Motivations for Lightwave Communications

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通信工程专业英语Unit9：WDM

Application scenarios of WDM
• Backbone networks: WDM technology is widely used in backbone networks to provide high-speed and large-capacity data transmission services. It can effectively improve the network capacity and transmission speed, and is an important technology to support the development of the Internet.
The Development History of WDM
The first WDM system was developed in the early 1970s, but it was not widely used until the 1990s due to technical difficulties and high cost.
Frequency-division Multiplexing (FDM)
In FDM, different optical signals are generated at different frequencies,
allowing them to be transmitted simultaneously through the same
Communication Engineering Professional English Unit9: WDM
目录
• introduction • The basic principles of WDM • Key Technologies of WDM • The advantages and challenges

The behavior of light in photonic crystals

The behavior of light in photoniccrystalsHave you ever wondered how light interacts with matter? Photonic crystals are fascinating materials that can manipulate the behavior of light in a unique way. In this article, we will explore the physics behind photonic crystals and the potential applications of these materials.What are photonic crystals?A photonic crystal is an artificial material that has a periodic structure on the scale of the wavelength of light. This means that the material has a repeated pattern that can interact with light in a controlled way. The periodic structure of photonic crystals can be created using various techniques, such as lithography, self-assembly, and holography.How do photonic crystals affect light?Photonic crystals can affect light in several ways. One of the most important effects is the photonic bandgap. A photonic bandgap is a range of wavelengths of light that cannot propagate through the photonic crystal. This is similar to the electronic bandgap in semiconductors, which blocks the flow of electrons in certain energy regions.The photonic bandgap arises from the interference of the electromagnetic waves within the periodic structure of the photonic crystal. When the wavelength of light is comparable to the distance between the features of the crystal, the wave experiences constructive and destructive interference, leading to the formation of the bandgap. The size and location of the bandgap can be engineered by adjusting the periodicity and shape of the photonic crystal.Another effect that photonic crystals can have on light is the modification of its dispersion relation. The dispersion relation describes the relationship between the wavelength and the direction of light propagation in a certain material. In photonic crystals, the dispersion relation can be altered by introducing defects or changing thestructure of the crystal. This can lead to the formation of photonic modes that have novel properties, such as slow light or supercollimation.Applications of photonic crystalsThe unique properties of photonic crystals have led to a wide range of applications in science and technology. One of the most promising applications is in the field of optical computing. Photonic crystals can be used as waveguides and resonators to create compact and efficient devices for signal processing and communication.Another application of photonic crystals is in the field of solar energy. The bandgap of photonic crystals can be tuned to match the absorption spectrum of solar cells, leading to higher efficiency and reduced waste heat. Photonic crystals can also be used as anti-reflection coatings to enhance the absorption of light in solar panels.Photonic crystals also have potential applications in the field of sensing. The high sensitivity of photonic crystal sensors to changes in the refractive index or chemical composition of the surrounding environment can be used for the detection of biomolecules, gases, and pollutants.ConclusionIn conclusion, photonic crystals are fascinating materials that can manipulate the behavior of light in a controlled way. The photonic bandgap and modification of the dispersion relation are two of the most important effects that photonic crystals can have on light. The unique properties of photonic crystals have led to a wide range of applications in science and technology, including optical computing, solar energy, and sensing. As research in photonic crystals continues to advance, we can expect to see even more exciting applications in the future.。

单模光纤的基模计算

单模光纤的基模计算课程设计任务书学⽣姓名：专业班级：电⼦0902指导教师：洪建勋⼯作单位：信息⼯程学院题⽬: 单模光纤的基模计算初始条件：计算机、beamprop软件要求完成的主要任务:1、课程设计⼯作量：2周2、技术要求：（1）学习beamprop软件。

（2）设计⼀个单模光纤，分析单模光纤的电磁场分布，并研究输⼊光波波长、纤芯折射率、纤芯半径对单模光纤传输模式的影响。

（3）对单模光纤的电磁场分布和传输模式进⾏beamprop软件仿真⼯作。

3、查阅⾄少5篇参考⽂献。

按《武汉理⼯⼤学课程设计⼯作规范》要求撰写设计报告书。

全⽂⽤A4纸打印，图纸应符合绘图规范。

时间安排：对单模光纤进⾏设计仿真⼯作，完成课设报告的撰写。

提交课程设计报告，进⾏答辩。

指导教师签名：年⽉⽇系主任（或责任教师）签名：年⽉⽇⽬录摘要光纤通信是利⽤光导纤维来传输光波信号。

光纤通信作为现代通信的主要传输⼿段，在现代通信⽹中起着重要作⽤。

⾃光纤通信问世以来，整个通信领域发⽣了⾰命的变化，它使⾼速率、⼤容量的通信成为可能。

单模光纤是在给定的波长上，只能传输单⼀基模的光纤。

单模光纤相⽐于多模光纤可⽀持更长传输距离，更⼤的宽带，这对于⾼码速传输是⾮常重要的。

关键词：光纤，通信，基膜，宽带AbstractOptical fiber communication transmits light wave signals with fiber material. As the main means of transmission of the modern communication, optical fiber communication plays an important role in modern communication networks. Since the advent of optical fiber communication, the entire field of communications has undergone revolutionary changes, and it enableshigh-speed, large-capacity communication possible.Single-mode fiber can only transfer a single fundamental mode fiber in a given wavelength. Compared to multimode fiber, single-mode fiber can support longer transmission distance and the greater broadband. This is very important for high code rate transmission.Keywords: Optical fiber, communication, fundamental mode, broadban1 绪论光纤通信技术从光通信中脱颖⽽出，已成为现代通信的主要⽀柱之⼀，在现代电信⽹中起着举⾜轻重的作⽤。

Teleportation and spin squeezing utilizing multimode entanglement of light with atoms

a r X i v :q u a n t -p h /0511174v 1 17 N o v 2005Teleportation and spin squeezing utilizing multimode entanglement of light withatomsK.Hammerer 1,E.S.Polzik 2,3,J.I.Cirac 11Max-Planck–Institut f¨u r Quantenoptik,Hans-Kopfermann-Strasse,D-85748Garching,Germany2QUANTOP,Danish Research Foundation Center for Quantum Optics,DK 2100Copenhagen,Denmark3Niels Bohr Institute,DK 2100Copenhagen,Denmark We present a protocol for the teleportation of the quantum state of a pulse of light onto the collective spin state of an atomic ensemble.The entangled state of light and atoms employed as a resource in this protocol is created by probing the collective atomic spin,Larmor precessing in an external magnetic ﬁeld,oﬀresonantly with a coherent pulse of light.We take here for the ﬁrst time full account of the eﬀects of Larmor precession and show that it gives rise to a qualitatively new type of multimode entangled state of light and atoms.The protocol is shown to be robust against the dominating sources of noise and can be implemented with an atomic ensemble at room temperature interacting with free space light.We also provide a scheme to perform the readout of the Larmor precessing spin state enabling the veriﬁcation of successful teleportation as well as the creation of spin squeezing.PACS numbers:03.67.Mn,32.80.QkI.INTRODUCTIONQuantum teleportation -the disembodied transport of quantum states -has been demonstrated so far in sev-eral seminal experiments dealing with purely photonic [1]or atomic [2]systems.Here we propose a protocol for the teleportation of a coherent state carried initially by a pulse of light onto the collective spin state of ∼1011atoms.This protocol -just as the recently demonstrated direct transfer of a quantum state of light onto atoms [3]-is particularly relevant for long distance entanglement distribution,a key resource in quantum communication networks [4].Our scheme can be implemented with just coherent light and room-temperature atoms in a single vapor cell placed in a homogeneous magnetic ﬁeld.Existing proto-cols in Quantum Information (QI)with continuous vari-ables of atomic ensembles and light [4]are commonly de-signed for setups where no external magnetic ﬁeld is ap-plied such that the interaction of light with atoms meets the Quantum non-demolition (QND)criteria [5,6].In contrast,in all experiments dealing with vapor cells at room-temperature [3,7]it is,for technical reasons,ab-solutely essential to employ magnetic ﬁelds.In experi-ments [3,7]two cells with counter-rotating atomic spins were used to comply with both,the need for an exter-nal magnetic ﬁeld and the one for an interaction of QND character.So far it was believed to be impossible to use a single cell in a magnetic ﬁeld to implement QI protocols,since in this case -due to the Larmor precession -scat-tered light simultaneously reads out two non-commuting spin components such that the interaction is not of QND type.In this paper we do not only show that it is well possible to make use of the quantum state of light and atoms created in this setup but we demonstrate that -for the purpose of teleportation [8,9]-it is in factbetter to do so.As compared to the state resulting from the common QND interaction the application of an external magnetic ﬁeld enhances the creation of correlations between atoms and light,generating more and qualitatively new,multimode type of entanglement.The results of the paper can be summarized as follows:(i )Larmor precession in an external magnetic ﬁeld enhances the creation of entanglement when a collective atomic spin is probed with oﬀ-resonant light.The resulting entanglement involves multiple modes and is stronger as compared to what can be achieved in a comparable QND interaction.(ii )This type of entangled state can be used as a resource in a teleportation protocol,which is a simple generalization of the standard protocol [8,9]based on Einstein-Podolsky-Rosen (EPR)type of entanglement.For the experimentally accessible parameter regime the teleportation ﬁdelity is close to optimal.The protocol is robust against imperfections and can be implemented with state of the art technique.(iii )Homodyne detection of appropriate scattering modes of light leaves the atomic state in a spin squeezed state.The squeezing can be the same as attained from a comparable QND measurement of the atomic spin [10,11].The same scheme can be used for atomic state read-out of the Larmor precessing spin,necessary to verify successful teleportation.We would like to note that it was shown recently in [12]that the eﬀect of a magnetic ﬁeld can enhance the capacity of a quantum memory in the setup of two cells.Teleportation in the setup of a single cell without mag-netic ﬁeld was addressed in [13].The paper is organized as follows:The three points above are presented in sections II,III and IV,in this order.Some of the details in the calculations of sections III and IV are moved to appendices B and C.2II.INTERACTIONWe consider an ensemble of N at Alkali atoms with total ground state angular momentum F ,placed in a constant magnetic ﬁeld causing a Zeeman splitting of Ωand ini-tially prepared in a fully polarized state along x .The collective spin of the ensemble is then probed by an oﬀresonant pulse which propagates along z and is linearly polarized along x .Thorough descriptions of this inter-action and the ﬁnal state of light and atoms after the scattering can befoundin [14,15,16,17,18]and espe-cially in [19,20,21,22]for the speciﬁc system we have in mind.We derive the ﬁnal state here with a special focus on the eﬀects of Larmor precession and light prop-agation in order to identify the light modes which are actually populated in the scattering process.In appendix A we show that the interaction is ade-quately described by a HamiltonianH =H at +H li +V,H at =Ω√N ph N at F a 1σΓ/2A ∆where N ph is the over-all number of photons in the pulse,a 1is a constant characterizing the ground state’s vector polarizability,σis the scattering cross section,Γthe decay rate,∆the detuning and A the eﬀective beam cross section.Changing to a rotating frame with respect to H at by deﬁning X I (t )=exp(−iH at t )X exp(iH at t )and evaluat-ing the Heisenberg equations for these operators yields the following Maxwell-Bloch equations∂t X I (t )=κT cos(Ωt )p (0,t ),(2a)∂t P I (t )=κT sin(Ωt )p (0,t ),(2b)(∂t +c∂z )x (z,t )=κcT[cos(Ωt )P I (t )−sin(Ωt )X I (t )]δ(z ),(∂t +c∂z )p (z,t )=0,where ∂t (z )denotes the partial derivative with respect to t (z ).These equations have a clear interpretation.Light noise coming from the ﬁeld in quadrature with the classi-cal probe piles up in both,the X and P spin quadrature,but it alternately aﬀects only one or the other,changing with a period of 1/Ω.Conversely atomic noise adds to the in phase ﬁeld quadrature only and the signal comes alternately from the X and P spin quadrature.The out of phase ﬁeld quadrature is conserved in the interaction.To solve this set of coupled equations it is convenient to introduce a new position variable,ξ=ct −z ,to elim-inate the z dependence.New light quadratures deﬁned by ¯x (ξ,t )=x (ct −ξ,t ),¯p (ξ,t )=p (ct −ξ,t )also have a simple interpretation:ξlabels the slices of the pulse moving in and out of the ensemble one after the other,starting with ξ=0and terminating at ξ=cT .The Maxwell equations now read∂t ¯p (ξ,t )=0,(2c)∂t ¯x (ξ,t )=κcT[cos(Ωt )P I (t )−sin(Ωt )X I (t )]δ(ct −ξ).(2d)The solutions to equations (2a,2b,2c)areX I (t )=X I (0)+κT t 0d τcos(Ωτ)¯p (cτ,0),(3a)P I (t )=P I (0)+κT t 0d τsin(Ωτ)¯p (cτ,0),(3b)¯p (ξ,t )=¯p (ξ,0)(3c)and the formal solution to (2d)is¯x (ξ,t )=¯x (ξ,0)+(3d)+κT [cos(Ωξ/c )P I (ξ/c )−sin(Ωξ/c )X I (ξ/c )].As mentioned before,both atomic spin quadratures are aﬀected by light but,as is evident from the solutions for X (t ),P (t ),they receive contributions from diﬀerent and,in fact,orthogonal projections of the out-of-phase ﬁeld.As we will show in the following,the corresponding projections of the in-phase ﬁeld carry in turn the signal of atomic quadratures after the interaction.It is there-fore convenient to explicitly introduce operators for these modes [21].We deﬁne a cosine component before the in-teractionp in c = T Td τcos(Ωτ)¯p (cτ,0),(4a)x in c =TTd τcos(Ωτ)¯x (cτ,0)(4b)and a sine component p in s ,x ins with cos(Ωτ)replaced by sin(Ωτ).In frequency space these modes consist of spec-tral components at sidebands ωc ±Ωand are closely re-lated to the sideband modulation modes introduced in3[26]for the description of two photon processes.It is eas-ily checked that these modes are asymptotically canon-ical,[x in c ,p in c ]=[x in s ,p ins ]=i [1+O (n −10)]≃i ,and inde-pendent,[x in c ,p in s ]=O (n −10)≃0,if we assume n 0≫1for n 0=ΩT ,the pulse length measured in periods of Larmor precession.In terms of these modes the atomic state after the in-teraction X out =X I (T ),P out =P I (T )is given by X out =X in +κ2p inc ,P out =P in +κ2p ins .(5a)The ﬁnal state of cosine (sine)modes is de-scribed by x out c(s),p outc(s),deﬁned by equations (4)with ¯x (cτ,0),¯p (cτ,0)replaced by ¯x (cτ,T ),¯p (cτ,T )respec-tively.Since the out-of-phase ﬁeld is conserved we have triviallyp out c =p in c ,p out s =p in s .(5b)Deriving the corresponding expressions for the cosine andsine components of the ﬁeld in phase,x out c ,x outs ,raises some diﬃculties connected to the back action of light onto itself.This eﬀect can be understood by noting that a slice ξof the pulse receives a signal of atoms at a time ξ/c [see equation (3d)]which,regarding equations (3a,3b),in turn carry already the integrated signal of all slices up to ξ.Thus,mediated by the atoms,light acts back on itself.The technicalities in the treatment of this eﬀect are given in appendix B where we identify relevant ”back action modes”,x c ,1,p c ,1,x s ,1,p s ,1,in terms of which one can express x out c =x in c +κ2P in +κ√2 2p in s ,1,(5c)x out s=x in s −κ2X in−κ√2 2p in c ,1.(5d)The last two terms in both lines represent the eﬀect of back action,part of which involves the already deﬁned cosine and sine components of the ﬁeld in quadrature.The remaining part is subsumed in the back action modes which are again canonical and independent from all other modes.Equations (5)describe the ﬁnal state of atoms and the relevant part of scattered light after the pulse has passed the atomic ensemble and are the central result of this section.Treating the last terms in equations (5c,5d)as noise terms,it is readily checked by means of the separa-bility criteria in [27]that this state is fully inseparable,i.e.it is inseparable with respect to all splittings be-tween the three modes.For the following teleportation protocol the relevant entanglement is the one between atoms and the two light modes.Figure 1shows the von Neumann entropy E vN of the reduced state of atoms in its dependence on the coupling strength κand in com-parison with the entanglement created without magnetic ﬁeld in a pure QND interaction of atoms and light.The amount of entanglement is signiﬁcantly enhanced.FIG.1:Von Neumann Entropy of the reduced state of atoms versus coupling strength kappa for the state of equation 5(full line)and for the state generated without magnetic ﬁeld in a pure QND interaction (dashed line)with the same cou-pling strength.Application of a magnetic ﬁeld signiﬁcantly enhances the amount of light-atom entanglement.III.TELEPORTATION OF LIGHT ONTOATOMSIn this section we will show how the multimode entan-glement between light and atoms generated in the scat-tering process can be employed in a teleportation proto-col which is a simple generalization of the standard proto-col for continuous variable teleportation using EPR-type entangled states [8,9].We ﬁrst present the protocol and evaluate its ﬁdelity and then analyze its performance un-der realistic experimental conditions.A.Basic protocolFigure 2depicts the basic scheme which,as usually,consists of a Bell measurement and a feedback operation.Input The coherent state to be teleported is encoded in a pulse which is linearly polarized orthogonal to the classical driving pulse and whose carrier frequency lies at the upper sideband,i.e.at ωc +Ω.The pulse envelope has to match the one of the classical pulse.As is shown in appendix B,canonical operators y,q with [y,q ]=i de-scribing this mode can conveniently be expressed in terms of cosine and sine modulation modes,analogous to equa-tions (4),deﬁned with respect to the carrier frequency.One ﬁndsy =12(y s +q c ),q =−12(y c −q s ).(6)A coherent input amounts to having initially ∆y 2=∆q 2=1/2and an amplitude y , q with mean photon number n ph =( y 2+ q 2)/2.Bell measurement This input is combined at a beam splitter with the classical pulse and the scattered light.At the ports of the beam splitter Stokes vector compo-nents S y and S z are measured by means of standard po-larization measurements.Given the classical pulse in xFIG.2:Scheme for teleportation of light onto atoms:As de-scribed in section II,a classical pulse(linearly polarized along x)propagating along the positive z direction is scattered oﬀan atomic ensemble contained in a glass cell and placed in a constant magneticﬁeld B along x.Classical pulse and scat-tered light(linearly polarized along y)are overlapped with a with a coherent pulse(linearly polarized along z)at beam splitter B S.By means of standard polarization measurements Stokes vector components S y and S z are measured at one and the other port respectively,realizing the Bell measurement. The Fourier components at Larmor frequencyΩof the corre-sponding photocurrents determine the amount of conditional displacement of the atomic spin which can be achieved by ap-plying a properly timed transverse magneticﬁeld b(t).See section III A for details.polarization this amounts to a homodyne detection of in-and out-of-phaseﬁelds of the orthogonal polarization component.The resulting photocurrents are numerically demodulated to extract the relevant sine and cosine com-ponents at the Larmor frequency[20].Thus one eﬀec-tively measures the commuting observables˜x c=12 x out c+y c,˜x s=12 x out s+y s ,(7)˜q c=12 p out c−q c ,˜q s=12 p out s−q s .Let the respective measurement results be given by ˜Xc,˜X s,˜Q c and˜Q s.Feedback Conditioned on these results the atomic state is then displaced by an amount˜X s−˜Q c in X and −˜X c−˜Q s in P.This can be achieved by means of two fast radio-frequency magnetic pulses separated by a quar-ter of a Larmor period.In the ensemble average theﬁnal state of atoms is simply given byXﬁn=X out+˜x s−˜q c,Pﬁn=P out−˜x c−˜q s.(8)This description of feedback is justiﬁed rigorously in ap-pendix C.Relating these expressions to input operators,weﬁnd by means of equations(5),(6)and(7)Xﬁn= 1−κ√2 2p in c+12x in s−16 κ2 P in−121−κ√√2 2p in s,1+q.(9b)This is the main result of this section.Teleportationﬁdelity Taking the mean of equations (9)with respect to the initial state all contributions due to input operators and back action modes vanish such that Xﬁn = y and Pﬁn = q .Thus,the am-plitude of the coherent input light pulse is mapped on atomic spin quadratures as desired.In order to prove faithful teleportation also the variances have to be con-served.It is evident from(9)that theﬁnal atomic spin variances will be increased as compared to the coherent input.These additional terms describe unwanted excess noise and have to be minimized by a proper choice of the couplingκ.As aﬁgure of merit for the telepor-tation protocol we use theﬁdelity,i.e.squared over-lap,of input andﬁnal state.Given that the means are transmitted correctly theﬁdelity is found to be F= 2 (1+2(∆Xﬁn)2)(1+2(∆Pﬁn)2) −1/2.The variances of theﬁnal spin quadratures are readily calculated tak-ing into account that all modes involved are independent and have initially a normalized variance of1/2.In this way a theoretical limit on the achievableﬁdelity can be derived depending solely on the coupling strengthκ.In ﬁgure3we take advantage of the fact that the amount of entanglement between light and atoms is a monotonously increasing function ofκsuch that we can plot theﬁ-delity versus the entanglement.This has the advantage that we can compare the performance of our teleporta-tion protocol with the canonical one[8,9]which uses a two-mode squeezed state of the same entanglement as a resource and therefore maximizes the teleportationﬁ-delity for the given amount of entanglement.No physical state can achieve a higherﬁdelity with the same entan-glement.This follows from the results of[30]where it was shown that two-mode squeezed states minimize the EPR variance(and therefore maximize the teleportation ﬁdelity)for given entanglement.The theoreticalﬁdelity achievable in our protocol is maximized forκ≃1.64cor-responding to F≃.77.But also for experimentally more feasible values ofκ≃1can theﬁdelity well exceed the classical limit[28,29]of1/2and,moreover,compari-son with the values achievable with a two-mode squeezed state shows that our protocol is close to optimal.FIG.3:(a)Theoretical limit on the achievableﬁdelity F ver-sus entanglement between atoms and light measured by the von Neumann entropy E vN of the reduced state of atoms.The grey area is unphysical.For moderate amounts of entangle-ment our protocol is close to optimal.(b)Coupling strengthκversus entanglement.The dashed lines indicate the maximal ﬁdelity of F=.77which is achieved forκ=1.64.B.Noise eﬀects and Gaussian distributed input Under realistic conditions the teleportationﬁdelity will be degraded by noise eﬀects like decoherence of the atomic spin state,light absorption and reﬂection losses and also because the coupling constantκis experimen-tally limited to valuesκ≃1.On the other hand the classicalﬁdelity bound to be beaten will be somewhat higher than1/2since the coherent input states will nec-essarily be drawn according to a distribution with aﬁnite width in the mean photon number¯n.In this section we analyze the eﬃciency of the teleportation protocol un-der these conditions and show that it is still possible to surpass any classical strategy for the transmission and storage of coherent states of light[28,29].During the interaction atomic polarization decays due to spontaneous emission and collisional relaxation.In-cluding a transverse decay theﬁnal state of atoms is given byX out= √βf X,(10a) P out= √βf P.(10b)as follows from the discussion in appendix A.βis the atomic decay parameter and f X,f P are Langevin noise operators with zero mean.Their variance is experimen-tally found to be close to the value corresponding to a coherent state such that f2X = f2P =1/2.Light absorption and reﬂection losses can be taken into account in the same way asﬁnite detection eﬃciency.For example the statistics of measurement outcome˜X s will not stem from the signal mode˜x s alone but rather from the noisy mode√ǫfx,swhereǫis the photon loss parameter and f x,s is a Langevin noise operator of zero mean and variance f2x,s =1/2.Analogous expres-sions have to be used for the measurements of˜x c,˜q s and ˜q c which will be adulterated by Langevin terms f x,c,f q,s and f q,c respectively.In principle each of the measure-ment outcomes can be fed back with an independently chosen gain but for symmetry reasons it is enough to distinguish gain coeﬃcients g x,g q for the measurement outcomes of sine and cosine components of x and q re-spectively.Including photon loss,ﬁnite gain and atomic decay,as given in(10),equations(8),describing theﬁnal state of atoms after the feed back operation,generalize toXﬁn= βf X+g x √ǫf x,s (11a)−g q √ǫf q,c ,Pﬁn= βf P−g x √ǫf x,c (11b)−g q √ǫf q,s .For non unit gains a given coherent amplitude( y , q ) will not be perfectly teleported onto atoms and the cor-respondingﬁdelity will be degraded by this mismatch according toF( y , q )=2[1+2(∆Xﬁn)2][1+2(∆Pﬁn)2]·exp−( y − Xﬁn )21+2(∆Pﬁn)2 .If the input amplitudes are drawn ac-cording to a Gaussian distribution p( y , q )=exp[−( y 2+ q 2)/2¯n]/2π¯n with mean photon number¯n the averageﬁdelity[with respect to ( y , q )]is readily calculated.The exact expression in terms of initial operators can then be derived by means of equations(5),(6),(7)and(11)but is not particularly enlightening.Inﬁgure4we plot the averageﬁdelity, optimized with respect to gains g x,g q,in its dependence on the atomic decayβfor various values of photon loss ǫ.We assume a realistic valueκ=0.96for the coupling constant and a mean number of photons¯n=4for the distribution of the coherent input.For feasible values ofβ,ǫ 0.2the averageﬁdelity is still well above the classical bound on theﬁdelity[28,29].This proves that the proposed protocol is robust against the dominating noise eﬀects in this system.The experimental feasibility of the proposal is illus-trated with the following example.Consider a sam-ple of N at=1012Cesium atoms in a glass cell placed in a constant magneticﬁeld along the x-direction caus-ing a Zeeman splitting ofΩ=350kHz in the F=4 ground state multiplet.The atoms are pumped into m F=4and probed on the D2(F=4→F′=3,4,5)FIG.4:(a)Averageﬁdelity achievable in the presenceof atomic decayβ,reﬂection and light absorption lossesǫ=8%,12%,16%,couplingκ=0.96and Gaussian dis-tributed input states with mean photon number¯n=4.Theﬁ-delity benchmark is in this case5/9(dashed line).(b)Respec-tive optimal values for gains g x(solid lines)and g q(dashedlines).transition.The classical pulse contains an overall num-ber of N ph=2.51013photons,is detuned to the blueby∆=1GHz,has a duration T=1ms and can have an eﬀective cross section of A≃6cm2due to thermalmotion of atoms.Under these conditions the tensor polarizability can be neglected(∆/ωhfs≃10−1).Also n0=ΩT=350justiﬁes the use of independent scatter-ing modes.The couplingκ≃1and the depumping ofground state populationη≃10−1as desired.IV.SPIN SQUEEZING AND STATE READ-OUTIn this section we present a scheme for reading out either of the atomic spin components X,P by means of a probe pulse interacting with the atoms in the one way as described in section II.The proposed scheme allows one,on the one hand,to verify successful receipt of the coherent input subsequent to the teleportation protocol of section III and,on the other hand,enables to generate spin squeezing if it is performed on a coherent spin state. It is well known[15,31]and was demonstrated exper-imentally[10,11]that the pure interaction V,as given in equation(1),can be used to perform a QND measure-ment of either of the transverse spin components.At ﬁrst sight this seems not to be an option in the scenario under consideration since the local term H at,account-ing for Larmor precession,commutes with neither of the spin quadratures such that the total Hamiltonian does not satisfy the QND criteria[5,6].As we have shown in section II Larmor precession has two eﬀects:Scattered light is correlated with both transverse components andsuﬀers from back action mediated by the atoms.Thus, in order to read out a single spin component one has to overcome both disturbing eﬀects.Our claim is that this can be achieved by a simultane-ous measurement of x outc,p outs,p outs,1or x outs,p outc,p outc,1 if,respectively,X or P is to be measured.In the follow-ing we consider in particular the former case but every-thing will hold with appropriate replacements also for a measurement of P.As shown inﬁgure5the set of observablesx outc,p outs,p outs,1can be measured simultaneously by a measurement of Stokes component S y after aπ/2rota-tion is performed selectively on the sine component of the scattered light.The cosine component of the corre-sponding photocurrent will give an estimate of x outcandthe sine component of p outs.Multiplying the photocur-rent’s sine component by the linear function deﬁning the back action mode,equation(B1),will give in additionan estimate of p outs,1.Note that theﬁeld out of phase is conserved in the interaction such thatp outs,1=p in s,1,p outc,1=p in c,1,(12) i.e.the results will have shot noise limited variance.It is then evident from equation(5c)that the respective photocurrents together with an a priori knowledge ofκare suﬃcient to estimate the mean X .The conditional variances after the indicated measure-ments are∆X2|{x out c,p out s,p out s,1}=(∆X in)222,(13b)corresponding to a pure state.Obviously the variance in X is squeezed by a factor(1+κ2/2)−1.Note that the squeezing achieved in a QND measurement without magneticﬁeld but otherwise identical parameters is given by(1+κ2)−1.From this we conclude that the quality of the estimate for X ,as measured f.e.by input-output coeﬃcients known from the theory of QND measurements [5,6],can be the same as in the case without Larmor precession albeit only for a higher couplingκ. Equations(13)are conveniently derived by means of the formalism of correlation matrices [32].For the operator valued vector R=(X,P, x c,p c,x s,p s,x c,1,p c,1,x s,1,p s,1)equations(5),(12) and(B2)deﬁne via R out=S(κ) R in a symplectic linear transformation S(κ).The contributions of p in c,2andp in s,2to x outs,1and x outc,1as given in(B2)are treated as noise and do not contribute to the symplectic trans-formation S but enter the input-output relation for the correlation matrix as an additional noise term as follows.The correlation matrix is as usually deﬁned byγi,j=tr{ρ(R i R j+R j R i)}.The initial state is then an10×10identity matrix and theﬁnal state is γout=S(κ)S(κ)T+γnoise where the diagonal matrixFIG.5:Scheme for spin measurement:After the scattering a π/2rotation is performed on the scattered light modulated at the Larmor frequency such as to aﬀect only the sine(cosine) component.Standard polarization measurement of S y and appropriate postprocessing allows to read out the mean of X(P),leaving the atoms eventually in a spin squeezed state.γnoise=diag[0,0,0,0,0,0,1,0,1,0](κ/2)4/15accountsfor noise contributions due correlations to second order back action modes c.f.equations(B2).In order to evaluate the atomic variances after a measurement ofx out c ,p outs,p outs,1the correlation matrixγout is split upinto blocks,γout= A C C T Bwhere A is the2×2subblock describing atomic variances. Now,the state A′after the measurement can be found by evaluating[32]A′=A−limx,n→∞C1(∆−iΓ/2) a01+ia1 F×(A3)8 with real dimensionless coeﬃcients a j of order unity andΓthe excited states’decay rate.The non-hermitian partof the resulting Hamilton operator describes the eﬀectof light absorption and loss of ground state populationdue to depumping in the course of interaction.In thefollowing we will focus on the coherent interaction and,for the time being,take into account only the hermitiancomponent.The eﬀects of light absorption and atomicdepumping are treated below.Coherent interaction Since scattering of light occurspredominantly in the forward direction[22]it is legiti-mate to adopt a one dimensional model such that the(negative frequency component of the)electricﬁeld prop-agating along z is given byE(−)(z,t)=E(−)(z) ey+E(−)(z,t) e xE(−)(z)=ρ(ωc) b dωa†(ω)e−ikzE(−)(z,t)=ρ(ωc)ωc/4πǫ0Ac and A denotes the pulse’scross sectional area,N ph the overall number of photonsin the pulse and T its duration.We restrict theﬁeldin x polarization to the classical probe pulse,since onlythe coupling of atoms to the y polarization is enhancedby the coherent probe.Furthermore we implicitly assumefor the classical pulse a slowly varying envelope such thatit arrives at z=0at t=0and is then constant fora time bining this expression for theﬁeld withexpressions(A2)and(A3)for the atomic polarizability inequation(A1)yieldsV=−i κ4πJTbdω d zj(z) a(ω)e−i[(k c−k)z−ωc t]−h.c.where we deﬁned a dimensionless coupling constant κ=N ph Ja1σΓ/2A∆withσthe scattering cross sec-tion on resonance.We now deﬁneﬁeld quadratures for spatially localized modes[24,25]asx(z)=14πbdω a(ω)e−i(k c−k)z+h.c. ,(A4a)p(z)=−i4πbdω a(ω)e−i(k c−k)z−h.c. (A4b)with commutation relations[x(z),p(z′)]=icδ(z−z′) where the delta function has to be understood to have a width on the order of c/b.Since we assumed thatΩ≪b, the time it takes for such a fraction of the pulse to cross the ensemble is much smaller than the Larmor period 1/Ω.During the interaction with one of these spatiallylocalized modes the atomic state does not change appre-ciable and we can simplify the interaction operator to V= κ(JT)−1/2J z p(0)where J z= i F(i)z and we as-sumed that the ensemble is located at z=0and changedto a frame rotating at the carrier frequencyωc.A last approximation concerns the description of theatomic spin state.Initially the sample is prepared in acoherent spin state with maximal polarization along x, i.e.in the eigenstate of J x with maximal eigenvalue J. We can thus make use of the Holstein-Primakoﬀapprox-imation[23]which allows to describe the spin state as a Gaussian state of a single harmonic oscillator.The ﬁrst step is to express collective step up/down operators (along x),J±=J y±iJ z,in terms of bosonic creation and annihilation operators,[b,b†]=11,asJ+=√11−b†b/2J b,J−=√11−b†b/2J. It is easily checked that these operators satisfy the correct commutation relations[J+,J−]=2J x if one identiﬁes J x=J−b†b.The fully polarized initial state thus corresponds to the ground state of the harmonic oscillator.Note that this map-ping is exact.Under the condition that b†b ≪J one can approximate J+≃√2Jb†and therefore J z≃−i 2and P=−i(b−b†)/√。

光场调控英语

Light Field Manipulation: A Revolution inOptics and Its ApplicationsIn the realm of optics, light field manipulation has emerged as a cutting-edge technology, promising unprecedented control over the propagation and interaction of light. This field, often referred to as "light field engineering" or "light field调控," involves the precise manipulation of the amplitude, phase, polarization, and wavelength of light, enabling the creation of novel optical phenomena and devices with unique functionalities.The concept of light field manipulation dates back to the early days of optics, but significant progress has been made in recent years due to advancements in nanotechnology, materials science, and computational methods. This has led to the development of a range of innovative optical devices and systems that have revolutionized various fields, including imaging, communications, and energy conversion. One of the most significant applications of light field manipulation is in the field of computational imaging. By precisely controlling the light field, researchers have been able to create novel imaging systems that offerunprecedented resolution, depth of field, and dynamic range. These systems, known as light field cameras or plenoptic cameras, capture not only the intensity of light but alsoits direction, enabling the reconstruction of the three-dimensional scene with unprecedented fidelity.Another important area where light field manipulation has found widespread application is in optical communications. By manipulating the phase and polarizationof light, researchers have been able to develop high-capacity optical fiber communication systems that can transmit information at unprecedented speeds and distances. These systems are critical for enabling the global internet and high-speed data networks.In addition to its applications in imaging and communications, light field manipulation is also finding uses in areas such as energy conversion and quantum information processing. By controlling the light field at the nanoscale, researchers have been able to developefficient solar cells and photodetectors that convert sunlight into electricity with unprecedented efficiency. Similarly, the precise control of light-matter interactionsusing light field manipulation offers the potential for novel quantum devices and algorithms that could revolutionize computing and information processing.The future of light field manipulation looks even more promising. With the continued development of advanced materials and nanotechnologies, as well as the increasing availability of powerful computational resources, we can expect to see even more innovative applications of light field manipulation in areas such as biomedicine, security, and defense.Overall, light field manipulation represents a significant leap forward in our ability to control and manipulate light. Its impact on optics and its applications is likely to be profound, enabling the creation of novel devices and systems with unprecedented capabilities and functionalities. As we continue to explore the frontiers of light field manipulation, we stand on the cusp of a new era in optics that will transform our world in ways we can only imagine.**光场调控：光学领域的革命及其应用**在光学领域，光场调控已经成为一项尖端技术，它承诺对光的传播和相互作用进行前所未有的控制。

大学-光学的培训教材

2
Historical Overview
Discover the milestones and key discoveries that have shaped the field of optics throughout history.
3
Modern Applications
Learn about the wide range of modern applications of optics, from telecommunications to imaging technology.
Endoscopy
Learn how fiber optics enables minimally invasive procedures and allows doctors to visualize internal organs.
Polarization of Light
1 Polarizing Filters
Future Trends in Optics
Quantum Optics
Explore the emerging field of quantum optics and its revolutionary applications in computing, communication, and cryptography.
Diagnostic Imaging Laser Surgery
Discover how optics plays a vital role in medical imaging techniques like X-rays, CT scans, and MRI.
Explore the use of lasers in various surgical procedures, including laser eye surgery and skin treatments.

Optical Fiber Communications光纤通讯知识课件

– Region originally used for first single-mode fibers
• Extended band (E-band): 1360 to 1460 nm
– Operation extends into the high-loss water-peak region
School of Electrical and Electronic Enginesering, Hubei University of Technology
School of Electrical and Electronic Enginesering, Hubei University of Technology
• In a vacuum the speed of light c is equal to the wavelength λ times the frequency ν, so that c=λν
• The relationship between the energy of a photon and its frequency (or wavelength) is determined by Planck’s Law E = hν where h = 6.63 × 10–34 J-s = 4.14 × 10–15 eV-s is Planck’s constant.
• There is an extremely large choice of remotely accessible programs and information databases
7
1.1 Motivations (2)
Advantages of optical fibers

微波技术相关国际刊物投稿指南

微波技术相关国际刊物投稿指南电子与通信技术文献（德国）内容范围刊载天线与传输、固态电子学、信息论、信息技术、微波通信与网络、电路与系统理论、量子电学等方面的原始论文、简讯与书评。

投稿地址Indexed inManaging Editor Eng.Ind.Dr.Ing.R.Pauli,Fischmuhle3 Sci.AbstrD-84419 Schwindegg,Germany Sci.Cit.Ind.IEE Proceedings-A :Science ,Measurement and Technology 英国电气工程师学会志，A辑：科学，测量与技术内容范围刊载材料科学、电学、磁学、测量仪器、工程管理、设计、医学与生物医学工程系统的应用等方面的论文。

投稿地址Indexed inThe Managing Editor Math.R.IEE Proceedings-Science, Measurement and Tech. Met. Abstr.Publishing Dept., Inst. of Electrical Engineers Sic. Abstr.Michael Faraday House, Six Hills Way, Stevenage Sci. Cit. Ind.Herts.SG1 2AY,United Kingdom.IEE Proceedings-B: Electric Power Applications 英国电气工程师学会志，B辑：电力应用内容范围刊载电力设备的设计以及电力工业与非工业领域的应用与开发方面的论文。

投稿须知See IEE Proceedings-A Indexed in投稿地址Math.R.The Managing Editor Sci.Abstr.IEE Proceedings-Electric Power Applications Sci. Cit. Ind.Publishing Dept., Institution of Electrical EngineersMichael Faraday House, Six Hills Way, StevenageHerts. SG1 2AY,United KingdomIEE Proceedings-C: Generation, Transmission and Distribution 英国电气工程师学会杂志，C辑：发电，输电与配电内容范围刊载发电机的操纵与控制、发电机辅助生产线与系统、电力系统设计，操作与控制、电力系统生产线及测量方面的论文。

光学通信英语作文模板范文

光学通信英语作文模板范文Optical Communication。

With the rapid development of technology, optical communication has become an essential part of our daily lives. It has revolutionized the way we communicate, providing faster, more reliable, and secure transmission of information. In this article, we will explore the basics of optical communication, its advantages, and its applications in various fields.First and foremost, let's understand what optical communication is. Optical communication is a method of transmitting information using light as the carrier. It involves the use of optical fibers, which are thin, flexible, and transparent fibers made of glass or plastic. These fibers are capable of transmitting large amounts of data over long distances at high speeds. The process of optical communication involves converting electrical signals into optical signals, transmitting these signalsthrough the optical fibers, and then converting them back into electrical signals at the receiving end.One of the key advantages of optical communication is its high bandwidth. Optical fibers have a much larger bandwidth compared to traditional copper wires, allowing them to transmit a greater amount of data in a shorter amount of time. This makes optical communication ideal for applications that require high-speed data transmission, such as internet connections, telecommunication networks, and data centers.Another advantage of optical communication is its low signal loss. Optical fibers have the ability to transmit signals over long distances with minimal loss of signal strength. This is due to the fact that light travels through the fibers in a straight line, without being affected by external interference or environmental factors. As a result, optical communication offers a more reliable and stable transmission of information compared to other communication methods.Furthermore, optical communication is also highly secure. Since light signals are transmitted through the fibers, they are not susceptible to electromagnetic interference or eavesdropping. This makes optical communication an ideal choice for transmitting sensitiveand confidential information, such as financial transactions, government communications, and military operations.The applications of optical communication are vast and diverse. In the field of telecommunications, optical communication is used to transmit voice, data, and video signals over long distances, providing high-speed internet connections, cable television, and telephone services to consumers and businesses. In addition, optical communication is also used in the healthcare industry for medical imaging, diagnostics, and remote patient monitoring. It is also widely used in the transportation industry for traffic management, vehicle tracking, and navigation systems.Moreover, optical communication plays a crucial role inthe field of scientific research and education. It is used in laboratories and research facilities for the transmission of data from scientific instruments, such as telescopes, microscopes, and particle accelerators. In addition, optical communication is used in educational institutions for distance learning, online courses, and virtual classrooms.In conclusion, optical communication has revolutionized the way we transmit information, offering faster, more reliable, and secure communication methods. Its high bandwidth, low signal loss, and security make it an ideal choice for a wide range of applications in various fields. As technology continues to advance, the potential for optical communication to further improve and expand its capabilities is limitless. It is clear that optical communication will continue to play a vital role in shaping the future of communication and technology.。

微波反射技术的英文表达

微波反射技术的英文表达Title: Microwave Reflection Technology: Bridging the Gap Between Theory and ApplicationMicrowave reflection technology, a cornerstone in the field of electromagnetic engineering, plays a pivotal role in modern communication systems and radar technology. This essay delves into the core principles of microwave reflection, its diverse applications, and the challenges it presents to researchers and engineers.At the heart of microwave reflection technology lies the concept of electromagnetic wave reflection. When microwaves encounter a surface, a portion of the energy is reflected back, while the rest is absorbed or transmitted. The behavior of these reflected waves is governed by the laws of physics, particularly the Fresnel equations, which describe the reflection and transmission coefficients at the interface between two media.The reflection coefficient, denoted by Γ, is a complex number that quantifies how much of the incident wave is reflected. It depends on the properties of the media, such as the dielectric constant and conductivity, as well as the angle ofincidence and the polarization of the wave. Understanding and manipulating these variables is crucial for optimizing the performance of microwave systems.The applications of microwave reflection technology span various domains, each leveraging its unique properties to solve complex problems.Radar Technology: Radar systems, which rely on microwave reflection for object detection, have been revolutionized by the ability to analyze reflected signals. By measuring the phase and amplitude of the reflected signals, radar can accurately determine the position, velocity, and even the shape of distant objects, making it indispensable in military, meteorological, and civilian navigation applications Microwave Imaging: In medical diagnostics, microwave reflection is used in imaging technologies such as microwave tomography and radar imaging. These systems can detect anomalies in the human body by analyzing the reflected microwave signals, offering a non-invasive alternative toX-rays.Quality Control in Manufacturing: In industries that require non-destructive testing, microwave reflection is used to inspect materials for defects and ensure quality. Thetechnology can detect changes in the material's properties, such as moisture content and density, without causing damage.Despite its widespread applications, microwave reflection technology faces significant challenges that hinder its full potential. These include the complexity of designing systems that can efficiently manipulate microwave signals, the need for accurate models to predict wave behavior in complex environments, and the integration of microwave technology into emerging fields such as 5G communications and quantum computing.Future advancements in microwave reflection technology will likely focus on miniaturization, integration with other technologies, and the development of intelligent systems capable of dynamic adaptation to changing conditions. Research into new materials and manufacturing techniques will also play a critical role in overcoming current limitations and expanding the capabilities of microwave systems.In conclusion, microwave reflection technology, with its foundational principles and broad applications, is a vital area of research and development. As we continue to push the boundaries of what is possible, the future of microwavereflection technology promises to be as exciting as it is transformative.。

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• • • •
Short band (S-band): 1460 to 1530 nm (shorter than C-band) Conventional band (C-band): 1530 to 1565 nm (EDFA region) Long band (L-band): 1565 to 1625 nm (longer than C-band) Ultra-long band (U-band): 1625 to 1675 nm
• Increase in PC storage capacity and processing power
– 20G hard drives were fine around 2000; now standard is 160G – Laptops ran at 300 MHz; now the speed is over 3 GHz
• More and more bandwidth-hungry services are appearing
– Web searching, home shopping, high-definition interactive video, remote education, telemedicine and e-health, high-resolution editing of home videos, blogging, and large-scale high-capacity escience and Grid computing
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Motivations (1)
• Lifestyle changes from Internet growth and use
– Average phone call lasts 3 minutes – Average Internet session is 20 minutes
• There is an extremely large choice of remotely accessible programs and information databases
2014-8-12
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Motivations (2)
Advantages of optical fibers
• Long Distance Transmission: The lower transmission losses in fibers compared to copper wires allow data to be sent over longer distances. • Large Information Capacity: Fibers have wider bandwidths than copper wires, so that more information can be sent over a single physical line. • Small Size and Low Weight: The low weight and the small dimensions of fibers offer a distinct advantage over heavy, bulky wire cables in crowded underground city ducts or in ceiling-mounted cable trays. • Immunity to Electrical Interference: The dielectric nature of optical fibers makes them immune to the electromagnetic interference effects. • Enhanced Safety: Optical fibers do not have the problems of ground loops, sparks, and potentially high voltages inherent in copper lines. • Increased Signal Security: An signal is well-confined within the fiber and an opaque coating around the fiber absorbs any signal emissions.
Motivations for Lightwave CommunicationsE-Band S-Band C-Band L-Band U-Band 1260 1360 1460 1530 1565 1625 1675
Wavelength (nm)
2014-8-12
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• Original band (O-band): 1260 to 1360 nm
– Region originally used for first single-mode fibers
• Extended band (E-band): 1360 to 1460 nm
– Operation extends into the high-loss water-peak region