US-20260128794-A1 - OPTICAL TRANSMISSION DEVICE AND OPTICAL TRANSMISSION SYSTEM

US20260128794A1US 20260128794 A1US20260128794 A1US 20260128794A1US-20260128794-A1

Abstract

An optical transmission device is configured to receive and process an optical signal received via an optical transmission line, the optical transmission device including: an output unit configured to output information concerning deviation of an amplitude characteristic of the received optical signal; a tunable optical filter (TOF) configured to filter the received optical signal; a controller configured to control a setting of the TOF based on the information concerning the deviation of the amplitude characteristic.

Inventors

TOMOHIRO NAGANUMA
Naoya Okada
Joji Terashi

Assignees

FUJITSU LIMITED

Dates

Publication Date: 20260507
Application Date: 20251104
Priority Date: 20241105

Claims (11)

1 . An optical transmission device configured to receive and process an optical signal received via an optical transmission line, the optical transmission device comprising: an output unit configured to output information concerning deviation of an amplitude characteristic of the received optical signal; a tunable optical filter (TOF) configured to filter the received optical signal; a controller configured to control a setting of the TOF based on the information concerning the deviation of the amplitude characteristic.
2 . The optical transmission device according to claim 1 , wherein the controller variably controls a center frequency of the TOF, based on information concerning the deviation of the amplitude characteristic.
3 . The optical transmission device according to claim 1 , wherein the controller calculates the deviation of the amplitude characteristic using an output of a waveform monitor for the received optical signal or a compensation coefficient of an adaptive equalization circuit.
4 . The optical transmission device according to claim 1 , wherein the controller compares an absolute value of the deviation of the amplitude characteristic with a threshold value, and controls the setting of the TOF in a direction so that the absolute value of the deviation of the amplitude characteristic decreases, when the absolute value of the deviation of the amplitude characteristic is greater than the threshold value.
5 . The optical transmission device according to claim 1 , wherein the controller selects whether to change the setting of the TOF for a predetermined signal type that includes at least one of a baud rate and a multilevel degree which are parameters of a plurality of signal types of the received optical signal.
6 . The optical transmission device according to claim 1 , wherein the controller sets a center frequency of the TOF to a value different from a center frequency of a signal band of the received optical signal.
7 . The optical transmission device according to claim 1 , further comprising an optical amplifier configured to optically amplify the received optical signal, wherein the information concerning the deviation of the amplitude characteristic is information concerning the deviation of the amplitude characteristic after optical amplification.
8 . The optical transmission device according to claim 1 , wherein the TOF has a bandpass optical filter characteristic.
9 . An optical transmission system, comprising: a first optical transmission device configured to transmit an optical transmission signal to an optical transmission line; and a second optical transmission device configured to receive an optical reception signal via the optical transmission line, wherein the first optical transmission device transmits the optical transmission signal, and the second optical transmission device includes: an output unit configured to output information concerning deviation of an amplitude characteristic of the optical reception signal; a first tunable optical filter (TOF) configured to filter the optical reception signal; a first controller configured to control setting of the first TOF based on the information concerning the deviation of the amplitude characteristic.
10 . The optical transmission system according to claim 9 , wherein the output unit transmits the information concerning the deviation of the amplitude characteristic to the first optical transmission device, and the first optical transmission device includes: a second TOF configured to filter the optical transmission signal; a second controller configured to control the setting of the second TOF based on the received information concerning the deviation of the amplitude characteristic.
11 . An optical transmission system, comprising: a first optical transmission device configured to transmit an optical transmission signal to an optical transmission line; and a second optical transmission device configured to receive an optical reception signal via the optical transmission line, wherein the first optical transmission device includes: a TOF configured to filter the optical transmission signal; a controller configured to control setting of the TOF based on information concerning a deviation of an amplitude characteristic, and the second optical transmission device includes an output unit configured to output the information concerning the deviation of the amplitude characteristic to the first optical transmission device.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2024-193774, filed on Nov. 5, 2024, the entire contents of which are incorporated herein by reference. FIELD The embodiments discussed herein are related to an optical transmission device and an optical transmission system. BACKGROUND Optical amplifiers are used in recent optical transmission systems. An optical amplifier is provided, for example, in a reconfigurable optical add/drop multiplexer (ROADM) or the like on a transmission path, or is provided in an optical transceiver to amplify transmission/reception optical power. By using an optical amplifier, the number of electrical repeaters that are conventionally used may be reduced, whereby reductions in the cost and power of the system may be realized. One method for realizing increases in the capacity of an optical communication system is to increase the capacity per wave of an optical signal. The transmission capacity per wave is related to the baud rate of the optical signal. By increasing the baud rate, the transmission capacity may be increased without changing the reception sensitivity. On the other hand, problems arise such as stricter requirements for the band characteristics of the transmitting and receiving devices and increased in power consumption of the optical transmission device. One prior art involves adjusting an optical channel spectrum by varying the frequency of an optical filter based on the bit error rate (BER) to reduce the influence of asymmetric filtering. In addition, there is a technique for correcting variations in characteristics of a balanced receiver by controlling the amplitude and delay of an optical signal. In addition, there is a technique in which distortion is reduced by a compensation signal obtained by using a filtering operation to thereby extract a pilot tone included in a received signal. Another technique mitigates the effects of frequency dependent imbalances between the IQ subchannels of receiver channels and recovers data based on pre-stored calibration data. In addition, there is a technology in which a loss difference of an optical signal for each wavelength generated in a wavelength multiplexed signal is compensated by a loss compensator. For example, refer to Published Japanese-Translation of PCT Application, Publication No. 2022-519282, Japanese Laid-Open Patent Publication No. 2008-219765, U.S. Patent Application Publication No. 2014/0286642, U.S. Patent Application Publication No. 2012/0057863, and Japanese Laid-Open Patent Publication No. H11-275020. SUMMARY According to an aspect of an embodiment, an optical transmission device is configured to receive and process an optical signal received via an optical transmission line, the optical transmission device including: an output unit configured to output information concerning deviation of an amplitude characteristic of the received optical signal; a tunable optical filter (TOF) configured to filter the received optical signal; a controller configured to control a setting of the TOF based on the information concerning the deviation of the amplitude characteristic. An object and advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the disclosure. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram depicting an optical transmission device according to a first embodiment. FIG. 2 is a graph depicting an example of amplification characteristics of an optical amplifier. FIG. 3A is an explanatory diagram of deviation of amplitude characteristics for each baud rate. FIG. 3B is an explanatory diagram of deviation of amplitude characteristics for each baud rate. FIG. 4 is a diagram depicting an example of internal functions of a DSP according to the first embodiment. FIG. 5 is an explanatory diagram of control of tilt in signal band by changing a center frequency of a TOF. FIG. 6 is a graph depicting an example of frequency characteristics of a compensation coefficient of an adaptive equalization circuit. FIG. 7A is an explanatory diagram of an example of calculating tilt in the signal band from a tap number. FIG. 7B is an explanatory diagram of an example of calculating tilt in the signal band from a tap number. FIG. 8 is a flowchart depicting a control example of the optical transmission device according to the first embodiment. FIG. 9 is a table depicting a setting example of whether to perform control for a signal type. FIG. 10 is a diagram depicting an optical transmission system according to a second embodiment. DESCRIPTION OF EMBODIMENTS First, problems associated with the conventional techniques are discussed. For example, as the baud rate of the optical signal