Photonic vector signal generation employing a novel optical direct-detection in-phase/quadrature-phase upconversion

This work demonstrates the feasibility of the generation of an RF direct-detection vector signal using optical in-phase/quadrature-phase (I/Q) upconversion. The advantage of the proposed transmitter is that no electrical mixer is needed to generate the RF signal. Therefore, I/Q data of RF signals are processed at baseband at the transmitter, which is independent of the carrier frequency of the generated RF signal. A 10 Gb/s 16 quadrature amplitude modulation signal is experimentally demonstrated. Following transmission over a 50 km single-mode fiber, the power penalty is negligible. Moreover, I/Q imbalance of the proposed transmitter is studied and compensated by digital signal processing, which is both numerically and experimentally verified.     

基于数字调制技术的核磁共振射频脉冲发生器

在核磁共振（NMR）领域,射频脉冲信号的质量、形状对NMR性能及应用有着重要影响.本文基于现场可编程门阵列（FPGA）和直接数字频率合成（DDS）芯片AD9910设计了一种硬件结构更为简单的NMR射频脉冲发生器,实现了射频脉冲各项参数的数字化调制.其频率、相位、振幅的控制精度分别达到了32位、16位和14位,脉冲调制的时间精度为0.01 μs,可灵活生成持续时间不小于0.1 μs、载波频率不高于400 MHz的各类软脉冲和硬脉冲.同时,针对脉冲序列的特点建立了"脉冲+延时"的基础模型,提出了一种通用性更强的列表式脉冲序列控制方案,精简了对上级控制单元的控制需求.此外,对射频脉冲信号的频谱特性进行了理论分析,并采用Hanning窗对软脉冲的包络波形进行了优化处理,仿真和实验结果表明,Hanning窗可以有效抑制软脉冲的频谱泄漏问题.     

一种用于高场MRI的多源射频发射机

介绍了高场磁共振成像（MRI）多源发射技术的原理,提出了一种用于高场MRI系统的多源射频信号发射机.它能并行输出多路频率、相位、幅度,可快速独立调节的射频脉冲信号.该射频发射机的实现基于单片现场可编程门阵列（FPGA）和多通道数模转换器（DAC）芯片,FPGA读取预存于双端口随机存取存储器（RAM）中的射频信号参数,并利用读取的参数分别实现每路信号的直接数字频率合成（DDS）和信号调制等核心功能,获得多路数字射频信号;FPGA输出的数字信号经过高性能DAC转化为模拟信号,即所需要的射频信号.该射频发射机在设计中大量采用软件无线电技术,即利用Xilinx提供的IP核实现DDS和信号调制等主要功能,具有集成度高、体积小、灵活度高的优点,同时,该设计可以大大缩短开发时间,有效降低实现的难度和成本,为高场MRI谱仪的多源射频发射机的设计研制提供了一种低成本、高效、高性价比的方案.     

A cost-effective 100-Gb/s transmitter with low-speed optoelectronic devices and high spectral efficiency

A 100-Gb/s high-speed optical transmitter is proposed and experimentally demonstrated. Based on frequency-quadrupling technique, two sub-channels with a fixed 50-GHz spacing are obtained from one laser source. Using return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) modulation format and polarization multiplexing (PolMux), only low-speed electronic devices of 12.5 GHz are needed for the 100-Gb/s transmitter. This eliminates the need of ultrahigh-speed optoelectronic devices and thus greatly reduces the cost. The experimental results show that this transmitter can achieve good performance in dispersion tolerance of a 25-km single mode fiber (SMF).     

EER–LINC RF transmitter architecture for high PAPR signals using switched power amplifiers

Digital radio communications uses nowadays different modulation schemes with high data rate possibilities. Designing a multi-standard linearized transmitter is an interesting goal for which OFDM (Orthogonal Frequency Division Multiplex) modulation is the worst case at the moment. Transmission of multi-carrier signals like OFDM ones are subject to high dynamic variation, quantified by the PAPR (Peak to Average Power Ratio) signal property. Nonlinearities occurring at the power amplification part implies the transmitter to be linearized for preserving the information integrity. This paper presents a new multi-standard linearized RF transmitter architecture based on both EER and LINC techniques. The goal is to cancel the influence of the high PAPR of an OFDM signal as soon as possible in the different steps of the transmitter. In order to maintain the overall efficiency, the use of switched PAs is promoted, which is possible thanks to the constant (envelope) power property occurring by the proposed EER–LINC method. New circuit designs are necessary, and comparison with classical EER and LINC solutions is discussed.     

Using distributed nonlinear dynamics for public key encryption

We introduce a new method for asymmetric (public key/private key) encryption exploiting properties of nonlinear dynamical systems. A high-dimensional dissipative nonlinear dynamical system is distributed between transmitter and receiver, so we call the method distributed dynamics encryption (DDE). The transmitter dynamics is public, and the receiver dynamics is hidden. A message is encoded by modulation of parameters of the transmitter, and this results in a shift of the overall system attractor. An unauthorized receiver does not know the hidden dynamics in the receiver and cannot decode the message. We present an example of DDE using a coupled map lattice.     

Design and development of a new architecture of sliceable bandwidth variable transponder

In this paper we propose a new sliceable bandwidth variable transponder (SBVT) architecture with the separate analysis on the transmitter and receiver section. In transmission section we propose a distance module (DM) which is a programmable module. It divides a data stream/main stream (which employs a super-channel) into sub-stream and assigned modulation technique to each sub-stream based on their light path distance detailing the concept of sub-channel. In this paper, we have also proposed an algorithm for the distance module. Next we propose a modulation and transmission module (M&TM), where, planar light wave circuit (PLC) is used for enabling three modulation techniques (PM-16QAM, PM-QPSK and PM-BPSK). Finally, we propose the receiving section, which is designed to support three modulation techniques. It consists of two demodulator circuits, one for PM-16QAM/PM-QPSK and the other for PM-BPSK. In this proposed work, we focus on the multi-mode interference (MMI) devices (MMI coupler and MMI splitter) because of their photonic integration technology which is necessary for the implementation of SBVT. Lastly, we propose an elastic optical node architecture which removes the limitations of previously discussed node architecture for long distance communication.     

Synchronization of chaos in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers

Synchronization of chaos is achieved experimentally in unidirectionally coupled external-cavity vertical-cavity surface-emitting semiconductor lasers operating in an open-loop regime. Synchronization is observed when the polarization of the transmitter is perpendicular to the polarization (x polarization) of the free-running receiver. The ratio of transmitter output to y-polarized receiver output power shows normal (positive-slope) synchronization. However, inverse (negative-slope) synchronization is found to arise between the transmitter output and the x-polarized receiver output power.     

Design of full-duplex and multifunction bidirectional CMOS transceiver for optical interconnect applications

This work presents a full-duplex and multifunction bidirectional transceiver for optical interconnect application. The transceiver utilizes a common limiting amplifier/gain stage, thus reducing total chip area and total power consumption. While providing a full-duplex bidirectional transmission with the aid of a hybrid circuit between the electrical input/output (I/O) and the optoelectronic signals from the transmitter and receiver circuits, it also allows for a half-duplex operation with the aid of a switch between the transimpedance amplifier signals and the transmitter electrical input from the I/O port. The multifunction bidirectional CMOS transceiver is designed in a 0.13 µm Si-CMOS technology, with power dissipation of 79 and 54.4 mW for the transmitter and receiver, respectively. It shows a 3-dB bandwidth of 5.58 and 5.69 GHz for the transmitter and the receiver respectively and with a 3-dB gain of 66.14 and 69.6 dB, in full-duplex mode. The transceiver operates up to 7 Gb/s in full-duplex mode.     

Ka波段分布作用速调管发射机实验系统

介绍一个Ka波段分布作用速调管(EIK)发射机的实验系统,使用的核心器件是一只国产分布作用速调管样管,中心频率为35.01 GHz,脉冲输出功率为10 kW,最大工作比0.5%。该实验系统是为Ka/W波段双频毫米波测云仪发射机关键器件国产化进行的预研。实验系统一方面要对EIK样管的性能进行全面测试,对EIK样管在应用中可能存在的问题进行分析;另一方面优化发射机电路,满足EIK样管最佳工作要求。实验结果表明,国产Ka波段分布作用速调管技术取得了长足的进步,Ka波段大功率EIK发射机将进入实用阶段。     

Thermal effect analysis on crosstalk and performance of optoelectronic transmitter modules for optical interconnects

This paper presents thermal analysis on crosstalk and performance of optoelectronic transmitter modules and also demonstrates the thermal analysis for efficient heat dissipation for the transmitter modules. The thermal crosstalk model for analysis is based on interconnects parameters for vertically stacked and horizontally packaged optoelectronic transmitter modules. While the analytical expression is used to estimate the thermal critical frequency, f _{crit_th} , above which signals become severely deteriorated, a Teflon-based thermal printed circuit board (PCB) has been designed for packaging the optoelectronic transmitter modules to ensure efficient heat dissipation. The thermal and performance analysis of the packaged modules show that the chips operate at temperatures below the f _{crit_th} , which is apt for reliable data and signal transmission.     

Compensation for multimode fiber dispersion by adaptive optics

Adaptive optics is used to compensate for modal dispersion in digital transmission through multimode fiber (MMF). At the transmitter, a spatial light modulator (SLM) controls the launched field pattern. An estimate of intersymbol interference (ISI) caused by modal dispersion is formed at the receiver and fed back to the transmitter, where the SLM is adjusted to minimize ISI. Error-free transmission of 10 Gbit/s non-return-to-zero signals through standard 50 microm graded-index MMFs up to 11.1 km long is demonstrated. It is shown that a single SLM can compensate for modal dispersion across a 600 GHz bandwidth.     

Optimizing receiver and transmitter layout in optical wireless multi spot configuration access link

The study of indoor optical wireless (OW) environment is complicated by the difficulty of obtaining accurate impulse response for a large number of transmitter/receiver locations. An accurate impulse response for a given receiver location requires not only direct path, but also reflections up to nth order. The impulse response obtained is only valid for a specific location and for specific receiver parameters. If a receiver moves, the impulse response has to be recalculated. In this paper, we utilize an efficient approach for calculating optical wireless channel to study the optimal region of transmitters and receivers in a multi spot diffusing configuration. This paper takes advantage of an efficient calculation technique to study the optimal layout of receiver locations and transmitter locations in multi spot diffusing environment. Received power and delay spread are used as metrics to optimize receiver and transmitter layouts.     

Average capacity optimization in free-space optical communication system over atmospheric turbulence channels with pointing errors

A model is proposed to study the average capacity optimization in free-space optical (FSO) channels, accounting for effects of atmospheric turbulence and pointing errors. For a given transmitter laser power, it is shown that both transmitter beam divergence angle and beam waist can be tuned to maximize the average capacity. Meanwhile, their optimum values strongly depend on the jitter and operation wavelength. These results can be helpful for designing FSO communication systems.     

Development of lasers for spaceborne Doppler wind lidar applications

During the course of years, various activities have been carried out at CESI (incorporating now former CISE Innovative Technologies labs) on Doppler wind lidar (DWL) for spaceborne applications. Historically, the first activities were related to the development of a CO₂ laser transmitter for the DWL development with coherent (heterodyne) detection technique. More recently, efforts have been directed to the technology of neodymium solid-state laser transmitter with direct detection (edge technique). Presently, a work in course involves a team of European firms including CESI and is devoted to the breadboarding of a diode-pumped UV laser for DWL application.     

Injection locked Fabry-Perot laser diodes for WDM passive optical network spare function

In this paper, a protection scheme for transmitters in wavelength-division-multiplexing passive optical network (WDM-PON) has been proposed and demonstrated. If any downstream transmitter encounters problems at the central office (CO), the interrupted communication can be restored immediately by injecting a Fabry-Perot laser diode (FP-LD) with the upstream lightwave corresponding to the failure transmitter. Compared with the conventional methods, this proposed architecture provides a cost-effective and reliable protection scheme employing a common FP-LD. In the experiment, a 1:36 protection capability was implemented with a 2.5 Gbit/s downstream transmission capability.     

Electromagnetic wave interactions with a metamaterial cloak

We establish analytically the interactions of electromagnetic wave with a general class of spherical cloaks based on a full wave Mie scattering model. We show that for an ideal cloak the total scattering cross section is absolutely zero, but for a cloak with a specific type of loss, only the backscattering is exactly zero, which indicates the cloak can still be rendered invisible with a monostatic (transmitter and receiver in the same location) detection. Furthermore, we show that for a cloak with imperfect parameters the bistatic (transmitter and receiver in different locations) scattering performance is more sensitive to eta(t)=square root micro(t)/epsilon(t) than n(t)=square root micro(t)epsilon(t).     

Performance limits of pico-cell systems using radio-over-fiber techniques with an electroabsorption modulator

We investigate the performance limits of a pico-cell system using the radio- over-fiber technique with an electroabsorption modulator (EAM) in a 2.4 GHz wireless local area network (WLAN) environment. To understand the performance limits of the system using an EAM as the optical transceiver, we vary the optical modulation index (OMI) of the transmitter for different bias voltages to the EAM. Power margins in the links are found to estimate a possible service range, and packet loss rates (PLRs) in the pico-cell system are measured to evaluate the transmission performance. The total service range can be extended up to 3 m by adjusting the OMI of the transmitter for different applied bias voltages to the EAM.     

Reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links with spatial diversity

In the scenario of first laser communication relay satellite being launched into geostationary earth orbit, we evaluate the reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links in presence of turbulence and various weather conditions using spatial diversity technique. In channel modeling, Beer Lambert Law incorporates the weather effects. The log-normal probability density function (pdf) models weak turbulence and gamma–gamma pdf moderate to strong turbulence. Using the combined channel state pdf, bit error rate (BER) expressions are derived for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. From the BER plots, we evaluate the minimum average received power required to achieve a desired BER for all three schemes for different channel conditions. Subsequently, minimum transmitter power requirement is evaluated for both uplink and downlink using the range equation. It is observed that presence of moderate, light and thin fog cause additional power requirement. Also, among the three schemes, M-PPM scheme requires the least transmitter power, followed by M-DPPM and OOK schemes. Further, it is seen that the transmitter diversity or multiple input single output technique reduces the uplink minimum transmitter power requirement, whereas for downlink aperture averaging and receiver diversity or single input multiple output techniques can achieve the same. The power requirement for uplink is 8–10 dB more as compared to downlink in presence of turbulence and various weather conditions.     

Improved analog optical link performance with quantum phase amplification

A degenerate parametric amplifier at the transmitter can improve the power efficiency of a small-signal phase-modulated optical transmission system by acting as a phase amplifier. For a parametric power gain H, the total transmitter power requirement is reduced by a factor of H(2) compared with that of a conventional phase-modulated system.