Fiber-optic Interference Research Articles

A laser-based automatic interference refractometer for control of the gradient of the index of refraction of plane-parallel glass elements

A laser-based fiber-optic interference refractometer for use in automatic control of the gradient of the index of refraction of large plane-parallel glass optical elements with resolution on the order of 8·10–7 cm–1 and absolute error at most 2·10–5 cm–1 is proposed.

A Theoretical Study of the Temperature Sensor Based on the LP01-LP02 Intermodal Interference in Optical Fiber with a Liquid Core

We theoretically propose the temperature sensor based on optical fiber consisting of fused silica and core of 2.5 μm radius filled in with toluene. In such an optical fiber the intermodal interference of modes LP01-LP02 shows a characteristic dependence of the equalization wavelength λ0 on temperature. The optical fiber sensor was theoretically investigated in the temperature range of 0-40 °C, where the equalization wavelength λ0 for modes LP01-LP02 changes from 1284.2 nm to 844.1 nm. Such considerable wavelength change with temperature favors this sensor for temperature measurements with sensitivity better than 0.1 °C.

Fiber-optic interferometric refractometer for deep-water monitoring

A method is proposed for organizing deep-water refractometric studies and fiber-optic interference systems for precise monitoring of the absolute refractive index of sea water at depths up to 1000 m with measuring probes submerged independently or together with underwater equipment.

Closed-loop phase stepping in a calibrated fiber-optic fringe projector for shape measurement

Active homodyne feedback control can be used to stabilize an interferometer against unwanted phase drifts introduced by, for example, temperature gradients. The technique is commonly used in fiber-optic sensors to maintain the fiber at its most sensitive (quadrature) position. We describe an extension of the technique to introduce stabilized, pi/2-rad phase steps in a full-field interferometer. The technique was implemented in a single-mode, fiber-optic interference fringe projector used for shape measurement and can be easily applied to other fiber- or bulk-optic interferometers, for example, speckle pattern and holographic interferometers. Fresnel reflections from the distal fiber ends undergo a double pass in the fibers and interfere at the fourth port of a directional coupler. The interference intensity (and hence phase) is maintained at quadrature by feedback control to a phase modulator in one of the fiber arms. Stepping between quadrature positions (separated by pi rad for light undergoing a double pass) introduces stabilized phase steps in the projected fringes (separated by pi/2 rad for a single pass). A root-mean-square phase stability of 0.61 mrad in a 50-Hz bandwidth and phase step accuracy of 1.17 mrad were measured.

Suppression of Manakov soliton interference in optical fibers.

In this paper, we study the interaction of two vector solitons in the Manakov equations that govern pulse transmission in randomly birefringent fibers. Under the assumptions that these solitons initially are well separated and having nearly the same amplitudes and velocities but arbitrary polarizations, we derive a reduced set of ordinary differential equations for both solitons' parameters. We then solve this reduced system analytically. Our analytical solutions show that, when two Manakov solitons have the same amplitude and phases, their collision distance steadily increases as their initial polarizations change from parallel to orthogonal. In particular, the collision distance at orthogonal polarizations is of the order of the square of the collision distance at parallel polarizations. When the Manakov solitons have different amplitudes, a quasiequidistant bound state can be formed. The degrees of position and amplitude oscillations in this bound state diminish as the initial polarizations change from parallel to orthogonal. With a combination of launching Manakov solitons along orthogonal polarizations and at unequal amplitudes, Manakov-soliton interference is almost completely suppressed. These theoretical results are in excellent agreement with our direct numerical simulations.

Fiber-optic interference refractor for investigating aqueous media

A circuit of a modified laser fiber-optic interference refractometer is described. Using the modified refractometer it is possible to measure the absolute indices of refraction of water at depths down to 10 m in an automatic mode. The capabilities of the modified design are discussed and the measurement error is estimated.

Fiber-optic Moiré Interference Principle

A novel fiber-optic interference method called fiber-optic Moiré interferometry has been developed and demonstrated. Fiber-optic moiré interference is based on the special relative positions and the polarization directions of three HiBi fiber ends. A helium–neon laser and three HiBi fibers are used to configure a moiré interferometer in our experiments. The optical field intensity distribution function of the moiré interference pattern is analyzed and the simulation results as compared with experimental interference patterns are given.

Temperature measurement of end gas under knocking condition in a spark-igniyion engine by laser interferometry

Knocking is one of the most significant problems that limits the efficiency of an internal combustion engine. It is caused by autoignition of the unburned gas ahead of the flame. In order to understand the knock phenomenon, it is important to measure the temperature of the unburned gas. In this study, with polarization preserving fibers, the laser interference measurement of the unburned gas temperature was performed in a constant-volume and a specially designed engine which could be ignited only once. The engine was fueled with n- butane , oxygen and argon, and was operated under knocking conditions. When the density of the gas changes, the change of the optical path length of the test beam corresponds to the change of the refractive index. The temperature history of the unburned gas was determined by measuring the pressure and the change of interference signal. The optical fiber interference system had the advantage of resisting mechanical vibration because the test and reference beams were transmitted in the same optical fiber and were separated only in the test section.

Temperature Measurement of End Gas under Knocking Condition in a S. I. Engine by Laser Interferometry.

Knock is one of the most significant problems that limit the efficiency of an internal combustion engine. It is caused by autoignition of the unburned gas ahead of the flame. In order to understand the knock phenomenon, it is important to measure the temperature of unberned gas. In this study, with polarization maintaining optical fibers, the laser interference measurement of unburned gas temprature was performed in a constant volume vessel and a specially designed engine which could be ingited only once. The engine fueled with n-butane, oxygen and argon, was operated under knocking conditions. When the density of the gas changes, the change of the optical path length of test beam corresponds to the change of refractive index. The temperature history of the unburned gas was determined by measuring the pressure and the change of interference signal. The optical fiber interference system had the advantage of resisting mechanical vibration because test and reference beams were transmitted in the same optical fiber and were seperated only in the test section.

Experimental Study of Interference in Optical Fibers

Feasibility of fiber optics for the measurement of the degree of coherence was confirmed experimentally. A diffraction pattern of the light from optical fibers was recorded on a photographic film and the pattern was analyzed in terms of spatial frequency by the diffraction method. The degree of coherence was evaluated from the diffraction powers associated with the interference between fibers. Despite the complex behavior of photographic emulsions, experimental results assure the feasibility of the method. The spatial and temporal coherence of a helium-neon laser are presented, which were obtained by this method.