# Is there a phase shift associated with twisted nematic LCDs?

• JohnDoes
In summary, the conversation discusses the possibility of a phase shift in light entering a twisted nematic liquid crystal display when a voltage is applied to manipulate the polarization. The individual is looking for articles on this topic and information on the mathematical relationship between voltage and phase shift. The conversation also mentions the potential use of liquid crystals in beam steering and the speaker is looking for someone who may have more information on the topic.
JohnDoes
Hello,

As it says in the title, I would like to know if the light entering a twisted nematic liquid crystal display experiences any kind of phase shift specifically when applying a voltage to manipulate the polarisation of the light.

If it is the case, could someone point me towards any articles that describe this? I have had a look myself on Google etc., though most of the papers that seem related are only accessible through membership.

Also, if anyone knows the sort of maths behind it e.g. applying x amount of voltage/polarisation induces y amount of phase shift, whether it applies for a specific TN LCD device or in general, that would be great.

Thank you.

Yes. There is almost definitely a shift. Twisting of polarization is equivalent to having difference of refraction index for right-polarized and left-polarized light. (See Faraday Effect for some details.) So I would expect a difference in phase between on and off states. But there might be an overall index of refraction change as well, so I have no idea how you'd go about estimating the total.

I can tell you that people would be looking into this, because there have been applications of liquid crystals in beam steering, where phases are really important. I could probably even point you to people who would know, depending on how important this is.

Thank you for the reply K^2. I ask this particular question because it regards a particular design project that I am working on. My project involves finding some programmable "micromirror" device that can create bespoke changes for the phase of light. I happen to have access to a projector that uses a TN device; if it does the stuff I need it to do, with some reverse engineering, it could be just the thing.

If you could point me towards anyone who knows more I'd appreciate it.

## What is a twisted nematic LCD?

A twisted nematic LCD (TN LCD) is a type of liquid crystal display (LCD) that uses a twisted nematic liquid crystal to control the polarization of light passing through the display. This allows for the display of images and text on electronic devices such as smartphones, televisions, and computer monitors.

## What is a phase shift in relation to twisted nematic LCDs?

A phase shift in a twisted nematic LCD refers to the change in the orientation of the liquid crystal molecules when an electric field is applied. This change in orientation allows for the manipulation of light passing through the display, resulting in the display of different images or colors.

## Is there a phase shift associated with all twisted nematic LCDs?

Yes, all twisted nematic LCDs rely on a phase shift to control the polarization of light passing through the display. However, the amount of phase shift may vary depending on the specific design and technology used in the display.

## How is the phase shift controlled in twisted nematic LCDs?

The phase shift in twisted nematic LCDs is controlled by applying an electric field to the liquid crystal molecules. This electric field is generated by thin film transistors (TFTs) located behind each pixel on the display, which can be individually controlled to produce the desired phase shift and display the desired image or color.

## Can the phase shift be adjusted in twisted nematic LCDs?

Yes, the phase shift in twisted nematic LCDs can be adjusted by varying the strength of the electric field applied to the liquid crystal molecules. This can be done through the use of different voltages or pulse durations, allowing for a wide range of images and colors to be displayed on the screen.

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