Demonstration of monolithic optical injection locking for directly modulated RF photonic links

Optical injection locking has been a known method for increasing the modulation performance of semiconductor lasers. Such benefits include increased modulation bandwidth, increased linearity, lower chirp and lower noise. For analog photonic applications the increased bandwidth and linearity are of main concern for the distribution of high frequency analog signals with maximum fidelity. Previous experiments involving optical injection locked lasers are typically done using a monolithic semiconductor laser as the slave and an external cavity semiconductor laser as the master. Such setups are ideal for laboratory use but often are impractical for real life implementation. Particularly, the external cavity laser is prone to vibration and the injection ration (coupling from the master laser into the slave) is limited by the coupling efficiency and polarization mismatch.; Optical injection locking using a single monolithic distributed feedback (DFB) laser with two separate gain sections is demonstrated for the first time. With a relatively strong grating, each section can be made to operate independently and at different wavelengths. By varying the bias current, the two sections can be tuned closer to each other such that injection locking occurs. Since the master and slave laser share the same waveguide, very high injection ratios can be achieved. Under injection locked conditions the modulation bandwidth is increased from 12 GHz to 23 GHz. An increase of 20dB in linearity is also observed. The increase in modulation performance is on par with our experimental observations using an isolated master laser. This monolithic approach offers reduced size, weight and power consumption compared to external modulation schemes; making it ideal for analog photonic applications.; A finite difference time domain model based on coupled traveling waves is developed to accurately model this dual section DFB laser. The model takes into account various optical modes and the spatial variations along the cavity length. The simulated performance is in good agreement with experimental results. Comparison to the classical lumped element laser rate equations is also done to highlight the benefits of using a distributed model.