Manufacturing of laser diode modules: Integration and automation of laser diode-fiber alignment and RIN characterization

Laser diode-fiber alignment and relative intensity noise (RIN) characterization are two crucial steps to the manufacturing of fiber pigtailed laser diode modules. Integrating both steps into a single automatic process can increase yield, improve the throughput and reduce manufacturing cost. This work presents a novel scheme of the integrated laser-diode-to-fiber alignment and RIN testing automation for the manufacturing of Fabry-Perot (FP) laser diode module hosted in a low cost isolator-free coaxial-type package. It is demonstrated that the value of RIN is not only determined by the intrinsic spontaneous emission of the laser diode, but also strongly dependent on the fiber-laser alignment and pigtailing process. It is experimentally determined, for the first time, that regardless of the type of lensed fiber employed for fiber-laser coupling, and with or without the presence of angular misalignment, there is an optimal fiber-laser alignment location at which the RIN value reaches its minimum. Moreover, it is observed that both RIN minimization and laser power coupling maximization occur at the same fiber-laser alignment position.