Specialty Optical Fibers Handbook

order modes, the TE

01

(H

01

), and TM

01

(E

01

) modes of the circular core fiber,

transform into eHE

01

and oEH

01

hybrid modes without circular symmetry [29–

31]. The first higher order mode of the elliptical core fiber, eHE

01

, depends on the

ellipticity and the normalized cutoff wavelength is defined by an empirical

expression from Dyott [32]:

V

bcutoff

¼ 2:405(b=a)

0:6275

(16:4)

The second higher order mode depends on the ellipticity and Dn. For practical

values of Dn and ellipticity 0:38 < b=a < 1, the oEH

01

mode is the second higher

order mode. However, when b=a < 0:38, a mode is borrowed from the third set

of higher order modes. The third set of higher order modes is based on the

splitting of the circular HE

21

mode into the eHE

21

and oHE

21

modes. Conse-

quently, ...