Speaker: Ramesh K. Gupta (EE13D204)
Abstract: Directional couplers (DCs) are widely used for the realization of integrated silicon photonics devices such as power splitter (PS) , microring resonator (MRR), Mach-Zehnder interferometer (MZI), polarization ﬁlters, DBR based wavelength ﬁlters, etc. in silicon-on-insulator (SOI) platform. A DC operating uniformly over a wider wavelength range is a long time demand for an integrated silicon photonics chip. Especially, wavelength independent ﬁgure of merits of certain integrated optical components/devices (e.g. uniform Q-value/extinction of an MRR, uniform extinction ratio of an MZI, uniform power splitting ratio of a PS) reduce the design complexity and overall fabrication costs of a chip. There are few recently demonstrated designs of DCs oﬀer uniform power splitting over a broad wavelength range. However, such DCs have extra design parameters (e.g. subwavelength grating period and phase controlling section) to be controlled accurately for any decisive performances. Moreover, such DCs may not be useful for the design of compact microring resonators.
We have demonstrated a new design of wavelength independent directional coupler (DC) in siliconon-insulator (SOI) with a device layer thickness of 220 nm. Semi-analytical coupled mode theory is used to optimize a nearly wavelength independent design of DC, operating in TE-polarization (λ ∼ 1550 nm). The transmission characteristics of fabricated DCs are found to be indeed wavelength independent over a bandwidth of 100 nm (1525 nm ≤ λ ≤ 1625 nm), consistent with the theoretical predictions. The average excess loss of such directional couplers is evaluated as ∼ 0.8 dB and there are scopes for its further reduction. These DCs are then used further to demonstrate integrated optical building blocks like power splitters (2 × 2, 1 × 4), Mach-Zehnder interferometers (2 × 2), and all-pass microring resonators. Their performances are also found to be uniform and thermooptically reconﬁgurable within the wavelength range mentioned and thus making them suitable for integrated silicon photonics for broadband applications. In PhD Seminar-I, I presented detail design and experimental demonstration of wavelength DC (WIDC). In this talk (PhD Seminar-II), I am going to focus on the demonstration of ultra-broadband and reconﬁgurable silicon photonics devices designed with WIDCs.
All are cordially invited.