فهرست مطالب mahmood seifouri

In this paper, we proposed a two-channel demultiplexer based on two-dimensional (2D) photonic crystal (PhC) circular nano-resonator. the structure consists of two photonic crystal filters. At first, we analyze the photonic crystal filter. In this analysis, the structure is optimized by scanning the radius of nano-resonators central rods and radius of scattering rods. The results reveal that the average quality factor, average transmission coefficient, average crosstalk, and average channel width are respectively obtained as 3506.9, 94.3%, -25.35 dB, and 0.45 nm. The advantages of this design is simple structure and small size, which can be used in WDM systems.

n this paper, the generation of a highly broadband supercontinuum spectrum has numerically been investigated in a suspended As2Se3 based ridge waveguide. By changing the dimensions of the proposed waveguide, the dispersion has been engineered to achieve a suitable profile with the two zero-dispersion wavelengths as well as the lower magnitude and flat anomalous dispersion regime. Due to the high refractive index contrast between the core and cladding, the propagated light has been highly confined in the core and as a result, a high optical nonlinear coefficient has been obtained. Simulation results show that when the pump pulses with a width of 100 fs and peak power of 1KW at the wavelength of 2150 nm are injected into the designed

In this paper, Using a 2D photonic crystal and a novel square ring resonator,several compact and simple structures have been introduced in the present paper toconstruct optical add/drop filters and multi-channel filter. The difference structures hasbeen designed and simulated by using the proposed square ring resonator and differentdropping waveguides. To do analyses, the finite-difference time-domain method and theplane wave expansion have been used. The three add/drop filters can separate thewavelength of 1554 nm with a transmission coefficient of 100 %, quality factor of 1295and bandwidth of 1.2 nm. The models of structures are simulated by the RSOFT CADLayoutsoftware. The results, flexibility and simplicity of structures have caused fromtheir used to designing of an optical multi-channel filter with a channel spacing of 1.5nm. The advantages of this design include the channel spacing, quality factor,transmission coefficient and bandwidth which are suitable for applicability in opticalcommunication systems such as wavelength division multiplexing systems.

Ring resonators have always been referred to as a highly flexible structure for designing optical devices. In this study, we have designed and simulation a four channel optical demultiplexer using square photonic crystal ring resonator. The square lattice constant for this purpose structure is used. The purposed structure has an average crosstalk, transmission coefficient, quality factor and channel spacing of -14.5 dB, 90%, 858 and 1.6 nm, respectively. To obtain the photonic band gap of the structure, the plane wave expansion (PWE) method has been used and the finite-difference time-domain (FDTD) method has been also used to analyze the optical behavior of the structure. The good results obtained from designing and simulating optical demultiplexer structure such as narrower channel spacing indicate the high flexibility of this structure and ring resonator for being used in designing optical devices as well as their suitability for being used in wavelength division multiplexing (WDM) systems.

Taking advantage of chemical potential (μ_c) one layer and multi layers graphene nano ribbons, we designed and analyzed performance of plasmonic switches at mid-IR wavelengths. By slight varying the chemical potential of graphene, significant resonance shifts (∆λ) and modulation depth (MD) achieved. Finite element method numerical simulation show that plasmonic switch made of hexagonal boron nitride (hBN)/Graphene suffering relatively large MD and wavelength shifts with N=6, and varying μ_c from 0.3eV- 0.4eV, 14 dB and 2.8 µm, respectively. The proposed structure could be useful for research in compact and largely tunable mid-infrared photonic devices to realize on-chip CMOS optoelectronic systems.

In this paper, an optical filter based on a two dimensional photonic crystal ring resonator (PCRR) with triangular lattice is designed and presented. For this purpose, the effects of positioning, arrangement and the number of the inner rods of he dual-curved PCRR on the performance characteristics of our optical filter such as the transmission coefficient and the quality factor have been fully investigated. Calculation results show that a transmission coefficient of 100% with a quality factor of 2400 at the operating wavelength of nearly 1576 nm can be achieved. The proposed optical filter comparatively performs better than the previously reported ones. In addition, this structure can be used for the design of optical multi-channel demultiplexer. To study the photonic band gap of our structure, the plane wave expansion (PWE) method has been used and the finite-difference time-domain (FDTD) method has also been employed to analyze the optical behavior of the proposed device.

Waveguides with low confinement loss, low chromatic dispersion, and low nonlinear effects are used in optical communication systems. Optical fibers can also be employed in such systems. Besides optical fibers, photonic crystal fibers are also highly suitable transmission media for optical communication systems. In this paper, we introduce two new designs of index-guiding photonic crystal fiber (IGPCF) with characteristics appropriate for optical communications. In the first proposed design with a hexagonal structure having a defect at the center, the chromatic dispersion at the wavelength of 1550 nm is less than 1 ps/(nm.km). In the second design with a hexagonal structure having air holes with unequal diameters, nearly zero dispersion at the wavelength range of 1370 to 1380 nm is achieved. At the same time, for the latter design, at the wavelength of 1550 nm, the chromatic dispersion slope is1 ps/(km.nm), the confinement loss is less than 10-9 dB/km, and the nonlinear coefficient reaches 3.690 W-1.km-1.

In this paper a hexagonal Photonic Crystal Fiber (PCF) structure with Unequal hole size in silica core is proposed. By compromising between dispersion, Effective Area, confinement loss and the number of propagation modes, the higher orders of dispersion can be reduced significantly. Simulation results demonstrate that, zero flattened dispersion with very low slope over a wide wavelength range of 1.2μm to 1.6μm in abnormal dispersion region with single mode propagation can be achieved. By passing a 28fs laser pulse with a maximum power of 5kw in a 15cm long of such a PCF, supercontinuum output spectrum is simulated over the wavelength range of 1.4μm to 1.62μm.

In this paper, we report a new design of As2Se3 chalcogenide glass photonic crystal fiber (PCF) with ultra-flattened dispersion at mid-infrared wavelength range. We have used the plane wave expansion method (PWE) for designing the structure of As2Se3 glass PCF at different wavelength windows. In the proposed structure with hole to hole spacing and, the negative dispersion is -1025 ps/nm/km at the wavelength of 1.55µm and also an ultra-flattened dispersion is achieved at the wavelength range of 3.5-18μm. Hence such PCFs have a high potential to be used as dispersion compensating fibers at 1.55µm wavelength in optical communication systems. The ultra-flattened dispersion at the wavelength range of 3.5-18μm can be employed to achieve high power supercontinuum generation. The nonlinear coefficient of the proposed PCF is at the wavelength of 1.55µm. Chalcogenide glasses are known to have both high transparency and nonlinearity in a wide range of infrared wavelengths compared to silica glasses.

RGC structure is used to neutralize the effect of optical sensor parasitic capacitance at input of broadband transimpedance in an optical link Because of its very low input impedance. In this paper, an improved RGC structure is proposed. This improved structure is simulated using ADS in 0.18μm CMOS platform. The simulation results show that the structure provides transimpedance of 60dBΩ at the bandwidth interest of 9GHz. With such a bandwidth, this structure can be used in optical telecommunication systems based SONET OC-192 protocols. Similarly, our results illustrate that, the proposed structure provides higher gain-bandwidth product than in comparison with previous similar design. Consequently there is no requirement for an additional gain stage following the RGC structure in the conventional transimpedance amplifier design. Therefore, both the power consumption and input referred noise current spectral density will decreases.