Abstract: A liquid mixing ratio detecting sensor has cylindrical holder which is immersed in sulfuric acid solution. The holder is filled with silicone oil. A glass plate is placed within the holder. A light emitting diode emits light beams which enter the glass plate through its vertical side, and totally reflect from a boundary between the glass plate and the sulfuric acid solution. The light beams coming out from the glass plate is reflected by a reflection plate to enter into the glass plate through its vertical side, and totally reflected from a reference boundary between the glass plate and the silicone oil when a refractive index of the sulfuric acid solution is greater than that of silicone oil. On the other hand, the light beams entered into the glass plate refracts at the reference boundary to fall on a photo diode when the refractive index of the sulfuric acid solution decreases to be smaller than that of silicone oil.

Abstract: A fibre sensor used for the measurement of ambient refractive index has a tapered end. The taper of the optical fibre generates cladding modes which undergo multiple reflections at the external surface of the fibre, and therefore gives high sensitivity to the ambient index. A tapered fibre is also relatively immune to contamination by adhering droplets when the end reflection is used since the droplets tend to move to the point of greatest radius, which tends to be away from the point where the Fresnel reflection of interest occurs. The reflection from the tapered end of a multimode fibre is measured as a function of ambient refractive index. In contrast to a square-cleaved fibre, the reflection from a tapered fibre is monotonically related to the ambient index, removing an ambiguity that occurs when refractive index is measured by Fresnel reflection at normal incidence. Tapered optical fibres are suitable for probes to identify the interface between immiscible liquids.

Abstract: A refractive index FOCS has a fiber optic core with a partly light transmissive thin metal film clad of an effective thickness and light transmissivity so that transmission through the core is strongly affected by the refractive index of a surrounding liquid or vapor medium. The metal clad and surrounding medium produce a localized refractive index at the core interface which modulates light transmission through the core as a function of the medium refractive index. The clad is made of platinum, or also of gold, rhodium, palladium, nickel, iron, cobalt, ruthenium, iridium, osmium, zinc, copper, silver, chronium, molybdenum, tungsten, vanadium, niobium, tantalum, titanium, zirconium or hafnium. The clad is also made of oxides of these metals, or metal compounds or alloys. With a fluorescent tip, the changes in the fluorescent signal are a measure of the medium refractive index. With a reflective tip, the changes in the reflected signal are measured.

Abstract: The characteristic parameters of a semiconductor laser (1) acting as an amplifier and brought to bistable operating conditions are determined. The output power (I2) of laser (1) is measured as a function of the power (I1) of an amplitude-modulated optical input signal to determine the laser hysteresis loop; the switching points (P1, P2) between the two stable states of the laser (1) are identified, the input and output power values relevant to such points are memorized, and at least the value of the non-linear refractive index coefficient (n.sub.2) of the material used to fabricate the laser (1) as determined starting from the power values relevant to at least one of said points (P1, P2). By exploiting the power values relevant to both switching points (P1, P2) also the amplification factor (A), the finesse parameter (F) of the passive cavity of the laser (1) and the wavelength difference (.lambda.1-.lambda.

Abstract: A scale for use in critical angle hand refractometers of conventional design permitting direct numerical readout of every scale division.

Abstract: An improved sampling system is provided for on-line monitoring of a liquid such as a process liquor in a paper mill or the like. The sampling system includes, in general terms, an improved sampling probe for circulating process liquor from a process tank or the like to a sensor device such as a refractometer for monitoring of selected parameters. The sampling probe includes intake and return conduits having ends nested within an open-ended probe housing disposed within the process tank, such that the intake and return conduit ends are shielded from direct contact with large particulate settling within the tank. The intake and return conduit ends are further arranged for intersection of liquor flow streams associated therewith at a position inset within the probe housing to generate turbulence which tends to sweep large particulate away from the probe while maintaining smaller particulate in suspension to avoid probe clogging.

Abstract: A sensor uses the principle of surface plasmon resonance (SPR) to monitor the progress of the reaction between a sample and a sensitive layer (for example an antibody layer). The layer is applied to the rear surface of a metallic film formed on the surface of an optically transmissive component in the form of a hemicylindrical lens and slide. Collimated light from a source is applied via a lens which focuses the incoming beam to a focus at a point to form a fan-shaped spread of light incident at the point. The light is internally reflected at the point, and emerges from the component to be applied to a dectector array which latter is electronically scanned. The angle of incidence of the light at the point is such as to span that angle which gives rise to surface plasmon resonance, together with a range of angles thereabout so that the progress of the resonant condition, as the reaction between the sample and the sensitive layer proceeds, can be monitored.

Abstract: A differential, sequential detector, and method, for detecting refractive index gradients in a sample and for producing an output signal approximating a derivative of the refractive index gradient utilizes two closely spaced, parallel probe light beams passing through the sample with the beams separated along the direction of any expected gradient to be detected. A sensor is arranged to measure and produce an output signal proportional to the difference in movement of the two beams. The sensor is preferably arranged so that only complementing portions of each beam will fall on the sensing area of the sensor so that parallel movement of the beams will change equally the respective complementary portions sensed to maintain a constant output from the sensor, but movement of one beam relative to the other beam will produce a change in the sensor output proportional to the relative movement and approximating the derivative of refractive index gradient causing the relative beam movement.

Abstract: The index of refraction of a liquid is measured using an optical fiber refractometer having a light transmitting optical fiber by immersing a portion of the optical fiber in the liquid and launching light into one end of the optical fiber at a selected non-zero launch angle with respect to the fiber axis. Light transmitted through the optical fiber is detected at the other end of the optical fiber and a determination is made of the index of refraction of the liquid in accordance with the detected light and the selected non-zero launch angle. By varying the launching angles of the light the range of the refractometer is increased. The light transmitting optical fiber is provided with a region having at least one tapered portion for further increasing the range of the refractometer. The tapered portion of the optical fiber is disposed between a refractive end of the optical fiber and the light source for providing single-ended operation.

Abstract: Properties of thin films are monitored in real time by measuring the interactions of the light from an injection laser diode with the thin film adjacent to one of the facets of the laser diode by an associated photodetector. Thickness, index of refraction and other properties can be measured as a function of the output power, slope efficiency and threshold current of the laser diode.

Abstract: A differential refractometer is described capable of measuring the refractive index charge, dn, of a transparent fluid corresponding to a change dc of the concentration of a solute in said fluid. The fluid is restricted to a fine capillary within a transparent material such as glass. Incident upon the capillary at an angle close to the critical angle is a fine light beam incident from said transparent material. The axes of the light beam and capillary intersect at a point within the capillary defining thereby a plane within which the refraction occurs. A position sensing device is placed to measure the displacement of the beam twice refracted during its passage through the capillary, said measure being used to generate a numerical value of the ratio dn/dc.

Abstract: Concentration gradients in samples to be evaluated are detected by measuring the deflection of a probe light beam passed through the sample using the principals of Schlieren optics. Specific chemical compounds in a sample can be detected and identified by supplying excitation energy to the sample where such energy is selected to be absorbed by the chemical compound to be specifically identified and not by other compounds in the sample. The absorption of the excitation energy by the absorbing compound produces a temperature gradient within the sample which causes deflection of the probe light beam and signals representative of such deflection may be separated from signals representative of deflections caused by other refractive index gradient present in the sample. A light emitting diode may be used to generate the probe light beam.

Abstract: A monochromatic light beam scans a silica reference and a translucent body, both submerged in index matching fluid and the deflection angle of the beam is measured as it exits the reference, the translucent body and the fluid. This deflection angle of the light beam exiting the reference is compared with the undeflected beam passing through only the fluid. The difference, if any, is used to offset the measurements of the deflection angles of the light beam exiting the translucent body to correct them so that the profile is referenced to the index of silica.

Abstract: An improved frequency locking circuit suitable for indirectly locking an optical frequency f.sub.0 to a radio frequency f.sub.1 or of locking the radio frequency to the optical frequency. A beam of optical frequency f.sub.0 is modulated by a compound signal which is the sum of a signal at frequency f.sub.2 and an FM subcarrier at frequency f.sub.1 that is phase modulated at frequency f.sub.3 to produce a phase modulated beam. The phase modulated beam is filtered by a filter having a transfer function having a characteristic frequency f.sub.f. A pair of control signals are generated that are proportional respectively to the amplitudes of two components of the filtered signal at frequencies f.sub.2, f.sub.3. These control signals are separately used in a pair of servo loops to separately establish fixed values of f.sub.0 /f.sub.f and f.sub.1 /f.sub.f. By using an optical cavity of the filter, the frequency locking circuit may be used for measuring the refractive index of a gas.

Abstract: A method and means for a spatial and temporal probe for laser generated plumes based on density gradients includes generation of a plume of vaporized material from a surface by an energy source. The probe laser beam is positioned so that the plume passes through the probe laser beam. Movement of the probe laser beam caused by refraction from the density gradient of the plume is monitored. Spatial and temporal information, correlated to one another, is then derived.

Abstract: Two methods for determination of thickness of a film of known material that is mounted on one face of a solid substrate of known material are disclosed, using: (1) inversion of an optical beam reflectivity equation; or (2) determination of the film thickness that minimizes the variance of the optical beam reflectivity, computed at each of a predetermined sequence of optical beam wavelengths. Four methods for determination of the (real) refractive index of a film of known thickness mounted on a face of a solid substrate of known material are disclosed, using: (1) minimization of absolute differences of computed and measured optical beam reflectivity, summed over a sequence of known film thicknesses, for assumed values of the refractive index; (2 and 3) two iterative techniques of promote convergence of an estimate of the index to a final value of the refractive index; or (4) solution of a quadratic equation whose coefficients are slowly varying functions of the solution variable.

Abstract: The discriminating device comprises an optical coupler (4) having at least three ends (5 to 8) to which are connected a semiconductor source of light (1) whose intensity is modulated, a semiconductor photoconductor (2) and an optical probe constituted by a multi-mode optical fibre (3) whose end has a pointed shape. This discriminating device is in particular applicable in a device for measuring the voluminal fraction of at least one fluid of a current of non-mixible fluids.

Abstract: A detector device for determining the mixing ratio of gasoline and alcohol includes a flint glass plate, one side of which is placed to be in direct contact with a mixing liquid of gasoline and alcohol, a light emitting diode is located at the other side of the flint glass plate to be opposite to the mixing liquid so that light beams emitted from the diode enter the flint glass plate to be incident on a boundary between the plate and the mixing liquid and a photo diode having a rectangular shape and located in coplanar relationship with the light emitting diode to receive the light beams totally reflected from the boundary.

Abstract: Several specific types of optical sensors capable of measuring temperature, pressure, force, acceleration, radiation and electrical fields, fluid level, vapor pressure, and the like, are disclosed, along with an electro-optical system for detecting the optical signal developed by the sensor. One such probe utilizes a convex shaped structure consisting of an elastomeric material attached to an end of an optical fiber, the elastomeric material being coated with a luminescent material, a combination that is capable of measuring both temperature and pressure. Such a probe is also specifically adapted for measuring surface temperature by making a good physical contact with the surface being measured. Another such probe utilizes a similar structure but of a non-elastomeric material for the purpose of detecting both temperature and either index of refraction or vapor pressure changes.

Abstract: A thermal wave imaging apparatus generates a real time image of the surface and subsurface of an opaque solid object. A.C. electrical signals indicative of the configuration of the surface and subsurface of the object which are generated during a thermal wave scan of the object by a first heating beam which generates a localized temperature gradient on the object and a deflectable second probe beam heating beam, which deflection is detected by a detection device mounted adjacent to the object, are stored in an image memory under the control of a central processor. A refresh counter generates sequential, incremental signals used to control the X and Y axis deflection of a display monitor. Such signals also address the image memory and generate output data controlling the intensity of the display point at each generated X and Y axis deflection point.

Abstract: An apparatus for measuring the refractive index of liquid particularly suitable for use in an ink-jet printing system is provided. The apparatus includes a light emitting diode and a photodiode which are optically coupled by an optical fiber which in turn is partly immersed in a liquid to be measured. In one aspect, the wavelength of light emitted from the light emitting diode is so set to be outside a light absorption wavelength range of the liquid to be measured. In another aspect, provision is made of a temperature dependent resistor which changes its electrical resistance depending on the temperature of the liquid to be measured so as to vary the level of the driving current to be applied to the light emitting diode thereby varying the amount of light to be emitted.

Abstract: The optical sensor for the detection of specific substances and refractive index changes in gaseous, liquid, solid and porous samples is composed of integrated optical elements. It consists of a waveguiding film (1) equipped with a diffraction grating (4) and applied onto a substrate (2). For the selective detection of a specific substance contained in the sample (3) a selectively chemisorbing additional layer (5) covers the film (1) at least in the grating region. The sample (3) is applied at least in the grating region either directly onto the waveguiding film (1) or onto the selectively chemisorbing additional layer (5). Chemisorption of the substance, which is contained in the sample (3) and is to be detected, to the selectively chemisorbing additional layer (5) results in a further adlayer (6) coating the waveguiding film (1).

Abstract: An apparatus (31) and method for measuring the refractive index of an optical recording medium substrate (34) wherein an angle of incidence of a polarized beam (33) is set at an oblique angle of incidence with the substrate (34), the polarized direction of the polarized beam (33) is varied for the substrate (34) in this state, the transmitted or reflected light beam by the substrate is received by a light receiving means (36) through a light analyzer means (35) in the crossed Nichol state and the received light amount for the polarized angle is measured and is compared with a theoretical formula so that the refractive index in the thickness direction of the substrate can be measured.

Abstract: A device for measuring optical properties is provided which is equipped with an exciting light source for emitting exciting light to the sites to be measured of a sample, a light intensity modulator for modulating the exciting light, a probe light source for emitting probe light and a detector for receiving the probe light. The device is characterized by comprising an intensity distribution modifying means for bringing the maximum intensity portion of said probe light close to the sample when the probe light emitted from the probe light source reaches the site to be measured or the vicinity thereof. A method for measuring optical properties using the device is also provided. This device is useful particularly for measurement of the light absorption characteristics of a monomolecular film spread on a liquid surface.

Abstract: Concentration gradients in samples to be evaluated are detected by measuring the deflection of a probe light beam passed through the sample using the principals of Shlieren optics. Specific chemical compounds in a sample can be detected and identified by supplying excitation energy to the sample where such energy is selected to be absorbed by the chemical compound to be specifically identified and not by other compounds in the sample. The absorption of the excitation energy by the absorbing compound produces a temperature gradient within the sample which causes deflection of the probe light beam and signals representative of such deflection may be separated from signals representative of deflections caused by other refractive index gradients present in the sample. A light emitting diode may be used to generate the probe light beam.

Abstract: A method is disclosed for determining the refractive index profile of an optical fiber wherein light from an intense optical source is focused at the bare fiber end portion of the test fiber. A small amount of light will be coupled into the optical fiber where for the short length of uncoated fiber only cladding modes are excited. The index of refraction is determined directly by analyzing the intensity distribution emitted from the optical fiber with a lens system having a limited numerical aperture.

Abstract: Parallel light rays are applied to a cylinder and true exit positions of the rays from the cylinder are measured, phantom exit positions for the incident rays are calculated by using a mathematical function representing a phantom refractive index profile, and the mathematical function is modified so as to minimize the sum of the squared differences between the true and phantom exit positions.

Abstract: A method for automatically determining the refractive index profile of a lightguide preform.

Abstract: A method and an apparatus for the precise determination of the compressibility factor of a gas sample are disclosed. Two grating interferometers are coupled together with one interferometer defining a refractive index interferometer adapted to provide a signal of information related to the refractive index of the gas sample and the other interferometer defining a pressure interferometer adapted to provide another signal of information related to the pressure of the gas sample whereby to permit measurement of the refractive index as a function of pressure. Each interferometer is capable of dividing a linearly polarized monochromatic laser beam into a measuring beam and a reference beam and causing the measuring beam and reference beam to travel along respective optical paths extending in close parallel relationship over predetermined optical path lengths.

Abstract: An optical refractometer for automatically determining the principal indices of a specimen receives an incident radiation beam which is reflected by a first rotatable mirror onto a reflecting surface of a first elliptical mirror wherein the axis of rotation of the first rotatable surface extends through a first focus of the first elliptical mirror. A hemicylinder has a center of curvature at a second focus of the first elliptical mirror and rotatably and translatably mounts a specimen about a first axis and along second and third axes, respectively, such that a portion of the specimen is located at the second focus to receive the reflected incident beam from the first rotatable surface. A second elliptical mirror has third and fourth foci and a second surface for reflecting the incident radiation beam from the second elliptical mirror with an axis of rotation extending through the fourth focus with the third focus being at the first axis coincident with the second focus for producing a reflected beam output.

Abstract: A system and method for monitoring the state of a crystal (C) which is suspended in a solution is disclosed which includes providing a light source (10) for emitting a beam (12) of light along an optical axis (X). A collimating lens is arranged along the optical axis for collimating the emitted beam to provide a first collimated light beam (16) consisting of parallel light rays. The solution and crystal are contained in a transparent container (18). By passing the first collimated light beam through the container, a number of the parallel light rays are deflected off of the surfaces of said crystal being monitored according to the refractive index gradient to provide a deflected beam (19) of deflected light rays. A focusing lens (22) is arranged along the optical axis for focusing the deflected rays (32, 34, 48, 50) towards a desired focal point (24a). A knife edge (24) is arranged in a predetermined orientation at the focal point; and a screen (26) is provided.

Abstract: A recirculating optical/electronic closed loop feedback process and appars in which nanosecond light pulses are triggered by a pulse generator upon arrival of previous signals that have just completed a round trip through the closed loop feedback system. The optical path is comprised of a light source and a detector between which is mounted beam forming optics that guide the light beam from the light source through a transparent vessel having a semitransparent medium therein whose refractive index and/or transparencies are measured. The electronic portion is comprised of a pulse amplifier for amplifying the detected light beam that in turn is repetitively applied to a high rate pulse generator to retrigger the light source through a pulse counter that records the number of signal circulations which pass through the closed loop during a given time to indicate the change of transmissivity of said medium.

Abstract: The invention is directed to an arrangement for determining the spectral characteristic of the refractive index of a liquid or a gas wherein the specimen is enclosed between two boundary surfaces spaced apart between 1 and 50 .mu.m. The surfaces are at least approximately parallel to each other. The boundary surfaces cause interferences when illuminated with white light passing through the surfaces. The interferences are measured by a spectrometer in their wavelength-dependent course and are thereafter evaluated.

Abstract: A method of measuring the velocity of a fluid by noninstrusive means comprises passing a pump laser beam pulse through the fluid wherein the fluid contains a constituent absorbing the wavelength of the laser so that a temperature gradient, and therefore an index of refraction gradient, occurs in the laser beam path; and a probe laser beam is passed transverse to the pump laser beam and is deflected by the heated portion of the fluid; measuring the beam deflection and calculating from that the fluid velocity. After the pump pulse the amount of deflection reaches a peak value and then decreases at a rate independent of the concentration of the absorbing constituent. Where the pump laser beam has a Gaussian spatial profile, the deflection signal decreases according to: exp-2(v+/a).sup.2, where v is the velocity; t is time; and a is a constant representing the pump laser beam radius.

Abstract: Surface inhomogeneities of a piece of glass are detected by disposing the glass piece in interfacial relation to an optical medium and reflecting light at a predetermined angle of incidence from the glass surface - optical medium interface along a scan path, through at least a portion of the optical medium. The optical medium is selected to have a refractive index equal to the bulk refractive index of the piece of glass. The intensity of the light reflected from the glass along the scan path is monitored to indicate surface inhomogeneities and the location thereof on the glass surface.

Abstract: A refractometer comprises a light source, an angle prism and an optical system in a casing so mounted that the optical system focuses an image of a diaphragm at said light source upon a double photodiode located beyond the prism and supported by an oblique surface of the casing. The ratio of the output of one photodiode to the output of the double photodiode is measured to register the index of refraction.

Abstract: Method for determining a refractive index of an object in which the object is illuminated with a slit pattern of illumination light to form an optical section of the section of the object and the optical section is observed in two directions to determine apparent thickness of the optical section in these directions. Operations are carried out to obtain the refractive index of the object from the apparent thickness of the optical section.

Abstract: A thermal wave imaging apparatus generates a real time image of the surface and subsurface of an opaque solid object. A.C. electrical signals indicative of the configuration of the surface and subsurface of the object which are generated during a thermal wave scan of the object by a first heating beam which generates a localized temperature gradient on the object and a deflectable second probe beam heating beam, which deflection is detected by a detection device mounted adjacent to the object, are stored in an image memory under the control of a central processor. A refresh counter generates sequential, incremental signals used to control the X and Y axis deflection of a display monitor. Such signals also address the image memory and generate output data controlling the intensity of the display point at each generated X and Y axis deflection point.

Abstract: The apparatus described basically includes a vessel (10) which has a horizontal transparent window (11) and contains an index liquid (12). An optical fiber (13) is mounted in this vessel perpendicular to the window (11). Light (14) is launched and focused by a condenser (15) onto fiber (13). The light cone of aperture angle (2.beta.) due to the guided and leaky modes is eliminated using an annular mirror (16) that reflects the remaining portion of the aperture light cone (2.alpha.) escaping laterally from the fiber. This light reflected by the mirror (16) is focused by an annular condenser (18) and reflected onto a detector (20) by a flat mirror (19) with a hole in the center. Measuring the amount of light received by the detector (20) allows the refractive index of the fiber to be determined.

Abstract: The invention relates to a measuring window for a process refractometer. Process refractometers are commonly used in the industry for continuous measurement of the concentration of a solution. The wall of the refractometer facing the process solution is provided with a window which must satisfy the requirement that the passage of light rays satisfies certain criteria, that the sealing is reliable, that the fastening is firm and that the wall facing the process and the window form a planar surface. The transparent portion of the window according to the invention comprises a roof prism embedded in a V-shaped groove in the process wall. Each wall of the V-groove is provided with a sealing abutting against the prism, and the third side of the prism forms a continuous plane with the process wall.

Abstract: A system for determining the index of refraction of a sample fluid in which light from a collimated light source is directed through a light pervious cell in which sample and reference fluids are held. The light from the collimated light source which is transmitted through the cell is deflected and is then directed through a pair of gratings to establish patterns. When the cell contains a reference fluid therein, first patterns are established, and second patterns are then established by replacing the reference fluid with the sample fluid. A measurement of the change between the first patterns and the second patterns is used for determining the index of refraction of the sample fluid.

Abstract: Optical apparatus for determining for example by display on an oscilloscope the refractive index profile across an optical fibre including an ellipsoidal reflector and a scanning system for a laser beam directed towards one focus of the ellipsoidal reflector at which point the fibre to be examined is placed and including a detector which is relatively small in size situated at the other focus of the ellipsoidal reflector.

Abstract: A fiber optic directional coupler comprises a pair of bases, with respective longitudinal, arcuate grooves formed therein on confronting faces thereof, for mounting a pair of optical fibers in close proximity. A portion of the cladding is removed from each of the fibers to form planar facing surfaces which permits the spacing between the fiber cores to be within a predetermined critical zone so that guided modes of the fibers interact, through their evanescent fields, to cause light to be transferred by evanescent field coupling between the fibers. The coupler is "tuned" to a desired coupling efficiency by offsetting the planar facing surfaces to increase the spacing between the fiber cores. A method of manufacture of the coupler includes procedures which permit the coupler halves to be made symmetrical. The method also permits couplers having given coupling characteristics to be reproduced.

Abstract: To determine the radial profile of the refractive index of a substantially cylindrical transparent object such as an optical fibre or optical fibre preform, the object is illuminated with a collimated beam of light incident at an angle to the axis of the cylindrical object differing substantially from 90 degrees and measuring the refraction angle at which light leaves a substantially plane endface as a function of the radial position on the endface.

Abstract: A method of sensing the optical deflection function of an approximately cylindrical object, such as an optical fibre preform, comprises illuminating the object with collimated light; focusing the transmitted light so that in the focal plane the distance of the light from the optical axis is linearly proportional to the angle through which light has been deviated by the object; optically modulating the focused light so that a property of the light varies as a function of said distance, and calculating the deflection function from the modulated light. The modulations may be spatial or temporal. The refractive index profile can also be calculated.

Abstract: The present invention provides a thermal imaging method to evaluate the surface and subsurface properties of a material and is based on techniques of optical beam deflection thermal imaging. The invention uses a localized excitation source, such as an optical beam, to provide localized heating of the sample surface. A surface thermal gradient is induced on the sample surface as heat flows, in three dimensions, from the area of localized excitation into the test material. The surface temperature gradient causes a thermal refractive lens to be generated in the fluid (gas or liquid) adjacent to the sample surface. An optical probe beam is directed through the thermal lens and is deflected by changes in a refractive index of the thermal lens. Changes in the refractive index are induced by variations of the surface temperature. In this manner, a detailed surface temperature profile can be generated which reveals surface and subsurface properties of the material tested.

Abstract: A photoconductor having a passageway therethrough is employed in practicing the refractive near-field method of determining the index of refraction profile of an optical fiber as a technique of eliminating leaky mode contribution to detected power.

Abstract: Equipment and method for mapping an object using moire deflectometry wherein collimated radiation deflected from the object is used to generate a moire pattern and wherein by measuring linear deflections in the pattern, variations in characteristics of the object is determined.

Abstract: Apparatus and a method for analyzing the refractive index profile of a cylindrical, transparent optical waveguide preform, utilizing a scanning light beam to traverse a fixed preform and a refractor to direct light deflected by the preform onto a displacement sensor, is described.

Abstract: An optical fluid analyzing apparatus is shown comprising transparent means (12,13) of known refractive index (n.sub.1) providing a cell (14) for receiving a fluid sample of unknown refractive index (n.sub.2). A diffraction grating 10 is formed in an inner wall (11) of the cell. A light source (15) is positioned at an incident angle (.theta..sub.0) with a grating to satisfy the Bragg condition. A pair of detectors (16, 17) intercept the 0th order and 1st order diffracted light. Circuitry (18) responds to signals generated by the detectors to provide an output indicative of the refractive index of the sample.