Bouchaib Hraimel

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.

Enhanced Spurious-Free Dynamic Range Using Mixed Polarization in Optical Single Sideband Mach–Zehnder Modulator

We analyze in theory, simulation, and experiment the spurious-free dynamic range (SFDR) for a radio-over-fiber system using an optical single sideband (OSSB) Mach-Zehnder modulator (MZM) that is linearized using mixed polarization. The mixed polarization OSSB MZM makes use of a dual-electrode z-cut LiNbO3 MZM, where a linear polarizer is placed in front and in behind the optical modulator, respectively. It is found that intermodulation distortion can be suppressed significantly regardless of modulation index. Thus intermodulation induced power fading and crosstalk via fiber chromatic dispersion for a given RF carrier is reduced compared to using the conventional OSSB MZM. Improvements of ~ 13 dB in SDFR is predicted in theory, simulation, and demonstrated experimentally.

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.

Optical Single-Sideband Modulation With Tunable Optical Carrier to Sideband Ratio in Radio Over Fiber Systems

We show that an optical modulator that consists of an integrated dual parallel Mach-Zehnder modulator (dMZM) can be used for obtaining not only optical single-side band modulation but also tunability of optical carrier to sideband ratio (OCSR) simultaneously. Such a modulator will be vital for optimizing the performance of radio over fiber links by improving modulation efficiency and receiver sensitivity and by removing fiber chromatic dispersion induced RF power fading. It is shown that a wide range of OCSR tunability can be obtained by altering bias voltage of dMZM, and optimum OCSR, to maximize the output RF power, depends on RF modulation index and extinction ratio of the integrated dMZM. Good agreement between theory, simulation, and experiment is obtained. For typical extinction ratio and low modulation index, it is found that an OCSR of 0 dB is optimum to maximize RF carrier power. However, for multiband orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) radio, the best error vector magnitude (EVM) of -21.8 dB is obtained experimentally at an OCSR of ~5.4 dB due to avoidance of clipping induced nonlinear distortion.

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.

Performance Analysis of a Photonic-Assisted Periodic Triangular-Shaped Pulses Generator

We propose and analyze a photonic-assisted periodic triangular-shaped pulses generator, in which a continuous wave (CW) laser is connected to a dual electrode Mach-Zehnder modulator (De-MZM), and then the De-MZM is connected with a normal dispersion fiber or element. A radio frequency (RF) sinusoid directly drives the De-MZM to obtain optical subcarrier modulation with optical carrier suppression. By carefully setting the physical parameters, the generated harmonics of optical intensity can be corresponding to the Fourier components of typical periodic triangular pulses. Numerical simulations reveal that modulation index must be set to 2.305 and bias voltage drift must be within a range from from the minimum transmission of the De-MZM. In addition, the dispersion must be set correctly to suppress the primary distortion of 4th order harmonics.

Performance Improvement of Radio-Over Fiber Links Using Mixed-Polarization Electro-Absorption Modulators

We analyze, in theory, simulation, and experiment the spurious-free dynamic range (SFDR) for a radio-over-fiber (RoF) system using a polarization-dependent electro-absorption modulator (EAM) that is linearized using mixed polarization. The mixed-polarization EAM makes use of a polarization-dependent EAM, where a linear polarizer is placed in front of and behind the optical modulator. It is found that improvements of more than 8.1 and 9.5 dB in SDFR for back to back and after 20 km of fiber transmission, respectively, are predicted in theory and simulation and verified experimentally. Suppression of second-order nonlinear distortion is also investigated by simulation and experiment. Moreover, closed forms of the adjacent channel power ratio and third-order intermodulation distortion to carrier power ratio of an orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) signal are presented for an RoF link using mixed-polarization EAM. Finally, mixed-polarization EAM is verified for improving the error vector magnitude of the OFDM UWB signal over fiber by more than 3 dB.

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.

Experimental Demonstration of Mixed-Polarization to Linearize Electro-Absorption Modulators in Radio-Over-Fiber Links

We experimentally investigate optical mixed polarization for the linearization of an electro-absorption modulator (EAM) in radio-over-fiber links. A linear polarizer is used before and after a polarization-dependent EAM. Thus, both transverse-electric and transverse-magnetic polarized lights are simultaneously modulated by different amounts. By carefully optimizing two polarization angles, the third-order intermodulation distortion (IMD3) is suppressed. The linearization leads to suppression of the IMD3 by more than 16 dB and improvement of spurious-free dynamic range by 8.1 and 9.5 dB for back-to-back and after 20 km of fiber transmission, respectively, compared to the nonlinearization case.