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.     

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.     

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.     

Characteristics of Gbit/s optical receiver sensitivity and long-span single-mode fiber transmission at 1.3 µm

Sensitivity of a 1.3 μm Ge APD receiver was measured at data rates ranging from 100 Mbits/s to 2 Gbits/s, using a high-speed GaAs FET RZ driver, low-noise Si bipolar transistor (BIT) receiver amplifier, and a highly sensitive TD comparator. The required received optical level at a 10^-9error rate was -31.9 dBm for 2 Gbits/s with a Ge APD/Si BIT front end having a 50 Ω input impedance. A Ge APD/ GaAs FET front end, with a 500 Ω input impedance, brought about 2 dB improvement at 100 Mbits/s, as compared with a Ge APD/Si BIT (50 Ω) front end. A coupling loss of 4 dB, achieved by a hemispherical microlens tipped on a single-mode fiber, and a low fiber loss of 0.57 dB/km, including splice loss, enabled 44.3 km single-mode fiber transmission at 2 Gbits/s. The 1.3 μm transmission system has a data rate repeater-spacing product of 88.6 (Gbit/s)km. Prospects of Gbit/s receiver sensitivity and the 2 Gbit/s transmission system, with more than 50 km repeater spacing, are also discussed.     

Repeater spacing of 280 Mbit/s single-mode fiber-optic transmission system using 1.55 µm laser diode source

This paper describes an attainable repeater spacing for a high bit-rate single-mode fiber-optic transmission in the 1.55 μm wavelength region where laser mode partition noise comes to be significant. An expression for evaluating mode partition noise is given as the form involving the influence of laser spectral fluctuations under high bit-rate modulation, together with the intersymbol interference and the equalized pulse shape in tile optical receiver. After the validity of its numerical results is confirmed experimentally, the resulting evaluation of laser mode partition noise is connected to a systematic discussion on the attainable repeater spacing of a 280 Mbit/s fiber-optic transmission system operating at 1.55 μm, along with fiber loss versus dispersion tradeoffs. This discussion permits the attainable repeater spacing to be 60-70 km for the combination of a laser diode with 1.5-2.0 nm spectrum broadening and a fiber with the loss of 0.5 dB/km and the dispersion of 4-6 ps/km - nm.     

Optical Fiber Submarine Cable System Development at KDD

An optical fiber submarine cable system using longwavelength and single-mode optical fiber is expected to provide economical long-haul digital transmission. This paper describes the recent research and development on an optical fiber submarine cable system for international communication at the KDD Research and Development Laboratories. An experimental model including cable and repeaters has been designed and manufactured. An experimental repeater of 1.3 μm and 280 Mbits/s was laid at a depth of 1500 m and its fundamental performance was measured in November 1981. Test production of longlength cable having a single continuous length of 30 km became possible in the end of 1981. In early June 1982, the experimental system with a 50 km cable length and two repeaters operating at 300 Mbits/s and 1.3 μm wavelength was laid in a loop into the Sagami Bay from the KDD Ninomiya Submarine Cable Landing Station.     

Design considerations for the structural optimization of a single-mode fiber

Design considerations are made for the structural optimization of single-mode fibers used in high-bit-rate and long-haul transmission systems in the long-wavelength region. As the basic fiber parameters, a combination of the spot size W0and the effective cutoff wavelength λceis newly chosen, because the combination is found to suitably describe various actual index profiles which deviate from an ideal step-index profile. A procedure to specify the usable range of W0and λceis established, whereby the overall transmission-line loss in one repeater section is calculated using simple expressions for fiber intrinsic loss, excess loss in the cabling process, and splice loss, etc. The optimum values for a 400 Mbit/s transmission system operating at 1.3 μm with a repeater spacing of 20 km are obtained asW_{0} = 5.0 pm 0.5mum and 1.1 μmleqlambda_{ce}leq 1.28 mum taking into consideration the additional requirement for the possible use atlambda=1.55 mum     

800 Mbit/s optical transmission experiments with dispersion-free fibres at 1.5 ?m

By using dispersion-free single-mode fibres at 1.5 ?m, where silica fibres have minimum loss, an optical transmission experiment was successfully carried out at 800 Mbit/s with 20 km repeater spacing. Error rate against receiving optical level characteristics showed that the optical power penalty caused by fibre dispersion is negligible after long line transmission at 1.5 ?m.     

The SL Undersea Lightguide System

A digital optical fiber undersea cable system targeted for transatlantic service in 1988 is now under development at Bell Laboratories. The system uses single-mode fibers to carry data at a bit rate of 280 Mbits/s. Using digital speech compression techniques, a total system capacity of over 35 000 two-way voice channels can be realized. With laser transmitters at 1.3 μm, repeater spacings are expected to exceed 35 km. This paper discusses system parameters, repeaters, fiber and cable design, terminal equipment, and system measurements.     

Single and multimode fiber bandwidth measurements with single and multilongitudinal mode lasers operating at 0.8-, 1.3-, and 1.5-µm wavelength

The bandwidth characteristics of single and multimode optical fibers have been investigated with single and multilongitudinal mode laser sources operating at 0.8, 1.3, and 1.5 μm. It is shown that single-mode fiber with a cutoff wavelength of 1.3 μm can support 1 Gb/s transmission over at least 7.5 km with a 0.8-μm laser source.     

1.5 m optical transmission experiments using very low-loss single-mode fibres

By using an InGaAsP semiconductor laser emitting at 1.5 ?m, where silica fibre loss is at a minimum, single-mode fibre transmission experiments were successfully carried out at 100 Mbit/s with about 30 km repeater spacing, 400 Mbit/s transmission characteristics using 20 km fibres are also reported.     

Design and performance of ultra-low-loss single-mode fiber cable in 1.5-µm wavelength region

The structural optimization of single-mode fiber for use in the 1.5-μm wavelength region is made with the aim of minimizing the total transmission-line loss over a repeater section. For example, the optimum ranges of the mode-field radius w0and effective cutoff wavelength λceare determined as 5.5 μmleq w_{0} leq 6.5 mum and 1.35μmleq lambda_{ce} leq 1.53 mum for high bit-rate transmission systems with a repeater spacing of 80 km. Based upon the design, ultra-low-loss single-mode fiber cables are fabricated. The average loss of 108 fibers in the cables is 0.19 dB/km at 1.55 μm. The total loss of a 216-km-long fiber link containing 107 splice points was 46.3 dB. Good loss stability at high temperatures as well as during the cable manufacturing processes, are achieved by the appropriate choices of coating materials and optimized fiber parameters.     

1.3 ?m/1.5 ?m bidirectional WDM optical-fibre transmission system experiment at 144 Mbit/s

Results are reported of a 1.3 ?m/1.5 ?m bidirectional WDM transmission system experiment operating at 144 Mbit/s over 58 km of cabled single-mode fibre. Regenerators used Bell Laboratories-developed 1.3 and 1.5 ?m InGaAsP semiconductor lasers, InGaAs PIN diodes, microwave monolithic amplifiers and optical bidirectional couplers.     

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.     

British Telecom 565 Mbit/s lightline system

British Telecom is currently developing a 565 Mbit/s trunk optical fibre system which incorporates both multiplexing and line transmission. The system will operate at 1.3 μm over single-mode fibre with a 30 km repeater spacing. Extensive use is being made of ECL uncommitted logic arrays (ULAs) manufactured at British Telecom Research Laboratories (BTRL) and derived from the reliable ECL 40 process as used in submarine cable system integrated circuits. Details of the system design are presented together with the initial results of a laboratory system built out of commercially available components to establish confidence in the design.     

Trends in long-wavelength single-mode transmission systems and demonstrations in japan

Long-wavelength single-mode optical fiber transmission technology has recently made rapid progress and is now moving into the commercial operation stage. This paper describes the present state of this technology focusing on the research and development work in the Electrical Communication Laboratories. Based on the results of experiments on optical devices and on preliminary system feasibility analysis, it is shown that, at the present time, an optical wavelength in the 1.3 μm band is desirable for large capacity transmission from the viewpoint of attainable repeater spacings. A field trial plan of a 400 Mbit/s optical transmission system for a long-haul trunk which can compete economically with existing digital transmission systems is outlined.     

Single-mode fiber design for long haul transmission

By using simple yet accurate approximations for the propagation characteristics of a single-mode optical fiber, we obtain a simple model for the total loss and chromatic dispersion of single-mode fiber transmission lines as a function of the operating conditions such as splice offset, microbending loss, bends, etc. This model is then applied to typical cases of terrestrial and submarine systems and we obtain single-mode fiber designs which are stable with respect to slight operating condition changes for both 1.3 and 1.55 μm wavelengths. It appears that the same fiber can be used at 1.3 μm for both terrestrial and submarine systems, and even for 1.55 μm terrestrial systems if monochromatic sources become available at this wavelength. A general comparison between the two wavelengths is carried out and shows under which conditions the 1.55 μm wavelength is of practical interest. It is emphasized that the availability of monochromatic sources at 1.55 μm would make a major breakthrough for the repeater spacing.     

1.55-μm fiber-optic transmission experiments for long-spansubmarine cable system design

Results of 1.55-μm transmission experiments at 140, 280, and 565 Mb/s involving conventional and dispersion-shifted single-mode fibers along the Fabry-Perot laser diode (FP-LD) and distributed-feedback laser diode (DFB-LD) optical sources are discussed. The results show which combination of optical fiber and optical source best meet the requirement of long repeater spacing for each bit rate. The results indicate that to achieve repeater spacing more than 100 km with dispersion-shifted fibers and FP-LD optical sources will impose strict requirements on both the optical fibers and the optical sources even at 280 Mb/s. Alternatively, systems using DFB-LD optical sources will not degrade the transmission performances and will considerably loosen requirements on the fibers and optical sources. A combination of dispersion-shifted fibers and DFB-LD optical sources can further loosen the requirements on the fibers and optical sources in 560-Mb/s systems     

Long-wavelength optical fiber communication

Recent research on long-wavelength lightwave communication utilizing the wavelength region between 1.3 and 1.6 µm is reviewed with an eye toward future system development. The attraction of the long-wavelength region is the availability of the ultimately low-loss and wide-band features of the silica fiber, where minimum loss is 0.27 dB/km at a wavelength of 1.3 µm and 0.16 dB/km at 1.55 µm. The single-mode fiber has found its first significant applications in long-wavelength systems. The specific characteristics of lightwave components are discussed with focus on physical fundamentals. The practical performance of fibers and lightwave devices is surveyed. The dynamic properties of long-wavelength laser diodes are discussed in relation to fiber characteristics. The noise characteristics of long-wavelength detectors are considered for the purpose of specifying the repeater spacing. Some system studies are reviewed, for example, 1.3-µm-wavelength lightwave systems, which have demonstrated bandwidth-distance products of about 40 GHz ċ km. Various approaches to extend the capacity of long-wavelength lightwave transmission are given. In the future, the 1.5-µm wavelength system could operate at the lowest loss wavelength region extending from 1.5 to 1.65 µm. Much higher performance, for example, bandwidth-distance products of 185 GHz ċ km, achieved by further continuation of research and development on lightwave sources as well as fibers. Because of the author's familiarity with work in Japan, that work is emphasized and most frequently cited.     

Deep sea trial of 1.55 μm optical fibre submarine cable system

The first 6000 m deep sea trial of a 1.55 μm optical fibre submarine cable system was successfully conducted in the Pacific Ocean, near Torishima Island, in January 1988. By using 1.55 μm loss-minimised single-mode fibre cables and submerged fully monolithic Si-IC regenerators with DFB lasers, excellent transmission performances at 140, 280 and 565 Mbit/s were obtained through 150 km repeater spacings, respectively