Measurement Of Refractive Index Profile Research Articles

Measurement of refractive-index profiles in optical-fibre preforms by spatial-filtering technique

A nondestructive technique based on spatial filtering is presented for measuring the refractive-index profile in an optical-fibre preform. The method is simple, accurate and has sufficient resolution to enable detailed profiles of single-mode preforms to be obtained.

Holographic measurement of refractive-index profile of optical fibre preform

A holographic method of measuring the refractive-index profile of an optical fibre preform is presented. It uses the principle of shearing interferometry. The method is simple and allows measurements to be repeated even after the preform has been withdrawn for fibre drawing.

Measurement of refractive-index profile and transmission characteristics of a single-mode optical fiber from its exit-radiation pattern

A new exit-radiation pattern method for measuring the refractive-index profile of a single-mode fiber is proposed and used experimentally. In this method the profile is computed from the far-field exit-radiation pattern of the H(11) mode at the end of the single-mode fiber. This method can be applied to a cabled fiber, and the propagation constant, field profile, and group delay of the H(11) mode, and the single-mode limit can be obtained as well as the index profile. The principle, computer simulations, experimental setup, and experimental results are first described. The profile obtained shows a good agreement with that obtained from the interference fringe pattern measured before drawing the fiber. Computations of the group delay of the H(11) mode and the single-mode limit from the measured exit-radiation pattern are discussed.

Nondestructive measurement of refractive index profiles of optical fiber preform rods

Nondestructive measurement of refractive index profiles of optical fiber preform rods

Practical application of the refracted near-field technique for the measurement of optical fibre refractive index profiles

Both the theoretical basis and experimental realization of the refracted near-field technique for the direct measurement of optical fibre profiles are presented. The technique requires minimal sample preparation, no computation and is applicable to both single and multimode fibres. Both the core and the cladding are profiled. After outlining the problems associated with other techniques, the use of this method for the measurement of fibre profile, numerical aperture and geometry is discussed. Leaky mode rejection and resolution are treated in detail. A fitting procedure for determining theα-value of a profile is given. The experimental apparatus is fully discussed. Results are presented to illustrate both the applicability of the technique to single and multimode fibres and also the rejection of leaky modes. The experimental sensitivity is shown sufficient to reveal an index fluctuation having a wavelength < 1μm and an amplitude of < 0.0001.

Single-mode-fiber refractive-index profile measurement by reflection method

A new technique for measuring the refractive index profile of single-mode fibers based on the reflection method is described, and experimental results are demonstrated. When the core radius of a test fiber is only a few times larger than the laser beam spot size, the reflected power distribution does not indicate the refractive index correctly. However, the true index profile can be calculated from the beam spot size and the reflected power distribution with high accuracy: 0.3-microm spatial resolution and 5% relative refractive-index resolution are obtained for practical single-mode fibers.

Near field and far field power distributions in a multimode graded fibre

It is shown in this paper that the near field and far field power distributions corresponding to any distribution of rays in an arbitrary graded fibre, reach a steady state along the fibre. This steady state is usually a function of the input distribution of rays and of the refractive index profile of the fibre. The case of parallel beam injection is considered and an analytical expression for the near field power distributions for any arbitrary profile is found. This suggests a new method of refractive index profile measurement which is free of leaky ray corrections and can be very sensitive near the optimum profile for time dispersion.

Doped crystals for integrated optics

Detailed measurements of dopant concentration and refractive index profiles in two diffused optical waveguide systems are reported (LiNbO 3: Ti, MgO: Cu). Relevance of the result to theoretical models of index perturbation and to device application are discussed.

A new technique for refractive index profile measurement in multimode optical fibres

A new technique for refractive index profile measurement in multimode optical fibres

Elimination of errors due to sample polishing in refractive index profile measurements by interferometry

The surface contouring caused by routine polishing of fibers and preforms in preparation for measurement of the refractive index profile has been studied. By observation of the surface interference fringes the effect of polishing on doped preforms is visualized. It is found that composition-dependent thickness variations occur which can cause a sizable error in the refractive index variation deduced by interference measurements in performs (several percent) and in fibers (∼50%). The difficulty is eliminated by several minutes of additional polishing on a hard lap.

Atmospheric Refractivity Studies with Airborne Microwave Refractometer

An airborne microwave refractometer was used for measurement of refractive index profiles in the Kanpur-Nainital region. Details of the instrument and experiments are described in this paper. Average refractivity profiles obtained from the data are plotted. Fine structure of refractivity shows scale of turbulence of the order of tens of meters and mean squared refractivity fluctuations about 10−11 for heights upto 2300 meters. The exponent of the wave number dependence of refractivity spectrum has a range of 3 to 5.

Radio refractive index investigations over Bass Strait, Southern Australia

Radio refractive index profile measurements between 500 and 5000 feet were made over Bass Strait (Australia) during January and March 1966, using a microwave refractometer car-tied in a light aircraft. During these flights continuous radio propagation measurements at 173 MHz and 1.9 GHz were made over paths at points along which the profiles were measured. Supporting meteorological observations were also made. The measured refractive index profiles and associated weather conditions are described, and possible mechanisms to account for the observed relations between propagation behavior, refractive index, and meteorological data are discussed. The measurements show the progressive development of a strong superrefractive layer near 3000 feet, resulting from a subsidence inversion. This layer produced enhanced signals on the 173-MHz over-horizon radio path, due mostly to partial reflection at the layer and at some times possibly to trapping. Fading on the 1.9 GHz optical path probably resulted from trapping.

The construction and performance of an airborne microwave refractometer

The paper describes the construction of a Birnbaum-type microwave refractometer and its application in studies of refractive-index variations at heights up to 20000ft. Practical problems encountered in airborne measurements are discussed in detail. Some typical results are given which illustrate the performance obtained in measurements of refractive-index profiles and discontinuities.