Abstract

Fiber optic local area networks, microwave and optical phased arrays, multiplexers/demultiplexers, and signal processing systems demand distributive couplers with low excess loss as well as low loss deviation. Various techniques, including biconical fusion and channel waveguide, have been experimentally tried out to construct 1 × N couplers, with N less than 100. However, these conventional techniques have disadvantages of poor reproducibility, high insertion loss, and large loss deviation among output ports. A new 1 × 516 multimode fiber optic coupler was fabricated using semiautomated apparatuses, a submicron accuracy alignment technique, and a GRIN lens. The multimode glass fibers have a core diameter of 50 µm and cladding diameter of 125 µm. To minimize the fractional loss at the interface facet of a GRIN lens, the multimode fibers are precisely etched to 40-µm diameter. The well-arranged fiber bundle is then accurately aligned with the GRIN lens and the input fiber. The outputs of the 1 × 516 fiber coupler are individually identified employing an image processing system. Calibration, test, and data recording of the couplers were performed by a multichannel computer-aided measurement system. The 1 × 516 coupler has an excess loss of 5.25 dB and a loss deviation of ±2.5 dB. The excess loss varies less than ±0.2 dB over the temperature range from −20 to ±60°C.

© 1989 Optical Society of America