http://hdl.handle.net/10397/319 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5802 Title: Fiber-tip micro-cavity for temperature and transverse load sensing<br/><br/>Authors: Ma, Jun; Ju, Jian; Jin, Long; Jin, Wei; Wang, Dongning<br/><br/>Abstract: A low cost fiber-optic micro-cavity interferometric sensor is presented. The micro-cavity is fabricated at the fiber tip by splicing a silica capillary to a single mode fiber and then heating/melting the capillary to form a microsphere with an internal air cavity. Applications of the micro-cavity sensor for temperature and traverse load measurements are demonstrated. The sensor has small size and good mechanical strength, and may be used in high temperature environment.<br/><br/>Description: DOI: 10.1364/OE.19.012418 Mon, 20 Jun 2011 00:00:00 GMT http://hdl.handle.net/10397/5801 Title: Highly sensitive bending sensor based on Er³⁺-doped DBR fiber laser<br/><br/>Authors: Lu, Weisheng; Guo, Tuan; Wong, Allan C. L.; Tam, Hwa-yaw; He, Sailing<br/><br/>Abstract: A short cavity Er³⁺-doped distributed-Bragg-reflector (DBR) fiber laser with a low polarization beat frequency has been demonstrated for bending measurement. The polarization beat frequency of the DBR laser is extremely sensitive to bending and can measure curvature changes as small as 1.8 × 10⁻² m⁻¹. Excellent agreement between experimental and theoretical results was obtained for bending curvatures from 0 m⁻¹ to 58.8 m⁻¹ with corresponding changes in beat frequency from 18.6 MHz to 253 MHz. The sensor is insensitive to temperature fluctuations and has a temperature coefficient of the beat frequency of -25.4 kHz/°C, making the temperature compensation unnecessary in most practical applications. The very low beat frequency of the DBR fiber laser makes frequency downconversion unnecessary. This can greatly simplify the demodulation scheme and thus, allow the realization of low-cost but highly sensitive optical bending sensor systems.<br/><br/>Description: DOI: 10.1364/OE.18.017834 Mon, 16 Aug 2010 00:00:00 GMT http://hdl.handle.net/10397/5800 Title: Intermodal coupling of supermodes in a twincore photonic crystal fiber and its application as a pressure sensor<br/><br/>Authors: Liu, Zhengyong; Tse, Vincent; Wu, Chuang; Chen, Daru; Lu, Chao; Tam, Hwa-yaw<br/><br/>Abstract: In this paper, we experimentally demonstrated the fabrication and hydrostatic pressure characteristics of a twin-core photonic crystal fiber (TC-PCF). Mode couplings in the TC-PCF for x- and y-polarizations were analyzed simultaneously using group effective index of guiding modes. The output spectrum of the TC-PCF was modulated due to the combined couplings of the two polarizations. To the best of our knowledge, it is the first time to measure hydrostatic pressure through the dual-polarization mode coupling in a TC-PCF. The measured sensitivity of the pressure sensor was -21pm/MPa. The length of the TC-PCF used for pressure measurement was 20cm, which is much shorter than pressure sensor based on PM-PCF, and does not require any external polarizing components, meaning that it is a good candidate for compact pressure sensor.<br/><br/>Description: DOI: 10.1364/OE.20.021749 Mon, 10 Sep 2012 00:00:00 GMT http://hdl.handle.net/10397/5799 Title: Simultaneous and independent multi-parameter monitoring with fault localization for DSP-based coherent communication systems<br/><br/>Authors: Shen, Thomas Shun Rong; Lau, Alan Pak Tao; Yu, Changyuan<br/><br/>Abstract: Digital signal processing (DSP)-based coherent communications have become standard for future high-speed optical networks. Implementing DSP-based advanced algorithms for data detection requires much more detailed knowledge of the transmission link parameters, resulting in optical performance monitoring (OPM) being even more important for next generation systems. At the same time, the DSP platform also enables new strategies for OPM. In this paper, we propose the use of pilot symbols with alternating power levels and study the statistics of the received power and phase difference to simultaneously and independently monitor the carrier frequency offset between transmitter and receiver laser, laser linewidth, number of spans, fiber nonlinearity parameters as well as optical signal-to-noise ratio (OSNR) of a transmission link. Analytical predictions are verified by simulation results for systems with full chromatic dispersion (CD) compensation per span and 10% CD under-compensation per span. In addition, we show that by monitoring the changes in the statistics of the received pilot symbols during network operation, one can locate faults or OSNR degradations along a transmission link without additional monitoring equipments at intermediate nodes, which may be useful for more efficient dynamic routing and network management.<br/><br/>Description: DOI: 10.1364/OE.18.023608 Mon, 08 Nov 2010 00:00:00 GMT