3-Fiber 1550nm SLED Source for IMU Applications

A novel, 14-pin Butterfly (BTF) light source module, incorporating a broadband Superluminescent Light-Emitting Diode (SLED) at 1550 nm, has been developed for inertial measurement unit (IMU) applications. The compact BTF module integrates micro-optical lenses, a flatpack optical isolator, a monolithic 1:3 beam divider and other components on a temperature-controlled, free-space optical bench platform and is delivering, at an SLED current of 300 mA, more than 3.5 mW of output power at each of the three polarization-maintaining (PM) output fibers with a polarization extinction ratio (PER) larger than 18 dB.

1. Optical Module Architecture and Build

The optical module is a standard 14-pin BTF package (housing 20.8mm x 12.7mm) where a ceramic plate, which acts as an optical bench, is mounted on top of a high-performance thermo-electric cooler. The SLED chip is soldered on a ceramic submount that is mounted on the optical bench. The optical output beam of the SLED is collimated by a micro-optical lens (1.0mm x 1.0mm) with an efficiency of more than 90%. The collimated output beam propagates through a double-stage, flatpack optical isolatorbefore being deflected into a monolithic 1:3 beam divider that is delivering three free-space output beams of equal power to an array of three PM output fibers. The fiber coupling into each output fiber is accomplished using narrow focusing lenses that are individually aligned to achieve nearly identical output power values across all three fibers. The coupling efficiency from free space into the PM fibers is better than 50% for each output, resulting in a high electro-optical efficiency. The 3D CAD layout of this module is shown in Figure 1, a photograph of an open module is shown in Figure 2.