International Journal of Optics and Photonics
Year:2017 | Volume:11 | Issue:1|Papers Count:7

The modulation response, relative intensity noise (RIN) and frequency noise (FN) characteristics of quantum dot (QD) lasers are investigated theoretically in the presence of an external optical beam. Using small signal analysis of the rate equations for carriers and photons, it is demonstrated that by injecting excess carriers into the QDs excited state through optical pumping, the modulation response of QD laser enhances and its bandwidth increases. The external optical pump also helps QD laser to turn on during shorter delay time. Further, it is deduced that the RIN level of QD laser reduces and the damping factor increases due to external beam. Moreover, the frequency noise level of QD laser and correspondingly its linewidth decreases by applying the optical beam.

For a fiber optical surface plasmon resonance (SPR) sensor a short part of its cladding should be removed to coat a thin layer of a metal. Usually this is problematic when an optical fiber with small core diameter is used. In this paper, a new method using miter droplet of the HF acid for short fiber optical taper fabrication is reported. Using this method in a multi-mode optical fiber with the core/cladding size of 50.125 mm a 2 mm long taper with 40 mm diameter is fabricated. Roughness of its surface is investigated using an atomic force microscopy. The measured mean value of the roughness is about 8 nm. A 60 nm thin layer of pure silver is coated on the taper surface in order to investigate its performance using a fiber optical SPR sensor. Using this SPR fiber sensor measurement of the lead concentrations in water ranging from 0.1 to 10 part per million (ppm) is reported.

In this study, we have theoretically investigated the effect of electron stopper layer on internal temperature distribution of high performance vertical cavity surface-emitting laser emitting at 1305 nm. Simulation software PICS3D, which selfconsistently combines the 3D simulation of carrier transport, self-heating, gain computation and wave-guiding, was used. Simulation results show that change the electron stopper layer properties affect the internal temperature distribution of the device. The temperature of the active region increases compared with the original device. Comparison of temperature distribution in devices with different electron stopper layer confirms that optimized structure operates at maximum temperature.

Nanostructures of noble metal materials have been used in organic solar cells for enhancement of performance and light trapping. In this study, we have introduced branched silver cauliflower-like nanopatterns as sub-wavelength structured metal grating in organic solar cells. Self-assembled fabrication process of branched nanopatterns was carried out on a bio-template of cicada wing nanonipple arrays using a gas aggregation dc magnetron sputtering nanocluster source without size filtration. The branched nanostructures provide surface gaps with dimensions near the organic exciton diffusion length, which prevents recombination of charge carriers. An increased power conversion efficiency of 14.8% compared to that of the planar device was achieved mainly due to the enhancement in the short-circuit current density. Besides, these branched cauliflower-like nanopatterns had enhanced optical light absorption in the solar cell as a result of enhancing the optical path length of the reflected light in the active layer and plasmonic effects of the noble metal material.

We solve the coupled mode equations governing the chalcogenide nonlinear fiber Bragg gratings (FBGs) numerically, and obtain the bistability characteristics. The characteristics of the chalcogenide nonlinear FBGs such as: switching threshold intensity, bistability interval and on-off switching ratio are studied. The effects of FBG length and its third order nonlinear refractive index on FBG characteristics are investigated. We obtain an interesting result that independent of the third order nonlinear refractive index; there exists an optimum FBG length of about 6 mm at which the on-off switching ratio becomes maximized. It is also found that by increasing the nonlinearity, the maximum value of on-off switching ratio decreases. The results of this paper can be mainly used for designing alloptical switches and memories.

Considering a temperature dependent two-level quantum system, we have numerically solved the Landau-Zener transition problem. The method includes the incorporation of temperature effect as a thermal noise added Schrödinger equation for the construction of the Hamiltonian. Here, the obtained results which describe the changes in the system including the quantum states and the transition probabilities are investigated and discussed. The results successfully describe the behavior of the transition probabilities by sweeping the temperature.

The semi-classical model of atomfield interaction has been fully studied for some multilevel atoms, e.g. Vee, L , Cascade , Y, and inverted Y and so on. This issue is developed into the full-quantum electrodynamics formalism, where the probe and coupling electromagnetic fields are quantized. In this article, we investigate the full-quantum model of absorption and dispersion spectrum of trapped four-levels inverted Y type atoms, interacting with a probe beam of photons as well as two-mode trapped coupling photons. It is shown that the measurement of the maximum of absorption of the probe field and its detuning gives us simply the number of two-mode coupling photons, individually. An experimental setup for this non-demolition photon counting method is proposed and the numbers of coupling photons are obtained analytically.