Design of hollow optical fiber for mode division multiplexing

1. Mahdi KASMI 1
, Faouzi BAHLOUL 1
, Yong Soo LEE 2
, Kyunghwan Ken OH 2
, Sofien MHATLI 1
, Rabah ATTIA 1
A study is presented of the hollow optical fiber (HOF) properties needed to achieve 10-mode multiplexing transmission. A combination of mode division multiplexing (MDM)
processing with optical LP mode separation is proposed to prevent the need for MDM computation. The impact of modal properties as chromatic dispersion and the differential
mode delay of the HOF on mode multiplexing are discussed.
DESIGN OF HOLLOW OPTICAL FIBER FOR MODE DIVISION MULTIPLEXINGDESIGN OF HOLLOW OPTICAL FIBER FOR MODE DIVISION MULTIPLEXING
1. University of Carthage, SERCOM laboratory, Tunisia Polytechnic School, EPT, B.P. 743, 2078, Tunisia, E-mail : faouzi.bahloul@enit.rnu.tn
2 Yonsei University, Institute of Physics and Applied Physics, Seoul 120-749, South Korea
Conclusion
Geometric Description
Uncoupled MDM using HOF
Optimized fiber design of HOF with three modes has been proposed.
 We have identified the structure with low DMD and with low chromatic dispersion for LP01, LP11 and LP21.
 We have showed the optimum values of air hole radius.
 The HOF with three-LP modes is adapted to weakly coupled mode-division-multiplexed systems.
Description
Hollow optical fiber (HOF) has three layered structure, central air hole, two
concentric rings and cladding.
Parameters
The hole radius r1.
The two rings core-cladding refractive index differences Δ+ and Δ- and
their radius r2 and r3.
The parameters of the HOF are chosen r2 = 3.7µm, and r3 = 4.7µm,
respectively.
The refractive index of the cladding is 1.444 at the wavelength 1550 nm.
Δ+
and Δ-
were 1.968% and 0.064% respectively.
 First, we study the impact of the air hole size on the mode properties of
the proposed fiber. We show that the effective index of 10 guided
modes can be separated by the method of adding a circular air hole of
appropriate size in the fiber center. When r1 decreases, the difference of
effective index (Δneff) can reach to the highest value.
Variation of the effective indices (neff ) of LP01, LP11, LP21 modes in HOF as
a function of the radius of the first ring r1.
The refractive indices of the silica
(cladding) and the ring cores at
different wavelengths are calculated
using the Sellmeier equation. When
the air hole radius r1 is fixed at the
optimized value of 0.6 μm, the
effective refractive indices and the
effective index difference (Δneff)
between all adjacent guided modes
of all the 10 guided modes as a
function of wavelength were
calculated.
Effective refractive indices (neff) of
all guided modes (b) Δneff between
all adjacent guided modes, as a
function of the wavelength of λ, for
the 10-mode HOF with with r1 =0.6
μm, r2 = 3.7µm, r3 = 4.7µm and
rcladding= 62.5 μm, respectively. Δ+
and
Δ-
were 1.968% and 0.064%
0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
1,444
1,448
1,452
1,456
1,460
1,464
neff
r1
(µm)
LP01y
LP01x
LP11ay
LP11ax
LP11bx
LP11by
LP21bx
LP21by
LP21ax
LP21ay
1,50 1,52 1,54 1,56 1,58 1,60 1,62 1,64
1,445
1,450
1,455
1,460
neff
λ (µm)
LP01y
LP01x
LP11ay
LP11ax
LP11bx
LP11by
LP21bx
LP21by
LP21ax
LP21ay
1,50 1,52 1,54 1,56 1,58 1,60 1,62 1,64
0,000
0,002
0,004
0,006
0,008
0,010
LP01y
-LP01x
LP01x
-LP11ay
LP11ay
-LP11ax
LP11ax
-LP11bx
LP11bx
-LP11by
LP11by
-LP21bx
LP21bx
-LP21by
LP21by
-LP21ax
LP21ax
-LP21ay
∆neff
λ (µm)
1,50 1,52 1,54 1,56 1,58 1,60 1,62 1,64
-100
-80
-60
-40
-20
0
20
Dispersion(ps/nm.km)
λ (µm)
LP01y
LP11by
LP21ax
1,50 1,52 1,54 1,56 1,58 1,60 1,62 1,64
0
2
4
6
8
10
12
14
16
18
20
DMD(ns/km)
λ (µm)
LP01 to LP11
LP11 to LP21
LP01 to LP21
Modal wavelength dependency over the C+L
band of the designed HOF showing (a) the
group
velocity dispersion (b) the differential mode
delay.
The modal wavelength dependency of the
designed fiber over the whole C+L band
also is investigated. The chromatic
dispersions and the differential mode delay
of the first three modes (LP01, LP11 and
LP21) as a function of wavelength were
calculated. The maximum chromatic
dispersion for all guided modes is about -90
ps∕nm.km over the C+L band. The HOF
should support a specific number of well-
guided modes with low DMD, and low
coupling between modes.
Refractive index profile of a HOF.