JP2006157811A - Optical transmission method and apparatus for decreasing transmission error - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a transmission error in high-speed transmission of an optical signal. <P>SOLUTION: Multi-mode optical signals emitted from a light emitting element are coupled to be made incident to one end face of an optical transmission medium 62, and multi-mode optical signals transmitted in the optical transmission medium 62 are received by being made incident to a light receiving element 66 coupled on another end face of the optical transmission medium 62. Thus, when performing optical communication, optical signals of a single or multiple mode groups selected to be settled within a range of inter-mode difference, with which a transmission error can be settled within an allowable range, are extracted and only the optical signals of a mode selection group limiting the inter-mode difference a little are read, thereby decreasing the transmission error. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical transmission method and an optical transmission apparatus that reduce transmission errors when transmitting an optical signal in a plurality of modes emitted from a light emitting element.

  In recent years, in the field of optical communications, where digital devices such as electronic devices are connected to each other to perform high-speed signal long-distance transmission, which is impossible with electrical transmission, electrical signals are converted into optical signals (transmitters). Light is incident on the light guide medium (such as an optical fiber) by the optical coupling means on the transmission side, an optical signal is transmitted through the light guide medium, and light is incident on the receiver from the light coupling medium by the optical coupling means on the reception side. An optical transmission device (optical link system) configured to convert an optical signal into an electrical signal at a receiver is used.

  In the field of optical communication related to such optical transmission equipment, a multimode optical fiber such as plastic optical fiber (multimode optical fiber) is used to transmit a signal of about 100 megabits per second at a distance of about several tens of meters. Such applications are being applied to digital optical communication over a relatively short distance.

  Conventionally, when digital optical communication is performed by connecting digital devices to each other, as illustrated in FIG. 8, each digital device 10, 11 and each corresponding end of the optical fiber cable 12 are respectively connected to connectors. 14 and 16 are generally used for detachable connection.

  As illustrated in FIG. 9, the connectors 14 and 16 are configured to detachably connect the optical fiber connecting device 18 to the object 20 optically and mechanically. The optical fiber connection device 18 is a so-called male connector of the optical fiber 12, while the object 20 is a female connector installed in the digital devices 10 and 11. The optical fiber connection device 18 includes a main body 22 and an insertion terminal 24. The main body 22 is held by the user in order to insert the insertion terminal 24 into the insertion hole 26 of the object 20 or to pull out the insertion terminal 24 from the insertion hole 26. Doubles as

  The corresponding end portions of the optical fiber 12 are exposed at the end surfaces of the insertion terminal 24. The insertion terminal 24 is, for example, a columnar or prismatic member, and a retaining portion is provided in the middle thereof. The retaining portion fits into a recess provided in the insertion hole 26 of the object 20 to keep the optical fiber connecting device 18 and the object 20 optically and mechanically connected. .

  A lens 28 and a light receiving element 30 (or a light emitting element 32) are disposed on the inner bottom of the insertion hole 26 of the object 20.

  The optical fiber connection device 18 is configured so that the end of the optical fiber 12 faces the lens 28 and the light receiving element 30 (or the light emitting element 32) in a connected state in which the insertion terminal 24 is fitted in the insertion hole 26 of the object 20. To be configured.

  When the light receiving element 30 is installed on the object 20 of one connector 14, an optical signal guided through the optical fiber 12 is received by the light receiving element 30 through the lens 28. When the light emitting element 32 is installed on the object 20 of the other connector 16, an optical signal generated by the light emitting element 32 enters the end of the optical fiber 12 through the lens 22.

  The one connector 14 is configured such that the light energy emitted from the end of the optical fiber 12 when received by the light receiving element 30 through the lens 28 becomes the maximum amount. At the same time, the other connector 16 is configured such that the optical energy generated when the light signal generated by the light emitting element 32 enters the end of the optical fiber 12 through the lens 28 is maximized.

  In this way, the digital devices 10 and 11 and the corresponding end portions of the optical fiber cable 12 are optically connected to the optical fiber connection device 18 and the object 20 so that the energy coupling efficiency is optimum. The optical signal generated by the light emitting element 32 is transmitted to the other device side through the optical fiber 12 and received by the light receiving element 30 in a state of being mechanically connected to each other and received by the light receiving element 30, thereby allowing digital optical communication between digital devices. An optical transmission device (optical link means) has been proposed (see, for example, Patent Document 1).

However, when the optical fiber connection device 18 and the object 20 configured as described above are used in an optical transmission device, the optical signal is guided from the transmitter that converts an electrical signal into an optical signal by the optical coupling means on the transmission side. The main purpose is to combine the optical coupling structure of the optical element and the optical transmission medium for making light incident on the medium (optical fiber, etc.) so that the light energy from the transmitter is maximized to the light guide medium. And At the same time, the optical transmission apparatus configured as described above is provided between the light guide medium and the receiver in order to cause the optical signal transmitted through the light guide medium to enter the receiver and convert the optical signal into an electrical signal. The optical coupling structure between the optical element and the optical transmission medium is mainly intended to couple the optical energy from the optical transmission medium to the receiver so as to be as large as possible. For this reason, the optical coupling structure that focuses on coupling the optical element and the optical transmission medium so as to maximize the light energy as much as possible cannot prevent transmission errors in high-speed transmission. is there.
JP 2000-137150 A

  In view of the above-described problems, the present invention provides a new optical transmission method capable of reducing transmission errors in high-speed transmission of optical signals, and an optical transmission device using the optical transmission method for reducing transmission errors of optical signals. It is intended to provide to.

  The optical transmission method according to claim 1 is an optical transmission method for transmitting an optical signal of a plurality of modes emitted from a light emitting element through an optical transmission medium and receiving the light signal to the light receiving element, wherein the plurality of modes emitted from the light emitting element. The selected mode is selected to enter the optical transmission medium, and the propagation time difference in the optical transmission medium between the selected modes is within a range where transmission errors can be accommodated. Features.

  According to the above-described optical transmission method, one or a plurality of mode groups that can fall within a transmission time difference within a permissible range can be selected and extracted as an optical signal of the mode selection group. Since only the optical signals in the mode selection group with a small difference are read, transmission errors can be reduced.

  An optical transmission device according to claim 2 is an optical transmission device including a light emitting element that emits an optical signal of a plurality of modes, an optical transmission medium that transmits the optical signal, and a light receiving element that receives the optical signal. And a mode selection means for selecting a mode of a part of the optical signal, and the mode selection means is provided between the light emitting element and the optical transmission medium or between the optical transmission medium and the light receiving element.

  According to a third aspect of the present invention, in the optical transmission device according to the second aspect, the mode selecting means includes a plurality of modes emitted from the light emitting element, and the propagation time difference in the optical transmission medium is within a permissible range. It is characterized by selecting a part of modes that can be accommodated.

  According to a fourth aspect of the present invention, in the optical transmission apparatus according to the second aspect, the mode selection means is in the optical transmission medium among the light emitting surfaces of the mode selection means that emits light from the light emitting element or the optical transmission medium. This is a member having an opening or a window at a position where a part of modes in which a transmission error is within an allowable range exists.

  With the configuration as described above, the mode selection means selects one or a plurality of mode groups as optical signals of the mode selection group so as to be within the range of the propagation time difference within which the transmission error can be within the allowable range. Since only the optical signals of the mode selection group extracted and selected by the mode selection means are received, transmission errors can be reduced.

  According to the optical transmission method and the optical transmission apparatus for reducing transmission errors of the present invention, there is an effect that transmission errors can be reduced in high-speed transmission of optical signals.

(First embodiment)
A first embodiment of the present invention relating to an optical transmission method and an optical transmission apparatus for reducing transmission errors will be described with reference to FIGS.

  As shown in FIG. 1, the optical transmission apparatus (optical link system) according to the first embodiment is installed in a transmitter 50 having a circuit for converting an inputted electric signal into an optical signal, and the transmitter 50. Receptacle 52, a receiver 54 having a circuit for converting an optical signal into an electrical signal and outputting it, a receptacle 56 installed in the receiver 54, and a receptacle 52 of the transmitter 50 optically and mechanically. An input plug 58 as an optical coupling means to be coupled is installed at one end, and an output plug 60 as an optical coupling means to be optically and mechanically coupled to the receptacle 56 of the receiver 54 is installed at the other end. And an optical fiber (multimode optical fiber) 62 (which may be a flat light guide or the like) as a transmission medium.

  In this optical transmission device, a light emitting element 64 as an optical element is arranged inside the receptacle 52, and a light receiving element 66 as an optical element is arranged inside the receptacle 56.

  Furthermore, this optical transmission apparatus is configured as a multimode optical beam transmission system. In this optical transmission device, a receptacle 52 and an input plug 58 are provided so as to reduce transmission errors when transmitting an optical signal with a multi-mode light beam (multiple modes), and to keep the transmitted optical energy moderate. A receptacle 56 and an output plug 60 are configured.

  In this optical transmission device, as a method for reducing transmission errors, when an optical signal is transmitted in a plurality of modes by the optical transmission device, the transmission error is within an allowable range among the transmittable optical signals in a plurality of modes. A method is adopted in which only an optical signal of a mode selection group, which is one or a plurality of mode groups selected so as to fall within a range of propagation time differences that can be accommodated, is extracted and used for transmission / reception of signals.

  In such an optical transmission device, when an optical signal is transmitted using the multimode optical fiber 62, the propagation time of each mode is different, so that mode dispersion occurs and pulse separation occurs due to the difference in mode group speed. It is considered that transmission errors increase when optical signals of all such modes are used for signal exchange.

  Therefore, one or a plurality of mode groups whose group delay difference between the modes is within the allowable range of transmission errors are selected and extracted as the optical signals of the mode selection group, and only the optical signals of this mode selection group are used. To send and receive signals.

  For example, in the method for reducing the transmission error of this optical transmission apparatus, a higher order from the fundamental mode having a mode number of 0 that can be transmitted using the multimode optical fiber 62 to the maximum number of guided modes. One or more mode groups corresponding to the low-order modes that are relatively on the basic mode side within the allowable range of transmission errors among all the modes leading to the mode as the optical signal of the mode selection group select.

  Alternatively, in the method for reducing the transmission error of this optical transmission device, a single number corresponding to a higher-order mode on the side of the maximum number of modes relatively guided within the allowable range of the transmission error. Alternatively, a plurality of mode groups are selected as optical signals for the mode selection group.

  Furthermore, in the method for reducing the transmission error of this optical transmission device, it corresponds to the number of modes intermediate between the fundamental mode side and the maximum number of guided modes within the allowable range of the transmission error. One or a plurality of mode groups may be selected as the optical signal of the mode selection group.

  In the method for reducing the transmission error of the optical transmission apparatus, one or more mode groups selected so as to fall within the range of the propagation time difference within which the transmission error can be within an allowable range are included in the mode selection group. Since only the optical signals of the mode selection group that are selected and extracted as optical signals and the difference in propagation time is limited are read, transmission errors can be reduced.

  Next, an optical coupling structure for reducing transmission errors between an optical element and an optical transmission medium for reducing transmission errors as mode selection means provided in the optical transmission apparatus will be described with reference to FIG.

  In the optical coupling structure for reducing transmission errors between the optical element, which is the mode selection means shown in FIG. 2, and the optical transmission medium, the receptacle 52 and the input plug 58 are configured to be so-called butt coupling.

  In the receptacle 52, the optical element package 70 is disposed below the coupling insertion hole 68 provided in the housing 82. In the optical element package 70 installed in the receptacle 52 of the transmitter 50, a light emitting element 64 is arranged on the inner bottom surface of a package 70A made of ceramic or the like (which may be a metal package or a resin package), and light is emitted from the light emitting element 64. A window portion 70B for transmitting the multi-mode light beam and emitting it to the outside is provided. The optical element package 70 is configured to be connected to the circuit of the transmitter 50 by an electrode terminal 72 projecting from the bottom surface of the package 70A.

  In this receptacle 52, the opening limiting member 100 constituting the transmission error reducing means is disposed adjacent to the outside of the window portion 70 </ b> B of the optical element package 70. The aperture limiting member 100 has a predetermined shape and a predetermined size so that a single or a plurality of mode groups that can be accommodated within a transmission error tolerance range can be selected and extracted as an optical signal of the mode selection group on the light shielding plate. The opening 102 is formed by drilling.

  The opening restricting member 100 configured in this manner is arranged with its periphery fixed to the inner surface of the housing 82 facing the optical element package 70 side. The opening limiting member 100 may be installed in the window portion 70B of the optical element package 70.

  Although not shown, the receptacle 56 on the receiver 54 side has the same configuration as the receptacle 52 on the transmitter 50 side except that a light receiving element 66 is installed instead of the light emitting element 64. The aperture limiting member 100 installed in the receptacle 56 is provided with one or a plurality of aperture limiting members 100 that fall within an allowable transmission error range by applying an optical signal emitted from the end face of the optical fiber 62 to the aperture 102 drilled in the light shielding plate. An optical signal of a mode selection group that is a mode group is emitted from the opening 102 to the light receiving element 66. The opening 102 provided in the opening limiting member 100 may be configured as a transmission window that transmits a light beam.

  The input plug 58 for connection to the receptacle 52 includes a multimode optical fiber at the center of the insertion portion 58A for insertion into the coupling insertion hole 68 and along the central axis of the coupling insertion hole 68. The ferrule 74 to which the end of the optical fiber 62 is attached is integrally configured. Also, the output plug 60 is equivalent to the input plug 58, and the optical fiber 62 is arranged in the center of the insertion portion 60A for insertion into the coupling insertion hole 68 and along the central axis of the coupling insertion hole 68. The ferrule 74 to which the end of the above is attached is integrally installed.

  The input plug 58 (or the output plug 60) configured in this manner is inserted into the insertion hole 68 for coupling 58A (or the insertion portion 60A), and then the receptacle 52 (or the receptacle 56). Butt-joined.

  An opening limiting member 100 constituting transmission error reducing means disposed between the receptacle 52 (or the receptacle 56) and the input plug 58 (or the output plug 60) butt-coupled to the receptacle 52 is provided. The shape and size of the opening 102 are obtained by experiment and set to an appropriate value. That is, the opening 102 of the opening limiting member 100 constituting the transmission error reducing means is variously changed in shape and size, and the relationship with the amount of transmission error is obtained by experiment and evaluated. Is set to an appropriate value that can reduce transmission errors.

  Here, it is determined in consideration of the effect that the transmission error is reduced as the size of the opening 102 is narrowed down, and the limitation of the energy coupling efficiency in transmitting light energy.

  Furthermore, this optical transmission apparatus may be configured such that the opening limiting member 100 is provided in at least one of the receptacle 52 of the transmitter 50 or the receptacle 56 of the receiver 54.

  Next, another configuration example of an optical coupling structure for reducing transmission errors between an optical element and an optical transmission medium, which is mode selection means for reducing transmission errors, will be described with reference to FIG.

In the optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 3, the receptacle 52 and the input plug 58 are so-called butt coupled, and further on the optical element side. The optical axis as the center line of the light beam and the optical axis as the center line of the core of the optical fiber 62 are shifted while maintaining a parallel state (decentered).

  That is, in the optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 3, the coupling insertion hole 68 portion in the receptacle 52 (or receptacle 56) is formed as required by the light emitting element 64. (Or the light receiving element 66) is decentered in a predetermined state, and light is emitted when the insertion portion 58A (insertion portion 60A) is inserted into the coupling insertion hole 68 and coupled by butt coupling. Butt coupling while maintaining a state where the optical axis as the center line of the optical path set on the element 64 (or light receiving element 66) side and the optical axis as the center line of the core of the optical fiber 62 are decentered by a predetermined amount in parallel. To be configured.

  In the thus configured optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 3, the irradiation range of the laser beam irradiated from the light emitting element 64 on the incident surface of the optical fiber 62 R and the end face C of the fiber core of the optical fiber 62 are shifted as illustrated in FIG. 4, and the transmission is selected corresponding to the portion where the laser beam irradiation range R and the end face C of the fiber core overlap. Since only the optical signal of the mode selection group that is one or a plurality of mode groups that fall within the error tolerance range can be taken out and transmitted by the optical fiber 62, a transmission error can be prevented by the optical transmission device using this. Can be reduced.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.

  In the second embodiment, the transmitter 52 side receptacle 52 (or the receiver 54 side receptacle 56) for constituting the optical coupling means is provided with a condenser lens 80.

  In the receptacle 52 on the transmitter 50 side (or the receptacle 56 on the receiver 54 side) using this condensing lens, as shown in FIG. 5, the bottom of the coupling insertion hole 68 provided in the housing 82 of the receptacle 52 (56). A light guide opening 84 is formed in the surface. In the housing 82, a condenser lens 80 is disposed on the optical element package 70 side from the light guide opening 84.

  In the housing 82, the optical element package 70 is disposed on the optical path condensed by the condenser lens 80. In the optical element package 70, a light emitting element 64 (or a light receiving element 66) is disposed on the inner bottom surface of the metal package, and a multimode light beam emitted from the light emitting element 64 is transmitted and emitted to the outside (or light). A window portion 70B for transmitting a multi-mode light beam emitted from the fiber 62 and allowing it to enter the light receiving element 66 is provided. The optical element package 70 is configured to be connected to the circuit of the transmitter 50 by an electrode terminal 72 projecting from the bottom surface of the package 70A.

  Further, in the optical coupling means using this condensing lens, the aperture limiting member 100 constituting the transmission error reducing means is disposed adjacent to the optical element package 70 side of the condensing lens 80. The aperture limiting member 100 has a predetermined shape and a predetermined size so that a single or a plurality of mode groups that can be accommodated within a transmission error tolerance range can be selected and extracted as an optical signal of the mode selection group on the light shielding plate. The opening 102 is formed by drilling.

  The opening limiting member 100 configured as described above is arranged with its peripheral end side fixed to the inner peripheral surface of the opening in which the condenser lens 80 in the housing 82 is installed. The opening limiting member 100 may be disposed on the window 70B side of the optical element package 70 or on the optical fiber 62 side from the condenser lens 80.

  Although not shown, the receptacle 56 on the receiver 54 side has the same configuration as the receptacle 52 on the transmitter 50 side except that a light receiving element 66 is installed instead of the light emitting element 64. In the aperture limiting member 100 installed in the receptacle 56, the optical signal emitted from the end face of the optical fiber 62 is applied to the aperture 102 drilled in the light shielding plate portion of the aperture limiting member 100, so that the transmission error is within the allowable range. An optical signal of a mode selection group that is one or a plurality of mode groups that can be accommodated is emitted from the aperture 102 to the light receiving element 66 via the condenser lens 80. The opening 102 provided in the opening limiting member 100 may be configured as a transmission window that transmits a light beam.

  The input plug 58 (or the output plug 60) configured in this manner is inserted into the insertion hole 68 for coupling 58A (or the insertion portion 60A), and then the receptacle 52 (or the receptacle 56). To join.

  Further, an opening limiting member 100 constituting transmission error reducing means, which is disposed between the receptacle 52 (or the receptacle 56) and the input plug 58 (or the output plug 60) coupled thereto, The shape and size of the opening 102 are obtained by experiment and set to an appropriate value.

  Furthermore, this optical transmission apparatus may be configured such that the opening limiting member 100 is provided in at least one of the receptacle 52 of the transmitter 50 or the receptacle 56 of the receiver 54.

  Next, another configuration example of an optical coupling structure for reducing transmission errors between an optical element for reducing transmission errors and an optical transmission medium, which is mode selection means, will be described with reference to FIG.

  In the optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 6, the optical axis as the center line of the light beam on the optical element side and the center line of the core of the optical fiber 62 The optical axis is shifted while maintaining a parallel state (decentered state).

  That is, in the optical coupling structure for reducing the transmission error between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 6, the coupling insertion hole 68 portion in the receptacle 52 (or the receptacle 56) is provided as the light emitting element as necessary. The condensing lens 80 and the optical element package 70 disposed in the receptacle 52 (or the receptacle 56) are configured so as to be eccentric to a predetermined state with respect to the 64 (or the light receiving element 66), and an optical fiber as necessary. 62 is configured to be eccentric to a predetermined state.

  In the optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 6 configured as described above, the insertion portion 58A (insertion portion 60A) is inserted into the coupling insertion hole 68. Thus, the optical axis as the center line of the optical path set on the light emitting element 64 (or the light receiving element 66) side and the optical axis as the center line of the core of the optical fiber 62 are offset by a predetermined amount in parallel. Join while keeping the centered state.

  In the optical coupling structure for reducing transmission errors between the optical element and the optical transmission medium, which is the mode selection means shown in FIG. 6 configured as described above, the laser beam irradiated from the light emitting element 64 on the incident surface of the optical fiber 62 is collected. The irradiation range S focused and irradiated by the optical lens 80 and the end face C of the fiber core of the optical fiber 62 are shifted as illustrated in FIG. Only the optical signal of the mode selection group, which is one or a plurality of mode groups that are selected corresponding to the portion where S and the end face C of the fiber core overlap and falls within the allowable range of transmission errors, is extracted. Since transmission is possible using the fiber 62, transmission errors can be reduced with an optical transmission device using the fiber 62.

  Since the configuration, operation, and effects of the second embodiment other than those described above are the same as those of the first embodiment described above, the same members are denoted by the same reference numerals, and the detailed description thereof is omitted. Description is omitted. Further, the present invention is not limited to the first or second embodiment described above, and it is needless to say that various other configurations can be taken without departing from the gist of the present invention.

It is a schematic structure explanatory drawing which shows the principal part of the optical transmission apparatus using the mode selection means of this invention. It is explanatory drawing which shows the coupling | bonding state of the optical element and optical transmission medium which are the mode selection means concerning 1st Embodiment of this invention. It is explanatory drawing which shows the coupling | bonding state in the optical element, the optical transmission medium, and another structural example which is the mode selection means concerning 1st Embodiment of this invention. In another configuration example of the optical coupling structure of the optical element and the optical transmission medium, which is the mode selection unit according to the first embodiment of the present invention, the irradiation range of the laser beam on the incident surface of the optical fiber, and the fiber core It is explanatory drawing which shows the state shifted with the end surface. It is explanatory drawing which shows the optical element, the optical transmission medium, and the coupling | bonding state which are the mode selection means concerning 2nd Embodiment of this invention. It is explanatory drawing which shows the coupling | bonding state in the other structural example of the optical element and optical transmission medium which is the mode selection means concerning 2nd Embodiment of this invention. In another configuration example of the optical coupling structure of the optical element and the optical transmission medium, which is the mode selection unit according to the second embodiment of the present invention, the irradiation range of the laser beam on the incident surface of the optical fiber, and the fiber core It is explanatory drawing which shows the state shifted with the end surface. It is explanatory drawing which illustrates the optical transmission system which connects the conventional digital apparatus mutually and performs digital optical communication. It is explanatory drawing which illustrates the conventional optical fiber connection apparatus which can be attached and detached optically and mechanically.

Explanation of symbols

50 Transmitter 52 Receptacle 54 Receiver 56 Receptacle 58 Input Plug 58A Insertion Port 60 Output Plug 60A Insertion Port 62 Optical Fiber 64 Light Emitting Element 66 Light Receiving Element 68 Coupling Insertion Hole 70 Optical Element Package 80 Condensing Lens 82 Housing 84 Conduction Optical aperture 100 aperture limiting member 102 aperture

Claims (4)

An optical transmission method for transmitting an optical signal of a plurality of modes emitted from a light emitting element via an optical transmission medium and receiving the light on a light receiving element,
While selecting a part of a plurality of modes emitted from the light emitting element and entering the optical transmission medium,
An optical transmission method characterized in that a propagation time difference in the optical transmission medium between the selected partial modes is within a range in which a transmission error can be accommodated. A light emitting element that emits an optical signal of a plurality of modes;
An optical transmission medium for transmitting optical signals;
In an optical transmission device comprising a light receiving element for receiving an optical signal,
Mode selection means for selecting a part of the plurality of modes of the optical signal;
An optical transmission apparatus comprising the mode selection unit between the light emitting element and the optical transmission medium or between the optical transmission medium and the light receiving element.   The mode selecting means selects a part of modes in which a propagation time difference in the optical transmission medium can keep a transmission error within an allowable range among a plurality of modes emitted by the light emitting element. The optical transmission device according to claim 2.   The mode selection means can transmit a transmission error within an allowable range due to a difference in propagation time in the optical transmission medium among light emitting surfaces in the mode selection means that emit light from the light emitting element or the optical transmission medium. The optical transmission device according to claim 2, wherein the optical transmission device is a member having an opening or a window at a position where some modes exist.

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