JP2001296456A - Optical coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical coupler that can attain reduction in cost and size. SOLUTION: The optical coupler is constituted of a light emitting element 57 for converting an electrical signal 100Z and transmitting an optical signal 100 for communication, a light receiving element 58 for receiving communication optical signal 200D and converting it to an electrical signal 200X, a silicon substrate 52 on which the light emitting element 57 and the light receiving element 58 are installed, an optical fiber 54 which is connected at one end to the light receiving element 57, and an optical connector 55 which is provided at the other end of the optical fiber 54. On the silicon substrate 52, a fiber guide groove 53 is formed which has a bend 60 for fixing the optical fiber 54. The light receiving element 58 is installed facing this bend 60 of the fiber guide groove 53, for the purpose of receiving the light 200D for the bend loss released from a curved part 90 of the optical fiber 54 that is fixed in the fiber guide groove 53.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical coupler for converting a communication optical signal transmitted and received by an optical communication network into an electric signal.

[0002]

2. Description of the Related Art With the recent progress of high-speed and large-capacity communication networks, even in low-speed subscriber lines having relatively low communication speeds, optical communication using optical fibers has been carried out from telecommunication networks using electric wires. Switching to a network has begun. For example, NTT
(Registered trademark) has begun to introduce an optical access system commonly called a π system. The π system is an SLT (subscriber line terminal equipment) that converts between a digitized electric signal and an optical signal for communication in a station, which is schematically described;
FTM (optical wiring module) that performs multi-branch and multiplexing of optical signals for communication in a station and subscriber lines (optical communication lines), and provided at a part that becomes a key point near each user's home (home, etc.) An ONU (optical line termination circuit) for converting a communication optical signal and an electric signal of a subscriber line (optical communication line)
This is a system composed of an LT, FTM, and an optical fiber that connects between ONUs. In the π system, light having a wavelength of 1.3 μm is used as a communication optical signal used for optical communication. The π system has a function of monitoring a failure or an accident such as a break in a communication line of an optical communication network, and uses light having a wavelength of 1.55 μm band for the function. However, the light in the 1.55 μm band is used only for monitoring a failure such as a break in a communication line or an accident as described above, and is unnecessary for optical communication. The portion where the optical signal for use is input to the ONU needs to have a function of blocking light in the 1.55 μm band. At present, an optical coupler is used to realize each function required for the ONU. The optical coupler separates the received signal by receiving the communication optical signal in the optical fiber by the light receiving element as it is, and transmits the transmission signal by sending the transmission signal as it is to the optical fiber as the communication optical signal by the light emitting element. The signal is being synthesized. However, the optical signal for communication as described above has advantages in that the signal is transmitted at high speed and the frequency band is wide, but the optical signal has a higher linearity than the electric signal. Therefore, it has the disadvantage that it is difficult to separate the received signal from other signals and to combine the transmitted signal with other signals. As a method of separating a received signal by an optical coupler and combining a transmitted signal, for example, a glass plate having a dielectric multilayer film formed on the surface thereof, such as a half mirror, is placed at 45 degrees with respect to a traveling direction of a communication optical signal. A method using a beam splitter that separates received light and combines transmitted light by arranging it in an inclined manner, or
Conventionally, a method using a fusion type coupler formed by fusing a plurality of optical fibers has been used.
A method using a PLC (planar optical circuit) optical coupler having an optical waveguide formed on a quartz glass or silicon (Si) substrate has been used.

FIG. 5 is a diagram schematically showing transmission and reception of a communication optical signal using a conventional PLC optical coupler. FIG.
Is a schematic view, and, for example, a covering portion or a reinforcing member constituting an actual optical fiber is not described because it does not relate to propagation or leakage of an optical signal of the present application. The optical coupler 1 is communicatively connected to an optical coupler 1a on the other side via an optical communication network 20. In the optical communication network 20, a communication network side optical connector 22 is provided at an end of the communication network side optical fiber 21, 21a.
22a, the optical coupler 1 and the optical coupler 1
a provided on each of the coupler-side optical connectors 6, 6a to be described later.
And can be connected. Hereinafter, since the optical couplers 1 and 1a have the same configuration, only the optical coupler 1 will be described. The optical coupler 1 is a planar optical circuit (hereinafter, PLC) that separates the communication optical signal 600 and combines the communication optical signal 500.
2) and silicon dioxide (Si)
O ₂ ), and a Y branch circuit portion 3 formed by using
a long-wavelength light cutoff filter 4 provided at a connection between the Y-branch circuit unit 3 and a coupler input / output optical fiber 5 described later to cut off only the line monitoring optical signal 300 of long-wavelength light of μm or more; A coupler input / output optical fiber 5 for transmitting and receiving the optical signals 500A and 600A to and from the optical communication network 20,
A coupler-side optical connector 6 provided at an end of the coupler input / output optical fiber 5 on the optical communication network 20 side, and a laser diode (hereinafter, referred to as a light emitting element) that converts a transmission signal 500Z of an electric signal into a communication optical signal 500. LD) 9),
The communication optical signal 500 output from the LD 9 is
0, a coupler output optical fiber 8 that guides the communication optical signal 600B output from the PLC 2 to the PD 10, and a light receiving element that converts the communication optical signal 600B into an electric signal reception signal 600X. A photodiode (hereinafter, referred to as PD) 10.

Here, the communication optical signal 600A input to the optical communication network 20 side end of the Y branch circuit section 3 is transmitted to the other two ends of the Y branch circuit section 3 by 50%. Signal 600
B, 600C. Conversely, PLC2
Is transmitted to the coupler output optical fiber 8 and is 50% of the communication optical signal 600A received from the optical communication network 20. The communication optical signal 600A is also output to the coupler input optical fiber 7 side by 50% by passing through the PLC2.
There is no adverse effect on the communication optical signal 500 output from D9, so this is not a problem. Also, 50% of the communication optical signal 500 input from the LD 9 to the Y branch circuit section 3 is output from the end of the Y branch circuit section 3 on the optical communication network 20 side to the coupler input / output optical fiber 5, and the remaining 50% of
Is leaked out of the waveguide of the Y-branch circuit unit 3 and is not used.
Conversely, the communication optical signal 500A output to the coupler input / output optical fiber 5 through the PLC 2 is an output corresponding to 50% of the communication optical signal 500 output from the LD 9.
On the other hand, the line monitoring optical signal 300 output from the switching station or the relay station of the optical communication network 20 is cut off by the long-wavelength light cutoff filter 4 and is not input to the PLC 2, but is input to the PD 1.
0 does not receive the line monitoring optical signal 300. As described above, when the transmission loss of the optical communication network 20 or the like is ignored, the communication optical signal 500 transmitted from the optical coupler 1 side is used.
Is transmitted to the optical communication network 20 by passing through the PLC 2 so that a communication optical signal 500A corresponding to 50% of the communication signal 500A is transmitted to the optical communication network 20.
The communication optical signal 600A received from the optical communication network 20
Is transmitted through the PLC 2a in the optical coupler 1a, and the communication optical signal 600B corresponding to 50% of the
Input to 0. That is, the communication optical signal 500 transmitted from the optical coupler 1 side
The communication optical signal becomes 0%, and when it is received by the optical coupler 1a of the other party, the communication optical signal further becomes 50%. Therefore, the communication signal 500B corresponding to 25% of the original communication optical signal 500 Is received by the PD 10a in the optical coupler 1a of the other party, is converted into an electric signal, and the received signal 500X
Is output. In the same manner as above, the communication optical signal 600B transmitted from the other optical coupler 1a side also has a communication signal 600B equivalent to 25% of the original communication optical signal 600.
Is received by the PD 10 in the optical coupler 1 of the other party, is converted into an electric signal, and the received signal 600X is output.
In this way, in the optical access system (π system) introduced by NTT, the optical coupler using the PLC 2 is turned on while monitoring the line with the line monitoring optical signal 300.
U (optical line termination circuit) for signal light (wavelength 1.3
(μm band).

[0005]

SUMMARY OF THE INVENTION However, PLC
In order to form an optical waveguide such as the Y branch circuit unit 3 on the PLC _2, a thick film of silicon dioxide (SiO ₂ ) is formed on the PLC ₂ , and the thick film is etched to a depth of 10 μm or more. A step of performing When the long-wavelength light cutoff filter 4 is installed to cut off the optical signal 300 for line monitoring, the Y-branch circuit unit 3 and the coupler input / output optical fiber 5
Since the method of inserting and bonding the long-wavelength light cutoff filter 4 to the connection portion with the filter is used, a step of inserting and bonding the separately prepared long-wavelength light cutoff filter 4 is required.
Each of these steps increases the cost of the optical coupler due to the high level of difficulty and the number of steps. However, as described above, the optical coupler, which is an ONU (optical line termination circuit), is provided at a portion that becomes a screw point near each user's house (home, etc.), and therefore, it is desired that the cost be low. . Further, the long-wavelength light cutoff filter 4 cannot be made very small because it needs to be bonded to the PLC 2, but as described above, the optical coupler is provided at a portion that becomes a spiral point near each user's house (home or the like). Therefore, miniaturization is desired. The present invention has been made to solve the conventional problems as described above, and an object of the present invention is to provide an optical coupler that can be reduced in size and cost.

[0006]

In order to achieve the above object, an optical coupler according to the present invention of claim 1 comprises a light emitting element for converting an electric signal into a communication optical signal and transmitting the signal, and a communication optical signal. A light receiving element for receiving and converting the light to an electric signal; a silicon substrate on which the light emitting element and the light receiving element are installed; an optical fiber having one end connected to the light emitting element; and an optical fiber fixed to the other end of the optical fiber An optical connector, comprising: a fiber guide groove having a bent portion for fixing an optical fiber is formed on the silicon substrate; and the light receiving element is fixed to the fiber guide groove. In order to receive the received light emitted from the bent portion of the optical fiber, the optical fiber is installed facing the bent portion of the fiber guide groove. According to a second aspect of the present invention, in the optical coupler according to the first aspect, a converging lens for receiving the received light corresponding to the bending loss is provided. According to a third aspect of the present invention, in the optical coupler according to the first or second aspect, a long-wavelength blocking film for blocking an optical signal for line monitoring is formed on an end face of the optical fiber in the optical connector. It is characterized by.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on illustrated embodiments. FIG. 1 is a diagram schematically illustrating transmission and reception of an optical signal for communication using the optical coupler according to the first embodiment of the present invention. In FIG. 1, the conventional PL shown in FIG.
Portions having the same functions as those of the C optical coupler are denoted by the same reference numerals, and redundant description will be omitted. As shown in FIG. 1, the optical coupler 51 of the present embodiment is communicatively connected to the optical coupler 51a of the other party via the optical communication network 20. The communication network side optical connectors 22 and 22a of the optical communication network 20 can be connected to the optical coupler 51 and each of the coupler side optical connectors 55 and 55a described later provided in the optical coupler 51a. Hereinafter, since the optical couplers 51 and 51a have the same configuration, the optical coupler 51
Will be described only. The optical coupler 51 includes a silicon substrate 52, a fiber guide groove 53 having a substantially L-shaped bent portion 60 formed on the surface of the silicon substrate 52,
An optical fiber 54 fitted and fixed in the fiber guide groove 53, a coupler-side optical connector 55 installed at an end of the optical fiber 54 on the side of the optical communication network 20, and an optical communication of the optical fiber 54 inside the coupler-side optical connector 55. End surface 62 on the side of net 20
A long-wavelength light blocking film 56 formed above to block light in the 1.55 μm band is connected to the other end of the optical fiber 54 and disposed at the innermost portion of the fiber guide groove 53 to convert an electric signal. A laser diode (hereinafter referred to as LD) 57 which is a light emitting element for transmitting a communication optical signal, and an optical fiber which is installed facing the groove bending portion 60 of the fiber guide groove 53 and is fixed to the fiber guide groove 53 And a photodiode (hereinafter, referred to as PD) 58 that is a light receiving element that receives the received light corresponding to the bending loss emitted from the fiber bending portion 90 and converts the received light into an electric signal. In the present embodiment, the optical fiber 54 is fitted into the substantially L-shaped fiber guide groove 53 and fixed, so that the received signal can be reduced from the leaked received light (bending loss of the received light), which has not been conventionally used. Can be taken out.

FIG. 2 is an enlarged sectional view showing a groove bending portion 60 in the fiber guide groove 53 of the silicon substrate 52. In the drawings, the enlargement ratio of each part is shown with a smaller dimensional difference than the actual ratio for convenience of explanation. The optical fiber 54 used in this embodiment is called a step index type, and propagates light (communication optical signal) in the core section 80 while being totally reflected. The optical fiber 54 in FIG. 2 has a clad 70 and a core 8 covered around the clad 70 by removing the coating and the like (not shown).
It is composed of only 0. Generally, the diameter of the core 80 is about 10 μm, and the diameter of the clad 70 is 12 μm.
It is about 5 μm. The material is core part 80, clad part 7
Although 0 is quartz, the refractive index differs depending on the mixing ratio of germanium dioxide or the like, and the refractive index of the core portion 80 is slightly higher (about 0.3%). Therefore, the light (communication optical signal) inside the core unit 80 is as shown in FIG.
If the inner critical angle θ1 is, for example, 80 degrees or more, the core 8
The light is totally reflected at a boundary surface between 0 and the cladding portion 70.
The optical fiber 54 in the fiber guide groove 53 is linear in the groove linear portion 61 and becomes a fiber linear portion 91, but is bent in an arc at the groove bent portion 60 and becomes a fiber curved portion 90. . In the fiber straight portion 91,
Since the critical angle θ1 is 80 degrees or more, the light (communication optical signal) is totally reflected at the interface between the core section 80 and the cladding section 70.
Since the angle 2 is equal to or less than 80 degrees, the light (communication optical signal) is not totally reflected at the boundary surface between the core portion 80 and the clad portion 70, and is transmitted to the outside through the clad portion 70. The bent portion of the optical fiber 54 (the fiber bending portion 9
The light leaked to the outside from 0) and emitted is conventionally not used at all, and is called a bending loss.

In this embodiment, the fiber bending portion 90
The light receiving element P is located at a position where a communication optical signal (received signal 200D) corresponding to a bending loss leaked and emitted from the optical disc can be incident.
By arranging D58, it was configured to be able to receive the received signal 200D. In the case of the present embodiment, the reception signal 200 transmitted through the core 80 of the fiber bending section 90 is used.
The ratio between the light amount of C and the light amount of the received signal 200D corresponding to the bending loss is about 90% and 10%. Therefore, about 10% (about several dB) of the received signal 200A becomes the light amount of the received signal 200B received by the PD 58, but this does not pose a problem if the intensity level of the received signal 200A is sufficient. Further, by changing the shape of the groove bending portion 60 so as to further increase the degree of bending, the degree of bending of the fiber bending portion 90 is increased, and the ratio of the amount of light of the reception signal 200D is increased to, for example, about 50%. Is also possible. The transmission signal 100 transmitted from the LD 57 is emitted as the transmission signal 100B corresponding to the bending loss by about 10% in the fiber bending section 90, but the intensity level of the transmission signal 100A is about 90% of the transmission signal 100Z. There is no problem because there is enough. The above is the optical coupler 51
The operation on the optical coupler 51a side is shown in FIG.
As shown in (1), the transmission signal 200 is transmitted from the LD 57a, and the transmission signal 200A having a light intensity of 90% is transmitted to the optical communication network 20. Then, the transmission signal 200A of the optical coupler 51a is received as the reception signal 200A of the optical coupler 51. Conversely, the transmission signal 10 on the optical coupler 51 side
0A is received as the reception signal 100A on the optical coupler 51a side. In the present embodiment, for example, 90% of the amount of light transmitted from the LD 57a is transmitted as the transmission signal 200A on the optical coupler 51a side, and 10% of the reception signal 200A is received on the optical coupler 51 side. 9% of the light amount of the transmitting LD 57a on the optical coupler 51a side can be received by the PD 58 on the optical coupler 51 side. this is,
Although the light quantity is smaller than 25% of the transmitting light emitting element that can be received by the PDs 10 and 10a as the light receiving elements in the conventional optical couplers 1 and 1a shown in FIG. 5, this is not a problematic level. As described above, the light receiving ratio of the PDs 58 and 58a can be increased to, for example, close to 50% by changing the shape of the groove bending portion 60.

FIG. 3 is an enlarged perspective view of the coupler-side optical connector 55 and the long-wavelength light blocking film 56 inside the coupler-side optical connector 55. When the coupler-side optical connector 55 and the communication network-side optical connector 22 are connected, the end face 62 of the coupler-side optical fiber 54 and the end face of the communication network-side optical fiber 21 are arranged at positions facing each other. 5
1 and the optical communication network 20 can transmit and receive the communication optical signals 100A and 200A in the 1.3 μm band.
Here, in the present embodiment, since the long wavelength blocking film 56 is formed on the end face 62 of the coupler-side optical fiber 54, the line monitoring optical signal 300 in the 1.55 μm wavelength band transmitted from the optical communication network 20 is Are blocked by the long wavelength blocking film 56 and do not enter the optical coupler 51. Similarly, since the long-wavelength blocking film 56a is also formed on the end face 62a of the coupler-side optical fiber 54a, the line monitoring optical signal 300 does not enter the optical coupler 51a. In the present embodiment, the long-wavelength blocking film 56 is formed on the end face 62 of the coupler-side optical fiber 54, and the long-wavelength blocking film 56a is formed on the end face 62 of the coupler-side optical fiber 54a.
Since it is formed at a, it is not necessary to adhere and fix the long-wavelength cutoff filter 4 and the like having a different configuration to the silicon substrate 52 unlike the conventional PLC optical coupler, and a compact optical coupler can be manufactured. FIG. 4 is an enlarged sectional view showing a groove bending portion 60 in a fiber guide groove 53 of a silicon substrate 52 according to a second embodiment of the present invention. In the drawings, the enlargement ratio of each part is shown with a smaller dimensional difference than the actual ratio for convenience of explanation. In the present embodiment, for example, a condenser lens 59 such as a hemispherical lens or a cylindrical lens is arranged at the position where the PD 58 is installed in the silicon substrate 52 in the first embodiment, and the PD 58 is located at the focal position of the condenser lens 59. Was placed. Other configurations are the same as those of the first embodiment. In the present embodiment, the fiber bending portion 90
The communication optical signal (received signal 200D) corresponding to the bending loss leaked and emitted from the light source is collected by the condensing lens 59 as a received signal 200E directed to the focal point on the PD 58, so that the received light (received signal 200D) ) Can efficiently obtain the received signal 200X (electrical signal). For example, even if the received light (received signal 200D) is attenuated to a weak level, it can be reliably received by condensing. The received signal 200X can be obtained from the signal 200D. In the above embodiments, the fiber guide groove 53 is used.
Is formed in a substantially L-shape and has a right angle portion, but for example, the groove bending portion 60 may be curved in accordance with the curvature of the fiber bending portion 90. In addition, the fiber guide groove 53 of each of the above embodiments has a substantially L-shaped shape in which the groove linear portion 61 bends at a substantially right angle at the groove bending portion 60. However, the bending angle of the groove bending portion 60 is substantially a right angle. It is not limited, for example, several dB from the fiber bending portion 90.
Any other angle may be used as long as the received light (communication optical signal corresponding to the bending loss) of the degree (about 10% of the whole received light) leaks.

[0011]

As described above, according to the first aspect of the present invention, there is no need to form an optical waveguide by forming a thick film such as silicon dioxide (SiO ₂ ) on a silicon substrate and then etching it. Since only the fiber guide groove for fixing the optical fiber is provided on the silicon substrate by bending, the optical coupler can be manufactured at low cost. Claim 2
Since the present invention includes a condensing lens for converging a communication optical signal corresponding to a bending loss leaked and emitted from the fiber bending portion toward a focal point on the light receiving element, the received signal can be efficiently converted from the received light. Can be obtained, and even if the received light is attenuated to a weak level, it is possible to reliably receive the received light and obtain a received signal by focusing. According to the third aspect of the present invention, since a long-wavelength blocking film for blocking an optical signal for line monitoring is formed on an end face of an optical fiber in an optical connector, a small-sized optical coupler can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating transmission and reception of a communication optical signal using an optical coupler according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a groove bending portion in a fiber guide groove of a silicon substrate.

FIG. 3 is an enlarged perspective view of a coupler-side optical connector and a long-wavelength light blocking film inside the coupler-side optical connector.

FIG. 4 is an enlarged sectional view showing a groove bending portion in a fiber guide groove of a silicon substrate according to a second embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating transmission and reception of a communication optical signal using a conventional PLC optical coupler.

[Explanation of symbols]

20 optical communication network, 21, 21a communication network side optical fiber,
22, 22a Communication network side optical connector, 51, 51a Optical coupler, 52, 52a Silicon substrate, 53, 53a
Fiber guide groove, 54, 54a Coupler side optical fiber, 55, 55a Coupler side optical connector, 56, 56a
Long wavelength light blocking film, 57, 57a Laser diode (LD: light emitting element), 58, 58a Photodiode (PD: light receiving element), 60, 60a Groove, 61,
61a groove linear portion, 62, 62a end face, 90, 90a
Fiber bending section, 91, 91a fiber straight section,
100, 100A, 100B, 100C Optical coupler 51
Transmission signal (communication optical signal) = reception signal of the optical coupler 51a, transmission signal (electric signal) of the 100Z optical coupler 51,
100X Received signal (electric signal) of optical coupler 51a, 2
00, 200A, 200B, 200C Optical coupler 51a
Transmission signal (communication optical signal) = reception signal of optical coupler 51, transmission signal (electric signal) of 200Z optical coupler 51a, reception signal (electric signal) of 200X optical coupler 51, 300 line monitoring optical signal

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04B 10/135 10/13 10/12 F term (reference) 2H036 NA01 QA12 QA22 QA53 2H037 AA01 BA02 BA12 CA06 DA03 DA04 DA12 2H047 KA02 MA07 QA02 TA44 5F089 AA01 AC10 AC16 CA03 CA20 GA01 5K002 BA16 BA31 BA33 FA01

Claims (3)

[Claims] 1. A light emitting element for converting an electric signal into an optical signal for communication and sending it, a light receiving element for receiving the optical signal for communication and converting it to an electric signal, and the light emitting element and the light receiving element are provided. An optical coupler comprising a silicon substrate, an optical fiber having one end connected to the light emitting element, and an optical connector fixed to the other end of the optical fiber, wherein an optical fiber is provided on the silicon substrate. A fiber guide groove having a bent portion for fixing is formed, and the light receiving element receives the light emitted from the curved portion of the optical fiber fixed to the fiber guide groove. An optical coupler characterized by being installed facing a bent portion. 2. The optical coupler according to claim 1, further comprising: a condenser lens for receiving the received light corresponding to the bending loss. 3. The optical coupler according to claim 1, wherein a long wavelength blocking film for blocking an optical signal for line monitoring is formed on an end face of the optical fiber in the optical connector.