Comparison and Analysis between APD and PIN Functionality in an Optical Communication System

This project compares the performances of conventional PIN photodiode with APD photodiode in an optical communication system. The project developer optimized the photo detectors for various parameters and simulated the project with Opti System software. The results showed that APD photo detectors are a good candidate for communication systems than PIN photo detectors.

CE 3.1 Project Information
Name of the project: Comparison and Analysis between APD and PIN Functionality
in an Optical Communication System
Location of the project: Please fill
Project Duration: Please fill
Organization: Please fill
Role and Designation during the time: Project Developer
CE 3.2 Project Background
CE 3.2.1 Characteristics of the project
The avalanche photodiode or APD is a reverse biased diode. The major difference
between APD is that the absorption of photons is better than PIN. Within the fibre optic
communication, few of the major factors could affect the overall affect the system quality
that causes lesser desirable communication within two optical networks. Hence, the
optimization of the systems eventually become inevitable for telecommunication. In this
project, I have compared the performances of conventional PIN photodiode with APD
photodiode. I even set-up the respective optimized system of optical transmission for
obtaining the greatest performance after simulation with the help of Opti System software. I
have shown the APD photo detectors as a good candidate for the communication systems
than PIN photo detectors, for their availability of internal gain. I noted that the maximum Q-
factor that was produced by each and every detector, was being heavily impacted by the
respective shot and thermal noises with APD. Therefore, in the project, I had to compare the

performances of APD and PIN and check the results if the responsivity and multiplication
gain is increasing.
CE 3.2.2 Objectives developed for the project
This particular project for Comparison and Analysis between APD and PIN
Functionality in an Optical Communication System came up into mind while completing the
course of advanced optical communication. I showed extra interest in this particular course
and hence decided to execute the project. I wanted to check the performances of the two
photodiodes of APD and PIN after elimination of probable performance degradations.
Therefore, for obtaining accurate results from the project, I eventually developed few
objectives, which are given below:
 To optimize photo detectors for several parameters like dark current, shot noise, gain,
thermal noise, responsivity and extinction ratio.
 To properly explore the respective performances of APD and PIN in terms of the
Maximum Q-Factor.
 To complete simulation process for the optimized communication system so that it
could be helpful in analysis of devices under the significant development for provided
link distance.
 To predict the overall performance of the optical communication system with the help
of simulation process.
 To execute the entire process of simulation and with the help of OptiSystem software.
 To eliminate every probable performance degradations even before implementation of
the definite hardware.

Project Supervisor
Project
Developer (Me)
Head of the
Department
CE 3.2.3 My area of work
I was being hired as the project developer for this specific project of Comparison and
Analysis between APD and PIN Functionality in an Optical Communication System. As I
had major interest in the optical communication system, I did not face any issue while
completing the project all by myself. I had executed several similar telecommunications
projects on optical communication previously and thus I had the confidence to execute this
project. My project supervisor identified my strengths in the course and selected me as the
project developer.
CE 3.2.4 Project Group
Figure 1: People involved in the project
CE 3.2.5 My responsibilities throughout the project
For completing the tasks, I was subsequently assigned for the work to compare and
contrast the performances of photo diodes of APD and PIN for any optical communication
system. I at first completed the course and cleared my doubts regarding the project. I

understood that photo detectors play the most significant role within the performance of
photo receiver. I had to optimize the photo detectors for various parameters such as dark
current, shot noise, gain, thermal noise, responsivity and extinction ratio. My main goal was
to find out the maximum Q factor and thus I investigated the performances of APD and PIN.
I also had for simulating this project in respect of the parameters of performance with the
help of Opti System software and then improve and analyse the results of the proposed
optical communication systems.
CE 3.3 Distinctive Activity
CE 3.3.1 Comprehending the Theory of Project
In this project, I had used my theoretical knowledge of advanced communication
system course. I considered the specifications of avalanche photo detector and PIN photo
detector. I checked that the major sources of noise of the PIN photo diode are the thermal as
well as shot noises. As these two types of sources of the noise are independent statistically,
the complete noise at the provided bandwidth B was being expressed as follows:
Where were the photo current, radiation of background and the dark
current, R was an equivalent resistor that was being determined by each and every device.
As per local field theory, this total noise that was equivalent of the APD was written:
F was the excessive noise factor.

Figure 2: Signal to noise ratios for two configurations of the front end of an optical
receiver: Photo detectors (PIN or APD) with an amplifier
Regarding designing procedure, I selected Opti System software as it was perfect for
this project.
CE 3.3.2 Engineering knowledge and skills applied in the project
I had correctly applied my understanding of core acquaintance of electrical and
electronics engineering. I had to apply my knowledge and skills of optical communication
system and photo detectors. Since, I had to compare the two results, it was required to have a
deep understanding of APD and PIN. For simulation, I have applied my knowledge of Opti
System software and hence I was able to integrate the project appropriately.
CE 3.3.3 Accomplishment and Task Performed
For the accomplishment of the project, I had to simulate the project with Opti System
software. This particular software helped me in following a distinct flow within the entire
project.

Figure 3: Flowchart of the project
I selected three components of optical transmitters, optical transmission lines as well
as optical receivers for the project. A PSBS or pseudo random bit sequence has generated the
pulsed electrical signals that were next utilized as the modulation input. The signals were
being split in two distinct outputs signals that were then detected by PIN Photo diode (PIN-
PD) as well as the APD Photo diode (APDPD). Moreover, these were being converted to
electrical output signal once again.
Regarding simulation, I checked that the sources of nominal laser diode selected
wavelength was of 1550 nm, with the output power being set to 0 dBm. The respective rise as
well as fall time for laser signals were equal to 0.05 bit. The respective insertion losses of 1
dB and the depth 100 dB were taken into consideration for the 4th order low-pass filter. The
system specification is provided below:

Table 2: System Specifications
The optical transmission line comprises of several functions.
Figure 4: Optical Transmission Line
I have made the complete set up of Opti System for completion of simulation. I
connected the oscilloscope as well as Eye Diagram analyser with 3R Regenerator.

Figure 5: Systematic layout of simulation set-up (Opti System)
I created the optimized system and analysed the results and graphs. I eve calculated
maximum Q factor at the receiver. The optimum value of fibre length was around 50 km for
both APD and PIN devices. I even compared the APD gain with maximum Q factor.
Figure 6: APD gain versus Maximum Q-Factor
Thus, I noted that APD has higher maximum Q factor as gain increases, maximum Q
factor decreases. I obtained APD gain of 2-30dB. Finally, I compared the APD responsivity
with maximum Q factor with PIN responsivity with maximum Q factor.

Figure 7: Comparison of APD Responsivity with Maximum Q-Factor compared with
PIN Responsivity with Maximum Q-Factor
CE 3.3.4 Identified issues and their solutions
3.3.4.1 Issues
One of the problems, which I have confronted within the project was during
completing the simulation process. I was not being able to analyse the simulation result for
the optimized system and was unable to calculate the maximum Q-factor. For this particular
reason, I was unable to improve the devices with the increasing extinction ratio. The second
issue that I have eventually faced in this particular project of APD and PIN photo detectors
was while evaluation of dark current for PIN and APD. Due to this issue, I was even unable
to compare them and get the result of better performances.
3.3.4.2 Solutions

To resolve the first issue faced within the project, I had provided the solution of doing
the simulation once again. This time the result was perfect. We swept the distinct extinction
ratio, as well as then calculates the maximum Q Factor at receiver. I was also successful in
improving both the devices in respect to increment the extinction ratio. I took this optimum
value for the fibre length was more than 50km for the PIN and APD devices.
Figure 4: Maximum Q Factor vs Extinction ratio with ER; bit rate=10 Gb/s, APD
gain=3 dB, input power=0 dB, optical fibre length=50 km
For the second issue, I calculated and found out that the dark current for APD as well
as PIN were 10-50 nA and 1-10 nA respectively. Thus, after comparing, I understood that
APD could eventually perform well since it comprises of high Maximum Q Factor.
CE 3.3.5 Plan to produce creative and innovative works
My principal plan was to create the most advanced with the original efforts by
efficiently working with the supervisor of project. I have even sub divided my mechanisms
flawlessly and then considerably made sure that I had accomplished each and every
individual parts with the high efficiency and efficacy.

CE 3.3.6 Collaborative Work
I along with my project supervisor had to complete this project work together. I even
had to test the project functionalities quickly for proper identification of every error within
the project and then accomplished our work easily.
CE 3.4 Project Review
CE 3.4.1 Project Overview
I have documented as well as noted each and every result while the integration of my
experiment. I also have used my core understanding of circuit designing to complete the
comparison of APD and PIN perfectly and appropriately. I have also used Opti System
software for the purpose of simulation.
CE 3.4.2 My Contribution to work
I have effectively compared and analysed between APD and PIN functionality within
an optical communication system, since I was the project developer. My other contribution to
this project was to integrate the entire system effectively and properly.