Optical circuits providing a time delay to signals modulated on optical carriers are considered important for optical communication systems and phased array antennas. A continuously tunable optical delay line is demonstrated in low-cost CMOS compatible LPCVD planar waveguide technology. The device consists of three cascaded ringresonator all-pass filters with fixed circumference of 2 cm (delay of 0.12 ns and FSR of 8.4 GHz). The measured group delay ranges from 0 ns up to 1.2 ns with a bandwidth of 500 MHz and delay ripple smaller than 1 ps, which is in accordance with the calculations
