Jianbin Fu

Linearized analog photonic links based on a dual-parallel polarization modulator

A linearized analog photonic link (APL) is proposed based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of two polarization beam splitters and two polarization modulators (PolMs). Theoretical analysis shows that the APL is potentially free from the third-order nonlinear distortion if a polarization controller placed before the DPPolM is carefully adjusted. A proof-of-concept experiment is carried out. A reduction of the third-order intermodulation components as high as 40 dB and an improvement of the spurious-free dynamic range as large as 15.5 dB is achieved as compared with a single PolM-based link. The DPPolM-based APL is simple, compact, and power efficient since it requires only one laser, one modulator, and one photodetector.

Photonic approach to the simultaneous measurement of the frequency, amplitude, pulse width, and time of arrival of a microwave signal

A photonic approach to the simultaneous measurement of the frequency, pulse amplitude (PA), pulse width (PW), and time of arrival (TOA) of an unknown pulsed microwave signal is proposed and demonstrated. The measurement is performed based on optical carrier-suppressed modulation, complementary optical filtering, low-speed photodetection, and electrical signal processing. A proof-of-concept experiment is carried out. A frequency measurement range of 2-11 GHz with a measurement error for frequency, PA, PW, and TOA within ±0.1 GHz, ±0.05 V, ±1 ns, and ±0.16 ns is achieved.

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.

Fiber-connected UWB sensor network for high-resolution localization using optical time-division multiplexing.

A fiber-connected ultra-wideband (UWB) sensor network for high-resolution localization which consists of a central station and several sensor nodes is proposed and demonstrated. To make the central station easily identify the received UWB pulses from different sensor nodes, optical time-division multiplexing (OTDM), realized by inserting a certain length of optical fiber between every two sensor nodes, is implemented. Due to the OTDM technology, the UWB pulses received by different sensors are mapped into different time slots, so neither parameter estimation nor clock synchronization is required in the UWB sensor node. All complex signal processing is completed in the central station, which greatly improve the localization accuracy and simplify the system. A proof-of-concept experiment for two-dimensional localization is demonstrated. Spatial resolution as high as 3.9 cm is achieved.

UWB-over-fiber sensor network for accurate localization based on optical time-division multiplexing

An impulse radio (IR) ultra-wideband (UWB) over fiber sensor network for accurate localization based on optical time-division multiplexing (OTDM) is proposed and demonstrated. Neither clock synchronization nor parameter estimation is required in the proposed UWB sensor nodes. All complex signal processing is completed in the central station, which can greatly improve the localization accuracy and simplify the UWB sensor system. A proof-of-concept experiment is carried out. Two-dimension localization with centimeter-level spatial resolution is achieved.

A photonic-assisted transceiver with wavelength reuse for distributed UWB radar

A photonic-assisted transceiver with wavelength reuse for distributed ultra-wideband (UWB) radar is proposed and demonstrated. The transceiver converts an input optical phase modulated signal into an optical UWB pulse train based on phase modulation to intensity modulation conversion using a fiber Bragg grating, and performs wavelength reuse by re-modulating the phase modulated optical signal via an intensity modulator. The transceiver is applied in a UWB ranging radar. A centimeter level accuracy is achieved.

Photonic microwave bandpass filter based on optical single-sideband polarization modulation for long-reach radio over fiber applications

A two-tap dispersion-insensitive photonic microwave bandpass filter based on optical single-sideband (SSB) polarization modulation is proposed for long-reach radio over fiber applications. The optical SSB polarization modulation, which generates two complementary intensity-modulated signals along two orthogonal polarization directions, is implemented by a polarization modulator (PolM) followed by an optical filter. With a polarization maintaining fiber (PMF) to introduce a time delay, a two-tap dispersion-insensitive photonic microwave bandpass filter is obtained. The proposed filter is used to shape a Gaussian pulse to an ultra-wideband (UWB) signal. After 40-km fiber transmission, no distortion in the waveform of the UWB signal is observed.

A fiber-distributed bistatic ultra-wideband radar based on optical time division multiplexing

A fiber-distributed bistatic ultra-wideband (UWB) radar based on optical time division multiplexing (OTDM) is proposed and demonstrated. The proposed radar consists of a central office (CO) and two spatially separated transceivers. OTDM technology is implemented by inserting a certain length of optical fiber between the two radar transceivers, so the UWB pulses received by different transceivers can be identified by the time slots they are presented in. The UWB pulses emitted from different transceivers are designed to have opposite polarities, so it is easy to identify which transceiver the echo UWB pulse is emitted from. Therefore, the information of target in the radar coverage area can be extracted with single-channel cooperative signal processing in the CO. In addition, wavelength-reuse is applied in each transceiver to simplify the system and polarization division multiplexing is employed to avoid optical interference. An experiment is carried out, showing that 2-D localization with centimeter-level accuracy can be achieved.

A fiber-distributed multistatic ultra-wideband radar

A fiber-distributed multistatic ultra-wideband (UWB) radar is proposed and demonstrated. The proposed radar includes a central office (CO), two transmitters and a receiver which are connected by optical fibers. The UWB pulses generated by the two transmitters are designed to have opposite polarities using the complementary transmission and reflection responses of an FBG, so that it is easy to identify in the CO which transmitter the echo pulse is from. An experiment is carried out. 2-D localization of a target is realized using the proposed radar. The localization accuracy is of centimeter level.

Length measurement of long optical fiber with sub-millimeter resolution

Knowing the exact length of long optical fiber is of great importance to interferometry-based optical sensors, fiber-connected antenna arrays and other microwave photonic applications. This paper reviews recent efforts on long optical fiber length measurement with sub-millimeter resolution, including optical time domain reflectometers, optical frequency domain reflectometers, and optical backscatter reflectometers based on microwave frequency sweeping. Techniques to improve the measurement resolution and to reduce the measurement error are discussed.