All-optical operation holds promise as the future of computing technology, and key components will include miniaturized waveguides (WGs) and optical switches that control narrow bandwidths. Nanowires (NWs) offer an ideal platform for nanoscale WGs, but their utility has been limited by the lack of comprehensive coupling scheme and of band selectivity. Here, we introduce a NW geometric superlattice (GSL) that allows controlled, narrow-band guiding in Si NWs through direct coupling of a Mie resonance with a bound guided state (BGS). Periodic diameter modulation in a GSL creates a Mie-BGS coupled-excitation that manifests as a scattering dark state with a pronounced scattering dip in the Mie resonance envelope. The frequency of the coupled mode, tunable from the visible to near-infrared, is determined by the pitch of the GSL and exhibits a Fourier-transform limited bandwidth. Using a combined GSL-WG system, we demonstrate spectrally-selective guiding and optical switching at telecommunication wavelengths, highlighting the potential to use NW GSLs for the design of on-chip optical components.
To exploit photonics technologies for in vivo studies in life science and biomedicine, it is necessary to efficiently deliver light energy to the target objects embedded deep within complex biological tissues. However, light waves diffuse randomly inside complex media due to multiple scattering, and only a small fraction reaches the target object. Here we present a method to counteract the random diffusion and to focus ‘snake-like’ multiple-scattered waves to the embedded target. To realize this, we experimentally identified time-gated reflection eigenchannels that have extraordinarily large reflectance at a specific flight time where most of the multiple-scattered waves have interacted with the target object. By injecting light to these eigenchannels, we achieved more than 10-fold enhancement in light energy delivery compared to ordinary wave diffusion cases. This method works up to depths of approximately 2 times the transport mean free path at which target objects are completely invisible by ballistic optical imaging. This work will lay a foundation for enhancing the working depth of imaging, sensing, and light stimulation.
We investigate optical characteristics of the ultra-small zero-cell cavities that consist of two, four and three shifted lattice
points in square- and triangular-lattice photonic crystal structures. Mode volumes and Q factors of these cavities are
systematically studied using three-dimensional finite-difference-time-domain simulation. In particular, an extremely
small mode volume of ~0.015 μm<sup>3</sup> [~1.5 (λ/2<i>n</i><sub>slab</sub>)<sup>3</sup>] is obtained in the triangular-lattice three-hole-shifted cavity. In an
experiment, we demonstrate optically pumped room-temperature lasing action with a low lasing threshold of ~130 μW in
a square-lattice two-hole-shifted cavity. The operation of this ultra-small laser is unambiguously confirmed by the
numerical simulation based on the actual fabricated structures.
Recent progress toward wavelength-scale photonic crystal lasers is summarized. To realize the ultimate laser, one needs to have a wavelength-scale photonic crystal cavity that is lossless. As a candidate for this ultimate laser, the two-dimensional unit-cell photonic crystal laser compatible with current injection is proposed. Experimental demonstration of the low-threshold two-dimensional photonic crystal lasers in the triangular lattice and the square lattice will be discussed. The very high quality factor in excess of 1,000,000 is theoretically predicted from the wavelength-scale resonator supporting the whispering-gallery-like photonic crystal mode.
Recent progress toward wavelength-scale photonic crystal lasers is summarized. Lasing characteristics of two possible configurations of the unit-cell photonic crystal laser that has a central node through which current could be supplied. The very high quality factor in excess of 100,000 is theoretically expected from a square lattice unit-cell photonic crystal resonator. Applications of photonic crystals to other forms of active devices are also briefly discussed.
Novel square lattice photonic band gap lasers are realized at room temperature from single cell photonic crystal slab micro-cavities fabricated in InGaAsP materials emitting at 1.5 micrometers . This single cell photonic band gap laser operates in the new class of two-dimensional mode to be classified as the smallest possible whispering gallery mode with genuine energy null at the center. The low-loss nondegenerate mode with modal volume of 0.1 ((lambda) /2)<SUP>3</SUP> demonstrates a spectrometer-limited below-threshold quality factor > 2000 and a theoretical quality factor of > 10,000. Threshold incident peak pump power of 0.8 mW is achieved from this whispering-gallery-type laser mode. The other class of photonic crystal lasers is also observed outside the photonic band gap of the square lattice, operating in the mode characteristically one-dimensional.