共查询到20条相似文献,搜索用时 15 毫秒
1.
Rajat Kumar Singh Rajiv Srivastava Yatindra Nath Singh 《Optical and Quantum Electronics》2007,39(14):1153-1165
Optical packet switching provides high speed, data rate/format transparency, efficient use of bandwidth and flexibility. The
major problem in the implementation of “all-optical” switching is contention which occurs when two or more packets arrive
at the same time for the same destination. To resolve the contention, we have proposed an optical packet switch architecture
based on WDM loop buffer memory in the feedback configuration. In that architecture, the contending packets are stored in
a loop buffer module, and routed in the free time slots. The buffering duration in the recirculating loop is limited by a
circulation limit. The analysis was been done to obtain the maximum number of allowed circulations. This paper proposes improved
version of that optical packet switch architecture, to increase the number of maximum allowed circulations. The modification
is done either by adding an extra erbium doped fiber amplifier (EDFA) in the original switch or by replacing the core space
switch with arrayed waveguide grating (AWG). The performance analysis has been done by the simulations. 相似文献
2.
Continuous-wave (CW) performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) at room
and elevated temperatures is investigated with the aid of the comprehensive fully self-consistent optical-electrical-thermal-gain
model. A standard OC GaInNAs/GaAs double-quantum-well VCSEL emitting the 1.3-μm radiation is used as a typical modern VCSEL
structure. The oxide aperture is placed at the anti-node position of an optical standing wave within a VCSEL cavity. The desired
single-fundamental-mode (SFM) operation has been found to be expected only in VCSELs equipped with relatively small active
regions of diameters equal or smaller than 10 μm. Therefore a proton implantation used as an radial additional confinement
of the current spreading from the upper annular contact towards the centrally located active region is proposed and its impact
on the VCSEL performance is investigated. The above structure modification has been found to enable a radical improvement
in the VCSEL performance. In particular, in this case, the SFM VCSEL operation is possible even in VCSELs with quite large
active regions and for much wider ambient-temperature range than in the standard OC VCSELs. 相似文献
3.
基于扩展的自旋反转模型,对光反馈诱发下长波长垂直腔面发射激光器中的低功耗偏振开关进行了理论研究.研究表明:长波长垂直腔面发射激光器在自由运行下未能获得的偏振开关现象,可以通过引入中等强度的偏振旋转光反馈来实现.对比强弱两种不同的线性色散效应,发现了一些有趣的现象:弱线性色散条件下更易于在低注入电流下获得偏振开关,并且产生偏振开关所需的反馈强度具有更大的调控范围;强色散效应中未能始终获得偏振开关,会出现两模共存区,并且偏振开关出现的注入电流值较高.同时,观察到的偏振模跳变和多偏振开关现象类似于短波长垂直腔面发射激光器,因而证实这两类激光器在偏振开关的本质规律上是相似的.此外,还对长波长垂直腔面发射激光器不易在低注入电流下获得偏振开关的原因进行了分析,并给出了合理的解释. 相似文献
4.
We theoretically investigate the synchronization performance of the polarization modes of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where the master VCSEL subjects to polarization-preserved optical feedback and the slave VCSEL subjects to polarization-preserved optical injection. We demonstrate that high synchronization can be achieved between corresponding polarization components of the master laser and the slave laser. We also analyze the influence of the internal mismatched parameters on the synchronization performance. Furthermore, this system is used to dual-channel communication and the different transmitted digital information is respectively recovered at each polarization branch of the slaver laser successfully with the encryption scheme of chaos masking (CM). The results open an opportunity for multichannel chaotic communication by utilizing different polarization components in single-mode or multi-transverse-mode VCSELs. 相似文献
5.
基于周期性极化铌酸锂晶体的线性电光效应耦合波理论,数值研究了电光调制对外部光反馈垂直腔表面发射激光器(VCSEL)输出矢量混沌偏振模的操控.研究结果表明,VCSEL输出的偏振度随着电光晶体的长度或施加于电光晶体的外电场强度成周期性转换,控制一定的施加外电场强度和晶体的长度,激光器的不同参数下引起初始混沌偏振态都可以转换为其他任意混沌偏振态.特别是合理选择一定的施加外电场强度或晶体长度,VCSEL输出的任意混沌偏振模可以转换为完全一致的两线性混沌偏振模(x和ŷ偏振),即两线性混沌偏振模的能量能够达到稳定和完全均衡. 相似文献
6.
The polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback are studied experimentally. It is thereby demonstrated that polarization-selective optical feedback can be utilized to entirely eliminate VCSEL polarization switching over the entire device operating range. 相似文献
7.
William Arveson 《Communications in Mathematical Physics》2000,211(1):63-83
A mathematical notion of interaction is introduced for noncommutative dynamical systems, i.e., for one parameter groups of
*-automorphisms of endowed with a certain causal structure. With any interaction there is a well-defined “state of the past” and a well-defined
“state of the future”. We describe the construction of many interactions involving cocycle perturbations of the CAR/CCR flows
and show that they are nontrivial. The proof of nontriviality is based on a new inequality, relating the eigenvalue lists
of the “past” and “future” states to the norm of a linear functional on a certain C
*-algebra.
To the memory of Irving Segal
Received: 12 October 1999 / Accepted: 21 October 1999 相似文献
8.
As quantum information science approaches the goal of constructing quantum computers, understanding loss of information through
decoherence becomes increasingly important. The information about a system that can be obtained from its environment can facilitate
quantum control and error correction. Moreover, observers gain most of their information indirectly, by monitoring (primarily
photon) environments of the “objects of interest.” Exactly how this information is inscribed in the environment is essential
for the emergence of “the classical” from the quantum substrate. In this paper, we examine how many-qubit (or many-spin) environments
can store information about a single system. The information lost to the environment can be stored redundantly, or it can
be encoded in entangled modes of the environment. We go on to show that randomly chosen states of the environment almost always
encode the information so that an observer must capture a majority of the environment to deduce the system’s state. Conversely,
in the states produced by a typical decoherence process, information about a particular observable of the system is stored
redundantly. This selective proliferation of “the fittest information” (known as Quantum Darwinism) plays a key role in choosing
the preferred, effectively classical observables of macroscopic systems. The developing appreciation that the environment
functions not just as a garbage dump, but as a communication channel, is extending our understanding of the environment’s
role in the quantum-classical transition beyond the traditional paradigm of decoherence. 相似文献
9.
The correlations of the linear and circular polarizations in the system of two photons have been theoretically investigated.
The polarization of a two-photon state is described by the one-photon Stokes parameters and by the components of the correlation
“tensor” in the Stokes space. It is shown that in the case of two-photon decays π0 → 2γ, η → 2γ, K
L
0 → 2γ, K
S
0 → 2γ and the cascade process |0〉 → |1〉 + γ → |0〉 + 2γ(|0〉 and |1〉 are states with the spin 0 and 1, respectively) the final
two-photon state represents a characteristic example of the entangled (nonfactorizable) state, and the correlations between
the Stokes parameters in all these decays have the purely quantum character: the incoherence inequalities of the Bell type
for the components of the correlation “tensor”, established previously for the case of classical “mixtures”, are violated.
The general analysis of the registration procedure for two correlated photons by two one-photon detectors is performed. 相似文献
10.
Mirjana?Bo?i? Milena?Davidovi? Teodora?L.?Dimitrova Salvador?Miret-Artés ángel?S.?Sanz Antoine?Weis 《Journal of Russian Laser Research》2010,31(2):117-128
We study experimentally and theoretically the influence of light polarization on the interference patterns behind a diffracting
grating. Different states of polarization and configurations are considered. The experiments are analyzed in terms of electromagnetic
energy (EME) flow lines, which can be eventually identified with the paths followed by photons. This gives rise to a novel
trajectory interpretation of the Arago–Fresnel laws for polarized light, which we compare with interpretations based on the
concept of “which-way” (or “which-slit”) information. 相似文献
11.
D. Supper J. Pfeiffer M. Ilzhöfer Ch. Giuliani Ch. Degen A.P. Lima A. Ramakrishnan G. Ebbinghaus G. Steinle 《Optics Communications》2006,267(2):447-450
We present long-wavelength vertical-cavity surface emitting laser (VCSEL) with a new approach for control of singlemode emission at 1285 nm wavelength. The VCSELs show singlemode optical output powers of 1.0 mW and a serial resistance between 70 Ω and 100 Ω. 相似文献
12.
A vibronic charge-transfer exciton, which is a pair of Jahn-Teller electron and hole polarons, is considered as a possible
cause of the appearance of the Müller phase in the virtual ferroelectric SrTiO3 and the “green” luminescence in the virtual ferroelectric KTaO3. The two “green” luminescence bands can be associated with emission from two states of a typical intrinsic defect, viz.,
a vibronic charge-transfer exciton trapped by an oxygen vacancy and an isolated vibronic charge-transfer exciton. In both
cases the “green” luminescence corresponds to the recombination of the electron and the hole in the vibronic charge-transfer
exciton, which is accompanied by the emission of light. The properties of the Müller phase can be attributed to mixing of
the normal state and states of the vibronic charge-transfer exciton phase when they interact with polarization in the soft
SrTiO3 matrix under the conditions of a pseudo-Jahn-Teller (pseudo-JT) effect on a soft TO mode of the displacement type. In this
case the vibronic charge-transfer exciton phase forming the low-lying excited states has “order-disorder” degrees of freedom
and exists at temperatures significantly below the point of the order-disorder ferroelectric transition in SrTiO3 at T=T
Q≈37 K. The corresponding lowering of the symmetry of the vibronic charge-transfer exciton phase to polar symmetry leads to
the possibility of a long-period incommensurate phase in such excited states, which arises as a result of the appearance of
a Lifshitz invariant. The valence-band state making the largest contribution of the pseudo-JT effect corresponds to a wave
vector equal to the critical wave vector of the incommensurate vibronic charge-transfer exciton phase. When the temperature
is lowered, the pseudo-JT distortion increases down to ∼T
Q and subsequently saturates in accordance with the saturation of the dielectric constant. The basic assumption in the model
is that the temperature T=T
Q corresponds to the narrow temperature range for the transition from an intermediate to a strong pseudo-JT effect under the
conditions for the realization of polarization tunneling states. The appearance of a significant admixture of states of the
modulated ferroelectric vibronic charge-transfer exciton phase to the ground state under the conditions for the realization
of polarization tunneling states at low temperatures provides an explanation for the principal properties of the Müller phase.
Fiz. Tverd. Tela (St. Petersburg) 40, 907–909 (May 1998) 相似文献
13.
We analyze theoretically the effect of polarization mode competition on the synchronization of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs). Chaos in the master laser is induced by delayed optical feedback, and the slave laser is subject to isotropic optical injection from the master VCSEL. We show that the synchronization quality can be enhanced when the chaotic regime in the master VCSEL involves both fundamental orthogonal linearly polarized modes. 相似文献
14.
Botao Zhang 《Optics Communications》2011,284(12):3011-3013
Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with ultrafast optical modulation. After injection of a subpicosecond laser pulse into the VCSEL cavity, nonlasing modes were excited and produced optical beating in the emission of the VCSEL. After these oscillations have died down, when the VCSEL is operating at high power and when the injected laser pulses exceed a power threshold as well, the injected laser pulses can induce the lasing to switch to a normally nonlasing mode with crossed polarization. Our measurements of the decay time of the nonlasing modes at low injected pulse energy are consistent with the interpretation of this switching as enabled by increased lifetime of the nonlasing modes at high power. 相似文献
15.
An experimental study has been presented of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) operating in the 850 nm region of the electromagnetic spectrum. In this regard, various relevant VCSEL samples with numerous oxide aperture sizes have been fabricated and characterized. Thorough investigations of the electrical as well as optical characteristics of the fabricated samples have been performed, which include the overall device performance as a function of the oxidize aperture sizes. It is reported that the VCSELs with oxide aperture size <10 μm require low threshold currents (<1 mA). Further, the differential quantum efficiencies up to 28% corresponding to wall-plug efficiencies of up to 15% were measured for a number of these devices. 相似文献
16.
E. Z. Kuchinskii N. A. Kuleeva I. A. Nekrasov M. V. Sadovskii 《Journal of Experimental and Theoretical Physics》2008,107(2):281-287
We discuss the problem of a possible “violation” of the optical sum rule in the normal (nonsuperconducting) state of strongly
correlated electronic systems, using our recently proposed DMFT + Σ approach applied to two typical models: the “hot spot”
model of the pseudogap state and the disordered Anderson-Hubbard model. We explicitly demonstrate that the general Kubo single-band
sum rule is satisfied for both models, but the optical integral itself is in general dependent on temperature and characteristic
parameters, such as the pseudogap width, correlation strength, and disorder scattering, leading to an effective “violation”
of the optical sum rule, which may be observed in experiments.
The text was submitted by the authors in English. 相似文献
17.
This paper investigates stimulated emission and absorption near resonance for a driven system of interacting two-level atoms.
Microscopic kinetic equations for the density matrix elements of N-atom states including atomic motion are built, taking into account atom-field and atom-atom interactions. Analytical solutions
are given for the resulting macroscopic equations in different limits, for a system composed of a strong coherent “pump” field
and a weak counter-propagating “probe” field. It was shown that the existence of a dipole-dipole (long-range) interaction
between atoms separated by distance less than the pump wave-length can cause the formation of periodic polarization and population
structures (gratings in time and space) in the pumped medium without a probe field. The magnitude of pump induced population
grating can have a strong dependence on the relation between the pump field detuning and the polarization decay rate. The
“interaction” between pump and probe induced polarization/population gratings through a dipole-dipole interaction mechanism
causes the absorption line shape asymmetry. Under certain conditions, this asymmetry is revealed in increasing probe gain
for the “red”-shifted (relative to pump) probe and suppressing the gain for the “blue”-shifted probe field when pump is “red”-shifted
relative to the ensemble averaged resonant frequency. The theoretical results are consistent with experimental data for the
probe gain or absorption as the function of frequency and the dependance of the gain on atomic density for sodium vapor when
the pump laser is tuned near the D
2 line. Here the dependance of gain on particle density was explained in the terms of the long-range interaction between the
atoms. 相似文献
18.
Y. Ding W. J. Fan D. W. Xu C. Z. Tong Y. Liu L. J. Zhao 《Applied physics. B, Lasers and optics》2010,98(4):773-778
We present the fabrication process and experimental results of 850-nm oxide-confined vertical cavity surface emitting lasers
(VCSELs) fabricated by using dielectric-free approach. The threshold current of 0.4 mA, which corresponds to the threshold
current density of 0.5 kA/cm2, differential resistance of 76 Ω, and maximum output power of more than 5 mW are achieved for the dielectric-free VCSEL with
a square oxide aperture size of 9 μm at room temperature (RT). L–I–V characteristics of the dielectric-free VCSEL are compared with those of conventional VCSEL with the similar aperture size,
which indicates the way to realize low-cost, low-power consumption VCSELs with extremely simple process. Preliminary study
of the temperature-dependent L–I characteristics and modulation response of the dielectric-free VCSEL are also presented. 相似文献
19.
Continuous-wave (CW) performance of modern 1.3-μm InAsP/InGaAsP multi-quantum-well (MQW) tunnel-junction vertical-cavity surface-emitting
diode lasers (TJ-VCSELs) is investigated using our comprehensive self-consistent simulation model to suggest their optimal
design for room and elevated temperatures. For increasing ambient temperatures, an increase in the VCSEL threshold current
has happened to be mostly associated with the Auger recombination. Nevertheless, the InAsP/InGaAsP VCSELs have been found
to exhibit encouraging thermal behaviour with the quite high value of maximal operating temperature of 350 K. It has been
found that 5-μm devices seem to be the most optimal ones because they demonstrate both the room temperature (RT) threshold
current equal to only 0.55 mA and maximum operating temperature equal to as much as 345 K. For these devices, the characteristic
temperature T0 is equal to 92 K for 290–305 K, 51 K for 310–325 K and 29 K for 330–345 K. Therefore, the InAsP/InGaAsP VCSELs
have been found to offer very promising performance both at room and elevated temperatures as sources of the carrier 1.3-μm
wave in the fibre optical communication using silica fibres. 相似文献
20.
V. P. Karassiov 《Journal of Russian Laser Research》2005,26(6):484-513
The notion and main features of polarization states of light are discussed within the framework of classical and quantum optics.
This notion is shown to be correctly defined for arbitrary light beams only within quantum optics by using the P-quasispin formalism developed earlier. Polarization states of quantum light are shown to be fully described by a polarization
density operator (PDO) obtained via reducing the total field density operator. Theoretical foundations are given for quantum
tomography of polarization states of light fields considered as a way of measuring PDO. Herewith, the main attention is paid
to a method where proper polarization tomographic observables (PDO “measurers”) are used. The method is shown to be adequately
formulated by means of quasi-spectral tomographic expansions of PDO in special operator bases (given by finite sums of partially
orthogonal projectors), which determine probability distributions of tomographic observables as expansion coefficients. Matrix
versions of such “tomographic” PDO representations are obtained. In particular, projections of these expansions on quasiclassical
operator bases, determining polarization quasiprobability functions, are given. An example of experimental implementation
of polarization tomography of unpolarized light (biphoton radiation with hidden polarization) is analyzed. 相似文献