In this post we want to discuss about mode of user select in lumerical.So we here define and discuss about some parameters in lumerical.

If you work with lumerical you can see some of these parameters TE Polarization fraction and TE/TM fraction.I found a link that describe it very well.

**TE Polarization fraction and TE/TM fraction definition:**

Since the TE/TM polarization definition can vary in different application areas, here is a mathematical definition of the "TE polarization fraction" and "TE/TM fraction" from Knowledge Base58 in order to avoid any confusion:

The "TE polarization fraction Ex" for propagation along the z direction is defined by the following equation:

where |Ex|^2+|Ey|^2 corresponds to |E_parallel|^2 (since we are considering the polarization of the modes, we only consider the fields parallel to the mode cross section). For propagation along the x/y direction (ie. "TE polarization fraction Ey/Ex"), this is similarly defined:

and

"TE/TM fraction" is defined by the following equations:

and

where and refers to the field component in the direction of propagation (ie. perpendicular to the mode cross section).

**Now we want to distinguish TE or TM mode just by looking at TE/TM fraction ?**

i found a good link that it explain it very good please see it and this.So we concluded that:

Fig1:User select Mode,x axis is direction of wave propogation

The "TE/TM fraction (%)" indicates if the mode is TE or TM because it calculates how much longitudinal component of E or H is there compared to the total field. For example, in the 1D mode analysis of a slab waveguide, TE mode by definition is the one whose E_longitudinal = 0. Hence, "Transverse Electric".

However, back to the real 2D profile, you will find there are no pure TE or TM modes. Those modes, we conventionally call TE or TM, are rather Quazi-TE or Quazi-TM. Their longitudinal components never vanish.

In view of the above, the higher the TE fraction, the more the mode is TE. But I think the comparison between the TE and TM fractions has little to do with determining TE or TM especially when the fraction values are close like in your case.

So we concluded that we can not see mode from view point ideal, they are relative.

Fig2:TE and TM Modes

For more info and review about mode please see this link.Finally i will share here some points: