JP7590732B2 - Asymmetric bidirectional optical transmission module - Google Patents

Description

The present invention relates to an optical fiber connector including a reflective objective coupler, and an asymmetric bidirectional optical transmission module including an optical fiber to which the optical fiber connector is connected. The reflective objective coupler referred to here is an optical coupler having an optical system that performs wavefront transformation using a combination of multiple reflecting mirrors, similar to a reflective objective lens.

It is known that the optical paths along which light propagates within an optical fiber can be classified as the optical fiber's guided modes. For example, one or more guided modes appear within a single optical fiber depending on parameters such as the physical dimensions of the core and cladding regions of the optical fiber, the refractive index, wavelength, and angle of incidence. In multimode optical fibers that can have multiple guided modes, a method of transmitting a signal in each of the multiple guided modes is called a mode division multiplexing communication method, and technological development of this mode division multiplexing communication method has been underway for some time.

For example, the optical communication system of Patent Document 1 realizes mode division multiplexing communication by dividing upstream and downstream optical signals into a low-order mode group and a high-order mode group, which have significantly different propagation angles, and transmitting them using a single multimode optical fiber.

Specifically, the optical signal forming the low-order mode group from the low-order mode group light source is emitted from the aperture of the mode multiplexer/demultiplexer along the central axis of the multimode optical fiber, propagates through the multimode optical fiber, and enters the low-order mode group detector.

The optical signal that forms the higher-order mode group from the higher-order mode group light source is reflected by two mirrors to become convergent light, which converges near the end face of the multimode optical fiber and enters the multimode optical fiber at a greater angle to the central axis than the optical signal from the lower-order mode group light source. The optical signal that forms the entered higher-order mode group is reflected by two mirrors from the other end of the multimode optical fiber via the mode multiplexer/demultiplexer and enters the higher-order mode group detector.

JP 2019-169780 A

However, in conventional technology, depending on the type of refractive index distribution in the multimode optical fiber, interference may occur between the upstream and downstream optical signals, or high-speed signals may not be transmitted. In addition, the reflective objective lens using two mirrors in conventional technology may result in low coupling efficiency to the optical fiber.

The present invention has been made in consideration of the problems inherent in the conventional technology. The object of the present invention is to provide an optical fiber capable of high-speed communication in which multiple different core parts are appropriately arranged and interference between uplink and downlink optical signals is appropriately reduced, as well as an asymmetric bidirectional optical transmission module capable of improving the coupling efficiency to the optical fiber.

An optical fiber connector including a reflective objective coupler according to an aspect of the present invention, and an asymmetric bidirectional optical transmission module including an optical fiber, wherein the optical fiber connector further includes a first light-emitting element having a first numerical aperture and a first wavelength, and a first light emitted from the first light-emitting element is incident on the end face of the optical fiber via the reflective objective coupler, and a second light-receiving element that receives a second light emitted from a second light-emitting element having a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength, propagates through the optical fiber, and is preferably configured such that the second light propagates through a first core portion of the optical fiber, and the first light propagates through a second core portion including the first core portion of the optical fiber.

An optical fiber connector including a reflective objective coupler according to another aspect of the present invention, and an asymmetric bidirectional optical transmission module including an optical fiber, wherein the optical fiber connector further includes a first light receiving element that receives, via the reflective objective coupler, a first light emitting element that is radiated from a first light emitting element having a first numerical aperture and a first wavelength, propagates through the optical fiber, and is radiated from an end face of the optical fiber, and a second light emitting element that has a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength, and into whose end face the second light radiated from the second light emitting element is incident, and it is preferable that the second light propagates through a first core portion of the optical fiber, and the first light propagates through a second core portion including the first core portion of the optical fiber.

Another aspect of the present invention is an optical fiber connector including a reflective objective coupler, and an asymmetric bidirectional optical transmission module including an optical fiber, in which an optical fiber connector included in the asymmetric bidirectional optical transmission module is connected to one end of the optical fiber, and an optical fiber connector included in the asymmetric bidirectional optical transmission module is connected to the other end of the optical fiber.

The present invention makes it possible to provide an optical fiber capable of high-speed communication in which multiple different core parts are appropriately arranged and interference between uplink and downlink optical signals is appropriately reduced, and an asymmetric bidirectional optical transmission module including an optical fiber connector that can improve the coupling efficiency to the optical fiber.

FIG. 1 is a schematic diagram showing an example of implementation of a communication system including an asymmetric bidirectional optical transmission module according to the present embodiment. 1A is a schematic diagram showing an enlarged cross section of the optical fiber of FIG. 1 according to the present embodiment, (B) another schematic diagram showing an enlarged cross section of the optical fiber of FIG. 1 according to the present embodiment, and (C) a schematic diagram showing an enlarged longitudinal cross section of the optical fiber of FIG. 1 according to the present embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of the optical fiber connector of FIG. 1 according to the present embodiment. 1 is a schematic diagram showing an example of an asymmetric bidirectional optical transmission module according to an embodiment of the present invention; 5A to 5C are diagrams illustrating a method for defining the relative positions of optical elements according to the present embodiment. 6A and 6B are diagrams illustrating a method for defining the numerical aperture of the second mirror according to the present embodiment. 1A and 1B are schematic diagrams illustrating an example of an initial model when designing an optical element according to the present embodiment. FIG. 8 is a schematic diagram illustrating optical paths in the schematic diagram of FIG. 7 according to the present embodiment. FIG. 8 is a schematic diagram illustrating an optical path when the optical element is optimally designed based on the schematic diagram of FIG. 7 according to this embodiment. 11 is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, using the overall module length as a parameter. FIG. 11 is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, using the diameter of the second core portion as a parameter. FIG. 11 is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, using the numerical aperture of the second core portion as a parameter. FIG. 13 is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, using the numerical aperture of the second mirror as a parameter. FIG. (A) is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to this embodiment and the optical coupling efficiency with the optical fiber, with the total module length fixed at 30 mm and the numerical aperture of the second mirror as a parameter; (B) is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to this embodiment and the optical coupling efficiency with the optical fiber, with the total module length fixed at 50 mm and the numerical aperture of the second mirror as a parameter; (C) is a diagram showing the results of calculations of the relationship between the relative position of the optical element according to this embodiment and the optical coupling efficiency with the optical fiber, with the total module length fixed at 70 mm and the numerical aperture of the second mirror as a parameter; 1A is a diagram showing the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, the numerical aperture of the second mirror is fixed to 0.8, and the numerical aperture of the second core portion is used as a parameter, and (B) is a diagram showing the relationship between the relative position of the optical element according to the present embodiment and the optical coupling efficiency with the optical fiber, the numerical aperture of the second mirror is fixed to 0.9, and the numerical aperture of the second core portion is used as a parameter. The relationship between the relative position of the optical element and the optical coupling efficiency with the optical fiber when the numerical aperture of the second mirror is 0.4 and 0.5 is added to the diagram of FIG. 13 relating to this embodiment. This is a diagram illustrating the relationship between the numerical aperture of the second mirror and the optical coupling efficiency with the optical fiber, extracted from FIG. 16 according to this embodiment.

The following describes in detail an example of an optical fiber, an optical fiber connector, and an asymmetric bidirectional optical transmission module including an optical fiber and an optical fiber connector according to the present embodiment, with reference to the drawings. Note that the embodiments described below are comprehensive or specific examples. The numerical values, shapes, materials, components, component installation positions and connection forms, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the scope of the present disclosure. Furthermore, among the components in the following embodiments, components that are not described in an independent claim that indicates a superordinate concept are described as optional components. Furthermore, the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

(1) Overview of the configuration of an asymmetric bidirectional optical transmission module including an optical fiber and an optical fiber connector, and a communication system including the asymmetric bidirectional optical transmission module. FIG. 1 is a schematic diagram showing an overview of the configuration relationship of an asymmetric bidirectional optical transmission module 300 including an optical fiber 100, an optical fiber connector 200a, and an optical fiber connector 200b according to the present embodiment, and a communication system 400.

An imaging start signal as an electrical signal (not shown) is transmitted to the optical fiber connector 200a from a control unit 10 including a CPU (Central Processing Unit) (not shown). The imaging start signal input to the optical fiber connector 200a is converted from an electrical signal to an optical signal b1 by the first light-emitting element 240a and transmitted in the optical fiber 100 via the optical module 220a. The optical signal b1 transmitted in the optical fiber 100 is input to the first light-receiving element 240b via the optical module 220b of the optical fiber connector 200b and converted into an imaging start signal as an electrical signal (not shown). The imaging start signal converted into an electrical signal is input to an imaging device 20 such as a CCD camera, and the imaging device 20 starts imaging the surroundings. Image information captured by the imaging device 20 is input as an image signal to the second light-emitting element 230b of the optical fiber connector 200b. The image signal, which is an electrical signal input to the second light-emitting element 230b, is converted into an optical signal b2 and transmitted in the optical fiber 100 via the optical module 210b. The optical signal b2 transmitted through the optical fiber 100 is input to the second light receiving element 230a via the optical module 210a of the optical fiber connector 200a and converted into an image signal as an electrical signal (not shown). The image signal, which is an electrical signal, is input to the control unit 10, where image processing is performed. Note that the transmission speeds of the control signal, including the imaging start signal, and the data signal, including the image signal, in the optical fiber 100 are different. The transmission speed of the data signal is generally faster than the transmission speed of the control signal. In addition, the optical fiber 100, the first light emitting element 240a, the first light receiving element 240b, the second light emitting element 230b, and the second light receiving element 230a have frequency bands in which they can operate in accordance with the transmission speed.

In the above overview, the control unit 10 was described as a device that processes electrical signals connected to the optical fiber connector 200a, but the device that is connected to the optical fiber connector 200a is not limited to the control unit 10. Any electronic device that transmits and receives information to the outside can be connected to the optical fiber connector 200a. Similarly, in the above overview, the imaging device 20 was described as a device that operates by electrical signals connected to the optical fiber connector 200b, but the device that is connected to the optical fiber connector 200b is not limited to the imaging device 20. Any electronic device that transmits and receives information to the outside can be connected to the optical fiber connector 200b.

(2) Individual Outlines of the Optical Fiber, the Optical Fiber Connector, and the Asymmetric Bidirectional Optical Transmission Module The individual outlines of the optical fiber, the optical fiber connector, and the asymmetric bidirectional optical transmission module according to this embodiment will be further described with reference to FIGS.

(2.1) Overview of Optical Fiber FIG. 2 is a cross-sectional view showing an image of an optical fiber 100 according to this embodiment. As shown in FIG. 2A, the cross section of the optical fiber 100 has a quadruple (four-layer) structure consisting of a first core and a first clad concentrically arranged, and a second core and a second clad on the outside of the first core and a first clad. However, as shown in FIG. 2B, the first clad and the second core can be combined in the same layer, so that it can have at least a triple (three-layer) structure. That is, a first core portion (first core) 101 having a GI (Graded Index Fiber) structure is arranged inside the concentric circle of the cross section of the optical fiber 100. A second core portion (second core) 102 having a SI (Step-Index Fiber) structure is arranged outside the first core portion 101. The first core portion 101 and the second core portion 102 make it possible to spatially separate an upstream optical signal and a downstream optical signal within the optical fiber 100, making it an optical fiber capable of high-speed communication. In the case of the three-layer structure of FIG. 2(B), the refractive index of the first core is set to be smaller than the refractive index of the second core, and in the case of the four-layer structure of FIG. 2(A), the refractive index of the first core is not determined by the refractive index of the second core.

(2.2) Overview of the Optical Fiber Connector FIG. 3 is a schematic diagram showing an image of the optical fiber connector 200a according to the present embodiment. Inside the optical fiber connector 200a, a reflective objective coupler is disposed as an optical module 220a. The reflective objective coupler includes a first mirror 221a and a second mirror 222a. The first mirror 221a has a curved surface that is appropriately designed, and the second mirror is conical. The reflective surface of the first mirror 221a can be represented by an n-th degree polynomial (n is a natural number equal to or greater than 3). An optical signal emitted from a light source is reflected by the conical second mirror 222a, and the optical signal reflected by the second mirror 222a is reflected by the appropriately designed aspherical first mirror 221a, coupled to the end face of the optical fiber 100, and propagates through the second core portion 102 of the optical fiber 100. In this case, by making the second mirror conical, it becomes possible to couple a low emission angle component with high brightness in the light emitted from the light source with the optical fiber 100, so that it becomes possible to improve the coupling efficiency between the light source and the optical fiber 100. Note that in FIG. 3, the first light emitting element 240a is shown as the light source. Also, the reflective objective coupler can be realized with the same structure on the transmitting side and the receiving side. When the reflective objective coupler is used on the receiving side, it is possible to arrange a light receiving element such as a PD (Photo Diode) instead of the light source. Also, it is possible to make the coupling efficiency between the reflective objective coupler on the transmitting side and the optical fiber 100 approximately the same as the coupling efficiency between the reflective objective coupler on the receiving side and the optical fiber 100.

(2.3) Overview of the asymmetric bidirectional optical transmission module Fig. 4 is a schematic diagram showing an image of an asymmetric bidirectional optical transmission module 300 according to this embodiment. An optical fiber connector 200a and an optical fiber connector 200b incorporating a reflective objective coupler are connected to both ends of an optical fiber 100. In this specification, the optical fiber connector 200a and the optical fiber connector 200b may be collectively referred to as the optical fiber connector 200.

First, the flow of transmission and reception of optical signals transmitted by the first core portion 101 of the optical fiber 100 will be described. In FIG. 4, a case where an optical signal is transmitted from the optical fiber connector 200b to the optical fiber connector 200a will be described. However, since the first core portion 101 does not have a directionality of optical signals, if the optical fiber connector 200 is appropriately selected, it is also possible to transmit the optical signal in the opposite direction through the first core portion 101.

The optical signal emitted from the second light emitting element 230b built into the optical fiber connector 200b is converted into parallel light by the collimator lens 211b, and the converted parallel light is incident on the first core portion 101 of the optical fiber 100 by the condenser lens 212b. The optical module 210b shown in FIG. 1 includes the collimator lens 211b and the condenser lens 212b, but the configuration of the optical module 210b is not limited to this. For example, it is also possible for the optical module 210b to be composed of a single lens, and for the single lens to include the functions of the collimator lens 211b and the condenser lens 212b.

In the optical fiber connector 200a, the optical signal emitted from the first core portion 101 is converted into parallel light by the collimator lens 212a, and the converted parallel light is collected by the collecting lens 211a and is incident on the second light receiving element 230a. The optical module 210a shown in FIG. 1 includes the collimator lens 212a and the collecting lens 211a, but the configuration of the optical module 210a is not limited to this. For example, it is also possible for the optical module 210a to be composed of a single lens, and for the single lens to include the functions of the collimator lens 212a and the collecting lens 211a.

In the above cases, it is preferable that the collimator lens 211b and the condenser lens 211a are disposed at the same relative position in the optical fiber connector 200. It is also preferable that the collimator lens 212a and the condenser lens 212b are disposed at the same relative position in the optical fiber connector 200. It is also preferable that the second light receiving element 230a and the second light emitting element 230b are disposed at the same relative position in the optical fiber connector 200.
In addition, although the optical transmission module and the optical fiber are arranged coaxially in FIG. 4, it is also possible to bend the optical axis by using a mirror or the like on each connection surface or within the optical transmission module.

Next, the flow of transmission and reception of optical signals transmitted by the second core portion 102 of the optical fiber 100 will be described. In FIG. 4, a case where an optical signal is transmitted from the optical fiber connector 200a to the optical fiber connector 200b will be described. However, since the second core portion 102 does not have a directionality of the optical signal, if the optical fiber connector 200 is appropriately selected, it is also possible to transmit the optical signal in the opposite direction through the second core portion 102.

The optical signal emitted from the first light-emitting element 240a is reflected by the cone-shaped second mirror 222a as described above. The optical signal reflected by the second mirror 222a is reflected by the first mirror 221a having an appropriately designed curved surface, coupled to the end face of the optical fiber 100, and propagates through the second core portion 102 of the optical fiber 100. The optical module 220a shown in FIG. 1 includes the first mirror 221a and the second mirror 222a, but the details of the configuration including the optical module 220a and the first light-emitting element 240a will be described later. Furthermore, the optical signal propagated through the second core portion 102 is emitted from the other end face of the optical fiber 100, reflected by the first mirror 221b in the direction of the second mirror 222b, and the optical signal reflected by the second mirror 222b is incident on the first light-receiving element 240b. The optical module 220b shown in FIG. 1 includes a first mirror 221b and a second mirror 222b, but details of the configuration including the optical module 220b will be described later.

In the above cases, it is preferable that the first mirror 221a and the first mirror 221b are arranged at the same relative position in the optical fiber connector 200. It is also preferable that the second mirror 222a and the second mirror 222b are arranged at the same relative position in the optical fiber connector 200. It is also preferable that the first light-emitting element 240a and the first light-receiving element 240b are arranged at the same relative position in the optical fiber connector 200. In this embodiment, the first mirror 221a and the first mirror 221b may be collectively referred to as the first mirror 221. In addition, the second mirror 222a and the second mirror 222b may be collectively referred to as the second mirror 222.

In addition, in the optical fiber connector 200a, when the first light receiving element 240b is placed at the position of the first light emitting element 240a, it is possible to place the second light emitting element 230b at the position of the second light receiving element 230a. In the optical fiber connector 200b, it is possible to place the second light receiving element 230a at the position of the second light emitting element 230b, and place the first light emitting element 240a at the position of the first light receiving element 240b.

(3) Details of the Optical Fiber, the Optical Fiber Connector, and the Asymmetric Bidirectional Optical Transmission Module The optical fiber 100 will be described in detail with reference to Fig. 2. The optical fiber connector 200 will be described in detail with reference to Figs. 3, 5, and 6. Furthermore, the asymmetric bidirectional optical transmission module 300 will be described in detail with reference to Fig. 4.

となり、第２コア部内の伝搬光に対する開口数は

となる。 (3-1) Details of the Optical Fiber FIG. 2C, which is an enlarged cross-sectional view of the optical fiber 100 in FIG. 1, will be described in more detail. As shown in FIG. 2C, the first core portion 101 of the GI structure is disposed inside the concentric circle of the cross-section of the optical fiber 100. Also, the second core portion 102 of the SI structure is disposed outside the first core portion 101. The diameter of the optical fiber 100 is preferably 500 to 1000 μm, but is not limited to this value, and the diameter of the optical fiber 100 may be thinner than 500 μm or thicker than 1000 μm. The optical signal b2 input to the first core portion 101 is transmitted by meandering between the side surfaces of the first core portion 101 around the central axis C1 inside the first core portion 101 of the GI structure. A cladding layer is formed on the outer periphery of the first core portion 101 (not shown), and the optical signal b2 remains inside the first core portion 101. The optical signal b1 incident on the second core portion 102 is transmitted by meandering between the side surfaces of the second core portion 102 around the central axis C1 inside the second core portion 102 of the SI structure. A clad layer is formed on the outer periphery (not shown) of the second core portion 102, and the optical signal b1 remains inside the second core portion 102. In this way, the upstream optical signal/downstream optical signal can be spatially separated within the optical fiber 100. In addition, the material of the core portion and the clad portion of the optical fiber 100 is preferably made of a material having high transparency and low optical propagation loss such as glass or plastic, but is not limited to glass and plastic. It is also possible to adopt any material having high transparency, low optical propagation loss, and controllable refractive index for the core portion and the clad portion of the optical fiber 100. In addition, it is also possible to configure the first core portion 101 and the second core portion 102 with different materials. In addition, the numerical aperture for the propagating light in the first core portion is

The numerical aperture for the light propagating in the second core portion is

It becomes.

の場合においては侵入した光信号ｂ１のほとんどはそのまま第２コア部１０２に突き抜けることになる。 By using a semiconductor light emitting element as the light source, it is possible to miniaturize the entire system. For example, a semiconductor light emitting element capable of transmitting a high-speed signal of several Gbps or more can be used for the optical signal b2. As an example, a vertical cavity surface emitting laser (VCSEL) that is a semiconductor light emitting element capable of operating at a high frequency can be used as the second light emitting element 230b. Also, for example, a semiconductor light emitting element capable of transmitting a medium-speed signal of about several Mbps, which is slower than the VCSEL, can be used for the optical signal b1. As an example, an LED (light emitting diode) can be used as the first light emitting element 240a for the semiconductor light emitting element capable of transmitting a medium-speed signal. By using these light sources, it may be possible to prevent optical signal interference between the upstream optical signal and the downstream optical signal, and to prevent signal attenuation due to band limitation by propagating the optical signal through a core having core characteristics corresponding to each propagation band. Note that the optical signal b1 transmitted by the second core portion 102 may enter the first core portion 101, but in a general setting,

In the case of (a), most of the intruding optical signal b1 passes through to the second core portion 102 as it is.

(3-2) Details of the Optical Fiber Connector As shown in FIG. 3, the reflective objective coupler includes an aspherical first mirror 221a and a conical second mirror 222a. The spatial distance between the aspherical first mirror 221a and the first light-emitting element 240a is preferably 10 to 30% of the total length of the reflective objective coupler. In addition, it is preferable to arrange the light source of the optical signal b1 in the optical fiber connector 200 so that the numerical aperture (NA) of the second mirror 222 with respect to the light source is 0.8 or more. The total length of the reflective objective coupler means the distance from the first mirror 221a to the position where the optical signal b1 is focused along the central axis C1 of the optical fiber 100.

(Regarding the relationship between the arrangement of the first mirror, the second mirror, and the first light emitting element 240a, and the overall length of the reflective objective coupler)
5 is a schematic diagram showing the positional relationship between the aspherical first mirror 221a, the conical second mirror 222a, and the first light emitting element 240a in the optical fiber connector 200a. The light emitted from the first light emitting element 240a is reflected by the conical second mirror 222a toward the aspherical first mirror 221a, and the light reflected by the aspherical first mirror 221a is collected at the end face of the optical fiber 100.

The intersection point between the central axis C1 of the optical fiber 100 and the aspheric first mirror 221a is x1, the intersection point between the central axis C1 and the first light-emitting element 240a is x2, and the intersection point between the focal point of the light reflected by the first mirror 221a and the central axis C1 is x3. In this case, the spatial distance from x1 to x2 is l2, the spatial distance from x1 to x3 is l1, and (l2/l1) x 100 is defined as the relative position [%] of the light-emitting/light-receiving element. In FIG. 5, the relative position of the light-emitting/light-receiving element indicates the relative position of the first light-emitting element 240a in the optical fiber connector 200a. In the optical fiber connector 200b, the relative position [%] of the first light-receiving element 240b is defined in the same way as in the optical fiber connector 200a. The spatial distance l1 may also be referred to as the total length of the reflective objective coupler. Therefore, the spatial distance between the aspherical first mirror 221 and the first light-emitting element 240a being 10-30% of the total length of the reflective objective coupler means that the relative position [%] of the light-emitting and light-receiving elements is 10-30%.

If the relative position [%] of the light emitting/receiving element is large, the overall length of the reflective objective coupler may become long, and the overall length of the optical fiber connector 200 may become long. In this case, the optical fiber connector 200 may become large. Also, if the relative position [%] of the light emitting/receiving element is large, in order to supply a sufficient amount of light to the optical fiber 100, the second mirror 222 needs to be enlarged or moved, and the optical fiber connector 200 may become large. On the other hand, if the relative position of the light emitting/receiving element is small, there is a possibility that the second mirror 222 will not be able to use the far-field pattern (light distribution pattern at a long distance where the size of the light source can be ignored) of the first light emitting element 240a. There is also a possibility that the second mirror 222 will be affected by the heat generated by the first light emitting element 240a.

(Regarding the numerical aperture (NA) of the second mirror 222 with respect to the light source of the optical signal b2)
6 is a schematic diagram showing an enlarged view of a portion including the first light-emitting element 240a and the cone-shaped second mirror 222a in FIG. 5. As described above, the light emitted from the first light-emitting element 240a is reflected by the cone-shaped second mirror 222a toward the aspherical first mirror 221a. In this case, the numerical aperture of the second mirror 222 is defined as sin θ, which is the sine of the maximum angle θ between the central axis C1 and the light emitted from the first light-emitting element 240a among the light reflected toward the first mirror 221a. Since the light emitted from the first light-emitting element 240a has a light distribution characteristic in which the angle from the central axis C1 is greatly expanded, the numerical aperture of the second mirror is one of the important factors in order to obtain the required light intensity.

(3-2-1) Design Procedure for Optical Fiber Connector As described above, the optical coupling efficiency between the optical element and the optical fiber 100 in the optical fiber connector 200 changes depending on the relative positional relationship of the optical element to the optical fiber 100. Therefore, a method for simulating the change in coupling efficiency will be described.

(Early model)
FIG. 7 is a diagram showing a schematic diagram of an initial arrangement relationship between the spherical first mirror 221c, the conical second mirror 222a, the first light emitting element 240a, and the optical fiber 100. Optimization of the arrangement of each optical element is started from the initial arrangement relationship. The total length l1 of the reflective objective coupler is set to an arbitrary distance, and the first light emitting element 240a is arranged at an arbitrary position on the central axis C1 of the optical fiber 100. The first mirror 221c is made spherical with the total length l1 of the reflective objective coupler as the radius of curvature. Specifically, the arrangement method of the initial model will be described with a focus on the arrangement method of the second mirror 222a. The second mirror 222a is arranged so that the numerical aperture of the second mirror 222a satisfies a significant arbitrary value, and the point x1 on the diameter of the second mirror 222a is an intersection point with the straight line l3 that satisfies the numerical aperture sin α of the first core portion 101. However, since the second mirror 222a is located at the position shown in FIG. 7, the position farthest from the first light-emitting element 240a along the central axis C1 is appropriate. For example, when the numerical aperture of the first core is 0.2, the above α is 11.5 degrees. Next, a method for determining the conical surface angle γ will be described. The conical surface angle γ of the second mirror 222a is determined so that the light emitted from the light emission center of the first light-emitting element 240a to the central axis C1 is incident from the second mirror 222a to the intersection x2 of the first mirror 221c and the above straight line l3. Note that when determining the conical surface angle γ, it is assumed that a conical surface with an angle γ also exists at the apex of the cone. The radius l4 of the conical base of the second mirror 222a is the length of the perpendicular line from the intersection x1 to the central axis C1. The arrangement of the initial model thus determined is shown in FIG. 7.

Figure 8 is a schematic diagram showing the path of light when light is emitted from the first light-emitting element 240a in the initial arrangement in Figure 7. As is clear from Figure 8, the light reflected from the spherical first mirror 221c travels in a direction away from the optical fiber 100, rather than toward the end face of the optical fiber 100.

(optimization)
The spherical first mirror 221c is changed to an aspheric surface represented by an n-th order polynomial (n is a natural number of 3 or more), and the coefficients are changed to optimize the light emitted from the first light-emitting element 240a on the end surface of the optical fiber 100. FIG. 9 shows the result of the calculation process in which the surface shape of the first mirror 221c in FIG. 7 is changed to an aspheric surface, and the light emitted from the first light-emitting element 240a is condensed on the end surface of the optical fiber 100. Next, the relationship between the relative position [%] of the light-emitting/light-receiving element and the coupling efficiency [%] will be described with the total length of the reflective objective coupler, the core diameter of the second core portion 102, the NA of the second core portion 102, and the NA of the second mirror 222 as parameters. Note that the aspheric surface of the first mirror 221a in the following description is an aspheric surface represented by a 12th order polynomial.

(When the total length of the reflective objective coupler is used as a parameter)
FIG. 10 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the total length l1 of the reflective objective coupler in FIG. 7 is changed from 10 mm to 70 mm. In the following figures, l1 may be described as the total length of the module. The vertical axis shows the coupling efficiency [%], which expresses the ratio in percentage of the intensity of the light incident on the second core portion 102 of the optical fiber 100 to the intensity of the light emitted from the first light emitting element 240a. The horizontal axis expresses the relative position of the light emitting/receiving element described above in percentage. In FIG. 10, the diameter of the second core portion 102 is 500 μm, the numerical aperture of the second core portion 102 is 0.5, and the numerical aperture of the second mirror 222 is 0.8, and the relative position of the light emitting/receiving element is changed from 10.0% to 50.0%. As can be seen from the plot in Fig. 10, when the total length l1 of the reflective objective coupler was changed between 10 mm and 70 mm, no significant difference was observed in the change in coupling efficiency with respect to the relative position of the light emitting and receiving elements. In other words, when the total length l1 of the reflective objective coupler was between 10 mm and 70 mm, it was found that the coupling efficiency had a maximum value when the relative position of the light emitting and receiving elements was between 10.0% and 20.0%.

(When the diameter of the second core portion 102 is used as a parameter)
11 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the diameter of the second core portion 102 in FIG. 7 is changed from 200 μm to 1000 μm. As in FIG. 10, the vertical axis shows the coupling efficiency [%], which expresses the ratio of the intensity of the light incident on the second core portion 102 of the optical fiber 100 to the intensity of the light emitted from the first light emitting element 240a in percentage. The horizontal axis shows the relative position of the light emitting/receiving element in percentage. In FIG. 11, the total length l1 of the reflective objective coupler is set to 10 mm, the numerical aperture of the second core portion 102 is set to 0.5, and the numerical aperture of the second mirror 222 is set to 0.8, and the relative position of the light emitting/receiving element is changed from 10.0% to 50.0%. When the diameter of the second core portion 102 is increased, the amount of light incident on the optical fiber 100 increases, and therefore the coupling efficiency increases. However, even if the diameter of the second core portion 102 changes, the relative position of the light emitting/receiving element at which the maximum value of the coupling efficiency appears is between 10.0% and 20.0%, and it can be seen that there is little change in the relative position of the point at which the maximum value appears.

(When the numerical aperture _NA2 of the second core portion 102 is used as a parameter)
12 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the numerical aperture _NA2 of the second core portion 102 in FIG. 7 is changed from 0.3 to 0.6. As in FIG. 10, the vertical axis shows the coupling efficiency [%], which is expressed as a percentage of the ratio of the intensity of the light incident on the second core portion 102 of the optical fiber 100 to the intensity of the light emitted from the first light emitting element 240a. In FIG. 12, the total length l1 of the reflective objective coupler is 10 mm, the diameter of the second core portion 102 is 500 μm, and the numerical aperture of the second mirror 222 is 0.8, and the relative position of the light emitting/receiving element is changed from 10.0% to 50.0%. When the numerical aperture of the second core portion 102 is increased, the amount of light incident on the optical fiber 100 increases, so the coupling efficiency tends to increase. 12, when the numerical aperture of the second core portion 102 is increased and the relative position [%] of the light emitting/receiving element is decreased, some areas of light are vignetted due to the arrangement of the optical elements, and therefore the tendency of the plot differs between the cases where the numerical aperture of the second core portion 102 is small and the case where the numerical aperture of the second core portion 102 is large. However, it can be seen that even if the numerical aperture of the second core portion 102 is changed, the relative position of the light emitting/receiving element at which the maximum value of the coupling efficiency appears is between 10.0% and 30.0%.

(When the numerical aperture of the second mirror is used as a parameter)
Fig. 13 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the numerical aperture of the second mirror 222 in Fig. 7 is changed from 0.6 to 0.9. As in Fig. 10, the vertical axis shows the coupling efficiency [%], which is expressed in percentage as the ratio of the intensity of the light incident on the second core portion 102 of the optical fiber 100 to the intensity of the light emitted from the first light emitting element 240a. In Fig. 13, the total length l1 of the reflective objective coupler is 50 mm, the diameter of the second core portion 102 is 500 μm, and the numerical aperture of the second core portion 102 is 0.5, and the relative position of the light emitting/receiving element is changed from 10.0% to 50.0%. When the numerical aperture of the second mirror is increased, the amount of light reflected by the second mirror increases, and the amount of light incident on the optical fiber 100 increases, so that the coupling efficiency tends to increase. 13, when the numerical aperture of the second mirror 222 is increased, it may be difficult to secure the numerical aperture unless the relative positions of the light emitting and receiving elements are increased. However, when the numerical aperture of the second mirror 222 is 0.7 or more, it is expected that the relative positions of the light emitting and receiving elements at which the maximum value of the coupling efficiency appears will be between 10.0% and 30.0%, even if the numerical aperture of the second mirror 222 changes. It can also be seen that when the numerical aperture of the second mirror 222 is 0.7 or more, the maximum value of the coupling efficiency is 40.0% or more when the relative positions of the light emitting and receiving elements are between 10.0% and 30.0%.

(When the numerical aperture of the second mirror is used as a parameter and the total length of the reflective objective coupler is changed)
Fig. 14 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the total length of the reflective objective coupler is changed from 50 mm in Fig. 13 to the front or rear with the numerical aperture of the second mirror as a parameter. Fig. 14(A) shows the case where the total length of the reflective objective coupler is 30 mm, Fig. 14(B) is the same as Fig. 13, and Fig. 14(A) shows the case where the total length of the reflective objective coupler is 70 mm. From Figs. 14(A) to (C), when the numerical aperture of the second mirror 222 is 0.7 or more, it is expected that the relative position of the light emitting/receiving element at which the maximum value of the coupling efficiency appears will be between 10.0% and 30.0%, even if the numerical aperture of the second mirror 222 is changed.

(When the numerical aperture of the second mirror is changed with the numerical aperture of the second core portion 102 as a parameter)
15 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the numerical aperture of the second mirror is changed to 0.8 and 0.9 with the numerical aperture of the second core portion 102 as a parameter. Fig. 15(A) shows the case where the numerical aperture of the second mirror is 0.8, and Fig. 15(B) shows the case where the numerical aperture of the second mirror is 0.9. The maximum value or the local maximum value of the coupling efficiency changes depending on the numerical aperture of the second core portion 102, but it is expected that the relative position of the light emitting/receiving element where the maximum value of the coupling efficiency appears will be between 10.0% and 30.0%.

(When the numerical aperture of the second mirror is added as a parameter)
16 is a diagram showing the relationship between the relative position [%] of the light emitting/receiving element and the coupling efficiency [%] when the numerical aperture of the second mirror is set to 0.4 and 0.5 in FIG. 13. When the numerical aperture of the second mirror is set to 0.4 and 0.5, no significant change in the coupling efficiency is observed when the relative position of the light emitting/receiving element is between 10% and 30%. Therefore, as described above, when the numerical aperture of the second mirror 222 is 0.7 or more, it can be seen that the maximum value of the coupling efficiency is 40.0% or more when the relative position of the light emitting/receiving element is between 10.0% and 30.0%.

Figure 17 is a diagram extracted from Figure 16 of this embodiment showing the relationship between the numerical aperture of the second mirror and the optical coupling efficiency with the optical fiber. From the plot in Figure 17, it can be seen that when the numerical aperture of the second mirror is between 0.6 and 0.8, the slope of the graph tends to change from a concave direction to a convex direction. In particular, Figure 17 shows that the tendency of the maximum coupling efficiency to change above and below the numerical aperture of the second mirror of 0.7 may change. For example, when the numerical aperture of the second mirror is 0.7 or more and less than 1, it is possible to assume that the maximum coupling efficiency has a tendency to gradually approach a peak value as the numerical aperture of the second mirror is increased. Conversely, when the numerical aperture of the second mirror is less than 0.7, it can be seen from Figure 17 that the maximum coupling efficiency drops sharply as the numerical aperture of the second mirror is reduced.

In addition, in the figures showing the graphs above, it is shown that there is no solution when there are no plots at positions where the relative positions of the light emitting and receiving elements are less than 30%.

Furthermore, it is preferable that the light source of the optical signal b2 and the light source of the optical signal b1 are provided as semiconductor chips and are mounted in the optical fiber connector 200. In this embodiment, the calculations were performed assuming that the size of the semiconductor chip of the light-emitting element or the light-receiving element is 200 μm × 200 μm (length × width).

As mentioned above, if the core diameter is the same, the larger the numerical aperture of the optical fiber, and if the numerical aperture is the same, the larger the core diameter of the optical fiber, the higher the coupling efficiency.

As described above, the positional relationship of the optical elements in the asymmetric bidirectional optical transmission module 300 is preferably as follows. In the direction of the central axis C1 of the optical fiber, the distance l2 between the first mirror 221a and the first light-emitting element 240a is preferably in the range of 10% to 30% of the distance l1 from the first mirror 221a to the position where the first light reflected by the first mirror is focused. Similarly, in the direction of the central axis of the optical fiber 100, the distance l2 between the first mirror 221b and the first light-receiving element 240b is preferably in the range of 10% to 30% of the distance l1 to the end face of the fiber from which the first light incident on the first mirror 221b is emitted.

The above configuration makes it possible to improve the efficiency of light coupling between the optical fiber and the light entering and exiting the optical fiber. In particular, when the range of ((l2/l1) x 100) is between 10% and 30%, the peak of the light coupling efficiency with the optical fiber appears.

As described above, it is preferable that the numerical aperture of the second mirrors 222a, 222b of the asymmetric bidirectional optical transmission module 300 is greater than or equal to 0.7 and less than 1.

According to the above configuration, when the numerical aperture of the second mirror is changed, the peak of the optical coupling efficiency with the optical fiber appears in the range of 10% to 30% of the value of ((l2/l1) x 100) when the numerical aperture of the second mirror is in the range of 0.7 or more and less than 1.

The above-described configuration of the asymmetric bidirectional optical transmission module 300 makes it possible to provide an optical fiber capable of high-speed communication by appropriately arranging multiple different core parts and appropriately reducing interference between uplink and downlink optical signals. It is also possible to provide an asymmetric bidirectional optical transmission module that includes an optical fiber connector that can improve the coupling efficiency to the optical fiber.

(Variation 1)
In the above embodiment, the second light receiving element 230a and the optical module 210a are mainly described as being separated from each other, but it is also possible to configure the second light receiving element 230a and the optical module 210a as one unit. For example, it is also possible to integrate a single lens having a collimating function and a condensing function on the light receiving surface of the second light receiving element 230a with the second light receiving element 230a. An example of the second light receiving element 230a is a light receiving semiconductor element such as a photodiode or a phototransistor. In addition, in the above embodiment, the second light emitting element 230b and the optical module 210b are mainly described as being separated from each other, but it is also possible to configure the second light emitting element 230b and the optical module 210b as one unit. For example, it is also possible to integrate a single lens having a collimating function and a condensing function on the light emitting surface of the second light emitting element 230b with the second light emitting element 230b. An example of the second light emitting element 230b is the VCSEL, which is the semiconductor laser described above.

(Variation 2)
In the above embodiment, the first core portion 101 has been described as being a multimode optical fiber with a GI structure. However, the first core portion 101 is not limited to being a multimode optical fiber with a GI structure. For example, the first core portion 101 may be a single mode optical fiber. In this case, it is preferable that the second core portion 102 is a multimode optical fiber with an SI structure. Even when the first core portion 101 is a single mode optical fiber, it is possible to make the signal transmission speed of the first core portion 101 faster than the signal transmission speed of the second core portion 102. In addition, in order to make the signal transmission speed of the first core portion 101 about 1 Gbps or 1 Gbps or more, the description has been given mainly on the case where a VCSEL is used as the second light-emitting element 230b, but the second light-emitting element 230b is not limited to a VCSEL. For example, it may be possible to use any laser as the second light-emitting element 230b as long as it has a gigahertz frequency band.

The following describes the characteristics of the asymmetric bidirectional optical transmission module 300 including the optical fiber 100 and optical fiber connector 200 of this embodiment.

The optical fiber connector 200a including the reflective objective coupler according to the first aspect of the present disclosure, and the optical fiber connector 200a in the asymmetric bidirectional optical transmission module 300 including the optical fiber 100, preferably include the following configuration. The optical fiber connector 200a preferably includes a first light-emitting element 240a having a first numerical aperture and a first wavelength. The first light emitted from the first light-emitting element 240a is preferably incident on the end face of the optical fiber 100 via the reflective objective coupler. In addition, the optical fiber connector 200a preferably includes a second light-receiving element 230a having the following configuration. The second light-receiving element 230a preferably receives the second light emitted from the second light-emitting element 230b having a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength, propagates through the optical fiber 100, and is emitted from the end face of the optical fiber 100. It is also preferable that the second light propagates through the first core portion 101 of the optical fiber 100, and the first light propagates through the second core portion 102 that includes the first core portion 101 of the optical fiber.

The above configuration makes it possible to realize an optical fiber capable of high-speed communication with multiple cores appropriately arranged to appropriately reduce interference between uplink and downlink optical signals, and an optical fiber connector that can improve the coupling efficiency to the optical fiber.

The optical fiber connector 200b including a reflective objective coupler according to the second aspect of the present disclosure, and the optical fiber connector 200b in the asymmetric bidirectional optical transmission module 300 including an optical fiber 100, preferably include the following configuration. The optical fiber connector 200b preferably includes a first light receiving element 240b having the following configuration. The first light receiving element 240b preferably receives the first light emitted from the first light emitting element 240a having a first numerical aperture and a first wavelength, propagates through the optical fiber 100, and is emitted from the end face of the optical fiber 100 via the reflective objective coupler. In addition, the optical fiber connector 200b preferably includes a second light emitting element 230b having a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength. It is preferable that the second light emitted from the second light emitting element 230b is incident on the end face of the optical fiber 100. It is preferable that the second light propagates through the first core portion 101 of the optical fiber 100, and the first light propagates through the second core portion 102 including the first core portion 101 of the optical fiber 100.

The above configuration makes it possible to realize an optical fiber capable of high-speed communication with multiple cores appropriately arranged to appropriately reduce interference between uplink and downlink optical signals, and an optical fiber connector that can improve the coupling efficiency to the optical fiber.

The optical fiber connector 200 including a reflective objective coupler and the asymmetric bidirectional optical transmission module 300 including an optical fiber 100 according to the third aspect of the present disclosure preferably include an optical fiber connector 200 having the following configuration. That is, the asymmetric bidirectional optical transmission module 300 preferably has an optical fiber connector 200a according to the first aspect connected to one end of the optical fiber 100. The asymmetric bidirectional optical transmission module 300 preferably has an optical fiber connector 200b according to the second aspect connected to the other end of the optical fiber 100.

The above configuration makes it possible to realize an appropriate asymmetric bidirectional optical transmission module by using an optical fiber capable of high-speed communication in which multiple cores with different characteristics are appropriately arranged and interference between uplink and downlink optical signals is appropriately reduced, and an optical fiber connector that can improve the coupling efficiency to the optical fiber.

The first light-emitting element 240a of the asymmetric bidirectional optical transmission module 300 according to the fourth aspect of the present disclosure is preferably a non-coherent light source, and the second light-emitting element 230b is preferably a coherent light source.

The above configuration makes it possible to realize an asymmetric bidirectional optical transmission module that can appropriately set the transmission speed of uplink and downlink optical signals by appropriately arranging multiple different cores and appropriately selecting the characteristics of the light transmitted through the cores in relation to the characteristics of the cores.

The first light-emitting element 240a of the asymmetric bidirectional optical transmission module 300 according to the fifth aspect of the present disclosure is preferably an LED (light emitting diode), and the second light-emitting element 230b is preferably a laser light source.

The above configuration makes it possible to realize an asymmetric bidirectional optical transmission module that can appropriately set the transmission speed of uplink and downlink optical signals by appropriately arranging multiple different cores and appropriately selecting the characteristics of the light transmitted through the cores in relation to the characteristics of the cores.

The numerical aperture of the first core portion 101 of the optical fiber 100 of the asymmetric bidirectional optical transmission module 300 according to the sixth aspect of the present disclosure is preferably smaller than the numerical aperture of the second core portion 102. The first core portion 101 is preferably an optical fiber with a graded index fiber (GI) structure or a single mode optical fiber. The second core portion 102 is preferably located in the cladding portion on the outer periphery of the first core portion 101, and the second core portion 102 not including the first core portion 101 is preferably an optical fiber with a step-index fiber (SI) structure. The first core portion 101 and the second core portion 102 are preferably capable of propagating light in both directions.

According to the above configuration, in a transmission system in which the transmission speeds of upstream and downstream signals are different, it becomes possible to properly perform two-way communication using a single optical fiber having a GI structure or a single-mode optical fiber structure within an SI structure.

The reflective objective coupler of the asymmetric bidirectional optical transmission module 300 according to the seventh aspect of the present disclosure preferably includes an aspherical first mirror 221 and a conical second mirror 222. The second mirror 222a preferably reflects the light emitted from the first light-emitting element 240a in the direction of the first mirror 221a, and the first mirror 221a preferably focuses the light reflected by the second mirror 222a on the end face of the optical fiber 100. Alternatively, the first mirror 221b preferably reflects the light emitted from the end face of the optical fiber 100 in the direction of the second mirror 222b, and the second mirror 222b preferably focuses the light reflected by the first mirror 221b on the first light-receiving element 240b.

The above configuration allows components such as reflective objective couplers to be configured in an appropriate arrangement, which reduces the cost of components and the manufacturing costs associated with manufacturing precision, making it possible to reduce component and manufacturing costs. Also, compared to conventional single-core bidirectional links, it is possible to minimize the internal configuration of the connector to accommodate the desired transmission speed.

The second light receiving element 230a of the asymmetric bidirectional optical transmission module 300 according to the eighth aspect of the present disclosure is preferably located between the second mirror 222a and the optical fiber 100, and the first light emitting element 240a is preferably located between the second mirror 222a and the first mirror 221a. The second light emitting element 230b is preferably located between the second mirror 222b and the optical fiber 100, and the first light receiving element 240b is preferably located between the second mirror 222b and the first mirror 221b.

The above configuration makes it possible to position the reflective objective coupler, the light emitting element, and the light receiving element in appropriate positions, thereby improving the efficiency of coupling between the light entering and exiting the optical fiber and the optical fiber.

The positional relationship of the optical elements in the asymmetric bidirectional optical transmission module 300 according to the ninth aspect of the present disclosure is preferably as follows. In the direction of the central axis C1 of the optical fiber, the distance l2 between the first mirror 221a and the first light emitting element 240a is preferably in the range of 10% to 30% of the distance l1 from the first mirror 221a to the position where the first light reflected by the first mirror is focused. In the direction of the central axis C1 of the optical fiber 100, the distance l2 between the first mirror 221b and the first light receiving element 240b is preferably in the range of 10% to 30% of the distance l1 to the end face of the fiber from which the first light incident on the first mirror 221b is emitted.

The above configuration allows the reflective objective coupler, light emitting element, and light receiving element to be positioned in appropriate positions, improving the efficiency of light coupling between the light entering and exiting the optical fiber and the optical fiber. In particular, the peak of the light coupling efficiency with the optical fiber appears when the range of ((l2/l1) x 100) is between 10% and 30%.

The numerical aperture of the second mirrors 222a, 222b of the asymmetric bidirectional optical transmission module 300 according to the tenth aspect of the present disclosure is preferably 0.7 or more and less than 1.

According to the above configuration, when the numerical aperture of the second mirror is changed, the peak of the optical coupling efficiency with the optical fiber appears in the range of 10% to 30% of the value of ((l2/l1) x 100) when the numerical aperture of the second mirror is in the range of 0.7 or more and less than 1.

(Supplementary description of the embodiment)
The block diagrams used in the description of the above-mentioned embodiments show functional blocks. The method of realizing each functional block is not particularly limited. For example, each functional block may be realized using one device that is physically or logically coupled, or may be realized using two or more devices that are physically or logically separated and directly or indirectly connected to each other.

When the control unit 10 and/or the imaging device 20 are configured with multiple hardware elements, the functional blocks (not shown) of the control unit 10 and/or the imaging device 20 are realized by any one of the hardware elements or a combination of the hardware elements. Examples of the hardware elements include a processor, memory, storage, a communication device, an input device, an output device, a bus, etc.

In this case, each function of the control unit 10 and/or the imaging device 20 is realized by loading a specific software or program onto hardware such as a processor and memory. Specifically, each function is realized by loading specific software onto the hardware, causing the processor to perform calculations and control the reading and writing of data in the memory and storage.

In this disclosure, the determination may be made based on a value represented by one bit (0 or 1), a Boolean (true or false) value, or a comparison of numerical values (e.g., a comparison with a predetermined value).

The process steps, sequences, flow charts, etc. of each aspect, variation, or embodiment described herein may be reordered unless inconsistent. For example, the methods described in this disclosure present elements of various steps using an example order and are not limited to the particular order presented.

In addition, the information, parameters, etc. described in this disclosure may be expressed using absolute values, may be expressed using relative values from a predetermined value, or may be expressed using other corresponding information.

The names used for the parameters described above are not limiting in any way. Furthermore, the formulas etc. using these parameters may differ from those explicitly disclosed in this disclosure. The various names are not limiting in any way.

The terms "connected," "coupled," or any variation thereof, mean any direct or indirect connection or coupling between two or more elements. It may also include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The coupling or connection between the elements may be physical, logical, or a combination thereof.

As used in this disclosure, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

Any reference to elements using designations such as "first," "second," etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient way to distinguish between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed or that the first element must precede the second element in some way.

The word "part" in the configuration of each of the above devices may be replaced with "means," "device," etc.

When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, similar to the term "comprising." Additionally, the term "or," as used in this disclosure, is not intended to be an exclusive or.

In this disclosure, where articles have been added through translation, such as a, an, and the in English, this disclosure may include that the nouns following these articles are in the plural form.

In this disclosure, the term "A and B are different" may mean "A and B are different from each other." The term may also mean "A and B are each different from C." Terms such as "separate" and "combined" may also be interpreted in the same way as "different."

Each aspect/embodiment described in this disclosure may be used alone, in combination, or switched depending on the execution. In addition, notification of specific information (e.g., notification that "X is the case") is not limited to being done explicitly, but may be done implicitly (e.g., not notifying the specific information).

Although the embodiments have been described in detail with reference to the drawings, the present invention is not limited to the contents described in the above embodiments. Furthermore, the components described above include those that a person skilled in the art would easily imagine and those that are substantially the same. Furthermore, the configurations described above can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 10 control unit 20 imaging device 100 optical fiber 101 first core portion 102 second core portion 200a, 200b optical fiber connector 221a, 221b first mirror 222a, 222b second mirror 230a second light receiving element 230b second light emitting element 240a first light emitting element 240b first light receiving element 300 asymmetric bidirectional optical transmission module 400 communication system

Claims (7)

An optical fiber connector including a reflective objective coupler, and an asymmetric bidirectional optical transmission module including an optical fiber,
The optical fiber connector includes:
a first light-emitting element having a first numerical aperture and a first wavelength, wherein a first light emitted from the first light-emitting element is incident on an end face of the optical fiber via the reflective objective coupler;
a second light receiving element configured to receive second light emitted from a second light emitting element having a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength, propagating through the optical fiber, and emitting second light from the end face;
the reflective objective coupler includes an aspherical first mirror and a conical second mirror, the second mirror reflecting light emitted from the first light emitting element in a direction toward the first mirror, and the first mirror focusing the light reflected by the second mirror onto an end face of the optical fiber;
In the central axis direction of the optical fiber,
a distance between the first mirror and the first light-emitting element is in a range of 10% to 30% of a distance from the first mirror to a position where the first light reflected by the first mirror is collected;
the numerical aperture of the second mirror is equal to or greater than 0.7 and less than 1;
an asymmetric bidirectional optical transmission module, in which the second light propagates through a first core portion of the optical fiber, and the first light propagates through a second core portion including the first core portion of the optical fiber; An optical fiber connector including a reflective objective coupler, and an asymmetric bidirectional optical transmission module including an optical fiber,
The optical fiber connector includes:
a first light receiving element that receives, via the reflective objective coupler, a first light that is emitted from a first light emitting element having a first numerical aperture and a first wavelength, propagates through the optical fiber, and is emitted from an end face of the optical fiber;
The second light emitting element further includes a second numerical aperture smaller than the first numerical aperture and a second wavelength different from the first wavelength, and a second light radiated from the second light emitting element is incident on the end surface,
the reflective objective coupler includes a first aspherical mirror and a second conical mirror, the first mirror reflecting light emitted from an end face of the optical fiber in a direction toward the second mirror, and the second mirror collecting the light reflected by the first mirror onto the first light receiving element;
In the central axis direction of the optical fiber,
a distance between the first mirror and the first light receiving element is in a range of 10% to 30% of a distance to the end face of the optical fiber from which the first light incident on the first mirror is emitted;
the numerical aperture of the second mirror is equal to or greater than 0.7 and less than 1;
an asymmetric bidirectional optical transmission module, in which the second light propagates through a first core portion of the optical fiber, and the first light propagates through a second core portion including the first core portion of the optical fiber; An optical fiber connector including a reflective objective coupler, and an asymmetric bidirectional optical transmission module including an optical fiber,
an optical fiber connector included in the asymmetric bidirectional optical transmission module according to claim 1 is connected to one end of the optical fiber;
An asymmetric bidirectional optical transmission module, wherein an optical fiber connector included in the asymmetric bidirectional optical transmission module according to claim 2 is connected to the other end of the optical fiber. 4. The asymmetric bidirectional optical transmission module according to claim 3, wherein the second light receiving element is located between the second mirror and the optical fiber, the first light emitting element is located between the second mirror and the first mirror, the second light emitting element is located between the second mirror and the optical fiber, and the first light receiving element is located between the second mirror and the first mirror. The asymmetric bidirectional optical transmission module according to claim 1 , wherein the first light-emitting element is a non-coherent light source, and the second light-emitting element is a coherent light source. 6. The asymmetric bidirectional optical transmission module according to claim 5 , wherein the first light emitting element is an LED (light emitting diode), and the second light emitting element is a laser light source. 7. The asymmetric bidirectional optical transmission module according to claim 1, wherein the numerical aperture of the first core portion of the optical fiber is smaller than the numerical aperture of the second core portion, the first core portion is an optical fiber with a graded index fiber (GI) structure or a single mode optical fiber, the second core portion is located in a cladding portion on an outer periphery of the first core portion, the second core portion not including the first core portion is an optical fiber with a step-index fiber (SI) structure, and the first core portion and the second core portion are capable of propagating light in both directions.

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