Optical testing of silicon photonics is especially challenging, as optical fibers must be precisely positioned in 3D space, and perfectly angled, relative to the device under test. Devices may take many forms, requiring solutions for test on-wafer or in singulated die form, for single fibers or fiber arrays, and for vertical grating couplers or edge couplers. Sophisticated software and finely tuned motorized multi-axis positioning systems are required to ensure optimum fiber alignment for every device, on each wafer, at every temperature. Accurate optical instrumentation completes the test cell.