RF sub-band de-multiplexing for ultra-wide band optical digital coherent detection

1. A method for data transmission, comprising radio frequency (RF) mixing to down-convert in-phase and quadrature parts of a photo-detected electrical RF band signal to baseband for data conversion;

controlling a mixing phase of an electrical local oscillator (LO) at one or more RF mixing modules;

selecting one of the RF sub-bands to be down-converted to baseband after coherent photo-detection; and

performing RF sub-band de-multiplexing for ultra-wide band optical digital coherent detection; and

providing LO phase control to perform sub-band de-multiplexing without the use of baseband signal inversion to minimize unmatched signal path and using LO phase control to perform sub-band switching.

2. The method of claim 1 , comprising receiving ultra-wide band optical channel containing a plurality of sub-bands.

3. The method of claim 1 , comprising using one set of coherent receivers to convert multiple sub-bands to mixed electrical signal lanes.

4. The method of claim 1 , comprising using RF mixers to perform IQ mixing on input signal lanes to down-convert RF sub-bands to baseband lanes.

5. The method of claim 1 , comprising using RF IQ mixing to de-multiplex a set of high bandwidth lanes into multiple sets of bandwidth lanes each containing a sub-band.

6. The method of claim 1 , comprising applying parallel sets of digital signal processors (DSPs) with analog to digital conversion bandwidth requirements to handle multiple sub-bands.

7. The method of claim 1 , comprising switching RF sub-bands during RF de-multiplexing to predetermined DSP for data recovery.

8. The method of claim 1 , comprising picking positive or negative side-bands by a phase relationship between I and Q.

9. The method of claim 1 , comprising obtaining in-phase and quadrature components for a sideband by rotating mixing LO phases by 90 degrees, while maintaining a phase difference between two beating arms at 90 degrees.

10. The method of claim 1 , wherein during a positive sideband down-conversion, an I mixing arm phase lags by 90 degrees while the I mixing arm phase leads by 90 degrees for a negative sideband down-conversion.

11. The method of claim 1 , comprising de-multiplexing a positive sideband S p _ x and a negative side band S n _ x with a relationship:

S x ′=( I x ′+jQ x ′)=( S p _ x e jω RF t +S n _ x e −jω RF t )·cos θ+( S p _ y e jω RF t +S n _ y e −jω RF t )·sin θ.

12. The method of claim 1 , comprising down-converting one sideband using homodyne coherent detection.

13. The method of claim 1 , wherein the selecting one of the RF sub-bands comprises choosing either at a positive side or a negative side relative to an optical carrier.

14. The method of claim 1 , comprising sharing coherent mixer, laser, and balanced photo-detectors for two or more sets of RF sub-bands to de-multiplex an optical channel containing multiple RF sub-bands.

15. The method of claim 1 , wherein each RF sub-band is down converted to baseband signals separately for parallel analog to digital sampling with a bandwidth requirement.