Chunhui Qi

Millimeter-wave radio-over-fiber system based on two-step heterodyne technique

We theoretically demonstrate an improved two-step-heterodyne-based, millimeter-wave, radio-over-fiber system. With the millimeter-wave mixer and a fiber Bragg grating located in the base station, two-step heterodyne is achieved. The proposed scheme has the merit of good system performance and high suppression of unwanted frequency tones, which is verified by numerical simulations.

An Improved Radio Over Fiber System With High Sensitivity and Reduced Power Degradation by Employing a Triangular CFBG

We propose and demonstrate a prototype for an improved intensity modulation direct detection (IMDD)-based radio over fiber (RoF) system by employing a homemade triangular chirped fiber Bragg grating (CFBG). In the scheme, an intensity modulator first modulates the lightwave with millimeter-wave driving signals to realize optical double-sideband (DSB) modulation, and then the output DSB signals pass though a triangular CFBG. Because the triangular CFBG is with a negative slop in spectrum, the lower sideband experiences higher attenuation than the upper sideband, which means the optical single sideband with carrier (OSSB+C) modulation can be easily implemented. The process of triangular CFBG also improves the link performance by balancing optical carrier-to-sideband ratio. As our scheme only uses a commercially used intensity modulator and homemade triangular CFBGs, the system is guaranteed with cost-effective architecture and good performance.

60 GHz millimeter-wave generator based on a frequency-quadrupling feed-forward modulation technique

We propose and analyze a prototype of a 60 GHz millimeter-wave (mm-wave) generator. In the scheme, two lasers with a 70 GHz frequency interval serve as sources. Then a frequency-quadrupling feed-forward modulation technique is employed to generate two phase correlated sidebands with a 60 GHz interval. The desired sidebands can be selected by using standard optical interleavers. In our work, a 60 GHz mm-wave signal free of phase noise can be achieved. The employed technique can also be extended to frequency 8-tupling.

Photonic frequency-quadrupling scheme for millimeter-wave generation by employing feed-forward modulation technique

We theoretically analysis and numerically verify a frequency-quadrupling scheme which is capable of generating millimeter-wave (mm-wave) signals. The scheme is based on dual wavelength feed-forward modulation technique, which circumvents the need for direct modulation at mm-wave frequency band, providing potential for two-tone optical sources. The analytical models for transmission through a dispersive medium are confirmed by numerical simulations. Results of this study demonstrate that such a scheme offer realistic solutions to support future wireless systems.

Simulation analysis of a photonic ultrawideband pulse generator by using a dual-parallel Mach–Zehnder modulator

This study analyzes a photonic ultrawideband pulse generator by using a dual-parallel Mach-Zehnder modulator. A simple configuration capable of generating two popular types of ultrawideband pulse shape, Gaussian monocycle and doublet, is proposed. The generated ultrawideband pulses have very high quality, and the exact waveform is tunable with respect to parameter settings. By changing the time delay between two-path driving pulses applied to the upper and lower sub-Mach-Zehnder modulator of the dual-parallel Mach-Zehnder modulator, the generated ultrawideband pulses can be switched from Gaussian monocycle to doublet. The proposal is first analyzed and then validated by simulations. Results of the study demonstrate that it can offer a realistic solution to photonic ultrawideband pulse generation.

Flat microwave photonic filter based on hybrid of two filters

A new microwave photonic filter (MPF) hybrid of two filters that can realize both multiple taps and a flat bandpass or bandstop response is presented. Based on the phase character of a Mach?Zehnder modulator (MZM), a two taps finite impulse response (FIR) filter?is obtained as the first part. The second part is obtained by taking full advantage of the wavelength selectivity of the fiber Bragg grating (FBG) and the gain of a erbium-doped fiber (EDF). Combining the two filters, the flat bandpass or bandstop response is realized by changing the couplers factor k, the reflectivity of FBG1 R1 or the gain of the EDF g. Optimizing the system parameters, a flat bandpass response with amplitude depth of more than 45?dB is obtained at k = 0.5, R1 = 0.33, g = 10, and a flat bandstop response is also obtained at k = 0.4, R1 = 0.5, g = 2. In addition, the free-spectral range (FSR) can be controlled by changing the length of the EDF and the length difference between two MZMs. The method is proved feasible by some experiments. Such a method offers realistic solutions to support future radio-frequency (RF) optical communication systems.

Corrections to “An Improved Radio Over Fiber System With High Sensitivity and Reduced Power Degradation by Employing a Triangular CFBG” [Apr 1, 2010 516-518]

Corrections to the paper “An Improved Radio Over Fiber System With High Sensitivity and Reduced Power Degradation by Employing a Triangular CFBG” is given.

Frequency-octupling millimeter-wave generation based on optical two-step self-heterodyne technique

A cost-effective frequency-quadrupling scheme which is capable of generating high frequency millimeter-wave (mm-wave) signal is theoretically proposed. By employing optical two-step self-heterodyne technique, this scheme is easy to realize and have a high efficiency. Base on this scheme, a frequency-octupling frequency component is generated. This proposed scheme is a viable solution for the future ultra-high frequency mm-wave applications. (4 pages)

Key factors in getting high Q values for finite- and infinite-impulse-response microwave photonic filters

In this brief-article the effect of the number of taps on the quality (Q) for infinite- and finite-impulse-response microwave photonic filters (IIRMPFs and FIRMPFs) is analyzed. For FIRMPFs, an increas of Q with the number of taps from 2 to 10 is deduced by analyzing the free spectrum ranges with 3-dB bandwidths. For IIRMPFs, a pretty high Q can be realized when the product of the coefficient and the gain in the feedback loop equals 1. Our analytical results are verified by a typical IIRMPF structure based on a fiber Bragg grating (FBG), and the Q value can be increased up to 804 by using two FBGs with reflectivities of 50% and 99.5%, respectively.

Optical ultra-wideband pulse generation and distribution using a dual-electrode Mach-Zehnder modulator

A novel approach to generate and distribute ultra-wideband (UWB) pulses in optical domain is investigated. In this proposed scheme, a dual-electrode Mach-Zehnder modulator (DE-MZM) is biased at its quadrature point so as to realize the linear response. Then the intensity of output optical field can be assumed to the subtraction of two input Gaussian pulses. If the input Gaussian pulses are with the same sharp parameters but different time delays, a quasi-monocycle-waveform UWB signal can be generated. If the input Gaussian pulses are with different amplitudes and full-width at half-maximum (FWHM), a quasi-doublet-waveform UWB signal can be generated. A transmission of the UWB signals through a 25-km single mode fiber is carried out successfully. The results in both temporal and frequency domains are also presented.