Conclusions
In principle, WDM ADC using LPFs and DSP works!
The optical part mixes high-frequency with low-frequency components by aliasing. This is a hybrid opto-electronic RF-mixer.
The main advantages of LPF are lower bandwidth and reduction of noise in the system due to limited bandwidth.
The LPF should be designed for a flat-frequency system response.
LPFs should have matched frequency response.
An anti-aliasing filter is required at the modulator RF input.
To obtain moderate ADC performance (ENOB > 6 and > 40 GS/s):
- Relatively long optical pulses (e.g. 28 ps) can be used in the system minimizing optical-pulse amplitude noise.
- Optical-pulse jitter must be less than s = 100 fs.
- The received optical power per detector must be greater than ~ 1 mW.
ENOB > 10 and > 40 GS/s requires jitter s < 3 fs and received optical power > 10 mW per channel