Designing biasing circuits that are made to match both types of MZM technologies (LiNbO₃ and InP) requires high voltage and current ranges; see Table 8-1. The Optical Internetworking Forum (OIF) recommends four differential IQ bias and two differential phase bias inputs; see Figure 8-1. This differential signaling scheme helps minimize crosstalk and noise between channels, which otherwise potentially results in a complicated bias control algorithm. While an ideal dither tone is a sine wave, generating a sine wave is cumbersome in a largely digital circuit domain. A square wave is relatively easier to generate through digital circuits, and is also usable, provided that the bandwidth of this dither signal is less than the low cutoff frequency of the receiver (that is, 100 kHz or 1 MHz as per OIF). Passive RC filters with a cutoff frequency less than 100 kHz are usable at the DAC output for LiNbO₃ modulators, which have a very small bias current requirement. For InP modulators that are mainly used with optical modules, typically requiring a receiver low cutoff frequency of MHz, choose RC values so that the power dissipation across the resistors is small.

For smooth detection of the dither signal at the MZM output, use two orthogonal dither frequency sources for the I and Q arms. The amplitude of the dither waveform is typically 0.5% to 2.5% of the dc bias voltage, which is mainly governed by the design implementation.