TWI570397B - Optical evaluation of lenses and lens molds - Google Patents

Description

Optical evaluation techniques for lenses and lens molds Refer to related application

The present application claims priority to Provisional Application No. 62/037,966, the disclosure of which is incorporated herein by reference in its entirety in its entirety in the entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire entire all And the priority of the present application, which is incorporated herein by reference. The full text of the two provisional applications is hereby incorporated by reference.

In a particular aspect, the present disclosure is directed to methods and tools for describing the geometric and optical properties of molded lenses that are used in consumer products and that are manufactured by diamond transfer molding. The present disclosure is more concerned with the manufacture of optical components including such molded lenses, as well as the manufacture of consumer products including such optical components.

The market for miniaturized cameras used in smart phones, mobile phones, tablets, portable computers, automobiles and trucks is expanding rapidly. The image quality requirements of state-of-the-art cameras are forcing manufacturers to develop complex optical components consisting of many aspherically molded lenses.

Figure 1 illustrates an exemplary optical assembly consisting of four molded plastic lenses. In particular, the assembly illustrated in U.S. Patent No. 7,777,972 comprises four lenses, four lenses being arranged in front of the phase plane 170 of the assembly to form an image on the sensor. The lens elements are arranged in a first lens group having a non-spherical convex side 101, an aspherical convex side 102, and a first lens element 100 having a positive refractive index. The assembly also includes a second lens group including second lens element 110, third lens element 120, and fourth lens element 130.

The second lens element 110 having a negative refractive index has an aspherical convex side 111 and an aspherical concave side 112. The third lens element 120 has an aspherical concave side 121 and an aspherical convex side 122. The fourth lens element 130 has an aspherical convex side surface 131 and an aspherical concave image side surface 132. The aperture stop 140 is positioned between the first lens element 100 and the imaged object. The infrared filter 150 is disposed between the image side surface 132 of the fourth lens element 130 and the image plane 170. The infrared filter 150 does not affect the focal length of the imaging optical lens assembly. The sensor cover glass 160 is arranged between the infrared filter 150 and the image plane 170, and the sensor cover glass 160 does not affect the focal length of the imaging optical lens assembly.

Generally, a curved lens surface is rotationally symmetric about an axis, and the axes on each surface are nominally on a common axis (the optical axis of the assembly). The common slice visibility of the lens face axis is important to the optical performance of the overall assembly. It is also important that the curvature of each lens face is the gap between each lens surface, ie the thickness of the lens and the gap between adjacent lenses.

Thus, each individual lens typically includes a plurality of sheet visibility and gap references, fabricated with sufficiently small tolerances. The curved functional optical faces illustrated in Figure 1 are laminated together to provide proper alignment of the final lens assembly. These benchmarks are generally Provided by an additional non-optical active area on each lens that forms a loop around the edge of the active lens portion. When assembled, the non-optical portions of the lens are stacked together relative to one another, and the overall lens assembly design requires alignment and spacing of the lens portions.

Because of the tight manufacturing tolerances, in many cases conventional measuring instruments (such as contact probes and gauges, tactile profilometers, inspection microscopes) are no longer able to achieve the required accuracy or measurement reproducibility. In addition, at the manufacturing level, measurement instruments used to measure certain lens properties, such as refractive index or birefringence, are not commercially available. Therefore, the measurement instrument is missing until today.

The methods and apparatus of the present disclosure can be used to evaluate the size and optical properties of a transparent sample, particularly a lens comprising a curved effective face area, and including nominally flat, parallel upper and lower surface areas, for example, in a component These lenses are positioned on the body.

In an embodiment, the apparatus includes an optical metrology system for measuring the relative position of the nominally parallel upper and lower surface regions of the sample and using two or more of the nominally parallel upper and lower surface regions from the sample The information obtained from the optical and physical thicknesses calculated at multiple locations is evaluated by the data processing system for the optical and dimensional characteristics of the sample.

Alternatively, or additionally, the method and apparatus of the present disclosure evaluates transparent samples by combining three-dimensional surface topographical information (eg, height contours) with two-dimensional images (eg, intensity distribution) on the upper and lower surfaces of the sample. The dimensional properties of (eg lenses). The topographical message and two images can be obtained from the same side of the sample.

The method and apparatus can be used in a production environment.

In general, the sample may be a lens that includes curved upper and lower effective surface areas (eg, having optical power), as well as areas that are not used for additional upper and lower surfaces of the light guide. The areas that are not used for the additional upper and lower surfaces of the light guide are used to mechanically position the lenses in the assembly. These portions may have planar parallel surfaces. The curved portion may be referred to as an active portion, while the other (eg, planarly parallel portions) are inactive portions. The sample may have a surface area that is a convex or concave, spherical or aspherical effective portion.

The upper and lower surfaces of the inactive portion may be nominally flat or conical and may include a nominally circular feature or boundary that is nominally concentric with the apex of the effective area region.

The sample can be a lens for use in a camera assembly of a portable electronic device.

In general, the dimensional characteristics may include the position of the apex of the effective surface area relative to a reference feature of the additional surface area (eg, a nominally circular reference feature). In some embodiments, the lens apex is evaluated from a three-dimensional swept surface topography map, and the reference features are located in a two-dimensional image of the component. Two-dimensional images can be extracted from the same data collection as a three-dimensional map, or can be part of a separate step.

The dimensional characteristics may include the relative heights of the upper and lower vertex features of the sample. Such measurements may rely on additional information from the optical and physical thicknesses calculated at two or more locations of the nominally parallel upper and lower surface regions of the sample.

In some embodiments, the method includes compensating for the refractive properties of the lens when traversing the sample to determine its lateral position.

In some embodiments, the device includes a component holder that includes an auxiliary reference surface. This auxiliary reference surface can be nominally flat and located a distance below the optical component that, during testing, reflects through the optical component and back to the component and measures the light of the detection tube.

In some embodiments, the device includes a component fixture, an optical metrology system, and a data processing system. The component holder has both an auxiliary reference surface and a clamp for the at least partially transparent sample. The optical metrology system measures the position of the auxiliary reference surface and the upper and lower surface areas of the nominally parallel sample. The data processing system evaluates the optical and dimensional properties of the sample using information derived from optical and physical thicknesses calculated from two or more locations of the nominally parallel upper and lower surface regions of the sample.

In some embodiments, the complete measurement cycle includes a separate measurement of the topography of the auxiliary reference surface.

In some embodiments, the device includes element(s) to change the polarization state of light used in the measurement system (eg, polarizer and/or wave plate) to evaluate and/or compensate for the birefringence properties of the material of the sample. .

In some embodiments, the field of view of the optical metrology device extends beyond the lateral extent of the optical component to be tested. To improve accuracy and reduce drift sensitivity, the system performs an additional measurement of the position of the reference surface relative to the internal reference of the reference surface where the reference surface is not covered by the optical component.

In some embodiments, the optical metrology device is a coherent scanning interferometer. For example, the optical metrology device can be a coherent scanning interferometer that scans the optical axis nominally parallel to the optical component to be tested. The homology characteristics of the light source can be selected to increase (eg, maximize) the signal to noise ratio of the interfering signal (for sweeping via components) Collected by each transparent interface encountered in the process of drawing).

In some embodiments, the coherent scanning interferometer automatically adjusts the source coherence characteristics to enhance (eg, maximize) the signal to noise ratio based on measurements or nominal information about the thickness and optical properties of the component.

In some embodiments, measurements of the measured samples in a plurality of azimuthal directions relative to the instrument are combined to produce a final result with reduced systematic error.

In some embodiments, a confocal microscope configuration is used to detect the position of the transparent interface of the sample by scanning.

In some embodiments, a focus sensing or structured illumination measuring device is used to detect the position of the transparent interface of the sample by scanning.

In some embodiments, a focus sensing or structured illumination measuring device is used to detect the position of the transparent interface by scanning.

In some embodiments, the radiant light used for the measurement is selected in the ultraviolet, visible, or infrared spectrum. The measurement is best performed in the spectral domain, which is close to the spectral domain in which the optical components are designed.

In certain embodiments, apparatus and methods can be used to describe the thickness and refractive index of a molded lens. Alternatively, or in addition, these methods and apparatus can be used to describe the thickness and lateral distance between features (e.g., critical features) of the molded lens.

In general, a typical lens forming process relies on precise alignment of the two molds facing each other. The distance between the dies defines the thickness of the molded part. The lens thickness is a key parameter for the performance of the final lens assembly. The disclosed method and apparatus can provide process control signals for the thickness from vertex to vertex Information, for example, is provided in sub-micron accuracy.

The thickness variation across the lens provides a quantitative information about the relative tilt of the two halves of the lens, and another parameter is often critical to the final lens imaging capability. The tilt or parallelism error is another process control parameter that can be measured by the disclosed apparatus and method.

The refractive index within the lens and its variation also provide information about process control. Refractive index changes or stress birefringence beyond tolerance indicate problems with the injection molding process. These two parameters affect the imaging performance of the optical component. With the disclosed apparatus and method, these two parameters can be quantitatively evaluated for process control.

The lateral centering between the dies defines the centering of the apex to the apex of the lens and is another key parameter for the final lens capability. The disclosed method and apparatus centering the top to the apex can provide process control information, for example, with a precision of ten microns.

The parameters of the forming process also affect the fill factor within the mold, so the apex height and centering correspond to the positioning features. The vertices beyond the tolerance to the height of the feature and the centering of the vertices to the features may point to problems with the injection molding process. These two parameters affect the imaging performance of the optical component. With the disclosed method and apparatus, two parameters are quantitatively evaluated for process control.

Various aspects of the invention are summarized below.

In the general case, in the first aspect, the method of the present invention is used to determine a message relating to a transparent optical element composed of an active portion (e.g., a lens portion) and an inactive portion (e.g., a plane-parallel portion). The active portion includes at least one curved surface and an inactive portion including the opposing first and second surfaces, the method comprising: Directing the metered light to the transparent optical element; detecting reflected light from at least one location on the first surface of the inactive portion; detecting at least one from the first surface corresponding to the inactive portion Reflected light of the position on the second surface of the position; determining a message about the inactive portion based on the detected light; and evaluating the transparent optical element based on the information about the inactive portion.

Embodiments of the method may include one or more of the following features and/or other features. For example, coherent scanning interference (CSI) can be used to perform surface measurements of the first and second surfaces of the inactive portion. Alternatively, the surface measurements of the first and second surfaces of the inactive portion can be performed using a confocal microscope.

The information about the inactive portion may include a height profile of the first surface of the inactive portion and a height profile of the second surface of the inactive portion. The information about the inactive portion may include a physical thickness profile or an optical thickness profile of the inactive portion.

The information in the inactive portion may include a message regarding the refractive index of the material forming the transparent optical element. For example, the information about the refractive index may include the group index of refraction of the material and/or the phase index of the material. The information about the refractive index may include a message regarding the change in refractive index between different positions of the inactive portion. The information about the refractive index may include information about the birefringence of the material (e.g., plastic) that forms the transparent optical element.

In some embodiments, the method further includes detecting the reflected light from the reflection of the reference feature on the fixture supporting the transparent optical element, and determining the information about the reference feature based on the detected light from the reference feature. The measured light reflected from the reference feature can be reflected from a position corresponding to at least one location on the first surface of the inactive portion (eg, imaged to the same location of the detector). From the reference Before and after the test feature is reflected, the measurement light can be transmitted by a transparent optical element. In some embodiments, the transparent optical element is not on the optical path of the reflected measurement light from the reference feature. In some cases, the method can include detecting the reflected light from the reflection of the clamp at the second location, the second location being different than the at least one location corresponding to the first surface of the inactive portion.

For the first polarization, the measured light can be detected and the second polarization is different from the first polarization.

Based on the information about the inactive portion, evaluating the transparent optical element can include inferring a message regarding the size or optical characteristics of the active portion.

In some embodiments, the inactive portion is a tilt control interlock of the transparent optical elements. The at least one curved surface of the effective portion may be a spherical surface or an aspherical surface. The active portion may include a second curved surface relative to the first curved surface.

The information about the active portion may include a birefringence message about the material forming the lens portion. The message about the active portion may include a message regarding the change in the refractive index of the material forming the lens portion.

Evaluating transparent optical components can include determining whether a transparent optical component meets specification requirements, and specification requirements are based on non-active portions of the message. The inactive portion can surround the circumference of the active portion.

In still another aspect, the method of forming an optical component of the present invention comprises: determining a message of a transparent optical component using the foregoing method, wherein the transparent optical component is a lens; and fixing with respect to one or more other lenses in the lens barrel The lenses form an optical component. The method can include securing the optical assembly relative to a sensor to provide a module of the digital camera.

In general, in another aspect, the system of the present invention is for determining information about a transparent optical component comprising an active portion (e.g., a lens portion) and an inactive portion (such as a planar parallel portion), the effective portion including at least A curved surface and an inactive portion include first and second surfaces opposite to each other, the system comprising: a clamp for supporting the transparent optical component; an optical instrument including the light source, the detector, and the optical component, when the transparent optical component is supported On the fixture, the optical elements are arranged to direct light from the light source to the transparent optical element, and the reflected light from the transparent optical element is directed to the detector; and an electronic controller is in communication with the detector. Based on the detected light from the corresponding locations of the first and second surfaces of the inactive portion, the electronic controller is programmed to determine the message regarding the inactive portion.

Embodiments of the system may include one or more of the following features and/or other features. For example, the optical instrument can be an optical swept surface topography instrument such as a coherent scanning interferometer or a confocal microscope.

The fixture can include reference features located in the optical path of the optical instrument. In some embodiments, the reference feature is a planar reflector. The clamp can include a bracket that positions the transparent optical element at a distance from the reference feature. The clamp can include an actuator for rotating the transparent optical element relative to the optical axis of the optical instrument.

The light source can provide light with a variable spectrum.

The optical instrument can include a polarization module configured to polarize light from the source. The polarization module can also be configured to selectively polarize light from the source in an orthogonal polarization state.

In general, in still another aspect, the method of the present invention is used to determine information about a transparent optical element having a lens portion Dividing into plane parallel portions, the method comprising: using an optical instrument to obtain a height information (such as a surface profile), the height information being about a first surface of the transparent optical element and a second surface of the transparent optical element opposite the first surface; using optical An instrument obtains an intensity map (eg, an image) of the intensity of the first surface and the second surface; and determines one or more features of the at least one of the first surface and the second surface on the transparent optical element based on the height information and the intensity map Size message.

Embodiments of the method may include one or more of the following features and/or other features. For example, the optical instrument can be a coherent scanning interference microscope or a confocal microscope.

The height information about the first and second surfaces may individually include surface contours of the first and second surfaces. The method of claim 1, wherein the intensity map is determined based on a continuous intensity box (collected by a multi-element detector using an optical instrument). For a continuous intensity box, the intensity map is determined by averaging the intensity of each element in the multi-element detector. Using an optical instrument to obtain an intensity map can include determining the intensity of each element of the multi-element detector relative to a corresponding location of the best focus of the first and second surfaces of the optical instrument.

The size message may include the location of the apex of the first or second surface, another feature relative to the first or second surface. In some cases, the size message is the lateral distance between the vertex and other features, and the lateral distance is the distance measured on a plane that is nominally parallel to the parallel portion of the plane. Other features may be features of planar parallel portions located on the first or second surface. Other features may be a circular feature with a nominal center located at the apex. Other features may be the steps of the first and/or second surface of the parallel planar portion.

An optical instrument can be used to measure the first surface facing the light The instrument measures a transparent optical target and measures the transparent optical target with the second surface facing the optical instrument. The data obtained from the measurement of the transparent optical target of the first surface facing the optical instrument can be used to determine the position of the apex of the lens portion of the first surface. The data obtained from the measurement results of the transparent optical target of the first surface facing the optical instrument can determine the position of the apex of the lens portion of the first surface with respect to the position of the feature of the plane parallel portion of the first surface. The data obtained from the measurement results of the transparent optical target of the first surface facing the optical instrument can determine the position of the feature of the plane parallel portion of the first surface with respect to the position of the feature of the plane parallel portion of the second surface. The data obtained from the measurement results of the transparent optical target of the second surface facing the optical instrument can determine the position of the apex of the lens portion of the second surface with respect to the position of the apex of the first surface.

The sizing message can include a refraction effect resulting from the tilt of the transparent optical element relative to the optical instrument. The size information considering the effect of the refraction can be the position of features on the surface of the transparent optical element on the opposite side of the optical instrument.

An optical instrument can be used to measure a transparent optical target relative to a first azimuth of the axis of the optical instrument, the optical instrument being operable for a second azimuth (different from the first azimuth) relative to the axis for transparent optics Measurement of the target. The sizing message may include data obtained from the measurement of the transparent optical element of the first azimuth, determining a size message for the one or more features, and determining the size information may include the amount of transparent optical element at the second azimuth The resulting data determines the size information about one or more features. Determining the size information may include reducing based on the size information obtained by the first and second azimuth angles The error of the size message.

The method can include determining whether the transparent optical component meets the specification requirements based on the size message.

In another aspect, the system of the present invention is used to determine information about a transparent optical component, the system comprising: an optical instrument and an electronic controller, the electronic controller is in communication with the optical instrument, and the electronic controller is programmed to cause the system to perform the foregoing The method of the form.

Embodiments of the system may include one or more other aspects.

In general, in another aspect, the method of the present invention is used to determine a message about a target having a curved portion and a planar portion, the curved portion including a first curved surface having a vertex and an axis defining the target, the method comprising: Measuring the light guide to the target; detecting the light reflected from the first curved surface of the curved portion; detecting the reflected light reflected from at least one of the other surfaces of the target; and determining the curved portion based on the detected light The message of the vertices of the first surface.

Embodiments of the method may include one or more of the following features and/or other features. For example, the target can be a transparent optical element, such as a lens element (eg, a molded lens element). In some embodiments, the target is a portion of a mold of an optical component, such as a mold for one side of the lens component.

The curved portion may include a second curved surface opposite to the first curved surface, the second curved surface having a vertex, and the information about the apex of the first curved surface includes a thickness of the lens between the apex of the first surface and the apex of the second surface, the thickness of the lens Measured along the optical axis.

The curved portion may include a second curved surface opposite to the first curved surface, the second The surface has vertices, and the information about the vertices of the first surface includes a lateral offset between the vertices of the first surface and the vertices of the second surface, the lateral offset being measured along a plane orthogonal to the optical axis.

The measuring light can be guided to the target by the optical instrument, and the first curved surface faces the optical instrument when the equivalent metering is reflected. Determining the information about the vertices of the first surface may include determining the position of the vertices. The at least one other surface may include other surfaces facing the optical instrument, and determining the information about the vertices of the first curved surface further includes determining, on at least one other surface, a lateral offset between the orthogonal vertices and the feature of interest The plane of the optical axis measures the lateral offset. At least one other surface may include a surface that faces away from the optical instrument, and determining the information about the apex of the first curved surface further comprises: determining a lateral offset, orthogonal to features on the surface of the optical instrument, and facing the optical instrument The plane of the optical axis between the features of interest on the other surface measures the lateral offset. The curved portion may include a second curved surface relative to the first curved surface, and determining the information about the vertices of the first curved surface includes determining a position of a vertex of the second curved surface. Determining the information about the vertices of the first surface may include determining the thickness of the curved portion based on the positions of the vertices of the first and second curved surfaces along the optical axis. In some embodiments, determining the information about the vertices of the first surface comprises determining a lateral offset between the vertices of the first surface and the vertices of the second surface, and measuring the lateral offset at a plane orthogonal to the optical axis Based on: (i) a lateral offset between the apex of the first curved surface and the feature of interest on the other surface facing the optical instrument; (ii) the feature of interest and the off-axis optics on the other surface facing the optical instrument A lateral offset between the features of interest on the surface of the instrument; (iii) a lateral offset between the apex of the second curved surface and the feature of interest on the surface of the optical instrument.

Determining the message regarding the vertices of the first surface may include determining a message regarding the tilt of at least one surface of the planar portion, and considering the tilt when determining a message regarding the vertices of the first surface. The message about tilt is the tilt angle α _tilt relative to the optical axis of the optical instrument (used to direct the measured light to the object).

The method can include adjusting an azimuth of the target relative to the optical instrument (for directing the measurement light to the object) after detecting the photometric light, and repeating detecting from the first curved surface and from at least one other after adjusting the azimuth angle Surface measurement light. The method can include, after the azimuth adjustment, determining an additional message regarding the vertices of the first surface based on the detected measurements.

In some embodiments, the method includes changing the polarization state of the measurement light after detecting the measurement light, and repeating the detection of the measurement light from the first curved surface and from the at least one other surface after the polarization state is changed. The method can include determining a birefringence information about the target based on the detected measured light before or after the polarization state changes.

The method can include evaluating the target based on the information about the vertices of the first surface. Assessing the target may include determining whether the target satisfies the specification requirements based on the message regarding the vertices of the first surface.

The plane portion can be the tilt control interlock of the target. The at least one curved surface of the curved portion may be an aspherical surface. The planar portion may surround the circumference of the curved portion.

In still another aspect, a method of forming an optical component of the present invention comprises: using the foregoing method, determining a message about a target, wherein the target is a lens; and fixing the lens relative to one or more other lenses in the lens barrel to form Optical components. The method can include fixing the optical group relative to one sensor Pieces to provide a module for a digital camera.

In still another aspect, a system of the present invention is for determining a message about a target having a curved portion and a planar portion, the curved portion having a first curved surface having a vertex and defining an axis of the target, the system comprising: a clamp for a support target; an optical instrument comprising a light source, a detector, and an optical component, the optical component being arranged to direct light from the light source to the target, the target being supported on the fixture, the reflected light of the target being guided to the detector; and the electronic controller, In communication with the detector, based on the first surface from the target and at least one detected light from the other surface, the electronic controller is programmed to determine a message regarding the apex of the first surface.

Embodiments of the system may include features in one or more of the following features and/or other aspects. For example, the optical instrument can be an optical swept surface topography instrument such as a coherent scanning interferometer or a confocal microscope.

The clamp can include an actuator configured to redirect the target relative to the optical instrument. For example, the actuator can be configured to rotate the object relative to the optical axis of the optical instrument.

The optical instrument can include a set of polarizing films configured to polarize light from the light source. In the orthogonal polarization state, the polarization module can be configured to selectively polarize light from the source (eg, using one or more polarizers and/or wave plates).

The detector can be a multi-element detector (eg, a CMOS array or a CCD array), and the optical instrument can be assembled to image the surface of the target to a multi-element detector.

The light source can change its spectral output. For example, the light source can include two or more LEDs of different colors. The relative light intensity from two or more LEDs is varied while changing the color of the light. The light source can be a visible light and/or an infrared source.

Other aspects and advantages of the invention will be apparent from the description which follows.

100‧‧‧First lens element

101‧‧‧Aspherical convex side

102‧‧‧Aspherical convex side

110‧‧‧second lens element

111‧‧‧Aspherical convex side

112‧‧‧Aspherical concave side

120‧‧‧ third lens element

121‧‧‧Aspherical concave side

122‧‧‧Aspherical convex side

130‧‧‧Fourth lens element

131‧‧‧Aspherical convex side

132‧‧‧Aspherical concave side

140‧‧‧Aperture stop

150‧‧‧Infrared filter

160‧‧‧Sensor cover glass

170‧‧‧ image plane

200‧‧‧ lens

201‧‧‧Optical measuring instruments

210‧‧‧ Planar parallel

211‧‧‧ surface

212‧‧‧ surface

220‧‧‧ lens part

221‧‧‧ surface

222‧‧‧ surface

300‧‧‧CSI microscope

301‧‧‧Electronic processor

302‧‧‧Light source

304‧‧‧ Input light

306‧‧‧ Interference target

308‧‧‧Relay optics

310‧‧‧Relay optics

312‧‧ ‧ splitter

314‧‧‧瞳 plane

315‧‧‧Aperture stop

316‧‧‧virtual line

317‧‧‧Main solid line

318‧‧‧ objective lens

320‧‧ ‧ splitter

322‧‧‧Test light

324‧‧‧Test surface

326‧‧‧ platform

328‧‧‧ reference light

330‧‧‧Reference optics

332‧‧‧Combined light

334‧‧‧Electronic detector

336‧‧‧Relay lens

338‧‧ ‧ stop

340, 342, 344, 346‧‧‧ polarizing elements

350‧‧‧Mobile platform

400‧‧‧ fixture

410‧‧‧Support structure

420‧‧‧ reference plane

421‧‧‧ outside part

422‧‧‧ inner part

500‧‧‧flow chart

510, 520, 530, 540, 550, 560, 570, 580, 590‧ ‧ steps

700‧‧‧Flowchart

710, 720‧‧ steps

800‧‧‧ Flowchart

810, 820, 830, 840, 850, 860, 870, 880 ‧ ‧ steps

900‧‧‧ lens

910‧‧‧Inactive part

911‧‧ plane

912‧‧‧ plane

914c‧‧‧ Focus on the center of the feature, the upper surface

914i‧‧‧ edge

Edge of 914o‧‧

512c‧‧‧About the center of the feature, the lower surface

Edge of 915i‧‧

Edge of 915o‧‧

916‧‧‧ plane

917‧‧‧ plane

Edge of 918‧‧

Edge of 919‧‧

920‧‧‧Efficient part

921‧‧‧ upper surface

922‧‧‧ lower surface

923‧‧‧ vertex

924‧‧‧ vertex

1400‧‧‧flow chart

1405, 1410, 1415, 1420, 1425, 1430, 1435, 1440, 1445, 1450, 1455, 1460, 1465‧‧ steps

1600‧‧‧flow chart

1605, 1610, 1615, 1620, 1625, 1630, 1635, 1640, 1645, 1650, 1655, 1660, 1665, 1670, 1675‧‧ steps

1800‧‧‧flow chart

1805, 1810, 1815, 1820, 1825, 1830, 1835, 1840, 1845, 1850, 1855‧‧‧ steps

1900‧‧‧ lens mold

1912‧‧‧Outer plane

1914‧‧‧Ladder

1914o‧‧‧ outer edge

1916‧‧‧ inner plane

1921‧‧‧ Surface

Vertex of 1923‧‧‧

2000‧‧‧ Flowchart

2001‧‧‧Flowchart

2010, 2020, 2030, 2040, 2050, 2060, 2070‧ ‧ steps

2011, 2021, 2031, 2041, 2051, 2061, 2071 ‧ ‧ steps

2100‧‧‧Flowchart

2101‧‧‧Flowchart

2110, 2120, 2130, 2140, 2150, 2160, 2170, 2180‧‧ steps

T‧‧‧ thickness

1 is a cross-sectional view of an imaging optical lens assembly.

Figure 2A is a side view of a lens sample to be tested.

Figure 2B is a top view of the lens sample to be tested in Figure 2A.

Figure 3 is a schematic illustration of a coherent scanning interference microscope.

4A is a side view of a lens sample to be tested mounted on a jig having a reference surface.

4B and 4C are side views of the lens sample and fixture of FIG. 4A, illustrating two steps in the measurement process.

5 is a flow chart showing the flow of a coherence scanning interferometry (CSI) application and the steps illustrated in FIGS. 4B and 4C.

6A and 6B are side views showing the measuring steps of another embodiment.

Figure 7 is a flow chart showing the flow of an embodiment using coherent scanning interference and the steps illustrated in Figures 6A and 6B.

Figure 8 is a flow chart showing an embodiment of measuring the birefringence between the upper and lower parallel faces of the lens.

Figure 9 is a side view of another lens sample to be tested.

Figure 10 is a top plan view of the lens sample to be tested in Figure 9.

11 is another top view of the lens sample to be tested in FIG. Carefully depicted in the horizontal direction of interest, in order to illustrate the exaggeration of the decenter.

Figure 12 is a schematic diagram showing the apparent and actual optimal focal length position of the feature of interest measured through the sample.

Figure 13 is a side elevational view of the lens sample to be tested of Figure 9. Here, the surface of the concave lens faces the optical instrument.

Figure 14 is a flow chart showing the flow of an embodiment using CSI.

Figure 15A is a schematic diagram showing the apparent and actual position of the feature of interest for the refraction effect correction.

Figure 15B illustrates the tilt and lateral offset of the azimuth due to refraction.

Figure 16 is a flow chart showing the flow of another embodiment using CSI.

17A and 17B are top views showing the orientation of the lens in different samples and instruments.

Figure 18 is a flow chart showing the flow of still another embodiment using CSI.

Figure 19 is a side view of the lens mold to be tested.

Fig. 20A is a flow chart showing the flow of characteristic analysis of a lens.

Fig. 20B is a flow chart showing the flow of characteristic analysis of another lens.

21A and 21B are flowcharts showing the flow of characteristic analysis of a forming process of a lens.

Referring to Figures 2A and 2B, lens 200 includes an inactive planar parallel portion 210 and an active lens portion 220. In this example, the planar parallel portion includes two nominally flat, nominally parallel surfaces 211 and 212. Here, the "nominally" reference is the design of the lens. Nominal flatness and nominal parallelism may occur with appreciable deviations, such as from manufacturing tolerances. The lens portion 220 is a meniscus lens having an upper convex surface 221 and a lower concave surface 222. Generally come Said surfaces 221 and 222 can be spherical or aspherical. Planar planar surfaces 211 and 212, for example, can be features formed on the sample. In the final assembly, the alignment and fixation lenses are assisted with respect to one or more lenses.

The optical measuring instrument 201 is used to evaluate the optical properties of some of the lenses 200, in particular including the uniformity of the refractive index and the birefringence of the residual stress, and dimensional features such as the thickness of the lens, including but not limited to the thickness T, in the figure It is a function of coordinates x, y (such as the Cartesian coordinate system shown in Figure 2A). The method of the present disclosure evaluates the optical properties and actual dimensions of the region between the plane parallel surfaces 211 and 212 by measuring. These measurements can be used as an indicator of the overall optical and dimensional properties of the lens.

In general, optical metrology instrument 201 can be one of a variety of different instruments capable of performing spectroscopic surface topography measurements of lens 200. Examples of instruments include coherence scanning interferometry (CSI) (eg, "coherent scanning interference" revealed in P. de Groot, optical measurement of surface topography, edited by R. Leach, chapt. 9, pp .187-208, (Springer Verlag, Berlin, 2011)), Imaging Confocal Microscopy (as disclosed in R. Artigas, "Imaging Confocal Microscopy", Optical Measurement of Surface Topography, edited by R. Leach, chapt .11, pp. 237-286, (Springer Berlin Heidelberg, 2011)), structured illumination microscopes (as disclosed in XMColonna de Lega, "Using Modulated Illumination Non-Contact Surface Characteristics Analysis", US Patent (2014)), Focus sensing (eg uncovered in F. Helmli's "Focus Change Instrument", Optical Measurement of Surface Topography, edited by R. Leach, chapt.7, pp. 131-166, (Springer Berlin Heidelberg, 2011)) Or a wavelength-tuned Fourier transform phase shifting interferometry (FTPSI) system (such as exposing In L.L. Deck, "Fourier Transform Phase Offset Interference", in Applied Optics 42 (13), 2354-2365 (2003)).

Referring to FIG. 3, as an example, one optical metrology tool suitable for describing lens 200 is CSI microscope 300. In the present system, light source 302 directs input light 304 through relay optics 308, 310 and beam splitter 312 to interference target 306. The relay optics 308, 310 are imaged by a source 302 extending in space, imaging the input light 304 onto the pupil plane 314 of the aperture stop 315 and the corresponding interference target 306 (as indicated by the virtual edge 316 and the main solid line 317).

In the embodiment of FIG. 3, the interference target 306 is of the Mirau type and includes an objective lens 318, a beam splitter 320, and a parametric surface 322. The beam splitter 320 separates the input light 304 into test light 122 and reference light 328, the test light 122 is directed to the lens 200 supported by the platform 326, and the reference light 328 is reflected by the reference surface 322. The objective lens 318 individually focuses the test light and the reference light onto the test surface and the reference surface. The reference optics 330 supporting the reference surface 322 are coated to reflect only the focused reference light such that most of the input light passes through the reference optics before being separated by the beam splitter 320.

After being reflected from the test and reference surfaces, the test light is recombined with the reference light by the beam splitter 320 to form combined light 332. It is delivered by beam splitter 312 and relay lens 336 to form an optical interference pattern on electronic detector 334 (for example, a multi-element CCD or CMOS detector). The intensity distribution of the optical interference pattern passing through the detector is measured by different components of the detector and stored in an electronic processor 301 (eg, a stand-alone or networked computer, or a processor integrated with other components of the system). Analyze. The relay lens 336 images different points on the focal plane of the target 306 onto the corresponding detector 334 point.

Field stop 338 between relay optics 308 and 310 defines the area of test surface 324 that is illuminated by test light 122. After reflection of the lens 200 and the reference surface, the combined light 332 forms a secondary image of the source at the pupil plane 314 of the objective lens.

Optionally, polarizing elements 340, 342, 344, and 346 define the polarization states of the test and reference light that are directed to the respective test and reference planes, and the combined light of the polarization states is directed to the detector. According to an embodiment, each of the polarizing elements may be a polarizer (eg, a linear polarizer), a phase difference plate (such as a half or quarter wave plate), or a similar optical element that affects the polarization state of the incident beam. Again, in some embodiments, one or more polarizing elements may not be present. Further, according to the present embodiment, the beam splitter 312 may be a polarization beam splitter or a non-polarization beam splitter. In general, because of the presence of polarizing elements 340, 342, and/or 346, the polarization state of test light 322 at test surface 324 can be a function of the azimuthal position of light in pupil plane 314.

In the presently illustrated embodiment, source 302 provides illumination of broadband wavelengths (e.g., a full-width illumination spectrum is half maximum greater than 20 nanometers, half maximum greater than 50 nanometers, or optimally, more than 100 nanometers). For example, the source 302 can be a white light diode (LED), a filament of a halogen bulb, an arc lamp such as a neon or a so-called supercontinuum source, using a nonlinear effect in the optical material to produce a wide range. Source spectrum (>200 nm). The broadband of the wavelength corresponds to a finite coherence length. The mobile platform 350 adjusts the relative optical path length between the test and reference light to produce an optical interference signal at each of the detector elements. For example, in the embodiment of FIG. 3, the mobile platform 350 is a piezoelectric transducer, The interference target 306 is coupled to adjust the distance between the test surface and the interference target and thereby change the relative optical path length between the test light and the reference light of the detector.

Referring back to FIG. 2A, the optical instrument 201 looks down the lens 200 in a viewing direction parallel to the z-axis shown in FIG. 2A. In the figure, S1 and S2 individually represent the reflected light from the nominal upper and lower plane parallel surfaces 211 and 212 of the lens 200. In the measurement data acquisition, the system collects the height information of these surfaces in x, y and z in the global coordinate system. This coordinate system is established by optical instrument 201. Ideally, the axis of rotation of the lens surface is nominally aligned parallel to the z-axis.

The measurement information of the upper surface 211 of the lens 200 is obtained by reflection of light in the air (signal "S1" in the figure). Individually, in the figure, the measurement information of the lower surface 212 of the lens 200 is derived from the reflection of light within the lens material (signal "S2").

Considering a specific example of a CSI microscope system such as system 300, the relative distance T between the upper surface 211 and the lower surface 212 of a particular coordinate x, y is given as T = T' / n _G (1) where T ' is the apparent or measured optical thickness, determined by CSI microscopy or by tuning the FTPSI with wavelengths using homology information, and at low NA (eg 0.06 or less), n _G is the group velocity index ( At high NA, such as 0.2 or higher, the n _G value can be varied due to the effect of the tilt angle, resulting in an effective group velocity index). Conversely, when confocal, structural illumination or focus sensing is used, signal S2 will appear at a higher position z. In this example, the physical thickness is given by T = nT" (2) where T" is the apparent or measured optical thickness as measured by a confocal or related focus-sensitive instrument, and n is the phase velocity refraction rate.

The thickness map T'(x, y) or T"(x, y) provides information about the uniformity and average of the physical thickness T(x, y), as well as the optical properties of the lens 200, as exemplified by the refractive index n _G (x, y) or n (x, y). In some examples, the average of the composition's uniformity and size, optical properties, is sufficient to control in the process of lens 200.

If desired, additional information such as thickness map T(x, y) or optical refractive index n(x, y) can be obtained by other means, such as by contact profilometers (eg, disclosed in P. Scott's "borrowing contact" The latest development in the measurement of aspheric surfaces of probe instruments, Proc. SPIE 4927, 199-207 (2002), can be supplemented by measurements made by optical metrology instrument 201, allowing separation and independent evaluation of refractive index from physical thickness effect.

Although the characterization of the lens described above relies only on the height profile information of the surfaces 211 and 212, the characterization of the lens can utilize other information. For example, in some embodiments, a particular reference fixture is included to provide additional optical information. Referring to FIG. 4A, in some embodiments, the lens 200 is mounted on a clamp 400 having an embedded reference surface 420. In FIG. 4A, S1, S2, and S3 represent the reflected light of the upper and lower surfaces (211 and 212) of interest of the lens 200 and the upper surface 420 of the reference jig, which are measured by the distance T along the z-axis. _Air is separated by the lower lens surface 212.

The clamp 400 includes a support structure 410 and a reflective upper surface 420. Lens 200 rests on the support structure 410, the lens is positioned on a T _air distance from the reflecting surface 420. The support structure 410 may be comprised of a plurality of struts or walls on opposite sides of the lens 200, or may be a single cylindrical support separated by an outer portion 421 of the reflective surface 420. The jig 400 can be tailor-made specifically for the lens 200, and can be replaced with another jig when equivalently measuring lenses of different shapes.

4B and 4C illustrate the measurement of the entire area of the planar parallel portion 210 of the lens 200 using two successive measurement steps of the optical instrument 201. According to the process 500 of FIG. 5, the measurement information provided by these steps includes height profile measurements of the surfaces 211, 212, and 420 to complete the characterization of the optical and geometric properties of the lens. In the figure, the apparent height measurements Z _{1, ... 4} each correspond to the reflected light S1 ... S4.

In the first step, as shown in FIG. 4B, measurement information for the three surfaces 211, 212, and 420 is collected (steps 510, 520, 530). Therein, the lower surface 212 and the auxiliary reference surface 420 are measured through the lens material and thus correspond to the apparent height. Measurement information for the three surfaces is collected without the need to adjust the position of the lens on the fixture.

In a second step, as shown in Figure 4C, the lens is removed by the clamp 400 (step 540) and the secondary reference surface 420 is measured a second time (signal S4) (step 550).

The measurement information is combined to produce a map of the thickness and refractive index profile between the upper and lower parallel surfaces of the lens element. For the homology scanning interferometer and the comparable interferometric instrument, after obtaining the apparent height information Z _1,...4 , the physical and optical thickness maps are: T ( x, y ) = z ₁ ( x, y ) - z ₂ ( x,y )+ z ₃ ( x,y )- z ₄ ( x,y ) (3)

T' ( x,y )= z ₁ ( x,y )- z ₂ ( x,y ). (4)

Next, the map of the group velocity index is n _G ( x, y ) = T' ( x, y ) / T ( x, y ). (5)

Equivalent systems rely on confocal, structured illumination or focus-sensing surface profilometers, and equations (4) and (5) become T" ( x, y ) = z ₁ ( x, y ) - z ₂ ( x, y ), (6)

n = T / T" . (7)

The thickness map provides information about the average thickness of the lens and possible tilt between the two sides of the lens based on the change in thickness measured from one side of the lens to the other. The refractive index map provides information about the possible refractive index gradients for the entire lens area.

As an optional additional step, knowing the dispersion of the nominal refractive index of the material within the lens, it is often possible to change the group index to the phase index: n = Transform ( n _G ). (8)

In some cases, the transformation can be as simple as adding a constant. For example, the added constant is Where n(k) is the nominal refractive index of the material (referred to by the manufacturer or measured by some method), expressed as a function of wavenumber, and K ₀ is the number of centroid waves used to measure the spectral band. Other transformations are possible, such as a lookup table or polynomial function. The transform polynomial produces a function of the known refractive index of the test sample by fitting the data points of the group refractive index (using the instrument).

In order to improve the accuracy of the process, it is also possible to add a measurement. For example, referring to FIGS. 6A, 6B, and 7, in some embodiments, for the S5 reflected from the jig reference surface of the optical path, the additional measurement z ₅ (x, y) is simultaneously applied to the lens image by the lens 200. Capture (in step 710 of flowchart 700). For example, for an example where the clamp can be moved between two measurement steps, this additional information can provide an overall height displacement of the clamp relative to the optical instrument. This message can correct the measurement result of z ₄ (x, y), for example, by providing a combination of the displacement amount or the displacement amount, the tip and tilt compensation for the change of the clamp position between the measurements (step 720) ).

In some embodiments, the measurements are repeated for different configurations of the instrument such that data is collected substantially in different spectral distributions. For example, the center of the first spectral distribution is between 400 nm and 490 nm, the center of the second spectral distribution is between 490 nm and 590 nm, and the center of the third spectral distribution is located at 590 nm and 700 N. Between meters. Each spectral distribution provides an independent measure of the optical properties of the lens material. A plurality of measurements of the group velocity index or the phase velocity index can then be combined to derive an estimate of the change in optical properties of the material in wavelength (or dispersion). And/or used to control the process, which can be used to verify that the material is within tolerance. In the example where the instrument measures the refractive index of the group (as in a chirped interferometer), the estimation of the dispersion is further used to calculate an estimate of the refractive index, for example, by using the product of the first derivative of the centroid number. . In some embodiments, the multi-spectral distribution is present at the same time, and the instrument collects the data obtained from the scan data acquisition. The multi-spectral band is separated at the side detector, for example, using a color sensitive element (a CCD or CMOS camera equipped with a color filter) to separate the detectors. Alternatively, the return light from the sensor is separated in space by a dichroic optical element that reflects or delivers a particular spectral component to the plurality of monochrome sensors. A minimum of two spectral bands are needed to estimate the dispersion of the material.

While the foregoing measurements can be performed using polarized or unpolarized light, additional information about the lens 200 using polarized light can also be collected by drop. example For example, referring to Figure 8, the problem is revealed by the fabrication of a lens (or other partially transparent sample) that can determine the optical property information about the polarization dependence of the lens, including the effects of stress birefringence. In most cases, lenses with no stress and corresponding stress birefringence are the design goals of process control.

The presence of stress birefringence in the sample can be monitored by observing its effect on the planar parallel regions of the sample. Here, the metrology process outlined in flowchart 500 or in flowchart 700 is performed at least twice, with each complete data acquisition cycle being performed in different polarization states of the illumination light used by the metrology system. Conventional polarizers and/or wave plates are used to manipulate the polarization state of the optical metrology instrument.

For example, as shown in flowchart 800, the first measurement is performed with illumination light linearly linearly polarized along the x-direction, and the first measurement is repeated linearly with illumination light linearly polarized along the y-direction. In some embodiments, the polarization direction is aligned relative to a reference feature on lens 200. For example, where the lens is an injection-molded lens, the reference feature can correspond to a gate that is the location where the exit material enters the mold cavity.

The collected plurality of refractive index maps are then combined to provide a quantitative measure of the birefringence present in the lens material. For example, in step 870, the birefringence effect is calculated from the measurement results. In step 880, an average refractive index is calculated from the measured value. Birefringence, for example, can be manifested as the difference in optical path through the lens, as shown in step 870 of flowchart 800. Here, the cumulative effect of the birefringence through the lens is calculated as B ( x, y ) = [ n ₂ ( x, y ) - n ₁ ( x, y )] ^T (9)

And the average refractive index (as shown in step 880) is

Similarly, birefringence can be expressed as the difference in optical path length per unit length within the material. The phase velocity refractive index n _1,2 corresponds to two polarization directions. For process control, these refractive indices can be suitably represented by group refractive index measurements (for example, following measurements from CSI microscopes). In addition, for some process control cases, the measurement of optical thickness variation is B' ( x, y ) = T' ₂ ( x, y ) - T' ₁ ( x, y ) (11) or B "( x , y )= T " ₂ ( x,y )- T " ₁ ( x,y ) (12)

It may be sufficient to use the simple configuration in Figure 2A.

Although the foregoing embodiments relate to metrology, measurements of non-active regions of the lens (e.g., planar parallel portions) are described, and information about the lens is generally inferred from these characterizations. Other embodiments are also possible. For example, measurements can also be made and directly describe the effective portion of the lens.

Referring to Figures 9 and 10, the sample lens 900 under test includes an effective portion 920 having a curved surface and an inactive portion. The inactive portion consists of several nominal planes that surround the active portion. 9 is a side view of the lens 900, and FIG. 10 is a top view. The effective portion 920 corresponds to the upper convex surface 921 and the lower convex surface 922. Upper surface 921 has a vertex 923 that is nominally aligned with the same axis along apex 924 of lower surface 922.

The inactive portion is offset from the inner and outer planar surfaces on each side of the lens 900 by a series of planar, annular surfaces having stepped features. In general, the surface of the inactive portion, for example, may include features formed on the sample, assist in alignment and clamping of the lens during final assembly, and/or relative pairs of lens features The measurement is more convenient. In this example, the upper side of the inactive portion includes planes 912 and 916. Step 914 separates planes 912 and 916, step 914 contacts surface 912 at edge 914o, and contacts 916 at edge 914i. Surface 916 contacts upper convex surface 921 at edge 918.

The underside of the inactive portion includes planes 911 and 917. Step 915 separates faces 911 and 917. Step 915 contacts surface 911 at edge 915o and surface 917 at edge 915i. Face 917 contacts lower concave surface 922 at edge 919.

The optical metrology instrument 201 is used to evaluate some of the dimensional features of the lens 900, including but not limited to the apex-to-apex thickness T _Apex and the relative x, y lateral offset of the surface feature position (see common axis z), including (but not limited to) vertex center and aligned surface features. These measurements were made by measuring the top surface profile to determine the position of the three-dimensional vertices, the relative three-dimensional position, and the topography of other surface features. These measurements are an indicator of the dimensional characteristics of the lens as a whole.

As shown in FIG. 9, during operation, the optical instrument 201 looks down the sample in a viewing direction parallel to the z-axis, corresponding to the optical axis of the instrument 201. In the measurement data acquisition, in the x, y, z of the global coordinate system, the system collects height and intensity information on the surface of interest.

The measurement information for vertex 923 is derived from the reflection of light in the air (signal S _UA in Figure 9), such as the measurement information in other features of interest on the upper surface (signal S _UF in Figure 9). Individually, the measurement information of the feature of interest on the lower surface is derived from the reflected light within the lens material (signal S _LF in Figure 9).

Considering a specific example of a CSI microscope system, as shown in Figure 3, the general signal S _UA is processed to generate a height message, which is then analyzed to determine the three-dimensional position P _UA of the vertex 923. The height information derived from the signal S _UF can be combined with P _UA to determine H _UA , at the apex height of z, relative to the upper surface-surface 912 of the feature of interest. The same height information can also be used to determine the position of the upper surface edge feature, for example, the upper surface of the attention feature 912 is a nominally rounded edge. Alternatively, or in addition, the signal S _UF can be processed to generate an intensity message, which is then analyzed to determine the position of the upper surface edge feature 914o.

S _LF is a non-interference intensity signal that can be analyzed to determine the position of the lower surface edge feature 915o. Referring to Fig. 12, S _LF can be measured at the optimum focus Z position by the microscope system, as shown in Fig. 12, at the x, y position, with respect to the focal plane of the upper surface, replaced by T _BF . For the thickness T _feature and the refractive index n, which is a nearly vertical incident angle, T _BF can be calculated as: T _BF = T _feature / n (13)

For this calculation, the thickness and refractive index can be assumed to be nominal or previously measured by other means, such as using the same instrument or caliper. Depending on the accuracy required for a given application, it may be more advantageous to compensate for the effects of spherical aberration from the refraction through the lens material and calculate a correction for T _BF , using the following formula:

Wherein NA represents the numerical aperture of the optical instrument.

The lateral position of the upper surface vertex C _UA is given by the x, y coordinate of P _UA . The location of other features of interest may be defined in other ways, for example, as the center of the measured edge location, indicated as C _UF and C _{LF in} FIG. The lateral distance between these locations corresponds to the offset between the axes parallel to the z-axis, implicit to the reference plane, and in some cases to the planar features of the upper surface. For example, the inter-feature lateral distance XY _Feature can be calculated as: XY _Feature = C _UF - C _LF (14)

Similarly, the lateral distance from the top surface vertex to the feature XY _UAF can be calculated as: XY _UAF = C _UA - C _UF (15)

In some cases, the XY _{Feature is} sufficient to control the process in the manufacture of the lens, for example, as a tool for lateral alignment of the mold halves. Similarly, the XY _UAF, along with the relative vertex height H _UA , is sufficient for identifying the problem of lens formation. For example, the expected size deviation of these mold halves from the upper surface.

It is necessary to explicitly measure the dimensional characteristics between the upper surface apex and the lower surface apex, such as the vertex thickness T _Apex or the inter- vertex lateral distance XY _Apex in FIG. 9, corresponding to C _UA and C _LA as shown in FIG. The lateral distance between. In some embodiments, referring to FIG. 13, this may be by an additional measurement lens 900 oriented with the lower surfaces 911, 917, and 922 facing the optical instrument 201 while facing the optical instrument 201 with respect to the upper surface of the lens 900. The measurements are taken to maintain the azimuth of the orbit. Using a method similar to that described in the first measurement, the second measurement provides H _LA , P _LA and the lateral distance XY _{LAF of the} lower surface vertex to the feature, corresponding to the lateral distance between C _LA and C _LF : XY _LAF = C _LA - C _LF (16)

It should be noted that for the particular geometry depicted in Figure 13, _HLA is negative.

In some cases, this second measurement provides an independent measurement of the XY _Feature .

In some embodiments, the instrument is first measured from the surface of the lens and then the other is measured, and the resulting measurement information is combined according to the flow 1400 shown in FIG. 14 to produce a measurement of the full vertex thickness. The lateral distance of the desire. In this embodiment, the sequence of steps is as follows: First, the lens 900 is positioned such that the upper surface faces the metrology instrument 201 (step 1405). In this configuration, the metrology instrument 201 measures the height profile at least in the region of the apex of the upper surface and calculates the position of the upper vertex (step 1410). The lens 900 is in the same position, and for the upper feature of interest, the instrument 201 measures the height profile and intensity distribution, such as edge 914o (step 1415). In step 1420, the system then calculates the upper vertex height H _UA , the lateral distance from the upper vertex to the feature XY _UAF (as in equation (15)).

For the measurement of the lower surface features, the metrology instrument 201 and the lens 900 measure relative to each other such that the lower feature of interest, such as the edge 915o, is in the best focus position (step 1425). This position can be determined using the nominal or measured values of T _feature and n. At this location, the instrument measures the intensity distribution of the features (step 1430). Using the message from the intensity distribution, the system calculates (in step 1435) the lateral offset XY _{Feature of} an inter-feature.

Next, lens 900 is flipped and positioned with its lower surface facing instrument 201 (step 1440). At this position, the height profile is measured in the region of the lower vertex 924, and the lower vertex position P _{LA is} calculated (step 1445). Then, for one or more features on the lower surface (eg, edge 915o), the system measures the height profile and intensity distribution in step 1450. Using this measurement, the system calculates a lateral distance H _LA from the lower vertex to the feature XY _LAF (step 1455).

In step 1460, the vertex thickness T _Apex can be calculated as: T _Apex = H _UA + T _feature + H _LA (17)

Finally, at step 1465, the inter- vertex lateral distance XY _Apex corresponds to the lateral distance between C _UA and C _LA and can be calculated from the following, where the superscript represents whether the parameter is obtained from the upper surface measurement or the lower surface measurement: XY _Apex = XY _UAF ^upper +( XY _Feature ) ^upper - XY _LAF ^lower (18)

If the lower surface measurement provides an independent measure of the lateral distance of the _feature XY _Feature , the following expression can optionally be used to reduce the potential statistical variability: XY _Feature = 0.5[ XY _Feature ^upper + XY _Feature ^lower ] (19 )

XY _Apex = XY _UAF ^upper + XY _Feature - XY _LAF ^lower (20)

In some embodiments, as previously discussed with reference to Figures 4A-4C, the apparatus can include a component holder that includes a nominally flat reflective surface that is placed under the sample such that the reflected light propagating through the sample is oriented Measuring instrument. Such an embodiment can improve the contrast of the intensity images acquired using the optical instrument 201.

In some embodiments, information about x, y spatial variations in the region (including features of interest) may be utilized to more accurately determine the size features. For example, the message may include a refractive index n(x, y), a thickness T(x, y), and a map of surface topography S _UA (x, y) and S _LA (x, y), and the like.

Referring to Figures 15A and 15B, the planar areas of the lens to be tested appear to be parallel, but in practice the ideal is likely to be deviated. For example, the best fit plane through the up and down attention features may deviate from parallel. This can result in a tilt of the non-parallel portion of the first measurement (upper surface towards the instrument) relative to the second measurement (lower surface facing instrument). For example, individual non-parallel features relative to the upper and lower surfaces may adjust the tilt of the component. The tilt of these opposing components forms a wedge angle W that can be derived from the thickness map T(x,y) and incorporated into the dimensional features. For example, the vertex thickness T _Apex can be expressed as: T _Apex = f _ApexZ ( H _UA , T _feature , H _LA , W ) (21)

The lateral distance XY _Feature and XY _Apex can be expressed as: XY _Feature = f _FeatureXY ( C _UF , C _LF , W ) (22)

XY _Apex = f _ApexXY ( XY _UAF , XY _Feature , XY _LAF , W ) (23)

Figure 9 illustrates the lower surface edge measured by the upper surface interface, which appears to be perpendicular to the optical axis of the sweeping surface topography, but in practice it is possible to deviate from the ideal. Moreover, such a deviation may have a dependency of (x, y), for example, a change in local tilt in the surface topography map S _UA (x, y). Figure 15A illustrates the position of interest at a particular lateral position through a material thickness T having a refractive index n through a beam amount, first encountering a surface tilt α _tilt relative to the vertical.

Due to the refraction effect, the lateral offset ΔL that focuses on the apparent and actual lateral position is approximately: Δ L = T sin( α _refr ) (24) where sin( α _refr ) and sin( α ) according to Snell's law _Tilt ) Correlation: sin( α _refr )=sin( α _tilt )/ n . (25) Therefore, Δ L is: Δ L = T sin( α _tilt )/ n . (26)

In Figure 15A, the thickness T is depicted as a measure of the thickness of the sample in the same orientation as the expected direction of the beam. For some embodiments, T may correspond to a thickness along the optical axis. This potential difference in the effect of ΔL, which is commonly encountered with small α _tilt values, is negligible.

In the XY plane, the local tilt α _tilt has some azimuthal orientation θ _tilt . As shown in Fig. 15B, the lateral offset ΔL has the same azimuthal orientation. The x, y coordinate corrections where the position of the focus is noticeable are: △x=△ L . Cos( θ _tilt ) (27)

△y=△ L . Sin( θ _tilt ) (28)

In general, the refractive index n, the thickness T, the tilt α _tilt, and the azimuthal direction θ _tilt depend on the lateral position (x, y), so ΔL is usually a function of (x, y). A refraction correction can be applied to each measured edge point, and the set of corrected edge points can then be analyzed as needed to produce a corrected position of the feature of interest.

Referring to Figure 16, depicted in flowchart 1600, an illustrative embodiment illustrates a tilt angle having a lens. Here, the lens is first positioned as its upper surface area vector measuring instrument (step 1605), and the instrument is used to measure the height profile of the upper vertex region, and from the measurement, the upper vertex position P _{UA is} calculated (step 1610). . The system then measures the height and intensity distribution for the upper feature of interest (such as surface 914 or the edge on the upper surface) (step 1615). From this measurement, the system calculates the upper feature center C _UF . In step 1620, the system then calculates the upper vertex height H _UA and the lateral distance from the upper vertex to the feature XY _UAF . For the next measurement, using the nominal and measured values of T _feature and n, the system moves the lens relative to the optical instrument such that the underlying features of interest (such as planes or edges) are in a best focus position (steps) 1625). In this position, the system measures the intensity distribution of the underlying features and measures the apparent edge position of the lower surface (step 1630). For the lateral offset ΔL, these measurements are corrected by the system. A local refractive index n, a tilt α _tilt, and a thickness T are used for each edge position (step 1635). Using the corrected edge position, the system calculates the position C _LF of the center of the lower feature (step 1640). The positions with the upper and lower features (C _UF and C _LF ) and the wedge angle W, the system calculates the lateral offset XY _{Feature of the feature} (step 1645). Here, the wedge angle corresponds to the tilt in the thickness map of the lens.

Next, in step 1650, the lens is flipped such that the lower surface faces the optical instrument (step 1650) and the height profile of the lower vertex region is acquired (step 1655). The lower vertex position P _{LA is} calculated from this height contour system. The system then measures the height profile and intensity distribution of the underlying surface features of interest (step 1660). The information obtained from steps 1655 and 1660 is then used to calculate the lower surface vertex height H _LA and the lower vertex to feature lateral distance XY _LAF (step 1665). Using this value for H _{LA and} with the values of H _UA and T _feature , the system calculates the vertex thickness T _Apex (step 1670). Using XY _UAF , XY _LAF , XY _Feature, and W, the system also calculates the value of the lateral offset of the inter-vertex XY _Apex (step 1675).

In some embodiments, the sample is measured in two or more azimuthal directions relative to the optical instrument. By obtaining independent measurements of the dimensional characteristics of the lens in different azimuthal directions, the system can combine these independent measurements to reduce system errors in the final reported dimensional characteristics.

Examples of sources of systematic error include misalignment between the optical axis and the scan axis, lateral or axial misalignment of the illumination, and deviations in the tilt of the sample.

In some cases, the systematic error has a component that is independent of the orientation of the sample. For example, the reported lateral distance between two particular features may be skewed by some offset at the instrument coordinates (Δx _bias , _{Δy bias} ). This deviation can depend on the particular sample characteristics being measured. In such a case, in determining the lateral distance, the sample is measured relative to the instrument in an azimuthal direction θ ₀ and the sample is measured in the azimuthal direction θ ₁₈₀ relative to the instrument, where θ ₁₈₀ is offset 180 relative to θ _{0 .} °, can reduce the systematic error by combining these two measurements. As shown in Figures 17A and 17B, this corresponds to a relative azimuthal rotation of 180° between the sample coordinates (x _sample , y _sample ) and the instrument coordinates (x _instr , y _instr ). This relative azimuthal orientation can be achieved by sample clamping or by aligning the salient features of the component itself. For example, the sample support can include a rotary table and a ruler that can be manually or automatically rotated about the optical axis of the optical instrument in the desired number.

Referring to Figure 18, a flow chart 1800 illustrates an exemplary method of utilizing sample rotation. This process combines the sequence of measurements with respect to the four differently oriented lenses of the instrument:

- Position in orientation orientation θ ₀ , upper surface facing instrument

- Position in orientation orientation θ ₁₈₀ , upper surface facing instrument

- Position in orientation orientation θ ₀ , lower surface facing instrument

- Position in orientation orientation θ ₁₈₀ , lower surface facing instrument

Specific steps are as follows. First, the lens is positioned such that its upper surface faces the optical instrument and is in the azimuthal direction θ ₀ (step 1805). In this orientation, the system performs continuous height and intensity distribution measurements and calculates versus The value of (step 1810).

For the next measurement sequence, the lens is positioned with its upper surface facing the optical instrument and positioned in the azimuthal direction θ ₁₈₀ (step 1815). In this orientation, the system performs continuous height and intensity distribution measurements and calculates versus The value of (step 1820).

For subsequent measurement sequences, the lens is positioned with its lower surface facing the optical instrument and positioned in the azimuthal direction θ ₀ (step 1825). In this orientation, the system performs continuous height and intensity distribution measurements and calculates The value of (step 1830).

For the final measurement sequence, the lens is positioned such that its lower surface faces the optical instrument and is in the azimuthal direction θ ₁₈₀ (step 1835). In this orientation, the system performs continuous height and intensity distribution measurements and calculates The value of (step 1840). Among them, the order of measurement made in these relative orientations is not important and can be determined by convenience.

The calculated value is then used to calculate in each direction versus The lateral distance between the vertices of the constituent values (step 1845). Finally, using these constituent values, the system calculates the lateral distance between the vertices (Step 1850) and the lateral distance from the final vertex to the feature versus (Step 1855).

The final reported lateral distance XY ^final is calculated by combining the corresponding lateral distances measured at θ ₀ and θ ₁₈₀ , respectively XY ⁰ and XY ¹⁸⁰ : XY ^final = f _Combine ( XY ⁰ , XY ¹⁸⁰ ) (29)

The foregoing equations can be applied to the lateral distances of interest, including those previously discussed, such as the lateral distance XY _{Feature of the feature} , the vertex-to-feature lateral distances XY _UAF and XY _LAF, and the lateral distance XY _Apex between the vertices. If the measurement of the lateral distance is in the reference sample frame, that is, relative to the sample coordinates (x _sample , y _sample ), in some cases, the combined function can simply be the arithmetic mean of the measured values. . Alternatively, or in addition, in a single step, some operations can map the results of the tool reference frame to the sample reference frame. It is possible that other operations may account for previously determined residual tool deviations.

As mentioned earlier, another potential source of measurement error is The birefringence of the material in the product. In some cases, measurements obtained using instruments with multiple polarized states (eg, using polarizers and/or wave plates) can reduce measurement errors by combining multiple measurements. This can be further combined with a change in the relative azimuthal orientation of the sample relative to the instrument.

The apparatus and method described above allow for the evaluation of transparent samples during production, particularly including lenses (including curved effective surface areas and planar parallel areas as substitutes) to determine the size and optical properties of the sample. Transparent samples include lenses, such as molded lenses, which are part of a multi-lens lens assembly, such as a portion of a digital camera. Such lens assemblies are widely used in cameras in mobile devices, such as cell phones, smart phones, and tablets, among other examples.

In some embodiments, the above method can be applied to the determination of a mold for making a lens. For example, referring to FIG. 19, the sample to be tested may be a half lens mold 1900. This mold includes a curved surface 1921 corresponding to the effective area of the lens formed using the mold. Surface 1921 has a vertex 1923. The mold also includes a planar portion that is comprised of a first inner plane 1916 and a second outer plane 1912. The plane is separated by a step 1914. In describing the measurement of the mold 1900, the outer edge 1914o of the step 1914 can serve as a feature of interest. The outer plane 1912 is offset from the apex 1923 by the height H _A measured along the z-axis of the instrument 201. Mold 1900 performs characterization by obtaining a high profile and intensity distribution, for example, a height profile and intensity distribution from surface 1921 (via light S _A ) and outer plane 1912 (light S _F ). For example, the message regarding the vertex position and the lateral offset of the vertex to the edge of the feature of interest can be determined by the description of the aforementioned lens 900.

The technique is illustrated in the flowcharts in Figures 20A and 20B Possible application. Flowchart 2000 in Figure 20A illustrates the characteristic analysis technique of the lens using the thickness and birefringence measurements as described above (step 2010). In step 2020, based on these measurements, the system will derive values for thickness, parallelism, average refractive index, refractive index gradient, and birefringence. These values are next compared to the predetermined specifications of these parameters (step 2030).

For those lenses that do not meet specifications, the lens is rejected (step 2040) and the system concludes that the corresponding forming location is outside of the process control target (step 2050). For those lenses that meet the specifications, the lens is classified as thickness (step 2060) and the corresponding formed portion is reported to be within the process control target (step 2070).

Flowchart 2001 in Figure 20B illustrates lens characterization techniques using measurements of vertex-to-feature height, vertex thickness, inter-vertex lateral distance, and inter-feature lateral distance. Here, in a first step 2011, the measurements as described above derive the position of the various features of the lens from the height and intensity data. In step 2021, based on these measurements, the system will derive values from vertex to feature height, vertex thickness, lateral apex lateral distance, and lateral distance between features. These values are then compared to the predetermined specifications of these parameters (step 2031).

For those lenses that do not meet the specifications, the lens is rejected (step 2041) and the system derives the corresponding forming location beyond the process control target (step 2051). For those lenses that meet the specifications, the lenses are classified into thickness bins (step 2061) and the corresponding forming locations are reported to be within the process control target (step 2071).

Measurement techniques can also be used to analyze the characteristics of the molding process used to make the lens. The flow chart in FIG. 21A and FIG. 21B shows the molding process. An example of sexual analysis.

In the process illustrated by flowchart 2100 in FIG. 21A, a first step 2110 is to measure the thickness and birefringence of the inactive portion of the lens. Based on these measurements, the system analyzes the thickness, parallelism, average refractive index, refractive index gradient, and birefringence of the lens (step 2120). Based on this analysis, the relative positions of the two halves of the mold are adjusted to meet the thickness and parallelism specifications (step 2130). The forming process parameters (eg, temperature and ramp rate, lens material composition, injection pressure) are adjusted to meet the specifications of the refractive index (step 2140).

Flowchart 2101 is depicted in FIG. 21B, which is a measurement of the height profile of the lens surface and the lateral position of the apex and features. Based on these measurements, the system determines and derives the vertex-to-feature height, vertex thickness, lateral distance between the vertices, and the lateral distance of the features (step 2160). Based on this analysis, the relative positions of the two halves of the mold are adjusted to meet the thickness and lateral centering specifications (step 2130). Forming process parameters (such as temperature and ramp rate, lens material composition) are adjusted to meet the vertex-to-feature functional specifications (step 2140).

Although the above flow chart illustrates the separation of birefringence and thickness measurements and the measurement of vertices and features, in some embodiments, the two sets of measurements can be combined, for example, to improve the characteristics of the lens and/or Or lens shaping.

While certain embodiments have been described, other embodiments are possible. For example, although lens 200 and lens 900 are both meniscus lenses, more generally, other types of lenses can also be characterized using the disclosed techniques. For example, convex convex lenses, concave concave lenses, plano-convex lenses, and plano-concave lenses. The lens surface can be aspherical. In some embodiments, the surface of the lens can be packaged A points of inflection, in which the concave portion of the surface changes. An example of such a surface is the surface 132 shown in FIG.

In addition, a variety of alignment features can be used in addition to those described above. For example, while the planar surfaces of lenses 200 and 900 are annular surfaces, other geometries are possible. Discrete features, such as raised portions on the surface, sags, or simply marked on the surface, can be used as features in the above-described measurements.

While the present specification generally focuses on the measurement of optical components, a related category of applications is the measurement of the mold used to make the injection molded lens. In this case, a mold exhibits all of the features present on the lens, i.e., the feature is an effective optical surface and one or more position, center or alignment references. For the side of the lens, the illustrated measurement steps are easy to apply. For example, the instrument is used to measure the center position and height of the apex of the optical surface relative to the mechanical reference. Other measurement steps include characterization of the steps between the outer datums and the angle of the steep conical centering datum.

In some embodiments, such as when the component under test is larger than the field of view of the optical instrument, measurements of different regions of the component can be stitched together to provide measurement of the entire component. An exemplary technique for splicing measurements is disclosed in J. Roth and P. de Groot, "Wide Field Scanning White Light Interference on Rough Surfaces," Proc. ASPE Spring Conference, Surface Measurement Progress, 57-60 (1997).

In some embodiments, additional corrections can be applied to improve measurement accuracy. For example, a correction of the phase change in the reflective properties of the surface can be applied. See, for example, P. de Groot, J. Biegen, J. Clark, X. Colonna de Lega, and D. Grigg, "Measurement of the optical dimensions of industrial parts. Involved in, Applied Optics 41 (19), 3853-3860 (2002).

In some embodiments, the component can be measured from more than one viewing angle, or measured from both sides. See, for example, P. de Groot, J. Biegen, J. Clark, X. Colonna de Lega, and D. Grigg, "Optical Interference in Measuring Geometrical Dimensions of Industrial Parts," Applied Optics 41 (19), 3853- 3860 (2002).

The results of the measurements can be combined with other measurements, for example, including probe measurements in the form of aspheric surfaces, as disclosed, for example, in P. Scott's "Recent Development of Aspheric Measurement by Contact Probe Instruments" ", 4927, 199-207 (2002).

Various data processing methods can be applied. For example, a method suitable for measuring a plurality of surfaces (using a homology scanning interferometer) can be used. See, for example, P.J. de Groot and X. CXolonna de Lega, "Analysis and Analysis of Transparent Membranes by Interference Microscopy", Proc. SPIE 7064, 706401-1 706401-6 (2008).

In accordance with the methods and figures illustrated herein, the calculations associated with the above described measurements and analysis can be implemented in standard programming techniques used in computer programs. The code is applied to the input data to perform the functions described herein and to generate an output message. The output message can be applied to one or more output devices, such as a display. Each program can be implemented in a high-level program or object-oriented programming language to communicate with a computer system. However, the program can be implemented in a combination of language or mechanical language, if desired. In any case, the language can compile a language or a translation language. In addition, the program can be run on a pre-programmed application specific integrated circuit for this purpose.

Each such computer program is optimally stored on a storage medium or device (eg, ROM, CD or disk), which can be used by general purpose or dedicated programmable Brain reading, when the storage medium or device is read by a computer to perform the procedures described herein for configuring and operating the computer. The computer program can also reside in the cache or main memory during program execution. The correction method can also be implemented, at least in part, as a computer readable storage medium, configured with a computer program, wherein the storage medium so configured causes the computer to operate in a particular and predetermined manner to perform the functions described herein.

Other embodiments are within the scope of the following patent application.

200‧‧‧ lens

201‧‧‧Optical measuring instruments

210‧‧‧ Planar parallel

211‧‧‧ surface

212‧‧‧ surface

220‧‧‧ lens part

221‧‧‧ surface

222‧‧‧ surface

T‧‧‧ thickness

Claims (35)

A method of determining a message about a transparent optical element, the transparent optical element comprising a lens portion and a planar parallel portion, the lens portion comprising at least one curved surface, the planar parallel portion comprising an opposite first and a second surface, The method includes: directing the measured light to the transparent optical element; detecting reflected light from at least one location on the first surface of the planar parallel portion; the at least corresponding to the first surface a position of a position detecting a reflected light from the second surface of the parallel portion of the plane; determining a message about the parallel portion of the plane based on the detected light; and based on the information about the parallel portion of the plane The transparent optical element was evaluated. The method of claim 1, wherein the surface measurement of the first and second surfaces of the planar parallel portion is performed by a coherent scanning interferometer. The method of claim 1, wherein the surface measurement of the first and second surfaces of the planar parallel portion is performed by a confocal microscope. The method of claim 1, wherein the message regarding the parallel portion of the plane comprises: a height profile of the first surface of the parallel portion of the plane and a height profile of the second surface of the parallel portion of the plane. The method of claim 1, wherein the message regarding the parallel portion of the plane comprises: a physical thickness profile or an optical thickness profile of the parallel portion of the plane. The method of claim 1, wherein the parallel portion of the plane The message includes information about a refractive index of a material forming the transparent optical component. The method of claim 6, wherein the message regarding the refractive index comprises: a refractive index of the material. The method of claim 6, wherein the message regarding the refractive index comprises: a phase refractive index of the material. The method of claim 6, wherein the message regarding the refractive index comprises: a message relating to a change in refractive index between different positions of the parallel portions of the plane. The method of claim 6, wherein the message regarding the refractive index comprises: a message regarding the birefringence of the material forming the transparent material. The method of claim 1, further comprising: detecting the reflected light from a reference feature on a fixture, the fixture supporting the transparent optical component, and based on the detection from the reference feature Light, decides the message about the reference feature. The method of claim 11, wherein the reflected light from the reference feature is reflected at a location corresponding to the at least one location of the first surface of the planar parallel portion. The method of claim 12, wherein the metering light is transmitted by the transparent optical element before and after being reflected by the reference feature. The method of claim 12, wherein the transparent optical element is not located on the optical path of the measured light reflected from the reference feature. The method of claim 12, further comprising: at a position different from the at least one position of the first surface corresponding to the parallel portion of the plane A second position detects the reflected light from the fixture. The method of claim 1, wherein the metering is detected with a first polarization, and thereafter, the measuring light is detected with a second polarization different from the first polarization. The method of claim 1, wherein evaluating the transparent optical element comprises inferring a message regarding the size or optical properties of the lens portion based on the information about the parallel portion of the plane. The method of claim 1, wherein the planar parallel portion is an oblique control interlock of the transparent optical element. The method of claim 1, wherein the at least one curved surface of the lens portion is an aspherical surface. The method of claim 1, wherein the lens portion comprises: a first curved surface and a second curved surface opposite to each other. The method of claim 1, wherein the message regarding the lens portion comprises: a birefringence message about a material forming the lens portion. The method of claim 1, wherein the message regarding the lens portion comprises: a message relating to a change in refractive index of a material forming the lens portion. The method of claim 1, wherein the evaluating the transparent optical component comprises determining whether the transparent optical component conforms to a specification based on the information about the parallel portion of the plane. The method of claim 1, wherein the planar parallel portion is located near a circumference of the lens portion. A method of forming an optical component, comprising: determining a message about the transparent optical component using the method of claim 1 wherein the transparent optical component is a lens; and relative to one or more other lenses in the lens barrel, The lens is fixed to form the optical component. The method of claim 25, further comprising: fixing the optical component relative to a sensor to provide a module of a digital camera. a system for determining a message about a transparent optical element, the transparent optical element comprising a lens portion and a planar parallel portion, the lens portion comprising at least one curved surface and the planar parallel portion comprising opposing first and second surfaces, The system comprises: a fixture for supporting the transparent optical component; an optical instrument comprising a light source, a detector and a plurality of optical components, the optical components being arranged when the transparent optical component is supported by the clamp Directing light from the light source to the transparent optical element and directing reflected light from the transparent optical element to the detector; and an electronic controller communicating with the detector based on the plane from The detected light of the first portion of the parallel portion and the corresponding position of the second surface, the electronic controller is programmed to determine a message about the parallel portion of the plane. A system as claimed in claim 27, wherein the optical instrument is an optical swept surface topographer. The system of claim 28, wherein the optical surface profiler is a coherent scanning interferometer. Such as the system of claim 28, wherein the optical surface morphology The instrument is a confocal microscope. A system of claim 27, wherein the fixture comprises: a reference feature located on an optical path of the light from the optical instrument. The system of claim 31, wherein the reference feature is a flat reflector. The system of claim 31, wherein the fixture comprises: a pedestal positioned to position the transparent optical element a distance from the reference feature. The system of claim 27, wherein the optical instrument comprises: a polarizing film set assembled to polarize light from the light source. A system of claim 34, wherein the set of polarizing films is configured to selectively polarize light from the source in an orthogonal polarization state.