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In Part I, a new internally coded time hoping optical code division multiple access (TH/OCDMA) scheme for fiber optic communication systems has been proposed and its multiple access performance has been evaluated using optical orthogonal code (OOC). Due to low cardinality of OOCs with a correlation value of 1, the capability of the proposed scheme could not be utilized effectively for an increasing number of simultaneous users. In this part, we consider applying the internally coded technique introduced in part one to the frame time hopping/OCDMA scheme. We evaluate the multiple access performance of the system for the three detectors introduced in Part I. Our results demonstrate the capability of the internally coded TH/CDMA scheme to substantially increase the maximum number of simultaneous users when using FTH codes instead of OOCs. Index Terms--Chip-level receiver, correlation receiver, error correcting codes, fiber-optic CDMA, frame time hoping, super orthogonal codes.

Some of the optical parameters of the bent multimode graded-index (GRIN) optical fiber in terms of indices of refraction, where the bending stresses broke the radial symmetry, are evaluated by use of multiple-beam Fizeau fringes. The variation of the index difference between the cladding index and core index in both the compression and tensile fiber regions is measured. The accuracy of measuring the index is [+ or -] 1 x [10.sup.-4]. The spatial resolution of the method is 1.39 [micro]m. Evaluation of the acceptance angle, the numerical aperture, and the V number profiles of the bent fiber from the interference pattern at both sides of the bent fiber are presented. The fraction of the mode number lost has been evaluated. The method was used to study the influence of compression on diminishing the index difference that leads to a dissipation of energy and a considerable mode loss. It is obvious from the experimental data that the change of the index difference due to bending strongly affects the fraction of propagating mode number, especially at the small radii of curvature. Ignoring the variation of the index difference we evaluating the number of propagated modes number leads to an insufficient determination of the mode loss. It subsequently leads to an incorrect determination of the mode dispersion and the interface loss in bent GRIN fibers. The study confirms that the deviation of the guide axis from straightness with the radius of curvature of less than 1 cm could lead to a significant fraction mode loss. OCIS codes: 060.2270, 120.3180, 060.0060, 120.0120, 000.2190, 060.2400.

We demonstrate a multimode-fiber bundle reference scheme in a photorefractive volume hologram and discuss its angular/spatial selectivity both experimentally and theoretical]y. We measure the angular/ spatial selectivity, changing distances between the photorefractive crystal and the output facet of the multimode-fiber bundle. The distance variation leads to a beam-size change in the reference beam, however, the object-beam size was fixed in all cases. The dependence of the angular/spatial selectivity for random-pattern (RP) referencing on a hologram dimension was examined and the characteristics compared with those derived from Gaussian referencing. Experimental results show that the RP referencing makes little contribution to the enhancement in angular selectivity, even though it leads to a considerable enhancement in spatial selectivity. The angular selectivity is mainly dependent on the dimension of a volume hologram, even with RP referencing. It is also noteworthy that the use of an RP beam can cause some high-frequency noise in the angular-multiplexing regime, which should be avoided in a hologram memory system. Nonetheless, the spatial selectivity of the RP referencing shows nearly no dependence on hologram dimension, and is mainly dependent on the transversal speckle size of the random-pattern beam. These characteristics can also be verified by the numerical results presented here, which are in good agreement with the experimental results. OCIS codes: 090.0090, 030.6140, 210.2860.

Fiber infrastructures in future personal communication systems (PCS's) must minimize remote antenna size and cost, and facilitate system maintenance and upgradeability. These goals can be met by a centralized PCS infrastructure using analog fiber-optic links. It is essential that the relationship between optical-link quality in terms of spurious-free dynamic range (SFDR) and PCS quality of service be accurately quantified so that optical device and other infrastructure design requirements can be determined. This paper presents a comprehensive wireless/optical simulation model which combines wireless system characteristics (such as fading, cochannel interference, diversity, and power control) with the noise and nonlinearities of fiber-optic links. Results of the simulation indicate that representative SFDR requirements for fiber infrastructures in PCS systems are in the 72-83 dB [multiplied by] [Hz.sup.2/3] range. The impact of varying environmental characteristics as quantified by distance loss and shadowing variance is between 7-10 dB. A larger distance loss or lower shadowing variance result in lower SFDR requirements. The required automatic gain control (AGC) accuracy decreases as the SFDR increases. These results indicate that either distributed feedback (DFB) or Fabry-Perot (FP) semiconductor laser diodes can be used in the implementation of PCS infrastructures. Index Terms - Analog fiber, dynamic range, fading, infrastructure, laser, PCS, power control, SFDR, wireless.

Polycrystalline silver halide fibers were thermally treated by a variety of heating and quenching procedures. For each procedure, the recrystallization process and the grain-size distribution were investigated. The absorption and scattering coefficients at 10.6 [[micro]meter] and the infrared transmittance spectra in the 3-20 [[micro]meter] wavelength range were also measured. Treatment at temperatures above 170 [degrees] C and long time intervals generally lead to an increase in grain size, with a dependent increase in absorption and scattering coefficients at 10.6 [[micro]meter]. Heating only to temperatures below 170 [degrees] C reduced the absorptive and scattering losses. The Rayleigh-Gans scattering model was utilized to describe the scattering behavior. A model involving cation vacancies localized at charged dislocations or casual divalent impurities is suggested to explain the infrared absorption of the fibers.

The effectiveness of surface-bonded and embedded optical fibers for the detection of ultrasonic Lamb waves in 2-3-mm-thick steel, carbon-fiber-reinforced plastic (CFRP) and glass-reinforced plastic (GRP) plates are compared. A novel integrating ultrasonic sensor was achieved using the signal arm of an actively stabilized 633-nm homodyne Mach-Zehnder fiber interferometer which was either bonded directly to the plate surface or spliced to single-mode fibers embedded within a composite plate during manufacture. An embedded fiber is shown to be about 20 times more sensitive to Lamb wave motions than a surface-bonded fiber. However, the latter may be more practical. Key words: Smart structures, fiber-optic sensors, ultrasound, composite materials, nondestructive testing.

Fiber-optic transmission of Q-switched ruby laser pulses is limited by fiber damage owing to the high laser-beam intensities. Pulse stretching with a semiconductor-based control circuit for the Pockels cell of the ruby laser to reduce the peak intensities is described. Pulses with durations from 200 ns to 1 [[micro]second] and a coherence length of [approximately]3 m were generated. These pulses were coupled into multimode optical fibers to investigate the transmission characteristics and the limits of transmittable pulse energies. Stretched pulses can be transmitted in quartz fibers with a 600-[[micro]meter] core diameter to pulse energies of 300 mJ, which is an increase by a factor of 4 compared with standard Q-switched pulses. It is expected that beam guiding of ruby laser pulses by fiber optics will significantly facilitate the use of holographic interferometry in technical applications such as vibration analysis. Key words: Pulse stretching, ruby laser, fiber-optic transmission

A method of measuring the complex modulation of a Bragg grating is derived from a one-dimensional model of light propagating in an optical fiber. Interference fringes between the Bragg grating and a reference air-gap reflector are measured, and a Fourier transform of the interference fringes generated as a laser is swept through the wavelength is used to compute the complex modulation function of the Bragg grating over a restricted domain. Supporting data, taken by temperature tuning a distributed feedback diode laser, are shown.

Gain measurements are carried out for different lengths of three types of erbium-doped silica fiber with different pump powers at 1480 nm. From these measurements a relation is established for each type of fiber between gain and the attenuation factor of the pump power. This relation is in complete agreement with the one predicted by an analytic model based on overlapping factors, which makes it possible to obtain methods for the experimental characterization of doped fibers.

Time-resolved laser-induced fluorescence spectroscopy and fiber optics show potential as tools for detecting environmental pollutants in water and soil. On-site laser probe is useful for practical applications as it is simplified by time-integrated data accumulation of fluorescence intensities in an 'early' and in a 'late' time window with regard to the excitation pulse. Its capability for on-line monitoring of petroleum products is demonstrated in various applications and results from field measurements in an industrial oil separator are reported.

Accurate forms for the [LP.sub.nm] modes (n = 0 and n [greater than or equal to] 2) in a uniform circular-core curved fiber are given. We show that the [LP.sub.nm] modes (n [greater than or equal to] 2) are composed of two spatially orthogonal components and that, to the zeroth order, there is no special polarization axis for the LP modes in a uniform circular-core curved fiber.

Fiber-optic radiance microprobes, increasingly applied for measurements of internal light fields in living tissues, provide three-dimensional radiance distribution solids and radiant energy fluence rates at different depths of turbid samples. These data are, however, distorted because of an inherent feature of optical fibers: nonuniform angular sensitivity. Because of this property a radiance microprobe during a single measurement partly underestimates light from the envisaged direction and partly senses light from other directions. A theory of three-dimensional equidistant radiance measurements has been developed that provides correction for this instrumental error using the independently obtained function of the angular sensitivity of the microprobe. For the first time, as far as we know, the measurements performed with different radiance microprobes are comparable. An example of application is presented. The limitations of this theory and the prospects for this approach are discussed. Key words: Optics of living tissue, radiance measurements, fiber-optic microprobe, three-dimensional picture of light field in turbid media.

The variation in the green intensity ratio (2[H.sub.11/2] and 4[S.sub.3/2] energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 [degrees] C), autocalibrated fiber-optic temperature sensor. Key words: Fiber-optic sensors, rare-earth-doped fiber, fluorescence.

Among the improvements planned for the 1997-98 upgrade of the D0 detector at Fermilab are installation of a scintillating-fiber central tracker and a lead-scintillator central preshower counter read out with wave-shifting fibers. Because of space limitations, fibers in both systems may need to undergo bends with fairly small radii, and the resulting stresses and strains may cause light losses. This paper presents results of a study of the effects of deformation on fiber light transmission. Particular emphasis is placed on the new multiclad fibers developed by Kuraray.

Propagation of [Ga.sub.x][In.sub.1-x][As.sub.y][P.sub.1-y] light-emitting-diode radiation through an optical fiber was found to affect its spectral curve very strongly, and the origin of this effect was analyzed. Various kinds of fibers were found to induce interferencelike modulations superimposed on the smooth spontaneous spectral curve of the diodes. We were able to show that when a monomode polarization-preserving fiber is used, the modulations are mostly due to intermodal interference. Key words: Guiding in optical fibers, diode-fiber coupling, spontaneous electroluminescence.

The butt-coupling loss between different tapered rectangular waveguides and a standard single-mode optical fiber has been calculated. Losses as low as 0.16 dB can be reached for waveguides with a refractive-index contrast in the range of 0.5% to 1.96%. The fabrication tolerance are such that practical devices with coupling losses below 0.25 dB are feasible. Key words: Coupling loss, optical waveguides, integrated optics.

Raman fiber optic chemical sensors provide remote in situ characterization capability. One application of Raman fiber optic chemical sensors is the characterization of the contents of nuclear waste tanks. In these tanks it is expected that approximately 20 meters of optical fiber will be exposed to radiation levels between 100 and 1000 rads/hour. In support of this work two silica optical fiber types (one a communications grade fiber and the other nominally radiation resistant) have been tested at the radiation levels expected in the tanks. Luminescence and Raman scattering measurements have been performed in situ with 488-nm excitation on two types of silica optical fiber exposed to a constant low to moderate dose rate of gamma radiation of 880 rads(Si)/hour from a 60Co source for a total dose of greater than 45 krads. The nominally radiation-resistant fiber was also excited with 514.5-nm and near-infrared 830-nm laser radiation. The rate of the silica Raman signal fdecrease is more than three times greater for the visible excitation wavelengths than for the 830-nm excitation for the radiation resistant fiber. The behavior of the 650-nm photoluminescence line upon irradiation was different for the two fibers studied, both in terms of the shift of the 650-nm line and rate of increase of the normalized photoluminescence intensity. In all cases the photoluminescence from the fibers was less than the Raman intensity. No radioluminescence was observed in either fiber. The radiation resistant fiber exhibited photobleaching effects on the Raman transmission when photoannealed with 488-nm laser light.

Optical-fiber strain gauges with asymmetric etched structures have been analyzed, fabricated, and tested. These sensors are very sensitive with a gauge factor as high as 170 and a flat frequency response to at least 2.7 kHz. The gauge factor depends on the asymmetry of the etched structures and the number of etched sections. To understand the physical principles involved, researchers have used structural analysis programs based on a finite-element method to analyze fibers with asymmetric etched structures under tensile stress. The results show that lateral bends are induced on the etched fibers when they are stretched axially. To relate the lateral bending to the optical attenuation, we have also employed a ray-tracing technique to investigate the dependence of the attenuation on the structural deformation. Based on the structural analysis and the ray-tracing study parameters affecting the sensitivity have been studied. These results agree with the results of experimental investigations.

A mathematical model that describes a fiber-to-fiber holographic connector is presented. We consider both single- and double-image cases for the reconstruction of the second hologram. A comparative study of the two coupling conditions is presented. Fourier analysis of the coupling equation enables us to study the linearity of the system.

A simple analytical model is developed for the evaluation of interfacial shearing stress at the glass fiber surface in dual-coated optical fiber specimens subjected to tension. The analysis has been performed for pull-out testing and in situ evaluation of Young's (shear) modulus of the primary coating material and is aimed at assessment of the effect of the materials properties and the specimen's geometry on the magnitude and distribution of interfacial shearing stress. It is shown that the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. It is concluded that, while currently used 1-cm-long specimens with approximately 30-micrometer-thick primary coatings are acceptable, shorter specimens (say, 5 mm long) are expected to result in more stable experimental data. The results obtained can be useful for comparing the adhesive strength of the primary coating material in fibers of different lengths and with different coating designs, as well as for the evaluation of Young's (shear) modulus of this material from the measured axial displacement of the glass fiber.

The stress intensity factor K(sub I) along the front edge of a growing small crack in a silica optical fiber was evaluated by 3-D boundary element analysis based on the crack geometry observed during the delayed fracture test. The variation of K(sub I) was shown to be little along the front of the growing crack. The crack velocity in the direction normal to the crack front was able to be expressed as a power function of K(sub I) at each position on the crack front. The crack velocity was also shown to be larger at a position closer to the fiber surface for each value of K(sub I).

Thermal effects caused by launching conditions in a C[O.sub.2] laser beam delivery that uses metallic hollow waveguides is investigated. It is found that front-end clipping is the main cause of thermal loading and generates a steep temperature gradient at the fiber front end while the continuous beam attenuation produces a temperature distribution declining slowly along the waveguide. Key words: Hollow waveguides, C[O.sub.2] beam delivery.

A study is conducted to explore the mechanism of spectral broadening in erbium doped fiber (EDF) lasers, with the inclusion of a dispersion shifted fiber (DSF) in the cavity for pump powers less than 200 mW. The application of the optical communication system is confirmed by the generated broadband that is demultiplexed in the C-band.

A new, to our knowledge, method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. We inject light from a 4-ns rise-time pulsed broadband flash lamp into fibers of various lengths and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning a range of approximately 3000 [Angstrom] are recorded from a single flash-lamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength-dependent attenuation is also determined from the signal intensifies. The method is demonstrated with experiments using a step-index 200-[Mu]m-diameter Si[O.sub.2] fiber. The results agree with the transit time determined from the bulk glass refractive index to within [+ or -] 0.035% for the visible (4000-7200-[Angstrom]) spectrum and 0.12% for the LTV (2650-4000-[Angstrom]) spectrum and with the attenuation specified by the fiber manufacturer to within [+ or -] 10%. [C] 2001 Optical Society of America OCIS codes: 060.2300, 060.2310.

This paper reviews the fundamental concepts and basic theory of polarization mode dispersion (PMD) in optical fibers. It introduces a unified notation and methodology to link the various views and concepts in Jones space and Stokes space. The discussion includes the relation between Jones vectors and Stokes vectors, rotation matrices, the definition and representation of PMD vectors, the laws of infinitesimal rotation, and the rules for PMD vector concatenation.

This paper reports on a dc-20-GHz InP heterojunction bipolar transistor (HBT) active mixer, which obtains the highest gain-bandwidth product (GBP) thus far reported for a direct-coupled analog mixer integrated circuit (IC). The InP HBT active mixer is based on the Gilbert transconductance multiplier cell and integrates RF, local oscillator, and IF amplifiers. High-speed 70-GHz [f.sub.T] and 160-GHz [f.sub.max] InP HBT devices along with microwave matching accounts for its record performance. Operated as a down-converter mixer, the monolithic microwave integrated circuit achieves an RF bandwidth (BW) from dc-20 GHz with 15.3-dB gain and benchmarks a factor of two improvement in GBP over state-of-the-art analog mixer IC's [1]-[9]. Operated as an up-converter, direct-digital modulation of a 2.4-Gb/s [2.sup.31] - 1 pseudorandom bit sequence (PRBS) onto a 20-GHz carrier frequency resulted in a carrier rejection of a 28 dB, clock suppression of 45 dBc, and less than a 50-ps demodulated eye phase jitter. The analog multiplier was also operated as a variable gain amplifier, which obtained 20-dB gain with a BW from dc-18 GHz, an third-order intercept of 12 dBm, and over 25 dB of dynamic range. A single-ended peak-to-peak output voltage of 600 mV was obtained with a [+ or -] 35-mV 15 Gb/s [2.sup.5] - 1 PRBS input demonstrating feasibility for OC-192 fiber-telecommunication data rates. The InP-based analog multiplier IC is an attractive building block for several wide-band communications such as those employed in satellites, local multipoint distribution systems, high-speed local area networks, and fiber-optic links. Index Terms--Fiber optics, InP HBT, limiter, mixer, multiplier, VGA.

Microbend mode strippers/scramblers are commonly assumed to remove higher order modes uniformly. In fact, they only remove higher order modes propagating in the plane of the microbends, resulting in an elliptical output pattern from a circular fiber.