Multi-core optical attenuator, method for optical attenuation adjustment thereof, and multi-core optical fiber attenuation system

Abstract

The application discloses a multi-core optical attenuator, an optical attenuation adjusting method thereof and a multi-core optical fiber attenuation system, and relates to the technical field of optical attenuators.The multi-core optical attenuator comprises a multi-core optical fiber having a plurality of cores; a plurality of grating formation areas arranged along the axial direction of the multi-core optical fiber; each grating formation area is used for forming a long-period grating in the multi-core optical fiber; the long-period grating is phase-matched and coupled with the fundamental mode of the corresponding core in the multi-core optical fiber at a preset working wavelength, so as to couple the signal light of the corresponding core to a cladding mode and attenuate the signal light; wherein the periods of the grating formation areas are different and correspond to different cores respectively; and a controller is coupled with each grating formation area and used for independently adjusting the coupling strength of each grating formation area to the corresponding core, so as to independently control the attenuation amount of each core. In this way, independent addressing and continuous attenuation adjustment of each core can be realized under the premise of not being demultiplexed into single-core optical fibers, and the reliability of the device is improved.

Description

Technical Field

[0001] This invention relates to the field of optical attenuator technology, and in particular to a multi-core optical attenuator and its optical attenuation adjustment method, and a multi-core optical fiber attenuation system. Background Technology

[0002] As the transmission capacity of single-mode fiber approaches the limit of nonlinear capacity, space-division multiplexing (SDM) technology has become an important direction for improving capacity. Multi-core fiber (MCF) constructs multiple spatial channels by setting multiple independent fiber cores within a shared cladding. In practical systems, MCF requires online devices such as variable optical attenuators (VOAs) for optical power management. However, in traditional engineering practice, MCF is usually demultiplexed into multiple single-core fibers using fan-in and fan-out devices, and then connected to single-core VOAs for processing. This results in a linear increase in the number of devices, size, insertion loss, and cost with the number of cores, and the multiple fusion splices and connection points reduce reliability. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-core optical attenuator and its optical attenuation adjustment method, as well as a multi-core optical fiber attenuation system, which can achieve independent addressing and continuous attenuation adjustment of each fiber core without demultiplexing it into a single-core optical fiber, thereby improving device reliability.

[0004] To address the aforementioned technical problems, this invention provides a multi-core optical attenuator, comprising: Multi-core optical fiber, which has multiple fiber cores; Multiple grating forming regions are sequentially arranged along the axial direction of the multi-core optical fiber; each grating forming region is used to form a long-period grating in the multi-core optical fiber, and the long-period grating is phase-matched with the fundamental mode of the corresponding fiber core in the multi-core optical fiber at a preset operating wavelength, so as to couple the signal light of the corresponding fiber core to the cladding mode for attenuation; wherein, the periods of each grating forming region are different, and they correspond to different fiber cores respectively; The controller, coupled to each of the grating forming regions, is used to independently adjust the coupling strength of each grating forming region to its corresponding fiber core, so as to independently control the attenuation of each fiber core.

[0005] To address the aforementioned technical problems, the present invention also provides a multi-core optical fiber attenuation system, comprising: the multi-core optical attenuator as described above; and further comprising: A fan-in device is disposed at the input end of the multi-core optical fiber; the multiple output ports of the fan-in device are optically coupled to multiple fiber cores respectively; the fan-in device is used to inject each input optical signal into the corresponding fiber core respectively; A fan-out device is disposed at the output end of the multi-core optical fiber, and the multiple input ports of the fan-out device are respectively optically coupled to the multiple fiber cores; the fan-out device is used to demultiplex the multiple optical signals output from the multiple fiber cores and output them respectively.

[0006] To address the aforementioned technical problems, the present invention also provides a method for adjusting the optical attenuation of a multi-core optical attenuator, comprising: Multiple grating forming regions are arranged along the axial direction of the multi-core optical fiber; each grating forming region has a different period, and each grating forming region is used to form a long-period grating in the multi-core optical fiber; At a preset operating wavelength, the fundamental mode of the corresponding fiber core in the multi-core optical fiber is coupled to the cladding mode using the long-period grating, so that the signal light of the corresponding fiber core is attenuated. The coupling strength of each grating forming region to its corresponding fiber core is independently adjusted using a controller, thereby independently controlling the attenuation of each fiber core.

[0007] The beneficial effects of the present invention are as follows: The multi-core optical attenuator provided by the present invention sets multiple grating forming regions arranged sequentially along the axial direction on the multi-core optical fiber. Each grating forming region has a different grating period, so that each grating forming region is only phase-matched coupled with the fundamental mode of the corresponding fiber core at a preset operating wavelength, coupling the signal light of the fiber core to the cladding mode for attenuation. At the same time, grating forming regions with different periods correspond to different fiber cores, realizing core-by-core addressing. The controller is coupled to each grating forming region and independently adjusts the coupling strength of each grating forming region, so that the attenuation of each fiber core can be set and controlled individually. Thus, independent and continuous attenuation adjustment of each fiber core is achieved without demultiplexing the multi-core optical fiber into a single-core optical fiber. Furthermore, the number and size of devices are greatly reduced, insertion loss and cost are significantly reduced, reliability is improved, and the spatial integration advantages of space division multiplexing are retained. The above-mentioned multi-core optical attenuator has no fiber core end face interruption and no free space optical path throughout the entire process, has high return loss and does not require optical path alignment.

[0008] In addition, the present invention also provides a corresponding multi-core optical fiber attenuation system and optical attenuation adjustment method for multi-core optical attenuators, which have the same or corresponding technical features as the multi-core optical attenuators mentioned above, and have the same effect. Attached Figure Description

[0009] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1This is a schematic diagram of the structure of a multi-core optical attenuator provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the overall structure of the four-core optical attenuator provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure of a heterogeneous four-core optical fiber provided in an embodiment of the present invention; Figure 4 A schematic diagram of the transmission spectrum and isolation of each fiber core under the action of a single long-period grating provided in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the adjustable range of fiber core attenuation as a function of the corrugated pressure plate pressing amount, provided in an embodiment of the present invention. Figure 6 This is a flowchart of the optical attenuation adjustment method for a multi-core optical attenuator provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the structure of a multi-core optical fiber attenuation system provided in an embodiment of the present invention. Detailed Implementation

[0011] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0012] It should be noted that, in the description of this invention, 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. The terms "first," "second," etc., used in this invention are used to distinguish similar objects and are not used to describe a specific order or sequence.

[0013] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] An embodiment of the present invention provides a multi-core optical attenuator. Figure 1 This is a schematic diagram of the structure of a multi-core optical attenuator provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the multi-core optical attenuator includes: Multi-Core Fiber (MCF) 1, has multiple fiber cores; Multiple grating forming regions are arranged sequentially along the axis of the multi-core optical fiber 1. Each grating forming region is used to form a long-period grating in the multi-core optical fiber 1. The long-period grating is phase-matched with the fundamental mode of the corresponding fiber core in the multi-core optical fiber 1 at a preset working wavelength to couple the signal light of the corresponding fiber core to the cladding mode for attenuation. The periods of each grating forming region are different and correspond to different fiber cores. Controller 2 is coupled to each grating forming region and is used to independently adjust the coupling strength of each grating forming region to its corresponding fiber core, so as to independently control the attenuation of each fiber core.

[0015] It should be noted that multi-core fiber 1 refers to an optical fiber containing multiple independent cores within a single shared cladding. A long-period grating (LPG) is a periodic perturbation of refractive index or stress with a period on the order of tens to hundreds of micrometers introduced along the fiber axis. At the resonant wavelength that satisfies the phase-matching condition, it couples the core fundamental mode to the cladding mode, which propagates in the same direction. The fundamental mode is the lowest-order mode propagating in an optical fiber; under single-mode conditions, it is LP. 01 Cladding modes are modes that propagate within the fiber cladding, their energy being transmitted within the cladding and unable to propagate stably along the fiber core. Phase-matched coupling refers to the resonant transfer of energy from the fiber core fundamental mode to the cladding mode when phase-matching conditions are met, forming a coupling process from the fiber core fundamental mode to the co-propagating cladding mode. In this invention, each grating forming region and its corresponding fiber core satisfy the phase-matching condition at a preset operating wavelength, thereby achieving selective energy transfer from the fiber core fundamental mode to the cladding mode. The signal light coupled to the cladding mode is lost because it cannot propagate stably within the cladding, resulting in attenuation at that resonant wavelength.

[0016] In the multi-core optical attenuator provided in this embodiment of the invention, multiple grating forming regions arranged sequentially along the axial direction are set on the multi-core optical fiber 1. Each grating forming region has a different grating period, so that each grating forming region is only phase-matched coupled with the fundamental mode of the corresponding fiber core at a preset operating wavelength, and the signal light of the fiber core is coupled to the cladding mode for attenuation. At the same time, grating forming regions with different periods correspond to different fiber cores, realizing core-by-core addressing. The controller 2 is coupled to each grating forming region and independently adjusts the coupling strength of each grating forming region, so that the attenuation of each fiber core can be set and controlled individually. Thus, independent and continuous attenuation adjustment of each fiber core is achieved without demultiplexing the multi-core optical fiber 1 into a single-core optical fiber. Furthermore, the number and size of devices are greatly reduced, insertion loss and cost are significantly reduced, reliability is improved, and the spatial integration advantages of space division multiplexing are retained. The multi-core optical attenuator has no fiber core end face interruption and no free space optical path throughout the entire process, has high return loss and does not require optical path alignment.

[0017] Furthermore, in a specific implementation, in the multi-core optical attenuator provided in the embodiments of the present invention, the multi-core optical fiber 1 can be a heterogeneous multi-core optical fiber, and the effective refractive index of the fundamental mode of each core of the heterogeneous multi-core optical fiber is different; at a preset operating wavelength, each grating forming region and the fundamental mode of the corresponding core satisfy the phase matching condition, while each grating forming region and the fundamental modes of the other cores among the multiple cores except the corresponding core do not satisfy the phase matching condition.

[0018] In practice, heterogeneous multi-core fiber refers to a multi-core fiber in which the refractive index profile or effective refractive index of each core is intentionally designed to be different from the others. The phase-matching condition refers to the relationship between the grating period Λ and the operating wavelength λ, and the effective refractive index n of the fiber core's fundamental mode. co cladding mode effective refractive index n cl The relationship between them satisfies Λ=λ / (n) co -n cl The relationship between the core fundamental mode and the cladding mode is as follows: Under this condition, the propagation constants of the core fundamental mode and the cladding mode are equal, and the core fundamental mode and the cladding mode achieve phase synchronization.

[0019] In this invention, by designing each fiber core to have a different effective refractive index of the fundamental mode, each fiber core possesses its own unique phase matching condition. When the period of a certain grating forming region is set to a specific value, at a preset operating wavelength, this period can only enable the fundamental mode of the fiber core corresponding to that specific value to satisfy the phase matching condition, while other fiber cores, due to their different effective refractive indices of the fundamental mode, do not satisfy the phase matching condition at this period, and therefore no coupling attenuation occurs.

[0020] Taking a four-core optical fiber as an example, the effective refractive indices of the fundamental mode of the four cores are designed to be approximately 1.443875, 1.444079, 1.444282, and 1.444480, respectively. The difference in effective refractive index of the fundamental mode between adjacent cores is approximately 2 × 10⁻⁶. -4 Although the difference is small, it is sufficient to give each fiber core a different phase-matching wavelength. The period of each grating forming region is set to a different value corresponding to this difference, so that at the preset operating wavelength, each grating forming region causes attenuation only in the corresponding fiber core. This makes it possible to address one fiber core per period, with an isolation of more than 30 dB between each fiber core at the preset operating wavelength.

[0021] Furthermore, in a specific implementation, in the multi-core optical attenuator provided in the embodiments of the present invention, the grating forming region can be a mechanically inductive long-period grating forming region; the mechanically inductive long-period grating forming region can include a pressure-applying element and a driving mechanism; the pressure-applying element is disposed toward the multi-core optical fiber 1, and the pressure-applying element is used to apply periodic pressure to the multi-core optical fiber 1 to induce periodic perturbations in the refractive index in the multi-core optical fiber 1; the driving mechanism is coupled to the controller 2, and the output end of the driving mechanism is connected to the pressure-applying element, and the driving mechanism is used to drive the pressure-applying element to change the magnitude of the pressure applied to the multi-core optical fiber 1 in response to the command of the controller 2.

[0022] In implementation, the mechanically inductive long-period grating is a long-period grating that can be loaded and unloaded mechanically induced on an optical fiber. The pressure-applying element is positioned facing the multi-core optical fiber 1, and its surface facing the fiber has a periodic undulating structure. When the driving mechanism drives the pressure-applying element to press against the multi-core optical fiber 1, the periodic undulating structure of the pressure-applying element applies periodic pressure to the fiber, causing periodic micro-bending deformation in the axial direction, thereby inducing periodic refractive index perturbations within the fiber, forming a long-period grating. The driving mechanism is coupled to a controller 2. The control signal from the controller 2 is converted into a mechanical driving force by the driving mechanism, changing the pressure between the pressure-applying element and the multi-core optical fiber 1. When the applied pressure increases, the amplitude of the refractive index perturbation in the fiber increases accordingly, and the coupling coefficient of the long-period grating increases; when the pressure decreases, the coupling coefficient decreases; when the pressure is unloaded to zero, the fiber recovers its deformation, the refractive index perturbation disappears, and the grating returns to a lossless state. Therefore, by sending commands from the controller 2 to change the driving force of the driving mechanism, the coupling strength of the long-period grating can be continuously adjusted, thereby continuously adjusting the attenuation of the corresponding fiber core. This mechanical induction method has the advantages of repeated loading and unloading, continuous adjustment, and reset to zero loss. Moreover, the entire optical path is an all-fiber structure with no fiber core end face interruption and high return loss.

[0023] It should be added that this invention can use a permanently written long-period grating to replace the mechanically inductive grating. Specifically, a multi-period superimposed long-period grating is directly written into each core of the multi-core fiber 1 using ultraviolet laser, carbon dioxide laser, or femtosecond laser core-by-core writing. The coupling strength is then tuned using thermo-optical methods (changing the refractive index by heating) or tapering methods (changing the grating period by applying axial stress to draw the fiber into a tapered shape). This scheme can also achieve core-by-core addressing and continuous attenuation adjustment, but once the grating is written, it is permanent and cannot be unloaded.

[0024] Furthermore, this invention can also use inter-core coupled long-period gratings to replace mechanically inductive gratings. Specifically, the period of the grating forming region is taken as the beat length between two adjacent fiber cores, causing the fundamental mode of the signal fiber core to resonantly couple to a dedicated high-loss dumping core. This dumping core dissipates the signal light energy through leakage, and the amount transferred is the attenuation. Each fiber core pair uses its own different period to achieve selective addressing. This scheme is suitable for multi-core optical fibers with specific core layouts.

[0025] Furthermore, in a specific implementation, in the multi-core optical attenuator provided in the embodiments of the present invention, the pressure-applying element can be a pressure plate with a periodic corrugated structure; the driving mechanism can be an actuator. The actuator can be used to drive the pressure plate to be pressed vertically into the multi-core optical fiber 1; the amount of pressing between the pressure plate and the multi-core optical fiber 1 is adjusted by the actuator.

[0026] Accordingly, the multi-core optical attenuator may also include an angular registration structure disposed between the multi-core optical fiber 1 and the pressure plate; the angular registration structure can be used to fix the angular orientation relationship between the pressure direction of the pressure plate and the core layout of the multi-core optical fiber 1.

[0027] In implementation, a pressure plate with a periodic corrugated structure has equally spaced periodic corrugations on its surface facing the multi-core optical fiber 1. The spacing of these corrugations corresponds to the period of the long-period grating of the pressure plate. An actuator (such as a piezoelectric actuator, stepper motor, miniature hydraulic cylinder, or electromagnet drive mechanism) drives the pressure plate to press vertically into the multi-core optical fiber 1. The amount of pressure applied between the pressure plate and the multi-core optical fiber 1 determines the magnitude of the pressure applied to the optical fiber, thereby determining the amplitude of the refractive index disturbance and the coupling strength. The multi-core optical fiber 1 is placed on a support base, and the pressure plate presses down on the optical fiber from above, with the optical fiber located between the pressure plate and the support base. An angular registration structure is used to fix the angular orientation relationship between the pressure direction of the pressure plate and the core layout of the multi-core optical fiber 1. This structure can be an orientation reference plane located on the outer edge of the multi-core optical fiber 1, a non-circular cladding structure, or a marker core within the optical fiber. The angular registration structure ensures that the multi-core fiber 1 does not rotate relative to the pressure plate in the axial direction, thus ensuring that the pressure direction of the pressure plate is always aligned with the target fiber core, avoiding coupling efficiency fluctuations caused by angular drift of the fiber core. In this embodiment, taking a four-core fiber as an example, the angular registration structure uses a flat sectional surface located at the bottom of the cladding outer edge as the orientation reference plane. This flat sectional surface has a fixed angular positional relationship with the square arrangement of the four fiber cores, ensuring that the pressure direction of each pressure plate always maintains a fixed angle with the four-core layout, thereby ensuring stable coupling efficiency of each grating forming region to its corresponding fiber core.

[0028] It should be added that the multi-core optical fiber 1 of the present invention can also be a homogeneous multi-core optical fiber, in which case a single mechanically induced long-period grating with rotatable azimuth can be used. Specifically, for homogeneous multi-core optical fibers with the same or substantially the same effective refractive index of the fundamental mode in each core, a mechanically induced long-period grating that can rotate around the fiber axis is set. By changing the pressure azimuth angle of the grating, directional selective attenuation is achieved according to the angular position of each core relative to the bending plane. This scheme can address different cores at different times by rotating the azimuth angle, and is suitable for application scenarios with high cost or volume requirements.

[0029] Furthermore, in a specific implementation, the multi-core optical attenuator provided in the embodiments of the present invention may further include: a detector, disposed at the output end of the multi-core optical fiber 1, for detecting the output optical power of each fiber core; the input end of the controller 2 is coupled to the output end of the detector, and the controller 2 is used to output driving signals to each grating forming region according to the output optical power, so as to adjust the coupling strength of each grating forming region respectively, so that the output optical power of each fiber core tends to be consistent.

[0030] In implementation, a detector is positioned at the output end of the multi-core fiber 1. It performs beam-splitting tap detection on the optical signals of each fiber core at the output end to obtain the actual output optical power of each core. The detector's output end is coupled to the input end of the controller 2. After receiving the output optical power data of each fiber core, the controller 2 compares it with a preset target value or the average value among the fiber cores, calculates the target attenuation required for each fiber core, and then sends independent drive signals to the drive mechanisms of the corresponding grating forming areas to adjust the push-in amount of each grating forming area, thereby adjusting the attenuation of each fiber core individually. This makes the output optical power of each fiber core tend to be consistent or reach its respective set target value. This can compensate in real time for inconsistencies between cores caused by factors such as fiber manufacturing errors, ambient temperature drift, input optical power fluctuations, and device aging, achieving active power balancing of each fiber core. This balancing is effective throughout the entire attenuation dynamic range and is unaffected by changes in the operating point.

[0031] It should be noted that the controller 2 and the detector can be integrated in the same housing to form an integrated monitoring and control module. This integrated monitoring and control module has both signal receiving function (receiving the output optical power signal from the detector) and signal output function (outputting drive signals to the drive mechanism of each grating forming area), thereby integrating monitoring and control functions into one, which is beneficial to reduce device size, simplify external wiring, and improve system integration.

[0032] Furthermore, in a specific implementation, the multi-core optical attenuator provided in the embodiments of the present invention may further include: a cladding mode stripper, which covers at least a portion of the outer surface of the multi-core optical fiber 1 located in the grating formation region, for absorbing optical signals coupled from the fiber core to the cladding mode.

[0033] In implementation, the cladding mode stripping layer can be a high-refractive-index coating material covering the outer surface of the multi-core fiber 1, with a refractive index higher than that of the fiber cladding. When the fiber core fundamental mode is coupled to the cladding mode, the cladding mode propagates within the cladding, and its energy distribution extends to the interface between the cladding and the coating. Because the refractive index of the cladding mode stripping layer is higher than that of the cladding, the cladding mode no longer satisfies the total internal reflection condition at the interface, thus leaking into the stripping layer and being absorbed and lost, unable to return to the fiber core. The cladding mode stripping layer covers at least a portion of the outer surface of the multi-core fiber 1 located in each grating forming region, ensuring that the energy of the coupled cladding mode is dissipated in a timely manner, suppressing crosstalk and transmission ripple caused by the cladding mode recoupling back to the fiber core during subsequent propagation. In this embodiment, the cladding mode stripping layer can be a high-refractive-index UV-curable acrylate coating material, coated on the outer surface section of the multi-core fiber 1 passing through each grating forming region.

[0034] Furthermore, in a specific implementation, in the multi-core optical attenuator provided in the embodiments of the present invention, the pressure application directions of the pressure application elements of two adjacent grating forming regions are orthogonal.

[0035] In implementation, long-period gratings may have different coupling efficiencies for light with different polarization states, thus introducing polarization-dependent loss (PDL), which is the difference in insertion loss of the device for incident light with different polarization states, measured in dB. When the pressure directions of two adjacent grating forming regions are orthogonal to each other, that is, the pressure directions of the first and second grating forming regions differ by 90 degrees in a plane perpendicular to the fiber axis, the polarization-dependent losses introduced by each region are opposite in direction, and can be partially or completely canceled out in the overall device, thereby reducing the polarization-dependent loss of the entire multi-core optical attenuator. Taking a four-core fiber as an example, the pressure direction of the first grating forming region is set to be horizontal, the pressure direction of the second grating forming region is set to be vertical, the third grating forming region is set to be horizontal again, and the fourth grating forming region is set to be vertical, and so on, so that the overall loss of each polarization state tends to be balanced after cascading. In this way, without adding additional components, effective suppression of polarization-dependent loss can be achieved simply by the spatial arrangement of the grating forming regions.

[0036] Furthermore, in a specific implementation, in the multi-core optical attenuator provided in the embodiments of the present invention, a torsion structure can be provided on the multi-core optical fiber 1 between two adjacent grating forming regions; the torsion structure can be used to torsion the multi-core optical fiber 1 around its own axis by a preset angle.

[0037] In implementation, a torsion structure is disposed on a multi-core fiber 1 between two adjacent grating forming regions. This structure causes the multi-core fiber 1 to twist around its own axis by a predetermined angle (e.g., 90 degrees). Through this torsion structure, as the optical signal propagates from one grating forming region to the next, its polarization state rotates relative to the fiber core layout, effectively changing the pressure direction of the next grating forming region relative to the optical polarization state. This effect is equivalent to an alternative where the pressure directions of adjacent grating forming regions are orthogonal, and it also reduces the polarization-dependent loss of the entire device. This torsion structure can be a fiber segment subjected to torsional stress, or a fusion twist artificially introduced during fiber splicing. This approach, along with the approach where the pressure direction is orthogonal, can be used alone or in combination to achieve better polarization-dependent loss suppression.

[0038] In the multi-core optical attenuator provided in the embodiments of the present invention, as a specific embodiment of the present invention, the multi-core optical fiber is a heterogeneous four-core optical fiber 11. The following is in conjunction with... Figures 2 to 5 The four-core implementation is further described below.

[0039] Figure 2 This is a schematic diagram of the overall structure of a four-core optical attenuator provided in an embodiment of the present invention. Figure 2 As shown, the four-core optical attenuator includes: a heterogeneous four-core optical fiber 11; and a first grating forming region, a second grating forming region, a third grating forming region, and a fourth grating forming region arranged sequentially along the axial direction of the heterogeneous four-core optical fiber 11. The four grating forming regions have the same structure but different periods: the i-th grating forming region consists of a periodic... The system comprises a corrugated pressure plate 2i and an actuator 3i that drives its lifting and lowering (i=1, 2, 3, 4, corresponding to numbers 21-24 and 31-34), with each corrugated pressure plate located above the optical fiber 1. Specifically, each grating forming area includes a first corrugated pressure plate 21, a second corrugated pressure plate 22, a third corrugated pressure plate 23, and a fourth corrugated pressure plate 24, and a first actuator 31, a second actuator 32, a third actuator 33, and a fourth actuator 34 that respectively drive the lifting and lowering of each corrugated pressure plate; a support base 4 located below the heterogeneous four-core optical fiber 11, which penetrates the four grating forming areas and provides pressure support for each corrugated pressure plate; and a controller 2. Each corrugated pressure plate 21 to 24 is located above the heterogeneous four-core optical fiber 11, and each actuator 31 to 34 drives the corresponding corrugated pressure plate to press against the heterogeneous four-core optical fiber 11 on the support base 4. The outer surface of the heterogeneous four-core optical fiber 11, passing through each grating forming region, is coated with a cladding mode stripping layer 16. The fan-out device 6 demultiplexes the four cores into four single-core outputs and sets a tap for each core. The output power of each core is sent to the controller 2 via the first detector 71, the second detector 72, the third detector 73, and the fourth detector 74, respectively. The controller 2 outputs drive signals to the four actuators 31 to 34, independently controlling the pressing amount of the pressure plates in each grating forming region. The period of the first corrugated pressure plate 21 is Λ1, the period of the second corrugated pressure plate 22 is Λ2, the period of the third corrugated pressure plate 23 is Λ3, and the period of the fourth corrugated pressure plate 24 is Λ4, and Λ1, Λ2, Λ3, and Λ4 are all different.

[0040] Figure 3 This is a schematic diagram of the cross-sectional structure of a heterogeneous four-core optical fiber provided in an embodiment of the present invention. Figure 3 As shown, the heterogeneous four-core fiber 11 has four cores arranged in a square within a common cladding 15, namely the first core 11, the second core 12, the third core 13, and the fourth core 14. The spacing between adjacent cores is approximately 40 μm, and the outer diameter of the common cladding 15 is approximately 125 μm. Each core has a recessed channel 17 on its outer periphery. The recessed channel 17 is a ring-shaped region with a refractive index lower than that of the cladding, used to suppress crosstalk between adjacent cores. An orientation reference plane (located at the outer edge of the common cladding 15) is provided. Figure 3The bottom flat section serves as the angular registration reference, ensuring that the pressure direction of each corrugated pressure plate remains fixed relative to the angular layout of the four cores. The four cores use the same core radius, but their relative refractive index difference Δ is designed to be different from each other. The relative refractive index difference Δ is defined as the ratio of (core refractive index minus cladding refractive index) to the cladding refractive index. The relative refractive index difference Δ1 of the first core 11 is approximately 0.36%, and its fundamental mode effective refractive index is approximately 1.443875; the relative refractive index difference Δ2 of the second core 12 is approximately 0.37%, and its fundamental mode effective refractive index is approximately 1.444079; the relative refractive index difference Δ3 of the third core 13 is approximately 0.38%, and its fundamental mode effective refractive index is approximately 1.444282; the relative refractive index difference Δ4 of the fourth core 14 is approximately 0.39%, and its fundamental mode effective refractive index is approximately 1.444480. The difference in the fundamental mode effective refractive index between adjacent cores is approximately 2 × 10⁻⁶. -4 This difference gives each fiber core its own unique phase matching conditions, which forms the basis for core-by-core phase matching addressing.

[0041] In the four-core embodiment, the coupling mechanism of the long-period grating is as follows. After the i-th corrugated plate induces a long-period grating on the heterogeneous four-core fiber 11 with a period Λi, at the resonant wavelength that satisfies the phase-matching condition, the fundamental mode of the i-th fiber core is coupled to the cladding mode that propagates in the same direction. The phase-matching condition is: λ res,i =(n eff,i -n clad,eff )×Λi; Where, λ res,i Let n be the resonant wavelength of the i-th fiber core. eff,i Let n be the effective refractive index of the fundamental mode of the i-th fiber core. clad,eff Let n be the effective refractive index of the selected cladding mode, and Λi be the period of the grating forming region. Since the four fiber cores share the same cladding, n... clad,eff The period is approximately the same for each core, about 1.4400. Taking the working wavelength λ0 = 1550nm, the periods required for each fiber core to resonate exactly at 1550nm are: Λ1≈400μm, Λ2≈380μm, Λ3≈362μm, Λ4≈346μm.

[0042] Figure 4 This is a schematic diagram showing the transmission spectrum and isolation of each fiber core under the action of a single long-period grating, provided in an embodiment of the present invention. Figure 4As shown, under the action of the first corrugated pressure plate 21 (period Λ1 ≈ 400 μm), the resonance of the first fiber core 11 is exactly located at the working wavelength of 1550 nm, resulting in significant attenuation. However, under the same period Λ1, the resonance wavelengths of the second fiber core 12 are approximately 1632 nm, the third fiber core 13 are approximately 1713 nm, and the fourth fiber core 14 are approximately 1792 nm, all far from the working wavelength of 1550 nm. Therefore, there is almost no coupling or attenuation at 1550 nm. Thus, period Λ1 only causes significant attenuation in the first fiber core 11, while the isolation for the other three cores is greater than 30 dB. Similarly, period Λ2 only causes resonance and attenuation in the second fiber core 12 at 1550 nm, period Λ3 only causes resonance and attenuation in the third fiber core 13 at 1550 nm, and period Λ4 only causes resonance and attenuation in the fourth fiber core 14 at 1550 nm. Ultimately, by cascading the four grating forming regions, addressable attenuation corresponding to one fiber core per cycle was achieved. An isolation greater than 30dB between each core means that, at the preset operating wavelength, the attenuation of any grating forming region to its non-corresponding fiber core is at least 30dB less than the attenuation to its corresponding fiber core, ensuring that crosstalk between cores is negligible during core-by-core adjustment.

[0043] Figure 5 This is a schematic diagram illustrating the adjustable range of fiber core attenuation as a function of the corrugated pressure plate in an embodiment of the present invention. At the resonant wavelength, after passing through a length of L... i After the i-th grating formation region is reached, the transmittance of the i-th fiber core satisfies: T i =cos 2 (κ i ·L i ); Among them, T i Let κ be the transmittance of the i-th fiber core. i L is the coupling coefficient of the grating forming region, which is proportional to the refractive index perturbation amplitude, i.e., proportional to the amount of pressure applied by the corrugated plate; i This is the length of the grating forming region along the axis of the multi-core fiber. Increasing the indentation makes κ... i ·L i As the transmittance T increases from 0 to π / 2, the transmittance T i The decrease from 1 to 0 corresponds to an attenuation A. i =-10·log 10 (cos²(κ i ·L i The value increases continuously from 0 dB. The length L of each grating forming region is taken as... i Approximately 20 mm, in κ i ·L iWithin a range not exceeding π / 2, the adjustable attenuation range of a single core is 0 to 25 dB and continuously adjustable. Releasing the pressure plate immediately restores the insertion loss to near zero (minimum insertion loss less than 0.5 dB), and the adjustment resolution is better than 0.1 dB (mainly determined by the stepping accuracy of the actuator). Since the four grating forming areas are driven independently by four actuators, the attenuation of the four cores can be set independently without affecting each other.

[0044] In the application of four-core attenuation equalization, the fan-out device 6 taps each core, and the first detector 71 to the fourth detector 74 measure the output power of each core in real time and send it to the controller 2. The controller 2 aims to make the output power of the four cores tend to be consistent, and adjusts the push-in amount of the four actuators 31 to 34 respectively, thereby actively correcting the attenuation of each fiber core. Since the attenuation of each fiber core can be set independently, this method can compensate for the inconsistency between cores caused by fiber manufacturing errors, temperature drift, and input power fluctuations, and achieve equalization of each core at the full attenuation operating point.

[0045] In the operation of the four-core embodiment, the incident light is injected into each core of the four-core optical fiber 1 through the fan-in device 5; the controller 2 drives the actuators 31 to 34 respectively according to the target attenuation or equalization target of each core, so that the corrugated pressure plates 21 to 24 press against the four-core optical fiber 1 with the corresponding pressing amount; each grating forming region resonates and couples only to the corresponding core at the working wavelength according to its dedicated period Λ1 to Λ4, transferring part of the power of the core into the cladding mode, and dissipating it through the cladding mode stripping layer 16; the attenuated light of each core is demultiplexed and output through the fan-out device 6, and is simultaneously fed back to the controller 2 by the detectors 71 to 74 through the taps, forming core-by-core control.

[0046] In the four-core embodiment, to reduce polarization-dependent loss, the pressure directions (bending planes) of adjacent grating forming regions can be made orthogonal to each other. That is, in a plane perpendicular to the fiber axis, the pressure direction of the first grating forming region differs from that of the second grating forming region by 90 degrees, the second from the third by 90 degrees, and the third from the fourth by 90 degrees, so that the overall loss of each polarization state tends to be balanced after cascading. Alternatively, an approximately 90-degree fiber twist can be introduced into the multi-core fiber between adjacent grating forming regions, which can also achieve the effect of reducing polarization-dependent loss. Both schemes can be used individually or in combination. To compensate for the influence of temperature on the resonant wavelength, the temperature of the support base 4 can be controlled, or a working wavelength locking function can be introduced into the controller 2. This multi-core optical attenuator has no fiber core end face interruption and no free space optical path throughout its entire process, and the return loss is greater than 50dB.

[0047] The multi-core optical attenuator provided in this invention can be applied to various scenarios. For example, in a space-division multiplexing optical transmission system, the multi-core optical attenuator can be directly connected in series in a multi-core optical fiber transmission link to independently adjust the transmitted optical power of each fiber core. This compensates for inter-core power deviations caused by manufacturing differences, bending loss differences, or uneven power distribution across different wavelength channels, thereby improving system performance. In gain equalization applications of erbium-doped fiber amplifiers (EDFAs), the multi-core optical attenuator can be placed at the output end of the EDFA to independently control the power attenuation of the amplified optical signal in each fiber core, making the output power of each fiber core more consistent and achieving gain flatness in the EDFA. In a wavelength division multiplexing (WDM) system, the multi-core optical attenuator can be used in conjunction with different operating wavelength settings to selectively attenuate specific wavelength signal light in each fiber core, achieving power equalization between channels. In fiber optic sensing systems, this multi-core optical attenuator can independently control the attenuation of the return signal light from each sensing fiber core to match the dynamic range of different sensing channels. In space-constrained applications such as data center optical interconnects, this multi-core optical attenuator, due to its small size, low insertion loss, and high reliability, can be directly integrated into multi-core fiber optic transmission links, significantly saving space and reducing system complexity.

[0048] In the above embodiments, the multi-core optical attenuator has been described in detail. Based on the same inventive concept, the embodiments of the present invention also provide an optical attenuation adjustment method for the multi-core optical attenuator and corresponding embodiments for electronic devices.

[0049] This invention also provides a method for adjusting the optical attenuation of the above-mentioned multi-core optical attenuator. Figure 6 This is a flowchart illustrating the optical attenuation adjustment method for a multi-core optical attenuator provided in an embodiment of the present invention. Figure 6 As shown, the optical attenuation adjustment method may specifically include the following steps: S601. Multiple grating forming regions are arranged along the axial direction of the multi-core optical fiber; each grating forming region has a different period, and each grating forming region is used to form a long-period grating in the multi-core optical fiber.

[0050] In a possible implementation, the multi-core fiber can be a heterogeneous multi-core fiber, where each core has a different effective refractive index of its fundamental mode. The period of each grating forming region is set according to the difference between the effective refractive index of the fundamental mode and the effective refractive index of the cladding mode of its corresponding core, such that at a preset operating wavelength, the period of each grating forming region only satisfies the phase matching condition with the fundamental mode of its corresponding core, and does not satisfy the phase matching condition with the fundamental modes of other non-corresponding cores. The grating forming regions are arranged sequentially along the axis of the multi-core fiber and do not overlap.

[0051] S602. At a preset operating wavelength, a long-period grating is used to couple the fundamental mode of the corresponding fiber core in the multi-core fiber to the cladding mode, so that the signal light of the corresponding fiber core is attenuated.

[0052] In a possible implementation, when the optical signal propagates along the multi-core optical fiber through each grating forming region, each long-period grating, at a preset operating wavelength, only causes phase-matched coupling between the fundamental mode and the cladding mode of its corresponding fiber core, transferring a portion of the signal power of that fiber core from the fundamental mode to the cladding mode. The signal light coupled to the cladding mode is dissipated through the cladding mode stripping layer and does not return to the fiber core, thereby causing attenuation in the fiber core at the preset operating wavelength.

[0053] S603. The coupling strength of each grating forming region to its corresponding fiber core is independently adjusted by the controller, so as to independently control the attenuation of each fiber core.

[0054] In a possible implementation, the controller sends independent control signals to the driving mechanisms of each grating forming region. Each driving mechanism, in response to the control signal, changes the pressure applied to the multi-core optical fiber by its corresponding pressure-applying element, thereby independently adjusting the coupling coefficient of each long-period grating and enabling each fiber core to achieve its set target attenuation. This adjustment is continuous, and the grating forming regions do not interfere with each other. The invention may further include: detecting the output optical power of each fiber core; and the controller adjusting the coupling strength of each grating forming region according to the output optical power, so that the output optical power of each fiber core tends to be consistent.

[0055] In the optical attenuation adjustment method of the multi-core optical attenuator provided in the embodiments of the present invention, independent addressing and continuous attenuation adjustment of each core in the multi-core optical fiber can be achieved by executing the above steps S601 to S603, without having to demultiplex the multi-core optical fiber into a single-core optical fiber.

[0056] Since the embodiments of the optical attenuation adjustment method correspond to the embodiments of the multi-core optical attenuator, please refer to the description of the embodiments of the multi-core optical attenuator for the embodiments of the optical attenuation adjustment method, which will not be repeated here. Furthermore, it has the same beneficial effects as the multi-core optical attenuator mentioned above.

[0057] Furthermore, in a specific implementation, the optical attenuation adjustment method of the multi-core optical attenuator provided in the embodiments of the present invention may further include: twisting the multi-core optical fiber around its own axis by a preset angle between two adjacent grating forming regions to reduce polarization-dependent loss.

[0058] For more detailed information on the working process of each of the above steps, please refer to the relevant content disclosed in the foregoing embodiments, which will not be repeated here.

[0059] Based on the same inventive concept, embodiments of the present invention also provide a multi-core optical fiber attenuation system. Figure 7This is a schematic diagram of the structure of a multi-core fiber attenuation system provided in an embodiment of the present invention. Figure 7 As shown, the multi-core fiber optic attenuation system includes the aforementioned multi-core optical attenuator, fan-in device 5, and fan-out device 6. The fan-in device 5 is located at the input end of the multi-core fiber; its multiple output ports are optically coupled to multiple fiber cores. The fan-in device 5 can inject each input optical signal into its corresponding fiber core. The fan-out device 6 is located at the output end of the multi-core fiber, and its multiple input ports are optically coupled to multiple fiber cores. The fan-out device 6 can demultiplex and output the multiple optical signals from the multiple fiber cores. This multi-core fiber optic attenuation system can be directly applied to multi-core fiber optic transmission links without requiring significant modifications to the link, making it convenient to use.

[0060] Furthermore, in a specific implementation, in the multi-core fiber attenuation system provided in the embodiments of the present invention, the detector can be integrated into the fan-out device 6. The fan-out device 6 is equipped with a beam splitter for each output optical signal, and the detector detects the optical power of each optical signal through the beam splitter. This eliminates the need for a separate detector and additional optical path connections, making the system more compact and reducing insertion loss.

[0061] Since the principle of this multi-core fiber attenuation system is similar to that of the aforementioned multi-core optical attenuator, the implementation of this multi-core fiber attenuation system can be found in the implementation of the multi-core optical attenuator, and the repetition will not be repeated.

[0062] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0063] The foregoing has provided a detailed description of the multi-core optical attenuator and its optical attenuation adjustment method, as well as the multi-core optical fiber attenuation system provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only intended to help understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. A multi-core optical attenuator, characterized in that, include: Multi-core optical fiber, which has multiple fiber cores; Multiple grating forming regions are sequentially arranged along the axial direction of the multi-core optical fiber; each grating forming region is used to form a long-period grating in the multi-core optical fiber, and the long-period grating is phase-matched with the fundamental mode of the corresponding fiber core in the multi-core optical fiber at a preset operating wavelength, so as to couple the signal light of the corresponding fiber core to the cladding mode for attenuation; wherein, the periods of each grating forming region are different, and they correspond to different fiber cores respectively; The controller, coupled to each of the grating forming regions, is used to independently adjust the coupling strength of each grating forming region to its corresponding fiber core, so as to independently control the attenuation of each fiber core.

2. The multi-core optical attenuator according to claim 1, characterized in that, The multi-core optical fiber is a heterogeneous multi-core optical fiber, and the fundamental mode effective refractive index of each core of the heterogeneous multi-core optical fiber is different. At the preset operating wavelength, each grating forming region satisfies the phase matching condition with the fundamental mode of the corresponding fiber core, while each grating forming region does not satisfy the phase matching condition with the fundamental modes of the other fiber cores among the multiple fiber cores except the corresponding fiber core.

3. The multi-core optical attenuator according to claim 1, characterized in that, The grating forming area is a mechanically inductive long-period grating forming area; the mechanically inductive long-period grating forming area includes a pressure-applying element and a driving mechanism; The pressure-applying element is disposed toward the multi-core optical fiber, and the pressure-applying element is used to apply periodic pressure to the multi-core optical fiber to induce periodic perturbations in the refractive index in the multi-core optical fiber. The drive mechanism is coupled to the controller, and the output end of the drive mechanism is connected to the pressure-applying element. The drive mechanism is used to drive the pressure-applying element to change the pressure applied to the multi-core optical fiber in response to the instructions of the controller.

4. The multi-core optical attenuator according to claim 3, characterized in that, The pressure-applying element is a pressure plate with a periodic corrugated structure; the driving mechanism is an actuator; the actuator is used to drive the pressure plate to press vertically into the multi-core optical fiber; the amount of pressing between the pressure plate and the multi-core optical fiber is adjusted by the actuator; The multi-core optical attenuator also includes an angular registration structure disposed between the multi-core optical fiber and the pressure plate; the angular registration structure is used to fix the angular orientation relationship between the pressure direction of the pressure plate and the core layout of the multi-core optical fiber.

5. The multi-core optical attenuator according to claim 1, characterized in that, Also includes: A detector is installed at the output end of the multi-core optical fiber to detect the output optical power of each fiber core. The input terminal of the controller is coupled to the output terminal of the detector. The controller is used to output driving signals to each of the grating forming regions according to the output optical power, so as to adjust the coupling strength of each of the grating forming regions and make the output optical power of each fiber core tend to be consistent.

6. The multi-core optical attenuator according to claim 1, characterized in that, Also includes: A cladding mode stripping layer covers at least a portion of the outer surface of the multi-core optical fiber located in the grating forming region, and is used to absorb optical signals coupled from the fiber core to the cladding mode.

7. The multi-core optical attenuator according to claim 3, characterized in that, The pressure application directions of the pressure application elements in two adjacent grating forming regions are orthogonal.

8. The multi-core optical attenuator according to claim 3, characterized in that, A torsion structure is provided on the multi-core optical fiber between two adjacent grating forming regions; the torsion structure is used to torsion the multi-core optical fiber around its own axis by a preset angle.

9. A multi-core optical fiber attenuation system, characterized in that, Including the multi-core optical attenuator as described in any one of claims 1 to 8; further comprising: A fan-in device is disposed at the input end of the multi-core optical fiber; the multiple output ports of the fan-in device are optically coupled to multiple fiber cores respectively; the fan-in device is used to inject each input optical signal into the corresponding fiber core respectively; A fan-out device is disposed at the output end of the multi-core optical fiber, and the multiple input ports of the fan-out device are respectively optically coupled to the multiple fiber cores; the fan-out device is used to demultiplex the multiple optical signals output from the multiple fiber cores and output them respectively.

10. A method for adjusting the optical attenuation of a multi-core optical attenuator as described in any one of claims 1 to 8, characterized in that, include: Multiple grating forming regions are arranged along the axial direction of the multi-core optical fiber; each grating forming region has a different period, and each grating forming region is used to form a long-period grating in the multi-core optical fiber; At a preset operating wavelength, the fundamental mode of the corresponding fiber core in the multi-core optical fiber is coupled to the cladding mode using the long-period grating, so that the signal light of the corresponding fiber core is attenuated. The coupling strength of each grating forming region to its corresponding fiber core is independently adjusted using a controller, thereby independently controlling the attenuation of each fiber core.

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