US Patent 7194012 Laser driver circuit for externally modulated lasers

Systems and methods for biasing an externally modulated laser. An inductorless bias T network is provided that includes a terminating resistor in series with a capacitor. The capacitor is an open circuit for a bias signal and a virtual ground for an RF signal. Thus, the RF signal is terminated by the terminating resistor without dissipating the bias signal through a ground return path of the RF signal. Using a charge pump inverter, a positive supply can be used to positively bias a laser and negatively bias the external modulator through the terminating resistor. A negative power supply is not required. A swing voltage provided by the RF signal causes the external modulator to modulate the light emitted by the laser.