Long-Distance Transmission of AM-VSB CATV Systems Using Fabry-Perot Laser Diode and Fiber Bragg Grating

This study presented a directly modulated 1550 nm NTSC AM-VSB CATV longdistance transmission system using Fabry-Perot laser diode, optical isolator, fiber Bragg grating, quarter-split-band, and wavelength-division multiplexing techniques. Good carrier-to-noise ratio ( ≥48 dB), composite second-order ( ≥64 dB), and composite triple-beat ( ≥60 dB) performances were obtained after a 100 km standard single-mode fiber transmission. Our proposed system does not use an externally modulated 1550 nm transmitter and a sophisticated stimulated Brillouin scattering suppression technique. It reveals a prominent technique with simpler and more economical advantages than that of externally modulated 1550 nm transmission system.     

Dispersion Compensation in Externally Modulated Transmission System Using Chirped Fiber Grating

We present an externally modulated NTSC AM-VSB erbium-doped fiber amplifier (EDFA)-repeated system in the 1550 nm region which uses a chirped fiber grating (CFG) as a dispersion compensation device. In contrast to the conventional externally modulated fiber optical CATV systems, either with or without dispersion compensation fiber (DCF), good performances of carrier-to-noise ratio (CNR) S 50 dB, composite second order (CSO) S 74 dB, and composite triple beat (CTB) S 65 dB were achieved for the full channel band after a 100-km single-mode fiber (SMF) transmission.     

Analysis of dispersion compensation by chirped fiber grating in directly and externally modulated CATV systems

The dispersion compensation effect of the chirped fiber grating (CFG) is analyzed theoretically, and analytic expressions are derived for composite second-order (CSO) distortion in analog modulated sub-carrier multiplexed (AM-SCM) cable television (CATV) systems with externally and directly modulated transmitters. Simulations are given for the two kinds of modulations and for standard single mode fiber and non-zero dispersion shift fiber (NZDSF) systems. The results show that CFG could be used as a dispersion compensator in directly modulated systems, but its dispersion coefficient should be adjusted much more precisely than the externally modulated system. The requirements for the NZDSF system could be loosened much. It is proposed that directly modulated source may be used as a transmitter in CATV systems combined with tunable CFG dispersion compensator being adjusted precisely, which may be more cost-effective than externally modulation technology.     

Analysis of dispersion compensation for position-dependence in externally modulated CATV lightwave systems by using chirped fiber grating

The dispersion compensation characteristics of the chirped fiber grating (CFG) for different dispersion compensation positions are analyzed in externally modulated cable television (CATV) lightwave system and the analytic expression of the composite second order (CSO) distortion is derived. The analyses give a reasonable explanation for the position-dependent effect of CFG dispersion compensator, which was found in practical systems. Moreover, the theoretical result is also verified by an experiment. It is believed that the theory will be helpful in designing optical CATV fiber links with nodes at proper positions both for intensity amplification and dispersion compensation.     

Transmission Performance Improvement in Microwave/Millimeter-Wave Optical System Using Chirped Fiber Grating

A chirped fiber grating (CFG) written by the moving fiber/phase mask scanning beam technique with a uniform mask is used to demonstrate the dispersion compensation in the externally modulated microwave/millimeter-wave over fiber system. It is found that the use of the CFG is an efficient way to compensate for the severe RF power degradation induced by the fiber chromatic dispersion, which results in a significant improvement in the transmission performance. The signal to noise ratio is improved from 4.8 dB to 24.4 dB when 10.58 GHz RF signal carrying 5 Mbit/s QPSK format data is transmitted over 35 km single mode fiber.     

外调制CATV光发射机中并行结构预失真补偿技术

针对外调制式CATV光发射机中固有的非线性复合三阶差拍(CTB)失真,提出了一种并行结构的预失真补偿电路技术,并进行了详细的理论分析.在此基础上设计制作了基于互补型二极管阵列的预失真非线性补偿电路,实现了50～550MHz宽频带内CTB补偿15dB～18dB,同时对二次失真没有影响.     

10 Gb/s TDM passive optical networks using four wavelengths multiplexed channels

We propose a new architecture for 10 Gb/s upstream traffic in TDM-PON using externally injection-locked Fabry-Perot laser diodes (FP-LDs) in each optical network unit (ONU). Four directly modulated 2.5 Gb/s FP-LDs were injection-locked by continuous wave (CW) carriers distributed from the optical line terminal (OLT). Hence, a total of 10 Gb/s upstream traffic can be achieved. Experimental results show negligible power penalty at a transmission of 25 km standard single mode fiber (SMF) without dispersion compensation. The performance of the injection-locked FP-LD is also studied.     

全固双层芯色散补偿光子晶体光纤的研究与设计

为了补偿光纤色散对高速信号传输的限制,提出一种全固双层芯色散补偿光子晶体光纤.首先对该光纤模式耦合特性进行理论分析,然后利用多极法进行模拟计算,得到该光纤包层结构参数与色散值以及相位匹配波长之间的关系,并对其规律进行研究.通过优化光纤结构参数,得到在1 550nm处,色散值达到-32 620ps/(nm·km)、损耗为0.29dB/km、与标准单模光纤的熔接损耗为4.77dB的色散补偿光纤.该光纤可补偿1 910多倍长度的SMF-28单模光纤的色散,补偿能力远大于常规色散补偿光纤.与空气孔-石英结构色散补偿光子晶体光纤相比,全固色散补偿光子晶体光纤具有易制备、易与传统通信光纤熔接等优点.     

A hybrid high-gain double-pass erbium-doped fiber amplifier with dispersion compensation feedback loop

A new double-pass erbium-doped fiber amplifier (DP-EDFA) using chirped fiber Bragg grating (CFBG) is reported here showing a gain of 53.4 dB and noise figure (NF) of 5.36 dB. The proposed amplifier at the same time provides dispersion compensation through the use of CFBG.     

Electrical nonlinearity pre-compensation for CO-OFDM system

An electrical nonlinearity pre-compensation (ENPC) combined nonlinearity with chromatic dispersion method is introduced for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system. Comparing with existed only nonlinearity pre-compensation (NL Pre-comp) method, ENPC method is not only suitable for low-dispersion fiber system, but also effective for high dispersion fiber transmission system without optical dispersion compensation. For 40 Gbit/s 20 × 80 km standard single mode fiber (SSMF) system, ENPC method can improve the nonlinear threshold (NLT) (for Q > 10 dB) about 2.7, 1.2, and 1.0 dB, and the maximum Q factor about 1.2, 0.4, and 0.3 dB for 2, 8, and 16 ps/nm/km fiber systems, respectively. The method allow the CO-OFDM system can avoid using optical dispersion compensation even for high dispersion fiber system with higher input power, and the 2-step ENPC solution does not increase more computation complexity compared with NL pre-comp method.     

Directly Modulated 10 Gb/s Signal Transmission over 320 km of Negative Dispersion Fiber for Regional Metro Network

We demonstrate the transmission of directly modulated 10-Gb/s WDM signals over 320 km of negative dispersion fiber (dispersion:-2.5 ps/km/nm @1550 nm) without dispersion compensation. The results indicate that a regional metro WDM network could be implemented cost-effectively by using the proposed negative dispersion fiber and direct modulated lasers.     

采用光纤拉曼放大改善1550 nm外调制有线电视系统的组合二阶失真指标

为克服长距离光纤有线电视（CATV）系统中采用高增益掺铒光纤放大器（EDFA）所带来的非线性损伤．对在残留边带调幅（AM—VSB）外调制光纤有线电视系统中采用光纤分布拉曼放大时的组合二阶失真（CSO）进行了,理论研究。根据拉曼放大对信号光强的增益作用。导出了分布拉曼放大条件下的薛定谔方程。并采用微扰法解出了存在拉曼分布放大时,残留边带调幅外调制有线电视系统中．自相位调制（SPM）导致的组合二阶失真的解析表达式。相应数值计算结果表明．相对于采用掺铒光纤放大器功放．采用相同放大倍数的分布托曼放大可使长距离系统中自相位调制导致的组合二阶失真性能改善10dB以上。因此可以得出结论：在长距离残留边带调幅凋制的有线电视系统中,采用分布式光纤拉曼放大可以较好地改善由自相位调制导致的组合二阶失真恶化。     

Optimally gain-flattened and dispersion-managed C + L-band hybrid amplifier using a single-wavelength pump laser

We propose a hybrid C-band erbium-doped fiber amplifier (EDFA) and L-band Raman fiber amplifier (RFA) using a single pump laser diode. The optimum pump sharing ratio to EDFA/RFA is 1/10 with a total pump power of 660 mW. Using multiple fiber Bragg gratings (FBGs) with various reflectivities at different positions along the dispersion compensation fiber, the optimum dispersion compensation and power equalization for C + L-band channels are simultaneously realized. With an input power of −20 dBm/ch, the signal power variation among the channels is reduced from 9.8 dB to less than ±0.5 dB. Two pump reflectors are introduced to increase the pumping efficiency.     

Fiber to the Classrooms: Internet over Fiber Optical CATV System

This study proposed and demonstrated a directly modulated NTSC AM-VSB 77-channel plus Internet access system using a Fabry-Perot (FP) laser diode, an optical isolator, fiber Bragg grating (FBG), wavelength-division-multiplexing (WDM), channel conversion and two-way communication techniques over an existing multimode fiber (MMF) on the author’s campus. Performances of carrier-to-noise ratio (CNR) of >43dB composite second order (CSO) of >53dB and composite triple beat (CTB) of >53dB were obtained over a 2-km MMF transmission. The proposed two-way communication system is simple and suitable for fiber to the classrooms application.     

Broadband dispersion compensation of conventional single mode fibers using microstructure optical fibers

This paper presents a microstructure optical fiber for dispersion compensation in a wide range of wavelengths. The finite-element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed novel dispersion compensating fiber shows that it is possible to obtain a larger negative dispersion coefficient of about −130 to −360 ps/(nm km), better dispersion slope compensation, better compensation ratio, and lower confinement losses less than 10⁻² dB/km in the entire telecommunication (1400–1600 nm) band by using a modest number of design parameters and very simple cladding design.     

CSO/CTB/BER performances improvement in a bi-directional hybrid DWDM system

Experimental verifications of the feasibility of using chirped fiber grating (CFG) as the dispersion compensation device in a bi-directional hybrid dense-wavelength-division-multiplexing (DWDM) system to reduce the dispersion and cross-phase modulation (XPM) induced crosstalk were proposed and demonstrated. Not only channel capacity was increased, but also good performances of carrier-to-noise ratio (CNR) > 50 dB, composite second order (CSO) >72 dB, composite triple beat (CTB) >69 dB and low bit error rate (BER) < 10-9 were achieved in our proposed system over a 50-km single-mode fiber (SMF) transport.     

Stable wavelength-tuning laser in single-frequency by optical-injected Fabry-Perot laser diode and RSOA for long fiber distance propagation

In this demonstration, we propose and experimentally investigate a stable wavelength-tuning laser configuration by using self-seeded Fabry-Perot laser diode (FP-LD) and external-injected reflective semi-conductor optical amplifier (RSOA). Here, this proposed laser can be tuned in the wavelength range of 1534.05 to 1553.00 nm with a 1.1 nm tuning-step. And the output powers and side-mode suppression ratios (SMSRs) are measured at −5.3 to 4.6 dBm and 31.2 to 50.1 dB/0.05 nm, respectively. And, the proposed laser also can be directly modulated at 2.5 Gb/s on-off keying (OOK) modulation format and propagates 75 km single-mode fiber (SMF) with no optical amplifier and dispersion compensation.     

Directly modulated lasers in negative dispersion fiber links

In the paper the impact of frequency chirp of directly modulated lasers is considered in context of high-speed data transmission over negative dispersion fiber. Chirp/dispersion induced signal distortions are described, and detailed investigations of their influence on 10 Gb/s transmission system performance are presented. The desired laser chirp characteristics and optimal driving conditions are determined. It is also demonstrated that directly modulated laser with low chirp offers similar or even better dispersion tolerance than unchirped (externally modulated) source. Experimental verification of described investigations is presented at the end.     

Reduction in timing jitter by chirp selection for externally modulated return to zero optical soliton pulse at 10 Gb/s

We investigate the chirp selection of externally modulated RZ soliton pulse at 10 Gb/s for fiber optical communication systems for the reduction in timing jitter. We have chosen single arm Mach-Zehnder amplitude modulator with sin² electrical shaped input-output (P-V) characteristic and its chirp range has been varied in the range of −5 to 5. The timing jitter, Q factor and bit error rate (BER) generated for the chirp range has been studied for various fiber lengths and post compensation has been demonstrated to reduce the timing jitter. The number of fixed output amplifiers after every 60 km span is varied from 2 to 10 and corresponding accumulated ASE noise has been studied to manage timing jitter and BER in permissible range, i.e. 5 ps and 10⁻⁹, respectively. It is observed that when two fiber spans are taken then the compensating fiber length for the system is less than 20 km for each case of the chirp considered. For 10 fiber spans, the compensating fiber length increases in the range 60-90 km depending upon the value of chirp taken. Finally it is shown that the chirp value of external modulator should be set to either 0 or −1 for externally modulated RZ soliton pulse in 10 Gb/s optical communication system which makes the system more insensitive to the timing jitter and the selection of dispersion compensating fiber length.     

啁啾光纤光栅对光纤CATV系统中二阶非线性失真的改善

在理论上，我们利用光波的时域场包络方程分析了光纤CATV系统中的二阶非线性失真问题和获得理论的表达式，且分析的结果和数值模拟的结果很好的吻合。在实验上，利用啁啾光纤光栅的调谐特性来改变系统的色散补偿量进行了125公里的光纤CATV的系统实验，很好的证实了以上的理论推导。理论和实验的结果都证实适当的选择啁啾光纤光栅的色散补偿量可以很好的改善系统二阶非线性失真的性能。