In this presentation, I report on the self-organized photonic crystals (PCs) of organic and polymer materials for laser
applications. Here the self-organized PCs correspond to chiral liquid crystals (CLCs) and colloidal crystals (CCs). First,
CLC molecules self-organize the supramolecular helical arrangement by the helical twisting power like as 1-D PC
structure. When the fluorescent dye-doped CLC is optically excited with a linearly polarized beam, the laser emission
appears at the photonic band gap (PBG) edge(s) of CLC hosts. The optically excited laser emission shows circularly
polarized characteristic, even though the excitation beam is linearly polarized. Applying voltages to the optically excited
CLC cells enables reversible switching of the laser action as a result of changes in the supramolecular helical structure of
CLC host. Moreover, we succeed in the phototunable laser emission by using photoreactive CLCs. Second research
topic is establishment of new potential utilities of CC structures of polymer micro-particles. Monodispersed micro-particles
have an intrinsic capability to self-assemble the face-centered cubic lattice structures like as 3-D PCs on
substrates from the suspension solutions. The highly ordered architectures of colloidal particles are called as the CCs.
The laser cavity structure consists of an intermediate light-emitting layer of a fluorescent dye sandwiched between a pair
of polymeric CC films. Optical excitation of the device gives rise to the laser oscillation within the photonic band-gap of
the CC films. Interestingly, the laser action can be generated by optical excitation even though the CC laser device of
all-polymer materials becomes bent shape by mechanical stress.
The solar-to-electric power conversion efficiency of dye sensitized solar cells can be greatly enhanced by integrating a porous and highly reflecting photonic crystal in the device. The light harvesting enhancement is based on the enlargement of optical absorption caused by longer matter-radiation interaction time, which takes place at certain ranges of wavelengths. Photons are localized within the dye-sensitized electrode due to the effect of the photonic crystal, so the probability of optical absorption, and therefore the photogenerated current, is enhanced. The proposed photonic crystals are porous to allow a proper flow of the electrolyte through it and to prevent the introduction of internal resistance in the cell, which might alter the charge transport dynamics.
We here proposed a new kind of ultra-compact filters based on Fano resonances on patterned single crystalline silicon
nanomembranes (SiNM), which were fabricated and transferred onto transparent substrates like PET plastic and glass
substrates, using a wet transfer process. The angular and polarization dependent transmission characteristics of the filter
are experimentally investigated. The filter transmission characteristics are insensitive to the incident angle and
polarization for surface-normal incidence. For other incident angle conditions, the transmission peaks/dips shift,
according to the modal dispersion properties, as verified with the simulated modal dispersion curves. Both surface-normal
and angle-dependent filter transmission measurement results agree well with the numerical simulations.
In view of an electrically pumped photonic crystal-based semiconductor optical amplifier (SOA), we investigate optical mode propagation in 2D PhC waveguides in the presence of metal contacts for carrier injection. Our photonic crystal (PhC) devices are manufactured in the InP/InGaAsP material system. For the loss measurements, we have fabricated contact strips as narrow as 300nm with a sub-50nm placing accuracy on top of W3 waveguides. We study the influence of their position and width on optical power transmission through passive waveguides with respect to viability for future active devices. Our experimental results are complemented by numerical studies (FDTD, plane-wave expansion method).
We discuss recent our recent progress on functional photonic crystals devices and circuits for classical and quantum
information processing. For classical applications, we have demonstrated a room-temperature-operated, low
threshold, nanocavity laser with pulse width in the picosecond regime; and an all-optical switch controlled with
60 fJ pulses that shows switching time on the order of tens of picoseconds. For quantum information processing,
we discuss the promise of quantum networks on multifunctional photonic crystals chips. We also discuss a new
coherent probing technique of quantum dots coupled to photonic crystal nanocavities and demonstrate amplitude
and phase nonlinearities realized with control beams at the single photon level.
In this paper, we review some of our works on tuning the slow-light effect and superprism effect in photonic crystals from a synergistic perspective. The dispersive effects in a generic photonic crystal structure are classified into the longitudinal dispersion and angular dispersion according to their orientations with respect to the direction of light propagation. The slow-light effect originates from the longitudinal dispersion whereas the superprism effect originates primarily from the angular dispersion. The ability to tune these two categories of dispersive effects leads to several interesting topics of photonic crystal research, including slow-light photonic crystal modulators and superprism demultiplexers and sensors. We will discuss commonality and difference between the tunings of these two effects.
Photonic crystal microcavities with multi-hole defects were simulated using finite difference time domain (FDTD)
analysis. Subwavelength, multi-hole defects (MHD) offer a significant increase in defect surface area without
compromising the quality factor of the photonic crystal. Calculations of the increase in surface area compared to a
traditional, single hole defect are performed for MHD structures with varying subwavelength defect hole size,
subwavelength defect hole spacing, and effective defect radius. For active photonic crystal applications, the resonance
wavelength and quality factor of several different MHD photonic crystal structures was calculated as a function of the
dielectric constant of the defect. MHD photonic crystals can be designed to enable large changes in resonance
wavelength for small changes in defect dielectric constant. These structures would be advantageous for applications in
biosensing and optical switching.
Proc. SPIE 7031, Functional periodically poled-crystals for powerful intracavity CW difference-frequency-generation of widely tunable high spectral purity IR radiation, 70310K (29 August 2008); doi: 10.1117/12.794638
We present a novel tunable highly-coherent tunable source of IR radiation, based on difference-frequency generation
inside a miniature Ti:sapphire ring laser cavity by means of periodically-poled LiNbO3. Single mode
operation of the Ti:sapphire laser is provided by injection locking from an external-cavity diode laser and a
tunable-laser-injected fiber amplifier provides the signal radiation for the mixing. Such a source can be used in
spectroscopic set-ups for high sensitivity molecular sensing. Additional features are provided by properly altering
key properties of the 1-D photonic crystal.
The far-field focusing properties of two dimensional photonic crystals based flat lens with rod-type honeycomb
lattice are investigated using finite difference time domain (FDTD) method. The results match the wave-beam negative
refraction law with relative refractive index of -1. But, the image qualities are limited by low transmission at large
incident angles. To improve the image qualities, the effects of interface on the far-field image in a two-dimensional
honeycomb photonic crystal are investigated. It is found that the image qualities can be improved by modifying the
radius of rod near the surface of photonic crystals slab.