Polarization diversity detection performance of 2.5-Gb/s CPFSKregenerators intended for field use

2.5-Gb/s continuous-phase frequency-shift keying (CPFSK) regenerators are studied in laboratory and field experiments. A polarization diversity receiver is constructed with newly designed automatic gain and automatic frequency controllers. It achieves a sensitivity fluctuation of about 0.5 dB against all input signal polarization states. The automatic gain control is used in the intermediate-frequency circuits of the receiver and stably operates over 15 dB of input signal power variation. The automatic frequency control (AFC) is sufficiently stable to withstand a 30-kHz input signal polarization variation between two orthogonal linear polarization modes. AFC stability is maintained even if the environmental temperature of the laser diode modules fluctuates from 15 to 35 C. The polarization fluctuation in both cases results in only 0.1-dB degradation in receiver sensitivity     

Modulation and demodulation techniques in optical heterodyne PSKtransmission systems

Modulation and demodulation techniques are described for an optical PSK heterodyne transmission system operating at 560 Mb/s and 1.2 Gb/s. Performance limitations affecting the receiver sensitivity in a 1.2-Gb/s DPSK system, such as laser phase noise, phase modulation depth, IF center frequency deviation, and local laser power, are studied. High receiver sensitivities for PSK systems were achieved. The applicability of the Mach-Zehnder modulator as a phase modulator for 1.2-Gb/s DPSK is also demonstrated. A 1.2-Gb/s DPSK transmission of over 100 km, using polarization diversity with novel polarization-insensitive automatic frequency control in an attempt to overcome signal fading caused by polarization fluctuation in the transmitting fiber, is also described. A receiver sensitivity of less than -42.8 dBm and varying within 1.4 dB for all states of polarization was achieved. A multichannel high-definition TV (HDTV) transmission experiment using a DPSK polarization-diversity tunable receiver is described     

雷达极化问题和铁氧体变极化技术

描述了雷达极化问题的基本概念,提出了两类铁氧体全(变)极化器的机制。从理论上解决了这种器件的收发功能,并介绍了它在极化雷达中可实现极化扫描和接收的功能。     

Modulating the Ferromagnet/Molecule Spin Hybridization Using an Artificial Magnetoelectric

Spin‐polarized charge transfer at the interface between a ferromagnetic (FM) metal and a molecule can lead to ferromagnetic coupling and to a high spin polarization at room temperature. The magnetic properties of these interfaces can not only alter those of the ferromagnet but can also stabilize molecular spin chains with interesting opportunities toward quantum computing. With the aim to enhance an organic spintronic device's functionality, external control over this spin polarization may thus be achieved by altering the ferromagnet/molecule interface's magnetic properties. To do so, the magnetoelectric properties of an underlying ferroelectric/ferromagnetic interface are utilized. Switching the ferroelectric polarization state of a PbZr_0.2Ti_0.8O₃ (PZT) bottom layer within a PZT/Co/FePc‐based (Pc ‐ phthalocyanine) device alters the X‐ray magnetic circular dichroism of the Fe site within the phthalocyanine molecular top layer. Thus, how to electrically alter the magnetic properties of an interface with high spin polarization at room temperature is demonstrated. This expands electrical control over spin‐polarized FM/molecule interfaces, which is first demonstrated using ferroelectric molecules, to all molecular classes.     

38-krad/s 3.8-Grad Broadband Endless Optical Polarization Tracking Using LiNbO$_{3}$ Device

We demonstrate automatic endless optical polarization tracking over 3.8 Grad at up to 38-krad/s control speed with mean/maximum polarization errors of 0.068/0.185 rad. Without polarization fluctuations, mean/maximum polarization errors are 0.05/0.1 rad. Small-signal control time constant is about 2 $mu$s. Function is maintained over the wavelength range 1505–1570 nm.      

Analysis of Degree of Polarization as a Control Signal in PMD Compensation Systems Aided by Polarization Scrambling

The performance of degree of polarization (DOP) is investigated as a control signal in polarization-mode dispersion (PMD) compensation systems aided by polarization scrambling. The relation between the input and output polarization states of a signal propagating through a polarization scrambler and a PMD-induced optical fiber is described by a 3 $,times,$3 Stokes transfer matrix. The average DOP of the output signal over a period of polarization scrambling is derived as an alternative to the conventional DOP-based control signal, i.e., minimum DOP. In the presence of first- and all-order PMDs, the performance of the average and minimum DOPs in monitoring of differential group delay (DGD) for different data formats (i.e., RZ and NRZ) is evaluated. The performance of the two control signals are further investigated by calculating the outage probability of a feedforward first-order PMD compensation system. The results show that the average DOP outperforms the minimum DOP and also gives a wider DGD monitoring range.      

Radiation and depolarization of multibeam offset reflectors fed bymultimode pyramidal horns

The depolarization contents of the radiating currents on the surface of a multibeam offset parabola are minimized, for different beams, using multimode pyramidal horn feeds. Small percentages of the TE ₁₁ and TE₂₀ modes are used, respectively, for vertical and horizontal polarizations, in combination with the fundamental TE₁₀ mode. The mixture ratio increases for feeds with higher pointing angles to the reflector surface. Additionally, the beams that are away from the symmetry plane, suffer changes in the polarization bearing angles, which increase for further beams. Far radiated fields are computed from the depolarization minimized reflector currents, using both the orthogonal components of the linear polarization, for a 3M offset reflector with a diameter-to-focal-length ratio of unity, at 4 GHz. Minimized depolarization levels of around -40 dB for vertical polarization, and of around -34 dB for horizontal polarization are found. The linearly and circularly polarized diagonal horn feeds yield symmetric pencil beams. Their polarization, however, is quite high and difficult to control for linear polarization. For circular polarization, to the contrary, the depolarization is quite low     

Liquid-crystal polarization stabilizers on fiber arrays

We have built polarization stabilizer arrays of ultrathin liquid-crystal (LC) polarization controller (PC) arrays and a tap-type photodetector array on a fiber array. The ultrathin (35-/spl mu/m-thick) LC cells are inserted into trenches cut across the fiber array, which is affixed to V grooves in a glass plate and are used to change the phase of 1.55-/spl mu/m lights from 0.5 to 3.9/spl pi/ with the application of less than 3 Vrms. Two cascaded ultrathin LC cells, where the directions of alignment of the LCs are rotated by 45/spl deg/ relative to each other, are capable of converting light with an arbitrary input polarization to the transverse electric (TE) or transverse magnetic (TM) polarization. We fabricated a multichannel TE- and TM-polarization stabilizer of the previously mentioned 16-channel LC PC array and a feedback system made up of a multichannel tap-type photodetector array, sheet polarizer, and a computer and analog-to-digital converters. Feedback control was applied to maximize and minimize the tapped light, to convert an arbitrary input polarization to TM or TE output polarization, and stabilize it in the given state.     

Arbitrarily polarized slot radiators in bifurcated waveguide arrays

The feasibility of obtaining arbitrary polarization in both one- and two-dimensional arrays of slots in dual mode bifurcated Waveguides has been demonstrated. The radiating element consists of a pair of crossed slots in the sidewall of a bifurcated rectangular waveguide that couple to even and odd waveguide modes. One linear polarization is excited by the even or "sum" mode and the orthogonal linear polarization is excited by the odd or "difference" mode. By superposing the sum and difference modes in the proper amplitude and phase, any arbitrary polarization can be realized. A two-dimensional array consisting of eight waveguide linear arrays, ferrite phase shifters for scanning in the plane normal to the linear arrays, and a feed network for power distribution and polarization control was constructed. Good radiation performance for various polarizations was obtained. In the case of linear polarization, the cross polarization component was on the order of -25 dB and in the case of circular polarization, the axial ratio was on the order of 1 dB. The polarization was controlled with a ferrite phase shifter. Close-in sidelobes of better than 20 dB were obtained for all polarizations. The preceding performance characteristics were obtained over a scan range ofpm20degand over a 6 percent frequency band.     

Comparison of polarization handling methods in coherent opticalsystems

The authors compare three polarization handling methods in coherent optical systems. These methods are: endless polarization control, polarization diversity, and data-induced polarization switching. These methods are also compared with active, data-synchronous polarization switching. It is seen that endless polarization control is potentially the most powerful candidate, however, the choice of polarization control devices remain questionable. Polarization diversity is as versatile as polarization control and is potentially the fastest method; however, it yields lower receiver sensitivity. Endless control or a well-designed diversity receiver should be used for coherent trunk systems. Data-induced polarization switching is restricted to frequency-shift-keying (FSK) systems. It promises a loss span similar to that of diversity, but is far simpler, which makes it recommendable for FSK distribution systems     

2π空间全天空偏振观测系统研制与验证

在遥感观测中,天空偏振模式是大气效应的重要特征。它描述了全天空的偏振信息分布,大气效应对偏振观测的影响巨大,因此研究大气的偏振光效应是根本,它可以为减小大气效应对偏振图像的影响提供新思路。由于不同的区域和不同的观测条件对应于不同的天空偏振模式,研制天空偏振模式观测的仪器则成为了必要的前提。文中的重点在于设计一个全天空偏振观测仪器,通过精度测量,验证它的可用性。文中首先介绍了仪器的主要组成部分,包括仪器机械结构,光学设计以及电路控制,然后分析仪器的控制策略以及控制精度,最后通过对比试验,结果显示该天空偏振观测仪器可靠。     

A Mueller matrix formalism for modeling polarization effects inerbium-doped fiber

The effects of erbium anisotropy in erbium-doped fiber lasers, sources, and amplifiers are examined. Starting from basic ion properties, inversion and gain equations are derived analytically to describe polarization dependencies. A novel matrix form of the Er³⁺ rate equations is presented to propagate powers and polarization states. These equations are then numerically integrated and compared to experimentally observed polarization hole burning and polarization dependent gain. The theoretical predictions agree strongly with experiment in all cases     

All-fiber-optic polarization state azimuth control: application toFaraday rotation

An all fiber-optic system for the control and modulation of the azimuth of a linearly polarized beam is described. The experimental configuration is basically that of a Mach-Zehnder interferometer but with the birefringence of the two fiber arms controlled to produce orthogonal circular states of polarization which recombine in the final directional coupler. Azimuth control is then achieved by relative phase modulation using a piezo-electric element. The system has required the use of monomode fiber directional couplers of accurately characterized polarization properties, and the development of fiber linear retarders. The application of the system in the measurement of electric currents via Faraday rotation is described, although extensions to other types of optical instrument are equally feasible     

Polarization-Engineered Enhancement-Mode High-Electron-Mobility Transistors Using Quaternary AlInGaN Barrier Layers

Group III nitride heterostructures with low polarization difference recently moved into the focus of research for realization of enhancement-mode (e-mode) transistors. Quaternary AlInGaN layers as barriers in GaN-based high-electron-mobility transistors (HEMTs) offer the possibility to perform polarization engineering, which allows control of the threshold voltage over a wide range from negative to positive values by changing the composition and strain state of the barrier. Tensile-strained AlInGaN layers with high Al contents generate high two-dimensional electron gas (2DEG) densities, due to the large spontaneous polarization and the contributing piezoelectric polarization. To lower the 2DEG density for e-mode HEMT operation, the polarization difference between the barrier and the GaN buffer has to be reduced. Here, two different concepts are discussed. The first is to generate compressive strain with layers having high In contents in order to induce a positive piezoelectric polarization compensating the large negative spontaneous polarization. Another novel approach is a lattice-matched Ga-rich AlInGaN/GaN heterostructure with low spontaneous polarization and improved crystal quality as strain-related effects are eliminated. Both concepts for e-mode HEMTs are presented and compared in terms of electrical performance and structural properties.     

Electrooptic guided-wave device for general polarization transformations

We propose and analyze a novel optical waveguide device which performs general polarization transformations under electrical control. By combining an electrooptic TEleftrightarrowTM mode converter and two variable phase shifters in a unique optical wavegnide circuit, an input signal with arbitrary elliptical polarization can be converted to any desired polarization. This device is well suited for active polarization control of an optical signal received from a long single-mode fiber.     

Fast Adaptive Polarization and PDL Tracking in a Real-Time FPGA-Based Coherent PolDM-QPSK Receiver

Fast polarization changes of 40 krad/s and 6-dB polarization-dependent loss (PDL) are tracked in a 2.8-Gb/s real-time coherent quadrature phase-shift keying receiver. The tolerance against fast polarization changes and PDL is measured for different polarization control time constants. The sensitivity penalty of the receiver at a polarization change speed of 40 krad/s is 0.7 dB at bit-error rate (BER) of $1times 10^{-3}$, with a BER floor of $6.1times 10^{-7}$. With an additional PDL of 6 dB, these figures become 1.7 dB and $9.6times 10^{-6}$, respectively.      

Gain saturation properties of a semiconductor gain medium withtensile and compressive strain quantum wells

Gain saturation properties of a multiple-quantum-well structure with both tensile and compressively strained quantum wells are investigated analytically. This type of structure has recently been experimentally demonstrated to serve as a basis for the implementation of a two-polarization/two-frequency laser and polarization insensitive travelling wave(TW) amplifier. The performance of these devices strongly depends on the interaction between the TE and TM gains of the structure. The gain medium model appropriate for this type of structure is developed and the rate equation approach is used to describe the saturation properties of TE/TM gains and the coupling between the TE and TM gains due to gain saturation. The minimum amount of coupling between the two is governed by the basic symmetry of the light-hole wavefunction which interacts with photons of both polarization: photon cross-coupling. The finite rate of carrier escape from the quantum wells provides for carrier induced coupling between the populations of the two well types and therefore also couples TE and TM gains: carrier cross-coupling. The performance of a polarization insensitive amplifier, laser, and polarization control element is evaluated as a function of the amount of carrier cross-coupling, which is a structure dependent parameter. A structure with high degree of cross-coupling is desirable for polarization insensitive TW amplifier, while two-polarization lasers and polarization control elements require minimum cross-coupling     

Feed-forward continuous and complete polarization control with a PLZT rotatable-variable waveplate and inline polarimeter

A Pb/sub 1-x/La/sub x/(Zr/sub y/Ti/sub z/)/sub 1-x/4/O/sub 3/ (PLZT) electrooptic ceramic variable-rotatable waveplate and a compact inline polarimeter have been used to develop a fast feed-forward-controlled module for the continuous and complete conversion of polarization. This requires the control of only two parameters: the direction /spl theta/ and strength of the applied voltage V/sub 0/. Feed-forward control speed is fast, taking only 24 /spl mu/s. The chip plates were made by cutting T-shaped trenches into the four sides of a 500/spl times/400/spl times/300-/spl mu/m/sup 3/ PLZT chip and coating the trenches with electrodes. The PLZT waveplate is inserted into a 330-/spl mu/m gap between thermally expanded core fibers. The input polarization states are monitored by a newly developed compact and fast inline polarimeter, which is placed in front of the polarization controller. The optimum /spl theta/ and V/sub 0/ values for the required conversion are calculated by a computer, and the corresponding voltages are then applied to PLZT waveplate.     

基于光学零差偏振探测和锁相的合束激光偏振控制

激光偏振合束是提升窄线宽光纤激光亮度的重要技术,能实现多路激光的共孔径合束输出,同时维持较高的光束质量和线偏振态。文中探索和研究了基于线性锁相技术的合束激光偏振控制系统,详细分析和建立了光零差偏振检测物理模型和线性锁相控制环路的数学模型。利用高精度的光零差技术对合束激光的偏振相位进行检测,并通过快速实时反馈进行激光锁相,获得了输出功率为279 mW的线偏振态激光。锁相控制后,合束激光的偏振消光比达到19.3 dB,控制带宽高达39.6 kHz,剩余相位噪声为710-4 rad/Hz（1 Hz）和310-4 rad/Hz。当提高激光输出总功率达1 W时,偏振消光比维持在~15 dB,其限制因素在于光功率波动引入的相位噪声和光斑空间模式不匹配。     

Polarization characteristics of index-guided surface-emitting lasers with tilted pillar structure

We report precise control of polarization states for index-guided surface-emitting lasers by tilted-etching of the laser pillar. Circular laser pillars were etched by tilting the substrate toward ~110 or ~11~0 direction with an angle of 15/spl deg/-30/spl deg/ using reactive ion beam etching. For the laser device with a diameter of 7-10 /spl mu/m, we observed selectivity of the polarization state. We found a dominant polarization with an electric field perpendicular to the tilted direction of laser pillar. The maximum orthogonal polarization suppression ratio was about 25 dB. The selectivity of polarization in the tilted laser pillar devices is interpreted to be originated from the difference in optical losses for the two waves polarized to ~110 and ~11~0 directions.