JP4267402B2 - Wavelength division multiplexing system - Google Patents

Description

  The present invention relates to a wavelength division multiplexing system using a multimode fiber.

  A multimode fiber (hereinafter sometimes referred to as “MMF”) such as a graded index type fiber (hereinafter referred to as “GI fiber”) has a large core diameter and a high aperture. It is widely used as an optical LAN transmission line.

  Accompanying the demand for high-speed optical LAN, the accuracy in controlling the refractive index profile of the GI fiber has been improved, and the performance limit is almost reached. In order to further increase the transmission bandwidth of the GI fiber, it is necessary to perform wavelength division multiplexing (WDM).

  However, in the GI fiber, the optimum refractive index profile greatly depends on the wavelength of the signal light propagating in the fiber. Therefore, a GI fiber having a refractive index profile optimized at a specific wavelength has a problem that it cannot be applied to wavelength division multiplexing because the transmission bandwidth becomes very small at different wavelengths (for example, non-patent literature). 1).

FIG. 19 shows a GI fiber having a core diameter of 50 μm and an outer diameter of 125 μm (maximum relative refractive index difference Δ = 0.01, core radius a = 25 μm, each having a refractive index profile optimized at wavelengths λ ₀ = 850 nm and 1300 nm. ) OFL (Overfilled-Launch) band (see the standard IEC 60793-1-49).

 From FIG. 19, it can be seen that when the wavelength is away from the optimum wavelength (850 nm and 1300 nm, respectively), the transmission bandwidth decreases rapidly.

In addition, in the calculations related to FIG. 19 and all the following calculations, the material dispersion coefficients of pure quartz and germanium-added quartz are shown in Document A (Noriyoshi Shibata, Takao Edahiro, “Refractive index dispersion characteristics of glass for optical fibers”, Vol.OQE80-114, pp.85-90, 1980), and the material dispersion coefficient of fluorine-added quartz is described in Document B (JW Fleming, “Material dispersion in lightguide glasses”, Electron Lett. , Vol.14, pp.326-328, 1978), and the RMS spectral width of incident light is 0.35 nm. Further, the calculation of the transmission bandwidth is performed based on the group delay of each mode calculated from the refractive index profile (K. Okamoto, “Comparison of calculated and measured imperial fibers”, Appl. Opt., Vol. .18, pp. 2199-2206, 1979).
Takayoshi Ohkoshi, Katsunari Okamoto, Kazuo Hoba, “Optical Fiber”, Chapter 7, pp. 182-184, Ohmsha, 1984

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a wavelength division multiplexing system that enables wavelength division multiplexing using a multimode fiber.

In order to solve the above problems, the present invention is a wavelength division multiplexing system including a multimode fiber and one or more dispersion compensating fibers, and is connected between the multimode fiber and one dispersion compensating fiber. The dispersion compensating fiber is converted into light having a wavelength λ _m among light having wavelengths λ ₁ , λ ₂ , λ ₃ ,..., Λ _n propagated to the multimode fiber. is intended to have a optimized refractive index profile as inter-modal dispersion is minimized for said wavelength filter selects the light having the wavelength lambda _m is supplied to the dispersion compensating fiber, and, Wavelengths λ ₁ and λ ₂ propagated by the multimode fiber have the property of preserving the electromagnetic field distribution in the multimode fiber when the optical signal is separated for each wavelength. , Λ ₃ ,..., Λ _n , when extracting light having one wavelength λ _m , the light having the wavelength λ _m is separated by the wavelength filter and incident on the dispersion compensating fiber. Provided is a wavelength division multiplexing system in which the light of the wavelength λ _m is extracted after compensating the inter-mode dispersion of the light of the wavelength λ _m by a dispersion compensating fiber .

The present invention is a wavelength division multiplexing system comprising a multimode fiber and one or more dispersion compensating fibers, comprising a wavelength filter connected between the multimode fiber and one dispersion compensating fiber, The dispersion compensating fiber minimizes inter-mode dispersion with respect to light of one wavelength λ _m among light of wavelengths λ ₁ , λ ₂ , λ ₃ ,..., Λ _n propagated to the multimode fiber. The wavelength filter selects the light of the wavelength λ _m and supplies it to the dispersion compensating fiber, and separates the optical signal for each wavelength. the der those having a property to save an electromagnetic field distribution in a multi-mode fiber, the wavelength lambda ₁ propagated by a multimode _fiber, lambda _2, lambda _3, · · ·, the lambda _n light to When taking out the light of one wavelength lambda _m the out, after compensating the inter-mode dispersion of the light having the wavelength lambda _m by the dispersion compensating fiber, as taken to separate the light of the wavelength lambda _m by the wavelength filter An improved wavelength division multiplexing system is provided.

  In the wavelength division multiplexing system configured as described above, the wavelength filter includes a dielectric multilayer filter and two collimator lenses disposed so as to face each other via the dielectric multilayer filter. Is preferred.

The wavelength division multiplexing system having the above-described configuration, the multi-mode fiber is the core diameter 50 [mu] m, graded index fibers with a cladding diameter of 125 [mu] m, the wavelength 770nm, 790nm, 810nm, 830nm, 850nm, 870nm, 890nm, 910nm, all 1300nm it is also possible to transmit bandwidth in the channel is to exceed 2 GHz · miles.

The wavelength division multiplexing system having the above-described configuration, the multi-mode fiber core diameter 50 [mu] m, a graded index fiber having a cladding diameter of 125 [mu] m, the wavelength 850 nm, 870 nm, 890 nm, 910 nm, 3 GHz transmission band width in all channels of 930nm・ It can also exceed km .

In the wavelength division multiplexing system configured as described above, the multimode fiber is a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm, and has wavelengths of 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 The transmission bandwidth in all the channels of nm, 1360 nm, and 1380 nm may be greater than 5 GHz · km.

In the wavelength division multiplexing system having the above configuration , the channel spacing is preferably 20 nm .

The wavelength division multiplexing system of the present invention includes a wavelength filter connected between a multimode fiber and one dispersion compensation fiber, and the dispersion compensation fiber has wavelengths λ ₁ , λ ₂ , λ ₃ ,..., λ _n having a refractive index profile optimized for light of wavelength λ _m , and the wavelength filter selects light of wavelength λ _m and dispersion compensating fiber By supplying to the optical fiber, it is possible to realize wavelength division multiplexing of a multimode fiber, which has been impossible until now. By realizing the wavelength division multiplexing of the multimode fiber, the transmission rate of the multimode fiber can be dramatically improved.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

The wavelength division multiplexing system of the present invention is a wavelength division multiplexing system including a multimode fiber and one or more dispersion compensating fibers, and a wavelength connected between the multimode fiber and one dispersion compensating fiber. comprising a filter, the dispersion compensating fiber wavelength lambda ₁ to be propagated to the multi-mode _fiber, lambda _2, lambda _3, · · ·, are optimized for light of one wavelength lambda _m of the light lambda _n The wavelength filter selects the light of wavelength λ _m and supplies it to the dispersion compensating fiber.

  By the way, by optimizing the length ratio between a dispersion compensating fiber (hereinafter sometimes abbreviated as “DCF”) and a multimode fiber and connecting them together, intermode dispersion of the multimode fiber is achieved. Thus, a large transmission bandwidth can be realized even at a wavelength different from the wavelength at which the refractive index profile of the multimode fiber is optimized. However, in order to perform wavelength division multiplexing using this method, it is necessary to preserve (do not change) the electromagnetic field distribution in the multimode fiber when the optical signal is separated for each wavelength.

Therefore, in the present invention, optimal and multi-mode fiber, the wavelength lambda ₁ to be propagated to the multi-mode _fiber, lambda _2, lambda _3, · · ·, for one light of the wavelength lambda _m of the light lambda _n By connecting a dispersion compensating fiber having a refractive index profile through a wavelength filter that selects light of wavelength λ _m , the electromagnetic field distribution in the multimode fiber is preserved, and the multimode fiber is used. Enabled wavelength division multiplexing.

  Examples of the wavelength filter used in the present invention include those having a property of not changing the electromagnetic field distribution in the multimode fiber when the optical signal is separated for each wavelength. Examples of such a wavelength filter include a dielectric multilayer filter, a fiber grating filter, etc. Among these, in particular, the dielectric multilayer filter is disposed so as to face the dielectric multilayer filter. It is preferable to have two collimator lenses.

FIG. 1 is a schematic cross-sectional view showing an example of a wavelength filter used in the present invention.
The wavelength filter includes a dielectric multilayer filter 1, a first collimator lens 2 and a second collimator lens 3 disposed so as to face each other with the dielectric multilayer filter 1 interposed therebetween, and a cylindrical member that accommodates them. 4, an optical fiber 11 for the incident port P ₁ , an optical fiber 12 for the reflection port P ₂ , and an optical fiber 13 for the output port P ₃ .

  In this wavelength filter, the dielectric multilayer filter 1 is disposed almost at the center inside the cylindrical member 4 and fixed with an adhesive or the like. Further, the first collimator lens 2 and the second collimator lens 3 are inserted into the cylindrical member 4 from both opening ends of the cylindrical member 4, and these are opposed to each other through the dielectric multilayer filter 1. Are arranged to be. Further, the first collimator lens 2 and the second collimator lens 3 are fixed to the cylindrical member 4 with an adhesive 5.

  The optical fiber 11 and the optical fiber 12 are fixed to the first collimator lens 2 with an adhesive. On the other hand, the optical fiber 13 is fixed to the second collimator lens 3 with an adhesive.

Examples of the dielectric multilayer filter 1 include thin films such as SiO ₂ and Ta ₂ O ₅ having different refractive indexes, each having a thickness of about several tens to several hundreds of nanometers, and several layers to several hundreds of layers stacked. Can be mentioned. Such a dielectric multilayer filter 1 has a property of reflecting light of a specific wavelength and transmitting light of other wavelengths.

  Examples of the first collimator lens 2 and the second collimator lens 3 include cylindrical lenses made of a fiber type lens having a graded index type refractive index distribution.

  Examples of the cylindrical member 4 include a cylindrical member made of a material having low moisture permeability, such as metal, resin, and glass.

  Examples of the adhesive 5 include an epoxy adhesive and a silicon adhesive.

  Single mode fibers are used as the optical fibers 11, 12, and 13.

In this wavelength filter, light incident from the incident port P ₁ (light having wavelengths λ ₁ , λ ₂ ,..., Λ _n ) is converted into parallel light by the first collimator lens 2, and the dielectric multilayer The light enters the membrane filter 1. In this dielectric multilayer filter 1, light having a specific wavelength (for example, wavelength λ ₁ ) is reflected and enters the reflection port P ₂ . In addition, light of other wavelengths (for example, wavelengths λ ₂ ,..., Λ _n ) passes through the dielectric multilayer filter 1 and is condensed again by the second collimator lens ₃ and enters the output port P ₃ . To do.

According to the wavelength filter having such a configuration, light reflected by the dielectric multilayer filter 1 (light having a wavelength λ ₁ ) can also be transmitted through the dielectric multilayer filter 1 (wavelengths λ ₂ ,. _n light) does not significantly change the electromagnetic field distribution in the multimode fiber connected to the wavelength filter.

By the way, the relative refractive index difference profile Δ _DCF of the dispersion compensating fiber is expressed by the following equation (1).
[Delta] _DCF = [Delta] _optimum + b [[Delta] _optimum- [Delta] _target ] (1)
Here, _Δoptimum represents a relative refractive index difference profile of a fiber having the widest band with respect to a desired wavelength, _Δtarget represents a relative refractive index difference profile of a fiber that is a _target of dispersion compensation, and b represents a target fiber (for example, multi-fiber It is a constant representing the ratio of the length of the mode fiber) and the dispersion compensating fiber.

The dispersion compensation fiber designed in this way can play a role of dispersion compensation at wavelengths other than the design wavelength by changing the length. For example, assuming that the target fiber is optimized at the wavelength λ _target and the dispersion compensating fiber is designed to fully compensate with a length L _design for a certain design wavelength λ _design , λ _target and λ _design It is possible to completely compensate for an appropriate wavelength L _medium <L _design for a wavelength λ _{medium in} between.

  Using this mechanism, when the wavelength order of the light to be demultiplexed is set to monotonically increase or monotonously decrease, the tendency of dispersion compensation required for each dispersion compensation fiber becomes the same. In the simplest case, all dispersion compensating fibers can have the same relative index difference profile.

  For this reason, in the present invention, a dispersion-compensating fiber that is optimized for the wavelength of each channel in wavelength division multiplexing is used.

By the way, wavelength multiplexing in a wavelength division multiplexing system using a multimode fiber is realized by applying a wavelength multiplexing system similar to that in the case of a single mode fiber.
However, in a wavelength division multiplexing system using a multimode fiber, inter-mode dispersion of light propagating through the multimode fiber cannot be compensated at once over the entire use wavelength region. Therefore, wavelength demultiplexing by this wavelength division multiplexing system is realized by using a combination of the above-described wavelength filter and dispersion compensating fiber.

FIG. 2 is a schematic diagram showing a first embodiment of the wavelength division multiplexing system of the present invention.
The wavelength division multiplexing system of this embodiment includes one multimode fiber 21, four wavelength filters 31, 32, 33, 34, five optical fibers 41, 42, 43, 44, 45, and three dispersion compensations. The optical fiber 51, 52, and 53 are schematically configured.

In this wavelength division multiplexing system, the output end of the multimode fiber 21 and the incident port of the wavelength filter 31 including the optical fiber 41 for the reflection port and the optical fiber 42 for the output port are connected. Further, the optical fiber 42, input port of the wavelength filter 32 provided with a dispersion compensation fiber 51 for reflection port and the optical fiber 43 for output port is connected. Further, the optical fiber 43, input port of the wavelength filter 33 provided with a dispersion compensation fiber 52 for reflection port and the optical fiber 44 for output port is connected. Further, the optical fiber 44, input port of the wavelength filter 34 provided with a dispersion compensation fiber 53 for reflection port and the optical fiber 45 for output port is connected.

  By adopting such a configuration, this wavelength division multiplexing system has a structure in which the multimode fiber 21 and the dispersion compensating fibers 51, 52, 53 are connected in parallel.

Next, wavelength demultiplexing using this wavelength division multiplexing system will be described.
In this wavelength division multiplexing system, first, a wavelength filter that selects light of wavelength λ ₁ from light (light of wavelengths λ ₁ , λ ₂ ,..., Λ _n ) incident on the wavelength filter 31 from the multimode fiber 21. 31 separates the light of the optimized wavelength (wavelength with optimized refractive index profile) λ ₁ of the multimode fiber 21. This light already has minimum inter-mode dispersion, so there is no need for further dispersion compensation.

Subsequently, a wavelength filter that selects light of wavelength λ ₂ from light (light of wavelengths λ ₂ , λ ₃ ,..., Λ _n ) transmitted through the wavelength filter 31 and incident on the wavelength filter 32 from the optical fiber 42. 32 separates the light of wavelength λ ₂ and enters the dispersion compensating fiber 51. Here, as the dispersion compensating fiber 51, an optical fiber optimized so as to minimize the inter-mode dispersion of the light having the wavelength λ ₂ is used. Therefore, the light of wavelength λ ₂ has a large transmission bandwidth.

Subsequently, a wavelength filter that selects light having wavelength λ ₃ from light (light having wavelengths λ ₃ , λ ₄ ,..., Λ _n ) transmitted through wavelength filter 32 and incident on wavelength filter 33 from optical fiber 43. The light having the wavelength λ ₃ is separated by 33 and is incident on the dispersion compensating fiber 52. Here, the dispersion compensating fiber 52, is used that between the optical mode of the dispersion of the wavelength lambda ₃ is optimized so as to minimize. Accordingly, light of the wavelength lambda ₃ is made to have a large transmission bandwidth.

Subsequently, a wavelength filter that selects light of wavelength λ ₄ from light (light of wavelengths λ ₄ , λ ₅ ,..., Λ _n ) transmitted through the wavelength filter 33 and incident on the wavelength filter 34 from the optical fiber 44. 34 separates the light of wavelength λ ₄ and enters the dispersion compensating fiber 53. Here, the dispersion compensating fiber 53, is used that between the optical mode of the dispersion of the wavelength lambda ₄ is optimized so as to minimize. Accordingly, light of the wavelength lambda ₄ comes to have a large transmission bandwidth.

The light transmitted through the wavelength filter 34 (light having wavelengths λ ₅ ,..., Λ _n ) is emitted from the optical fiber 45.

  In this embodiment, the wavelength division multiplexing system using four wavelength filters and three dispersion compensating fibers is shown. However, the wavelength division multiplexing system of the present invention is not limited to this, and the dispersion compensating fiber is not limited to this. It is sufficient that at least one is used.

FIG. 3 is a schematic diagram showing a second embodiment of the wavelength division multiplexing system of the present invention.
The wavelength division multiplexing system of this embodiment includes one multimode fiber 61, four wavelength filters 71, 72, 73, 74, three dispersion compensating fibers 81, 82, 83, and five optical fibers 91, 92. , 93, 94, 95.

  In this wavelength division multiplexing system, the emission end of the multimode fiber 61 and the incident port of the wavelength filter 71 including the optical fiber 91 for the reflection port are connected. Further, the emission port of the wavelength filter 71 and the incident end of the dispersion compensating fiber 81 are connected. Furthermore, the output end of the dispersion compensating fiber 81 and the incident port of the wavelength filter 72 including the optical fiber 92 for the reflection port are connected.

  Hereinafter, similarly, the output port of the wavelength filter 72 and the incident end of the dispersion compensating fiber 82 are connected, and the incident end of the wavelength filter 73 including the output end of the dispersion compensating fiber 82 and the optical fiber 93 for the reflection port is used. The port is connected. The output port of the wavelength filter 73 and the incident end of the dispersion compensation fiber 83 are connected, and the output end of the dispersion compensation fiber 83, the optical fiber 94 for the reflection port, and the optical fiber 95 for the output port are provided. The incident port of the wavelength filter 74 is connected.

  By adopting such a configuration, this wavelength division multiplexing system has a structure in which the multimode fiber 61 and the dispersion compensating fibers 81, 82, 83 are connected in series.

Next, wavelength demultiplexing using this wavelength division multiplexing system will be described.
In this wavelength division multiplexing system, first, a wavelength filter that selects light of wavelength λ ₁ from light (light of wavelengths λ ₁ , λ ₂ ,..., Λ _n ) incident on the wavelength filter 71 from the multimode fiber 61. 71 separates light of the optimized wavelength (wavelength with optimized refractive index profile) λ ₁ of the multimode fiber 61. This light already has minimum inter-mode dispersion, so there is no need for further dispersion compensation.

Subsequently, light that has passed through the wavelength filter 71 (light with wavelengths λ ₂ , λ ₃ ,..., Λ _n ) is incident on the dispersion compensating fiber 81, and the light that has propagated through the dispersion compensating fiber 81 enters the wavelength filter 72. incident, separates the light of the wavelength lambda ₂ by the wavelength filter 72 for selecting light having a wavelength lambda _2. Here, as the dispersion compensating fiber 81, an optical fiber optimized so as to minimize the inter-mode dispersion of the light having the wavelength λ ₂ is used. Therefore, the light of wavelength λ ₂ has a large transmission bandwidth.

Subsequently, light that has passed through the wavelength filter 72 (light with wavelengths λ ₃ , λ ₄ ,..., Λ _n ) is incident on the dispersion compensating fiber 82, and the light that has propagated through the dispersion compensating fiber 82 enters the wavelength filter 73. incident, separates the light of the wavelength lambda ₃ by the wavelength filter 73 for selecting light having a wavelength lambda _3. Here, the dispersion compensating fiber 82, is used that between the optical mode of the dispersion of the wavelength lambda ₃ is optimized so as to minimize. Accordingly, light of the wavelength lambda ₃ is made to have a large transmission bandwidth.

Subsequently, light that has passed through the wavelength filter 73 (light with wavelengths λ ₄ , λ ₅ ,..., Λ _n ) is incident on the dispersion compensating fiber 83, and the light that has propagated through the dispersion compensating fiber 83 enters the wavelength filter 74. incident, separates the light of the wavelength lambda ₄ by the wavelength filter 74 for selecting light of a wavelength lambda _4. Here, the dispersion compensating fiber 83, is used that between the optical mode of the dispersion of the wavelength lambda ₄ is optimized so as to minimize. Accordingly, light of the wavelength lambda ₄ comes to have a large transmission bandwidth.

Then, light that has passed through the wavelength filter 74 (light having wavelengths λ ₅ ,..., Λ _n ) is emitted from the optical fiber 95.

  In this embodiment, the wavelength division multiplexing system using four wavelength filters and three dispersion compensating fibers is shown. However, the wavelength division multiplexing system of the present invention is not limited to this, and the dispersion compensating fiber is not limited to this. It is sufficient that at least one is used.

  In addition, the wavelength division multiplexing system of the present invention may be configured by combining a parallel connection of a multimode fiber and a dispersion compensating fiber and a serial connection.

In the wavelength division multiplexing system of the present invention, when a graded index type fiber having a core diameter of 50 μm and a cladding diameter of 125 μm is used as a multimode fiber, the wavelengths are 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, and 910 nm. The transmission bandwidth in all the channels of 1300 nm exceeds 2 GHz · km. The transmission bandwidth is represented by the product of the transmission rate that can be transmitted and the distance of the optical fiber, and indicates the transmission capacity of the optical fiber.
Therefore, the wavelength division multiplexing system of the present invention has a high transmission rate and enables wavelength division multiplexing in all channels of wavelengths 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, and 1300 nm.

Furthermore, in the wavelength division multiplexing system of the present invention, when a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm is used as a multimode fiber, transmission in all channels of wavelengths 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm. The bandwidth exceeds 3 GHz · km.
Therefore, the wavelength division multiplexing system of the present invention has a high transmission rate and enables wavelength division multiplexing in all channels of wavelengths 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm.

In the wavelength division multiplexing system of the present invention, when a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm is used as the multimode fiber, the wavelengths are 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, and 1360 nm. , The transmission bandwidth in all channels of 1380 nm exceeds 3 GHz · km.
Therefore, the wavelength division multiplexing system of the present invention has a high transmission rate and enables wavelength division multiplexing in all channels having wavelengths of 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, 1360 nm, and 1380 nm.

  In the wavelength division multiplexing system of the present invention, the interval between the channels is preferably 20 nm. Thus, even if the laser emission wavelength is not accurately controlled by the cooler, interference between channels due to the influence of temperature or the like can be minimized, and a system can be constructed at low cost.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

Example 1
In this embodiment, CWDM (Coarse WDM) is illustrated as an example of a wavelength division multiplexing system in which a multimode fiber and a dispersion compensating fiber are connected in parallel via a wavelength filter.
A 10-channel CWDM having wavelengths λ = 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, 930 nm, and 1300 nm was used.

As the multimode fiber, a fiber that is optimized at a wavelength of 850 nm and has a refractive index profile with a relative refractive index difference Δ = 0.01 and a core radius a = 25 μm to the power of α is used.
As the dispersion compensating fibers, those having refractive index profiles optimized for wavelengths λ = 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, 930 nm and 1300 nm were used.

  The dispersion compensation fiber corresponding to the wavelengths λ = 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm has a length ratio b = 50. Further, the dispersion compensating fiber corresponding to the wavelength λ = 1300 nm has a length ratio b = 10.

Here, FIG. 4 is a graph showing the refractive index profile of the target fiber (target, multimode fiber) and the dispersion compensating fiber for each wavelength.
FIG. 5 shows a 1 km long multimode fiber and a dispersion corresponding to wavelengths λ = 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm, having the refractive index profile as shown in FIG. It is a graph which shows the relationship between the length of a dispersion compensation fiber, and a transmission bandwidth, when a compensation fiber is connected.
FIG. 6 shows the length and transmission of a dispersion compensating fiber when a multi-mode fiber having a length of 1 km is connected to a dispersion compensating fiber having a refractive index profile as shown in FIG. 4 and corresponding to a wavelength λ = 1300 nm. It is a graph which shows the relationship with a bandwidth.

  From the results of FIGS. 4 to 6, the wavelength demultiplexing performance for the multimode fiber as shown in Table 1 was obtained.

(Example 2)
In this embodiment, an example of a wavelength division multiplexing system in which a multimode fiber and a dispersion compensating fiber are connected in series via a wavelength filter is shown.
A 5-channel wavelength division multiplexing system having wavelengths λ = 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm was used.

As the multimode fiber, a fiber that is optimized at a wavelength of 850 nm and has a refractive index profile with a relative refractive index difference Δ = 0.01 and a core radius a = 25 μm to the power of α is used.
Each of the dispersion compensating fibers had the same refractive index profile with a wavelength λ = 930 nm as a design wavelength and a length ratio b = 50.

Here, FIG. 7 is a graph showing the refractive index profiles of the target fiber (target, multimode fiber), the optimized fiber (optimum) at the wavelength of 890 nm, and the dispersion compensating fiber.
FIG. 8 is a graph showing the relationship between the length of the dispersion compensating fiber and the transmission bandwidth when the multimode fiber having a length of 1 km is connected to the dispersion compensating fiber having the refractive index profile as shown in FIG. It is.

  From the results of FIGS. 7 and 8, the wavelength demultiplexing performance for the multimode fiber as shown in Table 2 was obtained.

FIG. 9 is a schematic diagram showing a schematic configuration of a wavelength division multiplexing system in which a multimode fiber and a dispersion compensating fiber are connected in series via a wavelength filter in this embodiment.
In this wavelength division multiplexing system, the multimode fiber 101, the wavelength filter 111, the dispersion compensation fiber 121, the wavelength filter 112, the dispersion compensation fiber 122, the wavelength filter 113, the dispersion compensation fiber 123, the wavelength filter 114, and the dispersion compensation fiber 124 are arranged in this order. It is connected.

When the length of the multimode fiber 101 is L, the total length of the dispersion compensating fibers 121, 122, 123, and 124 is 0.0164L, and the wavelength filters 111, 112, 113, and 114 are placed at appropriate positions in the middle. is set up.
In addition, a serial connection wavelength division multiplexing system as shown in FIG. 9 may be connected in parallel in a channel corresponding to the wavelength λ = 1300 nm, and may be configured by parallel connection and series connection.

(Example 3)
In this embodiment, another example of a wavelength division multiplexing system in which a multimode fiber and a dispersion compensating fiber are connected in series via a wavelength filter is shown.
A 5-channel wavelength division multiplexing system having wavelengths λ = 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm was used.

As the multimode fiber, a fiber that is optimized at a wavelength of 850 nm and has a refractive index profile with a relative refractive index difference Δ = 0.01 and a core radius a = 25 μm to the power of α is used.
Each of the dispersion compensating fibers had the same refractive index profile with the wavelength λ = 930 nm as the design wavelength and the length ratio b = 10.

Here, FIG. 10 is a graph showing refractive index profiles of the target fiber (target, multimode fiber), the optimized fiber (optimum) at the wavelength of 890 nm, and the dispersion compensating fiber.
FIG. 11 is a graph showing the relationship between the length of the dispersion compensating fiber and the transmission bandwidth when the multimode fiber having a length of 1 km is connected to the dispersion compensating fiber having the refractive index profile as shown in FIG. It is.

  From the results of FIGS. 10 and 11, the wavelength demultiplexing performance for the multimode fiber as shown in Table 3 was obtained. The difference between the third embodiment and the second embodiment is only the value of the length ratio b. When Example 3 and Example 2 were compared, it was confirmed that the dispersion compensation fiber was longer, but a larger transmission bandwidth was obtained.

(Example 4)
In this embodiment, an example of a wavelength division multiplexing system using both parallel connection and series connection in connection between a multimode fiber and a dispersion compensating fiber via a wavelength filter is shown.
A 10-channel wavelength division multiplexing system having wavelengths λ = 850 nm, 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, 1360 nm, and 1380 nm was used.

As the multimode fiber, a fiber having a refractive index profile optimized at a wavelength of 1300 nm and having a relative refractive index difference Δ = 0.01 and a core radius a = 25 μm to the power of α is used.
The dispersion compensating fiber (DCF1) for wavelengths λ = 1320 nm, 1340 nm, 1360 nm, and 1380 nm had the same refractive index profile with the wavelength λ = 1380 nm as the design wavelength and the length ratio b = 50.
The dispersion compensating fiber (DCF2) for the wavelengths λ = 1220 nm, 1240 nm, 1260 nm, and 1280 nm has the same refractive index profile with the wavelength λ = 1220 nm as the design wavelength and the length ratio b = 50.
The dispersion compensating fiber (DCF3) for the wavelength λ = 850 nm has a refractive index profile with the wavelength λ = 850 nm as the design wavelength and the length ratio b = 10.

Here, FIG. 12 is a graph showing the refractive index profile of the target fiber (target, multimode fiber) and each dispersion compensating fiber.
FIG. 13 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multimode fiber having a length of 1 km is connected to a dispersion compensating fiber designed for a wavelength λ = 1220 nm.
FIG. 14 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multimode fiber having a length of 1 km is connected to a dispersion compensating fiber designed for a wavelength λ = 1380 nm.
FIG. 15 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multimode fiber having a length of 1 km is connected to a dispersion compensating fiber designed for a wavelength λ = 850 nm.

  From the results of FIGS. 12 to 15, the wavelength demultiplexing performance for the multimode fiber as shown in Table 4 was obtained.

FIG. 16 is a schematic diagram showing a schematic configuration of a wavelength division multiplexing system using both parallel connection and series connection in connection between a multimode fiber and a dispersion compensating fiber via a wavelength filter.
In this wavelength division multiplexing system, the multimode fiber 101, wavelength filter 141, wavelength filter 142, dispersion compensation fiber 151, wavelength filter 143, dispersion compensation fiber 152, wavelength filter 144, dispersion compensation fiber 153, wavelength filter 145, dispersion compensation fiber are used. 154 are connected in this order. In addition, the wavelength filter 146 is connected to the wavelength filter 141, and the wavelength filter 146, the dispersion compensation fiber 155, the wavelength filter 147, the dispersion compensation fiber 156, the wavelength filter 148, the dispersion compensation fiber 157, the wavelength filter 149, and the dispersion compensation fiber 158 are this. Connected in order. Further, a dispersion compensating fiber 159 is connected to the wavelength filter 146.

  When the length of the multimode fiber 131 is L, the total length of the dispersion compensating fibers 151, 152, 153, 154, 155, 156, 157, 158, 159 is 0.1708L, and the wavelength filters 141, 142, 143, 144, 145, 146, 147, 148, 149 are installed at appropriate locations along the way.

(Example 5)
In this embodiment, another example of a wavelength division multiplexing system in which a multimode fiber and a dispersion compensating fiber are connected in parallel via a wavelength filter is shown.
A 9-channel wavelength division multiplexing system having wavelengths λ = 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, 1360 nm, and 1380 nm was used.

As the multimode fiber, an optical fiber optimized at a wavelength of 850 nm and having a refractive index profile of the power of α with a maximum relative refractive index difference Δ = 0.02, a core radius a = 31.25 μm, and a cladding diameter of 125 μm was used.
In the dispersion compensation fiber for channels except for the wavelength λ = 1330 nm, each channel wavelength is set as a design wavelength, and the length ratio b = 50.

Here, FIG. 17 is a graph showing the refractive index profile of the target fiber (target, multimode fiber) and each dispersion compensating fiber.
FIG. 18 is a graph showing the relationship between the length of the dispersion compensating fiber and the transmission bandwidth when the multimode fiber having a length of 1 km is connected to each dispersion compensating fiber.

  From the results of FIGS. 17 and 18, the wavelength demultiplexing performance for the multimode fiber as shown in Table 5 was obtained.

  The wavelength division multiplexing system of the present invention can also be applied to a dense wavelength division multiplexing (DWDM) system.

It is a schematic sectional drawing which shows an example of the wavelength filter used by this invention. 1 is a schematic diagram showing a first embodiment of a wavelength division multiplexing system of the present invention. It is a schematic diagram which shows 2nd embodiment of the wavelength division multiplexing system of this invention. It is a graph which shows the refractive index profile of the dispersion compensation fiber for a target fiber and each wavelength. 5 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multi-mode fiber having a length of 1 km is connected to each dispersion compensating fiber having a refractive index profile as shown in FIG. 5 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multi-mode fiber having a length of 1 km is connected to each dispersion compensating fiber having a refractive index profile as shown in FIG. It is a graph which shows the refractive index profile of the target fiber, the optimization fiber at the time of wavelength 890nm, and a dispersion compensation fiber. FIG. 8 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a 1 km long multimode fiber is connected to a dispersion compensating fiber having a refractive index profile as shown in FIG. 7. It is a schematic diagram which shows schematic structure of the wavelength division multiplexing system with which the multimode fiber and the dispersion compensation fiber were connected in series via the wavelength filter. It is a graph which shows the refractive index profile of the target fiber, the optimization fiber at the time of wavelength 890nm, and a dispersion compensation fiber. 11 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multimode fiber having a length of 1 km and a dispersion compensating fiber having a refractive index profile as shown in FIG. 10 are connected. It is a graph which shows the refractive index profile of a target fiber and each dispersion compensation fiber. It is a graph which shows the relationship between the length of a dispersion compensation fiber, and a transmission bandwidth when connecting a multimode fiber having a length of 1 km and a dispersion compensation fiber designed for a wavelength λ = 1220 nm. It is a graph which shows the relationship between the length of a dispersion compensation fiber, and a transmission bandwidth when connecting a multimode fiber with a length of 1 km and a dispersion compensation fiber designed for a wavelength λ = 1380 nm. 7 is a graph showing the relationship between the length of a dispersion compensating fiber and the transmission bandwidth when a multimode fiber having a length of 1 km is connected to a dispersion compensating fiber designed for a wavelength λ = 850 nm. FIG. 2 is a schematic diagram showing a schematic configuration of a wavelength division multiplexing system that uses both parallel connection and series connection in connection between a multimode fiber and a dispersion compensating fiber via a wavelength filter. It is a graph which shows the refractive index profile of a target fiber and each dispersion compensation fiber. It is a graph which shows the relationship between the length of a dispersion compensation fiber, and a transmission bandwidth when a multimode fiber having a length of 1 km is connected to each dispersion compensation fiber. It is a graph which shows the wavelength characteristic of the transmission bandwidth of GI fiber which has the refractive index profile optimized by wavelength (lambda) ₀ = 850nm and 1300nm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Dielectric multilayer filter, 2 ... 1st collimator lens, 3 ... 2nd collimator lens, 4 ... Cylindrical member, 5 ... Adhesive, 11, 12, 13, .. Optical fiber, 21, 61... Multimode fiber, 31, 32, 33, 34, 71, 72, 73, 74... Wavelength filter, 41, 42, 43, 44, 45, 91, 92, 93, 94, 95... Optical fiber, 51, 52, 53, 81, 82, 83.

Claims (7)

A wavelength division multiplexing system comprising a multimode fiber and one or more dispersion compensating fibers,
A wavelength filter connected between the multimode fiber and one dispersion compensating fiber;
The dispersion compensating fiber minimizes inter-mode dispersion with respect to light of one wavelength λ _m among light of wavelengths λ ₁ , λ ₂ , λ ₃ ,..., Λ _n propagated to the multimode fiber. Having a refractive index profile optimized to be
The wavelength filter has a property of selecting the light of the wavelength λ _m and supplying it to the dispersion compensating fiber and preserving the electromagnetic field distribution in the multimode fiber when separating the optical signal for each wavelength. And
The multimode wavelength lambda ₁ propagated through the _{fiber, λ 2, λ 3, ···} , when taking out the light of one wavelength lambda _m of the light lambda _n, light having the wavelength lambda _m by the wavelength filter The light is incident on the dispersion-compensating fiber, compensated for inter-mode dispersion of the light having the wavelength λ _m by the dispersion-compensating fiber, and then the light having the wavelength λ _m is extracted. Division multiplexing system. A wavelength division multiplexing system comprising a multimode fiber and one or more dispersion compensating fibers,
A wavelength filter connected between the multimode fiber and one dispersion compensating fiber;
The dispersion compensating fiber minimizes inter-mode dispersion with respect to light of one wavelength λ _m among light of wavelengths λ ₁ , λ ₂ , λ ₃ ,..., Λ _n propagated to the multimode fiber. Having a refractive index profile optimized to be
The wavelength filter has a property of selecting the light of the wavelength λ _m and supplying it to the dispersion compensating fiber and preserving the electromagnetic field distribution in the multimode fiber when separating the optical signal for each wavelength. And
When taking out light of one wavelength λ _m out of light of wavelengths λ ₁ , λ ₂ , λ ₃ ,..., Λ _n propagated by the multimode fiber, the dispersion compensating fiber uses the wavelength λ _m A wavelength division multiplexing system, wherein after compensating for inter-mode dispersion of light, the wavelength filter separates and extracts the light of wavelength λ _m .   3. The wavelength filter includes a dielectric multilayer filter and two collimator lenses disposed so as to face each other with the dielectric multilayer filter interposed therebetween. The wavelength division multiplexing system described in 1.   The multi-mode fiber is a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm, and has a transmission bandwidth of 2 GHz in all channels of wavelengths 770 nm, 790 nm, 810 nm, 830 nm, 850 nm, 870 nm, 890 nm, 910 nm, and 1300 nm. The wavelength division multiplexing system according to any one of claims 1 to 3, wherein the wavelength division multiplexing system exceeds km.   The multimode fiber is a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm, and has a transmission bandwidth exceeding 3 GHz · km in all channels of wavelengths 850 nm, 870 nm, 890 nm, 910 nm, and 930 nm. The wavelength division multiplexing system according to any one of claims 1 to 3.   The multimode fiber is a graded index fiber having a core diameter of 50 μm and a cladding diameter of 125 μm, and has a transmission bandwidth of 5 GHz in all channels having wavelengths of 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, 1360 nm, and 1380 nm. The wavelength division multiplexing system according to any one of claims 1 to 3, wherein the wavelength division multiplexing system exceeds km. 7. The wavelength division multiplexing system according to claim 4 , wherein the channel interval is 20 nm.

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