It is basically for reducing coupling loss by using VCSELs

1. DAFFODIL INTERNATIONAL UNIVERSITY
Presentation on
Optical fiber communication
Group members:
 Md. Mehedi Hasan-#151-33-2391
 Md. Mahmudul Hasan-#151-33-2346
 Shuvo Kumar Das-#151-33-2312
 Md. Nishat Jaman-#151-33-2336
 Md Shaminur Rahman-#151-33-2467
 Md AbdulWahed-#151-33-2601

2. Low-lossLightCouplingDesign
forMultimodePolymerOpticalWaveguides
withVCSELLightSources
Optical Fiber:
a thin flexible fiber with a glass core through which light signals can be sent with
very little loss of strength.
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
Elements of optical fiber
 Glass core
 Glass cladding
 Primary buffer
 Secondary buffer

3. Fiber optic Communication
For gigabits and beyond gigabits transmission of data, the fiber optic
communication is the ideal choice. This type of communication is used to
transmit voice, video, telemetry and data over long distances and local area
networks or computer networks.

4. Classification of optical Fiber
Single Mode Fibers:
SMF can be described as a strand of fiber made of glass; they usually measure
about 8.3 to 10 microns in diameter with a single transmission mode. This fiber
permits only a single mode of light measured at 1310 or 1550 nm due to the
very narrow diameter if the core.
Types of Single mode fiber
 Non dispersion-shifted fiber (NDSF)
 Dispersion-Shifted Fibers (DSF)
 Non-Zero-Dispersion-shifted fibers (NZ-DSF)
.

5. Classification of optical Fiber
Multi-Mode Fibers:
The MMF fibers permit the passage of multiple modes of light through it.
They have a larger diameter than the SMF which is usually in the order of
50, 62.5 or 100 micrometers .Wavelength for the MMF is remarkably high,
reaching values between 3000 to 3500 feet with significant distortions that
occur at the receiving end leading to failure in transmission.
Types of Multimode fiber
 Step-Index Multimode Fiber
 Graded-Index Multimode Fiber

6. Losses of Optical Fiber Communication
When a beam of light carrying signals travels through the core of fiber optic, the
strength of the light will become lower. Thus, the signal strength becomes
weaker. This loss of light power is generally called fiber optic loss or attenuation.
 Intrinsic Fiber Core Attenuation
 Light absorption
 Scattering
 Bending loss
 Coupling loss

7. low coupling loss with VCSELs and PDs
What is VSSELs:
The vertical-cavity surface-
emitting laser, or VCSEL is a
type of semiconductor laser
diode with laser beam emission
perpendicular from the top
surface, contrary to conventional
edge-emitting semiconductor
lasers which emit from surfaces
formed by cleaving the individual
chip out of a wafer. VCSELs are
used in various laser products,
including computer mice, fiber
optic communications, laser
printers, and smartglasses.

8. low coupling loss with VCSELs and PDs
Advantages of VCSELs:
Manufacturability: All-vertical construction enables the use of traditional
semiconductor manufacturing equipment to keep fabrication costs down
Integrability: Semiconductor manufacturing and wafer integration of VCSELs is
compatible with detectors and other circuitry
Reliability: VCSELs do not have the failure modes of traditional laser structures
such as dark line defects. Also, because VCSELs can be implemented in arrays
and have very long wear out life, they are not vulnerable to catastrophic optical
damage like systems based on a single or few LEDs or EELs
Testability: VCSELS can be completely tested and burned-in while still in wafer
form. This increases manufacturing yield and lowers cost
Scalability: VCSELs can be easily fabricated into one or two dimensional arrays
to scale power output to match specific application requirements

9. Comparison To VCSELs over LED and LASER

10. Lowest possible coupling loss
The coupling loss between the waveguides and VCSEL sources is accurately
evaluated by applying the cut-back Method and defining the waveguide core
size that realizes the lowest coupling loss with VCSELs both theoretically and
experimentally.
EXPERIMENTAL PROCEDURE
The cut-back method has been widely used to measure the propagation loss of
long optical fibers. the cut-back method has also been applied to short
waveguides.
Cut-back method:
In the cut back method, the output optical power from the various length of
waveguides are measured by cutting the waveguide sample.

11. Experimental Procedure
 First, the length to be cut should be long enough to observe the output power
change is sufficiently larger than the measurement error. In this paper, a laser
diode (LD) emitting at 1550 nm is used for the light source to satisfy this
condition
 Second, the surface smoothness of the waveguide facets has to be consistent
for all the different length conditions. In this paper, the same abrasive paper
is used to polish the facet after cutting the waveguide with a razor to stabilize
the facet smoothness.
 Third, the output power should be measured under, at least, three
different waveguide lengths.

12. Optimum Core Size
Ray-trace simulation software, ‘Zemax’ is used to calculate the coupling loss of the
waveguide. Figure 1 shows the simulation model that assumes an optical link
composed of two wave guides connected by a 50-μm core GI MMF
The NA of the light source is set to 0.35 assuming the emitted light beam from
widely deployed VCSELs which directly excites the waveguide.