Abstract
Group-index independent coupling to a silicon-on-insulator (SOI) based band-engineered photonic crystal (PCW) waveguide is presented. A single hole size is used for designing both the PCW coupler and the band-engineered PCW to improve fabrication yield. Efficiency of several types of PCW couplers is numerically investigated. An on-chip integrated Fourier transform spectral interferometry device is used to experimentally determine the group-index while excluding the effect of the couplers. A low-loss, low-dispersion slow light transmission over 18 nm bandwidth under the silica light line with a group index of 26.5 is demonstrated, that corresponds to the largest slow-down factor of 0.31 ever demonstrated for a PCW with oxide bottom cladding.
Highlights
The slow light effect in photonic crystal waveguides (PCW) provides a strong light-matter interaction, which enhances absorption, non-linearity and gain per unit length [1,2], with several applications ranging from low-power and compact optical modulation [3] to gas detection [4]
In order to numerically investigate the efficiencies of different couplers, we simulate transmission through a structure consisting of a ridge silicon waveguide, 8 periods of a fast light region, and 13 periods of the designed band-engineered PCW
We find that using the step coupler design, the best coupling into the designed engineered PCW is at least 4% more efficient over the low-dispersion bandwidth compared to coupling into a laterally shifted lattice design with nearly similar Slow down factor (SF) = 0.28 and ng = 25.5
Summary
The slow light effect in photonic crystal waveguides (PCW) provides a strong light-matter interaction, which enhances absorption, non-linearity and gain per unit length [1,2], with several applications ranging from low-power and compact optical modulation [3] to gas detection [4]. Band engineering techniques that do not require multiple hole-sizes, such as changing the positions of the first two rows [12] or lattice-shifting [13,18], provide the advantage of higher yield and reproducibility Among these techniques, lattice-shifting makes it easier to target a desired group velocity over a bandwidth of interest since these two parameters can be tuned relatively independently [13]. Efficient optical coupling and slow-light operation over a large optical bandwidth provides a means for realization of larger optical bandwidth and high speed compact PCW based modulators. An example of such devices will be reported elsewhere
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