S. Alifah

The SCM/WDM system model for radio over fiber communication link

Subcarrier Multiplexing (SCM) is multiple radio frequency (RF) carrying signal to transmit through optical fiber using single wavelength. The most significant advantage of SCM in optical communications is its ability to place different optical carriers together closely. On the other hand, Wavelength Division Multiplexing (WDM) is a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart. In WDM each laser is modulated at a given speed, and the total aggregate capacity being transmitted along the high-bandwidth fiber is the sum total of the bit rates of the individual lasers. In this work, we investigate various issues in this scenario in order to provide a cost-effective, high performance solution for high speed data rates by the available bandwidth of the electrical and optical components. Therefore, SCM must be used in conjunction with WDM to utilize any significant fraction of the fiber bandwidth. The results is present higher bandwidth for long distance communication system (SMF, 150 km) by using SCM/WDM for Radio over Fiber. Therefore, the efficiency of bandwidth utilization of SCM is expected to be much better than conventional optical WDM.

Laser transmitter feed-forward linearization system for radio over fiber application

This paper introduces a laser transmitter feed-forward linearization system for Radio over Fiber application at frequency 5.2GHz. The system was modeled and simulated in Optisystem 8.0. Theoretical simulation has shown a reduction in the distortion to 20dB and above.

A review for development of feedforward linearisation system on radio over fiber links

Radio over fiber technology provides the efficient and cost effective solution for increased bandwidth demand in wireless area but suffer from performance degradation due to optical transmitter nonlinearity that generates distortion of inband, harmonic and intermodulation in modulating RF signal. A feedforward linearisation is a powerful technique that prefers because can reduce the broadband distortion in microwave/millimeter wave frequencies, reduce the all orders of distortion and the laser relative intensity noise (RIN) simultaneously. This paper reviewed the research progress of feedforward linearisation system in radio over fiber application. Feedforward linearisation system was reported that can suppress third-order intermodulation distortion (IMD3) from 10-20 and RIN reduction from 1-10 dB simultaneously at operating frequency from 0-5 GHz with linearization bandwidth 500-850 MHz. The highest operating frequency is 5.2 GHz with 10 dB IMD3 reduction on 500 MHz linearization bandwidth. Therefore, feedforward linearisation system can improved the RoF performance by linearity improvement so that the system can operate at broadband frequency.

The feedforward linearization system of optical transmitter for Free space optical (FSO) link

Free-space optics (FSO) or Free-space photonics (FSP), is refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere, which provides the wireless solution for the demand of high speed data rate and obtain broadband communications. The problem in implementing this technology is the performance reduction due to the nonlinearity present in the directly modulated optical transmitter, hence causes the inband, harmonic and intermodulation distortion in the modulated signal. The technique of feedforward distortion compensation is one of the better solution that prefers because, it can reduce the broadband distortion in modulated optical signal of wavelength 1550 nm which is suitable for wireless optical communication, also reduces all the other higher orders of distortion and the laser relative intensity noise (RIN) simultaneously. In this paper a novel design of the free space optical link non-linearity correction of the optical transmitter i.e. laser diode at frequency 5.2 GHz bandwidth used for IEEE802.11a standard and wavelength of 1550 nm employing the feedforward linearization technique is presented.

Nonlinear mitigation loop of a novel feedforward laser transmitter for radio over fiber link

The nonlinearity of a laser diode is a significant cause of limitation on the performance of every optical communication system especially in radio over fiber links considering radio frequency optically modulated signal. The amplitude and phase matching of a feedforward linearization loop is critical for optimum distortion reduction. In this paper, the influence of component parameters on the amplitude and phase matching of a novel feedforward laser transmitter design is presented employing a mathematical analysis and simulation with Optisystem 10.0. The mathematical and simulation results show that the system is influenced by fewer component parameters compared to previous works. This reduces the complexity of loop adjustment. In addition, the simulation results show that the system can reduce the third intermodulation distortion for up to 31 dB with the best achievable amplitude and phase matching.

An Improved Laser Transmitter Using Feedforward Linearization Technique for Radio Over Fiber Communication System

Several linearization techniques such as predistortion, feedback, quasi feedforward and feedforward which have been proposed are suggested to improve the linearity of a laser transmitter specifically for Radio over Fibre communication system. In general, feedforward linearization technique is known to be more effective since it can achieve reduction in all orders of distortion for large bandwidth and high frequency without needing to know the nonlinear characteristics of lasers. In this paper, we propose an improved feedforward laser transmitter design. The theoretical study shows that the proposed design is less sensitive since the distortion suppression is influenced by fewer parameters compared to other reported works. The simulation results show that the proposed system can achieve the optimum distortion reduction around 30 dB by only adjusting the coupling coefficient of both optical couplers in the distortion cancellation loop, while the phase is matched and the signal is cancelled optimally in signal cancellation loop. Previous works based on feedforward linearization technique will also be reviewed through some papers and patents.

Simultaneous Noise Reduction and Linearity Improvement of Optical Feedforward Transmitter for Radio over Fiber Systems

One of the major concern for the system is the issue of noise and interference. The majority source of nonlinearity come from laser diode nonlinearity. Likewise, the linearity improvement of optical transmitter is very important to enhance system performance in term of dynamic range. This paper demonstrated the simultaneous noise reduction and linearity improvement of optical transmitter using proposed feedforward linearization scheme for radio over fiber system. The system performance is predicted based on the simulation result in term of third order intermodulation distortion (IMD3) and relative intensity noise (RIN) reduction. The results show that simultaneous reduction of IMD3 up to 33 dB and RIN up to 20 dB employing the proposed system.