Theoretical spectrum of noisy optical pulse trains

The intensity of an ideal optical pulse train is often modeled as an exact periodic repetition of a given pulse-shape function with constant amplitude and width. Therefore, the ideal intensity power spectrum is a pure line power spectrum. However, spontaneous-emission noise due to amplification media, electronic noise due to modulators, or even intentional modulations result in period-to-period fluctuations of the pulse amplitude, width, or arrival time. The power spectrum of this so-called noisy optical pulse train is then composed of a line spectrum added to a band spectrum. This study shows that the optical pulse train intensity is cyclostationary under usual assumptions on the fluctuations. This property allows us to derive the exact optical pulse train power spectrum. A general closed-form expression that takes into account the three noise manifestations (jitter, amplitude, and width modulations) is provided. Particular expressions are given for usual cases of interest such as the jitter and amplitude modulation model, for given fluctuation probability distributions, and pulse-shape functions.     

Investigation of the propagation of an ultrasound pulse in a dispersed fractal medium

Results are presented of an experimental determination of the fractal parameters of crushed sand particles. Results of measurements of the propagation of an acoustic pulse through a mass of sand having various degrees of dispersion are used to determine the fractional exponent in the dependence of the propagation velocity on the ultrasound wavelength. A wave equation in fractional derivatives is proposed to describe the propagation of ultrasonic waves in a dispersed medium. Pis’ma Zh. Tekh. Fiz. 25, 14–18 (June 12, 1999)     

A model for the data-handling system in digital fiber-optic transmission

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 24–26, October, 1991.     

Long-haul dense wavelength division multiplexing between a chaotic optical secure channel and a conventional fiber-optic channel

The purpose of this paper is to numerically investigate dense wavelength division multiplexing (DWDM) transmission between a chaotic optical secure channel and a conventional fiber-optic channel. A 2.5 Gbits/s secure message masked by the chaotic optical secure channel and a 10 Gbits/s message sequence carried by the conventional fiber-optic channel can be realized simultaneously when the channel spacing is 0.8?nm. The results show that the Q-factors of the recovered messages can be increased significantly when the launched optical power is reduced appropriately. The deterioration of the quality of communication caused by fiber dispersion can be compensated noticeably on the condition that the symmetrical dispersion compensation scheme is adopted. In addition, the secure message is masked by chaos shift keying in the chaotic optical secure channel. The multiplexing distance between the chaotic optical secure channel and the conventional fiber-optic channel is up to 500?km.     

Stabilization of a fiber-optic two-arm interferometer for ultra-short pulse signal processing applications

We experimentally demonstrate a stable ultrafast first-order temporal differentiator using a fiber-optic Michelson interferometer incorporating a simple feedback stabilization control, which is based on dithering a single wavelength cw reference. Feedback control signals are acquired by a phase-lock-loop and used for automatically adjusting and maintaining the resonance wavelength of the differentiator at the pulse center wavelength without dithering or disturbing the interferometer arms. Picosecond odd-symmetry Hermite-Gaussian waveforms using the implemented first-order differentiator have been stably generated. The demonstrated stabilization system should prove useful for a wide range of ultrafast pulse processing and analysis applications based on the use of two-arm interferometers.     

Electromagnetic plane-wave pulse transmission into a Lorentz half-space

The propagation of an electromagnetic plane-wave signal obliquely incident upon a Lorentz half-space is studied analytically. Time-domain asymptotic expressions that increase in accuracy with propagation distance are derived by application of uniform saddle point methods on the Fourier-Laplace integral representation of the transmitted field. The results are shown to be continuous in time and comparable with numerical calculations of the field. Arrival times and angles of refraction are given for prominent transient pulse features and the steady-state signal.     

Metrological support of measurements of the parameters of fiber-optic data transmission systems

The present state of metrological support for measurements of fiber-optical data transmission systems and their components is considered. The results of research at the All-Russia Research Institute of Optophysical Measurements to construct a complex State Special Standard in this area, working standards and an appropriate checking scheme are presented.     

Unification of measurements of the average power of optical radiation in fiber-optic transmission systems

The current status of measurement uniformity, the design and characteristics of new standard calorimeters and high-precision apparatus, and a hierarchical testing sequence are discussed in application to instruments for measuring the average power of optical radiation in fiber-optic transmission systems. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 31–37, August, 2000.     

The transmission capacity of a nonlinear classical communication channel

The transmission capacity of a nonlinear classical communications channel that does not obey the well-known Shannon formula describing a linear additive channel is analyzed. According to the Landauer principle, no finite energy is required to transmit a bit of information, which, in principle, makes reversible data transmission possible. The process of data transmission is analyzed using a model of the transmitting medium representing a ferroelectric crystal possessing a center of symmetry. Using this model, it is possible to trace an analogy between the process of bit setting and transmission, on the one hand, and the violation of the lattice symmetry as a result of the second-order phase transition at the Curie temperature, on the other hand. An expression for the transmission capacity is obtained using the well-known cnoidal solution of the corresponding nonlinear equations in the absence of damping. The transmission capacity of an arbitrary nonlinear classical communication channel is estimated.     

Standard apparatus for measuring polarization mode dispersion in fiber-optic data transmission systems

Methods and instruments for ensuring the uniformity of polarization mode dispersion measurements in fiber-optic data transmission systems are described. The results of the development of a standard measuring instrument and working standards of the unit of dispersion are presented. The results of metrological investigations of a standard measuring instrument are also given.     

Standard equipment for instruments for the measurement of chromatic dispersion in fiber-optic information transmission systems

A technique and procedure for the development of standard equipment for instruments used in the measurement of chromatic dispersion in fiber-optic information transmission systems are described. An analysis of the errors of the standard equipment is presented. Results of studies of the standard equipment and working standard of chromatic dispersion are also presented.     

Information transmission using a synchronous chaotic response with filtering in the communication channel

A principle is proposed for obtaining a chaotic synchronous response in a driven nonlinear oscillatory system under conditions where the signal of the driving chaotic system is filtered by the coupling channel. Music and speech signals are used to demonstrate the efficiency of applying this principle to transmit information through a channel having a limited frequency band. Pis’ma Zh. Tekh. Fiz. 25, 71–77 (August 26, 1999)     

Data transmission through a radio channel using masking oscillations

A scheme of data transmission through a radio channel masked by chaotic oscillations is considered. A mathematical model describing the system is formulated in the case of chaotic oscillations generated in two separated frequency bands. The results of a numerical analysis of the model are presented. It is demonstrated that hidden data transmission in such a channel is possible.     

Analysis of a high-speed fiber-optic spectrometer for fiber-optic sensor signal processing

A novel high-speed fiber-optic spectrometer has been demonstrated in our previous work. The high-speed spectrum measurement is enabled by translating the spectral-domain signal into a time-domain signal through a dispersion element. We present a mathematical model that accurately describes the relationship between the optical spectrum to be measured and the dispersed time-domain signal. Based on the model, the effects of the key parameters on the performance of the spectrometer are investigated in detail using numerical simulation. The analysis is useful for the design and application of such spectrometers.     

Stability of a fiber-optic magnetometer

The stability of a fiber-optic magnetometer employing metallic glass ribbons was examined over a period of more than 10 h. The magnetometer can be operated either in the open magnetic loop or the closed magnetic loop configuration. The short-term minimum detectable magnetic field for ≈ 10 cm of sensor fiber length was less than 2 gamma in the dc to 1-Hz bandwidth. Long-term stability of approximately 10 gamma was achieved in the closed magnetic loop configuration.     

On the effect of noisy measurements of the regressor in functional linear models

We consider the estimation of the slope function in functional linear regression, where a scalar response Y is modelled in dependence of a random function X, when Y and only a panel Z ₁,…,Z _L of noisy measurements of X are observable. Assuming an i.i.d. sample of (Y,Z ₁,…,Z _L ) of size n we propose an estimator of the slope which is based on a dimension reduction technique and additional thresholding. We derive in terms of both the sample size n and the panel size L a lower bound of a maximal weighted risk over a certain ellipsoid of slope functions and a certain class of covariance operators associated with the regressor X. It is shown that the proposed estimator attains this lower bound up to a constant and hence it is minimax-optimal. The results are illustrated considering different configurations which cover in particular the estimation of the slope as well as its derivatives.     

Application of fiber-optic bragg grating sensors in monitoring environmental loads of overhead power transmission lines

We demonstrate the capability of using fiber-optic sensors for measurements on environmental loads on a high-power, overhead transmission line. A trial system with three Bragg gratings, including a temperature reference, was installed on a 160-m span of a 60-kV line. An interrogation system with a tunable distributed Bragg reflector laser source was used. Several measurements of the induced loads on a conductor were recorded in various wind conditions. In particular, aeolian vibrations were frequently observed, and several measurements of this phenomenon were made. The results correlate well with simple theoretical predictions and visual observations.