Mar 2009, Volume 2 Issue 1
    

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  • Research articles
    Homeostatic photobiomodulation
    Timon Chengyi LIU , Ruochun LIU , Ling ZHU , Jianqin YUAN , Min HU , Songhao LIU ,
    2009, 2(1): 1-8. https://doi.org/10.1007/s12200-009-0010-3
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    Photobiomodulation (PBM) is a modulation of laser irradiation or monochromatic light (LI) on biosystems, which stimulates or inhibits biological functions but does not result in irreducible damage. LI might be of low intensity LI (LIL) (about 10 mW/cm2), or moderate intensity LI (MIL) (102―103 mW/cm2). PBM of LIL or MIL (LPBM or MPBM) is studied from the homeostatic viewpoint in this paper. Homeostasis is redefined as the function-specific homeostasis (FSH), a negative-feedback response of a biosystem which maintains the function-specific conditions inside it. PBM is classified into two kinds, the FSH-specific PBM (fPBM) and developmental PBM (dPBM). For fPBM, there is no PBM of LI on the function in FSH, but there is PBM of LI on the function far from FSH. dPBM can disrupt FSH. It can be found that LPBM is an fPBM, and whether MPBM is fPBM or dPBM depends on MIL dose and cell sensitivity. Low level LI therapy is just clinical applications of fPBM, so that it is a cellular rehabilitation.
  • Research articles
    Simulation of 40 Gbit/s NRZ to RZ format conversion based on sum-frequency generation using a PPLN loop mirror
    Jian WANG , Junqiang SUN , Weiwei ZHANG , Zhefeng HU ,
    2009, 2(1): 9-14. https://doi.org/10.1007/s12200-008-0074-5
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    A novel scheme of all-optical format conversion is proposed and simulated from non-return-to-zero (NRZ) to return-to-zero (RZ) at 40 Gbit/s by exploiting sum-frequency generation (SFG) in a periodically poled lithium niobate loop mirror (PPLN-LM). The conversion performance is analyzed, including eye diagrams, conversion efficiency, pulse width ratio, duty cycle, Q-factor, extinction ratio, and tunability. It is found that the signal wavelength can be tuned in a wide wavelength range by properly changing the pump wavelength.
  • Research articles
    Performance analysis of a hybrid OCDMA/WDM system
    Hui YAN , Kun QIU , Yun LING ,
    2009, 2(1): 15-20. https://doi.org/10.1007/s12200-009-0001-4
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    The performance of the hybrid optical code-division multiple-access (OCDMA) and wavelength division multiplexing (WDM) network is analyzed. End-to-end bit error rate (BER) of the network adopting error correction coding is calculated, and the expressions which show spectral efficiency performance, including the effects of polarization mode dispersion (PMD), are derived. The result demonstrates that PMD can decrease spectral efficiency dramatically. Analysis of the blocking performance with and without orthogonal optical codes (OOCs) and wavelength conversion shows that OOC and wavelength can improve the performance of the network. Since the wavelength conversion is much more costly than OOC conversion, a scheme for spare placement wavelength conversion is introduced to balance the cost and performance.
  • Research articles
    All-optical clock extraction for CSRZ modulation data
    Zhixin CHEN , Xin JIN , Huaihu CAO , Jian WANG ,
    2009, 2(1): 21-27. https://doi.org/10.1007/s12200-009-0009-9
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    This paper demonstrates a theoretical investigation on clock extraction from carrier-suppressed return-to-zero (CSRZ) modulation format data at 40?Gbit/s by using a semiconductor optical amplifier (SOA)-based ring laser. A completely numerical analysis about the clock characteristics at 40?Gbit/s is done, which is an effective guide for the experiment and necessary to optimize system performance. The crucial parameters, including the pulse width, energy of the CSRZ data signals and influence of SOA bias current, are analyzed because they determine the quality of the recovered clock pulses. Meanwhile, simulation results show that high-quality clock extraction from 27―1 pseudo-random binary sequence (PRBS) CSRZ data at 40?Gbit/s can be achieved by using higher power assisting continuous-wave (CW) light into a SOA-based ring laser.
  • Research articles
    Fabrication of buried channel optical waveguide splitter
    Zigang ZHOU ,
    2009, 2(1): 28-30. https://doi.org/10.1007/s12200-008-0042-0
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    An electric field technique was developed to fabricate buried channel waveguides on optical glass. A voltage of 800 V was applied on the glass to accelerate the field-driven ion exchange process by expeditiously replacing host sodium ions in the glass with silver ions. As a result, the optical loss for channel waveguides was measured using the edge coupling technique with a He-Ne laser. Loss of 0.35 dB/cm was obtained for the channel waveguides with 25 μm in depth, which is relatively low for waveguides of such depth at red wavelength band.
  • Research articles
    Low-power 1×2 all-optical switching in a silicon double coupler microring resonator*
    Dou NA , Chunfei LI ,
    2009, 2(1): 31-34. https://doi.org/10.1007/s12200-008-0066-5
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    Low-power 1×2 optical switching in a double coupler ring resonator (DCRR) made by a silicon nanoscale waveguide based on two photon absorption (TPA) is analyzed theoretically. The TPA originates from a femtosecond pump light at 400 nm, which enters the DCRR together with a CW signal light at 1.55 mm through the input port. TPA makes the silicon free-carrier concentration change, which is proportional to the change of reflective index. Our numerical simulation shows that when average pump power reaches 2 mW, it will induce the 10−3 refraction-index change and the π-phase shift of signal light, after which 1×2 all-optical switching can be realized.
  • Research articles
    Analysis of mode-field half widths of two kinds of single-mode waveguides
    Lianhuang LI , Fuyuan GUO ,
    2009, 2(1): 35-39. https://doi.org/10.1007/s12200-008-0077-2
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    The mode-field half widths of two kinds of single-mode waveguides are investigated. Based on the maximal matching efficiency method, the relationship between the mode-field half width and normalized frequency is analyzed. Furthermore, two equations of mode-field half widths as a function of normalized frequency are proposed through mathematical modeling and the curve fitting method. Numerical calculations indicate that they are accurate within a parameter range.
  • Research articles
    All-optical ultra-wideband pulse generation based on semiconductor optical amplifiers*
    Jianji DONG , Xinliang ZHANG , Dexiu HUANG ,
    2009, 2(1): 40-49. https://doi.org/10.1007/s12200-008-0082-5
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    Several all-optical methods for ultra-wideband (UWB) pulse generation based on various nonlinearities of single semiconductor optical amplifiers (SOAs), namely cross phase modulation (XPM), cross gain modulation (XGM), and a hybrid of self phase modulation (SPM) and XGM, have been demonstrated. In the first method, UWB doublet pulses are realized with XPM. The input optical Gaussian pulse will be converted to two polarity-reversed monocycle pulses by a blue shifted and a red shifted optical bandpass filters respectively. These two monocycle pulses are then combined with proper time delay to generate two polarity-reversed doublet pulses. Second, two polarity-reversed monocycle pulses are obtained based on XGM of the SOA and group delay of the single mode fiber (SMF). In the scheme, two polarity-reversed Gaussian pulses are generated due to XGM, and then the mixed signal is converted to a monocycle shape due to the group delay of the SMF. Finally, we present UWB doublet generation based on SPM. The monocycle pulse is generated from a dark return-to-zero (RZ) signal and converted to a doublet pulse by injecting an additional probe signal with the SMF transmission. For the first time and to the best of our knowledge, we report that the generated doublet pulses are transmitted over 5?km SMF by proper dispersion compensation without distortion. The configuration of our all-optical methods is compact and simple. The feasibility to implement the pulse shape modulation and pulse polarity modulation is discussed.
  • Research articles
    Progress of photonic crystal fibers and their applications
    Wei CHEN , Jinyan LI , Peixiang LU ,
    2009, 2(1): 50-57. https://doi.org/10.1007/s12200-009-0002-3
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    In this article, the fabrication technologies of photonic crystal fibers (PCFs) and their applications at home and abroad were formulated at length, especially in fields such as large mode-area active PCFs, fiber lasers, birefringence fibers, sensors, high nonlinear PCFs, frequency transformation, dispersion compensation PCFs, wideband communication for optical network systems, and photonic band-gap fibers. Finally, according to the above analysis, the prospects and developing trends of PCFs were presented.
  • Research articles
    A simple method for measuring dynamic phase changes in a homodyne interferometric fiber-optic sensor
    Zefeng WANG , Yongming HU , Zhou MENG , Ming NI ,
    2009, 2(1): 58-60. https://doi.org/10.1007/s12200-008-0075-4
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    A simple but reliable measurement method for the dynamic phase shift in a passive homodyne interferometric fiber-optic sensor is proposed. The amplitude of the dynamic phase shift is calculated directly from the photodetector output. A Mach-Zehnder interferometer with a PZT, which is used to generate the simulation signal, is constructed. The experimental results obtained using this simple method are well in agreement with the results given by the standard phase generated carrier (PGC) method, which shows the validity of the results. This new method has the advantages of simplicity of operation, no active element in the sensing head, no modulation to the laser, large dynamic range and working bandwidth, etc. It can be used for the dynamic phase shift measurement of various interferometric fiber-optic sensors.
  • Research articles
    10 W CW ytterbium-doped fiber laser with 4 × 1 fused fiber bundle combiner
    Jihuang ZHANG , Chao YANG , Chuan HUANG , Yuhua LI , Nengli DAI , Peixiang LU , Zuowen JIANG , Wei CHEN , Jinyan LI ,
    2009, 2(1): 61-63. https://doi.org/10.1007/s12200-008-0039-8
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    An ytterbium-doped double-clad fiber laser with one-end pumped by four 915 nm laser diodes (LDs) combined by a homemade multimode fused fiber bundle combiner is proposed. The combiner, fused by splicing four fiber pigtails from diodes, exhibits a good capability of low-loss and a high efficiency of 92.7%. The fiber laser, which can generate a continuous-wave (CW) up to 10.3 W output power at 1104 nm with a homemade D-shape inner cladding ytterbium-doped fiber, is demonstrated. The slope efficiency is about 65% and the optical-to-optical conversion efficiency with respect to the pump power is 46% at its maximum output laser power.
  • Research articles
    3-dimensional fiber Bragg grating strain and displacement sensing system based on a cylinder structure
    Jianhua LUO , Bo LIU , Yuwen LAN , Shuzhong YUAN , Guiyun KAI , Xiaoyi DONG ,
    2009, 2(1): 64-67. https://doi.org/10.1007/s12200-008-0043-z
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    A novel 3-dimensional fiber Bragg grating (FBG) strain and displacement sensing system based on a cylinder structure was proposed. Three FBGs, fixed in the outer surface of the cylinder at the same level according to a 120° angle interval, were used as sensing elements. In principle, the three FBGs have some fixed relationship when a strain F is put on the cylinder. Based on the principles of physics and mathematics, theoretical derivations and the experimental set-up were shown. According to the experimental results, this sensor could measure the size and angles of the strain or displacement accurately.
  • Research articles
    Fabrication and characteristics of double-clad fiber Bragg gratings
    Lijun LI , Wande FAN , Shenggui FU , Yange LIU , Shuzhong YUAN , Xiaoyi DONG ,
    2009, 2(1): 68-75. https://doi.org/10.1007/s12200-008-0058-5
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    A double-clad fiber Bragg grating (DCFBG) is a kind of grating which is directly written into the core of a double-clad fiber (DCF). Because of its special structure, DCFBGs have potential applications in fiber communication and sensing. In this paper, some of the recent studies on DCFBG are reviewed, and the photosensitivity and thermal decay of DCFBG fabricated in different DCFs are investigated. The DCFBGs of diversiform reflectivity are fabricated, and the maximum reflectivity of the grating is 99.9%. Finally, the special characteristics of DCFBG, such as nonlinear and stress, are illustrated.
  • Research articles
    Polarization beam splitter based on photonic crystal fibers
    Ke WEN , Rong WANG , Jingyuan WANG , Jianhua LI ,
    2009, 2(1): 76-80. https://doi.org/10.1007/s12200-008-0061-x
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    Polarization beam splitters (PBSs) are a special kind of coupler. They can split incoming light from a single fiber into two orthogonally polarized beams. They are usually used in coherent optical communication systems, optical sense systems and optical measurement systems. In this paper, two kinds of mechanisms of the PBSs based on photonic crystal fibers (PCFs) are discussed. The full-vector finite element method (FEM) was employed to analyze propagating properties, while the full-vector beam propagation method (BPM) was applied to analyze preferences of the splitters. The results show that it is possible to achieve a compact PBS with high extinction ratio.
  • Research articles
    Short cavity single-frequency all-fiber Er/Yb co-doped laser
    Ming ZHAO , Yubin GUO , Xuanguo SHEN , Tianshu WANG ,
    2009, 2(1): 81-85. https://doi.org/10.1007/s12200-009-0003-2
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    A 5-cm-long Er/Yb co-doped all-fiber laser is studied. Two fiber Bragg gratings (FBGs) are written in the Er/Yb co-doped sensitive fiber using UV beams. A 980?nm pumping laser diode (LD) is used, and output wavelength is selected by two FBGs. The single-frequency laser is achieved at 1544.68?nm. The 3?dB spectrum width is 0.08?nm, while the side mode suppression ratio is 55?dB. The maximum output power exceeds 4?mW for pump power of 140?mW and the stability is less than ±0.01?dB. Single-frequency operation is verified using a scanning Fabry-Perot (F-P) interferometer. Relative intensity noise is less than −100?dB. A 10?Gbit/s code rate is used in the fiber laser transmission experiment. A good optical eye diagram is received after 21?km single-mode fiber transmission. A simple distributed Bragg reflection(DBR) fiber laser array is designed. The wavelength difference of output laser array is 0.8?nm, conforming to the ITU―T channel spacing standard of wavelength-division multiplexing systems.
  • Research articles
    Laser micro-cladding electronic pastes for fabrication of MIM thick film capacitors
    Yu CAO , Xiangyou LI , Xiaoyan ZENG ,
    2009, 2(1): 86-91. https://doi.org/10.1007/s12200-009-0008-x
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    Two direct-write processing methods – direct material deposition by microPen and Nd:YAG laser micro-cladding – are integrated with computer-aided design/computer-aided manufacturing (CAD/CAM) technology for the fabrication of passive electronic components. A basic two-step procedure of the laser micro-cladding electronic paste (LMCEP) process for thick film pattern preparation is presented. In particular, metal-insulator-metal (MIM) type thick film capacitors are fabricated on ceramic substrates by the LMCEP process. Multilayer structures of the MIM thick film capacitors are demonstrated and discussed. Results of the frequency characteristics test show that the MIM thick film capacitors fabricated by the LMCEP process have excellent direct current (DC) voltage stability (<2.48%), excellent frequency stability (<2.6%) and low dissipation factor (<0.6%), which are sufficient for many megahertz applications.
  • Research articles
    Full-color OLEDs based on conjugated materials
    Bo QU , Zhijian CHEN , Lixin XIAO , Fangwen LUO , Qihuang GONG ,
    2009, 2(1): 92-102. https://doi.org/10.1007/s12200-009-0005-0
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    Since 1987, the possibility of realizing a new generation display based on organic light-emitting diodes (OLEDs) has inspired much interest in both academic and industrial groups. This review elucidates recent process in materials for OLEDs, approaches to improve electroluminescent properties of devices, and recent works based on conjugated materials in our laboratory.
  • Research articles
    Plasma photonic crystal
    Wei LI , Yong ZHAO , Ruizhen CUI , Haitao ZHANG ,
    2009, 2(1): 103-107. https://doi.org/10.1007/s12200-009-0004-1
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    Plasma photonic crystals are presented in this paper. A plasma photonic crystal can control the propagation of electromagnetic waves. Similar to other photonic crystals, the permittivity of a plasma photonic crystal is distributed as periodic arrays. The properties of periodic arrays of plasma can broaden the range of frequency and enhance the efficiency of beam-wave interaction. In special uses, the behavior of plasma shows that it has properties of photonic crystals.
  • Research articles
    Effect of indium distribution on optical properties in InGaAs/GaAs quantum wells
    Guozhi JIA , Jianghong YAO , Yongchun SHU , Xiaodong XIN , Biao PI ,
    2009, 2(1): 108-112. https://doi.org/10.1007/s12200-008-0047-8
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    The effect of In surface segregation and diffusion on the transition energy of an InGaAs/GaAs strained quantum well (QW) was investigated theoretically. Diffusion equations and the Schrödinger equation on the InGaAs/GaAs QW were solved numerically. The energy shifts under different diffusion lengths were simulated. When the width of QW, L, is larger than 5 nm, the change rate of the transition energy is very minimal at the initial stage of the annealing process for wide QW, and the transition energy has a rapid blue shift with an increase of the diffusion length. When L is smaller than 5 nm, the transition energy is very sensitive to the diffusion length. The change rate of transition energy increases with a decrease in QW width.
  • Research articles
    AlGaN solar-blind photodetectors grown by low pressure MOCVD
    Xiaoyan WANG , Xiaoliang WANG , Baozhu WANG , Junxue RAN , Hongling XIAO , Cuimei WANG , Guoxin HU ,
    2009, 2(1): 113-117. https://doi.org/10.1007/s12200-009-0006-z
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    AlxGa1−xN ternary alloys are very attractive materials for application to ultraviolet (UV) photodetection. In this work, high Al content AlxGa1−xN films are grown on sapphire substrate by low pressure metalorganic chemical vapor deposition (MOCVD). The Al content in the AlxGa1−xN epilayer is estimated to be 54% by high resolution X-ray diffraction (HRXRD) and Vegard’s law. The full width at half maximum (FWHM) of the rocking curve for the Al0.54Ga0.46N (0002) is about 597 arcsec. According to the transmittance measurement result, our sample is suitable for fabricating solar-blind photodetectors. The observed Fabry-Perot fringes in the transmission region indicate that high optical quality is obtained. Solar-blind metal-semiconductor-metal (MSM) photodetectors based on the MOCVD-grown Al0.54Ga0.46N film are fabricated and tested. The detector has a low dark current of about 31?pA under a bias voltage of 5?V. An UV/visible contrast of about four orders of magnitude is observed and responsivity increases with increments of the bias voltage.