Multimode-Coupled High-Frequency Photoreceiver

Current airborne military communications and electronic warfare systems require low SWaP, rugged fiber optics detectors for airborne military communications and electronic warfare systems.  A typical 1 GHz-km graded index multi-mode (MM)50 µm fiber supports 20 GHz communication bandwidth over 50 m fiber length and 50 GHz bandwidth over 20 m fiber length. In both cases, all optical modes of the multimode fiber might contain energy. A typical solution for high bandwidth applications uses butt-to-butt coupling from the fiber end to a small, 10 µm to 35 µm-sized receiver. This approach, however, does not work well because it results in large losses (2 to 7 dB) and, more importantly, due to vibrations-related variability of power distribution across the modes in the fiber output. Because of the latter, the fraction of signal power delivered to the detector becomes variable as energy distribution across the modes changes. This causes spurious modulation of the signal at the photodetector output. SA Photonics’ GRIN-Lens Optical Coupler (GLOC) system provides the capability to efficiently couple signals from multimode fibers to small photoelectric detectors, supporting high bandwidth and stability of operation against modal distribution of energy in the fiber in wide temperature, vibrations and pressure rages.