Discussion of cutoff wavelength in optical fibres its defination measurements specifications optical fibre refractive index profiles, Total Internal Reflection, specifications for ITU G 657, 655A ,G655A,D

1. CUTOFF WAVELENGTH
I N F I B R E O P T I C S
JUNE 21 2021 Mon
CREATED BY GORAKHVANJARE

2. TABLE OF
CONTENTS • INTRODUCTION
• DEFINATION
• REFRACTIVE INDEX
• TOTAL INTERNAL REFLECTION
• MEASURMENTS SPECIFICATIONS
• MEASURMENTS PROCEDURE
• REFERENCES
©GV4779

3. INTRODUCTIO
N
INTRODUCTION
IzaaA
n optical fibre is a flexible transparent fibre made
by drawing glass silica, Optical fibres are used to
transmit light between the two ends of the fibre
and wide uses in fibre optic communications.
Where they permit transmission over longer
distances at higher bandwidth [data transfer rates]
than electrical cables.
Optical fiber goes under various measurements
parameter in which cut-off wavelength is one of
important parameter of them, cut-off wavelength
is important for single mode fibres as it is the
characteristic unique to single mode fibres.

4. ut-off wavelength is the wavelength above
which an optical fibre will allow single
mode transmission. In other words the
wavelength below which multimode
transmission starts.
DEFINATION
Single mode fibre design to have
one mode for propagation typically
SMF used in telecommunication
cables having core diameter 8㎛
and MFD 9㎛.
For multimode fibres cutoff wavelength is
not important why? The answer is simple
as the defination of cutoff wavelength
itself is the wavelength below which
multimode transmission starts hence
cutoff is a single mode fibre characteristic.
C

5. To understand cut off it is better to think about the
analogy of a road having a width of 10 meters.
Theoretically, if the car width is 5 meters, then two
cars can travel in that road. If the car width is 5.1,
only one car can travel in that road at a time. Then,
5.1 is the cut-off for this road.
Cut-off wavelength is important for single mode
optical fibers as it is the characteristic unique to
single mode optical fibers. Cut-off wavelength is
the minimum wavelength below which a single
mode fiber will act as multimode fibers, meaning
it will allow propagation of more than one mode
at a time. Thus it is clear that cut-off wavelength
determines the fate of single mode transmission.
ITU-T recommendation for single mode fibers ITU-T
G.652 specify a cut-off wavelength of less than or
equal to 1260nm. This means the wavelength below
1260nm is acceptable for a single mode.
10m

6. REFRACTIVE INDEX
he cutoff wavelength is determined by fibres
refractive index profile the length and bend of the
fibre Refractive index is measure of bending of a ray
of light when passing one medium into another.
Optical fibers typically include a core surrounded by a
transparent cladding material with a lower index of
refraction. Light is kept in the core by the phenomenon
of total internal reflection. which causes the fiber to act as
a waveguide. Optical fibre rely on total internal reflection
for their operation
T
Refractive Index
Optical fibres work even
when the fibre is bent

7. TTOTAL INTERNAL
REFLECTION
• When light is incident upon a medium of
lesser index of refraction, the ray is bent away
from the normal, so the exit angle is greater
than the incident angle. Such reflection is
commonly called “internal reflection". The exit
angle will then approach 90° for some critical
incident angle θc, and for incident angles
greater than the critical angle there will be
total internal reflection.
• Example of Total Internal Reflection
MIRAGE : It is an optical illusion that is
responsible for the appearance of the water
layer at short distances in a desert or on the
road. Mirage is an example of total internal
reflection which occurs due to atmospheric
refraction.
Fig: Total internal reflection
•There appear to be water on the road
though there is not.

8. MEASUREMENT
SPECIFICATIONS
SCOPE → This part of IEC 60793 establishes uniform
requirements for measuring the cut-off wavelength of
single-mode optical fibre, thereby assisting in the
inspection of fibres and cables for commercial
purposes.
METHOD USED →IEC 60793 Optical Fibres-
Part 1-44: [INTERNATIONAL
TELECOMMUNICATION UNION]ITU-T G650 1
TIA/EIA FOTP 80…
INSTRUMENT →
PK2200

9. MEASURMENT INSTRUMENT
SPECIFICATION
PARAMETER MACHINE UNIT
FIBRE CUTOFF (SMF
G650)
PK 2200 nm
CABLE CUTOFF PK 2200 nm
The cutoff wavelength of single
mode fibers depends on the
fiber length and bend
conditions.

10. CUTOFF SPECIFICATIONS FOR ITU-T G.657A1,G.657A2
PARAMETERS G.657A1, E1 G.657A2 ,E2(200㎛) G.657 E3
CUTOFF WAVELENGTH 1160㎚ to 1360㎚ 1160㎚ to 1360㎚ 1160㎚ to 1360㎚
CABLE CUTOFF
WAVELENGTH
≤ 1260㎚ ≤ 1260㎚ ≤ 1260㎚
CLADDING DIAMETER 125.0 ±0.7㎛ 125.0. ±0.7㎛ 125.0 ±0.7㎛
MODE FIELD DIAMETER 9.1 ± 0.4㎛ at 1310㎚ 8.6 to 9.2㎛ at 1310㎚ 8.6 to 9.2㎛ at 1310㎚
• CABLE CUTOFF ONLY CONSIDER WHEN CUTOFF
WAVELENGTH VALUE EXCEEDS ABOVE 1320nm
E2
E1
NEW

11. CABLE CUTOFF SPECIFICATIONS FOR DOF ITU-T
G655E.G656, G.655.C
TYPE A
TYPE Q
PARAMETERS G.655E(TYPE Q) G.655.C (TYPE A)
CUTOFF WAVELENGTH ▁ ▁ ▁ ▁
CABLE CUTOFF WAVELENGTH ≤ 1450㎚ ≤ 1450㎚
CLADDING DIAMETER 125.0 ±0.7㎛ 125.0. ±0.7㎛
MODE FIELD DIAMETER AT 1550
1550㎚
9.6 ± 0.4㎛ at 1550㎚ 9.2 ± 0.5㎛ at 1550㎚

12. Determining the cutoff wavelength of a single mode fiber
involves finding the wavelength above which the power
transmitted through the fiber decreased abruptly. This power
decrease occurs when the second-order mode propagating in
the fiber is cut off. The cutoff wavelength of single mode
fibers depends on the fiber length and bend conditions. The
effects of length and bending are different on different fibers
Cutoff wavelength may be measured on uncabled or cabled
single mode fibers. A slightly different procedure is used in
each case, but the basic measurment process is the same. The
test method for uncabled single mode fiber cutoff wavelength
is EIA/TIA-455-80. The test method for cabled single mode
fiber cutoff wavelength is EIA/TIA-455-170.
MEASUREMENT
PROCEDURES
EIA/TIA-455-80 →September 1, 1998. FOTP- 80 Measurement of
Cut-Off Wavelength of Single-Mode Fiber by Transmitted Power. This
method is intended to measure the cut-off wavelength of single-
mode fiber by determining the wavelength at which the fiber
transmission abruptly changes.

13. • Each test method describes the test equipment (input
optics, mode filters, and cladding-mode strippers)
necessary for the test.
BEND REFERENCE TECHNIQUE (FIBRE CUTOFF) : the cutoff
wavelength was measured using bend reference technique
described by fiber optic test procedure (FOTP)-80, on a 2 meter
single mode fabricated silica fiber using the experimental setup
viz; Photon Kinetics Model 2200.

14. G 657 A1
FIBRE CUTOFF MEASURMENT FOR ITU-T
G 657
A2
E1 E2
• Scan the fibre ID
• Enter operator ID
• Enter length as 2mtr
• Take 2mtr length fibre
• Cleave it
• Select the menu for
measuring cutoff
wavelength
• Lay the fibre on flat surface
instrument table give 28㎝
loop
• Allign the input and output
ends of the fibre specimens
to the detection optics
• Press F1 to measure fibre
cutoff wavelength then give
6㎝ guide loop press F1 after
measurment the value as
E3

15. CABLE CUTOFF WAVELENGTH (MULTIMODE
REFERENCE)
• When fibre cutoff greater than 1320㎚ from top end it goes for
cable cutoff
PROCEDURE FOR CABLE CUTOFF FOR ITU-T G
697 A1,A2
E2
E1
The test sample shall be 22 m of
uncabled fiber coiled into a loop with a
minimum 280㎜ to conservatively
simulate cabling effects. To simulate the
effects of a splice organizer, apply two
loop of 80㎜ diameter near one end, as
shown in Figure
FOR ITU-T G655E.656(DOF), G.655.C,D(DOF) SMF IN THIS
TYPE OF FIBRE CUTOFF DOES NOT MEASURE AT 1310㎚ AS
ITS CUTOFF ALREADY HIGH SO IT CAN BE MEASURE AT
1550㎚ IN CABLE CUTOFF.
TYPE
A
TYPE
Q
◇◆◇◆◇◆◇◆◇◆◇◆

16. REFERENCES
• https://www.researchgate.net/publi
cation/37464067_Cut-
off_wavelength_measurement
• https://standards.globalspec.com
• https://www.stl.tech/optical-
interconnect-products/optical-
fibre-cable/
• Optiwave
• https://fibercore.humaneticsgroup.
com/services-
support/fiberpaedia/c/cut-
wavelength

17. END OF PRESENTATION
END OF PRESENTATION