Polarization management device, polarization management method, and method for manufacturing polarization management device

Abstract

The application discloses a polarization management device, a polarization management method and a preparation method of the polarization management device, and belongs to the technical field of integrated photonics and optical communication. The application is characterized in that a ferroelectric thin film waveguide layer is arranged, the ferroelectric thin film waveguide layer comprises a first port, a second port and a third port; the first port is a signal input port and is used for inputting incident light; the incident light comprises a first polarization mode and / or a second polarization mode; the second port is a signal output port; and the third port is selectively used as a polarization state monitoring port or a signal output port. By using the high refractive index enhanced mode restriction capability of the ferroelectric thin film material and combining the intrinsic optical anisotropy, the differential transmission of the first polarization mode and the second polarization mode is realized, meanwhile, by using the refractive index adjustability of the ferroelectric thin film material, the third port can be selectively switched between the polarization state monitoring port and the signal output port, and the efficient polarization beam splitting management and the integration of various polarization management functions are realized in the same device.

Description

Technical Field

[0001] This application relates to the fields of integrated photonics and optical communication technology, and in particular to a polarization management device, a polarization management method, and a method for fabricating the polarization management device. Background Technology

[0002] With the rapid development of optical communication, data center interconnection, and integrated optics technologies, achieving efficient, compact, and multifunctional polarization management on photonic chips has become a critical technical challenge that urgently needs to be addressed. Existing polarization beam splitters (PBS) mainly face the following technical difficulties: (1) Limited polarization extinction ratio. Due to the low refractive index of the material (n≈1.97), the existing silicon-based platform has limited mode confinement capability. The polarization extinction ratio (PER) of the TE mode is usually only about 23dB, which is difficult to meet the high signal-to-noise ratio requirements of high-speed optical communication systems.

[0003] (2) Single function and lack of integrated polarization management capability. The existing PBS only realizes the polarization beam splitting function, and the TM mode is still output from a certain port. If it is necessary to filter out TM crosstalk or suppress polarization noise, an additional polarization filter must be cascaded, which increases the system complexity and insertion loss.

[0004] (3) Lack of real-time polarization state monitoring function. The existing PBS cannot provide real-time information on the purity of the input polarization state. The system needs to rely on external polarization monitoring equipment, which increases cost and size.

[0005] (4) Lack of dynamic reconfigurability. The existing passive PBS has a fixed beam splitting ratio and output port status, which cannot be dynamically adjusted according to system requirements, thus limiting its application in reconfigurable optical networks.

[0006] Therefore, how to simultaneously achieve efficient polarization beam splitting management and the integration of multiple polarization management functions in a single device is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of this application is to provide a polarization management device, a polarization management method, and a method for fabricating a polarization management device, thereby achieving efficient polarization beam splitting management and integration of multiple polarization management functions in a single device.

[0008] To achieve the above objectives, this application provides a polarization management device, comprising: Substrate; A buried oxide layer is disposed on the surface of the substrate; A ferroelectric thin-film waveguide layer is disposed on the surface of the buried oxide layer; the ferroelectric thin-film waveguide layer includes a first port, a second port, and a third port; The first port is a signal input port for inputting incident light; the incident light includes a first polarization mode and / or a second polarization mode. The second port is a signal output port; The third port is selectively used as either a polarization state monitoring port or a signal output port; the polarization state monitoring port is used to monitor the polarization state of the incident light. The first polarization mode is output from the second port and / or the third port; the transmission loss of the second polarization mode in the ferroelectric thin film waveguide layer is greater than the transmission loss of the first polarization mode in the ferroelectric thin film waveguide layer. The upper cladding layer is disposed on the surface of the ferroelectric thin film waveguide layer.

[0009] Optionally, the ferroelectric thin-film waveguide layer includes a cascaded first asymmetric directional coupler and a second asymmetric directional coupler; The first asymmetric directional coupler includes a first waveguide and a second waveguide; both the first waveguide and the second waveguide are disposed on the surface of the buried oxide layer, and the first waveguide and the second waveguide are spaced apart along a first direction; The second asymmetric directional coupler includes a second waveguide and a third waveguide; the third waveguide is disposed on the surface of the buried oxide layer, and the second waveguide and the third waveguide are spaced apart along the first direction; The input end of the first waveguide is the first port, and the output end of the first waveguide is the second port; The output of the third waveguide is the third port.

[0010] Optionally, the width of the first waveguide is 0.5μm-1.0μm, including the values ​​at both ends; The width of the second waveguide is 1.5μm-2.5μm, including the values ​​at both ends; The width of the third waveguide is equal to the width of the first waveguide; The gap width between the first waveguide and the second waveguide is 500nm-800nm, including the values ​​at both ends; The gap width between the third waveguide and the second waveguide is equal to the gap width between the first waveguide and the second waveguide.

[0011] Optionally, the polarization management device further includes: An electrical signal control component is used to control the electrical signal applied to the ferroelectric thin-film waveguide layer, so that the third port can be selectively used as the polarization state monitoring port or the signal output port.

[0012] To achieve the above objectives, this application also provides a polarization management method applied to the aforementioned polarization management device, comprising: The third port can be selectively used as either the polarization state monitoring port or the signal output port; The incident light is input into the first port; When the third port is used as the polarization state monitoring port, the first polarization mode is output from the second port, and the polarization state of the incident light is monitored through the third port; When the third port is used as the signal output port, the first polarization mode is output from the second port and / or the third port.

[0013] Optionally, monitoring the polarization state of the incident light through the third port includes: The change in the polarization state of the incident light is monitored by monitoring the change in the output power of the third port.

[0014] Optionally, the polarization management device includes the electrical signal control component; The step of selectively using the third port as either the polarization state monitoring port or the signal output port includes: By controlling the electrical signal applied to the ferroelectric thin-film waveguide layer, the third port can be selectively used as either the polarization state monitoring port or the signal output port.

[0015] Optionally, the step of selectively using the third port as either the polarization state monitoring port or the signal output port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer includes: By controlling the electrical signal applied to the ferroelectric thin-film waveguide layer to be zero, the third port is made into the polarization state monitoring port.

[0016] Optionally, the step of selectively using the third port as either the polarization state monitoring port or the signal output port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer includes: By applying the electrical signal to the ferroelectric thin-film waveguide layer, the third port is made into the signal output port.

[0017] To achieve the above objectives, this application also provides a method for fabricating a polarization management device, comprising: Provide substrate; A buried oxide layer is formed on the surface of the substrate; A ferroelectric thin-film waveguide layer is formed on the surface of the buried oxide layer. The ferroelectric thin-film waveguide layer includes a first port, a second port, and a third port. The first port is a signal input port for inputting incident light. The incident light includes a first polarization mode and / or a second polarization mode. The second port is a signal output port. The third port is selectively used as a polarization state monitoring port or the signal output port. The polarization state monitoring port is used to monitor the polarization state of the incident light. The first polarization mode is output from the second port and / or the third port. The transmission loss of the second polarization mode in the ferroelectric thin-film waveguide layer is greater than the transmission loss of the first polarization mode in the ferroelectric thin-film waveguide layer. An upper cladding layer is formed on the surface of the ferroelectric thin-film waveguide layer to obtain the polarization management device.

[0018] Optionally, a ferroelectric thin-film waveguide layer is formed on the surface of the buried oxide layer, comprising: A ferroelectric thin film is deposited on the surface of the buried oxide layer; The ferroelectric thin film is subjected to polarization treatment; The polarized ferroelectric thin film is patterned to form the ferroelectric thin film waveguide layer.

[0019] Optionally, after forming the upper cladding layer on the surface of the ferroelectric thin-film waveguide layer, the method further includes: An electrical signal control component is prepared; the electrical signal control component is used to control the electrical signal applied to the ferroelectric thin film waveguide layer, so that the third port can be selectively used as the polarization state monitoring port or the signal output port.

[0020] Obviously, the polarization management device provided in this application, by setting a ferroelectric thin-film waveguide layer, utilizes the high refractive index of the ferroelectric thin-film material to enhance mode confinement capabilities, and combines this with its intrinsic optical anisotropy to achieve differentiated transmission of the first polarization mode and the second polarization mode. Simultaneously, the adjustable refractive index of the ferroelectric thin-film material allows the third port to selectively switch between a polarization state monitoring port and a signal output port. Thus, multiple polarization management functions are integrated into a single device, including efficient polarization beam splitting, intrinsic polarization mode blocking, real-time polarization state monitoring, and dynamically adjustable output state. Compared with existing technologies, it has the following advantages: (1) The polarization extinction ratio is significantly improved. By replacing the traditional silicon-based material with a ferroelectric thin film waveguide layer, the high refractive index of the ferroelectric thin film material enhances the mode confinement capability, thereby significantly improving the extinction ratio of the first polarization mode and thus significantly improving the device performance.

[0021] (2) Integration of polarization beam splitting and built-in filtering functions. By utilizing the intrinsic optical anisotropy of ferroelectric thin film materials, the first polarization mode is efficiently output while the second polarization mode is intrinsically suppressed due to its greater transmission loss. Crosstalk and polarization noise of the second polarization mode can be filtered out without the need for an additional polarization filter. The two functions of polarization beam splitting and polarization filtering are integrated in the same device, avoiding the increase in size, insertion loss and system complexity caused by cascading additional devices.

[0022] (3) It has a real-time polarization state monitoring function. The third port is configured as a polarization state monitoring port. By using this port to monitor the polarization state of the incident light, the change of polarization state can be sensed in real time on the same device. On-chip self-testing can be achieved without external polarization monitoring equipment, which reduces the system cost and size.

[0023] (4) The output state is dynamically adjustable. By utilizing the adjustable refractive index of the ferroelectric thin film material, the third port can be switched between the polarization state monitoring port and the signal output port, realizing the dynamic activation of the dormant port and the reconfiguration of the device function. Existing passive polarization beam splitters do not have this reconfigurable capability.

[0024] (5) High functional integration and compact device structure. Applying ferroelectric thin film materials to waveguide integrated devices realizes the leap of ferroelectric materials from free-space optical devices to waveguide integrated devices, opening up new avenues for the application of ferroelectric thin film materials in photonic integrated circuits.

[0025] This application also provides a polarization management method applied to the aforementioned polarization management device, which can achieve high-performance polarization management. It integrates multiple functions such as polarization state monitoring, dynamic control of output path, and natural processing of second polarization mode in the same method flow, and can achieve integrated processing of polarization beam splitting, filtering and monitoring without additional operation.

[0026] This application also provides a method for fabricating a polarization management device, which can produce the above-mentioned polarization management device and has the advantages of simple process and compatibility with CMOS process, making it suitable for mass production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 A top view of a polarization management device in the XY direction provided in an embodiment of this application; Figure 2A cross-sectional view of a polarization management device in the YZ direction provided in an embodiment of this application; Figure 3 A flowchart illustrating a polarization management method provided in an embodiment of this application; Figure 4 A flowchart illustrating a method for fabricating a polarization management device as provided in this application embodiment; Figure 5 The transmission spectrum of a polarization management device provided in this application under C-band and TE mode incident light; Figure 6 The PER curve of a polarization management device under C-band and TE mode incident light is provided in the embodiments of this application. Figure 7 A normalized electric field intensity distribution of a polarization management device under C-band and TE-mode incident light, provided in an embodiment of this application; Figure 8 The transmission spectrum of a polarization management device under C-band, TM mode incident light provided in this application embodiment; Figure 9 A normalized electric field intensity distribution of a polarization management device under C-band, TM mode incident light, provided in an embodiment of this application; Figure 10 The transmission spectrum of a polarization management device provided in this application under O-band and TE mode incident light; Figure 11 The PER curve of a polarization management device provided in this application embodiment under O-band and TE mode incident conditions.

[0029] The annotations in the attached figures are explained as follows: 11-Substrate; 12-Buried oxide layer; 13-Ferroelectric thin film waveguide layer; 131-First waveguide; 132-Second waveguide; 133-Third waveguide; 41-First port; 42-Second port; 43-Third port. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] With the rapid development of optical communication, data center interconnection, and integrated optics technologies, achieving efficient, compact, and multifunctional polarization management on photonic chips has become a critical technical problem that urgently needs to be solved. Polarization beamsplitters (PBSs) are core components in photonic integrated circuits (PICs) for achieving polarization diversity. Their basic function is to spatially separate the two orthogonal polarization states—transverse electric (TE) and transverse magnetic (TM)—in the incident light and output them from different ports.

[0032] Currently, existing polarization beam splitter implementation schemes mainly include the following categories: (1) Silicon-based asymmetric directional coupler type polarization beam splitter rotator. This type of device uses an asymmetric directional coupler (ADC) and realizes the polarization beam splitting and rotation function on a silicon-based platform by constructing the effective polarization refractive index condition. It has the advantages of compact structure, high extinction ratio and large manufacturing tolerance.

[0033] (2) Lithium niobate thin film Mach-Zehnder interferometer type polarization beam splitter. This type of device uses a multimode interference coupler (MMI) and a phase shifter cascaded to form a Mach-Zehnder interferometer (MZI) structure, realizing the polarization beam splitting function on the thin film lithium niobate (LNOI) platform.

[0034] However, the aforementioned existing technical solutions still have many drawbacks: (1) Limited polarization extinction ratio. Because the existing silicon-based ADC-PBS is limited by the low refractive index contrast of the material (n≈1.97), the mode confinement capability is insufficient. Therefore, the TE mode extinction ratio (PER) is only about 23dB, which is difficult to meet the requirements of high-speed optical communication systems for higher signal-to-noise ratio and lower bit error rate, thus limiting the further improvement of system transmission capacity and transmission distance.

[0035] (2) Single function and lack of integrated polarization management capability. Because the design goal of the existing PBS is only polarization beam splitting, the TM mode is still output from the cross port. Therefore, if the system needs to filter out TM crosstalk or suppress polarization noise, an independent polarization filter must be cascaded at the output, which leads to increased device size, accumulated insertion loss and significantly increased system complexity.

[0036] (3) Lack of real-time polarization state monitoring function. Because the output ports of the existing PBS are all signal output ports, they do not have the ability to sense the purity of the input polarization state. Therefore, when the input polarization state drifts due to factors such as temperature change and fiber vibration, the system cannot sense this change through the PBS itself and must rely on external polarization monitoring equipment, which increases the system cost and complexity.

[0037] (4) Lack of dynamic reconfigurability. Because existing silicon-based ADC-PBS are all passive devices and do not have electric field control function, their beam splitting ratio and output port status are fixed after manufacturing and cannot be dynamically adjusted according to system requirements, which limits their application in reconfigurable optical networks, adaptive optics and other scenarios.

[0038] Therefore, this application provides a polarization management device that, by setting a ferroelectric thin-film waveguide layer, utilizes the high refractive index of the ferroelectric thin-film material to enhance mode confinement capabilities, and combines this with its intrinsic optical anisotropy to achieve differentiated transmission of the first polarization mode and the second polarization mode. Simultaneously, the tunable refractive index of the ferroelectric thin-film material allows the third port to selectively switch between a polarization state monitoring port and a signal output port. This achieves efficient polarization beam splitting management and integration of multiple polarization management functions within a single device. It can be widely applied in optical communication, polarization multiplexing systems, coherent optical communication, quantum optics, and integrated optical circuits.

[0039] Please refer to Figure 1 and Figure 2 , Figure 1 This is a top view of a polarization management device in the XY direction provided in an embodiment of this application. Figure 2 A cross-sectional view of a polarization management device in the YZ direction provided in an embodiment of this application, where the upper cladding is not shown. The polarization management device provided in this embodiment may include: Substrate 11; A buried oxide layer 12 is disposed on the surface of the substrate 11; A ferroelectric thin-film waveguide layer 13 is disposed on the surface of the buried oxide layer 12; the ferroelectric thin-film waveguide layer 13 includes a first port 41, a second port 42 and a third port 43. The first port 41 is a signal input port used to input incident light; the incident light includes a first polarization mode and / or a second polarization mode. The second port 42 is a signal output port; The third port 43 is selectively used as a polarization state monitoring port or a signal output port; the polarization state monitoring port is used to monitor the polarization state of the incident light. The first polarization mode is output from the second port 42 and / or the third port 43; the transmission loss of the second polarization mode in the ferroelectric thin film waveguide layer 13 is greater than the transmission loss of the first polarization mode in the ferroelectric thin film waveguide layer 13. The upper cladding is disposed on the surface of the ferroelectric thin film waveguide layer 13.

[0040] It is understood that the substrate 11 is used to support the entire device structure. In some embodiments, the specific type of substrate 11 is not limited; for example, the material of the substrate 11 may include silicon. It is understood that the silicon substrate 11 is compatible with CMOS processes and has mature processing technology, facilitating large-scale production.

[0041] It is understood that the buried oxide layer 12 is used to isolate the substrate 11 from the ferroelectric thin-film waveguide layer 13, preventing light energy leakage to the substrate 11. In some embodiments, the specific type of the buried oxide layer 12 is not limited; for example, the material of the buried oxide layer 12 may include a silicon dioxide (SiO2) layer. It is understood that the refractive index of SiO2 is much lower than that of the ferroelectric thin-film waveguide layer 13, which can create a good refractive index contrast, confining the light field to propagate within the ferroelectric thin-film waveguide layer 13. In some embodiments, the specific thickness of the buried oxide layer 12 is not limited; for example, the thickness of the buried oxide layer 12 can be 2μm-4μm, including the values ​​at both ends. It is understood that a larger buried oxide layer 12 provides better isolation to the substrate 11, but excessive thickness increases the fabrication difficulty and cost of the device.

[0042] This embodiment does not limit the specific types of the first and second polarization modes. For example, the first polarization mode can be a TE mode, and the second polarization mode can be a TM mode. It is understood that ferroelectric thin film materials have intrinsic optical anisotropy, that is, the difference in in-plane / out-of-plane refractive index and absorption caused by ferroelectric polarization, which makes the transmission loss of different polarization modes in ferroelectric thin film waveguides different, among which the transmission loss of the TM mode is significantly higher than that of the TE mode.

[0043] This embodiment does not limit the specific type of ferroelectric thin-film waveguide layer 13. For example, the material of the ferroelectric thin-film waveguide layer 13 may include lead zirconate titanate (PZT), lanthanum-doped lead zirconate titanate (PLZT), or barium titanate (BTO). It is understood that these ferroelectric materials all possess high refractive indices and intrinsic optical anisotropy, while also exhibiting the Pockels effect, making them ideal materials for realizing polarization management and electro-optic reconfigurable functions. In some embodiments, the refractive index of lead zirconate titanate at a wavelength of 1550 nm can be 2.4; the electro-optic coefficient of lead zirconate titanate can be 200 pm / V, approximately 6-7 times that of LNOI; the thermo-optic coefficient can be used for temperature compensation calculations, and the thermo-optic coefficient of lead zirconate titanate can be 1.5 × 10⁻⁶. -4 K -1 .

[0044] This embodiment does not limit the specific thickness of the ferroelectric thin-film waveguide layer 13. For example, the thickness H of the ferroelectric thin-film waveguide layer 13 can be 300nm-700nm, including the values ​​at both ends. Preferably, H can be 500nm. It is understood that the thickness of the waveguide layer affects the number of transmission modes and the confinement effect in the waveguide. Too thin a layer will result in insufficient mode confinement, while too thick a layer may introduce higher-order mode interference.

[0045] This embodiment does not limit the specific structure of the ferroelectric thin film waveguide layer 13. For example, the ferroelectric thin film waveguide layer 13 may include a cascaded first asymmetric directional coupler and a second asymmetric directional coupler. The first asymmetric directional coupler may include a first waveguide 131 and a second waveguide 132; both the first waveguide 131 and the second waveguide 132 are disposed on the surface of the buried oxide layer 12, and the first waveguide 131 and the second waveguide 132 are spaced apart along the first direction Y. The second asymmetric directional coupler may include a second waveguide 132 and a third waveguide 133; the third waveguide 133 is disposed on the surface of the buried oxide layer 12, and the second waveguide 132 and the third waveguide 133 are spaced apart along the first direction Y; in this structure, the first waveguide 131 is the input waveguide, the second waveguide 132 is the bridging waveguide, and the third waveguide 133 is the output waveguide; The input end of the first waveguide 131 is the first port 41, and the output end of the first waveguide 131 is the second port 42. In this structure, the second port 42 is a Bar port (a straight-through port, which refers to a port where the optical signal continues to be transmitted at the output end along the same waveguide as the input port). The output of the third waveguide 133 is the third port 43. In this structure, the third port 43 is a cross port (a port where the optical signal is switched to another different waveguide at the output).

[0046] It is understandable that asymmetric directional couplers achieve polarization beam splitting by using mode coupling between two waveguides with different widths: when the effective refractive index of a specific mode in the two waveguides satisfies the phase matching condition, the mode couples from one waveguide to the other; when the phase matching condition is not met, the mode maintains its original path of transmission. By properly designing the waveguide width and gap, the second polarization mode can satisfy the phase matching condition while the first polarization mode does not, thus achieving polarization beam splitting.

[0047] In other embodiments, the cascaded first and second asymmetric directional couplers can also employ a Mach-Zehnder interferometer (MZI) structure or a multimode interferometer (MMI) structure. It is understood that the MZI structure achieves polarization beam splitting through interference effects, but typically requires a longer device size; the MMI structure achieves polarization beam splitting based on self-image effects, but typically requires lengths of several hundred micrometers or more.

[0048] In other embodiments, a single-stage asymmetric directional coupler structure may also be used. It is understood that the single-stage asymmetric directional coupler structure is simpler, but its polarization extinction ratio is typically lower than that of a cascaded structure.

[0049] In some embodiments, the specific structure of each waveguide is not limited. For example, the first waveguide 131, the second waveguide 132, and the third waveguide 133 may include strip waveguides or ridge waveguides. A ridge waveguide includes a planar layer and a ridge layer disposed on the surface of the planar layer. It is understood that strip waveguides have a simple fabrication process but weak mode confinement capability; ridge waveguides enhance mode confinement through the ridge layer and are suitable for small bending radii and compact designs.

[0050] In some embodiments, the specific shape of each waveguide is not limited, for example: The first waveguide 131 can be a straight waveguide in the coupling region and a curved waveguide at the end of the coupling region, with the curved waveguide bending towards the side away from the second waveguide 132. The second waveguide 132 is a straight waveguide; The third waveguide 133 can be a straight waveguide in the coupling region and a curved waveguide at the end of the coupling region, with the curved waveguide curving away from the side away from the second waveguide 132.

[0051] Understandably, the curved design of the first waveguide 131 and the third waveguide 133 can maintain a sufficient distance between the waveguide and the middle region to prevent unnecessary crosstalk of the optical signal in the uncoupled region.

[0052] In some embodiments, the relative positions of the waveguides are not limited. For example, the first waveguide 131, the second waveguide 132, and the third waveguide 133 are arranged in a staggered manner along the second direction X. The second direction X (i.e., the light propagation direction, specifically the light propagation direction in the straight waveguide of the first waveguide 131) is perpendicular to the first direction Y. In some embodiments, the second waveguide 132 may include a first coupling region and a second coupling region arranged sequentially along the second direction X. The projection of the first coupling region along the first direction Y overlaps with the first waveguide 131, and the projection of the second coupling region along the first direction Y overlaps with the second waveguide 132. It is understood that the first waveguide 131 and the third waveguide 133 overlap with different segments of the second waveguide 132 in the second direction X, so that the two-stage coupling regions are arranged sequentially in space rather than overlapping, thereby avoiding mode interference and crosstalk that may occur when two-stage coupling occurs simultaneously in the same area.

[0053] In some embodiments, the coupling length of each coupler is not limited, for example: The coupling length L of the first asymmetric directional coupler c1 It can be 40μm-70μm, including both ends; preferably, L c1 It can be 55μm; The coupling length L of the second asymmetric directional coupler c2 The coupling length L with the first asymmetric directional coupler c1 equal.

[0054] Understandably, the coupling length determines the interaction distance required for a mode to be fully coupled from one waveguide to another, and is a key parameter affecting the polarization extinction ratio.

[0055] In some embodiments, the specific structural parameters of each waveguide are not limited, for example: The width W1 of the first waveguide 131 can be 0.5μm-1.0μm, including the values ​​at both ends; preferably, W1 can be 0.75μm. The width W2 of the second waveguide 132 can be 1.5μm-2.5μm, including the values ​​at both ends; preferably, W2 can be 2μm. The width W3 of the third waveguide 133 can be equal to the width W1 of the first waveguide 131; The gap width W between the first waveguide 131 and the second waveguide 132 gap1 The wavelength is 500nm-800nm, including both ends; preferably, W gap1 It can be 650nm; The gap width W between the third waveguide 133 and the second waveguide 132 gap2 The gap width W between the first waveguide 131 and the second waveguide 132 gap1 equal.

[0056] Understandably, the width W1 of the first waveguide 131 and the width W3 of the third waveguide 133 are equal (W3=W1), and both are narrower than the width W2 of the second waveguide 132 (W1≠W2). This allows the first waveguide 131 and the third waveguide 133 to support fundamental mode transmission, while the second waveguide 132, due to its larger width, can support higher-order modes. This width configuration allows the effective refractive indices of the first polarization mode (TE0 mode) transmitted in the first waveguide 131 and the second polarization mode (TM1 mode) transmitted in the second waveguide 132 to be matched or mismatched through design, thereby determining whether the modes couple and forming the basis for achieving polarization selectivity.

[0057] Understandably, the above-mentioned ranges of waveguide widths and coupling gaps take into account both process feasibility and polarization beam splitting performance: if the waveguide width is too narrow, it will weaken mode confinement, while if it is too wide, it may introduce higher-order mode interference; if the coupling gap is too small, it will increase the process difficulty and may introduce mode interference, while if it is too large, it will reduce coupling efficiency.

[0058] In some embodiments, the polarization management device may further include: An electrical signal control component is used to control the electrical signal applied to the ferroelectric thin film waveguide layer 13, so that the third port 43 can be selectively used as a polarization state monitoring port or a signal output port.

[0059] Understandably, the electrical signal control component can change the refractive index of the ferroelectric thin-film waveguide layer 13 by applying an electrical signal, thereby altering the phase matching condition of the cascaded asymmetric directional coupler, reallocating the optical path, and enabling selective switching of the third port 43 between two functions. The refractive index change satisfies the following: Δn=-½·n 3 ·r 33 ·(V / d); In the formula, n is the refractive index of the ferroelectric thin-film waveguide layer 13, and r 33 denoted as the electro-optic coefficient of the thin-film waveguide layer, V as the applied bias voltage, and d as the electrode spacing.

[0060] In some embodiments, the specific control method of the polarization state monitoring port is not limited. For example, when the electrical signal control component does not apply an electrical signal to the ferroelectric thin film waveguide layer 13, the third port 43 is used as the polarization state monitoring port.

[0061] Understandably, when no electrical signal is applied, the refractive index of the ferroelectric thin-film waveguide layer 13 does not change, and the phase matching condition of the cascaded asymmetric directional coupler remains in its initial design state. At this time, the third port 43 is in normal operating condition (without electro-optic tuning). In normal operating condition, the output power of the third port 43 is extremely low (approximately -42dB in TE mode and below -24dB in TM mode). Therefore, the third port 43 can be configured as a polarization state monitoring port. By monitoring abnormal increases in the output power of the third port 43, changes in the input polarization state can be sensed in real time. For example, when the input polarization state changes from a pure TE mode to one mixed with TM mode components or when the TE polarization direction rotates, the power of the third port 43 increases from an extremely low reference value (e.g., -42dB) to a detectable level (e.g., -30dB or higher), thereby achieving on-chip self-monitoring without the need for external polarization monitoring equipment.

[0062] In some embodiments, when the third port 43 serves as a polarization state monitoring port, the monitoring results can be provided as a feedback signal to the active polarization controller or the system alarm module. It is understood that when an increase in power is detected at the third port 43, it indicates that the input polarization state has deteriorated. The active polarization controller can adjust and compensate for the input polarization state in real time based on this feedback signal, while the system alarm module can issue a warning message, thereby forming a closed-loop polarization control at the system level to ensure the transmission quality and stability of the optical communication system.

[0063] In some embodiments, the specific control method of the signal output port is not limited. For example, when the electrical signal control component applies an electrical signal to the ferroelectric thin-film waveguide layer 13, the third port 43 is used as the signal output port. It is understood that after the electrical signal is applied, the refractive index of the ferroelectric thin-film waveguide layer 13 changes due to the linear electro-optic effect, and the phase matching condition of the cascaded asymmetric directional coupler changes accordingly. Modes that did not originally meet the coupling condition are coupled, and the output power of the third port 43 becomes continuously adjustable with voltage changes. By controlling the voltage, the state switching of the third port 43 from a monitoring port to a signal output port can be realized: from extremely low power (below -40dB) to continuously adjustable power, achieving dynamic activation of the extremely low output port and reconfiguration of device function. Existing passive polarization beamsplitters do not possess this reconfigurable capability.

[0064] In some embodiments, when the third port 43 serves as a signal output port, the first polarization mode can be output simultaneously from both the second port 42 and the third port 43 (with an adjustable beam splitting ratio), or it can be output entirely from the third port 43. It is understood that the specific allocation ratio depends on the voltage value of the applied electrical signal. By continuously adjusting the voltage, the power allocation ratio of the first polarization mode between the second port 42 and the third port 43 can be continuously varied, thus flexibly adapting to the needs of different application scenarios. This function can be used to implement a 1×2 optical switch or an adjustable beam splitting ratio function, providing a flexible polarization management scheme for reconfigurable optical networks.

[0065] This embodiment does not limit the specific structure of the electrical signal control component. For example, the electrical signal control component may include at least one pair of electrodes. It is understood that the pair of electrodes includes a positive electrode and a negative electrode. A bias voltage can be applied to the ferroelectric thin film waveguide layer 13 through the electrodes, and the refractive index of the waveguide can be changed by utilizing the electro-optic effect of the ferroelectric thin film material.

[0066] This embodiment does not limit the specific type of electrode. For example, the electrode material may include Au, Al, Ti / Au, or other low-resistivity metals. It is understood that low-resistivity metals can reduce the transmission loss of high-frequency signals and improve the efficiency of electro-optic tuning.

[0067] This embodiment does not limit the specific form of the electrode. For example, the electrode may include a traveling wave electrode, a lumped electrode (LE), or a coplanar waveguide (CPW) electrode. It is understood that traveling wave electrodes are suitable for high-speed electro-optic tuning, enabling speed matching between microwaves and light waves to obtain a larger modulation bandwidth; LE electrodes are suitable for low-frequency modulation and have a simpler structure; CPW electrodes are suitable for high-frequency modulation, but their fabrication process is more complex.

[0068] This embodiment does not limit the specific location of the electrodes. For example, the electrodes can be disposed on both sides or the top of the ferroelectric thin-film waveguide layer 13; the extension direction of the electrodes is consistent with the extension direction of the ferroelectric thin-film waveguide layer 13. It is understood that the shape of the electrodes is consistent with that of the waveguide (the electrodes also conform to the bent shape when the waveguide is bent) to ensure that a uniform electric field is applied to the entire waveguide, thereby achieving effective electro-optic tuning.

[0069] This embodiment does not limit the specific spacing between the positive and negative electrodes. For example, the spacing between adjacent positive and negative electrodes can be 300nm-1000nm, including the values ​​at both ends. Preferably, the spacing between adjacent positive and negative electrodes can be 500nm. It is understood that the closer the electrode spacing, the greater the electric field strength generated under the same voltage, and the higher the modulation efficiency; however, too close a spacing will increase the manufacturing difficulty and may introduce metal absorption losses.

[0070] This embodiment does not limit the specific value of the bias voltage. For example, the driving voltage can be 0-30V, including the values ​​at both ends. Preferably, the driving voltage can be 0-20V, including the values ​​at both ends. It is understood that the higher the voltage, the wider the electro-optic tuning range, but excessively high voltage will increase power consumption and may affect device stability. A driving voltage within 20V can achieve effective refractive index tuning.

[0071] It is understood that the upper cladding layer is used to protect the ferroelectric thin-film waveguide layer 13. This embodiment does not limit the specific type of the upper cladding layer; for example, the material of the upper cladding layer may include SiO2. This embodiment does not limit the specific thickness of the upper cladding layer; for example, the thickness of the upper cladding layer may be 2μm-3μm, including the values ​​at both ends.

[0072] In some embodiments, the refractive index of the upper cladding layer may be lower than that of the ferroelectric thin-film waveguide layer 13 to ensure that the optical field is confined to the ferroelectric thin-film waveguide layer 13 for transmission. In some embodiments, the refractive index of the upper cladding layer may be 1.45, and the refractive index of the ferroelectric thin-film waveguide layer 13 may be 2.4.

[0073] Based on the above embodiments, this application, by setting a ferroelectric thin-film waveguide layer 13, utilizes the high refractive index of the ferroelectric thin-film material to enhance mode confinement capabilities, and combines this with its intrinsic optical anisotropy to achieve differentiated transmission of the first polarization mode and the second polarization mode. Simultaneously, the adjustable refractive index of the ferroelectric thin-film material allows the third port 43 to selectively switch between a polarization state monitoring port and a signal output port. This integrates multiple polarization management functions, including efficient polarization beam splitting, intrinsic polarization mode blocking, real-time polarization state monitoring, and dynamically adjustable output state, within the same device. Compared with the prior art, it has the following beneficial effects: (1) The polarization extinction ratio is significantly improved. The ferroelectric thin film waveguide layer 13 is used to replace the traditional silicon-based material. The high refractive index of the ferroelectric thin film material enhances the mode confinement ability, which significantly improves the extinction ratio of the first polarization mode, thereby significantly improving the device performance.

[0074] (2) Integration of polarization beam splitting and built-in filtering functions. By utilizing the intrinsic optical anisotropy of ferroelectric thin film materials, the first polarization mode is efficiently output while the second polarization mode is intrinsically suppressed due to its greater transmission loss. Crosstalk and polarization noise of the second polarization mode can be filtered out without the need for an additional polarization filter. The two functions of polarization beam splitting and polarization filtering are integrated in the same device, avoiding the increase in size, insertion loss and system complexity caused by cascading additional devices.

[0075] (3) It has a real-time polarization state monitoring function. The third port 43 is configured as a polarization state monitoring port. By using this port to monitor the polarization state of the incident light, the change of polarization state can be sensed in real time on the same device. On-chip self-detection can be achieved without external polarization monitoring equipment, which reduces the system cost and size.

[0076] (4) The output state is dynamically adjustable. By utilizing the adjustable refractive index of the ferroelectric thin film material, the third port 43 can be switched between the polarization state monitoring port and the signal output port, realizing the dynamic activation of the dormant port and the reconfiguration of the device function. Existing passive polarization beam splitters do not have this reconfigurable capability.

[0077] (5) High functional integration and compact device structure. Applying ferroelectric thin film materials to waveguide integrated devices realizes the leap of ferroelectric materials from free-space optical devices to waveguide integrated devices, opening up new avenues for the application of ferroelectric thin film materials in photonic integrated circuits.

[0078] Please refer to Figure 3 , Figure 3 A flowchart illustrating a polarization management method provided in this application embodiment. This polarization management method, applied to the aforementioned polarization management device, may include: S101: Enables the third port to be selectively used as a polarization state monitoring port or a signal output port.

[0079] In some embodiments, the specific method of selecting the function of the third port is not limited. For example, when the polarization management device includes an electrical signal control component, the third port can be selectively used as a polarization state monitoring port or a signal output port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer. It is understood that the electrical signal control component can change the refractive index of the ferroelectric thin-film waveguide layer by applying an electrical signal, thereby changing the phase matching condition of the cascaded asymmetric directional coupler, redistributing the optical path, and achieving selective switching of the third port between the two functions.

[0080] In some embodiments, the specific control method of the polarization state monitoring port is not limited. For example, the third port can be used as a polarization state monitoring port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer to be zero. It is understood that when no electrical signal is applied, the refractive index of the ferroelectric thin-film waveguide layer does not change, and the phase matching condition of the cascaded asymmetric directional coupler remains in its initial design state. At this time, the third port is in normal operation (without electro-optic tuning). In normal operation, the output power of the third port is extremely low (approximately -42dB in TE mode and below -24dB in TM mode). Therefore, the third port can be configured as a polarization state monitoring port. By monitoring the abnormal increase in the output power of the third port, the change in the input polarization state can be sensed in real time. For example, when the input polarization state changes from a pure TE mode to one mixed with TM mode components or when the TE polarization direction rotates, the power of the third port increases from an extremely low reference value (e.g., -42dB) to a detectable level (e.g., -30dB or higher), thereby achieving on-chip self-detection without the need for external polarization monitoring equipment.

[0081] In some embodiments, when the third port serves as a polarization state monitoring port, the monitoring results can be provided as a feedback signal to the active polarization controller or the system alarm module. It is understood that when an increase in power is detected at the third port, it indicates that the input polarization state has deteriorated. The active polarization controller can adjust and compensate for the input polarization state in real time based on this feedback signal, while the system alarm module can issue a warning message, thereby forming a closed-loop polarization control at the system level to ensure the transmission quality and stability of the optical communication system.

[0082] In some embodiments, the specific control method of the signal output port is not limited. For example, by applying an electrical signal to the ferroelectric thin-film waveguide layer, the third port can be used as a signal output port. It is understood that after applying the electrical signal, the refractive index of the ferroelectric thin-film waveguide layer changes due to the linear electro-optic effect, and the phase matching condition of the cascaded asymmetric directional coupler changes accordingly. Modes that did not originally meet the coupling condition begin to couple, and the output power of the third port becomes continuously adjustable with voltage changes. By controlling the voltage, the state switching of the third port from a monitoring port to a signal output port can be achieved: from extremely low power (below -40dB) to continuously adjustable power, realizing the dynamic activation of the extremely low output port and the reconfiguration of device function. Existing passive polarization beamsplitters do not possess this reconfigurable capability.

[0083] In some embodiments, when the third port serves as a signal output port, the first polarization mode can be output simultaneously from both the second and third ports (with an adjustable beam splitting ratio), or it can be output entirely from the third port. It is understood that the specific allocation ratio depends on the voltage value of the applied electrical signal. By continuously adjusting the voltage, the power allocation ratio of the first polarization mode between the second and third ports can be continuously varied, thus flexibly adapting to the needs of different application scenarios. This function can be used to implement a 1×2 optical switch or an adjustable beam splitting ratio function, providing a flexible polarization management scheme for reconfigurable optical networks.

[0084] S102: Input incident light at the first port.

[0085] In some embodiments, the specific method of inputting incident light is not limited; for example, the incident light can be input to the first port by coupling.

[0086] S103: When the third port is used as a polarization state monitoring port, the first polarization mode is output from the second port, and the polarization state of the incident light is monitored through the third port; When the third port is used as a signal output port, the first polarization mode is output from the second port and / or the third port.

[0087] In some embodiments, the specific method of monitoring the polarization state is not limited. For example, the change in the polarization state of the incident light can be monitored by monitoring the change in the output power of the third port. It is understood that when the input polarization state is a pure first polarization mode (such as the TE mode), the output power of the third port is a very low reference value (e.g., -42dB); when the input polarization state deteriorates (e.g., a second polarization mode component is introduced or the first polarization direction is rotated), the output power of the third port will increase detectably (e.g., from -42dB to -30dB or higher). By monitoring the power change at the third port, the change in the input polarization state can be sensed in real time and provided as a feedback signal to the active polarization controller or system alarm module. This monitoring function does not rely on any external polarization testing equipment, achieving on-chip self-detection.

[0088] Based on the above embodiments, this application is applied to the above-mentioned polarization management device, which can realize high-performance polarization management and integrate multiple functions such as polarization state monitoring, output path dynamic control and second polarization mode natural processing in the same method flow. It can realize the integrated processing of polarization beam splitting, filtering and monitoring without additional operation.

[0089] Please refer to Figure 4 , Figure 4 A flowchart illustrating a method for fabricating a polarization management device according to an embodiment of this application. The method for fabricating a polarization management device according to an embodiment of this application may include: S201: Provides a substrate.

[0090] This embodiment does not limit the specific type and structural parameters of the substrate. For details, please refer to the above embodiments, which will not be repeated here.

[0091] S202: A buried oxide layer is formed on the substrate surface.

[0092] This embodiment does not limit the specific type and structural parameters of the buried oxide layer. For details, please refer to the above embodiment, which will not be repeated here.

[0093] This embodiment does not limit the specific method of forming the buried oxide layer. For example, the buried oxide layer can be grown on the substrate surface by thermal oxidation.

[0094] S203: A ferroelectric thin-film waveguide layer is formed on the surface of the buried oxide layer; The ferroelectric thin-film waveguide layer includes a first port, a second port, and a third port; the first port is a signal input port for inputting incident light; the incident light includes a first polarization mode and / or a second polarization mode; the second port is a signal output port; the third port is selectively used as a polarization state monitoring port or a signal output port; the polarization state monitoring port is used to monitor the polarization state of the incident light; the first polarization mode is output from the second port and / or the third port; the transmission loss of the second polarization mode in the ferroelectric thin-film waveguide layer is greater than the transmission loss of the first polarization mode in the ferroelectric thin-film waveguide layer.

[0095] This embodiment does not limit the specific method of forming the ferroelectric thin-film waveguide layer; for example, the following methods can be used: Step 31: Deposit a ferroelectric thin film on the surface of the buried oxide layer.

[0096] This embodiment does not limit the specific method of depositing ferroelectric thin films. For example, ferroelectric thin films can be deposited on the surface of buried oxide layers using the sol-gel method, RF magnetron sputtering, chemical vapor deposition (CVD) or pulsed laser deposition (PLD).

[0097] In some embodiments, the specific process conditions for depositing ferroelectric thin films are not limited; for example, PZT thin films are used as an example: The sol-gel method may include: preparing a PZT precursor sol using lead acetate, n-propanezirconium oxypropane, and isopropanetitanium oxypropane as starting materials and 2-methoxyethanol as a solvent; uniformly coating the PZT precursor sol onto the surface of the buried oxide layer by spin coating, with each layer undergoing pyrolysis treatment (300°C-400°C) after spin coating, repeated multiple times to achieve the target thickness of the ferroelectric thin film; and subjecting the PZT precursor sol to rapid thermal annealing (RTA) treatment (650°C-750°C) to crystallize the film into a perovskite structure, thus obtaining the PZT thin film. A typical component of the PZT thin film is Pb(Zr) 0.52 Ti 0.48 )O3.

[0098] The radio frequency magnetron sputtering method may include: using a PZT ceramic target as the target material, sputtering atmosphere of Ar / O2 mixed gas (Ar / O2 flow ratio ≈ 45: 0.65), sputtering pressure of 0.52 Pa-0.54 Pa, substrate temperature of 200°C, and radio frequency power of 160 W; after deposition, rapid thermal annealing (RTA) is used to crystallize the PZT thin film. Understandably, CVD can produce high-quality thin films, but the equipment cost is high; PLD can precisely control the composition of thin films, but it is difficult to guarantee uniformity.

[0099] Step 32: Polarize the ferroelectric thin film.

[0100] It is understandable that polarization treatment of the deposited ferroelectric thin film can impart stable ferroelectric anisotropy. Polarization treatment is a key process step in enabling ferroelectric thin films to acquire intrinsic optical anisotropy.

[0101] In some embodiments, the specific method of polarization processing is not limited; for example, the following methods may be used: Step 321: Prepare a temporary electrode on the surface of the ferroelectric thin film.

[0102] In some embodiments, the specific method of preparing the temporary electrode is not limited; for example, the temporary electrode can be prepared by sputtering a point electrode onto the surface of a ferroelectric thin film.

[0103] In some embodiments, the specific type of point electrode is not limited; for example, the material of the point electrode may include Pt or Au.

[0104] Step 322: Apply a DC electric field through a temporary electrode at a preset temperature to orient the electric dipoles inside the ferroelectric thin film along the direction of the electric field.

[0105] This embodiment does not limit the specific process conditions of step 322, which can be determined according to the actual situation.

[0106] In some embodiments, the electric field direction may be parallel to the thickness direction of the ferroelectric thin film (i.e., perpendicular to the substrate surface direction) to ensure maximum out-of-plane remanent polarization.

[0107] Step 323: Remove the temporary electrode after polarization is complete.

[0108] In some embodiments, the specific process conditions for polarization treatment are not limited. For example, the process conditions for polarization treatment may include: The polarization electric field strength can be 100kV / cm-300kV / cm, including the values ​​at both ends; preferably, the electric field strength can be 200kV / cm. The polarization temperature can be between 100°C and 180°C, including both ends; preferably, the polarization temperature can be 120°C. The polarization time can be 10 minutes to 30 minutes, including both ends; preferably, the polarization time can be 20 minutes.

[0109] Step 33: Pattern the polarized ferroelectric thin film to form a ferroelectric thin film waveguide layer.

[0110] In some embodiments, the specific type and structural parameters of the ferroelectric thin film are not limited. For details, please refer to the above embodiments, which will not be repeated here.

[0111] In some embodiments, the specific method of graphical processing is not limited; for example, the following methods may be used: Step 331: Perform photolithography on the polarized ferroelectric thin film to define the pattern of the ferroelectric thin film waveguide layer.

[0112] It is understandable that the pattern of a ferroelectric thin-film waveguide layer refers to the planar pattern of the waveguide included in the ferroelectric thin-film waveguide layer, which can be determined according to the specific structure of the waveguide.

[0113] In some embodiments, the specific method of photolithography is not limited; for example, the following methods may be used: Coating: Spin-coat positive photoresist (such as AZ5214 type) onto the surface of the polarized ferroelectric thin film. The photoresist thickness can be selected according to the subsequent etching depth requirements, such as 1μm-3μm. After coating, pre-bake (soft bake) on a hot plate at 90°C-100°C to remove the solvent in the photoresist.

[0114] Exposure: Ultraviolet lithography (UV Lithography) or electron beam lithography (EBL) is used to project the pattern of the ferroelectric thin film waveguide layer onto the photoresist surface through a mask; among them, electron beam lithography is suitable for pattern definition with submicron precision (in this embodiment, the waveguide width accuracy requirement is ±20nm). Development: The exposed sample is immersed in the corresponding developer and developed, then rinsed with deionized water and dried with N2 to form a photoresist mask; subsequently, a hard bake is performed to enhance the photoresist mask's resistance to etching.

[0115] Step 332: Based on the photoresist mask, etch the ferroelectric thin film until the preset depth is reached, and then stop to form a ferroelectric thin film waveguide layer.

[0116] In some embodiments, the specific value of the preset depth is not limited, and can be determined according to the specific structure of the ferroelectric thin film waveguide layer.

[0117] In some embodiments, the etching depth can be precisely controlled by controlling the etching time.

[0118] In some embodiments, the specific etching method is not limited, and any dry etching method can be used. For example, inductively coupled plasma reactive ion etching (ICP-RIE) can be used to perform anisotropic etching on the ferroelectric thin film to obtain the ferroelectric thin film waveguide layer.

[0119] In some embodiments, the specific process conditions for anisotropic etching are not limited. For example, the process conditions for anisotropic etching may include: The etching gas can be an Ar / CHF3 mixture, with the CHF3 volume fraction being 30%-40%, including both ends. The ICP power (i.e., plasma source power) can be 500W-2000W, including the values ​​at both ends; The RF bias power (i.e., substrate bias power) can be 300W-500W, including the values ​​at both ends; The chamber pressure can be 10mTorr-30mTorr (approximately 1.3Pa-4.0Pa), including the values ​​at both ends; The etching rate can be 100 nm / min.

[0120] Step 333: Remove residual photoresist mask. In some embodiments, the specific method for removing residual photoresist mask is not limited. For example, oxygen plasma ashing (O2 Plasma Ashing) can be used to remove the residual photoresist mask, followed by ultrasonic cleaning with acetone, isopropyl alcohol (IPA), and deionized water, and then drying with N2. If necessary, piranha solution (H2SO4:H2O2=3:1) can be used for cleaning to remove organic residues, but the cleaning time must be strictly controlled to avoid corrosion of the ferroelectric thin film waveguide layer.

[0121] Understandably, when the ferroelectric thin-film waveguide layer adopts a strip waveguide structure, only the first photolithography, first etching, and first resist stripping are required sequentially. However, when the ferroelectric thin-film waveguide layer adopts a ridge waveguide structure (including a planar layer and a ridge layer), the first photolithography, first etching, and first resist stripping are required sequentially to form the initial planar layer; the initial planar layer is then subjected to a second photolithography, second etching, and second resist stripping to form the final planar layer and ridge layer. The specific process flow can be referenced from the above steps, and the specific process parameters can be determined based on the waveguide structure used in the ferroelectric thin-film waveguide layer. When the ferroelectric thin-film waveguide layer adopts a ridge waveguide structure, the patterns during the two photolithography steps are the planar layer pattern and the ridge layer pattern, respectively; the etching depths are the initial thickness of the ferroelectric thin film and the thickness of the ridge layer, respectively (i.e., the initial thickness of the ferroelectric thin film minus the remaining thickness of the planar layer).

[0122] S204: An upper cladding is formed on the surface of a ferroelectric thin-film waveguide layer to obtain a polarization management device.

[0123] In some embodiments, the specific type and structural parameters of the cladding are not limited. For details, please refer to the above embodiments, which will not be repeated here.

[0124] In some embodiments, the specific method of forming the upper cladding is not limited. For example, the upper cladding can be formed on the surface of the ferroelectric thin film waveguide layer by means of plasma enhanced chemical vapor deposition (PECVD) or magnetron sputtering.

[0125] In some embodiments, after step S204, the process may further include: mechanically polishing the input and output faces of the polarization management device to form smooth faces, so as to facilitate subsequent coupling and alignment with the fiber array or lens fiber.

[0126] In some embodiments, if it is necessary to implement the function of dynamically adjustable output state, step S204 may further include: An electrical signal control component is prepared; the electrical signal control component is used to control the electrical signal applied to the ferroelectric thin film waveguide layer, so that the third port can be selectively used as a polarization state monitoring port or a signal output port.

[0127] It is understandable that the electrical signal control component changes the refractive index of the ferroelectric thin film waveguide layer by applying an electrical signal, thereby changing the phase matching condition of the cascaded asymmetric directional coupler, redistributing the optical path, and realizing the selective switching of the third port between the polarization state monitoring port and the signal output port.

[0128] This embodiment does not limit the specific structure and structural parameters of the electrical signal control component. For details, please refer to the above embodiment, which will not be repeated here.

[0129] This embodiment does not limit the specific method of fabricating the electrical signal control component. For example, when the electrical signal control component includes electrodes, the following methods can be used: Electrodes are fabricated sequentially using photolithography, metal deposition (electron beam evaporation or magnetron sputtering), and lift-off processes.

[0130] Based on the above embodiments, this application can prepare the above-mentioned polarization management device, which has the advantages of simple process and compatibility with CMOS process, and is suitable for mass production.

[0131] The functions of the polarization management device described above are illustrated below with specific examples.

[0132] Example 1: C-band polarization management device.

[0133] This embodiment provides a polarization management device that can operate in the C-band, i.e., the range of 1530nm-1565nm.

[0134] like Figure 1 As shown, the device, from top to bottom, includes a first waveguide 131 (input waveguide, width W1), a second waveguide 132 (bridging waveguide, width W2), and a third waveguide 133 (output waveguide, width W3, W3=W1). Equal-width gaps (gap width W1) are provided between the first waveguide 131 and the second waveguide 132, and between the second waveguide 132 and the third waveguide 133. gap1 =W gap1 These components form a cascaded asymmetric directional coupler. The output of the first waveguide 131 is the first signal output port (Port1), and the output of the third waveguide 133 is the second signal output port (Port2).

[0135] like Figure 2 As shown, the cross-sections of the device from bottom to top are as follows: Substrate 11: Made of silicon material with a thickness of 500 μm; Buried oxide layer 12: Made of SiO2 material, with a thickness of 4μm; Ferroelectric thin film waveguide layer 13: made of PZT ferroelectric thin film material with a thickness of 500 nm; Upper cladding: made of SiO2 material, with a thickness of 3μm; Waveguide parameters: W1=0.75μm, W2=2.0μm, W3=0.75μm, W gap1 =W gap2 =640nm, L c1 =L c2 =55μm.

[0136] The performance of the device in the C-band of this embodiment is as follows: When the TE mode is incident: The transmittance of the first port 41 is greater than -1dB; The third port 43 has a transmittance of less than -42dB (extremely low output). The polarization extinction ratio is greater than 41dB, which is better than existing silicon-based PBS (about 23dB) and an improvement of about 18dB.

[0137] When the TM model is incident: The transmittance of the first port 41 is less than -24dB; The transmittance of the third port 43 is less than -24dB; The TM mode is intrinsically blocked, and there is no obvious output from either of the two output ports.

[0138] Please refer to Figure 5 , Figure 5 The transmission spectrum of a polarization management device provided in this application under C-band and TE mode incident light. Figure 5 In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (dB). The Port1 curve is approximately -1dB, and the Port2 curve is approximately <-42dB, indicating that the TE mode outputs efficiently from the first output port, while the second output port has almost no output.

[0139] Please refer to Figure 6 , Figure 6 The PER curve of a polarization management device provided in this application embodiment under C-band and TE mode incident conditions. Figure 6 In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents PER (dB). PER > 41dB across the entire wavelength range indicates that the device has an extremely high polarization extinction ratio.

[0140] Please refer to Figure 7 , Figure 7 The normalized electric field intensity distribution of a polarization management device under C-band and TE-mode incident conditions is provided in the embodiments of this application. Figure 7 In the test, the TE mode energy is concentrated in the first waveguide 131 and output from Port1, proving that no mode coupling of the TE mode occurs in the device.

[0141] Please refer to Figure 8 , Figure 8 The transmission spectrum of a polarization management device provided in this application under C-band, TM mode incident light. Figure 8 In the test, the transmittance of both Port1 and Port2 was below -24 dB, proving that the TM mode was intrinsically blocked.

[0142] Please refer to Figure 9 , Figure 9 The normalized electric field intensity distribution of a polarization management device under C-band, TM mode incident conditions is provided in the embodiments of this application. Figure 9 In the process, the energy of the TM mode is dissipated during transmission, and neither port has a valid output.

[0143] Example 2: O-band polarization management device.

[0144] This embodiment provides a polarization management device capable of operating in the O-band, i.e., the range of 1260nm-1360nm. The device structure and materials are the same as in Embodiment 1.

[0145] The performance of the device in the O-band of this embodiment is as follows: When the TE mode is incident: The transmittance of the first port 41 is greater than -3dB; The transmittance of the third port 43 is less than -37dB to -47dB; The polarization extinction ratio is approximately 34dB-44dB.

[0146] Please refer to Figure 10 , Figure 10 The transmission spectrum of a polarization management device provided in this application under O-band and TE mode incident light. Figure 10 In the figure, the Port1 curve is approximately -3dB, and the Port2 curve is approximately -37dB to -47dB, indicating that the TE module outputs efficiently from the first output port, while the second output port has almost no output.

[0147] Please refer to Figure 11 , Figure 11 The PER curve of a polarization management device provided in this application embodiment under O-band and TE mode incident conditions. Figure 11 In the entire wavelength range, the polarization extinction ratio (PER) is approximately 34 dB to 44 dB.

[0148] The O-band is the core band for short-range optical interconnects in data centers. In this embodiment, the PER of the TE mode in the O-band reaches 34dB-44dB, which verifies the application potential of the PZT platform in short-range communication.

[0149] Example 3: Electro-optically activatable polarization management device.

[0150] Based on Example 1, this embodiment further provides traveling wave electrodes on both sides or top of the ferroelectric thin film waveguide layer 13. The material is Ti / Au, and the thickness is 10nm / 100nm.

[0151] Working principle: In the zero-voltage state, the device operates in the polarization beam splitting and monitoring mode described in Example 1, with the third port 43 having extremely low output power (below -42dB) as a polarization state monitoring port. When a DC bias voltage (0-20V) is applied to the ferroelectric thin-film waveguide layer 13 through the electrodes, the refractive index of the ferroelectric thin-film waveguide layer 13 changes due to the Pockels effect, and the amount of refractive index change satisfies: Δn=-½·n 3 ·r 33 ·(V / d); In the formula, n is the refractive index of the ferroelectric thin-film waveguide layer 13, and r 33 denoted as the electro-optic coefficient of the thin-film waveguide layer, V as the applied bias voltage, and d as the electrode spacing; The change in refractive index alters the phase matching condition of the cascaded asymmetric directional coupler, causing the output power of the third port 43 to increase continuously with voltage changes.

[0152] This document uses specific examples to illustrate the principles and implementation methods of this application. The various embodiments are progressive, with each embodiment focusing on its differences from others. Similar or identical parts between embodiments can be referred to interchangeably. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this application. For those skilled in the art, various improvements and modifications can be made to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of this application.

[0153] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

Claims

1. A polarization management device, characterized in that, include: Substrate; A buried oxide layer is disposed on the surface of the substrate; A ferroelectric thin-film waveguide layer is disposed on the surface of the buried oxide layer; The ferroelectric thin-film waveguide layer includes a first port, a second port, and a third port; The first port is a signal input port for inputting incident light; the incident light includes a first polarization mode and / or a second polarization mode. The second port is a signal output port; The third port can be selectively used as either a polarization state monitoring port or a signal output port. The polarization state monitoring port is used to monitor the polarization state of the incident light; The first polarization mode is output from the second port and / or the third port; the transmission loss of the second polarization mode in the ferroelectric thin film waveguide layer is greater than the transmission loss of the first polarization mode in the ferroelectric thin film waveguide layer. The upper cladding layer is disposed on the surface of the ferroelectric thin film waveguide layer.

2. The polarization management device according to claim 1, characterized in that, The ferroelectric thin-film waveguide layer includes a cascaded first asymmetric directional coupler and a second asymmetric directional coupler. The first asymmetric directional coupler includes a first waveguide and a second waveguide; both the first waveguide and the second waveguide are disposed on the surface of the buried oxide layer, and the first waveguide and the second waveguide are spaced apart along a first direction; The second asymmetric directional coupler includes a second waveguide and a third waveguide; the third waveguide is disposed on the surface of the buried oxide layer, and the second waveguide and the third waveguide are spaced apart along the first direction; The input end of the first waveguide is the first port, and the output end of the first waveguide is the second port; The output of the third waveguide is the third port.

3. The polarization management device according to claim 2, characterized in that, The width of the first waveguide is 0.5μm-1.0μm, including the values ​​at both ends; The width of the second waveguide is 1.5μm-2.5μm, including the values ​​at both ends; The width of the third waveguide is equal to the width of the first waveguide; The gap width between the first waveguide and the second waveguide is 500nm-800nm, including the values ​​at both ends; The gap width between the third waveguide and the second waveguide is equal to the gap width between the first waveguide and the second waveguide.

4. The polarization management device according to any one of claims 1 to 3, characterized in that, Also includes: An electrical signal control component is used to control the electrical signal applied to the ferroelectric thin-film waveguide layer, so that the third port can be selectively used as the polarization state monitoring port or the signal output port.

5. A polarization management method, applied to the polarization management device according to any one of claims 1 to 4, characterized in that, include: The third port can be selectively used as either the polarization state monitoring port or the signal output port; The incident light is input into the first port; When the third port is used as the polarization state monitoring port, the first polarization mode is output from the second port, and the polarization state of the incident light is monitored through the third port; When the third port is used as the signal output port, the first polarization mode is output from the second port and / or the third port.

6. The polarization management method according to claim 5, characterized in that, The monitoring of the polarization state of the incident light through the third port includes: The change in the polarization state of the incident light is monitored by monitoring the change in the output power of the third port.

7. The polarization management method according to claim 5 or 6, characterized in that, The polarization management device includes the electrical signal control component; The step of selectively using the third port as either the polarization state monitoring port or the signal output port includes: By controlling the electrical signal applied to the ferroelectric thin-film waveguide layer, the third port can be selectively used as either the polarization state monitoring port or the signal output port.

8. The polarization management method according to claim 7, characterized in that, The step of selectively using the third port as either the polarization state monitoring port or the signal output port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer includes: By controlling the electrical signal applied to the ferroelectric thin-film waveguide layer to be zero, the third port is made into the polarization state monitoring port.

9. The polarization management method according to claim 7, characterized in that, The step of selectively using the third port as either the polarization state monitoring port or the signal output port by controlling the electrical signal applied to the ferroelectric thin-film waveguide layer includes: By applying the electrical signal to the ferroelectric thin-film waveguide layer, the third port is made into the signal output port.

10. A method for fabricating a polarization management device, characterized in that, include: Provide substrate; A buried oxide layer is formed on the surface of the substrate; A ferroelectric thin-film waveguide layer is formed on the surface of the buried oxide layer; The ferroelectric thin-film waveguide layer includes a first port, a second port, and a third port; the first port is a signal input port for inputting incident light; the incident light includes a first polarization mode and / or a second polarization mode; the second port is a signal output port; the third port is selectively used as a polarization state monitoring port or the signal output port; the polarization state monitoring port is used to monitor the polarization state of the incident light; the first polarization mode is output from the second port and / or the third port; the transmission loss of the second polarization mode in the ferroelectric thin-film waveguide layer is greater than the transmission loss of the first polarization mode in the ferroelectric thin-film waveguide layer. An upper cladding layer is formed on the surface of the ferroelectric thin-film waveguide layer to obtain the polarization management device.

11. The method for fabricating the polarization management device according to claim 10, characterized in that, A ferroelectric thin-film waveguide layer is formed on the surface of the buried oxide layer, comprising: A ferroelectric thin film is deposited on the surface of the buried oxide layer; The ferroelectric thin film is subjected to polarization treatment; The polarized ferroelectric thin film is patterned to form the ferroelectric thin film waveguide layer.

12. The method for fabricating the polarization management device according to claim 10 or 11, characterized in that, After forming the upper cladding layer on the surface of the ferroelectric thin-film waveguide layer, the method further includes: An electrical signal control component is prepared; the electrical signal control component is used to control the electrical signal applied to the ferroelectric thin film waveguide layer, so that the third port can be selectively used as the polarization state monitoring port or the signal output port.

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