October 18, 2017
1 EEET2392 Project
Wavelength Division Multiplexing (WDM) is a common technique used in optical communication networks to increase the data capacity of a single optical fibre. By using different wavelengths, many optical communication channels can be transmitted simultaneously in an optical fibre.
In a WDM transmission system, a multiplexer is used at the transmitter to combine (multi-plex) several wavelength channels together. At the receiver, different wavelength channels are separated by a WDM demultiplexer.
A WDM demultiplexer can be constructed from cascaded add-drop ring resonators [1, 2] as illustrated in Fig. 1.
Figure 1. WDM demultiplexer based on cascaded add-drop ring resonators
The wavelength response of a WDM demultiplexer is illustrated in Fig. 2
Figure 2. WDM demultiplexer wavelength response
Some important characteristics of a WDM are: - Channel bandwidth(BW): 3 dB bandwidth of
a wavelength channel - Channel spacing (CS): wavelength spacing between adjacent channels -
Insertion loss (IL): IL = 10 log10 Pout at the center wavelength of a channel - Cross-talk (XT): XT =
10 log10 Pout,j+1 is the difference in the output power of the adjacent channel (channel j+1) and a
channel (channel j). - Free Spectral Range (FSR)
 Xuezhe Zheng, Ivan Shubin, Guoliang Li, Thierry Pinguet, Attila Mekis, Jin Yao, Hiren Thacker, Ying Luo, Joey Costa, Kannan Raj, John E. Cunningham, and Ashok V. Krishnamoorthy, -A tunable 1x4 silicon CMOS photonic wavelength multiplexer/demultiplexer for dense optical interconnects,- Opt. Express 18, 5151-5160 (2010)
 Philippe P. Absil, Peter De Heyn, Pieter Dumon, Dries Van Thourhout, Peter Verheyen, Shankar Selvaraja, Guy Lepage, Marianna Pantouvaki, Michal Rakowski, Joris Van Campenhout, -Advances in silicon photonics WDM devices,- Proc. SPIE 9010, Next-Generation Optical Net-works for Data Centers and Short-Reach Links, 90100J (2014/02/19)
In this project, you will design a WDM demultiplexer based on add-drop ring resonators. The specifications of your demultiplxer depend on your student number.
Run the below code cell and enter your student number to obtain the demultiplexer specifica-tions
In [ ]: student_number = raw_input(-Enter your student number, without s, eg 1234567, then press from eeet2392.wdm_specs import *
The designed WDM demultiplexer must also satisfy the following requirements: - All ring resonators must be critically coupled. - The gap between waveguides in the directional couplers must not be smaller than 200 nm - The FSR range of all ring resonators must be at least four times the channel spacing
Design a demultiplxer to meet the above requirements. You need to work out the length of all rings, the gap and length of all directional couplers. For this project, you can assume that the effect of the bend sections on the coupling ratios of the directional couplers is negilible.
You also must use ASP PDK in your design. You will learn about PDK in week 10. To use ASP PDK you need to import asp_silicon_photonics.technology instead to default silicon pho-tonic technology, ie import asp_silicon_photonics.technology instead of from technologies import silicon_photonics
Create a PCell for the demultiplexer. The PCell must contain the Layout view and other views required for circuit simulation.
Simulate the designed demultiplexer and plot the wavelength response of all channels and the through port. From the simulation results, determine the bandwidth, insersion loss, cross talk of each channel. Discuss what you can do to increase the bandwidth, reduce the insersion loss and reduce the cross-talk.
Attach grating couplers from the PDK to all input and output ports of the demultiplexer to form a completed demultiplexer device ready to be interfaced to optical fibres. All grating cou-plers must be spaced 50 mm apart horizontally. Generate the GDS file for your final device. Simu-late your demultiplexer with grating couplers.
Discuss the effect (if there is any) of the input and output grating couplers on the performance of the designed WDM demultiplexer.
Investigate the effects of the variation in the waveguide width on the performance of the de-signed WDM demultiplexer. Extra marks will be given if you can investigate the effect of silicon core layer thickness variation or temperature variation on the demultiplexer performance.
1.3 Project submission
You will need to submit: - This notebook - A report summarising your design process, the results and your discussion. Detailed instructions on the structure of the report will be provided later. The report will need to be submitted via the submission link on Blackboard.
The due date for the notebook and report submission is Thursday October 19 at 23:59 (Week 13). Late submission will be penalised at 5% of the total available marks per 6 hours for up to 48 hours. Submission more than 48 hours after the deadline will not be marked.
You are also required to demonstrate your design (ie running the notebook) to your course lecturer on Friday October 20. Time and location for project demonstration will be announced later.
This is an individual project. Each student will have different set of specifications based on your student number. Do not copy designs or reports from other students. If two design notebooks or reports are found to be similar, mark penalty will be applied for both notebooks or reports.
Important: Plagiarism is academic misconduct and you will be penalised and reported to RMIT senior officer for academic misconduct
1.5 Your project design starts from here
Add new cells and enter code to work on your design. All of your calculation, design and simu-lation should be contained in this notebook.
Before each code cell you need include some explanation of what are you trying to achieve with that code cell. Use markdown cell to enter your text. You should use headings to organise your notebook into sections
In [ ]:
In [ ]:
By submitting this project I agree that all the work was done by me and that I have not copied anything from anyone else.