Abstract
In this paper, we design a waveguide on photonic crystal slab for propagation of low-dispersion slow light. By shifting the air holes adjacent to the waveguide, we obtain a photonic crystal waveguide with a group index of 25 in 25 nm bandwidth which results in a group index bandwidth product of 0.366. To take the advantages of low dispersion slow light generated in this engineered waveguide, we next focus on low coupling efficiency limitation. A low group index coupler is proposed to increase the transmission of the light to the slow mode in the low dispersion bandwidth. By using the proposed coupler and adjusting the structural parameters, the coupling efficiency to low dispersion slow light is improved 11 dB compared to the transmission without the coupler.
Highlights
Slow light technology plays an important role in the future of optical buffers, optical logical gates, and optical signal processing
In a Photonic crystal waveguide (PCW) slow light can be realized by modifying its structure
The slow light generated in a PCW can be used in several applications, such as optical delay lines or buffers and enhanced light-matter interaction [1]–[3]
Summary
Slow light technology plays an important role in the future of optical buffers, optical logical gates, and optical signal processing. Photonic crystal waveguide (PCW) is widely used in generation of slow light. In a PCW slow light can be realized by modifying its structure. This works for a desired wavelength and provides larger bandwidths compared with other methods, such as electromagnetically induced transparency. There are two main limitations in realization of slow light in PCW: 1) the group velocity dispersion (GVD) in slow light region, and 2) low efficiency of coupling light from strip waveguide to the slow light PCW. GVD occurs when the group velocity of light depends on optical frequency or wavelength. The GVD parameter is defined as β2 = ∂/∂ω(1/vg) = (∂2k)/(∂ω2), where k is the phase constant, ω is the angular frequency and vg is the group velocity of signal. The dispersion parameter Dλ is defined as
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