EP-4738727-A1 - OPTICAL RECEIVER, OPTICAL TRANSMITTER, AND OPTICAL COMMUNICATION FAULT MONITORING METHOD

Abstract

One aspect of the present invention provides an optical reception device including a monitoring unit configured to: optimize a polarization state by rotating each of a reference signal received in such a way as to be close to a reception signal and the reception signal; compute a power profile for each polarization for the signal with the optimized polarization state; and compute a power difference between the polarizations from the power profile for each polarization, and identify an occurrence position and a value of a polarization-dependent impairment from an occurrence position and a difference amount of the computed difference.

Inventors

• TAKAHASHI MINAMI
• SASAI TAKEO
• YAMAZAKI ETSUSHI
• KISAKA YOSHIAKI

Assignees

• NTT, Inc.

Dates

Publication Date

20260506

Application Date

20230630

Claims (4)

1. An optical reception device comprising a monitoring unit configured to: optimize a polarization state by rotating each of a reference signal received in such a way as to be close to a reception signal and the reception signal; compute a power profile for each polarization for the signal with the optimized polarization state; and compute a power difference between the polarizations from the power profile for each polarization, and identify an occurrence position and a value of a polarization-dependent impairment from an occurrence position and a difference amount of the computed power difference.
2. An optical transmission device comprising a polarization state optimization unit that optimizes a polarization state for an optical transmission signal, wherein the polarization state optimization unit acquires the polarization state in a vicinity where a difference between polarizations becomes large by feedback from a reception side, causes changes back and forth with reference to the acquired polarization state, sets a change amount as a maximum value when the change amount falls below a lower limit threshold, and optimizes the polarization state.
3. A method of monitoring impairments in optical communication, the method comprising: by a polarization-multiplexed optical reception device, optimizing a polarization state by rotating a reference signal received in such a way as to be close to a reception signal; computing a power profile for each polarization for the signal with the optimized polarization state; and computing a power difference between the polarizations from the power profile for each polarization, and identifies an occurrence position and a value of an impairment related to optical communication from an occurrence position and a difference amount of the computed power difference.
4. The method of monitoring impairments in optical communication according to claim 3, comprising: optimizing the polarization state; estimating a perturbation term using the optimized signal and a signal that is an estimated linear solution; and computing a power profile for each polarization using the estimated perturbation term.

Description

TECHNICAL FIELD The present invention relates to a technology of an optical reception device, an optical transmission device, and a method of monitoring impairments in optical communication. BACKGROUND ART Polarization-dependent impairments such as polarization-dependent loss (PDL) and polarization mode dispersion (PMD) are one of major limiting factors that lower signal quality in polarization-multiplexed digital coherent systems required for high capacity and long range transmission (see, for example, Non Patent Literature 1). The polarization mode dispersion is mode dispersion in which light propagating in two different polarization modes along a waveguide changes in speed in these modes due to external factors such as defects, temperature, and stress unique to the waveguide. In a case where high PMD locally exists in a transmission link such as laid fiber, a transmission rate of the system for correct operation is limited. Therefore, in order to maintain a secure network, a reliable technology for detecting and measuring the position of PMD is important. Polarization-dependent loss is defined as a ratio of maximum output power to minimum output power for all polarization states, and is loss that appears in various link components such as a fiber coupler, a wavelength selective switch (WSS), and an erbium-doped fiber amplifier (EDFA). In general, the polarization state of an optical signal is not temporally maintained along the fiber, and thus polarization angles between the polarization state of the optical signal and various devices are formed in random directions. Therefore, the PDL behaves as probabilistically varying loss, resulting in a probabilistic variation in system performance. For this reason, it is necessary to design a margin assuming the worst case in order to secure reliability during operation life and avoid a system stop. The accumulated margin of individual PDL components increases ambiguity in signal quality estimation and limits the transmission rate. By accurately monitoring distributed PDLs that randomly and simultaneously occur in multiple span links, it is possible to avoid the worst case design and maximize the transmission rate. Citation List Non Patent Document Non Patent Document 1: Takeo Sasai, Masanori Nakamura, et al., "0.77-dB Anomaly Loss Localization Based on DSP-Based Fiber-Longitudinal Power Estimation Using Linear Least", 2023 Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA, 2023, W1H.4 SUMMARY OF INVENTION Technical Problem However, since power and dispersion that depend on polarization are impairments that require analysis for each polarization and have a property of depending on the polarization state, statistical processing and control of the polarization state are required, and this makes measurement difficult. Furthermore, it has been difficult to accurately acquire the true value and the position of a loss only by reception-side signal processing without using a dedicated measuring instrument. In view of the above circumstances, an object of the present invention is to provide a technology capable of estimating loss and mode dispersion that depend on polarization in components in an optical transmission link. Solution to Problem One aspect of the present invention provides an optical reception device including a monitoring unit configured to: optimize a polarization state by rotating each of a reference signal received in such a way as to be close to a reception signal and the reception signal; compute a power profile for each polarization for the signal with the optimized polarization state; and compute a power difference between the polarizations from the power profile for each polarization, and identify an occurrence position and a value of a polarization-dependent impairment from an occurrence position and a difference amount of the computed power difference. One aspect of the present invention provides an optical transmission device including: a polarization state optimization unit that optimizes a polarization state for an optical transmission signal, in which the polarization state optimization unit acquires the polarization state in a vicinity where a difference between polarizations becomes large by feedback from a reception side, causes changes back and forth with reference to the acquired polarization state, sets a change amount as a maximum value when the change amount falls below a lower limit threshold, and optimizes the polarization state. One aspect of the present invention provides a method of monitoring impairments in optical communication, the method including: by a polarization-multiplexed optical reception device, optimizing a polarization state by rotating a reference signal received in such a way as to be close to a reception signal; computing a power profile for each polarization for the signal with the optimized polarization state; and computing a power difference between the polarizations from the powe