Systems and methods for optical modulation index calibration in a CATV network

1. An active splitter comprising:

a unit operating as a splitter in a forward direction and an active combiner in a reverse direction, the combiner having a plurality of inputs that each receive an upstream optical signal from a respective optical network unit (ONU) and combines them to create a combined electrical signal at an output;

a transmitter that receives the combined electrical signal and converts the combined signal to a reverse path optical signal, the transmitter adjusting at least one of power output and gain to maintain a constant ratio between optical modulation index at the output and optical modulation index at an input,

wherein the active splitter has a first gain setting optimized for optical network units (ONUs) transmitting a first reverse spectrum and a second gain setting optimized for ONUs transmitting a reverse spectrum limited to an amount less than the first reverse spectrum,

wherein the active splitter is configured for transmitting the first reverse spectrum; and

a multiplexer that multiplexes the reverse path optical signal with a forward path optical signal.

2. The active splitter of claim 1 where the constant ratio of optical modulation index at the output is maintained irrespective of the respective optical power received at the plurality of inputs.

3. The active splitter of claim 2 where the optical modulation index at the output is set to the optical modulation index of the plurality of inputs.

4. The active splitter of claim 2 where the optical modulation index at the output is set to an adjustable fraction of the optical modulation index of the plurality of inputs.

5. A system comprising a head end, a plurality of optical network units (ONUs), and at least one active splitter, the active splitter comprising:

a unit operating as a splitter in a forward direction and an active combiner in a reverse direction, the combiner having a plurality of inputs that each receive an upstream optical signal from a respective optical network unit (ONU) and combines them to create a combined electrical signal at an output;

a transmitter that receives the combined electrical signal and converts it to a reverse path optical signal at a calibrated level;

a multiplexer that multiplexes the reverse path optical signal with a forward path optical signal;

where the active splinter at least one of: (i) calibrates ay least one of its own reverse transmission optical power level and RF signal gain to that of at least one other device, and in response to a downstream signal; (ii) calibrates at least one of its own reverse transmission optical power level and RF signal gain to that of at least one other device, and in response to an upstream signal; or (iii) calibrates at least one of a reverse transmission optical power level and RF signal gain of another device using a downstream signal sent from the active splitter to the other device.

6. The system of claim 5 where the active splitter is capable of decoding received forward path communication signals.

7. The system of claim 5 where the active splitter is capable of receiving a forward path communication signal, modulating the received forward path communication signal, and outputting the modulated forward path signal to another device.

8. The system of claim 5 where the active splitter is capable of instructing a second active splitter to adjust its reverse transmission power level.

9. The system of claim 5 where the active splitter constructs a system map comprising topology information, the topology information including at least one of: (i) serial numbers of other active splitters operatively connected to the active splitter; (ii) serial numbers of ONUs operatively connected to the active splitter.

10. The system of claim 9 where said active splitter is capable of using the map to report system status information and said topology information to a head end.

11. The system of claim 10 where said system status information includes the status of said active splitter.

12. The system of claim 10 where an upstream active splitter communicates with and monitors a downstream active splitter.

13. The system of claim 9 where said active splitter is capable of detecting at least one of an input level to an active splitter from an ONU, and chattering ONUs.

14. The system of claim 13 capable of disabling detectors of at least one of defective ONUs and chattering ONUs.

15. The system of claim 9 where the active splitter is capable of automatically triggering route redundancy by monitoring upstream transmission over a first link and switching upstream traffic to a second link if the first link is non-operative.

16. The system of claim 5 where the head end is capable of instructing an active splitter to initiate a self-calibration procedure.

17. The system of claim 5 where the reverse transmit level of all other active splitters connected to and downstream from said active splitter are equalized to an optimized level.

18. The system of claim 17 where said reverse transmit level of any downstream active splitter is equalized to said optimized level automatically at the startup of said downstream splitter.

19. The system of claim 5 where the active splitter is capable of receiving and decoding an upstream signal, and communicating with an upstream device using the decoded upstream signal.

20. The system of claim 5 where calibration occurs automatically.

21. The system of claim 5 , where at least one optical network unit (ONU) is capable of adjusting at least one of output power level or gain, in response to an instruction received by said ONU in a downstream signal.

22. The system of claim 5 , where at least one ONU can receive an assigned port number.

23. The system of claim 5 , where at least one ONU can respond to a status monitoring request.

24. The system of claim 5 , where at least one ONU can send its serial number and/or status information to an upstream device.

25. The system of claim 5 where the head end includes a calibrated receiver that provides a constant RF output level based on a modulation index of an input signal, by adjusting a gain on the RF output level as a function of optical input level.

26. The system of claim 25 where the calibrated receiver has two RF outputs, at least one directly connected to a CMTS that lacks any RF combining network and lacks any RF splitting network.

27. An active splitter comprising:

a unit operating as a splitter in a forward direction and an active combiner in a reverse direction, the combiner having a plurality of inputs that each receive an upstream optical signal from a respective optical network unit (ONU) and combines them to create a combined electrical signal at an output;

a transmitter that receives the combined electrical signal and converts the combined signal to a reverse path optical signal, the transmitter adjusting at least one of power output and gain to maintain a constant ratio between optical modulation index at the output and optical modulation index at an input,

wherein the constant ratio of optical modulation index at the output is maintained irrespective of the respective optical power received at the plurality of inputs; and

a multiplexer that multiplexes the reverse path optical signal with a forward path optical signal.

28. The active splitter of claim 27 having a first gain setting optimized for ONUs that can transmit a first reverse spectrum and a second gain setting optimized for ONUs that transmit a reverse spectrum limited to an amount less than the first reverse spectrum, and where the active splitter can transmit the first reverse spectrum.

29. The active splitter of claim 28 where the optical modulation index at the output is set to the optical modulation index of the plurality of inputs.

30. The active splitter of claim 28 where the optical modulation index at the output is set to an adjustable fraction of the optical modulation index of the plurality of inputs.