Showing papers in "Journal of Lightwave Technology in 1984"
TL;DR: In this paper, a vector H -field finite-element method has been used for the solution of optical waveguide problems, where the permittivity of the guiding structures can be an arbitrarily tensor, only limited to being lossless.
Abstract: A vector H -field finite-element method has been used for the solution of optical waveguide problems. The permittivity of the guiding structures can be an arbitrarily tensor, only limited to being lossless. To extend the domain of the field representation, infinite elements have been introduced. To eliminate spurious solutions and to improve eigenvectors, a penalty function method has been introduced. To show the validity and usefulness of this formulation, computed results are illustrated for step channel waveguide, diffused channel waveguide, anisotropic channel waveguide, and channel waveguide directional couplers.
373 citations
TL;DR: In this paper, a circular metallic hollow waveguide with inner dielectric multilayers was designed with the emphasis on low-loss transmission of the HE 11 mode for the infrared.
Abstract: A circular metallic hollow waveguide with inner dielectric multilayers is designed with the emphasis on low-loss transmission of the HE 11 mode for the infrared. The effects of absorptions and variations of thickness of coated dielectric materials are discussed and are shown to be small on the minimum attainable transmission losses. Mode structure and transmission properties are also clarified for the general class of hollow waveguides by using a normalized surface impedance and admittance.
323 citations
TL;DR: In this article, state-of-the-art optical multi/demultiplexers (MUX/DEMUX) and WDM system design is reviewed and various system applications are also summarized.
Abstract: Wavelength-division-multiplexing (WDM) technology is now recognized as one of the key technologies in optical communications systems. This is because it has great potential to enhance system design and flexibility. This paper reviews state-of-the-art optical multi/demultiplexers (MUX/DEMUX) and WDM system design. Various system applications are also summarized.
309 citations
TL;DR: In this paper, the principles of operation of fiber-optic gyroscopes are reviewed along with methods to reduce their effect on the rotation-rate signal, and a direction of future research and possible applications are indicated.
Abstract: The principles of operation of fiber-optic gyroscopes are reviewed. Performance-limiting phenomena are discussed along with methods to reduce their effect on the rotation-rate signal. Current technology and performance of state-of-the-art systems are presented. Finally, a direction of future research and possible applications are indicated.
307 citations
TL;DR: A comprehensive summary of recent work in the area of heavy metal fluoride glasses has been generated for those seeking more detailed information on this topic as mentioned in this paper, which includes discussions on glass compositions, preparation, structure, fiber drawing characteristics, and intrinsic and extrinsic optical properties.
Abstract: A comprehensive summary is provided on the subject of heavy metal fluoride glasses. This includes discussions on glass compositions, preparation, structure, fiber drawing characteristics, and intrinsic and extrinsic optical properties. Other relevant glass and fiber characteristics such as strength, durability, and thermal Shock resistance are also outlined. Particular emphasis is given to the measurements of optical attenuation in fluoride glasses and their potential for use in ultralow-loss fiber optic waveguides. An excellent bibliography of recent work in the area of heavy metal fluoride glasses has been generated for those seeking more detailed information on this topic.
258 citations
TL;DR: In this article, a theory describing the effect of the FM noise on the bit error rate (BER) performance of various heterodyne and homodyne schemes was developed and the feasibility of the phase shift keying (PSK) scheme using semiconductor lasers was also discussed on the basis of analysis and experimentation.
Abstract: In coherent optical communication schemes, the FM noises of the transmitter and/or the local oscillator seriously deteriorate the receiver sensitivity. A theory is developed describing the effect of the FM noise on the bit-error rate (BER) performance of various heterodyne and homodyne schemes. To verify the theory, the BER of a phase-shift keying (PSK) heterodyne system is measured. The feasibility of the PSK scheme using semiconductor lasers is also discussed on the basis of analysis and experimentation.
203 citations
TL;DR: In this article, the authors re-examine the optical receiver design in view of these different requirements, namely, high receiver sensitivity, wide dynamic range, transparent to the operating bit rate, unrestricted data format, and fast acquisition time.
Abstract: The technology of optical-fiber systems is advancing rapidly. Parallel to the development of long-haul telecommunication systems in the gigabits per second data rates operating in the long-wavelength region is the wide penetration of optical-fiber systems in local area networks, video trunking and distribution, sensors, etc. These diversified applications impose different and often conflicting constraints on the optical receiver. This paper re-examines the optical receiver design in view of these different requirements, namely, high receiver sensitivity, wide dynamic range, transparent to the operating bit rate, unrestricted data format, and fast acquisition time. Design tradeoffs between conflicting receiver requirements are considered in detail. In particular, the sensitivity of high-capacity long-wavelength transmission systems is emphasized. The state-of-the-art performance of photodetectors and low-noise amplifiers is discussed. We show that dark current of avalanche photodiodes (APD's) is the main factor limiting the sensitivity of long-wavelength optical receivers. In addition, as an example, we report on the design and experimental performance of a hybridized low-noise optical receiver amplifier capable of more than 2-Gbits/s operation. The input noise spectral density achieved is 9 pA/ \sqrt{Hz} with a noise corner frequency of 920 MHz, corresponding to an equivalent noise resistance of 120 Ω.
200 citations
TL;DR: In this paper, the high-frequency modulation characteristics of InGaAsP ridge waveguide and etched mesa buried heterostructure (EMBH) laser at 1.55 μm and 1.3 μm are investigated.
Abstract: The high-frequency modulation characteristics of InGaAsP ridge waveguide lasers at 1.55 μm and etched mesa buried heterostructure (EMBH) lasers at 1.3 μm are investigated. Small-signal and large-signal circuit models are developed for both devices, and the main factors which influence the high-frequency modulation response are established. It is shown that the electrical parasitics in the chip dominate the small-signal frequency response of the EMBH laser and limit the large-signal turn-on and turn-off times. The small-signal and large-signal responses of both devices show strong damping of the relaxation oscillations. This damping can be modeled accurately using field-dependent optical gain compression in the rate equations.
193 citations
TL;DR: In this article, the authors analyzed the coupling at bends in optical fibers supporting one or only a few guided modes by considering the local normal modes for the corresponding straight waveguide and determined the correction to these matrix elements due to the longitudinal strain in a bent fiber.
Abstract: Mode coupling at bends in optical fibers supporting one or only a few guided modes is analyzed by considering the local normal modes for the corresponding straight waveguide. Matrix elements giving the strength of coupling between guided modes at a corner bend, and for coupling between guided modes and radiation modes, are calculated as a function of guiding strength for this "geometrical" effect. The correction to these matrix elements due to the longitudinal strain in a bent fiber is also determined. The increase in propagation constant for the fundamental mode of a fiber wrapped in a coil of constant radius is calculated from information on the coupling strengths and mode propagation constants. The phase shift and attenuation of the fundamental mode caused by a spatially periodic microbending of the fiber axis are also considered. Finally, potential applications of these effects in fiber-optic devices such as mode converters, phase shifters, switches, and sensors are discussed.
180 citations
TL;DR: In this paper, a new theory of backscattering in single-mode fibers is presented, which allows backscatter waveforms to be predicted for fibers of any refractive-index profile or scattering-loss distribution.
Abstract: A new theory of backscattering in single-mode fibers is presented. It allows backscatter waveforms to be predicted for fibers of any refractive-index profile or scattering-loss distribution. The results agree with experimental data and provide confirmation of an earlier, more restricted theory.
167 citations
TL;DR: In this article, the authors reported that appropriate glass compositions for drawing low-loss fibers are limited to the narrow ranges in the glass-forming regions and suggested that ultralow loss cannot be achieved due to the existence of the weak absorption tail.
Abstract: Chalcogenide glass fibers for mid-infrared transmission have been fabricated in As-S, As-Ge-Se, and Ge-S glass systems using high purity materials. The preparation of unclad, Teflon FEP clad, and chalcogenide glass clad fibers and their transmission loss characteristics are reported. It is found that appropriate glass compositions for drawing low-loss fibers are limited to the narrow ranges in the glass-forming regions. The minimum losses obtained are 35 dB/km at 2.44μm for As 40 S 60 unclad fiber, 182 dB/km at 2.12 μm for As 38 Ge 5 Se 57 unclad fiber, and 148 dB/km at 1.68 μm for Ge 20 S 80 unclad fiber. It is shown that hydrogen impurity absorptions and short-wavelength weak absorption tails seriously enhance loss in the fibers. It is also suggested that ultralow loss cannot be achieved due to the existence of the weak absorption tail. However, it is expected that the chalcogenide glass fibers can be used in short fiber-length applications such as in the remote monitoring and delivery of CO laser radiation. This is due to their wide operating wavelength ranges of 0.9-6\mu m for As-S, 1.3-9\mu m for As-Ge-Se, and 0.8-5\mu m for Ge-S, in which losses can be reduced to below 1 dB/m.
TL;DR: State-of-the-art and systems applications of single-mode wavelength-division multiplexing (WDM) devices are described and development trends and problems of the new technology are discussed.
Abstract: State-of-the-art and systems applications of single-mode wavelength-division multiplexing (WDM) devices are described. The performance characteristics required differ depending on whether the method of operation is one-way or two-way. Development trends and problems of the new technology are discussed.
TL;DR: In this article, an analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber, based on the thermoelastic displacement c potential in which the principle of superposition applies.
Abstract: An analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber. The method is based on the thermoelastic displacement c potential in which the principle of superposition applies. The method is applicable to any fiber structure. Its application to fibers with isolated stress-producing regions and a variety of core shapes is demonstrated. The optimum fiber parameters required to achieve maximum material birefringence for fibers with circular or bow-tie shaped stress regions are given. It is also shown that the thermal stresses tend to make the bow-tie fiber more crack-resistant than the fiber with circular stress lobes.
TL;DR: In this paper, an asymmetric interferometric channel waveguide modulator in Ti:LiNbO 3 at 0.83-μm wavelength was used for X-, Y-and Z -cut substrates.
Abstract: Measurements are described on asymmetric interferometric channel waveguide modulators in Ti:LiNbO 3 at 0.83-μm wavelength. Modulation voltages and device transmissions are compared for X-, Y- and Z -cut substrates. An interferometer intrinsic phase bias of \sim\pi/2 allows linear modulation and we have observed linearity over 67 dB for a 3-kHz bandwidth. This dynamic range is limited by optical damage effects, of which the photovoltaic effect is the most critical.
TL;DR: In this article, a simple model of mode partition noise is developed, which is valid for semiconductor lasers operating CW, having a single active region and oscillating primarily in one dominant mode.
Abstract: A simple model of mode partition noise is developed, which is valid for semiconductor lasers operating CW, having a single active region and oscillating primarily in one dominant mode. It is shown that the intensity fluctuations in the nonlasing modes occur with characteristic times of a few nanoseconds and have exponential probability distributions. We show that the lasing mode is able to follow adiabatically fluctuations in the nonlasing modes in such a way that the total intensity remains constant. Our model quantitatively accounts for the observations of Linke et al. that the frequency of "dropouts" in the lasing-mode intensity decreases exponentially with the ratio of average intensities of the lasing and nonlasing modes, and that in digital communication applications a ratio of about 50 is required to reduce the resulting bit-error probability to \lsim 10^{-9} . We also account for the probability distribution of the lasing-mode intensity, which was observed by Liu et al to be exponential at low intensity and Gaussian at high intensity. The exponential fluctuations constitute partition noise induced in the lasing mode by large Gaussian fluctuations in the field amplitude of the nonlasing mode. Additional noise sources associated with the carrier density and the lasing-mode field produce Gaussian behavior at high intensities plus a negligible broadening of the low-intensity exponential tail.
TL;DR: In this paper, a quasi-index-guided single-lobe ridge waveguide laser was shown to exhibit a transition from gain-guided to index-guided regime when the threshold current decreases rapidly, the lateral mode contracts, and the far field changes from a twin lobe to a single lobe pattern.
Abstract: In double-heterostructure stripe-geometry semiconductor lasers an effective lateral index step \Delta n_{L} over the stripe region can be induced through evanescent-field coupling. Such a quasi-index-guided device exhibits a transition from the gain-guided to the index-guided regime when \Delta n_{L} is progressively increased. Using parameters appropriate to a 1.3-μm InGaAsP laser, the transition is shown to occur around \Delta n_{L} \sim 5 \times 10^{-3} . The exact value of \Delta n_{L} depends on the extent of carrier-induced antiguiding. In the transition region the threshold current decreases rapidly, the lateral mode contracts, and the far field changes from a twin-lobe to a single-lobe pattern. Our analysis suggests that a quasi-index-guided device operates most efficiently for values of \Delta n_{L} at which the index-guided regime is just approached. With a further increase of \Delta n_{L} , the mismatch between the gain and mode profiles leads to lower differential quantum efficiencies. Among other structures, the analysis is applicable to a ridge waveguide laser. For a 1.3-μm laser the optimum \Delta n_{L} can be obtained using 0.2-μm-thick cladding layers for a 0.2-μm thick active layer.
TL;DR: In this paper, a preform deformation technique was used to make both polarization-preserving and single-polarization fibers with circular cores, low loss, and excellent polarization holding.
Abstract: High-birefringence optical fibers have been fabricated using a preform deformation technique in which an initially round preform is locally heated and squeezed from two sides. This technique has been used to make both polarization-preserving and single-polarization fibers. A novel feature of these new fibers is their rectangular shape which facilitates location of the principal axes and increases resistance to polarization breakdown from external perturbations. These fibers have circular cores, low loss, and excellent polarization holding.
TL;DR: In this paper, the phase bias offset due to a finite polarizer extinction ratio is greatly reduced by incoherent effects, and may be further reduced by using a depolarized source or by appropriate orientation of the polarizer transmission axis.
Abstract: Polarizer requirements for fiber-optic gyroscopes with high-birefringence fiber and broad-band sources are investigated theoretically by employing a model with a single coupling center between polarization modes. The phase bias offset due to a finite polarizer extinction ratio is greatly reduced by incoherent effects, and may be further reduced by using a depolarized source or by appropriate orientation of the polarizer transmission axis. Some experimental data is presented which supports the theoretical model.
TL;DR: In this paper, the effect of lens aberration on coupling efficiency and loss penalty due to misalignment for a laser diode to single-mode fiber couplers was studied.
Abstract: This paper studied the effect of lens aberration on coupling efficiency and loss penalty due to misalignment for a laser diode to single-mode fiber couplers. The theoretical results were in very good agreement with experimental values and the validity of the present analysis was confirmed. The paper made clear that coupling loss is dominated by aberration and proposed some basic approaches to improving coupling efficiency.
TL;DR: In this paper, the effects of self-phase modulation (an optical wave acting on itself) and cross phase modulation (one optical wave modulating a channel at a different wavelength) on the nonlinear refractive index of silica is analyzed.
Abstract: Phase noise in angle-modulated optical-fiber communication systems arising from optical power fluctuations is analyzed. The nonlinear refractive index of silica is the physical mechanism which converts power fluctuations into phase fluctuations. The effects of self-phase modulation (an optical wave acting on itself) and cross-phase modulation in wavelength-division multiplexed (WDM) systems (one optical wave modulating a channel at a different wavelength) have been calculated. The phase noise generated in single-channel systems is negligible for laser fluctuations less than 1-mW rms. In WDM systems containing as few as four channels the phase noise exceeds tolerable levels (0.15 rad) for power fluctuation of 1 mW in each channel.
TL;DR: In this paper, a long-distance low-loss silica optical-fiber link connected to a compact absorption cell was employed to realize a fully optical highly sensitive fiber gas sensor for low-level CH 4 gas in conjunction with a highly radiant InGaAsP light-emitting diode (LED) at 1.66 μm.
Abstract: A long-distance low-loss silica optical-fiber link connected to a compact absorption cell was employed to realize a fully optical highly sensitive fiber gas sensor for low-level CH 4 gas in conjunction with a highly radiant InGaAsP light-emitting diode (LED) at 1.66 μm. By using a dielectric interference filter which replaces a monochromator to simplify the system configuration and operation, a 2-km-long silica fiber link was demonstrated to be capable of achieving reproducibly the detection sensitivity of nearly 700 ppm for CH 4 gas in air, i.e., 1.3 percent of the lower explosion limit of CH 4 density. This high sensitivity verifies a potential for major applications to strategic points within the environment, like industrial and mining complexes as well as urban and residential areas. This result also indicates that the purely optical gas-sensor system based on ultralow loss optical-fiber networks, incorporating LED's or laser diodes, can be extensively utilized for the real-time remote measurement and surveillance of a number of dangerous, explosive, and toxic gases in the near-infrared region.
TL;DR: In this paper, light beam switching in a four-port channel waveguide was achieved using electrooptic modulation of epitaxially grown PLZT thin film on sapphire.
Abstract: Light beam switching in a four-port channel waveguide has been achieved using electrooptic modulation of epitaxially grown PLZT thin film on sapphire. The switches exhibited a low drive voltage of 4.7 V with a switching speed of higher than 1 GHz.
TL;DR: In this paper, a visibility concept was introduced to calculate modal noise power, noise bandwidth, and nonlinear distortion at fiber connecting points, and it was shown that a 3dB connection loss limits effective signal-to-noise ratio (SNR) to 22 dB in high-bit-rate digital systems and in analog systems, the SNR is improved more than 20 dB by using a superimposed pulse modulation with a frequency that is 100 times the baseband signal bandwidth.
Abstract: Modal noise at fiber connecting points is studied theoretically and experimentally. Simple formulas for calculating modal-noise power, noise bandwidth, and nonlinear distortions are obtained by introducing a visibility concept. Modal noise for multimode operating LD is also analyzed. These theoretical results are applied to high-bit-rate digital systems and analog systems using direct IM. Then, it is shown that a 3-dB connection loss limits effective signal-to-noise ratio (SNR) to 22 dB in high-bit-rate digital systems, and that in analog systems, the SNR is improved more than 20 dB by using a superimposed pulse modulation with a frequency that is 100 times the baseband signal bandwidth.
TL;DR: In this paper, the authors demonstrated a statistical measurement technique to characterize the mode partition in injection lasers. And they showed that the dominant mode of a TJS (AlGaAs) laser contains on the average 1.6 percent of the total output power, there is a probability of 10-6, that it carries 30 percent of total output.
Abstract: We have demonstrated a statistical measurement technique to characterize the mode partition in injection lasers. In the steady state small nonlasing side modes have distributions similar to that of a narrow-band Gaussian noise. There is a certain probability that they carry a significant portion of the total output. For example, if a side mode of a TJS (AlGa)As laser contains on the average 1.6 percent of the total output power, there is a probability of 10-6, that it carries 30 percent of the total output. Distributions of main modes of a multimode laser can be matched by beta distributions with properly selected parameters. In addition to dc conditions, this technique has also been used to study the transient behavior of injection lasers. The dominant mode has been shown to start from a noise distribution.
TL;DR: In this paper, a large variety of quaternary 1.3 and 1.5-μm injection lasers were directly modulated at bit rates up to 2 Gbit/s using a drive circuit known to have a flat response up to speeds more than twice this high.
Abstract: Samples of a large variety of quaternary 1.3- and 1.5-μm injection lasers were directly modulated at bit rates up to 2 Gbit/s using a drive circuit known to have a flat response up to speeds more than twice this high. The resulting optical signals were detected and analyzed for eye degradation and bit error rates. It was found that some lasers were capable of modulation at rates exceeding 2 Gbit/s without degradation while others exhibited significant eye closure at bit rates as low as 300 Mbit/s. A clear correlation was found between high-speed capability and the absence of a current blocking junction. That is, the lasers capable of the fastest modulation were of the simplest geometries: ridge guide and oxide stripe. Buried heterostructure (BH) and buried crescent (BC) lasers both showed significant speed limitations. The modulation bandwidths of the various lasers were also investigated using small-signal sinusoidal modulation and the measured half-power bandwidths were consistent with the large-signal modulation results. The shape of typical modulation transfer characteristics is consistent with a simple RC rolloff with RC products of ≳ 400 ps for buried crescent lasers, ∼ 150 ps for buried heterostructure lasers, and < 60 ps for ridge guide lasers. These results apply also to samples which had been processed to form cleaved-coupled-cavity (C3) lasers for mode stabilization.
TL;DR: In this article, two 2 × 2 switches with fiber pigtails have been made with insertion loss of ∼3- and ∼14-dB crosstalk isolation with a 70-V operating voltage.
Abstract: Polarization-independent single-mode optical cross points with low loss have been fabricated for \lambda = 1.3-\mu m wavelength. Waveguide design, coupling strength equalization for the two polarizations, fabrication tolerances, and the performance of several Ti:LiNbO 3 directional-coupler switches are presented. Two 2 × 2 switches have been made with fiber pigtails. The switches have an insertion loss of ∼3- and \sim-14 -dB crosstalk isolation with a 70-V operating voltage. A 4 × 3 switch had similar performance but higher insertion loss.
TL;DR: This work reviews recent progress in coupling devices for monomode fiber systems, with an eye towards practical performance limits in the near future, and discusses planar lenses which are being developed for various applications.
Abstract: We review recent progress in coupling devices for monomode fiber systems, with an eye towards practical performance limits in the near future. Emphasis is placed on key subjects such as laser-to-fiber coupling and packaging, connectors, and splicing. In addition, we also discuss planar lenses which are being developed for various applications.
TL;DR: In this paper, a ring waveguide fabricated by ion exchange in glass was used to measure resonance in a multimode ring and the authors reported finesses of better than 20 making possible the measurement of frequency deviations to 10-4A, and temperature variations to 0.002°C.
Abstract: We report observation of resonance in a ring waveguide 4 cm in diameter fabricated by ion exchange in glass. The observed finesse of four was explained in terms of loss per unit length and coupling efficiency onto and off of the ring. A large nonresonant background was attributed to mode-mixing in the multimode ring and to an observed depolarization. The ability to measure resonance in a multimode waveguide ring was due to the fact that only the highest order mode was directionally coupled out. Estimates predict finesses of better than 20 making possible the measurement of frequency deviations to 10-4A, and temperature variations to 0.002°C. With improvements, this may also be a viable device for inertial rotation sensing.
TL;DR: In this paper, a method for forming bends in waveguides in III-V semiconductors by reflection off an etched vertical wall is proposed for providing wave-guiding through 90° with negligible loss.
Abstract: Bent-guide structures will undoubtedly play an important role in increasing packing density in future integrated optical circuits. A method for forming bends in waveguides in III-V semiconductors by reflection off an etched vertical wall is proposed for providing wave-guiding through 90° with negligible loss.
TL;DR: In this paper, loss values of 4 dB/km at 2 μm and 15 dB/ km at 2.4 μm were obtained for an antimony-doped germanium-oxide glass optical fiber prepared by a VAD method incorporating a dehydration process.
Abstract: Loss values of 4 dB/km at 2 μm and 15 dB/km at 2.4 μm were obtained for an antimony-doped germanium-oxide glass optical fiber prepared by a VAD method incorporating a dehydration process.