JPH01113708A - Optical multiplexing/demultiplexing module - Google Patents

Abstract

PURPOSE:To use a single mode fiber as well as a multimode fiber as the transmission optical fiber by giving the double structure of a core part to be a single mode waveguide and a core part to be a multimode waveguide to the core part of an optical fiber for input/output. CONSTITUTION:The core part of an optical fiber 3 for input/output has the double structure where the core part to be a single mode waveguide 20 and the core part to be a multimode waveguide 21 are formed on the same axis. Three steps of refractive index are given to the refractive index distribution on the end face of the optical fiber 3 to form this core part. In this constitution, the light having a wavelength lambda1 emitted from a light emitting element 1 is efficiently coupled to the single mode waveguide 20, and the light having a wavelength lambda2 propagated in the multimode waveguide 21 is coupled to a photodetector 2. Thus, the single mode fiber as well as the multimode fiber can be used as the transmission optical fiber, and an inconvenience that modules are prepared for them independently of each other in a conventional device is resolved.

Description

[Detailed description of the invention] [Industrial application field].

The present invention relates to an optical multiplexing/demultiplexing module incorporating a light emitting element and a light receiving element used for bidirectional transmission by propagating light of different wavelengths through a single optical transmission line.

[Prior Art] Fig. 6 is a configuration diagram showing a conventional optical multiplexing/demultiplexing module disclosed, for example, in "243 Single Mode Fiber Multiplexing/Demultiplexing Module" of the 1985 National Conference of the Optical and Radio Division of the Institute of Electronics and Communication Engineers. be. In the figure, 1 is the wavelength λ! 2 is a light receiving element; 3 is an optical input/output fiber using a single mode fiber for optical input/output;
4 is a collimating lens that converts the light of wavelength λ1 emitted from the light emitting element 1 into a parallel beam; 5 is a condensing lens for condensing the light onto the light receiving element 2; and 6 is the collimating lens 4 that converts the light into a parallel beam. Optical input/output fiber 3 for light with wavelength λ1
A common boat lens 7 is used to convert the light of wavelength ^2 emitted from the optical input/output fiber 3 into a parallel beam; 7 is the collimating lens 4. Condensing lens 5
．． A pentaprism installed between common boat lenses 6, 8 is a wavelength λ formed on the side of the pentaprism 7.
1 is a filter that transmits light of wavelength λ2 and reflects light of wavelength λ2; 9 is a mirror formed on the other side of pentaprism 7;
is a spacer prism inserted between the collimating lens 4 and the filter 8, and 11 is the wavelength λ! converted by the collimating lens 4. 12 is a parallel light beam of wavelength λ2 converted by the common boat lens 6, 13 is a case fixing each of the above components, and 14a is a light beam formed at the other end of the optical input/output fiber 3. A connector 15 is a transmission line fiber using a single mode fiber for the transmission line.
4b is an optical connector formed at the end of the transmission line fiber 15.

Next, the operation of the above-described conventional optical multiplexing/demultiplexing module will be explained. Light with a wavelength λ1 emitted from the light emitting element 1 is converted into a parallel beam 11 by the collimator lens 4, passes through the spacer prism 10, and enters the filter 8. Here, the filter 8 has a wavelength λ! Therefore, the parallel light beam 11 with wavelength λ1 passes through the filter 8 and becomes a Ventab filter.
The light enters the rhythm 7, passes through the pentaprism 7, and enters the common boat lens 6. Here, the parallel light beam 11 with the wavelength λ1 is condensed by the common boat lens 6 and input to the optical input/output fiber 3, and furthermore, the optical connector 14a,
The signal is coupled to the transmission line fiber 15 connected at 14'b, propagates through the transmission line fiber 15, and is sent to another station. On the other hand, the light of wavelength λ2 that has propagated through the transmission line fiber 15 from another station propagates through the optical input/output fiber 3 connected by the optical connectors 14a and 14b, and then exits from the end and is shared by the optical input/output fiber 3. The light enters the boat lens 6. Here, the light of wavelength λ2 is converted into a parallel light beam 12 and is passed through the pentaprism 7.
The light passes through the filter and enters the filter 8. Here, filter 8
reflects the light of wavelength λ2, so the parallel light beam 1 of wavelength λ2
2 is reflected and enters a mirror 9 formed on the other side of the pentaprism 7. Here, the parallel light beam 12 with the wavelength λ2 is further reflected and eventually changes its direction by 90 degrees and enters the condenser lens 5, and is condensed onto the light receiving element 2 by the condenser lens 5.

The reason why a single mode fiber is used as the optical input/output fiber 3 as described above is that a single mode fiber is used as the transmission line fiber 15. For example, consider using FIG. 7 the case where a multimode fiber is used as the optical input/output fiber 3 regardless of whether a single mode fiber is used as the transmission line fiber 15.

FIG. 7 is a configuration diagram showing a connecting portion when a single mode fiber and a multimode fiber are connected in the optical connector of FIG. 6. In the figure, 16 is the core portion of the multimode fiber used as the optical input/output fiber 3;
7 is a core portion of a single mode fiber used as the transmission line fiber 15, and 18 is a joint surface between the multimode fiber and the single mode fiber. The multimode fiber can propagate light in many propagation modes to the core portion 16. On the other hand, the core portion 17 of the single mode fiber can only propagate light in one of the lowest propagation modes. Therefore, when coupling light from a multimode fiber to a single mode fiber, most of the light in the multimode fiber that does not match the propagation mode of the single mode fiber is not coupled and is lost. On the other hand, when coupling from a single mode fiber to a multimode fiber, all of the light that has propagated through the single mode fiber is coupled to the multimode fiber. Therefore, when a single mode fiber is used as the transmission line fiber 15,
When a multimode fiber is used as the optical input/output fiber 3,
Most of the light of wavelength ^1 coupled from the light emitting element 1 to the optical input/output fiber 3 is lost at the bonding surface 18;
All of the light of wavelength λ2 that has propagated through the transmission line fiber 15 is coupled to the optical input/output fiber 3. On the other hand, if a multimode fiber is used as the transmission line fiber 15 and a single mode fiber is used as the optical input/output fiber 3, the optical input/output fiber 3
All the light of wavelength λ1 coupled to transmission line fiber 1
However, most of the light of wavelength λ2 that has propagated through the transmission line fiber 15 is lost at the joint surface 18.

As mentioned above, in order to perform good optical transmission for both sending and receiving, when a single mode fiber is used as the transmission line fiber 15, it is necessary to use a single mode fiber as the optical input/output fiber 3. On the other hand, when a multimode fiber is used as the transmission line fiber 15, a multimode fiber must be used as the optical input/output fiber 3. For optical multiplexing/demultiplexing modules in which a single mode fiber is used as the output fiber 3, only a single mode fiber can be used as the transmission line fiber 15 and a multimode fiber cannot be used. This indicates that in an optical multiplexing/demultiplexing module in which a multimode fiber is used as the output fiber 3, a multimode fiber cannot be used as the transmission line fiber 15, and a single mode fiber cannot be used.

[Problems to be Solved by the Invention] Since the conventional optical multiplexing/demultiplexing module described above is configured as described above, the optical multiplexing/demultiplexing module using a single mode fiber as the optical input/output fiber 3 has the following problems. , only a single mode fiber can be used as the transmission line fiber 15, and if a multimode fiber is used as the transmission line fiber 15, a separate optical combiner with a new multimode fiber provided in the optical input/output fiber 3 is used. There was a problem in that a wave module had to be prepared.

The present invention was made to solve these problems, and an object of the present invention is to obtain an optical multiplexing/demultiplexing module that can use both single mode fiber and multimode fiber as transmission line fibers.

[Means for Solving the Problems] The optical multiplexing/demultiplexing module according to the present invention includes a core portion of an optical input/output fiber that is divided into a single mode waveguide core portion and a multimode waveguide core portion. It has a double core structure held coaxially.

[Operation] In the optical multiplexing/demultiplexing module of this invention, the core portion of the optical input/output fiber is a double core having a core portion serving as a single mode waveguide and a core portion serving as a multimode waveguide on the same axis. Because of this structure, there is no loss of light due to coupling whether a single mode fiber or multimode fiber is used as the transmission line fiber, so the optical multiplexing/demultiplexing module can be replaced with a transmission line fiber. The inconvenience can be resolved.

[Embodiment] FIG. 1 is a block diagram showing an optical multiplexing/demultiplexing module which is an embodiment of the present invention, and each reference numeral 1, 2 and 4 to 14a, 14b
In Fig. 0, which is the same as the conventional example shown in Fig. 6 above, 3 is an optical input/output fiber according to the present invention;
Unlike the conventional example shown in FIG. 6, it has a double core structure. 19 is a double core portion of optical input/output fiber 3;
0 is a single mode waveguide, 21 is a multimode waveguide,
The single mode waveguide 20 and the multimode waveguide 21 are coaxially formed. The wavelength λlσ light emitted from the light emitting element 1 is efficiently coupled to the single mode waveguide 20 of the optical input/output fiber 3. As shown, the light emitting element 1. Collimating lens 4. The common boat lens 6 is being adjusted. In addition, in the coupling system between the optical input/output fiber 3 and the light receiving element 2, the light having the wavelength λ2 propagating through the multimode waveguide 21 of the optical input/output fiber 3 is efficiently coupled. Condensing lens 5. The light receiving element 2 has been adjusted.

Figures 2 and 3 are configuration diagrams for explaining the effects of the optical multiplexing/demultiplexing module in Figure 1, and Figures 4 and 5 are optical input/output fibers constituting the optical multiplexing/demultiplexing module in Figure 1. FIG.

Next, the operation of the optical multiplexing/demultiplexing module which is an embodiment of the invention described above will be explained. The light of wavelength λ1 emitted from the light emitting element 1 is converted into a parallel beam 1 by the collimating lens 4.
1, the spacer prism 10. Filter 8
．． The light passes through the pentaprism 7 and enters the single mode waveguide 20 of the optical input/output fiber 3 through the common boat lens 6.

On the other hand, the light with the wavelength λ2 propagating through the multimode waveguide 21 of the optical input/output fiber 3 is converted into a parallel light beam 12 by the common boat lens 6, and then converted into a parallel light beam 12 by the filter 8. The light is reflected by the mirror 9 and coupled to the light receiving element 2 by the condensing lens 5. Here, since multimode light emitted from the multimode waveguide 21 of the optical input/output fiber 3 is coupled to the light receiving element 2, the lowest mode of this multimode light is propagated. Naturally, the light propagating through the single mode waveguide 20 is also coupled to the light receiving element 2.

In the optical multiplexing/demultiplexing module having such a structure, both cases in which a single mode fiber and a multimode fiber are used as the transmission line fiber 15 will be described.

First, the case where a single mode fiber is used as the transmission line fiber 15 as shown in FIG. 2 will be described. The light of wavelength λ1 emitted from the light emitting element 1 shown in FIG.
0. The light of wavelength λ1 propagated through the single mode waveguide 20 of the optical input/output fiber 3 is transmitted to the optical connector 14.
a.

It is coupled to the single mode fiber transmission line fiber 15 connected at 14b. On the other hand, the light with the wavelength λ2 propagating through the transmission line fiber 15, which is a single mode fiber, is coupled to the single mode waveguide 20 of the optical input/output fiber 3 connected by the optical connectors 14a and 14b. . The light having the wavelength λ2 coupled to the single mode waveguide 20 of the optical input/output fiber 3' is coupled to the light receiving element 2 as described above.

Next, the case where a multimode fiber is used as the transmission line fiber 15 as shown in FIG. 3 will be described. The light having the wavelength λl emitted from the light emitting element 1 shown in FIG. 3 enters the single mode waveguide 20 of the optical input/output fiber 3 as described above. The light of wavelength λ1 propagated through the single mode waveguide 20 of the optical input/output fiber 3 is transmitted to the optical connector 14a,
The light is incident on the core portion 16 of the multimode fiber transmission line fiber 15 connected at 14b. At this time, since the multimode fiber can propagate multimode light including at least the mode of the single mode waveguide 20, the light of wavelength λ1 is efficiently coupled to the transmission line fiber 15 of the multimode fiber. On the other hand, the light with the wavelength λ2 propagating through the transmission line fiber 15 of the multimode fiber is transmitted to the optical connectors 14a and 14b.
The light enters the optical input/output fiber 3 connected at . Here, since the propagation mode of the light with wavelength λ2 propagated through the transmission line fiber 15 of the multimode fiber is multimode,
Only a small amount of light is coupled to the single mode waveguide 20 of the optical input/output fiber 3. However, since the other light is coupled to the multimode waveguide 21 of the optical input/output fiber 3, all the light of wavelength ^2 that has propagated through the multimode fiber transmission line fiber 15 is input/output. fiber 3
is combined with The wavelength λ coupled to the single mode waveguide 20 and multimode waveguide 21 of this optical input/output fiber 3
The light of No. 2 is coupled to the light receiving element 2 as described above.

As described above, if a double-structured fiber having a single mode waveguide 20 and a multimode waveguide 21 coaxially is used as the optical input/output fiber 3, a single mode fiber and a multimode fiber can be used as the transmission line fiber 15. It becomes possible to use both mode fibers.

Next, the refractive index distribution in the cross section of the optical input/output fiber 3 having the single mode waveguide 20 and the multimode waveguide 21 coaxially will be explained. In FIG. 4, the horizontal axis represents the distance from the central axis of the cross section of the optical input/output fiber 3, and the vertical axis represents the refractive index. The refractive index is constant at the refractive index n1 from the center to the radius a, and at the position of the radius a, the refractive index decreases to nl, and gradually decreases in a parabolic shape until the radius reaches the radius, and becomes the refractive index n3 at the radius a. It has a refractive index distribution. Furthermore, there is at least Ja
The relational expression of nl nl−nl)<λ holds true.

At this time, the area within the radius a becomes one core, which satisfies the above relational expression, thereby forming a single mode waveguide 2o. Moreover, the inside of the radius becomes a graded index type multimode waveguide 21.

FIG. 5 shows another example of the refractive index distribution shown in FIG. The refractive index shown in Figure 5 is the refractive index n from the center to the radius a.
1. The refractive index is n3 up to the radius, and the refractive index is n3 beyond the radius.
It has a refractive index distribution that decreases stepwise. Furthermore, there is a distance of at least 4a nl between the radius a, the refractive index n1, the refractive index n2, and the wavelength λ of the light propagating in the fiber.
The relational expression nl −n3×λ holds true. At this time,
The area within the radius a becomes a single mode waveguide 20, and the area within the radius a becomes a step index type multimode waveguide 21.

[Effects of the Invention] As explained above, the present invention has a core part of an optical input/output fiber in an optical multiplexing/demultiplexing module, in which the core part that becomes a single mode waveguide and the core part that becomes a multimode waveguide are coaxially arranged. Since it has a double core structure, it has the excellent effect of providing an optical multiplexing/demultiplexing module that can use both single mode fiber and multimode fiber as a transmission line fiber. be.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical multiplexing/demultiplexing module which is an embodiment of the present invention, FIGS. 2 and 3 are configuration diagrams for explaining the effects of the optical multiplexing/demultiplexing module of FIG. 1, and FIG. 5 is an explanatory diagram showing the refractive index distribution of the cross section of the optical input/output fiber constituting the optical multiplexing/demultiplexing module of FIG. 1, FIG. 6 is a configuration diagram showing a conventional optical multiplexing/demultiplexing module, and FIG. 7 FIG. 7 is a configuration diagram showing a connecting portion when a single mode fiber and a multimode fiber are connected in the optical connector of FIG. 6; In the figure, 1... light emitting element, 2... light receiving element, 3
...Light input/output fiber, 4...Collimating lens, 5...Condensing lens, 6...Common boat lens, 7
...Penta prism, 8...Filter, 9...Mirror, 10...Spacer prism, 11.12...
Parallel light beam, 13... Case, 14a, 14b... Optical connector, 15... Transmission line fiber, 16.17.
... Core part, 18... Joint surface, 19... Double core part, 20... Single mode waveguide, 21... Multimode waveguide. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 4 Figure 5111

Claims (3)

[Claims] (1) In a light synthesis/demultiplexing module consisting of at least one light emitting element, at least one light receiving element, a light wavelength multiplexing/demultiplexing element, and an optical fiber, the cross section of the optical fiber is coaxial. It has a double core structure, and one core of the double core is a single mode waveguide, and the other core of the double core is a multimode waveguide. Optical multiplexing/demultiplexing module. (2) As the above-mentioned optical fiber, the refractive index distribution of the cross section of this optical fiber is constant at a refractive index n_1 from the center of the optical fiber outward to a distance of radius a, and
At the position, the refractive index decreases to n_2, which is lower than the refractive index n_1, and continuously decreases from the refractive index n_2 in a parabolic manner from radius a to radius b, and at radius b or more, the refractive index n_3
It has a refractive index distribution shape such that the above refractive index n_1
, n_2, the radius a, and the wavelength λ of the light used, at least the relational expression 4a√{2n_1(n_1-n_2)}<λ holds. The optical multiplexing/demultiplexing module according to item 1. (3) As the optical fiber, the refractive index distribution of the cross section of this optical fiber is constant at a refractive index n_1 from the center of the optical fiber outward to a distance of radius a, and
At the position, the refractive index n_2 is lower than the refractive index n_1, and the refractive index n_2 is constant from radius a to radius b, and at the position of radius b, the refractive index n_2 is lower than the refractive index n_2.
It has a step-like refractive index distribution shape that decreases to _3,
At least 4a√{2n_1(n_1-n
_2)}<λ The optical multiplexing/demultiplexing module according to claim 1, characterized in that an optical fiber is used that satisfies the relational expression: _2)}<λ.