Performance Evaluation of Multimode Fiber-Based Optical OFDM Communication System

The most significant limitation of data transmission in Multimode Fibers (MMFs) is intermodal dispersion due to the propagation velocity of each of the guided mode is different. This paper addresses this problem by adopting optical Orthogonal Frequency Division Multiplexing (OFDM) scheme to compensate intermodal dispersion and to enhance the bandwidth-distance product of MMF. The optical OFDM scheme adopted here is based on treating the signal fading due to intermodal dispersion in MMFs in a similar manner to that caused by multipath effect in wireless channels. A MATLAB simulink model is developed for the optical OFDM system. Simulation results are reported for 1Gbps link operating with different digital subcarrier modulation schemes to assess the impact of various parameters on system performance. The results indicate clearly that a Bit Error RateBER) of 10-5 can be achieved for a 1Gbps, 1km (10ns-dispersion) link operating with 1550nm, -23.6dBm laser and 16- Quadrature Amplitude Modulation (QAM) subcarrier modulation scheme

Using Low-Density Parity-Check Codes to Reduce the Effect of Laser Line width For Optical Communication

The performance of coherent optical communication systems is degraded significantly by the phase noise of the semiconductor lasers. The phase noise is induced by spontaneous emission in the laser cavity and yields broadening in the laser linewidth. This paper addresses the application of the Low-Density Parity-Check (LDPC) codes as Forward Error Correcting (FEC) codes to relax the laser linewidth requirement. These codes are applied to three types of heterodyne optical receivers (BPSK, DPSK and QPSK) operating with finite laser linewidth

Generating of Chaotic Signals by using Semiconductor Laser with Optical Feedback

This paper addresses theoretically generating the chaotic signals by using semiconductor laser diode of 1550 nm with optical feedback. The performance of a semiconductor laser subjected to a delay optical feedback was investigated using rate equations that describe the temporal variation of photon density, carrier density, and the phase of the lasing field. The simulation results show how semiconductor lasers are sensitive to external optical perturbations and how rich chaotic signal with large information can be generated with controlled optical feedback

Investigation of Raman Amplification In Photonic Crystal Fibers

In this paper, Raman amplification characteristics in photonic crystal fibers (PCFs) are investigated in details. Performance comparsion between PCF-based Raman amplifier and other conventional fiber-based counterparts is presented. The simulated results reported here can be used as a guide line to design PCF-based Raman amplifier that outperforms the conventional fiber amplifiers. Raman gain as high as 33 dB can be obtained with a well designed PCF even at low pump power of 300 mW

Advanced avalanche photodiode receivers in optical communications.

This thesis is concerned with a detailed study of the performance of superlattice avalanche photodiodes (SAPDs) and the implications for high bit rate direct-detection optical fibre communication systems. In these advanced detectors the electron to hole ionisation rate ratio is artificially enhanced through selective heating of the electron distribution to reduce the excess noise associated with the randomness of the avalanche multiplication and to ensure high gain-bandwidth product. Thus SAPDs are suitable for long wavelength applications (1.3-1.6 pm) where most compound semiconductor materials otherwise have comparable electron and hole ionisation rates. A comprehensive discrete ionisation model is developed to assess the performance of SAPDs; emphasis being placed on the gain, excess noise factor, gain moment generating function (MGF), and gain-bandwidth product. The model is quite flexible and it is found that other device impairments such as dark current and the number of ionisations per stage caused by the injected carrier can be readily incorporated into the formulation. The performance of optical receivers employing SAPDs is examined using a Gaussian approximation (GA) and taking into account the influence of various device impairments. To assess the accuracy of GA a rigorous statistical analysis is developed using a MGF formulation. New signal designs for optical communications devised specifically for APD receivers are described. These signals achieve simultaneously both zero intersymbol interference and zero telegraph distortion with respect to a depressed optimum threshold and are thus well suited to untimed transmission. Importantly, they also offer improved tolerance to alignment jitter when they used in conventional fully retimed receivers

Advanced avalanche photodiode receivers in optical communications.

This thesis is concerned with a detailed study of the performance of superlattice avalanche photodiodes (SAPDs) and the implications for high bit rate direct-detection optical fibre communication systems. In these advanced detectors the electron to hole ionisation rate ratio is artificially enhanced through selective heating of the electron distribution to reduce the excess noise associated with the randomness of the avalanche multiplication and to ensure high gain-bandwidth product. Thus SAPDs are suitable for long wavelength applications (1.3-1.6 pm) where most compound semiconductor materials otherwise have comparable electron and hole ionisation rates. A comprehensive discrete ionisation model is developed to assess the performance of SAPDs; emphasis being placed on the gain, excess noise factor, gain moment generating function (MGF), and gain-bandwidth product. The model is quite flexible and it is found that other device impairments such as dark current and the number of ionisations per stage caused by the injected carrier can be readily incorporated into the formulation. The performance of optical receivers employing SAPDs is examined using a Gaussian approximation (GA) and taking into account the influence of various device impairments. To assess the accuracy of GA a rigorous statistical analysis is developed using a MGF formulation. New signal designs for optical communications devised specifically for APD receivers are described. These signals achieve simultaneously both zero intersymbol interference and zero telegraph distortion with respect to a depressed optimum threshold and are thus well suited to untimed transmission. Importantly, they also offer improved tolerance to alignment jitter when they used in conventional fully retimed receivers

Design Investigation of 4 × 4 Nonblocking Hybrid Plasmonic Electrooptic Switch

This paper proposes a compact, plasmonic-based 4 × 4 nonblocking switch for optical networks. This device uses six 2 × 2 plasmonic Mach-Zehnder switch (MZS), whose arm waveguide is supported by a JRD1 polymer layer as a high electro-optic coefficient material. The 4 × 4 switch is designed in COMSOL environment for 1550 nm wavelength operation. The performance of the proposed switch outperforms those of conventional (nonplasmonic) counterparts. The designed switch yields a compact structure ( 500 × 70   µ m 2 ) having V π L = 12   V · µ m , 1.5 THz optical bandwidth, 7.7 dB insertion loss, and −26.5 dB crosstalk. The capability of the switch to route 8 × 40 Gbps WDM signal is demonstrated successfully