Volume 33, Issue 33

A fundamental requirement in the design of an optical receiver is the achievement of high sensitivity and broad bandwidth. These two features are very important in getting reliable system. In this project a receiver circuit based on Photo parametric Amplifier (PPA), which is suggested as one of the alternative for receiver detection and amplification techniques is fully described. The PPA mode of operation involves optical detection and amplification within a single device. It is able to provide selectivity and sensitivity at the same time, as required for wireless optical communications. The most common problem that any communication system might face is the noise which must be eliminated or at least reduce it. In order to reduce the noise, filters have been implemented before the signal is passes through an amplifier. In this project an Up converter has been placed at the transmitter circuit in order to obtain high frequency, while at the receiver circuit, filters has been placed with Down converter to obtain the desired frequency. Photo diode, PIN type has been used to detect any incoming signal at the receiver circuit. Results showed that the output signal has been improved; with addition power strength and noise reduction which showed that photo parametric amplifier is more reliable and suitable to be used in wireless optical communication system.

This paper forces on the monitoring and compensation of optical telecommunication channels by using Optical add drop multiplexers (OADM) in an Optical orthogonal frequency division multiplexing (OOFDM) system. An adaptive fiber nonlinearity precompensation (AFNP) scheme is also proposed to solve the fiber nonlinearity in coherent optical orthogonal frequency division multiplexed networks (CO-OFDM). Optical performance monitoring (OPM) at end-terminals is applied to channel identification in this paper. It is considered to be high efficiency and a cost efficient technique in low-dynamic system.

Based on the prescribed ABCD matrix for refraction by hemispherical lens under paraxial approximation, we formulate an analytical expression of coupling efficiency of a laser diode to a single mode circular core graded index fiber via a hemispherical lens on the tip of the fiber. The analysis involves Gaussian field distribution for both the source and the fiber and consideration of allowable aperture provided by the hemispherical lens. In order to find out the suitable refractive index profile for maximum coupling efficiency, we investigate the coupling optics for different profile exponents in graded index refractive index profile. In this context two different laser diodes emitting wavelengths 1.3 μm and 1.5 μm are employed for the concerned study. It is found that the graded index fiber having triangular refractive index profile is the most efficient one for the said two wavelengths of practical importance. Our formalism is simple and executable with little computation. The results found should be of tremendous importance to the designer of such coupling in the field of optimum launch optics.

In order to minimize the average end to end delay for data transporting in hybrid wireless optical broadband access network, a novel routing algorithm named MSTMCF (minimum spanning tree and minimum cost flow) is devised. The routing problem is described as a minimum spanning tree and minimum cost flow model and corresponding algorithm procedures are given. To verify the effectiveness of MSTMCF algorithm, extensively simulations based on OWNS have been done under different types of traffic source.

We compared the bit-error-rate (BER) and throughput performance of coherent time-spreading (TS) and spectral phase encoding (SPE) optical code division multiple access (OCDMA) systems. The results indicate that for the short input pulse (250–300 fs pulsewidth), SPE-OCDMA can in principle yield a substantial throughput advantage over TS-OCDMA systems.

The paper presents a method for the development of a new class of zero cross correlation optical code for Optical Code Division Multiple Access (OCDMA) system using Spectral Amplitude Coding. The proposed code is called Modified Zero Cross Correlation Code (MZCC). The code has minimum length and can be constructed quite simply for any number of users and for any code weights. The code has better spectrum slicing properties and noise performance in term of Bit Error Rate. The Modified Zero Cross Correlation Code will be demonstrated in simulation using OptiSys. 6.0 to observe noise performance which is better as compared to the existing Zero Cross Correlation Code.

In this paper, we will study, via simulation, the transmission of DVB-C channels over an external modulated optical link using a Mach-Zehnder modulator (MZM). We will also observe the consequences of biasing the MZM near its transmission minimum point, which allows higher carrier to noise ratio at the transmitter, but increases second-order distortion at the receiver.

Self-phase modulation (SPM) effect on performance of 40 Gbit / s (3 × 13.33 Gbit / s) optical duty-cycle division multiplexing (O-DCDM) over 400 km (5 × 80 km) standard single mode fiber (SSMF) based on three different dispersion compensation schemes is investigated by simulation. The result shows that the SPM effect is very strong in dispersion pre-compensation compared to post-compensation. Further reduction in SPM effect is observed by combination of pre- and post-compensation with the optimum pre-compensation value of around 215 ps / nm. The simulation is performed at different launched power into dispersion compensation fiber (DCF). The range between {-}6 to {-}8 dBm is observed as the optimum power for all dispersion compensation schemes. The highest SPM threshold is observed when dispersion pre- and post-compensation are used together, which is around +6.7 dBm. In addition, the optimum range of launched power into SSMF for different transmission distances from 80 km to 1280 km is also presented.

A recursive algorithm for a non-uniform amplitude beam propagating through a sub-wavelength grating is proposed in this paper. This method is based on Maxwell's equations and the continuity of the tangential components of the electric and magnetic field vectors, and gives an exact complete solution. And we illustrate a propagation of a Gaussian beam through a grating in detail.

It is well accepted that radiation propagates in the free space (without obstacles) in a spherical wave form as well as in a plane wave form. Almost all observed phenomena such as interference, diffraction etc are explained satisfactorily on the basis of spherical wave propagation with a slight alteration in the mathematical treatment. However, one of the fundamental aspects, namely the intensity of the radiation as a function of the distance still remains an unsolved problem as the intensity varies with 1/ (distance) 2 when one represents the propagation in terms of spherical waves while it is independent of the distance if it is considered as a plane wave. In order to understand this puzzle, the propagation by a spherical wave form is reexamined. It is found that conversion of fields into particle (vice versa), via the field quantization process, explains several dilemma related with the radiation propagation.