Optical module with MU connector interface using self-alignment technique by solder-bump chip bonding

We applied a self-alignment technique that uses solder-bump chip bonding for alignment between photonic devices and optical fibers in optical modules, and achieved a compact and simple MU-type connectorized receiver module that requires no optical-axis adjustment. In our scheme, coupling a photonic device to a fiber is basically done by simple butt-joining, which is automatically accomplished by solder-bump bonding the device onto a platform with an optical fiber glued by a ceramic ferrule. To achieve this, we fabricated a 10×10 mm alumina chip-carrier with a 1.25-mm-diameter zirconia ferrule which had a 10/125-μm-diameter single-mode fiber inside it. The alignment accuracy between the fiber and the solderable patterns of the chip-carrier was below 5 μm (cumulative distribution of 50%). A prototype receiver module was fabricated using a photodiode with 180-μm-diameter active area (bandwidth of 800 MHz@-3 dB). The receiver conformed to the MU connector standard, so an MU plug can be connected by pushing it on. Degradation of the photodiode´s bandwidth was hardly seen. Submicron alignment (Ave.=0.5 μm) resulting from a 15-sample chip-bonding experiment using 32 25-μm-diameter micro-solder bumps suggests that our new scheme would be applicable to ultra-high-speed PD-to-fiber coupling in receiver modules, or to LED- or VCSEL-to-fiber coupling in transmitter modules after improving the fabrication accuracy of the optical ferrule integrated chip-carrier