A 30 channel, 2 km fiber optic data transmission system has been installed in Hawaii for use in the DSCS satellite network. Data rates to 20 Mb/s with bit error rates less than 10-8 can be accommodated. Over three hundred (300) single fiber optical connectors were installed with an average loss of only 1 dB. Designed for a worst case signal-to-noise ratio (peak signal/rms noise) of 30:1, an average of 52:1 was achieved ranging from 34:1 to 66:1. Five, six fiber optical cable traversed the underground duct system. Multimode dispersions (FWHM) in the fibers ranged from 0.2 nsec/km to 4.8 nsec/km. Fiber/cable attenuations ranged from 4.8 to 7.7 dB/km at 0.85 μm.
Fiber optics can be used for several multiterminal data distribution applications. Some of these applications use fiber optic solutions that are cost-effective using presently available technology. These applications include intrafacility communications, electric power monitor and control, and railroad command control and communications. Intrafacility communications include telephone, data, video and high quality facsimile within a building or group of buildings. Electric power monitor and control includes both monitoring and controlling of power transmission between the power control center and substations as well as within the substation switch yard.
The Navy's commitment to the application of data bus technology to shipboard internal communication stems from the necessity of reducing cable congestion and weight. The Shipboard Data Multiplex System is a general purpose data bus system intended to take the place of most of the point-to-point cabling and associated hardware presently used for information transfer aboard ships of the Fleet. It uses both frequency and time multiplexing of a two-level set of redundant interconnections to provide a highly reliable data bus capable of distributing all forms of periodic and aperiodic signals. We report here a demonstration of the feasibility of substituting fiber optics for the coaxial cable presently used by this system. Primary concerns were whether the interface hardware could handle the FDM signals on the bus without excessive distortion and degradation of their signal to noise ratios. This paper describes methods used to demonstrate that the intermodulation distortion and signal-to-noise ratio requirements of the SDMS can be met by the necessary interface components.
The fundamental application of guided wave optical systems has been to communications. The principles and components which have been developed for guided wave optical communications systems are finding applications in a diverse number of information processing areas. This paper will review promising applications in these areas of information processing, including non-impact printing systems, high density memory systems, display systems, high-speed facsimile systems, and potential medical applications.
Fiberoptics are utilized in medicine by fields which have classically used light for either diagnosis or treatment. The specialities that have adopted the use of lasers have included the light for treatment and diagnosis group and those who have a problem with hemostasis in their treatment regimen. Table 1 lists the specialities which utilizes the diagnostic applications of fiberoptics. The diagnostic applications can be divided into the use of coherent fiber bundles for visualization and incoherent fiber bundles for illumination. Endoscopy is the introduction of a tube containing both coherent and incoherent fiber bundles into body orifices either natural or man made. Peritonoscopy inspects the abdomen through a small incision and enables the physician to observe from the reproduction tract in the pelvis to the dome of the liver. Gastrointestinal endoscopy uses these techniques through different instruments to explore the upper tract through the mouth or the lower tract through the anus. Pulmonary endoscopy called bronchoscopy enters the respiratory tract through the mouth. Urology investigates the bladder in cystoscopy through the urethra. All these diagnostic applications can also take biopsies through these instruments for diagnoses of anatomical abnormalities visualized through the endoscopic instruments.
The interaction of laser radiation with blood vessels is treated analytically using a model based on experimental data by considering the steady-state approached by the system. The factors controlling the relative performance of different lasers in closing vessels are uncovered and discussed. Carbon dioxide, Argon and Nd:YAG lasers are compared. An explanation of laser stimulated vessel wall disruption is found. Evidence suggests that coagulation is enhanced by the local presence of radiation energy. The theory shows why Argon laser radiation has a more destructive effect on the perivascular tissue than Nd:YAG laser radiation in closing vessels of the same size.
This review paper describes the status of optical fiber technology in Canada. Work on optical fiber communications started in 1972 at Bell-Northern Research and the Communications Research Centre. Since then several other industrial organizations, universities, and government organizations have contributed to the development of the technology. Work on optimized, compatible components and initial system studies have led to several experimental trial systems. These systems will be described and current results will be summarized.
Several, multi-video channel, transmission methods using optical fibers have been demonstrated. These use an LED or laser light source and can be either analog or digital. The current limitation on multiple channel analog transmission is light source linearity. Several methods of improving linearity are being developed. At the high signal levels needed for amplitude modulated multiple channel video transmission PIN diodes are the preferred receiver. At present, 12 channel, analog transmission using a laser has been achieved over a single fiber for a length of one kilometer.
The important design considerations for a fiber-optic television trunk line using both analog and digital approaches are given. The decision processes for selecting the approach for a given application requirement are discussed. Important link model parameters for an actual 12 channel, 8 km CATV supertrunk are shown with photographs of operating commercial hardware.
An analysis has been made of several bi-directional coupling schemes that allow duplex transmission over a single optical fiber through the use of wavelength separation. Three basic generic types of couplers have been considered: prism, grating, and dichroic mirror. Included in the analysis is a detailed comparison with respect to throughput loss, internal crosstalk and external crosstalk rejection of two potential implementations of each generic type. The throughput loss calculation includes the effect of scattering and absorption from component surfaces and volumes, and an approximate calculation of losses due to basic diffraction limitations. A detailed crosstalk analysis based on the estimated scattering mainly from component surfaces has also been performed.
The key component for any fiber data bus system is the fiber coupler. Since multimode single-strand fiber is used as a communication link in a data bus system, multimode fiber couplers must be designed and used. The simultaneous presence of many modes in multimode fibers renders the powerful coupled node theory which is based on the concept of phase matching among single modes, useless in predicting the coupling length of the multimode fiber coupler. Because of the close proximity of the coupling elements, results obtained according to other perturbation techniques are also questionable. In this presentation we shall first mention the available theories and experiments on multimode couplers, then a new technique based on the computer solution of wave equations will be introduced and applied to various realistic multimode couplers made with graded-index fibers. Practical aspects of the problem will be emphasized.
The recent development of low loss single mode optical fiber waveguides for light has made possible a new class of inertial reference devices built on the principal of a closed loop interferometer. Light circulating through the loop in both directions experiences a relative phase delay proportional to rotation rate about the loop axis. This paper derives the phase delay and discusses signal detection, signal processing techniques and error sources. It is concluded that synchronous modulation and demodulation and an active gain control at the signal calculational level are required to eliminate drift errors. Potential performance is extraordinarily good; rotation rate sensitivity of a few milli-arc seconds per second and angular position random walk errors of an arc second per square root hour appear feasible.
One of the quantities to be determined in building low noise fiber ring interferometer gyroscopes is the temperature sensitivity of the dispersion term in the Fresnel drag coefficient. Some experiments have been performed to show that the Fresnel drag measurement is useable for determining the size and the temperature dependence of dispersion in single mode fibers. The limits of accuracy of such an experiment will be discussed.
An optical time domain reflectometer is described which combines in one instrument the basic capability to analyze several important fiber characteristics. The device uses the polarization properties of light to enable high sensitivity fault detection close to the fiber input end; its probe pulse temporal characteristics and high gain photodetector in combination provide excellent discontinuity location resolution in long lossy fibers, and give an indication of fiber dispersion at large bandwidths.
A technique using an electro-optic phase modulator has been developed to add a ±90 degree phase shift to the Sagnac interferometer gyro. The introduction of the phase shift produces maximum sensitivity at low angular rates. The modulated output of the gyro is detected and processed by a single channel ac coupled sample and hold amplifier. The amplifier output is normalized to compensate for laser output and preamplifier gain drift.
There seem to be no technological or material problems impeding the development of integrated optical circuits (IOC's) which cannot be overcome. Instead the largest stumbling block is the lack of clearly defined application areas in which IOC's can perform in a unique or clearly superior way. In the long run, high data-rate optical communications may be the driving forces. In the near term, we must look to specialized signal- and data-processing tasks.
Considerable progress has been made in thin film optical devices and optical fiber waveguides over the past few years. Most of the research and development effort to date in fiber optics and "integrated optics" has been directed toward communications applications. Recently, it has been realized that there are also important potential uses for these technologies in military systems for processing wideband information and for sensing physical quantities. This paper reviews these anticipated applications including signal delay, matched filtering, A/D conversion, rf spectrum analysis, logic, pressure sensing, and rotation rate sensing.
Directional couplers, filters, modulators, switches, sources, etc., are being built either in ferroelectrics or in semiconductors. These devices make more likely the incorporation of integrated-optics technology into the rapidly growing field of optical communication.
Monolithic, integrated optical designs for high-spectral-radiance, GaAs/GaAℓAs laser sources are discussed. The sources described are designed to emit up to one watt of power in a CW, room-temperature operating mode. Specifically discussed are integrated optical techniques and devices for minimizing source spectral linewidth, maximizing source power, and achieving optimal output beam apodization.
In this paper we discuss the integration of various optical components into semiconductor injection lasers in order to improve their properties, thereby enhancing the utility of these lasers. These optical components include 2-dimensional waveguides, optical gratings, prisms and interferometric structures. The paper is divided into four sections; the first of which is a brief review of heterostructure waveguides and laser diodes. Successive sections then describe the utility of integrated optical techniques to control transverse modes, the longitudinal modes and the radiation pattern of lasers.
Reductions in power consumption and improvements in reliability have made AlGaAs stripe-contact hetero-junction lasers well-suited for many fiber-optic data systems of present interest. Although the beam pattern of some of these lasers is in the form of a stable single lobe, instabilities in the lateral direction are often observed, and require further attention for fibers with small acceptance angles. For long-distance, high-data-rate fiber systems, heterojunction lasers with emission wavelengths beyong 1 μm are being developed. Such lasers of InGaAsP/InP have many attractive properties, but suffer from carrier leakage at short wavelengths (1.0-1.2 μm) and elevated temperatures.
The fundamentals of noncollinear coplanar guided-wave acoustooptics and some of the more recent progress on application of the resulting devices are summarized in this paper. First, basic interaction mechanisms, configurations, and key acoustical and optical parameters are discussed. A number of wideband device configurations which employ isotropic/anisotropic Bragg diffractions and multiple surface acoustic waves together with the results obtained using optical waveguides in Y-cut LiNb03 substrate are then described. Finally, typical performance figures that have been obtained with applications using the resulting wideband devices, emphasizing those being carried out at the author's institution, including high-resolution light beam deflectors, very high-scanning rate light beam deflectors, spectrum analyzers, convolvers, pulse compressors, and tunable optical filters are given. Further improvements in performance figures as well as implementation of other types of signal processors are possible. These applications constitute some of the attractive ones in future wideband multichannel integrated/fiber optic communication and signal processing systems.
Military radar environments require wideband, high resolution, high probability of intercept RF receivers for signal sorting. An Integrated Optical RF Spectrum Analyzer utilizing the Bragg diffraction of guided optical waves by surface acoustic waves has great potential for furnishing that capability. Besides having projected performance competitive with other technologies, Integrated Optics offers reduced size and cost. The state-of-the art of optical waveguide componentry has now progressed sufficiently to make possible the development of a feasibility model of such a circuit.
An integrated optical system for comparing one set of voltage signals to a reference set will be described. The processor utilizes a hologram written in an outdiffused LiNb03 waveguide to effectively subtract the input signal voltage set from one or many reference sets as a means of pattern recognition. Parallel processing in a one-dimensional format should make possible comparison rates of 100 MHz for data sets containing as many as 100 information channels. The envisioned system contains the following components: A end-fired laser, a metallized-photoresist grating beam splitter and two polished-edge mirrors to form an integrated interferometer, a waveguide hologram in the area of beam recombination, and a lens to project the processed beam onto a butt-coupled detector. In the reference arm of the interferometer, a simple electrode pair is utilized to generate the phase shift required for holographic subtraction, while in the signal arm, a more complicated N-channel electrode structure is employed to electrooptically convert voltage information to spatial phase information on the guided wave. Efforts to build and characterize a three-channel system with integrated beam splitter, mirror, electrodes, and hologram are presented.
Signal processing applications for integrated optical devices which have been proposed and currently under active study include rf spectrum analysis, analog to digital conversion, heterodyne optical reception, pulse compression, digital logic, and correlation filtering. For these applications, integrated optics offers the potential of improved performance due to the lower power consumption and higher speed which results from miniaturization. Once fabrication problems have been solved, several fundamental effects must be considered as limits on performance. For example, acoustic velocity and attenuation taken together determine the achievable time-bandwidth product for integrated optic acoustic devices just as they do for their larger bulk equivalents. Power requirements of integrated optical devices can present problems of optical or electrical damage caused by the increased energy density resulting from miniaturization. In devices such as the spectrum analyzer in which signals are represented by deflected light beams in the plane of the waveguide, the quality and design of the various components such as lenses and couplers and the guides themselves, set performance limits on application of integrated optic processors.
Integrated optoelectronic devices will be considered in which optical fibers are coupled to optical channel waveguides and in which both optical slab and channel waveguides are coupled to detectors. Use of Si02/Si substrates allows formation of low loss waveguides, smooth V-groove channels for both channel waveguides and fiber support channels and sophisticated detector configurations such as charge-coupled device (CCD) linear arrays. We will discuss a slab waveguide-CCD detector coupling structure which has been experimentally characterized by a high degree of uniformity along the linear array, minimal excessive optical scattering and very low charge transfer inefficiency. Coupling of light from optical fibers to channel waveguides and from an array of channel waveguides to a CCD linear array is demonstrated. Applications of the various device structures considered to integrated optical spectrum analysis, optical transversal filtering, and time multiplexing of a number of fiber optical communication channels are discussed.
Modulation and defelction are two basic functions needed in any optical communication and data transmission systems. High speed modulation may be accomplished through various physical mechanisms, only modulators based on linear electrooptic effects (Pockels effect) and acoustooptic effects are of practical use in the visible and near infrared regions. A brief review of the physical principles and schemes to achieve intensity modulation are presented, leading to the establishment of the basic device parameters. Various integraed electrooptic modulators are discussed.
Four-port switches which operate independently of the polarization state of incident light are necessary for use with optical fibers which do not preserve polarization. We will review the present state of development of such a switch in Ti-diffused LiNb03 and the progress of end-fire coupling experiments between the switch and single mode optical fibers. Likely applications of such a switch in future optical fiber systems will be discussed.