Pump laser control circuit for an optical transmission system

• US 5,343,320 A
• Filed: 08/03/1992
• Issued: 08/30/1994
• Est. Priority Date: 08/03/1992
• Status: Expired due to Term

• Current Assignee: AT&T Submarine Systems, Inc. (Johnson Controls International plc)
• Original Assignee: AT&T, Inc.
• Inventors: Anderson, Cleo D.
• Primary Examiner(s): HSU, ALPUS
• Application Number:
  US07/926,629
• Time in Patent Office: 757 Days
• Field of Search: 359/134, 359/160, 359/173, 359/174, 359/176, 359/177, 359/341, 359/345, 359/179, 359/159, 372/6, 372/70, 372/72, 372/29, 372/30, 385/142
• US Class Current: 398/157
• CPC Class Codes: H04B 10/077 using a supervisory or additional signal
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04B 10/291 in which processing or amplification is carried out without conversion of the main signal from optical form
• CPC Class Codes: H04B 10/2912 characterised by the medium used for amplification or processing
• CPC Class Codes: H04B 10/2939 Network aspects
• CPC Class Codes: H04B 10/298 Two-way repeaters, i.e. repeaters amplifying separate upward and downward lines

Abstract

An optical transmission system, especially useful in undersea applications, includes an optical path between two terminals with one or more repeaters located between the terminals for amplifying optical communications signals flowing in the optical path. The repeaters contain optical fiber amplifiers driven by pump lasers. The average optical power produced by the pump lasers is controlled in proportion to the magnitude of electrical line current produced by a controllable constant current source located in one of the terminals. This is achieved by regulator circuits which are responsive to a signal related to the magnitude of the line current and signals related to the actual optical output of the pump lasers. The magnitude of the line current may be conveniently set at the terminals so that the lowest bit error rate is achieved in the transmission system. Alternatively, the magnitude of the line current may also be set to at some minimum level to achieve an acceptable bit error rate and low pump laser and fiber amplifier aging.

Claims

1. An optical transmission system, comprising:

a controllable line current source for producing a substantially constant current of a predetermined magnitude;

an optical fiber amplifier which amplifies optical communications signals carried by the transmission system;

a circuit responsive to the magnitude of the line current comprising a pump laser for controlling the gain of the fiber amplifier in substantial proportion to the predetermined magnitude of the constant current in which the pump laser produces an optical power output which is directed to a section of doped fiber in the optical fiber amplifier;

the circuit controlling the gain of the fiber amplifier further comprising;

a current reference circuit which produces a current signal having a magnitude proportional to the magnitude of the constant current;

a circuit for producing a current signal having a magnitude representing the magnitude of the optical power output produced by the pump laser; and

a regulator for controlling the optical power output of the laser in accordance with any difference between the magnitude of the current signals produced by the current reference circuit and the circuit for producing a current signal representing the magnitude of the optical power output of the pump laser.

2. The transmission system of claim 1, in which the circuit for producing a current signal having a magnitude representing the magnitude of the optical power output of the pump laser comprises a monitor diode responsive to the optical power output of the pump laser.

3. The transmission system of claim 1, further comprising:

a summing junction producing an output signal related to the difference between the magnitudes of the current reference signal and the current signal representing the magnitude of the optical power output of the pump laser;

an amplifier for increasing the magnitude of the output signal from the summing junction;

a shunt regulator responsive to the increased magnitude output signal from the summing junction which controls drive current to the pump laser.

4. An optical underwater transmission system, comprising:

first and second shore terminals;

a first optical path for carrying optical communications signals from the first shore terminal to the second shore terminal;

a second optical path for carrying optical communications signals from the second shore terminal to the first shore terminal;

a plurality of repeaters spaced at predetermined distances along the first and second optical paths in which each repeater includes a fiber amplifier for amplifying the optical communications signals in those paths;

a constant current source in one of the first and second shore terminals for providing substantially constant electrical current of a predetermined magnitude for the repeaters;

a pump laser in each of the repeaters for producing optical power which causes the fiber amplifiers to amplify the optical communications signals;

a means for controlling the average optical power produced by the pump lasers in the plurality of repeaters in response to the magnitude of the constant current;

the means for controlling the average optical power comprising

a regulator for causing some or all of the constant current to flow through the pump laser; and

a circuit responsive to the magnitude of the constant current and the optical power output of the pump laser for controlling the regulator to cause an amount of the constant current to flow through the pump laser such that the optical power produced by the pump laser is a desired amount proportional to the magnitude of the line current.