Operational Characteristics of Photodiodes used as Photo
detectors in Optical System.
Shahd Tantawi
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Princess Sumaya
University for Technology, [email protected]
Abstract – A Photo diodes is a pin
semiconductor .Its main rule is to convert optical light signal into electrical
current.
In this paper, we will focus on photo
diodes working as photo detectors and their characteristics Photo detectors
should have high sensitivity, low noise, low cost and high reliability.
INTRODCTION
Photodiodes are used at the receiver side of an
optical fiber .Their main job is to convert the optical light signal to an
electrical signal carrying the requested data. The requirements for a photodetector are like those of an optical source. It must have high
sensitivity, low cost ,fast response, low noise, , and high reliability.requirements
There are two types of photo destectors PIN photodiodes and Avalanche photodiodes .
pin Photodiodes
They are the most common photo detectors .The
consist of p and n regions with a The reverse-biased pn junction has a
region, named the depletion region which is depleted of charge carriers and where a
large built-in electric field opposes flow of electrons from the n-side to the p-side. When such a
p–n junction is illuminated with light on one side, electron–hole pairs are
created through absorption. The resulting current is proportional to the
incident optical power. Thus a reverse-biased p–n junction acts as a
photo detector and is referred to as the p–n photodiode.
Avalanche
From
exam paper
OBJECTIVE
The goal of this experiment is to study the characteristics of photo detectors .It
focuses on the sensitivity of the photodiodes .The sensitivity of photodiodes
is define the ratio of the generated current and incident optical light power
as a small current proportional the light intensity is generated. The
sensitivity is proportional the wavelength of light.Thus, an experiment testing
photodiode sensitivity to LED optical wavelength is studied and .
+
METHODLOGY
The implementation of the experiment was done in two was
:on the MCM40 optical fiber trainer kit & using Optiwave software and both
lead to the same results.
On MCM40 kit, we started with powering up the module and
removing all the jumpers. Then we started by connecting the LED 820nm with the
Photodiode 820 nm using the required kit jumpers to implement the
connection and through optical fiber
cables .Then we used the voltmeter and the DC oscilloscope to read the results after
the LED optical source emitted the light and after it was received and
transmitted to an electrical current by the photo detector. The same steps were
repeated to form a mix and match procedure for the LED 820 nm optical source
emitting light received by a 660nm photodiode, LED 660 nm optical source
emitting light received by a 660nm photodiode and LED 660 nm optical source
emitting light received by a 820nm photodiode. The voltmeter and oscilloscope
results were recorded for each case.
In Optiwave
software , the experiment implementation started by generating bits by a pseudo
random bit sequence generator entering an NRZ pulse generator and into an LED
optical light source .The LED optical source output was connected to Optical
Power Meter and Optical spectral analyzer to read the optical power value .Also
the LED optical source was connected to an optical fiber with a photo detector
at the end of it .The photo detector output was connected to electrical power
meter visualize and Oscilloscope visualize and BER analyzer.This same
experiement was repeated for 4 cases
·
LED 820 nm optical source
emitting light received by a 820nm photodiode.
·
LED 820 nm optical source
emitting light received by a 660nm photodiode.
·
LED 660 nm optical source
emitting light received by a 660nm photodiode and
·
LED 660 nm optical source
emitting light received by a 820nm photodiode.
The power meter visualize and Oscilloscope visualize results were recorded for each case.
RESULTS AND SIMULATION
The kit experiment and the Optiwave experiments
were done successfully and seamlessly reaching consistent results and
conclusion.
The summary of the results of the simulation
and kit results are shown below
·
LED 660 nm optical source
emitting light received by a 660nm photodiode and
·
LED 660 nm optical source
emitting light received by a 820nm photodiode.
·
LED 820 nm optical source
emitting light received by a 820nm photodiode.
·
LED 820 nm optical source
emitting light received by a 660nm photodiode.
Figure 1: Optiwave design
.
LED 660 nm optical source emitting light received by a
820nm photodiode
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LED 820 nm optical source
emitting light received by a 820nm photodiode.
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LED 820 nm optical source
emitting light received by a 660nm photodiode.
Conclusion
Results table
As for the kit experiment we have arrived to the same
results and number patterns and using the voltmeter and oscilloscope to arrive
to the results.
Conclusion
•
In
the case when PD1 (820nm) is connected with LED 2 (660nm) the detected voltage is lower than the
voltage detected when connecting PD1(820nm ) with LED 1 (820nm) because PD1
reaches its maximum sensitivity at 820nm .
•
In
the case when PD2 (660nm) is connected with LED 1 (820nm) the detected voltage
is lower than the voltage detected when PD2 (660nm) is connected with LED 1
(660nm) (actually it coincides with the voltage measured without optical
signal), because the photodiode PD2 reaches its maximum sensitivity at 660 nm
and the attenuation of the fiber is higher at 820 nm than at 660 nm.
•
Therefore
it can be concluded that that photo diode PD1 reaches its maximum sensitivity
at 660 nm and PD2 at 820 nm.
Referecnces
Abbreviation
Led
Pd
Pin
