Ehsān Shāh Hosseini

PhD student, Photonics, GaTech

MS in electrical engineering GaTech 2008

BS in electrical engineering, Sharif University, Tehran 2003

I am currently a PhD student in the ``Photonics Research Group'' working with Dr. Ali Adibi. My main research concentration has been visible range microdisk resonators fabricated in silicon nitride.

Research

Optical resonators, with the capability of trapping and storing photons for long periods of time, are essential parts of the optical integrated systems. Two common structures,  used extensively in today’s integrated circuits, are photonic crystal cavities and traveling wave resonators (microrings, microdisks, and microtoroids).

Realization of whispering
gallery mode (WGM) resonators in silicon-based material systems has great benefits, such as ease of fabrication, integrability with mature silicon (Si) electronics, and low cost. These novel structures have already been demonstrated on silicon oxide (SiO2), silicon, and silicon nitride (Si3N4) materials. While SiO2 micro-toroid and micro-sphere resonators have shown the highest Q’s, their size and lack of chip-scale integrability (because of the bulky fiber taper coupling scheme) result in complications in using them for integrated photonics applications. On the other hand, Si microdisks on oxide substrates have recently been shown to be capable of achieving high quality factors (Q > 10^6) while being coupled to planar optical waveguides.

Integrated nanophotonics in the visible range of the spectrum could serve as a new platform for sensing and optical data processing applications. Photonic structures that guide and manipulate light in the visible spectral range are not as well investigated as their IR counterparts. Nevertheless, this spectral range is important for applications such as biological sensing (e.g., using fluorescence and surface enhanced Raman spectroscopy (SERS)), and visible wavelength reconfigurable optical signal processing (for applications such as LiDAR). By adding light generation and detection in the visible range (using Si) to the Si3N4 photonic device on the same substrate, it is possible to develop all visible nanophotonic components, including sources, modulators, waveguide components, and detectors on a monolithic CMOS-compatible photonic chips; thereby forming complete system-on-chip solutions.

Despite their good performance in the infrared (IR) region, Si resonators suffer from significant material loss in the visible range of the optical spectrum, making them unsuitable for visible light applications. Unlike silicon, low Si content, LPCVD Si3N4 offers a very low material loss throughout the optical range (wavelengths from 300 nm to several microns), and a moderately high refractive index (n ≈ 2). Thus, provided that the Si3N4 layer is optically isolated from the lossy Si substrate, it can guide the visible light without significant loss in this wavelength range. Nevertheless, most of the research on silicon nitride has been concentrated on infrared (IR) or near infrared (NIR) applications.

The few reported works on Si3N4 photonic crystals and microring resonators in the visible range were of considerably lower fabrication quality compared with their Si counterparts. In my research, monolithic, high Q, compact Si3N4/SiO2 resonators are demonstrated in the visible range, and critical coupling of the resonators to in-plane waveguides is also demonstrated (at λ =652-660 nm)

Publications

• E. Shah Hosseini, P. Alipour, A. Atabaki and A. Adibi, “Athermal PDMS clad silicon nitride microdisk resonators,’’ in preparation.
• E. Shah Hosseini, S. Yegnanarayanan, A. Atabaki , M. Soltani, and A. Adibi, “Systematic design and fabrication of high-Q pulley-coupled planar silicon nitride microdisk resonators,” in preparation.
• P. Alipour, E. Shah Hosseini, A. Eftekhar, B. Momeni, and A. Adibi, “Athermal performance in high-Q polymer-clad silicon microdisk resonators,” in preparation.
• B. Momeni, E. Shah Hosseini, and A. Adibi, “Planar Photonic crystal microspectrometers in silicon-nitride for the visible range,” Opt. Express 17(19), 2009.
• E. Shah Hosseini, S. Yegnanarayanan, A. Atabaki, M. Soltani, and A. Adibi, “High quality planar silicon nitride microdisk resonators for integrated photonics in the visible wavelength range,” Opt. Express 17(17), 2009.      
• B. Momeni, E. Shah Hosseini, M. Askari, M. Soltani, and A Adibi, “Integrated photonic crystal spectrometers for sensing applications,” Opt. Commun. 282(15), 2009.
• B. Momeni, S. Yegnanarayanan, M. Soltani, A. Eftekhar, E. Shah Hosseini, and A. Adibi, “Silicon nanophotonic devices for integrated sensing,” J. Nanophoton. 3, 2009.
• B. Momeni, M. Chamanzar, E. Shah Hosseini, M. Askari, M. Soltani, and A. Adibi, “Strong angular dispersion using higher bands of planar silicon photonic crystals,” Opt Express 16(18), 2008.
• A. Atabaki, E. Shah Hosseini, B. Momeni, and A. Adibi, “Enhancing the guiding bandwidth of photonic crystal waveguides on silicon-on-insulator,” Opt. Lett. 33(22), 2008.