一种微型化制造的双腔结构芯片原子钟87Rb蒸汽腔

碱金属蒸汽腔是芯片原子钟（CSACs）中重要的核心部件之一,其微型化制造具有重要的实用价值,同时也非常具有挑战性。采用MEMS 技术批量化制作了具有双腔结构的芯片原子钟87Rb 蒸汽腔阵列。在阳极键合过程中,通过原位化学反应产生纯净的87Rb 元素蒸汽,缓冲气体（N2）采用反充的方法充入到87Rb 蒸汽腔内以保证缓冲气体的压强可以精确的控制。所设计的双腔结构可以防止原位化学反应中产生的杂质阻挡光路,从而能够提高探测到的光信号的强度。通过原子钟桌面系统测试,得到了87Rb 元素D1 线的光学吸收谱和用于芯片原子钟锁频的误差信号,在90℃时,87Rb 元素D1 线纠偏信号的线宽（波峰与波谷间距）可达到0.53 kHz。测试结果表明,双腔结构的87Rb 蒸汽腔满足芯片原子钟或其他芯片级原子器件的设计要求。     

Quarter-micrometer gate ion-implanted GaAs MESFET's with an f1 of 126 GHz

The fabrication and characterization of a 0.25-μm-gate, ion-implanted GaAs MESFET with a maximum current-gain cutoff frequency f_t of 126 GHz is reported. Extrapolation of current gains from bias-dependent S-parameters at 70-100% of I _dss yields f₁'s of 108-126 GHz. It is projected that an f₁ of 320 GHz is achievable with 0.1-μm-gate GaAs MESFETs. This demonstration of f₁'s over 100 GHz with practical 0.25-μm gate length substantially advances the high-frequency operation limits of short-gate GaAs MESFETs     

Dependence of the frequency shift of the optical-microwave doubleresonance signal in the Cs D2 line on the pumpingfrequency and power of a GaAs semiconductor laser

The OMDR (optical-microwave double resonance) effect in the Cs D₂ line was studied for realizing a gas-cell-type Cs atomic frequency standard. A glass cell containing Cs with buffer gases (Ar/N₂=1.26, total pressure=39 torr) was placed in a TE₀₁₂ mode microwave cavity at a temperature of 45°C and was pumped using a GaAs semiconductor laser frequency locked to an external interferometer tuned to the 6P_3/2 (F=2,3,4)←6 S_1/2(F=3) transition. The OMDR signal appearing at the resonance to the F=4←3 hyperfine transition of the 6S_1/2 state shifted with detuning of the laser frequency and with change of the laser and microwave powers. The dependence of the shift on these variables around an optimum operating condition was obtained as, Δν_MW[Hz]=-(0.31±0.02) {1+(0.44±0.15) (ΔP_L/P_L)} Δν_L [MHz]-10(ΔV_MW/V _MW)     

Delay analysis of a packet voice multiplexer by the ΣDi/D/1 queue

The performance of a statistical multiplexer whose inputs consist of a superposition of voice packet streams is studied. The delay for such a system is analyzed by solving the ΣD_i/ D/1 queue. The analytic method can be used to find the approximate mean delay for an arbitrarily large number of trunks and the approximate delay distribution when the number of trunks is less than 100. An efficient hybrid simulation of the packet voice multiplexer which can be used to find the delay distribution for a large number of trunks is presented. In addition, easily computable error bounds for the present approximation are provided, and the accuracy of the M/ D/1 approximation is investigated     

Thermal shifts of the spectral lines in the 4F3/2 to 4I11/2 manifold of anNd:YAG Laser

A report is presented of the thermal shifts of eleven of the twelve lines from the ⁴F_3/2 Stark energy levels to the ⁴I_11/2 energy levels in an Nd:YAG laser for a temperature change from 20-200°C. The thermal shift difference between the Stark sublevels R₁, R₂ in ⁴F_3/2 is found to be about -0.6±0.6 cm^-1/100°C. Within experimental uncertainty, all of the lasing lines either moved to longer wavelength or remained unchanged with increasing temperature     

Image restoration by convex projections using adaptive constraintsand the L1 norm

A new projection method based on the row action projection (RAP) algorithm for image restoration is presented. The new implementation is computationally attractive and facilitates local adaption of projection operators. The local mean and the least L₁ norm set of solutions are used as constraints. Computer simulations illustrate the new methods to be very competitive in restoring missing spectral components of a degraded image     

Measurement of the stimulated emission cross section for the 4F3/2-4I13/2transition of Nd3+ in YAlO3 crystal

A method for the simultaneous measurement of the stimulated emission cross section and fluorescence lifetime by studying the relation between laser parameters and the laser relaxation oscillation frequency is discussed. The stimulated emission cross section for the ⁴F_3/2-⁴I_13/2 transition of Nd³⁺ ion in YAP crystal was measured to be (22±1)×10^-20 cm²     

On algebraic decoding of the Z4-linearCalderbank-McGuire code

The quaternary Calderbank-McGuire (see Des., Codes Cryptogr., vol.10, no.2, 1997) code is a Z₄-linear code of length 32 which has 2³⁷ codewords and a minimum Lee distance of 12. The Gray map of this code is known to be a nonlinear binary (64, 2³⁷,12) code. The Z₄-linear Calderbank-McGuire code can correct all errors with Lee weight ⩽5. An algebraic decoding algorithm for the code is presented in this paper. Furthermore, we discuss an alternative decoding method which takes advantage of the efficient BCH decoding algorithm     

Binary images of cyclic codes over Z4

We determine all linear cyclic codes over Z₄ of odd length whose Gray images are linear codes (or, equivalently, whose Nechaev-Gray (1989) image are linear cyclic codes or are linear cyclic codes)     

0.33-μm gate-length millimeter-wave InP-channel HEMTs with highf1 and fmax

The fabrication of 0.33-μm gate-length AlInAs/InP high electron mobility transistors (HEMTs) is reported. These InP-channel devices have f_t values as high as 76 GHz, f_max values of 146 GHz, and maximum stable gains of 16.8, 14, and 12 dB at 10, 18, and 30 GHz, respectively. The extrinsic DC transconductances are as high as 610 mS/mm; with drain-source breakdown voltages exceeding 10 V. The effective electron velocity in the InP channel is estimated to be at least 1.8×10⁷ cm/s, while the f_tL_g product is 29 GHz-μm. These results are comparable to the best reported results for similar InGaAs-channel devices     

Local fractional population measurement of the upper state 4I13/2 of an erbium-doped fiber amplifier

A method of measuring the local fractional population of the upper state ⁴I_13/2 of an erbium-doped amplifier is investigated. The local fractional population is related theoretically by EDF parameters to the local spontaneous emission (SE) power that leaks laterally from the EDF. The proportional constant between the fractional population and the detected SE power is determined experimentally by measuring saturated spontaneous emission power. The local fractional population of a 19.7 m-long EDF, pumped with a 1.48 μm light and injected with a 1.552 μm signal light, was measured by detecting the local SE power with a Ge photodiode having a diameter of 2 mm. The measured fractional population coincides with the calculated value     

Performance characteristics of an injection-controlledelectron-beam pumped XeF(C→A) laser system

Characteristics of an injection-controlled electron-beam pumped XeF(C→A) laser are investigated with emphasis on efficient wideband tuning and scaling issues. Using a quasi-CW dye laser as an injection source, data are obtained that describe the laser characteristics over a wide parameter range. A high-Z electron-beam backscattering reflector inside the laser reaction cell improved the electron-beam energy deposition by 40%, resulting in an increase of the amplified laser output by more than a factor of four. Efficient and continuous wavelength tuning between 470 and 500 nm is achieved with an output energy density of ~1 J/l, and an intrinsic efficiency of ~1% throughout the entire tuning region     

Gain measurements on the KrF(B→X), XeF(B→X), and XeF(C→A) lasertransitions in an XeF(C→A) laser gas mixture

Optimum energy extraction from an electron-beam-pumped XeF(C →A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(C→ A) transition, but also in the ultraviolet (UV) region for the competing XeF(B→X) and KrF(B→X ) transitions. The authors report gain measurements on the XeF(C→A) transition and small-signal gain and absorption coefficients at or near both the XeF(B→X ) (351 and 353 nm) and KrF(B→X) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(C→A) kinetics is discussed     

Measurement of mode partition characteristics of laser diodesmodulated by M-sequences

A method which permits the determination of k-values of laser diodes modulated by M-sequences is described. With this method, the mode partition characteristics of laser diodes in actual operating conditions can be measured. Measurements at frequencies which are lower by two orders of magnitude compared with conventional methods are possible     

Analysis of erbium-doped fiber amplifiers pumped in the4I15/2-4I13/2 band

A theoretical model for the amplifiers predicts gain coefficients of around 2 dB per milliwatt of launched pump power, in close agreement with previously reported measurements. The model is also used to determine the optimal pump wavelength λ_opt that maximizes the amplifier gain. It is shown that the latter is insensitive to pump detuning near λ_opt=1.48 μm, within a 20 nm range, which indicates that broadband, multimode laser diode pump sources and pumps with narrow linewidths should yield identical gain performance     

Two chi-square statistics for determining the orders p andq of an ARMA (p, q) process

The &thetas;, λ, and η functions have been previously proposed for use in choosing the autoregressive and moving-average orders of an ARMA (q, p) process visually. Two chi-square statistics associated with these three functions are presented and used here to determine the orders of an ARMA process statistically. It is shown that the two statistics are asymptotically equivalent to the Quenouille-Walker's goodness-of-fit test statistic, which is a Lagrange multiplier test statistic. Some numerical examples are presented to illustrate the usefulness of the two chi-square statistics as well as the three functions in ARMA modeling     

Scaling characteristics of the XeF (C→A)excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C→A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F₂, NF₃ , Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C→A) laser operation     

l1-optimal estimation for discrete-time linearsystems

A linear multichannel estimation problem with discrete-time linear shift-invariant models is formulated in the time domain as a minimum l¹ norm approximation problem. It is shown, using some key results from optimization theory, that solving the approximation problem is equivalent to solving a sequence of linear programming problems which terminates when an optimal or near-optimal solution is reached. The motivation for considering an l¹ -optimal design versus l²- or H^∞-optimal designs is presented. A sample problem is solved to illustrate the computational procedure, as well as to compare the relative performances of the l¹-, l² and H^∞-optimal estimators in a practical situation     

A single-hop F2 propagation model forfrequencies above 30 MHz and path distances greater than 4000 km

Standard textbook explanations of ionosphere propagation suggest that 30 MHz and 4000 km are the limiting frequency and distance for single-hop communications. During the peak of sunspot cycle 22, however, there have been hundreds of reports of F₂ communications exceeding great-circle distance of 4200 km at 50 MHz. It is shown that parabolic F₂ ionospheric models explain this propagation irregularity, although textbooks and reference books fail to show that such long distances at VHF are possible     

Theory of an efficient N×N passive opticalstar coupler

A method for configuring an efficient N×N optical passive star coupler is introduced. It makes the construction of a one-piece coupler possible and thus eliminates the excess loss problem associated with cascade couplers and reduces the structural complexity. The authors show that a 100% efficiency figure can be achieved through the entire array by using a properly designed space-varying refractive-index slab. The authors give a mathematical analysis of the space-varying refractive-index slab and examine spatial frequencies of the required refractive-index pattern. The authors demonstrate how the wave-mixing method can be utilized as one possible method of configuring such a slab, using a constant temporal optical frequency involving nonlinear media such as photorefractive crystals