Optical transmission system, optical transmission apparatus and wavelength spacing measurement apparatus

Patent metadata

Field	Value
Publication number	US-9698905-B2
Application number	US-201514712195-A
Country	US
Kind code	B2
Filing date	May 14, 2015
Priority date	Jun 25, 2014
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

An optical transmission system includes comprising: a first optical transmission apparatus to transmit wavelength-multiplexed optical signals; and a second optical transmission apparatus to receive the wavelength-multiplexed optical signals, the second optical transmission apparatus including: a receiver to perform digital coherent reception; a wavelength spacing monitor to transform a reception signal obtained by the digital coherent reception from a time domain signal to a frequency domain spectrum signal, and to monitor wavelength spacing of the spectrum signal; and a transmitter to transmit, to the first optical transmission apparatus, wavelength control information according to a monitor result obtained by the wavelength spacing monitor or the monitor result, wherein the first optical transmission apparatus includes: a receiver to receive the wavelength control information or the monitor result; and a control unit to control the wavelength spacing based on the wavelength control information or the monitor result received by the receiver.

First claim

What is claimed is:

1. An optical transmission system comprising:
a first optical transmission apparatus configured to transmit wavelength-multiplexed optical signals; and
a second optical transmission apparatus configured to receive the wavelength-multiplexed optical signals, the second optical transmission apparatus comprising:
a receiver configured to perform digital coherent reception of the wavelength-multiplexed optical signals;
a wavelength spacing monitor configured to transform a reception signal obtained by the digital coherent reception from a time domain signal to a frequency domain spectrum signal, and to monitor wavelength spacing of the wavelength-multiplexed optical signals transformed to the spectrum signal; and
a transmitter configured to transmit, to the first optical transmission apparatus, wavelength control information according to a monitor result obtained by the wavelength spacing monitor or the monitor result,

wherein the first optical transmission apparatus comprises:
a receiver configured to receive the wavelength control information or the monitor result; and
a processor configured to control the wavelength spacing of the wavelength-multiplexed optical signals based on the wavelength control information or the monitor result received by the receiver,

wherein the wavelength spacing monitor detects the wavelength spacing by comparing power of the spectrum signal with a specific power value and detects, as the wavelength spacing, spacing having a largest distance between frequencies at which the power exceeds the specific power value.

2. The optical transmission system according to claim 1 , wherein the wavelength spacing monitor detects a direct current level of the power of the spectrum signal, and sets the specific power value at a power level obtained by subtracting a predetermined power value from the direct current level.

3. The optical transmission system according to claim 1 , wherein the wavelength spacing monitor varies the specific power value, calculates the distance between frequencies obtained based on each of the varied specific power values, and detects the largest distance among the calculated distances as the wavelength spacing.

4. The optical transmission system according to claim 1 ,
wherein the wavelength spacing monitor:
detects, by comparing power of the spectrum signal with the specific power value, an edge frequency of a signal component corresponding to a first wavelength equivalent to a spectrum whose center frequency is a frequency corresponding to a wavelength of a local light source used for the digital coherent reception, the first wavelength being contained in the spectrum signal; and
detects wavelength spacing between the first wavelength and a second wavelength adjacent to the first wavelength, based on data indicating a relationship between the wavelength spacing to be detected and a power of the spectrum signal at a frequency shifted by a predetermined frequency offset from the edge frequency toward the second wavelength.

5. The optical transmission system according to claim 1 ,
wherein the wavelength spacing monitor:
detects, by comparing power of the spectrum signal with the specific power value, a center frequency of a signal component corresponding to a first wavelength equivalent to a spectrum whose center frequency is a frequency corresponding to a wavelength of a local light source used for the digital coherent reception, the first wavelength being contained in the spectrum signal;
detects a ratio between power of the spectrum signal at a frequency shifted from the center frequency toward a second wavelength adjacent to the first wavelength by a first frequency offset, and power of the spectrum signal at a frequency shifted from the center frequency toward the second wavelength by a second frequency offset which is larger than the first frequency offset; and
detects the wavelength spacing between the first and second wavelengths based on data indicating a relationship between the ratio and the wavelength spacing to be detected.

6. The optical transmission system according to claim 1 , wherein the spectrum signal is a signal obtained by performing a fast-Fourier transform on the reception signal obtained by the digital coherent reception.

7. The optical transmission system according to claim 1 , wherein the spectrum signal is a signal obtained by: performing a fast-Fourier transform on the reception signal obtained by the digital coherent reception; and then performing a moving average on the fast-Fourier-transformed signal.

8. The optical transmission system according to claim 1 ,
wherein the transmitter performs frequency modulation to superimpose the wavelength control information or the monitor result onto a transmission optical signal to be transmitted to the first optical transmission apparatus, and
wherein the receiver of the first optical transmission apparatus performs frequency demodulation on the transmission optical signal to detect the superimposed wavelength control information or monitor result.

9. The optical transmission system according to claim 1 , wherein the processor controls the wavelength spacing to have a constant spacing by: setting, as a reference wavelength, one of a plurality of wavelengths contained in the wavelength-multiplexed optical signals; and controlling another of the plurality of wavelengths.

10. An optical transmission apparatus comprising:
a receiver configured to perform digital coherent reception of wavelength-multiplexed optical signals;
a wavelength spacing monitor configured to transform a reception signal obtained by the digital coherent reception from a time domain signal to a frequency domain spectrum signal, and to monitor wavelength spacing of the wavelength-multiplexed optical signals transformed to the spectrum signal; and
a transmitter configured to transmit, to another optical transmission apparatus, wavelength control information according to a monitor result obtained by the wavelength spacing monitor or the monitor result,
wherein the wavelength spacing monitor detects the wavelength spacing by comparing power of the spectrum signal with a specific power value and detects, as the wavelength spacing, spacing having a largest distance between frequencies at which the power exceeds the specific power value.

11. The optical transmission apparatus according to claim 10 ,
wherein the receiver is configured to receive the wavelength control information or the monitor result transmitted from another optical transmission apparatus, and
wherein the optical transmission apparatus further comprises a processor configured to control the wavelength spacing of the wavelength-multiplexed optical signals based on the wavelength control information the monitor result received by the receiver.

12. A wavelength spacing measurement apparatus comprising:
a receiver configured to perform digital coherent reception of wavelength-multiplexed optical signals; and
a wavelength spacing monitor configured to transform a reception signal obtained by the digital coherent reception from a time domain signal to a frequency domain spectrum signal, and to monitor wavelength spacing of the wavelength-multiplexed optical signals transformed to the spectrum signal,
wherein the wavelength spacing monitor detects the wavelength spacing by comparing power of the spectrum signal with a specific power value and detects, as the wavelength spacing, spacing having a largest distance between frequencies at which the power exceeds the specific power value.

Assignees

• Fujitsu Ltd

Inventors

• Saito Taku
• Komaki Kosuke
• Endo Taketo

Classifications

• H04B10/0799

  Monitoring line transmitter or line receiver equipment · CPC title

• H04B10/0779

  Monitoring line transmitter or line receiver equipment · CPC title

• H04B10/07957 Primary

  Monitoring or measuring wavelength · CPC title

• H04B2210/074

  using a superposed, over-modulated signal · CPC title

• H04J14/0256

  at the optical channel layer · CPC title