A bidirectional 60 GHz RoF system based on FWM in a semiconductor optical amplifier

In this study, a bidirectional 60 GHz RoF systems based on four-wave mixing (FWM) in semiconductor optical amplifier (SOA) is proposed. Two key techniques are included in such a scheme, namely, generation of 60 GHz modulating signals and distribution of 60 GHz local oscillator. The analytical model is theoretically analyzed and then confirmed by numerical simulations. Results of this study demonstrate that such a scheme can offer realistic solutions to support future mobile broad-band applications.     

60 GHz Radio over Fiber Technology for Wireless Access by employing Narrow-Angle PSK Modulation

This paper investigates two key techniques used in 60 GHz Radio over Fiber (RoF) technology for wireless access, namely, the generation of 60 GHz signals and the distribution of 60 GHz local oscillator (LO). In the proposed model, a 60 GHz PSK signal is generated by a heterodyne of two subcarriers with narrow-angle PSK (NA-PSK) modulation, whose phase shift is equal to one half that of a normal PSK signal. Then we use a 60 GHz mixer to frequency mix two PSK signals in two different bands, 60 GHz and baseband. By doing this, the modulation information can be fully eliminated, resulting in a 60 GHz LO. In the wireless terminal, coherent demodulation is realized by a self-mixing of the transmitted 60 GHz PSK signal and LO. Thus no millimeter-wave (mm-wave) band oscillator is needed in the wireless terminal.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

Impact of interferometer delay time on the performance of ODSB-SC RoF system with wavelength interleaving

In this paper, we investigate the impact of interferometer delay time in a 5 Gb/s optical double sideband-suppressed carrier (ODSB-SC) RoF system transmitting two wavelength interleaved radio frequency (RF) signals at 10 and 15 GHz over an optical fiber. Here, an optical Mach–Zehnder modulator is used for both optical carrier suppression and signal modulation. At the receiver, delay interferometer is used for the separation of RF frequency signals. We analyze the performance of the RoF system by varying the value of delay time of interferometer from 0.02 to 0.14 ns. The result shows that the RoF system performance is optimum for the time delay of 0.1 ns. Further, the optical spectrums, RF spectrums and eye diagrams of two interleaved RF signals have been compared.     

All optical arbitrary waveform generation by optical frequency comb based on cascading intensity modulation

We propose and experimentally demonstrate an all optical arbitrary waveform generation by optical frequency comb (OFC) based on cascading intensity modulation. By selecting spectral lines of interest from OFC through optical filters, 10 GHz, 20 GHz, and 60 GHz sinusoidal signals with low phase noise and more complex waveforms, including ultra-short pulse, half-wave cosine, and single frequency modulated MMW signals, are generated easily.     

Analysis of an optical mm-wave generation scheme with frequency octupling using two cascaded Mach-Zehnder modulators

We propose a novel method to generate optical mm-wave signals with frequency octupling using two cascaded Mach-Zehnder modulators (MZMs). First, the scheme is investigated both theoretically and by simulation, and results show that an 80 GHz mm-wave is generated by a 10 GHz RF oscillator. Then, an analytical expression is developed to describe the performance of the scheme. The influences caused by non-ideal factors are discussed in detail, and undesired sidebands suppression ratios are plotted and analyzed. At last a RoF system using the mm-wave generation scheme is demonstrated and its BER curves indicate that the performance of the system is still good even if the parameters deviate from the ideal values to a certain degree.     

Performance improvement and wavelength reuse in millimeter-wave radio-over-fiber links incorporating all-fiber optical interleaver

Simultaneous downlink performance improvement and uplink wavelength reuse in a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) system by using a simple and cost-effective all-fiber optical interleaver are proposed and demonstrated. The MMW RoF downlink performance improvement is based on suppressing optical carrier-to-sideband ratio (OCSR), with which the mechanism is confirmed by theoretic analysis and derived experimental results. Measured results show that, by suppressing OCSR using a fabricated all-fiber optical interleaver, the downlink optical receiver sensitivity is improved about 2.1 dB. The downlink data rate is 1.25 Gbit/s and the carrier frequency is 58.1 GHz; the link consists of 6 km optical single-mode fiber and 1 m wireless connection. On the other hand, with the interleaver suppressing downlink OCSR, simultaneously an optical carrier is recovered from the RoF downlink and is reused for RoF uplink transmission. The uplink is operated at 62.9 GHz and the data rate is the same 1.25 Gbit/s. With the recovered optical carrier, a laser-free remote access point is achieved. The principle, structure, and fabrication of an all-fiber optical interleaver are also presented in this paper.     

Simulative investigation the impact of optical amplification techniques on single- and dual-electrode MZM and direct modulator's in single-tone RoF system

Since the introduction of erbium-doped fiber amplifier (EDFA) in optical fiber communication systems at 1550 nm, the fiber loss is no longer considered as the limiting factor but the fiber dispersion and chirp parameters play an important role in degrading the performance of optical communication systems. Further, the invention of external modulators of Mach-Zehnder (MS) type minimizes the transmission power penalty due to fiber chromatic dispersion as these modulators are consider almost chirp-free modulators. Also, better suppression of nonlinear distortions consists of harmonic distortions (HDs) and intermodulation distortions (IMDs) were achieved by using Mach-Zehnder external modulator [8]. In this work, a simulation comparison of external- and direct-modulation schemes using different optical amplifiers; SOA and EDFA in single-tone RoF system is reported. A single-tone channel of 20 GHz is transmitted over single-mode fiber (SMF) either externally modulated by using single-electrode (SEMZM) - and dual-electrode (DEMZM) - Mach-Zehnder modulator or by direct-modulation scheme. Better improvements in the measurement of received RF power of a 20 km linked single-tone RoF system are achieved by using SEMZM with EDFA, which means maximum optical link is achieved between Central Office (CO) and Base Station (BS). Further, this scheme provides better BER as compare to other schemes discussed in this paper.     

A novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators

We propose a novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators (MZMs) for the first time. First, the scheme is investigated theoretically, which suggests that it can be used for sextupling, 12-tupling, and 18-tupling mm-wave generation. Then simulation results are given, 60 GHz mm-wave is generated from 5 GHz, or 10 GHz RF oscillator based on frequency 12-tupling or sextupling, and 90 GHz mm-wave is generated from 5 GHz RF oscillator based on frequency 18-tupling. The optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are analyzed by simulation, in which several non-ideal factors are taken into consideration. Results indicate that all the three mm-wave generation methods are practical and very good performance can be obtained when the extinction ratio of the MZM is 30 dB, even if the extinction ratio of the MZM is 20 dB, the performance is still good, especially for the sextupling mm-wave generation method, whose performance is excellent and insensitive to the extinction ratio of MZM, the non-ideal RF driving voltage and the non-ideal DC bias. At last, we set up a RoF system by simulation to verify the transmission performance of the scheme. The BER performance and eye diagrams are given.     

EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz^2/3 for an optical input power of − 6 dBm.     

Power penalty in multitone radio-over-fibre system employing direct and external modulation with optical amplifiers

This paper presents a multitone RoF system employing a central station and a remote antenna station to transmit modulated microwave or mm-wave signals. Two configurations of the system employing direct and external modulation are presented. First, at the central station, the modulating signal is directly and externally modulated at 1549.5 and 1550.5 nm, respectively, and the combined signal is then transmitted using wireless mode. In the second configuration, the combined signal is transmitted over 20 km to the remote antenna station using optical fibre connectivity. At the remote antenna station, both channel wavelengths are separated and amplified with an EDFA and SOA and are detected. The demonstration results show that there exists a small power penalty between the direct and the external modulation. But a large power penalty is reported depending upon the choice of optical amplifier viz. EDFA or SOA. Better performance is recorded in later case. The results also show that power is being distributed among the operating frequency and sidebands adjacent to it after transmission over a fibre link.     

基于外调制器的全双工无线信号光传输系统

提出了一种基于双平行马赫 增德尔调制器的全双工矢量信号传输系统。传统的光学倍频技术只适用于NRZ (not return to zero) 等强度调制格式,而不适用于无线通信中常用的MPSK、MQAM等矢量信号调制技术,用传统的倍频技术生成光毫米波后,用滤波器将其2个边带分开,在其中一个边带上调制矢量信号,这样幅度和相位信息被正确保留,且使用了8倍频模块,降低了传输过程中对光电器件的带宽要求。理论分析和仿真结果表明:通过此方法产生的携带在60 GHz载波上的625 Msymbol/s的4QPSK信号,经过20 km单模光纤传输后,误差向量幅度损耗可以忽略不计。     

Generation of optical carrier suppression millimeter-wave signal using one dual-parallel MZM to overcome chromatic dispersion

In this paper, we have proposed a novel approach to generate optical carrier suppression (OCS) mm-wave with signal only carried by one first-order sideband using a dual-parallel MZM in radio-over-fiber (RoF) system, and the transmission performance was also investigated. As the optical mm-wave signal is transmitted along the fiber, there is no time shift of the data symbols resulting from the group velocity dispersion in the fiber because the signal is only modulated on one sideband. The simulation results showed that the eye diagram keeps open and clear even when the optical mm-wave signals are transmitted over 96-km and the power penalty is about 1-dB after fiber transmission distance of 60-km, which is quite consistent with our theoretical analysis. Furthermore, the proposed OCS optical mm-wave generation approach is also used in a full-duplex RoF link based on wavelength reuse at the base station for the uplink due to another pure sideband without carrying data. The bidirectional 2.5-Gbit/s data is successfully transmitted over 40-km standard single mode fiber with less than 0.5-dB power penalty in the simulation. Both the unidirectional RoF downlink and the full-duplex RoF system have good performance.     

一种基于相干检测的双向输出信号频率可选的光纤无线系统

提出了一种单光源、双向输出信号频率可选的光纤无线系统,该系统在单光源条件下,利用相干检测技术、数字信号处理技术,结合并行相位调制器以及波长选择开关结构,在上下行链路实现基带信号、多个毫米波信号输出.仿真验证表明,针对20Gbit/s 16-QAM调制信号,经30km光纤传输,系统下行输出信号频率实现0~60GHz可选,其传输最小矢量误差为6.53%(0GHz)~7.61%(60GHz);上行输出信号频率实现0~120GHz可选,其传输最小矢量误差为6.89%(0GHz)~8.30%(120GHz).理论分析和仿真结果表明,该系统双向链路均可实现频率可选的信号输出,且双向传输具有较好的性能表现.     

A subcarrier demultiplexing scheme based on a coefficient-switchable microwave photonic filter in radio-over-fiber systems

A flexible method for subcarrier demultiplexing in radio-over-fiber (RoF) systems is proposed and experimentally demonstrated. The subcarrier demultiplexer is realized by a coefficient-switchable microwave photonic filter, which is based on biasing Mach–Zehnder modulator (MZM) at different transmission slopes. The 2.4 GHz and 2.7 GHz subcarrier signals both modulated with 100 Mbps on-off keying (OOK) data are transmitted and demultiplexed in the RoF system. The experimental result shows that each of the two subcarriers can be individually selected out with the other one well depressed. The proposed subcarrier demultiplexing scheme is simple, feasible, cost-effective and has good potential applications in the multiplexed RoF systems.     

Infrasound signal classification based on spectral entropy and support vector machine

The operation speed of the algorithm is the critical factor in the real-time monitoring of infrasound signals. The existing methods mainly focus on how to improve the accuracy of classification and can’t be used in real time monitoring because of their slow running speed. We adopt spectral entropy into the feature extraction of infrasound signals. Combined with the support vector machine algorithm, the proposed method effectively extracted the signal features meanwhile greatly improved the operation efficiency. Experimental results show that the running speed of the proposed method is 1.0 s, which is far less than 4.7 s of the comparison method. So the proposed method can be applied in real-time monitoring of earthquakes, tsunamis, landslides and other infrasound events.     

Single-sideband modulated radio-over-fiber system based on long period fiber grating

We present a prototype for optical single-sideband (SSB) modulated radio-over-fiber (RoF) system by employing a long period fiber grating (LPFG). A LPFG with 13.78 nm base width of transmission spectrum and 0?23.2 dB of transmission depth was designed by using commercial software. Then it is used in RoF SSB modulation scheme. In the scheme, a Mach?Zehnder modulator modulates the light wave with millimeter-wave driving signals to realize optical double-sideband (ODSB) modulation, the generated ODSB modulation signals pass through a LPFG. Due to the negative slope in transmission spectrum, the lower sideband experiences higher attenuation than the upper sideband. Thus the conversion from ODSB to optical single sideband with carrier (OSSB + C) can be easily achieved by using only one LPFG. Also, the carrier to sideband ratio (CSR) can be reduced by using a LPFG, results show the CSR can be decreased from 12.49 dB to 1.1 dB.     

Employing inverse return-to-zero and Manchester formats for uplink wavelength reuse in RoF systems

The inverse return-zero (IRZ) modulation format and Manchester format were investigated as wavelength reusing schemes in the RoF downlink systems. Since both of the modulation formats featured power remaining in the bit slot regardless of the bit value, the downlink optical carrier can be reused as the uplink light source. The performances of two formats were analyzed in the symmetrical and asymmetrical duplex RoF system. It was found that IRZ is more suitable for symmetrical system, and the duty cycle of IRZ pulse is the critical factor on the asymmetrical RoF system performance. However the Manchester format demonstrated the large system tolerance on asymmetrical duplex RoF system with the receiver sensitivity degradation within 1 dB.     

Gigabit-converged wired and wireless networks for simultaneous multi-services transmission

A novel architecture of converged radio-over-fiber(RoF) and wavelength division multiplexed passive optical network(WDM-PON) system,namely RoF-WDM-PON,is demonstrated.20-GHz 1-Gb/s radio frequency(RF) signals and 1-Gb/s baseband(BB) signals are simultaneously generated and transmitted using optical carrier suppression(OCS) modulation techniques.The proposed scheme is compatible with the conventional RoF and PON system.25-km single-mode fiber(SMF) transmission is successfully achieved.     

A full-duplex radio-over-fiber system using direct modulation laser to generate optical millimeter-wave and wavelength reuse for uplink connection

In this paper, we present a full-duplex radio-over-fiber system incorporating both optical millimeter-wave (mm-wave) generation and wavelength reuse for uplink connection. The optical double sidebands (DSB) signal is generated by using only one inexpensive broadband direct modulation laser (DML), to which a mixing RF signal is applied. An optical interleaver is then used to separate the first-order optical sidebands from the optical carrier of optical DSB signal. The separated first-order optical sidebands are beat to generate mm-wave signal that has double the frequency of the RF drive signal, while the separated optical carrier is reused as light source to remodulate uplink signal. Both detailed theoretical analysis and experiments to demonstrate the feasibility of the proposed system are presented. Experiment result shows that the bidirectional 2.5 Gb/s data can be successfully transmitted over 40 km standard single-mode fiber (SSMF) with less than 2 dB power penalty.