Fused tapered couplers are typically cladding-mode devices although the effect of the core is not always negligible. Tapers of single fibers may be used as a building-block to their understanding. If the tapering is not slow, then higher-order mode coupling effects occur. This degrades the coupling between fibers in a fused coupler. However such an effect in a single fiber may be usefully exploited as a basis for interferometric type devices. Accordingly, we review the transmission properties of biconically tapered fibers and propagation mechanisms involved therein, giving reference to fused tapered couplers. Furthermore, we consider tapering as a means of field access and manipulation, provide a comparison with polishing and etching, and discuss applications such as simple in-line modulation and filtering.
We present here the results of a theoretical study of the insertion loss and isolation of WDM couplers manufactured by the fused biconical taper process. Included in this study are single devices, identical concatenated devices and non-identical concatenated devices.
Wavelength Division Multiplexing (WDM), a method for combining a multiplicity of different wavelength signals onto a single optical fiber, is finding increasing usage in optical fiber communications systems. Most commonly, WDM's are used in long haul communications to increase the transmission capacity on trunks, and in datacomm applications where high-isolation, bi-directional transmission is required.
A simplified model is presented that accurately predicts the coupling limitations of asymmetric fused multimode star (mxn) couplers fabricated from fibers with arbitrary core radii and numerical aperture values. The model assumes that the following conditions within the coupling region are met: a) the ratio of the cladding thickness between adjacent cores to the core radius (t/r) is much greater than 0.1, b) each fiber has an identical core index profile coefficient, c) the refractive index of each fiber's cladding is identical, and d) the fibers are substantially tapered. The model is shown to be equally applicable to symmetric couplers fused from identical fibers. In addition, experimental results supporting the model are presented.
Assemblies of fiber polarizers and ploarization maintaining directional couplers have been produced in D fiver without intermediate splices. The lowest loss achieved in initial attempts to produce two-component coupler-ploarizer asseblies is 0.66dB. The stability of wide temerature range. The main applicaion for such assemblies is for interfermetric sensors, including fiver gyroscopes.
A new design of Y-type end-fused single-mode fiber directional couplers has been suggest ed, and its optimum parameters with which it is possible to obtain losses of 0,5-1 dB have been determined. Cross-talk attenuation between reverse channels exceeds 60 dB. It has been found by experiments that transmission coefficients of the developed couplers are stable at wavelength variations. Furthermore, Y-type directional couplers maintain polarization state of the propagating radiation. Simple Michelson interferometer based on Y-type fiber optic directional couplers with a new optical fringe visibility registration system for the narrow linewidth( ▵V) = 10 kHz - 1 MHz) analysis of the single-frequency lasers has been created.
The performance of lightly fused, sharply tapered 313 fiber optic couplers is analyzed in the presence of errors in the fiber separations. Particular attention is paid to the calculation of the degradation of the coupling ratio uniformity due to unequal fiber separations.
There is growing interest in the use of wavelength-division-multiplexing for providing wideband switched services in the local network. In some proposed network structures it is important to be able to multiplex as many channels as possible in the 1250 - 1600 nm operating window of single-mode fibre. A conventional wavelength multiplexer consists of a fibre array, a single lens and a diffraction grating. Although capable of producing low insertion losses, this device has a narrow channel bandwidth with respect to the channel spacing. This relative bandwidth is given approximately by the ratio of the fibre core and cladding diameters ( 10/125 for standard single-mode fibre ). In order to multiplex multi-longitudinal-mode lasers with a spectral width perhaps as high as 5 nm, large channel spacings are required. In this paper, improved designs of wavelength-division-multiplexer are described which provide greater channel packing density than conventional multiplexers.
Fiber optic switches which use the "moving fiber" principle to obtain low insertion loss and mode independence are discussed. Because the precisely-cleaved endfaces of the fibers are accurately aligned in close proximity, most of the modes can be transferred, and losses kept to a minimum (typically 0.6 dB). Due to the mature technology of electromechanical relays, and the low inertia associated with moving fibers instead of moving mirrors, prisms, or lenses, the switches are very reliable. Both bypass and fully-reversible versions will be discussed. The loopback capability of the fully-reversible switch makes possible an extended range of applications, including dual attachment station bypass and self-healing ring "wrap around".
An induced redistribution of modal power among guided modes was investigated experimentally and theoretically. This technique can be successfully applied to a variety of novel fiber optic devices: sensors, switches and modulators, resulting in improved performance and unique characteristics. The sensors employing this technique were found to be inherently more sensitive than other intensity type sensors and can be used to sense various phenomena, such as pressure, vibration and temperature.
This paper analyzes the characteristics of single-mode fiber (SMF) components using graded-index-rod (GRIN-rod) lenses. The coupling efficiency of the SMF to GRIN-rod lens to SMF coupling system is derived in the general case. The problem is simplified by using the reciprocal field method. All solutions are in closed form.
Optical fiber networks for public communications are moving toward the subscribers and therefore feeder optical cables with relative great amount of fibers are needed. A 120 fibers cable has been designed with ten UV curable acrilate coated fibers accommodate together inside each plastic loose tube, and twelve these tubes are stranded around a central strength member resulting in a high packaging density construction. A cable prototipe has been manufactured and some tests was made under conditions which simulate the situations found during installation and after due to hostile environments.
As STc) connectors become popular in a diversified connector market, emphasis is being placed on economics related to connector and termination costs, along with performance. As users become better educated in connector technologies, manufacturers must constantly improve on existing technologies while further endeavoring to create better, more innovative products. In this paper, we will present OFTI's design advances evident in its STC connector. Among the topics to be discussed will be design enhancements making the STC a "user friendly" connector. Optical and mechanical performance are primary concerns when a connector is designed. We carry design one step further by focusing on termination requirements, allowing connector assembly to be as efficient as possible. The STC rear body design allows faster installation while maintaining connector/cable integrity. Optical and environmental performance of different connector ferrule materials will be discussed along with rear body materials. Complete performance test data will also be presented.
This paper describes the design and development of a novel range of expanded beam connectors that are fully field terminable, of high performance and are suited for use in a diversity of harsh environments. Detailed consideration is given to the Series 900 hermaphrodite connectors developed primarily for use with field deployable military communication systems.
The introduction of linear networks with greater than 20 nodes has been inhibited by the loss associated with conventional discrete couplers. Typical excess and insertion loss are 0.5 dB and 1.0 dB respectively. This paper describes the development of a low loss, tunable coupling ratio tap which enables the expansion of linear networks to a hundred nodes or more. It analyzes the characteristics of the coupler and shows the impact on system design and performance.
About 50 different fiber optic rotary connectors, or fiber optic slip rings, have been built or described in the literature. These are devices for transmitting fiber optic signals across a rotating interface. The simplest are single channel slip rings where two multimode fibers face each other across a rotary interface. Losses are in the 3-4 dB range, or 1.5-3 dB if lenses are used to inject or collect light across the air gap, and light can be transmitted in either direction. Multiple channel optical slip rings have the advantage of redundancy and transmitting more data, omitting the necessity of multiplexing, while possibly freeing the rotational axis of the slip ring for a microwave, hydraulic, or pneumatic rotary joint. A number of different designs have been advanced which can be grouped into (1) concentric annular fiber bundles, (2) circular waveguides comprising open reflective channels or transparent dielectrics in the form of rings, rods, tubes, or wrapped fiber, (3) derotating intermediate optical components comprising prisms, mirrors, or fiber bundles, and (4) coaxial arrangement of mirrors and lenses rotating synchronously. These devices are primarily for large diameter multimode fiber and are often described for passive or active operation, i.e., they may incorporate active light sources and receivers rather than passively transmitting light supplied by optical fiber. The technical challenge in building a multiple, off-axis fiber optic slip ring is having incoming light available for transmission over 360Ã‚Â° of rotation, transmitting the light across the rotational interface with minimum light loss, dispersion, and modulation, then collecting sufficient light on the receiving side for further transmission. Important causes of light loss in optical slip rings are axial and angular misalignment of the two rotating members, Fresnel losses, and lens to fiber misalignment. During operation losses may result from dust; fogging, breakage, aging, elevated temperatures, and radiation. The system designer must carefully consider matching the slip ring to the light modulation method to avoid degrading or distorting signal transmission. An ideal optical slip ring would be passive, off-axis, bidirectional, achromatic, and capable of supporting any size single or multimode fiber.
Nonimaging optical transformers and their potential applications in fiber optics are dis-cussed. A newly discovered nonimaging optical design is described in detail. The new design known as 01/02 transformer, transforms a Lambertian source with an angular divergence 01 to a Lambertian source with an angular divergence Θ2, while preserving the phase space volume. Its potential applications are in launching light into multi-mode fibers as well as inter-connecting optical fibers. It is particularly in the interconnect problem that very low losses are of critical importance.
Avalanche photodiodes (APDs) capable of providing useful gain at microwave frequencies are vital components for future multi-gigabit/s lightwave transmission systems. To date, the APD structure that has shown the most promise for high frequency operation consists of a wide-bandgap multiplication region and a narrow-bandgap absorbing layer separated by a transition region to reduce charge accumulation at the heterojunction interfaces (SAGM-APD). InP/InGaAsP/InGaAs APDs of this type have exhibited bandwidths as high as 8 GHz and gain-bandwidth products of 70 GHz. In this paper we discus the physical effects that determine their speed and project performance limits.
We report on monolithically integrated 1 x 12 arrays of InGaAs PIN detectors and InGaAsP LEDs for use in long wavelength optical communication system applications. The detectors are sensitive in the wavelength region of 0.95 μm - 1.65 μm, and the high radiance LEDs emit at 1.30 μm. The devices utilize Si V-block fiber-array connectors for accurate alignment between the 12 devices and 12 fibers. The resultant structures are built in a 14-pin, dual in-line package.
Planar InGaAs/InP APD's having a SAM structure have been fabricated making use of ion implantation of silicon as the n-type source for achieving multiplication in the InP region. Quantum efficiencies greater than 80% and gains greater than 50 have been achieved. Noise measurements indicate multiplied bulk dark currents less than 1 nA for a device of diameter 50 micrometers. For certain conditions of the fabrication parameters, response times less than 1 ns are achieved without the use of an intermediate quaternary layer between the InGaAs and InP regions.
Due to their inherent technological simplicity, pin and Schottky photo-detectors are prime candidates for optoelectronic integration. We review different detector structures for .8 pm and 1.3 ium/1.55 /um operation with special emphasis on integrateability for large-bandwidth receivers, present experimental results, and discuss problems related to these devices. While a bandwidth potential > 20 GHz can be demonstrated for all these structures, minimum-size requirements pose a limit on the bandwidth in systems applications.
In this paper, we present data on the electrical characteristics and the optical response of photodetectors integrated on GaAs substrates with FET devices. We compare the differences between devices fabricated on globally implanted areas versus the undoped semi-insulating regions of the same wafer.
In optical recording, the use of single-mode fibres can considerably increase the coupling efficiency of the laser light into the light path. Important here is the performance of the laser-to-fibre coupler used. A mathematical treatment of different kinds of laser-to-fibre couplers is presented using scalar diffraction theory in order to obtain the field incident on the front end of the fibre. In this case the coupling efficiency of a laser-to-fibre coupler, using an aberrated light source (astigmatism) with an asymmetric far-field pattern, can easily be calculated.
In this paper an all fiber technique is described which reduces laser frequency jitter and provides absolute frequency referencing for laser diodes. The system utilizes a narrow band wavelength division multiplexer (WDM) as the reference cavity. The laser current is adjusted such that its emission frequency corresponds to the mid-point of the WDM transfer function. Thus, laser frequency fluctuations are translated into changes in the transmitted power through the WDM. An electronic servo is used to drive the laser injection current to maintain the emission frequency at the desired value.
Degradation modes of high power GaAlAs infrared lasers in accelerated life tests were investigated. Two modes were observed: gradual and rapid degradation. The latter degradation mode suddenly occurred after the gradual degradation mode. In order to clarify the cause of the rapid degradation, we compared them with artificially stressed degradation modes.