A novel four-air-hole multicore dual-mode large-mode-area fiber: Proposal and design

A novel four-air-hole multicore dual-mode large-mode-area optical fiber is proposed in this paper. The characteristics of the mode field distribution, the operating wavelength, the effective area A_eff and the bending loss of fundamental modes are calculated. The influence of the structural parameters on the operating wavelength, the effective index n_eff and the effective area of fundamental modes is also discussed. This fiber makes the second-order modes TE₀₁ and TM₀₁ cut-off while increasing the effective area of fundamental modes, which can realize strictly dual-mode operation. The maximum effective area of fundamental modes is approximately 4025 μm². The single-mode operation can be also realized by adjusting the structural parameters. This fiber is simple to fabricate, and flexible to design. It can be used for large-mode-area high-power optical fiber laser and amplifier.     

Diagrammatic Separation of Different Crystal Structures of A2BX4 Compounds Without Energy Minimization: A Pseudopotential Orbital Radii Approach

The A₂BX₄ family of compounds manifest a wide range of physical properties, including transparent conductivity, ferromagnetism, and superconductivity. A 98% successful diagrammatic separation of the 44 different crystal structures of 688 oxide A₂BX₄ compounds (96% for 266 oxide‐only) is described by plotting the total radius of the A atom R_A versus the radius of the B atom R_B for many A₂BX₄ compounds of known structure types and seeking heuristically simple, straight boundaries in the R_A versus R_B plane that best separate the domains of different structure types. The radii are sums R_A = R_s(A) + R_p(A) of the quantum‐mechanically calculated “orbital radii” R_s(R_p), rather than empirical radii or phenomenological electronegativity scales. These success rates using first‐principles orbital radii uniformly exceed the success rates using classic radii. Such maps afford a quick guess of the crystal structure of a yet unmade A₂BX₄ compound by placing its atomic orbital radii on such maps and reading off its structure type.     

折反式大口径、大视场、宽光谱光学系统

在地面的目标探测光学系统多采用大口径(500 mm)同轴光学系统的前提下,系统探测的大视场和宽光谱就成了亟待解决的问题。设计了附带小口径球面透射校正镜组的折反式光学系统,利用该校正镜组校正了系统由于大相对口径、大视场和宽光谱带来的像差,使系统达到了预定的指标要求。其中只有主反射镜面形为二次非球面,设计参数也易于加工。在相应的实例要求下,用ZEMAX光学设计软件进行了优化评价,并给出了该系统的对星观测结果。该光学系统设计的口径为Ф750 mm,相对孔径为1:1.32,视场为4 ,光谱范围为500~800 nm,系统实际探测能力在15 Mv以上。该系统结构简单,均采用普通玻璃材料,成本低,成像质量良好。     

一种优越的光外差中频稳定装置

一种优越的相干光通信系统中频稳定装置已经研制出来.该装置可以实现对光外差中频频率的高度稳定,且所稳定的光外差中频频率可以自由调节.本装置用于一个采用1.52μmHe-Ne气体激光器的相干光纤通信系统中,光外差中频在整个TV频道范围内都能跟踪稳定.相对于光频的频率稳定度优于10-9.通信系统传输的图象信号得到了满意的稳定接收.     

Excess low frequency noise/I-V studies in p-on-n MBE LWIR Hg1−xCdxTe detectors

Excess low frequency noise is investigated for the first time in infrared MBE grown LWIR Hg_1−xCd_xTe double layer planar heterostructure (DLPH) detectors grown on lattice matched substrates. LWIR detectors having R₀A_opt values at 40K in the 10¹–10⁷ Θ-cm² range have been characterized as a function of temperature between 120 and 20K. Detectors with R₀A_opt≥10³Θ-cm² at 40K have theoretical diffusion limited performance down to 78K and detectors with R₀A_opt ≥10⁵ Θ-cm² at 40K are within a factor of two of theoretical diffusion limited performance for T>65K. Activation energies extracted from noise (V_d=−100 mV) and dark current (V_d=−100 mV) vs temperature measurements were detector dependent. The activation energy for detectors with R₀A_opt≈10⁶ Θ-cm² at 40K is ∼0.90*E_g to 0.99*E_g. The noise measured between 78 and 105K in the intermediate performance (R₀A_opt∼10³–10⁴ Θ-cm² at 40K) detectors are higher than the noise measured in the higher performance (R₀A_opt∼10⁵–10⁷ Θ-cm²) detectors. In addition, the excess low frequency noise and the dark current at −100 mV in the intermediate and poor (R₀A_opt∼10¹ Θ-cm²) performance detectors are temperature independent. For each detector measured, the activation energy extracted from noise (V_d=−100 mV) vs temperature measurements is equal to the activation energy extracted from the total dark current (V_d=−100 mV) vs temperature measurements. For different dark current mechanisms, the excess low frequency noise varies with temperature and also with area within statistical accuracy in the same manner as the total dark current through the detector. At 78K, the Tobin¹⁴ expression holds in the general sense for equal area detectors dominated by different current mechanisms and also for detectors with a wide range of implant dimensions (A_imp=3.85×10⁻⁷ cm² to A_imp=6.25×10⁻⁴ cm²). Following measurements, the detectors were stripped of the passivation and overlaying metal layers and dressed by a defect etch to reveal defects in each detector. A correlation among noise, leakage current and defect type has been determined for each detector.     

Small two-dimensional arrays of mid-wavelength infrared HgCdTe diodes fabricated by reactive ion etching-induced p-to-n-type conversion

The reactive ion etching (RIE) technique has been shown to produce high-performance n-on-p junctions by localized-type conversion of p-type mid-wavelength infrared (MWIR) HgCdTe material. This paper presents variable area analysis of n-on-p HgCdTe test diodes and data on two-dimensional (2-D) arrays fabricated by RIE. All devices were fabricated on x = 0.30 to 0.31 liquid-phase epitaxy (LPE) grown p-type (p = ∼1 × 10¹⁶ cm⁻³) HgCdTe wafers obtained from Fermionics Corp. The diameter of the circular test diodes varied from 50 μm to 600 μm. The 8 × 8 arrays comprised of 50 μm × 50 μm devices on a 100-μm pitch, and all devices were passivated with 5000 ? of thermally deposited CdTe. At temperatures >145 K, all devices are diffusion limited; at lower temperatures, generation-recombination (G-R) current dominates. At the lowest measurement temperature (77 K), the onset of tunneling can be observed. At 77 K, the value of 1/R₀A for large devices shows quadratic dependence on the junction perimeter/area ratio (P/A), indicating the effect of surface leakage current at the junction perimeter, and gives an extracted bulk value for R₀A of 2.8 × 10⁷ Ω cm². The 1/R₀A versus P/A at 195 K exhibits the well-known linear dependence that extrapolates to a bulk value for R₀A of 17.5 Ω cm². Measurements at 77 K on the small 8 × 8 test arrays were found to demonstrate very good uniformity with an average R₀A = 1.9 × 10⁶ Ω cm² with 0° field of view and D* = 2.7 × 10¹¹cm Hz^1/2/W with 60° field of view looking at 300 K background.     

Current mechanisms in VLWIR Hg1−xCdxTe photodiodes

VLWIR (_c∼15 m to 17 m at 78 K) detectors have been characterized as a function of temperature to determine the dominant current mechanisms impacting detector performance. I_d−V_d curves indicate that VLWIR detectors are diffusion limited in reverse and near zero bias voltages down to temperatures in the 40 K range. At 30 K the detectors are limited by tunneling currents in reverse bias. Since the detectors are diffusion limited near zero bias down to 40 K, the R₀A_imp versus temperature data represents the diffusion current performance of the detector as a function of temperature. The detector spectral response measurement and active layer thickness are utilized to calculate the HgCdTe layer x value and the optical activation energy E_{a optical}. The activation energy, E_{a electrical}, obtained from the measured diffusion limited R₀A_imp versus temperature data is not equal to the activation energy, E_{a optical}, obtained from the spectral response measurement for all x values measured. E_{a electrical}=^*E_{a optical}, where ranges between 0.64 and 1.0 For cutoff wavelengths in the 9 m at 78 K, E_{a electrical}=E_{a optical}. E_{a electrical}=0.65^* E_{a optical} have been measured for_c=17 m at 78 K detectors. As the band gap energy decreases to values in the range of 70 meV and lower, it is reasonable to expect a more dominant role of band tailing effects on the transport properties of the material system. In such a picture, one would expect the optical band gap to be unmodified, whereas the intrinsic concentration could be enhanced from its value for the ideal semiconductor. Such a picture could explain the observed behavior. Further probing experiments and modeling efforts will help clarify the physics of this behavior.     

Uniformity in HgCdTe diode arrays fabricated by reactive ion etching

Two-dimensional, midwavelength infrared (MWIR) HgCdTe detector arrays have been fabricated using reactive ion etching (RIE). Detector-to-detector uniformity has been studied in the devices fabricated with CdTe- and ZnS-passivation layers. Mapping of the doping profile, passivant/HgCdTe interface electrical properties, and diode impedance-area product (R₀A_j) in a two-dimensional array of diodes has been carried out. Temperature and perimeter/area dependence of the dark current are studied to identify the bulk and surface current components. Maximum R₀A_j=2×10⁷ Θcm² was achieved in CdTe-passivated, 200×200 μm² diode arrays. It demonstrates that CdTe-passivated, RIE-processed HgCdTe is a feasible technology.     

Thermally Stable Transparent Resistive Random Access Memory based on All‐Oxide Heterostructures

An all‐oxide transparent resistive random access memory (T‐RRAM) device based on hafnium oxide (HfO_x) storage layer and indium‐tin oxide (ITO) electrodes is fabricated in this work. The memory device demonstrates not only good optical transmittance but also a forming‐free bipolar resistive switching behavior with room‐temperature R_OFF/R_ON ratio of 45, excellent endurance of ≈5 × 10⁷ cycles and long retention time over 10⁶ s. More importantly, the HfO_x based RRAM carries great ability of anti‐thermal shock over a wide temperature range of 10 K to 490 K, and the high R_OFF/R_ON ratio of ≈40 can be well maintained under extreme working conditions. The field‐induced electrochemical formation and rupture of the robust metal‐rich conductive filaments in the mixed‐structure hafnium oxide film are found to be responsible for the excellent resistance switching of the T‐RRAM devices. The present all‐oxide devices are of great potential for future thermally stable transparent electronic applications.     

Photosensitivity of In-SiO2-Cd0.28Hg0.72Te structures with a nontransparent field electrode

The photoeffect in a metal-insulator-semiconductor (MIS) structure that incorporated a Cd_0.28Hg_0.72Te compound, a low-temperature pyrolitic SiO₂, and an In layer with a thickness of 500 nm and an area of 0.5×0.5 mm² was studied. For a MIS structure with a nontransparent field electrode, the observed photoeffect consists in variation in the capacitance and high-frequency electrical conductivity of the MIS structure; this photoeffect is caused by photocarriers that are formed outside the MIS structure and reach this structure either due to diffusion or along the surface channel. This happens if the MIS structure is in the state of inversion; in this case, an eddy electric current formed crosses the induced p-n junction and closes on itself at the MIS structure periphery. It is assumed that this current and the extra voltage across the p-n junction are related by the Shockley formula. The following parameters were evaluated: the coefficient β in the Shockley formula (β characterizes the nonideality of the p-n junction); the product R ₀ A of the resistance for zero bias by the area of the p-n junction; and the surface area ΔS of collection of the charge carriers. It was found that β=1.52, R ₀ A=2.7×10⁵ Ω cm², and ΔS corresponds to a stripe that goes along the MIS-structure perimeter and has a width of 15 μm. The MIS structure studied is considered as a photodetector. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 7, 2000, pp. 822–826. Original Russian Text Copyright ? 2000 by Ovsyuk, Vasil’ev, Mashukov.     

An internal calibration technique for pseudobinary systems by auger electron spectroscopy

An internal calibration technique has been developed for the quantitative analysis of pseudobinary systems by means of Auger electron spectroscopy without the need for stan-dards of known composition. This technique has been used for analyzing PbO-In₂O₃ two-phase films and A1N-A1₂ O₃ , AlAs-GaAs, and GaP-InP solid solutions. The technique is applicable to systems of the type (AC_m) (BC_n)_1-x if the Auger intensities measured for elemens A, B, and C are given by the linear relationships I = xI_A ^**, I_B = (l-x)I_B ^*, and I_C = xI_C ^** + (l-x)I_{C C} ^* where I_A ^** and I_C ^** are the inten-sities for pure AC_m and I_B ^* and I* are the intensities for pure BC_n . To determine whether this criterion is satisfied, a series of Auger measurements is made on regions of dif-ferent composition within a single specimen (e.g., on speci-mens in which a concentration variation exists across the surface or surfaces exposed by repeated sputter-etching of a sample with an in-depth composition gradient), and plots of I_A vs I_B and I_C/I_B vs I_A/I_B are made. If these plots are linear over tne range of compositions investigated, it is assumed that the above linear relationships are valid over the whole range of the pseudobinary system. It is then possible to construct linear calibration plots of I_A, I_B , and I_C vs x for the whole composition range.     

Some results on sensitivity and robust stability of input-output systems governed by integral and differential equations

We consider input-output systems (not necessarily of feedback type) on the time domain [0, ) which are governed by nonlinear vector integral or differential equations that relate the input and the output. Assuming that these equations depend on a parameterA, describing perturbations, which is allowed to vary in a vicinity of a nominal valueA ₀ in a linear space, we study how strongly the output is affected by changes of (a)A ₀ when the input is fixed (insensitivity), and (b) the input whenA is fixed withA A ₀ being not too large (robust stability).The results are based on the theory of input-output systems over abstract extended spaces given in Parts I and II of [3]. We discuss nominal systems described by nonlinear Volterra and differential equations, and consider two types of possible perturbations. We also prove a simple result on systems governed by singular differential equations whose perturbations can change the order of the system.     

Optical transitions in MnGa2Se4

The dependence of the absorption coefficient on incident photon energy in a MnGa₂Se₄ single crystal has been investigated in the temperature range 110?C295 K. Using group-theory analysis of the electron state symmetry and comparison of the symmetry of the energy spectrum of MnGa₂Se₄ and its isoelectronic analogs, a conclusion about the character of optical transitions has been drawn. It is shown that the features observed at 2.31 and 2.45 eV are related to the intracenter transitions ⁶ A ₁ ¹ ?? ⁴ T ₂(⁴ G) and ⁶ A ₁ ² ?? ⁴ T ₂(⁴ G). The ⁶ A ₁ state is split by the crystal field.     

光折变自适应光外差探测的实验研究

利用国产光折变晶体构成一个自适应光外差的实验系统，观察到中频外差输出，并给出了系统的探测灵敏度、自准直性以及接收视场等特性的实验结果。     

Advances in composition control for 16 µm LPE P-on-n HgCdTe heterojunction photodiodes for remote sensing applications at 60K

With good composition control in both p-type cap and n-type base LPE layers, it is possible to make barrier-free two-layer P-on-n HgCdTe heterojunction photodiodes with very long cutoff wavelengths. Diode arrays with good R_oA operability, good quantum efficiency, and low 1/f noise at 60K have been demonstrated at cutoff wavelengths to 16.3μm. The diode performance continues to improve at lower temperatures, following a diffusion-current trend to at least 35K. Measured R_oA values of 2×10⁵ ohm-cm² for an 18 μm cutoff at 35K are the highest reported at this very long wavelength. A simple defect model applied to the area dependence of R_oA at 40K implied a defect areal density of 3×10⁴ cm⁻² and a defect impedance of 3×10⁶ ohm.     

Ultrahigh Energy Density of Antiferroelectric PbZrO3-Based Films at Low Electric Field

Dielectric capacitors play a vital role in advanced electronics and power systems as a medium of energy storage and conversion. Achieving ultrahigh energy density at low electric field/voltage, however, remains a challenge for insulating dielectric materials. Taking advantage of the phase transition in antiferroelectric (AFE) film PbZrO₃ (PZO), a small amount of isovalent (Sr²⁺) / aliovalent (La³⁺) dopants are introduced to form a hierarchical domain structure to increase the polarization and enhance the backward switching field E_A simultaneously, while maintaining a stable forward switching field E_F. An ultrahigh energy density of 50 J cm⁻³ is achieved for the nominal Pb_0.925La_0.05ZrO₃ (PLZ5) films at low electric fields of 1 MV cm⁻¹, exceeding the current dielectric energy storage films at similar electric field. This study opens a new avenue to enhance energy density of AFE materials at low field/voltage based on a gradient-relaxor AFE strategy, which has significant implications for the development of new dielectric materials that can operate at low field/voltage while still delivering high energy density.     

Electrical Characterization of Different Passivation Treatments for Long-Wave Infrared InAs/GaSb Strained Layer Superlattice Photodiodes

Silicon dioxide (SiO₂), silicon nitride (Si _x N _y ), and zinc sulfide (ZnS) with ammonium sulfide [(NH₄)₂S] as a prepassivation surface treatment were compared as passivants for InAs/GaSb strained layer superlattice detectors with a 0% cutoff wavelength of ∼10 μm. SiO₂ did not show significant improvement and the zero-bias resistance-area product (R ₀ A) was 0.72 Ω-cm² at 77 K. Si _x N _y passivation showed a nominal improvement with an R ₀ A value of 4.1 Ω-cm² at 77 K. ZnS with (NH₄)₂S treatment outperformed others significantly, improving the R ₀ A value to 492 Ω-cm² at 77 K. Variable-area diode measurements indicated a bulk-limited R ₀ A value of 722 Ω-cm². ZnS-passivated diodes exhibited maximum surface resistivity with a value of 2500 Ω-cm.     

Composition-Dependent Photoluminescence Properties and Anti-Counterfeiting Applications of A2AgX3 (A = Rb,Cs; X = Cl,Br, I)

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue-emitting all-inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A₂AgX₃ (A = Rb, Cs; X = Cl, Br, I) through solid-state synthesis is reported. In contrast to the Cu(I) analogs, A₂AgX₃ are broad-band emitters sensitive to A and X site substitutions. First-principle calculations show that defect-bound excitons are responsible for the observed main PL peaks in Rb₂AgX₃ and that self-trapped excitons (STEs) contribute to a minor PL peak in Rb₂AgBr₃. This is in sharp contrast to Rb₂CuX₃, in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A₂AgX₃ significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A₂AgX₃ are prepared and successfully used in anti-counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A₂AgX₃ suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.     

Transient processes in gunn diodes

The influence of transient processes on the parameters of Gunn logic devices and Gunn generators is considered. For Gunn logic devices the dependence of the switching time on the load resistance R₁ is calculated and the criteria limiting the possible values of $\text{R}{}_1\text{R}{}_0$ (where R₀ is the low field resistance of the Gunn diode) are derived. The simple criterion of the Gunn generation modes is obtained. This criterion allows the prediction of what mode of generation (transit, hybrid or LSA) should take place if the oscillation frequency and the diode parameters are known. For the transit modes in a parallel resonant circuit the change of the resonant frequency due to the diode connection is estimated and the criterion which should be met by the diode parameters and the load resistance is derived. In particular this criterion sets up a limitation of the maximum diode length for the quenched mode at a given frequency. The simple calculation of the basic generation parameters is presented for the case when the Gunn diode operates in a series resonant circuit.