Fei Zeng

Ultrawideband Impulse Radio Signal Generation Using a High-Speed Electrooptic Phase Modulator and a Fiber-Bragg-Grating-Based Frequency Discriminator

We propose a novel approach to generating ultrawideband impulse radio signals in the optical domain. The proposed system consists of a laser source, an electrooptic phase modulator (EOPM), a fiber Bragg grating (FBG), and a photodetector (PD). The light source is phase modulated by an electrical Gaussian pulse train via the EOPM. The optical phase modulation to intensity modulation conversion is achieved by reflecting the phase modulated light at the slopes of the FBG that serves as a frequency discriminator. Electrical monocycle or doublet pulses are obtained at the output of the PD by locating the wavelength of the optical carrier at the linear or the quadrature slopes of the FBG reflection spectrum. The use of the proposed configuration to implement pulse polarity and pulse shape modulation in the optical domain is discussed. Experimental measurements in both temporal and frequency domains are presented

Optical ultrawideband monocycle pulse generation based on cross-gain modulation in a semiconductor optical amplifier

A novel method for generating ultrawideband (UWB) monocycle pulses based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. Thanks to the XGM in the SOA, a pair of polarity-reversed optical Gaussian pulses is generated at the output of the SOA, to which a Gaussian pulse pump and a continuous-wave probe are applied. The two polarity-reversed optical pulses are then time delayed by two cascaded fiber Bragg gratings to introduce a time delay difference. A UWB monocycle pulse with a full width at half-maximum of 48 ps and a fractional bandwidth of 188% is generated at the output of a high-speed photodetector.

All-Fiber Ultrawideband Pulse Generation Based on Spectral Shaping and Dispersion-Induced Frequency-to-Time Conversion

An approach to generating and distributing ultrawideband (UWB) pulses based on optical spectral shaping and frequency-to-time conversion using all-fiber components is proposed and demonstrated. In the system, the spectrum of an ultrashort pulse from a mode-locked fiber laser is spectrally shaped by an all-fiber spectrum shaper, to produce a monocycle- or a doublet-shaped power spectrum. Thanks to the frequency-to-time conversion in a dispersive fiber, time-domain optical pulses exhibiting the user-defined shape of the optical power spectrum are obtained. Experiments based on the proposed approach are carried out. UWB monocycle or doublet pulses are generated

An approach to ultrawideband pulse generation and distribution over optical fiber

We propose a novel approach to generating and distributing ultrawideband (UWB) pulse signals over optical fiber. The proposed system consists of a single-wavelength laser source, an electrooptic phase modulator (EOPM), a length of single-mode fiber (SMF), and a photodetector (PD). The combination of the EOPM, the SMF link, and the PD forms an all-optical microwave bandpass filter, which is used to generate a UWB signal with a spectrum meeting the regulation of the Federal Communication Commission. Gaussian doublet pulses are obtained at the receiver front-end, which can provide several gigahertz bandwidths for applications in high-bit-rate UWB wireless communications. Experimental results measured in both temporal and frequency domains are presented.

Millimeter-Wave Frequency Tripling Based on Four-Wave Mixing in a Semiconductor Optical Amplifier

An approach to generating a frequency-tripled millimeter-wave (mm-wave) signal based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is experimentally demonstrated. In the proposed system, two phase-correlated optical wavelengths generated by an optical phase-locked loop (OPLL) are used as two pumps to generate the FWM process in the SOA. Two idlers with a wavelength spacing three times that of the two pump wavelengths are obtained. The two pump wavelengths are then removed by two cascaded fiber Bragg gratings serving as an optical notch filter. By beating the two idlers at a photodetector, an mm-wave with a frequency that is three times that of the OPLL reference source is generated

Single-longitudinal-mode fiber ring laser employing an equivalent phase-shifted fiber Bragg grating

A novel single-longitudinal-mode (SLM) fiber ring laser that incorporates an equivalent phase-shifted fiber Bragg grating acting as an ultra-narrow bandpass filter in the laser cavity is proposed. The equivalent phase-shifted fiber Bragg grating has an ultra-narrow transmission bandwidth which ensures an SLM lasing. Stable SLM operation without mode hopping is demonstrated.

Photonic Generation of Microwave Signals Based on Pulse Shaping

A novel approach to generating microwave signals based on optical pulse shaping is proposed and experimentally demonstrated. The proposed system consists of a femtosecond pulse laser source, a Sagnac-loop filter (SLF), a dispersive element, and a photodetector. The spectrum of the femtosecond pulse is shaped by the SLF that has a sinusoidal spectral response. Thanks to the frequency-to-time conversion in the dispersive element, time-domain pulse exhibiting the shape of the optical power spectrum is obtained. Depending on the free-spectral range of the SLF and the total dispersion of the dispersive element, signals with frequencies up to terahertz can be generated. A model to describe the signal generation is developed. Experimental results agree well with the theoretical analysis

All-optical microwave bandpass filter with negative coefficients based on a phase modulator and linearly chirped fiber Bragg gratings

A novel all-optical microwave bandpass filter with negative coefficients is presented. Positive and negative coefficients are obtained through conversion from phase modulation to intensity modulation by passing the phase-modulated optical carriers through chirped fiber Bragg gratings having group-delay responses with positive and negative slopes. A two-tap transversal microwave filter with one negative coefficient is experimentally implemented.

All-optical microwave bandpass filters implemented in a radio-over-fiber link

An all-optical microwave bandpass filter implemented in a radio-over-fiber (RoF) link is proposed and demonstrated. The filter consists of an optical phase modulator, a length of high birefringence (Hi-Bi) fiber, a 25-km singlemode fiber and a narrow linewidth laser source. Different time delays are achieved when the two orthogonal polarization modes are traveling along the Hi-Bi fiber. The baseband resonance is eliminated by use of the optical phase modulator in combination with the 25-km single-mode fiber serving as a dispersive device. The proposed filter is immune to optical interference because of the orthogonality of the two polarization modes. A two-tap all-optical microwave bandpass filter with a null-to-null bandwidth of 8.7 GHz and a notch rejection level greater than 30 dB implemented in the 25-km RoF link is demonstrated.

All-optical microwave bandpass filter with negative coefficients based on PM-IM conversion

A novel technique for obtaining negative coefficients for the implementation of all-optical microwave bandpass filters is presented. In the proposed approach, the negative coefficients are obtained by locating the optical carriers at the opposite slopes of the transfer function of an optical filter, to convert the phase-modulated signal to intensity-modulated signal, with phase inversion of the radio-frequency modulating signals. A two-tap microwave bandpass filter with negative coefficients is demonstrated.