Fault tolerant fiber optic transmission system

• US 5,278,688 A
• Filed: 10/18/1991
• Issued: 01/11/1994
• Est. Priority Date: 04/24/1990
• Status: Expired due to Term

• Current Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Original Assignee: Ortel Corporation (Emcore Corporation)
• Inventors: Blauvelt, Henry A., Ury, Israel
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US07/781,072
• Time in Patent Office: 816 Days
• Field of Search: 359/127, 359/133, 359/110, 359/111, 359/162, 359/164, 359/173, 359/124, 359/125, 359/188, 359/132, 385/31
• US Class Current: 398/91
• CPC Class Codes: H04B 10/032 using working and protection systems H04J14/0287 takes precedence
• CPC Class Codes: H04J 14/0279 WDM point-to-point architectures
• CPC Class Codes: H04J 14/0294 Dedicated protection at the optical channel (1+1)

Abstract

A fault tolerant fiber optic system has a plurality of lasers modulated by the same signal source. The signals from the lasers are conveyed to an optical coupler by single mode optical fibers. The signals from all of the lasers are mixed in the optical coupler, producing an output signal which is an average of the input signals from the lasers. The optical coupler has a plurality of output single mode fibers which can transmit the averaged signal to a number of optical receivers. By optically combining the signals in phase with each other, the failure of any laser decreases signal strength, but does not disable the system. Surprisingly, the averaging also has the capability of improving the carrier to noise and carrier to distortion ratios for the system, since noise and distortion from the lasers are not correlated and are diminished by a factor of N where N is the number of lasers.

Claims

1. A fault tolerant fiberoptic system comprising:

first means for producing a first optical signal on a first signal mode optical fiber;

second means for producing a second optical signal on a second single mode optical fiber;

input means coupled to the first and second means for modulating the first and second means for producing first and second optical signals with the same amplitude modulated signal;

coupler means connected to the fibers for mixing the first and second optical signals;

a plurality of single mode optical fiber outputs from the coupler means for transmitting an optical signal on each of the optical fiber outputs which is an average of the first and second optical signals.

2. A fiberoptic system as recited in claim 1 wherein the means for producing optical signals each comprise a semiconductor laser.

3. A fiberoptic system as recited in claim 1 wherein the means for producing optical signals each comprise a laser and wherein the wavelength of each laser is sufficiently different from the wavelength of each other laser that the frequency difference between the lasers does not lie within the bandwidth of the signal.

4. A fault tolerant fiberoptic system comprising:

a first modulated input light source having a first optical fiber output for transmitting a single mode optical signal;

a second modulated input light source having a second optical fiber output for transmitting a single mode optical signal;

input means for modulating both of the light sources with the same signal;

an optical coupler having as parallel inputs the first and second optical fibers, the signal paths from the means for modulating through the light sources to the optical coupler having similar phase delays so that the modulated signals from the two light sources are in phase with each other at the input to the optical coupler; and

at least one single mode output optical fiber from the optical coupler, each such output fiber having single mode signals which is an average of the signals from the first and second optical fibers.

5. A fiberoptic system as recited in claim 4 wherein the light sources each comprise a semiconductor laser.

6. A fiberoptic system as recited in claim 4 wherein the light sources each comprise a laser and wherein the wavelength of each laser is sufficiently different from the wavelength of each other laser that the frequency difference between the lasers does not lie within the bandwidth of the signal.

7. A fiberoptic system as recited in claim 4 comprising a plurality of single mode output optical fibers.

8. A fault tolerant fiberoptic system comprising:

a first light source having a first modulated single mode optical signal output;

a second light source having a second single mode optical modulated signal output;

input means for modulating both of the light sources with the same signal;

an optical coupler;

a first single mode optical fiber connecting the first light source to a first input to the optical coupler;

a second single mode optical fiber connecting the second light source to a second input to the optical coupler, the first and second optical fibers each having a length such that the second optical signal is in phase with the first optical signal; and

a plurality of output single mode optical fibers connected to the optical coupler for transmitting signals combined from the first and second optical fibers.

9. A fiberoptic system as recited in claim 8 wherein the light sources each comprise a semiconductor laser.

10. A fiberoptic system as recited in claim 8 wherein the light sources each comprise a laser and wherein the wavelength of each laser is sufficiently different from the wavelength of each other laser that the frequency difference between the lasers does not lie within the bandwidth of the signal.

11. A fault tolerant fiberoptic system comprising:

a plurality of light sources;

means for modulating all of the light sources with the same signal;

an optical coupler;

a single mode input optical fiber connected between the output of each of the light sources and an input of the optical coupler, each of the input optical fibers having a length such that the optical signals in all of the fibers are in phase with each other at the input to the optical coupler; and

a plurality of single mode output optical fibers connected to outputs of the optical coupler for transmitting signals which is an average of the signals from the plurality of input optical fibers.

12. A fiberoptic system as recited in claim 11 wherein the light sources each comprise a semiconductor laser.

13. A fiberoptic system as recited in claim 11 wherein the light sources each comprise a laser and wherein the wavelength of each laser is sufficiently different from the wavelength of each other laser that the frequency difference between the lasers does not lie within the bandwidth of the signal.

14. A method for minimizing modulator noise and distortion in a fiberoptic system comprising the steps of:

introducing a first modulated optical signal into a first single mode optical fiber;

introducing a second modulated optical signal into a second single mode optical fiber, the modulation of the second optical signal being the same as the first optical signal;

optically combining the first and second modulated signals with the two modulations being in phase with each other; and

extracting a plurality of modulated single mode optical signals, each of the extracted signals being an average of of the first and second modulated signals.

15. A method as recited in claim 14 wherein each optical fiber has a length sufficient for delivering the signals in phase.

16. A method as recited in claim 14 wherein the difference in frequency between the light sources does not lie within the bandwidth of the signal.

17. A method for minimizing modulator noise and distortion in a fiberoptic system comprising the steps of:

producing the same modulated optical signal on each of at least two single mode optical fibers;

feeding the modulated signals into an optical coupler in phase with each other for mixing of the two modulated signals; and

transmitting a signal from the coupler on each of a plurality of single mode optical fibers, the signal on each of the fibers from the coupler being an average of the two modulated signals.

18. A method as recited in claim 17 wherein each optical signal is produced by a laser modulated by a single signal source and comprising the step of adjusting the optical signal path length so that the signals are in phase with each other.