COMPACT LENS TESTER

For lens testing, a telecentric lens aims light from a light source on an exit pupil formed relative to a device lens of a device-under-test. A sensor receives light from the device-under-test.

BACKGROUND INFORMATION

The subject matter disclosed herein relates to a compact lens tester.

BRIEF DESCRIPTION

An apparatus for lens testing is disclosed. The apparatus includes a light source, a telecentric lens, and a sensor. The telecentric lens aims light from the light source on an exit pupil formed relative to a device lens of a device-under-test. The sensor receives light from the device-under-test.

A system for lens testing is also disclosed. The system includes a light source, a telecentric lens, a sensor, and the dynamic fixture. The telecentric lens aims light from the light source on an exit pupil formed relative to a device lens of a device-under-test. The sensor receives light from the device-under-test. The dynamic fixture actively aligns at least one of the device-under-test and the sensor.

A method for lens testing is further disclosed. The method acquires pixel charge contents of an image pattern from a sensor that receives light from a device-under-test. The light is aimed from a light source on an exit pupil formed relative to a device lens of the device-under-test by a telecentric lens. The method further computes device-under-test characteristics from the pixel charge contents.

DETAILED DESCRIPTION

The schematic flowchart diagrams and/or schematic block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations. It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Although various arrow types and line types may be employed in the flowchart and/or block diagrams, they are understood not to limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only an exemplary logical flow of the depicted embodiment.

Optical devices, such as cameras, instruments, lenses, sensors, and combinations thereof are often tested to assure that the optical device performs as designed. Unfortunately, suitable testers can be bulky and/or expensive. The embodiments described herein employ a telecentric lens that aims light on an exit pupil disposed relative to a device lens of a device-under-test to reduce the size and cost of a lens tester. In addition, the embodiments may employ a sensor of the device-under-test to characterize the device lens and/or device-under-test. The embodiments are further scalable to support the testing of a wide variety of device lenses and/or optical devices as will be described hereafter.

FIG. 1Ais a schematic diagram of a lens tester100of the embodiments. In the depicted embodiment, the lens tester100includes a light source101comprising a source102, a collimating lens106, and a test pattern110. In one embodiment, the test pattern110is an optical diffuser. The optical diffuser may have a diffuser angle of expansion of less than ±10 degrees relative to a beam108. The source102may be selected from the group consisting of a point source102, an extended source102, and a plurality of sources102. The light source101and/or source102may emit substantially polychromatic radiation or substantially monochromatic radiation. The light source101and/or source102may emit light in a specified frequency in the group consisting of 190-390 nanometers (nm), 390-780 nm, and above 780 nm.

The exiting beam from the collimating lens106is the beam108, being incident on the test pattern110. Then, ray bundles112carrying the object information from the test pattern110are refracted by the lens114that collimates them aiming them at the exit pupil116. The lens tester100further includes a telecentric lens114. The telecentric lens114may have a numerical aperture of not greater than 0.5. Alternatively, the telecentric lens114may have a numerical aperture of greater than 0.5. In one embodiment, the telecentric lens114is an eyepiece. An exit pupil116may be disposed relative to a device lens of a device-under-test. In one embodiment, the exit pupil116is disposed outside of the telecentric lens114. Table 1 illustrates one embodiment of a prescription for a telecentric lens114.

In one embodiment, a prescription for the telecentric lens114minimizes a merit function comprising a location of the exit pupil116, ray height, a field-of-view, and/or a collimation of rays in ray bundles112for the device-under-test.

In one embodiment, the source102emits a light beam104which is collimated by the collimating lens106. The exiting beam from the collimating lens106is the beam108, and is incident on the test pattern110. In one embodiment, the test pattern110comprises an optical diffuser. Ray bundles112carrying the object information from the test pattern110are refracted by the telecentric lens114. The telecentric lens114collimates the ray bundles112, aiming the ray bundles112at the exit pupil116. Since the lens114is telecentric, the distance from the test pattern110has a very large tolerance without compromising lens tester performance. As a result, the lens tester100may be easily scaled to test a variety of optical devices and/or lenses. For descriptive purposes, light traversing the lens tester100may be referred to as the light beam104, the beam108, and the ray bundles112.

FIG. 1Bshows a side view schematic diagram of light paths104/108/112through a lens tester100. Exemplary light paths of the light beam104, the beam108, and the ray bundles112are shown.

FIG. 1Cis a side view schematic diagram of the lens tester100with a dynamic fixture130. The dynamic fixture130may motivate the device-under-test120through one or more degrees of freedom. The dynamic fixture130may align the device-under-test120with the lens tester100and/or sensor222. In one embodiment, the dynamic fixture130aligns the device-under-test120based on characteristics of ray bundles112received at the sensor222.

FIG. 1Dis a side view schematic diagram of the lens tester100with dynamic fixtures130. In the depicted embodiment, a first dynamic fixture130aligns the device-under-test120and a second dynamic fixture130aligns the sensor222.

FIG. 1Eis a schematic diagram of an optical diffuser110and the manner by which the optical diffuser110diffuses the incident beam108into a diffused ray bundle112expanding with a diffuser angle of expansion133.

FIG. 2Ais a schematic diagram of the lens tester100with a device-under-test120. The device-under-test120may include one or more device lenses121. In the depicted embodiment, the device-under-test120is the telecentric lens114rotated at 180 degrees.

The source102may emit the light beam104which is collimated by the collimating lens106. The beam108exiting the collimating lens106is incident on the test pattern110. The ray bundles112carrying the object information from the test pattern110pass through the telecentric lens114. The telecentric lens114collimates the ray bundles112. The telecentric lens114further aims the ray bundles112at the exit pupil116. In the depicted embodiment, the device-under-test120is an instance of the telecentric lens114inverted at 180 degrees. The device-under-test120focuses the ray bundles220onto the sensor222, thus imaging the test pattern110. The exit pupil116may be formed before the device-under-test120along the ray bundles112and within the device-under-test120along the ray bundles112.

FIG. 2Bshows a side view schematic diagram of light paths through the lens tester100and telecentric lens device-under-test120ofFIG. 2A. Exemplary light paths of the light beam104, the beam108, and the ray bundles112are shown.

FIGS. 3A-Dare the calculated values for the lens tester100with the device-under-test120illustrated inFIGS. 2A-B.FIG. 3Ais a plot of MTF vs. spatial frequency, wherein the fields125are indicated in millimeters of object height and the diffraction limited curve is shown as well for sagittal S and tangential T planes including a S difference limit338, a T difference limit339, S 0.0, 3.0 mm340, T 3.0, 3.0 mm341, S 5.0, 0.0 mm342, T 0.0, 5.0 mm343, S 3.0, 5.0 mm344, T 5.0, 3.0 mm345, S 5.0, 3.0 mm345, S 0.0, 0.0 mm346, T 3.0, 0.0 mm347, S 3.0,5.0 mm348, T 5.0, 5.0 mm349, T 0.0, 0.3 mm351, S 3.0, 0.0 mm350, S 5.0, 5.0 mm352, and T 5.0, 0.0353. The graph indicates that the lens tester100facilitates image resolution in excess of 1/2/30 nm, namely about 16 micrometers (μm).

FIG. 4Ais a side view schematic diagram of the lens tester100with a compact compound lens device-under-test120. In the depicted embodiment, the device lens121is a compound lens. In addition, the sensor222is native to the device-under-test120.

In one embodiment, the source102emits a light beam104which is collimated by the collimating lens106. The beam108from the collimating lens106is incident on the test pattern110. From the test pattern110, ray bundles112carrying the object information from the test pattern110pass through the telecentric lens114. The telecentric lens114collimates the ray bundles112. The telecentric lens114further aims the ray bundles112on the exit pupil116. The exit pupil116may coincide with the entrance pupil of the device-under-test120, which in the depicted embodiment is located inside the device-under-test120. The compound lens device-under-test120images the test pattern110onto the sensor222through a protective window420.

FIG. 4Bshows a side view schematic diagram of light paths through the lens tester100and the compact compound lens device-under-test120ofFIG. 4A. Exemplary light paths of the light beam104, the beam108, and the ray bundles112are shown.

FIGS. 5A-Dare the calculated values for the lens tester100with the compact compound lens device-under-test120illustrated inFIGS. 4A-B.FIG. 5Ais a plot of MTF vs. spatial frequency, wherein the fields125are indicated in millimeters of object height and the diffraction limited curve is shown as well for sagittal S and tangential T planes for an difference limit319, S 0.0, 0.0 mm320, T 0-0 mm321, S 0.0, 3.5 mm322, T 0.0, 3.5 mm323, S 3.0, 0.0 mm324, T 3.0, 0.0 mm325, S 3.0, 3.5 mm326, T 3.0, 3.5 mm327, S 3.0, 0328, T 3.0, 0.0329, S 4.5, 0.0330, T 4.5, 0.0,331, S 4.5, 3.5332, T 4.5, 3.5333, S 4.5 0.0334, T 4.5, 0.0335, and S 0.0, 0.0326.

FIG. 5Care plots of field curvature vs. field125in mm and distortion vs. field125in percent, showing 830 nm 310, 850 nm312, and 870 nm314in the tangential plane T and the sagittal plane S.

FIG. 6illustrates a front view of a test pattern110with a periodic pattern based on the USAF 1951 optical test pattern. The repetitive pattern of the test pattern110facilitates testing a lens resolution at various field positions by a uniform object. Although the USAF 1951 optical test pattern is shown, any pattern may be employed. The test pattern110facilitates testing a wide variety of device-under-test120and/or device lenses121.

FIG. 7Ais a side view schematic diagram of a light source101with a beam homogenizer710. The beam homogenizer710may be selected from the group consisting of a single optical element, a microlens array, an engineered diffuser, and a diffractive optical element. The source102emits an expanding beam104that is then collimated by the collimator lens106, from which a beam108is transmitted through the beam homogenizer710, from which emerges a collimated and homogenized beam712. For descriptive purposes, light traversing the lens tester100may be referred to as the homogenized beam712. The homogenized beam712is incident on a test pattern110and ray bundles112carry the object information from the test pattern110. In an embodiment, the source102emits a Gaussian beam104that has a Gaussian profile. The Gaussian profile remains constant over the collimator lens106, but becomes homogenized over the beam homogenizer710. In one embodiment, the beam homogenizer710is realized in a single optical element.

FIG. 7Bis a plot of irradiance distribution700versus lateral space of calculated profiles of the beam108ofFIG. 7A.

FIG. 7Cis a plot of a footprint of irradiance distribution700of calculated profiles of the beam108ofFIGS. 7A-B.

FIG. 7Dis a plot of a footprint of irradiance700vs. lateral space721of calculated profiles for the homogenized beam712ofFIG. 7A. In the shown embodiment,90% of the power emitted from the source is transmitted into the homogenized ray bundles112.FIG. 7Eis a plot of a footprint of irradiance700of the calculated profiles for the homogenized beam712ofFIG. 7A. Table 2 details one embodiment of a prescription for the beam homogenizer710.

Table 3 details one alternate embodiment of a prescription for the beam homogenizer210.

FIG. 7Fis a plot of footprints of irradiance distribution700of calculated profiles for the beam108and the homogenized beam712. The irradiance distribution700aof the beam108is superimposed on the irradiance distribution700bof the homogenized beam712. In one embodiment, at least 90 percent of the optical power is transmitted through the beam homogenizer710.

FIG. 7Gis a side view schematic diagram of light paths through a light source102with beam homogenizer710. The light paths include the light beam104, beam108, and homogenized beam712.

FIG. 8Ais a side view schematic diagram of the lens tester100illuminated by a light source101with a beam homogenizer710. The source102emits an expanding beam104that is then collimated by a collimating lens106. The beam108is transmitted through a beam homogenizer710, from which emerges as a collimated and homogenized beam712, becoming incident on the test pattern110. The ray bundles116carrying the object information of the test pattern110pass through the telecentric lens114that collimates the ray bundles112, aiming the ray bundles112at the exit pupil116. Since the lens114is telecentric, the distance from the test pattern110has a very large tolerance without compromising the lens tester performance.

FIG. 8Bshows a side view schematic diagram of light paths through the lens tester100with beam homogenizer710ofFIG. 8A. The light paths include the collimated light beam104, collimated beam108, homogenized beam712, and ray bundles112.

FIG. 9Ais a side view schematic of a lens tester100without a test pattern110. In the depicted embodiment, the lens tester100includes sources102and a telecentric lens114. The sources102may comprise a plurality of light sources102such as multiple Light Emitting Diodes (LED), laser diodes, vertically emitting semiconductor lasers and/or the like. The sources102emit the ray bundles112that pass through and are refracted by the telecentric lens114. The telecentric lens114collimates the ray bundles112and focuses the ray bundles112at the exit pupil116. Since the telecentric lens114is telecentric, the distance from the sources102have a very large tolerance without compromising the lens tester performance.

FIG. 9Bis a side view schematic of light paths through a lens tester100without a test pattern110ofFIG. 9A. The light paths include the ray bundles112.

FIG. 10is a schematic block diagram of a computer400. In the depicted embodiment, the computer400includes a processor405, memory410, and communication hardware415. The memory410may store code. The processor405may execute the code. The communication hardware415communicates with other devices such as the sensor222.

FIG. 11is a flow chart diagram of a method500of computation of the device-under-test characteristics. The method500may compute the characteristics of the device-under-test120. The method500may be performed by the lens tester100, the sensor222, and/or the computer400.

The method500starts, and in one embodiment, the sensor222acquires505pixel charge contents on which photons corresponding to an image pattern of the test pattern110are converted to electrons. The telecentric lens114together with the device-under-test120form an image from light emitted by the light source101. In a certain embodiment, the image is of the test pattern110shown inFIG. 6. The processor405may receive the pixel charge contents from the image of the test pattern110as binary data and using one or more algorithms compute510the device-under-test characteristics. The processor405may further determine515if the device-under-test120and/or the sensor222are aligned relative to the lens tester100. If the device-under-test120and/or sensor222are not aligned, the processor405may motivate520the dynamic fixture130to better align the device-under-test120and/or sensor222. After motivating the dynamic fixture130, the sensor222further acquires505additional pixel charge contents.

If the device-under-test120and sensor222are aligned with the lens tester100, the sensor222may acquire525pixel charge contents as described in step505. The processor405may receive the pixel charge contents of the image representation of the test pattern110and using one or more algorithms compute530the device-under-test characteristics. In one embodiment, the processor405computes530the device-under-test characteristics sequentially for a given zone of the field-of-view of the telecentric lens114and/or the sensor220. The device-under-test characteristics may include but are not limited to MTF, relative illumination (RI), and distortion of the image for a given zone. The lens tester100may continue acquiring525pixel charge contents and computing530characteristics until determining535that all the zones have been scanned. If all the zones have been scanned, the lens tester100may output540the characteristics and the method500ends. The characteristics may be output by being displayed. In an embodiment, the computed characteristic value are transmitted electronically to another electronic device, such as another computer400.

Testers for optical devices are often bulky and expensive. The embodiments employ a telecentric lens114to focus light on the exit pupil116disposed relative to the device lens121of the device-under-test120. The telecentric lens114supports of large tolerance in the distance from the test pattern110to the device lens121and/or sensor222. As a result, the size and cost of the lens tester100is reduced. In addition, the use of the telecentric lens114allows the lens tester100to be easily scaled for a plurality of optical device sizes and focal lengths.