JP2022164394A - Mode characteristic compensator, multimode amplification system, and mode multiplex transmission system - Google Patents

Abstract

To enable an intensity difference between modes to be compensated, even for four or more modes.SOLUTION: A mode characteristic compensator provided with a mode multiplex-demultiplex function for multiplexing four or more basic modes to a main waveguide in mutually different modes and demultiplexing the four or more modes of the main waveguide for each mode in the basic modes. includes a coupler for coupling basic modes propagating the main waveguide and a non-contact parallel waveguide to a higher order mode of the main waveguide and causing mode conversion to occur between itself and the main waveguide. Each of the couplers includes a plurality of coupling parts, and a delay-amount variable delay part for causing a propagation delay to occur between the parallel waveguide and the main waveguide. The delay amount of the delay part included with the coupler is predetermined so that the intensity difference between the modes outputted from the main waveguide is smaller than the intensity difference between the basic modes.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a device capable of compensating intensity differences of four or more modes, and a multimode amplification system and mode multiplex transmission system comprising the same.

In mode multiplexing transmission, an MDL (Mode Dependent Loss) compensator that compensates for the loss difference between modes in a multimode transmission path has been proposed (see, for example, Non-Patent Documents 1 and 2). Non-Patent Document 1 is a spatial MDL compensator that compensates for the loss difference between the three modes, and Non-Patent Document 2 is a PLC (Planar Lightwave Circuit) type MDL compensation that compensates for the loss difference between the three modes. It is a vessel. On the other hand, a multiplexer/demultiplexer that enables 6-mode mode multiplex transmission has been proposed (see, for example, Non-Patent Document 3).

T. Mizuno et al. , "Mode dependent loss equalizer and impact of MDL on PDM-16QAM few-mode fiber transmission," ECOC2015, P5.9 (2015) N. Sugawara et al. , "3-Mode PLC-Based Mode Dependent Loss Equalizer in MDM Transmission," OECC2019, TuE2-2 (2019) N. Hanzawa et al. , "Demonstration of PLC-based six-mode multiplexer for mode division multiplexing transmission," ECOC2015, P2.6 (2015)

Non-Patent Documents 1 and 2 can compensate for the intensity difference between the three modes, but no device has been realized that dynamically compensates the intensity difference for each mode for more than three modes.

The present disclosure aims to make it possible to compensate for intensity differences between modes, even with four or more modes.

The modal characteristic compensator of the present disclosure is
A mode characteristic compensator having a mode multiplexing/demultiplexing function of multiplexing four or more fundamental modes into a main waveguide in mutually different modes and demultiplexing the four or more modes of the main waveguide in the fundamental mode for each mode,
A coupler that couples a fundamental mode propagating in a parallel waveguide that is not in contact with the main waveguide to a higher-order mode of the main waveguide to cause mode conversion with the main waveguide,
Said couplers are each:
a plurality of coupling portions that couple a higher-order mode predetermined for each coupler from the parallel waveguide to the main waveguide;
A delay section with a variable delay amount disposed between the plurality of coupling sections, wherein the parallel waveguide and the main waveguide are not coupled and a propagation delay difference is generated between the parallel waveguide and the main waveguide. When,
with
The delay amount of the delay unit provided in the coupler is determined so that the intensity difference between the modes output from the main waveguide is smaller than the intensity difference between the fundamental modes.

The multimode amplification system of the present disclosure comprises:
a multimode optical amplifier for amplifying a wavelength multiplexed signal having multiple modes;
a mode demultiplexer that demultiplexes the amplified wavelength multiplexed signal for each mode;
a wavelength gain compensator that performs wavelength gain compensation for each mode demultiplexed by the mode demultiplexer;
Compensating a gain difference between wavelength-gain-compensated wavelength-multiplexed signals, converting the wavelength-multiplexed signal after compensating for the gain difference into a mode before demultiplexing by the mode demultiplexer, and combining the signals. a modal characteristic compensator;
Prepare.

The mode multiplexing transmission system of the present disclosure is
a transmitter that emits n (n is an integer equal to or greater than 4) wavelength-multiplexed signals;
a mode characteristic compensator of the present disclosure that multiplexes n wavelength multiplexed signals into mode multiplexed signals of different modes;
a multimode fiber that propagates a mode-multiplexed signal multiplexed by the mode characteristic compensator;
a mode demultiplexer that separates the mode-multiplexed signal propagated through the multimode fiber for each mode;
a receiver that demultiplexes and receives the n wavelength multiplexed signals demultiplexed by mode by the mode demultiplexer by wavelength;
Prepare.

According to the present disclosure, it is possible to compensate for intensity differences between modes even with four or more modes.

It is a figure explaining the modal characteristic compensator which concerns on this embodiment. It is an example of the structure of a coupler. FIG. 2 shows an illustration of coupler structural parameters. An example of structural parameter values for each coupler is shown. Waveguide width and effective refractive index in coupler 24 (WINC#4) are shown. Fig. 2 shows a schematic diagram of a joint of a WINC structure; An example of the transmittance from the LP11a mode to the LP11a mode and from the LP11b to the LP21a mode with respect to the coupling length L _c , (a) g = 5.5 μm, (b) g = 6.5 μm, (c) g = 7 0.5 μm is shown. Shows the properties of equations (5) and (6) for L _d . An example of wavelength characteristics with respect to temperature is shown. 1 shows a configuration example of a multimode amplification system according to this embodiment. 1 shows a configuration example of an optical transmission system according to this embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In addition, in this specification and the drawings, constituent elements having the same reference numerals are the same as each other.

(Embodiment example 1)
FIG. 1 is a diagram for explaining the modal characteristic compensator of this embodiment. The modal characteristic compensator of this embodiment is a 6-mode mode multiplexer/demultiplexer in the case where all waveguides have a constant height h, and further has a function of compensating the loss difference/gain difference of the 6 modes. In FIG. 1, as an example of the present disclosure, six fundamental modes (LP01) modes are input, and six different modes (LP01 mode, LP11a mode, LP11b mode, LP21a mode, LP21b mode, LP02 mode) are combined. Give an example.

The mode characteristic compensator further includes m (m is an integer of 3 or more) side waveguides 15 to 19 which are not in contact with the main waveguide 11 and the sub waveguides 12 and 13 and have couplers. In the side waveguides 15 to 19, the effective refractive index of the propagating mode exclusively matches the effective refractive index of the m higher-order modes on the lower-order side of the main waveguide 11 for the desired light wavelength range. It is characterized by

FIG. 1 shows a configuration example when m=5, the side waveguide 15 has a coupler 21-2, the side waveguide 16 has a coupler 21-3, the side waveguide 17 has a coupler 21-4, The side waveguide 18 has a coupler 21-5 and the side waveguide 19 has a coupler 21-6. Each coupler causes mode conversion with the main waveguide 11 and transfers optical power. In FIG. 1, the coupler is labeled as "coupler".

The modal characteristic compensator comprises at least one intermediate waveguide 14 which is not in contact with the main waveguide 11, sub-waveguides 12, 13 and side waveguides 15-19. The main waveguide 11, the sub-waveguides 12 and 13, the intermediate waveguide 14 and the side waveguides 15 to 19 have the same waveguide height h. and at least one of the side waveguides 15-19 includes a mode rotator 25, 26 for converting the LP11a mode to the LP11b mode. The main waveguide 11 also includes a taper 31 whose waveguide width increases continuously in the longitudinal direction and converts the E31 mode coupled from the sub waveguide 12 to the main waveguide 11 by the coupler 22 into the E13 mode. The main waveguide 11 also includes a taper 32 that continuously decreases in waveguide width in the longitudinal direction and transforms the E13 and E31 modes into the LP21b and LP02 modes. By using a WINC divider (wavelength-independent coupler type arbitrary branching ratio divider) described later for each coupler provided in this 6-mode multiplexer/demultiplexer, dynamic mode control by a heater becomes possible.

FIG. 2 shows an example of the structure of the WINC divider provided for each coupler 21-24 (coupler1, coupler2, coupler3, coupler4). Coupler 21 includes couplers 21-2 to 21-6. Each of the couplers 21 to 24 in FIG. 1 is illustrated by omitting a plurality of coupling portions as described above.

Each coupler is composed of two parallel waveguides 111 and 112, and has a plurality of coupling portions 121 and 122 to create a propagation delay difference between the parallel waveguides 111 and 112 between the coupling portions 121 and 122. It has a delay unit 123 . The port #1 is arranged at the end of the waveguide 111 on the side of the coupling section 121, the port #2 is arranged on the end of the waveguide 112 on the side of the coupling section 121, and the port #2 is arranged on the end of the waveguide 111 on the side of the coupling section 122. A port #3 is arranged at the end, and a port #4 is arranged at the end of the waveguide 112 on the coupling section 122 side.

The delay unit 123 has a heater for adjusting the delay amount ΔL. In the coupling parts 121 and 122, parameters such as the coupling length Lc and the waveguide spacing _g are set so that about half the power of the propagating mode, for example, 0.4 to 0.6 times, is transferred to the other waveguide. . In FIG. 2, "3 dB mode divider" is described as an example. The length L ₁ of the waveguide 111 of the delay section is represented by L _m +2L _d . The length L ₂ of the waveguide 112 of the delay section is represented by L ₁ +ΔL. By appropriately designing parameters such as the widths w1 and _w2 of the waveguides ₁₁₁ and 112, the height h, the waveguide spacing _g , and the coupling length Lc, and adjusting the delay amount ΔL with the heater, the mode intensity ratio can be changed. That is, since the intensity can be adjusted for each mode, it is possible to compensate for the intensity difference of each mode.

上式により、Ｌ_ｄとＲが定まれば、ｓ_ｄを求めることができる。 FIG. 3 shows an explanatory diagram of the structural parameters of each coupler. An example is shown in which the waveguide 20 bends with a radius of curvature R and bends in the opposite direction into an S shape at an angle θ. The length s _d in the x-axis direction, the radius R, and the length L _d in the z-axis direction are related by the following formula.

If L _d and R are determined by the above formula, s _d can be obtained.

FIG. 4 shows an example of structural parameter values for each coupler. In the coupler 21 (WINC#1), the LP01 mode input from the input port #2 becomes the LP11a mode in the output port #3, and in the coupler 22 (WINC#2), the LP11a mode input from the input port #2 becomes the output port #. 3 is the E31 mode, the LP11a mode input from the input port #2 of the coupler 23 (WINC#3) is the E31 mode of the output port #3, and the coupler 24 (WINC#4) is input from the input port #2. LP11b mode is converted to LP21a mode at output port #3.

FIG. 5 shows the waveguide width and effective refractive index in WINC#4. Coupler 24 (WINC#4) is desired to excite the LP11b mode to the LP21a mode at a desired ratio. On the other hand, the LP11a mode is converted to the LP01 mode. FIG. 6 shows a schematic diagram of the coupling portion of the WINC structure in the coupler 24. As shown in FIG. As shown in FIG. 6, the LP11a mode must pass through the main waveguide 11 as it is, and the LP11b mode must be designed to split into the LP21a mode by 3 dB.

FIG. 7 shows the _LP11a mode to LP11a mode ( The transmission from port #1 to port #3) and the transmission from LP11b mode to LP21a mode (port #2 to port #3) are shown. For example, when g = 7.5 µm and L _c = 10 mm, the transmittance from the LP11a mode to the LP11a mode (port #1 to port #3) is approximately 1, and from the LP11b mode to the LP21a mode (port #2 to port #3 ) is approximately 0.5. Therefore, when g=7.5 μm and L _c =10 mm, the LP11a mode passes through the main waveguide 11 as it is, and the LP11b mode is split into the LP21a mode by 3 dB. By adjusting the waveguide spacing g and the coupling length Lc in this way, the _LP11a mode passes through the main waveguide 11 as it is, and the LP11b mode is split into the LP21a mode by 3 dB.

As described above, it is possible to realize a device that adjusts the intensity of each mode with the WINC divider structure for each of the six modes and compensates for the inter-mode loss difference and mode gain difference.

Note that the modal characteristics compensator of the present disclosure functions as a mode demultiplexer that outputs a fundamental mode in which intensity differences between modes are compensated for by inputting mode-multiplexed signals of six modes from the opposite direction. Therefore, the present disclosure can provide a mode multiplexer/demultiplexer that can compensate for intensity differences between modes. In addition, although 6 modes are illustrated in this embodiment, compensation for mode loss difference and gain difference can be realized with an arbitrary number of modes by using the WINC structure for each mode.

(Embodiment example 2)
In this embodiment, an example of adjusting the delay amount ΔL between the waveguides 111 and 112 in the delay section as a design for reducing the wavelength dependence of the 6-mode mode characteristic compensator will be described.

The output power of LP11a mode light from port #3 when LP01 mode light is incident on port #2 in FIG. 2 is expressed by the following equation.

Here, A3 is the complex amplitude of port #3 in _FIG . Further, when the propagation constants of the coupling (even-odd) modes of the coupling portions 121 and 122 and the modes propagating through the waveguides 111 and 112 are β _e , β _o , β ₁ and β ₀ respectively,
(Number 3)
q=(β _e −β _o )/2
δ = (β ₁ - β ₀ )/2
Δφ=β ₀ (L ₂ +L _c )−β ₁ (L ₁ +L _c )
and Here, _L1 is the length of waveguide ₁₁₁ in the delay section, and L2 is the length of waveguide 112 in the delay section.

となる。 Now, assuming that the center wavelength is 1550 nm, the LP11a and LP01 modes of the waveguides 111 and 112 are phase-matched (δ=0) at the center wavelength, and the coupling sections 121 and 122 are designed to operate appropriately (qL _c =π/4 ), the output power of the LP11a mode light from the port #3 when the LP01 mode light is incident on the port #2 is

becomes.

なお、ｋ＝（ｑ^２－δ^２）^１／２、λ_０は光の波長、ｋ（波数）を２π／λ_０、Ｎ_１、Ｎ_２はそれぞれ導波路１１１、１１２の群屈折率である。 In order to obtain a transmittance close to 100% in a wide band, the above equation should be 1 and the wavelength dependence of Δφ should be small. Therefore, the conditional expression for broadband design is as follows.

Note that k=(q ² −δ ² ) ^1/2 , λ ₀ is the wavelength of light, k (wavenumber) is 2π/λ ₀ , N ₁ and N ₂ are the group refractive indices of the waveguides 111 and 112, respectively. .

FIG. 8 shows the characteristics of equations (5) and (6) for _Ld . 8A shows the characteristics of WINC#1, FIG. 8B shows the characteristics of WINC#2, FIG. 8C shows the characteristics of WINC#3, and FIG. 8D shows the characteristics of WINC#4. Therefore, L _d of WINC#1 to #4 is selected so that the value of equation (6) is close to 0 and the value of equation (5) is close to 1. For example, WINC#1: L _d =2618 μm, WINC#2: L _d =10626 μm, WINC#3: L _d =6590 μm, WINC#4: L _d =3408 μm provides a broadband design. Lm is 4000 _μm for all WINCs. Other structural parameters are as shown in FIG.

FIG. 9 shows an example of wavelength characteristics with respect to temperature. 9A shows the characteristics of WINC#1, FIG. 9B shows the characteristics of WINC#2, FIG. 9C shows the characteristics of WINC#3, and FIG. 9D shows the characteristics of WINC#4. As shown in FIG. 9, at each wavelength, when the temperature is 80°, the transmittance decreases to about 60%, and when the temperature is 0°, the transmittance can be increased to nearly 100%. Therefore, by adjusting the temperature of the heater of the delay section 123 of the waveguide 112, the intensity of the mode can be adjusted over a wide band.

(Embodiment 3)
FIG. 10 shows a configuration example of a multimode amplification system according to the present disclosure. A configuration example of gain compensation for six modes (LP01, LP11a, LP11b, LP21a, LP21b, and LP02 modes) is shown. Each mode is converted into the LP01 mode, which is the fundamental mode, by a mode demultiplexer 82 in the subsequent stage of a 6-mode multimode EDFA (Erbium-Doped Fiber-Optical Amplifier) 81 . When the signal input to the multimode EDFA 81 is a wavelength multiplexed signal, the mode demultiplexer 82 demultiplexes the amplified wavelength multiplexed signal for each mode. Each wavelength-multiplexed signal passes through a wavelength gain compensator (DWG compensation) 83, and gain difference compensation between wavelengths is performed for each mode.

After that, they are multiplexed by a mode multiplexer 84 having a function of compensating for gain differences between modes. At this time, the wavelength gain compensator 83 converts to the mode before demultiplexing by the mode demultiplexer 82 and multiplexes. The mode multiplexer 84 can use the mode characteristic compensator of the present disclosure described in the first and second embodiments. Therefore, the gain difference between wavelength-multiplexed signals whose wavelength gain is compensated by the wavelength gain compensator 83 can be compensated.

It should be noted that it is not necessary to use all 6 modes, excitation may be performed by limiting the number of modes, all 6 modes may be separated by a mode demultiplexer, or only limited modes may be demultiplexed. can be Also, instead of the multimode EDFA 81, any multimode optical amplifier capable of amplifying a wavelength multiplexed signal having a plurality of modes can be used.

FIG. 11 shows a configuration example of a mode multiplexing transmission system according to the present disclosure. In this system, a wavelength multiplexed signal transmitter 91 that transmits n wavelength multiplexed signals, a wavelength multiplexed signal receiver 92 that demultiplexes and receives the n wavelength multiplexed signals, and signals from each wavelength multiplexed signal transmitter 91 mode multiplexer 93 for multiplexing wavelength multiplexed signals into mode multiplexed signals of different modes; mode multiplexer 94 for separating mode multiplexed signals for each mode; mode multiplexer 93 and mode multiplexer 94; and a multimode fiber 95 having n modes to be connected. At least one of the mode multiplexer 93 and the mode demultiplexer 94 uses the mode characteristic compensator described in the first or second embodiment.

The mode multiplexer 93 multiplexes the n wavelength multiplexed signals into mode multiplexed signals of different modes. Since the mode-multiplexed transmission system of the present disclosure includes the mode characteristic compensator of the present disclosure, mode-multiplexed signals with little intensity difference between modes can be transmitted through the multimode fiber 95 .

Also, the mode demultiplexer 94 separates the n mode multiplexed signals propagated through the multimode fiber 95 for each mode. As a result, n wavelength multiplexed signals are output from the mode demultiplexer 94 . Since the mode multiplexing transmission system of the present disclosure includes the mode characteristics compensator of the present disclosure, even if there is an intensity difference between the modes in the mode multiplexed signal, the intensity difference between the modes is compensated for and uniform intensity is obtained. of wavelength multiplexed signals can be output to the receiver 92 .

A transmission repeater may have a multimode amplifier 96 and also a gain compensator 97 . The multimode amplifier 96 and gain compensator 97 can adopt the configuration shown in FIG. For example, the multimode amplifier 96 has a multimode EDFA 81 , and the gain compensator 97 has a mode demultiplexer 82 , a wavelength gain compensator 83 and a mode multiplexer 84 .

In this specification, an embodiment relating to a planar lightwave circuit using a glass-based material has been described, but the material may of course be other. For example, a planar lightwave circuit using a semiconductor such as Si or InGaAsP or an organic substance such as a polymer can obtain the same effect as the embodiment described in this specification. In addition, the wavelength band used is about 1.5 to 1.6 μm in the embodiment described in this specification, but even in the mid-infrared region (2 μm or more) with a longer wavelength or the visible light band I do not care.

As described above, the modal characteristic compensator of the present disclosure is
An optical multiplexer for multiplexing 6 modes into a main waveguide,
couplers (21-24) that couple each mode into the main waveguide,
a WINC divider;
means for varying the delay amount ΔL of the delay section of each WINC divider (heater for adjusting the temperature of the delay section);
By adjusting the delay amount ΔL of the delay unit provided in each coupler, it is possible to compensate for the intensity difference of each mode. Thereby, the modal characteristic compensator of this embodiment functions as a modal loss difference/gain difference compensator.

Here, the modal characteristic compensator of the present disclosure is
a main waveguide (11) capable of propagating n (n is an integer equal to or greater than 4) modes and having a tapered portion in which the width of the waveguide changes continuously in the longitudinal direction;
Waveguides (12 to 16) that are non-contact with the main waveguide 11 and have coupling portions that cause mode conversion with the main waveguide and transfer optical power;
on a substrate, wherein
A waveguide 1 capable of propagating a mode of m (m is an integer equal to or greater than 2) and a waveguide 2 (112) parallel to the waveguide 1 (111),
Each of the waveguides 1 and 2 arranged in parallel has two or more adjacent coupling portions,
having a delay waveguide portion between the coupling portions, which is a region in which the waveguides are not coupled;
A phase delay difference Δτ of the light wave generated in the delay section of the waveguide 1 and the waveguide 2 is adjusted by the delay amount ΔL of the delay section,
In the portion where the waveguide 1 and the waveguide 2 are close to each other,
The waveguide width and height are adjusted such that the effective refractive index of the mode propagating in the waveguide 2 exclusively matches the effective refractive index of m−1 modes of the waveguide 1 for the desired wavelength range of light.・The relative refractive index difference is adjusted,
The length of the coupling portion and the waveguide spacing at the coupling portion are determined so that 0.4 to 0.6 times the optical power guided through the waveguide 2 by mode conversion is propagated through the waveguide 1. Equipped with a mode multiplexer/demultiplexer,
It is characterized by being able to adjust the intensity for each mode,
The LP11a mode coupled from the side waveguide 15 to the main waveguide 11 passes through the main waveguide 11 as it is,
The LP01 mode of the intermediate waveguide 14 is split 3 dB into the LP21a mode of the main waveguide 11 and the LP01 mode of the intermediate waveguide 14,
adopted the configuration.

(Effect of the present disclosure)
For the 6-mode modal characteristic compensator, it is possible to dynamically adjust the strength of the mode by using the WINC structure. , it is possible to compensate for the modal gain difference.

(Points of this disclosure)
Applying a WINC divider to a four or more mode Asymmetric Directional Coupler (ADC) allows control of dynamic inter-mode gain differential compensation by the heater.
In particular, by appropriately designing the waveguide spacing g and the coupling length Lc, the _LP11a mode can pass through the main waveguide 11 as it is, and the LP11b mode can be divided into the LP21a modes by 3 dB.

The present disclosure can be applied to the information and communications industry.

11: main waveguides 12, 13: sub waveguides 14: intermediate waveguides 15, 16, 17, 18, 19: side waveguides 20: waveguides 21-2, 21-3, 21-4, 21-5, 21 -6, 22, 23, 24: Coupler 81: Multimode EDFA
82: Mode demultiplexer 83: Wavelength gain compensator 84: Mode multiplexer 91: Wavelength multiplexed signal transmitter 92: Wavelength multiplexed signal receivers 93, 94: Mode multiplexer/demultiplexer 95: Multimode fiber 96: Multimode Amplifier 97: Gain Compensators 111, 112: Waveguides 121, 122: Coupling Section 123: Delay Section

Claims (6)

A mode characteristic compensator having a mode combining/demultiplexing function, combining four or more fundamental modes in different modes to a main waveguide, and demultiplexing the four or more modes of the main waveguide by the fundamental mode for each mode, ,
A coupler that couples a fundamental mode propagating in a parallel waveguide that is not in contact with the main waveguide to a higher-order mode of the main waveguide to cause mode conversion with the main waveguide,
Said couplers are each:
a plurality of coupling portions that couple a higher-order mode predetermined for each coupler from the parallel waveguide to the main waveguide;
A delay section with a variable delay amount disposed between the plurality of coupling sections, wherein the parallel waveguide and the main waveguide are not coupled and a propagation delay difference is generated between the parallel waveguide and the main waveguide. When,
with
The delay amount of the delay unit provided in the coupler is determined such that the intensity difference between the modes in the main waveguide is smaller than the intensity difference between the fundamental modes.
Modal compensator. each of the couplers includes a heater for adjusting the temperature of the delay section;
The delay amount of the delay unit is adjusted by adjusting the temperature of the delay unit.
2. A modal characteristic compensator according to claim 1. The main waveguide has a tapered portion in which the width of the waveguide changes continuously in the longitudinal direction,
the taper converts E13 and E31 modes to LP21b and LP02 modes;
3. A modal characteristic compensator according to claim 1 or 2. The coupling portion has a waveguide width, a high and a relative refractive index difference,
The waveguide spacing between the parallel waveguide and the main waveguide and the coupling length of the waveguide spacing at the coupling portion are 0.4 to 0.6 times the optical power guided through the parallel waveguide by mode conversion. defined to propagate in the main waveguide,
A modal characteristic compensator according to any one of claims 1 to 3. a multimode optical amplifier for amplifying a wavelength multiplexed signal having multiple modes;
a mode demultiplexer that demultiplexes the amplified wavelength multiplexed signal for each mode;
a wavelength gain compensator that performs wavelength gain compensation for each wavelength multiplexed signal demultiplexed by the mode demultiplexer;
2. Compensating a gain difference between wavelength-gain-compensated wavelength-multiplexed signals, converting the wavelength-multiplexed signals after compensating for the gain difference into a mode before demultiplexing by the mode demultiplexer, and combining the signals. 4. A modal characteristic compensator according to any one of 4;
A multimode amplification system with a transmitter that emits n (n is an integer equal to or greater than 4) wavelength-multiplexed signals;
5. The mode characteristic compensator according to any one of claims 1 to 4, which multiplexes n wavelength multiplexed signals into mode multiplexed signals of different modes;
a multimode fiber that propagates a mode-multiplexed signal multiplexed by the mode characteristic compensator;
a mode demultiplexer that separates the mode-multiplexed signal propagated through the multimode fiber for each mode;
a receiver that demultiplexes and receives the n wavelength multiplexed signals demultiplexed by mode by the mode demultiplexer by wavelength;
A mode multiplexed transmission system comprising:

Images