By Topic

Lightwave Technology, Journal of

Issue 8 • Date Aug 1990

Filter Results

Displaying Results 1 - 16 of 16
  • Numerical simulation of the nonlinear response of a p-i-n photodiode under high illumination

    Page(s): 1137 - 1144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A theoretical study and a model for the numerical simulation of the nonlinear electrical response, including the harmonic-generation rate calculation, of a p-i-n InGaAs photodiode under high-illumination conditions are discussed. The device structure is described. An algorithm, which is based on a finite-difference calculation, is used to calculate the temporal electrical response of the device to a microwave optical input signal. The different harmonics in the power spectrum are obtained using the fast Fourier transform (FFT) calculation. This model is a tool for designing the p-i-n photodiode and determining the conditions for its utilization in order to avoid the electrical response nonlinearity View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A design of waveguide collimating lenses in the presence of anisotropic aberrations

    Page(s): 1187 - 1191
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    Anisotropic aberration correction is discussed on the basis of the extraordinary-ray ray-tracing method. Two closed analytical forms of anisotropic-aberration-free profiles are derived. The two profiles are referred to as pseudoelliptic and pseudohyperbolic, and a comparison is made between the two surfaces. The latter profiles are aberration-free in an isotropic medium. A design limit in the aperture angle is investigated. The relationship between the aperture and the energy reflection coefficient is investigated using the Fresnel formula. The pseudo-hyperbolic surface has a lower energy reflection coefficient in focusing and the pseudo-elliptic surface has a lower energy reflection coefficient in collimating View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection of high-frequency ultrasound with a polarization-maintaining fiber

    Page(s): 1221 - 1227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    The effect of a high-frequency ultrasound wave incident normally upon a polarization-maintaining optical fiber is investigated theoretically and experimentally. Two different mechanisms accounting for the birefringence change in the fiber resulting from radial strain produced by the ultrasonic wave are identified and studied. A polarization-maintaining fiber can respond to lower frequencies than a single-mode fiber in the polarimetric mode. Moreover, it does so with better sensitivity and requires no real-time control of the polarization state of the input light. The frequency separating the ranges of significance of the two mechanisms is experimentally found to be about 1 MHz (in water). The principle and the realization of a polarimetric ultrasonic sensor using a polarization-maintaining fiber are also described View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simulation and measurement of radiation loss at multimode fiber macrobends

    Page(s): 1250 - 1256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A ray-tracing model for simulating light propagation in bent multimode fibers is described. The model takes modal effects into account. Calculations of the bend loss using this model are compared with measurements. Reasonable agreement with measured bend losses is obtained by including a realistic modal power distribution (MPD) in the simulation. For situations in which the power per mode in each principle mode group is constant, the simulations predict fractional loss curves as a function of the normalized group number m/M that are independent of wavelength. These curves can be used to predict bend losses in other constant radius bends as long as the MPD is known. The emission pattern of the radiated light has been calculated and qualitative agreement with the measured pattern found. It is suspected that the differences between simulation and experiment might be explained if the exact shape of the fiber in the bend were known and taken into account View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Approximate solutions for modal propagation in channel dielectric waveguides

    Page(s): 1198 - 1206
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    A method allowing the approximate modal solutions of a truly two-dimensional-channel, dielectric waveguide to be evaluated easily is presented. In principle, the approximation can be applied iteratively until an arbitrary numerical accuracy is achieved. The application of the method to planar optical waveguides is illustrated; the results obtained for a step semicircular channel guide are presented as an example. It is shown that, within its limitations, the method provides an approximation that lies within 1% of the converged value View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Polarization- and wavelength-insensitive guided-wave optical switch with semiconductor Y junction

    Page(s): 1192 - 1197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A polarization- and wavelength-insensitive semiconductor guided-wave optical switch with a Y junction is proposed. The switch exhibits a digital response with respect to current, allowing its use as a wavelength-insensitive 1×2 optical switch. The switching characteristics are analyzed by using the beam propagation method, and a design example is given. The polarization- and wavelength-insensitive switching operation has been confirmed with a fabricated GaAs/GaAlAs switch at wavelengths of 1.3 and 1.55 μm, and the on/off ratio exceeded 20 dB at an injection current of 250 mA at these wavelengths View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of finite rib waveguides by matrix methods

    Page(s): 1228 - 1234
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    The modal structure of finite lateral extent waveguides differs from that of the associated infinite structures by the presence of additional guided modes arising from the boundary conditions and by the discrete representation of the continuum modes. These differences are analyzed for a rib waveguide using matrix methods. The origin of the additional modes and their evolution with changing system parameters are discussed. The development of localized modes from delocalized modes is of particular interest, as is the evolution of radiation modes into discrete, localized modes of higher order as the rib increases in height. These developments are followed in detail and the changes in modal character are related to the properties of the finite system's dispersion curves. Illustrations of the effect of increasing system size on the localized and delocalized modes are given View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optical-fiber resonant rings based on polarization-dependent couplers

    Page(s): 1212 - 1220
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    A theoretical and experimental analysis has been carried out on optical-fiber resonant rings based on polarization-dependent couplers. The analysis includes the use of optical-fiber polarization splitters and polarization-preserving fiber as particular cases. Two resonant configurations are presented and their sensor applications discussed. The changes of polarizations that take place in the ring are used as an effective distributed coupling which in one configuration feeds power into a resonance, and in the other introduces a variable attenuation, changing the effective losses of the resonant mode. The experimental characteristics of the system enable detection of small polarization changes. The experimental characteristics of a resonant ring about 2.5-m long and a polarization-selecting coupler are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Accuracy of approximate methods for the evaluation of chromatic dispersion in dispersion-flattened fibers

    Page(s): 1145 - 1150
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The accuracy of three approximate methods of estimating chromatic dispersion in dispersion-flattened fibers is examined. In these methods, the material dispersion of fiber is approximated by (a) the dispersion of pure fused silica, (b) the dispersion of the core material, and (c) the weighted average of material dispersion of various layers of the fiber. The actual values and three approximate values of the dispersion are calculated and compared for fibers with two, three, and four cladding regions. Examples of satisfactory and poor accuracy are given. The accuracy of approximate methods depends on the index differences and their first- and second-order derivatives with respect to wavelength. The smaller the index differences and their derivatives, the smaller the error in the approximate dispersion. However, small index differences along do not guarantee small errors. For GeO2-doped fibers, the accuracy of approximate methods b and c is much better than that of method a View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Integrated optical architectures for tapped delay lines

    Page(s): 1167 - 1176
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    An integrated optics (IO) device that is an implementation of an IO tapped delay line is discussed. It is capable of performing discrete convolution of an optical pulse sequence with a preset digital function. Several architectures for the device are presented. A systematic realization of the preset function samples that permits efficient utilization of all the input light power and maximization of the output signal-to-noise ratio (SNR) for the device is discussed. A detailed analysis of what determines the number of preset samples that can be realized and how to realize them on a LiNbO3 crystal is given. Two digital filter design examples are presented, and the quantization error effects on their performance are examined. The same architectures are shown to implement digital-to-analog (D/A) conversion and systolic multiplication of a Toeplitz matrix with a vector having the form of optical pulses View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Random coupling theory of single-mode optical fibers

    Page(s): 1235 - 1242
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    A random coupling theory is developed for analyzing the propagation characteristics of the polarization state of light in single-mode optical fibers (including conventional and polarization maintaining fibers) under random disturbances. The basic idea is that the disturbances that a fiber suffers in practice continuously change with time and space, so time-varying coupling will occur along the fiber between two linearly polarized modes HE11 that may propagate in the fiber. A coupled-mode equation of single-mode fibers under random disturbances is derived and solved rigorously with few assumptions. A random coupled-mode equation is derived considering time and space variation. Analytic solutions are obtained and used for analyzing the effect of random birefringence, polarization dispersion, polarization fluctuation, and evolution of the degree of polarization in single-mode fibers and for characterizing fiber properties View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Realization of broad-band phase devices by using W-type eccentric-core optical fibers

    Page(s): 1207 - 1211
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    Axially nonsymmetric W-type optical fibers are proposed as broadband phase devices for optical-fiber systems to provide the Fresnel's rhomb retarder in classical optical systems. Propagation characteristics of the W-type eccentric-core optical fibers are investigated theoretically using the boundary-integral method. The results of the numerical analysis indicate that such broadband phase devices can be realized by using the wavelength-dependent birefringence of axially nonsymmetric W-type optical fibers. It is theoretically found in the case of eccentric cores that a relative bandwidth of 18.2% with a phase retardation error of 2% is realizable without the propagation of higher-order mode waves View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of intrinsic phase mismatch on linear modulator performance of the 1×2 directional coupler and Mach-Zehnder interferometer

    Page(s): 1177 - 1186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    The performance of 1×2 directional couplers and Mach-Zehnder interferometers as linear modulators is compared. Models describing the operation of each device, incorporating the intrinsic phase mismatch Δβ0 which is present in nonideal devices, are developed. Distributions of Δβ0 are obtained for each device and are shown to be independent of device type. Linear dynamic range and sensitivity measurements showing how Δβ0 affects performance agree with theory. The additional effect of the coupling coefficient in the 1×2 directional coupler is demonstrated. This information can be used to predict device yield when combined with the measured Δβ0 distributions View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Statistical treatment of the evolution of the principal states of polarization in single-mode fibers

    Page(s): 1162 - 1166
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    A simple relationship is found for the evolution of the principal states of polarization (PSPs) and their differential group delay in fiber links. A simple expression is found, using the relationship, for the probability of the differential group delay (DGD), considering the evolution of the PSPs as a Brownian motion. The theory has been verified experimentally on an optical cable composed of 12 single-mode, shifted-dispersion fibers 2.2-km long. The results show that the DGD grows as the square root of the length when the length of the fiber is far larger than the correlation length of the perturbation. The measured value of DGD can vary substantially in two fibers belonging to the same ensemble, and in the same fiber, considering two frequencies differing by more than 5 nm View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Beam expanding fiber using thermal diffusion of the dopant

    Page(s): 1151 - 1161
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1008 KB)  

    A beam-expanding fiber (BEF) for embedding optical devices has been fabricated by utilizing thermally induced Ge diffusion in silica single-mode fibers (SMFs). The preparation of fiber samples and their heat treatment is described, and the effect of heat on Ge dopant distribution and diffusion is discussed. Modal-intensity distributions were studied and found to confirm the broadening of the modal field distribution after heat treatment of the fiber. Localized heat treatment to obtain BEFs is considered, and device characteristics are discussed. The BEF can arbitrarily change the spot size of a propagating mode without changing the normalized frequency View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fiber misalignment measurement method by the reflected light from fibers

    Page(s): 1243 - 1249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    A simple method for detecting misalignment of fiber axes is described. Bidirectional misalignment of the fiber axis is measured through images observed in one direction. The bidirectional components of fiber axis misalignment are measured using images created by reflected light from the fibers. The image observed for each fiber consists of a single bright line, a great advantage when processing images. The characteristics of the intensity distribution of reflected light from fibers determined by computer simulation and experiments are examined. Based on these results, the principle of the method for detecting optical-fiber positions is explained. It is shown that the accuracy of the axis misalignment measurement is defined as a standard deviation of 0.61 μm for a single fiber and 0.86 μm for a fiber ribbon; the accuracy of the measurement may allow further improvement by using an image sensor with higher resolution View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

The Journal of Lightwave Technology contains articles on current research, applications and methods used in lightwave technology and fiber optics.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Peter J. Winzer
Alcatel-Lucent Bell Labs