Composite modulated optical switch and method of conditioning

Abstract

The application relates to the technical field of optical switches, in particular to a composite-modulation optical switch and a modulation method, which comprises a first silicon nitride waveguide for receiving input light; a second silicon nitride waveguide for receiving output light; a transition waveguide arranged between the first silicon nitride waveguide and the second silicon nitride waveguide; the width of the transition waveguide is smaller than that of the first silicon nitride waveguide and the second silicon nitride waveguide; a first protective layer, the first protective layer at least wraps the transition waveguide, a lithium niobate layer is arranged above the protective layer, and a spacing layer with a certain thickness is formed between the transition waveguide and the lithium niobate layer; metal electrodes are arranged at two ends of the lithium niobate layer, and the metal electrodes are used for connecting a power supply. The composite modulation scheme of the lithium niobate layer and the transition waveguide can reduce the process difficulty of the optical switch on the basis of improving the modulation performance.

Description

Technical Field

[0001] This invention relates to the field of optical switch technology, specifically to a composite modulation optical switch and its modulation method. Background Technology

[0002] An optical switch is an optical device with one or more optional transmission ports, which is used to physically switch or logically operate optical signals in optical transmission lines or integrated optical circuits.

[0003] During the operation of an optical switch, one or more channels in the optical switch need to be modulated with signals.

[0004] For example, patent application CN113900280A discloses a polarization-independent optical switch. The optical switch has a symmetrical structure and includes: a lower cladding layer, a lithium niobate waveguide layer, an upper cladding layer, and a silicon nitride layer. The lithium niobate waveguide layer is integrated above the lower cladding layer, and the silicon nitride layer is above the lithium niobate waveguide layer. The upper cladding layer fills the space between the lithium niobate waveguide layer and the silicon nitride layer. A uniform beam splitting multimode interference coupler and the upper half of the interlayer coupling structure are sequentially etched in the silicon nitride layer along the light propagation direction. The lower half of the interlayer coupling structure and a polarization-independent modulation waveguide are etched in the lithium niobate waveguide layer. Metal electrodes are fabricated on both sides of the polarization-independent modulation waveguide of the lithium niobate waveguide layer, and the positions of the metal electrodes are adjusted according to the modulation characteristics of the lithium niobate waveguide layer.

[0005] For example, patent application CN117092836A discloses an electro-optic switch. This electro-optic switch is fabricated based on electro-optic materials and includes a substrate, a single-mode input waveguide, an interferometer waveguide, a single-mode output waveguide, and a beamsplitter with an adjustable beam splitting ratio. The beamsplitter employs a multimode interference coupler or a dual-mode interferometer structure and utilizes the electro-optic effect of the aforementioned electro-optic material. Specifically, the beamsplitter includes a substrate, a buffer layer, a waveguide core, a cladding layer, and a tuning electrode; the waveguide core is made of a lithium niobate thin film.

[0006] In other words, existing technologies attempt to modulate light using lithium niobate waveguide layers, hoping to leverage the material advantages of lithium niobate to improve modulation speed and reduce modulation loss.

[0007] However, the applicant noted that in practical applications, the modulation speed that lithium niobate waveguides can actually improve is still limited. Therefore, there is an urgent need for a modulation scheme that can further improve the modulation speed. Summary of the Invention

[0008] The purpose of this invention is to provide a composite modulation optical switch that partially solves or alleviates the above-mentioned shortcomings in the prior art, improves the effective modulation speed of lithium niobate, and allows the performance of lithium niobate to be fully utilized in optical switch modulation.

[0009] To solve the aforementioned technical problems, the present invention specifically adopts the following technical solution: A first aspect of the present invention is to provide a composite modulation optical switch, comprising: The first silicon waveguide is used to receive the input light; A second silicon waveguide for receiving the output light; Furthermore, a transition waveguide is provided between the first silicon waveguide and the second silicon waveguide; the width of the transition waveguide is smaller than that of the first silicon waveguide and smaller than that of the second silicon waveguide. A first protective layer is provided, which at least wraps the transition waveguide, and a lithium niobate layer is disposed above the protective layer. A spacer layer of a certain thickness is formed between the transition waveguide and the lithium niobate layer in the first protective layer. The transition waveguide, the spacer layer and the lithium niobate layer form a composite interface. Metal electrodes are provided at both ends of the lithium niobate layer, and the metal electrodes are used to connect to a power source. Specifically, when the input light propagates along the direction from the first silicon waveguide to the transition waveguide, a first portion of the input light enters the lithium niobate layer, and a second portion of the input light is transmitted to the transition waveguide. Furthermore, when the metal electrode is energized, the refractive index of the lithium niobate layer will also change under the action of voltage, thereby modulating the phase of the first part of the light; Subsequently, after the first portion of light and the second portion of light leave the composite interface, they merge in the second silicon waveguide to form the final output light.

[0010] In some embodiments, the material of the first protective layer is silicon oxide.

[0011] In some embodiments, the first portion of light accounts for a first proportion of the input light that is greater than or equal to 30% and less than 100%.

[0012] In some embodiments, the first ratio is greater than or equal to 40%.

[0013] In some embodiments, the first ratio is greater than or equal to 50%.

[0014] In some embodiments, the length of the lithium niobate layer is 3-20 mm; and / or, the width of the first silicon waveguide or the second silicon waveguide is 200-300 nm. In some embodiments, the thickness of the spacer layer is less than 500 nm; In some embodiments, a second protective layer is provided on the lithium niobate layer.

[0015] In some embodiments, the second protective layer covers the metal electrode.

[0016] The present invention also provides a method for adjusting an optical switch, comprising the steps of: S101, providing an optical switch as described in any one of the embodiments; S102: Select the corresponding standard adjustment voltage based on the standard input light intensity selected by the user; S103, the optical switch initiates the modulation process in response to the standard adjustment voltage; S104, during the modulation process, the coupling fast detection index is obtained by monitoring the output light; S105, based on the comparison between the coupling fast detection index and the set coupling index, determine whether the standard adjustment voltage needs to be corrected.

[0017] In some embodiments, S105 includes: Calculate the degree of difference between the stated fast coupling index and the set coupling index; When the degree of difference is less than or equal to the first difference threshold, the coupling rapid detection index continues to be monitored. When the degree of difference is greater than the first difference threshold and less than the second difference threshold, supplementary detection is performed using coupled supplementary detection indicators; When the degree of difference is greater than or equal to the second difference threshold, a voltage regulation step is performed.

[0018] In some embodiments, the coupling supplementary detection index includes: the variation trend of the second harmonic with temperature; correspondingly, the supplementary detection steps include: The amplitudes of the first and second harmonics are measured at the first temperature. At least one second harmonic amplitude is measured at at least one second temperature; The variation trend of the second harmonic with temperature is calculated based on the amplitude of the first and second harmonics and at least one second and second harmonic amplitude. If the voltage change trend increases with increasing temperature, a voltage regulation step is executed; if the voltage change trend remains constant with increasing temperature, an auxiliary suggestion is given to advise the user to check whether the optical fiber or light source is faulty.

[0019] Beneficial technical effects: This application proposes a composite modulation scheme based on lithium niobate, which splits the optical path through a transition waveguide and a lithium niobate layer, allowing the light to be divided into two beams to form a composite beam. This splitting method in the transition waveguide and the lithium niobate layer waveguide can reduce the modulation pressure on the lithium niobate layer to a certain extent.

[0020] From another perspective, it can control the size of the composite modulation optical switch while improving modulation efficiency.

[0021] Furthermore, the applicant also attempts to provide a low-cost, high-efficiency restrictive regulation scheme that can autonomously adjust the voltage at a specific stage to appropriately compensate for the regulation error caused by device drift, while minimizing over-regulation or mis-regulation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0023] Figure 1 This is a schematic diagram of the modulation region of an optical switch in the prior art; Figure 2 This is a schematic diagram of the modulation region of an exemplary optical switch in this application; Figure 3 This is a schematic cross-sectional view of an exemplary modulation region of this application; Figure 4 This is a flowchart illustrating a method in an exemplary embodiment of this application.

[0024] 1. Metal electrode; 2. Lithium niobate layer; 3. Transition waveguide; 4. Silicon layer; 5. First protective layer; 6. Second protective layer; 7. First silicon waveguide; 8. Second silicon waveguide; 9. Modulation waveguide; 10. Output waveguide. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] In this document, suffixes such as "module," "part," or "unit" used to denote elements are used only for the purpose of illustrative purposes and have no specific meaning in themselves. Therefore, "module," "part," or "unit" may be used interchangeably.

[0027] In this document, the terms "upper," "lower," "inner," "outer," "front," "rear," "one end," and "the other end," 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 the present invention and for 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 the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0028] In this document, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] In this document, "and / or" includes any and all combinations of one or more of the listed related items.

[0030] In this article, "multiple" means two or more, that is, it includes two, three, four, five, etc.

[0031] As used in this specification, the term "about" typically means + / -5% of the value, more typically + / -4% of the value, more typically + / -3% of the value, more typically + / -2% of the value, even more typically + / -1% of the value, and even more typically + / -0.5% of the value.

[0032] In this specification, certain embodiments may be disclosed in a range-bound format. It should be understood that this "range-bound" description is merely for convenience and brevity and should not be construed as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered as having specifically disclosed all possible subranges and the individual numerical values ​​within those ranges. For example, a description of the range 1-6 should be considered as having specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the individual numbers within those ranges, such as 1, 2, 3, 4, 5, and 6. This rule applies regardless of the breadth of the range.

[0033] In existing optical switches, there are two modulation schemes: 1) Modulation using silicon waveguides: Figure 1A partial structural schematic diagram of an optical switch is shown. In existing optical switches, an exemplary optical switch includes a modulation region comprising: The first silicon nitride for input light and the second silicon nitride for output light (i.e., output waveguide 10). A modulation waveguide 9 (i.e., a silicon waveguide) is disposed between the first silicon nitride and the second silicon nitride; wherein the silicon nitride is mainly used for light transmission, while the silicon waveguide is mainly used for light modulation.

[0034] Typically, a silicon waveguide is placed on top of the silicon carbide waveguide.

[0035] The modulation process for silicon waveguides and silicon nitride waveguides is as follows: The optical signal is first transmitted through a silicon nitride waveguide. When modulation of the optical signal is required, the optical signal is transitioned from the silicon nitride waveguide to the silicon waveguide and modulated thereon.

[0036] For example, by applying a voltage to a silicon waveguide, the refractive index can be changed using the plasma dispersion effect, thereby altering the phase of light.

[0037] For example, a doped region can be fabricated on a silicon waveguide. Applying a voltage to this region changes the concentration of free carriers inside the silicon waveguide, which in turn causes a change in the refractive index of the silicon material. Consequently, the phase of the light will also change.

[0038] In other words, in the traditional approach, when modulating light, 100% of the light is located on the silicon waveguide.

[0039] 2) Modulation using lithium niobate: For example, CN113900280A discloses a polarization-independent optical switch in which light enters a lithium niobate layer during modulation, is modulated in the lithium niobate layer, and then returns to the silicon nitride waveguide.

[0040] In other words, in this scheme, when the light is modulated, 100% of the light will be located on the lithium niobate layer and fully modulated by the lithium niobate.

[0041] However, the applicant noted that the modulation of lithium niobate has many drawbacks in practical applications: 1) Too large size: Lithium niobate is large in size, which can lead to an oversized optical switch, making it difficult to expand the scale of the switch.

[0042] 2) Actual modulation speed remains difficult to improve: Although lithium niobate material itself has high-speed modulation performance, the actual modulation speed improvement is limited. The applicant found that since the modulation mode of lithium niobate material relies on voltage control, the higher the voltage, the higher the modulation speed. However, higher voltage also places higher demands on the supporting electronic control system. Therefore, in reality, the improvement in modulation speed by lithium niobate is very limited. In contrast to the traditional single modulation mode, this application proposes a composite modulation scheme based on lithium niobate and provides a voltage regulation scheme based on composite interface monitoring for the composite modulation scheme.

[0043] Example 1: like Figure 2 As shown, the modulation region includes: A first silicon waveguide 7 (equivalent to the light input end, or a part of the input end) is used for input light and a second silicon waveguide 8 (equivalent to the light output end, or a part of the output end) is used for output light. A transition region (which can be a silicon nitride waveguide, and therefore can also be called a transition waveguide 3) is provided between the first silicon waveguide 7 and the second silicon waveguide 8, and the waveguide width of the transition region is smaller than the width of the first silicon waveguide 7 and the second silicon waveguide 8 on both sides; and a lithium niobate layer 2 is provided on the transition region.

[0044] In this process, a composite interface is formed between the lithium niobate layer 2 and the transition waveguide 3.

[0045] For example, the first silicon waveguide and the second silicon waveguide are respectively connected to optical fibers to realize the input and output of light.

[0046] Preferably, the lithium niobate layer is disposed on the lower layer of silicon nitride. For example, the lithium niobate layer can be disposed on silicon nitride by bonding.

[0047] Specifically, in this embodiment, some of the light will enter the lithium niobate layer, while some of the light can remain in the silicon nitride waveguide in the transition region. For example, in some embodiments, the light entering the lithium niobate layer is about 30%-100% of the original input light.

[0048] For example, in some embodiments, the light entering the lithium niobate layer is more than 40% of the original light.

[0049] For example, in some embodiments, the light entering the lithium niobate layer is more than 50% of the original light.

[0050] For example, in some embodiments, the light entering the lithium niobate layer is more than 60% of the original light.

[0051] For example, in some embodiments, only a portion of the original light enters the lithium niobate layer, meaning that at least a portion of the light enters the silicon nitride waveguide.

[0052] For example, in some embodiments, the width of lithium niobate is approximately 0.5-2 mm, such as preferably 1 mm.

[0053] For example, in some embodiments, the length of lithium niobate is approximately 3mm-20mm.

[0054] For example, in some embodiments, the width of SiN is approximately 200-300 nm and the thickness is approximately 300-400 nm.

[0055] For example, such as Figure 2 As shown, the optical switch in this embodiment includes: First silicon waveguide 7 for receiving input light; The second silicon waveguide 8 is used to receive the output light; Furthermore, a transition waveguide is provided between the first silicon waveguide 7 and the second silicon waveguide 8; the width of the transition waveguide is smaller than that of the first silicon waveguide 7 and the second silicon waveguide 8. See Figure 3 As shown, the optical switch further includes: a first protective layer 5 (such as a silicon oxide layer), the first protective layer 5 at least wraps the transition waveguide 3 (such as a silicon nitride waveguide), and a lithium niobate layer 2 is disposed above the protective layer, the first protective layer forming a spacer layer of a certain thickness between the transition waveguide and the lithium niobate layer; wherein, the transition waveguide, the spacer layer and the lithium niobate layer sequentially form a composite interface.

[0056] Metal electrodes 1 are provided at both ends of the lithium niobate layer, and the metal electrodes 1 are used to connect to a power source.

[0057] In this embodiment, the composite interface can refer to the region where the lithium niobate layer and the silicon nitride layer are in contact with each other or optically coupled through an intermediate dielectric layer (such as a silicon dioxide cladding). The spacer layer serves both a protective function and a degree of light isolation, separating the light between the lithium niobate layer and the silicon oxide waveguide.

[0058] Specifically, when the input light propagates along the direction from the first silicon waveguide to the transition waveguide, a first portion of the input light enters the lithium niobate layer, and a second portion of the input light is transmitted to the transition waveguide. Furthermore, when the metal electrode is energized, the refractive index of the lithium niobate layer will also change under the action of voltage, thereby modulating the phase of the first part of the light; Subsequently, the first portion of light and the second portion of light are combined in the second silicon nitride waveguide to form the final output light.

[0059] From another perspective, the input light will be synchronously transmitted in both the lithium niobate and silicon nitride waveguides to form a composite light mode (or composite light). When this composite light passes through the composite interface region, a portion of the composite light will undergo a phase change under the modulation of the lithium niobate. Subsequently, after leaving the composite interface region, the light in the lithium niobate layer will return to the silicon nitride waveguide and merge with the original light in the silicon nitride waveguide to form a new output light.

[0060] For example, in some embodiments, the first and second silicon waveguides may be silicon nitride waveguides or silicon oxynitride waveguides.

[0061] For example, in some embodiments, a second protective layer 6 is provided on the lithium niobate layer. Figure 3 As shown, the second protective layer 6 is connected to the first protective layer 5 to cover the lithium niobate layer and the metal electrode 1.

[0062] Figure 3 A cross-sectional schematic diagram of an optical switch in this exemplary embodiment is shown, which includes: a silicon waveguide (or silicon layer 4); a silicon oxide layer (i.e., a first protective layer 5) is disposed above the silicon waveguide, and a silicon nitride layer (i.e., a transition waveguide 3) is disposed inside the silicon oxide layer, which encapsulates the silicon nitride layer, thereby providing a certain degree of protection.

[0063] A lithium niobate layer 2 is disposed above the silicon oxide layer, and metal electrodes 1 are connected to both ends of the lithium niobate layer 2. The metal electrodes are used to apply an adjustable voltage to the lithium niobate. A protective layer (such as a silicon oxide layer, i.e., a second protective layer 6) is wrapped around the lithium niobate layer and the metal electrodes.

[0064] In this embodiment, a certain gap is provided between the lithium niobate layer and the silicon nitride layer, and the length of this gap is preferably within 500 nm.

[0065] By physically separating the lithium niobate layer and the silicon nitride layer with a silicon oxide layer, the optical crosstalk problem between the different layers can be reduced.

[0066] In this embodiment, lithium niobate is used for modulation, which can achieve a higher modulation bandwidth.

[0067] Example 2: This invention provides a voltage regulation method for the aforementioned composite mode optical switch. To facilitate understanding of the operation of this regulation method, the modulation process of the optical switch will be briefly described first.

[0068] First, when the optical switch initiates modulation, a specific voltage (also known as a regulating voltage or modulation voltage) is applied to the lithium niobate layer by energizing the two metal electrodes. This voltage alters the phase of the light passing through the lithium niobate layer, thus regulating the phase of the first portion of the light. Therefore, a phase difference exists between the first and second portions of the light when they are finally combined. When they are combined, interference occurs due to this phase difference, causing a change in the optical power (equivalent to light intensity) of the combined output light, thereby achieving light modulation.

[0069] Therefore, in practical operation, different voltages can be selected to achieve the corresponding modulation purpose based on the final required output light intensity. Furthermore, it is understandable that after the optical switch is fabricated, since the physical modulation architecture (such as the structure of lithium niobate or silicon nitride waveguides) is fixed, the required modulation voltage for the same input light intensity but different output light intensity requirements is usually also fixed. In other words, there is a specific mapping relationship between the output light intensity or phase difference and the modulation voltage. Based on this mapping relationship, in practical operation, the optical switch can autonomously select different voltages according to the actual working objective.

[0070] However, the applicant noted that with prolonged operation of the optical switch, the performance or architecture of its internal components may drift to some extent (e.g., defects may occur at the composite interface). In response, the applicant attempted to provide a low-cost, high-efficiency limiting regulation scheme to appropriately compensate for regulation errors caused by component drift by autonomously adjusting the voltage at specific stages, while minimizing over-regulation or mis-regulation.

[0071] Specifically, see Figure 4 As shown, the method provided in this embodiment includes: S101, providing an optical switch as described in any of the above embodiments; S102: Select the corresponding standard adjustment voltage based on the standard input light intensity selected by the user; S103, the optical switch initiates the modulation process in response to the standard adjustment voltage; S104, During the modulation process, the output light is monitored to obtain the coupling fast detection index; S105, based on the comparison between the coupling fast detection index and the set coupling index, determine whether the standard adjustment voltage needs to be corrected.

[0072] For example, in some embodiments, at least one set of standard test conditions can be set for the optical switch. This set of standard test conditions includes: standard input light intensity, standard adjustment voltage, and standard output light intensity (i.e., output light power). For instance, when the optical switch is set to operate within a reasonable range, when it receives a standard input light intensity and modulates it with a standard adjustment voltage, the corresponding output light power has a standard value. However, if, when using the same standard input light intensity and standard adjustment voltage, the final output light power deviates from the standard value, it may indicate that the optical switch is outside its reasonable operating range, suggesting a potential malfunction or hidden danger.

[0073] It is understood that the adjustment method in this invention can be applied to the factory setting stage of the optical switch, or it can be periodically adjusted during the operation of the optical switch.

[0074] For example, in some embodiments, the coupling fast detection index can be any of the following: the magnitude of the insertion loss change, the magnitude of the extinction ratio change.

[0075] Insertion loss (IL) is the power lost when light travels from the input to the output of an optical switch. The power loss can be calculated by comparing the standard output light intensity determined under standard test conditions with the measured output light intensity.

[0076] Specifically, the magnitude of the insertion loss variation can be defined as the magnitude of the insertion loss variation over time or temperature.

[0077] For example, the insertion loss of an optical switch can be continuously measured at at least two temperature points, thereby calculating the trend of the insertion loss of the optical switch at at least two temperature points.

[0078] Among them, the extinction ratio refers to the ratio of the optical power in the "on" state to the optical power in the "off" state measured at the output port of the optical switch, and the trend of the extinction ratio refers to the extent to which the extinction ratio changes with environmental conditions (such as time or temperature).

[0079] In some embodiments, S105 includes: Calculate the degree of difference between the stated fast coupling index and the set coupling index; When the degree of difference is less than or equal to the first difference threshold, the coupling rapid detection index continues to be monitored. When the degree of difference is greater than the first difference threshold and less than the second difference threshold, supplementary detection is initiated using coupled supplementary detection indicators (i.e., supplementary detection strategy is executed). When the degree of difference is greater than or equal to the second difference threshold, a voltage regulation step is performed.

[0080] In some embodiments, the voltage regulation step involves: correcting the standard regulation voltage until the output light meets a set condition (e.g., the output light intensity meets a set standard intensity), and recording the current correction condition. This correction condition can be a correction coefficient, such as corrected regulation voltage = standard regulation voltage * correction coefficient. This correction coefficient can be used or referenced in subsequent modulation processes.

[0081] Similarly, taking the trend of insertion loss as an example, the graded evaluation mechanism in this embodiment is explained as follows: In this embodiment, if the trend of insertion loss (hereinafter referred to as the trend) is very small (e.g., within the first difference threshold), it can be considered as normal measurement noise and no additional adjustment is required. When the trend shows relatively obvious signs, but still does not exceed the red line (e.g., greater than the first difference threshold, but still less than the second difference threshold), the supplementary inspection strategy for the composite interface will be initiated first, without directly correcting the adjustment voltage. Alternatively, when the trend is already very obvious (e.g., exceeding the second difference threshold), then direct correction of the adjustment voltage is allowed.

[0082] For example, in some embodiments, the magnitude of the insertion loss variation is the magnitude of the insertion loss variation over time. For example, after the optical switch has been operating for a period of time, its coupling efficiency can be monitored periodically. For instance, standardized monitoring can be set up after 7 days, 14 days, and 21 days of optical switch operation, and the insertion loss variation during these periods can be recorded. If a significant increase in insertion loss is detected, voltage regulation can be considered.

[0083] It is understood that the test cycle in this embodiment can be set by the user. For example, it can follow the normal operation of the optical switch and record multiple test points at intervals. Alternatively, the user can choose to pause the normal operation of the optical switch during non-busy periods and complete the test of the optical switch briefly and intensively.

[0084] In this embodiment, the supplementary inspection strategy is to further activate other auxiliary indicators related to coupling efficiency and re-inspect the optical switch in order to eliminate, as far as possible, situations that are highly likely to be caused by other faults or error factors (e.g., avoiding voltage regulation due to light source or fiber failure).

[0085] In this embodiment, voltage adjustment will employ a gradient adjustment method. Specifically, during the voltage adjustment step, multiple adjustments can be made step-by-step to determine a suitable voltage adjustment value. For example, when the actual output optical power is observed to be too low, the original standard adjustment voltage can be appropriately increased to obtain a first correction voltage (the increase can be preset). If the first correction voltage still does not meet the detection condition (i.e., the actual output optical power still does not reach the standard output optical intensity), the first correction voltage is further appropriately increased to obtain a second correction voltage. This process continues until the Nth correction voltage meets the detection condition, at which point the Nth correction voltage is used as the final correction adjustment voltage.

[0086] In this embodiment, by using gradient adjustment, the magnitude of the correction voltage can be limited to a certain extent, avoiding additional faults such as nonlinear distortion, power consumption surge, or even dielectric layer breakdown caused by excessive correction voltage. At the same time, moderately limiting the voltage magnitude also helps maintain high modulation efficiency.

[0087] In this embodiment, the gradient adjustment scheme is preferably limited to activation only in special stages (such as when the trend of change is very obvious, or when other faults are properly eliminated through supplementary inspection). This allows the appropriate adjustment voltage to be found autonomously through gradient adjustment, while avoiding over-adjustment of the voltage in non-composite fault scenarios (i.e., errors caused by non-composite interface defects, such as fiber aging).

[0088] For example, when the light source ages or the optical fiber bends, problems such as decreased input optical power or increased output coupling loss may occur. For instance, when the light source ages, the input optical power may fail to reach the expected standard input light intensity (e.g., it may only be about 80% of the original standard input light intensity), thus reducing the final output optical power (e.g., the measured output optical power may only be about 70% of the standard output light intensity). In this case, even increasing the voltage will not restore the output optical power to the standard value. However, this embodiment aims to use a low-cost fast detection method to quickly determine the error. In this situation, it may be difficult to distinguish the specific root cause of the fault, so a voltage adjustment step may be initiated when the light source is aging. Furthermore, since the voltage adjustment step is a gradient adjustment, the measured output optical power may slightly increase after several adjustments (e.g., to 75% of the standard output light intensity), which may initially mislead the gradient adjustment procedure. That is, it may seem that the adjustment can increase the light intensity, but in reality, even after multiple cycles of adjustment, it cannot be restored to the final standard output light intensity. This misleading information may lead to an unlimited increase in the adjustment voltage, which not only fails to solve the problem but also introduces new risks due to excessive voltage.

[0089] The hierarchical and segmented restrictive adjustment mechanism based on coupling efficiency observation in this embodiment can mitigate the risk of misadjustment caused by non-coupling efficiency through segmented screening and hierarchical setting of observation angles. In other words, this embodiment performs special screening at at least two levels: 1) Select coupling detection indicators (such as coupling fast detection and coupling supplementary detection indicators) that are more correlated with coupling efficiency, so as to observe the quality of the composite interface with the help of coupling detection indicators, thereby reducing the interference of other observation factors or changing factors to a certain extent.

[0090] For example, insertion loss is extremely sensitive to the efficiency of the coupling interface; once the coupling efficiency of the interface changes, it is more likely to cause significant fluctuations than normal changes. Another example is that when the temperature changes drastically, the thermal stress between the interfaces may be amplified, leading to an increase in the interfacial spacing and thus a change in the light field distribution (e.g., instead of 50% of the light entering lithium niobate, only about 45% actually enters), which may cause significant fluctuations in the extinction ratio (ER).

[0091] 2) First, select rapid testing methods with minimal intervention to quickly inspect the composite interface. For example, insertion loss and extinction ratio are mainly monitored at the output end (e.g., measuring optical power), thus achieving low-cost rapid testing. Furthermore, when the rapid testing indicators show some anomalies, but the degree of anomaly is relatively low, then an interventional supplementary testing strategy targeting the composite interface is initiated. Therefore, through step-by-step and tiered testing, the reliability and effectiveness of the testing can be improved while controlling the degree of intervention (i.e., reducing testing costs).

[0092] In some embodiments, the coupling supplementary detection index includes: the second harmonic variation trend. Correspondingly, the supplementary detection steps include: The amplitudes of the first and second harmonics are measured at a first temperature (typically room temperature, such as approximately 25°C); At least one second harmonic amplitude is measured at at least one second temperature; The variation trend of the second harmonic component with temperature is calculated based on the amplitude of the first and second harmonics and at least one second harmonic amplitude. If the trend shows that the change increases with increasing temperature, then the voltage regulation step is executed; if the trend shows that the change remains constant with temperature, then auxiliary suggestions are given, such as suggesting that the user check whether there are quality problems with the optical fiber or light source at the output end, such as whether the optical fiber is bent or contaminated, or whether the light source is aging or has other faults.

[0093] For example, the trend of the second harmonic component with temperature can be characterized by the proportion of increase or decrease of the second harmonic component within a unit temperature range.

[0094] For example, the trend of the second harmonic component changing with temperature over the entire cycle can also be characterized by the average of the increase or decrease ratios over multiple unit temperature intervals.

[0095] Preferably, the first temperature is lower than the second temperature, meaning that the low temperature can be measured first and then the high temperature can be measured, thereby improving the detection efficiency.

[0096] It should be noted that maintaining constancy in this embodiment does not mean that the trend of change is necessarily zero, but rather that the trend of change fluctuates only within a very small range. For example, if the magnitude of change (such as the increase or decrease ratio) is less than the set range, it is tended to be considered to be in a constant state.

[0097] For example, the procedure for supplementary detection based on the second harmonic is as follows: First, at 25°C, a small-amplitude, low-frequency sinusoidal pilot signal (frequency f) is superimposed on the regulated voltage. Then, the amplitude A1 of the second harmonic component at frequency 2f in the output light is detected through spectrum analysis or a lock-in amplifier. Next, the temperature is raised to approximately 60°C, and the same sinusoidal pilot signal is again added to the regulated voltage. The amplitude A2 of the second harmonic component is recorded. If A2 is significantly larger than A1, it is considered that the second harmonic component increases with increasing temperature.

[0098] Furthermore, in this embodiment, when the fast detection index appears in an ambiguous range, intervention detection is performed through the second harmonic (i.e., intervention conditions are directly set in the voltage, i.e., a sinusoidal pilot signal is superimposed), which can directly evaluate whether there is nonlinear distortion at the composite interface, thereby helping to further eliminate interference from non-interface factors.

[0099] In fact, this embodiment is based on a segmented and graded conservative correction strategy, which aims to compensate for the modulation deficiency caused by the composite interface as much as possible, while avoiding over-adjustment (such as excessively high voltage) or misadjustment. That is, it avoids new errors caused by high voltage (such as additional offset caused by high operating temperature).

[0100] It should be noted that when optical switch performance drifts, the usual recommendation is to increase the adjustment voltage. However, in the composite modulation mode used in this application, since the modulation pressure is transferred to the lithium niobate layer, and the lithium niobate layer needs to achieve full optical power modulation based on partial optical modulation, a relatively high voltage is required to meet this requirement. However, excessively high voltage can also easily lead to excessive power consumption and heat generation, thereby exacerbating the stress risk at the composite interface (such as causing cracking of the composite interface).

[0101] In response, this embodiment provides a restrictive adjustment mechanism for composite interfaces, namely, restrictively guiding the increase of voltage. This enables autonomous correction under high probability errors caused by composite interfaces, while avoiding overcorrection (such as increasing voltage but failing to solve the error, and instead causing additional hidden dangers due to excessive voltage).

[0102] The adjustment method in this embodiment can be used for factory adjustment of optical switches. Therefore, this method can correct subtle deviations between manufacturing and design processes by adjusting the adjustment voltage.

[0103] It is important to understand that the optical switch in this embodiment employs a modulation architecture combining lithium niobate and silicon nitride waveguides. However, due to the significant difference in the thermal expansion coefficients of lithium niobate and silicon nitride waveguides, the composite process places extremely high demands on it. Even slight deviations in the process can easily lead to drift in the optical switch during operation, such as cracks forming at the composite interface.

[0104] For example, in an exemplary optical switch embodiment, the proportion of light in the lithium niobate layer is 50% (corresponding to the first portion of light), and correspondingly, the proportion of light in the silicon nitride waveguide (i.e., transition waveguide) is 50% (corresponding to the second portion of light). Therefore, when the first portion of light is modulated using a first voltage, the final output light can maintain a first intensity.

[0105] However, after a period of operation, the interface layer (e.g., the protective layer) between lithium niobate and the silicon nitride waveguide may experience local delamination due to defects (such as voids generated during the manufacturing process, or crack changes caused by inconsistent thermal expansion coefficients). In this case, only about 45% of the light actually passes through the lithium niobate layer, while the remaining approximately 55% is transmitted through the silicon nitride waveguide. The decrease in the proportion of light passing through the lithium niobate layer means a reduction in the proportion of the optical field effectively participating in electro-optic modulation. To achieve the same phase change (e.g., π), this embodiment will use a stronger electric field for compensation. That is, in this embodiment, a higher voltage (i.e., increasing the first voltage) will be required to appropriately compensate for the error caused by the defects at the composite interface.

[0106] The purpose of this invention is to specifically adjust for quality defects at composite interfaces, while avoiding over-adjustment that could lead to the concealment or neglect of other faults. For example, the applicant has noted that when the light source ages or the optical fiber bends, the power (or intensity) of the final output light may also decrease, and the feedback in the coupling loss index may exhibit a similar phenomenon to the delamination of the composite interface. However, through the aforementioned step-by-step, segmented detection mechanism, the interference of other non-composite interface faults on the adjustment process can be appropriately reduced.

[0107] It should be noted that, in this document, 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 a process, method, article, or apparatus. Unless otherwise specified, 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 that element.

[0108] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a computer terminal (which may be a mobile phone, computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0109] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A composite modulation optical switch, characterized in that, include: The first silicon waveguide used to receive the input light; A second silicon waveguide for receiving the output light; Furthermore, a transition waveguide is provided between the first silicon waveguide and the second silicon waveguide; the width of the transition waveguide is smaller than that of the first silicon waveguide and smaller than that of the second silicon waveguide. A first protective layer is provided, which at least wraps the transition waveguide, and a lithium niobate layer is disposed above the protective layer. A spacer layer of a certain thickness is formed between the transition waveguide and the lithium niobate layer in the first protective layer. The transition waveguide, the spacer layer and the lithium niobate layer form a composite interface. Metal electrodes are provided at both ends of the lithium niobate layer, and the metal electrodes are used to connect to a power source. Specifically, when the input light propagates along the direction from the first silicon waveguide to the transition waveguide, a first portion of the input light enters the lithium niobate layer, and a second portion of the input light is transmitted to the transition waveguide. Furthermore, when the metal electrode is energized, the refractive index of the lithium niobate layer will also change under the action of voltage, thereby modulating the phase of the first part of the light; Subsequently, after the first portion of light and the second portion of light leave the composite interface, they merge in the second silicon waveguide to form the final output light.

2. The optical switch according to claim 1, characterized in that, The material of the first protective layer is silicon oxide.

3. The optical switch according to claim 1, characterized in that, The first portion of light accounts for a first proportion of the input light that is greater than or equal to 30% and less than 100%.

4. The optical switch according to claim 3, characterized in that, The first proportion is greater than or equal to 40%.

5. The optical switch according to claim 3, characterized in that, The first proportion is greater than or equal to 50%.

6. The optical switch according to claim 1, characterized in that, The length of the lithium niobate layer is 3-20 mm; and / or the width of the first silicon waveguide or the second silicon waveguide is 200-300 nm. And / or, the thickness of the spacer layer is less than 500 nm; And / or, a second protective layer is provided on the lithium niobate layer.

7. The optical switch according to claim 6, characterized in that, The second protective layer covers the metal electrode.

8. A method for adjusting an optical switch, characterized in that, Including the following steps: S101, providing an optical switch as described in any one of claims 1-7; S102: Select the corresponding standard adjustment voltage based on the standard input light intensity selected by the user; S103, the optical switch initiates the modulation process in response to the standard adjustment voltage; S104, during the modulation process, the coupling fast detection index is obtained by monitoring the output light; S105, based on the comparison between the coupling fast detection index and the set coupling index, determine whether the standard adjustment voltage needs to be corrected.

9. The method according to claim 8, characterized in that, S105 includes: Calculate the degree of difference between the stated fast coupling index and the set coupling index; When the degree of difference is less than or equal to the first difference threshold, the coupling rapid detection index continues to be monitored. When the degree of difference is greater than the first difference threshold and less than the second difference threshold, supplementary detection is performed using coupled supplementary detection indicators; When the degree of difference is greater than or equal to the second difference threshold, a voltage regulation step is performed.

10. The method according to claim 9, characterized in that, The coupling supplementary detection index includes: the variation trend of the second harmonic with temperature; correspondingly, the supplementary detection steps include: The amplitudes of the first and second harmonics are measured at the first temperature. At least one second harmonic amplitude is measured at at least one second temperature; The variation trend of the second harmonic with temperature is calculated based on the amplitude of the first and second harmonics and at least one second and second harmonic amplitude. If the voltage change trend increases with increasing temperature, a voltage regulation step is executed; if the voltage change trend remains constant with increasing temperature, an auxiliary suggestion is given to advise the user to check whether the optical fiber or light source is faulty.

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