International Journal of

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In this paper we present an in-depth review on the trends and the directions taken by the researchers worldwide in Optical Code Division Multiple Access (OCDMA) systems. We highlight those trends and features that are believed to be essential to the successful introduction of various OCDMA techniques in communication systems and data networks in near future. In particular we begin by giving a comprehensive review on the constructions of optical orthogonal codes (OOC). In our system study we first focus and discuss on various OCDMA techniques such as 1-D, 2-D and spectrally-encoded ultrashort light pulse CDMA, and discuss their pros and cons. A comprehensive discussion takes place on all important aspects of each OCDMA technique. In particular, we elaborate on enabling technologies that are needed prior to full scale consideration of OCDMA in communication systems. We extend our discussion to various data networks, including fiber-based and wireless to indicate the directions and the applications that OCDMA systems are considered for. It is believed that OCDMA once fully developed and matured will be an inseparable part of advanced optical communication systems and networks due to its various desirable features and functionalities, in not so distant future.

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In this paper the Phase-Matching bandwidth, effective nonlinear coefficient and the walk-off angle within the effective bandwidth of the LiGa(SexS1-x)2 biaxial nonlinear crystals are calculated using the Genetic algorithm (GA). This calculation is held for all tree principle XY, YZ and XZ planes individually. The results are shown the accuracy of the applied algorithm is quite qualified.

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We generalized the squeeze and displacement operators of the one-dimensional harmonic oscillator to the three-dimensional case and based on these operators we construct the corresponding coherent and squeezed states. We have also calculated the Wigner function for the three-dimensional harmonic oscillator and from the analysis of time evolution of this function, the quantum Liouville equation is also presented. Further properties of the quantum states including Mandel’s 􀡽 and quadrature squeezing parameters are discussed as well.

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We proposed and analyzed implementation of the single-qutrit quantum gates based on stimulated Raman adiabatic passage (STIRAP) between magnetic sublevels in atoms coupled by pulsed laser fields. This technique requires only the control of the relative phase of the driving fields but do not involve any dynamical or geometrical phases, which make it independent of the other interaction details: detuning and pulse shapes, areas and durations. The suggested techniques are immune to spontaneous emission since the qubit and qutrit manipulation proceeds through non-absorbing dark states. In this paper, taking proper timing of the Rabi frequencies allows us to transfer the population of the system to a desired superposition of the ground states with the highest fidelity. We also obtained and implemented single-qutrit unitary gates, for transferring of the population of the system with different initial and final states.

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The Photoexcited carrier lifetime (τ) and peak to valley transmission difference (ΔTp-v) in direct and indirect band gap crystals has been investigated by the use of single beam open and closed aperture z-scan technique using frequency doubled Nd:YAG laser. The peak to valley transmission difference (ΔTp-v) is found to be of the order of 10-2 in case of direct band gap crystals and of the order of 10-3 in case of indirect band gap crystals. The carrier life time (τ) is found to be in nanoseconds range in case of direct band gap crystals and picoseconds range in case of indirect band gap crystals. Lower value of (τ) and (ΔTp-v) in case of indirect band gap crystals can be attributed to the reduction in the value of carrier density (N) and small value of nonlinear phase shift ( Δϕ ),respectively.

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In this paper, properties of reflection phase in one-dimensional quaternary photonic crystals combining dispersive meta-materials and positive index materials are investigated by transfer matrix method. Two omnidirectional band gaps are located in the band structure of considered structure. However, we limit our studies to the frequency range of the second wide band gap. We observe that the value of the reflection phase difference between TE and TM waves can be controlled by changing the incident angle and frequency. Also, the results show that the reflection phase difference in the second band gap increases by increasing the incident angle, and remains almost unchanged in a broad frequency band. Furthermore, at two points near to the edges of the gap the reflection phase difference keeps almost zero in spite of the change of incident angle. Based on these properties, phase compensators and omni-directionally synchronous reflectors and also polarizers can be designed.

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We present the procedure for designing a high speed and low power all-optical analog to digital converter (AO-ADC), by integrating InGaAsP semiconductor optical amplifier (SOA) with InP based photonic crystal (PhC) drop filters. The self-phase modulation in the SOA can shift the frequency of the Gaussian input pulse. The two output PhC based drop filters are designed to appropriately code the frequency-shifted analog signals by the SOA, converting them to four desired digital output levels. Our numerical results show that in an appropriately designed AO-ADC, the center wavelength (1572 nm) of an amplitude modulated Gaussian pulse of 1.8 ps width and 1.56 pJ energy can be shifted by 6.7 nm, by the SOA, and then be quantized and coded to four digital levels (00, 01, 10, and 11). The two point-defect PhC drop filters, compensating the effect of the frequency shift by SOA, minimize the AO-ADC integral and differential nonlinearity errors.

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The well-established Fresnel diffraction occurs as an opaque object partially obstructs the passage of a coherent beam of light. In this process, the amplitude of the optical wave experiences a discontinuous change that leads to peculiar bright and dark fringes near the ray optics border of the beam. The fringe pattern varies very slowly by distance from the object and away from the beam border the diffraction effect is negligible. These behaviors have limited the applications of the conventional Fresnel diffraction very severely. In this article, we introduce a new kind of Fresnel diffraction that occurs due to discontinuous change in phase or phase gradient, in a part of a coherent beam of light. The change splits the beam into two diffracting wavefronts with common border that interfere with each other. In this kind of diffraction, the fringes may appear in the central part of the beam and their locations and visibilities are very sensitive to the phase change. Therefore, the researchers have utilized the effect in the measurements of different physical quantities, with high accuracy, using modest equipment. In this article, we use the Fresnel diffraction from the semi-infinite opaque screen (knife- edge) as the building block to describe the introduced effect, diffraction from the phase steps, and discuss its different aspects. We simulate the implied diffraction patterns, investigate the patterns by experiments, elaborate on the unique features of the effect, and present some interesting applications.

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The simulation results of a 10-kW heat capacity slab laser are presented. Two different schemes for optical pumping with high-power laser diodes are investigated. The simulation of optical pumping using ZEMAX software demonstrates a uniform pump distribution within the laser slabs. Additionally, the temperature distribution in the laser slab is examined using COMSOL. The findings for two distinct laser designs reveal that increasing the slab dimensions reduces the temperature distribution and thermal issues. Furthermore, cooling schemes indicate that the cooling phase of a 10-kW HCL falls within the range of 20-40 seconds. A comparison of water and air cooling of the optically pumped slabs during the cooling phase demonstrates that water cooling is more efficient than air cooling. The simulation results confirm that the proposed laser will be an efficient device for laser material processing. A focused 10-kW HCL laser will melt the steel sheet after less than 1 s at 1490 K.

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The spatial self-phase modulation (SSPM) method was used to study the nonlinear optical responses of hydraulic oil containing dispersed nanosheets of reduced graphene oxide (rGO), hydroxylated rGO (rGO-OH), and carboxylated rGO (rGO-COOH). The intensity-dependent number of observed symmetric diffraction rings was analyzed to estimate the samples' thermally induced nonlinear refractive indexes and lead to estimated thermo-optical coefficients. Based on the observed symmetric diffraction rings, the nonlinear refraction coefficient and thermo-optical coefficient of samples were estimated to be in the order of magnitude of 10^-6 cm²/W and 10^-2 K^-1, respectively. The results indicated that the presence of rGO derivatives significantly enhanced the optical nonlinearity of hydraulic oil.