An informal introduction to PICs design: ‘We’re not in Kansas anymore’
From Science to the real world
The first thing you realize when designing a PIC is that scientific papers are a good reading material, but not a user’s manual. Actual PICs design requires software tools, fabrication deviation and characterization knowledge. So, be prepared to invest time, money and brainpower to bring your idea to life. From our experience, it is important not only to be able to simulate and layout your idea but also to consider that different fabrication processes (and even foundries) can severely impact your theoretical performance, so be prepared for characterize and optimize (but that’s another topic to address)
Software saves time…
Software can make your life much easier and, we don’t mean only in terms of usability and time, which is already quite something. But choosing the right software can be of big help if you are planning to reuse /escalate your design capabilities. Additionally, most of commercial software tools are incorporating functionalities that can help you bridging the simulation to reality gap, such as convergence tests, montecarlo simulations… Understanding the software modules can really help you to speed up your design by choosing the right tool.
…but not money
Even though you can find open photonic design software tools, if your design is going to be fabricated or included in a bigger structure, you will probably need to go for proprietary tools. The good news are that most of these tools are licensed module based, so you may be able to encompass your software investment to your design phase. The bad news is that going for an end customer design will probably require the full suite, so our advice is get a good understanding of your alternatives and your requirements and plan and budget in advance.
Yes, even with the most comprehensive software suite, at some point you will require programming for layout development, scripting simulations, geometrical structure modifications, integration with other simulation tools or even combination with other designs. So, do not leave aside programming as it underpins photonics design just as much as Maxwell equation resolution.
It is not only about software, hardware plays a role
Most of Photonic design tools conversation pivot around software capabilities, but software runs on hardware….and hardware has the ability to make your software fly or just crawl. Thus, plan your design environment considering that hardware needs to be capable of fully powering your software tools (RAM, cores, servers/cloud…
Design ahead for fabrication
Unless you just want to have a theoretical useless design, our recommendation is that you plan ahead for fabrication and characterization. Consider in your design as much input from the foundry you are planning to fabricate with as possible, e.g., minimum minimum feature spacing, available materials and thicknesses for the different layers, maximum core layer thickness deviation, waveguide propagation losses, to name a few. Remember that fabrication is not only costly but time consuming, so you will probably want to ensure that your design is as feasible as possible in terms of fabrication processes.
Layout for characterization
And finally you have your chip home, and it is time for measurements, and oopsss!…Anticipating your design layout will facilitate its characterization not only in terms of lab set up but also to anticipate the parameters and corresponding test structures that can be interesting in order to measure the design performance properly.