A 3-bit true-time-delay lines device having a packing density of 5 lines/cm 2 with a minimum delay step of 100 ps is designed, fabricated and demonstrated. This device is based on substrate guided wave propagation combined with slanted photopolymer volume phase gratings. In this paper, we report the delay and bandwidth measurements for the 3-bit delay lines fabricated on BK-7 glass substrates with a substrate bouncing angle of 45 . The power fluctuation among the outputs due to the cascading fanout effect (a serious drawback for real system applications) is experimentally investigated as well. A power fluctuation controlled to within 610% is achieved. A femtosecond laser pulse is sent through the device and a bandwidth measurement of up to 2.5 THz is obtained. The delay step is measured by employing an ultrafast photodetector together with a sampling scope. The true-time-delay device presented herein has the potential to be integrated with photodetector arrays due to its planar structure on a single substrate together with the surface normal fan-in and fan-out features.

We report a high packing density true-time-delay rea (-5 delay lines/cm2) and ultrawide ray antennae, true-time delay, holo-UTURE phased-array antennas (PAA' s) satisfying the wide bandwidth requirements must implement true-timedelay (TTD) steering techniques such that the far field pattern is independent of frequency. In the TTD approach, the path difference between two radiators is compensated by lengthening the microwave feed to the radiating element with a shorter path to the microwave phase-front. These are usually accomplished by lossy and bulky metallic waveguide feeds, inducing high cost and heavy weight. There have been great interests in photonic true-time-delays for PAA applications in recent years[1]- [3]. This requires the photonic system to offer true-timedelay transmission paths for the microwave signals that are distributed to array elements. Compared to electronic phaseshifters, photonic TTD's offers wide bandwidth, compact size, reduced weight and very low RF interference.