共查询到20条相似文献,搜索用时 15 毫秒
1.
A wavelength-tunable, single-frequency GaInAsP-InP laser diode using an intracavity electrooptic LiNbO3 crystal as the wavelength selective component is discussed. Wavelength tuning is achieved by applying a driving voltage on the crystal electrodes. First results indicate a tuning rate of 1 GHz/V over a tuning range of about 4 nm. This performance was obtained using a nonoptimized X -cut, Z -propagating LiNbO3 crystal. A potential tuning rate of 6.5 GHz/V is possible with reasonable improvements 相似文献
2.
An LiNbO3 optical integrated circuit pigtailed with two single-mode fibres, which allows time-division two-dimensional velocity measurement, is discussed. To detect time-division multiplexed beat signals corresponding to velocity components v X and v γ of a moving object, a waveguide switch is integrated on a Z -propagating LiNbO3 substrate of 28×7 mm2 in addition to a waveguide interferometer with a frequency shifter. In the optical IC, either v X or v γ could be measured selectively with signal-to-noise ratio of 20 dB by driving an electronic gate placed after a photodiode in synchronization with the waveguide switch 相似文献
3.
A single-stage low-sidelobe weighted-coupled integrated acoustooptic tunable filter (IAOTF) operating at the optical wavelength of 1.31 μm has been realized on a Y -cut X -propagating LiNbO3 substrate for the first time. The weighted-coupling, which enabled the achievement of low-sidelobe levels, was facilitated by focused surface acoustic waves generated by a curved interdigital transducer. First sidelobe levels as low as -17.6 dB have been obtained. Optical bandwidth of 4 nm and tuning range of 170 nm for an interaction length of 6 mm were also accomplished 相似文献
4.
Reports a theory for calculating the coupling length L c of Ti:LiNbO3 single-mode waveguide directional couplers from process parameters and operating wavelength. Estimates are accurate to within a factor of 2 compared with published experimental results for z -cut y -propagating LiNbO3 devices for 0.63 μm⩽λ⩽1.56 μm. Use of this formalism to assess acceptable process parameter and wavelength tolerances is demonstrated 相似文献
5.
The first demonstration of Bragg reflector grating filters in Ti:LiNbO3 single-mode channel guides is reported. Filter bandwidths as narrow as 0.14 nm centred at 1.476 μm have been achieved for TE polarisation in Y -cut (X -propagating) material 相似文献
6.
Various Y -cut Z -propagating lithium niobate YZ -LiNbO3 substrate configurations are investigated to develop efficient ways of confining the wave energy in surface acoustic-wave (SAW) microsensors based on waveguide structure. The core and cladding regions for the SAW waveguide sensors have been titanium in-diffused or out-diffused and in some cases metal overlays have been used. By varying the diffusion conditions, the SAW velocities in these regions can be controlled such that a channeled region with interface wave-reflection is produced while minimizing the wave-velocity-difference between the cladding and the core 相似文献
7.
Secret key agreement by public discussion from common information 总被引:15,自引:0,他引:15
Maurer U.M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1993,39(3):733-742
The problem of generating a shared secret key S by two parties knowing dependent random variables X and Y , respectively, but not sharing a secret key initially, is considered. An enemy who knows the random variable Z , jointly distributed with X and Y according to some probability distribution P XYZ, can also receive all messages exchanged by the two parties over a public channel. The goal of a protocol is that the enemy obtains at most a negligible amount of information about S . Upper bounds on H (S ) as a function of P XYZ are presented. Lower bounds on the rate H (S )/N (as N →∞) are derived for the case in which X =[X 1, . . ., X N], Y =[Y 1, . . ., Y N] and Z =[Z 1, . . ., Z N] result from N independent executions of a random experiment generating X i, Y i and Z i for i =1, . . ., N . It is shown that such a secret key agreement is possible for a scenario in which all three parties receive the output of a binary symmetric source over independent binary symmetric channels, even when the enemy's channel is superior to the other two channels 相似文献
8.
Shamai S. Wyner A.D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1990,36(6):1428-1430
Let {X n}, {Y n} be independent stationary binary random sequences with entropy H ( X ), H (Y ), respectively. Let h (ζ)=-ζlogζ-(1-ζ)log(1-ζ), 0⩽ζ⩽1/2, be the binary entropy function and let σ(X )=h -1 (H (X )), σ(Y )=h -1 (H (Y )). Let z n=X n⊕Y n , where ⊕ denotes modulo-2 addition. The following analog of the entropy-power inequality provides a lower bound on H (Z ), the entropy of {Z n}: σ(Z )⩾σ(X )*σ(Y ), where σ(Z )=h -1 (H (Z )), and α*β=α(1-β)+β(1-α). When {Y n} are independent identically distributed, this reduces to Mrs. Gerber's Lemma from A.D. Wyner and J. Ziv (1973) 相似文献
9.
The authors report a wavelength independent TE-TM mode convertor used as a waveguide electrooptic modulator in a coherence modulated system. The modulation voltages thus obtained (20 V) are about 10 times lower than those previously reported in earlier coherence modulated devices. The modulator is a strip waveguide fabricated on Y -cut Z -propagation, Ti-indiffused LiNbO3. When used in conjunction with a birefringent plate and polarizers, the modulator is shown to imprint on light a signal encoded into an optical delay greater than the source coherence length. Demonstration of the device is reported using a highly multimode laser diode at 820 nm 相似文献
10.
Optimal pump wavelength in the4I 15/2-4I 13/2 absorption band for efficient Er3+-doped fiberamplifiers
Zyskind J.L. Giles C.R. Desurvire E. Simpson J.R. 《Photonics Technology Letters, IEEE》1989,1(12):428-430
The authors report the measured gain of a highly efficient erbium-doped fiber amplifier pumped at wavelengths between 1.46 and 1.51 μm. The optimal pump wavelength, λopt, was determined to be 1.475 μm. At this wavelength, the maximum gain coefficients for signals at 1.531 and 1.544 μm were 2.3 and 2.6 dB/mW, respectively. At λopt, high gains ranging from 32 dB at pump power P p=20 mW up to 40 dB at P p=80 mW were obtained. These modest pump powers are within the capabilities of currently available 1.48-μm diode lasers. The width about λopt for 3-dB gain variation exceeded 27 nm for P p=10 mW and 40 nm for P p >20 mW. With this weak dependence on pump wavelength, single-longitudinal-mode lasers do not have a significant advantage over practical Fabry-Perot multimode pump lasers 相似文献
11.
Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H S , output admittance Y s, and the y -parameter model of the switching converter. The criteria are listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T , line-to-output transfer function A gf , and output impedance Z of requirement is given, an input filter with H s and Y s can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H s⩽1 (may be relaxed to 3-6 dB), and Y s is larger than the curves of the graphical illustration, perhaps using 6 dB as a rule-of-thumb minimum separation 相似文献
12.
Gorgucci E. Scarchilli G. Chandrasekar V. 《Geoscience and Remote Sensing, IEEE Transactions on》1992,30(5):853-858
A method that uses the properties of rain medium itself to obtain accurate weather radar system gain calibration is discussed. This technique is based on the principle that the rainfall rate measured using absolute reflectivity (Z ) and differential reflectivity ( Z DR) is the same as that obtained from specific differential phase (K DP). The measurements required for this technique are Z , Z DR, and K DP. The rainfall rate estimates obtained from Z and Z DR are compared with the estimates obtained from K DP. The scatter plot between the two rainfall estimates should lie close to a 1:1 line, and any systematic deviation from this line can be removed by appropriately adjusting the system gain. It is noted that Z DR can be calibrated accurately because it is a differential power measurement, and K DP is obtained from differential phase measurement, which is unaffected by system calibration. The sensitivity and accuracy of this technique are studied, and theoretical and simulation results for C -band frequencies are presented 相似文献
13.
Loeliger H.-A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(6):1675-1682
Recently, linear codes over Z M (the ring of integers mod M ) have been presented that are matched to M -ary phase modulation. The general problem of matching signal sets to generalized linear algebraic codes is addressed based on these codes. A definition is given for the notion of matching. It is shown that any signal set in N -dimensional Euclidean space that is matched to an abstract group is essentially what D. Slepian (1968) called a group code for the Gaussian channel. If the group is commutative, this further implies that any such signal set is equivalent to coded phase modulation with linear codes over Z M. Some further results on such signal sets are presented, and the signal sets matched to noncommutative groups and the linear codes over such groups are discussed 相似文献
14.
Proton-exchanged Z -cut LiNbO3 planar waveguides formed using phosphoric acid were characterized optically. The refractive index profile and the diffusion parameters were studied systematically. These waveguides have propagation losses of less than 1 dB/cm and exhibit properties that are different from those obtained using benzoic acid. The index profile is not a simple step function and can be modeled accurately by a polynomial expression. A maximum surface index increase of 0.145 was measured at a 0.633-μm wavelength. The diffusion constant D 0 and the activation energy Q for the proton-exchange process using this acid were found to be 6.43×108 μm2/h and 82.91 kJ/mol, respectively. The annealing properties of these waveguides were also established, and the effects of annealing on surface index change and waveguide depth increase were found to follow a power-law relationship 相似文献
15.
Fortier P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(2):391-393
A conjecture is proven on the number of points on shells for the shifted Z 4 and the shifted Z 8 lattices. Furthermore, the results are extended to any shifted Z 4n lattice (n =0, 1, . . .). These results provide an easy way to compute the number of points on shells for the type of lattices used in the design of multidimensional signal sets or in vector coding 相似文献
16.
Sutter K. Bosshard C. Ehrensperger M. Gunter P. Twieg R.J. 《Quantum Electronics, IEEE Journal of》1988,24(12):2362-2366
Single crystals of 2-methyl-4-nitro-N -methylaniline (MNMA) have been grown from the melt. The crystal structure was determined (orthorhombic, Pna2I (2 mm), Z =4, a =17.788(6) Å, b =11.893(4) Å, c =3.907(2) Å). The refractive indexes n a and n c were measured between 500 and 700 nm [ n a(633 nm)=2.148(10), n c(633 nm)=1.520(3)]. The nonlinear optical susceptibilities coefficients r 31=8 pm/V and r 33=7.5 pm/V were determined. Most optical properties can be explained in terms of molecular orientation and polarizability 相似文献
17.
A new organic electrooptic crystal, 2,6-dibromo-N-methyl-4-nitroaniline, is reported. The crystal structure was determined by X-ray diffraction (orthorhombic, space group Fdd2, point group mm2, Z =16, a =11.745 Å, b =29.640 Å, c =10.807 Å). The refractive indexes were measured at several wavelengths between 500 and 1100 nm (at 632.8 nm, n a=1.90, n b=1.62, and n c=1.48) and fit the data to a single oscillator Sellmeier equation. A report is presented on measurements of the linear electrooptic effect, yielding the combined coefficients n a 3r 13-n c3 r 33, as well as the first known measurements of the quadratic electrooptic effect in an organic crystal, yielding the coefficients r 42 and r 51 at 514.5, 632.8, and 810 nm. Good agreement is found between the observed dispersion in the electrooptic coefficients and that predicted by the simple two-level dispersion model 相似文献
18.
Hamada N. Sauerbrey R. Wilson W.L. Jr. Tittel F.K. Nighan W.L. 《Quantum Electronics, IEEE Journal of》1988,24(8):1571-1578
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 相似文献
19.
Aydin K. Yang Zhao Seliga T.A. 《Geoscience and Remote Sensing, IEEE Transactions on》1989,27(1):57-66
An attenuation correction procedure is proposed and evaluated by simulations using raindrop size distribution obtained from ground-based disdrometer measurements. The results show that under certain conditions it is possible to retrieve C -band reflectivity factor (Z H) and differential reflectivity (Z DR) radar observables affected by attenuation along rain-filled propagation paths. Rainfall rates estimated from Z H and Z DR with and without attenuation correction are compared to determine the effects of attenuation and the capability of the correction procedure to account for it 相似文献
20.
One of the Doppler radars operated by the National Severe Storms Laboratory can measure the difference between propagation phase constants K Dp at horizontal and vertical polarization. This study examines the use of this parameter K Dp in addition to the reflectivity factor Z H and the differential reflectivity Z DR, to obtain information about rain and hail. It is shown from theory and experiments that a third parameter of the drop size distribution, obtained from K DP, can be used to support Z DR measurement and/or to point out mixed-phase hydrometeors. Quantitative information on hail size distribution can be obtained for small hailstones when their major axes are nearly vertically aligned, giving rise to negative Z DR and K DP values 相似文献