What is Interferometric Modulator?

Interferometric Modulator (IMOD)is a display technology. It uses the interference of light for display. It is a light modulator that has an electrical switch. It can both emit light to appear colorful and absorb light to appear black. It is also called Mirasol. It creates various colors by using the interference principle. It uses the interference of the reflected light to show different colors. It uses very little power and can also be seen in sunlight. 

Need for Interferometric Modulator

There have been several electronic devices that are made. These electronic devices need technologies that help them stay charged so that less power is drained and also lesser electricity is needed to power it. The display technologies also needed a way by which they could have a lesser strain on the eyes. Keeping all this in mind, the Interferometric Modulator Technology was developed to solve all such problems. 

History 

1. The primary display was made on walls of caves with materials such as rocks and blood and leaves. Later, pen and paper were used to display things.
2. Then, the shift was made into electronic displays. The cathode ray tube was used in 1897. It used an electron gun and fluorescence for display. The several display technologies followed such as Flip-flap/disc display (1957), Monochrome plasma display (1964), LED display (1968), Thin film transistor LCD (1986), OLED in 2003, and Electronic paper in 2004.
3. Gyricon was the first kind of E-paper and was developed by Xerox. Gyricon uses polyethylene spheres of 2 colors, black and white. The black part is negatively charged while the white part is positively charged.
4. The application of voltage decides which color is visible to us. These spheres are suspended in oil, so they can rotate freely when voltage is applied and placed in a transparent silicone sheet.
5. E-paper technologies are several such as Gyricon, Electrophoretic Displays, Electrowetting displays, Electrofluidic display and Mirasol, etc.

Technologies Used 

1. Glass substrate: This is a substrate made of glass. Each pixel in an interferometric modulator is coated with this substance. This is a substrate displaying transparent properties.
2. Reflective membrane: This is a thin membrane that uses the property of reflection for image construction. The reflective membrane is placed beneath the glass substrate. This membrane is a conductor of electricity.
3. Stack: This is semi-transparent in nature and does not absorb or reflect all the light. It is made up of a thin film.
4. Air gap: Various colors on the screen are a result of varying air gap present. The gap is present between the glass substrate and the reflective membrane. Due to the application of voltage, there is an increase or decrease in the air gap that results in the formation of various colored pixels.

Working Principle

1. The pixel contains a thin film coated glass substrate.
2. Beneath this, there is a reflective membrane that is also conductive in nature.
3. When voltage is applied to this, it is attracted to the glass. 
4. This is when we see black pixels. The state is named Collapsed state.
5. The application of lower voltage makes the membrane return to its original position.
6. This is also called the Open state. The open state is seen as a colored pixel. The color of the pixel is a result of the interference of light.
7. A pixel in Mirasol comprises several sub-pixels.
8. The membrane is capable of moving with respect to a semitransparent thin film stack.
9. Mirasol behaves as an optical resonant.
10. The reflected color is different according to the air gap.
11. When the membrane is completely attracted to glass, it behaves as an induced absorber.
12. All incident light is absorbed and a black pixel is seen.
13. It is this binary operation of Mirasol that is used in flat panel displays.
14. It uses ambient lighting and pixels can be seen in sunlight as well.

Bistability

IMOD technology possesses bistability. This nature allows IMOD to have almost 0 power drainage when the display is unchanged. This is due to the electro-mechanical properties of Mirasol (aka IMOD). Bistability allows better battery life. IMOD displays do not refresh the screens as the LCD does. This is done in the following steps : 
First stage:  

• The IMOD membrane is put in an open state at a bias voltage.
• A short positive write voltage is applied to it which makes it reach the collapsed state.

Second Stage: 

• The write pulse is removed while IMOD continues in the collapsed state due to the application of the bias voltage.
• A short un-write voltage is applied which makes it reach the open state.

Color generation  

1. Several sub-pixels make up an RGB pixel as the brightness of the pixel is not adjusted. An array of colors represents different brightness levels of pixels.
2. There are 3 such arrays, one each of colors, Red, Blue and Green. This display is composed of a cavity. IMOD contains a reflective membrane and a stack made of the thin film.
3. When light is incident on the IMOD it reflects from the reflective membrane as well as the top of the stack. Some light waves have constructive interference while others have destructive interference.
4. The wavelengths of light that follow constructive interference are visible to the human eye as they are brighter than that of destructive interference. This is the most efficient use of light as it is reflected and not absorbed in which case, it loses its energy.

Applications 

1. It can be used in MP3 players.
2. Cell phone’s secondary and main displays can be made with this.
3. Portable Bluetooth accessories use Interferometric Modulator.
4. Handheld / wrist-worn GPS devices use this technology.
5. It is used in E-books, camcorders, computer monitors, wall-mounted TVs, etc.

It has some industrial applications like: 

1. Gaming devices that use Interferometric Modulator.
2. Digital TV and DVD players use the Interferometric Modulator.
3. Medical imaging makes use of it.
4. It is used in Automotive navigation.
5. Digital camera and camcorder screens can be made using this.

Advantages  

1. It has Industry compatibility and can be manufactured by the same industries that are used to manufacture the LCD without any extra effort of constructing new industries and factories. This makes it easily available.
2. Display for All Conditions- It can be used in bright sunlight and also in freezing temperatures where LCD does not function due to the use of liquid.
3. It provides great Readability and can also be read in sunlight because it uses ambient lighting.
4. Lesser power is consumed as compared to other displays due to its bistable nature and also because it has a very less refresh rate and almost 0 battery drainage when the picture on the screen in not changed.
5. It has a consistent contrast quality and also has real-like image processing. The images that appear have brightness which is more than its competitors and the images look true to life.
6. It is robust and sound. It is made up of inorganic materials that are not prone to environmental effects such as UV radiation and temperature changes. This also makes Mirasol displays very durable.
7. It is easy to integrate (because of the same industries manufacturing Mirasol that earlier manufactured LCD) and is safe from a business point of view, offering better experience at a lesser risk.

Disadvantages 

1. It is difficult to see in the dark because it uses ambient lighting.
2. It uses ambient lighting so it would always need light in the surroundings.
3. It has a ghosting effect. The images may not be present but their shadows would still be visible.
4. There are other technologies that are industry standards with similar features.
5. It has a low refresh rate. It cannot be used for highly interactive devices.