Yanli Ran

Vibration Fiber Sensors Based on SM-NC-SM Fiber Structure

A novel vibration sensor based on the single mode (SM)-no core (NC)-SM fiber structure is proposed and experimentally sensing results demonstrated. By numerical simulation, we use an NC fiber (NCF) as the multimode waveguide structure for the multimode interference (MMI) sensing. Through intensity demodulation, the vibration sensing structure can detect continuous vibration disturbances with the frequencies of ranging from 100 Hz to 29 kHz and the inherent frequency of cantilever slab of 700 Hz. The frequency sensing resolution is 1 Hz in real-time monitoring. The proposed compact structure is easy to fabricate and has low cost.

Interrogation of Ultrashort Bragg Grating Sensors Using Shifted Optical Gaussian Filters

Ultrashort fiber Bragg gratings (FBGs) possess significant potential as weak sensing units for distributed measurements, the exploitation of which, however, have been usually limited by their inherent wide spectra which is undesirable for most traditional wavelength measurements. In this letter, we propose to use shifted optical Gaussian filters to interrogate such wide spectrum gratings. However, instead of acting like Gaussian edge filters as previously done, to take advantage of spectral feature of ultrashort gratings, here they have a role which is more like shifted matched filters. The measurement inherits the important features of a common shifted Gaussian filter interrogation technique, namely its high flexibility, natural insensitivity to intensity variations, promising future for multichannel interrogation, and a potentially wider measuring range relative to common intensity-based approaches. We believe that this simple concept for ultrashort Bragg gratings should offer the strong foundation for their future applications in distributed measurements. Interrogation of a strain-tuned ultrashort grating was accomplished, with a wide sensitivity tuning range from 2.8 to 10.4 dB/nm achieved.

Static/dynamic strain sensing applications by monitoring the correlation peak from optical wideband chaos

We present a new sensing demodulation approach by monitoring the amplitude changes of correlation peak through using optical wideband chaos. For the static strain sensing, the reflection intensity of optical wideband chaos can be modulated by the strain induced wavelength spacing between the wavelength division multiplexing (WDM) device and the sensing grating. Thus, the relative amplitude change (RAC) of correlation peak is mainly determined by the change of chaotic reflection intensity. For the dynamic strain sensing, the reflection intensity of optical wideband chaos can be modulated by the fast fluctuant evanescent wave on a section of no-core fiber (NCF). Thus, the response from correlation peaks RAC is mainly according to the dynamic strain frequency. The experimental measurements show that a high strain sensing sensitivity of 7.04*10-3 RAC/με is achieved within the measurement range of 900 με during the static strain test. While in the dynamic test, the demodulation can detect the vibration frequency of 6 kHz located at 6 km long. This demodulation method can simultaneously achieve static/dynamic sensing and precisely locating the fiber break point with the high accuracy of several centimeters, making it very easy for network maintenance.

Ultra-short FBG based distributed sensing using shifted optical Gaussian filters and microwave-network analysis

Ultrashort fiber Bragg gratings (US-FBGs) have significant potential as weak grating sensors for distributed sensing, but the exploitation have been limited by their inherent broad spectra that are undesirable for most traditional wavelength measurements. To address this, we have recently introduced a new interrogation concept using shifted optical Gaussian filters (SOGF) which is well suitable for US-FBG measurements. Here, we apply it to demonstrate, for the first time, an US-FBG-based self-referencing distributed optical sensing technique, with the advantages of adjustable sensitivity and range, high-speed and wide-range (potentially >14000 με) intensity-based detection, and resistance to disturbance by nonuniform parameter distribution. The entire system is essentially based on a microwave network, which incorporates the SOGF with a fiber delay-line between the two arms. Differential detections of the cascaded US-FBGs are performed individually in the network time-domain response which can be obtained by analyzing its complex frequency response. Experimental results are presented and discussed using eight cascaded US-FBGs. A comprehensive numerical analysis is also conducted to assess the system performance, which shows that the use of US-FBGs instead of conventional weak FBGs could significantly improve the power budget and capacity of the distributed sensing system while maintaining the crosstalk level and intensity decay rate, providing a promising route for future sensing applications.

TDM interrogation of intensity-modulated USFBGs network based on multichannel lasers

We report a large-scale multi-channel fiber sensing network, where ultra-short FBGs (USFBGs) instead of conventional narrow-band ultra-weak FBGs are used as the sensors. In the time division multiplexing scheme of the network, each grating response is resolved as three adjacent discrete peaks. The central wavelengths of USFBGs are tracked with the differential detection, which is achieved by calculating the peak-to-peak ratio of two maximum peaks. Compared with previous large-scale hybrid multiplexing sensing networks (e.g., WDM/TDM) which typically have relatively low interrogation speed and very high complexity, the proposed system can achieve interrogation of all channel sensors through very fast and simple intensity measurements with a broad dynamic range. A proof-of-concept experiment with twenty USFBGs, at two wavelength channels, was performed and a fast static strain measurements were demonstrated, with a high average sensitivity of ~0.54dB/µƐ and wide dynamic range of over ~3000µƐ. The channel to channel switching time was 10ms and total network interrogation time was 50ms.

Deformation independent FBG strain sensor based on speckle pattern processing

In this paper we demonstrate a vision based strain retrieving method for FBG sensor Bragg wavelength shift demodulation. We use noteworthy wavelength dependent speckle pattern spatial information as a fingerprint and implement content-based speckle pattern retrieval software.

Demonstration of low pulse repetition frequency erbium-doped fiber lasers

We demonstrate a low pulse repetition frequency (LPRF) Q-switched erbium-doped fiber (EDF) lasers based on acoustic optical modulator (AOM). The single wavelength fiber laser has a stable output at 1553 nm. In Q-switched operation, a pulse train with 3.3μs width and a repetition rate of 1kHz is obtained. The dual wavelength fiber laser is based on fiber Bragg gratings (FBGs) and a Faraday rotator mirror (FRM) as the laser cavity, which has a stable output at 1545 nm and 1557 nm with similar peak power and same repetition rate.