Engineering Communication For Optical Communication: Comparison And Analysis Between APD And PIN Functionality

Discuss about the Engineering Communication For Optical Communication.

 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.

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.

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. 

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.

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: 

Characteristics of the project

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:  

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.

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.

 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. 

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.   

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.    

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. 

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. 

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.

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. 

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.

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.

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. 

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.

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.