JP2004045825A - Optical transmitting and receiving apparatus and optical transceiver system, and optical transceiver method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitting and receiving apparatus which can transmit and receive light signals with an optical fiber, can suppress near-end reflection at a low cost and is high in receiving efficiency, an optical transceiver system and an optical transceiver method. <P>SOLUTION: The optical transmitting and receiving apparatus 1 is provided with a transmission section 4 which is connected to the optical fiber 2 having an end 2a of a convex shape axisymmetric to a central axis, emits a transmission signal and makes the signal incident on the optical fiber 2 from the end 2a, and a reception section 3 which receives the reception signal from the end 2a of the optical fiber 2 and performs single-fiber two-way communications. The transmission section 4 emits the transmission light in such a manner that that the exit position of the transmission light to the plane perpendicular to the normal taken down from the exit position of the transmission light to the central axis of the optical fiber 2 and inclusive of the central axis of the optical fiber 2 in such a manner that the exit position of the transmission light in the transmission section 4 and the incident position of the transmission light in the optical fiber 2 exist on the sides opposite to each other. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for transmitting and receiving optical signals in two directions using a single multi-mode optical fiber such as a plastic optical fiber as a transmission medium used in home communication, communication between electronic devices, LAN (Local Area Network), and the like. The present invention relates to an optical transmission / reception device, an optical transmission / reception system, and an optical transmission / reception method capable of two-way bidirectional communication.
[0002]
[Prior art]
Conventionally, in an optical communication device that transmits and receives signal light using a single optical fiber as a transmission medium, the near-end reflected return light generated by using a single transmission path is incident on the light receiving element as noise. The mainstream is to suppress the transmission light by performing the polarization separation inherent to the reflected light.
[0003]
As one example, Japanese Patent Application Laid-Open Nos. 4-96437 and 10-153720 disclose apparatuses configured to separate the near-end reflected return light of transmission light from reception light using a polarization beam splitter. ing.
[0004]
As shown in FIG. 15, an optical communication transmitting / receiving device described in Japanese Patent Application Laid-Open No. 4-96437 has an LED 101, a PD (light receiving element) 102, lenses 103 and 104, a PBS (polarizing beam splitter) 105, and an aperture 106. It comprises 107 and 108, and transmits and receives signal light via the optical fiber 109.
[0005]
Here, the light emitting point of the LED 101 is located at the focal position of the lens 103, and the optical fiber 109 is located at the focal position of the lens 104.
[0006]
The light emitted from the optical fiber 109 becomes light 111 which is substantially parallel light by the lens 104. Then, of the light 111 that has become substantially parallel light, the P wave is reflected by the PBS 105 and received by the PD 102.
[0007]
Light emitted from the LED 101 becomes light 110 that is substantially parallel light by the lens 103. The P wave of the substantially parallel light 110 is reflected by the PBS 105 and does not pass through the PBS 105.
[0008]
On the other hand, the S-wave of the light 110 that has become substantially parallel light passes through the PBS 105, is condensed by the lens 104, and enters the optical fiber 109. Here, 4% of the light condensed on the end face of the optical fiber 109 is reflected, passes through the lens 104 again, and reaches the PBS 105.
[0009]
The rotation of the polarization plane does not occur in the reflection at the end face of the optical fiber 109 and the transmission through the lens. Therefore, the near-end reflected return light (light reflected by the end face of the optical fiber 109) passes through the PBS 105 and does not enter the PD 102. Each of the apertures 106, 107, and 108 cuts a component that is not parallel light and is generated by aberration of a lens.
[0010]
Further, as shown in FIG. 16, the optical transmitting and receiving device described in Japanese Patent Application Laid-Open No. H10-153720 has a Si substrate 201, an LD (semiconductor laser) 203, a heat sink 202 of the LD 203, a PD 204, a prism 205, a PBS 206, a package 207, A lens 208, a socket for an optical fiber 210 and a connector 209 are provided.
[0011]
The PD 204 is formed on the Si substrate 201. The prism 205 also serves as a base for the PBS 206. Here, unlike the configuration shown in FIG. 15, the PBS 206 is designed to transmit a P wave and reflect an S wave.
[0012]
The light emitted from the LD 203 has S-polarization characteristics, and most of the light is reflected by the PBS 206 and the optical path is changed. Then, after being further NA-converted by the lens 208, the light enters the optical fiber 210.
[0013]
On the other hand, the light emitted from the optical fiber 210 is condensed by the lens 208, and then transmitted only by the PBS 206 through the PBS 206 to enter the PD 204. The near-end reflected return light reflected at the end face of the optical fiber 210 does not rotate the polarization plane in the reflection at the end face of the optical fiber 210 and the transmission through the lens, so that the S-polarized light component is maintained and reflected by the PBS 206 to reach the PD 204. do not do.
[0014]
However, the configurations described in JP-A-4-96437 and JP-A-10-153720 use PBS. Since the PBS is expensive, the cost of the entire optical system in the device increases.
[0015]
Performing such costly two-way optical communication is not preferable in the current situation where two-way communication is required for all devices.
[0016]
Therefore, when transmission and reception are performed with one optical fiber, it can be said that it is preferable to perform transmission and reception separation in space without using a polarization separation element such as PBS so as to reduce the cost.
[0017]
In addition, since the PBS formed of the multilayer dielectric film is generally formed on the surface of a prism or the like, the place where it can be used is limited, and this is an obstacle to miniaturization of the optical transceiver.
[0018]
Further, since one polarization component of the received light is reflected, the signal itself is weakened, and the S / N is deteriorated.
[0019]
Therefore, an optical transceiver for preventing reflection of transmission light at the end of an optical fiber without using a PBS is described in JP-A-11-237535.
[0020]
As shown in FIG. 17, the optical transmitting and receiving apparatus includes a light emitting unit 302 for emitting a first optical signal S1 and a direction R1 different from a direction for emitting a second optical signal S2 from an end 311a of an optical fiber 311. An optical device 320 for causing the first optical signal S1 of the light emitting means 302 to enter the incident end of the optical fiber 311 and a light receiving means 305 for receiving the second optical signal S2 emitted from the end 311a of the optical fiber 311 And
[0021]
When the first optical signal S1 enters the end 311a of the optical fiber 311, the light receiving unit 305 receives the reflected light S3 generated by the reflection of the first optical signal S1 at the end 311a of the optical fiber 311. It is located outside the area.
[0022]
This prevents the first optical signal S1 emitted from the light emitting means 302 from being reflected by the end 311a of the optical fiber 311 and entering the light receiving element 305.
[0023]
[Problems to be solved by the invention]
However, in the configuration described in Japanese Patent Application Laid-Open No. H11-237535, in order for light to propagate in the optical fiber 311, the radiation angle of the optical fiber 311 substantially defined by the numerical aperture (NA) of the optical fiber must be within the range. The light emitting element of the light emitting means 302 must be arranged.
[0024]
For this reason, the second optical signal S2 transmitted and emitted through the optical fiber 311 is coupled to the light receiving element of the light receiving means 305, and the light emitted from the light emitting element is reflected by the end 311a of the optical fiber 311. In order to prevent the light receiving element from being coupled to the light receiving element, the light receiving element needs to be considerably small with respect to the emission area of the light from the optical fiber 311. Therefore, the receiving efficiency of this optical transmitting and receiving device is reduced.
[0025]
The present invention has been made in view of the above problems, and an object of the present invention is to enable transmission and reception of an optical signal by using a single optical fiber, to suppress near-end reflection at low cost, and to improve reception efficiency. An object of the present invention is to provide an optical transmission / reception device, an optical transmission / reception system, and an optical transmission / reception method.
[0026]
[Means for Solving the Problems]
In order to solve the above problem, the optical transmitting and receiving device of the present invention is connected to an optical fiber having a convex end that is axially symmetric with respect to a central axis, emits a first optical signal, and outputs the first optical signal from the end. An optical transmitting and receiving apparatus, comprising: a light transmitting means for entering the optical fiber; and a light receiving means for receiving a second optical signal from an end of the optical fiber, wherein the optical transmitting and receiving apparatus performs single-core bidirectional communication. Means for transmitting the light to a plane perpendicular to a perpendicular drawn from the emission position of the first optical signal in the optical transmission means to the central axis of the optical fiber and including the central axis of the optical fiber; The first optical signal is emitted such that an emission position of the first optical signal in the means and an incident position of the first optical signal in the optical fiber are located on opposite sides.
[0027]
According to the above configuration, the optical transmitting / receiving device is connected to the optical fiber having a convex end that is axially symmetric with respect to the central axis of the optical fiber, and the optical transmitting unit is provided with a symmetric plane (in the optical transmitting unit). An emission position of the first optical signal in the optical transmission means with respect to a plane perpendicular to a perpendicular drawn from the emission position of the first optical signal to the central axis of the optical fiber and including the central axis of the optical fiber; The first optical signal is emitted such that the incident position of the first optical signal on the optical fiber is located on the opposite side.
[0028]
Therefore, even if a part of the first optical signal is reflected at the end of the optical fiber as reflected return light (near-end reflection), the reflected return light is reflected in a direction away from the central axis of the optical fiber. Become.
[0029]
As a result, the reflected return light does not enter the optical receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0030]
Further, by separating the first optical signal and the second optical signal in space without using a polarization separation element such as a PBS (polarization beam splitter), it is possible to reduce the cost and size of the optical system. . This makes it possible to use a low-cost and easy-to-handle optical system.
[0031]
Further, when the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means.
[0032]
Therefore, the size of the light receiving means can be increased, and the receiving efficiency of the light receiving means can be improved.
[0033]
As described above, it is possible to provide an optical transmitting and receiving apparatus having a signal quality that is almost the same as that of the two-core system even though it is a single-core bidirectional optical communication system using one optical fiber.
[0034]
In the above optical transmitting and receiving apparatus, the optical transmitting means includes: a light emitting means for generating a first optical signal; and an optical system for condensing the first optical signal generated by the light emitting means on an end of the optical fiber. The system is arranged such that a plane (a plane perpendicular to a perpendicular line drawn from the emission position of the first optical signal in the optical transmitting means to the central axis of the optical fiber and including the central axis of the optical fiber) is reflected from the optical system. It is preferable that the light is collected so that the emission position of the first optical signal and the incident position of the first optical signal on the optical fiber are located on opposite sides.
[0035]
According to the above configuration, the first optical signal can be efficiently focused on the optical fiber using the optical system.
[0036]
Even if a part of the first optical signal from the optical system is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber. .
[0037]
Therefore, the reflected return light does not enter the light receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0038]
In the above optical transmitting and receiving apparatus, it is preferable that the first optical signal has the same optical path as the optical path of the optical signal out of the second optical signal from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber.
[0039]
According to the above configuration, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction further away from the central axis of the optical fiber. Can be.
[0040]
Therefore, the reflected return light does not enter the optical receiving means, the occurrence of crosstalk noise can be suppressed, and the S / N can be improved.
[0041]
In the above optical transmitting and receiving apparatus, a part of the first optical signal has the same optical path as the optical path of the optical signal having the maximum radiation angle among the optical signals emitted from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber. Is preferred. Here, the maximum radiation angle refers to a radiation angle having an optical path having the largest angle (radiation angle) from the central axis of the optical fiber in an optical path of an optical signal emitted from a certain emission position.
[0042]
According to the above configuration, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is surely reflected in a direction away from the central axis of the optical fiber. be able to.
[0043]
Therefore, the reflected return light does not enter the optical receiving means, the occurrence of crosstalk noise can be suppressed, and the S / N can be improved.
[0044]
In the above optical transmitting and receiving apparatus, a part of the first optical signal has a maximum radiation angle of light emitted from the vicinity of the outer periphery farthest from the emission position of the first optical signal on the surface of the end of the optical fiber. It is preferable to have the same optical path as the optical path of the optical signal having
[0045]
According to the above configuration, a part of the first optical signal can be reliably reflected in a direction away from the central axis of the optical fiber, and the occurrence of crosstalk noise can be suppressed.
[0046]
In addition, the light transmitting means can be arranged in a region distant from the central axis of the optical fiber, so that the light receiving region of the light receiving means for the second optical signal can be made larger.
[0047]
Therefore, it is possible to improve the receiving efficiency of the optical receiving means.
[0048]
In the above optical transmitting and receiving apparatus, it is preferable that the optical receiving means is provided on the central axis of the optical fiber extending from the end of the optical fiber toward the optical transmitting and receiving apparatus.
[0049]
According to the above configuration, it is possible to improve the receiving efficiency of the optical receiving unit.
[0050]
In the above optical transmitting and receiving apparatus, it is preferable that the optical receiving unit is provided closer to the end of the optical fiber than the optical transmitting unit.
[0051]
According to the above configuration, for example, the optical receiving unit can efficiently receive the second optical signal with the smallest possible optical system.
[0052]
An optical transmitting and receiving system according to the present invention includes an optical fiber having a convex end that is axially symmetric with respect to a central axis, an optical transmitting unit that emits a first optical signal and causes the optical fiber to enter the optical fiber from the end, An optical receiving system for receiving a second optical signal from an end of the optical fiber, wherein the optical transmitting and receiving system performs single-core bidirectional communication, wherein An emission position of the first optical signal in the optical transmission means, with respect to a plane perpendicular to a perpendicular line drawn to the central axis of the optical fiber and including the central axis of the optical fiber, It is characterized in that the incident position of the first optical signal is located on the opposite side.
[0053]
According to the above configuration, the end of the optical fiber has a convex shape that is axially symmetric with respect to the central axis of the optical fiber, and the optical transmitting unit is configured to have a plane of symmetry (from the emission position of the first optical signal in the optical transmitting unit). With respect to a plane perpendicular to the perpendicular drawn to the central axis of the optical fiber and including the central axis of the optical fiber), the emission position of the first optical signal in the optical transmission means and the position of the first optical signal in the optical fiber The first optical signal is emitted such that the incident position is located on the opposite side.
[0054]
Therefore, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber.
[0055]
As a result, the reflected return light does not enter the optical receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0056]
In addition, since the end of the optical fiber has a convex shape that is axially symmetric with respect to the central axis of the optical fiber, light of the first optical signal that has entered the optical fiber can be largely refracted at the end. . Therefore, the first optical signal can be efficiently propagated.
[0057]
Furthermore, by separating the first optical signal and the second optical signal in space without using a polarization separation element, it is possible to reduce the cost and size of the optical system. This makes it possible to use a low-cost and easy-to-handle optical system.
[0058]
In the case where the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means.
[0059]
Therefore, the size of the light receiving means can be increased, and the receiving efficiency of the light receiving means can be improved.
[0060]
In the above optical transmitting and receiving system, it is preferable that the surface of the end portion of the optical fiber is spherical. Alternatively, in the above optical transmitting and receiving system, it is preferable that the end portion of the optical fiber is a cone or a truncated cone.
[0061]
According to the above configuration, the end of the optical fiber has a convex shape that is axisymmetric with respect to the central axis of the optical fiber.
[0062]
Therefore, light incident on the optical fiber of the first optical signal can be refracted greatly at the end. As a result, the first optical signal can be efficiently propagated.
[0063]
Further, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected away from the central axis of the optical fiber. Therefore, it is possible to provide an optical transmission / reception system having a good S / N.
[0064]
In the above optical transmitting and receiving system, the core of the optical fiber is preferably made of plastic.
[0065]
According to the above configuration, since the plastic is easy to process, the shape of the optical fiber is easy to process. Therefore, it becomes easy to process the surface of the end portion of the optical fiber into, for example, a spherical surface or to adjust the size of the diameter of the optical fiber.
[0066]
In the above optical transmitting and receiving system, the optical path of the optical signal having the maximum radiation angle is obtained when the part of the first optical signal is emitted from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber in the second optical signal. It is preferable to have the same optical path as
[0067]
According to the above configuration, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is surely reflected in a direction away from the central axis of the optical fiber. be able to.
[0068]
Therefore, the reflected return light does not enter the optical receiving means, the occurrence of crosstalk noise can be suppressed, and the S / N can be improved.
[0069]
The optical transmitting and receiving method according to the present invention is characterized in that the first optical signal from the optical transmitting means is made incident on the convex optical fiber whose end is axially symmetric with respect to the central axis from the end, and the end of the optical fiber is An optical transmission / reception method for performing single-core bidirectional communication by receiving a second optical signal from the optical fiber, comprising: a perpendicular line drawn from an emission position of the first optical signal in the optical transmission means to a central axis of the optical fiber. The first light is provided at an end of the optical fiber on the side opposite to the emission position of the first optical signal in the optical transmission means with respect to a plane including the central axis of the optical fiber. It is characterized in that a signal is incident.
[0070]
According to the above method, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber. Become.
[0071]
Therefore, the reflected return light does not enter the light receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0072]
Further, by separating the first optical signal and the second optical signal in space without using a polarization separation element, it is possible to reduce the cost and size of the optical system. This makes it possible to use a low-cost and easy-to-handle optical system.
[0073]
Further, when the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means. Therefore, the size of the light receiving means can be increased, and the receiving efficiency of the light receiving means can be improved.
[0074]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of the present invention will be described below with reference to FIGS.
[0075]
FIG. 2 shows a configuration of a main part of an optical communication link (optical transmission / reception system) including the optical transmission / reception device according to the present embodiment. As shown in FIG. 1, the optical communication link includes an optical transmitting / receiving device 1 and an optical fiber 2.
[0076]
The optical transceiver 1 is disposed at both ends of the optical fiber 2 so as to be optically connected to the optical fiber 2. The configuration of the optical transmitting and receiving apparatus 1 which is a characteristic configuration in the present embodiment will be described later.
[0077]
The optical fiber 2 bidirectionally transmits modulated light (optical signal) suitable for transmission based on the data signal to be transmitted.
[0078]
The core of the optical fiber 2 has, for example, a diameter of about 1 mm and is made of plastic. The numerical aperture NA of the optical fiber 2 is 0.3. As shown in FIG. 1, the end 2a of the optical fiber 2 is subjected to spherical processing with a radius of 1.5 mm.
[0079]
Since the core of the optical fiber 2 is made of plastic which is easy to process, the surface of the end 2a of the optical fiber 2 is processed into, for example, a spherical surface, or the size of the diameter of the optical fiber 2 is adjusted. It becomes easy to do.
[0080]
As shown in FIG. 1, since the end 2 a has a spherical shape, the optical axis of the light emitted from a certain emission position in the optical fiber 2 is aligned with the optical transmitting / receiving device 1 side of the optical fiber 2. It is inclined toward the central axis.
[0081]
Here, the emitted light when the surface of the end 2a is a spherical surface (the end 2a is a spherical end surface) will be described in comparison with Comparative Example 1 where the end is flat.
[0082]
FIG. 13 is a diagram illustrating light emitted from the optical fiber 22 in Comparative Example 1.
[0083]
As shown in FIG. 13, in Comparative Example 1, the light axis of the light emitted from a certain emission position in the light emitted from the end 22 a is the central axis of the optical fiber 22 (indicated by a dashed line in the figure). And become almost parallel.
[0084]
On the other hand, as shown in FIG. 1, of the light emitted from the optical fiber 2 in the present embodiment, the optical axis of the light emitted from a certain emission position is Tilted toward the central axis. That is, the optical axes of the respective radiated lights from the optical fiber 2 intersect on the side of the optical transceiver 1 from the end 2a.
[0085]
That is, in the radiation light in the case where the end 2a has a spherical end surface, the radiation angle of the light ray radiated most from the central axis side of the optical fiber 2 becomes maximum. On the other hand, the radiation angle of a light beam radiated away from the central axis of the optical fiber 2 is smaller than usual (in the case of a flat surface (see FIG. 13)).
[0086]
As shown in FIG. 1, in the light emitted from the optical fiber 2, the emission angle of the light beam emitted from the center axis side of the optical fiber 2 becomes the largest at the outer peripheral portion (end) of the optical fiber 2. (Outermost periphery of the portion 2a).
[0087]
Here, FIG. 4 shows a configuration of the optical fiber 2 (solid line in the figure) whose end 2a has a spherical end face and the optical fiber 22 (dotted line in the figure) whose end 22a has a flat surface. FIG. 4 shows, out of the light emitted from the ends 2a and 22a, the light emitted from the vicinity of the outer periphery of the ends 2a and 22a and emitted most toward the central axis of the optical fibers 2.22. .
[0088]
As shown in FIG. 4, the radiation angle on the central axis side of the optical fiber 2 (the angle between the light ray of the radiation light and the central axis of the optical fiber) is such that the light emitted from the end 2 a is closer to the end 22 a Is larger than the outgoing light. Here, the state of light emitted from the optical fiber 2 (a part of the emitted light) when excited by a light source having an excitation NA of 0.6 is shown.
[0089]
That is, if the propagation angle in the optical fiber 2 is the same, the radiation angle with respect to the central axis of the optical fiber 2 becomes larger when the light emitting end is on the spherical end face than on the flat end face. The light ray having the maximum radiation angle having the optical path indicated by S20 when it is a flat surface becomes S10 having a larger radiation angle when it is formed on a spherical end face.
[0090]
This is because the end 2a has a spherical end surface, so that the end 2a works like a lens. For this reason, as the light emitted from the outer peripheral portion of the end 2a, the optical path thereof is refracted more (the radiation angle from the optical fiber 2 becomes larger).
[0091]
The shape of the end 2a is a convex shape, and is not particularly limited as long as the shape is axially symmetric with respect to the central axis of the optical fiber 2. For example, a vertex is located on the central axis of the optical fiber 2. It may be a certain cone (the end surface is a conical surface) or a truncated cone.
[0092]
When the surface of the end 2a is a spherical surface, it is preferable that the spherical surface has a large curvature.
[0093]
FIG. 3 shows the intensity distribution pattern of the emitted light (1 m, 20 m, steady state) for each transmission distance (1 m, 20 m, steady state) when the light is excited by the light source having the excitation NA of 0.6 and the light is transmitted using the optical fiber 2. 4 is a graph showing a far field pattern (hereinafter, referred to as FFP). In FIG. 3, the vertical axis represents relative intensity when the intensity of light having a radiation angle of 0 ° (emitted light traveling on the central axis of the optical fiber) is set to 1, and the horizontal axis represents the radiation angle (°) (light in the optical path). (Angle from the central axis of the fiber 2).
[0094]
Here, since the numerical aperture NA of the optical fiber 2 is set to 0.3, the propagating light corresponding to the numerical aperture NA larger than 0.3 attenuates in the originally steady state, and becomes a leaky mode. It should show the smallest FFP shown.
[0095]
However, when the transmission distance is short, the light beam in the leaky mode is not sufficiently attenuated, and the pattern has a large radiation angle as shown in FIG. 3 as the FFP with the transmission distance of 1 m and 20 m. As the distance becomes longer, the FFP becomes smaller and finally becomes an FFP close to a steady state. That is, when the transmission distance is short, it is understood that light having a numerical aperture NA or more of the optical fiber 2 is sufficiently transmitted.
[0096]
Hereinafter, the configuration of the optical transceiver 1, an optical signal (second optical signal) received by the optical transceiver 1, and an optical signal (first optical signal) transmitted from the optical transceiver 1 will be described.
[0097]
First, the configuration of the optical transceiver 1 will be described. As shown in FIG. 1, the optical transmitting / receiving device 1 includes a receiving unit (optical receiving unit) 3 and a transmitting unit (optical transmitting unit) 4.
[0098]
Usually, in order to perform single-core bidirectional communication, an optical signal (received light) received by the optical transceiver 1 and an optical signal (transmitted light) transmitted from the optical transceiver 1 are polarized by a PBS (polarizing beam splitter) or the like. Separation using a separation element is costly.
[0099]
Performing such costly two-way optical communication is not preferable in the current situation where two-way communication is required for all devices.
[0100]
Therefore, when transmission and reception are performed with one optical fiber, it can be said that it is preferable to perform transmission and reception separation in space without using a polarization separation element such as PBS so as to reduce the cost.
[0101]
When separating transmission and reception in space, considering that a transmission / reception unit is integrated on the end face of an optical fiber of about 1 mm using a large-diameter optical fiber, the area ratio between the transmission unit and the reception unit affects the reception efficiency. However, this further affects the S / N (Signal to Noise Ratio) (SNR).
[0102]
In general, under such conditions, it is advisable to reduce the size of the transmitting section that is easy to narrow down to a small beam and increase the size of the receiving section that is difficult to narrow down to a small beam.
[0103]
However, no matter how small the beam to be transmitted is, the size that can be mounted in a range of 1 mm is limited, so that the mechanical interference between the receiving unit and the transmitting unit, that is, the overlapping of the receiving unit and the transmitting unit is considered. To avoid this, the receiving unit has to be reduced to some extent.
[0104]
In addition, the transmission light is reflected on the end face of the optical fiber (near-end reflection), so that crosstalk noise of the transmission / reception light easily occurs.
[0105]
Therefore, the optical transmitting and receiving device 1 of the present embodiment includes the receiving unit 3 and the transmitting unit 4 as described above.
[0106]
As shown in FIG. 6, the receiving unit 3 has a lens 31 as an optical system and a photodiode 32 as a light receiving element. Further, the transmission unit 4 includes a lens 41 as an optical system and a photodiode (light emitting unit) 42 as a light emitting element.
[0107]
As described above, in order to improve the receiving efficiency, it is preferable to increase the size of the receiving unit 3 and reduce the size of the transmitting unit 4.
[0108]
In general, as shown in FIG. 3, the intensity distribution of the light emitted from the optical fiber 2 has a Gaussian shape, and the intensity on the central axis of the optical fiber 2 is the strongest.
[0109]
Therefore, in order to improve the receiving efficiency, it is preferable that a part of the receiving unit 3 exists on the central axis of the optical fiber 2.
[0110]
The arrangement of the receiving unit 3 and the transmitting unit 4 is not particularly limited. For example, as shown in FIG. 5, the receiving unit 3 is arranged close to the end 2a of the optical fiber 2, and the transmitting unit 4 may be arranged at a position farther from the receiving unit 3 and the transmission light may be narrowed down to be coupled to the optical fiber 2. Thereby, the transmission light from the optical fiber 2 can be efficiently received by the smallest possible optical system.
[0111]
Next, the arrangement of the receiving unit 3 and the transmitting unit 4 will be described in detail.
[0112]
By the way, as shown in FIG. 1, the light emitted from the optical fiber 2 clearly shows the density since the end 2a is a spherical end face.
[0113]
On the other hand, as shown in FIG. 13, the emission angle of the emitted light from the optical fiber 22 is constant at any radiation position on the end 22a because the end 22a has a flat surface. Therefore, the light emitted from the end face 22a is averaged without being sparse and dense.
[0114]
Accordingly, when the end 2a has a spherical end surface, the transmitting unit 4 is arranged in a region where emitted light is sparse, and the receiving unit 3 is arranged so as to include a dense region. Efficiency can be maximized.
[0115]
In addition, it is preferable that the transmission light be incident as close to the outer peripheral portion as possible of the end 2a. In other words, the transmission light is shifted to a light beam (the incident angle to the end portion 2a becomes the maximum) which travels in the opposite direction to the light having the maximum emission angle among the lights emitted from the vicinity of the outer periphery of the end portion 2a. Just fine. Thus, the size of the receiving unit 3 can be increased, and the receiving efficiency can be maximized.
[0116]
Normally, for example, when the transmitting unit 4 is arranged near the central axis of the optical fiber 2 and transmission light is made incident on the optical fiber 2, the receiving unit 3 cannot be arranged near the optical axis. Thereby, the receiving efficiency of the receiving unit 3 is reduced.
[0117]
Further, FIG. 14 shows the transmitting and receiving unit 4 in the optical transmitting and receiving apparatus 1 shown in FIG. 1 for each of the case where the end of the optical fiber has a spherical end surface and the case where the end of the optical fiber has a flat surface. The relationship between the distance D (mm) from the central axis of the optical fiber 2 and the receiving efficiency (%) of the receiving unit 3 is shown.
[0118]
Accordingly, when the distance D (division ratio between the receiving unit 3 and the transmitting unit 4) from the central axis of the optical fiber 2 in the transmitting unit 4 is the same, higher receiving efficiency is obtained when the spherical end face is used. You can see that it is.
[0119]
Thus, it is preferable that the receiving unit 4 is provided on the central axis of the optical fiber 2 extending from the end 2 a of the optical fiber 2 to the optical transmitting / receiving device 1 side. Thereby, the receiving efficiency in the receiving unit 3 can be improved.
[0120]
Next, coupling of transmission light to the optical fiber 2 when the end 2a has a spherical end face will be described with reference to FIG.
[0121]
Here, the transmission light S11 is incident substantially near the outer peripheral portion of the end 2a, and is perpendicular to a perpendicular drawn from the emission position of the transmission light S11 in the transmission unit 4 to the central axis of the optical fiber 2, In addition, the transmission light S11 is incident on a plane including the central axis of the optical fiber 2 (hereinafter, referred to as a symmetry plane) on the side opposite to the emission position of the transmission light S11.
[0122]
At this time, as shown in FIG. 11, the transmission light S11 becomes the propagation light S12, and propagates while being reflected in the optical fiber 2. That is, the transmission light S11 can be coupled to the optical fiber 2.
[0123]
On the other hand, the transmission light S13 is incident on the same side of the symmetry plane as the emission position of the transmission light S13.
[0124]
At this time, the transmission light S13 becomes leakage light S14, and goes out of the optical fiber 2 without propagating through the optical fiber 2. That is, the transmission light S13 does not couple to the optical fiber 2.
[0125]
As described above, the transmission light is incident on the opposite side to the emission position of the transmission light with respect to the symmetry plane, so that the transmission light can be reliably coupled to the optical fiber 2.
[0126]
Next, near-end reflection of transmission light at the end 2a of the optical fiber 2 will be described.
[0127]
First, the incident position of the transmission light emitted from the photodiode 42 of the transmission unit 4 at the end 2a will be described with reference to FIG. Hereinafter, of the transmitted light, the light reflected at the incident position is referred to as reflected return light.
[0128]
In the drawing, the incident positions A, B, and C are such that the incident position of the transmission light and the position of the photodiode 42 are opposite to the symmetry plane X.
[0129]
On the other hand, the incident position D is such that the incident position of the transmission light and the position of the photodiode 42 are on the same side with respect to the symmetry plane X.
[0130]
Here, since the end portion 2a has a spherical end surface, the reflected return light of the transmission light incident on the incident positions A, B, and C is reflected at the incident positions A, B, and C at the near end, and is received. The light is reflected outside the reception area of the unit 3.
[0131]
On the other hand, the reflected return light of the transmitted light that has entered the incident position D is not reflected outside the reception area of the receiving unit 3 even if it is reflected at the incident position D at the near end. That is, the reflected return light from the incident position D is often coupled to the receiving area of the receiving unit 3.
[0132]
When the reflected return light is coupled to the receiving area of the receiving unit 3 as described above, it becomes crosstalk noise, and the S / N at the receiving unit 3 is reduced.
[0133]
However, in the optical transmitting and receiving apparatus 1 according to the present embodiment, the reflected light is reflected by returning the transmission light from the transmission unit 4 to the opposite side of the transmission light with respect to the symmetry plane X. It is possible to prevent the receiving unit 3 from being coupled to, for example, the photodiode 32.
[0134]
Therefore, it is possible to improve the S / N in the optical transmitting and receiving device 1.
[0135]
The incident position of the transmission light may be near the outer periphery of the end 2a farthest from the emission position of the transmission light in the transmission unit 4 (on the extension line connecting the emission position and the central axis of the optical fiber 2). preferable.
[0136]
Thereby, it is possible to reliably prevent the reflected return light from being incident on the light receiving unit 3.
[0137]
At this time, it is not always necessary to excite the photodiode 42 at an angle equal to or smaller than the numerical aperture NA of the optical fiber 2, and if it is excited with a light ray within the effective NA indicating a propagation angle of a predetermined distance as shown in FIG. Good.
[0138]
Hereinafter, transmission light and reception light when the receiving unit 3 includes the lens 31 and the photodiode 32 and the transmitting unit 4 includes the lens 41 and the photodiode 42 will be described with reference to FIG.
[0139]
In FIG. 7, radiated light emitted from the vicinity of the outer periphery of the surface of the end portion 2a is referred to as radiated light S15 (S15a to S15c), and the light having the largest radiation angle of the radiated light S15 is referred to as radiated light S15b.
[0140]
The transmission light S16 emitted from the photodiode 42 is incident on the end 2a via the lens 41, propagates in the optical fiber 2 as propagation light S17, and is reflected at the near end as reflected return light N18.
[0141]
Here, the optical path of the transmission light S16 is opposite to the optical path of the emission light S15b. That is, the incident position of the transmission light S16 on the end 2a is on the opposite side of the emission position of the transmission light S16 in the transmission unit 4, that is, the emission position of the transmission light S16 from the lens 41 with respect to the symmetry plane.
[0142]
As described above, when the transmission light S16 is incident near the outer peripheral portion of the convex end portion 2a, the incident surface is greatly inclined outward with respect to the central axis of the optical fiber 2. Therefore, most of the transmission light S16 is refracted on the surface of the end 2a and becomes the propagation light S17, which propagates through the optical fiber 2.
[0143]
Further, a part of the transmission light S16 becomes the reflected return light N18, and the reflected return light N18 is reflected in a direction away from the central axis of the optical fiber 2. Therefore, crosstalk noise is less likely to occur, and S / N can be improved.
[0144]
Further, the transmitting unit 4 can be made relatively smaller than the receiving unit 3, and therefore the receiving unit 3 can be made larger. Thereby, the receiving efficiency of the receiving unit 3, that is, the photodiode 32 can be improved.
[0145]
Thus, it is possible to provide the optical transceiver 1 having a signal quality that is almost the same as that of the two-core system even though it is a single-core bidirectional optical communication system using one optical fiber 2.
[0146]
The photodiode 42 is not particularly limited as long as it is a light-emitting element that emits light, and may be, for example, an LD (Laser Diode) or an LED (Light Emitting Diode).
[0147]
Further, as the optical system, the receiving unit 3 has been described using the lens 31, but the present invention is not limited to this. For example, the light collecting mirror 5 shown in FIG. 8 may be used.
[0148]
Hereinafter, the case where the incident position of the transmission light S16 on the end 2a is on the same side as the emission position of the transmission light S16 in the transmission unit 4, that is, the emission position of the transmission light S16 from the lens 41 with respect to the symmetry plane, This will be described as Comparative Example 2 with reference to FIG.
[0149]
In FIG. 9, radiated light emitted from the vicinity of the outer periphery of the surface of the end 2a is referred to as radiated light S15 (S15a / S15b), and light having the largest radiation angle out of the emitted light radiated from the end 2a is radiated. The light is S15b.
[0150]
The transmission light S36 emitted from the photodiode 42 is incident on the end 2a via the lens 41, propagates through the optical fiber 2 as light S37, or leaks from the optical fiber 2, and as reflected return light N38. Near-end reflection.
[0151]
Here, the angle (spread angle) of the transmission light S36 from the central axis of the optical fiber 2 is smaller than that of the emission light S15b emitted from the opposite side of the symmetry plane. Note that the transmission light cannot be coupled to the optical fiber 2 even if the transmission light enters the optical fiber at an angle equal to or larger than the spread angle of the radiation emitted from the incident position of the end face 2a.
[0152]
Therefore, even if the transmission light S36 is incident so that the spread angle at the incident position becomes the largest, as shown in FIG. 9, the reflected return light N38 is transmitted to the reception unit 3 (the lens 31 or the photodiode 32). The light is easily incident (coupled), and crosstalk is likely to occur in the receiving unit 3.
[0153]
Also, referring to FIG. 10, it is assumed that the receiving unit 23 of the comparative example 1 shown in FIG. 13 includes a lens 25 and a photodiode 26, and the transmitting unit 24 includes a lens 28 and a photodiode 27. It will be described as.
[0154]
In FIG. 10, radiated light emitted from near the outer peripheral portion of the surface of the end 22a is referred to as radiated light S45 (S45a / S45b), and light having the largest radiation angle among radiated light emitted from the end 22a is radiated light. S45b is set.
[0155]
The transmission light S46 emitted from the photodiode 27 is incident on the end 22a via the lens 28, becomes light S47, and is reflected at the near end as reflected return light N48.
[0156]
Here, the surface of the end portion 22a is a flat surface, and the refraction effect of the incident light cannot be obtained as much as the end portion 2a which is a spherical end surface.
[0157]
Therefore, even if the transmission light S46 is excited from the same position and angle as the transmission light S16 to the end 2a whose surface is a spherical end surface as shown in FIG. 7, the light S47 does not propagate through the optical fiber 2, and 2 will leak.
[0158]
Further, even if the transmission light S46 is excited from the same position and the same angle as the transmission light S16 to the end 2a whose surface shown in FIG. 7 is a spherical end surface, the reflected return light N48 is smaller in the optical fiber 2 than the reflected return light N18. Is not reflected away from the central axis of
[0159]
Therefore, the ratio of the reflected return light N48 to the reception unit 23 and the coupling to the reception area (photodiode 26) increases. As a result, the combined reflected return light N48 becomes crosstalk noise, and the S / N is degraded.
[0160]
As described above, the transmission light from the transmission unit 4 is made incident on the end 2a and the reception light from the end 2a is received on the optical fiber 2 whose end 2a is axisymmetric with respect to the central axis. Thus, single-core bidirectional communication is performed. In addition, a plane perpendicular to a perpendicular line drawn from the emission position of the transmission light in the transmission unit 4 to the central axis of the optical fiber 2 and including the central axis of the optical fiber 2 (a plane of symmetry). The transmission light is made incident on the end 2a of the optical fiber 2 on the side opposite to the emission position of the transmission light.
[0161]
That is, in an optical transmission / reception system that includes the optical fiber 2, the transmission unit 4, and the reception unit 3 and performs single-core two-way communication, the emission position of the transmission light in the transmission unit 4 and the incidence of the transmission light in the optical fiber 2 The position is opposite to the plane of symmetry.
[0162]
Therefore, even if a part of the transmission light is reflected as reflected return light at the end 2 a of the optical fiber 2, the reflected return light is reflected in a direction away from the central axis of the optical fiber 2.
[0163]
As a result, the reflected return light does not enter the receiving unit 3 and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0164]
In addition, since the end 2a of the optical fiber 2 has a convex shape that is axially symmetric with respect to the center axis of the optical fiber 2, the light that has entered the optical fiber 2 out of the transmission light is largely refracted at the end 2a. be able to. Therefore, the transmission light can be efficiently propagated in the optical fiber 2.
[0165]
Further, by separating the transmission light and the reception light in space without using a polarization separation element, the cost and size of the optical system can be reduced. This makes it possible to use a low-cost and easy-to-handle optical system.
[0166]
Further, when the transmitting light and the receiving light are separated in space, the transmitting unit 4 can usually be smaller than the receiving unit 3.
[0167]
Therefore, the size of the receiving unit 3 can be increased, and the receiving efficiency of the receiving unit 3 can be improved.
[0168]
【The invention's effect】
As described above, the optical transmitting and receiving device of the present invention is connected to an optical fiber having a convex end that is axially symmetric with respect to the central axis, emits a first optical signal, and from the end to the optical fiber. An optical transmitting and receiving apparatus comprising: an optical transmitting means for inputting light; and an optical receiving means for receiving a second optical signal from an end of the optical fiber, wherein the optical transmitting and receiving apparatus performs single-core bidirectional communication. The optical transmission means is perpendicular to a perpendicular line drawn from the emission position of the first optical signal to the central axis of the optical fiber, and is located on the plane including the central axis of the optical fiber. The first optical signal is emitted such that the emission position of one optical signal and the incident position of the first optical signal on the optical fiber are located on opposite sides.
[0169]
Thereby, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber (near-end reflection), the reflected return light is reflected in a direction away from the central axis of the optical fiber. It becomes.
[0170]
Therefore, the reflected return light does not enter the light receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0171]
Further, by separating the first optical signal and the second optical signal in space without using a polarization separation element such as a PBS (polarization beam splitter), it is possible to reduce the cost and size of the optical system. . This makes it possible to use a low-cost and easy-to-handle optical system.
[0172]
Further, when the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means.
[0173]
Therefore, the size of the light receiving means can be increased, and the receiving efficiency of the light receiving means can be improved.
[0174]
As a result, it is possible to provide an optical transmitting and receiving apparatus having a signal quality almost the same as that of the two-core optical communication system even though it is a single-core bidirectional optical communication system using one optical fiber.
[0175]
The optical transmitting and receiving apparatus of the present invention is configured such that the optical transmitting unit includes a light emitting unit that generates a first optical signal, and an optical system that condenses the first optical signal generated by the light emitting unit on an end of the optical fiber, The optical system moves from the optical system to a plane (a plane that is perpendicular to a perpendicular line drawn from the emission position of the first optical signal in the optical transmitting means to the central axis of the optical fiber and includes the central axis of the optical fiber). The light is condensed so that the emission position of the first optical signal and the incident position of the first optical signal on the optical fiber are located on opposite sides.
[0176]
Thereby, the first optical signal can be efficiently focused on the optical fiber using the optical system.
[0177]
Even if a part of the first optical signal from the optical system is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber. .
[0178]
Therefore, the reflected return light does not enter the light receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, there is an effect that the S / N can be improved.
[0179]
The optical transmitting and receiving apparatus according to the present invention is configured such that the first optical signal has the same optical path as the optical path of the optical signal out of the second optical signal from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber.
[0180]
Thus, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light can be reflected further away from the central axis of the optical fiber.
[0181]
Therefore, the reflected return light is not incident on the light receiving means, the generation of crosstalk noise can be suppressed, and the S / N can be improved.
[0182]
In the optical transmitting and receiving apparatus of the present invention, a part of the first optical signal has the same optical path as the optical path of the optical signal having the maximum radiation angle among the optical signals emitted from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber. It is a configuration to have.
[0183]
Thus, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light can be surely reflected in a direction away from the central axis of the optical fiber.
[0184]
Therefore, the reflected return light is not incident on the light receiving means, the generation of crosstalk noise can be suppressed, and the S / N can be improved.
[0185]
In the optical transmitting and receiving apparatus of the present invention, a part of the first optical signal has a maximum radiation of the light emitted from the vicinity of the outer periphery farthest from the emission position of the first optical signal on the surface of the end of the optical fiber. This is a configuration having the same optical path as the optical path of the optical signal having an angle.
[0186]
Thereby, it is possible to surely reflect a part of the return light of the first optical signal in a direction away from the central axis of the optical fiber, and to suppress occurrence of crosstalk noise.
[0187]
Also, the light transmitting means can be arranged in a region separated from the central axis of the optical fiber, and accordingly, the light receiving region of the second light signal in the light receiving means can be made larger. Therefore, there is an effect that the receiving efficiency of the optical receiving means can be improved.
[0188]
The optical transceiver of the present invention is configured such that the optical receiving means is provided on the central axis of the optical fiber extending from the end of the optical fiber to the optical transceiver.
[0189]
Thereby, there is an effect that the receiving efficiency in the optical receiving unit can be improved.
[0190]
The optical transmitting and receiving apparatus according to the present invention has a configuration in which the optical receiving unit is provided closer to the end of the optical fiber than the optical transmitting unit.
[0191]
Thus, in the optical receiving means, for example, there is an effect that the second optical signal can be efficiently received by an optical system as small as possible.
[0192]
An optical transmitting and receiving system according to the present invention includes an optical fiber having a convex end that is axially symmetric with respect to a central axis, an optical transmitting unit that emits a first optical signal and causes the optical fiber to enter the optical fiber from the end, An optical receiving system for receiving a second optical signal from an end of the optical fiber, wherein the optical transmitting and receiving system performs single-core bidirectional communication, wherein An emission position of the first optical signal in the optical transmission means, with respect to a plane perpendicular to a perpendicular line drawn to the central axis of the optical fiber and including the central axis of the optical fiber, It is characterized in that the incident position of the first optical signal is located on the opposite side.
[0193]
Thus, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber.
[0194]
As a result, the reflected return light does not enter the optical receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0195]
In addition, since the end of the optical fiber has a convex shape that is axially symmetric with respect to the central axis of the optical fiber, light of the first optical signal that has entered the optical fiber can be largely refracted at the end. . Therefore, the first optical signal can be efficiently propagated.
[0196]
Furthermore, by separating the first optical signal and the second optical signal in space without using a polarization separation element, it is possible to reduce the cost and size of the optical system. This makes it possible to use a low-cost and easy-to-handle optical system.
[0197]
In the case where the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means.
[0198]
Therefore, it is possible to increase the size of the light receiving means, and it is possible to improve the receiving efficiency of the light receiving means.
[0199]
The optical transmitting / receiving system of the present invention has a configuration in which the surface of the end of the optical fiber is spherical. Alternatively, the optical transmitting and receiving apparatus of the present invention has a configuration in which the end portion of the optical fiber is a cone or a truncated cone.
[0200]
Thereby, the end of the optical fiber has a convex shape that is axially symmetric with respect to the central axis of the optical fiber. Therefore, light incident on the optical fiber of the first optical signal can be refracted greatly at the end. As a result, the first optical signal can be efficiently propagated.
[0201]
Further, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected away from the central axis of the optical fiber. Therefore, there is an effect that an optical transmission / reception system having a good S / N can be provided.
[0202]
The optical transmission / reception system of the present invention has a configuration in which the core of the optical fiber is made of plastic.
[0203]
Thus, the plastic can be easily processed, so that the shape of the optical fiber can be easily processed. Therefore, there is an effect that it becomes easy to process the surface of the end portion of the optical fiber into, for example, a spherical surface, or to adjust the diameter of the optical fiber.
[0204]
In the optical transmitting and receiving system of the present invention, a part of the first optical signal is an optical signal having the maximum radiation angle in the optical signal emitted from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber in the second optical signal. The configuration has the same optical path as the optical path.
[0205]
Thus, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light can be surely reflected in a direction away from the central axis of the optical fiber.
[0206]
Therefore, the reflected return light is not incident on the light receiving means, the generation of crosstalk noise can be suppressed, and the S / N can be improved.
[0207]
The optical transmitting and receiving method according to the present invention is characterized in that the first optical signal from the optical transmitting means is made incident on the convex optical fiber whose end is axially symmetric with respect to the central axis from the end, and the end of the optical fiber is An optical transmission / reception method for performing single-core bidirectional communication by receiving a second optical signal from the optical fiber, comprising: a perpendicular line drawn from an emission position of the first optical signal in the optical transmission means to a central axis of the optical fiber. The first light is provided at an end of the optical fiber on the side opposite to the emission position of the first optical signal in the optical transmission means with respect to a plane including the central axis of the optical fiber. This is a configuration in which a signal is incident.
[0208]
According to the above method, even if a part of the first optical signal is reflected as reflected return light at the end of the optical fiber, the reflected return light is reflected in a direction away from the central axis of the optical fiber. Become.
[0209]
Thereby, the reflected return light does not enter the optical receiving means, and the occurrence of crosstalk noise can be suppressed. Thereby, the S / N can be improved.
[0210]
Further, by separating the first optical signal and the second optical signal in space without using a polarization separation element, it is possible to reduce the cost and size of the optical system. This makes it possible to use a low-cost and easy-to-handle optical system.
[0211]
Further, when the first optical signal and the second optical signal are separated in space, the optical transmitting means can usually be made smaller than the optical receiving means. Therefore, it is possible to increase the size of the light receiving means, and it is possible to improve the receiving efficiency of the light receiving means.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a main part of an optical transceiver according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of a main part of an optical communication link including the optical transceiver illustrated in FIG. 1;
FIG. 3 is a graph showing FFP when light is excited by a light source having an excitation numerical aperture NA of 0.6 and light is transmitted using the optical fiber shown in FIG. 2;
FIG. 4 is a diagram showing a configuration in a case where an end face of an optical fiber is spherical and a configuration in a case where it is flat
FIG. 5 is a diagram illustrating a configuration of an optical transmitting and receiving apparatus when a receiving unit is arranged closer to an optical fiber than a transmitting unit;
FIG. 6 is a diagram illustrating a configuration of a transmission unit and a reception unit.
FIG. 7 is a diagram illustrating transmission light and reception light when a transmission unit and a reception unit include a lens and a photodiode.
FIG. 8 is a diagram illustrating a configuration of an optical transmitting and receiving device when a condensing mirror is used for an optical system.
FIG. 9 is a diagram illustrating optical paths of transmission light and reception light in Comparative Example 2.
FIG. 10 is a diagram illustrating optical paths of transmission light and reception light in Comparative Example 3.
FIG. 11 is a diagram illustrating coupling of transmission light incident on an optical fiber.
FIG. 12 is a diagram illustrating a relationship between an incident position of transmission light and a position of a photodiode in a transmission unit.
FIG. 13 is a diagram showing emitted light in Comparative Example 1 using an optical fiber having a flat end surface.
FIG. 14 shows the distance D (mm) from the center axis of the optical fiber in the transmitting unit and the receiving distance for each of the case where the end of the optical fiber has a spherical end surface and the case where it has a flat surface. 6 is a graph showing a relationship with a receiving efficiency (%) of a unit.
FIG. 15 is a diagram illustrating a configuration of a conventional optical transmission / reception device.
FIG. 16 is a diagram showing a configuration of another conventional optical transmitting / receiving device.
FIG. 17 is a diagram showing a configuration of still another conventional optical transmission / reception device.
[Explanation of symbols]
1 Optical transceiver
2 Optical fiber
3 Receiver (optical receiving means)
4 Transmission unit (optical transmission means)
5 Condensing mirror (optical system)
31 lenses
32 Photodiode
41 lens (optical system)
42 Photodiode (light emitting means)
S16 Transmission light (first optical signal)
S15 Received light (second optical signal)
N18 reflected return light

Claims (14)

An optical transmission means connected to an optical fiber having a convex end that is axially symmetric with respect to a central axis, for emitting a first optical signal and causing the first optical signal to enter the optical fiber from the end, and an end of the optical fiber And an optical receiving unit for receiving a second optical signal from
The optical transmission means is perpendicular to a perpendicular drawn from the emission position of the first optical signal in the optical transmission means to the central axis of the optical fiber, and with respect to a plane including the central axis of the optical fiber, The first optical signal is emitted such that an emission position of the first optical signal in the optical transmission unit and an incident position of the first optical signal in the optical fiber are located on opposite sides. Optical transceiver. The light transmitting unit includes a light emitting unit that generates the first optical signal, and an optical system that collects the first optical signal generated by the light emitting unit at an end of the optical fiber,
The optical system converges such that an emission position of the first optical signal from the optical system and an incident position of the first optical signal on the optical fiber are located on opposite sides with respect to the plane. The optical transmitting / receiving device according to claim 1, wherein: 2. The optical signal according to claim 1, wherein the first optical signal has the same optical path as an optical path of an optical signal of the second optical signal, which is emitted from the vicinity of an outer peripheral portion on a surface of an end of the optical fiber. 3. Optical transceiver. A part of the first optical signal has the same optical path as the optical path of the optical signal having the maximum radiation angle among the optical signals emitted from the vicinity of the outer peripheral portion on the surface of the end of the optical fiber. The optical transceiver according to claim 3. A part of the first optical signal is an optical signal having a maximum radiation angle among light emitted from the vicinity of the outermost part farthest from the emission position of the first optical signal on the surface of the end of the optical fiber. The optical transmitting and receiving apparatus according to claim 3, wherein the optical transmitting and receiving apparatus has the same optical path as the optical path. 2. The optical transceiver according to claim 1, wherein the optical receiving means is provided on a central axis of the optical fiber extending from an end of the optical fiber toward the optical transceiver. 2. The optical transceiver according to claim 1, wherein the optical receiving unit is provided closer to an end of the optical fiber than the optical transmitting unit. An optical fiber having a convex end that is axially symmetric with respect to a central axis, an optical transmitting unit that emits a first optical signal and causes the optical fiber to enter the optical fiber from the end, An optical receiving and receiving system for receiving a second optical signal, the optical transmitting and receiving system for performing single-core bidirectional communication,
The optical transmission means is perpendicular to a perpendicular line drawn from the emission position of the first optical signal to the central axis of the optical fiber, and includes a central axis of the optical fiber. An optical transmitting / receiving system, wherein an emission position of a first optical signal and an incident position of the first optical signal in the optical fiber are located on opposite sides. The optical transmission / reception system according to claim 8, wherein a surface of an end portion of the optical fiber is spherical. The optical transmission / reception system according to claim 8, wherein the end of the optical fiber has a conical shape. The optical transmitting and receiving system according to claim 8, wherein the end of the optical fiber has a truncated cone shape. The optical transmission and reception system according to claim 8, wherein the core of the optical fiber is made of plastic. A part of the first optical signal has the same optical path as the optical path of the optical signal having the maximum radiation angle in the optical signal of the second optical signal emitted from the vicinity of the outer peripheral portion on the end surface of the optical fiber. The optical transmission / reception system according to claim 8, comprising: The first optical signal from the optical transmission means is made incident on the convex optical fiber whose end is axially symmetric with respect to the central axis from the end, and the second optical signal is received from the end of the optical fiber. By doing, an optical transmission and reception method for performing single-core bidirectional communication,
The optical transmission means is perpendicular to a perpendicular line drawn from the emission position of the first optical signal to the central axis of the optical fiber, and includes a central axis of the optical fiber. An optical transmission / reception method, characterized in that the first optical signal is incident on an end of the optical fiber opposite to the emission position of the first optical signal.

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