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(a) Microscope picture of the TTD beamformer based on a 1*4 MMI and PCWs. (b) SEM picture of the enlarged view of the 1*4 MMI power splitter. (c) Enlarged view of the S-bends that increase the waveguide separations. (d) and (e) SEM pictures of the PCW region containing photonic crystal taper and slow light PCW region.
Transmission spectra of the channels containing 1–3 mm PCWs.
(a) A schematic of the measurement setup of a PCW-based TTD module. Measurement results of phase vs. frequency relation for (b) channel-2, (c) channel-3, and (d) channel-4. Measurement results were normalized to the strip waveguide (channel-1). The horizontal line (black) in (b), (c), and (d) represents the normalized phase shift of channel-1. From top to bottom, each color line represents the measurements performed at λ = 1548 nm, 1552 nm, 1562 nm, and 1568 nm, respectively.
Wavelength-tunable time delay for all four channels.
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