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Frontiers of Optoelectronics

, Volume 2 Issue 2

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Status and prospects for phosphor-based white LED packaging
Zongyuan LIU, Sheng LIU, Kai WANG, Xiaobing LUO
Front Optoelec Chin. 2009, 2 (2): 119-140.
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The status and prospects for high-power, phosphor-based white light-emitting diode (LED) packaging have been presented. A system view for packaging design is proposed to address packaging issues. Four aspects of packaging are reviewed: optical control, thermal management, reliability and cost. Phosphor materials play the most important role in light extraction and color control. The conformal coating method improves the spatial color distribution (SCD) of LEDs. High refractive index (RI) encapsulants with high transmittance and modified surface morphology can enhance light extraction. Multi-phosphor-based packaging can realize the control of correlated color temperature (CCT) with high color rendering index (CRI). Effective thermal management can dissipate heat rapidly and reduce thermal stress caused by the mismatch of the coefficient of thermal expansion (CTE). Chip-on-board (CoB) technology with a multi-layer ceramic substrate is the most promising method for high-power LED packaging. Low junction temperature will improve the reliability and provide longer life. Advanced processes, precise fabrication and careful operation are essential for high reliability LEDs. Cost is one of the biggest obstacles for the penetration of white LEDs into the market for general illumination products. Mass production in terms of CoB, system in packaging (SiP), 3D packaging and wafer level packaging (WLP) can reduce the cost significantly, especially when chip cost is lowered by using a large wafer size.

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Differential absorption optical coherence tomography with strong absorption contrast agents of gold nanorods
Ming WEI, Jun QIAN, Qiuqiang ZHAN, Fuhong CAI, Arash GHARIBI, Sailing HE
Front Optoelec Chin. 2009, 2 (2): 141-145.
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Plasmon-resonant gold nanorods (GNRs) are demonstrated as strong absorption contrast agents for optical coherence tomography (OCT). OCT imaging of tissue phantoms doped with GNRs of different resonant wavelengths and concentrations is studied. To utilize the high absorption property of GNRs, a differential absorption OCT imaging is introduced to retrieve the absorption information of GNRs from conventional backscattered signals. It is shown that the contrast of the OCT image can be enhanced significantly when the plasmon resonant wavelength of the GNRs matches the central wavelength of the OCT source.

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POEM 2008 makes its debut a success
Xiaochun XIAO, Weiwei DONG, Qingming LUO
Front Optoelec Chin. 2009, 2 (2): 146-147.
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Can communications and sensors work together in one network?
Xinwan LI, Jianping CHEN
Front Optoelec Chin. 2009, 2 (2): 148-152.
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With the development of both optical fiber-based communication and sensation, one interesting topic has been pointed out. How to connect those mountains of sensors to detect the signal in a large area, and how to make the cost of sensing system lower enough should be studied. A network of sensors is a good option. All sensing equipments, including the interrogators and the sensors, will be internetworking together. However, fiber optic communication networks have been developed very well over the past two decades. Is it necessary to rebuild a new network for sensors? In this paper, some new technologies in the two areas of fiber optic sensors and fiber optic communication will be addressed. Then, the available overlay architecture of a fiber optic sensors network will be presented. Finally, a polymorphous optical burst switching (POBS)-based architecture will be proposed, which can support all kinds of services, including digital data optical circuit/burst/packet switching and analog fiber optic sensor signal circuit/burst switching, etc.

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Engineering modes in optical fibers with metamaterial
Min YAN, Niels Asger MORTENSEN, Min QIU
Front Optoelec Chin. 2009, 2 (2): 153-158.
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In this paper, we report a preliminary theoretical study on optical fibers with fine material inclusions whose geometrical inhomogeneity is almost indistinguishable by the operating wavelength. We refer to such fibers as metamaterial optical fibers, which can conceptually be considered as an extension from the previously much publicized microstructured optical fibers. Metamaterials can have optical properties not obtainable in naturally existing materials, including artificial anisotropy as well as graded material properties. Therefore, incorporation of metamaterial in optical fiber designs can produce a new range of fiber properties. With a particular example, we will show how mode discrimination can be achieved in a multimode Bragg fiber with the help of metamaterial. We also look into the mean field theory as well as Maxwell-Garnett theory for homogenizing a fine metamaterial structure to a homogeneous one. The accuracies of the two homogenization approaches are compared with full-structure calculation.

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Temperature performance of Raman scattering in data fiber and its application in distributed temperature fiber-optic sensor
Deming LIU, Shuang LIU, Hairong LIU
Front Optoelec Chin. 2009, 2 (2): 159-162.
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A wavelength division multiplexer (WDM) was used to extract the Raman scattering signal from a data fiber. The temperature performance of Raman scattering spectrum was studied theoretically and experimentally. On the base of this study, a distributed fiber-optic temperature sensor (DFTS) system was developed. The sensing distance was 4?km. The temperature accuracy and the distance resolution reached to±1°C and±1?m, respectively. The system is stable and adequate for commercial usage, such as the power industry, the underground tunnel, the subway, and the pipe laying, and also for the mission applications, such as the warship and the airplane.

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Photonic crystal fiber with novel dispersion properties
Shuqin LOU, Shujie LOU, Tieying GUO, Liwen WANG, Weiguo CHEN, Honglei LI, Shuisheng JIAN
Front Optoelec Chin. 2009, 2 (2): 170-177.
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Our recent research on designing microstructured fiber with novel dispersion properties is reported in this paper. Two kinds of photonic crystal fibers (PCFs) are introduced first. One is the highly nonlinear PCF with broadband nearly zero flatten dispersion. With introducing the germanium-doped (Ge-doped) core into highly nonlinear PCF and optimizing the diameters of the first two inner rings of air holes, a new structure of highly nonlinear PCF was designed with the nonlinear coefficient up to 47 W-1·km-1 at the wavelength 1.55 μm and nearly zero flattened dispersion of ±0.5 ps/(km·nm) in telecommunication window (1460-1625 nm). Another is the highly negative PCF with a ring of fluorin-doped (F-doped) rods to form its outer ring core while pure silica rods to form its inner core. The peak dispersion -1064 ps/(km·nm) in 8 nm full width at half maximum (FWHM) wavelength range and -365 ps/(km·nm) in 20 nm (FWHM) wavelength range can be reached by adjusting the structure parameters. Then, our recent research on the fabrication of PCFs is reported. Effects of draw parameters such as drawing temperature, feed speed, and furnace temperature on the geometry of the final photonic crystal fiber are investigated.

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Deuterium treatment of low water peak fiber
Xinwei QIAN, Deming LIU, Feng TU
Front Optoelec Chin. 2009, 2 (2): 178-181.
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The deuterium (D2) treatment of low water peak single-mode fiber (LWP-SMF) after drawing has been investigated. The D2 treatment time and concentration have important effect on fiber’s properties after D2 treatment. The insufficient treatment of D2 cannot ensure fiber resistant to hydrogen aging, whereas excessive treatment of D2 will result in excess loss on fiber at 1383 nm. The optimization on viscosity match between the core and the cladding is helpful on problem solving of excess loss after the D2 treatment. However, by designing proper time and D2 concentration in the D2 treatment process, it can produce fiber with good hydrogen aging resistance and low excess loss and lower the cost of the D2 treatment process.

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Transmission-type SPR sensor based on coupling of surface plasmons to radiation modes using a dielectric grating
Changkui HU, Deming LIU
Front Optoelec Chin. 2009, 2 (2): 182-186.
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A transmission-type surface plasmon resonance (SPR) sensor is presented. In the transmission-type SPR structure, surface plasmon waves are outcoupled to radiation modes by the use of dielectric grating on a thin-film layer of Ag. Compared with the traditional reflection-type SPR sensor, the new method provides larger detectable range, which might be useful to investigate thick targets such as in cell analysis. Theoretical simulations show that the structures provide high transmission efficiency for surface plasmon resonance and the devices present extremely linear sensing characteristics. Furthermore, it is found that the transmission efficiency and the refractive index detection sensitivity of the SPR sensor can be improved by the use of a lower refractive index glass prism.

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Polarization characteristics of subwavelength aluminum wire grating in near infrared
Changkui HU, Deming LIU
Front Optoelec Chin. 2009, 2 (2): 187-191.
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Rigorous coupled wave analysis (RCWA) was used to investigate the polarization characteristics of subwavelength aluminum wire grating in near infrared. Upon exposure to the atmosphere, a layer of Al2O3 forms rapidly on the aluminum wires, so the effect of metal oxide layers on the polarization properties is modeled and analyzed. It is shown that subwavelength aluminum wire grating with oxide layers forming on the wires still offers excellent polarization properties. As the thickness of the oxide layer increases, the transmission coefficient increases, but the extinction ratio decreases. In addition, a magnesium fluoride (MgF2) layer was proposed to deposit between the aluminum wires and the substrate to enhance transmission coefficient. The theoretical research shows that subwavelength aluminum grid grating has high transmission coefficient and extinction ratio in near infrared, as well as uniform performance with wide variations in the angle of incidence. These features with their small size make it desirable for use in optical communication and allow more compact component designs.

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Stable and high-performance multiwavelength erbium-doped fiber laser based on fiber delay interferometer
Shuang LIU, Junqiang SUN, Ping SHUM
Front Optoelec Chin. 2009, 2 (2): 195-199.
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In this paper, we proposed a novel scheme to realize the multiwavelength erbium-doped fiber lasers. By adding a length of dispersion shifted fiber (DSF) in the ring cavity, we can suppress the cavity mode competition resulting from homogeneous line broadening (HLB) effect. In addition, a comb filter based on fiber delay interferometer (DI) is used for frequency selecting. To enhance the extinction ratio while maintaining the free space range (FSR), the proposed isolator-assisted double-pass DI is utilized into the laser cavity, and a stable 7-wavelength simultaneous lasing spaced at 21.5 GHz is accordingly achieved with an extinction ratio of higher than 40 dB. The lasers are stable with a maximum power fluctuation per channel of less than 0.6 dB during an hour test.

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Multiple-wavelength transmitter for WDM optical network
Shuang LIU, Deming LIU, Junqiang SUN
Front Optoelec Chin. 2009, 2 (2): 200-203.
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Optical network based on wavelength-division multiplexing (WDM) technology will be a most active research topic in the 21st century. This paper describes a WDM multiple-wavelength transmitter and several key corresponding devices for optical network, including amplified spontaneous emission (ASE) spectrum-sliced multiple-wavelength optical source, optical add/drop multiplexer (OADM), semiconductor optical amplifier (SOA), as well as the spectrum noise suppression scheme. The new research results are reported, and the applications of these developed devices are also introduced.

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High-power EDFA applied in distributed optical fiber Raman temperature sensor system
Xu ZHANG, Deming LIU, Hairong LIU, Qizhen SUN, Zhifeng SUN, Ziheng XU, Wengang WANG
Front Optoelec Chin. 2009, 2 (2): 210-214.
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In this paper, a high-power erbium-doped fiber amplifier (EDFA) for the temperature sensor system is theoretically designed and experimentally demonstrated. It consists of an erbium-doped fiber that is pumped bidirectionally with two 980-nm high-power laser diodes (LDs). At the EDFA input, an optical isolator (ISO) is used to ensure that the signal pulse transmits forward only. After that, a wavelength division multiplexer (WDM) is employed to combine the forward pump laser (980 nm) and incident optical pulse (1550 nm) into the erbium-doped fiber for direct amplification in the optical domain. At the EDFA output, another WDM couples the backward pump laser (980 nm) into the erbium-doped fiber and outputs the amplified optical pulse (1550 nm) with an ISO followed to isolate the backscattering light. According to this structure, we carried out the experiment in the condition as follows. For 980 nm pump LD, the operating current is 590 mA, and the setting temperature is 25°C. For EDFA, the length of erbium-doped fiber is 12.5 m, and the power of 1550 nm input signal is 1.5 mW. As a result, the power of pump LD is 330 mW, and the power uncertainty is 0.5%. The power of EDFA output at 1550 nm is 300 mW, and the power uncertainty is±3 mW.

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Design of distributed Raman temperature sensing system based on single-mode optical fiber
Ziheng XU, Deming LIU, Hairong LIU, Qizhen SUN, Zhifeng SUN, Xu ZHANG, Wengang WANG
Front Optoelec Chin. 2009, 2 (2): 215-218.
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The distributed optical fiber temperature sensor system based on Raman scattering has developed rapidly since it was invented in 1970s. The optical wavelengths used in most of the distributed temperature optical fiber sensor system based on the Raman scattering are around from 840 to 1330?nm, and the system operates with multimode optical fibers. However, this wavelength range is not suitable for long-distance transmission due to the high attenuation and dispersion of the transmission optical fiber. A novel distributed optical fiber Raman temperature sensor system based on standard single-mode optical fiber is proposed. The system employs the wavelength of 1550?nm as the probe light and the standard communication optical fiber as the sensing medium to increase the sensing distance. This system mainly includes three modules: the probe light transmitting module, the light magnifying and transmission module, and the signal acquisition module.

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Distributed optical fiber perturbation sensing system based on Mach-Zehnder interferometer
Wengang WANG, Deming LIU, Hairong LIU, Qizhen SUN, Zhifeng SUN, Xu ZHANG, Ziheng XU
Front Optoelec Chin. 2009, 2 (2): 229-232.
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A novel distributed optical fiber vibration-sensing system based on Mach-Zehnder interferometer has been designed and experimentally demonstrated. Firstly, the principle of Mach-Zehnder optical path interferometer technique is clarified. The output of the Mach-Zehnder interferometer is proportional to the phase shift induced by the perturbation. Secondly, the system consists of the laser diode (LD) as the light source, fiber, Mach-Zehnder optical interferometers as the sensing units, a 1×N star fiber-optic coupler, an N×1 fiber-optic coupler, a photodiode (PD) detector, and a computer used in signal processing. The entire monitoring region of this system is divided into several small zones, and each small monitoring zone is independent from each other. All of the small monitoring zones have their own sensing unit, which is defined by Mach-Zehnder optical interferometer. A series of sensing units are connected by the star fiber-optic couplers to form a whole sensing net. Thirdly, signal-processing techniques are subsequently used to calculate the phase shift to estimate whether intruders appear. The sensing system is able to locate the vibration signal simultaneously, including multiple vibrations at different positions, by employing the time-division multiplexed (TDM) technique. Finally, the operation performance of the proposed system is tested in the experiment lab with the conditions as follows: the number of the sensing units is 3, the length of the sensing fiber is 50 m, and the wavelength of the light diode is 1550 nm. Based on these investigations, the fiber surrounding alert system is achieved. We have experimentally demonstrated that the sensing system can measure both the frequency and position of the vibration in real time, with a spatial positional resolution better than 50 m in an area of 1 km2.

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FBG sensing temperature characteristic and application in oil/gas down-hole measurement
Shaomin LI, Xiaoying LIU, Chong LIU
Front Optoelec Chin. 2009, 2 (2): 233-238.
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Fiber Bragg gratings (FBGs) have been used to sense numerous parameters such as strain, temperature, and pressure. Cost-effective multipoint measurements have been achieved by connecting FBGs in parallel, serial, and other topologies as well as by using spatial, wavelength, and time-domain multiplexing techniques. This paper presents a method of measuring temperature of the oil/gas down-hole. Detailed contents include the basic theory and characteristics of fiber gratings, analysis of the sensing mechanism of fiber-optic gratings, and the cross-sensitivity effect between temperature and strain; the method of making the light-source of the fiber-optic gratings and the technology of measuring wavelength shift, building an experimental system of the temperature measurement, and dealing with the experimental data. The paper makes a comparison of several kinds of FBG sensing systems used in oil/gas down-hole to measure temperature and the analysis of the experimental results of building the temperature measurement system. It demonstrates that the fiber-optic grating sensing method is the best choice in all methods of measuring temperature in oil/gas down-hole, which has a brilliant applied prospect.

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16 articles