Passive alignment of an optical fiber on a multi-layer ceramic module for radio-over-fiber applications

The low-temperature co-fired ceramics technology is a successful and space-qualified technology enabling three-dimensional microwave design. Now we are pursuing an important step further towards multi-functional multi-purpose hybrid assembly technologies: combining ceramic technology with optical fiber technology. In such systems, fiber alignment is a crucial issue. Extra gadgets used for the fiber alignment make the system more complex and bulky. Considering the many features offered by the ceramic multi-layer technology for size reduction, it is advantageous to use this technology for the passive alignment of an optical fiber above the optical source. In this paper, the passive fiber alignment employing flip-chip mounting of a vertical cavity surface emitting laser in a ceramic substrate is presented. We have studied the performance of the resulting optical link with respect to figures typical for radio-over-fiber applications, namely the link gain, noise figure, and the spurious-free dynamic range and compared the results with a link where the VCSEL was wire bonded to the circuit.