Fiber-optic delay line devices for GigaHertz signal processing

Single mode optical fiber is an excellent delay medium for broadband signal processing because it exhibits extremely low loss and dispersion. Two new forms of a fiber delay line are presented, each capable of performing a variety of signal processing functions. In the macrobend tapped delay line, the optical signal is tapped by forming sharp bends in a fiber coil. A 16-tap device with 1 ns tap intervals has been demonstrated as a 1 Gb/s sequence generator and matched filter. A 19-tap device was demonstrated as a frequency filter with a fundamental passband at 1 GHz. The v-groove tapped delay line makes use of arrays of silicon v-grooves to precisely align and position an array of adjustable evanescently coupled fiber taps. A 4-tap v-groove device was used as a 500 Mb/s sequence generator and matched filter. A similar 7-tap device was demonstrated as a discretely variable delay line, and as a programmable filter whose fundamental passband could be varied in discrete steps from 69 MHz to 1.67 GHz. Both of the delay line designs presented appear to be extendable to include large numbers of closely spaced taps.