Single GRIN-lens directional couplers

Two types of small, rugged, gradient-index (GRIN) rod-lens directional couplers have been made. One is a three-port directional coupler and the other is an asymmetric four-port coupler. Each coupler can have various splitting ratios from 1:1 to 20:1. Excess insertion loss is less than 1.0 dB, and directivity is greater than 30 dB for the three-port couplers, while these same figures are 1.2 dB and 40 dB for the asymmetric four-port couplers. The couplers are stable between −40 and +80°C.