveguide width changes and their lengths is also equal. This overcomes the influence of manufacturing and temperature fluctuations on the optical filter, improving its stability. Furthermore, considering the solvability of the aforementioned constraints, the aforementioned phase shifters can have at least three waveguide widths (preferably four) to ensure that the aforementioned constraints can be practically achieved.

[0027] The following will combine Figures 1-4The optical filter and wavelength division multiplexing device provided in this application are described in detail.

[0028] Example optical filter:

[0029] As mentioned above, to overcome the aforementioned technical problems, this application provides an optical filter based on the Mach-Zehnder interferometer principle. Considering that this application mainly improves its phase-shifting section, the optical filter provided in this application omits other structures (such as the 3dB directional couplers at both ends), which can be adjusted according to actual needs (such as cascading multiple devices).

[0030] Figure 1 This is a schematic diagram of the structure of an optical filter provided in some embodiments of this application.

[0031] like Figure 1 As shown, the optical filter 100 provided in this application mainly includes a first waveguide 110 and a second waveguide 120. In this application, phase adjustment is not achieved directly using the length difference between the first waveguide 110 and the second waveguide 120, but rather by constructing multiple phase shifters within the first waveguide 110 and the second waveguide 120. That is, the first waveguide 110 includes a first phase shifter group, and the second waveguide 120 includes a second phase shifter group.

[0032] The first phase shifter group can refer to the collection of phase shifters within the first waveguide 110. The second phase shifter group can refer to the collection of phase shifters within the second waveguide 120. Within each phase shifter group, the phase shifter can refer to waveguide structures with different waveguide widths and therefore different effective refractive indices, while waveguide structures with the same waveguide width can be considered as a single phase shifter.

[0033] Based on the principle of phase shifting within a Mach-Zehnder interferometer, the basic requirements for any phase shifter i in the first phase shifter group and any phase shifter j in the second phase shifter group are as follows:

[0034] as well as .

[0035] Where w is the waveguide width of the corresponding phase shifter, L is the pure phase shifting arm length of the corresponding phase shifter, and n eff n is the effective refractive index of the waveguide corresponding to the phase shifter. g Here, λ is the group refractive index of the waveguide corresponding to the phase shifter, λ is the center wavelength, and FSR is the free spectral range of the Herzödel interference structure. Furthermore, the aforementioned m is actually Δφ / 2π, and can be any even number, typically a three-digit value.

[0036] Considering that the aforementioned temperature mainly affects the aforementioned equation, it is reflected in the effect of n effThe influence of temperature is λ. Combining this with the aforementioned difference relationship, to eliminate the influence of temperature, the effects caused by temperature can be controlled to cancel each other out. That is, the temperature influence of the first phase shifter group in the first waveguide 110 is the same as the temperature influence of the second phase shifter group in the second waveguide 120.

[0037] Considering that in a phase shifter, phase delay is represented as the product of the effective refractive index and the corresponding pure phase shift arm length, and taking into account the aforementioned multiple phase shifters and the influence of temperature changes on the effective refractive index, the aforementioned "temperature-induced effects cancel each other out" can be specifically characterized as the sum of the products of the first fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase shift arm length of the corresponding phase shifter equal to the sum of the products of the first fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase shift arm length of the corresponding phase shifter. Here, the first fluctuation factor reflects the numerical fluctuation of the effective refractive index under temperature changes.

[0038] Considering that the first waveguide 110 and the second waveguide 120 are configured as a single optical device, the temperature changes of the two waveguides are the same. The aforementioned first wave factor can reflect Δn under ΔT. eff .

[0039] Considering the approximately linear relationship between temperature and effective refractive index, the aforementioned effects can be characterized by the following equation:

[0040] Where T is temperature. Furthermore, considering that the effective refractive index is generally dimensionless, this formula can be understood as a pure numerical calculation when both sides have uniform units (mainly uniform length units).

[0041] Similar to the aforementioned effect of temperature, the fabrication process generally affects the waveguide width of the structure, thus affecting the effective refractive index. Therefore, adjustments can be made based on a similar principle to that of temperature. Specifically, the sum of the products of the second fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase-shifting arm length of the corresponding phase shifter is equal to the sum of the products of the second fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase-shifting arm length of the corresponding phase shifter. Here, the second fluctuation factor reflects the numerical fluctuation of the effective refractive index under changes in the waveguide width of the phase shifter.

[0042] The fluctuations in waveguide width caused by the fabrication process are generally small and can be considered as derivatives at the corresponding width. Similar to the logic of the aforementioned equation, the waveguides affected by the fabrication process can have the same effect in both the first waveguide 110 and the second waveguide 120, thus canceling each other out, and can be represented by the following equation:

[0043] Similar to the formula mentioned above, this formula can also be understood as a purely numerical calculation.

[0044] Considering that the relationship between waveguide width and effective refractive index is often nonlinear, the aforementioned differential of effective refractive index based on width can generally be understood as the derivative at the corresponding width.

[0045] Both of the aforementioned differential results can be determined through testing. During testing, this can be determined based on the change in effective refractive index at temperature for waveguides of different widths. And for... It can be determined based on the effective refractive index variation (i.e., the derivative at the corresponding point) under different waveguide widths.

[0046] Preferably, to further avoid changes in the aforementioned effects caused by variations in the waveguide width, a waveguide width with an effective refractive index that is approximately linear at that width can be selected. This approximate linearity can be determined by the second derivative threshold condition of the effective refractive index based on the width, or by the trend of change in the curve.

[0047] Therefore, based on the aforementioned requirements, for any phase shifter i in the first phase shifter group and any phase shifter j in the second phase shifter group, the following requirements are satisfied as a whole:

[0048] .

[0049] Considering the arbitrary choice of m mentioned above, when the phase shifter has three different waveguide widths (i.e., a total of three L variables), the L in the aforementioned equation may have a solution. When there are four or more waveguide widths, the L in the equation must have a solution.

[0050] Therefore, each phase shifter in the first phase shifter group and the second phase shifter group has at least three different widths.

[0051] As an example only, Figure 1 In the first waveguide 110, the first phase shifter group may include a first phase shifter 131 and a second phase shifter 132. The waveguide width of the first phase shifter 131 is w1, and its length is L1. The waveguide width of the second phase shifter 132 is w2, and its length is L2. The second phase shifter group of the second waveguide 120 may include a third phase shifter 133 and a fourth phase shifter 134. The waveguide width of the third phase shifter 133 is w3, and its length is L3. The waveguide width of the fourth phase shifter 134 is w4, and its length is L4. Furthermore, the width of the main body structure of the aforementioned first waveguide 110 and second waveguide 120 is w0.

[0052] Therefore, the lengths of the aforementioned phase shifters should satisfy the following equation:

[0053] .

[0054] In the aforementioned formula, the waveguide width is generally selected in advance, so that each differential result can be predetermined. λ and FSR are determined according to the optical requirements of the device. m is generally arbitrarily chosen as an even number (generally >100).

[0055] In practical configurations, phase shifters are often distributed across different waveguides based on their waveguide width. That is, one waveguide may contain only phase shifters with larger waveguide widths, while another waveguide may contain phase shifters with smaller waveguide widths. In actual setups, the wider phase shifters are generally the actual phase shifters used to process the beam, while the narrower phase shifters are generally compensations for the wider ones.

[0056] Therefore, the optical filter provided in this application is configured based on the Mach-Zehnder interferometer principle and has two waveguides, each containing multiple phase shifters. To overcome manufacturing and temperature errors in the optical filter, the lengths of the aforementioned phase shifters are constrained so that the effective refractive indices of the phase shifters on both sides are equal to the sum of the product of the differential of the temperature and the length, and the effective refractive index of the phase shifters is equal to the sum of the product of the differential of the width and the length. This overcomes the influence of manufacturing errors and temperature fluctuations on the optical filter, improving its stability. Furthermore, considering the solvability of the aforementioned constraints, the aforementioned phase shifters can have at least three waveguide widths (preferably four) to ensure that the aforementioned constraints can be practically achieved.

[0057] Furthermore, considering the different waveguide widths of the phase shifters, in order to effectively connect the various phase shifters in the waveguide and avoid the impact of abrupt changes in waveguide width on the phase, the optical filter is also provided with multiple width transition structures 140 on the first waveguide 110 and the second waveguide 120. The width transition structures 140 can be set between segments with different waveguide widths, and the two structures with different widths are matched by the gradual change in width of the width transition structure 140 itself.

[0058] Specifically, to achieve a waveguide width transition, the two ends of the width transition structure 140 present interfaces with different waveguide widths, the waveguide width of which is consistent with the waveguide structure it connects to. The width transition structure 140 exhibits a gradually changing waveguide width between the two interfaces to match the different waveguide widths at both ends. The waveguide width of the width transition structure 140 between the two interfaces is a monotonic transformation based on the waveguide widths of the two interfaces. In the figure, this is presented as a linear change, resulting in a straight-line appearance; in other cases, it can also be a non-linear change, resulting in a curved appearance.

[0059] For example, in the first waveguide 110, the aforementioned width transition structure 140 is provided between the first waveguide 110 body and the first phase shifter 131, between the first phase shifter 131 and the second phase shifter 132, and between the second phase shifter 132 and the first waveguide 110 body. In the second waveguide 120, the aforementioned width transition structure 140 is provided between the second waveguide 120 body and the third phase shifter 133, between the third phase shifter 133 and the fourth phase shifter 134, and between the fourth phase shifter 134 and the second waveguide 120 body.

[0060] It should be noted that the aforementioned arrangement may be adjusted according to actual needs. For example, in the first waveguide 110, a branch body of w0 can also be set between the first phase shifter 131 and the second phase shifter 132, and a corresponding width transition structure can be set.

[0061] In some embodiments, the material and fabrication method of the width transition structure 140 are generally the same as those of other structures within the waveguide. In optical integration, the waveguide and its internal phase shifters and width transition structures are generally etched based on substrate materials such as lithium niobate (LiNbO3).

[0062] In some embodiments, the width transition structure 140 itself may also have a certain influence. To eliminate this influence, the two waveguides should have the same width transition and the same arrangement to offset the influence of the width transition structure 140. That is, the number, type, and arrangement order of each width transition structure in the width transition structure group formed by the width transition structure in the first waveguide 110 and the width transition structure group formed by the width transition structure in the second waveguide 120 are the same.

[0063] To further illustrate this point, this application provides another schematic diagram of an optical filter structure ( Figure 2 ).

[0064] like Figure 2 As shown, within the first waveguide 110, except Figure 1 In addition to the width transition structure 140 shown, the system also includes width transition structures 140 disposed between the second waveguide 120 body and the third phase shifter 133 (w0→w3), between the third phase shifter 133 and the fourth phase shifter 134 (w3→w4), and between the fourth phase shifter 134 and the second waveguide 120 body (w4→w0), and these width transition structures 140 are disposed after the aforementioned second phase shifter 132. Similarly, width transition structures 140 are also disposed between the first waveguide 110 body and the first phase shifter 131 (w0→w1), between the first phase shifter 131 and the second phase shifter 132 (w1→w2), and between the second phase shifter 132 and the first waveguide 110 body (w2→w0) before the third phase shifter 133 on the second waveguide 120.

[0065] Therefore, when the phase shifters in the two waveguides have different widths, the width transition structure can be set in the same way, thereby canceling out the influence of the width transition structure on the beam through the two waveguides.

[0066] Furthermore, considering that the width transition structure 140 is often used to offset width changes, the actual installation order of the width filtering devices installed in areas where there are no width changes is not required. For example, the width transition structure 140 installed in the first waveguide 110 corresponding to the second waveguide 120 can be arbitrarily placed in a suitable area.

[0067] In some embodiments, the aforementioned phase shifters can be formed based on a conventional Mach-Zehnder interference structure, i.e., corresponding phase shifting arms exist on both waveguides, and a phase shifter is formed based on the difference in their arm lengths. That is, the optical filter 100 includes multiple pairs of phase shifting arms with different widths. Two phase shifting arms in a pair are respectively disposed in the first waveguide 110 and the second waveguide 120 with the same waveguide width and different waveguide degrees, and are configured as phase shifters in the target waveguide.

[0068] The target waveguide is the phase-shifting arm pair with the longer phase-shifting arm length between the first and second waveguides, and the pure phase-shifting arm length of the phase shifter is the difference in length between the corresponding phase-shifting arm pairs in the two waveguides.

[0069] To further illustrate the foregoing, this application is based on Figure 1 The phase shifter structure provides a schematic diagram of an optical filter containing a pair of phase shifting arms. Figure 3 ).

[0070] like Figure 3 As shown, based on the aforementioned four phase shifters, the aforementioned optical filter 100 may include a first phase shifter pair 151, a second phase shifter pair 152, a third phase shifter pair 153, and a fourth phase shifter pair 154. Specifically, the first phase shifter pair 151 corresponds to the first phase shifter 131, the second phase shifter pair 152 corresponds to the second phase shifter 132, the third phase shifter pair 153 corresponds to the third phase shifter 133, and the fourth phase shifter pair 154 corresponds to the fourth phase shifter 134.

[0071] Based on the aforementioned correspondence, that is, the waveguide length L of the first phase shifting arm pair 151 in the first waveguide 110 is the first phase shifting arm first waveguide component. 1.1 The waveguide length L of the first phase shifter pair 151 in the second waveguide 120 is greater than the first phase shifter pair 151 in the second waveguide 120. 1.2 The first waveguide 110 is configured as the first phase-shifting arm to the target waveguide 151 and forms a phase shifter on the first waveguide 110, with waveguide length L1 = L 1.1 -L 1.2Other phase-shifting arms are similar and will not be described in detail here.

[0072] Correspondingly, the aforementioned width transition structure 140 can be set at both ends of the phase shift arm in each phase shift arm pair, without the need to set an additional width transition structure on the waveguide.

[0073] The phase shifter based on the aforementioned configuration allows the width transition structure to be set based on the actual waveguide width, avoiding errors in the width and length aspects of the width transition structure. For example, an additional width transition structure may create a certain width at the junction, affecting the pure phase shift arm length of the phase shifter on the other side. For instance, within the first waveguide 110, the width transition structure 140 from w0 to w3 and the transition structure 140 from w3 to w4 may form a structure with a width of w3 and a length of l at the junction, thereby reducing the pure phase shift arm length L3-l of the third phase shifter 133 within the second waveguide 120.

[0074] Furthermore, to improve the stability of the device, the phase-shifting arms in the multiple phase-shifting arm pairs in the first waveguide 110 and the second waveguide 120 are arranged in the same order, and the shorter lengths of the phase-shifting arms are the same. That is, in the aforementioned... Figure 4 In the diagram, the phase-shifting arms of each waveguide are ordered as first, second, third, and fourth. The waveguide length L of the second waveguide component of the aforementioned first phase-shifting arm... 1.2 = Waveguide length L of the second waveguide component of the second phase shifter arm 2.2 = Waveguide length L of the first waveguide component of the third phase-shifting arm 3.1 = Waveguide length L of the first waveguide component of the fourth phase-shifting arm 4.1 =L ref (Generally denoted as the reference length). The length of each phase-shifting arm pair within the target waveguide can then be directly set based on the pure phase-shifting arm length, reducing computational complexity.

[0075] In practical integrated photonic circuits, considering that the aforementioned optical filters mainly adjust phase based on length, they may occupy a large amount of space and affect the integration of other structures. In actual fabrication, the waveguides of the aforementioned optical filters can often be bent, thereby adjusting their length in the direction perpendicular to the extension direction, thus reducing the space occupied by the optical filters.

[0076] In practical structures, the waveguide of an optical filter often has a concave bend. This application can integrate the phase shifter into the bend so that the length adjustment of the phase shifter does not affect the space occupied by the optical filter in the extension direction.

[0077] Furthermore, to achieve a symmetrical arrangement of the two bent segments, the aforementioned phase shifter can be split into phase shifting structures of equal length and symmetrically arranged within the corresponding segments. This phase shifter can be combined with the aforementioned phase shifting arm pair so that the actual allocated length corresponds to the length of the phase shifting arm in the waveguide component (e.g., L1+Lref).

[0078] To illustrate this point, this application also provides a schematic diagram of the structure of an optical filter involving bending. Figure 4 ).

[0079] like Figure 4 As shown, each waveguide may include an upstream phase-shifting section, a connecting section, and a downstream phase-shifting section. The upstream and downstream phase-shifting sections refer to the regions on either side of the bend along the beam propagation direction within the corresponding waveguide. Specifically, the upstream phase-shifting region refers to the waveguide structure before the beam reaches the bend after entering the waveguide structure. The upstream phase-shifting region also refers to the waveguide structure after the beam passes the bend. The connecting section connects the upstream and downstream phase-shifting sections at both ends and generally refers to the bend within the waveguide. The upstream and downstream phase-shifting sections (within tolerances) are perpendicular to the waveguide's extension direction. Furthermore, considering connections to other devices or within devices, the waveguide may also include a reset section to restore the end direction to the waveguide's own extension direction.

[0080] like Figure 4 As shown, the first waveguide 110 may include a first upstream phase-shifting section 111, a first connecting section 112, and a first downstream phase-shifting section 113. The second waveguide 120 may include a second upstream phase-shifting section 121, a second connecting section 122, and a second downstream phase-shifting section 123.

[0081] Each pair of phase-shifting structures within the waveguide can be symmetrically arranged within two phase-shifting sections. That is, at least one pair of phase-shifting structures is symmetrically arranged within the upstream and downstream phase-shifting sections based on the connecting section. Each pair of phase-shifting structures includes two phase-shifting structures of equal length and width respectively arranged in the upstream and downstream phase-shifting sections.

[0082] Based on the principle of Mach-Zehnder interference structures, a phase-shifting structure pair corresponds to a phase shifter, and the total length of the phase-shifting structures in the pair matches the pure phase-shifting arm length of the corresponding phase shifter. When the aforementioned phase-shifting arm pair is not involved, the total length of the phase-shifting structure pair is the pure phase-shifting arm length of the corresponding phase shifter. When a phase-shifting arm pair is involved, the total length of the phase-shifting structure pair is the waveguide branch length of the corresponding phase-shifting arm of the phase shifter, and the pure phase-shifting arm length needs to be determined by subtracting it from the waveguide branch length of the phase-shifting arm in another waveguide (see the above description for details).

[0083] To simplify the complexity, only the first phase shifter 131 is set in the first waveguide 110 and only the third phase shifter 133 is set in the second waveguide 120. No corresponding phase shifter arms are set in other waveguides. Other phase shifters can also be set up in a similar way.

[0084] Based on the aforementioned configuration requirements, the first phase shifter 131 can correspond to the first phase shifting structure pair. The first upstream phase shifting component 161 of the first phase shifting structure pair is located in the first upstream phase shifting section 111, and the first downstream phase shifting component 162 is located in the first downstream phase shifting section 113. The third phase shifter 133 can correspond to the third phase shifting structure pair. The third upstream phase shifting component 163 of the third phase shifting structure pair is located in the second upstream phase shifting section 121, and the third downstream phase shifting component 164 is located in the second downstream phase shifting section 123.

[0085] Considering the case where no phase shift arm pair is set, the length of the first phase downstream component 162 is equal to the length of the first phase upstream component 161, which is 0.5 * the pure phase shift arm length L1 of the first phase shifter 131. The length of the third phase downstream component 164 is equal to the length of the third phase upstream component 163, which is 0.5 * the pure phase shift arm length L3 of the third phase shifter 133.

[0086] In some embodiments, considering that the waveguide branch bodies of the first and second waveguides also have a certain width and are of the same width, they can actually constitute a phase shifter. That is, the branch body structure of the first waveguide has a different length than the branch body structure of the second waveguide, so that the branch body structure forms a phase shifter based on the length difference in the longer waveguide. Here, the waveguide branch body can refer to the main structure of the waveguide. That is, the structure when no other waveguide structure (such as the aforementioned phase shifter) is provided (such as the aforementioned connection section).

[0087] Based on the aforementioned length differences of the waveguide branch body, this is generally reflected in the length differences of the connecting sections. For example, the aforementioned Figure 4 In the case where the length of the first connecting section 112 is greater than the length of the second connecting section 122, the length difference can be used to construct a phase shifter based on a similar principle to the aforementioned phase shifter arm pair.

[0088] Furthermore, in actual structures, the bending dimensions of the bending regions of the two waveguides are generally the same, and the aforementioned length difference of the connecting section is actually reflected (or understood as) the length difference of the connecting section entering the phase-shifting section.

[0089] thus, Figure 4 The optical filter shown may also serve as an optical filter that satisfies the aforementioned optical constraints in practical applications.

[0090] The various embodiments provided in this application can be combined. Based on this, this application also provides a schematic diagram of an optical filter that includes both phase-shifting arm pairs and phase-shifting structure pairs. Figure 5 ).

[0091] like Figure 5 As shown, both the upper and lower waveguides of the optical filter are equipped with four different waveguide widths of phase-shifting structure pairs. Phase-shifting structure pairs with the same waveguide width in different waveguides can be equivalent to a single phase-shifting arm. It should be noted that the lengths marked in the figure represent the total length of the phase-shifting structure pair.

[0092] Furthermore, the width w0 of the two waveguides is the same as their length, thus not forming an additional phase shifter.

[0093] Exemplary wavelength division multiplexing devices and optical quantum computers:

[0094] Based on the aforementioned optical filters, wavelength division multiplexing (WDM) structures in integrated photonic circuits can be constructed. Specifically, this application also provides an exemplary block diagram of a WDM structure ( Figure 6 ).

[0095] like Figure 6 As shown, the wavelength division multiplexing (WDM) structure 600 can be composed of multiple optical filters 100 (three are shown in the figure), and the optical filters 100 can separate different wavelength components of the light beam by configuring parameters. For specific configuration procedures, please refer to the relevant descriptions of wavelength division multiplexing structures based on Mach-Zehnder interferometers, which will not be repeated here.

[0096] Based on the same principle, this application also provides an optical device, which may include the optical filter provided in any embodiment of this application or the wavelength division multiplexing structure provided in this application.

[0097] In practical applications, the optical filters and wavelength division multiplexing structures provided in this application can be realized based on basic materials such as lithium niobate (LiNbO3) and integrated into optical quantum computers. An optical quantum computer is a quantum computing device that uses photons (light particles) as qubits for information processing.

[0098] A quantum computer primarily consists of a single-photon source, a quantum chip, and a detection system. The single-photon source generates high-quality single photons, which serve as the carriers of qubits, through laser excitation of quantum dots or spontaneous parametric down-conversion (SPDC). The quantum processor is composed of optical components such as optical fibers, waveguides, beam splitters, phase modulators, and mirrors to achieve optical transmission and logical operations (e.g., Hadamard gates, CNOT gates). The detection system measures the final state of the photons (e.g., polarization or path) and outputs the calculation results. For detailed descriptions of the specific processing procedures of a quantum computer, please refer to the relevant technical descriptions; they will not be elaborated upon here.

[0099] In practical applications, the optical filter and wavelength division multiplexing structure provided in this application can be used in various components of the aforementioned optical quantum computer. That is, one or more of the single-photon source, optical quantum chip, and single-photon detector in the optical quantum computer include the optical filter provided in this application.

[0100] For example, single-photon sources can be used to verify quantum randomness and manipulate single-photon quantum states through optical filters. Optical quantum chips can achieve programmable optical paths using the aforementioned optical filters (i.e., interferometers), beam splitters, and phase modulators. Single-photon detectors can infer the phase value of the source result by adding a phase delay to the optical filter.

[0101] Therefore, optical quantum computers involving the aforementioned optical filters or wavelength division multiplexing devices are also within the scope of protection of this application.

[0102] The embodiments of the present invention disclosed above are merely illustrative of the invention. The embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An optical filter, characterized in that, It includes a first waveguide and a second waveguide, wherein the first waveguide and the second waveguide form a Mach-Zehnder interference structure; The first waveguide includes a first phase shifter group, and the second waveguide includes a second phase shifter group, wherein each phase shifter in the first phase shifter group and the second phase shifter group has at least three different waveguide widths; The sum of the products of the first fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase shift arm length of the corresponding phase shifter is equal to the sum of the products of the first fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase shift arm length of the corresponding phase shifter; the sum of the products of the second fluctuation factor of the effective refractive index of each phase shifter in the first phase shifter group and the pure phase shift arm length of the corresponding phase shifter is equal to the sum of the products of the second fluctuation factor of the effective refractive index of each phase shifter in the second phase shifter group and the pure phase shift arm length of the corresponding phase shifter, wherein the first fluctuation factor reflects the numerical fluctuation of the effective refractive index under temperature change, and the second fluctuation factor reflects the numerical fluctuation of the effective refractive index under waveguide width change of the phase shifter.

2. The optical filter according to claim 1, characterized in that, For any phase shifter i in the first phase shifter group and any phase shifter j in the second phase shifter group, the following requirements must be met: ； Where w is the waveguide width of the corresponding phase shifter, L is the pure phase shifting arm length of the corresponding phase shifter, and n eff n is the effective refractive index of the waveguide corresponding to the phase shifter. g λ is the group refractive index of the waveguide corresponding to the phase shifter, λ is the center wavelength, m is any even number, FSR is the free spectral range of the Herzundell interference structure, and T is the temperature.

3. The optical filter according to claim 1, characterized in that, The waveguide includes an upstream phase-shifting section, a connecting section, and a downstream phase-shifting section, wherein the two ends of the connecting section are respectively connected to the upstream phase-shifting section and the downstream phase-shifting section; At least one pair of phase shifting structures is symmetrically arranged in the upstream phase shifting section and the downstream phase shifting section based on the connecting section. Each pair of phase shifting structures includes two phase shifting structures of equal length and width respectively arranged in the upstream phase shifting section and the downstream phase shifting section. Each pair of phase shifting structures corresponds to a phase shifter, and the total length of the phase shifting structures in the pair matches the pure phase shifting arm length of the corresponding phase shifter.

4. The optical filter according to claim 1, characterized in that, The first waveguide and the second waveguide also include multiple width transition structures, which are disposed at least between segments where the waveguide width changes.

5. The optical filter according to claim 4, characterized in that, The number, type, and arrangement order of the width transition structures in the first waveguide width transition structure group and the second waveguide width transition structure group are the same.

6. The optical filter according to claim 1, characterized in that, The optical filter includes multiple pairs of phase-shifting arms with different widths. Two phase-shifting arms in each pair are respectively disposed in the first waveguide and the second waveguide with the same waveguide width and different waveguide degrees, and are configured as phase shifters in the target waveguide. Wherein, the target waveguide is the one with the longer phase shift arm length in the first waveguide and the second waveguide of the phase shifter pair, and the pure phase shift arm length of the phase shifter is the difference in length between the corresponding phase shift arm pairs in the two waveguides.

7. The optical filter according to claim 6, characterized in that, The phase shifting arms in the plurality of phase shifting arm pairs in the first waveguide and the second waveguide are arranged in the same order, and the shorter length of each phase shifting arm in the plurality of phase shifting arms is the same.

8. The optical filter according to claim 1, characterized in that, Both the first waveguide and the second waveguide include branch body structures of the same width. The branch body structures of the first waveguide and the second waveguide have different lengths, so that the branch body structures form a phase shifter based on the length difference in the longer waveguide.

9. A wavelength division multiplexing device, characterized in that, The wavelength division multiplexing device includes at least a plurality of optical filters according to any one of claims 1 to 8, wherein the plurality of optical filters are cascaded based on different center wavelengths to separate different wavelength signals of the input beam.

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 an optical filter as described in any one of claims 1-8.

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