Negative luminescence from mid-wave infrared HgCdTe diode arrays

A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm². The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature.     

Competitive technologies of third generation infrared photon detectors

Hitherto, two families of multielement infrared (IR) detectors are used for principal military and civilian infrared applications; one is used for scanning systems (first generation) and the other is used for staring systems (second generation). Third generation systems are being developed nowadays. In the common understanding, third generation IR systems provide enhanced capabilities like larger number of pixels, higher frame rates, better thermal resolution as well as multicolour functionality and other on-chip functions. In the paper, issues associated with the development and exploitation of materials used in fabrication of third generation infrared photon detectors are discussed. In this class of detectors two main competitors, HgCdTe photodiodes and quantum well IR photoconductors (QWIPs) are considered. The performance figures of merit of state-of-the-art HgCdTe and QWIP focal plane arrays (FPAs) are similar because the main limitations come from the readout circuits. However, the metallurgical issues of the epitaxial layers such as uniformity and number of defected elements are the serious problems in the case of long wavelength infrared (LWIR) and very LWIR (VLWIR) HgCdTe FPAs. It is predicted that superlattice based InAs/GaInSb system grown on GaSb substrate seems to be an attractive to HgCdTe with good spatial uniformity and an ability to span cutoff wavelength from 3 to 25 μm.     

HgCdTe buried multi-junction photodiodes fabricated by the liquid phase epitaxy

This article reports the parameters and characteristics of the new type of HgCdTe buried photodiodes operated at near-room temperature (T=200–300 K) in long wavelength infrared spectral range. The liquid phase epitaxy (LPE) Hg_1−xCd_xTe (x=0.16–0.20) layers were grown on holes etched in (1 0 0) CdZnTe substrate. Prior to layer deposition, the CdZnTe substrate has been etched to form the bars on 30 μm centers and 20-μm depth. Next, 20-μm thick HgCdTe epitaxial layer has been grown from Te-rich solution. The type of conductivity was controlled by deliberately doping with indium (n-type) and Sb (p-type). The Nomarski microscopy showed that the surface of specially prepared layers was flat and the composition of layers, measured by Fourier transform infrared microscopy, was homogenous. Samples were cleaved and examined in cross section by scanning electron microscopy. Finally, serial connected multi-junction photodiodes have been fabricated. It is shown that LPE can be used to realise advanced bandgap engineered multi-junction structures. This conclusion is supported by device quality characteristics: spectral response and detectivity.     

High performance uncooled InAsSbP/InGaAs photodiodes for the 1.8–3.4 μm wavelength range

Room temperature In_0.97Ga_0.03As photodiodes with an InAs_0.36Sb_0.20P_0.44 transparent window layer operating in the mid-infrared region over the wavelength range 1.8–3.4 μm are reported. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes were grown on p-type (100) InAs substrates by liquid phase epitaxy (LPE). Basic detector characteristics have been measured and compared with other detectors in this wavelength range. The typical detectivity of the photodiodes is 1.2 × 10¹⁰ cm Hz^1/2/W at room temperature, which compares very favourably with that of TE cooled HgCdTe and is at least three times that of cooled PbSe photoconductors. The InAs_0.36Sb_0.20P_0.44/In_0.97Ga_0.03As heterojunction photodiodes offer the advantage of increased sensitivity and extended wavelength response at room temperature compared with that of currently available commercial photodetectors, making them an attractive alternative for a number of mid-infrared applications including optical gas sensors and infrared spectrometers.     

连续波光参量振荡器定向红外干扰

介绍了基于光纤激光器泵浦的光学参量振荡器发展现状及其在定向红外干扰技术中的应用前景,对定向红外干扰技术的一些基本原理进行了讨论。利用自研的一台基于光纤激光器泵浦的连续波光学参量振荡器,通过周期调谐的方式分别实现3.414,3.630和3.820 m的瓦级中红外激光输出。采用这3个波长的激光对中红外热像仪进行了干扰原理性实验。对比实验结果可以得出:对于3.820 m波长的中红外激光,当其辐照的HgCdTe探测器前功率密度大于10 W/cm2量级时,在传输750 m距离后,热像仪实现饱和效果并且非饱和区域图像灰度级发生较大变化,达到了掩盖有用信号的目的。     

HgCdTe avalanche photodiodes: A review

This paper presents a comprehensive review of fundamental issues, device architectures, technology development and applications of HgCdTe based avalanche photodiodes (APD). High gain, above 5×10³, a low excess noise factor close to unity, THz gain-bandwidth product, and fast response in the range of pico-seconds has been achieved by electron-initiated avalanche multiplication for SWIR, MWIR, and LWIR detector applications involving low optical signals. Detector arrays with good element-to-element uniformity have been fabricated paving the way for fabrication of HgCdTe-APD FPAs.     

实用化少模光纤的研究

针对大容量光纤通信系统,设计了一种实用化的椭圆纯硅芯少模光纤,给出了光纤的设计原理与参考标准,运用全矢量有限元法结合完美匹配层边界条件分析了光纤的传输特性.在1.4~1.65μm波长处,光纤处于稳定的HE_(11)和HE_(21)双模运转,模式有效折射率差大于1.8×10~(-3),避免了模间耦合和串扰;在工作波长1.55μm处,HE_(11)和HE_(21)模的色散系数分别为19.61和4.41ps/(nm·km),色散斜率分别为0.048和0.002ps/(nm~2·km),模场面积分别为97.17和143.96μm2,模式的衰减系数均小于0.21dB/km.该光纤的传输特性基本符合G.652和G.655光纤标准,可利用现有成熟的"预制棒拉丝工艺"制备,同时与波分复用技术相结合可以成倍提升光网络的传输容量,对于下一代通信网络带宽的提升具有重要意义.     

介质/金属结构太赫兹空芯光纤的传输特性

理论分析了金属、介质/金属结构空芯光纤在THz波段的模式结构和传输特性.金属空芯光纤支持TE11模式,介质/金属空芯光纤的介质膜厚在取最优值时支持HE11模式.对于波长为200μm的太赫兹波,内径为1 mm的两种空芯光纤,TE11和HE11模式的损耗分别为8.4 dB/m和2 dB/m.为优化介质/金属结构宅芯光纤的传输性能,分析了金属和介质材料的光学常数对衰减系数的影响.基于几种已发表的金属在太赫兹波段的光学常数,计算结果表明铝是最好的选择;初步测量结果显示,在各种树脂材料中聚乙烯在THz波段吸收较小,并且其折射率接近介质膜的最优值1.41,为太赫兹波空芯光纤中介质膜材料的理想选择.     

Transmission experiments in the 1.2-1.6 μm wavelength region using graded-index optical fiber cables

Optical fiber transmission systems with extremely long repeater spacing are very attractive for various applications both in land and undersea communication systems. This paper describes the results of transmission experiments, using low-loss fibers in the 1.2-1.6 μm wavelength region. Graded-index optical fibers having an optimum profile at 1.27 μm were manufactured in cables. Average bandwidth was 1,275 MHz-km, and the average optical loss was 0.6 dB/km. The 52.6-km and 62.3-km repeater spacings were realized at 100 Mb/s and 32 Mb/s transmission, respectively, using InGaAsP/InP LD and Ge-APD. The 21.5-km and 12.0-km repeater spacings at 32 Mb/s were also realized by 1.2μm and 1.5μm LEDS, respectively.     

Review of fiber optical communications

This paper will discuss recent advances in optical fiber, fiber cabling, and light source technology. These advances will make it possible for widespread applications of fiber optical communications in the very near future. Developments in fiber waveguide have made possible the long distance transmission of high data rate information over a single fiber waveguide. Of the various fiber types, four are currently receiving the most attention because of their attenuation, dispersion, and cost characteristics. Semiconductor injection lasers have been developed that have lifetimes exceeding 10,000 hours with projected lifetimes extending beyond 100,000 hours. Receiver technology is well developed and avalanche photodiodes provide high sensitivity receiver performance for most data bandwidths of interest.     

一种新的低非线性宽带色散补偿微结构光纤的设计

采用矢量光束传输法对空气孔包层呈正六边形分布的微结构光纤的色散和非线性特性进行了数值模拟。通过分别调节内三层空气孔的直径和包层空气孔节距,设计了一种低非线性宽带色散补偿微结构光纤。该光纤在波长1.55 μm处具有－3 235.8 ps/nm/km的大负色散,可在以1.55 μm为中心的100 nm宽带波长范围对相当于自身长度190倍的普通单模传输光纤进行宽带色散补偿(色散补偿率偏移在0.5%以内),同时该光纤可在此宽带波长范围内保持非线性系数低于5 W^-1·km^-1。     

Single-mode and tunable VCSELs in the near- to mid-infraredInvited Paper

Single-mode, long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the near- to mid-infrared covering the wavelength range from 1.3 to 2.3μm are presented. This wide spectral emission range opens applications in gas sensing and optical interconnects. All these lasers are monolithically grown in the InGaA1As-InP material system utilizing a buried tunnel junction (BTJ) as current aperture. Fabricated with a novel high-speed design with reduced parasitics, bandwidths in excess of 10 GHz at 1.3 and 1.55 μm have been achieved. Therefore, the coarse wavelength division multiplexing (CWDM) wavelength range of 1.3 to 1.6 μm at 10 Gb/s can be accomplished with one technology. Error-free data-transmission at 10 Gb/s over a fiber link of 20 km is demonstrated. One-dimensional arrays have been fabricated with emission wavelengths addressable by current tuning. Micro-electro-mechanical system (MEMS) tunable devices provide an extended tuning range in excess of 50 nm with high spectral purity. All these devices feature continuous-wave (CW) operation with typical single-mode output powers exceeding 1 mW. The operation voltage is around 1 - 1.5 V and power consumption is as low as 10 - 20 mW. Furthermore, we have also developed VCSELs based on GaSb, targeting at the wavelength range from 2.3 to 3.0 μm. The functionality of tunable diode laser spectroscopy (TDLS) systems is shown by presenting a laser hygrometer applying a 1.84-μm VCSEL.     

Ultra-high-precision mid-IR spectrometer II: system description and spectroscopic performance

The development and spectroscopic performance evaluation of an ultra-sensitive, mid-IR spectrometer is reported. The laser system is based upon difference-frequency generation (DFG) at ～3.5 μm by mixing a DFB diode laser at 1562 nm and a DFB fiber laser at 1083 nm using a periodically poled LiNbO₃ crystal. DFG radiation was coupled to a 100?m optical path length astigmatic Herriott cell. Sensitive and selective spectroscopic detection of formaldehyde was performed with second-harmonic detection using Peltier-cooled HgCdTe detectors. By applying computer lock-ins, dual-beam optical noise subtraction, focus matching, thermal stabilization, active wavelength control, and advanced signal processing a sensitivity corresponding to an absorbance ～1.6×10^-7 is achieved for 260 s of averaging.     

复自相干度度量超连续谱相干性

引入复自相干度来度量同一脉冲产生的超连续谱的相干性, 并对其进行了实验研究. 采用Mach-Zehnder干涉仪, 测量700 ps脉冲抽运光子晶体光纤产生的超连续谱的相干性. 实验测得超连续谱不同波长成分的相干长度均大于40 μm, 在长波区可达225 μm. 超连续谱的整个光谱区域各谱成分的相干度有差异, 但复自相干度的模平均值为0.461, 相干性较好, 可以满足如光测量、光学传感等很多应用.     

Application of a WGM optical fiber probe fabricated by 3D printing technology for glucose concentration measurement

This study proposes a method for manufacturing a whispering gallery mode (WGM) optical fiber probe used for measuring glucose. The principle of the WGM optical fiber probe consists of the bending interference that occurs between the core mode and cladding mode. 3D printing technology was used to create a mold for the optical fiber sensor so that the bent optical fiber sensor was fixed within the mold to ensure a stable bend radius. This method of fabrication allows for easier installation and replacement of the resulting optical fiber compared to WGM optical fiber sensors fabricated by traditional methods. The results of the concentration test showed that as the glucose aqueous solution concentration increased from 0 to 10%, the wavelength was red shifted and the transmission loss gradually increased. At a bend radius of 3.1 mm and an etching diameter of 46 μm, the wavelength sensitivity was 1.475 nm/% and the R-squared value was 0.983, indicating an extremely high sensitivity. These results confirm that the WGM optical fiber probe created in this study can be used to measure glucose concentrations with high sensitivity, and that it is relatively easy to manufacture, install, and replace. Therefore, the proposed WGM optical fiber probe exhibits good performance and is suitable for use as a glucose concentration sensor.     

Material considerations for third generation infrared photon detectors

In the paper, issues associated with the development and exploitation of materials used in fabrication of third generation infrared photon detectors are discussed. In this class of detectors two main competitors, HgCdTe photodiodes and quantum well photoconductors are considered. The performance figures of merit of state-of-the-art HgCdTe and QWIP focal plane arrays (FPAs) are similar because the main limitations come from the readout circuits. The metallurgical issues of the epitaxial layers such as uniformity and number of defected elements are the serious problems in the case of long wavelength infrared (LWIR) and very LWIR (VLWIR) HgCdTe FPAs. It is predicted that superlattice based InAs/GaInSb system grown on GaSb substrate seems to be an alternative to HgCdTe with good spatial uniformity and an ability to span cutoff wavelength from 3 to 25 μm. In this context the material properties of type II superlattices are considered more in detail.     

飞秒脉冲泵浦光子晶体光纤产生1.3μm区域的光谱展宽

采用OPA产生的中心波长为1.2759 μm、平均输出功率为30 mW、重复频率为250 kHz、脉冲宽度为250 fs的光脉冲作为泵浦源,研究了PCF输出光谱随泵浦焦点与光纤端面的相对移动的光谱演变.在纤芯直径为2.0 μm、长度为1.8 m的光子晶体光纤中获得了近700 nm的光谱展宽,展宽的光谱从1.09 μm到1.79 μm,分析认为是高阶孤子的分裂和四波混频导致的光谱展宽,而在1.4 μm左右的光谱凹陷是由于光纤中OH离子的吸收造成的.PCF输出的光谱可应用在WDM通信和光互连网的超短脉冲多通道光源中.     

Maximization of repeater spacing in ultrawide-wavelength-division multiplexing optical communication systems based on multipumped laser diodes

We show that the amplifier bandwidth can be further increased and the gain spectrum can be tailored if one uses pumping with multiple laser wavelengths. We consider the wide-gain amplifier where four sets of multipumps are employed. We process two multiplexing techniques in long haul transmission cables where the number of channels is up to 9600 in ultrawide-wavelength-division multiplexing (UWWDM) with employment of the ultrawide-space-division multiplexing (UW-SDM) technique to merge the number of links up to 400 in the optical-fiber core over wide ranges of affecting sets of parameters. As well as the repeater spacing using a multi-pumping Raman amplifier, we investigate N _R pumps in the optical pumping wavelength (from 1.36 to 1.44 μm) to amplify optical channels where the optical wavelength range (1.45–1.65 μm) satisfies near infrared optical transmission region.     

Simple design of optical fiber displacement sensor using a multimode fiber coupler

A simple design sensor is demonstrated using a fabricated multimode plastic fiber coupler in conjunction with reflective intensity modulation technique. The performances of this sensor are investigated for different light sources. This sensor uses only one fiber for sending and receiving the light and therefore only the back slope exists. The sensor shows the highest performance with the use of yellow light source, which has the highest intensity and the smallest beam divergence. The sensitivity, linear range, resolution and dynamic range of the sensor are obtained at 0.0001 mV/μm, 1500 μm, 70 μm, and 5.0 mm, respectively. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for real field applications.     

Investigation on optical transmission spectra of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

The optical transmission spectra from 0.3 to 11 μm of relaxor ferroelectric single crystals (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) were systematically studied at room temperature in this paper. The crystal is transparent between 0.45 and 5.5 μm and becomes completely absorbing around 0.4 μm in near UV region and 10 μm in infrared region. But the wavelength cutoff in near UV is much sharper than the long wavelength cutoff. As compared with other configurations, tetragonal single crystals possess the optimal transmission properties. The optical transmittance in the wavelength region from 0.45 to 5.5 μm is about 70%. The results show that tetragonal PMN-xPT single crystals are promising for a wide range of optical applications. Some discussions about the oxygen-octahedra structure that determines the basic energy level of the crystals are also presented on the optical properties of PMN-xPT single crystals.