We propose a dispersion flattened and high birefringence terahertz photonic crystal fiber using roll up method with
PTFE. The PCF made of this method shows dispersion flatness by the air region between PTFE tubes around core and
high birefringence by asymmetric mode distributions. When using rod with Dout = 1mm, dispersion of the proposed THz PCF has a slope of 0.4ⅹ10-2 near 0.848 THz and the value of the then is about 0.21 ps/THz.cm. In this structure, the order of birefringence is 10-3 and the order of confinement loss is about 10-11 dB/m.
The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.
We present that the carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film depends
on the incidence angle of photoexciting beam. At higher incidence angles of photoexciting beam, the modulation
efficiency of terahertz transmission due to TM-polarized excitation is distinctly higher than one due to TE-polarized
excitation. We find that this phenomenon is due to the enhancement of carrier injection which is expected when the
incident light is more transmitted through the organic thin film.
We have proposed a hybrid square-lattice PCF using two different sized air holes and conventional square lattice
cladding structure. Based on the plane wave expansion method and finite element method, we numerically investigated it
polarization and dispersion properties compared to the conventional square lattice photonic crystal fiber. From the
numerical results, it is shown that the proposed structure provides high birefringence and still maintains negative
dispersion property. Numerical results show that the birefringence of the hybrid square-lattice PCF reaches 10-2. The
value and slope of the chromatic dispersion are also negative over the C band.
We investigate the terahertz (THz) transmission characteristics of complex slot arrays with various order of rotation symmetry. Our experimental results reveal that an asterisk-shaped aperture with sixfold rotational symmetry is the most appropriate shape for realizing polarization-independent, highly efficient, and frequency-selective transmission of THz radiation. A systematic understanding of the THz transmission characteristics is useful for achieving versatile platforms and custom-designed metallic devices with specific electromagnetic responses.
We investigate subwavelength confinement of terahertz electromagnetic surface modes in a three-dimensional
region with coupled slot structures. Two-dimensional resonance focusing on a subwavelength slot converts to
three-dimensional subwavelength confinement, due to sharp edge confinement effect on asymmetric
plasmonic structure, at the center position of the slot structures which consists of two or more slots. We also
report on the polarization independent confinement of terahertz electromagnetic surface modes beyond
diffraction limit. The structure which consists of radially arranged subwavelength slots located at a same
center position shows the polarization-independent terahertz three-dimensional subwavelength confinement.
Photonic quasicrystals are unique structures having long-range order but no periodicity. It has been found that
quasiperiodic structures give rise to unusual phenomena and properties that have not been observed in periodic
structures. Recently, it has been reported that introducing quasi-periodic structures of microscopic air holes in optical
fibers can give rise to a unique dispersion property such as almost zero ultra-flattened chromatic dispersion and large
mode area dispersion compensating fiber.
In this paper, we introduce a ring core photonic quasicrystal fiber (PQF) and its optical properties are theoretically
analyzed. The chromatic dispersion properties of doped ring core PQF, are investigated along with their dependence on
the proposed defect parameters using 3D full-vectorial Beam Propagation Method (BPM) and plane wave expansion
method.
We propose an index-guiding supersqure lattice PCF with two missing air holes as a defect core and analyze the
polarization properties using a plane wave expansion method. From the numerical results, the proposed fiber is an
absolutely single polarization single mode over the wide wavelength range from 1 to 2μm where only the slow axis
mode is guided and the fast axis mode becomes a radiative mode.
We propose a dual-core photonic quasicrystal fiber with six-fold symmetry that may be useful in compensating
chromatic dispersion of a single-mode fiber. The geometry of the proposed photonic quasicrystal fiber is described and
then the behaviors of effective index and chromatic dispersion are calculated according to the structural parameters. The
dual-core fiber is composed of a pure silica inner core and an outer core that is formed by reducing the diameter of air
holes in the third cladding layer. We investigate the dependence of the effective indices of inner core and outer core, the
fundamental super mode, and the effect of chromatic dispersion on the structural parameters by using plane wave
expansion method.
The dual-core photonic quasicrystal fiber has a large negative chromatic dispersion value of approximately -2000 ps
nm-1 km-1 over optical communication band around 1.5μm. Introducing quasicrystal structures in the dual-core optical
fibers can improve the capability of dispersion compensation of the fibers significantly.
A further insight into the prior concept of polarization sensitive optical coherence tomography system intended for non-laboratory
conditions is brought forward and an experimental proof-of-concept is presented. A phenomenological model
is adopted from the theory of light depolarization in crystalline polymers and modified to yield a simplified algorithm for
mapping depolarization ratio in dermis. The algorithm could distinguish between dermal layers with depleted collagen
content and normal dermis of normal perilesional skin. Dermis is simulated by bireringent lamellae of collagen arranged
chaotically in multiple layers parallel to the skin surface. Both the design concept and the model imply the sub-millimeter
tumor thickness as a proofed prognostic factor and an important criterion for complementary functional
diagnostics of skin cancers at their early phase of vertical growth. Choice of the model is inspired by similarity of
structural and optical properties between liquid-crystal collagen fibers in dermis and birefringent crystalline lamellae in
polymer materials. The numerical computation based on the model allowing for real characteristics of dermis gives
plausible interpreting of depolarization peculiarities caused by collagen depletion. Feasibility is discussed of exploiting
fiber optic analogs of achromatic retarders. Fabrication of the fiber retarders is shown to be realistic by making use of the
photonics technology possessed by the authors.
A challenge is accepted to identify depth resolved optical birefringence of turbid media, particularly human skin using
polarization sensitive optical coherence tomography under external environmental perturbations, e.g. under application
conditions in clinics and hospitals. A novel concept is advanced and respective design is elaborated for a system which
comprises a source of low-coherence light, a tandem of a readout interferometer and a sensing interferometer with reference
and sample arms, and a handheld probe integrated into the sensing interferometer through polarization-maintaining fibers.
The system provides fast electro-optic switching over orthogonal polarization components of a measurand light beam at the
same output from the sensing interferometer. At said output either of the aforementioned components remains perpendicular
to the polarization plane of light in the reference arm. For either of the components the readout interferometer compensates
optical path length differences in the sensing interferometer within a given interval of depth in the sample, and evolves
spatial fringes which are read out by optoelectronic means without any mechanical scanning in depth. The fringes are devoid
of cross-correlation artifacts inasmuch as the readout interferometer recombines coherently the measurand beam and the
reference beam having mutually orthogonal polarizations only.
A novel wavelength swept broadband source based on an ultrashort pulse laser and an external tunable filter was
proposed for application of frequency domain-optical coherence tomography (FD-OCT). The laser beam coupled into
the single mode fiber, which provided 0.5-nm instantaneous spectral linewidth with 1-mW average output power, was
tuned from 740 nm to 850 at a 1 kHz repetition rate. The system with an axial resolution of 5 &mgr;m performed OCT
imaging of air-gap between glass plates proving potential about the application of pulse laser source to FD-OCT
system. The proposed swept source scheme could be applied for the implementation of ultra-high resolution FD-OCT
system based on a supercontinuum source with an ultra-short pulse laser and a high nonlinear optical fiber.
We investigate the characteristics of resonant mode of a cavity with two-dimensional (2D) photonic crystal (PC) mirrors using the finite difference time domain simulation. The employed PC mirrors are composed of a square array of dielectric rods in air. As the dielectric constant of the rods increases, the frequency of resonant mode decreases whereas its Q factor increases. However, both the frequency and Q factor of a resonant mode increases as the number of dielectric rod increases. To clarify the mechanism that determines the frequency of resonant modes, we have studied the characteristics of resonant modes of one-dimensional PC cavities made of PCs. Our study of one-dimensional PC cavity demonstrates that both the phase change due to the reflection at the surface of PC mirror and the optical path length between PC mirrors play important roles in the determination of the position of resonant frequency. We also discuss the tunable PC filters implemented with the PC mirrors composed of some materials, such as liquid crystal, whose dielectric constant depends on an external field. In this case, the phase change due to the reflection can be controlled by changing the dielectric constant of liquid crystals in the PC mirrors.
The effects of liquid crystal (LC) infiltration on the photonic band gaps (PBGs) of two-dimensional (2D) metallic photonic crystals (PCs)are investigated by theoretical calculation. Contrary to the LC-infiltrated dielectric photonic crystals, the infiltration of LCs into 2D metallic PCs is found to enlarge PBGs and create another PBGs in a frequency range higher than that of the original PBG. The change of refractive index due to the phase transition of LCs affects both edges of PBGs so that the positions of PBGs show rather large temperature dependence near the phase transition temperature. Thus metallic PCs infiltrated with LCs can overcome the drawbacks of LC infiltration in dielectric PCs, i.e., the band gap narrowing and weak tunabilty of band gap. The usefulness of LC infiltration in the implementation of 2D or 3D tunable metallic photonic crystals is also discussed.
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