Method and apparatus for obtaining information for mode dispersion compensation

Abstract

To provide a method for obtaining an optical processing condition, which can be corresponded to a high-speed signal, and can be corresponded to a transmission channel of which a mode scattering amount is large for compensating a mode scattering in a small calculation time and a small power consumption for a mode dispersion compensation.SOLUTION: A method for acquiring information for a mode dispersion compensation in order to obtain an optical processing condition for compensating a mode scattering in a mode division multiplex transmission using a multimode fiber, contains: an optical transmission step of transmitting an optical probe signal from a mode multiplexer in each mode of the first mode to Mth mode of the mode division multiplex transmission, and transmitting the multimode fiber; a frequency response measurement step of measuring a frequency response of a complex amplitude of the optical probe signal that has transferred the multimode fiber; and an information acquisition step for the mode dispersion compensation for acquiring the information for the mode dispersion compensation containing a group delay difference and a loss difference between the modes in the mode division multiplex transmission by using the frequency response of the complex amplitude of the first mode to the Mth mode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for acquiring information used in modal dispersion compensation, and an apparatus for implementing the method. [Background technology]

[0002] Mode division multiplexing (MDM) can increase the transmission capacity per optical fiber by modulating and multiplexing individual signals onto multiple propagation modes in multimode fiber (MMF). Although the propagation modes of MMF are orthogonal to each other in the spatial electric field distribution of light, they can couple during transmission due to spatial perturbations in the refractive index distribution that occur during MMF manufacturing and slight bending during installation. Furthermore, each propagation mode has a different propagation constant, resulting in differences in group delay time and transmission loss. Such inter-mode coupling, group delay difference, and loss difference are collectively called modal dispersion and are factors that degrade signal transmission quality. Degraded signals can be compensated for by performing multiple-input, multiple-output (MIMO) processing after reception. However, the computational complexity of MIMO processing increases with the number of modes, the number of signal modulations, and the transmission distance.

[0003] Furthermore, current optical fiber networks use wavelength division multiplexing transmission, which multiplexes multiple different wavelengths, and routing is performed using each wavelength as an optical path. Therefore, if mode division multiplexing transmission is introduced into optical networks, it is conceivable that routing would be performed using each transmission mode as an optical path. However, as mentioned above, modal dispersion occurs, which requires MIMO processing at each node where an optical switch is located, which is not realistic due to the power consumption and calculation delays. For this reason, optical switches for MMF have not been studied very much at present.

[0004] As techniques that can compensate for modal dispersion without MIMO processing, all-optical MIMO processing (see Non-Patent Document 1 below) and wavefront compensation using optical phase conjugation (OPC) technology (see Patent Document 1 below: Japanese Patent No. 6202499) have been proposed. Generally, mode coupling is expressed by a unitary matrix U. In all-optical MIMO processing using an optically integrated arbitrary unitary device, the optically integrated arbitrary unitary device is used to convert an optical signal that has propagated through an MMF and has undergone mode coupling into a U -1 Mode coupling is compensated for by converting the phase shifter into the Mach-Zehnder interferometer. As optical integrated arbitrary unitary devices, devices that combine a Mach-Zehnder interferometer with a phase shifter and a multimode interferometer with a phase shifter have been proposed. Both are implemented in a lightwave planar circuit, and modal dispersion can be compensated for by controlling the voltage applied to the phase shifter.

[0005] On the other hand, in wavefront compensation using OPC technology, the wavefront of the optical signal propagating through the MMF from the receiving end to the transmitting end is captured as an image in a computer using a wavefront sensor with an image sensor, and then the wavefront of the signal light to be transmitted is modulated using a spatial light modulator (SLM) to create a wavefront with the sign of the captured wavefront inverted. This operation generates a phase-conjugated signal light, which propagates in the reverse direction from the transmitting end to the receiving end, thereby compensating for mode coupling caused by the MMF. These conventional methods can compensate for mode coupling without converting the optical signal into an electrical signal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6202499 [Non-patent literature]

[0007] [Non-Patent Document 1] A. Annoni, E. Guglielmi, M. Carminati1, G. Ferrari1, M. Sampietro1, DAB Miller, A. Melloni, and F. Morichetti, “Unscrambling light - automatically undoing strong mixing between modes,” Light Sci. Appl. 6, e17110 (2017). Summary of the Invention [Problem to be solved by the invention]

[0008] In conventional techniques, compensation for modal dispersion in mode division multiplexing transmission requires a lot of calculation time and power consumption. Furthermore, conventional optical MIMO processing compensates for modal dispersion in the optical time domain, making it difficult to handle high-speed signals. Furthermore, conventional optical MIMO processing does not easily support transmission paths with large amounts of modal dispersion. The present invention aims to solve, for example, one or more of the above problems. [Means for solving the problem]

[0009] One invention is based on the finding that by measuring the frequency response of the complex amplitude of each mode in mode division multiplexing transmission, information used for modal dispersion compensation, including group delay differences and loss differences between modes in mode division multiplexing transmission, can be obtained.

[0010] The present invention relates to a method for acquiring information for mode dispersion compensation to obtain optical processing conditions for compensating for mode dispersion in mode division multiplexing transmission using a multimode fiber. For the purpose of explanation, it is assumed that the mode division multiplexing transmission includes modes 1 to M (M is an integer). Then, this method includes an optical propagation step, a frequency response measurement step, and a modal dispersion compensation information acquisition step. The optical propagation step is a step for transmitting an optical probe signal from the mode multiplexer for each of the first to Mth modes of mode division multiplexing transmission, and propagating the signal through the multimode fiber. The frequency response measurement step is a step for measuring the frequency response of the complex amplitude of the optical probe signal propagated through the multimode fiber (the frequency response of the complex amplitude of the 1st mode to the Mth mode). The modal dispersion compensation information acquisition process is a process for acquiring modal dispersion compensation information including the group delay difference and loss difference between modes in mode division multiplexing transmission, using the frequency responses of the complex amplitudes of the first to Mth modes. This process involves obtaining a frequency response matrix H that compiles the frequency responses of the complex amplitudes of the first to Mth modes into an M × M matrix. a step of performing singular value decomposition on the frequency response matrix H to obtain a matrix Λ containing functions of the group delay difference and loss difference between modes in mode division multiplexing transmission as elements of a diagonal matrix; Preferably, it contains:

[0011] The next invention relates to a mode division multiplexing transmission method using a multimode fiber, which uses the modal dispersion compensation information obtained by the above method. This method includes a mode multiplexing step, a propagation step, a mode separation step, and a mode dispersion compensation step. The mode multiplexing process is a process for obtaining a mode division multiplexed signal by mode multiplexing an optical signal in a mode multiplexer. The propagation process is the process in which the mode division multiplexed signal propagates through the multimode fiber. The mode separation process is a process for obtaining mode-separated signals by separating the modes of a mode division multiplexed signal propagated through a multimode fiber using a mode separator. The modal dispersion compensation step is a step for performing optical processing based on modal dispersion compensation information on the mode-separated signal to perform modal dispersion compensation.

[0012] The next invention relates to an apparatus 1 for acquiring information for modal dispersion compensation for obtaining optical processing conditions for compensating for modal dispersion in mode division multiplexing transmission using a multimode fiber. This apparatus 1 has a transmission path 3, a frequency response measurement unit 5, and a modal dispersion compensation information acquisition unit 7. This apparatus 1 can be used in a mode division multiplexing transmission system. This system has a propagation unit, a mode separation unit, and a modal dispersion compensation unit. These apparatuses and systems are intended to realize the methods described above. [Effects of the Invention]

[0013] In this invention, for example, the transfer function H, which is the frequency response for each mode of the transmission line, is calculated in advance, and the inverse matrix H of the transfer function is calculated in the optical frequency domain for a signal degraded by mode dispersion. -1 Therefore, according to this invention, modal dispersion compensation by digital MIMO processing is not required, and calculation time and power consumption can be significantly reduced. Furthermore, while conventional optical MIMO processing performs modal dispersion compensation in the optical time domain, the present invention performs modal dispersion compensation in the optical frequency domain, making it possible to handle higher-speed signals. Furthermore, the amount of modal dispersion that can be compensated for by this invention depends greatly on the measurement resolution of the optical spectrum in the transfer function measurement section, the resolution of the spectrometer in the modal dispersion compensation section, and the number of complex amplitude modulators. Therefore, by configuring a system using components with good performance for these parameters, it is possible to accommodate transmission paths with large amounts of modal dispersion. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a conceptual diagram showing an example of the configuration of a system for implementing a modal dispersion compensation method. [Figure 2] FIG. 2 is a flowchart for explaining each step of the method for acquiring information for mode dispersion compensation. [Figure 3] FIG. 3 is a conceptual diagram showing an example of the configuration of the mode dispersion compensator. [Figure 4]FIG. 4 is a flowchart for explaining each step of the mode division multiplexing transmission method. [Figure 5] FIG. 5 is a conceptual diagram showing another example of the configuration of a system for implementing a modal dispersion compensation method. [Figure 6] FIG. 6 is a conceptual diagram showing an example of use of the present invention. [Figure 7] FIG. 7 is a conceptual diagram showing the overall analytical model in the embodiment. [Figure 8] FIG. 8 is a conceptual diagram showing an analytical model of a transmission path in this embodiment. [Figure 9] FIG. 9 is a constellation diagram, instead of a drawing, showing the constellation of a received signal in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes embodiments of the present invention with reference to the drawings. The present invention is not limited to the embodiments described below, and also includes appropriate modifications of the embodiments below within the scope obvious to those skilled in the art.

[0016] Information acquisition for modal dispersion compensation Figure 1 is a conceptual diagram showing an example of the configuration of a system for implementing a modal dispersion compensation method. As shown in Figure 1, this system has multiple light sources corresponding to each mode, multiple modulators corresponding to each light source that modulate the light from each light source, and a signal generation unit that provides modulation signals to the multiple modulators. Furthermore, each of the multiple optical signals appropriately modulated by the modulators is combined with the corresponding probe light. Multiple multiplexing units are also present. The multiplexed light from the multiple light sources and the corresponding probe light are combined in a mode multiplexer to obtain a mode-division multiplexed signal. The mode-division multiplexed signal is transmitted to a mode separator via a transmission line. For each optical signal mode-separated by the mode separator, the corresponding optical complex amplitude is measured using an optical complex amplitude meter. The measurement results are processed to determine the transfer function of the transmission line. In the example shown in Figure 1, an inverse matrix calculation unit calculates information for modal dispersion compensation. The modal dispersion compensation unit performs mode compensation for each mode-separated light based on the obtained information for modal dispersion compensation. The mode-compensated light is received by a receiver. In a system for realizing a modal dispersion compensation method, information for performing modal compensation is obtained, and mode compensation is performed based on the obtained information before transmitting a mode division multiplexed signal.

[0017] 2 is a flowchart for explaining each step of the method for acquiring information for modal dispersion compensation. Each step for acquiring information for modal dispersion compensation will be explained below.

[0018] Optical propagation process The optical propagation step (S101) is a step for transmitting an optical probe signal from the mode multiplexer for each of the first to Mth modes of mode division multiplexing transmission, and propagating the signal through the multimode fiber. In this step, probe light from the light source is input to the transmission line 3 having M propagation modes via the i-th port of the mode multiplexer. In other words, the i-th spatial mode is selectively excited in the transmission line 3. The light source can be a single-pulse light source, a coherent wideband light source such as a supercontinuum light source, or a wavelength-swept laser light source. The transmission line 3 is a multimode fiber (MMF). Multimode fibers (MMF) include few-mode fibers (FMF) with a reduced number of propagation modes, and coupled multicore fibers. Within the transmission line 3, due to modal dispersion, the probe light selectively excited as the i-th mode undergoes energy transfer to each mode, and each mode experiences different group delay and loss.

[0019] Frequency response measurement The frequency response measurement step (S102) is a step for measuring the frequency response of the complex amplitude of the optical probe signal propagated through the multimode fiber (the frequency response of the complex amplitude of the 1st mode to the Mth mode). The optical probe signal propagating through the multimode fiber is separated into each mode using a mode separator. Then, the complex amplitude including the intensity and phase of the probe light that has been subjected to modal dispersion is measured by an optical complex amplitude measurement device after being separated into each mode via the mode separator. In this case, a coherent receiver or an optical spectrum analyzer can be used as the optical complex amplitude measurement device.

[0020] Modal dispersion compensation information acquisition process The mode dispersion compensation information acquisition step (S103) is a step for acquiring mode dispersion compensation information including the differential group delay and differential loss between modes in mode division multiplexing transmission, using the frequency responses of the complex amplitudes of the first to Mth modes. This step preferably includes the steps of: obtaining a frequency response matrix H in which the frequency responses of the complex amplitudes of the first to Mth modes are organized into an M × M matrix; and performing singular value decomposition on the frequency response matrix H to obtain a matrix Λ including functions of the differential group delay and differential loss between modes in mode division multiplexing transmission as elements of a diagonal matrix.

[0021] When a coherent receiver is used as an optical complex amplitude measurement device, what is measured is the impulse response in each mode when an optical signal (e.g., a pulse signal) is input to the i-th mode of the transmission line. For this reason, the frequency response h can be obtained by performing an optical Fourier transform or a digital Fourier transform by dispersing the signal using an optical bandpass filter or the like. 11 (w), h 21 (w),…,h M1 (w) is obtained. On the other hand, when an optical spectrum analyzer is used as an optical complex amplitude measurement device, the frequency response can be obtained without Fourier transform. MM By combining all these frequency responses into an MxM matrix, the transfer function of the MMF shown in equation (1) can be obtained.

[0022]

number

[0023] Furthermore, when the transfer function H(w) is subjected to singular value decomposition, the following equation (2) is obtained.

[0024]

number

[0025] where ω is the angular frequency, U and V are the coupling efficiencies of each mode at the input and output, respectively, α1(ω), α2(ω), …, α M (ω) is the loss of each mode, β1(ω), β2(ω), …, β M (ω) is the propagation constant of each mode, and L is the fiber length of the transmission line. U and V are random unitary matrices. The central diagonal matrix on the right side of equation (2), which is the singular value of H(ω), represents the group delay difference and loss difference between modes. Finally, the inverse matrix calculation unit calculates H(ω), which is the inverse matrix of H(ω). -1In the conventional technology described above, the singular values ​​of H(ω) are not included in the compensation, which causes the problem of not being able to compensate for the differential mode group delay and differential loss. This embodiment is just one example, and the light source and optical complex amplitude measurement device are not limited to any particular form as long as they can obtain the frequency response of the transmission path.

[0026] Modal dispersion compensation FIG. 3 is a conceptual diagram showing an example of the configuration of the modal dispersion compensation unit. This example corresponds to the modal dispersion compensation unit in the device shown in FIG. 1. As shown in FIG. 3, this modal dispersion compensation unit has a spectrometer connected to a mode separator, an optical separator (e.g., a beam splitter) connected to each optical element, an optical complex amplitude modulator connected to the optical separator, and an optical coupler (beam combiner) connected to the optical complex amplitude modulator. A signal based on modal dispersion compensation information (in this example, a signal from the inverse matrix calculation unit) is input to the optical complex amplitude modulator, and appropriate modulation is performed. Each step for performing modal dispersion compensation will be explained below.

[0027] 4 is a flowchart for explaining each step of the mode division multiplexing transmission method. Each step of the mode division multiplexing transmission method will be explained below.

[0028] Mode multiplexing process The mode multiplexing step (S201) is a step for obtaining a mode division multiplexed signal by mode multiplexing an optical signal using a mode multiplexer. The light from the light source is modulated by a modulator to obtain a signal a(t) = (a1(t), a2(t), ..., a M (t)) T The signal is modulated to a frequency and then mode-multiplexed by a mode combiner to obtain a mode-division multiplexed signal.

[0029] Propagation process The propagation step (S202) is a step in which the mode division multiplexed signal propagates through the multimode fiber. The mode division multiplexed signal obtained in the mode multiplexing step is input to the transmission path. In the transmission path 3, each signal is subjected to modal dispersion. In other words, H(ω) acts on each signal. At this time, since H(ω), which is the transfer function of the MMF, is a frequency response, the spectrum A(ω) = (A1(ω), A2(ω), ..., A M (ω)) T The product H(ω)A(ω) is obtained. This transmission path 3 (propagation path) is the transmission path 3 in the device shown in FIG.

[0030] Mode Separation Process The mode separation step (S203) is a step for obtaining mode-separated signals by mode-separating the mode-division multiplexed signals propagated through the multimode fiber using a mode separator. The mode-division multiplexed signals propagated through the multimode fiber are separated into their respective modes by the mode separator (mode separation unit).

[0031] Modal dispersion compensation process The mode dispersion compensation step (S204) is a step for performing optical processing based on the mode dispersion compensation information on the mode-separated signal to perform mode dispersion compensation. After mode dispersion compensation, the mode division multiplexed signal is transmitted. In this way, the mode division multiplexed signal that has undergone mode dispersion compensation can be transmitted. Each mode (each element of H(ω)A(ω)) is incident on the mode dispersion compensation section. In the mode dispersion compensation section shown in Figure 3, the signal is first split into optical frequencies by a spectrometer, and then each mode is branched into M by a beam splitter. A diffraction grating, prism, arrayed waveguide grating (AWG), etc. can be used as the spectrometer. The M × M split and separated signals are then subjected to a complex amplitude modulator to obtain the H(ω) calculated in the transfer function measurement section. -1 After each element of is integrated, the corresponding signals are combined by the beam combiner. In this way, H(ω) -1 H(ω)A(ω). And, H(ω) -1H(ω) is cancelled out, and only A(ω) is obtained. A spatial light modulator or a lithium niobate electro-optic modulator (LN modulator) can be used as a complex amplitude modulator. After that, by passing through the spectrometer again, each optical frequency is added together, and the original signal a(t) = (a1(t), a2(t), ..., a M (t)) T is obtained and received by the receiver. This is just an example, and the spectrometer and complex amplitude modulator are not limited to any particular form as long as they are capable of complex amplitude modulation in the optical frequency domain.

[0032] Another configuration example Figure 5 is a conceptual diagram showing another example of the configuration of a system for implementing a modal dispersion compensation method. In the example shown in Figure 5, M probe beams are individually modulated into known signals such as pseudorandom codes by a modulator. It is preferable to generate the signals so that they are uncorrelated. The modulated probe beams are then simultaneously injected into the transmission path via the respective ports of a mode multiplexer. Similar to the above configuration, each probe beam is subjected to modal dispersion, and H(ω) acts on it. The modal dispersion-affected probe beams are then separated into their respective modes by a mode separator and measured by an optical complex amplitude measurement device. The signals are then converted into digital signals, and modal dispersion is digitally compensated for by a multiple-input, multiple-output (MIMO) processor consisting of a butterfly-type finite impulse response (FIR) filter with M inputs and M outputs. The code determination circuit then determines the coefficients of the FIR filter so that the output of the FIR filter matches the original signal. The determined FIR filter coefficients are the impulse responses in each mode. Therefore, H(ω) can be obtained by Fourier transforming the FIR filter coefficients. In this form, the inverse matrix calculation unit calculates the inverse matrix of H(ω), H(ω) -1 In this configuration, the light source and modulator can be used in common with those used in the modal dispersion compensation process. Also, in this configuration, the modal dispersion compensation process has the same configuration and function as the system shown in Figure 1.

[0033] The transfer function H(ω), which is the frequency response for each mode of the transmission line, is calculated in advance, and the inverse matrix H(ω) of the transfer function is calculated in the optical frequency domain for signals degraded by modal dispersion. -1 Modal dispersion is compensated for by applying the modal dispersion compensation technique. This eliminates the need for modal dispersion compensation using digital multiple-input multiple-output (MIMO) processing, significantly reducing computation time and power consumption. Furthermore, while conventional optical MIMO processing performs modal dispersion compensation in the optical time domain, our method performs modal dispersion compensation in the optical frequency domain, making it possible to handle higher-speed signals. Furthermore, the amount of modal dispersion that can be compensated for using this method is highly dependent on the measurement resolution of the optical spectrum in the transfer function measurement section, the resolution of the spectrometer in the modal dispersion compensation section, and the number of complex amplitude modulators. Therefore, configuring a system using components with good performance for these parameters makes it possible to handle transmission paths with large amounts of modal dispersion.

[0034] Usage example Figure 6 is a conceptual diagram showing an example of the use of this invention. As described above, the present invention can be used for signal compensation in optical submarine cables and terrestrial optical fiber transmission lines using multimode fiber, few-mode fiber, or coupled multicore fiber with multiple propagation modes. Furthermore, since it can also compensate for chromatic dispersion, which is synonymous with modal dispersion when the number of modes is one, it can also be applied to optical fiber transmission lines using conventional single-mode fiber. Furthermore, this invention can also be applied to optical networks. As described above, optical fiber optical networks switch paths using optical signals as they are. In conventional systems, MIMO processing, which requires conversion to digital signals, has problems such as delays due to processing time, losses due to photoelectric conversion, and power consumption. As shown in Figure 6, application of this invention eliminates the need for digital MIMO processing, enabling the realization of a mode-selective optical switch for MMF, FMF, and coupled multicore fiber. [Example]

[0035] The effects of the present invention will be shown below by numerical analysis of form 1. Figure 7 shows an overall analytical model in this embodiment, and Figure 8 shows an analytical model of the transmission line in this embodiment. Table 1 shows analytical parameters.

[0036] Table 1. Analysis parameters in the examples [Table 1]

[0037] The transmission path was assumed to be a three-mode fiber with three propagation modes and modeled using the split-step method as shown in Figure 8. The signal used was a 25 GBaud polarization-multiplexed 16-level quadrature amplitude modulation (DP-16QAM) pseudorandom-coded signal (PRBS). Therefore, the number of propagation modes was six (two polarization modes × three spatial modes). However, the present invention does not limit the number of propagation modes or modulation format. To reduce modal dispersion to some extent, the transmission path was assumed to combine two fibers with negative differential mode group delay and one fiber with positive differential mode group delay. Figure 9 shows the constellation of the received signal. It can be seen from Figure 9 that applying the present invention compensated for modal dispersion, and the signal constellation distribution was clearly distinguishable. Furthermore, there were no received bit errors for these parameters. These results confirm that the present invention can compensate for modal dispersion, including mode coupling, differential mode group delay, and differential mode loss. [Industrial Applicability]

[0038] This invention can be used in the information and communications industry. [Explanation of symbols]

[0039] 1-mode dispersion compensation information acquisition device 3 Transmission Line 5 Frequency response measurement section 7-mode dispersion compensation information acquisition unit

Claims

1. A method for obtaining information for modal dispersion compensation to obtain optical processing conditions for compensating for modal dispersion in mode division multiplexing transmission using a multimode fiber, comprising: the mode division multiplexing transmission includes up to M-th modes (M is an integer of 2 or more), For each of the first to Mth modes of the mode division multiplexing transmission, an optical propagation step of transmitting an optical probe signal from a mode multiplexer and propagating the optical probe signal through the multimode fiber; a frequency response measurement step of measuring a frequency response of the complex amplitude of the optical probe signal propagated through the multimode fiber; and a modal dispersion compensation information acquisition step of acquiring modal dispersion compensation information including a group delay difference and a loss difference between modes in the mode division multiplexing transmission, using frequency responses of complex amplitudes of the first mode to the Mth mode, The modal dispersion compensation information acquisition step includes: obtaining a frequency response matrix H by arranging the frequency responses of the complex amplitudes of the first mode to the Mth mode into an M×M matrix; performing singular value decomposition on the frequency response matrix H to obtain a matrix Λ containing functions of differential group delay and differential loss between modes in the mode division multiplexing transmission as elements of a diagonal matrix; Including, method.

2. A mode division multiplexing transmission method using a multimode fiber, which uses modal dispersion compensation information obtained by the method of claim 1, comprising: a mode multiplexing step of mode-multiplexing an optical signal by the mode multiplexer to obtain a mode division multiplexed signal; a propagation step in which the mode division multiplexed signal propagates through the multimode fiber; a mode separation step of mode-separating the mode division multiplexed signal propagated through the multimode fiber by a mode separator to obtain a mode-separated signal; a mode dispersion compensation step of performing optical processing based on the mode dispersion compensation information on the mode separated signal to perform mode dispersion compensation; A method comprising:

3. An apparatus (1) for acquiring modal dispersion compensation information for obtaining optical processing conditions for compensating for modal dispersion in mode division multiplexing transmission using a multimode fiber, comprising: the mode division multiplexing transmission includes up to M-th modes (M is an integer of 2 or more), For each of the first to Mth modes of the mode division multiplexing transmission, a transmission path (3) for transmitting an optical probe signal from the mode multiplexer and propagating the optical probe signal through the multimode fiber; a frequency response measurement unit (5) that measures the frequency response of the complex amplitude of the optical probe signal propagated through the multimode fiber; a modal dispersion compensation information acquisition unit (7) that acquires modal dispersion compensation information including a group delay difference and a loss difference between modes in the mode division multiplexing transmission using frequency responses of complex amplitudes of the first mode to the Mth mode, The modal dispersion compensation information acquisition unit (7) a frequency response matrix H is obtained by collecting the frequency responses of the complex amplitudes of the first mode to the Mth mode into an M×M matrix, and the frequency response matrix H is subjected to singular value decomposition to obtain a matrix Λ containing functions of the group delay difference and the loss difference between the modes in the mode division multiplexing transmission as elements of a diagonal matrix, thereby obtaining the modal dispersion compensation information; Device.

4. A mode division multiplexing transmission system including the acquisition device (1) for modal dispersion compensation information according to claim 3, The system further comprises a modal dispersion compensator (9) that performs optical processing based on the modal dispersion compensation information on the mode-separated signal to perform modal dispersion compensation.

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