Light Localizations in Photonic Crystal Line Defect Waveguides

Abstract

In this paper, we discuss unique light localizations in photonic crystal line defect waveguides based on two different concepts. The first concept is an additional defect doping that breaks the symmetry of the line defect. Even though such a defect is open to the line defect, the optical field is well confined around the defect at cutoff frequencies of the line defect. This expands the design flexibility of microcavities and allows effective mode controls such as the single-mode operation. The lasing action of such cavities in a GaInAsP photonic crystal slab was experimentally observed by photopumping at room temperature. The second concept is a chirping of the waveguide structure. The photonic band of a waveguide mode has a band edge, at which the group velocity becomes zero. The band-edge condition shifts in a chirped line defect waveguide, so guided light reaches a zero group velocity point and is localized. A macroscopic behavior of this phenomenon was experimentally observed in a waveguide fabricated into a silicon-on-insulator substrate. In addition, a microscopic behavior was theoretically investigated, which suggested its applicability to a group delay device.

Experimental demonstration of a four-port photonic crystal cross-waveguide structure

“…This is because its mode frequency lies just above the top edge of the WG2 second band diagram in this design, and it has a different mode symmetry compared with the WG1 fundamental waveguide mode. [23][24][25] In conclusion, a multi-mode InP PhC cavity structure has been designed and fabricated. The structure consists of two crossing waveguides intersecting in a single cell cavity.…”

Multiple slow waves and relevant transverse transmission and confinement in chirped photonic crystals

“…This is true for the structures with and without defects. Some details of the above-mentioned connections between different characteristics have been studied for various PhC based structures, e.g., see [4,6,7,[10][11][12]15]. In this section, we investigate which confinement scenarios and values of Q-factor are typical for configurations A and B.…”

“…The use of periodic structures such as photonic crystals (PhCs) and metastructures look promising from the point of view of overcoming these difficulties. Different features and manifestations of slow light in one-and twodimensional PhCs with [2,4,6,7] and without [1,3,[8][9][10] defects have been studied. The interest in slow-wave regimes in these structures has been stimulated by the possible applications, such as buffers for the time-domain processing of optical signals and the compression of optical energy.…”

“…Moreover, slow-wave phenomena have been found in some types of one-dimensional PhCs without defects (e.g., frozen modes) [1,9]. Strong field localization is often associated with small group velocity and, thus, with large values of g n in defect [4,6] and slot [7] PhC waveguides. At the same time, slow waves enable high-Q regimes [11,12].…”

“…In fact, such defect modes are also associated with slow light, because they typically show a quite flat dispersion. On the other hand, strong field enhancement also occurs inside the slabs of defect-free PhCs where 6 10 Q  can be achieved [10]. In fact, the connection between the large values of g n , strong field localization, and large Q values is evident, regardless of whether the slab contains structural defects or not.…”