Temperature tunable random laser using superconducting materials

We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very sensitive to the system temperature.     

A New Spectral Triple over a Space of Connections

A new construction of a semifinite spectral triple on an algebra of holonomy loops is presented. The construction is canonically associated to quantum gravity and is an alternative version of the spectral triple presented in [1].     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

Fourier-wavelet regularized deconvolution (ForWaRD) for lidar systems based on TEA-CO2 laser

Lidar is an efficient tool for remotely measuring physical quantities or detecting targets. To improve the range resolution in long pulse lidars, such as lidar systems based on TEA-CO₂ lasers, deconvolution methods were used by previous investigators. Deconvolution is a noise sensitive process. In order to avoid noise amplification during the deconvolution process, the Fourier-wavelet regularized deconvolution method is used to deconvolve and denoise the back-scattered lidar signal simultaneously. This method is applied to lidar systems based on the TEA-CO₂ laser and the results are compared to nitrogen tail clipping method. Numerical simulation shows, in comparison to the clipping nitrogen tail technique, by using the ForWaRD method; the range resolution and working distance of the lidar is improved and the clipping tail apparatus is also eliminated.     

Theoretical study of hybrid TEA–CO2 lasers

Temporal and spatial analysis of dynamics of hybrid transversely excited atmospheric pressure (TEA)–CO₂ lasers is studied using two different models with four and eight energy levels. These models are used for simulation of the laser and computing the output energy. Effects of several parameters such as input energies and gas mixture concentrations (especially presence of CO molecules) are also studied.     

The moment method for fiber Raman amplifier gain ripple minimization

We aim to propose a novel fiber Raman amplifier modeling based on the moment method, which is previously introduced for modeling the inhomogeneous Erbium doped fiber amplifiers and recently employed to analyze the fiber Raman amplifier with continuous pump spectrum. In this model, the number of governing equations is independent of the number of signals and according to the degree of accuracy it is proportional to the number of pumps. This method is employed to analyze the Raman fiber amplifiers with an arbitrary input signal line shape and to minimize the gain ripple of the fiber Raman amplifier with respect to the pump powers and pump frequencies.     

The effect of probe-Ohmic environment coupling type and probe information flow on quantum probing of the cutoff frequency

This work aims to compare results of dissipating and pure dephasing single-qubit probes in characterizing the cutoff frequency of a harmonic reservoir Ohmic spectral density. In particular, we proved that a dissipating single-qubit improves the estimation precision of the cutoff frequency estimator. The information backflow and outflow of the dissipating and the dephasing single-qubit are compared. The relation between the quantum Fisher information and the information outflow and backflow of the probe is obtained. The results show that difference between the values of information outflow and backflow of a dissipating single-qubit is larger than a dephasing single-qubit. So, a single-qubit probe extracts more information from an Ohmic reservoir by increasing the difference between the values of information outflow and backflow of the probe.     

Gain ripple minimization in the wide-band SCISSOR Raman amplifier

A side coupled integrated spaced sequence (SCISSOR) of Silicon or Chalcogenide glass microrings of different diameter are considered as a wide-band Raman amplifier. Because the two-photon absorption (TPA) losses in Chalcogenide glass are less than that of Silicon, it is shown that Chalcogenide microrings are suitable for wide-band Raman amplifier in the telecommunication bandwidth (1.5 μm). The Lagrange unknown multiplier method is employed to minimize the gain ripple of the amplifier versus the pump and system parameters.     

Polarization maintaining optical fiber multi-intruder sensor

In this paper, an optical fiber multi-intruder sensor based on polarization maintaining optical fiber (PMF), without any interferometric fiber loop, is introduced. To map the local coordinates of intruders on the beating spectrum of the output modes, radiation from a ramp frequency modulated laser is injected at the input of PMF optical fiber sensor. It is shown that the local coordinates and some characteristics of intruders can be obtained by the measurement of the frequencies and amplitudes of the output mode beating spectrum. Generally the number of beating frequencies is more than the number of intruders. Among the beating frequencies, a group with maximum signal to noise ratio is chosen. The short Fourier denoising method is employed to increase the sensor resolution. Because the output signal is the superposition of finite numbers of discrete frequencies this method is a powerful tool for denoising even for negative signal to noise ratio.