Alireza Mowla

Design of a flat-gain multipumped distributed fiber Raman amplifier by particle swarm optimization

The pumping scheme of multipumped distributed fiber Raman amplifiers is optimized by a powerful method called particle swarm optimization. By use of particle swarm optimization, we optimize both pump powers and frequencies of multipumped Raman amplifiers with a high number of pumps. Particle swarm optimization is a fast and effective method, and it surpasses other optimization methods, such as the genetic algorithm, for optimizing fiber amplifiers. It is shown that the computational efficiency of particle swarm optimization is significantly better than that of the genetic algorithm, reducing the time of computation to one third, and its implementation is more straightforward. A gain bandwidth of 92.1 nm and a gain variation of 0.49 dB in the range of 1524.5-1616.6 nm are obtained by this method, using ten backward pumps in a 60-km-long amplifier. The gain variation reduction is due to the inclusion of pump frequencies in the optimization process.

Effect of the optical system on the Doppler spectrum in laser-feedback interferometry

We present a comprehensive analysis of factors influencing the morphology of the Doppler spectrum obtained from a laser-feedback interferometer. We explore the effect of optical system parameters on three spectral characteristics: central Doppler frequency, broadening, and signal-to-noise ratio. We perform four sets of experiments and replicate the results using a Monte Carlo simulation calibrated to the backscattering profile of the target. We classify the optical system parameters as having a strong or weak influence on the Doppler spectrum. The calibrated Monte Carlo approach accurately reproduces experimental results, and allows one to investigate the detailed contribution of system parameters to the Doppler spectrum, which are difficult to isolate in experiment.

A Novel Design Approach for Erbium-Doped Fiber Amplifiers by Particle Swam Optimization

A novel design approach for erbium-doped fiber amplifiers is proposed based on particle swarm optimization algorithm. The main six parameters of the EDFAs including: pumping wavelength, input signal power, fiber numerical aperture, erbium-doped area radius, erbium concentration, and the fiber length are optimized utilizing a fast and efficient method called particle swarm optimization algorithm. In this paper, a combination of fiber amplifier bandwidth, gain, and flatness are taken into account as objective function and the results are presented for different pump powers. Our investigation shows that particle swarm optimization algorithm outperforms genetic algorithm in convergence speed, straightforwardness, and coping with high- dimensional spaces, when the parameters of EDFA are to be optimized. It has been shown that the required time for the optimization of the fiber amplifier parameters is reduced four times by using particle swarm optimization algorithm, compared to genetic algorithm method.

Wideband Gain Flattened Hybrid Erbium-doped Fiber Amplifier/Fiber Raman Amplifier

An optimal wideband gain flattened hybrid erbium-doped fiber amplifier/fiber Raman amplifier (EDFA/FRA) has been introduced. A new and effective optimization method called particle swarm optimization (PSO) is employed to find the optimized parameters of the EDFA/FRA. Numerous parameters which are the parameters of the erbium-doped fiber amplifier (EDFA) and the fiber Raman amplifier (FRA) define the gain spectrum of a hybrid EDFA/FRA. Here, we optimize the length,

Optimum design of a hybrid erbium-doped fiber amplifier/fiber Raman amplifier using particle swarm optimization.

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Concurrent Reflectance Confocal Microscopy and Laser Doppler Flowmetry to Improve Skin Cancer Imaging: A Monte Carlo Model and Experimental Validation

concentration, and pump power and wavelength of the EDFA and also pump powers and wavelengths of the FRA to obtain the flattest operating gain spectrum. Hybrid EDFA/FRA with 6-pumped- and 10-pumped-FRAs have been studied. Gain spectrum variations are 1.392 and 1.043 dB for the 6-pumped- and 10-pumped-FRAs, respectively, in the 108.5 km hybrid EDFA/FRAs, with 1 mW of input signal powers. Dense wavelength division multiplexing (DWDM) system with 60 signal channels in the wavelength range of 1529.2-1627.1 nm, i.e. the wide bandwidth of 98 nm, is studied. In this work, we have added FRAs pump wavelengths to the optimization parameters to obtain better results in comparison with the results presented in our previous works.

A compact laser imaging system for concurrent reflectance confocal microscopy and laser doppler flowmetry

We propose and optimize a hybrid erbium-doped fiber amplifier/fiber Raman amplifier (EDFA/FRA). A large number of parameters of a wide-band hybrid amplifier consisting of an erbium-doped fiber amplifier (EDFA) and a fiber Raman amplifier (FRA) have been optimized using an effective and fast global optimization method called particle swarm optimization. Two types of hybrid EDFA/FRA with six- and 10-pumped FRAs have been optimized. A large number of variables affect the hybrid EDFA/FRA performance, thus we need a global optimization method to be able to deal with these variables. Particle swarm optimization helps us to find optimum parameters of a hybrid EDFA/FRA and reduce the gain spectrum variations to 2.91 and 2.03 dB for the six and 10 pumped FRAs, respectively. The optimum design supports the amplification of 60 signal channels in the wavelength range of 1529.2-1627.1 nm for a wavelength-division multiplexing system.

Self-mixing sensing system based on uncooled vertical-cavity surface-emitting laser array: linking multichannel operation and enhanced performance

Optical interrogation of suspicious skin lesions is standard care in the management of skin cancer worldwide. Morphological and functional markers of malignancy are often combined to improve expert human diagnostic power. We propose the evaluation of the combination of two independent optical biomarkers of skin tumours concurrently. The morphological modality of reflectance confocal microscopy (RCM) is combined with the functional modality of laser Doppler flowmetry, which is capable of quantifying tissue perfusion. To realize the idea, we propose laser feedback interferometry as an implementation of RCM, which is able to detect the Doppler signal in addition to the confocal reflectance signal. Based on the proposed technique, we study numerical models of skin tissue incorporating two optical biomarkers of malignancy: (i) abnormal red blood cell velocities and concentrations and (ii) anomalous optical properties manifested through tissue confocal reflectance, using Monte Carlo simulation. We also conduct a laboratory experiment on a microfluidic channel containing a dynamic turbid medium, to validate the efficacy of the technique. We quantify the performance of the technique by examining a signal to background ratio (SBR) in both the numerical and experimental models, and it is shown that both simulated and experimental SBRs improve consistently using this technique. This work indicates the feasibility of an optical instrument, which may have a role in enhanced imaging of skin malignancies.

Confocal laser feedback tomography for skin cancer detection

We propose a compact laser feedback interferometry imaging system for concurrent reflectance confocal microscopy and laser Doppler flowmetry. This system acquires both confocal reflectance and Doppler signals in a confocal architecture to image dynamic turbid media with higher contrast than a system operating in either modality and is coherent in nature. In a confocal optical configuration, reflectance confocal microscopy provides information about scattering from within a small volume centered around the focal point of the confocal system, and laser Doppler flowmetry provides information about the velocity of moving scatterers within the same volume. Raster scanning the sample enables the concurrent creation of two images, containing independent information, from a well-specified depth within the sample. Concurrent spatial mapping of these independent sensing modalities affords improvement in the capability of the imaging system by obtaining additional information from both morphological and functional features of the dynamic turbid medium at depths penetrable by near-infrared lasers. We realize the idea using a laser feedback interferometry imaging system scanning a microfluidic channel that contains a dynamic turbid medium. We show the effectiveness of this integrated imager quantitatively through the improvement of the signal-to-background ratio of a combined (multiplication) image.

Diffuse reflectance imaging for non-melanoma skin cancer detection using laser feedback interferometry

We compare the performance of a self-mixing (SM) sensing system based on an uncooled monolithic array of 24×1 vertical-cavity surface-emitting lasers (VCSELs) in two modes of operation: single active channel and the concurrent multichannel operation. We find that the signal-to-noise ratio of individual SM sensors in a VCSEL array is markedly improved by multichannel operation, as a consequence of the increased operational temperature of the sensors. The performance improvement can be further increased by manufacturing VCSEL arrays with smaller pitch. This has the potential to produce an imaging system with high spatial and temporal resolutions that can be operated without temperature stabilization.