Fiber Pigtailed Multimode Laser Module Based on Passive Device Alignment on an LTCC Substrate

Abstract

A concept that utilizes structured planar substrates based on low-temperature cofired ceramics (LTCC) as a precision platform for a miniature passive alignment multimode laser module is demonstrated. The three-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves, and cavities for the laser-to-fiber coupling. The achieved passive alignment accuracy allows high coupling efficiency realizations of multimode fiber pigtailed laser modules. Thick-film printing and via punching can be incorporated in order to integrate electronic assemblies directly on the optomechanical platform. The platform is scalable, and it allows embedding of subsystems, such as silicon optical bench (SiOB), but it also provides the interface for larger optical systems. Temperature management of high-power laser diodes is achieved by realizing heat dissipation structures and a cooling channel into the LTCC substrate. The measured maximum laser metallization temperature was 70degC when a thermal power of 0.5 W was applied at the laser active area using a liquid cooling of 50 mL/min. The measured maximum temperature of the laser surface was about three times higher without liquid cooling. Optical coupling efficiency of the multimode laser systems was simulated using optical systems simulation software. The nominal coupling efficiency between 100times1 mum stripe laser and 62.5/125-mum graded index fiber (NA=0.275) was 0.37. The simulated coupling efficiency and alignment tolerances were verified by prototype realization and characterization. The measured alignment tolerance values between laser and fiber in AT prototype series were Deltax=7.7 mum, Deltay=7.6 mum, and Deltaz=10.8 mum (SD values). The corresponding values in A2 prototype series were Deltax=3.1 mum, Deltay=9.1 mum, and Deltaz=10.2 mum. The measured average coupling efficiency was 0.28 in AT series and 0.31 in A2 series. The coupling efficiencies of all operational prototypes varied from 0.05 to 0.43