VAD single mode fiber with depressed cladding layer has been developed. Fabricated fibers have a germanium doped core of index difference ▵+ = 0.2~ 0.3% and a fluorine doped cladding layer of negative index difference ▵- = 0.1~0.4%. The cladding to core diameter ratio is 5 to 9, and the transmission loss is less than 0.5 dB/km at 1.311m. Bending loss increase due to lateral pressure was found to be equal to that of the matched cladding fiber whose index difference ▵ is equal to the total index difference of the depressed cladding fiber (▵ = ▵+ + ▵-). The chromatic dispersion, however, was rather similar to that of the matched cladding fiber which has the same concentration of germanium in the core, or the same positive index difference (▵ = ▵+), yielding the low dispersion at 1.3 μm. The fusion splice loss was also confirmed to be as small as the matched cladding fiber. The low transmission loss was maintained throughout the cabling process.

A numerical study has been made into the accuracy of the equivalent step-index (ESI) description of monomode fibres. It is primarily concerned with the measurement of ESI parameters without knowledge of the refractive index profile, rather than the theoretical generation of the best parameters when both the field and profile are known. It is then found that the ESI parameters afford an adequate description of mode cut-off but can give rise to significant errors in dispersion (for dispersion shifted fibres) and for the mode field width. Contrary to popular belief, it is shown that the Gaussian approximation leads to significant errors.

The effects of fibre drawing tension on the optical properties of various monomode fibre designs is examined. High drawing tensions were found to give low optical loss. Grading the refractive index profile was found to reduce the drawing-induced loss considerably. Fibres with high germania content show the largest drawing effects.

The optical attenuation and chromatic dispersion of single-mode fiber is reviewed on the basis of an optimum fiber design for 1.3 μm operation. Two designs of optical fiber cable and their optical performance are discussed.

This paper will review a systematic procedure that is being used to tailor optical properties of single-mode lightguides for specific research applications. It requires the coordinated implementation of computer-aided modeling with glass processing technology and state of the art diagnostic measurement procedures.

Procedural modification in making chalogenide glass and optical fibers has resulted in the reduction, and, in some cases, the elimination of water and hydrogen absorption bands. As a result of this new approach, transmission in the 2.5μm (4000 cm ^-1) to 7 μm (1428 cm^-1) region is improved by dB loss of two orders of magnitude. The methods are as fol-lows: 1. Elimination of hydrogen sulfide absorption bands from As2S3 glass by selectively doping the glass with a fraction of ppm As₂0₃ to act as a hydrogen getter. 2. Elimination of water absorption bands from As₂S₃ glass by baking out the quartz ampoule at 900°C under high vacuum and by using vacuum-distilled elemental powdered sulfur as a starting material. Sulfur is known to be fairly hygroscopic, especially in the powdered form. Thus, it is a potential source of H₂O contamination.

The wide variety of measurements used to characterize monomode fibers are reviewed from the viewpoints of laboratory, factory and field environments. The preferred methods are indicated, and emerging standards are also noted. A number of the more recent references to the literature are given.

Single mode fiber communication systems and the associated technologies are developing. With regard to fibers, final decisions have yet to be'reached as to which parameters are most critical for system performance. This paper will discuss the measurement of three fiber parameters which have been identified as required by system designers. These are: attenuation rate at the wavelength of operation, "effective cutoff wavelength," and mode field diameter. Special emphasis will be placed upon the modifications required to indus-trialize the laboratory measurement techniques to implement "state of the art" measurements in the factory.

Previous work has demonstrated that group-delay spectra in single-mode fibers can be measured with 0.1 psec resolution by a white-light crosscorrelation technique. An application would be to pretest short fibers before drawing an entire preform. This could be particularly useful for achieving high draw yield for fibers whose dispersion spectra are sensitive to core diameter. This paper describes measurements of minimum-dispersion spectra that were obtained using 4 m lengths of fiber that were cut from each end of kilometer-long quadruple-clad, triangular-index, and step-index depressed-clad fibers. The axial uniformity of fiber dispersion was found to be very good. Results show that averaging dispersion spectra using short fiber segments from each end produces excellent agreement when compared with the dispersion spectrum determined from conventional pulse-delay measurements on a long length of fiber.

We review the techniques available for long wavelength single mode reflectometry and describe in detail a coherent reflectometer operating at 1.15μm with a dynamic range of 30dB at 80 metres resolution.

Because their cores are not perfectly circular or because of stress, inherent to the structure or externally applied, practical single mode fibers are birefringent. These sources of birefringence are reviewed briefly. A simple model for the fiber consists of a combination of one linearly birefringent element and one circularly birefringent element. Depending on the magnitude of the birefringence, different techniques of evaluating the parameters of the model may be suitable. Several methods appropriate for low and high birefringence fiber are described and some of their advantages and disadvantages outlined. In an idealized single mode optical fiber, in which none of the structural or optical parameters varies with the azimuthal coordinate, all polarization states within the fundamental mode are degenerate; that is, neither the phase nor group velocity depends on polarization. In practice, however, this degeneracy is usually lifted by non-circularity of the core, by inherent stress in the guiding structure, or by stress resulting from bending, pressure, or twisting. Light entering the fiber with an arbitrary polarization state will then be resolved into a pair of orthogonal polarization states that propagate with different velocities. As a phase shift develops between them, the state of polarization will vary periodically along the fiber. The orthogonal states may be linear, circular, or in general elliptical, depending on the specific mechanisms involved.

Optical fibers have potentially good characters for active use in geophysics. In this paper we describe a practical approach to this use taking into account the physics and geophysics limitations. Some suggestions are made for the design of complete and operational systems. The economic data are also correlated with the technological possibilities. We conclude with a description of wide-range applications.

A technique that can be used for the closed-loop operation of dynamically biased optical fiber gyroscopes is discussed. The source wavelength dependence of the scale factor is considerably suppressed and the dynamic range of this system is limited only by that of the phase modulator used. Preliminary experimental results using an all-fiber gyroscope are compared with theoretical predictions.

A series of fiber-optic acoustic sensors based on the Sagnac interferometer are described. Features of these sensors include filtering of low-frequency signal components, use of a laser light source as an amplifier, and selection of the mechanism whereby the acoustic signature is impressed upon the light beams propagating in the fiber coil.

A sensitive fiber optic accelerometer has been fabricated and tested. The device is applicable where high sensitivity and large dynamic range are required. The transducer consists of a single-mode optical fiber wrapped many times around a solid right circular cylinder to amplify the radial deformation of the cylinder under axial acceleration. Two of these cylinders can be implemented in a differential manner to make the device insensitive to common-mode effects. The sensitivity and dynamic range of the sensor can be tailored through a suitable choice of cylinder material or by mass loading techniques.

We have designed and tested a guided wave optical modulator for applications as an integrated optical voltage probe. This voltage probe consists of an injection laser diode (ILD) connected to a stress-induced polarization preserving fiber, an electro-optic coupled-channel waveguide modulator, a graded-index multimode fiber for the return optical signal, and an electronics box containing the necessary electronics for the driving of the ILD source and the detection of the return signal. The electronics box can be physically separated from the ILD source and the fiber-modulator assemblies for ease of installation in the field. The ILD and modulator assemblies are ruggedized and the fibers are cabled. This probe has been tested in the frequency range 10 kHz-200 MHz and at a dynamic range of 40 dB at 200 MHz bandwidth.

At the present time phase modulation in optical fiber systems for communication, devices such as all-fiber gyroscopes, and active compensators for Mach-Zehnder interferometers in fiber optic sensors, is accomplished by using piezoelectric cylinders with wrapped fibers. However, the PZT cylinder cannot be modulated at high frequencies (above ~ 1 MHz), and also also its weight and size is a disadvantage. Elasto-optic interaction and modulation of the light beam propagating in an optical fiber in the MHz region would be extremely desirable for such applications as: heterodyning, active compensator schemes, small fiber gyroscopes and other devices.

Because of the low loss and low dispersion properties of silica optical fibers in the 1 pm wavelength region, optical fiber communication systems are expected to have a wide applications area. This paper describes recent development on InP/InGaAsP injection lasers as a light source for communication systems in the 1.2~1.6 μm wavelength region. Important factors for these lasers are 1)mode control, 2)temperature characteristics, 3)light output power, and 4)reliability. Transverse mode control is essential to assure linearity in light against current output characteristic and stable coupling efficiency into single mode fiber. Threshold current reduction is important for high temperature operation and assurance of long lifetime. Many types of index-guiding lasers have been developed to satisfy these conditions, and the transmission system at 400 Mbit/s with 25 km repeater spacing is going to be5installed in Japan. MTTF of a laser diode for this system is estimated to be about 10 hours in the condition of 5 mW at 50°C. Submarine systems require higher reliability of the device and the certification of longer life is now urgent. Single longitudinal mode lasers are desirable to realize next generation transmission systems of long haul and high capacity. For this purpose, distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers have been developed, and room temperature CW operations have been achieved.

A circuit designed for direct modulation of semiconductor lasers at frequencies up to 2.5 GHz has been built in order to study the high speed modulation characteristics of injection lasers. The circuit provides flat (±1.0 dB) frequency response from 20 kHz to 2.6 GHz. An integral bias T network provides a dc bias port for laser prebias. A versatile experimental mounting fixture incorporating this circuit provides thermoelectric cooling of stud mounted lasers and allows for simultaneous measurements from both laser facets. The laser can be cooled or heated and an active feedback controller holds the stud temperature to ±0.05°C. This mounting fixture and circuit were recently employed in an experimental single mode fiber communications system employing a new Bell Labs mode stabilized laser at 1.5 μm. The system set a new length record of 119 km for unrepeatered transmission at a bit rate of 420 Mb/s. Distortion free modulation of injection lasers at speeds up to 2.0 Gb/s has been achieved.

The Atlanta Single-Mode Experiment successfully demonstrated the viability and economic attractiveness of single-mode fibers as waveguides in future telecommunication systems. This paper describes the main optical components used in this experiment, such as the depressed-refractive-index cladding single-mode fiber, the stranded cable design, a novel bonded-splice technique, and precision directly-molded and field-assembly-type biconic connectors. A two-channel WDM experiment was performed in the 1.3 micron wavelength region using interference-filter multiplexers, grating demultiplexers, and InGaAsP/InP buried-heterostructure lasers centered around 1.275 and 1.335 micron wavelengths. In addition, a bi-directional transmission experiment was performed in the 1.3/1.5 micron wavelength regions.

Optical transmission systems employing monomode fibre are capable of both long repeater spans and high capacity. The design considerations for such systems are discussed for both direct and coherent techniques. The results of monomode systems experiments which have been performed by the British Telecom Research Laboratories (BTRL) are presented.

Experimental aspects of the deep water (3000 fathoms = 5486 m) sea trial conducted in September, 1982 in the North Atlantic are described. We deployed the major portion of the 18.2 km cable with its 12 single mode fibers twice within a 60 hour period. We constructed a transmission test system that allowed us to make all measurements from the ship end of the cable. Observed changes in fiber loss and bit error rates from the effects on the fiber of immersion, tension, temperature, and pressure were very small and will be discussed along with other interesting aspects of the experiment. The test sets included programmable single mode optical attenuators which permitted automatic measurement of system margins at will during any phase of the experiment. Single mode connectors permitted us to recon-figure the fiber topology as needed. For a description of the SL system the reader is referred to reference 1.