The primary goal of the proposed Phase I SBIR effort is to investigate various schemes for implementing a built-in test circuit using integrated optoelectronic modules. The circuit will be implemented using OptiComp's (OCC) advanced optoelectronic modules which monolithically integrate VCSELs, detectors, and interconnecting waveguides. Using these unique optoelectronic circuits, advanced built-in test capabilities are enabled which could significantly enhance optical networks used in military/aerospace applications. The built-in test capabilities will detect transmitter, receiver, and cable failures in the high-performance networks implemented with these modules. OCC occupies a 7,000 square foot facility which includes a full service, backend semiconductor fabrication fabrication cleanroom and optoelectronic device integration laboratory, an optoelectronic testing area, and an MBE based crystal growth facility. OCCÂ’s design center includes optoelectronic based modeling software for VCSELs and waveguide structures, as well as full EDA schematic capture and mask layout. Benefit The proposed program will offer a dual-use commercialization opportunity for built in testing in optical interconnects and networks. These built-in testing capabilities are enabled by OCC's monolithic optoelectronic module technology which allows the integration of additional VCSELs and/or detectors for self diagnostics. This built-in test capability will be able to distinguish between transmitter, receiver, and cable failures. These optical networks, and their self diagnostics, have significant market potential, especially for demanding military and commercial optical networks such as those in avionics. Keywords fault tolerant, optical networks, waveguide, BIT, Built In Test, VCSEL, self diagnostics, detector