presented. The proposed tool is addressed to the students of optical communication courses, encouraging self consolidation of the subjects learned in lectures. The semiconductor laser model is based on the well known rate equations for the carrier density, photon density and optical phase. The direct modulation of the laser is considered with input parameters which can be selected by the user. Different options for the waveform, amplitude and frequency of the injected current are available, together with the bias point. Simulation results are plotted for carrier density and output power versus time. Instantaneous frequency variations of the laser output are numerically shifted to the audible frequency range and sent to the computer loudspeakers. This results in an intuitive description of the “chirp” phenomenon due to amplitude-phase coupling, typical of directly modulated semiconductor lasers. In this way, the student can actually listen to the time resolved spectral content of the laser output. By changing the laser parameters and/or the modulation parameters, consequent variation of the laser output can be appreciated in intuitive manner. The proposed educational tool has been previously implemented by the same authors with locally executable software. In the present manuscript, we extend our previous work to a web based platform, offering improved distribution and allowing its use to the wide audience of the web.
Optical filters are crucial elements in optical communications. The influence of cascaded filters in the optical signal will
affect the communications quality seriously. In this paper we will study and simulate the optical signal impairment
caused by different kinds of filters which include Butterworth, Bessel, Fiber Bragg Grating (FBG) and Fabry-Perot (FP).
Optical signal impairment is analyzed from an Eye Opening Penalty (EOP) and optical spectrum point of view. The
simulation results show that when the center frequency of all filters aligns with the laser’s frequency, the Butterworth
has the smallest influence to the signal while the F-P has the biggest. With a -1dB EOP, the amount of cascaded
Butterworth optical filters with a bandwidth of 50 GHz is 18 in 40 Gbps NRZ-DQPSK systems and 12 in 100 Gbps PMNRZ-
DQPSK systems. The value is reduced to 9 and 6 respectively for Febry-Perot optical filters. In the situation of
frequency misalignment, the impairment caused by filters is more serious. Our research shows that with a frequency
deviation of 5 GHz, only 12 and 9 Butterworth optical filters can be cascaded in 40 Gbps NRZ-DQPSK and 100 Gbps
PM-NRZ-DQPSK systems respectively. We also study the signal impairment caused by different orders of the
Butterworth filter model. Our study shows that although the higher-order has a smaller clipping effect in the
transmission spectrum, it will introduce a more serious phase ripple which seriously affects the signal. Simulation result
shows that the 2nd order Butterworth filter has the best performance.
This paper describes the theory and experimental results of a dynamic holographic wavelength filtering for use in optical telecommunication Coarse and Dense Wavelength Division Multiplexing (CWDM/DWDM) applications. The enabling component is a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) where dynamic holograms are implemented in real time; as a consequence, tuning of the filter is possible according to the light modulation. The great advantage of this FLC device is a polarization insensitivity operation, allowing low crosstalk and potential low loss in optical communications.
Other applications, such as demultiplexers and wavelength routers, have been studied and practical values have been obtained according to central wavelengths recommended in ITU G. 694.1 and G. 694.2. Lab experiments have demonstrated the capability of a phase FLC-SLM to diffract the incident light, according its wavelengths and the hologram patterns, for the use in the former applications.
The proliferation of high-bandwidth applications has created a growing interest in upgrading networks to deliver broadband services to homes and small businesses between network providers. There has to be a great efficiency between the total cost of the infrastructures and the services that can be offered to the end users. Coarse Wavelength Division Multiplexing (CWDM) is an ideal solution to the tradeoff between cost and capacity. This technology uses all or part of the 1270 to 1610 nm wavelength fiber range with optical channel separation about 20 nm. The problem in CWDM systems is that for a given reach the performance is not equal for all of transmitted channels because of the very different fiber attenuation and dispersion characteristics for each channel.
In this work, by means of an Optical Communication System Design Software, we study a CWDM network configuration, for lengths of up to 100 km, in order to achieve low Bit Error Rate (BER) performance for all optical channels. We show that the type of fiber used will have an impact on both the performance of the systems and on the bit rate of each optical channel. In the study, we use both on the already laid and widely deployed singlemode ITU-T G.652 optical fibers and on the latest "water-peak-suppressed" versions of the same fiber as well as G.655 fibers. We have used two types of DML. One is strongly adiabatic chirp dominated and another is strongly transient chirp dominated. The analysis has demonstrated that all the studied fibers have a similar performance when laser strongly adiabatic chirp dominated is used for lengths of up to 40 Km and that fibers with negative sign of dispersion has a higher performance for long distance, at high bit rates and throughout the spectral range analyzed. An important contribution of this work is that it has demonstrated that when DML are used it produces a dispersion accommodation that is function of the fiber length, wavelength and bit rate. This could put in danger the quality of a system CWDM if it is not designed carefully.
In the last few years, user requirements in data rate and bandwidth have grown enormously. A remarkable technological evolution has taken place in two major areas: transmission and interconnection networks. The role of photonic components and technologies in switched networks will mainly be determined by the enhanced functionality given by photonics, e.g., transparency, avoiding electronic bottlenecks. If switched data are kept in an optical format rather than electronic format, it allows the switch bandwidth to be as high as the fiber bandwidth. All-optical, space-division interconnects can be made using an acousto-optic beam deflector. The aim of this work is carry out an experimental analysis on the characteristics and behavior of an acousto-optic modulator (AOM) in order to determine its limitations for switching applications. Relevant parameters of the acousto-optic device have been derived from a theoretical study. This has allowed the identification of the parameters to be optimized in a switching application.
A neural network based system to identify images transmitted through a Coherent Fiber-optic Bundle (CFB) is presented. Patterns are generated in a computer, displayed on a Spatial Light Modulator, imaged onto the input face of the CFB, and recovered optically by a CCD sensor array for further processing. Input and output optical subsystems were designed and used to that end. The recognition step of the transmitted patterns is made by a powerful, widely-used, neural network simulator running on the control PC. A complete PC-based interface was developed to control the different tasks involved in the system. An optical analysis of the system capabilities was carried out prior to performing the recognition step. Several neural network topologies were tested, and the corresponding numerical results are also presented and discussed.
We demonstrate the operation and rapid reconfiguration of a 12 X 12 Acousto-Optic Photonic Crossbar (AOPC). This AOPC can implement any desired permutation, fan-in, or fan-out interconnection between any subset out of twelve single-mode input fibers into any subset out of twelve single-mode output fibers. The system uses one large-aperture Acousto- Optic Deflector (AOD) driven by a sum-of-tones RF-waveform produced by an arbitrary waveform generator and computed from an experimentally measured lookup table, thus reducing the control complexity of the system. The design, based on the momentum-space technique, includes optical and acoustical rotation for the AOD, in order to optimize the efficiency of the desired interconnections and minimize the undesirable negative first-order acoustooptic Bragg- diffractions. A limitation of this type of systems is the unavoidable reconfiguration (dead) time introduced by the AOD itself, which can result in crosstalk between the individual input channels during that period of time. In this paper, we experimentally investigate the reconfiguration time of this AOPC, by switching between two different crossbar patterns, and then measuring the time during which the detected signal can not be individually resolved for each input channel. Coupling efficiency problems and alignment procedures are also discussed and analyzed.
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