Fiber-optic Communication Links Research Articles

The design and realization of a high reliability semiconductor laser for single-mode fiber-optical communication links

Long-haul trunk telecommunication systems, particularly optical submarine cable systems, have especially demanding reliability requirements. The authors describe how the InGaAsP inverted-rib waveguide (IRW) laser was designed for use as the source for such single-mode systems by minimizing known degradation hazards. The results of an extensive reliability assurance program are summarized. This included wafer validation endurance tests, overstress tests, and package design and life tests. The results of 7 million life-test hours confirm that the IRW laser has extremely good reliability performance. >

GHz optical communication experiments using lead-salt laser diodes in the 3.5–5.5μm wavelength region

The modulation performance of lead-salt laser diodes suitable for mid-infrared fibre optic communication systems has been investigated. The electron and photon lifetime for a PbCdS laser have been determined to 3.1 ns and 3.3 ps, respectively. Moreover, an experiment using short lengths of fluoride fibres shows the feasibility of GHz fibre optic communication links in the mid-infrared region using lead-salt lasers if the potential ultra-low loss of mid-infrared optical fibres can be realized.

A low DC, self-clocking, two-color transmission code for optical communications

A new self-clocking channel code is demonstrated and compared to other codes used in digital communication systems. The new code requires two channels and is best suited for wavelength-multiplexed optical fiber transmission systems. An experimental demonstration of the proposed code in a fiber-optic communication link is reported and the code performance is analyzed.

Upper limit of bandwidth improvement by optical equalization of graded-index fibres

Optical equalization was suggested as a means for increasing the bandwidth of optical fibre communication links when non-optimal graded-index fibre profiles are available. In this paper it is shown that by proper choice of the length as well as of the index of the compensating fibre one can significantly increase the bandwidth capability of the link. An upper limit of this improvement is derived, which is much larger than that obtained with alternating fibres of equal lengths.

A Set of Fiber Optics Experiments

A set of ten experiments designed to introduce undergraduate electrical engineering students to the area of fiber optics is described. The projects include measurement of pertinent parameters of optical fibers, sources, and detectors (the major components of fiber optic systems), the construction of a simple fiber optic communication link, the use of an optical fiber as a sensor of acoustic waves, and the making of a holographic optical element to serve as a fiber coupler. Although the experiments are expressly designed for a project-type laboratory, they are also suitable for other situations such as classroom demonstrations.

A 2 km Optical Fiber Communication Trial

This paper describes a recent field trial of an optical fiber communication link. The fixed point-to-point full duplex link used low loss multi-mode fibers fabricated by the CVD process in a simple cable structure. Fiber loss was approximately 4 dB/km before cabling and up to 7 dB/km after cabling. Digital 5 Mbit/s throughput TDM terminals were used to multiplex a variety of signal sources, including voice and data onto the fibers. Cabled fiber losses over 2.3 km were low enough to permit the use of incoherent infrared LED's as sources and silicon PIN photodiodes as receivers. 'Vee' groove splices were employed to connect fibers in the field. Installation was by standard cable laying techniques and no special problems were encountered.

Receiver Sensitivity of Optical Fiber Communication Systems: The Effects of Channel Characteristics and Receiver Filter Design

The receiver sensitivity of a moderate bit rate optical fiber communication link is investigated. The effect of both power conversion among the guided modes of the fiber and power loss to the radiation field from the guided modes is examined. Three different receiver filter designs are considered; a zero-forcing equalization procedure and two filters which do not compensate for the pulse dispersion introduced by the optical fiber channel. The degree of sophistication required in the detection process is a function of the mode coupling and attenuation parameters and the numerical results provide useful quantitative information for this aspect of system design. In particular, the channel parameter values for which processing techniques are required to compensate for pulse dispersion can be obtained from the results.

Wide-bandwidth high-radiance gallium-arsenide light-emitting diodes for fibre-optic communication

High-radiance GaAs l.e.d.s with 3 dB modulation bandwidths exceeding 500 MHz have been fabricated from p-n junction layers prepared with very high zinc acceptor doping levels. This development will permit the use of l.e.d.s in near-gigahertz or gigabit/s optical-fibre communication links.