Showing papers on "Step-index profile published in 1985"

Power transfer in fused biconical-taper single-mode fiber couplers: dependence on external refractive index

Abstract: It is demonstrated that through control of the refractive index surrounding a fused biconical-taper single-mode coupler the coupling coefficient can be changed from 0% to 96%. Data are also presented that show the coupling mechanism cannot be attributed to power transfer between the modal fields guided by the fiber cores in the taper-waist region. The results support the model of the coupling mechanism as a beat phenomenon between modes guided by a glass core with a dumbbell cross section and an external refractive index.

Ultraviolet reflecting mirror

Abstract: An ultraviolet reflecting mirror comprises a substrate, a high reflection factor film provided on the substrate and having a film thickness of at least 250 Å and reflecting a light beam by the surface thereof, and a group of dielectric material layers comprising one or more sets of two layers of low refractive index film and high refractive index film provided on the high reflection factor film. The low refractive index film is provided on the high reflection factor film. The optical film thickness of the high refractive index film and the low refractive index film is approximately 1/4(2n-1)λ, where n is a natural number and λ is the design wavelength and 150nm≦λ≦300nm. The film thickness of at least one of the high refractive index film and the low refractive index film is 3λ/4.

Interference filter design using flip-flop optimization

Abstract: An antireflective optical film is placed between an incident media and a substrate to effect minimal reflectivity from the incident media-substrate interface over a broad spectral band. The film is designed by selecting a first material with a low refractive index and a second material with a high refractive index. A theoretical film is defined with a plurality of thin layers of equal thickness. The low refractive index or the high refractive index material is specified for each layer in the film. The reflectivity of the theoretical film is evaluated. The refractive index of one of the layers is changed to the alternate index and the reflectivity of the defined film is reevaluated. If the reflectivity of the film is improved, the alternate refractive index is assigned to the changed layer. The steps of changing, reevaluating, and assigning are repeated for each of the layers in the film until no further improvement in the reflectivity of the film is obtained. The thin layers may be defined with equal physical or optical thickness and should be substantially thinner than wavelengths within the spectral band to be reflected by the film. The initial refractive index profile may be defined with all of the layers having the low refractive index, all of the layers having the high refractive index, the layers having alternately low and high refractive indices, or such that the initial refractive index profile for the film approximates a predetermined gradient index profile.

Form birefringent cutoff polarizer and method

Abstract: The cladding and a portion of the core of a length of optical fiber are removed to form an interaction region. A form birefringent stack is positioned on the exposed core. The refractive index of the stack for polarizations parallel to the plane of the interaction region is approximately equal to the refractive index of the fiber core so that these polarizations radiate from the fiber. The refractive index of the stack for the polarization normal to the plane fo the interaction region is approximately equal to the refractive index of the cladding so that this polarization remains guided by the fiber. A photodetector forms an error signal from the polarization radiated from the fiber, and control circuitry processes the error signal to drive a polarization controller that adjusts the polarization of light input to the polarizer to minimize the error signal.

Study of refractive index of GeO(2):SiO(2) mixtures using deposited-thin-film optical waveguides: erratum.

Abstract: Refractive indices of deposited thin films of amorphous GeO2:SiO2 mixtures were determined by multimode optical waveguide measurement techniques at four different wavelengths and used to characterize waveguide properties as a function of material composition. The results indicate that the refractive index varies linearly with the mole fraction of GeO2 in the guide, while wavelength dispersion increases with heavier GeO2 dopant concentrations. This is consistent with previously reported findings for bulk samples and suggests that linear variation of the film’s compositional content is a viable method for obtaining refractive indices and dispersive properties needed to interface with other optical devices in integrated optics-type applications.

1.5mu-band zero dispersion single mode fiber

Abstract: PURPOSE:To make connection easy and make the core direct viewing method possible by changing stepwise the refractive index of the boundary part between the second core layer and a clad layer. CONSTITUTION:With respect to a fiber provided with the first core layer 1 having a refractive index n1 in the center, the second core layer 2 having a refractive index n2 lower than that of the first core layer, and a clad layer 3 having a refractive index n3 on the outside periphery of the second core layer, the refractive index on the boundary between the second core layer 2 and the clad layer 3 is changed stepwise. Since the refractive index on the boundary between the second core layer 2 and the clad layer 3 is changed stepwise in this manner, alignment is made easy to prevent the increase of connection loss and connection is made easy when optical fibers are connected by seeing cores.

Parametric study of depressed inner cladding single-mode fibers

Abstract: A parametric study on the depressed inner cladding (DIC) single-mode fibers shows the influence of the inner-cladding diameter on the effective cutoff wavelengths of the first two modes, determining a practical transmission window. The set of curves that is obtained can be considered universal, at least for a value of the inner-cladding/core index differences ratio close to 0.5. The behavior of the effective cutoff wavelengths is explained by studying the effective index of the modes and the fundamental mode diameter, this explanation being confirmed by a bending and microbending sensitivity test. It appears that DIC fibers optimized for long-range transmission should have an inner cladding to core diameter ratio greater than 3 and a relative depth of the inner cladding smaller than 0.5.

A new large-diameter optical fibre waveguide for operation in the TE01 mode

Abstract: It is shown that by using an optical fibre of 'tubular' structure, comprising a thin layer of higher refractive index sandwiched between a core and a cladding of lower refractive index, it is possible to transmit the TE01 mode in isolation with the HE11 mode virtually cut off. Possible advantages of this arrangement are discussed.

Constant polarization fiber with absolute single polarization band

Abstract: PURPOSE:To propagate light in only either of two orthogonal polarization modes by making an inside clad which surrounds a core smaller in refractive index than the core and making an outside clad larger in the refractive index than the inside clad. CONSTITUTION:A single-mode fiber has the inside and outside clads 2 and 3 and strain inducing members 5 around the core 1. Then the refractive index n1 of the inside clad 2 is made smaller than the refractive index n0 of the core 1 and the specific refractive index difference is set to 0.001-0.006; and the refractive index n2 of the outside clad 3 is made larger than the refractive index n1 and the radius ratio b/a of the core and clad 2 is set to 2-8. Therefore, when the core is stressed by the members 5 symmetrically about the axis to have birefringence, an absolute single polarization band is obtained almost at specific wavelength with which light in HE11 mode is not propagated and only light in HE1 mode is propagated, so that the sensitivity of a fiber sensor is increased greatly.

Wide-band low dispersion optical fiber

Abstract: PURPOSE:To obtain wide-band characteristics with small loss by providing three layers of clads whose refractive indexes are nearly equal to that of pure quartz glass and specified respectively outside a core and eliminating wavelength dispersion when wavelength is 1.3 and 1.7mum. CONSTITUTION:An optical fiber has the high-refractive-index core 1 in the center and the three layers of clads 2-4 around the core. The clad 2 is made of pure quartz glass and has a less refractive index. The clad 3 is relatively thick or 1.5 times as thick as the diameter of the core 1 and its refractive index is larger than that of the clad 2. The clad 4 has a refractive index substantially as large as the refractive index of the pure quartz glass. thus, the wavelength dispersion value is zero corresponding to at least two wavelengths in a wavelength area of 1.3-1.7mum and the small-loss, wide-band low dispersion optical fiber is manufactured efficiently.

A new large-diameter optical fibre waveguide for operation in

Abstract: It is shown that by using an optical fibre of 'tubular' structure, comprising a thin layer of higher refractive index sandwiched between a core and a cladding of lower refractive index, it is possible to transmit the TE~~ mode in isolation with the HE^^ mode virtually cut off. Possible advantages of this arrangement are discussed.

Factors Affecting the Refractive Index Distribution of Window Glass

Abstract: A 400-sample glass refractive index (RI) survey is reported. Differences in RI distribution between sheet and patterned glasses and between glass from old and young buildings are reported and discussed.

A numerical method for the analysis of single-mode low-dispersion graded-index fibers

Abstract: A numerical integration method for the calculation of the time dispersion of optical-fiber modes is introduced and used to determine the parameters of single-mode graded-index silica-based fibers for the 1.55-μm band. The method gives an accuracy on the order of 0.001 ps/km/nm, and it was possible to quantify the error in assuming the overall time dispersion to be the sum of the material and waveguide dispersions. The analysis indicates that when large material dispersion is to be neutralized by waveguide dispersion, the outer diameter of the cladding must be increased to avoid higher microbending losses. When the difference between the refractive indices at the center of the core and in the cladding decreases, the ratio between the cladding and core diameters must be increased.

Optical wavelength filter

Abstract: PURPOSE:To stabilize a fiber system by providing low refractive index parts having the refractive index lower than the refractive index of a clad so as to face each other with the core in the clad in-between and stretching part of the fiber in the longitudinal direction thereof. CONSTITUTION:A filter consists of the fiber 21 having the low refractive index, a stretching region 22, the core 23, the clad 24 and the low refractive index parts 25 installed to face each other with the core 23 in the clad 24 in-between. Part of the fiber 21 having the low refractive index parts 25 is heated and stretched to form the stretching region 22. The core diameter decreases as well with a decrease in the outside diameter of the clad in the region 22 and the electric field of light spreads to the clad 24. Then mode coupling arises between the electric field spreading in equal directions around the core 23 and the electric field around the region sandwiched by the parts 22 and the outside of the clad 24 and the transfer of light power arises. As a result, the wavelength of a small loss and the wavelength of a large loss exist periodically and function as a filter.

Improvements relating to optical fibres

Abstract: A method of producing a partially reflective splice between two optical fibers for use for example in an optical fibre hydrophone as described in our U.K. patent application No. 8220793, comprising spacing opposed faces of the fibres apart by a predetermined distance and filling this space with a UV setting cement having deliberatly a different refractive index to the fibres. The refractive index may be determined by the addition to the cement of an organic refractive index modifying liquid such as di-iodomethane. By suitable choice of spacing and refractive index the characteristics of a splice can be controlled to produce predetermined reflection.

Nondestructive Refractive Index Characterization Of Optical Fibers Using A Phase Contrast Scanning Optical Microscope

Abstract: A phase contrast heterodyne interference optical microscope for the precise characterization of optical path distribution across a transversely illuminated single or multi mode fiber is described. Using the Abel inversion algorithm in conjunction with this measurement, an exact profile of the refractive index can be extracted. The fiber is immersed in an index-matching liquid to ensure small optical path phase variation. This scheme is valid for any refractive index profile, assuming the fiber is cylindrically symmetric and its index of refraction is a function of the radial distance only. The technique is attractive since it requires minimum fiber preparation and has the potential of on-line index monitoring without breaking into the fiber. A brief theoretical analysis is given to illustrate the feasibility and potential of the proposed method.

Vibration Sensor Using Integrated Optical Coupling Element

Abstract: A vibration sensor based on a cantilever fiber and an integrated optical coupling element is presented. The main advantage of the device is its insensitivity to intensity variations of the source.

Nonlinear Refractive Index Of CS 2 At 10.6 µm

Abstract: We have measured the nonlinear refractive index n2 of CS2 at 10.6 μm using two different techniques. We find that n2 is (2.2 ± 0.7) x 1010 esu which is over an order of magnitude larger than its value in the visible.

Realization of intentionally introduced mode-coupling in optical fibers by downward axial vapor deposition

Abstract: Step-index optical fibers have been fabricated with a bandwidth increase over conventional ones of more than one order-of-magnitude. The improved performance value of approximately 600 MHz.km was achieved by mode-coupling due to intentionally introduced refractive index variations along the length of the preform. The preforms were fabricated by a soot deposition process called Downward Axial Vapor Deposition (DAVD), which allows for the perturbation of the soot stream, and hence the introduction of small index changes as a soot boule is being grown. The index perturbations which are spaced on the order of 1 μm in the preform and are a few percent of the total index difference, lead to a coupling length in the fiber of a few meters, as evidenced by far-field numerical aperture measurements. The invariance of the output mode pattern to input launch conditions also makes these fibers potentially useful as jumper and connector cables. This represents the first reported achievement of reduction in multimode pulse dispersion in optical fibers by mode-coupling introduced in the fabrication process, an idea awaiting implementation almost since fiber transmission became a practical reality.

Equivalent-Step Index Parameters For Predicting Single-Mode Fiber Dispersion

Abstract: We have defined new Equivalent Step-Index parameters for single-mode fibers having a graded core profile and/or a central index dip. These parameters are obtained from the actual index profile through simple analytical expressions with a straightforward physical interpretation. As compared to previous ESI theories, they allow a better accuracy in predicting the transmission characteristics of the fibers. In particular, the use of these ESI parameters with the usual models for calculating the chromatic dispersion in single mode fibers proves very efficient : the accuracy in predicting the zero dispersion wavelength is better than 2 nm for nearly step index fibers designed for the 1.3 μm window, and it remains better than 15 nm for triangular core profile fibers designed for the 1.55 μm window.

Step-Index Profile Microlenses Formed in Glass

Abstract: A step-index distribution in planar arrayed microlenses is obtained by field-assisted sodium-silver ion exchange in glass. The optical characteristics of the lenses depend only on the lens geometry and the value of the refractive index change.