Ultra-low NA refractive index profiling system and method for filtering highly disruptive diffraction effects

Abstract

To provide a method for determining a refractive index profile of an optical object having a cylindrical surface.SOLUTION: A method for determining a refractive index profile includes: (a) scanning a surface at a plurality of first scanning locations with a pinhole aperture in a path of one or more optical beams; (b) measuring a first deflection function based on detection of the optical beams after deflection by an optical object for each of the first scanning locations; (c) scanning the surface at a plurality of second scanning locations where the path of the optical beams is free of the pinhole aperture; (d) measuring a second deflection function based on detection of the optical beams after deflection by the optical object for each of the second scanning locations; (e) merging at least portions of the first and second deflection functions to obtain a composite deflection function; and (f) calculating the refractive index profile using the composite deflection function.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to refractive index measurements, and more particularly to a system and method for determining the refractive index profile of an optical object that reduces the effects of diffraction caused by material effects. [Background technology]

[0002] Transparent cylindrical objects such as fiber preforms, optical fibers, light pipes, light tubes, etc. are used in a variety of optical applications. It is often desirable to know the refractive index profile (RIP) of such objects, as the RIP can determine, for example, the waveguiding or other properties of the object. One way to determine the radial RIP of a cylindrical object is to scan the surface at multiple scan positions with one or more light beams impinging perpendicular to the longitudinal cylindrical axis of the object. The optical object can deflect the beam(s) and measure the deflection at each of the scan positions to define a deflection angle distribution. The RIP of the object can be reconstructed from the deflection angle distribution.

[0003] Unfortunately, this process can be subject to errors caused by mechanical features of the cylindrical object. For example, one method of manufacturing optical fiber is known as outside vapor deposition (OVD), where layers of fiber are deposited around a core or other substrate. Microlayer variations in the resulting material lead to significant diffraction when measuring the deflection function. As can be seen in Figure 8, diffraction inhibits accurate measurement of the deflection data, causing noise and inaccurate values ​​for the final reconstructed RIP.

[0004] U.S. Patent No. 9,989,458 (B2) seeks to provide a more accurate measurement of RIP for cylindrical glass bodies by identifying the zero order beam for deflection measurements and filtering the higher diffraction orders. However, additional information is required to achieve such filtering, and even after filtering is performed, there may be too much noise in the data to make an accurate determination.

[0005] European Patent Publication No. 3,889,581 (A1) attempts to improve the accuracy of the RIP calculation by measuring the deflection data at different wavelengths through a cylindrical object. However, when the separation between the diffraction orders is very small, the higher order filtering required can be very difficult. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for a method and system for accurately measuring deflection data for RIP reconstruction that can more easily and reproducibly enable better diffraction separation and significantly reduce the impact of material effects on RIP determination.

[0007] To meet these and other needs, the present disclosure provides a method for determining the refractive index profile of an optical object having a cylindrical surface and a longitudinal cylindrical axis. The method includes: (a) scanning a cylindrical surface of the optical object at a first plurality of scan locations with one or more light beams impinging perpendicular to a longitudinal cylindrical axis, where a pinhole aperture is disposed in a path of the one or more light beams upstream of the cylindrical surface; (b) measuring a first deflection function of the optical object for each of the first plurality of scan locations based on detection of the one or more light beams after deflection by the optical object; (c) scanning the cylindrical surface of the optical object at a second plurality of scan locations with one or more light beams impinging perpendicular to the longitudinal cylindrical axis, where no pinhole aperture is disposed in the path of the one or more light beams; (d) measuring a second deflection function of the optical object for each of the second plurality of scan locations based on detection of the one or more light beams after deflection by the optical object; (e) merging at least a portion of the first deflection function with at least a portion of the second deflection function to determine a composite deflection function; and (f) calculating a refractive index profile of the optical object using the composite deflection function.

[0008] In another aspect, the present disclosure provides a system for determining a refractive index profile of an optical object having a cylindrical surface and a longitudinal cylindrical axis, the system including a measurement cell configured to receive the optical object having a light input surface, a light output surface, and a cavity disposed therebetween, one or more light sources configured to emit one or more light beams toward the measurement cell, a stage configured to support the measurement cell, (d) an optical sensor configured to be positioned in the path of the one or more light beams downstream of the light output surface of the measurement cell, a pinhole aperture selectively movable in and out of the path of the one or more light beams upstream of the light input surface of the measurement cell, and a controller. The controller (i) initiates relative motion between the stage and the one or more light sources and the optical sensor with a pinhole aperture in the path of the one or more light beams to cause the one or more light beams to be incident on the cylindrical surface of the optical object perpendicular to the longitudinal cylindrical axis at a first plurality of scan locations; (ii) measures a first deflection function of the optical object for each of the first plurality of scan locations based on detection by the optical sensor of the one or more light beams after deflection by the optical object; and (iii) causes the one or more light beams to be incident on the cylindrical surface of the optical object perpendicular to the longitudinal cylindrical axis at a second plurality of scan locations. Initiating relative movement between the stage and the one or more light sources and the optical sensor with a pinhole aperture out of the path of the one or more light beams to impinge on a cylindrical surface of the body; (iv) measuring a second deflection function of the optical object for each of a second plurality of scan positions based on detection by the optical sensor of the one or more light beams after deflection by the optical object; (v) merging at least a portion of the first deflection function with at least a portion of the second deflection function to obtain a composite deflection function; and (vi) calculating a refractive index profile of the optical object using the composite deflection function.

[0009] At least a portion of the first deflection function may include deflection data for one or more of the first plurality of scan locations, and at least a portion of the second deflection function may include deflection data for one or more of the second plurality of scan locations. One or more of the first plurality of scan locations may be different from one or more of the second plurality of scan locations. The composite deflection function may further include a portion of the first deflection function corresponding to the first scan location where the deflected one or more light beams experience diffraction caused by microlayer structure refractive index variations in the optical body, and a portion of the second deflection function corresponding to the second scan location that encompasses a boundary between different materials or dopings in the optical body. The composite deflection function may further be formed by a portion of the second deflection function that extends from a radial edge location of the optical body to the stitching location, and by a portion of the first deflection function that extends from the stitching location toward the radial center of the optical body.

[0010] The pinhole aperture may have a diameter of about 25 micrometers to about 500 micrometers. More specifically, the pinhole aperture may have a diameter of about 50 micrometers to about 250 micrometers. The pinhole aperture may be provided on a rotatable wheel, where in one orientation of the rotatable wheel, the pinhole aperture is in the path of the one or more light beams and in at least one other orientation, the pinhole aperture is outside the path of the one or more light beams. The rotatable wheel may further include a plurality of pinhole apertures, each of the plurality of pinhole apertures having a different diameter than the others.

[0011] It is understood that the embodiments described herein can be used alone or in combination with each other. [Brief description of the drawings]

[0012] The following detailed description of the embodiments will be better understood when read in conjunction with the accompanying drawings, in which: It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities shown.

[0013] [Figure 1]FIG. 1 is a schematic block diagram of an exemplary deflection function measurement system. [Diagram 2] FIG. 2 is a top view of a rotatable wheel having multiple pinhole apertures. [Diagram 3] FIG. 3 is a deflectometric image showing significant diffraction separation as a result of use of the exemplary system of FIG. [Figure 4] FIG. 4 shows a comparison of the refractive index distribution calculated from data measured by a conventional deflection measurement system and the refractive index distribution calculated from deflection data measured using a pinhole. [Diagram 5] FIG. 5 is a flow diagram of a method for measuring deflection data and calculating a refractive index profile. [Figure 6] FIG. 6 is a comparison of deflection functions measured with a pinhole aperture and without a pinhole aperture, showing the stitching position between the two to form a composite deflection function. [Figure 7A] FIG. 7A is a comparison of the refractive index profile calculated from data measured by a conventional deflectometry system and the refractive index profile calculated using the method of FIG. [Figure 7B] FIG. 7B is an expanded view of the central portion of the plot in FIG. 7A. [Figure 8] FIG. 8 is a deflectometric image using a conventional system and method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Certain terminology is used in the following description for convenience only and is not limiting. The words "right", "left", "lower" and "upper" designate directions in the drawings to which reference is made. The words "inwardly" and "outwardly" refer, respectively, to directions toward and away from the geometric center of the device and indicated portions thereof. The terminology includes the above-listed words, derivatives thereof, and words of similar import. Furthermore, the words "a" and "an" as used in the claims and corresponding portions of the specification mean "at least one".

[0015] It should also be understood that the terms "about," "approximately," "generally," "substantially," and similar terms used herein when referring to dimensions or characteristics of components indicate that the described dimensions / characteristics are not precise boundaries or parameters, but do not exclude minor variations therefrom that are functionally similar. At a minimum, such references involving numerical parameters include variations that do not vary by the least significant digit using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.).

[0016] Referring now to FIG. 1, a schematic diagram of an exemplary embodiment of a system 100 that may be used to measure the deflection angular distribution function of a cylindrical optical object 11 is shown. The object 11 has a cylindrical surface 11a and a longitudinal cylindrical axis A that extends into the plane of the paper in FIG. 1. The optical object 11 may be circular in cross section, although other cross-sectional shapes may be used as well. The object 11 may be received in a measurement cell 9, which may have a light input surface 9a, a light output surface 9b, and a cavity 10 disposed therebetween. The light input surface 9a and the light output surface 9b may be transparent to one or more wavelengths of light and may be disposed parallel to one another as shown in FIG. 1, although any conventional measurement cell may be used. The object 11 may be received in the cavity 10, and the remainder of the cavity may be filled with a refractive index-adjusting fluid (not shown). In an exemplary embodiment, the refractive index-adjusting fluid is an oil having a refractive index that is close to, but not the same as, at least the refractive index of the light input surface 9a and the light output surface 9b of the measurement cell 9.

[0017] The system 100 may further include one or more light sources 1a-1c configured to emit a light beam towards the measurement cell 9 either directly or indirectly. Each of the light sources 1a-1c may be a laser diode or a similar light emitter. When two or more light sources 1a-1c are used, each light source 1a-1c may provide light of a different wavelength, although it is also possible that one or more light sources 1a-1c emit light having the same wavelength. The light sources 1a-1c may each emit a light beam that is received by one or more coupling fibers 2 that may deliver the light beam(s) to a beam conditioner 3. The coupling fiber(s) 2 may be single mode optical fibers (e.g. designed to carry a single mode of light: a transverse mode), although other types of coupling fibers or components for delivering the emitted light beam may be used as well. The beam conditioner 3 may modify the properties of the light beam(s).

[0018] In the embodiment shown in FIG. 1, the system 100 may include a first optical axis 15a and a second optical axis 15b. The first optical axis 15a in FIG. 1 coincides with one or more light beams emanating from the beam conditioner 3. The second optical axis 15b may intercept the light entrance surface 9a and the light exit surface 9b of the measurement cell 9 in operation. The first optical axis 15a may be parallel to the second optical axis 15b. In this example, the light beam first travels along the first optical axis 15a and is then redirected to the second optical axis 15b by a pair of off-axis reflectors 4a, 4b, which may be parabolic mirrors or the like. In an alternative embodiment, the beam conditioner 3 and the first reflector 4a may be a single component (not shown). The first reflector 4a may generate a collimated beam that is directed toward the second reflector 4b along a third optical axis 15c, which may be oriented perpendicular to the first optical axis 15a and the second optical axis 15b. The second reflector 4b may take the received collimated beam along a third optical axis 15c and focus the beam along a second optical axis 15b. Although the example shown in FIG. 1 has three optical axes 15a, 15b, 15c, any number of optical axes may be used as needed, including a single optical axis, if desired. Additionally, any number of optical elements, including reflectors, lenses, etc., may be used to redirect, collimate, or focus one or more light beams, as desired.

[0019] The focused beam reflecting from the second reflector 4b may pass through an optical shutter 6 before entering the measurement cell 9. In operation, the shutter 6 may remain in a closed position and may open when a pulsed control signal is applied. For example, the shutter 6 may remain open as long as the control voltage to the shutter 6 remains high. However, as soon as the voltage goes low, the shutter 6 may close, providing an inherent "fail-safe" operation, i.e., security. However, the shutter 6 may be operated in any conventional manner for deflection measurements.

[0020] One or more light beams may enter the measurement cell 9 through the light entrance surface 9a and impinge on the cylindrical surface 11a of the optical body 11 perpendicular to the longitudinal cylindrical axis A (e.g., 90°±5°). The light beams are refracted by the optical body 11 through a deflection angle, which may be defined by the path of the exiting light beam relative to the path of the originally entering light beam. The refracted light beams may exit the measurement cell 9 through the light exit surface 9b for detection by an optical sensor 14 downstream of the light exit surface 9b. The optical sensor 14 may be part of a camera 13, such as a line scan camera. The optical sensor 14 may be a CMOS sensor, a CCD sensor, or the like, and may include one or more rows of active pixels. The optical sensor 14 may transmit a corresponding detector signal to a controller 16, which will be described in more detail below. A filter 12 may be disposed between the measurement cell 9 and the optical sensor 14 and may help to prevent ambient light from adversely affecting the measurement. In the example of FIG. 1, filter 12 may be an infrared long-pass filter, although other types may be used as well.

[0021] Measuring the deflection function involves measuring the deflection angle across multiple scan positions (e.g., at varying heights relative to the central longitudinal axis A of the optical object 11). It is therefore useful to allow for relative movement of the measurement cell 9 with respect to the one or more light sources 1a-1c and the optical sensor 14. In FIG. 1 this is achieved by supporting the measurement cell 9 on a stage 7, which in this example is a linear stage configured to move the measurement cell 9 longitudinally relative to the optical sensor 14. The stage 7 may be motorized and movable based on commands received from the controller 16, although other methods for moving the stage 7 may be used as well.

[0022] 1, the object 11 in the measurement cell 9 is moved (e.g., scanned), but in alternative embodiments, other components (such as light sources 1a-1c or beam conditioner 3) may be simultaneously moved (e.g., scanned) relative to the object 11 (held stationary or moved in opposite directions) so that the light beam height can be varied to transmit the light beam through different portions of the optical object 11. Other arrangements for adjusting the scan position on the optical object 11 (e.g., a moveable mirror, etc.) may also be used.

[0023] The controller 16 may be a computer, for example, including a processor unit (e.g., CPU), a memory unit, and support circuits operatively interconnected. The processor may be or include any form of general-purpose computer processor that can be used in an industrial environment. The memory unit may include a computer-readable medium capable of storing instructions (e.g., software) that direct the processor to perform the methods described in detail below. The memory unit may be, for example, a random access memory, a read-only memory, a floppy or hard disk drive, or other form of digital storage device. In an exemplary embodiment, the instructions stored in the memory unit are in the form of software that, when executed by the processor, transforms the processor into a special-purpose processor that controls (i.e., directs or causes) the system 100 to perform one or more of the methods described below. The support circuits are operatively (e.g., electrically) coupled to the processor and may include cache, clock circuits, input / output subsystems, power supplies, control circuits, etc. It should be further understood that while the controller 16 is shown generally as a single component in this example, it may include multiple individual devices, with control functions being divided among the individual devices.

[0024] One or more of the light sources 1a-1c, the shutter 6, the stage 7, the optical sensor 14, and potentially other components may each be configured to transmit signals and data to, and receive signals and data from, the controller 16 along a number of data connections 17. The data connections 17 may be wired or wireless, and any conventional data connections 17 known to those of skill in the art are suitable.

[0025] To aid in the diffraction order separation, the pinhole aperture 5 may be selectively movable in and out of the path of the light beam upstream of the light entrance surface 9a of the measurement cell 9. In the example shown in FIG. 1, the pinhole aperture 5 may be positioned to be inserted in the beam path between the two off-axis reflectors 4a, 4b. However, the pinhole aperture 5 may be positionable at other positions along the beam path as well. The pinhole aperture 5 is preferably generally circular in shape, and the diameter may be selected as a function of the material (e.g., spacing of the microlayer structure, material composition, etc.) and / or size of the optical body 11, along with other considerations of the system 100. In particular, smaller pinhole apertures provide better diffraction order separation due to smoother deflection functions, but as the pinhole aperture becomes smaller, the aperture itself may generate its own diffraction. Smaller pinhole apertures are also more difficult to align, and an off-center aperture, even a few micrometers with a very small diameter, may cause a "half-moon shaped" beam profile, which causes problems further downstream. Smaller pinhole apertures also absorb more light intensity and require longer exposure times and therefore longer measurement times. Thus, the diameter of the pinhole aperture 5 may be a balance between being large enough to avoid the problems mentioned above, but small enough (with appropriate tolerances) to adequately separate the diffraction orders caused by the material. Generally, the diameter of the pinhole aperture 5 may be from about 25 micrometers to about 500 micrometers. More preferably, the diameter of the pinhole aperture 5 may be from about 50 micrometers to about 250 micrometers. In these diameter ranges, it has been found that the pinhole aperture 5 can generally adequately separate the diffraction orders caused by material differences to enable more accurate deflection measurements, while minimizing the adverse effects from the smaller aperture size.

[0026] In the example of FIG. 1, the pinhole aperture 5 is supported in a tray 8, which may be movable in response to commands from the controller 16. The pinhole aperture 5 may be held in the tray 8 by a snap-in engagement, a friction fit, a mechanical fastener, or the like. The pinhole aperture 5 may be removable from the tray 8 for replacement with another pinhole aperture (not shown) of a different diameter. The tray 8 may have an unobstructed opening (not shown) to allow conventional passage of the light beam, or may be moved completely out of the beam path if necessary. FIG. 2 shows an alternative example in which the pinhole aperture 5 is provided on a rotatable wheel 24, which may be mounted near the beam path in the system 100. In one rotational orientation of the rotatable wheel 24, the pinhole aperture 5 may be moved into the light beam path. In at least one other rotational orientation, the pinhole aperture 5 may be located outside the light beam path. In the example of FIG. 2, the rotatable wheel 24 includes an aperture 25 having a more conventional diameter for deflection measurements (e.g., 2 mm or more) and allowing substantially more light beam(s) to pass through than the pinhole aperture 5. FIG. 2 also shows that pinhole apertures 5′, 5″ of different diameters may be arranged on the rotatable wheel 24 and may be used as needed. In yet another embodiment, the pinhole aperture 5 may be formed by a mechanically adjustable iris (not shown), but it has been found that the blades of the iris may cause polygonal beam deformations and additional undesirable polygonal diffraction. Still other ways in which the pinhole aperture 5 can be moved in and out of the beam path may be used as well, for reasons that will be explained in more detail below.

[0027] FIG. 3 shows that the use of pinhole aperture 5 in the beam path produces a better separation of diffractions (compared to FIG. 8, for example), which allows for better deflection measurement accuracy with less noise in areas subject to material effects such as microlayer variations. As a result, RIP reconstructions in these regions are improved using a primarily hardware-centric solution, as shown in FIG. 4. However, it has been found that deflection measurements using pinhole aperture 5 in other regions, such as locations of transitions between different materials or dopings, can be adversely affected. Referring again to FIG. 4, sharp spikes in the deflection measurements can occur at material transition boundaries. RIPs in these areas using pinhole aperture 5 measurements are less accurate, as represented by the rounded curves and gradual declines in the RIPs calculated using the setup of FIG. 1, compared to conventional approaches that provide sharp spikes and relatively flat regions. For this reason, the method described below utilizes deflection measurements both with and without pinhole aperture 5.

[0028] FIG. 5 shows an exemplary embodiment of a method 500 for determining the RIP of the optical object 11, which may be executed by the controller 16 and / or other processing devices (not shown) using the system 100 shown in FIG. 1 or other embodiments. In step 501, the surface of the optical object 11 is scanned in a first plurality of scan positions by one or more light beams impinging perpendicularly to the longitudinal cylindrical axis A. To this end, the controller 16 may initiate a relative movement between the stage 7 and one or more light sources 1a-1c and the optical sensor 14 to achieve each of the first plurality of scan positions. A pinhole aperture 5 may be placed in the light beam path during the scanning process. In step 502, for each of the first plurality of scan positions, a first deflection function is measured in the optical sensor 14. For example, the first deflection function includes deflection data for one or more of the first plurality of scan positions.

[0029] In step 503, the surface of the optical object 11 is scanned at a second plurality of scan positions by one or more light beams impinging perpendicularly to the longitudinal cylindrical axis A. In this step, the light beam path is free of pinhole aperture 5 (i.e., there is no pinhole aperture 5 in the path of the light beam(s) during the scanning process). Again, the controller 16 may initiate relative movement between the stage 7 and one or more light sources 1a-1c and the optical sensor 14 to achieve each of the second plurality of scan positions. In step 504, a second deflection function is measured at the optical sensor 14 for each of the second plurality of scan positions. For example, the second deflection function includes deflection data for one or more of the second plurality of scan positions.

[0030] Thus, two deflection functions are measured for the optical object 11, one with the pinhole aperture 5 at a given location and one without the pinhole aperture 5. Although FIG. 5 shows the first deflection function (i.e. with the pinhole aperture 5) being measured first, in some embodiments the second deflection function (i.e. without the pinhole aperture 5) may be measured first and data using the pinhole aperture 5 may be acquired thereafter. In some embodiments, the system 100 may alternately measure the first and second deflection functions at each scan position. For example, the first deflection function may be measured for a particular scan position, then the pinhole aperture 5 may be removed and the second deflection function may be measured for the same scan position, after which the system 100 proceeds to the next scan position where the process may be repeated. In some embodiments, it may be possible to acquire the first and second deflection functions substantially simultaneously, such as by using multiple beam paths (not shown) or the like. The order in which the first and second deflection functions are acquired is not important to the method.

[0031] In step 505, a composite deflection function is generated by merging at least a portion of the first deflection function with at least a portion of the second deflection function. An example is shown in FIG. 6. The second deflection function in the curve ("no pinhole") shows sharp spikes on either side of the center of the optical body 11, which correspond to material or doping boundaries. However, as the second deflection function approaches the center position, microlayer variations cause noise in the measurement, shown as a large number of variable fluctuations in the curve. The first deflection function in which a 500 micrometer pinhole aperture 5 is introduced into the light beam path ("500 μm pinhole") shows a much smoother curve in which microlayer variations are present. This is because the diffraction orders are far enough apart that only the zeroth diffraction order can be extracted. However, the sharp transition at the material boundary does not reach the value found without the pinhole aperture 5.

[0032] The composite deflection function in this example is generated by merging a portion of the first deflection function corresponding to a first scan position where the deflected light beam or beams experience diffraction caused by microlayer structure refractive index variations in the optical body 11 (e.g., the second deflection function exhibits noise) and a portion of the second deflection function corresponding to a second scan position that encompasses a boundary between different materials or dopings in the optical body 11 (e.g., where a sharp spike occurs). The two deflection functions may be stitched together at the positions marked with an "X" in FIG. 6. That is, in this example, the composite deflection function uses the second deflection function data from the radial edge portion of the optical body 11 (or alternatively, a reference position inside or outside the radial edge of the optical body 11) until a sharp spike occurs proximate the measurement positions of -40 mm and 40 mm. In this example, between these two stitching positions, the composite deflection function uses the first deflection function data toward the radial center of the optical body. The stitching location can be placed where the two deflection functions overlap or intersect. In this example, the two deflection functions overlap just inside the short boundary spike, and the stitching location is preferably placed at that location to obtain an optimal composite deflection curve for calculating the RIP. However, the stitching location can be placed anywhere determined to obtain the desired data from the first or second deflection function. Although FIG. 6 shows one stitching location on each side of the center of the optical body 11, any number of stitching locations can be used if desired, such as when multiple discrete portions of each of the first or second deflection functions are used.

[0033] FIG. 6 shows that the first deflection function and the second deflection function each cover the same range of scan positions on the optical object 11. However, the first and second multiple scan positions need not be identical over that range. For example, if the stitching position is generally known in advance, the second deflection function may be measured for scan positions up to the stitching position or for scan positions slightly beyond the stitching position. The first deflection function may be similarly measured for scan positions approximately from the stitching position. This can speed up the measurement process by not spending time measuring deflection functions in areas that will not be used in the final composite deflection function. Other variations between the first and second multiple scan positions may be used as well.

[0034] Referring again to FIG. 5, in step 506, the RIP of the optical object 11 can be calculated from the composite deflection function. Mathematically, this can be achieved by numerical integration applying, for example, the inverse Abel transform (known in the literature and by those skilled in the art), the inverse Radon transform (for example, for non-radially symmetric optical objects 11), or other similar techniques. However, since the calculated RIP may suffer from well-known RI profiling measurement artifacts such as rounded boundaries near sharp RI steps, underestimated RI differences, etc., it is preferable to apply an improved evaluation method to the composite deflection function that can overcome these errors related to the measurement artifacts. Those skilled in the art may select a particular evaluation routine based on given circumstances, such as, but not limited to, the particular optical object 11 and the resulting characteristics in the composite deflection function. The deflection function is the basis for any of these methods. It is therefore understood that an improved, more accurate composite deflection function achieved according to the above-mentioned method will also result in a more accurate resulting RIP. 7A-7B show an exemplary comparison of RIPs calculated in conventional deflection measurement systems and techniques and RIPs calculated according to the above-described systems and methods. As can be seen, the RIPs are less noisy and show improved value determination, especially as one approaches the center of the optical object.

[0035] Although the above method has been described as utilizing two deflection functions to achieve a composite deflection function, more than two deflection functions may be used as well, if desired.

[0036] Those skilled in the art will recognize that the boundaries between operations described above are merely exemplary. Operations may be combined into a single operation, a single operation may be distributed into additional operations, and operations may be performed with at least partial overlap in time. Furthermore, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be changed in various other embodiments.

[0037] Although specific different embodiments are shown in the drawings, various individual elements or combinations of elements from different embodiments may be combined with each other according to the spirit and scope of the present disclosure. Thus, individual features described herein only with respect to one embodiment should not be construed as being incompatible with other embodiments described herein, but are otherwise encompassed by the present disclosure.

[0038] It will be appreciated by those skilled in the art that changes may be made to the above-described embodiments without departing from the broad concepts embodied herein. It is understood, therefore, that the disclosure is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the disclosure.

Claims

1. 1. A method for determining a refractive index profile of an optical object having a cylindrical surface and a longitudinal cylindrical axis, the method comprising: (a) scanning the cylindrical surface of the optical object at a first plurality of scan locations with one or more light beams impinging perpendicular to the longitudinal cylindrical axis, wherein a pinhole aperture is disposed in a path of the one or more light beams upstream of the cylindrical surface; (b) for each of the first plurality of scan locations, measuring a first deflection function of the optical object based on detection of the one or more light beams after deflection by the optical object; (c) scanning the cylindrical surface of the optical body at a second plurality of scan locations with one or more light beams impinging perpendicular to the longitudinal cylindrical axis, the pinhole aperture not being within the path of the one or more light beams; (d) for each of the second plurality of scan locations, measuring a second deflection function of the optical object based on detection of the one or more light beams after deflection by the optical object; (e) merging at least a portion of the first deflection function with at least a portion of the second deflection function to obtain a composite deflection function; (f) calculating the refractive index profile of the optical body using the composite deflection function; and A method comprising:

2. 2. The method of claim 1 , wherein the at least a portion of the first deflection function includes deflection data for one or more of the first plurality of scan locations and the at least a portion of the second deflection function includes deflection data for one or more of the second plurality of scan locations, the one or more of the first plurality of scan locations being different from the one or more of the second plurality of scan locations.

3. 3. The method of claim 1 or 2, wherein the composite deflection function includes a portion of the first deflection function corresponding to a first scan position where the deflected one or more light beams experience diffraction caused by microlayer structure refractive index variations in the optical object, and a portion of the second deflection function corresponding to a second scan position that encompasses a boundary between different materials or dopings in the optical object.

4. 3. The method of claim 1 or 2, wherein the composite deflection function is formed by a portion of the second deflection function that extends from a radial edge position of the optical body to a stitching position, and by a portion of the first deflection function that extends from the stitching position toward a radial center of the optical body.

5. The method of claim 1 , wherein the pinhole aperture has a diameter of about 25 micrometers to about 500 micrometers.

6. The method of claim 5 , wherein the pinhole aperture has a diameter of about 50 micrometers to about 250 micrometers.

7. 6. The method of claim 5, wherein the pinhole aperture is provided on a rotatable wheel, and in one orientation of the rotatable wheel, the pinhole aperture is in the path of the one or more light beams, and in at least one other orientation, the pinhole aperture is out of the path of the one or more light beams.

8. The method of claim 7 , wherein the rotatable wheel includes a plurality of pinhole apertures, each of the plurality of pinhole apertures having a different diameter than the others.

9. 1. A system for determining a refractive index profile of an optical object having a cylindrical surface and a longitudinal cylindrical axis, the system comprising: (a) a measurement cell configured to receive the optical object, the measurement cell having a light input surface, a light output surface, and a cavity disposed therebetween; (b) one or more light sources configured to emit one or more light beams towards the measurement cell; and (c) a stage configured to support the measurement cell; and (d) an optical sensor configured to be positioned in a path of the one or more light beams downstream of the light exit surface of the measurement cell; and (e) a pinhole aperture selectively movable in and out of the path of the one or more light beams upstream of the light entrance surface of the measurement cell; and (f) a controller, (i) commencing relative motion between the stage and the one or more light sources and the optical sensor with the pinhole aperture in the path of the one or more light beams to impinge the one or more light beams on the cylindrical surface of the optical object perpendicular to the longitudinal cylindrical axis at a first plurality of scan locations; (ii) for each of the first plurality of scan locations, measuring a first deflection function of the optical object based on detection by the optical sensor of the one or more light beams after deflection by the optical object; (iii) commencing relative motion between the stage and the one or more light sources and the optical sensor with the pinhole aperture out of the path of the one or more light beams to cause the one or more light beams to impinge on the cylindrical surface of the optical object perpendicular to the longitudinal cylindrical axis at a second plurality of scan locations; (iv) for each of the second plurality of scan locations, measuring a second deflection function of the optical object based on detection by the optical sensor of the one or more light beams after deflection by the optical object; (v) merging at least a portion of the first deflection function with at least a portion of the second deflection function to obtain a composite deflection function; (vi) a controller configured to calculate the refractive index profile of the optical body using the composite deflection function; and A system comprising:

10. 10. The system of claim 9, wherein the at least a portion of the first deflection function includes deflection data for one or more of the first plurality of scan locations and the at least a portion of the second deflection function includes deflection data for one or more of the second plurality of scan locations, the one or more of the first plurality of scan locations being different from the one or more of the second plurality of scan locations.

11. 11. The system of claim 9 or 10, wherein the controller is configured to obtain the composite deflection function by merging a portion of the first deflection function corresponding to a first scan position where the deflected one or more light beams undergo diffraction caused by microlayer structure refractive index variations in the optical object and a portion of the second deflection function corresponding to a second scan position that encompasses a boundary between different materials or dopings in the optical object.

12. 11. The system of claim 9 or 10, wherein the controller is configured to obtain the composite deflection function by merging a portion of the second deflection function that extends from a radial edge position of the optical body to a stitching position and a portion of the first deflection function that extends from the stitching position toward the radial center of the optical body.

13. The system of claim 9 , wherein the pinhole aperture has a diameter of about 25 micrometers to about 500 micrometers.

14. The system of claim 13 , wherein the pinhole aperture has a diameter of about 50 micrometers to about 250 micrometers.

15. 14. The system of claim 13, further comprising a rotatable wheel, the pinhole aperture being disposed on the rotatable wheel, and in one orientation of the rotatable wheel, the pinhole aperture being in the path of the one or more light beams, and in at least one other orientation, the pinhole aperture being out of the path of the one or more light beams.

16. 16. The system of claim 15, wherein the rotatable wheel includes a plurality of pinhole apertures, each of the plurality of pinhole apertures having a different diameter than the others.

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