Chirp Managed Laser and Applications

The chirp managed laser (CML) is an alternative transmitter technology that allows a directly modulated laser (DML) to be used in high-performance applications with a smaller size, lower power consumption, less device complexity, and lower cost. The CML comprises a DML and an isolated, passive optical filter. A key feature of the CML is its large tolerance to fiber dispersion, reaching over 360 km transmission at 10 Gb/s in standard single-mode fiber without dispersion compensation. The combination of adiabatic chirp from the laser and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are out of phase. This results in destructive intersymbol interference after fiber transmission. Other applications of CML are generation of advanced modulation formats, such as return-to-zero (RZ) alternate mark inversion, and RZ differential phase-shift keying. Tunable CML using DFB array, and sampled grating deterministic bit rate (DBR) technologies for 10 Gb/s metro applications have now been demonstrated. A four-element DBR array CML has also been demonstrated for 100 Gb/s metro applications. This paper reviews the principle of operation of CML and its various applications, as well as recent advances in CML-based devices.