Integrated photonic devices for fiber optic communication systems

Fabrication and epitaxial growth technology for III-V semiconductor devices have developed to the point where substantial levels of photonic integration are now feasible. Both highly complex and simple photonic integrated devices are currently the subjects of much active research and product development. These efforts are motivated by the many potential advantages of photonic integration, reduced size, lower power consumption, increased functionality, higher performance and above all else lower cost. We discuss two different examples of photonic integrated devices that demonstrate some of the significant performance advantages that can be achieved with this technology. Both devices are fabricated using our deep ridge buried heterostructure technology that combines both SAG and butt joint epitaxial techniques to obtain the maximum flexibility in the device design. The first device is a high-speed modulator with an integrated phase shifter that enables the transmitter chirp to be dynamically tuned. This enables the transmission performance to be optimized for different amounts of fiber dispersion. In this device the phase shifter can be driven either with a synchronous sinusoidal source or a complementary data modulation. By varying either the amplitude of the drive signal or the bias on the phase modulator the chirp of the transmitted optical pulses can be controlled. For synchronous sinusoidal or narrowband chirp control a single frequency drive signal synchronized with the data modulation is applied to the phase modulator. This signal can be used to apply either positive or negative chirp to the transmitted data bits by varying the phase and amplitude of the drive signal. A more sophisticated approach uses the complement of the data modulation signal to drive the phase modulator. This method referred to as broadband chirp control provides better compensation since it applies frequency chirp only to the transitions in the signal.