Saghaei's papers published in 2016, 2015, 2014, 2012 and 2011

[1] H. Saghaei, V. Heidari, M. Ebnali-Heidari, and M. R. Yazdani, “A systematic study of linear and nonlinear properties of photonic crystal fibers,” Optik, vol. 127, no. 24, pp. 11938–11947, 2016, doi: 10.1016/j.ijleo.2016.09.111.

In this paper, linear and nonlinear properties of photonic crystal fiber (PCF) are studied in terms of wavelength for triangular and square lattices to investigate the effects of changing the fiber dimensions including air-hole diameter, pitch size, and the number of air-hole rings on the dispersion profile and its nonlinear parameter. A chalcogenide-based PCF is proposed in this paper and modeled in the TCAD environment of Mode Solution software related to the Lumerical package. The finite difference eigenmode solver numerical method is utilized in the modeling and anisotropic perfectly matched layers (PML) are assumed as absorbing boundaries to be positioned outside the outer-most ring of the air-holes. Accordingly, the effects of changing each of the aforementioned parameters on the value and slope of dispersion and loss profiles as well as on its nonlinear parameter are systematically determined. For instance, numerical results achieved by the simulation results show that both the value and slope of dispersion profile are reduced by considering the diameter of air holes with a constant value and increasing the pitch size of the fiber. Moreover, considering a fixed value for the pitch size and increasing the air hole diameters lead to an increase of dispersion profile in terms of wavelength. Additionally, the numerical results show that an increase in the diameter of the air holes results in an increase in the nonlinear parameter. Further, the input source’s wavelength increase will result in the reduction of the nonlinear parameter.

[2] H. Saghaei, M. K. Moravvej-Farshi, M. Ebnali-Heidari, and M. N. Moghadasi, “Ultra-Wide Mid-Infrared Supercontinuum Generation in As40Se60 Chalcogenide Fibers: Solid Core PCF Versus SIF,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 22, no. 2, 2016, doi: 10.1109/JSTQE.2015.2477048.

Due to the pronounced scientific and technical attention paid to the mid-infrared spectral region, we focus on ultra-wide mid-infrared supercontinuum generation in As 40 Se 60 chalcogenide SIF and PCF - step-index and photonic crystal fibers - using a symmetrized split-step Fourier method (S-SSFM). Simulations reveal, in response to launching 100 fs input pulses of 50 kW peak powers, with near zero-dispersion wavelengths centered about λ 0 = 8.5 μm, into 50-mm long As 40 Se 60 SIF and solid core PCF, 8.5 and 11-μm supercontinua can be achieved, respectively. Moreover, numerical results also show, when ultra-short pulses of center wavelengths λ 0 = 12 μm are launched into those SIF and PCF, ripple-free spectra as wide as 10 and 13 μm can be attained, respectively. These spectra are useful for safe spectroscopic medical imaging diagnosis such as early cancer diagnostics, and other spectroscopic applications such as gas sensing and food quality control.

[3] H. Saghaei, M. Ebnali-Heidari, and M. K. Moravvej-Farshi, “Midinfrared supercontinuum generation via As_2Se_3 chalcogenide photonic crystal fibers,” Applied Optics, vol. 54, no. 8, p. 2072, 2015, doi: 10.1364/ao.54.002072.

Using numerical analysis, we compare the results of optofluidic and rod filling techniques for the broadening of supercontinuum spectra generated by As2Se3 chalcogenide photonic crystal fibers (PCFs). The numerical results show that when air-holes constituting the innermost ring in a PCF made of As2Se3-based chalcogenide glass are filled with rods of As2S3-based chalcogenide glass, over a wide range of mid-IR wavelengths, an ultra-flattened near-zero dispersion can be obtained, while the total loss is negligible and the PCF nonlinearity is very high. The simulations also show that when a 50 fs input optical pulse of 10 kW peak power and center wavelength of 4.6 μm is launched into a 50 mm long rod-filled chalcogenide PCF, a ripple-free spectral broadening as wide as 3.86 μm can be obtained.

[4] M. Ebnali-Heidari, H. Saghaei, F. Koohi-Kamali, M. Naser Moghadasi, and M. K. Moravvej-Farshi, “Proposal for Supercontinuum Generation by Optofluidic Infiltrated Photonic Crystal Fibers,” IEEE Journal on Selected Topics in Quantum Electronics, vol. 20, no. 5, 2014, doi: 10.1109/JSTQE.2014.2307313.

We propose a technique based on optofluidic infiltration to design a photonic crystal fiber (PCF) to control chromatic dispersion for supercontinuum generation. Selectively infiltrating the PCF air-holes with an optical fluid having an appropriate refractive index, we have achieved a PCF with low confinement loss and ultra-flattened near zero dispersion centered about λ ZD ~ 1325 nm, without a need for nano-scale geometrical tuning. Numerical simulations show that femto-second pulses, with center wavelengths within the range of 1250 nm ≤ λ 0 ≤ 1625 nm, can generate relatively flat supercontinuum spectra as wide as 640 to 1180 nm, passing through a 250-mm long PCF whose dispersion profile is engineered via selective optofluidic infiltration. Simulations also show that optical fluid with refractive index of n F = 1.32 for input signals having the aforementioned range of wavelengths result in the widest flat supercontinua. This is attributed to the smallest corresponding effective mode area as well as the smallest and flat corresponding dispersion both of which enhance the PCF nonlinearities.

[5] M. Ebnali-Heidari, F. Dehghan, H. Saghaei, F. Koohi-Kamali, and M. K. Moravvej-Farshi, “Dispersion engineering of photonic crystal fibers by means of fluidic infiltration,” Journal of Modern Optics, vol. 59, no. 16, pp. 1384–1390, 2012, doi: 10.1080/09500340.2012.715690.

We present a technique based on the optofluidic method to design a photonic crystal fiber (PCF) experiencing small dispersion over a broad range of wavelengths. Without nano-scale variation in the air-hole diameter or the lattice constant of Λ, or even changing the shape of the air holes, this approach allows us to control the dispersion of the fundamental mode in a PCF simply by choosing a suitable refractive index of the liquid to infiltrate into the air holes of the PCF. Moreover, one can design a different PCF such as a dispersion flattened fiber (DFF), dispersion shifted fiber (DSF), by utilizing fluids of various refractive indices.

[6] H. Saghaei, B. Seyfe, H. Bakhshi, and R. Bayat, “Novel approach to adjust the step size for closed-loop power control in wireless cellular code division multiple access systems under flat fading,” IET Communications, vol. 5, no. 11, pp. 1469–1483, 2011, doi: 10.1049/iet-com.2010.0029.

In this article, we study the power control (PC) process in wireless cellular code division-multiple access systems under flat fading and propose a novel approach to find an optimum step size for closed-loop power control algorithms. In this approach, an optimum step size will be computed from a proposed function. This function depends on system parameters such as, the number of co-channel users, processing gain, the period of PC, Doppler frequency, channel attenuation and the order of diversity. Based on this computation, the mobile station (MS) adjusts its transmit power optimally to decrease interference for other co-channel users. Simulation results for different sets of system parameters show that the proposed algorithm decreases the bit error rate, the outage probability at the base station (BS), and increases the battery life of the MS compared with other values of the step size. The performance of the proposed algorithm is compared with the fixed-step-size power control algorithm and superiority of its performance is confirmed by simulation results. Moreover, the upper and lower bounds of the outage probability and the received signal-to-interference ratio for the proposed algorithm at the BS will be calculated.