Long-distance gigabit-range optical fiber transmission experiments employing DFB-LD's and InGaAs-APD's

High-speed and long-distance transmission characteristics have been examined at 1.2, 2, and 4 Gbit/s, employing mesa structure DFB-DC-PBH LD transmitters and planar InGaAs APD receivers. High receiver sensitivities, -40 dBm at 1.2 Gbit/s, -37.4 dBm at 2 Gbit/s and -32.4 dBm at 4 Gbit/s, have been obtained employing high-speed and low noise InGaAs APD/FET receiver circuits. Long-span transmissions, 1.2-Gbit/s 170-km, 2-Gbit/s 141-km, and 4- Gbit/s 120-km at 1.55 μm, and 4-Gbit/s 74-km at 1.3 μm, have been performed. Power penalties caused by the LD wavelength chirping in the 1.5- μm wavelength region and error rate flooring caused by the LD side-mode oscillation in the 1.3- μm wavelength region are discussed. The transmission length is limited not only by the DFB LD wavelength chirping but also by the two-mode oscillation, which was observed at the pulse leading edge when LD bias current was near the threshold current. From the 1.3 μm wavelength 4-Gbit/s experiment, it was found that the pattern effect of the side-mode oscillation caused the error rate floor, when the LD bias current is set near the threshold current, and that the error rate floor disappeared when the bias current is set slightly above the threshold.     

Chirp-free transmission over 82.5 km of single mode fibers at 2 Gbit/s with injection locked DFB semiconductor lasers

The spectral and modulation characteristics of injection locked distributed feedback lasers operating at 1.5-μm wavelength have been investigated. The total elimination of excess chirp in directly modulated lasers by the injection locking technique has allowed us to perform transmission experiments over 82.5 km of single mode fibers at 2 Gbit/s without any measurable penalty related to dispersion. Device design parameters for efficient chirp suppression are also given.     

Gigabit/s optical receiver sensitivity and zero-dispersion single-mode fiber transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 μm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p+nn- Ge APD. The p+nn- Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55μm and a 10^-9error rate, which was 4 dB better than the receiving level with a p+n Ge APD. Detector performance at 1.3μm was also studied for comparison with performance at 1.55μm. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55μm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) . km at 1.55μm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3μm dispersion-free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

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.     

Computer simulation and noise analysis of the system performance of 1.55-µm single-frequency semiconductor lasers

A theoretical model for the noise analysis of the system performance of 1.55-μm single-frequency semiconductor lasers is presented. Computer simulations are used to analyze the role of various noise sources in a 1.7-Gbit/s transmission experiment where the data was transmitted over 69 km using a 1.56-μm distributed-feedback laser. The bit-error-rate curves generated from numerical simulations agree well with the results of the transmission experiment. The relative contributions of various noise sources in limiting the system performance are discussed and compared. In particular, we consider circuit noise, shot noise, laser intensity noise, mode-partition noise, parasitic reflections, and the frequency chirp.     

Very high speed intra-office optical link experiments for 0.4- and 1.6-Gbit/s trunk lines

Very high speed optical links are studied. Applicable areas for systems using light-emitting diodes (LED'S) or laser diodes (LD's) with short transmission length are clarified. A new type differential mode inversion (DMI) decoder is proposed and it is shown that the DMI code is suitable as the line code for very high speed intra-office optical links. By using DMI code. a 400-Mbit/s information rate optical transmission experiment employing a 1.3-μm InGaAsP LED and a 0.5-km graded-index multimode optical fiber (GIF) as well as a 1.6-Gbit/s information rate optical transmission experiment using a 1.3-μm InGaAsP/InP Fabry-Perot-type LD and a 10-km single-mode optical fiber (SMF) are carried out. These results show that the feasibility of a 400-Mbit/s intra-office optical link using the LED and GIF, as well as a 1.6-Gbit/s intra-office optical link using the LD and SMF, are confirmed and this optical transmission technology has high-speed performance up to 3.2 Gbit/s.     

445 Mbit/s transmission field experiment at 1.55-µm wavelength region over 80 km using undersea optical-fiber cable

New transmission equipment employing a 1.55-μm distributed feedback laser diode (DFB-LD) to overcome fiber dispersion has been tested at environmental conditions using 1.3-μm zero-dispersion fiber cable on the undersea section of route F-400M. The DFB-LD's dynamic spectrum characteristics, in relation to power penalty, were examined and a suitable laser prebias control level was obtained. Field experimental transmission lines operated error free for a two-month period, and applicability to 1.55-μm 445-Mbit/s systems of over 100 km was shown.     

1.3-µm BH laser performance at microwave frequencies

We have studied the performance of In1-xGaxAsyP1-yburied heterostructure (BH) 1.3-μm lasers in the microwave range. This study consisted of small-signal, large-signal, and digital pseudo-random word evaluation of these lasers. The small-signal study pointed out the impact of the oxide stripe capacitance on the laser response at microwave frequencies. The large-signal study uncovered basic laser non-linearities that affect the temporal response, spectral broadening, and wavelength chirp. Finally, digital pseudo-random word tests performed at 1.7 Gbit/s indicated that in spite of these inherent laser nonlinearities, the 1.3-μm BH lasers performed well enough to be considered as promising sources for gigabit optical communication systems.     

Dispersion compensation by active predistorted signal synthesis

Techniques for the synthesis of an optical signal predistorted to compensate for fiber dispersion are discussed theoretically. A scheme for very high bit rate (>10 Gbit/s) time-division-multiplexed transmission is proposed which neither requires extremely short pulse sources nor suffers from their inherent dispersion limitations. The rudimentary aspects of the techniques have been verified experimentally by demonstrating both enhanced and degraded transmission of a 4-GHz modulated signal at 1.55 μm over 10-30 km of optical fiber.     

8-Gbit/s transmission experiment over 68 km of optical fiber using a Ti:LiNbO3external modulator

We describe the performance of an experimental 1.5-μm lightwave transmission system operating at 8 Gbit/s over 68.3 km of single-mode fiber. The dispersion penalty is limited to 1 dB through the use of external modulation and is attributable to the intrinsic information bandwidth.     

High-speed optical pulse transmission at 1.29-µm wavelength using low-loss single-mode fibers

Optical-fiber transmission experiments in the 1.3-μm wavelength region are reported. GaInAsP/InP double-heterostructure semiconductor laser emitting at 1.293 μm is modulated directly in nonreturn-to-zero (NRZ) codes at digit rates tanging from 100 Mbit/s to 1.2 Gbit/s. Its output is transmitted through low-loss GeO2-doped single-mode silica fibers in 11-km lengths. Transmitted optical signals are detected by a high-speed Ge avalanche photodiode. Overall loss of the 11-km optical fibers, including 11 splices, is 15.5 dB at 1.3 μm. Average received optical power levels necessary for 10^-9error rate are -39.9 dBm at 100 Mbit/s and -29.1 dBm at 1.2 Gbit/s. In the present system configuration, the repeater spacing is limited by loss rather than dispersion. It seems feasible that a more than 30 km repeater spacing at 100 Mbit/s and a more than 20 km even at 1.2 Gbit/s can be realized with low-loss silica fiber cables, whose loss is less than 1 dB/km. Distinctive features and problems associated with this experimental system and constituent devices are discussed.     

初始啁啾补偿光纤色散效应的数值研究

以具有初始啁啾的高斯脉冲在单模光纤中的传输为例,分析、计算了线性初始啁啾对光纤二阶、三阶色散效应的影响,指出了初始啁啾进行色散补偿的适用范围和条件,并对二阶、三阶色散完全补偿光纤链路中40Gbit/s短脉冲传输效果进行了数值计算,结果表明,依据入射功率选择合适的初始啁啾,能使脉冲稳定传输距离大幅提升.     

10 Gbit/s transmission over 69 km of non-dispersion-shifted singlemode fibre with CPFSK direct modulation of 1.55 mu m BH DFB laser

With low chirp direct modulation of a commercially available lambda =1.55 mu m BH DFB laser module at 10 Gbit/s, a transmission experiment over 69 km of non-dispersion-shifted singlemode fibre was successfully performed. The scheme is based on optical FM by modulation of the injection current with subsequent conversion into intensity modulation by means of a fibre Mach-Zehnder interferometer.<>     

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

A DC-coupled wide dynamic range AGC amplifier IC for 560-Mbit/s optical transmission

A wide-band high-gain AGC amplifier stabilizing the output dc level against a broad gain variation is proposed and monolithically integrated using high-speed 1-μm Si-bipolar IC technology. The fabricated IC exhibits a maximum gain of 39 dB, gain dynamic range of 44 dB, bandwidth of 800 MHz, and output dc-level fluctuation of 8 mV, and realizes wide dynamic range and direct dc-coupling of the multistage AGC amplifier. Also, in order to examine the feasibility of the fabricated IC, a 1.5-μm-wavelength optical transmission experiment was carried out using DFB-LD and InGaAs-APD. Measured minimum received optical power for an error rate of 10^-9is -40 dBm at 560 Mbit/s and -38 dBm at 1.12 Gbit/s. Optical dynamic range of 30 dB is also achieved by using the fabricated IC and APD.     

Silicon bipolar decision circuit handling bit rates up to 5 Gbit/s

A high-speed silicon bipolar decision circuit is presented which operates up to 5 Gbit/s. It may serve as a subcomponent for integration in a regenerator/repeater circuit for multi-gigabit fiber-optic trunk lines. The circuit was implemented in a standard bipolar silicon technology featuring oxide-wall isolation, 2-μm emitter stripe widths, and a transit frequency of 9 GHZ atV_{CE} = 1V. The measured clock-phase-margin of the decision circuit at 4 Gbit/s corresponds to two thirds of a bit slot and to half a bit slot at 5 Gbit/s. The minimum input sensitivity at 4 Gbit/s is less than 150 mV.     

Practical limitations on optical amplifier performance

Practical issues are considered to determine if significant improvements in the sensitivity, of 1.55-μm optical receivers can be realized through the use of semiconductor laser preamplifiers. It is found that practical problems related to realizable values of population inversion parameter, input coupling losses, external optical filter requirements, polarization effects, and source laser stability make it unlikely that optical preamplifiers can approach their optimum performance at data rates below several Gbit/s. The most promising application of optical preamplifiers will therefore be to increase the sensitivity of receivers in future fiber optic communication systems operating at multigigabit data rates.     

Long-span single-mode fiber transmission characteristics in long wavelength regions

Experimental and analytical results on high-speed optical pulse transmission characteristics for long-span single-mode fibers by using InGaAsP lasers, emitting at 1.1, 1.3, and 1.5 μm, as well as a Ge-APD are reported. At 1.1 μm, 400 Mbit/s transmission experiments were successfully carried out with 20 km repeater spacing. At 1.3 μm, where single-mode fiber dispersions approach zero, error rate characteristics showed that optical power penalties at 100 Mbits/s and 1.2 Gbits/s are negligible even after 30 and 23 km fiber transmission, respectively. It was confirmed that a 1.6 Gbit/s transmission system has 15 km repeater spacing. At 1.5 μm, where silica fibers have ultimately minimum loss, single-mode fiber transmission experiments were carried out at 100 Mbits/s with about 30 km repeater spacing. 400 Mbit/s transmission characteristics using 20 km fibers were also studied. Fiber bandwidths, measured by optical pulse broadenings after 20 km transmission, were 24, 140, and 37 GHz . km . nm at 1.1, 1.3, and 1.5 μm, respectively. Progress in lasers, fibers, and optical delay equalizers at 1.5μm will bring about large-capacity transmission systems having about 150 km repeater spacing. These results reveal fiber dispersion characteristics in the long wavelength region essential to high data rate single-mode fiber transmission system design.     

正常色散光纤消啁啾的孤子传输实验

利用正常色散光纤消啁啾成功地进行了１Ｇｂｉｔ／ｓ，２３ｋｍ的光孤子传输，观察到了一阶和高阶孤子传输现象。在对光脉冲消啁啾过程中发现了一个新的现象：适当长度的正常色散光纤消啁啾不仅能够压窄负啁啾的脉宽，而且能够压窄频谱。     

1.3-µm BH laser performance at microwave frequencies

We have studied the performance of In1-xGaxAsyP1-yburied heterostructure (BH) 1.3-µm lasers in the microwave range. This study consisted of small-signal, large-signal, and digital pseudo-random word evaluation of these lasers. The small-signal study pointed out the impact of the oxide stripe capacitance on the laser response at microwave frequencies. The large-signal study uncovered basic laser non-linearities that affect the temporal response, spectral broadening, and wavelength chirp. Finally, digital pseudo-random word tests performed at 1.7 Gbit/s indicated that in spite of these inherent laser nonlinearities, the 1.3-µm BH lasers performed well enough to be considered as promising sources for gigabit optical communication systems.