Bruce Chow

Radio-over-Fiber Distributed Antenna System for WiMAX Bullet Train Field Trial

Wireless broadband access for mobile applications is an area of increasing growth. An international collaboration, led by the Taiwan Industrial Technology Research Institute (ITRI), has been working to implement a dedicated WiMAX network for a user field trial on the Taiwan High Speed Rail (THSR) bullet train system. Continuous wireless coverage at train speeds up to 300km/hr is challenging due to a number of critical issues, including handover at high speeds and coverage in challenging terrain such as tunnels. A Radio-over-Fiber (RoF) Distributed Antenna System (DAS) was developed by Corning Incorporated to address the critical issue of handover and increase the coverage for each WiMAX basestation. For a DAS deployment consisting of multiple discrete antennas, proper signal strength management is required because the maximum delay spread allowed by the WiMAX protocol is easily surpassed at realistic fiber ranges up to 9km. This paper reviews some of the initial results of the RoF DAS experiments in SongShan tunnel in Taipei. Error-free signal transmission was achieved when the difference in received power from two consecutive antennas was greater than 10dB.

Characterization of optical and mechanical modification of surface alignment layers for liquid crystal devices

Reliable performance of liquid crystal (LC) materials in display applications is critically dependent on the behavior of surface treatments that induce molecular alignment parallel to the cell windows. While general understanding of the nature of this effect has been available for some time, the detailed characteristics of the LC-surface interaction are not sufficiently well understood to enable reliable interface engineering. This is particularly true for new materials that might otherwise possess favorable qualities but cannot be reproducibly oriented in a device. Our work is concentrated on understanding optical and mechanical modification of organic monolayers that have been self- assembled on dielectric surfaces. We use vibrationally resonant sum-frequency generation and ellipsometry as well as non-optical techniques, such as contact angle testing, to evaluate the influence of these perturbations. We have been able to follow subtle conformation changes as well as more dramatic photochemical effects. The results help reveal the anchoring mechanisms and provide insight into ways of tailoring interfaces for new materials.

Evaluation of extended reach capability of 40G BiDi VCSEL-based WDM transmission over OM4 multimode fibers

40G BiDi is a commercial WDM transceiver with duplex LC connectivity for transmissions over multimode fibers. In this paper, we evaluate the transmission performance of 40G BiDi over OM4 fibers. We have carefully selected OM4 fibers with the lowest and highest peak wavelengths around 850 nm to evaluate the reach capability for 40G BiDi transmission. We demonstrated that the OM4 fiber with the lowest peak wavelength can transmit error free over 325 m while the OM4 fiber with the highest peak wavelength can transmit up to 350-390 m. In both cases, the maximum lengths are much longer than 150 m and 200 m specified for OM4 and wideband MMF transmissions, respectively. We also measured the transceiver encircled flux and found that it was tighter than the encircled flux standard, which may be a factor favoring long system reach at 900 nm.

Dual Core Optical Fiber for Distributed Brillouin Fiber Sensors

A dual core optical fiber is designed and fabricated for simultaneous measurements of strain and temperature in distributed Brillouin sensors. Brillouin frequency shift difference of 120 MHz between the two cores is demonstrated.

Relative acoustic sensitivity of standard telecom and specialty optical fiber cables for distributed sensing

Fiber Optic Distributed Acoustic Sensing (DAS) and Distributed Strain Sensing (DSS) systems have widespread use for asset and security monitoring. The acoustic signal from such sources as intruders, vehicles, or gunfire must be coupled from the earth to an optical fiber which is then interrogated by DAS system technology. Because the optical fiber is the sensing element, and because the cable is required to mediate the interaction of the fiber and its environment, the selection of the optical fiber, cable design, and deployment conditions are critical to the performance of the system. Cable designs specifically created for sensing are shown to achieve 20 dB higher signal-to-noise than standard telecom designs, which correspond to an enhanced sensing range of more than 30 meters. In addition, directly burying the sensing cable in the ground leads to 15 dB higher sensitivity than installing it in a duct. In many cases, standard cables for telecommunications applications are designed to isolate and protect the fibers from the external environment; therefore a cable designed for sensing applications and deployed specifically with this in mind leads to the highest sensitivity with the largest sensing range.