Date: 19th July 2017
Time: 4:00 P.M – 5 PM
Venue: ESB 244
Speaker: Gayathri M S (EE12D013)
Guide: Dr. Shanti Bhattacharya
Dr. Anil Prabhakar (Chairperson)
Dr. Ananth Krishnan (M)
Dr. Harishankar Ramachandran (M)
Dr. Kothiyal (M)
Dr. Manu Jaiswal t (M) ( PH)
In my first seminar, I discussed the design of polarization sensitive gratings and early fabrication results. This seminar continues this topic but addresses the fabrication issues in more detail. Polarization sensitive gratings are high aspect ratio structures in quartz glass. Due to their high aspect ratio, fabrication proves to be extremely challenging. Gratings with different profiles were fabricated. The difference in the fabrication methods to obtain a nearly rectangular grating profile and a triangular grating profile lies in the metal deposition step, while both are subjected to the same anisotropic etching processes. I will show how the sub-wavelength feature sizes of these gratings have been used to our advantage.
The second part of the seminar will focus on the analytical equations of the modal method that we have used to design these gratings. Even though applicable to gratings of all dimensions, the modal method results in a particularly simple implementation in the sub-wavelength regime. Although, the modal method, which was originally evolved for rectangular grating profiles back in the 1980s, it can also be used for grating of other shapes, such as, triangular or trapezium profiles. The usual way to compute the effective indices or phase is to apply the equations to the different lamellar layers into which these profiles can be decomposed. We propose a simpler way to calculate phase for these zero-order gratings by constructing ‘phase-equivalent’ blazed profiles.
Finally, different perspectives of the modal method are explored highlighting its similarity to other commonly used analysis techniques.
What can you expect from the talk?
- Challenges of fabrication of sub-wavelength high aspect ratio quartz gratings
- The ‘phase-equivalence’ concept to simplify design and analysis
Last but not the least, a deeper look into the modal method indicating that it is more than just a design tool.
All are cordially invited