We proposed a method for ultra-high group index slow light with high optical buffering performance based on photonic crystal waveguide coupled with a cavity. By introducing cavity analogous to rhombus shape in photonic crystal waveguide center, slow light properties and buffering performance are studied. Numerical results through plane-wave expansion method and model field distribution through finite-difference time domain method show that both the rhombus cavity radii and some discriminatory rods around rhombus cavity have a plentiful effect on slow light properties and buffering fulfillment. By adjusting the cavity rod radii, we obtained high group index of 5163 with buffering bit length Lbit about 17.968 μm and delay time Ts reaching to 51.967 ps through the waveguide-cavity length of 3.02 μm. Moreover, low group velocity dispersion can be achieved, with governable positive and negative values. To regulate the optimal parameters to increase the group index and demonstrate the delay time performance, some discriminatory rods around rhombus cavity are adjusted in the upper and lower edges confronting each other in the waveguide, and ultra-high group index as exceedingly large as 22350 is obtained that is extremely higher than previous studies. Simultaneously, the corresponding buffer bit length Lbit and delay time Ts reach respectively to 25.8279 μm and 225.7783 ps through the waveguide-cavity length of 3.0306 μm. We designed a simple structure but a more generalized that may contribute a requisite theoretical basis for potential industrial applications in the storage capacity properties of high group index for optical buffering and optical communication systems.
KEYWORDS: Electrons, Electromagnetism, Motion models, Extremely high frequency, Information technology, Tungsten, Electron beams, Laser systems engineering, Oxides, Electroluminescence
A physical model of obitron radiation is presented in this paper. Result of calculations according to this model agrees quite well with that obtained in obitron experiments. New ways are pointed out and new schemes are proposed fcr millimeter wave generation.
When evaluating the detection probability of a pulsed Gm-APD laser ranging system with a propagation path close to the ground, the detection probability limitation caused by the atmospheric turbulence cannot be ignored. Based on modulated Poisson model, the detection probability limitation due to the turbulence effects is investigated, and a cumulative pulses detection method is proposed to restrain the turbulence effects. The results show that the influence of the turbulence effects is equivalent to adding a new noise source to the echo intensity, the detection probability results in a worse situation with stronger turbulence effects, when the turbulence degree is 1.5 and the echo intensity is 10, the target detection probability decrease by 0.17, and the false alarm probability increases by 0.03. By utilizing the cumulative pulses detection technique, the target detection probability and false alarm probability improve by 0.3 and 0.07, respectively.
The wavelength dependence of the nonreciprocal phase shift (NPS) in a magneto-optical (MO) waveguide is investigated from the aspect of the geometrical structure. In an MO nonreciprocal waveguide, the effect of the waveguide dispersion on the NPS is being demonstrated to compensate the dispersion of the Faraday rotation coefficients. By accurately controlling the structure parameter of the MO waveguide, the wavelength-insensitive NPS can be obtained. According to this principle, we proposed the dual-wavelength nonreciprocal phase shifter at the wavelengths of 1.31 and 1.55 μm.
Detection of signals in the THz frequency region is important for applications of THz waves in many areas, such as in
medical imaging, forbidden-combined sensing, weapon monitoring, and wireless communications. Cooling system
operating under very low temperature, for eliminating the unwanted background THz radiation that exists everywhere in
room temperature, sets an obstacle for applications of conventional THz signal detecting systems. We present a
combined cavity that can pick out the useful signal in high sensitivity, while the influence of the background THz
radiation can be neglected in the detection. The combined cavity consists of a point-defect photonic-crystal resonator
and a photonic-crystal WGR. The two resonators are coupled together through optical tunneling to form the combined
cavity. Under proper operating parameters, the two resonators are in simultaneous resonance, and the field intensity in
the point-defect resonator can be thousands of times of that of an incoming THz signal for a given frequency, so that the
sensitivity of detection can be very high. Since the background THz radiation is not in resonance with the cavity, the
influence of it to the detection of THz signals wanted can be neglected, and thus cooling systems can be omitted. Plane
wave expansion method is used to determine the resonance wavelengths and mode patterns of the cavity. Finite-difference-
time-domain method is used to find the quality factors and to simulate the resonance process. Parameter
optimization and the conditions for simultaneous resonance of the two cavities are studied.
Based on a model of coupling Maxwell's equations with the rate equations of electronic population, the spatial-distribution
and spectrum-characteristics as well as amplified properties of defect modes such as lasing threshold,
saturated output in a single-defect active photonic crystal are investigated through finite-difference time-domain method.
Influences of the number of crystal periods and spatial profile on amplified feature are also analyzed. The results show
that the lasing threshold and saturated output depend directly on the number of crystal periods and the spatial profile of
defect modes; the defect mode with lower mode area has a low-threshold. Furthermore, the lasing threshold can be
further reduced as the saturated output increases if the number of crystal periods increase. Such a feature is important for
understanding of the interaction between optical gain and defect modes.
We systematically investigate realization of super narrow-pass-band and super narrow-transmission-angle filters with
one-dimensional defective photonic crystal hetero-structures through the transfer-matrix method. The structure consists
of a few different defective one-dimensional photonic crystal blocks. The influence of the relative bandwidth of the
defective layer, the number of periods, and the ratio of index of the high index material to the low index material in the
structures were studied. We find that when the relative width factor m and n of the defective layers are even numbers,
relatively narrower pass-angle will be achieved. When the number of periods of the structures increases, the pass-angle
will decrease exponentially. When the number of periods reaches 12, the pass-angle gets to be less than 0.002 degree. In
addition, higher ratio of the two indices in the structures corresponds to smaller transmission angle and narrower
wavelength pass-band.
Using a time-independent calculation based on self-consistent transfer matrix method, we numerically investigate
localized mode in a one-dimensional (1D) weakly disordered medium containing Lorentz dispersive material. The result
show that the random medium containing dispersive media has frequency-dependent localized modes. Such localized
modes strongly depend on dispersive parameters, such as transverse optical phonon frequency ω0, oscillator strength Χ0 and thickness of dispersive layer. The resonant frequency of such mode can be modified to shift by applying a dispersive
medium. By this study, we will acquire some knowledge of localized mode in dispersive disorder medium; furthermore,
this study suggests a method to realize tenability of localized mode, which is important for application of random laser.
We investigated the group-velocity dispersion of a one dimensional uniform photonic crystal by the optical transmission method. For application in optical communications, the wavelength should be near one of the two edges of a photonic bandgap. Four kinds of
dispersion-compensation may be obtained with a photonic crystal. Huge negative and positive group-velocity-dispersion (GVD) about a
zero-dispersion-point as large as 5.1 Tera- ps/nm/km by a photonic crystal of 100 periods can be realized. Such a value is about 50 Giga times the GVD of conventional dispersion-compensation fibers. The GVD reaches a maximum when the optical length ratio of the high refractive index material to the low refractive index material is 1.2 for given operating parameters. When we keep the optical length of each layer being constant, the GVD is found to increase rapidly with the refractive index ration of the high refractive index material to the low one and even more rapidly with the number of periods of a photonic crystal. Under quite common operating parameters, a thin piece of photonic crystal of 100 periods may play the role of an ordinary dispersion-compensation fiber with a length over 158
kilo-meters.
We propose a kind of planar photonic crystal micro-cavity which is truly two-dimensional and is composed of a line of periodic air-holes and a set of periodic air grooves both with defect. Unlike the photonic crystal micro-cavity formed by distributed Bragg reflection (DBR) layers and two dimensional holes in a semiconductor substrate, the micro-cavity proposed is a true two-dimensional planar structure that is easy for mass-production through die-press copying. Numerical simulations by the FDTD method show that there exist resonance modes inside the photonic bandgap. The resonance wavelength is mainly decided by the period and radius of the holes. The quality factor of the cavity is mainly decided by the number of periods of the holes and the grooves.
We investigate a complex cavity composed of three simple cavities, which are formed by three simple defects in a one-dimensional photonic crystal (PC), by the optical transmission method. We set two of the simple cavities to be the same, and let the cavity-length of the third one vary. Generally, two or more narrow resonant transmission modes emerge in the bandgap region; the position of one of them is basically fixed with different fine structures, in which exists a fixed crest, while the other modes wander in the bandgap region as the cavity-length of the third cavity varies. We find the optimized the relative coupling length being 0.447 for the complex cavity. Introducing the parameter - degree of rectangularity, we find that the complex PC cavity is much more close to an ideal narrow band-pass filter than a simple PC defect cavity. It is surprising that the degree of rectangularity is insensitive to the number of periods in the structures.
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