Highly accurate long-span chromatic dispersion measurement system by a new phase-shift technique

A highly accurate long span chromatic dispersion measurement system, which is based on a wavelength-division-multiplexing phase-shift technique and utilizes six laser diodes in1.2 sim 1.6 mum spectral region, has been developed. It is intrinsically free from error due to the fiber length variation caused by temperature changes under the measurement. The measurement accuracies of dispersion and Zero-dispersion wavelength are extremely good and within ±0.02 ps/km . nm and ±0.1 nm in 1250 ∼ 1450 nm spectral region in the case of a 10.5-km single-mode fiber measurement. The dynamic range is over 50 dB excluding system theS/Nmargin of 5 dB. Using this system, chromatic dispersion measurements of a 101.9-km pure-silica-core single-mode fiber and a 100.7 km concatenated dispersion-shifted single-mode fiber have been successfully carried out. The measured result has coincided with the arithmetical mean of those of constituent fibers.     

1.5-1.6 µm GaInAsP/InP dynamic-single-mode (DSM) lasers with distributed Bragg reflector

The theoretical bases and the experimental results of the dynamic behavior of1.5-1.6 mum GaInAsP/InP dynamic-single-mode (DSM) lasers with distributed Bragg reflector (DBR) are given. A condition for the single-mode operation of a rapidly modulated DBR laser, called a "dynamic-single-mode laser," and the dynamic spectral width were theoretically presented. Experimentally, buried-heterostructure distributed-Bragg-reflector integrated-twin-guide (BH-DBR-ITG) and buried-heterostructure butt-jointed-built-in distributed-Bragg-reflector (BH-BJB-DBR) lasers emitting at the wavelength of1.5-1.6 mum were directly modulated up to 3 GHz, and the stable single-mode operations were obtained in both types of lasers. The dynamic spectral width at the worst modulation condition was measured to be 0.27 nm, which was aboutfrac{1}{35}times smaller than that of conventional lasers.     

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.     

Chromatic dispersion measurements over a 50-km single-mode fiber

Chromatic dispersion has been measured over a 50-km-long single-mode fiber, using five sinusoidally modulated laser diodes. Results indicate that chromatic dispersion characteristics for single-mode fibers with 33-dB optical loss can be evaluated in the1.2-1.6-mum spectral region.     

Chromatic dispersion induced distortion of modulated monochromatic light employing direct detection

The spectrum of an intensity modulated (IM) and a combined intensity-frequency modulated (IM-FM) monochromatic light source has been generated. The amplitudes of the modulated carrier and the first three pairs of sidebands are plotted showing the influence of IM on an FM signal. The effects of first order chromatic dispersion on the baseband amplitude response and harmonic distortion are determined. The manner in which modulation type and depth, modulating frequency, wavelength, and fiber length alter harmonic distortion is presented. Numerical examples giving the amplitude response of a single-mode fiber system as well as the magnitude of the second- and third-harmonic distortion caused by chromatic dispersion are presented. Based on this material, the limits placed on analog transmission due to chromatic dispersion may be assessed.     

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     

Experimental Study on the Role of Chromatic Dispersion in Continuous-Wave Supercontinuum Generation

The influence of chromatic dispersion on continuous-wave (CW)-pumped supercontinuum (SC) generation in kilometer-long standard fibers is experimentally investigated. We perform our study by means of a tunable, high-power fiber ring laser pumping a dispersion-shifted fiber in the wavelength range of small and medium anomalous dispersion. Our results show that, at low input powers, chromatic dispersion plays a dominant role on nonlinear pump spectral broadening, giving rise to a broader spectrum when pumping just above the zero-dispersion wavelength of the fiber. At higher input powers, however, the width of the generated SC spectrum is mostly due to the Raman effect, hence more independent of the value of the chromatic dispersion coefficient. We show that, in this case, the optimum pumping wavelengths for SC generation are not so close to the zero-dispersion wavelength of the fiber as in the previous case. In these conditions, as the chromatic dispersion grows, we can obtain square-shaped and high-power density spectra, which seem extremely promising for applications in optical coherence tomography.      

Simple approximations for chromatic dispersion in single- mode fibers with various index profiles

Simple approximate formulas of chromatic dispersion and zero-chromatic dispersion wavelength are empirically derived for single-mode fibers with various index profiles having the deformations such as a central dip, hump, and/or tailing at a core cladding interface. These profiles are typical which are commonly obtained in current single-mode fibers. The approximation is based on the exact solution of vector-wave equation. These accuracies are better than 0.3 and 0.03 percent for the chromatic dispersion and zero-chromatic dispersion wavelength, respectively. With the aid of the simple approximations, the properties of chromaric dispersion and zero-chromatic dispersion wavelength for practical single-mode fibers are discussed. The relation between the chromatic dispersion and basic fiber parameters of single-mode fibers, effective cutoff wavelength of the LP11mode, and the spot-size of the LP01mode, are clarified.     

Chromatic-dispersion compensator using virtually imaged phasedarray

A new method for chromatic-dispersion compensation is proposed and demonstrated. This method can produce a chromatic dispersion practically in a wide range from -2000 to +2000 ps/nm and can compensate simultaneously for the dispersion of over 60 wavelength channels with 100-GHz spacing in a wavelength-division multiplexed (WDM) system that has a total bandwidth of over 50 nm. This method has further attractive features such as very small polarization-state dependence, mechanically variable chromatic dispersion, and potential for small packaging. It was experimentally confirmed that this method compensated for the chromatic dispersion accumulated through 110 km standard single-mode fiber (SMF) at 1.55-μm wavelength and that 10-Gb/s signal quality was clearly recovered after the 110-km transmission     

Optical Fiber Cable Measurements in the Field

The optical fiber cable measurement instruments developed by NTF for field use in the 1.3 μm wavelength are discussed. The properties of a stabilized optical light source for single-mode fiber attenuation measurement, optical time-domain reflectometer using a Q-switched Nd:YAG laser as a light source, and chromatic dispersion measurement instrument are described. From the measurement results, these instruments are revealed to be suitable in constructing and maintaining singlemode fiber optical transmission lines.     

Characteristics of dispersion free single-mode fiber in the 1.5 µm wavelength region

Characteristics of dispersion free single-mode fibers in the wavelength regions 1.5 and 1.3 μm are compared experimentally and theoretically. We consider the influence of the refractive index profile on dispersion, the tolerance limits of structure parameters for minimum dispersion, attainable fiber bandwidth, and transmission loss including splicing and bending losses. For a fiber designed for minimum dispersion at 1.5 μm, the measured fiber loss was less than 1 dB/km and bandwidth was 250 GHz. km. nm. The achievable minimum loss estimation shows the advantage of dispersion free fibers at the 1.5 μm wavelength over dispersion free fibers at 1.3 μm.     

888nm半导体抽运的60W皮秒激光振荡器模型

为了建立一个基于888nm半导体抽运的高平均功率和高效率皮秒激光振荡器的理论模型,采用模拟计算方法和谐振腔理论、ABCD定律、自洽条件以及连续被动锁模条件,利用激光晶体Nd:YVO4对波长888nm半导体抽运源的吸收特性和元件的相关参量、合适的腔模参量、实现稳定锁模的参量进行了理论分析和计算,并通过以上研究和模拟计算得到了皮秒振荡器模型的相关数据。结果表明,在120W的抽运功率下,激光器可以输出约61.5W的皮秒激光,光光转换效率51.3%。这一理论模型的建立对高平均功率和高效率皮秒激光振荡器的实验研究起着指导作用。     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

Analysis of CNR penalty of radio-over-fiber systems including the effects of phase noise from laser and RF oscillator

The effect of phase noises from a laser and an oscillator on radio-over-fiber (RoF) systems is analyzed and discussed with a power spectral density (PSD) function. A Mach-Zehnder modulator (MZM) and a phase shifter are employed to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. It is shown that a carrier-to-noise ratio (CNR) penalty is deeply related to the bandwidth of a receiver filter and the phase noise from a radio frequency (RF) signal oscillator rather than that from a laser in a small differential-delay environment and a direct detection scheme. The CNR penalty due to the increment of the laser linewidth from 10 to 624 MHz is almost 1.1 dB, while the increase of the RF-oscillator linewidth from 1 to 100 Hz results in about a 20-dB penalty at a 30-GHz 10-km transmission in a standard single-mode fiber (SSMF) with a fiber chromatic dispersion of 17 ps/km/spl middot/nm.     

光纤OFDM系统中的色散补偿技术研究

为了减小光纤的色度色散对光纤正交频分复用（OFDM）系统性能的影响,提出了将无线通信中的信道估计器引入光纤OFDM系统进行信道估计的色散补偿方法。在理论上分析了光纤的色度色散对于传输OFDM信号的影响,并在实验中采用梳状导频的形式,在每个OFDM码元的特定的子载波上插入导频,在接收端通过基于最小平方（LS）原则的LS估计器进行信道估计,得到了OFDM光纤传输的信道幅度响应和相位响应,通过使用LS估计器,直接调制的光OFDM信号在单模光纤中传输200km,误比特率低于10-6 ,功率代价小于2dB。结果表明,高频子载波较低频子载波更容易受到色散的影响,在光纤OFDM系统中引入信道估计器进行信道估计能够有效补偿由色度色散带来的相位偏移和幅度衰减。     

The effect of chirping-induced pulse shaping on the performance of11 Gbit/s lightwave systems

The influence of laser chirping, fiber chromatic dispersion, and receiver filtering on the shape of the pulses in 11 Gb/s lightwave transmission systems is discussed. Both the NRZ and RZ encoding formats are considered as well as positive and negative dispersion. The results quantify the sensitivity of the system performance to the receiver decision time, the maximum permissible deviation of the laser wavelength from the fiber zero dispersion wavelength, and the improvement in transmission performance offered by pulse compression arising from negative dispersion     

Dynamic spectral width of rapidly modulated 1.58 ?m GaInAsP/InP buried-heterostructure distributed-Bragg-reflector integrated-twin-guide lasers

The dynamic spectral width of a CW GaInAsP/InP buried-heterostructure distributed-Bragg-reflector integrated-twin-guide (BH-DBR-ITG) laser operating at a wavelength of 1.58 ?m was measured under direct modulation up to 3 GHz. The maximum dynamic spectral width at a modulation depth of 100% was measured to be 0.27 nm at the resonance-like frequency of 1.8 GHz. A possibility of wideband transmission of 1.55 ?m conventional single-mode fibre at 185 Gbit km is suggested.     

Profile dispersion effects on transmission bandwidths in graded index optical fibers

Transmission bandwidths of optical fibers would be maximized if their refractive index profiles were optimally graded. However, dispersive differences between fiber material constituents make the optimal power law profile exponent α depend on wavelength. This profile dispersion effect is significant for germanium borosilicate fibers and makes their observed transmission bandwidths change by more than 300 percent within a 650-1050 nm wavelength range. Measurements are made in spectrally filtered white light from a xenon arc lamp that is sinusoidally modulated by an electrooptic crystal. Reduction of sine wave envelope intensity due to transmission in a fiber gives its baseband frequency response. The functional dependence of bandwidth on wavelength is used to diagnose whether α is larger or smaller than the optimal value which minimizes intermodal dispersion at particular wavelengths.     

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.     

Phase-mismatch dependence of efficiency of wave generation through four-wave mixing in a single-mode optical fiber

The generation wave efficiency with respect to phase mismatch in the four-wave mixing process is clarified experimentally in a single-mode fiber transmission line at 825 nm wavelength. The generated power of approximately 20 pW is measured successfully for input signal powers below 1 mW by the technique utilizing a heterodyne receiver and lock-in detector. The calculated efficiency as a function of the equivalent frequency separation can well explain and reflect the results obtained experimentally. Furthermore, the efficiency at zero chromatic dispersion wavelengths of 1.3 and 1.55 μm is also discussed considering chromatic dispersion slope against wavelength.