The TFLN-DPIQ bias voltage controller from Plugtech is specifically designed for TFLN Thermo-optic (TO) dual-polarization IQ modulators. Its principle involves injecting dither signals of different frequencies, analyzing the working point errors of the Y-I, Y-Q, Y-P, X-I, X-Q and X-P arms of the modulator, and adjusting the six output bias voltages accordingly to keep the modulator in optimal working condition at all times.