Optical fibers have many applications in biomedical fields and daily life. They can transmit light signals over long distances with low loss and are immune to electromagnetic interference. Optical fibers are used for fiber-optic communication networks, illumination, imaging in confined spaces, and fiber optic sensors. Fibers typically include a transparent core surrounded by a cladding material with a lower refractive index to guide light through total internal reflection. Fibers that support many propagation paths are called multi-mode, while those that only support a single mode are called single-mode fibers. Optical fibers enable high-speed data transmission and have advantages over electrical cables such as huge data capacity, low signal loss, and lightweight design.

1. Optical fibers applications in biomedical &
daily life
By: Eman Kamel
Reham Mohamed
Mahmoud Khaled
An optical fiber (or optical fiber) is a flexible, transparent fiber made of
extruded glass (silica) or plastic, slightly thicker than a human hair. It can function
as a waveguide, or “light pipe”, to transmit light between the two ends of the
fiber. The field of applied science and engineering concerned with the design and
application of optical fibers is known as fiber optics.
Optical fibers are widely used in fiber-optic communications, where they permit
transmission over longer distances and at higher bandwidths (data rates) than
wire cables. Fibers are used instead of metal wires because signals travel along
them with less loss and are also immune to electromagnetic interference. Fibers
are also used for illumination, and are wrapped in bundles so that they may be
used to carry images, thus allowing viewing in confined spaces. Specially
designed fibers are used for a variety of other applications, including sensors
and fiber lasers.
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 total internal reflection. This causes the fiber to act as a waveguide.
Fibers that support many propagation paths or transverse modes are
called multi-mode fibers (MMF), while those that only support a single mode are
called single-mode fibers (SMF). Multi-mode fibers generally have a wider core
diameter, and are used for short-distance communication links and for
applications where high power must be transmitted. Single-mode fibers are used
for most communication links longer than 1,000 meters (3,300 ft).
• ,
Optical Fiber Communication:
Optical fibers can be used to transmit light and thus information over long
distances. Fiber-based systems have largely replaced radio transmitter systems
for long-haul optical data transmission. They are widely used for telephony, but

2. also for Internet traffic, long high-speed local area networks (LANs), cable TV
(CATV), and increasingly also for shorter distances within buildings. In most
cases, silica fibers are used, except for very short distances, where plastic optical
fibers can be advantageous.
Compared with systems based on electrical cables, the approach of optical
fiber communications (light wave communications) has advantages, the
most important of which are:
• - The capacity of fibers for data transmission is huge: a single silica
fibers can carry hundreds of thousands of telephone channels, utilizing only a
small part of the theoretical capacity. In the last 30 years, the progress
concerning transmission capacities of fiber links has been significantly faster than
e.g. the progress in the speed or storage capacity of computers.
• - The losses for light propagating in fibers are amazingly small: ≈
0.2 dB/km for modern single-mode silica fibers, so that many tens of kilometers
can be bridged without amplifying the signals.
• - A large number of channels can be re amplified in a single fiber amplifier,
if required for very large transmission distances.
• Due to the huge transmission rate achievable, the cost per transported bit
can be extremely low.
• - Compared with electrical cables, fiber-optic cables are very lightweight.
• - Fiber-optic cables are immune to problems that arise with electrical
cables, such as ground loops or electromagnetic interference (EMI). Such issues
are important, for example, for data links in industrial environments.
System Design:
The simplest type of fiber-optic communication system is a fiber-optic
link providing a point-to-point connection with a single data channel. Such a link
essentially contains a transmitter for sending the information optically, a
transmission fiber for transmitting the light over some distance, and a receiver.
The transmission fiber may be equipped with additional components such
as fiber amplifiers for regenerating the optical power or dispersion
compensators for counteracting the effects of chromatic dispersion. The article
on fiber-optic links gives more details.
A typical channel capacity for long-haul transmission is nowadays 2.5 or
10 GB/s; 40, 100 or even 160 GB/s may be used in the future. More advanced
systems increase the transmission capacity by simultaneously using several,

3. dozens or even hundreds of different wavelength channels (coarse or dense
wavelength division multiplexing). The main challenges are to suppress channel
cross-talk via nonlinearities, to balance the channel powers (e.g. with gain-
flattened fiber amplifiers), and to simplify the systems. Another approach is time
division multiplexing, where several input channels are combined by nesting in
the time domain, and solutions are often used to ensure that the sent ultra short
pulses stay cleanly separated even at small pulse-to-pulse spacing.
Another important development is that of systems which link many different
stations with a sophisticated fiber-optic network. This approach can be very
flexible and powerful, but also raises a number of non-trivial technical issues,
such as the need for adding or dropping wavelength channels, ideally in a fully
reconfigurable manner, or to constantly readjust the connection topology so as to
obtain optimum performance, or to properly handle faults so as to minimize their
impact on the overall system performance. As many different concepts (e.g.
concerning topologies, modulation formats, dispersion management, nonlinear
management, and software) and new types of devices (senders, receivers,
fibers, fiber components, electronic circuits) are constantly being developed, it is
not clear so far which kind of system will dominate the future of optical fiber
communications.
Advanced Fiber Designs:
• As carriers look to new amplifier and transmission technologies to
increase the capacity and distances that they can transmit information, Optical
fiber types will evolve to add further value to a network. The design of optical
fibers is a multi-dimensional balancing act which requires precise tuning of a
fiber’s optical characteristics to achieve a design that will maximize value when
installed a network. AS an example, Corning LEAF fiber was designed to provide
a balance between a large effective area to minimize non-linear effects and a low
dispersion across the 1550 nm region to reduce the costs associated with
dispersion compensation.
• Although, it has been the case for submarine cable systems for many
years, it is possible that within few years terrestrial networks may begin to
employ dispersion managed cables. The use of dispersion managed cables in
terrestrial network may be to facilitate very high TDM rates such as 80 Gb/s.
Such a terrestrial dispersion managed cable system would likely utilize two or
more different fibers distinctly optimized for different performance features.
These systems differ from those utilizing dispersion compensation modules in
that compensation is accomplished in distributed fashion as opposed to discrete

4. placement of modules. Of course there are numerous, primarily logistical, issues
that have so far precluded the use of dispersion managed cables terrestrially.
However, there have been recent demonstrations of TDM rates up to 80 Gb/s
utilizing managed cable with very real implications for terrestrial use.
•
Optical Fiber Sensors:
A fiber optic sensor is a sensor that uses optical fiber either as the sensing
element ("intrinsic sensors"), or as a means of relaying signals from a remote
sensor to the electronics that process the signals ("extrinsic sensors"). Fibers
have many uses in remote sensing. Depending on the application, fiber may be
used because of its small size, or because no electrical power is needed at the
remote location, or because many sensors can be multiplexed along the length of
a fiber by using light wavelength shift for each sensor, or by sensing the time
delay as light passes along the fiber through each sensor. Time delay can be
determined using a device such as an optical time-domain reflectometer and
wavelength shift can be calculated using an instrument implementing optical
frequency domain reflectometry.
Fiber optic sensors are also immune to electromagnetic interference, and do not
conduct electricity so they can be used in places where there is high
voltage electricity or flammable material such as jet fuel. Fiber optic sensors can
be designed to withstand high temperatures as well.
Compared with other types of sensors, fiber-optic sensors exhibit a
number of advantages:
-They consist of electrically insulating materials (no electric cables are
required), which makes possible their use e.g. in high-voltage environments.
• -They can be safely used in explosive environments, because there is no
risk of electrical sparks, even in the case of defects.
• -They are immune to electromagnetic interference (EMI), even to nearby
lightning strikes, and do not themselves electrically disturb other devices.
• -Their materials can be chemically passive, i.e., do not contaminate their
surroundings and are not subject to corrosion.
• -They have a very wide operating temperature range (much wider than is
possible for many electronic devices).
• -They have multiplexing capabilities: multiple sensors in a single fiber line
can be interrogated with a single optical source.

5. − Bragg Grating Sensors:
Fiber-optic sensors are often based on fiber Bragg gratings. The basic principle
of many fiber-optic sensors is that the Bragg wavelength (i.e., the wavelength of
maximum reflectivity) of a fiber Bragg grating depends not only on the Bragg
grating period but also on temperature and mechanical strain. For silica fibers,
the fractional response of the Bragg wavelength to strain is roughly 20% smaller
than the strain itself, since the direct effect of strain is to some extent reduced by
a decrease in refractive index. The temperature effect is close to that expected
from thermal expansion alone. The effects of strain and temperature can be
distinguished with various techniques (e.g. by using reference gratings which are
not subject to the strain, or by combining different types of fiber gratings), so that
both quantities are obtained at the same time. For pure strain sensing, the
resolution can be the range of a few με (i.e., relative length changes of a few
times 10−6
), and the accuracy may not be much lower. For dynamic
measurements (e.g. of acoustic phenomena), sensitivities better than 1 nε in a 1-
Hz bandwidth are achievable.
− Distributed Sensing:
Other fiber-optic sensors do not use fiber Bragg gratings as sensors, but rather
the fiber itself. The principle of sensing can then be based on Rayleigh
scattering, Raman scattering or Brillouin scattering. For example, optical time
domain reflectometry is a method where weak reflections can be localized using
a pulsed probe signal. It is also possible, e.g., to exploit the temperature or strain
dependence of the Brillouin frequency shift.
In some cases, the measured quantity is a kind of average over the full fiber
length. This is the case for certain temperature sensors but also for Sagnac
interferometers used as gyroscopes. In other cases, position-dependent
quantities (e.g. temperatures or strains) are measured. This is called distributed
sensing.
There are many alternative techniques. Some examples are:
• -Fiber Bragg gratings may be used in interferometric fiber sensors, where
they merely serve as reflectors, and the measured phase shift results from fiber
spans between them.

6. • -There are Bragg grating laser sensors, where a sensor grating forms the
end mirror of a fiber laser resonator, containing e.g. some erbium-doped fiber,
which receives some 980-nm pump light via the fiber line. The Bragg wavelength,
which depends on e.g. temperature or strain, determines the lasing wavelength.
This approach, which has many further variations, promises very high resolution
due to the small line width of such a fiber laser, and very high sensitivity.
• -In some cases, pairs of Bragg gratings are used as fiber Fabry–Pérot
interferometers, which can react particularly sensitively to external influences.
The Fabry–Pérot interferometer can also be made with other means, e.g. with a
variable air gap in the fiber.
• -Long-period fiber gratings are particularly interesting for multi-parameter
sensing (e.g. of temperature and strain), and alternatively for strain sensing with
very low sensitivity to temperature changes.
− Applications
Even after a number of years of development, fiber-optic sensors have still not
enjoyed great commercial success, since it is difficult to replace already well-
established technologies, even if they exhibit certain limitations. For some
application areas, however, fiber-optic sensors are increasingly recognized as a
technology with very interesting possibilities. This holds particularly for harsh
environments, such as sensing in high-voltage and high-power machinery, or in
microwave ovens. Bragg grating sensors can also be used to monitor the
conditions e.g. within the wings of airplanes, in wind turbines, bridges, large
dams, oil wells and pipelines. Buildings with integrated fiber-optic sensors are
sometimes called “smart structures”; they allow one to monitor the inside
conditions and to gain important information on the strain to which different parts
of the structure are subject, on aging phenomena, vibrations, etc. Smart
structures are a main driver for the further development of fiber-optic sensors.
Uses Of Optical Fibers in Biomedical:
With a global population that's both growing and living longer, the world's
healthcare providers are increasingly looking to advanced biomedical
instrumentation to enable more efficient patient diagnosis, monitoring, and
treatment. In this context, biomedical sensing applications of optical fiber are of

7. growing importance. At the same time, recent advances in minimally invasive
surgery (MIS) demand smaller disposable sensing catheters.
Endoscopic imaging applications of fiber-optics are well established, but the
intrinsic physical characteristics of optical fibers also make them extremely
attractive for biomedical sensing. Uncabled fibers (typically less than 250 μm
diameter) can be inserted directly into hypodermic needles and catheters, so that
their use can be both minimally invasive and highly localized—and fiber-optic
sensors (FOS) made with them can perform remote multipoint and
multiparameter sensing. Optical fibers are immune to electromagnetic
interference (EMI), chemically inert, nontoxic, and intrinsically safe. Their use will
not cause interference with the conventional electronics found in medical
theaters. And, most importantly, the immunity of fibers to electromagnetic and
radio frequency (RF) signals makes them ideal for real-time use during
diagnostic imaging with MRI, CT, PET, or SPECT systems, as well as during
thermal ablative treatments involving RF or microwave radiation.
***Fiber-optic biomedical sensors:
Optical fiber sensors comprise a light source, optical fiber, external transducer,
and photo detector. They sense by detecting the modulation of one or more of
the properties of light that is guided inside the fiber—intensity, wavelength, or
polarization, for instance. The modulation is produced in a direct and repeatable
fashion by an external perturbation caused by the physical parameter to be
measured. The measured of interest is inferred from changes detected in the
light property.
Fiber-optic sensors can be intrinsic or extrinsic. In an intrinsic sensor, the light
never leaves the fiber and the parameter of interest affects a property of the light
propagating through the fiber by acting directly on the fiber itself. In an extrinsic
sensor, the perturbation acts on a transducer and the optical fiber simply
transmits light to and from the sensing location.
Many different fiber-optic sensing mechanisms have been demonstrated already
for industrial applications.
and some for biomedical applications among which are
fiber Bragg gratings (FBG), Fabry-Perot cavities or external fiber Fabry-Perot
interferometer (EFPI) sensors, evanescent wave, Sagnac interferometer, Mach-
Zehnder interferometer, microbend, photo elastic , and others. By far the most
common, however, are based on EFPIs and FBGs. Spectroscopic sensors based
on light absorption and fluorescence are also common. Biomedical FOS can be
categorized into four main types: physical, imaging, chemical, and biological.

8. Physical sensors measure a variety of physiological parameters, like body
temperature, blood pressure, and muscle displacement. Imaging sensors
encompass both endoscopic devices for internal observation and imaging, as
well as more advanced techniques such as optical coherence tomography (OCT)
and photoacoustic imaging where internal scans and visualization can be made
non intrusively. Chemical sensors rely on fluorescence, spectroscopic, and
indicator techniques to identify and measure the presence of particular chemical
compounds and metabolic variables (such as pH, blood oxygen, or glucose
level). They detect specific chemical species for diagnostic purposes, as well as
monitor the body's chemical reactions and activity. Biological sensors tend to be
more complex and rely on biologic recognition reactions—such as enzyme-
substrate, antigen-antibody, or ligand-receptor—to identify and quantify specific
biochemical molecules of interest.
In terms of sensor development, the basic imaging sensors are the most
developed. Fiber-optic sensors for measurement of physical parameters are the
next most prevalent, and the least developed area in terms of successful
products is sensors for biochemical sensing, even though many FOS concepts
have been demonstrated.
Applications:
Dosage form analysis:
Dreassi and co workers have reported the application of an optical fiber probe for
quality control in the pharmaceutical industry. The system was used to
quantitatively determine the content of a number of pharmaceutical solid dosage
forms containing ibuprofen, and powders containing benzydamine an analogue
of cetrimide. A team from Burroughs-Well come have taken this one step ahead
and have performed identification tests on tablets through the plastic wall of the
blister packaging to distinguish between film coated and uncoated tablets and
between active and placebo forms. The technique satisfied the requirements of a
confirmation of identity test prior to use in a clinical trial.
Fiber optical scanning in TLC for drug identification:
Ahrens et al. proposed an organized toxicological analysis procedure using high-
performance thin layer chromatography in combination with fiber optical scanning
densitometry for recognition of drugs in biological samples. The technique
allowed parallel recording of chromatograms by identifying the drugs and
comparing their ultra violet spectra with the data obtained from library as a
reference spectra.

9. Determination of DNA oligomers:
Kleinjung and group demonstrated the binding of DNA oligonucleotides to
immobilized DNA targets using a fiber optic fluorescence sensor. 13 mer
oligonucleotides were attached to the core of a multimode fiber and the
complementary sequence was identified by using a fluorescent double stranded
specific DNA ligand. The evanescent field was used to differentiate between
bound and unbound species. The template DNA oligomer was immobilized either
by direct coupling to the activated sensor surface or using the avidin biotin bridge
to detect the single base mismatches in the target sequence.
***Endoscope:
Optical fibers are also used in endoscopes. The following is some of the parts of
an endoscope:
• Fiber optic bundles
• Light is guided to the area under investigation by non-coherent fiber optic
bundles (bundles where the optical fibers are not lined up at both ends).
However, the image must be transmitted back by a coherent fiber optic
bundle (a bundle where the optical fibers are lined up at both ends of the
fiber so that an image can be transmitted). In order to produce a clear
image, the shaft contains up to 10 000 fibrer!
• Pipes Water
• Carry water to wash the lens and keep the view clear.
• Operations channel
• Carries accessories to the distil end for surgery.
• Control cables
• Controls which way the distil end is bent.
• Additional optional channel
• Carries air or carbon dioxide to and from the distil end
Five medical procedures carried out using an endoscope:
• Arthroscopy
The endoscope is inserted through an incision in the skin near a joint
under investigation. This can be used to look at the joint and preform
operations such as removing torn tissues.
• Bronchoscopy

10. The endoscope is inserted through bronchial tubes within the lungs in
order to look at the airway and to remove any objects blocking the airway.
• Endoscope Biopsy
The endoscope is inserted through an incision or opening in the body that
leads to the area under investigation. Biopsy forceps are then used to take
a sample of tissue that can then be analysed by a pathologist.
• Gastroscopy (Also called Oesophagogastroduodenoscopy)
The endoscope is inserted down the throat to look for problems with the
oesophagus, stomach and duodenum such as bleeding or ulcers.
• Laparoscopy
The endoscope is inserted through an incision in the abdominal in order to
look at abdominal organs and perform minor surgery.