Volume 24, Issue 2

In this study a metal clad waveguide sensor with a metamaterial guiding layer is analyzed. Sensitivity of the proposed sensor is derived using dispersion and Fresenal’s equations for waveguiding mode and reflection mode. While efficiently analyzing and comparing the results with the existing one, some interesting findings are achieved. It is observed that the proposed sensor shows larger cover layer sensitivity and larger adlayer sensitivity compared to the dielectric guiding layer sensor due to adsorbtive properties of metamaterial. Henceforth, it concludes that the proposed sensor shows sensitivity improvement over a dielectric guiding layer sensor.

The paper presents experimental results of the lifetime of light induced excess carriers in the n−type silicon. The lifetimes of carriers of silicon crystals were analysed as a function of the intensity of light illuminating the sample. As a measurement method of the lifetime of carriers, the photoacoustic method in a transmission configuration with different surfaces was used. The dependence character was next analysed in the frame of the Shockley Reed Hall statistics in approximation of the light low intensity.

Optical sampling based on ultrafast optical nonlinearities is a useful technique to monitor the waveforms of ultrashort optical pulses. In this paper, we present a new implementation of optical waveform sampling systems by employing our newly constructed free–running mode–locked fibre laser with a tunable repetition rate and a low timing jitter, an all–optical waveform sampler with a highly nonlinear fibre (HNLF), and our developed computer algorithm for optical waveform display and measurement, respectively. Using a femtosecond fibre laser to generate the highly stable optical sampling pulses and exploiting the four–wave mixing effect in a 100m–long HNLF, we successfully demonstrate the all–optical waveform sampling of a 10GHz optical clock pulse sequence with a pulse width of 1.8 ps and a 80Gbit/s optical data signal, respectively. The experimental results show that waveforms of the tested optical pulse signals are accurately reproduced with a pulse width of 2.0 ps. This corresponds to a temporal resolution of 0.87 ps for optical waveform measurement. Moreover, the optical eye diagram of a 10Gbit/s optical data signal with a 1.8 ps pulse width is also accurately measured by employing our developed optical sampling system.

We propose and study a new technique for securing fibre data communication. The paper presents a method for optical encryption of information transmitted with a traditional fibre link. The encryption method uses a spatial light modulator which converts light pulses representing original data into pseudo-random patterns. A linear combination of light pulses with pseudo-random patterns provides a required encryption performance. The main element of the encryptor is the spatial light modulator which comprises a matrix of cells selectively transmitting or blocking the light beam depending on the pseudo-random configuration of cells. The encrypted information is transmitted through the optical fibre. The decryption process relies on a computational solving of linear program or greedy pursuit. We present a brief description of the method, theoretical analysis and results of numerical simulation. A physical model concept of the method is also presented.

Number of trace compounds (called biomarkers), which occur in human breath, provide an information about individual feature of the body, as well as on the state of its health. In this paper we present the results of experiments about detection of certain biomarkers using laser absorption spectroscopy methods of high sensitivity. For NO, OCS, C 2 H 6 , NH 3 , CH 4 , CO and CO(CH 3 ) 2 an analysis of the absorption spectra was performed. The influence of interferents contained in exhaled air was considered. Optimal wavelengths of the detection were found and the solutions of the sensors, as well as the obtained results were presented. For majority of the compounds mentioned above the detection limits applicable for medicine were achieved. The experiments showed that the selected optoelectronic techniques can be applied for screening devices providing early diseases detection.

The work presents doping characteristics and properties of high Si−doped InGaAs epilayers lattice−matched to InP grown by low pressure metal−organic vapour phase epitaxy. Silane and disilane were used as dopant sources. The main task of investigations was to obtain heavily doped InGaAs epilayers suitable for usage as plasmon−confinement layers in the construction of mid−infrared InAlAs/InGaAs/InP quantum−cascade lasers (QCLs). It requires the doping concentration of 1×10 19 cm –3 and 1×10 20 cm –3 for lasers working at 9 μm and 5 μm, respectively. The electron concentration increases linearly with the ratio of gas−phase molar fraction of the dopant to III group sources (IV/III). The highest electron concentrations suitable for InGaAs plasmon−contact layers of QCL was achieved only for disilane. We also observed a slight influence of the ratio of gas−phase molar fraction of V to III group sources (V/III) on the doping efficiency. Structural measurements using high−resolution X−ray diffraction revealed a distinct influence of the doping concentration on InGaAs composition what caused a lattice mismatch in the range of –240 ÷ –780 ppm for the samples doped by silane and disilane. It has to be taken into account during the growth of InGaAs contact layers to avoid internal stresses in QCL epitaxial structures.