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Homodyne Detection Theory

9008-045

 

Consider two optical beams mixing on a photodiode (square-law detector), as illustrated in 9008-047. Let the beams be given by:

 

Received signal beam electric field = Ercos(wrt + ),

Local-oscillator beam electric field = Eocoswot.

 

The photodetector current is given by:

I ~ (Er + Eo)2

I ~ [Ercos(wrt + ) + Eocoswot]2

I ~ Er2cos2(wrt + ) + 2ErEocos(wrt + ).coswot + Eo2cos2wot

 

Replacing wr by wo,

I ~ Er2[1 + cos2(wot + )] + ErEo[cos(2wot + ) + cos ]

+ Eo2[1 + cos2wot]

 

I ~ (Er + Eo)2 + ErEocos

 

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