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Homeostatic photobiomodulation
Timon Chengyi LIU , Ruochun LIU , Ling ZHU , Jianqin YUAN , Min HU , Songhao LIU ,
Front. Optoelectron.. 2009, 2 (1): 1-8.
https://doi.org/10.1007/s12200-009-0010-3
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.
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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 ,
Front. Optoelectron.. 2009, 2 (1): 9-14.
https://doi.org/10.1007/s12200-008-0074-5
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.
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All-optical clock extraction for CSRZ modulation
data
Zhixin CHEN , Xin JIN , Huaihu CAO , Jian WANG ,
Front. Optoelectron.. 2009, 2 (1): 21-27.
https://doi.org/10.1007/s12200-009-0009-9
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.
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All-optical ultra-wideband pulse generation based
on semiconductor optical amplifiers*
Jianji DONG , Xinliang ZHANG , Dexiu HUANG ,
Front. Optoelectron.. 2009, 2 (1): 40-49.
https://doi.org/10.1007/s12200-008-0082-5
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.
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Progress of photonic crystal fibers and their
applications
Wei CHEN , Jinyan LI , Peixiang LU ,
Front. Optoelectron.. 2009, 2 (1): 50-57.
https://doi.org/10.1007/s12200-009-0002-3
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.
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A simple method for measuring dynamic phase changes
in a homodyne interferometric fiber-optic sensor
Zefeng WANG , Yongming HU , Zhou MENG , Ming NI ,
Front. Optoelectron.. 2009, 2 (1): 58-60.
https://doi.org/10.1007/s12200-008-0075-4
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.
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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 ,
Front. Optoelectron.. 2009, 2 (1): 61-63.
https://doi.org/10.1007/s12200-008-0039-8
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.
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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 ,
Front. Optoelectron.. 2009, 2 (1): 64-67.
https://doi.org/10.1007/s12200-008-0043-z
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.
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Fabrication and characteristics of double-clad
fiber Bragg gratings
Lijun LI , Wande FAN , Shenggui FU , Yange LIU , Shuzhong YUAN , Xiaoyi DONG ,
Front. Optoelectron.. 2009, 2 (1): 68-75.
https://doi.org/10.1007/s12200-008-0058-5
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.
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Effect of indium distribution on optical properties
in InGaAs/GaAs quantum wells
Guozhi JIA , Jianghong YAO , Yongchun SHU , Xiaodong XIN , Biao PI ,
Front. Optoelectron.. 2009, 2 (1): 108-112.
https://doi.org/10.1007/s12200-008-0047-8
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.
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AlGaN solar-blind photodetectors
grown by low pressure MOCVD
Xiaoyan WANG , Xiaoliang WANG , Baozhu WANG , Junxue RAN , Hongling XIAO , Cuimei WANG , Guoxin HU ,
Front. Optoelectron.. 2009, 2 (1): 113-117.
https://doi.org/10.1007/s12200-009-0006-z
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.
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