Modern optical communication systems require tunable optical delay lines for synchronization of data packages.
Chirped fiber grating are typically used as a dispersive element for this application. Fiber-based schemes, however,
suffer from bulkiness, slow response and/or low time resolution. Integrated photonics on silicon is one alternative
approach. Several more advanced device architectures have been subsequently demonstrated on silicon, including ringresonator and photonic crystal (PhC) line-defect waveguide types.
The coauthors of this paper have recently proposed a novel class of tunable optical delay lines based on apodized
grating waveguides. It was shown that high bit-rate operation is achievable by cascading two complementary (inward
and outward) apodized gratings. In this paper, we have experimentally demonstrated our proposed approach and studied
performance of the fabricated delay lines for optical telecommunication applications.
The bit-rate was extracted from broadening of transform-limited input pulses of the measured dispersion of the
delay lines. Characterization of the compact delay lines shows that the single grating devices offer true-time delays as
long as 164 ps, tuning range of ~ 81 ps, and a minimum bit rate of ~ 15 Gb/s. The cascaded scheme offer true-time
delays of 82 ps and tuning range of 32 ps and can potentially operate at bit rates as high as 107 Gb/s.