Jianyu Zheng

Photonic microwave-signal-mixing technique using phase-coherent orthogonal optical carriers for radio-over-fiber application

An optical-assisted microwave-mixing technique based on orthogonal and phase-coherent optical carriers is proposed and demonstrated. High-quality binary-phase-shift keying, amplitude-shift keying, and on-off keying microwave modulation at 20 GHz implemented in the optical domain have been tested. The ultra-high-bandwidth response of the proposed mixing device is also analyzed and compared. The phase stability of the photonic microwave signal in the radio-over-fiber system is improved by the proposed signal mixing technique.

Fiber-distributed Ultra-wideband noise radar with steerable power spectrum and colorless base station

A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module. Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals. Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion. The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 5.2 GHz and 7.8 GHz or not. Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO. The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible.

Implementation of wavelength reusing upstream service based on distributed intensity conversion in ultrawideband-over-fiber system

We propose and demonstrate a simple scheme for generating the ultrawideband (UWB) signals and reusing the wavelength for upstream service simultaneously by using a distributed polarization modulation-to-intensity modulation convertor. Through adjusting the static phase difference between transverse electric and transverse magnetic modes of the optical carrier (OC) and the angle between the polarization direction of the OC and the principal axis of the polarizers, the UWB doublet-like signals were generated. Meanwhile, the error-free transmission of the upstream signals with bit rate of 1.25 Gbit/s over 10 km fiber is achieved. The power penalty resulting from the interference of downstream signals is less than 0.3 dB.

Photonic Generation of Ultrawideband (UWB) Pulse With Tunable Notch-Band Behavior

A photonic approach to generating the ultrawideband (UWB) pulses with tunable band-rejection behavior based on a negative coefficient two-tap microwave photonic filter is proposed and experimentally demonstrated. To avoid the interference between UWB and the Wireless Fidelity system, the UWB pulse with the “batwing” shape, which corresponds to the 5-GHz notch-band in frequency domain, is generated. Moreover, the band-notched position of the generated UWB signals could be tuned by adjusting the basic delay of the microwave photonic filter. Utilizing the optically tunable band-rejection character, the UWB systems can coexist with existing and future wireless network technologies almost without interference, as well as provide the opportunity for the combination between UWB-over-fiber and cognitive radio.

Widely-Tunable and Background-Free Ultra-Wideband Signals Generation Utilizing Polarization Modulation-Based Optical Switch

A simple widely-tunable and background-free ultra-wideband (UWB) pulse shaper by utilizing the polarization modulation-based optical switch is proposed and demonstrated. By virtue of the excellent switch isolation and the complementarity between two inverted baseband signals output from the optical switch, the local oscillator leakage signal and the low frequency components of the obtained UWB signals are suppressed very well. The UWB pulse with center frequency up to 28 GHz is generated.

Long-term stability improvement of tunable optoelectronic oscillator using dynamic feedback compensation

We propose and demonstrate a novel method to improve the long-term stability of the wideband tunable optoelectronic oscillator (OEO) where a dynamic compensation scheme is achieved to offset the parameter variation of the fiber. In our method, a 900 MHz calibration signal transmits in the fiber link of the OEOs feedback loop for establishing a servo system which can extract the time delay of the feedback loop. The time delay varies with the external environment because refractive index and length of the fiber fluctuate with ambient temperature variations. Taking the extracted information as the reference, the wavelength of the tunable laser used in the OEO can be controlled precisely and continually to offset the random delay fluctuation in the fiber. Consequently, the long-term stability of the microwave signal generated by the OEO can be optimized. The experiment results show that Allan deviation achieved in 1000-s averaging time is improved more than two orders of magnitude when the tunable OEO worked at 2.4 GHz.

Orthogonal Single-Sideband Signal Generation Using Improved Sagnac-Loop-Based Modulator

A novel microwave photonics technique that enables the modulation of orthogonal optical single-sideband (OSSB) by using an improved Sagnac-loop-based modulator is proposed and experimentally demonstrated. The dual-driving Mach-Zehnder modulator and polarization-maintaining fiber Bragg grating are integrated inside and outside the Sagnac loop, respectively, in order to realize the OSSB modulation and polarization-selective filtering. Therefore, the precisely defined orthogonal OSSB signal can be generated steadily at 20-GHz carrier frequency in the experiment.

Multiservice Wireless Transport Over RoF Link With Colorless BS Using PolM-to-IM Convertor

A new architecture of radio-over-fiber system with colorless base stations based on distributed polarization modulation-to-intensity modulation converter is proposed and demonstrated, which can simultaneously support the existing low radio frequency and millimeter-wave wireless services transmission. In the experiment, the orthogonal frequency-division-multiplexing downstream signals working at 0.3 and 54.8 GHz are received at the base station via 25-km fiber. Meanwhile, successful transmission of the upstream signal is implemented by reusing the light-wave. The experimental results are compatible with the theoretical prediction.

Photonic-Assisted Ultrawideband Pulse Generator With Tunable Notch Filtering Based on Polarization-to-Intensity Conversion

A photonic approach to generating ultrawideband (UWB) pulses with tunable band-rejection behavior and a chirp-free property, which is based on a nonlinear operated polarization-to-intensity converter, is proposed and demonstrated. As an initial phase shift of the incident light φ0 = π, a high-order UWB pulse fully satisfied the indoor mask regulated by the Federal Communications Commission was synthesized by a pair of polarity-inverted and doublet-like pulses at the output port of the polarization beam combiner. Moreover, the notch band will occur dynamically on the power spectra of the UWB signals from 3 to 16 GHz through adjusting the relative delay time between both doublet-like pulses from 333 to 62.5 ps due to the effect of microwave photonic filtering, which means that the spectrum-overlay-induced interference between UWB and other narrow-band communication systems could be real-time averted. In addition, the polarity switch of the synthesized UWB pulse could be implemented by adjusting angle α between the x-axis component of modulated light and the principal axis of the arm of transverse electric mode by the polarization controller.

Bidirectional multiband radio-over-fiber system based on polarization multiplexing and wavelength reuse.

A polarization multiplexing technique based on phase-shift-induced polarization modulation-to-intensity modulation (PloM-to-IM) convertor and a Mach-Zehnder modulator (MZM) is proposed to generate multi-band signals. Successful transmission of the traditional radio frequency, microwave (MW) and millimeter wave (MMW) signals is simultaneously achieved. Meanwhile, the intensity-constant optical carrier (OC) is reused for upstream 25-km transmission.