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We propose a novel multi-parameter sensing technique based on a Brillouin optical time domain reflectometry in the elliptical-core few-mode fiber, using higher-order optical and acoustic modes. Multiple Brillouin peaks are observed for the back scattering of both the LP01 mode and LP11 mode. We characterize the temperature and strain coefficients for various optical–acoustic mode pairs. By selecting the proper combination of modes pairs, the performance of multi-parameter sensing can be optimized. Distributed sensing of temperature and strain is demonstrated over a 0.5-km elliptical-core few-mode fiber, with the discriminative uncertainty of 0.28°C and 5.81 με for temperature and strain, respectively Refereed/Peer-reviewed

We demonstrate a novel complex Brillouin optical time-domain analysis (BOTDA) approach for distributed fiber sensing that detects the complex Brillouin spectrum. Unlike other approaches, we utilize the complex nonlinear least-square regression technique to determine the Brillouin frequency shift (BFS) directly in the complex domain. The reduction of BFS uncertainty with our approach is shown through theoretical analysis and is validated by both simulations and experiments. Compared with either the gain-based or the phase-based BOTDA approaches, our complex BOTDA can improve the sensing accuracy by a factor of 2 , which is equivalent to a 3 dB improvement in the power signal-to-noise ratio. Distributed temperature sensing is demonstrated over 40 km standard single-mode fiber. The experimental results agree well with the theoretical predictions of BFS uncertainty that confirms this considerable improvement. Refereed/Peer-reviewed

We propose a single-ended Brillouin-based sensor in elliptical-core few-mode optical fiber for multi-parameter measurement using spontaneousBrillouin scattering. Distributed sensing of temperature and strain is demonstrated over 0.5 km elliptical-core few-mode fiber. Refereed/Peer-reviewed

We propose the polarization-multiplexing (POL-MUX) using free-running TOSAs, with the direct-detection receiver required only the baseband bandwidth. A >100-Gb/s POL-MUX direct modulation is realized by 10G-class TOSA/ROSA with TOSA frequency offset from 0 to 250 GHz. Refereed/Peer-reviewed

We demonstrate a novel single-shot distributed Brillouin optical time domain analyzer (SS-BOTDA). In our method, dual-polarization probe with orthogonal frequency-division multiplexing (OFDM) modulation is used to acquire the distributed Brillouin gain spectra, and coherent detection is used to enhance the signal-To-noise ratio (SNR) drastically. Distributed temperature sensing is demonstrated over a 1.08 km standard single-mode fiber (SSMF) with 20.48 m spatial resolution and 0.59 °C temperature accuracy. Neither frequency scanning, nor polarization scrambling, nor averaging is required in our scheme. All the data are obtained through only one-shot measurement, indicating that the sensing speed is only limited by the length of fiber. Refereed/Peer-reviewed

We present coherent imaging for acquiring two-dimensional optical image that recovers amplitude and phase simultaneously. With coherent imaging, we detect few-mode-fiber modes with high extinction-ratio, and perform mode decomposition and differential mode delay measurement. Refereed/Peer-reviewed

We demonstrate a novel technique for distributed Brillouin frequency estimation by fitting the Brillouin transfer function directly in the complex domain. Experimental results show the uncertainty of Brillouin frequency can be significantly reduced compared with the approaches based solely on Brillouin gain or phase. Refereed/Peer-reviewed

The spinning in few-mode fiber with distributed long period gratings can dramatically reduce the DMD at 1550nm. The effective bandwidth and DMD can be further improved with frequency modulation in the spin profile. Refereed/Peer-reviewed

Frequency chirp used to be a transmission barrier for optical direct modulation (DM) systems. We reinvent DM by treating the chirp as complex modulation, which significantly increases the OSNR sensitivity of DM based coherent systems. Refereed/Peer-reviewed

A single-shot BOTDA technique is demonstrated to measure the distributed stimulated Brillouin spectrum by using dual-polarized OFDM probe and coherent detection, without frequency scanning, averaging or polarization scrambling. Refereed/Peer-reviewed

We propose a novel method for distributed measurement of temperature and strain using a few-mode fiber (FMF). High discrimination accuracies of 0.115 oC and 0.283 με are achieved, under a spatial resolution of 2.5 m. Refereed/Peer-reviewed

We report the first experiment of digital coherent detection of directly modulated signals that utilizes both phase and amplitude of the signals. A novel algorithm is proposed to take advantage of simultaneous detection of both phase and amplitude of the modulated signal. Using our proposed scheme, the experiment shows 6-dB improvement over the amplitude-only detection scheme. Refereed/Peer-reviewed

Complex imaging via coherent detection is proposed for acquiring two-dimensional (2-D) nearfield optical image that recovers amplitude and phase simultaneously. Based on the proposed complex imaging, we experimentally demonstrate the technique by detecting few-mode-fiber (FMF) modes with high extinction-ratio, and perform mode decomposition and differential mode delay (DMD) measurement. Refereed/Peer-reviewed

We propose a distributed grating-assisted few-mode fiber (DG-FMF) to reduce the differential mode delay (DMD).By introducing asymmetric long-period fiber gratings with random exposure directions in a step-index few-mode fiber during fiber manufacture process, the strong random mode coupling is generated along the entire length of the fiber.Simulation results show that mean DMD in the DG-FMF can be reduced to less than 12 ns at a distance of 100 km with a period of 514 μm and grating strength of 1 × 10-6. The DMD reduction in our DG-FMF is guaranteed within the entire C-band, and in a wide temperature range from-20°C to =60°C. Refereed/Peer-reviewed

We propose a unique few-mode fiber (FMF)-based multi-parameter optical-fiber sensor for distributed measurement of temperature and strain. We launch a pump and a probe signal through specific linearly polarized modes into a FMF, and monitor the Brillouin frequency shift (BFS) in each mode. By analyzing the temperature and strain coefficients of the BFS of the two lowest order (LP01, LP11) modes, discrimination of temperature and strain are successfully demonstrated, with an accuracy of 1.2°C and 21.9 με Refereed/Peer-reviewed

Complex imaging via coherent detection is proposed for acquiring two-dimensional nearfield optical image recovering amplitude and phase simultaneously. We experimentally demonstrate the technique using few-mode-fiber (FMF) modes with high extinction-ratio, and perform mode decomposition based on it. Refereed/Peer-reviewed