Mohmoud Mohamed

Frequency sixupler for millimeter-wave over fiber systems

In this work, we propose and investigate a novel technique for the generation of millimeter-wave (mm-wave), i.e. frequency sixuplexing technique. The proposed technique is comprised of two cascaded Mach- Zehnder modulators (MZMs). The first MZM, biased at maximum transmission, is only used for even-order optical harmonic generation, and then a second MZM, biased at minimum transmission, is used for both optical carrier suppression modulation and data signal modulation. As an example, we consider an RF at 10 GHz, which carries the data signal and drives the MZMs; and an mm-wave signal at 60 GHz, i.e. a frequency sixupler, is obtained. It is found that our proposed sixupler leads to an 8-dB higher RF power at 60 GHz and a 6-dB improvement in receiver sensitivity with comparison to the conventional technique, i.e. optical carrier suppression modulation. The generated mm-wave signal is robust to fiber chromatic dispersion. The proposed technique is verified by experiments.

Analysis of frequency quadrupling using a single Mach-Zehnder modulator for millimeter-wave generation and distribution over fiber systems

We comprehensively investigate three modulation techniques for the generation of millimeter-wave (mm-wave) using optical frequency quadrupling with a dual???electrode Mach-Zehnder modulator (MZM), i.e. Technique-A, Technique-B and Technique-C. For Technique-A, an RF signal drives the two electrodes of the MZM with maximum transmission bias, and this MZM is used for both the mm-wave generation and signal modulation. Technique-B is the same as Technique-A, but 180(0) phase shift between the two electrodes is applied. Technique-C is the same as Technique-B, but the MZM is only used for the mm-wave generation without signal modulation. It is found that Technique-B and Technique-C are better for frequency quadrupling than frequency doubling, tripling and sextupling. Both theoretical analysis and simulation show that the generated mm-wave suffers from constructive/destructive interaction due to fiber chromatic dispersion in Technique-A. However, the generated mm-wave is almost robust to fiber chromatic dispersion in Technique-B and Technique- C. It is found that Technique-C is the best in the quality of the generated mm-wave, especially when poor optical filtering is used. In addition, we develop a theory for calculation of Q-factor for mm-wave generation using the three modulation techniques. We consider an RF at 7.5 GHz and obtain an mm-wave at 30 GHz as an example, i.e. a frequency quadrupler. We evaluate the generation and distribution in terms of system Q-factor. The impact of RF modulation index, chromatic dispersion, MZM extinction ratio and optical filtering on Q-factor are investigated.

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of ~4% is optimum for optical transmitter with Mach-Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.

Precompensated Optical Double-Sideband Subcarrier Modulation Immune to Fiber Chromatic-Dispersion-Induced Radio Frequency Power Fading

We propose and demonstrate a new optical double-sideband modulation technique that is immune to fiber chromatic dispersion and thus free of dispersion-induced RF power fading. The proposed modulation technique also provides a 3 dB improvement of RF power compared with optical single-sideband modulation. The proposed modulation technique is analyzed in theory and simulation. It is shown that for a given fiber length an optimum electrical phase shift exists to completely cancel the dispersion-induced RF power fading. We verify this proposed modulation technique experimentally for a single-tone RF signal and for a multiband orthogonal frequency division multiplexing ultrawideband signal.

Frequency Quadrupler for Millimeter-Wave Multiband OFDM Ultrawideband Wireless Signals and Distribution Over Fiber Systems

Performance of millimeter-wave (mm-wave) multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) signal generation using a frequency-quadrupling technique and transmission over fiber is investigated by simulation and experiment, and the error vector magnitude (EVM) is used to evaluate the transmission quality. Frequency hopping within the first three bands of IEEE 802.15.3a has been used in experiments to obtain an MB-OFDM UWB signal. The frequency quadrupling can be achieved by using only one Mach-Zehnder modulator (MZM) and two cascaded MZMs. It is found that using one MZM is better than using two cascaded MZMs in the performance of mm-wave generation. For using one MZM, it is found that transmission through 20 km of fiber degrades the EVM by less than 0.5 dB compared with back-to-back. Also, the EVM is degraded by less than 1 and 0.25 dB for a bias drift of less than 20% and an extinction ratio of more than 10 dB, respectively. Moreover, the EVM of the system using one MZM is improved by more than 2.5 dB compared with the two cascaded MZMs. In addition, it is found that the minimum EVM required of -17 dB can be achieved by using a local oscillator modulation index of ~63% and 70% at least for using the one MZM and two cascaded MZMs, respectively.

Efficient Photonic Generation of Millimeter-Waves Using Optical Frequency Multiplication in Radio-over-fiber Systems

Photonic millimeter-wave (mm-wave) generation using optical frequency multiplication (OFM) is considered as a cost-effective solution in radio over fiber (RoF) systems. We comprehensively investigate the generation of mm-waves using high-order harmonic generation with a dual-electrode Mach-Zehnder modulator (DE-MZM) theoretically and experimentally, considering; the DE-MZM bias condition and finite extinction ratio. We consider three bias cases, i.e. maximum transmission bias (MATB), minimum transmission bias (MITB) and quadrature bias (QB). Our analysis shows that MATB is the best for the generation of mm-waves using the fourth order harmonics, and the generated mm-waves are almost immune to fiber dispersion. On the contrary, MITB is the best for the generation of mm-waves using the second or sixth-order harmonics, and the mm-waves generated are almost immune to fiber dispersion, too. Mm-waves generated with the QB always suffer from the impact of fiber dispersion.

Optical Generation of Millimeter-Wave Multiband OFDM Ultra-Wideband Wireless Signal and Distribution Over Fiber

Performance of millimeter-wave (MMW) multiband orthogonal frequency-division-multiplexing (OFDM) ultra-wideband (UWB) signal generation using optical frequency up-conversion and transmission over fiber is experimentally investigated. In this work, we propose an optical frequency quadrupling technique using two cascaded Mach-Zehnder modulators (MZMs) biased at quadrature and driven by the same local oscillator frequency but with 180° phase shift between the two MZMs. We demonstrate 30-GHz MMW wireless that carries three bands of OFDM UWB signals.

Investigation of the Performance of Multiband Orthogonal Frequency Division Multiplexing Ultrawideband Over Fiber Transmission Under the Presence of In-Band Interferers

Multiband (MB) orthogonal frequency division multiplexing (OFDM) ultrawideband (UWB) wireless, which provides high-data-rate access, must be distributed by use of optical fiber. UWB receivers are anticipated to operate under hostile interference environments. So the study of the coexistence of various communication standards with MB-OFDM UWB over fiber is an important issue. The performance of MB-OFDM UWB over fiber transmission system is investigated, considering the effect of in-band narrowband jammers such as WiMAX, MIMO WLAN, WLAN, and marine radar. Experiments were performed to show the effect of fiber transmission under various interferer power levels. It is found that in-band interferers can cause severe degradation in system performance if any interferer to the UWB peak power ratio is not held below a certain level. The results also show that MB-OFDM UWB over fiber transmission is more vulnerable to certain interferers such as WiMAX and radar signals than to the other in-band jammers.

Electrical Compensation of Fiber Chromatic Dispersion Induced RF Power Fading in Optical Double-Sideband Subcarrier Modulation

We present and demonstrate a new optical double-sideband modulation technique that is free of dispersion induced RF power fading. The predicted 3-dB RF power improvement over optical single sideband modulation is experimentally verified.

Photonic generation of millimeter-waves using two cascaded Electro-Absorption Modulators in radio-over-fiber systems

We propose a novel photonic millimeter-wave (mm-wave) generation technique using two cascaded Electro-Absorption Modulators (EAMs). The two cascaded EAMs are driven by the same low radio frequency (RF) signal but with certain phase shift to suppress odd-order optical sidebands and enhance second order sidebands to obtain frequency doubling and quadrupling. It is shown that RF modulation voltage, phase shift between the two EAMs, and their bias voltages are the keys to be adjusted to efficiently generate high quality mm-wave signal. Experimental proof of concept is also demonstrated.