Waveguiding, Modes, Organic LEDs

[needhelp87]

Hi everyone,

I was wondering if someone could please explain to me the concept of
waveguiding, coupling/coupled, and guiding mode.

Here is an application of these terms:

The photons emitted in the active region of OLEDs are
coupled into three types of modes: direct transmission into
the air, the glass total internal reflection mode, and the highindex
~ITO/organic! guided mode. Assuming Lambertian
light sources, the fractions of energy in the three modes have
been estimated as 0.2, 0.3, and 0.5, respectively.2 A number
of methods have been suggested for increasing the output
coupling efficiency. For example, random textures or ordered
microlens arrays have been employed on the top surface of
the glass substrate in order to minimize total internal
reflection.3,4 The thickness of the ITO layer has also been
controlled in order to reduce the energy in the high-index
layer.5 An integrated classical and quantum-mechanical weak
microcavity theory has been proposed in order to calculate
the efficiencies of each mode for OLED layered structure.6

I don't really understand HOW a photonic crystal helps "waveguide" these modes OUT of the OLED? I appreciate your help. Thanks!

Source: pbg.kaist.ac.kr/pdf_text/yjlee03APL.pdf

 

[needhelp87]

^ Bump ^

Please, any help is appreciated. I have a presentation due in a couple of days.

Thanks.

 

[sir-pinski]

Waveguiding refers to the process of confining and directing light within a specific structure, such as an optical fiber or a photonic crystal. In the context of Organic Light Emitting Diodes (OLEDs), waveguiding is used to control the propagation of photons emitted from the active region of the device.

Coupling or coupled modes refer to the interaction between different modes of light within the waveguide. In the case of OLEDs, the photons emitted from the active region can interact with different modes, such as direct transmission into the air, total internal reflection mode, and guided mode.

Guiding mode, also known as the high-index guided mode, refers to the mode that is confined and guided within the high-index layer, typically the Indium Tin Oxide (ITO) layer in OLEDs. This mode has the highest energy fraction among the three modes mentioned above.

In the context of increasing the output coupling efficiency in OLEDs, different methods are employed to manipulate the interaction between these modes. For instance, the use of random textures or microlens arrays on the top surface of the glass substrate can minimize the total internal reflection mode, allowing for more light to be emitted into the air. Similarly, controlling the thickness of the ITO layer can reduce the energy in the high-index guided mode, increasing the energy in the other modes and improving the overall efficiency of the device.

In summary, waveguiding, coupling modes, and guiding modes are all important concepts in understanding the behavior of light in OLEDs and how different structures and techniques can be used to manipulate and improve the efficiency of these devices. I hope this helps clarify the terms for you.