Variable optical attenuator and variable optical attenuation system

Abstract

To realize a variable optical attenuator capable of individually adjusting an amount of light propagating through a plurality of cores, with a simple configuration.SOLUTION: A variable optical attenuator 10 receives light propagating through a first optical fiber 41 having a plurality of cores, individually adjusts an amount of light having propagated through each core, and emits the light to a second optical fiber 42 having a plurality of cores. The variable optical attenuator 10 comprises separation optical systems 11, 12 that spatially separate a plurality of light beams emitted into a space from the plurality of cores of the first optical fiber 41, and optical attenuation means 15(a), 15(b) that can individually adjust an amount of attenuation of the plurality of light beams separated by the separation optical systems 11, 12.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a variable optical attenuator and a variable optical attenuation system suitable for an optical fiber having a plurality of cores such as multi-core fiber (MCF). More specifically, the present invention relates to a variable optical attenuator or the like capable of individually adjusting the amount of propagating light of a light beam emitted from each core of an MCF. [Background Art]

[0002] In response to the increasing traffic volume in optical fiber networks, space division multiplexing transmission (SDM) has been proposed to meet such demands, and multi-core fiber (MCF) has been proposed as one of such schemes. As an MCF, one having a plurality of optical propagation cores in a single optical fiber is known. It is also known that a fiber bundle formed by bundling a plurality of single-mode fibers (SMF) each having one core is used as a substitute for MCF.

[0003] For example, in optical transmission using MCF, loss differences between each core during connector connection or fusion splicing, and loss differences between each core when light passes through the MCF accumulate, resulting in loss differences between cores when light is transmitted over long distances. Further, when an MC-EDFA (optical amplifier) attempts to collectively amplify the light power propagating through the MCF, the amplification gain in each core differs due to the difference in the power of light input to each core, which may further increase the power difference of light propagating through each core. Therefore, a variable optical attenuator (VOA) for independently adjusting the power of light propagating through each core of the MCF is required.

[0004] Here, consider using existing technology to individually adjust the power of light propagating through each core of the MCF. In this case, a configuration is conceivable in which light from each core of the MCF is coupled to a plurality of SMFs by a branching device called a fan-out device, the power of each optical path is individually adjusted by a variable optical attenuator provided in each SMF, and then the plurality of SMFs are re-coupled to each core of the MCF by a multiplexing device called a fan-in device (see Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-195036 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in configurations using fan-out and fan-in devices as described above, the need for devices with physical waveguides leads to increased optical propagation loss due to losses within the devices and losses when connecting MCFs and SMFs to each device. Furthermore, the need to implement a number of variable optical attenuators corresponding to the number of cores in the MCF results in a complex and large overall device, leading to increased manufacturing costs.

[0007] Therefore, the main objective of the present invention is to realize a variable optical attenuator with a simple configuration that can individually adjust the amount of light propagating through multiple cores. [Means for solving the problem]

[0008] The inventors of the present invention diligently studied means to solve the problems of the prior art and found that a variable attenuator for an MCF can be realized with a simple configuration by first emitting and separating the light propagating through each core of an MCF into space, and by incorporating an optical attenuation means that can individually adjust the light intensity of each light beam within the spatial optical system. Based on this finding, the inventors realized that the problems of the prior art could be solved and completed the present invention. Specifically, the present invention has the following configuration.

[0009] The first aspect of the present invention relates to a variable optical attenuator 10. The variable optical attenuator 10 according to the present invention is used by being placed between a first optical fiber 41 and a second optical fiber 42. The first optical fiber 41 and the second optical fiber 42 are optical fibers having multiple cores, and a typical example is a multicore fiber (MCF). However, these are not limited to MCFs, and may be bundled fibers made by bundling multiple single-mode fibers (SMFs) having one core, or bundled fibers made by bundling multiple MCFs. Furthermore, the combination of the first optical fiber 41 and the second optical fiber 42 is not limited to a combination of MCFs or a combination of bundled fibers, and it is also possible to have a combination where one is an MCF and the other is a bundled fiber. The variable optical attenuator 10 according to the present invention has the function of individually adjusting the amount of light that is incident on the first optical fiber 41, propagates through each core, and outputs it to the second optical fiber 42. "Light intensity" is the total amount of light energy that passes through a certain surface within a certain time, and is a physical quantity that represents the strength (light power) of the optical signal propagating through an optical fiber.

[0010] The variable optical attenuator 10 comprises a separation optical system and an optical attenuation means. The separation optical system spatially separates multiple light beams emitted into space from multiple cores of the first optical fiber 41. The separation optical system is composed of, for example, multiple lenses. The separation optical system is configured to separate the multiple light beams in space and ultimately guide each light beam to each core of the second optical fiber 42. The optical attenuation means is configured to allow individual adjustment of the attenuation amount of the multiple light beams separated by the separation optical system. The optical attenuation means may attenuate the light beams by physically blocking a portion of the light beams, or it may be formed of a translucent material that allows adjustment of the transmittance of the light beams.

[0011] As described above, in this invention, light propagating through each core, such as an MCF, is emitted into space, and each light beam is separated by a separation optical system. Within this separation optical system, optical attenuation means are provided to individually adjust the light intensity of each light beam. This eliminates the need for connection devices such as fan-out and fan-in devices, thereby reducing light propagation loss. Furthermore, since this invention adjusts the light intensity of the light beams in space, optical equipment (individual variable attenuators) that adjusts the light intensity of light propagating through the core of the optical fiber is unnecessary. As a result, the entire device can be made simple and compact.

[0012] In the variable optical attenuator 10 according to the present invention, the optical attenuation means may include a plurality of light-shielding elements 15 that individually shield a plurality of optical beams. In this case, each of the plurality of light-shielding elements 15 is configured to allow individual adjustment of the amount of light shielding of the optical beam. For example, by shielding a portion of the beam width of the optical beam with the tip of the light-shielding element 15, the optical beam can be individually attenuated. Alternatively, the operation of the light-shielding elements 15 can be controlled by an actuator so that the amount of beam width shielded by the light-shielding element 15 can be adjusted. In this way, by using light-shielding elements 15, the amount of attenuation of the optical beam can be adjusted with a simple configuration.

[0013] In the variable optical attenuator 10 according to the present invention, the light-shielding element 15 (particularly the part that touches the light beam) may be made of an opaque material that does not transmit the light beam. Alternatively, the light-shielding element 15 may be composed of an optical member that can deflect the direction of the light beam, thereby cutting out a portion of the light beam from the optical path. By composing the light-shielding element 15 of an opaque material or a deflecting member in this way, the amount of attenuation of the light beam can be adjusted with a simple configuration.

[0014] In the variable optical attenuator 10 according to the present invention, the optical attenuation means may include a liquid crystal element 19 that can individually adjust the transmittance of multiple optical beams. With the liquid crystal element 19, the transmittance of the transmission region of each optical beam can be individually adjusted, so the amount of attenuation of the optical beams can be adjusted in a compact configuration.

[0015] In the variable optical attenuator 10 according to the present invention, the separation optical system may include a first lens 11, a second lens 12, a third lens 13, and a fourth lens 14. The first lens 11 receives each optical beam from each core of the first optical fiber 41 and widens the separation width by creating an angular difference in the optical paths of each optical beam. The second lens 12 receives each optical beam that has passed through the first lens 11 and arranges the optical paths of each optical beam substantially in parallel. The third lens 13 receives each optical beam that has passed through the second lens 12 and narrows the separation width of the optical paths of each optical beam. The fourth lens 14 receives each optical beam that has passed through the third lens 13 and couples the optical paths of each optical beam to the respective cores of the second optical fiber 42. In this case, it is preferable that the optical attenuation means is provided between the second lens 12 and the third lens 13. In this way, by configuring a separation optical system with multiple lenses, the propagation loss of each light beam can be suppressed.

[0016] In the variable optical attenuator 10 according to the present invention, the separation optical system may include a first lens (Figure 3: first lens 11), a second lens (Figure 3: fifth lens 16), a reflecting element 17, and a third lens (Figure 3: fourth lens 14). The first lens (11) receives each optical beam from each core of the first optical fiber 41 and widens the separation width by creating an angular difference in the optical path of each optical beam. The second lens (16) receives each optical beam that has passed through the first lens (11) and focuses each optical beam toward the subsequent reflecting element 17. The reflecting element 17 reflects each optical beam that has been focused by the second lens (16). The third lens (14) receives each optical beam that has been reflected by the reflecting element 17 and passed through the second lens (16) again, and couples the optical path of each optical beam toward the respective cores of the two optical fibers 42. In this case, it is preferable that the reflective element 17 is provided between the second lens (16) and the reflecting element 17. By using the reflecting element 17 in this way, the entire variable optical attenuator 10 can be made compact. Furthermore, since the optical path of the optical beam can be folded back by using the reflecting element 17, for example, the first optical fiber 41 and the second optical fiber 42 can be placed next to each other and coupled.

[0017] In the variable optical attenuator 10 according to the present invention, the reflective element 17 may transmit a portion of each light beam. An example of such a reflective element 17 is a half mirror. In this case, it is preferable that the variable optical attenuator 10 further includes a light detection means for detecting the amount of light of a portion of each light beam transmitted through the reflective element 17. In this case, the amount of attenuation of each beam by the light attenuation means is individually adjusted according to the amount of light detected by the light detection means. In this way, by using a portion of the light transmitted through the reflective element 17 as monitor light, the variable optical attenuator 10 can be controlled with a simple configuration.

[0018] A second aspect of the present invention is a variable optical attenuation system 100. The variable optical attenuation system 100 according to the present invention includes a variable optical attenuator 10 and a control device 30. The variable optical attenuator 10 relates to the first aspect, and the configuration thereof is as described above. The control device 30 detects the light amount of light propagating through each core of the second optical fiber 42, controls the light attenuating means according to the detected light amount, and individually adjusts the attenuation amount of each beam by the light attenuating means. Effects of the Invention

[0019] According to the present invention, a variable optical attenuator capable of individually adjusting the light amount of light propagating through a plurality of cores can be realized with a simple configuration. Brief Description of the Drawings

[0020] [Figure 1] Fig. 1 schematically shows one embodiment of a variable optical attenuation system. [Figure 2] Fig. 2 schematically shows a first embodiment of a variable attenuator. [Figure 3] Fig. 3 schematically shows a second embodiment of a variable attenuator. [Figure 4] Fig. 4 schematically shows a third embodiment of a variable attenuator. Mode for Carrying Out the Invention

[0021] Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to the modes described below, and also includes appropriate modifications within the range obvious to those skilled in the art from the modes described below.

[0022] Fig. 1 shows the overall configuration of a variable optical attenuation system 100. The variable optical attenuation system 100 mainly individually attenuates light propagating through a first optical fiber 41 having a plurality of cores, and couples the attenuated light to a second optical fiber 42 that also has a plurality of cores. In the present embodiment, the first and second optical fibers 41, 42 are each a multi-core fiber (MCF).

[0023] As shown in Figure 1, the variable optical attenuation system 100 comprises a variable optical attenuator 10, taps 20, and a control device 30. The variable optical attenuator 10 is the core of this system and has the function of individually attenuating the light propagating through each core of the first optical fiber 41. Details of the variable optical attenuator 10 will be described later. The taps 20 (also called optical couplers) branch a portion of the light propagating through each core of the second optical fiber 42 to single-mode fibers (SMFs) 43. For example, the number of SMFs 43 is the same as the number of cores in the second optical fiber 42; for example, if the second optical fiber 42 has 4 cores, then 4 SMFs 43 are provided. Each SMF 43 is connected to the control device 30. The control device 30 provides feedback control to the variable optical attenuator 10 based on the amount of light propagating through each SMF 43. In other words, the control device 30, although not shown in the figure, includes a photodetector that detects the amount of light branched to each SMF 43, and a computing device (such as a PC) that estimates the amount of light propagating through each core of the second optical fiber 42 from the detected light amount and sends a control signal to the variable optical attenuator 10 based on the estimated value. Known taps 20 and control device 30 can be used, respectively.

[0024] Next, the configuration of the variable optical attenuator 10 will be described in detail. Figure 2 shows a first embodiment of the variable optical attenuator 10. As shown in Figure 2, the variable optical attenuator 10 according to this embodiment is composed of a plurality of lenses 11 to 14 and a plurality of light-shielding elements 15. In this embodiment, the first optical fiber 41 and the second optical fiber 42 will be described using MCFs having four cores each as an example. However, the number of cores of the first and second optical fibers 41 and 42 is not limited to four, and may be, for example, two cores, five cores, six cores, or seven cores.

[0025] The output end of the first optical fiber 41 is connected to the input end of the variable optical attenuator 10. Since the inside of the variable optical attenuator 10 is hollow, the light propagating through each core of the first optical fiber 41 is emitted into the variable optical attenuator 10 from the output end of the first optical fiber 41. In this specification, light propagating through space in this manner is referred to as an "optical beam". The optical beams from each core of the first optical fiber 41 are emitted into the variable optical attenuator 10 while diffusing so as to expand the beam diameter.

[0026] Multiple light beams emitted from the first optical fiber 41 into the variable optical attenuator 10 all enter the first lens 11. The first lens 11 is a collimating lens with a front focal position at the exit end of the first optical fiber 41. Therefore, if a light beam enters the optical axis of the first lens 11, it is collimated (parallelized) and travels in a straight line along the optical axis of the first lens 11. However, as shown in the example in Figure 2, if a light beam enters the optical axis of the first lens 11 at a position offset from the optical axis, it is collimated and travels in a straight line with an angular difference from the optical axis of the first lens 11. Therefore, after passing through the first lens 11, the light beams emitted from each core of the first optical fiber 41 intersect at the rear focal position of the first lens 11 and are then gradually spatially separated. This increases the separation width of each light beam. Thus, the first lens 11 has the function of collimating multiple light beams and the function of expanding the separation width.

[0027] A second lens 12 is provided behind the first lens 11. The second lens 12 is a focusing lens, and its front focal position is aligned with the rear focal position of the first lens 11 (i.e., the intersection point of each light beam). As a result, the multiple light beams that have passed through the first lens 11 are sufficiently separated before entering the second lens 12, where they are focused and diffused while being aligned substantially parallel to each other. That is, as shown in Figure 2, each light beam that has passed through the second lens 12 is focused so that its beam diameter gradually decreases, converges at the rear focal position of the second lens 12, then diffuses again so that its beam diameter expands as it travels through space, and enters the third lens 13. At this time, the optical axes of each light beam are substantially parallel in the space between the second lens 12 and the third lens 13.

[0028] Furthermore, a condensing lens with a longer focal length than the first lens 11 is used as the second lens 12. That is, the spacing between each light beam between the second lens 12 and the third lens 13 can be changed by the ratio of the focal lengths of the first lens 11 (collimating lens) and the second lens 12 (condensing lens). For example, if a condensing lens with a focal length 10 times that of the first lens 11 is used as the second lens 12, the spacing between each light beam between the second lens 12 and the third lens 13 can be increased to 10 times the spacing between each core in the first optical fiber 41. From the viewpoint of ensuring sufficient spacing between each light beam, it is preferable that the second lens 12 has a focal length 2 times or more, 5 times or more, or 10 times or more that of the first lens 11.

[0029] As shown in Figure 2, the combination of the third lens 13 and the fourth lens 14 is positioned symmetrically to the combination of the first lens 11 and the second lens 12, with respect to the line connecting the focal points (convergence points) of each light beam as the axis of symmetry. In this way, the first to fourth lenses 11 to 14 constitute a relay optical system that couples the first optical fiber 41 and the second optical fiber 42.

[0030] To explain in more detail, a third lens 13 is provided behind the second lens 12. The third lens 13 is a collimating lens, and its front focal position is aligned with the rear focal position of the second lens 12 (i.e., the convergence point of each light beam). As shown in the example in Figure 2, when a light beam that has passed through the second lens 12 is incident at a position offset from the optical axis of the third lens 13, it is collimated and travels in a straight line with an angular difference from the optical axis of the third lens 13. As a result, the multiple light beams that have passed through the third lens 13 intersect at the rear focal position of the third lens 13, gradually reducing their separation width, and are then spatially separated again. This reduces the separation width of each light beam. Thus, the third lens 13 has the function of collimating multiple light beams and the function of reducing their separation width.

[0031] A fourth lens 14 is provided behind the third lens 13. The fourth lens 14 is a focusing lens, and its front focal position is aligned with the rear focal position of the third lens 13 (i.e., the intersection point of each optical beam). Furthermore, the rear focal position of the fourth lens 14 is aligned with the incident end of the second optical fiber 42. As a result, as shown in Figure 2, the optical beams that have passed through the fourth lens 14 are aligned substantially parallel to each other by the fourth lens 14 and focused onto each core of the second optical fiber 42. At this time, the optical axes of each optical beam are substantially parallel in the space between the fourth lens 14 and the second optical fiber 42. In this way, the first to fourth lenses 11 to 14 form a spatial optical system that optically couples the first optical fiber 41 and the second optical fiber 42.

[0032] Here, as shown in Figure 2, light-shielding elements 15 are placed between the second lens 12 and the third lens 13, each on the optical path of multiple light beams. The number of light-shielding elements 15 is the same as the number of light beams propagating in the space of the variable optical attenuator 10, that is, the number of cores in the first and second optical fibers 41 and 42. In Figure 2, two light-shielding elements 15(a) and (b) are drawn, but in reality, since the first and second optical fibers 41 and 42 have 4 cores, four light-shielding elements 15 are also provided.

[0033] The light-shielding element 15 is configured to individually shield the light beam and to allow individual adjustment of the amount of light shielding. Thus, the light-shielding element 15 is used to attenuate the light intensity of the light beam by shielding a portion of it. Specifically, the light-shielding element 15 is configured to shield only a portion of the beam width of the light beam and to allow adjustment of the beam width that is shielded. As a result, the amount of attenuation of each light beam is individually adjusted by each light-shielding element 15. In this invention, it is not intended that the light beam be completely blocked by the light-shielding element 15, but it may be possible to completely block the light beam depending on the application.

[0034] As mentioned above, the light-shielding element 15 blocks a portion of the beam width, so it is desirable to place it at a position on the optical path of each light beam where the beam width is as wide as possible. That is, as shown in Figure 2, the focal point of each light beam is located midway between the second lens 12 and the third lens 13, and the beam width of each light beam is smallest at this focal point. On the other hand, the beam width of each light beam increases as it gets closer to the second lens 12 and the third lens 13. For this reason, it is preferable to place each light-shielding element 15 at a position closer to the second lens 12 or closer to the third lens 13 than the focal point of each beam. For example, it is preferable to place half of the multiple light-shielding elements 15 (four light-shielding elements 15 in the example shown in Figure 2) at a position closer to the second lens 12 and the other half at a position closer to the third lens 13.

[0035] The light-shielding element 15 has a tip portion that contacts the light beam formed with an acute cross-section, allowing for fine adjustment of the amount of light shielding the light beam. Preferably, the light-shielding element 15, at least its tip portion, is made of an opaque material or a light-reflective material so as to shield a portion of the light beam. A light-shielding element 15 made of an opaque material makes the light beam opaque by absorbing it. The opaque material should have a transmittance to the light beam of, for example, 0 to 10% or 0 to 5%. Alternatively, a light-shielding element 15 made of a light-reflective material deflects the direction of the light beam, thereby cutting out a portion of the light beam from the optical path. Preferably, the polarization direction of the light beam is adjusted to avoid interference with other light beams.

[0036] Furthermore, as shown in Figure 2, the light-shielding element 15 is equipped with an actuator, and the amount of light shielding of the light beam is changed by operating the light-shielding element 15 with this actuator. However, if the light-shielding element 15 is inserted perpendicular to the optical axis of the light beam, the amount of light in the light beam will be rapidly attenuated, making it difficult to fine-tune the amount of attenuation. For this reason, it is preferable to insert the light-shielding element 15 from an oblique direction relative to the optical axis of the light beam. From this viewpoint, in this embodiment, a rotational motion mechanism that rotates the light-shielding element 15 is used as the actuator that operates the light-shielding element 15, rather than a linear motion mechanism. As a result, as shown in Figure 2, the tip of the light-shielding element 15 is inserted from an oblique direction relative to the optical axis of the light beam. A typical example of such a rotational motion mechanism is a motor. In addition, the operation of the actuators of the light-shielding element 15 is individually controlled by control signals from the control device 30 (see Figure 1) described above. In this way, by providing a light-shielding element 15 equipped with an individually controllable actuator in each of the optical paths of multiple light beams, the amount of light shielding (attenuation) of the light beams can be individually adjusted.

[0037] Next, with reference to Figure 3, a second embodiment of the variable optical attenuator 10 according to the present invention will be described. The second embodiment will be described focusing on the differences from the first embodiment described above, and components identical to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted.

[0038] The second embodiment shown in Figure 3 replaces the functions of the second lens 12 and the third lens 13 in the first embodiment shown in Figure 2 with a fifth lens 16 and a reflective element 17. In other words, in the second embodiment, a reflective element 17 is placed at the focal point (convergence point) of each light beam in order to realize the functions of the second lens 12 and the third lens 13 (see Figure 2) with a single fifth lens 16 (see Figure 3).

[0039] Specifically, the light beams emitted from each core of the first optical fiber 41 pass through the first lens 11, where they are collimated and the spacing between each light beam widens as they enter the fifth lens 16. The light beams are aligned in parallel and focused by the fifth lens 16. Therefore, in this side view, the fifth lens 16 functions as a focusing lens, similar to the second lens 12 shown in Figure 2. A reflecting element 17 is positioned at the rear focal point of the fifth lens 16. As a result, each light beam that has passed through the fifth lens 16 is focused on the surface of the reflecting element 17, reflected off the surface of the reflecting element 17, and enters the fifth lens 16 again. When each light beam enters the fifth lens 16 again, it is collimated by the fifth lens 16 and the spacing between each light beam narrows as it enters the fourth lens 14. Therefore, in this aspect, the fifth lens 16 functions as a collimating lens, similar to the third lens 13 shown in Figure 2. Each light beam is focused again by the fourth lens 14 and guided to the lenses of the second optical fiber 42.

[0040] Furthermore, in the second embodiment, as in the first embodiment, a light-shielding element 15 is provided on the optical path of each of the multiple light beams. The light-shielding element 15 is provided between the fifth lens 16 and the reflecting element 17. As shown in Figure 3, the light-shielding element 15 may be provided in the optical path (forward path) from when the light beam passes through the fifth lens 16 until it reaches the reflecting element 17, or it may be provided in the optical path (return path) from when the light beam reflected by the reflecting element 17 is re-entered the fifth lens 16. In this way, the same optical functions as in the first embodiment can be achieved in the second embodiment as well.

[0041] The reflective element 17 may reflect the entire amount of light beam, or it may be a so-called half-mirror that reflects a portion of the light beam and transmits the rest. When a half-mirror is used as the reflective element 17, as shown in Figure 3, a portion of the light beam that has passed through the reflective element 17 may be detected by the photodetector 18. The number of photodetectors 18 is the same as the number of light beams. In the example shown in Figure 3, only two photodetectors 18(a) and (b) are drawn, but in reality, four photodetectors 18 will be provided to correspond to four light beams. A general photodiode (PD) that converts the amount or intensity of light into an electrical signal can be used as the photodetector 18. The electrical signal detected by each photodetector 18 is transmitted to the control device 30 (see Figure 1) and used for individual control of the operation of the light-shielding element 15. Note that when the photodetectors 18 are built into the variable optical attenuator 10 as shown in Figure 3, the tap 20 and single-mode fiber 43 shown in Figure 1 can be omitted.

[0042] Next, with reference to Figure 4, a third embodiment of the variable optical attenuator 10 according to the present invention will be described. The third embodiment will also be described focusing on the differences from the first embodiment described above, and components identical to those in the first embodiment will be denoted by the same reference numerals, thus omitting their description.

[0043] The third embodiment shown in Figure 3 replaces the functions of the multiple light-shielding elements 15 in the first embodiment shown in Figure 2 with a single liquid crystal element 19. In other words, in the third embodiment, the liquid crystal element 19 is placed at a position through which all light beams pass, and the transmittance of the liquid crystal element 19 is controlled for each light beam transmission region, thereby individually adjusting the attenuation of each light beam.

[0044] Furthermore, any general-purpose liquid crystal element 19 capable of controlling the light transmittance for each region can be used. Specifically, the liquid crystal element 19 has a liquid crystal layer in which transparent electrodes are attached to both sides of a glass substrate, with transparent electrodes attached, arranged between two polarizing plates with different polarization directions. When a voltage is applied between the electrodes, the orientation of the liquid crystal molecules in the liquid crystal layer between them changes. This allows the light transmittance to be adjusted by combining the movement of the liquid crystal molecules with the polarization directions of the two polarizing plates. As shown in Figure 3, it is preferable to place the liquid crystal element 19 at the focal point of each light beam, i.e., at the rear focal point of the second lens 12. However, it is also possible to place the liquid crystal element 19 at a position closer to the second lens 12 or closer to the third lens 13 than the focal point of each beam.

[0045] In this way, the liquid crystal element 19 can be used as an optical attenuation means for individually adjusting the attenuation amount of multiple light beams. In this embodiment, since it is not necessary to place a light shielding element 15 for each light beam, the overall configuration of the variable optical attenuator 10 can be made more compact.

[0046] In this specification, embodiments of the present invention have been described with reference to the drawings in order to express the content of the present invention. However, the present invention is not limited to the above embodiments, and includes modifications and improvements that are obvious to those skilled in the art based on the matters described in this specification. [Explanation of Symbols]

[0047] 10... Variable optical attenuator 11... First lens 12...Second lens 13...Third lens 14…Fourth lens 15…Light-shielding element (light attenuation means) 16…Fifth lens 17…Reflector 18... Light-receiving element (light detection means) 19... Liquid crystal element (light attenuation means) 20... Tap 30... Control device 41...First optical fiber 42...Second optical fiber 43…Single-mode fiber 100…Variable optical attenuation system

Claims

1. A variable optical attenuator for receiving light propagating through a first optical fiber having multiple cores, individually adjusting the amount of light propagating through each core, and outputting it to a second optical fiber having multiple cores, A separation optical system for spatially separating multiple light beams emitted into space from the multiple cores, The system includes optical attenuation means capable of individually adjusting the attenuation amount of multiple light beams separated by the separation optical system, The separation optical system is Each optical beam from each core of the first optical fiber is incident on a first lens that widens the separation width by creating an angular difference in the optical path of each optical beam, A second lens into which each light beam that has passed through the first lens is incident, and which is used to arrange the optical paths of each light beam substantially in parallel, Each light beam that has passed through the second lens is incident on a third lens for narrowing the separation width of the optical paths of each light beam, The system includes a fourth lens into which each light beam that has passed through the third lens is incident and which couples the optical paths of each light beam to the respective cores of the second optical fiber, The rear focal position of the second lens and the front focal position of the third lens are aligned, and the light attenuation means is It is provided between the second lens and the third lens, Multiple light-shielding elements that individually block the multiple light beams, The system comprises multiple rotational motion mechanisms for rotating each of the multiple light-shielding elements, Half of the multiple light-shielding elements are positioned closer to the second lens than the focal point of the multiple light beams, and the other half are positioned closer to the third lens than the focal point. By rotating the light-shielding element using the aforementioned rotational motion mechanism, the amount of light shielding for each of the multiple light beams can be individually adjusted. Variable optical attenuator.

2. The light-shielding element is formed of an opaque material that does not transmit the light beam. The variable optical attenuator according to claim 1.

3. The light-shielding element is composed of an optical member that can deflect the direction of the light beam, thereby cutting off a portion of the light beam from the optical path. The variable optical attenuator according to claim 1.

4. A variable optical attenuator according to any one of claims 1 to 3, The system includes a control device that detects the amount of light propagating through each core of the second optical fiber, controls the optical attenuation means according to the detected amount of light, and individually adjusts the amount of attenuation of each beam by the optical attenuation means. Variable light attenuation system.

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