JP2013081054A - Mode multiplexed transmission system and mode multiplex transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize long distance large capacity transmission in a mode multiplexed transmission system.SOLUTION: A mode multiplexed transmission system according to the present invention includes a mode multiplexer and a mode demultiplexer. The mode multiplexer generates propagation light of the first high order or higher mode of signal light owing to nonlinear effects between signal light and pump light and converts it into mode multiplexed signal light having plural modes of propagation light multiplexed into a single wavelength. The mode demultiplexer generates basic mode light of signal light included in the mode multiplexed signal light owing to linear effects between the pump light and the mode multiplexed signal light and converts it into a plurality of signal light differing in wavelength.

Description

  The present invention relates to a mode multiplex transmission system and a mode multiplex transmission method that use a multimode optical fiber to increase transmission capacity.

  Currently, traffic in optical fiber networks is increasing, and transmission capacity can be increased by using various methods such as increasing the transmission speed, increasing the number of wavelength division multiplexing using wavelength division multiplexing (WDM) technology, and multi-level modulation. I have been trying to expand. However, it is expected that it will be difficult to expand the transmission capacity using existing transmission lines and conventional transmission methods in the future, so the expansion of the wavelength range, new transmission fibers, and new transmission methods have been studied. Yes.

  As a method for expanding the wavelength region, studies have been made to increase the transmission capacity by realizing WDM in a wide wavelength region using a wavelength band that is not currently used. However, since the transmission loss varies depending on the wavelength band, it is considered that the usable wavelength band is limited, and furthermore, it is difficult to realize an optical amplifier that can amplify over a wide wavelength range, so that WDM in a wide wavelength range is practically used. There are many challenges to reach.

  Therefore, in addition to wavelength multiplexing, a mode multiplexing transmission method using a multimode optical fiber as a transmission line and using a plurality of propagation modes has been proposed (see, for example, Patent Document 1 and Non-Patent Document 1).

JP-A-8-288911

C. P. Tsekrekos and A.M. M.M. J. et al. Koonen, “Mode-selective spatial filtering for increased robustness in a mode group diversity multiplexing link”, Opt. Lett. 32, 1041-1043 (2007) K. Inoue, “Four-Wave Mixing in an Optical Fiber in the Zero-Dispersion Wavelength Region”, IEEE Journal of Lighttw. Technol. , VOL. 10, NO. 11, NOVEMBER 1992. pp. 1553-1561 S. Savin, et al. “Tunable mechanically induced long-period fiber gratings”, OPTICCS LETTERS / Vol. 25, no. 10 / May 15,2000

  However, Patent Document 1 does not propose a method for exciting a desired higher-order mode.

  Also, as disclosed in Non-Patent Document 1, in a multiplexer that performs mode multiplexing, a method of coupling to different modes by changing the excitation position of a multimode optical fiber has been proposed. There is a method of receiving different modes of signal light with different receivers by changing the position of the light receiving portion of the receiver. However, this method has not proposed an accurate mode multiplexing / demultiplexing method and multiple mode multiplexing / demultiplexing methods, and the accuracy of multiplexing / demultiplexing deteriorates as the number of multiplexed modes increases. There is a problem that it is difficult to realize long-distance and large-capacity transmission because crosstalk exists between multiple signals.

  In view of this, the present invention aims at realizing long-distance and large-capacity transmission in a mode multiplex transmission system as a technique for solving this problem.

  In order to achieve the above object, the present invention solves the problem by using a mode multiplexing / demultiplexing device including a multimode optical fiber and an optical coupler.

  The mode multiplexing transmission system according to the present invention combines signal light having a different wavelength from a plurality of transmitters and pump light having a different wavelength from the plurality of transmitters, and uses a nonlinear effect between the pump light and the signal light. A mode multiplexing device that generates propagation light of the signal light of the first higher-order mode or higher and outputs a mode multiplexed signal light in which a plurality of modes of propagation light are multiplexed to one wavelength to a multimode optical fiber; The mode multiplexed signal light is input from the mode optical fiber, the pump light having the same wavelength as the pump light is combined with the mode multiplexed signal light, and the mode multiplexing is performed by the nonlinear effect of the pump light and the mode multiplexed signal light. And a mode demultiplexer that generates the fundamental mode light of the signal light included in the signal light and outputs the generated fundamental mode light of the signal light to a different receiver for each wavelength.

  Since the mode multiplexer multiplexes the signal light and the pump light, the signal light can be excited by a plurality of modes of propagation light. Since the mode demultiplexer multiplexes the mode multiplexed signal light and the pump light, the mode higher than the first higher order mode can be returned to the basic mode. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode multiplexing / demultiplexing can be suppressed in the mode demultiplexing device. Therefore, the mode multiplexing transmission system according to the present invention can realize long-distance and large-capacity transmission in the mode multiplexing transmission system.

  The mode multiplex transmission method according to the present invention combines signal light having a different wavelength from a plurality of transmitters and pump light having a different wavelength from the plurality of transmitters, and a nonlinear effect between the signal light and the pump light. A mode multiplexing procedure for generating propagation light of the first higher-order mode or higher of the signal light, and outputting mode multiplexed signal light, in which the propagation light of a plurality of modes is multiplexed to one wavelength, to a multimode optical fiber; The mode multiplexed signal light is input from a mode optical fiber, the mode multiplexed signal light and the pump light having the same wavelength as that of the pump light are combined, and the mode is caused by a nonlinear effect of the pump light and the mode multiplexed signal light. A mode demultiplexing procedure for generating basic mode light of the signal light included in the multiplexed signal light and receiving the generated basic mode light of the signal light by a plurality of receivers in order.

  Since the signal light and the pump light are multiplexed in the mode multiplexing procedure, it is possible to excite the signal light into a plurality of modes of propagation light. Since the mode multiplexed signal light and the pump light are multiplexed in the mode demultiplexing procedure, the mode higher than the first higher order mode can be returned to the basic mode. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode multiplexing / demultiplexing can be suppressed in the mode demultiplexing procedure. Therefore, the mode multiplexing transmission method according to the present invention can realize long-distance and large-capacity transmission in a mode multiplexing transmission system.

  The mode multiplexing device according to the present invention includes an optical coupler that multiplexes a plurality of signal lights having different wavelengths and pump light having different wavelengths and the nonlinear effect of the signal light and the pump light. A multimode optical fiber that generates propagating light that is higher than the first higher-order mode of light and converts the propagating light in a plurality of modes into mode multiplexed signal light that is multiplexed into one wavelength.

Here, the frequency of the pump light is ω ₁ , the frequency of the signal light is ω ₂ , and the frequency of light generated in the multimode optical fiber by four-wave mixing of light of frequency ω ₁ and light of frequency ω ₂ Is the ω ₃ , the effective refractive indexes n ₁ , n ₂ , and n ₃ of the propagation modes of the multimode optical fiber at the frequencies ω ₁ , ω ₂ , and ω ₃ are expressed by the following equations 1 and 2. Is done.

  Since the optical coupler combines the signal light and the pump light, it is possible to excite the signal light into a plurality of modes of propagation light in the multimode optical fiber. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode multiplexing can be suppressed by using a nonlinear effect between signal light and pump light. Therefore, the mode multiplexing apparatus according to the present invention can realize long-distance and large-capacity transmission in a mode multiplexing transmission system.

  A mode demultiplexing device according to the present invention includes a mode multiplexed signal light in which a plurality of modes of signal light are superimposed on the same wavelength, an optical coupler for combining pump light having different wavelengths from the mode multiplexed signal light, and the pump light. And a multimode optical fiber that generates basic mode light of the signal light included in the mode multiplexed signal light by a non-linear effect between the mode multiplexed signal light and converts it into a plurality of signal lights having different wavelengths.

Here, the frequency of the pump light is ω ₁ , the frequency of the signal light is ω ₂ , and the frequency of light generated in the multimode optical fiber by four-wave mixing of light of frequency ω ₁ and light of frequency ω ₂ Is the ω ₃ , the effective refractive indexes n ₁ , n ₂ , and n ₃ of the propagation modes of the multimode optical fiber at the frequencies ω ₁ , ω ₂ , and ω ₃ are expressed by the following equations 1 and 2. Is done.

  Since the optical coupler multiplexes the mode multiplexed signal light and the pump light, a mode higher than the first higher-order mode can be returned to the fundamental mode in the multimode optical fiber. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode demultiplexing can be suppressed by using a nonlinear effect between signal light and pump light. Therefore, the mode demultiplexer according to the present invention can realize long-distance and large-capacity transmission in a mode multiplexing transmission system.

  In the mode multiplexing method according to the present invention, a plurality of signal lights having different wavelengths and the signal light and pump lights having different wavelengths are combined, and a multimode optical fiber is combined by the optical multiplexing procedure. By propagating the combined light, a non-linear effect between the signal light and the pump light generates a propagation light higher than the first higher-order mode of the signal light, and the multi-mode propagation light is multiplexed into one wavelength. And a mode multiplexing procedure for converting into mode multiplexed signal light.

  Since the signal light and the pump light are multiplexed in the optical multiplexing procedure, it is possible to excite the signal light into a plurality of modes of propagation light in the mode multiplexing procedure. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode multiplexing can be suppressed by using a nonlinear effect between signal light and pump light. Therefore, the mode multiplexing method according to the present invention can realize long-distance and large-capacity transmission in a mode multiplexing transmission system.

  The mode demultiplexing method according to the present invention includes a mode multiplexing signal light in which a plurality of modes of signal light are superimposed on the same wavelength, and an optical multiplexing procedure for combining pump light having different wavelengths from the mode multiplexed signal light, and the pump By propagating the combined light combined in the optical combining procedure to a multimode optical fiber having a light wavelength of zero dispersion wavelength, the mode multiplexed signal light is caused by a nonlinear effect between the pump light and the mode multiplexed signal light. A mode demultiplexing procedure for generating the fundamental mode light of the signal light included in the signal light and converting it into a plurality of signal lights having different wavelengths.

  Since the mode multiplexed signal light and the pump light are multiplexed in the optical multiplexing procedure, the mode higher than the first higher-order mode can be returned to the basic mode in the mode demultiplexing procedure. Here, since FWM generally does not occur in different propagation modes, crosstalk in mode demultiplexing can be suppressed by using a nonlinear effect between signal light and pump light. Therefore, the mode demultiplexing method according to the present invention can realize long-distance and large-capacity transmission in a mode multiplexing transmission system.

According to the present invention, the accuracy of mode multiplexing and demultiplexing is good, loss during mode multiplexing and crosstalk during demultiplexing can be reduced, and the transmission distance can be expanded. Therefore, long-distance and large-capacity transmission can be realized in the mode multiplex transmission system.
Further, since the modes can be combined or demultiplexed with respect to the WDM signal, the number of multiplexing / demultiplexing devices can be reduced and the system can be constructed economically.

An example of the mode multiplexing transmission system which concerns on this embodiment is shown. An example of the structure of the mode multiplexer which concerns on this embodiment is shown. An example of the mode multiplexing principle of single signal light using FWM is shown. An example of the mode multiplexing principle of WDM signal light using FWM is shown. 2 shows an example of the configuration of a mode demultiplexer according to the present embodiment. An example of the mode demultiplexing principle of single signal light using FWM is shown. An example of the mode demultiplexing principle of WDM signal light using FWM is shown. The structural example of the multimode optical fiber which concerns on this embodiment is shown. An example of the wavelength dependence of the refractive index of a multimode optical fiber is shown. An example of the wavelength dependence of group velocity dispersion of a multimode optical fiber is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and are not limited to the following embodiments.

  FIG. 1 shows a mode multiplex transmission system according to this embodiment. The mode multiplexing transmission system according to the present embodiment includes a plurality of transmitters 91_1 to 91_N, a mode multiplexing device 92, a mode demultiplexing device 93, and a plurality of receivers 94_1 to 94_N. The mode multiplexing transmission method according to this embodiment includes a mode multiplexing procedure and a mode demultiplexing procedure in this order.

In the mode multiplexing procedure, the mode multiplexing device 92 generates signal lights x _{1 to} x _N having different wavelengths from the plurality of transmitters 91_1 to 91_N and pump lights p having different wavelengths from the signal lights x _{1 to} x _N. multiplexes pump light p and the signal light x ₁ optical signal x ₁ produces a first higher-order mode than the propagation light ~x _N by nonlinear effect with ~x _N, first-order modes more propagating light Outputs the mode multiplexed signal light x multiplexed into one wavelength to the multimode optical fiber 95.

In the mode demultiplexing procedure, the mode demultiplexing device 93 receives the mode multiplexed signal light y from the multimode optical fiber 95, combines the pump light p having the same wavelength as the pump light p with the mode multiplexed signal light y, The fundamental mode light of the signal light included in the mode multiplexed signal light y is generated by the nonlinear effect of the pump light p and the mode multiplexed signal light y. Thus, it is possible to generate a signal beam _y 1 ~y _N having the same wavelength as the signal light _x 1 ~x _N. Then, the mode demultiplexer 93 outputs the signal lights y _{1 to} y _N to different receivers 94_1 to 94_N for each wavelength.

N transmitters emanating from 91_1～91_N N kinds of signal light _x 1 ~x _N wavelengths, the mode multiplexing device 92 comprises a mode converter, are multiplexed, multi-mode optical fiber 95 is used as a transmission line Are converted into different modes. The combined signal lights x _{1 to} x _N propagate in the multimode optical fiber 95 as different propagation modes. The mode demultiplexer 93 installed on the emission side demultiplexes into N ports for each wavelength, and the N demultiplexed signal lights are received by N receivers 94_1 to 94_N. That is, N types of signal light can be transmitted in parallel. The signal light transmitted from the transmitter i and passed through the mode converter is denoted by x _i , and the signal light received by the receiver i is denoted by y _i . In the present invention, a mode multiplexer 92 and a mode demultiplexer 93 composed of an optical coupler and a multimode optical fiber are used.

  The mode multiplexer 92, the mode demultiplexer 93, and the multimode optical fiber 95 will be described below.

(Mode multiplexer 92)
FIG. 2 shows the configuration of the mode multiplexer 92 according to the present embodiment. The mode multiplexer 92 includes a WDM multiplexer 21, an optical coupler 22, and a multimode optical fiber 23. The mode multiplexing method according to the present embodiment includes an optical multiplexing procedure and a mode multiplexing procedure in this order.

In the optical multiplexing procedure, the optical coupler 22 combines the signal light x _{1 to} x _N and the pump light p.
Mode in multiplexing procedure, the multi-mode optical fiber 23, to generate a signal light x ₁ ~x _N and the first higher-order mode or of the propagation light of the signal light by nonlinear effect of pump light p, the first higher mode than Are propagated into mode multiplexed signal light multiplexed at one wavelength.

The signal light incident on the mode multiplexing device 92 is a plurality of signal lights having different wavelengths. The signal light x _{1 to} x _N is multiplexed on one fiber by the WDM multiplexer 21, and the wavelength of the signal light passes through the optical coupler 22. It is combined with one different pump light p. In the optical fiber 95, when the wavelength of the pump light p is close to the zero dispersion wavelength of each propagation mode of the multimode optical fiber 23, four-wave mixing (FWM), which is one of nonlinear phenomena, occurs. A new wavelength of light is generated. At this time, mode-multiplexed signal light x can be obtained by converting the input signal light x ₁ to x _N to the same wavelength and different propagation modes.

A specific method for obtaining the mode multiplexed signal light x will be described with reference to FIG.
When the frequency of the pump light p is ω ₁ and each frequency of the signal light x _{1 to} x _N is ω ₂ , the frequency ω ₃ of newly generated light satisfies the following phase matching condition.
(Equation 1)
2ω ₁ = ω ₂ + ω ₃
(Equation 2)
2n ₁ ω ₁ = n ₂ ω ₂ + n ₃ ω ₃
Here, n _{1 to} n ₃ are effective refractive indexes of the propagation modes of the multimode optical fiber 23 at the respective frequencies ω _{1 to} ω ₃ .

When the medium is a single mode optical fiber, n ₁ to n _{3 with} respect to ω ₁ to ω ₃ have a “one-to-one” relationship. However, in the case of a multimode optical fiber, the frequencies ω _{1 to} ω _Since there are a plurality of propagation modes for ₃ , there is a “one-to-many” relationship. In other words, N _{1 to} n ₃ in Equation 2 can be considered as N ³ combinations, where N is the number of propagation modes.

For example, as shown in FIG. 3, the zero dispersion wavelength of the LP01 mode, which is the fundamental mode, is λ _p, and the wavelength of the signal light incident in the LP01 mode is λ ₀ ′. Further, when the pump light is incident at λ _p , it is assumed that the wavelength of newly generated light satisfying Equations 1 to 2 is λ ₀ between the LP01 mode pump light and the signal light. When the light propagating across at LP11 mode higher mode is incident, mode LP01 mode wavelength lambda ₀ 'is converted into LP01 mode wavelength lambda _0, the wavelength lambda ₀ LP01 mode and the LP11 mode are multiplexed Multiple signal light can be obtained.

  Also, as shown in FIG. 4, even if the target is a WDM signal, mode multiplexed signal light can be generated collectively with a single pump light.

  FWM also occurs between the LP01 mode pump light and the LP11 mode signal light. However, since the zero dispersion wavelength is generally different in different propagation modes, the wavelength conversion efficiency by the FWM is abrupt as shown in Non-Patent Document 2. In the LP11 mode, no FWM is generated, and the FWM can be generated only during the LP01 mode.

In order to use high-order mode light for the incident signal, for example, a long-period fiber Bragg grating can be used as the multimode optical fiber 23. As shown in Non-Patent Document 2, the grating interval Λ for converting the fundamental mode to the higher-order mode at the wavelength λ is given by Equation 1. In Equation 1, n ₀ and n ₁ ^m respectively indicate the effective refractive index of the fundamental mode and the effective refractive index of the mth higher-order mode at the wavelength λ. The fiber grating spacing is determined by the structural parameters of the fiber used, the wavelength, and the mode order to be converted. After determining the wavelength to be used, numerical analysis is performed from the structural parameters of the fiber to calculate the effective refractive index of the fundamental mode and the desired higher-order mode. A necessary grating period is determined using these calculation results and Equation (3).
(Equation 3)
Λ = λ / (n ₀ −n ₁ ^m )

(Mode splitter 93)
FIG. 5 shows the configuration of the mode demultiplexer 93 according to this embodiment. The mode demultiplexer 93 includes an optical coupler 31, a multimode optical fiber 32, and a WDM demultiplexer 33. The mode demultiplexing method according to the present embodiment includes an optical multiplexing procedure and a mode demultiplexing procedure in this order.

In the optical multiplexing procedure, the optical coupler 31 combines the mode multiplexed signal light and the pump light.
In the mode demultiplexing procedure, the multimode optical fiber 32 generates the fundamental mode light of the signal lights x _{1 to} x _N included in the mode multiplexed signal light y by the nonlinear effect of the pump light and the mode multiplexed signal light, converting different plurality of signal lights _y 1 ~y _N.

  The incident mode multiplexed signal light y and pump light p having different wavelengths are incident on the multimode optical fiber 32, and FWM is generated in the multimode optical fiber 32. At this time, if the wavelength of the pump light is adjusted so as to satisfy the conditions of Equations 1 to 2 only for the specific mode from the mode multiplexed signal light of the same wavelength, only the signal light of the specific mode is renewed. A mode demultiplexer can be realized by converting the light into a wavelength and passing the light through a WDM spectrometer.

For example, as shown in FIG. 6, the wavelength of the mode multiplexed signal light in the LP01 mode and the LP11 mode is λ ₀ and the wavelength of the pump light in the LP01 mode is λ _p . When the wavelength of the pump light is close to the zero dispersion wavelength of the LP01 mode, light of the LP01 mode having the wavelength λ ₀ ′ that satisfies Equations 1 to 2 is generated. That is, the LP01 mode can be extracted from the mode multiplexed signal light of the LP01 mode and the LP11 mode, and a mode demultiplexing device can be realized by extracting by the WDM demultiplexer 33 in the subsequent stage.

  Further, as shown in FIG. 7, even if the target is a WDM signal, it is possible to generate mode multiplexed signal light collectively with a single pump light.

  Note that FWM is also generated between the LP01 mode pump light and the LP11 mode signal light. However, in general, different propagation modes have different zero-dispersion wavelengths, so that no FWM is generated, and the FWM is generated only between the LP01 modes. it can. That is, crosstalk in mode demultiplexing can be suppressed as compared with the conventional method.

(Multimode optical fiber 23)
Next, 32 structural examples used for the multimode optical fiber 23 used for the mode multiplexer 92 and the mode demultiplexer 93 will be described.
FIG. 8 shows the structure of a multimode optical fiber. The fiber has a staircase structure. This structure is used in a conventional dispersion-shifted fiber, and the structure dispersion can be increased negatively.

  As described above, in order to generate FWM and realize mode multiplexing or mode demultiplexing, the zero dispersion wavelength in each mode needs to be different. The dispersion in each mode is divided into material dispersion and structural dispersion, and the material dispersion in an optical fiber having the same material is equal in each mode. On the other hand, the structural dispersion is different in each mode, and it is necessary to have a structural dispersion value that cannot be ignored with respect to the material dispersion. At present, the structural dispersion value becomes negatively large by adopting a W-shaped refractive index distribution used in a dual-shaped core or dispersion compensating fiber as shown in FIG. Preferred as 23 and 32.

For example, FIG. 7 shows effective refractive indexes of the LP01 mode and the LP11 mode when a ₁ = 2.15 μm, a ₂ = 10 μm, Δ1 = 1%, and Δ2 = 0.2%. There are different effective refractive indexes for each mode, and there are four types of wavelengths (LP01-LP01, LP01-LP11, LP11-LP01, LP11-) between the pump light and the signal light that satisfy Equations 1 and 2 depending on the combination of modes. LP11) It can be seen that it is determined.

  FIG. 8 shows the group velocity dispersion values of the same fiber. It can be seen that the zero dispersion wavelength of the LP01 mode is 1550 nm, whereas the zero dispersion wavelength of the LP11 mode is 1390 nm.

That is, only one wavelength is converted by the FWM with respect to the mode multiplexed signal, and mode multiplexing / demultiplexing can be realized when the wavelength λ _p of the pump light _p is set as the zero dispersion wavelength of each mode.

  In this embodiment, only the FWM between the LP01 mode and the LP11 mode is dealt with. However, there are cases where Formulas 1 to 2 are satisfied even between different modes such as the LP01 mode and the LP11 mode.

  Using the mode multiplexing device 92, the mode demultiplexing device 93, and the multimode optical fiber 95 described above, an N number mode multiplex transmission system as shown in FIG. 1 is constructed. Using this system, N types of pump light corresponding to zero dispersion wavelengths of N types of propagation modes are incident on the multimode optical fiber, so that the mode multiplexer 92 that multiplexes the N modes and the N types of modes are separated. The mode demultiplexer 93 can be realized.

  The present invention is a transmission using a multimode optical fiber, and the frequency utilization efficiency is improved by using the mode, and a large capacity and long distance communication can be realized.

21: WDM multiplexer 22: optical coupler 23: multimode optical fiber 31: optical coupler 32: multimode optical fiber 33: WDM demultiplexers 91_1 to 91_N: transmitter 92: mode multiplexer 93: mode demultiplexer 94_1-94_N: Receiver

Claims (8)

Signal light having different wavelengths from a plurality of transmitters and the signal light are combined with pump light having different wavelengths, and higher than the first higher-order mode of the signal light due to nonlinear effects of the pump light and the signal light A mode multiplexer that generates a multi-mode optical fiber and generates a mode multiplexed signal light in which a plurality of modes of the propagated light are multiplexed into one wavelength;
The mode multiplexed signal light is input from the multimode optical fiber, the pump light having the same wavelength as the pump light is combined with the mode multiplexed signal light, and the non-linear effect between the pump light and the mode multiplexed signal light A mode demultiplexing device that generates the basic mode light of the signal light included in the mode multiplexed signal light, and outputs the generated basic mode light of the signal light to a different receiver for each wavelength;
A mode multiplex transmission system comprising: The signal light having a different wavelength from a plurality of transmitters and the signal light are combined with the pump light having different wavelengths, and the first higher-order mode of the signal light is increased by a non-linear effect of the signal light and the pump light. A mode multiplexing procedure for generating a multi-mode optical fiber and generating a mode multiplexed signal light in which a plurality of modes of propagation light are multiplexed into one wavelength;
The mode multiplexed signal light is input from the multimode optical fiber, the mode multiplexed signal light and the pump light having the same wavelength as the pump light are combined, and the nonlinear effect between the pump light and the mode multiplexed signal light is obtained. A mode demultiplexing procedure for generating the basic mode light of the signal light included in the mode multiplexed signal light, and receiving the generated basic mode light of the signal light by a plurality of receivers;
Mode multiplex transmission method. An optical coupler that combines a plurality of signal lights having different wavelengths and pump light having different wavelengths with the signal lights;
A non-linear effect between the signal light and the pump light generates propagation light of the signal light higher than the first higher-order mode, and converts the propagation light of a plurality of modes into mode multiplexed signal light multiplexed at one wavelength. And a mode optical device. The frequency of the pump light is ω ₁ , the frequency of the signal light is ω ₂ , and the frequency of light generated in the multimode optical fiber by four-wave mixing of the light of frequency ω _{1 and} the light of frequency ω ₂ is ω _3. , The effective refractive indexes n ₁ , n ₂ , n ₃ of the propagation modes of the multimode optical fiber at the frequencies ω ₁ , ω ₂ , ω ₃ are expressed by the following equations: Item 4. The mode multiplexer according to Item 3.
2ω ₁ = ω ₂ + ω ₃
2n ₁ ω ₁ = n ₂ ω ₂ + n ₃ ω ₃ A mode multiplexed signal light in which a plurality of modes of signal light are superimposed on the same wavelength, and an optical coupler for combining the mode multiplexed signal light with pump lights having different wavelengths;
A multimode optical fiber that generates a fundamental mode light of the signal light included in the mode multiplexed signal light by a nonlinear effect between the pump light and the mode multiplexed signal light, and converts the fundamental mode light into a plurality of signal lights having different wavelengths; A mode demultiplexer provided. The frequency of the pump light is ω ₁ , the frequency of the signal light is ω ₂ , and the frequency of light generated in the multimode optical fiber by four-wave mixing of the light of frequency ω _{1 and} the light of frequency ω ₂ is ω _3. , The effective refractive indexes n ₁ , n ₂ , n ₃ of the propagation modes of the multimode optical fiber at the frequencies ω ₁ , ω ₂ , ω ₃ are expressed by the following equations: Item 6. The mode demultiplexer according to Item 5.
2ω ₁ = ω ₂ + ω ₃
2n ₁ ω ₁ = n ₂ ω ₂ + n ₃ ω ₃ An optical multiplexing procedure for combining a plurality of signal lights having different wavelengths and pump light having different wavelengths with the signal lights;
Propagating light that is higher than the first higher-order mode of the signal light due to the nonlinear effect of the signal light and the pump light by propagating the combined light combined in the optical multiplexing procedure to a multimode optical fiber, A mode multiplexing method that sequentially includes a mode multiplexing procedure for converting a multimode propagation light into a mode multiplexed signal light multiplexed into one wavelength. A mode multiplexing signal light in which a plurality of modes of signal light are superimposed on the same wavelength and a mode multiplexing signal light for combining pump lights having different wavelengths;
By propagating the combined light combined in the optical combining procedure to a multimode optical fiber having the pump light wavelength of zero dispersion wavelength, the mode multiplexing is performed by a nonlinear effect between the pump light and the mode multiplexed signal light. A mode demultiplexing method that sequentially includes a mode demultiplexing procedure for generating basic mode light of the signal light included in signal light and converting it into a plurality of signal lights having different wavelengths.

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