Fiber-optic gyroscope with suppression of excess noise from the radiation source

A new optical system is proposed and investigated experimentally for a Sagnac fiber interferometer in which the excess noise of the wide-band radiation source is suppressed. A tenfold improvement in the sensitivity of a fiber-optic gyroscope with an erbium/ytterbium fiber superfluorescent light source was achieved experimentally. It is shown that the identity of the polarization characteristics of the interferometer channels plays an important role. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (September 26, 1998)     

Fiber ring laser with locked relaxation oscillations

An investigation is made of the locking of the relaxation oscillations in a fiber ring laser with an active medium of phosphorus aluminosilicate glass doped with erbium and ytterbium ions. It is shown that stable pulse-periodic emission in the 1.5 /gmm range can be achieved at a pulse repetition frequency between 80 and 160 kHz with a pulse length of 2–3 μs. A single-mode model is used to determine the laser parameters (the pumping rate and the photon lifetime in the cavity). Pis’ma Zh. Tekh. Fiz. 25, 24–28 (January 26, 1999)     

Dual-wavelength superfluorescent fiber emitter

The feasibility of constructing a dual-wavelength, spatially single-mode, superfluorescent fiber emitter on the basis of erbium optical fibers with pumping by multimode semiconductor lasers is demonstrated. The emitter is fabricated by all-fiber technology and has a power output in excess of 10 mW, an average emission wavelength of 1.54 μm, and a spectral resolution of 27.5 nm at component linewidths of 3 nm and 9 nm. The depolarization of the radiation from the emitter as it propagates in an anisotropic, single-mode fiber waveguide is investigated. Pis’ma Zh. Tekh. Fiz. 23, 37–42 (October 26, 1997)     

Structural and noise characterization of VO2 films on SiO2/Si substrates

Multi-technique structural and electrophysical investigations of VO₂ films on SiO₂/Si substrates are carried out to study the microscopic nature of fluctuator defects — sources of lowfrequency flicker noise. It is established that the noise intensity is determined by the magnitude of the microstress fluctuations 〈ε 〉={〈(δc/c)²〉}, where c is the lattice parameter along the c-axis parallel to [011] direction in the blocks of which the film is formed. The dimensions of the blocks were determined in the direction of the c-axis (t _c∼1000 Å). The suggestion is put forward that the samples contain two types of fluctuator defects: 1) V atoms jumping between the two nearest interstitial sites and 2) V atoms jumping between these interstitial sites near lattice defects. Pis’ma Zh. Tekh. Fiz. 23, 58–65 (July 12, 1997)     

Compensation of excess noise in a fiber-optic gyroscope with a 3×3 directional coupler

It is shown theoretically that the excess noise of the radiation source can be compensated in a fiber-optic gyroscope with a 3×3 ring directional coupler and a differential amplifier at the exit. This noise is one of the main factors limiting the precision of a fiber-optic gyroscope. Pis’ma Zh. Tekh. Fiz. 23, 36–38 (August 12, 1997)     

Effect of particle mass on the behavior of stochastic ratchets

Nonlinear Brownian motion in stochastic rachets is investigated by electronic simulation methods. It is shown experimentally that it is possible to sort particles by mass using a discrete random process, binary noise, as the source of the nonequilibrium stochastic ratchets. Pis’ma Zh. Tekh. Fiz. 24, 47–53 (January 26, 1998)     

Topological birefringence and combined Rytov-Magnus effect

It is shown that the symmetry properties of the locally isotropic inhomogeneous medium of an optical fiber cause circular and linear topological birefringence. The circular birefringence δn _C in graded-index fibers is ∼(λ/ρ)² (where λ is the wavelength and ρ is the core radius), while the linear birefringence is δn _L ∼(λ/ρ)³. This topological birefringence is characterized not only by the polarization basis (as in crystals for example) but also by the magnitude and sign of the topological charge of the guided vortex. This topological birefringence forms the basis of the instability of the fiber IV vortex and is observed experimentally as the combined Rytov-Magnus effect. Pis’ma Zh. Tekh. Fiz. 25, 41–46 (March 12, 1999)     

Use of high-purity AlxGa1−x as layers in epitaxial structures for high-power microwave field-effect transistors

The fabrication of high-purity layers of Al_xGa_1−x As solid solutions in the range 0⩽x⩽0.38 by molecular beam epitaxy is reported. The low-temperature photoluminescence spectra of these layers reveal predominantly the free exciton recombination line (X). The narrow width of the X line, the high intensity ratio of this line to that of the band-acceptor transition line, and the linear dependence of the X line intensity on the excitation power density in the range between 1×10⁻⁴ and 100V·cm⁻² indicate a low concentration of background impurities in these layers. Using this material in pseudomorphic AlGaAs/InGaAs/GaAs heterostructures for high-power microwave transistors produced devices with a specific saturated output power of 0.9 W/mm at 18 GHz. Pis’ma Zh. Tekh. Fiz. 25, 8–15 (August 12, 1999)     

Photoluminescence of II–IV–V2 and I–III–VI2 crystals passivated in a sulfide solution

An investigation was made to determine how chemical treatment of the surface of II–IV–V₂ and I–III–VI₂ semiconductor crystals (such as CdSiAs₂, ZnSnP₂, CuGaSe₂, and r-AgInS₂) using a solution of ammonium sulfide in tert-butyl alcohol influences their photoluminescence properties. It is shown that the photoluminescence intensity is enhanced substantially after treatment with the spectral profile and energy position of the band peaks remaining unchanged. Pis’ma Zh. Tekh. Fiz. 24, 17–22 (November 26, 1998)     

Radiation characteristics of a dense cesium plasma in the visible range

Calculations are made of the radiation spectrum from a cesium plasma column. It is shown that this plasma may serve as a light source with a high proportion of visible radiation and an almost continuous spectrum. The visible spectrum is formed mainly by bright recombination 6P and 5D continua whose thresholds are shifted in the long-wavelength direction. Pis’ma Zh. Tekh. Fiz. 23, 40–45 (December 26, 1997)     

Fiber-optic detector using a mid-infrared diode laser and an acoustooptic modulator

Data are given for an infrared detector based on a semiconductor injection laser, which operates at a wavelength of 3.3 μm and is coupled by a chalcogenide optical fiber to an acoustooptic modulator made from an amorphous Si-Te alloy. The beam modulation coefficient reaches 70% for a pulse duration ≳0.3 μs, making the detector well suited to gas-analysis applications. Pis’ma Zh. Tekh. Fiz. 23, 14–18 (October 26, 1997)     

White-light interferometry with depolarization of the radiation

It is shown that the precision of white-light interferometers with a single-mode fiber linking the sensing and processing interferometers can be enhanced by incorporating discrete or all-fiber “time-average” radiation depolarizers (Billings depolarizers). Relations are given to describe the dependence of the output signal and the “ zero” drift of white-light interferometers on the polarization characteristics of the optical channel. Relations are also presented for the elements of the Jones matrix of a Billings depolarizer. Pis’ma Zh. Tekh. Fiz. 23, 56–60 (July 26, 1997)     

Growth of GaN by molecular-beam epitaxy with activation of the nitrogen by a capacitive rf magnetron discharge

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (June 26, 1998)     

Recording of high-energy cosmic rays by observation of the radio signal reflected from the ionosphere

Feasibility is shown for a method of detecting superhigh-energy (>10²² eV) cosmic rays on the surface of Antarctica with an event rate acceptable for observation purposes. This situation can be attributed to various favorable circumstances such as 1) the large area of the continent (10⁶–10⁷ km²); 2) the location of the vast majority of the ice cap at an altitude of 3–4 km; 3) the low level of atmospheric noise because this area is as far as possible from the equatorial thunderstorm belt; and 4) the effective band of the radio pulse frequency spectrum (0–7 MHz) not exceeding the highest frequencies used. Estimates of the electromagnetic pulse intensity were made using previously published studies. Pis’ma Zh. Tekh. Fiz. 24, 65–68 (December 26, 1998)     

Excitation of a quasi-plane shear wave by a surface acoustic source producing normal stresses

The generation of elastic volume waves by a source which is widely used in acoustic flaw detection is considered. This source produces normal stresses at the boundary of an elastic solid. The source is large compared to the wavelength of the waves that are launched. The possibility of exciting a shear wave with a plane front in the near zone is established, and an estimate of its intensity is made. Pis’ma Zh. Tekh. Fiz. 23, 91–94 (December 12, 1997)     

Observation of a negative characteristic temperature for the threshold current of diode lasers for the 2.8 /gmm spectral range

A decrease in the lasing threshold with increasing temperature has been observed in InAs/InAsSbP laser heterostructures for the 2.7–2.9 μm spectral range at cryogenic temperatures (T=32–85 K). At temperatures below 50 K a negative characteristic temperature, T ₀=−70 K, was obtained for the threshold current. Characteristics of the temperature dependence of the threshold current and the laser output power were investigated. Pis#x2019;ma Zh. Tekh. Fiz. 23, 72–79 (November 26, 1997)     

Angular momentum of the fields of a few-mode fiber. III. Optical Magnus effect, Berry phase, and topological birefringence

It is shown that, on the one hand, the evolution of the angular rotation of the lines of nodes of the CP₁₁ mode is a manifestation of the optical Magnus effect in a few-mode fiber with a parabolic refractive index profile, and, on the other hand, the additional phase γ _b =±δβ ₂₁ z in CV and IV vortices is the Berry topological phase, which arises as a result of the cyclic change in the orientations of the orthogonal axes of dislocations. The splitting of the propagation velocities of orthogonal circularly polarized CV⁺ and IV⁻ modes in an LV vortex in a parabolic fiber is a manifestation of the phenomenon of topological birefringence of a few-mode fiber. The azimuth of the linear polarization of a vortex undergoes continuous angular rotation. In an optical fiber with a stepped index profile the CP₁₁ mode forms circularly polarized edge dislocation over lengths which are multiples of half the beat length, and over lengths which are odd multiples of the quarter beat length it forms linearly polarized fields with a purely screw dislocation. This transformation of edge and screw dislocations can be regarded formally as conversion of the polarizational angular momentum into orbital angular momentum. The conversion of angular momentum is a reflection of the dynamical unity of the optical Magnus effect and the Berry topological phase in the fields of a few-mode fiber. Pis’ma Zh. Tekh. Fiz. 23, 59–67 (December 12, 1997)     

Angular momentum of the fields of a few-mode waveguide: Conversion of the angular momentum

An analysis is made of the transformation of the angular momentum density in the field of an unstable IV vortex of a few-mode optical fiber. It is shown that the effect of mode dispersion of IV vortices is observed as the conversion of the polarization and orbital components of the electrodynamic angular momentum. The angular momentum defect may be recorded experimentally as a mechanical twist of the optical few-mode fiber. Formally the dispersion process resembles the conversion of the signs of the orbital and polarization components of the angular momentum density. A complex pseudopotential, whose real and imaginary parts characterize the field lines and lines of equal pseudopotential, is introduced to describe the energy flux density of the fiber vortex. The conversion of field states with equivalent partial ê ⁺ F ₁(R)exp{−iφ} and ê2⁻ F ₁(R)exp{+iφ} vortices was investigated experimentally. Pis#x2019;ma Zh. Tekh. Fiz. 23, 58–65 (November 26, 1997)     

Influence of degradation on the spectrum of voltage fluctuations in thick films of high-temperature superconductors

The noise parameters of high-temperature superconductors (yttrium barium cuprites) have been studied before and after degradation. The samples were thick films—10.5 mm×5.5 mm×8 μm—fabricated by magnetron sputtering on a ZrO substrate. A model is proposed for the onset of voltage fluctuations. The results of the measurements confirm that the observed noise spectrum is caused by fluctuations in the resistivity. Pis’ma Zh. Tekh. Fiz. 23, 91–94 (December 26, 1997)     

Dosimeter for real-time monitoring of nuclear radiation energy (dose) using a metal-gas-insulator-semiconductor structure

A new type of semiconducting dosimeter is proposed for real-time monitoring of nuclear radiation energy (dose). This dosimeter produces an electrical output signal directly proportional to the incident radiation dose (and not its intensity) and its sensitivity to this radiation dose can be controlled. Pis’ma Zh. Tekh. Fiz. 24, 64–69 (November 26, 1998)