Zonglei Li

Coherent BOTDA sensor with intensity modulated local light and IQ demodulation

Coherent Brillouin optical time domain analysis (BOTDA) sensing system with intensity modulated local (IML) light and fast IQ demodulation is proposed and demonstrated. IML light instead of phase modulated local (PML) light is utilized to reduce the coherent and multiple sidebands induced noises. A spatial resolution of 3-m and ± 1.8°C temperature accuracy at the far end of the fiber are obtained over 40-km sensing distance.

Self-Mixing Demodulation for Coherent Phase-Sensitive OTDR System

Phase-sensitive optical time domain reflectometry (Ф-OTDR) attracts much attention due to its capability of telling the type and position of an intrusion simultaneously. In recent decades, coherent Ф-OTDR has been demonstrated to realize long-distance detection. For coherent Ф-OTDR, there are three typical demodulation schemes in the reported studies. However, they still cannot realize real-time monitoring to satisfy practical demands. A simple and effective demodulation method based on self-mixing has been put forward to demodulate the beat signal in coherent Ф-OTDR. It not only saves a local electrical oscillator and frequency locked loop, but also demodulates the beat signal without residual frequency. Several vibrations with different frequency were separately applied at the same location of a 42.5 km fiber. The spatial resolution of 10 m and frequency response range from 8 Hz to 980 Hz have been achieved. The precise location with signal-to-noise ratio of 21.4 dB and broadband measurement demonstrate the self-mixing scheme can demodulate the coherent Ф-OTDR signal effectively.

Precise Brillouin gain and phase spectra measurements in coherent BOTDA sensor with phase fluctuation cancellation

In order to cancel phase fluctuation induced Brillouin gain spectrum (BGS) and Brillouin phase spectrum (BPS) distortions, a new scheme with phase fluctuation cancellation (PFC) is proposed to realize precise BGS and BPS measurements in coherent BOTDA sensors. We present comprehensive and theoretical analysis about the effect of phase fluctuation on the shape of BGS and BPS, and further design a new experimental setup to fully cancel phase fluctuation induced measurement errors. In our new scheme, the two signals sent into the in-phase/quadrature (I/Q) demodulator are almost the same except for the additional amplitude amplification and phase shift induced by Brillouin gain, thus a strict phase synchronization between them has been realized (i.e., PFC). Experimental results show that the biggest BFS decoding error induced by phase fluctuation is reduced from 4.9MHz to 0.4MHz over a 40-km sensing fiber.

Simultaneous transmission of multiple wireless services over fiber with reduced network complexities

We propose a scheme of a radio-over-fiber (RoF) network supporting the simultaneous transmission of radio frequency identification (RFID), Wi-Fi, and ZigBee services. All services share the same optical transmitter and receiver to reduce the network complexity. Error vector magnitude (EVM) values of 0.36%, 1.23%, and 0.25% can be achieved in the downlink for RFID, WiFi, and ZigBee signals, respectively. The corresponding EVM values in the uplink are 0.37%, 1.78%, and 0.29%, respectively. The scheme is verified over a 2 km RoF link where RFID, WiFi, and ZigBee master nodes can communicate normally with their slave nodes.

Phase fluctuation cancellation of anonymous microwave signal transmission in passive systems.

A phase fluctuation cancellation approach for anonymous microwave signal transmission over fiber link is proposed and demonstrated. Unlike most previous schemes that used for active systems, our proposal is suitable for passive systems by utilizing the optical signal feedback and electrical signal phase-locking. Experimental results show that phase drifts of 7.7-ps, 54-ps and 96-ps (RMS value) for 2.45-GHz signals could be reduced to 3.1-ps, 3.8-ps and 8.5-ps after 1-km, 10-km and 25-km SMF transmission over an eight-hour period, respectively. Overall system performance is limited by the coherent Rayleigh noise and could be further optimized.

Enhanced phase stability in passive analog photonic links with coherent Rayleigh noise reduction.

Minimizing phase fluctuation along passive analog fiber link is proposed and experimentally demonstrated. By utilizing three different optical wavelengths, we could significantly reduce the effect of coherent Rayleigh noise (CRN). In addition, a phase-locked loop is employed for dynamic phase fluctuation compensation. The RMS phase jitter within two-hour period is reduced to ~1.7131 ps over 40-km fiber link.

Coherent BOTDA Sensor With Single-Sideband Modulated Probe Light

In order to optimize the coherent Brillouin optical time domain analysis (BOTDA) sensor for more effective chromatic dispersion (CD) suppression, single-sideband intensity-modulated probe (IMP) light is utilized. Obvious Brillouin gain spectrum distortion due to CD observed in the double-sideband IMP case is successfully cancelled. Meanwhile, frequency preshift for local light generation in other coherent BOTDA sensors that have been reported recently can be avoided in our scheme, resulting in a reduction in system complexity. On the other hand, a logarithmic detector, instead of an inphase/quadrature demodulator, is applied to reduce half of the measurement time. A ~2-m spatial resolution and 0.97 °C temperature accuracy at the end of a 40-km sensing fiber are realized by using a 100-ns/80-ns differential pulsewidth pair.

Enhanced performance in coherent BOTDA sensor with reduced effect of chromatic dispersion.

An approach for reducing chromatic dispersion (CD) induced Brillouin gain spectrum (BGS) distortion and measurement instabilities in coherent Brillouin optical time domain analysis (BOTDA) sensing systems is proposed and experimentally demonstrated. By utilizing intensity modulated probe (IMP) instead of phase modulated probe (PMP), sensing performance is obviously improved. Reduction of ~6-MHz decoding error caused by the CD induced BGS distortion is achieved in the measurement of Brillouin frequency shift (BFS) along the whole 40-km sensing distance. Enhanced system stabilities are demonstrated by testing the BGS under different conditions.

Coherent BOTDA sensor with suppressed chromatic dispersion

Intensity modulated probe is utilized in coherent BOTDA sensor to reduce chromatic dispersion effect instead of phase modulated probe. Reduction of ~6-MHz decoding error in Brillouin gain spectrum is achieved along 40-km sensing distance.

Recent advances in coherent BOTDA sensor

Summary form only given. Recently, coherent detection has been utilized in Brillouin optical time domain analysis (BOTDA) sensors to improve the signal-to-noise ratio (SNR) and provide a new freedom of Brillouin frequency shift (BFS) measurement through Brillouin phase shift (BPS). The generation of probe light in coherent BOTDA sensor is usually based on double sideband (DSB) phase modulation (PM), which distorts the BGS in long-rang sensing due to its low immunization to chromatic dispersion (CD). In this work, a comparative investigation has been implemented among the coherent BOTDA sensors by utilizing probe light based on DSB-PM, DSB intensity modulation (IM) and single sideband (SSB) IM. Simulation and experimental results show that the Brillouin gain spectrum (BGS) distortion caused by CD in PM case can be reduced in IM case, on the other hand, the effect of CD on the BPS leads to decoding errors in both IM and PM cases.