Multiplexing and transmission of RF signals using an optical fiber

Ultrasonic non-destructive testing systems designed to control huge structures normally use several transducers in the reception stage. To avoid increasing the cost of electronics, a multiplexer is used to send all received signals to the same processing module. Traditionally, transmission of such signals is carried out using copper cables. For special applications (i.e. continuous monitoring of nuclear plants) metallic cables are not suitable because of their high sensitivity to electromagnetic perturbations. Moreover, the multiplexing is made electronically. When the distance between the transducers and the reception unit is large and/or electromagnetic noise is important, signal degradation takes place. The proposed system implements the transmission and multiplexing of ultrasonic electrical signals obtained by means of broadband transducers (up to 1 MHz), using an optical fiber. Optical fibers are made of dielectric materials (silica or plastic) so they are inherently passive to electromagnetic noise. Wavelength division multiplexing is utilized for adding channels to the system by means of fiber optic couplers and different light sources. The wavelengths of the optical signals utilized are located far apart in the optical spectrum in order to avoid serious crosstalk in transmission. The limit to the number of multiplexed channels depends on the optical fiber selected, the spectrum of the light sources and the wavelength division multiplexers or couplers utilized.     

Multichannel dispersion compensation using a silicon waveguide-based optical phase conjugator

We experimentally demonstrate dispersion compensation using a silicon-based optical phase conjugator. We achieve simultaneous transmission of four dense wavelength division multiplexing (DWDM) channels spaced at 100 GHz and operating at 10 Gbits/s over 320 km of standard fiber. The measured power penalty at bit error rate of 10(-9) is less than 0.3 dB.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

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Proposed Power-Equalized EDFA Modules Using Fiber Bragg Gratings with Various Reflectivities

We proposed and experimentally demonstrated two power-equalized erbium-doped fiber amplifier (EDFA) modules using fiber Bragg gratings (FBGs) with various reflectivities for individual channels. The transmission type power-equalized EDFA module is low-cost for its simple design, while the reflection type power-equalized EDFA module can suppress most of the amplified spontaneous emission noise. Both consist of a bidirectional EDFA, a set of FBG chains with suitable reflectivities, and an optical isolator/optical circulator. They can find potential applications in wavelength division multiplexing lightwave transmission systems.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

By introducing a convergent lens in the phase mask setup and by tilting appropriately the fiber from the phase mask, a linearly chirped fiber grating with an appropriate chirp can be obtained conveniently. Using this method, two groups of fiber gratings, each of them is composed of 8 overlaped linearly chirped fiber gratings but with different center reflection wavelength separations (～0.8 nm and ～1.6 nm, respectively) are fabricated. Experimental results show that, the compensators based on the two groups of fiber gratings can be used to compensate for the dispersion of 8×2.5 Gb/s transmission over 100 km of standard single-mode fiber for multiple channels in optical time-division multiplexing (OTDM) and densed wavelength division multiplexing (DWDM).     

A scheme of optical interconnection for super high speed parallel computer

An optical cross connection network which adopts coarse wavelength division multiplexing (CWDM) and data packet is introduced. It can be used to realize communication between multi-CPU and multi-MEM in parallel computing system. It provides an effective way to upgrade the capability of parallel computer by combining optical wavelength division multiplexing (WDM) and data packet switching technology. CWDM used in network construction, optical cross connection (OXC) based on optical switch arrays, and data packet format used in network construction were analyzed. We have also done the optimizing analysis of the number of optical switches needed in different scales of network in this paper. The architecture of the optical interconnection for 8 wavelength channels and 128 bits parallel transmission has been researched. Finally, a parallel transmission system with 4 nodes, 8 channels per node, has been designed.     

Tbit/s超大容量光纤通信系统的研究进展

Tbit/s超大容量光纤传输系统促进了光纤通信技术的发展。综述了采用波分复用技术(WDM)、光时分复用技术(OTDM)和WDM/OTDM混合方式的Tbit/s超大容量光传输系统的研究现状、技术实现方式及研究的最新进展。对各种传输系统的优缺点进行了评价,对Tbit/s光纤通信系统的前景作了展望。     

Spectral efficient hybrid wireless optical broadband access network (WOBAN) based on transmission of wireless MIMO OFDM signals over WDM PON

In this paper, a spectral efficient hybrid wireless optical broadband access network (WOBAN) is proposed and demonstrated based on the transmission of wireless multi-input multi-output orthogonal frequency division multiplexing (MIMO OFDM) signals over wavelength division multiplexing passive optical network (WDM PON). By using radio over fiber (ROF) techniques, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. It is a known fact that multiple wireless signals having the same carrier frequency cannot propagate over a single optical fiber at the same time, such as MIMO signals feeding multiple antennas in fiber wireless (FiWi) system. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. This technique allows four pairs of wireless MIMO OFDM signals with the same carrier frequency for each pair to be transmitted over a single optical fiber by using one optical source per wavelength. The crosstalk between the different MIMO channels with the same frequency is eliminated, since each channel is upconverted on specified wavelength with enough channel spacing between them. Also the maximum crosstalk level between the different MIMO channels with different frequencies is very low around ?76 dB. The physical layer performance of the proposed WOBAN is analyzed in terms of the bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR). The proposed WOBAN achieves 7.68 Gb/s data rate for 20 km for the optical back-end and 240 Mb/s for the outdoor wireless front-end.     

RSOA-basRSOA-based distributed access long reach hybrid WDM-TDM PON with OADMs

A distributed access scheme using optical add/drop multiplexers （OADMs） for long reach hybrid wavelength division multiplexing and time division multiplexing passive optical networks （WDM-TDM PONs） is proposed and demonstrated. Colorless operations are implemented by using commercially available reflective semiconductor optical amplifiers （RSOAs） at both the center office （CO） and the customer side. Four 1.25-Gb/s channels are successfully transmitted over 80-km single-mode fiber with four OADMs. The dynamic input power range of the RSOA is also investigated. Compared with traditional access schemes, the proposed scheme could cover the area along the feed fiber with no blind zone. The experimental results show that it could be an ideal solution for the next generation access networks.     

Gain Flattening Approach to Physical EDFA for 16 × 40 Gb/s NRZ-DPSK WDM Optical Communication Systems

We are using different approaches to gain flattening in EDFAs without using additional components; i.e., gain flattening filter, dispersion shift fiber, periodic gratings, etc. By using gain flatten approach 3, it is possible to achieve the transmission of sixteen channels at 40 Gb/s wavelength division multiplexing (WDM) over a transmission distance of 490 km by single-mode fiber and dispersion-compensating fiber at a span of 70 km with channel spacing of 200 GHz. We observed the bit error rate less than 10^-9 and power of received signal more than -5 dBm with NRZ-DPSK format.     

Control packet signaling mechanism using electronic code division multiple access for packet-based networks

We propose and experimentally demonstrate the feasibility of a control packet signaling technique using electronic code division multiple access for a wavelength division multiplexing packet-based network, whereby each wavelength channel is assigned a unique electronic code based label on a radio frequency subcarrier. Such a technique allows each wavelength channel to be electronically identified without requiring the use of a WDM demultiplexer. We experimentally demonstrate this technique with two wavelength channels each with 1.25 Gb/s baseband payload data and 10 Mb/s header coded onto an electronic code at 160 Mb/s. A performance study of the electronic code division multiple access based control signaling scheme in a wavelength division multiplexed packet-based access network is also performed in terms of the required power budget to monitor the electronic code division multiple access control signals in the presence of several sources of noise for error-free transmission of both payload data and electronic code division multiple access based control signals. It is shown that the modulation depth of each signal impacts the amount of required optical tap power. As the modulation depth of the electronic code division multiple access based control signal is increased, the required optical tap power is reduced. However, this increases the bit-error-rate for the payload data. Therefore, there lies a maximum and a minimum of the required tap optical power for the successful recovery of both signals. The lower bound of this range is usually determined by the successful recovery of electronic code division multiple access based control signal while the upper bound is determined by the successful recovery of payload data. The required optical tap power is analyzed for different transmission bit rates of the payload data for various receiver architecture scenarios without an optical amplifier at the receiver. The scalability analyses were repeated with an optical amplifier placed in the receiver terminal of the network. The resulting optical tap power that is required for the successful monitoring of the electronic code division multiple access based control signals are compared with that of the case without the amplifier.     

Gain Flattening Approach to Physical EDFA for 16 × 40 Gb/s NRZ-DPSK WDM Optical Communication Systems

We are using different approaches to gain flattening in EDFAs without using additional components; i.e., gain flattening filter, dispersion shift fiber, periodic gratings, etc. By using gain flatten approach 3, it is possible to achieve the transmission of sixteen channels at 40 Gb/s wavelength division multiplexing (WDM) over a transmission distance of 490 km by single-mode fiber and dispersion-compensating fiber at a span of 70 km with channel spacing of 200 GHz. We observed the bit error rate less than 10^-9 and power of received signal more than -5 dBm with NRZ-DPSK format.     

A Survivable Wavelength Division Multiplexing Passive Optical Network with Both Point-to-Point Service and Broadcast Service Delivery

Abstract

A survivable wavelength division multiplexing passive optical network enabling both point-to-point service and broadcast service is presented and demonstrated. This architecture provides an automatic traffic recovery against feeder and distribution fiber link failure, respectively. In addition, it also simplifies the protection design for multiple services transmission in wavelength division multiplexing passive optical networks.     

基于高非线性光纤的增益谱平坦拉曼光纤放大器研究

针对光纤通信中密集波分复用系统各信道的在线平坦光放大这一光通信问题,提出利用级联高非线性光纤来设计增益平坦的拉曼光纤放大器。对高非线性光纤(As S光纤)拉曼增益谱前后沿进行线性拟合处理,利用不同波长泵浦抽运同种光纤,实现前放大后增益补偿,并考虑信号光损耗不同,在输出端得到了一个近似固定的功率输出值,并分析了影响拉曼光纤放大器输出特性的因素。模拟结果表明:平均增益为20.45 dB,增益平坦度为0.15 dB。     

基于单个光纤光栅的Sagnac干涉仪的理论与实验研究

提出了一种结构新颖的Sagnac干涉仪,分析计算了所含光纤光栅分别为均匀Bragg光栅和线 性啁啾光栅时的透射响应,得到了均匀光栅Sagnac环的解析解,发现含均匀光栅时可得到间隔均匀的通带结构,而含啁啾光纤光栅时只能得到间隔非均匀的通带结构.这两种结构都可 能有应用价值,前者可用在密集波分复用系统中,后者可用在光纤传感领域中.实验制作了 两种通带间隔不同的、通带数分别为8和16的多通带滤波器,实验证实了理论计算得到的结果. 关键词： 光纤光栅 Sagnac干涉仪 光学滤波器     

基于磁光效应的二维三角晶格光子晶体模分复用器

随着全光通信的快速发展, 波分复用传输系统已不能满足高容量光网络的需求, 而模分复用技术利用有限的稳定模式作为独立信道传递信息, 可以成倍地提高系统容量和频谱效率, 是构建未来光网络的关键技术之一. 本文基于掺Bi复合稀土铁石榴石的磁光效应, 设计了1.55 μm波段的二维三角晶格光子晶体模分复用器. 在该光子晶体结构中引入缺陷, 形成模式分束波导, 通过外加磁场改变其在不同偏振模式下的磁导率, 从而控制TE, TM模式的传输, 实现了1.55 μm波段的模分复用. 利用平面波展开法和时域有限差分法对此模分复用器进行了能带和传输特性分析, 结果表明: TE和TM模式的透射率均高于92%, 信道隔离度分别为19.7 dB和42.1 dB. 这些特性在未来的大容量光传输系统中有着重要的应用前景.     

Mode division multiplexing: from photonic integration to optical fiber transmission [Invited]

To overcome the capacity crunch of optical communications based on the traditional single-mode fiber(SMF), different modes in a few-mode fiber(FMF) can be employed for mode division multiplexing(MDM). MDM can also be extended to photonic integration for obtaining improved density and efficiency, as well as interconnection capacity. Therefore, MDM becomes the most promising method for maintaining the trend of "Moore's law" in photonic integration and optical fiber transmission. In this tutorial, we provide a review of MDM works and cutting-edge progresses from photonic integration to optical fiber transmission, including our recent works of MDM low-noise amplification, FMF fiber design, MDM Si photonic devices, and so on. Research and application challenges of MDM for optical communications regarding long-haul transmission and short reach interconnection are discussed as well. The content is expected to be of important value for both academic researchers and industrial engineers during the development of next-generation optical communication systems,from photonic chips to fiber links.     

基于光码分多址技术的塑料光纤接入网探讨

本文通过对多信道光接入网复用和多址接入方式的分析,提出一种基于光码分多址(OCDMA)技术的塑料光纤接入网结构,同时给出了适合于多媒体信息业务传输的控制协议以及低成本的硬件实现方案,为实现光接入网的最终目标即光纤到办公室(FTTO)或光纤到家庭(FTTH)提供了一条有效的途径.     

Transmission performance of 20 × 10 Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on-off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor.The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems.The bit error rate (BER) for all channels observed is less than 10⁻¹⁰ up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.     

Novel schemes to generate multi-level modulation formats for ultra-capacity coherent detection transmission systems

We summarize several novel schemes to generate multi-level modulation formats for high capacity transmission system with high spectral efficiency. We show that multi-level 8QAM, 16QAM, 32QAM, and 64QAM （QAM： quatlrature amplitude modulation） optical signals can be generated by commercial optical and electrical devices. Employing these multilevel modulation formats, we have realized PDM-8QAM （PDM： polarization division multiplexing） 32 Tb/s and PDM-36QAM 64-Tb/s signals transmission over 580-and 320-km fibers, respectively.