Method for measuring optical characteristics and system thereof

Abstract

During initial start-up of an optical communication system, an ASE reference span loss is calculated based on transmitting power and received power of ASE light generated by an optical amplifier, and an OSC reference span loss is calculated based on the transmitting power and the received power of OSC light. During normal operation of the optical communication system, a span loss is calculated using the OSC light, and an amount of change in the span loss representing a difference between the span loss and the OSC reference span loss is calculated. A current span loss between a transmitting station and a receiving station is calculated by adding the amount of change in the span loss to the ASE reference span loss.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a wavelength characteristic of an optical fiber;

FIG. 2 is a diagram showing a configuration of a transmitting station and a receiving station;

FIG. 3 is a diagram schematically showing a procedure for measuring a span loss;

FIGS. 4A and 4B are diagrams showing a method for measuring a span loss between the transmitting station and the receiving station;

FIG. 5 is a diagram exemplifying generation of the ASE light;

FIG. 6 is a diagram showing an allocation of ASE light and OSC light;

FIGS. 7A and 7B are diagrams showing another method for measuring a span loss;

FIGS. 8A and 8B are diagrams showing a method for measuring optical receiving power in the receiving station;

FIGS. 9A and 9B are diagrams showing a method for measuring receiving power in the receiving station in the case where an optical amplifier in the transmitting station is operated under an automatic gain control; and

FIGS. 10A and 10B are diagrams showing a measurement method in the case of a different arrangement of photo detectors.

Claims

1. A measurement system which measures, in an optical communication system for transmitting WDM light in a predetermined signal wavelength band from a transmitting station to a receiving station, a span loss between the transmitting station and the receiving station, comprising: a reference light generation unit, provided in the transmitting station, for generating reference light having a wavelength component in the signal wavelength band;a first photo detector, provided in the transmitting station, for detecting the optical power of the signal wavelength band;a second photo detector, provided in the receiving station, for detecting the optical power of the signal wavelength band;a third photo detector, provided in the transmitting station, for detecting the optical power of control light having a wavelength which is allocated out of the signal wavelength band;a fourth photo detector, provided in the receiving station, for detecting the optical power of the control light;a first calculation unit for calculating a reference span loss from results detected by said first and second photo detectors when the reference light is being generated;a second calculation unit for calculating correction data from results detected by said third and fourth photo detectors; anda third calculation unit for calculating a span loss in the signal wavelength band by correcting the reference span loss using the correction data.

2. The measurement system according to claim 1, wherein said second calculation unit outputs, as the correction data, a difference between a first correction value determined during initial start-up of the optical communication system and a second communication correction value determined during operation of the optical communication system.

3. The measurement system according to claim 1, wherein, said reference light generation unit is an optical amplifier for amplifying an optical signal to be transmitted to the receiving station, andthe reference light is ASE light which is an output from the optical amplifier.

4. The measurement system according to claim 3, wherein the reference light is the ASE light generated by supplying pump light when no optical signal is inputted to the optical amplifier.

5. The measurement system according to claim 3, wherein said reference light generation unit comprises an optical filter transmitting a wavelength component in the signal wavelength band, andthe reference light is obtained by extracting a wavelength component in the signal wavelength band from the ASE light using the optical filter.

6. The measurement system according to claim 1, wherein said reference light generation unit comprises: a light source for generating an optical signal having a predetermined wavelength in the signal wavelength band; andan optical device for guiding the optical signal generated by the light source to a transmission line between the transmitting station and receiving station.

7. The measurement system according to claim 1, wherein, said first and second photo detectors are placed at a position where they detect the optical power of an optical signal including the control light, andthe control light is stopped when said first and second photo detectors detect the optical power in order for said first calculation unit to calculate the reference span loss.

8. A measurement system which measures, in an optical communication system for transmitting WDM light in a predetermined signal wavelength band from a transmitting station to a receiving station, optical received power in the receiving station, comprising: a reference light generation unit, provided in the transmitting station, for generating reference light having a wavelength component in the signal wavelength band;a first photo detector, provided in the receiving station, for detecting the optical power of the signal wavelength band;a second photo detector, provided in the transmitting station, for detecting the optical power of control light having a wavelength which is allocated out of the signal wavelength band;a third photo detector, provided in the receiving station, for detecting the optical power of the control light;a first detection unit for detecting reference received power from a result detected by said first photo detector while the reference light is being generated;a first calculation unit for calculating a first correction data from results detected by said second and third photo detectors; anda second calculation unit for calculating optical received power in the signal wavelength band by correcting the reference received power using the first correction data.

9. The measurement system according to claim 8, further comprising: a second detecting unit for detecting an optical loss between an add-drop multiplexer provided in the transmitting station and an optical amplifier for amplifying an optical signal to be transmitted to the receiving station with a constant gain; anda third calculation unit for calculating second correction data representing a difference between an optical loss determined by said second detection unit during initial start-up of the optical communication system and an optical loss determined by said second detection unit during operation of the optical communication system, wherein,said second calculation unit calculates the optical received power in the signal wavelength band by correcting the reference received power using the first and second correction data.

10. A method for measuring, in an optical communication system for transmitting WDM light in a predetermined signal wavelength band from a transmitting station to a receiving station, a span loss between the transmitting station to the receiving station, comprising: transmitting reference light having a wavelength component in the signal wavelength band from the transmitting station to the receiving station;detecting optical power of the reference light using a first photo detector provided in the transmitting station;detecting optical power of the reference light using a second photo detector provided in the receiving station;calculating a reference span loss from results detected by the first and second photo detectors;detecting optical power of control light having a wavelength which is allocated out of the signal wavelength band using a third photo detector provided in the transmitting station;detecting optical power of the control light using a fourth photo detector provided in the receiving station;calculating correction data from results detected by the third and fourth photo detectors; andcalculating a span loss in the signal wavelength band by correcting the reference span loss using the correction data.