Recirculating delay lines have been made using loops of single mode fiber that are closed, without splices, using one or more single mode fiber directional couplers. The use of an all single mode fiber system allows the accurate storage of high frequency analog or digital signals for long delay periods. Such devices can be used as wideband transient or buffer memories. Recirculating fiber loops are also useful as transversal filters that can exhibit uniform notch and bandpass filter characteristics over a wide range of frequencies from 1 MHz to 1.3 GHz.