Measurements of thermal effects on four-photon mixing conversion efficiency in an optical fiber

Thermal effects on the conversion efficiency of four-photon mixing (FPM) power in a silica optical fiber are measured. When the temperature of the fiber changes from 9 to 350 degrees C, the first Stokes power decreases with a temperature coefficient of -0.33%/ degrees C as the temperature increases to 200 degrees C and then becomes saturated with a further increase in temperature. This temperature characteristic of the first Stokes power reflects the temperature characteristics of the nonlinear refractive index of the fiber, which are similar to its FPM temperature dependence.     

Performance Enhancement for Optical Fast Frequency-hopping CDMA Systems by BCH Channel Coding

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Performance of run-length limited (4, 18) code for optical storage systems

In this paper, the authors investigate the performance of recently presented run-length limited (4, 18) code for high density optical storage systems. The construction of the code is described simply. The code has code rate R = 1/3 and density ratio (DR) = 1.67. The bit error rate (BER) performance for decision feedback equalizer (DFE) and partial response maximum likelihood (PRML) detector are simulated, considering signal-to-noise ratio (SNR) and optical channel jitter. The result shows that the performance of the code is acceptable. The encoder and decoder of the code are implemented by complex programmable logic device (CPLD) chip and the hardware resources required for encoder and decoder arelow.     

气相质谱法对小鼠体内甲苯二异氰酸酯代谢产物的鉴定分析

应用气相质谱测定小鼠体内甲苯二异氰酸酯(TDI)的代谢产物,并鉴别了其在机体中的代谢途径。TDI色谱条件为Supelco PTETM-5色谱柱(30 mm×0.25 mm×0.25 μm),起始柱温90 ℃保持30 min,以40 ℃·min-1升至280 ℃,保持5.25 min;汽化室温度250 ℃;载气为氦气,流速为1.0μL·min-1。TDI体内代谢产物色谱条件为30+2mX0.25+0.02mm 94%甲基、4%乙烯基键合相弹性石英毛细柱,起始温度30 ℃保持5 min,以8 ℃·min-1升至280 ℃,保持5 min。汽化室温度250 ℃;载气为氦气,流速1.0μL·min-1。质谱条件为电离方式EI,电离能量70eV,连接管温度280 ℃,扫描范围35～350μ;进样量1.0μL。结果表明2,4甲苯二异氰酸酯在血液、尿液、粪便中都被代谢成为2,4甲苯二胺。GC-MS法可有效分离并鉴定TDI体内代谢产物。     

Performance Enhancement for Optical Fast Frequency-hopping CDMA Systems by BCH Channel Coding

In this paper, the impact of optical beat noise on the performance of optical fast frequency-hopping code-division multiple-access (FFH OCDMA) networks is analyzed. BCH/FFH-OCDMA to reduce the impact of optical beat noise is proposed. It is shown that, BCH/FFH-OCDMA has much better performance under the same bit rate, same chip time and same number of available wavelengths. Another advantage for BCH/FFH-OCDMA is that the code length of one-coincidence sequence will be shorter, which can greatly reduce the difficulty of fabrication for fiber gratings.     

Single-shot distributed optical-fiber temperature sensing by the frequency-derived technique

We present, for the first time to our knowledge, a distributed optical-fiber temperature sensor, based on a pulsed laser, that provides distributed temperature measurement by use of a single pulse propagating in an optical fiber. The system uses the frequency-derived technique based on the optical Kerr effect. The performance of the system is investigated for the temperature range 33-150 degrees C. A linear relationship between the temperature and the derived frequency is obtained. The best temperature resolution was determined to be +/-1.2 degrees C. The best measured spatial resolution was 0.56 m.     

Accurate monitoring of an interferometric fiber-optic sensor with a multimode semiconductor laser

A technique for monitoring interferometric sensors by correlation of the optical signal from the sensor with the signal from a phase-modulated reference interferometer is described. The technique is applied to temperature measurement with a fiber Fabry-Perot sensing head. We extend the 7 degrees C unambiguous measurement range obtained with a 1.3-mum laser diode as the light source to 43 degrees C by adding a second laser diode emitting at 1.55mum . Experimentally, a rms phase-measurement error of +/-0.28rad , corresponding to a temperature error of +/-0.32 degrees C , was achieved with a low-quality multimode Fabry-Perot laser. The phase error was improved to +/-0.14rad , corresponding to a temperature error of +/-0.16 degrees C , by use of a distributed-feedback laser diode.     

GeO2-SiO2纳米复合材料的合成及其光学特性研究

运用溶胶-凝胶法合成了GeO2-SiO2纳米复合材料,探索了为pH在2的条件下通过水解Si(OC2H5)4和GeCl4合成GeO2-SiO2干胶的过程.在100～1 200℃下对干胶进行热处理.采用UV光谱法测定了材料的光学性质,观察到随热处理温度的升高,样品光谱的吸收边向长波方向移动.由于温度的影响,晶粒长大,带隙能量减小,纳米微晶的量子尺寸效应显示出来.经X射线衍射分析,观察到了随热处理温度的增高,材料结构从无序到有序的转变过程,直到1 100℃时,有明显的微晶生成,其尺寸为5～10nm.     

磷酸-氨水蒸沉γ晶型聚酰胺6的热行为研究

尼龙6是一种多晶型的半结晶高聚物。实验采用蒸沉法制备出尼龙6,首先通过XRD和FTIR的手段进行表征,与采用沸水处理的尼龙6样品表征结果对比,确定其为γ晶型,然后在130～211℃的温度范围内进行热处理,通过DSC研究其在低于熔点热处理时的整个热行为变化过程,并运用FTIR观察其在不同条件下热处理发生的晶型变化。发现蒸沉法制备的γ晶型尼龙6随着热处理温度的升高,整体结晶完善度以及晶片厚度随着处理温度的升高而增加。而且在这个过程中,样品厚度不同的晶片在不同温度下发生了γ晶型向α晶型的转化,最终在接近熔点(211℃)热处理时,样品变为以α晶型为主。     

在不同衬底上制备的ZnO薄膜透射率的研究

采用反应磁控溅射在不同结构衬底上生长ZnO薄膜,通过X-ray衍射(XRD)及透射光谱来分析薄膜的成膜情况,并得出在Al₂O₃/AlN复合基上溅射沉积的ZnO薄膜比单独在AlN薄膜衬底的结晶质量好且透过率也较高。而经不同的快速热退火温度验证,发现在400 ℃时,ZnO薄膜的结晶化及在(002)方向上的择优取向达到最好,并在可见光范围内的平均透过率达到88%以上。当退火温度超过450 ℃时,温度过高改变了ZnO薄膜的内部结构,使其氧原子和锌原子发生了较大距离的位移,导致薄膜内部缺陷的增多,从而存在过多的晶界,增加了其薄膜的散射机制,使光的透过性变差,退火温度为500 ℃时,薄膜的平均透过率为80%。     

Tunable optical add-drop multiplexer based on long-period fiber gratings for coarse wavelength division multiplexing systems

We propose and experimentally demonstrate a voltage-controllable add-drop multiplexer with a tunable coupler based on long-period fiber gratings (LPFGs). The tunable coupler is based on cladding mode coupling between two parallel LPFGs with divided coil heaters, which controls the resonant wavelength positions of the two LPFGs. The wavelength tunability of the tunable coupler is measured to be -0.45 nm/degrees C in the temperature range from 20 to 120 degrees C. The large tuning range of optical signals (approximately 50.54 nm) from 1502.32 to 1552.86 nm, which covers both the short (S) and the conventional (C) bands, is achieved. The channel isolation is as high as approximately 40 dB. It has several advantages, including a broad tuning range of wavelength in both the S- and C-bands, high channel isolation, no backreflection, and so on.     

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system

Temperature-insensitive dynamic pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum bandwidth modulation and optical power detection is proposed. A specifically designed double-hole cantilever beam is used to provide a pressure-induced axial strain gradient along the sensing FBG and is also used to modulate the reflection bandwidth of the grating. The bandwidth modulation is immune to spatially uniform temperature effects, and the pressure can be unambiguously determined by measuring the reflected optical power, avoiding the complex wavelength interrogation system. The system acquisition time is up to 85 Hz for dynamic pressure measurement, and the thermal fluctuation is kept less than 1.2% full-scale for a temperature range of -10 degrees C to 80 degrees C.     

原位漫反射红外光谱研究升温速率对HMX炸药热分解过程的影响

原位红外光谱法是一种新兴的动态研究方法。该方法具有原位实时监控和红外光谱精确分析物质化学结构的优点,能够实时跟踪材料在不同温度下的化学变化,测定材料的微观结构与温度的关系。采用原位漫反射红外光谱研究了炸药1,3,5,7-四硝基-1,3,5,7-四氮杂环辛烷(HMX)分别在每min 5, 10, 20和40 ℃四种不同升温速率下的热分解行为。研究结果表明：在5 ℃·min-1升温速率下,断裂的HMX环发生分子内结合,在10, 20和40 ℃·min-1升温速率下,断裂的HMX发生分子间成环,形成稳定的八元环结构。随着温度的升高,C—N键的断裂数率远高于N—N键的断裂速率。随着升温速率的增加,C—N键的起始分解温度增加,表明增加升温速率会引起HMX分解的滞后。检测到HMX的分解所释放出CO₂, N₂O, CO, NO, HCHO, HONO, NO₂和HCN共八种气体,升温速率的变化未改变HMX的分解机理。     

Analyses of constraints on high speed optical code division multiplexing access (OCDMA) link parameters due to fiber optic chromatic dispersion

In direct sequence-optical code division multiplexing access (DS-OCDMA) system networks, data rate and data spreading technique involved in such systems require a high chip rate. Transmission link in these systems is significantly affected by the fiber chromatic dispersion. In this study, we have developed and employed a simple model to estimate the G652 fiber dispersion effects. OCDMA technique has been employed to investigate fiber chromatic dispersion effects on multiple access interference (MAI). We have found that, at a short optical fiber length, the optical fiber dispersion has a significant impact on the high data rate transmission systems (higher than 750 Mbit/s). The performance and optimization of optical orthogonal code (OOC) in the OCDMA system is reported. We have demonstrated that, for a high data rate, even if dispersion compensated devices are not deployed, the BER can be significantly improved when the OOC desired length is selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a trade off between the limited dispersion effects and the MAI.     

BCH信道编码对降低快跳频OCDMA系统中色度色散的影响

提出BCH信道编码的方案来降低色度色散对降低快跳频OCDMA系统性能的影响.采用BCH信道编码后,单重合码的长度将变短,即可以用较少的波长数来构造码字,因此降低了色度色散的影响.分析结果表明,在相同的信息比特速率、脉元间隔、资用波长数的情况下,BCH信道编码能显著改善FFH-OCDMA系统的误码率性能.同时,由于单重合码的长度将变短,大大降低了光纤光栅的制作难度.由于BCH信道编码在电域中实现,其硬件技术已相当成熟,所以对整个BCH/FFH-OCDMA系统的代价影响不大.     

Photonic‐on‐a‐chip: a thermal actuated Mach‐Zehnder interferometer and a molecular thermometer based on a single di‐ureasil organic‐inorganic hybrid

An integrated photonic‐on‐a‐chip device based on a single organic‐inorganic di‐ureasil hybrid was fabricated for optical waveguide and temperature sensing. The device is composed by a thermal actuated Mach‐Zehnder (MZ) interferometer operating with a switching power of 0.011 W and a maximum temperature difference between branches of 0.89 ºC. The MZ interferometer is covered by a Eu³⁺/Tb³⁺ co‐doped di‐ureasil luminescent molecular thermometer with a temperature uncertainty of 0.1ºC and a spatial resolution of 13 µm. This is an uncommon example in which the same material (an organic‐inorganic hybrid) that is used to fabricate a particular device (a thermal‐actuated MZ interferometer) is also used to measure one of the device intrinsic properties (the operating temperature). The photonic‐on‐a‐chip example discussed here can be applied to sense temperature gradients with high resolution (10⁻³ ºC·µm⁻¹) in chip‐scale heat engines or refrigerators, magnetic nanocontacts and energy‐harvesting machines.     

HCCI燃烧过程化学发光光谱研究

在一台经改装单缸光学发动机机上,进行不同喷油策略和进气温度条件下均质压燃(HCCI)燃烧化学发光光谱实验研究。实验保证循环供油量一定,燃用正庚烷作为燃料,转速600 r.min-1,进气压力0.1MPa,控制2个不同的进气温度:95和125℃。化学发光光谱研究结果表明,低温反应阶段化学发光很弱,主要源于甲醛光谱;低温反应后期-负温度系数区-高温反应初始阶段主要发光来源还是甲醛光谱;高温反应阶段发光主要来源于CO—O*连续谱,同时在CO—O*连续谱上出现OH,HCO,CH,HCHO谱峰;高温反应后期化学发光明显减弱。与-30°ATDC喷油相比,-300°ATDC喷油时CO—O*连续谱发光强度更大,HCO和OH生成量更多,燃烧反应进行程度更深。较高进气温度下CO—O*连续谱发光强度更大,HCO和OH生成量更多。     

Approach to all-optical bipolar direct-sequence ultrawideband coding

An approach to all-optical bipolar direct-sequence ultrawideband (UWB) encoding for multiple access communications is proposed and demonstrated. The bipolar coding is performed based on electro-optic phase modulation and phase modulation to intensity modulation (PM-IM) conversion in a fiber Bragg grating (FBG) array that serves as a multichannel frequency discriminator. The chip number and the chip period of the code are determined by the number of FBGs and their physical separation. By locating the optical carriers that carry a Gaussian pulse at the left or right slopes of the FBG reflection spectra, bipolar direct-sequence UWB codes are generated. A bipolar UWB coding system with a code length of 4 is experimentally demonstrated.     

40 Gb/s, secure optical communication based upon fast reconfigurable time domain spectral phase en/decoding with 40 Gchip/s optical code and symbol overlapping

We propose and experimentally demonstrate a 40 Gb/s secure optical communication system with on-off-keying (OOK) modulation format by using a time domain spectral phase en/decoding scheme, which employs a highly dispersive element and high-speed phase modulator for introducing significant symbol overlapping for both the encoded and incorrectly decoded noiselike signals to enhance the information security against eavesdropping using a power detector. The influence of dispersion and chip modulation rate on the symbol overlapping of the incorrectly decoded signal has been analytically investigated and experimentally verified. Security enhancement for 40 Gb/s OOK data using fast reconfigurable 40 Gchip/s optical codes with code lengths of up to 1024 has been demonstrated and compared with a 10 Gb/s system.     

A novel scheme of two-dimension time-stacked wavelength-time optical code label for optical packet switching network

A novel scheme of time-stacked optical code label based on optical code division multiple (OCDM) technique for optical packet switching network is proposed, in which two-dimensional wavelength-time OCDM code is used as the optical label. Packet loss rate and system characteristic based on the proposed scheme are studied. Results show that less packet loss rate of proposed scheme can be achieved as compared with that of one-dimension time-stacked optical code label system.