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.     

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.     

The OS-280M Optical-Fiber Submarine Cable System

This paper describes the optical-fiber submarine cable system being developed by the Kokusai Denshin Denwa Company, Ltd. (KDD) for the transoceanic service in 1988. The system uses 1.3-μm single-mode fibers to carry digital signals operating at 280 Mbits/s. This paper discusses the system parameters, repeater design, cable design, and reliability evaluation. Furthermore, the results of a deep-sea trial at 7000-m sea depth carried out in February 1984 are reported.     

Repeater Fault Location for a Submarine Optical Fiber Cable Transmission System

This paper introduces a repeater fault location system for a repeated submarine optical fiber transmission system of 400 Mbits/ s at 1.3μm. The repeater fault location system is used in an out-of-service test. The fault locator transmits a test signal via a main optical fiber line, in order to make a loop-back path in one of the repeaters for returning the test signals via another main optical fiber line and to measure the bit error rate (BER) of the interrogated repeater. The test signal is a kind of pseudorandom signal that includes a low frequency component, which is assigned to the repeater as a supervisory frequency tone (SVT) signal. The BER is measured by counting the number of low frequency signal phase inversions in a time. This paper first describes the test signal generating method, SVT frequency allocation, and the filter design installed in a repeater. Next, there is a discussion of how the capability of the repeater fault locator has been experimentally verified by using two submarine repeaters, including four regenerative repeater units and three submarine optical fiber cables. As a result, a BER of less than5 times 10^{-6}is accurately measured.     

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.     

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.     

7000 m deep sea trial of OS-280M optical-fibre submarine cable system

The letter reports the 7000 m deep sea trial of an experimental OS-280M optical-fibre submarine cable system, consisting of a 24 km optical cable and two monolithic IC submarine repeaters, which was successfully carried out in February 1984.     

50 km, two-repeaters sea trial of optical-fibre submarine cable system

The experimental optical-fibre submarine cable system with 50 km cable and two repeaters was successfully laid in early June 1982. Optical loss changes of the cable during laying were less than 0.003 dB/km. The experiment will be continued during two or three years to obtain data on the cable and the repeaters.     

Optical fiber submarine cable systems

Optical fiber submarine cable systems especially developed for international systems throughout the world are reviewed, and the future technologies for optical fiber submarine cable systems are discussed. The discussion covers: system design; cable design and the fiber used; mechanical design of submarine optical repeaters; branching repeaters; repeater circuits; reliability; terminal equipment; repeater supervisory systems; initial system applications; and future trends     

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 Conceptional Design on Optical Frequency-Division-Multiplexing Distribution Systems with Optical Tunable Filters

Optical frequency-division-multiplexing distribution systems providing more than ten frequency multiplexed optical signals separated by on the order of gigahertz, distribute signals to plural receivers, where one of the signals is selected by a frequency selection switch (FS-SW). This paper describes the design of an optical frequency-divisionmultiplexing distribution system. Investigation is made of periodic filters for frequency division multiplexers and FS-SW, and the optical source, as well as single-mode fiber polarization mode dispersion. Preliminary transmission experiments using a bit rate of 450 Mbits/s, fiber length of 13 km, and frequency spacing of 11 GHz are also demonstrated at a 1.5 μm wavelength to show the design's suitability.     

High-Speed CMI Optical Intraoffice Transmission System: Design and Performance

This paper presents the design and performance features of a successfully developed optical intraoffice transmission system operating at 100-400 Mbits/s. The keys to the commercial realization of this simple, highly reliable, and low-cost system are the employment of the 1.3 μm LED and graded-index multimode fiber. Additionally important, the system makes use of coded mark inversion (CMI) coding to ensure bit sequence independence (BSI) and good error-monitoring capability. Experimental results have clarified the optimum bandwidth of the low-pass filter at the receiver end and the commercially attainable transmission distance. Furthermore, an available system gain of 15.4 dB is demonstrated through 400 Mbit/s transmission experiments. This value enables transmission over distances in excess of 4 km through multimode fiber (900 MHzcdotpkm, 0.8 dB/km).     

A design and experimental results of the OS-280M optical submarine repeater circuits

This paper describes the design philosophy and the experimental results of the optical submarine repeater for the OS-280M optical fiber submarine cable system to be installed across the ocean. This repeater which employs the information rate of 280 Mbit/s, the optical wavelength of 1.3 μ, and is implemented with monolithic ICs, features high reliability, long repeater spans, and the supervisory systems. The test results show that the average optical output power is - 1.4 dBm for the mark density of 1/2, the minimum average power of the optical input for the BER 10 is about -38 dBm at the room temperature, and other specifications are also well satisfied.     

Optical loss measurement results on an experimental optical fibre submarine cable of 30 km length

A continuous length of 30 km optical fibre submarine cable was successfully manufactured and laid on the sea bed about 1000 m deep. After the sea trial of 17 months, the cable was recovered from the sea bed. No significant degradation was observed in the optical loss of the recovered cable.     

Recent advances in submarine optical fiber cable transmission systems in Japan

Submarine optical fiber cable transmission systems are promising successors to existing submarine coaxial cable systems. This paper will review the history and the state of the art of the submarine optical fiber cable transmission technology, and the submarine optical fiber cable transmission systems named FS-400M and OS-280M being developed by NTT and KDD, respectively, in Japan.     

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.     

Optical Fiber System Applications Aspects in Future NTT Networks

This paper describes some aspects of optical fiber cable system applications in future NTT transmission networks, considering voice transmission as predominant even in future transmission networks in accordance with demand forecasts. The desirable optical fiber cable transmission system which should be developed and introduced is discussed taking into account optical fiber costs, demand estimates, pertinent technological developments, etc. It was concluded that the following process of introducing optical fiber cable transmission systems should be feasible. In the first step, approximately 32 Mbit/s and 100 Mbit/s digital transmission systems should be employed for short and medium haul trunks with heavy traffic using graded index optical fibers. A large capacity, long haul digital transmission system, such as a 400 Mbit/s system using graded index or, if possible, single mode optical fiber should be introduced next. The optical fiber cable costs at which fiber systems become economical, depend upon the application area. For short and medium haul systems, 40¢ per meter per core is required, but $2 per meter per core is sufficient for large capacity, long haul systems. For a short haul system operating at approximately 1.5 Mbits/s or 6 Mbits/s, the advantages of its introduction greatly depend on optical fiber costs which should be less than 20¢per meter per core.     

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.     

A Consideration of an Optical Coupler for Optical Submarine Transmission Laser Redundancy Systems

Theoretical and experimental results are described for a new optical coupler which consists of two laser diodes, two GRIN spherical rod lenses, a polarizing filter, and a single-mode fiber, and which employs laser diode polarization characteristics for an optical submarine transmission laser redundancy system. This optical coupler has two channels at 1.3 μm wavelength. Optical coupler loss values, which include coupling loss, polarization loss, and assembly loss, are 4.9 dB for one laser diode and 5.2 dB for another laser diode. Such loss values are almost the same as the conventional laser diode module loss for a single-mode fiber. This paper describes in detail a laser redundancy system in an optical submarine transmission system, structure and characteristics of an optical coupler, and experimental results on a high bit rate long-haul transmission system using the proposed optical coupler.     

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.