Optical Modulator Half-Wave Voltage Measurement Using Opposite-Phase Sine Waves

A simplified direct measurement of half-wave voltage (V
_π
) based on the optical modulator third harmonic distortions to sinusoidal signals in opposite phase is proposed and performed for a quadrature Mach-Zehnder optical modulator. Experimental results are obtained from dc up to 11 GHz. The tested device V
_π
value is 2.4 V for dc increasing to 3.8 Vat 10 GHz. A linear extrapolation predicts that V
_π
will be close to 10.5 V at 40 GHz, which is equivalent to the first harmonic for a 80 GBd transmission rate based on QPSK modulation.