Béatrice Cabon

Microwave-frequency conversion methods by optical interferometer and photodiode

Frequency conversion in fiber-optic systems like subcarrier multiplexed (SCM) systems is now to be used in many applications for both digital and analog signals. The performance of two different optoelectronic configurations, both used for frequency conversion in the microwave frequency range, are compared here. In the first case, mixing is achieved by a Mach-Zehnder (MZ) interferometer, while in the second case, photodiode mixing is presented. Experimental investigations are presented at the optical wavelength of 1.3 /spl mu/m. In both cases, promising results have been achieved.

Transmission of Multi-Band OFDM and Impulse Radio Ultra-Wideband Signals Over Single Mode Fiber

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using this figure of merit the direct modulation of distributed feedback (DFB) laser diode and the external modulation with Mach-Zehnder modulator (MZM) are compared in terms of their impact on UWB signals. Using intensive simulation we also compare MB-OFDM and IR-UWB in terms of their sensitivity to the distortions of a UWB over fiber link using error vector magnitude (EVM) as a figure of merit. An EVM measurement is accomplished for a MB-OFDM over fiber link. The impact of IR-UWB pulse shape on its resistance to the nonlinearity of modulation transfer function is also investigated.

Theoretical and experimental analysis of influence of phase-to-intensity noise conversion in interferometric systems

The noise power spectral density in interferometric systems was studied theoretically and experimentally. The influence of 1/f frequency modulation noise, white noise, and source dispersion are shown in the conversion of phase noise into intensity noise. The direct relative intensity noise (RIN) is compared with the RIN caused by phase-to-intensity noise conversion, and the root mean square of equivalent interferometer phase error was studied. The influence of the interferometer operating point is shown on the noise power spectrum. The results can be employed to estimate the influence of the these effects in phase-to-intensity noise conversion in radio-frequency-modulated optical links, which use either self-delayed interferences or interferometers. These results can be applied to optical signal processing, radar signal processing, etc., which often use interferometers.

Optimum Biasing of VCSEL Diodes for All-Optical Up-Conversion of OFDM Signals

Nonlinear behavior of vertical-cavity surface-emitting laser (VCSEL) diodes is exploited to perform all-optical up-conversion by second- and third-order mixing. We investigate and explain conditions for optimum frequency mixing with a common WLAN IEEE 802.11a signal. Then, we apply these findings to the transmission of an ultra-wideband (UWB) multiband-OFDM ECMA-368 signal over a fiber-optic link. We demonstrate direct modulation with the UWB signal up to 10.3 GHz and perform up-conversion to frequencies as high as 16 GHz, far beyond the cutoff frequency of the VCSEL diode.

Signal and noise conversions in RF-modulated optical links

The power spectral density of the optical intensity in RF modulated optical links is investigated theoretically and experimentally in interferometric systems with a good agreement. The influence of the Henry factor /spl alpha/ of directly modulated distributed feedback laser diodes is shown on the conversion of phase noise into intensity noise for the first time.

Impact of Phase Noise in 60-GHz Radio-Over-Fiber Communication System Based on Passively Mode-Locked Laser

In this paper, a radio-over-fiber (RoF) communication system at 60 GHz based on passively mode-locked laser diode (PMLLD) is presented and the performance of different electrical down-conversion methods (coherent and non-coherent down-conversion) for this communication system is studied. Impact of PMLLD phase noise on error vector magnitude (EVM) is also observed and a complete theory and experimental survey on using non-coherent down-conversion (envelope detector) to reduce error of system caused by phase instability of PMLLD is provided. The performance of envelope detector to down-convert the signal with OOK modulation in this communication system is observed using eye diagram and quality factor (Q factor) measurement.

Performance of interferometric systems for optical processing of microwave signals: influence of laser- and microwave-phase noises

An unbalanced Mach-Zehnder interferometer (UMZ) is used to convert microwave (MW) frequency modulation (FM) of a laser diode into intensity modulation (IM). In coherent interference regime, it is shown that parasite FM, induced by laser-phase noise and by MW-phase noise of the modulation source, causes negligible intensity noise, but significant phase noise in the photodetected intensity at the output of the UMZ. Theoretical study is realized in linear- and nonlinear-interference regimes. Results are validated experimentally.

Impact of Amplitude Noise in Millimeter-Wave Radio-Over-Fiber Systems

In this paper, a complete theoretical and experimental study of amplitude noise impact on performance of radio-over-fiber (RoF) communication system in millimeter-wave (MMW) frequency band is presented. A simulation method is also presented, using which one can determine the origin of the amplitude noise which has the most impact on error vector magnitude (EVM). This method is based on analyzing the trends of EVM versus received optical power. The impact of different optical and electrical noise such as relative intensity noise, shot noise and thermal noise on EVM is precisely studied employing experimental and theoretical analysis. In the proposed RoF system, two techniques are used to generate MMW signal, and the EVM results are compared from amplitude noise viewpoint. In the first technique, two independent distributed feedback lasers are used to generate MMW signal at the output of a photodetector, and the second technique is based on a passively mode-locked laser diode. Impact of optical sources phase noise on performance of the system is removed using a noncoherent down-conversion method based on envelope detector. Using this method, a very good matching between the experimental and the simulation results is observed.

Simultaneous transmission of gigabit wireline signal and ECMA 387 mmW over fiber using a single MZM in multi-band modulation

We propose a multi-band radio over fiber system compatible with wired and 60GHz band wireless transmission by implementing two-band modulation with a single Mach-Zehnder modulator. In this paper, broadband millimeter wave at 60 GHz band, which is compliant with the ECMA 387 standard, is generated by photodetection after 25 km long optical fiber transmission. Furthermore, baseband transmission, which feeds up the requirement of fiber-to-the-Home, has been realized simultaneously.

Up-Conversion of IQ Modulated Subcarriers with Dispersive Fiber for 60 GHz Radio-Over-Fiber Networks

An optical microwave mixing technique based on optical phase modulation and fiber chromatic dispersion is investigated for up-conversion of IQ modulated microwave subcarriers. Experiments with analog signals have validated up-conversion theory. Error Vector Magnitude measurements have shown low penalty induced by optical microwave up-conversion process on QAM signals within the 10 GHz band. For future radio-over-fiber networks, optical microwave up-conversion in the 60 GHz band is investigated. Application of this technique for high symbol rate IQ modulations for future 60 GHz radio-over-fiber networks is proposed