Testing LCD panels and liquid crystal test cells is one of the most common applications for Axometrics measurement systems. We revolutionized the industry when we introduced full-Mueller-matrix testing to this market in 2005.
Using our patented Mueller Matrix Method, Axometrics systems can measure all parameters a liquid crystal cell simultaneously:
- Cell gap
- Rubbing direction / Alignment direction on both the TFT and CF glass
- Twist angle
- Pre-tilt angle on both the TFT and CF glass
The measurement works on every mode of liquid crystal, including twisted, parallel rubbed, anti-parallel rubbed, vertically aligned, and hybrid cells. Our software includes an automatic detection function so you can successfully make measurements even if you do not already know what type of LC geometry you are testing.
Using AxoScan, the measurement is fast enough that you can scan a nearly unlimited number of XY points on a panel.
High-resolution XY scan of cell gap made by AxoScan
For making measurements inside of one pixel, the AxoStep imaging polarimeter is an ideal choice. This is important for Multi-domain designs, Investigating LC behavior near patterned electrodes, and analyzing bad or damaged pixels.
Cell gap and alignment direction variation within the subdomains of one pixel in a PSVA panel as measured by AxoStep.
Additionally, we offer solutions for measuring liquid crystal devices versus applied voltage, and temperature chambers for measuring gravity-induced cell gap defects (mura) when panels are heated and held vertically.
Another key measurement made for LCD panels is the off-axis retardation (Rth) of the color filter layers. It is known that large off-axis retardation of color filters can decrease the contrast ratio of a panel. The AxoScan’s ability to measure low retardation values proves useful in this application.
Off-axis retardation of a patterned color filter measured by AxoScan
Axometrics has worked closely with most of the world's leading LCD manufacturers to develop measurement solutions throughout the R&D, manufacturing, and QC stages of production. Contact us today to learn more.
Donec sagittis porta placerat. Mauris pharetra aliquet rhoncus. In egestas enim in massa imperdiet, id scelerisque nisl pulvinar. Praesent gravida nunc a justo vestibulum tempus. Nullam nunc tellus, faucibus id nisl sed, egestas pretium libero. Ut sed libero in dolor faucibus tempor in nec orci. Curabitur malesuada semper ligula, eu fringilla nunc pellentesque eget. Donec neque lacus, fermentum eu leo at, porttitor pellentesque eros. Proin at lobortis ligula, malesuada dignissim dolor. Integer mollis ac arcu non rhoncus.
Sed vestibulum efficitur diam, id consectetur odio elementum id. Aenean in metus lectus. Proin vitae ipsum a odio egestas blandit. Donec ullamcorper ut eros sed tincidunt. Vestibulum dignissim malesuada nisl elementum auctor. Donec eget nisl aliquam, elementum arcu pulvinar, lacinia tellus. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque eu purus quis massa pretium facilisis in in elit. Nulla lacinia, tellus sed dignissim pretium, sapien orci posuere odio, et luctus magna magna a leo. Quisque tincidunt urna leo, quis sagittis erat accumsan a. Nam ut purus id ex viverra accumsan. Morbi mollis blandit ipsum id ultrices. Nulla auctor eros a libero malesuada varius. Sed eu purus lacinia erat volutpat convallis eget non orci. Mauris tristique molestie purus nec maximus.
Morbi sit amet mollis diam. Suspendisse elementum vestibulum ornare. Pellentesque gravida in ante ac ultricies. Pellentesque pulvinar, lorem eget rutrum luctus, nulla arcu tempor augue, sed ullamcorper sem mauris eget nulla. Donec vitae hendrerit augue. Suspendisse id rutrum urna, in commodo ex. Aenean eu tincidunt lacus, ut tincidunt justo. Duis bibendum egestas erat, nec mollis odio ultrices ut.
Pellentesque ultricies libero sed erat ullamcorper mollis. Cras cursus ac arcu nec tempus. Etiam dignissim dolor accumsan leo ornare placerat eu at ex. Maecenas risus felis, lobortis nec molestie eu, mattis sed erat. Cras condimentum, nisi at fringilla luctus, tellus justo interdum eros, vitae gravida dui nisi pellentesque odio. Integer malesuada condimentum sapien. Nam convallis a dui quis aliquet. Nullam sollicitudin urna nisi, vel imperdiet tellus posuere eu. Aenean viverra tortor sed augue pretium hendrerit. Vestibulum euismod, risus at luctus lacinia, neque velit sodales orci, et sagittis odio metus et arcu. Aliquam erat volutpat. Etiam id rutrum dui. Proin turpis felis, bibendum vel dapibus eu, pulvinar ac ipsum. Aliquam eget leo sed orci pharetra scelerisque. Quisque finibus elementum nisi vel lacinia. Suspendisse tincidunt ultrices turpis, quis maximus metus sollicitudin non.
Overview
Birefringence is the difference in a material’s refractive index for difference incident polarization states of light. We define birefringence as Δn = nmax – nmin, where nmax and nmin are the maximum and minimum refractive indices for all possible launched polarization states.
As light passes through a birefringent material, the polarization state parallel to nmax will progressively lag further and further behind the polarization state aligned with nmin. This lag is called the 'retardance' or 'retardation'. In units of length, this retardation is simply δ = Δn t where t is the material thickness. In units of phase, where 360° is one wavelength, the retardance is δ = 360° Δn t / λ where λ is the wavelength of the light.
Most users wanting to map the birefringence of a sample are actually more interested in mapping the retardance. And while AxoScan and AxoStep do not directly measure birefringence, they both excel at retardance measurements. Or if the actual birefringence is needed, it is a simple matter of mechanically measuring the sample thickness and calculating birefringence from the measured retardance in degrees as Δn = δ λ / 360° t.
Our systems can measure retardance with levels as low as 0.01° or λ/36,000. If only a single measurement wavelength is used, the maximum retardance that can be measured is 180° or λ/2. Retardance values higher than 5,000° or approximately 14λ can be measured by testing multiple wavelengths and applying curve-fitting algorithms.
AxoScan completes a single-point retardance measurement in 0.03 seconds. Including time to move an XY stage, users can typically measure up to three locations per second allowing for high-resolution line scans and XY maps of samples. Typically AxoScan is used for testing samples with features larger than 3 mm.
AxoStep is an imaging microscope system that provides retardance measurements of every location within a image in 14 seconds. This allows for very high resolution maps of small areas. AxoStep is used for measuring features smaller than 3 mm.
Example Measurements
A 2 mm diameter injection-molded plastic lens measured with AxoStep reveals retardation near the filling gate. In addition to affecting polarization states, retardation will cause a phase error that distorts the optical wavefront produced by the lens resulting in lower-quality imaging.
The glass used to manufacture LCD panels requires very low internal stress so that it does not affect polarization states and so that the glass does not change dimensions when diced into smaller pieces. The figure below shows the very small stress pattern (less than 0.5 nm of retardation) present in a Gen 5 (1,100 mm x 1,300 mm) LCD glass substrate as measured by AxoScan.
In a Vickers test, a pyramidal diamond indenter is pressed into a sample to determine the hardness of the sample. An AxoStep system was used to map the resulting strain-induced birefringence when a glass plate was tested.
An AxoScan with the VRTF fixture is an ideal system for testing LCOS panels and other types of reflective displays. Since the fixture can be configured for transmission or reflection, with varying tilt and rotation angles, nearly all the polarization-critical components used in LCOS projectors and near-eye displays can be characterized.
AxoScan MMSP-VRTF-1-MSRS
Using our LCD view software, the cell gap, alignment direction, twist, and pre tilt angles of the liquid crystals within the LCOS can be measured. Note that measuring vertically aligned (VA) panels requires applying a voltage to the entire panel for cell gap testing.
Vacuum chuck for holding LCOS panels and applying voltage
For devices that need to be measured in retroreflection, it is possible to insert hey beam splitter into the measurement path as shown below.
Use of a calibrated beamsplitter allows retro-reflection measurements
By carefully measuring the Mueller matrix of the beamsplitter in both transmission and reflection, our software can mathematically remove the influence of the beamsplitter from the measurement leaving only the polarization properties of the sample behind.
United States