Polarization-mode dispersion measurements based on transmissionspectra through a polarizer

Routine characterization of polarization-mode dispersion (PMD) in single-mode fiber, both at the manufacturing stage and in installed systems, requires an easy-to-implement measurement technique. One method that is particularly simple to implement involves counting the number of extrema (i.e., maxima and minima) per unit wavelength interval in the transmission spectrum measured through a polarizer (analyzer) placed at the output of a test fiber. In this paper, we establish accurate equations relating both the extrema density and mean-level crossing densities in such spectra to the expected value of PMD. These equations are used to measure several fiber samples, and are compared to measured values obtained with a commercially available test set. It is shown that measuring both mean-level crossings and extrema densities provides a simple means for establishing whether a fiber is scaling as √L (long-length regime) or L (short-length regime). Using Monte Carlo simulations, the accuracy of the fixed-analyzer measurements is examined as a function of the width of the wavelength interval over which measurements are made. In addition, the simulations indicate that fixed-analyzer measurements are quite robust with respect to the presence of polarization-dependent loss (PDL) in the span, an important consideration for measurements in amplified systems     

Polarization mode dispersion measurements in an installed opticalfiber submarine cable

Highly accurate polarization mode dispersion (PMD) measurement using an interferometric detection technique with AC modulation is discussed. This technique, which searches for the interference fringe signal, was used to measure PMD in a 60 km long installed optical submarine cabled fiber 2500 m sea depth and to determine the fiber-length dependence of PMD. PMD measurement in 60-km-long installed optical submarine cabled fibers was confirmed to be less than about 0.7 ps. It was found that the fiber length dependence of the PMD measurement in the less than ~20-km-long cascaded uncabled fibers was proportional to √L; however, the PMD data in the long-length (over ~50 km long) fibers were slightly scattered     

White light dispersion measurements by one- and two-dimensionalspectral interference

White light dispersion measurements by and two-dimensional spectral interference are shown. One-dimensional white light spectral interference measurements allow accurate characterization of dispersion using weak optical fields. Two-dimensional spectral interference allows for real-time measurements since no post-processing is needed, and therefore can be used in situations where the optical properties of the elements under test vary in time. We demonstrate the applicability of the two methods for characterizing dispersive elements such as optical glasses and dielectric coatings     

Ultra-wideband slotline dispersion measurements using ring resonator

The design for an ultra-wideband coplanar waveguide-fed slotline ring resonator is presented. The broadband feed system permits dispersion measurements to be made over the frequency range 2?220 GHz using a single circuit and coplanar waveguide probes connected to a vector network analyser. Measured effective dielectric constant data from a number of different rings using thin-film copper on alumina is presented, and compared with a theoretical prediction using the spectral domain approach, the agreement being better than 3.5%.     

Analysis and correction of errors in a polarimeter for Faraday rotation measurements

Sources of error in polarization measurements on electromagnetic waves are investigated. A method is described for correcting the error in the measurement of a Faraday rotation in propagation from a geostationary satellite by calibrating the receiving system.     

Modal distribution of backscattered light in a step-index multimode fibre

The modal distribution of backscattered light has been measured for a low mode-mixing, step-index fibre. The modal distribution of the Rayleigh backscatter is shown to depend on that of the exciting pulse. The possibility of substantial errors arising in reflectometry measurements of splice and connector losses is demonstrated where the receiver is mode-selective.     

A compact in-line polarimeter using a Faraday rotator

We have developed a compact in-line polarimeter for monitoring the polarization of light in active fiber. It consists of two parts: a half-mirror inserted into a trench cut at a slant across the fiber so that it reflects a portion of the optical beam and the combination of a magnetized Faraday rotator plate sandwiched between mirrors and a four-channel detector.     

Chromatic dispersion measurements on long fibre lengths using LEDs

The chromatic dispersion of 50.7 km of single-mode fibre has been measured with a single edge-emitting LED using the phase-shift technique. For a 15 s measurement time the zero of chromatic dispersion is obtained with a standard deviation of 0.7 nm for a 50.7 km fibre length and 0.25 nm for a 38.0 km length.     

Modal dispersion and attenuation measurements of silicon nitrideand silicon oxynitride waveguides using a streak camera

By measuring short pulse propagation in silicon nitride and oxynitride waveguides fabricated on silicon, it has been possible to characterize both attenuation and group velocity dispersion accurately for the different modes that propagate. The method is self-calibrating, using the ratio between scattered light from forward and backward traveling pulses at a particular point on the waveguide. In principle, the group velocity data can be used to calculate the phase velocities for the different modes using known dispersion relations. The phase velocities were measured independently using a prism coupling technique, and the group velocities that could be derived from them matched the experimental data within a few percent. The resolution of the technique is limited mainly by amplitude fluctuations of the laser. The full-width-half-maximum resolution was at best about 12 ps but should be extendable to better than 5 ps     

Chromatic dispersion distribution measurement along a single-modeoptical fiber

A nondestructive measurement technique, which uses a four-wavelength bidirectional optical time domain reflectometer (OTDR) to measure the chromatic dispersion distribution along a single-mode fiber, is compared with the destructive interferometric technique. The experimental results obtained by this technique are in good agreement with those obtained by the interferometric technique. In addition, a measurement procedure is proposed for a transmission line composed of different types of single-mode fiber. These results show that this technique is extremely useful for the design of wavelength division multiplexer (WDM) and finite difference multiplexer (FDM) optical communication systems     

Calculation of dispersion and nonlinear effect limited maximum TDMand FDM bit rates of transform-limited pulses in single-mode opticalfibers

The dispersion-limited maximum time-division-multiplexed (TDM) bit rates and the optical nonlinear-effect-limited maximum frequency-division multiplexed (FDM) channel numbers in single-mode optical fibers have been calculated for transform-limited optical pulses. The total bit rate attainable with combinations of TDM and FDM on Gaussian-type transform-limited pulses is about 7 Tbt/s in the typical 15 THz wide low-loss region of single-mode fibers at each of 1.3 and 1.5 μm wavelength bands. The maximum total bit rate attainable with dispersion-shifted (DS) fibers in the Er-doped fiber amplifier (EDFA's) gain region of 1525-1565 nm is calculated to be about 2.3 Tbt/s, but reduces to 1.2 to 1.8 Tbt/s depending on fiber length for cases of a uniform TDM bit rate over the entire FDM channels. For DS fibers the four-wave mixing effect is a dominant effect limiting the channel power and the maximum FDM channel number, but for normal single-mode fibers the chromatic dispersion effect and cross-phase modulation (CPM) and stimulated Raman scattering (SRS) effects are dominant effects limiting the TDM bit rate and channel power, respectively     

Spectral properties of Rayleigh backscattered light fromsingle-mode fibers caused by a modulated probe signal

The statistical properties of Rayleigh backscattering from single-mode fibers are investigated, taking into account the modulation and the coherence of the source light. The autocorrelation function and the power spectral density of the backscattered field and intensity are derived. To describe the noise due to Rayleigh backscattering in bidirectional systems, the spectrum of the interference of backscattered light with reflected source light is also calculated. The measurements confirm the theoretical results. It is shown that, if no optical isolator is used and the laser diode is exposed to Rayleigh backscattering, the interaction between laser and fiber depends strongly on the modulation of the light     

Distributed dispersion measurements and control within continuously varying dispersion tapered fibers

We report the first continuous nondestructive measurement of dispersion along a fiber designed to have a continuously varying dispersion profile. This measurement highlights the flexibility of the measurement technique and illustrates the levels of accuracy [/spl ap/0.05 ps/(nm/spl middot/km)] that can be achieved when pulling long fibers with arbitrary dispersion profiles.     

Chromatic dispersion measurements over a 50-km single-mode fiber

Chromatic dispersion has been measured over a 50-km-long single-mode fiber, using five sinusoidally modulated laser diodes. Results indicate that chromatic dispersion characteristics for single-mode fibers with 33-dB optical loss can be evaluated in the1.2-1.6-mum spectral region.     

Analysis of quasi-parabolic reflectors with a microwave lamp installed at the input of a prismatic light guide

A technique for calculating a quasi-parabolic reflector containing a spherical electrodeless lamp in a translucent microwave resonator placed at the input of a prismatic light guide is considered. The light-intensity curves calculated with the ROTREF computer code are analyzed. These curves are calculated for admissible values of the reflector’s turning angle, different diameters of the prismatic light guide, and different shifts of the lamp along the reflector axis. The three most typical positions of the lamp inside the quasi-parabolic reflector are found and features of these positions are discussed.     

Multiplexing of optical fiber sensors using a frequency-modulated source and gated output

A novel method is proposed and demonstrated for multiplexing fiber-optic interferometric sensors using the FMCW technique. The method uses a gas laser whose optical frequency is modulated sinusoidally by an external modulator. The use of gating and appropriate signal processing can achieve low crosstalk between sensors. Experiments on two and three sensor systems are reported. The minimum detectable signal measured is 1 mrad/sqrt{Hz}and the crosstalk factor achieved is -35 dB. The major causes of crosstalk are also analyzed.     

Third-order dispersion compensation using a phase modulator

Compensation of third-order dispersion in a fiber-optic transmission system using a phase modulator is studied both theoretically and experimentally. A sinusoidal signal is used as modulation function, where the amplitude and phase delay are optimized. The 2-ps input pulses (160-Gb/s compatible) were transmitted through a 626-km fiber link, where the characteristic oscillating tail was measured with a 1.6-ps resolution optical sampling system. When applying the phase modulation, the oscillating tail was significantly suppressed. The pulses were also used in a 160-Gb/s transmission experiment, where the eye diagrams were measured with the sampling system. Numerical simulations and practical experiments showed excellent agreement.     

Measurement of a modulated DFB laser spectrum using gated delayedself-homodyne technique

The mixing of a modulated DFB laser with a CW local oscillator can be achieved with a single laser by using a gated modulation technique combined with an appropriate optical delay. Frequency chirp measurements up to ±22 GHz are demonstrated using this technique     

Birefringence and polarisation dispersion measurements in high-birefringence single-mode fibres

We have measured by white-light crosscorrelation the polarisation mode dispersion of a polarisation-maintaining single-mode fibre and its variation with wavelength. The results have been confirmed by birefringence measurements and by birefringence modelling.     

Crosspolarisation measurements using a composite feed

The crosspolarisation performance of reflector antennas fed by a low-crosspolarisation composite feed is investigated experimentally. It is found that an improvement of slightly better than 9 dB can be obtained with this feed, compared with the single-dipole feed. This confirms previously published theoretical findings.