Off-set Filtering Effect in SOA Based Optical Access Network

In-line and reflective semiconductor optical amplifiers (SOA and RSOA) can be effectively utilized as external optical intensity modulators. However the limited modulation bandwidth affects the application possibilities, because next generation access networks desire high transmission speed. Bandwidth enhancement can be achieved by means of optical equalization thanks to the chirping characteristics of semiconductor optical amplifier. The limited modulation transfer function can be combined with the converted phase modulation transfer function. Investigation of optical filter with optimal slope is a crucial challenge in this approach. The presented simulations describe the slope dependence of the modulation band. The model can take into account the different type of realizable optical filters. However there is a trade-off between modulation efficiency and modulation bandwidth due to the extra insertion loss of the set-off optical filter. In the paper theoretical and simulation investigations are presented with the result of improved modulation bandwidth

Synchronization and channel estimation in experimental M-QAM OFDM radio over fiber systems using CAZAC based training preamble

In this paper, we propose a new technique for synchronization and channel estimation in M-QAM OFDM radio over fiber (RoF) system by using constant amplitude zero auto-correlation (CAZAC) sequence based training preamble. Delay and correlate method is used to identify the training sequence in the received signal vector and to correct the symbol timing offset. For an optimum demodulation of OFDM signal, optimum down sampling offset position has to be identified before applying symbol timing algorithm. To solve this issue, we present the iterative method of finding optimum down sampling offset position. We show that the training preamble used for synchronization can also be applied to estimate the channel response using averaging technique. Moreover, we used the least square estimation based channel estimation method using pilot subcarriers and compare the results with training preamble based estimation

Novel Vestigial Sideband Modulation Scheme to Enhance the SNR in Radio Over Fiber Systems

The optical single sideband (OSSB) scheme is a common choice in radio over fiber system for compensating chromatic dispersion (CD) but it suffers from low signal to noise ratio (SNR).We present the novel technique for SNR improvement using unequal sideband intensity based modulation scheme, we name it optical vestigial sideband modulation scheme (OVSB). To analyze such scheme we use the series Mach-Zehnder modulator (MZM) and phase modulator (PM) configuration. In this configuration by operating MZM at quadrature point and properly tuning the PM index the individual intensity of the first order sidebands and higher order harmonics can be controlled independent to each other.The optimum operating point of PM for maximizing the SNR can be identified by reducing the harmonic distortion and increasing the first order sidebands power. We experimentally validated the proposed OVSB scheme generation method and provide its theoretical proof. We evaluate the symbol error rate (SER) performance using 4QAM signal for OSSB and OVSB and show the improved performance of OVSB scheme compared to OSSB scheme. We also discuss the harmonic distortion behavior of the series MZM and PM configuration

Experimental demonstration of multi-Gbps multi sub-bands FBMC transmission in mm-wave radio over a fiber system

The filter bank multicarrier (FBMC) modulation format is considered as a potential candidate for future wireless 5G due to its feature of high suppression for out-of-band emissions, which allows combining multiple sub-bands with very narrow band-gaps, and hence increases the overall wireless transmission capacity. In this paper, we experimentally demonstrate the generation of multi sub-bands FBMC signals at millimeter-wave (mm-wave) for radio-over-fiber (RoF) systems. The designed multi sub-bands FBMC system consists of 5 sub-bands of 800 MHz with inter sub-band gaps of 781.25 kHz. The composite 5 sub-bands FBMC signal is generated with no band-gap between dc to the first sub-band to preserve the bandwidth of the system. Each FBMC sub-band consists of 1024 sub-carriers and is modulated with uncorrelated data sequences. The aggregate FBMC signal is carried optically by externally modulating a free running laser and is converted to millimeter waves (mm-waves) by photomixing with another free running laser at a frequency offset of 53 GHz. At the receiver, the received electrical mm-wave signal is down-converted to an intermediate frequency (IF) and then post-processed using digital signal processing (DSP) techniques. With the use of the simple recursive least square (RLS) equalizer in the DSP receiver, the achieved aggregate data rate is 8 Gbps and 12 Gbps for 16 quadrature amplitude modulation (QAM), and 64 QAM, respectively with a total bandwidth of 4.2 GHz. The system performance is evaluated by measuring error vector magnitude (EVM) and bit error rate (BER) calculations

Photonic Approach to Phased Array Application

Many applications, including phased array antennas, require a significant and tunable time delay, which pure electrical methods cannot establish. A variable microwave true-time delay line utilizing a photonic approach is presented in this paper. The variation of the delay is achieved by the application of dispersive fiber and tunable laser. With this method, the tunable delay line can control multiple radiating elements. In this paper, both DWDM and CWDM solutions are theoretically investigated and compared. The experimental work applying DWDM tunable laser validates the theoretical analysis. Finally, the Phased array concept is presented, and the system simulation shows the operation. The suggested phased array feeding method requires only one laser source, an external intensity modulator, passive combiners, and dividers instead of multiple optical transmitters with multiplexers and demultiplexers

Distortion and noise problems of subcarrier multiplexed optical systems

In this paper investigation of subcarrier multiplexed optical subsystems for optically supported communication systems is presented. Noise and spurious free dynamic range are the main parameters, which are determined by the applied optical transmission. The frequency dependence of these parameters and optimal frequency chosen is presented

Vertical cavity surface emitting lasers in radio over fiber applications

Theoretical and experimental study of using direct modulated vertical cavity surface emitting lasers in radio over fiber applications is presented. The nonlinear distortion and signal to noise ratio are investigated and evaluated in case of short-range multi-carrier transmission. Nonlinear characterization and comparison of the different kind of semiconductor lasers are also presented