Performance evaluation of the different types offiber-chromatic-dispersion equalization for IM-DD ultralong-distanceoptical communication systems with Er-doped fiber amplifiers

We have evaluated the transmission performance of different fiber-chromatic-dispersion-equalization methodologies for ultralong distance IM-DD optical communication systems that use Er-doped fiber amplifier repeaters. The experiment used a 1000 km fiber loop consisting of 30 dispersion-shifted fiber spans and 31 Er-doped fiber amplifiers. We changed the insertion point of the normal single-mode fiber for equalization to change the shape of the accumulated chromatic dispersion. Comparison of the longest transmission distance and the width of the 9000 km transmissible window are discussed for several types of dispersion equalization. The results indicate that the best type of the dispersion equalization for ultralong distance IM-DD optical communication systems is to install dispersion-shifted fibers with short sections of normal single-mode fibers to compensate the accumulated dispersion     

The experimental study of the effect of fiber chromatic dispersionupon IM-DD ultra-long distance optical communication systems withEr-doped fiber amplifiers using a 1000 km fiber loop

We have evaluated the transmission performance difference of ultra-long distance optical communication systems with Er-doped fiber amplifier repeaters due to fiber chromatic dispersion effect. A 1000 km fiber loop with 31 Er-doped fiber amplifiers was used for the experiments. We have changed the system zero dispersion wavelength by changing the length of the normal single-mode fiber at the end of the fiber loop, and measured the bit-error-rate after transmission. Comparison of the longest transmission distance and the width of the 9000 km transmissible window were discussed for various system zero dispersion wavelengths. The results have shown that the difference between the gain peak wavelength of the amplifier chain and the system zero dispersion wavelength caused degradation of the system performance, and the degree of the degradation was almost symmetrical from the gain peak wavelength     

Adaptive dispersion equalization by monitoring relative phase shiftbetween spacing-fixed WDM signals

This paper proposes a novel adaptive dispersion equalization system that equalizes the temperature-induced dispersion fluctuation in long-span ultra-high-speed optical transmission systems. The system monitors the dispersion fluctuation by measuring the relative delay between two wavelength division multiplexed (WDM) signals, and equalizes the dispersion fluctuation by wavelength tuning. A variable-dispersion equalizer can be used instead of wavelength tuning. Adaptive equalization is successfully demonstrated in 40-Gb/s (8-ps-RZ pulses) 400-km transmission. Furthermore, the proposed equalization system is shown to be applicable to WDM systems that use dispersion and dispersion slope compensation. Since the sensitivity to the dispersion fluctuation is improved by extending the wavelength spacing of the signal and monitor channels, the system is shown to operate even when polarization-mode dispersion (PMD) of the transmission fiber must be taken into account     

25-Gb/s optical NRZ transmission over 40 km of single-mode fiber at 1550 nm without dispersion compensation

We present a method for transmitting 25-Gb/s optical nonreturn-to-zero signals at a wavelength of 1550 nm over a 40-km single-mode fiber without any dispersion compensation methods. We propose optimized self-phase modulation by varying parameters of the fiber launching power and the extinction ratio of optical non-return to zero signals to overcome severe signal distortions by the chromatic dispersion effect. Using the optimization of the self-phase modulation effect, we were able to transmit 25-Gb/s optical nonreturn-to-zero signals over a 40-km single-mode fiber, which can be applicable to passive optical networks with a single wavelength channel and a high split ratio. We demonstrated that the self-phase modulation effect can be controlled by the extinction ratio and the fiber launching power.     

Effects of water absorption peaks on transmission characteristics of LED-based lightwave systems operating near 1.3 µm wavelength

Chromatic dispersion effects on LED-based optical fiber systems are calculated as a function of transmission length and the LED central wavelength. The computer analysis includes the filtering effects of water absorption which reduces the spectral width of LED signal pulses. We show that the basebandwidth of multimode fiber systems can be significantly increased by offsetting the LED central wavelength above the wavelength at which minimum chromatic dispersion occurs in the fiber medium. Additional bandwidth degradation due to modal dispersion effects are not considered. However, the combined effects of optical loss and chromatic dispersion are used to calculate upper limits for repeater spacings in possible multimode wideband systems.     

Optimal design for direct-detection system with optical amplifiersand dispersion compensators

System performances of direct detection optical fiber communication systems with optical amplifiers and dispersion compensators are investigated theoretically and confirmed by experimental results for several different configurations. The experimental results agreed well with the calculated results. The theoretical calculation predicts that a 120-km repeaterless transmission of 10 Gb/s is possible through the standard single-mode fiber using only one commercial fiber amplifier and a dispersion compensation fiber at the receiving end     

Optical PSK synchronous heterodyne detection transmissionexperiment using fiber chromatic dispersion equalization

This letter demonstrates an 8-Gb/s optical PSK (phase shift keying) synchronous detection transmission experiment using external cavity laser diodes. A 188-km 1.3-μm zero-dispersion fiber is used as the transmission medium at the wavelength of 1.55 μm. Fiber chromatic dispersion is successfully compensated with a microstrip-line delay equalizer     

Advanced Optical Modulation Formats

Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity.     

Investigation into the temperature dependence of chromaticdispersion in optical fiber

The change in the chromatic dispersion of optical fiber with temperature is an important design parameter for 40-Gb/s systems. We derive an equation for the change in dispersion with a temperature that is more general than what has previously been published. We present experimental results for the change in fiber dispersion with temperature for six commercially available fiber types of interest for 40-Gb/s communication systems. In addition, we demonstrate that the empirical model developed by Ghosh et al in 1994 for the temperature-dependent index of refraction of SiO₂ can be used to accurately model the temperature dependence of the chromatic dispersion of a wide variety of optical fibers     

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40 Gb/s. The proposed approach shows great potential for future high data rate optical access networks.     

Lightwave single sideband wavelength self-tunable filter using anInP:Fe crystal for fiber-wireless systems

A new optical single sideband filter is presented to compensate for chromatic dispersion effects in fiber-wireless systems. The device is based on three dynamic Bragg gratings, which are generated in a photorefractive iron-doped indium phosphide (InP:Fe) crystal. This filter is controlled by the input optical double sideband signal itself, which makes it independent of the modulated optical carrier wavelength. In this paper, the principle of the device is presented and demonstrated. Experiments include a 14-km fiber transmission followed by a 3-m radio link carrying a 140-Mb/s binary phase-shift keyed data stream at 16 GHz     

Fiber Bragg grating fabrication for dispersion slope compensation

Group-delay dispersion slope causes signal deterioration in long-distance high-data-rate communication systems. We report the fabrication of high-quality apodized and chirped fiber gratings with dispersion slopes as high as -1800 ps/nm/sup -2/ over a 0.7-mn bandwidth-sufficient to compensate for the dispersion slope of >25000-km length of standard fiber at a wavelength of 1550 nm. We believe this is the first time that fiber Bragg gratings have been specifically designed and fabricated for dispersion slope compensation. The fabrication technique uses a standard unchirped phase mask and two scans of the inscribing UV beam.     

Waveform distortion evaluation for optical CPFSK heterodyne transmission

Waveform distortion of a continuous phase FSK signal due to fiber chromatic dispersion is measured. The transmission spacing is estimated to be 100 km at 5 Gbit/s with 1.55-μm wavelength. Also the 2-Gbit/s optical CPFSK heterodyne detection transmission experiment is reported. Since there is no chirping degradation, it is possible to transmit the signal through a 200-km single-mode fiber.     

Fourth-order dispersion compensation for 250-fs pulse transmissionover 139-km optical fiber

Record distance transmission of 250-fs pulses over 139-km optical fiber at 6-GHz repetition is realized by compensating chromatic dispersion up to fourth-order using a novel approach. The link is designed combining 108.5-km standard single-mode fiber (SMF), 17.5-km dispersion-shifted fiber, and 13-km negative-slope dispersion-compensating fiber to achieve both zero total chromatic dispersion and slope at the 1.55-μm carrier. Fourth-order pulse dispersion caused by the fiber dispersion curvature around 1.55 μm is then suppressed by adding the quadratic phase of opposite sign from excess SMF to produce 503-fs output. However, both higher quality and shorter 390-fs output is achieved after applying 6-GHz electrooptic phase modulation (3.5 π O-peak) to prestretched pulses and adding a further 50-m SMF to the link     

Compensation for chromatic dispersion and nonlinear effect in highdispersive coherent optical repeater transmission system

A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible     

Transmission limitations due to self-phase modulation in opticalPSK heterodyne detection systems employing chromatic dispersionequalization

Even if the amplitude of a phase-modulated optical signal is constant before transmission, amplitude modulation is caused by fiber chromatic dispersion. As a result, self-phase modulation (SPM) is induced. In optical heterodyne detection, SPM cannot be compensated for by the delay equalizer (electrical domain) used to compensate fiber chromatic dispersion. However, the transmission distance limitation of multi-repeatered coherent transmission systems has not been investigated in the presence of SPM. This paper theoretically and experimentally investigates the transmission distance achievable with a phase-shift-keying (PSK) heterodyne detection system employing in-line optical amplifiers and delay equalization. The calculated results show that equalization is effective when γP₀/2B²|β₂|<10 in the normal dispersion regime, and γP₀/2B²|β ₂|<15 in the anomalous dispersion regime. Furthermore, the increase in transmission distance achieved by using equalization is experimentally shown in an 8 Gb/s PSK heterodyne transmission experiment using a conventional single-mode (SM) fiber and in-line fiber amplifiers     

Automatic dispersion equalization for installing high-speed opticaltransmission systems

This paper proposes an optical transmission system with automatic dispersion equalization for exploitation of the fiber capacity without additional installation cost. The system has two operational modes: “measurement-mode” wherein dispersion is measured by phase-to amplitude-modulation conversion, and “data-transmission-mode” for providing telecommunication services. Dispersion equalization is realized by the accompanying use of dispersion compensating devices and wavelength tuning to the zero-dispersion of the optical fibers. Supervisory-channel communication enables remote operation. We demonstrate a simplified system; the dispersion of a 10 Gb/s-1000 km transmission line is successfully equalized in a fully automatic manner. Equalization with the preciseness of 10.1 mn from the zero-dispersion wavelength provides penalty free transmission or better performance with optical input power under the Brillouin threshold     

Optical Dispersion Compensator With$&#8811;$4000-ps/nm Tuning Range Using a Virtually Imaged Phased Array (VIPA) and Spatial Light Modulator (SLM)

We present an optical tunable chromatic dispersion compensator based on a virtually imaged phased-array and spatial light modulator providing both positive and negative dispersion. We demonstrate tunable dispersion compensation of 10-Gb/s positively chirped nonreturn-to-zero data signal over a range of$-4080sim+850$ps/nm (240-km single-mode fiber to 9.5-km dispersion-compensating fiber), which operates independent of the input state of polarization and has potential capability for wavelength-division multiplexing.     

Gigabit single-mode fiber transmission using 1.3-µm edge-emitting LEDs for broad-band subscriber loops

This paper describes gigabit single-mode fiber transmission using 1.3-μm edge-emitting LED's for broad-band subscriber loops, focusing on a method of calculation for maximum transmission distance and 1.2-Gbit/s and 600-Mbit/s transmission experiments. Gigabit single-mode fiber transmission is necessary for subscriber loops, especially in broad-band ISDN and optical CATV systems. Edgeemitting LED's are excellent light sources because of their high power launched into the fiber compared with surface-emitting LED's, and currently lower cost and higher reliability than laser diodes. The maximum transmission distance is carefully estimated by taking into account the wavelength dependence for both chromatic dispersion and loss of the single-mode fiber, and the possibility of gigabit transmission near the dispersion free wavelength 1.3 μm, is confirmed. Encouraged by the above results, we demonstrate 1.2-Gbi,t/s 10-km and 600-Mbit/s 20-km transmission experiments using a newly developed 1.3-μm edge-emitting LED and a new driver circuit with a simple response compensation circuit. These results show the proposed calculation method and the LED response compensation circuit to be powerful tools for the realization of low-cost gigabit single-mode fiber transmission using edge-emitting LED's.     

海底光缆用色散均衡光纤

介绍了一种带正色散的单模光纤,用来均衡常用于海底光缆中的非零色散位移光纤的负色散。这种光纤类似于常规单模光纤（Ｇ．６５２光纤）,但具有较低的衰减和较小的宏弯损耗。由于这种光纤应用常规的掺锗纤芯和纯ＳｉＯ２包层,与目前常用的纯ＳｉＯ２纤芯和掺氟包层的色散均衡光纤相比,在成本上具有较大的优越性。