Optical IQ ("In-phase" and "quadrature") modulation. Two individual optical signals are demodulated.
"In-phase" and "quadrature" Optical I/Q modulator consists of two independently-controlled Mach–Zehnder interferometers (MZI) whose outputs are combined.
The combining structure also includes a bias electrode that applies a phase delay between the two MZIs, allowing for the required phase control between the two modulator arms.
Tx
Digital Signal1
Electric field of Signal1
Digital Signal2
Electric field of Signal2
Electric field of Optical Signal (1+2)
Optical Power Signal (1+2)
Rx
Balanced Photodetector allows to recover original sinals.
Electric field of Signal1(PD1)
PD1 Signal
Electric field of Signal2
PD2 Signal
Interference of of Electric field (1-2)
Optical Power Signal (1-2)
-> Digital Signal 1 has been demodulated.
Electric field of Signal1(PD3)
PD3 Signal
Electric field of Signal4
PD4 Signal
Electric field of Signal2(PD4)
Interference of Electric field (3-4)
Optical Power Signal (3-4)
-> Digital Signal 2 has been demodulated.