Proble M 2 Direct Detection Heterodyne Detection If An Electro Optic Modulator Is Biased At The Quadrature Point And 1 (60.1 KiB) Viewed 38 times
Proble m 2. Direct Detection \& Heterodyne Detection If an electro-optic modulator is biased at the quadrature point and the amplitude of the input AC signal is small, the modulator acts as a classical amplitude modulator with an output optical spectrum as shown in Figure 1. Assume the optical frequency of the laser, vs is 193THz and the RF modulation frequency, fm is 10MHz. Figure 1. Output optical spectrum of MZM. a) For direct detection, the output of the MZM is connected directly to a photodetector as shown in Figure 2. Draw the output photocurrent power spectrum including the DC and AC components and show proportionality of these components to the electric field, ES
Figure L. Uirect-detection recerver. b) For heterodyne detection, a local oscillator (i.e. laser) with frequency vLO=vs−Δv and amplitude ELO is mixed with the output of the MZM onto a photodiode. In this example, let Δv=10GHz. The optical spectrum incident onto the photodiode is shown in Figure 3. For heterodyne detection, the MZM signal and local oscillator are combined and coupled to a photodetector as shown in Figure 4. Draw the output photocurrent power spectrum including the DC and AC components and show proportionality of these components to the electric fields, ES and ELO. Figure 3. Optical spectrum of local oscillator and MZM output that are combined on photodetector for heterodyne detection.
Figure 4. Heterodyne-detection receiver.
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