Interferometric waviness detection systems

An interferometer detection system, including a beam splitter receiving a collimated light signal and splitting the signal into a first light signal and a second light signal. The system includes a first mirror receiving and reflecting the first light signal along a first path. The system includes a second mirror receiving and reflecting the second light signal along a second path via a transparent material. The system includes a 2D photosensor array configured to receive from the beam splitter the reflected first light signal merged with the reflected second light signal double passing through the transparent material and configured to generate an interference fringe pattern. A non-sinusoidal interference fringe pattern indicates geometrical variation between a wavefront of the reflected first light signal along the first path and a wavefront of the reflected second light signal double passing through the transparent material along the second path.

TECHNICAL FIELD

The present invention relates generally to testing and detecting waviness (surface/refractive index irregularity) of flat transparent optical elements and displays, and more specifically to cover glass for displays and assembled display modules.

BACKGROUND

The waviness of a flat panel display is an important parameter for providing insight into lamination process control and for providing an indication of final product quality. It is becoming increasingly important for the display module to have absolute flatness quality. Any irregular pattern (waviness) can be seen by a corresponding user, especially if seen at a specific angle. An irregular pattern will consequently degrade the user experience.

It is in this context that embodiments arise.

SUMMARY

The present embodiments relate to solving one or more problems found in the related art, and more specifically include systems and methods for testing and detecting waviness (surface/refractive index irregularity) of flat transparent optical elements and displays.

An interferometric waviness detection system is disclosed and includes a beam splitter configured to receive a collimated light signal and split the collimated light signal into a first light signal traveling along a first path and a second light signal traveling along a second path. The detection system includes a first mirror configured to receive and reflect the first light signal along the first path. The detection system includes a second mirror configured to receive and reflect the second light signal along the second path via a transparent material that is located along the second path between the beam splitter and the second mirror. The detection system includes a 2D photosensor array configured to receive from the beam splitter the reflected first light signal along the first path merged with the reflected second light signal double passing through the transparent material along the second path and generate an interference fringe pattern. A non-sinusoidal interference fringe pattern indicates geometrical phase variation between a first wavefront of the reflected first light signal along the first path and a second wavefront of the reflected second light signal double passing through the transparent material along the second path.

A method for measuring waviness (e.g., non-uniform variation) in the flatness of a transparent optical material is disclosed. The method includes receiving a collimated light signal at a beam splitter. The method includes splitting the collimated light signal using the beam splitter into a first light signal traveling along a first path and a second light signal traveling along a second path. The method includes receiving the first light signal and reflecting the first light signal along the first path using a first mirror. The method includes receiving at a second mirror the second light signal through a transparent material located along the second path between the beam splitter and the second mirror. The method includes reflecting the second light signal received from the transparent material along the second path using the second mirror. The method includes merging using the beam splitter the reflected first light signal traveling along the first path and the reflected second light signal double passing through the transparent material along the second path. The method includes generating an interference fringe pattern from the reflected first light signal merged with the reflected second light signal. A non-sinusoidal interference fringe pattern indicates geometrical phase variation between a first wavefront of the reflected first light signal traveling along the first path and a second wavefront of the reflected second light signal double passing through the transparent material along the second path.

An interferometric waviness detection system is disclosed and includes a beam splitter configured to receive a collimated light signal having a first linear polarization and split the collimated light signal into a first light signal traveling along a first path and a second light signal traveling along a second path. The detection system includes a first quarter-wave plate. The detection system includes a mirror configured to receive and reflect the first light signal along the first path via the first quarter-wave plate located along the first path between the beam splitter and the mirror. The detection system includes a display module of a device under test (DUT) configured to receive and reflect the second light signal along the second path. The detection system includes a 2D photosensor array configured to receive from the beam splitter the reflected first light signal double passing through the first quarter-wave plate along the first path merged with the reflected second light signal along the second path and generate an interference fringe pattern. A non-sinusoidal interference fringe pattern indicates geometrical phase variation between a first wavefront of the reflected first light signal along the first path and a second wavefront of the reflected second light signal along the second path received by the beam splitter.

A method for measuring waviness (e.g., non-uniform variation) in the flatness of a transparent optical material is disclosed. The method includes receiving a collimated light signal having a first linear polarization at a beam splitter. The method includes splitting the collimated light signal using the beam splitter into a first light signal traveling along a first path and a second light signal traveling along a second path. The method includes receiving at a mirror the first light signal through a first quarter-wave plate located along the first path between the beam splitter and the mirror. The method includes reflecting the first light signal received from the first quarter-wave plate along the first path using the mirror. The method includes receiving the second light signal and reflecting the second light signal along the second path using a display module of a device under test (DUT). The method includes merging using the beam splitter the reflected first light signal double passing through the first quarter-wave plate along the first path and the reflected second light signal traveling along the second path. The method includes generating an interference fringe pattern from the reflected first light signal merged with the reflected second light signal. A non-sinusoidal interference fringe pattern indicates a geometrical phase variation between a first wavefront of the reflected first light signal along the first path and a second wavefront of the reflected second light signal along the second path received by the beam splitter.

These and other advantages will be appreciated by those skilled in the art upon reading the entire specification and the claims.

DETAILED DESCRIPTION

Generally speaking, the various embodiments of the present disclosure describe interferometer systems that can detect the degree of flatness of a transparent optical material (e.g., cover glass) and a display module with circular polarizer, wherein the interferometer systems are based on a Michelson interferometer setup. In particular, the interferometric waviness detection system of embodiments of the present disclosure distinctively determines the quality and/or degree of physical flatness of an optically transparent material or reflective material, such as one of the layers of a display module. Embodiments of the present disclosure use light wave interference to detect phase variation coming out of the transparent optical material caused by flatness variation, thickness variation, or refractive index variation. Embodiments of the present invention use a modified Michelson interferometer setup to detect thickness and/or refractive index uniformity over a transparent optical object area and/or a reflective material of a display module.

With the above general understanding of the various embodiments, example details of the embodiments will now be described with reference to the various drawings. Similarly numbered elements and/or components in one or more figures are intended to generally have the same configuration and/or functionality. Further, figures may not be drawn to scale but are intended to illustrate and emphasize novel concepts. It will be apparent, that the present embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order not to unnecessarily obscure the present embodiments.

FIG. 1illustrates a standard Michelson interferometer. A coherent laser110is collimated and aligned in such a way that after a beam splitter120splits the beam111into multiple beams, they are reflected from two separate mirrors101and102. The reflected beams are later combined by the beam splitter120onto a plane of sensor130. The intrinsic interferogram135gives an indication about wave front quality of the coherent collimated laser source110.

In particular, the coherent laser beam111may be collimated by a telescopic beam expander. The laser beam111then passes through beam splitter120configured to split the beam111equally (50:50). One arm of the laser beam111will be reflected ninety degrees (90°) and be bounced off from mirror101. This beam111A will pass directly through the beam splitter120to be received by the screen or sensor130.

The second arm of the laser beam111will first pass through the beam splitter120(e.g., without reflection) and then bounce off from mirror102. This bounced beam111B will then be reflected ninety degrees (90°) by the beam splitter120.

Once mirror101, mirror102and the laser110are aligned correctly, the beam111A off of mirror101and the beam111B off of mirror102will interfere with each other, and generate an interferogram (interference fringe pattern)135. In an ideal setup, a uniform interference fringe pattern is formed as there is no interference along either path.

Embodiments of the present invention provide for interferometric waviness detection systems and methods for implementing the same that each modify the Michelson interferometer setup to accommodate for different optical module waviness detections and inspections. and method for implementing the same.

FIG. 2Aillustrates various exemplary component layers of a mobile phone200, including a display module240having a display layer270and a transparent optical material250(e.g., cover glass/touch panel250a), the flatness of each being measured using embodiments of the present disclosure. The mobile phone is provided purely as an illustration of the use of a display module240and/or transparent optical material250, the flatness of each being measurable through embodiments of the present disclosure. Not all components of the mobile phone are illustrated. Other uses of the display module240and/or transparent optical material250are supported, whose flatness is measurable through embodiments of the present disclosure. For example, the display module240and/or transparent optical material250may be found in mobile devices with display screens, television screens, computer monitors, tablet devices, integrated display screens (e.g., integrated into dash of vehicle, desk surface, panel, etc.), portable communication devices, etc.

As shown, the mobile phone200includes a back cover210. A bottom shell220is interfaced with a face shell230to protect the circuit board225that is configured to provide functionality to the mobile phone200. The bottom shell220is configured to support a battery215, and is further configured to interface with the back cover210. The face shell230is configured to interface with and support a display module240. When fully assembled, the display module240includes a display layer270and cover glass/touch panel250a. The cover glass/touch panel250ais configured as a transparent material or transparent optical material250. When interfacing together all of the various components, the mobile phone200is configured in a convenient package suitable for handling by human hands.

FIG. 2Bis a cross section of the display module240having various layers, the flatness of each being measured using embodiments of the present disclosure. When fully assembled, the display module240includes a display layer270, such as a liquid crystal display (LCD), a circular polarizer260, and optically transparent cover glass/touch panel250a. In some configurations, the circular polarizer260may be integrated within the display layer270as is shown by the dotted outline surrounding both the display layer270and circular polarizer260. The display layer270is configured to provide a visual interface with a corresponding user, such as by displaying images that are viewable by the user. The display layer270may include one or more additional layers, though not herein described in full. Various technologies are used to build the display layer270typically configured as pixels providing colored light that are viewable by a user. These technologies include liquid-crystal displays (LCDs), light-emitting diodes (LEDs), organic light-emitting diodes (OLED), etc. The cover glass/touch panel250ais located adjacent to the display layer270or the circular polarizer260that is associated with the display layer270. Cover glass/touch panel250ais configured as a user interface, wherein the user may interact with the mobile phone200and/or provide input control through touching the glass or panel250ausing a stylus or one or more fingers.

When one or more layers of the display module240, including the display layer270and/or the cover glass/touch panel250a, are defective, the visual interfacing with the user suffers. For example, distorted images may be presented to the user that are caused by defects in the display layer270and/or the cover glass/touch panel250a. Slight distortions may degrade the user's viewing experience. Extreme distortion may introduce motion sickness for the user. As such, the layers of the display module240, such as the display layer270and/or the cover glass/touch panel250a, should be uniform, or flat, in order to provide the best viewing experience to the user.

In particular, uniform flatness of the top surface251of the cover glass/touch panel250aand top surface271of display layer270is desired for optimum viewing experience of the user. Embodiments of the present disclosure are configured to detect and/or measure the flatness of the top surface251of cover glass250aor other transparent material, and of the top surface271of display layer270or other reflective material. These embodiments are also capable of detecting and/or measuring the variation in thickness of the cover glass/touch panel250aor other transparent material250and/or the variation in the refractive index (or refractivity) across the cover glass/touch panel250aor other transparent material250. For example, embodiments of the present disclosure are configured to detect and/or measure the variation in thickness between the top surface251and bottom surface252of cover glass250aor other transparent material. Also, embodiments of the present disclosure are configured to detect and/or measure the variation in refractivity (e.g., index of refraction) between the top surface251and bottom surface252of the cover glass250a, or other transparent material.

FIG. 3Ais a block diagram of an interferometer waviness detection system300A configured to detect variation in flatness, variation in thickness, and/or variation of refractivity of a transparent optical material (e.g., cover glass/touch panel, display cover glass, thin film, optical thin film material, etc.), in accordance with one embodiment of the present disclosure. The interferometer waviness detection system300A uses light wave interference to detect phase variation between a reference signal and a signal coming out of a transparent optical material. The phase variation is caused by a variation in flatness, a variation in thickness, and/or a variation in the refractive index of the transparent optical material. As such, any waviness (e.g., non-uniformity or variation in flatness, thickness, and/or refractivity) in the transparent material is capable of being detected and analyzed with interferometer waviness detection system300A.

The interferometer waviness detection system300A includes a laser310that is configured to output a light signal. In one embodiment, the laser310outputs a coherent light signal, which emits continuous light waves of the same wavelength. The coherent light signal may be collimated when output from laser310, or may be collimated using a collimator device. A beam splitter320is configured to receive the collimated light signal311, and is further configured to split the collimated light signal311into a first light signal311atraveling along a first path (e.g., along a first arm) and a second light signal311btraveling along a second path (e.g., along a second arm). In one embodiment, the beam splitter320is configured as a fifty/fifty beam splitter which effectively splits the collimated light signal311evenly for purposes of generating interference fringe patterns and their analysis. In one embodiment, the first light signal is identical (e.g., same frequency and phase) to the second light signal, as output from the beam splitter320.

The interferometer waviness detection system300A includes mirror1, which is configured to receive and reflect the first light signal along the first path. The first light signal traveling along the first path may provide a reference signal. As an illustration, the first path may be broken into segments, as follows. In particular, the first light signal311ais reflected off the beam splitter320along the first segment311a-1of the first path. The first light signal311ais reflected off mirror1and travels along the second segment311a-2of the first path. The first light signal311athat is reflected off mirror1is transmitted or passed through the beam splitter320and travels along the third segment311a-3of the first path. A 2D photosensor array330is configured to receive the first light signal311athat is reflected off mirror1and passed through the beam splitter320. The 2D photosensor array330is configured to sense or detect light signals using one or more sensing technologies.

The interferometer waviness detection system300A includes mirror2, which is configured to receive and reflect the second light signal311balong the second path via a transparent material250. In particular, the transparent material250is located along the second path between the beam splitter320and mirror2. As an illustration, the second path may be broken into segments, as follows. The second light signal311bis transmitted or passed through the beam splitter320and travels along the first segment311b-1of the second path. The second light signal311bis transmitted or passed through the transparent material250(e.g., transparent optical material, cover glass, touch screen, etc.) and then travels along the second segment311b-2of the second path. As shown, the transparent material250is located along the second path between the beam splitter320and mirror2. The second light signal311bis reflected off mirror2and travels along the third segment311b-3of the second path. The second light signal311bis transmitted or passed through the transparent material250and then travels along the fourth segment311b-4of the second path. The second light signal311bis then reflected off the beam splitter320and then travels along the fifth segment311b-5of the second path. The 2D photosensor array330is configured to receive the second light signal311b, wherein the second light signal311bis reflected off mirror1, double passed through the transparent material250, and reflected off the beam splitter320.

As such, the 2D photosensor array330(e.g., sensor plane) is configured to receive from the beam splitter the reflected first light signal along the first path merged with the reflected second light signal double passing through the transparent material along the second path and generate an interference fringe pattern. The reflected second light signal311bmay have a shift in phase (though having the same frequency) when compared to the reflected first light signal311a, wherein the shift in phase may be caused by a geometrical variation (e.g., non-uniformity) in flatness, thickness, or refractivity (index of refraction) in the transparent material250. For example, the wavefront (i.e., second wavefront) of the second light signal311bmay be different than a wavefront (i.e., first wavefront) of the first light signal311awhen reaching the beam splitter320.

The interference fringe pattern or interferogram335provides an indication on whether there is a change in phase between the wavefronts of the first light signal311a(e.g., reflected off mirror1) and the second light signal311b(double passing through the transparent material250, reflected off mirror2, and reflected off the beam splitter320) as received by the 2D photosensor array330. That is, a phase variation between the wavefront of the first light signal311aand the wavefront of the second light signal311bas received by the 2D photosensor array330induces a disturbance in the resulting interferogram335. In particular, a non-sinusoidal interference pattern indicates geometrical phase variation between a wavefront of the reflected first light signal along the first path and a wavefront of the reflected second light signal double passing through the transparent material along the second path. That is, a non-uniform interference fringe pattern indicates a change in phase, which correlates to a variation in the flatness, or variation in thickness, or variation in refractivity of the transparent material250. In addition, a sinusoidal interference pattern indicates no abnormal change in phase between the wavefront of the reflected first light signal along the first path and the wavefront of the reflected second light signal double passing through the transparent material along the second path. That is, a uniform interference fringe pattern indicates no change in phase due to material non-uniformity, which correlates to no abnormal variation in the flatness, or thickness, or refractivity of the transparent material250. The information extracted from the interferogram335gives an indication as to the amount of variation in the flatness (e.g., degree of flatness), or thickness (degree of thickness), or refractivity of the transparent material250. For example, sinusoidal interference patterns represent that there is phase change between the two paths, and if the pattern is uniform that is a normal change in phase between the wavefront of the reflected first light signal along the first path and the wavefront of the reflected second light signal double passing through the transparent material along the second path. On the other hand, if the pattern is not uniform, this indicates abnormal change in phase due to material or geometric non-uniformity of the device.

FIG. 3Bis a top down view of the interferometer waviness detection system300A ofFIG. 3Athat is configured to detect variation in flatness, or thickness, or refractivity of a transparent optical material, in accordance with one embodiment of the present disclosure. The interferometer waviness detection system300A as shown inFIGS. 3A-3Bprovides one configuration for detecting the variation in the flatness (e.g., degree of flatness), or thickness (degree of thickness), or refractivity of the transparent material250. Other configurations are supported. For example, the transparent material may be located between the beam splitter320and mirror1(e.g., along the first path) instead of being located along the second path. Consistent between any configuration of the interferometer waviness detection system300A is that the physical distances between the beam splitter320and the mirror1or mirror2are identical (e.g., distance D1).

As shown inFIG. 3B, the components of the interferometer waviness detection system300A is located within support structure390. For example, the support structure390may be a physical housing, or a surface. Mirror1may be located on a track system340so that the location of mirror1with respect to the beam splitter320may be adjusted (e.g., fine-tuned). Track system340may also provide for adjusting the orientation of mirror1with respect to the beam splitter. In particular, mirror1is located a distance D1from the beam splitter, wherein the distance D1is measured from the point of the beam splitter where the collimated light signal311originating from laser310is reflected (along the first path) or transmitted (along the second path), such as a center point of the beam splitter320.

In addition, mirror2is located the same distance D1from the beam splitter. Though mirror2is shown as being fixed within outline390, mirror2may be on its own track system that provides for movement and/or orientation alignment of mirror2with respect to the beam splitter320. As previously introduced, the distance D1along the second path is measured from the point of the beam splitter where the collimated light signal311originating from laser310is reflected (along the first path) or transmitted (along the second path), such as a center point of the beam splitter320. When aligned, both mirror1and mirror2are each separated from the beam splitter320by distance D1. That is, a first distance between the first mirror and the beam splitter along the first path (e.g., as traveled by the first light signal) is approximately equal to a second distance between the second mirror and the beam splitter along the second path (e.g., as traveled by the second light signal). For example, the distance D1may be approximately 1 foot, or may be greater than 1 foot, or less than 1 foot. Because the distances D1between mirror1and mirror2and the beam splitter are nearly identical, no change in phase would be detected between the first light signal311aand the second light signal as received by the 2D photosensor array330when no transparent material or phase perturbation is placed within the interferometer waviness detection system300A, such as along the second path (or first path).

Holder350is located along the second path, and more particularly located between the beam splitter320and mirror2. Holder350is configured for holding, supporting, and/or clasping onto the transparent material250, such that the transparent material250is fixed in space with respect to the beam splitter320and mirror2. As shown, holder350is located a distance x from mirror2. The holder350may located anywhere along a line stretching between the beam splitter320and mirror2(e.g., along the second path). That is, the transparent material may be located anywhere between the beam splitter320and mirror2along the second path. The detection of the variation in the flatness, or variation in thickness, or variation in refractivity of the transparent material250will be similar no matter the location of the transparent material250between the beam splitter320and mirror2.

Holder350may be attached to the support structure390. Although holder350is shown fixed within the support structure390, holder350may also be located on a track system that provides for movement and/or orientation alignment of the transparent material250.

2D photosensor array330is configured to receive from the beam splitter320the reflected first light signal311aalong the first path merged with the reflected second light signal311b, passing through the transparent material again along the second path, and generate an interference fringe pattern or interferogram335. A computing device380may be coupled to the 2D photosensor array330in order to display, store, and/or analyze the interference fringe pattern335. For example, computing device380may be coupled via a wired connection381, or a wireless connection.

FIG. 3Cillustrates a cutaway view of the interferometer waviness detection system300A ofFIGS. 3A-3Btaken along a line drawn between points A-A inFIG. 3B, in accordance with one embodiment of the present disclosure. As shown inFIG. 3C, the interferometer waviness detection system300A may be enclosed and/or supported in support structure390, as previously introduced. In particular, a collimated light signal originating from light source310(e.g., laser) is provided to the beam splitter320, which splits the collimated light signal into a first light signal and a second light signal. The first light signal travels along a first path to be reflected off mirror1before returning back to the beam splitter320. The second light signal travels along a second path to pass through transparent material250, reflect off mirror2, and then pass through the transparent material250again before returning back to the beam splitter320. A 2D photosensor array is configured to receive from the beam splitter320the reflected first light signal merged with the reflected second light signal double passing through the transparent material and generate an interference pattern. Computing device380may be coupled to the 2D photosensor array330(e.g., wired or wireless connection, etc.) in order to display, store, and/or analyze the interference fringe pattern.

FIG. 3Dillustrates the placement of a transparent optical material in the interferometer waviness detection system300A ofFIGS. 3A-3C, and the different orientations of the transparent optical material within the detection system that still provide accurate detection of a variation in flatness, or thickness, or refractivity in the transparent material250, in accordance with one embodiment of the present disclosure.

An advantage of the interferometer waviness detection system300A is that the transparent material250can be located anywhere between the beam splitter320and mirror2. As shown inFIG. 3D, distance “x” may range between 0 to D1, to include 0 and D1(e.g., 0≤x≤D1). That is, transparent material250may be located anywhere on axis305between the beam splitter320and mirror2.

Another advantage of the interferometer waviness detection system300A is that the orientation of transparent material250need not be perfectly aligned with mirror2in order to detect a variation in flatness, or thickness, or refractivity of the transparent material250. That is, transparent material250need not be perfectly parallel with mirror2. For example, plane303of the transparent material250may be non-parallel to the plane304of mirror2within the interferometer waviness detection system300A. For example, transparent material250may be rotated on one or more of axis302and axis301. Purely as an example, transparent material250may be rotated by up to 5 degrees about each of axis302and axis301from a perfectly aligned orientation, such that the interferometer waviness detection system300A is still able to detect a variation in flatness, or thickness, or refractivity of the transparent material250. Purely as another example, transparent material250may be rotated by up to 10 degrees about each of axis302and axis301from a perfectly aligned orientation, such that the interferometer waviness detection system300A is still able to detect a variation in flatness, or thickness, or refractivity of the transparent material250. Purely as another example, transparent material250may be rotated by up to 15 degrees about each of axis302and axis301from a perfectly aligned orientation, such that the interferometer waviness detection system300A is still able to detect a variation in flatness, or thickness, or refractivity of the transparent material250. Purely as another example, transparent material250may be rotated by up to 30 degrees about each of axis302and axis301from a perfectly aligned orientation, such that the interferometer waviness detection system300A is still able to detect a variation in flatness, or thickness, or refractivity of the transparent material250. Of course, in other embodiments, plane303of the transparent material250may be parallel to the plane304of mirror2within the interferometer waviness detection system300A.

FIG. 4is a flow diagram400illustrating a method for measuring variation in flatness, or variation in thickness, or variation in refractivity of a transparent material, in accordance with one embodiment of the present disclosure. Flow diagram400may be implemented by the interferometer waviness detection system300A ofFIGS. 3A-3D, in embodiments to detect any waviness (e.g., non-uniformity and/or variation in flatness, thickness, and/or refractivity) of a transparent material (e.g., transparent optical material, cover glass/touch pane or panel, display cover glass, thin film, optical thin film material, etc.).

At410, the method includes receiving a collimated light signal at a beam splitter. The collimated light signal may originate from a light source, such as a laser providing a coherent beam of light, which is then collimated. The collimated light signal is received by the beam splitter, which then splits the collimated light signal at420into a first light signal and a second light signal. For example, the first light signal and the second light signal are identical, in one embodiment. The first light signal travels along a first path, and the second light signal travels along a second path.

At430, the method includes receiving the first light signal and reflecting the first light signal along the first path using a first mirror. The first light signal may be configured as a reference signal.

At440, the method includes receiving at a second mirror the second light signal along the second path. The second light signal is received at the second mirror after passing through a transparent material that is located along the second path between the beam splitter and the second mirror. At450, the method includes reflecting the second light signal along the second path using the second mirror, wherein the second light signal is received after passing through the transparent material. After reflection, the second light signal again passes through (e.g., a double pass) the transparent material.

At460, the method includes merging using the beam splitter the reflected first light signal traveling along the first path and the reflected second light signal double passing through the transparent material along the second path. That is, the reflected first light signal and the reflected second light signal are combined. At470, the method includes generating an interference pattern (e.g., interference fringe pattern) from the reflected first light signal merged with the reflected second light signal. For example, a 2D photosensor array is configured to receive the reflected first light signal merged with the reflected second light signal and sense and/or detect the merged light signals, such that the interference pattern may be generated. The interference pattern may be an interference fringe pattern or interferogram.

In particular, the interference pattern may show any change in phase between the reflected first light signal traveling along the first path and the reflected second light signal double passing through the transparent material along the second path. Any phase variation between the reflected first light signal the reflected second light signal double passing through the transparent material induces a disturbance in the interference pattern. In particular, a non-sinusoidal or non-uniform interference pattern indicates geometrical phase variation between a wavefront of the reflected first light signal and a wavefront of the reflected second light signal received at the beam splitter. The change in phase is caused by one or more of a variation in flatness, variation in thickness, and a variation in refractivity of the transparent material. Also, a sinusoidal or uniform interference pattern indicates no abnormal variation in phase between the reflected first light signal and the reflected second light signal received at the beam splitter. That is, no abnormal variation in phase indicates that there is uniform flatness, or uniform thickness, or uniform refractivity of the transparent material.

FIG. 5Ais a block diagram of an interferometer waviness detection system500A configured to detect flatness of a display module that acts as a reflecting mirror, in accordance with one embodiment of the present disclosure. The interferometer waviness detection system500A modifies a Michelson interferometer setup to detect and/or measure variation in flatness of a display module. In particular, the modified Michelson interferometer setup performing waviness detection includes an assembled display module as one of the reflecting elements. That is, a reflective optical object (such as an assembled display module with circular polarizer260, which consists of a quarter-wave plate260-A and a polarizer260-B) functions as a light reflecting mirror in the interferometer waviness detection system500A. The interferometer waviness detection system500A uses light wave interference to detect phase variation between a reference signal and a signal reflected off the assembled display module. The phase variation is caused by a variation in flatness of the assembled display module. As such, any waviness (e.g., non-uniform flatness) in the assembled display module is capable of being detected and analyzed with the interferometer waviness detection system500A. In particular, a resulting interferogram535gives an indication as to the quality of the reflective optical object, such as display module240.

The interferometer waviness detection system500A includes laser310that is configured as a light source that outputs a light signal. In one embodiment, the laser310outputs a coherent light signal, which emits continuous light waves of the same wavelength. The coherent light signal may be collimated when output from laser310, or may be collimated using a collimator device. In one embodiment, the collimated light signal511is configured as a linearly polarized electromagnetic wave. For instance, the collimated light signal511may be transmitted through a linear polarizer, or may be output as being linearly polarized from the light source, such the electric field oscillated in a vertical or horizontal direction, or any other direction perpendicular to the direction of propagation of the collimated light signal511. For example, in one implementation the collimated light signal511may be linearly polarized with linear P-polarization as received by the beam splitter320. In another implementation, the collimated light signal511may be linearly polarized with linear S-polarization as received by the beam splitter320.

Beam splitter320is configured to split the received collimated light signal511into a first light signal511atraveling along a first path (e.g., along a first arm) and a second light signal511btraveling along a second path (e.g., along a second arm). In one embodiment, the beam splitter320is configured as a fifty/fifty beam splitter which effectively splits the collimated light signal511evenly for purposes of generating interference fringe patterns and their analysis. In another embodiment, the first light signal511ais identical (e.g., same frequency and phase) to the second light signal511b, as output from the beam splitter320. In one embodiment, the beam splitter320comprises a non-polarizing beam splitter.

The interferometer waviness detection system500A includes a mirror, such as mirror1, which is configured to receive via a quarter-wave plate520the first light signal511a, and reflect the first light signal along the first path. The first light signal511atraveling along the first path may provide a reference signal. As an illustration, the first path may be broken into segments, as follows. In particular, the first light signal511ais reflected off the beam splitter320along the first segment511a-1of the first path. In the first segment511a-1of the first path, the first light signal511ais linearly polarized with linear P-polarization (e.g., a first linear polarization), as is shown inFIG. 5A. The first light signal511atravels from the beam splitter320and passes through the quarter-wave plate520before reaching the mirror1along the second segment511a-2. The quarter-wave plate520is located along the first path between the beam splitter320and mirror1. The quarter-wave plate520is configured to convert linearly polarized light to circularly polarized light, and vice versa. In the second segment511a-2of the first path, the first light signal511ais now circularly polarized in a clockwise direction, in one implementation, and as is shown inFIG. 5A. In another implementation, the first light signal511amay be circularly polarized in a counter-clockwise direction. Mirror1is configured to receive (after passing through the quarter-wave plate520) and reflect the first light signal511ain the third segment511a-3. Mirror1reverses the circular polarization of the first light signal511a. As such, in the third segment511a-3of the first path, the first light signal511ais now circularly polarized in a counter-clockwise direction. In the fourth segment511a-4of the first path, the first light signal511apasses again through the quarter-wave plate520which is configured to convert the light back to a linear polarization, but now is rotated by ninety degrees from the linear polarization of the first segment511a-1. That is, in the fourth segment511a-4of the first path, the first light signal511ais now linearly polarized with linear S-polarization (e.g., a second linear polarization). As such, the first light signal511adouble passes through the quarter-wave plate520and undergoes a rotation by ninety degrees (e.g., to a second linear polarization). In the fifth segment511a-5of the first path, the first light signal511apasses through the beam splitter320and is received by the 2D photosensor array330(e.g., sensor plane), wherein the first light signal511ais linearly polarized with linear S-polarization. The 2D photosensor array330is configured to sense or detect light signals using one or more sensing technologies.

The interferometric waviness detection system500A includes a reflective optical object that functions as a mirror in a modified Michelson interferometer setup. In particular, the interferometric waviness detection system500A includes the assembled display module240configured to display images, which includes a display layer270(configured to display pixel images) (e.g., LCD display, LED display, OLED display, etc.), circular polarizer260(which consists of a quarter-wave plate260-A and a polarizer260-B), and cover glass/touch panel250a, as previously introduced. The assembled display module240may be a device under test (DUT). The polarizer260-B of the circular polarizer260acts as a mirror, or reflector, and is configured to receive and reflect the second light signal511balong the second path. As an illustration, the second path may be broken into segments, as follows. The second light signal511bis transmitted or passed through the beam splitter320, and travels along the first segment511b-1of the second path. In the first segment511b-1of the second path, the second light signal511bis still linearly polarized with linear P polarization, as is shown inFIG. 5A. The second light signal511bpasses through the cover glass/touch panel250a. It is assumed that the cover glass/touch panel250ahas been previously tested (e.g., using interferometer waviness detection system300A ofFIG. 3A) and has been tested to have no waviness characteristics (e.g., no variation in flatness, or thickness, or refractivity) (according to specifications), and as such there is no abnormal change in phase when the light signal passes through the cover glass/touch panel250a. The second light signal511bthen passes through circular polarizer260, which includes a quarter-wave plate260-A configured to convert linearly polarized light to circularly polarized light (e.g., clockwise or counter-clockwise direction that is consistent with the operations of the quarter-wave plate520in the first arm), and vice versa. The circular polarizer260includes a polarizer260-B that is configured to receive and reflect a significant portion (e.g., most if not all) of the second light signal511balong the second path. Upon reflection, polarizer260-B reverses the circular polarization of the second light signal511b. The second light signal511bnow passes again (e.g., double passes) through the quarter-wave plate260-A, which is configured to convert the light back to a linear polarization, but now is rotated by ninety degrees from the linear polarization present in the first segment511b-1. As such, in the second segment511b-2of the second path, the second light signal511bis now linearly polarized with linear S-polarization (e.g., a second linear polarization).

In the third segment511b-3of the second light signal, the 2D photosensor array330(e.g., sensor plane) is configured to receive from the beam splitter320the reflected first light signal511adouble passed through the quarter-wave plate520along the first path merged with the reflected second light signal511balong the second path. As shown, the reflected first light signal511aand the reflected second light signal511bhave the same polarizations (e.g., linear S polarization if the collimated light signal has a linear P polarization, or linear P polarization if the collimated light signal511starts with a linear S polarization). This is because in the first path, the first light signal511adouble passes through the quarter-wave plate520with a reflection from mirror1, and in the second path, the second light signal511bdouble passes through the quarter-wave plate260-A in circular polarizer260of display module240with a reflection off of the polarizer260-B. In either path, the polarization switching (e.g., from linear P polarization to linear S polarization) allows wavefronts of the first light signal511areflected from mirror and the second light signal511breflected off the display module240to be combined at sensor plane with same state of polarization, thus generating interferogram or interference fringe pattern giving flatness information of the display module240.

In particular, the 2D photosensor array330is configured to generate an interference fringe pattern535. The reflected second light signal511bmay have a shift in phase when compared to the reflected first light signal511a, wherein the shift in phase may be caused by a variation (e.g., non-uniformity) in the flatness in the display module240, and more particularly the display layer270as translated to the polarizer260-B of the circular polarizer260. The interference fringe pattern or interferogram535provides an indication on whether there is a change in phase between the first light signal511a(e.g., reflected off mirror1and double passing through quarter-wave plate520) and the second light signal511b(reflecting off the display module240and reflecting off the beam splitter320) as received by the 2D photosensor array330. That is, a phase variation between the first light signal511aand the second light signal511bas received by the 2D photosensor array330induces a disturbance in the resulting interferogram535. In particular, a non-sinusoidal interference pattern indicates an abnormal change in phase (e.g., geometric phase variation) between a wavefront (e.g., first wavefront) of the reflected first light signal along the first path and a wavefront (e.g., second wavefront) of the reflected second light signal along the second path received by the beam splitter. That is, a non-uniform interference fringe pattern indicates a change in phase, which correlates to at least a variation in the flatness of the display module240, and in particular, of the display layer270(as translated to the polarizer260-B of the circular polarizer260). In addition, a sinusoidal interference fringe pattern indicates no abnormal variation in phase between the reflected first light signal along the first path and the reflected second light signal along the second path received by the beam splitter. That is, a uniform interference fringe pattern indicates no abnormal variation in phase, which correlates to no variation in the flatness of the display module240, and in particular no variation in the flatness of the display layer270(as translated to the polarizer260-B of the circular polarizer260). As such, the information extracted from the interferogram535gives an indication as to the amount of variation in the flatness (e.g., degree of flatness) of the display module240, and more particularly the display layer270of display module240. For example, sinusoidal interference patterns represent that there is phase change between the two paths, and if the pattern is uniform that is a normal change in phase between the wavefront of the reflected first light signal along the first path and the wavefront of the reflected second light signal along the second path. On the other hand, if the pattern is not uniform, this indicates abnormal change in phase due to material or geometric non-uniformity of the device

FIG. 5B-1is a top down view of the interferometer waviness detection system500A ofFIG. 5Athat is configured to detect variation in flatness of a display module (e.g., the display layer in the module), in accordance with one embodiment of the present disclosure. The interferometer waviness detection system500A as shown inFIGS. 5A and 5B-1provides one configuration for detecting the variation in the flatness (e.g., degree of flatness) of the display module240(e.g., display layer270). Other configurations are supported. For example, the display module may be located along the first path, and the mirror located on the second path. Consistent between any configuration of the interferometer waviness detection system500A is that the physical distances between the beam splitter320and mirror1, and between the beam splitter320and the display module (e.g., the polarizer260-B of the circular polarizer260) of the DUT are identical (e.g., distance D2).

As shown inFIG. 5B-1, the components of the interferometer waviness detection system500A is located within support structure590. For example, the support structure390may be a physical housing, or a surface. Mirror1may be located on a track system340so that the location of mirror1with respect to the beam splitter320may be adjusted (e.g., fine-tuned). Track system340may also provide for adjusting the orientation of mirror1with respect to the beam splitter. In particular, mirror1is located a distance D2from the beam splitter, wherein the distance D2is measured from the point of the beam splitter where the collimated light signal511originating from laser310is reflected (along the first path) or transmitted (along the second path), such as a center point of the beam splitter320.

When aligned, both mirror1and the display module240(e.g., the polarizer260-B of the circular polarizer260) held by holder550are each separated from the beam splitter320by distance D2. That is, a first distance between the mirror and the beam splitter along the first path (e.g., as traveled by the first light signal) is equal to a second distance between the display module (e.g., the polarizer260-B of the circular polarizer260) and the beam splitter along the second path (e.g., as traveled by the second light signal). The distance D2can be any value. For example, the distance D2may be approximately 1 foot, or may be greater than 1 foot, or less than 1 foot. Because the distances D2between mirror1and the display module240(e.g., the polarizer260-B of the circular polarizer260) and the beam splitter320are identical, no change in phase would be detected between wavefronts of the first light signal511aand the second light signal511bas received by the 2D photosensor array330when there is no variation in the flatness of the display module240, or more specifically no variation in the flatness of the display layer270(translated to the polarizer260-B of the circular polarizer260) in display module240.

In addition, the quarter-wave plate520is located along the first path between the beam splitter320and mirror1. As shown, quarter-wave plate520may be fixed with respect to support structure590. In other implementations, the position of quarter-wave plate520may be adjusted (e.g., located on a track system). The location of quarter-wave plate is not critical, and can be at any position between the beam splitter320and mirror1. As shown, quarter-wave plate520is located at a distance “y” from mirror1.

2D photosensor array330is configured to receive from the beam splitter320the reflected first light signal511adouble passing through the quarter-wave plate520along the first path merged with the reflected second light signal511b, double passing through the quarter-wave plate260-A and reflecting off the polarizer260-B (e.g., polarizer layer), both included in the circular polarizer260, along the second path, and generate an interference fringe pattern or interferogram535. A computing device380may be coupled to the 2D photosensor array330in order to display, store, and/or analyze the interference fringe pattern535. For example, computing device380may be coupled via a wired connection381, or a wireless connection.

FIG. 5B-2is a top down view of the interferometer waviness detection system500that is configured to detect flatness of a display module and/or a cover glass, in accordance with one embodiment of the present disclosure.FIG. 5B-2is similar toFIG. 5B-1except for the addition of mirror2in housing590′. In particular, the interferometer waviness detection systems300A and500A may be configured within the same support structure590′. For example, the interferometer waviness detection system500B ofFIG. 5B-2may be configured as either interferometer waviness detection system300A or interferometer waviness detection system500A. As an illustration, track system340allows mirror1to be at a distance D1from beam splitter320when configured as an interferometer waviness detection system300A, or to be at a distance D2from beam splitter320when configured as an interferometer waviness detection system500A, wherein D1is greater than D2. In particular, in the interferometer waviness detection system300A configuration as implemented in housing590′, mirror1and mirror2are each located at distance D1from beam splitter320. In this configuration, holder550is configured to hold, support, and/or clasp the transparent material250. Also, in the interferometer waviness detection system500A configuration as implemented in housing590′, mirror1and the DUT having the display module240(e.g., polarizer260-B of circular polarizer260) are each located at distance D2from the beam splitter320, wherein the holder550holding the DUT is configured to locate the display module240(e.g., polarizer260-B of circular polarizer260within display module240) of DUT at distance D2from beam splitter320. Holder550may interact or interface with track system565to position the DUT. Holder550is configured for holding, supporting, and/or clasping the DUT. As such, holder550is located on the second path, and more particularly, movably located between beam splitter320and mirror2.

FIG. 5C-1illustrates a cutaway view of the interferometer waviness detection system500A ofFIGS. 5A and 5B-1taken along a line drawn between points B-B ofFIG. 5B-1, in accordance with one embodiment of the present disclosure. As shown inFIG. 5C-1, the interferometer waviness detection system500A may be enclosed and/or supported in support structure590, as previously introduced. In particular, a collimated light signal originating from light source310(e.g., laser) is provided to the beam splitter320, which splits the collimated light signal to a first light signal and a second light signal. The first light signal travels along a first path via a quarter-wave plate520to be reflected off mirror1before returning back to the beam splitter320(after passing again through quarter-wave plate520). The second light signal travels along a second path to pass through the quarter-wave plate260-A of circular polarizer260, reflect off the polarizer260-B of the circular polarizer260, and then double pass through the quarter-wave plate260-A again before returning back to the beam splitter320. As shown, the display module240is held, supported, and/or clasped by holder550. Also, holder550may be located on a track system565, such that the display module240is movably positioned within the interferometer waviness detection system500A. A 2D photosensor array is configured to receive from the beam splitter320the reflected first light signal double passing through the quarter-wave plate520(and reflecting off mirror1) merged with the reflected second light signal double passing through the quarter-wave plate260-A of the circular polarizer260(and reflecting off the polarizer260-B) and generate an interference pattern (e.g., interference fringe pattern or interferogram). Computing device380may be coupled to the 2D photosensor array330(e.g., wired or wireless connection, etc.) in order to display, store, and/or analyze the interference fringe pattern.

FIG. 5C-2illustrates a cutaway view of the interferometer waviness detection system500B ofFIG. 5B-2taken along a line drawn between points C-C ofFIG. 5B-2, in accordance with one embodiment of the present disclosure.FIG. 5C-2is similar toFIG. 5C-1except for the addition of mirror2in housing590′. In particular, the interferometer waviness detection systems300A and500A may be configured within the same support structure590′ shown inFIG. 5C-2and as previously described in relation toFIG. 5B-2.

FIG. 6is a flow diagram illustrating a method for measuring variation in flatness of a display module, in accordance with one embodiment of the present disclosure. Flow diagram600may be implemented by the interferometer waviness detection system500A ofFIGS. 5A and 5B-1and/or interferometer waviness detection system500B ofFIG. 5B-2, in embodiments to detect any waviness (e.g., non-uniformity and/or variation in flatness) of a display module, and more particularly a display layer of the display module.

At610, the method includes receiving a collimated light signal at a beam splitter. The collimated light signal may originate from a light source, such as a laser providing a coherent beam of light, which is then collimated. The collimated light signal has a first linear polarization (e.g., linear P polarization, linear S polarization, etc.). The collimated light signal having a first linear polarization is received by the beam splitter, which then splits the collimated light signal at620into a first light signal and a second light signal. For example, the first light signal and the second light signal are substantially identical, in one embodiment. The first light signal travels along a first path, and the second light signal travels along a second path.

At630, the method includes receiving the first light signal at a mirror after passing through a quarter-wave plate. The quarter-wave plate may be located along the first path between the beam splitter and the mirror. The first light signal may be configured as a reference signal. At640, the first light signal passing through the quarter-wave plate is reflected off the mirror along the first path.

At650the method includes receiving the second light signal at an assembled display module of a DUT. In one implementation, the assembled display module includes a cover glass/touch panel, a circular polarizer (which consists of a quarter-wave plate and a polarizer), and a display layer. The polarizer of the circular polarizer acts as a reflector or mirror. As such, the second light signal after passing through the quarter-wave plate of the circular polarizer is reflected off the polarizer (e.g., polarizer layer) of the circular polarizer of the DUT along the second path.

At660, the method includes merging using the beam splitter the reflected first light signal double passing through the quarter-wave plate traveling along the first path (after reflection off mirror1) and the reflected second light signal double passing through the quarter-wave plate of the circular polarizer along the second path (after reflection off polarizer of the circular polarizer). The reflected first light signal received at the beam splitter has a second linear polarization (e.g., linear S polarization) that is rotated by ninety degrees from the first linear polarization (e.g., linear P polarization) of the collimated light signal511. In one embodiment, the reflected second light signal double passes through a quarter-wave plate of a circular polarizer of a display module (after reflection off the polarizer of the circular polarizer). In particular, the second light signal is received at the display module from the beam splitter after double passing through the quarter wave plate of the circular polarizer and reflecting off the polarizer of the circular polarizer before reaching the beam splitter. The reflected second light signal received at the beam splitter also has the second linear polarization (e.g., linear S polarization). That is, the reflected first light signal and the reflected second light signal have the same state of polarization when received by beam splitter and delivered to the sensor plane of the 2D photosensor array.

At670, the method includes generating an interference pattern (e.g., interference fringe pattern) from the reflected first light signal merged with the reflected second light signal. For example, a 2D photosensor array is configured to receive the reflected first light signal merged with the reflected second light signal and sense and/or detect the merged light signals, such that the interference pattern may be generated. The interference pattern may be an interference fringe pattern or interferogram.

In particular, the interference pattern may show any change in phase between the reflected first light signal double passing through the quarter-wave plate along the first path and the reflected second light signal double passing through the quarter-wave plate of the circular polarizer of the display module along the second path. Any phase variation between the reflected first light signal the reflected second light signal induces a disturbance in the interference pattern. In particular, a non-sinusoidal or non-uniform interference pattern indicates a geometrical phase variation (e.g., change in phase) between the wavefronts of the reflected first light signal and the reflected second light signal received at the beam splitter. The change in phase may be caused by a variation in flatness of the display module (e.g., display layer of display module). Also, a sinusoidal or uniform interference pattern indicates no abnormal variation in phase between the reflected first light signal and the reflected second light signal received at the beam splitter. That is, no abnormal variation in phase indicates that there is uniform flatness of the display module (e.g., display layer of display module).

FIGS. 7A-7Cillustrate various coverage areas of interference fringe patterns detecting flatness of a transparent optical material and/or a display module, in accordance with embodiments of the present disclosure.

For example,FIG. 7Aillustrates an interference fringe pattern735athat is configured to detect and/or measure a variation in flatness, or variation in thickness, or variation in refractivity of a transparent material250, wherein the interference fringe pattern735acovers most of the surface area of the transparent material250. Also,FIG. 7Aillustrates an interference fringe pattern735athat is configured to detect and/or measure a variation in flatness in a display module (e.g., display layer270of the display module), wherein the interference fringe pattern735acovers most of the surface area of the display model240(e.g., most of display layer270of display module240).

FIG. 7Billustrates an interference fringe pattern735bthat is configured to detect and/or measure a variation in flatness, or variation in thickness, or variation in refractivity of a transparent material250, wherein the interference fringe pattern735bcovers a small portion of the overall surface area of the transparent material250. Also,FIG. 7Billustrates an interference fringe pattern735bthat is configured to detect and/or measure a variation in flatness in a display module (e.g., display layer270of the display module), wherein the interference fringe pattern735bcovers a small portion of the overall surface area of the display module (e.g., display layer270of the display module).

FIG. 7Cillustrates an interference fringe pattern735cthat is configured to detect and/or measure a variation in flatness, or variation in thickness, or variation in refractivity of a transparent material250, wherein the interference fringe pattern735ccovers the entirety of the overall surface area of the transparent material250. Also,FIG. 7Cillustrates an interference fringe pattern735cthat is configured to detect and/or measure a variation in flatness in a display module (e.g., display layer270of the display module), wherein the interference fringe pattern735ccovers the entirety of the overall surface area of the display module (e.g., display layer270of the display module).

FIGS. 8A-8Fillustrate multiple interferograms providing simulated interference fringe patterns that detects and/or measures the variation in flatness, or variation in thickness, or variation in refractivity of a transparent optical material (e.g., cover glass/touch panel), or display module, in embodiments. In one implementation, each of the interference fringe patterns shown inFIGS. 8a-8F correlates to a corresponding contour of a surface of the tested material (e.g., transparent material250, or assembled display module240of the DUT, or display layer270of the assembled display module240of the DUT). In a corresponding interference fringe pattern, it may be determined that there is a change in phase between the reflected first light signal along the first path and the reflected second light signal in either the interferometer waviness detection system300A or the interferometer waviness detection system500A when there is more than one peak or valley in the interference pattern.

In particular,FIG. 8Aillustrates an interference fringe pattern exhibiting uniform phase variation, wherein the phase from the light signal varies uniformly thereby generating one nice peak810A. That is, the interference fringe pattern ofFIG. 8Ais uniform (e.g., exhibiting uniform phase variation between fringes), wherein each fringe represents one wavelength phase variation. Also, the interference fringe pattern has one peak810A (or valley), which exhibits uniformity of the fringe pattern off the peak in any direction. This indicates good results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 8Billustrates an interference fringe pattern exhibiting a phase variation. Although the interference fringe pattern ofFIG. 8Bis uniform (e.g., exhibiting uniform phase variation between fringes), wherein each fringe represents one wavelength phase variation, the peak810B is off-shifted from the center of the interference fringe pattern. This indicates poor results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 8Cillustrates an interference fringe pattern exhibiting a phase variation. The interference fringe pattern ofFIG. 8Cshows an X-shaped valley810C instead of uniform peak. This indicates poor results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 8Dillustrates an interference fringe pattern exhibiting a phase variation. The interference fringe pattern ofFIG. 8Dshows multiple peaks and/or valleys. In particular, the interference fringe pattern shows an X-shaped valley810D, and at least two X-shaped valleys820A and820B. This indicates poor results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 8Eillustrates an interference fringe pattern exhibiting a phase variation. The interference fringe pattern ofFIG. 8Eshows a non-uniform fringe pattern, wherein each fringe represents one wavelength phase variation. In particular, there is non-uniform phase variation between fringes. Also, the interference fringe pattern ofFIG. 8Eshows both a peak810E and a valley820E. This indicates poor results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 8Fillustrates an interference fringe pattern exhibiting a phase variation. The interference fringe pattern ofFIG. 8Fshows a non-uniform fringe pattern, wherein each fringe represents one wavelength phase variation. In particular, there is non-uniform phase variation between fringes. Also, the interference fringe pattern ofFIG. 8Fdoes not show either a distinctive peak or valley. This indicates poor results for the corresponding transparent material or display module (e.g., display layer of the display module).

FIG. 9shows a control module910for controlling the systems described above. Control module910may be configured within an example device used to perform aspects of the various embodiments of the present disclosure. For example,FIG. 9illustrates an exemplary hardware system900suitable for implementing a device in accordance with one embodiment. Hardware system900may be a computer system suitable for practicing embodiments of the disclosure, and may include processors, memory, and one or more interfaces. In particular, hardware system900includes a central processing unit or processor901for running software applications and optionally an operating system. Processor901may be one or more general-purpose microprocessors having one or more processing cores. Further, system900may include memory950for storing applications and data for use by processor901. Storage952provides non-volatile storage and other computer-readable media for applications and data, and may include fixed disk drives, removable disk drives, flash memory devices, and CD-ROM, DVD-ROM, Blu-ray, HD-DVD, or other optical devices, as well as signal transmission and storage media. The components of system900are connected via one or more data buses914.

The control module900may be employed to control devices in the system based in part on sensed values. For example only, the control module900may control one or more of coherent laser310, 2D photosensor array330, beam splitter320, mirror1, mirror2, holder350, holder550, quarter wave plate520, circular polarizer (not shown), track system340, track system560, and other sensors912based on the sensed values and other control parameters. The control module900will typically include one or more memory devices and one or more processors. Other computer programs stored on memory devices associated with the control module900may be employed in some embodiments.

There will typically be a user interface associated with the control module900. The user interface may include a display interface918configured for providing instructions to a display screen and/or graphical software displays of the testing systems, and user input devices920such as pointing devices, keyboards, touch screens, microphones, etc., which are used to communicate user inputs to the system900.

In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise testing systems. All of these systems may be integrated with electronics for controlling their operation before, during, and after testing. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein.

Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files).

The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” of all or a part of a fab host computer system, which can allow for remote access for testing. In some examples, a remote computer (e.g., a server) can provide testing processes to a system over a network, which may include a local network or the internet.

The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber.

As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, etc.

The following show a few additional embodiments which can be combined or integrated with the existing disclosed embodiments ofFIGS. 1-9and/or embodiments disclosed in the claims, or provide modifications that may cover other embodiments generated by combining the below disclosure with the existing disclosed embodiments ofFIGS. 1-9and/or embodiments disclosed in the claims.

A1. A method for measuring flatness, in accordance with one embodiment of the present disclosure. The method includes receiving a collimated light signal at a beam splitter. The method includes splitting using the beam splitter the collimated light signal into a first light signal traveling along a first path and a second light signal traveling along a second path. The method includes receiving the first light signal and reflecting the first light signal along the first path using a first mirror. The method includes receiving at a second mirror the second light signal passing through a transparent material located along the second path between the beam splitter and the second mirror. The method includes reflecting the second light signal received from the transparent material along the second path using the second mirror. The method includes merging using the beam splitter the reflected first light signal traveling along the first path and the reflected second light signal double passing through the transparent material along the second path. The method includes generating an interference fringe pattern from the reflected first light signal merged with the reflected second light signal. In the method, a non-sinusoidal interference fringe pattern indicates geometric phase variation between a first wavefront of the reflected first light signal traveling along the first path and a second wavefront of the reflected second light signal double passing through the transparent material along the second path.

A2. In accordance with another embodiment of the present disclosure, the method further includes setting a first distance between the first mirror and the beam splitter along the first path to be equal to a second distance between the second mirror and the beam splitter along the second path.

A3. In accordance with another embodiment of the present disclosure, the method further includes determining a change in phase between the first wavefront of the reflected first light signal along the first path and the second wavefront of the reflected second light signal double passing through the transparent material along the second path is caused by a variation in thickness of the transparent material or a variation in refractivity across the transparent material.

A4. Further, in the method, the transparent material comprises a cover glass for a display module, in accordance with one embodiment of the present disclosure.

A5. In accordance with another embodiment of the present disclosure, the method further includes receiving at the second mirror the second light signal from the beam splitter and through the transparent material. The method includes reflecting off the second mirror the received second light signal. The method includes receiving at the beam splitter the reflected second light signal double passing through the transparent material.

A6. In accordance with another embodiment of the present disclosure, the method further includes determining that there is a change in phase between the first wavefront of the reflected first light signal along the first path and the second wavefront of the reflected second light signal double passing through the transparent material along the second path when there is more than one peak or valley in the interference fringe pattern.

A7. In the method, a plane of the transparent material is non-parallel to a plane of the mirror, in accordance with one embodiment of the present disclosure.

A8. In the method, a plane of the transparent material is parallel to a plane of the mirror, in accordance with one embodiment of the present disclosure.

A9. In accordance with another embodiment of the present disclosure, the method further includes placing the transparent material at any point between the beam splitter and the second mirror along the second path.

A10. In the method, a sinusoidal interference fringe pattern indicates no abnormal variation in phase between the first wavefront of the reflected first light signal along the first path and the second wavefront of the reflected second light signal double passing through the transparent material along the second path, in accordance with one embodiment of the present disclosure.

A11. In accordance with another embodiment of the present disclosure, the method further includes generating a light signal. The method includes collimating the light signal to produce the collimated light signal.

B1. A method for measuring flatness, in accordance with one embodiment of the present disclosure. The method includes receiving a collimated light signal having a first linear polarization at a beam splitter. The method includes splitting using the beam splitter the collimated light signal into a first light signal traveling along a first path and a second light signal traveling along a second path. The method includes receiving at a mirror the first light signal through a first quarter-wave plate located along the first path between the beam splitter and the mirror. The method includes reflecting the first light signal received from the first quarter-wave plate along the first path using the mirror. The method includes receiving the second light signal and reflecting the second light signal along the second path using a display module of a device under test (DUT). The method includes merging using the beam splitter the reflected first light signal double passing through the quarter-wave plate along the first path and the reflected second light signal traveling along the second path. The method includes generating an interference fringe pattern from the reflected first light signal merged with the reflected second light signal. In the method, a non-sinusoidal interference fringe pattern indicates a geometric phase variation between the reflected first light signal along the first path and the reflected second light signal along the second path received by the beam splitter.

B2. In the method, the display module includes a circular polarizer including a second quarter-wave plate and a polarizer, and a display layer configured for displaying pixel images.

B3. In the method, the display layer includes a liquid-crystal display (LCD), or light emitting diode (LED) display, or an organic light emitting diode (OLED) display.

B4. In accordance with another embodiment of the present disclosure, the method further includes receiving at the mirror the first light signal via the first quarter-wave plate. The method includes reflecting off the mirror the received first light signal. The method includes receiving the reflected first light signal double passing through the first quarter-wave plate at the beam splitter, wherein the reflected first light signal received at the beam splitter has a second linear polarization that is rotated by ninety degrees from the first linear polarization. The method includes receiving from the beam splitter at the polarizer the second light signal passing through the second quarter-wave plate of the circular polarizer. The method includes reflecting off the polarizer the received second light signal. The method includes receiving at the beam splitter the reflected second light signal double passing through the second quarter-wave plate circular polarizer and having the second linear polarization.

B5. In accordance with another embodiment of the present disclosure, the method further includes setting a first distance between the mirror and the beam splitter along the first path to be equal to a second distance between the polarizer of the circular polarizer and the beam splitter along the second path.

B6. In the method, a change in phase between the first light signal traveling along the first path and the second light signal traveling along the second path is caused by a variation in flatness of the display module.

B7. In accordance with another embodiment of the present disclosure, the method further includes determining a change in phase between the reflected first light signal and the reflected second light signal when there is more than one peak or valley in the interference fringe pattern.

B8. In the method, the beam splitter comprises a non-polarizing beam splitter.

B9. In the method, a sinusoidal interference fringe pattern indicates no abnormal variation in phase between the reflected first light signal along the first path and the reflected second light signal along the second path received by the beam splitter.

B10. In accordance with another embodiment of the present disclosure, the method further includes generating a light signal. The method includes collimating the light signal to produce the collimated light signal.