Optical fibers are flexible, transparent strands made of silica or plastic that transmit light, commonly used in telecommunications due to their high bandwidth and low power loss. Hollow-core fibers uniquely guide light through a hollow core, utilizing photonic crystals to achieve lower signal loss and increased speed over traditional fibers. Key factors affecting optical fiber performance include dispersion, attenuation, and their applications range from communication to sensing and power delivery.

2. OPTICAL FIBER :-
•An optical fiber is a flexible, transparent fiber made by silica
or plastic .
•Optical fibers are used most often as a means to transmit
light between the two ends of the fiber and find wide usage
in fiber-optic communications, where they permit
transmission over longer distances and at
higher bandwidths (data rates) than wire cables. These Fibers
are used because signals travel along them with lesser
amounts of loss , fibers are also immune to
electromagnetic interference .

3. • Optical fibers typically include a transparent 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. Fibers
that support many propagation paths or transverse modes are
called multi-mode fibers , while those that support a single mode
are called single-mode fibers .
• The field of applied science and engineering concerned with the
design and application of optical fibers is known as fiber optics.

4. Advantages :-
• Fibre optic cables have a much greater bandwidth than metal cables. The
amount of information that can be transmitted per unit time of fibre over
other transmission media is its most significant advantage.
• An optical fibre offers low power loss. This allows for longer transmission
distances. In comparison to copper; in a network, the longest
recommended copper distance is 100m while with fibre, it is 2000m.
• An optical fibre has greater tensile strength than copper or steel fibres of
the same diameter. It is flexible, bends easily and resists most corrosive
elements that attack copper cable.
• Optical fibres are difficult to tap. As they do not radiate electromagnetic
energy, emissions cannot be intercepted.
• Fibre optic cables are much thinner and lighter than metal wires. They
also occupy less space with cables of the same information capacity.

5. Why Do We Need
HOLLOW CORE FIBER…..??

6. A hollow-core fiber is an optical fiber which guides light essentially within a
hollow region, unhindered through air. The light beam is confined to the hollow
core by the holes in the surrounding glass material, which looks like a
honeycomb in cross section and creates a strictly no-go region for light, so that
only a minor portion of the optical power propagates in the solid fiber material
(typically a glass). According to the standard physical mechanism for guiding
light in a fiber, this should not be possible: normally, the refractive index of
the fiber core has to be higher than that of the surrounding cladding material,
and there is no way of obtaining a refractive index of glass below that of air or
vacuum, at least in the optical region.

7. How does it work….??

8. • A different guiding mechanism can be used, based on a
photonic band gap, as can be realized in a photonic
crystal fiber with a certain structure. Such fibers are
also called Photonic Band Gap Fibers. The name air-
guiding fibers is less precise, because it is actually not
the air which provides the guidance.
• The secret to hollow-core fiber is doing away with the
cladding and replacing it with photonic crystals. The
light shoots down the hollow core, and when it strikes
the edge, the photonic crystals bounce the photons.

9. A photonic crystal is a periodic optical nanostructure that affects the
motion of photons in much the same way that ionic lattices affect
electrons in solids. Photonic crystals occur in nature in the form of
structural coloration—and, in different forms, promise to be useful in
a range of applications. Photonic crystals can, in principle, find uses
wherever light must be manipulated. Photonic crystals are composed
of periodic dielectric, metallo-dielectric—or even superconductor
microstructures or nanostructures . Photons (behaving as waves)
either propagate through this structure or not, depending on their
wavelength.

10. • By doing away with the plastic or glass, these
hollow-core fibers have lower signal loss ,allowing
for longer distances between repeaters, and the
increased speed of light ,about 30% faster.
• The fact that each fiber is physically separated
(single-spatial-mode) allows for higher
bandwidth, and any polarization of the light is
kept in tact .

11. Modes
They can be used just like other single mode optical
fibers
Also, this single mode in hollow core fibers has quasi
– Gaussian intensity distribution just as in the case of
optical fibers
Even though ,they can be used as single mode fibers
till date there exists no such hollow core fiber in which
light travels only in single mode i.e. It travels inside
this fiber in multi – mode also
In some cases , additional ‘surface’ modes also have
been detected in these fibers
But , the main drawback is that here too occurs
higher loss of regarding this mode as compared to
that in single mode
These multi - modes decay very rapidly too

12. In particular , for a hole radius ρ = 0.47 λ for λ
is hole spacing , the core supports a single
mode and no surface modes for core radii
between 0.8 λ and 1.1 λ

14. THE PARAMETERS ON WHICH FORMATION OF
OPTICAL FIBER DEPENDS
• The factors on which the formation of an
Optical fiber depends is:
• Dispersion
• Attenuation

15. WHAT IS DISPERSION?
• In optics, dispersion is the phenomenon in which the phase velocity
of a wave depends on its frequency.[1] Media having this common
property may be termed dispersive media. Sometimes the term
chromatic dispersion is used for specificity. Although the term is used in the field of optics to
describe light and other electromagnetic waves, dispersion in the same sense can apply to any
sort of wave motion such as acoustic dispersion in the case of sound and seismic waves,
in gravity waves (ocean waves), and for telecommunication signals propagating
along transmission lines (such as coaxial cable) or optical fiber.
• In optics, one important and familiar consequence of dispersion is the change in the angle
of refraction of different colors of light,[2] as seen in the spectrum produced by a
dispersive prism and in chromatic aberration of lenses. Design of compound achromatic lenses,
in which chromatic aberration is largely cancelled, uses a quantification of a glass's dispersion
given by its Abbe number V, where lowerAbbe numbers correspond to greater dispersion over
the visible spectrum. In some applications such as telecommunications, the absolute phase of a
wave is often not important but only the propagation of wave packets or "pulses"; in that case
one is interested only in variations of group velocity with frequency, so-called group-velocity
dispersion (GVD).

16. DISPERSION IN OPTICAL FIBERS.
• As the optical pulses travel the length of the
fiber, they are broadened or lengthened in
time. This is called dispersion. Because the
pulses eventually will become so out of step
that they begin to overlap each other and
corrupt the data, dispersion sets an upper
limit on the data-carrying capabilities of a
fiber.

17. TYPES OF DISPERSION.
• There are three principal causes for this
broadening of light:
• Chromatic Dispersion – Different
wavelengths travel at different velocities
down the fiber. Because typical light
sources provide power over a series or
range of wavelengths, rather than from a
single discrete spectral line, the pulses
must spread out along the length of the
fiber as they proceed. The high-speed
lasers used in communications have very
narrow spectral output specifications,
greatly reducing the effect of chromatic
dispersion.

18. • Modal Dispersion – Different fiber
modes reflect at different angles as
they proceed down the fiber.
Because each modal angle produces
a somewhat different path length for
the beam, the higher-order modes
reach the output end of the fiber
behind the lower-order modes.

19. • Waveguide Dispersion – This minor cause for
dispersion is due to the geometry of the fiber and
results in different propagation velocities for each of
the modes.

20. ATTENUATION.
• Signals lose strength as they are propagated
through the fiber; this is known as
beam attenuation. Attenuation is measured
in decibels (dB) with the relation:

21. • where Pin and Pout refer to the optical power going
into and coming out of the fiber. The table below
shows the power typically lost in a fiber for several
values of attenuation in decibels.
The attenuation of an optical fiber is wavelength
dependent. At the extremes of the transmission curve,
multiphoton absorption predominates. Attenuation is
usually expressed in dB/km at a specific wavelength.
Typical values range from 10 dB/km for step-index
fibers at 850 nm to a few tenths of a dB/km for single-
mode fibers at 1550 nm.

23. • There are several causes of attenuation in an optical fiber:
• Rayleigh Scattering – Microscopic-scale variations in the index of refraction of
the core material can cause considerable scatter in the beam, leading to
substantial losses of optical power. Rayleigh scattering is wavelength dependent
and is less significant at longer wavelengths. This is the most important loss
mechanism in modern optical fibers, generally accounting for up to 90 percent of
any loss that is experienced.
• Absorption – Current manufacturing methods have reduced absorption caused
by impurities (most notably water in the fiber) to very low levels. Within the
bandpass of transmission of the fiber, absorption losses are insignificant.
• Bending – Manufacturing methods can produce minute bends in the fiber
geometry. Sometimes these bends will be great enough to cause the light within
the core to hit the core/cladding interface at less than the critical angle so that
light is lost into the cladding material. This also can occur when the fiber is bent in
a tight radius (less than, say, a few centimeters). Bend sensitivity is usually
expressed in terms of dB/km loss for a particular bend radius and wavelength.

24. Applications
Some of the major application areas of optical fibers
are:
• Communications – Voice, data and video
transmission are the most common uses of fiber
optics, and these include:
– Telecommunications
– Local area networks (LANs)
– Industrial control systems
– Avionic systems
– Military command, control and communications
systems
They can be useful in future for telecommunications

25. • Sensing – Fiber optics can be used to deliver light
from a remote source to a detector to obtain pressure,
temperature or spectral information. The fiber also
can be used directly as a transducer to measure a
number of environmental effects, such as strain,
pressure, electrical resistance and pH. Environmental
changes affect the light intensity, phase and/or
polarization in ways that can be detected at the other
end of the fiber.
• Power Delivery – Optical fibers can deliver remarkably
high levels of power for tasks such as laser cutting,
welding, marking and drilling.
• Illumination – A bundle of fibers gathered together
with a light source at one end can illuminate areas
that are difficult to reach – for example, inside the
human body, in conjunction with an endoscope. Also,
they can be used as a display sign or simply as

26. • Another application , perhaps closer to fruition
, which can be successfully exploit these
advantages offered by air-guiding PCFs , is
the delivery of high-power continuous wave ,
nanosecond and sub-picosecond laser beams
, which are useful for marking , machining and
welding , laser – Doppler velocimetry ( deals
with the measurement of parameters related
to fluids ) , laser surgery and THz generation

27. REFFERENCES:-
www.osapublishing.org
science.sciencemag.org
www.rp-photonics.com
www.nktphotonics.com
wikipedia.org
www.orc.soton.ac.uk
EDU.photonics

28. THANKYOU
KARAN BHATIA