JP2004101809A - Optical communication module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and miniaturized full duplex type bidirectional optical communication module capable of reducing crosstalk caused by near-by reflection or diffused internal light by using simple configuration. <P>SOLUTION: The optical module capable of transmitting/receiving optical signals through a plastic optical fiber comprises a light emitting element for generating transmitting light, a light receiving element for receiving light outgoing from the plastic optical fiber, an optical component for converging the transmitting light/receiving light, and a receptacle having an opening into which a plug attached to the end of the plastic optical fiber is inserted. When the plug is inserted into the receptacle, a crosstalk prevention part for preventing the coupling of the transmitting light or scattered light in the optical communication module with the light receiving element is formed on the periphery of the leading part of the plug/plastic optical fiber. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical communication module capable of transmitting and receiving an optical signal in both directions, and more particularly to a plastic optical fiber as a transmission medium, which is used for home communication, communication between electronic devices, LAN (Local Area Network), and the like. The present invention relates to an optical communication module.
[0002]
2. Description of the Related Art Communication using an optical fiber as a transmission medium has been attracting attention since long-distance transmission and high-speed transmission are possible. As the optical fiber, a single mode fiber or a multimode fiber mainly made of glass is mainly used. Glass optical fiber (GOF) is used for long-distance and high-speed communication because of its small transmission loss and large transmission band. However, these optical fibers have a very small core diameter of 5 to 80 μm, and it is necessary to control alignment and coupling with an optical communication module with high precision, so that expensive optical fiber plugs and optical systems are required. Become.
[0003]
Also, with the recent trend toward lower loss and wider bandwidth of plastic optical fiber (POF), mounting of an optical communication module using POF as a transmission medium for home communication and communication between electronic devices is being studied. Compared to GOF, POF is still unsuitable for long-distance and high-speed transmission, but because it has a large diameter of about 1 mm, coupling with an optical communication module is easier than that of GOF. Can be easily inserted and removed, and thus there is an advantage that an inexpensive and easy-to-use optical communication link can be obtained.
[0004]
The characteristics of GOF and POF are greatly different, and optical communication modules that take advantage of the respective advantages have been developed. GOF has the advantage that long-distance and high-speed transmission is possible, but requires high-precision alignment technology and makes the optical communication module expensive. FIG. 4 shows an example of an optical communication module using GOF. The optical fiber 102 is attached to the plug 107 after being bonded to the ferrule 121 and processed at the end face. The optical communication module 101 includes a receptacle 110 having an opening into which a plug 107 is inserted, a transmission lens 106, and a light emitting element 104. As described in JISC-5970 and the like, each component has an accuracy on the order of several μm. In addition, it is necessary to assemble each component with high precision, and the optical communication module 101 is relatively expensive.
[0005]
FIG. 5 shows an example of an optical communication module using a POF. Since the POF has a large core diameter and does not require high-accuracy alignment, only a simple plug 107 can be used without an expensive ferrule. The plug 107 includes an optical mini jack (OMJ) used for transmitting an audio digital signal. The optical communication module 101 is composed of a light emitting element 104 formed integrally with a molded lens 106 and a receptacle 110. Since the POF has a large diameter, the shape accuracy thereof can be as large as several tens to 100 μm, and it is inexpensive. Thus, the optical communication module 101 that can be easily assembled is obtained. For example, the accuracy of the core diameter of the POF itself is defined as ± 60 μm in JISC-6837. 4 and 5 show the case of a transmission module used for one-way communication.
[0006]
On the other hand, in the case of an optical communication module using an optical fiber as a transmission medium, in addition to the one in which communication is performed in one direction as shown in FIGS. There is an optical communication module that performs the following. Conventionally, this type of optical communication module mainly uses two optical fibers. However, when two optical fibers are used, there are problems that it is difficult to reduce the size of the optical communication module and that the cost of the optical fibers increases as the transmission distance increases. For this reason, an optical communication module that performs full-duplex optical communication using one optical fiber has been proposed.
[0007]
In such an optical communication module, since transmission and reception are performed by the same optical fiber, it is important to prevent interference between transmission light and reception light. The main causes of the interference of the transmitted light with the received light include the case where the transmitted light is reflected on the end face of the optical fiber when entering the optical fiber (hereinafter referred to as “near-end reflection”) and the case where the transmitted light is reflected inside the optical communication module. There is one due to scattered light (hereinafter referred to as “internal light”).
[0008]
Further, in an optical communication link using an optical fiber as a transmission medium, it is important to couple received light emitted from the optical fiber to a light receiving element with high efficiency in order to obtain a high SN (Signal to Noise Ratio). .
[0009]
Conventionally proposed optical communication modules for single-core full-duplex communication include a method of separating transmission / reception light using a polarization separation element. That is, while the direction of polarization of the received light propagating through the optical fiber is random during the propagation, the direction of polarization of the reflected light (near-end reflection) of the transmitted light reflected at the end face of the optical fiber is the same. Therefore, by arranging a polarization separation element that reflects only the light having this polarization between the optical fiber and the light receiving element, it is possible to prevent interference due to near-end reflection. However, in this method, since about half of the received light is reflected by the polarization splitter, a reception loss of about 3 dB occurs, so that efficient use of light cannot be performed, and an inexpensive light emitting diode as a light emitting element is used. (LED) cannot be used.
[0010]
For this reason, Japanese Patent Application Laid-Open No. H11-27217 discloses a method in which transmission light is incident on a position shifted from the center of an optical fiber, and reception light emitted from another region of the optical fiber is received. This method will be described with reference to FIG. The transmission light 108 emitted from the light emitting element 104 is condensed by the transmission lens 106, is reflected by the rising mirror 115, and is incident on the end face of the optical fiber 102 at a position shifted from the center of the optical axis. Received light 109 emitted from the optical fiber 102 is coupled to the light receiving element 105. The end surface of the optical fiber 102 is processed into a curved surface or an inclined surface, and the reflected light 114 reflected on the end surface of the optical fiber 102 is reflected toward the outer periphery of the optical fiber 102, thereby preventing interference due to near-end reflection.
[0011]
FIG. 7 shows the relationship between the coupling position of the transmission light 108 on the end face of the optical fiber 102 and the reception area. In the method in which the transmission light 108 is incident on a position shifted from the center of the optical fiber 102, as shown in FIG. 7, the end face of the single-core optical fiber 102 is spatially divided into a transmission area where the transmission light 108 is incident and a reception area. To realize single-core full-duplex communication. In this method, by making the reception area larger than the transmission area, transmission / reception light can be separated with less loss than about 3 dB loss in the method using the polarization separation element. That is, in such a method, the reception efficiency can be improved by making the reception area larger (that is, making the transmission area smaller and making the light enter the outer periphery of the optical fiber 102). Since the core diameter is small in GOF, it is difficult to adopt this method of spatial separation. However, in POF, it is easy to spatially separate transmitted light and received light by using the large-diameter core. It is. Also, since it is not necessary to assemble with higher precision than the GOF and the optical system can be constituted by relatively simple and inexpensive optical components, the inexpensive optical communication module 102 for single-core full-duplex communication can be used. Can be obtained.
[0012]
Further, POF has a feature that the processing of the end face is easy. In the end face treatment by GOF, it is necessary to bond the cut fiber strand to a ferrule machined with high dimensional accuracy, and then to mirror-process with an expensive polishing device. On the other hand, POF has a large core diameter and does not require high-precision control, so there is no need for a ferrule. The wire is directly bonded to the plug, and the end face is pressed against a hot blade of any shape and melted easily. Can be processed. The end face shape of the optical fiber may be processed into an inclined surface, a spherical surface, or the like in addition to a plane perpendicular to the optical axis. In the GOF, an inclined surface is often used to prevent transmission light emitted from the light emitting element from being reflected at the end face of the optical fiber and being coupled to the light emitting element again to make the oscillation state unstable. On the other hand, in the POF, the precision of the optical system is low, the transmission light reflected on the end face of the optical fiber is hard to return to the light emitting element, and the communication speed is relatively low. However, when performing single-core full-duplex communication as described above, in order to prevent the reflected light 114 of the transmission light 108 from being coupled to the light receiving element 105 and causing interference due to near-end reflection, a spherical surface or an inclined surface is required. May be.
[0013]
FIG. 8 shows an example of a conventional plug shape for a plastic optical fiber, 102 denotes an optical fiber, and 107 denotes a plug (OMJ) 107. POF can be processed into an arbitrary shape by melting its end face with a hot plate. FIG. 8 shows a case where the end surface is a spherical surface. When the end face is melted in this way, the tip of the plug 7 has a tapered portion 12 whose inner diameter increases toward the tip as shown in FIG. By having the plug inclined portion 12, the molten POF spreads to this portion, so that the end face of the POF can be processed without causing chipping or burrs. That is, the front end of the POF has an enlarged portion 16 that is larger than the core diameter. The plug 107 is generally made of a metal such as stainless steel or aluminum because heat resistance is required. A flat portion 13 is formed at the tip of the plug 107 to maintain strength.
[0014]
[Patent Document 1]
JP-A-11-27217
Patent Document 1: JP-A-61-122614 FIG.
JISC-5970
JISC-6387
[0015]
[Problems to be solved by the invention]
However, the method disclosed in Japanese Patent Application Laid-Open No. 11-27217 can prevent interference due to reflection of transmission light at the end face of the POF, but can prevent interference due to light reflected by a plug or a receptacle. Can not. As described above, the POF is fixed to the plug, and the entire plug is inserted into the receptacle. In an optical communication module using a POF, the processing accuracy of each component is low in order to reduce the cost, and the transmission light is made incident on the outer peripheral portion of the POF to perform full-duplex communication by spatial separation. May be irradiated not on the end face of the POF but on a plug or a receptacle on the outer periphery thereof. For example, in the plug shown in FIG. 8, transmission light applied to the plug inclined portion 12 and the plug flat portion 13 is easily reflected or scattered on the light receiving element side, and is likely to cause interference.
[0016]
In addition, in communication between electronic devices, it is necessary to perform communication at a short distance of about 1 m, and since it can be easily inserted and removed, it is necessary to consider eye safety (eye safety). The amount of light (the amount of light emitted from the optical fiber) must be set low. However, when a semiconductor laser is used as the light source of the optical communication module, if the light amount of the light source itself is reduced, the following problem occurs.
[0017]
As shown in FIG. 9, the relationship between the drive current of the semiconductor laser and the optical output can be approximated by the characteristic of a broken line formed by two straight lines in a region where the optical output is not saturated. The area A is a laser oscillation area, and the area B is a spontaneous emission area. When a pulse current is input with a current larger than the threshold current (Ith) as the bias current, the extinction ratio increases because the light output increases even at the pulse signal “0”. On the other hand, if a current lower than Ith is taken as the bias current, the pulse width decreases (duty ratio changes) due to oscillation delay. Therefore, normally, the bias current is set near Ith. In this case, since the spontaneous emission light exists even when the pulse signal is “0”, the extinction ratio is determined from the ratio of the spontaneous emission light and the light output when the pulse signal is “1”. For example, in the case of a semiconductor laser having a spontaneous emission of 0.3 mW, it is necessary to set the maximum output (output when the pulse signal is "1") to 3 mW or more in order to make the extinction ratio 10 or more.
[0018]
That is, it is difficult to satisfy the extinction ratio when the transmission light amount is reduced by lowering the output of the semiconductor laser, and the duty ratio is changed when the bias current is reduced, causing a problem. For this reason, it is necessary to reduce the transmission light amount by lowering the coupling efficiency (transmission efficiency) between the light emitted from the semiconductor laser and the optical fiber. As a method of lowering the transmission efficiency, there is a method of reducing the amount of light by using a filter or a polarizing element having a low light transmittance, but the number of parts increases and the cost increases. For this reason, it is common to reduce the diameter of the transmission lens that collects the light emitted from the light emitting element and couples the light to the optical fiber, so that the light beam with a large emission angle is cut by the transmission lens.
[0019]
However, this method has a problem in that light that does not actually contribute to transmission (light cut by the transmission lens) increases, so that interference due to internal disturbance light is likely to increase. In particular, in order to perform full-duplex communication using one optical fiber, it is necessary to efficiently couple the received light radiated from the optical fiber to the light receiving element. However, when the receiving efficiency is increased, light due to near-end reflection or internal disturbance light is also efficiently received at the same time, and there is a problem that interference increases. Further, the internal disturbance light is also reflected by the plug or the receptacle toward the light receiving element 105, so that interference is likely to occur.
[0020]
These interferences can be dealt with by improving the accuracy of the components, but in that case, the feature that the optical communication module using the POF is inexpensive and easy to manufacture is impaired.
[0021]
On the other hand, Japanese Patent Application Laid-Open No. 61-122614 discloses a method of reducing stray light by attaching a light shielding material to a collimator lens used for an optical isolator.
[0022]
That is, by inserting a light shielding material between the semiconductor laser and the collimator lens, stray light generated in the lens is reduced, stray light is prevented from returning to the semiconductor laser, and the semiconductor laser can be driven stably. ing.
[0023]
However, this is to prevent the light emitted by itself from returning to its original state, and cannot prevent interference to the light receiving element, which is a problem in a full-duplex optical communication module using a single-core POF. In addition, the stray light in the lens is reduced, and stray light in the optical communication module and scattered light from an optical fiber plug or the like cannot be prevented. Further, the light emitting point of the semiconductor laser is minute, and it is sufficient to prevent return light to this light emitting point. However, in the optical communication module, it is necessary to separate the light from the received light. For this reason, it is more difficult to reduce the internal disturbance light. Furthermore, when inserting a light-shielding material, it is necessary to control the insertion accuracy, pay attention to adhesion, and to prevent deterioration due to aging, etc., resulting in high cost and performance problems.
[0024]
The present invention has been made in view of these problems, and enables full-duplex bidirectional communication with a single plastic optical fiber.Especially, crosstalk due to near-end reflection and internal disturbance light is achieved with a simple configuration. An inexpensive and small optical communication module that can be reduced is provided.
[0025]
[Means for Solving the Problems]
That is, the present invention relates to an optical communication module capable of transmitting and receiving an optical signal by using one plastic optical fiber, comprising: a light emitting element that generates transmission light; and a light receiving element that receives reception light emitted from the plastic optical fiber. A light receiving element, an optical component for condensing transmission light and / or reception light, and a receptacle having an opening for inserting a plug attached to an end of the plastic optical fiber. An interference prevention unit is provided around the plug and / or the tip of the plastic optical fiber when inserted into the receptacle, for preventing the transmission light or the scattered light inside the optical communication module from being coupled to the light receiving element. The present invention relates to an optical communication module characterized by being formed.
[0026]
The present invention further provides the following optical communication module.
The optical communication module according to the above, wherein the interference prevention unit is formed in a part of the receptacle.
[0027]
The optical communication module according to any one of the preceding claims, wherein the interference prevention portion has a conical shape whose diameter gradually increases from the side where the optical component is disposed toward the plastic optical fiber.
[0028]
The optical communication according to any one of the above, wherein the interference prevention portion has a tip on a side where the optical component is disposed, and has a shape inclined from an optical axis center on the plastic optical fiber side toward an outer peripheral direction. module.
[0029]
The optical communication module according to any one of the preceding claims, wherein the interference prevention unit is arranged so as to block light emitted from the optical component side so as not to irradiate the end of the plug.
[0030]
The plastic optical fiber has an enlarged portion whose end is larger than the core diameter at an end thereof, and the interference preventing portion shields a part of the enlarged portion from light emitted from the optical component side. The optical communication module according to any one of the above, wherein the optical communication module is arranged.
[0031]
The optical communication module according to any one of the above, wherein a part of the interference prevention unit and a part of the optical component are arranged in contact with each other.
[0032]
The optical communication module according to any one of the preceding claims, wherein the interference prevention unit is formed only in the vicinity of the end face of the plastic optical fiber where the transmission light is incident.
[0033]
The optical communication module according to any one of the above, wherein a surface of the interference prevention unit on a side facing the plastic optical fiber is inclined with respect to an optical axis of the plastic optical fiber.
[0034]
With the above-described configuration, full-duplex optical communication using one optical fiber with reduced interference due to internal disturbance light such as near-end reflection and stray light becomes possible.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
A first embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a schematic diagram showing a configuration of an optical communication link. The optical communication link 3 is connected to an optical fiber 2 for bidirectionally transmitting modulated light suitable for transmission based on a data signal to be transmitted, and optically coupled to both ends of the optical fiber 2. Each optical communication module 1 is provided.
[0036]
FIG. 2 is a schematic diagram illustrating an optical communication module according to the first embodiment of the present invention. The optical communication module 1 includes a light emitting element 4 for generating a transmission light 8 that is modulated light based on a data signal, a light receiving element 5 for receiving a reception light 9 from the optical fiber 2 and generating a data signal, A transmission lens 6 for condensing the light emitted from the element 4 and coupling it to the optical fiber 2, a rising mirror 15 for changing the direction of the transmission light 8 and coupling the same to the optical fiber 2, and a detachable optical fiber 2. And a receptacle 10 having an opening. The tip of the optical fiber 2 is bonded and fixed to a plug 7, and the optical fiber 2 and the optical communication module 1 are optically coupled by being inserted into an opening of a receptacle 10 which is a part of the optical communication module 1.
The light generated by the light emitting element 4 diverges radially according to the radiation angle of the light emitting element 4. The divergent light is converted into an arbitrary numerical aperture by the transmission lens 6 and collected. The condensed light changes its direction by the rising mirror 15 and enters the optical fiber 2. The position of the optical fiber 2 where the transmission light 8 is incident is on the outer periphery of the optical fiber 2. The transmission light 8 is converged on the end face of the optical fiber 2 into a substantially circle having a diameter of about several hundred μm. The POF has a large core diameter, so that the light-collecting area may be relatively large. Even if the light-collecting area is slightly misaligned, a part of the transmission light 8 may be incident on the optical fiber 2. And light can be collected by an inexpensive optical system. The reception light 9 emitted from the optical fiber 2 radiates at an emission angle determined by the numerical aperture of the optical fiber 2 and is coupled to the opposing light receiving element 5. As described above, when the transmission light 8 and the reception light 9 are spatially separated within the aperture of the optical fiber 2, the reception light 9 emitted from the position of the optical fiber 2 where the transmission light 8 is incident enters the light receiving element 5. Since the coupling is not performed, and the position of the optical fiber 2 where the transmission light 8 is incident is set at the outer peripheral portion of the optical fiber 2, the reception light 9 can be more efficiently coupled to the light receiving element 5.
[0037]
Part of the transmission light 8 entering the optical fiber 2 is reflected at the end face of the optical fiber 2 (reflected light 14). The reflected light 14 of the transmission light 8 from the optical fiber 2 is reflected in the outer peripheral direction of the optical fiber 2 because the end face of the optical fiber 2 is processed into a spherical surface, and is not coupled to the light receiving element 5 but is reflected at the near end. Interference can be prevented.
[0038]
Further, as described above, in the optical communication module 1 using POF as a transmission medium, the accuracy of the components is low in order to reduce the price, and the transmission light 8 is used to perform full-duplex communication by spatial separation. Since the light is incident on the outer peripheral portion of the fiber 2, a part of the transmission light 8 may be irradiated to the outer peripheral portion of the optical fiber 2 without being incident on the optical fiber 2 due to an axis deviation of the optical fiber 2. In the optical communication module 1, an interference prevention unit 11 is formed in a part of the receptacle 10. The interference prevention unit 11 is configured so that the transmission light 8 and the internal disturbance light in the optical communication module 1 are not irradiated to the enlarged part 16 formed at the time of processing the end face of the optical fiber 2, the inclined part 12 and the flat part 13 of the plug 7. Are located.
[0039]
The interference prevention unit has a configuration in which a part of the plug is arranged to shield light from the optical component side, so that interference due to reflection and scattering from the plug can be reduced.
[0040]
Although the plastic optical fiber has an enlarged portion whose diameter is larger than the core diameter at the end thereof, the interference preventing portion is arranged so as to shield part or all of the enlarged portion from the optical component side so as to shield light. In addition, interference due to reflection and scattering from the enlarged portion of the optical fiber and / or the inclined portion of the plug can be reduced.
[0041]
The inner wall of the receptacle 10 may be formed of a material having a high light absorption such as black. Since the plug 7 is generally formed of metal, by preventing the transmission of the transmission light 8 to the plug 7, the reflectance can be significantly reduced, and interference due to near-end reflection can be reduced. In addition, by forming the interference prevention unit integrally with the receptacle, it is possible to improve the assembly accuracy.
[0042]
The surface of the interference prevention unit 11 on which the optical components are arranged has a conical shape whose diameter increases from the distal end of the optical fiber 2 toward the optical fiber. The interference prevention section has a conical shape along the end face of the optical fiber, so it is possible to reliably shield the enlarged portion of the optical fiber and the optical fiber plug, thereby reducing interference due to near-end reflection and internal disturbance light. can do. That is, the transmission light 8 originally applied to the inclined portion 12 and the flat portion 13 of the plug 7 is applied to the interference preventing portion 11 and is reflected toward the outer periphery of the optical fiber 2 (second reflected light 17) by this conical shape. Therefore, interference due to near-end reflection can be more reliably prevented.
[0043]
Furthermore, since the interference prevention unit has an inclined shape that extends from the side where the optical components of the optical communication module are arranged toward the optical fiber, the transmission light 8 kicked by the transmission lens 6 and the optical communication module 1 The internally disturbed light scattered inside can be prevented from being reflected by the inclined portion toward the light receiving element 5 side, and can be prevented from being coupled to the light receiving element. Therefore, the transmission lens 6 having a small diameter can be used, and the problems of eye safety and extinction ratio can be easily solved.
[0044]
The side surface of the optical fiber of the interference prevention unit 11 may be conical, like the side surface of the optical component. However, by forming all or a part of the side surface along the outer periphery of the end surface of the optical fiber 2, the optical fiber 2 is It is possible to cope with any misalignment in any direction, and it is possible to reliably shield the enlarged portion 16 and the plug 7 of the optical fiber 2, and it is possible to reliably reduce interference due to near-end reflection and internal disturbance light. .
[0045]
Also, a case where a part of the light emitted from the optical fiber 2 is reflected by a part of the optical communication module 1 and is coupled to the optical fiber 2 again, propagates through the optical fiber 2 and is coupled to the optical communication module on the other side. (Interference due to reflection from the partner module). In order to prevent the interference due to the reflection of the partner module, the surface of the interference prevention unit 11 facing the optical fiber 2 (reflection-coupling prevention surface) is inclined with respect to the optical axis of the optical fiber 2 (the reflected light is transmitted through an (More specifically, about 10 ° for a numerical aperture of about 0.3). The light applied to the anti-reflection / coupling surface is reflected and returns to the optical fiber 2 side again. Interference due to reflection can be reduced.
[0046]
Furthermore, the interference prevention unit 11 also has a role as a stopper for positioning the plug 7 and the optical communication module 1. The insertion depth and position of the plug 7 are regulated by the interference prevention unit 11. Further, since each optical component is positioned with respect to the receptacle 10, both can be aligned via the receptacle 10.
[0047]
Next, each component of the optical communication module 1 shown in FIG. 2 will be described.
As the optical fiber 2, a large-diameter optical fiber 2 such as POF is used. The POF has a core made of a plastic having excellent light transmittance such as PMMA (Poly (methyl methacrylate) or polycarbonate) and a clad made of a plastic having a lower refractive index than the core. Since the diameter of the core can be easily increased from about 200 μm to about 1 mm as compared with the quartz optical fiber, the coupling adjustment with the optical communication module 1 is easy, and the inexpensive optical communication link 3 can be obtained. As shown in the present embodiment, when the transmission light 8 and the reception light 9 are spatially separated, it is preferable to use a core having a diameter of about 1 mm.
[0048]
As the light emitting element 4, a semiconductor laser or a light emitting diode (LED) is used. The wavelength of the light emitting element 4 is preferably a wavelength at which transmission loss of the optical fiber 2 to be used is small and inexpensive. For example, when a POF is used as the optical fiber 2, a semiconductor laser having a wavelength of 650 nm, which has a mass production effect for a DVD or the like, can be used. In addition, a monitor photodiode is disposed at the rear of the light emitting element 4 so that the light amount of the light emitting element 4 is kept constant.
[0049]
As the light receiving element 5, a photodiode having high sensitivity in the wavelength region of the light emitting element 4 by converting the intensity of the received modulated light into an electric signal is used. For example, a PIN photodiode made of silicon or an avalanche photodiode is used. And so on.
[0050]
The receptacle 10 is made of plastic, and is manufactured by injection molding or the like. It is preferable that the hue has a high absorptance at the used light wavelength such as black. The optical communication module 1 can be easily assembled by forming a positioning portion for aligning each optical component in the receptacle 10.
[0051]
As described above, by using the optical communication module 1 shown in the first embodiment, it is possible to prevent interference due to near-end reflection and internal light due to stray light, and a full-duplex system using one optical fiber 2. Optical communication becomes possible. In particular, since an optical system that is simple and inexpensive can be used, the optical communication module 1 that can be manufactured at low cost and easily can be obtained. Here, the interference prevention unit is provided in a part of the receptacle, but a configuration in which a light absorbing member is directly formed at the end of the fiber to shield light is also possible.
[0052]
(Second embodiment)
Next, a second embodiment will be described with reference to FIG. In the second embodiment, members having the same functions as those described in the first embodiment are assigned the same reference numerals as those in the first embodiment, and the description is omitted. . In the present embodiment, an optical communication module 1 having an optical system different from that of the first embodiment is shown.
[0053]
The transmission light 8 generated by the light emitting element 4 diverges radially according to the radiation angle of the light emitting element 4. Thereafter, the transmission light 8 is converted into an arbitrary numerical aperture by the transmission lens 6 and collected, passes through the optical member 18, and is coupled to the optical fiber 2. The reception light 9 emitted from the optical fiber 2 is reflected toward the light receiving element 5 by the light collecting mirror 19, and is collected by the light collecting mirror 19 having a curvature to be coupled to the light receiving element 5. The optical member 18 has a prism 20 which is inclined with respect to the optical axis of the optical fiber 2 on the surface from which the transmission light 8 is emitted, and refracts the transmission light 8 to make it enter the optical fiber 2. Further, a part of the condensing mirror 19 is arranged close to the optical fiber 2.
[0054]
Part of the transmission light 8 incident on the optical fiber 2 is reflected at the end face of the optical fiber 2. The reflected light of the transmission light 8 on the optical fiber 2 is shielded by the condenser mirror 19 and is not coupled to the light receiving element 5, so that interference due to near-end reflection can be prevented. In addition, interference due to internal disturbance light can be prevented by the light collecting mirror 19 since the transmitting unit and the receiving unit are separated. However, light reflected and scattered by the plug 7 of the optical fiber 2 and a part of the receptacle 10 may be scattered in an unexpected direction, and it is difficult to completely separate the scattered light. In order to prevent interference due to the scattered light, an interference prevention unit 11 is formed in a part of the receptacle 10.
[0055]
In this embodiment, the interference prevention unit 11 is formed only in the vicinity (near) where the transmission light 8 is incident. The interference preventing unit 11 is disposed so that the transmitting light 8 and the internal disturbance light in the optical communication module 1 are not irradiated to the enlarged part 16 formed at the time of processing the end face of the optical fiber 2, the inclined part 12 and the flat part 13 of the plug 7. The shape is an inclined shape that spreads from the side where the optical components are arranged toward the optical fiber 2 side. Since the transmission unit and the reception unit are separated by the condenser mirror 19, it is not necessary to form the interference prevention unit 11 on the reception unit side (the lower side in FIG. 3). Further, since the transmission and reception are separated in the vertical direction in FIG. 3 by the condensing mirror 19, the interference prevention unit 11 prevents the transmission light 8 from being reflected and scattered on the receiving unit side (lower side in FIG. 3). The shape is a shape having a slope such that the shape spreads from the side where the optical components are arranged toward the optical fiber 2 side.
[0056]
The optical member 18 (the mirror can be formed by evaporating metal) is made of plastic such as PMMA or polycarbonate, and is manufactured by injection molding or the like. Then, a metal thin film having high reflectivity, such as aluminum or gold, is formed on the side to be a reflection mirror (which is also a condensing mirror) by an evaporation method or the like. The optical member 18 includes a transmitting lens 6 for condensing the transmitting light 8 and coupling the transmitting light 8 to the optical fiber 2, a prism 20 for refracting the transmitting light 8 and entering the optical fiber 2, and a light emitting element (not shown). An uneven portion for positioning used for alignment with the light receiving element 5 and the light receiving element 4 is formed. As described above, since one optical member 18 has many functions, the number of constituent members can be significantly reduced, and the tolerance at the time of assembling can be reduced. Therefore, it is possible to obtain the low-cost and compact optical communication module 1. It becomes possible.
[0057]
A part of the optical member 18 is disposed in contact with or close to a part of the interference preventing unit 11. If there is an interval between the optical member 18 and the interference prevention unit 11, interference due to internal disturbance light is likely to occur due to reflected light therebetween. Further, the prism 20 refracts the transmission light 8 and causes the transmission light 8 to be inclined from the outer peripheral portion of the optical fiber 2 toward the inner peripheral portion. This makes it difficult for the transmission light 8 to irradiate the inclined portion 12 of the plug 7. Further, the interference prevention unit 11 is not formed on the receiving unit side. Part of the light emitted from the optical fiber 2 is also emitted from the enlarged portion 16 of the optical fiber 2. Therefore, the reception efficiency can be improved by not forming the interference prevention unit 11 on the receiving unit side.
[0058]
Also, a case where a part of the light emitted from the optical fiber 2 is reflected by a part of the optical communication module 1 and is coupled to the optical fiber 2 again, propagates through the optical fiber 2 and is coupled to the optical communication module on the other side. (Interference due to reflection from the partner module). In order to prevent the interference caused by the reflection of the partner module, the surface of the interference prevention unit 11 facing the optical fiber 2 (reflection-coupling prevention surface 21) is inclined with respect to the optical axis of the optical fiber 2 (the reflected light is reflected by the optical fiber 2). (It is about 10 ° for a numerical aperture of about 0.3). The light applied to the anti-reflection / coupling surface 21 is reflected and returns to the optical fiber 2 again. However, the light is not coupled to the optical fiber 2 because the reflection angle is increased by the anti-reflection / coupling surface 12. That is, the reflected light is converted by the reflection / coupling preventing surface 21 into an angle larger than the numerical aperture of the optical fiber 2. The prism 20 also has the same function, and reduces interference due to reflection from the partner module.
[0059]
The present embodiment is an example, and the present invention is characterized in that the interference prevention unit 11 is formed in a part of the receptacle 10, and it is needless to say that the present invention can be applied to other optical arrangements.
[0060]
【The invention's effect】
According to the present invention, a full-duplex bidirectional communication module using a single plastic optical fiber with reduced crosstalk due to near-end reflection and internal disturbance light can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating the configuration of an optical communication link according to the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of an optical communication module according to a first embodiment of the present invention.
FIG. 3 is a schematic diagram illustrating a configuration of an optical communication module according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram illustrating a configuration of an optical communication module using a glass optical fiber.
FIG. 5 is a schematic diagram illustrating a configuration of an optical communication module using a conventional plastic optical fiber.
FIG. 6 is a schematic configuration diagram illustrating a conventional optical communication module capable of full-duplex communication.
FIG. 7 is a view for explaining the relationship between the coupling position of the transmission light at the end face of the optical fiber and the reception area.
FIG. 8 is a diagram illustrating a plug shape for a conventional plastic optical fiber.
FIG. 9 is a graph illustrating the relationship between the current and the optical output of a semiconductor laser.
[Explanation of symbols]
1: Optical communication module
2: Optical fiber
3: Optical communication link
4: Light emitting element
5: receiving element
6: Transmission lens
7: Plug
8: Transmitted light
9: Received light
10: Receptacle
11: Interference prevention unit
12: Plug slope
13: Plug flat part
14: reflected light (near-end reflected light)
15: Start-up mirror
16: Enlargement section
17: Second reflected light
18: Optical member
19: Condensing mirror
20: Prism
21: Reflective coupling prevention surface
101: Optical communication module
102: Optical fiber
104: Light emitting element
105: light receiving element
106: Transmission lens
108: transmission light
109: Received light
110: Receptacle
114: reflected light (near-end reflection)
115: Start-up mirror
121: Ferrule

Claims (9)

An optical communication module capable of transmitting and receiving an optical signal using a single plastic optical fiber, comprising: a light emitting element for generating transmission light; a light receiving element for receiving reception light emitted from the plastic optical fiber; An optical component for condensing light and / or received light; and a receptacle having an opening for inserting a plug attached to an end of the plastic optical fiber, wherein the plug is inserted into the receptacle. Forming an anti-interference portion around the tip of the plug and / or the plastic optical fiber to prevent the transmission light or the scattered light inside the optical communication module from being coupled to the light receiving element. Optical communication module. The optical communication module according to claim 1, wherein the interference prevention unit is formed in a part of the receptacle. 3. The optical communication module according to claim 1, wherein the interference prevention unit has a conical shape whose diameter gradually increases from a side where the optical component is disposed toward the plastic optical fiber. . 4. The interference prevention section according to claim 1, wherein the interference prevention section has a tip on a side where the optical component is disposed, and has a shape inclined from an optical axis center on the plastic optical fiber side toward an outer peripheral direction. The optical communication module according to the above. The optical communication module according to any one of claims 1 to 4, wherein the interference prevention unit is arranged so as to block light irradiated from the optical component side so as not to irradiate an end of the plug. The plastic optical fiber has an enlarged portion whose end is larger than the core diameter at an end thereof, and the interference preventing portion shields a part of the enlarged portion from light emitted from the optical component side. The optical communication module according to claim 1, wherein the optical communication module is arranged. The optical communication module according to claim 1, wherein a part of the interference prevention unit and a part of the optical component are arranged in contact with each other. The optical communication module according to any one of claims 1 to 7, wherein the interference prevention unit is formed only in the vicinity of the end face of the plastic optical fiber where the transmission light is incident. 9. The optical communication module according to claim 1, wherein a surface of the interference prevention unit facing the plastic optical fiber is inclined with respect to an optical axis of the plastic optical fiber.

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